Bio


Zhenan Bao joined Stanford University in 2004. She is currently a K.K. Lee Professor in Chemical Engineering, and with courtesy appointments in Chemistry and Material Science and Engineering. She is a member of the National Academy of Engineering and National Academy of Inventors. She founded the Stanford Wearable Electronics Initiative (eWEAR) and is the current faculty director. She is also an affiliated faculty member of Precourt Institute, Woods Institute, ChEM-H and Bio-X. Professor Bao received her Ph.D. degree in Chemistry from The University of Chicago in 1995 and joined the Materials Research Department of Bell Labs, Lucent Technologies. She became a Distinguished Member of Technical Staff in 2001. Professor Bao currently has more than 400 refereed publications and more than 60 US patents. She served as a member of Executive Board of Directors for the Materials Research Society and Executive Committee Member for the Polymer Materials Science and Engineering division of the American Chemical Society. She was an Associate Editor for the Royal Society of Chemistry journal Chemical Science, Polymer Reviews and Synthetic Metals. She serves on the international advisory board for Advanced Materials, Advanced Energy Materials, ACS Nano, Accounts of Chemical Reviews, Advanced Functional Materials, Chemistry of Materials, Chemical Communications, Journal of American Chemical Society, Nature Asian Materials, Materials Horizon and Materials Today. She is one of the Founders and currently sits on the Board of Directors of C3 Nano Co., a silicon valley venture funded company. She is Fellow of AAAS, ACS, MRS, SPIE, ACS POLY and ACS PMSE. She was a recipient of the L'Oreal UNESCO Women in Science Award in 2017. She was awarded the ACS Applied Polymer Science Award in 2017, ACS Creative Polymer Chemistry Award in 2013 ACS Cope Scholar Award in 2011, and was selected by Phoenix TV, China as 2010 Most influential Chinese in the World-Science and Technology Category. She is a recipient of the Royal Society of Chemistry Beilby Medal and Prize in 2009, IUPAC Creativity in Applied Polymer Science Prize in 2008, American Chemical Society Team Innovation Award 2001, R&D 100 Award, and R&D Magazine Editors Choice Best of the Best new technology for 2001. She has been selected in 2002 by the American Chemical Society Women Chemists Committee as one of the twelve Outstanding Young Woman Scientist who is expected to make a substantial impact in chemistry during this century. She is also selected by MIT Technology Review magazine in 2003 as one of the top 100 young innovators for this century. She has been selected as one of the recipients of Stanford Terman Fellow and has been appointed as the Robert Noyce Faculty Scholar, Finmeccanica Faculty Scholar and David Filo and Jerry Yang Faculty Scholar.

Academic Appointments


Administrative Appointments


  • Director, Stanford Wearable Electronics Initiative (eWEAR) (2016 - Present)

Honors & Awards


  • Applied Polymer Science Award, American Chemical Society (ACS) (2017)
  • Member, National Academy of Inventors, National Academy of Inventors (2017)
  • Women in Science Award, L'Oreal Foundation and UNESCO (2017)
  • Member, National Academy of Engineering, National Academy of Engineering (2016)
  • ACS POLY Fellow, American Chemical Society (ACS) Polymer Division (POLY) (2014)
  • Andreas Acrivos Award for Professional Progress in Chemical Engineering, American Institute of Chemical Engineers (AICHE) (2014)
  • MRS Fellow, Materials Research Society (MRS) (2014)
  • ACS Polymer Division Carl S. Marvel Creative Polymer Chemistry Award, American Chemical Society (ACS) (2013)
  • Honorary Guest Professorship, Soochow University, China (2013)
  • AAAS Fellow, American Association for the Advancement of Science (AAAS) (2012)
  • Cheung Kong Scholar, Li Ka Shing Foundation and Chinese Ministry of Education (2012)
  • Honorary Guest Professorship, Nanjing Industry University, China (2012)
  • ACS Fellow, American Chemical Society (ACS) (2011)
  • ACS PMSE Fellow, American Chemical Society (ACS) Polymer Science and Engineering (PMSE) division (2011)
  • Most influential Chinese in the World, Science and Technology Category, Phoenix TV (2011)
  • Founder, Board of Directors, C3 Nano Co. (2010-present)
  • Honorary Si Yuan Chair Professorship, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China (2010-2013)
  • David Filo and Jerry Yang Faculty Scholar, Stanford University (2009-2012)
  • The Royal Society of Chemistry 2009 Beilby Medal and Prize, Stanford University (2009)
  • IUPAC Award, Polymer International (2008)
  • SPIE Fellow, SPIE (2008)
  • 50 Awards in the Innovator category, Nanotech Briefs (2007)
  • Featured in Women in SPIE Optics Planner calendar, SPIE (2007)
  • Ranked 4 among the Top 20 most cited authors in the field of Organic Thin Film Transistors, ISI (2007)
  • Teaching Excellence Award, Stanford Society of Women Engineering (2007)
  • Sloan Research Fellowship, Alfred P. Sloan Foundation (2006)
  • Du Pont Science and Technology Award, DuPont (2005)
  • Finmeccanica Faculty Scholar, Stanford University (2004-2008)
  • Terman Fellow, Stanford University (2004-2007)
  • Robert Faculty Scholar, Stanford University (2004-2005)
  • Robert Noyce Faculty Scholar, Stanford University (2004-2005)
  • 3M Faculty Award, 3M (2004)
  • Best Mentor Award, University Relations of Lucent Technologies (2003)
  • Top 100 young innovators for this century, MIT Technology Review (2003)
  • Zhu Kezhen Distinguished Lecturer, Zhejiang University, Hangzhou city, Zhejiang province, China (2003)
  • Elizabeth Crosby Lecturer, University of Michigan, Department of Material Sciences and Engineering (2002)
  • Team Innovation Award, American Chemical Society (2002)
  • Eastman Lecturer, University of Akron, Department of Polymer Science (2001)
  • Editor's Choice of the "Best of the Best" in new technology, R&D Magazine (2001)
  • R&D 100 Award for the work on Printed Plastic Circuits for Electronic Paper Displays, R&D Magazine (2001)
  • Top 10 Research Breakthroughs for work on large scale integrated circuits based on organic materials, Science Magazine (2000)
  • Top 100 Young Engineers, National Academy of Engineering (2000)

Boards, Advisory Committees, Professional Organizations


  • International Advisory Board, J. Am. Chem. Soc. (2015 - Present)
  • Associate Editor, Chemical Science (2014 - 2016)
  • International Editorial Advisory Board, Materials Horizon (2013 - Present)
  • International Editorial Advisory Board, Advanced Materials (2013 - Present)
  • International Editorial Advisory Board, Nanoscale (2012 - Present)
  • International Editorial Advisory Board, Chemical Communications (2012 - Present)
  • International Editorial Advisory Board, Advanced Energy Materials (2012 - Present)
  • Board of Directors, C3 Nano, Co. (2011 - Present)
  • International Editorial Advisory Board, Nature Asia Materials (2011 - Present)
  • International Editorial Advisory Board, ACS Nano (2011 - Present)
  • International advisory board member, LG Display (2010 - Present)
  • Conference Chair, Gordon Research Conference on Electronic Processes in Organic Materials (2010 - 2010)
  • Board Member, National Academies Board on Chemical Sciences and Technology (2009 - 2012)
  • Executive Committee Member/Member-at-Large, Division of Polymer Materials Science and Engineering, American Chemical Society (2009 - 2012)
  • Associate Editor, Synthetic Metals (2009 - 2011)
  • International Editorial Advisory Board, Chemistry of Materials (2006 - 2011)
  • Scientific Advisory Board Member, Plastic Electronics Foundation (2006 - 2009)
  • Associate Editor, Polymer Review (2004 - 2008)
  • Board of Directors, Material Research Society (MRS) (2003 - 2005)
  • International Editorial Advisory Board, Materials Today (2002 - Present)
  • Meeting chair, Materials Research Society Spring Meeting (2002 - 2002)
  • International Editorial Advisory Board, Advanced Functional Materials (2001 - 2005)
  • Executive Committee Member/Member-at-Large, Division of Polymer Materials Science and Engineering, American Chemical Society (2000 - 2006)

Professional Education


  • PhD, The University of Chicago (1995)

2017-18 Courses


All Publications


  • Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Lei, T., Guan, M., Liu, J., Lin, H., Pfattner, R., Shaw, L., McGuire, A. F., Huang, T., Shao, L., Cheng, K., Tok, J. B., Bao, Z. 2017; 114 (20): 5107-5112

    Abstract

    Increasing performance demands and shorter use lifetimes of consumer electronics have resulted in the rapid growth of electronic waste. Currently, consumer electronics are typically made with nondecomposable, nonbiocompatible, and sometimes even toxic materials, leading to serious ecological challenges worldwide. Here, we report an example of totally disintegrable and biocompatible semiconducting polymers for thin-film transistors. The polymer consists of reversible imine bonds and building blocks that can be easily decomposed under mild acidic conditions. In addition, an ultrathin (800-nm) biodegradable cellulose substrate with high chemical and thermal stability is developed. Coupled with iron electrodes, we have successfully fabricated fully disintegrable and biocompatible polymer transistors. Furthermore, disintegrable and biocompatible pseudo-complementary metal-oxide-semiconductor (CMOS) flexible circuits are demonstrated. These flexible circuits are ultrathin (<1 μm) and ultralightweight (∼2 g/m(2)) with low operating voltage (4 V), yielding potential applications of these disintegrable semiconducting polymers in low-cost, biocompatible, and ultralightweight transient electronics.

    View details for DOI 10.1073/pnas.1701478114

    View details for Web of Science ID 000401314700044

    View details for PubMedID 28461459

  • Separation of Semiconducting Carbon Nanotubes for Flexible and Stretchable Electronics Using Polymer Removable Method ACCOUNTS OF CHEMICAL RESEARCH Lei, T., Pochorovski, I., Bao, Z. 2017; 50 (4): 1096-1104

    Abstract

    Electronics that are soft, conformal, and stretchable are highly desirable for wearable electronics, prosthetics, and robotics. Among the various available electronic materials, single walled carbon nanotubes (SWNTs) and their network have exhibited high mechanical flexibility and stretchability, along with comparable electrical performance to traditional rigid materials, e.g. polysilicon and metal oxides. Unfortunately, SWNTs produced en masse contain a mixture of semiconducting (s-) and metallic (m-) SWNTs, rendering them unsuitable for electronic applications. Moreover, the poor solubility of SWNTs requires the introduction of insulating surfactants to properly disperse them into individual tubes for device fabrication. Compared to other SWNT dispersion and separation methods, e.g., DNA wrapping, density gradient ultracentrifugation, and gel chromatography, polymer wrapping can selectively disperse s-SWNTs with high selectivity (>99.7%), high concentration (>0.1 mg/mL), and high yield (>20%). In addition, this method only requires simple sonication and centrifuge equipment with short processing time down to 1 h. Despite these advantages, the polymer wrapping method still faces two major issues: (i) The purified s-SWNTs usually retain a substantial amount of polymers on their surface even after thorough rinsing. The low conductivity of the residual polymers impedes the charge transport in SWNT networks. (ii) Conjugated polymers used for SWNT wrapping are expensive. Their prices ($100-1000/g) are comparable or even higher than those of SWNTs ($10-300/g). These utilized conjugated polymers represent a large portion of the overall separation cost. In this Account, we summarize recent progresses in polymer design for selective dispersion and separation of SWNTs. We focus particularly on removable and/or recyclable polymers that enable low-cost and scalable separation methods. First, different separation methods are compared to show the advantages of the polymer wrapping methods. In specific, we compare different characterization methods used for purity evaluation. For s-SWNTs with high purity, i.e., >99%, short-channel (smaller than SWNT length) electrical measurement is more reliable than optical methods. Second, possible sorting mechanism and molecular design strategies are discussed. Polymer parameters such as backbone design and side chain engineering affect the polymer-SWNT interactions, leading to different dispersion concentration and selectivity. To address the above-mentioned limiting factors in both polymer contamination and cost issues, we describe two important polymer removal and cycling approaches: (i) changing polymer wrapping conformation to release SWNTs; (ii) depolymerization of conjugated polymer into small molecular units that have less affinity toward SWNTs. These methods allow the removal and recycling of the wrapping polymers, thus providing low-cost and clean s-SWNTs. Third, we discuss various applications of polymer-sorted s-SWNTs, including flexible/stretchable thin-film transistors, thermoelectric devices, and solar cells. In these applications, polymer-sorted s-SWNTs and their networks have exhibited good processability, attractive mechanical properties, and high electrical performance. An increasing number of studies have shown that the removable polymer approaches can completely remove polymer residues in SWNT networks and lead to enhanced charge carrier mobility, higher conductivity, and better heterojunction interface.

    View details for DOI 10.1021/acs.accounts.7b00062

    View details for Web of Science ID 000399859800047

    View details for PubMedID 28358486

  • Highly stretchable polymer semiconductor films through the nanoconfinement effect SCIENCE Xu, J., Wang, S., Wang, G. N., Zhu, C., Luo, S., Jin, L., Gu, X., Chen, S., Feig, V. R., To, J. W., Rondeau-Gagne, S., Park, J., Schroeder, B. C., Lu, C., Oh, J. Y., Wang, Y., Kim, Y., Yan, H., Sinclair, R., Zhou, D., Xue, G., Murmann, B., Linder, C., Cai, W., Tok, J. B., Chung, J. W., Bao, Z. 2017; 355 (6320): 59-?

    Abstract

    Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.

    View details for DOI 10.1126/science.aah4496

    View details for Web of Science ID 000391739900042

    View details for PubMedID 28059762

  • The rise of plastic bioelectronics NATURE Someya, T., Bao, Z., Malliaras, G. G. 2016; 540 (7633): 379-385

    Abstract

    Plastic bioelectronics is a research field that takes advantage of the inherent properties of polymers and soft organic electronics for applications at the interface of biology and electronics. The resulting electronic materials and devices are soft, stretchable and mechanically conformable, which are important qualities for interacting with biological systems in both wearable and implantable devices. Work is currently aimed at improving these devices with a view to making the electronic-biological interface as seamless as possible.

    View details for DOI 10.1038/nature21004

    View details for Web of Science ID 000389716800032

    View details for PubMedID 27974769

  • Intrinsically stretchable and healable semiconducting polymer for organic transistors NATURE Oh, J. Y., Rondeau-Gagne, S., Chiu, Y., Chortos, A., Lissel, F., Wang, G. N., Schroeder, B. C., Kurosawa, T., Lopez, J., Katsumata, T., Xu, J., Zhu, C., Gu, X., Bae, W., Kim, Y., Jin, L., Chung, J. W., Tok, J. B., Bao, Z. 2016; 539 (7629): 411-415

    Abstract

    Thin-film field-effect transistors are essential elements of stretchable electronic devices for wearable electronics. All of the materials and components of such transistors need to be stretchable and mechanically robust. Although there has been recent progress towards stretchable conductors, the realization of stretchable semiconductors has focused mainly on strain-accommodating engineering of materials, or blending of nanofibres or nanowires into elastomers. An alternative approach relies on using semiconductors that are intrinsically stretchable, so that they can be fabricated using standard processing methods. Molecular stretchability can be enhanced when conjugated polymers, containing modified side-chains and segmented backbones, are infused with more flexible molecular building blocks. Here we present a design concept for stretchable semiconducting polymers, which involves introducing chemical moieties to promote dynamic non-covalent crosslinking of the conjugated polymers. These non-covalent crosslinking moieties are able to undergo an energy dissipation mechanism through breakage of bonds when strain is applied, while retaining high charge transport abilities. As a result, our polymer is able to recover its high field-effect mobility performance (more than 1 square centimetre per volt per second) even after a hundred cycles at 100 per cent applied strain. Organic thin-film field-effect transistors fabricated from these materials exhibited mobility as high as 1.3 square centimetres per volt per second and a high on/off current ratio exceeding a million. The field-effect mobility remained as high as 1.12 square centimetres per volt per second at 100 per cent strain along the direction perpendicular to the strain. The field-effect mobility of damaged devices can be almost fully recovered after a solvent and thermal healing treatment. Finally, we successfully fabricated a skin-inspired stretchable organic transistor operating under deformations that might be expected in a wearable device.

    View details for DOI 10.1038/nature20102

    View details for Web of Science ID 000388161700050

    View details for PubMedID 27853213

  • Skin-inspired organic electronic materials and devices MRS BULLETIN Bao, Z. 2016; 41 (11): 897-902
  • Pursuing prosthetic electronic skin. Nature materials Chortos, A., Liu, J., Bao, Z. 2016; 15 (9): 937-950

    Abstract

    Skin plays an important role in mediating our interactions with the world. Recreating the properties of skin using electronic devices could have profound implications for prosthetics and medicine. The pursuit of artificial skin has inspired innovations in materials to imitate skin's unique characteristics, including mechanical durability and stretchability, biodegradability, and the ability to measure a diversity of complex sensations over large areas. New materials and fabrication strategies are being developed to make mechanically compliant and multifunctional skin-like electronics, and improve brain/machine interfaces that enable transmission of the skin's signals into the body. This Review will cover materials and devices designed for mimicking the skin's ability to sense and generate biomimetic signals.

    View details for DOI 10.1038/nmat4671

    View details for PubMedID 27376685

  • A highly stretchable autonomous self-healing elastomer NATURE CHEMISTRY Li, C., Wang, C., Keplinger, C., Zuo, J., Jin, L., Sun, Y., Zheng, P., Cao, Y., Lissel, F., Linder, C., You, X., Bao, Z. 2016; 8 (6): 619-625

    View details for DOI 10.1038/NCHEM.2492

    View details for Web of Science ID 000376529000020

  • Stretchable Self-Healing Polymeric Dielectrics Cross-Linked Through Metal-Ligand Coordination JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Rao, Y., Chortos, A., Pfattner, R., Lissel, F., Chiu, Y., Feig, V., Xu, J., Kurosawa, T., Gu, X., Wang, C., He, M., Chung, J. W., Bao, Z. 2016; 138 (18): 6020-6027

    Abstract

    A self-healing dielectric elastomer is achieved by the incorporation of metal-ligand coordination as cross-linking sites in nonpolar polydimethylsiloxane (PDMS) polymers. The ligand is 2,2'-bipyridine-5,5'-dicarboxylic amide, while the metal salts investigated here are Fe(2+) and Zn(2+) with various counteranions. The kinetically labile coordination between Zn(2+) and bipyridine endows the polymer fast self-healing ability at ambient condition. When integrated into organic field-effect transistors (OFETs) as gate dielectrics, transistors with FeCl2 and ZnCl2 salts cross-linked PDMS exhibited increased dielectric constants compared to PDMS and demonstrated hysteresis-free transfer characteristics, owing to the low ion conductivity in PDMS and the strong columbic interaction between metal cations and the small Cl(-) anions which can prevent mobile anions drifting under gate bias. Fully stretchable transistors with FeCl2-PDMS dielectrics were fabricated and exhibited ideal transfer characteristics. The gate leakage current remained low even after 1000 cycles at 100% strain. The mechanical robustness and stable electrical performance proved its suitability for applications in stretchable electronics. On the other hand, transistors with gate dielectrics containing large-sized anions (BF4(-), ClO4(-), CF3SO3(-)) displayed prominent hysteresis due to mobile anions drifting under gate bias voltage. This work provides insights on future design of self-healing stretchable dielectric materials based on metal-ligand cross-linked polymers.

    View details for DOI 10.1021/jacs.6b02428

    View details for Web of Science ID 000375889100044

    View details for PubMedID 27099162

  • Hierarchical N-Doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor JOURNAL OF THE AMERICAN CHEMICAL SOCIETY To, J. W., He, J., Mei, J., Haghpanah, R., Chen, Z., Kurosawa, T., Chen, S., Bae, W., Pan, L., Tok, J. B., Wilcox, J., Bao, Z. 2016; 138 (3): 1001-1009

    Abstract

    Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry's law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultrasmall pores (d < 0.5 nm) and preservation of nitrogen moieties, essential for enhanced CO2 affinity. Furthermore, our described work provides a strategy to initiate developments of rationally designed porous conjugated polymer structures and carbon-based materials for various potential applications.

    View details for DOI 10.1021/jacs.5b11955

    View details for Web of Science ID 000369044400047

    View details for PubMedID 26717034

  • Removable and Recyclable Conjugated Polymers for Highly Selective and High-Yield Dispersion and Release of Low-Cost Carbon Nanotubes. Journal of the American Chemical Society Lei, T., Chen, X., Pitner, G., Wong, H. P., Bao, Z. 2016; 138 (3): 802-805

    Abstract

    High-purity semiconducting single-walled carbon nanotubes (s-SWNTs) with little contamination are desired for high-performance electronic devices. Although conjugated polymer wrapping has been demonstrated as a powerful and scalable strategy for enriching s-SWNTs, this approach suffers from significant contaminations by polymer residues and high cost of conjugated polymers. Here, we present a simple but general approach using removable and recoverable conjugated polymers for separating s-SWNTs with little polymer contamination. A conjugated polymer with imine linkages was synthesized to demonstrate this concept. Moreover, the SWNTs used are without prepurifications and very low cost. The polymer exhibits strong dispersion for large-diameter s-SWNTs with high yield (23.7%) and high selectivity (99.7%). After s-SWNT separation, the polymer can be depolymerized into monomers and be cleanly removed under mild acidic conditions, yielding polymer-free s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize polymer. This approach enables isolation of "clean" s-SWNTs and, at the same time, greatly lowers costs for SWNT separation.

    View details for DOI 10.1021/jacs.5b12797

    View details for PubMedID 26731376

  • Fast and reversible thermoresponsive polymer switching materials for safer batteries NATURE ENERGY Chen, Z., Hsu, P., Lopez, J., Li, Y., To, J. W., Liu, N., Wang, C., Andrews, S. C., Liu, J., Cui, Y., Bao, Z. 2016; 1
  • Ultrahigh electrical conductivity in solution-sheared polymeric transparent films. Proceedings of the National Academy of Sciences of the United States of America Worfolk, B. J., Andrews, S. C., Park, S., Reinspach, J., Liu, N., Toney, M. F., Mannsfeld, S. C., Bao, Z. 2015; 112 (46): 14138-14143

    Abstract

    With consumer electronics transitioning toward flexible products, there is a growing need for high-performance, mechanically robust, and inexpensive transparent conductors (TCs) for optoelectronic device integration. Herein, we report the scalable fabrication of highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PSS) thin films via solution shearing. Specific control over deposition conditions allows for tunable phase separation and preferential PEDOT backbone alignment, resulting in record-high electrical conductivities of 4,600 ± 100 S/cm while maintaining high optical transparency. High-performance solution-sheared TC PEDOT:PSS films were used as patterned electrodes in capacitive touch sensors and organic photovoltaics to demonstrate practical viability in optoelectronic applications.

    View details for DOI 10.1073/pnas.1509958112

    View details for PubMedID 26515096

    View details for PubMedCentralID PMC4655535

  • A skin-inspired organic digital mechanoreceptor SCIENCE Tee, B. C., Chortos, A., Berndt, A., Nguyen, A. K., Tom, A., McGuire, A., Lin, Z. C., Tien, K., Bae, W., Wang, H., Mei, P., Chou, H., Cui, B., Deisseroth, K., Ng, T. N., Bao, Z. 2015; 350 (6258): 313-?

    View details for DOI 10.1126/science.aaa9306

    View details for Web of Science ID 000362838700039

    View details for PubMedID 26472906

  • Flow-enhanced solution printing of all-polymer solar cells NATURE COMMUNICATIONS Diao, Y., Zhou, Y., Kurosawa, T., Shaw, L., Wang, C., Park, S., Guo, Y., Reinspach, J. A., Gu, K., Gu, X., Tee, B. C., Pang, C., Yan, H., Zhao, D., Toney, M. F., Mannsfeld, S. C., Bao, Z. 2015; 6

    View details for DOI 10.1038/ncomms8955

    View details for Web of Science ID 000360346700010

  • A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing NATURE COMMUNICATIONS Chou, H., Nguyen, A., Chortos, A., To, J. W., Lu, C., Mei, J., Kurosawa, T., Bae, W., Tok, J. B., Bao, Z. 2015; 6

    View details for DOI 10.1038/ncomms9011

    View details for Web of Science ID 000360351600003

  • Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework ACS CENTRAL SCIENCE To, J. W., Chen, Z., Yao, H., He, J., Kim, K., Chou, H., Pan, L., Wilcox, J., Cui, Y., Bao, Z. 2015; 1 (2): 68-76
  • H-Bonded Supramolecular Polymer for the Selective Dispersion and Subsequent Release of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Pochorovski, I., Wang, H., Feldblyum, J. I., Zhang, X., Antaris, A. L., Bao, Z. 2015; 137 (13): 4328-4331

    Abstract

    Semiconducting, single-walled carbon nanotubes (SWNTs) are promising candidates for applications in thin-film transistors, solar cells, and biological imaging. To harness their full potential, however, it is necessary to separate the semiconducting from the metallic SWNTs present in the as-synthesized SWNT mixture. While various polymers are able to selectively disperse semiconducting SWNTs, the subsequent removal of the polymer is challenging. However, many applications require semiconducting SWNTs in their pure form. Toward this goal, we have designed a 2-ureido-6[1H]-pyrimidinone (UPy)-based H-bonded supramolecular polymer that can selectively disperse semiconducting SWNTs. The dispersion purity is inversely related to the dispersion yield. In contrast to conventional polymers, the polymer described herein was shown to disassemble into monomeric units upon addition of an H-bond-disrupting agent, enabling isolation of dispersant-free, semiconducting SWNTs.

    View details for DOI 10.1021/jacs.5b01704

    View details for Web of Science ID 000352752000014

    View details for PubMedID 25815604

  • Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care NATURE COMMUNICATIONS Chen, L. Y., Tee, B. C., Chortos, A. L., Schwartz, G., Tse, V., Lipomi, D. J., Wong, H. P., McConnell, M. V., Bao, Z. 2014; 5

    View details for DOI 10.1038/ncomms6028

    View details for Web of Science ID 000343935600001

  • Skin-inspired electronic devices MATERIALS TODAY Chortos, A., Bao, Z. 2014; 17 (7): 321-331
  • Semiconducting polymer nanoparticles as photoacoustic molecular imaging probes in living mice. Nature nanotechnology Pu, K., Shuhendler, A. J., Jokerst, J. V., Mei, J., Gambhir, S. S., Bao, Z., Rao, J. 2014; 9 (3): 233-239

    Abstract

    Photoacoustic imaging holds great promise for the visualization of physiology and pathology at the molecular level with deep tissue penetration and fine spatial resolution. To fully utilize this potential, photoacoustic molecular imaging probes have to be developed. Here, we introduce near-infrared light absorbing semiconducting polymer nanoparticles as a new class of contrast agents for photoacoustic molecular imaging. These nanoparticles can produce a stronger signal than the commonly used single-walled carbon nanotubes and gold nanorods on a per mass basis, permitting whole-body lymph-node photoacoustic mapping in living mice at a low systemic injection mass. Furthermore, the semiconducting polymer nanoparticles possess high structural flexibility, narrow photoacoustic spectral profiles and strong resistance to photodegradation and oxidation, enabling the development of the first near-infrared ratiometric photoacoustic probe for in vivo real-time imaging of reactive oxygen species-vital chemical mediators of many diseases. These results demonstrate semiconducting polymer nanoparticles to be an ideal nanoplatform for developing photoacoustic molecular probes.

    View details for DOI 10.1038/nnano.2013.302

    View details for PubMedID 24463363

  • Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method. Nature communications Yuan, Y., Giri, G., Ayzner, A. L., Zoombelt, A. P., Mannsfeld, S. C., Chen, J., Nordlund, D., Toney, M. F., Huang, J., Bao, Z. 2014; 5: 3005-?

    Abstract

    Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.

    View details for DOI 10.1038/ncomms4005

    View details for PubMedID 24398476

  • An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film. Nature communications Pan, L., Chortos, A., Yu, G., Wang, Y., Isaacson, S., Allen, R., Shi, Y., Dauskardt, R., Bao, Z. 2014; 5: 3002-?

    View details for DOI 10.1038/ncomms4002

    View details for PubMedID 24389734

  • Highly stable organic polymer field-effect transistor sensor for selective detection in the marine environment. Nature communications Knopfmacher, O., Hammock, M. L., Appleton, A. L., Schwartz, G., Mei, J., Lei, T., Pei, J., Bao, Z. 2014; 5: 2954-?

    Abstract

    In recent decades, the susceptibility to degradation in both ambient and aqueous environments has prevented organic electronics from gaining rapid traction for sensing applications. Here we report an organic field-effect transistor sensor that overcomes this barrier using a solution-processable isoindigo-based polymer semiconductor. More importantly, these organic field-effect transistor sensors are stable in both freshwater and seawater environments over extended periods of time. The organic field-effect transistor sensors are further capable of selectively sensing heavy-metal ions in seawater. This discovery has potential for inexpensive, ink-jet printed, and large-scale environmental monitoring devices that can be deployed in areas once thought of as beyond the scope of organic materials.

    View details for DOI 10.1038/ncomms3954

    View details for PubMedID 24389531

  • Selective metal deposition at graphene line defects by atomic layer deposition. Nature communications Kim, K., Lee, H., Johnson, R. W., Tanskanen, J. T., Liu, N., Kim, M., Pang, C., Ahn, C., Bent, S. F., Bao, Z. 2014; 5: 4781-?

    Abstract

    One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene's line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphene's grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt-graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively.

    View details for DOI 10.1038/ncomms5781

    View details for PubMedID 25179368

  • One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films. Nature communications Giri, G., Li, R., Smilgies, D., Li, E. Q., Diao, Y., Lenn, K. M., Chiu, M., Lin, D. W., Allen, R., Reinspach, J., Mannsfeld, S. C., Thoroddsen, S. T., Clancy, P., Bao, Z., Amassian, A. 2014; 5: 3573-?

    View details for DOI 10.1038/ncomms4573

    View details for PubMedID 24736391

  • Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries NATURE CHEMISTRY Wang, C., Wu, H., Chen, Z., McDowell, M. T., Cui, Y., Bao, Z. 2013; 5 (12): 1043-1049

    View details for DOI 10.1038/NCHEM.1802

    View details for Web of Science ID 000327450500014

  • Stretchable and self-healing polymers and devices for electronic skin PROGRESS IN POLYMER SCIENCE Benight, S. J., Wang, C., Tok, J. B., Bao, Z. 2013; 38 (12): 1961-1977
  • 25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress ADVANCED MATERIALS Hammock, M. L., Chortos, A., Tee, B. C., Tok, J. B., Bao, Z. 2013; 25 (42): 5997-6037
  • Direct growth of aligned graphitic nanoribbons from a DNA template by chemical vapour deposition. Nature communications Sokolov, A. N., Yap, F. L., Liu, N., Kim, K., Ci, L., Johnson, O. B., Wang, H., Vosgueritchian, M., Koh, A. L., Chen, J., Park, J., Bao, Z. 2013; 4: 2402-?

    View details for DOI 10.1038/ncomms3402

    View details for PubMedID 23989553

  • Effects of Odd-Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Akkerman, H. B., Mannsfeld, S. C., Kaushik, A. P., Verploegen, E., Burnier, L., Zoombelt, A. P., Saathoff, J. D., Hong, S., Atahan-Evrenk, S., Liu, X., Aspuru-Guzik, A., Toney, M. F., Clancy, P., Bao, Z. 2013; 135 (30): 11006-11014

    Abstract

    Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5'bis(4-alkylphenyl)-2,2'-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling.

    View details for DOI 10.1021/ja400015e

    View details for Web of Science ID 000322752900031

    View details for PubMedID 23822850

  • Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nature materials Diao, Y., Tee, B. C., Giri, G., Xu, J., Kim, D. H., Becerril, H. A., Stoltenberg, R. M., Lee, T. H., Xue, G., Mannsfeld, S. C., Bao, Z. 2013; 12 (7): 665-671

    Abstract

    Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach-termed fluid-enhanced crystal engineering (FLUENCE)-that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm(2) V(-1) s(-1) and 11 cm(2) V(-1) s(-1). FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics.

    View details for DOI 10.1038/nmat3650

    View details for PubMedID 23727951

  • Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. Nature communications Wu, H., Yu, G., Pan, L., Liu, N., McDowell, M. T., Bao, Z., Cui, Y. 2013; 4: 1943-?

    View details for DOI 10.1038/ncomms2941

    View details for PubMedID 23733138

  • Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mei, J., Diao, Y., Appleton, A. L., Fang, L., Bao, Z. 2013; 135 (18): 6724-6746

    Abstract

    The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm(2)/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.

    View details for DOI 10.1021/ja400881n

    View details for Web of Science ID 000318839300001

    View details for PubMedID 23557391

  • Flexible Wireless Temperature Sensors Based on Ni Microparticle-Filled Binary Polymer Composites ADVANCED MATERIALS Jeon, J., Lee, H., Bao, Z. 2013; 25 (6): 850-855

    View details for DOI 10.1002/adma.201204082

    View details for Web of Science ID 000314653300006

    View details for PubMedID 23233317

  • Stable Li-ion Battery Anodes by In-situ Polymerization of Conducting Hydrogel to Conformally Coat Silicon Nanoparticles Nature Comm. Wu, H., Yu, G., Pan, L., Liu, N., McDowell, M., T., Bao, Z. 2013; 4: 1943

    View details for DOI 10.1038/ncomms2941

  • Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring. Nature communications Schwartz, G., Tee, B. C., Mei, J., Appleton, A. L., Kim, D. H., Wang, H., Bao, Z. 2013; 4: 1859-?

    Abstract

    Flexible pressure sensors are essential parts of an electronic skin to allow future biomedical prostheses and robots to naturally interact with humans and the environment. Mobile biomonitoring in long-term medical diagnostics is another attractive application for these sensors. Here we report the fabrication of flexible pressure-sensitive organic thin film transistors with a maximum sensitivity of 8.4 kPa(-1), a fast response time of <10 ms, high stability over >15,000 cycles and a low power consumption of <1 mW. The combination of a microstructured polydimethylsiloxane dielectric and the high-mobility semiconducting polyisoindigobithiophene-siloxane in a monolithic transistor design enabled us to operate the devices in the subthreshold regime, where the capacitance change upon compression of the dielectric is strongly amplified. We demonstrate that our sensors can be used for non-invasive, high fidelity, continuous radial artery pulse wave monitoring, which may lead to the use of flexible pressure sensors in mobile health monitoring and remote diagnostics in cardiovascular medicine.

    View details for DOI 10.1038/ncomms2832

    View details for PubMedID 23673644

  • Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains Nature Materials Diao, Y., Tee, B., C-K., Giri, G., Xu, J., Kim, D., H., Becerril, H., A., Bao, Z. 2013; 12: 665-671

    View details for DOI 10.1038/nmat3650

  • Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring Nature Comm. Schwartz, G., Tee, B., C-K., Mei, J., Appleton, A., L., Kim, H., D, Wang, H., Bao, Z. 2013; 4: 1859

    View details for DOI 10.1038/ncomms2832

  • An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film Nature Comm. Pan, L., Chortos, A., Yu, G., Wang, Y., Isaacson, S., Allen, R., Bao, Z. 2013
  • A Flexible Bimodal Sensor Array for Simultaneous Sensing of Pressure and Temperature Adv. Mater. Tien, N., T., Jeon, S., Kim, D., I., Trung, T., Q., Jang, M., Hwang, B., U., Bao, Z. 2013
  • Stretchable LEDs: Light-emitting electronic skin Nature Photonics Vosgueritchian, M., Tok, J., B.-H., Bao, Z. 2013; 7: 769-771
  • Direct Growth of Aligned Graphitic Nanoribbons from a DNA Template by Chemical Vapour Deposition Nature Comm. Sokolov, A., N., Yap, F., L., Liu, L., Kim, K., Ci, L., Johnson, O., B., Bao, Z. 2013; 4: 2402
  • 25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress Adv. Mat. Hammock, M., L., Chortos, A., Tee, B., C-K., Tok, J., B.-H., Bao, Z. 2013; 25: 5997-6038
  • Ultra-High Mobility Transparent Organic Thin Film Transistors Via an Off-Center Spin-Coating Method Nature Comm. Yuan, Y., Giri, G., Ayzner, A., L., Zoombelt, A., P., Mannsfeld, S., C.B., Chen, J., Bao, Z. 2013
  • Highly stable organic polymer field-effect transistor sensor for selective detection in the marine environment Nature Comm. Knopfmacher, O., Hammock, M., L., Appleton, A., L., Schwartz, G., Mei, J., Lei, T., Bao, Z. 2013
  • An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications NATURE NANOTECHNOLOGY Tee, B. C., Wang, C., Allen, R., Bao, Z. 2012; 7 (12): 825-832

    Abstract

    Pressure sensitivity and mechanical self-healing are two vital functions of the human skin. A flexible and electrically conducting material that can sense mechanical forces and yet be able to self-heal repeatably can be of use in emerging fields such as soft robotics and biomimetic prostheses, but combining all these properties together remains a challenging task. Here, we describe a composite material composed of a supramolecular organic polymer with embedded nickel nanostructured microparticles, which shows mechanical and electrical self-healing properties at ambient conditions. We also show that our material is pressure- and flexion-sensitive, and therefore suitable for electronic skin applications. The electrical conductivity can be tuned by varying the amount of nickel particles and can reach values as high as 40 S cm(-1). On rupture, the initial conductivity is repeatably restored with ∼90% efficiency after 15 s healing time, and the mechanical properties are completely restored after ∼10 min. The composite resistance varies inversely with applied flexion and tactile forces. These results demonstrate that natural skin's repeatable self-healing capability can be mimicked in conductive and piezoresistive materials, thus potentially expanding the scope of applications of current electronic skin systems.

    View details for DOI 10.1038/NNANO.2012.192

    View details for Web of Science ID 000312003700019

    View details for PubMedID 23142944

  • Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Pan, L., Yu, G., Zhai, D., Lee, H. R., Zhao, W., Liu, N., Wang, H., Tee, B. C., Shi, Y., Cui, Y., Bao, Z. 2012; 109 (24): 9287-9292

    Abstract

    Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (~480 F·g(-1)), unprecedented rate capability, and cycling stability (~83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (~0.3 s) and superior sensitivity (~16.7 μA · mM(-1)). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.

    View details for DOI 10.1073/pnas.1202636109

    View details for Web of Science ID 000305511300024

    View details for PubMedID 22645374

  • 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium Iodide as a New Air-Stable n-Type Dopant for Vacuum-Processed Organic Semiconductor Thin Films JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wei, P., Menke, T., Naab, B. D., Leo, K., Riede, M., Bao, Z. 2012; 134 (9): 3999-4002

    Abstract

    2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I) was synthesized and employed as a strong n-type dopant for fullerene C(60), a well-known n-channel semiconductor. The coevaporated thin films showed a maximum conductivity of 5.5 S/cm at a doping concentration of 8.0 wt% (14 mol%), which is the highest value reported to date for molecular n-type conductors. o-MeO-DMBI-I can be stored and handled in air for extended periods without degradation and is thus promising for various organic electronic devices.

    View details for DOI 10.1021/ja211382x

    View details for Web of Science ID 000301550800018

    View details for PubMedID 22324847

  • Chemical and Engineering Approaches To Enable Organic Field-Effect Transistors for Electronic Skin Applications ACCOUNTS OF CHEMICAL RESEARCH Sokolov, A. N., Tee, B. C., Bettinger, C. J., Tok, J. B., Bao, Z. 2012; 45 (3): 361-371

    Abstract

    Skin is the body's largest organ and is responsible for the transduction of a vast amount of information. This conformable material simultaneously collects signals from external stimuli that translate into information such as pressure, pain, and temperature. The development of an electronic material, inspired by the complexity of this organ is a tremendous, unrealized engineering challenge. However, the advent of carbon-based electronics may offer a potential solution to this long-standing problem. In this Account, we describe the use of an organic field-effect transistor (OFET) architecture to transduce mechanical and chemical stimuli into electrical signals. In developing this mimic of human skin, we thought of the sensory elements of the OFET as analogous to the various layers and constituents of skin. In this fashion, each layer of the OFET can be optimized to carry out a specific recognition function. The separation of multimodal sensing among the components of the OFET may be considered a "divide and conquer" approach, where the electronic skin (e-skin) can take advantage of the optimized chemistry and materials properties of each layer. This design of a novel microstructured gate dielectric has led to unprecedented sensitivity for tactile pressure events. Typically, pressure-sensitive components within electronic configurations have suffered from a lack of sensitivity or long mechanical relaxation times often associated with elastomeric materials. Within our method, these components are directly compatible with OFETs and have achieved the highest reported sensitivity to date. Moreover, the tactile sensors operate on a time scale comparable with human skin, making them ideal candidates for integration as synthetic skin devices. The methodology is compatible with large-scale fabrication and employs simple, commercially available elastomers. The design of materials within the semiconductor layer has led to the incorporation of selectivity and sensitivity within gas-sensing devices and has enabled stable sensor operation within aqueous media. Furthermore, careful tuning of the chemical composition of the dielectric layer has provided a means to operate the sensor in real time within an aqueous environment and without the need for encapsulation layers. The integration of such devices as electronic mimics of skin will require the incorporation of biocompatible or biodegradable components. Toward this goal, OFETs may be fabricated with >99% biodegradable components by weight, and the devices are robust and stable, even in aqueous environments. Collectively, progress to date suggests that OFETs may be integrated within a single substrate to function as an electronic mimic of human skin, which could enable a large range of sensing-related applications from novel prosthetics to robotic surgery.

    View details for DOI 10.1021/ar2001233

    View details for Web of Science ID 000302033000005

    View details for PubMedID 21995646

  • Tuning charge transport in solution-sheared organic semiconductors using lattice strain NATURE Giri, G., Verploegen, E., Mannsfeld, S. C., Atahan-Evrenk, S., Kim, D. H., Lee, S. Y., Becerril, H. A., Aspuru-Guzik, A., Toney, M. F., Bao, Z. 2011; 480 (7378): 504-U124

    Abstract

    Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π-π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π-π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 Å to 3.08 Å. We believe that 3.08 Å is the shortest π-π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π-π distance of 3.04 Å has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm(2) V(-1) s(-1) for unstrained films to a high mobility of 4.6 cm(2) V(-1) s(-1) for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.

    View details for DOI 10.1038/nature10683

    View details for Web of Science ID 000298318000056

    View details for PubMedID 22193105

  • Siloxane-Terminated Solubilizing Side Chains: Bringing Conjugated Polymer Backbones Closer and Boosting Hole Mobilities in Thin-Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mei, J., Kim, D. H., Ayzner, A. L., Toney, M. F., Bao, Z. 2011; 133 (50): 20130-20133

    Abstract

    We introduce a novel siloxane-terminated solubilizing group and demonstrate its effectiveness as a side chain in an isoindigo-based conjugated polymer. An average hole mobility of 2.00 cm(2) V(-1) s(-1) (with a maximum mobility of 2.48 cm(2) V(-1) s(-1)), was obtained from solution-processed thin-film transistors, one of the highest mobilities reported to date. In contrast, the reference polymer with a branched alkyl side chain gave an average hole mobility of 0.30 cm(2) V(-1) s(-1) and a maximum mobility of 0.57 cm(2) V(-1) s(-1). This is largely explained by the polymer packing: our new polymer exhibited a π-π stacking distance of 3.58 Å, while the reference polymer showed a distance of 3.76 Å.

    View details for DOI 10.1021/ja209328m

    View details for Web of Science ID 000298713600028

    View details for PubMedID 22122218

  • Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes NATURE NANOTECHNOLOGY Lipomi, D. J., Vosgueritchian, M., Tee, B. C., Hellstrom, S. L., Lee, J. A., Fox, C. H., Bao, Z. 2011; 6 (12): 788-792

    Abstract

    Transparent, elastic conductors are essential components of electronic and optoelectronic devices that facilitate human interaction and biofeedback, such as interactive electronics, implantable medical devices and robotic systems with human-like sensing capabilities. The availability of conducting thin films with these properties could lead to the development of skin-like sensors that stretch reversibly, sense pressure (not just touch), bend into hairpin turns, integrate with collapsible, stretchable and mechanically robust displays and solar cells, and also wrap around non-planar and biological surfaces such as skin and organs, without wrinkling. We report transparent, conducting spray-deposited films of single-walled carbon nanotubes that can be rendered stretchable by applying strain along each axis, and then releasing this strain. This process produces spring-like structures in the nanotubes that accommodate strains of up to 150% and demonstrate conductivities as high as 2,200 S cm(-1) in the stretched state. We also use the nanotube films as electrodes in arrays of transparent, stretchable capacitors, which behave as pressure and strain sensors.

    View details for DOI 10.1038/NNANO.2011.184

    View details for Web of Science ID 000298248300011

    View details for PubMedID 22020121

  • Selective dispersion of high purity semiconducting single-walled carbon nanotubes with regioregular poly(3-alkylthiophene)s NATURE COMMUNICATIONS Lee, H. W., Yoon, Y., Park, S., Oh, J. H., Hong, S., Liyanage, L. S., Wang, H., Morishita, S., Patil, N., Park, Y. J., Park, J. J., Spakowitz, A., Galli, G., Gygi, F., Wong, P. H., Tok, J. B., Kim, J. M., Bao, Z. 2011; 2

    Abstract

    Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around SWNTs. However, no sorting of sc-SWNTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-SWNTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-SWNTs. Our approach enables direct film preparation after a simple centrifugation step. Using the sorted sc-SWNTs, we fabricate high-performance SWNT network transistors with observed charge-carrier mobility as high as 12 cm(2) V(-1) s(-1) and on/off ratio of >10(6). Our method offers a facile and a scalable route for separating sc-SWNTs and fabrication of electronic devices.

    View details for DOI 10.1038/ncomms1545

    View details for Web of Science ID 000297686500028

    View details for PubMedID 22086341

  • 3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ko, S., Verploegen, E., Hong, S., Mondal, R., Hoke, E. T., Toney, M. F., McGehee, M. D., Bao, Z. 2011; 133 (42): 16722-16725

    Abstract

    We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.

    View details for DOI 10.1021/ja207429s

    View details for Web of Science ID 000296678200004

    View details for PubMedID 21970371

  • From computational discovery to experimental characterization of a high hole mobility organic crystal NATURE COMMUNICATIONS Sokolov, A. N., Atahan-Evrenk, S., Mondal, R., Akkerman, H. B., Sanchez-Carrera, R. S., Granados-Focil, S., Schrier, J., Mannsfeld, S. C., Zoombelt, A. P., Bao, Z., Aspuru-Guzik, A. 2011; 2

    Abstract

    For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm(2) V(-1) s(-1), respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm(2) V(-1) s(-1) reported to date.

    View details for DOI 10.1038/ncomms1451

    View details for Web of Science ID 000294806500030

    View details for PubMedID 21847111

  • Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers NATURE MATERIALS Mannsfeld, S. C., Tee, B. C., Stoltenberg, R. M., Chen, C. V., Barman, S., Muir, B. V., Sokolov, A. N., Reese, C., Bao, Z. 2010; 9 (10): 859-864

    Abstract

    The development of an electronic skin is critical to the realization of artificial intelligence that comes into direct contact with humans, and to biomedical applications such as prosthetic skin. To mimic the tactile sensing properties of natural skin, large arrays of pixel pressure sensors on a flexible and stretchable substrate are required. We demonstrate flexible, capacitive pressure sensors with unprecedented sensitivity and very short response times that can be inexpensively fabricated over large areas by microstructuring of thin films of the biocompatible elastomer polydimethylsiloxane. The pressure sensitivity of the microstructured films far surpassed that exhibited by unstructured elastomeric films of similar thickness, and is tunable by using different microstructures. The microstructured films were integrated into organic field-effect transistors as the dielectric layer, forming a new type of active sensor device with similarly excellent sensitivity and response times.

    View details for DOI 10.1038/nmat2834

    View details for Web of Science ID 000282134700025

    View details for PubMedID 20835231

  • Water-stable organic transistors and their application in chemical and biological sensors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Roberts, M. E., Mannsfeld, S. C., Queralto, N., Reese, C., Locklin, J., Knoll, W., Bao, Z. 2008; 105 (34): 12134-12139

    Abstract

    The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

    View details for DOI 10.1073/pnas.0802105105

    View details for Web of Science ID 000258905700009

    View details for PubMedID 18711145

  • Self-sorted, aligned nanotube networks for thin-film transistors SCIENCE LeMieux, M. C., Roberts, M., Barman, S., Jin, Y. W., Kim, J. M., Bao, Z. 2008; 321 (5885): 101-104

    Abstract

    To find use in electronics, single-walled carbon nanotubes need to be efficiently separated by electronic type and aligned to ensure optimal and reproducible electronic properties. We report the fabrication of single-walled carbon nanotube (SWNT) network field-effect transistors, deposited from solution, possessing controllable topology and an on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs are tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network in which nanotube chirality separation and simultaneous control of density and alignment occur in one step during device fabrication. Micro-Raman experiments corroborate device results as a function of surface chemistry, indicating enrichment of the specific SWNT electronic type absorbed onto the modified dielectric.

    View details for DOI 10.1126/science.1156588

    View details for Web of Science ID 000257320800045

    View details for PubMedID 18599781

  • Soluble regioregular polythiophene derivatives as semiconducting materials for field-effect transistors CHEMISTRY OF MATERIALS Bao, Z. N., Lovinger, A. J. 1999; 11 (9): 2607-2612
  • Lithium Metal Anodes with an Adaptive "Solid-Liquid" Interfacial Protective Layer JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, K., Pei, A., Lee, H. R., Kong, B., Liu, N., Lin, D., Liu, Y., Liu, C., Hsu, P., Bao, Z., Cui, Y. 2017; 139 (13): 4815-4820

    Abstract

    Lithium metal is an attractive anode for the next generation of high energy density lithium-ion batteries due to its high specific capacity (3,860 mAh g(-1)) and lowest overall anode potential. However, the key issue is that the static solid electrolyte interphase cannot match the dynamic volume changes of the Li anode, resulting in side reactions, dendrite growth, and poor electrodeposition behavior, which prevent its practical applications. Here, we show that the "solid-liquid" hybrid behavior of a dynamically cross-linked polymer enables its use as an excellent adaptive interfacial layer for Li metal anodes. The dynamic polymer can reversibly switch between its "liquid" and "solid" properties in response to the rate of lithium growth to provide uniform surface coverage and dendrite suppression, respectively, thereby enabling the stable operation of lithium metal electrodes. We believe that this example of engineering an adaptive Li/electrolyte interface brings about a new and promising way to address the intrinsic problems of lithium metal anodes.

    View details for DOI 10.1021/jacs.6b13314

    View details for Web of Science ID 000398764000034

    View details for PubMedID 28303712

  • Characterization and Understanding of Thermoresponsive Polymer Composites Based on Spiky Nanostructured Fillers ADVANCED ELECTRONIC MATERIALS Chen, Z., Pfattner, R., Bao, Z. 2017; 3 (1)
  • Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing ORGANIC ELECTRONICS Gu, K. L., Zhou, Y., Gu, X., Yan, H., Diao, Y., Kurosawa, T., Ganapathysubramanian, B., Toney, M. E., Bao, Z. 2017; 40: 79-87
  • High-Performance Lithium Metal Negative Electrode with a Soft and Flowable Polymer Coating ACS ENERGY LETTERS Zheng, G., Wang, C., Pei, A., Lopez, J., Shi, F., Chen, Z., Sendek, A. D., Lee, H., Lu, Z., Schneider, H., Safont-Sempere, M. M., Chu, S., Bao, Z., Cui, Y. 2016; 1 (6): 1247-1255
  • Comparison of the Morphology Development of Polymer-Fullerene and Polymer-Polymer Solar Cells during Solution-Shearing Blade Coating ADVANCED ENERGY MATERIALS Gu, X., Yan, H., Kurosawa, T., Schroeder, B. C., Gu, K. L., Zhou, Y., To, J. W., Oosterhout, S. D., Savikhin, V., Molina-Lopez, F., Tassone, C. J., Mannsfeld, S. C., Wang, C., Toney, M. F., Bao, Z. 2016; 6 (22)
  • Inducing Elasticity through Oligo-Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers ADVANCED FUNCTIONAL MATERIALS Wang, G. N., Shaw, L., Xu, J., Kurosawa, T., Schroeder, B. C., Oh, J. Y., Benight, S. J., Bao, Z. 2016; 26 (40): 7254-7262
  • A Stiff and Healable Polymer Based on Dynamic-Covalent Boroxine Bonds ADVANCED MATERIALS Lai, J., Mei, J., Jia, X., Li, C., You, X., Bao, Z. 2016; 28 (37): 8277-8282

    Abstract

    A stiff and healable polymer is obtained by using the dynamic-covalent boroxine bond to crosslink PDMS chain into 3D networks. The as-prepared polymer is very strong and stiff, and can bear a load of more than 450 times its weight. When damaged, it can be completely healed upon heating after wetting.

    View details for DOI 10.1002/adma.201602332

    View details for Web of Science ID 000386103600024

    View details for PubMedID 27387198

  • A Highly Stretchable and Autonomous Self-Healing Polymer Based on Combination of Pt center dot center dot center dot Pt and pi-pi Interactions MACROMOLECULAR RAPID COMMUNICATIONS Mei, J., Jia, X., Lai, J., Sun, Y., Li, C., Wu, J., Cao, Y., You, X., Bao, Z. 2016; 37 (20): 1667-1675
  • Investigation of a Solution-Processable, Nonspecific Surface Modifier for Low Cost, High Work Function Electrodes. ACS applied materials & interfaces Hinckley, A. C., Wang, C., Pfattner, R., Kong, D., Zhou, Y., Ecker, B., Gao, Y., Bao, Z. 2016; 8 (30): 19658-19664

    Abstract

    We demonstrate the ability of the highly fluorinated, chemically inert copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to significantly increase the work function of a variety of common electrode materials. The work function change is hypothesized to occur via physisorption of the polymer layer and formation of a surface dipole at the polymer/conductor interface. When incorporated into organic solar cells, an interlayer of PVDF-HFP at an Ag anode increases the open circuit voltage by 0.4 eV and improves device power conversion efficiency by approximately an order of magnitude relative to Ag alone. Solution-processable in air, PVDF-HFP thin films provide one possible route toward achieving low cost, nonreactive, high work function electrodes.

    View details for DOI 10.1021/acsami.6b05348

    View details for PubMedID 27428045

  • All-Polymer Solar Cells Employing Non-Halogenated Solvent and Additive CHEMISTRY OF MATERIALS Zhou, Y., Gu, K. L., Gu, X., Kurosawa, T., Yan, H., Guo, Y., Koleilat, G. I., Zhao, D., Toney, M. F., Bao, Z. 2016; 28 (14): 5037-5042
  • Tunable Polyaniline-Based Porous Carbon with Ultrahigh Surface Area for CO2 Capture at Elevated Pressure ADVANCED ENERGY MATERIALS He, J., To, J. W., Psarras, P. C., Yan, H., Atkinson, T., Holmes, R. T., Nordlund, D., Bao, Z., Wilcox, J. 2016; 6 (14)
  • Capacitance Characterization of Elastomeric Dielectrics for Applications in Intrinsically Stretchable Thin Film Transistors ADVANCED FUNCTIONAL MATERIALS Kong, D., Pfattner, R., Chortos, A., Lu, C., Hinckley, A. C., Wang, C., Lee, W., Chung, J. W., Bao, Z. 2016; 26 (26): 4680-4686
  • Non-Conjugated Flexible Linkers in Semiconducting Polymers: A Pathway to Improved Processability without Compromising Device Performance ADVANCED ELECTRONIC MATERIALS Schroeder, B. C., Chiu, Y., Gu, X., Zhou, Y., Xu, J., Lopez, J., Lu, C., Toney, M. F., Bao, Z. 2016; 2 (7)
  • Mechanically Durable and Highly Stretchable Transistors Employing Carbon Nanotube Semiconductor and Electrodes ADVANCED MATERIALS Chortos, A., Koleilat, G. I., Pfattner, R., Kong, D., Lin, P., Nur, R., Lei, T., Wang, H., Liu, N., Lai, Y., Kim, M., Chung, J. W., Lee, S., Bao, Z. 2016; 28 (22): 4441-?

    Abstract

    Mechanically durable stretchable trans-istors are fabricated using carbon nanotube electrical components and tough thermoplastic elastomers. After an initial conditioning step, the electrical characteristics remain constant with strain. The strain-dependent characteristics are similar in orthogonal stretching directions. Devices can be impacted with a hammer and punctured with a needle while remaining functional and stretchable.

    View details for DOI 10.1002/adma.201501828

    View details for Web of Science ID 000377123500014

    View details for PubMedID 26179120

  • 3D Porous Sponge-Inspired Electrode for Stretchable Lithium-Ion Batteries ADVANCED MATERIALS Liu, W., Chen, Z., Zhou, G., Sun, Y., Lee, H. R., Liu, C., Yao, H., Bao, Z., Cui, Y. 2016; 28 (18): 3578-?

    Abstract

    A stretchable Li4 Ti5 O12 anode and a LiFePO4 cathode with 80% stretchability are prepared using a 3D interconnected porous polydimethylsiloxane sponge based on sugar cubes. 82% and 91% capacity retention for anode and cathode are achieved after 500 stretch-release cycles. Slight capacity decay of 6% in the battery using the electrode in stretched state is observed.

    View details for DOI 10.1002/adma.201505299

    View details for Web of Science ID 000376250600021

    View details for PubMedID 26992146

  • Role of Polymer Structure on the Conductivity of N-Doped Polymers ADVANCED ELECTRONIC MATERIALS Naab, B. D., Gu, X., Kurosawa, T., To, J. W., Salleo, A., Bao, Z. 2016; 2 (5)
  • Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing. ACS applied materials & interfaces Shaw, L., Hayoz, P., Diao, Y., Reinspach, J. A., To, J. W., Toney, M. F., Weitz, R. T., Bao, Z. 2016; 8 (14): 9285-9296

    Abstract

    The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used to tune polymer alignment in a one-step deposition process not requiring substrate patterning or any postdeposition treatment.

    View details for DOI 10.1021/acsami.6b01607

    View details for PubMedID 26985638

  • A Stretchable Graphitic Carbon/Si Anode Enabled by Conformal Coating of a Self-Healing Elastic Polymer ADVANCED MATERIALS Sun, Y., Lopez, J., Lee, H., Liu, N., Zheng, G., Wu, C., Sun, J., Liu, W., Chung, J. W., Bao, Z., Cui, Y. 2016; 28 (12): 2455-2461
  • Impact of Polystyrene Oligomer Side Chains on Naphthalene Diimide-Bithiophene Polymers as n-Type Semiconductors for Organic Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Kurosawa, T., Chiu, Y., Zhou, Y., Gu, X., Chen, W., Bao, Z. 2016; 26 (8): 1261-1270
  • The Effects of Cross-Linking in a Supramolecular Binder on Cycle Life in Silicon Microparticle Anodes. ACS applied materials & interfaces Lopez, J., Chen, Z., Wang, C., Andrews, S. C., Cui, Y., Bao, Z. 2016; 8 (3): 2318-2324

    Abstract

    Self-healing supramolecular binder was previously found to enhance the cycling stability of micron-sized silicon particles used as the active material in lithium-ion battery anodes. In this study, we systematically control the density of cross-linking junctions in a modified supramolecular polymer binder in order to better understand how viscoelastic materials properties affect cycling stability. We found that binders with relaxation times on the order of 0.1 s gave the best cycling stability with 80% capacity maintained for over 175 cycles using large silicon particles (∼0.9 um). We attributed this to an improved balance between the viscoelastic stress relaxation in the binder and the stiffness needed to maintain mechanical integrity of the electrode. The more cross-linked binder showed markedly worse performance confirming the need for liquid-like flow in order for our self-healing polymer electrode concept to be effective.

    View details for DOI 10.1021/acsami.5b11363

    View details for PubMedID 26716873

  • Tuning the Morphology of Solution-Sheared P3HT:PCBM Films ACS APPLIED MATERIALS & INTERFACES Reinspach, J. A., Diao, Y., Giri, G., Sachse, T., England, K., Zhou, Y., Tassone, C., Worfolk, B. J., Presselt, M., Toney, M. F., Mannsfeld, S., Bao, Z. 2016; 8 (3): 1742-1751

    Abstract

    Organic bulk heterojunction (BHJ) solar cells are a promising alternative for future clean-energy applications. However, to become attractive for consumer applications, such as wearable, flexible, or semitransparent power-generating electronics, they need to be manufactured by high-throughput, low-cost, large-area-capable printing techniques. However, most research reported on BHJ solar cells is conducted using spin coating, a single batch fabrication method, thus limiting the reported results to the research lab. In this work, we investigate the morphology of solution-sheared films for BHJ solar cell applications, using the widely studied model blend P3HT:PCBM. Solution shearing is a coating technique that is upscalable to industrial manufacturing processes and has demonstrated to yield record performance organic field-effect transistors. Using grazing incident small-angle X-ray scattering, grazing incident wide-angle X-ray scattering, and UV-vis spectroscopy, we investigate the influence of solvent, film drying time, and substrate temperature on P3HT aggregation, conjugation length, crystallite orientation, and PCBM domain size. One important finding of this study is that, in contrast to spin-coated films, the P3HT molecular orientation can be controlled by the substrate chemistry, withPSS substrates yielding face-on orientation at the substrate-film interface, an orientation highly favorable for organic solar cells.

    View details for DOI 10.1021/acsami.5b09349

    View details for Web of Science ID 000369044100024

    View details for PubMedID 26771274

  • Compact Roll-to-Roll Coater for in Situ X-ray Diffraction Characterization of Organic Electronics Printing. ACS applied materials & interfaces Gu, X., Reinspach, J., Worfolk, B. J., Diao, Y., Zhou, Y., Yan, H., Gu, K., Mannsfeld, S., Toney, M. F., Bao, Z. 2016; 8 (3): 1687-1694

    Abstract

    We describe a compact roll-to-roll (R2R) coater that is capable of tracking the crystallization process of semiconducting polymers during solution printing using X-ray scattering at synchrotron beamlines. An improved understanding of the morphology evolution during the solution-processing of organic semiconductor materials during R2R coating processes is necessary to bridge the gap between "lab" and "fab". The instrument consists of a vacuum chuck to hold the flexible plastic substrate uniformly flat for grazing incidence X-ray scattering. The time resolution of the drying process that is achievable can be tuned by controlling two independent motor speeds, namely, the speed of the moving flexible substrate and the speed of the printer head moving in the opposite direction. With this novel design, we are able to achieve a wide range of drying time resolutions, from tens of milliseconds to seconds. This allows examination of the crystallization process over either fast or slow drying processes depending on coating conditions. Using regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) inks based on two different solvents as a model system, we demonstrate the capability of our in situ R2R printing tool by observing two distinct crystallization processes for inks drying from the solvents with different boiling points (evaporation rates). We also observed delayed on-set point for the crystallization of P3HT polymer in the 1:1 P3HT/PCBM BHJ blend, and the inhibited crystallization of the P3HT during the late stage of the drying process.

    View details for DOI 10.1021/acsami.5b09174

    View details for PubMedID 26714412

  • Semiconducting Carbon Nanotubes for Improved Efficiency and Thermal Stability of Polymer-Fullerene Solar Cells ADVANCED FUNCTIONAL MATERIALS Salim, T., Lee, H., Wong, L. H., Oh, J. H., Bao, Z., Lam, Y. M. 2016; 26 (1): 51-65
  • Dispersion of High-Purity Semiconducting Arc-Discharged Carbon Nanotubes Using Backbone Engineered Diketopyrrolopyrrole (DPP)-Based Polymers ADVANCED ELECTRONIC MATERIALS Lei, T., Pitner, G., Chen, X., Hong, G., Park, S., Hayoz, P., Weitz, R. T., Wong, H. P., Bao, Z. 2016; 2 (1)
  • Impact of the Crystallite Orientation Distribution on Exciton Transport in Donor-Acceptor Conjugated Polymers ACS APPLIED MATERIALS & INTERFACES Ayzner, A. L., Mei, J., Appleton, A., DeLongchamp, D., Nardes, A., Benight, S., Kopidakis, N., Toney, M. F., Bao, Z. 2015; 7 (51): 28035-28041

    Abstract

    Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their extended electronic wave functions, they often form semicrystalline thin films. In this work, we aim to understand whether distribution of crystallographic orientations affects exciton diffusion using a low-band-gap polymer backbone motif that is representative of the donor/acceptor copolymer class. Using the fact that the polymer side chain can tune the dominant crystallographic orientation in the thin film, we have measured the quenching of polymer photoluminescence, and thus the extent of exciton dissociation, as a function of crystal orientation with respect to a quenching substrate. We find that the crystallite orientation distribution has little effect on the average exciton diffusion length. We suggest several possibilities for the lack of correlation between crystallographic texture and exciton transport in semicrystalline conjugated polymer films.

    View details for DOI 10.1021/acsami.5b02968

    View details for Web of Science ID 000369448200008

    View details for PubMedID 26292836

  • Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors SCIENTIFIC REPORTS Wang, C., Lee, W., Kong, D., Pfattner, R., Schweicher, G., Nakajima, R., Lu, C., Mei, J., Lee, T. H., Wu, H., Lopez, J., Diao, Y., Gu, X., Himmelberger, S., Niu, W., Matthews, J. R., He, M., Salleo, A., Nishi, Y., Bao, Z. 2015; 5

    View details for DOI 10.1038/srep17849

    View details for Web of Science ID 000366284000001

    View details for PubMedID 26658331

  • Fabrication of flexible pressure sensors with microstructured polydimethylsiloxane dielectrics using the breath figures method JOURNAL OF MATERIALS RESEARCH Miller, S., Bao, Z. 2015; 30 (23): 3584-3594
  • Conjugated polymer sorting of semiconducting carbon nanotubes and their electronic applications NANO TODAY Wang, H., Bao, Z. 2015; 10 (6): 737-758
  • A Sensitive and Biodegradable Pressure Sensor Array for Cardiovascular Monitoring ADVANCED MATERIALS Boutry, C. M., Nguyen, A., Lawal, Q. O., Chortos, A., Rondeau-Gagne, S., Bao, Z. 2015; 27 (43): 6954-?
  • Partially-Screened Field Effect and Selective Carrier Injection at Organic Semiconductor/Graphene Heterointerface NANO LETTERS Shih, C., Pfattner, R., Chiu, Y., Liu, N., Lei, T., Kong, D., Kim, Y., Chou, H., Bae, W., Bao, Z. 2015; 15 (11): 7587-7595

    View details for DOI 10.1021/acs.nanolett.5b03378

    View details for Web of Science ID 000364725400062

    View details for PubMedID 26496513

  • Shape-Controlled, Self-Wrapped Carbon Nanotube 3D Electronics ADVANCED SCIENCE Wang, H., Wang, Y., Tee, B. C., Kim, K., Lopez, J., Cai, W., Bao, Z. 2015; 2 (9)
  • Effect of Chemical Structure on Polymer-Templated Growth of Graphitic Nanoribbons ACS NANO Liu, N., Kim, K., Jeong, H. Y., Hsu, P., Cui, Y., Bao, Z. 2015; 9 (9): 9043-9049

    View details for DOI 10.1021/acsnano.5b03134

    View details for Web of Science ID 000361935800042

    View details for PubMedID 26267798

  • Diketopyrrolopyrrole-Based Semiconducting Polymer Nanoparticles for In Vivo Photoacoustic Imaging. Advanced materials Pu, K., Mei, J., Jokerst, J. V., Hong, G., Antaris, A. L., Chattopadhyay, N., Shuhendler, A. J., Kurosawa, T., Zhou, Y., Gambhir, S. S., Bao, Z., Rao, J. 2015; 27 (35): 5184-5190

    Abstract

    Diketopyrrolopyrrole-based semiconducting polymer nanoparticles with high photostability and strong photoacoustic brightness are designed and synthesized, which results in 5.3-fold photoacoustic signal enhancement in tumor xenografts after systemic administration.

    View details for DOI 10.1002/adma.201502285

    View details for PubMedID 26247171

    View details for PubMedCentralID PMC4567488

  • n-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions. Chemistry (Weinheim an der Bergstrasse, Germany) Zhang, S., Naab, B. D., Jucov, E. V., Parkin, S., Evans, E. G., Millhauser, G. L., Timofeeva, T. V., Risko, C., Brédas, J., Bao, Z., Barlow, S., Marder, S. R. 2015; 21 (30): 10878-10885

    Abstract

    Dimers of 2-substituted N,N'-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer CC bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2 , yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2 ) dissociation and of D2 -to-A electron transfer, D2 reacts with A to form D(+) and A(-) by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D(+) /0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. -1.9 V vs. FeCp2 (+/0) ) (Cp=cyclopentadienyl) due to cancelation of trends in the D(+/0) potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed.

    View details for DOI 10.1002/chem.201500611

    View details for PubMedID 26088609

  • Diketopyrrolopyrrole (DPP)-Based Donor-Acceptor Polymers for Selective Dispersion of Large-Diameter Semiconducting Carbon Nanotubes SMALL Lei, T., Lai, Y., Hong, G., Wang, H., Hayoz, P., Weitz, R. T., Chen, C., Dai, H., Bao, Z. 2015; 11 (24): 2946-2954

    Abstract

    Low-bandgap diketopyrrolopyrrole (DPP)-based polymers are used for the selective dispersion of semiconducting single-walled carbon nanotubes (s-SWCNTs). Through rational molecular design to tune the polymer-SWCNT interactions, highly selective dispersions of s-SWCNTs with diameters mainly around 1.5 nm are achieved. The influences of the polymer alkyl side-chain substitution (i.e., branched vs linear side chains) on the dispersing yield and selectivity of s-SWCNTs are investigated. Introducing linear alkyl side chains allows increased polymer-SWCNT interactions through close π-π stacking and improved C-H-π interactions. This work demonstrates that polymer side-chain engineering is an effective method to modulate the polymer-SWCNT interactions and thereby affecting both critical parameters in dispersing yield and selectivity. Using these sorted s-SWCNTs, high-performance SWCNT network thin-film transistors are fabricated. The solution-deposited s-SWCNT transistors yield simultaneously high mobilities of 41.2 cm(2) V(-1) s(-1) and high on/off ratios of greater than 10(4) . In summary, low-bandgap DPP donor-acceptor polymers are a promising class of polymers for selective dispersion of large-diameter s-SWCNTs.

    View details for DOI 10.1002/smll.201403761

    View details for Web of Science ID 000356444600014

    View details for PubMedID 25711378

  • Effect of Spacer Length of Siloxane-Terminated Side Chains on Charge Transport in Isoindigo-Based Polymer Semiconductor Thin Films ADVANCED FUNCTIONAL MATERIALS Mei, J., Wu, H., Diao, Y., Appleton, A., Wang, H., Zhou, Y., Lee, W., Kurosawa, T., Chen, W., Bao, Z. 2015; 25 (23): 3455-3462
  • Tuning Local Molecular Orientation-Composition Correlations in Binary Organic Thin Films by Solution Shearing ADVANCED FUNCTIONAL MATERIALS Ma, W., Reinspach, J., Zhou, Y., Diao, Y., McAfee, T., Mannsfeld, S. C., Bao, Z., Ade, H. 2015; 25 (21): 3131-3137
  • Structural and Electrical Investigation of C-60-Graphene Vertical Heterostructures ACS NANO Kim, K., Lee, T. H., Santos, E. J., Jo, P. S., Salleo, A., Nishi, Y., Bao, Z. 2015; 9 (6): 5922-5928

    Abstract

    Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C60 thin film on graphene. The assembled film structure of C60 on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C60 film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C60 crystal and graphene lattice directions are found, and van der Waals ab initio calculations support the observed phenomena. Moreover, using C60-graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10(3). Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications.

    View details for DOI 10.1021/acsnano.5b00581

    View details for Web of Science ID 000356988500032

    View details for PubMedID 26027690

  • Bulky End-Capped [1]Benzothieno[3,2-b]benzothiophenes: Reaching High-Mobility Organic Semiconductors by Fine Tuning of the Crystalline Solid-State Order ADVANCED MATERIALS Schweicher, G., Lemaur, V., Niebel, C., Ruzie, C., Diao, Y., Goto, O., Lee, W., Kim, Y., Arlin, J., Karpinska, J., Kennedy, A. R., Parkin, S. R., Olivier, Y., Mannsfeld, S. C., Cornil, J., Geerts, Y. H., Bao, Z. 2015; 27 (19): 3066-3072

    Abstract

    A series of bulky end-capped [1]benzothieno[3,2-b]benzothiophenes (BTBTs) are developed in order to tune the packing structure via terminal substitution. A coupled theoretical and experimental study allows us to identify 2,7-di-tert-butylBTBT as a new high-performance organic semiconductor with large and well-balanced transfer integrals, as evidenced by quantum-chemical calculations. Single-crystal field-effect transistors show a remarkable average saturation mobility of 7.1 cm(2) V(-1) s(-1) .

    View details for DOI 10.1002/adma.201500322

    View details for Web of Science ID 000354487700016

    View details for PubMedID 25855909

  • Epitaxially Grown Strained Pentacene Thin Film on Graphene Membrane SMALL Kim, K., Santos, E. J., Lee, T. H., Nishi, Y., Bao, Z. 2015; 11 (17): 2037-2043

    Abstract

    Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.

    View details for DOI 10.1002/smll.201403006

    View details for Web of Science ID 000354226500007

    View details for PubMedID 25565340

  • Large-area formation of self-aligned crystalline domains of organic semiconductors on transistor channels using CONNECT PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Park, S., Giri, G., Shaw, L., Pitner, G., Ha, J., Koo, J. H., Gu, X., Park, J., Lee, T. H., Nam, J. H., Hong, Y., Bao, Z. 2015; 112 (18): 5561-5566

    Abstract

    The electronic properties of solution-processable small-molecule organic semiconductors (OSCs) have rapidly improved in recent years, rendering them highly promising for various low-cost large-area electronic applications. However, practical applications of organic electronics require patterned and precisely registered OSC films within the transistor channel region with uniform electrical properties over a large area, a task that remains a significant challenge. Here, we present a technique termed "controlled OSC nucleation and extension for circuits" (CONNECT), which uses differential surface energy and solution shearing to simultaneously generate patterned and precisely registered OSC thin films within the channel region and with aligned crystalline domains, resulting in low device-to-device variability. We have fabricated transistor density as high as 840 dpi, with a yield of 99%. We have successfully built various logic gates and a 2-bit half-adder circuit, demonstrating the practical applicability of our technique for large-scale circuit fabrication.

    View details for DOI 10.1073/pnas.1419771112

    View details for Web of Science ID 000353953800030

    View details for PubMedID 25902502

  • High performance top contact fused thiophene-diketopyrrolopyrrole copolymer transistors using a photolithographic metal lift-off process ORGANIC ELECTRONICS Xie, Y., Ouyang, S., Wang, D., Lee, W., Bao, Z., Matthews, J. R., Niu, W., Bellman, R. A., He, M., Fong, H. H. 2015; 20: 55-62
  • Large-Area Assembly of Densely Aligned Single-Walled Carbon Nanotubes Using Solution Shearing and Their Application to Field-Effect Transistors ADVANCED MATERIALS Park, S., Pitner, G., Giri, G., Koo, J. H., Park, J., Kim, K., Wang, H., Sinclair, R., Wong, H. P., Bao, Z. 2015; 27 (16): 2656-2662

    Abstract

    Dense alignment of single-walled carbon nanotubes over a large area is demonstrated using a novel solution-shearing technique. A density of 150-200 single-walled carbon nanotubes per micro-meter is achieved with a current density of 10.08 μA μm(-1) at VDS = -1 V. The on-current density is improved by a factor of 45 over that of random-network single-walled carbon nanotubes.

    View details for DOI 10.1002/adma.201405289

    View details for Web of Science ID 000353298900013

    View details for PubMedID 25788393

  • High-Areal-Capacity Silicon Electrodes with Low-Cost Silicon Particles Based on Spatial Control of Self-Healing Binder ADVANCED ENERGY MATERIALS Chen, Z., Wang, C., Lopez, J., Lu, Z., Cui, Y., Bao, Z. 2015; 5 (8)
  • Effect of Solution Shearing Method on Packing and Disorder of Organic Semiconductor Polymers CHEMISTRY OF MATERIALS Giri, G., Delongchamp, D. M., Reinspach, J., Fischer, D. A., Richter, L. J., Xu, J., Benight, S., Ayzner, A., He, M., Fang, L., Xue, G., Toney, M. F., Bao, Z. 2015; 27 (7): 2350-2359

    View details for DOI 10.1021/cm503780u

    View details for Web of Science ID 000353176100013

  • N-Type Conjugated Polymer-Enabled Selective Dispersion of Semiconducting Carbon Nanotubes for Flexible CMOS-Like Circuits ADVANCED FUNCTIONAL MATERIALS Wang, H., Li, Y., Jimenez-Oses, G., Liu, P., Fang, Y., Zhang, J., Lai, Y., Park, S., Chen, L., Houk, K. N., Bao, Z. 2015; 25 (12): 1837-1844
  • Enhancement of ambipolar characteristics in single-walled carbon nanotubes using C-60 and fabrication of logic gates APPLIED PHYSICS LETTERS Park, S., Nam, J. H., Koo, J. H., Lei, T., Bao, Z. 2015; 106 (10)

    View details for DOI 10.1063/1.4914476

    View details for Web of Science ID 000351397600059

  • Thermotropic Phase Transition of Benzodithiophene Copolymer Thin Films and Its Impact on Electrical and Photovoltaic Characteristics CHEMISTRY OF MATERIALS Ko, S., Kim, D. H., Ayzner, A. L., Mannsfeld, S. C., Verploegen, E., Nardes, A. M., Kopidakis, N., Toney, M. F., Bao, Z. 2015; 27 (4): 1223-1232

    View details for DOI 10.1021/cm503773j

    View details for Web of Science ID 000350192500013

  • Highly skin-conformal microhairy sensor for pulse signal amplification. Advanced materials Pang, C., Koo, J. H., Nguyen, A., Caves, J. M., Kim, M., Chortos, A., Kim, K., Wang, P. J., Tok, J. B., Bao, Z. 2015; 27 (4): 634-640

    Abstract

    A bioinspired microhairy sensor is developed to enable ultraconformability on nonflat surfaces and significant enhancement in the signal-to-noise ratio of the retrieved signals. The device shows ≈12 times increase in the signal-to-noise ratio in the generated capacitive signals, allowing the ultraconformal microhair pressure sensors to be capable of measuring weak pulsations of internal jugular venous pulses stemming from a human neck.

    View details for DOI 10.1002/adma.201403807

    View details for PubMedID 25358966

  • Significant enhancement of infrared photodetector sensitivity using a semiconducting single-walled carbon nanotube/c60 phototransistor. Advanced materials Park, S., Kim, S. J., Nam, J. H., Pitner, G., Lee, T. H., Ayzner, A. L., Wang, H., Fong, S. W., Vosgueritchian, M., Park, Y. J., Brongersma, M. L., Bao, Z. 2015; 27 (4): 759-765

    Abstract

    A highly sensitive single-walled carbon nanotube/C60 -based infrared photo-transistor is fabricated with a responsivity of 97.5 A W(-1) and detectivity of 1.17 × 10(9) Jones at 1 kHz under a source/drain bias of -0.5 V. The much improved performance is enabled by this unique device architecture that enables a high photoconductive gain of ≈10(4) with a response time of several milliseconds.

    View details for DOI 10.1002/adma.201404544

    View details for PubMedID 25607919

  • Highly skin-conformal microhairy sensor for pulse signal amplification. Advanced materials Pang, C., Koo, J. H., Nguyen, A., Caves, J. M., Kim, M., Chortos, A., Kim, K., Wang, P. J., Tok, J. B., Bao, Z. 2015; 27 (4): 634-640

    View details for DOI 10.1002/adma.201403807

    View details for PubMedID 25358966

  • An imaging and analysis toolset for the study of Caenorhabditis elegans neurodevelopment Conference on Optical Methods in Developmental Biology III Christensen, R., Bokinsky, A., Santella, A., Wu, Y., Marquina, J., Kovacevic, I., Kumar, A., Winter, P., McCreedy, E., Mohler, W., Bao, Z., Colon-Ramos, D., Shroff, H. SPIE-INT SOC OPTICAL ENGINEERING. 2015

    View details for DOI 10.1117/12.2082394

    View details for Web of Science ID 000353408400003

  • Solvent effects on polymer sorting of carbon nanotubes with applications in printed electronics. Small Wang, H., Hsieh, B., Jiménez-Osés, G., Liu, P., Tassone, C. J., Diao, Y., Lei, T., Houk, K. N., Bao, Z. 2015; 11 (1): 126-133

    Abstract

    Regioregular poly(3-alkylthiophene) (P3AT) polymers have been previously reported for the selective, high-yield dispersion of semiconducting single-walled carbon nanotubes (SWCNTs) in toluene. Here, five alternative solvents are investigated, namely, tetrahydrofuran, decalin, tetralin, m-xylene, and o-xylene, for the dispersion of SWCNTs by poly(3-dodecylthiophene) P3DDT. The dispersion yield could be increased to over 40% using decalin or o-xylene as the solvents while maintaining high selectivity towards semiconducting SWCNTs. Molecular dynamics (MD) simulations in explicit solvents are used to explain the improved sorting yield. In addition, a general mechanism is proposed to explain the selective dispersion of semiconducting SWCNTs by conjugated polymers. The possibility to perform selective sorting of semiconducting SWCNTs using various solvents provides a greater diversity of semiconducting SWCNT ink properties, such as boiling point, viscosity, and surface tension as well as toxicity. The efficacy of these new semiconducting SWCNT inks is demonstrated by using the high boiling point and high viscosity solvent tetralin for inkjet-printed transistors, where solvent properties are more compatible with the inkjet printing head and improved droplet formation.

    View details for DOI 10.1002/smll.201401890

    View details for PubMedID 25138541

  • Few-layer, large-area, 2D covalent organic framework semiconductor thin films CHEMICAL COMMUNICATIONS Feldblyum, J. I., McCreery, C. H., Andrews, S. C., Kurosawa, T., Santos, E. J., Duong, V., Fang, L., Ayzner, A. L., Bao, Z. 2015; 51 (73): 13894-13897

    View details for DOI 10.1039/c5cc04679c

    View details for Web of Science ID 000360398900006

  • Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation JOURNAL OF PHYSICAL CHEMISTRY LETTERS Ayzner, A. L., Nordlund, D., Kim, D., Bao, Z., Toney, M. F. 2015; 6 (1): 6-12

    View details for DOI 10.1021/jz502253r

    View details for Web of Science ID 000347513700002

  • Understanding Polymorphism in Organic Semiconductor Thin Films through Nanoconfinement JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Diao, Y., Lenn, K. M., Lee, W., Blood-Forsythe, M. A., Xu, J., Mao, Y., Kim, Y., Reinspach, J. A., Park, S., Aspuru-Guzik, A., Xue, G., Clancy, P., Bao, Z., Mannsfeld, S. C. 2014; 136 (49): 17046-17057

    Abstract

    Understanding crystal polymorphism is a long-standing challenge relevant to many fields, such as pharmaceuticals, organic semiconductors, pigments, food, and explosives. Controlling polymorphism of organic semiconductors (OSCs) in thin films is particularly important given that such films form the active layer in most organic electronics devices and that dramatic changes in the electronic properties can be induced even by small changes in the molecular packing. However, there are very few polymorphic OSCs for which the structure-property relationships have been elucidated so far. The major challenges lie in the transient nature of metastable forms and the preparation of phase-pure, highly crystalline thin films for resolving the crystal structures and evaluating the charge transport properties. Here we demonstrate that the nanoconfinement effect combined with the flow-enhanced crystal engineering technique is a powerful and likely material-agnostic method to identify existing polymorphs in OSC materials and to prepare the individual pure forms in thin films at ambient conditions. With this method we prepared high quality crystal polymorphs and resolved crystal structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), including a new polymorph discovered via in situ grazing incidence X-ray diffraction and confirmed by molecular mechanic simulations. We further correlated molecular packing with charge transport properties using quantum chemical calculations and charge carrier mobility measurements. In addition, we applied our methodology to a [1]benzothieno[3,2-b][1]1benzothiophene (BTBT) derivative and successfully stabilized its metastable form.

    View details for DOI 10.1021/ja507179d

    View details for Web of Science ID 000346544200021

    View details for PubMedID 25333565

  • Large-Scale Production of Graphene Nanoribbons from Electrospun Polymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, N., Kim, K., Hsu, P., Sokolov, A. N., Yap, F. L., Yuan, H., Xie, Y., Yan, H., Cui, Y., Hwang, H. Y., Bao, Z. 2014; 136 (49): 17284-17291

    Abstract

    Graphene nanoribbons (GNRs) are promising building blocks for high-performance electronics due to their high electron mobility and dimensionality-induced bandgap. Despite many past efforts, direct synthesis of GNRs with controlled dimensions and scalability remains challenging. Here we report the scalable synthesis of GNRs using electrospun polymer nanofiber templates. Palladium-incorporated poly(4-vinylphenol) nanofibers were prepared by electrospinning with controlled diameter and orientation. Highly graphitized GNRs as narrow as 10 nm were then synthesized from these templates by chemical vapor deposition. A transport gap can be observed in 30 nm-wide GNRs, enabling them to function as field-effect transistors at room temperature. Our results represent the first success on the scalable synthesis of highly graphitized GNRs from polymer templates. Furthermore, the generality of this method allows various polymers to be explored, which will lead to understanding of growth mechanism and rational control over crystallinity, feature size and bandgap to enable a new pathway for graphene electronics.

    View details for DOI 10.1021/ja509871n

    View details for Web of Science ID 000346544200045

    View details for PubMedID 25407608

  • Selective solution shearing deposition of high performance TIPS-pentacene polymorphs through chemical patterning JOURNAL OF MATERIALS RESEARCH Giri, G., Miller, E., Bao, Z. 2014; 29 (22): 2615-2624
  • Stretchable Energy-Harvesting Tactile Electronic Skin Capable of Differentiating Multiple Mechanical Stimuli Modes ADVANCED MATERIALS Park, S., Kim, H., Vosgueritchian, M., Cheon, S., Kim, H., Koo, J. H., Kim, T. R., Lee, S., Schwartz, G., Chang, H., Bao, Z. 2014; 26 (43): 7324-7332
  • Self-Assembled Monolayers of Cyclohexyl-Terminated Phosphonic Acids as a General Dielectric Surface for High-Performance Organic Thin-Film Transistors ADVANCED MATERIALS Liu, D., He, Z., Su, Y., Diao, Y., Mannsfeld, S. C., Bao, Z., Xu, J., Miao, Q. 2014; 26 (42): 7190-7196
  • Electronic Readout Enzyme-Linked Immunosorbent Assay with Organic Field-Effect Transistors as a Preeclampsia Prognostic ADVANCED MATERIALS Hammock, M. L., Knopfmacher, O., Ng, T. N., Tok, J. B., Bao, Z. 2014; 26 (35): 6138-?

    Abstract

    Organic field-effect transistor (OFET) sensors can meet the need for portable and real-time diagnostics. An electronicreadout enzyme-linked immunosorbent assay using OFETs for the detection of a panel of three biomarkers in complex media to create a pre-eclampsia prognostic is demonstrated, along with biodetection utilizing a fully inkjet-printed and flexible OFET to underscore our ability to produce disposable devices.

    View details for DOI 10.1002/adma.201401829

    View details for Web of Science ID 000342148600013

    View details for PubMedID 25047764

  • Tunable Flexible Pressure Sensors using Microstructured Elastomer Geometries for Intuitive Electronics ADVANCED FUNCTIONAL MATERIALS Tee, B. C., Chortos, A., Dunn, R. R., Schwartz, G., Eason, E., Bao, Z. 2014; 24 (34): 5427-5434
  • High performance organic thin film transistors using chemically modified bottom contacts and dielectric surfaces ORGANIC ELECTRONICS Xie, Y., Cai, S., Shi, Q., Ouyang, S., Lee, W., Bao, Z., Matthews, J. R., Bellman, R. A., He, M., Fong, H. H. 2014; 15 (9): 2073-2078
  • A Three-Dimensionally Interconnected Carbon Nanotube-Conducting Polymer Hydrogel Network for High-Performance Flexible Battery Electrodes ADVANCED ENERGY MATERIALS Chen, Z., To, J. W., Wang, C., Lu, Z., Liu, N., Chortos, A., Pan, L., Wei, F., Cui, Y., Bao, Z. 2014; 4 (12)
  • Comparing the Device Physics and Morphology of Polymer Solar Cells Employing Fullerenes and Non-Fullerene Acceptors ADVANCED ENERGY MATERIALS Bloking, J. T., Giovenzana, T., Higgs, A. T., Ponec, A. J., Hoke, E. T., Vandewal, K., Ko, S., Bao, Z., Sellinger, A., McGehee, M. D. 2014; 4 (12)
  • A Rapid and Facile Soft Contact Lamination Method: Evaluation of Polymer Semiconductors for Stretchable Transistors CHEMISTRY OF MATERIALS Wu, H., Benight, S. J., Chortos, A., Lee, W., Mei, J., To, J. W., Lu, C., He, M., Tok, J. B., Chen, W., Bao, Z. 2014; 26 (15): 4544-4551

    View details for DOI 10.1021/cm502271j

    View details for Web of Science ID 000340346300029

  • Using in-Situ Polymerization of Conductive Polymers to Enhance the Electrical Properties of Solution-Processed Carbon Nanotube Films and Fibers ACS APPLIED MATERIALS & INTERFACES Allen, R., Pan, L., Fuller, G. G., Bao, Z. 2014; 6 (13): 9966-9974

    Abstract

    Single-walled carbon nanotubes/polymer composites typically have limited conductivity due to a low concentration of nanotubes and the insulating nature of the polymers used. Here we combined a method to align carbon nanotubes with in-situ polymerization of conductive polymer to form composite films and fibers. Use of the conducting polymer raised the conductivity of the films by 2 orders of magnitude. On the other hand, CNT fiber formation was made possible with in-situ polymerization to provide more mechanical support to the CNTs from the formed conducting polymer. The carbon nanotube/conductive polymer composite films and fibers had conductivities of 3300 and 170 S/cm, respectively. The relatively high conductivities were attributed to the polymerization process, which doped both the SWNTs and the polymer. In-situ polymerization can be a promising solution-processable method to enhance the conductivity of carbon nanotube films and fibers.

    View details for DOI 10.1021/am5019995

    View details for Web of Science ID 000338979900010

    View details for PubMedID 24914703

  • Large-area, transparent, and flexible infrared photodetector fabricated using p-N junctions formed by N-doping chemical vapor deposition grown graphene. Nano letters Liu, N., Tian, H., Schwartz, G., Tok, J. B., Ren, T., Bao, Z. 2014; 14 (7): 3702-3708

    Abstract

    Graphene is a highly promising material for high speed, broadband, and multicolor photodetection. Because of its lack of bandgap, individually gated P- and N-regions are needed to fabricate photodetectors. Here we report a technique for making a large-area photodetector on the basis of controllable fabrication of graphene P-N junctions. Our selectively doped chemical vapor deposition (CVD) graphene photodetector showed a ∼5% modulation of conductance under global IR irradiation. By comparing devices of various geometries, we identify that both the homogeneous and the P-N junction regions contribute competitively to the photoresponse. Furthermore, we demonstrate that our two-terminal graphene photodetector can be fabricated on both transparent and flexible substrates without the need for complex fabrication processes used in electrically gated three-terminal devices. This represents the first demonstration of a fully transparent and flexible graphene-based IR photodetector that exhibits both good photoresponsivity and high bending capability. This simple approach should facilitate the development of next generation high-performance IR photodetectors.

    View details for DOI 10.1021/nl500443j

    View details for PubMedID 24927382

  • Highly Stable Carbon Nanotube Top-Gate Transistors with Tunable Threshold Voltage ADVANCED MATERIALS Wang, H., Cobb, B., van Breemen, A., Gelinck, G., Bao, Z. 2014; 26 (26): 4588-?

    Abstract

    Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time.

    View details for DOI 10.1002/adma.201400540

    View details for Web of Science ID 000339565100028

    View details for PubMedID 24789423

  • Morphology control strategies for solution-processed organic semiconductor thin films ENERGY & ENVIRONMENTAL SCIENCE Diao, Y., Shaw, L., Bao, Z., Mannsfeld, S. C. 2014; 7 (7): 2145-2159

    View details for DOI 10.1039/c4ee00688g

    View details for Web of Science ID 000337977600005

  • Highly stretchable transistors using a microcracked organic semiconductor. Advanced materials Chortos, A., Lim, J., To, J. W., Vosgueritchian, M., Dusseault, T. J., Kim, T., Hwang, S., Bao, Z. 2014; 26 (25): 4253-4259

    View details for DOI 10.1002/adma.201305462

    View details for PubMedID 24740928

  • Effective Solution- and Vacuum-Processed n-Doping by Dimers of Benzimidazoline Radicals. Advanced materials Naab, B. D., Zhang, S., Vandewal, K., Salleo, A., Barlow, S., Marder, S. R., Bao, Z. 2014; 26 (25): 4268-4272

    View details for DOI 10.1002/adma.201400668

    View details for PubMedID 24753007

  • Effect of Non-Chlorinated Mixed Solvents on Charge Transport and Morphology of Solution-Processed Polymer Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Lee, W., Giri, G., Diao, Y., Tassone, C. J., Matthews, J. R., Sorensen, M. L., Mannsfeld, S. C., Chen, W., Fong, H. H., Tok, J. B., Toney, M. F., He, M., Bao, Z. 2014; 24 (23): 3524-3534
  • The Large-Area, Solution-Based Deposition of Single-Crystal Organic Semiconductors ISRAEL JOURNAL OF CHEMISTRY Shaw, L., Bao, Z. 2014; 54 (5-6): 496-512
  • High Performance All-Polymer Solar Cell via Polymer Side-Chain Engineering. Advanced materials Zhou, Y., Kurosawa, T., Ma, W., Guo, Y., Fang, L., Vandewal, K., Diao, Y., Wang, C., Yan, Q., Reinspach, J., Mei, J., Appleton, A. L., Koleilat, G. I., Gao, Y., Mannsfeld, S. C., Salleo, A., Ade, H., Zhao, D., Bao, Z. 2014; 26 (22): 3767-3772

    View details for DOI 10.1002/adma.201306242

    View details for PubMedID 24664632

  • High performance tetrathienoacene-DDP based polymer thin-film transistors using a photo-patternable epoxy gate insulating layer ORGANIC ELECTRONICS Shi, Q., Xie, Y., Cai, S., Lee, W., Bao, Z., Matthews, J. R., Simonton, K. L., Myers, T. E., Bellman, R. A., He, M., Fong, H. H. 2014; 15 (5): 991-996
  • VLSI-Compatible Carbon Nanotube Doping Technique with Low Work-Function Metal Oxides. Nano letters Suriyasena Liyanage, L., Xu, X., Pitner, G., Bao, Z., Wong, H. P. 2014; 14 (4): 1884-1890

    Abstract

    Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, as-made carbon nanotube field effect transistors (CNFETs) are p-type in ambient, and a consistent and reproducible n-type carbon nanotube (CNT) doping technique has yet to be realized. In addition, for very large scale integration (VLSI) of CNT transistors, it is imperative to use a solid-state method that can be applied on the wafer scale. Herein we present a novel, VLSI-compatible doping technique to fabricate n-type CNT transistors using low work-function metal oxides as gate dielectrics. Using this technique we demonstrate wafer-scale, aligned CNT transistors with yttrium oxide (Y2Ox) gate dielectrics that exhibit n-type behavior with Ion/Ioff of 10(6) and inverse subthreshold slope of 95 mV/dec. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses confirm that slow (∼1 Å/s) evaporation of yttrium on the CNTs can form a smooth surface that provides excellent wetting to CNTs. Further analysis of the yttrium oxide gate dielectric using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques revealed that partially oxidized elemental yttrium content increases underneath the surface where it acts as a reducing agent on nanotubes by donating electrons that gives rise to n-type doping in CNTs. We further confirm the mechanism for this technique with other low work-function metals such as lanthanum (La), erbium (Er), and scandium (Sc) which also provide similar CNT NFET behavior after transistor fabrication. This study paves the way to exploiting a wide range of materials for an effective n-type carbon nanotube transistor for a complementary (p- and n-type) transistor technology.

    View details for DOI 10.1021/nl404654j

    View details for PubMedID 24628497

  • Tuning the threshold voltage of carbon nanotube transistors by n-type molecular doping for robust and flexible complementary circuits. Proceedings of the National Academy of Sciences of the United States of America Wang, H., Wei, P., Li, Y., Han, J., Lee, H. R., Naab, B. D., Liu, N., Wang, C., Adijanto, E., Tee, B. C., Morishita, S., Li, Q., Gao, Y., Cui, Y., Bao, Z. 2014; 111 (13): 4776-4781

    Abstract

    Tuning the threshold voltage of a transistor is crucial for realizing robust digital circuits. For silicon transistors, the threshold voltage can be accurately controlled by doping. However, it remains challenging to tune the threshold voltage of single-wall nanotube (SWNT) thin-film transistors. Here, we report a facile method to controllably n-dope SWNTs using 1H-benzoimidazole derivatives processed via either solution coating or vacuum deposition. The threshold voltages of our polythiophene-sorted SWNT thin-film transistors can be tuned accurately and continuously over a wide range. Photoelectron spectroscopy measurements confirmed that the SWNT Fermi level shifted to the conduction band edge with increasing doping concentration. Using this doping approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants. We observed an unprecedented noise margin of 28 V at VDD = 80 V (70% of 1/2VDD) and a gain of 85. Additionally, robust SWNT complementary metal-oxide-semiconductor inverter (noise margin 72% of 1/2VDD) and logic gates with rail-to-rail output voltage swing and subnanowatt power consumption were fabricated onto a highly flexible substrate.

    View details for DOI 10.1073/pnas.1320045111

    View details for PubMedID 24639537

  • High-yield sorting of small-diameter carbon nanotubes for solar cells and transistors. ACS nano Wang, H., Koleilat, G. I., Liu, P., Jiménez-Osés, G., Lai, Y., Vosgueritchian, M., Fang, Y., Park, S., Houk, K. N., Bao, Z. 2014; 8 (3): 2609-2617

    Abstract

    We describe herein a high-yield method to selectively disperse semiconducting CoMoCAT (CO disproportionation on Co-Mo catalysts) single-walled carbon nanotubes (SWNTs) with regioregular poly(3-alkylthiophenes) polymers. We observed that the dispersion yield was directly related to the length of the polymer's alkyl side chains. Molecular dynamics simulations in explicit toluene (real toluene molecules) indicate that polythiophenes with longer alkyl side chains bind strongly to SWNTs, due to the increased overall surface contact area with the nanotube. Furthermore, the sorting process selectively enriches smaller-diameter CoMoCAT SWNTs with larger bandgaps, which is ideal for solar cell applications. Compared to the larger diameter sorted HiPco (High-Pressure CO) SWNTs, solar cells fabricated using our sorted CoMoCAT SWNTs demonstrated higher open-circuit voltage (Voc) and infrared external quantum efficiency (EQE). The Voc achieved is the highest reported for solar cells based on SWNT absorbers under simulated AM1.5 solar illumination. Additionally, we employed the sorted CoMoCAT SWNTs to fabricate thin film transistors with excellent uniformity and device performance.

    View details for DOI 10.1021/nn406256y

    View details for PubMedID 24484388

  • Sequentially solution-processed, nanostructured polymer photovoltaics using selective solvents ENERGY & ENVIRONMENTAL SCIENCE Kim, D. H., Mei, J., Ayzner, A. L., Schmidt, K., Giri, G., Appleton, A. L., Toney, M. F., Bao, Z. 2014; 7 (3): 1103-1109

    View details for DOI 10.1039/c3ee43541e

    View details for Web of Science ID 000333203900028

  • Lead candidates for high-performance organic photovoltaics from high-throughput quantum chemistry - the Harvard Clean Energy Project ENERGY & ENVIRONMENTAL SCIENCE Hachmann, J., Olivares-Amaya, R., Jinich, A., Appleton, A. L., Blood-Forsythe, M. A., Seress, L. R., Roman-Salgado, C., Trepte, K., Atahan-Evrenk, S., Er, S., Shrestha, S., Mondal, R., Sokolov, A., Bao, Z., Aspuru-Guzik, A. 2014; 7 (2): 698-704

    View details for DOI 10.1039/c3ee42756k

    View details for Web of Science ID 000331413700023

  • A flexible bimodal sensor array for simultaneous sensing of pressure and temperature. Advanced materials Tien, N. T., Jeon, S., Kim, D., Trung, T. Q., Jang, M., Hwang, B., Byun, K., Bae, J., Lee, E., Tok, J. B., Bao, Z., Lee, N., Park, J. 2014; 26 (5): 796-804

    Abstract

    Diverse signals generated from the sensing elements embedded in flexible electronic skins (e-skins) are typically interfered by strain energy generated through processes such as touching, bending, stretching or twisting. Herein, we demonstrate a flexible bimodal sensor that can separate a target signal from the signal by mechanical strain through the integration of a multi-stimuli responsive gate dielectric and semiconductor channel into the single field-effect transistor (FET) platform.

    View details for DOI 10.1002/adma.201302869

    View details for PubMedID 24493054

  • Ultrafast energy transfer from rigid, branched side-chains into a conjugated, alternating copolymer JOURNAL OF CHEMICAL PHYSICS Griffin, G. B., Lundin, P. M., Rolczynski, B. S., Linkin, A., McGillicuddy, R. D., Bao, Z., Engel, G. S. 2014; 140 (3)

    View details for DOI 10.1063/1.4855156

    View details for Web of Science ID 000330614400056

  • Side Chain Engineering in Solution-Processable Conjugated Polymers CHEMISTRY OF MATERIALS Mei, J., Bao, Z. 2014; 26 (1): 604-615

    View details for DOI 10.1021/cm4020805

    View details for Web of Science ID 000330416900050

  • High-Mobility, Aligned Crystalline Domains of TIPS-Pentacene with Metastable Polymorphs Through Lateral Confinement of Crystal Growth. Advanced materials Giri, G., Park, S., Vosgueritchian, M., Shulaker, M. M., Bao, Z. 2014; 26 (3): 487-493

    Abstract

    Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals. This lateral confinement causes aligned crystal growth, and the smallest patterns of 0.5 μm wide solvent wetting regions promotes formation of highly strained, aligned, and single-crystalline TIPS-pentacene regions with mobility as high as 2.7 cm(2) V(-1) s(-1) .

    View details for DOI 10.1002/adma.201302439

    View details for PubMedID 24133041

  • Probing the interfacial molecular packing in TIPS-pentacene organic semiconductors by surface enhanced Raman scattering JOURNAL OF MATERIALS CHEMISTRY C Xu, J., Diao, Y., Zhou, D., Mao, Y., Giri, G., Chen, W., Liu, N., Mannsfeld, S. C., Xue, G., Bao, Z. 2014; 2 (16): 2985-2991

    View details for DOI 10.1039/c3tc32581d

    View details for Web of Science ID 000334123800020

  • Nanostructured conductive polypyrrole hydrogels as high-performance, flexible supercapacitor electrodes JOURNAL OF MATERIALS CHEMISTRY A Shi, Y., Pan, L., Liu, B., Wang, Y., Cui, Y., Bao, Z., Yu, G. 2014; 2 (17): 6086-6091

    View details for DOI 10.1039/c4ta00484a

    View details for Web of Science ID 000333580700016

  • Swelling of Polymer Dielectric Thin Films for Organic-Transistor-Based Aqueous Sensing Applications CHEMISTRY OF MATERIALS Verploegen, E., Sokolov, A. N., Akgun, B., Satija, S. K., Wei, P., Kim, D., Kapelewski, M. T., Bao, Z., Toney, M. F. 2013; 25 (24): 5018-5022

    View details for DOI 10.1021/cm4032013

    View details for Web of Science ID 000329137800022

  • Side-Chain Engineering of Isoindigo-Containing Conjugated Polymers Using Polystyrene for High-Performance Bulk Heterojunction Solar Cells CHEMISTRY OF MATERIALS Fang, L., Zhou, Y., Yao, Y., Diao, Y., Lee, W., Appleton, A. L., Allen, R., Reinspach, J., Mannsfeld, S. C., Bao, Z. 2013; 25 (24): 4874-4880

    View details for DOI 10.1021/cm4024259

    View details for Web of Science ID 000329137800006

  • Thiol-ene Cross-Linked Polymer Gate Dielectrics for Low-Voltage Organic Thin-Film Transistors CHEMISTRY OF MATERIALS Wang, C., Lee, W., Nakajima, R., Mei, J., Kim, D. H., Bao, Z. 2013; 25 (23): 4806-4812

    View details for DOI 10.1021/cm403203k

    View details for Web of Science ID 000328437300021

  • Conjugated Polymer-Mediated Polymorphism of a High Performance, Small-Molecule Organic Semiconductor with Tuned Intermolecular Interactions, Enhanced Long-Range Order, and Charge Transport CHEMISTRY OF MATERIALS Chen, J., Shao, M., Xiao, K., He, Z., Li, D., Lokitz, B. S., Hensley, D. K., Kilbey, S. M., Anthony, J. E., Keum, J. K., Rondinone, A. J., Lee, W., Hong, S., Bao, Z. 2013; 25 (21): 4378-4386

    View details for DOI 10.1021/cm403039y

    View details for Web of Science ID 000327045000029

  • Mechanistic Study on the Solution-Phase n-Doping of 1,3-Dimethyl-2-aryl-2,3-dihydro-1H-benzoimidazole Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Naab, B. D., Guo, S., Olthof, S., Evans, E. G., Wei, P., Millhauser, G. L., Kahn, A., Barlow, S., Marder, S. R., Bao, Z. 2013; 135 (40): 15018-15025

    Abstract

    The discovery of air-stable n-dopants for organic semiconductor materials has been hindered by the necessity of high-energy HOMOs and the air sensitivity of compounds that satisfy this requirement. One strategy for circumventing this problem is to utilize stable precursor molecules that form the active doping complex in situ during the doping process or in a postdeposition thermal- or photo-activation step. Some of us have reported on the use of 1H-benzimidazole (DMBI) and benzimidazolium (DMBI-I) salts as solution- and vacuum-processable n-type dopant precursors, respectively. It was initially suggested that DMBI dopants function as single-electron radical donors wherein the active doping species, the imidazoline radical, is generated in a postdeposition thermal annealing step. Herein we report the results of extensive mechanistic studies on DMBI-doped fullerenes, the results of which suggest a more complicated doping mechanism is operative. Specifically, a reaction between the dopant and host that begins with either hydride or hydrogen atom transfer and which ultimately leads to the formation of host radical anions is responsible for the doping effect. The results of this research will be useful for identifying applications of current organic n-doping technology and will drive the design of next-generation n-type dopants that are air stable and capable of doping low-electron-affinity host materials in organic devices.

    View details for DOI 10.1021/ja403906d

    View details for Web of Science ID 000326356400025

    View details for PubMedID 24011269

  • A rapid and efficient self-healing thermo-reversible elastomer crosslinked with graphene oxide. Advanced materials Wang, C., Liu, N., Allen, R., Tok, J. B., Wu, Y., Zhang, F., Chen, Y., Bao, Z. 2013; 25 (40): 5785-5790

    View details for DOI 10.1002/adma.201302962

    View details for PubMedID 23946261

  • Solution-Grown Organic Single-Crystalline p-n Junctions with Ambipolar Charge Transport ADVANCED MATERIALS Fan, C., Zoombelt, A. P., Jiang, H., Fu, W., Wu, J., Yuan, W., Wang, Y., Li, H., Chen, H., Bao, Z. 2013; 25 (40): 5762-?

    Abstract

    Organic single-crystalline p-n junctions are grown from mixed solutions. First, C60 crystals (n-type) form and, subsequently, C8-BTBT crystals (p-type) nucleate heterogeneously on the C60 crystals. Both crystals continue to grow simultaneously into single-crystalline p-n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single-crystalline p-n junctions.

    View details for DOI 10.1002/adma.201302605

    View details for Web of Science ID 000330773400011

    View details for PubMedID 23956037

  • High Mobility N-Type Transistors Based on Solution-Sheared Doped 6,13-Bis(triisopropylsilylethynyl)pentacene Thin Films. Advanced materials Naab, B. D., Himmelberger, S., Diao, Y., Vandewal, K., Wei, P., Lussem, B., Salleo, A., Bao, Z. 2013; 25 (33): 4663-4667

    Abstract

    An N-Type organic thin-film transistor (OTFT) based on doped 6,13-Bis(triisopropylsilylethynyl)pentacene is presented. A transition from p-type to n-type occurrs with increasing doping concentrations, and the highest performing n-channel OTFTs are obtained with 50 mol% dopant. X-ray diffraction, scanning Auger microscopy, and secondary ionization mass spectrometry are used to characterize the morphology of the blends. The high performance of the obtained transistors is attributed to the highly crystalline and aligned nature of the doped thin films.

    View details for DOI 10.1002/adma.201205098

    View details for PubMedID 23813467

  • Aligned SWNT Films from Low-Yield Stress Gels and Their Transparent Electrode Performance ACS APPLIED MATERIALS & INTERFACES Allen, R., Fuller, G. G., Bao, Z. 2013; 5 (15): 7244-7252

    Abstract

    Carbon nanotube films are promising for transparent electrodes for solar cells and displays. Large-area alignment of the nanotubes in these films is needed to minimize the sheet resistance. We present a novel coating method to coat high-density, aligned nanotubes over large areas. Carbon nanotube gel dispersions used in this study have aligned domains and a low yield stress. A simple shearing force allows these domains to uniformly align. We use this to correlate the transparent electrode performance of single-walled carbon nanotube films with the level of partial alignment. We have found that the transparent electrode performance improves with increasing levels of alignment and in a manner slightly better than what has been previously predicted.

    View details for DOI 10.1021/am401592v

    View details for Web of Science ID 000323241100066

    View details for PubMedID 23823600

  • Observation of orientation-dependent photovoltaic behaviors in aligned organic nanowires APPLIED PHYSICS LETTERS Oh, J. H., Wong, L. H., Yu, H., Park, Y. J., Kim, J. M., Bao, Z. 2013; 103 (5)

    View details for DOI 10.1063/1.4817299

    View details for Web of Science ID 000322723000099

  • Ultra-Smooth and Ultra-Strong Ion-Exchanged Glass as Substrates for Organic Electronics ADVANCED FUNCTIONAL MATERIALS Kaefer, D., He, M., Li, J., Pambianchi, M. S., Feng, J., Mauro, J. C., Bao, Z. 2013; 23 (25): 3233-3238
  • Atomic layer deposition of high-k dielectrics on single-walled carbon nanotubes: a Raman study NANOTECHNOLOGY Liyanage, L. S., Cott, D. J., Delabie, A., Van Elshocht, S., Bao, Z., Wong, H. P. 2013; 24 (24)

    Abstract

    Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, to realize a carbon nanotube field effect transistor (CNTFET) with excellent gate control, the high-k dielectrics between the CNT and the metal gate must have superb electrical properties and extremely high uniformity. Thus it is essential to understand the interactions between high-k materials and the SWCNTs to effectively control the transistor characteristics. In this study, we investigate the effects of atomic layer deposited (ALD) high-k dielectrics (Al2O3 and HfO2) on SWCNTs using Raman spectroscopy. We subjected the SWCNTs to various ALD cycles and studied the nucleation and growth of ALD dielectrics at defect sites using scanning electron microscopy and transmission electron microscopy images. We analyzed these samples using Raman spectroscopy and x-ray photoelectron spectroscopy. The Raman peak shifts of the G-peak and the 2D (G') peaks suggest doping and stress induced effects on the CNTs by the surrounding high-k oxide environment. Trends in the G-peak FWHM and G/D-peak ratios were identified and compared between Al2O3 and HfO2. We confirmed the ALD-deposited HfO2 is polycrystalline using x-ray diffraction and analyzed dielectric-CNT bonding states using XPS measurements. This study provides insights on the effects of ALD high-k materials on SWCNTs for future high-speed transistor applications.

    View details for DOI 10.1088/0957-4484/24/24/245703

    View details for Web of Science ID 000319384300021

    View details for PubMedID 23696347

  • Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors. ACS nano Hammock, M. L., Knopfmacher, O., Naab, B. D., Tok, J. B., Bao, Z. 2013; 7 (5): 3970-3980

    Abstract

    Biodetection using organic field-effect transistors (OFETs) is gaining increasing interest for applications as diverse as food security, environmental monitoring, and medical diagnostics. However, there still lacks a comprehensive, empirical study on the fundamental limits of OFET sensors. In this paper, we present a thorough study of the various parameters affecting biosensing using an OFET decorated with gold nanoparticle (AuNP) binding sites. These parameters include the spacing between receptors, pH of the buffer, and ionic strength of the buffer. To this end, we employed the thrombin protein and its corresponding DNA binding aptamer to form our model detection system. We demonstrate a detection limit of 100 pM for this protein with high selectivity over other proteases in situ. We describe herein a feasible approach for protein detection with OFETs and a thorough investigation of parameters governing biodetection events using OFETs. Our obtained results should provide important guidelines to tailor the sensor's dynamic range to suit other desired OFET-based biodetection applications.

    View details for DOI 10.1021/nn305903q

    View details for PubMedID 23597051

  • Tuning the Dirac Point in CVD-Grown Graphene through Solution Processed n-Type Doping with 2-(2-Methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole. Nano letters Wei, P., Liu, N., Lee, H. R., Adijanto, E., Ci, L., Naab, B. D., Zhong, J. Q., Park, J., Chen, W., Cui, Y., Bao, Z. 2013; 13 (5): 1890-1897

    Abstract

    Controlling the Dirac point of graphene is essential for complementary circuits. Here, we describe the use of 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole (o-MeO-DMBI) as a strong n-type dopant for chemical-vapor-deposition (CVD) grown graphene. The Dirac point of graphene can be tuned significantly by spin-coating o-MeO-DMBI solutions on the graphene sheets at different concentrations. The transport of graphene can be changed from p-type to ambipolar and finally n-type. The electron transfer between o-MeO-DMBI and graphene was additionally confirmed by Raman imaging and photoemission spectroscopy (PES) measurements. Finally, we fabricated a complementary inverter via inkjet printing patterning of o-MeO-DMBI solutions on graphene to demonstrate the potential of o-MeO-DMBI n-type doping on graphene for future applications in electrical devices.

    View details for DOI 10.1021/nl303410g

    View details for PubMedID 23537351

  • p-Channel Field-Effect Transistors Based on C-60 Doped with Molybdenum Trioxide ACS APPLIED MATERIALS & INTERFACES Lee, T. H., Luessem, B., Kim, K., Giri, G., Nishi, Y., Bao, Z. 2013; 5 (7): 2337-2341

    Abstract

    Fullerene (C60) is a well-known n-channel organic semiconductor. We demonstrate that p-channel C60 field-effect transistors are possible by doping with molybdenum trioxide (MoO3). The device performance of the p-channel C60 field-effect transistors, such as mobility, threshold voltage, and on/off ratio is varied in a controlled manner by changing doping concentration. This work demonstrates the utility of charge transfer doping to obtain both n- and p-channel field-effect transistors with a single organic semiconductor.

    View details for DOI 10.1021/am3026568

    View details for Web of Science ID 000317549100007

    View details for PubMedID 23446111

  • Scalable Synthesis of Fused Thiophene-Diketopyrrolopyrrole Semiconducting Polymers Processed from Nonchlorinated Solvents into High Performance Thin Film Transistors CHEMISTRY OF MATERIALS Matthews, J. R., Niu, W., Tandia, A., Wallace, A. L., Hu, J., Lee, W., Giri, G., Mannsfeld, S. C., Xie, Y., Cai, S., Fong, H. H., Bao, Z., He, M. 2013; 25 (5): 782-789

    View details for DOI 10.1021/cm303953e

    View details for Web of Science ID 000316168800017

  • Hybrid nanostructured materials for high-performance electrochemical capacitors NANO ENERGY Yu, G., Xie, X., Pan, L., Bao, Z., Cui, Y. 2013; 2 (2): 213-234
  • Look fast: Crystallization of conjugated molecules during solution shearing probed in-situ and in real time by X-ray scattering PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Smilgies, D., Li, R., Giri, G., Chou, K. W., Diao, Y., Bao, Z., Amassian, A. 2013; 7 (3): 177-179
  • Scalable and Selective Dispersion of Semiconducting Arc-Discharged Carbon Nanotubes by Dithiafulvalene/Thiophene Copolymers for Thin Film Transistors ACS NANO Wang, H., Mei, J., Liu, P., Schmidt, K., Jimenez-Oses, G., Osuna, S., Fang, L., Tassone, C. J., Zoombelt, A. P., Sokolov, A. N., Houk, K. N., Toney, M. F., Bao, Z. 2013; 7 (3): 2659-2668

    Abstract

    We report a simple and scalable method to enrich large quantities of semiconducting arc-discharged single-walled carbon nanotubes (SWNTs) with diameters of 1.1-1.8 nm using dithiafulvalene/thiophene copolymers. Stable solutions of highly individualized and highly enriched semiconducting SWNTs were obtained after a simple sonication and centrifuge process. Molecular dynamics (MD) simulations of polymer backbone interactions with and without side chains indicated that the presence of long alkyl side chains gave rise to the selectivity toward semiconducting tubes, indicating the importance of the roles of the side chains to both solubilize and confer selectivity to the polymers. We found that, by increasing the ratio of thiophene to dithiafulvalene units in the polymer backbone (from pDTFF-1T to pDTFF-3T), we can slightly improve the selectivity toward semiconducting SWNTs. This is likely due to the more flexible backbone of pDTFF-3T that allows the favorable wrapping of SWNTs with certain chirality as characterized by small-angle X-ray scattering. However, the dispersion yield was reduced from pDTFF-1T to pDTFF-3T. MD simulations showed that the reduction is due to the smaller polymer/SWNT contact area, which reduces the dispersion ability of pDTFF-3T. These experimental and modeling results provide a better understanding for future rational design of polymers for sorting SWNTs. Finally, high on/off ratio solution-processed thin film transistors were fabricated from the sorted SWNTs to confirm the selective dispersion of semiconducting arc-discharge SWNTs.

    View details for DOI 10.1021/nn4000435

    View details for Web of Science ID 000316846700086

    View details for PubMedID 23402644

  • A Comparison of the Properties of Two Structurally Equivalent but Regiochemically Different Mono-Alkylated Polybithiophenes Prepared Through AABB-Type Stille Polycondensation JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Lundin, P. M., Giri, G., Bao, Z. 2013; 51 (4): 908-915

    View details for DOI 10.1002/pola.26448

    View details for Web of Science ID 000314150500018

  • Comparison of the Photovoltaic Characteristics and Nanostructure of Fullerenes Blended with Conjugated Polymers with Siloxane-Terminated and Branched Aliphatic Side Chains CHEMISTRY OF MATERIALS Kim, D. H., Ayzner, A. L., Appleton, A. L., Schmidt, K., Mei, J., Toney, M. F., Bao, Z. 2013; 25 (3): 431-440

    View details for DOI 10.1021/cm303572d

    View details for Web of Science ID 000315018500020

  • High-Performance Phototransistors Based on Single-Crystalline n-Channel Organic Nanowires and Photogenerated Charge-Carrier Behaviors ADVANCED FUNCTIONAL MATERIALS Yu, H., Bao, Z., Oh, J. H. 2013; 23 (5): 629-639
  • Oriented, polymer-stabilized carbon nanotube films: influence of dispersion rheology NANOTECHNOLOGY Allen, R., Bao, Z., Fuller, G. G. 2013; 24 (1)

    Abstract

    Thin carbon nanotube films have great potential for transparent electrodes for solar cells and displays. One advantage for using carbon nanotubes is the potential for solution processing. However, research has not been done to connect solution rheological properties with the corresponding film characteristics. Here we study the rheological properties of single-walled carbon nanotube/polythiophene composite dispersions to better understand the alignment that can be achieved during deposition. Several parameters are varied to explore the cause of the alignment and the requirements of achieving a uniform, aligned carbon nanotube/polythiophene film. By understanding the dispersions thoroughly, the film quality can be predicted.

    View details for DOI 10.1088/0957-4484/24/1/015709

    View details for Web of Science ID 000312272500031

    View details for PubMedID 23221393

  • A review of fabrication and applications of carbon nanotube film-based flexible electronics NANOSCALE Park, S., Vosguerichian, M., Bao, Z. 2013; 5 (5): 1727-1752

    Abstract

    Flexible electronics offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags. Carbon nanotubes (CNTs) are a promising material for flexible electronics, both as the channel material in field-effect transistors (FETs) and as transparent electrodes, due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. In this feature article, we review the recent progress of CNTs in flexible electronics by describing both the processing and the applications of CNT-based flexible devices. To employ CNTs as the channel material in FETs, single-walled carbon nanotubes (SWNTs) are used. There are generally two methods of depositing SWNTs on flexible substrates-transferring CVD-grown SWNTs or solution-depositing SWNTs. Since CVD-grown SWNTs can be highly aligned, they often outperform solution-processed SWNT films that are typically in the form of random network. However, solution-based SWNTs can be printed at a large-scale and at low-cost, rendering them more appropriate for manufacturing. In either case, the removal of metallic SWNTs in an effective and a scalable manner is critical, which must still be developed and optimized. Nevertheless, promising results demonstrating SWNT-based flexible circuits, displays, RF-devices, and biochemical sensors have been reported by various research groups, proving insight into the exciting possibilities of SWNT-based FETs. In using carbon nanotubes as transparent electrodes (TEs), two main strategies have been implemented to fabricate highly conductive, transparent, and mechanically compliant films-superaligned films of CNTs drawn from vertically grown CNT forests using the "dry-drawing" technique and the deposition or embedding of CNTs onto flexible or stretchable substrates. The main challenge for CNT based TEs is to fabricate films that are both highly conductive and transparent. These CNT based TEs have been used in stretchable and flexible pressure, strain, and chemical and biological sensors. In addition, they have also been used as the anode and cathode in flexible light emitting diodes, solar cells, and supercapacitors. In summary, there are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.

    View details for DOI 10.1039/c3nr33560g

    View details for Web of Science ID 000314931900002

    View details for PubMedID 23381727

  • Cooperative Spectrum Sensing With Adaptive Energy Threshold Control and Efficient Data Fusion 2nd IEEE/CIC International Conference on Communications in China (ICCC) Ling, X., Bao, Z., Wen, H., Wu, B., Xu, S., Pan, L. IEEE. 2013: 362–367
  • A Novel X-band Differential Bandpass Filter Based on Oversized Substrate Integrated Waveguide Cavity Cross Strait Quad-Regional Radio Science and Wireless Technology Conference (CSQRWC) Jin, C., Chen, J., Chu, H., Bao, Z. IEEE. 2013: 62–65
  • Tuning the Dirac Point in CVD-Grown Graphene through Solution Processed n-Type Doping with 2-(2-Methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole Nano Lett. Wei, P., Liu, N., Lee, H., R., Adijanto, E., Ci, L., Naab, B., D., Bao, Z. 2013; 13: 1890-1897
  • Effects of Odd-Even Side Chain Length of Alkyl-Substituted Diphenyl-bithiophenes on First Monolayer Thin Film Packing Structure J. Am. Chem. Soc. Akkerman, H., B., Mannsfeld, S., C.B., Kaushik, A., P., Verploegen, E., Burnier, L., Zoombelt, A., P., Bao, Z. 2013; 135: 11006-11014
  • A Rapid and Efficient Self-Healing Thermo-Reversible Elastomer Crosslinked with Graphene Oxide Adv. Mater. Wang, C., Liu, N., Allen, R., Tok, J., B.-H., Wu, Y., Zhang, F., Bao, Z. 2013; 25: 5785-5790
  • Confined organization of fullerene units along high polymer chains JOURNAL OF MATERIALS CHEMISTRY C Fang, L., Liu, P., Sveinbjornsson, B. R., Atahan-Evrenk, S., Vandewal, K., Osuna, S., Jimenez-Oses, G., Shrestha, S., Giri, G., Wei, P., Salleo, A., Aspuru-Guzik, A., Grubbs, R. H., Houk, K. N., Bao, Z. 2013; 1 (36): 5747-5755

    View details for DOI 10.1039/c3tc31158a

    View details for Web of Science ID 000323578000020

  • Observation of orientation-dependent photovoltaic behaviors in aligned organic nanowires Appl. Phys. Lett. Oh, J., H., Wong, L., H., Yu, H., Park, Y., J., Kim, J., M., Bao, Z. 2013; 103: 53304
  • Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors ACS Nano Hammock, M., L., Knopfmacher, O., Naab, B., D., Tok, J., B., Bao, Z. 2013; 7: 3970-3980
  • High Mobility N-Type Transistors Based on Solution-sheared Doped TIPS-pentacene Thin Films Adv. Mat. Naab, B., D., Himmelberger, S., Diao, Y., Vandewal, k., Wei, P., Lussem, B., Bao, Z. 2013; 25: 4663-4667
  • Solution-Grown Organic Single-Crystalline p-n Junctions with Ambipolar Charge Transport Adv. Mater. Fan, C., Zoombelt, A., P., Jiang, H., Fu, W., Wu, J., Yuan, W., Bao, Z. 2013
  • Mechanistic Study on the Solution-Phase n-Doping of 1,3-Dimethyl-2-aryl-2,3-dihydro-1H-benzoimidazole Derivatives J. Am. Chem. Soc. Naab, B., D., Guo, S., Olthof, S., Evans, E. G., B., Wei, P., Millhauser, G., L., Bao, Z. 2013
  • Toward high-mobility organic field-effect transistors: Control of molecular packing and large-area fabrication of single-crystal-based devices MRS BULLETIN Li, H., Giri, G., Tok, J. B., Bao, Z. 2013; 38 (1): 34-42
  • A comparison of two air-stable molecular n-dopants for C-60 ORGANIC ELECTRONICS Menke, T., Wei, P., Ray, D., Kleemann, H., Naab, B. D., Bao, Z., Leo, K., Riede, M. 2012; 13 (12): 3319-3325
  • Toward mechanically robust and intrinsically stretchable organic solar cells: Evolution of photovoltaic properties with tensile strain SOLAR ENERGY MATERIALS AND SOLAR CELLS Lipomi, D. J., Chong, H., Vosgueritchian, M., Mei, J., Bao, Z. 2012; 107: 355-365
  • A simple droplet pinning method for polymer film deposition for measuring charge transport in a thin film transistor ORGANIC ELECTRONICS Li, H., Mei, J., Ayzner, A. L., Toney, M. F., Tok, J. B., Bao, Z. 2012; 13 (11): 2450-2460
  • Evaluation of Solution-Processable Carbon-Based Electrodes for All-Carbon Solar Cells ACS NANO Ramuz, M. P., Vosgueritchian, M., Wei, P., Wang, C., Gao, Y., Wu, Y., Chen, Y., Bao, Z. 2012; 6 (11): 10384-10395

    Abstract

    Carbon allotropes possess unique and interesting physical, chemical, and electronic properties that make them attractive for next-generation electronic devices and solar cells. In this report, we describe our efforts into the fabrication of the first reported all-carbon solar cell in which all components (the anode, active layer, and cathode) are carbon based. First, we evaluate the active layer, on standard electrodes, which is composed of a bilayer of polymer sorted semiconducting single-walled carbon nanotubes and C(60). This carbon-based active layer with a standard indium tin oxide anode and metallic cathode has a maximum power conversion efficiency of 0.46% under AM1.5 Sun illumination. Next, we describe our efforts in replacing the electrodes with carbon-based electrodes, to demonstrate the first all-carbon solar cell, and discuss the remaining challenges associated with this process.

    View details for DOI 10.1021/nn304410w

    View details for Web of Science ID 000311521700114

    View details for PubMedID 23113673

  • Manipulating the Morphology of P3HT-PCBM Bulk Heterojunction Blends with Solvent Vapor Annealing CHEMISTRY OF MATERIALS Verploegen, E., Miller, C. E., Schmidt, K., Bao, Z., Toney, M. F. 2012; 24 (20): 3923-3931

    View details for DOI 10.1021/cm302312a

    View details for Web of Science ID 000310095100012

  • TIPS-pentacene crystalline thin film growth ORGANIC ELECTRONICS Akkerman, H. B., Li, H., Bao, Z. 2012; 13 (10): 2056-2062
  • Dispersion of single walled carbon nanotubes in amidine solvents NANOTECHNOLOGY Barman, S. N., Pan, D., Vosgueritchian, M., Zoombelt, A. P., Galli, G., Bao, Z. 2012; 23 (34)

    Abstract

    The excellent electronic and material properties of single walled carbon nanotubes (SWNTs) makes this nanomaterial very attractive for incorporation into flexible and stretchable electronics. However, the widespread application of SWNTs in electronic devices is still limited. To purify, process and place SWNTs, appropriate solvents for dispersion are needed. However, a fundamental understanding of the reasons why certain solvents are capable of dispersing SWNTs is still missing. Here we report on two new potential solvents containing amidine moieties, 1,8-diazabicycloundec-7-ene (DBU) and 1,5-diazabicyclo(4.3.0)non-5-ene (DBN). Even though these solvents' molecular structures differ by only two -CH(2)- groups, we found that DBU is capable of dispersing SWNTs, while DBN is not. We carried out density functional theory (DFT) calculations to investigate the interaction between DBU and DBN, and we elucidated the reasons for the different performances of the two solvents. DBU has a preferential edge-on interaction with the SWNT, thus allowing for a higher solvent coverage than DBN. In addition, the CH(2)-SWNT interaction present for DBU substantially increases the adsorption energy compared to DBN. Our results point to the important interplay between the interaction of pi electrons, nitrogen lone pairs and the -CH(2)- groups present in aprotic solvent molecules and the delocalized pi electrons in SWNTs.

    View details for DOI 10.1088/0957-4484/23/34/344011

    View details for Web of Science ID 000307812000012

    View details for PubMedID 22885377

  • Work function recovery of air exposed molybdenum oxide thin films APPLIED PHYSICS LETTERS Irfan, I., Turinske, A. J., Bao, Z., Gao, Y. 2012; 101 (9)

    View details for DOI 10.1063/1.4748978

    View details for Web of Science ID 000308408100070

  • Engineering the metal gate electrode for controlling the threshold voltage of organic transistors APPLIED PHYSICS LETTERS Chung, Y., Johnson, O., Deal, M., Nishi, Y., Murmann, B., Bao, Z. 2012; 101 (6)

    View details for DOI 10.1063/1.4739511

    View details for Web of Science ID 000307862400089

  • Strong and Stable Doping of Carbon Nanotubes and Graphene by MoOx for Transparent Electrodes NANO LETTERS Hellstrom, S. L., Vosgueritchian, M., Stoltenberg, R. M., Irfan, I., Hammock, M., Wang, Y. B., Jia, C., Guo, X., Gao, Y., Bao, Z. 2012; 12 (7): 3574-3580

    Abstract

    MoO(x) has been used for organic semiconductor doping, but it had been considered an inefficient and/or unstable dopant. We report that MoO(x) can strongly and stably dope carbon nanotubes and graphene. Thermally annealed MoO(x)-CNT composites can form durable thin film electrodes with sheet resistances of 100 Ω/sq at 85% transmittance plain and 85 Ω/sq at 83% transmittance with a PEDOT:PSS adlayer. Sheet resistances change less than 10% over 20 days in ambient and less than 2% with overnight heating to 300 °C in air. The MoO(x) can be easily deposited either by thermal evaporation or from solution-based precursors. Excellent stability coupled with high conductivity makes MoO(x)-CNT composites extremely attractive candidates for practical transparent electrodes.

    View details for DOI 10.1021/nl301207e

    View details for Web of Science ID 000306296200037

    View details for PubMedID 22694046

  • Transparent, Optical, Pressure-Sensitive Artificial Skin for Large-Area Stretchable Electronics ADVANCED MATERIALS Ramuz, M., Tee, B. C., Tok, J. B., Bao, Z. 2012; 24 (24): 3223-3227

    Abstract

    Optical pressure sensors are highly responsive and are unaffected by surrounding parameters such as electronic noise, humidity, temperature, etc. A new type of optical pressure sensor is described that demonstrates the stretchability and transparency of a polydimethylsiloxane waveguide, while also serving as a substrate. The pressure sensors are both robust and easy to fabricate over a large area.

    View details for DOI 10.1002/adma.201200523

    View details for Web of Science ID 000305450500009

    View details for PubMedID 22641411

  • Using Nitrile Functional Groups to Replace Amines for Solution-Deposited Single-Walled Carbon Nanotube Network Films ACS NANO Opatkiewicz, J. P., LeMieux, M. C., Liu, D., Vosgueritchian, M., Barman, S. N., Elkins, C. M., Hedrick, J., Bao, Z. 2012; 6 (6): 4845-4853

    Abstract

    Amine-terminated self-assembled monolayers (SAMs) can be utilized to selectively adsorb semiconducting single-walled carbon nanotubes (S-SWNTs), but are not ideal. Formation of these monolayer films from silanes can be dramatically influenced by atmospheric and other processing conditions, resulting in poor-quality SAMs or irreproducible results. The surface sorting method of fabricating these semiconducting nanotube networks (SWNTnts) can become ineffective if the functionalized surface is not smooth with high amine density. However, by replacing the amine with a nitrile group, SAM formation can be made more controllable and reproducible. Upon SWNT deposition, the nitrile group was found to not only adsorb higher density SWNTnts but also sort the nanotubes efficiently, as shown by micro-Raman spectroscopy. Upon testing these SWNTnts for device performance, these thin-film transistors (TFTs) were also found to yield higher quality devices than those fabricated on amine surfaces. Overall, these results expand the applicability of surface sorting and SWNT adsorption to other organic functionalities for nanotube separation. This report provides an outline of the merits and characterization of using the nitrile functional group for the separation and adsorption of SWNTs and its integration in network TFTs.

    View details for DOI 10.1021/nn300124y

    View details for Web of Science ID 000305661300031

    View details for PubMedID 22588018

  • In Situ Hetero End-Functionalized Polythiophene and Subsequent "Click" Chemistry With DNA MACROMOLECULAR RAPID COMMUNICATIONS Lee, J. K., Ko, S., Bao, Z. 2012; 33 (10): 938-942

    Abstract

    It is demonstrated that bifunctionalized polythiophenes involving thiol and azide end-functional groups can be synthesized by chain-growth Suzuki-Miyaura type polymerization. The bifunctionalized polythiophenes are successfully characterized by 1H NMR, gel permeation chromatography (GPC), and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). Furthermore, the azide end-group reacts with DNA via "click chemistry" to form a polythiophene/DNA hybrid structure, which is characterized by ESI-MS. The described synthetic approaches will lead to the synthesis of novel multi-block copolymers as well as biomolecule-based conjugated polymer structures.

    View details for DOI 10.1002/marc.201100686

    View details for Web of Science ID 000304192400008

    View details for PubMedID 22354688

  • High-Performance Transistors and Complementary Inverters Based on Solution-Grown Aligned Organic Single-Crystals ADVANCED MATERIALS Li, H., Tee, B. C., Giri, G., Chung, J. W., Lee, S. Y., Bao, Z. 2012; 24 (19): 2588-2591

    View details for DOI 10.1002/adma.201200151

    View details for Web of Science ID 000303795700008

    View details for PubMedID 22461243

  • Graphene-sponges as high-performance low-cost anodes for microbial fuel cells ENERGY & ENVIRONMENTAL SCIENCE Xie, X., Yu, G., Liu, N., Bao, Z., Criddle, C. S., Cui, Y. 2012; 5 (5): 6862-6866

    View details for DOI 10.1039/c2ee03583a

    View details for Web of Science ID 000303251500019

  • Recent advances in flexible and stretchable electronics, sensors and power sources SCIENCE CHINA-CHEMISTRY Tok, J. B., Bao Zhenan, Z. A. 2012; 55 (5): 718-725
  • Organic Transistors with Ordered Nanoparticle Arrays as a Tailorable Platform for Selective, In Situ Detection ACS NANO Hammock, M. L., Sokolov, A. N., Stoltenberg, R. M., Naab, B. D., Bao, Z. 2012; 6 (4): 3100-3108

    Abstract

    The use of organic transistors as sensing platforms provides a number of distinct advantages over conventional detection technologies, including their tunability, portability, and ability to directly transduce binding events without tedious and expensive labeling procedures. However, detection efforts using organic transistors lack a general method to uniquely specify and detect a target of interest. While highly sensitive liquid- and vapor-phase sensors have been previously reported, detection has been restricted either to the serendipitous interaction of the analyte molecules with the organic semiconductor or to the covalent functionalization of the semiconductor with receptor groups to enhance specificity. However, the former technique cannot be regularly relied upon for tailorable sensing while the latter may result in unpredictable decreases in electronic performance. Thus, a method to provide modular receptor sites on the surface of an organic transistor without damaging the device will significantly advance the field, especially regarding biological species detection. In this work, we utilized a block copolymer to template ordered, large-area arrays of gold nanoparticles, with sub-100 nm center-to-center spacing onto the surface of an organic transistor. This highly modular platform is designed for orthogonal modification with a number of available chemical and biological functional groups by taking advantage of the well-studied gold-thiol linkage. Herein, we demonstrate the functionalization of gold nanoparticles with a mercury-binding oligonucleotide sequence. Finally, we demonstrate the highly selective and robust detection of mercury(II) using this platform in an underwater environment.

    View details for DOI 10.1021/nn204830b

    View details for Web of Science ID 000303099300027

    View details for PubMedID 22397363

  • Controlled Conjugated Backbone Twisting for an Increased Open-Circuit Voltage while Having a High Short-Circuit Current in Poly(hexylthiophene) Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ko, S., Hoke, E. T., Pandey, L., Hong, S., Mondal, R., Risko, C., Yi, Y., Noriega, R., McGehee, M. D., Bredas, J., Salleo, A., Bao, Z. 2012; 134 (11): 5222-5232

    Abstract

    Conjugated polymers with nearly planar backbones have been the most commonly investigated materials for organic-based electronic devices. More twisted polymer backbones have been shown to achieve larger open-circuit voltages in solar cells, though with decreased short-circuit current densities. We systematically impose twists within a family of poly(hexylthiophene)s and examine their influence on the performance of polymer:fullerene bulk heterojunction (BHJ) solar cells. A simple chemical modification concerning the number and placement of alkyl side chains along the conjugated backbone is used to control the degree of backbone twisting. Density functional theory calculations were carried out on a series of oligothiophene structures to provide insights on how the sterically induced twisting influences the geometric, electronic, and optical properties. Grazing incidence X-ray scattering measurements were performed to investigate how the thin-film packing structure was affected. The open-circuit voltage and charge-transfer state energy of the polymer:fullerene BHJ solar cells increased substantially with the degree of twist induced within the conjugated backbone--due to an increase in the polymer ionization potential--while the short-circuit current decreased as a result of a larger optical gap and lower hole mobility. A controlled, moderate degree of twist along the poly(3,4-dihexyl-2,2':5',2''-terthiophene) (PDHTT) conjugated backbone led to a 19% enhancement in the open-circuit voltage (0.735 V) vs poly(3-hexylthiophene)-based devices, while similar short-circuit current densities, fill factors, and hole-carrier mobilities were maintained. These factors resulted in a power conversion efficiency of 4.2% for a PDHTT:[6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) blend solar cell without thermal annealing. This simple approach reveals a molecular design avenue to increase open-circuit voltage while retaining the short-circuit current.

    View details for DOI 10.1021/ja210954r

    View details for Web of Science ID 000302191900036

    View details for PubMedID 22385287

  • Contacting nanowires and nanotubes with atomic precision for electronic transport APPLIED PHYSICS LETTERS Qin, S., Hellstrom, S., Bao, Z., Boyanov, B., Li, A. 2012; 100 (10)

    View details for DOI 10.1063/1.3692585

    View details for Web of Science ID 000301655500059

  • Highly Effective Separation of Semiconducting Carbon Nanotubes verified via Short-Channel Devices Fabricated Using Dip-Pen Nanolithography ACS NANO Park, S., Lee, H. W., Wang, H., Selvarasah, S., Dokmeci, M. R., Park, Y. J., Cha, S. N., Kim, J. M., Bao, Z. 2012; 6 (3): 2487-2496

    Abstract

    We have verified a highly effective separation of semiconducting single-walled carbon nanotubes (sc-SWNTs) via statistical analysis of short-channel devices fabricated using multipen dip-pen nanolithography. Our SWNT separation technique utilizes a polymer (rr-P3DDT) that selectively interacts with and disperses sc-SWNTs. Our devices had channel lengths on the order of 300-500 nm, with an average of about 3 SWNTs that directly connected the source-drain electrodes. A total of 140 SWNTs were characterized, through which we have observed that all of the SWNTs exhibited semiconducting behavior with an average on/off current ratio of ~10(6). Additionally, we have characterized 50 SWNTs after the removal of rr-P3DDT, through which we have again observed semiconducting behavior for all of the SWNTs with similar electrical characteristics. The relatively low average on-conductance of 0.0796 μS was attributed to the distribution of small diameter SWNTs in our system and due to the non-ohmic Au contacts on SWNTs. The largely positive threshold voltages were shifted toward zero after vacuum annealing, indicating that the SWNTs were doped in air. To the best of our knowledge, this is the first time numerous SWNTs were electrically characterized using short-channel devices, through which all of the measured SWNTs were determined to be semiconducting. Hence, our semiconducting single-walled carbon nanotube sorting system holds a great deal of promise in bringing forth a variety of practical applications in SWNT electronics.

    View details for DOI 10.1021/nn204875a

    View details for Web of Science ID 000301945900064

    View details for PubMedID 22352426

  • The effect of pH and DNA concentration on organic thin-film transistor biosensors ORGANIC ELECTRONICS Khan, H. U., Roberts, M. E., Johnson, O., Knoll, W., Bao, Z. 2012; 13 (3): 519-524
  • High-Mobility Field-Effect Transistors from Large-Area Solution-Grown Aligned C-60 Single Crystals JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, H., Tee, B. C., Cha, J. J., Cui, Y., Chung, J. W., Lee, S. Y., Bao, Z. 2012; 134 (5): 2760-2765

    Abstract

    Field-effect transistors based on single crystals of organic semiconductors have the highest reported charge carrier mobility among organic materials, demonstrating great potential of organic semiconductors for electronic applications. However, single-crystal devices are difficult to fabricate. One of the biggest challenges is to prepare dense arrays of single crystals over large-area substrates with controlled alignment. Here, we describe a solution processing method to grow large arrays of aligned C(60) single crystals. Our well-aligned C(60) single-crystal needles and ribbons show electron mobility as high as 11 cm(2)V(-1)s(-1) (average mobility: 5.2 ± 2.1 cm(2)V(-1)s(-1) from needles; 3.0 ± 0.87 cm(2)V(-1)s(-1) from ribbons). This observed mobility is ~8-fold higher than the maximum reported mobility for solution-grown n-channel organic materials (1.5 cm(2)V(-1)s(-1)) and is ~2-fold higher than the highest mobility of any n-channel organic material (~6 cm(2)V(-1)s(-1)). Furthermore, our deposition method is scalable to a 100 mm wafer substrate, with around 50% of the wafer surface covered by aligned crystals. Hence, our method facilitates the fabrication of large amounts of high-quality semiconductor crystals for fundamental studies, and with substantial improvement on the surface coverage of crystals, this method might be suitable for large-area applications based on single crystals of organic semiconductors.

    View details for DOI 10.1021/ja210430b

    View details for Web of Science ID 000300460600049

    View details for PubMedID 22239604

  • Fabrication of organic semiconductor crystalline thin films and crystals from solution by confined crystallization ORGANIC ELECTRONICS Akkerman, H. B., Chang, A. C., Verploegen, E., Bettinger, C. J., Toney, M. F., Bao, Z. 2012; 13 (2): 235-243
  • Highly Conductive and Transparent PEDOT:PSS Films with a Fluorosurfactant for Stretchable and Flexible Transparent Electrodes ADVANCED FUNCTIONAL MATERIALS Vosgueritchian, M., Lipomi, D. J., Bao, Z. 2012; 22 (2): 421-428
  • Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates CHEMISTRY OF MATERIALS Lipomi, D. J., Lee, J. A., Vosgueritchian, M., Tee, B. C., Bolander, J. A., Bao, Z. 2012; 24 (2): 373-382

    View details for DOI 10.1021/cm203216m

    View details for Web of Science ID 000299367500018

  • Micro-imprinted prism substrate for self-aligned short channel organic transistors on a flexible substrate APPLIED PHYSICS LETTERS Jeon, J., Tee, B. C., Murmann, B., Bao, Z. 2012; 100 (4)

    View details for DOI 10.1063/1.3679119

    View details for Web of Science ID 000300064500064

  • Mechanistic Considerations of Bending-Strain Effects within Organic Semiconductors on Polymer Dielectrics ADVANCED FUNCTIONAL MATERIALS Sokolov, A. N., Cao, Y., Johnson, O. B., Bao, Z. 2012; 22 (1): 175-183
  • Impact of regioregularity on thin-film transistor and photovoltaic cell performances of pentacene-containing polymers JOURNAL OF MATERIALS CHEMISTRY Jiang, Y., Hong, S., Oh, J. H., Mondal, R., Okamoto, T., Verploegen, E., Toney, M. F., McGehee, M. D., Bao, Z. 2012; 22 (10): 4356-4363

    View details for DOI 10.1039/c2jm15483h

    View details for Web of Science ID 000300250200027

  • 5,11-Conjugation-extended low-bandgap anthradithiophene-containing polymer exhibiting enhanced thin-film order and field-effect mobility CHEMICAL COMMUNICATIONS Jiang, Y., Mei, J., Ayzner, A. L., Toney, M. F., Bao, Z. 2012; 48 (58): 7286-7288

    Abstract

    Anthradithiophene was incorporated in a polymer structure by extending its conjugation from the 5,11-positions, through in situ desilylation followed by acetylenic coupling with a dibromo-monomer. The resulting polymer showed largely redshifted order in a thin film as well as order in thin film, forming lamellar structures out of the substrate plane. As a result, it exhibits field-effect hole mobilities, on the order of 0.1 cm(2) V(-1) s(-1), a ten to hundred-fold improvement as compared to previous acene-containing polymers.

    View details for DOI 10.1039/c2cc32473c

    View details for Web of Science ID 000305624500018

    View details for PubMedID 22699310

  • Themed issue on "organic optoelectronic materials'' JOURNAL OF MATERIALS CHEMISTRY Hu, W., Bao, Z., Muellen, K. 2012; 22 (10): 4134-4135

    View details for DOI 10.1039/c1jm90199k

    View details for Web of Science ID 000300250200001

  • Wafer-Scale Fabrication and Characterization of Thin-Film Transistors with Polythiophene-Sorted Semiconducting Carbon Nanotube Networks ACS NANO Liyanage, L. S., Lee, H., Patil, N., Park, S., Mitra, S., Bao, Z., Wong, H. P. 2012; 6 (1): 451-458

    Abstract

    Semiconducting single-walled carbon nanotubes (SWCNTs) have great potential of becoming the channel material for future thin-film transistor technology. However, an effective sorting technique is needed to obtain high-quality semiconducting SWCNTs for optimal device performance. In our previous work, we reported a dispersion technique for semiconducting SWCNTs that relies on regioregular poly(3-dodecylthiophene) (rr-P3DDT) to form hybrid nanostructures. In this study, we demonstrate the scalability of those sorted CNT composite structures to form arrays of TFTs using standard lithographic techniques. The robustness of these CNT nanostructures was tested with Raman spectroscopy and atomic force microscope images. Important trends in device properties were extracted by means of electrical measurements for different CNT concentrations and channel lengths (L(c)). A statistical study provided an average mobility of 1 cm(2)/V·s and I(on)/I(off) as high as 10(6) for short channel lengths (L(c) = 1.5 μm) with 100% yield. This highlights the effectiveness of this sorting technique and its scalability for large-scale, flexible, and transparent display applications.

    View details for DOI 10.1021/nn203771u

    View details for Web of Science ID 000299368300055

    View details for PubMedID 22148677

  • A Cell-Compatible Conductive Film from a Carbon Nanotube Network Adsorbed on Poly-L-lysine ACS NANO Lin, D. W., Bettinger, C. J., Ferreira, J. P., Wang, C. L., Bao, Z. 2011; 5 (12): 10026-10032

    Abstract

    Single-walled carbon nanotubes (SWNTs) have shown promise for use in organic electronic applications including thin film transistors, conducting electrodes, and biosensors. Additionally, previous studies found applications for SWNTs in bioelectronic devices, including drug delivery carriers and scaffolds for tissue engineering. There is a current need to rapidly process SWNTs from solution phase to substrates in order to produce device structures that are also biocompatible. Studies have shown the use of surfaces covalently functionalized with primary amines to selectively adsorb semiconducting SWNTs. Here we report the potential of substrates modified with physisorbed polymers as a rapid biomaterials-based approach for the formation of SWNT networks. We hypothesized that rapid surface modification could be accomplished by adsorption of poly-L-lysine (PLL), which is also frequently used in biological applications. We detail a rapid and facile method for depositing SWNTs onto various substrate materials using the amine-rich PLL. Dispersions of SWNTs of different chiralities suspended in N-methylpyrrolidinone (NMP) were spin coated onto various PLL-treated substrates. SWNT adsorption and alignment were characterized by atomic force microscopy (AFM) while electrical properties of the network were characterized by 2-terminal resistance measurements. Additionally, we investigated the relative chirality of the SWNT networks by micro-Raman spectroscopy. The SWNT surface density was strongly dependent upon the adsorbed concentration of PLL on the surface. SWNT adsorbed on PLL-treated substrates exhibited enhanced biocompatibility compared to SWNT networks fabricated using alternative methods such as drop casting. These results suggest that PLL films can promote formation of biocompatible SWNT networks for potential biomedical applications.

    View details for DOI 10.1021/nn203870c

    View details for Web of Science ID 000298316700079

    View details for PubMedID 22053708

  • High-Mobility Air-Stable Solution-Shear-Processed n-Channel Organic Transistors Based on Core-Chlorinated Naphthalene Diimides ADVANCED FUNCTIONAL MATERIALS Lee, W., Oh, J. H., Suraru, S., Chen, W., Wuerthner, F., Bao, Z. 2011; 21 (21): 4173-4181
  • Improving the Performance of Lithium-Sulfur Batteries by Conductive Polymer Coating ACS NANO Yang, Y., Yu, G., Cha, J. J., Wu, H., Vosgueritchian, M., Yao, Y., Bao, Z., Cui, Y. 2011; 5 (11): 9187-9193

    View details for DOI 10.1021/nn203436j

    View details for Web of Science ID 000297143300081

    View details for PubMedID 21995642

  • Carrier mobility in pentacene as a function of grain size and orientation derived from scanning transmission X-ray microscopy ORGANIC ELECTRONICS Braeuer, B., Kukreja, R., Virkar, A., Akkerman, H. B., Fognini, A., Tyliszczak, T., Bao, Z. 2011; 12 (11): 1936-1942
  • Enhancing the Supercapacitor Performance of Graphene/MnO2 Nanostructured Electrodes by Conductive Wrapping NANO LETTERS Yu, G., Hu, L., Liu, N., Wang, H., Vosgueritchian, M., Yang, Y., Cui, Y., Bao, Z. 2011; 11 (10): 4438-4442

    Abstract

    MnO2 is considered one of the most promising pseudocapactive materials for high-performance supercapacitors given its high theoretical specific capacitance, low-cost, environmental benignity, and natural abundance. However, MnO2 electrodes often suffer from poor electronic and ionic conductivities, resulting in their limited performance in power density and cycling. Here we developed a "conductive wrapping" method to greatly improve the supercapacitor performance of graphene/MnO2-based nanostructured electrodes. By three-dimensional (3D) conductive wrapping of graphene/MnO2 nanostructures with carbon nanotubes or conducting polymer, specific capacitance of the electrodes (considering total mass of active materials) has substantially increased by ∼20% and ∼45%, respectively, with values as high as ∼380 F/g achieved. Moreover, these ternary composite electrodes have also exhibited excellent cycling performance with >95% capacitance retention over 3000 cycles. This 3D conductive wrapping approach represents an exciting direction for enhancing the device performance of metal oxide-based electrochemical supercapacitors and can be generalized for designing next-generation high-performance energy storage devices.

    View details for DOI 10.1021/nl2026635

    View details for Web of Science ID 000295667000073

    View details for PubMedID 21942427

  • Stretchable, elastic materials and devices for solar energy conversion ENERGY & ENVIRONMENTAL SCIENCE Lipomi, D. J., Bao, Z. 2011; 4 (9): 3314-3328

    View details for DOI 10.1039/c1ee01881g

    View details for Web of Science ID 000294306900015

  • Solution-Processed Graphene/MnO2 Nanostructured Textiles for High-Performance Electrochemical Capacitors NANO LETTERS Yu, G., Hu, L., Vosgueritchian, M., Wang, H., Xie, X., McDonough, J. R., Cui, X., Cui, Y., Bao, Z. 2011; 11 (7): 2905-2911

    Abstract

    Large scale energy storage system with low cost, high power, and long cycle life is crucial for addressing the energy problem when connected with renewable energy production. To realize grid-scale applications of the energy storage devices, there remain several key issues including the development of low-cost, high-performance materials that are environmentally friendly and compatible with low-temperature and large-scale processing. In this report, we demonstrate that solution-exfoliated graphene nanosheets (∼5 nm thickness) can be conformably coated from solution on three-dimensional, porous textiles support structures for high loading of active electrode materials and to facilitate the access of electrolytes to those materials. With further controlled electrodeposition of pseudocapacitive MnO(2) nanomaterials, the hybrid graphene/MnO(2)-based textile yields high-capacitance performance with specific capacitance up to 315 F/g achieved. Moreover, we have successfully fabricated asymmetric electrochemical capacitors with graphene/MnO(2)-textile as the positive electrode and single-walled carbon nanotubes (SWNTs)-textile as the negative electrode in an aqueous Na(2)SO(4) electrolyte solution. These devices exhibit promising characteristics with a maximum power density of 110 kW/kg, an energy density of 12.5 Wh/kg, and excellent cycling performance of ∼95% capacitance retention over 5000 cycles. Such low-cost, high-performance energy textiles based on solution-processed graphene/MnO(2) hierarchical nanostructures offer great promise in large-scale energy storage device applications.

    View details for DOI 10.1021/nl2013828

    View details for Web of Science ID 000292849400059

    View details for PubMedID 21667923

  • Stretchable Organic Solar Cells ADVANCED MATERIALS Lipomi, D. J., Tee, B. C., Vosgueritchian, M., Bao, Z. 2011; 23 (15): 1771-?

    View details for DOI 10.1002/adma.201004426

    View details for Web of Science ID 000289531800014

    View details for PubMedID 21491510

  • Pentacene Based Organic Thin Film Transistors as the Transducer for Biochemical Sensing in Aqueous Media CHEMISTRY OF MATERIALS Khan, H. U., Roberts, M. E., Knoll, W., Bao, Z. 2011; 23 (7): 1946-1953

    View details for DOI 10.1021/cm103685c

    View details for Web of Science ID 000289029400039

  • Aryl-Perfluoroaryl Substituted Tetracene: Induction of Face-to-Face pi-pi Stacking and Enhancement of Charge Carrier Properties CHEMISTRY OF MATERIALS Okamoto, T., Nakahara, K., Saeki, A., Seki, S., Oh, J. H., Akkerman, H. B., Bao, Z., Matsuo, Y. 2011; 23 (7): 1646-1649

    View details for DOI 10.1021/cm200356y

    View details for Web of Science ID 000289029400004

  • The Phase Behavior of a Polymer-Fullerene Bulk Heterojunction System that Contains Bimolecular Crystals JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS Miller, N. C., Gysel, R., Miller, C. E., Verploegen, E., Beiley, Z., Heeney, M., McCulloch, I., Bao, Z., Toney, M. F., McGehee, M. D. 2011; 49 (7): 499-503

    View details for DOI 10.1002/polb.22214

    View details for Web of Science ID 000288541400003

  • Solution-Shear-Processed Quaterrylene Diimide Thin-Film Transistors Prepared by Pressure-Assisted Thermal Cleavage of Swallow Tails JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Oh, J. H., Lee, W., Noe, T., Chen, W., Koenemann, M., Bao, Z. 2011; 133 (12): 4204-4207

    Abstract

    A scalable synthesis of swallow-tailed quaterrylene diimides (STQDIs) and a method for the solution processing of sparingly soluble quaterrylene diimide (QDI) thin films are described. The pressure-assisted thermal cleavage of swallow tails yields crystalline QDI layers with electron mobility up to 0.088 cm(2) V(-1) s(-1). The developed method opens up a new route toward the solution processing of higher rylene diimides with poor solubility.

    View details for DOI 10.1021/ja110486s

    View details for Web of Science ID 000291715300015

    View details for PubMedID 21375243

  • The effect of amine protonation on the electrical properties of spin-assembled single-walled carbon nanotube networks NANOTECHNOLOGY Opatkiewicz, J. P., LeMieux, M. C., Patil, N. P., Wei, H., Mitra, S., Bao, Z. 2011; 22 (12)

    Abstract

    Amine-terminated self-assembled monolayers (SAMs) have been shown to selectively adsorb semiconducting single-walled carbon nanotubes (sc-SWNTs). Previous studies have shown that when deposited by spin coating, the resulting nanotube networks (SWNTnts) can be strongly influenced by the charge state of the amine (primary, secondary, and tertiary). When the amine surfaces were exposed to varying pH solutions, the conductivity and overall quality of the resulting fabricated networks were altered. Atomic force microscopy (AFM) topography had shown that the density of the SWNTnts was reduced as the amine protonation decreased, indicating that the electrostatic attraction between the SWNTs in solution and the surface influenced the adsorption. Simultaneously, μ-Raman analysis had suggested that when exposed to more basic conditions, the resulting networks were enhanced with sc-SWNTs. To directly confirm this enhancement, Ti/Pd contacts were deposited and devices were tested in air. Key device characteristics were found to match the enhancement trends previously observed by spectroscopy. For the primary and secondary amines, on/off current ratios were commensurate with the Raman trends in metallic contribution, while no trends were observed on the tertiary amine (due to weaker interactions). Finally, differing SWNT solution volumes were used to compensate for adsorption differences and yielded identical SWNTnt densities on the various pH-treated samples to eliminate the influence of network density. These results further the understanding of the amine-SWNT interaction during the spin coating process. Overall, we provide a convenient route to provide SWNT-based TFTs with highly tunable electronic charge transport through better understanding of the influence of these specific interactions.

    View details for DOI 10.1088/0957-4484/22/12/125201

    View details for Web of Science ID 000287448200001

    View details for PubMedID 21317495

  • Controlling Electric Dipoles in Nanodielectrics and Its Applications for Enabling Air-Stable n-Channel Organic Transistors NANO LETTERS Chung, Y., Verploegen, E., Vailionis, A., Sun, Y., Nishi, Y., Murmann, B., Bao, Z. 2011; 11 (3): 1161-1165

    Abstract

    We present a new method to manipulate the channel charge density of field-effect transistors using dipole-generating self-assembled monolayers (SAMs) with different anchor groups. Our approach maintains an ideal interface between the dipole layers and the semiconductor while changing the built-in electric potential by 0.41-0.50 V. This potential difference can be used to change effectively the electrical properties of nanoelectronic devices. We further demonstrate the application of the SAM dipoles to enable air-stable operation of n-channel organic transistors.

    View details for DOI 10.1021/nl104087u

    View details for Web of Science ID 000288061500043

    View details for PubMedID 21323381

  • Syntheses of Organic Molecule-DNA Hybrid Structures ACS NANO Lee, J. K., Jung, Y. H., Tok, J. B., Bao, Z. 2011; 5 (3): 2067-2074

    Abstract

    Investigation of robust and efficient pathways to build DNA-organic molecule hybrid structures is fundamentally important to realize controlled placement of single molecules for potential applications, such as single-molecule electronic devices. Herein, we report a systematic investigation of synthetic processes for preparing organic molecule-DNA building blocks and their subsequent elongation to generate precise micrometer-sized structures. Specifically, optimal cross-coupling routes were identified to enable chemical linkages between three different organic molecules, namely, polyethylene glycol (PEG), poly(p-phenylene ethynylene) (PPE), and benzenetricarboxylate, with single-stranded (ss) DNA. The resulting DNA-organic molecule hybrid building blocks were purified and characterized by both denaturing gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS). The building blocks were subsequently elongated through both the DNA hybridization and ligation processes to prepare micrometer-sized double-stranded (ds) DNA-organic molecule hybrid structures. The described synthetic procedures should facilitate future syntheses of various hybrid DNA-based organic molecular structures.

    View details for DOI 10.1021/nn1032455

    View details for Web of Science ID 000288570600062

    View details for PubMedID 21323343

  • Microfluidic Arrays for Rapid Characterization of Organic Thin-Film Transistor Performance ADVANCED MATERIALS Bettinger, C. J., Becerril, H. A., Kim, D. H., Lee, B., Lee, S., Bao, Z. 2011; 23 (10): 1257-?

    View details for DOI 10.1002/adma.201003815

    View details for Web of Science ID 000288170700010

    View details for PubMedID 21381125

  • Halogenated Materials as Organic Semiconductors CHEMISTRY OF MATERIALS Tang, M. L., Bao, Z. 2011; 23 (3): 446-455

    View details for DOI 10.1021/cm102182x

    View details for Web of Science ID 000286691100010

  • Selective Surface Chemistry Using Alumina Nanoparticles Generated from Block Copolymers LANGMUIR Stoltenberg, R. M., Liu, C., Bao, Z. 2011; 27 (1): 445-451

    Abstract

    Developing orthogonal surface chemistry techniques that perform at the nanoscale is key to achieving precise control over molecular patterning on surfaces. We report the formation and selective functionalization of alumina nanoparticle arrays generated from block copolymer templates. This new material provides an alternative to gold for orthogonal surface chemistry at the nanometer scale. Atomic force microscopy and X-ray photoelectron spectroscopy confirm these particles show excellent selectivity over silica for phosphonic and carboxylic acid adsorption. As this is the first reported synthesis of alumina nanoparticles from block copolymer templates, characterizations via Fourier transform infrared spectroscopy, Auger electron spectroscopy, and transmission electron microscopy are presented. Reproducible formation of alumina nanoparticles was dependent on a counterintuitive synthetic step wherein a small amount of water is added to an anhydrous toluene solution of block copolymer and aluminum chloride. The oxidation environment of the aluminum in these particles, as measured by Auger electron spectroscopy, is similar to that of native aluminum oxide and alumina grown by atomic layer deposition. This discovery expands the library of available surface chemistries for nanoscale molecular patterning.

    View details for DOI 10.1021/la104094h

    View details for Web of Science ID 000285560400060

    View details for PubMedID 21133369

  • Thin Film Structure of Triisopropylsilylethynyl-Functionalized Pentacene and Tetraceno[2,3-b]thiophene from Grazing Incidence X-Ray Diffraction ADVANCED MATERIALS Mannsfeld, S. C., Tang, M. L., Bao, Z. 2011; 23 (1): 127-?

    View details for DOI 10.1002/adma.201003135

    View details for Web of Science ID 000285723400015

    View details for PubMedID 21104808

  • The Shear Flow Processing of Controlled DNA Tethering and Stretching for Organic Molecular Electronics ACS NANO Yu, G., Kushwaha, A., Lee, J. K., Shaqfeh, E. S., Bao, Z. 2011; 5 (1): 275-282

    Abstract

    DNA has been recently explored as a powerful tool for developing molecular scaffolds for making reproducible and reliable metal contacts to single organic semiconducting molecules. A critical step in the process of exploiting DNA-organic molecule-DNA (DOD) array structures is the controlled tethering and stretching of DNA molecules. Here we report the development of reproducible surface chemistry for tethering DNA molecules at tunable density and demonstrate shear flow processing as a rationally controlled approach for stretching/aligning DNA molecules of various lengths. Through enzymatic cleavage of λ-phage DNA to yield a series of DNA chains of various lengths from 17.3 μm down to 4.2 μm, we have investigated the flow/extension behavior of these tethered DNA molecules under different flow strengths in the flow-gradient plane. We compared Brownian dynamic simulations for the flow dynamics of tethered λ-DNA in shear, and found our flow-gradient plane experimental results matched well with our bead-spring simulations. The shear flow processing demonstrated in our studies represents a controllable approach for tethering and stretching DNA molecules of various lengths. Together with further metallization of DNA chains within DOD structures, this bottom-up approach can potentially enable efficient and reliable fabrication of large-scale nanoelectronic devices based on single organic molecules, therefore opening opportunities in both fundamental understanding of charge transport at the single molecular level and many exciting applications for ever-shrinking molecular circuits.

    View details for DOI 10.1021/nn102669b

    View details for Web of Science ID 000286487300035

    View details for PubMedID 21126082

  • High Mobility Air-Stable Solution-Shear-Processed n-Channel Organic Transistors Based on Core-Chlorinated Naphthalene Diimides Adv. Funct. Mater. Lee, W.-Y., Oh, J., H., Suraru, S., Chen, W.-C, Würthner, F., Bao, Z. 2011; 21: 4173-4181
  • Solvent additives and their effects on blend morphologies of bulk heterojunctions JOURNAL OF MATERIALS CHEMISTRY Salim, T., Wong, L. H., Braeuer, B., Kukreja, R., Foo, Y. L., Bao, Z., Lam, Y. M. 2011; 21 (1): 242-250

    View details for DOI 10.1039/c0jm01976c

    View details for Web of Science ID 000285067300031

  • Side chain engineering of fused aromatic thienopyrazine based low band-gap polymers for enhanced charge carrier mobility JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Verploegen, E., Becerril, H. A., Toney, M. F., Bao, Z. 2011; 21 (5): 1537-1543

    View details for DOI 10.1039/c0jm02491k

    View details for Web of Science ID 000286332000032

  • Synthesis of regioregular pentacene-containing conjugated polymers JOURNAL OF MATERIALS CHEMISTRY Okamoto, T., Jiang, Y., Becerril, H. A., Hong, S., Senatore, M. L., Tang, M. L., Toney, M. F., Siegrist, T., Bao, Z. 2011; 21 (20): 7078-7081

    View details for DOI 10.1039/c1jm10643k

    View details for Web of Science ID 000290167200006

  • Molecular n-type doping for air-stable electron transport in vacuum-processed n-channel organic transistors APPLIED PHYSICS LETTERS Oh, J. H., Wei, P., Bao, Z. 2010; 97 (24)

    View details for DOI 10.1063/1.3527972

    View details for Web of Science ID 000285481000079

  • 2,9-Dibromopentacene: Synthesis and the role of substituent and symmetry on solid-state order SYNTHETIC METALS Okamoto, T., Reese, C., Senatore, M. L., Tang, M. L., Jiang, Y., Parkin, S. R., Bao, Z. 2010; 160 (23-24): 2447-2451
  • Full-Swing and High-Gain Pentacene Logic Circuits on Plastic Substrate IEEE ELECTRON DEVICE LETTERS Jeon, J., Murmann, B., Bao, Z. 2010; 31 (12): 1488-1490
  • Fabrication and Evaluation of Solution-Processed Reduced Graphene Oxide Electrodes for p- and n-Channel Bottom-Contact Organic Thin-Film Transistors ACS NANO Becerril, H. A., Stoltenberg, R. M., Tang, M. L., Roberts, M. E., Liu, Z., Chen, Y., Kim, D. H., Lee, B., Lee, S., Bao, Z. 2010; 4 (11): 6343-6352

    Abstract

    Reduced graphene oxide (RGO) is an electrically conductive carbon-based nanomaterial that has recently attracted attention as a potential electrode for organic electronics. Here we evaluate several solution-based methods for fabricating RGO bottom-contact (BC) electrodes for organic thin-film transistors (OTFTs), demonstrate functional p- and n-channel devices with such electrodes, and compare their electrical performance with analogous devices containing gold electrodes. We show that the morphology of organic semiconductor films deposited on RGO electrodes is similar to that observed in the channel region of the devices and that devices fabricated with RGO electrodes have lower contact resistances compared to those fabricated with gold contacts. Although the conductivity of RGO is poor compared to that of gold, RGO is still an enticing electrode material for organic electronic devices possibly owing to the retention of desirable morphological features, lower contact resistance, lower cost, and solution processability.

    View details for DOI 10.1021/nn101369j

    View details for Web of Science ID 000284438000008

    View details for PubMedID 20945927

  • Dip-Pen Nanolithography of Electrical Contacts to Single Graphene Flakes ACS NANO Wang, W. M., Stander, N., Stoltenberg, R. M., Goldhaber-Gordon, D., Bao, Z. 2010; 4 (11): 6409-6416

    Abstract

    This study evaluates an alternative to electron-beam lithography for fabricating nanoscale graphene devices. Dip-pen nanolithography is used for defining monolayer graphene flakes and for patterning of gold electrodes through writing of an alkylthiol on thin films of gold evaporated onto graphene flakes. A wet gold etching step was used to form the individual devices. The sheet resistances of these monolayer graphene devices are comparable to reported literature values. This alternative technique for making electrical contact to 2D nanostructures provides a platform for fundamental studies of nanomaterial properties. The merits of using dip-pen nanolithography include lack of electron-beam irradiation damage and targeted patterning of individual devices with imaging and writing conducted in the same instrument under ambient conditions.

    View details for DOI 10.1021/nn101324x

    View details for Web of Science ID 000284438000015

    View details for PubMedID 20945878

  • In Situ, Label-Free DNA Detection Using Organic Transistor Sensors ADVANCED MATERIALS Khan, H. U., Roberts, M. E., Johnson, O., Foerch, R., Knoll, W., Bao, Z. 2010; 22 (40): 4452-4456

    View details for DOI 10.1002/adma.201000790

    View details for Web of Science ID 000284000900003

    View details for PubMedID 20859935

  • Effects of Thermal Annealing Upon the Morphology of Polymer-Fullerene Blends ADVANCED FUNCTIONAL MATERIALS Verploegen, E., Mondal, R., Bettinger, C. J., Sok, S., Toney, M. F., Bao, Z. 2010; 20 (20): 3519-3529
  • Synthesis and characterization of soluble indolo[3,2-b]carbazole derivatives for organic field-effect transistors ORGANIC ELECTRONICS Boudreault, P. T., Virkar, A. A., Bao, Z., Leclerc, M. 2010; 11 (10): 1649-1659
  • Effect of Surface Chemistry on Electronic Properties of Carbon Nanotube Network Thin Film Transistors ACS NANO Vosgueritchian, M., LeMieux, M. C., Dodge, D., Bao, Z. 2010; 4 (10): 6137-6145

    Abstract

    Thin films of single-walled carbon nanotubes (SWNTs) are a viable nanomaterial for next generation sensors, transistors, and electrodes for solar cells and displays. Despite their remarkable properties, challenges in synthesis and processing have hindered integration in current electronics. Challenges include the inability to precisely assemble and control the deposition of SWNT films on a variety of surfaces and the lack of understanding of the transport properties of these films. Here, we utilize an optimized "dry transfer" technique that facilitates the complete intact transfer of SWNT films between different surfaces. We then show the effect of surface chemistry on the electronic properties of SWNT films. By isolating the effect of the surface, we gain insight into the fundamental transport properties of SWNTs on surfaces with different chemical functionalities. Thin film transistor (TFT) characteristics, corroborated with μ-Raman spectroscopy, show that by using different surface chemical functionalities it is possible to alter the electronic properties of SWNT films. This opens up another route to tune the electronic properties of integrated SWNT films.

    View details for DOI 10.1021/nn1012226

    View details for Web of Science ID 000283453700085

    View details for PubMedID 20857943

  • Driving High-Performance n- and p-type Organic Transistors with Carbon Nanotube/Conjugated Polymer Composite Electrodes Patterned Directly from Solution ADVANCED MATERIALS Hellstrom, S. L., Jin, R. Z., Stoltenberg, R. M., Bao, Z. 2010; 22 (37): 4204-?

    Abstract

    We report patterned deposition of carbon nanotube/conjugated polymer composites from solution with high nanotube densities and excellent feature resolution. Such composites are suited for use as electrodes in high-performance transistors of pentacene and C(60), with bottom-contact mobilities of > 0.5 and > 1 cm(2) V(−1) s(−1), respectively. This represents a clear step towards development of inexpensive, high-performance all-organic circuits.

    View details for DOI 10.1002/adma.201001435

    View details for Web of Science ID 000283392000017

    View details for PubMedID 20626010

  • Organic Semiconductor Growth and Morphology Considerations for Organic Thin-Film Transistors ADVANCED MATERIALS Virkar, A. A., Mannsfeld, S., Bao, Z., Stingelin, N. 2010; 22 (34): 3857-3875

    Abstract

    Analogous to conventional inorganic semiconductors, the performance of organic semiconductors is directly related to their molecular packing, crystallinity, growth mode, and purity. In order to achieve the best possible performance, it is critical to understand how organic semiconductors nucleate and grow. Clever use of surface and dielectric modification chemistry can allow one to control the growth and morphology, which greatly influence the electrical properties of the organic transistor. In this Review, the nucleation and growth of organic semiconductors on dielectric surfaces is addressed. The first part of the Review concentrates on small-molecule organic semiconductors. The role of deposition conditions on film formation is described. The modification of the dielectric interface using polymers or self-assembled mono-layers and their effect on organic-semiconductor growth and performance is also discussed. The goal of this Review is primarily to discuss the thin-film formation of organic semiconducting species. The patterning of single crystals is discussed, while their nucleation and growth has been described elsewhere (see the Review by Liu et. al).([¹]) The second part of the Review focuses on polymeric semiconductors. The dependence of physico-chemical properties, such as chain length (i.e., molecular weight) of the constituting macromolecule, and the influence of small molecular species on, e.g., melting temperature, as well as routes to induce order in such macromolecules, are described.

    View details for DOI 10.1002/adma.200903193

    View details for Web of Science ID 000282793600007

    View details for PubMedID 20715062

  • Effects of Dispersion Conditions of Single-Walled Carbon Nanotubes on the Electrical Characteristics of Thin Film Network Transistors ACS APPLIED MATERIALS & INTERFACES Barman, S. N., LeMieux, M. C., Baek, J., Rivera, R., Bao, Z. 2010; 2 (9): 2672-2678

    Abstract

    To facilitate solution deposition of single-walled carbon nanotubes (SWNTs) for integration into electronic devices they need to be purified and dispersed into solutions. The vigorous sonication process for preparing these dispersions leads to large variations in the length and defect density of SWNTs, affecting the resulting electronic properties. Understanding the effects of solution processing steps can have important implications in the design of SWNT films for electronic applications. Here, we alter the SWNTs by varying the sonication time, followed by deposition of sub-monolayer SWNT network films onto functionalized substrates. The corresponding electrical performance characteristics of the resulting field effect transistors (FETs) are correlated with SWNT network sorting and morphology. As sonication exposure increases, the SWNTs shorten, which not only affects electrical current by increasing the number of junctions but also presumably leads to more defects. The off current of the resulting transistors initially increased with sonication exposure, presumably due to less efficient sorting of semiconducting SWNTs as the defect density increases. After extended sonication, the on and off current decreased because of increased bundling and fewer percolation pathways. The final transistor properties are influenced by the nanotube solution concentration, density, alignment, and the selectivity of surface sorting of the SWNT networks. These results show that in addition to chirality, careful consideration of SWNT dispersion conditions that affect SWNT length, bundle diameter, and defect density is critical for optimal SWNT-FET performance and potentially other SWNT-based electronic devices.

    View details for DOI 10.1021/am1005223

    View details for Web of Science ID 000282017700029

    View details for PubMedID 20738099

  • Tuning the Optoelectronic Properties of Vinylene-Linked Donor-Acceptor Copolymers for Organic Photovoltaics MACROMOLECULES Ko, S., Mondal, R., Risko, C., Lee, J. K., Hong, S., McGehee, M. D., Bredas, J., Bao, Z. 2010; 43 (16): 6685-6698

    View details for DOI 10.1021/ma101088f

    View details for Web of Science ID 000280855000023

  • Anthradithiophene-Containing Copolymers for Thin-Film Transistors and Photovoltaic Cells MACROMOLECULES Jiang, Y., Okamoto, T., Becerril, H. A., Hong, S., Tang, M. L., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2010; 43 (15): 6361-6367

    View details for DOI 10.1021/ma1001639

    View details for Web of Science ID 000280743300017

  • Contact engineering for organic semiconductor devices via Fermi level depinning at the metal-organic interface PHYSICAL REVIEW B Liu, Z., Kobayashi, M., Paul, B. C., Bao, Z., Nishi, Y. 2010; 82 (3)
  • High-Performance Air-Stable n-Type Organic Transistors Based on Core-Chlorinated Naphthalene Tetracarboxylic Diimides ADVANCED FUNCTIONAL MATERIALS Oh, J. H., Suraru, S., Lee, W., Koenemann, M., Hoeffken, H. W., Roeger, C., Schmidt, R., Chung, Y., Chen, W., Wuerthner, F., Bao, Z. 2010; 20 (13): 2148-2156
  • Use of a 1H-Benzoimidazole Derivative as an n-Type Dopant and To Enable Air-Stable Solution-Processed n-Channel Organic Thin-Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wei, P., Oh, J. H., Dong, G., Bao, Z. 2010; 132 (26): 8852-?

    Abstract

    We present here the development of a new solution-processable n-type dopant, N-DMBI. Our experimental results demonstrated that a well-known n-channel semiconductor, [6,6]-phenyl C(61) butyric acid methyl ester (PCBM), can be effectively doped with N-DMBI by solution processing; the film conductivity is significantly increased by n-type doping. We utilized this n-type doping for the first time to improve the air-stability of n-channel organic thin-film transistors, in which the doping can compensate for the electron traps. Our successful demonstration of n-type doping using N-DMBI opens up new opportunities for the development of air-stable n-channel semiconductors. It is also potentially useful for application on solution-processed organic light-emitting diodes and organic photovoltaics.

    View details for DOI 10.1021/ja103173m

    View details for Web of Science ID 000279561200019

    View details for PubMedID 20552967

  • X-ray Microscopy Imaging of the Grain Orientation in a Pentacene Field-Effect Transistor CHEMISTRY OF MATERIALS Braeuer, B., Virkar, A., Mannsfeld, S. C., Bernstein, D. P., Kukreja, R., Chou, K. W., Tyliszczak, T., Bao, Z., Acremann, Y. 2010; 22 (12): 3693-3697

    View details for DOI 10.1021/cm100487j

    View details for Web of Science ID 000278684000016

  • Induced Sensitivity and Selectivity in Thin-Film Transistor Sensors via Calixarene Layers ADVANCED MATERIALS Sokolov, A. N., Roberts, M. E., Johnson, O. B., Cao, Y., Bao, Z. 2010; 22 (21): 2349-2353

    View details for DOI 10.1002/adma.200903305

    View details for Web of Science ID 000279100200010

    View details for PubMedID 20376848

  • Nanotubes on Display: How Carbon Nanotubes Can Be Integrated into Electronic Displays ACS NANO Opatkiewicz, J., LeMieux, M. C., Bao, Z. 2010; 4 (6): 2975-2978

    Abstract

    Random networks of single-walled carbon nanotubes show promise for use in the field of flexible electronics. Nanotube networks have been difficult to utilize because of the mixture of electronic types synthesized when grown. A variety of separation techniques have been developed, but few can readily be scaled up. Despite this issue, when metallic percolation pathways can be separated out or etched away, these networks serve as high-quality thin-film transistors with impressive device characteristics. A new article in this issue illustrates this point and the promise of these materials. With more work, these devices can be implemented in transparent displays in the next generation of hand-held electronics.

    View details for DOI 10.1021/nn101092d

    View details for Web of Science ID 000278888600003

    View details for PubMedID 20565139

  • Band structure measurement of organic single crystal with angle-resolved photoemission APPLIED PHYSICS LETTERS Ding, H., Reese, C., Maekinen, A. J., Bao, Z., Gao, Y. 2010; 96 (22)

    View details for DOI 10.1063/1.3446849

    View details for Web of Science ID 000278404800029

  • Parallel Fabrication of Electrode Arrays on Single-Walled Carbon Nanotubes using Dip-Pen-Nanolithography-Patterned Etch Masks LANGMUIR Park, S., Wang, W. M., Bao, Z. 2010; 26 (9): 6853-6859

    Abstract

    This article presents a novel application of using dip-pen nanolithography (DPN) to fabricate Au electrodes concurrently in a high-throughput fashion through an etch resist. We have fabricated 26 pairs of electrodes, where cleanly etched electrode architectures, along with a high degree of feature-size controllability and tip-to-tip uniformity, were observed. Moreover, electrode gaps in the sub-100-nm regime have been successfully fabricated. Conductivity measurements of multiple electrodes in the array were all comparable to that of bulk Au, confirming the reliability and the low-resistance property of the electrodes. Finally, as a demonstration of electrode functionality, SWNT devices were fabricated and the electrical properties of an SWNT device were measured. Hence, our experimental results validate DPN as an effective tool in generating high-quality electrodes in a parallel manner with mild, simple processing steps at a relatively low cost.

    View details for DOI 10.1021/la904170w

    View details for Web of Science ID 000276969700114

    View details for PubMedID 20163131

  • Biomaterials-based organic electronic devices POLYMER INTERNATIONAL Bettinger, C. J., Bao, Z. 2010; 59 (5): 563-567

    Abstract

    Organic electronic devices have demonstrated tremendous versatility in a wide range of applications including consumer electronics, photovoltaics, and biotechnology. The traditional interface of organic electronics with biology, biotechnology, and medicine occurs in the general field of sensing biological phenomena. For example, the fabrication of hybrid electronic structures using both organic semiconductors and bioactive molecules has led to enhancements in sensitivity and specificity within biosensing platforms, which in turn has a potentially wide range of clinical applications. However, the interface of biomolecules and organic semiconductors has also recently explored the potential use of natural and synthetic biomaterials as structural components of electronic devices. The fabrication of electronically active systems using biomaterials-based components has the potential to realize a large set of unique devices including environmentally biodegradable systems and bioresorbable temporary medical devices. This article reviews recent advances in the implementation of biomaterials as structural components in organic electronic devices with a focus on potential applications in biotechnology and medicine.

    View details for DOI 10.1002/pi.2827

    View details for Web of Science ID 000277767500001

  • Low-voltage and short-channel pentacene field-effect transistors with top-contact geometry using parylene-C shadow masks APPLIED PHYSICS LETTERS Chung, Y., Murmann, B., Selvarasah, S., Dokmeci, M. R., Bao, Z. 2010; 96 (13)

    View details for DOI 10.1063/1.3336009

    View details for Web of Science ID 000276275300063

  • Influence of Electrostatic Interactions on Spin-Assembled Single-Walled Carbon Nanotube Networks on Amine-Functionalized Surfaces ACS NANO Opatkiewicz, J. P., LeMieux, M. C., Bao, Z. 2010; 4 (2): 1167-1177

    Abstract

    Preferential interactions between self-assembled monolayers (SAMs) terminated with amine functional groups and single-walled carbon nanotubes (SWNTs) were exploited to produce nanotube networks (SWNTnts) via spin coating. We provide insight into the mechanisms of this system while simultaneously demonstrating a facile approach toward controllable arrays of SWNTnts. The chirality, density, and alignment of the SWNTnt was heavily influenced by adsorption onto amine-functionalized surfaces that were exposed to varying pH solutions, as evidenced by atomic force microscopy (AFM) and Raman spectroscopy. This pH treatment altered the charge density on the surface, allowing for the examination of the contribution from electrostatic interaction to SWNT adsorption and SWNTnt characteristics. Secondary and tertiary amines with methyl substitutions were utilized to confirm that adsorption and chirality specific adsorption is largely due to the nitrogen lone pair, not the neighboring hydrogen atoms. Thus, the nature of adsorption is predominantly electrostatic and not due to van der Waals forces or localized polarization on the SWNTs. Moreover, the overall density of SWNTnts is different for the various amines, indicating that the accessibility to the lone pair electrons on the nitrogen plays a crucial role in SWNT adsorption. With greater understanding of the amine-SWNT interaction, these findings can be utilized to control SWNTnt formation for the precise integration into electronic devices.

    View details for DOI 10.1021/nn901388v

    View details for Web of Science ID 000274635800073

    View details for PubMedID 20112967

  • Thiophene-rich fused-aromatic thienopyrazine acceptor for donor-acceptor low band-gap polymers for OTFT and polymer solar cell applications JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Becerril, H. A., Verploegen, E., Kim, D., Norton, J. E., Ko, S., Miyaki, N., Lee, S., Toney, M. F., Bredas, J., McGehee, M. D., Bao, Z. 2010; 20 (28): 5823-5834

    View details for DOI 10.1039/c0jm00903b

    View details for Web of Science ID 000279565900008

  • Organic Thin-Film Transistors Fabricated on Resorbable Biomaterial Substrates Adv. Mater. Bettinger, C., Bao, Z. 2010; 22: 651-655
  • A Crystal-Engineered Hydrogen-Bonded Octachloroperylene Diimide with a Twisted Core: An n-Channel Organic Semiconductor ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Gsaenger, M., Oh, J. H., Koenemann, M., Hoeffken, H. W., Krause, A., Bao, Z., Wuerthner, F. 2010; 49 (4): 740-743
  • Organic Light-Emitting Diodes on Solution-Processed Graphene Transparent Electrodes ACS NANO Wu, J., Agrawal, M., Becerril, H. A., Bao, Z., Liu, Z., Chen, Y., Peumans, P. 2010; 4 (1): 43-48

    Abstract

    Theoretical estimates indicate that graphene thin films can be used as transparent electrodes for thin-film devices such as solar cells and organic light-emitting diodes, with an unmatched combination of sheet resistance and transparency. We demonstrate organic light-emitting diodes with solution-processed graphene thin film transparent conductive anodes. The graphene electrodes were deposited on quartz substrates by spin-coating of an aqueous dispersion of functionalized graphene, followed by a vacuum anneal step to reduce the sheet resistance. Small molecular weight organic materials and a metal cathode were directly deposited on the graphene anodes, resulting in devices with a performance comparable to control devices on indium-tin-oxide transparent anodes. The outcoupling efficiency of devices on graphene and indium-tin-oxide is nearly identical, in agreement with model predictions.

    View details for DOI 10.1021/nn900728d

    View details for Web of Science ID 000273863400007

    View details for PubMedID 19902961

  • Fused aromatic thienopyrazines: structure, properties and function JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Bao, Z. 2010; 20 (47): 10568-10576

    View details for DOI 10.1039/c0jm01840f

    View details for Web of Science ID 000284542600001

  • Energetics and stability of pentacene thin films on amorphous and crystalline octadecylsilane modified surfaces JOURNAL OF MATERIALS CHEMISTRY Virkar, A. A., Mannsfeld, S. C., Bao, Z. 2010; 20 (13): 2664-2671

    View details for DOI 10.1039/b921767c

    View details for Web of Science ID 000275662400018

  • Solution Assembly of Organized Carbon Nanotube Networks for Thin-Film Transistors ACS NANO LeMieux, M. C., Sok, S., Roberts, M. E., Opatkiewicz, J. P., Liu, D., Barman, S. N., Patil, N., Mitra, S., Bao, Z. 2009; 3 (12): 4089-4097

    Abstract

    Ultrathin, transparent electronic materials consisting of solution-assembled nanomaterials that are directly integrated as thin-film transistors or conductive sheets may enable many new device structures. Applications ranging from disposable autonomous sensors to flexible, large-area displays and solar cells can dramatically expand the electronics market. With a practical, reliable method for controlling their electronic properties through solution assembly, submonolayer films of aligned single-walled carbon nanotubes (SWNTs) may provide a promising alternative for large-area, flexible electronics. Here, we report SWNT network TFTs (SWNTntTFTs) deposited from solution with controllable topology, on/off ratios averaging greater than 10(5), and an apparent mobility averaging 2 cm(2)/V.s, without any pre- or postprocessing steps. We employ a spin-assembly technique that results in chirality enrichment along with tunable alignment and density of the SWNTs by balancing the hydrodynamic force (spin rate) with the surface interaction force controlled by a chemically functionalized interface. This directed nanoscale assembly results in enriched semiconducting nanotubes yielding excellent TFT characteristics, which is corroborated with mu-Raman spectroscopy. Importantly, insight into the electronic properties of these SWNT networks as a function of topology is obtained.

    View details for DOI 10.1021/nn900827v

    View details for Web of Science ID 000272846000043

    View details for PubMedID 19924882

  • Interplay between Energetic and Kinetic Factors on the Ambient Stability of n-Channel Organic Transistors Based on Perylene Diimide Derivatives CHEMISTRY OF MATERIALS Oh, J. H., Sun, Y., Schmidt, R., Toney, M. F., Nordlund, D., Koenemann, M., Wuerthner, F., Bao, Z. 2009; 21 (22): 5508-5518

    View details for DOI 10.1021/cm902531d

    View details for Web of Science ID 000271756400019

  • Micrometer-Sized DNA-Single-Fluorophore-DNA Supramolecule: Synthesis and Single-Molecule Characterization SMALL Lee, J. K., Jaeckel, F., Moerner, W. E., Bao, Z. 2009; 5 (21): 2418-2423

    Abstract

    The synthesis of single-fluorophore-bis(micrometer-sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single-molecule level is reported. A fluorophore-bis(oligodeoxynucleotide) triblock is synthesized via the amide-coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with lambda-DNA fragments on the micrometer length scale. The successful synthesis of the micrometer-sized DNA-single-fluorophore-DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single-molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single-molecule electronic devices after metallization of the DNAs.

    View details for DOI 10.1002/smll.200900494

    View details for Web of Science ID 000271791100011

    View details for PubMedID 19517486

  • Dip-Pen Nanolithography of Electrical Contacts to Single-Walled Carbon Nanotubes ACS NANO Wang, W. M., LeMieux, M. C., Selvarasah, S., Dokmeci, M. R., Bao, Z. 2009; 3 (11): 3543-3551

    Abstract

    This paper discusses a method for the direct patterning of Au electrodes at nanoscale resolution using dip-pen nanolithography, with proof-of-concept demonstrated by creating single-walled carbon nanotube devices. This technique enables insight into three key concepts at the nanoscale: using dip-pen nanolithography as an alternative to electron-beam lithography for writing contacts to carbon nanotubes, understanding the integrity of contacts and devices patterned with this technique, and on a more fundamental level, providing a facile method to compare and understand electrical and Raman spectroscopy data from the same isolated carbon nanotube. Electrical contacts to individual and small bundle single-walled carbon nanotubes were masked by an alkylthiol that was deposited via dip-pen nanolithography on a thin film of Au evaporated onto spin-cast, nonpercolating, and highly isolated single-walled carbon nanotubes. A wet Au etching step was used to form the individual devices. The electrical characteristics for three different single-walled carbon nanotube devices are reported: semimetallic, semiconducting, and metallic. Raman analysis on representative devices corroborates the results from AFM imaging and electrical testing. This work demonstrates a technique for making electrical contact to nanostructures of interest and provides a platform for directly corroborating electrical and optical measurements. The merits of using dip-pen nanolithography include flexible device configuration (such as varying the channel length and the number, size, and orientation of contacts), targeted patterning of individual devices with imaging and writing conducted in the same instrument under ambient conditions, and negligible damage to single-walled carbon nanotubes during the fabrication process.

    View details for DOI 10.1021/nn900984w

    View details for Web of Science ID 000271951200029

    View details for PubMedID 19852486

  • Sorted and Aligned Single-Walled Carbon Nanotube Networks for Transistor-Based Aqueous Chemical Sensors ACS NANO Roberts, M. E., LeMieux, M. C., Bao, Z. 2009; 3 (10): 3287-3293

    Abstract

    Detecting trace amounts of analytes in aqueous systems is important for health diagnostics, environmental monitoring, and national security applications. Single-walled carbon nanotubes (SWNTs) are ideal components for both the sensor material and active signal transduction layer because of their excellent electronic properties and high aspect ratio consisting of entirely surface atoms. Submonolayer arrays, or networks of SWNTs (SWNTnts) are advantageous, and we show that topology characteristics of the SWNT network, such as alignment, degree of bundling, and chirality enrichment strongly affect the sensor performance. To enable this, thin-film transistor (TFT) sensors with SWNTnts were deposited using a one-step, low-cost, solution- based method on a polymer dielectric, allowing us to achieve stable low-voltage operation under aqueous conditions. These SWNT-TFTs were used to detect trace concentrations, down to 2 ppb, of dimethyl methylphosphonate (DMMP) and trinitrotoluene (TNT) in aqueous solutions. Along with reliable cycling underwater, the TFT sensors fabricated with aligned, sorted nanotube networks (enriched with semiconductor SWNTs) showed a higher sensitivity to analytes than those fabricated with random, unsorted networks with predominantly metallic charge transport.

    View details for DOI 10.1021/nn900808b

    View details for Web of Science ID 000271106100055

    View details for PubMedID 19856982

  • Tuning Crystalline Solid-State Order and Charge Transport via Building-Block Modification of Oligothiophenes ADVANCED MATERIALS Reese, C., Roberts, M. E., Parkin, S. R., Bao, Z. 2009; 21 (36): 3678-?
  • Fabrication of low-cost electronic biosensors MATERIALS TODAY Sokolov, A. N., Roberts, M. E., Bao, Z. 2009; 12 (9): 12-20
  • Low-voltage transistor sensors based on organic semiconductors and carbon nanotube networks Roberts, M. E., LeMieux, M. C., Mannsfeld, S. C., Bao, Z. AMER CHEMICAL SOC. 2009
  • Synthesis of Acenaphthyl and Phenanthrene Based Fused-Aromatic Thienopyrazine Co-Polymers for Photovoltaic and Thin Film Transistor Applications CHEMISTRY OF MATERIALS Mondal, R., Miyaki, N., Becerril, H. A., Norton, J. E., Parmer, J., Mayer, A. C., Tang, M. L., Bredas, J., McGehee, M. D., Bao, Z. 2009; 21 (15): 3618-3628

    View details for DOI 10.1021/cm900788e

    View details for Web of Science ID 000268523300021

  • Crystalline Ultrasmooth Self-Assembled Monolayers of Alkylsilanes for Organic Field-Effect Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ito, Y., Virkar, A. A., Mannsfeld, S., Oh, J. H., Toney, M., Locklin, J., Bao, Z. 2009; 131 (26): 9396-9404

    Abstract

    Crystalline self-assembled monolayers (SAMs) of organosilane compounds such as octadecyltrimethoxysilane (OTMS) and octadecyltrichlorosilane (OTCS) were deposited by a simple, spin-casting technique onto Si/SiO(2) substrates. Fabrication of the OTMS SAMs and characterization using ellipsometry, contact angle, atomic force microscopy (AFM), grazing angle attenuated total reflectance Fourier transform infrared (GATR-FTIR) spectroscopy and grazing incidence X-ray diffraction (GIXD) are described. The characterization confirms that these monolayers exhibit a well-packed crystalline phase and a remarkably high degree of smoothness. Semiconductors deposited by vapor deposition onto the crystalline OTS SAM grow in a favorable two-dimensional layered growth manner which is generally preferred morphologically for high charge carrier transport. On the OTMS SAM treated dielectric, pentacene OFETs showed hole mobilities as high as 3.0 cm(2)/V x s, while electron mobilities as high as 5.3 cm(2)/V x s were demonstrated for C(60).

    View details for DOI 10.1021/ja9029957

    View details for Web of Science ID 000267633300056

    View details for PubMedID 19518097

  • Self-Sorted Nanotube Networks on Polymer Dielectrics for Low-Voltage Thin-Film Transistors NANO LETTERS Roberts, M. E., LeMieux, M. C., Sokolov, A. N., Bao, Z. 2009; 9 (7): 2526-2531

    Abstract

    Recent exploitations of the superior mechanical and electronic properties of carbon nanotubes (CNTs) have led to exciting opportunities in low-cost, high performance, carbon-based electronics. In this report, low-voltage thin-film transistors with aligned, semiconducting CNT networks are fabricated on a chemically modified polymer gate dielectric using both rigid and flexible substrates. The multifunctional polymer serves as a thin, flexible gate dielectric film, affords low operating voltages, and provides a platform for chemical functionalization. The introduction of amine functionality to the dielectric surface leads to the adsorption of a network enriched with semiconducting CNTs with tunable density from spin coating a bulk solution of unsorted CNTs. The composition of the deposited CNT networks is verified with Raman spectroscopy and electrical characterization. For transistors at operating biases below 1 V, we observe an effective device mobility as high as 13.4 cm(2)/Vs, a subthreshold swing as low as 130 mV/dec, and typical on-off ratios of greater than 1,000. This demonstration of high performance CNT thin-film transistors operating at voltages below 1 V and deposited using solution methods on polymeric and flexible substrates is an important step toward the realization of low-cost flexible electronics.

    View details for DOI 10.1021/nl900287p

    View details for Web of Science ID 000268138600003

    View details for PubMedID 19499894

  • The Role of OTS Density on Pentacene and C-60 Nucleation, Thin Film Growth, and Transistor Performance ADVANCED FUNCTIONAL MATERIALS Virkar, A., Mannsfeld, S., Oh, J. H., Toney, M. F., Tan, Y. H., Liu, G., Scott, J. C., Miller, R., Bao, Z. 2009; 19 (12): 1962-1970
  • Precise Structure of Pentacene Monolayers on Amorphous Silicon Oxide and Relation to Charge Transport ADVANCED MATERIALS Mannsfeld, S. C., Virkar, A., Reese, C., Toney, M. F., Bao, Z. 2009; 21 (22): 2294-?
  • Cross-Linked Polymer Gate Dielectric Films for Low-Voltage Organic Transistors CHEMISTRY OF MATERIALS Roberts, M. E., Queralto, N., Mannsfeld, S. C., Reinecke, B. N., Knoll, W., Bao, Z. 2009; 21 (11): 2292-2299

    View details for DOI 10.1021/cm900637p

    View details for Web of Science ID 000266708700017

  • Polymer-Assisted Direct Deposition of Uniform Carbon Nanotube Bundle Networks for High Performance Transparent Electrodes ACS NANO Hellstrom, S. L., Lee, H. W., Bao, Z. 2009; 3 (6): 1423-1430

    Abstract

    Flexible transparent electrodes are crucial for touch screen, flat panel display, and solar cell technologies. While carbon nanotube network electrodes show promise, characteristically poor dispersion properties have limited their practicality. We report that addition of small amounts of conjugated polymer to nanotube dispersions enables straightforward fabrication of uniform network electrodes by spin-coating and simultaneous tuning of parameters such as bundle size and density. After treatment in thionyl chloride, electrodes have sheet resistances competitive with other reported carbon nanotube based transparent electrodes to date.

    View details for DOI 10.1021/nn9002456

    View details for Web of Science ID 000267533600016

    View details for PubMedID 19422197

  • Solution-processed flexible organic transistors showing very-low subthreshold slope with a bilayer polymeric dielectric on plastic APPLIED PHYSICS LETTERS Liu, Z., Oh, J. H., Roberts, M. E., Wei, P., Paul, B. C., Okajima, M., Nishi, Y., Bao, Z. 2009; 94 (20)

    View details for DOI 10.1063/1.3133902

    View details for Web of Science ID 000266342800065

  • Isotropic transport in an oligothiophene derivative for single-crystal field-effect transistor applications APPLIED PHYSICS LETTERS Reese, C., Roberts, M. E., Parkin, S. R., Bao, Z. 2009; 94 (20)

    View details for DOI 10.1063/1.3129162

    View details for Web of Science ID 000266342800026

  • Liquid-Crystalline Semiconducting Copolymers with Intramolecular Donor-Acceptor Building Blocks for High-Stability Polymer Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kim, D. H., Lee, B., Moon, H., Kang, H. M., Jeong, E. J., Park, J., Han, K., Lee, S., Yoo, B. W., Koo, B. W., Kim, J. Y., Lee, W. H., Cho, K., Becerril, H. A., Bao, Z. 2009; 131 (17): 6124-6132

    Abstract

    The ability to control the molecular organization of electronically active liquid-crystalline polymer semiconductors on surfaces provides opportunities to develop easy-to-process yet highly ordered supramolecular systems and, in particular, to optimize their electrical and environmental reliability in applications in the field of large-area printed electronics and photovoltaics. Understanding the relationship between liquid-crystalline nanostructure and electrical stability on appropriate molecular surfaces is the key to enhancing the performance of organic field-effect transistors (OFETs) to a degree comparable to that of amorphous silicon (a-Si). Here, we report a novel donor-acceptor type liquid-crystalline semiconducting copolymer, poly(didodecylquaterthiophene-alt-didodecylbithiazole), which contains both electron-donating quaterthiophene and electron-accepting 5,5'-bithiazole units. This copolymer exhibits excellent electrical characteristics such as field-effect mobilities as high as 0.33 cm(2)/V.s and good bias-stress stability comparable to that of amorphous silicon (a-Si). Liquid-crystalline thin films with structural anisotropy form spontaneously through self-organization of individual polymer chains as a result of intermolecular interactions in the liquid-crystalline mesophase. These thin films adopt preferential well-ordered intermolecular pi-pi stacking parallel to the substrate surface. This bottom-up assembly of the liquid-crystalline semiconducting copolymer enables facile fabrication of highly ordered channel layers with remarkable electrical stability.

    View details for DOI 10.1021/ja8095569

    View details for Web of Science ID 000265755800036

    View details for PubMedID 19354240

  • High-Performance Air-Stable n-Channel Organic Thin Film Transistors Based on Halogenated Perylene Bisimide Semiconductors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Schmidt, R., Oh, J. H., Sun, Y., Deppisch, M., Krause, A., Radacki, K., Braunschweig, H., Koenemann, M., Erk, P., Bao, Z., Wuerthner, F. 2009; 131 (17): 6215-6228

    Abstract

    The syntheses and comprehensive characterization of 14 organic semiconductors based on perylene bisimide (PBI) dyes that are equipped with up to four halogen substituents in the bay area of the perylene core and five different highly fluorinated imide substituents are described. The influence of the substituents on the LUMO level and the solid state packing of PBIs was examined by cyclic voltammetry and single crystal structure analyses of seven PBI derivatives, respectively. Top-contact/bottom-gate organic thin film transistor (OTFT) devices were constructed by vacuum deposition of these PBIs on SiO(2) gate dielectrics that had been pretreated with n-octadecyl triethoxysilane in vapor phase (OTS-V) or solution phase (OTS-S). The electrical characterization of all devices was accomplished in a nitrogen atmosphere as well as in air, and the structural features of thin films were explored by grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM). Several of those PBIs that bear only hydrogen or up to two fluorine substitutents at the concomitantly flat PBI core afforded excellent n-channel transistors, in particular, on OTS-S substrate and even in air (mu > 0.5 cm(2) V(-1) s(-1); I(on)/I(off) > 10(6)). The best OTFTs were obtained for 2,2,3,3,4,4,4-heptafluorobutyl-substituted PBI 1a ("PTCDI-C4F7") on OTS-S with n-channel field effect mobilities consistently >1 cm(2) V(-1) s(-1) and on-to-off current rations of 10(6) in a nitrogen atmosphere and in air. For distorted core-tetrahalogenated (fluorine, chlorine, or bromine) PBIs, less advantageous solid state packing properties were found and high performance OTFTs were obtained from only one tetrachlorinated derivative (2d on OTS-S). The excellent on-to-off current modulation combined with high mobility in air makes these PBIs suitable for a wide range of practical applications.

    View details for DOI 10.1021/ja901077a

    View details for Web of Science ID 000265755800047

    View details for PubMedID 19354212

  • Lyotropic Liquid-Crystalline Solutions of High-Concentration Dispersions of Single-Walled Carbon Nanotubes with Conjugated Polymers SMALL Lee, H. W., You, W., Barman, S., Hellstrom, S., LeMieux, M. C., Oh, J. H., Liu, S., Fujiwara, T., Wang, W. M., Chen, B., Jin, Y. W., Kim, J. M., Bao, Z. 2009; 5 (9): 1019-1024

    View details for DOI 10.1002/smll.200800640

    View details for Web of Science ID 000266184500004

    View details for PubMedID 19291730

  • Flexible, plastic transistor-based chemical sensors ORGANIC ELECTRONICS Roberts, M. E., Mannsfeld, S. C., Stoltenberg, R. M., Bao, Z. 2009; 10 (3): 377-383
  • Correlating Carrier Type with Frontier Molecular Orbital Energy Levels in Organic Thin Film Transistors of Functionalized Acene Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Reichardt, A. D., Wei, P., Bao, Z. 2009; 131 (14): 5264-5273

    Abstract

    We investigate the relationship between the charge carrier type in organic thin film transistors (OTFTs) and molecular energy levels. We examine a series of functionalized acenes that collectively have their HOMOs range from -4.9 eV to -5.6 eV and LUMOs range from -2.8 eV to -3.7 eV, as measured by cyclic voltammetry. Placed together, these 20 molecules allow us to chart the transition from OTFTs that display only hole transport, to ambipolar, to solely electron transport. Specifically, we note that for octadecyltrimethoxysilane (OTS) treated substrates, with top contact gold electrodes, electron injection and transport occurs when the LUMO < -3.15 eV, while hole injection and transport ceases when the HOMO < -5.6 eV. Ambipolar transport prevails when molecules have HOMO/ LUMO levels within the aforementioned range. This is seen across channel lengths ranging from 50-150 microm and using only gold as electrodes. This empirical plot is the first time such a detailed study has been made on the onset of charge injection and transport for a class of organic semiconductors. It provides guidelines for future molecular design.

    View details for DOI 10.1021/ja809659b

    View details for Web of Science ID 000265039000053

    View details for PubMedID 19317404

  • Solution-processed, high-performance n-channel organic microwire transistors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Oh, J. H., Lee, H. W., Mannsfeld, S., Stoltenberg, R. M., Jung, E., Jin, Y. W., Kim, J. M., Yoo, J., Bao, Z. 2009; 106 (15): 6065-6070

    Abstract

    The development of solution-processable, high-performance n-channel organic semiconductors is crucial to realizing low-cost, all-organic complementary circuits. Single-crystalline organic semiconductor nano/microwires (NWs/MWs) have great potential as active materials in solution-formed high-performance transistors. However, the technology to integrate these elements into functional networks with controlled alignment and density lags far behind their inorganic counterparts. Here, we report a solution-processing approach to achieve high-performance air-stable n-channel organic transistors (the field-effect mobility (mu) up to 0.24 cm(2)/Vs for MW networks) comprising high mobility, solution-synthesized single-crystalline organic semiconducting MWs (mu as high as 1.4 cm(2)/Vs for individual MWs) and a filtration-and-transfer (FAT) alignment method. The FAT method enables facile control over both alignment and density of MWs. Our approach presents a route toward solution-processed, high-performance organic transistors and could be used for directed assembly of various functional organic and inorganic NWs/MWs.

    View details for DOI 10.1073/pnas.0811923106

    View details for Web of Science ID 000265174600009

    View details for PubMedID 19299506

  • Direct Patterning of Organic-Thin-Film-Transistor Arrays via a "Dry-Taping" Approach ADVANCED MATERIALS Liu, S., Becerril, H. A., LeMieux, M. C., Wang, W. M., Oh, J. H., Bao, Z. 2009; 21 (12): 1266-?
  • Controlled Deposition of Crystalline Organic Semiconductors for Field-Effect-Transistor Applications ADVANCED MATERIALS Liu, S., Wang, W. M., Briseno, A. L., Mannsfeld, S. C., Bao, Z. 2009; 21 (12): 1217-1232
  • Chlorination: A General Route toward Electron Transport in Organic Semiconductors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Oh, J. H., Reichardt, A. D., Bao, Z. 2009; 131 (10): 3733-3740

    Abstract

    We show that adding chlorine atoms to conjugated cores is a general, effective route toward the design of n-type air-stable organic semiconductors. We find this to be true for acenes, phthalocyanines, and perylene tetracarboxylic diimide (PDI)-based molecules. This general finding opens new avenues in the design and synthesis of organic semiconductors. We compared a series of fluoro- and chloro-functionalized acenes, phthalocyanines, and PDI-based molecules. The acenes synthesized showed high and balanced ambipolar transport in the top-contact organic field effect transistor (OFET) geometry. The electron-withdrawing halogen groups lowered the LUMO and the charge injection barrier for electrons, such that electron and hole transport occurred simultaneously. If the chlorine added does not distort the planarity of the conjugated core, we found that the chloro-functionalized molecules tend to have a slightly smaller HOMO-LUMO gap and a lower LUMO level than the fluoro-containing molecules, both from calculations and cyclic voltammetry measurements in solution. This is most likely due to the fact that Cl contains empty 3d orbitals that can accept pi-electrons from the conjugated core, while F does not have energetically accessible empty orbitals for such delocalization.

    View details for DOI 10.1021/ja809045s

    View details for Web of Science ID 000264792600065

    View details for PubMedID 19243143

  • Detailed Characterization of Contact Resistance, Gate-Bias-Dependent Field-Effect Mobility, and Short-Channel Effects with Microscale Elastomeric Single-Crystal Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Reese, C., Bao, Z. 2009; 19 (5): 763-771
  • Experimental Study and Statistical Analysis of Solution-Shearing Processed Organic Transistors Based on an Asymmetric Small-Molecule Semiconductor IEEE TRANSACTIONS ON ELECTRON DEVICES Liu, Z., Becerril, H. A., Roberts, M. E., Nishi, Y., Bao, Z. 2009; 56 (2): 176-185
  • Pentaceno[2,3-b]thiophene, a Hexacene Analogue for Organic Thin Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Mannsfeld, S. C., Sun, Y., Becerril, H. A., Bao, Z. 2009; 131 (3): 882-?

    Abstract

    Hexacene and larger fused rings remain elusive targets for chemists. Here, we report a hexacene-like molecule containing six linearly fused rings, specifically a pentacene molecule fused with a terminal thiophene ring, pentaceno[2,3-b]thiophene. It can be purified and isolated as a purple-black powder at ambient conditions. This molecule has a low HOMO-LUMO gap of 1.75 eV in o-DCB and an optical band gap of 1.58 eV in thin film. Top contact organic thin film transistors (OTFTs) were made, and atomic force microscopy (AFM) reveals a dendritic thin film growth characteristic of pentacene. An OTFT mobility of 0.574 cm(2)/V s was measured for pentaceno[2,3-b]thiophene under nitrogen.

    View details for DOI 10.1021/ja808142c

    View details for Web of Science ID 000264791600005

    View details for PubMedID 19125619

  • Overestimation of the field-effect mobility via transconductance measurements and the origin of the output/transfer characteristic discrepancy in organic field-effect transistors JOURNAL OF APPLIED PHYSICS Reese, C., Bao, Z. 2009; 105 (2)

    View details for DOI 10.1063/1.3029587

    View details for Web of Science ID 000262970900112

  • Patterning of alpha-Sexithiophene Single Crystals with Precisely Controlled Sizes and Shapes CHEMISTRY OF MATERIALS Liu, S., Mannsfeld, S. C., Wang, W. M., Sun, Y., Stoltenberg, R. M., Bao, Z. 2009; 21 (1): 15-17

    View details for DOI 10.1021/cm802806t

    View details for Web of Science ID 000262266500006

  • Transistor and solar cell performance of donor-acceptor low bandgap copolymers bearing an acenaphtho[1,2-b]thieno[3,4-e]pyrazine (ACTP) motif JOURNAL OF MATERIALS CHEMISTRY Becerril, H. A., Miyaki, N., Tang, M. L., Mondal, R., Sun, Y., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2009; 19 (5): 591-593

    View details for DOI 10.1039/b819210c

    View details for Web of Science ID 000262547000003

  • Solution-processed, high-performance n-channel organic nanowire transistors Proc. Nat. Acad. Sci. USA Oh, J., H., Lee, H., W., Mannsfeld, S., C.B., Stoltenberg, R., M., Jung, E., Jin, Y., W., Bao, Z. 2009; 106: 6065-6070
  • Chlorination: a general route towards electron transport in organic semiconductors J. Am. Chem. Soc. Tang, M., L., Oh, J., H., Reichardt, A., D., Bao, Z. 2009; 131: 3733-3740
  • Solution Assembly of Transistor Arrays Based on Sorted Nanotube Networks for Large-scale Flexible Electronic Applications 47th Annual Symposium of the Society-for-Information-Display LeMieux, M. C., Roberts, M., Opatkiewicz, J., Bao, Z., Patil, N., Mitra, S. SOC INFORMATION DISPLAY. 2009: 877–879
  • Material and device considerations for organic thin-film transistor sensors JOURNAL OF MATERIALS CHEMISTRY Roberts, M. E., Sokolov, A. N., Bao, Z. 2009; 19 (21): 3351-3363

    View details for DOI 10.1039/b816386c

    View details for Web of Science ID 000266269300003

  • New indolo[3,2-b]carbazole derivatives for field-effect transistor applications JOURNAL OF MATERIALS CHEMISTRY Boudreault, P. T., Wakim, S., Tang, M. L., Tao, Y., Bao, Z., Leclerc, M. 2009; 19 (19): 2921-2928

    View details for DOI 10.1039/b900271e

    View details for Web of Science ID 000265919300008

  • Molecular design for improved photovoltaic efficiency: band gap and absorption coefficient engineering JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Norton, J. E., Miyaki, N., Becerril, H. A., Verploegen, E., Toney, M. F., Bredas, J., McGehee, M. D., Bao, Z. 2009; 19 (39): 7195-7197

    View details for DOI 10.1039/b915222a

    View details for Web of Science ID 000270382400004

  • Influence of Molecular Structure And Film Properties on the Water-Stability and Sensor Characteristics of Organic Transistors CHEMISTRY OF MATERIALS Roberts, M. E., Mannsfeld, S. C., Tang, M. L., Bao, Z. 2008; 20 (23): 7332-7338

    View details for DOI 10.1021/cm802530x

    View details for Web of Science ID 000261335200021

  • Oligothiophene based organic semiconductors with cross-linkable benzophenone moieties SYNTHETIC METALS Virkar, A., Ling, M., Locklin, J., Bao, Z. 2008; 158 (21-24): 958-963
  • Highly Efficient Patterning of Organic Single-Crystal Transistors from the Solution Phase ADVANCED MATERIALS Mannsfeld, S. C., Sharei, A., Liu, S., Roberts, M. E., McCulloch, I., Heeney, M., Bao, Z. 2008; 20 (21): 4044-?
  • Synthesis and characterization of pentacene- and anthradithiophene-fluorene conjugated copolymers synthesized by Suzuki reactions MACROMOLECULES Okamoto, T., Jiang, Y., Qu, F., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2008; 41 (19): 6977-6980

    View details for DOI 10.1021/ma800931a

    View details for Web of Science ID 000259859800020

  • Aging Susceptibility of Terrace-Like Pentacene Films JOURNAL OF PHYSICAL CHEMISTRY C Yang, H., Yang, L., Ling, M., Lastella, S., Gandhi, D. D., Ramanath, G., Bao, Z., Ryu, C. V. 2008; 112 (42): 16161-16165

    View details for DOI 10.1021/jp8055224

    View details for Web of Science ID 000260129400001

  • Direct Patterning of Gold Nanoparticles Using Dip-Pen Nanolithography ACS NANO Wang, W. M., Stoltenberg, R. M., Liu, S., Bao, Z. 2008; 2 (10): 2135-2142

    Abstract

    Various methods for the patterned assembly of metal nanoparticles have been developed in order to harness their unique electrical and optical properties for device applications. This paper discusses a method for direct writing of Au nanoparticles at nanoscale resolution using dip-pen nanolithography. First, a procedure was developed for increasing the loading of Au nanoparticles onto AFM tips to prolong patterning life. AFM tips were subsequently imaged by scanning electron microscopy to determine ink coverage and to gain insight into the deposition process. Next, surface interactions, relative humidity, and writing speed were controlled to determine an optimal range of conditions for deposition. Various ink-substrate combinations were studied to elucidate the dependence of deposition on interactions between Au nanoparticles and the substrate surface; inks consisted of positively and negatively charged particles, and substrates were SiO(2) surfaces modified as hydrophilic or hydrophobic and interacted electrostatically or covalently with Au nanoparticles. Results indicate that a highly hydrophilic surface is required for Au nanoparticle deposition, unless covalent binding can occur between the Au and substrate surface. The optimal range of relative humidity for patterning was found to be 40-60%, and Au nanoparticle deposition was not sensitive to writing speeds ranging from 0.01 to 2 microm/s.

    View details for DOI 10.1021/nn8005416

    View details for Web of Science ID 000260503100022

    View details for PubMedID 19206460

  • Synthesis of DNA-organic molecule-DNA triblock oligomers using the amide coupling reaction and their enzymatic amplification JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lee, J. K., Jung, Y. H., Stoltenberg, R. M., Tok, J. B., Bao, Z. 2008; 130 (39): 12854-?

    Abstract

    Precise electrical contact between single-molecule and electrodes is a first step to study single-molecule electronics and its application such as (bio)sensors and nanodevices. To realize a reliable electrical contact, we can use DNA as a template in the field of nanoelectronics because of its micrometer-scaled length with the thickness of nanometer-scale. In this paper, we studied the reactivity of the amide-coupling reaction to tether oligodeoxynucleotides (ODNs) to organic molecules and the elongation of the ODNs by the polymerase chain reaction (PCR) to synthesize 1.5 kbp dsDNA-organic molecule-1.5 kbp dsDNA (DOD) triblock architecture. The successful amide-coupling reactions were confirmed by electrospray ionization mass spectrometry (ESI-MS), and the triblock architectures were characterized by 1% agarose gel electrophoresis and atomic force microscope (AFM). Our result shows that this strategy is simple and makes it easy to construct DNA-organic molecule-DNA triblock architectures and potentially provides a platform to prepare and investigate single molecule electronics.

    View details for DOI 10.1021/ja8044458

    View details for Web of Science ID 000259553700009

    View details for PubMedID 18763775

  • FLEXIBLE ELECTRONICS Stretching our imagination NATURE NANOTECHNOLOGY LeMieux, M. C., Bao, Z. 2008; 3 (10): 585-586

    View details for DOI 10.1038/nnano.2008.296

    View details for Web of Science ID 000260314300006

    View details for PubMedID 18838993

  • Trialkylsilylethynyl-functionalized tetraceno[2,3-b]thiophene and anthra[2,3-b]thiophene organic transistors CHEMISTRY OF MATERIALS Tang, M. L., Reichardt, A. D., Siegrist, T., Mannsfeld, S. C., Bao, Z. 2008; 20 (14): 4669-4676

    View details for DOI 10.1021/cm800644y

    View details for Web of Science ID 000257666300022

  • Self-assembly, molecular packing, and electron transport in n-type polymer semiconductor nanobelts CHEMISTRY OF MATERIALS Briseno, A. L., Mannsfeld, S. C., Shamberger, P. J., Ohuchi, F. S., Bao, Z., Jenekhe, S. A., Xia, Y. 2008; 20 (14): 4712-4719

    View details for DOI 10.1021/cm8010265

    View details for Web of Science ID 000257666300027

  • High-performance organic thin-film transistors through solution-sheared deposition of small-molecule organic semiconductors ADVANCED MATERIALS Becerril, H. A., Roberts, M. E., Liu, Z., Locklin, J., Bao, Z. 2008; 20 (13): 2588-?
  • Organic solar cells with solution-processed graphene transparent electrodes APPLIED PHYSICS LETTERS Wu, J., Becerril, H. A., Bao, Z., Liu, Z., Chen, Y., Peumans, P. 2008; 92 (26)

    View details for DOI 10.1063/1.2924771

    View details for Web of Science ID 000257424500068

  • Functionalized asymmetric linear acenes for high-performance organic semiconductors ADVANCED FUNCTIONAL MATERIALS Tang, M. L., Reichardt, A. D., Okamoto, T., Miyaki, N., Bao, Z. 2008; 18 (10): 1579-1585
  • Ambipolar, high performance, acene-based organic thin film transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Reichardt, A. D., Miyaki, N., Stoltenberg, R. M., Bao, Z. 2008; 130 (19): 6064-?

    Abstract

    We present a high performance, ambipolar organic field-effect transistor composed of a single material. Ambipolar molecules are rare, and they can enable low-power complementary-like circuits. This low band gap, asymmetric linear acene contains electron-withdrawing fluorine atoms, which lower the molecular orbital energies, allowing the injection of electrons. While hole and electron mobilities of up to 0.071 and 0.37 cm2/V.s, respectively, are reported on devices measured in nitrogen, hole mobilities of up to 0.12 cm2/V.s were found in ambient, with electron transport quenched. These devices were fabricated on octadecyltrimethoxysilane-treated surfaces at a substrate temperature of 60 degrees C.

    View details for DOI 10.1021/ja8005918

    View details for Web of Science ID 000255620200004

    View details for PubMedID 18412338

  • Microstructure of oligofluorene asymmetric derivatives in orgranic thin film transistors CHEMISTRY OF MATERIALS Yuan, Q., Mannsfeld, S. C., Tang, M. L., Roberts, M., Toney, M. F., Delongchamp, D. M., Bao, Z. 2008; 20 (8): 2763-2772

    View details for DOI 10.1021/cm800071r

    View details for Web of Science ID 000255019300026

  • Introducing organic nanowire transistors MATERIALS TODAY Briseno, A. L., Mannsfeld, S. C., Jenekhe, S. A., Bao, Z., Xia, Y. 2008; 11 (4): 38-47
  • Thin film structure of tetraceno[2,3-b]thiophene characterized by grazing incidence X-ray scattering and near-edge X-ray absorption fine structure analysis JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yuan, Q., Mannsfeld, S. C., Tang, M. L., Toney, M. F., Luening, J., Bao, Z. 2008; 130 (11): 3502-3508

    Abstract

    Understanding the structure-property relationship for organic semiconductors is crucial in rational molecular design and organic thin film process control. Charge carrier transport in organic field-effect transistors predominantly occurs in a few semiconductor layers close to the interface in contact with the dielectric layer, and the transport properties depend sensitively on the precise molecular packing. Therefore, a better understanding of the impact of molecular packing and thin film morphology in the first few monolayers above the dielectric layer on charge transport is needed to improve the transistor performance. In this Article, we show that the detailed molecular packing in thin organic semiconductor films can be solved through a combination of grazing incidence X-ray diffraction (GIXD), near-edge X-ray absorption spectra fine structure (NEXAFS) spectroscopy, energy minimization packing calculations, and structure refinement of the diffraction data. We solve the thin film structure for 2 and 20 nm thick films of tetraceno[2,3-b]thiophene and detect only a single phase for these thicknesses. The GIXD yields accurate unit cell dimensions, while the precise molecular arrangement in the unit cell was found from the energy minimization and structure refinement; the NEXAFS yields a consistent molecular tilt. For the 20 nm film, the unit cell is triclinic with a = 5.96 A, b = 7.71 A, c = 15.16 A, alpha = 97.30 degrees, beta = 95.63 degrees, gamma = 90 degrees; there are two molecules per unit cell with herringbone packing (49-59 degree angle) and tilted about 7 degrees from the substrate normal. The thin film structure is significantly different from the bulk single-crystal structure, indicating the importance of characterizing thin film to correlate with thin film device performance. The results are compared to the corresponding data for the chemically similar and widely used pentacene. Possible effects of the observed thin film structure and morphology on charge carrier mobility are discussed.

    View details for DOI 10.1021/ja0773002

    View details for Web of Science ID 000253951900062

    View details for PubMedID 18293975

  • Evaluation of solution-processed reduced graphene oxide films as transparent conductors ACS NANO Becerril, H. A., Mao, J., Liu, Z., Stoltenberg, R. M., Bao, Z., Chen, Y. 2008; 2 (3): 463-470

    Abstract

    Processable, single-layered graphene oxide (GO) is an intriguing nanomaterial with tremendous potential for electronic applications. We spin-coated GO thin-films on quartz and characterized their sheet resistance and optical transparency using different reduction treatments. A thermal graphitization procedure was most effective, producing films with sheet resistances as low as 10(2) -10(3) Omega/square with 80% transmittance for 550 nm light. Our experiments demonstrate solution-processed GO films have potential as transparent electrodes.

    View details for DOI 10.1021/nn700375n

    View details for Web of Science ID 000254408000014

    View details for PubMedID 19206571

  • Organic semiconductor-carbon nanotube bundle bilayer field effect transistors with enhanced mobilities and high on/off ratios APPLIED PHYSICS LETTERS Liu, S., Mannsfeld, S. C., LeMieux, M. C., Lee, H. W., Bao, Z. 2008; 92 (5)

    View details for DOI 10.1063/1.2841033

    View details for Web of Science ID 000253016500082

  • "Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N '-bis(heptafluorobutyl)-3,4 : 9,10-perylene diimide"(vol 91, art no 212107, 2007) APPLIED PHYSICS LETTERS Oh, J. H., Liu, S., Bao, Z., Schmidt, R., Wuerthner, F. 2008; 92 (4)

    View details for DOI 10.1063/1.2839368

    View details for Web of Science ID 000252860400130

  • Adding new functions to organic semiconductor nanowires by assembling metal nanoparticles onto their surfaces JOURNAL OF MATERIALS CHEMISTRY Briseno, A. L., Mannsfeld, S. C., Formo, E., Xiong, Y., Lu, X., Bao, Z., Jenekhe, S. A., Xia, Y. 2008; 18 (44): 5395-5398

    View details for DOI 10.1039/b809228c

    View details for Web of Science ID 000260620300014

  • High performance organic thin film transistor through solution sheared deposition of small molecule organic semiconductors Adv. Mater. Becerril, H., A., Roberts, M., Liu, Z., Locklin, J., Bao, Z. 2008; 20: 2588-2594
  • High-resolution measurement of the anisotropy of charge transport in single crystals ADVANCED MATERIALS Reese, C., Bao, Z. 2007; 19 (24): 4535-?
  • Tunable thin-film crystalline structures and field-effect mobility of oligofluorene-thiophene derivatives CHEMISTRY OF MATERIALS Shin, T. J., Yang, H., Ling, M., Locklin, J., Yang, L., Lee, B., Roberts, M. E., Mallik, A. B., Bao, Z. 2007; 19 (24): 5882-5889

    View details for DOI 10.1021/cm0710599

    View details for Web of Science ID 000251150900022

  • Enhancement in open circuit voltage through a cascade-type energy band structure APPLIED PHYSICS LETTERS Sista, S., Yao, Y., Yang, Y., Tang, M. L., Bao, Z. 2007; 91 (22)

    View details for DOI 10.1063/1.2817935

    View details for Web of Science ID 000251324600089

  • Selective nucleation of organic single crystals from vapor phase on nanoscopically rough surfaces ADVANCED FUNCTIONAL MATERIALS Mannsfeld, S. C., Briseno, A. L., Liu, S., Reese, C., Roberts, M. E., Bao, Z. 2007; 17 (17): 3545-3553
  • Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N '-bis(heptafluorobutyl)3,4 : 9,10-perylene diimide APPLIED PHYSICS LETTERS Oh, J. H., Liu, S., Bao, Z., Schmidt, R., Wuerthner, F. 2007; 91 (21)

    View details for DOI 10.1063/1.2803073

    View details for Web of Science ID 000251105500020

  • Core-fluorinated rerylene bisimide dyes: Air stable n-channel organic semiconductors for thin film transistors with exceptionally high on-to-off current ratios ADVANCED MATERIALS Schmidt, R., Ling, M. M., Oh, J. H., Winkler, M., Koenemann, M., Bao, Z., Wuerthner, F. 2007; 19 (21): 3692-?
  • Synthesis, characterization, and field-effect transistor performance of pentacene derivatives ADVANCED MATERIALS Okamoto, T., Senatore, M. L., Ling, M., Mallik, A. B., Tang, M. L., Bao, Z. 2007; 19 (20): 3381-?
  • Selective crystallization of organic semiconductors on patterned templates of carbon nanotubes ADVANCED FUNCTIONAL MATERIALS Liu, S., Briseno, A. L., Mannsfeld, S. C., You, W., Locklin, J., Lee, H. W., Xia, Y., Bao, Z. 2007; 17 (15): 2891-2896
  • Perylenediimide nanowires and their use in fabricating field-effect transistors and complementary inverters NANO LETTERS Briseno, A. L., Mannsfeld, S. C., Reese, C., Hancock, J. M., Xiong, Y., Jenekhe, S. A., Bao, Z., Xia, Y. 2007; 7 (9): 2847-2853

    Abstract

    Perylenetetracarboxyldiimide (PTCDI) nanowires self-assembled from commercially available materials are demonstrated as the n-channel semiconductor in organic field-effect transistors (OFETs) and as a building block in high-performance complementary inverters. Devices based on a network of PTCDI nanowires have electron mobilities and current on/off ratios on the order of 10(-2) cm2/Vs and 10(4), respectively. Complementary inverters based on n-channel PTCDI nanowire transistors and p-channel hexathiapentacene (HTP) nanowire OFETs achieved gains as high as 8. These results demonstrate the first example of the use of one-dimensional organic semiconductors in complementary inverters.

    View details for DOI 10.1021/nl071495u

    View details for Web of Science ID 000249501900055

    View details for PubMedID 17696562

  • Synthesis of solution-soluble pentacene-containing conjugated copolymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Okamoto, T., Bao, Z. 2007; 129 (34): 10308-?

    View details for DOI 10.1021/ja0725403

    View details for Web of Science ID 000249035200005

    View details for PubMedID 17685520

  • Probing the anisotropic field-effect mobility of solution-deposited dicyclohexyl-alpha-quaterthiophene single crystals ADVANCED FUNCTIONAL MATERIALS Mannsfeld, S. C., Locklin, J., Reese, C., Roberts, M. E., Lovinger, A. J., Bao, Z. 2007; 17 (10): 1617-1622
  • Solution-assisted assembly of organic semiconducting single crystals on surfaces with patterned wettability LANGMUIR Liu, S., Wang, W. M., Mannsfeld, S. C., Locklin, J., Erk, P., Gomez, M., Richter, F., Bao, Z. 2007; 23 (14): 7428-7432

    Abstract

    Two efficient approaches to assembling organic semiconducting single crystals are described. The methods rely on solvent wetting and dewetting on substrates with patterned wettability to selectively direct the deposition or removal of organic crystals. Substrates were functionalized with different self-assembled monolayers (SAMs) to achieve the desired wettabilities. The assembly of different organic crystals over centimeter-squared areas on Au, SiO2, and flexible plastic substrates was demonstrated. By designing line features on the substrate, the alignment of crystals, such as CuPc needles, was also achieved. As a demonstration of the potential application of this assembly approach, arrays of single-crystal organic field-effect transistors were fabricated by patterning organic single crystals directly onto and between transistor source and drain electrodes.

    View details for DOI 10.1021/1a700493p

    View details for Web of Science ID 000247487200004

    View details for PubMedID 17547427

  • Solution deposited liquid crystalline semiconductors on a photoalignment layer for organic thin-film transistors APPLIED PHYSICS LETTERS Fujiwara, T., Locklin, J., Bao, Z. 2007; 90 (23)

    View details for DOI 10.1063/1.2746937

    View details for Web of Science ID 000247145500036

  • Resistance switching in a polystyrene film containing Au nanoparticles JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Tsukamoto, T., Liu, S., Bao, Z. 2007; 46 (6A): 3622-3625
  • Correlating molecular structure to field-effect mobility: The investigation of side-chain functionality in phenylene - Thiophene oligomers and their application in field effect transistors CHEMISTRY OF MATERIALS Sung, A., Ling, M. M., Tang, M. L., Bao, Z., Locklin, J. 2007; 19 (9): 2342-2351

    View details for DOI 10.1021/cm070117n

    View details for Web of Science ID 000245900100031

  • Air-stable n-channel organic semiconductors based on perylene diimide derivatives without strong electron withdrawing groups ADVANCED MATERIALS Ling, M., Erk, P., Gomez, M., Koenemann, M., Locklin, J., Bao, Z. 2007; 19 (8): 1123-1127
  • Non-destructive probing of the anisotropy of field-effect mobility in the rubrene single crystal SYNTHETIC METALS Ling, M., Reese, C., Briseno, A. L., Bao, Z. 2007; 157 (6-7): 257-260
  • Organic single-crystal field-effect transistors MATERIALS TODAY Reese, C., Bao, Z. 2007; 10 (3): 20-27
  • Fabrication of field-effect transistors from hexathiapentacene single-crystal nanowires NANO LETTERS Briseno, A. L., Mannsfeld, S. C., Lu, X., Xiong, Y., Jenekhe, S. A., Bao, Z., Xia, Y. 2007; 7 (3): 668-675

    Abstract

    This paper describes a simple, solution-phase route to the synthesis of bulk quantities of hexathiapentacene (HTP) single-crystal nanowires. These nanowires have also been successfully incorporated as the semiconducting material in field-effect transistors (FETs). For devices based on single nanowires, the carrier mobilities and current on/off ratios could be as high as 0.27 cm2/Vs and >103, respectively. For transistors fabricated from a network of nanowires, the mobilities and current on/off ratios could reach 0.057 cm2/Vs and >104, respectively. We have further demonstrated the use of nanowire networks in fabricating transistors on mechanically flexible substrates. Preliminary results show that these devices could withstand mechanical strain and still remain functional. The results from this study demonstrate the potential of utilizing solution-dispersible, nanostructured organic materials for use in low-cost, flexible electronic applications.

    View details for DOI 10.1021/nl0627036

    View details for Web of Science ID 000244867400023

    View details for PubMedID 17288487

  • Complementary inverter using high mobility air-stable perylene di-imide derivatives APPLIED PHYSICS LETTERS Ling, M., Bao, Z., Erk, P., Koenemann, M., Gomez, M. 2007; 90 (9)

    View details for DOI 10.1063/1.2695873

    View details for Web of Science ID 000244591700107

  • Structural transitions of nanocrystalline domains in regioregular poly(3-hexyl thiophene) thin films J. Poly. Sci. Part B: Poly. Phys. Yang, H., C., Shin, T., J., Bao, Z., Ryu, C., Y. 2007; 45: 1303-1312
  • Design, Synthesis, and Transistor Performance of Organic Semiconductors Organic Thin Film Transistors Mallik, A., B., Locklin, J., J., Mannsfeld, S., Reese, C., Roberts, M., Senatore, M. edited by Bao, Z., Locklin, J., J. CRC Press. 2007
  • Probing Non-destructive probing of the anisotropy of field-effect mobility in the rubrene single crystal Syn. Met. Ling, M., M., Reese, C., Briseno, L., Alejandro, Bao, Z. 2007; 157: 257-260
  • Solubility-driven thin film structures of regioregular poly(3-hexyl thiophene) using volatile solvents Appl. Phys. Lett. Yang, H., H., LeFevre, S., W., Ryu, C., Y., Bao, Z. 2007; 90: 172116
  • Air Stable n-Channel Organic Semiconductors for Thin Film Transistors Based on Fluorinated Derivatives of Perylene Diimides Chem. Mater. Chen, H., Z., Ling, M., M., Mo, X., Shi, M., M., Bao, Z. 2007; 19: 816-824
  • Structure property relationships: Asymmetric oligofluorene-thiophene molecules for organic TFTs CHEMISTRY OF MATERIALS Tang, M. L., Roberts, M. E., Locklin, J. J., Ling, M. M., Meng, H., Bao, Z. 2006; 18 (26): 6250-6257

    View details for DOI 10.1021/cm0623514

    View details for Web of Science ID 000242935500028

  • High-performance organic semiconductors: Asymmetric linear acenes containing sulphur JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Okamoto, T., Bao, Z. 2006; 128 (50): 16002-16003

    Abstract

    Two new linear acenes with fused thiophene units have been synthesized. These acenes have conjugation lengths between anthracene and pentacene. Thin films of these linear molecules were characterized by ultraviolet spectroscopy, X-ray diffraction, atomic force microscopy (AFM), and field-effect transistor measurements. Submonolayer AFM studies show growth that greatly resembles pentacene, while thin-film growth is dendritic. Mobilites as high as 0.47 cm2 V-1 s-1 have been found for the tetraceno[2,3-b]thiophene and are as high as 0.15 cm2 V-1 s-1 for anthra[2,3-b]thiophene.

    View details for DOI 10.1021/ja066824j

    View details for Web of Science ID 000242825600037

    View details for PubMedID 17165730

  • Patterning organic single-crystal transistor arrays NATURE Briseno, A. L., Mannsfeld, S. C., Ling, M. M., Liu, S., Tseng, R. J., Reese, C., Roberts, M. E., Yang, Y., Wudl, F., Bao, Z. 2006; 444 (7121): 913-917

    Abstract

    Field-effect transistors made of organic single crystals are ideal for studying the charge transport characteristics of organic semiconductor materials. Their outstanding device performance, relative to that of transistors made of organic thin films, makes them also attractive candidates for electronic applications such as active matrix displays and sensor arrays. These applications require minimal cross-talk between neighbouring devices. In the case of thin film systems, simple patterning of the active semiconductor layer minimizes cross-talk. But when using organic single crystals, the only approach currently available for creating arrays of separate devices is manual selection and placing of individual crystals-a process prohibitive for producing devices at high density and with reasonable throughput. In contrast, inorganic crystals have been grown in extended arrays, and efficient and large-area fabrication of silicon crystalline islands with high mobilities for electronic applications has been reported. Here we describe a method for effectively fabricating large arrays of single crystals of a wide range of organic semiconductor materials directly onto transistor source-drain electrodes. We find that film domains of octadecyltriethoxysilane microcontact-printed onto either clean Si/SiO(2) surfaces or flexible plastic provide control over the nucleation of vapour-grown organic single crystals. This allows us to fabricate large arrays of high-performance organic single-crystal field-effect transistors with mobilities as high as 2.4 cm(2) V(-1) s(-1) and on/off ratios greater than 10(7), and devices on flexible substrates that retain their performance after significant bending. These results suggest that our fabrication approach constitutes a promising step that might ultimately allow us to utilize high-performance organic single-crystal field-effect transistors for large-area electronics applications.

    View details for DOI 10.1038/nature05427

    View details for Web of Science ID 000242805400052

    View details for PubMedID 17167482

  • Hexathiapentacene: Structure, molecular packing, and thin-film transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Briseno, A. L., Miao, Q., Ling, M., Reese, C., Meng, H., Bao, Z., Wudl, F. 2006; 128 (49): 15576-15577

    Abstract

    In this communication we report the electrical characteristics of hexathiapentacene (HTP) and emphasize the unusual chemical structure and molecular packing. We report field-effect mobilities as high as 0.04 cm2 V-1 s-1 and current on/off ratios of >105. With crystallographic evidence of unusually long S-S bonds compared to normal S-S bonds, we have suggested a unique resonance structure similar to trithiapentalene, which well explains the bonding characteristics of HTP. This work appears to be the first to determine its molecular structure/packing mode and to study its application in organic transistors.

    View details for DOI 10.1021/ja066088j

    View details for Web of Science ID 000242575300014

    View details for PubMedID 17147352

  • Assembly and alignment of metallic nanorods on surfaces with patterned wettability SMALL Liu, S., Tok, J. B., Locklin, J., Bao, Z. 2006; 2 (12): 1448-1453

    View details for DOI 10.1002/smll.200600275

    View details for Web of Science ID 000242275800011

    View details for PubMedID 17193004

  • Copper hexafluorophthalocyanine field-effect transistors with enhanced mobility by soft contact lamination ORGANIC ELECTRONICS Ling, M., Bao, Z. 2006; 7 (6): 568-575
  • High-performance organic semiconductors based on fluorene-phenylene oligomers with high ionization potentials ADVANCED MATERIALS Locklin, J., Ling, M. M., Sung, A., Roberts, M. E., Bao, Z. 2006; 18 (22): 2989-?
  • High-performance microscale single-crystal transistors by lithography on an elastomer dielectric APPLIED PHYSICS LETTERS Reese, C., Chung, W., Ling, M., Roberts, M., Bao, Z. 2006; 89 (20)

    View details for DOI 10.1063/1.2388151

    View details for Web of Science ID 000242100200042

  • Air-stable n-channel copper hexachlorophthalocyanine for field-effect transistors APPLIED PHYSICS LETTERS Ling, M., Bao, Z., Erk, P. 2006; 89 (16)

    View details for DOI 10.1063/1.2362976

    View details for Web of Science ID 000241405200123

  • High-performance organic single-crystal transistors on flexible substrates ADVANCED MATERIALS Briseno, A. L., Tseng, R. J., Ling, M., Falcao, E. H., Yang, Y., Wudl, F., Bao, Z. 2006; 18 (17): 2320-?
  • Effect of morphology on organic thin film transistor sensors ANALYTICAL AND BIOANALYTICAL CHEMISTRY Locklin, J., Bao, Z. N. 2006; 384 (2): 336-342

    Abstract

    This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.

    View details for DOI 10.1007/s00216-005-0137-z

    View details for Web of Science ID 000234299600004

    View details for PubMedID 16328249

  • Organic Single-Crystal Complementary Inverters Appl. Phys. Lett. Briseno, A., Tseng, R., Ling, M., Chen, H., Bao, Z., Falcao, E. 2006; 89: 222111
  • Molecular conductance measurements through printed Au nanodots Appl. Phys. Lett. Jiang, W., Garfunkel, E., Zhitenev, N., B., Abusch-Magder, D., Tennant, D., M, Bao, Z. 2006; 89: 113107
  • High Performance Organic Semiconductors Based on Fluorene-phenylene Oligomers with High Ionization Potentials Adv. Mater. Locklin, J., Ling, M., M., Sung, A., Roberts, M., Bao, Z. 2006; 18: 2989-2992
  • Thickness Dependence of Microstructure in Semiconducting Films of an Oligofluorene Derivative J. Am. Chem. Soc. DeLongchamp, D., M., Ling, M., M., Roberts, M., Jung, Y., S., Fischer, D., A., Lin, E., Bao, Z. 2006; 128: 16579-12586
  • High Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur J. Am. Chem. Soc. Tang, M., L., Okamoto, T., Bao, Z. 2006; 128: 160002-160003
  • Patterning Organic Semiconductors Using ‘Dry’ Poly(dimethylsiloxane) Elastomeric Stamps for Thin Film Transistors J. Am. Chem. Soc. Briseno, A., L., Roberts, M., Ling, M., M., Moon, H., Bao, Z. 2006; 128: 3880-3881
  • Control of Topography, Stress and Diffusion at Molecule-metal Interface Nanotechnology Zhitenev, N., B., Jiang, W., Erbe, A., Bao, Z., Garfunkel, E., Tennant, D., M 2006; 17: 1272-1277
  • Transistor Performance of Top, Rough Surface of Pentacene Measured by Laminated, Double Insulated-Gate Supported on a Poly(dimethylsiloxanes) Base Structure Appl. Phys. Lett. Ling, M., M., Li, D., W., Bao, Z. 2006; 88: 33502
  • Organic Single Crystals: Tools for the Exploration of Charge Transport Phenomena in Organic Materials J. Mater. Chem. Reese, C., Bao, Z. 2006; 16: 329-333
  • Optimizing the thin film morphology of organic field-effect transistors: The influence of molecular structure and vacuum deposition parameters on device performance POLYMER REVIEWS Locklin, J., Roberts, M. E., Mannsfeld, S. C., Bao, Z. 2006; 46 (1): 79-101
  • Nanowire lithography: Fabricating controllable electrode gaps using Au-Ag-Au nanowires NANO LETTERS Liu, S. H., Tok, J. B., Bao, Z. N. 2005; 5 (6): 1071-1076

    Abstract

    A method to fabricate nanowire electrodes possessing controllable gaps is described. The method relies on electrochemical deposition and selective chemical etching or heating to selectively remove the Ag segment of Au-Ag-Au nanowires. Because the thickness of the Ag segment directly dictates the size of the nanogap, the gap width can be easily controlled during the nanowire fabrication process. Herein, we demonstrate gaps with 2 microm, 100 nm and 20 nm widths via the above-mentioned approaches. In addition, we observed that small gaps (approximately 20 nm) can be formed through annealing Au-Ag-Au nanowires at 200 degrees C in air. Electrical contact between nanowire electrodes and contact pads is studied. Using nanowire electrodes with a 100 nm gap, we subsequently fabricate organic field effect transistors (FETs) with regioregular poly(3-hexylthiophene).

    View details for DOI 10.1021/nl050581w

    View details for Web of Science ID 000229729900014

    View details for PubMedID 15943445

  • Organic Thin Film Transistors Based on Cyclohexyl-substituted Organic Semiconductors Chem. Mater. Locklin, J., Li, D., W., Mannsfeld, S., C.B., Borkent, E., J., Meng, H., Advincula, R., Bao, Z. 2005; 17: 3366-3374
  • Molecular Nano-junctions Formed with Different Metallic Electrodes Nanotechnology Zhitenev, N., B., Erbe, A., Bao, Z., Jiang, W., Garfunkel, E. 2005; 16: 495-500
  • Conducting AFM and 2D GIXD Studies on Pentacene Thin Films J. Am. Chem. Soc. Yang, H., Shin, T., J., Ling, M., M., Cho, K., Ryu, C., Y., Bao, Z. 2005; 127: 11542-11543
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  • Metallic contact formation for molecular electronics: interactions between vapor-deposited metals and self-assembled monolayers of conjugated mono- and dithiols LANGMUIR de Boer, B., Frank, M. M., Chabal, Y. J., Jiang, W. R., Garfunkel, E., Bao, Z. 2004; 20 (5): 1539-1542

    Abstract

    We present grazing-incidence Fourier transform infrared and AFM data of Au, Al, and Ti vapor-deposited onto self-assembled monolayers (SAMs) of conjugated mono- and dithiols. SAMs of 4,4'''-dimercapto-p-quaterphenyl, 4,4"-dimercapto-p-terphenyl, and 4,4'-dimercapto-p-biphenyl have reactive thiols at the SAM/vacuum interface that interact with vapor-deposited Au or Al atoms, preventing metal penetration. Conjugated monothiols lack such metal blocking groups, and metals (Au, Al) can penetrate into their SAMs. Vapor deposition of Ti onto conjugated mono- and dithiol SAMs and onto hexadecanethiol SAMs destroys the monolayers.

    View details for DOI 10.1021/la0356349

    View details for Web of Science ID 000189241500002

    View details for PubMedID 15801409

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