Bio


Novel materials and processing techniques for large-area and flexible electronic/photonic devices. Polymeric materials for electronics, bioelectronics, and biosensors. Electrochemical devices for neuromorphic computing. Defects and structure/property studies of polymeric semiconductors, nano-structured and amorphous materials in thin films. Advanced characterization techniques for soft matter.

Administrative Appointments


  • Department Chair, Stanford University/Materials Science and Engineering (2019 - Present)

Honors & Awards


  • Walter J. Gores Award for Excellence in Teaching, Stanford University (2016)
  • Highly Cited Researcher in Materials Science, ISI/Clarivate (2015-)
  • Tau Beta Pi Award for Excellence in Undergraduate Teaching, Stanford University (2013)
  • Early Career Award, SPIE (2010)
  • CAREER Award, NSF (2007-2011)
  • Untenured Faculty Award, 3M (2007-2009)
  • Outstanding Performance Award, PARC (2003, 2004)
  • Award for Outstanding Students Abroad, Italian University Council (1997)
  • John Tyssowski Memorial Fellow, UC Berkeley (1997)
  • Fellow, Fulbright (1995-2000)

Program Affiliations


  • Stanford SystemX Alliance

Professional Education


  • PhD, UC Berkeley, Materials Science (2001)

Current Research and Scholarly Interests


Novel materials and processing techniques for large-area and flexible electronic/photonic devices. Polymeric materials for electronics, bioelectronics, and biosensors. Electrochemical devices for neuromorphic computing. Defects and structure/property studies of polymeric semiconductors, nano-structured and amorphous materials in thin films. Advanced characterization techniques for soft matter.

2018-19 Courses


Stanford Advisees


All Publications


  • Parallel programming of an ionic floating-gate memory array for scalable neuromorphic computing SCIENCE Fuller, E. J., Keene, S. T., Melianas, A., Wang, Z., Agarwal, S., Li, Y., Tuchman, Y., James, C. D., Marinella, M. J., Yang, J., Salleo, A., Talin, A. 2019; 364 (6440): 570-+
  • High-mobility, trap-free charge transport in conjugated polymer diodes NATURE COMMUNICATIONS Nikolka, M., Broch, K., Armitage, J., Hanifi, D., Nowack, P. J., Venkateshvaran, D., Sadhanala, A., Saska, J., Mascal, M., Jung, S., Lee, J., McCulloch, I., Salleo, A., Sirringhaus, H. 2019; 10
  • The role of the third component in ternary organic solar cells NATURE REVIEWS MATERIALS Gasparini, N., Salleo, A., McCulloch, I., Baran, D. 2019; 4 (4): 229–42
  • Increased charge carrier mobility and molecular packing of a solution sheared diketopyrrolopyrrole-based donor-acceptor copolymer by alkyl side chain modification JOURNAL OF MATERIALS CHEMISTRY C Hambsch, M., Erdmann, T., Chew, A. R., Bernstorff, S., Salleo, A., Kiriy, A., Voit, B., Mannsfeld, S. B. 2019; 7 (12): 3665–74

    View details for DOI 10.1039/c8tc06255b

    View details for Web of Science ID 000463831800027

  • Influence of Water on the Performance of Organic Electrochemical Transistors CHEMISTRY OF MATERIALS Savva, A., Cendra, C., Giugni, A., Torre, B., Surgailis, J., Ohayon, D., Giovannitti, A., McCulloch, I., Di Fabrizio, E., Salleo, A., Rivnay, J., Inal, S. 2019; 31 (3): 927–37
  • Role of the Anion on the Transport and Structure of Organic Mixed Conductors ADVANCED FUNCTIONAL MATERIALS Cendra, C., Giovannitti, A., Savva, A., Venkatraman, V., McCulloch, I., Salleo, A., Inal, S., Rivnay, J. 2019; 29 (5)
  • Mechanisms for Enhanced State Retention and Stability in Redox-Gated Organic Neuromorphic Devices ADVANCED ELECTRONIC MATERIALS Keene, S., Melianas, A., van de Burgt, Y., Salleo, A. 2019; 5 (2)
  • Additive solution deposition of multi-layered semiconducting polymer films for design of sophisticated device architectures JOURNAL OF MATERIALS CHEMISTRY C Murrey, T. L., Guo, K., Mulvey, J. T., Lee, O. A., Cendra, C., Bedolla-Valdez, Z. I., Salleo, A., Moulin, J., Hong, K., Moule, A. J. 2019; 7 (4): 953–60

    View details for DOI 10.1039/c8tc05652h

    View details for Web of Science ID 000459571400015

  • Optics of Perovskite Solar Cell Front Contacts. ACS applied materials & interfaces Hossain, M. I., Hongsingthong, A., Qarony, W., Sichanugrist, P., Konagai, M., Salleo, A., Knipp, D., Tsang, Y. H. 2019; 11 (16): 14693–701

    Abstract

    The front contact has a major impact on the electrical and optical properties of perovskite solar cells. The front contact is part of the junction of the solar cell and must provide lateral charge transport to the terminals and should allow for an efficient light incoupling, while having low optical losses. The complex requirements of the perovskite solar front contact will be described and the optics of the front contact will be investigated. It will be shown that the front contact has a distinct influence on the short-circuit current and energy conversion efficiency. Metal oxide films were investigated as potential front contacts. The incoupling of light in the solar cell is investigated by three-dimensional finite-difference time-domain optical simulations and optical measurements of experimentally realized self-textured zinc oxide films. The zinc oxide films were prepared by metal-organic chemical vapor deposition at low temperatures. Furthermore, the influence of free carrier absorption of metal oxide films on the optics of low bandgap and/or tandem solar cells is investigated. Guidelines are provided on how to choose the doping concentration and thickness of the metal oxide films. Finally, it will be shown that by selecting an optimal front contact design the short-circuit current and energy conversion efficiency can be increased by at least 15%.

    View details for PubMedID 30900443

  • Parallel programming of an ionic floating-gate memory array for scalable neuromorphic computing. Science (New York, N.Y.) Fuller, E. J., Keene, S. T., Melianas, A., Wang, Z., Agarwal, S., Li, Y., Tuchman, Y., James, C. D., Marinella, M. J., Yang, J. J., Salleo, A., Talin, A. A. 2019

    Abstract

    Neuromorphic computers could overcome efficiency bottlenecks inherent to conventional computing through parallel programming and read out of artificial neural network weights in a crossbar memory array. However, selective and linear weight updates and <10 nanoampere read currents are required for learning that surpasses conventional computing efficiency. We introduce an ionic floating-gate memory (IFG) array based upon a polymer redox transistor connected to a conductive-bridge memory (CBM). Selective and linear programming of a transistor array is executed in parallel by overcoming the bridging voltage threshold of the CBMs. Synaptic weight read-out with currents <10 nanoampere is achieved by diluting the conductive polymer in an insulating channel to decrease the conductance. The redox transistors endure >1 billion 'read-write' operations and support >1 megahertz 'read-write' frequencies.

    View details for PubMedID 31023890

  • Redefining near-unity luminescence in quantum dots with photothermal threshold quantum yield. Science (New York, N.Y.) Hanifi, D. A., Bronstein, N. D., Koscher, B. A., Nett, Z., Swabeck, J. K., Takano, K., Schwartzberg, A. M., Maserati, L., Vandewal, K., van de Burgt, Y., Salleo, A., Alivisatos, A. P. 2019; 363 (6432): 1199–1202

    Abstract

    A variety of optical applications rely on the absorption and reemission of light. The quantum yield of this process often plays an essential role. When the quantum yield deviates from unity by significantly less than 1%, applications such as luminescent concentrators and optical refrigerators become possible. To evaluate such high performance, we develop a measurement technique for luminescence efficiency with sufficient accuracy below one part per thousand. Photothermal threshold quantum yield is based on the quantization of light to minimize overall measurement uncertainty. This technique is used to guide a procedure capable of making ensembles of near-unity emitting cadmium selenide/cadmium sulfide (CdSe/CdS) core-shell quantum dots. We obtain a photothermal threshold quantum yield luminescence efficiency of 99.6 ± 0.2%, indicating nearly complete suppression of nonradiative decay channels.

    View details for PubMedID 30872520

  • Diffraction imaging of nanocrystalline structures in organic semiconductor molecular thin films. Nature materials Panova, O., Ophus, C., Takacs, C. J., Bustillo, K. C., Balhorn, L., Salleo, A., Balsara, N., Minor, A. M. 2019

    Abstract

    The properties of organic solids depend on their structure and morphology, yet direct imaging using conventional electron microscopy methods is hampered by the complex internal structure of these materials and their sensitivity to electron beams. Here, we manage to observe the nanocrystalline structure of two organic molecular thin-film systems using transmission electron microscopy by employing a scanning nanodiffraction method that allows for full access to reciprocal space over the size of a spatially localized probe (~2 nm). The morphologies revealed by this technique vary from grains with pronounced segmentation of the structure-characterized by sharp grain boundaries and overlapping domains-to liquid-crystal structures with crystalline orientations varying smoothly over all possible rotations that contain disclinations representing singularities in the director field. The results show how structure-property relationships can be visualized in organic systems using techniques previously only available for hard materials such as metals and ceramics.

    View details for DOI 10.1038/s41563-019-0387-3

    View details for PubMedID 31160799

  • High-Throughput Open-Air Plasma Activation of Metal-Oxide Thin Films with Low Thermal Budget ACS APPLIED MATERIALS & INTERFACES Tak, Y., Hilt, F., Keene, S., Kim, W., Dauskardt, R. H., Salleo, A., Kim, H. 2018; 10 (43): 37223–32

    Abstract

    Sputter-processed oxide films are typically annealed at high temperature (activation process) to achieve stable electrical characteristics through the formation of strong metal-oxide chemical bonds. For instance, indium-gallium-zinc oxide (IGZO) films typically need a thermal treatment at 300 °C for ≥1 h as an activation process. We propose an open-air plasma treatment (OPT) to rapidly and effectively activate sputter-processed IGZO films. The OPT effectively induces metal-oxide chemical bonds in IGZO films at temperatures as low as 240 °C, with a dwell time on the order of a second. Furthermore, by controlling the plasma-processing conditions (scan speed, distance a between plasma nozzle and samples, and gas flow rate), the electrical characteristics and the microstructure of the IGZO films can be easily tuned. Finally, OPT can be utilized to implement a selective activation process. Plasma-treated IGZO thin-film transistors (TFTs) exhibit comparable electrical characteristics to those of conventionally thermal treated IGZO TFTs. Through in-depth optical, chemical, and physical characterizations, we confirm that OPT simultaneously dissociates weak chemical bonds by UV radiation and ion bombardment and re-establishes the metal-oxide network by radical reaction and OPT-induced heat.

    View details for PubMedID 30288973

  • Unraveling the Effect of Conformational and Electronic Disorder in the Charge Transport Processes of Semiconducting Polymers ADVANCED FUNCTIONAL MATERIALS Chew, A. R., Ghosh, R., Pakhnyuk, V., Onorato, J., Davidson, E. C., Segalman, R. A., Luscombe, C. K., Spano, F. C., Salleo, A. 2018; 28 (41)
  • Progress in Poly (3-Hexylthiophene) Organic Solar Cells and the Influence of Its Molecular Weight on Device Performance ADVANCED ENERGY MATERIALS Wadsworth, A., Hamid, Z., Bidwell, M., Ashraf, R. S., Khan, J. I., Anjum, D. H., Cendra, C., Yan, J., Rezasoltani, E., Guilbert, A. Y., Azzouzi, M., Gasparini, N., Bannock, J. H., Baran, D., Wu, H., de Mello, J. C., Brabec, C. J., Salleo, A., Nelson, J., Laquai, F., McCulloch, I. 2018; 8 (28)
  • Biomimetic Electronic Devices for Measuring Bacterial Membrane Disruption ADVANCED MATERIALS Pitsalidis, C., Pappa, A., Porel, M., Artim, C. M., Faria, G. C., Duong, D. D., Alabi, C. A., Daniel, S., Salleo, A., Owens, R. M. 2018; 30 (39): e1803130

    Abstract

    Antibiotic discovery has experienced a severe slowdown in terms of discovery of new candidates. In vitro screening methods using phospholipids to model the bacterial membrane provide a route to identify molecules that specifically disrupt bacterial membranes causing cell death. Thanks to the electrically insulating properties of the major component of the cell membrane, phospholipids, electronic devices are highly suitable transducers of membrane disruption. The organic electrochemical transistor (OECT) is a highly sensitive ion-to-electron converter. Here, the OECT is used as a transducer of the permeability of a lipid monolayer (ML) at a liquid:liquid interface, designed to read out changes in ion flux caused by compounds that interact with, and disrupt, lipid assembly. This concept is illustrated using the well-documented antibiotic Polymixin B and the highly sensitive quantitation of permeability of the lipid ML induced by two novel recently described antibacterial amine-based oligothioetheramides is shown, highlighting molecular scale differences in their disruption capabilities. It is anticipated that this platform has the potential to play a role in front-line antimicrobial compound design and characterization thanks to the compatibility of semiconductor microfabrication technology with high-throughput readouts.

    View details for PubMedID 30117203

  • Spectral Signatures and Spatial Coherence of Bound and Unbound Polarons in P3HT Films: Theory Versus Experiment JOURNAL OF PHYSICAL CHEMISTRY C Ghosh, R., Chew, A. R., Onorato, J., Pakhnyuk, V., Luscombe, C. K., Salleo, A., Spano, F. C. 2018; 122 (31): 18048–60
  • Approaching Perfect Light Incoupling in Perovskite and Silicon Thin Film Solar Cells by Moth Eye Surface Textures ADVANCED THEORY AND SIMULATIONS Qarony, W., Hossain, M., Dewan, R., Fischer, S., Meyer-Rochow, V., Salleo, A., Knipp, D., Tsang, Y. 2018; 1 (8)
  • Polymorphism controls the degree of charge transfer in a molecularly doped semiconducting polymer MATERIALS HORIZONS Jacobs, I. E., Cendra, C., Harrelson, T. F., Valdez, Z., Faller, R., Salleo, A., Moule, A. J. 2018; 5 (4): 655–60

    View details for DOI 10.1039/c8mh00223a

    View details for Web of Science ID 000437187900003

  • A Universal Platform for Fabricating Organic Electrochemical Devices ADVANCED ELECTRONIC MATERIALS Duong, D. T., Tuchman, Y., Chakthranont, P., Cavassin, P., Colucci, R., Jaramillo, T. F., Salleo, A., Faria, G. C. 2018; 4 (7)
  • Molecularly selective nanoporous membrane-based wearable organic electrochemical device for noninvasive cortisol sensing. Science advances Parlak, O., Keene, S. T., Marais, A., Curto, V. F., Salleo, A. 2018; 4 (7): eaar2904

    Abstract

    Wearable biosensors have emerged as an alternative evolutionary development in the field of healthcare technology due to their potential to change conventional medical diagnostics and health monitoring. However, a number of critical technological challenges including selectivity, stability of (bio)recognition, efficient sample handling, invasiveness, and mechanical compliance to increase user comfort must still be overcome to successfully bring devices closer to commercial applications. We introduce the integration of an electrochemical transistor and a tailor-made synthetic and biomimetic polymeric membrane, which acts as a molecular memory layer facilitating the stable and selective molecular recognition of the human stress hormone cortisol. The sensor and a laser-patterned microcapillary channel array are integrated in a wearable sweat diagnostics platform, providing accurate sweat acquisition and precise sample delivery to the sensor interface. The integrated devices were successfully used with both ex situ methods using skin-like microfluidics and on human subjects with on-body real-sample analysis using a wearable sensor assembly.

    View details for PubMedID 30035216

  • Optimized pulsed write schemes improve linearity and write speed for low-power organic neuromorphic devices JOURNAL OF PHYSICS D-APPLIED PHYSICS Keene, S. T., Melianas, A., Fuller, E. J., van de Burgt, Y., Talin, A., Salleo, A. 2018; 51 (22)
  • Copper interstitial recombination centers in Cu3N PHYSICAL REVIEW B Yee, Y., Inoue, H., Hultqvist, A., Hanifi, D., Salleo, A., Magyari-Kope, B., Nishi, Y., Bent, S. F., Clemens, B. M. 2018; 97 (24)
  • Improving Quantum Yield of Upconverting Nanoparticles in Aqueous Media via Emission Sensitization NANO LETTERS Wisser, M. D., Fischer, S., Siefe, C., Alivisatos, A., Salleo, A., Dionne, J. A. 2018; 18 (4): 2689–95

    Abstract

    We demonstrate a facile method to improve upconversion quantum yields in Yb,Er-based nanoparticles via emission dye-sensitization. Using the commercially available dye ATTO 542, chosen for its high radiative rate and significant spectral overlap with the green emission of Er3+, we decorate the surfaces of sub-25 nm hexagonal-phase Na(Y/Gd/Lu)0.8F4:Yb0.18Er0.02 upconverting nanoparticles with varying dye concentrations. Upconversion photoluminescence and absorption spectroscopy provide experimental confirmation of energy transfer to and emission from the dye molecules. Upconversion quantum yield is observed to increase with dye sensitization, with the highest enhancement measured for the smallest particles investigated (10.9 nm in diameter); specifically, these dye-decorated particles are more than 2× brighter than are unmodified, organic-soluble nanoparticles and more than 10× brighter than are water-soluble nanoparticles. We also observe 3× lifetime reductions with dye adsorption, confirming the quantum yield enhancement to result from the high radiative rate of the dye. The approach detailed in this work is widely implementable, renders the nanoparticles water-soluble, and most significantly improves sub-15 nm nanoparticles, making our method especially attractive for biological imaging applications.

    View details for PubMedID 29589449

  • Chemically Responsive Elastomers Exhibiting Unity-Order Refractive Index Modulation. Advanced materials (Deerfield Beach, Fla.) Wu, D. M., Solomon, M. L., Naik, G. V., Garcia-Etxarri, A., Lawrence, M., Salleo, A., Dionne, J. A. 2018; 30 (7)

    Abstract

    Chameleons are masters of light, expertly changing their color, pattern, and reflectivity in response to their environment. Engineered materials that share this tunability can be transformative, enabling active camouflage, tunable holograms, and novel colorimetric medical sensors. While progress has been made in creating artificial chameleon skin, existing schemes often require external power, are not continuously tunable, and may prove too stiff or bulky for applications. Here, a chemically tunable, large-area metamaterial is demonstrated that accesses a wide range of colors and refractive indices. An ordered monolayer of nanoresonators is fabricated, then its optical response is dynamically tuned by infiltrating its polymer substrate with solvents. The material shows a strong magnetic response with a dependence on resonator spacing that leads to a highly tunable effective permittivity, permeability, and refractive index spanning negative and positive values. The unity-order index tuning exceeds that of traditional electro-optic and photochromic materials and is robust to cycling, providing a path toward programmable optical elements and responsive light routing.

    View details for PubMedID 29315902

  • Organic electrochemical transistors NATURE REVIEWS MATERIALS Rivnay, J., Inal, S., Salleo, A., Owens, R. M., Berggren, M., Malliaras, G. G. 2018; 3 (2)
  • Fused electron deficient semiconducting polymers for air stable electron transport NATURE COMMUNICATIONS Onwubiko, A., Yue, W., Jellett, C., Xiao, M., Chen, H., Ravva, M., Hanifi, D. A., Knall, A., Purushothaman, B., Nikolka, M., Flores, J., Salleo, A., Bredas, J., Sirringhaus, H., Hayoz, P., McCulloch, I. 2018; 9: 416

    Abstract

    Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

    View details for PubMedID 29379022

  • Organic Electronics for Point-of-Care Metabolite Monitoring TRENDS IN BIOTECHNOLOGY Pappa, A., Parlak, O., Scheiblin, G., Mailley, P., Salleo, A., Owens, R. M. 2018; 36 (1): 45–59
  • Organic Electronics for Neuromorphic Computing NATURE ELECTRONICS Burgt, Y. v., Melianas, A., Keene, S. T., Malliaras, G., Salleo, A. 2018; 1 (7): 386-397
  • Organic Electronics for Point-of-Care Metabolite Monitoring. Trends in biotechnology Pappa, A. M., Parlak, O., Scheiblin, G., Mailley, P., Salleo, A., Owens, R. M. 2018; 36 (1): 45–59

    Abstract

    In this review we focus on demonstrating how organic electronic materials can solve key problems in biosensing thanks to their unique material properties and implementation in innovative device configurations. We highlight specific examples where these materials solve multiple issues related to complex sensing environments, and we benchmark these examples by comparing them to state-of-the-art commercially available sensing using alternative technologies. We have categorized our examples by sample type, focusing on sensing from body fluids in vitro and on wearable sensors, which have attracted significant interest owing to their integration with everyday life activities. We finish by describing a future trend for in vivo, implantable sensors, which aims to build on current progress from sensing in biological fluids ex vivo.

    View details for PubMedID 29196057

  • Structural Effects of Gating Poly(3-hexylthiophene) through an Ionic Liquid ADVANCED FUNCTIONAL MATERIALS Guardado, J. O., Salleo, A. 2017; 27 (32)
  • Improving the electrical performance of solution processed oligothiophene thin-film transistors via structural similarity blending JOURNAL OF MATERIALS CHEMISTRY C Leydecker, T., Favaretto, L., Duc Trong Duong, Zappala, G., Borjesson, K., Licciardello, A., Salleo, A., Melucci, M., Orgiu, E., Samori, P. 2017; 5 (21): 5048–54

    View details for DOI 10.1039/c7tc00748e

    View details for Web of Science ID 000402872400002

  • On the transient response of organic electrochemical transistors ORGANIC ELECTRONICS Faria, G. C., Duong, D. T., Salleo, A. 2017; 45: 215-221
  • Long-Term Structural Evolution of an Intercalated Layered Semiconductor ADVANCED FUNCTIONAL MATERIALS Chew, A. R., Fonseca, J. J., Dubon, O. D., Salleo, A. 2017; 27 (14)
  • Negative Isotope Effect on Field-Effect Hole Transport in Fully Substituted C-13-Rubrene ADVANCED ELECTRONIC MATERIALS Ren, X., Bruzek, M. J., Hanifi, D. A., Schulzetenberg, A., Wu, Y., Kim, C., Zhang, Z., Johns, J. E., Salleo, A., Fratini, S., Troisi, A., Douglas, C. J., Frisbie, C. D. 2017; 3 (4)
  • Hierarchical Aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor NANO ENERGY Parlak, O., Mishra, Y. K., Grigoriev, A., Mecklenburg, M., Luo, W., Keene, S., Salleo, A., Schulte, K., Ahuja, R., Adelung, R., Turner, A. P., Tiwari, A. 2017; 34: 570-577
  • Reducing the efficiency-stability-cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells. Nature materials Baran, D., Ashraf, R. S., Hanifi, D. A., Abdelsamie, M., Gasparini, N., Röhr, J. A., Holliday, S., Wadsworth, A., Lockett, S., Neophytou, M., Emmott, C. J., Nelson, J., Brabec, C. J., Amassian, A., Salleo, A., Kirchartz, T., Durrant, J. R., McCulloch, I. 2017; 16 (3): 363-369

    Abstract

    Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V.

    View details for DOI 10.1038/nmat4797

    View details for PubMedID 27869824

  • A non-volatile organic electrochemical device as a low-voltage artificial synapse for neuromorphic computing. Nature materials van de Burgt, Y., Lubberman, E., Fuller, E. J., Keene, S. T., Faria, G. C., Agarwal, S., Marinella, M. J., Alec Talin, A., Salleo, A. 2017

    Abstract

    The brain is capable of massively parallel information processing while consuming only ∼1-100 fJ per synaptic event. Inspired by the efficiency of the brain, CMOS-based neural architectures and memristors are being developed for pattern recognition and machine learning. However, the volatility, design complexity and high supply voltages for CMOS architectures, and the stochastic and energy-costly switching of memristors complicate the path to achieve the interconnectivity, information density, and energy efficiency of the brain using either approach. Here we describe an electrochemical neuromorphic organic device (ENODe) operating with a fundamentally different mechanism from existing memristors. ENODe switches at low voltage and energy (<10 pJ for 10(3) μm(2) devices), displays >500 distinct, non-volatile conductance states within a ∼1 V range, and achieves high classification accuracy when implemented in neural network simulations. Plastic ENODes are also fabricated on flexible substrates enabling the integration of neuromorphic functionality in stretchable electronic systems. Mechanical flexibility makes ENODes compatible with three-dimensional architectures, opening a path towards extreme interconnectivity comparable to the human brain.

    View details for DOI 10.1038/nmat4856

    View details for PubMedID 28218920

  • Towards 3D organic solar cells NANO ENERGY Knipp, D., Jovanov, V., Tamang, A., Wagner, V., Salleo, A. 2017; 31: 582-589
  • Sequential Doping Reveals the Importance of Amorphous Chain Rigidity in Charge Transport of Semi-Crystalline Polymers. The journal of physical chemistry letters Chew, A. R., Ghosh, R., Shang, Z., Spano, F. C., Salleo, A. 2017; 8 (20): 4974–80

    Abstract

    Sequential doping is a promising new doping technique for semicrystalline polymers that has been shown to produce doped films with higher conductivity and more uniform morphology than conventional doping processes, and where the dopant placement in the film can be controlled. As a relatively new technique, however, much work is needed to understand the resulting polymer-dopant interactions upon sequential doping. A combination of infrared spectroscopy and theoretical simulations shows that the dopants selectively placed in the amorphous regions in the film via sequential doping result in highly localized polarons. We find that the presence of dopants within the amorphous regions of the film leads to an increase in conjugation length of the amorphous chains upon doping, increasing film connectivity and hence improving the overall conductivity of the film compared with the conventional doping processes.

    View details for PubMedID 28949140

  • Anomalous Charge Transport in Conjugated Polymers Reveals Underlying Mechanisms of Trapping and Percolation ACS CENTRAL SCIENCE Mollinger, S. A., Salleo, A., Spakowitz, A. J. 2016; 2 (12): 910-915

    Abstract

    While transport in conjugated polymers has many similarities to that in crystalline inorganic materials, several key differences reveal the unique relationship between the morphology of polymer films and the charge mobility. We develop a model that directly incorporates the molecular properties of the polymer film and correctly predicts these unique transport features. At low degree of polymerization, the increase of the mobility with the polymer chain length reveals trapping at chain ends, and saturation of the mobility at high degree of polymerization results from conformational traps within the chains. Similarly, the inverse field dependence of the mobility reveals that transport on single polymer chains is characterized by the ability of the charge to navigate around kinks and loops in the chain. These insights emphasize the connection between the polymer conformations and the transport and thereby offer a route to designing improved device morphologies through molecular design and materials processing.

    View details for DOI 10.1021/acscentsci.6b00251

    View details for Web of Science ID 000390865300008

    View details for PubMedID 28058280

    View details for PubMedCentralID PMC5200932

  • Trade-Off between Trap Filling, Trap Creation, and Charge Recombination Results in Performance Increase at Ultralow Doping Levels in Bulk Heterojunction Solar Cells ADVANCED ENERGY MATERIALS Shang, Z., Heumueller, T., Prasanna, R., Burkhard, G. F., Naab, B. D., Bao, Z., McGehee, M. D., Salleo, A. 2016; 6 (24)
  • The Roles of Structural Order and Intermolecular Interactions in Determining Ionization Energies and Charge-Transfer State Energies in Organic Semiconductors ADVANCED ENERGY MATERIALS Graham, K. R., Ndjawa, G. O., Conron, S. M., Munir, R., Vandewal, K., Chen, J. J., Sweetnam, S., Thompson, M. E., Salleo, A., McGehee, M. D., Amassian, A. 2016; 6 (22)
  • Naphthalenediimide Polymers with Finely Tuned In-Chain p-Conjugation: Electronic Structure, Film Microstructure, and Charge Transport Properties. Advanced materials Erdmann, T., Fabiano, S., Milián-Medina, B., Hanifi, D., Chen, Z., Berggren, M., Gierschner, J., Salleo, A., Kiriy, A., Voit, B., Facchetti, A. 2016; 28 (41): 9169-9174

    Abstract

    Naphthalenediimide-based random copolymers (PNDI-TVTx) with different π-conjugated dithienylvinylene (TVT) versus π-nonconjugated dithienylethane (TET) unit ratios (x = 100→0%) are investigated. The PNDI-TVTx-transistor electron/hole mobilities are affected differently, a result rationalized by molecular orbital topologies and energies, with hole mobility vanishing but electron mobility decreasing only by ≈2.5 times when going from x = 100% to 40%.

    View details for DOI 10.1002/adma.201602923

    View details for PubMedID 27572671

  • Signatures of Intracrystallite and Intercrystallite Limitations of Charge Transport in Polythiophenes MACROMOLECULES Vakhshouri, K., Smith, B. H., Chan, E. P., Wang, C., Salleo, A., Wang, C., Hexemer, A., Gomez, E. D. 2016; 49 (19): 7359-7369
  • Dual-Characteristic Transistors Based on Semiconducting Polymer Blends ADVANCED ELECTRONIC MATERIALS Lu, G., Di Pietro, R., Koelln, L. S., Nasrallah, I., Zhou, L., Mollinger, S., Himmelberger, S., Koch, N., Salleo, A., Neher, D. 2016; 2 (10)
  • Bandgap Restructuring of the Layered Semiconductor Gallium Telluride in Air. Advanced materials Fonseca, J. J., Tongay, S., Topsakal, M., Chew, A. R., Lin, A. J., Ko, C., Luce, A. V., Salleo, A., Wu, J., Dubon, O. D. 2016; 28 (30): 6465-6470

    Abstract

    A giant bandgap reduction in layered GaTe is demonstrated. Chemisorption of oxygen to the Te-terminated surfaces produces significant restructuring of the conduction band resulting in a bandgap below 0.8 eV, compared to 1.65 eV for pristine GaTe. Localized partial recovery of the pristine gap is achieved by thermal annealing, demonstrating that reversible band engineering in layered semiconductors is accessible through their surfaces.

    View details for DOI 10.1002/adma.201601151

    View details for PubMedID 27171481

  • Enhancing Quantum Yield via Local Symmetry Distortion in Lanthanide-Based Upconverting Nanoparticles ACS PHOTONICS Wisser, M. D., Fischer, S., Maurer, P. C., Bronstein, N. D., Chu, S., Alivisatos, A. P., Salleo, A., Dionne, J. A. 2016; 3 (8): 1523-1530
  • Roadmap on optical energy conversion JOURNAL OF OPTICS Boriskina, S. V., Green, M. A., Catchpole, K., Yablonovitch, E., Beard, M. C., Okada, Y., Lany, S., Gershon, T., Zakutayev, A., Tahersima, M. H., Sorger, V. J., Naughton, M. J., Kempa, K., Dagenais, M., Yao, Y., Xu, L., Sheng, X., Bronstein, N. D., Rogers, J. A., Alivisatos, A. P., Nuzzo, R. G., Gordon, J. M., Wu, D. M., Wisser, M. D., Salleo, A., Dionne, J., Bermel, P., Greffet, J., Celanovic, I., Soljacic, M., Manor, A., Rotschild, C., Raman, A., Zhu, L., Fan, S., Chen, G. 2016; 18 (7)
  • ORGANIC DEVICES. Avoid the kinks when measuring mobility. Science McCulloch, I., Salleo, A., Chabinyc, M. 2016; 352 (6293): 1521-1522

    View details for DOI 10.1126/science.aaf9062

    View details for PubMedID 27339971

  • High-efficiency and air-stable P3HT-based polymer solar cells with a new non-fullerene acceptor NATURE COMMUNICATIONS Holliday, S., Ashraf, R. S., Wadsworth, A., Baran, D., Yousaf, S. A., Nielsen, C. B., Tan, C., Dimitrov, S. D., Shang, Z., Gasparini, N., Alamoudi, M., Laquai, F., Brabec, C. J., Salleo, A., Durrant, J. R., McCulloch, I. 2016; 7

    Abstract

    Solution-processed organic photovoltaics (OPV) offer the attractive prospect of low-cost, light-weight and environmentally benign solar energy production. The highest efficiency OPV at present use low-bandgap donor polymers, many of which suffer from problems with stability and synthetic scalability. They also rely on fullerene-based acceptors, which themselves have issues with cost, stability and limited spectral absorption. Here we present a new non-fullerene acceptor that has been specifically designed to give improved performance alongside the wide bandgap donor poly(3-hexylthiophene), a polymer with significantly better prospects for commercial OPV due to its relative scalability and stability. Thanks to the well-matched optoelectronic and morphological properties of these materials, efficiencies of 6.4% are achieved which is the highest reported for fullerene-free P3HT devices. In addition, dramatically improved air stability is demonstrated relative to other high-efficiency OPV, showing the excellent potential of this new material combination for future technological applications.

    View details for DOI 10.1038/ncomms11585

    View details for Web of Science ID 000377909600001

    View details for PubMedID 27279376

    View details for PubMedCentralID PMC4906164

  • Core/Shell Approach to Dopant Incorporation and Shape Control in Colloidal Zinc Oxide Nanorods CHEMISTRY OF MATERIALS Mehra, S., Bergerud, A., Milliron, D. J., Chan, E. M., Salleo, A. 2016; 28 (10): 3454-3461
  • 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)
  • Near infrared laser annealing of CdTe and in-situ measurement of the evolution of structural and optical properties JOURNAL OF APPLIED PHYSICS Simonds, B. J., Misra, S., Paudel, N., Vandewal, K., Salleo, A., Ferekides, C., Scarpulla, M. A. 2016; 119 (16)

    View details for DOI 10.1063/1.4947186

    View details for Web of Science ID 000375929900039

  • Characterizing the Polymer:Fullerene Intermolecular Interactions CHEMISTRY OF MATERIALS Sweetnam, S., Vandewal, K., Cho, E., Risko, C., Coropceanu, V., Salleo, A., Bredas, J., McGehee, M. D. 2016; 28 (5): 1446-1452
  • Time- and Temperature-Independent Local Carrier Mobility and Effects of Regioregularity in Polymer-Fullerene Organic Semiconductors ADVANCED ELECTRONIC MATERIALS Sher, M., Bartelt, J. A., Burke, T. M., Salleo, A., McGehee, M. D., Lindenberg, A. M. 2016; 2 (3)
  • Strain effects on the work function of an organic semiconductor. Nature communications Wu, Y., Chew, A. R., Rojas, G. A., Sini, G., Haugstad, G., Belianinov, A., Kalinin, S. V., Li, H., Risko, C., Brédas, J., Salleo, A., Frisbie, C. D. 2016; 7: 10270-?

    Abstract

    Establishing fundamental relationships between strain and work function (WF) in organic semiconductors is important not only for understanding electrical properties of organic thin films, which are subject to both intrinsic and extrinsic strains, but also for developing flexible electronic devices. Here we investigate tensile and compressive strain effects on the WF of rubrene single crystals. Mechanical strain induced by thermal expansion mismatch between the substrate and rubrene is quantified by X-ray diffraction. The corresponding WF change is measured by scanning Kelvin probe microscopy. The WF of rubrene increases (decreases) significantly with in-plane tensile (compressive) strain, which agrees qualitatively with density functional theory calculations. An elastic-to-plastic transition, characterized by a steep rise of the WF, occurs at ∼0.05% tensile strain along the rubrene π-stacking direction. The results provide the first concrete link between mechanical strain and WF of an organic semiconductor and have important implications for understanding the connection between structural and electronic disorder in soft organic electronic materials.

    View details for DOI 10.1038/ncomms10270

    View details for PubMedID 26831362

    View details for PubMedCentralID PMC4740348

  • 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

    Abstract

    Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10(-10) S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water.

    View details for DOI 10.1038/srep17849

    View details for PubMedID 26658331

  • Microstructural and Electronic Origins of Open-Circuit Voltage Tuning in Organic Solar Cells Based on Ternary Blends ADVANCED ENERGY MATERIALS Mollinger, S. A., Vandewal, K., Salleo, A. 2015; 5 (23)
  • Toward Conductive Mesocrystalline Assemblies: PbS Nanocrystals Cross-Linked with Tetrathiafulvalene Dicarboxylate CHEMISTRY OF MATERIALS Andre, A., Zherebetskyy, D., Hanifi, D., He, B., Khoshkhoo, M. S., Jankowski, M., Chasse, T., Wang, L., Schreiber, F., Salleo, A., Liu, Y., Scheele, M. 2015; 27 (23): 8105-8115
  • Solid Solutions of Rare Earth Cations in Mesoporous Anatase Beads and Their Performances in Dye-Sensitized Solar Cells SCIENTIFIC REPORTS Cavallo, C., Salleo, A., Gozzi, D., Di Pascasio, F., Quaranta, S., Panetta, R., Latini, A. 2015; 5

    View details for DOI 10.1038/srep16785

    View details for PubMedID 26577287

  • Engineering semiconducting polymers for efficient charge transport MRS COMMUNICATIONS Himmelberger, S., Salleo, A. 2015; 5 (3): 383-395
  • Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers. Proceedings of the National Academy of Sciences of the United States of America Wang, S., Fabiano, S., Himmelberger, S., Puzinas, S., Crispin, X., Salleo, A., Berggren, M. 2015; 112 (34): 10599-10604

    Abstract

    Efficiency, current throughput, and speed of electronic devices are to a great extent dictated by charge carrier mobility. The classic approach to impart high carrier mobility to polymeric semiconductors has often relied on the assumption that extensive order and crystallinity are needed. Recently, however, this assumption has been challenged, because high mobility has been reported for semiconducting polymers that exhibit a surprisingly low degree of order. Here, we show that semiconducting polymers can be confined into weakly ordered fibers within an inert polymer matrix without affecting their charge transport properties. In these conditions, the semiconducting polymer chains are inhibited from attaining long-range order in the π-stacking or alkyl-stacking directions, as demonstrated from the absence of significant X-ray diffraction intensity corresponding to these crystallographic directions, yet still remain extended along the backbone direction and aggregate on a local length scale. As a result, the polymer films maintain high mobility even at very low concentrations. Our findings provide a simple picture that clarifies the role of local order and connectivity of domains.

    View details for DOI 10.1073/pnas.1501381112

    View details for PubMedID 26261305

    View details for PubMedCentralID PMC4553794

  • Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Wang, S., Fabiano, S., Himmelberger, S., Puzinas, S., Crispin, X., Salleo, A., Berggren, M. 2015; 112 (34): 10599-10604
  • Miscibility and Acid Strength Govern Contact Doping of Organic Photovoltaics with Strong Polyelectrolytes MACROMOLECULES Le, T. P., Shang, Z., Wang, L., Li, N., Kesava, S. V., O'Connor, J. W., Chang, Y., Bae, C., Zhu, C., Hexemer, A., Gomez, E. W., Salleo, A., Hickner, M. A., Gomez, E. D. 2015; 48 (15): 5162-5171
  • The Effect of Processing Additives on Energetic Disorder in Highly Efficient Organic Photovoltaics: A Case Study on PBDTTT-C-T:PC71 BM. Advanced materials Gao, F., Himmelberger, S., Andersson, M., Hanifi, D., Xia, Y., Zhang, S., Wang, J., Hou, J., Salleo, A., Inganäs, O. 2015; 27 (26): 3868-3873

    Abstract

    Energetic disorder, an important parameter affecting the performance of organic photovoltaics, is significantly decreased upon the addition of processing additives in a highly efficient benzodithiophene-based copolymer blend (PBDTTT-C-T:PC71 BM). Wide-angle and small-angle X-ray scattering measurements suggest that the origin of this reduced energetic disorder is due to increased aggregation and a larger average fullerene domain size together with purer phases.

    View details for DOI 10.1002/adma.201405913

    View details for PubMedID 26016473

  • Percolation, Tie-Molecules, and the Microstructural Determinants of Charge Transport in Semicrystalline Conjugated Polymers ACS MACRO LETTERS Mollinger, S. A., Krajina, B. A., Noriega, R., Salleo, A., Spakowitz, A. J. 2015; 4 (7): 708-712
  • The Effect of Processing Additives on Energetic Disorder in Highly Efficient Organic Photovoltaics: A Case Study on PBDTTT-C-T:PC71 BM. Advanced materials Gao, F., Himmelberger, S., Andersson, M., Hanifi, D., Xia, Y., Zhang, S., Wang, J., Hou, J., Salleo, A., Inganäs, O. 2015; 27 (26): 3868-3873

    View details for DOI 10.1002/adma.201405913

    View details for PubMedID 26016473

  • Control of Rubrene Polymorphs via Polymer Binders: Applications in Organic Field-Effect Transistors CHEMISTRY OF MATERIALS Jo, P. S., Duong, D. T., Park, J., Sinclair, R., Salleo, A. 2015; 27 (11): 3979-3987
  • 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

  • Molar Mass versus Polymer Solar Cell Performance: Highlighting the Role of Homocouplings CHEMISTRY OF MATERIALS Vangerven, T., Verstappen, P., Drijkoningen, J., Dierckx, W., Himmelberger, S., Salleo, A., Vanderzande, D., Maes, W., Manca, J. V. 2015; 27 (10): 3726-3732
  • Role of Side-Chain Branching on Thin-Film Structure and Electronic Properties of Polythiophenes ADVANCED FUNCTIONAL MATERIALS Himmelberger, S., Duong, D. T., Northrup, J. E., Rivnay, J., Koch, F. P., Beckingham, B. S., Stingelin, N., Segalman, R. A., Mannsfeld, S. C., Salleo, A. 2015; 25 (17): 2616-2624
  • Direct Correlation of Charge Transfer Absorption with Molecular Donor:Acceptor Interfacial Area via Photothermal Deflection Spectroscopy JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Buchaca-Domingo, E., Vandewal, K., Fei, Z., Watkins, S. E., Scholes, F. H., Bannock, J. H., de Mello, J. C., Richter, L. J., Delongchamp, D. M., Amassian, A., Heeney, M., Salleo, A., Stingelin, N. 2015; 137 (16): 5256-5259

    Abstract

    Here we show that the charge transfer (CT) absorption signal in bulk-heterojunction solar cell blends, measured by photothermal deflection spectroscopy, is directly proportional to the density of molecular donor:acceptor interfaces. Since the optical transitions from the ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both the donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer:fullerene interface. The latter is ∼100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment as 0.3 D and the electronic coupling between the ground and CT states to be on the order of 30 meV.

    View details for DOI 10.1021/ja512410f

    View details for Web of Science ID 000353931500004

    View details for PubMedID 25856143

  • Symmetry-Breaking Charge Transfer in a Zinc Chlorodipyrrin Acceptor for High Open Circuit Voltage Organic Photovoltaics JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Bartynski, A. N., Gruber, M., Das, S., Rangan, S., Mollinger, S., Trinh, C., Bradforth, S. E., Vandewal, K., Salleo, A., Bartynski, R. A., Bruetting, W., Thompson, M. E. 2015; 137 (16): 5397-5405

    Abstract

    Low open-circuit voltages significantly limit the power conversion efficiency of organic photovoltaic devices. Typical strategies to enhance the open-circuit voltage involve tuning the HOMO and LUMO positions of the donor (D) and acceptor (A), respectively, to increase the interfacial energy gap or to tailor the donor or acceptor structure at the D/A interface. Here, we present an alternative approach to improve the open-circuit voltage through the use of a zinc chlorodipyrrin, ZCl [bis(dodecachloro-5-mesityldipyrrinato)zinc], as an acceptor, which undergoes symmetry-breaking charge transfer (CT) at the donor/acceptor interface. DBP/ZCl cells exhibit open-circuit voltages of 1.33 V compared to 0.88 V for analogous tetraphenyldibenzoperyflanthrene (DBP)/C60-based devices. Charge transfer state energies measured by Fourier-transform photocurrent spectroscopy and electroluminescence show that C60 forms a CT state of 1.45 ± 0.05 eV in a DBP/C60-based organic photovoltaic device, while ZCl as acceptor gives a CT state energy of 1.70 ± 0.05 eV in the corresponding device structure. In the ZCl device this results in an energetic loss between E(CT) and qV(OC) of 0.37 eV, substantially less than the 0.6 eV typically observed for organic systems and equal to the recombination losses seen in high-efficiency Si and GaAs devices. The substantial increase in open-circuit voltage and reduction in recombination losses for devices utilizing ZCl demonstrate the great promise of symmetry-breaking charge transfer in organic photovoltaic devices.

    View details for DOI 10.1021/jacs.5b00146

    View details for Web of Science ID 000353931500031

    View details for PubMedID 25826321

  • Strain-induced modification of optical selection rules in lanthanide-based upconverting nanoparticles. Nano letters Wisser, M. D., Chea, M., Lin, Y., Wu, D. M., Mao, W. L., Salleo, A., Dionne, J. A. 2015; 15 (3): 1891-1897

    Abstract

    NaYF4:Yb(3+),Er(3+) nanoparticle upconverters are hindered by low quantum efficiencies arising in large part from the parity-forbidden nature of their optical transitions and the nonoptimal spatial separations between lanthanide ions. Here, we use pressure-induced lattice distortion to systematically modify both parameters. Although hexagonal-phase nanoparticles exhibit a monotonic decrease in upconversion emission, cubic-phase particles experience a nearly 2-fold increase in efficiency. In-situ X-ray diffraction indicates that these emission changes require only a 1% reduction in lattice constant. Our work highlights the intricate relationship between upconversion efficiency and lattice geometry and provides a promising approach to modifying the quantum efficiency of any lanthanide upconverter.

    View details for DOI 10.1021/nl504738k

    View details for PubMedID 25647523

  • Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matrices NATURE COMMUNICATIONS El Gemayel, M., Borjesson, K., Herder, M., Duong, D. T., Hutchison, J. A., Ruzie, C., Schweicher, G., Salleo, A., Geerts, Y., Hecht, S., Orgiu, E., Samori, P. 2015; 6

    Abstract

    The fabrication of multifunctional high-performance organic thin-film transistors as key elements in future logic circuits is a major research challenge. Here we demonstrate that a photoresponsive bi-functional field-effect transistor with carrier mobilities exceeding 0.2 cm(2) V(-1) s(-1) can be developed by incorporating photochromic molecules into an organic semiconductor matrix via a single-step solution processing deposition of a two components blend. Tuning the interactions between the photochromic diarylethene system and the organic semiconductor is achieved via ad-hoc side functionalization of the diarylethene. Thereby, a large-scale phase-segregation can be avoided and superior miscibility is provided, while retaining optimal π-π stacking to warrant efficient charge transport and to attenuate the effect of photoinduced switching on the extent of current modulation. This leads to enhanced electrical performance of transistors incorporating small conjugated molecules as compared with polymeric semiconductors. These findings are of interest for the development of high-performing optically gated electronic devices.

    View details for DOI 10.1038/ncomms7330

    View details for Web of Science ID 000352718000001

    View details for PubMedID 25739864

  • Optical measurement of doping efficiency in poly(3-hexylthiophene) solutions and thin films PHYSICAL REVIEW B Wang, C., Duong, D. T., Vandewal, K., Rivnay, J., Salleo, A. 2015; 91 (8)
  • Organic electronics: Something out of nothing. Nature materials Salleo, A. 2015; 14 (11): 1077–78

    View details for PubMedID 26366846

  • Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells JOURNAL OF MATERIALS CHEMISTRY A Qian, D., Liu, B., Wang, S., Himmelberger, S., Linares, M., Vagin, M., Muller, C., Ma, Z., Fabiano, S., Berggren, M., Salleo, A., Inganas, O., Zou, Y., Zhang, F. 2015; 3 (48): 24349-24357

    View details for DOI 10.1039/c5ta06501a

    View details for Web of Science ID 000366163000022

  • Efficiency Enhancement of Gallium Arsenide Photovoltaics Using Solution-Processed Zinc Oxide Nanoparticle Light Scattering Layers JOURNAL OF NANOMATERIALS Kang, Y., Liang, D., Mehra, S., Huo, Y., Chen, Y., Christoforo, M. G., Salleo, A., Harris, J. S. 2015
  • Branched and linear A(2)-D-A(1)-D-A(2) isoindigo-based solution-processable small molecules for organic field-effect transistors and solar cells RSC ADVANCES Tomassetti, M., Ouhib, F., Cardinaletti, I., Verstappen, P., Salleo, A., Jerome, C., Manca, J., Maes, W., Detrembleur, C. 2015; 5 (104): 85460-85469

    View details for DOI 10.1039/c5ra17660c

    View details for Web of Science ID 000363179900037

  • Multi-phase microstructures drive exciton dissociation in neat semicrystalline polymeric semiconductors JOURNAL OF MATERIALS CHEMISTRY C Paquin, F., Rivnay, J., Salleo, A., Stingelin, N., Silva-Acuna, C. 2015; 3 (41): 10715-10722

    View details for DOI 10.1039/c5tc02043c

    View details for Web of Science ID 000363252200006

  • Modular synthetic design enables precise control of shape and doping in colloidal zinc oxide nanorods JOURNAL OF MATERIALS CHEMISTRY C Mehra, S., Chan, E. M., Salleo, A. 2015; 3 (27): 7172-7179

    View details for DOI 10.1039/c5tc01216c

    View details for Web of Science ID 000357416500028

  • Semi-transparent perovskite solar cells for tandems with silicon and CIGS ENERGY & ENVIRONMENTAL SCIENCE Bailie, C. D., Christoforo, M. G., Mailoa, J. P., Bowring, A. R., Unger, E. L., Nguyen, W. H., Burschka, J., Pellet, N., Lee, J. Z., Graetzel, M., Noufi, R., Buonassisi, T., Salleo, A., McGehee, M. D. 2015; 8 (3): 956-963

    View details for DOI 10.1039/c4ee03322a

    View details for Web of Science ID 000352274600021

  • Optically switchable transistors comprising a hybrid photochromic molecule/n-type organic active layer JOURNAL OF MATERIALS CHEMISTRY C Boerjesson, K., HERDER, M., Grubert, L., Duong, D. T., Salleo, A., Hecht, S., Orgiu, E., Samori, P. 2015; 3 (16): 4156-4161

    View details for DOI 10.1039/c5tc00401b

    View details for Web of Science ID 000352870400041

  • Solution-Processed Field-Effect Transistors Based on Dihexylquaterthiophene Films with Performances Exceeding Those of Vacuum-Sublimed Films ACS APPLIED MATERIALS & INTERFACES Leydecker, T., Duc Trong Duong, D. T., Salleo, A., Orgiu, E., Samori, P. 2014; 6 (23): 21248-21255

    Abstract

    Solution-processable oligothiophenes are model systems for charge transport and fabrication of organic field-effect transistors (OFET) . Herein we report a structure vs function relationship study focused on the electrical characteristics of solution-processed dihexylquaterthiophene (DH4T)-based OFET. We show that by combining the tailoring of all interfaces in the bottom-contact bottom-gate transistor, via chemisorption of ad hoc molecules on electrodes and dielectric, with suitable choice of the film preparation conditions (including solvent type, concentration, volume, and deposition method), it is possible to fabricate devices exhibiting field-effect mobilities exceeding those of vacuum-processed DH4T transistors. In particular, the evaporation rate of the solvent, the processing temperature, as well as the concentration of the semiconducting material were found to hold a paramount importance in driving the self-assembly toward the formation of highly ordered and low-dimensional supramolecular architectures, confirming the kinetically governed nature of the self-assembly process. Among the various architectures, hundreds-of-micrometers long and thin DH4T crystallites exhibited enhanced charge transport.

    View details for DOI 10.1021/am506245v

    View details for Web of Science ID 000346326600081

    View details for PubMedID 25380324

  • The Crucial Influence of Fullerene Phases on Photogeneration in Organic Bulk Heterojunction Solar Cells ADVANCED ENERGY MATERIALS Zusan, A., Vandewal, K., Allendorf, B., Hansen, N. H., Pflaum, J., Salleo, A., Dyakonov, V., Deibel, C. 2014; 4 (17)
  • Organic electrochemical transistors as impedance biosensors MRS COMMUNICATIONS Faria, G. C., Duong, D. T., Salleo, A., Polyzoidis, C. A., Logothetidis, S., Rivnay, J., Owens, R., Malliaras, G. G. 2014; 4 (4): 189-194
  • Plasmon-Enhanced Upconversion JOURNAL OF PHYSICAL CHEMISTRY LETTERS Wu, D. M., Garcia-Etxarri, A., Salleo, A., Dionne, J. A. 2014; 5 (22): 4020-4031

    Abstract

    Upconversion, the conversion of photons from lower to higher energies, is a process that promises applications ranging from high-efficiency photovoltaic and photocatalytic cells to background-free bioimaging and therapeutic probes. Existing upconverting materials, however, remain too inefficient for viable implementation. In this Perspective, we describe the significant improvements in upconversion efficiency that can be achieved using plasmon resonances. As collective oscillations of free electrons, plasmon resonances can be used to enhance both the incident electromagnetic field intensity and the radiative emission rates. To date, this approach has shown upconversion enhancements up to 450×. We discuss both theoretical underpinnings and experimental demonstrations of plasmon-enhanced upconversion, examining the roles of upconverter quantum yield, plasmonic geometry, and plasmon spectral overlap. We also discuss nonoptical consequences of including metal nanostructures near upconverting emitters. The rapidly expanding field of plasmon-enhanced upconversion provides novel fundamental insight into nanoscale light-matter interactions while improving prospects for technological relevance.

    View details for DOI 10.1021/jz5019042

    View details for Web of Science ID 000345542900014

  • Plasmon-Enhanced Upconversion. journal of physical chemistry letters Wu, D. M., García-Etxarri, A., Salleo, A., Dionne, J. A. 2014; 5 (22): 4020-4031

    Abstract

    Upconversion, the conversion of photons from lower to higher energies, is a process that promises applications ranging from high-efficiency photovoltaic and photocatalytic cells to background-free bioimaging and therapeutic probes. Existing upconverting materials, however, remain too inefficient for viable implementation. In this Perspective, we describe the significant improvements in upconversion efficiency that can be achieved using plasmon resonances. As collective oscillations of free electrons, plasmon resonances can be used to enhance both the incident electromagnetic field intensity and the radiative emission rates. To date, this approach has shown upconversion enhancements up to 450×. We discuss both theoretical underpinnings and experimental demonstrations of plasmon-enhanced upconversion, examining the roles of upconverter quantum yield, plasmonic geometry, and plasmon spectral overlap. We also discuss nonoptical consequences of including metal nanostructures near upconverting emitters. The rapidly expanding field of plasmon-enhanced upconversion provides novel fundamental insight into nanoscale light-matter interactions while improving prospects for technological relevance.

    View details for DOI 10.1021/jz5019042

    View details for PubMedID 26276488

  • Enhancing Fullerene-Based Solar Cell Lifetimes by Addition of a Fullerene Dumbbell ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Schroeder, B. C., Li, Z., Brady, M. A., Faria, G. C., Ashraf, R. S., Takacs, C. J., Cowart, J. S., Duong, D. T., Chiu, K. H., Tan, C., Cabral, J. T., Salleo, A., Chabinyc, M. L., Durrant, J. R., McCulloch, I. 2014; 53 (47): 12870-12875

    Abstract

    Cost-effective, solution-processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon-based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long-term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM-based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability.

    View details for DOI 10.1002/anie.201407310

    View details for Web of Science ID 000344793400035

    View details for PubMedCentralID PMC4241035

  • Role of Molecular Weight Distribution on Charge Transport in Semiconducting Polymers MACROMOLECULES Himmelberger, S., Vandewal, K., Fei, Z., Heeney, M., Salleo, A. 2014; 47 (20): 7151-7157

    View details for DOI 10.1021/ma501508j

    View details for Web of Science ID 000343949500017

  • Enhanced Photovoltaic Performance of Indacenodithiophene-Quinoxaline Copolymers by Side-Chain Modulation ADVANCED ENERGY MATERIALS Dang, D., Chen, W., Himmelberger, S., Tao, Q., Lundin, A., Yang, R., Zhu, W., Salleo, A., Mueller, C., Wang, E. 2014; 4 (15)
  • Direct Observation of Doping Sites in Temperature-Controlled, p-Doped P3HT Thin Films by Conducting Atomic Force Microscopy ADVANCED MATERIALS Duong, D. T., Hung Phan, H., Hanifi, D., Jo, P. S., Thuc-Quyen Nguyen, T. Q., Salleo, A. 2014; 26 (35): 6069-?

    Abstract

    The distribution of dopant sites in doped poly(3-hexylthiophene) (P3HT) thin films is characterized using optical absorption, grazing-incidence X-ray diffraction, and conducting atomic force microscopy (c-AFM). It is shown that dopant sites can be directly observed using c-AFM and that the solution temperature dramatically impacts phase separation and conductivity in spin-cast films.

    View details for DOI 10.1002/adma.201402015

    View details for Web of Science ID 000342148600002

  • Direct observation of doping sites in temperature-controlled, p-doped P3HT thin films by conducting atomic force microscopy. Advanced materials Duong, D. T., Phan, H., Hanifi, D., Jo, P. S., Nguyen, T., Salleo, A. 2014; 26 (35): 6069-6073

    Abstract

    The distribution of dopant sites in doped poly(3-hexylthiophene) (P3HT) thin films is characterized using optical absorption, grazing-incidence X-ray diffraction, and conducting atomic force microscopy (c-AFM). It is shown that dopant sites can be directly observed using c-AFM and that the solution temperature dramatically impacts phase separation and conductivity in spin-cast films.

    View details for DOI 10.1002/adma.201402015

    View details for PubMedID 25060970

  • Contact Doping with Sub-Monolayers of Strong Polyelectrolytes for Organic Photovoltaics ADVANCED ENERGY MATERIALS Mor, G. K., Jones, D., Le, T. P., Shang, Z., Weathers, P. J., Woltermann, M. K., Vakhshouri, K., Williams, B. P., Tohran, S. A., Saito, T., Verduzco, R., Salleo, A., Hickner, M. A., Gomez, E. D. 2014; 4 (13)
  • A New Tetracyclic Lactam Building Block for Thick, Broad-Bandgap Photovoltaics JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kroon, R., Mendaza, A. D., Himmelberger, S., Bergqvist, J., Backe, O., Faria, G. C., Gao, F., Obaid, A., Zhuang, W., Gedefaw, D., Olsson, E., Inganas, O., Salleo, A., Muller, C., Andersson, M. R. 2014; 136 (33): 11578-11581

    Abstract

    A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on π-stacking of the polymer backbone, which was retained in PTNT:fullerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 5% for >200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of >4% could be retained when thick active layers of ∼400 nm were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials.

    View details for DOI 10.1021/ja5051692

    View details for Web of Science ID 000340737900005

    View details for PubMedID 25056482

  • Mechanism of Crystallization and Implications for Charge Transport in Poly(3-ethylhexylthiophene) Thin Films ADVANCED FUNCTIONAL MATERIALS Duong, D. T., Ho, V., Shang, Z., Mollinger, S., Mannsfeld, S. C., Dacuna, J., Toney, M. F., Segalman, R., Salleo, A. 2014; 24 (28): 4515-4521
  • Importance of the donor:fullerene intermolecular arrangement for high-efficiency organic photovoltaics. Journal of the American Chemical Society Graham, K. R., Cabanetos, C., Jahnke, J. P., Idso, M. N., El Labban, A., Ngongang Ndjawa, G. O., Heumueller, T., Vandewal, K., Salleo, A., Chmelka, B. F., Amassian, A., Beaujuge, P. M., McGehee, M. D. 2014; 136 (27): 9608-9618

    Abstract

    The performance of organic photovoltaic (OPV) material systems are hypothesized to depend strongly on the intermolecular arrangements at the donor:fullerene interfaces. A review of some of the most efficient polymers utilized in polymer:fullerene PV devices, combined with an analysis of reported polymer donor materials wherein the same conjugated backbone was used with varying alkyl substituents, supports this hypothesis. Specifically, the literature shows that higher-performing donor-acceptor type polymers generally have acceptor moieties that are sterically accessible for interactions with the fullerene derivative, whereas the corresponding donor moieties tend to have branched alkyl substituents that sterically hinder interactions with the fullerene. To further explore the idea that the most beneficial polymer:fullerene arrangement involves the fullerene docking with the acceptor moiety, a family of benzo[1,2-b:4,5-b']dithiophene-thieno[3,4-c]pyrrole-4,6-dione polymers (PBDTTPD derivatives) was synthesized and tested in a variety of PV device types with vastly different aggregation states of the polymer. In agreement with our hypothesis, the PBDTTPD derivative with a more sterically accessible acceptor moiety and a more sterically hindered donor moiety shows the highest performance in bulk-heterojunction, bilayer, and low-polymer concentration PV devices where fullerene derivatives serve as the electron-accepting materials. Furthermore, external quantum efficiency measurements of the charge-transfer state and solid-state two-dimensional (2D) (13)C{(1)H} heteronuclear correlation (HETCOR) NMR analyses support that a specific polymer:fullerene arrangement is present for the highest performing PBDTTPD derivative, in which the fullerene is in closer proximity to the acceptor moiety of the polymer. This work demonstrates that the polymer:fullerene arrangement and resulting intermolecular interactions may be key factors in determining the performance of OPV material systems.

    View details for DOI 10.1021/ja502985g

    View details for PubMedID 24932575

  • 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

  • Correlated Donor/Acceptor Crystal Orientation Controls Photocurrent Generation in All-Polymer Solar Cells ADVANCED FUNCTIONAL MATERIALS Schubert, M., Collins, B. A., Mangold, H., Howard, I. A., Schindler, W., Vandewal, K., Roland, S., Behrends, J., Kraffert, F., Steyrleuthner, R., Chen, Z., Fostiropoulos, K., Bittl, R., Salleo, A., Facchetti, A., Laquai, F., Ade, H. W., Neher, D. 2014; 24 (26): 4068-4081
  • Toward bulk heterojunction polymer solar cells with thermally stable active layer morphology JOURNAL OF PHOTONICS FOR ENERGY Cardinaletti, I., Kesters, J., Bertho, S., Conings, B., Piersimoni, F., d'Haen, J., Lutsen, L., Nesladek, M., Van Mele, B., Van Assche, G., Vandewal, K., Salleo, A., Vanderzande, D., Maes, W., Manca, J. V. 2014; 4
  • Modeling of the effect of intentionally introduced traps on hole transport in single-crystal rubrene PHYSICAL REVIEW B Dacuna, J., Desai, A., Xie, W., Salleo, A. 2014; 89 (24)
  • Increased open-circuit voltage of organic solar cells by reduced donor-acceptor interface area. Advanced materials Vandewal, K., Widmer, J., Heumueller, T., Brabec, C. J., McGehee, M. D., Leo, K., Riede, M., Salleo, A. 2014; 26 (23): 3839-3843

    Abstract

    The charge carrier lifetime in small molecule: C60 photovoltaic devices is increased by reducing the physical interface area availabe for recombination. For donor contents below 10%, the gain in open-circuit voltage (Voc ) depends logarithmically on the interface area while the energy of the interfacial charge-transfer state ECT remains invariant.

    View details for DOI 10.1002/adma.201400114

    View details for PubMedID 24664888

  • 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

  • Tuning the plasmonic absorption of metal reflectors by zinc oxide nano particles: Application in thin film solar cells NANO ENERGY Palanchoke, U., Kurz, H., Noriega, R., Arabi, S., Jovanov, V., Magnus, P., Aftab, H., Salleo, A., Stiebig, H., Knipp, D. 2014; 6: 167-172
  • Charge Transport Orthogonality in All-Polymer Blend Transistors, Diodes, and Solar Cells ADVANCED ENERGY MATERIALS Fabiano, S., Himmelberger, S., Drees, M., Chen, Z., Altamimi, R. M., Salleo, A., Loi, M. A., Facchetti, A. 2014; 4 (6)
  • On the Efficiency of Charge Transfer State Splitting in Polymer: Fullerene Solar Cells ADVANCED MATERIALS Albrecht, S., Vandewal, K., Tumbleston, J. R., Fischer, F. S., Douglas, J. D., Frechet, J. M., Ludwigs, S., Ade, H., Salleo, A., Neher, D. 2014; 26 (16): 2533-2539

    Abstract

    The field dependence and yield of free charge carrier generation in polymer:fullerene blends with varying energetic offsets is not affected when the excitation energy is varied from above band-gap to direct CT state excitation. Instead, the ability of the CT state to split is dictated by the energetic offset between the relaxed CT state and the charge separated (CS) state.

    View details for DOI 10.1002/adma.201305283

    View details for Web of Science ID 000334386600011

    View details for PubMedID 24574091

  • The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Steyrleuthner, R., Di Pietro, R., Collins, B. A., Polzer, F., Himmelberger, S., Schubert, M., Chen, Z., Zhang, S., Salleo, A., Ade, H., Facchetti, A., Neher, D. 2014; 136 (11): 4245-4256

    Abstract

    We investigated the correlation between the polymer backbone structural regularity and the charge transport properties of poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)], a widely studied semiconducting polymer exhibiting high electron mobility and an unconventional micromorphology. To understand the influence of the chemical structure and crystal packing of conventional regioregular P(NDI2OD-T2) [RR-P(NDI2OD-T2)] on the charge transport, the corresponding regioirregular polymer RI-P(NDI2OD-T2) was synthesized. By combining optical, X-ray, and transmission electron microscopy data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of all of the polymer films, which were then correlated to the electron mobilities in electron-only diodes. By carefully selecting the preparation conditions, we were able to obtain RR-P(NDI2OD-T2) films with similar crystalline structure along the three crystallographic axes but with different orientations of the polymer chains with respect to the substrate surface. RI-P(NDI2OD-T2), though exhibiting a rather similar LUMO structure and energy compared with the regioregular counterpart, displayed a very different packing structure characterized by the formation of ordered stacks along the lamellar direction without detectible π-stacking. Vertical electron mobilities were extracted from the space-charge-limited currents in unipolar devices. We demonstrate the anisotropy of the charge transport along the different crystallographic directions and how the mobility depends on π-stacking but is insensitive to the degree or coherence of lamellar stacking. The comparison between the regioregular and regioirregular polymers also shows how the use of large planar functional groups leads to improved charge transport, with mobilities that are less affected by chemical and structural disorder with respect to classic semicrystalline polymers such as poly(3-hexylthiophene).

    View details for DOI 10.1021/ja4118736

    View details for Web of Science ID 000333435500026

    View details for PubMedID 24524296

  • A direct measurement of the electronic structure of Si nanocrystals and its effect on optoelectronic properties JOURNAL OF APPLIED PHYSICS Mustafeez, W., Majumdar, A., Vuckovic, J., Salleo, A. 2014; 115 (10)

    View details for DOI 10.1063/1.4868299

    View details for Web of Science ID 000333083100024

  • High-resolution x-ray analysis of graphene grown on 4H-SiC (000(1)over-bar) at low pressures JOURNAL OF MATERIALS RESEARCH Capanoa, M. A., Capano, B. M., Morisette, D. T., Salleo, A., Lee, S., Toney, M. F. 2014; 29 (3): 439-446
  • Very Low Band Gap Thiadiazoloquinoxaline Donor-Acceptor Polymers as Multi-tool Conjugated Polymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Steckler, T. T., Henriksson, P., Mollinger, S., Lundin, A., Salleo, A., Andersson, M. R. 2014; 136 (4): 1190-1193

    Abstract

    Here we report on the synthesis of two novel very low band gap (VLG) donor-acceptor polymers (Eg ≤ 1 eV) and an oligomer based on the thiadiazoloquinoxaline acceptor. Both polymers demonstrate decent ambipolar mobilities, with P1 showing the best performance of ∼10(-2) cm(2) V(-1) s(-1) for p- and n-type operation. These polymers are among the lowest band gap polymers (≲0.7 eV) reported, with a neutral λmax = 1476 nm (P2), which is the farthest red-shifted λmax reported to date for a soluble processable polymer. Very little has been done to characterize the electrochromic aspects of VLG polymers; interestingly, these polymers actually show a bleaching of their neutral absorptions in the near-infrared region and have an electrochromic contrast up to 30% at a switching speed of 3 s.

    View details for DOI 10.1021/ja410527n

    View details for Web of Science ID 000330598600009

    View details for PubMedID 24422463

  • Structure-property relationships of oligothiophene-isoindigo polymers for efficient bulk-heterojunction solar cells ENERGY & ENVIRONMENTAL SCIENCE Ma, Z., Sun, W., Himmelberger, S., Vandewal, K., Tang, Z., Bergqvist, J., Salleo, A., Andreasen, J. W., Inganas, O., Andersson, M. R., Muller, C., Zhang, F., Wang, E. 2014; 7 (1): 361-369

    View details for DOI 10.1039/c3ee42989j

    View details for Web of Science ID 000329550700025

  • Sub-bandgap laser annealing of room temperature deposited polycrystalline CdTe Conference on Laser Processing and Fabrication for Solar, Displays, and Optoelectronic Devices III Simonds, B. J., Misra, S., Paudel, N., Vandewal, K., Salleo, A., Ferekides, C., Scarpulla, M. A. SPIE-INT SOC OPTICAL ENGINEERING. 2014

    View details for DOI 10.1117/12.2062178

    View details for Web of Science ID 000348841600010

  • Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nature materials Vandewal, K., Albrecht, S., Hoke, E. T., Graham, K. R., Widmer, J., Douglas, J. D., Schubert, M., Mateker, W. R., Bloking, J. T., Burkhard, G. F., Sellinger, A., Fréchet, J. M., Amassian, A., Riede, M. K., McGehee, M. D., Neher, D., Salleo, A. 2014; 13 (1): 63-68

    Abstract

    Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

    View details for DOI 10.1038/nmat3807

    View details for PubMedID 24240240

  • Semi-Transparent Polymer Solar Cells with Excellent Sub-Bandgap Transmission for Third Generation Photovoltaics ADVANCED MATERIALS Beiley, Z. M., Christoforo, M. G., Gratia, P., Bowring, A. R., Eberspacher, P., Margulis, G. Y., Cabanetos, C., Beaujuge, P. M., Salleo, A., McGehee, M. D. 2013; 25 (48): 7020-7026

    Abstract

    Semi-transparent organic photovoltaics are of interest for a variety of photovoltaic applications, including solar windows and hybrid tandem photovoltaics. The figure shows a photograph of our semi-transparent solar cell, which has a power conversion efficiency of 5.0%, with an above bandgap transmission of 34% and a sub-bandgap transmission of 81%.

    View details for DOI 10.1002/adma.201301985

    View details for Web of Science ID 000328707300020

    View details for PubMedID 24123497

  • Spray Deposition of Silver Nanowire Electrodes for Semitransparent Solid-State Dye-Sensitized Solar Cells ADVANCED ENERGY MATERIALS Margulis, G. Y., Christoforo, M. G., Lam, D., Beiley, Z. M., Bowring, A. R., Bailie, C. D., Salleo, A., McGehee, M. D. 2013; 3 (12): 1657-1663
  • The impact of molecular weight on microstructure and charge transport in semicrystalline polymer Semiconductors poly(3-hexylthiophene), a model study PROGRESS IN POLYMER SCIENCE Koch, F. P., Rivnay, J., Foster, S., Mueller, C., Downing, J. M., Buchaca-Domingo, E., Westacott, P., Yu, L., Yuan, M., Baklar, M., Fei, Z., Luscombe, C., McLachlan, M. A., Heeney, M., Rumbles, G., Silva, C., Salleo, A., Nelson, J., Smith, P., Stingelin, N. 2013; 38 (12): 1978-1989
  • Re-evaluating the role of sterics and electronic coupling in determining the open-circuit voltage of organic solar cells. Advanced materials Graham, K. R., Erwin, P., Nordlund, D., Vandewal, K., Li, R., Ngongang Ndjawa, G. O., Hoke, E. T., Salleo, A., Thompson, M. E., McGehee, M. D., Amassian, A. 2013; 25 (42): 6076-6082

    Abstract

    The effects of sterics and molecular orientation on the open-circuit voltage and absorbance properties of charge-transfer states are explored in model bilayer organic photovoltaics. It is shown that the open-circuit voltage correlates linearly with the charge-transfer state energy and is not significantly influenced by electronic coupling.

    View details for DOI 10.1002/adma.201301319

    View details for PubMedID 23897581

  • A general relationship between disorder, aggregation and charge transport in conjugated polymers NATURE MATERIALS Noriega, R., Rivnay, J., Vandewal, K., Koch, F. P., Stingelin, N., Smith, P., Toney, M. F., Salleo, A. 2013; 12 (11): 1037-1043

    View details for DOI 10.1038/NMAT3722

    View details for Web of Science ID 000326099300020

  • Re-evaluating the Role of Sterics and Electronic Coupling in Determining the Open-Circuit Voltage of Organic Solar Cells ADVANCED MATERIALS Graham, K. R., Erwin, P., Nordlund, D., Vandewal, K., Li, R., Ndjawa, G. O., Hoke, E. T., Salleo, A., Thompson, M. E., McGehee, M. D., Amassian, A. 2013; 25 (42): 6076-6082
  • A general relationship between disorder, aggregation and charge transport in conjugated polymers. Nature materials Noriega, R., Rivnay, J., Vandewal, K., Koch, F. P., Stingelin, N., Smith, P., Toney, M. F., Salleo, A. 2013; 12 (11): 1038-1044

    Abstract

    Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

    View details for DOI 10.1038/nmat3722

    View details for PubMedID 23913173

  • Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Noriega, R., Salleo, A., Spakowitz, A. J. 2013; 110 (41): 16315-16320

    Abstract

    Existing models for the electronic properties of conjugated polymers do not capture the spatial arrangement of the disordered macromolecular chains over which charge transport occurs. Here, we present an analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior.

    View details for DOI 10.1073/pnas.1307158110

    View details for Web of Science ID 000325395600023

    View details for PubMedID 24062459

    View details for PubMedCentralID PMC3799354

  • 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

  • Structural Factors That Affect the Performance of Organic Bulk Heterojunction Solar Cells MACROMOLECULES Vandewal, K., Himmelberger, S., Salleo, A. 2013; 46 (16): 6379-6387

    View details for DOI 10.1021/ma400924b

    View details for Web of Science ID 000323811100001

  • Photocurrent Enhancement from Diketopyrrolopyrrole Polymer Solar Cells through Alkyl-Chain Branching Point Manipulation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Meager, L., Ashraf, R. S., Mollinger, S., Schroeder, B. C., Bronstein, H., Beatrup, D., Vezie, M. S., Kirchartz, T., Salleo, A., Nelson, J., McCulloch, L. 2013; 135 (31): 11537-11540

    Abstract

    Systematically moving the alkyl-chain branching position away from the polymer backbone afforded two new thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT-T) polymers. When used as donor materials in polymer:fullerene solar cells, efficiencies exceeding 7% were achieved without the use of processing additives. The effect of the position of the alkyl-chain branching point on the thin-film morphology was investigated using X-ray scattering techniques and the effects on the photovoltaic and charge-transport properties were also studied. For both solar cell and transistor devices, moving the branching point further from the backbone was beneficial. This is the first time that this effect has been shown to improve solar cell performance. Strong evidence is presented for changes in microstructure across the series, which is most likely the cause for the photocurrent enhancement.

    View details for DOI 10.1021/ja405934j

    View details for Web of Science ID 000323019400032

    View details for PubMedID 23876163

  • Color in the Corners: ITO-Free White OLEDs with Angular Color Stability. Advanced materials Gaynor, W., Hofmann, S., Christoforo, M. G., Sachse, C., Mehra, S., Salleo, A., McGehee, M. D., Gather, M. C., Lüssem, B., Müller-Meskamp, L., Peumans, P., Leo, K. 2013; 25 (29): 4006-4013

    Abstract

    High-efficiency white OLEDs fabricated on silver nanowire-based composite transparent electrodes show almost perfectly Lambertian emission and superior angular color stability, imparted by electrode light scattering. The OLED efficiencies are comparable to those fabricated using indium tin oxide. The transparent electrodes are fully solution-processable, thin-film compatible, and have a figure of merit suitable for large-area devices.

    View details for DOI 10.1002/adma.201300923

    View details for PubMedID 23670954

  • Solution-Processable Zirconium Oxide Gate Dielectrics for Flexible Organic Field Effect Transistors Operated at Low Voltages CHEMISTRY OF MATERIALS Park, Y. M., Desai, A., Salleo, A., Jimison, L. 2013; 25 (13): 2571-2579

    View details for DOI 10.1021/cm303547a

    View details for Web of Science ID 000321809700002

  • Conformational Disorder Enhances Solubility and Photovoltaic Performance of a Thiophene-Quinoxaline Copolymer ADVANCED ENERGY MATERIALS Wang, E., Bergqvist, J., Vandewal, K., Ma, Z., Hou, L., Lundin, A., Himmelberger, S., Salleo, A., Muller, C., Inganas, O., Zhang, F., Andersson, M. R. 2013; 3 (6): 806-814
  • One-Step Macroscopic Alignment of Conjugated Polymer Systems by Epitaxial Crystallization during Spin-Coating ADVANCED FUNCTIONAL MATERIALS Muller, C., Aghamohammadi, M., Himmelberger, S., Sonar, P., Garriga, M., Salleo, A., Campoy-Quiles, M. 2013; 23 (19): 2368-2377
  • Solution processed zinc oxide nanopyramid/silver nanowire transparent network films with highly tunable light scattering properties. Nanoscale Mehra, S., Christoforo, M. G., Peumans, P., Salleo, A. 2013; 5 (10): 4400-4403

    Abstract

    Metal nanowire transparent networks are promising replacements to indium tin oxide (ITO) transparent electrodes for optoelectronic devices. While the transparency and sheet resistance are key metrics for transparent electrode performance, independent control of the film light scattering properties is important to developing multifunctional electrodes for improved photovoltaic absorption. Here we show that controlled incorporation of ZnO nanopyramids into a metal nanowire network film affords independent, highly tunable control of the scattering properties (haze) with minimal effects on the transparency and sheet resistance. Varying the zinc oxide/silver nanostructure ratios prior to spray deposition results in sheet resistances, transmission (600 nm), and haze (600 nm) of 6-30 Ω □(-1), 68-86%, and 34-66%, respectively. Incorporation of zinc oxide nanopyramid scattering agents into the conducting nanowire mesh has a negligible effect on mesh connectivity, providing a straightforward method of controlling electrode scattering properties. The decoupling of the film scattering power and electrical characteristics makes these films promising candidates for highly scattering transparent electrodes in optoelectronic devices and can be generalized to other metal nanowire films as well as carbon nanotube transparent electrodes.

    View details for DOI 10.1039/c3nr00863k

    View details for PubMedID 23575765

  • The chemical and structural origin of efficient p-type doping in P3HT ORGANIC ELECTRONICS Duong, D. T., Wang, C., Antono, E., Toney, M. F., Salleo, A. 2013; 14 (5): 1330-1336
  • Effects of Confinement on Microstructure and Charge Transport in High Performance Semicrystalline Polymer Semiconductors ADVANCED FUNCTIONAL MATERIALS Himmelberger, S., Dacuna, J., Rivnay, J., Jimison, L. H., McCarthy-Ward, T., Heeney, M., McCulloch, I., Toney, M. F., Salleo, A. 2013; 23 (16): 2091-2098
  • Ultrathin Body Poly(3-hexylthiophene) Transistors with Improved Short-Channel Performance ACS APPLIED MATERIALS & INTERFACES Wang, C., Rivnay, J., Himmelberger, S., Vakhshouri, K., Toney, M. F., Gomez, E. D., Salleo, A. 2013; 5 (7): 2342-2346

    Abstract

    The microstructure and charge transport properties of binary blends of regioregular (rr) and regiorandom (RRa) poly(3-hexylthiophene) (P3HT) are investigated. X-ray diffraction of the blended films is consistent with a vertically separated structure, with rr-P3HT preferentially crystallizing at the semiconductor/dielectric interface. Thin film transistors made with these blended films preserve high field effect mobility with rr-P3HTcontent as low as 5.6%. In these dilute blends, we estimate that the thickness of rr-P3HT in the channel is only a few nanometers. Significantly, as a result of such an ultrathin active layer at the interface, short channel effects due to bulk currents are eliminated, suggesting a new route to fabricate high-performance, short-channel, and reliable organic electronic devices.

    View details for DOI 10.1021/am3027103

    View details for Web of Science ID 000317549100008

    View details for PubMedID 23429794

  • Vertical Confinement and Interface Effects on the Microstructure and Charge Transport of P3HT Thin Films JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS Jimison, L. H., Himmelberger, S., Duong, D. T., Rivnay, J., Toney, M. F., Salleo, A. 2013; 51 (7): 611-620

    View details for DOI 10.1002/polb.23265

    View details for Web of Science ID 000315860100015

  • Low-Temperature Processed Ga-Doped ZnO Coatings from Colloidal Inks JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Della Gaspera, E., Bersani, M., Cittadini, M., Guglielmi, M., Pagani, D., Noriega, R., Mehra, S., Salleo, A., Martucci, A. 2013; 135 (9): 3439-3448

    Abstract

    We present a new colloidal synthesis of gallium-doped zinc oxide nanocrystals that are transparent in the visible and absorb in the near-infrared. Thermal decomposition of zinc stearate and gallium nitrate after hot injection of the precursors in a mixture of organic amines leads to nanocrystals with tunable properties according to gallium amount. Substitutional Ga(3+) ions trigger a plasmonic resonance in the infrared region resulting from an increase in the free electrons concentration. These nanocrystals can be deposited by spin coating, drop casting, and spray coating resulting in homogeneous and high-quality thin films. The optical transmission of the Ga-ZnO nanoparticle assemblies in the visible is greater than 90%, and at the same time, the near-infrared absorption of the nanocrystals is maintained in the films as well. Several strategies to improve the films electrical and optical properties have been presented, such as UV treatments to remove the organic compounds responsible for the observed interparticle resistance and reducing atmosphere treatments on both colloidal solutions and thin films to increase the free carriers concentration, enhancing electrical conductivity and infrared absorption. The electrical resistance of the nanoparticle assemblies is about 30 kΩ/sq for the as-deposited, UV-exposed films, and it drops down to 300 Ω/sq after annealing in forming gas at 450 °C, comparable with state of the art tin-doped indium oxide coatings deposited from nanocrystal inks.

    View details for DOI 10.1021/ja307960z

    View details for Web of Science ID 000315936700032

    View details for PubMedID 23394063

  • Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors NATURE COMMUNICATIONS Lu, G., Blakesley, J., Himmelberger, S., Pingel, P., Frisch, J., Lieberwirth, I., Salzmann, I., Oehzelt, M., Di Pietro, R., Salleo, A., Koch, N., Neher, D. 2013; 4

    Abstract

    Polymer transistors are being intensively developed for next-generation flexible electronics. Blends comprising a small amount of semiconducting polymer mixed into an insulating polymer matrix have simultaneously shown superior performance and environmental stability in organic field-effect transistors compared with the neat semiconductor. Here we show that such blends actually perform very poorly in the undoped state, and that mobility and on/off ratio are improved dramatically upon moderate doping. Structural investigations show that these blend layers feature nanometre-scale semiconductor domains and a vertical composition gradient. This particular morphology enables a quasi three-dimensional spatial distribution of semiconductor pathways within the insulating matrix, in which charge accumulation and depletion via a gate bias is substantially different from neat semiconductor, and where high on-current and low off-current are simultaneously realized in the stable doped state. Adding only 5 wt% of a semiconducting polymer to a polystyrene matrix, we realized an environmentally stable inverter with gain up to 60.

    View details for DOI 10.1038/ncomms2587

    View details for Web of Science ID 000318873900042

    View details for PubMedID 23481396

  • Recombination in Polymer:Fullerene Solar Cells with Open-Circuit Voltages Approaching and Exceeding 1.0 V ADVANCED ENERGY MATERIALS Hoke, E. T., Vandewal, K., Bartelt, J. A., Mateker, W. R., Douglas, J. D., Noriega, R., Graham, K. R., Frechet, J. M., Salleo, A., McGehee, M. D. 2013; 3 (2): 220-230
  • PEDOT:gelatin composites mediate brain endothelial cell adhesion JOURNAL OF MATERIALS CHEMISTRY B Bongo, M., Winther-Jensen, O., Himmelberger, S., Strakosas, X., Ramuz, M., Hama, A., Stavrinidou, E., Malliaras, G. G., Salleo, A., Winther-Jensen, B., Owens, R. M. 2013; 1 (31): 3860-3867

    View details for DOI 10.1039/c3tb20374c

    View details for Web of Science ID 000321905900016

  • Solution processed zinc oxide nanopyramid/silver nanowire transparent network films with highly tunable light scattering properties Nanoscale Mehra, S., Christoforo, M., G., Peumans, P., Salleo, A. 2013; 5: 4400
  • Efficient charge generation by relaxed charge-transfer states at organic interfaces Nature Materials, Advance Online Vandewal, K., Albrecht, S., Hoke, E., T., Graham, K., R., Widmer, J., Douglas, J., D., Salleo, A. 2013
  • 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. 2013; 25: 4663
  • Color in the corners: ITO-free white OLEDs with angular color stability Advanced Materials Gaynor, W., Hofmann, S., Christoforo, G., M., Sachse, C., Mehra, S., Salleo, A. 2013; 25: 4006
  • 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

  • Role of confinement and aggregation in charge transport in semicrystalline polythiophene thin films PHYSICAL REVIEW B Duong, D. T., Toney, M. F., Salleo, A. 2012; 86 (20)
  • Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale CHEMICAL REVIEWS Rivnay, J., Mannsfeld, S. C., Miller, C. E., Salleo, A., Toney, M. F. 2012; 112 (10): 5488-5519

    View details for DOI 10.1021/cr3001109

    View details for Web of Science ID 000309628100012

    View details for PubMedID 22877516

  • Estimation of the spatial distribution of traps using space-charge-limited current measurements in an organic single crystal PHYSICAL REVIEW B Dacuna, J., Xie, W., Salleo, A. 2012; 86 (11)
  • Optically switchable transistor via energy-level phototuning in a bicomponent organic semiconductor NATURE CHEMISTRY Orgiu, E., Crivillers, N., Herder, M., Grubert, L., Paetzel, M., Frisch, J., Pavlica, E., Duong, D. T., Bratina, G., Salleo, A., Koch, N., Hecht, S., Samori, P. 2012; 4 (8): 675-679

    Abstract

    Organic semiconductors are suitable candidates for printable, flexible and large-area electronics. Alongside attaining an improved device performance, to confer a multifunctional nature to the employed materials is key for organic-based logic applications. Here we report on the engineering of an electronic structure in a semiconducting film by blending two molecular components, a photochromic diarylethene derivative and a poly(3-hexylthiophene) (P3HT) matrix, to attain phototunable and bistable energy levels for the P3HT's hole transport. As a proof-of-concept we exploited this blend as a semiconducting material in organic thin-film transistors. The device illumination at defined wavelengths enabled reversible tuning of the diarylethene's electronic states in the blend, which resulted in modulation of the output current. The device photoresponse was found to be in the microsecond range, and thus on a technologically relevant timescale. This modular blending approach allows for the convenient incorporation of various molecular components, which opens up perspectives on multifunctional devices and logic circuits.

    View details for DOI 10.1038/NCHEM.1384

    View details for Web of Science ID 000306696300019

    View details for PubMedID 22824901

  • Scalable Fabrication of Strongly Textured Organic Semiconductor Micropatterns by Capillary Force Lithography ADVANCED MATERIALS Jo, P. S., Vailionis, A., Park, Y. M., Salleo, A. 2012; 24 (24): 3269-3274

    Abstract

    Strongly textured organic semiconductor micropatterns made of the small molecule dioctylbenzothienobenzothiophene (C(8)-BTBT) are fabricated by using a method based on capillary force lithography (CFL). This technique provides the C(8)-BTBT solution with nucleation sites for directional growth, and can be used as a scalable way to produce high quality crystalline arrays in desired regions of a substrate for OFET applications.

    View details for DOI 10.1002/adma.201200524

    View details for Web of Science ID 000305450500017

    View details for PubMedID 22605625

  • Electrothermal phenomena in zinc oxide nanowires and contacts APPLIED PHYSICS LETTERS LeBlanc, S., Phadke, S., Kodama, T., Salleo, A., Goodson, K. E. 2012; 100 (16)

    View details for DOI 10.1063/1.4703935

    View details for Web of Science ID 000303128500048

  • A Selenophene-Based Low-Bandgap Donor-Acceptor Polymer Leading to Fast Ambipolar Logic ADVANCED MATERIALS Kronemeijer, A. J., Gili, E., Shahid, M., Rivnay, J., Salleo, A., Heeney, M., Sirringhaus, H. 2012; 24 (12): 1558-1565

    Abstract

    Fast ambipolar CMOS-like logic is demonstrated using a new selenophene-based donor-acceptor polymer semiconductor. The polymer exhibits saturation hole and electron mobilities of 0.46 cm(2) /Vs and 0.84 cm(2) /Vs. Inverters are fabricated with high gains while three-stage ring oscillators show stable oscillation with an unprecedented maximum frequency of 182 kHz at a relatively low supply voltage of 50 V.

    View details for DOI 10.1002/adma.201104522

    View details for Web of Science ID 000301523600007

    View details for PubMedID 22351605

  • 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

  • The Mechanism of Burn-in Loss in a High Efficiency Polymer Solar Cell ADVANCED MATERIALS Peters, C. H., Sachs-Quintana, I. T., Mateker, W. R., Heumueller, T., Rivnay, J., Noriega, R., Beiley, Z. M., Hoke, E. T., Salleo, A., McGehee, M. D. 2012; 24 (5): 663-?

    Abstract

    Degradation in a high efficiency polymer solar cell is caused by the formation of states in the bandgap. These states increase the energetic disorder in the system. The power conversion efficiency loss does not occur when current is run through the device in the dark but occurs when the active layer is photo-excited.

    View details for DOI 10.1002/adma.201103010

    View details for Web of Science ID 000299466600009

    View details for PubMedID 21989825

  • Effect of Miscibility and Percolation on Electron Transport in Amorphous Poly(3-Hexylthiophene)/Phenyl-C-61-Butyric Acid Methyl Ester Blends PHYSICAL REVIEW LETTERS Vakhshouri, K., Kozub, D. R., Wang, C., Salleo, A., Gomez, E. D. 2012; 108 (2)

    Abstract

    Recent evidence has demonstrated that amorphous mixed phases are ubiquitous within mesostructured polythiophene-fullerene mixtures. Nevertheless, the role of mixing within nanophases on charge transport of organic semiconductor mixtures is not fully understood. To this end, we have examined the electron mobility in amorphous blends of poly(3-hexylthiophene) and phenyl-C(61)-butyric acid methyl ester. Our studies reveal that the miscibility of the components strongly affects electron transport within blends. Immiscibility promotes efficient electron transport by promoting percolating pathways within organic semiconductor mixtures. As a consequence, partial miscibility may be important for efficient charge transport in polythiophene-fullerene mixtures and organic solar cell performance.

    View details for DOI 10.1103/PhysRevLett.108.026601

    View details for Web of Science ID 000298991400022

    View details for PubMedID 22324702

  • Laser-Based Synthesis of Nanomaterials in the Solid State Conference on Lasers and Electro-Optics (CLEO) Salleo, A. IEEE. 2012
  • High-Mobility Ambipolar Transistors: Properties and Function Conference on Organic Field-Effect Transistors XI Kronemeijer, A. J., Gili, E., Shahid, M., Rivnay, J., Salleo, A., Heeney, M., Sirringhaus, H. SPIE-INT SOC OPTICAL ENGINEERING. 2012

    View details for DOI 10.1117/12.940782

    View details for Web of Science ID 000326639600003

  • Solution-grown n-type ZnO nanostructures: synthesis, microstructure and doping Handbook of ZnO and Related Materials Noriega, R., Mehra, S., Salleo, A. edited by Feng, Z., C. Taylor and Francis/CRC Press. 2012: 1
  • Controlled conjugated backbone twisting for an increased open-circuit voltage while having a high short-circuit current in poly(hexyl)thiophene derivatives J. Am. Chem. Soc. Ko, S., Hoke, E., Pandey, L., Hong, S., Mondal, R., Rajib, R., Salleo, A. 2012; 134: 5222
  • Effect of Miscibility and Percolation on Electron Transport in Amorphous Poly(3-Hexylthiophene)/Phenyl-C61-Butyric Acid Methyl Ester Blends Phys. Rev. Lett. Vakhshouri, K., Kozub, D., R., Wang, C., Salleo, A., Gomez, E., D. 2012; 108: 26601
  • Electrothermal phenomena in zinc oxide nanowires and contacts Appl. Phys. Lett. LeBlanc, S., Phadke, S., Kodama, T., Salleo, A., Goodson, K., E. 2012; 100: 163105
  • Title: Using Alignment and 2D Network Simulations to Study Charge Transport Through Doped ZnO Nanowire Thin Film Electrodes ADVANCED FUNCTIONAL MATERIALS Phadke, S., Lee, J., West, J., Peumans, P., Salleo, A. 2011; 21 (24): 4691-4697
  • Modeling space-charge-limited currents in organic semiconductors: Extracting trap density and mobility PHYSICAL REVIEW B Dacuna, J., Salleo, A. 2011; 84 (19)
  • Relation between Microstructure and Charge Transport in Polymers of Different Regioregularity JOURNAL OF PHYSICAL CHEMISTRY C McMahon, D. P., Cheung, D. L., Goris, L., Dacuna, J., Salleo, A., Troisi, A. 2011; 115 (39): 19386-19393

    View details for DOI 10.1021/jp207026s

    View details for Web of Science ID 000295245500060

  • Morphology-Dependent Trap Formation in High Performance Polymer Bulk Heterojunction Solar Cells ADVANCED ENERGY MATERIALS Beiley, Z. M., Hoke, E. T., Noriega, R., Dacuna, J., Burkhard, G. F., Bartelt, J. A., Salleo, A., Toney, M. F., McGehee, M. D. 2011; 1 (5): 954-962
  • Real-Time Observation of Poly(3-alkylthiophene) Crystallization and Correlation with Transient Optoelectronic Properties MACROMOLECULES Boudouris, B. W., Ho, V., Jimison, L. H., Toney, M. F., Salleo, A., Segalman, R. A. 2011; 44 (17): 6653-6658

    View details for DOI 10.1021/ma201316a

    View details for Web of Science ID 000294585600006

  • Effect of Acene Length on Electronic Properties in 5-, 6-, and 7-Ringed Heteroacenes ADVANCED MATERIALS Goetz, K. P., Li, Z., Ward, J. W., Bougher, C., Rivnay, J., Smith, J., Conrad, B. R., Parkin, S. R., Anthopoulos, T. D., Salleo, A., Anthony, J. E., Jurchescu, O. D. 2011; 23 (32): 3698-?

    View details for DOI 10.1002/adma.201101619

    View details for Web of Science ID 000294977300012

    View details for PubMedID 21732562

  • Steric Control of the Donor/Acceptor Interface: Implications in Organic Photovoltaic Charge Generation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Holcombe, T. W., Norton, J. E., Rivnay, J., Woo, C. H., Goris, L., Piliego, C., Griffini, G., Sellinger, A., Bredas, J., Salleo, A., Frechet, J. M. 2011; 133 (31): 12106-12114

    Abstract

    The performance of organic photovoltaic (OPV) devices is currently limited by modest short-circuit current densities. Approaches toward improving this output parameter may provide new avenues to advance OPV technologies and the basic science of charge transfer in organic semiconductors. This work highlights how steric control of the charge separation interface can be effectively tuned in OPV devices. By introducing an octylphenyl substituent onto the investigated polymer backbones, the thermally relaxed charge-transfer state, and potentially excited charge-transfer states, can be raised in energy. This decreases the barrier to charge separation and results in increased photocurrent generation. This finding is of particular significance for nonfullerene OPVs, which have many potential advantages such as tunable energy levels and spectral breadth, but are prone to poor exciton separation efficiencies. Computational, spectroscopic, and synthetic methods were combined to develop a structure-property relationship that correlates polymer substituents with charge-transfer state energies and, ultimately, device efficiencies.

    View details for DOI 10.1021/ja203235z

    View details for Web of Science ID 000293768400055

    View details for PubMedID 21688785

  • Precipitation of silicon nanoclusters by laser direct-write OPTICS EXPRESS Mustafeez, W., Lee, D., Grigoropoulos, C., Salleo, A. 2011; 19 (16): 15452-15458

    Abstract

    The ability to use a laser to direct-write tracks of localized emission enhancement in PECVD-deposited Silicon rich oxide (SRO) films is demonstrated. For this purpose, 400 nm thick SRO films with varying excess Si content were irradiated with loosely focused 355 nm, 12 ps pulses at 80 MHz while being translated at 2mm/s. Mapping of areas irradiated with energies between 4.7 nJ and 5.5 nJ/pulse exhibits regions with the largest emission enhancement. Raman and photoluminescence (PL) measurements suggest precipitation of amorphous and crystalline Si nanoclusters. In the most emissive regions, the PL efficiency of the laser-annealed films was ~70% of that obtained by standard oven-annealing processes. Stress in Si crystals in some areas is identified as leading to quenching of the PL and is hypothesized to be caused by the densification of SRO matrix.

    View details for Web of Science ID 000293339200072

    View details for PubMedID 21934909

  • Drastic Control of Texture in a High Performance n-Type Polymeric Semiconductor and Implications for Charge Transport MACROMOLECULES Rivnay, J., Steyrleuthner, R., Jimison, L. H., Casadei, A., Chen, Z., Toney, M. F., Facchetti, A., Neher, D., Salleo, A. 2011; 44 (13): 5246-5255

    View details for DOI 10.1021/ma200864s

    View details for Web of Science ID 000292417800024

  • Quantitative analysis of lattice disorder and crystallite size in organic semiconductor thin films PHYSICAL REVIEW B Rivnay, J., Noriega, R., Kline, R. J., Salleo, A., Toney, M. F. 2011; 84 (4)
  • A Boltzmann-weighted hopping model of charge transport in organic semicrystalline films JOURNAL OF APPLIED PHYSICS Kwiatkowski, J. J., Jimison, L. H., Salleo, A., Spakowitz, A. J. 2011; 109 (11)

    View details for DOI 10.1063/1.3594686

    View details for Web of Science ID 000292214700082

  • Structural origin of gap states in semicrystalline polymers and the implications for charge transport PHYSICAL REVIEW B Rivnay, J., Noriega, R., Northrup, J. E., Kline, R. J., Toney, M. F., Salleo, A. 2011; 83 (12)
  • Room-Temperature Fabrication of Ultrathin Oxide Gate Dielectrics for Low-Voltage Operation of Organic Field-Effect Transistors ADVANCED MATERIALS Park, Y. M., Daniel, J., Heeney, M., Salleo, A. 2011; 23 (8): 971-974

    View details for DOI 10.1002/adma.201003641

    View details for Web of Science ID 000287669000003

    View details for PubMedID 21341309

  • Using Alignment and 2D Network Simulations to Study Charge Transport Through Doped ZnO Nanowire Thin Film Electrodes Advanced Functional Materials Phadke, S., Lee, J., Y., West, J., Peumans, P., Salleo, A. 2011; 21: 4691
  • Room-Temerature Fabrication of Ultra-Thin Oxide Gate Dielectrics for Low-Voltage Operation of Organic Field Effect Transistors Advanced Materials Park, Y., M., Daniel, J., Heeney, M., Salleo, A. 2011; 23: 971
  • Organic Semiconductors in Transistor Applications Organic Electronics Vol.II: More Materials and Applications James, D., Smith, D., Heeney, M., Anthopoulos, T., Salleo, A., McCulloch, I. edited by Klauk, H. Wiley-VCH Verlag. 2011: 1
  • Charge Transport Theories in Organic Semiconductors Organic Electronics Vol.II: More Materials and Applications Noriega, R., Salleo, A. edited by Klauk, H. Wiley-VCH Verlag. 2011: 1
  • Laser-Synthesized Epitaxial Graphene ACS NANO Lee, S., Toney, M. F., Ko, W., Randel, J. C., Jung, H. J., Munakata, K., Lu, J., Geballe, T. H., Beasley, M. R., Sinclair, R., Manoharan, H. C., Salleo, A. 2010; 4 (12): 7524-7530

    Abstract

    Owing to its unique electronic properties, graphene has recently attracted wide attention in both the condensed matter physics and microelectronic device communities. Despite intense interest in this material, an industrially scalable graphene synthesis process remains elusive. Here, we demonstrate a high-throughput, low-temperature, spatially controlled and scalable epitaxial graphene (EG) synthesis technique based on laser-induced surface decomposition of the Si-rich face of a SiC single-crystal. We confirm the formation of EG on SiC as a result of excimer laser irradiation by using reflection high-energy electron diffraction (RHEED), Raman spectroscopy, synchrotron-based X-ray diffraction, transmission electron microscopy (TEM), and scanning tunneling microscopy (STM). Laser fluence controls the thickness of the graphene film down to a single monolayer. Laser-synthesized graphene does not display some of the structural characteristics observed in EG grown by conventional thermal decomposition on SiC (0001), such as Bernal stacking and surface reconstruction of the underlying SiC surface.

    View details for DOI 10.1021/nn101796e

    View details for PubMedID 21121692

  • Unconventional Face-On Texture and Exceptional In-Plane Order of a High Mobility n-Type Polymer ADVANCED MATERIALS Rivnay, J., Toney, M. F., Zheng, Y., Kauvar, I. V., Chen, Z., Wagner, V., Facchetti, A., Salleo, A. 2010; 22 (39): 4359-?

    Abstract

    Substantial in-plane crystallinity and dominant face-on stacking are observed in thin films of a high-mobility n-type rylene-thiophene copolymer. Spun films of the polymer, previously thought to have little or no order are found to exhibit an ordered microstructure at both interfaces, and in the bulk. The implications of this type of packing and crystalline morphology are discussed as they relate to thin-film transistors.

    View details for DOI 10.1002/adma.201001202

    View details for Web of Science ID 000284000700005

    View details for PubMedID 20623753

  • Microstructural Characterization and Charge Transport in Thin Films of Conjugated Polymers ADVANCED MATERIALS Salleo, A., Kline, R. J., Delongchamp, D. M., Chabinyc, M. L. 2010; 22 (34): 3812-3838

    Abstract

    The performance of semiconducting polymers has been steadily increasing in the last 20 years. Improved control over the microstructure of these materials and a deeper understanding of how the microstructure affects charge transport are partially responsible for such trend. The development and widespread use of techniques that allow to characterize the microstructure of semiconducting polymers is therefore instrumental for the advance of these materials. This article is a review of the characterization techniques that provide information used to enhance the understanding of structure/property relationships in semiconducting polymers. In particular, the applications of optical and X-ray spectroscopy, X-ray diffraction, and scanning probe techniques in this context are described.

    View details for DOI 10.1002/adma.200903712

    View details for Web of Science ID 000282793600005

    View details for PubMedID 20607787

  • Indacenodithiophene Semiconducting Polymers for High-Performance, Air-Stable Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Zhang, W., Smith, J., Watkins, S. E., Gysel, R., McGehee, M., Salleo, A., Kirkpatrick, J., Ashraf, S., Anthopoulos, T., Heeney, M., McCulloch, I. 2010; 132 (33): 11437-11439

    Abstract

    High-performance, solution-processed transistors fabricated from semiconducting polymers containing indacenodithiohene repeat units are described. The bridging functions on the backbone contribute to suppressing large-scale crystallization in thin films. However, charge carrier mobilities of up to 1 cm(2)/(V s) for a benzothiadiazole copolymer were reported and, coupled with both ambient stability and long-wavelength absorption, make this family of polymers particularly attractive for application in next-generation organic optoelectronics.

    View details for DOI 10.1021/ja1049324

    View details for Web of Science ID 000281066400019

    View details for PubMedID 20677750

  • Quantification of Thin Film Crystallographic Orientation Using X-ray Diffraction with an Area Detector LANGMUIR Baker, J. L., Jimison, L. H., Mannsfeld, S., Volkman, S., Yin, S., Subramanian, V., Salleo, A., Alivisatos, A. P., Toney, M. F. 2010; 26 (11): 9146-9151

    Abstract

    As thin films become increasingly popular (for solar cells, LEDs, microelectronics, batteries), quantitative morphological and crystallographic information is needed to predict and optimize the film's electrical, optical, and mechanical properties. This quantification can be obtained quickly and easily with X-ray diffraction using an area detector in two sample geometries. In this paper, we describe a methodology for constructing complete pole figures for thin films with fiber texture (isotropic in-plane orientation). We demonstrate this technique on semicrystalline polymer films, self-assembled nanoparticle semiconductor films, and randomly packed metallic nanoparticle films. This method can be immediately implemented to help understand the relationship between film processing and microstructure, enabling the development of better and less expensive electronic and optoelectronic devices.

    View details for DOI 10.1021/la904840q

    View details for Web of Science ID 000277928100199

    View details for PubMedID 20361783

  • Probing the electrical properties of highly-doped Al:ZnO nanowire ensembles JOURNAL OF APPLIED PHYSICS Noriega, R., Rivnay, J., Goris, L., Kaelblein, D., Klauk, H., Kern, K., Thompson, L. M., Palke, A. C., Stebbins, J. F., Jokisaari, J. R., Kusinski, G., Salleo, A. 2010; 107 (7)

    View details for DOI 10.1063/1.3360930

    View details for Web of Science ID 000276795400081

  • Transmission electron microscopy of solution-processed, intrinsic and Al-doped ZnO nanowires for transparent electrode fabrication 13th International Conference on Electron Microscopy Kusinski, G. J., Jokisaari, J. R., Noriega, R., Goris, L., Donovan, M., Salleo, A. WILEY-BLACKWELL. 2010: 443–49

    Abstract

    A solution-based chemistry was used to synthesize intrinsic and Al-doped (1% and 5% nominal atomic concentration of Al) ZnO nanostructures. The nanowires were grown at 300 degrees C in trioctylamine by dissolving Zn acetate and Al acetate. Different doping conditions gave rise to different nanoscale morphologies. The effect of a surfactant (oleic acid) was also investigated. An electron microscopy study correlating morphology, aspect ratio and doping of the individual ZnO wires to the electrical properties of the spin coated films is presented. HRTEM revealed single crystalline [0001] wires.

    View details for DOI 10.1111/j.1365-2818.2009.03289.x

    View details for Web of Science ID 000274551700047

    View details for PubMedID 20500415

  • Microstructural Origin of High Mobility in High-Performance Poly(thieno-thiophene) Thin-Film Transistors ADVANCED MATERIALS Wang, C., Jimison, L. H., Goris, L., McCulloch, I., Heeney, M., Ziegler, A., Salleo, A. 2010; 22 (6): 697-?

    View details for DOI 10.1002/adma.200902303

    View details for Web of Science ID 000274910200004

    View details for PubMedID 20217772

  • Materials and Applications for Large Area Electronics: Solution-Based Approaches CHEMICAL REVIEWS Arias, A. C., MacKenzie, J. D., McCulloch, I., Rivnay, J., Salleo, A. 2010; 110 (1): 3-24

    View details for DOI 10.1021/cr900150b

    View details for Web of Science ID 000274255700002

    View details for PubMedID 20070114

  • Materials and Applications for Large-Area Electronics: Solution-Based Approaches Chemical Reviews Arias, A., C., MacKenzie, D., McCulloch, I., Rivnay, J., Salleo, A. 2010; 110: 3
  • Microstructural Origin of High-Mobility in High-Performance Poly(thieno-thiophene) Thin Film Transistors Advanced Materials Wang, C., Jimison, L., H., Goris, L., McCulloch, I., Heeney, M., Ziegler, A., Salleo, A. 2010; 22: 697
  • Unconvention Face-On Texture and Exceptional In-Plane Order of a High Mobility n-Type Polymer Advanced Materials Rivnay, J., Toney, M., F., Zheng, Y., Kauvar, I., V., Chen, Z., Wagner, V., Salleo, A. 2010; 22: 4359
  • Light trapping in thin-film silicon solar cells with submicron surface texture OPTICS EXPRESS Dewan, R., Marinkovic, M., Noriega, R., Phadke, S., Salleo, A., Knipp, D. 2009; 17 (25): 23058-23065

    Abstract

    The influence of nano textured front contacts on the optical wave propagation within microcrystalline thin-film silicon solar cell was investigated. Periodic triangular gratings were integrated in solar cells and the influence of the profile dimensions on the quantum efficiency and the short circuit current was studied. A Finite Difference Time Domain approach was used to rigorously solve the Maxwell's equations in two dimensions. By studying the influence of the period and height of the triangular profile, the design of the structures were optimized to achieve higher short circuit currents and quantum efficiencies. Enhancement of the short circuit current in the blue part of the spectrum is achieved for small triangular periods (P<200 nm), whereas the short circuit current in the red and infrared part of the spectrum is increased for triangular periods (P = 900nm) comparable to the optical wavelength. The influence of the surface texture on the solar cell performance will be discussed.

    View details for Web of Science ID 000272761300083

    View details for PubMedID 20052232

  • Large modulation of carrier transport by grain-boundary molecular packing and microstructure in organic thin films NATURE MATERIALS Rivnay, J., Jimison, L. H., Northrup, J. E., Toney, M. F., Noriega, R., Lu, S., Marks, T. J., Facchetti, A., Salleo, A. 2009; 8 (12): 952-958

    Abstract

    Solution-processable organic semiconductors are central to developing viable printed electronics, and performance comparable to that of amorphous silicon has been reported for films grown from soluble semiconductors. However, the seemingly desirable formation of large crystalline domains introduces grain boundaries, resulting in substantial device-to-device performance variations. Indeed, for films where the grain-boundary structure is random, a few unfavourable grain boundaries may dominate device performance. Here we isolate the effects of molecular-level structure at grain boundaries by engineering the microstructure of the high-performance n-type perylenediimide semiconductor PDI8-CN2 and analyse their consequences for charge transport. A combination of advanced X-ray scattering, first-principles computation and transistor characterization applied to PDI8-CN2 films reveals that grain-boundary orientation modulates carrier mobility by approximately two orders of magnitude. For PDI8-CN2 we show that the molecular packing motif (that is, herringbone versus slip-stacked) plays a decisive part in grain-boundary-induced transport anisotropy. The results of this study provide important guidelines for designing device-optimized molecular semiconductors.

    View details for DOI 10.1038/NMAT2570

    View details for PubMedID 19898460

  • Ordering of Poly(3-hexylthiophene) Nanocrystallites on the Basis of Substrate Surface Energy ACS NANO Meredig, B., Salleo, A., Gee, R. 2009; 3 (10): 2881-2886

    Abstract

    Molecular dynamics simulations are used to study the influence of functionalized substrates on the orientation of poly(3-hexylthiophene) (P3HT) nanocrystallites, which in turn plays a critical role in P3HT-based transistor performance. The effects of alkyl-trichlorosilane self-assembled monolayer packing density, packing order, and end-group functionality are independently investigated. Across these factors, the potential energy surface presented by the substrate to the P3HT molecules is determined to be the main driver of P3HT ordering. Surprisingly, disordered substrates with a smoothly varying potential energy landscape are found to encourage edge-on P3HT orientation, while highly ordered substrates have undesirable potential energy wells that reduce the edge-on orientation of P3HT because of substrate-side-chain interactions.

    View details for DOI 10.1021/nn800707z

    View details for Web of Science ID 000271106100005

    View details for PubMedID 19746953

  • Dual-gate organic thin film transistors as chemical sensors APPLIED PHYSICS LETTERS Park, Y. M., Salleo, A. 2009; 95 (13)

    View details for DOI 10.1063/1.3242372

    View details for Web of Science ID 000270458000079

  • Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene) ADVANCED MATERIALS Jimison, L. H., Toney, M. F., McCulloch, I., Heeney, M., Salleo, A. 2009; 21 (16): 1568-?
  • Intrinsic and Doped Zinc Oxide Nanowires for Transparent Electrode Fabrication via Low-Temperature Solution Synthesis 50th Electronic Materials Conference Goris, L., Noriega, R., Donovan, M., Jokisaari, J., Kusinski, G., Salleo, A. SPRINGER. 2009: 586–95
  • Semiconducting Thienothiophene Copolymers: Design, Synthesis, Morphology, and Performance in Thin-Film Organic Transistors ADVANCED MATERIALS McCulloch, I., Heeney, M., Chabinyc, M. L., DeLongchamp, D., Kline, R. J., Coelle, M., Duffy, W., Fischer, D., Gundlach, D., Hamadani, B., Hamilton, R., Richter, L., Salleo, A., Shkunov, M., Sporrowe, D., Tierney, S., Zhong, W. 2009; 21 (10-11): 1091-1109
  • Large modulation of carrier transport by grain-boundary molecular packing and microsctructure in organic thin films Nature Materials Rivnay, J., Jimison, L., H., Northrup, J., E., Toney, M., F., Noriega, R., Lu, S., Salleo, A. 2009; 8: 952
  • Flexible Electronics: Materials and Applications edited by Salleo, A., Wong, W., S. Springer Verlag. 2009
  • Light Trapping in Thin Film Silicon Solar Cells with Periodic Pyramid Texture Optics Express Devan, R., Marinkovic, M., Noriega, R., Phadke, S., Salleo, A., Knipp, D. 2009; 17: 23058
  • Dual gate organic thin film transistors as chemical sensors Applied Physics Letters Park, Y., M., Salleo, A. 2009; 95: 133307
  • Materials and Novel Patterning methods for Flexible Electronics Flexible Electronics: Materials and Applications Wong, W., S., Chabinyc, M., L., Ng, T., N., Salleo, A. edited by Wong, W., W., Salleo, A. Springer Verlag. 2009: 1
  • Charge Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regio-Regular Poly(3-hexylthiophene) Advanced Materials Jimison, L., H., Toney, M., F., McCulloch, I., Heeney, M., Salleo, A. 2009; 21: 1568
  • Correlating the microstructure of thin films of poly[5,5-bis(3-dodecyl-2-thienyl)-2,2-bithiophene] with charge transport: Effect of dielectric surface energy and thermal annealing PHYSICAL REVIEW B Jimison, L. H., Salleo, A., Chabinyc, M. L., Bernstein, D. P., Toney, M. F. 2008; 78 (12)
  • Interfacial effects in thin films of polymeric semiconductors JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Rivnay, J., Jimison, L. H., Toney, M. F., Preiner, M., Melosh, N. A., Salleo, A. 2008; 26 (4): 1454-1460

    View details for DOI 10.1116/1.2952454

    View details for Web of Science ID 000258494400036

  • Connecting electrical and molecular properties of semiconducting polymers for thin-film transistors MRS BULLETIN Chabinyc, M. L., Jimison, L. H., Rivnay, J., Salleo, A. 2008; 33 (7): 683-689
  • Connecting Electrical and Molecular Properties of Semiconducting Polymers for Thin Film Transistors MRS Bulletin Chabinyc, M., Jimison, L., H., Rivnay, J., Salleo, A. 2008; 33: 683-689
  • Correlating the microstructure of thin films of Poly[5,5’-bis(3-dodecyl-2-thienyl)-2,2’-bithiophene] with charge transport: effect of dielectric surface energy and thermal annealing. Physical Review B Jimison, L., H., Salleo, A., Chabinyc, M., L., Toney, M., F. 2008; 78: 19
  • Solution based self-assembly of an be array of polymeric thin-film transistors ADVANCED MATERIALS Salleo, A., Arias, A. C. 2007; 19 (21): 3540-?
  • Charge transport in polymeric transistors MATERIALS TODAY Salleo, A. 2007; 10 (3): 38-45
  • Microstructure, charge transport and trapping in anisotropic polymeric thin film transistors IEEE LEOS Summer Topical Meeting 2007 Jimison, L. H., Rivnay, J., Toney, M. F., Salleo, A. IEEE. 2007: 206–207
  • Bias stress effects in organic thin film transistors 2007 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM PROCEEDINGS - 45TH ANNUAL Ng, T. N., Chabinyc, M. L., Street, R. A., Salleo, A. 2007: 243-?
  • Solution Based Self-Assembly of an Array of Polymeric Thin-Film Transistors Advanced Materials Salleo, A., Arias, A., C. 2007; 19: 3540
  • Jet printing flexible displays MATERIALS TODAY Street, R. A., Wong, W. S., Ready, S. E., Chabinyc, I. L., Arias, A. C., Limb, S., Salleo, A., Lujan, R. 2006; 9 (4): 32-37
  • Micro-structural effects on the performance of poly(thiophene) field-effect transistors Conference on Organic Field-Effect Transistors V Salleo, A., Jimison, L. H., Donovan, M. M., Chabinyc, M. L., Toney, M. F. SPIE-INT SOC OPTICAL ENGINEERING. 2006

    View details for DOI 10.1117/12.681171

    View details for Web of Science ID 000243028900005

  • Toolset for printed electronics DIGITAL FABRICATION 2006, FINAL PROGRAM AND PROCEEDINGS Ready, S. E., Wong, W. S., Arias, A., Salleo, A., Apte, R. B., Chabinyc, M. L., Street, R. A. 2006: 17-20
  • Stability of organic transistors Organic Electronics Salleo, A., Chabinyc, M., L. edited by Klauk, H. Wiley-VCH Verlag. 2006: 1
  • Jet printing flexible displays Materials Today Street, R., A., Wong, W., S., Ready, S., E., Chabinyc, M., L., Arias, A., C., Limb, S., Salleo, A. 2006; 9: 32
  • Microstructural effects on the performance of poly(thiophene) thin-film-transistors Salleo, A., Jimison, L., H., Donovan, M., M., Chabinyc, M., L., Toney, M., F. 2006
  • Printing methods and materials for large-area electronic devices PROCEEDINGS OF THE IEEE Chabinyc, M. L., Wong, W. S., Arias, A. C., Ready, S., Lujan, R. A., Daniel, J. H., Krusor, B., Apte, R. B., Salleo, A., Street, R. A. 2005; 93 (8): 1491-1499
  • Polymer thin-film transistor arrays patterned by stamping ADVANCED FUNCTIONAL MATERIALS Salleo, A., Wong, W. S., Chabinyc, M. L., Paul, K. E., Street, R. A. 2005; 15 (7): 1105-1110
  • Transport in polycrystalline polymer thin-film transistors PHYSICAL REVIEW B Street, R. A., Northrup, J. E., Salleo, A. 2005; 71 (16)
  • Reversible and irreversible trapping in poly(thiophene) thin-film-transistors Applied Physics Letters Salleo, A., Endicott, F., Street, R., A. 2005; 86: 263505
  • Printed active-matrix TFT arrays for x-ray imaging MEDICAL IMAGING 2005: PHYSICS OF MEDICAL IMAGING, PTS 1 AND 2 Street, R. A., Wong, W. S., Ready, S., Lujan, R., Arias, A. C., Chabinyc, M. L., Salleo, A., Apte, R., Antonuk, L. E. 2005; 5745: 7-17

    View details for DOI 10.1117/12.593521

    View details for Web of Science ID 000229929500002

  • Polymer thin-film-transistor arrays patterned by stamping Advanced Functional Materials Salleo, A., Wong, W., S., Chabinyc, M., L., Paul, K., E., Street, R., A. 2005; 15: 1105
  • Printing Methods and Materials for Large-Area Electronic Devices Chabinyc, M., L., Wong, W., S., Arias, A., C., Ready, S., E., Lujan, R., Daniel, J., H., Salleo, A. 2005
  • Transport in polycrystalline polymer TFTs Physical Review B Street, R., A., Northrup, J., E., Salleo, A. 2005; 71: 165202
  • Materials requirements and fabrication of active matrix arrays of organic thin-film transistors for displays CHEMISTRY OF MATERIALS Chabinyc, M. L., Salleo, A. 2004; 16 (23): 4509-4521

    View details for DOI 10.1021/cm049647z

    View details for Web of Science ID 000225078600013

  • Lamination method for the study of interfaces in polymeric thin film transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Chabinyc, M. L., Salleo, A., Wu, Y. L., Liu, P., Ong, B. S., Heeney, M., McCulloch, I. 2004; 126 (43): 13928-13929

    Abstract

    A method for the fabrication of polymeric thin-film transistors (TFTs) by lamination is described. Poly(dimethylsiloxane) stamps were used to delaminate thin films of semiconducting polymers from silicon wafers coated with a self-assembled monolayer (SAM) formed from octyltrichlorosilane. These supported films were laminated onto electrode structures to form coplanar TFTs. The fabrication process was used to make TFTs with poly(3-hexylthiophene), P3HT, and poly[5,5'-bis(3-dodecyl-2-thienyl)-2,2'-bithiophene], PQT-12. TFTs, where these polymers were laminated onto gate dielectrics coated with SAMs from octyltrichlorosilane, had effective field-effect mobilities of 0.03 and 0.005 cm2/(V s), respectively. TFTs where PQT-12 was laminated onto gate dielectrics that were not coated with a SAM also had mobility of 0.03 cm2/(V s). In contrast, TFTs fabricated by spin-coating PQT-12 onto the same structure had mobilities ranging from 10-3 to 10-4 cm2/(V s). These results suggest that the lower mobilities of polymer TFTs made with hydrophilic gate dielectrics are caused by molecular ordering in the semiconducting film rather than electronic effects of dipolar groups at the interface.

    View details for DOI 10.1021/ja044884o

    View details for Web of Science ID 000224873600026

    View details for PubMedID 15506746

  • All jet-printed polymer thin-film transistor active-matrix backplanes APPLIED PHYSICS LETTERS Arias, A. C., Ready, S. E., Lujan, R., Wong, W. S., Paul, K. E., Salleo, A., Chabinyc, M. L., Apte, R., Street, R. A., Wu, Y., Liu, P., ONG, B. 2004; 85 (15): 3304-3306

    View details for DOI 10.1063/1.1801673

    View details for Web of Science ID 000224679300103

  • Localized state effects in polymer thin film transistors JOURNAL OF NON-CRYSTALLINE SOLIDS Street, R. A., Salleo, A., Chabinyc, M., Paul, K. 2004; 338: 607-611
  • Kinetics of Bias-stress and Bipolaron formation in regio-regular poly(thiophene) Physical Review B Salleo, A., Street, R., A. 2004; 23 (70): 235324
  • Printed polymer transistors and display backplanes Arias, A., C., Ready, S., E., Lujan, R., A., Wong, W., S., Paul, K., E., Chabinyc, M., L., Salleo, A. 2004
  • Short-channel effects in regio-regular poly(thiophene) thin-film transistors Chabinyc, M., L., Lu, J., P., Salleo, A., Street, R., A. 2004
  • Materials requirements and fabrication of active matrix arrays of organic thin-film-transistors for displays special issue of Chemistry of Materials on Organic Electronics Chabinyc, M., L., Salleo, A. 2004; 23 (16): 4509
  • Intrinsic hole mobility and trapping in regio-regular poly(thiophene) Physical Review B Salleo, A., Chen, T., W., Volkel, A., Wu, Y., Liu, P., Ong, B., S. 2004; 7 (70): 115311
  • Organic Electronics Flexible Flat Panel Displays Apte, R., B., Ong, B., S., Street, R., A., Salleo, A., Chabinyc, M., L., Arias, A., C. edited by Crawford, G., P. 2004: 1
  • Localized state effects in polymer thin-film transistors Journal of Non-Crystalline Solids Street, R., A., Salleo, A., Chabinyc, M., L. 2004; 338-340: 607
  • Lamination Method for the Study of Interfaces in Polymeric Thin Film Transistors Journal of the American Chemical Society-Communication Chabinyc, M., L., Salleo, A., Wu, Y., Liu, P., Ong, B., S., Heeney, M. 2004; 43 (126): 13928
  • All jet-printed polymer thin film transistor active-matrix backplanes Applied Physics Letters Arias, A., C., Ready, S., E., Lujan, R., Wong, W., S., Paul, K., E., Salleo, A. 2004; 15 (85): 3304
  • Bipolaron mechanism for bias-stress effects in polymer transistors PHYSICAL REVIEW B Street, R. A., Salleo, A., Chabinyc, M. L. 2003; 68 (8)
  • Light-induced bias stress reversal in polyfluorene thin film transistors Journal of Applied Physics Salleo, A., Street, R., A. 2003; 1 (94): 471
  • Printed polymer transistor arrays for displays and imaging Paul, E., Wong, W., S., Chabinyc, M., L., Salleo, A., Ready, S., E., Apte, R., B. 2003
  • Bipolaron mechanism for bias-stress effects in organic transistors Physical Review B Street, R., A., Salleo, A., Chabinyc, M., L. 2003; 8 (68): 85316
  • Laser driven phase transformations in amorphous silica Nature Materials Salleo, A., Taylor, S., T., Martin, M., C. 2003; 12 (2): 796
  • Polymer thin-film transistors with chemically modified dielectric interfaces APPLIED PHYSICS LETTERS Salleo, A., Chabinyc, M. L., Yang, M. S., Street, R. A. 2002; 81 (23): 4383-4385

    View details for DOI 10.1063/1.1527691

    View details for Web of Science ID 000179481900024

  • Organic polymeric thin-film transistors fabricated by selective dewetting APPLIED PHYSICS LETTERS Chabinyc, M. L., Wong, W. S., Salleo, A., Paul, K. E., Street, R. A. 2002; 81 (22): 4260-4262

    View details for DOI 10.1063/1.1524301

    View details for Web of Science ID 000179340800054

  • Contact effects in polymer transistors Applied Physics Letters Street, R., A., Salleo, A. 2002; 15 (81): 2887
  • Fabrication processes for polymeric organic transistors Salleo, A., Chabinyc, M., L., Paul, K., E., Apte, R., B., Street, R., A., Ong, B., S. 2002
  • Continuous-wave InGaN laser diodes on copper and diamond substrates Journal of Materials Research Wong, W., S., Kneissl, M., Treat, D., W., Panero, M., Miyashita, N., Salleo, A. 2002; 4 (17): 1
  • Organic Polymeric Thin Film Transistors Fabricated by Selective Dewetting Applied Physics Letters Chabinyc, M., L., Wong, W., S., Salleo, A., Paul, K., E., Street, R., A. 2002; 22 (81): 4260
  • High-resolution jet printing for fabrication of a Si:H thin film transistors and arrays Wong, W., S., Ready, S., E., Matusiak, R., White, S., D., Lu, J., P., Ho, J., H., Salleo, A. 2002
  • Polymer thin-film transistors with chemically modified dielectric interfaces Applied Physics Letters Salleo, A., Chabinyc, M., L., Street, R., A., Yang, M., S. 2002; 23 (81): 4383
  • Energy deposition at front and rear surfaces during picosecond laser interaction with fused silica Applied Physics Letters Salleo, A., Génin, F., Y., Feit, M., D., Teepe, A., M., Sands, T., Russo, R., E. 2001; 19 (78): 2840
  • Role of light intensification by cracks in optical breakdown on surfaces Journal of the Optical Society of America A Génin, F., Y., Salleo, A., Pistor, T., V., Chase, L., L. 2001; 10 (18): 2607
  • Rear surface laser damage on 355 nm silica optics due to Fresnel diffraction at front surface contamination particles Applied Optics Génin, F., Y., Feit, M., D., Kozlowski, M., R., Rubenchik, A., M., Salleo, A., Yoshiyama, J. 2000; 21 (39): 3654-3663
  • Machining of transparent materials using an IR and UV nanosecond pulsed laser Applied Physics A Salleo, A., Sands, T., Génin, F., Y. 2000; 6 (71): 601-608
  • Integration of GaN Thin Films with Dissimilar Substrate Materials by Pd-In Metal Bonding and Laser Liftoff Journal of Electronic Materials Wong, W., S., Wengrow, A., B., Cho, Y., Salleo, A., Quitoriano, N., J., Cheung, N., W. 1999; 12 (28): 1409-13
  • Crack propagation in fused silica during UV and IR ns-laser illumination. Salleo, A., Chinsio, R., Génin, F., Y. edited by Exarhos et al., G., J. 1999
  • Modeling of laser-induced surface cracks in silica at 355 nm Feit, M., D., Campbell, J., Faux, D., Génin, F., Y., Kozlowski, M., R., Rubenchik, A., M., Salleo, A. edited by Exarhos et al., G., J. 1998
  • Characterization of nodular and thermal defects in hafnia/silica multilayer coatings using optical, photothermal, and atomic force microscopy Stolz, C., J., Yoshiyama, J., M., Salleo, A., Wu, Z., L., Green, J., Krupka, R. edited by Exarhos et al., G., J. 1998
  • Laser-induced damage of fused silica at 355 nm initiated at scratches Salleo, A., Génin, F., Y., Yoshiyama, J., Stolz, C., J., Kozlowski, M., R. edited by Exarhos et al., G., J. 1998
  • Pulse-shape and pulse-length scaling of ns pulse laser damage threshold due to rate limiting by thermal conduction. Feit, M., D., Rubenchik, A., M., Salleo, A., Eimerl, D. edited by Exarhos et al., G., J. 1998
  • Effects of polishing, etching, cleaving, and water leaching on the UV laser damage of fused silica Yoshiyama, J., Génin, F., Y., Salleo, A., Thomas, I., Kozlowski, M., R., Sheehan, L., M. edited by Exarhos et al., G., J. 1998
  • Influence of external mechanical loadings (creep, fatigue) on oxygen diffusion during nickel oxidation. Oxidation of Metals Moulin, G., Arevalo, P., Salleo, A. 1996; 1-2 (45): 153-181
  • High temperature reactivity of different forms of carbon at low oxygen fugacity Solid State Ionics, Diffusions & Reactions Gozzi, D., Guzzardi, G., Salleo, A. 1996; 3-4 (83): 177-189