Professional Education


  • Doctor of Philosophy, National Taiwan University (2015)

Stanford Advisors


All Publications


  • Multi-scale ordering in highly stretchable polymer semiconducting films. Nature materials Xu, J., Wu, H., Zhu, C., Ehrlich, A., Shaw, L., Nikolka, M., Wang, S., Molina-Lopez, F., Gu, X., Luo, S., Zhou, D., Kim, Y., Wang, G. N., Gu, K., Feig, V. R., Chen, S., Kim, Y., Katsumata, T., Zheng, Y., Yan, H., Chung, J. W., Lopez, J., Murmann, B., Bao, Z. 2019

    Abstract

    Stretchable semiconducting polymers have been developed as a key component to enable skin-like wearable electronics, but their electrical performance must be improved to enable more advanced functionalities. Here, we report a solution processing approach that can achieve multi-scale ordering and alignment of conjugated polymers in stretchable semiconductors to substantially improve their charge carrier mobility. Using solution shearing with a patterned microtrench coating blade, macroscale alignment of conjugated-polymer nanostructures was achieved along the charge transport direction. In conjunction, the nanoscale spatial confinement aligns chain conformation and promotes short-range pi-pi ordering, substantially reducing the energetic barrier for charge carrier transport. As a result, the mobilities of stretchable conjugated-polymer films have been enhanced up to threefold and maintained under a strain up to 100%. This method may also serve as the basis for large-area manufacturing of stretchable semiconducting films, as demonstrated by the roll-to-roll coating of metre-scale films.

    View details for PubMedID 30988452

  • Characterization of Hydrogen Bonding Formation and Breaking in Semiconducting Polymers under Mechanical Strain MACROMOLECULES Gasperini, A., Wang, G., Molina-Lopez, F., Wu, H., Lopez, J., Xu, J., Luo, S., Zhou, D., Xue, G., Tok, J., Bao, Z. 2019; 52 (6): 2476–86
  • Synthesis and Properties of Soluble Fused Thiophene Diketopyrrolopyrrole-Based Polymers with Tunable Molecular Weight MACROMOLECULES Niu, W., Wu, H., Matthews, J. R., Tandia, A., Li, Y., Wallace, A. L., Kim, J., Wang, H., Li, X., Mehrotra, K., Bao, Z., He, M. 2018; 51 (23): 9422–29
  • Effect of Nonconjugated Spacers on Mechanical Properties of Semiconducting Polymers for Stretchable Transistors ADVANCED FUNCTIONAL MATERIALS Mun, J., Wang, G., Oh, J., Katsumata, T., Lee, F. L., Kang, J., Wu, H., Lissel, F., Rondeau-Gagne, S., Tok, J., Bao, Z. 2018; 28 (43)
  • Enhanced Charge Transport and Stability Conferred by Iron(III)-Coordination in a Conjugated Polymer Thin-Film Transistors ADVANCED ELECTRONIC MATERIALS Wu, H., Rondeau-Gagne, S., Chiu, Y., Lissel, F., To, J. F., Tsao, Y., Oh, J., Tang, B., Chen, W., Tok, J., Bao, Z. 2018; 4 (9)
  • Efficient and UV-stable perovskite solar cells enabled by side chain-engineered polymeric hole-transporting layers JOURNAL OF MATERIALS CHEMISTRY A Tsai, C., Li, N., Lee, C., Wu, H., Zhu, Z., Wang, L., Chen, W., Yan, H., Chueh, C. 2018; 6 (27): 12999–3004

    View details for DOI 10.1039/c8ta03608j

    View details for Web of Science ID 000438548800013

  • Nonhalogenated Solvent Processable and Printable High-Performance Polymer Semiconductor Enabled by Isomeric Nonconjugated Flexible Linkers MACROMOLECULES Wang, G., Molina-Lopez, F., Zhang, H., Xu, J., Wu, H., Lopez, J., Shaw, L., Mun, J., Zhang, Q., Wang, S., Ehrlich, A., Bao, Z. 2018; 51 (13): 4976–85
  • Enhancing Molecular Alignment and Charge Transport of Solution-Sheared Semiconducting Polymer Films by the Electrical-Blade Effect ADVANCED ELECTRONIC MATERIALS Molina-Lopez, F., Wu, H., Wang, G., Yan, H., Shaw, L., Xu, J., Toney, M. F., Bao, Z. 2018; 4 (7)
  • Quadruple H-Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yan, X., Liu, Z., Zhang, Q., Lopez, J., Wang, H., Wu, H., Niu, S., Yan, H., Wang, S., Lei, T., Li, J., Qi, D., Huang, P., Huang, J., Zhang, Y., Wang, Y., Li, G., Tok, J., Chen, X., Bao, Z. 2018; 140 (15): 5280–89

    Abstract

    Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-1-3) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-2 was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m2), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics.

    View details for PubMedID 29595956

  • Deformable Organic Nanowire Field-Effect Transistors ADVANCED MATERIALS Lee, Y., Oh, J., Kim, T., Gu, X., Kim, Y., Wang, G., Wu, H., Pfattner, R., To, J. F., Katsumata, T., Son, D., Kang, J., Matthews, J. R., Niu, W., He, M., Sinclair, R., Cui, Y., Tok, J., Lee, T., Bao, Z. 2018; 30 (7)
  • Soft Poly(butyl acrylate) Side Chains toward Intrinsically Stretchable Polymeric Semiconductors for Field-Effect Transistor Applications MACROMOLECULES Wen, H., Wu, H., Aimi, J., Hung, C., Chiang, Y., Kuo, C., Chen, W. 2017; 50 (13): 4982–92
  • n-Type Doped Conjugated Polymer for Nonvolatile Memory. Advanced materials Lee, W., Wu, H., Lu, C., Naab, B. D., Chen, W., Bao, Z. 2017

    Abstract

    This study demonstrates a facile way to efficiently induce strong memory behavior from common p-type conjugated polymers by adding n-type dopant 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole. The n-type doped p-channel conjugated polymers not only enhance n-type charge transport characteristics of the polymers, but also facilitate to storage charges and cause reversible bistable (ON and OFF states) switching upon application of gate bias. The n-type doped memory shows a large memory window of up to 47 V with an on/off current ratio larger than 10 000. The charge retention time can maintain over 100 000 s. Similar memory behaviors are also observed in other common semiconducting polymers such as poly(3-hexyl thiophene) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene], and a high mobility donor-acceptor polymer, poly(isoindigo-bithiophene). In summary, these observations suggest that this approach is a general method to induce memory behavior in conjugated polymers. To the best of the knowledge, this is the first report for p-type polymer memory achieved using n-type charge-transfer doping.

    View details for DOI 10.1002/adma.201605166

    View details for PubMedID 28234405

  • Isoindigo-Based Semiconducting Polymers Using Carbosilane Side Chains for High Performance Stretchable Field-Effect Transistors MACROMOLECULES Wu, H., Hung, C., Hong, C., Sun, H., Wang, J., Yamashita, G., Higashihara, T., Chen, W. 2016; 49 (22): 8540–48
  • 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

  • Effect of Spacer Length of Siloxane-Terminated Side Chains on Charge Transport in Isoindigo-Based Polymer Semiconductor Thin Films ADVANCED FUNCTIONAL MATERIALS Mei, J., Wu, H., Diao, Y., Appleton, A., Wang, H., Zhou, Y., Lee, W., Kurosawa, T., Chen, W., Bao, Z. 2015; 25 (23): 3455-3462
  • A Rapid and Facile Soft Contact Lamination Method: Evaluation of Polymer Semiconductors for Stretchable Transistors CHEMISTRY OF MATERIALS Wu, H., Benight, S. J., Chortos, A., Lee, W., Mei, J., To, J. W., Lu, C., He, M., Tok, J. B., Chen, W., Bao, Z. 2014; 26 (15): 4544-4551

    View details for DOI 10.1021/cm502271j

    View details for Web of Science ID 000340346300029