All Publications

  • Tough and Water-Insensitive Self-Healing Elastomer for Robust Electronic Skin ADVANCED MATERIALS Kang, J., Son, D., Wang, G., Liu, Y., Lopez, J., Kim, Y., Oh, J., Katsumata, T., Mun, J., Lee, Y., Jin, L., Tok, J., Bao, Z. 2018; 30 (13): e1706846


    An electronic (e-) skin is expected to experience significant wear and tear over time. Therefore, self-healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e-skin. However, previously reported elastomers and especially self-healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch-insensitive high stretchability (1200%), high toughness of 12 000 J m-2 , and autonomous self-healing even in artificial sweat. The tough self-healing materials enable the wafer-scale fabrication of robust and stretchable self-healing e-skin devices, which will provide new directions for future soft robotics and skin prosthetics.

    View details for DOI 10.1002/adma.201706846

    View details for Web of Science ID 000428793600027

    View details for PubMedID 29424026

  • Skin electronics from scalable fabrication of an intrinsically stretchable transistor array NATURE Wang, S., Xu, J., Wang, W., Wang, G., Rastak, R., Molina-Lopez, F., Chung, J., Niu, S., Feig, V. R., Lopez, J., Lei, T., Kwon, S., Kim, Y., Foudeh, A. M., Ehrlich, A., Gasperini, A., Yun, Y., Murmann, B., Tok, J., Bao, Z. 2018; 555 (7694): 83-+


    Skin-like electronics that can adhere seamlessly to human skin or within the body are highly desirable for applications such as health monitoring, medical treatment, medical implants and biological studies, and for technologies that include human-machine interfaces, soft robotics and augmented reality. Rendering such electronics soft and stretchable-like human skin-would make them more comfortable to wear, and, through increased contact area, would greatly enhance the fidelity of signals acquired from the skin. Structural engineering of rigid inorganic and organic devices has enabled circuit-level stretchability, but this requires sophisticated fabrication techniques and usually suffers from reduced densities of devices within an array. We reasoned that the desired parameters, such as higher mechanical deformability and robustness, improved skin compatibility and higher device density, could be provided by using intrinsically stretchable polymer materials instead. However, the production of intrinsically stretchable materials and devices is still largely in its infancy: such materials have been reported, but functional, intrinsically stretchable electronics have yet to be demonstrated owing to the lack of a scalable fabrication technology. Here we describe a fabrication process that enables high yield and uniformity from a variety of intrinsically stretchable electronic polymers. We demonstrate an intrinsically stretchable polymer transistor array with an unprecedented device density of 347 transistors per square centimetre. The transistors have an average charge-carrier mobility comparable to that of amorphous silicon, varying only slightly (within one order of magnitude) when subjected to 100 per cent strain for 1,000 cycles, without current-voltage hysteresis. Our transistor arrays thus constitute intrinsically stretchable skin electronics, and include an active matrix for sensory arrays, as well as analogue and digital circuit elements. Our process offers a general platform for incorporating other intrinsically stretchable polymer materials, enabling the fabrication of next-generation stretchable skin electronic devices.

    View details for DOI 10.1038/nature25494

    View details for Web of Science ID 000426247600036

    View details for PubMedID 29466334

  • 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)
  • Stretchable Polymer Semiconductors for Plastic Electronics ADVANCED ELECTRONIC MATERIALS Wang, G., Gasperini, A., Bao, Z. 2018; 4 (2)
  • Understanding the Impact of Oligomeric Polystyrene Side Chain Arrangement on the All-Polymer Solar Cell Performance ADVANCED ENERGY MATERIALS Kurosawa, T., Gu, X., Gu, K. L., Zhou, Y., Yan, H., Wang, C., Wang, G., Toney, M. F., Bao, Z. 2018; 8 (2)
  • The Effects of Counter Anions on the Dynamic Mechanical Response in Polymer Networks Crosslinked by Metal-Ligand Coordination JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Rao, Y., Feig, V., Gu, X., Wang, G., Bao, Z. 2017; 55 (18): 3110–16

    View details for DOI 10.1002/pola.28675

    View details for Web of Science ID 000406937100029

  • Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains ADVANCED FUNCTIONAL MATERIALS Schroeder, B. C., Kurosawa, T., Fu, T., Chiu, Y., Mun, J., Wang, G., Gu, X., Shaw, L., Kneller, J. E., Kreouzis, T., Toney, M. F., Bao, Z. 2017; 27 (34)
  • Highly stretchable polymer semiconductor films through the nanoconfinement effect SCIENCE Xu, J., Wang, S., Wang, G. N., Zhu, C., Luo, S., Jin, L., Gu, X., Chen, S., Feig, V. R., To, J. W., Rondeau-Gagne, S., Park, J., Schroeder, B. C., Lu, C., Oh, J. Y., Wang, Y., Kim, Y., Yan, H., Sinclair, R., Zhou, D., Xue, G., Murmann, B., Linder, C., Cai, W., Tok, J. B., Chung, J. W., Bao, Z. 2017; 355 (6320): 59-?


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

    View details for DOI 10.1126/science.aah4496

    View details for Web of Science ID 000391739900042

    View details for PubMedID 28059762

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


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

    View details for DOI 10.1038/nature20102

    View details for Web of Science ID 000388161700050

    View details for PubMedID 27853213

  • Inducing Elasticity through Oligo-Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers ADVANCED FUNCTIONAL MATERIALS Wang, G. N., Shaw, L., Xu, J., Kurosawa, T., Schroeder, B. C., Oh, J. Y., Benight, S. J., Bao, Z. 2016; 26 (40): 7254-7262