Kang Jiheong, Mun Jaewan, Zheng Yu, Koizumi Masato, Matsuhisa Naoji, Wu Hung-Chin, Chen Shucheng, Tok Jeffrey B-H, Lee Gae Hwang, Jin Lihua, Bao Zhenan
Department of Chemical Engineering, Stanford University, Stanford, CA, USA.
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea.
Nat Nanotechnol. 2022 Dec;17(12):1265-1271. doi: 10.1038/s41565-022-01246-6. Epub 2022 Nov 10.
Semiconducting polymer thin films are essential elements of soft electronics for both wearable and biomedical applications. However, high-mobility semiconducting polymers are usually brittle and can be easily fractured under small strains (<10%). Recently, the improved intrinsic mechanical properties of semiconducting polymer films have been reported through molecular design and nanoconfinement. Here we show that engineering the interfacial properties between a semiconducting thin film and a substrate can notably delay microcrack formation in the film. We present a universal design strategy that involves covalently bonding a dissipative interfacial polymer layer, consisting of dynamic non-covalent crosslinks, between a semiconducting thin film and a substrate. This enables high interfacial toughness between the layers, suppression of delamination and delocalization of strain. As a result, crack initiation and propagation are notably delayed to much higher strains. Specifically, the crack-onset strain of a high-mobility semiconducting polymer thin film improved from 30% to 110% strain without any noticeable microcracks. Despite the presence of a large mismatch in strain between the plastic semiconducting thin film and elastic substrate after unloading, the tough interface layer helped maintain bonding and exceptional cyclic durability and robustness. Furthermore, we found that our interfacial layer reduces the mismatch of thermal expansion coefficients between the different layers. This approach can improve the crack-onset strain of various semiconducting polymers, conducting polymers and even metal thin films.
半导体聚合物薄膜是可穿戴和生物医学应用中软电子器件的关键元件。然而，高迁移率的半导体聚合物通常很脆，在小应变（<10%）下很容易断裂。最近，通过分子设计和纳米限域，已报道了半导体聚合物薄膜本征机械性能的改善。在此，我们表明，调控半导体薄膜与衬底之间的界面性质可显著延迟薄膜中微裂纹的形成。我们提出了一种通用的设计策略，即在半导体薄膜与衬底之间共价键合一个由动态非共价交联组成的耗散性界面聚合物层。这使得层间具有高界面韧性，抑制分层并使应变离域。结果，裂纹萌生和扩展显著延迟至更高的应变。具体而言，高迁移率半导体聚合物薄膜的裂纹起始应变从30%提高到110%应变，且无任何明显的微裂纹。尽管卸载后塑性半导体薄膜与弹性衬底之间存在较大的应变失配，但坚韧的界面层有助于维持粘结以及卓越的循环耐久性和稳健性。此外，我们发现我们的界面层降低了不同层之间热膨胀系数的失配。这种方法可提高各种半导体聚合物、导电聚合物甚至金属薄膜的裂纹起始应变。
