Wang Yifei, Nasreen Shamima, Kamal Deepak, Li Zongze, Wu Chao, Huo Jindong, Chen Lihua, Ramprasad Rampi, Cao Yang
Electrical Insulation Research Center, Institute of Materials Science, University of Connecticut, 97 N Eagleville Road, Storrs, Connecticut 06269, United States.
School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta, Georgia 30332, United States.
ACS Appl Mater Interfaces. 2021 Sep 29;13(38):46142-46150. doi: 10.1021/acsami.1c12854. Epub 2021 Sep 14.
Metal-polymer interface plays a crucial role in controlling the dielectric performance in all flexible electronics. Ideally, the formation of the Schottky barrier due to the large band offset of the electron affinity of the polymer over the work function of the electrode should sufficiently impede the charge injection. Arguably, however, such an injection barrier has hardly been indisputably verified in polymer-metal junctions due to the ever-existing surface states, which dramatically compromise the barrier thus leading to undesired high electrical conduction. Here, we demonstrate experimentally a clear negative correlation between the breakdown strength and the density of surface states in polymer dielectrics. The existence of surface states reduces the effective barrier height for charge injection, as further revealed by density functional theory calculations and photoinjection current measurements. Based on these findings, we present a surface engineering method to enhance the breakdown strength with the application of nanocoatings on polymer films to eliminate surface states. The density of surface states is reduced by 2 orders of magnitude when the polymer is coated with a layer of two-dimensional hexagonal boron nitride nanosheets, leading to about 100% enhancement of breakdown strength. This work reveals the critical role played by surface states on electrical breakdown and provides a versatile surface engineering strategy to curtail surface states, broadly applicable for all polymer dielectrics.
金属-聚合物界面在所有柔性电子产品的介电性能控制中起着至关重要的作用。理想情况下，由于聚合物的电子亲和势与电极功函数之间存在较大的能带偏移而形成的肖特基势垒应能充分阻碍电荷注入。然而，可以说，由于始终存在的表面态，这种注入势垒在聚合物-金属结中几乎从未得到无可争议的验证，表面态极大地削弱了势垒，从而导致不希望出现的高电导率。在此，我们通过实验证明了聚合物电介质的击穿强度与表面态密度之间存在明显的负相关。密度泛函理论计算和光注入电流测量进一步表明，表面态的存在降低了电荷注入的有效势垒高度。基于这些发现，我们提出了一种表面工程方法，通过在聚合物薄膜上应用纳米涂层来消除表面态，从而提高击穿强度。当聚合物涂覆一层二维六方氮化硼纳米片时，表面态密度降低了2个数量级，击穿强度提高了约100%。这项工作揭示了表面态在电击穿中所起的关键作用，并提供了一种通用的表面工程策略来减少表面态，广泛适用于所有聚合物电介质。
