Tuning Surface States of Metal/Polymer Contacts Toward Highly Insulating Polymer-Based Dielectrics

Abstract

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 everexisting 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.

Deep Well Trapping of Hot Carriers in a Hexagonal Boron Nitride Coating of Polymer Dielectrics

“…While the key point of this study is the deep potential located in the BN coating layer, other experiments such as photocurrent injection measurement can also provide complementary information such as barrier height between the electrode and the polymer as well as the surface states. A recent study of hBN using photocurrent injection measurements has indeed showed the ability of hBN nanocoats to reduce surface states at polymer−metal interfaces, 40 further corroborating the carrier trapping reported here.…”

High-energy-density polymer dielectrics via compositional and structural tailoring for electrical energy storage

“…The polymer-based dielectrics must withstand ever-increasing and enormous operating electric fields, but a clear negative correlation between U e and E b of surface states in polymer dielectrics has been demonstrated experimentally ( Wang et al., 2021 ). The surface state dramatically reduces the charge injection barrier height lead to high electrical conduction.…”

Molecular Simulation of Electron Traps in Epoxy Resin/Graphene Oxide Nanocomposites

“…Epoxy resin (EP) is widely used in the insulation of electrical equipment and electronic devices. However, the distortion of the electric field induced by space charge injection caused by high field and temperature gradient aggravates the breakdown and electrical tree of insulation materials [ 1 , 2 , 3 , 4 ], which seriously threatens the safe and stable operation of power equipment. Therefore, it is urgent to study high-performance direct current insulation materials.…”