Atomistic Modeling of Charge Injection Into Dielectric Polymers

Electrical degradation and electric field distortion in polymers are inherently determined by their charge transfer and charge injection properties. In this contribution, we have proposed a first-principles-based multi-scale modeling approach for describing charge injection into dielectric polymers. First-principles calculations and molecular dynamics (MD) simulations are performed to determine the microscopic physical quantities that enter the non-empirical formula describing charge injection. It is shown that, among the several well-known charge injection models, the disorder-based injection model is relatively appropriate for modeling carrier injection from the electrode into dielectric polymers. From a theoretical point of view, the field emission (FE) and the thermal emission (TE) models are unsuitable for describing charge injection into dielectrics, and the agreement between experimental data and the injection current predicted by these models is most likely accidental. According to the disorder-based injection model, in line with the experimental findings, the simulated injection current increases rapidly at the field above
$10^{{2}}$
kV/mm. The computational results indicate that the carriers would be injected from the amorphous region rather than from the crystalline region and that the impurity or interface states play a crucial role in charge injection. Novel non-empirical theoretical models taking into account these mid-gap states are required to describe the injection current into dielectric polymers.