Revelation of charge injection barrier at metal/thermal degraded epoxy resin interface by molecular dynamics and first-principles calculation

Molecular defects caused by the thermally degraded epoxy resin (EP) play significant roles in space charges of insulation in high-voltage power devices. This paper investigates the influence of molecular by-products of thermal degraded EP on charge injection at the electrode/EP interface. Interface structure models of the Cu (111) electrode/EP thermal decomposition molecules were studied by molecular simulation. Thermally degraded EP introduces CO, CO2, CH2O, H2O, and various small organic molecules. Compared to that of pure EP (3.08 eV), the majority of molecular defects enhance electron injection by reducing the electron injection barrier. Ethylene and vinyl alcohol reduce the electron injection barrier (∼1.6 eV). The carbon–carbon double bond (C=C) exhibits a significant decrease in the injection barrier. However, the hole injection barrier for all molecular products is higher than that of the epoxy molecular fragment. Except for formaldehyde and phenol molecules, space charge accumulation at the interface increases with the thermal degradation of EP. The Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectra of the aged EP samples verify the molecular dynamics simulation results. The findings are useful for improving the reliability of insulation in high-power density electric devices.