Effect of Square Wave Electric Field on Electroluminescence in Polyimide: Testing and Modeling

Under square wave electric fields, charge transport and associated energy dissipation drive the aging and degradation of polymer insulations. During this process, part of the energy is released in the form of photon emission namely electroluminescence (EL). As one of the excitation mechanisms of EL, charge recombination links the charge dynamics with energy transfer, providing a point for revealing the underlying physical mechanisms of EL. In this paper, the effect of the square wave parameters on EL in polyimide (PI) is experimentally and numerically investigated. A recombination dynamics simulation based on the bipolar charge transport (BCT) model is adopted to reproduce the EL performance under square wave voltage with a wide frequency range. Further analysis indicates that EL behavior is determined by the charge distribution under the square wave electric field. The intensity and distribution of recombination-induced EL are jointly regulated by frequency and rise time, which exhibits characteristic turning points related to these two square wave parameters. Moreover, EL is likely to concentrate near the interface of the material, suggesting that the insulation aging caused by energy dissipation may be a long-term evolution of gradual penetration from the interface to the interior.