Charge transport and dissipative processes in insulating polymers: Experiments and model

Electroluminescence in insulating polymers signs the existence of potentially harmful excited states because the excess energy can be released through degraded pathways, opening the way to chemical degradation. Excitation mechanisms involve impact excitation/ionization by hot carriers or bi-polar charge recombination. In order to discuss the relative contribution of these processes to light emission in polyethylene, we introduce a numerical model of charge transport postulating a recombination-controlled electroluminescence. Model outputs and experimental measurements are compared for three different protocols of dc voltage application considering especially the simulated recombination rate and the measured light emission. A fairly good agreement is found between model and experiment when considering electroluminescence under constant dc stress. The model fails to describe the measurement under time-varying dc stress suggesting that excitation by hot carriers should be taken into account.