Simulation on the influence of bipolar charge injection and trapping on surface potential decay of polyethylene

The surface potential decay (SPD) properties of low-density polyethylene (LDPE) are determined by charge injection and volume charge transport properties. We adopt a bipolar charge transport (BCT) model to investigate the SPD properties of LDPE with the consideration of time dependent charging process. The non-linear charge continuity equation in the BCT model is solved by a finite differential weighted essentially nonoscillatory (WENO) method that is high stable and high order accurate. Poisson's equation is resolved by Boundary Element method (BEM). We obtain the analytical and numerical SPDs in the case of single charge carrier injection and the agreement of analytical and numerical results is excellent. After analyzing the numerical SPD and space charge results at bipolar charge injection, we find that SPD crossover phenomena occur when the hole injection barrier between the insulator and the grounded electrode is relative low. The SPD crossover occurs when the grid voltage exceeds a threshold value. Moreover, it is also found that the SPD crossover is affected by charge trapping/detrapping properties.