Estimation of the charge injection of low-density polyethylene in a double-layer structure: From mathematical fitting to simulation

Polymer materials have excellent electrical insulation properties and play a crucial role in high-voltage direct current equipment. Unlike the electric field–current relationship at the low-density polyethylene (LDPE)/Al interface with a single-layer LDPE sample, which approximates the Schottky relationship, this study employed a double-layer sample structure to establish unipolar conditions, thereby eliminating the influence of extraction current, displacement current, and electric field distortion present under bipolar conditions. The electric field–current relationship at different temperatures was derived. The relationship between the injection current and the electric field mathematically fit the Poole–Frenkel effect, rather than the Schottky effect, and the charge injection barrier, the trap depth, and carrier mobility were calculated. To validate the obtained parameters, this paper proposes an improved bipolar charge transport model and conducts simulations of space charge, current, and electric field. The simulation results with the Poole–Frenkel injection parameters fit the dynamics of space charge and current under different voltages and temperatures well. The temporal evolution of the electric field and the injection current under various conditions, along with their correlation, demonstrates remarkable agreement with the experimental results. In contrast, simulation results based on the approximate Schottky parameters obtained under bipolar conditions did not match the experimental outcomes. It indicates that the Poole–Frenkel effect is more accurate for describing the charge injection process, especially in the analysis of space charge and current dynamic characters.