Numerical Capacitance Analysis of Single-Layer OLEDs Based on the Master Equation

We present the simulations of the small-signal capacitance characteristics of organic light-emitting diodes based on the master equation for a 3-D lattice solved under the sinusoidal steady-state condition. Small-signal measurements and current-voltage characteristics by Martens et al. can be simultaneously reproduced with appropriate parameters. According to our simulations, the frequently observed effect of a negative differential capacitance at low frequencies is affected by several parameters. It becomes more pronounced with longer recombination lifetime, lower injection barrier, and higher energetic disorder.