Electrostatic capacitance in single and double layer organic diodes

The electrostatic capacitance-voltage characteristics of single and double layer organic diodes are explored by numerical simulation and theoretical analysis. For single layer devices, the capacitance in the high voltage limit is approximately 3/2 times the geometric capacitance C0 for unipolar carrier injection or ambipolar injection with high recombination rates, and 4/πC0 for symmetric ambipolar injection with low recombination rates. For double layer devices, the capacitance is determined by the relative charge distribution at the contacts, in the bulk region of the two layers, and at their interface. The charge distribution is affected by the injection barrier height and by exciplex-controlled interface recombination.