Modeling the low-voltage regime of organic diodes: Origin of the ideality factor

This paper investigates the physics of single-layer organic diodes in the low-voltage regime. A simple analytical model is developed to describe the current-voltage characteristics of the device. At variance with what is often reported in the literature, the operating mechanism of the organic diode is closer to that of the p-n junction than that of the conventional Schottky diode. The influence of an exponential distribution of traps is also analyzed. Alongside a drastic reduction of the current at above-diffusion-potential regime, traps introduce a substantial ideality factor in the low-voltage current. Two-dimensional physically based simulations are carried out in order to ascertain the validity of our model. By including trap effects, device simulation could fairly fit the experimental data of the organic diodes made of vacuum-evaporated pentacene. (C) 2011 American Institute of Physics. [doi:10.1063/1.3660221]