Theory of Hole Injection and Conductivity in Organic Materials

Abstract

The relationship between current and applied voltage is calculated for a process in which a given number of charge carriers of one sign is injected into matter which contains only a negligible density of charges of the opposite sign. Diffusion effects are taken into account approximately. The current‐voltage relationship depends strongly on the image force exerted on the injected carriers near the electrode. The calculated current‐voltage curve agrees qualitatively with that observed in anthracene under light excitation. The voltage at which saturation is approached can be calculated and depends upon a recombination velocity of the injected charge with the injecting electrode, and upon the image force. Different saturation voltages for various electrodes can be explained by a difference in recombination velocities. The dependence of the saturation voltage upon the intensity of the saturation current is also explained. For anthracene, the recombination between holes and a water electrode is expressed as a velocity much greater than thermal velocities.