Charge injection and recombination at the metal-organic interface

We consider the mechanism of charge injection from metals into amorphous organic semiconductors. By first treating charge recombination at the interface as a hopping process in the image potential, we obtain an expression for the surface recombination rate. The principle of detailed balance is then used to determine the injection current. This simple approach yields the effective Richardson constant for injection from metal to organic, and provides a means to derive the electric field dependence of thermionic injection. The result for the net current, injected minus recombination, is in agreement with a more exact treatment of the drift-diffusion equation.