Extremely Non-Equilibrium Hopping Transport and Photogeneration Efficiency in Organic Semiconductors: An Analytic Approach

An analytical model of highly nonequilibrium hopping transport of charge carriers in disordered organic semiconductors has been developed. In particular, the initial time interval is considered when transport is controlled by hops down in energy. The model is applied to the calculation of the separation probability of geminate pairs in a semiconductor with a Gaussian energy distribution of localized states. This probability determines the photogeneration efficiency. The temperature dependence of the separation probability is obtained and shown to be much weaker than predicted by the classical Onsager model, in agreement with experiment and Monte Carlo simulations. The field dependence is taken into account using a modified effective temperature method.