The stochastic character of hopping transport in organic disordered semiconductors makes Monte Carlo method natural for simulations of charge generation and transport. We model the separation probability of geminate pairs formed as a result of dissociation of molecular excitations, varying temperature, applied electric field and thickness of the semiconductor layer. Particular attention is paid to how the initial energy distribution of carriers, as well as the localization radius of their wave functions, affect the photoseparation efficiency. We neglect neither long-distance hops nor energy and spatial (off-diagonal) disorder. At lower temperatures, the pair separation probability may differ significantly from the predictions of the well-known Onsager model, both upward and downward. The results obtained reveal remarkably strong dependence of photogeneration efficiency on carrier localization in the case of quasi-equilibrium initial energy distribution at low temperature or large energy disorder. Oppositely, rather weak dependence is found in the case of nonequilibrium transport. We attribute this to the effect of long jumps from deep states. These findings could extend our knowledge of photogeneration in organic solar cells and permit developing theoretical recommendations for synthesizing novel materials.
Litvinenko et al. (Tue,) studied this question.