Separation of geminate charge-pairs at donor-acceptor interfaces in disordered solids

Using an extension of the Onsager model of exciton dissociation in the bulk of a disordered solid, we determine the separation probability of geminate electron-hole pairs following exciton dissociation by charge-transfer at a donor-acceptor interface. The donor-acceptor interface confines the electron and hole in their respective layers, leading to charge separation with a probability that is significantly higher than predicted by bulk theory. The model explains the surprisingly high carrier collection efficiencies observed in organic donor-acceptor photovoltaic cells, and correctly predicts the voltage-dependence of the photocurrent which differs substantially from that of conventional inorganic semiconductor p-n junctions and may ultimately limit the power conversion efficiency of organic donor-acceptor photovoltaic cells. (C) 2004 Elsevier B.V. All rights reserved.