Theory to exciton dissociation at the interface between a conjugated polymer and an electron acceptor

Experimental studies evidence that excitons in organic materials can efficiently dissociate into free electrons and holes at an intrinsic donor/acceptor interface despite the strong Coulomb attraction between the charges provided by the low dielectric constant in organics. Using a semi-analytic theory for the dissociation probability of electron-hole pairs we show that although delocalization of charge carriers along the polymer chains can help the carriers to overcome the Coulomb potential barrier, this effect is not enough to explain the efficient and field-independent dissociation of pairs at the interfaces. Furthermore we study the influence of the dipole layer built in the dark at the donor/acceptor interface considering two distinct forms of this dipole layer: a continuous layer and a system of discrete dipoles. In the latter case very high dissociation probabilities can be reached. The main effect here is provided by the quantization energy of holes restrained by the adjacent dipoles. (C) 2011 Elsevier B.V. All rights reserved.