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

It is a matter of controversy why excitons can efficiently dissociate into free electrons and holes at an intrinsic donor-acceptor interface despite the strong Coulomb interaction between the charges provided by the low dielectric constant in organic materials. We suggest an analytic theory based on the recently developed exact solution for the dissociation problem [Phys. Rev. Lett. 100, 196602 (2008)] and show that delocalization of charge carriers along the polymer chains can help the carriers to overcome the Coulomb potential barrier. The main effect here is provided by the kinetic energy of charge carriers caused by quantization. Neglecting the quantization effects leads to underestimation of the dissociation probability by at least an order of magnitude. Particular attention in our study is given to the calculation of carrier energies, which shows that the parabolic approximation together with the first-order correction is sufficient to calculate such energies in most cases.