Photogeneration of Charge Carriers in Organic Solar Cells: The Role of Nonequilibrium States for Electrons and Holes

The aim of this study is to consider the photogeneration of charge carriers in nano-structured blends of the donor (D) and acceptor (A) materials. The optical excitation photons absorbed in one of these materials produce intramolecular excitons which can diffuse into the D–A interface and form interfacial CT states at the interface. The interfacial CT state dissociates into a geminate pair of the nonequilibrium mobile electron and hole. In this study, an empirical model describing thermalization of the nonequilibrium charges within the Coulomb well is proposed. The efficiency of the interfacial CT state’s dissociation into a pair of free charges is found as a function of the electric field applied, effective temperature, and diffusion length of the nonequilibrium electron-hole pairs.