The Relationship between the Electric Field-Induced Dissociation of Charge Transfer Excitons and the Photocurrent in Small Molecular/Polymeric Solar Cells

A bulk heterojunction system consisting of a soluble poly(p-phenylenevinylene) donor and a small molecular electron acceptor based on Vinazene (2-vinyl-4,5-dicyanoimidazole) has been investigated with respect to the correlation between field-induced emission quenching and free charge carrier formation. Transient and steady-state emission properties measured at different voltages indicate that emissive charge transfer (CT) excitons formed at the heterojunction are prone to direct field-induced dissociation. However, the split-up of these CT excitons cannot fully account for the photocurrents observed on the very same devices. It is proposed that the formation of free carriers involves a nonemissive precursor and that the recombination of this precursor does not proceed via the formation of CT excitons.