Dielectric Screening To Reduce Charge Transfer State Binding Energy in Organic Bulk Heterojunction Photovoltaics

Reaching high efficiencies in organic photovoltaics is often limited by dissociating charge transfer states at electron donor–acceptor interfaces due to their large binding energies and rapid geminate recombination. By adding a high-permittivity small molecule, camphoric anhydride, at 20 wt % to a polymer–fullerene bulk heterojunction photovoltaic device, we increased the film permittivity, reduced the charge transfer state energy, and increased the power conversion efficiency by 75%. At higher concentrations, the camphoric anhydride begins to crystallize and phase separate from the bulk heterojunction, causing the permittivity and power conversion efficiency to decrease. Adding camphoric anhydride in low concentrations is an effective strategy to increase permittivity and reduce recombination at the donor–acceptor interface and as a result increase organic photovoltaic efficiency in bulk heterojunction devices.