Organic photovoltaic cells with high open circuit voltages based on pentacene derivatives

Heterojunction organic photovoltaic devices were fabricated using C60 as the electron acceptor and several pentacene derivatives with triisopropylsilylethynyl functional groups as the electron donor. The open circuit voltage (Voc) of functionalized pentacene-based cells is significantly higher (0.57–0.90 V) than for cells based on unsubstituted pentacene (0.24 V), due to the higher oxidation potentials of these pentacene derivatives. The performance of pentacene derivative cells is limited by lower current densities than the reference pentacene/C60 cell. The absorption spectra of films and solutions of pentacene derivatives closely resemble one another, leading us to conclude that these films are amorphous in nature. Weak intermolecular coupling in the derivative films results in lower charge mobility and shorter exciton diffusion lengths relative to pentacene.