Benzo[c]thiophene-C60 diadduct: an electron acceptor for p-n junction organic solar cells harvesting visible to near-IR light.

We synthesized a new 56-π-electron fullerene derivative through a Diels-Alder cycloaddition of benzo[c]thiophene that featured a relatively low temperature, closer to stoichiometric use of the diene, and easy product purification. The 56-π-electron benzo[c]thiophene diadduct (BTCDA) has a LUMO energy level of 0.09 to 0.18 eV higher than that of 58-π-electron fullerenes, and therefore, the BTCDA-based organic photovoltaic device exhibited a higher open-circuit voltage and power-conversion efficiency (PCE). When used with a binary-donor system, including visible-light-harvesting tetrabenzoporphyrin (BP) and near-IR-harvesting titanyl phthalocyanine (TiOPc), the device had a PCE that was 1.5-3 times higher (2.8%) than that for devices with BP or TiOPc alone because the binary-donor device can utilize light between λ=350 and 950 nm.