Benzochalcogenodiazole-based donor-acceptor-acceptor molecular donors for organic solar cells.

Four new molecules with a donor–acceptor–acceptor (D-A-A) configuration, in which 2,1,3-benzoxadiazole or 2,1,3-benzoselenodiazole were adopted as the central bridging acceptor, were synthesized as electron donors for small-molecule organic solar cells. In conjunction with two previously reported 2,1,3-benzothiadiazole-based compounds, the influences of the benzochalcogenodiazole acceptor unit and the ditolylarylamine donor moiety on the molecular structure, electrochemical behavior, and optical properties of the materials were investigated systematically to obtain a clear structure–property relationship. Vacuum-deposited hybrid planar mixed-heterojunction devices fabricated with the new donors and C70 as the acceptor showed power conversion efficiencies in the range of 2.9–4.3 % under 1 sun (100 mW cm−2) AM 1.5 G simulated solar illumination. The current density–voltage characteristics of solar cells at various light intensities were measured, which revealed a high bimolecular recombination.