Synthesis of TPD–thiophene-based small molecule donor for organic photovoltaic cells

The donor–acceptor–donor (D–A–D) type small molecule, TPD2T, was synthesized by the Stille coupling reaction and consisted of the electron-withdrawing thiene[3,4-c]pyrrole-4,6-dione (TPD) unit as an electron-accepting (A) core and electron-rich bithiophene units as electron-donating (D) groups. The absorption maximum of the TPD2T film was observed at 460 nm, and was broader and red-shifted compared to that in solution (λ_max = 450 nm). Organic photovoltaic cells fabricated with the conventional and inverted structures both exhibited similar power conversion efficiencies of 0.14–0.15%. Despite the low short-circuit current values, the TPD2T devices showed high open-circuit voltages of over 1.0 V owing to the relatively low-lying HOMO level of TPD2T (−5.4 eV).