Rational design of π-bridges for ambipolar DPP-RH-based small molecules in organic photovoltaic cells

We report the synthesis of a series of A1–π–A2–π–A1-type small molecules, DPP2T-RH, DPPFT-RH, and DPPT-RH, in which thiophene and furan were introduced to bridge the two strong electron-withdrawing units of DPP and rhodanine (RH). Interestingly, these DPP-RH-based small molecules exhibited ambipolar characteristics, showing photovoltaic performance both as donors and acceptors in combination with PC71BM and P3HT, respectively. The best power conversion efficiencies were obtained from DPPFT-RH (1.77%) and DPP2T-RH (1.28%) as donor and acceptor, respectively. Their physical properties, film packing ability, and photovoltaic performances were fine-tuned by rational design of the π-bridges.