All-conjugated donor–acceptor graft/block copolymers as single active components and surfactants in all-polymer solar cells

In this work, we report the synthesis of all-conjugated donor–acceptor (D–A) graft/block copolymers via an externally-initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, end-functional electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized via KCTP initiated by the Ni(COD)2-activated PNDI complexes. Therefore, a series of D–A graft copolymers and ABA-type (P3HTs were initiated from both ends of PNDI) triblock copolymers were successfully synthesized. The polymers were used to fabricate polymer thin film transistors and the results indicated that all the polymers exhibited moderate charge mobilities ranging from 10−4 to 10−3 cm2 V−1 s−1, and they could be further improved by thermal annealing. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active components or as surfactants. A power conversion efficiency (PCE) of 0.22 % with open circuit voltage (Voc) = 0.55 V, short circuit current density (Jsc) = 0.64 mA/cm2, and fill factor (FF) = 0.62 was recorded by using the donor–acceptor all-conjugated block copolymer as acceptor, and a PCE of 2.28 % with Voc = 0.61 V, Jsc = 7.00 mA/cm2, and FF = 0.54 was obtained when PNDI was used as a surfactant.