High open-circuit voltage polymer solar cells based on D–A copolymer of indacenodithiophene and fluorine-substituted benzotriazole

Abstract A medium band gap D–A copolymer of indacenodithiophene (IDT) and fluorinated dithienylbenzotriazole (FBTA), PIDT-FBTA, was synthesized for the application as donor material in polymer solar cells (PSCs). PIDT-FBTA showed deeper highest occupied molecular orbital (HOMO) energy level due to the strong electron-withdrawing difluorine substitution on benzotriazole acceptor unit in the D–A copolymer. The PSCs based on PIDT-FBTA:PC 70 BM (1:3) exhibited a high V oc of 0.90 V and a power conversion efficiency (PCE) of 3.62% under the illumination of AM 1.5G, 100 mW cm −2 . The device performance was further improved by methanol treatment with PCE increased to 4.90% and V oc increased to 0.92 V.