Synthesis and photovoltaic properties of a D–A copolymer of dithienosilole and fluorinated-benzotriazole

An alternative D–A copolymer of a dithienosilole (DTS) donor unit and a fluorinated-benzotriazole (FBTA) acceptor unit with a thiophene π-bridge, PDTS-DTFBTA, was designed and synthesized, for application as a donor material in polymer solar cells (PSCs). PSCs based on PDTS-DTFBTA : PC₇₀BM (1 : 1, w/w) with thermal annealing at 120 °C for 10 min showed a PCE of 3.93% with a V_oc of 0.64 V, which is slightly improved in comparison with its analogous polymer (PDTS-DTBTA) without the fluorine substitution. By using indene-C₆₀ bisadduct (ICBA) instead of PC₇₀BM as acceptor, the PCE was improved to 4.99% with a high V_oc of 0.85 V. PDTS-DTFBTA is the first reported fluorinated D–A copolymer which shows improved photovoltaic performance with ICBA as acceptor compared to PCBM.