Synthesis and photovoltaic properties of a new donor-acceptor conjugated polymer based on fluorinated benzothiadiazole units

A novel fluorinated copolymer (PDTSffBT) based on dithienosilole donor unit and fluorinated benzothiadiazole acceptor unit has been synthesized for polymer solar cells. This copolymer exhibits a deeper HOMO energy level compared to that of hydrogenated benzothiadiazole-based copolymer (PDTSBT), resulting in high open-circuit voltages well exceeding 0.75 V. The introduction of the two electron-withdrawing fluorine atoms on the benzothiadiazole unit also leads to an increase in the molar extinction coefficient as well as the interchain interaction in the PDTSffBT copolymer with respect to its analogue PDTSBT copolymer. Power conversion efficiency (PCE) of the device using PDTSffBT:PC₇₁BM as active layer (2.93 %) is much higher than of a PDTSBT:PC₇₁BM (1.64 %) counterpart under identical conditions.