Two new fluorinated copolymers based on thieno[2,3-f]benzofuran for efficient polymer solar cells

Abstract

Two new copolymers named TBFPF-BT and TBFPF-BO, composed of a fluorine substituted thieno[2,3-f]benzofuran donor unit and benzothiadiazole/benzooxadiazole acceptor unit, have been synthesized as the donor materials for polymer solar cell (PSC) applications. Both polymers presented wide absorptions (300–800 nm) in the UV-Vis region. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels were −5.28/−3.60 eV and −5.38/−3.69 eV for TBFPF-BT and TBFPF-BO, respectively. PSCs with the blends of TBFPF-BT/TBFPF-BO and PC₇₁BM (1 : 2, w/w) as photoactive layers exhibited relatively low photovoltaic performances. After optimizing with 1% 1,8-diiodooctane (DIO) as additive, dramatic changes in short-circuit current density (J_sc) and fill factor (FF) were seen, with PCE up to 6.80% and 5.98% under AM 1.5, 100 mW cm⁻² for TBFPF-BT and TBFPF-BO, respectively. Compared to TBFPF-BO, the higher PCE mainly benefits from the higher hole mobility and better morphology for the TBFPF-BT and PC₇₁BM blend film.