Novel donor-acceptor polymers based on 7-perfluorophenyl-6H-[1,2,5]thiadiazole[3,4-g]-benzoimidazole for bulk heterojunction solar cells

Three new fluorinated D-A type conjugated polymers based on a novel building unit 7-perfluorophenyl-6H-[1,2,5] thiadiazole[3,4-g]benzoimidazole have been synthesized through a Sitlle coupling reaction. The as-prepared polymers exhibit a narrow band gap (from 1.31 to 1.34 eV) and low lying energy levels with lowest occupied molecular orbital (LUMO) energy levels of -3.95, -3.97 and -4.15 eV, respectively. These polymers exhibit excellent solubility in common organic solvents due to the introduction of perfluorophenyl and long alkyl sidechains. The power conversion efficiency (PCE) of solar cells based on these as-prepared polymers and PC71BM could reach as high as 1.92%. Our results could provide a simple strategy for designing high performance D-A polymers based on this unit and a potential to further improve their performance.