Synthesis and Photovoltaic Properties of Poly(5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo-[c][1,2,5]-thiadiazole-9,9-dioctylfluorene)

A donor–acceptor type conjugated polymer poly(5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo-[c] [1,2,5]-thiadiazole-9,9-dioctylfluorene) (POTBTF) based on octyloxy-containing benzothiadiazole (OTBT) and octyl-containing fluorine (F) was synthesized by Suzuki coupling reaction. The polymer possesses a narrow bandgap and strong light harvesting ability with excellent thermal stability and reasonable solubility. POTBTF exhibited a broad absorption from 300 to 600 nm with an absorption peak at 543.8 nm. The power conversion efficiency of the polymer solar cell based on POTBTF/PC71BM (1:3, w/w) reached 1.77% with a short-circuit current density of 6.69 mA/cm2, an open-circuit voltage of 0.71 V, and a fill factor of 0.374 under AM 1.5 G irradiation (100 mW/cm2) without annealing or any additives. The results indicate that introducing long alkoxy side chains into benzothiadiazole would not only improve the solubility of the polymers but also maintain the planarity of molecule conformation, and therefore, enhance the performance of photovoltaic devices.