Efficient bulk heterojunction solar cells with copolymers based on fluorene, dithienylbenzothiadiazole, and thiophene derivatives

Three copolymers, PFTpBt, PFbCNTpBt, and PFC6TpBt, which are based on dioctylfluorene, dithienylbenzothiadiazole, and thiophene derivatives with different functional groups, were synthesized via a Suzuki reaction. The copolymers were characterized by NMR, GPC, TGA, UV–vis absorption, and electrochemical cyclic voltammetry. Thermogravimetric analysis showed that the copolymers exhibited good thermal stability. The optical, electrochemical, photovoltaic properties, and hole mobility of the copolymers were investigated and discussed. The polymer solar cell based on PFTpBt had the best performance, with a power conversion efficiency (PCE) of 2.17% under the illumination of AM 1.5, 100 mW/cm2.

Research highlights
► Three copolymers based on dioctylfluorene, dithienylbenzothiadiazole and thiophene derivatives with different functional groups were synthesized via a Suzuki reaction.
► The UV-vis absorption spectra in the solid state and the hole mobilities of the copolymers changed when incorporating thiophene units with different functional groups.
► The polymer solar cell based on PFTpBt had the best performance, with a power conversion efficiency (PCE) of 2.17%.