D-A copolymers based on lactam acceptor unit and thiophene derivatives for efficient polymer solar cells

D-A copolymers PTTBDTP and PBTBDTP based on lactam acceptor unit BDTP and thieno[3,2-b]thiophene (TT) or 2,2′-bithiophene (BT) were synthesized. The effect of TT and BT on optical, electrochemical, crystallinity and other properties of the polymers were fully investigated. Compared with PTTBDTP, PBTBDTP possessed better UV-vis absorption ability, better crystallinity and higher hole mobility. Therefore, PSCs based on PBTBDTP:PC71BM achieved a PCE of 6.86%, which is higher than that of PTTBDTP:PC71BM cells (5.84%).192