Dialkylthio benzo[1,2-b:4,5-b′]difuran polymer for efficient organic photovoltaics with solvent treatment in active layers

•The facile synthesis of dialkylthiobenzo[1,2-b:4,5-b']difuran.•The electrochemical characterization of polymer PBDFs-DTBTff.•The enhancement of solvent additive and THF vapor treatment on device performance.•The demonstration of the highest PCE of 5.48% for PBDFs-DTBTff based devices.

The facile synthesis of dialkylthio substituted benzo[1,2-b:4,5-b′]difuran unit via a straightforward palladium-catalyzed carbon–sulfur bond formation reaction is reported. A novel donor–acceptor alternating copolymer was further developed by Stille coupling. The optical and electrochemical properties of the polymer have been carefully studied. The photovoltaic performance by blending the copolymer with [6,6]-phenyl-C71-butyric acid methyl ester were explored in both conventional and inverted solar cell devices. Solvent additive and vapor treatment exhibit positive effects on the device performance. The best devices delivered a power conversion efficiency of 5.48%, with an active layer processed from chloroform solutions with 1,8-diiodooctane (3%) and 30 s tetrahydrofuran vapor treatment.