A 2-(trifluoromethyl)thieno[3,4-b]thiophene-based small-molecule electron acceptor for polymer solar cell application

A new TbT unit 2-(trifluoromethyl)thieno[3,4-b]thiophene is designed and synthesized for developing small-molecule acceptor. A small molecule acceptor ATT-8 with an indacenodithiophene (ITD) core, two rhodanine ending-groups, and two TbT linkers were constructed. A wide-bandgap polymer donor PBDB-T is selected to fabricate bulk-heterojunction solar cells with ATT-8 acceptor. The as-cast film device delivers a PCE of 4.80% with an open circuit voltage (Voc) of 0.955 V, a short-circuit current (Jsc) of 10.32 mA cm−2 and a fill factor (FF) of 48.71%. Further optimization via additive and thermal annealing (TA) promotes PCE of the device to 7.31% with a Voc of 0.804 V, a Jsc of 13.90 mA cm−2, and an FF of 65.42%.