Design a thieno[3,2-b]thiophene bridged nonfullerene acceptor to increase open-circuit voltage,short-circuit current-density and fill factor via the ternary strategy

In this study,we report a new small molecule acceptor(named TT-4 F)which uses 3,6-dimethoxylthieno[3,2-b]thiophene(TT)as theπ-bridge.Addition of 0.05 weight ratio amount of TT-4 F into the host binary blend of PTB7-Th:IEICO-4 F,resulting in a ternary blend in a weight ratio of 1:1:0.05,enables increased open-circuit voltage(Voc),short-circuit curre nt-density(Jsc),and fill-factor(FF)at the same time.Finally,12.1%efficiency is obtained.Compared to the 3-(2-ethylhexyloxylthiophene)bridge on IEICO-4 F,the additional methoxyl group on the TT-6 position is involved in the lowest unoccupied molecular orbital(LUMO)and the largerπ-system on TT increases the electron-donating nature,both of which help to raise the LUMO level,one reason of the increased Voc.Upon addition of 0.05 TT-4 F,the hole mobility is increased,the monomolecular recombination is reduced,and the charge dissociation and collection is enhanced.All of these contribute to the increased Jsc and FF.