Random terpolymers for high-performance semitransparent polymer solar cells

A lot of binary copolymers have been designed and synthesized for non-fullerene polymer solar cells (PSCs). However, some binary donor-acceptor copolymers exhibited unsatisfactory optical absorption and photovoltaic performance, which are based on 2D-conjugated bithienyl-benzodithiophene (BDTT) and fluorobenzotriazole. Herein, we employed random copolymerization approach to construct terpolymers (named as J28, J55, J82), which outperform binary copolymers in non-fullerene PSCs. Non-fullerene PSCs based on J55: ITIC (1.0:1.0) without any additive (DIO) demonstrate a VOC of 0.83 V, a JSC of 17.23 mA cm-2, a FF of 63.67% and a PCE of 9.19% (a PCE of 5.85% for J52:ITIC, 1.0:1.0; a PCE of 8.16% for J60:ITIC, 1.0:1.0). Semitransparent polymer solar cells (ST-PSCs) based on J55:ITIC showed a VOC of 0.84 V, a JSC of 15.60 mA cm-2, a FF of 51.19%, a PCE of 6.73% with an AVT of 22.06%. This work demonstrates that fluorobenzotriazole and BDTT with branched alkyl and branched alkylthio based terpolymers could have higher photovoltaic performance via random copolymer approach and also meet the balance of two key parameters of power conversion efficiencies and average visible transmittance in ST-PSCs.