New ternary copolymer P(BDTT-PDBT) was prepared.
The optical band gap was 1.72 eV.
The HOMO/LUMO levels were −5.45 eV/−3.73 eV.
The hole mobility of P(BDTT-PDBT) was 3.2 × 10−3 cm2 V−1 s−1.
The PSCs made from P(BDTT-PDBT) offered maximum PCE of 5.73%.