Low bandgap copolymer of 1,4-diketopyrrolo[3,4-c]pyrrole and thieno[3,2-b]thiophene: Synthesis and applications in polymer solar cells and field-effect transistors

► We synthesized a copolymer of thienothiophene and pyrrolopyrrole-dione, DH-PTTDPP. ► FETs based on DH-PTTDPP showed a hole mobility of 2.5 × 10−3 cm2 V−1 s−1. ► Polymer solar cell based on DH-PTTDPP/PC70BM showed an efficiency of 1.90%.