A heptacyclic acceptor unit developed for D–A copolymers used in polymer solar cells†
Thiophene rings in the pentacyclic unit TPTI were replaced with thieno[3,2-b]thiophene moieties to produce a new fused-ring acceptor unit TTP. A D–A copolymer PBDTTTP was synthesized via copolymerizing TTP and benzo[1,2-b:4,5-b′]dithiophene (BDT). PBDTTTP possessed an optical bandgap of 2.11 eV, a deep HOMO level of −5.43 eV, and partial crystallinity. PBDTTTP:PC71BM solar cells gave a PCE of 5.53%, and the maximum Voc reached 1 V.