A weak donor/strong acceptor alternating copolymer for efficient bulk heterojunction solar cells

A new alternating copolymer, CO-BDT–DTBT, designed with the “weak donor/strong acceptor” strategy has been synthesized and characterized. This strategy was tested by constructing a library of polymers employing alkanoyloxy-substituted benzodithiophene (BDT) as the weak donor, and benzothiadiazole (BT) as the strong acceptor. CO-BDT–DTBT has a low HOMO energy level of −5.62 eV, and as a result a BHJ device containing CO-BDT–DTBT blended with PC71BM was found to exhibit a high VOC of 0.88 V. These findings confirm that “weak donor/strong acceptor” polymers are a promising new class of alternating copolymers for polymer solar cell applications.