Benzo[1,2-b:4,5-b′]dithiophene and Thieno[3,4-c]pyrrole-4,6-dione Based Donor-π-Acceptor Conjugated Polymers for High Performance Solar Cells by Rational Structure Modulation

A series of benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-c]pyrrole-4,6-dione (BDT-TPD) based copolymers (P1–P4) with D-π-A structures are designed and synthesized. When the π bridges change from 2,2′-bithiophene to thieno[3,2-b]thiophene and then to 3-hexylthieno[3,2-b]thiophene, the performance of the polymer photovoltaic devices shows significant improvement. Especially, the device based on P4 with alkylthienyl-substituted BDT and π bridge of 3-hexylthieno[3,2-b]thiophene exhibits power conversion efficiency as high as 7.71%, and the short-circuit current of the cells is up to 13.70 mA cm–2. The results indicate that the modulation of π bridges is a feasible way to achieve highly efficient polymer solar cells.