Synthesis and Photovoltaic Properties of Thieno[3,4-c]pyrrole-4,6-dione-based donor-acceptor Copolymers

Three donoracceptor (DA) 1,3-di(thien-2-yl)thieno [3,4-c]pyrrole-4,6-dione-based copolymers, poly{9,9-dioctylfluorene-2,7-diyl-alt-1,3-bis(4-hexylthien-2-yl)-5-octylthieno[3,4-c]pyrrole-4,6-dione}, poly{N-(1-octylnonyl)carbazole-2,7-diyl-alt-1,3-bis(4-hexylthien-2-yl)-5-octylthieno[3,4-c]pyrrole-4,6-dione}, and poly {4,8-bis(2-ethylhexyloxyl) benzo[1,2-b:3,4-b']dithiophene-alt-1,3-bis(4-hexylthien-2-yl)-5-octylthieno[3,4-c] pyrrole-4,6-dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep-lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open-circuit potential when they are used in photovoltaic cells. Bulk-heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC71BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open-circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm2). (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012