New conjugated copolymers, P1-P3, based on dithiafulvalene-fused entity and different conjugated segments have been synthesized. Incorporation of electron-deficient conjugated segments into the conjugated copolymers results in red shifting the absorption band and lowering the hole mobility. Bulk heterojunction solar cells using on these polymers as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the acceptor were fabricated by solution process. The cells based on the blend of P1-P3/PC61BM (1:1, w/w) have power conversion efficiencies (PCEs) ranging from 0.53 to 0.93%. Among these, the cell of P1/PC61BM exhibited the highest open-circuit voltage at 0.85 V, and the cell of P3/PC61BM exhibited the best PCE at 0.93% with the short-circuit current (J(SC)) of 4.88 mA/cm(2). (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 2121-2129, 2012