Three alternating donoracceptor copolymers have been synthesized by Stille coupling polymerization of 2,6-(trimethyltin)4,8-bis(5-dodecylthiophene-2-yl)benzo[1,2-b:4,5-b]dithiophene with 1,3-dibromo-5-hexylthieno[3,4-c]pyrrole-4,6-dione, 4,7-dibromo-1,3-benzothiadiazole, and 5,7-dibromo-2,3-didodecylthieno[3,4-b]pyrazine, respectively. The synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The thienopyrroledione copolymer displayed a power conversion efficiency of 3.00% which was increased to 3.86% by application of the additive 1,8-diiodooctane (DIO). Tapping mode atomic force microscopy analysis indicated that there was an increase in the phase separation between polymer and PCBM, leading to an improvement in the performance upon the addition of DIO. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 26222630