Four new donoracceptor (donor) [DA(D)], PBDT-PTQ, PBDT-PTTQ, PBDT-TQ, and PBDT-TTQ, bearing the same backbone of alternative benzodithiophene (BDT) and quinoxaline units but with phenylene thienyl, phenylene di-thienyl, thienyl and di-thienyl groups (other donors), respectively, at the acceptor quinoxaline units, were designed and synthesized to investigate the impacts of the conjugated side chains at the acceptor units on the photovoltaic properties of polymers. The power conversion efficiencies (PCEs) of the polymer solar cells (PSCs) based on PBDT-TQ:[6,6]-phenyl-C-70-butyric acid methyl ester (PC70BM) and PBDT-PTQ:PC70BM reach to 4.39 and 3.58%, respectively, which are 43 and 17% higher, respectively, than that of a reported alkylphenyl substituted polymer with the same main chain. However, the PCEs based on PBDT-TTQ and PBDT-PTTQ, in which an additional thiophene is added at a side chain of PBDT-TQ and PBDT-PTQ, respectively, decline. The mechanism how the conjugated side chains affect the performance of the PSCs is also discussed. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1565-1572