Two new low bandgap alternating polyfluorene copolymers based on dioctylfluorene and donor-acceptor-donor monomers have been synthesized via a Suzuki polymerization reaction. The resulting copolymers have low optical bandgaps at 1.99-1.98 eV The bulk heterojunction polymer solar cells were fabricated with the conjugated polymers as the electron donor and 6.6-phenyl C-61-butyric acid methyl ester as the electron acceptor. The power conversion efficiencies of the solar cells based on copolymers 1 and 2 are 0.37 and 0.42%, respectively, under the illumination of AM 1.5, 100 mW/cm(2). The results indicate that the two copolymers are promising conjugated polymers for polymer solar cells. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5336-5343, 2009