Two donor acceptor-type alternating copolymers consisting of 2,1,3-benzoselenadiazole and carbazole derivatives with thiophene or selenophene pi-bridges were synthesized by Suzuki cross-coupling polymerization, and their optical, electrochemical, and photovoltaic properties were compared. The selenophene pi-bridged copolymer (PCz-DSeBSe) exhibited a smaller band-gap (1.82 eV) than the thiophene-bridged polymer (PCz-DTBSe; 1.89 eV). PCz-DSeBSe also showed a deeper highest occupied molecular orbital energy level (-5.36 eV) than PCz-DTBSe (-5.20 eV). Moreover, the PCz-DSeBSe thin film showed higher crystallinity and hole mobility than the PCz-DTBSe thin film. Organic photovoltaic devices were fabricated using the polymers as the donors and [6,61-phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor. The device using PCz-DSeBSe showed a higher open circuit voltage (V-oc), short circuit current density (J(sc)), and power conversion efficiency (PCE) than that using PCz-DTBSe. The fabricated indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/PCz-DSeBSe:PC71BM/LiF/AI device showed the maximum PCE of 2.88% with a J(sc) of 7.87 mA/cm(2), an V-oc of 0.80 V, and a fill factor of 0.50 under AM 1.5G irradiation (100 mW/cm(2)). (C) 2014 Elsevier Ltd. All rights reserved.