Low-band gap selenophene-based polymers were synthesized. Their optoelectronic and photovoltaic properties and space-charge limited currents were compared with those of the related thiophene-based polymers. The band gaps of the Se-based derivatives were approximately 0.05-0.12 eV lower than those of their thiophene counterparts. Organic photovoltaic (OPV) devices based on the blends of these polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-71 (PC71BM) were fabricated, and the maximum power conversion efficiency of the OPV device based on PSPSBT and PC71BM was 3.1%with a short-circuit current density (J(sc)) of 9.3 mA cm(-2), an open-circuit voltage (V-oc) of 0.79 V, and a fill factor of 0.42under AM 1.5 G illumination (100 mW cm(-2)). (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4550-4557