To develop conjugated polymers with low bandgap, deep HOMO level, and good solubility, a new conjugated alternating copolymer PC-DODTBT based on N-9'-heptadecanyl-2,7-carbazole and 5, 6-bis(octyloxy)-4,7di(thiophen-2-yl) benzothiadiazole was synthesized by Suzuki cross-coupling polymerization reaction. The polymer reveals excellent solubility and thermal stability with the decomposition temperature (5% weight loss) of 327 degrees C. The HOMO level of PC-DODTBT is -5.11 eV, indicating that the polymer has relatively deep HOMO level. The hole mobility of PC-DODTBT as deduced from SCLC method was found to be 2.03 x 10(-4) cm(2)/Versus Polymer solar cells (PSCs) based on the blends of PC-DODTBT and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) with a weight ratio of 1:2.5 were fabricated. Under AM 1.5 (AM, air mass), 100 mW/cm(-2) illumination, the devices were found to exhibit an open-circuit voltage (V-oc) of 0.73 V, short-circuit current density (J(sc)) of 5.63 mA/cm(-2), and a power conversion efficiency (PCE) of 1.44%. This photovoltaic performance indicates that the copolymer is promising for polymer solar cells applications. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 99-107, 2012