Conjugated polymers having good electrochemical and thermal stability are highly desired in optoelectronics. We report a new polythiophene consisting of alternating 4,4'-didodecyl-2,2'-bithiophene and terthiophene units (HPL1) synthesized via Stille coupling reaction. The optical band gap of HPL1 (1.92 eV) is similar to that of regioregular poly(3-hexylthiophene) (rr-P3HT, 1.89 eV). In comparison to rr-P3HT, the HPL1 when subjected to the cyclic voltammetry as thin film shows much superior electrochemical stability and a lower highest occupied molecular orbital energy level (-4.87 eV for rr-P3HT and -4.95 eV for HPL1). The transient photoluminescence study of HPL1 and rr-P3HT shows that both materials have two exciton decay processes, and the excitons of rr-P3HT are quenched more quickly. The onset decomposition, Td for rr-P3HT (465 degrees C) is 4 degrees C lower than HPL1 (469 degrees C). Preliminary photovoltaic study disclosed that the polymer solar cell based on HPL1:[6,6]-phenyl-C61-butyric acid methyl ester blend showed a power conversion efficiency of 0.63%, with a Voc of 0.6 V, and a short circuit current (Jsc) of 2.79 mA similar to cm-2 under AM 1.5 illumination (100 mW similar to cm-2). The whole study provided an important example to design new electrochemically and thermally stable polymers with longer exciton life time for application in bulk heterojunction polymer solar cells. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012