Polymer photovoltaic solar cells using poly(2,6-bis(3-alkylthiophen-2-yl)dithieno-[3,2-b;2',3'-d]thiophene) (PBTDT) as the donor is demonstrated. The UV-vis spectra show that PBTDT has strong absorption in the visible spectrum. By adjusting the ratio of PBTDT to[6,6]-phenyl C61-butyric acid methylester(PCBM) and optimizing the annealing temperature, the PBTDT-based polymer solar cells show a power conversion efficiency of 0.42% under 100 mW/cm(2) AM1.5G simulated sunlight. (C) 2009 Elsevier B.V. All rights reserved.