A new low band gap silole-containing conjugated polymer, PSBTBT, was designed and synthesized. Photovoltaic properties of PSBTBT were initially investigated, and an average power conversion efficiency (PCE) of 4.7 % with a best PCE of 5.1 % was recorded under illumination (AM 1.5G, 100 mW/cm(2)). The response range of the device covers the whole visible range from 380 to 800 nm. These results indicate that PSBTBT is a promising polymer material for applications in polymer solar cells.