A new soluble conjugated copolymer based on 2,7-dibenzosilole and 4,7-dithien-2-yl-2,1,3benzothiadiazole units has been synthesized (PBSDTBT). Bulk heterojunction solar cell devices are fabricated using this material as the donor and [6,6]-phenyl-C-61 butyric acid methyl ester (PCBM) as the acceptor. The power conversion efficiency is 1.6% under AM1.5 illumination. This material also shows a good V-oc (0.97 V). The results are quite promising considering the relatively large bandgap (1.9 eV) of this polymer.