A novel donor–acceptor–donor oligomer, 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene-5,5-dioxide (37HPTDBTSO) with a dibenzothiophene-5,5-dioxide core and end-cap phenylene–thiophene moieties, was synthesized using Stille cross-coupling reactions. The functional properties, including the optical and electrochemical properties, were investigated. Using 37HPTDBTSO and phenyl-C61-butyric acid methyl ester (PCBM) as a photoactive layer, bulk-heterojunction solar cell devices were fabricated by a spin-coating technique. 37HPTDBTSO was found to be a valuable electron donor. The device had a high open circuit voltage of 0.85 V and the highest power conversion efficiency of 0.84% when the weight ratio of 37HPTDBTSO to PCBM was 1:1.5. These results indicate that the new oligomer is a promising solution-processable photovoltaic material.