Polymeric materials are promising for solar cell applications. High-molecular-weight and soluble poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3 '-benzothiadiazole)] is synthesized by either a Stille or Suzuki coupling reaction. Electrochemical and optical characterization of this thermally and air-stable polymeric material is reported, and bulk heretojunction polymer/fullerene photovoltaic devices are fabricated.