The dye sensitization method for bulk heterojunction polymer solar cells is applied to polymer/polymer solar cells composed of conjugated donor and acceptor polymers. The power conversion efficiency is successfully improved by addition of a near-infrared (NIR) dye. Spectroscopic analysis and J-V characteristics indicate that the dye molecules effectively contribute to the charge generataion through direct absorption of NIR light and also through the energy transfer from the donor polymers, according to the cascaded HOMO and LUMO potentials. These results demonstrate the versatility of dye sensitization as a useful method for improving the conversion efficiency of photovoltaics.