In this manuscript, we report high-performance polymer photovoltaic cells with P3HT:PCBM film prepared from polymer solution added with 1-dodecanethiol (P3HT and PCBM are poly (3-hexylthiophene) and [6,6]-phenyl-C(61)-butyric acid methyl ester, respectively). The addition of 1-dodecanethiol into polymer solution resulted in remarkable enhancement in the energy conversion efficiency of polymer photovoltaic cells. The efficiency enhancement for the device with a P3HT:PCBM (1:2 w/w) film is more significant than for the device with a P3HT:PCBM (1:1 w/w) film. Devices with energy conversion efficiency as high as 4% were demonstrated with a thick P3HT:PCBM film prepared by a quick drying process. (C) 2009 Elsevier B.V. All rights reserved.