We have studied the lifetime improvement of organic solar cells based on conjugated polymer:fullerene blends using a UV absorbing film. The cell using P3HT and PCBM-71 exhibited a conversion efficiency of similar to 4.3%, but it decreased with increase in illumination time. The conversion efficiency of the cells with and without UV film decreased to 6.6% and 37.6%, respectively, after 24 h of light exposure under AM1.5. The UV exposure appears to change the P3HT polymer network such that the defects are generated, resulting in the degradation of cell efficiency. It is found that the conversion efficiency of the cell having a 4 um UV blocking layer is higher than that without a UV layer after 12 h of illumination under 120 mW/cm(2). (C) 2009 Elsevier B.V. All rights reserved.