We demonstrate the enhancement of the device performance in polymer: PCBM blend photovoltaic cells by insertion of C60 interlayer between the active layer and the upper electrode. The active layer was fabricated by spin coating of a polymer {(poly(2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene)(MEH-PPV) or (poly(3-hexylthiopene)(P3HT) and fullerene derivative [5,6]-phenyl-C61-butyric acid methyl ester(PCBM)}, then the C60 interlayer and LiF/Al electrode were deposited. The both polymer cells with C60 interlayer showed significant increase in the power conversion efficiency compared to cells without the C60 layer.