The solar cells based on the blend of MEH-PPV(poly(2-methoxy-5-(2'-ethylhexyloxy) -1,4-phenylene vinylene)) and PCBM (1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61) as acceptor were fabricated. The thickness dependence of the performance of solar cells was studied. The results showed that the solar cells with active layer thickness of 100 nm have the best performance. Increasing device thickness resulted in an increase of charge recombination and a lowering of the fill factor, which leads to lower overall power conversion efficiency. The reasons for the S-shaped kink in the thick device were also analyzed. Influence of the cathode material on the performance of the devices was discussed. The results showed that the solar cells using LiF/Al as the negative electrode formed ohmic contacts at the cathode and anode, which favored the collecting of the charge, increased the transmission of the charge and the absorption of solar light, and improved the performance of the solar cell.