We fabricated organic solar cell (OSC) devices using blended solution of MDMO-PPV: PCBM-C-61. The electrical properties of the devices were investigated as a function of the photoactive layer thicknesses and by addition of LiF interlayer. The devices having photoactive layer under 200nm has shown the best efficiency. The electrical characteristics were degraded by decreasing photoactive layer thicknesses. The devices with 200nm of photoactive layer without LiF interlayer have shown the best electrical characteristics, which were 0.49% of PCE, 41.5% of fill factor and 1.4mA/cm(2) of J(SC). Similar trends were observed by adding LiF interlayer between active layer and Al cathode. As a result, the efficiency of the OSC devices was more enhanced by adding LiF interlayer. The power conversion efficiency was improved up to 32% (PCE = 0.65%) when compared with the devices without LiF interlayer (PCE-0.49%).