In this work, small molecule organic photovoltaic cells based on copper phthalocyanine (CuPc)/C-60 hetrojunction were fabricated. To have a good band structure matching between the work function of the anode and the highest occupied molecular orbital of the organic material the introduction of a buffer layer is necessary. Efficiency of devices shows a strong improvement when the metal oxides such as molybdenum oxide (MoO3) and tungsten oxide (WO3) were used as buffer layer between the ITO anode and active layer. The effect of MoO3 and WO3 thickness on the performance of the photovoltaic devices was investigated and compared. The thickness of each buffer layer was optimized to have better hole transport. Also the devices' performance was analyzed based on the surface roughness of bare ITO, and ITO, which covered with WO3 and MoO3. It was found that the anode buffer layer thickness is a very important factor in controlling the electrical characteristics of the organic photovoltaic devices. It is shown that the best results are obtained with a 4 nm MoO3. (C) 2011 Elsevier By. All rights reserved.