Organic solar cells (OSCs) have become the most potential photoelectric converter.In this paper ,a Cu(I) complex was synthesized and employed in OSCs as cathode buffer layer.The experimental results show that the power conversion efficiency (PCE) of OSCs is closely associate d with the thickness of cathode buffer layer.Under AM 1.5solar illumination,the PCE increases in early stage and then decreases when the structure of OSCs is ITO/CuPc (20nm)/C60(40nm)/CuBB (x )/Al (100nm).When the thickness of CuBB is 8nm,the maximum efficiency is 0.94%.This can be unders tood as follows. CuBB has a good electron mobility,when thin CuBB layer decorates the cathode,whi ch can provide a good ohmic contact and is in favor of electron transport.However,when the CuBB laye r exceeds 8nm,series resistor will increase and the electron won′t transport through cathode buffer layer,then the power conversion efficiency decreases.