PIN organic solar cells with the structure of ITO/V₂O₅/rubrene/C₇₀:rub rene/C₇₀/BCP/Al were fabricated,using rubrene,rubrene and C₇₀ mixi ng layer,and C₇₀ as P,I and N layers,respectively.The thickness effect of the mixing layer on the performance of the cells is reveale d,indicating that the optimized device performance is obtained at thickness of 5nm.The power conversion efficie ncy of the optimized cell is as high as 1.58% and the short-circuit current is up to 4.365mA·cm－2,which ar e 140.3% and 129.7% more than those of the PN device.We suggest that the insertion of the I layer increa ses the separation ratio of the excitons,leading to the enhancement of th e device performance.