Bilayer cells with the structure of ITO/Rubrene/C70/bathocuproine(BCP)/Al were fabricated.The effects of BCP layer on the performance of the cells and its mechanism were studied by inserting BCP with different thicknesses between C70 and Al as buffer layer.The experiental results show that the power conversion efficiency of the cell is as high as 1.78% with 6 nm BCP,and the open-circuit voltage is up to 0.901 V simultaneously.Compared with the device without buffer layer,the power conversion efficiency,short-circuit current,open-circuit voltage and filling factor of Rubrene/C70 heterojunction solar cells with 6 nm BCP are enhanced by 432.9%,74.8%,95.4% and 55.5%,respectively.