Organic solar cells with structure of ITO/MoO3（5 nm）/Rubrene（50 nm）/C60（45 nm）/Rubrene（0, 3, 5.5, 9.5 nm）/Al（130 nm） were prepared. The rubrene layer near the Al cathode was used as the electron transporting layer. Compared with that of the control device without the electron transporting layer, the open circuit voltage, fill factor and power conversion efficiency of the device with 5.5 nm rubrene layer were increased from 0.68 V, 0.488, 0.315% to 0.86 V, 0.574, 0.490%, respectively. The analysis of the experimental results shows that when hot Al atoms are directly deposited on C60 layer, the C60 layer is undermined and a high work function is formed, which leads to a weaker built-in electric field and a poorer performance. When the rubrene layer is inserted, a significant improvement in device performance is achieved due to the formation of defect states in rubrene layer during Al deposition. Further experimental results of single-electron devices show that energy levels of the defect states are lower than that of the lowest unoccupied molecular orbital of C60.
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