Inverted polymer solar cell with P3HT:PC61BM as an active layer is fabricated based on Al2O3/MoO3 composite anode buffer layer. Effects of Al2O3/MoO3 composite anode buffer layers with the Al2O3 precursor solutions of different concentrations on the device performance are investigated. It can be found that the Al2O3/MoO3 composite anode buffer layer can effectively enhance the photovoltaic performance and device stability of inverted polymer solar cell. The open-circuit voltage (Voc), short-circuit current (Jsc), filling factor (FF), and photoelectric conversion efficiency (PCE) are 0.64 V, 8.62 mA/cm2, 63.86%, and 3.85% respectively for the control device with MoO3 single buffer layer. In addition, with the increase of the concentration of Al2O3 precursor solution, the photovoltaic performance of the inverted polymer solar cell with Al2O3/MoO3 composite anode buffer layer is gradually improved. For the Al2O3 precursor solution of 0.15%, the photovoltaic performance of the device reaches an optimal value, and the corresponding Voc, Jsc, FF, and PCE are 0.65 V, 11.04 mA/cm2, 64.46%, and 4.64%, respectively. The Jsc and PCE significantly increase by 28% and 20%, respectively, compared with those of the control device with MoO3 single buffer layer. Moreover, after 80 days of measuring the device lifetime, the PCE of the device with the composite anode buffer layer remains at 76% of the original value while the PCE with the single buffer layer is reduced below 50%. The improvement of the device performance should be attributed to the PC61BM receptor near the anode dissolved and washed by isopropyl alcohol solvent from the Al2O3 precursor solution. At the same time, a large number of pits on the surface of the active layer are filled with Al2O3 to make it more smoothly contact the composite anode buffer layer. Therefore, the contact resistance between the active layer and the anode decreases, which enhances hole collection performance of the anode. Simultaneously, the Al2O3 layer can passivate the active layer of the device, thus improving the photovoltaic performance and device stability of inverted polymer solar cell.
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