Among the n-type metal oxide materials used in the planar perovskite solar cells, zinc oxide (ZnO) is a promising candidate to replace titanium dioxide (TiO2) due to its relatively high electron mobility, high transparency, and versatile nanostructures. Here, we present the application of low temperature solution processed ZnO/Al-doped ZnO (AZO) bilayer thin film as electron transport layers (ETLs) in the inverted perovskite solar cells, which provide a stair-case band profile. Experimental results revealed that the power conversion efficiency (PCE) of perovskite solar cells were significantly increased from 12.25 to 16.07% by employing the AZO thin film as the buffer layer. Meanwhile, the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) were improved to 20.58 mA/cm2, 1.09V, and 71.6%, respectively. The enhancement in performance is attributed to the modified interface in ETL with stair-case band alignment of ZnO/AZO/CH3NH3PbI3, which allows more efficient extraction of photogenerated electrons in the CH3NH3PbI3 active layer. Thus, it is demonstrated that the ZnO/AZO bilayer ETLs would benefit the electron extraction and contribute in enhancing the performance of perovskite solar cells.
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