The effect of electron transportation layer (ETL) PCBM film thickness was investigated for the performance of inverted structure perovskite solar cells. The charge transportation study was carried by Mott-Schottky analysis. The result shows the charge transportation status of different electron thickness. A thicker PCBM layer could provide better diode property, while the thinner layer would lead to higher short circuit current. For this perovskite fabrication method, the thicker film worked better. This study reveals the optimization of PCBM depends on various factors, like cathode, and perovskite films. To further improve the efficiency of devices, the perovskite film and the design of device structure are needed to be optimized.