Despite recent increases in perovskite solar cell (PSC) efficiencies, long-term stability remains a barrier to manufacturing and marketing. SnO2 electron transport layers enable the low-temperature processing of planer n-i-p structured PSCs. However, ultraviolet radiation damages to the interface between the electron transport layer and the perovskite (PVK), which is a significant issue for n-i-p configuration. Herein, the insertion of a thin CeO2 passivation layer between the SnO2 and PVK is investigated to block the interface degradation. This CeO2 layer improves charge extraction and reduces defects in the PVK/CeO2 interface, resulting in 22.71% power conversion efficiency (PCE) compared to the pristine SnO2 PSC devices, which has a PCE of 20.7%. In addition, after 1700 h of storage at room temperature and 5%-8% RH (dry box), the PCE stability of the reinforced SnO2-CeO2 PSC devices drops from 22% to 19%, whereas that of the pristine SnO2 PSC devices drops from 20% to 16%.