Stability issues and high material cost constitute the biggest obstacles of a perovskite solar cell (PVSC), hampering its sustainable development. Herein, we demonstrate that, after suitable surface modification, the low-cost cerium oxide (CeO x ) nanocrystals can be well dispersed in both polar and nonpolar solvents and easily processed into high-quality electron transport layers (ETLs). The inverted PVSC with the configuration of “NiMgLiO/MAPbI3/6,6-phenyl-C61-butyric acid methyl ester (PCBM)/CeO x ” has achieved a high efficiency up to 18.7%. Especially, the corresponding devices without encapsulation can almost keep their initial PCEs in 30% humidity-controlled air in the dark for 30 days and also show no sign of degradation after continuous light soaking and maximum power point tracking for 200 h in a N2 atmosphere. These results have been proved to be associated with the dual functions achieved by the PCBM/CeO x bilayer ETLs in both efficient electron extraction and good chemical shielding. Furthermore, an all inorganic interfacial layer based PVSC with the configuration of “NiMgLiO/MAPbI3/CeO x ” has also achieved a promising efficiency of 16.7%, reflecting the potential to fabricate efficient PVSCs with extremely low cost.