Herein, solution‐processed 2D Nb2O5(001) nanosheets (c‐Nb2O5 NS) are prepared and combined with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) as an electron transport layer (ETL) for inverted inorganic CsPbI2Br perovskite solar cells (PeSCs). The PeSCs with a c‐Nb2O5/PC61BM bilayer ETL yield a high power conversion efficiency (PCE) up to 11.74%, remarkably outperforming the devices with only PC61BM (9.10%) and those with the state‐of‐the‐art ZnO/C60 ETL (10.65%) prepared under the same conditions. More importantly, the nonencapsulated PeSCs with c‐Nb2O5 exhibit a high thermal stability with only 20% PCE loss after 400 h thermal aging at 85 °C. Such an impressive performance and a high stability can be attributed to the introduction of c‐Nb2O5(001) NS with favorable band levels, strong acid nature, and the small lattice fringe spacing along the large lateral (001) surface, which not only facilitate the electron transport, blocking the hole transport, but also contribute to defect passivation and retard the iodine ions diffusion toward the Ag electrode. This study thus provides a deeper insight for the interfacial design in inverted inorganic PeSCs and contributes to PCE improvement in the future.