Research on the air stability of perovskite solar cells (PSCs) has attracted great attention in the field of photovoltaics. Although devices based on lead halide perovskites show outstanding efficiency, their commercialization is hampered by the instability of the perovskite under exposure to moisture in ambient air. The use of mesoporous scaffolds has been considered as a promising method to protect the perovskite from moisture ingress. Here, we demonstrate a TiO2/Al2O3 bilayer as the mesoporous scaffold to enhance the air stability of PSCs. PSCs based on the TiO2/Al2O3 mesoporous scaffold were assembled in ambient air at a relative humidity (RH) of over 65%, delivering a champion power conversion efficiency (PCE) of 16.84%. More importantly, PSCs based on TiO2/Al2O3 retained 82% of their initial PCE after storage in ambient air for 2000 h without any encapsulation. In comparison, PSCs based on a single layer of mesoporous TiO2 retained only 57% of their initial PCE. In addition, the TiO2/Al2O3 mesoporous scaffold shows no reduction in light transmission in the visible region in comparison to a single layer of TiO2, indicating its potential to be used for semi-transparent and tandem PSC applications.