Abstract Owing to the superior optoelectronic properties of perovskite materials, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been increased dramatically within several years, but the poor thermal, humidity, and light stability of these PSC devices hinders the progress to their practical application. We obtained an inspiration from two-dimensional (2D) Ruddlesden–Popper perovskite solar cells with good photovoltaic performance and placed the organic-inorganic hybrid perovskite layer inside two fully-inorganic CsPbI3 perovskite layers in the cubic α phase. The middle layer has lower stability than the two outer ones, which protect the middle layer by impeding the organic ions of the organic-inorganic hybrid perovskite middle layer from diffusing outside and causing damage to neighbor CTLs. Water molecules from air are also obstructed from reaching the hybrid perovskite layer. We used 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) ionic liquid and 3-(decyldimethylammonio) propane-1-sulfonate (DDMAPS) and obtained phase-stable fully-inorganic α phase CsPbI3. The constructed PSCs have extremely high stabilities and high PCEs. After 1000 h of illumination under AM1.5 illumination in air at 60 °C (Humility: ~60%), PSCs with a sandwich structure of three perovskite layers maintain nearly all the original PCE of 21.32%, while those without that only remain 76.63%.