Stabilization of Inorganic Perovskite Solar Cells with a 2D Dion–Jacobson Passivating Layer

Abstract Inorganic metal halide perovskites such as CsPbI 3 are promising for high‐performance, reproducible, and robust solar cells. However, inorganic perovskites are sensitive to humidity, which causes the transformation from the black phase to the yellow δ, non‐perovskite phase. Such phase instability has been a significant challenge to long‐term operational stability. Here, a surface dimensionality reduction strategy is reported, using 2‐(4‐aminophenyl)ethylamine cation to construct a Dion–Jacobson 2D phase that covers the surface of the 3D inorganic perovskite structure. The Dion–Jacobson layer mainly grows at the grain boundaries of the perovskite, effectively passivating surface defects and providing favourable interfacial charge transfer. The resulting inorganic perovskite films exhibit excellent humidity resistance when submerged in an aqueous solution (isopropanol:water = 4:1 v/v) and exposed to a 50% humidity air atmosphere. The Dion–Jacobson 2D/3D inorganic perovskite solar cell (PSC) achieves a power conversion efficiency (PCE) of 19.5% with a V oc of 1.197 eV. It retains 83% of its initial PCE after 1260 h of maximum power point tracking under 1.2 sun illumination. The work demonstrates an effective way for stabilizing efficient inorganic perovskite solar cells.