In situ formation of a 2D/3D heterostructure for efficient and stable CsPbI2Br solar cells

Forming a 2D capping layer has been recognized as an effective strategy to improve both efficiency and stability of organic-inorganic perovskite solar cells. However, constructing a 2D/3D heterostructure is difficult for inorganic perovskites due to their resistance to cation exchange reaction. Here, we report an effective in situ growth method to form a 2D/3D heterostructure for inorganic CsPbI2Br perovskite. The 2D capping layer was found to form a type-II heterojunction with 3D perovskites, facilitating hole extraction at the perovskite/hole transport layer interface. When exposed to a humid environment, the 2D/3D perovskite films showed greatly enhanced phase stability as compared to the pristine 3D perovskite films. As a result, the optimized 2D/3D CsPbI2Br device reached a power conversion efficiency of 14.5% with improved short-circuit current and significantly enhanced device moisture stability.