Realizing Stable and Luminescent 3D Perovskites via Photo‐Induced Transformation of Quasi‐2D Phases

Abstract Traditional 3D perovskites, being remarkably effective in solar cells and light‐emitting diodes (LEDs), exhibit poor stability under illumination and moisture, limiting their real‐life applications. Recent advancements in perovskite‐based devices have utilized combinations of 2D and 3D perovskites to improve stability. However, high ion mobility can lead to the formation of quasi‐2D phases at interfaces during fabrication, whose behavior remains unclear. Previous studies indicate that quasi‐2D perovskites are less stable and may transform into 3D phases under illumination, but the underlying mechanisms have yet to be investigated. In this work, the light‐induced transformation of quasi‐2D phenylethylammonium cesium lead bromide PEA ₂ Cs _{n −1} Pb _n Br _{3 n +1} perovskite is demonstrated to stable 3D CsPbBr ₃ perovskite. The process is initiated by light excitation, which triggers a reaction with surrounding moisture and oxygen molecules. PbO and Pb(OH) ₂ species form within the material which passivate defects and significantly enhance the photoluminescence and stability of the 3D phase. The simple synthesis method, followed by UV treatment, provides a direct method to stable and luminescent 3D perovskite, making it promising for solar cell, LEDs and photodetector applications.