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

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 PEA₂Cs_n-1Pb_nBr₃ _n ₊₁ perovskite is demonstrated to stable 3D CsPbBr₃ 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.