Light/heating/humidity induced reversible transformation between CsPb2Br5 and CsPbBr3 for switchable photoluminescence and heterostructure diodes

CsPb₂Br₅ has attracted a tremendous attention recently owing to its high stability and unusual optical properties. However, the transformation between CsPb₂Br₅ and CsPbBr₃ has yet been fully understood and the origin of the bright green emission in CsPb₂Br₅ is still under debate. In this work, we elucidate the mechanism of the abnormal green emission in CsPb₂Br₅ and reveal the light/heating/humidity induced reversible transformation between CsPb₂Br₅ and CsPbBr₃. The detailed structure characterization indicates the successful synthesis of pure phase CsPb₂Br₅, which exhibits a non-luminous feature. Remarkably, after the treatment of ultraviolet laser irradiation or annealing, the pure phase CsPb₂Br₅ can be transformed partially or completely into CsPbBr₃, yielding an unexpected bright green emission. In addition, the transformed CsPbBr₃ can be converted back to CsPb₂Br₅ under the humidity environment, demonstrating the reversible transformation and photoluminescence switch. Interestingly, CsPbBr₃ derived from transformed CsPb₂Br₅ exhibits superior emission properties such as higher photoluminescence stability, compared with the one-spot directly synthesized CsPbBr₃. Moreover, the light induced transformation facilitates the fabrication of CsPb₂Br₅/CsPbBr₃ nano-heterostructure diodes with a high rectification ratio. These results provide an important insight into the photophysics and transformation mechanism of all-inorganic Cs-Pb-Br perovskites for photonics/electronics device applications.