Controlled Structural Transformation in Sb‐Doped Indium Halides A3InCl6 and A2InCl5∙H2O Yields Reversible Green‐to‐Yellow Emission Switch

Abstract Lead halide perovskites have demonstrated promising emission tunability achieved by composition engineering, which makes them viable in several potential applications. Determining how to effectively control the crystalline structural transformation and composition in lead‐free halide perovskites is of great importance. Herein, a controllable synthetic method is reported to obtain the 0D metal halide perovskite derivatives (Cs 1− x Rb x ) 2 InCl 5 ∙H 2 O and (Cs 1− x Rb x ) 3 InCl 6 , through synergistic regulation of the Cs/Rb feed ratios and the reaction solvent. When hydrochloric acid (HCl) is used as the reaction solvent, (Cs 1− x Rb x ) 2 InCl 5 ∙H 2 O is obtained at a high Cs/Rb feed ratio greater than 2:1, while (Cs 1− x Rb x ) 3 InCl 6 is obtained at a low Cs/Rb feed ratio of less than 2:5. However, when anhydrous methanol (MeOH) is used as the reaction solvent, only the (Cs 1− x Rb x ) 3 InCl 6 structure is obtained at all Cs/Rb feed ratios. In addition, a reversible crystalline structural transformation is demonstrated between (Cs 0.67 Rb 0.33 ) 2 InCl 5 ∙H 2 O and (Cs 0.67 Rb 0.33 ) 3 InCl 6 by immersing the as‐prepared products into MeOH and HCl sequentially, which generates a novel green/yellow reversible emission switch. The Sb 3+ ion self‐trapped exciton emission and stability of the synthesized (Cs 1− x Rb x ) 2 InCl 5 ∙H 2 O and (Cs 1− x Rb x ) 3 InCl 6 are systematically investigated. The results are helpful for promoting the diverse photonics and optoelectronics applications of these environmentally stable perovskite derivatives.