Transformation of Cs3Bi2Br9 to Cs2AgBiBr6 Lead‐Free Perovskite Microcrystals Through Cation Exchange

Abstract All‐inorganic lead‐free Cs 2 AgBiBr 6 double perovskites have gained significant attention due to their potential as stable and nontoxic photoactive semiconductors. Currently, it remains challenging to synthesize homogeneous microcrystals (MCs) exhibiting excellent properties, which are necessary for large‐area device integration. This work proposes a two‐step synthesis approach involving the introduction of a foreign silver cation to transform the 0D layered Cs 3 Bi 2 Br 9 to 3D Cs 2 AgBiBr 6 perovskite structure. This work has studied the cation exchange (CE) transformation mechanism by isolating intermediates to be able to follow the evolution of the crystal lattice as well as the structural and optical properties over time. Moreover, complete CE results in phase‐pure, highly crystalline Cs 2 AgBiBr 6 MCs exhibiting excellent photonic properties, superior to their counterparts synthesized by anti‐solvent precipitation. These findings highlight the potential of CE‐induced transformation as a means of synthesizing novel, stable perovskites.