Surfactant-Free Synthesis of the Full Inorganic Perovskite CsPbBr3: Evolution and Phase Stability of CsPbBr3 vs CsPb2Br5 and Their Photocatalytic Properties

In the present study, the successful fabrication, through a surfactant-free one-pot synthesis in ethanol solution, of the all-inorganic halide perovskite CsPbBr3 has been achieved. The phase formation has been obtained for the first time, using the β-diketonate complexes [Pb(hfa)2diglyme]2 and Cs(hfa) (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2-methoxyethyl ether) and Br2 as the precipitating agent. The growth of CsPb2Br5 microcrystals has been obtained and stabilized under specific synthetic conditions, by controlling the phase transition from CsPbBr3 to CsPb2Br5 as well. The entire process was operated under acid-catalyzed conditions without any need of humidity control and hazardous organic solvents. The control of the aging time and the phase stability during the heat treatment represent the key points in order to selectively and reproducibly obtain the CsPbBr3 or CsPb2Br5 phases. Structural, morphological, and compositional characterizations of the final product show the formation of square microcrystals, with a grain size of up to 3 μm, of the pure and stable perovskite CsPbBr3 phase. Finally, promising results in photocatalytic degradation tests using rhodamine B solution have been obtained under UV light (λ = 360 nm) and visible light, showing high degradation yields of up to 81.9% and 58.4% for CsPbBr3 and CsPb2Br5, respectively.