Solventless mechanochemical synthesis of Sn-based halide perovskite microcrystals with high stability tracked by photoluminescence spectroscopy

Developing solvent-free methods to synthesize lead-free perovskites is of practical importance from the viewpoint of sustainability. In this work, we use a facile mechanochemical approach to synthesize a series of lead-free Sn-based halide perovskite microcrystals (powders) in ambient conditions directly from precursor powders (CsX and SnX₂ (X = I, Br, Cl)) without any solvent. Such an approach is energy-saving and avoids the use of toxic solvents. There exists phase evolution during the mechanochemical processing of the precursor powders with CsSn₂Br₅ to CsSnBr₃ in the first hour and finally into the stabilized phase of Cs₂SnBr₆ after 28 days and with Cs₂SnCl₄ to CsSnCl₃ in the first hour and finally to the stabilized phase of Cs₂SnCl₆ after 36 days. The stabilized Cs₂SnI₆ powders emit light centered at 930 nm under the excitation of 785 nm, and the stabilized Cs₂SnBr₆ powders emit light centered at 682 nm under the excitation of 365 nm. Both the stabilized Cs₂SnI₆ and Cs₂SnBr₆ powders exhibit excellent long-term structural and optical stabilities, and the Cs₂SnBr₆ powders have a better thermal stability than the Cs₂SnI₆ powders. This work likely offers a green-route synthesis of lead-free halide perovskites towards large-scale manufacturing and industrialization.