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.