Mechanisms of mechanochemical synthesis of cesium lead halides: pathways toward stabilization of α-CsPbI3

Cesium lead iodide with cubic perovskite structure (α-CsPbI₃) is gaining significant interest in photovoltaic applications due to its excellent absorbance of the visible solar light and other attractive optoelectronic properties. However, the synthesis of stable α-CsPbI₃ poses a significant challenge. Mechanochemical synthesis is emerging as a suitable method for the preparation of cesium lead halides. This work investigates the ball milling-induced synthesis of cesium lead halides perovskite phase using halide mixing or doping approaches. The synthesis in the CsI + PbI₂, CsBr + PbBr₂, CsBr + PbI₂, and CsI + PbI₂ + NdI₃ mixtures and halide exchange reactions in the CsPbBr₃ + 3KI and CsBr + PbBr₂ + 3KI systems are investigated to elucidate the mechanism of this process. Then, CsPb(I₁₋ₓBrₓ)₃ and CsPb(₁₋y)NdyI₃ materials with different x and y ratios are prepared, and their stability is probed in the air using light absorption spectroscopy. These results suggest that Nd doping is more efficient in the stabilization of the perovskite structure than partial replacement of iodine with bromine. Microstructure observations reveal the existence of two different product formation mechanisms depending on the mechanical properties of reactants. The results reveal that the milling temperature has a significant impact on the reaction kinetics. The produced particles nucleate and grow at the reactant interface and retard the synthesis reaction by creating a diffusion barrier. Extended milling reduces the product particle size and creates fresh contact between reactants, thus facilitating reaction completion.