How does the halide exchange reaction affect the crystal structure and optical properties of MAPbBr3?

Label:chem

Topic
The halide exchange reaction involves substituting halide ions within the perovskite structure, which can alter the material's composition and optical properties. Understanding these changes is crucial for optimizing the performance of perovskite-based devices.

From: "Tuning emission and bandgap dynamics of MAPbBr₃ single crystals through halide exchange with methyl iodide", Chemical Physics Impact, Volume 10, June 2025, 100807
Answer
The halide exchange reaction significantly affects both the crystal structure and optical properties of MAPbBr3. Initially, MAPbBr3 crystals exhibit a cubic crystal structure with a space group of m3m and a lattice constant of 5.940 Å. As iodide ions replace bromide ions, the bandgap decreases from 2.26 eV to 1.7 eV, and the emission spectrum shifts from green (540 nm) to red (730 nm). Elemental analysis shows a change in the atomic molar ratio of bromine to lead from approximately 3:1 to a lower bromine content, indicating the formation of a mixed halide perovskite, MAPb(Br/I)3. The presence of vacancies in the crystal lattice facilitates the diffusion of iodide ions, enabling efficient halide exchange. These changes in crystal structure and optical properties highlight the dynamic nature of the halide exchange process and its direct impact on the material's optoelectronic characteristics.
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