Structure of Mixed\nHalide Perovskite Nanocrystals\nat Various Length Scales

Understanding the internal structure and bonding of lead\nhalide\nperovskite nanocrystals (NCs) is crucial to designing stable materials\nfor various applications. In this work, we probe the extent of alloying\nand phase segregations in mixed halide perovskites at three length\nscales using a combination of optical spectroscopy, X-ray diffraction\n(XRD), extended X-ray absorption fine structure (EXAFS), and Raman\nspectroscopy. We observe domain-free mixed halide solid solutions\nwith randomly distributed halide ions about the Pb center with several\ndistinct but dynamically changing [PbCl<sub><i>x</i></sub>Br<sub>6–<i>x</i></sub>]<sup>4–</sup> environments\nwith only Pb–Cl and Pb–Br bonds. They are also sensitive\nto the changes in the unit cell dimensions resulting from the substitution\nof Br by Cl, obeying Vegard’s law. Further, we reveal that\nweak octahedral bonding drives the consistent alteration of the halide\nenvironment. These studies provide insights into the chemical bonding\ndriving the improved stability and performance pivotal for designing\nadvanced optoelectronic devices.