Structure of Mixed Halide Perovskite Nanocrystals at Various Length Scales

Abstract

Understanding the internal structure and bonding of lead halide perovskite nanocrystals (NCs) is crucial to designing stable materials for various applications. In this work, we probe the extent of alloying and phase segregations in mixed halide perovskites at three length scales using a combination of optical spectroscopy, X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and Raman spectroscopy. We observe domain-free mixed halide solid solutions with randomly distributed halide ions about the Pb center with several distinct but dynamically changing [PbCl x Br 6−x ] 4− environments with only Pb−Cl and Pb−Br bonds. They are also sensitive to the changes in the unit cell dimensions resulting from the substitution of Br by Cl, obeying Vegard's law. Further, we reveal that weak octahedral bonding drives the consistent alteration of the halide environment. These studies provide insights into the chemical bonding driving the improved stability and performance pivotal for designing advanced optoelectronic devices.