Atomic insights of stable, monodispersed CsPbI${}_{3-x}$Br${}_x$ (x = 0, 1, 2, 3) nanocrystals synthesized by modified ligand cell

Synthesis of monodispersed, stable halide, and mixed halide perovskite nanocrystals by hot-injection approach is still challenging due to the fast reaction kinetics and unrevealed ligand chemistry. The atomic scale imaging of perovskite nanocrystals using transmission electron microscopy (TEM) is also challenging because of their structural degradation due to high electron dose and soft nature of perovskites. Here, a novel technique is proposed to synthesize pure cubic phase, monodispersed, stable CsPbX${}_3$ (X = I/Br) nanocrystals by simply modifying ligand chemistry using olive oil, which also leads to realization of tuneable composition mixed halide perovskites by simple physical mixing. Here, the atomic scale images and the probable distribution of Cs, Pb, and I/Br atoms in single halide and mixed halide perovskites via high-resolution TEM microscopy are presented. The estimated atomic distance (Pb-Pb and Pb-I/Br) is strongly corroborated with the VESTA structure. Interestingly, the lattice constant (d-value) of the synthesized nanocrystals is smaller (≈3%) than the theoretical predicted one, leading to a higher phase stability in laboratory ambient conditions (45-55% humidity, 300 K). The theoretical analysis using density functional theory enlightens the understanding of higher stability of CsPbI${}_2$Br along with the maximum optical absorption in the visible regime, as a preferable material for the photovoltaic applications. (© 2022 Wiley‐VCH GmbH)