Unveiling Electron Dose-Induced Phase Decomposition and Energy Kinetics in Cu-Doped CsPbI₃ Nanocrystals

Abstract

Atomic-scale examination of lead halide perovskites is currently a subject of growing interest for applications in the optimization of perovskite-based photovoltaic and optoelectronic devices. While transmission electron microscopy (TEM) is a powerful tool to characterize these electron-sensitive materials at the atomic scale, it induces structural and chemical modifications along with other undesirable artifacts. Here, we investigate the phase stability of nominally Cu-doped CsPbI 3 nanocrystals, with enhanced structural stability as compared to their pristine counterparts, against electron irradiation using high-resolution TEM at ambient conditions. Our findings reveal a significant transformation from the cubic to the orthorhombic phase at a dose of ∼3 × 10 3 e − /Å 2 . Analysis of the beam energy deposited per unit cell, along with the evolution of lattice energy with varying cell dimensions, as obtained from density functional theory, provides valuable insights into the mechanisms governing the beaminduced phase decomposition process, corroborated by the phonon dispersion of the system, which is not yet reported. At a critical dose of ∼1.68 × 10 6 e − /Å 2 , the lattice undergoes complete and irreversible degradation. Thus, our study demonstrates real-time in situ beam-induced phase decomposition in Cu-doped CsPbI 3 for the first time, with an estimation of the electron dose limits below which beam-induced alterations are minimal, allowing accurate imaging and analysis of perovskites.