Exploring the Structural and Optical Response of Halide Perovskites Using High-Energy Electrons

Abstract

This thesis aims to investigate the nanoscale morphology, crystallography, composition, and optoelectronic structure of halide perovskites, a promising candidate for next-generation optoelectronic materials, using high-energy electron-beam microscopy techniques. This work addresses the stability challenge of PSCs from a material science perspective by understanding and controlling their complicated nanostructure. The unique macroscopic properties of lead halide perovskites are dictated by their nanostructure, which has direct ramifications on device performance and operational stability. The thesis starts by reviewing hybrid halide perovskites and their heterogeneity at multiple lengthscales, and the different electron microscopy techniques used and developed in this work. It then reports in three experimental chapters the study of degradation mechanisms under an electron and X-ray beam using 4D-scanning transmission microscopy (4D-STEM), the development of cathodoluminescence (CL-SEM) to probe the optical properties of halide perovskites at the nanoscale, and the development of strategies to push the limits of 4D-STEM towards in-situ and operando conditions. The study demonstrates that high-energy electron probes are a powerful tool for studying perovskites at the nanoscale, and each experimental chapter addresses a specific technique development to enable new modalities of electron microscopy on halide perovskites. With these developments, this thesis yields valuable fundamental insights into the phase and operational stability of the beam-sensitive hybrid lead perovskites at the nanoscale.