UC Berkeley

Halide perovskites are emerging new semiconductors that have excellent optoelectronic performance. The great optical efficiency has triggered research in all fields of physical sciences, including electronic property studies, chemical synthesis, electrical engineering, and structural characterization. Different from traditional covalent semiconductors such as silicon or II-VI semiconductors, halide perovskites resemble ionic crystals to have lower mechanical strength, solution processability, and dynamical lattices. The uniqueness of halide perovskites evades conventional categorization so that renewed conceptual frameworks are necessary. Generally speaking, in the field of physical chemistry of halide perovskites, both the structural and electronic properties of this class of material are of great interest. The coupling between structural dynamics and electronic behaviors contributes to the intriguing carrier dynamical phenomena, such as the formation of polaron, delayed photoluminescence, dynamical screening of hot carriers, etc. The major obstacle to unravel the unprecedented properties of halide perovskites has been the lack of control over the atomic configuration of perovskite microstructures, which requires both synthetic and characterization advancement. Therefore, this Dissertation centers around the structural and carrier Dynamics of low-dimensional halide perovskites by making use of atomically defined nanostructures and advanced spectroscopic/microscopic tools.

After a brief background introduction to halide perovskites, I discuss the scientific questions to be addressed in this Dissertation. In Chapter 2 and 3, I focus on a material platform composed of one-dimensional halide perovskite nanowires. With this material platform, an optical scaling law is observed and explained with Monte Carlo simulation. In these two chapters, I demonstrate the power of well-defined perovskite nanostructures and how to use these nanostructures to resolve intriguing carrier dynamics of halide perovskites in general. In Chapter 4, I introduce synthesis of atomically thin halide perovskite nanostructures. Both one-dimensional atomically thin nanowires and two-dimensional atomically thin nanosheets are used as case studies to demonstrate the advanced synthetic control over the atomic structure of halide perovskites. Electron microscopy is used to resolve the structure of atomic resolution. In Chapter 5, I select the atomically thin nanowires as a material platform to study the transient structural dynamics of halide perovskite nanostructures. Ultrafast electron camera is used to resolve the structural dynamics with millisecond resolution while atomic spatial resolution is maintained. I thoroughly investigate the structural behaviors of one-dimensional halide perovskites under electron beams and demonstrate the resilient while mobile lattice dynamics as a unique character of halide perovskites. Finally, in Chapter 6, I summarize the Dissertation by providing an outlook and new perspectives on the study of halide perovskites. Overall, this Dissertation is aimed to address the structural and electronic properties of halide perovskite with an emphasis on the synthetic control. The research logic of this Dissertation can be used as a new paradigmatic framework for the future exploration and investigation of this emerging new material.