UC Berkeley

Lead halide perovskites are the subject of great interest owing to the unique photophysical properties of perovskites where elucidating the nature of those properties highly relies on the understanding the photophysics of semiconducting materials. Upon photoexcitation, excited electrons and holes are generated, where bound electron-hole pair is called an exciton, what decides the optoelectronic properties depends on how charges carriers are relaxed back to their ground state. Given that the charges carriers can be coupled to lattice vibrations, called phonons, while relaxing, taking a closer look at how the structural fluctuations produced by the lattice affects the behavior of charge carriers is crucial to elucidate the microscopic origin of the properties of semiconducting materials. However, including the dynamical effects of phonons is in general difficult. Although the study on how phonons affect the properties of free charges has a long history, there still remains active open area for studying how excitonic properties are altered by the interaction with phonons. Especially for perovskites, the complex structure and anharmonic nature makes theoretical study even more challenging.

Herein, in this thesis, we explore the properties of lead halide perovskites in various dimensions by using an atomistic molecular dynamics simulations, allowing us to capture all orders of anharmonicity. For the system of layered perovskites with bulky organic molecules, it is showed that how the anharmonicity of organic molecules affects the vibrational relaxation dynamics following photoexcitation. And for a system of single chain perovskite nanowire, we are able to analyze the structural dynamics. In terms of studying excitonic properties in bulk perovskites, with this explicit anharmonic perovskite lattice, we describe quantum particles with path integral framework and we have developed a Gaussian field theory to describe the effective interactions between electrons and holes as mediated by the perovskite lattice using path integral molecular dynamics, illustrating the method of use to study exceptional excitonic properties of perovskites. Lastly, we end this by briefly introducing the application of this framework for studying the multiparticle excitations in perovskite nanocrystals.