Lead Halide Perovskite Nanocrystals: Photophysical and Photochemical Dynamics

Abstract

Lead halide perovskites nanocrystals (LHP NCs) are a recent novel material of ‘high-defect tolerance’ that has been synthesized which have provided a new platform for opto-electronic devices, such as photovoltaics and light-emitting diodes. Development of these materials for commercial devices requires a thorough understanding of their photo-physical properties. A comprehensive understanding of photo-physical properties involves studying the interplay between light-matter interactions, which produce photo-excited charge carriers and govern radiative recombination mechanism, carrier-lattice interactions, which play a dominate role in non-radiative dynamics such as hot-carrier cooling and recombination, and the NC surface chemistry which plays an important role in passivating surface sites which can potentially act as non-radiative recombination centers. In chapter 1 a review of the photo-physical phenomena and electronic processes which occur in materials is established and the motivation for incorporating nanomaterials into opto-electronic devise is provided. Chapter 2 describes in formal details the theoretical methods used to compute electronic structure, light-matter interactions, and carrier-lattice interactions are. Chapter 3 overviews simple physical models, such as particle-in-a-box photo-physics and two-level Redfield theory, which give intuition on how to understand the results of the research. Finally chapters 4-7 are devoted to original research on charge-carrier dynamics within a LHP NC atomistic model as free carriers, bound polarons, in the presence of surface defects, and finally in the presence of transition metal dopants. Chapter 4 provides computational evidence of slow electron cooling due to strong electronic confinement and large spin-orbit coupling contributed from Pb2+ 6p orbitals. Chapter 5 considers the effect of polaron formation on hot-carrier dynamics with the prediction of low efficiency polaron infrared photoluminescence. Chapter 6 provides mechanism for ‘defect tolerance’ due to bright electron surface trap states that form due to polaron reorganization. Chapter 7 models dual exciton-dopant luminescence due to Mn2+ doping.