Synthesis, Self-assembly and Regrowth of Lead Halide Perovskite Nanocrystals

Abstract

Over the last decade, impressive development in lead halide perovskites (LHPs) have made them leading candidate materials for photovoltaics (PVs), X-ray scintillators, and light-emitting diodes (LEDs). The success of LHPs NCs in lighting and display applications is mainly originated from their high photoluminescence quantum yield (PLQY), narrow emission, sizable bandgap, and cost-effective fabrication. Consequently, a comprehensive understanding of the design principles of LHP NCs will fuel further innovations in their optoelectronic applications.

This dissertation centers on the synthesis and self-assembly of LHP NCs. At first, we investigate the capability of colloidal synthetic routine to engineer the shape, size, and dimensionality of the resulting LHPs NCs (chapter 2), including 0D nanospheres, 2D nanoplates, and 3D nanocubes. Starting from the LHPs NCs, nanoplates (chapter 3), nanowires (chapter 4), and superstructures (chapter 5) are successfully achieved via various self-assembly strategies. In chapter 3, we present a liquid-air interfaces-assisted self-assembly technique to obtain micro-scale CsPbBr3 nanoplates from as-synthesized nanoscale NCs. The AC-HRTEM offered an atomic-level observation during the structural evolution and revealed an oriented attachment-mediated assembly mechanism. The assembled CsPbBr3 nanoplates exhibited ultrahigh stability under X-ray energy dispersive spectroscopy (EDS) mapping conditions (300-kV electron beam), and the first atomic-resolution EDS elemental mapping data of LHP NCs were acquired. In chapter 4, we demonstrate an efficient green-chemistry approach for the self-assembly of CsPbBr3 NCs into 1D nanowires and nanobelts via the light induction. As an elegant and promising green-chemistry approach, light-induced self-assembly represents a rational method for designing perovskites. In chapter 5, we will explore the self-assembly of CsPbBr3 NCs into superstructures to overcome the ‘green gap’ to achieve a pure green emission with high PLQY for realizing next-generation vivid displays.

In summary, we systematically investigated the mechanisms of LHP NC self-assembly, the kinetics of their morphological evolution and phase transitions, and driving forces that govern the self-assembly process. The assembled LHP NCs manifest desirable properties (e.g., superfluorescence, improved photoluminescence lifetime, enhanced stability against moisture, light, electron-beam irradiation, and thermal-degradation) that translate into dramatic improvements in device performance.