Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Chemistry

Major

Chemistry

First Advisor

Javier Vela

Abstract

As the global population increases and our dependence on technology grows, we need to

develop technologies that can generate energy cleanly and efficiently without releasing harmful

pollutants into the environment. This thesis describes the synthesis and characterization of new

and emerging solar cell materials including methylammonium lead mixed halide perovskites,

cesium germanium halide perovskites, and alkali bismuth dichalcogenides.

We begin by characterizing the methylammonium lead mixed halide perovskites by 207Pb

solid state nuclear magnetic resonance (ssNMR) spectroscopy. When these materials are prepared

in solution, we observe the presence of dopants and semicrystalline phases that survive and persist

even upon annealing. We develop a novel solid phase synthesis that successfully eliminates these

semicrystalline phases; however, dopants still persist. Our results are consistent with the presence

of miscibility gaps and spontaneous spinodal decomposition of mixed-halide perovskites at room

temperature. These results suggest that better optoelectronic properties and improved device

performance may be achieved through careful manipulation of the different phases and

nanodomains present in these materials.

Next, because many technologically relevant semiconductors are composed of toxic (Cd,

Pb, As) or relatively scarce (Li, In) elements, we describe the synthesis of nanocrystals of two new

ternary semiconductor families: cesium germanium halide perovskites and alkali bismuth

dichalcogenides. We achieve size control of cesium germanium halide perovskite nanocrystals by

varying cysteammonium halide ligands in an aqueous synthesis. We observe a variety of

morphologies including pyramidal, hexagonal, and spheroidal. We successfully dope Mn2+ into

the lattice for the first time with incorporations up to 29% in bulk and 16% in nano samples. We

also report a facile, low-temperature, and size-tunable (4–28 nm) solution phase synthesis of

ternary alkali bismuth dichalcogenides. We observe 1.20–1.45 eV band gaps that all fall within

the ideal range for solar cells with high extinction coefficients in the 104–106 cm-1 M-1 range. We

computationally investigate the lowest energy superstructures that result from “coloring” that is

caused by mixed-cation sites present in the rock salt lattice. The syntheses reported in this

dissertation unlock two new classes of low cost and environmentally friendly semiconductors that

show properties of interest for applications in energy conversion.

Copyright Owner

Bryan Anthony Rosales

Language

en

File Format

application/pdf

File Size

142 pages

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