Date of Award
Doctor of Philosophy
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.
Bryan Anthony Rosales
Rosales, Bryan Anthony, "Synthesis and advanced spectroscopy of new and emerging energy materials" (2019). Graduate Theses and Dissertations. 17088.