UC Santa Barbara

The focus of this dissertation was on the preparation and analysis of new materials related to hybrid halide perovskites, AMX3, where A = a small organic cation, M = a divalent heavy metal, and X = a halogen. It sought to understand the fundamental reasons for why the hybrid perovskites work as excellent optoelectronic materials, and to use this information to design new, stable, and less toxic materials.

This dissertation first sought to understand whether disparate slabs of metaliodide octahedra could be electronically coupled using electronically functional organic molecules, as this could create more stable and potentially more functional materials. A well-known organic compound made famous during the advent of organic metals, tetrathiafulvalene, was used to prepare three new hybrid materials [(TTF)Pb2I5, (TTF)BiI4, and (TTF)4BiI6] with some found to behave like semiconductors with 3D electronic connectivity, even though they were structurally 1D or 2D materials. This discovery supported our original hypothesis that a more stable, layered, hybrid perovskite material could potentially exist using functional organic molecules as both structural and electronic components.

This work then extended its focus to study platinum based hybrid perovskites, A2PtI6 (A = small organic cation), and examined the effect of increasing cation size in Pt based vacancy ordered hybrid perovskite materials (VOHPs). This study was pertinent to our fundamental understanding of VOHPs, as by establishing structural trends caused by the small organic cations, and how different metals (Pt) behaved in these systems, future avenues for material design could be opened. It was found that the hydrogen bonding of the small organic cation to the iodides of the [PtI6]2- octahedra were quite significant as cation size increased, as these interactions dictated final structure and subsequent optical properties of these materials.

In the process of understanding iodide containing hybrid perovskites, serendipitous discoveries of polyiodides were made along the way. These works include understanding the effect of hydrogen bonding in the formation of hybrid platinum oligo- and polyiodides, as well as resolving the 200 years old mystery as to what happens when starch combines with iodine.

In summary, the work presented herein is reflective of the many diverse preparation and characterization techniques needed to complete these projects: solution and solid state synthesis, and single crystal and bulk material characterization techniques ranging from crystallography, calorimetry, and optical spectroscopy. It is also a testament to the social aspect of science, as to complete this work, many collaborations needed to be formed.