Hybrid Perovskite Design through Composition and its Impact on Growth and Morphology
Williams, Spencer Thomas
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Hybrid perovskite solar cells (PVSCs) have emerged into the academic and industrial communities as a potentially transformative alternative to prevailing silicon technologies. PVSCs have rapidly increased in efficiency in the brief time they have been in the research spotlight, but fundamental material challenges like Pb-toxicity, ionic diffusivity, and stability impede efforts toward commercialization. This has led to significant world-wide investments in the compositional engineering of CH3NH3PbI3, one of the most commonly studied hybrid perovskites for photovoltaics. Throughout the course of this effort, a significant amount of work has been directed at modifying each site in the hybrid perovskite lattice, but the complexity inherent to this material system has complicated rational design. This dissertation presents a series of case studies aimed at elucidating the role that each site in the CH3NH3PbI3 lattice plays in mediating material growth and structural evolution. Chapters 2 and 3 present experimental investigations of the role that halide anion and organic cation sites play in transformation, respectively. Chapter 4 presents a conceptual overview that connects this understanding to the many other techniques being developed to control CH3NH3PbI3 growth. Chapter 5 expands on this conceptual footing to mount a survey of the periodic table to identify species with the potential to modify the metal cation site, and Chapter 6 mounts a focused investigation of transition metal inclusion in CH3NH3PbI3. Relationships between composition, growth, morphology, and resulting properties are uniquely complex in this relatively new class of material. As a whole, the work presented in this dissertation provides a framework to untangle this complexity and rationally motivate continued compositional engineering to eventually facilitate technology translation. Chapter 7 summarizes relationships between composition, growth, and structure along with presenting broader perspective to direct continued efforts toward Pb replacement. A selection of key figures from each chapter are reproduced in this concluding chapter to allow a non-specialist reader to draw value out of this dissertation without requiring a close reading of each topic covered.