Dissertation
Tailoring perovskite functionality with fluoridation topochemistry
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2022
DOI:
https://doi.org/10.17918/00001206
Abstract
Topochemistry is the chemical modification of a material while preserving its crystalline integrity. In instances where bottom-up synthesis of a complex material may be difficult or impossible to control, topochemistry offers a precise route of engineering properties through post-synthesis treatment. My work applies fluoridation topochemistry to perovskite materials for spatial chemical and physical property modifications. Perovskite oxides - with the formula ABO3 in which A tends to be an alkali, alkaline earth, or rare earth metal, and B tends to be a transition or post-transition metal - offer a wide variety of tunable optoelectronic and magnetic properties. Lateral patterning of these properties can enable new architectures in oxide-based electronic, magnetic memory, spintronic, and ionic devices. I laterally pattern such properties in perovskite film SrFeO3-[delta] by combining photolithography with reduction/oxidation and fluoridation topochemistries to fabricate laterally-heterostructured films of SrFeO3, reduced SrFeO2.5, and fluoridated phase SrFeO2F. I also demonstrate that the chemical stability of SrFeO2F enables dynamically-control patterned properties through selective reversible redox chemistry of oxide phases. In a second, related yet quite different materials class, the hybrid organic/inorganic lead halide perovskites, I demonstrate that fluoridation topochemistry exerts strong influence over the dynamics of photoinduced charge carriers, with significant implications for photovoltaic devices. Issues in these materials arise from the weak bonding at crystalline surfaces and interfaces. I test the hypothesis that topochemically applied fluoride, selectively added at the surface of hybrid perovskite thin films improves surface chemistry through strong bonding. Under optimized conditions, fluoridation improves the photoinduced charge carrier lifetimes by three-fold. Meanwhile, "overfluoridation" leads to the generation of PbF2 which is identified herein to act as an electron-acceptor for the conduction band of the perovskite.
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Details
- Title
- Tailoring perovskite functionality with fluoridation topochemistry
- Creators
- Benjamin M. Lefler
- Contributors
- Steven J. May (Advisor)Aaron T. Fafarman (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xiv, 131 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991018526907404721