| Summary: | There is an unmet need for thin film photovoltaic (PV) technology that features low materials cost, high performance and reliability, and compatibility with low-cost manufacturing. Chalcogenide perovskite materials show promise to meet these criteria but are at an early stage of development. Other promising optoelectronic materials, such as lead halides perovskites, have shown remarkable strides in optoelectronic performance, but they are plagued with issues of toxicity and stability. Chalcogenide perovskites have been proposed as potential replacements for these lead halide perovskites, but there is a dearth of information on their fundamental material properties. Recent theoretical studies have demonstrated that chalcogenide perovskite materials have suitable band gaps for a single-junction solar cell, and these results are backed by experimental studies on bulk sample morphologies. In order to determine the technological potential of this material class, it is important to understand their structure-property correlations, as well as study it in thin-film form. In this thesis, we focus on materials in the Ba-Zr-S system, particularly BaZrS3 and Ba3Zr2S7 . Although the band gap of these materials have been experimentally determined, there are still many unknown material properties, including absorption coefficients, carrier mobilities, and carrier diffusion lengths. High-quality thin film samples of chalcogenide perovskites will enable measurements of these properties. This thesis has two main goals: 1) to further investigate and characterize bulk properties of these materials for optoelectronic applications and 2) realize the synthesis of thin films, enabling further measurements and paving the way for device fabrication. We connect optoelectronic performance to both intrinsic and extrinsic material properties, using a suite of characterization techniques. We also demonstrate the first-of-a-kind synthesis of epitaxial chalcogenide perovskite thin films using molecular beam epitaxy (MBE), and show encouraging results on alloying and defect control. This thesis advances the current knowledge of chalcogenide perovskites both in terms of properties and processing, and sets the stage for realizing chalcogenide perovskite optoelectronics.
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