Shining Light on Metal Halide Perovskite Stability with Nanoscale Optical Characterization

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Mitigating the detrimental effects of climate change will require technological advances in renewable energy. In the last decade, hybrid metal halide perovskite thin films have shown increasing success as active layers in solar cells, demonstrating power conversion efficiencies rivaling those of silicon. Despite these successes, issues with stability and concerns about toxicity have kept these materials from widespread commercialization. At the center of both issues is the polycrystalline microstructure inherent to these films, which introduces heterogeneity in optoelectronic properties and energy landscape and can limit charge transport and efficiency. However, identifying routes for improvement is difficult because measurements of bulk optoelectronic properties cannot adequately probe this heterogeneity. A need therefore exists for optoelectronic studies on the nanoscale to fully understand the relationship between microstructure, stability, and charge transport. This project will address these issues by pioneering the combined use of THz and photoluminescence (PL) scattering near-field microscopy (SNOM) to map static and dynamic optoelectronic properties at the nanoscale. This project will specifically focus on mixed-halide and mixed lead-tin materials for the use in tandem solar cells as they are central to both the stability concerns and the commercial efforts of the field. Through comparison with traditional microscopy and ultrafast spectroscopy measurements, THz/PL-SNOM measurements will unravel the mechanisms whereby both intrinsic and extrinsic factors affect optoelectronic performance. By analyzing methods employed to improve stability including passivation and A-site cation mixing, this project will provide a roadmap for the materials engineering of stable and efficient perovskite thin films.