Shining Light on Metal Halide Perovskite Stability with Nanoscale Optical Characterization

减轻气候变化的有害影响需要可再生能源的技术进步。在过去的十年中，混合金属卤化物钙钛矿薄膜作为太阳能电池的有源层已经越来越成功，显示出与硅相媲美的功率转换效率。尽管取得了这些成功，但稳定性问题和对毒性的担忧使这些材料无法广泛商业化。这两个问题的核心是这些薄膜固有的多晶微观结构，它引入了光电特性和能量景观的异质性，并限制了电荷传输和效率。然而，确定改进的途径是困难的，因为体光电特性的测量不能充分探测这种异质性。因此，需要在纳米尺度上进行光电研究，以充分了解微观结构、稳定性和电荷输运之间的关系。该项目将通过开创太赫兹和光致发光（PL）散射近场显微镜（SNOM）的结合使用来解决这些问题，以绘制纳米尺度上的静态和动态光电特性。该项目将特别关注用于串联太阳能电池的混合卤化物和混合铅锡材料，因为它们是该领域稳定性问题和商业努力的核心。通过与传统显微镜和超快光谱测量的比较，太赫兹/PL-SNOM测量将揭示影响光电性能的内在和外在因素的机制。通过分析提高稳定性的方法，包括钝化和a位阳离子混合，本项目将为稳定高效的钙钛矿薄膜的材料工程提供路线图。

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.