CAREER: Optoelectronic Local Probes Measuring Microstructural Degradation and Recovery Under Accelerated Environmental Stressors

摘要：半导体中的缺陷对现代电子产品的性能和稳定性起着至关重要的作用。因此，研究这些缺陷的能力对于生产可靠、高性能的电子产品是非常重要的，而这些电子产品是现代经济的基础。现有的方法通常测量属性，但没有足够的分辨率来解决它们出现的长度尺度上的缺陷。因此，现有的方法只能提供有限的关于独特的局部属性的信息。本CAREER项目旨在建立一个创新的测量平台，可以直接观察微结构光电器件的载流子动力学。基于金属卤化物钙钛矿的太阳能电池将是这项工作的重点。这样的设备具有出色的性能，但稳定性差，对实际应用构成了基本挑战。缺陷化学，离子迁移和微观结构特征都被认为是稳定性差的罪魁祸首，但潜在的物理机制尚未完全了解。PI的研究团队将在受控的环境条件下使用局部光学和电子探针来研究钙钛矿的微观结构，并阐明性能下降的原因。这一基本认识将有助于指导钙钛矿的合理设计和合成，以实现坚固可靠的太阳能电池。PI的研究愿景与教育计划相结合，旨在为广泛的学生，特别是犹他州的年轻女学生，产生对太阳能和电子显微镜的好奇心和兴奋感。该项目将让本科生和研究生参与研究，并促进来自代表性不足群体的学生参与STEM。一个具有流媒体视频和教育资源的互动网站将有助于向美国和国外的公众传播研究成果。技术摘要：金属卤化物钙钛矿非常适合光伏应用，特别是太阳能电池。这种新型半导体具有低成本的加工、丰富的化学和结构多样性、可调谐的带隙、独特的缺陷容忍度和“自我修复”能力。尽管付出了相当大的努力，但钙钛矿太阳能电池稳定性差的潜在物理机制尚未完全了解。许多已建立的表征技术测量平均性能，其长度尺度远远大于电子和结构不均匀性，其量级为典型晶粒尺寸（1微米）。为了应对这一挑战，PI使用了一种创新的测量平台，可以直接实时观察钙钛矿在单个微观结构、表面和界面水平上的降解动力学。通过在扫描电子显微镜系统中集成光电探针（例如，低能电子束，近场光子源）与孤立/混合环境应力源，研究小组旨在可视化钙钛矿在退化和恢复过程中的局部缺陷（例如，移动离子）和载流子动力学。除了原位电和光学成像，该团队正在设计和制造单个晶粒和晶界上的小纳米触点，用于定量分析在单个和混合应力下微观结构中的离子迁移和局部载流子传输。研究小组将应用基于修正泊松漂移和扩散的二维/三维分析和数值模型来分析纳米接触收集的定量数据集。这项CAREER研究将为单结钙钛矿太阳能电池的“性能-微观结构-应力源”关系提供全面的知识，并为减轻环境恶化提供一般指导方针。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract:Defects in semiconductors play a critical role in the performance and stability of modern electronics. The ability to interrogate such defects is therefore of great importance in producing reliable, high-performance electronics that underly the modern economy. Existing methods often measure properties without sufficient resolution to resolve defects on the length scales that they occur. Thus, existing methods provide limited information about the unique local properties. This CAREER project aims to establish an innovative measurement platform that can directly observe the carrier dynamics of microstructured optoelectronic devices. Solar cells based on metal halide perovskites will be the focus of this work. Such devices have remarkable performance, but poor stability, posing a basic challenge for real-world applications. Defect chemistry, ion migration, and microstructural characteristics have all been considered as culprits for the poor stability, but the underlying physical mechanisms are not fully understood. The PI’s research team will use local optical and electrical probes under controlled environmental conditions to study the microstructure of perovskites and elucidate reasons for performance degradation. This fundamental understanding will help to guide the rational design and synthesis of perovskites for robust and reliable solar cells. The PI’s research vision is integrated with an educational plan that aims to generate curiosity and excitement for solar energy and electron microscopy for a broad range of students, with a particular focus on young women students in Utah. The PI will involve undergraduate and graduate students in research and promote the participation of students from underrepresented groups in STEM. An interactive website with streaming videos and educational resources will assist in disseminating the research findings to the general public in the US and abroad.Technical Abstract:Metal halide perovskites are ideally suited for photovoltaic applications, particularly solar cells. This novel class of semiconductors features low-cost processing, rich chemical and structural diversity, tunable bandgaps, and unique defect tolerance and “self-healing” capabilities. Despite considerable efforts, the underlying physical mechanisms for the inferior stability of perovskite solar cells are not fully understood. Many established characterization techniques measure the averaged properties, on a length scale far greater than that of the electronic and structural inhomogeneity, which is on the order of the typical grain size ( 1 micrometer). To tackle this challenge, the PI uses an innovative measurement platform that can directly observe the degradation kinetics of perovskites at the level of individual microstructures, surfaces, and interfaces in real-time. By integrating optoelectronic probes (e.g., low-energy electron beam, near-field photon source) with isolated/mixed environmental stressors in a scanning electron microscope system, the research team aims to visualize the local defects (e.g., mobile ions) and charge carrier dynamics during deterioration and recovery in the perovskites. In addition to the in-situ electrical and optical imaging, the team is designing and fabricating small nanocontacts on individual grains and grain boundaries for quantitative analysis of ion migration and local carrier transport within the microstructures under both individual and mixed stressors. The research team will apply 2D/3D analytical and numerical models based on modified Poisson drift and diffusion to analyze the quantitative datasets collected with nanocontacts. This CAREER research will provide comprehensive knowledge on the “performance-microstructure-stressor” relationship of single-junction perovskite solar cells and general guidelines to mitigate the environmental deterioration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.