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

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.