CAREER: Integrated X-ray Ptychography and Optical Luminescence to Understand the Interplay between Local Structural Dynamics and Optoelectronic States

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Nontechnical description: Large scale deployment of solar cells and low-cost light emitting diodes (LEDs) present an enormous opportunity to reduce the environmental impact of today's energy technologies. The halide perovskites offer a potentially disruptive lower-cost alternative to existing traditional semiconductors used in solar cells and LEDs now. This project develops new nanoscale characterization approaches to better understand how these emerging halide perovskite materials grow and help eliminate defects in the resulting crystals. Understanding crystallization and degradation pathways to synthesize high-quality, robust halide perovskite thin films can facilitate their deployment to achieve society-wide impacts on the energy footprint. As part of this effort, a systematic approach to broadening participation of underrepresented minorities in STEM with a focus on photovoltaics and nanoscience education is incorporated in this project. Educational activities engage students at the high school, undergraduate, and graduate levels, including establishing a Solar Summer Bootcamp, where local high school students fabricate and test solar cells, building an appreciation for the science behind modern solar cell materials and enabling students hands-on experience at the frontiers of science.Technical description: This project investigates how the nanoscale variations in chemistry and structure in complex halide perovskites determines their stability. To do so, this project adds a new dimension to X-ray characterization at the nanoscale, providing insight into optoelectronic material properties by measuring light given off by optoelectronic materials under X-ray irradiation, i.e. X-ray excited optical luminescence. The project team develops the application of X-ray excited optical luminescence and ptychography techniques to the halide perovskites at synchrotron-based nanoprobe X-ray beamlines. Using this suite of nanoscale characterization techniques, the research team quantifies the relationship between local composition, structure, and electronic states with state-of-the-art spatial resolution. In a cycle of iterative feedback to improve perovskite crystal quality and stability, the project examines the crystallization and degradation reaction mechanisms in the halide perovskite materials using in situ experiments. The flexibility and wide applicability of the tools developed in this project creates a powerful experimental platform for achieving synchronous insight into the relationship between the electronic, chemical, and structural properties that determine functional performance in optoelectronic materials.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.