CAREER: CAS: Broadband UV-NIR Ultrafast Photochemistry Imaged in Space and Time

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Elham Ghadiri of Wake Forest University is advancing time-resolved microscopies and using them to visualize how the fundamental photochemical charge-transfer processes taking place in solar light-harvesting materials are affected by the microscopic structure of their local surroundings. Capturing these charge-transfer processes is challenging, however, as they take place in times approaching a millionth of a billionth of a second, and the time scales vary from one point to another in a material on nanometer length scales. Dr. Ghadiri and her students are developing femtosecond optical microscopy techniques that can visualize the fundamental photochemical reactions in light-harvesting semiconductors made from earth-abundant materials. Their discoveries could lead to a better understanding of complex photochemical processes that take place in highly heterogenous materials, as well as help to develop design criteria for efficient light-harvesting materials used in future clean energy generation and storage applications. In partnership with the WFU sustainability program, the Ghadiri group will engage in community outreach using research-based educational platforms designed to educate people of all ages about the role of sustainable solar devices in daily life as one aspect of climate change mitigation. The Ghadiri group will develop ultrafast microscopy and spectroscopy methods to allow the visualization of fundamental photoinduced reaction dynamics in complex and heterogeneous solar energy conversion materials. The primary focus is on semiconductors that are highly light-absorbing and that are based on earth-abundant elements, which makes them promising candidates for sustainable energy conversion applications. The performance of solar cells fabricated from the materials depends on the efficiency of ultrafast and fast electron and proton transfer reactions that occur independently, and in competition with each other. Ultrafast transient absorption and diffuse reflectance microscopies will be used to probe the dynamics on sub-micron length scales and ultrafast time scales with broad spectral coverage. The project aims to provide an in-depth spatiotemporal analysis of charge carrier processes that are central to solar cell function. The advancement of microscopy tools that push the limits of conventional time-resolved spectroscopy is a potential broader impact of the work.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.