CAS-SC: Uncovering Mechanistic Details of Photo-Induced Charge Transfer in Thin Films of Photoactive Materials with In situ and Operando Transient Absorption Spectroscopy

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Elizabeth Young of Lehigh University is using sophisticated time-resolved spectroscopies to study photoactive chemical conversion devices under operational conditions. Photochemical cells operate by absorbing light from the sun and use that light energy to drive chemical reactions. The efficiency of the device is the net result of a series of interdependent fundamental processes, including light absorption, charge separation, and charge migration, as well as the collection of charges that can be used to drive chemical reactions. The separated charges can also undergo unproductive recombination within the device, resulting in loss of efficiency. Each of these interconnected processes depends heavily on the types of materials used within the cell, making it necessary to study a functional system rather than the individual parts in isolation. Dr. Young and her students will use femtosecond pump-probe methods to study photoactive devices under potential bias and steady-state illumination. Their discoveries could further our understanding of the complex kinetic networks that are central to the functioning of the chemical conversion devices needed for sustainable chemistry applications. The project will also provide research opportunities for students, thus contributing to the development of the Nation's scientific workforce. This project centers on the use of transient absorption spectroscopy coupled with electrochemical and photolysis techniques to quantify charge transfer dynamics in semiconductor material stacks that undergo photo-induced charge transfer. The project will utilize atomically precise, extremely thin absorbing chalcogenide materials synthesized using atomic layer deposition. Such materials are particularly well suited because layer thicknesses and compositions can be finely tuned to enable systematic study in both planar and nanostructured devices. The influence of an applied electrochemical potential and steady-state illumination (i.e., the most realistic operating conditions for photovoltaics and photoelectrical chemical cells) on charge-carrier dynamics and charge transfer kinetics will be quantified to determine how steady-state conditions influence ultrafast lifetimes and charge transfer kinetics. Such work could ultimately provide insight into the function and efficiency of devices such as photovoltaic and photoelectrochemical cells.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.