Modeling of Charge Transfer Processes in Heterostructured Nanocomposites

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The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division at the National Science Foundation supports Professors Kilina, Kilin, and Kryjevski of North Dakota State University to develop computational methods that model light-induced processes taking place in quantum dots (tiny pieces of crystalline solids that are one billionth of a meter in size). Developing sustainable and efficient energy sources is one of the greatest challenges facing mankind. One attractive solution is solar-based fuel cells that utilize the sun's energy to produce hydrogen from water. This hydrogen can then be used as a fuel, producing only water when it is burned (combined with oxygen). However, high cost, and low efficiency and durability are the main factors that hinder the large-scale use of this solar cells. One way to meet these challenges is to utilize quantum dots. Attaching a molecule to the quantum dot surface alters its ability to capture light. This modification can significantly enhance the efficiency of solar energy conversion to chemical energy. This research may result in more efficient solar cell components. Computational predictions guide the rational design of novel, cost-effective materials for energy applications. This project also provides educational and research experiences for high school, undergraduate and graduate students in computational chemistry and materials chemistry modeling. Remote training/research activities are offered to increase participation of female and Native American students. The project helps prepare a diverse STEM workforce with the skills and knowledge critical for the real-world design of novel materials for energy applications.The research team creates and implements novel quantum chemistry methods capable of accurately modeling the photoexcited dynamics in extended nanostructures with complex surfaces and interfaces. Specifically, this methodology is suitable for the Janus-type quantum dots composed of two different semiconductors, such as PbS(e)/CdS(e), and covalently functionalized by organic dyes, to determine the conditions that govern the dynamics of charge transfer in the presence of other competing processes, such as carrier multiplication, energy transfer, phonon-mediated carrier relaxation and carrier recombination. These computations are useful for interpreting data from time-resolved optical spectroscopy and guiding new experimental probes. Knowledge of the dependence of charge and exciton transfer efficiency on the surface and interface effects is critical for controlling the photoexcited processes via chemical engineering of quantum dot/dye composites, thus improving their functionality for energy conversion applications.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.