Elucidating Physical and Electronic Interactions in Ternary Blend Organic Solar Cells

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Solar energy is among the most attractive renewable energy sources, providing motivation for fundamental research to enable low-cost technologies that are adaptable for a variety of applications. Among these, thin film organic photovoltaic cells (based on small organic molecules and polymers) are a potentially suitable option. This technology provides a path towards a lightweight, flexible platform for integration of renewable electricity production capacity into building infrastructure. Of the organic solar cells under study, ternary blend cells have demonstrated the potential for state-of-the-art efficiency. In addition, the technology amends itself to simple device fabrication methods that are compatible with existing continuous roll-to-roll processing manufacturing methods. This project will address fundamental research into the mechanisms that govern the active layer of material, the polymer blend, in order to increase efficiency of the resulting device. The project will focus on the complex physical and electronic interactions in the ternary polymer blend mixture that determines the cell's solar conversion efficiency. The research plan of the project is coupled with a cohesive educational plan that benefits community college students as well as University of Southern California (USC) undergraduates and graduate students. Community college students from Cerritos College (Norwalk, CA) will be hosted each summer to participate in the research project. These students are largely from under-represented groups in STEM and many are first generation college students. The project also involves collaborations with laboratories in Germany and Denmark. Undergraduate and graduate students (from Cerritos and USC) will also work closely with the international collaborators, including graduate student exchange for an extended international research experience. Finally, the project includes efforts toward developing write-to-learn pedagogies are being pursued in undergraduate organic chemistry courses at USC with the goal of facilitating learning and student retention. The focus of the fundamental research project is to expand the understanding of the role of miscibility of synergistic components in ternary blend organic solar cells, specifically those based on two donor polymers and one molecular acceptor. Specific interests are centered on how physical relationships influence the open circuit voltage and on the development of a more global picture of favorable electronic interactions between components. The objectives of the project are: to elucidate the fundamental physical and electronic interactions between synergistic components and clarify the mechanism of operation; to establish the limits of effective electronic relationships between synergistic donor components, specifically focusing on the maximum effective highest occupied molecular orbital offset; and to develop rational design rules for synergistic components. This work will be executed through a combination of polymer synthesis, basic electronic and structural characterization, device characterization and theory. Achievement of the stated objectives should lead to an enhanced fundamental understanding of the ternary blend platform and the path to clear design principles for new donor and acceptor components.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.