Christopher Bardeen of the University of California-Riverside is supported by the Chemical Structure, Dynamics and Mechanisms Program in the Division of Chemistry to carry out research to probe how exciton structure impacts excited state dynamics in molecular crystal systems, with an emphasis on processes relevant for organic photovoltaic materials. The research plan is designed to accomplish three objectives. First, the team will continue their collaborative work on using time-resolved luminescence spectroscopy and theory to characterize delocalized exciton states in polyacene molecular crystals. Second, the dynamics and reaction mechanism of singlet fission, a process whereby a absorption of a single photon leads to the creation of two excitons, and potentially two electron-hole pairs, will be studied. Crystalline tetracene will be a model system for clarifying how this unique relaxation process works. Third, energy migration in organic systems, which plays an important role in determining solar cell efficiencies, will be studied using a modified version of the optical transient grating experiment. The goal will be to measure exciton diffusion lengths of 20 nm or less by using a combination of standing waves and high dynamic range detection.
The overall thrust of this research is to generate fundamental insights into how exciton properties like delocalization can affect singlet fission and exciton diffusion, thus providing a way to assess the ultimate potential of crystalline organic materials for photovoltaic applications. This understanding in turn could aid in the design of improved materials for solar cells and address an important societal problem: the need for clean, inexpensive, and renewable energy. Graduate students and postdoctoral associates will be trained in technologically vital areas. Outreach activities to local elementary schools which enroll a majority population of students from underrepresented groups in science will also be initiated.
