Topic: Mechanistic Insights into Solar Light Harvesting using Multispectral Multidimensional Spectroscopy

Speaker: Dr. Yin Song - University of Michigan

Host: Professor James McCusker

Date: Friday, March 15, 2019

Time: 9:00 AM

Location: CEM 481 E & W

More Information:

Understanding how sunlight is captured, transferred and stored in both artificial and natural solar harvesting systems is not only critical at a fundamental level, but also provides useful guidance for the design of next-generation optoelectronic devices. A grand challenge is to map the energy flow and conversion in these systems, which often span a wide range of time scales—from femtosecond to seconds. Traditional spectroscopic methods for following these processes are often poorly suited for studying light-harvesting systems which generally contain complex and heterogeneous materials with highly-congested spectra and dynamics. In this talk, I will first describe advances we have made in developing multispectral multidimensional spectroscopy (MMDS), i.e., which greatly extends the kinetic and structural information available from one of the most advanced forms of time-resolved optical spectroscopy. I will then discuss general strength and applications of MMDS, followed by two recent applications. One example is organic solar cells (OSCs) which are considered promising candidates for potential building-integrated photovoltaic applications. However, the mechanism of charge separation and the role of coherence in these materials are still under debate. I will show how we have used MMDS to disentangle alternative charge-separation pathways in OSCs and explore the effect of coherence on charge separation. In another application I will discuss our studies of two essential pigments—chlorophyll a and bacteriochlorophyll a—which form the basis of most natural photosynthetic architectures and play vital roles in photosynthetic energy and charge transfer. Open questions remain about the interplay of vibrational and electronic states within the main absorption band and its impact on the photoexcited dynamics. I will discuss our recent efforts to use polarized MMDS to unravel vibronic structure of these pigments and their photoinduced relaxation dynamics.