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Chemistry & Materials Forum No. 141: Ultrafast Singlet Fission for Energy Applications (Dr. Yi Rao)
发布时间:2019-10-31 浏览次数:

Dr. Yi Rao from the Department of Chemistry and Biochemistry at Utah State University, delivered a talk, ' Ultrafast Singlet Fission for Energy Applications' on Jun. 24th, 2019 by invitation. It was hosted by Prof. Juncheng Hu.

In this talk, Dr. Rao discussed about ultrafast singlet fission in acenes. Singlet fission is known to improve solar energy utilization by circumventing the Shockley-Queisser thermodynamic limit. In the process of singlet fission, two essential steps are the formation of a correlated triplet pair and its subsequent quantum decoherence. However, the nature of the triplet pair as well as its formation and decoherence mechanisms still remain elusive. As an example, we examine both essential steps in single crystalline hexacene and show remarkable anisotropy of the overall singlet fission rate along different crystal axes, namely the long a axis and the short b axis. The triplet pair which formation is facilitated by electronic coupling and phonon relaxation, emerges on the same ultrafast timescales of ca. 200fs along both the crystal axes upon photo-excitation, thus making quantum decoherence the critical step for directional anisotropy of singlet fission. The distinct quantum decoherence rates are ascribed to the notable difference on their associated energy loss according to the Redfield quantum dissipation theory, which suggests an experimentally consistent ~100% faster formation of decoupled triplet dimer along the b axis than its counterpart along the a axis. The hybrid experimental/theoretical framework presented in our study will not only further our understanding of singlet fission, but also shed light on the systematic design of new materials for the third-generation solar cells.

Dr. Rao received his doctor's degree from Institute of Chemistry, Chinese Academy of Sciences in 2003. He worked as a postdoctoral fellow at Prof. Eisenthal's group at Department of Chemistry in Columbia University from 2003 to 2007. Then he was co-employed as Associate Research Scientist by both prof. Nicholas J. Turro and prof. Kenneth B. Eisenthal at Department of Chemistry in Columbia University from 2007 to 2013. In 2013, he joined prof. Tony F. Heinz's group studied material science at Department of Physics in Columbia University. In 2014 he joined the Department of Chemistry in Temple University as research associate professor and started independent research. In 2017 he became an Assistant Professor at Department of Chemistry and Biochemistry in Utah State University. His research was funded by Natural Science Foundation of the United States, ARO, and Honda Inc.. His research has involved ultrafast spectroscopy, surface science, photochemistry, materials science, biophysical chemistry, environmental science and many other fields. He has more than 40 scientific publications at Naturechemistry, PNAS, Nanoletter, JPC and JCP. His current research focuses on ultrafast charge transfer in energy and material chemistry, and interface chemistry in Environmental Science.


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