Woodruff School of Mechanical Engineering

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Excitons Charge-Transfer states, Charge-Separated states, and Carriers: The Importance of Charge Delocalization


Dr. Garry Rumbles


National Renewable Energy Laboratory


Wednesday, April 19, 2017 at 3:00:00 PM


EBB Building, Room Children's Healthcare of Atlanta Seminar Room


John Reynolds


Although OPV devices have increased in solar harvesting efficiency, there remains much debate surrounding the mechanism by which the active medium absorbs solar radiation and creates high yields of free, mobile carriers that do not immediately recombine. The uncertainty arises from the low dielectric constant of the active material, normally a conjugated polymer and a fullerene, which lack the ability to screen the coulombic interaction between charges This presentation will discuss the role of charge delocalization on producing a charge-separated state, where the electron and hole are created at a larger distance than that found in a charge-transfer state. It will examine the important role of the solid-state microstructure of the polymer and its impact on delocalizing the hole, and also on the aggregation properties of the electron acceptor and its role on delocalizing the electrons. In addition, the role that time-resolved microwave conductivity (fp-TRMC) plays in helping to unravel this story will be explained.


Professor Garry Rumbles is a Laboratory Fellow in the Chemistry and Nanoscience Center at the National Renewable Energy Laboratory (NREL) in Golden, Colorado and holds affiliated faculty positions in the Departments of Chemistry at University of Colorado Boulder, Colorado State University and Imperial College London. He is also the Associate Director for research of the Renewable and Sustainable Energy Institute (RASEI), a joint institute between CU-Boulder and NREL. Prior to joining NREL in 2000, he was a member of physical chemistry faculty at Imperial College. He gained his undergraduate degree in Chemistry with Electronics from the University of Southampton in 1980, and his PhD in Photochemistry from the University of London in 1984. His graduate work was carried out in the Davy Faraday Research Laboratory in the Royal Institution, London. He was a Postdoc, first with Prof. George Atkinson at the University of Arizona and then Prof. Edward KC Lee at UC Irvine, before returning to the UK (with an American wife). His current research interests are in solar energy with a focus on the basic science of solar photoconversion processes and photoinduced electron transfer processes in polymer-based nanostructured interfaces. His primary research expertise lies in photochemistry and laser spectroscopy with a special interest in the photophysics of conjugated polymers. He has published over 200 articles, and is a Fellow of the Royal Society of Chemistry (UK).