SEMINAR ANNOUNCEMENT Title: Carrier Dynamics and Multiple Exciton Generation in Semiconductor Nanocrystals: Applications to Third Generation Solar Photon Conversion By: A.J. Nozik, Center for Basic Sciences (National Renewable Energy Laboratory) and Department of Chemistry (University of Colorado) Location: FRNY G140, 3:30 PM, Tuesday, January 16th, 2006 Abstract: In order to utilize solar power for the production of electricity and fuel on a massive scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency and low capital cost ($/m2). One potential, long-term approach to high efficiency is to utilize the unique properties of semiconductor quantum dot nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient exciton multiplication or enhanced photopotential through hot electron transport and transfer processes. To achieve these desirable effects it is necessary to understand and control the dynamics of electron relaxation, cooling, multiple exciton generation (MEG), transport, and interfacial electron transfer of the photogenerated carriers with fs to ns time resolution. At NREL, we have been studying these fundamental dynamics in bulk and nanoscale semiconductors (quantum dots, quantum wires, and quantum wells) using femtosecond transient absorption, photoluminescence, and THz spectroscopy. This work will be summarized and recent advances in creating multiple excitons from a single photon will be discussed, including a unique model to explain efficient MEG based on the coherent superposition of multiple excitonic states. Various possible configurations for quantum dot solar cells that could produce ultra-high conversion efficiencies for the production of solar fuels and electricity will be discussed, along with associated thermodynamic calculations that show the theoretical gains in solar photon conversion efficiency for both electricity and fuel production. ________________________________ Arthur J. Nozik Dr. Arthur J. Nozik is a Senior Research Fellow <http://www.nrel.gov/research_fellows/nozik.html> at NREL and Professor Adjoint <http://www.colorado.edu/chem/DEC/people/nozika.html> in the Chemistry Department at the University of Colorado, Boulder. He received his B.Ch.E. from Cornell University in 1959 and his Ph.D. in Physical Chemistry from Yale University in 1967. Before joining NREL in 1978, then known as the Solar Energy Research Institute, he conducted research at the Allied Chemical Corporation and American Cyanamid Corporation. Dr. Nozik's research interests include size quantization effects in semiconductor quantum dots and quantum wells, and the applications of these nanostructures to solar photon conversion, photogenerated carrier relaxation dynamics in semiconductor structures, photoelectrochemistry of semiconductor-molecule interfaces, photoelectrochemical energy conversion, photoelectrolysis of water to hydrogen, photocatalysis, optical, magnetic and electrical properties of solids, and Mössbauer spectroscopy. He has published more than 160 papers and book chapters in these fields and holds 11 U.S. patents. He has served on numerous scientific review and advisory panels and received several awards in solar energy research. Dr. Nozik has been a senior editor of The Journal of Physical Chemistry since 1993. He is a fellow of both the American Physical Society and the American Association for the Advancement of Science and a member of the American Chemical Society, the Electrochemical Society, the American Association for the Advancement of Science, the Materials Research Society, and the Society of Photo Optical Instrument Engineers. Selected Publications 1. R. Ellingson, M. Beard, J. Johnson, P.Yu, O.I. Micic, A. Shaebev, Al. L. Efros, and A.J. Nozik, "Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots," Nano Letters, 5, 865 (2005). 2. A.J. Nozik, "Exciton Multiplication and Relaxation Dynamics in Quantum Dots: Applications to Ultrahigh-Efficiency Solar Photon Conversion," Inorganic Chemistry (Forum) 44, 6893 (2005). 3. Pingrong Yu, Matthew C. Beard, Randy J. Ellingson, Suzanne Ferrere, Calvin Curtis, John Drexler, Fred Luiszer, and Arthur J. Nozik, "Absorption Cross Section and Related Optical Properties of Colloidal InAs Quantum Dots," J. Phys. Chem., in press (2005). 4. J. L. Blackburn, D. C. Selmarten, R. J. Ellingson, M. Jones, O. Micic, and A.J. Nozik, "Electron and Hole Transfer from Indium Phosphide Quantum Dots," J. Phys. Chem. B 109, 2625 (2005). 5. P.R. Yu, J.M. Nedeljkovic, P.A. Ehrenkiel, R.J. Ellingson, and A.J. Nozik, "Size dependent femtosecond electron cooling dynamics in CdSe quantum rods," Nano Letters, 4, 1089 (2004). 6. L. Langof, L. Fradkin, E. Ehrenfreund, E. Lifshitz, O.I. Micic, A.J. Nozik, "Colloidal InP/ZnS core-shell nanocrystals studied by linearly and circularly polarized photoluminescence," Chem. Phys. 297, 93 (2004).
