Multiple exciton generation in semiconductor quantum dots and applications to third generation solar photon conversion

PHYS 210

Arthur J. Nozik, anozik@nrel.gov1, Randy J. Ellingson2, Matthew C. Beard, matthew_beard@nrel.gov3, Joseph Luther, joseph_luther@nrel.gov3, Justin C. Johnson3, Matthew D Law4, and Qing Song4. (1) NREL, 1617 Cole Blvd, Golden, CO 80401, (2) Energy Sciences, National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401, (3) Center for Basic Sciences, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, (4) Energy Sciences, NREL, 1617 Cole Blvd, Golden, CA 80401
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 (delivered watts/m2) and low capital cost ($/m2). One potential, long-term approach to high efficiency is to utilize the unique properties of quantum dot nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer. To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, multiple exciton generation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers with femtosecond (fs) to ns time resolution. We have been studying these fundamental dynamics in various bulk and nanoscale semiconductors (quantum dots (QDs), quantum rods/wires, and quantum wells)using fs - ns transient absorption, photoluminescence, and THz spectroscopy. Recently, we predicted the generation of more than one electron-hole pair (exciting as excitons in QDs) per absorbed photon would be an efficient process in QDs . This prediction has been confirmed by several groups using various spectroscopies over the past few years in several types of QDs. Very efficient and ultrafast multiple exciton generation (MEG) from absorbed single high energy photons has been reported in PbSe, PbS, PbTe, CdSe, InAs and Si QDs. Efficient MEG may greatly enhance the conversion efficiency of solar cells that incorporate QDs for both solar electricity and solar fuel (e.g., H2) production. Aspects of this work will be summarized and recent advances will be discussed. Various configurations for quantum dot solar cells for ultrahigh conversion efficiencies for the production of electricity and solar fuels will be presented, along with progress in developing such new types of solar cells.
 

Spectroscopy, Chemistry, and Imaging through Nanophotonics
8:00 AM-12:00 PM, Tuesday, April 8, 2008 Morial Convention Center -- Rm. 345, Oral

Division of Physical Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008