May 24, 2005 |
"We have shown that solar cells based on quantum
dots theoretically could convert more than 65 percent of the sun's energy into
electricity, approximately doubling the efficiency of solar cells."
- Arthur Nozik, NREL
Golden, Colorado [RenewableEnergyAccess.com] Researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have shown that nanotechnology may greatly increase the amount of electricity produced by solar cells.
In a paper published in a May issue of the American Chemical Society's Nano
Letters journal, an NREL team found that tiny "nanocrystals," also
known as "quantum dots," produce as many as three electrons from one
high energy photon of sunlight. When today's photovoltaic (PV) solar cells
absorb a photon of sunlight, the energy gets converted to at most one electron,
and the rest is lost as heat.
The research demonstrates the potential for solar PV cells that reduce wasteful
heat and maximize the amount of the sun's energy that is converted to
electricity - a key step toward making solar energy more cost-competitive with
conventional power sources.
The NREL research team, led by Arthur Nozik, included Randy Ellingson, Matt
Beard, Justin Johnson, Pingrong Yu, and Olga Micic, and worked in collaboration
with theorists Alexander Efros and Andrew Shabaev of the Naval Research
Laboratory (NRL) in Washington, D.C.
The findings are further confirmation of pioneering work by Nozik, who in 2000
predicted that quantum dots could increase the efficiency of solar cells,
through a process now termed "multiple exciton generation," or
"MEG". Last year, Richard Schaller and Victor Klimov of Los Alamos
National Laboratory in New Mexico were the first to demonstrate the electron
multiplication phenomenon predicted by Nozik, using quantum dots made from lead
selenide.
"We have shown that solar cells based on quantum dots theoretically could
convert more than 65 percent of the sun's energy into electricity, approximately
doubling the efficiency of solar cells," Nozik said. The best cells today
convert about 33 percent of the sun's energy into electricity.
The NREL and NRL researchers' paper also describes a new theoretical foundation
for the multiple exciton generation process that is based on certain unique
aspects of quantum theory.
The recent work demonstrates MEG in quantum dots of a second semiconductor
material, lead sulfide.
The NREL/NRL work not only shows higher overall efficiency for multiple exciton
generation, it also establishes that the process occurs with lower photon
energies, meaning it could make use of an even greater portion of the sun's
light spectrum.
Beyond potential use for photovoltaic cells, similar quantum dot technology may
someday be used in photoelectrochemical cells, which could become a clean and
renewable way to produce hydrogen directly from water and sunlight.
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