Monday, May 23, 2005
Golden, Colo. — 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
solar cells absorb a photon of sunlight, the energy gets
converted to at most one electron, and the rest is lost as
The research demonstrates the potential for solar, or photovoltaic,
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
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
"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
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
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.
NREL is the U.S. Department of Energy's primary national
laboratory for renewable energy and energy efficiency research
and development. NREL is operated for DOE by Midwest Research
Institute and Battelle.
For further information contact NREL Public Affairs at (303)