GOLDEN, Colo., July 25 U.S. Energy Department researchers and Innovalight Inc. have found that quantum dot materials may improve efficiency of silicon solar cells.
Researchers at the department's National Renewable Energy Laboratory have shown that a new and important effect called Multiple Exciton Generation occurs efficiently in silicon nanocrystals. MEG results in the formation of more than one electron per absorbed photon.
In a paper published Tuesday in the initial online version of the American Chemical Society's Nano Letters Journal, an NREL team reported that silicon nanocrystals, or quantum dots, obtained from Innovalight can produce more than one electron from single photons of sunlight that have wavelengths less than 420 nanometers. When photovoltaic solar cells absorb a photon of sunlight, about 50 percent of the incident energy is lost as heat. MEG provides a way to convert some of this energy lost as heat into additional electricity.
Innovalight Inc. is a thin-film solar cell developer based in Santa Clara, Calif.
Silicon is the dominant semiconductor material used in solar cells, representing more than 93 percent of the photovoltaic cell market. Until this discovery, MEG had been reported over the past two years to occur only in nanocrystals (also called quantum dots) of semiconductor materials that are not presently used in commercial solar cells, and which contained environmentally harmful materials such as lead.
The new result opens the door to the potential application of MEG for greatly enhancing the conversion efficiency of solar cells based on silicon because more of the sun's energy is converted to electricity.
This is a key step toward making solar energy more cost-competitive with conventional power sources.
Copyright 2007 by UPI
