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Quantum Effect Discovered Could Increase Silicon Photovoltaic Efficiency
Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), in collaboration with Innovalight, Inc. have discovered a unique quantum effect in silicon nanocrystals which could make photovoltaic solar cells more energy efficient.
Researchers found a new effect called multiple exciton generation (MEG) occurs efficiently in silicon nanocrystals. MEG results in the formation of more than one electron per absorbed photon.
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, according to NREL.
Silicon nanocrystals obtained from Innovalight can produce more than one electron from single photons of sunlight that have wavelengths less than 420 nm, accoding to NREL. When today’s 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.
In addition to efficiently extracting the electrons from the quantum dots in solar cells, future research is directed toward producing MEG at wavelengths that have a greater overlap with the solar spectrum, as well as producing a much sharper onset of the MEG processes with decreasing wavelength of the photons, according to NREL.