Green Car Congress  
Go to GCC Discussions forum About GCC Contact  RSS Subscribe Twitter headlines

« Westinghouse to Provide Four AP1000 Nuclear Power Plants in China; Buys Pebble Bed Modular Reactor Company | Main | Toyota Announces Development of Plug-In Hybrid; First Manufacturer to Have PHEV Certified for Public Road Use in Japan »

Print this post

Researchers Find MEG Effect in Silicon Nanocrystals; May Improve Efficiency of Silicon Solar Cells

25 July 2007

Researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL), collaborating with Innovalight, Inc., have shown that an important effect called Multiple Exciton Generation (MEG) can occur efficiently in colloidal silicon nanocrystals. MEG results in the formation of more than one electron per absorbed photon.

This represents the first report of MEG within silicon semiconductor NCs. MEG has previously been reported 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 (PbSe, PbS, PbTe, CdSe, and InAs).

Silicon is the dominant semiconductor material used in present day solar cells, representing more than 93% of the photovoltaic cell market. 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.

In a paper published on 24 July 24 in the initial on-line 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 nm.

When today’s photovoltaic solar cells absorb a photon of sunlight, about 50% of the incident energy is lost as heat. MEG provides a way to convert some of this energy lost as heat into additional electricity.

The silicon nanocrystals produced by Innovalight, Inc., a thin-film solar cell developer based in Santa Clara, California, were studied at NREL as part of a collaboration between NREL and Innovalight scientists. The NREL team consisted of Matthew C. Beard, Kelly P. Knutsen, Joseph M. Luther, Qing Song, Wyatt Metzger, Randy J. Ellingson and Arthur J. Nozik.

The findings represent an important extension of the range of semiconductor materials that exhibit MEG and are a further confirmation of pioneering work by Nozik, who in 1997 predicted that semiconductor quantum dots could exhibit efficient electron multiplication and hence increase the efficiency of solar cells.

To date, all experiments showing the production of more than one electron per absorbed photon have been based on various types of optical spectroscopy. In a solar cell device it is necessary to extract the electrons produced in the quantum dots and pass them through an external circuit to generate electrical power. Such experiments are currently underway at NREL, Innovalight and other laboratories to demonstrate that MEG can indeed lead to enhanced solar cell efficiencies.

Calculations at NREL by Mark Hanna and Nozik have shown that the maximum theoretical efficiency of quantum dot solar cells exhibiting optimal MEG is about 44% with normal unconcentrated sunlight and 68% with sunlight concentrated by a factor of 500 with special lenses or mirrors. Today’s conventional solar cells that produce one electron per photon have maximum efficiencies of 33% and 40%, respectively, under the same solar conditions.

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.

Resources:

July 25, 2007 in Power Generation, Solar | Permalink | Comments (1) | TrackBack (0)

TrackBack

TrackBack URL for this entry:
http://www.typepad.com/services/trackback/6a00d8341c4fbe53ef00e3981bbbc08833

Listed below are links to weblogs that reference Researchers Find MEG Effect in Silicon Nanocrystals; May Improve Efficiency of Silicon Solar Cells:

Comments

Woo hoo!!! We're now only 20 years away from having a rechargeable solar cell phone.

Our kids will be having convo's on the phone saying "Hold up, I need to get closer to the window to charge my phone."

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Green Car Congress © 2014 BioAge Group, LLC. All Rights Reserved. | Home | BioAge Group