New technique developed at MIT could enable a major boost in solar-cell efficiency.

[OKIsItJustMe]

http://web.mit.edu/press/2013/photon-to-electron-conversion.html

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For Immediate Release: April 18, 2013
contact: Kimberly Allen, MIT News Office
email: [e-mail] phone: [phone]

[font size=5]Special deal on photon-to-electron conversion: Two for one![/font]

[font size=4]New technique developed at MIT could enable a major boost in solar-cell efficiency.[/font]

[font size=3]CAMBRIDGE, Mass. — Throughout decades of research on solar cells, one formula has been considered an absolute limit to the efficiency of such devices in converting sunlight into electricity: Called the Shockley-Queisser efficiency limit, it posits that the ultimate conversion efficiency can never exceed 34 percent for a single optimized semiconductor junction.

Now, researchers at MIT have shown that there is a way to blow past that limit as easily as today’s jet fighters zoom through the sound barrier — which was also once seen as an ultimate limit.

Their work appears this week in a report in the journal Science, co-authored by graduate students including Daniel Congreve, Nicholas Thompson, Eric Hontz and Shane Yost, alumna Jiye Lee ’12, and professors Marc Baldo and Troy Van Voorhis.

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While today’s commercial solar panels typically have an efficiency of at most 25 percent, a silicon solar cell harnessing singlet fission should make it feasible to achieve efficiency of more than 30 percent, Baldo says — a huge leap in a field typically marked by slow, incremental progress. In solar cell research, he notes, people are striving “for an increase of a tenth of a percent.”

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http://dx.doi.org/10.1126/science.1232994

[caraher]

1. Big by the standards of the field, perhaps

Incremental efficiency increases are largely irrelevant to spreading solar PV.

Bear in mind that while you get 2 electrons per photon, each electron has less energy. In fact, from their research paper:

...fission does not itself increase the power efficiency of a solar cell. It potentially doubles the photocurrent at the cost of losing at least half the open circuit voltage.

They do discuss some tweaks that might make the cells just squeak past the Shockley-Queisser limit, but multiple junction cells already surpass that figure (I believe the record is just over 40% efficiency). The economics are far more important than breaking efficiency records for most power applications (spacecraft power systems might be one exception).

[FogerRox]

2. SpectroLab 39.2%

[OKIsItJustMe]

3. Solar Junction/NREL 44% (Three junction concentrator)

http://www.democraticunderground.com/112740638
http://www.nrel.gov/news/features/feature_detail.cfm/feature_id=2055

[font face=Serif][font size=5]Award-Winning PV Cell Pushes Efficiency Higher[/font]
[font size=4]December 28, 2012[/font]
[font size=3]It takes outside-the-box thinking to outsmart the solar spectrum and set a world record for solar cell efficiency. The solar spectrum has boundaries and immutable rules. No matter how much solar cell manufacturers want to bend those rules, they can't.

So how can we make a solar cell that has a higher efficiency than the rules allow?

That's the question scientists in the III-V Multijunction Photovoltaics Group at the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) faced 15 years ago as they searched for materials they could grow easily that also have the ideal combinations of band gaps for converting photons from the sun into electricity with unprecedented efficiency.

A band gap is an energy that characterizes how a semiconductor material absorbs photons, and how efficiently a solar cell made from that material can extract the useful energy from those photons.

"The ideal band gaps for a solar cell are determined by the solar spectrum," said Daniel Friedman, manager of the NREL III-V Multijunction Photovoltaics Group. "There's no way around that."

But this year, Friedman's team succeeded so spectacularly in bending the rules of the solar spectrum that NREL and its industry partner, Solar Junction, won a coveted R&D 100 award from R&D Magazine for a world-record multijunction solar cell. The three-layered cell, SJ3, converted 43.5% of the energy in sunlight into electrical energy — a rate that has stimulated demand for the cell to be used in concentrator photovoltaic (CPV) arrays for utility-scale energy production.

Last month, that record of 43.5% efficiency at 415 suns was eclipsed with a 44% efficiency at 947 suns. Both records were verified by NREL. This is NREL's third R&D 100 award for advances in ultra-high-efficiency multijunction cells. CPV technology gains efficiency by using low-cost lenses to multiply the sun's intensity, which scientists refer to as numbers of suns.

Friedman says earlier success with multijunction cells — layered semiconductors each optimized to capture different wavelengths of light at their junctions — gave NREL a head start.

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[FogerRox]

4. In the lab? SPectrolabs have been produced for about 2 years