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Triple-junction solar cell design could break 50 percent conversion barrier

January 17, 2013
Triple-junction solar cell design could break 50 percent conversion barrier
Schematic diagram of a multi-junction solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency (Photo: U.S. Naval Research Laboratory)
Schematic diagram of a multi-junction solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency (Photo: U.S. Naval Research Laboratory)
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Reported timeline of solar cell energy conversion efficiencies (Photo: National Renewable Energy Laboratory (USA))
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Reported timeline of solar cell energy conversion efficiencies (Photo: National Renewable Energy Laboratory (USA))
Schematic diagram of a multi-junction solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency (Photo: U.S. Naval Research Laboratory)
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Schematic diagram of a multi-junction solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency (Photo: U.S. Naval Research Laboratory)

The current world record for triple-junction solar cell efficiency is 44 percent, but a collaboration between the U.S. Naval Research Laboratory (NRL), the Imperial College of London, and MicroLink Devices Inc. has led to a multi-junction photovoltaic cell design that could break the 50 percent conversion efficiency barrier under concentrated solar illumination.

Presently, the best examples of traditional silicon solar cells top out at around 25 percent efficiency, whereas multi-junction cells have achieved more than 40 percent. Multi-junction solar cells contain several layers of semiconducting material stacked one on top of another, each designed to absorb a different wavelength of light, thereby boosting their efficiency. On top, high band gap semiconductor material absorbs the short wavelength radiation, while longer wavelengths are absorbed by the layers below.

The key to the new multi-junction cell design was identifying what are known as "InAlAsSb quaternary alloys" as a high band gap material that can be grown lattice-matched to an indium phosphide (InP) substrate. Used in the team's multi-junction solar cell, the alloys could achieve a maximum direct band gap of 1.8 electron volts (eV), which is higher than commonly used materials that, when lattice-matched to InP, result in a maximum of 1.4 eV.

"This research has produced a novel, realistically achievable, lattice-matched, multi-junction solar cell design with the potential to break the 50 percent power conversion efficiency mark under concentrated illumination," said Robert Walters, Ph.D., NRL research physicist.

The Naval Research Lab, MicroLink, and the Rochester Institute of Technology will develop the technology over the next three years with funding from the U.S. Department of Energy (DoE) and the Advanced Research projects Agency-Energy (ARPA-E). ARPA-E projects develop technology that is promising but too early for private-sector investment.

Source: Naval Research Laboratory

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EnvironmentEnergyPhotovoltaicEfficiencySolar CellNaval Research Laboratory
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14 comments
splatman
I always ask myself, is it efficiency that matters or total system $/kWh produced over the lifetime of the cell?
JBar
50% using concentration...I wonder what the attenuation is of the concentrator. More importantly, what is the material cost per kwatt generated?
BeWalt
Splatman: It depends.
In applications where space is limited or weight is crucial, such as satellites or high-flying electric relay platforms (24-7 planes) to replace communication satellites, efficiency is everything, because one needs to carry as little as possible and has to get out as much as possible.
In applications where space doesn't matter, such as powering a large home in a suburb, cost per kW rules. If the home owner only needs to cover half of his roof to make 80% of his power (and that depends on efficiency of house and appliances), then the only thing he cares about is how much cash to pay to get there.
Henry Davis
Just a thought, why is 50% a barrier? Milestone perhaps?
grtbluyonder
Solar cells have always "almost" become economically viable, have "almost" achieved good efficiency but never in actuality. I used to design solar arrays for satellites and the target successful market price touted in the 1970's was 25 cents for a 2X2cm silicon solar cell. The price never came even close and still isn't. This is likely just another lab toy. There are thousands of variants of almost, soon, perhaps, etc. etc. etc. They have a lot in common with fuel cells in terms of their seemingly "almost" commercialization and economic viability.
slayerwulfe
to: BeWalt please try to think outside of 'roof' as the geophysical orientation that u have to contend with in any installation situation.low installations on a proper surface R much easier to align & maintain.
BeWalt
Henry: There is no 50%-barrier as such. It's just a good round number that would be nice to pass. Just like the 100mph-barrier in a car. Or my personal 180lbs-barrier, uhm, different story.
You have a number, you aim higher, and try harder, and are happy to get there once it happens. Or lower, whatever.
The thing with solar cells is that once upon a time, "experts" said solar cells could never be made with more than "x" % efficiency. Until they realized they had not known enough to make that statement. Between making the statement and the realization, decades can pass. True for pretty much all technologies.
The silicon solar cell efficiency barrier was once thought to be around 30%. Then they started cooking up multilayer-multicompound-cells and thought it would be 40% which at some point was passed. So let's have a look at the number 50 now. It's more exciting than watching baseball!
Sure, there's no way to get close to or make more than 100%. But for theoretical considerations as of now, based on hypothetical multi-multi-super-dooper cells made from Indium Gallium Nitride, people have taken the word "seventy" into their mouths, some 10 years ago, in Berkeley, California. And then, as usually, got bashed for it by "experts".
It's a great spectacle. Get the chips, sit back and enjoy.
Stephen N Russell
How much to produce said solar cells for home use. Radical if doable.
Norman Welch
I've been hearing about solar cells for decades now, but the only cells available seem to be early 80's surplus at best. When will some of the newer technology become available for the average person to purchase? nw9784@yahoo.com
Mike Kling
Seems like my whole adult life (and I'm 59) we've been a decade away from practical fusion power and three years away from economically feasible solar energy. For the last 5 years I've been reading gizmag I have read about 1000 "ground breaking" developments in solar energy. Sooooooo..... does anybody know when the hell I'll finally be able to put solar cells on my roof that will, in the long run, be cheaper than buying oil/coal produced electricity?
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