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Research record breaking solar cell efficiency from new InGaN crystals

Published on October 28th, 2013 | by Tina Casey

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Record Breaking Solar Cell Efficiency From A “Perfect Crystal”

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October 28th, 2013 by
 
Gallium is already on its way to becoming the workhorse of the solar tech field, and now it looks like the soft metal is is on track to become a thoroughbred. A team of US scientists has hit upon an improved method for growing indium gallium nitride (InGaN) crystals that could lead to record-breaking solar cell efficiency. So far the method has resulted in a film of InGaN that has “almost ideal characteristics.”

To ice the cake, an analysis of the film revealed the precise reason why the results of the new InGaN growing method were so good, which could lead to further improvements in LED technology as well as solar cells.

A Perfect InGaN Crystal

Nitride refers to a compound of nitrogen, in this case in conjunction with indium, a soft silvery-white, zinc-like metal, as well as gallium.

record breaking solar cell efficiency from new InGaN crystals

InGaN LED light by Christian Pelant.

If InGaN already rings a bell, you might be thinking of the world record-setting concentrating solar cell module developed by the company Amonix. That module is based on a record setting solar cell developed by Solar Junction, that incorporates  a layer of antimony-doped InGaN.

Gallium in particular is an effective material for LEDs as well as solar cells due to its band gap characteristics, most familiarly in CIGS thin film solar cells (CIGS is the semiconductor copper-indium-gallium-(di)selenide). The potential has barely been scratched, though.

Arizona State University and the Georgia Institute of Technology collaborated on the new method, which addressed the problem at its core. The obstacle has been irregularities in the atomic structure of the crystal, as explained by ASU team leader Fernando Ponce:

Being able to ease the strain and increase the uniformity in the composition of InGaN is very desirable, but difficult to achieve. Growth of these layers is similar to trying to smoothly fit together two honeycombs with different cell sizes, where size difference disrupts a periodic arrangement of the cells.

The new method is called metal modulated epitaxy. It is a variation of the epitaxial deposition method first developed at Bell Labs in the 1960′s, which involves applying a thin layer of material to a substrate that takes on the crystal structure of the lower layer.

The result was a more film that resembles a perfect crystal, both in its uniformity of structure and in the desirable trait of luminosity.

As for why the improvement occurred, the analysis credited “strain relaxation at the first atomic layer of crystal growth.”

We Built This Next-Generation Solar Cell

Solar cell efficiency is not the only factor leading to a drop in the cost of solar power, since the “soft costs” of installing a solar system still account for a considerable chunk of change.

However, solar cell efficiency is still a key factor, and if the new findings translate from the lab to commercial development, let’s throw ourselves a taxpayer appreciation party.


The latest development has roots in a 2008 paper published by Georgia Tech team leader Alan Doolittle with other collaborators, titled “Metal modulation epitaxy growth for extremely high hole concentrations above 1019cm−3 in GaN.” It described how the metal modulated epitaxy method yielded an enhanced doping efficiency of up to 10 percent, which compares favorably to the 1 percent efficiency under the conventional method.

That research was funded by grants from the Office of Naval Research, the Air Force Office of Scientific Research, and the Defense Advanced Research Projects Agency as well as the National Science Foundation.

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About the Author

Tina Casey specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



  • mds

    Tina,
    Good article. Nice to have a window into developments from lab research.
    Check this out:

    http://www.greencarcongress.com/2013/10/20131022-a123solid.html

    I would definitely use the word “breakthrough” even though it has not been made a commercial product yet. If it does make it to commercial production it looks like that will happen fast, given the manufacturing connections with A123/Wanxiang Group.
    mike

  • JamesWimberley

    “Gallium is already on its way to becoming the workhorse of the solar tech field”. No it is not. Silicon cells (silicon doped with tiny amounts of phosphorus and boron) hold 89% of the market and the share is not going down. The very high efficiency cells you describe, made with exotic materials and elaborate fabrication, are the $100,000 thoroughbreds of the business; far too difficult and expensive for ordinary use. What path do you imagine for them ever to achieve economies of scale and replace the true workhorses?

    • mds

      CIGS, like it discusses. >20% in the lab. <15% in production. Reason is because it likes to be a multi-crystal. Crystal boundaries make reduce efficiency. Same for mSi verses cSi. If this method can solve that problem at low-cost-of-manufacture for CIGS then she's correct it will lead to significantly lower cost thin-film CIGS PV. I thought that was stated clearly and fairly even if the "workhorse" claim was a little exaggerated.

    • dynamo.joe

      Well, as the immortal James W Mayer used to say back when I was in grad school, “Ga is the material of the future….and it always will be”.

      • mds

        Hmmm “always” is a very long time. His psychic must have been much better than my psychic.

    • mds
  • Syros

    “The result was a more film that resembles…”
    Something is missing here.

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