Clean Power solar cell efficiency

Published on January 25th, 2014 | by Tina Casey


Color This New Solar Cell Efficiency Breakthrough Blue

January 25th, 2014 by  

If you had to pick the best color for solar cell efficiency off the top of your head, yellow – as in sunlight – would probably get the nod. However, there is a lot of efficiency to be mined in the blue end of the spectrum. The problem is, blue light has excess energy that conventional solar cell materials can’t capture efficiently, and away it goes in the form of heat.

That makes finding a cheap, blue light-friendly solar cell material one of the keys to kicking solar cell efficiency up to the next level while keeping costs down, and researchers over at Argonne National Laboratory and the University of Texas at Austin believe they have found just such a one.

solar cell efficiency

Blue light by bigpresh.

Harvesting Blue Light For Solar Cell Efficiency

The material in question is copper indium selenide (CIS), which is a close cousin of CIGS (a combination of copper, indium, gallium, and selenium) the go-to material for thin film solar cells.

The thin film angle is important to solar cell affordability because, although thin film is not as efficient as the gold standard (that would be silicon), it is far more inexpensive to manufacture and it has a greater range of applications.

The new Argonne solar cell research pivots on the manufacturing process to harvest more light from the blue end of the spectrum.

To deposit thin films of CIS, the researchers used a fabrication method called photonic curing. In photonic curing, you heat and cool the top layer of a material in less than a second. Aside from binding the materials, photonic curing also vaporizes organic molecules.

Once the organic molecules are out of the way, that leaves the field clear for multiple exciton generation, and thus greater efficiency in blue light conversion (in other words, one high-energy photon is stimulating multiple excitons, instead of just one exciton per photon).

Before you get too excited about all those excitons bouncing around, researcher Brian Korgel of the University of Texas cautions that the labwork looks promising, but it’s the relationship between manufacturing and multiple exciton generation that will make the technology competitive in the marketplace:

The holy grail of our research is not necessarily to boost efficiencies as high as they can theoretically go, but rather to combine increases in efficiency to the kind of large-scale roll-to-roll printing or processing technologies that will help us drive down costs.

The cost of solar power is already sinking like a stone and apparently it hasn’t nearly hit bottom yet.

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About the Author

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+.

  • Ronald Brakels

    I’m going to be really, really, really annoying and point out that sunlight isn’t yellow, it’s white. So why does the sun look yellow then? I don’t know! But I don’t think it is yellow. When I photograph the sun it comes out white. I suspect the sun looks yellow because the only times we normally actually see it are around dusk and dawn, although how our brains perceive colour may also be involved rather than just atmospheric effects.

    • Peter Gray

      You’re right, Ronald. As I remember, the peak of the solar spectrum reaching the ground is about in the middle of our visual range, which produces the even mixture of colors we call “white.” Our perceptions can get a lot of things backward, starting with the notion that red/orange/yellow light is “warm” and green/blue is “cool,” when the opposite is true. We also complain that fluorescent lights are unnaturally too blue or white, while incandescents are a more natural yellow, like sunlight. But put in a tube that simulates real daylight (like my wife does for indoor photography), and it’s much hotter (bluer) than a normal fluorescent.

      Our extremely wide range of visual sensitivity leads to similar misperceptions. For example, we might describe some situation as being half as bright as another, while the actual light flux is 50 or 100 times less.

      I enjoy these bits of tech trivia as well, so thanks for pointing it out.

      • sean

        the colour temperature is actually slightly yellow, however it is usually too bright to notice.

        Using incandescents for lighting is horribly inefficient, and as you pointed out, very hot. Use LEDs and you escape this “increased heating to obtain higher colour temperatures.

        • Peter Gray

          To answer Sean and dynamo Joe, yes, the atmosphere takes out 1/4 or so of the blue end of a spectrum that starts with a blue tilt (

          I’m well aware of the waste from incandescents, but I wasn’t referring to that – I somewhat misused “hotter” as shorthand for “higher color temperature,” which gets at another common confusion, between heat and temperature.

          You seem to be under that misunderstanding as well! A higher-temp incandescent will produce _less_ waste heat per lumen than a cooler one. That’s why halogen bulbs are quite hot, but more efficient. Likewise, dimming lots of incandescents, instead of turning some off and leaving the rest at full power, is a terrible way to conserve energy.

          Not as bad as trying to use an open refrigerator to cool off on a hot day (yes, it has happened!), but close…

          • Ronald Brakels

            Thanks everyone for your replies on the colour of the sun. It is an interesting topic.

    • dynamo.joe

      maybe it’s because the blue light is preferentially scatter, causing the sky to be blue and leaving the redder end of the spectrum?

      • Peter Gray

        Yes, see reply above…

  • Peter Forint

    I wanted to share this on LinkedIn and add my comments, but your sharing plugin doesn’t allow it. Please reconfigure or use a different plugin. Thanks!

  • J_JamesM

    Keep on plugging away, and eventually these innovations will add up.

  • Steve Grinwis

    Always cool to hear of new innovation.

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