Clean Power

Published on January 30th, 2013 | by James Ayre


Super-Efficient Solar Cells Possible Through Use Of Exotic Form Of Silicon, Generating More Than One Electron-Hole Pair Per Photon

January 30th, 2013 by  

By utilizing an exotic form of silicon, silicon BC8, it is very likely possible to significantly raise the efficiency of solar cells, according to new research headed by the University of California, Davis.


Solar cells currently in use generate one electron-hole pair for every photon that hits them, and are capable of a theoretical maximum efficiency of ‘only’ 33%. But by utilizing nano-particles of an exotic form of silicon known as silicon BC8, it is possible for each photon to generate multiple electron-hole pairs.

“This approach is capable of increasing the maximum efficiency to 42%, beyond any solar cell available today, which would be a pretty big deal,” said lead author Stefan Wippermann, a postdoctoral researcher at UC Davis. “In fact, there is reason to believe that if parabolic mirrors are used to focus the sunlight on such a new-paradigm solar cell, its efficiency could reach as high as 70 percent.”

Silicon nano-particles, on their own, are capable of generating more than one electron-hole pair, because of an effect called “quantum confinement.”

“But with nanoparticles of conventional silicon, the paradigm works only in ultraviolet light,” Wippermann said. “This new approach will become useful only when it is demonstrated to work in visible sunlight.”

That’s where BC8 comes in, because of its ability to generate multiple pairs even with only visible light.

BC8 is a form of silicon that is formed under very high pressure but that remains stable at normal pressures, similar to the way that diamond is a form of carbon formed at extreme pressure but stable at normal ones.

“This is more than an academic exercise. A Harvard-MIT paper showed that when normal silicon solar cells are irradiated with laser light, the energy the laser emits may create a local pressure high enough to form BC8 nanocrystals. Thus, laser or chemical pressure treatment of existing solar cells may turn them into these higher-efficiency cells,” said co-author Gergely Zimanyi, professor of physics at UC Davis.

The new research was just published January 25th in the journal Physical Review Letters.

Source: University of California Davis (UCD)
Image Credits: Stefan Wippermann/UC Davis

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • mds

    Very interesting, but you’re going to have to explain how a concentrator can increase efficiency of conversion. Normally, for CPV, efficiency is measured as a percentage of the light collection area, so the concentrator allows less PV material to be used to convert sunlight from a larger area, but it does not increase the efficiency of conversion. In fact, the reflectors or lenses used cannot be perfect (that’s life), so CPV typically has a few percentage points LESS efficiency than the PV cells used.
    Increasing efficiency from 42% to 70% by using a concentrator is either:
    (a) a mis-quote
    (b) what he’s saying is not properly explained
    or (c) it’s nonsense.
    {I mean no offense here. I hope you will forgive me for being blunt and to the point. I appreciate the article. This is really amazing solar science. I’m just trying to improve understanding, maybe just mine, by pointing out an apparent flaw in the information given.}

  • That 70% efficiency would make concentrating systems really worth it.

    Of course, it is still a question of economics but the method may not raise prices significantly.

    • Otis11

      And there’s always the fact that until energy is to cheap to care (which I don’t see on the horizon) people/organizations/companies will continue to research technologies to make even the “out there” concepts of today a reality in a few decades, if not sooner.

      Interesting piece!

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