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Solar Cells Use IR Radiation

For the first time, European researchers have made short-wavelength IR radiation usable with the assistance of a practical up-converter. The research team from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, together with their colleagues at the University of Bern, Switzerland, and the Heriot-Watt University in Edinburgh, Scotland, has developed technology that transforms infra-red into usable light.

The concept has been known about since the 1960s. However, it has only been investigated in connection with solar cells since 1996. Thermal radiation from the sun is largely lost on most silicon solar cells. Up-converters are able to transform the infrared radiation into usable light, however. The researchers have now for the first time successfully adapted this effect for use in generating power.

Solar cells see only a portion of solar radiation: approximately 20% of the energy contained in the solar spectrum is unavailable to cells made of silicon. They are unable to utilize a part of the infrared radiation, the short-wavelength IR radiation, for generating power.

“We have been able to adapt both the solar cells and the up-converter so as to obtain the biggest improvement in efficiency so far,” explained Stefan Fischer happily, a scientist at ISE. Silicon solar cells theoretically convert about 30% of sunlight falling upon them into electrical power. Up-converters could increase this portion to a level of 40%.

As solar radiation falls on the solar cells, they absorb the visible and near-infrared light. The infrared portion is not absorbed, however. It goes right through them. On the back-side, the radiation runs into the up-converter — essentially a microcrystalline powder made of sodium yttrium fluoride embedded in a polymer. Part of the yttrium has been replaced by the scientists with the element erbium, which is active in the optical range and responsible in the end for the up-conversion.

A two-sided silicon solar cell -- positioned here on aluminum cylinders -- is illuminated from above by an infrared laser.(Courtesy Fraunhofer Institute for Solar Energy Systems)

A two-sided silicon solar cell — positioned here on aluminum cylinders — is illuminated from above by an infrared laser.
(Courtesy Fraunhofer Institute for Solar Energy Systems)

As the light falls on this up-converter, it excites the erbium ions. That means they are raised to a higher energy state. You can imagine this reaction like climbing up a ladder: an electron in the ion uses the energy of the light particle to climb up the first step of the ladder. A second light particle enables the electron to climb to the second step, and so on. An ion that has been excited in this manner can jump down from the highest step or state. In doing so, it emits light with an energy equal to all of the light particles that have helped the electron to climb on up. The up-converter collects, so to speak, the energy of several of these particles and transfers it to a single one. This has so much energy then that the solar cells see it and can utilize it.

Researchers had to adapt the solar cells in order to be able to employ an up-converter such as this. Normally, metal is vapor-deposited on the backside, enabling current to flow out of the solar cells — so no light can shine through normally.

“We equipped the solar cells with metal lattices on the front and rear sides so that IR light can pass through the solar cells. In addition, the light can be used by both faces of the cell — we call this a bi-facial solar cell,” explained Fischer. Scientists have applied specialized anti-reflection coatings to the front and rear sides of the solar cell. These cancel reflections at the surfaces and assure that the cells absorb as much light as possible. “This is the first time we have adapted the anti-reflection coating to the backside of the solar cell as well. That could increase the efficiency of the modules and raise their energy yields. The first companies are already trying to accomplish this by implementing bi-facial solar cells.”

For more information about the research see Solar cells utilize thermal radiation.

Editor's note: This article originally appeared on EE Times Europe.

14 comments on “Solar Cells Use IR Radiation

  1. t.alex
    December 2, 2013

    We have long known solar energy efficiency is pretty low and we always need huge area of coverage for solar panels to achieve decent amount of energy for proper use. 

    This research is pretty amazing enhancement by exploiting IR radiation. How long more will it take to mass-produce this technology?

  2. Daniel
    December 2, 2013

    “The research team from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, together with their colleagues at the University of Bern, Switzerland, and the Heriot-Watt University in Edinburgh, Scotland, has developed technology that transforms infra-red into usable light.”

    Paul, am not clear about this statement.  For more than a decade infra red lights are using in military and avionic domain for surveillance, night vision, target acquisition etc. its alos widely using for Non-military applications like remote temperature sensing, short raned wireless communication, weather forecasting etc.

  3. Daniel
    December 2, 2013

    “We have long known solar energy efficiency is pretty low and we always need huge area of coverage for solar panels to achieve decent amount of energy for proper use”

    Alex, that's depends up on the efficiency of PV cells and nothing related to solar light. We have to develop good PV panels, which can convert all the solar light to energy.

  4. SP
    December 4, 2013

    This is very good from environment perspective. Looking at limited resources this generation has and what upcoming generations will get, its the need of hour that this must be materialized. ANd the governments need to strongly support it.

  5. FLYINGSCOT
    December 4, 2013

    Scotland is doing a lot of great research in renewable energy technologies (wind, water, wave) and has a fantastic reputation in research in general.  I found it doubly impressive that Scotland is at the forefront of solar reasearch considering it is one of the wettest, cloudiest places on earth…..only kidding.

  6. Adeniji Kayode
    December 4, 2013

    @ t.alex, I agree with you on that, for some time now, I have been wondering why solar energy is generally accepted as the best form of alternative energy to crude and yet seems the most expensive and due to different factors- seems to be unreliable. This research should at least bring us close to much more success in solar power.

  7. Daniel
    December 4, 2013

    “Looking at limited resources this generation has and what upcoming generations will get, its the need of hour that this must be materialized. ANd the governments need to strongly support it.'

    SP, today's imagination is tomorrow's innovation and technology. Things are happening in that direction, the innovative ideas or imaginations from science fiction stories and moves are paving the way to have R&D in similar direction.

  8. _hm
    December 5, 2013

    This is wonderful idea. We covered visible, near IR and IR. What are other spectrum band yet to explore?

     

  9. t.alex
    December 6, 2013

    Jacob, that's right. I mean if the efficiency is high, with the same area we can get more electricity for our needs. 

  10. Adeniji Kayode
    December 7, 2013

    @jacob, I agree with you on that. some of those gadgets that were kind of lirs or film tricks of time past are the realities of today. who would jave believed then that PC would metamorphosis into tabs today. This age would usher in an era where almost anything would be possible.

  11. Daniel
    December 8, 2013

    “I mean if the efficiency is high, with the same area we can get more electricity for our needs. “

    Alex, as of now that's the only drawback with PV cells. the efficiency of PV cells has to be increased for a better production from the same panel.

  12. Daniel
    December 9, 2013

    “I agree with you on that. some of those gadgets that were kind of lirs or film tricks of time past are the realities of today. who would jave believed then that PC would metamorphosis into tabs today. This age would usher in an era where almost anything would be possible”

    Adeniji, let's hope for the best!!!

  13. SunitaT
    February 22, 2014

    This innovation in technology, no doubt gives us hope that the solar cell might someday convert the full spectrum of light i.e. from Ultra-violet to Infra-red into electric power efficiently, making solar cells the most popular and coveted alternative source of energy in near future.

  14. SunitaT
    February 22, 2014

    @_hm: Well we do have the ultraviolet(UV), near UV portions of spectrum yet to be covered efficiently, though the good news is there have been some technologies already out of research-hub, that use some multi layered amorphous semiconductors, where each layer is doped specifically to absorb a particular wavelength.

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