Nav: Home

Solar cells utilize thermal radiation

November 13, 2013

There is more to solar radiation than meets the eye: sun- burn develops from unseen UV radiation, while we sense infrared radiation as heat on our skin, though invisible to us. Solar cells also 'see' only a portion of solar radiation: ap- proximately 20 percent 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.

Researchers of 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, have now for the first time made a portion of this radiation usable with the assistance of a practical up-converter. The technology that transforms infra- red into usable light has been known about since the 1960s. However, it has only been investigated in connection with solar cells since 1996. "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," reports Stefan Fischer happily, a scientist at ISE. The potential is big: silicon solar cells theoretically convert about thirty percent of sunlight falling upon them into electrical power. Up-converters could increase this portion to a level of forty percent.

A ladder for light particles

However, how does the up-converter manage to utilize the infrared radiation for the solar cells? 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 Part of the yttrium has been replaced by the scientists with the element erbium, which is active in the optical range and responsible in the end for the up-conversion.

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 sec- ond 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 elec- tron 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 vapour-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," explains 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," says Fischer, emphasizing the potential of the approach.
-end-


Fraunhofer-Gesellschaft

Related Solar Cells Articles:

Solar cells more efficient thanks to new material standing on edge
Researchers from Lund University in Sweden and from Fudan University in China have successfully designed a new structural organization using the promising solar cell material perovskite.
Printable solar cells just got a little closer
A University of Toronto Engineering innovation could make printing solar cells as easy and inexpensive as printing a newspaper.
A big nano boost for solar cells
Solar cells convert light into electricity. While the sun is one source of light, the burning of natural resources like oil and natural gas can also be harnessed.
Game changer for organic solar cells
Researchers develop a simple processing technique that could cut the cost of organic photovoltaics and wearable electronics.
Physics, photosynthesis and solar cells
A University of California, Riverside assistant professor has combined photosynthesis and physics to make a key discovery that could help make solar cells more efficient.
Throwing new light on printed organic solar cells
Researchers at the University of Surrey have achieved record power conversion efficiencies for large area organic solar cells.
A new way to image solar cells in 3-D
Berkeley Lab scientists have developed a way to use optical microscopy to map thin-film solar cells in 3-D as they absorb photons.
Toward 'greener,' inexpensive solar cells
Solar panels are proliferating across the globe to help reduce the world's dependency on fossil fuels.
A new technique opens up advanced solar cells
Using a novel spectroscopic technique, EPFL scientists have made a much-needed breakthrough in cutting-edge photovoltaics.
OU physicists developing new systems for next generation solar cells
University of Oklahoma physicists are developing novel technologies with the potential to impact utility-scale energy generation, increase global energy capacity and reduce dependence on fossil fuels by producing a new generation of high efficiency solar cells.

Related Solar Cells Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Moving Forward
When the life you've built slips out of your grasp, you're often told it's best to move on. But is that true? Instead of forgetting the past, TED speakers describe how we can move forward with it. Guests include writers Nora McInerny and Suleika Jaouad, and human rights advocate Lindy Lou Isonhood.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...