Nanowire solar cells raise efficiency limit

March 24, 2013
Nanowire crystals are used as the solar cells. The image (left) shows a SEM (Scaning Electron Microscope) image of GaAs nanowire crystal grown on a Silicon substrate. A TEM (Transmission Electron Microscope) image (middle) shows a single nanowire. Further zooming in on the crystal structure, using STEM (Scanning Transmission Electron Microscope) imaging, shows the actual atomic columns (right). Credit: Niels Bohr Institute

Scientists from the Nano-Science Center at the Niels Bohr Institut, Denmark and the Ecole Polytechnique Fédérale de Lausanne, Switzerland, have shown that a single nanowire can concentrate the sunlight up to 15 times of the normal sun light intensity. The results are surprising and the potential for developing a new type of highly efficient solar cells is great.

Due to some unique physical properties of nanowires, the limit of how much energy we can utilize from the sun's rays is higher than previous believed. These results demonstrate the great potential of development of nanowire-based , says PhD Peter Krogstrup on the surprising discovery that is described in the journal Nature Photonics.

The research groups have during recent years studied how to develop and improve the quality of the nanowire crystals, which is a cylindrical structure with a diameter of about 10,000 part of a human hair. The nanowires are predicted to have great potential in the development not only of solar cells, but also of future quantum computers and other electronic products.

The figure shows that the sun's rays are drawn into a nanowire, which stands on a substrate. At a given wavelength the sunlight is concentrated up to 15 times. Consequently, there is great potential in using nanowires in the development of future solar cells. Credit: Niels Bohr Institute

It turns out that the nanowires naturally concentrate the sun's rays into a very small area in the crystal by up to a factor 15. Because the diameter of a nanowire crystal is smaller than the wavelength of the light coming from the sun it can cause resonances in the intensity of light in and around nanowires. Thus, the resonances can give a concentrated sunlight, where the energy is converted, which can be used to give a higher conversion effeciency of the sun's energy, says Peter Krogstrup, who with this discovery contributes to that the research in based on nanowires get a real boost.

New efficiency limit

The typical efficiency limit - the so-called "Shockley-Queisser Limit" - is a limit, which for many years has been a landmark for solar cells efficiency among researchers, but now it seems that it may be increased.

It's exciting as a researcher to move the theoretical limits, as we know. Although it does not sound like much, that the limit is moved by only a few percent, it will have a major impact on the development of solar cells, exploitation of nanowire solar rays and perhaps the extraction of energy at international level. However, it will take some years years before production of solar cells consisting of nanowires becomes a reality, says Peter Krogstrup who just completed his PhD at the Niels Bohr Institute, University of Copenhagen.

The research is conducted in collaboration with the Laboratory des Matériaux Semiconducteurs, Ecole Polytechnique Fédérale de Lausanne, the Foundation and the company SunFlake A / S. Their scientific findings work support results published in the journal Science in January. Here, a group of researchers from Lund, showed that the sun's rays was sucked into the due to the high amount of power that their solar cell produced.

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1.2 / 5 (5) Mar 24, 2013
This is excellent news. With luck and government support, solar power and other alternatives should begin to displace the stranglehold of coal and oil.
3.7 / 5 (3) Mar 24, 2013
So what is their new efficiency record?
3 / 5 (2) Mar 24, 2013
Ho hum...
5 / 5 (3) Mar 24, 2013
Shockley Queisser puts the limit for single band gap cells at 41 percent. (Multi-bandgap cells can have more than that).

What they have shown here is that even single bandgap cells can be better than previously thought - which is big, because manufacturing a single bandgap cell is much easier than multi-bandgap cells.
2.7 / 5 (7) Mar 24, 2013
This is excellent news. With luck and government support, solar power and other alternatives should begin to displace the stranglehold of coal and oil.

No government support please. Every time governments get involved in the energy industry, energy gets more expensive, just look at the cost of a barrel of oil coming from the middle east, $100/barrel all because those governments run the business over there. The world is awash in oil yet the price remains little changed because governments like to manipulate much of our daily lives to the benefit of the political class.
4.5 / 5 (2) Mar 24, 2013
Benni: "The world is awash in oil yet the price remains little changed because governments like to manipulate much of our daily lives to the benefit of the political class."

Could you be more specific regarding your statement that the world is awash in oil? Total output has sat at about 80 million barrels a day - for about the past 8 years. There are some significant finds around the world - but output stays pretty flat - as new oil discoveries are just keeping abreast with old ones that are going dry. The appetite for energy in India and China is increasing - hence the great push for development of all alternatives - as it does not seem feasible to hope we can increase oil production much above current levels. Do you have some source for you 'awash' statement?
5 / 5 (1) Mar 25, 2013
Increasing that number would appear to be the entire justification for the research.

"So what is their new efficiency record?" - JRI

and yet the article doesn't provide it.

Thus the author of the article doesn't comprehend the basic reason for the research.

Dumber than dirt.
1 / 5 (1) Mar 25, 2013
It would be nice to see what they are thinking the new numbers are, I would agree VendicarE. Anyone know what type of solar cells they would apply to? What do they mean by
"However, it will take some years years before production of solar cells consisting of nano wires becomes a reality" That could mean 3,6,10 or am I just asking too much. Does this change the linear progression curve of development into an asymptotic curve? Let's explore all workable energy solutions!
not rated yet Mar 25, 2013
Apparently this was shown back in 2006 and there are 11 patents on it.They increase the solar cell efficiency by up to 18% but weather this is an additional percentage increase or a percentage of the current efficiency i can not tell. Here is the blog from 2006 highlighted by a guy called Bob Crowley in a duplicate of this article in (rdmag . com)
microphonium . blogspot . ie/search?q=solar

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