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The new solar coating, made from a special nanomaterial may not look like much, but it helps solar cells to be 42 percent more efficient, making them close to being cost competitive. Best of all it can be easily produced with existing infrastructure.  (Source: Rensselaer/Shawn Lin)
New coated cell 43 percent more efficient, can be easily produced with current production lines

Solar breakthroughs are relatively commonplace.  However, typically they are iterative -- small increases by a percent or two in efficiency.  Researchers at the Rensselaer Polytechnic Institute have invented a new solar cell that is anything but iterative as it blows away past offerings by a large margin; something RPI calls a "game-changer" for the solar business.

Against relatively cheap coal power, solar -- like nuclear and wind -- has struggled to compete from a purely economic standpoint.  Worse yet, it trails wind and nuclear in terms of how close it is to being cost competitive.  The light at the end of the tunnel is that solar have shown the highest gains in efficiency of any alternative energy source, making its future look very bright.

The new RPI solar cell is a normal cell covered in a special anti-reflective coating which traps sunlight from nearly every angle and part of the spectrum.  The new cell is near perfect; it absorbs 96.21 percent of the sunlight shined on it, while a normal cell could only absorb 67.4 percent.  That 43 percent efficiency boost, coupled with mass production, if properly implemented could place solar on the verge of competing unsubsidized with coal power, at last.

Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university’s Future Chips Constellation describes the breakthrough, stating, "To get maximum efficiency when converting solar power into electricity, you want a solar panel that can absorb nearly every single photon of light, regardless of the sun’s position in the sky.  Our new antireflective coating makes this possible."

Most materials have a mixture of light absorbing (anti-reflective) and light reflecting properties, depending on the angle and wavelength of light.  For example, eyeglasses allow light to pass through on direct angles, but begin to reflect light at sharper angles.  Solar panels in their current form operate with similar mixed character.  In order to improve efficiency, mechanical components must be added to turn to panel to face the sun.  This system entails significant cost and loss of energy efficiency, as well as a great maintenance burden.

With Professor Lin's discovery, the world's first cost-efficient static solar arrays could be produced.  No matter what angle the sun was at, nearly all sunlight would be absorbed and converted to power.  Professor Lin describes, "At the beginning of the project, we asked ‘would it be possible to create a single antireflective structure that can work from all angles?’ Then we attacked the problem from a fundamental perspective, tested and fine-tuned our theory, and created a working device."

Rensselaer physics graduate student Mei-Ling Kuo helped Professor Lin investigate various antireflective coatings.  Their eventual choice was a nanomaterial, consisting of several fine anti-reflective sheets.  Normal antireflective coatings consist of one sheet, which absorbs light at a specific wavelength.  By stacking seven separate layers into a composite coat, they were able to absorb nearly the entire spectrum.  Furthermore, the staggered nature of the layers "bent" the flow of sunlight to a favorable angle, trapping it in the coating.  This means that if light manages to reflect off a lower layer, it will be sent back down by the upper layers.

Each layer was made from a special nanomaterial consisting of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle.  The material was grown through standard chemical vapor deposition techniques, and could be applied to the manufacturing of most standard solar cells, including III-V multi-junction and cadmium telluride cells.

On a microscopic level the nanomaterial looks like a forest of tiny, densely packed trees.  Each layer is 50 nm to 100 nm thick.

The team hopes to bring their technology quickly to market, as it will require little in the way of manufacturing line changes. The research is detailed in the paper "Realization of a Near Perfect Antireflection Coating for Silicon Solar Energy", published in the journal Optics Letters.

Besides Lin and Kuo, the other researchers listed as co-authors on the paper were E. Fred Schubert, Wellfleet Senior Constellation Professor of Future Chips at Rensselaer; Research Assistant Professor Jong Kyu Kim; physics graduate student David Poxson; and electrical engineering graduate student Frank Mont.

The research was funded with the help of funding from the U.S. Department of Energy’s Office of Basic Energy Sciences, as well as the U.S. Air Force Office of Scientific Research.

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RE: so how about actual efficiency?
By LTG on 11/5/2008 10:26:13 AM , Rating: 2
When previous record efficiencies are mentioned to be around 25%, doesn't that number already assume an optimal light angle?

If so, that means this new technology would still allow only ~25%, just at more times during the day.

I don't know which but this is a big distinction!

RE: so how about actual efficiency?
By kattanna on 11/5/2008 10:36:09 AM , Rating: 5
from my reading, even at optimal sun angle cells now only capture 67% of the light with the balance being lost and reflected out. the new coating does 2 things

at optimal angle it now captures 97%, instead of 67%

and even at non optimal angles it captures 97%, so therefore you no longer need mechanized panels that have to track the sun, instead allowing for much cheaper and easier maintenaince systems.

and since its a "simple" coating, it can be applied to existing cell manufacture lines to instantly boost them.

RE: so how about actual efficiency?
By General Disturbance on 11/5/2008 12:11:21 PM , Rating: 1
Yah, but we still have winter in the north. You still need direct incidence to get really warm.

RE: so how about actual efficiency?
By Bruneauinfo on 11/5/2008 7:01:37 PM , Rating: 2
yeah!! and what about us Matrix fanatics that are living down here near the core of the earth where it's still warm!?!?!? it's not economically feasible to tunnel to the surface to connect any of this to our power grid!

RE: so how about actual efficiency?
By jlips6 on 11/5/2008 8:49:44 PM , Rating: 2
fool, we blackened the sun anyway remember?
The robots first ran on sunlight-... wait...

RE: so how about actual efficiency?
By pixelslave on 11/5/2008 9:33:44 PM , Rating: 3
Yah, but we still have winter in the north. You still need direct incidence to get really warm.

Solar panels need the light, not the warmness of the sun.

RE: so how about actual efficiency?
By AssBall on 11/6/2008 10:42:35 AM , Rating: 2
Maybe you should learn how solar panels work before you start typing. Look up INFRARED.

By TheOtherBubka on 11/5/2008 9:30:40 PM , Rating: 2
Clearing the FUD here. First, it is an accomplishment in 'extending' the angle of incidence range of anti-reflection coatings. However, in terms of increasing the efficiency of Si, all optics coating engineers will tell you a simple 1/4 wavelength anti-reflection coating will help but a 3 layer anti-reflection coating (as the authors made) is much better. For example see
Took an InP cell and increased it's efficiency from 11.96% to 19.43%. BUT, what the authors Jason is citing here do not point out is that the processing for this type of coating is extremely expensive. Although the materials are sputtered down, the top 2 coatings of the picture have to be done at fairly oblique angles to the sputtering target where material utilization goes down and the ability to cover large areas decreases. Keep this in mind when they have had to increase the complexity substantially to accomplish what can be accomplished through other engineering methods.

RE: so how about actual efficiency?
By JLL55 on 11/5/2008 10:47:08 AM , Rating: 2
the 25% incorporates inefficiencies in the conversions and transmission IIRC. So this is trying for the lowest hanging fruit of absorption (increased absorption = increased electricity production). Similar to gas where a large percentage (anyone know the number) is lost to heat and light and inefficiency in force transfer (hence the things like microspray injection for gas engines increases surface area of gas molecules to all more efficient burning while the force transfer and heat and light inefficiency still exist.

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