Carbon nanotubes could make efficient solar cells

September 10, 2009 By Anne Ju
In a carbon nanotube-based photodiode, electrons (blue) and holes (red) - the positively charged areas where electrons used to be before becoming excited - release their excess energy to efficiently create more electron-hole pairs when light is shined on the device. Image: Nathan Gabor

( -- Cornell researchers fabricated, tested and measured a simple solar cell called a photodiode, formed from an individual carbon nanotube.

Using a instead of traditional silicon, Cornell researchers have created the basic elements of a solar cell that hopefully will lead to much more efficient ways of converting light to electricity than now used in calculators and on rooftops.

The researchers fabricated, tested and measured a simple solar cell called a photodiode, formed from an individual carbon nanotube. Reported online Sept. 11 in the journal Science, the researchers -- led by Paul McEuen, the Goldwin Smith Professor of Physics, and Jiwoong Park, assistant professor of chemistry and chemical biology -- describe how their device converts light to electricity in an extremely efficient process that multiplies the amount of electrical current that flows. This process could prove important for next-generation high efficiency , the researchers say.

"We are not only looking at a new material, but we actually put it into an application -- a true solar cell device," said first author Nathan Gabor, a graduate student in McEuen's lab.

The researchers used a single-walled carbon nanotube, which is essentially a rolled-up sheet of , to create their solar cell. About the size of a , the nanotube was wired between two electrical contacts and close to two electrical gates, one negatively and one positively charged. Their work was inspired in part by previous research in which scientists created a diode, which is a simple transistor that allows current to flow in only one direction, using a single-walled nanotube. The Cornell team wanted to see what would happen if they built something similar, but this time shined light on it.

Shining lasers of different colors onto different areas of the nanotube, they found that higher levels of photon energy had a multiplying effect on how much was produced.

Further study revealed that the narrow, cylindrical structure of the carbon nanotube caused the electrons to be neatly squeezed through one by one. The electrons moving through the nanotube became excited and created new electrons that continued to flow. The nanotube, they discovered, may be a nearly ideal photovoltaic cell because it allowed electrons to create more electrons by utilizing the spare energy from the light.

This is unlike today's solar cells, in which extra energy is lost in the form of heat, and the cells require constant external cooling.

Though they have made a device, scaling it up to be inexpensive and reliable would be a serious challenge for engineers, Gabor said.

"What we've observed is that the physics is there," he said.

Provided by Cornell University (news : web)

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5 / 5 (1) Sep 10, 2009
Ok, so it again comes down to the more basic problem of mass-producing high quality carbon nanotubes. These little things have promise in so many applications, I am glad to see more work being done.
One thing though, whoever figures out how to mass produce quality nanotubes first will have a huge market to fill.
4 / 5 (2) Sep 10, 2009
So many questions...
The nanotube, they discovered, may be a nearly ideal photovoltaic cell because it allowed electrons to create more electrons by utilizing the spare energy from the light.

What does "ideal photavoltaic cell" mean? Does it mean a possibility to convert 99% or more of sunlight's power, utilizing the complete spectrum of Sun's projected light, or just that it's really, really good?

Also, does this have potentials in something like computer circuit development?

Lastly, when this technology has been pulled into the army for development of solar powerd weaponry, how long will we have to wait for this technology to be commercially available?
5 / 5 (3) Sep 10, 2009
given the enormous rewards, why is the government not making a manhattan project out of the goal of making cheaply producible carbon nanotubes.
5 / 5 (2) Sep 10, 2009
How accurate is this? Last time I looked outside, light hitting my roof wasn't coherent as a laser. If they use regular non-coherent streams of photons, how much does the efficiency of their solarcell go down?
Sep 10, 2009
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not rated yet Sep 10, 2009
It would be an interesting combination... photo voltaic nano-threads in space in the Earth's magnetic field could reveal a very large amount of electrical energy... sending it back to Earth... well.
not rated yet Sep 10, 2009
MorituriMax, yes sunlight is incoherent. I wonder if that would effect the efficiencies of these. Of course there are simple ways to split the spectrum but making them coherent requires energy...

One more question. At this size can they be put into glass, fabric, paneling, etc? This would allow more collection area. Office windows that act as solar panels, clothing that slowly recharges your gadgets, sides of buildings collecting energy.

But like everyone said the mass production problem means a long.... wait.
not rated yet Sep 11, 2009
Google "Optical Rectenna" for more information on this technology.
not rated yet Sep 11, 2009
For a laugh --

You ever think it is funny that carbon nanotubes are like God's little fixit for the 21st century. I mean it is like witch medicine of the 19th century -- got a problem try carbon nanotubes not only will the problem be solved but the effeciency will be through the roof and the power consumption minimal -- btw if the nanotubes don't work just unroll it into graphene and that will probably solve the problem. -- Really ?? -- at this rate next thing you know nanotubes places in the body will create stem cells and if accelerated to .9c will form dark matter. These things are GREAT.

not rated yet Sep 11, 2009
"The electrons moving through the nanotube became excited and created new electrons that continued to flow." Is this counter to law of conservation of matter?
not rated yet Sep 11, 2009
nematic liquid crystal polymers sandwiched in these tubes would offer a functional photodiode motor assemblies
not rated yet Sep 12, 2009
This sounds like a simple dipole antenna. I see no reason that this technology couldn't be tweaked into a fractal shape similar to a cellphone antenna, giving it broadband reception as well as wide angle reception.
not rated yet Sep 12, 2009

Thing is, they are like a fix-all miracle solution. It is because they are so small and tailorable (in theory) that they can be tweaked to mimic other substances (or some that do not yet exist) and do cool stuff.
not rated yet Sep 18, 2009
What is limiting our ability to mass-produce nanotubes?

This 2005 study describes the currently achievable rate: "...sheets are produced at up to seven meters per minute by the coordinated rotation of a trillion nanotubes per minute for every centimeter of sheet width"


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