First all-carbon solar cell

Oct 31, 2012 by Mark Shwartz
This shows the new all-carbon solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. Credit: Mark Shwartz / Stanford University

(Phys.org)—Stanford University scientists have built the first solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today.

The results are published in the Oct. 31 online edition of the journal ACS Nano.

"Carbon has the potential to deliver high performance at a low cost," said study senior author Zhenan Bao, a professor of chemical engineering at Stanford. "To the best of our knowledge, this is the first demonstration of a working solar cell that has all of the components made of carbon. This study builds on previous work done in our lab."

Unlike rigid silicon that adorn many rooftops, Stanford's thin film prototype is made of that can be coated from solution. "Perhaps in the future we can look at alternative markets where flexible carbon are coated on the surface of buildings, on windows or on cars to generate electricity," Bao said.

The coating technique also has the potential to reduce manufacturing costs, said Stanford graduate student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz.

"Processing silicon-based solar cells requires a lot of steps," Vosgueritchian explained. "But our entire device can be built using simple coating methods that don't require expensive tools and machines."

This video is not supported by your browser at this time.
Stanford Professor Zhenan Bao talks about the carbon solar cell research.

Carbon nanomaterials

The Bao group's experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin film solar cell, the electrodes are made of conductive metals and (ITO). "Materials like indium are scarce and becoming more expensive as the demand for solar cells, touchscreen panels and other grows," Bao said. "Carbon, on the other hand, is low cost and Earth-abundant."

For the study, Bao and her colleagues replaced the silver and ITO used in conventional electrodes with graphene – sheets of carbon that are one atom thick –and single-walled carbon nanotubes that are 10,000 times narrower than a human hair. "Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties," Bao said.

For the active layer, the scientists used material made of carbon nanotubes and "buckyballs" – soccer ball-shaped carbon molecules just one nanometer in diameter. The research team recently filed a patent for the entire device.

"Every component in our solar cell, from top to bottom, is made of carbon materials," Vosgueritchian said. "Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes."

One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1 percent – much lower than commercially available solar cells. "We clearly have a long way to go on efficiency," Bao said. "But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically."

Improving efficiency

The Stanford team is looking at a variety of ways to improve efficiency. "Roughness can short-circuit the device and make it hard to collect the current," Bao said. "We have to figure out how to make each layer very smooth by stacking the nanomaterials really well."

The researchers are also experimenting with carbon nanomaterials that can absorb more light in a broader range of wavelengths, including the visible spectrum.

"Materials made of carbon are very robust," Bao said. "They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit."

The ability of carbon solar cells to out-perform conventional devices under extreme conditions could overcome the need for greater efficiency, according to Vosgueritchian. "We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress," he said. "But obviously we want the highest efficiency possible and are working on ways to improve our device."

"Photovoltaics will definitely be a very important source of power that we will tap into in the future," Bao said. "We have a lot of available sunlight. We've got to figure out some way to use this natural resource that is given to us."

Explore further: Atom-thick CCD could capture images: Scientists develop two-dimensional, light-sensitive material

More information: pubs.acs.org/doi/full/10.1021/nn304410w

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User comments : 13

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JoeBlue
1.4 / 5 (10) Oct 31, 2012
I don't think that would be reducing the carbon footprint of the power source....

Caliban
3.7 / 5 (3) Oct 31, 2012
I don't think that would be reducing the carbon footprint of the power source....



Yeah, but if it's not in the atmospere, then that sort of makes it a moot point. This would make it possible to use recaptured waste CO2 as a material from which to produce these panels.


JoeBlue
2.5 / 5 (8) Oct 31, 2012
I don't think that would be reducing the carbon footprint of the power source....



Yeah, but if it's not in the atmospere, then that sort of makes it a moot point. This would make it possible to use recaptured waste CO2 as a material from which to produce these panels.




^^ Does not understand satire...
Caliban
5 / 5 (2) Nov 01, 2012
I don't think that would be reducing the carbon footprint of the power source....



Yeah, but if it's not in the atmospere, then that sort of makes it a moot point. This would make it possible to use recaptured waste CO2 as a material from which to produce these panels.




^^ Does not understand satire...


In this case, I confess that the satirical tone escaped me.

Please accept my apologies.

TheQuietMan
5 / 5 (1) Nov 01, 2012
What would be cool is if it were really easy to fabricate. Cost is bigger consideration than efficiency IMO.
Lurker2358
1 / 5 (2) Nov 01, 2012
What would be cool is if it were really easy to fabricate. Cost is bigger consideration than efficiency IMO.


It's sort of impossible to predict scaled production costs based solely on laboratory experiments.

Wouldn't it be useful to take a computerized physics model, and adapt an additional program to generate all possible configurations of the materials to form a single cell (an evolutionary algorithm,) try all possibilities and see which work best in the model?

Then take like the best candidates from each family of solutions and actually make them and see which work best in the real world.

DARPA did something similar with an antennae they were trying to make a while back, and it worked.
Mike_Massen
1 / 5 (2) Nov 01, 2012
Genetic algorithms in software gave been around for almost 20 years and can produce some interesting 'designs' for things like filters, fractal antennas etc. The physical variant of genetic algorithms has also been in use as a pilot test methodology for a few years and ever since 3D printing became rather more widespread... Extending it to permutations of laboratory techniques to assess production models in materials processing is a sensible approach and from my own direct experience has been trialled in a few labs around the world for other purposes. Those in common knowledge now are the fuel production genetic experiments, Eg. yeasts modified to produce major component of diesel fuels...

It is amazing how much goes on in real private labs which doesn't see the light of day in terms of internet access, ie. There is so much not published or accessible on the net...
SteveL
not rated yet Nov 03, 2012
One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light
"Materials made of carbon are very robust," Bao said. "They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit."
Would these work best in a hybrid solar thermal process? Seems that these could pick up the near infrared from a solar thermal system. They didn't provide the appropriate temperature, but it looks like these can stand some heat.
SteveL
not rated yet Nov 03, 2012
Wouldn't it be useful to take a computerized physics model, and adapt an additional program to generate all possible configurations of the materials to form a single cell (an evolutionary algorithm,) try all possibilities and see which work best in the model?

Then take like the best candidates from each family of solutions
Sounds a lot like what they are doing at folding@home.
http://folding.st.../Science
antialias_physorg
5 / 5 (2) Nov 04, 2012
It's sort of impossible to predict scaled production costs based solely on laboratory experiments.

At least one can predict that the source material is dirt cheap compared to any other system on the market - and that it's also virtually impossible for that material to come in short supply even if this technology were to be scaled up massively.
DHStrongheart
not rated yet Nov 06, 2012
The author mentions that they're working at improving efficiency, but does not give figures for the current efficiency of this solar technology....
Trigonometry
not rated yet Nov 11, 2012
"One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1 percent"

less than 1%
Mike_Massen
1 / 5 (2) Nov 11, 2012
There are lots of sources of "near infra red" such as around the vessels that use solar for thermal power Eg as in Spain, plethora of industries etc.

There is plenty of heat around and with mirrors can increase this substantially, with various dichroic (old meaning) reflectors or prisms so any near infrared of the appropriate frequencies goes to the carbon cells (higher freq to conventional silicon cells) & which, being made of carbon could handle really intense levels ie High temperatures.

Its surprising people on this so far haven't considered or thought to comment there are staggering numbers of places where near infra red is usable as sources for these and improved versions of carbon solar cells...?

If the cost is low enough it could well be standard fare in so many places...!

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