Getting a charge out of solar 'paint'

February 14, 2011 By Miles O'Brien and Marsha Walton
Energy generated from renewable sources has long promised to satisfy demands for more and cleaner electricity. Because renewable sources, such as sunlight and wind, can produce greatly fluctuating amounts of energy, they are most effectual when excess energy can be stored until it's needed. Credit: Prof. Gutierrez/Prof. Hermanovicz/Prof. Lee, University of California-Berkeley

Have you seen those big, bulky, breakable photovoltaic cells that now collect the sun's rays? Well, what if solar energy could be harnessed using tiny collectors that could be spray painted on a roof, a wall or even a window?

The science of converting sunlight into is more than a century old, but the reality of doing it efficiently and affordably is ongoing.

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"Not only does it involve fundamental science in terms of physics and chemistry, and in some cases biology, but there are major engineering challenges as well," notes Brian Korgel, a nanomaterials chemist at the University of Texas at Austin.

Korgel and his colleagues are a new breed of , looking for answers to the world's big problems.

"There was a time where the field of chemical engineering had a reputation of being really conservative. You'd get your degree in chemical engineering, and you'd work for a chemical plant with a hard hat or in a giant refinery," says Korgel.

That's no longer the only option.

"Chemical engineers are now able to take these new chemicals, like nanomaterials, and we're trying to create the technologies that can meet the global challenge of, say, energy sustainability. We're taking chemistry, we're inventing new ways to actually make materials that can't be made any other way," he continues.

With support from the National Science Foundation (NSF), that's what Korgel and his team are doing to create solar cells that are light, flexible, efficient and--often the biggest obstacle--affordable.

"It's challenging to get high efficiencies of conversion. For example, the basic single junction solar cell is fundamentally limited to an efficiency of 30 percent. So, if you made a perfect solar cell, the highest efficiency would be 30 percent," explains Korgel at his Austin lab.

Currently, manufacturing cells with anything near that level of efficiency requires high heat, a vacuum and is very expensive. Korgel's approach, using nanotechnology, is completely different.

"What we're doing right now in my research group is making nanocrystals. We're focused on 'CIGS'--copper, indium, gallium, selenide--and we make small particles of this inorganic material that we can disperse in a solvent, creating an ink or paint," he says.

This solar "paint" would have the same function as the large photovoltaic (PV) solar collectors on buildings and "solar farms" around the world.

Korgel describes the tiny collection devices as a "solar sandwich."

"So these devices are 'sandwiches,' where you have the metal contact on the bottom and metal contact on the top to extract the charge out; and the middle part is the part that absorbs out the light," explains Korgel.

This paint, made of the CIGS nanocrystals, can be sprayed on plastic, glass and even fabric to create a solar cell.

"So what we're able to do is create radically new ways of depositing inorganic films to make , and so we're trying to meet this challenge of much lower cost of manufacturing," he says.

One way to create these cells on a very large scale would be to print them on thin, flexible sheets, the same way huge presses now print newspapers. "And the final product would ideally look something like today's shingles," says Vahid Akhavan, one of Korgel's graduate research assistants. "You want to produce something that is very user friendly. So you could go to your local hardware store, buy them and install them on your roof."

These shingles would do double duty, generating electricity while serving as roofing material. They would be also stand up better in bad weather, such as hail and windstorms, than some of today's more fragile solar collectors.

A lot of challenges need to be conquered before solar energy becomes so commonplace. High on that list is improving the efficiency of these nanomaterial cells. "Right now, we have made devices that have an efficiency of 3 percent, and to be commercial, you really need to be at 10 percent," says Korgel. "But I think we can get to 10 percent. Those are just engineering challenges; they are not necessarily easy, but they are not fundamental roadblocks."

Depending on what part of the world is looking to transition to , that improved efficiency is critical.

"I did my post-doc in Dublin, Ireland, so I know cloudy days with five hours of sunlight," says Korgel. "So if you want to use solar, you need to have efficient devices that can harvest the sun under those conditions."

Another obstacle will be determining what raw materials can be used if this technology can be mass produced. The copper, indium, gallium, and selenide are not all cheap or readily available.

"Ultimately, thinking much further out, you want to go with a technology where you use elements that are earth-abundant," says Korgel.

One possibility is silicon, which is made from sand, abundant across our planet. But extracting the silicon from the sand is now an incredibly energy-intensive process and the chemicals it takes to do that are pretty harsh on the environment.

Korgel, his students and colleagues see all those problems as having answers. And he's also motivated by non-scientists eager to wean the world from diminishing fossil fuels.

"Everyone realizes this is a major problem, and so many people want to see it solved and are incredibly enthusiastic and supportive of the scientific and engineering community. And it's inspiring," says Korgel. "What it's given me is a deep appreciation of how important this problem of meeting energy sustainability is. It drives you further on to try and meet that need."

The Korgel lab is also investigating medical uses for nanomaterials. "These nanomaterials have unique properties. They might be fluorescent and give off light, they can be magnetically responsive. If you shine light on them, they can generate heat. So you can take all of these unique properties, and then they're so small that they can flow around in your bloodstream and get into organs," he says.

For example, a nano probe could detect a cancer cell and then deliver the medicine to kill it. "So, if you could come up with a nanoscopic unit that could detect a variety of different types of cancers or different diseases and then carry out a therapy of some sort, that would be a big deal," he says.

Explore further: Lower-cost solar cells to be printed like newspaper, painted on rooftops

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12 comments

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Eikka
not rated yet Feb 14, 2011
If you shine light on them, they can generate heat.


Somehow I don't see the significance of that. I mean, black paint anyone?
d_robison
not rated yet Feb 14, 2011
If you shine light on them, they can generate heat.


Somehow I don't see the significance of that. I mean, black paint anyone?


I also read somewhere that it had been discovered that if you stick your hand in water, your hand gets wet...

Anyways, the article is ok and the idea is really cool, but a large problem I can see with something like this is during the winter months in places that do see snow. Snow covers the roof, most of the light gets reflected off the snow, no energy gathered. Even with a fairly steep roof you can still get a small layer of snow that could disable these shingles (anyone who lives in the northeast U.S. definitely knows about this problem first hand). However, if they were also put on the sides of the house I suppose you could gather a small amount of energy.
StillWind
2.3 / 5 (4) Feb 14, 2011
[ a large problem I can see with something like this is during the winter months in places that do see snow. Snow covers the roof, most of the light gets reflected off the snow, no energy gathered.


The real problem is in the perception that solar energy is capable of replacing carbon based fuels.
Solar is not and never will be a replacement for traditional fuels, with the possible exception of space based environments, solar will only be an adjunct to those fuel sources.
While i certainly agree that solar power should be developed to our best ability, continuing with a lie will only ensure that this technology gets left in the dust, since nearly every other fuel source is more efficient and economically viable. OTOH, if we recognize it for the niche that ti is, we can finally start to create a realistice energy strategy.
Glyndwr
2.5 / 5 (2) Feb 14, 2011
[ a large problem I can see with something like this is during the winter months in places that do see snow. Snow covers the roof, most of the light gets reflected off the snow, no energy gathered.


The real problem is in the perception that solar energy is capable of replacing carbon based fuels.
Solar is not and never will be a replacement for traditional fuels, with the possible exception of space based environments, solar will only be an adjunct to those fuel sources.
While i certainly agree that solar power should be developed to our best ability, continuing with a lie will only ensure that this technology gets left in the dust, since nearly every other fuel source is more efficient and economically viable. OTOH, if we recognize it for the niche that ti is, we can finally start to create a realistice energy strategy.


the whole point of science is that we dont know the answer 100%. Never say never
robbor
not rated yet Feb 14, 2011
hey, where do I get those shingles...oh,another 15 years, you say.
Bog_Mire
not rated yet Feb 14, 2011
snow will melt with a little heat.
MarkyMark
not rated yet Feb 15, 2011
This is a good bit of reaserarch which could one day help with ower energy needs, note i say helps as for now i dont see solar replacing fossil fuels ( one day tho who knows some suprise discovery may change that). As for snow covering roof shingles i agree it is a problem but not an impossable one to solve with a little enginuity. At least you can spray this stuff on walls and windows limiting the snow problem.
LivaN
not rated yet Feb 15, 2011
a large problem[...]snow, no energy gathered.


The real problem is in the perception that solar energy is [...] ti is, we can finally start to create a realistice energy strategy.


the whole point of science is that we dont know the answer 100%. Never say never


Solar power relies on the sun, which you may or may not realise sets in the evening. Add to that the decrease in it's intensity in relation to weather effects and you have a power supply that is not constant or even consistent.

It is not possible in the foreseeable future to have solar power replace carbon fuels without additional support. Nuclear power is a great candidate to supplement solar power and together they may be able to replace carbon fuels. Solar power alone is currently 100% not able to do so.
Grallen
not rated yet Feb 15, 2011
Solar CAN be used to replace fossil fuels. Use solar generated electricity to split water. Your can sell or ditch the oxygen. You can run your car on the hydrogen.

This strategy is already used (Google: "DIY Hydrogen"). It would be nice if it was cheap enough to become widespread.
Eikka
not rated yet Feb 15, 2011
Solar CAN be used to replace fossil fuels. Use solar generated electricity to split water. Your can sell or ditch the oxygen. You can run your car on the hydrogen.

This strategy is already used (Google: "DIY Hydrogen"). It would be nice if it was cheap enough to become widespread.


If only it wasn't so darn inefficient to do so. That kinda makes it... how would I put it... pointless.

And to scale the process up, you'd have to find a vast source of pure water, which in practice means desalination plants, which in practice means more energy used than you can get out of the panels.
PPihkala
not rated yet Feb 15, 2011
I wonder why people seem to be forgetting the existing solar collectors with much better efficiency? Namely Solar heat collectors, preferably vacuum tubes that work even in sub-freezing temperatures. Collect that heat and use it to replace the energy needed for heating or use it for adsorbtion driven cooling. That is existing tech, but everyone is trying to make electricity from solar, which is much harder and costlier and currently giving out laughable efficienses. Besides, heat is much easier to store than electricity. All one needs is big warm water storage tank.
kaasinees
1 / 5 (1) Feb 15, 2011
Vacume tubes actually REQUIRE energy, becuase of entropy, and there are always particles coming from vaccum enclosure itself. So no vacumes dont work. And how does vacume tubes collect heat?
The problem with SOLAR PANELS(or better yet photovoltacs), which you are refering to is that they cant absorb all wavelengths of light, only a narrow band, that is why their efficiency "sux", there is alot of research that can make solar panels better, i havent seen them in production processes yet though.

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