New material promises better solar cells

New material promises better solar cells
Sunlight is converted into electrical current in a layered structure.

Researchers at the Vienna University of Technology show that a recently discovered class of materials can be used to create a new kind of solar cell.

Single are combined to create novel materials with completely new properties. Layered oxide heterostructures are a new class of materials, which has attracted a great deal of attention among materials scientists in the last few years. A research team at the Vienna University of Technology, together with colleagues from the USA and Germany, has now shown that these heterostructures can be used to create a new kind of extremely efficient ultra-thin .

Discovering new material properties in computer simulations

"Single atomic layers of different oxides are stacked, creating a material with which are vastly different from the properties the individual oxides have on their own", says Professor Karsten Held from the Institute for , Vienna University of Technology. In order to design with exactly the right physical properties, the structures were studied in large-scale computer simulations. As a result of this research, the scientists at TU Vienna discovered that the oxide heterostructures hold great potential for building solar cells.

New material promises better solar cells
Elias Assmann (left) and Karsten Held (right) demonstrate the idea behind the new solar cell: Light is absorbed by a layered structure, free charge carrieres are produced and electric current starts to flow.
Turning light into electricity

The basic idea behind solar cells is the . Its simplest version was already explained by Albert Einstein in 1905: when a photon is absorbed, it can cause an electron to leave its place and electric current starts to flow. When an electron is removed, a positively charged region stays behind – a so called "hole". Both the negatively charged electrons as well as the holes contribute to the electrical current.

"If these electrons and holes in the solar cell recombine instead of being transported away, nothing happens and the energy cannot be used", says Elias Assmann, who carried out a major part of the computer simulations at TU Vienna. "The crucial advantage of the new material is that on a microscopic scale, there is an electric field inside the material, which separates electrons and holes." This increases the efficiency of the solar cell.

Two isolators make a metal

The oxides used to create the material are actually isolators. However, if two appropriate types of isolators are stacked, an astonishing effect can be observed: the surfaces of the material become metallic and conduct electrical current. "For us, this is very important. This effect allows us to conveniently extract the charge carriers and create an electrical circuit", says Karsten Held. Conventional solar cells made of silicon require metal wires on their surface to collect the charge carriers – but these wires block part of the light from entering the solar cell.

Not all photons are converted into with the same efficiency. For different colors of light, different materials work best. "The oxide heterostructures can be tuned by choosing exactly the right chemical elements", says Professor Blaha (TU Vienna). In the computer simulations, containing Lanthanum and Vanadium were studied, because that way the materials operate especially well with the natural light of the sun. "It is even possible to combine different kinds of materials, so that different colors of light can be absorbed in different layers of the solar cell at maximum efficiency", says Elias Assmann.

Putting theory into practice

The team from TU Vienna was assisted by Satoshi Okamoto (Oak Ridge National Laboratory, Tennessee, USA) and Professor Giorgio Sangiovanni, a former employee of TU Vienna, who is now working at Würzburg University, Germany. In Würzburg, the new solar cells will now be build and tested. "The production of these solar cells made of oxide layers is more complicated than making standard silicon solar cells. But wherever extremely high efficiency or minimum thickness is required, the new structures should be able to replace silicon cells", Karsten Held believes.

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More information: … ysRevLett.110.078701
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User comments

Feb 12, 2013
"The oxides used to create the material are actually isolators. However, if two appropriate types of isolators are stacked..."
Perhaps the author meant "insulators"

Feb 12, 2013
lol, yeah, insulators no doubt.

Translation humor aside:

I'm not holding my breath until they actually manage to fabricate one AND demonstrate that it works. Then there's the added complications of durability and manufacturing. If the material is too prone to defects and such then it may not be useful, for example.

There are a TON of ideas like this floating around right now, but none of them seem to be 100% ready for prime time yet.

Some of the best work I've seen recently in this field is coming out of MIT. I'd keep my eye on them if you're interested in advanced thin film solar cells.

Feb 12, 2013
Perhaps the author meant "insulators"

Probably. (The german word for insulator is 'Isolator'. Looks like a translation SNAFU)

The abstract (from the link at the bottom of the article) sounds extremely promising, though - because it adresses all of the things that impact solar cells:
- fast charge separation
- gradual band gap for full spectrum conversion
- minimal material requirements

Feb 12, 2013
This is getting ridiculous. Almost every day there is an article about some awesome discovery that *should* allow to create better solar cells. Like the child who cries wolf, at some point people won't pay attention anymore.

Feb 12, 2013
You're welcome.

Anyone who posts in clear contravention to forum guidelines deserves no less for his complete regard to netiquette.

Feb 12, 2013
@DavidW: You're off-topic and you hardly make sense.

Feb 12, 2013
Who really knows the perfect time? If we discover too fast it appears that extinction is a really possibility, sooner, rather than later. But then if all humans are going to eventually die, then perhaps less suffing now is better? The truth is what tells us that life is important. The truth says to try to do the most good. The real power rests with the truth. This is the power that we people need to remember.

The truth tells us? Would that be in English? Mandarin Chinese? In Maths? Did the truth speak to ya about staying out in the sun to long and letting your brain getting short-circuited? I think that is about as close to the truth and this topic ya're going to get.

Feb 12, 2013
DavidW, did the truth say to ya anything about the subject of this article?

Maybe the truth told ya to not bother reading the article and just jump on in with the "truth's" whisperings in your ears. They have medication for those type of truths.

Feb 12, 2013
Come dude. you think you have a point? huh? I'll be more than happy to debate you in front of everyone you know witnessing the truthful facts, crying and shaking in disbelief... as you try to find excuses for your bad behaviour. Any day, bring it on. Until then, sit down and shut up.

Is that a general Dude? Or a specific Dude? If it's a general generic dude, I'm game. But I've got to head home for now,,,,, tomorrow maybe? Spend the night productively, I'll spend mine sleeping. Toot-A-Loo.

Feb 13, 2013
Mmmmm ... more layers? Although each layer/interface is but one more barrier for power flow to jump.

Of interest in this regard: The shady side could also be a thermal-voltiac layer. A possible improvement in overall power through put. (All Solar photo-voltiac cells get hot on the Sunny side, this temperature differential IS power untapped.)

Feb 13, 2013
... Perhaps the author meant "insulators"

Isolators v. insulators, a semantic / language difference, most likely. The Viennese think different? Not!

Feb 15, 2013

David, our purpose it to create super advanced technologies and then combine them with advanced technologies developed by life in other create a hyper technology that becomes one with the universe (merges with the fabric of the universe).

Thats the best i can think of.

Feb 17, 2013
This is not a game.


So exactly why are you wasting your life playing "fairy in the sky" again?

Feb 17, 2013
"This is getting ridiculous. Almost every day there is an article about some awesome discovery that *should* allow to create better solar cells. Like the child who cries wolf, at some point people won't pay attention anymore."

We are putting great effort into solar cell efficiency. There is a chart on the efficiency over time on wikipedia (don't have the link) but If you look, we are making stead progress. I don't think on this subject that there will be great leaps, just incremental ones. Although at some point like many technological development curves, it might just go Asymptotic since most tech curves go that way or into S-Curves.

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