UCLA researchers create highly transparent solar cells for windows that generate electricity

[OKIsItJustMe]

http://newsroom.ucla.edu/portal/ucla/ucla-researchers-create-highly-236698.aspx

[font face=Serif][font size=5]UCLA researchers create highly transparent solar cells for windows that generate electricity[/font]

By Jennifer Marcus | July 20, 2012

[font size=3]UCLA researchers have developed a new transparent solar cell that is an advance toward giving windows in homes and other buildings the ability to generate electricity while still allowing people to see outside. Their study appears in the journal ACS Nano.

The UCLA team describes a new kind of polymer solar cell (PSC) that produces energy by absorbing mainly infrared light, not visible light, making the cells nearly 70% transparent to the human eye. They made the device from a photoactive plastic that converts infrared light into an electrical current.

"These results open the potential for visibly transparent polymer solar cells as add-on components of portable electronics, smart windows and building-integrated photovoltaics and in other applications," said study leader Yang Yang, a UCLA professor of materials science and engineering, who also is director of the Nano Renewable Energy Center at California NanoSystems Institute (CNSI).

Yang, who is also the holder of the Carol and Lawrence E. Tannas, Jr., Endowed Chair in Engineering, added that there has been intense world-wide interest in so-called polymer solar cells. "Our new PSCs are made from plastic-like materials and are lightweight and flexible," he said. "More importantly, they can be produced in high volume at low cost."

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[silverweb]

1. Awesome.

[font color="navy" face="Verdana"]This is news I've been longing to hear. Let's make this stuff available and start using it fast!!

[jillan]

2. Yes!!! This is great news! And lately great news is hard to find.

[drm604]

3. Use this for cellphone screens

and every time you take it out of your pocket it will get a small charge.

I wonder if this would be worthwhile for car windows?

[AtheistCrusader]

7. o.0

[drm604]

12. I don't understand your post.

[AtheistCrusader]

13. Even a 100% dedicated solar panel of that size is useless to keep your phone topped off.

The technology being discussed here generates useful voltages on the scale of buildings. Maybe useful as a trickle charger for electric cars. From a maintenence, keeping it topped off perspective.

A charger that can do your cell phone in a few hours, like the Nomad 7, is the size of a laptop. You'd also need the backlight of the phone to be more powerful to overcome the opacity of the charger panel, if it's absorbing 25% of the light that passes through.

[drm604]

21. Then just explain that rather than posting some cryptic characters.

[limpyhobbler]

4. cool. nt

[rhett o rick]

5. GE will buy it and squash it. nm

[PamW]

6. LOW EFFICIENCY!!

Yes - you can make solar cells that are transparent; but they are LOW EFFICIENCY!!!

It's simple physics, from the Conservation of Energy.

For any given photon impinging on the solar cell window; either the energy of that photon is going to be turned into electricity by the solar cell function; or the photon is allowed to pass through so it can light the room.

You can't make 100% of the energy do BOTH things simultaneously; i.e. getting 100% of the light value AND 100% of the electric value. The sum total of the light energy plus the total electrical energy has to equal the total energy value of the photons impinging on the window.

You can't have your cake and eat it too.

PamW

[AtheistCrusader]

8. I'll take 20-25%

That's excellent. There is so much surface area to install this on. Most exterior business windows are tinted to some degree anyway.

[PamW]

15. These cells don't get 20%

Solar cells that are opaque will do well to turn 20% of the energy in the photons to electricity. The rest winds up as heat.

These cells have the additional inefficiency that they let through photons to light the room; in which case none of the photons energy can be captured as electricity. ( Photons are quanta - you don't get to absorb part of a photon. )

The fact that these cells are transparent, of necessity means that they can't be as efficient as cells using the same material / electric energy capture scheme that are opaque.

If you let through photons to light the room; those are just photons that your electric energy capture scheme doesn't get to work on.

Simple.

PamW

[AtheistCrusader]

17. I mean, I'll take 20% opacity.

Saves on window tinting. I know the yield will be low, like 3-4% something like that.

[Spitfire of ATJ]

9. That's the point. It's not tranparent to infrared.

Any color in any object you can name has that color because it absorbs all the colors of the visible spectrum EXCEPT the color of the object itself which it reflects back and that is why it is seen by the eye as that color. This thing must be in the color of infrared.

Now the question is if they can make it economically viable for owners of highrises to consider replacing all of the glass in the building with this stuff.

[PamW]

14. WRONG!!! WRONG!!! WRONG!!!

You don't understand why objects are the color they are. Evidently you've never studied quantum mechanics.

It has to do with the energy levels of the electron orbitals in the object's atoms. Let's say we have 3 levels; a ground state and two excited states.

Level 3 ---

Level 2 ---


Level 1 ---


Suppose the difference in energy between level 1 and level 3 corresponds to blue light. Suppose the difference between level 2 and level 3 corresponds to yellow light, and the difference between level 1 and level 2 corresponds to green light.

Then the atom can absorb a photon of blue light and an electron moves from level 1 to level 3. That electron then falls to level 2 and emits a photon of yellow light. The electron then falls back to ground state going from level 2 to level 1 and emits a photon of green light.

That's how an element absorbs blue, and then emits yellow and green.

Teachers often tell the scheme you did to elementary school children; but it's actually WRONG!!

Word to the wise; don't try to contradict a PhD Physicist like myself on the subject of Physics when your knowledge of the subject is grade school level.

PamW

[Spitfire of ATJ]

18. "Word to the wise; don't try to contradict a PhD Physicist like myself"

There were tons of PhD Physicists who were saying the sound barrier couldn't be broken.

Before that, they claimed the light bulb was impossible.

I tried to keep it simple in layman's terms and got jumped on for it.

Besides, who cares if it's not efficient? I'll get better as they refine it. Recognize a breakthrough when you see it.

[Nederland]

20. There were tons of PhD Physicists who were saying the sound barrier couldn't be broken.

Name one.

[PamW]

29. MYTH - "Old Wives Tale"

It's purely a MYTH that physicists and engineers said that the sound barrier couldn't be broken.

It has been know for a LONG, LONG time that the crack of a whip is due to the tip going super-sonic. So there can't be any physical laws that are violated by going faster than sound.

There were engineering concerns about whether one could get jet / rocket engines that could produce enough power to compensate for the immense drag caused when one goes super-sonic. The shock-wave that is the "bow wave" of a supersonic aircraft saps lots of energy. Until recently, the only way to go supersonic was to use after-burners on the jet engines. That limited super-sonic flight to a few tens of minutes.

The new F-22 stealth fighter is the first craft that has "super-cruise" and can go super-sonic without the use of after-burners on the engines.

I don't care how efficient it is. It is merely a scheme to "borrow from Peter to pay Paul". Any energy that is converted into electricity comes out of that which could otherwise be used for lighting. You can't "double count" the energy and use a given incident photon for both lighting and electricity; regardless of how efficient you get.

You do understand that, don't you?

PamW

[Spitfire of ATJ]

30. They talked about the "sonic wall" and a lot of pilots died trying to break through.

http://www.pbs.org/wgbh/nova/transcripts/2412barrier.html

#!

[PamW]

31. Difficult vs Impossible

You do realize that there is a difference between "difficult" and "impossible", don't you?

No physicist said that going super-sonic was going to be easy. There are very challenging issues of control, since controls often work "backwards" in the super sonic regime. A craft like the Space Shuttle returning from orbit can only be flown "fly by wire" since the reaction of the control surfaces are different depending on the speed. For a desired control input; the direction of movement of the control surfaces depends on the local sonic conditions, and hence it takes a computer to figure out which way to move the control surfaces.

However, it's not impossible; just difficult. That's why ultimately, we could do it.

Now going super-luminal; that is going faster than the speed of light in a vacuum IS prohibited by the Laws of Physics.

It's an "Old Wives" tale that physicists once said super-sonic flight was impossible, or that heavier than air flight is impossible. Take flight for instance. Prior to the 20th century, we didn't know how to do it; but we knew it could be done, and that the laws of Physics didn't forbid it. After all, birds fly. If the laws of Physics forbid it; then birds couldn't fly either.

PamW

[Spitfire of ATJ]

32. Why don't you go back even further. Some scientists claimed going over 60mpg

would suck all of the air out of a railroad coach and everyone would suffocate.

The electric light was described as being against the laws of physics at one time too.

Scientists argue constantly with some of the most highly regarded in their fields being wrong throughout the history of science. Besides, I'll trust the word of people who were involved in the project that said there were scientists and engineers who claimed it was impossible.

As far as FTL, that's true. All FTL in science fiction does a cheat of one kind or another. Time warp and space fold or leaving this realm into another and returning at the destination are the most common. I don't rule anything out. Especially since we are just starting.

There were people who watched the moon landing who had crossed the prairie in a covered wagon.

[PamW]

16. Infra-red energies are less than the band gap

Sorry but infra-red photons don't help you make electricity.

Infra-red photons have energy less than the energy band gap between the valence band and the conduction band.

In fact, not all visible light photons have enough energy to cross the band gap.

That's what gives you the "quantum efficiency" limit for solar cells. Google "quantum efficiency" and solar cells and look it up.

http://en.wikipedia.org/wiki/Solar_cell_efficiency

However, solar cells operate as quantum energy conversion devices, and are therefore subject to the "thermodynamic efficiency limit". Photons with an energy below the band gap of the absorber material cannot generate a hole-electron pair, and so their energy is not converted to useful output and only generates heat if absorbed.


None of the infra-red photons have enough energy to cross the band gap.

PamW

[Spitfire of ATJ]

19. "None of the infra-red photons have enough energy to cross the band gap."

So we should scrap this article as bunk?

[AtheistCrusader]

22. Error!

"Sorry but infra-red photons don't help you make electricity."

Not through Photo-voltaic, but you can with a thermocouple

[OKIsItJustMe]

23. Perhaps you should take the time to read the actual paper (rather than the press release.)

(There’s a link to it in the OP.)

http://pubs.acs.org/doi/pdf/10.1021/nn3029327

[font face=Serif][font size=5]Visibly Transparent Polymer Solar Cells Produced by Solution Processing[/font]

…

[font size=4]ABSTRACT[/font]

[font size=3]Visibly transparent photovoltaic devices can open photovoltaic applications in many areas, such as building-integrated photovoltaics or integrated photovoltaic chargers for portable electronics. We demonstrate high-performance, visibly transparent polymer solar cells fabricated via solution processing. The photoactive layer of these visibly transparent polymer solar cells harvests solar energy from the near-infrared region while being less sensitive to visible photons. The top transparent electrode employs a highly transparent silver nanowire—metal oxide composite conducting film, which is coated through mild solution processes. With this combination, we have achieved 4% power-conversion efficiency for solution-processed and visibly transparent polymer solar cells. The optimized devices have a maximum transparency of 66% at 550 nm.

…

Conclusions and Prospects. We have demonstrated high-performance, solution-processed, visibly transparent polymer solar cells through the incorporation of near-infrared light-sensitive polymer and using silver nanowire composite films as the top transparent electrode. The near-infrared photoactive polymer PBDTT-DPP absorbs more near-infrared light but is less sensitive to visible light, balancing solar cell performance and transparency in the visible wavelength region. The transparent top electrode is a fully solution-processed silver nanowire-based composite film, which is compatible with common PSC materials. With this combination, we have achieved ~4% power-conversion efficiency for the solution-processed and visibly transparent solar cells, while the devices have high transparency, 66% at 550 nm. These results open the potential for visibly transparent polymer solar cells as add-on components of multijunction photovoltaic devices, smart windows, and building-integrated photovoltaics and in other applications.

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[PamW]

24. Exactly what I wanted to see...

The above post is exactly what I wanted to see. It documents what I suspected from the press release.

The power conversion efficiency for these solar cells are indeed very low at 4% efficiency.

Additionally, the solar cell function reduces the transparency, and hence light transmission properties relative to glass by about 34% ( 66% transmission ).

So there you have it in a nutshell. Of the incident photon energy, these cells give you 4% of your incident energy as electricity, and you pay for that with 34% reduction in light transmission.

It had to be something like that. There's NEVER a "free lunch" with energy. You can't "win" and the laws of physics never even let you break even. You just have to learn to live with that since there's nothing you can do about it. Yet so many are always looking for that "free lunch" which costs them more than it's worth.

PamW

[XemaSab]

25. Most office windows are shaded anyways

While this technology is far from mature, it's an interesting first step in a promising direction.

[Exen Trik]

10. But in the infrared?

The point of this is that it isn't a visible light solar cell, it's infrared. It even reduces heat passing through so it saves energy needed to cool the building. Of course this isn't terribly efficient yet as far as the area it takes goes, but think about how much glass used. Entire skyscrapers coated with this kind of technology makes a damn nice dent in the power they use.

The coating is going to be cheap, it costs nothing in terms of space, and it can replace normal tinting for shading and reducing heat. That sounds an awful lot like having your cake AND eating it, to me.

All that remains is to see just how cheap and how efficient it can get. But this is a great start in a very promising direction.

[PamW]

27. Again...

Again you must have misread something.

Inra-red photons have energies below the value of the valence band to conduction band gap energy.

So you don't get photovoltaic electrons from infra-red photons.

PamW

[OKIsItJustMe]

11. How efficiently do your windows produce electricity today?

This would be 100% more efficient than a standard window.

[PamW]

26. The problem is...

The problem is that you pay for the electric production with decreased light input to the room.

The worst thing would be to take that new electricity and use it to light the room. The inefficiencies in conversion from light to electricity and back to light would make it a net loser to just using the light photons directly.

It all depends on how much light you need for the room.

If you have all the light you need, and you are drawing the shades to keep some out; then it would be OK to use the excess light to convert to electricity.

However, if you don't have enough light for the room, or have exactly as much as you need; turning some of it into electricity will be a net loser.

Just remember that the laws of physics don't let you use light photons twice. For each photon that goes into the window; you can either let it pass as light or turn it into electricity with the loss of illumination potential.

I'm just cautioning against "double counting" of energy; you can't get the full lighting potential of the incidents photons, while simultaneously using them to make electricity.

I have no problem with the technology. Just don't "double count" energy.

PamW

[OKIsItJustMe]

28. "The problem is that you pay for the electric production with decreased light input to the room."

How much will you miss the near-infrared?