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Counterintuitive “LED-type” solar cell breaks efficiency record

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April 24, 2012

The record-breaking Alta Devices solar cell (Photo: Joe Foster, Alta Devices)

The record-breaking Alta Devices solar cell (Photo: Joe Foster, Alta Devices)

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When you think of a solar cell, you probably think of something designed to absorb as much sunlight as possible. What you probably don't think of is something that is also capable of emitting light. Nonetheless, that’s exactly what a new prototype device designed more like an LED does, and it recently set an efficiency record for flat-plate single junction solar cells.

The cell was created by Alta Devices, a California-based company co-founded by University of California, Berkeley professor of electrical engineering Eli Yablonovitch. Together with graduate student Owen Miller, he worked out a mathematical principle which states that “the better a solar cell is at emitting photons, the higher its voltage and the greater the efficiency it can produce.”

Eli Yablonovitch and Owen Miller, who worked out the theory for the new solar cell (Photo:...
Eli Yablonovitch and Owen Miller, who worked out the theory for the new solar cell (Photo: Eli Yablonovitch)

The prototype cell incorporates a gallium arsenide semiconductor. Electrons within that material are knocked loose to flow freely by the energy of photons in sunlight. As the electrons are knocked loose by the existing photons, other photons are generated in the process.

So far, that’s the same principle that’s at work in most conventional solar cells. However, the prototype cell is designed to let these new photons escape as easily as possible (in part, via a highly-reflective rear mirror surface), which in turn raises the voltage that it is able to produce.

The technology allowed the prototype to achieve an efficiency of 28.3%, which broke the previous record of 26%. Yablonovitch hopes that researchers building on his work may be able to achieve a figure of 30% within a few years.

Although the record-breaking device is a flat-plate single junction cell (meaning it is only capable of absorbing light waves within a given frequency), the principle it uses is said to apply to all types of solar cells.

Source: The Optical Society

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
21 Comments

When are people going to stop announcing vapor-ware and produce something that the public can buy.

S Michael
24th April, 2012 @ 07:02 pm PDT

s Michael

I think this was just a research finding, not an actual product.

bio-power jeff
25th April, 2012 @ 05:26 am PDT

Yablonovitch is not a vapor-ware seller, he is a very sound physicist who has already published several fundamental papers in optics/photovoltaics. Maybe some of you have heard about the 4n^2 law, which states that the maximum energy density one could ever achieve in an optical medium is proportional to the square of the index of refraction of the medium (n^2). Well, this is one of Yablonovitch's contribution to solar cells. Just to say, even if the "LED-type" seems counterintuitive, I would not be surprised that Yablonovitch has just made a new beautiful contribution to our understanding of the photovoltaic conversion phenomena.

RicardoTheron
25th April, 2012 @ 06:47 am PDT

What I think S Michael means is that we keep reading about higher and higher efficiency products but this does not translate in affordable products we can use.

Francois Parent
25th April, 2012 @ 09:56 am PDT

There is always a time gap before a result of a scientific research can be applied in mass production. There are lot of technological problems to solve. Especially, if some industry leaders have another interests.

Imhof Iván
25th April, 2012 @ 11:20 am PDT

Still waiting for my mr. Fusion, this does however greatly enhance the understanding of photovoltaics. I pray i can hand my son a world of tron like power so he can concentrate on better things than survival

MasterG
25th April, 2012 @ 11:28 am PDT

it seems like every month we hear of some new development in PV technology, higher efficiency, cheaper manufacturing, less costly materials, etc.... current PV products have an efficiency of... what, 20%? i think it'll need at least another 10% before solar power really takes off, but that probably will not be for another ten years.

mikewax
25th April, 2012 @ 01:21 pm PDT

Nice stuff. While other groups are trying to squeeze an extra 2% from Mono-C solar cells, this guy is breaking new ground.

The nay-sayers will be left with behind with their heads in the sand and their certainty intact.

Mirmillion
25th April, 2012 @ 04:43 pm PDT

... regardless of the nay-sayers, I want to thank you Professor Yablonovitch and Owen Miller for your success, on behalf of my grandson... truly a great achievement. Pure genius IMHO

Brent Eagleson
25th April, 2012 @ 06:20 pm PDT

Suddenly! It's 1940! "Let there be light" by Robert A. Heinlein, writing as Lyle Monroe.

RAH used many pen names so it wouldn't look like he was writing nearly half the stories in the pulp magazines - which he was. ;)

http://en.wikipedia.org/wiki/Let_There_Be_Light_(short_story)

It's a story about solid-state light emitting panels that can also convert light into electricity.

Yablonovitch-Miller doesn't have the same ring to it as Douglas-Martin. ;)

Gregg Eshelman
26th April, 2012 @ 01:37 am PDT

please put this stuff in LOWES, i just bought my 1st house and am dying to go solar. right now it's a HUGE investment that takes years to return on. give me something i can carry up a ladder and plug into an outlet, i don't care if it's 10% effective, just make it cheap and available!!!!!!!

johnweythek
26th April, 2012 @ 03:45 am PDT

The biggest percentage gains are still in becoming more efficient in our USE of the electricity we currently generate. With an electric bill of around $45/mo., it would take me at least twenty years to pay off a conversion to solar power, much as I would like to get off the grid.

Rich Mansfield
26th April, 2012 @ 10:33 am PDT

Re Lag in Manufacturing... after Invention.

The lag often amazingly corresponds to the time it takes for the original patent to expire, 20 years....

Unless the inventor can capitalise on his/her invention noone else is going to put money in, especially in a new fiend, when they know that if they are ready to market in 20 years (short term plan) ir wait a while and buy the patent after the hype has gone, and the inventor realises that he can't afford to get his great idea to market...

Many things aren't vapourware, it is just that the money often isn't there for good ideas. only the status quo.

MD
27th April, 2012 @ 02:07 am PDT

I am not a power hog. I think I would easily live on a photovoltaic system with a 20% yield. I have seen several systems I was financially capable of buying as first advertised but due to changes in philosophy the systems were never marketed to individual buyers. Systems originally described as potentially for decentralization of power to individual homes and businesses with power yields from 1KWH to 5KWH systems. Then the system comes to market with ratings like 25KWH to 500KWH and a price tag to match. The people apparently give in to the utilities and only sell systems that are much larger than most or all homes cannot possibly use and for dollars more than we can hope to pay.

If even one of these systems were marketed for the average home, the company would make billions if not trillions of dollars. Allowing for a 30 year warranty most companies once established would have to diversify as the first few years they would sell 90-95% of what they would sell in a 30 year run. But every country could become energy self sufficient. Machiavelli's dream (assuming "The Prince" was not satire or sarcasm). Add the uses like photovoltaic condensers for extracting water from the air and deserts go away. Then if we can finally get our gonads out of control we could all have all the food and water we need.

I have compared to my neighbors a low utility bill but I would still gladly pay $15,000 to $20,000 for a system that would last for 20-30 years. Utility costs only go up.

NatalieEGH
28th April, 2012 @ 10:13 pm PDT

@NatalieEGH,

Both natural gas and electricity produced therefrom are falling in price due to shalegas recovery techniques. Solar is yesterday. Some CO2 is tolerable lest we produce an ice age.

qwester
30th April, 2012 @ 07:06 am PDT

@kwester - the only problem with the shalegas is that we are basically selling our souls to the devil for cheaper natural gas. Fracking is a vile, environment-raping process that companies don't even bother to do correctly, making it even worse than it should be.

This nation and this world simply has to stop relying on burning crap to power our lives. The population growth in less wealthy countries like China means that they are accelerating their burning of the worst materials creating more and more pollution. America is hardly exempt - I live 20 miles from Niagara Falls, but all the hydro power in my backyard is shipped to NYC and my lights burn off a coal power plant. Makes no sense.

Firehawk70
6th May, 2012 @ 08:46 pm PDT

Oh and by the way - "Some CO2 is tolerable lest we produce an ice age. " is about as backwards thinking as I've ever heard. An ice age is exactly what we will get with more CO2!!!

The film "Day After Tomorrow" is based on solid paleoclimatological evidence. A rise in CO2 precedes the ice age for the very reason presented in the film - all the fresh water in the melting ice caps destabilizes the gulf stream's salt conveyor system. That results in less heat in the northern hemisphere - aka ice age.

Firehawk70
6th May, 2012 @ 08:50 pm PDT

Let's not start talking about paleoclimatological evidence like it is anything more than someone's best guess. We really need to come to grips with the FACT that scientific ideas, theories, postulations are just that. I'm not saying that an educated guess isn't a worthwhile thing. Just not so worthwhile as to give others the right to cram legislation and other forms of control down our collective throats.

Here's an idea let's start using LFTR technology to produce substantially all of our electricity then save the petroleum for other uses. Do the research and get behind it. Let's have the USA lead the way to clean cheap energy. I believe in more energy for everyone on the planet. Solar although plentiful can also raise temperatures (oh no!). Imagine every home having large heat absorbing and radiating black panels. LFTR keep repeating it to everyone you know. Solar may be part of the answer but not a large part. Annoyingly you buy them at X% efficiency and they lose a goodly portion of that efficiency every year. LFTR!

Dr. Veritas
11th May, 2012 @ 08:43 pm PDT

I'm sorry to all you naysayers out there who must work for the power industry. The fact is if you actually did the math you would realize that Solar is and has been cheaper than traditional power. I can put in a solar installation right now that would cost less for the same amount of kwh provided than traditional power sources. In addition, I can do that with unsubsidized solar vs. subsidized traditional sources. The fact is that no one want's to invest in solar power until it's free to them because they are scared of change and anything that upsets the status quo such as going from a monthly power bill + Mortgage to a slightly higher mortgage payment with no power bill is just too much for them. Even now that we have developed "Free" solar through financing here in NC folks are having trouble because it sounds too good to be true and folks are so beat up from being taken advantage of by big banks and small time crooks that they just don't want to take any unnecessary risks no matter how small or beneficial until someone they trust has already taken that risk. Even with other folks having already done it many of them won't try it because they looked at it two years ago. People don't realize that solar drops in cost an estimated 30% every year. Finally, folks often think "well it would be a good idea next year" without realizing that every year government and utility incentives go away as utilities meet their RPS standards mean more net cost even as the cost of materials is getting lower. I have run the numbers 100 ways to sunday the time to get into solar is before 2012 ends.

Zachary Burgess-Hicks
18th June, 2012 @ 02:01 pm PDT

It makes sense, if its photons that knock electrons loose in a solar cell. Ive wondered this, if the solar cell was made of a material that absorbs light and glows, like those plastic stars you can stick on your ceiling or some key pads on a cell phone and so forth, those materials absorb photons and release them in the dark. So a solar cell made of such should do better.

Stephen Dickens
16th September, 2012 @ 05:29 pm PDT

Zachary Burgess if you invested the money you used for your solar panels in a coal company today, after 5 years how many solar panels the size of the one you have today would you be able to buy?

katgod
2nd October, 2012 @ 05:39 pm PDT
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