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A close up of a single ball, 300 nm across. The ball is made up of 15 nm grains.  (Source: University of Washington)

Millions of the balls compose a layer of the solar cell.  (Source: University of Washington)

The thin light-absorbing zinc oxide surface, pictured here in a picture from a scanning electron microscope, is about 10 um thick, and composed of the popcorn ball like structures.  (Source: University of Washington)
While not very tasty, these balls are extra efficient

With gas prices going up, refining capacity stretched to its max, and the reality that fossil fuels will eventually be depleted settling in, interest in alternative energy solutions of various types is at an all time high.  Among these is renewed vigor in the solar power industry.  From building massive new plants to new ground breaking research, the rather old field of solar power, is adapting quickly to the latest tech.

The University of Washington just made another breakthrough in solar power, that while humorous sounding, certainly offers serious gains.  Researchers at the university studying solar cell configurations discovered that by implementing a popcorn ball design -- tiny spheres clumped into bigger porous spheres -- efficiency in cheap solar cells was near doubled.

The dramatic improvement was included in findings presented at the national meeting of the American Chemical Society in New Orleans.  Lead author Guozhong Cao, a UW professor of materials science and engineering, states, "We think this can lead to a significant breakthrough in dye-sensitized solar cells."

Dye-sensitive cells have been in vogue since early pioneering research in 1991.  The cells have the advantage of being flexible, cheaper, and easier to manufacture than brittle silicon solar cells.  Rough surfaces have been a focus in the dye-sensitive field's research, with researchers reach efficiencies of approximately 10 percent capture of the suns energy absorbed.  This efficiency is only about half that of traditional silicon solar cells found on roof tops and calculators but with the lower price its is enough to stay competitive with the silicon cells.

The University of Washington researchers looked to compare homogeneous rough surfaces with various clumped designs, instead of trying to maximize the efficiency of the well researched homogeneous rough surface.  One dilemma that researchers faced was the size of the grains used.  Bigger grains, closer to the visible wave length of light cause the light to bounce around inside the thin-light absorbing surface, increasing the probability that it will be absorbed.  On the other hand, small grains have a bigger surface area per volume, increasing absorbtion.

Explains Cao, "You want to have a larger surface area by making the grains smaller.  But if you let the light bounce back and forth several times, then you have more chances of capturing the energy."

Other researchers have tried unsuccessfully to improve efficiency by mixing small and large grains.  The UW researchers instead took tiny 15 nm grains and clumped them together into 300 nm agglomerations, essentially making large grains composed of small grains, an approach that resembles macroscopic scale popcorn balls.

Each gram of the material has an incredible surface area of 1,000 square feet per gram covered in light absorbing pigment.  Thanks to the complex design light also gets trapped inside the larger balls, increasing absorption remarkably.  The researchers were surprised at their success, saying it surpassed even their best hopes.  Says Cao, "We did not expect the doubling.  It was a happy surprise."

The overall efficiency was 2.4 percent for small grains only, the current highest efficiency achieved for the material (there are higher efficiency materials, hence the 10 percent in commercial designs).  The popcorn-ball design showed an overall efficiency of 6.2 percent, a 258 percent increase in efficiency.  Cao states, "The most significant finding is the amount of increase using this unique approach."

The research used the pigment zinc oxide, which is of lower efficiency than the commercially used titanium oxide, but easier to work with during experiments.  Titanium oxide layers are expected to show similar gains.  Cao gives an update on this explaining, "We first wanted to prove the concept in an easier material. Now we are working on transferring this concept to titanium oxide."

While titanium oxide cells currently have a record efficiency of 11 percent, the researchers hope that by using the new method they can by far surpass this old record, possibly even surpassing silicon cell efficiencies.  Such progress could make silicon cells, used for decades, obsolete, replaced by cheaper, more efficient, flexible cells.

The research was funded by the National Science Foundation, the Department of Energy, Washington Technology Center and the Air Force Office of Scientific Research.  The postdoctoral research was co-authored by Qifeng Zhang, research associate Tammy Chou and graduate student Bryan Russo all in the UW material sciences department, and Samson Jenekhe, a UW professor of chemical engineering.

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RE: Here's the simple solution
By killerroach on 4/14/2008 9:01:20 AM , Rating: 2
And the Native Americans also usually didn't live much past the age of 40 back then. I think there's probably more than a few people on these forums who would not take too kindly to that sort of an "improvement" of getting back to those sorts of ways, and suggesting mass depopulation coupled with ZPG in order to "conserve resources" sounds rather, shall we say, selfish... "things for me, but not for thee."

RE: Here's the simple solution
By AntiM on 4/14/2008 10:08:47 AM , Rating: 2
I admit that one man's utopia is another's nightmare. I don't see how you can call me selfish. Is it possible for us to continue with our present rate of consumption and pollution ? Do you want to leave future generations with an overpopulated, polluted, decimated planet? I'm willing to cut down on my consumption. I'm willing to not reproduce. (no wise cracks please!) I'm pretty sure that with our present knowledge, humans can live well past 40, and with a healthier lifestyle, probably much longer than we do today. I'm willing to make sacrifices for the betterment of the planet. What are you doing besides sitting there spewing out carbon dioxide?

RE: Here's the simple solution
By maven81 on 4/14/2008 1:44:03 PM , Rating: 2
I was just thinking about it this morning while glancing at all the people on the train with their various widgets... The truth is, the human race can not survive without technology. If you had simply advocated reducing the population growth that's one thing, but you're also suggesting we return to our roots so to speak, and live in some sort of agrarian society.
What that would do is halt any kind of progress. Humans lived like that for thousands of years, and did not progress anywhere. They didn't become more intelligent, they didn't gain any knowledge about the world around them, didn't find ways to deal with the most basic illnesses and so on. I realize you're implying we just keep our current level of technology, but if you abandon development knowledge will slowly decay until we can't even remember how anything works and how to fix it.
We got here through technology (even spears are a technology), to deny that is to deny who we are.

"We basically took a look at this situation and said, this is bullshit." -- Newegg Chief Legal Officer Lee Cheng's take on patent troll Soverain

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