Solar cell efficiency receives a transparent boost

Aug 22 - Houston Chronicle

Think about this during these dog days of summer: Researchers are working to capture the sun's rays more efficiently and turn them into electricity, using a see-through solar panel no thicker than a plastic grocery bag.

Officials with Phillips 66 said Tuesday that their partnership with California startup Solarmer Energy and a Chinese university has yielded the most efficient polymer-based organic solar cell yet, a milestone that puts them closer to marketing the technology.

Byron Johnson, manager of sustainability technologies at Houston-based Phillips 66, said the work reflects the company's commitment to renewable technologies, even though its core business remains rooted in the oil industry.

"Most of our work involves petrochemicals," he said. "That is our business. But we want to understand all energy sources and also participate in them."

His division works with biofuels, along with other renewable energy sources, including solar.

Vishal Shrotriya, a spokesman for Solarmer, said the partnership with Phillips 66 and South China University of Technology began two years ago, before Phillips 66 split from ConocoPhillips.

Solarmer, based in El Monte, Calif., originally licensed the organic solar cell technology from the University of California at Los Angeles, Shrotriya said.

Unlike conventional silicon solar panels, polymer-based organic solar cells are thin and flexible. They're also far less expensive to manufacture, Shrotriya said.

But they also are less efficient at converting sunlight to electricity.

The partnership announced Tuesday that its technology had been certified by the Newport Technology & Application Center's Photovoltaic Lab in Long Beach, Calif., as achieving 9.31 percent efficiency -- that is, the percent at which the technology converts photons, or sunlight, to electrons, or electricity.

Commercially viable?

That's a record for power conversion efficiency for polymer-based photovoltaic cells, although Johnson said the technology will have to reach 12 percent to 15 percent efficiency to become commercially viable.

Silicon solar panels typically operate at about 20 percent efficiency, Shrotriya said.

He and Johnson said organic solar cells offer some advantages over silicon solar panels, despite being less efficient.

They're cheaper, for one thing.

Silicon panels typically cost three to five times as much to make, Johnson said.

Light-weight, flexible

Silicon panels also are more fragile, while organic solar cells are light-weight and flexible.

Johnson suggested they could be taken to remote locations, for camping or military use. Ultimately, he said, they may be used to power buildings, rolled across the windows like tinted film.

"They're transparent, and sunlight could come through and generate enough electricity for the building itself," Johnson said.

Andrew Barron, a professor of chemistry and materials science at Rice University, said the 9.31 percent efficiency rate is an achievement.

But he said organic solar technology also has some inherent drawbacks. It degrades far more quickly than silicon solar technology, he said, giving it a relatively short lifespan.

And silicon technology is becoming cheaper, making the cost differential less important, Barron said.

"It's a nice technical advance," he said. "It sets a benchmark for other people to try to improve. But it's not going to be a commercial reality anytime soon unless they have a significant change in performance."

jeannie.kever@chron.com

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