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posted: 7/30/2011 6:00 AM

Solar cells may be printed on plain paper

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  • A laminated paper solar cell is connected to an LCD screen to demonstrate that it is producing power from ambient sunlight.

      A laminated paper solar cell is connected to an LCD screen to demonstrate that it is producing power from ambient sunlight.
    The Washington Post

 
The Washington Post

NEW YORK -- The next generation of solar cells may be printed on ordinary paper.

Engineers at Massachusetts Institute of Technology have created ultrathin paper cells that gather enough juice to power an LCD clock and can be glued to a briefcase, stapled to a hat or folded into a pocket. The research is a first step toward a cheap and lightweight source of renewable energy that, within two years, may be used for everything from charging an iPad to warming up clothing, researchers said.

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"Rather than confining solar power to rooftops or solar farms, paper photovoltaics can be used virtually anywhere, making energy ubiquitous," said Karen Gleason, associate dean of engineering research at MIT in Cambridge, Mass., and leader of the team that produced the cells.

Paper cells would have the potential to create a new market based on the popularity of low-power electronic devices that are now mostly fed by batteries, such as Apple's iPads and mobile phones, said Jeffrey Bencik, director of research at Kaufman Bros., a New York-based investment firm. That new market may grow to as much as $470 million by 2020, according to an April report by Lux Research, a Boston-based advisory firm.

"It's not competing with traditional solar panels out there at all," Bencik said in a telephone interview.

The research, funded by Eni, Italy's biggest oil company, was described by MIT engineers in a paper published July 8 in the journal Advanced Materials.

Competitors racing to develop other low-cost, flexible cells include Solarmer Energy Inc. in El Monte, Calif, and Lowell, Mass.-based Konarka Technologies Inc. Both companies produce organic photovoltaics, but have yet to find the combination of efficiency and production capabilities that enable large-scale commercial use, said Jason Eckstein, a researcher at Lux. Konarka's cells are applied on plastic, a material more expensive than paper.

Almost all solar cells now are made from silicon. They generate power by converting energy from light into charged current, a process called the photovoltaic effect.

While these devices provide power to both huge consumers, such as satellites and homes, and small ones, such as hand-held calculators, they're expensive. Crystalline and thin-film solar cells, the two most-common technologies available, rely on cutting wafers from large blocks of silicon material or depositing thin layers of rare earth materials like tellurium and indium onto glass.

MIT's ultrathin cells are made using a new technique that avoids damaging high temperatures and corrosive liquids involved in traditional methods, Gleason said in a telephone interview.

The bottom layer and the active layer, where combinations of electrons and positively charged ions interact to create an electrical current, are composed of abundant organic elements like carbon, oxygen, and copper, Gleason said.

"Nothing that we're using is potentially expensive," she said. Paper substrate is 1,000 times cheaper than glass, "which takes up almost 40 percent of the cost of the typical module."

Because of the low cost and the adaptability of the materials, Umberto Vergine, vice president of research for Rome- based Eni, envisions a wide array of markets.

"The flexibility of the cells and the versatility of sizes and shapes can provide solutions for many outdoor products including boating equipment, tents, sun-shields or even clothing," Vergine said in an email. "There's a wide choice out there. The Eni and MIT teams are working now to pick the right one to get to the market."

The project also answers a need among energy companies, such as Eni, that are being increasingly nudged by governments to find green energy alternatives, said Richard Griffith, an oil and gas analyst at London-based Evolution Securities.

"They'll keep an investment interest in these things because one of them may be the prize winner in the future," Griffith said in an interview.

The MIT research team that created the paper cells is almost three years ahead of pace, according to Gleason.

The engineers produced the first working paper solar cells in September 2010. A few months later, the prototype was able to keep an LCD clock working.

Cell efficiencies need to be improved before the devices can reach consumers, and plans to boost efficiency are in place. The print cells now operate at less than 2 percent efficiency, and plans to reach 8 percent -- enough to power a mobile phone -- within two years are in place, said Vladimir Bulovic, director of the Solar Frontiers Center at MIT.

Once that work is completed, "there is a great deal of things this can do for the gizmo world," he said in a telephone interview.

Gleason, the project's team leader said the results announced this month are just the first step in a long process.

"I'm very optimistic that within a year we'll see substantially improved efficiency," Gleason said. "No matter what the commercialization pathway is, part of it would be scaling up the process to where you could generate larger scale prototypes."

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