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Energy

Making a Soft Cell

New solar technologies are finding their way into prototypes.

Plastic solar cells can’t yet compete with conventional silicon photovoltaics for efficiently producing large-scale power. But they’ve become good enough that at least one company, Lowell, MA-based Konarka, has moved past the proof-of-concept phase and is putting them into products.

The Army, Air Force, and Textronics, a company based in Wilmington, DE, are now incorporating Konarka’s cells into the structures of tents for powering computers and the fabric of handbags for charging cell-phone and laptop batteries.

Konarka’s solar cells are printed or coated on rolls of plastic – much like photographic film. Tiny particles embedded in the film then absorb light and spit out electrons, which are transported by an electrolyte and harvested by electrodes.

So far, the company has demonstrated that its cells can charge cell-phone batteries, extending talking time, or even eliminating the need to plug into an outlet – assuming one lives somewhere like Phoenix and isn’t addicted to the device.

Konarka has also shown that the materials in its solar cells can be tuned to absorb and reflect different wavelengths of light; and, unlike traditional photovoltaic materials, the plastic substrate can conform to irregular shapes. According to one of Konarka’s partners, Textronics, the end-product can even be made to feel like ordinary cloth.

In anticipation of growing demand, Konarka has also partnered with a German printing company, Kurz, to manufacture its plastic-film solar cells on a large scale. Such a ramping up, however, will depend on when and if third parties are satisfied that the cells can be smoothly integrated into their own products.

Konarka’s efforts reflect a growing push toward cheap solar (see “Solar-Cell Rollout,” Technology Review, July 2004). The ultimate goal is to make solar power, which now costs 4 to 5 times as much as grid electricity, competitive with fossil fuels. It’s a challenge that could become easier if fuel prices continue to rise.

One approach involves making the photovoltaic materials out of electrically conductive polymers and nanostructures called fullerenes, or buckyballs. When such elements were first tried as solar cells, they were grossly inefficient, converting a mere one to two percent of light energy to electricity.

In recent months, though, by rearranging the polymers and buckyballs, several research teams – led by physicist David Carroll from Wake Forest; Alan Heeger, a co-founder and chief scientist of Konarka and a Nobel Laureate at the University of California at Santa Barbara; and Yang Yang of the University of California at Los Angeles – have improved the flow of electricity, approximately doubling the material’s ability to convert light into electricity. If researchers can get the performance to double again, the material will be efficient enough to compete with traditional solar technologies.

The next step – making solar cells that can compete with fossil fuels – will mean overcoming even more obstacles. For example, one way to improve the percentage of light converted into electricity is to increase the amount light actually absorbed by the cell. According to Sean Shaheen, a solar specialist at the National Renewable Energy Laboratory (NREL) in Golden, CO, this could be done by creating materials that absorb more colors in the spectrum, an idea he’s currently working on.

Such research into new solar technologies is going forward in both industrial and academic labs. Its researchers are confident that it will lead to more efficient and cheaper solar-cell devices, finding more and more applications, and eventually lessening our dependence on fossil fuels.

For now, according to Konarka, solar looks good for soldiers and trendy shoppers.

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