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Researchers are developing organic photovoltaic cells that can be ?painted? or ?printed? onto a thicker plastic backing layer ' like an overhead projector transparency.
New research on flexible solar cells is rapidly increasing their efficiency and affordability, as well as the potential applications of solar power.
An international research consortium is developing a new generation of solar cells called “organic photovoltaics.” Massachusetts-based manufacturer Konarka Inc. already markets some flexible solar cell products, and is working with the consortium partners to make the next generation more than twice as powerful.
Science activity for students
Solar cells can be likened roughly to penlight batteries. In an AA cell, a chemical reaction drives electrons from the positive (+) to the negative (-) pole, while in solar cells, the energy of light moves electrons. When a photon of light strikes a solar cell, it generates a pair of positive and negative charge carriers. When the pair separates inside the cell, they make current.
Silicon was first used for solar cells because it is relatively efficient at converting sunlight to energy. But silicon is expensive and brittle, so it must be encased in heavy glass or plastic protective panels. Still, organic cells complement rather than compete with silicon, and each technology has different applications, says NRC’s Dr. Ye Tao.
A solar cell that folds like a road map
NRC’s solar cells are made of thin layers of an organic plastic called polycarbazole. These flexible active layers can be “painted” or “printed” onto a thicker plastic backing layer — like an overhead projector transparency — that can be rolled or folded like tough, light, portable road maps.
According to Dr. Tao, due to their mechanical flexibility, these solar cells can make electricity when spread over irregular shapes such as briefcases, backpacks, tents, store awnings — even entire buildings. They can also form a dual-purpose semi-transparent window coating that may be tinted any colour, producing power while creating an interior mood and/or exterior pattern.
“We can’t make our solar cells very thick, so why not make their thinness an advantage?” asks Dr. Tao. “We can use a part of the light spectrum to generate electricity and still let part of the spectrum inside.”
However, compared with an amorphous silicon solar cell of the same area, polycarbazole cells are less efficient. The best amorphous silicon solar converts about 9 percent of the light energy that strikes it into electricity. Organics convert even less, but Dr. Tao says NRC’s research is narrowing the gap quickly. “When we started this project, their efficiency was around 3 percent and we’ve brought it up to 7 percent,” he says. “We hope to reach 8 percent by early next year.”
As organic solar cells approach the efficiency of amorphous silicon, they promise lower-cost solar power. The current lowest price for amorphous silicon cells is around $2 per watt, whereas “for polymer solar cells, we expect that by 2012, one watt will cost about 80 cents,” Dr Tao says.
This project is funded by Sustainable Development Technology Canada, a not-for-profit foundation created by the Government of Canada.
Electricity where you need it
Plugging a camp fridge into a tent in the woods? Running a music player from a nylon backpack? Using a storefront awning to provide some electricity? All of these applications are possibilities thanks to flexible organic photovoltaics.
NRC industry partner Konarka is testing earlier generation organic solar cells in consumer and military markets. One application now undergoing military testing, which is likely to resonate with consumers as well, is a tent covered by flexible polymer solar panels that power communications equipment inside.
“You can print the organic solar cells on flexible substrates, so you can use them for tents, awnings and even clothing, bags or packaging,” says Dr. Tao. “And because you have a flexible substrate, you can make these solar cells like you print newspapers. Of course, the main advantage is their low cost — it's much cheaper than the existing technology.”