ARCHIVED - A new twist on solar cells
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December 22, 2009— Ottawa, Ontario
Plugging a camp fridge into a tent in the woods? Running your music player from a nylon backpack? Using a storefront awning to light the store? Recharging a camera or cell phone from a sheet of plastic that folds and stows like a roadmap? All of these scenarios are becoming near-future possibilities thanks to a new generation of flexible solar cells called "organic photovoltaics."
Organic photovoltaics may soon be affordable and powerful enough to significantly expand the solar power market. They're being developed by scientists at the NRC Institute for Microstructural Sciences (NRC-IMS) in a consortium that includes Université Laval, St-Jean Photochemicals, Inc. and Konarka, Inc, an organic solar cell developer and producer based in Massachusetts.
More energy from sunlight strikes Earth in an hour than the whole planet currently uses each year. But right now, photovoltaics generate only about a millionth of our electricity. And electricity generated by silicon photovoltaics cost 5–6 times more than hydro, nuclear or fossil-fuel generation.
Hard, glossy blue silicon solar cell panels are now common on chain hardware and home-renovation store shelves. But they, like silicon computer chips, must be manufactured in vacuum chambers and scrupulously protected "clean rooms." The panels made from silicon solar cells are bulky and heavy because fragile silicon must be bonded to a rigid glass or plastic substrates to protect them from breakage.
The consortium solves these issues by replacing silicon with a low-cost, semiconductor polymer called polycarbazole. Polycarbazole can be managed in factories without special facilities, and high speed rotary printing presses can be adapted to apply a thin layer of the substance, much like ink, to a flexible plastic base.
Dr. Ye Tao, head of the NRC-IMS team, says their consortium partner Konarka is already running a U.S. plant that can print functioning, metre-wide solar cells at 10 metres per minute. While the organic cells are currently less efficient than amorphous silicon, which can convert about 9.5 percent of the light energy that strikes it into electricity, he hopes that polycarbazole's efficiency can reach 8 percent by the end of 2010 at a lower cost.
There is a huge potential market for the organic solar cells, both in consumer and military applications, such as flexible, portable chargers for personal electronics, and solar-powered military tents that power communications and computer equipment. "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."
Solar energy generation, while not new in Canada, so far remains limited mostly to applications such as charging batteries for emergency communications. Large rooftop solar panels that power buildings exist mainly as a costly option requiring subsidies, or for users in remote locations that are not connected to the grid.
The promise of solar power
But Dr. Tao takes a big-picture view. He notes that the bulk of Canadians' electricity now comes from the grid, fed by large generating plants that primarily burn increasingly expensive fossil fuels and emit carbon. Making solar electricity generation cost-effective for consumer applications will relieve the grid in the future — and hence benefit the environment.
"If you look at the amortization period and the cost of the electricity you get from silicon solar panels, you'll pay about 40 or 50 cents a kilowatt hour (KwH)," he says. "Right now, if you use electricity from the grid, you pay 10 cents per KwH. But if you have a cheaper organic solar cell with a price comparable to 10 cents per KwH, more people will adopt it and you will reduce energy use from the grid. When you take these loads off the grid, you will no longer need as much coal or natural gas."
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