13 April 2010

Closing In On A Carbon-Based Solar Cell

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To make large sheets of carbon available for light collection, Indiana University Bloomington chemists have devised an unusual solution - attach what amounts to a 3-D bramble patch to each side of the carbon sheet

Using that method, the scientists say they were able to dissolve sheets containing as many as 168 carbon atoms, a first.
The scientists' report will appear in a future issue of Nano Letters, an American Chemical Society journal.

"Our interest stems from wanting to find an alternative, readily available material that can efficiently absorb sunlight," said chemist Liang-shi Li, who led the research. "At the moment the most common materials for absorbing light in solar cells are silicon and compounds containing ruthenium. Each has disadvantages."

Their main disadvantage is cost and long-term availability. Ruthenium-based solar cells can potentially be cheaper than silicon-based ones, but ruthenium is a rare metal on Earth, as rare as platinum, and will run out quickly when the demand increases.

Carbon is cheap and abundant, and in the form of graphene, capable of absorbing a wide range of light frequencies. Graphene is essentially the same stuff as graphite (pencil lead), except graphene is a single sheet of carbon, one atom thick. Graphene shows promise as an effective, cheap-to-produce, and less toxic alternative to other materials currently used in solar cells. But it has also vexed scientists.

For a sheet of graphene to be of any use in collecting photons of light, the sheet must be big. To use the absorbed solar energy for electricity, however, the sheet can't be too big. Unfortunately, scientists find large sheets of graphene difficult to work with, and their sizes even harder to control.


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