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May 02, 2007

90% pure quantum dots for better solar cells made

Rice University scientists today revealed a breakthrough method for producing molecular specks of semiconductors called quantum dots, a discovery that could clear the way for better, cheaper solar energy panels. One way towards cheaper solar cells is to make them out of quantum dots. Prior research by others has shown that four-legged quantum dots, which are called tetrapods, are many times more efficient at converting sunlight into electricity than regular quantum dots. The best previous method produced 30 percent of particles as tetrapods, while the new method makes 90% tetrapods.

Significantly, these tetrapods are made of cadmium selenide, which have been very difficult to make, until now. The essence of the new recipe is to use cetyltrimethylammonium bromide instead of the standard alkylphosphonic acid compounds. Cetyltrimethylammonium bromide happens to be safer – it's used in some shampoos, for example – and it's much cheaper than alkylphosphonic acids. For producers looking to eventually ramp up tetrapod production, this means cheaper raw materials and less purification steps, Wong said.

"One of the major bottlenecks in developing tetrapod-based solar cell devices has been removed, namely the unavailability of high-quality tetrapods of the cadmium selenide kind," Wong said. "We might be able to make high-quality nanoshapes of other compositions also, using this new synthesis chemistry."

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