Method for Cheaper Quantum Dots

Research by Michael Wong (left) and Rice University scientists at Rice's Center for Biological and Environmental Nanotechnology (CBEN), 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.

Quantum dots interact with light in unique ways, to give off different-colored light or to create electrons and holes, due partly to their tiny size, partly to their shape and partly to the material they're made of. Rice scientists have developed a new chemical method for making four-legged cadmium selenide quantum dots, which previous research has shown to be particularly effective at converting sunlight into electrical energy.

Quantum dots are "megamolecules" of semiconducting materials that are smaller than living cells. 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. But, principal investigator Michael Wong, assistant professor of chemical and biomolecular engineering said the problem is that there is still no good way of producing tetrapods. Current methods lead to a lot of particles with uneven-length arms, crooked arms, and even missing arms. Even in the best recipe, 30 percent of the prepared particles are not tetrapods, he said.

CBEN's formula produces same-sized particles, in which more than 90 percent are tetrapods. 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.

The research, by Wong and his graduate student Subashini Asokan with CBEN Director Vicki Colvin and graduate student Karl Krueger appears this week in the journal Small.