Michael Wong and scientists at Rice’s Centre for Biological and Environmental Nanotechnology used a 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. They interact with light in unique ways, to give off different-coloured 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.
One way towards cheaper solar cells is to make them out of quantum dots. Prior research 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, Wong 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 per cent of the prepared particles are not tetrapods, he said.
CBEN’s formula produces same-sized particles, in which more than 90 per cent are 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, which is safer, much cheaper and uses less purification steps.
‘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.’