Jayakanth Ravichandran, an assistant professor in the USC Mork Family Department of Chemical Engineering and Materials Science, believes in a purpose for the supposed chaff of the periodic table: transition metals. Using these seemingly valueless elements, he designs new and complex materials in a bid to create new power sources for energy.
“The goals of alchemy aren’t exactly what we do, but we are doing it in a very indirect manner,” said Ravichandran, of the USC Viterbi School of Engineering. “Our goal is to ask this question: The periodic table has a lot of elements. Can you take simple, seemingly useless elements and put them together in a certain fashion to make functional materials out of them?”
One focus of the USC research group is to develop new materials for solar energy conversion. Solar cells convert sunlight into electricity and have been made with silicon for decades. Yet silicon isn’t ideal for prominent reasons. For one, silicon is extracted from sand, an energy-intensive process that doesn’t offset the carbon used in production for several years. And solar cells require a large quantity of silicon to achieve efficiency.
For half a century, scientists have worked to develop new classes of materials for solar cells. A class called perovskite halides was found to work as well as silicon, but it contained undesirable elements like lead or cadmium that are unstable, toxic and/or scarce. To replace these suboptimal choices, Ravichandran, whose background is in metallurgy, does research on transition metal perovskite chalcogenides, a new class of materials that are benign and extremely abundant.
USC Viterbi PhD student Shanyuan Niu and other students in Ravichandran’s research group prepared high-quality samples of these materials and studied their optical properties. Preliminary measurements show that these materials have potential use as solar cells and require 100 times less material to absorb the same amount of light as silicon. As a result, these materials have potential for several opto-electronic applications, such as devices that convert electrical signals into light and vice versa.
“It is very clear that we need to diversify our energy portfolio for the long-term future,” Ravichandran said. “There will always be a hard limit to non-renewable resources, even if the current predictions of when these resources run out are off by several years. Even if one looks beyond the energy applications, these are new semiconductors which have been the building blocks of our information age.”
Scratching the surface
Ravichandran thinks they are just scratching the surface of the new materials’ potential. Most important to him is being prepared for the resource scarcity of materials for a variety of new technologies in the future.
“In some sense, if you don’t invest in basic innovative materials research, the technologies you might think are feasible may not happen at all,” Ravichandran said. “You need to be able to have a large database of materials and know how to prepare them for use in any technology, whether the technology is relevant today or becomes so in the future.”
Ravichandran’s group’s paper on the subject was published in Advanced Materials. The team collaborated with USC Viterbi Assistant Professor Rehan Kapadia’s research group and a University of Missouri research team led by David Singh.