The Modern Alchemist

| February 9, 2017

Jayakanth Ravichandran seeks to employ overlooked elements of the periodic table for use in future technologies.

Jayakanth Ravichandran (far right) and his USC Viterbi research team. Photo credit: Valentina Suarez

Jayakanth Ravichandran likens his research to the ancient field of alchemy in which followers believed base metals like lead could be transformed into noble ones like gold and silver.

Ravichandran, an assistant professor in the USC Mork Family Department of Chemical Engineering and Science, believes in a purpose for the supposed chaff of the periodic table: the transition metals. Using these seemingly valueless elements, he designs new and complex materials in the hopes to create new power sources for energy and device applications

“The goals of alchemy aren’t exactly what we do, but we are doing it in a very indirect manner,” Ravichandran said. “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 Ravichandran’s 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 salient reasons. For one, silicon is extracted from sand, an energy-intensive process that doesn’t offset the carbon used in production for several years. As well, solar cells require a large quantity of silicon to achieve good 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 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 Ph.D. 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. Hence, these materials have potential for several opto-electronic applications, which are 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.”

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 this subject, Bandgap Control via Structural and Chemical Tuning of Transition Metal Perovskite Chalcogenides, was recently published in Advanced Materials. The team collaborated with USC Viterbi Assistant Professor Rehan Kapadia’s research group and a research team led by David Singh at the University of Missouri.