Javier Vela from Iowa State University. Photo: Christopher Gannon and courtesy of the Iowa State University College of Liberal Arts and Sciences.
Javier Vela from Iowa State University. Photo: Christopher Gannon and courtesy of the Iowa State University College of Liberal Arts and Sciences.

Lead-containing perovskites may make effective semiconducting materials for use in solar cells, but one serious problem with them is that they contain lead, which is toxic. So Javier Vela and the chemists in his Iowa State University research group have been searching for materials to replace the perovskite semiconductors that have proved so promising and efficient at converting sunlight into electricity?

What materials could produce semiconductors that worked just as well, but were safe and abundant and inexpensive to manufacture?

"Semiconductors are everywhere, right?" Vela said. "They're in our computers and our cell phones. They're usually in high-end, high-value products. While semiconductors may not contain rare materials, many are toxic or very expensive."

Vela, an Iowa State associate professor of chemistry and an associate of the US Department of Energy's Ames Laboratory, directs a lab that specializes in developing new, nanostructured materials. While thinking about the problem of lead in solar cells, he watched a conference presentation by researchers from Massachusetts Institute of Technology that suggested possible substitutes for perovskites in semiconductors.

Inspired by this, Vela and Iowa State graduate students Bryan Rosales and Miles White decided to focus on sodium-based alternatives and started an 18-month search for a new kind of semiconductor. Their work was supported by Vela's five-year, $786,017 CAREER grant from the US National Science Foundation; CAREER grants are the foundation's most prestigious awards for early career faculty.

The chemists came up with a compound made up of: sodium, which is cheap and abundant; bismuth, which is relatively scarce but is overproduced during the mining of other metals, making it cheap; and sulfur, the fifth most common element on Earth. The researchers report their discovery in a paper in the Journal of the American Chemical Society.

"Our synthesis unlocks a new class of low-cost and environmentally friendly ternary (three-part) semiconductors that show properties of interest for applications in energy conversion," the chemists wrote in their paper. In fact, Rosales is already working on creating solar cells that use the new semiconducting material.

Vela said that varying the synthesis conditions – reaction temperature and time, choice of metal ion precursors, adding certain ligands – allows the chemists to control the material's structure and the size of its nanocrystals. And that allows them to change and fine tune the material's properties.

Several of the material's properties are already ideal for solar cells, such as its band gap – the amount of energy required for a light particle to knock an electron loose. Unlike other materials used in solar cells, it is also stable when exposed to air and water.

So the chemists think they have a material that will work well in solar cells, but without the toxicity, scarcity or costs. "We believe the experimental and computational results reported here," they wrote in their paper, "will help advance the fundamental study and exploration of these and similar materials for energy conversion devices."

This story is adapted from material from Iowa State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.