Perovskites Without Lead for Optoelectronics

A barium zirconium sulfide thin film – the basis for a new class of LEDs and solar cells. (Source: D. Levere, U. Buffalo)

Scientists have created thin films made from barium zirconium sulfide (BaZrS3) and confirmed that the materials have alluring elec­tronic and optical properties predicted by theorists. The films combine excep­tionally strong light absorption with good charge transport – two qualities that make them ideal for appli­cations such as photo­voltaics and light-emitting diodes.

In solar panels, for example, experimental results suggest that BaZrS3 films would be much more efficient at converting sunlight into electricity than tradi­tional silicon-based materials with identical thick­nesses, says lead researcher Hao Zeng, PhD, professor of physics in the Univer­sity at Buffalo College of Arts and Sciences. This could lower solar energy costs, especially because the new films performed admirably even when they had imper­fections.

“For many decades, there have been only a handful of semi­conductor materials that have been used, with silicon being the dominant material,” Zeng says. “Our thin films open the door to a new direction in semi­conductor research. There’s a chance to explore the potential of a whole new class of materials.” BaZrS3 belongs to the class of materials of chalco­genide perov­skites, which are nontoxic, earth-abundant compounds. In recent years, theorists have calculated that various chalco­genide perovskites should exhibit useful electronic and optical properties, and these predictions have captured the interest and imagination of experi­mentalists like Zeng.

BaZrS3 is not a totally new material. Zeng looked into the history of the compound, and found infor­mation dating back to the 1950s. “It has existed for more than half a century,” he says. “Among earlier research, a company in Niagara Falls produced it in powder form. I think people paid little attention to it.” But thin films – not powder – are needed for appli­cations such as photo­voltaics and LEDs, so that’s what Zeng’s team set out to create.

The researchers crafted their BaZrS3 films by using a laser to heat up and vaporize barium zirconium oxide. The vapor was deposited on a sapphire surface, forming a film, and then converted into the final material through a chemical reaction called sulfuri­zation. “Semiconductor research has tradi­tionally been highly focused on conven­tional materials,” Hui says. “This is an opportunity to explore something new. Chalco­genide perovskites share some similarities to the widely researched halide perov­skites, but do not suffer from the toxicity and instability of the latter materials.”

“Now that we have a thin film made from BaZrS3, we can study its funda­mental properties and how it might be used in solar panels, LEDs, optical sensors and other appli­cations,” Wei says. (Source: U. Buffalo)

Reference: X. Wei et al.: Realization of BaZrS3 chalcogenide perovskite thin films for optoelectronics, Nano Energy 104317 (2019); DOI: 10.1016/j.nanoen.2019.104317

Link: Spin and Nanomagnetism Group, Dept. of Physics, University at Buffalo, The State University of New York, Buffalo, USA

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