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Fool's Gold

The study of pyrite, or "fool's gold," led researchers at Oregon State University to the discovery of a new class of materials with promise for solar energy. Image: Oregon State University

Pyrite, better known as "fool's gold," was familiar to the ancient Romans and has fooled prospectors for centuries—but has now helped researchers at Oregon State University discover related compounds that offer new, cheap, and promising options for solar energy.

These new compounds, unlike some solar cell materials made from rare, expensive, or toxic elements, would be benign and could be processed from some of the most abundant elements on Earth. Findings on them have been published in Advanced Energy Materials.

Iron pyrite itself has little value as a future solar energy compound, the scientists say, just as the brassy, yellow-toned mineral holds no value compared to the precious metal it resembles. But for more than 25 years it was known to have some desirable qualities that made it of interest for solar energy, and that spurred the recent research.

The results have been anything but foolish.

"We've known for a long time that pyrite was interesting for its solar properties, but that it didn’t actually work," says Douglas Keszler, a distinguished professor of chemistry at OSU. "We didn't really know why, so we decided to take another look at it. In this process we've discovered some different materials that are similar to pyrite, with most of the advantages but none of the problems.

"There's still work to do in integrating these materials into actual solar cells," Keszler says. "But fundamentally, it's very promising. This is a completely new insight we got from studying fool's gold."

Pyrite was of interest early in the solar energy era because it had an enormous capacity to absorb solar energy, was abundant, and could be used in layers 2,000 times thinner than some of its competitors, such as silicon. However, it didn’t effectively convert the solar energy into electricity.

In the new study, the researchers found out why. In the process of creating solar cells, which takes a substantial amount of heat, pyrite starts to decompose and forms products that prevent the creation of electricity.

Based on their new understanding of exactly what the problem was, the research team then sought and found compounds that had the same capabilities of pyrite but didn’t decompose. One of them was iron silicon sulfide.

"Iron is about the cheapest element in the world to extract from nature, silicon is second, and sulfur is virtually free," Keszler says. "These compounds would be stable, safe, and would not decompose. There's nothing here that looks like a show-stopper in the creation of a new class of solar energy materials."

Work to continue the development of the materials and find even better ones in the same class will continue at the National Renewable Energy Laboratory in Colo., which collaborated on this research.

SOURCE
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