If Fool’s Gold Fails In Solar Cells, Try Its Cousin

Pyrite, or iron sulfide, has proved to be fool’s gold for photovoltaics, failing to help solar cells reach theoretical predictions of 20% efficiency, the ratio of sunlight in to electricity out. Researchers could strike actual gold, however, with a cousin of pyrite, nanocrystalline Fe₂GeS₄ (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja408333y). Previous theoretical work showed that not only would Fe₂GeS₄ readily absorb visible light, much like pyrite, but the germanium cousin would be more thermodynamically stable. To assess Fe₂GeS₄’s photovoltaic promise, Amy L. Prieto and Sarah J. Fredrick of Colorado State University synthesized Fe₂GeS₄ nanocrystals and used UV-visible spectrometry to find that they absorb visible light. From photoelectrochemical tests, the researchers found that when exposed to green light, thin films of Fe₂GeS₄ produce a modest current. Fe₂GeS₄ may be appealing to solar-cell makers because it’s chemically simpler and less expensive than other photovoltaic materials, the researchers suggest, though they haven’t yet determined the material’s optoelectronic properties. Devising ways to cut air exposure to reduce oxidation and tweaking film thickness should boost its current density, the researchers add.