04 January 2011
Fool’s gold, or pyrite iron persulfide (FeS2), is a waste product of mining that also happens to be a semiconductor. Researchers from the University of California, Irvine, may have found a good use for this abundantly available mineral by using it to create thin films that could be useful for thin-film solar cells.
The researchers say just 10% of the pyrite disposed of each year in six US states could, in principle, be used to make an enormous ~3.5 TW of power (assuming 10% cell efficiency and a conservative 5 micron-thick pyrite active layer).
Although there’s much work to be done until that principle is a real possibility, iron pyrite has characteristics beyond its abundance that make it very promising for use in solar cells. It has a suitable band gap (Eg = 0.95 eV), an adequate minority carrier diffusion length (100-1000 nm), and strong light absorption (R > 105 cm-1 for h? > 1.3 eV).
Past attempts to use the material for photovoltaic devices have shown high quantum efficiencies and photocurrents but small photovoltages. However, the material hasn’t been heavily studied. The University of California researchers wanted to try making high-quality thin films using pyrite nanocrystals, with the aim of using the film in photovoltaics.
They first synthesized well-dispersed single-crystalline colloidal iron pyrite nanocrystals using a hot-injection method. Sintering layers of the nanocrystals in sulfur at 500 to 600°C produced large-grain polycrystalline pyrite films that could be used as the active layer in solar cells. The sintered film were stable for at least one month in air, and the researchers say that standard photovoltaic encapsulants and barrier coatings should be able to manage oxidation. Next, they plan to optimize the film microstructure and study the electrical and optical properties of the film.
If this work keeps moving in a positive direction, the pyrite nanocrystals could be used to fabricate inexpensive, large-area photovoltaics using roll-to-roll deposition of the nanocrystals or painting them onto flexible substrates.
Pyrite image by Hannes Grobe (Creative Commons).
Research Paper: Colloidal Iron Pyrite (FeS2) Nanocrystal Inks for Thin-Film Photovoltaics, J. Am. Chem. Soc., DOI: 10.1021/ja1096368.
Written by Nancy Lamontagne, Contributing Editor - US