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Fool’s Gold for Solar Panels

Researchers identify promising materials for supplying the world’s electricity needs.
February 23, 2009

One of the best materials for making cheap solar cells is iron pyrite (better known as fool’s gold), according to researchers at the University of California, Berkeley, and Lawrence Berkeley National Laboratory.

The researchers recently published an article in Environmental Science and Technology that surveys 23 semiconducting materials with properties that make them promising for converting sunlight into electricity. They evaluated the cost and abundance of these materials to determine which would work well for low-cost solar cells that could be made in numbers large enough to supply the world’s electricity needs. Today’s solar cells are mostly made from silicon–which is costly to refine and purify–or from thin films of cadmium telluride, which contain relatively rare or toxic elements, making it difficult or impossible to scale them up to provide all of the world’s electricity.

The researchers argue that research should be directed at materials that are cheap and abundant enough to easily supply the world’s energy needs. Iron sulfide (pyrite), or fool’s gold, stood out from all the other options, followed closely by amorphous silicon, a material used in some solar cells today. They estimate that these materials could provide 100 to 1,000 times the world’s current electricity needs.

But there may be a catch. While in theory, fool’s gold may shine as a solar-cell material, achieving the theoretical performance levels will be challenging. From another study published in 2000:

About 20 years ago pyrite (FeS2) was proposed as a promising candidate for [prospective] usage as photovoltaic absorber material for thin film solar cells. Among its physical properties–the very high absorption coefficient and a suitable energy bandgap (Eg≈0.95 eV) for photovoltaic energy conversion–also its nontoxicity and its composition from abundant elements were considered as particular advantages of pyrite.

However, the promises could not be fulfilled. Though the quantum efficiencies and the photocurrents were reasonably high for single crystalline pyrite samples, the open circuit voltages never exceeded about 200 mV at room temperature, much too low compared to the band gap of pyrite. The highest efficiency reported so far is about 2.8 %.

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