As Good As Gold Gets

Iron pyrite, otherwise known as fool’s gold, is a fool no more. One of the most abundant minerals in the earth’s crust, it is often discarded without a thought. Now, however, it is being taken very seriously by UC Irvine chemistry professor Matt Law and his team.

“This is something that is basically just thrown away,” Law said. “It just sits there in an open mine when it is possible that there’s some really great importance in it.”

What makes fool’s gold so attractive are its many benefits, as opposed to only one flaw. Not only is it earth abundant — meaning it would not suffer from price problems — it is also non-toxic.

The major downside is that its iron-to-sulfur ratio is difficult to control. The missing sulfur causes voltage problems so Law is trying to find ways to improve that ratio by making more sulfur stay in the pyrite crystal.

“What we are doing is making an ink that is user-friendly, something we can spray on a surface,” Law said. “We get that ink onto the surface and begin sintering it.”

In order to use the pyrite, researchers first try to produce a homogenous, thin film. Using semiconductor nanoparticles, they create a colloidal suspension, similar to milk, making sure that the pure mineral particles don’t fall out of the solution.

Sintering is a process that involves heat to merge the small particles into one big sheet of material. The result is a solid film composed of many crystals. The bigger the crystals, the easier it is to collect electrical current from the film.

“Successfully making this stable and usable nanocrystal ink was the proudest moment for us,” Law said. “It was a culmination of a lot of work by three students in the group. So many different syntheses were attempted, but they never panned out – we either couldn’t keep the material in the ink or it wasn’t completely pure.”

Ultimately, what Law and his team hope to do is create pyrite solar cells to replace the current silicon panels that are most commonly used. They would be deployed in a similar fashion, either in solar farms or integrated onto buildings.
“Iron pyrite will probably be able to produce the same amount of power and convert sunlight into electricity at pretty much the same rate as it is being transferred now,” Law said.

Finally, and possibly the most importantly, it would likely be cheaper than existing technologies. The use of solution processing, rather than vacuum processing, would help keep the temperatures low and, essentially, the costs down. The biggest selling point, though, is pyrite’s availability.

“Iron pyrite most definitely has a cost advantage,” Law said. “Although it depends on the manufacturing process, it will be made as cheap as possible.”

The only thing that would potentially deter this from being much more inexpensive is the fact that there are a lot of layers that make up a solar panel. Law hopes to ensure that all the layers can be produced inexpensively.

Law has actually been interested in pyrite since graduate school. When his friend introduced him to the mineral and its potential uses in solar cells, he initially assumed that it must have a “fatal flaw.” As he read more about it, however, he became convinced that it had a lot of potential and deserved more work.

“In the 1980s and 90s, pyrite was investigated by several groups in Europe, but the research fizzled out because of both the low voltage and low efficiency. I thought I could figure out what’s wrong with this material and develop the chemistry to fix it. I knew, in my mind, that it was something worthy of trying,” Law said.

Now, four UCI professors, 15 UCI graduate students and postdoctoral scholars are participating in this research, which is being funded by the National Science Foundation for the next three years. Still, Law and his team have a number of steps to go before pyrite solar cells become a reality.

He hopes to better understand the optical properties of iron pyrite, which include how much light it can absorb.

“We know that pyrite absorbs strongly, but we want to quantify it,” Law said.

They also look to create another technique to make the material completely flat and filled in, with no pores, which would make the solar cell perform better, because of the better film morphology.

Finally, they hope to understand the behavior of their “ink,” such as how long its shelf life is, what happens to it before and after the sintering process and what evaporates from the film during processing. All of this will help to make the film even better, and the best starting point to making this real is to create the highest quality pyrite layers possible.

“Ultimately, I think we have a very good team of collaborators, and a great chance to solve the voltage problem, which could make pyrite very important for alternative energy,” Law said.

The response from the scientific community, as well as the public in general, has been positive, with many expressing interest and curiosity in iron pyrite.

“Having economical solar technology that can scale to really large areas could have an enormous impact on the global energy picture,” Law said. “We could make an astounding amount of solar energy with iron pyrite.”