CREDIT: Dennis Schroeder / www.nrel.gov
A promising new solar cell technology just got an added boost from two separate teams of researchers, who successfully replaced its lead component with non-hazardous tin.
The technology in question is composed of crystalline structures called perovskite, whose usefulness in solar cells was discovered back in 2009. They yielded a record-setting pace of improved efficiency in solar conversion — how much of the light energy that hits the cell actually gets converted into electricity — but their traditional structure involved lead. And obviously, having a hazardous element in the solar arrays on your roof would make any business or homeowner nervous.
But two separate research teams — one publishing in Nature Photonics, and the other in Energy & Environmental Science — just demonstrated successful perovskite solar cell technology using tin instead. Unlike lead, tin is not easily absorbed by, and has no known natural role in, human biology, making it a low-toxicity chemical. On the downside, the two teams demonstrated solar conversion efficiencies of only 5.73 percent and 6.4 percent, respectively. Most traditional solar cells get between 15 and 25 percent, and the more advanced forms are reaching the theoretical maximum of over 30 percent.
However, lead perovskites were only at 3.8 percent back in 2009. As of now, they’ve hit 15 to 16 percent and are still rising. That is an unprecedented speed in improvement — an increase of 400 percent in solar conversion efficiency in less than five years. By contrast, traditional solar cells only increased their performance by 50 percent in their first five years. Should tin perovskites mimic the rate set by their lead-based brethren, they’ll have brought a non-hazardous recipe of materials to a very promising technology.
“There is no reason this new material can’t reach an efficiency better than 15 percent,” said Mecouri Kanatzidis, one of the researchers who published in Nature Photonics. “Tin and lead are in the same group in the periodic table, so we expect similar results.”
Tin perovskite also brings potential economic advantages: it’s cheap and easy to make, and can be integrated into a standard manufacturing process.
“It doesn’t require high-temperature processing. You can just dip glass into two chemicals and get the material to form on it,” said Joey Luther, a senior scientist at the Energy Department’s National Renewable Energy Laboratory (NREL).
That said, the breakthrough is still a possibility, not a guarantee. The technology will still have to be demonstrated outside the lab, at a commercial manufacturing scale that’s affordable and durable.
“The field is growing fast, but that’s because there is so much to do,’ Luther continued. “Every technique that everyone has used for every solar cell in the past, they want to try it on perovskite solar cells to see what they can learn. Anytime you jump into a new material, you need to get a feel for how it works — you just have to play around for a while.”