Turning Lead Into Gold...Er, Solar Panels | KCET
Turning Lead Into Gold...Er, Solar Panels
The MIT team, led by professors Angela M. Belcher and Paula T. Hammond, was studying a relatively new family of solar cell based on a promising semiconductor material called organolead halide perovskite. Cheap to synthesize, organolead halide perovskite solar panels have reached efficiencies near those of commercially available solar panels. In one study, perovskite-based solar cells converted up to 16 percent of the sunlight hitting them to electricity.
But there's a problem: though it offers the promise of cheaper solar power, making organolead halide perovskite requires a source of lead. Lead mining is one of the most environmentally destructive activities humans engage in. So Belcher, Hammond, and their team took a look at a source of lead that's already been mined: the ubiquitous lead-acid auto battery.
The team published a paper describing their work in the journal Energy & Environmental Science in late July.
In the U.S., lead-acid batteries are perhaps the most commonly recycled commodity, surpassing aluminum and glass by a wide margin. Of the more than 125 million lead-acid batteries discarded in the U.S. each year -- a staggering number when you think about it -- more than 98 percent are turned over to the nation's lead recycling industry.
But a two percent discard rate of 125 million plus lead acid batteries still works out to millions of pounds of lead discarded improperly each year in the U.S., and the problem is significantly worse in countries without a robust lead recycling industry. What's more, some industry watchers predict that lead-acid batteries may start to decline in popularity as lithium-ion batteries get cheaper, and that might mean less demand for the lead we currently recycle. Finding a new use for that lead could solve a significant waste disposal problem.
According to the MIT team, the process by which lead from old batteries is recovered for organolead halide perovskite is relatively simple, mainly taking place at low temperatures. The team produced a video of the process, which looks remarkably low-tech (though kids, don't try this at home unless your home is equipped with hazmat safety equipment:
The active layer of lead-laden pereskovite in a solar panel would be about half a micrometer thick. (It would take about 200 of those layers to equal the thickness of a standard sheet of inkjet printer paper.) That means that a single lead-acid battery could provide enough lead to power 30 typical homes with perovskite solar panels.
There's a dark gray elephant in the room, of course; wouldn't taking lead from used car batteries and putting thin layers of it in relatively fragile solar panels on our homes and workplaces pose a potentially serious risk of heavy metal exposure? Study co-author Po-Yen Chen, an MIT grad student, says that's a risk we can mitigate by encapsulating the lead layer inside other materials. "The process to encapsulate them will be the same as for polymer cells today," Chen told MIT's David Chandler. "That technology can be easily translated."
Chen added that the lead-bearing perovskite can be recovered and recycled once a solar panel reaches the end of its useful life, likely decades after purchase.
Admittedly, that probably won't reassure those ReWire readers who are especially conscious of the dangers of lead poisoning, including those veteran environmental justice activists who recall the difficult struggle in the 1970s to ban lead content in residential house paint.
Still, it's an interesting discovery, and if it prompts more work on turning an environmental liability into an environmental boon, it's hard to fault the team from MIT for trying. That's especially considering the potential benefit to people in developing countries, who often rely on moving lead acid batteries by hand from a central charging station to their homes in order to have a little bit of electrical power. Having one thirtieth of that lead in stationary solar panels on their roof or in their yard will likely seem like a huge step forward.
For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.
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