MIT researchers have developed a simple procedure for making a promising type of solar cell using lead recovered from discarded lead-acid car batteries—a practice that could benefit both the environment and human health. As new lead-free car batteries come into use, old batteries would be sent to the solar industry rather than to landfills. And if production of this new, high-efficiency, low-cost solar cell takes off—as many experts think it will—manufacturers’ increased demand for lead could be met without additional lead mining and smelting. Laboratory experiments confirm that solar cells made with recycled lead work just as well as those made with high-purity, commercially available starting materials. Battery recycling could thus support production of these novel solar cells while researchers work to replace the lead with a more benign but equally effective material.
Much attention in the solar community is now focused on an emerging class of crystalline photovoltaic materials called perovskites. The reasons are clear: The starting ingredients are abundant and easily processed at low temperatures, and the fabricated solar cells can be thin, lightweight, and flexible—ideal for applying to windows, building facades, and more. And they promise to be highly efficient.
Unlike most advanced solar technologies, perovskites are rapidly fulfilling that promise. “When perovskite-based solar cells first came out, they were a few percent efficient,” says Angela Belcher, the James Mason Crafts Professor in biological engineering and materials science and engineering at MIT. “Then they were 6 percent efficient, then 15 percent, and then 20 percent. It was really fun to watch the efficiencies skyrocket over the course of a couple years.” Perovskite solar cells demonstrated in research labs may soon be as efficient as today’s commercial silicon-based solar cells, which have achieved current efficiencies only after many decades of intensive research and development.
Research groups are now working to scale up their laboratory prototypes and to make them less susceptible to degradation when exposed to moisture. But one concern persists: The most efficient perovskite solar cells all contain lead.
That concern caught the attention of Belcher and her colleague Paula Hammond, the David H. Koch (1962) Professor in Engineering and head of the Department of Chemical Engineering at MIT. Belcher and Hammond have spent decades developing environmentally friendly synthesis procedures to generate materials for energy applications such as batteries and solar cells. Although lead is toxic, in consumer devices it can be encapsulated in other materials so it can’t escape and contaminate the environment, and it can be recovered from retired devices and used to make new ones. But lead mining and refining raise serious health and environmental issues ranging from the release of toxic vapors and dust to high energy consumption and greenhouse gas emissions. Therefore, research teams worldwide—including Belcher and Hammond—have been actively seeking a replacement for the lead in perovskite solar cells. But so far, nothing has proved nearly as effective.
Recognizing the promise of this technology and the difficulty of replacing the lead in it, in 2013 the MIT researchers proposed an alternative. “We thought, what if we got our lead from another source?” Belcher recalls. One possibility would be discarded lead-acid car batteries. Today, old car batteries are recycled, with most of the lead used to produce new batteries. But battery technology is changing rapidly, and the future will likely bring new, more efficient options. At that point, the 250 million lead-acid batteries in U.S. cars today will become waste—and that could cause environmental problems.
“If we could recover the lead in those batteries and use it to make perovskite solar cells, it’d be a win-win situation,” Belcher says.