Materials scientists say they have taken nearly 300-year-old toxic waste—a stockpile of spherical lead bullets from the 16th and 17th centuries, contaminated with carbon residue, metallic impurities and the dull patina of oxidation—and transformed it into a critical component for solar panels.
And not just any solar panels, but perovskite solar panels: one of the most Cost effective and energy efficient forms of solar energy in today’s market..
Researchers at Germany’s Jülich Research Center in Erlangen said their new technique “recycles” highly contaminated lead bullets into high-purity, commercial-grade lead iodide, a compound needed in bulk to make the best of these perovskite solar cells. The team’s results produced solar panels capable of converting sunlight into electricity with a competitive efficiency of 21%. For contextTop-of-the-line perovskite solar cells made with more pristine starting ingredients currently harvest energy with an efficiency of just over 27%.
“Perovskite solar cells rely on high-purity lead iodide,” physicist and study co-author Ian Marius Peters said in a statement. post on LinkedIn sharing the study“But lead is toxic and requires a lot of resources to extract and refine.”
“Millions of tons of lead already exist in waste streams that remain underutilized,” Peters added. “This work shows that legacy toxic waste can be converted into a resource for clean energy.”
Take out the lead
Peters and his colleagues selected this pile of time-ravaged Renaissance musket and harquebus ammunition primarily as a proof of concept for their new method. According to their new study, published In March of this year, in the journal Cell Reports Physical Science, they bought the “musket ball fragments” (as you probably would) from someone on eBay. The bullets, they wrote, were intentionally chosen as “an exceptionally challenging raw material model” for manufacturing high-purity lead iodide. In other words, they did it expressly to demonstrate that their process would work even with old, very dirty lead full of chemical impurities.
Their recycling method has two essential steps. First, two electrodes made from melted and reshaped lead bullets were immersed in a solvent mixture of acetonitrile and dissolved iodine with an electric current flowing through this liquid bath. The process, according to the team, produced lead iodide with remarkably high purity. The team also noted that this new method also had ecological benefits, limiting the use of chemicals and producing less lead-contaminated wastewater.
In the second step, this high-purity, mustard-yellow lead iodide powder was used to grow perovskite crystals using a technique known as reverse temperature crystallization, which uses heat, rather than cold, to induce the correct formation of molecules and crystalline forms.
According to Peters, this low-cost refinement method produced perovskite solar cells that were “statistically indistinguishable from devices made with commercial 5N precursors.” (5N here is industry jargon for a material with 99.999% purity. If you can believe it, and I admit I’m having trouble myself, 5N is short for “five nines”).
Closing the cycle
The researchers said they undertook this project as a means to capture the “estimated 30% to 40% of lead waste” that is effectively abandoned at the end of its industrial life cycle. An entirely new system, similar to the efficient recycling of lead-acid car batteries, would be needed to help boost perovskite solar cell (PSC) production.
“Sustainable sourcing of lead is imperative for scaling up PSCs,” the authors wrote.
PErovskites are a broad category of solar cells (and do not necessarily need lead in their crystalline structure to function), but it has been these lead-based versions that have proven to be the most efficient at converting sunlight into electricity.
“Consistently over time, lead-based devices continue to improve their performance,” said Tonio Buonassisi, director of the MIT Photovoltaics Research Laboratory. said MIT News in 2022, “none of the other compositions came close in terms of electronic performance.”
According to Buonassisi, lead halide perovskite solar cells have been the main focus of perovskite researchers for more than a decade. Among the material’s many benefits over traditional silicon-based solar panels, perovskites can be easily woven Fabric-like solar cells made from incredibly light and flexible polymeric materials.. Perovskites can also be mixed to make perovskite-silicon hybrid solar panels, where they have accomplished Impressive efficiency of 36%, higher than either of them alone.
“You can mix and match atoms and molecules in the structure,” Buonassisi said. “Perovskites are highly tunable, like a crystal structure of the kind you can build your own adventure.”
