Solar energy is, with the permission of wind energy, the renewable energy that has stood out the most and best in the energy transition on a global scale. There are already solar parks everywhere: from fields that They fill the emptied Spain to deserts passing through the tibetan plateau and also in high seas either in lakes. And although the most common technology is crystalline silicon, perovskite is the great promise. There is a compelling reason to bet on perovskite: a record efficiency certified in a laboratory. up to 26%.
However, a large-scale deployment of perovskite solar cells requires a large-scale, sustainable supply of high-purity lead iodide. We have come across lead: a toxic element whose mining is not exactly sustainable. On the not-so-good side, recycling it to the required purity levels is a technical challenge that a German research team at the Helmholtz Institute in Erlangen-Nuremberg has just solved. And in what way: have achieved converting 17th century musket balls into high-performance solar cells.
The idea. It consists of a process of upcycling (upcycling) in two stages: first a non-aqueous electrochemical route and then purification through the crystallization of single crystals, quite different from traditional methods based on strong acids and large volumes of water.
To demonstrate the robustness of their method, the team used lead bullets from the 16th and 17th centuries as raw material, a truly complicated material in that it contains carbon residues, metallic inclusions and oxidation patina. If the process can clean up this type of historical residue, it can handle virtually anything you throw at it (obviously any lead residue).
Recycling bullets into solar cells transforms lead waste into a clean energy source.
Why is it important. Perovskite solar cells require extraordinarily pure lead iodide, and achieving that level of purity from contaminated waste was until now a challenge without a practical solution that this research has solved: the team manufactured solar cells with their recycled material and obtained 21% efficiency, practically identical to the 22% of devices manufactured from industrial synthesis.
Beyond the technical result, the process solves two problems at the same time: it offers a way to supply the enormous demand for lead iodide that will be generated by the take-off of perovskite solar cells without resorting to new mining and at the same time eliminates a toxic pollutant whose current management is expensive and environmentally problematic.
Context. As we mentioned above, lead is an abundant waste: it comes from used car batteries, electronic scrap, construction materials or ammunition, among others. Lead recycling is dominated by car batteries, which have very high recovery rates in developed countries. The problem is in the rest: In 2018, only 48% of the world’s residual lead at the end of its useful life was recovered and in more dispersed flows such as electronics or construction, the recovery is even lower.
Conventional recycling returns metallurgical-grade lead, useful for batteries and alloys, but far from what the solar industry requires. In addition, they are slow processes that generate toxic gases such as nitrogen oxides and large quantities of contaminated wastewater, up to 70 liters per kilogram of lead iodide produced. Traditional high-temperature purification methods are expensive and complex. More robust, adaptable and cleaner extraction and purification methods are needed for perovskite technology to truly scale.
How they do it. The bullets are cleaned with dilute nitric acid, melted and molded into rods that act as electrodes in an electrochemical cell with acetonitrile and dissolved iodine. When current is applied, lead reacts directly with iodine and precipitates as lead iodide with 94% efficiency. Doing it this way, in a non-aqueous medium, is a deliberate decision to avoid introducing impurities that would accelerate the degradation of the perovskite.
The resulting lead iodide still contains metallic impurities, so it is not suitable for solar cells. That is why it is subjected to a second purification stage through crystallization at a controlled temperature for about 70 hours. The process is exceptionally selective: as the crystal grows, it expels contaminating metals such as silver or copper, raising the purity of the material to levels comparable to or even higher than the highest quality commercial standard.
Yes, but. The process works and the results are solid, but scale matters: at the laboratory level, productivity is just 0.05 grams per hour and each purification cycle lasts about 70 hours. The leap to an industrial scale requires solving the recovery of organic solvents, controlling the passivation of the electrodes and substantially improving the productivity of the process.
The research team does not hide it: the chemistry is proven, but the distance from the laboratory to a real production plant is long and will determine whether we end up seeing perovskite panels made with recycled lead or if this remains like a shiny piece of paper in a drawer.
In Xataka | Germany has had a crazy idea to solve one of the problems of renewables: covering a lake with solar panels
In Xataka | 800 meters deep in a 175 million year old rock: Germany’s solution to nuclear waste
GIPHY App Key not set. Please check settings