Eco-Friendly Recycling of Thin-Film Solar Cells

There are two primary types of solar cells on the market today: silicon-based cells, which make up 90% of the market, and thin-film cells. Thin-film solar cells, including Copper Indium Gallium Selenide (CIGS) cells, are the most efficient and versatile technology available, but their production leads to waste that contains both hazardous substances and valuable metals. Recovering these metals is crucial for both economic and environmental reasons, but current methods are costly and not environmentally friendly.

Ioanna Teknetzi, Burcak Ebin and Stellan Holgersson, Chalmers University of Technology, Sweden, have developed a method that recovers metals efficiently from CIGS solar cells and is more environmentally friendly than previous methods of recycling. The team was able to recover 100 % of the silver and 85 % of the indium at room temperature using a leaching process with 2 M HNO₃ and a surface to liquid ratio (A:L) of 1:3 cm²/mL for 24 hours. Silver and indium are the most valuable elements found in these cells.

The researchers also explored conditions for selectively leaching out contaminants, thus ensuring high-purity streams and thus their reuse in new products. To achieve mild leaching conditions, nitric acid concentrations were kept below 2 M and room temperature was maintained.

When leaching with 0.5 M HNO₃, the researchers found that 85% of Ag and 30% of In were extracted under the same conditions as before, resulting in lower contamination levels. Additionally, leaching with 0.1 M HNO₃ showed potential for achieving higher purity of Ag by initially selectively leaching Zn for 1 hour.

The selective leaching process involves placing the solar cell in a container with HNO₃ at the desired temperature, using agitation to facilitate dissolution of metals in the acid solution. The different metals are leached out at different times, allowing the process to be stopped before all the metals dissolve, resulting in higher purity. Once the leaching is complete, the desired metals are in the solution as ions, which can be purified and reused in the manufacturing of new solar cells.

The researchers found that their method reduces risks and costs while also improving purity through selective leaching of contaminants. Further optimization of the method is necessary to develop a viable metal recovery process from CIGS solar cells.