Solar cell silver, indium recycling tech

Swedish researchers at the Chalmers University of Technology have developed a recovery method for recycling 100% of the silver and about 85% of the indium contained in thin-film solar cells in an environmentally friendly, room temperature process.

"The problem is that the demand for indium and silver is high, and increased production is accompanied by a growing amount of production waste, which contains a mixture of valuable metals and hazardous substances," the scientists said. "Being able to separate attractive metals from other substances, therefore, becomes extremely valuable, both economically and environmentally, as they can be reused in new products."

Thin-film solar cells using a combination of copper, indium, gallium, and selenide (CIGS) are by far the most effective of today's commercially available technologies. Being thin and flexible, they can be adapted for many different applications.

Though the most common photovoltaic cells are still silicon-based, which accounts for 90% of the market, thin-film solar cells are rising in popularity and production.

Thin-film sheets may be used to generate electricity increasingly in places where bulkier photovoltaic cells cannot be used, such as curved surfaces on buildings and cars; lightweight applications like chargers for handheld devices and wearables; remotely placed electronics like parking meters, roadway and traffic sign lighting, emergency phones or radio transmitters, and much more.

Recycling various metals in mixed waste is often done through a chemical bath process called leaching which varies in types and amounts of acids and toxic waste effluent.

Ioanna Teknetzi and her colleagues at the Chalmers University of Technology considered both maximum purity and environmental sustainability when developing acidic leaching solutions that would offer a greener way to recover metals from recycled thin-film solar cells.

"We also have to use chemicals, but nowhere near as much as with previous leaching methods. To check the purity of the recovered indium and silver, we also measured the concentrations of possible impurities and saw that optimization can reduce these," Teknetzi said.

The researchers' methodology was to first analyze a cell's material, chemical composition, particle size and thickness. The cell is then placed in an acid solution and agitated to facilitate the dissolution of metals.

Leaching effectiveness and chemical reactions were then analyzed in samples taken throughout the process. Different metals separate at different times, so the process can be paused selectively which allows the metals to be extracted at higher levels of purity.

When the leaching is complete, the desired metals are suspended in the solution as ions and can be easily reused in the manufacture of new solar cells.

In addition to high-purity silver and indium, the research team says their leaching method can be used to selectively recover the other metals found in CIGS solar cells.

"It is crucial to remove any contamination and recycle so that the material becomes as clean as possible again," Teknetzi pointed out, "Until now, high heat and a large amount of chemicals have been used to succeed, which is an expensive process that is also not environmentally friendly."

The team's hope is that their research and metals recovery methodology will inspire optimization of the recycling process and pave the way for its large-scale use.

Further details from their CIGS solar cell recycling research can be read at Valuable metal recycling from thin film CIGS solar cells by leaching under mild conditions published in the April 2023 edition of ScienceDirect's Solar Materials and Solar Cells journal.