Greener method for recycling thin-film solar cells

Though silicon-based solar panels dominate with about 90 per cent of the market share, thin-film solar cells are growing in popularity, particularly in commercial and high-end applications. CIGS (Copper Indium Gallium Selenide) cells are some of the best performing, but the precious metals - indium and silver in particular – are in high demand and can be difficult to recover at end-of-life.

The Chalmers team used acid leaching to separate the metals from the other cell material, demonstrating that it is possible to recover 100 per cent of the silver and about 85 per cent of the indium. The process, described in the journal Solar Energy Materials and Solar Cells, takes place at room temperature without adding heat.

“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”, said Ioanna Teknetzi, PhD student at Chalmers’ Department of Chemistry and Chemical Engineering.

“We took into account both purity and environmentally friendly recycling conditions and studied how to separate the metals in the thin-film solar cells in acidic solutions through a much ‘kinder’ way of using a method called leaching. We also have to use chemicals, but nowhere near as much as with previous leaching methods.”

The film from the solar cell is first analysed with respect to material, chemical composition, particle size and thickness. The cell is then placed in a container with an acid solution at the desired temperature, where agitation is used to facilitate dissolution of the metals in the acid solution – the leaching process.

The different metals are leached at different times, meaning that the process can be stopped before all the metals begin to dissolve, which in turn contributes to achieving higher metal purity. When the leaching is complete, the desired metals are in the solution in the form of ions and can then easily be purified and reused in the manufacture of new solar cells.

“It takes one day, which is slightly longer than traditional methods, but with our method, it becomes more cost-effective and better for the environment,” said Dr Burcak Ebin, researcher at Chalmers’ Department of Chemistry and Chemical Engineering.

“Our hopes are that our research can be used as a reference to optimise the recycling process and pave the way for using the method on a larger scale in the future.”