Researchers at Chalmers University of Technology in Sweden have developed a process which opens the door to more efficient recovery of precious metals from thin-film solar cells.
The method is also claimed to be more environmentally friendly than previous methods of recycling and paves the way for ‘more flexible and highly efficient solar cells’.
There are two mainstream types of solar cells. The most common is silicon-based and accounts for 90% of the market. The other is thin-film solar cells which have three main sub-technologies, one of which is known as CIGS (copper, indium gallium, selenide) and consists of a layer of different metals, including indium and silver.
Thin-film solar cells are by far the most effective of today’s commercially available technologies. They can also be made bendable and adaptable, which means that they can be used in many different areas.
The problem is that the demand for indium and silver is high and increased production is accompanied by a growing amount of waste which contains a mixture of valuable metals and hazardous substances. Being able to separate target metals from other substances becomes extremely valuable, both economically and environmentally, as they can be reused in new products.
‘It is crucial to remove any contamination and recycle so that the material becomes as clean as possible,’ says Ioanna Teknetzi, a PhD student at the department of chemistry and chemical engineering who, together with Burcak Ebin and Stellan Holgersson, have published the results of their research in the journal Solar Energy Materials and Solar Cells. ‘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.’
Their research shows that a ‘greener’ recycling process can have the same outcome. ‘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,’ Teknetzi explains.
‘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 optimisation can reduce these.’
100% silver recovery
The process takes place at room temperature without adding heat and the researchers have shown it is possible to recover 100% of the silver and about 85% of the indium.
‘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,’ adds Burcak Ebin. ‘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.’
1. The film in the solar cell is analysed for material, chemical composition, particle size and thickness. The cell is placed in a container with an acid solution at the desired temperature and agitation dissolves the metals in a leaching process.
2. Leaching effectiveness and chemical reactions are assessed by analysing samples taken at specific times during the process. The various metals are leached at different times, meaning the process can be stopped before the metals begin to dissolve, which in turn contributes to achieving higher purity.
3. When the leaching is complete, the desired metals are within the solution in the form of ions and can be easily purified and reused in the manufacture of new solar cells.
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