Unique process to recycle rare metals from solar cells production leftovers

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The Midsummer Duo line is an extremely compact thin film production tool that utilizes Midsummer`s own developed CIGS solar cell technology (Photo: Midsummer AB)

Stockholm, Sweden — Midsummer, a leading supplier of production lines for cost effective manufacturing of flexible thin film CIGS solar cells, has developed a unique process to recover leftover rare metals such as indium and gallium when manufacturing thin film CIGS solar cells. The unique process will extensively reduce thin film CIGS (Copper Indium Gallium Selenide) manufacturing material costs. The process recovers the material that is left from the sputtering targets (30 to 40 per cent) and ends up on the masks in the machine.

The unique process to recycle the CIGS-material that does not end up on the solar cell has been developed in close co-operation with Professor Christian Ekberg and PhD-student Anna Gustafsson at the Swedish Chalmers University of Technology.

“Normally when recycling these kinds of materials you usually melt down the materials unrefined. But this new and unique method is far subtler as the process makes it possible to remove all the selenium before dissolving the material in its components with various acids,” said Sven Lindström, CEO, Midsummer. “Gallium and Indium are expensive rare earth materials and this unique process makes it possible for us to drastically reduce the material costs while at the same time conserve the earth’s limited resources”.

Selenium is separated from the metals

The unique feature of this process is that it removes selenium by oxygen and thus makes it easier to process the remaining oxidized metals. This is very good as selenium may in some reactions create toxic gases. “The CIGS material is grinded to a powder and oxygen is allowed to flow over the material”, said Anna Gustafsson, PhD-student at the Swedish Chalmers University of Technology. “The method allows SeO2 to be formed and all the selenium is separated from the metals. The separated selenium can then be reformed at very high purity (over 5N purity, 99.999%) so it can easily be reused in the solar cell production process without further purification.”

Midsummer has recently developed a high-efficient process for cadmium-free CIGS on stainless steel with sputtering. By using sputtering in all processing steps, the process cycles in the manufacturing of solar cells can be drastically shortened, the solar cells can be made cadmium-free and also made on stainless steel substrates suitable for light weight flexible modules – all contributing to a highly competitive method to manufacture thin film CIGS cells with high efficiencies. The process is a completely dry process and also an all-vacuum process, with less stringent requirements for clean-rooms etc.

Buffer without any cadmium

Using Midsummer’s innovative solar cell manufacturing process by sputtering, solar cells can be made on stainless steel – suitable for flexible modules – and without any cadmium in the buffer layer. Cadmium and its compounds are highly toxic and exposure to this metal is known to cause cancer and other illnesses. Avoiding cadmium in the manufacturing process is desirable for the sake of the production staff and it makes it generally easier to commence manufacturing of thin film CIGS solar cells.

Thin film CIGS solar panels are thinner and lighter than traditional silicon solar cells made of glass. They are also non-toxic (no cadmium) and can be made frameless, thus ideal for buildings and moving vehicles in cities. They are flexible and can be bent.

More information can be found under midsummer.se.

Source: Midsummer AB