Midsummer www.midsummer.se , 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 manufacturing material costs.

In close co-operation with Professor Christian Ekberg and PhD-student Anna Gustafsson at the Swedish Chalmers University of Technology, Midsummer has developed aunique process to recycle the CIGS-material that does not end up on the solar cell. The process recovers the material that is left from the sputtering targets (30 to 40 per cent) and what ends up on the masks in the machine.

“Normally when recycling these kinds of materials you usually melt down the materialsunrefined. 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”.

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 thematerial”, 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 withhigh efficiencies. The process is a completely dry process and also an all-vacuum process, with less stringent requirements for clean-rooms etc.

Using Midsummer’s revolutionary 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 themanufacturing process is desirable for the sake of the production staff and it makes it generally easier to commence manufacturing of thin film CIGS solarcells.

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 areflexible and can be bent.

Midsummer is a Swedish company with its roots in the optical disc manufacturing equipment and the photo mask industries. With expertise in utilizing sputtering for fast and efficient manufacturing processes, Midsummer has developed production lines for highly efficient and cost-effective manufacturing of flexible thin film CIGS solar cells.

Midsummer’s CIGS cells looks like crystalline silicon solar cells, but are made on stainless steel substrates. This makes the cells suitable not only for regular solar panels, but also for flexible, light weight panels that can be used on membrane roofs, landfills or other structures where the traditional glass modules cannot be applied.