Cooperation: Swedish solar energy expert Midsummer and Chalmers University of Technology

Midsummer AB, Elektronikhöjden 6, 175 43 JÄRFÄLLA, SWEDEN
Midsummer AB, Elektronikhöjden 6, 175 43 JÄRFÄLLA, SWEDEN

Swedish solar energy expert Midsummer and Chalmers University of Technology develops a unique process to recycle rare metals

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 manufacturing material costs.

In close cooperation with Professor Christian Ekberg and PhD-student Anna Gustafsson at the Swedish Chalmers University of Technology, Midsummer has developed a unique 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 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”.

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.

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 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.

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.

About Midsummer

Midsummer is a leading supplier of equipment for cost effective manufacturing of CIGS thin film flexible solar cells. Midsummer’s turnkey manufacturing lines have a small footprint, are perfectly scalable and allow for small-scale production of solar cells and modules.

Midsummer’s customers are thin film solar cell manufacturers all over the world. CIGS flexible solar modules are growing in popularity thanks to their low weight, flexibility and durability. Applications are e.g. floating modules, vehicles, landfills, portable power generation and membrane roofs on factories, offices and other structures that are not strong enough for traditional glass modules.

Founded in 2004 by people with a background from the optical disc manufacturing equipment and the photo mask industry, Midsummer has its head office in Stockholm, Sweden. Midsummer was the fastest growing greentech company in EMEA (Europe, Middle East and Africa) in 2007-2011 (according to Deloitte).

About CIGS thin film solar cells

CIGS stands for copper-indium-gallium-selenium, a metal alloy that converts the energy of light directly into electricity by the photovoltaic effect (PV). The CIGS absorber is deposited on a stainless steel substrate, along with electrodes on the front to collect current. The cells are then connected in series and covered by a protective layer of plastic to form a flexible solar module.

Since a stainless steel substrate is used, the modules can be made without glass. The CIGS solar modules are therefore much lighter, flexible and can be made frameless, to suit applications where traditional silicon solar cells cannot be used, e.g. on structures that are uneven, moving or weak.

CIGS solar cells are manufactured by sputtering the material onto 156×156 mm stainless steel substrates. The solar cells from Midsummer are free of cadmium, a toxic material usually used in CIGS and other thin film solar cells.

Flexible CIGS solar modules are gaining market share thanks to its high efficiency, low weight, flexibility and durability. There have been significant improvements in CIGS cell efficiency, with Midsummer achieving aperture area efficiency in excess of 15.8 per cent in an all-vacuum process.

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