Flexible Films for Photovoltaics

Flexible plastic films are now being used to protect solar cells from the elements, a move that could significantly reduce the production cost of manufacturing a photovoltaic module. Instead of working with individual glass plates, the solar cells could be printed onto a plastic film and then encapsulated with the barrier film – photovoltaics on a roll.

The film and packaging development was led by Dr. Klaus Noller from the Fraunhofer Institute for Process Engineering and Packaging IVV, along with Dr. Sabine Amberg-Schwab from the Fraunhofer Institute for Silicate Research ISC, who is an expert in hybrid polymers, called ORMOCERs – an in-house development of the ISC. She and her team worked almost 20 years on developing a coating material on the basis of ORMOCER that can be used as an effective barrier against oxygen and water vapor. What has been created is a barrier lacquer that the researchers combined with another known barrier material: silicon dioxide.

Dr. Sabine Amberg-Schwab and Dr. Klaus Noller have developed a specially coated polymer film that is ideally suited for encapsulating inorganic solar cells. (Image: Dirk Mahler)

"The results were astounding," said Amberg-Schwab: "A barrier effect that is far better than could be expected from adding only the two layers. The reasons for this are special effects that are generated between the two materials."

For the ideal application on a film, the team developed an ORMOCER coating material that is easy to process and cure. The damp heat test was a particular obstacle: the cured lacquer coating must remain stable at 85 degrees Celsius and 85 percent humidity. The solar cells on the roof or the facade are intended to withstand extreme weather conditions and temperatures as long as possible.

The team is faced with the challenge of developing a process with which the barrier layers can be applied to the film perfectly and economically. This was achieved with a roll-to-roll process. The painting line was optimized continuously to meet the special requirements: The ORMOCERs must be applied in a dust-free environment, with the layer thickness being extremely thin, yet as a continuous film. During this, the coated side must not touch a roller at any time. That would damage the layer. The patented process makes it possible to manufacture tough, high-barrier films in a cost-effective and environmentally friendly way.

Industrial partners are already using this process. Amberg-Schwab and Noller will receive one of the three 2011 Joseph von Fraunhofer Prizes for their developments.

For more information, visit: www.isc.fraunhofer.de