Fraunhofer researchers develop decorative films for BIPV

Fraunhofer Institute for Electron Beam and Plasma Technology (FEP) researchers are using roll-to-roll nanoimprint lithography to produce visually seamless building-integrated photovoltaics (BIPV) modules.

Fraunhofer FEP researchers are developing aesthetically appealing finishes for BIPV. The project is funded by the German Federal Ministry for Economic Affairs and Energy.

The institute’s Design-PV project is testing decorative films for facade elements, finished using roll-to-roll nanoimprint lithography (NIL). Fraunhofer FEP said NIL fabricates surface topographies on polymer films with feature sizes from a few hundred nanometers to the millimeter range in a continuous roll-to-roll process.

Several designs made by Surteco GmbH, one of five project partners, have been applied to PV-active and non-active facade elements and tested by the Hamelin-based Institute for Solar Energy Research (ISFH).

Dr. Steffen Günther, project manager at Fraunhofer FEP, said ISFH tests found the PV modules with decorative finishes are visually indistinguishable from conventional facade elements. “Depending on the finish, [the decorative modules] achieve up to 80% of the performance of uncovered comparison modules,” Günther added.

Fraunhofer FEP said that adhesive strength of the decorative film on the module’s front glass and the metal layer of the facade elements has been a key challenge.

Researchers found the coating must adhere reliably to the ETFE (ethylene tetrafluoroethylene) film substrate. ETFE must be specially treated before coating due to its low surface adhesion. A plasma process has been developed to roughen the ETFE interface layer on a nanometer scale, significantly improving decorative layer adhesion, Fraunhofer FEP said.

The team said it is confident “these advances will contribute to further increasing the acceptance of BIPV solutions in architecture.” Design-PV will continue testing additional designs and colors and assessing long-term stability and weather resistance.

In February, a team from the Fraunhofer Institute for Solar Energy Systems (ISE) developed colored solar panels that can be integrated into a building’s exterior while maintaining high efficiency.