The implementation of novel usage concepts, however, still faces several challenges, mostly concerning the required service life of electronic components and their direct integration into building envelopes, especially when these are of lightweight construction or comprise flexible membrane roofing systems or façades.
The flex 25 project team made key progress in the integration of electronic components in flexible, film-based building envelope areas. A prominent example for the targeted type of building envelope is the façade of the Munich Allianz-Arena, which is constructed of fluoropolymer films. A roll-to-roll process was used functionalize the films with a multi-layer-coating to protect integrated electronic components from water vapor and UV light.
Flexible electronic solutions are trendy in nearly all areas of every day life: fitness trackers that come as bracelets with bendable displays or flexible solar cells working as smart phone battery chargers.
The flex 25 project had the main goal to transfer existing vacuum and controlled atmosphere coating processes to weatherproof film substrates to add ultra-barrier properties against water vapor and oxygen while at the same time maintaining a high optical transmission after coating. The resulting surface-functionalized plastic film had to be suitable for the encapsulation of flexible electronic components. Large area façades and membrane roofings are usually not suitable to carry the weight of conventional glass encapsulated solar panels, but film-based solar cells are 40 times lighter and allow an integration into membrane roofs.
The flex 25 researchers at the Fraunhofer Institutes FEP, ISC and IVV have developed an economically viable and technologically beneficial alternative to glass encapsulation. It is based on the ultra-barrier concept of POLO-High Barrier, which was adapted to work for the coating of weatherproof fluoropolymer films like ETFE. Now, the concept is ready for a pilot-scale production of functional films with ultra-barrier properties against water vapor and oxygen, which are suitable for e.g. the encapsulation of organic opto-electronic components such as organic light-emitting diodes (OLEDs) or flexible solar cells.
The functional film is based on a multiple layer concept that includes specific hybrid polymers (ORMOCERs) and at least one metal oxide layer (illustrated below). ORMOCERs are a class of material developed by the Fraunhofer Institute for Silicate Research ISC. ORMOCER lacquers are suitable for wet chemical roll-to-roll coating processes. They have good gas barrier properties and they protect underlying layers and encapsulated components against degradation from UV radiation when provided with integrated UV absorbers.
The metal oxide layers were applied at the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP. In combination with ORMOCER layers, they provide an ideal barrier against the diffusion of water vapor and oxygen to the encapsulated components. It was possible to apply zinc-tin oxide or aluminum oxide layers by adapting the process to the specific mechanical and surface properties of ETFE films. This enabled a large-area roll-to-roll process with reactive dual magnetron sputtering of the ETFE films under vacuum.
In their joint project, the three Fraunhofer Institutes accomplished to develop a robust manufacturing process in pilot scale to apply barrier coatings of consistent quality to fluoropolymer films as substrate.
The next step after the successful completion of the project is bringing the gained knowledge to application. Some issues still need further attention, such as the long-term weathering stability, heat and moisture resistance. Also, a good permeation barrier film is not yet a device – successful demonstration of the deposition of electronically active functional stacks on fluoropolymer webs is the next milestone towards the direct integration of the new film solution in building envelopes.