Fraunhofer has developed a new method of providing high-area polymer films with an anti-reflective film layer through the utilisation of plasma-etching. The development was unveiled at the recent International Vacuum Conference and will be used to help provide solar cells with optimal light conditions.
The anti-reflective layer programme, named PolAR, was developed by an alliance including Rodenstock, Southwall Europe, Leica Microsystems and Fraunhofer’s IOF and FEP programmes. The project was funded by the Federal Ministry of Economics and Technology and focussed on developing a roll-to-roll process to manufacture anti-reflective polymer films.
The manufacture process creates minute indentations while also enhancing the base roughness of the film. The indentations are smaller in size than the wavelengths of visible light, this prevents light scattering and keeps the film clear. Whilst this process is ongoing, the depressions change the refraction index between the film and external medium continuously, this can dramatically reduce the optical reflection. Optical reflection on PET films, for example, may be reduced from 12% to 0.2%.
Prior to the development of this method, anti-reflective coating demanded a four-layer coating, the application of which can adversely affect the flexibility of thin-films. Though the process of impregnating films with anti-reflective coatings, named the moth eye principle, has been known for a long time, Fraunhofer has developed a novel process that is suitable for mass-production in roll-to-roll plants. In Fraunhofer’s pilot plants several meters of film can be processed per minute.
Fraunhofer has already applied the anti-reflective process to triacetate cellulose, fluoropolymer and lacquered films.