Development of innovative coatings for sun protection glasses based on the theory of the optimal spectral transmittance

Abstract

In this work new coatings for sun protection glasses for windows and glass facades were developed. These coatings improve the reduction of the energy input by solar radiation in comparison to the best sun protection glasses on the market. They reduce the cooling load of buildings and therefore contribute to the measures to reduce global climatic changes on earth. The new developed coatings are multilayer systems which are based on the principle of Fabry-Perot interference filters. The thin film multilayer systems are deposited on glass by magnetron sputtering under high vacuum conditions. The materials used in those coatings are silver, zinc oxide, titanium dioxide and silicon dioxide. Different coating designs were developed based on two bandpass filters, a metal-dielectric and an enhanced metal-dielectric filter. They were optimised to have a low energy load coefficient τe /τv and at the same time a stable colour appearance and a colour neutral light transmittance τv . The new coatings have energy load coefficients τe /τv between 0.339 and 0.398. For comparison one of the best commercial sun protection glass has an energy load coefficient of τe /τv = 0.429. A theoretical limit for this coefficient was determined to be at 0.334 if colour neutrality of the transmitted light is required.