Optical interference coatings for coloured building integrated photovoltaic modules: Predicting and optimising visual properties and efficiency

Abstract

The presented work is focusing on optical interference coatings on the back side of the front glass for crystalline silicon-based photovoltaic modules. We present results on how such coatings can be designed to obtain desired visual properties combined with a limited loss in power conversion efficiency. This colouring technology may therefore be very attractive for building integrated photovoltaics. Coating design parameters such as number of layers, design wavelength, layer thicknesses, and layer refractive indices affect both the visual appearance parameters and the efficiency. Important colour parameters are lightness, chroma, and hue, and we demonstrate how these colour parameters are influenced by the design parameters of the optical interference coating.Using optical interference coatings to create colours results in colours that are dependent on the observation angle. We have introduced a new parameter for quantification of angular colour dependence. Our results show that the angular colour dependence can be reduced by increasing the refractive indices of the interference coating.For many building projects it may be highly desired to combine high power conversion efficiency with certain visual properties. The results from our work also indicate some of the possibilities and challenges in this regard.