Solar optical properties of thin films of Cu, Ag, Au, Cr, Fe, Co, Ni and Al

The optical properties of metal coated glass substrates have been investigated. Thin films of various thicknessesof the noble metals: Cu, Ag, Au, the transition metals: Cr, Fe, Co, Ni and the free electron-like metal Al were thermally evaporated onto glass substrates. The front and backside reflectance and the transmittance between 0.35 and 15 μm were measured. The obtained data were used to calculate the integrated values of solar reflection and transmission as a function of metal film thickness. The application of metal films on domestic windows as sun-screens and heat-mirrors are discussed. It is concluded that Cu is the best coating in a window system if good heat insulating properties are desired. This is due to its ability to remain continuous at very thin film thicknesses. An infra-red reflectance of 86 per cent combined with a solar transmittance of 55 per cent was obtained for a 70film. For solar heat-protection Au-films are found to be superior owing to their transmittance peak in the middle of the visible wavelength region. The transition metals are less selective than the noble metals, but due to their flat response-curves in the visible range they cause a smaller change in colour of the transmitted and reflected light.