Protective and Highly Reflective Multi-Layer Thin Films for Solar Thermal Reflectors /

Abstract

Energy from the sun light is being used to produce the electricity by solar PV and solar thermal power plants. Concentrators used in solar thermal power plants use coatings that have to survive in all environmental conditions. There are two kinds of reflectors 1st surface reflectors (reflect light from the front) and second surface reflectors (in which light is reflected from the back side). Reflectance of the 1st surface reflectors is more than 2nd surface reflectors but they need protection from the severe weathering conditions. In this regard, Multilayer reflective and protective thin films of the Chromium, Silver, Aluminum and Silica were prepared on the glass substrate. These thin films were coated by using Physical Vapor Deposition technique. Chromium (20nm) was used as the adhesive layer between the glass and reflective layers of the Aluminum (100 nm) and Silver (130nm) that were coated by using thermal evaporation method. The protective layer of Silica (200nm) for these reflecting thin films was coated by RF-sputtering. These thin films were then characterized by using X-ray diffraction, Scanning electron microscope, Atomic force microscope and UV-VIS-IR spectroscopy. The characterization results showed a compact and homogeneous surface morphology of the thin films and surface roughness measured by AFM also resulted roughness as low as 7 nm in case of Ag thin film. Prepared thin films showed very high reflectance upto 92%, 89% for the Ag and Al respectively even after performing the tape test for the adhesion the thin films showed about 85% and above reflectance that makes them suitable for the application in solar thermal power plants.