Development of transparent heat mirrors based on metal oxide thin film structures

Abstract

The aim of this work is the preparation of RF sputtered indium–tin oxide (ITO) thin films for application as transparent heat mirrors. The heat mirrors are important elements for the photothermal solar energy conversion. In combination with moderate spectral selectivity of the solar absorbers they could increase the efficiency of the solar collector. The optical properties of ITO and double-layer ITO with titanium dioxide (TiO 2) structures in the visible and infrared ranges were investigated. The films were deposited on glass substrates by RF sputtering technique. Tin-doped indium, as well as titanium targets was used. The influence of the In–Sn target composition and the deposition parameters on the film properties were studied. The films' surface morphology and structure were investigated by SEM, TEM and XRD, the composition was studied applying electron probe microanalyzer (EPMA). The thicknesses of the films were determined by the laser ellipsometry method. The measurements in the infrared range were performed on Fourier transform infrared spectrophotometer (FTIR). The single layer ITO structures showed reflectance in the infrared range not exceeding 50% at longer wavelengths. The double layer structures with TiO 2 under layer showed increased reflectance in the infrared range with high visible transmittance reaching 85%.