Sol-Gel Deposited Highly Transparent Electrically Conductive and Infrared Reflective Metaloxide Thin Films to Improve Thermal Comfort and to Reduce Thermal Emittance

Abstract

The aim of this work is to comprehensively study sol-gel derived aluminumdoped zinc oxide (AZO) and tin-doped indium oxide (ITO) coatings for highly transparent electrically conductive and infrared reflective surfaces to improve the thermal comfort and to reduce the thermal emittance of a glazing. Therefore, multilayered polycrystalline transparent conductive oxide (TCO) thin films have been prepared on soda-lime glass slides by using an inorganic sol-gel process and the dip-coating technique. The functional layers were crystallized on the substrate and subsequently annealed in a reducing atmosphere to enhance the number of free charge carriers. Significant characteristics of the coatings, such as crystallinity, surface morphology, layer thickness, electrical conductivity, as well as the optical properties in a large spectral range between 0.25 and 35 μm were analyzed using UV-VIS- and IR-spectroscopy, SEM-, XRD- and 4-point conductivity measurements. The obtained samples are highly transparent with a visual transmittance above 0.85 and show specific resistivities of up to 1.6·10-3 Ω·cm for the zinc-based, and of up to 3.0·10-4 Ω·cm for the indium-based coatings. Applying an optimized multilayered coating with at most 500 nm is sufficient to reduce the surface emittance of a glazing from 0.89 to less than 0.40 for both types of TCO coatings in the infrared