Low-emitting surfaces prepared by applying transparent aluminum-doped zinc oxide coatings via a sol–gel process

Polycrystalline transparent conductive oxide thin films based on aluminum-doped zinc oxide (AZO) have been prepared on soda-lime glass by using an inorganic sol–gel process and the dip-coating technique. The multilayered films were crystallized on the substrate and subsequently annealed in a reducing atmosphere to enhance the number of free charge carriers. Significant characteristics of the functional coatings, such as crystallinity, surface smoothness, layer thickness, electrical conductivity, as well as the optical properties in a large spectral range between 0.25 and 35 μm were analyzed. 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. Applying an optimized AZO-coating with at most 500 nm is sufficient to reduce the surface emittance from 0.89 to less than 0.45 in the infrared.