Nanoporous silica antireflective coatings for solar heat collectors

To increase the efficiency of solar energy collection, low reflective coatings in the solar spectrum must be used for solar heat collectors. Nanoporous silica films can form broadband antireflectance in the region. Based on a base/acid two-step catalysed tetraethoxysilane (TEOS) system and the sol-gel process, the nanoporous antireflective silica coatings were prepared by dipcoating and annealing in air or ammonia atmosphere. Abrasion tests of the porous silica coatings indicate that treated coatings have scratch-resistant properties. The films were characterised by ellipsometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Reflectance spectra were recorded with a spectrophotometer. Based on optimised design, the average reflectance of the obtained coatings in the solar spectrum is less than 2%. Finally, a strengthening mechanism of the films is discussed.