Fabrication of robust, self-cleaning, broad-band TiO2-SiO2 double-layer antireflective coatings with closed-pore structure through a surface sol-gel process

Multifunctional antireflective (AR) coatings are widely used in fields of optical devices, flat-panel displays, windows and solar cell devices. In this paper, silica (SiO2) and titanium dioxide (TiO2) nano-materials were used as building blocks to construct multifunctional AR coatings. The surface of the SiO2 coating derived from SiO2 nanoparticles consists of a large number of nanopores, and its refractive index is tuned conveniently from 1.19 to 1.45 by controlled incorporation of TiO2 into these nanopores through a surface sol-gel process. By tuning the coating structure, substrates with double-layer TiO2-SiO2 coatings presented a maxium transmittance of 98.4% and average transmittance as high as 97.7% over the visible and near infrared region. The nanocomposite TiO2-SiO2 coatings demonstrated a good hydrophilicity, favorable robustness and high photocatalytic activity. In addition, the double-layer TiO2-SiO2 coatings had a long-term durability after accelerated-aging test, while the porous SiO2 coatings with a great of open nanopores showed a severe decrease. This double-layer TiO2-SiO2 coatings have the benefit of designing, fabricating, and developing multifunctional AR coatings with broadband transmittance, high photocatalytic activity and high environmental stability, which makes them extremely appealing for applications in lenses, solar photovoltaic cells, etc.. Moreover, this work not only provides an alternative way to tune the refractive indices of AR coatings, but also opens up a new avenue towards broadband AR coatings. (C) 2018 Elsevier B.V. All rights reserved.