A broadband antireflective coating based on a double-layer system containing mesoporous silica and nanoporous silica

A double-layer broadband antireflective (AR) coating with excellent transmittance was successfully fabricated using two kinds of silica coatings. The excellent optical performance in a wide wavelength range came from a reasonable refractive index gradient from air to the substrate produced by the mesopores in the bottom-layer silica coating and the particle-packed pores in the top-layer silica coating. The maximum transmittance of the broadband AR coating was approximated to 100.0% at the peak value and above 99.6% in the visible region from 400 to 800 nm. Meanwhile, the average transmittance of the coating was more than 99.0% over the range of 360 to 920 nm. In addition, the double-layer broadband silica AR coating showed strong mechanical performance and good environmental stability. This work provides an alternative way to prepare a broadband AR coating for some applications in energy harvesting and optical devices.