The design of energy-saving photonic multilayer structure induced near-infrared (NIR) blockage

Abstract

Energy-saving window that selectively blocks near-infrared (NIR) is a promising technology to save energy consumption. However, it is hard to achieve both high transmittance in visible light and high reflectance in NIR for the energy-saving windows. Here, we demonstrate a TiO2/Ag/TiO2/SiO2/TiO2 multilayer on a glass substrate to selectively block NIR while maintaining high transmittance to visible light. We first design and optimize the thickness of a TiO2/Ag/TiO2 structure; the metal layer reflects NIR and the dielectric layers increase transmittance of visible light with zero reflection condition. To further enhance NIR-blocking capability, we implement a TiO2 back reflector with a SiO2 spacer to TiO2/Ag/TiO2 structure. The back reflector can induce additional Fresnel reflection without sacrificing transmittance to visible light. The optimal TiO2 (32 nm)/Ag (22 nm)/TiO2 (30 nm)/ SiO2 (100 nm)/TiO2 (110 nm)/glass shows solar energy rejection 89.2% (reflection 86.5%, absorption 2.7%) in NIR, visible transmittance 69.9% and high long-wave (3 ≤ λ ≤ 20 μm) reflectance > 95%. This proposed visible-transparent, near-infrared-reflecting multilayer film can be applied to the windows of buildings and automobiles to reduce the energy consumption.