Photonic Multilayer Structure Induced High Near-Infrared (NIR) Blockage as Energy-Saving Window

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, a TiO₂ /Ag/TiO₂ /SiO₂ /TiO₂ multilayer is demonstrated on a glass substrate to selectively block NIR while maintaining high transmittance to visible light. The thickness of a TiO₂ /Ag/TiO₂ structure is first design and optimized; the metal layer reflects NIR and the dielectric layers increase transmittance of visible light with zero reflection condition. To further enhance NIR-blocking capability, a TiO₂ back reflector is implemented 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.