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

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2021-07, Vol.17 (29), p.e2100654-n/a
• Main Authors: Kim, Jiwon, Baek, Sangwon, Park, Jae Yong, Kim, Kwang Ho, Lee, Jong‐Lam
• Format: Article
• Language: English
• Subjects: Blocking; Design optimization; Energy consumption; Glass substrates; Light reflection; multilayer structure; Multilayers; Nanotechnology; Near infrared radiation; near‐infrared reflection; Reflectance; Silicon dioxide; Solar energy; Titanium dioxide; Transmittance; transparent energy‐saving window
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202100654

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. A highly transparent window film with high near‐infrared (NIR) reflection is designed by electromagnetic simulations. A photonic multilayer film combining a dielectric/metal/dielectric structure with a TiO2 back reflector shows both high NIR reflection (93.9%) and visible transparency (72%). The low NIR absorption (4.1%) prevents second heat source and promises a higher solar energy shielding effect than conventional methods.