Improvement of near infrared reflectance of TiO₂/SiO₂/TiO₂ multilayer structure for energy efficiency window applications

A TiO₂/SiO₂/TiO₂ multilayer structure was prepared by the sol-gel process and spin-coating methods and used to reflect near infrared (NIR) light. For the efficient NIR reflectance, higher refractive index TiO₂ film and lower refractive index SiO₂ film are desired. Porous film structure resulted in a lower refractive index compared to the solid film case by the inclusion of air molecules (n = 1). To increase the refractive index of the TiO₂ film, TiCl4 post treatment was used to fill the pores in the TiO₂ film. The refractive index of the TiO₂ film filled with the secondary TiO₂ nanoparticles increased owing to the minimization of the air gap. The UV-Vis-NIR spectrophotometeric data show that the multilayer structure with the TiCl₄-treated TiO₂ film has a higher NIR reflectance than that of the untreated TiO₂ film. The transfer matrix calculation for the NIR reflectance of the multilayer structure shows good agreement with the experimental data. Therefore, the multilayer structure formed with the TiCl₄-treated TiO₂ film showed improvement of NIR reflectance than that with the untreated TiO₂ film.