Optical modulation and fabrication of two-dimensional VO₂(M)-AgSiO₂ shell/core composite photonic crystal structures

The high phase transition temperature, low solar modulation efficiency, and unfavorable brown-yellow color have limited the practical application of VO₂-based smart windows. By embedding a hexagonal close-packed monolayer array of SiO₂ into the monoclinic VO₂(M)–Ag composite film using an electron-beam evaporation system, a two-dimensional VO₂(M)–AgSiO₂ shell/core photonic crystal composite material was formed. Due to the increased contact area between Ag and VO₂(M) within the composite material, the concentration of free electrons in VO₂(M) increases, causing the phase transition to occur at a lower temperature of 52.2 °C. With the embedded SiO₂ array, the solar modulation efficiency is enhanced to 25.4%, and the visible light modulation efficiency increases by nearly 7 times. Additionally, the grating effect of the photonic crystal significantly diffracts light around the 600 nm wavelength, reducing the strong absorption of VO₂(M) in the shortwave range and diluting its inherent brown-yellow color. By embedding the SiO₂ array into the VO₂(M)–Ag composite film, this approach simultaneously achieves a reduction in phase transition temperature, enhancement of solar modulation efficiency, and color adjustment of the film, providing a reference for the practical application of VO₂ in smart windows.