The thermochromic characteristics of ITO/VO₂ composite films on SiO₂ nanospheres

As a promising thermochromic material for smart windows, VO₂-based films have received extensive attention. To enhance the luminous transmittance (T_lum) of thermochromic smart windows without seriously affecting the solar modulation efficiency (ΔT_sol), this paper prepared VO₂ films by rapid thermal annealing of sputtered vanadium thin films on an ordered SiO₂ nanosphere array, and then the ITO as antireflection layer was deposited on VO₂ film by reactive magnetron sputtering. The surface morphology, crystal structure and optical transmittance of the films were characterized by Scanning Electron Microscopy, X-ray diffraction and UV–VIS–NIR spectrophotometer, respectively. The SiO₂ nanospheres provide continuous refractive index gradient, while the deposition of the ITO antireflection layer creates conditions for thin film interference, thereby synergistically reducing surface reflection in the VO₂-based smart window. Compared with the planar VO₂ thin film (T_lum, 39.1%), the ITO/VO₂/SiO₂ composite structure can significantly increase the T_lum from 39.1 to 55.5%, an increase of nearly 16.4%, while the ΔT_sol is basically unchanged. The results provide an effective strategy for improving the performance of smart windows.