Rational design of HSNs/VO2 bilayer coatings with optimized optical performances and mechanical robustness for smart windows

For vanadium dioxide (VO 2 )-based smart windows, insufficient optical performances, including luminous transmittance ( T lum ) and solar modulation efficiency ( ΔT sol ), have always been the main problems hindering their practicality as energy-efficient windows, which have attracted numerous studies in recent years. However, the improved T lum are always obtained at the expense of ΔT sol , and vice versa. In this work, we report a controllable interfacial engineering strategy for the fabrication of multifunctional hollow SiO 2 nanospheres (HSNs)/VO 2 bilayer coatings with tunable optical performance and mechanical robustness on the basis of finite difference time domain (FDTD) calculation. The theoretical calculation predicted that the T lum of the bilayer coatings can be enhanced from 42.7% to 55.2% without sacrificing the ΔT sol . Surprisingly, experiments showed that not only the T lum of the optimized bilayer coating increased to 53.8% from 21.4%, but also the ΔT sol enhanced from 9.8% up to 17.2%. It is believed that the outstanding optical performance comes from the low refractive index of HSNs as well as good dispersibility of VO 2 nanoparticles . Moreover, the pencil hardness test , tap peeling test and sand impact abrasion test showed remarkable mechanical robustness of the bilayer coating, which makes it highly attractive for application in the windows of high-rise buildings.