Surface And Interface Engineering For Improving The Optical Performances Of VO₂-based Thermochromic Smart Windows

As the by-production of economic growth and industrialization,he growing appetite for energy and increasingly environmental crime have become the global issues that attracted a great attention into development of approaches for energy saving and emission reduction.In our daily,life,energy consumption in buildings is inevitable and is responsible for 40%of total global energy consumption.As the function of heating and cooling,air-conditioner has become an indispensable domestic appliance to provide us with a comfortable environment.However,the use of air-conditioner accounts for near half of building’s energy consumption.Meanwhile,the windows,as the main pathway for energy exchange,are regarded as one of the most energy-inefficient components in buildings.Previously,scientists have developed some glass with passively improved thermal insulation performances,such as commercial insulating glass and low-E glass.In recent years,smart windows that can actively regulate the amount of transmitted heat in response to the ambient temperature change have received much attention.VO₂ undergoes an ultra-fast and reversible semiconductor-metal phase transition at ca.68°C,accompanied with dramatic change of infrared transmittance.VO₂ is highly transparent to infrared light when the ambient temperature is lower that its phase transition temperature,while its infrared transmittance significantly decreases at metallic phase.In this regard,VO₂thin films can intelligently regulate the amount of transmitted solar energy Superabundant solar radiation transmitted through the window would increase the indoor cooling load in summer,and high surface emissivity of the ordinary glazing would lead to significant heat loss in winter.Currently,the basic investigation in VO₂ thin films focuses on how to income the insufficient luminous transmittance and solar modulation efficiency.Noticeably,these two parameters are trade-off relationship.Improved luminous transmittance can be obtained at the expense of solar modulation efficiency,and vice versa.For the former one,antireflective methods could solve the problem to some extent.While the latter one has to be shoveled by plasmonic enhancement.In this work,based on the above idea,the simple and low process was used to modify the VO₂ thin films or nanoparticles.The VO₂ smart windows with antireflective,thermochromic and mechanical robustness.The research contents and corresponding results are summarized as follows:1.Bifunctional template-induced VO₂@SiO₂ dual-shell hollow nanospheres based coatings for smart windowsAn ingenious bifunctional template-induced approach for the synthesis of VO₂@SiO₂ dual-shell hollow nanospheres（DSHNs）and the preparation of DSHNs-based thermochromic coatings.Then the sequential mechanism for the formation of DSHNs was discussed.The corresponding smart coatings was prepared by dip-coating method.The VO₂@SiO₂DSHNs-based coating achieved enhanced luminous transmittance of61.8%and solar modulation efficiency of 12.6%as compared with that of bare VO₂ coatings(T_lum=42.5%,ΔT_sol=7.8%).Energy-saving tests also demonstrated that the as-prepared DSHNs-based coatings have desired solar energy-blocking ability.More importantly,the bifunctional template induced-method provided a new thought for the future investigation of VO₂-based core-shell structures.2.Rational design of HSNs/VO₂ bilayer coatings with enhanced optical performances and mechanical robustness for smart windowsIn the theoretical simulation,the luminous transmittance of the hybrid coating could be improved from 42.7%to 55.2%without sacrificing the solar modulation efficiency.Then glass substrate was dip-coated with hollow SiO₂ nanospheres and vanadium precursor sol,followed by annealing treatment.Experiments showed that the luminous transmittance was improved from 21.4%to 53.8%,which is agreed with the calculated results.Surprisingly,the solar modulation efficiency was improved from9.8%to 17.3%,much higher than the expected results.The analysis results of the morphology and optical spectra of as-prepared coatings demonstrated that the increased solar modulation efficiency could be attributed to the plasmonic enhancement.3.Three-layered hollow nanospheres based coatings with ultrahigh-performance of energy-saving,anti-reflection,and self-cleaning for smart windows.An ingenious SiO₂-TiO₂-VO₂ three-layered hollow nanospheres was designed and synthesized,which exhibited an excellent balance between luminous transmittance（74%）and solar modulation efficiency（12%）.Meanwhile,a new computation model was proposed,which allows to rapidly obtain the optical constants of nanostructured coatings.The experimental and simulated results indicated that the refractive of the hybrid thin films was reduced from 2.25 to 1.33,and the reflectance index in the visible region was reduced from 22.3%to 5.3%.The composite thin film also showed its natural energy saving,superhydrophilic and self-cleaning performances.