Photoelectric Properties Of Vanadium Dioxide Films Under Different Film Layers

In modern city,in order to improve daylighting factor and aesthetics,glass curtain wall area constitutes increasing gradually for buildings.To avoid the poor energy-saving and serious energy consumption problem of ordinary glass,energy-saving coating glass is used,of which the most common are low-e coating glass.However,optical spectrum of low-e coating glass is fixed,and the energy-saving effect is limited.Due to the infrared transmittance abrupt change in phase transition process,and the phase transition temperature is closing to room temperature,the VO₂ smart window has become one of hot research topics in recent years.In this thesis,to lower phase transition temperature,improve transmittance in visible range and solar infrared modulation ratio of VO₂ thin films,the influence of buffer layer,antireflective layer and sandwich structure on VO₂ photoelectric performance are researched.VO₂ thin films were fabricated by DC reactive magnetron sputtering on different buffer layers of 100 nm Al₂O₃ and TiO₂,respectively.All buffer layers were prepared by electron beam evaporation at room temperature.The results show that the buffer layers induced the crystallization of VO₂ phase,and enhanced photoelectric performance of the VO₂ thin films.Meanwhile,the phase transition temperatures of VO₂ films are reduced in some degree.The thin film prepared on TiO₂ buffer layer exhibits high microstructure and phase transition performance.The photoelectric properties of the VO₂ thin films grown on Ti pre-fabricated layers were studied.The results show that Ti pre-fabricated layers change the c-axis length of the VO₂ crystals,and the phase transition temperature of VO₂ thin films reduced as low as 45°C.Ti pre-fabricated layers oxidized into TiO₂ in VO₂ thin film deposition process for high temperature,which results in visible light transmittance improving due to interference effect between TiO₂ and VO₂ layers.High transparent MgF₂,Al₂O₃ and TiO₂ thin films were deposited on VO₂ thin films as antireflective layers,respectively.Experimental results show that thetransmittance in visible range and solar energy modulation ratio of the VO₂ thin films are significantly improved by adding the antireflective layer.Moreover,the performance of the VO₂ thin films with double antireflective layer is better than the single antireflective layer of the thin films.Among them,the transmittance waveform of the sample consisted of VO₂ / TiO₂ / Al₂O₃ is the most similar to ideal model.Calculation results reveal that the solar energy modulation ability is nearly 10% in full spectra,and nearly 35% in near infrared range,which exceed up to 13% compared to single VO₂ thin film.VO₂ thin films deposited on the MgF₂ bufferlayers with good crystallization.results show that MgF₂ films were decomposed and part of Mg²⁺ and F-doped into VO₂ in its growing process at high temperature,which caused phase transition temperature decreasing of the VO₂ thin films,blue shifting of absorb edges in the spectra,and enhancement of the visible transmittance.However,the solar energy modulation ability drops significantly in dense energy range from 750 nm to 1250 nm,which lead to decreasing of the solar energy modulation ability in full spectrum and in near infrared spectrum.Sandwich structure of MgF₂ / VO₂ / MgF₂ multilayer films was also investigated,which exhibits better visible transmittance and solar energy modulation ability than that of single VO₂ thin film or only MgF₂ buffer layer.The maximum transmittance is as high as 55% and the best energy modulation ability in full solar range and near infrared range,which is 7.64% and 27.46%,respectively.