Preparation Of Nano Vanadium Oxide And It's Application In Radiative Cooling

As a passive cooling method,radiative cooling is energy-saving and pollution-free.It is in line with the policy of green and sustainable development.It has been widely accepted as a new idea to effectively alleviate global warming.Recently,due to the significant changes in the optical parameters of the materials before and after the phase change,phase change materials such as VO₂ and GST have been tried to be used in the development of radiative cooling composite film to realize the intelligent radiative cooling function that can adjust its own radiation characteristics according to external excitations.In this paper,based on the principle of resonance absorption of the Fabry-Perot cavity,a transparent intelligent radiative cooling composite film based on VO₂ is designed and prepared.The radiative cooling composite film has good transmittance in the visible light band,and realizes the adjustment of the active radiative cooling performance in the infrared band.The research content and innovations of this article can be summarized as follows:(1)Focusing on the phase change characteristics of VO₂ film,the process of preparing ultra-thin VO₂ film on amorphous substrate based on DC magnetron sputtering method was explored and optimized.When the deposition temperature decreases and the annealing temperature increases,the content of V⁵⁺in the VO₂ film increases,thereby widening the optical band gap of the film,and the transmittance of the VO₂ film can be increased from 57.68%to 72.62%.Secondly,the high temperature transmittance peak of the ultra-thin VO₂ film in the visible light region is greater than the low temperature transmittance peak,which is consistent with the conclusions of the literature.In addition,the optical phase transition temperature(33°C-45°C)of the ultra-thin VO₂ film(thickness23nm)prepared under all process parameters is much lower than the theoretical 68°C.This is because the stress of the ultra-thin VO₂ film from the substrate is close to the complete state,causing the energy band to move,which makes the d_?energy band and the^*energy band more likely to coincide,and the electrons in the d_?energy band move Toward the^*energy band,weakening the correlation between the electrons in the original energy band,making the film more inclined to the metallic state at this time,resulting in a lower phase transition temperature.(2)Based on the principle of the resonance absorption of the Fabry-Perot cavity,a transparent intelligent radiative cooling composite film is designed.The radiative cooling composite film has good visible light transmittance,low emission in the low temperature state of the infrared band,and high emission under the high temperature state,thereby realizing the adjustment of the active radiative cooling performance.And through the simulation calculation,the influence mechanism of the thickness of the crucial films on the optical performance of the radiative cooling composite film is analyzed in detail.(3)With reference to the aforementioned simulation results,an intelligent radiative cooling composite film based on ultra-thin VO₂ film was prepared,and analyzed,characterized and tested for infrared emissivity.The results show that the emissivity of the prepared radiative cooling composite film changes obviously with the change of external temperature in the infrared band.Under the optimal film parameters,the emissivity modulation??of the radiative cooling composite film in the"atmospheric window"band(8-138))is as high as 0.714,which is the largest infrared emissivity modulation in the current research on the radiative cooling composite film based on VO₂film.At the same time,its visible light waveband transmittance(48.11%)also meets the lighting requirements of energy-saving glass(>40%).Finally,through calculation and analysis of its radiative power,it is found that the intelligent radiative cooling composite film exhibits the functional characteristics of absorbing solar energy at low temperature and radiating heat through the"atmospheric window"at high temperature during the day.