Method for preparing m-phase vo2 film by photo-assisted spray pyrolysis and m-phase vo2 film prepared by the method

Abstract

The application provides a method for preparing an M-phase VO2 film by a light-assisted spray pyrolysis method and the M-phase VO2 film prepared by the method, and belongs to the field of nanometer materials. The method comprises the following steps: (1) preparing a vanadium dioxide spraying liquid: adding vanadium oxyacetonylacetone into anhydrous methanol, stirring and aging to obtain a vanadium dioxide spraying liquid with ultraviolet photosensitive properties; (2) preparing a vanadium dioxide film: introducing the vanadium dioxide spraying liquid in step (1) into an atomizer and spraying onto a substrate coated with a TiO2 anatase phase under ultraviolet light irradiation to obtain the M-phase VO2 film. The method enables vanadium ions to be chelated in the sol by stirring, and the vanadium dioxide spraying liquid has ultraviolet photosensitive properties. The purity of the VO2(M) film is improved by introducing a titanium dioxide transition layer, and the microstructure of the VO2(M) film is improved by ultraviolet light irradiation, thereby improving the visual transmittance and solar light regulation rate of the VO2(M) film.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials, specifically relating to a method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis and the M-phase VO2 thin films prepared by this method. Background Technology

[0002] Faced with the current severe problems of building energy consumption and energy shortages, experts point out that building energy conservation is the most promising and direct effective method among various energy-saving approaches. Among the various components of a building, windows are among the largest energy consumers because their heat transfer coefficient is much higher than that of walls. In recent years, intelligent energy-saving windows based on environmental stimulus responses have attracted researchers' interest, such as electrochromic, mechanochromic, photochromic, and thermochromic intelligent windows. Among them, intelligent windows based on vanadium dioxide (VO2, M phase) thermochromic thin films have broad application prospects.

[0003] Among current preparation methods, the complexity of VO2 thin film preparation processes, low production efficiency, and difficulty in scaling up are key issues hindering the development of smart windows. There are various methods for preparing VO2 thin films, such as magnetron sputtering, electron beam evaporation, pulsed laser deposition, and the sol-gel method. Among these, physical deposition processes like magnetron sputtering, vacuum evaporation, and pulsed laser deposition involve expensive equipment, resulting in high film production costs and unsuitability for large-area film deposition. While the sol-gel method has relatively lower costs, its limitations in the coating process make it difficult to achieve large-scale production. Furthermore, another approach for smart window applications involves first preparing vanadium dioxide powder, then coating it onto the glass surface with an organic adhesive, followed by drying to obtain vanadium dioxide coated glass. This method has complex process steps, and the thick coating affects transmittance, while the coating adhesion is relatively poor. Therefore, developing a simple, efficient, and easily scalable VO2(M) thin film deposition method is of great significance for the industrialization of smart windows.

[0004] Spray pyrolysis technology combines the advantages of both gas-phase and liquid-phase methods, featuring simple processes, short preparation cycles, the ability to achieve large-area film formation, and high adhesion between the film and the substrate. However, traditional spray pyrolysis technology results in large-particle VO2 films with uneven size distribution, sometimes making it difficult to obtain a dense film structure, and can also lead to the mixed growth of M-phase and B-phase VO2. VO2 has various allotropes, such as VO2(M), VO2(A), VO2(B), VO2(C), VO2(D), and VO2(R), among which only VO2(M) possesses near-room-temperature thermochromic properties, which can be used for energy-saving applications in smart windows. When VO2(M) contains other VO2 phases, its thermochromic properties are significantly reduced. Therefore, obtaining a single-phase VO2(M) is a crucial prerequisite for realizing smart window applications.

[0005] Existing reports frequently mention the use of spray pyrolysis to prepare vanadium dioxide powder, but the conditions described are not directly applicable to thin film preparation. While a patent (application number 201610147983.0) involves the preparation of VO2(M) nanopowder and thin films using spray pyrolysis, the raw materials and process parameters differ from this invention. Furthermore, the patent's accompanying drawings primarily depict the powder and do not report the phase structure and thermochromic properties of the VO2 thin film, which are crucial for smart window applications. Additionally, a patent (application number 201610408843.4) describes a method for preparing VO2 multilayer films using sputtering, which involves expensive equipment and a complex process, requiring the preparation of auxiliary layers such as seed layers and buffer layers before the VO2 thin film can be manufactured. In conclusion, given the current technological conditions, achieving simple, efficient, and large-scale preparation of VO2(M) thin films for smart windows remains challenging.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing VO2(M) thin films by photo-assisted spray pyrolysis.

[0008] The technical solution of the present invention is as follows:

[0009] This invention provides a method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, comprising the following steps:

[0010] (1) Preparation of vanadium dioxide spray solution: Add vanadium acetylacetonate to anhydrous methanol, stir and age to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties;

[0011] (2) Preparation of vanadium dioxide thin film: The vanadium dioxide spray liquid from step (1) is introduced into the atomizer and sprayed onto the substrate coated with anatase phase TiO2 under ultraviolet irradiation to obtain M phase VO2 thin film.

[0012] In this invention, anhydrous methanol is used as the solvent. On the one hand, vanadium acetylacetonate dissolves well in anhydrous methanol; on the other hand, after vanadium acetylacetonate dissolves in anhydrous methanol, stirring allows vanadium ions to chelate in the sol, forming a stable ring structure that exhibits ultraviolet photosensitive properties. The purity of the VO2(M) film is improved by introducing a titanium dioxide transition layer, and the microstructure of the VO2(M) film is further improved by ultraviolet irradiation, thereby enhancing its visible transmittance and solar modulation efficiency.

[0013] In one specific embodiment, the specific steps of stirring and aging in step (1) are as follows: stirring at room temperature for 4~8 h under light-proof conditions, and then aging for 24~72 h; preferably, filtration is required before aging.

[0014] In one specific embodiment, in step (1), the concentration of vanadium dioxide spray solution is controlled at 0.01~0.10 mol / L.

[0015] In this invention, the concentration of the vanadium dioxide spray solution is controlled at 0.01~0.10 mol / L. If the concentration of the vanadium dioxide spray solution is too low, the film formation rate will be too slow; if the concentration is too high, the atomization efficiency will decrease, and the uniformity of the film will also deteriorate.

[0016] In one specific embodiment, in step (2), the ultraviolet radiation is preferably an ultraviolet irradiation lamp; more preferably, a high-pressure mercury lamp, wherein the main wavelength of the ultraviolet irradiation lamp is 365 nm and the power density is 50~200 mW / cm². 2 .

[0017] In this invention, the ultraviolet absorption peak of the vanadium dioxide spray liquid is above 300nm, and the main wavelength of the ultraviolet irradiation lamp is controlled at 365nm, which can effectively absorb the vanadium dioxide spray liquid.

[0018] In one specific embodiment, the ultraviolet irradiation lamp is fixed next to the atomizer and moves synchronously with the atomizer.

[0019] In one specific embodiment, in step (2), the compressed air flow rate of the atomizer is 5-15 L / min; the atomizer moves along the X / Y direction of the plane where the substrate is located, with a moving speed of 15-120 mm / s in the X direction and a moving speed of 0.5-5 mm / s in the Y direction.

[0020] In this invention, the moving speed in the X and Y directions directly affects the coating effect of vanadium dioxide spray liquid on the substrate. Too fast or too slow a moving speed in the X and Y directions may result in the vanadium dioxide spray liquid not adequately covering the entire substrate plane during the spraying process. Through repeated exploration, the applicant discovered that controlling the moving speed in the X direction to 15~120 mm / s and the moving speed in the Y direction to 0.5~5 mm / s achieves a better coating effect for the vanadium dioxide spray liquid on the substrate.

[0021] In one specific embodiment, in step (2), the distance between the end of the atomizer nozzle and the substrate is 30~70 mm.

[0022] In this invention, the distance between the end of the atomizer nozzle and the substrate is 30~70 mm. If the spraying distance is too small, the deposition rate is too fast and the film is uneven; if the spraying distance is too large, more mist will be lost and the deposition rate will be too slow.

[0023] In one specific embodiment, in step (2), the number of sprayed layers is 1 to 10.

[0024] In this invention, the number of coating layers is 1 to 10. When the number of coating layers reaches 10, the visible transmittance of the VO2 film is already very low. If the thickness is further increased, it will not be of much significance for the application of smart windows. Generally, the more coating layers there are, the thicker the film is, the lower the visible transmittance is, but the higher the sunlight modulation rate is, and vice versa.

[0025] In one specific embodiment, in step (2), the substrate is one of a glass substrate, a silicon wafer or a ceramic substrate; the temperature of the substrate is 420~480℃; and the thickness of the anatase phase TiO2 is 60-90nm.

[0026] In this invention, the substrate temperature is controlled at 420~480℃. 420~480℃ is the growth window for the M-phase VO2. If the temperature is too high or too low, impurity phases will be generated, such as the B-phase VO2, sodium vanadium oxide, or even other valence state vanadium oxides. The thickness of the anatase phase TiO2 is 60-90nm. If the anatase phase TiO2 is too thick, it will affect the visible transmittance of the film; if the anatase phase TiO2 is too thin, it cannot effectively block the diffusion of substrate ions, such as sodium ions in the glass substrate, which can easily diffuse into the film.

[0027] The present invention also provides an M-phase VO2 thin film prepared according to the above method.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. VO2 has various crystal structures, such as VO2(M), VO2(A), VO2(B), VO2(C), and VO2(R), but only VO2(M) exhibits thermochromic properties and can be used as a smart window. However, conventional spray pyrolysis methods for preparing VO2(M) often contain the VO2(B) phase, which significantly affects the film performance. The present invention involves spraying anatase-structured titanium dioxide onto a substrate, using this anatase-structured titanium dioxide as a transition layer to deposit a VO2(M) film. The presence of this transition layer in the anatase-structured titanium dioxide film both blocks the diffusion of ions from the substrate and alters the substrate surface state, inhibiting the growth of VO2(B) and achieving the preparation of a single-phase VO2(M) film.

[0030] 2. Applying ultraviolet (UV) irradiation during spray pyrolysis has two main effects. First, the absorption and activation of UV light by the photosensitive groups in the vanadium dioxide microdroplets promotes the decomposition of organic components in the droplets, improves the uniformity of VO2 film grain distribution, and reduces the generation of abnormal particles. Second, the surface free energy of the TiO2 transition layer increases under UV irradiation, enhancing the adsorption of VO2 microdroplets and improving the microstructure of VO2 to some extent, ultimately increasing its visible transmittance and solar modulation efficiency.

[0031] 3. In this invention, VO2(M) films can be obtained by direct spraying without the need for subsequent heat treatment, which greatly shortens the preparation cycle of VO2(M) films. Attached Figure Description

[0032] Figure 1 This is the X-ray diffraction pattern of the VO2(M) thin film prepared in Example 1 of the present invention;

[0033] Figure 2 This is a transmittance curve of the VO2(M) thin film prepared by the method in Example 2 of the present invention;

[0034] Figure 3 The X-ray diffraction pattern of the VO2 thin film prepared in Comparative Example 1 is shown below.

[0035] Figure 4 This is the X-ray diffraction pattern of the VO2 thin film prepared in Comparative Example 2. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] The following examples calculate the visible transmittance and solar susceptibility using the following formulas (1) to (3).

[0038] (1)

[0039] (2)

[0040] (3)

[0041] In the formula, T ( λ ) is the thin film at wavelength λ Transmittance at that location lum ( λ ) is the human visual acuity function. sol ( λ The solar radiation spectrum is given when the atmospheric mass is 1.5 and the solar altitude angle is 37°. T lum Δ represents the visible transmittance. T sol This refers to the solar moderating rate.

[0042] Example 1

[0043] This embodiment provides a method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, including the following steps:

[0044] (1) Preparation of vanadium dioxide spray solution: 1.6 g of vanadium acetylacetonate was added to 60 mL of anhydrous methanol, stirred at room temperature in the dark for 8 h, filtered and aged for 50 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.1 mol / L.

[0045] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a soda-lime glass substrate coated with anatase TiO2 (approximately 90 nm) under ultraviolet radiation lamp conditions to obtain VO2(M) thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: substrate temperature 480℃, compressed air flow rate of the atomizer 10 L / min, distance between the nozzle end of the atomizer and the substrate 60 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 50 mm / s and 5 mm / s respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm and the power density is approximately 60 mW / cm². 2 Ten layers were sprayed across the entire substrate plane, with a thickness of approximately 140 nm.

[0046] X-ray diffraction tests were performed on the VO2(M) thin film prepared in this embodiment. The X-ray diffraction pattern is shown below. Figure 1 As shown. By Figure 1 It can be seen that, apart from the diffraction peak of the TiO2 transition layer, only the VO2(M) diffraction peak appeared, and no VO2(B) or other impurity diffraction peaks were detected. The VO2(M) thin film prepared in this embodiment has a single phase and no impurity phase.

[0047] The transmittance of the VO2(M) film prepared in this embodiment was tested, and the visible transmittance was 26% and the solar light modulation rate was 13%.

[0048] Example 2

[0049] This embodiment provides a method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, including the following steps:

[0050] (1) Preparation of vanadium dioxide spray solution: 1.0g of vanadium acetylacetonate was added to 75 mL of anhydrous methanol, stirred at room temperature in the dark for 6 h, filtered and aged for 36 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.05mol / L.

[0051] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a soda-lime glass substrate coated with anatase TiO2 (approximately 60 nm) under ultraviolet radiation lamp conditions to obtain VO2(M) thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: substrate temperature 450℃, compressed air flow rate of the atomizer 8L / min, distance between the nozzle end of the atomizer and the substrate 45 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 20 mm / s and 2 mm / s respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm and the power density is approximately 90 mW / cm². 2 The substrate is coated with three layers, each approximately 90 nm thick.

[0052] X-ray diffraction tests were performed on the VO2(M) thin film prepared in this embodiment, and it was found that the VO2(M) thin film had a single phase and no impurities.

[0053] The transmittance of the VO2(M) thin film prepared in this embodiment was measured, and the transmittance curve is shown in the figure below. Figure 2 As shown. According to Figure 2 The transmittance curve is used to calculate the visible transmittance of the VO2(M) film prepared by the method of the present invention using the above formulas (1) to (3). T lum The solar moderating efficiency is 41%, Δ T sol The rate is 6%, which is higher than the solar modulation rate of a single-layer VO2(M) thin film (approximately 4%).

[0054] Example 3

[0055] This embodiment provides a method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, including the following steps:

[0056] (1) Preparation of vanadium dioxide spray solution: 0.4 g of vanadium acetylacetonate was added to 150 mL of anhydrous methanol, stirred at room temperature in the dark for 4 h, filtered and aged for 72 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.01 mol / L.

[0057] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a sapphire wafer coated with anatase phase TiO2 (approximately 60 nm) under ultraviolet radiation lamp conditions to obtain VO2(M) thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: the temperature of the sapphire wafer is 420℃, the compressed air flow rate of the atomizer is 5 L / min, the distance between the nozzle end of the atomizer and the sapphire wafer is 30 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 15 mm / s and 0.5 mm / s, respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm, and the power density is approximately 200 mW / cm². 2 The substrate is coated with one layer, which is approximately 30 nm thick.

[0058] X-ray diffraction tests were performed on the VO2(M) thin film prepared in this embodiment, and it was found that the VO2(M) thin film had a single phase and no impurities.

[0059] The transmittance of the VO2(M) film prepared in this embodiment was tested, and the visible transmittance was 70% and the solar light modulation rate was 3%.

[0060] Example 4

[0061] This embodiment provides a method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, including the following steps:

[0062] (1) Preparation of vanadium dioxide spray solution: 1.0g of vanadium acetylacetonate was added to 60 mL of anhydrous methanol, stirred at room temperature in the dark for 6 h, filtered and aged for 24 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.05mol / L.

[0063] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a soda-lime glass substrate coated with anatase phase TiO2 (approximately 60 nm) under ultraviolet radiation lamp conditions to obtain VO2(M) thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: substrate temperature 450℃, compressed air flow rate of the atomizer 15 L / min, distance between the nozzle end of the atomizer and the substrate 70 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 120 mm / s and 5 mm / s respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm and the power density is approximately 50 mW / cm². 2 Five layers are sprayed across the entire substrate plane, with a thickness of approximately 50 nm.

[0064] X-ray diffraction tests were performed on the VO2(M) thin film prepared in this embodiment, and it was found that the VO2(M) thin film had a single phase and no impurities.

[0065] The transmittance of the VO2(M) film prepared in this embodiment was tested, and the visible transmittance was 65% and the solar light modulation rate was 4%.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing VO2 thin films by light-assisted spray pyrolysis, comprising the following steps:

[0068] (1) Preparation of vanadium dioxide spray solution: 1.6 g of vanadium acetylacetonate was added to 60 mL of anhydrous methanol, stirred at room temperature in the dark for 8 h, filtered and aged for 50 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.1 mol / L.

[0069] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a soda-lime glass substrate without any transition layer under ultraviolet radiation lamp conditions to obtain a VO2 thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: substrate temperature 480℃, compressed air flow rate of the atomizer 10 L / min, distance between the nozzle end of the atomizer and the substrate 60 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 50 mm / s and 5 mm / s respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm and the power density is about 60 mW / cm². 2 Ten layers were sprayed across the entire substrate plane, with a thickness of approximately 140 nm.

[0070] X-ray diffraction tests were performed on the VO2 thin film prepared in this comparative example. The X-ray diffraction pattern is shown below. Figure 3 As shown. By Figure 3 It can be seen that the thin film phases obtained in this comparative example are VO2(B) and NaV6O. 15 When there is no transition layer, the Na in the glass substrate during the spraying process... + It diffuses into the thin film to form NaV6O. 15 The VO2(B) phase is obtained, but the VO2(M) phase cannot be obtained.

[0071] The transmittance of the VO2 film prepared in this comparative example was tested, and the visible transmittance was 24% and the solar light modulus was 0.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing VO2 thin films by light-assisted spray pyrolysis, comprising the following steps:

[0074] (1) Preparation of vanadium dioxide spray solution: 1.6 g of vanadium acetylacetonate was added to 60 mL of anhydrous methanol, stirred at room temperature in the dark for 8 h, filtered and aged for 50 h to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties, with a concentration of 0.1 mol / L.

[0075] (2) Preparation of vanadium dioxide thin film: Vanadium dioxide spraying liquid is loaded into an atomizer and sprayed onto a soda-lime glass substrate with a SiO2 transition layer (approximately 90 nm) under ultraviolet radiation lamp conditions to obtain a VO2 thin film. The ultraviolet radiation lamp is fixed next to the atomizer. The spraying parameters are set as follows: substrate temperature 480℃, compressed air flow rate of the atomizer 10 L / min, distance between the nozzle end of the atomizer and the substrate 60 mm, the atomizer moves along the XY direction of the plane where the substrate is located at speeds of 50 mm / s and 5 mm / s respectively, the main wavelength of the ultraviolet radiation lamp is 365 nm and the power density is approximately 60 mW / cm². 2 Ten layers were sprayed across the entire substrate plane, with a thickness of approximately 140 nm.

[0076] X-ray diffraction tests were performed on the VO2 thin film prepared in this comparative example. The X-ray diffraction pattern is shown below. Figure 4 As shown. By Figure 4 It can be seen that the thin film phases obtained in this comparative example are VO2(B) and VO2(M). The mass fraction of the VO2(M) phase was estimated to be approximately 8% by fitting using Jade software.

[0077] The transmittance of the VO2 film prepared in this comparative example was tested, and the visible transmittance was 23% and the solar light modulation rate was 1%.

[0078] Table 1. Comparison of substrate, visible transmittance, and solar modulation between the examples and comparative examples.

[0079]

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing M-phase VO2 thin films by light-assisted spray pyrolysis, characterized in that, Includes the following steps: (1) Preparation of vanadium dioxide spray solution: Add vanadium acetylacetonate to anhydrous methanol, stir and age to obtain vanadium dioxide spray solution with ultraviolet photosensitive properties. (2) Preparation of vanadium dioxide thin film: The vanadium dioxide spray liquid from step (1) is introduced into the atomizer and sprayed onto the substrate coated with anatase phase TiO2 under ultraviolet light irradiation to obtain M phase VO2 thin film. The substrate is one of glass, silicon, or ceramic; the substrate temperature is 420–480℃; and the thickness of the anatase TiO2 phase is 60–90 nm.

2. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1, characterized in that, In step (1), the specific steps of stirring and aging are as follows: stirring at room temperature for 4 to 8 hours under light-proof conditions, and then aging for 24 to 72 hours.

3. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 2, characterized in that, It needs to be filtered before aging.

4. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1, characterized in that, In step (1), the concentration of vanadium dioxide spray solution is controlled at 0.01 to 0.10 mol / L.

5. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1, characterized in that, In step (2), ultraviolet radiation is carried out using an ultraviolet irradiation lamp.

6. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 5, characterized in that, The ultraviolet irradiation lamp has a main wavelength of 365nm and a power density of 50–200mW / cm². 2 .

7. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 5, characterized in that, The ultraviolet irradiation lamp is fixed next to the atomizer and moves synchronously with the atomizer.

8. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1 or 7, characterized in that, In step (2), the compressed air flow rate of the atomizer is 5-15 L / min; the atomizer moves along the X / Y direction of the plane where the substrate is located, with a moving speed of 15-120 mm / s in the X direction and a moving speed of 0.5-5 mm / s in the Y direction.

9. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1, characterized in that, In step (2), the distance between the end of the atomizer nozzle and the substrate is 30-70 mm.

10. The method for preparing M-phase VO2 thin films by photo-assisted spray pyrolysis according to claim 1, characterized in that, In step (2), the number of sprayed layers is 1 to 10.

11. The M-phase VO2 thin film prepared by the method according to any one of claims 1-10.

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