TWI405827B - Tungsten oxide film for smart window - Google Patents

Abstract

A tungsten oxide film for a smart window. The tungsten oxide film is formed by a method including following steps. A coating material including a first precursor, a fuel, and a solvent is prepared. The first precursor includes tungsten powder, tungsten nitrate, tungsten sulfate, tungsten acetate, or a combination thereof. The fuel includes thiourea, urea, glycine, citric acid, or a combination thereof. The solvent includes water, hydrogen peroxide, ethyl alcohol, or a combination thereof. A coating layer is formed by applying the coating material onto a substrate. A tungsten oxide film is formed by annealing the coating layer.

Description

Tungsten oxide film for smart windows

This invention relates to an oxide film, and more particularly to a metal oxide film.

Oxide films have been widely used in traditional industries, semiconductor processes, and optoelectronics industries. At present, the preparation method of the oxide film can be roughly classified into a gas phase method and a solution method. However, gas phase processes such as evaporation or sputtering preparation methods require the use of expensive equipment, the speed of vacuum evacuation of the vacuum system limits the process speed, and the size of the reaction chamber also makes the process difficult to enlarge.

Solution methods such as gels or other aqueous solution preparation methods have problems in that the process is cumbersome and time-consuming and the characteristics of the oxide film are not easily controlled. For example, an aqueous solution for preparing a tungsten oxide film is firstly stirred with tungsten water and hydrogen peroxide for 6 hours to uniformly mix and remove excess hydrogen peroxide, then acetic acid is added to the solution and refluxed for 12 hours, and then the solution is evacuated to remove The solvent, followed by the addition of the surfactant to the solution, was stirred for about 1 hour, and then the impurities in the solution were centrifuged to leave a clear liquid, and then the resulting clear liquid was coated on a substrate and subjected to a heating step to obtain a tungsten oxide film. In addition, the process steps of the general solution method need to be precisely controlled to be reproducible. Otherwise, the process parameters are slightly inaccurate, for example, the time of stirring of the solution is different or the time of solution placement is different, and an oxide film of the same nature cannot be obtained.

Embodiments of the present invention provide a tungsten oxide film for use in a smart window. The method of forming the tungsten oxide film includes the following steps. Prepare the coating. The coating includes a first precursor, a fuel, and a solvent. The first precursor comprises tungsten powder, tungsten nitrate, tungsten sulfate, tungsten acetate or a combination thereof. The fuel includes thiourea, urea, glycine, citric acid or a combination of the above. The solvent includes water, hydrogen peroxide, alcohol, or a combination thereof. A coating is applied to the substrate to form a coating. An annealing step is performed to make the coating into a tungsten oxide film.

Embodiments of the present invention provide an oxide film and a method of forming the same. In an embodiment, the oxide film may include a metal oxide, and the metal may include, for example, tungsten, nickel, titanium, zinc, copper, silver, or a combination thereof.

The method of forming an oxide film includes the following steps. A coating is prepared that includes a first precursor, a fuel, and a solvent. A coating is applied to the substrate to form a coating. An annealing step is performed to cause the coating to become an oxide film. The method for forming an oxide film according to an embodiment of the present invention is simple, rapid, and reproducible. The method of forming the oxide film does not require the use of expensive or complicated equipment, and thus the cost is low. In addition, it can be applied to a large-area substrate. The morphology and properties of the oxide film can be controlled by the parameters of the modulation process.

The fuel includes thiourea, urea, glycine, citric acid or a combination of the above. The fuel releases thermal energy or gas during the preparation of the coating or during the annealing step, and thus the method of the embodiment of the present invention can form an oxide film at a lower annealing temperature or have a hole in the oxide film.

The solvent includes water, hydrogen peroxide, alcohol, or a combination thereof.

The first precursor includes a first metal powder, a first metal nitrate, a first metal sulfate, a first metal acetate, or a combination thereof, wherein the first metal may include, for example, tungsten, nickel, titanium, zinc, copper, silver Or a combination of the above. For example, in some embodiments, a nickel oxide film is formed, wherein the first precursor used can include nickel powder, nickel nitrate, nickel sulfate, nickel acetate, or a combination thereof. In some embodiments, a tungsten oxide film is formed, wherein the use of the first precursor can include, for example, tungsten powder, tungsten nitrate, tungsten sulfate, tungsten acetate, or a combination thereof.

The substrate may comprise glass or a transparent conductive oxide such as indium tin oxide (ITO), tin oxide fluoride (FTO), or the like.

The weight of the first precursor: the weight of the fuel can be 1:0.02-22. For example, in some embodiments a nickel oxide film is formed wherein the weight of the first precursor used: the weight of the fuel can be from 1:0.1 to 1.64. In some embodiments, a tungsten oxide film is formed wherein the weight of the first precursor used: the weight of the fuel can be from 1:0.3 to 2.24.

Fuel weight: The weight of the solvent can be 1:0.01~100. For example, in some embodiments in which a nickel oxide film is formed, the weight of the fuel: the weight of the solvent is 1:9 to 60. In some embodiments in which a tungsten oxide film is formed, the weight of the fuel: the weight of the solvent may be 1:0.03-40.

In an embodiment, the coating may further comprise a second doped precursor. The second doped precursor can, for example, comprise a second metal powder, a second metal nitrate, a second metal sulfate, a second metal acetate, or a combination thereof. The second metal includes tungsten, nickel, titanium, zinc, copper, silver or a combination thereof. The second metal is different from the first metal. The weight of the first precursor: the weight of the second doped precursor is 1: 0.001 to 0.1. A doped metal oxide film such as a doped nickel oxide film or a doped tungsten oxide film or the like can be formed using a coating comprising a second doped precursor.

In an embodiment, the method of preparing the coating is to place a material such as a first precursor, a fuel and a solvent (and a second precursor) in a container and stir to uniformly mix. The time taken from the time the materials are placed together to the time of mixing and mixing well can be less than one hour. In some embodiments, the coating can be obtained in as little as about 5 minutes. Therefore, the method of forming the oxide film is fast. In addition, the coating has excellent stability, and the prepared coating can exhibit reproducibility even after standing for a long period of time, for example, over a period of more than 24 hours.

In an embodiment, the annealing step may have a temperature of from 300 ° C to 550 ° C. For example, in some embodiments in which a nickel oxide film is formed, the temperature of the annealing step may be, for example, 350 ° C to 450 ° C. In some embodiments in which a tungsten oxide film is formed, the temperature of the annealing step may be, for example, 300 ° C to 550 ° C.

In an embodiment, the annealing step may take from 10 minutes to 6 hours, preferably from 10 minutes to 60 minutes.

Tungsten oxide film

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, the weight of the first precursor: the weight of the fuel is 1:0.4-2, the weight of the fuel: the weight of the solvent is 1 : 15~25, the annealing step temperature is 425 ° C to 550 ° C, and the annealing step is 10 minutes to 60 minutes, the tungsten oxide film is a cracked tungsten oxide film.

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, the weight of the first precursor: the weight of the fuel is 1:0.2 to 0.4, and the weight of the fuel: the weight of the solvent is 1 : 15 to 25, the annealing step is performed at a temperature of 425 ° C to 550 ° C, and the annealing step is performed for 10 minutes to 60 minutes, the tungsten oxide film is a tungsten oxide film having pores, or the tungsten oxide film has a crystal phase.

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, the weight of the first precursor: the weight of the fuel is 1:0.2 to 0.4, and the weight of the fuel: the weight of the solvent is 1 : 15~25, the annealing step temperature is 300 ° C to 425 ° C, and the annealing step is 10 minutes to 60 minutes, the tungsten oxide film is a flat tungsten oxide film, or the tungsten oxide film has an amorphous phase.

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is urea, the weight of the first precursor: the weight of the fuel is 1:0.2 to 0.4, and the weight of the fuel: the weight of the solvent is 1:15. ~25, the annealing step temperature is 425 ° C to 550 ° C, and the annealing step is 10 minutes to 60 minutes, the tungsten oxide film is a flat tungsten oxide film.

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is glycine, the weight of the first precursor: the weight of the fuel is 1:0.2 to 0.4, and the weight of the fuel: the weight of the solvent is 1 : 15 to 25, the annealing step is performed at a temperature of 425 ° C to 550 ° C, and the annealing step is performed for 10 minutes to 60 minutes, and the tungsten oxide film is a tungsten oxide film having pores.

In some embodiments, when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is citric acid, the weight of the first precursor: the weight of the fuel is 1:0.2 to 0.4, and the weight of the fuel: the weight of the solvent is 1 : 15 to 25, the annealing step is performed at a temperature of 425 ° C to 550 ° C, and the annealing step is performed for 10 minutes to 60 minutes, and the tungsten oxide film is a tungsten oxide film having pores.

The tungsten oxide film of the embodiment of the invention has excellent electrochromic properties and is suitable for various electrochromic components such as smart windows, electrochromic glass, color changing sunglasses, color changing automobile rearview mirrors, display billboards, Electronic paper displays and the like can also be applied to industries such as solar cells and semiconductors. Specific examples of forming a tungsten oxide film are exemplified below, and the analysis results of the tungsten oxide film are explained.

Example 1

The method of forming the tungsten oxide film includes the following steps. First, 1.5 g of tungsten powder (Merk) was dissolved in 9 ml, 30% hydrogen peroxide (Sigma-Aldrich) and 1 ml of deionized water (volume of hydrogen peroxide: volume of water: 9:1), and then 0.45 g of thiourea (Sigma). The above solution was added (weight of tungsten powder: weight of water plus hydrogen peroxide: weight of thiourea 1:6:0.3), and then the solution was stirred until the solvent was volatilized to a weight of 4.5 g of the solution, thereby obtaining a coating. The coating was spin-coated on an ITO or FTO substrate (ITO coated glass or FTO coated glass (Solarnix: sheet resistance: 8 Ω/sq)) to form a coating. Then, the substrate is subjected to an annealing step to change the coating into a tungsten oxide film, wherein the heating parameter sets the first heating rate to rise from room temperature to 350 ° C / 10 minutes; the second heating rate is from 350 ° C to 450 ° C /5 minutes; constant temperature heating conditions were maintained at 450 ° C for 30 minutes; and cooled to room temperature.

From the results of a scanning electron microscope (SEM) (JEOL JSM-6700 or JSM-7000) (Attachment 1), the tungsten oxide film of Example 1 (formed on the FTO substrate) was a film having pores.

Example 2

The tungsten oxide film was formed in a similar manner to Example 1, in which thiourea was replaced by urea. The analysis result of SEM (Attachment 2) showed that the tungsten oxide film of Example 2 was a flat film.

Example 3

The tungsten oxide film was formed in a similar manner to Example 1, in which thiourea was replaced by glycine. The analysis result of SEM (Attachment 3) shows that the tungsten oxide film of Example 3 is a film having pores.

Example 4

The tungsten oxide film was formed in a similar manner to Example 1, in which thiourea was replaced by citric acid. The analysis result of SEM (Attachment 4) shows that the tungsten oxide film of Example 4 is a film having pores.

Example 5

The tungsten oxide film was formed in a similar manner to Example 1, in which the weight of the tungsten powder: the weight of water plus hydrogen peroxide: the weight of the thiourea was changed to 1:6:0.81. The analysis result of SEM (Attachment 5) shows that the tungsten oxide film of Example 5 is a film having cracks.

Example 6

The tungsten oxide film was formed in a similar manner to Example 1, in which the weight of the tungsten powder: the weight of water plus hydrogen peroxide: the weight of the thiourea was changed to 1:6:0.4. The analysis result of SEM (Attachment 6) shows that the tungsten oxide film of Example 6 is a film having pores.

Example 7

The method for forming the tungsten oxide film is similar to that of the first embodiment, wherein the temperature of the annealing step is changed to 400 ° C, that is, the parameter is set to a first heating rate from room temperature to 350 ° C / 10 minutes; the second heating rate is The temperature was raised from 350 ° C to 400 ° C / 5 minutes; the constant temperature heating condition was maintained at 400 ° C for 30 minutes; and the temperature was lowered to room temperature. The analysis result of SEM (Attachment 7) showed that the tungsten oxide film of Example 7 was a flat film.

Example 8

The method of forming the tungsten oxide film was similar to that of Example 1, in which the temperature of the annealing step was changed to 500 °C. The analysis result of SEM (Attachment 8) shows that the tungsten oxide film of Example 8 is a film having pores.

Comparative example

The tungsten oxide film was formed in a similar manner to Example 1, in which thiourea was not added to the coating. The SEM analysis results (Annex 9) show that the tungsten oxide film of the comparative example is a flat film.

Structural properties analysis of thin films

Fig. 1 shows diffraction data of monoclinic tungsten oxide (WO ₃ ) (ICDD-PDF No. 01-072-0677), and test pieces of ITO substrate, Example 1, Example 7 and Comparative Example ( An X-ray diffraction (XRD) (Rigaku DMAX-2000/PC) pattern of a tungsten oxide film formed on an ITO substrate. Fig. 2 shows a Raman (JEOL JEM-2100F) pattern of the test pieces of Example 1, Example 7 and Comparative Example.

As is apparent from Fig. 1, the tungsten oxide thin films of Example 1 and Comparative Example have a polycrystalline structure and contain a monoclinic phase tungsten oxide thin film. The test piece of Example 7 showed only the peak of the ITO substrate. It can be seen from Fig. 2 that the scattering peaks of the Raman spectra at 805 cm ^-1 , 714 cm ^-1 , 327 cm ^-1 and 272 cm ^-1 verify that the tungsten oxide films of Example 1 and Comparative Examples contain monoclinic crystals. phase. Compared with the Raman spectra of Example 1 and Comparative Example, the Raman spectrum of the sample of Example 7 was weaker and wider at positions of 805 cm ^-1 and 714 cm ^-1 .

The test piece of Example 7 was also analyzed by TEM (Attachment 10). The results of the selected area electron diffraction (SAED) pattern showed that the test piece of Example 7 did not have a well-ordered crystalline structure, which was consistent with the results of the XRD pattern and the Raman spectrum. . Bright-field image (BFI), dark-field image (DFI) and high-resolution transmission electron microscope (HRTEM) images show that the oxide film of Example 7 contains nanocrystal oxidation. A nanocrystalline tungsten oxide having an average diameter of about 5 nm and buried in an amorphous tungsten oxide matrix. In addition, the d-spacing is about 0.37~0.38nm from both the SAED pattern and the HRTEM image.

Thin film optical properties analysis

The optical properties of the test piece can be performed using a three-electrode system, an electrochromic (EC) device (two-electrode system), and an ultraviolet-visible near-infrared light spectrometer (US-VIS-NIR spectrophotometer) (JASCO). V-670) for analysis.

The three-pole system uses a potentiostat (Autolab, PGSTAT302N), and the electrolyte is a 1M lithium perchlorate (LiClO ₄ ) (Sigma-Aldrich) solution in which the solvent is propylene carbonate (PC). ) (Alfa Aesar). A test piece (a tungsten oxide film was formed on the FTO substrate), a Pt line, and an Ag/AgCl system were used as a working electrode, a counter electrode, and a reference electrode, respectively.

The electrochromic device is provided with a 60 μm thick hot-melt resin between an ITO counter electrode and a test piece (a tungsten oxide film is formed on the FTO substrate, and the tungsten oxide film is oriented toward the ITO opposite electrode). Separate spacers (Solaronix, SA) were separated from each other, and the LiClO ₄ /PC electrolyte was introduced into the space between the test piece and the opposite electrode of the ITO by capillary action.

In a three-pole system or electrochromic device, when a negative bias is applied to the test piece, Li ions in the electrolyte are embedded in a transparent tungsten oxide (WO ₃ ) film (Attachment 11) to become colored oxide. A tungsten (Li _x WO ₃ ) film (Attachment 12), as shown in the following chemical equation:

When a positive bias is applied to the test piece, Li ions are removed from the tungsten oxide film, causing the colored tungsten oxide film to fade.

Fig. 3, Fig. 4, and Fig. 5 show the light transmittance and transmittance of the test pieces of Example 1, Example 7, and Comparative Example, respectively. The "initial preparation" in the figure indicates the light transmittance curve of the initially prepared test piece. The "color state" indicates the light transmittance curve of the tungsten oxide film of the initially prepared test piece after discoloration by a three-pole system. The "faded state" represents the light transmittance curve of a colored tungsten oxide film after fading by a three-pole system. "Transmittance change" means the result of the "faded state" curve after the "color state" curve is deducted.

Referring to FIGS. 3 to 5, the transmittance of visible light of the test pieces initially prepared in Example 1, Example 7 and Comparative Example was about 80%.

Referring to FIGS. 3 to 5, after the tungsten oxide film of the initially prepared test piece is fitted with Li ions of 20 mC cm ^-2 and discolored, the light transmittance is lowered. For example, the transmittance of the test piece of the comparative example to the light having a wavelength of 632 nm was lowered to 25%, the test piece of Example 1 was lowered to 20%, and the test piece of Example 7 was even lowered to 10% or less.

Referring to Figures 3 to 5, the light transmittance of the test piece of Example 7 after fading of the colored tungsten oxide film is similar to that at the time of initial preparation. The light transmittance of the test piece of Example 1 after fading of the colored tungsten oxide film was slightly lower than that at the time of initial preparation. On the other hand, the degree of light transmittance of the test piece of the comparative example was decreased to be larger than that of the first embodiment. Thus, for example, in the result of the change in the transmittance at the position of the wavelength of 632 nm, the tungsten oxide film of Example 7 has the largest amount, about 70%.

Fig. 6 is a view showing the charge density and optical density of the test pieces of Example 1, Example 7 and Comparative Example by reacting with Li ions at a fixed current density of 10 μAcm ^-2 by an electrochromic device ( Optical density; OD) relationship curve. From the slope of the curve, the coloration efficiency (CE) of the test pieces of Example 1, Example 7 and the comparative example was determined to be 6 cm ² C ^-1 , 37 cm ² C ^-1 and 7 cm ² C ^{- respectively. 1} . The color change efficiency of the test piece of Example 7 was significantly higher than that of the test piece of the comparative example.

The test pieces of Example 1, Example 7 and Comparative Example were repeatedly applied with positive and negative voltages for 200 seconds using an electrochromic device to discolor and color test pieces. In the embodiment, the test piece is colored when the applied voltage is -3 V. When the applied voltage is 3 V, the test piece is faded. Figure 7 shows the penetration of the test piece in the first test cycle (applied with a voltage of 3 V for 50 seconds at 50 seconds and then applied with a voltage of -3 V at 250 seconds) to light with a wavelength of 632 nm. Referring to Fig. 7, the results show that the test piece of Example 7 has the largest change in transmittance, about 60%, which is consistent with the results of Figs. 3 to 5. The color time and fading time of Example 7 (defined by the time when the transmittance was changed by 40%) were 8 seconds and 11 seconds, respectively. The transmittance of the test piece of the comparative example was less than 40%.

In addition to the color change efficiency and reaction time, the durability of the electrochromic material is also an important factor to be considered. Figure 8 shows the penetration of the test piece with light at a wavelength of 632 nm during 50 test cycles. The test piece of Example 7 had a 40% change in transmittance after 30 cycles of color/fading. The test pieces of Example 1 and Comparative Example showed only about 10% change in transmittance after a few color/fading cycles. As a result, the durability of the test piece of Example 7 was better than that of the comparative example.

Fig. 9, Fig. 10, and Fig. 11 show the test pieces of the first embodiment, the seventh embodiment, and the comparative example, respectively, by the three-pole system (the second, the tenth, the tenth, the fifth, and the 1000th) The relationship between the applied voltage in the color/fade cycle and the current density measured at this voltage (CV curve). Referring to Fig. 9, the CV curve of the test piece of Example 1 was not changed to a large extent. Referring to Fig. 10, the CV curve of the test piece of Example 7 was changed, but the area enclosed therein did not change much, which indicates that the test piece of Example 7 had good reliability. Referring to Fig. 11, after the color/fade cycle, the area surrounded by the CV curve of the test piece of the comparative example has a tendency to gradually decrease, which indicates that the test piece of the comparative example is not reliable.

Smart window

Figure 12 is a schematic view showing a smart window using a tungsten oxide film. Figure 13 shows the JV curve of a smart window bright state using a tungsten oxide film. Figure 14 shows the change in transmittance of a smart window using a tungsten oxide film in a short-circuit state when it is alternately lighted and light off. Referring to FIG. 12, the smart window includes an opposite ITO substrate 2 and an FTO substrate 4. The tungsten oxide film 6 and the Pt film 8 are provided on the FTO substrate 4. The Pt film 8 surrounds the tungsten oxide film 6. A film composed of TiO ₂ nanoparticles 10 is provided on the ITO substrate 2. The TiO ₂ nanoparticle 10 is adsorbed with a dye 12 (N719 dye). An electrolytic solution 14 (a propylene carbonate solution containing 0.5 M LiI and 5 mM I ₂ ) was provided between the ITO substrate 2 and the FTO substrate 4 . Smart windows use dye-sensitized solar cells. As can be seen from the results of Fig. 13, the open circuit voltage (Voc) of the smart window is 0.22 V. The short circuit current density (Jsc) is 2.13 mA. The fill factor (FF) is 0.27. The conversion efficiency is 0.12 (%). As can be seen from the results of Fig. 14, the smart window has a low light transmittance in the case of illumination. It has a high light transmittance without illumination.

Example 9

In this case, a nickel oxide film is formed. The nickel oxide film is formed in a similar manner to that in Example 1, in which the first precursor in the coating is nickel acetate and the fuel is urea. Weight of nickel acetate: weight of water plus hydrogen peroxide: the weight of urea is 1:0.1:5.66. The analysis results of SEM (Annex 13, 14) showed that the nickel oxide film of Example 9 was a flat film.

Example 10

The nickel oxide film was formed in a similar manner to Example 1, in which the first precursor in the coating was nickel nitrate. Weight of nickel nitrate: weight of water plus hydrogen peroxide: The weight of thiourea is 1:0.1:3.44.

Fig. 15 shows that the test piece of Example 10 was repeatedly applied with positive and negative voltages for 600 seconds using an electrochromic device to discolor and color test pieces. Fig. 16 is a graph showing the relationship between the charge density and the optical density in the reaction of the test piece of Example 10 with an OH ion at a fixed current density of 50 μAcm ^-2 by an electrochromic device. From the slope of the curve, the color change efficiency of the test piece of Example 10 was found to be 28 cm ² C ^-1 .

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

2. . . ITO substrate

4. . . FTO substrate

6. . . Tungsten oxide film

8. . . Pt film

10. . . TiO ₂ nanoparticle

12. . . dye

14. . . Electrolyte

Fig. 1 shows the diffraction data of monoclinic tungsten oxide, and the X-ray diffraction pattern of the ITO substrate, the test pieces of Example 1, Example 7, and the comparative example.

Fig. 2 shows Raman spectra of the test pieces of Example 1, Example 7 and Comparative Example.

Fig. 3 is a graph showing changes in light transmittance and transmittance of the test piece of Example 1.

Fig. 4 is a graph showing changes in light transmittance and transmittance of the test piece of Example 7.

Fig. 5 shows changes in light transmittance and transmittance of the test piece of the comparative example.

Fig. 6 is a graph showing the relationship between the charge density and the optical density of the test pieces of Example 1, Example 7 and Comparative Example.

Fig. 7 shows the transmittance of the test pieces of Example 1, Example 7 and Comparative Example in the first test cycle for light having a wavelength of 632 nm.

Figure 8 shows the transmittance of the test pieces of Example 1, Example 7 and Comparative Example for light having a wavelength of 632 nm during 50 test cycles.

Fig. 9 is a graph showing the relationship between voltage and current density in the color/fading cycle of the test piece of Example 1.

Fig. 10 is a graph showing the relationship between voltage and current density in the color/fading cycle of the test piece of Example 7.

Figure 11 shows the relationship between voltage and current density in the color/fade cycle of the test piece of the comparative example.

Figure 12 is a schematic view showing a smart window using a tungsten oxide film.

Figure 13 shows the J-V curve of a smart window using a tungsten oxide film in a bright state.

Figure 14 shows the change in transmittance of a smart window using a tungsten oxide film when it is alternately illuminated and not illuminated in a short circuit condition.

Figure 15 shows the penetration of light in Example 10 during the test cycle.

Fig. 16 is a graph showing the relationship between the charge density and the optical density of the test piece of Example 10.

2. . . ITO substrate

4. . . FTO substrate

6. . . Tungsten oxide film

8. . . Pt film

10. . . TiO ₂ nanoparticle

12. . . dye

14. . . Electrolyte

Claims (12)

A tungsten oxide film for use in a smart window, wherein the method for forming the tungsten oxide film comprises: preparing a coating comprising a first precursor, a fuel and a solvent, the first precursor comprising a tungsten powder, a tungsten nitrate, a tungsten sulfate, a tungsten acetate or a combination thereof, the fuel comprising thiourea, urea, glycine, citric acid or a combination thereof, the solvent comprising water, hydrogen peroxide, alcohol, or a combination thereof; The coating is applied to a substrate to form a coating; and an annealing step is performed to cause the coating to become a tungsten oxide film. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, and the weight of the first precursor is: The weight of the fuel is 1:0.4~2, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 °C to 550 °C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having cracks. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, and the weight of the first precursor is: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 ° C to 550 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having pores. A tungsten oxide film for use in a smart window according to claim 3, wherein the porous tungsten oxide film has a crystalline phase. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, and the weight of the first precursor is: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 ° C to 550 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having a crystalline phase. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, and the weight of the first precursor is: The weight of the fuel is 1: 0.2 to 0.4, the weight of the fuel: the weight of the solvent is 1:15 to 25, the temperature of the annealing step is 300 ° C to 425 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a flat tungsten oxide film. The tungsten oxide film for use in a smart window according to claim 6, wherein the flat tungsten oxide film has an amorphous phase. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is thiourea, and the weight of the first precursor is: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 300 ° C to 425 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having an amorphous phase. The tungsten oxide film applied to the smart window according to claim 1, wherein the first precursor is a tungsten powder, the solvent is hydrogen peroxide, the fuel is urea, and the weight of the first precursor: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 ° C to 550 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a flat tungsten oxide film. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is glycine, and the weight of the first precursor is: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 ° C to 550 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having pores. The tungsten oxide film applied to the smart window according to claim 1, wherein when the first precursor is tungsten powder, the solvent is hydrogen peroxide, the fuel is citric acid, and the weight of the first precursor is: The weight of the fuel is 1:0.2~0.4, the weight of the fuel: the weight of the solvent is 1:15~25, the temperature of the annealing step is 425 ° C to 550 ° C, and the time of the annealing step is 10 minutes to 60 minutes. The tungsten oxide film is a tungsten oxide film having pores. The tungsten oxide film for use in a smart window according to the first aspect of the invention, wherein the tungsten oxide film is a doped tungsten oxide film, and in the step of preparing the coating, the coating further comprises a second Doping the precursor, the second doping precursor comprises a second metal powder, a second metal nitrate, a second metal sulfate, a second metal acetate or a combination thereof, the second doping precursor The metal of the object comprises nickel, titanium, zinc, copper, silver or a combination thereof, the metal of the second doped precursor is different from the metal of the first precursor, the weight of the first precursor: the second doping The weight of the precursor is 1: 0.001~0.1.