Phase-change material-based high-functionality transparent thermal radiative cooling film and method for manufacturing same

Abstract

The present invention relates to a large-area radiative cooling film and a method for manufacturing same. The radiative cooling film can be produced to exhibit excellent emissivity and infrared transmittance, by synthesizing highly crystalline single-crystal vanadium dioxide through a chemical vapor deposition method, and optimizing the structure thereof, such as the vanadium dioxide pattern, spacing, and the thickness of each layer. In addition, the method for manufacturing a radiative cooling film can improve process speed and stability through a film thinning process based on dry transfer, and enables the manufacture of a large-area radiative cooling film.

Description

High-performance transparent thermal radiation cooling film based on phase change material and method for manufacturing the same

[0001] The present invention relates to a large-area thermal radiation cooling film and a method for manufacturing the same.

[0002] Vanadium (V) is a hard transition metal with excellent ductility and malleability. Its oxide, vanadium dioxide (VO2), exhibits a monoclinic phase structure below its phase transition temperature of 68°C, allowing it to optically transmit infrared radiation and act as an electrical insulator. Conversely, above the phase transition temperature, it transforms into a rutile phase structure, which blocks infrared radiation optically and acts as an electrical conductor, exhibiting the characteristic of a very rapid "metal-insulator transition" (MIT). Therefore, vanadium dioxide has recently been attracting attention as a key next-generation material for sensors, optical devices, memory devices, and smart windows.

[0003] Conventionally, when forming a vanadium dioxide thin film using a dry method, the process is carried out under high-temperature conditions, making it difficult to form the thin film directly on flexible and stretchable substrates that are sensitive to heat. Therefore, the vanadium dioxide thin film was formed by first forming the thin film on a growth substrate and then transferring it to a stretchable substrate or the like.

[0004] However, thin films formed by dry methods are composed of small grain-sized crystals, which can cause problems such as partial detachment during the transfer process, or cracks or lifting of the film due to mechanical deformation such as bending or tension on the substrate even after transfer is completed. In addition, conventional transfer processes use a method of transferring a vanadium dioxide thin film by etching the growth substrate, which has the disadvantage of being difficult to apply to large-area thin films due to issues with process time and etching uniformity, and in particular, there is a problem of risk associated with the use of etching solutions.

[0005] The objective of the present invention is to synthesize single-crystal vanadium dioxide having high crystallinity using chemical vapor deposition (CVD), optimize the structure to provide a radiative cooling film having high emissivity, and a method for manufacturing the same.

[0006] To achieve the above objective, the present invention provides a radiation cooling film characterized by comprising an infrared reflective layer sequentially stacked; a dielectric layer; a phase change layer comprising crystalline vanadium dioxide; and a protective layer, wherein the thickness of the phase change layer is 50 nm to 1000 nm.

[0007] In addition, the present invention provides a method for manufacturing a radiation cooling film comprising: (a) forming a phase change layer on a polymer coating layer; (b) forming a dielectric layer on the phase change layer; (c) forming an infrared reflective layer on the dielectric layer; and (d) transferring a film in which the polymer coating layer, the phase change layer, the dielectric layer, and the infrared reflective layer are sequentially laminated onto a substrate, wherein the phase change layer comprises crystalline vanadium dioxide, and in step (a), the phase change layer is formed with a thickness of 50 nm to 1000 nm.

[0008] The radiative cooling film according to the present invention can exhibit excellent emissivity and infrared transmittance by synthesizing single-crystal vanadium dioxide with high crystallinity through chemical vapor deposition and optimizing the structure, such as the vanadium dioxide pattern, spacing, and thickness of each layer.

[0009] In addition, the method for manufacturing a radiative cooling film according to the present invention can improve process speed and stability through a thin film formation process based on dry transfer, and can manufacture a large-area radiative cooling film.

[0010] FIG. 1 is a cross-sectional view of a radiative cooling film according to one embodiment of the present invention.

[0011] FIG. 2 is a flowchart illustrating a method for manufacturing a radiative cooling film according to one embodiment of the present invention.

[0012] FIG. 3 is a photograph of a radiant cooling film manufactured by a method for manufacturing a radiant cooling film according to one embodiment of the present invention.

[0013] FIG. 4 is a photograph (a) and optical microscope images (b, c) of a phase change layer in a radiative cooling film according to one embodiment of the present invention.

[0014] FIG. 5 is an image of a phase change layer in a radiation cooling film according to one embodiment of the present invention, taken with an atomic force microscope (a), a scanning electron microscope (b), and a transmission electron microscope (c).

[0015] FIG. 6 is a photograph (a) and lamin spectroscopic analysis result (b) before and after a phase change layer is dry-transferred from a radiative cooling film according to one embodiment of the present invention.

[0016] Figure 7 is the result of performing an infrared (IR) band optical characteristic analysis on a radiative cooling film according to one embodiment of the present invention.

[0017] Figure 8 is the result of simulating the infrared (IR) band optical characteristics of a radiative cooling film according to one embodiment of the present invention.

[0018] Figure 9 is the result of performing an analysis of the infrared (IR) band optical characteristics according to the type of metal in the infrared reflective layer of a radiative cooling film according to one embodiment of the present invention.

[0019] Figure 10 is the result of simulating the infrared (IR) band optical characteristics according to the thickness of the dielectric layer of a radiative cooling film according to one embodiment of the present invention.

[0020] Figure 11 is the result of performing an analysis of infrared (IR) band optical characteristics according to the thickness of the dielectric layer of a radiative cooling film according to one embodiment of the present invention.

[0021] Figure 12 is the result of performing an analysis of infrared (IR) band optical characteristics according to the type of dielectric layer of a radiative cooling film according to one embodiment of the present invention.

[0022] Figure 13 is the result of simulating the infrared (IR) band optical characteristics according to the thickness of the phase change layer of a radiative cooling film according to one embodiment of the present invention.

[0023] Figure 14 is the result of performing an analysis of infrared (IR) band optical characteristics according to the thickness of the phase change layer of a radiative cooling film according to one embodiment of the present invention.

[0024] Figure 15 is the result of simulating the infrared (IR) band optical characteristics according to the thickness of the protective layer of a radiative cooling film according to one embodiment of the present invention.

[0025] Figure 16 is the result of performing an analysis of infrared (IR) band optical characteristics according to the thickness of the protective layer of a radiative cooling film according to one embodiment of the present invention.

[0026] Figures 17 and 18 are graphs showing the infrared transmittance and emissivity according to the size and spacing of the vanadium dioxide thin film applied to the radiative cooling film structure.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Since the present invention is susceptible to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing. In the attached drawings, the dimensions of the structures are shown enlarged compared to the actual dimensions for the clarity of the present invention.

[0028] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0029] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0030] Meanwhile, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0031]

[0032] FIG. 1 is a cross-sectional view of a radiative cooling film structure according to one embodiment of the present invention.

[0033] Referring to FIG. 1, the radiative cooling film structure of the present invention may include an infrared reflective layer (100) stacked sequentially; a dielectric layer (200); a phase change layer (300) containing crystalline vanadium dioxide; and a protective layer (400).

[0034] The infrared reflective layer (100) may have a high reflectivity and low absorption loss for light in the infrared region of about 8 to 13 μm wavelength, which is the transmission window region. In one embodiment, the infrared reflective layer (100) may include one or more selected from the group consisting of silver (Ag), gold (Au), silver nanowires (Ag NWs) and indium tin oxide (ITO).

[0035] The thickness of the infrared reflective layer (100) may be about 0.05 μm or more, for example, about 50 nm to 1000 nm or about 50 nm to 500 nm. In addition, if the infrared reflective layer includes silver (Ag) nanowires, the resistance value of the infrared reflective layer (100) may be about 5 ohms or less or about 1 to 5 ohms.

[0036] The dielectric layer (200) has a dielectric constant or refractive index sufficient to cause phase inversion of the target infrared light at the interface with the infrared reflecting layer (100), and can have low absorption loss for the infrared light in the transmission window region.

[0037] In one embodiment, the dielectric layer (200) may include one or more selected from the group consisting of poly(methyl methacrylate, PMMA), boron nitride (BN), polyethylene, polystyrene, silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon nitride (Si3N4), germanium (Ge), zinc sulfide (ZnS), calcium fluoride (CaF2), magnesium fluoride (MgF2), etc.

[0038] The thickness of the dielectric layer (200) may be about 0.2 μm to 5 μm, about 0.5 μm to 3 μm, or about 1 μm to 2 μm.

[0039] By including the dielectric layer (200) as described above, the radiation cooling film structure according to the present invention can exhibit excellent infrared transmittance.

[0040] The phase change layer (300) may include a vanadium dioxide (VO2) single crystal. Based on a phase transition temperature of about 68°C, the single crystal vanadium dioxide has a monoclinic crystal phase and exhibits insulating properties below the phase transition temperature, so it may have a relatively low reflectance for infrared rays in the transmission window region, and at a temperature exceeding the phase transition temperature, it has a rutile crystal phase and exhibits metallic properties, so it may have a relatively high reflectance for infrared rays in the transmission window region.

[0041] The phase change layer (300) may include a vanadium dioxide thin film covering the entire area of ​​the dielectric layer (200), or a patterned vanadium dioxide thin film that exposes a portion of the entire area of ​​the dielectric layer (200). The patterned vanadium dioxide thin film may be a single crystal formed by two or more plate-shaped single crystals separated from each other and densely formed.

[0042] In one embodiment, in order to increase optical transmittance while minimizing emissivity reduction, the vanadium dioxide thin film constituting the phase change layer (300) may be patterned to have a filling rate of about 25 to 70%. At this time, the filling rate represents the ratio of the area occupied by the patterned vanadium dioxide thin film to the entire upper surface area of ​​the dielectric layer (200). In one embodiment, the patterned vanadium dioxide thin film may have a structure in which vanadium dioxide thin film patterns formed linearly on the phase change layer (300) are arranged at regular intervals, or in which polygonal or circular vanadium dioxide thin film patterns are arranged in a checkerboard shape.

[0043] The vanadium dioxide single crystal may have an average particle size of 10 μm to 1000 μm, 30 μm to 700 μm, or 50 μm to 500 μm.

[0044] The thickness of the phase change layer (300) may be 50 nm to 1000 nm, 50 nm to 500 nm, or 50 nm to 100 nm.

[0045] By including the phase change layer (300) as described above, a radiative cooling film having excellent emissivity based on Fabry-Perot resonance can be provided.

[0046] The protective layer (400) is an anti-oxidation layer and may include one or more selected from the group consisting of polyimide (PI), polyethylene, and poly(methyl methacrylate).

[0047] The thickness of the protective layer (400) may be 0.25 μm to 2.5 μm, 0.5 μm to 2.0 μm, or 1.0 μm to 1.5 μm.

[0048] By including the protective layer (400) as described above, excellent infrared transmittance is exhibited, and the durability of the radiation cooling film structure can be improved by preventing oxidation of the phase change layer containing vanadium dioxide.

[0049] The radiative cooling film according to an embodiment of the present invention applies a patterned single-crystal vanadium dioxide thin film pattern with high crystallinity through chemical vapor deposition, thereby exhibiting excellent emissivity and high optical transmittance. Such a radiative cooling film can be applied to windows, exterior materials, etc., of buildings and automobiles, and in this case, can bring about energy saving efficiency.

[0050]

[0051] FIG. 2 is a flowchart illustrating a method for manufacturing a radiative cooling film structure according to one embodiment of the present invention.

[0052] Referring to FIG. 2 together with FIG. 1, the method for manufacturing a radiative cooling film structure of the present invention may include: (a) a step of forming a phase change layer (300); (b) a step of forming a dielectric layer (200) on the phase change layer (300); (c) a step of forming an infrared reflective layer (300) on the dielectric layer (200); and (d) a step of transferring a film structure in which the phase change layer (300), the dielectric layer (200), and the infrared reflective layer (100) are sequentially stacked onto a substrate.

[0053] The step (S110) of forming the phase change layer can be formed by transferring a vanadium dioxide single crystal thin film onto the polymer protective layer (400) through a dry transfer method.

[0054] In one embodiment, the phase change layer (300) may be formed with a thickness of about 50 nm to 1000 nm, about 50 nm to 500 nm, or about 50 nm to 100 nm.

[0055] By forming the phase change layer (300) as described above, there are no restrictions on the process temperature, the process speed and stability can be improved, and there are advantages such as the ability to form an independent structure even on thin materials, and a radiative cooling film structure having excellent emissivity can be provided.

[0056] In one embodiment, the step (S110) of forming the phase change layer may include: forming a vanadium dioxide thin film on a growth substrate; applying a polymer solution for forming a protective layer (400) onto the vanadium dioxide thin film to form a polymer coating layer; attaching a release tape to the laminated polymer coating layer; and mechanically peeling the vanadium dioxide thin film from the growth substrate.

[0057] In another embodiment, the step (S110) of forming the phase change layer may include: forming a vanadium dioxide thin film on a growth substrate; patterning the vanadium dioxide thin film; applying a polymer solution for forming a protective layer (400) onto the patterned vanadium dioxide thin film to form a polymer coating layer; attaching a release tape to the laminated polymer coating layer; and mechanically peeling the patterned vanadium dioxide thin film from the growth substrate.

[0058]

[0059] As described above, when a phase change layer is formed using a dry transfer method, the process time can be significantly reduced compared to a wet transfer method using an etching solution, process stability can be ensured, and a large-area thin film can be formed. In addition, since the process is not carried out under high-temperature conditions, there is an advantage that the exfoliated vanadium dioxide thin film can be transferred to a desired substrate without any limitations on the material.

[0060] The step (S111) of forming the vanadium dioxide thin film can form a vanadium dioxide single-crystal thin film by chemical vapor deposition, and in this case, a plate-shaped single crystal can be formed and a flat thin film can be formed.

[0061] In one embodiment, the step (S111) of forming the vanadium dioxide thin film may form a vanadium dioxide thin film or a patterned vanadium dioxide thin film. The patterned vanadium dioxide thin film may be a single crystal in which two or more plate-shaped single crystals are separated from each other and densely formed.

[0062] In one embodiment, to increase optical transmittance while minimizing emissivity reduction, the vanadium dioxide thin film may be patterned to have a filling rate of about 25 to 70%. For example, the vanadium dioxide single crystals may be arranged with spaced-apart spaces between them, and the arrangement may be linear or checkerboard.

[0063] The above chemical vapor deposition method can be performed in an Ar / O2 gas atmosphere under conditions of a temperature of 400 to 1000°C, specifically 600 to 900°C, a pressure of 0.01 to 10 Torr, specifically 0.05 to 5 Torr, and a time of 1 to 10 hours, specifically 3 to 7 hours. When the above ranges are satisfied, the average size of the plate-shaped single crystals included in the vanadium dioxide single-crystal thin film is formed on a micro scale, which is preferred, but is not limited thereto.

[0064] The growth substrate may be a silicon wafer, quartz glass, tempered glass, metal, metal oxide, or a composite material thereof.

[0065] The step of laminating the polymer coating layer is a step of laminating the polymer coating layer by applying a polymer solution onto the vanadium dioxide thin film.

[0066] The polymer included in the polymer solution for forming the protective layer above may be formed on the phase change layer by applying an antioxidant material comprising one or more selected from the group consisting of polyimide (PI), polyethylene, and poly(methyl methacrylate), but is not limited thereto.

[0067] The above polymer solution includes one or more solvents selected from the group consisting of methylylrolidone, chlorobenzene, chloroform, tetrahydronaphthalene, tetrachlorobenzene, tetrahydrofuran, toluene, xylene, and indole, but is not limited thereto.

[0068] The above polymer solution may be applied by spin coating, bar coating, or drop casting methods, and when a thermosetting resin is used, it may further include curing means such as heat or ultraviolet rays if necessary, but is not limited thereto.

[0069] In one embodiment, the thickness of the polymer coating layer can be formed to a thickness of about 0.25 μm to 2.5 μm, about 0.5 μm to 2.0 μm, or about 1.0 μm to 1.5 μm.

[0070] The polymer coating layer described above acts as a protective layer (400), thereby enabling the manufacture of a radiative cooling film structure that exhibits excellent infrared transmittance, and can improve the durability of the radiative cooling film by preventing oxidation of the phase change layer containing vanadium dioxide.

[0071] The step of attaching the above-mentioned release tape is the step of attaching the release tape on the above-mentioned polymer coating layer.

[0072] Mechanical peeling of a vanadium dioxide single-crystal thin film can be performed using the adhesive force between the above peeling tape and the polymer coating layer, and the peeling tape can be removed after the mechanical peeling of the vanadium dioxide single-crystal thin film is performed.

[0073] The step of mechanically peeling off the vanadium dioxide thin film is a step of mechanically peeling off the vanadium dioxide thin film having the polymer coating layer laminated thereon from the growth substrate.

[0074] By mechanically peeling the vanadium dioxide thin film from the growth substrate by applying physical force with the peeling tape, the risk of explosion or fire caused by the etching solution and the risk of damage to the vanadium dioxide thin film caused by the etching solution, which occur when the growth substrate is etched and removed in the conventional manner, can be eliminated, and there is an advantage of significantly reducing the process time required for etching, washing, and drying. The mechanical peeling means may be achieved by peeling one end of the peeling tape in a 904-degree direction, but is not limited thereto.

[0075] In the step (S120) of forming the dielectric layer, the dielectric layer (200) may be formed on the phase change layer (300) using one or more materials selected from the group consisting of poly(methyl methacrylate, PMMA), boron nitride (BN), polyethylene, polystyrene, silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon nitride (Si3N4), germanium (Ge), zinc sulfide (ZnS), calcium fluoride (CaF2), magnesium fluoride (MgF2), etc.

[0076] In one embodiment, the dielectric layer (200) may be formed with a thickness of about 0.2 μm to 5 μm, about 0.5 μm to 3 μm, or about 1 μm to 2 μm.

[0077] By forming a dielectric layer (200) as described above, the radiation cooling film structure according to the present invention can have excellent emissivity.

[0078] In the step (S130) of forming an infrared reflective layer (100) on the dielectric layer (200), the infrared reflective layer (100) may be formed on the dielectric layer (200) using one or more materials selected from the group consisting of silver (Ag), gold (Au), silver nanowires (Ag NWs), and indium tin oxide (ITO).

[0079] In one embodiment, the infrared reflective layer may be formed with a thickness of about 0.05 μm or more, about 50 nm to 1000 nm, or about 50 nm to 500 nm.

[0080] The step (S140) of transferring the above-described laminated film onto a substrate is a step of attaching the film, which is laminated in the order of the protective layer (400), the phase change layer (300), the dielectric layer (200), and the infrared reflective layer (100), onto a substrate.

[0081] In one embodiment, after forming an adhesive resin layer on the substrate, the infrared reflective layer of the laminated film can be attached to the adhesive resin layer through a dry transfer method to perform the transfer of the laminated film.

[0082] The above description may include one or more types selected from glass substrates, silicon substrates, and PET substrates, but is not limited thereto.

[0083] In one embodiment, after transferring the laminated film onto the substrate, the release tape attached to one surface of the polymer coating layer can be removed.

[0084] As described above, when forming a film laminated on a substrate using a dry transfer method, the process time can be significantly reduced compared to a wet transfer method using an etching solution, process stability can be ensured, and large-area thin film formation is possible. In addition, since the process is not carried out under high-temperature conditions, there is an advantage that the exfoliated vanadium dioxide thin film can be transferred to a desired substrate without any limitations on the material.

[0085] In one embodiment, after the step (S140) of transferring the laminated film onto a substrate, a step of removing the polymer coating layer may be additionally included optionally. The step of removing the polymer coating layer may be performed using one or more solvents selected from the group consisting of methylpyrrolidone (NMP) and xylene. The step of removing the polymer coating layer is a step of removing the polymer coating layer formed on the phase change layer, and the radiative cooling film manufactured thereby does not have a protective layer formed on the phase change layer.

[0086]

[0087] Hereinafter, to aid in understanding the present invention, examples and the like will be described in detail. However, the following examples and the like are merely illustrative of the content of the present invention and the scope of the present invention is not limited to the following examples and the like. The examples and the like of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0088] [Example 1] Vanadium dioxide (VO2) / PMMA / Au 50 nm / substrate

[0089] A 2-inch diameter vanadium dioxide thin film was formed on a silicon substrate with a silicon oxide film deposited using chemical vapor deposition (CVD) under conditions of a temperature of 600–900°C, a pressure of 0.05–5 Torr, and a time of 3–7 hours.

[0090] Then, a polymer solution containing 12 wt% of a polyimide polymer in a mixed solvent of methylpyrrolidone (NMP) and xylene was applied to the vanadium dioxide thin film by spin coating at a speed between 3000 rpm and 5000 rpm for 1 minute, and the temperature was raised to 200°C to vaporize the solvent and deposit a polymer coating layer. Next, a thermal release tape (REVALPHA, Nitto) was attached to the polymer coating layer, and the thermal release tape was slowly pulled in a vertical direction of the silicon substrate to mechanically peel off the vanadium dioxide thin film from the silicon substrate.

[0091] A PMMA dielectric layer was formed by applying a solution containing PMMA to the vanadium dioxide layer using a spin coating or bar coating method at a speed of 2000 rpm to 5000 rpm for 1 minute to achieve a uniform thickness, and then heating at approximately 110°C for 10 minutes to sufficiently remove the solvent. Then, an infrared reflective layer was formed by slowly vacuum depositing a 50 nm thick gold thin film on the PMMA dielectric layer using an electron beam deposition system at a pressure of approximately 10-5 Torr and a speed of approximately 0.5 Å / sec.

[0092] Then, a UV-curable resin (Norland optical adhesives, Norland) was applied to a PET substrate to form an adhesive resin layer. Subsequently, the adhesive resin layer of the PET substrate was brought into contact with the infrared reflective layer, and the two layers were bonded by irradiating with a UV lamp until the UV energy reached 3 J / cm2. Afterward, the thermal release tape was removed by heating to 110°C, and a film in which a vanadium dioxide single-crystal thin film, a dielectric layer, and an infrared reflective layer were sequentially laminated was transferred onto the PET substrate. At this time, the polyimide polymer coating layer formed on the upper layer of the transferred vanadium dioxide single-crystal thin film was removed using NMP or xylene solvent to produce a vanadium dioxide (VO2) / PMMA / Au 50 nm / substrate radiative cooling film, and the image is shown in Fig. 3. Fig. 3(a) is an image of the vanadium dioxide thin film after dry transfer, and (b) is an image of the radiative cooling film produced in an actual size of 4 inches (approx. 10 cm).

[0093]

[0094] [Example 2] PI / Vanadium Dioxide (VO2) / PMMA / Au 50 nm / Substrate

[0095] A radiative cooling film with a PI / vanadium dioxide (VO2) / PMMA / Au 50nm / substrate structure was prepared in the same manner as in Example 1, except that a film having a vanadium dioxide single crystal thin film / dielectric layer / infrared reflective layer sequentially laminated on a PET substrate was transferred onto a PET substrate and the polyimide polymer coating layer was not removed.

[0096]

[0097] [Comparative Example 1] Vanadium dioxide (VO2) / substrate

[0098] A radiative cooling film with a vanadium dioxide (VO2) / substrate structure was prepared by directly growing vanadium dioxide on a silicon substrate or quartz substrate on which a silicon oxide film of 50 nm to 1 μm was deposited via the chemical vapor deposition (CVD) method shown in Example 1.

[0099]

[0100] [Comparative Example 2] Vanadium dioxide (VO2) / Au 50nm / substrate

[0101] After removing vanadium dioxide (Comparative Example 1) grown directly on a substrate from the substrate using a thermal release tape, 50 nm of Au was formed on the vanadium dioxide using a vacuum deposition process. Finally, by transferring it to a glass substrate using heat, a radiative cooling film with a vanadium dioxide (VO2) / Au 50 nm / substrate structure was prepared.

[0102]

[0103] [Experimental Example 1] Vanadium Dioxide Analysis

[0104] A vanadium dioxide layer with a diameter of 2 inches was formed on quartz glass using chemical vapor deposition (CVD) under conditions of a temperature of 600–900°C, a pressure of 0.05–5 Torr, and a time of 3–7 hours in an Ar / O2 gas atmosphere, and an analysis of the thickness and crystals of the vanadium dioxide layer was performed, and the results are shown in Figures 4 and 5.

[0105] Referring to Figure 4, vanadium dioxide with a size of 2 inches was synthesized on quartz glass based on chemical vapor deposition, and it was confirmed that the crystal size of vanadium dioxide was 50 to 100 μm.

[0106] Referring to Fig. 5, the results of imaging the synthesized vanadium dioxide using an atomic force microscope (AFM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM) show that the vanadium dioxide has a thickness of 100 to 200 nm and was synthesized as a single crystal.

[0107]

[0108] [Experimental Example 2] Dry Transfer Technology

[0109] The 2-inch vanadium dioxide (thickness: 100 to 200 nm) synthesized in Experimental Example 1 was dry-transferred onto a desired substrate (PET) using an adhesive polymer and a heat release tape, and the vanadium dioxide layer transferred to the substrate was analyzed by Raman spectroscopy, and the results are shown in Figure 6.

[0110] Looking at Figure 6, it can be confirmed that high-speed transfer of vanadium dioxide onto a desired substrate is possible without the use of a chemical solution, and through Raman analysis before and after transfer, it can be confirmed that there is no significant change in the characteristics of vanadium dioxide. It can be seen that the peak observed at 520 cm⁻¹ before transfer is due to the substrate and does not appear on the PET substrate after transfer.

[0111]

[0112] [Experimental Example 3]

[0113] Infrared (IR) band optical characteristics analysis was performed on the radiative cooling films prepared in Example 1, Comparative Example 1, and Comparative Example 2, and is shown in Figures 7 and 8.

[0114] Looking at Figure 7, it can be seen that when only vanadium dioxide (VO2) is included on the substrate, the emissivity value decreases above the phase change temperature, and when there is an infrared reflective layer and vanadium dioxide on the substrate, there is no change in the emissivity value regardless of the phase change temperature. On the other hand, when there is a phase change layer and a dielectric layer, polymethyl methacrylate (PMMA), it can be seen that the emissivity value increases above the phase change temperature.

[0115] Figure 8 shows the results of a simulation of the change in emissivity according to the thickness of the dielectric layer in the film of Example 1, and it can be seen that the change in emissivity of the film according to the thickness is significant.

[0116]

[0117] [Experimental Example 4] Experiment according to the type of metal in the infrared reflective layer

[0118] Infrared (IR) band optical characteristics analysis was performed on radiative cooling films prepared by the method of Example 2, with different types of metal in the infrared reflective layer, and is shown in Fig. 9.

[0119] Looking at Figure 9, it was confirmed that when silver or gold is used, a significant change in emissivity occurs in the 8–13 μm wavelength range due to infrared reflection, and in the case of silver nanowires, the lower the resistance, the greater the infrared reflection effect. In the case of ITO, although infrared reflection is not significant, it was confirmed that it is a material capable of reflecting infrared while being transparent in the visible light region. Therefore, it can be seen that when silver or gold is included, the thickness of the infrared reflective layer is optimally 0.05 μm or more, and when silver nanowires are included, the film's resistance value is optimally 5 ohms or less.

[0120]

[0121] [Experimental Example 5] Experiment according to the dielectric layer

[0122] Infrared (IR) band optical characteristics were analyzed for radiative cooling films with different dielectric layer thicknesses prepared by the method of Example 2, and are shown in Figures 10 and 11.

[0123] Looking at Figures 10 and 11, it can be seen that when the dielectric layer thickness is thin, the change in emissivity before and after the phase change temperature is small, and it was confirmed that the change in emissivity is large at 1 to 2 μm. In addition, it was confirmed that the change in emissivity decreases when the dielectric layer is too thick. Therefore, it can be seen that the optimal thickness of the dielectric layer is 1 to 2 μm.

[0124] In addition, an analysis of infrared (IR) band optical characteristics was performed on a radiative cooling film prepared by changing the dielectric layer to boron nitride (BN) in the radiative cooling film prepared by the method of Example 2, and is shown in Fig. 12.

[0125] Looking at Figure 12, it was confirmed that the film fabricated using boron nitride nanotubes did not absorb much infrared light in the 8–13 μm region. Therefore, it can be seen that boron nitride nanotubes can be used instead of PMMA when forming a dielectric layer on the film.

[0126]

[0127] [Experimental Example 6] Experiment according to the thickness of the phase change layer

[0128] Infrared (IR) band optical characteristics were analyzed for radiative cooling films with different thicknesses of the phase change layer prepared by the method of Example 2, and are shown in Figures 13 and 14.

[0129] Looking at Figure 13, simulation results show that the change in emissivity decreases significantly when the thickness of the vanadium dioxide thin film synthesized by chemical vapor deposition increases from 50 nm to 500 nm. In Figure 13, the solid line represents the vanadium dioxide thin film at 30°C, and the dotted line represents the vanadium dioxide thin film at 100°C. These results are observed identically in the experimental data in Figure 14, where it can be seen that the change in emissivity decreases significantly when the actual vanadium dioxide thin film increases from 100 nm to 500 nm. Therefore, it was confirmed that the optimal thickness of the phase change layer is 0.05 to 0.1 μm, which exhibits a high change in emissivity.

[0130]

[0131] [Experimental Example 7] Experiment according to the thickness of the protective layer

[0132] Infrared (IR) band optical characteristics analysis was performed on radiative cooling films with different thicknesses of the protective layer prepared by the method of Example 2, and is shown in Figures 15 and 16.

[0133] Looking at Figures 15 and 16, it can be seen that the emissivity changes when the thickness of the upper polyimide layer is changed. Therefore, it was confirmed that the optimal thickness of the phase change layer is approximately 1 μm, or about 1 to 1.5 μm.

[0134]

[0135] [Experimental Example 8] Transmittance and Emissivity of Vanadium Dioxide Thin Film According to Fill Factor

[0136] Figures 17 and 18 are graphs showing the infrared transmittance and emissivity according to the size and spacing of the vanadium dioxide thin film applied to the radiative cooling film structure.

[0137] Referring to Fig. 17, it was found that the infrared transmittance of the radiative cooling film structure decreased as the filling rate of the vanadium dioxide thin film patterns forming the phase change layer increased.

[0138] Specifically, the maximum infrared transmittance of a radiative cooling film structure with a phase change layer (filling rate 69.4%) having a structure in which square vanadium dioxide patterns with widths and lengths of 15 μm are spaced apart by 3 μm was measured to be about 23%, whereas the maximum infrared transmittance of a radiative cooling film structure with a phase change layer (filling rate 25%) having a structure in which square vanadium dioxide patterns with widths and lengths of 10 μm are spaced apart by 10 μm was measured to be about 62%.

[0139] Referring to Fig. 18, it was shown that the emissivity of the radiative cooling film structure improves as the filling rate of the vanadium dioxide thin film patterns forming the phase change layer increases.

[0140] Specifically, it was confirmed that a radiative cooling film structure with a phase change layer having a structure in which square vanadium dioxide patterns with width and length of 5 μm are spaced apart by 3 μm (filling rate approximately 39%), a phase change layer having a structure in which square vanadium dioxide patterns with width and length of 10 μm are spaced apart by 3 μm (filling rate approximately 59.17%), a phase change layer having a structure in which square vanadium dioxide patterns with width and length of 15 μm are spaced apart by 3 μm (filling rate approximately 69.4%), and a phase change layer having a structure in which square vanadium dioxide patterns with width and length of 10 μm are spaced apart by 5 μm (filling rate approximately 44.4%) were applied exhibited relatively excellent emissivity characteristics.

[0141] Considering the above results, the vanadium dioxide thin film pattern of the phase change layer can be formed to have an infrared transmittance and emissivity of about 30 to 70% in terms of filling rate.

[0142]

[0143] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0144] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. Infrared reflective layers stacked sequentially; dielectric layers; and phase change layers comprising crystalline vanadium dioxide, A radiation cooling film characterized by the thickness of the phase change layer being 50 nm to 1000 nm.

2. In Paragraph 1, A radiation cooling film further comprising a protective layer on the above-mentioned phase change layer.

3. In Paragraph 1, The infrared reflective layer comprises one or more materials selected from the group consisting of silver (Ag), gold (Au), silver nanowires (Ag NWs), and indium tin oxide (ITO), forming a radiation cooling film.

4. In Paragraph 1, The above dielectric layer comprises one or more materials selected from the group consisting of poly(methyl methacrylate, PMMA), boron nitride (BN), polyethylene, and polystyrene, forming a radiation cooling film.

5. In Paragraph 2, The above protective layer is a radiative cooling film comprising one or more selected from the group consisting of polyimide (PI), polyethylene, and poly(methyl methacrylate).

6. In Paragraph 1, A radiative cooling film characterized by the fact that the thickness of the infrared reflective layer is 0.05 μm or more.

7. In Paragraph 1, A radiation cooling film characterized by the thickness of the dielectric layer being 0.2 to 5 μm.

8. In Paragraph 2, A radiative cooling film characterized by the thickness of the protective layer being 0.25 to 2.5 μm.

9. In Paragraph 1, The above phase change layer is a radiation cooling film comprising a vanadium dioxide thin film or a patterned vanadium dioxide thin film.

10. In Paragraph 9, A radiation cooling film characterized by the above-mentioned patterned vanadium dioxide thin film being arranged with spaced-apart spaces between vanadium dioxide single crystals. 11.(a) A step of forming a phase change layer on a polymer coating layer; (b) a step of forming a dielectric layer on the phase change layer; (c) forming an infrared reflective layer on the dielectric layer; and (d) a step of transferring a film having a polymer coating layer, a phase change layer, a dielectric layer, and an infrared reflective layer sequentially laminated onto a substrate; comprising, The above phase change layer comprises crystalline vanadium dioxide, and A method for manufacturing a radiation cooling film, characterized by forming a phase change layer with a thickness of 50 nm to 1000 nm in step (a) above.

12. In Paragraph 11, A method for manufacturing a radiation cooling film, further comprising, after step (d) above, a step (S150) of transferring the laminated film onto a substrate and then removing the polymer coating layer.

13. In Paragraph 11, The above step (a) is a step of forming a vanadium dioxide thin film on a growth substrate (a-1); (a-2) A step of applying a polymer solution onto the vanadium dioxide thin film formed above to deposit a polymer coating layer; (a-3) A step of attaching a release tape to the laminated polymer coating layer; and (a-4) A method for manufacturing a radiation cooling film comprising the step of mechanically peeling off the vanadium dioxide thin film from the growth substrate.

14. In Paragraph 13, A method for manufacturing a radiative cooling film, characterized in that, in step (a-2) above, the polymer coating layer is formed on a phase change layer by applying an antioxidant material comprising one or more selected from the group consisting of polyimide (PI), polyethylene, and poly(methyl methacrylate).

15. In Paragraph 12, A method for manufacturing a radiative cooling film characterized by forming a polymer coating layer with a thickness of 0.25 to 2.5 μm in step (a-2) above.

16. In Paragraph 11, A method for manufacturing a radiation cooling film, characterized in that, in step (b) above, the dielectric layer is formed on an infrared reflective layer by applying one or more materials selected from the group consisting of poly(methyl methacrylate), PMMA, boron nitride (BN), polyethylene, and polystyrene.

17. In Paragraph 11, A method for manufacturing a radiative cooling film, characterized in that, in step (c) above, the infrared reflective layer is formed on a substrate by applying one or more metal particles selected from the group consisting of silver (Ag), gold (Au), silver nanowires (Ag NWs), and indium tin oxide (ITO).

18. In Paragraph 11, A method for manufacturing a radiation cooling film characterized by forming a dielectric layer with a thickness of 0.2 to 5 μm in step (b) above.

19. In Paragraph 11, A method for manufacturing a radiative cooling film characterized by forming an infrared reflective layer with a thickness of 0.05 μm or more in step (c) above.

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