A color cooling optical film and a method of making the same

Abstract

This invention discloses a colored cooling optical thin film and its preparation method. The thin film, from bottom to top, comprises a metal layer M, a first dielectric layer D1, an absorption layer A, a second dielectric layer D2, a third dielectric layer D3, and a fourth dielectric layer D4, stacked together. The metal layer M, the first dielectric layer D1, and the absorption layer A constitute a color layer, used to control the spectral characteristics in the visible light band to achieve a fixed color and high reflectivity in the near-infrared band. The second dielectric layer D2 and the third dielectric layer D3 constitute a near-infrared enhancement layer, used to improve the reflectivity in the near-infrared band. The fourth dielectric layer D4 is an anti-reflection layer, used to reduce residual reflection in the visible light band and protect the underlying film layers. The thin film of this invention can achieve a colored appearance with high absorption in the 400nm-800nm ​​visible light band and a cooling effect with high reflectivity in the 800nm-2500nm near-infrared band.

Description

Technical Field

[0001] This invention relates to the field of cooling film technology, and in particular to a colored cooling optical film and its preparation method. Background Technology

[0002] Color generation primarily relies on two mechanisms: pigment color (chemical color) and structural color (physical color). Traditional pigment color depends on the selective absorption of light by molecules at specific wavelengths. While widely used, it suffers from problems such as easy fading and environmental impact. In contrast, structural color produces color by controlling physical effects such as interference and diffraction of light through micro- and nano-structures. It boasts significant advantages such as high stability, environmental friendliness, non-toxicity, and high color saturation, making it an important development direction for novel color rendering technologies.

[0003] In the realization of structural colors, researchers have explored various technical approaches. For example, Chinese patent CN121005870A discloses a method for synthesizing a high-refractive-index-difference bottle brush block polymer and a biodegradable structural color material, which utilizes self-assembled photonic crystals to achieve broadband structural colors. Chinese patent CN120848084A discloses a high-purity structural color device and color rendering method based on metasurfaces, which combines interference and resonance effects on all-dielectric metasurfaces to obtain high-purity colored light. However, these solutions often face challenges such as complex design, difficult fabrication, or high cost, limiting their large-scale application.

[0004] On the other hand, in the field of radiation-cooling thin films, the technical goal is to maximize the reflection of sunlight to reduce heat load. For example, Chinese patent CN120648141A discloses a SiO2 / TiO2 / PMMA radiation-cooling thin film and its preparation method, proposing a multilayer film based on SiO2 / TiO2 / PMMA; Chinese patent CN119826389A discloses a dual-selective all-inorganic radiation-cooling thin film and its preparation method, employing a design of a metal reflective layer and a selective emission layer; Chinese patent CN120269884A discloses a daytime radiation-cooling coating, daytime radiation-cooling material, its preparation method and application, employing a porous structure design, which can achieve efficient daytime cooling, but its high reflectivity spectral characteristics usually cover the entire visible light band, resulting in the film's appearance inevitably being white or light-colored.

[0005] There is a huge market demand for dark-colored materials (such as building facades and automotive paint). Traditional cooling materials, in order to maximize the reflection of sunlight for cooling, typically maintain high reflectivity across the entire solar spectrum (including visible and near-infrared light), which inevitably results in a white or light-colored appearance. Traditional dark-colored materials achieve their dark appearance by broadband absorption of visible light, but they usually absorb both visible and near-infrared light simultaneously, leading to severe solar heat accumulation and a dramatic temperature rise under sunlight. This presents a fundamental contradiction between "dark-colored heat absorption" and "efficient cooling," creating a technological bottleneck in the industry.

[0006] Therefore, a significant contradiction exists in current technology: efficient cooling requires high reflectivity, while the aesthetic appeal of dark colors requires high absorption. Developing a thin film that can balance dark or color visual performance with efficient daytime radiative cooling capacity has become a key technological challenge that urgently needs to be overcome in this field, and it also has significant market application value. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a colored cooling optical film, which has a high average absorption rate in the visible light region, a certain reflectivity in a specific wavelength range, and can achieve a certain color. In certain applications, it can achieve color changes or fixed colors. It also has high reflectivity in the near-infrared band of 800nm-2500nm, which enables it to achieve a good cooling effect.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows: This invention provides a color cooling optical film, which comprises, from bottom to top, a metal layer M, a first dielectric layer D1, an absorption layer A, a second dielectric layer D2, a third dielectric layer D3, and a fourth dielectric layer D4 stacked together; The metal layer M, the first dielectric layer D1, and the absorption layer A constitute a color layer, which is used to regulate the spectral characteristics of the visible light band to achieve a fixed color and high reflectivity in the near-infrared band. The second dielectric layer D2 and the third dielectric layer D3 constitute a near-infrared enhancement layer to improve the reflectivity in the near-infrared band. The fourth dielectric layer D4 is an anti-reflection layer, used to reduce residual reflection in the visible light band and protect the underlying film layer. The film has a high absorption rate in the 400nm-800nm ​​visible light band to achieve a colored appearance, and a high reflectivity in the 800nm-2500nm near-infrared band for cooling effect.

[0009] Furthermore, the thickness of the metal layer M is 50 nm or more, and the material is selected from at least one of gold, silver, aluminum, copper, titanium, nickel, chromium and iron.

[0010] Furthermore, the thicknesses of the first dielectric layer D1, the second dielectric layer D2, the third dielectric layer D3, and the fourth dielectric layer D4 are each independent and range from 1 nm to 600 nm. The material is a fully dielectric thin film material with a refractive index between 1.2 and 3 in the wavelength range of 400 nm to 800 nm.

[0011] Furthermore, the all-dielectric thin film material is selected from at least one of magnesium fluoride, silicon dioxide, zinc oxide, iron oxide, silicon nitride, aluminum oxide, aluminum fluoride, cerium fluoride, lanthanum chloride, sodium hexachloroaluminate, neodymium fluoride, barium fluoride, calcium fluoride, lithium fluoride, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, niobium oxide, lanthanum titanate, yttrium oxide, zinc sulfide, silicon nitride, bismuth oxide, cerium oxide, and chromium oxide.

[0012] Furthermore, the thickness of the absorption layer A is 1nm-150nm, and the material is a material with an extinction coefficient of 0.2-4 in the wavelength range of 400nm-800nm, selected from at least one of platinum, nickel, titanium, chromium, iron oxide, germanium, tungsten, single crystal silicon and polycrystalline silicon.

[0013] Furthermore, the thin film also includes a phase change layer P, which is disposed between the first dielectric layer D1 and the absorption layer A. The metal layer M, the first dielectric layer D1, the phase change layer P, and the absorption layer A constitute a color layer, which is used to regulate the spectral characteristics of the visible light band to achieve color change and high reflectivity in the near-infrared band.

[0014] Furthermore, the phase change layer P has a thickness of 1nm-30nm and is made of a phase change material with an extinction coefficient of 0.5-4 in the wavelength range of 400nm-800nm, selected from at least one of vanadium dioxide, GST, GSST, GeTe, antimony sulfide and antimony selenide.

[0015] Furthermore, the thin film has a symmetrical structure, with the metal layer M as the center, and the first dielectric layer D1, the absorption layer A, the second dielectric layer D2, the third dielectric layer D3 and the fourth dielectric layer D4 arranged symmetrically on both sides in sequence, forming a stacked structure of D4D3D2AD1MD1AD2D3D4. Alternatively, the thin film may have a symmetrical structure, with the metal layer M as the center and the first dielectric layer D1, phase change layer P, absorption layer A, second dielectric layer D2, third dielectric layer D3 and fourth dielectric layer D4 arranged symmetrically on both sides, forming a stacked structure of D4D3D2APD1MD1PAD2D3D4.

[0016] This invention also provides a method for preparing a colored cooling optical film, which requires providing a colored cooling optical film as described above, and includes the following steps: Step 1: Design the thin film structure according to user requirements, specifically: (1) If the user requires the design of an asymmetric fixed color film, the film structure is: MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (2) If the user requires the design of an asymmetric variable color thin film, the thin film structure is: MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (3) If the user requires the design of a symmetrical fixed color film, the film structure is: D4D3D2AD1MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (4) If the user requires the design of a symmetrical variable color thin film, the thin film structure is: D4D3D2APD1MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. Step 2: Adjust the material and thickness of each layer in the thin film structure so that the thin film has high absorption in the visible light band of 400nm to 800nm ​​and high reflectivity in the near-infrared band of 800nm ​​to 2500nm. Step 3: Determine the structural parameters required to prepare the thin film structure based on the design results. The structural parameters include the total number of layers, the material used for each layer, the thickness of each layer, and the distribution between each layer. Step 4: Place the substrate into the cavity of the film-forming device; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between each layer, the first layer, the second layer, ... up to the last layer of the thin film structure are grown sequentially on the substrate to complete the preparation of the thin film.

[0017] Furthermore, the substrate is selected from polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate / polymethyl methacrylate composite, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene, or polydifluoroethylene. In step 5, the first layer, the second layer, and so on, of the thin film structure are grown sequentially on the substrate using physical vapor deposition. The physical vapor deposition method includes ion beam sputtering deposition, magnetron sputtering deposition, electron beam evaporation, or electron beam evaporation ion-assisted deposition.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention achieves "intelligent" band-specific management of the solar spectrum through ingenious membrane design. It achieves high absorption in the visible light band to present a dark color, while achieving high reflectivity in the near-infrared band to block heat input. This realizes functional integration and successfully combines the traditionally mutually exclusive functions of "dark appearance" and "daytime radiative cooling" into one, providing a revolutionary solution.

[0019] 2. Superior design, flexible structure, excellent performance, and easy fabrication. The membrane structure of this invention is scientifically designed with clearly defined functions. For the color layer (MD1PA / MD1A), the Fabry-Perot resonance principle is used to generate selective or broadband strong absorption in the visible light band, precisely controlling the color. For the near-infrared enhancement layer (D2D3), the reflectivity in the near-infrared band is drastically increased through interference effects, "accelerating the upscaling" and ensuring the cooling effect. The AR layer (D4) further reduces residual reflection of visible light, making the color purer and darker, and protecting the internal membrane layers. This allows for diverse colors and performance; by adjusting the thickness and material of each layer (especially D1, P, A, D2, D3), black can be achieved to meet different application scenarios and aesthetic requirements.

[0020] 3. This invention utilizes a wide range of materials and employs mature manufacturing processes. The selection of materials for the metal layer, dielectric layer, phase change layer, and absorber layer is broadly defined, avoiding reliance on specific scarce materials and facilitating cost control and mitigating supply chain risks. The physical vapor deposition (PVD) technologies employed (such as magnetron sputtering and electron beam evaporation) are mature and standardized industrial processes, easily enabling large-scale, low-cost manufacturing with promising industrialization prospects. This invention provides two core structures. For asymmetric structures, the thin film can be deposited on various substrates, including rigid substrates (such as glass and polished metal) and flexible substrates (such as PET, PI, PC / PMMA, etc.). This significantly expands its application scenarios, allowing it to be used in robust outdoor building materials as well as in flexible wearable devices or flexible electronic product casings requiring bending. For symmetric structures, the optical properties are identical regardless of the light's incidence, allowing them to be fragmented and incorporated into automotive paint for spraying. Simultaneously, the proposed symmetric structure design (centered on the metal layer) helps to counteract internal stresses within the film, improving its mechanical stability and durability.

[0021] 4. This invention has wide applications, huge market potential, and significant social benefits. Its technical characteristics enable it to penetrate multiple high-value markets and solve core industry pain points. In the construction and energy conservation field, it can be used on dark-colored building facades and roofs, significantly reducing air conditioning energy consumption while maintaining aesthetic design, thus contributing to the development of green buildings. In the automotive industry, it can be used on dark car paint and window films, significantly reducing interior temperatures in summer, improving driving comfort, reducing air conditioning energy consumption, and increasing the driving range of electric vehicles. In the electronics field, it can be used on the dark-colored casings of smartphones, laptops, and other devices, meeting market preferences while preventing overheating and ensuring performance and lifespan. In the field of outdoor facilities and precision instruments, it can be used on the casings of 5G base stations and power cabinets, ensuring stable operation of equipment at high temperatures; when used on the inner walls of precision instruments, it can absorb stray light, reduce thermal noise, and improve measurement accuracy. It can also be applied to special clothing, photovoltaic panel backsheets, etc., with broad prospects. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the asymmetric film structure of a colored cooling optical thin film (fixed color) according to the present invention.

[0024] Figure 2 This is a schematic diagram of the asymmetric film structure of a color cooling optical thin film (color-changing) according to the present invention.

[0025] Figure 3 This is a schematic diagram of a symmetrical film system structure of a colored cooling optical thin film (fixed color) according to the present invention.

[0026] Figure 4 This is a schematic diagram of a symmetrical film system structure of a color cooling optical thin film (color-changing) according to the present invention.

[0027] Figure 5 This is a reflection spectrum of a colored cooling optical thin film (variable color asymmetric structure) of the present invention in the 400nm-2500nm band under vertical incidence before phase transition.

[0028] Figure 6 This is a chromaticity coordinate diagram of one embodiment of a color cooling optical thin film (variable color asymmetric structure) of the present invention under vertical incidence before phase transition.

[0029] Figure 7This is a reflection spectrum of a colored cooling optical thin film (variable color asymmetric structure) of the present invention in the 400nm-2500nm band under vertical incidence after phase transition.

[0030] Figure 8 This is a chromaticity coordinate diagram under perpendicular incidence after phase transition, representing one embodiment of a color-cooled optical thin film (variable color asymmetric structure) of the present invention.

[0031] Figure 9 This is the absorption spectrum of a second embodiment of the colored cooling optical thin film (fixed color asymmetric structure) of the present invention, under vertical incidence at 400nm-800nm.

[0032] Figure 10 This is a reflection spectrum of a second embodiment of a colored cooling optical thin film (fixed color asymmetric structure) of the present invention in the 800nm-2500nm band under vertical incidence.

[0033] Figure 11 This is the absorption spectrum of a color cooling optical thin film (color-changing asymmetric structure) according to a third embodiment of the present invention, under vertical incidence in the 400nm-800nm ​​band after the introduction of a phase change layer.

[0034] Figure 12 This is a reflection spectrum of the 800nm-25nm band under vertical incidence after introducing a phase change layer in a third embodiment of the color cooling optical thin film (color-changing asymmetric structure) of the present invention.

[0035] Figure 13 This is a reflection spectrum of a fourth embodiment of a colored cooling optical thin film (fixed color symmetrical structure) of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0036] Figure 14 This is a reflection spectrum of a fourth embodiment of a colored cooling optical thin film (fixed color symmetrical structure) of the present invention in the 800nm-2500nm band under vertical incidence.

[0037] Figure 15 This is a chromaticity coordinate diagram under vertical incidence, representing a fourth embodiment of the color cooling optical thin film (fixed color symmetrical structure) of the present invention. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please see Figures 1-15 The present invention provides a color cooling optical film, wherein the film comprises, from bottom to top, a metal layer M, a first dielectric layer D1, an absorption layer A, a second dielectric layer D2, a third dielectric layer D3 and a fourth dielectric layer D4 stacked together; The metal layer M, the first dielectric layer D1, and the absorption layer A constitute a color layer, which is used to regulate the spectral characteristics of the visible light band to achieve a fixed color and high reflectivity in the near-infrared band. The second dielectric layer D2 and the third dielectric layer D3 constitute a near-infrared enhancement layer, which is used to accelerate the ramp-up speed of light from the light band to the near-infrared band and improve the reflectivity of the near-infrared band. The fourth dielectric layer D4 is an anti-reflection layer (AR layer), used to reduce residual reflection in the visible light band and protect the underlying film layer. The film has a high absorption rate in the 400nm-800nm ​​visible light band to achieve a colored appearance, and a high reflectivity in the 800nm-2500nm near-infrared band for cooling effect.

[0040] In this embodiment, the thickness of the metal layer M is 50 nm or more, and the material is selected from at least one of gold (Au), silver (Ag), aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), chromium (Gr), and iron (Fe). A thickness of 50 nm or more can improve reflectivity, reflecting visible light that has not been absorbed by the absorption layer back into the absorption layer, thereby improving the absorption rate in the visible light band.

[0041] In this embodiment, the thicknesses of the first dielectric layer D1, the second dielectric layer D2, the third dielectric layer D3, and the fourth dielectric layer D4 are independent and range from 1 nm to 600 nm. The material is a fully dielectric thin film material with a refractive index between 1.2 and 3 in the wavelength range of 400 nm to 800 nm.

[0042] In this embodiment, the all-dielectric thin film material is selected from at least one of magnesium fluoride (MgF2), silicon dioxide (SiO2), aluminum oxide (Al2O3), zinc oxide (ZnO), iron oxide (Fe2O3), silicon nitride (Si3N4), aluminum fluoride (AlF3), cerium fluoride (CeF3), lanthanum chloride (LaF3), sodium hexachloroaluminate (Na3AlF6), neodymium fluoride (NdF3), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), tantalum oxide (Ta2O5), titanium oxide (TiO2), hafnium oxide (HfO2), zirconium oxide (ZrO2), niobium oxide (Nb2O5), lanthanum titanate (La2Ti2O7), yttrium oxide (Y2O3), zinc sulfide (ZnS), bismuth oxide (Bi2O3), cerium oxide (CeO2), and chromium oxide (Cr2O3).

[0043] In this embodiment, the thickness of the absorption layer A is 1nm-150nm, and the material is a material with an extinction coefficient of 0.2-4 in the wavelength range of 400nm-800nm, selected from at least one of platinum (Pt), nickel (Ni), titanium (Ti), chromium (Cr), iron oxide (Fe2O3), germanium (Ge), tungsten (W), single-crystal silicon (Si), and polycrystalline silicon. In this embodiment, the thin film further includes a phase change layer P, which is disposed between the first dielectric layer D1 and the absorption layer A. The metal layer M, the first dielectric layer D1, the phase change layer P, and the absorption layer A constitute a color layer, used to control the spectral characteristics in the visible light band to achieve color change and high reflectivity in the near-infrared band. Color changes can be achieved by utilizing the phase change characteristics of phase change materials. Furthermore, since most phase change materials have a high extinction coefficient in the visible light band, the synergistic absorption of the phase change layer P and the absorption layer A in the visible light band can achieve a higher absorption rate than a single absorption layer A. In other words, the phase change layer plays a role in color change and enhancing visible light absorption.

[0044] In this embodiment, the thickness of the phase change layer P is 1nm-30nm, and the material is a phase change material with an extinction coefficient of 0.5-4 in the wavelength range of 400nm-800nm, selected from at least one of vanadium dioxide (VO2), GST (Ge2Sb2Te5), GSST (Ge2Sb2Se4Te1), GT (GeTe), antimony sulfide (Sb2S3), and antimony selenide (Sb2Se3).

[0045] In this embodiment, the thin film has a symmetrical structure. With the metal layer M as the center, a first dielectric layer D1, an absorption layer A, a second dielectric layer D2, a third dielectric layer D3 and a fourth dielectric layer D4 are symmetrically arranged on both sides in sequence to form a stacked structure of D4D3D2AD1MD1AD2D3D4. Alternatively, the thin film may have a symmetrical structure, with the metal layer M as the center and the first dielectric layer D1, phase change layer P, absorption layer A, second dielectric layer D2, third dielectric layer D3 and fourth dielectric layer D4 arranged symmetrically on both sides, forming a stacked structure of D4D3D2APD1MD1PAD2D3D4.

[0046] The entire membrane structure is described in detail below: According to the theory of light propagation in thin-film systems, light travels through the layered medium in the form of a plane electromagnetic wave. For absorbing materials, a complex refractive index needs to be introduced. ,in, n For refractive index, k The extinction coefficient is [value]. The wavelength is [wavelength]. A plane wave along a given Light intensity propagating along the axis As shown in the following formula: (1) In the formula, The intensity of the incident light. Let be the absorption coefficient of the material. From equation (1), it can be seen that, under the condition of a constant incident wavelength, the attenuation of light in the medium is related to the distance of the incident light into the medium. z and extinction coefficient k Related. For the same distance z The larger the extinction coefficient, the greater the attenuation of light. The extinction coefficient plays a crucial role in the absorption of materials.

[0047] Therefore, the attenuation of incident light in the visible light band can be increased by selecting materials with high extinction coefficients in the visible light band. Thus, this invention utilizes materials with high extinction coefficients in the visible light band as the absorption layer, such as nickel (Ni), titanium (Ti), iron oxide (Fe2O3), germanium (Ge), chromium (Cr), tungsten (W), and silicon (Si).

[0048] Phase change materials (PCMs) are materials that undergo rapid, reversible phase transitions under specific conditions (such as thermal, optical, and electrical signals), accompanied by significant changes in optical constants such as refractive index and extinction coefficient. This alters their optical path length, enabling spectral manipulation. Furthermore, some PCMs exhibit high extinction coefficients in the visible light band, enhancing visible light absorption and achieving deeper colors. Therefore, vanadium dioxide (VO2), GST (Ge2Sb2Te5), GSST (Ge2Sb2Se4Te1), and GT (GeTe) can be used as phase change layers.

[0049] For a multilayer film structure like MD1PA, the optical properties of each layer can be accurately calculated using the characteristic matrix method, and its characteristic matrix is ​​shown in equation (2): (2) Where j is the corresponding layer number, For the phase thickness of the layer, It is the complex refractive index. It is the physical thickness. It is the refractive index angle. Its optical admittance. The system matrix of the entire multilayer film structure is the product of the characteristic matrices of each film layer. The characteristic matrix of the MD1PA structure is expressed as shown in equation (3): (3) The generalized reflectivity R and transmittance T of the system can be calculated from the matrix elements: (4) (5) After the incident light enters the MD1PA cavity, the physical optical path length for one round trip between the interfaces is 2nd; simultaneously, the reflection phases of the two reflecting interfaces are respectively... and When the total optical path difference satisfies the following conditions for constructive interference: + (6) The resonant wavelength is obtained as follows: (7) According to equation (7), the position of the resonant wavelength can be controlled by changing the refractive index and thickness of D1, and the materials used for P and A, so as to obtain the desired reflection spectrum.

[0050] Using only a single-layer MD1PA structure results in a slow near-infrared upslope. Therefore, a near-infrared enhancement layer is needed to accelerate the upslope. The structure of the near-infrared enhancement layer is D2D3. After introducing the near-infrared layer, the base layer structure is considered as a whole. When near-infrared light reaches the bottom metal M, it is reflected back due to the high reflectivity of metal M. Constructive interference occurs between the near-infrared reflected light at interfaces A / D2, D2 / D3, and D3 / D4. According to equation (7), by adjusting the thickness and material of D2D3, the upslope of near-infrared light near the visible light range can be achieved, i.e., the rate of increase in reflectivity for wavelengths beyond 800nm ​​can be realized.

[0051] When realizing a black cooling film, high broadband absorption in the visible light band is required. Broadband absorption in the visible light band cannot be achieved solely by the base layer and the near-infrared enhancement layer. Therefore, a low-refractive-index material is needed as the AR film to reduce residual reflection in the visible light band and thus improve its absorption rate. According to equation (2), the characteristic matrix of the entire MD1PAD2D3D4 structure is: (8) Its equivalent admittance is: (9) in, The admittance of the substrate is considered. Adding a layer of low-refractive-index material reduces the equivalent admittance Y of the entire system. Treating the overall structure as a single-layer film, the reflectance formula is used... ,in, Let R be the refractive index of air. According to the reflectance formula, adding a layer of low-refractive-index material reduces R, lowering the residual reflection of the entire structure and increasing the absorption of visible light, thus achieving black. In some applications, a stable color is required. In this case, the phase transition layer can be removed, and only the MD1AD2D3D4 structure can be retained, achieving good color and cooling effects.

[0052] This invention also provides a method for preparing a colored cooling optical film, which requires providing a colored cooling optical film as described above, and includes the following steps: Step 1: Design the thin film structure according to user requirements, specifically: (1) If the user requires the design of an asymmetric fixed color film, the film structure is: MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (2) If the user requires the design of an asymmetric variable color thin film, the thin film structure is: MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (3) If the user requires the design of a symmetrical fixed color film, the film structure is: D4D3D2AD1MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (4) If the user requires the design of a symmetrical variable color thin film, the thin film structure is: D4D3D2APD1MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. Step 2: Adjust the material and thickness of each layer in the thin film structure so that the thin film has high absorption in the visible light band of 400nm to 800nm ​​and high reflectivity in the near-infrared band of 800nm ​​to 2500nm. Step 3: Determine the structural parameters required to prepare the thin film structure based on the design results. The structural parameters include the total number of layers, the material used for each layer, the thickness of each layer, and the distribution between each layer. Step 4: Place the substrate into the cavity of the film-forming device; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between each layer, the first layer, the second layer, ... up to the last layer of the thin film structure are grown sequentially on the substrate to complete the preparation of the thin film.

[0053] In this embodiment, the substrate is selected from polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate (PET), cellulose triacetate (TAC), polymethyl methacrylate (PMMA), polycarbonate / polymethyl methacrylate composite (PC / PMMA), polyimide (PI), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl butyral (PVB), ethylene vinyl acetate copolymer (EVA), polyurethane elastomer (TPU), polytetrafluoroethylene (PTFE), fluoroethyl propylene (FEP), or polydifluoroethylene (PVDF). In step 5, the first layer, the second layer, and so on, of the thin film structure are grown sequentially on the substrate using physical vapor deposition (PVD). The physical vapor deposition method includes ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB), or electron beam evaporation ion-assisted deposition (EBD-IAD).

[0054] Example 1 like Figure 2 As shown, this structure consists of seven layers, comprising a substrate and, from bottom to top, a stacked metal layer M (Ag), a first dielectric layer D1 (SiO2), a phase change layer P (GSST), an absorption layer A (Ge), a second dielectric layer D2 (Si3N4), a third dielectric layer D3 (Fe2O3), and a fourth dielectric layer D4 (MgF2), totaling seven layers. The substrate is a K9 glass deposition film with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thickness of each layer is shown in Table 1. A colored cooling film (color-changing) can be prepared according to the thickness values ​​given in Table 1. Before the phase change material undergoes a phase change, its vertically incident reflection spectrum is as follows... Figure 5 As shown, in the visible light band (400-800nm), it has a peak reflectance of 70.3% at 715nm, and an average reflectance of 90.2% in the near-infrared band (800-2500nm), achieving a good cooling effect. Its chromaticity coordinates are as follows... Figure 6 As shown, the corresponding chromaticity coordinates are x=0.5168, y=0.3775, which corresponds to orange. After the phase transition, its perpendicularly incident reflectance spectrum is as follows... Figure 7 As shown, in the visible light band (400-800nm), it has a peak reflectance of 47.2% at 757nm, and an average reflectance of 66.4% in the near-infrared band (800-2500nm), achieving a good cooling effect. Its chromaticity coordinates are as follows... Figure 8 As shown, the corresponding chromaticity coordinates are x=0.3564, y=0.2061, which is a purplish-red.

[0055] Table 1. Film thickness parameters for one of the embodiments (unit: nm)

[0056] Example 2 In some applications where color-changing functionality is not required, removing the phase change layer P and retaining the remaining structure can still achieve good cooling of colored thin films, such as... Figure 1 As shown, this structure consists of six layers, comprising a substrate and, from bottom to top, a metal layer M (Al), a first dielectric layer D1 (Al2O3), an absorber layer A (Ni), a second dielectric layer D2 (BaF2), a third dielectric layer D3 (ZnO), and a fourth dielectric layer D4 (CaF2), for a total of six layers. The substrate is a K9 glass deposition film with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thickness of each layer is shown in Table 2. A colored cooling film (fixed color) can be prepared according to the thickness values ​​given in Table 2. Figure 9 The absorption spectrum of the visible light band (400nm-800nm) under vertical incidence is shown in Example 2. The average absorption rate reaches 91.7%, which can achieve black. Figure 10 The image shows the reflection spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 2. The average reflectivity of this film system can reach 62.4%, which shows that it has a good reflection effect on the near-infrared band and can effectively achieve the cooling effect.

[0057] Table 2. Film thickness parameters for Example 2 (unit: nm)

[0058] Example 3 Based on Example 2, adding a phase change layer P can enhance absorption and achieve a deeper black color. For example... Figure 2 As shown, this structure consists of seven layers, comprising a substrate and, from bottom to top, a stacked metal layer M (Al), a first dielectric layer D1 (Al2O3), a phase change layer P (GST), an absorption layer A (Ni), a second dielectric layer D2 (BaF2), a third dielectric layer D3 (ZnO), and a fourth dielectric layer D4 (CaF2), for a total of seven layers. The substrate is a K9 glass deposition film with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thickness of each layer is shown in Table 3. A colored cooling film can be fabricated according to the thickness values ​​given in Table 3. Figure 11 The absorption spectrum of the visible light band (400nm-800nm) under vertical incidence is shown in Example 3. The average absorption rate reaches 96.7%, which can achieve black. Figure 12The image shows the reflection spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 3. The average reflectivity of this film system can reach 60%, demonstrating its excellent reflection effect on the near-infrared spectrum and its ability to effectively achieve cooling.

[0059] Table 3. Film thickness parameters for one of the embodiments (unit: nm)

[0060] Example 4 To broaden the scope of applications, the structure can be made symmetrical. For example... Figure 3 As shown, this structure consists of 11 layers: a substrate Sub, two symmetrical metal layers M (Pt), a first dielectric layer D1 (MgF2), an absorber layer A (Si), a second dielectric layer D2 (Fe2O3), a third dielectric layer D3 (Si3N4), and a fourth dielectric layer D4 (BaF2), totaling eleven layers. The substrate is a K9 glass film with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thickness of each layer is shown in Table 4. A red cooling film can be prepared according to the thickness values ​​given in Table 4. Figure 13 The image shows the reflection spectrum of the visible light band (400nm-800nm) under vertical incidence in Example 6. As can be seen from the image, in the red light band, the peak reflectance of this film system at 800nm ​​is 65.3%, and the average reflectance reaches 47.6%. Compared with other visible light bands, it has a higher reflectance in the red light band. Figure 14 The image shows the reflection spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 6. As can be seen from the image, the average reflectivity of the film system can reach 82.8% in the near-infrared band, demonstrating its excellent reflection effect on the near-infrared and its ability to effectively achieve a cooling effect. Figure 15 The image shows the chromaticity coordinates of Embodiment Six under vertical incidence. The chromaticity coordinates of this embodiment are (0.3820, 0.2739), and its luminance value L=17.2, demonstrating that a good red structural color can be achieved.

[0061] Table 4. Film thickness parameters for Example 6 (unit: nm)

[0062] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A colored cooling optical thin film, characterized in that, The thin film comprises, from bottom to top, a metal layer M, a first dielectric layer D1, an absorber layer A, a second dielectric layer D2, a third dielectric layer D3, and a fourth dielectric layer D4, which are stacked together. The metal layer M, the first dielectric layer D1, and the absorption layer A constitute a color layer, which is used to regulate the spectral characteristics of the visible light band to achieve a fixed color and high reflectivity in the near-infrared band. The second dielectric layer D2 and the third dielectric layer D3 constitute a near-infrared enhancement layer to improve the reflectivity in the near-infrared band. The fourth dielectric layer D4 is an anti-reflection layer, used to reduce residual reflection in the visible light band and protect the underlying film layer. The film has a high absorption rate in the 400nm-800nm ​​visible light band to achieve a colored appearance, and a high reflectivity in the 800nm-2500nm near-infrared band for cooling effect.

2. The colored cooling optical thin film as described in claim 1, characterized in that, The thickness of the metal layer M is 50 nm or more, and the material is selected from at least one of gold, silver, aluminum, copper, titanium, nickel, chromium and iron.

3. The colored cooling optical film as described in claim 1, characterized in that, The thicknesses of the first dielectric layer D1, the second dielectric layer D2, the third dielectric layer D3, and the fourth dielectric layer D4 are independent and range from 1 nm to 600 nm. The material is a fully dielectric thin film material with a refractive index between 1.2 and 3 in the wavelength range of 400 nm to 800 nm.

4. The colored cooling optical film as described in claim 3, characterized in that, The all-dielectric thin film material is selected from at least one of magnesium fluoride, silicon dioxide, aluminum oxide, zinc oxide, iron oxide, silicon nitride, aluminum fluoride, cerium fluoride, lanthanum chloride, sodium hexachloroaluminate, neodymium fluoride, barium fluoride, calcium fluoride, lithium fluoride, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, niobium oxide, lanthanum titanate, yttrium oxide, zinc sulfide, silicon nitride, bismuth oxide, cerium oxide, and chromium oxide.

5. A colored cooling optical thin film as described in claim 1, characterized in that, The thickness of the absorption layer A is 1nm-150nm, and the material is a material with an extinction coefficient of 0.2-4 in the wavelength range of 400nm-800nm, selected from at least one of platinum, nickel, titanium, chromium, iron oxide, germanium, tungsten, single crystal silicon and polycrystalline silicon.

6. The colored cooling optical thin film as described in claim 1, characterized in that, The thin film further includes a phase change layer P, which is disposed between the first dielectric layer D1 and the absorption layer A. The metal layer M, the first dielectric layer D1, the phase change layer P, and the absorption layer A constitute a color layer, which is used to regulate the spectral characteristics of the visible light band to achieve color change and high reflectivity in the near-infrared band.

7. A colored cooling optical thin film as described in claim 6, characterized in that, The phase change layer P has a thickness of 1nm-30nm and is made of a phase change material with an extinction coefficient of 0.5-4 in the wavelength range of 400nm-800nm, selected from at least one of vanadium dioxide, GST, GSST, GeTe, antimony sulfide and antimony selenide.

8. A colored cooling optical thin film as described in claim 6, characterized in that, The thin film has a symmetrical structure, with the metal layer M as the center, and the first dielectric layer D1, the absorption layer A, the second dielectric layer D2, the third dielectric layer D3 and the fourth dielectric layer D4 arranged symmetrically on both sides, forming a stacked structure of D4D3D2AD1MD1AD2D3D4. Alternatively, the thin film may have a symmetrical structure, with the metal layer M as the center and the first dielectric layer D1, phase change layer P, absorption layer A, second dielectric layer D2, third dielectric layer D3 and fourth dielectric layer D4 arranged symmetrically on both sides, forming a stacked structure of D4D3D2APD1MD1PAD2D3D4.

9. A method for preparing a colored cooling optical thin film according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Design the thin film structure according to user requirements, specifically: (1) If the user requires the design of an asymmetric fixed color film, the film structure is: MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (2) If the user requires the design of an asymmetric variable color thin film, the thin film structure is: MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (3) If the user requires the design of a symmetrical fixed color film, the film structure is: D4D3D2AD1MD1AD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. (4) If the user requires the design of a symmetrical variable color thin film, the thin film structure is: D4D3D2APD1MD1PAD2D3D4, where M represents the metal layer, D1 represents the first dielectric layer, P represents the phase change layer, A represents the absorption layer, D2 represents the second dielectric layer, D3 represents the third dielectric layer, and D4 represents the fourth dielectric layer. Step 2: Adjust the material and thickness of each layer in the thin film structure so that the thin film has high absorption in the visible light band of 400nm to 800nm ​​and high reflectivity in the near-infrared band of 800nm ​​to 2500nm. Step 3: Determine the structural parameters required to prepare the thin film structure based on the design results. The structural parameters include the total number of layers, the material used for each layer, the thickness of each layer, and the distribution between each layer. Step 4: Place the substrate into the cavity of the film-forming device; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between each layer, the first layer, the second layer, ... up to the last layer of the thin film structure are grown sequentially on the substrate to complete the preparation of the thin film.

10. The method for preparing a colored cooling optical film as described in claim 9, wherein the substrate is selected from polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate / polymethyl methacrylate composite material, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene, or polydifluoroethylene; In step 5, the first layer, the second layer, and so on, of the thin film structure are grown sequentially on the substrate using physical vapor deposition. The physical vapor deposition method includes ion beam sputtering deposition, magnetron sputtering deposition, electron beam evaporation, or electron beam evaporation ion-assisted deposition.

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