A black radiation-cooling thin film and its preparation method

Abstract

This invention discloses a black radiation-cooling thin film and its preparation method. The thin film comprises, from bottom to top, a substrate Sub, a black reflective module, and a radiation module. The structure of the black reflective module, from bottom to top, is MD1AD2, where M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer. The structure of the radiation module, from bottom to top, is (A'1A'2A'3). s L, where A'1, A'2, and A'3 are the first, second, and third absorption layers, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is a low refractive index protective layer; and s is the number of stacked periods, s≥1. This invention achieves good cooling performance while maintaining a black color.

Description

Technical Field

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

[0002] Nature is like an endless scroll of color, its magnificent color-producing mechanisms primarily attributed to two categories: pigment colors and structural colors. Pigment colors, also known as chemical colors, originate from specific chemical molecular structures within substances. These structures selectively absorb energy of certain wavelengths of visible light, while reflecting or transmitting the remaining wavelengths. Once received by the human eye, the brain interprets these colors as we perceive them, such as the vibrant green of plants given by chlorophyll, and the myriad hues of various paints and dyes. In contrast, structural colors are a clever physical method of color production. They do not rely on chemical pigments but rather on the precise microscopic structures of an object's surface (such as photonic crystals and gratings) that cause physical effects like interference, diffraction, or scattering of light, thus "weaving" together ever-changing colors. The iridescence of soap bubbles, the brilliance of peacock feathers, and the azure of the sky are all masterpieces of structural colors. Compared to chemical pigments, structural colors typically possess significant advantages such as high stability (resistant to fading), environmental friendliness, non-toxicity, and superior color saturation and brightness.

[0003] Among the many colors, black occupies a unique and important position. It is not only a favorite symbol of classicism and professionalism in the fashion world and industrial design (such as clothing, automotive paint, and electronic products), but also shines brightly in the scientific research field due to its special optical properties. Black materials can achieve broadband and efficient absorption in the visible light band (400-800nm), making them an ideal choice for absorbing stray light and improving image contrast, and are widely used in precision optical instruments. However, the other side of "black" is its efficient conversion of light energy. It is precisely this near-full-band absorption of visible light that makes black objects more prone to heat accumulation under illumination, facing significant thermal challenges—rapid heating, which may lead to performance degradation or shortened lifespan of devices. Solar radiation energy is distributed across a wide band of 400-2500nm; therefore, the core technology for creating a "cool" black material lies in: while maintaining perfect blackness in the visible light band, it must efficiently reflect near-infrared light in the 0.8-2.5µm band to isolate the main source of heat.

[0004] To achieve the ultimate black color, researchers have explored various technological approaches. Metamaterial absorption structures can precisely capture light waves through artificially designed subwavelength units; carbon nanotube arrays utilize their extremely low reflectivity and huge specific surface area to construct near-ideal "light traps"; in addition, there are various organic polymer structures and precisely designed planar thin film stacks. For example, Chinese invention publication CN120060781A proposes a gradient structure from a "base layer" to a "transition layer" and then to a "blackening functional layer." This design not only optimizes optical performance but also solves the problem of the film's mechanical robustness. The base layer (metallic elements and carbides) ensures a strong bond with the substrate; the transition layer (metal carbides and a small amount of carbon) alleviates interlayer stress; and the functional layer (metal carbides and a large amount of carbon) is mainly responsible for light absorption. Another Chinese invention publication CN118027475A provides a method for preparing a weather-resistant agricultural black polyethylene film. By blending two types of loaded antioxidants (diatomaceous earth-based and attapulgite-based) with polyethylene, lubricant, and black masterbatch into blown film, the resulting mulch film exhibits excellent weather resistance, can be recycled for three years, and retains high mechanical properties. This method aims to improve recycling rates, address white pollution, and reduce usage costs.

[0005] Meanwhile, radiation-cooling thin-film technology, as another powerful tool against overheating, has also made significant progress. Its goal is to efficiently reflect sunlight and enhance infrared radiation heat dissipation. Chinese invention publication CN120648141A proposes a three-layer structure based on SiO2 / TiO2 / PMMA. This design cleverly achieves high reflectivity in the ultraviolet, visible, and near-infrared bands, and exhibits high emissivity in the mid-infrared atmospheric window band, thereby achieving a cooling effect below ambient temperature, with low manufacturing costs. Chinese invention publication CN119826389A employs a composite architecture of a "metal reflective layer + selective emission dielectric film." The metal layer reflects most of the solar spectrum, while the carefully designed dielectric film layer generates sharp emission peaks in the atmospheric window band (8-13µm, etc.), greatly improving radiation-cooling efficiency. The Chinese invention with publication number CN120269884A proposes a porous daytime radiation cooling coating. It enhances sunlight reflection through the mixing of materials such as barium sulfate, yttrium oxide, and alumina and the design of a porous structure. It also enhances infrared emission capability by leveraging a large specific surface area, demonstrating the powerful potential of material microstructure in thermal management.

[0006] However, a key contradiction remains: to achieve a deep black color, the material must have extremely high absorptivity in the visible light band, but this leads to the accumulation of solar energy and significant temperature increases; conversely, to achieve radiative cooling, the material must have high reflectivity in the solar spectrum (especially near-infrared), but inevitably retains considerable reflectivity in the visible light band, which makes the material typically appear white or light-colored. Integrating these seemingly contradictory properties of "ultimate blackness" and "efficient cooling" is a challenging and cutting-edge research topic. Therefore, developing a pure black thin film capable of achieving significant radiative cooling is not only an extreme challenge to optical design, materials science, and thermal management technology, but will also open up new application paradigms for high-end electronic device appearance, the automotive industry, building energy conservation, and special equipment requiring a black appearance and sensitive to temperature, possessing extremely significant scientific research value and industrial application prospects. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a black radiation-cooling thin film that achieves high absorption in the visible light band of 400nm-800nm, high reflectivity in the near-infrared band of 800nm-2500nm, and high emissivity in the atmospheric window band of 8000nm-13000nm, thereby achieving good cooling effect while achieving blackness.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows: This invention provides a black radiation-cooling thin film, which, from bottom to top, comprises: a substrate Sub, a black reflective module, and a radiation module; the structure of the black reflective module, from bottom to top, is MD1AD2, wherein: M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer; the structure of the radiation module, from bottom to top, is (A'1A'2A'3). s L, where: A'1, A'2 and A'3 are the first absorption layer, the second absorption layer and the third absorption layer, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is the low refractive index protective layer; s is the number of stacked periods, s≥1; The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

[0009] Furthermore, the thickness of the metal layer M is greater than 50 nm; the material of the metal layer M is selected from one of gold, silver, aluminum, copper, iron, nickel, chromium, titanium, germanium and niobium.

[0010] Furthermore, the thickness of the first dielectric layer D1 ranges from 1 nm to 100 nm; the thickness of the second dielectric layer D2 ranges from 50 nm to 400 nm; the refractive index of the materials of the first dielectric layer D1 and the second dielectric layer D2 in the wavelength range of 400 nm–800 nm is between 1.2 and 3, and is selected from at least one of magnesium fluoride, silicon dioxide, 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, chromium oxide, cerium oxide, neodymium oxide, and zinc oxide.

[0011] Furthermore, the thickness of the visible light absorbing layer A ranges from 1 nm to 30 nm; the material of the visible light absorbing layer A has an extinction coefficient between 0.2 and 4 in the wavelength range of 400-800 nm, and is selected from at least one of nickel, titanium, chromium, iron oxide, germanium, single crystal silicon, polycrystalline silicon, antimony sulfide, antimony selenide, vanadium dioxide, GST, GSST and GT.

[0012] Furthermore, the thickness of the second absorption layer A'2 ranges from 50 nm to 300 nm, and the thicknesses of the first absorption layer A'1 and the third absorption layer A'3 range from 1 nm to 600 nm; the materials of the first absorption layer A'1, the second absorption layer A'2, and the third absorption layer A'3 have a refractive index between 1.2 and 3 in the wavelength range of 0.3-0.8 μm, and an extinction coefficient between 0.05 and 3 in the wavelength range of 8-13 μm, and are selected from one of SiO2, TiO2, Al2O3, SiN, Si3N4, and Ta2O5. The first absorption layer A'1 and the third absorption layer A'3 are selected from the same or different materials, but must have a different refractive index than the material of the second absorption layer A'2.

[0013] Furthermore, the low refractive index protective layer L has a refractive index between 1.2 and 3.0 in the wavelength range of 0.3 μm–2.5 μm, an extinction coefficient between 0 and 0.5, and an extinction coefficient between 0 and 3 in the wavelength range of 8 μm–13 μm. Its material is magnesium fluoride or silicon dioxide, and its thickness ranges from 50 nm to 200 nm.

[0014] Furthermore, the material of the substrate Sub 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.

[0015] This invention provides a method for preparing the black radiation-cooling thin film described above, comprising the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubMD1AD2(A'1A'2A'3). s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the first layer, the second layer, ... up to the last layer of the thin film structure are deposited sequentially on the substrate Sub using physical vapor deposition or chemical vapor deposition. The first layer is a metal layer M, the second layer is a first dielectric layer D1, the third layer is a visible light absorption layer A, the fourth layer is a second dielectric layer D2, the fifth layer is a first absorption layer A'1, the sixth layer is a second absorption layer A'2, the seventh layer is a third absorption layer A'3, and the last layer is a low refractive index protective layer L. Step 6: During the deposition of the metal layer M, an inert protective gas is introduced to prevent material oxidation; Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

[0016] This invention provides a black radiation-cooling thin film, the thin film consisting of a substrate Sub and a symmetrical structure L (A'3A'2A'1) with a metal layer M as the center of symmetry. s D2AD1MD1AD2(A'1A'2A'3) sThe structure consists of L, where M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer; A'1, A'2, and A'3 are the first, second, and third absorption layers, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is a low refractive index protective layer; and s is the number of stacked periods, where s≥1. The MD1AD2 structure and the D2AD1M structure constitute a black reflective module, and (A'1A'2A'3) n L-structure and L(A'3A'2A'1) n The structure consists of a radiation module; The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

[0017] This invention provides a method for preparing the black radiation-cooling thin film described above, comprising the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubL(A'3A'2A'1). s D2AD1MD1AD2(A'1A'2A'3) s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the first layer, the second layer, ..., up to the last layer of the thin film structure are deposited sequentially on the substrate Sub using physical vapor deposition or chemical vapor deposition. Step 6: During the deposition of the metal layer M, an inert protective gas is introduced to prevent material oxidation; Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. Through precise micro-nano structure design, these two seemingly contradictory properties have been successfully unified. Firstly, there is the exceptional blackness: the film boasts an average absorption rate of over 96% in the 400-800nm ​​visible light band, with some embodiments exceeding 98%. This means it reflects almost no visible light, providing the human eye with a deep, pure black visual experience, fully meeting the stringent aesthetic and brand recognition requirements of high-end consumer electronics (such as smartphones and camera bodies), the automotive industry (black car paint), and architectural design. Secondly, there is the highly efficient heat dissipation capability: the film cleverly achieves spectral management, strictly limiting heat absorption to the visible light range, while achieving a high reflectivity of over 90% or even 95% in the near-infrared band (800-2500nm), the main source of solar heat, effectively isolating most of the heat input at its source. Meanwhile, it exhibits a high emissivity of over 70% in the mid-infrared "atmospheric window" band (8-13um), with some embodiments reaching as high as 90%, enabling it to efficiently radiate absorbed or generated heat through the atmosphere into the cold space, achieving passive cooling.

[0019] 2. Utilizing a modular design, complex optical requirements are broken down into two core modules: The black reflective module (MD1AD2) consists of a bottom metal layer (M) serving as a near-infrared reflector; the middle visible light absorption layer (A) and the first dielectric layer (D1) form a Fabry-Perot resonant cavity, which efficiently consumes visible light by "trapping" it in the absorption layer through interference, thus achieving broadband absorption. This design offers higher light absorption efficiency and purer colors than simply relying on high-loss materials.

[0020] Radiation module ((A'1A'2A'3)) s L): Composed of two or three media materials with different refractive indices stacked together, it acts as a spectral separator. It is "transparent" to visible light, allowing it to be transmitted to the black module below where it is absorbed; at the same time, it is "opaque" to mid-infrared light, thus achieving high emissivity.

[0021] "Gradient cavity" design: To overcome the narrow transmission spectrum of traditional Fabry-Perot cavities, this invention employs (A'1A'2A'3). s The cavity parameter gradient design cascades multiple microcavities with slightly different resonant wavelengths, thereby forming a high and flat transmission platform in the visible light band. This ensures that light can enter the lower black reflective module uniformly and efficiently throughout the entire visible light band, which is key to achieving pure black and efficient cooling.

[0022] Admittance matching technology: Through precise calculation and design, the equivalent optical admittance of the radiation module is matched with that of the black reflection module, minimizing the residual reflection of visible light at the interface and further pushing the visible light absorption rate to the theoretical limit.

[0023] 3. This invention provides two core structures. For asymmetric structures, the thin films 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 greatly expands its application scenarios, allowing it to be used in robust outdoor building materials as well as in flexible electronic device housings requiring bending. For symmetric structures, the optical properties are the same regardless of which side the light incident from, so they can be pulverized into film fragments and incorporated into automotive paint for spraying. Simultaneously, the proposed symmetric structure design (symmetric about the metal layer) helps to counteract internal stresses in the film, improving its mechanical stability and durability. By adjusting the film thickness, stacking cycle number, and material combination, the optical properties of the thin film can be adjusted within a certain range to meet specific balance requirements for blackness, cooling efficiency, and cost in different application scenarios. Attached Figure Description

[0024] 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.

[0025] Figure 1 This is a schematic diagram of an asymmetric film system structure of a black radiation-cooling thin film according to the present invention.

[0026] Figure 2 This is a schematic diagram of a symmetrical film system structure of a black radiation-cooling thin film according to the present invention.

[0027] Figure 3 This is the absorption spectrum of a black radiation-cooling thin film according to an embodiment of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0028] Figure 4 This is a reflection spectrum of a black radiation-cooling thin film according to an embodiment of the present invention in the 800nm-2500nm band under vertical incidence.

[0029] Figure 5 This is the absorption spectrum of a black radiation-cooling thin film according to an embodiment of the present invention in the 8000nm-13000nm band under vertical incidence.

[0030] Figure 6 This is the absorption spectrum of a black radiation-cooling thin film according to a second embodiment of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0031] Figure 7 This is a reflection spectrum of a black radiation-cooling thin film according to a second embodiment of the present invention in the 800nm-2500nm band under vertical incidence.

[0032] Figure 8 This is the absorption spectrum of a black radiation-cooling thin film according to a second embodiment of the present invention in the 8000nm-13000nm band under vertical incidence.

[0033] Figure 9 This is the absorption spectrum of a black radiation-cooling thin film according to a third embodiment of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0034] Figure 10 The image shows the reflection spectrum of a black radiation-cooling thin film according to a third embodiment of the present invention in the 800nm-2500nm band under vertical incidence.

[0035] Figure 11 This is the absorption spectrum of a black radiation-cooling thin film according to a third embodiment of the present invention in the 8000nm-13000nm band under vertical incidence.

[0036] Figure 12 This is the absorption spectrum of a black radiation-cooling thin film according to a fourth embodiment of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0037] Figure 13 The image shows the reflection spectrum of a black radiation-cooling thin film according to a fourth embodiment of the present invention in the 800nm-2500nm band under vertical incidence.

[0038] Figure 14 The absorption spectrum of a black radiation-cooling thin film according to Embodiment 4 of the present invention in the 8000nm-13000nm band under vertical incidence is shown.

[0039] Figure 15 This is the absorption spectrum of a black radiation-cooling thin film according to Embodiment 5 of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0040] Figure 16 The image shows the reflection spectrum of a black radiation-cooling thin film according to Embodiment 5 of the present invention in the 800nm-2500nm band under vertical incidence.

[0041] Figure 17 The absorption spectrum of a black radiation-cooling thin film of the present invention in the 8000nm-13000nm band under vertical incidence is shown in Embodiment 5.

[0042] Figure 18 This is the absorption spectrum of a black radiation-cooling thin film according to Embodiment Six of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0043] Figure 19 The image shows the reflection spectrum of a black radiation-cooling thin film according to Embodiment Six of the present invention in the 800nm-2500nm band under vertical incidence.

[0044] Figure 20 The absorption spectrum of a black radiation-cooling thin film of the present invention in the 8000nm-13000nm band under vertical incidence is shown in Embodiment Six.

[0045] Figure 21 This is the absorption spectrum of a black radiation-cooling thin film according to Embodiment 7 of the present invention in the 400nm-800nm ​​band under vertical incidence.

[0046] Figure 22 This is the reflection spectrum of a black radiation-cooling thin film according to Embodiment 7 of the present invention in the 800nm-2500nm band under vertical incidence.

[0047] Figure 23 This is the absorption spectrum of a black radiation-cooling thin film according to Embodiment 7 of the present invention in the 8000nm-13000nm band under vertical incidence. Detailed Implementation

[0048] 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.

[0049] Please see Figure 1This invention discloses a black radiation-cooling thin film, comprising, from bottom to top: a substrate (Sub), a black reflective module, and a radiation module; the structure of the black reflective module, from bottom to top, is MD1AD2, wherein: M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer, which utilizes the underlying high-reflectivity metal layer and visible light absorption layer to achieve broadband absorption in the visible light band and high reflectivity in the near-infrared band; the structure of the radiation module, from bottom to top, is (A'1A'2A'3). s L, where A'1, A'2 and A'3 are the first absorption layer, the second absorption layer and the third absorption layer, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band. L is a low refractive index protective layer, and s is the number of stacked periods, s≥1. It has good admittance matching with the black reflective module, which can effectively reduce the residual reflection of the black reflective module, and has good emissivity in the 8-13μm band. The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

[0050] The following is a detailed description of the entire membrane structure: Since light enters the thin film through a radiation module, it needs to have high transmittance in the visible light band to prevent the radiation module from interfering with the visible light spectrum. A traditional Fabry-Perot filter consists of a resonant cavity and two mirrors. Its transmission spectrum has a very sharp peak, and its narrow bandwidth and uneven top make it unsuitable for broadband high transmittance in the visible light band. Therefore, "cavity parameter gradient design" is used to achieve broadband high transmittance in the visible light band. The core idea is to cascade multiple Fabry-Perot resonant cavities, but the resonant wavelength (i.e., center wavelength) of each cavity is designed to be slightly different.

[0051] Transmission of a single Fabry-Perot cavity It can be described by the following function: (1) in, This represents the peak transmittance for a structure with no absorption in the entire dielectric. The expression for F is R is the reflectivity of the mirror; the larger the value of F, the narrower the transmission peak. It is the phase difference for a single round trip, and its expression is: When the resonance condition is met, i.e. The expression for the center wavelength can be obtained as follows: (2) When N such filters are cascaded, the total transmittance is the product of the individual transmittances: (3) Wherein, the phase difference of the i-th cavity is .

[0052] Different optical thicknesses are set for N different resonant cavities. According to equation (2), they have different resonant wavelengths. The phase difference formula for each cavity can be rewritten around its center wavelength, letting By applying a Taylor expansion approximation, the relationship between phase difference and wavelength detuning can be obtained: (4) The transmittance function of each cavity can be viewed as a peak around its center wavelength.

[0053] Total transmittance of cascaded system It is the transmittance of all these cavities The product. By making By artificially creating a series of misaligned transmittance peaks in the target wavelength region, it is possible to maintain a high level of transmittance across the entire target wavelength region, forming a high and flat passband plateau; while on both sides, since there is at least one... A sharp drop, resulting in a decrease in total transmittance. It also drops sharply, thus forming a steep cutoff edge.

[0054] For a multilayer film structure, the optical properties of each layer can be accurately calculated using the characteristic matrix method, and its characteristic matrix is ​​shown in equation (5): (5) 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 MD1AD2 structure is expressed as shown in equation (6): (6) Assume the admittance of the substrate is Treating the MD1AD2 structure and the substrate as a subsystem, the equivalent admittance of the subsystem can be obtained as: (7) Radiation modules (A'1A'2A'3) n The characteristic matrix expression of the L-structure is shown in equation (8): (8) Combining the radiation module with the subsystem, the equivalent admittance of the entire structure is: (9) The equivalent refractive index of the radiation module can then be obtained. By treating the radiation module as the incident medium and adjusting its optical thickness to match its equivalent refractive index with the admittance of the subsystem, the desired result is achieved. This reduces the residual reflection of the black reflective module, thereby increasing its absorption rate in the visible light band.

[0055] According to Kirchhoff's laws, under thermal equilibrium conditions, the absorptivity of an object equals its emissivity. Therefore, the radiative layer needs to be made of a material with strong absorption in the 8-13µm range. At the same time, to ensure high transparency in the visible light band, the material selected for the radiative layer should have high transmittance in the 0.3-2.5µm range. Therefore, in the radiative layer units A'1A'2A'3, a material with high transparency in the visible light band and strong absorption in the 8-13µm range is selected as layer A'2. One or two materials with different refractive indices and high transparency in the visible light band and high absorption in the 8-13µm range are selected as A'1 and A'3, respectively. That is, the materials used for A'1 and A'3 can be the same or different to achieve high absorption in the 8-13µm range.

[0056] For the black reflective module, a high absorption rate of visible light is achieved by using an absorbing material with a high extinction coefficient. In terms of the propagation theory of light in thin-film systems, light propagates through the layered medium in the form of a plane electromagnetic wave. For the absorbing material, a complex refractive index needs to be introduced. Where n is the refractive index and k is the extinction coefficient. The wavelength is... A plane wave along a given The intensity of light propagating along the axial direction is as follows: (10) In the formula, The intensity of the incident light. Let be the absorption coefficient of the material. From equation (10), 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. It is related to the extinction coefficient k. For the same distance... The higher the extinction coefficient, the greater the attenuation of light; the extinction coefficient plays a crucial role in the absorption of materials. 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 spectrum. Since highly reflective metallic materials, such as silver, gold, and aluminum, have high reflectivity in the near-infrared band, a thick layer of highly reflective metal can be used as the underlayer to achieve high reflectivity in the near-infrared band.

[0057] In this embodiment, the thickness of the metal layer M is 50 nm or more, preferably 100 nm to 200 nm. In order to improve the reflectivity, visible light that is not absorbed by the visible light absorption layer is reflected back into the visible light absorption layer, thereby improving the absorption rate in the visible light band. The material of the metal layer M is selected from one of gold (Au), silver (Ag), aluminum (Al), copper (Cu), iron (Fe), nickel (Ni), chromium (Cr), titanium (Ti), germanium (Ge) and niobium (Nb).

[0058] In this embodiment, the thickness of the first dielectric layer D1 ranges from 1 nm to 100 nm, preferably from 10 nm to 90 nm; the thickness of the second dielectric layer D2 ranges from 50 nm to 400 nm, preferably from 100 nm to 400 nm; the materials of the first dielectric layer D1 and the second dielectric layer D2 are in the range of 400 nm–800 nm. The refractive index in the nm wavelength range is between 1.2 and 3, and is selected from at least one of magnesium fluoride (MgF2), silicon dioxide (SiO2), aluminum oxide (Al2O3), 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), silicon nitride (Si3N4), bismuth oxide (Bi2O3), cerium oxide (CeO2), chromium oxide (Cr2O3), magnesium oxide (MgO), neodymium oxide (Nd2O3), and zinc oxide (ZnO).

[0059] In this embodiment, the thickness of the visible light absorption layer A (an absorbing material with high absorption in the visible light band) ranges from 1 nm to 30 nm, preferably from 5 nm to 15 nm; the material of the visible light absorption layer A has an extinction coefficient between 0.2 and 4 in the wavelength range of 400-800 nm, and is selected from at least one of nickel (Ni), titanium (Ti), chromium (Cr), iron oxide (Fe2O3), germanium (Ge), single crystal silicon, polycrystalline silicon, antimony sulfide (Sb2S3), antimony selenide (Sb2Se3), vanadium dioxide (VO2), GST (Ge2Sb2Te5), GSST (Ge2Sb2Se4Te1), and GT (GeTe).

[0060] In this embodiment, the thickness of the second absorption layer A'2 ranges from 50 nm to 300 nm, and the thicknesses of the first absorption layer A'1 and the third absorption layer A'3 range from 1 nm to 600 nm. The materials of the first absorption layer A'1, the second absorption layer A'2, and the third absorption layer A'3 (which have high absorption in the 8-13 μm range) have a refractive index between 1.2 and 3 in the 0.3-0.8 μm wavelength range and an extinction coefficient between 0.05 and 3 in the 8-13 μm wavelength range. They are selected from one of SiO2, TiO2, Al2O3, SiN, Si3N4, and Ta2O5. The first absorption layer A'1 and the third absorption layer A'3 are selected from the same or different materials, but they must have different refractive indices than the material of the second absorption layer A'2.

[0061] In this embodiment, the low refractive index protective layer L has a refractive index between 1.2 and 3.0 in the wavelength range of 0.3 μm–2.5 μm, an extinction coefficient between 0 and 0.5, and an extinction coefficient between 0 and 3 in the wavelength range of 8 μm–13 μm. Its material is magnesium fluoride (MgF2) or silicon dioxide (SiO2), and its thickness ranges from 50 nm to 200 nm.

[0062] In this embodiment, the material of the substrate Sub 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).

[0063] The present invention provides a method for preparing a black radiation-cooling thin film according to the above, comprising the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubMD1AD2(A'1A'2A'3). s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the thin film structure is sequentially deposited on the substrate Sub using physical vapor deposition (PVD), either as the first layer, the second layer, and so on, up to the last layer. The first layer is a metal layer M, the second layer is a first dielectric layer D1, the third layer is a visible light absorption layer A, the fourth layer is a second dielectric layer D2, the fifth layer is a first absorption layer A'1, the sixth layer is a second absorption layer A'2, the seventh layer is a third absorption layer A'3, and the last layer is a low refractive index protective layer L. The thin film is prepared using standard deposition processes such as ion beam sputtering deposition (IBS), magnetron sputtering deposition (MS), electron beam evaporation (EB), or electron beam evaporation ion-assisted deposition (EBD-IAD). These processes have decades of experience in the optical coating and semiconductor industries, with widespread equipment availability and good process controllability, making them very suitable for large-scale, low-cost manufacturing.

[0064] Step 6: When depositing the metal layer M, an inert protective gas is introduced to prevent the material from oxidizing. When depositing the metal, in order to prevent the material from reacting with the gas and causing changes in the optical constant, oxygen or other reactive gases cannot be introduced. Only protective gases such as argon are added to maintain the deposition process.

[0065] Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

[0066] Please see Figure 2 The present invention discloses a black radiation-cooling thin film, wherein the thin film comprises a substrate Sub and a symmetrical structure L (A'3A'2A'1) with a metal layer M as the center of symmetry. s D2AD1MD1AD2(A'1A'2A'3) s The structure consists of L, where M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer; A'1, A'2, and A'3 are the first, second, and third absorption layers, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is a low refractive index protective layer; and s is the number of stacked periods, where s≥1. The MD1AD2 structure and the D2AD1M structure constitute a black reflective module, and (A'1A'2A'3) s L-structure and L(A'3A'2A'1) s The structure consists of a radiation module; The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

[0067] The present invention provides a method for preparing a black radiation-cooling thin film according to the above, comprising the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubL(A'3A'2A'1). s D2AD1MD1AD2(A'1A'2A'3) s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the first layer, the second layer, ..., up to the last layer of the thin film structure are deposited sequentially on the substrate Sub using physical vapor deposition or chemical vapor deposition. Step 6: During the deposition of the metal layer M, an inert protective gas is introduced to prevent material oxidation; Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

[0068] Example 1 like Figure 1 As shown, the thin film structure consists of a substrate Sub, a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Ag), a first dielectric layer D1 (MgF2), a visible light absorption layer A (Cr), and a second dielectric layer D2 (MgF2); the overall structure of the radiation module is (A'1A'2A'3). s The film L consists of a low-refractive-index protective layer L (SiO2), a first absorption layer A'1 (TiO2), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (TiO2). The gradient cavity consists of s stacked cycles, forming a structure of A'1A'2A'3, where s is 4. The original film system has a total of 17 layers. Since the first absorption layer A'1 and the third absorption layer A'3 are made of the same material, they are merged, resulting in a total of 14 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 1. A black radiation cooling film can be prepared according to the thickness values ​​given in Table 1. Figure 3 The image shows the absorption spectrum of the film system in the visible light band (400nm-800nm) under vertical incidence in Example 1. As can be seen from the image, the average absorption rate of the film system can reach 97.8% in the visible light band, which shows that it has high absorption in the visible light band and can achieve black structural color very well. Figure 4 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 1. As can be seen from the image, the average reflectance of this film system can reach 70.1% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 5 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 1. As can be seen from the image, the average absorptivity of the film system can reach 92.6% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0069] Table 1: Film Thickness Parameters for Example 1 (Unit: nm)

[0070] Example 2 like Figure 1 As shown, the thin film structure consists of a substrate (Sub), a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Ag), a first dielectric layer D1 (LaTiO3), a visible light absorption layer A (GST), and a second dielectric layer D2 (MgF2). The overall structure of the radiation module is (A'1A'2A'3). s The film L consists of a low-refractive-index protective layer L (MgF2), a first absorption layer A'1 (TiO2), a second absorption layer A'2 (Al2O3), and a third absorption layer A'3 (SiO2). The gradient cavity consists of s stacked cycles, forming a structure of A'1A'2A'3, where s is 3. The film system comprises a total of 14 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 2. A black radiation cooling film can be fabricated according to the thickness values ​​given in Table 2. Figure 6 The image shows the absorption spectrum of the film system in the visible light band (400nm-800nm) under vertical incidence in Example 2. As can be seen from the image, the average absorption rate of the film system can reach 92.8% in the visible light band, which shows that it has high absorption in the visible light band and can achieve black structural color very well. Figure 7 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 2. As can be seen from the image, the average reflectance of this film system can reach 95% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 8 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 2. As can be seen from the image, the average absorption rate of the film system can reach 75% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0071] Table 2. Film thickness parameters for Example 2 (unit: nm)

[0072] Example 3 like Figure 1As shown, the thin film structure consists of a substrate Sub, a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Ag), a first dielectric layer D1 (SiO2), a visible light absorption layer A (GST), and a second dielectric layer D2 (MgF2); the overall structure of the radiation module is (A'1A'2A'3). s The film L consists of a low-refractive-index protective layer L (MgF2), a first absorption layer A'1 (Ta2O5), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (Al2O3). The gradient cavity has s stacked periods, forming an A'1A'2A'3 structure. Here, s is 3, and the film system comprises a total of 14 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 3. A black radiation cooling film can be fabricated according to the thickness values ​​given in Table 3. Figure 9 The image shows the absorption spectrum of the film system in the visible light band (400nm-800nm) under vertical incidence in Example 3. As can be seen from the image, the average absorption rate of the film system can reach 92.8% in the visible light band, which shows that it has high absorption in the visible light band and can achieve black structural color very well. Figure 10 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 3. As can be seen from the image, the average reflectance of this film system can reach 82.8% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 11 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 3. As can be seen from the image, the average absorptivity of the film system can reach 90.1% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0073] Table 3. Film thickness parameters for Example 3 (unit: nm)

[0074] Example 4 like Figure 1 As shown, the thin film structure consists of a substrate Sub, a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Al), a first dielectric layer D1 (LaTiO3), a visible light absorption layer A (Ge), and a second dielectric layer D2 (MgF2); the overall structure of the radiation module is (A'1A'2A'3). sThe film L consists of a low-refractive-index protective layer L (MgF2), a first absorption layer A'1 (TiO2), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (Si3N4). The gradient cavity has s stacked periods, forming an A'1A'2A'3 structure. Here, s is 3, and the film system comprises a total of 14 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 black radiation cooling film can be fabricated according to the thickness values ​​given in Table 4. Figure 12 The image shows the absorption spectrum of the film system in the visible light band (400nm-800nm) under vertical incidence in Example 4. As can be seen from the image, the average absorption rate of the film system can reach 90.3% in the visible light band, which shows that it has high absorption in the visible light band and can achieve black structural color very well. Figure 13 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 4. As can be seen from the image, the average reflectance of this film system can reach 85.3% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 14 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 4. As can be seen from the image, the average absorptivity of the film system can reach 89.4% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0075] Table 4. Film thickness parameters for Example 4 (unit: nm)

[0076] Example 5 like Figure 1 As shown, the thin film structure consists of a substrate Sub, a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Ag), a first dielectric layer D1 (SiO2), a visible light absorption layer A (GST), and a second dielectric layer D2 (SiO2). The overall structure of the radiation module is (A'1A'2A'3). sThe film L consists of a low-refractive-index protective layer L (SiO2), a first absorption layer A'1 (Ta2O5), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (Ta2O5). The gradient cavity consists of s stacked periods, forming an A'1A'2A'3 structure. Here, s is 5. The original film system has a total of 20 layers. Since the first absorption layer A'1 and the third absorption layer A'3 use the same material, they are merged, resulting in a total of 16 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 5. A black radiation cooling film can be prepared according to the thickness values ​​given in Table 5. Figure 15 The image shows the absorption spectrum of the film system in the visible light band (400nm-800nm) under vertical incidence in Example 5. As can be seen from the image, the average absorption rate of the film system can reach 98% in the visible light band, which shows that it has high absorption in the visible light band and can achieve black structural color very well. Figure 16 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 5. As can be seen from the image, the average reflectance of this film system can reach 94.8% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 17 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 5. As can be seen from the image, the average absorptivity of the film system can reach 90.6% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0077] Table 5. Film thickness parameters for Example 5 (unit: nm)

[0078] Example 6 like Figure 1 As shown, the thin film structure consists of a substrate Sub, a black reflective module, and a radiation module. The black reflective module is composed of an asymmetric FP cavity with an MD1AD2 structure, consisting of a metal layer M (Cu), a first dielectric layer D1 (MgF2), a visible light absorption layer A (GST), and a second dielectric layer D2 (MgF2). The overall structure of the radiation module is (A'1A'2A'3). sThe film L consists of a low-refractive-index protective layer L (MgF2), a first absorption layer A'1 (Al2O3), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (Si3N4). The gradient cavity consists of s stacked cycles, forming a structure of A'1A'2A'3, where s is 4. The film system comprises a total of 17 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 6. A black radiation cooling film can be fabricated according to the thickness values ​​given in Table 6. Figure 18 The image shows the absorption spectrum of the visible light band (400nm-800nm) under vertical incidence in Example 6. As can be seen from the image, the average absorption rate of this film system can reach 90% in the visible light band, demonstrating its high absorption in the visible light band and its ability to achieve a black structural color. Figure 19 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 6. As can be seen from the image, the average reflectance of this film system can reach 83.1% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 20 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 6. As can be seen from the image, the average absorptivity of the film system can reach 80.1% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0079] Table 6. Film thickness parameters for Example 6 (unit: nm)

[0080] Example 7 like Figure 2 As shown, the thin film structure consists of a substrate Sub and L(A'3A'2A'1). s D2AD1MD1AD2(A'1A'2A'3) s The structure is composed of an L-shaped layer. For symmetrical structures, the optical properties are the same regardless of the direction of light incidence; therefore, it is only necessary to analyze the film structure on one side. The black reflective module consists of an asymmetric FP cavity with an MD1AD2 structure, composed of a metal layer M (Ag), a first dielectric layer D1 (SiO2), a visible light absorption layer A (GST), and a second dielectric layer D2 (SiO2). The overall structure of the radiation module is (A'1A'2A'3). sThe film L consists of a low-refractive-index protective layer L (SiO2), a first absorption layer A'1 (Ta2O5), a second absorption layer A'2 (SiO2), and a third absorption layer A'3 (Ta2O5). The gradient cavity consists of s stacked cycles, forming a structure of A'1A'2A'3, where s is 4. The original film system has a total of 33 layers. Since the first absorption layer A'1 and the third absorption layer A'3 are made of the same material, they are merged, resulting in a total of 27 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 7. A black radiation cooling film can be prepared according to the thickness values ​​given in Table 7. Figure 21 The image shows the absorption spectrum of the visible light band (400nm-800nm) under vertical incidence in Example 7. As can be seen from the image, the average absorption rate of this film system can reach 96% in the visible light band, demonstrating its high absorption in the visible light band and its ability to achieve a black structural color. Figure 22 The image shows the reflectance spectrum of the near-infrared band (800nm-2500nm) under vertical incidence in Example 7. As can be seen from the image, the average reflectance of this film system can reach 92.4% in the near-infrared band, demonstrating its excellent reflectance effect in the near-infrared region. Figure 23 The image shows the absorption spectrum of the film system in the atmospheric window band (8000nm-13000nm) under vertical incidence in Example 7. As can be seen from the image, the average absorptivity of the film system can reach 90.15% in the atmospheric window band, which shows that it has a high emissivity in the atmospheric window band and can effectively achieve the cooling effect.

[0081] Table 7. Film thickness parameters for Example 7 (unit: nm)

[0082] 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 black radiation-cooling thin film, characterized in that, The thin film comprises, from bottom to top: a substrate Sub, a black reflective module, and a radiation module; the structure of the black reflective module, from bottom to top, is MD1AD2, where: M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer; the structure of the radiation module, from bottom to top, is (A'1A'2A'3). s L, where: A'1, A'2 and A'3 are the first absorption layer, the second absorption layer and the third absorption layer, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is the low refractive index protective layer; s is the number of stacked periods, s≥1; The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

2. The black radiation-cooling thin film as described in claim 1, characterized in that, The thickness of the metal layer M is greater than 50 nm; the material of the metal layer M is selected from one of gold, silver, aluminum, copper, iron, nickel, chromium, titanium, germanium and niobium.

3. The black radiation-cooling thin film as described in claim 1, characterized in that, The thickness of the first dielectric layer D1 ranges from 1 nm to 100 nm; the thickness of the second dielectric layer D2 ranges from 50 nm to 400 nm; the refractive index of the materials of the first dielectric layer D1 and the second dielectric layer D2 in the wavelength range of 400 nm–800 nm is between 1.2 and 3, and is selected from at least one of magnesium fluoride, silicon dioxide, 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, chromium oxide, magnesium oxide, neodymium oxide, and zinc oxide.

4. The black radiation-cooling thin film as described in claim 1, characterized in that, The thickness of the visible light absorbing layer A ranges from 1 nm to 30 nm; the material of the visible light absorbing layer A has an extinction coefficient between 0.2 and 4 in the wavelength range of 400-800 nm, and is selected from at least one of nickel, titanium, chromium, iron oxide, germanium, single crystal silicon, polycrystalline silicon, antimony sulfide, antimony selenide, vanadium dioxide, GST, GSST and GT.

5. The black radiation-cooling thin film as described in claim 1, characterized in that, The thickness of the second absorption layer A'2 ranges from 50 nm to 300 nm, and the thicknesses of the first absorption layer A'1 and the third absorption layer A'3 range from 1 nm to 600 nm. The materials of the first absorption layer A'1, the second absorption layer A'2, and the third absorption layer A'3 have a refractive index between 1.2 and 3 in the wavelength range of 0.3-0.8 μm and an extinction coefficient between 0.05 and 3 in the wavelength range of 8-13 μm. They are selected from one of SiO2, TiO2, Al2O3, SiN, Si3N4, and Ta2O5. The first absorption layer A'1 and the third absorption layer A'3 are selected from the same or different materials, but they must have different refractive indices than the material of the second absorption layer A'2.

6. The black radiation-cooling thin film as described in claim 1, characterized in that, The low-refractive-index protective layer L has a refractive index between 1.2 and 3.0 in the wavelength range of 0.3 μm–2.5 μm, an extinction coefficient between 0 and 0.5, and an extinction coefficient between 0 and 3 in the wavelength range of 8 μm–13 μm. The material is magnesium fluoride or silicon dioxide, and the thickness ranges from 50 nm to 200 nm.

7. The black radiation-cooling thin film as described in claim 1, characterized in that, The substrate Sub is made of a material 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.

8. A method for preparing a black radiation-cooling thin film according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubMD1AD2(A'1A'2A'3). s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the first layer, the second layer, ... up to the last layer of the thin film structure are deposited sequentially on the substrate Sub using physical vapor deposition or chemical vapor deposition. The first layer is a metal layer M, the second layer is a first dielectric layer D1, the third layer is a visible light absorption layer A, the fourth layer is a second dielectric layer D2, the fifth layer is a first absorption layer A'1, the sixth layer is a second absorption layer A'2, the seventh layer is a third absorption layer A'3, and the last layer is a low refractive index protective layer L. Step 6: During the deposition of the metal layer M, an inert protective gas is introduced to prevent material oxidation; Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

9. A black radiation-cooling thin film, characterized in that, The thin film consists of a substrate Sub and a symmetrical structure L (A'3A'2A'1) with the metal layer M as the center of symmetry. s D2AD1MD1AD2(A'1A'2A'3) s The structure consists of L, where M is a metal layer, D1 is a first dielectric layer, A is a visible light absorption layer, and D2 is a second dielectric layer; A'1, A'2, and A'3 are the first, second, and third absorption layers, respectively, which have absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band; L is a low refractive index protective layer; and s is the number of stacked periods, where s≥1. The MD1AD2 structure and the D2AD1M structure constitute a black reflective module, and (A'1A'2A'3) n L-structure and L(A'3A'2A'1) n The structure consists of a radiation module; The thin film has a high absorption rate in the 400-800 nm visible light band to present a black appearance, a high reflectivity in the 800-2500 nm near-infrared band to reduce solar thermal gain, and a high emissivity in the 8-13 μm atmospheric window band to achieve radiative cooling.

10. A method for preparing a black radiation-cooling thin film according to claim 9, characterized in that, Includes the following steps: Step 1: Based on the target color and cooling performance requirements, determine the film structure as SubL(A'3A'2A'1). s D2AD1MD1AD2(A'1A'2A'3) s L, where: Sub represents the substrate, M represents the metal layer, D1 represents the first dielectric layer, A represents the visible light absorption layer, D2 represents the second dielectric layer, A'1 represents the first absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'2 represents the second absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, A'3 represents the third absorption layer with absorption in the 8μm-13μm band and high transmission in the 0.3μm-2.5μm band, L represents the low refractive index protective layer, s represents the number of stacked periods, s≥1; Step 2: Adjust the thickness and material of each layer in the thin film structure to make the thin film black, with high near-infrared reflectivity and high absorption in the 8-13µm band; 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 in each layer, the thickness of each layer, and the distribution between the layers. Step 4: Provide a flat substrate (Sub) and place it in the vacuum chamber of the film deposition equipment; Step 5: Based on the total number of layers, the material used in each layer, the thickness of each layer, and the distribution between layers, the first layer, the second layer, ..., up to the last layer of the thin film structure are deposited sequentially on the substrate Sub using physical vapor deposition or chemical vapor deposition. Step 6: During the deposition of the metal layer M, an inert protective gas is introduced to prevent material oxidation; Step 7: After all film layers are deposited, the black radiation-cooling thin film is obtained.

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