Solar absorber with multilayer film structure

Abstract

The invention provides a solar absorber with a multilayer film structure, and belongs to the technical field of solar absorption devices, the structure of the solar absorber is a multilayer Fabry-Perot resonance unit formed by alternately stacking metal layers and dielectric layers, the metal layers are used as substrates, and the dielectric layers are used as uppermost protective films; the material of the metal layer is TiN, and the material of the dielectric layer is SiO2; the Fabry-Perot resonance unit is composed of a TiN layer serving as a reflecting layer and a SiO2 layer serving as a transparent layer; an optical resonant cavity is formed between every two reflecting layers; multiple times of reflection, interference and absorption of light can be achieved through superposition of multiple unit film layers and based on the Fabry-Perot resonance principle, the reflection spectrum of the multi-layer film solar absorber within the range of 0.38-0.78 microns (visible light wave band) is changed by changing the thickness of SiO2 at the bottommost layer, the multi-layer film structure shows different colors, and the multi-layer film solar absorber has the advantages of being capable of achieving multi-layer film solar absorption. The optical camouflage device can be applied to different environments such as deserts, oceans and jungles.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar energy absorption devices, and in particular, relates to a multi-layer film structure solar energy absorber. Background Art

[0002] A solar absorber is a structure that converts incident solar radiation energy into thermal energy. It is widely used in the fields of energy utilization and aerospace. With the continuous growth of energy demand and the increasingly prominent environmental problems caused by traditional energy, solar energy, as an abundant, clean and renewable energy source, has received widespread attention and in-depth research. As a key component for solar energy utilization, the improvement of the performance of solar absorbers is crucial to the efficiency of solar energy utilization. Considering the shortcomings of traditional solar absorbers in terms of absorption capacity and spectral response range, it is difficult to fully realize the absorption of the full spectrum, which limits the further improvement of solar energy conversion efficiency. For example, some common absorbers cannot achieve a wide absorption band and a high absorption rate at the same time, the absorption performance at different angles is unstable, and there are problems such as the absorption efficiency decreasing with temperature. The photolithography process required in the production process of traditional solar absorbers has problems such as high cost, complex process, and long time consumption, and harmful chemicals are also produced in the process. Summary of the invention

[0003] In order to overcome the limitations of traditional solar absorbers and increase the absorption band width and light absorption rate of solar absorbers, based on the Fabry-Pérot (FP) resonance principle, the present invention proposes a multi-layer film structure solar absorber, which is formed by superimposing unit film layers composed of multiple layers of different film layers. The multi-layer film structure can achieve multiple reflections, interferences and absorption of light through the combination of different materials and the design of film layer thickness, refractive index and other parameters, thereby significantly improving the performance of the absorber.

[0004] Based on this, the multi-layer film structure solar absorber of the present invention is realized by the following technical solutions:

[0005] The structure of the solar absorber is a multi-layer FP resonance unit in which metal layers and dielectric layers are alternately stacked, with the metal layer as the base and the dielectric layer as the topmost protective film;

[0006] The metal layer has good reflection characteristics in the main waveband of solar radiation, and the real part of the dielectric constant is generally negative;

[0007] The dielectric layer has good window characteristics in the main waveband of solar radiation, and generally has a small imaginary part of the dielectric constant;

[0008] By changing the thickness of the dielectric layer close to the substrate, the reflection spectrum of the multilayer film solar absorber in the range of 0.38 μm to 0.78 μm is changed, so that the multilayer film structure displays different colors.

[0009] Furthermore, the metal layer is a TiN layer, which provides a stable support, good thermal stability and reflective performance.

[0010] Furthermore, the dielectric layer is a SiO2 layer, which prevents the metal layer from being oxidized and improves the spectral absorption rate.

[0011] Furthermore, the FP resonance unit is composed of a TiN layer as a reflective layer and a SiO2 layer as a transparent layer; every two reflective layers and the transparent layer in between form a TiN-SiO2-TiN optical resonance cavity.

[0012] Furthermore, light near the resonance wavelength first passes through the outermost SiO2 protective film and enters the TiN layer; part of the light is reflected, and the other part passes through the TiN layer and enters the optical resonant cavity structure composed of TiN-SiO2-TiN;

[0013] Once the light enters the optical resonant cavity (TiN-SiO2-TiN structure), the light will be reflected multiple times between the TiN layers because SiO2, as a transparent layer, satisfies the FP resonance condition. During each reflection, the light will interact with each layer of material, and part of the light will be absorbed and converted into heat energy. Multiple reflections will eventually be consumed in the solar absorber, thereby realizing the consumption and energy conversion of light energy in the solar absorber.

[0014] Furthermore, the amplitude and width of the FP resonance are adjusted by the thickness of the thin film reflector; the resonance wavelength depends on the thickness of the transparent layer and is predicted by the following formula:

[0015]

[0016] Where n is the refractive index of the transparent layer, k is an odd number, λ is the wavelength, and h is the thickness of the transparent layer. By precisely controlling the thickness of the transparent layer, the light is reflected multiple times between the reflective layer and the transparent layer, and then constructive interference occurs at a specific wavelength to form a resonant absorption peak, thereby improving the absorption efficiency of the solar absorber at this wavelength.

[0017] Furthermore, the colors of the multilayer film structures with different thicknesses of the bottom SiO2 layer are displayed in the CIE 1931x-y chromaticity diagram. By calculating the reflectivity of the multilayer film structure under different bottom SiO2 layer thickness conditions, the structural color of the multilayer film structure solar absorber is determined by the following formula:

[0018]

[0019] Among them, δ is a constant, D 65It is the most commonly used artificial daylight with a color temperature of 6500K among standard light sources. R(λ) is the reflectivity of the multilayer film structure solar absorber. X, Y, and Z are the CIE standard color matching functions of human vision, corresponding to the three primary colors of red, green, and blue respectively. The color of the multilayer film structure solar absorber is determined by its position in the two-dimensional chromaticity diagram and is represented by coordinates x and y.

[0020] A method for preparing the solar absorber: the preparation method is a magnetron sputtering method;

[0021] First, the chamber of the magnetron sputtering device is evacuated to a vacuum state, and TiN and SiO2 targets are installed on the sputtering cathode;

[0022] Then, argon gas is flushed into the chamber as a sputtering gas, and appropriate sputtering power and sputtering time are set. TiN and SiO2 materials are alternately deposited on the substrate by a deposition method to form a multilayer film structure solar absorber in which the metal layers and dielectric layers are alternately stacked.

[0023] Beneficial effects of the present invention:

[0024] The present invention uses high melting point materials TiN and SiO2 for the reflective layer and the transparent layer, which makes the absorber have better thermal stability under the condition of solar thermal utilization. In addition, compared with precious metals such as gold and silver, these two materials are cheaper, further reducing the manufacturing cost of the solar absorber.

[0025] The multi-layer coating structure of the present invention uses oxide as a protective layer, which does not require photolithography and achieves structural protection and anti-oxidation effects, while greatly improving the spectral absorption rate. Taking a single cycle as an example, the average spectral absorption is increased from 0.74 to 0.85.

[0026] The present invention changes the color of the overall structure by changing the thickness of the bottom layer SiO2. In the prior art, ZnS is often used in the outermost layer to change the color, but ZnS will produce certain harmful gases and cause pollution when used in solar absorbers, while SiO2 will not, and the cost of SiO2 is lower.

[0027] The solar absorber designed in the present invention is applied in the visible light to near infrared band. Compared with the prior art, the absorption band of the present invention is wider, which can reach 0.3μm-2.5μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the solar absorber of the present invention; wherein (1) is a metal layer, the material of which is TiN, and (2) is a dielectric layer, the material of which is SiO2.

[0029] Figure 2 This is a line graph of “wavelength-absorption rate” when the number of cycles is 0 to 3.

[0030] Figure 3 This is the "angle-average absorption rate" line graph when the incident light is TM and TE waves.

[0031] Figure 4 It is a bar graph of “Number of cycles - average absorption rate”.

[0032] Figure 5 This is the “wavelength-absorption rate” line graph with / without a protective layer.

[0033] Figure 6 The reflectance spectra and colors of the multilayer structure under different h3, wherein (a) is the structural reflectance spectrum of different h3 (SiO2) thicknesses in the embodiment, and (b) is the chromaticity coordinates of different bottom SiO2 layer thicknesses marked in the CIE 1931x-y chromaticity diagram. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0036] Combination Figures 1 to 6 , the present invention proposes a multi-layer film structure solar absorber.

[0037] The structure of the solar absorber is a multi-layer FP resonance unit in which metal layers 1 and dielectric layers 2 are alternately stacked, with the metal layer 1 as the base and the dielectric layer 2 as the topmost protective film.

[0038] The metal layer 1 has good reflection characteristics in the main waveband of solar radiation (0.3 μm-2.5 μm), and the real part of the dielectric constant is generally negative;

[0039] The dielectric layer 2 has good window characteristics in the main waveband of solar radiation (0.3 μm-2.5 μm), and the imaginary part of the dielectric constant is generally small (<0.1);

[0040] By changing the thickness of the dielectric layer 2 close to the substrate, the reflection spectrum of the multilayer film solar absorber in the range of 0.38 μm to 0.78 μm is changed, so that the multilayer film structure displays different colors.

[0041] Adding a protective layer on the top layer of the multilayer film structure can achieve multiple purposes: preventing structural oxidation, enhancing solar energy absorption (anti-reflection), and optical camouflage (changing the reflection spectrum of 0.38μm-0.78μm and thus changing the color display).

[0042] Implementation example Figure 1 As shown, the illustrated solar absorber is a multilayer film structure composed of multiple units with TiN as the substrate, each unit is composed of thin films of TiN and SiO2, wherein the thickness of TiN in the unit is d, and the thickness of SiO2 in the unit is h.

[0043] The metal layer 1 is a TiN layer, which provides a stable support, good thermal stability and reflective performance.

[0044] The dielectric layer 2 is a SiO2 layer, which prevents the metal layer from being oxidized and improves the spectral absorption rate.

[0045] The specific physical principle is: when two parallel and smooth reflectors are spaced a certain distance apart, and light of a specific wavelength is irradiated on one of the reflectors, the light will be reflected multiple times between this reflector and the other reflector, thus forming interference. If the phase difference between adjacent reflected waves is an integer multiple of the wavelength, the reflected waves will produce constructive interference, resulting in an increase in the intensity of the transmitted light; and when the phase difference is an odd multiple of half the wavelength, the reflected waves will undergo destructive interference, resulting in a maximum reflectivity and a minimum transmittance, i.e., FP resonance, thereby increasing the light absorption rate.

[0046] Therefore, only when the frequency of the incident light is infinitely close to the natural frequency of the optical resonant cavity, a strong standing wave will be generated in the cavity, thereby causing resonance. The light intensity distribution in the cavity will form a stable standing wave pattern, and the energy of the light will accumulate and enhance in the cavity, causing the amplitude of the transmitted light to reach a maximum value at a specific frequency.

[0047] Combining the Fabry-Perot resonance principle, the FP resonance unit is composed of a TiN layer as a reflective layer and a SiO2 layer as a transparent layer; every two reflective layers and the transparent layer in between form a TiN-SiO2-TiN optical resonant cavity.

[0048] When light enters the solar absorber, part of it is transmitted and the other part is reflected into the optical resonant cavity. The light is reflected multiple times between the reflective layer and the transparent layer. The reflective properties of the reflective layer enable the light to reflect back and forth in the multi-layer film structure, which cooperates with the optical properties of the transparent layer to meet the conditions of FP resonance. Therefore, at a specific wavelength, the amplitude of the transmitted light wave can reach a maximum value, while the amplitude of the reflected light wave can reach a minimum value, thereby improving the light absorption rate.

[0049] For light near the resonance wavelength, it first passes through the outermost SiO2 protective film, and the combination of the wavelength close to the resonance wavelength and the optical properties of each layer of material at this wavelength allows the light to pass through the TiN layer and enter the cavity, and then enter the TiN layer;

[0050] Since TiN has certain reflection and absorption characteristics in certain bands, part of the light will be reflected, but for the light near the resonance wavelength, part of it will pass through the TiN layer and enter the optical resonant cavity structure composed of TiN-SiO2-TiN;

[0051] Once the light enters the optical resonant cavity (TiN-SiO2-TiN structure), since SiO2 as a transparent layer meets the FP resonance conditions (appropriate thickness and refractive index), the light will be reflected multiple times between the TiN layers; during each reflection process, the light will interact with each layer of material, and part of the light will be absorbed and converted into heat energy. Multiple and multi-layer reflections are finally consumed in the solar absorber, thereby realizing the consumption and energy conversion of light energy in the solar absorber.

[0052] like Figure 2 As shown in the figure, when the wavelength is small (about 0.3-0.5μm), the absorbers with different period numbers corresponding to different broken lines have high absorptivity for light in this band, close to 1, which is caused by the intrinsic properties of TiN. When the period N=0, the absorptivity decreases significantly with the increase of wavelength, but with the increase of the period number N, the absorptivity of the absorber at a wavelength of 0.5-2.5μm gradually increases and approaches 1.

[0053] like Figure 3 As shown, the average absorption rates of TM and TE gradually decrease with the increase of the angle. When the angle is about 50°, the average absorption rates of TM and TE begin to decrease significantly, but the average absorption rates at 60° are still over 80%.

[0054] like Figure 4 As shown, when the period is 1, the average absorption rate is 0.8522. As the number of periods increases, the average absorption rate gradually increases. When the number of periods tends to ∞, the average absorption rate can reach 0.9801.

[0055] like Figure 5 As shown, taking a single cycle as an example, the average spectral absorption of the solar absorber increases from 0.74 to 0.85 after adding the protective layer.

[0056] The amplitude and width of the FP resonance are tuned by the thickness of the thin film mirror; the resonance wavelength depends on the thickness of the transparent layer and is predicted by the following equation:

[0057]

[0058] Where n is the refractive index of the transparent layer, k is an odd number, λ is the wavelength, and h is the thickness of the transparent layer. By precisely controlling the thickness of the transparent layer, the light is reflected multiple times between the reflective layer and the transparent layer, and then constructive interference occurs at a specific wavelength to form a resonant absorption peak, thereby improving the absorption efficiency of the solar absorber at this wavelength.

[0059] The target wavelength band for solar energy collection is 0.3-2.5 μm, and the refractive index of SiO2 obtained at this wavelength is 1.45. Therefore, when k=1, the thickness of the transparent layer can be obtained to be 0.172 μm.

[0060] It should be noted that formula (1) is only an estimate of the FP resonance wavelength, which means that the thickness of the transparent layer can be limited to a suitable range. In order to obtain the best average spectral absorption, the thickness of each layer is limited to a specific range for simulation optimization: 0.001–0.05μm for the reflective layer and 0.1-0.3μm for the transparent layer. Taking the average spectral absorption in the range of 0.3-2.5μm as the optimization target, the optimized Figure 1 Schematic diagram of the proposed multilayer film solar absorber. Structural parameters d1 = 0.001 μm, d2 = 0.005 μm, d3 = 0.009 μm, h0 = h1 = h2 = h3 = 0.17 μm. The maximum average spectral absorption is 0.935.

[0061] The colors of multilayer film structures with different thicknesses of the bottom SiO2 layer are displayed in the CIE 1931x-y chromaticity diagram. By calculating the reflectivity of the multilayer film structure under different bottom SiO2 layer thicknesses, the structural color of the multilayer film structure solar absorber is determined by the following formula:

[0062]

[0063] Among them, δ is a constant, D 65 It is the most commonly used artificial daylight with a color temperature of 6500K among standard light sources. R(λ) is the reflectivity of the multilayer film structure solar absorber. X, Y, and Z are the CIE standard color matching functions of human vision, corresponding to the three primary colors of red, green, and blue, respectively. The color of the multilayer film structure solar absorber is determined by its position in the two-dimensional chromaticity diagram, which is represented by the coordinates x and y.

[0064] Figure 6(a) shows the structural reflectance spectra of different SiO2 layer thicknesses; in the embodiment, a three-periodic structure is used as an implementation case, and the structural color is adjusted by changing the thickness of h3. As the thickness of the bottom SiO2 layer increases, the reflectance peak gradually moves to a longer wavelength, and another peak gradually appears. Using the above formula, the chromaticity coordinates of different bottom SiO2 layer thicknesses are obtained, and these coordinates are marked in the CIE 1931x-y chromaticity diagram, as shown in Figure 6 (b) As shown in the figure, as the thickness of the bottom SiO2 layer increases, the designed structural color changes from yellow to red, purple, blue and green, showing a linear and significantly wide range of color changes. This shows that the structure is suitable for color camouflage. By adjusting the thickness of the bottom SiO2 layer, this multilayer film structure can be applied to different environments such as deserts, oceans and forests.

[0065] Reference Figure 6 (b) It can be seen that the present invention can be achieved by changing h n Due to the thickness of the multilayer film structure, the reflection spectrum of the multilayer film structure at 0.38μm-0.78μm changes, which makes the multilayer film structure show different colors.

[0066] The preparation scheme of the solar absorber is as follows:

[0067] The preparation method is a magnetron sputtering method;

[0068] First, the chamber of the magnetron sputtering device is evacuated to a vacuum state, and TiN and SiO2 targets are installed on the sputtering cathode;

[0069] Then, argon gas is flushed into the chamber as a sputtering gas, and appropriate sputtering power and sputtering time are set. TiN and SiO2 materials are alternately deposited on the substrate by a deposition method to form a multilayer film structure solar absorber in which the metal layer 1 and the dielectric layer 2 are alternately stacked.

[0070] The above is a detailed introduction to the multi-layer film structure solar absorber proposed in the present invention, and the principles and implementation methods of the present invention are explained. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A multi-layer film structure solar absorber, characterized in that: The structure of the solar absorber is a multi-layer Fabry-Perot resonance unit in which metal layers (1) and dielectric layers (2) are alternately stacked, with the metal layer (1) serving as a substrate and the dielectric layer (2) serving as an uppermost protective film; The metal layer (1) has good reflection characteristics in the main waveband of solar radiation, and the real part of the dielectric constant is generally negative; The dielectric layer (2) has good window characteristics in the main waveband of solar radiation, and generally has a small imaginary part of the dielectric constant; By changing the thickness of the dielectric layer (2) close to the substrate, the reflection spectrum of the multilayer film solar absorber in the 0.38μm-0.78μm band is changed, so that the multilayer film structure displays different colors.

2. The solar absorber according to claim 1, characterized in that: The metal layer (1) is a TiN layer, which provides a stable support, good thermal stability and reflective performance.

3. The solar absorber according to claim 2, characterized in that: The dielectric layer (2) is a SiO2 layer, which prevents the metal layer (1) from being oxidized and improves the spectral absorption rate.

4. The solar absorber according to claim 3, characterized in that: The Fabry-Perot resonance unit is composed of a TiN layer as a reflective layer and a SiO2 layer as a transparent layer; every two reflective layers and the transparent layer in between form a TiN-SiO2-TiN optical resonance cavity.

5. The solar absorber according to claim 4, characterized in that: For light near the resonance wavelength, it first passes through the outermost SiO2 protective film and enters the TiN layer; part of the light will be reflected, and the other part will pass through the TiN layer and enter the optical resonant cavity structure composed of TiN-SiO2-TiN; Once the light enters the optical resonant cavity composed of TiN-SiO2-TiN, since SiO2 as a transparent layer satisfies the Fabry-Perot resonance condition, the light will be reflected multiple times between the TiN layers; during each reflection process, the light will interact with each layer of material, and part of the light will be absorbed and converted into heat energy. Multiple reflections will eventually be consumed in the solar absorber, thereby realizing the consumption and energy conversion of light energy in the solar absorber.

6. The solar absorber according to claim 5, characterized in that: The amplitude and width of the Fabry-Perot resonance are adjusted by the thickness of the thin film mirror; the resonance wavelength depends on the thickness of the transparent layer and is predicted by the following equation: Where n is the refractive index of the transparent layer, k is an odd number, λ is the wavelength, and h is the thickness of the transparent layer. By precisely controlling the thickness of the transparent layer, the light is reflected multiple times between the reflective layer and the transparent layer, and then constructive interference occurs at a specific wavelength to form a resonant absorption peak, thereby improving the absorption efficiency of the solar absorber at this wavelength.

7. The solar absorber according to claim 6, characterized in that: The colors of multilayer film structures with different thicknesses of the bottom SiO2 layer are displayed in the CIE 1931x-y chromaticity diagram. By calculating the reflectivity of the multilayer film structure under different bottom SiO2 layer thicknesses, the structural color of the multilayer film structure solar absorber is determined by the following formula: Among them, δ is a constant, D 65 It is the most commonly used artificial daylight with a color temperature of 6500K among standard light sources. R(λ) is the reflectivity of the multilayer film structure solar absorber. X, Y, and Z are the CIE standard color matching functions of human vision, corresponding to the three primary colors of red, green, and blue respectively. The color of the multilayer film structure solar absorber is determined by its position in the two-dimensional chromaticity diagram and is represented by coordinates x and y.

8. A method for preparing a solar absorber according to any one of claims 1 to 7, characterized in that: The preparation method is a magnetron sputtering method; First, the chamber of the magnetron sputtering device is evacuated to a vacuum state, and TiN and SiO2 targets are installed on the sputtering cathode; Then, argon gas is flushed into the chamber as a sputtering gas, and appropriate sputtering power and sputtering time are set. TiN and SiO2 materials are alternately deposited on the substrate by a deposition method to form a multilayer film structure solar absorber in which the metal layer (1) and the dielectric layer (2) are alternately stacked.

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