CN114635105A

CN114635105A - Preparation method of double-texture surface solar selective absorption coating and coating

Info

Publication number: CN114635105A
Application number: CN202210392635.5A
Authority: CN
Inventors: 瓦西里·帕里诺维奇; 曾晓梅; 杨兵; 张俊; 张翔宇; 陈燕鸣; 黄家辉
Original assignee: Wuhan University WHU
Current assignee: Wuhan University WHU
Priority date: 2022-04-14
Filing date: 2022-04-14
Publication date: 2022-06-17
Anticipated expiration: 2042-04-14
Also published as: CN114635105B

Abstract

The invention provides a preparation method of a solar selective absorbing coating with double-texture surface and the coating, comprising the following steps: preparing magnetron sputtering equipment, placing a sputtering target material, an arc power supply, a turntable and a substrate, vacuumizing and heating; introducing high-purity Ar gas, setting substrate negative bias, starting an arc power supply, and etching the surface of the substrate with Ar to form a required texture surface under the action of the arc power supply; depositing a multi-layer absorption coating: turning off the arc power supply, rotating the turntable to make the substrate on the turntable parallel to the sputtering target, turning on the radio frequency power supply and setting parameters, and introducing high-purity Ar gas and oxygen into the chamberGas, sequentially setting different O₂the/Ar ratio is that the substances of the sputtering target material are sputtered and deposited on the substrate to form a gradient multilayer absorption coating; depositing an alloy oxide or pure metal oxide anti-reflective coating; passing Ar again through⁺Etching a secondary texturing appearance on the surface of the anti-reflection layer by using an ion beam; and finishing the preparation of the coating. The absorption performance and the high-temperature stability of the coating prepared by the method are greatly improved.

Description

Preparation method of double-texture surface solar selective absorption coating and coating

Technical Field

The invention belongs to the technical field of coating preparation, and particularly relates to a preparation method of a solar selective absorbing coating with a double-texture surface and the coating.

Background

Solar Spectrum Selective Absorbers (SSA) are the most direct way to convert solar radiation into thermal energy. From a thermodynamic perspective, concentrated solar systems are required to increase the efficiency of solar power generation systems. The radiation density on the surface of the absorber inevitably leads to the increase of the working temperature, and at present, a concentrating solar energy system based on a parabolic trough requires the working temperature to be higher than 600 ℃, so that the method has strict requirements on the long-term thermal stability of the wave-absorbing material, and the design of the selective wave-absorbing material capable of working at the temperature is a very difficult problem.

So to achieve a high spectral selectivity of the coating, the coating is required to:

in the solar radiation range, i.e., in the ultraviolet-visible-near infrared band (0.3 to 2.5 μm), it should be an ideal black body that absorbs as much sunlight as possible (the absorption α is 1 and the reflectance R is 0).

② in the infrared range (greater than 2.5 μm, no solar radiation), equivalent to an ideal mirror, black body thermal radiation e is released as little as possible (absorption α ═ emissivity e ═ 0, reflectance R ═ 1). Since the solar energy absorbing coating will cause self heat radiation loss in the infrared range (higher than 2.5 μm) when operating in the temperature range of 400-600 ℃, in order to reduce the black body heat radiation of the part as much as possible, the reflection rate can be increased, and the solar wave band is between 0.3-2.5 μm, even if the reflection rate is 1 in the wave band of more than 2.5 μm, no solar energy loss will be caused.

③ greater than 600 ℃ and even higher thermal stability, resistance to long-term exposure to humidity and to other environmental conditions.

At present, bimetallic ceramic coatings, transition metal carbide and nitride coatings, high-temperature transition metal oxide coatings and the like have been widely applied commercially at the temperature below 400 ℃, but at higher temperature, the reflectivity of the coatings is increased, the absorptivity is reduced, and the thermal stability still cannot meet the requirements of a new generation of concentrating solar energy systems.

Long-term research shows that one of the thermal failure mechanisms of the metal infrared reflector when the metal infrared reflector works in an outdoor high-temperature environment is that the surface of the absorption layer is oxidized, so that the reflection performance of infrared spectrum wave bands is reduced; another mechanism is that atomic diffusion occurs at high temperature in the absorber sub-layers (anti-reflection layer, absorber layer and infrared mirror), causing the SSA basic structure to be destroyed, degrading the absorption rate in the solar spectral band. The oxidation equation and the diffusion equation can be expressed as follows:

where c is the atomic concentration of the metal or oxygen, t is time, D is the diffusion coefficient, and Δ is the Laplace operator. The arbitrary solution of the diffusion equation is characterized by a relaxation time τ, which describes the duration of the diffusion process, i.e. the duration of complete oxidation or structural loss of the absorbing coating, which can be written as:

in the formula, l is the size of the region where the atomic concentration reaches equilibrium, and it is understood from the formula that the larger the diffusion region is, the longer the diffusion process is, and therefore, the longer the time for which the absorption coating layer is resistant to high temperature is. One way to improve the high temperature stability of the coating is to increase the feature size of the coating surface to extend the duration of complete oxidation or structural loss of the coating. (if the coating surface feature size d is comparable to the visible wavelength λ (about 500nm) it can be used as an absorber; if the wavelength of the incident radiation λ < d, the incident light will be scattered, thus enhancing the absorption; if λ > > d, the surface is considered to be a smooth reflective surface).

The most widely used SSAs today are cermet absorbers, the spectral absorption being achieved by metal particles of about 5-80nm diameter embedded in a dielectric matrix. There are also multilayer (dielectric-metal-dielectric) interference stack coatings consisting of two transparent dielectric layers with an absorbing metal layer between them of about 5-20nm thickness. The failure of the two at high temperature is caused by diffusion/oxidation of metal particles/layers in an oxide matrix, the surface characteristics are deformed due to the diffusion/oxidation process, the average characteristic size is no longer more than 500nm, and the surface loses the selective absorption. In recent years, researchers have found that under the condition of the same diffusion coefficient D, according to the formula (2), the texture surface can effectively enlarge the diffusion area and prolong the relaxation time due to the up-and-down fluctuant morphology, so that the texture surface can survive for a longer time at high temperature. Researchers adopt the catalyst technology, electrochemical treatment, hydrothermal method and other processes to construct self-assembled 2D nano-structures and foam nano-structures on the surfaces of transition metals, Fe-Cr-Ni alloys, metal ceramics and the like so as to improve the absorption performance and the high-temperature stability of the nano-structures, and the results show that the reflectivity is always higher than 0.1, the temperature resistance of the coating is effectively improved to 500 ℃, but the further breakthrough cannot be realized. Therefore, it is urgently needed to develop a solar energy absorbing coating which can resist high temperature and has excellent absorbing performance.

Disclosure of Invention

The invention aims to provide a preparation method of a double-texture surface solar selective absorbing coating aiming at the defects of the prior art, the coating prepared by the method is entirely deposited on a pre-prepared textured substrate, a gradient multilayer absorbing coating and an oxide layer are embedded to be used as a protective layer and an anti-reflection layer, and finally, the surface of a secondary rough texture structure is etched based on the textured surface, so that the formed double-texture surface prolongs the diffusion process, and the absorption performance and the high-temperature stability of the coating are improved.

In order to solve the technical problems, the invention adopts the following technical scheme:

a preparation method of a solar selective absorbing coating with a double-texture surface comprises the following steps:

step 1: preparing magnetron sputtering equipment, sequentially placing a sputtering target material, an arc power supply, a turntable and a substrate according to a preset distance and a preset direction, wherein the arc power supply comprises an arc power supply target material, and at the moment, the arc power supply target material is parallel to the substrate, and closing a cavity; starting a cooling system, vacuumizing until the vacuum degree in the chamber reaches an ideal value, and heating the chamber until the temperature reaches a target value;

step 2: etching a texture surface on a substrate: introducing high-purity Ar gas, setting substrate negative bias, starting arc power supply, and ionizing Ar into Ar under the action of the arc power supply⁺，Ar⁺Bombarding the substrate by ion beams under potential difference, and etching the surface of the substrate to prepare a required texture surface;

and step 3: depositing a multi-layer absorption coating: turning off the arc power supply, rotating the turntable to make the substrate on the turntable parallel to the sputtering target, turning on the radio frequency power supply and setting parameters, simultaneously introducing high-purity Ar gas and high-purity oxygen gas into the chamber, and performing sputtering under radio frequency and O conditions₂Sputtering the material of the sputtering target under the action of Ar mixed gas flow and depositing the material on the substrate, and gradually increasing O₂the/Ar ratio is adopted, and a gradient multilayer absorption coating which is wrapped on the texture surface of the substrate and has absorption performance is formed;

and 4, step 4: and (3) depositing an anti-reflection layer: further increasing O on the basis of the last layer of absorbing coating deposited in step 3₂Content ratio and keeping constant O₂The mixed gas flow of the/Ar ratio and the total flow fully oxidizes a target sputtering product, pure metal oxide or metal oxide such as high-entropy alloy oxide, AlCr oxide and the like is deposited on the multilayer absorption coating, the thickness of the mixed gas flow is about 50nm-200nm, the mixed gas flow is used as a protective layer and an anti-reflection layer, the texture surface is protected from being oxidized at high temperature, the surface reflection is inhibited, the reflectivity in a 0.3-2.5 mu m wave band can be effectively reduced, and the spectrum selection ratio is improved;

and 5: etching a secondary texture table on the anti-reflection layerDough making: rotating the turntable to make the substrate on the turntable parallel to the arc power source target material, introducing high-purity Ar gas, and setting the negative bias of the substrate, Ar⁺And etching the surface of the anti-reflection layer by using ion beams to prepare a required secondary texture surface so as to further increase the reflection performance of the anti-reflection layer, thereby completing the preparation of the solar selective absorption coating with the double-texture surface.

Further, in step 1, the vacuum degree in the chamber is 10^-3Pa, and the temperature in the chamber is between 100 and 300 ℃.

Further, the arc power supply comprises an arc power supply target, a trigger, an anode and an interception screen, and in the whole process of preparing the coating, the interception screen is always isolated between the substrate and the arc power supply target and is in a closed state, so that the substrate is protected from being influenced by chromium ions sputtered in the arc power supply target, and the chromium ions are blocked.

Furthermore, in the whole process flow, a two-step process for preparing the textured surface is designed, wherein the first time is to obtain a surface texture on the substrate to provide a basis for texturing the absorption coating and the anti-reflection layer, the second time is to etch a secondary texture surface on the surface of the anti-reflection layer with the texture appearance after the reflection layer is deposited, the texture surface on the substrate is to enable the substrate to have absorption performance, and simultaneously enable the deposited absorption coating and the deposited reflection layer to have the textured surface, so that the spectral absorption performance is further enhanced, and the secondary texture surface on the reflection layer is to increase the reflection performance of the anti-reflection layer.

Furthermore, the texture surfaces of the first time and the second time respectively comprise an undulating shape such as a cone shape, a column shape, a spherical shape, a sponge shape and the like, the specific shape depends on a plurality of parameters such as substrate bias voltage, etching time, distance between an arc power source target and a substrate, arc power source parameters, air pressure and the like, the texture surface means that an original flat surface has a coarsening phenomenon, the roughness is larger, when light irradiates to the surface, the surface can undergo multiple reflections until light intensity is completely absorbed by the texture surface, namely the rough surface is more beneficial to spectrum absorption, the texture surface can also increase the diffusion area of atoms in the coating, the diffusion process is prolonged, and the high-temperature stability is facilitated.

Further, the surface textures with different appearances are obtained by regulating and controlling the distance between the arc power source target and the substrate, the substrate bias voltage, the etching time, the voltage difference between the anode and the arc power source target and the airflow flow.

Furthermore, the arc power source target is a Cr target which is used as a cathode of the arc power source, and the distance between the arc power source target and the substrate is between 100mm and 400 mm.

Further, the voltage difference between the anode and the target of the arc power supply is between 20 and 80V, and the current is between 70 and 120A, so that glow discharge is realized to ionize Ar into Ar⁺The etching time in step 2 is 10-120 minutes, and the etching time in step 5 is 10-60 minutes.

Further, the flow rate of the Ar gas in step 2 and step 5 is between 0.5 and 2Pa, and the negative bias voltage of the substrate is set to be between-80V and-500V.

Further, O in step 3 and step 4₂The flow rate of the Ar mixed gas flow is generally 0.5-5Pa, but O₂In different ratios of Ar to O, step 3 is to form a mixture of oxide and alloy (or metal), O₂the/Ar ratio is between 1: 60 to 15: 60, step 4 to form pure oxide, O₂the/Ar ratio is between 1: 3 to 5:1, wherein Ar is used for bombarding the target material and sputtering the target material, O₂For oxidizing the sputtering products, depositing an oxide coating.

Further, the sputtering target is a target for providing a material for the solar spectrum absorption coating, and the sputtering targets in the step 3 and the step 4 are both pure alloys or pure metals, such as high-entropy alloy, AlTi, AlCr and the like; the absorption coating can be made of alloy materials or pure metal materials, such as high-entropy alloy, AlTi, AlCr and the like, and is designed into a multilayer structure, the layered structure is favorable for preventing diffusion and fusion among light absorption nanometer crystal grains in the coating at high temperature, inhibiting coarsening of the crystal grains, and improving the stability of the high-temperature structure and performance while meeting spectrum selective absorption. Gradient multilayer absorption coating by gradually increasing O₂Ratio of/Ar (O when depositing the first absorption coating layer)₂The ratio/Ar is between 1: 60 to 4: 60, depositing the last absorbing coating layer O₂The ratio/Ar is between 8: 60 to 15: 60) depositing an absorbing coating with the alloy or metal content higher than that of the oxide, and then gradually reducing the alloy or metal content to form oxygenThe gradient multilayer (5-10 layers) structure absorption coating with the increased compound ratio has the thickness of 8-20nm and the total thickness of 40-200 nm.

The anti-reflection layer is pure metal oxide or pure metal oxide, such as high-entropy alloy oxide, AlTi, AlCr oxide and the like, reduces the reflectivity of the surface, improves the transmittance of the surface, enables more solar radiation energy to enter the bottom layer absorption coating, simultaneously serves as a protective layer, protects the coating from being oxidized at high temperature, and has the thickness of 50-200 nm.

The invention also aims to provide a coating prepared by the preparation method of the solar selective absorbing coating with the double-texture surface.

Compared with the prior art, the invention has the beneficial effects that:

(1) compared with a solar energy absorbing coating with a traditional structure, the coating prepared by the invention has novel appearance and structure, is a combination of a secondary rough texture surface, the absorbing coating and an oxide anti-reflection layer (protective layer), improves the absorbing performance and the thermal stability of the coating under the combined action of the secondary rough texture surface, the absorbing coating and the oxide anti-reflection layer, and has the advantages of simple preparation process steps, less material consumption, controllability and repeatability;

(2) when the solar selective absorbing coating is prepared, firstly a flat substrate is etched to form a rough texture surface, then a plurality of absorbing coatings and oxidation layer anti-reflection layers are deposited, and finally a secondary texture surface is etched on the surface of the anti-reflection layer with the texture appearance to form a spectrum absorbing coating with a double-texture surface, wherein the spectrum absorbing coating has the following advantages:

the roughness of the surface of the secondary texture is further increased, when light irradiates the surface, the light can undergo more reflections on the surface until the light intensity is completely absorbed by the coating, the spectral absorptivity is improved, and the absorptivity in a solar spectrum wave band is increased from 0.36 to 0.92;

secondly, the characteristic size of the texture surface of the coating is equivalent to or even larger than the wavelength of incident radiation, the diffusion area of atoms in the coating is enlarged, and the diffusion process is prolonged, so that the high-temperature resistant time of the coating is increased, the high-temperature stability is facilitated, and the absorption rate of the coating in a solar spectrum waveband is still stable after the coating is annealed at a high temperature of 800 ℃ through experimental verification;

the texture surface forms prepared twice can be adjusted, and surface textures with different forms, such as particle forms, sponge forms and the like can be obtained by adjusting and controlling substrate bias voltage, etching time, the distance between an arc power source target and a substrate, arc power source parameters, air pressure and the like, wherein the characteristic dimension of the particle forms is 200nm-1 mu m, and the dimension of the sponge-like characteristic units is about 1 mu m in length and about 500nm in width;

(3) the substrate provided by the invention has a textured surface, can absorb solar radiation, has larger roughness in texture appearance, improves the adhesive force of the coating, and does not need to worry about the problems of cracking, falling off and the like of the absorption layer caused by large brittleness after high temperature.

(4) According to the invention, the gradient multilayer absorption coating is deposited on the surface of the textured substrate with absorption performance, and the layered structure is favorable for preventing diffusion and fusion among light absorption nano crystal grains in the coating at high temperature, inhibiting coarsening of the crystal grains, satisfying spectrum selective absorption and improving the stability of the high-temperature structure and performance.

(5) The surface of the absorption coating is deposited with an alloy oxidation layer or a metal oxidation layer, such as a high-entropy alloy oxide, an AlCr oxide, an AlTi oxide and the like, so that the high-temperature stability is good, the stainless steel texture surface can be protected from being oxidized at high temperature, and the high-temperature oxidation-resistant coating is also used as an anti-reflection layer, so that the optical performance of the absorption layer is further improved, compared with a stainless steel substrate which is only provided with the texture surface, no absorption layer and an oxide anti-reflection layer, the coating which is wrapped with the absorption layer, the anti-reflection layer and a secondary texture surface on the texture surface has better spectral selectivity, the reflectivity in a solar spectrum waveband is reduced (the reflectivity is reduced from 0.28 to 0.04, and the absorptivity is increased from 0.75 to 0.92), the reflectivity in an infrared waveband is increased (from 0.87 to 0.91), and the self heat radiation loss is reduced;

(6) the invention is not only suitable for solar spectrum absorption coatings, but also can be used for preparing other functional coatings, and corresponding texture surfaces can be prepared only by selecting proper substrates and parameters according to the application and performance requirements of target coatings, thereby having wide application fields.

Drawings

FIG. 1 is a schematic diagram of an apparatus for preparing a solar selective absorber coating with a double-textured surface according to an embodiment of the invention;

FIG. 2 is a schematic view of the substrate-coating topography change during the preparation of a dual textured surface coating in accordance with one embodiment of the present invention; FIG. 2(a) 13-substrate, FIG. 2(b) 14-surface textured substrate, FIG. 2(c) 15-multilayer absorptive coating and 16-antireflective layer (protective layer), FIG. 2(d) microtextured absorptive coating;

FIG. 3 is a SEM surface topography image of a solar selective absorber coating with a grain morphology surface texture according to one embodiment of the invention; wherein, fig. 3(a) is the original shape of a flat stainless steel substrate, fig. 3(b) is a surface texture stainless steel substrate in a particle form, and fig. 3(c) is a surface texture coating in a particle form comprising an alcrnbtatitisizr high-entropy alloy absorption coating and an oxide antireflection layer;

FIG. 4 is a graph of the reflectance measured across a full spectrum band for flat stainless steel, grain morphology surface texture stainless steel, and grain morphology surface texture solar selective absorber coating prior to annealing in accordance with one embodiment of the present invention; the method comprises the following steps of a-flattening a stainless steel substrate reflectivity map, b-a stainless steel substrate reflectivity map with a grain-shaped surface texture, c-a grain-shaped surface texture absorption coating reflectivity map containing an AlCrNbTaTiSiZr high-entropy alloy absorption coating and an oxide anti-reflection layer, and d-an ideal solar spectrum absorption coating reflectivity map;

FIG. 5 is a graph of the reflectance of a grain-morphology surface-textured solar selective absorber coating measured at a full-spectrum band before and after annealing in accordance with a second embodiment of the present invention; wherein, a is a reflectivity map of the grain-shaped surface texture absorbing coating before annealing, b is 800 ℃ and 30h is annealed, c is 800 ℃ and 60h is annealed, and d is an ideal solar spectrum absorbing coating reflectivity map;

FIG. 6 is an SEM surface topography image of the solar selective absorption coating with the spongy surface texture in the third example;

FIG. 7 is a reflectivity spectrum of the solar selective absorbing coating with the spongy surface texture, a-the reflectivity spectrum of the solar selective absorbing coating with the spongy surface texture, b-the reflectivity spectrum of the surface texture absorbing coating with the particle morphology, and c-the reflectivity spectrum of the ideal solar spectrum absorbing coating in the third example.

In FIG. 1: 1-target 1, 2-target 2, 3-turntable, 4 '-sample holder, 5' -substrate (sample), 6-molecular pump, mechanical pump set, 7-heating tube, 8-Ar gas flow, 9-O₂Airflow, 10-trigger, 11-anode, 12-interception screen.

Detailed Description

The technical solutions in the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

The invention provides a preparation method of a solar selective absorbing coating with a double-texture surface, which is suitable for substrates of any material and is also suitable for the field of other functional coatings. The method comprises the steps of preparing a substrate surface with a texture structure by an arc discharge method and magnetron sputtering, depositing a plurality of layers of absorption coatings and oxidation layer antireflection layers, finally etching a secondary texture surface on the surface of the antireflection layer with the texture appearance, wherein the layered absorption coatings can inhibit coarsening of light absorption grains, improve the stability of a high-temperature structure and performance while meeting spectrum selective absorption, improve the oxidation resistance of the coatings and the light transmittance of the surface by the antireflection layers, so that more solar radiation energy enters the bottom layer absorption coatings, prolong the diffusion process of the secondary texture surface, improve the absorption performance and the high-temperature stability, and meet the technical requirements of a new generation of concentrating solar energy system.

With reference to fig. 1, which is a schematic diagram of equipment, and fig. 2, which is a schematic diagram of substrate coating morphology change, the invention provides a solar selective absorbing coating with double-textured surface and a preparation method thereof, comprising the following steps:

(1) preparing an experimental environment: on a radio frequency magnetron sputtering PVD device, a sputtering target material 1, an arc power source target material 2, a turntable 3, a sample frame 4 and a substrate 5 are placed according to the positions shown in figure 1, at the moment, the substrate 5 is parallel to the arc power source target material 2, the surface of the substrate 5 is flat (see 13 in figure 2 (a)), a mechanical pump and a molecular pump group 6 are used for vacuumizing, a heating pipe 7 is simultaneously opened, and when the vacuum degree reaches an ideal value and the temperature reaches a target value; the vacuum degree is generally 10^-3Pa magnitude, the temperature in the cavity is determined by the application and performance of the coating, and is generally between 100 ℃ and 300 ℃;

(2) etching a texture surface on a flat substrate: introducing high-purity Ar gas 8, setting substrate negative bias voltage which is generally-100V to-500V, and realizing Ar⁺Etching ions; starting an arc power supply, wherein the arc power supply comprises an arc power supply target 2, a trigger 20, an anode 11 and an interception screen 12, and under the action of the voltage difference of the trigger 10, the anode 11 and the arc power supply target 2, arc enhanced glow discharge is formed, so that Ar is ionized into Ar⁺，Ar⁺Bombarding the substrate 5 by ion beams under the potential difference, and etching the surface of the substrate 5 to prepare a required rough texture surface 14, as shown in figure 2 (b); in order to protect the substrate 5 from the influence of the sputtered chromium ions, the interception shield 12 is in a closed state in the whole process; in this step, the flow rate of the Ar gas stream is generally between 0.5 and 2 Pa; the arc power source target material is Cr target, as cathode, and forms voltage difference with anode to implement stable discharge, the voltage difference between anode 11 and arc power source target material 2 is generally between 20-80V, and current is between 70-120A, so as to form arc enhanced glow discharge, and Ar is ionized into Ar under the action of voltage difference between anode 11 and arc power source target material 2⁺(ii) a The distance between the arc power source target and the substrate 5 is generally between 100mm and 400 mm;

(3) depositing a multi-layer absorption coating: turning off an arc source, rotating the turntable 3 clockwise by 90 degrees to enable the substrate 5 on the turntable 3 to be parallel to the sputtering target 1, turning on a radio frequency power supply and setting parameters, introducing high-purity Ar gas 8 and high-purity oxygen gas 9 into the chamber, and performing radio frequency and O₂Under the combined action of the Ar mixed gas flow, the substances of the sputtering target material 1 are sputtered and deposited on the substrate 5, and O is gradually increased in the deposition process₂Ratio of/Ar (O)₂the/Ar ratio is between 1: 60 to 15: increasing O layer by layer during deposition₂the/Ar ratio) to form a gradient multilayer absorption coating 15 which is wrapped on the textured surface of the substrate and has absorption performance;

(4) deposition of antireflective layer (protective layer): further increasing O on the basis of the last layer of absorbing coating deposited in step 3₂Content ratio (O)₂The ratio/Ar is between 1: 3 to 5: 1) and maintain constant O₂The mixed gas flow of the/Ar ratio and the total flow rate fully oxidizes the sputtering product of the target material, and pure gold oxide or metal oxide, such as high-entropy alloy oxide, AlTi, AlCr oxide and the like, is deposited on the multilayer absorption coating layer, the thickness of the pure gold oxide or metal oxide is about 50nm to 200nm, and the oxide can be used as a protective layer and an anti-reflection layer 16, as shown in figure 2 (c);

(5) etching a secondary texture surface on the anti-reflection layer: rotating the turntable to make the substrate 5 on the turntable parallel to the arc power source target 2, introducing high-purity Ar gas, and setting the substrate negative bias voltage Ar⁺And etching the surface of the anti-reflection layer by using an ion beam to prepare a required textured surface 17, as shown in fig. 2(d), so as to further increase the reflection performance of the anti-reflection layer, thereby completing the preparation of the solar selective absorbing coating with the double textured surface.

(6) And (3) verifying the high-temperature stability: annealing in a high temperature annealing furnace and carrying out a thermal stability test in air. And in the annealing process, a sample is taken out periodically for appearance measurement and optical performance characterization.

In the above steps, the texture surfaces 14 and 17 both include conical, cylindrical, spherical, spongy and other undulating features, the specific features depend on a plurality of parameters such as substrate bias voltage, etching time, distance between an arc power source target and a substrate, arc power source parameters, air pressure and the like, the texture surface means that the original flat surface has a roughening phenomenon, the roughness is larger, the surface can undergo more reflections when light is irradiated to the surface until the light intensity is completely absorbed by the texture surface, namely the rough surface is more beneficial to spectral absorption, the texture surface can also increase the diffusion area of atoms in the coating, the diffusion process is prolonged, and the high-temperature stability is facilitated.

The sputter target 1 provides a material for solar spectrum absorbing coatings, typically a pure alloy or a pure metal, such as a high alloyEntropy alloys, AlTi, AlCr, and the like; the substrate 5 may be a simple substrate or a substrate coated with a plating layer depending on the intended coating use and performance. In step 3 and step 4, O₂The flow rate of the Ar mixed gas flow is generally 0.5-5Pa, and O₂The ratio of Ar is 0-1, Ar is used for bombarding the target material and sputtering the target material, O₂For oxidizing the sputtering product, depositing an oxide coating.

The multilayer absorption coating 15 deposited on the textured substrate can be an alloy material or a pure metal material, such as a high-entropy alloy, and is designed into a multilayer structure, and the layered structure is favorable for preventing diffusion fusion among light absorption nano crystal grains in the coating at high temperature, inhibiting coarsening of the crystal grains, and improving the stability of the high-temperature structure and performance while meeting spectrum selective absorption. The multilayers being characterised by a gradual increase in O₂ratio/Ar (O when depositing the first absorption coating layer)₂The ratio/Ar is between 1: 60 to 4: 60, depositing the last absorption coating layer₂The ratio/Ar is between 8: 60 to 15: 60) firstly, depositing an absorption coating with alloy or metal content higher than that of the oxide, and then gradually reducing the alloy or metal content to form a gradient multilayer (5-10 layers) structure absorption coating with the oxide ratio increasing, wherein the thickness of each layer is 8-20nm, and the total thickness is 40-200 nm.

The pure metal oxide or metal oxide 16 deposited on the absorption coating has the thickness of about 50nm-200nm and is used as a protective layer and an anti-reflection layer, such as high-entropy alloy oxide, AlTi, AlCr oxide and the like, because the pure metal oxide or metal oxide has good high-temperature stability, the textured surface can be protected from being oxidized at high temperature, the surface reflection is inhibited at the same time, the reflectivity in a wave band of 0.3-2.5 mu m can be effectively reduced, and the spectral selectivity is improved.

The temperature is 600-800 ℃ and the time is 5 minutes to 2000 hours in the thermal stability test. The morphology measurement comprises SEM micro-morphology characterization and AFM surface roughness analysis.

The optical performance is characterized in that the reflectivity R of the coating with the thickness of 0.25-2.5 mu m is measured in a full spectrum wave band, and then the absorptivity alpha in a solar spectrum wave band, the self thermal radiance epsilon in an infrared wave band and the spectrum absorption selectivity alpha/epsilon are respectively calculated.

Conversion formula of absorption rate and reflectivity of the coating in the solar spectrum band (0.3-2.5 μm):

the conversion formula of the self emissivity and the reflectivity of the coating in an infrared band (2.5-25 mu m) is as follows:

in the above formula, R, α, and ∈ are respectively reflectance, absorptance, and thermal emissivity, and it can be seen that the higher the reflectance R is, the lower the coating absorptance α and thermal emissivity ∈ are.

The present invention is further illustrated by the following specific examples, which are not to be construed as limiting the invention.

Example one:

the invention provides a preparation method of a solar selective absorbing coating with double-textured surface, the surface morphology of the prepared texture is adjustable, and surface textures with different appearances can be obtained by regulating substrate bias voltage, etching time, the distance between an arc power source target 2 and a substrate 5, arc power source parameters, air pressure and the like;

by taking the preparation of the textured surface in a particle form, stainless steel as a substrate, high-entropy alloy as an absorption layer, and high-entropy alloy oxide as an anti-reflection layer as an example of the surface textured solar selective absorption coating as shown in fig. 1, 3 and 4, the coating with the absorption layer and the anti-reflection layer wrapped on the textured surface and the secondary textured surface have better spectral selectivity compared with the stainless steel substrate with only the textured surface, no absorption layer and no oxide anti-reflection layer.

(1) Preparing an experimental environment: on a radio frequency magnetron sputtering PVD device, according to the illustration of fig. 1, an AlCrNbTaTiSiZr target (Al: Cr: Nb: Ta: Ti: Si: Zr ═ 15:15:15:15:15:10), a Cr target at the position of an arc power source target 2, and a flat stainless steel sheet at the position of a substrate 5 are placed at the positions of a sputtering target 1, and the surface is as illustrated in fig. 3 (a); at this time, the arc power source target 2 is parallel to the substrate 5 with a distance 16 therebetween0mm, the sputtering target 1 is vertical to the arc power source target 2, the interception screen 12 is closed, and the sputtering target is vacuumized to 5 multiplied by 10 by a mechanical pump and a molecular pump set 6^-3Pa, simultaneously opening the heating pipe 7, and setting the temperature in the cavity to be 150 ℃;

(2) etching a texture surface on a flat stainless steel substrate: introducing high-purity Ar gas 8 of 0.6Pa, setting the negative bias voltage of the substrate to-200V, closing the interception screen 12, starting an arc power supply, setting the voltage difference between the anode 11 and the target 2 to be 60V and the current to be 90A, forming arc enhanced glow discharge, and ionizing Ar into Ar⁺，Ar⁺Bombarding the substrate by ion beams under potential difference for 60min, and etching the surface of the substrate to prepare a grain-shaped texture surface, as shown in FIG. 3 (b);

(3) depositing a multi-layer absorption coating: turning off an arc source, clockwise rotating the turntable 3 by 90 degrees to 5' to enable a stainless steel sheet on the turntable 3 to be parallel to the AlCrNbTaTiSiZr high-entropy alloy sputtering target material 1, turning on a radio frequency power supply and setting parameters, and simultaneously introducing high-purity Ar gas 8 and high-purity O into the chamber₂9, total pressure 1.5Pa, at radio frequency and O₂And 5 layers of multi-layer gradient absorption coatings wrapped on the surface of the textured substrate are formed on the substrate 5 under the action of Ar mixed gas flow, in order to ensure that the coatings have excellent absorption performance, the absorption coatings with the high-entropy alloy content higher than that of the high-entropy alloy oxide need to be preferentially deposited, then the content of the high-entropy alloy is gradually reduced, and the absorption coatings with the gradient multi-layer structure with the high-entropy alloy oxide ratio increased are formed₂Flow ratio/Ar, in this example, 5 absorber coatings were deposited, O of each absorber coating₂The flow ratio/Ar is set to 3: 60. 5: 60. 6: 60. 7: 60. 10: 60, i.e. with distance from the substrate, O₂The flow ratio of Ar/5 layers is 15nm, 5 layers are all mixtures of high-entropy alloys and oxides thereof, the content of the high-entropy alloy in the first layer is the highest, and the content of the oxide in the last layer is the highest;

(4) depositing a pure high-entropy alloy oxide anti-reflection layer: further increasing O on the basis of the last layer of absorbing coating deposited in step 3₂The content ratio is 1: 1, and maintain constant O₂Mixed gas flow with a/Ar ratio and a total gas pressure of 1.5Pa, sputteringPure AlCrNbTaTiSiZr oxide is ejected and deposited on the surface of the absorption coating to be used as an anti-reflection layer, and the thickness is 70 nm;

(5) etching a secondary texture surface on the anti-reflection layer: rotating the turntable to make the stainless steel sheet on the turntable parallel to the arc power source target 2, introducing 0.6Pa high-purity Ar gas 8, setting the substrate negative bias voltage to-200V, turning off the interception screen 12, turning on the arc power source, setting the voltage difference between the anode 11 and the target 2 to be 60V, the current to be 90A, and Ar⁺And bombarding the anti-reflection layer by the ion beam under the potential difference for 30min, and etching a secondary texture surface on the anti-reflection layer to form a particle shape, as shown in a figure 3(c), so that the preparation of the solar selective absorption coating with the double-texture surface is completed.

(6) And (3) testing performance: and measuring the surface appearance and the reflection spectrum.

The SEM surface morphology is shown in fig. 3, where fig. 3(a) is the original morphology of a flat stainless steel substrate, fig. 3(b) is a surface texture stainless steel substrate in a particle morphology, fig. 3(c) is a surface texture coating in a particle morphology comprising an alcrnbtatitisizr high-entropy alloy absorption coating and an oxide antireflection layer, and the average roughness of the three surfaces is 21nm, 125nm, and 130nm in this order. As can be seen from FIG. 3, through Ar⁺The etched stainless steel surface is no longer flat, and the textured surface is composed of spherical particles with diameters of 200nm-1.5 μm as shown in fig. 3(b), and the granular surface morphology can make the substrate have absorption performance. Depositing AlCrNbTaTiSiZr high-entropy alloy absorbing coating and an oxide anti-reflection layer, and performing secondary etching to obtain spherical particles with a particle size of 100nm-1.0 μm, wherein the secondary textured SEM morphology is shown in FIG. 3 (c).

The reflection spectrum is shown in fig. 4, wherein a in fig. 4 is a reflectance spectrum of a flat stainless steel substrate (i.e., the reflectance spectrum in fig. 3 (a)), b in fig. 4 is a reflectance spectrum of a grain-shaped surface texture stainless steel substrate (i.e., the reflectance spectrum in fig. 3 (b)), c in fig. 4 is a reflectance spectrum of a grain-shaped surface texture absorption coating containing an alcrnbtitisizr high-entropy alloy absorption coating and an oxide anti-reflection layer (i.e., the reflectance spectrum in fig. 3 (c)), and d in fig. 4 is a reflectance spectrum of an ideal solar spectrum absorption coating. As can be seen from FIG. 4, curve c is closer to the ideal map d, b times, with a being the farthest; therefore, the absorption performance of the texture surface is superior to that of a flat stainless steel substrate, the spectral absorption rate is improved to a great extent, and after the AlCrNbTaTiSiZr high-entropy alloy absorption coating and the oxide anti-reflection layer are wrapped and subjected to secondary etching, the coating has higher anti-reflection performance, and the optical performances such as the absorption rate of the absorption layer are further improved:

firstly, in a solar spectrum waveband less than 2.5 mu m, the value of a curve c is closer to 0, the reflectivity of the curve c is as low as 0.04, the absorptivity reaches 0.92, the reflectivity of a curve b is as low as 0.28 and is 7 times of that of the curve c, which shows that the combination of a high-entropy alloy absorption coating, an oxide anti-reflection layer and a secondary etching process effectively reduces the reflectivity in the waveband of 0.3-2.5 mu m, the absorption rates alpha of the high-entropy alloy absorption coating, the oxide anti-reflection layer and the secondary etching process in the solar spectrum waveband (0.3-2.5 mu m) are respectively 0.36, 0.75 and 0.92, and the coating which contains an AlCrNbTaTiSiZr high-entropy alloy absorption coating and the oxide anti-reflection layer and has a grain shape texture surface is most beneficial to the absorption of a solar spectrum;

secondly, in an infrared band larger than 2.5 microns, the reflectivity of a curve c is increased fastest and finally reaches 0.91 along with the increase of the wavelength, and curves b and a are 0.87 and 0.84 in sequence, which means that the grain-shaped surface texture absorption coating containing the AlCrNbTaTiSiZr high-entropy alloy absorption coating and the oxide antireflection layer has the lowest heat radiation in the infrared band and the highest energy utilization rate.

Example two:

with reference to fig. 5, on the basis of the first example, the high-temperature stability of the grain-shaped dual-texture surface solar selective absorption coating with stainless steel as the substrate, high-entropy alloy as the absorption layer, high-entropy alloy oxide as the protective layer, and anti-reflection layer is further verified.

(1) Preparing an experimental environment: as in example one;

(2) etching a texture surface on a flat stainless steel substrate: as in example one;

(3) depositing a multi-layer absorption coating: as in example one;

(4) depositing a pure high-entropy alloy oxide anti-reflection layer: as in example one;

(5) etching a secondary texture surface on the anti-reflection layer: as in example one;

(6) testing the performance before annealing: measuring the surface topography, reflection spectrum, as shown in FIG. 4, and analyzing the result as in example one;

(7) and (3) verifying the high-temperature stability: and (3) carrying out a thermal stability test in the air in a high-temperature annealing furnace, setting the annealing temperature to be 800 ℃, and taking out samples at regular intervals of 30h and 60h for carrying out appearance measurement and optical performance characterization.

The absorption coating of the pure gold oxide-coated particle-shaped surface texture has no change in surface appearance before annealing, after annealing at 800 ℃ for 30h and after annealing at 800 ℃ for 60h, the particle-shaped texture is obvious, the roughness has a slight increasing trend, and the roughness is 130nm, 141nm and 153nm in sequence.

The reflection spectrum is shown in fig. 5, wherein a in fig. 5 is a reflectivity spectrum of the grain-shaped surface texture absorption coating before annealing (i.e. the reflectivity spectrum before annealing in fig. 3 (c)), b and c in fig. 5 are respectively a reflectivity spectrum of the grain-shaped surface texture absorption coating after annealing at 800 ℃ for 30h and 60h, d is a reflectivity spectrum of an ideal solar spectrum absorption coating, and the absorptances α of a-c in a solar spectrum waveband (0.3-2.5 μm) are respectively 0.92, 0.95 and 0.97. It can be seen that the reflectance spectrum before and after annealing changes little, the lowest value of the reflectance is stabilized at about 0.04 in the solar spectrum band (0.3-2.5 μm), and the highest value of the reflectance is stabilized at 0.88 in the infrared band higher than 2.5 μm, which indicates that the rough secondary texture surface of the coating effectively increases the diffusion region and process, the coating can maintain the original spectrum absorption performance at high temperature, the AlCrNbTaTiSiZr high-entropy alloy oxide has good high-temperature stability, the existence of the AlCrNbTaTiSiZr high-entropy alloy oxide further protects the stainless steel texture surface and the absorption coating from being oxidized at high temperature, and the AlCrNbTaTiSiZr high-entropy alloy oxide-containing grain morphology surface texture absorption coating has good high-temperature stability. To illustrate the effects of the present invention, Table 1 shows the absorbance α and surface roughness R of each sample in example one and example two_q。

Example three:

the invention can also prepare surface textures with other appearances by regulating and controlling substrate bias voltage, etching time, the distance between the arc power source target 2 and the substrate 5, arc power source parameters, air pressure and the like, and takes the preparation of a spongy texture surface, a stainless steel as a substrate, a high-entropy alloy as an absorption layer, a high-entropy alloy oxide as a protective layer and a double-texture surface solar selective absorption coating of an anti-reflection layer as an example by combining the graphs of fig. 6 and 7.

(1) Preparing an experimental environment: the distance between the arc power source target 2 and the substrate 5 is shortened to 120mm, and others are as in the first example;

(2) etching a texture surface on a flat stainless steel substrate: bombardment time was increased to 90min, others as example one;

(3) depositing a multi-layer absorption coating: monolayer absorption coating thickness was 18nm, others as example one;

(4) depositing a pure metal oxide anti-reflection layer: the thickness of the anti-reflection layer is 75nm as in example one;

(5) etching a secondary texture surface on the anti-reflection layer: bombardment time was increased to 60min, others as example one;

(6) and (3) testing the performance: and measuring the surface appearance and the reflection spectrum.

The SEM surface morphology is shown in fig. 6, and it can be seen from fig. 6 that the texture morphology obtained by changing the distance between the arc power source target 2 and the substrate 5 and the etching time of two times is also greatly changed, the texture surface in fig. 6 is like a sponge, the roughness of the coating surface is 150nm, the feature unit size is about 1 μm long and about 500nm wide, and the feature size is larger than the particle surface, which can further enhance the absorption performance of the coating.

The reflection spectrum is shown in fig. 7, wherein a in fig. 7 is a reflectivity spectrum of a sponge-shaped surface texture absorption coating comprising a high-entropy alloy absorption coating and an oxide antireflection layer (i.e. the reflectivity spectrum of fig. 6), b in fig. 7 is a reflectivity spectrum of a coating with a grain-shaped texture surface (i.e. the reflectivity spectrum of fig. 3 (c)), and c in fig. 7 is an ideal solar spectrum absorption coating reflectivity spectrum. As can be seen from FIG. 7, curve a is closer to the ideal spectrum c, b times;

in a solar spectrum waveband less than 2.5 mu m, the value of a curve a is closer to 0, the reflectivity of the curve a is as low as 0.01, the absorptivity reaches 0.98, the reflectivity of a curve b is as low as 0.04, which is 4 times of that of the curve a, and the sponge-shaped surface texture absorption coating is more beneficial to reducing the reflectivity in the waveband of 0.3-2.5 mu m compared with the particle-shaped texture surface, so that the spectrum selection ratio is improved, and the absorption of the solar spectrum is more beneficial;

secondly, in an infrared band larger than 2.5 mu m, along with the increase of the wavelength, the reflectivity of the curves a and b is 0.83 and 0.91 in sequence, and the reflectivity of the curve b is higher, which means that the granular surface texture absorption coating has lower heat radiation in the infrared band and the utilization rate of energy is higher.

Example four:

on the basis of the first example, the temperature of the chamber is 100 ℃, the distance between the arc power source target 2 and the substrate 5 is prolonged to 400mm, the bombardment time of the step 2 is prolonged to 120min, the substrate is negatively biased to-500V, the bombardment time of the step 5 is shortened to 10min, and in the step 3, O of each layer of absorption coating₂The flow ratio of/Ar is set to 1: 60. 3: 60. 5: 60. 6: 60. 8: 60, step 4, O₂The flow ratio of/Ar is 1: 3, the other steps are the same as the first example, the required solar selective absorption coating is prepared, the thickness of a single-layer absorption coating is 10nm, the thickness of an anti-reflection layer is 50nm, the surface roughness of the coating is 120nm, the coating is flatter, the texture is more round and fine, the coating is composed of a plurality of spherical particles with the diameters of 50nm-500nm, the reflectivity of the coating is as low as 0.05 and the absorptivity reaches 0.89 in a solar spectrum band smaller than 2.5 microns, and the reflectivity of the coating reaches 0.86 in an infrared band larger than 2.5 microns.

Example five:

on the basis of the first example, the distance between the arc power source target 2 and the substrate 5 is shortened to 100mm, the bombardment time in the step 2 is prolonged to 10min, the negative bias voltage of the substrate is minus 80V, the bombardment time in the step 5 is shortened to 20min, and in the step 3, O of each layer of absorption coating₂The flow ratio of/Ar is set to 2: 60. 4: 60. 5: 60. 7: 60. 12: 60, step 4, O₂The flow ratio/Ar is 2: 1, the other examples are the same as the first example, the required solar selective absorbing coating is prepared, and the other examples are the same as the first exampleSimilarly, the required solar selective absorption coating is prepared, the thickness of a single-layer absorption coating is 20nm, the thickness of an anti-reflection layer is 80nm, the surface roughness of the coating is 160nm, the coating is rougher and more spongelike, the size of a characteristic unit is about 1.2 microns long, the width is about 600nm, the reflectivity of the coating is as low as 0.02 and the absorptivity of the coating reaches 0.93 in a solar spectrum band smaller than 2.5 microns, and the reflectivity of the coating is as high as 0.82 in an infrared band larger than 2.5 microns.

Example six:

on the basis of the first example, the chamber temperature is set to 300 ℃, and O in the step 3 and the step 4 is added₂The total flow of Ar is increased to 3Pa, the flow of Ar gas in the step 2 and the step 5 is increased to 2Pa, and in the step 3, O of each layer of absorption coating₂The flow ratio of/Ar is set to 4: 60. 5: 60. 7: 60. 9: 60. 15: 60, step 4, O₂the/Ar flow ratio is 5:1, the other parts are the same as the first embodiment, the required solar selective absorption coating is prepared, the thickness of a single-layer absorption coating is 20nm, the thickness of an anti-reflection layer is 85nm, the surface roughness of the coating is 140nm, the reflectivity of the coating is as low as 0.02 in a solar spectrum waveband less than 2.5 microns, the absorptivity of the coating reaches 0.94, and the reflectivity of the coating is as high as 0.93 in an infrared waveband more than 2.5 microns. Meaning that the flow of Ar gas is increased in the

steps

2 and 5 to improve the etching strength and obtain a rougher surface to improve the anti-reflection performance and reduce the heat radiation, and O is increased in the steps 3 and 4₂The total flow of Ar can increase the thicknesses of the absorption coating and the anti-reflection layer, and further increase the spectral absorption performance of the coating.

Example seven:

on the basis of the first example, the total number of the absorbing coatings in the step 3 is increased to 8 layers, and in the step 3, the O of each absorbing coating layer₂The flow ratio of/Ar is set to 1: 60. 2: 60. 3: 60. 5: 60. 7: 60. 9: 60. 11: 60. 15: 60, otherwise identical to example one, to produce the desired solar selective absorber coating, a single absorber coating thickness of 15nm, an anti-reflective layer thickness of 70nm, and a coating layer thickness of 15nmThe surface roughness is 130nm, the reflectivity of the coating is as low as 0.03 and the absorptivity reaches 0.94 in a solar spectrum band smaller than 2.5 mu m, and the reflectivity of the coating is as high as 0.92 in an infrared band larger than 2.5 mu m. Meaning that increasing the number of absorbing coating layers can further increase the spectral absorption properties of the coating and reduce thermal radiation.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A preparation method of a double-texture surface solar selective absorption coating is characterized by comprising the following steps:

and 2, step: etching a texture surface on a substrate: introducing high-purity Ar gas, setting substrate negative bias, starting arc power supply, and ionizing Ar into Ar under the action of the arc power supply⁺，Ar⁺Bombarding the substrate by ion beams under potential difference, and etching the surface of the substrate to prepare a required texture surface;

and step 3: depositing a multi-layer absorption coating: turning off the arc power supply, rotating the turntable to make the substrate on the turntable parallel to the sputtering target, turning on the radio frequency power supply and setting parameters, simultaneously introducing high-purity Ar gas and high-purity oxygen gas into the chamber, and performing sputtering under radio frequency and O conditions₂Sputtering the material of the sputtering target under the action of Ar mixed gas flow and depositing the material on the substrate, wherein O is gradually increased in the deposition process₂the/Ar ratio is adopted so as to form a gradient multilayer absorption coating wrapped on the textured surface of the substrate;

and 4, step 4: depositing an anti-reflection layer:further increasing O on the basis of the last layer of absorbing coating deposited in step 3₂Content ratio and keeping constant O₂The mixed gas flow of the/Ar ratio and the total flow fully oxidizes the sputtering product of the target material, and pure alloy oxide or metal oxide with the functions of protection and antireflection is deposited on the multilayer absorption coating;

and 5: etching a secondary texture surface on the anti-reflection layer: rotating the turntable to make the substrate parallel to the arc power source target, introducing high purity Ar gas, setting negative bias of the substrate, Ar⁺And etching the surface of the anti-reflection layer by using ion beams to prepare a required secondary texture surface so as to further increase the reflection performance of the anti-reflection layer, thereby completing the preparation of the solar selective absorption coating with the double-texture surface.

2. The method for preparing the solar selective absorbing coating with the double-textured surface according to claim 1, wherein in the step 1, the vacuum degree in the cavity is 10^-3Pa, and the temperature in the chamber is between 100-300 ℃.

3. The method for preparing the solar selective absorption coating with the double-textured surface according to claim 1, wherein the arc power supply comprises an arc power supply target, a trigger, an anode and an interception screen, and the interception screen is always blocked between the substrate and the arc power supply target and is in a closed state in the whole process of preparing the coating.

4. The method for preparing the solar selective absorbing coating with the double-textured surface according to claim 1, wherein in the step 2 and the step 5, a two-step process for preparing the textured surface is designed, surface textures with different morphologies are obtained on the substrate by regulating and controlling the distance between the arc power source target and the substrate, the substrate bias voltage, the etching time, the voltage difference between the anode and the arc power source target and the Ar airflow flow, and the secondary textured surface is formed by etching the anti-reflection layer surface with the textured morphology again.

5. The method for preparing the solar selective absorbing coating with the double-textured surface according to claim 4, wherein the arc power source target is a Cr target which is used as a cathode of an arc power source and has a distance of 100mm-400mm from the substrate.

6. The method for preparing the solar selective absorbing coating with the double-textured surface according to claim 4, wherein the voltage difference between the anode of the arc power supply and the target of the arc power supply is 20-80V, the current is 70-120A, the etching time in step 2 is 10-120 minutes, and the etching time in step 5 is 10-60 minutes.

7. The method for preparing the solar selective absorbing coating with the double-textured surface according to claim 4, wherein the flow rate of Ar gas in the step 2 and the flow rate of Ar gas in the step 5 are both between 0.5 and 2Pa, and the negative bias voltage of the substrate is set to be between-80V and-500V.

8. The method for preparing the double-texture surface solar selective absorption coating according to claim 1, wherein O in the step 3 and the step 4₂The flow rate of the Ar mixed gas flow is 0.5-5 Pa;

wherein, in step 3, O₂the/Ar ratio is between 1: 60 to 15: 60, step 4, O₂The ratio/Ar is between 1: 3 to 5: 1.

9. the method for preparing the solar selective absorbing coating with the double-textured surface as claimed in claim 1, wherein in the step 3, the sputtering target is pure alloy or pure metal, and O is gradually increased₂the/Ar ratio is that an absorption coating with alloy or metal content higher than that of the oxide is deposited firstly, then the alloy or metal content is gradually reduced to form a gradient multilayer structure absorption coating with the oxide ratio increased, the thickness of each layer is between 8 and 20nm, and the total thickness is between 40 and 200 nm;

in step 4, the sputtering target is pure alloy or pure metal, and pure gold oxide or pure metal oxide is deposited to be used as a protective and anti-reflection functional layer, wherein the thickness of the anti-reflection functional layer is 50-200 nm.

10. A coating prepared by the method for preparing the double-texture surface solar selective absorbing coating according to any one of claims 1 to 9.