A photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer film

Abstract

The application relates to a photothermal selective absorber based on a Bi2Se3 / SiO2 alternating multilayer film, which belongs to the field of solar energy applications. The bottom layer is a metal substrate, the thickness of the substrate should be greater than the skin depth of incident light in the metal, which will ensure that the incident light cannot be transmitted after entering the coating; the SiO2 thin film and the Bi2Se3 thin film with different thicknesses are arranged alternately on the metal substrate to form an impedance matching control layer, the refractive index and the extinction coefficient of the Bi2Se3 / SiO2 alternating multilayer film are controlled through the thickness; the top layer of the Bi2Se3 thin film is a blackbody thermal radiation control function layer, the thermal radiation frequency domain is adjusted to the metal reflection region of the thin film through the thickness adjustment. The electrodes are increased at both ends of the top layer of the Bi2Se3 thin film to apply voltage, the electrical transport characteristics of each layer film are controlled through the voltage, which will change the refractive index and the extinction coefficient of the Bi2Se3 thin film, so as to adjust the equivalent impedance of different incident angles, and ensure that the Bi2Se3 / SiO2 alternating multilayer film always maintains the overall equivalent impedance matching state under each incident angle.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of solar energy technology and application, and particularly relates to a light-heat selective absorber based on Bi2Se3 / SiO2 alternate multilayer film. BACKGROUND

[0002] Solar light-heat conversion is the most direct and effective way for people to utilize solar energy, and has broad application prospects in the fields of solar hot water utilization, solar seawater desalination and solar light-heat power generation. The light-heat selective absorption coating is the most critical part of the solar light-heat conversion device, and its optical properties determine the heat trapping performance of the light-heat system. An ideal selective absorption coating should have an absorption rate of 100% in the solar strong radiation spectrum, so as to realize complete conversion of solar energy into heat, and an emission rate of 0 in the blackbody thermal radiation spectrum, so as to prevent secondary radiation of energy. That is, the light-heat selective absorption coating should meet the impedance matching in the solar strong radiation spectrum and the complete impedance mismatch in the blackbody thermal radiation spectrum. At present, the most widely studied light-heat selective absorption coatings mainly include metal ceramic type and surface superstructure type. The light-heat selective absorption coating of the metal ceramic type is difficult to further improve the light-heat conversion efficiency by only changing the metal particle concentration and size, and the mutual diffusion and aggregation between particles at high temperature will lead to changes in optical parameters, thereby weakening the spectral absorption performance. The light-heat selective absorption coating of the surface superstructure type has a wide frequency band advantage in the design of equivalent impedance matching by using surface plasmon resonance, but the non-uniformity of the surface structure will cause scattering of high-frequency light waves, making it difficult to further improve the light-heat conversion efficiency, and the micro-nano size superstructure processing also poses great challenges to the preparation process. In addition, the light-heat conversion efficiency of both types of light-heat selective absorption coatings depends on the incident angle of light, and it is impossible to achieve wide-angle spectral matching absorption.

[0003] Bi2Se3 is a typical third-generation topological insulator material, and its bulk phase has a large band gap. The surface state of the two-dimensional topological insulator material has a large adjustable space for electrical transport performance. By controlling the gate voltage, the surface conductance of the Bi2Se3 bulk can be significantly improved, and the high adjustability of the surface state electrical transport provides more space for impedance adjustment. At the same time, the concentration of the surface Dirac-type conduction carriers also affects the conductance loss, and changing the thickness of the topological insulator film can effectively adjust the impedance matching performance, which is conducive to achieving excellent spectral selective absorption and obtaining higher solar light-heat conversion efficiency. SUMMARY

[0004] In view of the problem that the existing light-heat conversion material is difficult to further improve the light-heat conversion efficiency, a light-heat selective absorber based on Bi2Se3 / SiO2 alternating multilayer film is proposed. The unique advantage of flexible and adjustable surface state electric transport of Bi2Se3 material is used for impedance matching design optimization in the light frequency band, so that the multilayer film realizes efficient light-heat conversion, and meanwhile the matching absorption of the solar strong radiation spectrum is maintained in a wide range of incident angles.

[0005] A light-heat selective absorber based on Bi2Se3 / SiO2 alternating multilayer film, the bottom layer of which is a metal substrate, and the specific metal material is not limited. The thickness of the substrate should be greater than the skin depth of the incident light in the metal, which will ensure that the incident light cannot be transmitted after entering the coating. The SiO2 film and the Bi2Se3 film of different thicknesses are arranged alternately on the metal substrate to form an impedance matching control layer. The refractive index and extinction coefficient of the Bi2Se3 / SiO2 alternating multilayer film are controlled by the topological surface state. The main means of controlling the topological surface state of the Bi2Se3 film is to change its refractive index and extinction coefficient by thickness control. The thickness of the Bi2Se3 / SiO2 alternating multilayer film is simulated and optimized by the finite difference time domain method, so that it is impedance matched in the solar strong radiation frequency domain, and the multilayer film realizes efficient absorption of the solar strong radiation spectrum. The topmost Bi2Se3 film is a blackbody thermal radiation control function layer. By adjusting the thickness of the film, the thermal radiation frequency domain is in the metal reflection region of the film, thereby reducing the infrared emissivity of the coating blackbody thermal radiation, and realizing efficient solar light-heat conversion of the coating. In addition, electrodes are added at both ends of the top Bi2Se3 film to apply voltage. The voltage can control the electric transport characteristics of each layer, which will effectively change the refractive index and extinction coefficient of the Bi2Se3 film, thereby flexibly adjusting the equivalent impedance of different incident angles, ensuring that the Bi2Se3 / SiO2 alternating multilayer film always maintains overall equivalent impedance matching state under each incident angle, and finally realizes wide-angle absorption of sunlight. The light-heat selective absorption structure based on the Bi2Se3 / SiO2 alternating multilayer film structure of the topological insulator can be prepared by a magnetron sputtering method, which has simple preparation process and mature process flow. In a vacuum environment, inert gas is used as the sputtering gas to deposit the bottom metal film on the substrate by the magnetron sputtering method, and then SiO2 film and Bi2Se3 film are deposited alternately. By changing the sputtering power, pressure, annealing temperature and other parameters, the quality and crystal growth orientation of the film can be controlled. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 Three-dimensional structure diagram of the light-heat selective absorber based on Bi2Se3 / SiO2 alternating multilayer film

[0007] Figure 2 Side view structure diagram of the light-heat selective absorber based on Bi2Se3 / SiO2 alternating multilayer film

[0008] Figure 3 Spectral absorption effect of photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer film

[0009] Figure 4 Spectral absorption effect of photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer film under wide-angle incidence DETAILED DESCRIPTION

[0010] A photothermal selective absorption coating based on Bi2Se3 / SiO2 alternating multilayer film structure is prepared by magnetron sputtering technology. Silicon wafer is used as the substrate, argon gas is used as the sputtering gas in a vacuum environment, Au, Bi2Se3 and SiO2 are used as the sputtering target material, and the sputtering time is controlled according to the required thickness of each layer and the deposition rate of different materials. First, a layer of gold film is sputtered on the silicon substrate, then SiO2 layers and Bi2Se3 layers are alternately deposited on the gold film, and finally a photothermal selective absorption coating based on Bi2Se3 / SiO2 alternating multilayer film structure is obtained. By applying voltage to control the electrical transport properties of each layer, the equivalent impedance at different incident angles can be flexibly adjusted to ensure that the Bi2Se3 / SiO2 alternating multilayer film always maintains an equivalent impedance matching state under an incident angle of 0-60°, thereby realizing wide-angle absorption of sunlight. The overall structure is shown in Figure 1 The photothermal selective absorption coating based on Bi2Se3 / SiO2 alternating multilayer film structure is shown in Figure 2 The first layer is an Au metal layer (thickness of 80-100 nm), the second layer is an SiO2 layer (thickness of 40-60 nm), the third layer is a Bi2Se3 layer (thickness of 80-100 nm), the fourth layer is an SiO2 layer (thickness of 100-120 nm), the fifth layer is a Bi2Se3 layer (thickness of 40-60 nm), and the sixth layer is an SiO2 layer (thickness of 60-80 nm). The photothermal selective absorber based on the Bi2Se3 / SiO2 alternating multilayer film structure has an average absorption rate of 94% in the high solar radiation spectral region of 0.3-2.5 μm and an infrared emissivity as low as 8% in the 2.5-25 μm region, with high-efficiency photothermal conversion performance. The spectral absorption effect is shown in Figure 3 The absorber has omnidirectional solar absorption capability and is not sensitive to incident angle, as shown in Figure 4 It has good absorption effect in a wide angle range of 0°-60°.

Claims

1. A photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer films, characterized by: The bottom layer is a metal substrate, the thickness of which should be greater than the skin depth of the incident light in the metal. This will ensure that the incident light cannot be transmitted out after entering the coating. SiO2 films and Bi2Se3 films of different thicknesses are alternately arranged on a metal substrate to form an impedance matching control layer. The refractive index and extinction coefficient of the Bi2Se3 / SiO2 alternating multilayer film are controlled by thickness. The top Bi2Se3 film is a blackbody thermal radiation control layer. By adjusting the film thickness, the thermal radiation frequency domain is placed in the metal reflection area of ​​the film. By adding electrodes at both ends of the top Bi2Se3 film and applying voltage, the electrical transport properties of each layer of the film can be regulated by voltage. This will change the refractive index and extinction coefficient of the Bi2Se3 film, thereby adjusting the equivalent impedance at different incident angles, ensuring that the Bi2Se3 / SiO2 alternating multilayer film always maintains an overall equivalent impedance matching state at all incident angles.

2. The photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer films according to claim 1, characterized in that: In a vacuum environment, an inert gas is used as the sputtering gas to deposit the underlying metal film on the substrate by magnetron sputtering, and then SiO2 film and Bi2Se3 film are alternately deposited in sequence. The film quality and film crystal growth orientation are controlled by changing one or more of the sputtering power, pressure, and annealing temperature.

3. The photothermal selective absorber based on Bi2Se3 / SiO2 alternating multilayer films according to claim 1, characterized in that: From bottom to top, the first layer is the Au metal substrate with a thickness of 80-100 nm; the second layer is the SiO2 layer with a thickness of 40-60 nm; the third layer is the Bi2Se3 layer with a thickness of 80-100 nm; the fourth layer is the SiO2 layer with a thickness of 100-120 nm; the fifth layer is the Bi2Se3 layer with a thickness of 40-60 nm; and the sixth layer is the SiO2 layer with a thickness of 60-80 nm.

Images