Cu2ZnSnS4-based visible light efficient absorber based on metasurface as well as preparation method and application of Cu2ZnSnS4-based visible light efficient absorber

Abstract

The invention relates to the field of micro-nano structure arrays and solar energy absorption, in particular to a super-surface-based Cu2ZnSnS4-based visible light efficient absorber as well as a preparation method and application of the super-surface-based Cu2ZnSnS4-based visible light efficient absorber. The solar visible light wave band absorption efficiency of the Cu2ZnSnS4-based series material is improved by utilizing the incident light regulation and control capability of the metasurface. The optical absorption cross section of incident light is increased through surface plasmon resonance of the metal aluminum nanodisk array; the frequency of action between incident light and the Cu2ZnSnS4-based series material is increased through cavity resonance of the Al2O3 medium nano hexahedron array; the refractive index jump gradient of incident light on the surface of the Cu2ZnSnS4-based series material is reduced through the free space impedance matching layer, so that the impedance matching condition is realized. And the three components are combined to form the visible light absorber with high absorption efficiency. The super-surface Cu2ZnSnS4-based visible light efficient absorber provided by the invention has the advantage of high visible light absorption rate.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano structure arrays and solar absorption, and particularly to a Cu2ZnSnS4-based visible light efficient absorber based on a metasurface, and a preparation method and application thereof. Background Art

[0002] The increasing cost of fossil fuels and the increasing impact of global warming have increased the urgency to find efficient renewable energy sources. As a renewable energy source, solar energy has attracted extensive attention. Due to the abundance, sustainability and cleanliness of solar energy, solar energy can be used for heating, cooling, power generation and thermochemical processes. Therefore, solar thermophotovoltaic systems have received much attention due to their effective method of converting solar energy into electrical energy. Cu2ZnSnS4 (CZTS) materials have broad application prospects in the fields of photocatalysis, photodetection and thin film solar cells due to their adjustable direct bandgap, non-toxicity, abundance, etc. However, compared with its theoretically predicted value, the actual photoelectric conversion efficiency of CZTS-based materials is often low, mainly due to the presence of many crystal defects, defect clusters and surface defects in the body, which will limit the collection of solar light and the transport of photo-generated electrons. Although element substitution, that is, replacing the atoms in the original absorption material with other element atoms, can adjust its defect density and improve the application performance. But the actual photoelectric conversion efficiency is still far lower than the theoretical value. One important reason is that the average absorption rate of CZTS-based materials in the entire visible light band is less than 0.7. This severely limits the performance of CZTS-based device.

[0003] A metasurface is an artificial micro-nano optical antenna with special electromagnetic characteristics arranged in a certain way to form a quasi-two-dimensional planar structure, which can realize flexible control of the phase, absorption, polarization, amplitude, etc. of incident light, and has important applications in optical lenses, super-resolution imaging and spectral enhancement. etc. The metasurface includes two major categories: metal array structures and dielectric array structures. The metal array structure can achieve selective absorption and scattering of light through the surface plasmon resonance effect associated with the collective oscillation of free electrons in the metal. In addition to the selective absorption and scattering of incident light related to the dielectric electromagnetic resonance mode, the dielectric array structure also has a cavity resonance mode (similar to a standing wave), which can further increase the absorption degree of the light-absorbing material for incident light. In addition, when incident light is incident on the surface of a high refractive index material, due to the too large gradient of the refractive index change, there will be an optical impedance mismatch with free space. Therefore, a transition layer dielectric film can be covered on the surface of the light-absorbing material to achieve impedance matching.

[0004] Therefore, combining the metal structure metasurface, dielectric structure metasurface, impedance matching layer and traditional solar absorption material is an effective method to achieve efficient absorption of sunlight and further improve the utilization rate of solar energy. Summary of the Invention

[0005] To solve the above problems, the present invention provides a metasurface-based Cu2ZnSnS4-based visible light efficient absorber, its preparation method and application. The metasurface-based Cu2ZnSnS4-based visible light efficient absorber provided by the present invention has the advantage of high visible light absorption rate.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a metasurface-based Cu2ZnSnS4-based visible light efficient absorber, which successively includes a metal substrate layer, a Cu2ZnSnS4-based thin film light absorption layer, and a free space impedance matching layer from bottom to top;

[0008] A metal aluminum nanodisk array and an Al2O3 dielectric nanohexahedron array are arranged on the Cu2ZnSnS4-based thin film light absorption layer;

[0009] The metal aluminum nanodisk array is arranged at a height of 65 nm from the metal substrate layer;

[0010] The Al2O3 dielectric nanohexahedron array is arranged on the top of the center of the metal aluminum nanodisk array.

[0011] Preferably, the metal substrate layer includes a silver thin film, and the thickness of the metal substrate layer is 100 nm.

[0012] Preferably, the Cu2ZnSnS4-based thin film light absorption layer includes all I2-II-IV-VI4 type compound semiconductor thin films such as CZTS, CZTSe, CZTSSe, ACZTS, CZTGS, etc., and the thickness of the Cu2ZnSnS4-based thin film light absorption layer is 500 nm.

[0013] Preferably, the free space impedance matching layer is an Al2O3 dielectric thin film with a refractive index of 1.7, and the thickness of the free space impedance matching layer is 40 nm.

[0014] Preferably, the thickness of the metal aluminum nanodisk array is 50 nm, the diameter is 160 nm, and the array period is 200 - 300 nm.

[0015] Preferably, the refractive index of the Al2O3 dielectric nanohexahedron array is 1.7, the thickness is 220 nm, the length is 200 nm, and the width is 200 nm.

[0016] The present invention also provides a preparation method of the metasurface-based Cu2ZnSnS4-based visible light efficient absorber according to the above technical solution, including the following steps:

[0017] S1. Use the metal substrate layer as the absorber support layer and the incident light reflection layer;

[0018] S2. Use the Cu2ZnSnS4-based thin film light absorption layer as the visible light absorption layer, and embed a metal aluminum nanodisk array at a position 65 nm above the upper surface of the metal substrate layer;

[0019] S3. Embed a dielectric nanohexahedron array on the surface of the Cu2ZnSnS4-based thin film light absorption layer and at the top of the center of the metal nanodisk array;

[0020] S4. Cover a free space impedance matching layer on the Cu2ZnSnS4-based thin film light absorption layer to obtain a Cu2ZnSnS4-based visible light high-efficiency absorber based on the metasurface.

[0021] The present invention also provides an application of the Cu2ZnSnS4-based visible light high-efficiency absorber based on the metasurface described in the above technical solution in improving the visible light absorption rate.

[0022] The present invention also provides an application of the Cu2ZnSnS4-based visible light high-efficiency absorber based on the metasurface described in the above technical solution in reducing the visible light reflectivity.

[0023] Preferably, the visible light reflectivity is reduced and the visible light absorption rate is increased in the range of 380-820 nm.

[0024] The present invention utilizes the incident light regulation ability of the metasurface to improve the solar visible light band absorption efficiency of CZTS-based materials. The surface plasmon resonance of the metal aluminum nanodisk array is used to increase the optical absorption cross-section of the incident light; the cavity resonance of the Al2O3 dielectric nanohexahedron array is used to increase the interaction times between the incident light and the CZTS-based materials; the free space impedance matching layer is used to reduce the refractive index jump gradient of the incident light on the surface of the CZTS-based materials, thereby realizing the impedance matching condition. The combination of the three forms a visible light absorber with high absorption efficiency.

[0025] Advantages of the present invention:

[0026] 1. Based on the surface plasmon resonance of the metal aluminum nanodisk array metasurface, the present invention greatly increases the absorption cross-section of long-wavelength sunlight.

[0027] 2. Based on the cavity resonance of the Al2O3 dielectric nanohexahedron array metasurface, the present invention greatly increases the interaction times between sunlight and traditional absorption materials.

[0028] 3. The free space impedance matching layer described in the present invention can reduce the reflection of the incident light on the upper surface of the sunlight absorption material, and maximize the absorption of the incident visible light. Description of the Drawings

[0029] Figure 1 Side sectional view of a CZTS-based visible light efficient absorber based on metasurface designed by the method of the present invention, where 1. metal substrate layer, 2. CZTS-based thin film light absorption layer, 3. dielectric nano-hexahedron array, 4. free space impedance matching layer, 5. metal nano-disk array, h1 is the thickness of the metal substrate layer, h2 is the thickness of the CZTS-based thin film light absorption layer, h3 is the thickness of the free space impedance matching layer, h0 is the thickness of the dielectric nano-hexahedron array, hd is the thickness of the metal nano-disk array, hz is the height 65 nm from the metal substrate layer, d is the diameter of a single metal nano-disk, and X / Y is the length and width of the dielectric nano-hexahedron, with the same size;

[0030] Figure 2 The dielectric hexahedron structure embedded in an array designed by the method of the present invention is absorber cross-section 1, where X is the size of the dielectric nano-hexahedron in the x direction, Y is the size of the dielectric nano-hexahedron in the y direction, Px is the period of the dielectric hexahedron structure in the x direction, and Py is the period of the entire structure in the y direction;

[0031] Figure 3 The metal disk structure embedded in an array designed by the method of the present invention is absorber cross-section 2, where Px is the period of the metal disk structure in the x direction, Py is the period of the metal disk structure in the y direction, and d is the diameter of a single metal disk structure;

[0032] Figure 4 Reflectivity comparison of the absorber designed by the method of the present invention, the single CZTS-based thin film layer (blue line), and the CZTS-based thin film layer combined with the impedance matching layer (red line). Detailed implementation mode

[0033] The present invention provides a CZTS-based visible light efficient absorber based on metasurface, which from bottom to top are a metal substrate layer, a CZTS-based thin film light absorption layer, and a free space impedance matching layer in sequence; a metal aluminum nano-disk array and an Al2O3 dielectric nano-hexahedron array are arranged on the CZTS-based thin film light absorption layer; the metal aluminum nano-disk array is arranged at a height of 65 nm from the metal substrate layer; and the Al2O3 dielectric nano-hexahedron array is arranged at the top of the center of the metal aluminum nano-disk array.

[0034] In the present invention, the metal substrate layer preferably includes a silver thin film, and the thickness of the metal substrate layer is preferably 100 nm. In the present invention, the thickness of the metal substrate layer is greater than the theoretical optical skin depth of the metal substrate layer (about 20 - 30 nm for visible light), so it can be considered that there is no transmitted light under the metal substrate layer.

[0035] In the present invention, the Cu2ZnSnS4-based thin film photoabsorbing layer preferably includes all I2-II-IV-VI4 type compound semiconductor thin films such as CZTS, CZTSe, CZTSSe, ACZTS, CZTGS, etc., and the thickness of the Cu2ZnSnS4-based thin film photoabsorbing layer is preferably 500 nm.

[0036] In the present invention, the free space impedance matching layer is preferably an Al2O3 dielectric thin film with a refractive index of 1.7, and the thickness of the free space impedance matching layer is preferably 40 nm. In the present invention, the free space impedance matching layer is mainly used to match the impedance between free space and CZTS-based materials, reducing the surface refractive index jump gradient, and this material can be different from the material of the dielectric tetragonal array.

[0037] In the present invention, the thickness of the metal aluminum nanodisk array is preferably 50 nm, the diameter is preferably 160 nm, and the array period is preferably 260 nm. In the present invention, the metal aluminum nanodisk array serves as an incident light resonance absorption auxiliary structure, and the material is preferably a metal material with strong surface plasmon resonance such as gold, silver, aluminum, etc. The range of the array periods Px and Py is both 200 - 800 nm, preferably both 260 nm. The wavelength range of efficient absorption includes but is not limited to the visible light wavelength range, and the actual wavelength range can be extended to 380 - 820 nm, with an incident angle of 0 - 70°.

[0038] In the present invention, the refractive index of the Al2O3 dielectric nanohexahedron array is preferably 1.7, the thickness is preferably 220 nm, the length is preferably 200 nm, and the width is preferably 200 nm. In the present invention, the dielectric nanohexahedron array (the side view is rectangular and the top view is square, and the six-sided shape is well reflected in the structure) aims to utilize its cavity resonance absorption characteristics, and its central axis coincides with the central axis of the metal nanodisk array. The range of the thickness h0 is 220 nm, and the range of the scale X - Y in the x and y directions is 60 - 740 nm. The dielectric refractive index is 1.7, and according to different device requirements, it can be a conductive dielectric or a non-conductive dielectric.

[0039] The present invention also provides a preparation method of a CZTS-based visible light efficient absorber based on the above technical solution, including the following steps:

[0040] S1. Using the metal substrate layer as the absorber support layer and the incident light reflection layer;

[0041] S2. Using the Cu2ZnSnS4-based thin film photoabsorbing layer as the visible light absorbing layer, and embedding the metal aluminum nanodisk array at a position 65 nm above the upper surface of the metal substrate layer therein;

[0042] S3. Embed an array of Al2O3 dielectric nano - hexahedrons at the top of the center of the metal aluminum nano - disk array on the surface of the Cu2ZnSnS4 - based thin - film photo - absorption layer;

[0043] S4. Cover a free - space impedance - matching layer on the Cu2ZnSnS4 - based thin - film photo - absorption layer to obtain a Cu2ZnSnS4 - based visible - light high - efficiency absorber based on a metasurface.

[0044] The present invention also provides an application of the Cu2ZnSnS4 - based visible - light high - efficiency absorber based on a metasurface as described in the above technical solution in improving the visible - light absorption rate. In the present invention, it is preferably to improve the visible - light absorption rate in the range of 380 - 820 nm.

[0045] The present invention also provides an application of the Cu2ZnSnS4 - based visible - light high - efficiency absorber based on a metasurface as described in the above technical solution in reducing the visible - light reflectivity. In the present invention, it is preferably to reduce the visible - light reflectivity in the range of 380 - 820 nm.

[0046] To further illustrate the present invention, the present invention will be described in detail below with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0047] Example 1

[0048] As Figures 1-4 shown, a Cu2ZnSnS4 - based (abbreviated as CZTS - based) visible - light high - efficiency absorber based on a metasurface and its design method:

[0049] S1. Use a silver thin - film with a thickness of 100 nm as the absorber support layer and the incident - light reflection layer;

[0050] S2. Use a CZTS (Cu2ZnSnS4) thin - film with a thickness of 500 nm as the visible - light absorption layer, and embed an array of metal aluminum nano - disks with a thickness of 50 nm and a diameter of 160 nm at a position 65 nm above the upper surface of the metal substrate, and the array period is 260 nm;

[0051] S3. Embed an array of Al2O3 dielectric nano - hexahedrons with a thickness of 220 nm, a length of 200 nm, a width of 200 nm, and a dielectric refractive index of 1.7 at the top of the center of the metal aluminum nano - disks on the CZTS thin - film surface;

[0052] S4. Finally, cover a 40 - nm - thick Al2O3 free - space impedance - matching layer, that is, a dielectric thin - film with a refractive index of 1.7, on the CZTS thin - film to form a CZTS - based visible - light high - efficiency absorber based on a metasurface.

[0053] By using two curl equations with time - dependence in Maxwell's equations

[0054]

[0055] Based on this, the electric field E, magnetic field H are related to the optical dielectric constant ε, magnetic permeability μ and conductivity σ of the material, and then according to the material reflectivity problem, the above equations are discretely processed and calculated by the finite-difference time-domain method in the Cartesian coordinate system. Then, based on the calculated electromagnetic field distribution, the energy flux is integrated on a specific target plane and compared with the total energy flux incident on the incident surface of the computational domain to obtain the reflectivity. During discretization, the entire space is discretized in the form of a cube, with the electric field components located at the centers of the cube edges, and the magnetic field components perpendicular to the centers of each face of the cube. In an isotropic medium, the Maxwell curl equations can be decomposed into six component equations in the Cartesian rectangular coordinate system:

[0056]

[0057] where E x , E y , E z , H x , H y , H z are the electric and magnetic field components of the electromagnetic field in the x, y, and z directions of the Cartesian rectangular coordinate system, respectively. Let i, j, and k represent the grid point position coordinates in the x, y, and z directions respectively, and Δx, Δy, and Δz represent the unit increments in the three spatial directions. Then, at any grid point in space at any time t n =n△t (n is an integer), the electric and magnetic field components of the electromagnetic field are respectively

[0058] E(iΔx, jΔy, kΔz)=E n (i,j,k)

[0059] H(iΔx, jΔy, kΔz)=H n (i,j,k)

[0060] Taking the electric field component and magnetic field component of the electromagnetic field in the x direction as an example, the time-domain difference equation for a specific space at any time under the first-order difference approximation is as follows

[0061]

[0062]

[0063] At this time, the electric and magnetic field components of each cube grid point in the computational domain are closely related on the time axis.

[0064] Calculations show that the average reflectivity of the visible light absorber in this embodiment in the range of 380 - 820 nm is 0.067( Figure 4Black line), with an average absorption rate of 93.3%.

[0065] Comparative Example 1

[0066] Different from Example 1, in this comparative example, only a dielectric impedance matching layer with a certain thickness is provided on the traditional CZTS material thin film.

[0067] S1. Use a silver thin film with a thickness of 100 nm as the absorber support layer and incident light reflection layer;

[0068] S2. Use a CZTS thin film with a thickness of 500 nm as the visible light absorption layer;

[0069] S3. Use a dielectric with a thickness of 40 nm and a refractive index of 1.7 as the incident surface impedance matching layer.

[0070] Calculation shows that when only a dielectric impedance matching layer with a refractive index of 1.7 and a thickness of 40 nm is provided on the traditional CZTS material thin film, the average reflectance in the range of 380 - 820 nm is 0.177 ( Figure 4 Red line), and the average absorption rate is only 82.3%.

[0071] Comparative Example 2

[0072] Different from Example 1, in this comparative example, there is only a traditional CZTS material thin film.

[0073] S1. Use a silver thin film with a thickness of 100 nm as the absorber support layer and incident light reflection layer;

[0074] S2. Use a CZTS thin film with a thickness of 500 nm as the visible light absorption layer.

[0075] Calculation shows that when there is only a traditional CZTS material thin film, the average reflectance in the range of 380 - 820 nm is 0.324 ( Figure 4 Blue line), and the average absorption rate is only 67.6%.

[0076] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A Cu2ZnSnS4-based visible light efficient absorber based on a metasurface, characterized in that: From bottom to top, they are the metal substrate layer, the Cu2ZnSnS4-based thin film light absorption layer, and the free space impedance matching layer; The Cu2ZnSnS4-based thin film light absorption layer is provided with a metal aluminum nano-disk array and an Al2O3 dielectric nano-hexahedron array; Disposing a metal aluminum nanodisk array at a height of 65 nm from the metal substrate layer; An Al2O3 dielectric nanohexahedron array is arranged on the top of the center of the metal aluminum nanodisk array.

2. The Cu2ZnSnS4-based visible light efficient absorber based on the supersurface according to claim 1 is characterized in that: The metal substrate layer includes a silver thin film, and the thickness of the metal substrate layer is 100 nm.

3. The Cu2ZnSnS4-based visible light efficient absorber based on a supersurface according to claim 1, characterized in that: The Cu2ZnSnS4-based thin film light absorption layer includes all I2-II-IV-VI4 type compound semiconductor thin films such as CZTS, CZTSe, CZTSSe, ACZTS, and CZTGS, and the thickness of the Cu2ZnSnS4-based thin film light absorption layer is 500nm.

4. The Cu2ZnSnS4-based visible light efficient absorber based on a supersurface according to claim 1, characterized in that: The free space impedance matching layer is an Al2O3 dielectric film with a refractive index of 1.7, and the thickness of the free space impedance matching layer is 40 nm.

5. The Cu2ZnSnS4-based visible light efficient absorber based on a supersurface according to claim 1, characterized in that: The thickness of the metal aluminum nano disk array is 50 nm, the diameter is 160 nm, and the array period is 200-300 nm.

6. The Cu2ZnSnS4-based visible light efficient absorber based on a supersurface according to claim 1, characterized in that: The Al2O3 medium nano hexahedron array has a refractive index of 1.7, a thickness of 220 nm, a length of 200 nm, and a width of 200 nm.

7. A method for preparing a Cu2ZnSnS4-based visible light efficient absorber based on a supersurface according to claim 1, characterized in that: The following steps are involved: S1. Using the metal substrate layer as an absorber support layer and an incident light reflection layer; S2. A Cu2ZnSnS4-based thin film light absorption layer is used as a visible light absorption layer, and a metal aluminum nanodisk array is embedded at a height of 65 nm from the upper surface of the metal substrate layer; S3. Al2O3 dielectric nanohexahedral array is embedded on the surface of the Cu2ZnSnS4-based thin film light absorption layer and on top of the center of the metal aluminum nanodisk array; S4. A free space impedance matching layer is covered on the Cu2ZnSnS4-based thin film light absorption layer to obtain a Cu2ZnSnS4-based visible light efficient absorber based on a metasurface.

8. Application of the Cu2ZnSnS4-based visible light efficient absorber based on a supersurface as described in any one of claims 1 to 6 in improving the visible light absorption rate.

9. Application of the Cu2ZnSnS4-based visible light efficient absorber based on a metasurface as described in any one of claims 1 to 6 in reducing visible light reflectivity.

10. The use according to claim 8 or 9, characterized in that: Reduce visible light reflectance and increase visible light absorptivity in the range of 380-820nm.

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