Metamaterial anti-reflection film for radioisotope thermophotovoltaic cell and preparation method and application thereof

Abstract

The invention discloses a metamaterial anti-reflection film for a radioactive isotope thermophotovoltaic cell and a preparation method and application of the metamaterial anti-reflection film. The invention relates to a metamaterial anti-reflection film for a radioactive isotope thermophotovoltaic cell, which is an all-dielectric metamaterial anti-reflection film. The all-dielectric metamaterial anti-reflection film sequentially comprises a first reflection layer, a second reflection layer and a Si nano resonance microstructure layer from bottom to top. The anti-reflection film provided by the invention has high flexibility, and the refractive index of the anti-reflection film and the reflection characteristic of electromagnetic waves can be regulated and controlled by adjusting the structural parameters of the metamaterial, so that the performance of the anti-reflection film in a target wave band and a wide angle range is accurately optimized; the high-efficiency anti-reflection effect of the near-infrared light band matched with the thermal photovoltaic module used by the radioisotope thermal photovoltaic cell is realized, the reflection loss of light is reduced, the photoelectric conversion efficiency is improved, and the overall electrical output performance of the radioisotope thermal photovoltaic cell is further improved.

Description

Technical Field

[0001] The present application relates to the field of nuclear power technology metamaterial technology, and specifically to a metamaterial anti-reflection film for radioisotope thermophotovoltaic cells and a preparation method and application thereof. Background Art

[0002] Radioisotope Thermophotovoltaic Battery (RTPVB) is a device that uses the thermal energy of the decay of radioisotope heat sources as the source term and converts it into electrical energy through the photovoltaic effect in the form of infrared radiation. It has the advantages of long working life, high volumetric power density, light structure, and strong environmental adaptability. It is regarded as an ideal power source type under extreme conditions such as deep space, deep sea, and polar regions.

[0003] Radioisotope thermophotovoltaic cells are mainly composed of radioisotope heat sources, thermal radiators, filters, and thermophotovoltaic modules. The radioisotope source deposits its decay energy inside itself and converts it into thermal energy. Its surface temperature can reach up to 1200K or above. The thermal radiator emits the thermal energy of the heat source in the form of infrared radiation, which is incident on the thermophotovoltaic module after being regulated by the filter, and converts the light energy into electrical energy through the photovoltaic effect. During the whole process, the components are coupled and regulated to achieve efficient energy conversion and electrical energy output. Among them, the thermophotovoltaic module, as a key component of the final electrical energy output, plays a particularly important role in the whole energy conversion process. However, due to the certain air impedance of the window layer material on the surface of the thermophotovoltaic module, about 30% of the incident photons are reflected, resulting in the loss of some photon energy. The thermophotovoltaic module cannot completely absorb the incident photons, which further affects the final electrical output performance and energy conversion efficiency of the radioisotope thermophotovoltaic cell.

[0004] At present, the commonly used method to reduce the photon reflection of thermal photovoltaic modules is to add anti-reflection film on the surface of thermal photovoltaic modules. The traditional anti-reflection film is an optical film composed of multiple layers of different materials or refractive index layers. It reduces or eliminates the reflected light on the optical surface through the interference effect between the layers, thereby improving the transmittance. However, since it is difficult to achieve efficient anti-reflection in the wide frequency band and wide angle range of near-infrared light, this traditional anti-reflection film cannot match the near-infrared light emitted by radioisotope heat sources well. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the art, the present application aims to provide a metamaterial anti-reflection film for radioisotope thermophotovoltaic cells and a preparation method and application thereof.

[0006] According to one aspect of the present application, a metamaterial anti-reflection film for a radioisotope thermophotovoltaic cell is provided.

[0007] The metamaterial anti-reflection film includes, from bottom to top, a first reflection layer, a second reflection layer and a Si tetrahedral nano-resonance microstructure layer.

[0008] According to some embodiments of the present application, the Si tetrahedral pyramids in the Si tetrahedral pyramid nano-resonance microstructure layer are regularly arranged.

[0009] According to some embodiments of the present application, the metamaterial anti-reflection film is an all-dielectric metamaterial anti-reflection film.

[0010] According to some embodiments of the present application, the upper side length of each Si tetrahedron is 70-100 nm; the lower side length is 150-200 nm; and the height is 300-400 nm.

[0011] According to some embodiments of the present application, the distance between every two Si tetrahedral pyramids is 70-100 nm.

[0012] According to some embodiments of the present application, the material of the first reflective layer includes: MgF2 or SiO2; the thickness of the first reflective layer is 40-70 nm.

[0013] According to some embodiments of the present application, the material of the second reflective layer includes: ZnS or TiO2; the thickness of the second reflective layer is 30-50 nm.

[0014] According to another aspect of the present application, a method for preparing the metamaterial anti-reflection film for the radioisotope thermophotovoltaic cell comprises:

[0015] sequentially preparing a first reflective layer and a second reflective layer on the surface of the thermophotovoltaic module;

[0016] Continue to prepare a Si layer on the surface of the second reflective layer;

[0017] A photoresist is coated on the surface of the Si layer, and a Cr layer is prepared after exposure and development, and etching is performed to obtain a Si nano-resonance microstructure layer.

[0018] According to some embodiments of the present application, the first reflective layer and the second reflective layer are prepared by chemical deposition.

[0019] According to some embodiments of the present application, the thickness of the Cr layer is 40-50 nm.

[0020] According to another aspect of the present application, the metamaterial anti-reflection film for radioisotope thermophotovoltaic cells prepared by the above preparation method is used to prepare thermophotovoltaic modules.

[0021] Compared with the prior art, this application has at least the following beneficial effects:

[0022] The present application provides a metamaterial anti-reflection film for radioactive isotope thermophotovoltaic cells. Compared with traditional anti-reflection films, the anti-reflection film of the present application has a high degree of flexibility. The refractive index of the composite material and the reflection characteristics of electromagnetic waves can be regulated by adjusting the structural parameters (such as size, shape, arrangement, etc.) of the metamaterial, thereby accurately optimizing its performance in the target band and wide angle range, achieving a high-efficiency anti-reflection effect in the near-infrared light band that matches the radioactive isotope thermophotovoltaic cells, reducing the reflection loss of light, improving the photoelectric conversion efficiency, and enhancing the overall performance of the thermophotovoltaic module.

[0023] The metamaterial anti-reflection film of the present application adds a high refractive index microstructure on the basis of a double-layer reflective layer film to form an all-dielectric metamaterial structure, which effectively changes the transmission field by stimulating appropriate surface current density and magnetic flux density, so that the low-bandgap thermal photovoltaic module can achieve efficient absorption of infrared photons.

[0024] The present application utilizes the electric resonance and magnetic resonance effects in metamaterials to achieve regulation of electromagnetic wave propagation characteristics through the design of their microstructures, adjust the reflection of electromagnetic waves at the interface between the medium and the anti-reflection film, achieve reflection cancellation, and thus achieve the purpose of anti-reflection.

[0025] The preparation method of the metamaterial anti-reflection film for radioisotope thermal photovoltaic cells of the present application is to prepare and process the designed anti-reflection film by magnetron sputtering, chemical vapor deposition, electron beam lithography, and plasma etching technology. Aiming at the problem of large photon reflection loss of thermal photovoltaic components in radioisotope thermal photovoltaic cells, a more efficient metamaterial anti-reflection film design is proposed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of a metamaterial anti-reflection film according to an exemplary embodiment of the present application.

[0027] Figure 2 This is a flow chart of the preparation process of the metamaterial anti-reflection film according to an exemplary embodiment of the present application.

[0028] Figure 3 This is a graph showing how the reflectivity of the metamaterial anti-reflection film and the Al2O3 / TiO2 anti-reflection film varies with wavelength according to an exemplary embodiment of the present application.

[0029] Figure 4 The graph is a quantum efficiency curve of an InGaAsP-3J thermophotovoltaic module with an anti-reflection film according to an exemplary embodiment and a comparative example of the present application.

[0030] Figure 5 This is a structural diagram and transmission spectrum of comparative example 2 of this application.

[0031] Figure 6 The blackbody thermal radiation power spectra at different temperatures in an exemplary embodiment of the present application.

[0032] Figure 7 The reflectivity of the metamaterial anti-reflection film according to the exemplary embodiment of the present application varies with the incident angle and wavelength. DETAILED DESCRIPTION

[0033] The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0034] It is particularly important to point out that similar substitutions and modifications made to the present application are obvious to those skilled in the art, and they are all deemed to be included in the present application. Relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application to implement and apply the technology of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0035] If no specific conditions are specified in this application, the preparation shall be carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, for which the manufacturers are not specified, are all conventional products that can be obtained commercially.

[0036] The application is described in detail below.

[0037] The metamaterial anti-reflection film used in the radioisotope thermophotovoltaic cell of the present application is an all-dielectric metamaterial anti-reflection film, such as Figure 1 As shown, it consists of a first reflection layer and a second reflection layer at the bottom and a Si nano-resonance microstructure at the top.

[0038] The Si nano-resonant microstructure at the top is composed of Si tetrahedral pyramids arranged regularly. Silicon has a high refractive index and relatively low optical loss in the visible light and near-infrared wavelength range, which can effectively reduce Ohm loss and improve the electromagnetic resonance intensity. The bottom is composed of a first reflective layer and a second reflective layer superimposed on each other. For example, the first reflective layer can be a thin layer of MgF2 or SiO2, and the second reflective layer can be ZnS or TiO2. The refractive index of the ZnS layer is higher than that of the MgF2 layer. The combination of decreasing refractive index can enhance the coupling effect between the incident photons and the window layer of the thermal photovoltaic module, and reduce the light loss when the light is transmitted to the semiconductor active absorption layer.

[0039] By adjusting the size parameters of each structure, the electromagnetic properties of light in the nanoscale range can be controlled to achieve a low reflection effect for incident photons.

[0040] Optionally, the structural parameters of the metamaterial anti-reflection film of the present application are: upper edge length a=70-100nm, lower edge length b=150-200nm, height h=300-400nm, unit distance d=70-100nm, and the thicknesses of the first reflective layer and the second reflective layer are 40-70nm and 30-50nm respectively.

[0041] The all-dielectric metamaterial anti-reflection film of the present application interacts with incident photons of different bands to excite multiple resonance modes (Mie resonance, FP resonance). This multi-resonance mode can broaden the reflectivity range of the anti-reflection film, and the reflectivity in the 900-2000nm band is less than 5%, so that the thermal photovoltaic module can achieve efficient photon absorption in the high quantum efficiency band. At a wavelength of 950nm, the Mie resonance radiation of the high refractive index Si nanostructure has a strong directionality, so it will produce strong forward and weak backward scattering characteristics, and the reflectivity is almost 0 at this time. At a wavelength of 1150nm, the all-dielectric metamaterial anti-reflection film of the present application exhibits FP resonance phenomenon, and the photon reflectivity is reduced to less than 5%.

[0042] The technical solution of the present application is further described below in conjunction with specific embodiments.

[0043] Example 1

[0044] A chemical deposition (CVD) system was used to sequentially deposit MgF2 with a thickness of 40 nm and ZnS with a thickness of 30 nm on the surface of the thermophotovoltaic module;

[0045] An inductively coupled plasma enhanced chemical vapor deposition system (ICPECVD) was used to plate 300 nm thick Si on the ZnS surface; PMMA photoresist was coated on the Si surface, and after coating, the photoresist was soft-dried at 90°C for 50 seconds;

[0046] The photoresist is exposed using a large electron beam exposure system, and the exposed sample is immersed in a positive photoresist developer for 40 seconds to dissolve the exposed photoresist and form a pattern array. After development, the sample is cleaned with clean water;

[0047] Use magnetron sputtering technology to plate 50nm thick Cr on the surface as a hard mask for subsequent etching;

[0048] The sample was immersed in acetone for 48 hours to remove the photoresist, and then ultrasonically cleaned in clean water for 10 minutes.

[0049] The Si layer was etched using an inductively coupled plasma etcher to form Si pillars. The sample was then immersed in a cerium ammonium nitrate solution for 10 minutes to remove the surface metal Cr, and the sample was cleaned using deionized water.

[0050] Example 2

[0051] A chemical deposition (CVD) system was used to sequentially deposit MgF2 with a thickness of 70 nm and ZnS with a thickness of 50 nm on the surface of the thermophotovoltaic module;

[0052] An inductively coupled plasma enhanced chemical vapor deposition system (ICPECVD) was used to deposit 350 nm thick Si on the surface of ZnS; PMMA photoresist was coated on the surface of Si, and after coating, the photoresist was soft-baked at 90° C. for 60 seconds;

[0053] The photoresist is exposed using a large electron beam exposure system, and the exposed sample is immersed in a positive photoresist developer for 60 seconds to dissolve the exposed photoresist to form a pattern array, and the sample is cleaned with deionized water after development;

[0054] Use magnetron sputtering technology to plate 45nm thick Cr on the surface as a hard mask for subsequent etching;

[0055] The sample was immersed in acetone for 48 hours to remove the photoresist, and then ultrasonically cleaned in deionized water for 10 minutes.

[0056] The Si layer was etched using an inductively coupled plasma etcher to form Si pillars. The sample was then immersed in a cerium ammonium nitrate solution for 10 minutes to remove the surface metal Cr, and the sample was cleaned using deionized water.

[0057] Example 3

[0058] A chemical deposition (CVD) system was used to sequentially deposit SiO2 with a thickness of 55 nm and TiO2 with a thickness of 35 nm on the surface of the thermophotovoltaic module;

[0059] An inductively coupled plasma enhanced chemical vapor deposition system (ICPECVD) was used to deposit 400 nm thick Si on the TiO2 surface; PMMA photoresist was coated on the Si surface, and after coating, the photoresist was soft-baked at 90°C for 60 seconds;

[0060] The photoresist is exposed using a large electron beam exposure system, and the exposed sample is immersed in a positive photoresist developer for 60 seconds to dissolve the exposed photoresist to form a pattern array, and the sample is cleaned with deionized water after development;

[0061] Use magnetron sputtering technology to plate 40nm thick Cr on the surface as a hard mask for subsequent etching;

[0062] The sample was immersed in acetone for 48 hours to remove the photoresist, and then ultrasonically cleaned in deionized water for 10 minutes.

[0063] The Si layer was etched using an inductively coupled plasma etcher to form Si pillars. The sample was then immersed in a cerium ammonium nitrate solution for 10 minutes to remove the surface metal Cr, and the sample was cleaned with clean water.

[0064] Comparative Example 1

[0065] Preparation of traditional Al2O3 / TiO2 anti-reflection film.

[0066] The substrate is placed in a reaction chamber, the deposition temperature is set at 1000°C, and the flow, pressure and ratio of the reaction gas are adjusted; an aluminum source precursor gas is introduced into the reaction chamber and chemically reacted with the oxygen source gas, the chemical reaction takes place on the surface of the substrate to generate an Al2O3 film; when the predetermined deposition time or the growth requirement of the Al2O3 film is reached, the supply of the precursor gas and the oxygen source gas is stopped; the reaction chamber is cooled to gradually cool the substrate and the Al2O3 film to room temperature.

[0067] The substrate is placed in a reaction chamber and the deposition temperature is set at 200°C; a titanium source precursor gas and an oxygen source gas are introduced into the reaction chamber and chemically reacted; the chemical reaction is carried out on the surface of the substrate to generate a TiO2 film.

[0068] Comparative Example 2

[0069] A metamaterial anti-reflection film is a structure in which a metal cube array is grown on a silicon oxide substrate.

[0070] like Figure 5 As shown in a, a two-dimensional metal cube array structure is designed on the battery surface, and the ultra-wideband transmission effect can be used to suppress reflection on the battery surface.

[0071] like Figure 5 As shown in Fig. b, the calculated transmission spectra at incident angles of 0° and 68°, respectively, where the geometric structure is dx=dy=320nm, wx=wy=80nm, h=320nm. The calculation results show that for ultra-wideband near-infrared (800-2000nm) incident light, the reflection can be effectively reduced and the transmission can be enhanced under the condition of large angle of incidence, and it is independent of polarization. At normal incidence, the transmission peak is located at around 1100nm, at which time the reflection is the lowest, the maximum transmission is about 90%, and the width is narrow.

[0072] like Figure 3 As shown, the metamaterial anti-reflection film of the present application can achieve a low reflection and high absorption effect of less than 5% in the 900-2000nm band.

[0073] Comparative Example 3

[0074] A multi-layer medium structure comprises: a substrate and an anti-reflection coating, wherein the anti-reflection coating comprises four layers, and the second layer is made of cubic gold nanoparticles.

[0075] This comparative example uses multiple layers of films with specific thickness and refractive index, so that after the incident light is reflected on the upper and lower surfaces of the film, the reflected light interferes or destructs, thereby achieving the effect of reducing reflection.

[0076] However, this traditional multi-layer film structure has a narrow low-reflection wavelength range and is heavily dependent on the optical properties of the material itself, which inevitably makes it impossible to meet the design goals of the anti-reflection film. The second refractive material uses cubic gold nanoparticles. When light interacts with the material, for lossy metal materials, the electric field enhancement inside the particles will increase the ohmic loss of the particles, generate heat energy loss, and cause photon energy loss. The specific anti-reflection effect is not mentioned in the patent, so it cannot be compared.

[0077] The technical solution of the present application is to add Si tetrahedral microstructures on the basis of a double-layer dielectric film. This periodic subwavelength all-dielectric metamaterial mainly utilizes the high refractive index characteristics of Si and the nanoscale structural size. When photons of appropriate wavelength interact with the Si microstructure, Mie resonance is excited. Each dielectric nanostructure can be regarded as a Huygens source, which can simultaneously excite electric dipole and magnetic dipole modes. By adjusting the structural size of the nanostructure, the equivalent electric susceptibility corresponding to its electric dipole mode and the equivalent magnetic polarizability corresponding to the magnetic dipole mode can be effectively regulated. When the electric resonance and the magnetic resonance meet the equilibrium condition, the reflection on the metamaterial surface will be eliminated, and at the same time, the phase manipulation of the transmitted light wave can cover the entire phase. In principle, the transmission efficiency of the dielectric Huygens metasurface light wave manipulation can reach 100%. At longer wavelengths, the metamaterial microstructure will excite Fabry-Pérot (FP) resonance, once again generating a low reflection band. The combination of the two resonances has broadened the anti-reflection wavelength range of the metamaterial, with a good low reflection effect.

[0078] Experimental example

[0079] The reflectivity of the anti-reflection films of Example 1 and Comparative Example 1 was tested.

[0080] The test results are as follows Figure 3As shown in the figure, it can be seen that the traditional Al2O3 / TiO2 anti-reflection film has a low reflection trough with a reflectivity of 3.8% at 800nm, and then the reflectivity gradually increases. After 2500nm, the reflectivity stabilizes at about 20%. The metamaterial anti-reflection film proposed in this design has double troughs at wavelengths of 935nm and 1600nm, which greatly broadens the wavelength range of low reflection, and the average reflectivity is less than 3%. In the range of 900-3000nm, the reflectivity of the metamaterial anti-reflection film of this design is lower than that of the traditional Al2O3 / TiO2 anti-reflection film, and can form a good match with the thermal radiation spectrum of the front end of the thermal photovoltaic module, ensuring the full utilization of photon energy.

[0081] Figure 4 The external quantum efficiency curve of the thermophotovoltaic module when using different anti-reflection films. The thermophotovoltaic module of this application uses an InGaAsP / InGaAsP / InGaAs triple-junction thermophotovoltaic module. Compared with the thermophotovoltaic module using the conventional Al2O3 / TiO2 anti-reflection film, the thermophotovoltaic module using the metamaterial anti-reflection film has a significantly improved external quantum efficiency, which indicates that the thermophotovoltaic module will generate more photocurrent. From the top cell to the bottom cell, it can be seen that the external quantum efficiency of each sub-cell gradually increases, especially the bottom cell, where the external quantum efficiency increases by 23% at most.

[0082] Figure 6 This is the blackbody thermal radiation power spectrum of the metamaterial anti-reflection film of the present application at different temperatures. It can be seen from the figure that the intensity of the blackbody thermal radiation power increases with the increase of temperature, and the peak value of the radiation spectrum also moves to the right, that is, blue shifts.

[0083] Figure 7 The figure shows the change of the reflectivity of the metamaterial anti-reflection film of the present application with the incident angle and wavelength. It can be seen from the figure that p-polarized light and s-polarized light have almost no effect on the reflection spectrum. As the incident angle increases, multiple reflection peaks appear in the reflection spectrum. In the range of 0-40°, it can be observed that the reflection spectrum has no obvious dependence on the incident angle. This shows that the metamaterial anti-reflection film of the present application has the characteristics of wide-angle response and polarization insensitivity.

[0084] The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A metamaterial anti-reflection film for radioisotope thermophotovoltaic cells, characterized in that: The metamaterial anti-reflection film comprises, from bottom to top, a first reflection layer, a second reflection layer and a Si tetrahedral nano-resonance microstructure layer.

2. The metamaterial anti-reflection film for radioisotope thermophotovoltaic cells according to claim 1, characterized in that: The Si tetrahedral pyramids in the Si tetrahedral pyramid nanoresonance microstructure layer are arranged regularly; Optionally, the metamaterial anti-reflection film is an all-dielectric metamaterial anti-reflection film.

3. The metamaterial anti-reflection film for radioisotope thermophotovoltaic cells according to claim 2, characterized in that: The upper side length of each Si tetrahedron is 70-100nm; the lower side length is 150-200nm; and the height is 300-400nm.

4. The metamaterial anti-reflection film for radioisotope thermophotovoltaic cells according to claim 3, characterized in that: The distance between two Si tetrahedral pyramids is 70-100 nm.

5. The metamaterial anti-reflection film for radioisotope thermophotovoltaic cells according to any one of claims 1 to 4, characterized in that: The material of the first reflective layer includes: MgF2 or SiO2; Optionally, the thickness of the first reflective layer is 40-70 nm.

6. The metamaterial anti-reflection film for radioisotope thermophotovoltaic cells according to any one of claims 1 to 4, characterized in that: The material of the second reflective layer includes: ZnS or TiO2; Optionally, the second reflective layer has a thickness of 30-50 nm.

7. A method for preparing a metamaterial anti-reflection film for a radioisotope thermophotovoltaic cell according to any one of claims 1 to 6, characterized in that: include: sequentially preparing a first reflective layer and a second reflective layer on the surface of the thermophotovoltaic module; Continue to prepare a Si layer on the surface of the second reflective layer; A photoresist is coated on the surface of the Si layer, and a Cr layer is prepared after exposure and development, and etching is performed to obtain a Si nano-resonance microstructure layer.

8. The preparation method according to claim 7, characterized in that: The first reflective layer and the second reflective layer are prepared by chemical deposition.

9. The preparation method according to claim 7, characterized in that: The thickness of the Cr layer is 40-50 nm.

10. A metamaterial anti-reflection film for a radioisotope thermophotovoltaic cell prepared by the preparation method according to any one of claims 7 to 9, used for preparing a thermophotovoltaic module with high efficiency in infrared photon absorption.

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