A hemispherical Bi₂Se₃ superstructure photothermal converter and its design method

Abstract

A photothermal converter based on a hemispherical Bi₂Se₃ superstructure belongs to the field of solar energy technology and applications. The stacked structure from bottom to top consists of: a metal substrate, a silica microsphere mask layer, and a Bi₂Se₃ thin film layer. The metal substrate is made of materials such as titanium and has a thickness greater than the skin depth (≥100 nm). The silica microsphere mask layer forms a close-packed array through self-assembly, with microspheres having a diameter of 200 nm. The Bi₂Se₃ thin film is prepared through conformal deposition, with a thickness ranging from several nanometers to hundreds of nanometers. This device utilizes the bulk-surface state synergistic effect of the topological insulator Bi₂Se₃, combined with Mie resonance excited by a hemispherical superstructure and plasmon coupling, to achieve an average high absorption rate of 97% in the 0.3–2.5 μm band and an emissivity as low as 0.07 in the 2.5–25 μm band. It exhibits stable absorption characteristics over a wide incident angle (0°–60°) and can be prepared in a low-cost and controllable manner through self-assembled microsphere masks and magnetron sputtering technology, providing a feasible solution for high-performance solar thermal conversion systems.

Description

Technical Field

[0001] This invention belongs to the field of solar energy technology and application, specifically relating to a hemispherical Bi2Se3 superstructure photothermal converter and its design method. Background Technology

[0002] Solar thermal conversion is the most direct and effective way for people to utilize solar energy, showing broad application prospects in many fields such as solar water heating systems, seawater desalination, and solar thermal power generation. The core performance of a solar thermal conversion system largely depends on the spectral selective absorption characteristics of its core component, the solar thermal converter. An ideal solar thermal converter should be able to achieve 100% perfect absorption in the spectral range where strong solar radiation is concentrated (approximately 0.3-2.5 μm), thereby maximizing the conversion of incident solar energy into heat energy; at the same time, in the infrared band dominated by blackbody thermal radiation (approximately 2.5-25 μm), its emissivity should approach zero, thereby suppressing energy loss caused by thermal radiation. This ideal characteristic requires the solar thermal converter to achieve good impedance matching in the solar spectral region and complete impedance mismatch in the infrared thermal radiation region.

[0003] Currently, widely studied photothermal converters are mainly divided into three categories: multilayer thin-film, metal-ceramic, and plasmonic superstructures. Multilayer thin-film photothermal converters suffer from insufficient absorption bandwidth in the high-radiation spectral region of the sun due to the dispersion characteristics of their constituent materials, thus limiting their photothermal conversion efficiency. Metal-ceramic photothermal converters cannot further improve their efficiency by simply changing the concentration and size of metal particles; moreover, particle diffusion or aggregation at high temperatures leads to changes in optical parameters, thereby weakening their spectral absorption performance. Plasmonic superstructure photothermal converters, achieved through periodic micro / nano structure design, exhibit powerful electromagnetic control capabilities. Flexible adjustment of periodic structural parameters facilitates highly tunable optical response characteristics in the target light band. However, in existing technologies, the efficient excitation and coupling of plasmons typically heavily relies on the lateral subwavelength structural size and nanoscale fabrication precision, posing a significant challenge to the feasibility of large-scale fabrication and the structural stability for long-term use. Furthermore, the performance of these devices is usually extremely sensitive to the incident angle of light, making it difficult to maintain stable and efficient absorption over a wide angle range. In summary, developing a novel photothermal converter that can balance high conversion efficiency, wide-angle absorption stability, low cost, and high fabrication feasibility is a key technical challenge that urgently needs to be overcome in this field.

[0004] Topological insulators, exemplified by Bi₂Se₃, exhibit a unique bulk-surface electronic state separation characteristic: the bulk phase possesses insulating properties with a band gap of approximately 0.3 eV, while the surface forms a band gap-free metallic state protected by time-reversal symmetry. This quantum property endows topological insulators with various advantages in spectral response modulation: mass Dirac fermions in the topological surface states can excite plasmons in the ultraviolet-visible region, significantly enhancing light-harvesting capabilities; the narrow-bandgap bulk states can generate intrinsic absorption in the near-infrared region, providing the possibility of achieving broadband strong absorption across the entire solar high-emissivity spectrum; simultaneously, the concentration of Dirac-type conduction carriers on the surface also affects conductivity loss. By changing the thickness of the topological insulator film, impedance matching performance can be effectively modulated, which is beneficial for achieving excellent spectrally selective absorption, thereby obtaining higher solar thermal conversion efficiency. Summary of the Invention

[0005] To address the bottlenecks in conversion efficiency improvement, strong dependence on incident angle, and complex fabrication processes faced by existing photothermal conversion materials, this invention proposes a photothermal converter based on a hemispherical Bi₂Se₃ superstructure. Its core objective is to overcome traditional design limitations by constructing a topological insulator / plasmon metamaterial composite system: on the one hand, utilizing the unique advantage of flexible and tunable surface state electrical transport in Bi₂Se₃, impedance matching in the optical frequency band is achieved, broadening the spectral response range; on the other hand, by exciting wide-angle Mie resonances through the hemispherical superstructure and synergizing with surface plasmon resonances, strong absorption of solar high-emissivity spectra and low emission of blackbody radiation spectra are achieved over a wide incident angle range. Furthermore, this superstructure can be fabricated using a simple self-assembled microsphere mask method, exhibiting both structural stability and good fabrication feasibility, thus providing a new solution for the design and fabrication of high-performance photothermal converters.

[0006] A hemispherical Bi₂Se₃ superstructure photothermal converter comprises, from bottom to top: a metal substrate, a monolayer close-packed silica microsphere mask, and a Bi₂Se₃ thin film. The metal substrate serves as both the support and reflective layer of the photothermal converter. Its thickness is greater than the skin depth of the incident light in the metal material, ensuring that the incident light is completely confined within the device, avoiding transmission loss. Simultaneously, plasmon polaritons can be excited at the interface between the metal substrate and the Bi₂Se₃ thin film, effectively enhancing the absorption of solar radiation spectrum. A monolayer close-packed silica microsphere mask covers the metal substrate. This mask layer is the key template for realizing the patterning of the hemispherical superstructure. Its unique spherical geometry has a three-dimensional isotropic curvature distribution, capable of exciting multi-order, degenerate, strong multipole Mie resonance modes. Coupled with surface plasmon polaritons, it provides more dimensions for controlling the spectral response, facilitating excellent spectrally selective absorption. In particular, the Mie modes dominated by the spherical structure have a significant advantage in wide-angle absorption due to the localization of the strong physical field within the cavity. Finally, a Bi₂Se₃ thin film was conformally deposited on the surface of the silica microsphere mask, with a thickness greater than or equal to the microsphere radius to ensure the stability of the superstructure. The Bi₂Se₃ thin film is the core functional material of this invention; its unique properties of bulk insulation and surface conductivity enable it to simultaneously support surface plasmon resonance and characteristic resonances of the dielectric material. This characteristic gives it significant advantages in broadband light absorption and high photothermal conversion efficiency when combined with the superstructure. Furthermore, by precisely controlling the thickness of the Bi₂Se₃ thin film, its refractive index and extinction coefficient can be altered, placing the device in the metallic reflection region of the material in the thermal radiation band, thereby significantly reducing the infrared emissivity corresponding to blackbody thermal radiation and ultimately achieving highly efficient photothermal conversion. The photothermal converter based on the hemispherical Bi₂Se₃ superstructure can be fabricated using a self-assembled microsphere mask method combined with magnetron sputtering, a simple and easy fabrication process. First, using a single layer of uniformly arranged silica microspheres as a mask, a micro-injection propulsion system is employed to assemble the single-layer silica microspheres at the air / water interface. By controlling key technologies such as the surface tension gradient of the fluid interface and dynamic equilibrium conditions, the controllable self-assembly of the single-layer densely packed silica microspheres is achieved. Then, the silica microsphere mask on the water surface is transferred to a metal substrate. Finally, using magnetron sputtering in a vacuum environment with an inert gas as the sputtering gas, the film growth quality is controlled by changing parameters such as sputtering power, pressure, and annealing temperature. The Bi2Se3 film is deposited on the surface of the microsphere mask plate on the metal substrate and in the gaps between adjacent microspheres, ultimately forming a hemispherical Bi2Se3 superstructure photothermal converter. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the three-dimensional structure of a photothermal converter based on a hemispherical Bi2Se3 superstructure;

[0008] Figure 2A schematic diagram of the cross-section of a periodic structural unit of a photothermal converter based on a hemispherical Bi2Se3 superstructure;

[0009] Figure 3 The spectral absorption characteristics of a photothermal converter based on a hemispherical Bi2Se3 superstructure;

[0010] Figure 4 The spectral absorption effect of a photothermal converter based on a hemispherical Bi2Se3 superstructure under wide-angle incident light is shown. Detailed Implementation

[0011] A photothermal converter based on a hemispherical Bi2Se3 superstructure, such as Figure 1 and Figure 2 As shown, the structure includes a metal substrate, a monolayer close-packed microsphere mask layer, and a Bi2Se3 thin film layer. The metal substrate is made of titanium, with no thickness limit, as long as it is greater than the skin depth (100 nm) of the incident light in the titanium layer. On the titanium substrate is a self-assembled monolayer close-packed silica microsphere array (microsphere diameter 200 nm). The adjacent microspheres, based on the self-assembly technology, have a natural spacing of 3-5 nm, and the microsphere array is tangent to the titanium substrate. A monolayer silica microsphere was assembled at the air / water interface using an injection micro-propulsion system. By controlling key parameters such as the fluid surface tension gradient and dynamic equilibrium conditions, the controllable self-assembly of the close-packed silica microspheres was achieved, followed by lift-and-transfer onto a titanium substrate. Magnetron sputtering was then used in a vacuum environment with argon as the sputtering gas and Bi₂Se₃ as the sputtering target. The sputtering time was controlled according to the required thickness and deposition rate to conformally deposit a 100 nm thick Bi₂Se₃ thin film on the silica microsphere array and between adjacent microspheres, ultimately yielding a hemispherical Bi₂Se₃ superstructure photothermal converter. The initial vacuum level of the magnetron sputtering system was set to 2 × 10⁻⁶. −4 During the sputtering process, argon is used as the working gas, with a flow rate controlled at 20 sccm and a working pressure maintained at 3.3 × 10⁻⁶ Pa. −4 Pa. During thin film deposition, the substrate was heated to 220 °C, the RF sputtering power was set to 10 W, and the deposition rate was 0.1 nm / s to ensure uniform deposition and film quality. Based on this structure, a hemispherical Bi₂Se₃ superstructure photothermal converter achieved an average absorptivity of 97% in the high-radiation solar spectrum region of 0.3–2.5 μm and an infrared emissivity as low as 0.07 in the 2.5–25 μm range, realizing excellent spectral selective absorption and high-efficiency photothermal conversion performance. The spectral absorption characteristics are as follows: Figure 3 As shown. Due to the strong localized Mie resonance dominated by the spherical superstructure, this photothermal converter is insensitive to the incident angle and possesses omnidirectional absorption capability of sunlight. Figure 4As shown, it exhibits good absorption performance within a wide angular range of 0°-60°. Therefore, the photothermal converter based on the hemispherical Bi2Se3 superstructure, with its spherical superstructure design and combined with the unique optical dispersion characteristics of Bi2Se3, possesses advantages in geometric stability, broadband spectral selective absorption, and wide-angle absorption characteristics, overcoming the limitations of traditional plasmonic superstructure photothermal conversion materials in terms of photothermal conversion efficiency and structural stability.

Claims

1. A hemispherical Bi₂Se₃ superstructure photothermal converter, characterized in that, From bottom to top, the structure comprises: a metal substrate, a monolayer close-packed silica microsphere mask, and a Bi₂Se₃ thin film. The metal substrate serves as the support and reflective layer of the photothermal converter, and its thickness is greater than the skin depth of the incident light in the metal material. A monolayer close-packed silica microsphere mask covers the metal substrate. Finally, a Bi₂Se₃ thin film with a thickness greater than or equal to the microsphere radius is conformally deposited on the surface of the silica microsphere mask.

2. The hemispherical Bi₂Se₃ superstructure photothermal converter according to claim 1, characterized in that, By constructing a topological insulator / plasmoelectric metamaterial composite system, the thickness of the Bi2Se3 thin film is precisely controlled to change its refractive index and extinction coefficient, so that the device is located in the solar spectral impedance matching region and the thermal radiation frequency domain metal emission region over a wide incident angle range.

3. A method for preparing a hemispherical Bi₂Se₃ superstructure photothermal converter as described in claim 1, characterized in that, It was prepared by combining a self-assembled microsphere mask method with magnetron sputtering.

4. A method for preparing a hemispherical Bi₂Se₃ superstructure photothermal converter as described in claim 1, characterized in that, The metal substrate is set to titanium metal, and its thickness is greater than the skin depth of the incident light in the titanium layer by 100 nm. On the titanium metal substrate, a self-assembled monolayer close-packed silica microsphere array is prepared. The microspheres have a diameter of 200 nm and the natural spacing between adjacent microspheres is 3~5 nm. The microsphere array is tangent to the titanium substrate. By controlling the sputtering time according to the required thickness and deposition rate, a Bi2Se3 thin film with a thickness of 100 nm was conformally deposited on the silica microsphere array and in the gaps between adjacent microspheres, finally obtaining a hemispherical Bi2Se3 superstructure photothermal converter.

5. A method for preparing a hemispherical Bi₂Se₃ superstructure photothermal converter as described in claim 1, characterized in that, The initial vacuum level of the magnetron sputtering system cavity is set to 2 × 10⁻⁶. −4 During the sputtering process, argon is used as the working gas, with a flow rate controlled at 20 sccm and a working pressure maintained at 3.3 × 10⁻⁶ Pa. −4 Pa. During thin film deposition, the substrate was heated to 220 °C, the RF sputtering power was set to 10 W, and the deposition rate was 0.1 nm / s.

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