Bionic moth eye and double-layer antireflection film composite structure, and preparation method and application thereof

Abstract

The application provides a bionic moth eye and double-layer anti-reflection film composite structure and a preparation method and application thereof, and belongs to the fields of photovoltaic technology and micro-nano optical technology. The composite structure comprises a planar silicon substrate, a double-layer anti-reflection film and a bionic moth eye nano structure layer; the double-layer anti-reflection film interferes and cancels out to reduce reflection, and the bionic moth eye nano structure layer provides a gradient refractive index transition, and the two cooperate to realize wideband anti-reflection at 300nm-1180nm. The planar silicon substrate takes into account efficient passivation, decoupling light management and carrier management. The application further discloses a preparation method of the composite structure: firstly, parameters of film layers and nano structures are cooperatively optimized by a finite difference time domain method combined with a particle swarm algorithm, then the double-layer film is plated in sequence by plasma enhanced chemical vapor deposition, and the moth eye array is formed at one time by ultraviolet nanoimprinting, and the process is simple and suitable for mass production. The composite structure can be applied to crystalline silicon solar cells, surface recombination is inhibited while short-circuit current is improved, and conversion efficiency is improved.

Description

Technical Field

[0001] This invention relates to the fields of photovoltaic technology and micro-nano optical technology, and in particular to a biomimetic moth eye and double-layer anti-reflective film composite structure, its preparation method and application. Background Technology

[0002] Crystalline silicon solar cells are currently the dominant technology in the photovoltaic market, and improving their photoelectric conversion efficiency is the core driving force for industry development. Short-circuit current density and open-circuit voltage are key parameters determining conversion efficiency; the former is limited by light-harvesting capability, while the latter is mainly affected by the surface carrier recombination rate. Therefore, an ideal cell surface structure must simultaneously achieve two major goals: minimizing optical reflection losses and maximally suppressing carrier surface recombination.

[0003] However, existing mainstream and emerging technologies are generally caught in a fundamental dilemma of "trading optoelectronic performance," making it difficult to achieve both goals simultaneously.

[0004] 1. Mainstream technologies: Random pyramid textured surface and anti-reflective coating:

[0005] Currently, the industry commonly uses wet chemical etching to prepare random pyramid textured surfaces, and then stacks SiN... x Antireflection / passivation films such as Al2O3 and TiO2. This technical approach has the following inherent drawbacks:

[0006] Process defects: Wet etching uses alkaline solutions, which can easily introduce metal ions such as sodium and potassium, causing contamination and damaging the minority carrier lifetime of the silicon wafer; at the same time, the etching process consumes 3-5 micrometer silicon layers, resulting in material waste and environmental problems.

[0007] Optical defects: The light-trapping ability of the pyramid structure is drastically reduced in the near-infrared band (especially above 1000nm), and its random size and distribution result in suboptimal anti-reflection effect over a wide spectral range.

[0008] Electrical defects: The huge specific surface area of ​​the three-dimensional textured surface and the lattice defects generated by etching lead to a significant increase in the interface state density, which becomes a strong recombination center for charge carriers, resulting in an increase in surface recombination current density and directly causing open circuit voltage loss.

[0009] In this design, light management (light trapping) and carrier management (passivation) functions are strongly coupled to the same rough interface, and any attempt to improve optical performance may degrade electrical performance. Furthermore, this technology is difficult to apply to novel high-efficiency battery structures.

[0010] 2. Emerging Technology: Nanowire / Nanopillar Arrays

[0011] In an effort to achieve a breakthrough, the industry has attempted to construct micro- and nanostructures such as nanowires and nanopillars on silicon surfaces to reduce reflection. However, this type of technology faces significant challenges:

[0012] Fabrication challenges: It is difficult to achieve large-scale, low-cost, and uniform fabrication of high aspect ratio nanostructures.

[0013] Performance challenges: The huge specific surface area of ​​nanostructures drastically exacerbates carrier surface recombination. Although optical reflectivity is reduced, the resulting electrical losses often offset the optical gains, failing to deliver a net improvement in battery efficiency.

[0014] In summary, existing technologies cannot simultaneously achieve efficient light capture and excellent surface passivation. Therefore, there is an urgent need to develop a novel surface structure that can fundamentally decouple light management and carrier management to overcome the long-standing bottleneck in the trade-off between optoelectronic performance. Summary of the Invention

[0015] The purpose of this invention is to provide a biomimetic moth eye-shaped composite structure with a double-layer antireflective film, its preparation method, and its applications, in order to solve the problem of photoelectric performance trade-off between light management and carrier management functions in the prior art. This composite structure achieves synergy between broadband antireflection and efficient surface passivation by integrating a biomimetic nanostructure and a specially designed double-layer film on a planar silicon substrate. Furthermore, its preparation method is feasible, low-cost, and suitable for large-scale production.

[0016] To achieve the above objectives, the present invention provides a biomimetic moth eye and double-layer antireflective film composite structure, comprising:

[0017] A planar silicon substrate is used to provide a carrier interface and achieve carrier passivation;

[0018] A double-layer antireflection film disposed on a planar silicon substrate is used to reduce light reflection through the interference cancellation effect;

[0019] A biomimetic moth-eye nanostructure layer is set on the double-layer antireflective film to provide a gradient refractive index transition from air to the double-layer antireflective film;

[0020] Among them, the biomimetic moth eye nanostructure layer and the double-layer antireflective film work synergistically to achieve 300nm. Broadband antireflection in the 1180nm band.

[0021] Preferably, the refractive index of the upper layer of the double-layer antireflective coating is in the range of 1.91. The refractive index of the lower layer is 2.03, and the refractive index range is 2.37. 2.71.

[0022] Preferably, the material combination of the double-layer antireflective film is selected from any of the following:

[0023] SiN x 1.91 / SiNx 2.71;

[0024] SiN x 1.91 / SiN x 2.37;

[0025] SiN x 2.03 / SiN x 2.37;

[0026] SiN x 2.03 / SiN x 2.71;

[0027] Or Si3N4 / TiO2.

[0028] Preferably, the biomimetic moth-eye nanostructure layer is a hexagonal periodic array composed of parabolic conical structures, with a refractive index of 1.56@589nm, and the geometric parameters of the conical structures satisfy the following: height of 300nm. 400nm, with a period of 290nm and a radius of 145nm.

[0029] This invention also provides a method for preparing a composite structure of a biomimetic moth eye and a double-layer antireflective film, comprising the following steps:

[0030] Structural Design and Optimization: Using the finite-difference time-domain method, the geometric parameters of the biomimetic moth-eye nanostructure layer and the material and thickness of the double-layer antireflective film were synergistically simulated and optimized to obtain the desired optical parameters at 300 nm. The 1180nm band has structural and film parameters with low weighted average reflectivity;

[0031] Structure fabrication: Based on the optimized parameters, a double-layer antireflection film was sequentially deposited on a planar silicon substrate, and a biomimetic moth-eye nanostructure layer was formed on the surface of the double-layer antireflection film using nanoimprinting technology.

[0032] Preferably, in the structural design and optimization, the particle swarm optimization algorithm is used to optimize the thickness of each layer of the double-layer antireflective coating within 1 nm. Optimization is performed within the 100nm range.

[0033] Preferably, in the fabrication of the structure, the deposition of the double-layer antireflective film is performed using plasma-enhanced chemical vapor deposition.

[0034] Preferably, nanoimprinting technology includes:

[0035] Use a rigid template with a biomimetic moth-eye structure pattern;

[0036] The structure is transferred to the imprinting adhesive layer by UV curing;

[0037] The structure is formed by roller imprinting and UV curing.

[0038] The present invention also provides an application of the above-described biomimetic moth eye and double-layer antireflective film composite structure in crystalline silicon solar cells.

[0039] Therefore, the present invention employs the above-mentioned biomimetic moth eye and double-layer antireflective film composite structure, its preparation method, and its application, and the beneficial technical effects are as follows:

[0040] (1) This invention integrates a biomimetic moth-eye nanostructure, a specially designed double-layer antireflective film, and a planar silicon substrate to achieve synergy and decoupling of optical antireflection and surface passivation functions. This structure fully utilizes the gradient refraction effect of the biomimetic structure over a wide spectral range and the interference effect of the dielectric thin film, which can reduce the reflection loss of the optoelectronic device surface. At the same time, the flat silicon substrate interface provides ideal conditions for applying a high-quality passivation layer, which can effectively suppress carrier surface recombination, thereby improving the light-harvesting ability while ensuring excellent electrical performance, and successfully overcoming the optoelectronic performance trade-off problem existing in traditional surface structures.

[0041] (2) The fabrication method proposed in this invention combines optical simulation optimization with efficient nanoimprinting technology, providing a clear and feasible technical path for the realization of composite structures. This method can not only accurately guide the acquisition of optimal structural parameters and ensure device performance, but also the nanoimprinting technology used has the potential for high throughput, high uniformity and low cost, overcoming some inherent defects of traditional wet etching or complex nanofabrication technologies, and laying the foundation for the large-scale application of this high-performance composite structure in crystalline silicon solar cells, photodetectors or other silicon-based optoelectronic devices. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the biomimetic moth eye structure layer;

[0043] Figure 2 This is a schematic diagram of a composite structure simulation model;

[0044] Figure 3 This is a flowchart of the nanoimprinting process;

[0045] Figure 4 Here are the FIB-SEM characterization images of the composite structure, where, Figure 4 Both (a) and (b) in the figure are FIB-SEM top views of the composite structure. Figure 4 (c) in the figure is a FIB-SEM side view of the composite structure; Figure 4(d) in the figure is a FIB-SEM cross-sectional view of the composite structure;

[0046] Figure 5 This is a graph showing the reflectance test results. Detailed Implementation

[0047] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0049] Example 1

[0050] This embodiment details the entire process of the composite structure of the present invention, from design optimization and simulation verification to actual fabrication and performance testing.

[0051] 1. Structural design and optimization.

[0052] Three-dimensional optical simulation and optimization were performed using the finite-difference time-domain method (FDTD). The simulation settings are as follows:

[0053] Simulation type: 3D; Silicon thickness: 200nm; Light source shape: plane wave; Plane wave type: Bloch / periodic; Light source incident axis: Z-axis; Wavelength range: 300nm 1180nm; Thickness optimization range: 1nm 100nm; X-axis boundary condition: symmetric; Y-axis boundary condition: antisymmetric; Z-axis boundary condition: perfectly matched layer; Monitor: frequency domain field and power.

[0054] The biomimetic moth-eye structure is a parabolic conical structure with a periodic arrangement of hexagonal arrays. Its model is output via a model script in FDTD, and a schematic diagram is shown below. Figure 1 As shown, its material refractive index =1.56@589nm. Parameter optimization was performed using parameter scanning in FDTD, with the following steps: The period of the moth-eye structure was fixed at 290nm, the radius at 145nm, and the scanning height range at 300nm. At 400nm, the optimal height for the lowest reflectivity was found to be 350nm; with the height fixed at 350nm and the scanning period fixed, the optimal period was finally determined to be 290nm. Therefore, the final optimized parameter for the moth eye structure is the height. =350nm, period =290nm, radius =145nm.

[0055] The double-layer antireflective coating consists of two dielectric films with different refractive indices, which are synergistically optimized. The possible combinations of dielectric materials are shown in Table 1.

[0056] Table 1. Combination of dielectric materials

[0057]

[0058] A schematic diagram of the complete model constructed in FDTD, including a planar silicon substrate, a double-layer antireflective film, and a biomimetic moth-eye structure, is shown below. Figure 2 As shown.

[0059] During the optimization process, a particle swarm optimization algorithm was used to collaboratively optimize the thickness of the bilayer films for various combinations. This algorithm finds the optimal solution by simulating the movement of a swarm of particles in the search space. In the optimization, the thickness of the two antireflection layers was selected as a variable, with each layer varying within a range of 1 nm. The optimization objective is to minimize 300nm to 100nm. The average reflectivity in the 1180nm band. The number of particles per generation was set to 50, with a maximum of 20 generations, and a total of 1000 simulations were performed to find the optimal solution.

[0060] The test results for parameter optimization show an average reflectance of the output wavelength from 300nm to 1180nm. The antireflection performance was evaluated using a weighted average reflectance under the AM0 and AM1.5 solar spectra. The calculation formula is as follows:

[0061] (1);

[0062] in, The values ​​are 0 and 1.5, representing the spectral type; The spectral reflectance of a material is expressed as wavelength. The function; Indicates AM1.5G or AM0G spectral irradiance (W·m -2 ·nm -1 ); This refers to the spectral wavelength; for solar cells, the wavelength range is typically 300 nm. 1100nm.

[0063] The reflectance curves obtained for each material combination were compared, and the results were calculated using formula (1). and After comparison, it was found that the optimal combination with the lowest reflectivity was the moth-eye structure SiN. X 2.03 / SiN X 2.71. The weighted average reflectance under this combination is... =3.58% and =3.64%.

[0064] 2. Electrical simulation.

[0065] The reflectivity curve data of the optimal structure obtained from FDTD was imported using Quokka electrical simulation software. The reflectivity was then calculated using the formula: transmittance. =1 reflectivity -Absorption rate Transmittance data were obtained. Electrical simulations were performed on the traditional pyramid structure, a single planar silicon structure, and the composite structure of this invention. The surface recombination current density of the planar silicon was set. 2mA / cm 2 pyramid structure 8mA / cm 2 Simulation results show that the battery using the composite structure of this invention has an open-circuit voltage (Voc) of 0.730V and a fill factor (FF) of 77.2%, while the traditional pyramid structure battery has a Voc of 0.723V and a fill factor (FF) of 76.3%. The structure of this invention significantly improves both the open-circuit voltage and the fill factor, and the short-circuit current density (Jsc) does not deteriorate.

[0066] 3. Structure preparation.

[0067] Based on the simulation optimization results, actual fabrication was carried out, and the nanoimprinting process flow is as follows: Figure 3 As shown:

[0068] Substrate preparation: A 2-inch monocrystalline silicon wafer was used, with the following specifications: P-type / 100 crystal orientation; thickness: 525. 25mm; Resistivity: 1 100 ohms cm.

[0069] Thin film deposition: Considering the actual process of depositing SiN with a refractive index of 2.71. X The film layer presents certain challenges. To reduce operational difficulties and costs, a suboptimal SiN film was employed. X 2.03 / SiN X The combination of 2.37, the combination of... =5.17% and =5.2%. A 36 nm thick SiN layer was sequentially deposited on a silicon substrate using plasma-enhanced chemical vapor deposition (PECVD). X 2.37 layers and 42nm thick SiN X 2.03 floors.

[0070] Nanoimprinting:

[0071] a. Apply mold working adhesive PS05 to the hard nickel template with the moth-eye structure pattern, so that it completely fills the moth-eye structure.

[0072] b. Use a PET (polyethylene terephthalate) film to contact the template. After complete contact, cure it with ultraviolet light and remove the nickel template. This leaves an inverted moth-eye structure on the middle PET layer.

[0073] c. Spin-coat the silicon wafer surface with double-layer antireflective coating with imprinting adhesive.

[0074] d. By using roller imprinting, the imprinting adhesive on the substrate material can fully contact and fill the structure on the PET.

[0075] e. After UV curing, the biomimetic moth eye structure is transferred onto the substrate after peeling, ultimately generating a composite structure of biomimetic moth eye and double-layer antireflective film.

[0076] 4. Characterization.

[0077] The morphology and properties of the prepared samples were characterized.

[0078] Structural characterization: The samples were observed using a ZEISS FIB-SEM. For example... Figure 4 For coating with 42.5nm SiNx 2.03 / 37.5nm SiNx 2.37 The FIB-SEM characterization image of the 2-inch silicon wafer after imprinting of the double-layer film shows that the hexagonal array is intact and the structure height is approximately 370 nm. 380nm, with approximately 400nm of residual adhesive.

[0079] Optical performance testing: using Shimadzu SolidSpec The 3700i UV spectrophotometer uses the integrating sphere method to measure reflectance. The test wavelength range is 260 nm. 1300nm. For example... Figure 5 As shown, the test results compare the experimental reflectance values ​​and FDTD simulation results of bare silicon and coated silicon wafers after nanoimprinting moth-eye structure treatment. It can be seen that bare silicon still has high reflectance after imprinting; the introduction of SiN... X After double-layer coating, the experimental reflectivity decreased significantly, and the simulated and experimental trends were roughly consistent, verifying the effectiveness of the present invention.

[0080] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art.

[0081] Therefore, this invention, employing the aforementioned biomimetic moth eye and double-layer antireflective film composite structure, its preparation method, and its application, can effectively overcome the bottleneck of photoelectric performance trade-offs faced by traditional crystalline silicon optoelectronic devices. Through structural innovation and process optimization, this solution achieves broadband high-efficiency antireflection while ensuring excellent interface passivation effects. Furthermore, its preparation process has promising prospects for industrial application, providing a reliable technical path for improving the overall performance of optoelectronic devices such as solar cells.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A biomimetic moth eye composite structure with a double-layer anti-reflective film, characterized in that, include: A planar silicon substrate is used to provide a carrier interface and achieve carrier passivation; A double-layer antireflection film disposed on a planar silicon substrate is used to reduce light reflection through the interference cancellation effect; A biomimetic moth-eye nanostructure layer is set on the double-layer antireflective film to provide a gradient refractive index transition from air to the double-layer antireflective film; Among them, the biomimetic moth eye nanostructure layer and the double-layer antireflective film work synergistically to achieve 300nm. Broadband antireflection in the 1180nm band; The material combination for the double-layer antireflective coating is selected from any of the following: Its x 1.91 / SiN x 2.71; Its x 1.91 / SiN x 2.37; Its x 2.03 / SiN x 2.37; Its x 2.03 / SiN x 2.71; Or Si3N4 / TiO2; The biomimetic moth-eye nanostructure layer is a hexagonal periodic array composed of parabolic conical structures. The material has a refractive index of 1.56 at 589 nm, and the geometric parameters of the conical structures satisfy the following: height 300 nm. 400nm, with a period of 290nm and a radius of 145nm.

2. The biomimetic moth eye and double-layer antireflective film composite structure according to claim 1, characterized in that, The refractive index of the upper layer of the double-layer antireflective coating ranges from 1.

91. The refractive index of the lower layer is 2.03, and the refractive index range is 2.

37. 2.

71.

3. The method for preparing the biomimetic moth eye and double-layer antireflective film composite structure as described in any one of claims 1 to 2, characterized in that, Includes the following steps: Structural Design and Optimization: Using the finite-difference time-domain method, the geometric parameters of the biomimetic moth-eye nanostructure layer and the material and thickness of the double-layer antireflective film were synergistically simulated and optimized to obtain the desired optical parameters at 300 nm. The 1180nm band has structural and film parameters with low weighted average reflectivity; Structure fabrication: Based on the optimized parameters, a double-layer antireflection film was sequentially deposited on a planar silicon substrate, and a biomimetic moth-eye nanostructure layer was formed on the surface of the double-layer antireflection film using nanoimprinting technology.

4. The method for preparing the biomimetic moth eye and double-layer antireflective film composite structure according to claim 3, characterized in that, In the structural design and optimization, the particle swarm optimization algorithm was used to optimize the thickness of each layer of the double-layer antireflective coating within 1 nm. Optimization is performed within the 100nm range.

5. The method for preparing the biomimetic moth eye and double-layer antireflective film composite structure according to claim 3, characterized in that, In the fabrication process, the double-layer antireflective film was deposited using plasma-enhanced chemical vapor deposition.

6. The method for preparing the biomimetic moth eye and double-layer antireflective film composite structure according to claim 3, characterized in that, Nanoimprint technology includes: Use a rigid template with a biomimetic moth-eye structure pattern; The structure is transferred to the imprinting adhesive layer by UV curing; The structure is formed by roller imprinting and UV curing.

7. The application of a biomimetic moth eye and double-layer antireflective film composite structure as described in any one of claims 1 to 2 in crystalline silicon solar cells.

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