WO2024027797A1 - 多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法 - Google Patents

多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法 Download PDF

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WO2024027797A1
WO2024027797A1 PCT/CN2023/111019 CN2023111019W WO2024027797A1 WO 2024027797 A1 WO2024027797 A1 WO 2024027797A1 CN 2023111019 W CN2023111019 W CN 2023111019W WO 2024027797 A1 WO2024027797 A1 WO 2024027797A1
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sub
cell
crystalline silicon
wavelength
light
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French (fr)
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吴颐良
陈怡华
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北京曜能光电科技有限公司
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    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
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    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
    • H01L31/0725—Multiple junction or tandem solar cells
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • H10K30/57—Photovoltaic [PV] devices comprising multiple junctions, e.g. tandem PV cells
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    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K39/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic radiation-sensitive element covered by group H10K30/00
    • H10K39/10—Organic photovoltaic [PV] modules; Arrays of single organic PV cells
    • H10K39/15—Organic photovoltaic [PV] modules; Arrays of single organic PV cells comprising both organic PV cells and inorganic PV cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/50—Organic perovskites; Hybrid organic-inorganic perovskites [HOIP], e.g. CH3NH3PbI3

Definitions

  • the present application relates to the technical field of solar cells, and in particular to a multi-junction solar cell, a perovskite crystalline silicon stacked cell, a crystalline silicon cell and a preparation method thereof.
  • multi-junction tandem solar cells such as double junctions and triple junctions ( Hereinafter referred to as multi-junction battery).
  • multi-junction tandem solar cells the perovskite/crystalline silicon tandem solar cells are currently attracting the most attention.
  • the theoretical photoelectric conversion efficiency of this tandem solar cell can be as high as 43%, which has been rapidly increased to 29.8%.
  • this The industrialization of tandem batteries is still subject to many limitations.
  • the multi-junction solar cells, perovskite crystalline silicon stacked cells, crystalline silicon cells and preparation methods provided by this application can improve the interface anti-reflection problem of stacked solar cells including perovskite/crystalline silicon, and the The solution is suitable for industrial production.
  • embodiments of the present application provide a multi-junction solar cell, including a first sub-cell and a second sub-cell located on the backlight surface of the first sub-cell, and the first sub-cell and the second sub-cell are
  • the structure of the battery interface is a sub-wavelength structure, and the period length of the sub-wavelength structure is less than the minimum wavelength of the absorption band of the second sub-battery.
  • the total thickness of all film layers between the light absorption layer of the first sub-cell and the light absorption layer of the second sub-cell is less than 100 nm.
  • the sub-wavelength structure is further configured to form a local electric field: the local electric field is formed between the upper surface and the lower surface of the light absorption layer of the first sub-cell, the local electric field causes the second
  • the migrating ions in the light-absorbing layer of a sub-cell are unevenly distributed on the upper and lower surfaces of the light-absorbing layer to leave channels for carriers to be extracted.
  • the height of the sub-wavelength structure is not less than 200 nm.
  • the second sub-cell is a crystalline silicon cell, and the period length of the sub-wavelength structure is not greater than 700 nm.
  • the sub-wavelength structure is located on the light-facing surface of the crystalline silicon cell.
  • the sub-wavelength structure is formed by a texturing process of crystalline silicon cells.
  • the second sub-cell uses a silicon substrate with nanotexture, so that the structure of the interface between the first sub-cell and the second sub-cell is a sub-wavelength structure.
  • the nano suede is nano pyramid suede or nano black silicon suede.
  • the length of the bottom side of the pyramid of the nano pyramid suede is 300 to 600 nm.
  • the texture height of the nano black silicon texture is not less than 200 nm.
  • the first sub-cell is a single-junction cell or a multi-junction cell; the material of the light-absorbing layer of the first sub-cell is selected from the group consisting of perovskite, gallium arsenide, aluminum gallium arsenide and gallium indium phosphide. one or more of them.
  • embodiments of the present application provide a perovskite crystalline silicon stacked battery, including a first sub-battery and a second sub-battery.
  • the first sub-battery is a perovskite battery
  • the second sub-battery It is a crystalline silicon cell
  • the perovskite cell includes a transparent conductive layer, a first transmission layer, a perovskite layer, and a second transmission layer; wherein one of the first transmission layer and the second transmission layer is electron transmission layer, and the other is a hole transmission layer
  • the structure of the light-facing surface of the crystalline silicon cell is a sub-wavelength structure, and the period length of the sub-wavelength structure is less than the minimum wavelength of the absorption band of the crystalline silicon cell.
  • embodiments of the present application further provide a crystalline silicon cell.
  • the light-facing surface structure of the crystalline silicon cell is a sub-wavelength structure, and the period length of the sub-wavelength structure is smaller than the absorption band of the crystalline silicon cell. minimum wavelength.
  • embodiments of the present application further provide a method for preparing a crystalline silicon cell, which includes: a textured surface preparation process.
  • the textured surface preparation process includes: providing a silicon substrate so that the silicon substrate forms a surface with a sub-wavelength structure. On the optical surface, the period length of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the crystalline silicon cell.
  • embodiments of the present application also provide a method for preparing a multi-junction solar cell, including: forming an interface with a sub-wavelength structure at the interface between the first sub-cell and the second sub-cell, and the sub-wavelength structure is The period length of the wavelength structure is smaller than the minimum wavelength of the absorption band of the second sub-cell.
  • Forming an interface with a sub-wavelength structure at the interface between the first sub-cell and the second sub-cell includes: in the preparation process of the second sub-cell, using a texturing process to form the second sub-cell.
  • the light-facing surface of the sub-wavelength structure includes: in the preparation process of the second sub-cell, using a texturing process to form the second sub-cell.
  • Figure 1 is a schematic diagram of a multi-junction solar cell provided by some embodiments of the present application.
  • Figure 2 is a schematic diagram of the calculation principle of the equivalent refractive index of the nanopyramid texture of a crystalline silicon cell
  • Figure 3 shows the integration of transmitted light energy in the wavelength range of 720-1150nm for the nanotexture with sub-wavelength structure provided in Experiment 1 of the present application and the planar structure, small texture structure and large texture structure produced by related technologies. Schematic diagram of the comparison of results;
  • Figure 4 is a simulated experimental diagram of the density distribution of migrating ions near a pyramid in a pyramid suede surface with a period length of 600 nm provided in Experiment 2 of the present application;
  • Figure 5 is a simulated experimental diagram of the relationship between the sum of the current density of the first sub-cell and the second sub-cell and the height of the sub-wavelength structure of the crystalline silicon/perovskite stacked cell provided in Experiment 3 of the present application;
  • Figure 6 is an electron micrograph of the nanosuede provided in Experiment 4 of this application.
  • Figure 7 is a reflectance diagram measured in the wavelength range of 300-1200nm for the crystalline silicon/perovskite stacked cell provided in Experiment 4 of this application (the bottom side lengths of the pyramids in the crystalline silicon cell are 320nm, 420nm and 580nm respectively. ).
  • Subwavelength structure refers to a periodic (or non-periodic) structure whose characteristic size is equivalent to or smaller than the operating wavelength.
  • the characteristic size of the sub-wavelength structure is smaller than the operating wavelength, and its reflectance, transmittance, polarization characteristics and spectral characteristics all show completely different characteristics from conventional optical elements, so it has greater application potential.
  • the period length of the sub-wavelength structure refers to the length of the above-mentioned periodic (or non-periodic) structure.
  • the characteristic size of the sub-wavelength structure can be understood as the average size of the unit structures that make up the sub-wavelength structure, or the statistical median value of the size of the unit structure, which generally takes the majority value (for example, more than 75% of the total number) The average value of the distribution interval.
  • the sub-wavelength structure refers to a structure composed of several protrusions in a periodic or non-periodic array on the surface of the layer structure
  • the unit structure in this application is the protrusions that make up the sub-wavelength structure
  • the period length of the sub-wavelength structure is the protrusion.
  • the bottom diameter can be shown as L in Figure 4.
  • the absorption band of crystalline silicon cells is mainly concentrated in 720nm-1200nm. Therefore, the size of the unit structure of the sub-wavelength structure in the solution of this application is less than 720nm, that is, it needs to be Find the size of most unit structures less than 720nm.
  • the size of the unit structure in the sub-wavelength structure is generally less than 700nm, which can achieve low reflection in the wavelength band greater than 700nm.
  • the perovskite light-absorbing layer is a layer of ionic crystals. Due to its simple low-temperature preparation process and the environmental pressure encountered during later operations, a large number of shallow energy level defects are easily produced in the perovskite light-absorbing layer; in addition, this shallow energy Level defects are also a type of ions that can migrate relatively freely in perovskite batteries, so they can also be called migrating ions. When a perovskite/crystalline silicon tandem cell with a planar structure or a large textured structure or a planar perovskite cell operates, these migrating ions will evenly cover the upper surface and surface of the perovskite light-absorbing layer during battery operation. At the lower surface, it is difficult to extract carriers, thereby reducing the filling factor and current density of the perovskite light-absorbing layer.
  • the traditional alkali etching texturing method uses anisotropic etching characteristics to form a pyramid-shaped (hereinafter referred to as pyramid) periodic structure on the surface of crystalline silicon (hereinafter referred to as pyramid) on the surface of crystalline silicon (crystalline direction 100).
  • the height of traditional pyramids is about 2 ⁇ m-6 ⁇ m.
  • the size of the pyramid can be controlled by adjusting the type or concentration of alkali solution, the scheme and ratio of alkali solution additives, reaction temperature and time.
  • the surface structure composed of the pyramids of the array is called nanopyramid texture.
  • Black silicon texture refers to the texture structure formed on the surface of crystalline silicon by wet method (metal-assisted chemical etching) or dry method (plasma etching).
  • the height of the microstructure of the traditional black silicon textured structure is about 2-5 ⁇ m.
  • the microstructure of the black silicon textured surface has a larger aspect ratio, so it is beneficial to light trapping.
  • the height of the microstructure in the black silicon texture can be adjusted by adjusting the process gas, solution concentration and etching time. When the period length of the microstructure of the black silicon suede and the height of the microstructure are both less than 1 ⁇ m, it is called nano black silicon suede.
  • planar structure There are currently three structures for the light-facing surface of crystalline silicon base cells in stacked batteries: planar structure, small suede structure, and large suede structure.
  • the planar structure has a large reflection loss of visible photons and near-infrared photons, so it is not suitable for industrial production.
  • the light-facing surface of the crystalline silicon bottom cell adopts a small suede structure with a height of 0.9-1.1 ⁇ m, the multiple reflection absorption principle of the pyramid surface of the small suede structure can be used to reduce near-infrared reflection loss.
  • this small textured structure requires the thickness of the perovskite light-absorbing layer to exceed 1 ⁇ m, and also requires high film quality of the perovskite light-absorbing layer, so the process is difficult and difficult to carry out industrial production.
  • the light-facing surface of the crystalline silicon bottom cell adopts a large textured structure with a height of 2-3 ⁇ m, although the near-infrared reflection loss of the large textured structure is relatively small, the perovskite light absorption layer and transmission layer are required to be conformal Crystalline silicon base cell covered with large suede structure, Generally, CVD and PVD deposition are required. The process is difficult, complex and costly. Currently, it is not possible to use solution methods suitable for industrial production.
  • the first sub-cell is stacked on the second sub-cell.
  • the interface between the first sub-cell and the second sub-cell is configured as a sub-wavelength structure.
  • a subwavelength structure is formed on the light-facing surface of the second sub-cell.
  • the period length of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the second sub-cell, and the wavelength of the incident light directed to the second sub-cell cannot identify microstructures smaller than the absorption band of the second sub-cell (i.e., the sub-wavelength structure of the present application).
  • these sub-wavelength structures can be equivalent to anti-reflective films with intermediate refractive index (between the bulk refractive index of the first sub-cell and the bulk refractive index of the second sub-cell) layer, which can effectively break through the optical difference between the first sub-cell and the second sub-cell, guide photons from the first sub-cell into the second sub-cell, thereby reducing the reflectivity of the second sub-cell's absorption band and improving the overall battery quality photon absorption and conversion efficiency.
  • intermediate refractive index between the bulk refractive index of the first sub-cell and the bulk refractive index of the second sub-cell
  • the surface of the second sub-cell is relatively flat, which reduces the film thickness and film quality requirements for the light-absorbing layer of the first sub-cell (the light-absorbing layer of the first sub-cell does not need to reach 1 ⁇ m ), thus reducing the process difficulty of the first sub-cell (so that the light-absorbing layer of the first sub-cell can be prepared by a solution method), which is beneficial to the industrial production of solar cells.
  • Some embodiments of the present application provide a multi-junction solar cell, including a first sub-cell and a second sub-cell located on the backlight surface of the first sub-cell.
  • the structure of the interface between the first sub-cell and the second sub-cell is a sub-wavelength structure.
  • the period length of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the second sub-cell.
  • the structure of the light-facing surface of the second sub-cell is the sub-wavelength structure, and each film layer of the first sub-cell is formed on the sub-wavelength structure of the light-facing surface.
  • the first sub-cell is stacked on the second sub-cell, and the incident light first passes through the first sub-cell and then enters the second sub-cell.
  • Each sub-cell has a corresponding main absorption band (hereinafter referred to as the absorption band), which is mainly determined by the bandgap width of its light-absorbing layer. At the same time, factors such as the material thickness, reflectivity and whether it is doped in the light-absorbing layer will also affect it. Specific value.
  • Each sub-cell can absorb light energy within the absorption band and efficiently It is converted into electrical energy efficiently and absorbs little or no light energy outside the absorption band.
  • a sub-wavelength structure is formed at the junction between the first sub-cell and the second sub-cell.
  • the sub-wavelength structure includes a plurality of unit structures, and the average size of the unit structures is smaller than the minimum wavelength of the absorption band corresponding to the second sub-cell. .
  • the first sub-battery is a perovskite cell (the Perovskite part shown in Figure 1)
  • the second sub-battery is a crystalline silicon cell (c shown in Figure 1 -Si sub cells part).
  • a sub-wavelength structure is formed at the junction of the perovskite cell and the crystalline silicon cell.
  • the size of the components of the sub-wavelength structure i.e. the size of the unit structure, which technicians call the period length of the sub-wavelength structure, will be unified as the period length below) Less than the minimum absorption wavelength of crystalline silicon cells.
  • the perovskite subcell is used as the top cell, and its absorption band is generally designed to be 300nm to 750nm.
  • the crystalline silicon subcell is used as the bottom cell, and its absorption band is generally designed to be 700nm to 1200nm.
  • the structure of the light-facing surface of the crystalline silicon sub-cell can be a sub-wavelength structure with a period length less than 700 nm, that is, the average size of the unit structures that make up the sub-wavelength structure can be Less than 700nm, or in other words, the size distribution of most sub-wavelength structures is within the range of less than 700nm.
  • the material of the light-absorbing layer of the above-mentioned first sub-cell can also be selected from wide-bandgap materials such as gallium arsenide (1.43eV), aluminum gallium arsenide (1.42eV-2.16eV), and gallium indium phosphide. Materials; In addition to crystalline silicon, the material of the light absorption layer of the second sub-cell can also be selected from copper indium gallium selenide (1.02eV-1.67eV, adjustable band gap), cadmium telluride (1.46eV), and narrow bandgap calcium titanium Narrow bandgap materials such as ore and gallium arsenide (1.424eV).
  • wide-bandgap materials such as gallium arsenide (1.43eV), aluminum gallium arsenide (1.42eV-2.16eV), and gallium indium phosphide. Materials; In addition to crystalline silicon, the material of the light absorption layer of the second sub-cell can also be selected from copper indium
  • the band gap width of the material of the light absorption layer of the first sub-cell is larger than the band gap width of the material of the light absorption layer of the second sub-cell. Therefore, the wide band gap material and the narrow band gap material here are relative. .
  • the unit structure in the sub-wavelength structure of the present application is preferably periodically distributed, and may also be a loose periodic distribution during specific implementation.
  • the sub-wavelength structures are mostly obtained through a wet texturing process or a dry texturing process.
  • the sub-wavelength structures generally include pyramid-shaped or nearly pyramid-shaped protrusions (hereinafter referred to as pyramids).
  • the unit structure of Dimension L is generally the average side length of the quadrilateral at the bottom of the pyramid or the median of the statistical distribution of side lengths. That is, the period length of the sub-wavelength structure can generally be the average side length of the quadrilateral at the bottom of the pyramid or the median of the statistical distribution of side lengths. Number, please refer to Figure 4 for details.
  • the sub-wavelength structure of this embodiment can be represented by micro protrusions distributed on the top film layer of the second sub-cell or micro protrusions formed by multiple local upward protrusions of the top film layer.
  • the average of the micro protrusions The bottom diameter or the median of the statistical bottom diameter distribution is smaller than the minimum value of the absorption band of the second sub-cell.
  • the shape of the tiny protrusions is, for example, Tetrahedron shape or pyramid shape.
  • the above-mentioned sub-wavelength structure can be formed integrally with the second sub-cell, or can be formed independently of the second sub-cell. As long as the characteristic size of the sub-wavelength structure is within a suitable size range, the stack can be made The battery only needs to achieve good anti-reflection effect in the absorption band of the second sub-battery.
  • the sub-wavelength structure at the interface between the first sub-cell and the second sub-cell can equivalently construct a refractive index between the first sub-cell and the second sub-cell between the first sub-cell and the second sub-cell.
  • the equivalent dielectric film layer between the bulk refractive index of the second sub-cell improves the optical difference between the first sub-cell and the second sub-cell, guides photons from the first sub-cell into the second sub-cell, and reduces the The reflectivity of the two sub-cells absorbs the wavelength band, which improves the photon absorption and conversion efficiency of the battery as a whole.
  • the material selection of the subwavelength structure meets the above requirements.
  • the sub-wavelength structure uses the same material as the second sub-cell or a material with a refractive index close to that of the second sub-cell, and the sub-wavelength structure is filled with a material that is the same as the first sub-cell or has a refractive index close to it, such as perovskite material.
  • the refractive index of the material with the sub-wavelength structure is close to that of the bulk material of the second sub-cell (the material of the light-absorbing layer of the second sub-cell).
  • the sub-wavelength structure can effectively construct a refractive index between the bulk phase of the first and second sub-cells.
  • the equivalent dielectric film layer between the refractive index can produce an anti-reflection effect on the light entering the second sub-cell (in other words, it can achieve an anti-reflection effect in the absorption band of the second sub-cell). This application specifically focuses on the sub-wavelength structure.
  • the material is not limited.
  • the shape of the unit structure of the sub-wavelength structure is a pyramid shape, and its material is the same as the second sub-cell; above the pyramid shape are the film layers of the perovskite sub-cell. Since each The perovskite light-absorbing layer is the thickest among the film layers, and the bulk refractive index of the second sub-cell refers to the refractive index of the perovskite light-absorbing layer.
  • the solution of this application is particularly suitable for stacked cells where the bulk refractive index difference between the first sub-cell and the second sub-cell is large, resulting in large interface reflection, such as perovskite/crystalline silicon stacked cells.
  • the refractive index of perovskite material is about 2.34-2.38
  • the refractive index of crystalline silicon is 3.42.
  • the present application can also provide microstructures on any film layer below the light absorption layer of the first sub-cell in Figure 1 or on the substrate of the stacked battery, so that the first sub-cell and the second sub-cell The junction is an interface with a sub-wavelength structure, thereby reducing the reflected light on the light-facing surface of the second sub-cell.
  • the crystalline silicon cell in the crystalline silicon/perovskite tandem cell can use a silicon substrate with pyramid texture, and the period length of the microstructure (i.e., pyramid) of the pyramid texture is smaller than the absorption capacity of the crystalline silicon.
  • the minimum wavelength of the waveband is, for example, less than 700nm, thus forming a sub-wavelength structure with an anti-reflection effect on the light-facing surface of the crystalline silicon cell.
  • the concentration of the alkali solution, the type and concentration of the additives, as well as the process temperature and time can be directly controlled in the texturing process of the silicon substrate of the crystalline silicon cell to control the microstructure of the texture formed on the surface of the silicon substrate ( For example, the size of the pyramid),
  • the size of the microstructure is made smaller than the minimum wavelength of the absorption band of the crystalline silicon cell, thereby forming a sub-wavelength structure at the interface between the first sub-cell and the second sub-cell, without the need for additional steps to form the sub-wavelength structure.
  • the above-mentioned second sub-cell includes at least one light absorption layer.
  • the above-mentioned second sub-cell may further include an anti-reflection layer and/or a metal electrode layer for collecting carriers.
  • the multi-junction solar cell of this embodiment may also include other film layers (such as composite layers or tunneling layers), or may further include other sub-cells, or Including other battery structures not mentioned, this embodiment does not limit them.
  • an interface with a sub-wavelength structure is formed at the junction of the first sub-cell and the second sub-cell, forming a bionic moth-eye structure, which can effectively break through the gap between the first sub-cell and the second sub-cell.
  • the optical difference guides photons from the first sub-cell into the second sub-cell, which can achieve low reflection in a wide wavelength band and a large range, thus improving the overall photon absorption and conversion efficiency of the cell.
  • the sub-wavelength structure is used to effectively construct a multi-layer anti-reflective film with a gradient transition of refractive index from the light-absorbing layer of the first sub-cell to the light-absorbing layer of the second sub-cell. layer.
  • the unit structure in the sub-wavelength structure is a wedge-shaped structure, so that the sub-wavelength structure is equivalent to equivalently constructing the light absorption from the light absorption layer of the first sub-cell to the second sub-cell.
  • the multi-layer anti-reflection coating layer with a gradual transition of refractive index gradient can improve the optical difference between the first and second sub-cells, guide photons from the first sub-cell into the second sub-cell, thereby reducing the absorption of the second sub-cell.
  • the reflectivity of the wavelength band improves the photon absorption and conversion efficiency of the battery as a whole.
  • FIG. 2(a) it is a schematic diagram of the nano-pyramid texture of a crystalline silicon cell, which is layered according to the thickness of 10nm.
  • each layer can be considered as a local crystalline silicon film with a thickness of 10nm plus the periphery.
  • dielectric film mainly the light absorption layer of the first sub-cell
  • the equivalent refractive index can be calculated with reference to the Lorentz-Lorenz equation.
  • the equivalent refractive index is related to the spatial ratio (space occupancy rate) of the two media in the film layer with equal thickness.
  • the sub-wavelength structure is equivalently constructed from the perovskite cell to the The refractive index gradient of the crystalline silicon cell is gradually transitioned into a multi-layer anti-reflection coating layer, and the equivalent multi-layer anti-reflection coating layer can guide photons in the near-infrared and infrared bands efficiently from the perovskite cell into the crystalline silicon cell. Width Low reflection is achieved within the wavelength band and large range (crystalline silicon absorption band), thereby increasing the light conversion rate of the crystalline silicon sub-cell.
  • (c) in Figure 2 is the equivalent multi-layer anti-reflective coating layer of (b) in Figure 2 .
  • medium 1 perovskite
  • medium 2 crystalline silicon
  • the occupancy rate of medium 2 in each layer continuously increases, and the occupancy rate of medium 1 continuously decreases. Therefore, the effective refractive index can also be realized from medium 1 Continuous change to medium 2.
  • the Fresnel reflectivity of each layer is also very small.
  • the medium occupancy of each layer gradually changes from 100% of medium 1 to 100% of medium 2, and the equivalent effective refractive index of each layer also gradually changes from the refractive index of medium 1 to the refractive index of medium 2.
  • the gradient from medium 1 to medium 2 can be achieved, and the desired anti-reflection effect can be obtained in the absorption band of the second battery.
  • the shape of the unit structure of the sub-wavelength structure is a pyramid shape. Because in the direction from medium 1 (perovskite) to medium 2 (crystalline silicon), the pyramid shape will make the medium occupancy and effective refractive index transition smoother, and the anti-reflection effect will be better.
  • the total thickness of all film layers between the light absorption layer of the first sub-cell and the light absorption layer of the second sub-cell is less than 100 nm.
  • the light absorption layer from the first sub-cell light absorption layer to the second sub-cell is equivalently constructed.
  • the multi-layer anti-reflection coating layer with gradual refractive index transition can well convert the sudden refractive index into a gradient equivalent refractive index, thereby reducing the sensitivity of reflection loss to the thickness of the interface layer, thus making the composite layer and transmission layer The design is more free.
  • the multi-junction solar cell forms an interface with a sub-wavelength structure at the junction of the first sub-cell and the second sub-cell, and by optimizing the height of the sub-wavelength structure, the interface between the first sub-cell and the second sub-cell can be Appropriate local electric fields are formed on the upper and lower surfaces of (such as perovskite cells).
  • the local electric field can cause the migrating ions in the light-absorbing layer of the first sub-cell to be unevenly distributed on the upper and lower surfaces of the light-absorbing layer of the first sub-cell, thereby leaving space for carriers to Channels that are freely extracted.
  • the height of the unit structure of the sub-wavelength structure corresponding to this appropriate local electric field is not less than 200nm.
  • the height of the unit structure specifically refers to the length of the unit structure in a direction substantially perpendicular to the solar cell substrate.
  • the height here can be understood as the average height of multiple unit structures that make up the entire sub-wavelength structure, or the statistical median height of multiple unit structures. For example, this condition is satisfied if the height distribution of not less than 75% of the unit structures is within a height range of not less than 200 nm.
  • the density of migrating ions in the perovskite light absorption layer is 10 16 per unit area (average distribution state).
  • the migrating ions will accumulate towards the interface.
  • the density at the interface It may be as high as 10 21 per unit area, thus forming an interface with very low conductivity, which is not conducive to carrier extraction.
  • the electric field distribution at the upper and lower interfaces of the perovskite light absorption layer will be uneven.
  • the migrating ions will be attracted by the electric field, and their density distribution at the interface will also be uneven.
  • FIG. 4 is a simulated experimental diagram of the density distribution of migrating ions in a sub-wavelength structure (pyramid suede) with a period length L of 600 nm. The color depth in the figure represents the packing density of migrating ions. The results show that near the pyramid's apex, the packing density of migrating ions is smallest, which can form a channel for carriers to be freely extracted.
  • cutting-edge sub-wavelength structures can reduce the impact of migrating ions and improve the long-term stability of tandem cells.
  • Figure 5 is a simulated experimental diagram of the relationship between the sum of the current densities of the first sub-cell and the second sub-cell and the sub-wavelength structure height of the crystalline silicon/perovskite stacked cell.
  • the experimental results show that when the height of the pyramid is less than 200nm, the sum of the current densities of the first sub-battery and the second sub-battery increases with the increase of the height of the pyramid; when the height of the pyramid is greater than or equal to 200nm, the sum of the current densities of the first sub-battery and the second sub-battery increases.
  • the sum of the current density slows down as the height of the pyramid increases and gradually approaches saturation; when the height of the pyramid is greater than 250nm, the sum of the current densities of the first sub-cell and the second sub-cell no longer changes as the height of the pyramid increases. Therefore, when the height of the sub-wavelength structure is not less than 200nm, the laminated battery can achieve good optical effects; when the height of the sub-wavelength structure is greater than or equal to 250nm, the laminated battery has better optical effects.
  • the experimental result parameters corresponding to this interval are better. Because when the height of the pyramid is greater than At 200nm (corresponding to the base length of the pyramid about 280nm), the sum of the current densities of the first sub-cell and the second sub-cell tends to be saturated, and the optical gain is extremely obvious, that is, the anti-reflection effect is also better, but the optical gain is not all converted into electrical gain. In the end, our experiments showed that the actual electrical parameters obtained by the pyramid texture are better when the period length is in the range of 300nm to 600nm.
  • the height of the unit structure of the sub-wavelength structure is not less than 200nm, and the period length L is not more than 700nm, and the optical anti-reflection effect is relatively good.
  • the nano black silicon texture has a period length in the range of 200nm to 400nm and a height of not less than 200nm, so that the actual effect of obtaining electrical parameters is better.
  • the sub-wavelength structure provided by this application will also cause great changes in the distribution of the built-in electric field of the first sub-cell light absorption layer.
  • the local built-in electric field intensity is reduced, which reduces the migration potential energy of migrating ions, which can improve the stability of the light-absorbing layer of the first sub-cell (such as a perovskite cell) and the stacked photovoltaic device.
  • the present application also provides a crystalline silicon/perovskite stacked cell using the sub-wavelength structure of the present application.
  • the light-facing surface of the crystalline silicon cell of the stacked cell adopts a height greater than 250nm and a period length less than 700nm.
  • Nano pyramid suede or nano black silicon suede Due to the heterogeneous structure of the nanopyramid suede or nanoblack silicon suede, local electric fields can be formed on the upper and lower surfaces of the perovskite light-absorbing layer. During battery operation, the local electric field can cause the perovskite light-absorbing layer to The migrating ions in the perovskite light-absorbing layer are unevenly distributed on the upper and lower surfaces, leaving a channel through which carriers can be freely extracted.
  • the perovskite light-absorbing layer with a special structure also causes a great change in the built-in electric field distribution of the perovskite light-absorbing layer.
  • the local electric field intensity is reduced, which reduces the migration potential energy of migrating ions, which is very important for perovskite cells and
  • the stability of perovskite/crystalline silicon stack photovoltaic devices is greatly helped.
  • the nano-pyramid texture or nano-black silicon texture of the specific size of the present application can improve the tolerance of perovskite top cells to shallow energy level defects, thereby improving the efficiency of stacked devices.
  • the period length of the above-mentioned sub-wavelength structure is further preferably no less than 200 nm and no more than 600 nm.
  • the sub-wavelength structure is in the range of 200nm to 600nm, it can achieve the following effects: (1) The interface has good anti-reflection or light trapping effect; (2) It can reduce the reflection loss on the interface layer (located between the light absorption layer of the first sub-cell and the second sub-cell). The thickness of the interface layer such as the transparent conductive electrode and the transmission layer between the light-absorbing layers of the two sub-cells is more freely designed; (3) The requirements for the film forming process of the first sub-cell are low.
  • the upper surface of the second sub-cell is relatively flat (compared to the large textured structure of crystalline silicon and the conventional small textured structure), and the light-absorbing layer (such as perovskite) of the first sub-cell does not have to be larger than With a 1 ⁇ m thick film, the requirements for film formation quality are also reduced, so that the light-absorbing layer of the first sub-cell can be prepared using a solution method, which is beneficial to the industrial production of solar cells.
  • the thickness of the perovskite light absorption layer At about 300 nanometers (from the top of the pyramid) or 800nm (from the lowest point of the pyramid), the electrical parameters of the stacked battery samples are relatively good.
  • the local electric field intensity of the built-in electric field formed by the light-absorbing layer of the first sub-cell is reduced, so that the migration potential energy of the migrating ions is reduced, which affects the light-absorbing layer of the first sub-cell and the components including the first sub-cell,
  • the second sub-cell greatly contributes to the stability of the stacked photovoltaic device.
  • the second sub-cell may be a crystalline silicon cell; in this case, the sub-wavelength structure may be formed through a texturing process of the crystalline silicon cell.
  • Crystalline silicon cells can be polycrystalline silicon cells or monocrystalline silicon cells.
  • the structure of crystalline silicon cells includes but is not limited to PERC (Passivated Emitter and Rear Cell, passivated emitter and rear contact), TOPCon (Tunnel Oxide Passivated Contact, tunnel oxide passivated contact) or HJT (silicon heterojunction, silicon heterojunction) structure.
  • the second sub-battery uses a silicon substrate with nanotexture.
  • the period length of the nanotexture is not less than 300nm and not greater than 600nm, which can form an anti-reflective sub-surface at the interface of the first sub-battery and the second sub-battery.
  • the sub-wavelength structure may be a nano-pyramid texture or a nano-black silicon texture.
  • Nanotexture refers to nano-scale microstructure texture, which can be achieved by alkali and additives, or a wet process of metal catalyzed chemical etching, or a dry process of plasma etching.
  • the above-mentioned first sub-cell is a single-junction cell or a multi-junction cell
  • the material of the light-absorbing layer of the first sub-cell can be selected from perovskite, cadmium telluride, copper indium gallium selenide, and gallium arsenide. , one or more of gallium indium phosphide and gallium aluminum arsenide.
  • Embodiments of the present application also provide a perovskite stacked battery, in which a first sub-battery and a second sub-battery are arranged in sequence from top to bottom along the light incident direction.
  • the first sub-battery is a perovskite battery
  • the The second sub-cell is a crystalline silicon cell;
  • the perovskite cell includes: a transparent conductive layer, a first transmission layer, a perovskite layer, and a second transmission layer; wherein the first transmission layer and the second transmission layer , one of which is the electron transport layer and the other is the hole transport layer;
  • the structure of the light-facing surface of the crystalline silicon cell is a sub-wavelength structure, and the period length of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the crystalline silicon cell.
  • the sub-wavelength structure can be formed through the first texturing process of the silicon substrate of the crystalline silicon cell.
  • the structure of the crystalline silicon cell includes but is not limited to PERC, TOPCon or HJT structure.
  • the size of the unit structure of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the crystalline silicon cell, so that the wavelength of the incident light directed to the crystalline silicon cell cannot identify its tiny structure, similar to the moth-eye structure of nanobionics, making it possible It effectively breaks through the optical difference between crystalline silicon cells and perovskite cells, and guides photons from the perovskite cells into the crystalline silicon cells, thereby reducing the reflectivity of the crystalline silicon cells in the absorption band and overall improving the photon absorption and performance of the stacked cells. Conversion efficiency.
  • the surface of crystalline silicon cells has a relatively large suede structure. It is flatter, and the quality requirements required for film formation of the perovskite layer are reduced. It can be prepared by a solution method,
  • Perovskite cells may also include anti-reflection layers and metal electrode layers.
  • the above-mentioned transparent conductive layer may include at least one of ITO, IZO, AZO, graphene and metal nanowires.
  • the general formula of the above-mentioned perovskite light-absorbing layer is ABX 3 , where A is a monovalent cation, including but not limited to one or more cations among lithium, sodium, potassium, cesium, rubidium, amine group or amidine group; B is a divalent cation.
  • Valent cations including but not limited to one of lead, tin, tungsten, copper, zinc, gallium, selenium, rhodium, germanium, arsenic, palladium, silver, gold, indium, antimony, mercury, iridium, thallium, bismuth, or Several cations;
  • X is a monovalent anion, including but not limited to one or more anions among iodine, bromine, chlorine or astatine.
  • the perovskite component in the perovskite light-absorbing layer can be, for example, Cs 0.05 FA 0.80 MA 0.15 PbI 2.55 Br 0.35 ; wherein Cs is cesium, FA is formamidine group, MA is methylamine group, and I is iodine.
  • the above-mentioned electron transport layer may include at least one of SnO 2 , TiO 2 , ZnO, ZrO 2 , fullerene and derivatives, TiSnO X and SnZnO X.
  • the hole transport layer includes PTAA, Poly-TPD, NiOx, P3HT, V 2 O 5 , MoOx, PEDOT:PSS, WOx, Spiro-OMeTAD, CuSCN, Cu 2 O, CuI, Spiro-TTB, F4-TCNQ, At least one of F6-TCNNQ, m-MTDATA and TAPC.
  • the above-mentioned sub-wavelength structure can also be configured as a multi-layer anti-reflection film layer that is equivalent to a gradient transition of refractive index from the perovskite light-absorbing layer to the light-absorbing layer of the crystalline silicon cell, and can be optimized by optimizing the sub-wavelength structure.
  • the wavelength structure is used to optimize the equivalent refractive index of the multi-layer anti-reflection coating to achieve the best anti-reflection effect.
  • the total thickness of all film layers between the perovskite light absorption layer and the light absorption layer of the crystalline silicon cell is less than 100 nm.
  • the above-mentioned sub-wavelength structure is further configured to form a local electric field formed between the upper surface and the lower surface of the light absorption layer of the first sub-cell, and the local electric field causes the first sub-cell to
  • the migrating ions in the light-absorbing layer of a sub-cell are unevenly distributed on the upper and lower surfaces of the light-absorbing layer to leave channels for carriers to be extracted.
  • the height of the above-mentioned sub-wavelength structure is not less than 200 nm.
  • the second sub-cell is a crystalline silicon cell, and the period length of the sub-wavelength structure is not greater than 700 nm.
  • the above-mentioned sub-wavelength structure is formed using a texturing process of crystalline silicon cells.
  • the above-mentioned second sub-cell is prepared using a silicon substrate with nanotexture, or a nanotexture is formed on the silicon substrate through a texturing process, and the nanotexture is a nanopyramid texture or a nanoblack silicon texture.
  • the nano When the suede is a nano-pyramid suede, the period length of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm; when the nano suede is a nano-black silicon suede, the height of the sub-wavelength structure is not less than 200 nm. And the period length is no more than 700nm.
  • the first sub-cell is a single-junction battery or a multi-junction battery; the material of the light-absorbing layer of the first sub-cell is selected from perovskite, cadmium telluride, copper indium gallium selenide, gallium arsenide, One or more of indium gallium phosphide and aluminum gallium arsenide.
  • Some embodiments of the present application also provide a three-junction solar cell.
  • the first sub-cell on the uppermost layer uses a light absorption layer of about 1.8ev;
  • the third sub-cell on the bottom layer uses a light absorption layer of about 1.2ev;
  • the third sub-cell in the middle uses a light absorption layer of about 1.2ev.
  • the second sub-cell uses a light absorbing layer of about 1.4ev.
  • the sub-wavelength structure described in this application can be provided on both the light-facing surface of the second sub-cell and the third sub-cell, wherein the period length of the sub-wavelength structure provided on the light-facing surface of the second sub-cell is is smaller than the minimum wavelength of the absorption band of the second sub-cell; the period length of the sub-wavelength structure provided on the light-facing surface of the third sub-cell is smaller than the minimum wavelength of the absorption band of the third sub-cell.
  • Embodiments of the present application also provide a bottom cell in a stacked battery.
  • the structure of the light-facing surface of the bottom cell is a sub-wavelength structure, and the period length of the sub-wavelength structure is less than the minimum wavelength of the absorption band of the bottom cell.
  • the bottom cell may be a crystalline silicon cell, and the period length of the sub-wavelength structure is not greater than 700 nm.
  • the surface of the bottom cell of this embodiment is relatively flat, and has good anti-reflection or light trapping effects in its own absorption band. It is suitable for use as the bottom cell of a stacked cell, which is beneficial to reducing the difficulty of film formation of the upper top cell and facilitating industrial production.
  • Embodiments of the present application also provide a crystalline silicon cell.
  • the structure of the light-facing surface of the crystalline silicon cell is a sub-wavelength structure, and the period length of the sub-wavelength structure is less than the minimum wavelength of the absorption band of the crystalline silicon cell.
  • the period length of the sub-wavelength structure is not greater than 700 nm.
  • the surface of the crystalline silicon cell of this embodiment is relatively flat, and has good anti-reflection or light trapping effect in the near-infrared and infrared bands (700-1200nm).
  • the relatively flat surface is conducive to reducing the difficulty of film formation of the upper top cell, and is suitable for laminate cells.
  • the bottom battery facilitates industrial production.
  • the above-mentioned sub-wavelength structure can also be configured as a multi-layer anti-reflection film layer that is equivalent to a gradient transition of refractive index from the top cell light absorption layer of the stacked cell to the crystalline silicon cell light absorption layer, and can be optimized through
  • the sub-wavelength structure is used to optimize the equivalent refractive index of the multi-layer anti-reflective coating to achieve the best anti-reflective effect.
  • the total thickness of all film layers between the top cell light absorption layer and the crystalline silicon light absorption layer is less than 100 nm.
  • the above-mentioned sub-wavelength structure is further configured to form the following local electric field: the local electric field is formed between the upper surface and the lower surface of the light absorption layer of the first sub-cell, and the local electric field causes the top cell to
  • the migrating ions in the light-absorbing layer are unevenly distributed on the upper and lower surfaces of the top cell light-absorbing layer to leave channels for carriers to be extracted.
  • the height of the above-mentioned sub-wavelength structure is not less than 200 nm.
  • the period length of the above-mentioned sub-wavelength structure is not greater than 700 nm.
  • the above-mentioned sub-wavelength structure is formed using a texturing process of crystalline silicon cells.
  • the above-mentioned second sub-cell is prepared by using a silicon substrate with nanotexture, or using a texturing process to form a nanotexture on the silicon substrate, and the nanotexture is a nanopyramid texture or a nanoblack silicon texture.
  • the nano suede is a nano pyramid suede
  • the period length of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm
  • the nano suede is a nano black silicon suede
  • the height of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm. Less than 200nm, and the period length is no more than 700nm.
  • Embodiments of the present application also provide a method for preparing a crystalline silicon cell, which includes: a textured surface preparation process.
  • the textured surface preparation process includes: providing a silicon substrate so that the silicon substrate forms a light-facing surface with a sub-wavelength structure.
  • the sub-wavelength structure is The period length of the structure is smaller than the minimum wavelength of the absorption band of the crystalline silicon cell.
  • the period length of the sub-wavelength structure is not greater than 700 nm.
  • the texture preparation process forms a nanotexture with a height greater than 300 nm and a period length less than 700 nm.
  • Nanotexture refers to a texture containing nanometer-scale microstructures, which can be achieved by alkali and additives, or a wet process of metal-catalyzed chemical etching, or a dry process of plasma etching.
  • embodiments of the present application provide a method for preparing a crystalline silicon battery, which can prepare a bottom battery suitable for use as a stacked battery.
  • the surface of the bottom battery is distributed with sub-wavelength structures with a period length less than 700 nm. Because the surface of this crystalline silicon cell is relatively flat when used as a bottom cell, it can reduce the difficulty of the top cell process and contribute to the industrial integration of the overall process of stacked cells.
  • the above-mentioned sub-wavelength structure can also be equivalently constructed as a multi-layer anti-reflection film layer with a gradient transition of refractive index from the light absorption layer of the top cell of the stacked cell to the light absorption layer of the crystalline silicon cell, and can be achieved by optimizing the sub-wavelength structure.
  • wavelength structure to optimize more Equivalent refractive index of the anti-reflective coating layer to achieve the best anti-reflective effect.
  • the total thickness of all film layers between the light absorption layer of the top cell and the crystalline silicon light absorption layer is less than 100 nm.
  • the above-mentioned sub-wavelength structure is further configured to form the following local electric field: the local electric field is formed between the upper surface and the lower surface of the light absorption layer of the first sub-cell, and the local electric field causes the top surface to
  • the migrating ions in the light-absorbing layer of the cell are unevenly distributed on the upper and lower surfaces of the light-absorbing layer of the top cell to leave channels for carriers to be extracted.
  • the height of the above-mentioned sub-wavelength structure is not less than 200 nm.
  • the period length of the above-mentioned sub-wavelength structure is not greater than 700 nm.
  • the above-mentioned sub-wavelength structure is formed using a texturing process of crystalline silicon cells.
  • the second sub-cell is prepared using a silicon substrate with nanotexture, or a nanotexture is formed on the silicon substrate through a texturing process, and the nanotexture is a nanopyramid texture or a nanoblack silicon texture.
  • the period length of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm; when the nano suede is a nano black silicon suede, the height of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm. Less than 200nm, and the period length is no more than 700nm.
  • Embodiments of the present application also provide a method for preparing a multi-junction solar cell, including: forming an interface of a sub-wavelength structure at the interface between the first sub-cell and the second sub-cell, and the period length of the sub-wavelength structure is is smaller than the minimum wavelength of the absorption band of the second sub-cell.
  • a method for preparing a multi-junction solar cell including: preparation of a first sub-cell and preparation of a second sub-cell.
  • the second sub-cell is The light-facing surface forms a sub-wavelength structure, and the period length of the sub-wavelength structure is smaller than the minimum wavelength of the absorption band of the second sub-cell.
  • the preparation method of the embodiment of the present application can solve the interface anti-reflection problem of tandem solar cells including perovskite/crystalline silicon, is well connected with existing processes, and is suitable for large-scale industrial production.
  • the above-mentioned sub-wavelength structure can also be equivalently constructed as a multi-layer anti-reflection film layer with a gradient transition of refractive index from the light-absorbing layer of the first sub-cell to the light-absorbing layer of the second sub-cell, and
  • the equivalent refractive index of the multi-layer anti-reflective coating can be optimized by optimizing the sub-wavelength structure to achieve the best anti-reflective effect.
  • the total thickness of all film layers between the light absorption layer of the first sub-cell and the light absorption layer of the second sub-cell is less than 100 nm.
  • the above-mentioned sub-wavelength structure is further configured to form the following local electric field: the local electric field is formed between the upper surface and the lower surface of the light absorption layer of the first sub-cell, and the local electric field causes the top surface to In the light absorbing layer of the battery
  • the migrating ions are unevenly distributed on the upper and lower surfaces of the light absorption layer of the first sub-cell to leave channels for carriers to be extracted.
  • the above-mentioned second sub-cell is a crystalline silicon cell
  • the height of the above-mentioned sub-wavelength structure is not less than 200 nm.
  • the period length of the above-mentioned sub-wavelength structure is not greater than 700 nm.
  • the second sub-cell is a crystalline silicon cell
  • the sub-wavelength structure can be formed using a texturing process of a crystalline silicon cell.
  • the second sub-cell is prepared using a silicon substrate with nanotexture, or a nanotexture is formed on the silicon substrate through a texturing process, and the nanotexture is a nanopyramid texture or a nanoblack silicon texture.
  • the period length of the nanotexture surface may be no less than 200 nm and no more than 600 nm.
  • the period length of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm; when the nano suede is a nano black silicon suede, the height of the sub-wavelength structure is not less than 300 nm and not greater than 600 nm. Less than 200nm, and the period length is no more than 700nm.
  • This embodiment provides a double-junction stacked battery.
  • the structure of the double-junction stacked battery is pin perovskite top cell/ITO/(n)poly-Si/SiO2/(n)c-Si. /(p+)c-Si/AlO x /SiO x N y /metal electrode
  • the pin perovskite top cell is a trans perovskite cell with a bandgap width of 1.67eV.
  • the crystalline silicon cell is a pin-structured TOPCon, and the poly-Si passivated contact is on one side of the crystalline silicon cell.
  • the front surface of the crystalline silicon cell (that is, the surface facing the incident light) is a nanotexture surface with an average pyramid height of 400nm (the angle between the hypotenuse and the base of the pyramid is 55 degrees, and the period length is about 560nm).
  • the specific method is to use KOH and additive solution etching on the surface of the silicon wafer with the (100) crystal orientation, and use the anisotropy of silicon to obtain a textured surface with a regular pyramid structure.
  • concentration of KOH, the type and concentration of additives, as well as the process temperature and time the size and uniformity of the pyramid structure can be controlled.
  • This embodiment provides a three-junction stacked cell.
  • its structure is nip perovskite top cell (bandgap width 1.8eV)/nip perovskite middle cell (bandgap width 1.4eV)/ ITO/(p)a-Si/(i)a-Si/(n)c-Si/(i)a-Si/(n)a-Si/ITO/metal electrode, among which, the crystalline silicon cell faces light
  • the surface is a nanosuede surface with an average microstructure height of 400nm.
  • the preparation method of the three-junction stacked battery is to bombard the surface of the crystalline silicon battery with high-energy plasma to form a nanotextured surface composed of the above microstructure, and then continue to prepare the subsequent film layers.
  • the equipment can eventually form an interface with a sub-wavelength structure at the interface between the crystalline silicon cell and the perovskite cell. Compared with the wet method, this method can obtain a sub-wavelength structure with a larger aspect ratio.
  • wet processes such as alkali polishing are used to remove damage on the surface of the crystalline silicon cell and impurities such as crystalline silicon and plasma reaction products remaining on the surface.
  • the absorption wavelength range of perovskite sub-cells is about 300nm-730nm, and the absorption wavelength range of crystalline silicon sub-cells is about 720nm-1000nm.
  • the nanotexture with subwavelength structure (period length 580nm) and the alkali polished surface structure, small texture structure and large texture structure produced by the existing technology are compared with the calculated light energy in the wavelength range of 720nm-1150nm. Integration is performed to obtain the numerical results shown in Figure 3.
  • the light transmission amount corresponding to the sub-wavelength structure nanotexture provided by this application is the largest, reaching 21.94mA/cm 2 , followed by the large texture structure (marked as large texture in the figure)
  • the anti-reflection advantage of the sub-wavelength structure nanotexture in the near infrared is better than that of the large textured structure, and is also better than that of the small textured structure and the planar structure.
  • FIG. 4 is a density distribution diagram of migrating ions.
  • the color depth in the figure represents the packing density of migrating ions. It can be intuitively seen that near the apex of the pyramid, the packing density of migrating ions is smallest, so a channel can be formed for carriers to be freely extracted.
  • FIG. 5 is a simulated experimental diagram of the relationship between the sum of the current density of the first sub-cell and the second sub-cell of the crystalline silicon/perovskite stacked cell and the height of the sub-wavelength structure (ie, the height of the pyramid in this experiment).
  • the results of this experiment show that when the height of the pyramid is less than 200nm, the sum of the current densities of the first sub-battery and the second sub-battery increases with the height of the pyramid; when the height of the pyramid is 200nm ⁇ 250nm, the sum of the current densities of the first sub-battery and the second sub-battery increases with the height of the pyramid.
  • the sum of the current densities of the sub-batteries slows down as the height of the pyramid increases and tends to saturation; when the height of the pyramid is greater than 250nm, the sum of the current densities of the first sub-battery and the second sub-battery reaches saturation and no longer changes with the height of the pyramid.
  • the height of the pyramid is 200nm ⁇ 250nm, that is, the sub-wavelength structure height 200nm ⁇ 250nm is the critical area to achieve optical gain.
  • the concentration of KOH, the type and concentration of the additives, and the process temperature and time are controlled to control the size and uniformity of the microstructure of the nanotexture surface to prepare nanotexture.
  • Surface crystalline silicon The microstructure of each sample was tested using an electron microscope, as shown in Figure 6. The measured period lengths of the nanotexture surface of the sample are 320nm, 420nm and 580nm respectively.
  • the battery preparation process was continued on the nanotextured crystalline silicon to prepare double-junction stacked battery 1, double-junction stacked battery 2 and double-junction stacked battery 3.
  • the structures of these double-junction stacked batteries are: Along the light incident direction, the sequence is p-i-n perovskite top cell/ITO/(n)a-Si/(i)a-Si/(n)c-Si/(i)a-Si/(p)a- Si/ITO/metal electrode. Then the reflectivity of double-junction tandem battery 1, double-junction tandem battery 2 and double-junction tandem battery 3 in the wavelength range of 300-1200nm is tested, as shown in Figure 7.
  • the double-junction tandem battery 1, double-junction tandem battery 2 and double-junction tandem battery 3 made of crystalline silicon corresponding to 320nm, 420nm and 580nm nanotexture have sub-wavelength structured nanotextures.
  • the size consistency of the surface unit structure is relatively good, with an extremely low reflectivity of close to 1% in the wavelength range of 450nm to 1000nm, and a moderate increase in reflectivity in the wavelength range of 1000nm to 1200nm, reaching a maximum of 30% at a wavelength of 1200nm.
  • the light trapping effect is better than any currently known crystalline silicon/perovskite double-junction tandem cells.
  • the double-junction tandem cell 3 made of nanotextured crystalline silicon with a period length of 580 nm has the best reflectance data.
  • test structure is a pure silicon wafer, that is, the optical test is directly performed on the silicon wafer or crystalline silicon cell formed with a sub-wavelength structure. Since the refractive index difference between the silicon wafer and air is too large (the refractive index of air is 1, the refractive index of crystalline silicon The coefficient is 3.6), the sub-wavelength structure will not be able to play a very good anti-reflection effect. In actual situations, there are some dielectric materials or top cell materials on the surface of the silicon wafer. Their refractive index is usually between the refractive index of air and the refractive index of crystalline silicon, which plays a good transition role. , so that the overall anti-reflection performance of the corresponding photovoltaic cells is better than that of photovoltaic cells with conventional suede structures or photovoltaic cells with small suede structures. volt battery.
  • the multi-junction solar cell includes a first sub-cell and a second sub-cell located on the backlight surface of the first sub-cell.
  • the structure of the interface between the first sub-cell and the second sub-cell is a sub-wavelength structure.
  • the period length of the wavelength structure is smaller than the minimum wavelength of the absorption band of the second sub-cell.
  • the multi-junction solar cells, perovskite crystalline silicon stack cells, crystalline silicon cells and preparation methods thereof disclosed in the present application are reproducible and can be applied in various industrial applications.
  • the multi-junction solar cells, perovskite crystalline silicon stack cells, crystalline silicon cells and preparation methods thereof of the present application can be applied in the field of solar cell technology.

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Abstract

本申请提供一种多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法，涉及太阳能电池技术领域，能够解决叠层太阳能电池的界面减反问题，在底层电池吸收的宽波段和大范围内实现低反射，并且解决方案适合大规模工业化生产。本申请提供的多结太阳能电池，包括第一子电池和位于所述第一子电池背光面的第二子电池，所述第一子电池与所述第二子电池的界面的结构为亚波长结构，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。

Description

多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法
相关申请的交叉引用
本申请要求于2022年8月5日提交中国国家知识产权局的申请号为202210940341.1、名称为“多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及太阳能电池技术领域，尤其涉及一种多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法。
背景技术
为提高太阳能电池对太阳光的利用效率，可以将具有不同禁带宽度的半导体材料组合起来，分别吸收不同波长范围的入射光，由此产生了双结、三结等多结叠层太阳能电池(以下简称多结电池)。多结叠层太阳能电池中目前最受关注的是钙钛矿/晶硅叠层太阳能电池，该叠层电池理论上的光电转换效率可高达43％，现已被快速提升至29.8％，但该叠层电池的产业化仍然受到很多限制。
技术问题
本申请提供的多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法，能够改善包括钙钛矿/晶硅在内的叠层太阳能电池的界面减反问题，并且该解决方案适用于工业化生产。
申请内容
第一方面，本申请的实施例提供一种多结太阳能电池，包括第一子电池和位于所述第一子电池背光面的第二子电池，所述第一子电池与所述第二子电池的界面的结构为亚波长结构，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。
可选地，所述第一子电池的光吸收层与所述第二子电池的光吸收层之间的所有膜层的总厚度小于100nm。
可选地，所述亚波长结构还被配置为形成局部电场：所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使所述第一子电池的光吸收层中的迁移离子不均匀地分布在所述光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
可选地，所述亚波长结构的高度不小于200nm。
可选地，所述第二子电池为晶硅电池，所述亚波长结构的周期长度不大于700nm。
可选地，所述亚波长结构位于所述晶硅电池的迎光面。
可选地，所述亚波长结构通过晶硅电池的制绒工艺形成。
可选地，所述第二子电池的采用具有纳米绒面的硅基底，使所述第一子电池与所述第二子电池的界面的结构为亚波长结构。
可选地，所述纳米绒面为纳米金字塔绒面或纳米黑硅绒面。
可选地，所述纳米金字塔绒面的金字塔的底部边长为300～600nm。
可选地，所述纳米黑硅绒面的绒面高度不小于200nm。
可选地，所述第一子电池为单结电池或多结电池；所述第一子电池的光吸收层的材料选自钙钛矿、砷化镓、铝砷化镓和磷化镓铟中的一种或多种。
第二方面，本申请的实施例提供一种钙钛矿晶硅叠层电池，包括第一子电池和第二子电池，所述第一子电池为钙钛矿电池，所述第二子电池为晶硅电池；所述钙钛矿电池包括透明导电层、第一传输层、钙钛矿层、第二传输层；其中，所述第一传输层和所述第二传输层其中之一为电子传输层，另一为空穴传输层；所述晶硅电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。
第三方面，本申请的实施例还提供一种晶硅电池，所述晶硅电池的迎光面结构为亚波长结构，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。
第四方面，本申请的实施例还提供一种晶硅电池的制备方法，包括：绒面制备工序，所述绒面制备工序包括：提供硅基底，使所述硅基底形成亚波长结构的迎光面，所述亚波长结构的周期长度小于所述晶硅电池吸收波段的最小波长。
第五方面，本申请的实施例还提供一种多结太阳能电池的制备方法，包括：使所述第一子电池与所述第二子电池的交界处形成亚波长结构的界面，所述亚波长结构的周期长度小于所述第二子电池吸收波段的最小波长。
使所述第一子电池与所述第二子电池的交界处形成亚波长结构的界面，包括：在所述第二子电池的制备工序中，利用制绒工艺使所述第二子电池形成所述亚波长结构的迎光面。
附图说明
图1为本申请一些实施例提供的多结太阳能电池的示意图；
图2为晶硅电池的纳米金字塔绒面的等效折射率计算原理示意图；
图3为本申请的实验1提供的具有亚波长结构的纳米绒面与相关技术制得的平面结构、小绒面结构和大绒面结构在波长720-1150nm范围内对透过光能进行积分的结果对比示意图；
图4为本申请的实验2提供的周期长度为600nm的金字塔绒面中一金字塔附近的迁移离子的密度分布模拟实验图；
图5为本申请的实验3提供的晶硅/钙钛矿叠层电池的第一子电池和第二子电池的电流密度总和与亚波长结构高度的关系模拟实验图；
图6为本申请的实验4提供的纳米绒面的电子显微图；
图7为本申请的实验4提供的晶硅/钙钛矿叠层电池在300-1200nm波长范围内测得的反射率图(晶硅电池中的金字塔的底部边长分别为320nm、420nm和580nm)。
具体实施方式
为使本申请实施例的目的、技术方案和优点更加清楚，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本文描述中使用的缩略语和关键术语
亚波长结构
亚波长结构是指结构的特征尺寸与工作波长相当或更小的周期(或非周期)结构。亚波长结构的特征尺寸小于工作波长，它的反射率、透射率、偏振特性和光谱特性等都显示出与常规光学元件截然不同的特征，因而具有更大的应用潜力。亚波长结构的周期长度指上述周期(或非周期)结构的长度。
在本申请中，亚波长结构的特征尺寸可以理解为组成亚波长结构的单元结构的平均尺寸，或单元结构的尺寸的统计中位值，一般取大部分数值(例如总数量的75％以上)分布区间的平均值。当亚波长结构指层结构表面上周期性或者非周期性阵列的若干凸起组成的结构时，本申请中的单元结构即为组成亚波长结构的凸起，亚波长结构的周期长度即凸起的底部直径，可参照图4中的L所示。
对于晶硅电池作为底电池的叠层电池，晶硅电池的吸收波段主要集中在720nm-1200nm，因此本申请方案中的亚波长结构的单元结构的尺寸小于720nm，即要 求大部分单元结构的尺寸小于720nm。具体实施时，为最大化晶硅电池的光吸收，亚波长结构中的单元结构的尺寸一般小于700nm，即可在大于700nm的波段实现低反射。
移动离子(或迁移离子)
钙钛矿光吸收层是一层离子晶体，由于其简单的低温制备工艺和后期运行中受到的环境压力，钙钛矿光吸收层中易产生大量的浅能级缺陷；此外，这种浅能级缺陷同时也是一种离子，可以在钙钛矿电池中可以相对自由地迁移，因此也可以称之为迁移离子。当平面结构或大绒面结构的钙钛矿/晶硅叠层电池或者平面钙钛矿电池工作时，这些迁移离子在电池运行过程中会均匀地覆盖在钙钛矿光吸收层的上表面和下表面处，导致载流子抽取困难，从而使得钙钛矿光吸收层的填充因子和电流密度降低。
纳米金字塔绒面
传统的碱刻蚀制绒方法是在晶硅表面(晶向100)，利用各向异性的刻蚀特性，在晶硅表面形成金字塔形状(以下简称金字塔)的周期结构。传统的金字塔的高度约为2μm-6μm。通过调控碱液的类型或浓度、碱液添加剂的方案和配比、反应温度和时间，可以调控金字塔的尺寸。当晶硅表面阵列的金字塔的周期长度以及金字塔的高度均小于1μm时，阵列的金字塔组成的表面结构称之为纳米金字塔绒面。
纳米黑硅绒面
黑硅绒面是指用湿法(金属辅助化学刻蚀)或者干法(等离子体刻蚀)在晶硅表面形成的绒面结构。传统的黑硅绒面结构的微结构的高度约为2-5μm，相对于碱刻蚀制绒方法，黑硅绒面的微结构具有更大的高宽比，因此有利于陷光。黑硅绒面中微结构的高度可以通过调整工艺气体、溶液浓度以及刻蚀时间来调整。当黑硅绒面的微结构的周期长度以及微结构的高度均小于1μm时，称之为纳米黑硅绒面。
目前的叠层电池中晶硅底电池的迎光面目前有三种结构：平面结构、小绒面结构与大绒面结构。当晶硅底电池的迎光面为经抛光处理的平面结构时，由于，平面结构对可见光子和近红外光子的反射损失较大，因此不适合产业化生产。当晶硅底电池的迎光面采用高度为0.9-1.1μm的小绒面结构时，可以利用小绒面结构的金字塔表面的多次反射吸收原理，减少近红外反射损失。但这种小绒面结构对于钙钛矿光吸收层的厚度要求超过1μm，对钙钛矿光吸收层的薄膜质量要求也高，故工艺难度大，难以进行工业化生产。当晶硅底电池的迎光面采用高度为2-3μm的大绒面结构时，虽然大绒面结构的近红外反射损失相对较小，但要求钙钛矿光吸收层与传输层能保形覆盖大绒面结构的晶硅底电池， 一般需要采用CVD和PVD沉积，工艺难度大、流程复杂、成本高，目前还无法使用适合工业化生产的溶液法制备。
对于包括第一子电池、第二子电池的太阳能电池，第一子电池层叠于第二子电池之上，本申请将第一子电池与第二子电池的界面配置为亚波长结构，例如可在第二子电池的迎光面形成亚波长结构。该亚波长结构的周期长度小于第二子电池的吸收波段的最小波长，射向第二子电池的入射光的波长无法识别尺寸小于第二子电池的吸收波段的微小结构(即本申请的亚波长结构)，因此根据光学理论，这些亚波长结构可以等效为具有中间折射率(介于第一子电池的体相折射率与第二子电池的体相折射率之间)的减反膜层，能有效突破第一子电池、第二子电池之间的光学差异，引导光子从第一子电池进入第二子电池，从而降低第二子电池吸收波段的反射率，从整体上提高电池的光子吸收及转化效率。此外，由于亚波长结构的尺寸较小，第二子电池表面相对平整，其对于第一子电池的光吸收层的膜厚和膜层质量要求降低(第一子电池的光吸收层无需达到1μm)，因此降低了第一子电池的工艺难度(使得第一子电池的光吸收层可以用溶液法制备)，有利于太阳能电池的工业化生产。
在之前的叠层电池应用中，普遍采用常规绒面结构(如金字塔尺寸在2μm以上)，或者小绒面结构(如金字塔尺寸在1μm左右)。对常规绒面结构和小绒面结构而言，由于吸收光的波长小于绒面结构的微结构大小，其降低反射的策略是以在电池内实现多次反射为目标，减少对外反射，从而提升光吸收；而本申请提供的叠层电池，是通过亚波长结构来降低光反射的策略来达到减少对外反射的目的。
下面结合具体实施例对本申请的技术方案进行说明。
本申请的一些实施例提供一种多结太阳能电池，包括第一子电池和位于第一子电池背光面的第二子电池，第一子电池与第二子电池的界面的结构为亚波长结构，该亚波长结构的周期长度小于第二子电池的吸收波段的最小波长。
可选地，作为一种实施方式，所述第二子电池的迎光面的结构为所述亚波长结构，第一子电池的各膜层形成于所述迎光面的亚波长结构之上。
本实施例的多结太阳能电池中，第一子电池层叠于第二子电池之上，入射光先穿过第一子电池，再进入第二子电池。每个子电池均有对应的主要吸收波段(以下简称吸收波段)，这个主要由其光吸收层的禁带宽度决定，同时光吸收层的材料厚度、反射率以及是否掺杂等因素也会影响其具体取值。每一子电池能将吸收波段内的光能吸收并高效 率转化为电能，对吸收波段之外的光能则吸收很少或者不吸收。
本实施例第一子电池与第二子电池的交界处形成有亚波长结构，该亚波长结构包括多个单元结构，所述单元结构的平均尺寸小于第二子电池对应的吸收波段的最小波长。
可选的，如图1所示，所述第一子电池为钙钛矿电池(如图1中所示的Perovskite部分)，第二子电池为晶硅电池(如图1中所示的c-Si sub cells部分)。钙钛矿电池与晶硅电池交界处形成亚波长结构，所述亚波长结构的组成部分的尺寸(即单元结构的尺寸，技术人员称之为亚波长结构的周期长度，以下统一为周期长度)小于晶硅电池最小吸收波长。
示例性地，对于晶硅/钙钛矿叠层电池，钙钛矿子电池作为顶电池，其吸收波段一般设计为300nm～750nm，晶硅子电池作为底电池，吸收波段一般设计为700nm～1200nm。当本实施例方案应用于晶硅/钙钛矿叠层电池时，晶硅子电池的迎光面的结构可为周期长度小于700nm的亚波长结构，即组成亚波长结构的单元结构的平均尺寸可小于700nm，或者说大部分亚波长结构的尺寸分布在小于700nm的范围内。
上述第一子电池的光吸收层的材料除宽带隙钙钛矿之外，还可以选择砷化镓(1.43eV)、铝砷化镓(1.42eV-2.16eV)和磷化镓铟等宽带隙材料；上述第二子电池的光吸收层的材料除了晶硅外，还可以选择铜铟镓硒(1.02eV-1.67eV，带隙可调)、碲化镉(1.46eV)、窄带隙钙钛矿和砷化镓(1.424eV)等窄带隙材料。本申请中第一子电池的光吸收层的材料的带隙宽度要大于第二子电池的光吸收层的材料的带隙宽度，因此此处的宽带隙材料与窄带隙材料是相对而言的。
另外，需要说明的是，本申请的亚波长结构中的单元结构优选周期性分布，具体实施时也可以是不严格的周期性分布。
示例性地，对于晶硅电池，其亚波长结构多通过湿法制绒工序或干法制绒工序得到，亚波长结构一般包括金字塔形状或者接近金字塔形状(以下简称金字塔)的凸起，其单元结构的尺寸L一般为金字塔的底部四边形的平均边长或边长统计分布的中位数，即所述亚波长结构的周期长度一般可为金字塔的底部四边形的平均边长或边长统计分布的中位数，具体可参照图4所示。
示例性地，本实施例的亚波长结构可以表现为分布在第二子电池的顶层膜层的微小凸起或者该顶层膜层多个局部向上凸起形成的微小凸起，微小凸起的平均底部直径或统计底部直径分布的中位数小于第二子电池的吸收波段的最小值。微小凸起的形状例如为 四面椎体形状或金字塔形状。
本领域技术人员可以理解的是，上述亚波长结构可以与第二子电池一体形成，也可以是独立于第二子电池形成，只要亚波长结构的特征尺寸在合适尺寸范围内，能够使叠层电池在第二子电池的吸收波段实现良好的抗反射效果即可。
本领域技术人员可以理解的是，第一子电池与第二子电池界面处的亚波长结构，能在第一子电池与第二子电池之间等效构建折射率介于第一子电池、第二子电池的体相折射率之间的等效介质膜层，从而改善第一子电池、第二子电池之间的光学差异，引导光子从第一子电池进入第二子电池，降低第二子电池吸收波段的反射率，从整体上提高电池的光子吸收及转化效率。亚波长结构的选材满足上述要求。
在一些实施例中，亚波长结构采用与第二子电池相同或者折射率接近的材料，亚波长结构的上方填充与第一子电池相同或者折射率接近的材料，例如钙钛矿材料。
亚波长结构的材料折射率与第二子电池的体相材料(第二子电池的光吸收层的材料)接近，亚波长结构能等效构建折射率介于第一、第二子电池体相折射率之间的等效介质膜层，能对进入第二子电池的光产生减反效果(换言之，能在第二子电池的吸收波段达到减反效果)，本申请对亚波长结构的具体材质并不做限定。
如图1所示，一些实施例中，亚波长结构的单元结构的形状为金字塔形状，其材质与第二子电池同材质；金字塔形状的上方为钙钛矿子电池的各膜层，由于各膜层中钙钛矿吸光层最厚，第二子电池体相折射率指钙钛矿吸光层的折射率。
本申请方案尤其适用于第一子电池、第二子电池体相折射率差异较大导致界面反射较大的叠层电池，例如钙钛矿/晶硅叠层电池。其中，钙钛矿材料折射率约为2.34-2.38，晶硅折射率为3.42。
本领域技术人员可以理解的是，本申请还可以在图1中第一子电池光吸收层以下的任意膜层或者叠层电池的基底上设置微结构，使得第一子电池、第二子电池交界处为亚波长结构的界面，从而降低第二子电池迎光面的反射光。
例如，在一些实施例中，晶硅/钙钛矿叠层电池中的晶硅电池可采用金字塔绒面的硅基底，且金字塔绒面的微结构(即金字塔)的周期长度小于晶硅的吸收波段的最小波长，例如小于700nm，这样在晶硅电池的迎光面形成具有减反效果的亚波长结构。在此实施例中，可以直接在晶硅电池的硅基底的制绒工艺中控制碱液的浓度、添加剂的种类和浓度，以及工艺温度和时间，控制硅基底表面形成的绒面的微结构(例如金字塔)的尺寸， 使微结构的尺寸小于晶硅电池的吸收波段的最小波长，从而在第一子电池、第二子电池交界面形成亚波长结构，无需额外增加形成亚波长结构的工序。
上述的第二子电池至少包括一层光吸收层。
上述的第二子电池还可进一步包括减反层，和/或，用于收集载流子的金属电极层。
另外，本实施例的多结太阳能电池除上述的第一子电池、第二子电池外，还可以包括其他膜层(例如复合层或隧穿层)，或者还可以进一步包括其他子电池，或包括其他未提及的电池结构，本实施例对此不做限定。
本实施例的多结太阳能电池，在其中的第一子电池、第二子电池交界处形成亚波长结构的界面，构成仿生蛾眼结构，能有效突破第一子电池、第二子电池之间的光学差异，引导光子从第一子电池进入第二子电池，可以在宽波段和大范围内实现了低反射，从而整体上提高电池的光子吸收及转化效率。
在一些实施例中，所述亚波长结构用于等效构建自所述第一子电池的光吸收层到所述第二子电池的光吸收层的折射率梯度渐变过渡的多层减反膜层。等效构建的各减反膜层，如果折射率过渡越平滑，减反效果越佳。因此，在一些实施例中，所述亚波长结构按等效折射率平滑过渡的方式构成。
在一些实施例中，亚波长结构中的单元结构为楔形结构，使所述亚波长结构相当于等效构建了自所述第一子电池的光吸收层到所述第二子电池的光吸收层的折射率梯度渐变过渡的多层减反膜层，能改善第一、第二子电池之间的光学差异，引导光子从第一子电池进入第二子电池，从而降低第二子电池吸收波段的反射率，从整体上提高电池的光子吸收及转化效率。
为便于理解，下面对亚波长结构原理进行简单介绍。如图2中(a)为晶硅电池的纳米金字塔绒面，按10nm的厚度等厚分层的示意图；图2的(a)中每层都可以认为是10nm厚度的局部晶硅膜加外围的介质膜(主要是第一子电池的光吸收层)，如图2中(b)所示。可以参照洛伦兹-洛伦兹(Lorentz-Lorenz)方程，计算等效折射率。等效折射率与等厚分层的膜层中两种介质的空间比值(空间占用率)相关，可通过优化亚波长结构各层中两种介质的空间比值(简化的模拟计算中，介于晶硅电池的光吸收层与钙钛矿电池的光吸收层之间的其他膜层厚度小，空间占比过小，可忽略不计)，将亚波长结构等效构建为自钙钛矿电池到晶硅电池的折射率梯度渐变过渡的多层减反膜层，且等效后的多层减反膜层能引导近红外及红外波段的光子高效地从钙钛矿电池进入晶硅电池，在宽 波段和大范围内(晶硅吸收波段)实现了低反射，从而增加晶硅子电池的光转化率。
图2中(c)为图2中(b)等效的多层减反膜层。从介质1(钙钛矿)向介质2(晶硅)的方向，每一层的介质2的占有率连续增加，介质1的占有率连续减小，因此，可以实现有效折射率也从介质1到介质2连续变化。此时，由于每层与相邻层的折射率差很小，所以各层的菲涅耳反射率也很小。每一层的介质占有率从100％的介质1向100％的介质2逐渐变化，每层等效的有效折射率也从介质1的折射率到介质2的折射率渐变。如上所述，通过优化本实施例的亚波长结构的横截面介质占有率能实现从介质1向介质2的渐变，在第二电池的吸收波段得到想要的减反效果。
优选地，亚波长结构的单元结构的形状为金字塔形状。因为从介质1(钙钛矿)向介质2(晶硅)的方向，金字塔形状会使得介质占有率和有效折射率过度更平滑，减反效果更佳。
在一些实施例中，所述第一子电池的光吸收层与所述第二子电池的光吸收层之间的所有膜层的总厚度小于100nm。
在第一子电池的光吸收层和第二子电池的光吸收层之间一般会有折射率更低的复合层和传输层，而两个子电池的光吸收层的折射率一般相对较大，因此界面处存在明显的折射率失配，而折射率失配会导致更多的反射损失。因此，第一子电池的光吸收层与第二子电池的光吸收层之间的所有膜层的总厚度小于100nm时，根据相关的等效介质理论，这些膜层在亚波长结构横截面所占的比例与第一子电池、第二子电池的光吸收层相比可忽略，因此通过优化亚波长结构，等效构建自第一子电池光吸收层到第二子电池的光吸收层的折射率渐变过渡的多层减反膜层，可以很好地将突变的折射率转化为梯度变化的等效折射率，从而降低反射损失对界面层厚度的敏感性，从而使复合层和传输层的设计更自由。
另外，在有些多结太阳能电池，如平面结构或者大绒面结构的钙钛矿/晶硅叠层电池或者平面钙钛矿电池中，迁移离子在电池运行过程中会均匀覆盖在钙钛矿上下界面处，导致载流子抽取困难，从而使得填充因子和电流密度降低。对于这一缺陷，本实施例提供的多结太阳能电池，在第一子电池、第二子电池的交界处形成亚波长结构的界面，并通过优化亚波长结构的高度，可以在第一子电池(如钙钛矿电池)的上表面和下表面处形成适当的局部电场。在电池运行过程中，该局部电场可以使第一子电池光吸收层中的迁移离子不均匀地分布在第一子电池的光吸收层的上表面和下表面，从而留出载流子可 被自由抽取的通道。实验证明，这个适当的局部电场对应的亚波长结构的单元结构的高度不小于200nm。单元结构的高度特指单元结构在与太阳能电池基底大体垂直的方向上的长度。具体实施时，此处的高度可理解为组成整个亚波长结构的多个单元结构的平均高度，或者多个单元结构统计意义上的高度中位数。例如，不低于75％的单元结构的高度分布在高度不小于200nm的范围内即满足这一条件。
假设钙钛矿光吸收层里面的迁移离子的密度是单位面积1016(平均分布状态)，在平面结构中，当有电场作用时，迁移离子会向界面处堆积，这个时候在界面处的密度可能高达单位面积1021，从而形成一个导电能力非常低的界面，不利于载流子抽取。但如果使用本申请所提供的亚波长结构，钙钛矿光吸收层的上下两个界面处的电场分布会是不均匀的，迁移离子受到电场的吸引，其密度在界面处的分布也会不均匀，可能有些地方迁移离子的密度为单位面积1021，而有些地方迁移离子的密度为单位面积1016，那载流子就可以绕过迁移离子堆积量大的地方，顺利的从迁移离子堆积量比较少的界面处发射出去。图4为周期长度L为600nm的亚波长结构(金字塔绒面)的迁移离子密度分布模拟实验图，图中用颜色深浅表示迁移离子的堆积密度。结果显示，在金字塔的塔尖附近，迁移离子的堆积密度最小，可以形成供载流子被自由抽取的通道。
钙钛矿电池刚制作完的时候一般迁移离子的量会比较少，不容易看出来。但是在长期运行以后，迁移离子的数量，即浅能级缺陷的数量会慢慢上升，进而逐渐影响转化效率。本申请通过亚波长结构降低迁移离子的影响，从而对叠层电池的长期稳定性产生有利的影响。
采用具有尖端的亚波长结构可降低迁移离子的影响，提高叠层电池的长期稳定性。
图5为晶硅/钙钛矿叠层电池的第一子电池和第二子电池的电流密度总和与亚波长结构高度的关系模拟实验图。实验结果显示，在金字塔高度小于200nm时，第一子电池和第二子电池的电流密度总和随金字塔的高度增加而增加；金字塔的高度大于等于200nm时，第一子电池和第二子电池的电流密度总和随金字塔的高度增加变缓，并逐渐趋于饱和；金字塔的高度大于250nm时，第一子电池和第二子电池的电流密度总和不再随金字塔的高度增加而变化。因此，当亚波长结构高度不小于200nm时，叠层电池可以实现很好的光学效果；亚波长结构的高度大于等于250nm时，叠层电池光学效果更好。
更进一步地，参照图7的反射率测试数据，作为亚波长结构的周期长度不小于300nm，且不大于600nm时，在这个区间对应的实验结果参数更佳。因为当金字塔高度大于 200nm(对应金字塔的底边长约280nm)时，第一子电池和第二子电池的电流密度总和趋于饱和，光学增益极为明显，也就是减反效果也更优，但是光学增益并不能全部转化为电学增益。最终我们的实验表明：金字塔绒面在周期长度300nm～600nm范围，实际获得电学参数效果更佳。
对于纳米黑硅绒面，所述亚波长结构的单元结构的高度不小于200nm，且周期长度L不大于700nm，光学减反效果比较好。优选地，纳米黑硅绒面在周期长度200nm～400nm的范围内且高度不小于200nm，实际获得电学参数效果更佳。
本申请提供的亚波长结构同时还会使第一子电池光吸收层的内建电场的分布产生极大的变化。局部的内建电场强度减小，使得迁移离子的迁移势能减小，可以提高第一子电池的光吸收层(例如钙钛矿电池)及叠层光伏器件的稳定性。
示例性地，本申请还提供一种采用本申请的亚波长结构的晶硅/钙钛矿叠层电池，该叠层电池的晶硅电池的迎光面采用高度大于250nm、且周期长度小于700nm的纳米金字塔绒面或纳米黑硅绒面。由于纳米金字塔绒面或纳米黑硅绒面的异性结构，可以在钙钛矿光吸收层的上表面和下表面处形成局部电场，在电池运行过程中，局部电场可以使钙钛矿光吸收层中的迁移离子不均匀地分布在钙钛矿光吸收层的上表面、下表面，从而留出载流子可被自由抽取的通道。异型结构的钙钛矿光吸收层同时导致钙钛矿光吸收层的内建电场分布产生极大的变化，局部的电场强度减小，使得迁移离子的迁移势能减小，对钙钛矿电池与钙钛矿/晶硅叠层光伏器件的稳定性有很大的帮助。换言之，本申请的特定尺寸的纳米金字塔绒面或纳米黑硅绒面，可以提高钙钛矿顶电池对浅能级缺陷的容忍度，从而使得叠层器件效率提升。
在一些实施例中，上述亚波长结构的周期长度进一步优选为不小于200nm，且不大于600nm。亚波长结构在200nm～600nm区间时，可以达到如下效果：(1)界面减反或陷光效果好；(2)可以降低反射损失对界面层(位于第一子电池的光吸收层与第二子电池的光吸收层之间的复合层和传输层等)的厚度的敏感性，两个子电池的光吸收层之间的透明导电电极和传输层等界面层的厚度设计更自由；(3)对第一子电池的成膜工艺的要求低。第二子电池的上表面相对比较平整(与晶硅的大绒面结构以及常规的小绒面结构相比而言)，第一子电池的光吸收层(例如钙钛矿)不必须是大于1μm的厚膜，对成膜质量的要求也降低，使第一子电池光吸收层可以使用溶液法制备，有利于太阳能电池的工业化生产。对于钙钛矿/晶硅电池，采用本申请的亚波长结构，钙钛矿光吸收层厚度 约300纳米(从金字塔塔尖处起算)或800nm(金字塔的最低处起算)，叠层电池样品的电学参数都比较好。(4)另外，第一子电池的光吸收层形成的内建电场的局部电场强度减小，使得迁移离子的迁移势能减小，对第一子电池的光吸收层以及包括第一子电池、第二子电池的叠层光伏器件的稳定性有很大的帮助。
在一些实施例中，上述第二子电池可以为晶硅电池；此时所述亚波长结构可通过晶硅电池的制绒工艺形成。晶硅电池可以是多晶硅电池或单晶硅电池。晶硅电池的结构包括但不限于PERC(Passivated Emitter and Rear Cell，钝化发射器和后部接触)，TOPCon(Tunnel Oxide Passivated Contact，隧穿氧化层钝化接触)或者HJT(silicon hetero junction，硅异质结)结构。
例如，第二子电池的采用具有纳米绒面的硅基底，纳米绒面的周期长度不小于300nm，且不大于600nm，可以在第一子电池、第二子电池的界面处形成抗反射的亚波长结构。所述亚波长结构可以为纳米金字塔绒面，或者纳米黑硅绒面。纳米绒面指纳米尺度的微结构绒面，可以通过碱和添加剂，或者金属催化化学刻蚀的湿法工艺，也可以使用等离子刻蚀的干法工艺来实现。
在一些实施例中，上述第一子电池为单结电池或多结电池，所述第一子电池的光吸收层的材料可以选择钙钛矿、碲化镉、铜铟镓硒、砷化镓、磷化镓铟和砷化镓铝中的一种或多种。
本申请实施例还提供一种钙钛矿叠层电池，沿光入射方向由上至下依次设置有第一子电池和第二子电池，所述第一子电池为钙钛矿电池，所述第二子电池为晶硅电池；所述钙钛矿电池包括：透明导电层、第一传输层、钙钛矿层、第二传输层；其中，所述第一传输层和所述第二传输层，其中之一为电子传输层，另一为空穴传输层；
所述晶硅电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度尺寸小于所述晶硅电池的吸收波段的最小波长。
所述亚波长结构可通过晶硅电池的硅基底的第一次制绒工艺形成，晶硅电池的结构包括但不限于PERC，TOPCon或者HJT结构。亚波长结构的单元结构的尺寸小于晶硅电池的吸收波段的最小波长，使射向晶硅电池的入射光的波长无法识别其微小的结构，类似于纳米仿生学的蛾眼结构，使其能有效突破晶硅电池与钙钛矿电池之间的光学差异，引导光子从钙钛矿电池进入晶硅电池，从而降低晶硅电池吸收波段的反射率，从整体上提高叠层电池的光子吸收及转化效率。此外，晶硅电池表面相对大绒面结构的晶硅电池 更平整，钙钛矿层成膜所需的质量要求降低，可以用溶液法制备，便于工业化生产。
钙钛矿电池还可以包括减反层和金属电极层。
晶硅电池和钙钛矿电池的中间还可存在一层复合层或者遂穿层，也可以没有，本申请对此不做限定。
上述透明导电层可以包括ITO、IZO、AZO、石墨烯和金属纳米线中的至少一种。
上述钙钛矿吸光层通式为ABX3，其中A为一价阳离子，包括但不限于锂、钠、钾、铯、铷、胺基或者脒基中的一种或几种阳离子；B为二价阳离子，包括但不限于铅、锡、钨、铜、锌、镓、硒、铑、锗、砷、钯、银、金、铟、锑、汞、铱、铊、铋、中的一种或几种阳离子；X为一价阴离子，包括但不限于碘、溴、氯或砹中的一种或几种阴离子。所述钙钛矿吸光层中的钙钛矿成分例如可以为Cs0.05FA0.80MA0.15PbI2.55Br0.35；其中Cs是铯，FA是甲脒基，MA是甲胺基，I是碘。
上述电子传输层可包括SnO2、TiO2、ZnO、ZrO2、富勒烯及衍生物、TiSnOX和SnZnOX中的至少一种。
所述空穴传输层包括PTAA、Poly-TPD、NiOx、P3HT、V2O5、MoOx、PEDOT:PSS、WOx、Spiro-OMeTAD、CuSCN、Cu2O、CuI、Spiro-TTB、F4-TCNQ、F6-TCNNQ、m-MTDATA和TAPC中的至少一种。
可选地，上述亚波长结构还可被配置为等效构建自钙钛矿光吸收层到晶硅电池的光吸收层的折射率梯度渐变过渡的多层减反膜层，并可通过优化亚波长结构来优化多层减反膜层的等效折射率，达到最佳减反效果。其中，钙钛矿光吸收层与晶硅电池的光吸收层之间的所有膜层的总厚度小于100nm。
可选地，上述亚波长结构还被配置为形成如下局部电场：所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使所述第一子电池的光吸收层中的迁移离子不均匀地分布在所述光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
可选地，上述亚波长结构的高度不小于200nm。
可选地，上述第二子电池采用晶硅电池，上述亚波长结构的周期长度不大于700nm。
可选地，上述亚波长结构利用晶硅电池的制绒工艺形成。
可选地，上述第二子电池制备时采用具有纳米绒面的硅基底，或者通过制绒工艺在硅基底上形成纳米绒面，所述纳米绒面为纳米金字塔绒面或者纳米黑硅绒面。所述纳米 绒面为纳米金字塔绒面时，所述亚波长结构的周期长度不小于300nm，且不大于600nm；所述纳米绒面为纳米黑硅绒面时，所述亚波长结构的高度不小于200nm，且周期长度不大于700nm。
可选地，所述第一子电池为电池单结或多结电池；所述第一子电池的光吸收层的材料选自钙钛矿、碲化镉、铜铟镓硒、砷化镓、磷化镓铟和砷化镓铝中的一种或多种。
上述叙述中多以两结太阳能电池为例进行说明，但本领域技术人员可以理解的是本申请技术方案还可以应用于三结、四结甚至更多结电池。
本申请的一些实施例还提供一种三结太阳能电池，最上层的第一子电池采用1.8ev左右的光吸收层；最下层的第三子电池采用约1.2ev的光吸收层，中间的第二子电池采用约1.4ev左右的光吸收层。在第一子电池与第二子电池的交界处，或者第二子电池与第三子电池的交界处采用本申请上述的亚波长结构的界面，同样可达到上面提到的提高界面减反效果从而提高电池的光子吸收及转化效率，降低反射损失对界面层厚度的敏感性及上层子电池的成膜工艺难度，增加叠层电池稳定性等有益效果。原理及方法大致类似，不再一一赘述。
在一些实施方式中，可以在第二子电池和第三子电池的迎光面均设置本申请所述的亚波长结构，其中，设置在第二子电池迎光面的亚波长结构的周期长度小于第二子电池的吸收波段的最小波长；设置在第三子电池迎光面的亚波长结构的周期长度小于第三子电池的吸收波段的最小波长。
本申请实施例还提供一种叠层电池中的底电池，所述底电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度小于所述底电池的吸收波段的最小波长。示例性地，底电池可为晶硅电池，所述亚波长结构周期长度不大于700nm。本实施例的底电池表面相对平整，且在自身的吸收波段减反或陷光效果好，适合做叠层电池的底电池，有利于降低上层顶电池成膜难度，便于工业化生产。
本申请实施例还提供一种晶硅电池，所述晶硅电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。示例性地，所述亚波长结构周期长度不大于700nm。
本实施例的晶硅电池表面相对平整，且在近红外及红外波段(700～1200nm)减反或陷光效果好，表面相对平整有利于降低上层顶电池成膜难度，适合做叠层电池的底电池，便于工业化生产。
可选地，上述亚波长结构还可配置为等效构建自叠层电池的顶电池光吸收层到晶硅电池光吸收层的折射率梯度渐变过渡的多层减反膜层，并可通过优化亚波长结构来优化多层减反膜层的等效折射率，达到最佳减反效果。其中，顶电池光吸收层与晶硅光吸收层之间的所有膜层的总厚度小于100nm。
可选地，上述亚波长结构还配置为形成下述的局部电场：所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使顶电池的光吸收层中的迁移离子不均匀地分布在顶电池光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
可选地，上述亚波长结构的高度不小于200nm。
可选地，上述亚波长结构的周期长度不大于700nm。
可选地，上述亚波长结构利用晶硅电池的制绒工艺形成。
可选地，上述第二子电池制备时采用具有纳米绒面的硅基底，或者利用制绒工艺在硅基底形成纳米绒面，所述纳米绒面为纳米金字塔绒面或者纳米黑硅绒面。所述纳米绒面为纳米金字塔绒面时，所述亚波长结构的周期长度不小于300nm，且不大于600nm；所述纳米绒面为纳米黑硅绒面时，所述亚波长结构的高度不小于200nm，且周期长度不大于700nm。
本申请实施例还提供一种晶硅电池的制备方法，包括：绒面制备工序，所述绒面制备工序包括：提供硅基底，使硅基底形成亚波长结构的迎光面，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。
所述亚波长结构周期长度不大于700nm。
在一些实施例中，绒面制备工序形成高度大于300nm，且周期长度小于700nm的纳米绒面。纳米绒面指包含纳米尺度的微结构的绒面，可以通过碱和添加剂，或者金属催化化学刻蚀的湿法工艺，也可以使用等离子刻蚀的干法工艺来实现。
如上所述，本申请实施例提供一种晶硅电池的制备方法，可以制备适合用作叠层电池的底电池，该底电池表层分布有周期长度小于700nm的亚波长结构。因该种晶硅电池作为底电池时表面相对平整，从而可降低顶电池工艺难度，有助于叠层电池的整体工艺产业化整合。
可选地，上述亚波长结构还可以等效构建自叠层电池的顶电池的光吸收层到晶硅电池光吸收层的折射率梯度渐变过渡的多层减反膜层，并可通过优化亚波长结构来优化多 层减反膜层的等效折射率，达到最佳减反效果。其中，顶电池的光吸收层与晶硅光吸收层之间的所有膜层的总厚度小于100nm。
可选地，上述亚波长结构还被配置为形成下述的局部电场：所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使顶电池的光吸收层中的迁移离子不均匀地分布在顶电池的光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
可选地，上述亚波长结构的高度不小于200nm。
可选地，上述亚波长结构的周期长度不大于700nm。
可选地，上述亚波长结构利用晶硅电池的制绒工艺形成。
可选地，上述第二子电池制备时采用具有纳米绒面的硅基底，或者通过制绒工艺在硅基底形成纳米绒面，所述纳米绒面为纳米金字塔绒面或者纳米黑硅绒面。
所述纳米绒面为纳米金字塔绒面时，所述亚波长结构的周期长度不小于300nm，且不大于600nm；所述纳米绒面为纳米黑硅绒面时，所述亚波长结构的高度不小于200nm，且周期长度不大于700nm。
本申请实施例还提供一种多结太阳能电池的制备方法，包括：在所述第一子电池与所述第二子电池的交界处形成亚波长结构的界面，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。
在一些实施例中，提供一种多结太阳能电池的制备方法，包括：第一子电池的制备和第二子电池的制备，所述第二子电池的制备工序中在所述第二子电池的迎光面形成亚波长结构，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。本申请实施例的制备方法能够解决包括钙钛矿/晶硅在内的叠层太阳能电池的界面减反问题，并且与现有工艺很好衔接，适合大规模工业化生产。
可选地，上述亚波长结构还可以等效构建自叠层电池的第一子电池的光吸收层到第二子电池的光吸收层的折射率梯度渐变过渡的多层减反膜层，并可通过优化亚波长结构来优化多层减反膜层的等效折射率，达到最佳减反效果。
其中，第一子电池的光吸收层与第二子电池的光吸收层之间的所有膜层的总厚度小于100nm。
可选地，上述亚波长结构还被配置为形成下述的局部电场：所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使顶电池的光吸收层中 的迁移离子不均匀地分布在第一子电池光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
可选地，上述第二子电池为晶硅电池，
可选地，上述亚波长结构的高度不小于200nm。
可选地，上述亚波长结构的周期长度不大于700nm。
可选地，上述第二子电池为晶硅电池，上述亚波长结构可利用晶硅电池的制绒工艺形成。
可选地，上述第二子电池制备时采用具有纳米绒面的硅基底，或者通过制绒工艺在硅基底形成纳米绒面，所述纳米绒面为纳米金字塔绒面或者纳米黑硅绒面。所述纳米绒面的周期长度可不小于200nm，且不大于600nm。
所述纳米绒面为纳米金字塔绒面时，所述亚波长结构的周期长度不小于300nm，且不大于600nm；所述纳米绒面为纳米黑硅绒面时，所述亚波长结构的高度不小于200nm，且周期长度不大于700nm。
为了进一步理解本申请技术方案，下面结合具体实施例进行说明。
实施例一
本实施例提供一种双结叠层电池，沿着光入射方向，双结叠层电池结构依次为p-i-n钙钛矿顶电池/ITO/(n)poly-Si/SiO2/(n)c-Si/(p+)c-Si/AlOx/SiOxNy/金属电极，p-i-n钙钛矿顶电池为反式钙钛矿电池，禁带宽度为1.67eV。晶硅电池为p-i-n结构的TOPCon，且晶硅电池单面poly-Si钝化接触。晶硅电池的前表面(即迎着入射光一侧的表面)为平均金字塔高度为400nm的纳米绒面(金字塔斜边与底边角度55度，周期长度约560nm)。具体的方法为在(100)晶向的硅片表面使用KOH与添加剂溶液刻蚀法，利用硅的各向异性得到正金字塔结构的绒面。通过控制KOH的浓度，添加剂的种类和浓度，以及工艺温度和时间，控制金字塔结构的大小以及均一性。
实施例二
本实施例提供一种三结叠层电池，沿着光入射方向，其结构依次为n-i-p钙钛矿顶电池(禁带宽度1.8eV)/n-i-p钙钛矿中电池(禁带宽度1.4eV)/ITO/(p)a-Si/(i)a-Si/(n)c-Si/(i)a-Si/(n)a-Si/ITO/金属电极，其中，晶硅电池的迎光面为微结构的平均高度为400nm的纳米绒面。该三结叠层电池的制备方法为在晶硅电池的表面用高能等离子体轰击使晶硅电池的表面形成上述微结构组成的纳米绒面，继续后续膜层制 备，最终可使晶硅电池与钙钛矿中电池的交界处形成亚波长结构的界面，此方法相较于湿法可以获得更大高宽比的亚波长结构。等离子工艺后使用碱抛等湿法工艺去除晶硅电池表面的损伤以及残留于表面的晶硅、等离子体反应生成物等杂质。
下面为本申请的实验数据
实验1：光学对比实验
对叠层电池而言，钙钛矿子电池的吸收波长的范围约为300nm-730nm，晶硅子电池的吸收波长的范围约为720nm-1000nm。将亚波长结构的纳米绒面(周期长度580nm)以及现有技术制得的碱抛平面结构、小绒面结构和大绒面结构在波长720nm-1150nm范围内，对按透过计算的光能进行积分，得到如图3中所示的数值结果。按图3所示的积分结果，本申请提供的亚波长结构的纳米绒面所对应的透光量最大，达到21.94mA/cm2，然后是大绒面结构(图中标示为大绒面)对应的透光量(21.35mA/cm2)和小绒面结构(图中标示为小绒面)对应的透光量(20.68mA/cm2)，最后是碱抛平面结构(图中标示为平面)对应的透光量(20.27mA/cm2)。但在此之前，本领域普遍认为，绒面结构中微结构的高度越高，陷光效果越好，因此为了达到更好的界面减反，太阳能电池中优先考虑大绒面结构，但大绒面结构要求上层光吸收层如钙钛矿层保形覆盖大绒面结构，因此工艺难度很大，难以工业化生产。对此，本申请通过形成特定周期长度例如周期长度为600nm的纳米绒面，既能获得比大绒面结构更佳的减反效果，又能为上层光吸收层如钙钛矿层提供相对较平整的基层平面，从而解决上述问题。通过实测钙钛矿/晶硅叠层电池的反射数据对比，亚波长结构的纳米绒面在近红外的减反优势优于大绒面结构，也优于小绒面结构和平面结构。
实验2：迁移离子模拟实验
构建周期长度L为600nm的金字塔绒面，在晶硅/钙钛矿叠层电池场景下模拟金字塔附近的电场以及在这样的电场中模拟迁移离子的迁移，稳定后提取迁移离子的密度分布数据。图4为迁移离子的密度分布图，图中用颜色深浅表示迁移离子的堆积密度。可以直观看出，在金字塔的塔尖附近，迁移离子的堆积密度最小，因此可以形成供载流子被自由抽取的通道。
实验3：亚波长结构高度模拟实验
构建单元结构的形状为金字塔形状，且周期长度L可变的晶硅/钙钛矿叠层模型，模拟叠层电池的第一子电池和第二子电池工作时的电流密度，提取第一子电池和第二子 电池的电流密度的数据并求和。图5为晶硅/钙钛矿叠层电池的第一子电池和第二子电池的电流密度总和与亚波长结构高度(即本实验中的金字塔的高度)的关系模拟实验图。本实验结果显示，当金字塔的高度小于200nm时，第一子电池和第二子电池的电流密度总和随金字塔的高度增加而增加；金字塔的高度为200nm～250nm时，第一子电池和第二子电池的电流密度总和随金字塔的高度增加变缓，并趋于饱和；金字塔的高度大于250nm时，第一子电池和第二子电池的电流密度总和达到饱和，不再随金字塔的高度变化。综上，金字塔的高度为200nm～250nm，即亚波长结构高度200nm～250nm是实现光学增益的临界区域。
实验3：晶硅/钙钛矿叠层电池实验
参照实施例一的方法，在进行纳米绒面刻蚀时通过控制KOH的浓度，添加剂的种类和浓度，以及工艺温度和时间，控制纳米绒面的微结构的大小以及均一性，制得纳米绒面晶硅。用电子显微镜测试各样品的微观结构，如图6所示。测得样片的纳米绒面的周期长度分别为320nm、420nm和580nm。分别在纳米绒面的晶硅上继续进行电池制备工艺，制备出双结叠层电池1、双结叠层电池2和双结叠层电池3，该些双结叠层电池的结构均为：沿着光入射方向，依次为p-i-n钙钛矿顶电池/ITO/(n)a-Si/(i)a-Si/(n)c-Si/(i)a-Si/(p)a-Si/ITO/金属电极。然后测试双结叠层电池1、双结叠层电池2和双结叠层电池3在300-1200nm波长范围内的反射率，如图7所示。可以看出，基于320nm、420nm和580nm的纳米绒面对应的晶硅制成的双结叠层电池1、双结叠层电池2和双结叠层电池3，其亚波长结构的纳米绒面的单元结构的尺寸一致性比较好，在450nm～1000nm波长范围内的具有接近1％的极低反射率，在1000nm～1200nm波长范围内反射率温和上升，最高在波长1200nm达到30％，比目前所知的任何晶硅/钙钛矿双结叠层电池的陷光效果都要好。其中，周期长度为580nm的纳米绒面的晶硅制成的双结叠层电池3的反射率数据最好。
本申请的实验直接基于叠层电池进行测试。如果测试结构是纯硅片，即直接对形成有亚波长结构的硅片或晶硅电池进行光学测试，由于硅片和空气的折射系数差异过大(空气的折射系数为1，晶硅的折射系数为3.6)，亚波长结构将不能起到非常优秀的减反射作用。而在实际情况中，在硅片表面会有一些介电材料，或者顶电池材料，他们的折射系数通常介于空气的折射系数和晶硅的折射系数之间，起到一个很好的过渡作用，使其对应的光伏电池的整体减反性优于常规绒面结构的光伏电池或者小绒面结构的光 伏电池。
以上所述，仅为本申请公开的具体实施方式，但本申请公开的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本申请公开的保护范围之内。因此，本申请公开的保护范围应该以权利要求的保护范围为准。
工业实用性
本申请提供一种多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法，涉及太阳能电池技术领域，能够改善包括钙钛矿/晶硅在内的叠层太阳能电池的界面减反问题，并且该解决方案适用于工业化生产。多结太阳能电池包括第一子电池和位于所述第一子电池背光面的第二子电池，所述第一子电池与所述第二子电池的界面的结构为亚波长结构，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。
此外，可以理解的是，本申请公开的多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法是可以重现的，并且可以应用在多种工业应用中。例如，本申请的多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法可以应用于太阳能电池技术领域。

Claims (15)

  1. 一种多结太阳能电池，包括第一子电池和位于所述第一子电池背光面的第二子电池，其中，所述第一子电池与所述第二子电池的界面的结构为亚波长结构，所述亚波长结构的周期长度小于所述第二子电池的吸收波段的最小波长。
  2. 如权利要求1所述的多结太阳能电池，其中，所述第一子电池的光吸收层与所述第二子电池的光吸收层之间的所有膜层的总厚度小于100nm。
  3. 如权利要求1所述的多结太阳能电池，其中，所述亚波长结构还被配置为形成局部电场，所述局部电场在所述第一子电池的光吸收层的上表面和下表面之间形成，所述局部电场使所述第一子电池的光吸收层中的迁移离子不均匀地分布在所述光吸收层的上表面和下表面，以留出供载流子被抽取的通道。
  4. 如权利要求3所述的多结太阳能电池，其中，所述亚波长结构的高度不小于200nm。
  5. 如权利要求1-4任一项所述的多结太阳能电池，其中，所述第二子电池为晶硅电池，所述亚波长结构的周期长度不大于700nm。
  6. 如权利要求5所述的多结太阳能电池，其中，所述亚波长结构位于所述晶硅电池的迎光面。
  7. 如权利要求5所述的多结太阳能电池，其中，所述亚波长结构利用晶硅电池的制绒工艺形成。
  8. 如权利要求5所述的多结太阳能电池，其中，所述第二子电池采用具有纳米绒面的硅基底，以使所述第一子电池与所述第二子电池的界面的结构为亚波长结构。
  9. 如权利要求8所述的多结太阳能电池，其中，所述纳米绒面为纳米金字塔绒面，且所述纳米金字塔绒面的金字塔的底部边长为300～600nm；或者，所述纳米绒面为纳米黑硅绒面，且所述纳米黑硅绒面的绒面高度不小于200nm。
  10. 如权利要求1-4、6～9任一项所述的多结太阳能电池，其中，所述第一子电池为单结电池或多结电池；所述第一子电池的光吸收层的材料选自钙钛矿、砷化镓、铝砷化镓和磷化镓铟中的一种或多种。
  11. 一种钙钛矿晶硅叠层电池，其中，包括第一子电池和第二子电池，所述第一子电池为钙钛矿电池，所述第二子电池为晶硅电池；
    所述钙钛矿电池包括透明导电层、第一传输层、钙钛矿光吸收层、第二传输层；其 中，所述第一传输层和所述第二传输层其中之一为电子传输层，另一为空穴传输层；
    所述晶硅电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。
  12. 一种晶硅电池，其中，所述晶硅电池的迎光面的结构为亚波长结构，所述亚波长结构的周期长度小于所述晶硅电池的吸收波段的最小波长。
  13. 一种晶硅电池的制备方法，包括：绒面制备工序，其中，所述绒面制备工序包括：提供硅基底，使所述硅基底形成亚波长结构的迎光面，所述亚波长结构的周期长度小于所述晶硅电池吸收波段的最小波长。
  14. 一种多结太阳能电池的制备方法，其中，包括：使所述第一子电池与所述第二子电池的交界处形成亚波长结构的界面，所述亚波长结构的周期长度小于所述第二子电池吸收波段的最小波长。
  15. 如权利要求14所述的多结太阳能电池的制备方法，其中，使所述第一子电池与所述第二子电池的交界处形成亚波长结构的界面，包括：在所述第二子电池的制备工序中，利用制绒工艺使所述第二子电池形成所述亚波长结构的迎光面。
PCT/CN2023/111019 2022-08-05 2023-08-03 多结太阳能电池、钙钛矿晶硅叠层电池、晶硅电池及其制备方法 WO2024027797A1 (zh)

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