Solar cell with low reflectivity at visible light wavelength and preparation process thereof

Abstract

The invention discloses a solar cell with low reflectivity at visible light wavelength and a preparation process thereof, and in the preparation process, (1) a cell antireflection film is of a three-layer structure prepared by adopting an evaporation process, and the three layers are respectively a 35.5 nm TiOx film, a 44 nm HfO2 film and a 52 nm Al2O3 film from the surface of the cell; (2) after manufacturing of an electrode metal grid line on the battery is completed, the surface of the battery is coated with black glue, black glue shielding is carried out on the metal grid line through the photoetching technology, black glue shielding is carried out on the metal grid line through the photoetching technology, and the interface reflectivity of the metal grid line is reduced; (3) blackening of the cover plate: manufacturing an antireflection film on the cover plate through an evaporation process so as to reduce the reflectivity of the surface of the cover plate; and after the antireflection film is finished, blackening the welding spot position of the battery by locally spraying black glue. According to the invention, the technical problem that the reflectivity (4%) of the solar cell within the wavelength range of 380-800nm is relatively high is solved.

Description

Technical Field

[0001] This invention belongs to the field of physical power source technology, and in particular relates to a solar cell with low reflectivity at visible light wavelengths and its fabrication process. Background Technology

[0002] Because solar cells exhibit significant specular reflection, which affects astronomical observations, a solar cell with low reflectivity in the visible light range is needed to reduce reflection. Generally, space-based solar cells have anti-reflection coatings on their surfaces to increase light absorption. These anti-reflection coated solar cells have a reflectivity of approximately 4% in the visible light range (380 nm–800 nm). To achieve a truly low-reflection effect, a cell with a reflectivity of less than 1% in this range has been proposed.

[0003] Against this backdrop, solar cells need to undergo optical processing to ensure that they have extremely low reflectivity in the visible light range, and that the optical processing of the cell surface does not affect or minimally affects the cell's photoelectric conversion efficiency. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a solar cell with low reflectivity in visible light wavelengths and its fabrication process, solving the technical problem that solar cells have a high reflectivity (4%) in the wavelength range of 380 nm to 800 nm.

[0005] This invention is implemented as follows: a fabrication process for a solar cell with low reflectivity in visible light wavelengths. The solar cell includes a solar cell body and a cover sheet. The fabrication process includes photolithography, upper electrode evaporation, isolation trench photolithography / etching, grid line blackening photolithography, anti-reflection film evaporation, solder joint photolithography and etching, lower electrode evaporation, electrode curing, dicing, and cover sheet bonding, wherein: (1) The antireflective coating of the battery is a three-layer structure prepared by vapor deposition process. Starting from the surface of the battery, it consists of 35.5 nm TiO2 layers. x A 44 nm HfO2 film and a 52 nm Al2O3 film; (2) After the metal grid lines of the upper electrode of the battery are fabricated, black glue is coated on the surface of the battery and the metal grid lines are masked by photolithography to reduce the interface reflectivity of the metal grid lines. (3) Blackening of the cover sheet: an anti-reflective film is made on the cover sheet by vapor deposition to reduce the reflectivity of the cover sheet surface; after the anti-reflective film is completed, the battery solder joints are blackened by local spraying of black glue.

[0006] Furthermore, the black adhesive is LTC-156 photoresist.

[0007] Furthermore, in step (3), an antireflection film evaporation process is performed on the rough surface of the cover plate using a dielectric film deposition equipment, and HfO2 film, MgF2 film, HfO2 film, MgF2 film, HfO2 film, and MgF2 film are deposited in sequence.

[0008] Furthermore, HfO2 films with a thickness of 24.6 nm, MgF2 films with a thickness of 27.5 nm, HfO2 films with a thickness of 61.7 nm, MgF2 films with a thickness of 22.3 nm, HfO2 films with a thickness of 40.3 nm, and MgF2 films with a thickness of 103.7 nm were deposited successively.

[0009] Furthermore, in step (3), the solder joints on the lower surface of the cover sheet are locally sprayed with black LTC-156 photoresist. After the cover sheet is sprayed, it is placed in an oven at 180°C for 10 minutes to bake and cure.

[0010] Furthermore, the solar cell is a triple-junction GaInP / GaAs / Ge solar cell.

[0011] The above-described fabrication process produces solar cells with low reflectivity at visible light wavelengths.

[0012] The advantages and technical effects of this invention are as follows: (1) Solar cell grid line (fine grid) blackening is to cover the grid line area with black photoresist to reduce the reflectivity of the grid line metal.

[0013] (2) Blackening of the cover plate solder joints involves spraying black glue on the lower surface of the cover plate to cover the solder joints of the battery, thereby reducing the reflectivity of the metal at the solder joints. (3) Anti-reflective film structure design: The light-receiving area of ​​the battery is optimized by designing the anti-reflective film system to reduce light reflection in the area and enhance the reflection effect.

[0014] (4) Cover film structure design: The surface of the battery is optimized by designing the cover antireflection film system to increase the light transmission of the battery, which is beneficial to the improvement of the battery's electrical performance efficiency and the reduction of surface reflection. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the cross-sectional structure of the battery.

[0016] Figure 2 This is a top view of the structure of a solar cell.

[0017] Figure 3 This is a schematic diagram of the cross-sectional structure of the anti-reflective coating on a solar cell.

[0018] Figure 4 This is a schematic diagram of the cross-sectional structure of the cover plate.

[0019] Figure 5 This is a top view of the cover plate.

[0020] Figure 6 This is a reflectance test chart of a battery prepared using the method of this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] The battery of this invention consists of a solar cell body and a cover plate. The technical solution adopted by this invention is: First, the antireflective coating structure is designed during the fabrication process of the battery antireflective coating. This invention designs a three-layer film, starting from the battery surface, consisting of TiOx (35.5 nm), HfO2 (44 nm), and Al2O3 (52 nm), as shown below. Figure 1 The antireflective film is fabricated using a vapor deposition process, which effectively reduces the reflectivity of the battery surface.

[0023] Secondly, after the metal grid lines on the battery's upper electrode are fabricated, the metal electrodes undergo a blackening design. This invention involves coating the battery surface with black adhesive (LTC-156 photoresist). Through photolithography, the metal grid lines are masked with black adhesive, reducing the interface reflectivity of the metal grid lines. By blackening the highly reflective metal surface (with a metal reflectivity exceeding 90%), the reflectivity of the grid line area can be reduced to approximately 8%, which is beneficial for reducing the overall reflectivity of the battery.

[0024] Finally, the cover sheet is selected and blackened. The cover sheet of this invention incorporates an antireflective film system; a design schematic is shown below. Figure 2 An antireflective coating is applied to the cover plate using a vapor deposition process. This coating effectively reduces the reflectivity of the cover plate surface. After the antireflective coating is completed, the cover plate undergoes a blackening treatment, specifically blackening the battery solder joints, which is achieved by locally spraying black adhesive. The purpose of blackening the cover plate is to blacken and shield the metal at the battery solder joints covered by the cover plate, achieving the same beneficial effect as blackening the grid lines.

[0025] To illustrate the above design, this invention provides a method for fabrication using a general process for manufacturing solar cells as an example.

[0026] The battery manufacturing process is as follows: The fabrication process of solar cell bodies includes photolithography, upper electrode evaporation, isolation trench photolithography / etching, grid line blackening photolithography, anti-reflection film evaporation, solder joint photolithography and etching, lower electrode evaporation, electrode curing, and dicing.

[0027] The cover glass manufacturing process includes antireflective film evaporation and cover glass blackening.

[0028] The design method for reducing solar cell antireflection protected by this invention mainly includes grid line blackening, antireflection film system design, and cover plate blackening. To increase the photoelectric conversion efficiency of the cell, the cover plate antireflection film system is optimized. To clearly define the order of the grid line blackening process, the antireflection film process, and the cover plate blackening process in the cell manufacturing process, this invention uses a triple-junction GaInP / GaAs / Ge solar cell as an example to briefly describe the entire process flow of a low-reflection cell.

[0029] Figure 1 This is a schematic diagram of the cross-sectional structure of the solar cell. In this diagram, 1-1 is the Ge substrate; 1-2 is the Ge sub-cell; 1-3 is the GaAs sub-cell; 1-4 is the GaInP sub-cell; 1-5 is the window layer; 1-6 is the CaP layer; 1-7 is the anti-reflective coating; 1-8 is the upper electrode metal layer; 1-9 is the lower electrode metal layer; 1-10 is the black adhesive (LTC-156 adhesive); 1-11 is the cover film adhesive; 1-12 is the glass cover film; and 1-13 is the anti-reflective coating on the glass cover film.

[0030] Figure 2 This is a top view of a solar cell structure. 2-1 is the fine grid; 2-2 is the main grid; and 2-3 is the solder joint.

[0031] Figure 3 It is an anti-reflective coating for solar cells ( Figure 1 The cross-sectional structure diagram is shown in Figure 1-7; where 3-1 is the solar cell and 3-2 is the TiO2. x (Thickness 35.5 nm), 3-3 is HfO2 (thickness 44.0 nm), 3-4 is Al2O3 (thickness 52.0 nm). Figure 4 It is a cover plate ( Figure 1 Schematic diagram of the cross-sectional structure of (1-12); where 4-1 is the cover plate; 4-2 is the rough surface of the cover plate (roughness Ra=0.4µm±0.1µm, Rt=1.6µm±0.2µm); 4-3 is HfO2 (in contact with the rough surface of the cover plate, thickness is 24.6nm), 4-4 is MgF2 (thickness is 27.5nm), 4-5 is HfO2 (thickness is 61.7nm), 4-6 is MgF2 (thickness is 22.3nm), 4-7 is HfO2 (thickness is 40.3nm), 4-8 is MgF2 (thickness is 103.7nm); 4-9 is black glue (LTC-156 glue).

[0032] Figure 5 It is a cover plate ( Figure 1A top view diagram (1-12); where 5-1 is the cover plate; 5-2 is the black adhesive (same as above). Figure 4 ,4-9).

[0033] The blackening of the solar cell grid lines (fine grids) in this invention involves blackening the grid line portion (...). Figure 2 2-1) It is covered by black photoresist, as shown in Figure 1-10, to reduce the reflectivity of the gate metal; the blackening of the cover plate solder joints is done on the lower surface of the cover plate ( Figure 4 Partially spray black glue onto 4-9) Figure 5 , 5-2), the solder joints of the battery ( Figure 2 (2-3) The reflectivity of the metal at the solder joint is reduced by shielding and covering the area to reduce the reflectivity of the metal; the anti-reflective film structure is designed to shield the light-receiving area of ​​the battery ( Figure 1 ,1-7) Through optimization of the antireflective coating system design ( Figure 3 ,3-2, 3-2, 3-3), reduce light reflection in this area and enhance the reflection effect; cover film structure design, optimize the battery surface through the design of the cover antireflection film system ( Figure 4 (4-3, 4-4, 4-5, 4-6, 4-7, 4-8) Increasing the light transmission of the battery is beneficial to improving the battery's electrical performance efficiency and reducing surface reflection; by adopting the above technical measures, the battery's reflectivity test curve is shown in [reference 4]. Figure 6 As shown.

[0034] The low-reflectivity structural design of the battery described in this invention includes blackening of the solar cell grid lines (fine grid), blackening of the cover plate solder joints, anti-reflection film structure design, cover plate film structure design, and selection of a frosted cover plate. Solar cells with any one or more of these designs are protected under this invention, regardless of the battery's substrate material, electrical performance, shape, or size. The solar cell described in this invention is a triple-junction GaInP / GaAs / Ge solar cell, such as... Figure 1 As shown, the battery is quadrilateral in shape, such as... Figure 2 As shown.

[0035] This invention uses an epitaxial wafer with a 3-junction GaInP / GaAs / Ge structure, and manufactures it according to the following process flow and method: Photolithography A: The purpose of using photolithography is to form the photolithographic pattern of the upper electrode (2-1, 2-2, 2-3).

[0036] Vapor deposition of upper electrode: Metal is deposited on the CaP layer (1-6) of the semi-finished battery using a vapor deposition process. After removing the photoresist, a metal pattern is formed on the upper electrode area (fine grid 2-1, main grid 2-2, 2-3).

[0037] CaP layer removal: The CaP layer in the light-receiving area (1-7) of the semi-finished battery is removed by wet etching process, with the aim of exposing the window layer (1-5) in this area.

[0038] The antireflective coating is deposited using a dielectric film deposition equipment on a semi-finished battery after the CaP layer removal process. TiO₂ is deposited sequentially. x Membrane (3-2, thickness controlled at 35.5 nm), HfO2 membrane (3-3, thickness controlled at 44.0 nm), Al2O3 membrane (3-4, thickness controlled at 52.0 nm).

[0039] Photolithography B uses black LTC-156 photoresist for the photolithography process. The purpose is to mask areas such as the fine gate (1-8 or 2-1) and the main gate (2-2) with black photoresist. A schematic diagram of the effect is shown below. Figure 1-1 0.

[0040] Vapor deposition of the lower electrode: The lower electrode metal is deposited on the substrate (1-9) of the semi-finished battery using a vapor deposition process.

[0041] The sintering process employs a high-vacuum annealing process to sinter the upper and lower electrodes (1-9) of the semi-finished battery, forming a good ohmic contact.

[0042] The dicing process uses a dicing device to cut the cells according to their dimensions.

[0043] The lead wires of the welding electrode are welded with metal interconnect strips at the battery welding point (2-3) and the lower electrode (1-9) respectively, serving as the lead ends of the upper and lower electrodes.

[0044] The cover plate coating was performed on the rough surface (4-2) of the cover plate using a dielectric film deposition equipment to deposit an antireflection film. HfO2 film (4-3, thickness 24.6nm), MgF2 film (4-4, thickness 27.5nm), HfO2 film (4-5, thickness 61.7nm), MgF2 film (4-6, thickness 22.3nm), HfO2 film (4-7, thickness 40.3nm), and MgF2 film (4-8, thickness 103.7nm) were deposited in sequence.

[0045] Blackening of the cover plate on the lower surface of the cover plate (see...) Figure 4-1 The solder joints (5-2) are partially sprayed with black LTC-156 photoresist. After the cover is sprayed, it is placed in an oven at 180℃ for 10 minutes to bake and cure.

[0046] The cover plate is attached using adhesive to bond the upper surface of the battery to the lower surface of the cover plate.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fabrication process for a solar cell with low reflectivity at visible light wavelengths, the solar cell comprising a solar cell body and a cover sheet, characterized in that, The fabrication process includes photolithography, upper electrode evaporation, isolation trench photolithography / etching, gate line blackening photolithography, anti-reflection film evaporation, solder joint photolithography and etching, lower electrode evaporation, electrode curing, dicing, and cover plate bonding, wherein: (1) The antireflective coating of the battery is a three-layer structure prepared by vapor deposition process. Starting from the surface of the battery, it consists of 35.5 nm TiO2 layers. x A 44 nm HfO2 film and a 52 nm Al2O3 film; (2) After the metal grid lines of the upper electrode of the battery are fabricated, black glue is coated on the surface of the battery and the metal grid lines are masked by photolithography to reduce the interface reflectivity of the metal grid lines. (3) Blackening of the cover sheet: an anti-reflective film is made on the cover sheet by vapor deposition to reduce the reflectivity of the cover sheet surface; after the anti-reflective film is completed, the battery solder joints are blackened by local spraying of black glue.

2. The fabrication process of the solar cell with low reflectivity in visible light wavelength according to claim 1, characterized in that, The black adhesive is LTC-156 photoresist.

3. The fabrication process of the solar cell with low reflectivity in visible light wavelength according to claim 1, characterized in that, In step (3), an antireflection film evaporation process is used on the rough surface of the cover plate using a dielectric film deposition equipment, and HfO2 film, MgF2 film, HfO2 film, MgF2 film, HfO2 film, and MgF2 film are deposited in sequence.

4. The fabrication process of the solar cell with low reflectivity in visible light wavelength according to claim 3, characterized in that, The following films were deposited sequentially: HfO2 film with a thickness of 24.6 nm, MgF2 film with a thickness of 27.5 nm, HfO2 film with a thickness of 61.7 nm, MgF2 film with a thickness of 22.3 nm, HfO2 film with a thickness of 40.3 nm, and MgF2 film with a thickness of 103.7 nm.

5. The fabrication process of a solar cell with low reflectivity in visible light wavelengths according to claim 1, characterized in that, In step (3), the solder joints on the lower surface of the cover plate are locally sprayed with black LTC-156 photoresist. After the cover plate is sprayed, it is placed in an oven at 180°C for 10 minutes to bake and cure.

6. The fabrication process of a solar cell with low reflectivity in visible light wavelength according to any one of claims 1-5, characterized in that, The solar cell is a triple-junction GaInP / GaAs / Ge solar cell.

7. A solar cell with low reflectivity in visible light wavelengths, prepared by the process described in any one of claims 1-6.

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