Gallium arsenide solar cell structure with positive electrode and negative electrode on same side and preparation method of gallium arsenide solar cell structure

Abstract

The invention provides a gallium arsenide solar cell structure with positive and negative electrodes on the same side and a preparation method thereof, and belongs to the technical field of solar cells. An epitaxial wafer is grown on a Ge substrate, an isolation groove and a positive electrode are arranged on a light receiving surface of the epitaxial wafer, negative electrodes are arranged in a backlight surface and the isolation groove of the epitaxial wafer, and antireflection films are arranged in other areas, except the positive electrode and the isolation groove, of the light receiving surface. According to the gallium arsenide solar cell structure with the positive electrode and the negative electrode on the same side, interconnection between the cell pieces is simpler and more convenient, so that the packaging technology is simplified, the piece distribution rate and the processing efficiency of the solar cell module are improved, and the reliability of the cell under the thermal cycle condition is improved; the series resistance of the solar cell is effectively reduced, and the conversion efficiency of the cell is improved; the preparation is easy, and industrial implementation is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and in particular relates to a gallium arsenide solar cell structure with positive and negative electrodes on the same side and its preparation method. Background Technology

[0002] Gallium arsenide (GaAs) solar cells are widely used in space energy systems and ground-based concentrated photovoltaic (CPV) systems due to their high conversion efficiency, excellent temperature characteristics, and radiation resistance. Traditional GaAs solar cells typically employ a structure where the positive and negative electrodes are located on opposite sides of the cell, with the front electrode (positive electrode) and the back electrode (negative electrode) extending from the light-receiving and back-shielding sides, respectively. However, this traditional electrode arrangement has several drawbacks:

[0003] (1) Difficulty in leading out the back electrode: When packaging the module, a relatively complicated interconnection process is required to lead out the back electrode, which is not only difficult to operate, but also easy to damage and contaminate the battery, affecting the battery performance, and also results in low processing efficiency, which seriously restricts the manufacturing cost.

[0004] (2) High series resistance: The current needs to pass through the entire battery structure longitudinally, resulting in high series resistance, which affects the fill factor;

[0005] (3) Low reliability: Under thermal cycling conditions, mechanical stress is easily generated due to the mismatch of the thermal expansion coefficients of the materials, which may lead to electrode detachment or battery rupture. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a gallium arsenide solar cell structure with positive and negative electrodes on the same side and its fabrication method, making the cells easier to interconnect and package; it can effectively reduce the series resistance of the solar cell and improve the cell's conversion efficiency.

[0007] The technical solution adopted in this invention is: a gallium arsenide solar cell structure with positive and negative electrodes on the same side, including an epitaxial wafer grown on a Ge substrate, wherein the light-receiving surface of the epitaxial wafer is provided with an isolation trench and a positive electrode, the back-light-receiving surface of the epitaxial wafer and the isolation trench are provided with a negative electrode, and the light-receiving surface, except for the positive electrode and the isolation trench, is provided with an anti-reflection film in other areas.

[0008] Furthermore, the width of the isolation trench is 100μm to 200μm, and it is formed on the Ge substrate.

[0009] Furthermore, the antireflective film is a titanium dioxide / aluminum oxide multilayer structure with a thickness of 100nm to 160nm.

[0010] Furthermore, the positive electrode adopts a metal grid structure.

[0011] Furthermore, the positive electrode is It has a multi-layered metal structure with a thickness of 4.8μm to 5.2μm.

[0012] Furthermore, the negative electrode adopts a rectangular solder joint structure.

[0013] Furthermore, the negative electrode of the backlight surface is an Al layer with a thickness of 9 μm to 11 μm.

[0014] Furthermore, the backlight surface is also provided with a seed layer, which is located between the epitaxial wafer and the negative electrode, using... It has a multi-layered metal structure with a thickness of 0.7μm to 1.3μm.

[0015] A method for fabricating a gallium arsenide solar cell with positive and negative electrodes on the same side includes the following steps:

[0016] An epitaxial layer is grown on the front side of a Ge substrate to form an epitaxial wafer;

[0017] Isolation grooves are etched on the light-receiving surface of the epitaxial wafer;

[0018] A positive electrode metal is deposited in the light-receiving surface of the epitaxial wafer and the isolation groove to form a positive electrode;

[0019] An antireflective film is deposited on the light-receiving surface of the epitaxial wafer;

[0020] Remove the antireflective film from the surface of the positive electrode and within the isolation groove;

[0021] A seed layer is deposited in the negative electrode region of the back surface of the epitaxial wafer;

[0022] Heat treatment is required;

[0023] The negative electrode is formed by vapor deposition of negative electrode metal on the back surface of the epitaxial wafer.

[0024] The epitaxial wafer is cut to form a solar cell.

[0025] Further, removing the antireflective film from the surface of the positive electrode and the isolation trench includes removing the antireflective film from the surface of the positive electrode using photolithography and wet etching, and removing the antireflective film from the isolation trench using solder joint overlay and solder joint etching.

[0026] The advantages and positive effects of this invention are:

[0027] (1) The gallium arsenide solar cell structure with positive and negative electrodes on the same side proposed in this application makes the interconnection between cells easier, thereby simplifying the packaging process; and through integrated interconnection design, it effectively improves the cell placement rate and processing efficiency of solar cell modules, which is particularly suitable for space applications; at the same time, the cell structure can also avoid the problem of electrode detachment caused by mismatch of thermal expansion coefficients, and improve the reliability of the cell under thermal cycling conditions.

[0028] (2) By designing the positive and negative electrodes on the same side, the current transmission path is effectively shortened and the series resistance of the solar cell is reduced; the photogenerated carriers can be directly transported laterally to the corresponding electrodes, avoiding the long path of transmission through the entire substrate, which can significantly improve the fill factor and thus improve the conversion efficiency of the cell.

[0029] (3) Using the method proposed in this application to prepare gallium arsenide solar cell structure with positive and negative electrodes on the same side, it is only necessary to add an etching isolation trench step to the existing gallium arsenide solar cell preparation process. The isolation trench can be completed by a single etching process and a single etching solution, which is easy to prepare and conducive to industrialization. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a battery structure according to a specific embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of a preparation method according to a specific embodiment of the present invention.

[0032] In the picture:

[0033] 1. Positive electrode; 2. Negative electrode; 3. Seed layer; 4. Antireflective coating; 5. Top cell; 6. First tunnel junction; 7. Middle cell; 8. Second tunnel junction; 9. Gradient buffer layer; 10. Bottom cell; 11. Bottom cell CAP layer. Detailed Implementation

[0034] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0035] like Figure 1 As shown, this embodiment of the invention proposes a gallium arsenide solar cell structure with positive and negative electrodes 2 on the same side, including an epitaxial wafer grown on a Ge substrate. The light-receiving surface of the epitaxial wafer is provided with an isolation trench and a positive electrode 1, and the back-light-receiving surface of the epitaxial wafer and the isolation trench are provided with a negative electrode 2. The other areas of the light-receiving surface, except for the positive electrode 1 and the isolation trench, are provided with an anti-reflection film 4. By setting the isolation trench, electrical isolation between the positive and negative electrode areas of the light-receiving surface of the epitaxial wafer is achieved, forming a gallium arsenide solar cell structure with positive and negative electrodes 2 on the same side.

[0036] Compared to the traditional gallium arsenide solar cell structure where the positive and negative electrodes 2 are located on opposite sides of the cell, the gallium arsenide solar cell structure with the positive and negative electrodes 2 on the same side simplifies the interconnection between cells, making it particularly suitable for series integrated module designs. More importantly, the design of the positive and negative electrodes 2 on the same side effectively shortens the current transmission path and reduces the series resistance of the solar cell. At the same time, photogenerated carriers can be directly transported laterally to the corresponding electrodes, avoiding long-path transmission through the entire substrate, which can significantly improve the fill factor and thus improve the cell's conversion efficiency.

[0037] Specifically, in this embodiment, the epitaxial wafer is a forward triple-junction solar cell structure, comprising, from top to bottom: a top cell 5, a first tunneling junction 6, a middle cell 7, a second tunneling junction 8, a gradient buffer layer 9, a bottom cell 10, and a bottom cell CAP layer 11. The upper surface of the top cell 5 is the light-receiving surface, and the lower surface of the bottom cell is the backlighting surface. An isolation groove and a positive electrode 1 are provided on the upper surface of the top cell 5, and a negative electrode 2 is located in the isolation groove and on the backlighting surface. Other areas on the upper surface of the top cell 5 are provided with an anti-reflection film 4.

[0038] Specifically, in this embodiment of the application, the width of the isolation trench is 100μm to 200μm and extends to the Ge substrate. Preferably, the depth of the isolation trench is 5μm to 10μm. With this setting, the positive electrode 1 and the negative electrode 2 can be separated while ensuring that the mechanical strength of the epitaxial wafer meets the usage requirements, thereby achieving a good electrical isolation effect.

[0039] Specifically, in the embodiments of this application, the antireflective film 4 can be one or more of aluminum oxide, silicon oxide, and titanium oxide, and can be a single-layer or multi-layer structure, which is not limited here; preferably, the antireflective film 4 is a titanium oxide / aluminum oxide multilayer structure with a thickness of 100nm to 160nm.

[0040] Specifically, in the embodiments of this application, the positive electrode 1 adopts a metal grid line structure, including a main grid line and a sub-grid line, to collect photogenerated carriers while reducing light shading losses.

[0041] Specifically, the positive electrode 1 can be one or more of Au, Ti, Ni, Ge, and Ag, and can be a single-layer structure or a multi-layer structure; preferably, in this embodiment, the positive electrode 1 is... It has a multi-layered metal structure with a thickness of 4.8μm to 5.2μm.

[0042] Specifically, in this embodiment, the negative electrode 2 adopts a rectangular solder joint structure, including multiple discrete metal solder joints, to achieve stable mechanical connection and efficient current transmission, thereby working together with the positive electrode 1 to improve the photoelectric conversion efficiency and reliability of the battery.

[0043] Specifically, the negative electrode 2 can be one or more of Cu, Al, and Ni, and can be a single-layer structure or a multi-layer structure. Preferably, in this embodiment, the negative electrode 2 on the backlight surface is an Al layer with a thickness of 9μm to 11μm.

[0044] Furthermore, to ensure the electroplating effect, a seed layer 3 is also provided on the backlight surface. The seed layer 3 is located between the epitaxial wafer and the negative electrode 2. Preferably, the seed layer 3 is made of... Multi-layered metal structure.

[0045] A method for fabricating a gallium arsenide solar cell with positive and negative electrodes on the same side, such as... Figure 2 As shown, it includes the following steps:

[0046] S1. An epitaxial layer is grown on the front side of a Ge substrate to form an epitaxial wafer;

[0047] S2. Etch isolation trenches on the light-receiving surface of the epitaxial wafer;

[0048] S3. Positive electrode metal is deposited in the light-receiving surface of the epitaxial wafer and in the isolation groove to form positive electrode 1;

[0049] S4. Deposit an anti-reflection film 4 on the light-receiving surface of the epitaxial wafer;

[0050] S5. Remove the antireflective film 4 from the surface of the positive electrode 1 and from the isolation groove;

[0051] S6. Seed layer 3 is deposited in the negative electrode area of ​​the backlight surface of the epitaxial wafer;

[0052] S7. Perform heat treatment;

[0053] S8. Deposit negative electrode metal onto the back surface of the epitaxial wafer to form negative electrode 2;

[0054] S9. Cut the epitaxial wafer to form a solar cell.

[0055] The following is a detailed explanation.

[0056] S1. An epitaxial layer is grown on the front side of the Ge substrate to form an epitaxial wafer, specifically as follows:

[0057] An epitaxial layer was grown on a Ge substrate using the MOCVD method to form a forward triple junction epitaxial wafer, which was grown sequentially as follows: bottom cell CAP layer 11, bottom cell 10, gradient buffer layer 9, second tunnel junction 8, middle cell 7, first tunnel junction 6, and top cell 5.

[0058] S2. Etching isolation trenches on the light-receiving surface of the epitaxial wafer, specifically:

[0059] Photoresist is applied to the light-receiving surface of the epitaxial wafer, which is then placed in a lithography machine. The lithography machine illuminates the isolation zone area through the photomask, and then the isolation zone area is developed using a developing solution.

[0060] The epitaxial wafer covered with a photoresist masking layer is immersed in a primary etching solution containing nitric acid / hydrobromic acid / buffer. After etching for 2-3 minutes, it is removed and placed in a resist remover to remove the protective adhesive. Finally, it is washed and dried to form an isolation tank.

[0061] S3. Positive electrode metal is deposited by vapor deposition on the light-receiving surface of the epitaxial wafer and within the isolation trench, specifically as follows:

[0062] Photoresist is applied to the light-receiving surface of the epitaxial wafer with isolation trenches, and then it is placed in a photolithography machine. The photolithography machine illuminates the electrode area and isolation trench area of ​​the light-receiving surface through the photolithography plate. Then, the positive electrode 1 area is developed using a developing solution, rinsed with deionized water, and then dried.

[0063] The epitaxial wafer is placed in a vacuum evaporation apparatus, and a positive electrode metal is deposited on the light-receiving surface and the isolation tank. The positive electrode metal is... The multilayer metal structure, with a thickness of 4.8μm to 5.2μm, includes several main gate lines and sub-gate lines. After the evaporation is completed, the epitaxial wafer is removed, and the photoresist is removed by immersion in acetone, leaving only the positive electrode metal pattern. It is then rinsed with deionized water and dried.

[0064] The completed epitaxial wafer has a positive electrode 1 formed on the light-receiving surface, and a positive electrode metal is provided in the isolation groove.

[0065] S4. Deposit an anti-reflection film 4 on the light-receiving surface of the epitaxial wafer;

[0066] After completing step S3, the epitaxial wafer is placed in a vacuum evaporation equipment, and an antireflection film 4 is deposited on the light-receiving surface. The antireflection film 4 is a multilayer structure of titanium oxide / aluminum oxide with a thickness of 100nm to 160nm.

[0067] The completed epitaxial wafer has an anti-reflection film 4 on the light-receiving surface, including inside the isolation groove.

[0068] S5. Remove the antireflective coating 4 from the surface of positive electrode 1 and inside the isolation groove:

[0069] The antireflection film 4 on the surface of the positive electrode 1 is removed by photolithography and wet etching, and the antireflection film 4 in the isolation trench is removed by solder joint overlay and solder joint etching.

[0070] Specifically, the process includes: coating the antireflection film 4 with photoresist, then placing it in a photolithography machine, the photolithography machine irradiating the positive electrode area and the isolation tank area through the photolithography plate, then using a developing solution to develop the positive electrode area and the isolation tank area, rinsing with deionized water and then drying.

[0071] The spin-dried epitaxial wafer is placed in an antireflective film etching solution (hydrofluoric acid: deionized water = 1:10) for 3 to 5 seconds to remove the antireflective film 4 from the surface of the positive electrode 1 and the isolation tank.

[0072] Then, rinse with deionized water, soak in acetone to remove the photoresist, and finally rinse with deionized water and spin dry.

[0073] The above method enables the simultaneous removal of the antireflective film 4 on the surface of the positive electrode 1 and the antireflective film 4 in the isolation groove.

[0074] S6. Seed layer 3 is deposited in the negative electrode area of ​​the backlight surface of the epitaxial wafer;

[0075] After completing step S5, the epitaxial wafer is placed in a vacuum evaporation apparatus, and a seed layer 3 is deposited on the negative electrode area of ​​the backlight surface of the epitaxial wafer. Seed layer 3 is... Multi-layered metal structure, 0.7μm to 1.3μm thick, removed after vapor deposition;

[0076] S7. Perform heat treatment, specifically:

[0077] After completing step S6, the epitaxial wafer is placed in a vacuum sintering apparatus and sintered at 350°C for 30 minutes in a vacuum environment. After cooling, it is taken out.

[0078] S8. Deposit negative electrode metal onto the back surface of the epitaxial wafer to form negative electrode 2;

[0079] The epitaxial wafer that has completed step S7 is placed in a vacuum evaporation equipment, and a negative electrode metal is deposited on the back surface of the epitaxial wafer. The negative electrode metal is Al with a thickness of 9μm to 11μm. After the evaporation is completed, the wafer is removed.

[0080] The negative electrode metal is connected to the positive electrode metal in the isolation tank to form negative electrode 2.

[0081] S9. Cut the epitaxial wafer into solar cells, specifically:

[0082] Place the epitaxial wafer that has completed step S8 into a mechanical dicing machine with the light-receiving side facing up, and dice the epitaxial wafer into solar cell cells of the required size according to the pre-made pattern.

[0083] The above method can be used to prepare gallium arsenide solar cell structures with positive and negative electrodes on the same side. It only requires adding an etching tank isolation tank step to the existing gallium arsenide solar cell preparation process. The isolation tank can be completed by a single etching process and a single etching solution, which is easy to prepare and conducive to industrialization.

[0084] The gallium arsenide solar cell structure with positive and negative electrodes on the same side prepared by this method makes the interconnection between cells easier, thereby simplifying the packaging process; furthermore, through integrated interconnection design, it effectively improves the cell placement rate and processing efficiency of solar cell modules, making it particularly suitable for space applications; at the same time, this cell structure can also avoid the problem of electrode detachment caused by mismatch in thermal expansion coefficients, improving the reliability of the cell under thermal cycling conditions.

[0085] By designing the positive and negative electrodes on the same side, the current transmission path is effectively shortened, reducing the series resistance of the solar cell. Photogenerated carriers can be directly transported laterally to the corresponding electrodes, avoiding long-path transmission through the entire substrate, which can significantly improve the fill factor and thus improve the conversion efficiency of the cell. In a specific embodiment, compared with a traditional gallium arsenide solar cell, the conversion efficiency of the gallium arsenide solar cell structure with the positive and negative electrodes on the same side can be improved by 0.5% to 1%.

[0086] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A gallium arsenide solar cell structure with positive and negative electrodes on the same side, characterized in that: The invention includes an epitaxial wafer grown on a Ge substrate, wherein the light-receiving surface of the epitaxial wafer is provided with an isolation trench and a positive electrode, the back-light-receiving surface of the epitaxial wafer and the isolation trench are provided with a negative electrode, and the other areas of the light-receiving surface, except for the positive electrode and the isolation trench, are provided with an anti-reflection film.

2. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 1, characterized in that: The isolation trench has a width of 100μm to 200μm and is formed on the Ge substrate.

3. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 1, characterized in that: The antireflective coating is a titanium dioxide / aluminum oxide multilayer structure with a thickness of 100nm to 160nm.

4. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 1, characterized in that: The positive electrode adopts a metal grid structure.

5. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 4, characterized in that: The positive electrode is It has a multi-layered metal structure with a thickness of 4.8μm to 5.2μm.

6. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 1 or 5, characterized in that: The negative electrode adopts a rectangular solder joint structure.

7. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 6, characterized in that: The negative electrode of the backlight surface is an Al layer with a thickness of 9 μm to 11 μm.

8. The gallium arsenide solar cell structure with positive and negative electrodes on the same side according to claim 7, characterized in that: The backlight surface is further provided with a seed layer, which is located between the epitaxial wafer and the negative electrode, using... It has a multi-layered metal structure with a thickness of 0.7μm to 1.3μm.

9. A method for fabricating a gallium arsenide solar cell with positive and negative electrodes on the same side, characterized in that, Includes the following steps: An epitaxial layer is grown on the front side of a Ge substrate to form an epitaxial wafer; Isolation grooves are etched on the light-receiving surface of the epitaxial wafer; A positive electrode metal is deposited in the light-receiving surface of the epitaxial wafer and the isolation groove to form a positive electrode; An antireflective film is deposited on the light-receiving surface of the epitaxial wafer; Remove the antireflective film from the surface of the positive electrode and within the isolation groove; A seed layer is deposited in the negative electrode region of the back surface of the epitaxial wafer; Heat treatment is required; The negative electrode is formed by vapor deposition of negative electrode metal on the back surface of the epitaxial wafer. The epitaxial wafer is cut to form a solar cell.

10. The method for preparing a gallium arsenide solar cell on the same side as the negative electrode according to claim 9, characterized in that: Removing the antireflective film from the surface of the positive electrode and the isolation trench includes removing the antireflective film from the surface of the positive electrode using photolithography and wet etching, and removing the antireflective film from the isolation trench using solder joint overlay and solder joint etching.

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