Reverse four-junction thin film gallium arsenide solar cell for space and preparation method of reverse four-junction thin film gallium arsenide solar cell

Abstract

The invention discloses a reverse four-junction thin film gallium arsenide solar cell for space and a preparation method, and belongs to the technical field of solar cells, the reverse four-junction thin film gallium arsenide solar cell for space adopts a reverse four-junction epitaxial structure, and a composite metal substrate is arranged on the back of an epitaxial layer of the reverse four-junction thin film gallium arsenide solar cell for space. The reverse four-junction thin film gallium arsenide solar cell for the space is characterized in that the epitaxial structure adopted by the reverse four-junction thin film gallium arsenide solar cell for the space can effectively improve the anti-irradiation performance of the thin film solar cell, meanwhile, the composite metal layer can enable the electrical performance of the solar cell not to be affected by bending, and the attachability of the solar cell is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a reverse quadruple-junction thin-film gallium arsenide solar cell for space use and a preparation method thereof. Background Art

[0002] Since the beginning of the 21st century, with the increasing demand for energy and the continuous reduction of traditional fossil fuel reserves, the search for renewable energy that can be efficiently utilized and is environmentally friendly has become a common goal of countries around the world. Among them, solar cells that convert solar energy into electrical energy have the advantages of being noise-free, pollution-free, inexhaustible, and not restricted by geographical location. They are the fastest-growing and most dynamic new energy research field in recent years.

[0003] Among the many types of solar cells, multi-junction gallium arsenide solar cells are currently the solar cells with the highest photoelectric conversion efficiency. They can absorb sunlight of different wavelengths through sub-cells with different band gaps, thereby improving the utilization rate of sunlight by the cells. In addition, gallium arsenide solar cells have much greater radiation resistance than silicon solar cells and are more suitable for space environments. Therefore, they are widely used in space vehicles, space stations, satellites and other fields.

[0004] While ensuring the photoelectric performance of GaAs solar cells, the solar cells can be made lightweight and flexible, thereby greatly improving the weight-to-power ratio of GaAs solar cells. This can effectively increase the carrying capacity of space vehicles and reduce launch costs. It has become an important research direction and focus of GaAs solar cell technology.

[0005] The inverted structure epitaxial layer is used to prepare AlGaInP / AlGaAs / / GaInAsP / GaInAs thin film epitaxial structure, and the composite metal substrate is prepared by electroplating or vacuum evaporation. This is an effective method for preparing flexible thin film gallium arsenide solar cells. Summary of the invention

[0006] In view of some problems existing in the existing technology, the present invention provides a reverse four-junction thin-film gallium arsenide solar cell for space use and a preparation method thereof. First, a reverse growth method is adopted to grow a four-junction thin-film epitaxial structure. In this state, a lower electrode seed layer and a composite metal structure are prepared. The epitaxial structure is transferred to a temporary substrate using a corrosion stripping technique. Then, processes such as upper electrode preparation, isolation groove etching, and anti-reflection film evaporation are carried out to obtain a flexible gallium arsenide cell with a reverse four-junction structure for space use.

[0007] The present invention is implemented as follows: a method for preparing a reverse quadruple-junction thin-film gallium arsenide solar cell for space use, comprising the following steps:

[0008] (1) Growing an inverse quadruple junction epitaxial layer on a GaAs substrate;

[0009] (2) preparing a lower electrode seed layer and a composite metal substrate on the backlight side of the epitaxial layer by evaporation-electroplating;

[0010] (3) completing the transfer of the epitaxial structure by a temporary film-substrate etching method, and preparing the upper electrode on the light-receiving surface of the epitaxial layer by a photolithography-evaporation-stripping method;

[0011] (4) using a photolithography-etching method to prepare the isolation groove, etching the cap layer on the light-receiving surface, and evaporating an anti-reflection film;

[0012] (5) Remove the anti-reflection film on the surface of the upper electrode by photolithography-etching method, and then perform slicing, cell stripping and cleaning.

[0013] In step (2), an Au-Zn-Au-Ag seed layer is evaporated on the backlight surface of the epitaxial wafer to a thickness of 1000-1500 nm, and a Cu / Ni composite metal is electroplated to a thickness of 10-100 μm.

[0014] In step (3), the substrate etching method is as follows: a mixed solution of sulfuric acid: deionized water: hydrogen peroxide = 1:1:8 is prepared according to a volume ratio, and after mixing and stirring evenly, the epitaxial wafer is placed in the etching for 2-3 hours. During the etching process, the solution temperature is controlled at 30-35°C.

[0015] In step (3), the upper electrode preparation method is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode and gate line area through the photomask and then uses a developer to reveal the area, the upper electrode metal is evaporated on the light-receiving surface after rinsing with deionized water and drying, the photoresist is removed by soaking with acetone, and only the upper electrode and gate line metal patterns are retained, which are then rinsed with deionized water and dried.

[0016] The upper electrode metal is a Au-Ge-Ag-Au multilayer metal structure with a thickness of 5 μm±0.2 μm.

[0017] In step (4), the isolation groove preparation method is as follows: a photolithography machine irradiates the isolation groove area through the photoresist plate and then uses a developer to develop the area, rinses with deionized water and spins dry, then corrodes in aqua regia solution for 90 seconds, soaks in acetone to remove the photoresist, rinses with deionized water and spins dry.

[0018] In step (4), the method for etching the cap layer is as follows: according to citric acid: hydrogen peroxide: deionized water = 1500g: 500ml: 1.5L, the mixture is stirred evenly and placed in a 40°C constant temperature water bath. After the solution temperature stabilizes, the epitaxial wafer is placed in the mixture and etched for 2 minutes.

[0019] In step (4), the anti-reflection film structure is a titanium oxide / aluminum oxide multilayer structure.

[0020] In step (5), the method for removing the anti-reflection film on the surface of the upper electrode is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode area through the photomask and then uses a developer to develop the area, the area is rinsed with deionized water and dried, and then placed in an anti-reflection film etching solution for etching for 10 seconds, the area is rinsed with deionized water and then soaked in acetone to remove the photoresist, and the area is rinsed with deionized water and then dried, wherein the anti-reflection film etching solution is hydrofluoric acid: deionized water = 1:10 according to the volume ratio.

[0021] The reverse quadruple-junction thin-film gallium arsenide solar cell for space use is prepared by the preparation method.

[0022] The advantages and positive effects of the present invention are:

[0023] 1. The present invention adopts an AlGaInP / AlGaInP / / GaInAsP / GaInAs (bandgap combination 2.0 / 1.57 / 1.2 / 0.9eV) reverse four-junction epitaxial structure. Compared with the AlGaInP / AlGaAs / GaInAs three-junction structure adopted in the prior art, the structure can effectively improve the radiation resistance of thin-film solar cells due to the introduction of the GaInAsP layer. The optimized bandgap combination can reduce the number of gradient buffer layers, reduce the difficulty and growth time of epitaxial growth, and reduce the total thickness of the epitaxial layer, which is conducive to the thin filmization of solar cells.

[0024] 2. In view of the problem that the metal stress of the lower electrode in the prior art is insufficiently controlled, resulting in severe warping of the solar cell and insufficient adherence, the present invention adopts a method of depositing a Cu / Ag composite metal layer on the lower electrode seed layer. This method not only strengthens the lower electrode, but also can control the stress of the flexible battery, thereby improving the adherence of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart of a reverse quadruple-junction thin-film gallium arsenide solar cell for space use prepared by the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of a reverse quadruple-junction thin-film gallium arsenide solar cell for space use prepared by the present invention;

[0027] Figure 3 It is a top view of the light-receiving surface of the reverse four-junction thin-film gallium arsenide solar cell for space prepared by the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] like Figure 1As shown, the method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use of the present invention comprises the following steps:

[0030] (1) Growing an inverse quadruple junction epitaxial layer on a GaAs substrate;

[0031] (2) preparing a lower electrode seed layer and a composite metal substrate on the backlight side of the epitaxial layer by evaporation-electroplating;

[0032] (3) completing the transfer of the epitaxial structure by a temporary film-substrate etching method, and preparing the upper electrode on the light-receiving surface of the epitaxial layer by a photolithography-evaporation-stripping method;

[0033] (4) using a photolithography-etching method to prepare the isolation groove, etching the cap layer on the light-receiving surface, and evaporating an anti-reflection film;

[0034] (5) Remove the anti-reflection film on the surface of the upper electrode by photolithography-etching method, and then perform slicing, cell stripping and cleaning.

[0035] In step (2), an Au-Zn-Au-Ag seed layer is evaporated on the backlight surface of the epitaxial wafer to a thickness of 1000-1500 nm, and a Cu / Ni composite metal is electroplated to a thickness of 10-100 μm.

[0036] In step (3), the substrate etching method is as follows: a mixed solution of sulfuric acid: deionized water: hydrogen peroxide = 1:1:8 is prepared according to a volume ratio, and after mixing and stirring evenly, the epitaxial wafer is placed in the etching for 2-3 hours. During the etching process, the solution temperature is controlled at 30-35°C.

[0037] In step (3), the upper electrode preparation method is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode and gate line area through the photomask and then uses a developer to reveal the area, the upper electrode metal is evaporated on the light-receiving surface after rinsing with deionized water and drying, the photoresist is removed by soaking with acetone, and only the upper electrode and gate line metal patterns are retained, which are then rinsed with deionized water and dried.

[0038] The upper electrode metal is a Au-Ge-Ag-Au multilayer metal structure with a thickness of 5 μm±0.2 μm.

[0039] In step (4), the isolation groove preparation method is as follows: a photolithography machine irradiates the isolation groove area through the photoresist plate and then uses a developer to develop the area, rinses with deionized water and spins dry, then corrodes in aqua regia solution for 90 seconds, soaks in acetone to remove the photoresist, rinses with deionized water and spins dry.

[0040] In step (4), the method for etching the cap layer is as follows: according to citric acid: hydrogen peroxide: deionized water = 1500g: 500ml: 1.5L, the mixture is stirred evenly and placed in a 40°C constant temperature water bath. After the solution temperature stabilizes, the epitaxial wafer is placed in the mixture and etched for 2 minutes.

[0041] In step (4), the anti-reflection film structure is a titanium oxide / aluminum oxide multilayer structure.

[0042] In step (5), the method for removing the anti-reflection film on the surface of the upper electrode is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode area through the photomask and then uses a developer to develop the area, the area is rinsed with deionized water and dried, and then placed in an anti-reflection film etching solution for etching for 10 seconds, the area is rinsed with deionized water and then soaked in acetone to remove the photoresist, and the area is rinsed with deionized water and then dried, wherein the anti-reflection film etching solution is hydrofluoric acid: deionized water = 1:10 according to the volume ratio.

[0043] The reverse quadruple-junction thin-film gallium arsenide solar cell for space use is prepared by the preparation method.

[0044] In order to further understand the content and features of the present invention, the following embodiments are given as examples and described in detail with reference to the accompanying drawings:

[0045] The embodiments described with reference to the accompanying drawings are exemplary rather than all embodiments. The dimensions of the various parts shown are not drawn in proportion to the actual dimensions. They are used to describe the present invention and should not be construed as limiting the present invention.

[0046] In the description of this embodiment, it is necessary to understand that the terms indicating orientation or positional relationship such as "up, down, top, bottom" are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and cannot be understood as a limitation on the present invention.

[0047] Example

[0048] Attachment Figure 1 , 2 As shown in the figure, the preparation of reverse quadruple-junction thin-film gallium arsenide solar cells for space use includes the following steps:

[0049] Step 1: Epitaxial layer 3 growth

[0050] An epitaxial layer 3 is grown on a GaAs substrate by using a MOCVD method, and its structure is an inverted quadruple junction structure.

[0051] Step 2: Evaporation of seed layer 2

[0052] The epitaxial wafer completed in step 1 is placed in a vacuum evaporation device, and a lower electrode seed layer 2 is evaporated on the backlight surface. The lower electrode seed layer 2 is a Au-Zn-Au-Ag multilayer metal structure with a thickness of 1μm±0.3μm. After the evaporation is completed, it is taken out.

[0053] Step 3: Heat Treatment

[0054] The epitaxial wafer completed in step 2 is placed in a vacuum sintering device, heated to 350° C. in a vacuum environment and sintered for 30 minutes, and then taken out after cooling down.

[0055] Step 4: Electroplating composite metal layer 1

[0056] After completing step 3, apply a protective film to the light-receiving surface of the epitaxial wafer to protect the epitaxial layer 3 from being affected by the electroplating process. Place the epitaxial wafer in a Cu electroplating tank, and use a DC electroplating method to electroplate metal Cu on the surface of the seed layer 2 with a thickness of 20μm to 25μm. After the electroplating is completed, take it out and rinse it with deionized water, then place the epitaxial wafer in a Ni electroplating tank, and use a DC electroplating method to electroplate metal Ni on the Cu surface with a thickness of 0.8μm to 1.2μm. After completion, take it out, rinse it with deionized water and dry it.

[0057] Step 5: Temporary substrate bonding

[0058] Evenly apply organic silica gel on the light-receiving surface of the epitaxial wafer after completing step 4, adhere a glass sheet with the same size and shape as the epitaxial wafer to the light-receiving surface of the epitaxial wafer, put it into a laminator and laminate it for 10 to 20 minutes, and set the lamination temperature to 60 to 110°C.

[0059] Step 6: Etching the substrate

[0060] The epitaxial wafer completed in step 5 is placed in a mixed solution of sulfuric acid: deionized water: hydrogen peroxide in a ratio of 1:1:8 to etch and remove the GaAs substrate.

[0061] Step 7: Prepare the upper electrode

[0062] refer to Figure 3 As shown, photoresist is applied to the light-receiving surface of the epitaxial wafer. After the photolithography machine irradiates the upper electrode 4 area through the photolithography plate, the area is revealed with a developer. After rinsing with deionized water and drying, the epitaxial wafer is placed in a vacuum evaporation device to evaporate the upper electrode metal on the light-receiving surface. The upper electrode metal is a Au-Ge-Ag-Au multilayer metal structure with a thickness of 5μm±0.2μm. After the evaporation is completed, the epitaxial wafer is taken out, and the photoresist is removed by soaking in acetone, leaving only the upper electrode 4 metal pattern, which is rinsed with deionized water and dried.

[0063] Step 8: Prepare the isolation groove

[0064] After completing step 7, apply photoresist on the light-receiving surface of the epitaxial wafer. After the photolithography machine irradiates the isolation groove area through the photomask, use a developer to reveal the area. Rinse with deionized water and spin dry. Then, corrode in aqua regia solution for 30 to 60 seconds. Remove the photoresist by soaking in acetone. Rinse with deionized water and spin dry.

[0065] Step 9: Etching the cap layer

[0066] Mix 1500g of citric acid, 500ml of hydrogen peroxide and 1.5L of deionized water, stir evenly and place in a constant temperature water bath at 35℃~42℃, put in the epitaxial wafer completed in step 3 after the solution temperature stabilizes, etch for 2min, take out, rinse with deionized water and spin dry.

[0067] Step 10: Evaporation of anti-reflection film 5

[0068] The epitaxial wafer completed in step 9 is placed in a vacuum evaporation device, and an anti-reflection film 5 is evaporated on the light-receiving surface. The anti-reflection film 5 is a titanium oxide / aluminum oxide multilayer structure with a thickness of 130nm±30nm.

[0069] Step 11: Remove the anti-reflection film on the upper electrode surface

[0070] After completing step 10, photoresist is applied to the light-receiving surface of the epitaxial wafer. The photolithography machine irradiates the upper electrode 4 area through the photomask and then uses a developer to develop the area. After rinsing with deionized water and drying, the wafer is placed in an anti-reflection film etching solution (hydrofluoric acid: deionized water = 1:10) for etching for 3s to 5s. After rinsing with deionized water, the wafer is soaked in acetone to remove the photoresist. The wafer is rinsed with deionized water and dried.

[0071] Step 12: Slicing

[0072] The epitaxial wafer completed in step 11 is placed in a laser scribing machine with the light-receiving surface facing upward, and the epitaxial wafer is scribed into solar cells of a desired size according to the pattern.

[0073] Step 13: De-substrate

[0074] The epitaxial wafer completed in step 12 is immersed in an acetone solution to completely separate the solar cell from the temporary substrate.

[0075] Step 14: Cleaning

[0076] The solar cell after step 13 is placed in acetone for cleaning, and after cleaning, a reverse quadruple-junction thin-film gallium arsenide solar cell for space use is obtained.

[0077] According to tests, the average photoelectric conversion efficiency of the reverse quadruple-junction thin-film gallium arsenide solar cells used in this space is higher than 30%, and the bending radius can reach 2.5cm.

[0078] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a reverse quadruple-junction thin-film gallium arsenide solar cell for space use, characterized in that: The following steps are involved: (1) Growing an inverse quadruple junction epitaxial layer on a GaAs substrate; (2) preparing a lower electrode seed layer and a composite metal substrate on the backlight side of the epitaxial layer by evaporation-electroplating; (3) completing the transfer of the epitaxial structure by a temporary film-substrate etching method, and preparing the upper electrode on the light-receiving surface of the epitaxial layer by a photolithography-evaporation-stripping method; (4) using a photolithography-etching method to prepare the isolation groove, etching the cap layer on the light-receiving surface, and evaporating an anti-reflection film; (5) Remove the anti-reflection film on the surface of the upper electrode by photolithography-etching method, and then perform slicing, cell stripping and cleaning.

2. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (2), an Au-Zn-Au-Ag seed layer is evaporated on the backlight surface of the epitaxial wafer to a thickness of 1000-1500 nm, and a Cu / Ni composite metal is electroplated to a thickness of 10-100 μm.

3. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (3), the substrate etching method is as follows: a mixed solution of sulfuric acid: deionized water: hydrogen peroxide = 1:1:8 is prepared according to a volume ratio, and after mixing and stirring evenly, the epitaxial wafer is placed in the etching for 2-3 hours. During the etching process, the solution temperature is controlled at 30-35°C.

4. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (3), the upper electrode preparation method is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode and gate line area through the photomask and then uses a developer to reveal the area, the upper electrode metal is evaporated on the light-receiving surface after rinsing with deionized water and drying, the photoresist is removed by soaking with acetone, and only the upper electrode and gate line metal patterns are retained, which are then rinsed with deionized water and dried.

5. The reverse quadruple-junction thin-film gallium arsenide solar cell for space use and the preparation method thereof according to claim 4, characterized in that: The upper electrode metal is a Au-Ge-Ag-Au multilayer metal structure with a thickness of 5 μm±0.2 μm.

6. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (4), the isolation groove preparation method is as follows: a photolithography machine irradiates the isolation groove area through the photoresist plate and then uses a developer to develop the area, rinses with deionized water and spins dry, then corrodes in aqua regia solution for 90 seconds, soaks in acetone to remove the photoresist, rinses with deionized water and spins dry.

7. The method for preparing a reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (4), the method for etching the cap layer is as follows: according to citric acid: hydrogen peroxide: deionized water = 1500g: 500ml: 1.5L, the mixture is stirred evenly and placed in a 40°C constant temperature water bath. After the solution temperature stabilizes, the epitaxial wafer is placed in the mixture and etched for 2 minutes.

8. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (4), the anti-reflection film structure is a titanium oxide / aluminum oxide multilayer structure.

9. The method for preparing the reverse quadruple-junction thin-film gallium arsenide solar cell for space use according to claim 1, characterized in that: In step (5), the method for removing the anti-reflection film on the surface of the upper electrode is as follows: photoresist is coated on the light-receiving surface of the epitaxial wafer, a photolithography machine irradiates the upper electrode area through the photomask and then uses a developer to develop the area, the area is rinsed with deionized water and dried, and then placed in an anti-reflection film etching solution for etching for 10 seconds, the area is rinsed with deionized water and then soaked in acetone to remove the photoresist, and the area is rinsed with deionized water and then dried, wherein the anti-reflection film etching solution is hydrofluoric acid: deionized water = 1:10 according to the volume ratio.

10. A reverse quadruple-junction thin-film gallium arsenide solar cell for space use made by the preparation method according to any one of claims 1 to 9.

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