Solar cell epitaxial structure and substrate stripping method thereof

Abstract

This invention discloses a solar cell epitaxial structure and its substrate lift-off method, belonging to the field of solar cell technology. The solar cell epitaxial structure provided by this invention includes a gallium arsenide substrate, a composite sacrificial layer, and an epitaxial layer stacked together. The composite sacrificial layer includes an AlAs first sacrificial layer, an N-GaAs second sacrificial layer, and an AlAs third sacrificial layer stacked starting from the gallium arsenide substrate; the thickness of the AlAs third sacrificial layer is 3-5 nm. The solar cell epitaxial structure provided by this invention can effectively reduce damage to the epitaxial wafer during substrate lift-off, improving the yield of the obtained epitaxial wafer. This invention also provides a substrate lift-off method for the above-mentioned solar cell epitaxial structure.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a solar cell epitaxial structure and a substrate stripping method thereof. Background Technology

[0002] By employing epitaxial layer lift-off technology, the epitaxial layer with flexible battery structure is separated from the rigid gallium arsenide substrate. The resulting flexible gallium arsenide solar cell retains the advantages of rigid gallium arsenide solar cells, such as high conversion efficiency, good temperature characteristics, and strong radiation resistance, while also being lighter and more flexible. This makes it a promising candidate for applications in fields such as satellites, drones, airships, and portable power banks where weight reduction and flexible surface attachment are required.

[0003] In related technologies, epitaxial layer lift-off techniques mainly employ two methods: the first involves using ammonia or sulfuric acid etching solutions to dissolve the entire GaAs substrate; the second uses HF solution to etch only the AlAs sacrificial layer in the epitaxial structure, allowing the gallium arsenide substrate to peel off. The resulting gallium arsenide substrate can be reused. To reduce production costs, the second method is generally used; however, this method has a significant drawback, which is a technical challenge in this field: during the lift-off process, the curling stress of the flexible metal substrate (located on the surface away from the rigid substrate) pulls on the epitaxial layer, causing localized damage. The size and location of this damage are not fixed, significantly affecting the battery's appearance and electrical properties, thus severely impacting production yield.

[0004] In summary, there is a need to provide an epitaxial structure for solar cells to facilitate the stripping of gallium arsenide substrates and improve product yield. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a solar cell epitaxial structure that can effectively reduce damage to the epitaxial wafer during substrate stripping and improve the yield of the obtained epitaxial wafer.

[0006] The present invention also provides a substrate stripping method in the above-mentioned solar cell epitaxial structure.

[0007] According to an embodiment of a first aspect of the present invention, a solar cell epitaxial structure is provided, the solar cell epitaxial structure comprising a gallium arsenide substrate, a composite sacrificial layer and an epitaxial layer stacked thereon;

[0008] The composite sacrificial layer includes an AlAs first sacrificial layer, an N-GaAs second sacrificial layer, and an AlAs third sacrificial layer stacked from the gallium arsenide substrate;

[0009] The thickness of the third sacrificial layer of AlAs is 3-5 nm.

[0010] The solar cell epitaxial structure according to embodiments of the present invention has at least the following beneficial effects:

[0011] (1) In traditional technology, only one sacrificial layer is usually set, or multiple sacrificial layers that can be corroded at the same time are set. As a result, when corroding the sacrificial layer, the corrosive liquid is prone to damage to the epitaxial layer.

[0012] This invention creatively employs a three-layer sacrificial structure. The second N-GaAs sacrificial layer is made of a different material than the other sacrificial layers, preventing it from being simultaneously corroded. The third sacrificial layer is relatively thin. In the stacked structure, specifically in the presence of the second N-GaAs sacrificial layer, the sidewall opening created by the corrosion of the third AlAs sacrificial layer is very small, preventing effective contact between the corrosive liquid and the third AlAs sacrificial layer, thus hindering its corrosion. Therefore, this invention, through adjustments to the structure, material, and thickness of the composite sacrificial layers, allows for the sequential corrosion of the first AlAs sacrificial layer, the second N-GaAs sacrificial layer, and the third AlAs sacrificial layer. Based on this:

[0013] When etching the first sacrificial layer of AlAs, the second sacrificial layer of N-GaAs will be damaged instead of the epitaxial layer; it is equivalent to transferring the unwanted damage to the second sacrificial layer of N-GaAs. Similarly, when etching the second sacrificial layer of N-GaAs, the epitaxial layer will not be damaged. Since the third sacrificial layer of AlAs is very thin and the etching time is very short, the damage to the epitaxial layer caused during the etching process can be ignored.

[0014] Furthermore, if the third sacrificial layer of AlAs is not included, and the goal of the present invention is achieved by adjusting the thickness of the second sacrificial layer of N-GaAs, it will be difficult to control the endpoint of the corrosion of the composite sacrificial layer due to the similarity of materials between the second sacrificial layer of N-GaAs and the epitaxial layer, which may easily cause damage to the epitaxial layer.

[0015] In other words, by adjusting the structure, material, and thickness of the composite sacrificial layer, the present invention can improve the yield of the epitaxial layer obtained during the gallium arsenide substrate stripping process.

[0016] (2) The material of the composite sacrificial layer selected in this invention has high lattice matching with the gallium arsenide (GaAs) substrate, which is conducive to the growth of high-quality epitaxial layers;

[0017] According to some embodiments of the present invention, the thickness of the AlAs first sacrificial layer is ≤20 nm. For example, it can be 10–18 nm. If the thickness of the AlAs first sacrificial layer is >20 nm, a longer etching time is required for complete etching. Within the above range, on the one hand, there is sufficient thickness to provide a larger corrosion sidewall opening, promoting the etching of the AlAs first sacrificial layer, and on the other hand, the etching time for etching the AlAs first sacrificial layer is saved to the greatest extent.

[0018] According to some embodiments of the present invention, the thickness of the first AlAs sacrificial layer is 14–16 nm. For example, it can be approximately 15 nm.

[0019] According to some embodiments of the present invention, the thickness of the N-GaAs second sacrificial layer is 100–200 nm. Specifically, it can be 110–130 nm. More specifically, it can be approximately 120 nm.

[0020] According to some embodiments of the present invention, the epitaxial layer includes an N-GaAs negative electrode contact layer, a GaInP top cell, a middle-top tunnel junction, a GaAs middle cell, a middle-bottom tunnel junction, an InGaAs bottom cell, and a P-GaAs positive electrode contact layer, which are sequentially stacked starting from the composite sacrificial layer.

[0021] According to some embodiments of the present invention, the thickness of the N-GaAs negative electrode contact layer is 180–350 nm. For example, it can be approximately 200 nm or 220 nm.

[0022] According to some embodiments of the present invention, the thickness of the GaInP top cell is 600–1000 nm. For example, it can be approximately 700 nm, 750 nm, or 800 nm.

[0023] According to some embodiments of the present invention, the thickness of the central-top tunnel junction is 20–30 nm. For example, it can be approximately 24 nm, 25 nm, or 26 nm.

[0024] According to some embodiments of the present invention, the thickness of the cell in the GaAs is 2500–4000 nm. For example, it can be approximately 2800 nm, 3000 nm, or 3200 nm.

[0025] According to some embodiments of the present invention, the thickness of the mid-bottom tunnel junction is 20–30 nm. For example, it can be approximately 24 nm, 25 nm, or 26 nm.

[0026] According to some embodiments of the present invention, the thickness of the InGaAs substrate is 4000–6500 nm. For example, it can be approximately 5000 nm, 5500 nm, or 5800 nm.

[0027] According to some embodiments of the present invention, the thickness of the P-GaAs positive electrode contact layer is 250–400 nm. For example, it can be approximately 270 nm, 300 nm, or 320 nm.

[0028] According to some embodiments of the present invention, the solar cell epitaxial structure further includes a flexible metal substrate disposed on the surface of the epitaxial layer away from the gallium arsenide substrate.

[0029] According to some embodiments of the present invention, the flexible metal substrate includes a copper substrate.

[0030] The thickness of the copper substrate is 15–30 μm. Specifically, it can be approximately 18 μm, 20 μm, or 25 μm.

[0031] According to some embodiments of the present invention, the method for setting the composite sacrificial layer in the solar cell epitaxial structure includes MOCVD (Metal-organic Chemical Vapor Deposition).

[0032] According to some embodiments of the present invention, the method for setting the epitaxial layer includes MOCVD.

[0033] According to some embodiments of the present invention, the method for setting the flexible metal substrate includes at least one of MOCVD and electroplating.

[0034] According to an embodiment of a second aspect of the present invention, a substrate stripping method for the aforementioned solar cell epitaxial structure is provided, the substrate stripping method comprising the following steps:

[0035] S1. Etch the AlAs first sacrificial layer with an aqueous HF solution A;

[0036] S2. The N-GaAs second sacrificial layer is corroded with an oxidizing ammonia solution;

[0037] S3. Etch the third sacrificial layer of AlAs with an aqueous solution of HF B.

[0038] Since the substrate lift-off method employs all the technical solutions of the solar cell epitaxial structure described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Specifically, the AlAs first sacrificial layer, N-GaAs second sacrificial layer, and AlAs third sacrificial layer can be sequentially etched away, resulting in a high-yield epitaxial wafer.

[0039] According to some embodiments of the present invention, in step S1, the concentration of HF in the HF aqueous solution A is 20-30 wt%. For example, it can be about 21 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 28 wt%, or 29 wt%.

[0040] For example, it can be prepared by mixing approximately 49 wt% concentrated HF aqueous solution and water at a volume ratio of 1:0.7 to 1.4. More specifically, it can be prepared by mixing at a volume ratio of approximately 1:0.9, 1:1, or 1:1.1.

[0041] According to some embodiments of the present invention, in step S1, the corrosion duration is 18 to 24 hours. For example, it can be approximately 20 hours.

[0042] In step S1, the gallium arsenide substrate is separated from other components, the first AlAs sacrificial layer is etched, and the surface of the second N-GaAs sacrificial layer is exposed.

[0043] According to some embodiments of the present invention, in step S2, the oxidizing agent in the oxidizing ammonia solution includes hydrogen peroxide.

[0044] According to some embodiments of the present invention, the concentration of the oxidant in the oxidizing ammonia solution is 0.6 to 0.85 wt%. Specifically, it may be about 0.7 wt% or about 0.75 wt%.

[0045] According to some embodiments of the present invention, the concentration of ammonia in the oxidizing ammonia solution is 0.5 to 0.75 wt%. The ammonia concentration is expressed as the concentration of NH3. Specifically, it may be about 0.6 wt% or about 0.7 wt%.

[0046] Specifically, the preparation method of the oxidizing ammonia solution includes mixing concentrated ammonia, concentrated hydrogen peroxide, and water. The concentration of the concentrated ammonia is 25-28 wt%. The concentration of the concentrated hydrogen peroxide is approximately 30 wt%. The volume ratio of the concentrated ammonia to the concentrated hydrogen peroxide is 1:0.8-1.2, for example, approximately 1:1. The volume ratio of the concentrated ammonia to water is 1:35-45, for example, approximately 1:40.

[0047] According to some embodiments of the present invention, in step S2, the corrosion includes vibration corrosion.

[0048] According to some embodiments of the present invention, in step S2, the corrosion duration is 0.5 to 1.5 minutes. For example, it can be approximately 1 minute.

[0049] Since the oxidizing ammonia solution used in step S2 does not react with the third sacrificial AlAs layer, the corrosion rate in step S2 can be relatively fast, and the requirement for corrosion duration is not very strict.

[0050] According to some embodiments of the present invention, in step S3, the concentration of HF in the HF aqueous solution B is 15-25 wt%. For example, it can be about 19 wt% or about 20 wt%.

[0051] Specifically, the preparation method of the HF aqueous solution B includes mixing a concentrated HF aqueous solution and water. The concentration of the concentrated HF aqueous solution is approximately 49 wt%. The volume ratio of the concentrated HF aqueous solution to water is 1:1.2 to 2.0. For example, it can be approximately 1:1.5.

[0052] According to some embodiments of the present invention, in step S3, the corrosion includes vibration corrosion.

[0053] According to some embodiments of the present invention, in step S3, the corrosion duration is 3 to 7 minutes. For example, it can be approximately 5 minutes.

[0054] According to some embodiments of the present invention, the process yield of the substrate stripping method is ≥95%. In this yield, "good product" refers to a product in which the epitaxial layer has not been corroded or damaged during the substrate stripping process.

[0055] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0056] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0057] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0058] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0059] Figure 1 This is a schematic diagram of the solar cell epitaxial structure provided in Embodiment 1 of the present invention.

[0060] Figure 2 This is a schematic diagram of the structure of the component obtained in step S1 of embodiment 2 of the present invention.

[0061] Figure 3 This is a schematic diagram of the structure of the component obtained in step S2 of embodiment 2 of the present invention.

[0062] Figure 4 This is a schematic diagram of the structure of the component obtained in step S3 of embodiment 2 of the present invention.

[0063] Figure label:

[0064] Gallium arsenide substrate 100;

[0065] Composite sacrificial layer 200, AlAs first sacrificial layer 210, N-GaAs second sacrificial layer 220, AlAs third sacrificial layer 230;

[0066] Epitaxial layer 300, N-GaAs negative electrode contact layer 310, GaInP top cell 320, middle-top tunnel junction 330, GaAs middle cell 340, middle-bottom tunnel junction 350, InGaAs bottom cell 360, P-GaAs positive electrode contact layer 370.

[0067] Flexible metal substrate 400. Detailed Implementation

[0068] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0069] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] Example 1

[0071] This example provides a solar cell epitaxial structure, comprising a gallium arsenide substrate 100, a composite sacrificial layer 200, an epitaxial layer 300, and a flexible metal substrate 400 stacked together; wherein:

[0072] The gallium arsenide substrate 100 has a size of 4 inches;

[0073] The composite sacrificial layer 200 consists of a 15nm thick AlAs first sacrificial layer 210, a 120nm thick N-GaAs second sacrificial layer 220, and a 3nm thick AlAs third sacrificial layer 230 stacked from the gallium arsenide substrate 100.

[0074] The epitaxial layer 300 is composed of an N-GaAs negative electrode contact layer 310 with a thickness of 200 nm, a GaInP top cell 320 with a thickness of 750 nm, a middle-top tunnel junction 330 with a thickness of 25 nm, a GaAs middle cell 340 with a thickness of 3000 nm, a middle-bottom tunnel junction 350 with a thickness of 25 nm, an InGaAs bottom cell 360 with a thickness of 5500 nm, and a P-GaAs positive electrode contact layer 370 with a thickness of 300 nm, which are stacked from the composite sacrificial layer 200.

[0075] The flexible metal substrate 400 is made of copper and has a thickness of 20 μm.

[0076] In this example, the composite sacrificial layer 200 and the epitaxial layer 300 are fabricated by MOCVD, and the flexible metal substrate 400 is fabricated by electroplating.

[0077] The solar cell epitaxial structure provided in this example is as follows: Figure 1 As shown.

[0078] Example 2

[0079] This example provides a substrate lift-off method for an epitaxial structure of a solar cell, with the following specific steps:

[0080] S1. The solar cell epitaxial structure obtained in Example 1 is placed in HF aqueous solution A with the flexible metal substrate 400 facing upward. After 20 hours of corrosion, the AlAs first sacrificial layer 210 is corroded and dissolved, exposing the surface of the N-GaAs second sacrificial layer 220, and the gallium arsenide substrate 100 falls off.

[0081] The HF aqueous solution A is prepared by mixing 49 wt% concentrated HF aqueous solution with water at a volume ratio of 1:1.

[0082] The structure of the component obtained in this step is as follows: Figure 2 As shown.

[0083] S2. Place the component obtained in step S1 into an oxidizing ammonia solution and agitate it for 1 minute to corrode it. The second sacrificial layer 220 of N-GaAs is corroded away, exposing the surface of the third sacrificial layer 230 of AlAs.

[0084] The oxidizing ammonia solution is a mixture of concentrated ammonia (25-28 wt%), concentrated hydrogen peroxide (about 30 wt%), and water in a volume ratio of 1:1:40.

[0085] The structure of the component obtained in this step is as follows: Figure 3 As shown.

[0086] S3. Place the component obtained in step S2 in HF aqueous solution B and shake it for 5 minutes to etch away the third sacrificial layer 230 of AlAs.

[0087] Among them, HF aqueous solution B is a mixture of concentrated HF aqueous solution (49wt%) and water at a volume ratio of 1:1.5.

[0088] The structure of the component obtained in this example is as follows: Figure 4 As shown.

[0089] Comparative Example 1

[0090] This example provides a solar cell epitaxial structure, which differs from Example 1 in that:

[0091] Excluding the 120nm thick N-GaAs second sacrificial layer 220 and the 3nm thick AlAs third sacrificial layer 230.

[0092] Comparative Example 2

[0093] This example provides a substrate lift-off method for a solar cell epitaxial structure. The specific steps differ from those in Example 2 as follows:

[0094] (1) The solar cell epitaxial structure obtained in Comparative Example 1 is adopted.

[0095] (2) Steps S2 to S3 are not included.

[0096] Test case

[0097] This example counts the number of good products out of 200 products obtained in Example 2 and Comparative Example 2 for different construction dates, and calculates the yield of Example 2 and Comparative Example 2. Good products refer to those where the N-GaAs negative electrode contact layer 310 is not corroded or damaged.

[0098] The results show that the substrate removal method provided in Comparative Example 2 has a process yield of 70-75%. The substrate removal method provided in Example 2 has a process yield of >95%.

[0099] Therefore, it can be seen that the solar cell epitaxial structure provided by the present invention, through the design of the composite sacrificial layer 200 structure, material and thickness, combined with the limitation of parameters in the substrate stripping method, can significantly improve the process yield.

[0100] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

Claims

1. A solar cell epitaxial structure, characterized by, The solar cell epitaxial structure includes a gallium arsenide substrate, a composite sacrificial layer, and an epitaxial layer stacked together. The composite sacrificial layer includes an AlAs first sacrificial layer, an N-GaAs second sacrificial layer, and an AlAs third sacrificial layer stacked from the gallium arsenide substrate; The thickness of the first sacrificial layer of AlAs is 10~18nm; The thickness of the second sacrificial layer of N-GaAs is 100~200nm; The thickness of the third sacrificial layer of AlAs is 3~5nm.

2. The solar cell epitaxial structure of claim 1, wherein The epitaxial layer includes an N-GaAs negative electrode contact layer, a GaInP top cell, a middle-top tunnel junction, a GaAs middle cell, a middle-bottom tunnel junction, an InGaAs bottom cell, and a P-GaAs positive electrode contact layer, which are sequentially stacked starting from the composite sacrificial layer; and / or, the solar cell epitaxial structure further includes a flexible metal substrate, which is disposed on the surface of the epitaxial layer away from the gallium arsenide substrate.

3. A method of substrate lift-off of a solar cell epitaxial structure according to any one of claims 1 to 2, characterized in that, The substrate stripping method includes the following steps: S1. Etch the AlAs first sacrificial layer with an aqueous HF solution A; S2. The N-GaAs second sacrificial layer is corroded with an oxidizing ammonia solution; S3. Etch the third sacrificial layer of AlAs with an aqueous solution of HF B.

4. The substrate peeling method according to claim 3, wherein In step S1, the concentration of HF in the HF aqueous solution A is 20~30wt%.

5. The substrate peeling method according to claim 3, wherein In step S2, the oxidizing agent in the oxidizing ammonia solution includes hydrogen peroxide.

6. The substrate peeling method according to claim 5, wherein The concentration of the oxidant in the oxidizing ammonia solution is 0.6~0.85wt%; and / or, the concentration of ammonia in the oxidizing ammonia solution is 0.5~0.75wt%.

7. The substrate peeling method according to claim 6, wherein In step S3, the concentration of HF in the HF aqueous solution B is 15~25wt%.

8. The substrate peeling method according to any one of claims 3 to 6, wherein In step S3, the corrosion includes vibration corrosion; and / or, in step S3, the corrosion duration is 3~7 minutes.

9. The substrate peeling method according to any one of claims 3 to 6, wherein The process yield of the substrate stripping method is ≥95%.

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