Multi-junction solar cell structure and preparation method thereof

Abstract

The invention discloses a multi-junction solar cell structure and a preparation method thereof, and relates to the technical field of solar cells, the multi-junction solar cell structure comprises a first substrate, a first ohmic contact layer, a plurality of sub-cells and a second ohmic contact layer, the second ohmic contact layer comprises a first sub-layer and a second sub-layer which are stacked in the direction deviating from the first substrate, the first sub-layer is a material layer containing In, the second sub-layer is a GaAs layer or a GaAsSb layer, namely, the first sub-layer containing In is further covered with the GaAs layer or the GaAsSb layer not containing In to serve as the second sub-layer, In atoms volatilized by the first sub-layer containing In to the reaction chamber are reduced or avoided, and the reaction efficiency is improved. According to the multi-junction solar cell structure and the preparation method thereof, resident In atoms in the reaction chamber are reduced, pollution and influence of the resident In atoms on the reaction chamber are reduced, the preparation yield of the multi-junction solar cell structure is improved, and good ohmic contact can be formed between the second sub-layer and the metal electrode.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a solar cell structure and a preparation method thereof. Background Art

[0002] Solar cells can directly convert solar energy into electrical energy and are an effective form of clean energy. III-V compound semiconductor solar cells have the highest conversion efficiency in the current material system. They also have the advantages of good high temperature resistance and strong radiation resistance. They are recognized as a new generation of high-performance and long-life space main power sources. The most studied gallium arsenide-based triple-junction solar cells currently use a lattice-matched GaInP / InGaAs / Ge structure and have been widely used in the aerospace field. However, the band gap combination of GaInP / InGaAs / Ge triple-junction solar cells is far from the optimal conditions of the solar spectrum, and its photoelectric conversion efficiency is difficult to further improve.

[0003] In recent years, the research focus has gradually shifted to bandgap-matched (Al)GaInP / GaAs / InGaAs triple-junction solar cells, whose theoretical efficiency can reach 50% under high-power concentration conditions. (Al)GaInP / GaAs / InGaAs triple-junction solar cells are usually inverted growth structures. Specifically, after forming stacked (Al)GaInP subcells, GaAs subcells, and InGaAs subcells on a GaAs substrate, the epitaxial wafer is bonded to a flexible PI substrate or an electroplated Cu substrate, and then flipped over and the GaAs substrate is peeled off, thereby preparing a flexible thin-film solar cell with a high weight-to-power ratio. The peeled GaAs substrate can be reused after processing, greatly reducing the cost of battery production.

[0004] However, in the process of preparing the epitaxial structure of the existing inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell, since the InGaAs material used in the InGaAs sub-cell close to the surface of the cell epitaxial structure has a high In component, and the surface of the cell epitaxial structure is usually an In-containing ohmic contact layer, after the In-containing ohmic contact layer is grown, the In atoms in the In-containing ohmic contact layer are easily volatilized and reside in the reaction chamber. When a new cell epitaxial structure continues to be prepared in the reaction chamber, the In atoms resident in the reaction chamber will nucleate in the new cell epitaxial structure to form defects, affecting the cell performance. Summary of the invention

[0005] To solve the above technical problems, the embodiments of the present application provide a multi-junction solar cell structure and a method for preparing the same, so as to reduce or avoid the In-containing ohmic contact layer located on the surface of the cell epitaxial structure from volatilizing In atoms into the reaction chamber, thereby reducing the resident In atoms in the reaction chamber, that is, reducing the contamination and impact of the resident In atoms on the reaction chamber, and improving the preparation yield of the multi-junction solar cell structure.

[0006] To achieve the above objectives, the present application provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides a multi-junction solar cell structure, comprising:

[0008] a first substrate;

[0009] A first ohmic contact layer, a plurality of sub-cells, and a second ohmic contact layer are located on one side of the first substrate and are stacked in a direction away from the first substrate;

[0010] The second ohmic contact layer includes a first sublayer and a second sublayer stacked in a direction away from the first substrate, the first sublayer is an In-containing material layer, and the second sublayer is a GaAs layer or a GaAsSb layer.

[0011] Optionally, the first sublayer is an InGaAs layer.

[0012] Optionally, the first sublayer is an AlInGaAs layer.

[0013] Optionally, the Al component x of the first sublayer satisfies: 0<x≤0.2.

[0014] Optionally, the thickness of the second sub-layer ranges from 10 nm to 100 nm, including endpoint values.

[0015] Optionally, the thickness of the first sublayer ranges from 100 nm to 500 nm, including endpoint values.

[0016] Optionally, the plurality of sub-cells include a first sub-cell, a second sub-cell, and a third sub-cell stacked in a direction away from the first substrate, a first tunnel junction is provided between the first sub-cell and the second sub-cell, and a second tunnel junction and a metamorphic buffer layer are provided between the second sub-cell and the third sub-cell, which are stacked in a direction away from the first substrate;

[0017] The first subcell is an AlGaInP subcell or a GaInP subcell, the second subcell is a GaAs subcell, and the third subcell is an InGaAs subcell.

[0018] Optionally, the metamorphic buffer layer is an AlGaInAs layer or a GaInP layer, and the metamorphic buffer layer includes an m-layer sequence stacked along the direction from the second sub-cell to the third sub-cell, m≥3, and m is an integer, the lattice constant of each layer of the sequence is greater than the lattice constant of the second sub-cell, and the lattice constant of each layer of the sequence increases along the direction from the second sub-cell to the third sub-cell, and the lattice constant of the m-th layer of the sequence is greater than the lattice constant of the third sub-cell.

[0019] Optionally, the In composition y of the first sublayer satisfies: 0.2≤y≤0.4.

[0020] Optionally, a sacrificial layer is further disposed between the first substrate and the first ohmic contact layer, and the sacrificial layer is an AlAs layer.

[0021] In a second aspect, an embodiment of the present application provides a method for preparing a multi-junction solar cell structure, comprising:

[0022] providing a first substrate;

[0023] A sacrificial layer, a first ohmic contact layer, a plurality of sub-cells and a second ohmic contact layer are formed on one side of the first substrate, wherein the second ohmic contact layer comprises a first sub-layer and a second sub-layer which are stacked in a direction away from the first substrate, wherein the first sub-layer is an In-containing material layer, and the second sub-layer is a GaAs layer or a GaAsSb layer;

[0024] Transferring the battery epitaxial structure formed by the first ohmic contact layer to the second ohmic contact layer onto a second substrate from one side of the second ohmic contact layer;

[0025] The sacrificial layer is corroded to peel off the first substrate.

[0026] Compared with the prior art, the above technical solution has the following advantages:

[0027] The multi-junction solar cell structure provided in the embodiment of the present application includes a first substrate and a first ohmic contact layer located on one side of the first substrate and stacked in a direction away from the first substrate, a plurality of sub-cells and a second ohmic contact layer, the second ohmic contact layer includes a first sub-layer and a second sub-layer stacked in a direction away from the first substrate, the first sub-layer is a material layer containing In, and the second sub-layer is a GaAs layer or a GaAsSb layer, that is, when forming the second ohmic contact layer on the surface layer of the cell epitaxial structure, the first sub-layer containing In is first grown, and then the GaAs layer or the GaAsSb layer is grown as the second sub-layer, so that not only the first sub-layer and the second sub-layer together constitute an ohmic contact layer to form a good ohmic contact with the metal electrode, but also, because the first sub-layer containing In is also covered with a GaAs layer or a GaAsSb layer as the second sub-layer, and the second sub-layer is a material layer not containing In, therefore, the volatilization of In atoms from the first sub-layer containing In to the reaction chamber can be reduced or avoided, thereby reducing the resident In atoms in the reaction chamber, that is, reducing the pollution and influence of the resident In atoms on the reaction chamber, and improving the preparation yield of the multi-junction solar cell structure. Furthermore, in the second ohmic contact layer, the second sublayer is closer to the metal electrode than the first sublayer, and the second sublayer is a GaAs layer or a GaAsSb layer, which can form a good ohmic contact with the metal electrode.

[0028] Other objects and advantages of the present application will be described in detail in the following embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A schematic cross-sectional view of a multi-junction solar cell structure provided in an embodiment of the present application;

[0031] Figure 2 For the general Figure 1 The schematic diagram of the intermediate structure of the multi-junction solar cell structure transferred from the first substrate to the second substrate;

[0032] Figure 3 For the general Figure 1 The schematic diagram of the structure of the multi-junction solar cell after the structure is transferred from the first substrate to the second substrate and the first substrate is removed;

[0033] Figure 4 for Figure 1 A specific cross-sectional schematic diagram of a multi-junction solar cell structure is shown.

[0034] Reference numerals:

[0035] First substrate-100; second substrate-110; first ohmic contact layer-200; multiple sub-cells 300; first sub-cell-310; second sub-cell-320; third sub-cell-330; first tunnel junction-340; second tunnel junction-350; metamorphic buffer layer-360; second ohmic contact layer-400; first sub-layer-410; second sub-layer-420; sacrificial layer-500; first window layer-311; first emitter region-312; first base region-313; first back field layer-314; second window layer-321; second emitter region-322; second base region-323; second back field layer-324; third window layer-331; third emitter region-332; third base region-333; third back field layer-334. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and need not be used to describe a specific order or sequential order. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances, which is only to describe the distinction mode adopted by the objects of the same attributes when describing in the embodiments of the present application. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, so that the process, method, system, product or equipment comprising a series of units need not be limited to those units, but may include other units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0038] Secondly, the present application is described in detail with reference to the schematic diagram. When describing the embodiments of the present application in detail, for the sake of convenience, the drawings showing the device structure will not be partially enlarged according to the general scale, and the schematic diagram is only an example, which should not limit the scope of protection of the present application. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0039] As described in the background technology section, in the process of preparing the epitaxial structure of the existing inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell, since the InGaAs material used in the InGaAs sub-cell close to the surface of the cell epitaxial structure has a higher In component, and the surface of the cell epitaxial structure is usually an In-containing ohmic contact layer, after the In-containing ohmic contact layer is grown, the In atoms in the In-containing ohmic contact layer are easily volatilized and reside in the reaction chamber. When a new cell epitaxial structure continues to be prepared in the reaction chamber, the In atoms resident in the reaction chamber will nucleate in the new cell epitaxial structure to form defects, affecting the cell performance.

[0040] In view of this, the present application provides a multi-junction solar cell structure. Figure 1 A cross-sectional schematic diagram of a multi-junction solar cell structure provided in an embodiment of the present application is shown. Figure 1 As shown, the multi-junction solar cell structure includes a first substrate 100 and a first ohmic contact layer 200, a plurality of sub-cells 300 and a second ohmic contact layer 400, which are stacked along a direction away from the first substrate 100 and located on one side of the first substrate 100, wherein the second ohmic contact layer 400 includes a first sublayer 410 and a second sublayer 420 stacked along a direction away from the first substrate 100, the first sublayer 410 is an In-containing material layer, and the second sublayer 420 is a GaAs layer or a GaAsSb layer.

[0041] Optionally, the first substrate 100 may be a GaAs substrate.

[0042] Optionally, the first ohmic contact layer 200 may be an n-type ohmic contact layer, for example, the first ohmic contact layer 200 may be an n-type GaAs layer, and the second ohmic contact layer 400 may be a p-type ohmic contact layer, but the present application does not limit this. Alternatively, the first ohmic contact layer 200 may be a p-type ohmic contact layer, and the second ohmic contact layer 400 may be an n-type ohmic contact layer.

[0043] It is understandable that the first ohmic contact layer 200 forms an ohmic contact with a metal electrode, and the second ohmic contact layer 400 forms an ohmic contact with another metal electrode, so as to facilitate the extraction of the current generated by the multiple sub-cells 300 absorbing sunlight.

[0044] It should be noted that the multi-junction solar cell structure provided in the embodiment of the present application may be an inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure. Figure 1As shown, the multiple sub-cells 300 may include a first sub-cell 310, a second sub-cell 320 and a third sub-cell 330 stacked in a direction away from the first substrate 100, a first tunnel junction 340 is arranged between the first sub-cell 310 and the second sub-cell 320, and a second tunnel junction 350 and a metamorphic buffer layer 360 stacked in a direction away from the first substrate 100 are arranged between the second sub-cell 320 and the third sub-cell 330; the first sub-cell 310 is an AlGaInP sub-cell or a GaInP sub-cell, the second sub-cell 320 is a GaAs sub-cell, and the third sub-cell 330 is an InGaAs sub-cell.

[0045] And, at this time, if Figure 1 As shown, a sacrificial layer 500 may be provided between the first substrate 100 and the first ohmic contact layer 200, and the sacrificial layer 500 may be an AlAs layer. That is, the sacrificial layer 500, the first ohmic contact layer 200, the first sub-cell 310, the first tunnel junction 340, the second sub-cell 320, the second tunnel junction 350, the metamorphic buffer layer 360, the third sub-cell 330 and the second ohmic contact layer 400 are stacked in a direction away from the first substrate 100 on one side of the first substrate 100, and the second ohmic contact layer 400 (especially the second sub-layer 420) is the surface layer of the cell epitaxial structure.

[0046] Furthermore, if Figure 2 As shown, the cell epitaxial structure composed of the first ohmic contact layer 200 to the second ohmic contact layer 400 is transferred onto the second substrate 110 from the side of the second ohmic contact layer 400 .

[0047] For example Figure 3 As shown, the sacrificial layer 500 (AlAs layer) is corroded by HF etching solution, and the first substrate 100 is peeled off. The second substrate 110 can be a PI substrate or an electroplated Cu substrate, which forms an ohmic contact with the second ohmic contact layer 400 as a metal electrode, and a metal electrode is also formed on the first ohmic contact layer 200 ( Figure 3 In this way, an inverted (Al)GaInP / GaAs / InGaAs triple junction solar cell structure can be formed.

[0048] However, the multi-junction solar cell structure provided in the embodiments of the present application is not limited to the inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure, but may also be a forward multi-junction solar cell structure, or a multi-junction solar cell structure of other materials. As long as the surface layer of the cell epitaxial structure is a material layer that makes ohmic contact and contains In during the epitaxial growth process of the multi-junction solar cell structure, the In atoms in the material layer that makes ohmic contact and contains In on the surface layer of the cell epitaxial structure are easily volatilized and remain in the reaction chamber, resulting in the problem that the In atoms remaining in the reaction chamber will nucleate in the new cell structure to form defects, thereby affecting the cell performance.

[0049] Based on this, the multi-junction solar cell structure provided in the embodiment of the present application forms a stacked first ohmic contact layer 200, a plurality of sub-cells 300 and a second ohmic contact layer 400 on one side of the first substrate 100 in a direction away from the first substrate 100, especially when forming the second ohmic contact layer 400 on the surface layer of the cell epitaxial structure, first grows a first sub-layer 410 containing In, and then grows a GaAs layer or a GaAsSb layer as the second sub-layer 420. In this way, not only the first sub-layer 410 and the second sub-layer 420 together constitute an ohmic contact layer to form a good ohmic contact with the metal electrode, but also, since the first sub-layer 410 containing In is also covered with a GaAs layer or a GaAsSb layer as the second sub-layer 420, and the second sub-layer 420 is a material layer that does not contain In, therefore, the volatilization of In atoms from the first sub-layer 410 containing In to the reaction chamber can be reduced or avoided, thereby reducing the resident In atoms in the reaction chamber, that is, reducing the pollution and influence of the resident In atoms on the reaction chamber, and improving the preparation yield of the multi-junction solar cell structure. Furthermore, in the second ohmic contact layer 400 , the second sublayer 420 is closer to the metal electrode than the first sublayer 410 , and the second sublayer 420 is made of a GaAs layer or a GaAsSb layer, which can form a good ohmic contact with the metal electrode.

[0050] Optionally, in some embodiments of the present application, the first sublayer 410 of the second ohmic contact layer 400 may be an InGaAs layer.

[0051] refer to Figure 3As shown, when the multi-junction solar cell structure provided by the embodiment of the present application is an inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure, if the first sublayer 410 in the second ohmic contact layer 400 is an InGaAs layer, then the first sublayer 410 (InGaAs layer) and the third subcell 330 (InGaAs subcell) and the second subcell 320 (GaAs subcell) are lattice-matched, which helps to reduce the defects and stress caused by lattice mismatch, thereby improving the overall performance and stability of the battery. In addition, the energy band structure of the InGaAs material makes the first sublayer 410 suitable as a p-type ohmic contact layer, which can effectively form a good energy level match with other parts of the battery, which is beneficial to the transmission and collection of carriers, and can also improve the contact characteristics between the battery and the metal electrode, reduce the contact resistance, and thus improve the current output and efficiency of the battery.

[0052] However, still refer to Figure 3 As shown, when the multi-junction solar cell structure provided by the embodiment of the present application is an inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure, after the sunlight is absorbed by the first subcell 310, the second subcell 320 and the third subcell 330 in sequence, there is usually excess light reaching the second ohmic contact layer 400 and the metal electrode (i.e., the second substrate 110) that forms an ohmic contact with the second ohmic contact layer 400. The metal electrode can be used to reflect the light to reflect the excess light back, so that each subcell can absorb the sunlight for the second time, thereby effectively reducing the thickness of the subcell and improving the performance of the solar cell. However, when the first sublayer 410 of the second ohmic contact layer 400 is an InGaAs layer, due to the small band gap of the InGaAs material, the first sublayer 410 may absorb part of the light, affecting the secondary absorption effect of the battery.

[0053] At this time, when the second sublayer 420 of the second ohmic contact layer 400 is a GaAs layer, since the band gap of the GaAs material is larger than the band gap of the InGaAs material, when the thickness of the second ohmic contact layer 400 remains unchanged, the second ohmic contact layer 400 is provided to include the first sublayer 410 (InGaAs layer) and the second sublayer 420 (GaAs layer). Compared with the second ohmic contact layer 400 being the first sublayer 410 (InGaAs layer) as a whole, it absorbs less light, thereby improving the secondary absorption effect of the battery.

[0054] However, when the second sublayer 420 of the second ohmic contact layer 400 is a GaAs layer, due to the lattice mismatch between the GaAs material and the InGaAs material of the third sub-cell 330 (InGaAs sub-cell) and the InGaAs material of the first sublayer 410 (InGaAs layer), the thickness of the second sublayer 420 can be set to be thinner. Optionally, the thickness of the second sublayer 420 ranges from 10nm to 100nm, including endpoint values, so that the second sublayer 420 (GaAs layer) is in a strained state to avoid the lattice mismatch affecting the device performance.

[0055] In addition, when the second sublayer 420 of the second ohmic contact layer 400 is a GaAsSb layer, the GaAsSb material is lattice matched with the InGaAs material of the third subcell 330 (InGaAs subcell) and the InGaAs material of the first sublayer 410 (InGaAs layer). However, the band gap of the GaAsSb material is relatively smaller than the band gap of the InGaAs material. To avoid the second sublayer 420 absorbing more light, the thickness of the second sublayer 420 can be set to be thinner. Optionally, the thickness of the second sublayer 420 ranges from 10nm to 100nm, including the end value, so that the overall absorption of light by the second ohmic contact layer 400 is substantially not increased.

[0056] Taking into account that the first sublayer 410 of the second ohmic contact layer 400 may absorb light when it is an InGaAs layer, thereby affecting the secondary absorption effect of the battery, another option is that in some embodiments of the present application, the first sublayer 410 of the second ohmic contact layer 400 may be an AlInGaAs layer. Since the band gap of the AlInGaAs material is large, the absorption of light by the second ohmic contact layer 400 can be significantly reduced, thereby improving the secondary absorption effect of the battery.

[0057] However, when the first sublayer 410 of the second ohmic contact layer 400 is an AlInGaAs layer, due to the presence of the Al component, it is difficult for the first sublayer 410 to form a good ohmic contact with the metal electrode. At this time, the second sublayer 420 of the second ohmic contact layer 400 is a GaAs layer or a GaAsSb layer, and the second sublayer 420 is closer to the metal electrode than the first sublayer 410. Therefore, the second sublayer 420 can form a good ohmic contact with the metal electrode.

[0058] Furthermore, when the second sublayer 420 of the second ohmic contact layer 400 is a GaAs layer, since the band gap of the GaAs material is also large, the absorption of light by the second ohmic contact layer 400 can be further reduced, thereby improving the secondary absorption effect of the battery. However, since the GaAs material is lattice mismatched with the InGaAs material of the third subcell 330 (InGaAs subcell), the thickness of the second sublayer 420 can be set to be thinner. Optionally, the thickness of the second sublayer 420 ranges from 10nm to 100nm, including the end value, so that the second sublayer 420 (GaAs layer) is in a strained state to avoid the lattice mismatch affecting the device performance.

[0059] When the second sublayer 420 of the second ohmic contact layer 400 is a GaAsSb layer, the GaAsSb material is lattice matched with the InGaAs material of the third subcell 330 (InGaAs subcell). However, the band gap of the GaAsSb material is relatively small. To avoid the absorption of light by the second sublayer 420, the thickness of the second sublayer 420 can be set to be thinner. Optionally, the thickness of the second sublayer 420 ranges from 10nm to 100nm, including the end value. Therefore, because the first sublayer 410 is an AlInGaAs layer, the absorption of light by the second ohmic contact layer 400 is significantly reduced, thereby improving the secondary absorption effect of the battery.

[0060] In summary, in the multi-junction solar cell structure provided in the embodiment of the present application, the first sublayer 410 of the second ohmic contact layer 400 may be an InGaAs layer or an AlInGaAs layer, and the second sublayer 420 of the second ohmic contact layer 400 may be a GaAs layer or a GaAsSb layer. The second sublayer 420 without In is used to reduce or avoid the first sublayer 410 containing In from volatilizing In atoms to the reaction chamber, thereby reducing the resident In atoms in the reaction chamber, that is, reducing the pollution and influence of the resident In atoms on the reaction chamber, and improving the preparation yield of the multi-junction solar cell structure. In addition, the first sublayer 410 and the second sublayer 420 together constitute an ohmic contact layer to form a good ohmic contact with the metal electrode, and further:

[0061] When the first sublayer 410 is an InGaAs layer and the second sublayer 420 is a GaAs layer, the advantages are that the first sublayer 410 (InGaAs layer) and the third subcell 330 (InGaAs subcell) and the second subcell 320 (GaAs subcell) are lattice-matched and energy-level-matched, which is conducive to forming a good ohmic contact; although the first sublayer 410 (InGaAs layer) may absorb part of the light due to its small band gap, the second sublayer 420 (GaAs layer) absorbs very little light and can still improve the secondary absorption effect of the battery; although the second sublayer 420 (GaAs layer) and the third subcell 330 (InGaAs subcell) and the first sublayer 410 (InGaAs layer) are lattice-mismatched, the thickness of the second sublayer 420 (GaAs layer) can be relatively thin, so that the second sublayer 420 is in a strained state, avoiding the lattice mismatch from affecting the device performance.

[0062] When the first sublayer 410 is an InGaAs layer and the second sublayer 420 is a GaAsSb layer, the advantages are that not only the first sublayer 410 (InGaAs layer) and the third subcell 330 (InGaAs subcell) and the second subcell 320 (GaAs subcell) are lattice-matched and energy-level-matched, which is conducive to forming a good ohmic contact, but also the second sublayer 420 (GaAsSb layer) is lattice-matched with the third subcell 330 (InGaAs subcell) and the first sublayer 410 (InGaAs layer); although the second sublayer 420 (GaAsSb layer) may absorb part of the light due to its small band gap, the thickness of the second sublayer 420 (GaAsSb layer) can be set to be thinner, so that the overall absorption of light by the second ohmic contact layer 400 is basically not increased.

[0063] When the first sublayer 410 is an AlInGaAs layer and the second sublayer 420 is a GaAs layer, the advantages are that, since the band gaps of the first sublayer 410 (AlInGaAs layer) and the second sublayer 420 (GaAs layer) are both large, the absorption of light by the second ohmic contact layer 400 can be significantly reduced, thereby improving the secondary absorption effect of the battery; although it is not easy for the first sublayer 410 (AlInGaAs layer) to form a good ohmic contact with the metal electrode, the second sublayer 420 (GaAs layer) is closer to the metal electrode than the first sublayer 410 (AlInGaAs layer), and the second sublayer 420 (GaAs layer) can form a good ohmic contact with the metal electrode; although the second sublayer 420 (GaAs layer) is lattice mismatched with the third subcell 330 (InGaAs subcell) and the first sublayer 410 (InGaAs layer), the thickness of the second sublayer 420 (GaAs layer) can be thinner, so that the second sublayer 420 is in a strained state, thereby avoiding the lattice mismatch from affecting the device performance.

[0064] When the first sublayer 410 is an AlInGaAs layer and the second sublayer 420 is a GaAsSb layer, the advantage is that, due to the large band gap of the first sublayer 410 (AlInGaAs layer), the absorption of light by the second ohmic contact layer 400 can be significantly reduced, thereby improving the secondary absorption effect of the battery; and, the second sublayer 420 (GaAsSb layer) is lattice matched with the third subcell 330 (InGaAs subcell); although the second sublayer 420 (GaAsSb layer) may absorb part of the light due to its small band gap, the thickness of the second sublayer 420 (GaAsSb layer) can be set to be thinner, so that due to the large band gap of the first sublayer 410 (AlInGaAs layer), the absorption of light by the second ohmic contact layer 400 can be significantly reduced, thereby improving the secondary absorption effect of the battery.

[0065] Furthermore, when the first sublayer 410 of the second ohmic contact layer 400 is an AlInGaAs layer, the Al composition x of the first sublayer 410 may be set to satisfy: 0<x≤0.2, so that the first sublayer 410 can also achieve the best ohmic contact with the metal electrode.

[0066] Based on any of the above embodiments, optionally, in some embodiments of the present application, regardless of whether the first sublayer 410 is an InGaAs layer or an AlInGaAs layer, the thickness of the first sublayer 410 may range from 100 nm to 500 nm, including endpoint values.

[0067] On the basis of any of the above embodiments, optionally, in some embodiments of the present application, regardless of whether the first sublayer 410 is an InGaAs layer or an AlInGaAs layer, the In component y of the first sublayer 410 satisfies: 0.2≤y≤0.4. Specifically, the In component of the InGaAs material of the third subcell 330 (InGaAs subcell) can be 0.3, and the In component y of the first sublayer 410 can also be 0.3 to facilitate lattice matching.

[0068] Specifically, in some embodiments of the present application, the multi-junction solar cell structure provided in the embodiments of the present application is an inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure, such as Figure 4 As shown, where:

[0069] The first ohmic contact layer 200 is an n-type GaAs layer;

[0070] The first sub-cell 310 includes a first window layer 311, a first emitter region 312, a first base region 313 and a first back field layer 314 stacked in a direction away from the first substrate 100, wherein the first window layer 311 may be an n-type AlInP layer, the first emitter region 312 may be an n-type AlGaInP layer, the first base region 313 may be a p-type AlGaInP layer, and the first back field layer 314 may be a p-type AlGaInP layer.

[0071] In the first tunnel junction 340 , the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, and the n-type doping may be Si or Te; the p-type layer may be a p-type AlGaAs layer, and the p-type doping may be C doping.

[0072] The second sub-cell 320 includes a second window layer 321, a second emitter region 322, a second base region 323 and a second back field layer 324 stacked in a direction away from the first substrate 100, wherein the second window layer 321 may be an n-type GaInP layer or an AlGaInP layer or an AlInP layer, the second emitter region 322 may be an n-type GaAs layer or an n-type GaInP layer, the second base region 323 may be a p-type GaAs layer, and the second back field layer 324 may be a p-type GaInP layer or a p-type AlGaAs layer.

[0073] In the second tunnel junction 350 , the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, and the n-type doping may be Si or Te; the p-type layer may be a p-type AlGaAs layer, and the p-type doping may be C doping.

[0074] The metamorphic buffer layer 360 may be an AlGaInAs layer or a GaInP layer, and its band gap is higher than that of the third subcell 330 (InGaAs subcell) to avoid light absorption. The metamorphic buffer layer 360 may include an m-layer sequence stacked along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell), where m≥3 and m is an integer. The lattice constant of each layer sequence in the metamorphic buffer layer 360 is greater than the lattice constant of the second subcell 320 (GaAs subcell), and the lattice constant of each layer sequence increases along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell), that is, the metamorphic buffer layer 360 is stacked in the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell). The structure plays a role of lattice transition between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell), effectively releasing the residual stress caused by lattice mismatch between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell), and effectively blocking the dislocations caused by lattice mismatch between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell) from extending to the active area of ​​the third subcell 330 (InGaAs subcell), thereby improving the performance of the multi-junction solar cell structure.

[0075] It can be understood that in the metamorphic buffer layer 360, the lattice constants of each layer sequence increase along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell). In this way, when the i+1th layer sequence with a relatively large lattice constant is grown on the ith layer sequence with a relatively small lattice constant, compressive stress will be generated, wherein 1≤i≤m-1. In addition, the lattice constant of the mth layer sequence in the metamorphic buffer layer 360 is set to be greater than the lattice constant of the third subcell 330, that is, the mth layer sequence is an overshoot layer. Then, when the third subcell 330 (InGaAs subcell) with a relatively small lattice constant is grown on the mth layer sequence with a relatively large lattice constant, tensile stress will be generated. Different from the compressive stress generated by the gradual increase of the lattice constant of the previous sequence, on the one hand, it can compensate for the residual stress generated by the previous sequence, and on the other hand, it can prevent the dislocation of the metamorphic buffer layer 360 from extending to the third subcell 330 (InGaAs subcell).

[0076] The third sub-cell 330 includes a third window layer 331, a third emitter region 332, a third base region 333 and a third back field layer 334 stacked in a direction away from the first substrate 100, wherein the third window layer 331 may be an n-type GaInP layer or an AlGaInP layer, the third emitter region 332 may be an n-type InGaAs layer or an n-type GaInP layer, the third base region 333 may be a p-type InGaAs layer, and the third back field layer 334 may be a p-type GaInP layer or a p-type AlInGaAs layer.

[0077] Accordingly, an embodiment of the present application further provides a method for preparing a multi-junction solar cell structure, the method comprising:

[0078] S100: Figure 1 As shown, a first substrate 100 is provided;

[0079] S200: Figure 1 As shown, a sacrificial layer 500, a first ohmic contact layer 200, a plurality of sub-cells 300 and a second ohmic contact layer 400 are formed on one side of the first substrate 100, and are stacked in a direction away from the first substrate 100. The second ohmic contact layer 400 includes a first sub-layer 410 and a second sub-layer 420 stacked in a direction away from the first substrate 100. The first sub-layer 410 is a material layer containing In, and the second sub-layer 420 is a GaAs layer or a GaAsSb layer.

[0080] S300: Figure 2 As shown, the cell epitaxial structure composed of the first ohmic contact layer 200 to the second ohmic contact layer 400 is transferred to the second substrate 110 from one side of the second ohmic contact layer 400;

[0081] S400: Figure 3 As shown, the sacrificial layer 500 is etched and the first substrate 100 is peeled off.

[0082] Optionally, the first substrate 100 may be a GaAs substrate.

[0083] Optionally, the first ohmic contact layer 200 may be an n-type GaAs layer.

[0084] Optionally, the first sublayer 410 of the second ohmic contact layer 400 may be an InGaAs layer or an AlInGaAs layer, and the second sublayer 420 of the second ohmic contact layer 400 may be a GaAs layer or a GaAsSb layer; when the first sublayer 410 is an AlInGaAs layer, its Al component x may satisfy: 0<x≤0.2.

[0085] Optionally, the thickness of the second sub-layer 420 ranges from 10 nm to 100 nm, including the endpoint values; the thickness of the first sub-layer 410 ranges from 100 nm to 500 nm, including the endpoint values.

[0086] Optionally, no matter the first sublayer 410 is an InGaAs layer or an AlInGaAs layer, the In composition y of the first sublayer 410 may satisfy: 0.2≤y≤0.4.

[0087] Optionally, the prepared multi-junction solar cell structure may be an inverted (Al)GaInP / GaAs / InGaAs triple-junction solar cell structure, such as Figure 4As shown, where:

[0088] The first sub-cell 310 includes a first window layer 311, a first emitter region 312, a first base region 313 and a first back field layer 314 stacked in a direction away from the first substrate 100, wherein the first window layer 311 may be an n-type AlInP layer, the first emitter region 312 may be an n-type AlGaInP layer, the first base region 313 may be a p-type AlGaInP layer, and the first back field layer 314 may be a p-type AlGaInP layer.

[0089] In the first tunnel junction 340 , the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, and the n-type doping may be Si or Te; the p-type layer may be a p-type AlGaAs layer, and the p-type doping may be C doping.

[0090] The second sub-cell 320 includes a second window layer 321, a second emitter region 322, a second base region 323 and a second back field layer 324 stacked in a direction away from the first substrate 100, wherein the second window layer 321 may be an n-type GaInP layer or an AlGaInP layer or an AlInP layer, the second emitter region 322 may be an n-type GaAs layer or an n-type GaInP layer, the second base region 323 may be a p-type GaAs layer, and the second back field layer 324 may be a p-type GaInP layer or a p-type AlGaAs layer.

[0091] In the second tunnel junction 350 , the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, and the n-type doping may be Si or Te; the p-type layer may be a p-type AlGaAs layer, and the p-type doping may be C doping.

[0092] The metamorphic buffer layer 360 may be an AlGaInAs layer or a GaInP layer, and its band gap is higher than that of the third subcell 330 (InGaAs subcell) to avoid light absorption. The metamorphic buffer layer 360 may include an m-layer sequence stacked along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell), where m≥3 and m is an integer. The lattice constant of each layer sequence in the metamorphic buffer layer 360 is greater than the lattice constant of the second subcell 320 (GaAs subcell), and the lattice constant of each layer sequence increases along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell), that is, the metamorphic buffer layer 360 is stacked in the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell). The structure plays a role of lattice transition between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell), effectively releasing the residual stress caused by lattice mismatch between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell), and effectively blocking the dislocations caused by lattice mismatch between the second subcell 320 (GaAs subcell) and the third subcell 330 (InGaAs subcell) from extending to the active area of ​​the third subcell 330 (InGaAs subcell), thereby improving the performance of the multi-junction solar cell structure.

[0093] It can be understood that in the metamorphic buffer layer 360, the lattice constants of each layer sequence increase along the direction from the second subcell 320 (GaAs subcell) to the third subcell 330 (InGaAs subcell). In this way, when the i+1th layer sequence with a relatively large lattice constant is grown on the ith layer sequence with a relatively small lattice constant, compressive stress will be generated, wherein 1≤i≤m-1. In addition, the lattice constant of the mth layer sequence in the metamorphic buffer layer 360 is set to be greater than the lattice constant of the third subcell 330, that is, the mth layer sequence is an overshoot layer. Then, when the third subcell 330 (InGaAs subcell) with a relatively small lattice constant is grown on the mth layer sequence with a relatively large lattice constant, tensile stress will be generated. Different from the compressive stress generated by the gradual increase of the lattice constant of the previous sequence, on the one hand, it can compensate for the residual stress generated by the previous sequence, and on the other hand, it can prevent the dislocation of the metamorphic buffer layer 360 from extending to the third subcell 330 (InGaAs subcell).

[0094] The third sub-cell 330 includes a third window layer 331, a third emitter region 332, a third base region 333 and a third back field layer 334 stacked in a direction away from the first substrate 100, wherein the third window layer 331 may be an n-type GaInP layer or an AlGaInP layer, the third emitter region 332 may be an n-type InGaAs layer or an n-type GaInP layer, the third base region 333 may be a p-type InGaAs layer, and the third back field layer 334 may be a p-type GaInP layer or a p-type AlInGaAs layer.

[0095] When a multi-junction solar cell structure is prepared using the method provided in the embodiment of the present application, a stacked first ohmic contact layer 200, a plurality of sub-cells 300, and a second ohmic contact layer 400 are formed on one side of the first substrate 100 in a direction away from the first substrate 100, and in particular, when the second ohmic contact layer 400 on the surface layer of the cell epitaxial structure is formed, a first sub-layer 410 containing In is first grown, and then a GaAs layer or a GaAsSb layer is grown as a second sub-layer 420. In this way, not only the first sub-layer 410 and the second sub-layer 420 together constitute an ohmic contact layer to form a good ohmic contact with the metal electrode, but also, since the first sub-layer 410 containing In is also covered with a GaAs layer or a GaAsSb layer as the second sub-layer 420, and the second sub-layer 420 is a material layer that does not contain In, the volatilization of In atoms from the first sub-layer 410 containing In to the reaction chamber can be reduced or avoided, thereby reducing the resident In atoms in the reaction chamber, that is, reducing the pollution and influence of the resident In atoms on the reaction chamber, and improving the preparation yield of the multi-junction solar cell structure. Furthermore, in the second ohmic contact layer 400 , the second sublayer 420 is closer to the metal electrode than the first sublayer 410 , and the second sublayer 420 is made of a GaAs layer or a GaAsSb layer, which can form a good ohmic contact with the metal electrode.

[0096] The various parts in this manual are described in a combination of parallel and progressive ways. Each part focuses on the differences from other parts, and the same or similar parts between the various parts can be referenced to each other.

[0097] With respect to the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other, so that professionals in the field can implement or use the present application. Various modifications to these embodiments will be apparent to professionals in the field, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-junction solar cell structure, characterized in that: include: a first substrate; A first ohmic contact layer, a plurality of sub-cells, and a second ohmic contact layer are located on one side of the first substrate and are stacked in a direction away from the first substrate; The second ohmic contact layer includes a first sublayer and a second sublayer stacked in a direction away from the first substrate, the first sublayer is an In-containing material layer, and the second sublayer is a GaAs layer or a GaAsSb layer.

2. The multi-junction solar cell structure according to claim 1, characterized in that: The first sublayer is an InGaAs layer.

3. The multi-junction solar cell structure according to claim 1, characterized in that: The first sublayer is an AlInGaAs layer.

4. The multi-junction solar cell structure according to claim 3, characterized in that: The Al composition x of the first sublayer satisfies: 0<x≤0.

2.

5. The multi-junction solar cell structure according to claim 1, characterized in that: The thickness of the second sub-layer ranges from 10 nm to 100 nm, including end points.

6. The multi-junction solar cell structure according to claim 1, characterized in that: The thickness of the first sublayer ranges from 100 nm to 500 nm, including end points.

7. The multi-junction solar cell structure according to any one of claims 1 to 6, characterized in that: The plurality of subcells include a first subcell, a second subcell, and a third subcell stacked in a direction away from the first substrate, a first tunnel junction is disposed between the first subcell and the second subcell, and a second tunnel junction and a metamorphic buffer layer are disposed between the second subcell and the third subcell, stacked in a direction away from the first substrate; The first subcell is an AlGaInP subcell or a GaInP subcell, the second subcell is a GaAs subcell, and the third subcell is an InGaAs subcell.

8. The multi-junction solar cell structure according to claim 7, characterized in that: The metamorphic buffer layer is an AlGaInAs layer or a GaInP layer, and includes an m-layer sequence stacked along the direction from the second sub-cell to the third sub-cell, m≥3, and m is an integer, the lattice constant of each layer of the sequence is greater than the lattice constant of the second sub-cell, and along the direction from the second sub-cell to the third sub-cell, the lattice constant of each layer of the sequence increases, and the lattice constant of the m-th layer of the sequence is greater than the lattice constant of the third sub-cell.

9. The multi-junction solar cell structure according to any one of claims 1 to 6, characterized in that: The In composition y of the first sublayer satisfies: 0.2≤y≤0.

4.

10. The multi-junction solar cell structure according to any one of claims 1 to 6, characterized in that: A sacrificial layer is further disposed between the first substrate and the first ohmic contact layer, and the sacrificial layer is an AlAs layer.

11. A method for preparing a multi-junction solar cell structure, characterized in that: include: providing a first substrate; A sacrificial layer, a first ohmic contact layer, a plurality of sub-cells and a second ohmic contact layer are formed on one side of the first substrate, wherein the second ohmic contact layer comprises a first sub-layer and a second sub-layer which are stacked in a direction away from the first substrate, wherein the first sub-layer is an In-containing material layer, and the second sub-layer is a GaAs layer or a GaAsSb layer; Transferring the battery epitaxial structure formed by the first ohmic contact layer to the second ohmic contact layer onto a second substrate from one side of the second ohmic contact layer; The sacrificial layer is corroded to peel off the first substrate.

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