Solar cell and method of manufacturing the same

Abstract

The application relates to the technical field of semiconductor electronic devices, and provides a solar cell and a preparation method thereof. The solar cell at least comprises a supporting substrate, an epitaxial active layer, a passivation protective layer, a first electrode and a second electrode. The supporting substrate has opposite first and second surfaces. The epitaxial active layer is arranged on the first surface. The surface of the epitaxial active layer facing the first surface has a defect area formed due to a growth process. The passivation protective layer is arranged on the epitaxial active layer and covers at least the defect area. The first electrode is arranged on the epitaxial active layer and away from the supporting substrate, and is electrically connected with the epitaxial active layer. The second electrode is arranged on the second surface of the supporting substrate and is electrically connected with the epitaxial active layer. The solar cell structure in the application can solve the problem of point light abnormality and local electric leakage caused by the defect area in the epitaxial active layer grown in an inverted mode, and can effectively improve the overall performance of the solar cell, such as light emission uniformity.

Description

Technical Field

[0001] This invention relates to the field of semiconductor electronic device technology, and in particular to a solar cell and its fabrication method. Background Technology

[0002] In conventional solar cells, the epitaxial active layer (or epitaxial stack) is typically grown in the forward direction. In non-single-junction structures, epitaxial wafers grown using lattice-matched designs result in significant differences in the bandgap of each sub-cell. This growth method leads to a low utilization rate of the solar spectrum. To improve the utilization rate of the solar spectrum, based on the principle of spectral matching, a process method using inverted growth of the epitaxial active layer with lattice mismatch is employed. This effectively reduces the energy loss caused by photoelectric mismatch between sub-cells in spatially lattice-matched forward-grown multi-junction cells, significantly improving the photoelectric conversion efficiency.

[0003] Currently, inverted growth is a major research direction for space-efficient multi-junction solar cells. However, lattice mismatch can reduce the quality of the epitaxial active layer, affecting the photoelectric conversion efficiency of the solar cell. To reduce the impact of epitaxial active layer defects caused by lattice mismatch, in addition to optimizing the growth of the epitaxial active layer, the solar cell structure can also be optimized during the fabrication process.

[0004] Due to the high dislocation density, flip-chip epitaxial active layer growth is more prone to defects than forward growth. In lattice-mismatched flip-chip solar cells, defects such as epitaxial droplets can appear on the surface of the epitaxial active layer. When the flip-chip epitaxial active layer structure is reversed to fabricate a solar cell, these droplets can cause abnormal illumination, localized leakage, and other phenomena, thus affecting the performance of the solar cell. In large-size solar cells, droplets in the epitaxial active layer cause excessively bright localized light emission, significantly impacting the uniformity of light emission. Therefore, eliminating droplet defects in the epitaxial active layer has become one of the urgent technical challenges to be solved by those skilled in the art. Summary of the Invention

[0005] To address the adverse effects of surface defects such as drop points in the epitaxial active layer of solar cells on their performance, this invention provides a solar cell and its fabrication method.

[0006] To achieve at least one or more of the aforementioned advantages, an embodiment of the present invention provides a solar cell comprising at least: a supporting substrate having opposing first and second surfaces; an epitaxial active layer disposed on the first surface of the supporting substrate, the surface of the epitaxial active layer facing the first surface having a defect region formed by the growth process; a passivation protective layer disposed on the epitaxial active layer and at least covering the defect region on the epitaxial active layer; a first electrode disposed on the epitaxial active layer and remote from the supporting substrate; and a second electrode disposed on the second surface of the supporting substrate.

[0007] In some embodiments, the supporting substrate may be a flexible substrate, such as Kovar alloy or PI (polyimide) film.

[0008] In some embodiments, the epitaxial active layer is fabricated using a flip-chip growth method. The epitaxial active layer can be a single-junction cell, a dual-junction cell, or a multi-junction cell. The number of junctions in the cell can be matched and set according to the actual functional requirements of the solar cell.

[0009] In some embodiments, the first electrode may consist of a pad and a gate line. The passivation protection layer is only disposed below the gate line, and there is no passivation protection layer below the pad.

[0010] In some embodiments, in a single or single solar cell, the distance between the passivation protective layer and the edge of the epitaxial active layer is not less than 5 micrometers. During the manufacturing process, this can avoid abnormal shedding of the epitaxial active layer at the edge of the wafer caused by the cutting of a wafer with multiple solar cells, thereby improving the yield.

[0011] In some embodiments, the passivation protective layer can be formed by PECVD deposition, ion magnetron sputtering, or electron beam evaporation.

[0012] In some embodiments, the passivation protective layer is made of at least one of silicon oxide, titanium oxide, aluminum oxide, and silicon nitride.

[0013] In some embodiments, the passivation protective layer is a single-layer film or a multi-layer film structure. The thickness of the passivation protective layer is greater than or equal to 100 nanometers and less than or equal to 1000 nanometers.

[0014] To achieve at least one or more of the aforementioned advantages, an embodiment of the present invention provides a method for preparing a solar cell, the method comprising at least the following steps.

[0015] Step S11: Growth of epitaxial active layer

[0016] A cutoff layer is grown on a substrate, and an epitaxial active layer is grown on the cutoff layer using MOCVD inverted growth technology to form a solar cell epitaxial wafer.

[0017] Step S12: Preparation of passivation protective layer

[0018] The surface of the epitaxial active layer, away from the substrate, has defect regions formed due to lattice mismatch during growth. A passivation protective layer is prepared on the epitaxial active layer using PECVD deposition or electron beam evaporation, and then photolithography and etching processes are used to ensure that the passivation protective layer at least covers the defect regions. Generally, the passivation protective layer is mainly placed at the corresponding locations of the defect regions on the epitaxial active layer. The total area of ​​the passivation protective layer is much smaller than the area of ​​its corresponding epitaxial active layer surface.

[0019] Step S13: Bonding

[0020] Bonding layers are deposited on the surface of a supporting substrate and on the surface of an epitaxial active layer with a passivation protective layer, respectively, and the epitaxial active layer is bonded to the supporting substrate through the bonding layers.

[0021] Step S14: Substrate peeling

[0022] Etching with a chemical solution is used to remove the substrate and the cutoff layer, and the flip-chip grown epitaxial active layer is flipped onto the support substrate, thereby achieving substrate stripping and transfer of the epitaxial active layer.

[0023] Step S15: Electrode fabrication (cutting / dicing)

[0024] A first electrode photolithography pattern is fabricated on the epitaxial active layer, and the first electrode metal is deposited and lifted to form the first electrode. A second electrode metal is deposited on the surface of the supporting substrate away from the bonding layer to form the second electrode. The electrodes are then fused, cut, and passivated to obtain a single or monolithic solar cell.

[0025] After the first electrode is fabricated, an anti-reflection film can be deposited on the surface of the first electrode in the epitaxial active layer to improve the absorption of the spectrum by the solar cell.

[0026] The solar cell and its preparation method provided by this invention have at least the following advantages:

[0027] 1. It can effectively avoid defects caused by growth drop points on the surface of the epitaxial active layer, which can lead to abnormal lighting and local leakage in some areas of the solar cell, thereby effectively improving the overall performance of the solar cell, such as the uniformity of light emission.

[0028] 2. The epitaxial active layer adopts a flip-chip growth method. The defect area generated by epitaxial growth is distributed in a local area on the surface of the last layer of epitaxial active region. Then, a passivation protective layer is provided on the local surface of the epitaxial active layer to cover the defect area. This setting can improve the bonding strength between the epitaxial active layer and the supporting substrate. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a side cross-sectional view of a defect area in an embodiment of the solar cell of the present invention;

[0031] Figure 2 for Figure 1 A schematic diagram of a top view of a solar cell structure is shown.

[0032] Figure 3 for Figure 1 The flowchart of the solar cell fabrication method shown is as follows; and

[0033] Figures 4a to 4d Based on Figure 3 The diagram shows a process flow diagram of one embodiment of the preparation method.

[0034] Reference numerals: 1-Solar cell, 00-Substrate, 01-Stop layer, 10-Supporting substrate, 10a-First surface, 10b-Second surface, 11-Bonding layer, 20-Epiaxial active layer, 21-Contact layer, 22-Top cell, 23-First tunnel junction, 24-Middle cell, 25-Second tunnel junction, 26-Buffer layer, 27-Bottom cell, 28-Defect region, 30-Passivation protection layer, 40-Antireflective coating, 50-First electrode, 60-Second electrode, 70-Pad, 71-Main grid line, 72-Secondary grid line. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be understood that the terms "center," "lateral," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and 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 therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. Additionally, the term "comprising" and any variations thereof mean "at least comprising."

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integrally formed connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are also intended to include the plural. It should also be understood that the terms “comprising” and / or “including” as used herein specify the presence of the stated features, integers, steps, operations, units, and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components, and / or combinations thereof.

[0039] Please see Figure 1 , Figure 1This is a side cross-sectional view of a defect area in an embodiment of the solar cell of the present invention. To achieve at least one or more of the aforementioned advantages, an embodiment of the present invention provides a solar cell 1, which includes at least: a supporting substrate 10, an epitaxial active layer 20, a passivation protective layer 30, a first electrode 50, and a second electrode 60. The supporting substrate 10 has opposing first surfaces 10a and second surfaces 10b. The epitaxial active layer 20 is disposed on the first surface 10a. The surface of the epitaxial active layer 20 facing the first surface 10a has a defect area 28 formed by the growth process. The passivation protective layer 30 is disposed on the epitaxial active layer 20 and at least covers the defect area 28. The first electrode 50 is disposed on the epitaxial active layer 20 and away from the supporting substrate 10, and is electrically connected to the epitaxial active layer 20. The second electrode 60 is disposed on the second surface 10b of the supporting substrate 10 and is electrically connected to the epitaxial active layer 20. The solar cell 1 can be a flexible solar cell.

[0040] The support substrate 10 can be a flexible substrate or a rigid substrate. When the support substrate 10 is a flexible substrate, its material can be at least one of alloy, semiconductor material, or PI (polyimide) film. In one embodiment, the flexible substrate can be a Kovar alloy substrate formed of an alloy of Fe, Co, and Ni. When the support substrate 10 is a rigid substrate, its material can be germanium (Ge).

[0041] The epitaxial active layer 20 can be formed by flip-chip growth, bonded and flipped onto the first surface 10a of the supporting substrate 10. In different embodiments, the epitaxial active layer 20 can be a single-junction cell, a dual-junction cell, or a multi-junction cell. The following and illustrations use a flexible solar cell 1 with an epitaxial active layer 20 structure having a multi-junction cell as an example for explanation.

[0042] The epitaxial active layer 20 may include, from top to bottom, a contact layer 21, a top cell 22, a first tunnel junction 23, a middle cell 24, a second tunnel junction 25, a buffer layer 26, and a bottom cell 27. The top cell 22 is made of GaInP (gallium indium phosphide), the middle cell 24 is made of GaAs (gallium arsenide), the buffer layer 26 can be a graded buffer layer, and the bottom cell 27 is made of InGaAs (indium gallium arsenide). The top cell 22, the middle cell 24, and the bottom cell 27 are connected via the first tunnel junction 23 and the second tunnel junction 25, respectively. The tunnel junction can generate a tunneling effect, allowing majority carriers to pass through while hindering minority carriers. The material of the tunnel junction can be any material that allows majority carriers to tunnel through. In some embodiments, the material of the tunnel junction can be doped gallium arsenide or gallium indium phosphide, etc.

[0043] See Figure 1In solar cell 1, the supporting substrate 10 and the epitaxial active layer 20 are bonded via a metal layer. Specifically, a bonding metal layer may be provided on the first surface 10a of the supporting substrate 10 (the upper surface in the figure). A bonding metal layer may be provided on the surface of the bottom cell 27 of the epitaxial active layer 20 facing the supporting substrate 10 (the lower surface in the figure). When the supporting substrate 10 and the epitaxial active layer 20 are bonded together, the bonding metal layers on the supporting substrate 10 and the bonding metal layers on the epitaxial active layer 20 are bonded together to form a bonding layer 11, thereby achieving bonding or adhesion. In some embodiments, the material of the bonding metal layer may be at least one or more of Ti, Pt, Au, Ni, and Sn, or different combinations thereof. The metal bonding layer may be a single-layer structure or a multi-layer structure.

[0044] The epitaxial active layer 20 may have defect regions 28 formed due to the growth process. The surface of the epitaxial active layer 20 facing the first surface 10a of the supporting substrate 10 has defect regions 28 formed due to the growth process. Figure 1 In the example, defect region 28 is located on the surface of the bottom cell 27 facing the supporting substrate 10 in the epitaxial active layer 20. Defect region 28 may be discontinuously distributed on the epitaxial active layer 20. Defect region 28 can cause abnormal performance of solar cell 1. Defect region 28 can be an uneven surface, such as bumps or protrusions on the epitaxial active layer 20; or it can be a groove or pit below the surface of the epitaxial active layer 20. For bumps or protrusions on the surface of the epitaxial active layer 20, they can be scraped flat. After scraping, a passivation protective layer 30 can be prepared on the surface of the epitaxial active layer 20 with defect region 28. Passivation protective layer 30 at least covers the grooves, pits, etc., below the surface of the epitaxial active layer 20. When the epitaxial active layer 20 is bonded to the supporting substrate 10, a bonding metal layer may be provided on the passivation protective layer 30.

[0045] The defect region 28 is not distributed across the entire surface of the epitaxial active layer 20, but rather is irregularly formed on a portion of the surface of the epitaxial active layer 20. Generally, a passivation protection layer 30 must cover the defect region 28 located below the gate line on the surface of the epitaxial active layer 20. It can be understood that the total area of ​​the passivation protection layer 30 is much smaller than the area of ​​its corresponding epitaxial active layer 20 surface.

[0046] Generally, multiple solar cells 1 are formed simultaneously on a wafer of a certain area. To reduce the impact of various processes on the performance of solar cells 1 and improve the yield of solar cells 1, the spacing between the passivation protective layer 30 and the edge of the epitaxial active layer 20 in a single solar cell 1 is not less than 5 micrometers. During the manufacturing process of solar cells 1, the limitation of this spacing can avoid abnormal edge chipping and detachment of the epitaxial active layer 20 at the edge of the wafer caused by the dicing of wafers with multiple solar cells 1.

[0047] The passivation protective layer 30 can be deposited on the epitaxial active layer 20 by PECVD deposition, ion magnetron sputtering, or electron beam evaporation. The passivation protective layer 30 can be a film layer, such as a single-layer or multi-layer structure. The material of the passivation protective layer 30 is at least one of silicon oxide, titanium oxide, aluminum oxide, and silicon nitride. The thickness of the passivation protective layer 30 is greater than or equal to 100 nanometers and less than or equal to 1000 nanometers, to form a protective coating on the defect region 28 and reduce the adverse effects of the defect region 28 on the solar cell 1.

[0048] To further explain, Figure 1 The example is a schematic cross-sectional view of a defect region on the epitaxial active layer 20 of a single solar cell 1. In an actual single solar cell 1, there are multiple irregularly distributed defect regions 28 on the surface of the bottom cell 27 of the epitaxial active layer 20 away from the top cell 22. When the defect regions 28 are cut in different directions and angles, at least one defect region 28 can be seen in the cross-sectional structure. Figure 1 Two defect regions 28 are shown as an example, but the example is not limited to this. Generally, a passivation protective layer 30 is retained only on the surface of the epitaxial active layer 20 having the defect regions 28. In actual products, in some specific embodiments, the defect regions 28 may be uneven and pitted, and the passivation protective layer 30 on the defect regions 28 may be dotted. Figure 1 In the example, the passivation protection layer 30 is schematically disposed across the entire surface of the bottom cell 27, only to illustrate the relative position of the passivation protection layer 30 in the solar cell 1, and does not represent its actual disposed area. In a single solar cell 1, for the epitaxial active layer 20, the passivation protection layer 30 is only disposed on the surface of the defect region 28. That is, on the surface of the epitaxial active layer 20 with the defect region 28, the passivation protection layer 30 is only locally disposed, and the total area of ​​the passivation protection layer 30 is much smaller than the area of ​​its corresponding epitaxial active layer 20 surface.

[0049] The solar cell 1 may further include a first electrode 50, a contact layer 21, an anti-reflection film 40, and a second electrode 60. The first electrode 50 is disposed on the epitaxial active layer 20 and away from the supporting substrate 10, and is electrically connected to the epitaxial active layer 20. The second electrode 60 is disposed on the second surface 10b of the supporting substrate 10 and is electrically connected to the epitaxial active layer 20. The contact layer 21 is disposed on the epitaxial active layer 20 and located below the first electrode 50. The anti-reflection film 40 is located on the surface of the epitaxial active layer 20 away from the supporting substrate 10, and covers the surface of the epitaxial active layer 20 and the surface of the grid lines of the first electrode 50. Figure 1 In this example, contact layer 21 is part of the epitaxial active layer 20 and is located on the upper surface of the top cell 22. The first electrode 50 is directly connected to the upper surface of the top cell 22 via contact layer 21. The contact layer 21 can be made of GaAs (gallium arsenide). Contact layer 21 serves as an ohmic contact layer between the first electrode 50 and the top cell 22, ensuring good electrical connection between the first electrode 50 and the epitaxial active layer 20. The antireflective coating 40 is located on the upper surface of the top cell 22 and covers the surface of the top cell 22 without a pad, thereby improving the absorption of the spectrum by the solar cell 1.

[0050] The antireflective coating 40 can be a single-layer, double-layer, or multi-layer structure. The material of the antireflective coating 40 can be oxides, nitrides, fluorides, etc. In some embodiments, the material of the antireflective coating 40 can be oxides, such as titanium dioxide (TiO2) or aluminum oxide (Al2O3). A double-layer antireflective coating 40 can be TiO2 and Al2O3. A triple-layer antireflective coating 40 can be TiO2, Al2O3, and MgF2. The materials of different layers in the antireflective coating 40 can have different reflectivities and / or refractive indices.

[0051] Figure 2 for Figure 1 The diagram shows a top-view structure of a solar cell. The first electrode 50 consists of a pad 70 and grid lines, which may include main grid lines 71 and secondary grid lines 72. Defect regions 28 covered by the passivation protective layer 30 are mainly distributed in the grid line region. Generally, the defect regions 28 are irregularly shaped, and their width is smaller than the width of the grid lines. In the illustration, for ease of drawing, the defect regions 28 are depicted as having a regular shape, used only to illustrate their distribution. The passivation protective layer 30 is only located below the corresponding grid lines; there is no passivation protective layer 30 below the pad 70.

[0052] See Figure 3 , Figure 3 for Figure 1 The flowchart illustrates the fabrication method of a solar cell. To achieve at least one or more of the aforementioned advantages, one embodiment of the present invention provides a method for fabricating a solar cell having the structure described above. Figure 3 The diagram illustrates a preferred method or process for fabricating flexible solar cells according to the present invention. However, the method and process for fabricating flexible solar cells in the present invention are not limited to these specific methods. Figure 3 As shown.

[0053] Combination Figure 3 See Figures 4a to 4d , Figures 4a to 4d Based on Figure 3 A schematic diagram of the process of one embodiment of the preparation method shown. Using... Figure 3 The method for preparing solar cells shown in the figure obtains the following: Figure 1 , Figure 2 The process method for the flexible solar cell shown is described below.

[0054] The fabrication method of solar cell 1 may include at least the following steps: growth of epitaxial active layer 20, preparation of passivation protective layer 30, bonding, substrate peeling, fabrication of electrodes 50 / 60, and dicing. The specific implementation process of each step is described below.

[0055] Step S11: Growth of epitaxial active layer 20

[0056] like Figure 4a As shown, a cutoff layer 01 is grown on a substrate 00 using metal-organic chemical vapor deposition (MOCVD) inverted growth technology, and then an epitaxial active layer 20 is grown on the cutoff layer 01 inverted. In the example shown, the substrate 00 can be made of GaAs (gallium arsenide), and the cutoff layer 01 can be made of GaInP (gallium indium phosphide).

[0057] The epitaxial active layer 20 may include a contact layer 21, a top cell 22, a first tunnel junction 23, a middle cell 24, a second tunnel junction 25, a buffer layer 26, and a bottom cell 27, which are sequentially disposed. The contact layer 21 may be made of GaAs (gallium arsenide), the top cell 22 of GaInP (gallium indium phosphide), the middle cell 24 of GaAs (gallium arsenide), and the bottom cell 27 of InGaAs (indium gallium arsenide).

[0058] Step S12: Preparation of passivation protective layer 30

[0059] like Figure 4a As shown, the surface of the flip-chip grown epitaxial active layer 20 away from the substrate 00 has a defect region 28 formed due to lattice mismatch during growth. See also... Figure 4bA passivation protection layer 30 is fabricated on the surface of the defect region 28 in the epitaxial active layer 20 using conventional semiconductor growth techniques. Conventional semiconductor growth techniques can include PECVD deposition, ion magnetron sputtering, or electron beam evaporation. Then, photolithography, etching, and localized photoresist application are used to simultaneously cover the defect region 28 on the epitaxial active layer 20 with the passivation protection layer 30 and photoresist. An etching process is then used to remove the passivation protection layer 30 from other areas of the epitaxial active layer 20 and the photoresist from the defect region 28, ensuring that the passivation protection layer 30 is formed on the epitaxial active layer 20 at least in the defect region 28.

[0060] Step S13: Bonding

[0061] like Figure 4c As shown, bonding metal layers can be deposited on the surface of the supporting substrate 10 and the surface of the epitaxial active layer 20 where the passivation protection layer 30 is provided by electron beam evaporation. The epitaxial active layer 20 can be bonded to the supporting substrate 10 via the bonding metal layer by Ni-Sn bonding process, and the bonding metal layer forms the bonding layer 11. In the example shown, the supporting substrate 10 can be a flexible substrate, such as a Kovar substrate.

[0062] Step S14: Substrate 00 peeling

[0063] like Figure 4d As shown, a chemical solution is used for etching to remove the substrate 00 and the stop layer 01 on it used for the growth of the epitaxial active layer 20. Then, the flip-chip grown epitaxial active layer 20 is flipped onto the support substrate 10. When removing the substrate 00 and the stop layer 01, a chemical solution (volume ratio) of NH4OH:H2O2:H2O = 2:3:2 can be used to remove the GaAs substrate 00, and a chemical solution (volume ratio) of HCl:H3PO4 = 1:1 can be used to remove the GaInP stop layer 01.

[0064] Step S15: Electrode fabrication (cutting / dicing)

[0065] like Figure 4dAs shown, after flip-chip grown epitaxial active layer 20 is flipped onto support substrate 10, electrodes are fabricated on epitaxial active layer 20 and support substrate 10, antireflective film 40 is deposited, and dicing and scribing are performed. A first electrode photolithography is performed on the upper surface of top cell 22 in epitaxial active layer 20, and the first electrode metal is deposited using a vapor deposition process. The first electrode photolithography layer is then peeled off to form first electrode 50. The first electrode metal is at least one of AuGeNi, Au, and Ag, or different combinations thereof. First electrode 50 can be a single-layer structure or a multi-layer structure. For example, in one specific embodiment, a front electrode pattern is prepared on contact layer 21 using a photolithography process, and a metal electrode is deposited using an electron beam evaporation metal deposition machine. This metal electrode can be a multi-layer structure composed of AuGeNi / Au / Ag / Au stacks.

[0066] The contact layer 21 on the epitaxial active layer 20, which does not contain the first electrode 50, is removed, leaving only the contact layer 21 between the epitaxial active layer 20 and the first electrode 50. An antireflective film 40 is deposited above the top cell 22 in the epitaxial active layer 20 using a vapor deposition process. The antireflective film 40 covers the area on the top cell 22 in the epitaxial active layer 20 where no pad is provided. The antireflective film 40 can be a multilayer structure, such as a stack formed by TiO2 / Al2O3. A second electrode metal is deposited on the surface of the supporting substrate 10 away from the bonding layer 11 to form the second electrode 60. Then, the wafer is fused, cut, and passivated to obtain a single or monolithic solar cell 1.

[0067] This invention provides a solar cell 1. During the fabrication process, the surface of the inverted epitaxial active layer 20 has defect regions 28 caused by lattice mismatch or other defects during growth. The defect regions 28 are dispersed across the surface of the epitaxial active layer 20. The presence of the defect regions 28 can cause abnormal illumination and localized leakage in parts of the solar cell 1. By providing a passivation protection layer 30 on the defect regions 28, the bonding strength between the epitaxial active layer and the supporting substrate can be improved, effectively enhancing the overall performance of the solar cell, such as luminous uniformity. For the entire surface of the epitaxial active layer 20 in the solar cell 1, the passivation protection layer 30 is only provided on the surface with the defect regions 28. This can be understood as the passivation protection layer 30 being provided only locally on the entire surface of the epitaxial active layer 20 with the defect regions 28. The total area of ​​the passivation protection layer 30 is much smaller than the area of ​​its corresponding epitaxial active layer 20 surface.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solar cell, characterized in that, include: A supporting substrate having opposing first and second surfaces, wherein the supporting substrate is a Kovar alloy flexible substrate; An epitaxial active layer is disposed on the first surface. The surface of the epitaxial active layer facing the first surface has discrete defect regions formed by lattice mismatch during flip-chip growth. The defect regions are pit-shaped. A passivation protective layer is disposed on the surface of the defect region of the epitaxial active layer, and only covers the defect region; The first electrode is disposed on the epitaxial active layer and away from the supporting substrate. The first electrode consists of a Pad and a gate line. The passivation protection layer is disposed only below the gate line. The passivation protection layer is not disposed below the Pad. as well as The second electrode is disposed on the second surface of the supporting substrate; The passivation protective layer is made of at least one of silicon oxide, titanium oxide, aluminum oxide, and silicon nitride.

2. The solar cell according to claim 1, characterized in that: The epitaxial active layer is a dual-junction cell or a multi-junction cell; the epitaxial active layer is formed by flip-chip growth.

3. The solar cell according to claim 1, characterized in that: The distance between the edge of the passivation protective layer and the edge of the epitaxial active layer is greater than or equal to 5 micrometers.

4. The solar cell according to claim 1, characterized in that: The passivation protective layer is a single-layer or multi-layer film structure, and the thickness of the passivation protective layer is greater than or equal to 100 nanometers and less than or equal to 1000 nanometers.

5. The solar cell according to claim 1, characterized in that: The passivation protective layer is formed by PECVD deposition, ion magnetron sputtering, or electron beam evaporation.

6. A method for preparing a solar cell, characterized in that, The preparation method includes: Epitaxial active layer growth: A cutoff layer is grown on a substrate, and an epitaxial active layer is grown on the cutoff layer using MOCVD inverted growth technology to form a solar cell epitaxial wafer; Passivation protection layer preparation: The surface of the epitaxial active layer away from the substrate has a defect region formed by lattice mismatch during flip-chip growth. The defect region is pit-shaped. A passivation protection layer is prepared on the epitaxial active layer by PECVD deposition or electron beam evaporation. The passivation protection layer covers only the defect region by photolithography and etching processes. Bonding: Bonding layers are deposited on the surface of a supporting substrate and on the surface of the epitaxial active layer where the passivation protection layer is provided, respectively, and the epitaxial active layer is bonded to the supporting substrate through the bonding layers; Substrate stripping: Etching with a chemical solution is used to remove the substrate and the cutoff layer, and the flip-chip grown epitaxial active layer is flipped onto the support substrate, which is a Kovar alloy flexible substrate; Electrode fabrication: A first electrode photolithography pattern is fabricated on the epitaxial active layer, and the first electrode metal is deposited and stripped to form the first electrode. A second electrode metal is deposited on the surface of the support substrate away from the bonding layer to form the second electrode. The electrode is then fused, cut, and passivated to obtain a single or monolithic solar cell.

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