Metal substrate multi-junction thin film solar cell and preparation method thereof

Abstract

The invention provides a metal substrate multi-junction thin film solar cell and a preparation method thereof. The preparation method of the metal substrate multi-junction thin film solar cell comprises the following steps: providing an epitaxial wafer, a temporary bonding film and a temporary supporting substrate; the epitaxial wafer comprises a growth substrate, and a flexible epitaxial structure is formed on the growth substrate; forming a flexible substrate on the surface of the flexible epitaxial structure; pasting a temporary bonding film on the surface of the flexible substrate; bonding the temporary support substrate and the temporary bonding film; ultraviolet light with the first wavelength is adopted for irradiation, so that the viscosity of the temporary bonding film is improved; etching to remove the growth substrate; manufacturing an electrode and an antireflection film on the flexible epitaxial structure; and irradiating by adopting ultraviolet light with a second wavelength to weaken the viscosity of the temporary bonding film, so that the temporary bonding film and the temporary supporting substrate are desorbed from the surface of the flexible substrate. According to the method disclosed by the invention, the combination stability of the temporary supporting substrate is improved by using the temporary bonding film, so that the preparation success rate of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a metal substrate multi-junction thin-film solar cell and a preparation method thereof. Background Art

[0002] With the rapid development of spacecraft, near-space platforms, and wearable devices, the performance requirements for solar cells are becoming increasingly stringent. Although traditional rigid GaAs solar cells have high photoelectric conversion efficiency, their heavy weight and poor plasticity limit their application in lightweight and complex curved applications.

[0003] Compared to traditional rigid GaAs solar cells, flexible thin-film GaAs solar cells offer advantages such as lightweight, configurability, and high specific power, making them a key research and development focus for the next generation of space energy technology. Flexible thin-film GaAs solar cells primarily consist of a flexible substrate, a flexible epitaxial structure, and an electrode structure. However, the flexible epitaxial structure of flexible thin-film GaAs solar cells is extremely thin, making it prone to shedding and cracking during device fabrication, making it difficult to manufacture flexible thin-film solar cells.

[0004] Therefore, in the current process of manufacturing flexible thin-film solar cells, attempts are being made to use a temporary support substrate on the surface of the flexible epitaxial structure to support and protect the flexible epitaxial structure, so as to reduce the phenomenon of the flexible epitaxial structure falling off and cracking during the subsequent lithography and evaporation processes. At present, the flexible substrates of mainstream flexible thin-film solar cells are mostly made of polyimide or metal copper, and their flexible epitaxial structures mostly use three-junction cell epitaxial layers, including lattice-matched GaInP / GaAs double-junction cell epitaxial layers, lattice-mismatched In 0.3 GaAs single junction cell epitaxial layer (mismatch of about 2%). In the flexible epitaxial structure of the solar cell (GaInP / GaAs / In 0.3In the process of combining a flexible GaAs structure with a temporary support substrate, it is usually performed by spin-coating an adhesive on the surface of the flexible substrate and the surface of the temporary support substrate, pressing the two together so that the flexible substrate and the temporary substrate are firmly and evenly bonded together, and then performing conventional device processes such as photolithography and electrode steaming, and then removing the temporary support substrate to complete the preparation of a flexible thin film gallium arsenide solar cell. For example, CN108269864A discloses a method of combining the flexible substrate and the temporary support substrate by spin-coating an adhesive on the surface of the flexible substrate and the temporary support substrate, and then pressing them together; CN107808911A discloses a method for transferring a micro-thin film epitaxial structure layer, by spin-coating an adhesive on the surface of the flexible substrate and the surface of the temporary support substrate, and laminating the surface of the flexible substrate on which the adhesive is spin-coated with the surface of the temporary support substrate, so as to achieve periodic and batch transfer operations of the thin film epitaxial structure layer. However, the above-mentioned traditional methods have the problems of insufficient adhesion between the flexible substrate and the temporary support substrate, and difficulty in thorough cleaning and removal due to excessive residual glue (adhesive) on the surface of the flexible substrate, which still directly affects the success rate of the preparation of flexible thin film solar cells.

[0005] In addition, as the requirements for photoelectric conversion of thin-film solar cells for various tasks continue to increase, it is urgent to develop four-junction, five-junction and other multi-junction GaAs thin-film solar cells. However, in the case of four-junction and above multi-junction cells (such as GaInP / GaAs / In 0.3 GaAs / In 0.6 In the process of manufacturing GaAs structures, the above-mentioned traditional method of combining a temporary support substrate also brings the following significant defects:

[0006] The flexible epitaxial structure of a four-junction or more multi-junction thin-film solar cell contains multiple lattice-mismatched sub-cell epitaxial layers (e.g., In 0.3 GaAs layer and In 0.6 GaAs layer, the mismatch between the two reaches 4%), which leads to a significant increase in the internal stress of the flexible epitaxial structure. The adhesion strength of traditional adhesives is difficult to resist the risk of interface delamination caused by high stress, and debonding is more likely to occur at the bonding interface between the flexible substrate and the temporary support substrate. Especially in the metal flexible substrate system, the difference in thermal expansion coefficient will further aggravate the debonding phenomenon.

[0007] Therefore, multi-junction thin-film solar cells urgently need to develop a new method for combining flexible substrates with temporary support substrates to optimize the manufacturing process of flexible thin-film solar cells and reduce adverse effects. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for bonding a flexible substrate to a temporary support substrate, which can significantly improve the stability of the bonding between the flexible substrate and the temporary support substrate, so as to be suitable for the preparation of metal substrate multi-junction thin-film solar cells (flexible thin-film solar cells with four junctions or more) with flexible epitaxial structures with greater internal stress; at the same time, it can also achieve higher cleanliness of the surface of the flexible substrate after the temporary support substrate is desorbed, so as to reduce the damage to the multi-junction thin-film solar cells caused by complex residual glue cleaning treatment.

[0009] In order to achieve the above object, the present invention provides a method for preparing a metal substrate multi-junction thin film solar cell, comprising:

[0010] Step 1: providing an epitaxial wafer, a temporary bonding film, and a temporary supporting substrate; the epitaxial wafer includes a growth substrate, and a flexible epitaxial structure is formed on the growth substrate;

[0011] Step 2, forming a flexible substrate on the surface of the flexible epitaxial structure;

[0012] Step 3, applying the temporary bonding film to the surface of the flexible substrate;

[0013] Step 4, bonding the temporary supporting substrate and the temporary bonding film;

[0014] Step 5, irradiating with ultraviolet light of a first wavelength to cause a photo-crosslinking reaction of the temporary bonding film material to increase the viscosity of the temporary bonding film;

[0015] Step 6, etching and removing the growth substrate;

[0016] Step 7, fabricating electrodes and anti-reflection films on the flexible epitaxial structure;

[0017] Step 8: irradiate with ultraviolet light of a second wavelength to decompose the temporary bonding film material, weaken the viscosity of the temporary bonding film, and desorb the temporary bonding film and the temporary supporting substrate from the surface of the flexible substrate.

[0018] Optionally, the first wavelength is 365nm to 400nm; the irradiation time of the ultraviolet light of the first wavelength is 3min to 5min; the energy of the ultraviolet light source of the first wavelength is ≥2500mJ / cm 2 .

[0019] Optionally, the second wavelength is 240nm to 280nm; the irradiation time of the ultraviolet light of the second wavelength is 5min to 10min; the energy of the ultraviolet light source of the second wavelength is ≥12000mJ / cm 2 .

[0020] Optionally, in step 3, when laminating the temporary bonding film, the laminating pressure applied is 0.3 MPa to 0.6 MPa, and the laminating temperature is 50° C. to 70° C.

[0021] Optionally, step 4 includes:

[0022] After pressing the temporary support substrate and the temporary bonding film surface, the temporary support substrate and the temporary bonding film are bonded.

[0023] Optionally, the bonding process parameters include: a process temperature of 50° C. to 100° C., and a bonding pressure of 500 mbar to 1000 mbar.

[0024] Optionally, the flexible epitaxial structure includes at least a four-junction cell epitaxial layer.

[0025] The present invention also provides a metal substrate multi-junction thin film solar cell, which is prepared by the above-mentioned metal substrate multi-junction thin film solar cell preparation method.

[0026] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0027] In the method of the present invention, a temporary bonding film is used instead of a traditional adhesive as the bonding interface between the flexible substrate and the temporary support substrate. The temporary bonding film can achieve enhanced or weakened viscosity under the irradiation of ultraviolet light of different specific wavelengths. On the one hand, the temporary bonding film undergoes a photocrosslinking reaction under the irradiation of long-wave ultraviolet light (365nm~400nm), which enhances the viscosity and significantly improves the bonding stability between the flexible substrate and the temporary support substrate, avoiding the debonding and separation phenomenon that is easy to occur in the flexible substrate in the subsequent process, thereby ensuring the success rate of the preparation of metal substrate multi-junction thin-film solar cells. , which is suitable for the preparation of four-junction and above multi-junction metal substrate multi-junction thin-film solar cells with greater internal stress; on the other hand, the temporary bonding film undergoes a decomposition reaction under the irradiation of short-wave ultraviolet light (240nm~280nm) and loses its viscosity. The temporary bonding film and the temporary substrate can be desorbed from the surface of the flexible substrate by themselves, realizing lossless separation from the surface of the flexible substrate. After the temporary bonding film is desorbed, the amount of residual glue on the surface of the flexible substrate is greatly reduced, the cleanliness is greatly improved, and the damage of the residual glue cleaning process to the metal substrate multi-junction thin-film solar cell is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention provides a process flow chart of a method for preparing a metal substrate multi-junction thin-film solar cell.

[0029] Figure 2 The present invention is a schematic diagram of the cross-sectional structure of an epitaxial wafer having a flexible epitaxial structure formed on a growth substrate.

[0030] Figure 3 The present invention is a schematic diagram of the cross-sectional structure of an epitaxial wafer having a flexible substrate formed on the surface of a flexible epitaxial structure.

[0031] Figure 4 This is a schematic diagram of the cross-sectional structure of an epitaxial wafer processed in step 3 of the present invention.

[0032] Figure 5 The process flow chart of the method for preparing a metal substrate multi-junction thin-film solar cell including the improved step 4 of the present invention is shown.

[0033] Figure 6 This is a schematic diagram of the cross-sectional structure of an epitaxial wafer processed in step 4 of the present invention.

[0034] Figure 7 This is a schematic diagram of the cross-sectional structure of an epitaxial wafer processed in step 6 of the present invention.

[0035] Figure 8 The present invention is a schematic diagram of the cross-sectional structure of an epitaxial wafer having a front gate line pattern electrode formed on a flexible epitaxial structure.

[0036] Figure 9 The figure is a schematic diagram of the cross-sectional structure of an epitaxial wafer with an anti-reflection film formed on a flexible epitaxial structure according to the present invention.

[0037] Description of the accompanying drawings:

[0038] Growth substrate 10

[0039] Peeling off the sacrificial layer 20

[0040] Flexible epitaxial structure 30

[0041] Metal seed layer 40

[0042] First metal layer 41

[0043] Second metal layer 42

[0044] Flexible substrate 50

[0045] Temporary bonding film 60

[0046] Temporary supporting substrate 70

[0047] Front grid line pattern electrode 80

[0048] Anti-reflection film 90. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] In the description of the present invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical connections; direct connections or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0052] The “multi-junction thin film solar cell” described herein refers to a thin film solar cell comprising multiple junction sub-cell epitaxial layers. For example, a four-junction thin film solar cell refers to a thin film solar cell comprising four junction sub-cell epitaxial layers.

[0053] As described in the background art, the conventional method of combining a flexible substrate with a temporary support substrate has at least the following problems:

[0054] (1) Insufficient interface bonding strength: On the one hand, for a flexible epitaxial structure containing multiple lattice-mismatched sub-cell epitaxial layers, its internal stress is relatively large. The internal stress is transmitted through the flexible substrate to the bonding interface between the flexible substrate and the temporary support substrate, which makes it easy for local warping or microcracks to occur at the interface, causing the temporary support substrate to debond and separate. On the other hand, for a flexible substrate made of metal material, since the thermal expansion coefficient of metal is larger than that of polyimide, when the temperature of the epitaxial wafer changes, it is more likely to further aggravate the debonding and separation of the temporary support substrate, thereby causing the flexible epitaxial structure to easily fall off and break.

[0055] (2) Residual adhesive contamination: After the preparation of the electrodes and anti-reflection film of the multi-junction thin-film solar cell, the temporary support substrate needs to be desorbed. However, after the temporary support substrate is desorbed, the adhesive is very likely to remain on the surface of the flexible substrate and is difficult to be completely cleaned and removed, resulting in increased roughness of the flexible substrate surface, which directly affects the cell performance (for example, causing the local resistance of the cell to increase, etc.) and the effective execution of the subsequent welding process.

[0056] To solve the above problems, the present invention provides a method for preparing a metal substrate multi-junction thin-film solar cell, which uses an ultraviolet (UV) temporary bonding film to replace the traditional bonding glue. The ultraviolet temporary bonding film exhibits different viscosities under ultraviolet light of different wavelengths. When performing the bonding process of the temporary support substrate, long-wave ultraviolet light is used to irradiate the ultraviolet temporary bonding film, and a photo-crosslinking reaction occurs inside the ultraviolet temporary bonding film, thereby improving the viscosity and significantly improving the bonding force between the flexible substrate and the temporary support substrate; and when performing the desorption and removal process of the temporary support substrate, short-wave ultraviolet light is used to irradiate the ultraviolet temporary bonding film, and the ultraviolet temporary bonding film loses its viscosity, thereby achieving self-desorption of the ultraviolet temporary bonding film and the temporary support substrate, so that the flexible substrate and the temporary support substrate do not need to use traditional adhesives to bond, thereby greatly improving the cleanliness of the flexible substrate surface after the temporary support substrate is desorbed, ensuring the cell performance of the metal substrate multi-junction thin-film solar cell, and providing a welding interface with good cleanliness for the subsequent welding process.

[0057] The present invention is described in detail below with reference to the accompanying drawings.

[0058] like Figure 1 As shown, the present invention provides a method for preparing a metal substrate multi-junction thin film solar cell, comprising:

[0059] Step 1: Provide an epitaxial wafer, a temporary bonding film, and a temporary supporting substrate; the epitaxial wafer includes a growth substrate, and a flexible epitaxial structure is formed on the growth substrate.

[0060] Figure 2 The schematic diagram of the cross-sectional structure of an epitaxial wafer with a flexible epitaxial structure formed on a growth substrate is shown. The growth substrate 10 has a front side and a back side opposite to each other. Figures 2 to 5 The cross-sectional structures shown are all formed on the back side of the growth substrate 10. In some embodiments, step 1 includes:

[0061] Step 1.1: forming a peeling sacrificial layer on the surface of the growth substrate.

[0062] The peeling sacrificial layer 20 serves as the separation interface between the growth substrate 10 and the subsequently formed flexible epitaxial structure 30. It can be dissolved by wet etching to separate the flexible epitaxial structure 30 from the growth substrate 10. Furthermore, the peeling sacrificial layer 20 also serves as an etch barrier during the subsequent etching process to remove the growth substrate, preventing damage to the flexible epitaxial structure 30. For example, the growth substrate 10 is made of gallium arsenide or germanium and has a thickness of 150 μm to 500 μm. The peeling sacrificial layer 20 is a stacked structure consisting of GaInP and AlInP layers (referred to as a GaInP / AlInP structure) with a thickness of 20 nm to 100 nm.

[0063] Step 1.2, sequentially forming the first junction sub-cell epitaxial layer to the last junction sub-cell epitaxial layer on the surface of the stripped sacrificial layer, so as to form a flexible epitaxial structure on the back side of the growth substrate.

[0064] Solar cells usually adopt the flip-chip growth method to form the flexible epitaxial structure 30, that is, the multi-junction cell epitaxial layers are grown on the growth substrate 10 in the order of the band gap from large to small. For a four-junction thin film solar cell, its flexible epitaxial structure consists of a GaInP layer (band gap of 1.9eV), a GaAs layer (band gap of 1.424eV), an In 0.3 GaAs layer (bandgap width is 1.0eV) and In 0.6 The flexible epitaxial structure of the five-junction thin-film solar cell consists of an AlGaInP layer (bandgap width of 2.05eV), an AlGaAs layer (bandgap width of 1.7eV), a GaAs layer (bandgap width of 1.424eV), an In 0.3 GaAs (bandgap width is 1.0eV) and In 0.6 It is composed of GaAs (bandgap width is 0.7eV).

[0065] As an example, the reaction chamber pressure for growing the flexible epitaxial structure 30 is 50 mbar and the temperature is 550-700°C. The metal organic sources used in the growth process include: trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), arsine (AsH3), and phosphine (PH3).

[0066] Step 2: forming a flexible substrate on the surface of the flexible epitaxial structure.

[0067] Figure 3 A schematic diagram of a cross-sectional structure of an epitaxial wafer having a flexible substrate formed on the surface of the flexible epitaxial structure is shown. In some embodiments, the flexible substrate 50 is formed by depositing a metal layer on the surface of the flexible epitaxial structure 30 using a metal evaporation or metal sputtering process, and the formation steps include:

[0068] Step 2.1, forming a metal seed layer on the surface of the flexible epitaxial structure; the metal seed layer comprises a first metal layer and a second metal layer stacked in sequence, and the first metal layer is close to the surface of the flexible epitaxial structure.

[0069] The metal seed layer 40 provides a uniform conductive surface for the subsequent fabrication of the flexible substrate 50. The first metal layer 41 may be made of at least one of Ti, Pt, Ni, and Cr, with a thickness of 50 nm to 100 nm. The second metal layer 42 may be made of Au, with a thickness of 300 nm to 800 nm.

[0070] Step 2.2: forming a flexible substrate on the surface of the metal seed layer.

[0071] The metal seed layer is connected to the electrodes of the electroplating equipment, and the epitaxial wafer is placed in the electroplating tank. The power is turned on to form a uniform and dense flexible substrate 50 on the surface of the metal seed layer. The thickness of the flexible substrate is controlled by parameters such as current and time to a value of 20 μm to 30 μm. The material of the flexible substrate can be any one or more of Cu, Cr, Ni, and Pt.

[0072] In some embodiments, after step 1 and before step 2, the epitaxial wafer is cleaned in a water bath using an electronic-grade cleaning solution or other decontamination agent, and can be further cleaned using an ultrasonic cleaning device to remove particles on the surface of the epitaxial wafer. After cleaning, the epitaxial wafer is dried.

[0073] Step 3: attaching the temporary bonding film to the surface of the flexible substrate.

[0074] The material of the temporary bonding film 60 is a composite photosensitive material. Under the irradiation of long-wave ultraviolet light (wavelength of 365nm~400nm), the temporary bonding film material undergoes a photocross-linking reaction to form a denser three-dimensional cross-linked network structure, so that the temporary bonding film 60 is more evenly attached to the surface of the flexible substrate 50, thereby increasing the effective contact area and thus improving the adhesion (viscosity). Under the irradiation of short-wave ultraviolet light (wavelength of 240nm~280nm), the temporary bonding film material undergoes a decomposition reaction so that the temporary bonding film 60 loses its viscosity and can be detached from the surface of the flexible substrate 50 by itself. In this embodiment, the temporary bonding film 60 can be purchased.

[0075] In some embodiments, the temporary bonding film 60 has opposite front and back sides, both sides of which are covered with release paper protective films (not shown). After peeling off the release paper protective film on one side of the temporary bonding film 60, the temporary bonding film 60 is applied to the surface of the flexible substrate 50 at a pressure of 0.3 MPa to 0.6 MPa and a temperature of 50°C to 70°C. The resulting cross-sectional structure is shown in FIG. Figure 4 .

[0076] Step 4: Bonding the temporary supporting substrate to the temporary bonding film.

[0077] In some embodiments, step 4 comprises:

[0078] After pressing the temporary support substrate and the temporary bonding film surface, the temporary support substrate and the temporary bonding film are bonded.

[0079] The temporary support substrate 70 may be made of a light-transmitting substrate material such as quartz, glass, or sapphire, and the light-transmitting wavelength thereof is ≥200 nm.

[0080] In some embodiments, the release paper protective film on the other side of the temporary bonding film 60 is peeled off, the surface of the temporary support substrate 70 is pressed against the surface of the temporary bonding film 60, and then the epitaxial wafer is placed in a bonding machine, and the temporary support substrate 70 and the temporary bonding film 60 are bonded under a vacuum environment, with a bonding temperature of 50°C to 100°C, a bonding pressure of 500mbar to 1000mbar, and a bonding time of 10min to 30min. The cross-sectional structure formed is shown in FIG. Figure 6 .

[0081] Step 5: irradiating with ultraviolet light of a first wavelength to cause a photo-crosslinking reaction in the temporary bonding film material, thereby increasing the viscosity of the temporary bonding film.

[0082] The first wavelength is 365nm to 400nm. The temporary bonding film is irradiated with ultraviolet light of this wavelength for 4 minutes, and the energy of the light source is ≥ 2500mJ / cm 2 The temporary bonding film 60 has increased viscosity under the irradiation of the ultraviolet light, so that the bonding stability between the temporary bonding film 60 and the flexible substrate 50 and the temporary supporting substrate 70 is significantly improved.

[0083] Step 6: etching and removing the growth substrate.

[0084] Starting from step 6, the epitaxial wafer is flipped vertically before subsequent processing, i.e., processing is performed from the front side of the growth substrate 10. In some embodiments, the growth substrate 10 is removed by wet etching. The etching solution used has a high chemical reaction rate with the growth substrate 10, and the etching removal of the growth substrate 10 can be completed in about 60 minutes, exposing the surface of the peeled sacrificial layer 20. In some embodiments, the etching solution includes, but is not limited to, any one of a mixed solution of ammonia and hydrogen peroxide, or a mixed solution of phosphoric acid and hydrogen peroxide.

[0085] After the etching and removal of the growth substrate 10 is completed, the epitaxial wafer is placed in a stripping sacrificial layer corrosion solution and immersed for 5 minutes to 10 minutes to remove the stripping sacrificial layer 20. In some embodiments, the corrosion solution includes but is not limited to any one of a hydrochloric acid solution and a mixed solution of hydrochloric acid and hydrofluoric acid. The epitaxial wafer after the removal of the growth substrate 10 and the stripping sacrificial layer 20 is placed in acetone and ethanol solutions in turn for ultrasonic cleaning for 5 minutes, then rinsed with deionized water and dried to obtain the following. Figure 7 The cross-sectional structure shown.

[0086] Step 7: Fabricate electrodes and anti-reflection films on the flexible epitaxial structure.

[0087] On the flexible epitaxial structure 30 above the temporary support substrate 70, conventional solar cell manufacturing processes such as photolithography, metal evaporation, and optical film evaporation are sequentially used to prepare the front grid line pattern electrode 80 and the anti-reflection film 90, and the epitaxial wafer is cut into the cell size by scribing. In some embodiments, step 7 includes:

[0088] Step 7.1, prepare a first photoresist coating (not shown) on the surface of the flexible epitaxial structure 30, dry it, expose it using a photolithography machine, and then develop it to obtain a front gate line lithography pattern on the flexible epitaxial structure 30.

[0089] Step 7.2, perform metal evaporation process.

[0090] The metal material used in the metal evaporation process is a front electrode material, which includes Au, Ag, AuGeNi alloy, etc.

[0091] Step 7.3: remove the first photoresist coating.

[0092] In some embodiments, after the metal evaporation process is completed, the epitaxial wafer is immersed in an acetone solution to remove the first photoresist coating and the metal material deposited on the first photoresist coating. After the removal is completed, the preparation of the front gate line pattern electrode 80 is completed, and the following is obtained: Figure 8The cross-sectional structure shown.

[0093] Step 7.4: prepare a second photoresist coating (not shown) on the surface of the flexible epitaxial structure and the front gate line pattern electrode, perform exposure processing using a photolithography machine, and then perform development processing to obtain an anti-reflection film photolithography pattern.

[0094] Step 7.5, performing an anti-reflection film evaporation process.

[0095] The anti-reflection film materials used in the anti-reflection film evaporation process include but are not limited to TiO x 、AlO x 、SiO x , any one or more of MgF2.

[0096] Step 7.6: remove the second photoresist coating.

[0097] In some embodiments, after the anti-reflection film evaporation process is completed, the epitaxial wafer is placed in an acetone solution for immersion treatment to remove the second photoresist coating and the anti-reflection film material deposited on the second photoresist coating. After the removal is completed, the preparation of the anti-reflection film 90 is completed, and the following is obtained: Figure 9 The cross-sectional structure shown.

[0098] Step 7.7, apply a dicing film to the back of the epitaxial wafer, and then use a dicing machine to cut the epitaxial wafer into battery size.

[0099] Step 8: irradiate with ultraviolet light of the second wavelength to decompose the temporary bonding film material, weaken the viscosity of the temporary bonding film, and desorb the temporary bonding film and the temporary supporting substrate from the surface of the flexible substrate.

[0100] The second wavelength is 240nm to 280nm. The temporary bonding film is irradiated with ultraviolet light of this wavelength for 5min to 10min, and the energy of the light source is ≥12000mJ / cm 2 The temporary bonding film 60 loses its viscosity under the irradiation of the ultraviolet light, so that the temporary bonding film 60 and the temporary supporting substrate 70 are self-desorbed, and finally a flexible thin film gallium arsenide solar cell monomer device is obtained.

[0101] In summary, in the method of the present invention, by attaching a temporary bonding film to the surface of the flexible epitaxial structure and pressing a temporary support substrate, and then coordinating with a conventional device preparation process, the success rate of preparing four-junction and five-junction flexible thin-film solar cells can be greatly improved. Since the viscosity of the temporary bonding film can change with the irradiation of ultraviolet light of different wavelengths, on the one hand, under the irradiation of long-wave ultraviolet light, the viscosity of the temporary bonding film is improved, which significantly improves the bonding force between the flexible substrate and the temporary support substrate, making the two firmly combined, avoiding the risk of interface stratification caused by the traditional bonding method using adhesives, and improving the success rate of preparing solar cells; on the other hand, the use of a temporary bonding film makes it possible for the surface of the flexible substrate to be combined with the temporary support substrate without the use of adhesives, etc. After the temporary support substrate is desorbed, the cleanliness of the surface of the flexible substrate is greatly improved due to the reduction of residual glue, eliminating the complicated residual glue cleaning step, and reducing the damage of the residual glue cleaning step to the metal substrate multi-junction thin-film solar cell.

[0102] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a metal substrate multi-junction thin film solar cell, characterized in that: Include: Step 1: providing an epitaxial wafer, a temporary bonding film, and a temporary supporting substrate; the epitaxial wafer includes a growth substrate, and a flexible epitaxial structure is formed on the growth substrate; Step 2, forming a flexible substrate on the surface of the flexible epitaxial structure; Step 3, applying the temporary bonding film to the surface of the flexible substrate; Step 4, bonding the temporary supporting substrate and the temporary bonding film; Step 5, irradiating with ultraviolet light of a first wavelength to cause a photo-crosslinking reaction of the temporary bonding film material to increase the viscosity of the temporary bonding film; Step 6, etching and removing the growth substrate; Step 7, fabricating electrodes and anti-reflection films on the flexible epitaxial structure; Step 8: irradiate with ultraviolet light of a second wavelength to decompose the temporary bonding film material, weaken the viscosity of the temporary bonding film, and desorb the temporary bonding film and the temporary supporting substrate from the surface of the flexible substrate.

2. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 1, wherein: The first wavelength is 365nm to 400nm; the irradiation time of the ultraviolet light of the first wavelength is 3min to 5min; the energy of the ultraviolet light source of the first wavelength is ≥2500mJ / cm 2 .

3. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 1, wherein: The second wavelength is 240nm to 280nm; the irradiation time of the second wavelength ultraviolet light is 5min to 10min; the energy of the second wavelength ultraviolet light source is ≥12000mJ / cm 2 .

4. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 1, wherein: In the step 3, when laminating the temporary bonding film, the laminating pressure applied is 0.3 MPa to 0.6 MPa, and the laminating temperature is 50° C. to 70° C.

5. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 1, wherein: The step 4 includes: performing a pressing process on the surface of the temporary supporting substrate and the surface of the temporary bonding film, and then bonding the temporary supporting substrate and the temporary bonding film.

6. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 5, wherein: The bonding process parameters include: a process temperature of 50° C. to 100° C., and a bonding pressure of 500 mbar to 1000 mbar.

7. The method for preparing a metal substrate multi-junction thin film solar cell according to claim 1, wherein: The flexible epitaxial structure at least includes a four-junction cell epitaxial layer.

8. A metal substrate multi-junction thin film solar cell, characterized in that: The solar cell is prepared by the method for preparing a metal substrate multi-junction thin film solar cell according to any one of claims 1 to 7.

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