Flexible solar cell and preparation method thereof

Abstract

The invention discloses a flexible solar cell and a preparation method thereof, and the preparation method comprises the following steps: providing a growth substrate, and growing a sacrificial layer on the growth substrate; growing an epitaxial structure on the sacrificial layer in an inverted manner; first slurry is printed on the first surface of the side, away from the growth substrate, of the epitaxial structure through a screen printing technology, the first slurry is sintered, a first electrode is prepared, and the first electrode is a flexible electrode and covers the whole first surface; providing a rigid substrate, and bonding the first electrode with the rigid substrate; removing the growth substrate and the sacrificial layer; second slurry is printed on the second surface of the side, away from the first electrode, of the epitaxial structure through the screen printing technology, the second slurry is sintered, a second electrode is prepared, the second surface comprises a metal area and a non-metal area, and the second electrode is located on the metal area; and de-bonding the first electrode with the rigid substrate. According to the invention, the preparation process of the flexible solar cell is simplified, and the production efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solar cells, and particularly relates to a flexible solar cell and a preparation method thereof. BACKGROUND

[0002] At present, commercial low-orbit satellites are developing rapidly, and as a key component, photovoltaic energy systems are mainly researched in the aspects of low cost, high photoelectric conversion efficiency and light weight.

[0003] At present, light flexible solar cells used in the space field mainly use photolithography combined with electron beam evaporation process to prepare front and back electrodes, and then use electrochemical deposition process to deposit flexible metal on the back electrode as a flexible substrate, or bond flexible organic film on the back electrode to form a flexible solar cell.

[0004] However, the preparation process of the flexible solar cell in the prior art is complex, the electrode preparation method of photolithography combined with electron beam evaporation process is time-consuming and high in cost, and it is difficult to realize mass production, and the flexible substrate needs additional semiconductor process flow, so that the preparation process of the whole device is more complicated. In addition, noble metal materials are mainly used to prepare front and back electrodes in the prior art, which greatly increases the cost of the flexible solar cell. Although researches have shown that ordinary metals such as copper can be used to replace noble metals as electrode materials, the stability and contact performance of these metals in the space environment are still difficult to meet the requirements, and it is still difficult to break through the limitations of the traditional preparation process.

[0005] Therefore, in view of the above technical problems, it is necessary to provide a flexible solar cell and a preparation method thereof. SUMMARY

[0006] The application aims to provide a flexible solar cell and a preparation method thereof, which can simplify the process flow and reduce the cost.

[0007] In order to achieve the above-mentioned purpose, the technical scheme provided by an embodiment of the application is as follows:

[0008] A preparation method of a flexible solar cell, the preparation method comprising the following steps:

[0009] providing a growth substrate and growing a sacrificial layer on the growth substrate;

[0010] flip growing an epitaxial structure on the sacrificial layer;

[0011] printing a first slurry on a first surface of the epitaxial structure away from the growth substrate by a screen printing process, and sintering the first slurry to prepare a first electrode, the first electrode being a flexible electrode and covering the entire first surface;

[0012] bonding the first electrode with the rigid substrate;

[0013] removing the growth substrate and the sacrificial layer;

[0014] printing a second paste on a second surface of the epitaxial structure by a screen printing process, the second surface including a metal region and a non-metal region, the second electrode being on the metal region;

[0015] unbonding the first electrode from the rigid substrate.

[0016] In an embodiment, the first paste includes an electrode paste and a dopant, the electrode paste being any one or more of copper paste, silver paste, aluminum paste, the dopant being any one or more of germanium, zinc; and / or,

[0017] the second paste being any one or more of copper paste, silver paste, aluminum paste.

[0018] In an embodiment, a first screen is used to print the first paste on the back of the epitaxial structure by a screen printing process, the first screen including a plurality of first screens and a plurality of second screens, the first screens and the second screens intersecting, the intersection of the first screens and the second screens forming knots.

[0019] In an embodiment, the wire diameter of the first screen is 10-20 μm, the wire diameter of the second screen is 10-20 μm, and the mesh number of the first screen is 350-400.

[0020] In an embodiment, a second screen is used to print the second paste on the front of the epitaxial structure by a screen printing process, the second screen being provided with a plurality of openings arranged in parallel, the width of the openings being 10-15 μm.

[0021] Another embodiment of the present application provides the technical solutions as follows:

[0022] A flexible solar cell includes an epitaxial structure, a first electrode and a second electrode, the epitaxial structure including a first surface and a second surface arranged oppositely, the first electrode being a flexible electrode and covering the entire first surface, the second surface including a metal region and a non-metal region, the second electrode being on the metal region.

[0023] In an embodiment, the first surface includes a first region and a second region, the height of the first electrode on the second region being higher than the height of the first electrode on the first region.

[0024] In an embodiment, the size of the second region is 1-2 μm.

[0025] In an embodiment, the thickness of the first electrode is 20-30 microns.

[0026] In an embodiment, the contact resistance of the first electrode is less than or equal to 10 -5 Ω·cm 2 .

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] The first electrode with both ohmic contact electrode and flexible substrate functions is prepared by using a screen printing process, and the flexible solar cell with excellent photoelectric conversion efficiency, good flexibility and bendability is obtained.

[0029] In the present application, the first electrode and the second electrode of the flexible solar cell are prepared by using a screen printing process, which simplifies the process flow and improves the production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] Figure 1 It is a structure schematic diagram of the flexible solar cell in embodiment 1 of the present application.

[0032] Figure 2 It is an optical microscope characterization diagram of the first electrode in embodiment 1 of the present application.

[0033] Figure 3 It is an atomic force microscope characterization diagram of the first electrode in embodiment 1 of the present application.

[0034] Figure 4 It is a flowchart of the preparation method of the flexible solar cell in embodiment 1 of the present application.

[0035] Figures 5a to 5g It is a process flowchart of the preparation method of the flexible solar cell in embodiment 1 of the present application.

[0036] Figure 6 It is a partial top view of the first screen in embodiment 1 of the present application.

[0037] Figure 7 It is a partial top view of the second screen in embodiment 1 of the present application.

[0038] MAIN REFERENCE NUMERALS EXPLANATION:

[0039] 11-back contact layer, 12-a plurality of sub-cell epitaxial structures, 13-window layer, 14-front contact layer, 21-first electrode, 22-second electrode, 30-inorganic anti-reflective film layer, 40-growth substrate, 50-sacrificial layer, 60-rigid substrate. DETAILED DESCRIPTION

[0040] In order to make the person skilled in the art better understand the technical solutions in the present disclosure, the technical solutions in the present disclosure will be described clearly and completely in the following with reference to the drawings in the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, not all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present disclosure.

[0041] The present disclosure discloses a preparation method of a flexible solar cell, comprising the following steps:

[0042] Providing a growth substrate and growing a sacrificial layer on the growth substrate;

[0043] Inverting and growing an epitaxial structure on the sacrificial layer;

[0044] Printing a first paste on a first surface of the epitaxial structure away from the growth substrate by a screen printing process, and sintering the first paste to prepare a first electrode, the first electrode being a flexible electrode and covering the whole first surface;

[0045] Providing a rigid substrate and bonding the first electrode with the rigid substrate;

[0046] Removing the growth substrate and the sacrificial layer;

[0047] Printing a second paste on a second surface of the epitaxial structure away from the first electrode by a screen printing process, and sintering the second paste to prepare a second electrode, the second surface comprising a metal region and a non-metal region, and the second electrode being located on the metal region;

[0048] Unbonding the first electrode from the rigid substrate.

[0049] The present disclosure further discloses a flexible solar cell comprising an epitaxial structure, a first electrode and a second electrode, the epitaxial structure comprising a first surface and a second surface arranged oppositely, the first electrode being a flexible electrode and covering the whole first surface, the second surface comprising a metal region and a non-metal region, and the second electrode being located on the metal region.

[0050] The present disclosure will be further described below in combination with specific examples.

[0051] Embodiment 1:

[0052] Referring to FIG. 1, the flexible solar cell in the embodiment includes an epitaxial structure, a first electrode 21 and a second electrode 22. The epitaxial structure includes a first surface and a second surface arranged oppositely. The first electrode 21 is a flexible electrode and covers the entire first surface. The second surface includes a metal region and a non-metal region. The second electrode 22 is located on the metal region. Figure 1 The flexible solar cell in the embodiment is a flexible III-V group solar cell, preferably a flexible gallium arsenide-based solar cell.

[0053] In other embodiments, the epitaxial structure can be a single-junction solar cell epitaxial structure, which includes, from bottom to top, a back contact layer, a base region, an emitter, a window layer and a front contact layer.

[0054] The flexible solar cell in the embodiment is a flexible III-V group solar cell, preferably a flexible gallium arsenide-based solar cell.

[0055] More specifically, the front contact layer 14 in the embodiment is an N-type (In)GaAs layer with a doping concentration of 3x1018cm-2, and the dopant includes but is not limited to any one or more of Si, C or Ge. The back contact layer 11 is a P-type InGaAs layer or a P-type Ge layer with a doping concentration of 5x1018cm-2, and the dopant includes but is not limited to any one or more of Zn or Be. 18 3 18 3

[0056] In addition, each of the plurality of sub-cell epitaxial structures 12 can include a front sub-contact layer, a back sub-contact layer and a sub-window layer arranged in a stack, and adjacent sub-cells can be connected by a tunnel junction.

[0057] Further, the thickness of the first electrode 21 is 20-30 μm, and the first electrode 21 covers the surface of the back contact layer 11.

[0058] Preferably, the first electrode 21 in the embodiment is a doped copper electrode, and the dopant includes but is not limited to any one or more of Ge or Zn. The doped copper electrode can collect photo-generated carriers (holes) while serving as a flexible substrate for the flexible solar cell at a sufficiently thin thickness, has excellent contact performance with a contact resistance less than or equal to 10 -5 2 Ω·cm, and is compatible with ohmic contact electrodes and flexible substrates.

[0059] Referring to FIG. 1, the flexible solar cell in the embodiment includes an epitaxial structure, a first electrode 21 and a second electrode 22. The epitaxial structure includes a first surface and a second surface arranged oppositely. The first electrode 21 is a flexible electrode and covers the entire first surface. The second surface includes a metal region and a non-metal region. The second electrode 22 is located on the metal region. Figure 2 Figure 3 ​​​​​​As shown, the surface morphology of the first electrode 21 in this embodiment is honeycomb-like, and the first surface of the epitaxial structure includes a first region and a second region, and the height of the first electrode on the second region is higher than that on the first region.

[0060] Specifically, the size of the second region is 1-2 μm. Due to the fluidity of the screen printing paste, the profile of the first electrode on the second region is approximately circular with a diameter of 1-2 μm after sintering. The honeycomb-like first electrode as the back electrode of the flexible solar cell can increase the light reflection efficiency, realize the secondary reflection of photons, and thus improve the utilization of light, which is conducive to improving the performance of the flexible solar cell.

[0061] More specifically, the second electrode 22 is located on the front contact layer, and the second electrode is a grid-shaped electrode with a narrow line width, and the line width of a single electrode or a single metal region is 15-20 μm, which can effectively collect photo-generated electrons.

[0062] In addition, it is worth noting that the front contact layer is also grid-shaped and corresponds to the position of the second electrode, and the window layer 13 is exposed between two adjacent single front contact layer structures, i.e., the area where the front contact layer is located is a metal region, and the area between two adjacent single front contact layer structures is a non-metal region.

[0063] The window layer 13 in this embodiment is formed with an inorganic anti-reflection film layer 30, which includes but is not limited to any one or more of a SiO2 layer, a Ti2O3 layer, a MgF2 layer, a ZnS layer, or an Al2O3 layer.

[0064] Referring to Figure 4 As shown, the preparation method of the flexible solar cell in this embodiment includes the following steps:

[0065] S1, referring to Figure 5a As shown, a growth substrate 40 is provided, and a sacrificial layer 50 is grown on the growth substrate 40.

[0066] The growth substrate 40 includes but is not limited to a gallium arsenide substrate or a germanium substrate, and the sacrificial layer 50 includes but is not limited to a GaInP layer or an AlAs layer.

[0067] S2, referring to Figure 5b As shown, the epitaxial structure is grown on the sacrificial layer 50 in an inverted manner.

[0068] Specifically, the epitaxial structure in this embodiment is a gallium arsenide-based multi-junction solar cell epitaxial structure, i.e., a front contact layer, a window layer, a plurality of sub-cell epitaxial structures, and a back contact layer are sequentially grown on the sacrificial layer, the front contact layer has a doping concentration of 3×1018 cm-3, the window layer is a p-type window layer, the plurality of sub-cell epitaxial structures are grown on the window layer, and the back contact layer is grown on the plurality of sub-cell epitaxial structures. 18 cm 3The N-type (In)GaAs layer contains dopants including, but not limited to, any one or more of Si, C, or Ge; the back contact layer has a doping concentration of 5 × 10⁻⁶. 18 cm 3 The P-type InGaAs layer or P-type Ge layer contains dopants including, but not limited to, any one or more of Zn and Be.

[0069] S3, Reference Figure 5c As shown, the first paste is printed on the entire first surface of the epitaxial structure away from the growth substrate by screen printing process, and the first paste is sintered to prepare the first electrode 21. The first electrode 21 is a flexible electrode and covers the entire first surface.

[0070] The first paste includes an electrode paste and a dopant. The electrode paste is any one or more of copper paste, silver paste, and aluminum paste, and the dopant is any one or more of germanium and zinc.

[0071] Preferably, in this embodiment, the electrode paste is copper paste, which is more cost-effective. By adding germanium or zinc dopants to conventional electrode paste, the tunneling probability of the prepared first electrode at the semiconductor interface can be significantly improved, the contact performance can be optimized, and the problem of poor stability of traditional metal electrodes can be solved.

[0072] Specifically, refer to Figure 6 As shown, in this embodiment, a first screen is used to print the first paste on the back of the epitaxial structure through a screen printing process. The first screen includes multiple first screens and multiple second screens. The first screens and the second screens intersect, and a mesh knot is formed at the intersection of the first screens and the second screens. During the printing process, the paste will accumulate at the mesh knot, so that a honeycomb-like first electrode is formed after sintering.

[0073] More specifically, the wire diameter of the first screen is 10μm~20μm, the wire diameter of the second screen is 10μm~20μm, and the mesh count of the first screen is 350~400.

[0074] In addition, this embodiment uses low-temperature annealing to sinter the first printed paste using the solid-phase regeneration principle, so as to promote the formation of ohmic contact between the first electrode and the back contact layer. The annealing temperature is set to less than or equal to 200°C, the annealing time is set to less than 1 hour, and the annealing environment includes, but is not limited to, any one of nitrogen, hydrogen-oxygen mixed atmosphere, and vacuum environment.

[0075] In this embodiment, screen printing technology is used to achieve rapid and uniform preparation of the first electrode, which solves the problems of high cost and low production efficiency of traditional metal electrode preparation. At the same time, the prepared first electrode serves as both an ohmic contact electrode and a flexible substrate, providing a new process route for the manufacturing of flexible gallium arsenide solar cells. This will help accelerate the commercialization of flexible III-V solar cell technology and provide strong support for the development of low-cost commercial aerospace.

[0076] S4, Reference Figure 5d As shown, a rigid substrate 60 is provided, and the first electrode 21 is bonded to the rigid substrate 60.

[0077] Among them, the rigid substrate 60 includes, but is not limited to, any one of gallium arsenide substrate, silicon substrate, silicon carbide substrate or glass substrate.

[0078] Specifically, the first electrode 21 is bonded to the rigid substrate 60 using a bonding machine or laminator by means of metal or bonding adhesive, including but not limited to organic hot melt adhesive or UV-curable adhesive.

[0079] S5, Participant Figure 5e As shown, the growth substrate 40 and the sacrificial layer 50 are removed.

[0080] Specifically, the growth substrate 40 and the sacrificial layer 50 are removed by a combination of dry etching and wet etching.

[0081] The wet etching solution is a mixture of ammonia and hydrogen peroxide. The temperature during the etching process is set to 30℃~50℃. Excessively high etching temperatures can easily lead to stress concentration in the bonding adhesive, resulting in delamination and cracks.

[0082] S6, Participant Figure 5f As shown, a second paste is printed on the second surface of the epitaxial structure away from the first electrode 21 by screen printing process, and the second paste is sintered to prepare the second electrode 22. The second surface includes a metal region and a non-metal region, and the second electrode 22 is located on the metal region.

[0083] The second paste is any one or more of copper paste, silver paste, and aluminum paste.

[0084] Specifically, refer to Figure 7 As shown, a second slurry is printed on the front side of the epitaxial structure using a second screen printing process. The second screen is a fully open screen, that is, it has several parallel openings with a width of 10μm to 15μm. The thickness of the prepared grid-shaped second electrode is 10μm, and the linewidth of a single electrode is 15μm to 20μm.

[0085] In the embodiment, a wide-spectrum xenon lamp transient sintering technology is used to promote the second electrode and the front contact layer to form an ohmic tunnel contact, and the sintering environment includes, but is not limited to, any one of nitrogen, a hydrogen-oxygen mixed atmosphere, and a vacuum environment.

[0086] In addition, after the preparation of the first electrode is completed, the front contact layer is etched by using a dry etching process or a wet etching process, and the window layer is exposed.

[0087] Preferably, a mixture of citric acid and hydrogen peroxide is used as a wet etching solution, and the front contact layer is wet etched at an etching temperature of 30-40 DEG C.

[0088] Further, the embodiment also includes preparing an inorganic anti-reflection film layer 30 on the window layer 13.

[0089] Specifically, the inorganic anti-reflection film layer 30 is deposited on the window layer 13 at a deposition temperature of 100-200 DEG C, and the inorganic anti-reflection film layer 30 includes, but is not limited to, any one or more of a SiO2 layer, a Ti2O3 layer, a MgF2 layer, a ZnS layer, or an Al2O3 layer.

[0090] S6、parting Figure 5g the first electrode and the rigid substrate.

[0091] Further, when a whole wafer is prepared, after the preparation of the inorganic anti-reflection film layer is completed, the whole wafer is divided into a plurality of single chips.

[0092] Specifically, the step includes:

[0093] 1. Using a wet etching process to etch the useless area between adjacent single chips from the window layer to the first electrode.

[0094] The wet etching solution is one or more of bromine water or a potassium iodate solution.

[0095] 2. Using laser scribing or a mechanical blade to cut the rigid substrate and the first electrode to separate the single chips.

[0096] The laser wavelength is 300-500 nm, and the blade thickness is 50 um.

[0097] After the separation of the single chips is completed, a thermal slip, ultraviolet light separation, or other mechanical or physical separation method is used to part the first electrode and the rigid substrate.

[0098] From the above technical solution, the present application has the following beneficial effects:

[0099] The application adopts a screen printing process to prepare the first electrode with the functions of ohmic contact electrode and flexible substrate, and obtains the flexible solar cell with excellent photoelectric conversion efficiency, good flexibility and bendability;

[0100] In the application, the first electrode and the second electrode of the flexible solar cell are prepared by using the screen printing process, so that the process flow is simplified and the production efficiency is improved.

[0101] It is apparent for those skilled in the art that the present disclosure is not limited to the details of the above exemplary embodiments, and the present disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of the present disclosure. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present disclosure is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present disclosure. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0102] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A method for fabricating a flexible solar cell, characterized in that, The preparation method includes the following steps: A growth substrate is provided, and a sacrificial layer is grown on the growth substrate; An epitaxial structure is grown on the sacrificial layer by flip-chip bonding. A first paste is printed on the first surface of the epitaxial structure away from the growth substrate using a screen printing process, and the first paste is sintered to prepare a first electrode. The first electrode is a flexible electrode and covers the entire first surface. A rigid substrate is provided, and the first electrode is bonded to the rigid substrate; Remove the growth substrate and the sacrificial layer; A second paste is printed on the second surface of the epitaxial structure on the side opposite to the first electrode using a screen printing process, and the second paste is sintered to prepare a second electrode. The second surface includes a metal region and a non-metal region, and the second electrode is located on the metal region. The first electrode is debonded to the rigid substrate.

2. The method for preparing a flexible solar cell according to claim 1, characterized in that, The first paste comprises an electrode paste and a dopant, wherein the electrode paste is any one or more of copper paste, silver paste, and aluminum paste, and the dopant is any one or more of germanium and zinc; and / or, The second paste is any one or more of copper paste, silver paste, and aluminum paste.

3. The method for preparing a flexible solar cell according to claim 1, characterized in that, A first paste is printed on the back of the epitaxial structure using a first screen printing process. The first screen includes multiple first screens and multiple second screens. The first screens and second screens intersect, and a knot is formed at the intersection of the first screens and the second screens.

4. The method for preparing a flexible solar cell according to claim 3, characterized in that, The wire diameter of the first screen is 10μm~20μm, the wire diameter of the second screen is 10μm~20μm, and the mesh count of the first screen is 350~400.

5. The method for preparing a flexible solar cell according to claim 1, characterized in that, A second paste is printed on the front side of the epitaxial structure using a second screen printing process. The second screen has several parallel openings with a width of 10μm to 15μm.

6. A flexible solar cell, characterized in that, The flexible solar cell includes an epitaxial structure, a first electrode, and a second electrode. The epitaxial structure includes a first surface and a second surface disposed opposite to each other. The first electrode is a flexible electrode and covers the entire first surface. The second surface includes a metal region and a non-metal region, and the second electrode is located on the metal region.

7. The flexible solar cell according to claim 6, characterized in that, The first surface includes a first region and a second region, wherein the height of the first electrode on the second region is higher than the height of the first electrode on the first region.

8. The flexible solar cell according to claim 7, characterized in that, The dimensions in the second region are 1μm to 2μm.

9. The flexible solar cell according to claim 6, characterized in that, The thickness of the first electrode is 20μm~30μm.

10. The flexible solar cell according to claim 6, characterized in that, The contact resistance of the first electrode is less than or equal to 10. -5 Ω·cm 2 .

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