A method for preparing a solar cell electrode and a solar cell

Abstract

The application discloses a preparation method of a solar cell electrode and a solar cell, and relates to the technical field of solar cells. The method comprises the following steps: providing a solar cell base body, at least one surface of the solar cell base body being provided with a conductive layer; covering an insulating protective layer on the surface of the solar cell base body with the conductive layer at intervals; depositing target metal ions on the outer side of the conductive layer which is not covered with the insulating protective layer by using an electrodeposition solution, and forming a target metal electrode with a nanotwin structure containing a coherent twin boundary by controlling the deposition current density. According to the embodiment, the target metal electrode with the nanotwin structure containing the coherent twin boundary can be formed, the surface oxidation rate of the target metal electrode is effectively reduced, a tin plating layer does not need to be formed on the surface of all the target metal electrodes, the use amount of tin is reduced, and the preparation cost of the battery is reduced.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a method for preparing a solar cell electrode and a solar cell. Background Technology

[0002] In the field of solar cell fabrication, silver, a metal with excellent conductivity, is mainly used to prepare solar cell electrodes. However, since silver is a precious metal, the cost of preparing solar cell electrodes is relatively high. Therefore, researchers are focusing on studying metals that can replace silver in preparing solar cells in order to reduce the cost of electrode preparation while maintaining good conductivity.

[0003] Currently, the industry widely uses metals such as copper to replace silver in electrode fabrication. However, other metals, including copper, have poor oxidation resistance, making the resulting metal electrodes prone to oxidation during solar cell operation. To address this issue, a tin plating layer is typically formed on the surface of the metal electrode to slow down the oxidation process. However, tin plating still contributes to the higher cost of solar cells. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a method for preparing a solar cell electrode and a solar cell, which can form a target metal electrode containing a nanotwin structure with coherent twin boundaries, effectively reducing the surface oxidation rate of the target metal electrode.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a solar cell electrode is provided, comprising: Step S1: Provide a solar cell substrate, wherein at least one surface of the solar cell substrate is provided with a conductive layer; Step S2: Cover the surface of the solar cell substrate with an insulating protective layer at intervals; Step S3: Deposit target metal ions on the outside of the conductive layer that is not covered by the insulating protective layer using an electrodeposition solution, and form a target metal electrode with a nanotwin structure containing coherent twin boundaries by controlling the deposition current density.

[0006] Optionally, the target metal electrode formed in step S3 includes a main gate electrode extending along a first direction and a fine gate electrode extending along a second direction and intersecting with the main gate electrode. The method further includes: step S4, setting a tin plating layer in the intersection area of ​​the main gate electrode and the fine gate electrode.

[0007] Optionally, the conductive layer includes a metal seed layer and / or a transparent conductive film; Preferably, when the conductive layer includes a metal seed layer, the thickness of the metal seed layer is 50nm-200nm.

[0008] Optionally, the target metal electrode is a copper electrode.

[0009] Optionally, the electrodeposition solution comprises: copper sulfate pentahydrate with a molar concentration of 0.5 mol / L to 2.5 mol / L, sulfuric acid with a molar concentration of 0.1 mol / L to 1.5 mol / L, chloride ions with a mass content of 15 ppm to 100 ppm, an accelerator with a mass content of 20 ppm to 550 ppm, and an inhibitor with a mass content of 50 ppm to 150 ppm; wherein the accelerator is used to promote the deposition of the target metal ions on the target crystal face during the deposition of the target metal ions on the outside of the conductive layer by the electrodeposition solution, and the inhibitor is used to inhibit the deposition of the target metal ions on non-target crystal faces.

[0010] Optionally, the accelerator includes at least one of: Janus Green, sodium 3-(benzothiazol-2-mercapto)-propanesulfonate, sodium polydithiodiethanesulfonate, polyethylene glycol, or sodium propyne sulfonate; Optionally, the promoter includes Janus Green at a mass content of 80ppm-120ppm.

[0011] Optionally, the accelerator includes sodium 3-(benzothiazole-2-mercapto)-propanesulfonate in a mass content of 10 ppm to 20 ppm.

[0012] Optionally, the accelerator includes sodium polydisulfide diethane sulfonate in a mass content of 130ppm-170ppm.

[0013] Optionally, the accelerator includes polyethylene glycol in a mass content of 55ppm-75ppm.

[0014] Optionally, the accelerator includes sodium propyne sulfonate in a mass content of 1 ppm to 3 ppm.

[0015] Optionally, the inhibitor includes at least one of sodium 3-mercapto-1-propanesulfonate, benzotriazole, polypropylene glycol, or methylbenzothiazole.

[0016] Optionally, the inhibitor comprises sodium 3-mercapto-1-propanesulfonate in a mass content of 10 ppm to 15 ppm.

[0017] Optionally, the inhibitor comprises benzotriazole at a mass content of 20 ppm to 30 ppm.

[0018] Optionally, the inhibitor comprises polypropylene glycol in a mass content of 8 ppm to 14 ppm.

[0019] Optionally, the inhibitor comprises methylbenzothiazole in a mass content of 4 ppm to 8 ppm.

[0020] Optionally, the deposition current density is 60 A / dm³. 2 -90A / dm 2 .

[0021] Optionally, step S3 includes: during the deposition of target metal ions, employing a forward pulse and a reverse waveform, wherein the peak deposition current density of the forward pulse is 70 A / dm². 2 -80A / dm 2 .

[0022] Optionally, the forward deposition time of the forward pulse is 18ms-40ms; the reverse pulse duration of the reverse waveform is 5ms-15ms, and the peak deposition current density during the reverse process is -25A / dm.

[0023] Optionally, step S3 further includes: performing gradient temperature control during the deposition of target metal ions; wherein the gradient temperature control includes at least two stages, the deposition current density in the first stage is greater than the deposition current density in the second stage, and the temperature in the first stage is lower than the temperature in the second stage. Optionally, the process parameters for gradient temperature control include: Phase 1: Deposition current density of 70 A / dm 2 -90A / dm 2 The temperature is 15℃-25℃, and the holding time is 0.5min-3min; Second stage: Deposition current density is 60 A / dm 2 -70A / dm 2 The temperature is 25℃-40℃, and the holding time is 3min-8min.

[0024] Optionally, step S2 includes: Step S21: Lay a full-surface positive photoresist on the surface of the solar cell substrate having the conductive layer; Step S22: Cover the positive photoresist with a first mask to expose the positive photoresist corresponding to the position where the target metal electrode is to be formed, expose it, and remove the first mask; Step S23: The exposed positive photoresist is developed using a first developing solution to remove the positive photoresist in the exposed area, thereby exposing the conductive layer at the position corresponding to the target metal electrode to be formed. Step S24: Thermally cure the remaining positive photoresist to form an insulating protective layer spaced over the conductive layer on the surface of the solar cell substrate.

[0025] Optionally, step S4 includes: A metal catalyst is deposited in the intersection region of the main gate electrode and the fine gate electrode using inkjet printing. The solar cell substrate containing the metal catalyst is annealed to dry and solidify the metal catalyst, thereby forming catalytic active sites. Tin plating is performed based on the catalytic active sites to form a tin plating layer in the intersection region of the main gate electrode and the fine gate electrode; Optionally, the metal catalyst is a palladium catalyst, etc.; preferably, the palladium catalyst comprises palladium nanoparticles with a particle size of 5 nm-20 nm, and the palladium loading in the palladium catalyst is 0.1-1 μg / mm. 2 ; Preferably, the annealing temperature is 80℃-120℃; Preferably, the thickness of the tin plating layer is 0.1μm-0.5μm.

[0026] Optionally, after step S3, the method further includes: Remove the insulating protective layer; Preferably, when the conductive layer includes a metal seed layer, after step S3, the method further includes: removing the portion of the metal seed layer corresponding to the insulating protective layer.

[0027] Optionally, the metal seed layer can be configured in the following ways: A metal seed layer is deposited on the surface of a solar cell substrate to which the target metal electrode is to be formed using magnetron sputtering; Preferably, the conditions for magnetron sputtering include: argon flow rate of 20 sccm-40 sccm, sputtering power of 80 W-300 W, gas pressure of 0.3 Pa-0.8 Pa, and deposition time of 3 min-8 min.

[0028] To achieve the above objectives, according to another aspect of the present invention, a solar cell is provided, comprising: A solar cell substrate, wherein at least one surface of the solar cell substrate is provided with a conductive layer; A target metal electrode containing a nanotwin structure with coherent twin boundaries is disposed on the outside of the aforementioned conductive layer.

[0029] Optionally, the crystal orientation of the nanotwin structure is (111) orientation.

[0030] Optionally, the target metal electrode is a copper electrode.

[0031] Optionally, the target metal electrode includes a main gate electrode extending along a first direction and a fine gate electrode extending along a second direction and intersecting the main gate electrode; The solar cell further includes a tin-plated layer disposed on the outer surface of the intersection region of the main grid electrode and the fine grid electrode.

[0032] One embodiment of the above invention has the following advantages or beneficial effects: a target metal electrode is formed on the outer layer of the conductive layer without an insulating protective layer on the surface of the solar cell substrate using an electrodeposition solvent. By adjusting the composition and ratio of the electrodeposition solution and the deposition current density, the target metal ions can be induced to deposit in a regular manner, forming a high-density twin array perpendicular to the deposition direction, thereby forming a target metal electrode with a nano-twin structure containing coherent twin boundaries. Since there are a large number of coherent twin boundaries in the target metal electrode, and the atomic arrangement of the coherent twin boundaries is relatively regular, the defect density is lower, and there are fewer oxygen permeation channels, the surface oxidation rate of the target metal electrode can be effectively reduced.

[0033] The further effects of the aforementioned unconventional alternative methods will be explained below in conjunction with specific implementation methods. Attached Figure Description

[0034] The accompanying drawings are provided to better understand the invention and are not intended to unduly limit the scope of the invention. Wherein: Figure 1 It is a schematic diagram of the crystal structure of copper electrodes in the prior art; Figure 2 This is a schematic flowchart of a method for preparing a solar cell electrode according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a first structure of a solar cell substrate according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a second structure of a solar cell substrate according to an embodiment of the present invention; Figure 5 This is a schematic diagram of a structure in which an insulating protective layer is provided on the surface of a solar cell substrate according to an embodiment of the present invention; Figure 6 This is a schematic diagram of a target metal electrode formed on the surface of a solar cell substrate according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the crystal structure of the target metal electrode according to an embodiment of the present invention; Figure 8 This is a top view of a solar cell substrate with a tin-plated layer according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a solar cell substrate with a tin-plated layer formed in the intersection area according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the structure of a solar cell according to an embodiment of the present invention.

[0035] Figure label: 1-Solar cell; 11-Solar cell substrate; 111-Conductive layer; 12-Insulating protective layer; 13-Target metal electrode; 131-Main grid electrode; 132-Fine grid electrode; 14-Tin plating layer Detailed Implementation

[0036] Currently, researchers in the industry mainly use metals such as copper to replace silver in the preparation of metal electrodes for solar cells. However, because other metals have poor oxidation resistance, the metal electrodes are prone to oxidation, which affects the photoelectric conversion efficiency of solar cells.

[0037] For example, regarding metallic copper, such as Figure 1 As shown, in ordinary copper crystal structures, the crystal orientation is random and the grain boundaries are disordered, which makes copper metal electrodes prone to carrier scattering during use. This causes the magnitude and direction of carrier movement to change continuously, limiting carrier transport efficiency.

[0038] Furthermore, because metallic copper is prone to oxidation, the atomic diffusion rate on the surface of metal electrodes prepared from it is relatively fast, with numerous diffusion paths, resulting in poor oxidation resistance. A common practice is to form a tin plating layer on its surface to slow down the oxidation rate. However, forming a tin plating layer on the surface of the metal electrode requires a large amount of tin, increasing manufacturing costs and potentially causing environmental pollution.

[0039] To address at least one problem existing in the prior art, embodiments of the present invention provide a method for preparing a solar cell electrode and a solar cell.

[0040] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0041] It should be noted that, in the embodiments of the present invention, the outer surface refers to the side away from the solar cell substrate. The outer side in the embodiments of the present invention refers to the side away from the solar cell substrate.

[0042] It should be noted that, unless otherwise specified, the embodiments of the present invention and the technical features thereof can be combined with each other.

[0043] Figure 2 This is a schematic diagram illustrating the main steps of a method for fabricating a solar cell electrode according to an embodiment of the present invention. Figure 2As shown, the method for preparing a solar cell electrode provided in this embodiment of the invention includes the following steps S1 to S3: Step S1: Provide a solar cell substrate 11, wherein at least one surface of the solar cell substrate 11 is provided with a conductive layer 111; Among them, the solar cell substrate 11 refers to a solar cell without a target metal electrode 13, including but not limited to tunnel oxide passivated contact (TOPCon) cells, heterojunction with intrinsic thin-layer (HJT) cells, interdigitated back contact (IBC) cells, perovskite cells, crystalline silicon-perovskite tandem cells, etc.

[0044] As an example, when the solar cell substrate 11 uses an HJT cell, the preparation method of the HTJ solar cell substrate 11 may include: using an n-type monocrystalline silicon wafer with a resistivity of 1Ω·cm-3Ω·cm as a silicon substrate, cleaning and texturing the silicon substrate to form a pyramid with a size of 2μm-5μm and a reflectivity of less than 5%, and then using chemical vapor deposition to form a stack of intrinsic amorphous silicon layer and P-type doped amorphous silicon, and a stack of intrinsic amorphous silicon and N-type doped amorphous silicon on the two surfaces of the silicon substrate, respectively, to obtain the HTJ solar cell substrate 11.

[0045] like Figure 3 As shown, when the solar cell substrate 11 is a solar cell that requires the target metal electrode 13 to be set on both sides, such as a TOPCon cell or an HJT cell, the aforementioned conductive layer 111 can be disposed on the two surfaces of the solar cell substrate 11 where the target metal electrode 13 needs to be set; for example... Figure 4 As shown, when the solar cell substrate 11 is a solar cell that requires the target metal electrode 13 to be set on one side, such as an IBC cell, the conductive layer 111 can be set only on the surface of the solar cell substrate 11 where the target metal electrode 13 needs to be set, or it can be set on both surfaces of the solar cell.

[0046] The aforementioned conductive layer 111 is mainly used for the lateral transport of charge carriers in the solar cell and can also serve as a transition layer between the target metal electrode 13 and the solar cell substrate 11, providing a growth nucleus for the subsequent fabrication of the target metal electrode 13. Due to its good conductivity, it is conducive to the electrodeposition of target metal ions, improves the adhesion between the target metal electrode 13 and the solar cell substrate 11, and reduces the contact resistance.

[0047] Step S2: Cover the surface of the solar cell substrate 11 with an insulating protective layer 12 at intervals; The insulating protective layer 12 is primarily used to prevent the deposition of target metal ions in locations where the target metal electrode is not required. It mainly covers the areas on the surface of the solar cell substrate 11 where the target metal electrode is not needed. For example, ... Figure 5 As shown, when the solar cell substrate 11 is a solar cell that requires target metal electrodes to be set on both sides, the insulating protective layer 12 covers the two surfaces of the solar cell substrate 11 with conductive layer 111 at intervals.

[0048] Step S3, as follows Figure 6 As shown, target metal ions are deposited on the outside of the conductive layer 111, which is not covered by the above-mentioned insulating protective layer 12, using an electrodeposition solution, and a target metal electrode 13 containing a nanotwin structure with coherent twin boundaries is formed by controlling the deposition current density.

[0049] The target metal electrode 13 is prepared on the outside of the conductive layer 111 that is not covered by the above-mentioned insulating protective layer 12 by electrodeposition. By setting the composition of the electrodeposition solution and the concentration of each component, the deposition current density, etc., the target metal ions form a nanotwin structure containing coherent twin boundaries during the deposition process.

[0050] The target metal ion can be a base metal with conductivity, such as copper, aluminum, nickel, etc., but is not limited to this.

[0051] Preferably, the target metal is copper, and the prepared target metal electrode 13 is a copper electrode.

[0052] By adjusting the composition of the electrodeposition solution, the concentration of each component, and the deposition current density, the target metal ions can be induced to arrange and deposit in a regular manner, forming a high-density twin array perpendicular to the deposition direction, containing a large number of coherent twin boundaries. Because the atomic arrangement of the target metal in the coherent twin boundaries is more regular and the defect density is low, oxygen permeation channels can be reduced, decreasing the probability of oxygen atoms entering the target metal electrode 13, thus slowing down the oxidation rate of the target metal electrode 13 and giving it good oxidation resistance, eliminating the need for a tin plating layer 14.

[0053] In an optional embodiment, when the target metal is copper, the electrodeposition solution comprises: copper sulfate pentahydrate with a molar concentration of 0.5 mol / L to 2.5 mol / L, sulfuric acid with a molar concentration of 0.1 mol / L to 1.5 mol / L, chloride ions with a mass content of 15 ppm to 100 ppm, an accelerator with a mass content of 20 ppm to 550 ppm, and an inhibitor with a mass content of 50 ppm to 150 ppm. The accelerator promotes the deposition of the target metal ions on the target crystal face during the deposition of the target metal ions on the outer side of the conductive layer using the electrodeposition solution, while the inhibitor inhibits the deposition of the target metal ions on non-target crystal faces. The accelerator and inhibitor work synergistically to achieve crystal face guidance, enabling preferential growth of grains on the target crystal face.

[0054] Chloride ions in the electrodeposition solution can be provided by hydrochloric acid.

[0055] As an example, in the above electrodeposition solution, the molar concentration of copper sulfate pentahydrate can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, or 2.5 mol / L, etc.; the molar concentration of sulfuric acid can be 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, or 1.5 mol / L, etc.; the mass content of chloride ions can be 15 ppm, 30 ppm, 50 ppm, 70 ppm, 80 ppm, or 100 ppm, etc.; the mass content of the promoter can be 20 ppm, 50 ppm, 100 ppm, 200 ppm, 280 ppm, 320 ppm, 400 ppm, or 550 ppm, etc.; and the mass content of the inhibitor can be 50 ppm, 70 ppm, 100 ppm, 120 ppm, 140 ppm, or 150 ppm, etc.

[0056] Optionally, the aforementioned accelerator includes at least one of: Janus Green, sodium 3-(benzothiazol-2-mercapto)-propanesulfonate, sodium polydisulfide diethanesulfonate, polyethylene glycol, or sodium propynyl sulfonate.

[0057] The aforementioned accelerators include Janus Green at a mass content of 80ppm-120ppm; sodium 3-(benzothiazole-2-mercapto)-propanesulfonate at a mass content of 10ppm-20ppm; sodium polydisulfide diethanesulfonate at a mass content of 130ppm-170ppm; polyethylene glycol at a mass content of 55ppm-75ppm; and sodium propyne sulfonate at a mass content of 1ppm-3ppm.

[0058] As an example, among the aforementioned accelerators, the mass content of Janus Green can be 80 ppm, 85 ppm, 90 ppm, 95 ppm, 100 ppm, 110 ppm, or 120 ppm, etc.; the mass content of sodium 3-(benzothiazole-2-mercapto)-propanesulfonate can be 10 ppm, 12 ppm, 15 ppm, 17 ppm, 19 ppm, or 20 ppm, etc.; the mass content of sodium polydisulfide diethanesulfonate can be 130 ppm, 140 ppm, 150 ppm, 160 ppm, or 170 ppm, etc.; the mass content of polyethylene glycol can be 55 ppm, 60 ppm, 65 ppm, 68 ppm, 70 ppm, or 75 ppm, etc.; and the mass content of sodium propyrynesulfonate can be 1 ppm, 1.3 ppm, 1.5 ppm, 1.7 ppm, 2.0 ppm, 2.5 ppm, or 3 ppm, etc.

[0059] Optionally, the above inhibitors include: sodium 3-mercapto-1-propanesulfonate, benzotriazole, polypropylene glycol, and methylbenzothiazole.

[0060] The above-mentioned inhibitors include sodium 3-mercapto-1-propanesulfonate with a mass content of 10ppm-15ppm; benzotriazole with a mass content of 20ppm-30ppm; polypropylene glycol with a mass content of 8ppm-14ppm; and methylbenzothiazole with a mass content of 4ppm-8ppm.

[0061] As an example, among the above inhibitors, the mass content of sodium 3-mercapto-1-propanesulfonate can be 10 ppm, 11 ppm, 12 ppm, 13 ppm, 14 ppm, or 15 ppm, etc.; the mass content of benzotriazole can be 20 ppm, 22 ppm, 24 ppm, 25 ppm, 27 ppm, or 30 ppm, etc.; the mass content of polypropylene glycol can be 8 ppm, 9 ppm, 10 ppm, 11 ppm, 12 ppm, 13 ppm, or 14 ppm, etc.; and the mass content of methylbenzothiazole can be 4 ppm, 5 ppm, 6 ppm, 7 ppm, or 8 ppm, etc.

[0062] It should be noted that the aforementioned promoters and inhibitors may also include other components, which will not be listed here.

[0063] Specifically, divalent copper ions provided by the electrodeposition solution are electrochemically reduced to monovalent copper ions. Under the action of a promoter, these monovalent copper ions are adsorbed onto the target crystal face. The thiol groups in the promoter of the electrodeposition solution provide sulfur... 2- Monovalent copper ions adsorbed onto the target crystal plane and S 2- They combine to form copper sulfide (Cu). +-S) bonds are used to promote the deposition of target metal ions on the target crystal plane. Then, monovalent copper ions are electrochemically reduced to generate copper atoms. Through the above electrochemical reaction, copper ions are continuously converted into copper atoms and grow on the crystal plane. Under the action of the inhibitor, monovalent copper ions are inhibited from adsorbing to non-target crystal planes, so as to inhibit the deposition of target metal ions on non-target crystal planes.

[0064] The crystal structure formed by copper atoms includes the (111) crystal plane, the (200) crystal plane, and the (220) crystal plane. The nanotwinned structure of copper has the (111) crystal plane as the twin boundary, and the target crystal plane is the (111) crystal plane. The non-target crystal planes are the (200) crystal plane and the (220) crystal plane.

[0065] The diffusion rate of copper atoms exhibits significant anisotropy across different crystal planes. The (111) plane shows the densest atomic arrangement, resulting in the slowest diffusion rate of copper atoms. Conversely, the (200) and (220) planes have larger interatomic gaps, leading to faster copper atom diffusion. Therefore, during copper atom electrodeposition, targeting the (111) plane and selectively oriented the copper grains to a structure dominated by the (111) plane can reduce the diffusion rate of copper atoms.

[0066] During the subsequent welding of tin-plated solder strips to the target metal electrode 13, copper atoms and tin atoms undergo atomic interdiffusion to form a copper-tin (Cu-Sn) brittle metal compound. The welding temperature during welding and the lamination temperature during the subsequent photovoltaic module lamination process may cause the atomic interdiffusion to continue, resulting in the continuous increase, thickening, and enlargement of the Cu-Sn brittle metal compound. This leads to a decrease in the mechanical strength and reliability of the welded surface, and may even cause problems such as interface cracking and solder strip detachment. In order to solve the above problems, this embodiment of the invention induces copper atoms to deposit on the (111) crystal plane during the electrodeposition process, which reduces the diffusion rate of copper atoms. This can reduce the generation rate of Cu-Sn brittle metal compound, avoid its excessive growth, and reduce the reliability problems of the module caused by excessive Cu-Sn brittle metal compound.

[0067] In one optional embodiment, the deposition current density is 60 A / dm³. 2 -90A / dm 2 As an example, the deposition current density could be 60 A / dm³. 2 65A / dm 2 70A / dm 2 80A / dm 2 85A / dm 2 or 90A / dm 2 wait.

[0068] By employing a higher deposition current density and adjusting the ratio of the electrodeposition solution, copper-sulfur (Cu) can be induced to form. + -S) bonds selectively adsorb at the (111) active site and inhibit their adsorption at the (200) or (220) active sites, increasing the peak intensity ratio at the (111) site. This results in the nanotwinned structures formed by the atoms of the target metal in the target metal electrode 13 having the same crystal orientation, and the crystal orientation being the (111) orientation. The crystal structure of the target metal electrode 13 is as follows: Figure 7 As shown, it basically does not include other crystal orientations or other crystal orientations are relatively few. It can be seen that the same crystal orientation can make the grains on the surface of the target metal electrode 13 more compact, and it is less likely to have surface curves such as steps or vacancies, thereby reducing the oxidation initiation point density and thus greatly reducing the surface oxidation rate of the target metal electrode 13.

[0069] In addition, using a high deposition current density to deposit target metal ions during the electrodeposition process can effectively improve preparation efficiency, reduce electrodeposition time, and lower preparation costs.

[0070] In an optional embodiment, step S3 may include: performing gradient temperature control during the deposition of target metal ions; wherein the gradient temperature control includes at least two stages, the deposition current density of the first stage is greater than the deposition current density of the second stage, and the temperature of the first stage is lower than the temperature of the second stage.

[0071] In the first stage, a high deposition current density and low temperature are used to form supersaturated copper ions on the cathode surface of the electrodeposition equipment. This promotes the directional generation of a large number of nanoscale twin composite nuclei by the target metal atoms, which have low thermodynamic nucleation work and slow kinetic atomic migration. This lays the foundation for the subsequent growth of a target metal layer with high twin density and (111) orientation. In the second stage, the temperature is increased to achieve rapid twin growth and lateral expansion at high temperature. The nucleation stage and the growth stage are decoupled by gradient temperature control.

[0072] Optionally, the process parameters for gradient temperature control include: Phase 1: Deposition current density of 70 A / dm 2 -90A / dm 2 The temperature is 15℃-25℃, and the holding time is 0.5min-3min; Second stage: Deposition current density is 60 A / dm 2 -70A / dm 2 The temperature is 25℃-40℃, and the holding time is 3min-8min.

[0073] As an example, in the gradient temperature controlled process parameters, the deposition current density in the first stage can be 70 A / dm³.2 80A / dm 2 85A / dm 2 or 90A / dm 2 The temperature in the first stage can be 15℃, 17℃, 19℃, 20℃, 22℃, or 25℃, and the holding time can be 0.5min, 0.8min, 1.0min, 1.2min, 1.5min, 2.0min, 2.5min, or 3.0min, etc.; the deposition current density in the second stage can be 60A / dm³. 2 62A / dm 2 64A / dm 2 65A / dm 2 67A / dm 2 or 70A / dm 2 The temperature of the second stage can be 25℃, 27℃, 30℃, 32℃, 35℃ or 40℃, etc., and the holding time can be 3.0min, 4.0min, 4.5min, 5.0min, 5.5min, 6.3min, 7.0min or 8.0min, etc.

[0074] In an optional embodiment, step S3 may include: employing a forward pulse and a reverse waveform during the deposition of target metal ions, wherein the peak deposition current density of the forward pulse is 70 A / dm². 2 -80A / dm 2 ; Optionally, the forward deposition time of the forward pulse is 18ms-40ms; the reverse pulse duration of the reverse waveform is 5ms-15ms, and the peak deposition current density during the reverse process is -25A / dm². 2 .

[0075] As an example, the forward deposition time of the forward pulse can be 18ms, 20ms, 24ms, 26ms, 30ms, 35ms, or 40ms, etc.; the duration of the reverse pulse of the reverse waveform can be 5ms, 7ms, 9ms, 10ms, 12ms, 13ms, or 15ms, etc.

[0076] By controlling the crystal growth kinetics with a positive pulse and a reverse waveform, more copper grains can be induced to grow on the (111) crystal plane, thus increasing the (111) orientation ratio.

[0077] In an optional embodiment, the target metal electrode 13 formed in step S3 may have different structures, with the following two structures as examples: The first structure: the target metal electrode 13 may include a main gate electrode 131 extending along a first direction and a fine gate electrode 132 extending along a second direction and intersecting the main gate electrode 131.

[0078] Among them, the fine grid electrode 132 is mainly used to collect charge carriers, and the main grid electrode 131 is mainly used to transfer the charge carriers collected by the fine grid electrode 132 to the outside of the solar cell.

[0079] The main grid electrode 131 has a wider linewidth and a greater thickness, and there are fewer of them on the surface of a solar cell; the fine grid electrode 132 has a narrower linewidth and a smaller thickness, and there are more of them on the surface of a solar cell, and they are arranged more densely.

[0080] Preferably, the first direction and the second direction are perpendicular to each other. As an example, in the surface of the solar cell substrate 11 where the target metal electrode 13 is disposed, the second direction is parallel to the wide side of the surface, and the first direction is parallel to the long side of the surface, so that the main grid electrode 131 and the fine grid electrode 132 intersect perpendicularly to form a "grid" structure.

[0081] When the target metal electrode 13 includes a main grid electrode 131 and a fine grid electrode 132, the method for fabricating the solar cell electrode may further include: step S4, depositing a tin plating layer 14 in the intersection region of the main grid electrode 131 and the fine grid electrode 132 to form a... Figure 8 and Figure 9 The structure shown.

[0082] The aforementioned tin plating layer 14 can reduce the welding temperature between the target metal electrode 13 and the solder ribbon, avoid damage to the solar cell substrate 11 due to excessively high welding temperature, form a strong connection between the target metal electrode 13 and the solder ribbon, reduce the probability of poor soldering, and isolate oxygen to inhibit the oxidation of the target metal electrode 13.

[0083] Furthermore, the intersection region of the main gate electrode 131 and the fine gate electrode 132 serves as a confluence channel between them. To ensure unimpeded carrier transport between them, a tin-plated layer 14 is provided in this region, which can further prevent oxidation of the main gate electrode 131 or the fine gate electrode 132 in this region. Compared with existing metal electrodes that form a tin-plated layer that completely covers the copper surface, the target metal electrode with a tin-plated layer only in the intersection region greatly reduces tin consumption and lowers manufacturing costs.

[0084] The second structure: the target metal electrode 13 may consist only of a fine gate electrode 132 extending along the second direction.

[0085] In this structure, a fine grid electrode 132 is primarily used to collect charge carriers, which are then transported to the outside of the solar cell via solder ribbons and busbars. By using only the fine grid electrode 132, the shading loss of the main grid electrode 131 can be eliminated, increasing the effective light-receiving area of ​​the solar cell and further improving the photoelectric conversion efficiency. Furthermore, the fine grid electrode 132 contains no tin, reducing electrode fabrication costs.

[0086] Specifically, step S4 above may include the following steps S41 to S43: Step S41: Deposit a metal catalyst in the intersection region of the main gate electrode 131 and the fine gate electrode 132 using inkjet printing. Optionally, the metal catalyst can be a palladium catalyst, comprising palladium nanoparticles with a particle size of 5 nm-20 nm, wherein the palladium loading is 0.1 μg / mm. 2 -1μg / mm 2 As an example, the palladium nanoparticles in the palladium catalyst can have particle sizes of 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, 18 nm, or 20 nm, etc., with a palladium loading of 0.1 μg / mm². 2 0.2μg / mm 2 0.4 μg / mm 2 0.6 μg / mm 2 0.8 μg / mm 2 or 1μg / mm 2 wait.

[0087] Step S42: Anneal the solar cell substrate 11 on which the above-mentioned metal catalyst is provided, and dry and solidify the above-mentioned metal catalyst to form palladium catalytic active sites. The annealing temperature mentioned above is 80℃-120℃. As an example, the annealing temperature can be 80℃, 90℃, 100℃, 110℃, or 120℃, etc.

[0088] Step S43: Tin plating is performed based on the palladium catalytic active sites to form a tin plating layer 14 in the intersection region of the main gate electrode 131 and the fine gate electrode 132, such as... Figure 8 and Figure 9 As shown; Specifically, the solar cell substrate 11, on which palladium catalytic active sites are formed, can be immersed in a tin plating bath. A tin plating layer 14 is formed in this region by reacting at the palladium catalytic active sites. The tin plating temperature can be 50±1℃. As an example, the tin plating temperature can be 49℃, 50℃, or 51℃, etc. The tin plating solution may include 10 g / L-12 g / L of stannous sulfate, 60 g / L-100 g / L of sodium citrate, 0.3 g / L-0.7 g / L of thiourea, a pH adjuster, and ammonia. The pH of the tin plating solution is adjusted to approximately 4.5 using the pH adjuster and ammonia. For example, the concentration of stannous sulfate in the tin plating solution may be 10 g / L, 10.5 g / L, 11 g / L, 11.5 g / L, or 12 g / L, etc.; the concentration of sodium citrate may be 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 90 g / L, or 100 g / L, etc.; and the concentration of thiourea may be 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, or 0.7 g / L, etc.

[0089] Preferably, the thickness of the tin plating layer 14 is 0.1 μm to 0.5 μm. As an example, the thickness of the tin plating layer 14 can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, or 0.5 μm, etc.

[0090] Furthermore, after tin plating is completed, deionized water can be used to rinse away any residual tin plating solution to prevent adverse reactions from the residual chemicals in the tin plating solution in subsequent processes.

[0091] By forming a tin-plated layer 14 at the intersection of the main gate electrode 131 and the fine gate electrode 132, and using inkjet printing to precisely control the formation position of the tin-plated layer 14, the structure of setting the tin-plated layer 14 on the surface of all target metal electrodes 13 is eliminated, reducing the amount of tin used and effectively reducing material costs.

[0092] In an optional embodiment, the conductive layer 111 includes a metal seed layer and / or a transparent conductive film, and the conductive layer 111 facilitates the subsequent electrodeposition of target metal ions.

[0093] When the conductive layer 111 is a transparent conductive film, the surface of the transparent conductive film can be electrolyzed to enhance its surface conductivity, which is more conducive to the deposition of target metal ions during the electrodeposition process.

[0094] Optionally, the method for preparing the transparent conductive film may include: depositing a transparent conductive film with a thickness of 50 nm to 150 nm on the surface of the solar cell substrate 11 where the target metal electrode 13 is to be disposed using physical vapor deposition. As an example, the thickness of the transparent oxide film may be 50 nm, 75 nm, 100 nm, 120 nm, or 150 nm.

[0095] Specific process parameters include: using a mixture of Ar and O2 as the sputtering gas, with an argon to oxygen flow rate ratio of 10:1-20:1, a sputtering power of 100W-300W, a sputtering pressure of 0.5Pa-1.5Pa, and a temperature of room temperature. As an example, in the fabrication process of transparent conductive films, the argon to oxygen flow rate ratio in the sputtering gas can be 10:1, 12:1, 15:1, 18:1, or 20:1, etc.; the sputtering power can be 100W, 130W, 150W, 200W, 250W, or 300W, etc.; and the sputtering pressure can be 0.5Pa, 0.7Pa, 0.9Pa, 1.0Pa, 1.3Pa, or 1.5Pa, etc.

[0096] When the conductive layer 111 is a metal seed layer, the metal of the metal seed layer can be copper, titanium, nickel, etc., and is not limited to these.

[0097] Preferably, the thickness of the metal seed layer is 50nm-200nm. As an example, the thickness of the metal seed layer can be 50nm, 75nm, 100nm, 125nm, 150nm, 175nm, or 200nm, etc.

[0098] Optionally, the above-mentioned method of setting the metal seed layer includes: setting the metal seed layer on the surface of the solar cell substrate 11 to which the target metal electrode 13 is to be formed by magnetron sputtering.

[0099] The conditions for magnetron sputtering include: argon flow rate of 20 sccm-40 sccm, sputtering power of 80 W-300 W, gas pressure of 0.3 Pa-0.8 Pa, and deposition time of 3 min-8 min. For example, the argon flow rate during magnetron sputtering can be 20 sccm, 25 sccm, 30 sccm, 35 sccm, or 40 sccm, etc.; the sputtering power can be 80 W, 100 W, 130 W, 150 W, 190 W, 250 W, or 300 W, etc.; the gas pressure can be 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.7 Pa, or 0.8 Pa, etc.; and the deposition time can be 3 min, 4 min, 5 min, 6 min, 7 min, or 8 min, etc.

[0100] Preferably, after the metal seed layer is formed, hydrofluoric acid can be used to treat the outer surface of the metal seed layer to remove surface oxides, improve the wettability of the metal seed layer surface, and facilitate the subsequent deposition of target metal ions.

[0101] When the conductive layer 111 is a transparent conductive film and a metal seed layer, the transparent conductive film can be disposed on the surface of the solar cell substrate 11, and the metal seed layer can be disposed on the outside of the transparent conductive film. Since the metal seed layer itself has good conductivity, there is no need to perform electrode treatment on the transparent conductive film.

[0102] The preparation methods and thickness ranges of transparent conductive films and metal seed layers are the same as those in the two cases mentioned above, and will not be repeated here.

[0103] In one alternative embodiment, the insulating protective layer 12 may include positive or negative photoresist.

[0104] When the insulating protective layer 12 includes positive photoresist, step S2 above may include: Step S21: A positive photoresist is laid on the entire surface of the solar cell substrate 11 having the conductive layer 111. Specifically, a film laminator can be used to uniformly coat the surface of the solar cell substrate 11 having the conductive layer 111 with photosensitive ink or photosensitive dry film for forming positive photoresist, with a thickness of 10μm-30μm; and then dry it at a temperature of 95℃-130℃ for 5min-10min to remove the solvent in the photosensitive ink or photosensitive dry film, so as to improve the uniformity and adhesion of the positive photoresist, thereby forming a uniform positive photoresist layer on the surface of the solar cell substrate 11 having the conductive layer 111.

[0105] As an example, the thickness of the photosensitive ink or photosensitive dry film can be 10μm, 15μm, 20μm, 25μm or 30μm, etc.; the drying temperature can be 95℃, 100℃, 105℃, 110℃, 115℃, 120℃ or 130℃, etc.; the drying time can be 5min, 6min, 7min, 8min, 9min or 10min, etc.

[0106] Step S22: Cover the positive photoresist with the first mask to expose the positive photoresist corresponding to the position of the target metal electrode 13 to be formed, expose it, and remove the first mask. The first mask is used to cover the portion of the positive photoresist where the target metal electrode 13 does not need to be set, and to expose the portion of the positive photoresist where the target metal electrode 13 needs to be set.

[0107] Specifically, an energy density of 100 mJ / cm³ can be used. 2 -300mJ / cm 2 The ultraviolet light exposure lasts 10-30 seconds, with a parallel light source wavelength of 365nm~436nm. After exposure, the thickness of the positive photoresist exposed on the first mask can be less than 20μm. As an example, the ultraviolet light energy density during exposure can be 100mJ / cm². 2 150mJ / cm 2 200mJ / cm 2 250mJ / cm 2 or 300mJ / cm 2Exposure time can be 10s, 15s, 20s, 25s or 30s, etc.; the wavelength of the parallel light source can be 365nm, 370nm, 380nm, 390nm, 400nm, 415nm or 436nm, etc.

[0108] Step S23: The positive photoresist after exposure is developed using the first developing solution to remove the positive photoresist in the exposed area, so that the conductive layer 111 is exposed at the position corresponding to the target metal electrode 13 to be formed. Specifically, the first developing solution can be a tetramethylammonium hydroxide aqueous solution with a volume percentage of 0.2%-0.6%, and the developing time can be 30s-120s. As an example, the volume percentage concentration of the tetramethylammonium hydroxide aqueous solution can be 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%, etc.; the developing time can be 30s, 50s, 75s, 100s, or 120s, etc.

[0109] After exposing the conductive layer 111 at the location where the target metal electrode 13 is to be formed, it can be rinsed with deionized water for 1 min to 3 min to remove residual first developing solution. As an example, rinsing with deionized water for 1 min, 1.5 min, 2 min, 2.5 min, or 3 min, etc., can be performed.

[0110] Step S24: Thermally cure the remaining positive photoresist to form an insulating protective layer 12 that is spaced over the surface of the solar cell substrate 11 having a conductive layer 111.

[0111] Specifically, the conditions for thermosetting positive photoresist may include: a curing temperature of 100℃-120℃ and a drying time of 10min-15min. As an example, the curing temperature may be 100℃, 105℃, 110℃, 115℃, or 120℃, etc.; and the drying time may be 10min, 11min, 12min, 13min, 14min, or 15min, etc.

[0112] By curing the positive photoresist, the stability of the remaining positive photoresist can be enhanced, its corrosion resistance can be improved, and the dimensional accuracy of the target metal electrode 13 prepared subsequently can be guaranteed.

[0113] When the insulating protective layer 12 includes negative photoresist, step S2 above may include: Step S21': A negative photoresist is laid on the entire surface of the solar cell substrate 11 having the conductive layer 111. Step S22': Use a second mask to cover the negative photoresist, expose the negative photoresist at the location where the target metal electrode 13 does not need to be formed, expose it, and remove the second mask. The second mask is used to cover the portion of the negative photoresist where the target metal electrode 13 is to be set, and to expose the portion of the negative photoresist where the target metal electrode 13 does not need to be set.

[0114] Step S23': The exposed negative photoresist is developed using a second developing solution to remove the negative photoresist corresponding to the position covered by the second mask (i.e., the unexposed area), so that the conductive layer 111 is exposed at the position corresponding to the target metal electrode 13 to be formed. Step S24': Thermally cure the remaining negative photoresist to form an insulating protective layer 12 on the surface of the solar cell substrate 11, which has a conductive layer 111, with the remaining negative photoresist intermittently covering it.

[0115] By setting an insulating protective layer 12, a groove is formed at the location where the target metal electrode 13 is to be set, which can limit the deposition area of ​​the target metal ions and improve the preparation accuracy of the target metal electrode 13.

[0116] In one alternative embodiment, such as Figure 10 As shown, after step S3, the above method further includes: removing the above-mentioned insulating protective layer 12.

[0117] Preferably, when the conductive layer 111 includes a metal seed layer, after step S3, the method further includes: removing the portion of the metal seed layer corresponding to the insulating protective layer 12, that is, retaining the metal seed layer between the target metal electrode 13 and the solar cell substrate 11.

[0118] It should be noted that when the conductive layer 111 includes a transparent conductive film, there is no need to remove the transparent conductive film.

[0119] According to an embodiment of the present invention, a method for preparing a solar cell electrode involves forming a target metal electrode 13 on the outer layer of a conductive layer 111 on the surface of a solar cell substrate 11 without an insulating protective layer 12 using an electrodeposition solvent. By adjusting the composition and ratio of the electrodeposition solution and the deposition current density, the target metal ions can be induced to deposit in a regular manner, forming a high-density twin array perpendicular to the deposition direction, thereby forming a target metal electrode 13 with a nano-twin structure containing coherent twin boundaries. Since there are a large number of coherent twin boundaries in the target metal electrode 13, and the atomic arrangement of the coherent twin boundaries is relatively regular, the defect density is lower, and there are fewer oxygen permeation channels, the surface oxidation rate of the target metal electrode 13 can be effectively reduced. Furthermore, it is not necessary to form a tin plating layer 14 on the surface of all target metal electrodes 13, thereby reducing the amount of tin used, lowering the battery manufacturing cost, and reducing environmental pollution caused by tin plating.

[0120] Understandably, before preparing the electrodes, there are different preparation methods for the solar cell substrate 11 depending on the type of solar cell substrate 11, which will not be elaborated here.

[0121] like Figure 10 As shown, this embodiment of the invention also provides a solar cell 1, which mainly includes: a solar cell substrate 11, at least one surface of the solar cell substrate 11 being provided with a conductive layer 111; and a target metal electrode 13 containing a nanotwin structure with coherent twin boundaries disposed outside the conductive layer 111.

[0122] In this embodiment of the invention, the target metal electrode 13 is formed by electrodeposition of target metal ions.

[0123] In an optional embodiment, the crystal orientation of the above-mentioned nanotwin structure is (111) orientation. The (111) crystal plane dominates in the nanotwin structure formed by the atoms of the target metal, which can reduce the diffusion rate of copper atoms, avoid the excessive growth of Cu-Sn brittle metal compounds in subsequent processes, and reduce the component reliability problems caused by Cu-Sn brittle metal compounds.

[0124] In an optional embodiment, the target metal electrode 13 includes a main gate electrode 131 extending along a first direction and a fine gate electrode 132 extending along a second direction and intersecting the main gate electrode 131.

[0125] The solar cell further includes a tin-plated layer 14 disposed on the outer surface of the intersection region of the main grid electrode 131 and the fine grid electrode 132.

[0126] The aforementioned tin plating layer 14 can reduce the welding temperature between the target metal electrode 13 and the solder ribbon, preventing excessively high welding temperatures from damaging the solar cell substrate 11. This ensures a strong connection between the target metal electrode 13 and the solder ribbon, reducing the probability of poor soldering, and also isolates oxygen, inhibiting the oxidation of the target metal electrode 13. Furthermore, it can prevent the oxidation of the main grid electrode 131 or the fine grid electrode 132 in this area.

[0127] In an optional embodiment, the conductive layer 111 comprises a transparent conductive film and / or a metal seed layer.

[0128] Specifically, when the conductive layer 111 is a transparent conductive film, the transparent conductive film covers the entire surface of the solar cell substrate 11; when the conductive layer 111 is a metal seed layer, the metal seed layer is disposed between the solar cell substrate 11 and the target metal electrode 13, and no metal seed layer is disposed on the portion of the solar cell substrate 11 where the target metal electrode 13 is not disposed; when the conductive layer 111 is a transparent conductive film and a metal seed layer, the transparent conductive film covers the entire surface of the solar cell substrate 11, the metal seed layer is disposed on the outer surface of the transparent conductive film and is disposed between the target metal electrode 13 and the transparent conductive film, and no metal seed layer is disposed on the portion of the solar cell substrate 11 where the target metal electrode 13 is not disposed.

[0129] According to an embodiment of the present invention, a solar cell is provided with a target metal electrode 13 containing a nanotwin structure of coherent twin boundaries. The target metal electrode 13 is formed by electrodeposition of target metal ions. Since there are a large number of coherent twin boundaries in the target metal electrode 13, and the atomic arrangement of the coherent twin boundaries is relatively regular, the defect density is lower, and there are fewer oxygen permeation channels, the surface oxidation rate of the target metal electrode 13 can be effectively reduced. Furthermore, it is not necessary to form a tin plating layer 14 on the surface of all the target metal electrodes 13, which reduces the amount of tin used, lowers the manufacturing cost of the solar cell, and can reduce environmental pollution caused by tin plating.

[0130] Example 1

[0131] Step A: Provide an HJT solar cell substrate, wherein an intrinsic amorphous silicon layer and an N-type doped amorphous silicon layer are stacked from the inside to the outside on one main surface of the HJT solar cell substrate, and an intrinsic amorphous silicon layer and a P-type doped amorphous silicon layer are stacked from the inside to the outside on the other main surface of the HJT solar cell substrate.

[0132] Step B: Transparent conductive films with a thickness of 80 nm and a sheet resistance of 50 Ω·cm are deposited on the outer sides of the N-type doped amorphous silicon layer and the P-type doped amorphous silicon layer respectively using physical vapor deposition (PVD). The PVD process conditions include: using a mixture of argon and oxygen as the sputtering gas, with an argon-to-oxygen flow rate ratio of 10:1, and a sputtering power of 250 W. Subsequently, a 150 nm thick metal seed layer is formed on the outer side of the transparent conductive film using magnetron sputtering. The process conditions include: using a Cu target, an argon flow rate of 40 sccm, a sputtering power of 180 W, a gas pressure of 0.5 Pa, and a deposition time of 5 min.

[0133] Step C: Using a laminator, uniformly coat the outer side of the metal seed layer with a photosensitive dry film, with a thickness of 15 μm. Dry at 80°C for 1 min to remove the solvent from the photosensitive dry film, forming a uniform positive photoresist layer. Cover the uniform positive photoresist surface with a first mask, using an energy density of 216 mmJ / cm². 2 Expose the sample to ultraviolet light at a wavelength of 415 nm for 30 seconds, then remove the first photomask. Use a 0.5% (v / v) tetramethylammonium hydroxide aqueous solution as the first developing solution and develop for 60 seconds to remove the positive photoresist in the exposed area, exposing the conductive layer at the location corresponding to the target metal electrode to be formed. Remove the first photomask again. Rinse with deionized water for 3 minutes to remove any residual first developing solution.

[0134] Step D: The patterned solar cell substrate is placed in an electrodeposition solution to electrodeposit copper atoms, forming a target metal electrode with a nanotwin structure containing coherent twin boundaries. The electrodeposition solution includes: copper sulfate pentahydrate with a molar concentration of 0.5 mol / L, sulfuric acid with a molar concentration of 0.2 mol / L, dilute hydrochloric acid with a mass content of 80 ppm, an promoter with a mass content of 350 ppm, and an inhibitor with a mass content of 50 ppm. The promoters include: Janus Green B at a mass content of 100 ppm, sodium 3-(benzothiazole-2-mercapto)-propanesulfonate at a mass content of 15 ppm, sodium polydisulfide diethanesulfonate at a mass content of 150 ppm, polyethylene glycol at a mass content of 65 ppm, and sodium propyne sulfonate at a mass content of 2 ppm; the inhibitors include: sodium 3-mercapto-1-propanesulfonate at a mass content of 13 ppm, benzotriazole at a mass content of 24 ppm, polypropylene glycol at a mass content of 11 ppm, and methylbenzothiazole at a mass content of 6 ppm. The deposition current density is 65 A / dm³. 2 The deposition time was 5 minutes, and the electrodeposition solution temperature was 20°C. Cu was induced by high current density. + -S bonds are selectively adsorbed at the (111) active site and inhibited from adsorbing at the (200) or (220) active sites to form the target metal electrode.

[0135] Step E: Deposit palladium catalyst in the intersection region of the main gate electrode and the aforementioned fine gate electrode using inkjet printing. The palladium loading of the palladium catalyst is 0.5 μg / mm². 2 The spacing between the cross regions is 210 μm. Then, the palladium catalyst is annealed at 100 °C to dry and solidify, forming palladium catalytic active sites. Tin plating is then performed based on these palladium catalytic active sites to form a 0.3 μm thick tin plating layer in the cross region between the main gate electrode and the fine gate electrode.

[0136] Step F: Remove the remaining positive photoresist and the portion of the metal seed layer corresponding to the positive photoresist to obtain the solar cell M1.

[0137] Example 2

[0138] Compared to Example 1, the difference lies in the use of a forward pulse + reverse waveform to control crystal growth kinetics during the electrodeposition process. The waveform design is as follows: the forward pulse is t... on =21ms, J p =74A / dm 2 The reverse is t off =6ms, J p =-25A / dm 2 The duty cycle is 1:4. The electrodeposition solution also contains bismuth ions at a mass concentration of 5.3 ppm, while the chloride ion mass concentration is reduced to 30 ppm.

[0139] In this design, the positive pulse is used to induce nucleation, while the negative waveform is used to eliminate hydrogen bubbles. The positive t... on Indicates the forward deposition time, forward J p This represents the peak deposition current density of the positive pulse; the reverse t... off Indicates the reverse pulse interval time, the reverse J p This represents the peak deposition current density during the reverse process.

[0140] Solar cell M2 was fabricated. The surface roughness Ra of its target metal electrode is 0.18 μm, the electrode tensile strength is 420 MPa, and the resistivity shift after damp heat aging is +1.2% (1000 h).

[0141] Example 3

[0142] Compared to Example 1, the difference lies in the use of gradient temperature control during the electrodeposition process, including: First stage: Deposition current density 82 A / dm³ 2 First stage: maintain at 20℃ for 1 min; Second stage: increase the temperature to 30℃ at a rate of 5℃ / min, then set the deposition current density to 65 A / dm³. 2 The solution was maintained for 5 minutes; the third stage involved natural cooling to room temperature. The electrodeposition solution also contained bismuth ions at a mass concentration of 5.3 ppm, while the chloride ion mass concentration was reduced to 30 ppm.

[0143] A solar cell M3 was prepared, in which the copper grain size in the target metal electrode is greater than 4 μm, the hardness of the target metal electrode is 2.1 GPa, and the electrode adhesion is 6.43 N / mm.

[0144] Example 4

[0145] The difference from Example 1 is that no promoters and inhibitors were added to the electrodeposition solution.

[0146] The prepared material had a series resistance of 1.85 mΩ·cm. 2 The solar cell M4 exhibits multiple peaks (111), (200), and (220) coexisting in the X-ray diffraction pattern of its target metal electrode, indicating the simultaneous presence of copper grains preferentially growing toward these three crystal planes, forming a multi-orientation coexisting crystal structure. The tin plating layer has a void ratio >12%, and the grating breakage rate in the EL image obtained by electroluminescence (EL) testing is 11%.

[0147] Example 5

[0148] The difference compared to Example 1 is that the deposition current density is 2 A / dm³. 2 .

[0149] A solar cell M5 was prepared, with a surface roughness Ra of the target metal electrode exceeding 1.3 μm.

[0150] Example 6

[0151] The difference compared to Example 1 is that the deposition current density is 5 A / dm³. 2 .

[0152] A solar cell M6 was prepared, with a surface roughness Ra of the target metal electrode greater than 1.3 μm.

[0153] Example 7

[0154] The difference compared to Example 1 is that the deposition current density is 10 A / dm³. 2 .

[0155] A solar cell M7 was prepared, with a surface roughness Ra of the target metal electrode greater than 1.3 μm.

[0156] The solar cells M1 to M7 prepared in Examples 1 to 7 above, as well as the target metal electrodes therein, were tested under the same conditions.

[0157] X-ray diffraction analysis

[0158] The XRD patterns of the target metal electrodes of solar cells M1 to M7 were obtained by X-ray diffraction (XRD) instrument, and the proportion of copper grains with (111) orientation was calculated.

[0159] Twin density calculation

[0160] Scanning electron microscopy (SEM) was used to obtain the target metal electrodes of solar cells M1 to M7, respectively. The number of twins in the test area was identified, and the twin density was calculated by the number of twins in the test area and the area of ​​the test area.

[0161] resistivity test

[0162] The resistivity of the target metal electrode of each solar cell was determined by using the four-probe method for measuring the resistivity of silicon wafers, according to the national standard GB / T 1552-2021 "Silicon Wafer Resistivity Measurement".

[0163] IV test

[0164] IV tests were performed on solar cells M1 to M7 respectively to obtain their IV curves under standard illumination. The initial series resistance (Rs) of each solar cell was determined based on the IV curves.

[0165] Damp heat test

[0166] The solar cells M1 to M7 were tested using the test method of the national standard GB / T 19394-2021. The increase in series resistance, the content of copper oxide (Cu2O) on the surface of the target metal electrode, and the total efficiency degradation of the solar cells after 1000h of damp heat test were recorded.

[0167] The data obtained after the above tests are shown in Table 1 below.

[0168] Table 1

[0169] As can be seen, compared with the solar cells M5-M7 prepared in Examples 5-7, the solar cell M1 prepared in Example 1 has a higher growth rate. In the preparation of the target metal electrode, a promoter and an inhibitor that can act as crystal guiding agents are added to the electrodeposition solution. A higher deposition current density is used, which can induce copper atoms to preferentially grow on the (111) crystal plane where the atomic arrangement is more compact, and inhibit the growth of copper atoms on the (200) crystal plane and the (220) crystal plane. The copper atoms in the target metal electrode exhibit a nanotwin structure with more coherent twin boundaries. The (111) orientation ratio and twin density are increased, which reduces the resistivity of the target metal electrode. As a result, the resistivity of the target metal electrode of solar cell M1 is close to that of single crystal copper (1.68 μΩ·cm), which effectively improves the oxidation resistance of the target metal electrode.

[0170] Compared to the solar cell M1 prepared in Example 1, the solar cell M2 prepared in Example 2 employed a forward pulse + reverse waveform to regulate crystal growth kinetics during electrodeposition, inducing more copper grains to grow on the (111) crystal plane, thus increasing the (111) orientation ratio. Furthermore, bismuth ions, which suppress dendrite formation, were added to the electrodeposition solution, and the competitive adsorption of promoters and inhibitors in the electrodeposition solution was reduced by decreasing chloride ions, resulting in a more regular crystal structure, higher twin density, reduced oxygen permeation channels, and lower resistivity of the target metal electrode. In damp heat testing, this demonstrated superior oxidation resistance. However, the electrodeposition solution used to regulate crystal plane orientation resulted in a side effect of increased series resistance in solar cell M2; therefore, the series resistance of solar cell M2 was slightly higher than that of solar cell M1 in Example 1.

[0171] Compared to the solar cell M1 prepared in Example 1, the solar cell M3 prepared in Example 3 adopted gradient temperature control during the electrodeposition process. In the first stage, a higher deposition current density was used to induce the rapid formation of nanotwin nuclei at low temperature. In the second stage, the rapid growth and lateral expansion of twins at high temperature were achieved. However, the lateral expansion of twins at high temperature may cause some copper grains to grow on the (200) or (220) crystal plane, which to some extent reduced the (111) orientation ratio and twin density. The oxygen permeation channels increased slightly, resulting in a higher initial Rs of solar cell M3 and slightly worse performance after damp heat testing.

[0172] Compared to the solar cells M1 to M3 prepared in Examples 1 to 3, the solar cell M4 prepared in Example 4 has a higher resistivity of the target metal electrode due to the absence of promoters and inhibitors in the electrodeposition solution and the higher deposition current density. Due to the anisotropy of the crystals, the copper grains grow rapidly on different crystal planes during the deposition process, resulting in random crystal orientation, disordered grain boundaries, (111) reduced orientation ratio and twin density, and island-like growth of the subsequent tin plating layer. This results in more surface defects at the interface between the tin plating layer and the target metal electrode, leading to poor damp heat test results.

[0173] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a solar cell electrode, characterized in that, include: Step S1: Provide a solar cell substrate, wherein at least one surface of the solar cell substrate is provided with a conductive layer; Step S2: Cover the surface of the solar cell substrate with an insulating protective layer at intervals; Step S3: Deposit target metal ions on the outside of the conductive layer that is not covered by the insulating protective layer using an electrodeposition solution, and form a target metal electrode with a nanotwin structure containing coherent twin boundaries by controlling the deposition current density.

2. The method for preparing a solar cell electrode according to claim 1, characterized in that, The target metal electrode formed in step S3 includes a main gate electrode extending along a first direction and a fine gate electrode extending along a second direction and intersecting with the main gate electrode. The method further includes: step S4, setting a tin plating layer in the intersection area of ​​the main gate electrode and the fine gate electrode.

3. The method for preparing a solar cell electrode according to claim 1, characterized in that, The conductive layer includes a metal seed layer and / or a transparent conductive film; Preferably, when the conductive layer includes a metal seed layer, the thickness of the metal seed layer is 50nm-200nm.

4. The method for preparing a solar cell electrode according to claim 1, characterized in that, The target metal electrode is a copper electrode; Preferably, the electrodeposition solution comprises: copper sulfate pentahydrate with a molar concentration of 0.5 mol / L to 2.5 mol / L, sulfuric acid with a molar concentration of 0.1 mol / L to 1.5 mol / L, chloride ions with a mass content of 15 ppm to 100 ppm, an accelerator with a mass content of 20 ppm to 550 ppm, and an inhibitor with a mass content of 50 ppm to 150 ppm; wherein the accelerator is used to promote the deposition of the target metal ions on the target crystal face during the deposition of the target metal ions on the outside of the conductive layer by the electrodeposition solution, and the inhibitor is used to inhibit the deposition of the target metal ions on non-target crystal faces; Optionally, the accelerator includes at least one of: Janus Green, sodium 3-(benzothiazol-2-mercapto)-propanesulfonate, sodium polydithiodiethanesulfonate, polyethylene glycol, or sodium propyne sulfonate; Optionally, the promoter includes Janus Green at a mass content of 80ppm-120ppm; Optionally, the accelerator includes sodium 3-(benzothiazol-2-mercapto)-propanesulfonate in a mass content of 10 ppm to 20 ppm; Optionally, the accelerator includes sodium polydisulfide diethane sulfonate in a mass content of 130ppm-170ppm; Optionally, the accelerator includes polyethylene glycol in a mass content of 55ppm-75ppm; Optionally, the accelerator includes sodium propyne sulfonate in a mass content of 1 ppm to 3 ppm; Optionally, the inhibitor includes: sodium 3-mercapto-1-propanesulfonate, benzotriazole, polypropylene glycol, and methylbenzothiazole; Optionally, the inhibitor comprises sodium 3-mercapto-1-propanesulfonate in a mass content of 10 ppm to 15 ppm; Optionally, the inhibitor comprises benzotriazole at a mass content of 20 ppm to 30 ppm; Optionally, the inhibitor comprises polypropylene glycol in a mass content of 8 ppm to 14 ppm; Optionally, the inhibitor comprises methylbenzothiazole in a mass content of 4 ppm to 8 ppm.

5. The method for preparing a solar cell electrode according to claim 1, characterized in that, The deposition current density is 60 A / dm. 2 -90A / dm 2 ; Optionally, step S3 includes: during the deposition of target metal ions, employing a forward pulse and a reverse waveform, wherein the peak deposition current density of the forward pulse is 70 A / dm². 2 -80A / dm; Optionally, the forward deposition time of the forward pulse is 18ms-40ms; the reverse pulse duration of the reverse waveform is 5ms-15ms, and the peak deposition current density during the reverse process is -25A / dm. Optionally, step S3 further includes: performing gradient temperature control during the deposition of target metal ions; wherein the gradient temperature control includes at least two stages, the deposition current density in the first stage is greater than the deposition current density in the second stage, and the temperature in the first stage is lower than the temperature in the second stage. Optionally, the process parameters for gradient temperature control include: Phase 1: Deposition current density of 70 A / dm 2 -90A / dm 2 The temperature is 15℃-25℃, and the holding time is 0.5min-3min; Second stage: Deposition current density is 60 A / dm 2 -70A / dm 2 The temperature is 25℃-40℃, and the holding time is 3min-8min.

6. The method for preparing a solar cell electrode according to claim 1, characterized in that, Step S2 includes: Step S21: Lay a full-surface positive photoresist on the surface of the solar cell substrate having the conductive layer; Step S22: Cover the positive photoresist with a first mask to expose the positive photoresist corresponding to the position where the target metal electrode is to be formed, expose it, and remove the first mask; Step S23: The exposed positive photoresist is developed using a first developing solution to remove the positive photoresist in the exposed area, thereby exposing the conductive layer at the position corresponding to the target metal electrode to be formed. Step S24: Thermally cure the remaining positive photoresist to form an insulating protective layer spaced over the conductive layer on the surface of the solar cell substrate.

7. The method for preparing a solar cell electrode according to claim 2, characterized in that, Step S4 includes: A metal catalyst is deposited in the intersection region of the main gate electrode and the fine gate electrode using inkjet printing. The solar cell substrate containing the metal catalyst is annealed to dry and solidify the metal catalyst, thereby forming catalytic active sites. Tin plating is performed based on the catalytic active sites to form a tin plating layer in the intersection region of the main gate electrode and the fine gate electrode; Optionally, the metal catalyst is a palladium catalyst; preferably, the palladium catalyst comprises palladium nanoparticles with a particle size of 5 nm-20 nm, and the palladium loading in the palladium catalyst is 0.1-1 μg / mm. 2 ; Preferably, the annealing temperature is 80℃-120℃; Preferably, the thickness of the tin plating layer is 0.1 μm-0.5 μm; Optionally, after step S3, the method further includes: Remove the insulating protective layer; Preferably, when the conductive layer includes a metal seed layer, after step S3, the method further includes: removing the portion of the metal seed layer corresponding to the insulating protective layer; Optionally, the metal seed layer can be configured in the following ways: A metal seed layer is deposited on the surface of a solar cell substrate to which the target metal electrode is to be formed using magnetron sputtering; Preferably, the conditions for magnetron sputtering include: argon flow rate of 20 sccm-40 sccm, sputtering power of 80 W-300 W, gas pressure of 0.3 Pa-0.8 Pa, and deposition time of 3 min-8 min.

8. A solar cell, characterized in that, include: A solar cell substrate, wherein at least one surface of the solar cell substrate is provided with a conductive layer; A target metal electrode containing a nanotwin structure with coherent twin boundaries is disposed on the outside of the conductive layer.

9. The solar cell according to claim 8, characterized in that, The crystal orientation of the nanotwin structure is (111) orientation; Optionally, the target metal electrode is a copper electrode.

10. The solar cell according to claim 8, characterized in that, The target metal electrode includes a main gate electrode extending along a first direction and a fine gate electrode extending along a second direction and intersecting the main gate electrode. The solar cell further includes a tin-plated layer disposed on the outer surface of the intersection region of the main grid electrode and the fine grid electrode.

Images