A copper plating solution, its preparation method and application

Abstract

This invention relates to a copper plating solution, its preparation method, and its application. The copper plating solution comprises the following components: copper pyrophosphate, a complexing agent, ammonia, a bath conditioner, a brightener, a pH adjuster, and water; the complexing agent is selected from potassium pyrophosphate or sodium pyrophosphate; the ammonia has a mass percentage concentration of 20%-30% and a volume concentration of 2-10 mL / L in the copper plating solution; the brightener has a mass concentration of 10-50 mg / L in the copper plating solution; and the pH value of the copper plating solution is 7.8-10. When used for copper plating of silver grid lines, it can ensure good electroplating results for the silver grid lines while reducing costs, and the silver grid lines are firmly attached and do not fall off, maintaining good conductivity.

Description

Technical Field

[0001] This invention belongs to the field of solar cells, specifically relating to a copper plating solution, its preparation method, and its application. Background Technology

[0002] The electrode grid lines in a solar cell play a role in collecting and conducting current. These grid lines can be made of silver or copper, among others. Silver grid lines offer superior conductivity but are more expensive, increasing the overall cost of the solar cell. While copper grid lines are cheaper, their conductivity is not as good as that of silver grid lines.

[0003] Electroplating copper onto silver grid lines can effectively reduce costs while maintaining good conductivity. However, traditional acidic copper plating solutions are prone to causing silver grid lines to detach under high current densities, affecting battery efficiency and reliability. Furthermore, achieving good electroplating results on silver grid lines is more difficult than on ordinary electroplated parts. Other existing copper plating solutions struggle to achieve satisfactory plating results on silver grid lines, such as a good plating appearance, including the good metallic luster of pure copper, uniform color without impurities, and no defects such as pinholes, pitting, detachment, or blackening. The challenge lies in ensuring good electroplating results on silver grid lines while reducing costs, maintaining a firm and non-detached plating, and preserving good conductivity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an improved copper plating solution to address the shortcomings and deficiencies of the prior art. When the copper plating solution is used for copper plating of silver grid lines, it can ensure good electroplating effect of copper plating of silver grid lines 8788 while reducing costs, and the silver grid lines are firm and do not fall off, maintaining good conductivity.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A copper plating solution comprising the following components: copper pyrophosphate, a complexing agent, ammonia, a bath conditioner, a brightener, a pH adjuster, and water; wherein the complexing agent is selected from potassium pyrophosphate or sodium pyrophosphate; the ammonia has a mass percentage concentration of 20%-30% and a volume concentration of 2-10 mL / L in the copper plating solution; the brightener has a mass concentration of 10-50 mg / L in the copper plating solution; and the pH value of the copper plating solution is 7.8-10.

[0007] In existing technologies, while silver electrode grid lines in solar cells exhibit good conductivity, they are expensive. Copper electrodes, on the other hand, are cheaper, but achieving good copper plating on silver electrode grid lines is often difficult, resulting in a poor plating appearance. Furthermore, traditional acidic copper plating solutions at high current densities can easily cause the silver grid lines to detach, affecting the cell's efficiency and reliability. The inventors of this application have discovered that by using copper pyrophosphate as the main copper salt, potassium pyrophosphate or sodium pyrophosphate as a complexing agent, and adding specific amounts of ammonia and a brightener, while controlling the pH of the plating solution within a suitable range, effective copper plating on silver grid lines can be achieved. This allows for cost reduction while ensuring good copper plating results on the silver grid lines, resulting in firmly attached silver grid lines that maintain good conductivity.

[0008] In this invention, copper pyrophosphate (Cu₂P₂O₇) is the main salt supplying copper ions to the plating solution. Potassium / sodium pyrophosphate is the main complexing agent in the copper plating solution; it reacts with copper ions to form potassium / sodium copper pyrophosphate, thus introducing pyrophosphate ions into the solution and achieving copper plating. The pH value of this invention is 7.8-10, which effectively prevents the hydrolysis of pyrophosphate, thereby improving the appearance of the electroplating.

[0009] The complexing agent potassium / sodium pyrophosphate in this invention can stabilize copper pyrophosphate complexes and prevent precipitation; it also improves coating quality, enhances the dispersion ability of the plating solution, and improves the anode dissolution. Potassium pyrophosphate is preferred, as potassium salts have higher solubility than sodium salts, higher potassium ion mobility, and higher conductivity in potassium salt solutions.

[0010] The ammonia solution in this invention can improve the appearance quality of the copper plating, enhance its gloss and adhesion, and promote anode dissolution. When the ammonia content is too low, the anode is prone to passivation and "copper powder" is produced. Furthermore, on the workpiece being plated (e.g., silver grid lines) at high current densities or edges, the plating may produce a white haze, roughness, or a dark color.

[0011] The bath builder in this invention can help the anode dissolve normally, prevent passivation, improve the dispersion ability of the plating solution, increase the current density, contribute to the buffering effect of pH value, and improve the brightness of the coating.

[0012] The gloss agent added in this invention adsorbs onto the cathode surface during electroplating, altering the deposition pattern of metal ions. This adsorption inhibits excessive grain growth, resulting in finer and more uniform grains in the plating layer. Furthermore, the gloss agent changes the electrochemical reaction process at the cathode, reducing cathode polarization and promoting the reduction and deposition of metal ions. This contributes to improving the brightness and uniformity of the plating layer. Moreover, by controlling the specific mass concentration of the gloss agent, this invention achieves optimal electroplating appearance while ensuring that the silver grid lines do not detach.

[0013] In some embodiments, the copper pyrophosphate in the copper plating solution has a mass concentration of 50–100 g / L.

[0014] In some embodiments, the complexing agent has a mass concentration of 200–300 g / L in the copper plating solution.

[0015] In some embodiments, the concentration of the bath-forming agent in the copper plating solution is 20–100 g / L.

[0016] In some embodiments, the mass percentage concentration of the ammonia solution is 25%-28%.

[0017] In some embodiments, the bath preparation agent is selected from one or more combinations of triammonium citrate, ammonium oxalate, potassium sodium tartrate, and ammonium nitrate.

[0018] In some embodiments, the gloss agent is selected from one or more combinations of 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, selenium disulfide, and isothiazolinone.

[0019] In some embodiments, the pH adjuster is selected from one or more combinations of sulfuric acid, hydrochloric acid, phosphoric acid, and citric acid.

[0020] In some embodiments, the pH adjuster is in the form of an aqueous solution, wherein the mass percentage concentration of the solute in the pH adjuster is 30%-98%.

[0021] In some embodiments, the copper plating solution is used for copper plating of silver grid lines in solar cells.

[0022] The present invention further provides a method for preparing the above-mentioned copper plating solution, the method comprising the steps of mixing the copper pyrophosphate, complexing agent, bath building agent, brightening agent, ammonia and water, and adjusting the pH to 7.8-10 using the pH adjusting agent.

[0023] The present invention further provides a method for electroplating copper onto silver grid lines of a solar cell. The method uses the silver grid lines of the solar cell as the cathode and performs electroplating in the presence of an anode and an electroplating solution, wherein the electroplating solution is the aforementioned electroplating solution of the present invention.

[0024] In some embodiments, the temperature of the electroplating solution is 40–60°C. Using this temperature results in a more uniform plating layer and a smoother surface.

[0025] In some embodiments, during the electroplating process, the electroplating solution is stirred or the cathode is moved. Stirring the electroplating solution or moving the cathode can result in a more uniform plating layer and a smoother surface.

[0026] In some embodiments, the average current density of the electroplating is 0.5–5 A / dm². 2 .

[0027] In some embodiments, the anode is selected from one or more combinations of soluble electrolytic copper plates, soluble electrolytic copper balls, and insoluble precious metal-coated titanium anode mesh.

[0028] In some embodiments, the area ratio of the cathode to the anode is 1:1 to 1:3.

[0029] The present invention further provides a solar cell grid line prepared by the above-mentioned electroplating copper plating method for the silver grid line of a solar cell, wherein the solar cell grid line includes a silver grid line and electroplated copper on the silver grid line.

[0030] The present invention further provides a solar cell including the aforementioned solar cell grid lines.

[0031] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0032] This invention utilizes copper pyrophosphate as the main copper salt, potassium pyrophosphate or sodium pyrophosphate as a complexing agent, and adds specific amounts of ammonia and brightener, while controlling the pH value of the electroplating solution within a suitable range. This allows for effective copper plating on silver grid lines, achieving good electroplating results while reducing costs. The silver grid lines are also firmly attached and do not fall off, maintaining good conductivity.

[0033] The electroplating solution of this invention has a simple composition, low cost, and good chemical stability. When used for copper plating of silver grid lines, no pre-plating or pretreatment of the silver grid lines is required to obtain a copper plating layer with fine crystals and good adhesion. The electroplating solution of this invention can be used for copper plating of silver grid lines in solar cells, avoiding the situation where the adhesion of silver grid lines decreases and leads to grid line detachment in traditional acidic plating solutions, and achieving a good electroplating appearance. Detailed Implementation

[0034] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0035] In this invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0036] Example 1

[0037] This embodiment provides a copper plating solution (formulation table shown in Table 1 below), and uses it for copper plating of silver grid lines in solar cells, as detailed below:

[0038] Clean the electroplating tank and interface equipment, including filters and pre-plating tanks, with hot water. Immerse the plating tank with 20 g / L dilute sulfuric acid and 2-3 g / L activated carbon, maintaining a temperature of 60°C and stirring for at least 8 hours. Drain the acid solution and rinse the tank and interface equipment with water. Immerse the plating tank and interface equipment with a 1% NaOH (10 g / L) solution, maintaining a temperature of 50-60°C, for at least 12 hours. Drain the alkaline solution and rinse thoroughly with water. Prepare the plating tank.

[0039] Prepare the plating bath using deionized water. Add deionized water (40-50℃) to approximately half the tank volume. While stirring, add the prescribed amount of potassium pyrophosphate and dissolve it completely. Add the prescribed amount of copper pyrophosphate in batches while stirring; this batching prevents the temperature from rising too quickly. After the copper pyrophosphate is completely dissolved, add cooling water to the operating level. Adjust the pH of the system to 8.6 using 50% sulfuric acid (pH adjuster). Cool the plating bath to 50-55℃ and add the prescribed amount of ammonia (25% concentration). Dilute the ammonia with water before adding it to the plating bath. Circulate and filter until the plating bath is clear. Add the prescribed amount of bath conditioner (triammonium citrate). Add the prescribed amount of gloss enhancer (2-mercaptobenzimidazole). The final electroplating solution is obtained.

[0040] The above-mentioned electroplating solution is used for silver grid line electroplating: During electroplating, the silver grid line cell is used as the cathode (wherein, the silver grid line is obtained by printing silver paste), and soluble electrolytic copper balls / plates are used as the anode. The electroplating solution is agitated by air bubbling, and the temperature of the electroplating solution is controlled at 45°C.

[0041] Examples 2-7

[0042] This embodiment provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Embodiment 1, except that the formulation composition and pH value of the plating solution are changed. See Table 1 below for details.

[0043] Example 8

[0044] This embodiment provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Embodiment 1, except that the stirring of the plating solution during electroplating is replaced by moving the cathode.

[0045] Comparative Examples 1-6

[0046] This comparative example provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Example 1, except that the formulation and pH value of the plating solution are changed (among which, changing the pH value may involve changing the amount of dilute sulfuric acid). See Table 1 below for details. In Comparative Examples 1-2, the amount of ammonia is changed; in Comparative Examples 3-4, the pH value is changed; and in Comparative Examples 5-6, the amount of brightener is changed.

[0047] Table 1. Electroplating solution formulations for each example and comparative example.

[0048]

[0049] Comparative Example 7

[0050] This comparative example provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Example 1, except that the electroplating process does not involve air bubbling to agitate the plating solution.

[0051] Comparative Example 8

[0052] This comparative example provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Example 1, except that the temperature of the plating solution is adjusted to 35°C during the electroplating process.

[0053] Comparative Example 9

[0054] This comparative example provides a copper plating solution and uses it for copper plating on silver grid lines of solar cells. The specific steps are basically the same as in Example 1, except that the plating solution in Example 1 is replaced with a commercial acidic sulfate copper plating solution.

[0055] The performance of the electrodes in the above embodiments and comparative examples was tested:

[0056] Appearance inspection standards: Visually inspected copper-plated surfaces show a pure copper metallic luster, are free from pollution, have a uniform color without impurities, and the plating layer is free from defects such as pinholes, pits, peeling, and blackening.

[0057] Adhesion test standards: The cross-cut test and the scratch test are used. After scratching the copper-plated surface with a knife, there should be no peeling or delamination of the copper plating surface; when tape is applied to the scratched area, there should be no peeling or delamination.

[0058] The results of the appearance inspection are shown in Table 2.

[0059] Table 2 Appearance Inspection Results

[0060]

[0061]

[0062] As can be seen from the comparison of Examples 1-3 and Comparative Examples 1-2, in the copper pyrophosphate plating process, the content of ammonia water will affect the performance of the plating solution and the quality of the plating layer. This is because ammonia water helps stabilize and transport copper ions. When ammonia water is insufficient, the stability of copper ions decreases, the deposition rate of the plating layer will slow down, and the production efficiency will be affected. When ammonia water is insufficient, defects such as pores and roughness may appear in the copper plating layer, and the surface smoothness and uniformity will decrease, affecting the appearance and performance of the finished product. When the ammonia water content is too high, it will change the chemical balance of the plating solution, resulting in unstable copper ion transport rate, making it difficult to control the deposition rate, and potentially causing uneven or rough plating layer.

[0063] As can be seen from the comparison of Examples 2, 4-5 and Comparative Examples 3-4, the pH value of the plating solution will affect the performance of the plating solution and the quality of the coating. If the pH is too high, the copper ions in the plating solution will combine with hydroxide ions to form copper hydroxide precipitate, resulting in a decrease in the effective copper ion concentration, thereby affecting the deposition efficiency and uniformity of the coating. If the pH value is too low, the solubility of copper ions in the plating solution will decrease, resulting in a decrease in the copper ion concentration, affecting the deposition efficiency, and the coating may become thinner or the deposition rate will slow down.

[0064] The comparison of Examples 1 and 5-6 shows that the role of gloss agents is to improve the gloss, smoothness, and uniformity of the coating. If the amount of gloss agent in the plating solution is too high or too low, it will adversely affect the quality of the coating. Insufficient gloss agent may result in a dull, rough, or cloudy surface, losing its original luster. However, excessive addition may lead to an overly smooth coating surface, resulting in excessive gloss, which may appear unnatural and form a rough or "foamy" surface.

[0065] The comparison between Examples 1 and Comparative Examples 7-8 shows that the temperature and agitation of the plating solution during electroplating affect the coating quality. When the plating solution temperature is too low, the current efficiency decreases significantly, leading to a slower deposition rate. This is because the dispersion ability of the plating solution and the cathode current efficiency decrease at low temperatures, resulting in coarser coating crystals and a darker color. When the electroplating solution is not agitated, anodic dissolution accelerates, and Cu... 2+ Excess, with P2O7 4- Insufficient mixing can easily lead to the formation of white copper pyrophosphate precipitate, resulting in a rough coating.

[0066] Adhesion test before electroplating: Battery cells with different types of silver paste (from different suppliers) were immersed in copper plating solution for 5 minutes, then removed, cleaned, and dried. A tensile test was then conducted using 3M tape. The results are shown in Table 3 below. It can be seen that the silver grid lines of the battery cells corresponding to the scheme in this application do not detach (i.e., various commercially available silver pastes can be used), while acidic copper plating solution will cause the silver grid lines to detach.

[0067] Table 3 Adhesion test results before electroplating

[0068]

[0069]

[0070] Post-electroplating adhesion test: Battery cells with different types of silver paste (from different suppliers) were immersed in a copper plating solution to deposit a 5μm thick copper layer. After removal, cleaning and drying, a tensile test was conducted using 3M tape. The results are shown in Table 4 below. It can be seen that the silver grid lines of the battery cells corresponding to the scheme in this application do not detach (i.e., various commercially available silver pastes can be used), while the acidic sulfate copper plating solution causes the silver grid lines to detach.

[0071] Table 4 Adhesion test after electroplating

[0072]

[0073] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0074] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A copper plating solution for silver grid lines in solar cells, characterized in that: The copper plating solution comprises the following components: copper pyrophosphate, complexing agent, ammonia, bath builder, gloss agent, pH adjuster, and water; the complexing agent is selected from potassium pyrophosphate or sodium pyrophosphate; the ammonia has a mass percentage concentration of 20%-30% and a volume concentration of 2-10 mL / L in the copper plating solution; the gloss agent has a mass concentration of 10-50 mg / L in the copper plating solution; the pH value of the copper plating solution is 7.8-10; the bath builder is selected from triammonium citrate; and the gloss agent is selected from 2-mercaptobenzimidazole. The copper pyrophosphate has a mass concentration of 50-100 g / L in the copper plating solution; the complexing agent has a mass concentration of 200-300 g / L in the copper plating solution.

2. The copper plating solution according to claim 1, characterized in that: The concentration of the bath-building agent in the copper plating solution is 20~100g / L.

3. The copper plating solution according to claim 1, characterized in that: The mass percentage concentration of the ammonia water is 25%-28%.

4. The copper plating solution according to claim 1, characterized in that: The pH adjuster is selected from one or more combinations of sulfuric acid, hydrochloric acid, phosphoric acid, and citric acid.

5. The copper plating solution according to claim 1, characterized in that: The pH adjuster is in the form of an aqueous solution, and the mass percentage concentration of the solute in the pH adjuster is 30%-98%.

6. A method for preparing a copper plating solution according to any one of claims 1-5, characterized in that: The preparation method includes the steps of mixing the copper pyrophosphate, complexing agent, bath building agent, gloss agent, ammonia and water, and adjusting the pH to 7.8-10 using the pH adjusting agent.

7. A method for electroplating copper onto silver grid lines of a solar cell, characterized in that: The method uses the silver grid line of a solar cell as the cathode and performs electroplating in the presence of an anode and an electroplating solution. The electroplating solution is the copper plating solution according to any one of claims 1-5. The temperature of the electroplating solution is 40~60℃. During the electroplating process, the electroplating solution is stirred or the cathode is moved.

8. The method for electroplating copper onto silver grid lines of a solar cell according to claim 7, characterized in that: The average current density of the electroplating is 0.5-5 A / dm 2 .

9. The method for electroplating copper onto silver grid lines of a solar cell according to claim 7, characterized in that: The anode is selected from one or more combinations of soluble electrolytic copper plates, soluble electrolytic copper balls, and titanium anode mesh coated with insoluble precious metals; and / or, the area ratio of the cathode to the anode is 1:1 to 1:

3.

10. A solar cell having grid lines, characterized in that: The grid lines are prepared by the electroplating copper plating method for solar cell silver grid lines according to any one of claims 7-9.

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