Copper plating electroplating solution as well as preparation method and application thereof

Abstract

The invention relates to a copper plating electroplating solution as well as a preparation method and application thereof. The copper plating electroplating solution comprises the following components: copper pyrophosphate, a complexing agent, ammonia water, a bath building agent, a gloss agent, a pH regulator and water, the complexing agent is selected from potassium pyrophosphate or sodium pyrophosphate; the mass percentage concentration of the ammonia water is 20%-30%, and the volume concentration of the ammonia water in the copper plating electroplating solution is 2-10 mL / L; the mass concentration of the gloss agent in the copper plating electroplating solution is 10 to 50 mg / L; and the pH value of the copper plating electroplating solution is 7.8-10. When the copper plating solution is used for silver grid line copper plating, on the premise that the cost is reduced, the silver grid line copper plating has a good plating effect, the silver grid line is firm and does not fall off, and good conductive performance is kept.

Description

Technical Field

[0001] The invention belongs to the field of solar cells, and in particular relates to a copper plating solution and a preparation method and application thereof. Background Art

[0002] The electrode grid lines of solar cells collect and conduct current in the cells. The electrode grid lines can be silver electrode grid lines or copper electrode grid lines. Among them, silver electrode grid lines have better conductivity, but they are more expensive, which will increase the cost of solar cells. Although copper electrode grid lines have lower costs, their conductivity is not as good as silver electrode grid lines.

[0003] By electroplating copper on the silver grid, the cost can be effectively reduced while maintaining good electrical conductivity. However, the traditional acidic copper electroplating solution easily causes the silver grid to fall off under high current density, affecting the efficiency and reliability of the battery. In addition, compared with ordinary electroplated parts, it is more difficult to achieve a good electroplating effect on the silver grid, and other copper plating solutions in the prior art are difficult to achieve a good electroplating effect on the silver grid, such as a good electroplated appearance, including good pure copper metallic luster, uniform color without impurities, and no pinholes, pitting, shedding, blackening and other defects in the coating. How to ensure that the copper plating of the silver grid has a good electroplating effect while reducing costs, and the silver grid is firm and does not fall off, and maintains good electrical conductivity is a difficulty. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an improved copper plating solution in view of 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 a good copper plating effect of the silver grid lines under the premise of reducing costs, and the silver grid lines are firm and do not fall off, maintaining good conductive properties.

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

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

[0007] In the prior art, although the silver electrode grid lines of solar cells have good electrical conductivity, they are expensive, while the price of copper electrodes is relatively low, but it is usually difficult to achieve a good electroplating copper plating effect on the silver electrode grid lines, it is difficult to achieve a good electroplating appearance, etc., and the use of traditional acidic electroplating copper plating solutions can easily cause the silver grid lines to fall off at high current density, affecting the efficiency and reliability of the battery. The inventors of the present application have found through research that by using copper pyrophosphate as the main copper salt, potassium pyrophosphate or sodium pyrophosphate as a complexing agent, adding a specific amount of ammonia water and a specific amount of a glossing agent, and controlling the pH value of the plating solution within a suitable range, it is possible to effectively electroplate copper on the silver grid lines, and to ensure that the copper plating of the silver grid lines has a good electroplating effect while reducing costs, and the silver grid lines are firm and do not fall off, and maintain good electrical conductivity.

[0008] The copper pyrophosphate (Cu 2 P 2 O 7 ) is the main salt for supplying copper ions to the plating solution. Potassium / sodium pyrophosphate is the main complexing agent in the copper plating solution, which forms potassium / sodium copper pyrophosphate with copper ions, so that the solution contains pyrophosphate, thereby achieving copper plating. The pH value of the present invention is 7.8-10, which can effectively prevent the hydrolysis of pyrophosphate, thereby improving the appearance of electroplating.

[0009] The complexing agent potassium / sodium pyrophosphate in the present invention can stabilize the copper pyrophosphate complex and prevent precipitation; at the same time, it can improve the quality of the coating, increase the dispersibility of the plating solution, and improve the dissolution of the anode. Among them, potassium pyrophosphate is preferred, the solubility of potassium salt is greater than that of sodium salt, the mobility of potassium ions is higher, and the potassium salt solution has higher conductivity.

[0010] The ammonia water in the present invention can improve the appearance quality of the copper coating, increase the glossiness and bonding strength of the coating, and promote the dissolution of the anode. When the ammonia water content is too low, the anode is easily passivated and "copper powder" is generated, and the coating of the plated workpiece (such as silver grid wire) at high current density or at the edge will produce white fog or roughness and dark color.

[0011] The bath building agent in the present invention can help the anode to dissolve normally, prevent passivation, improve the dispersibility of the plating solution, increase the current density, make a certain contribution to the buffering effect of the pH value, and improve the brightness of the coating.

[0012] The gloss agent added in the present invention is adsorbed on the cathode surface during the electroplating process, changing the deposition mode of metal ions. This adsorption can inhibit the excessive growth of grains, making the grains of the coating finer and more uniform; in addition, the gloss agent can change the electrochemical reaction process of the cathode, reduce cathode polarization, and promote the reduction deposition of metal ions. This helps to improve the brightness and uniformity of the coating. In addition, the present invention can achieve the optimal electroplating appearance effect by controlling the specific mass concentration of the gloss agent, while ensuring that the silver grid line does not fall off.

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

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

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

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

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

[0018] In some embodiments, the brightener 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 a combination of one or more 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, and 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 electroplating of silver grid lines of solar cells.

[0022] The present invention further provides a method for preparing the copper plating solution, which comprises the steps of mixing the copper pyrophosphate, a complexing agent, a bath building agent, a brightening agent, ammonia water 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 on solar cell silver grid lines, wherein the method uses the solar cell silver grid lines as cathodes 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. At this temperature, the plating layer can be more uniform and the surface can be smoother.

[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 make the coating more uniform and the surface smoother.

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

[0027] In some embodiments, the anode is selected from a combination of one or more of a soluble electrolytic copper plate, a soluble electrolytic copper ball, and an insoluble precious metal-coated titanium anode mesh.

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

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

[0030] The present invention further provides a solar cell comprising the solar cell grid line.

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

[0032] The present invention adopts copper pyrophosphate as the main copper salt, potassium pyrophosphate or sodium pyrophosphate as the complexing agent, adds a specific amount of ammonia water and a specific amount of brightener, and controls the pH value of the electroplating solution within a suitable range, so as to achieve effective copper electroplating on the silver grid line, and ensure that the copper plating of the silver grid line has a good electroplating effect, the silver grid line is firm and does not fall off, and maintains good conductive performance under the premise of reducing costs.

[0033] The electroplating solution of the present invention has simple ingredients, low cost and good chemical stability. When used for electroplating copper on silver grid lines, a copper plating layer with fine crystals and good bonding strength can be obtained without pre-plating or pre-treating the silver grid lines. The electroplating solution of the present invention can be used for copper plating of silver grid lines on solar cells, and can avoid the situation where the silver grid lines fall off due to the decrease in bonding strength in traditional acidic plating solutions, and can achieve a good electroplating appearance effect. DETAILED DESCRIPTION

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

[0035] In the present 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 (the formula is shown in Table 1 below), and it is used for copper plating of silver grid lines of solar cells, specifically as follows:

[0038] Use hot water to clean the electroplating tank and interface equipment, including filters, preparatory tanks, etc. Soak the plating tank, add 20g / L dilute sulfuric acid and 2-3g / L activated carbon, maintain the temperature at 60°C, and stir for at least 8 hours. Drain the acid and wash the tank and interface equipment with water. Soak the plating tank and interface equipment with 1% NaOH (10g / L) solution, maintain the temperature at 50-60°C, and soak for at least 12 hours. Drain the alkali solution and rinse with water. Prepare the preparation tank.

[0039] Use deionized water to build a bath. Add deionized water (40-50℃) to about 1 / 2 tank volume, add the formulated amount of potassium pyrophosphate while stirring to completely dissolve it. Add the formulated amount of copper pyrophosphate in batches while stirring. The purpose of adding in batches is to prevent the temperature from rising too quickly. After the copper pyrophosphate is completely dissolved, add cold water to the operating liquid level and adjust the pH of the system to 8.6 with 50% mass percent dilute sulfuric acid (pH adjuster). Cool the tank liquid to 50-55℃ and add the formulated amount of ammonia water (mass percent concentration is 25%). Before adding the ammonia water, dilute it with water and then add it to the tank liquid. Circulate and filter until the tank liquid is clear. Add the formulated amount of bath building agent (triammonium citrate). Add the formulated amount of gloss agent (2-mercaptobenzimidazole). Finally, the 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 silver paste printing), and the soluble electrolytic copper ball / copper plate is used as the anode. The electroplating solution is stirred by air bubbling, and the temperature of the electroplating solution is controlled to be 45°C.

[0041] Embodiment 2-7

[0042] This embodiment provides a copper plating solution, and uses it for copper plating of silver grid lines of solar cells. The specific steps are basically the same as those in Embodiment 1, except that the formula 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 of silver grid lines of solar cells. The specific steps are basically the same as those of Embodiment 1, except that 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 of solar cell silver grid lines. The specific steps are basically the same as those in Example 1, except that the formula composition and pH value of the plating solution are changed (wherein, changing the pH value may involve changing the amount of dilute sulfuric acid), as shown in Table 1 below. Wherein, the amount of ammonia water is changed in Comparative Examples 1-2, the pH value is changed in Comparative Examples 3-4, and the amount of brightener is changed in Comparative Examples 5-6.

[0047] Table 1 Electroplating solution formulas for various embodiments and comparative examples

[0048]

[0049] Comparative Example 7

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

[0051] Comparative Example 8

[0052] This comparative example provides a copper plating solution, and uses it for copper plating of silver grid lines of solar cells. The specific steps are basically the same as those of 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 of solar cell silver grid lines. The specific steps are basically the same as those in Example 1, except that the plating solution in Example 1 is replaced by a commercial acidic sulfate copper plating solution.

[0055] The performance tests were performed on the electrodes of the above embodiments and comparative examples:

[0056] Appearance inspection standard: Visual inspection shows that the copper-plated surface has a pure copper metallic luster, is pollution-free, has a uniform color and is free of impurities, and the plating layer has no defects such as pinholes, pitting, shedding, and blackening.

[0057] Adhesion test standard: Use the cross-cutting-tape pasting method and the scratch method. After scratching the copper-plated surface with a knife, there is no peeling or delamination on the copper-plated surface; use tape to stick on the scratched area, and there is no peeling or delamination.

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

[0059] Table 2 Appearance test results

[0060]

[0061]

[0062] From the comparison of Examples 1-3 and Comparative Examples 1-2, it can be seen that in the pyrophosphate copper plating process, the content of ammonia water will affect the performance of the plating solution and the quality of the coating, because ammonia water helps to stabilize and transport copper ions. When ammonia water is insufficient, the stability of copper ions is reduced, and the deposition rate of the coating will slow down, affecting production efficiency; when ammonia water is insufficient, the copper coating may have defects such as holes and roughness, and the surface finish and uniformity are reduced, affecting the appearance and performance of the finished product; excessive ammonia water content will change the chemical balance of the plating solution, resulting in unstable copper ion transmission rate and difficult to control deposition rate, which may cause uneven or rough coating.

[0063] From the comparison of Examples 2, 4-5 and Comparative Examples 3-4, it can be seen that the pH value of the plating solution will affect the performance of the plating solution and the quality of the coating; if the pH value is too high, the copper ions in the plating solution will combine with the hydroxide ions to form copper hydroxide precipitates, 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 the copper ions in the plating solution will be reduced, resulting in a decrease in the copper ion concentration, affecting the deposition efficiency, and the coating may become thinner or the deposition speed will slow down.

[0064] From the comparison between Example 1 and Comparative Examples 5-6, it can be seen that the function of the gloss agent is to improve the gloss, flatness and uniformity of the coating. If the gloss agent in the plating solution is too high / insufficient, it will have an adverse effect on the quality of the coating; if the gloss agent is insufficient, the coating may appear dull, rough or cloudy, and lose its original gloss; but if an excessive amount is added, the coating surface may be too flat, with excessive gloss, and may become unnatural, and form a rough or "foamy" surface.

[0065] From the comparison between Example 1 and Comparative Examples 7-8, it can be seen that the temperature during electroplating and the stirring of the plating solution have an impact on the quality of the coating. When the plating solution temperature is too low, the current efficiency will decrease significantly, resulting in a slower deposition rate. This is because the dispersion ability of the plating solution and the cathode current efficiency are reduced at low temperatures, and the coating crystals are coarse and dark in color. When the plating solution is not stirred, the anode dissolves faster, and Cu 2+ Excess, with P 2 O 7 4- If the coordination is not sufficient, white copper pyrophosphate precipitation is easily generated, resulting in a rough coating.

[0066] Adhesion test before electroplating: The battery cells with different types of silver paste (silver paste provided by different suppliers) were immersed in the copper plating solution for 5 minutes, taken out and cleaned and dried, and a tensile test was performed using 3M tape. The results are shown in Table 3. It can be seen that the silver grid lines of the battery cells corresponding to the solution of the present application do not fall off (that is, a variety of silver pastes on the market can be used), while the acidic copper electroplating solution will cause the silver grid lines to fall off.

[0067] Table 3 Adhesion test results before electroplating

[0068]

[0069]

[0070] Adhesion test after electroplating: Cells with different types of silver paste (silver paste provided by different suppliers) were placed in a copper plating solution to plate a 5μm thick copper layer, which was then taken out, cleaned and dried, and a tensile test was performed using 3M tape. The results are shown in Table 4. It can be seen that the silver grid lines of the cell corresponding to the solution of the present application do not fall off (i.e., a variety of silver pastes on the market can be used), while the acidic sulfate copper plating solution will cause the silver grid lines to fall off.

[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 their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0074] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A copper plating solution, characterized in that: The copper plating solution comprises the following components: copper pyrophosphate, a complexing agent, ammonia water, a bath building agent, a brightener, a pH regulator and water; the complexing agent is selected from potassium pyrophosphate or sodium pyrophosphate; the mass percentage concentration of the ammonia water is 20%-30%, and its volume concentration in the copper plating solution is 2-10 mL / L; the mass concentration of the brightener in the copper plating solution is 10-50 mg / L; the pH value of the copper plating solution is 7.8-10.

2. The copper plating solution according to claim 1, characterized in that: The mass concentration of the copper pyrophosphate in the copper plating solution is 50 to 100 g / L; and / or, the mass concentration of the complexing agent in the copper plating solution is 200 to 300 g / L; and / or, the mass concentration of the bath building agent in the copper plating solution is 20 to 100 g / 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 bath building agent is selected from a combination of one or more of triammonium citrate, ammonium oxalate, potassium sodium tartrate, and ammonium nitrate; and / or, the glossing agent is selected from a combination of one or more of 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, selenium disulfide, and isothiazolinone; and / or, the pH adjusting agent is selected from a combination of one or more of sulfuric acid, hydrochloric acid, phosphoric acid, and citric acid.

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

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

7. A method for electroplating copper for silver grid lines of solar cells, characterized in that: The method uses the silver grid line 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 copper plating solution according to any one of claims 1 to 5.

8. The method for electroplating copper for solar cell silver grid lines according to claim 7, characterized in that: The temperature of the electroplating solution is 40-60° C.; and / or, during the electroplating process, the electroplating solution is stirred or the cathode is moved.

9. The method for electroplating copper for solar cell silver grid lines according to claim 7, characterized in that: The average current density of the electroplating is 0.5 to 5 A / dm 2 ; and / or, the anode is selected from a combination of one or more of a soluble electrolytic copper plate, a soluble electrolytic copper ball, and an insoluble precious metal-coated titanium anode mesh; and / or, the area ratio of the cathode to the anode is 1:1-1:

3.

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

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