A method for electroplating a silicon solar cell

Abstract

The present invention discloses a method for electroplating a silicon solar cell. Before electroplating, the cell to be electroplated is pretreated, and the cell surface has laser grooves for electroplating. The pretreatment includes removing oil stains on the cell surface, removing the heat damage layer at the grooved part of the cell, and removing the oxide film at the grooved part of the cell. The cell is pretreated before electroplating to remove oil stains, heat damage layers and oxide films on the surface of the silicon substrate, providing a good deposition plane for subsequent electroplating, so that electroplating is performed on the cell after the pretreatment, and the obtained plated grid lines are uniform, dense, without broken grids, and not easy to fall off. The electroplated layer has good bonding strength with the cell, thereby ensuring the quality of the metal electrode of the silicon solar cell.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cell preparation, and in particular relates to an electroplating method for a silicon solar cell. Background Art

[0002] Electroplating technology has been widely used in the metal electrode manufacturing process of silicon solar cells, mainly based on the seed layer grid line electroplating method to replace the traditional cell screen printing method of electrode manufacturing. Electroplating generally uses a silver-containing electroplating solution, selects nickel / copper / silver three-layer plating, or uses nickel / copper / nickel three-layer plating to completely replace silver paste, thereby reducing the cost of silicon solar cells and making the product more competitive. In addition, the use of electroplating to make electrodes can also achieve thinner grid lines and low contact resistance, and can achieve double-sided electroplating, thereby creating higher cell efficiency.

[0003] Electroplating technology usually uses nickel plating as a seed layer and a barrier layer, that is, nickel is electroplated as a seed layer at the slot position of the cell, and then other metal layers are electroplated; however, due to the fact that a small amount of oil stains will adhere to the cell during the process and transportation before electroplating, and the slots for electroplating on the surface of the cell are generally laser slotted, but when the cell is laser slotted, the slotted part is heated by the instantaneous high energy of the laser, and a certain degree of thermal damage will occur; in addition, the substrate of the cell is a silicon wafer, and silicon has a strong affinity for oxygen, so that a dense oxide film is quickly formed on the slotted surface. Therefore, the above problems not only seriously hinder the firm bonding of the subsequent electroplating layer (especially the nickel plating layer as a seed layer) with the silicon substrate, thereby seriously affecting the quality of the metal electrode of the silicon solar cell; and on the cell obtained after electroplating, the broken grid is very obvious, resulting in the electroplating and the grid line being not uniform and dense enough. Summary of the invention

[0004] The object of the present invention is to overcome the above-mentioned shortcomings and provide a method for electroplating a silicon solar cell, which pre-treats the cell before electroplating so that the obtained plated grid lines are uniform, dense, without broken grids, and not easy to fall off. The electroplated layer has good bonding strength with the cell, thereby ensuring the quality of the metal electrode of the silicon solar cell.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for electroplating a silicon solar cell. Before electroplating, the cell to be electroplated is pretreated, and the surface of the cell has laser grooves for electroplating. The pretreatment includes the following steps:

[0007] S1. Remove oil stains from the surface of the battery cell;

[0008] S2, removing the thermal damage layer at the slotted part of the battery cell;

[0009] S3. Remove the oxide film on the slotted area of ​​the battery cell.

[0010] The above step S1 comprises:

[0011] S11, ultrasonic cleaning, wherein the cleaning solution used for cleaning comprises, by weight percentage, 3%-5% sodium carbonate, 1%-2% sodium silicate, 0.3%-0.5% fatty acid methyl ester ethoxylate sulfonate, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water;

[0012] S12, rinsing the battery cell after ultrasonic cleaning with deionized water.

[0013] During washing, the temperature of the cleaning liquid is set to 40-50° C., the ultrasonic cleaning frequency is set to 20-30 kHz, and the cleaning time is set to 60-180 s.

[0014] The above step S2 comprises:

[0015] S21, soaking the slotted side of the battery cell in an alkaline solution to remove the thermal damage layer at the slotted portion;

[0016] S22. Take out the battery cells from the alkaline solution and rinse them with deionized water.

[0017] The alkali solution, calculated by weight percentage, includes 5%-10% sodium hydroxide or potassium hydroxide, and the rest is deionized water.

[0018] The soaking time of the battery cell in the alkaline solution is set to 20-40s.

[0019] The above step S3 includes:

[0020] S31, soaking the slotted side of the battery cell in acid solution;

[0021] S32, taking the battery cell out of the acid solution and rinsing it with deionized water;

[0022] S33, drying the battery cells.

[0023] The acid solution, calculated by weight percentage, includes 4%-8% hydrofluoric acid, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water.

[0024] The battery cells are immersed in the acid solution for 15-30 seconds.

[0025] After the above pretreatment, electroplating is performed in the grooves of the battery cell.

[0026] Nickel is electroplated on the grooved portion of the battery cell to form a nickel plating layer.

[0027] During nickel electroplating, the slotted side of the cell is immersed in a stirred nickel electroplating solution, and the current density is set to 0.1-0.2A / dm2, the temperature of the nickel electroplating solution is set to 50-60°C, and the electroplating time is set to 8-12min.

[0028] The stirring is set to air stirring, and the stirring speed is set to 0.05L / min-0.1L / min.

[0029] The beneficial effects of the present invention are:

[0030] The cell is subjected to the above-mentioned pretreatment before electroplating to remove oil stains, heat damage layer and oxide film on the surface of the silicon substrate, and provide a good deposition plane for subsequent electroplating. Thus, electroplating is carried out on the cell after the above-mentioned pretreatment, and the obtained plated grid lines are uniform, dense, without broken grids, and not easy to fall off. The electroplated layer has good bonding strength with the cell, thereby ensuring the quality of the metal electrode of the silicon solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of a cell after electroplating without the pretreatment of the present application;

[0032] Figure 2 This is a schematic diagram of a battery cell after electroplating that has undergone pretreatment according to the present application. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention discloses a method for electroplating a silicon solar cell. Before electroplating, the cell to be electroplated is pretreated, and the surface of the cell has laser grooves for electroplating. The pretreatment includes the following steps:

[0035] S1. Remove oil stains from the surface of the battery cell;

[0036] S2, removing the thermal damage layer at the slotted part of the battery cell;

[0037] S3. Remove the oxide film on the slotted area of ​​the battery cell.

[0038] The above step S1 comprises:

[0039] S11, ultrasonic cleaning, wherein the cleaning solution used for cleaning is calculated by weight percentage and includes 3%-5% sodium carbonate, 1%-2% sodium silicate, 0.3%-0.5% fatty acid methyl ester ethoxylate sulfonate, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water.

[0040] Sodium carbonate and sodium silicate are both alkaline substances, which have a saponification effect on grease. When grease meets alkali, it will be decomposed into fatty acid salts that are soluble in water; fatty acid methyl ester ethoxylate sulfonate is a surfactant with very high cleaning ability; polyethylene glycol octyl phenyl ether is a surfactant that can promote the decomposition of grease. The cleaning liquid obtained by mixing the above ingredients according to the above ratio can effectively remove the oil stains on the surface of the battery cell. In addition, ultrasonic cleaning is used, so that the oil stains on the surface of the battery cell can be removed faster and more thoroughly.

[0041] When ultrasonic cleaning is used to remove oil stains, the temperature of the cleaning liquid is set to 40-50°C, the ultrasonic cleaning frequency is set to 20-30kHz, and the cleaning time is set to 60-180s. With such settings, combined with the cleaning liquid and ultrasonic cleaning, the oil stains on the battery cell can be completely cleaned.

[0042] Preferably, the temperature of the cleaning liquid can be set to 42, 45, 48, 49, 50° C. The ultrasonic cleaning frequency can be set to 22, 25, 26, 28 or 29 kHz. The cleaning time can be set to 70, 80, 100, 120, 150 or 160 seconds.

[0043] S12, rinsing the battery cell after ultrasonic cleaning with deionized water.

[0044] The floating oil still attached to the battery cell and the above-mentioned cleaning liquid can be washed away, so that there is no other attachment on the battery cell except deionized water. In this way, the battery cell is cleaned very cleanly, thereby preventing the components other than deionized water in the cleaning liquid from entering the subsequent processing steps and affecting the subsequent processing effect.

[0045] Even if there are other impurities on the battery cell besides the oil stains, after the above-mentioned ultrasonic cleaning and deionized water cleaning, the other impurities will be detached from the battery cell and cleaned away, thereby ensuring that the battery cell treated by S1 is very clean.

[0046] The above step S2 comprises:

[0047] S21. Soak the slotted side of the battery cell in alkaline solution.

[0048] The alkali solution, calculated by weight percentage, includes 5%-10% sodium hydroxide or potassium hydroxide, and the rest is deionized water.

[0049] The surface of the cell is a silicon nitride layer, but the high heat generated by the laser during laser grooving may damage the silicon underneath the silicon nitride, causing lattice defects, thus forming the thermal damage layer. Soaking the grooved side of the cell in an alkali solution can cause anisotropic corrosion of the silicon, removing the damaged part and leaving the silicon with a complete crystal form, thereby achieving the purpose of removing the thermal damage layer at the grooved part.

[0050] The soaking time of the battery cell in the alkaline solution is set to 20-40s. In this way, the heat loss of the slotted part of the battery cell can be removed, and the time used is short, which has both the speed and the effect of removing the heat damage layer of the slotted part.

[0051] S22, taking out the battery cell from the alkaline solution and rinsing it with deionized water so that there is no other attachment on the battery cell except the deionized water, thereby avoiding the reaction of the alkaline components with the acid solution in the subsequent step S3, thereby ensuring the effect of removing the oxide film at the grooved part in step 3, that is, ensuring the subsequent electroplating effect, that is, ensuring the quality of the electroplated electrode of the battery cell.

[0052] The above step S3 includes:

[0053] S31. Soak the slotted side of the battery cell in acid solution to remove the oxide film on the slotted portion.

[0054] The acid solution, calculated by weight percentage, includes 4%-8% hydrofluoric acid, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water.

[0055] The oxide film refers to silicon oxide generated by the reaction of silicon and oxygen. When the slotted side of the cell is immersed in acid solution, the hydrofluoric acid in the acid solution reacts with the silicon oxide to generate silicon fluoride gas, which is easily soluble in water, thereby removing the oxide film on the surface of the cell. In other words, the oxide film on the surface of the cell is dissolved by the acid solution erosion to expose the active interface, thereby ensuring the bonding strength between the subsequent electroplating layer and the silicon substrate.

[0056] Polyethylene glycol octylphenyl ether is a surfactant that can clean the dirt on the surface of the silicon wafer again, making the surface of the battery cell cleaner, that is, making the laser grooved part of the battery cell cleaner, thereby further ensuring the bonding strength between the subsequent electroplating layer and the silicon substrate.

[0057] In this embodiment, the battery cell is immersed in the acid solution for 15-30 seconds. Preferably, the immersion time is set to 18, 20, 22, 25, 28 or 20 seconds. The immersion time is set in this way so that the oxide film at the slotted part can be removed in a relatively short time.

[0058] S32. Take the battery cells out of the acid solution and rinse them with deionized water.

[0059] Similarly, the battery cells should be rinsed until there is no other attachment except deionized water, thus avoiding affecting the quality of the subsequent electroplating layer.

[0060] S33, drying the battery cells

[0061] That is, the battery cell rinsed with deionized water in step S31 is dried, which can be blow-dried or baked.

[0062] All the above-mentioned steps of rinsing the battery cells with deionized water and drying the cells may be carried out in any known and feasible manner, and are not the inventive point of the present invention, so they will not be described in detail here.

[0063] After the above pretreatment, electroplating is performed in the grooves of the battery cell.

[0064] In this embodiment, the electrode electroplating includes electroplating nickel in the grooves of the battery cell to form a nickel plating layer, and the nickel plating layer serves as a seed layer, because nickel can not only form a good ohmic contact with silicon, thereby ensuring a good ohmic contact between the entire fine grid and the battery cell; but the nickel plating layer can also serve as an isolation layer / barrier layer to effectively prevent the subsequent plating layers (such as copper plating layers, silver plating layers) from diffusing in the silicon layer.

[0065] When electroplating nickel, immerse the slotted side of the cell in a stirred nickel electroplating solution. Preferably, when electroplating nickel, the current density is set to 0.1-0.2A / dm2, the temperature of the nickel electroplating solution is set to 50-60°C, and the electroplating time is set to 8-12min. The setting of the electroplating parameters enables a better electroplating effect to be achieved in a relatively short time.

[0066] Preferably, the electroplating temperature is set to 52, 55, 57 or 58° C., and the electroplating time is set to 9, 10, 11 or 11.5 min.

[0067] Preferably, during nickel electroplating, the nickel electroplating solution is in a low-speed stirring state. The stirring is air stirring, and the stirring speed is set to 0.05L / min-0.1L / min, so that the nickel electroplating solution is in a low-speed stirring state. Preferably, the stirring speed is set to 0.06, 0.08, 0.09L / min.

[0068] Keeping the nickel plating solution in a stirring state during electroplating is conducive to the discharge of bubbles during the electroplating process; if it is not stirred, the concentration of the plating solution will become lower and lower, and the bubbles cannot be discharged in time, and some bubbles will be adsorbed on the silicon wafer, which is not conducive to the deposition of the nickel layer, and the area of ​​the cell adsorbed with bubbles will not be plated, and the grid will be broken. Low-speed air stirring is not only conducive to the deposition of the nickel layer, but also can make the plating solution in a more uniform state, so that the electroplating is more uniform, that is, the plating quality is better.

[0069] After nickel electroplating, the battery cell is taken out from the nickel electroplating solution, cleaned in deionized water, and then dried (either by drying or blowing), and then other subsequent electroplating layers are performed.

[0070] Figure 1 is a schematic diagram of a cell after electroplating that has not been pre-treated in this application. Figure 2 is a schematic diagram of a cell after electroplating after pretreatment according to the present invention, Figure 1 and Figure 2 It can be clearly seen that the above pretreatment of the cell before electroplating can remove the oil stains, thermal damage layer and oxide film on the surface of the silicon substrate, providing a good deposition plane for the subsequent electroplating layer. Electroplating is performed on the cell after the above pretreatment, and the obtained plating grid lines are uniform, dense, and without broken grids (such as Figure 2 The coating has good bonding strength with the cell and is not easy to fall off, thereby ensuring the quality of the metal electrode of the silicon solar cell. The cell processing step before pretreatment is not the focus of the present invention. The present invention is equivalent to adding a pretreatment step before the electroplating step in the general cell processing step. Therefore, the cell processing step before pretreatment is not described in detail here, and it can be any known and feasible step.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for electroplating a silicon solar cell, characterized in that: Before electroplating, the cell to be electroplated is pre-treated, and the cell surface has laser grooves for electroplating. The pre-treatment includes the following steps: S1. Remove oil stains from the surface of the battery cell; S2, removing the thermal damage layer at the slotted part of the battery cell; S3, removing the oxide film at the slotted part of the battery cell; The above step S1 comprises: S11, ultrasonic cleaning, wherein the cleaning solution used for cleaning comprises, by weight percentage, 3%-5% sodium carbonate, 1%-2% sodium silicate, 0.3%-0.5% fatty acid methyl ester ethoxylate sulfonate, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water; S12, rinsing the battery cell after ultrasonic cleaning with deionized water.

2. The electroplating method of silicon solar cell according to claim 1, characterized in that: During ultrasonic cleaning, the temperature of the cleaning solution is set to 40-50° C., the ultrasonic cleaning frequency is set to 20-30 kHz, and the cleaning time is set to 60-180 s.

3. The electroplating method of silicon solar cell according to claim 1, characterized in that: The above step S2 comprises: S21, soaking the slotted side of the battery cell in an alkaline solution; S22. Take out the battery cells from the alkaline solution and rinse them with deionized water.

4. The electroplating method of silicon solar cell according to claim 2, characterized in that: The above step S2 comprises: S21, soaking the slotted side of the battery cell in an alkaline solution; S22. Take out the battery cells from the alkaline solution and rinse them with deionized water.

5. The electroplating method of silicon solar cell according to claim 3 or 4, characterized in that: The alkali solution, calculated by weight percentage, includes 5%-10% sodium hydroxide or potassium hydroxide, and the rest is deionized water.

6. The electroplating method of silicon solar cell according to claim 5, characterized in that: The immersion time of the battery cell in the alkaline solution is set to 20-40s.

7. The electroplating method of a silicon solar cell according to any one of claims 1 to 4 and 6, characterized in that: The above step S3 includes: S31, soaking the slotted side of the battery cell in acid solution; S32, taking the battery cell out of the acid solution and rinsing it with deionized water; S33, drying the battery cells.

8. The electroplating method of silicon solar cell according to claim 7, characterized in that: The acid solution, calculated by weight percentage, includes 4%-8% hydrofluoric acid, 0.2%-0.4% polyethylene glycol octylphenyl ether, and the rest is deionized water.

9. The electroplating method of silicon solar cell according to claim 8, characterized in that: The battery cells are immersed in the acid solution for 15-30 seconds.

10. The electroplating method of a silicon solar cell according to any one of claims 1 to 4, 6, 8 to 9, characterized in that: After the above pretreatment, electroplating is performed in the grooves of the battery cell.

11. The electroplating method of silicon solar cell according to claim 10, characterized in that: Nickel is electroplated on the grooved portion of the battery cell to form a nickel plating layer.

12. The electroplating method of silicon solar cell according to claim 11, characterized in that: During nickel electroplating, the slotted side of the cell is immersed in a stirred nickel electroplating solution, and the current density is set to 0.1-0.2A / dm 2 , the temperature of the nickel electroplating solution is set to 50-60℃, and the electroplating time is set to 8-12min.

13. The electroplating method of silicon solar cell according to claim 12, characterized in that: The stirring is set to air stirring, and the stirring speed is set to 0.05L / min-0.1L / min.

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