Palladium-free nickel plating process for crystalline silicon solar cells and crystalline silicon solar cells

Abstract

The present invention provides a palladium-free nickel plating process for crystalline silicon solar cells and a crystalline silicon solar cell, and specifically relates to the technical field of solar cell preparation. The palladium-free nickel plating process comprises the following steps: A. printing an activation liquid on the surface of a silicon substrate, drying it, and then activating it to obtain a silicon substrate containing an activation layer; B. chemically nickel-plating the silicon substrate containing the activation layer to obtain a nickel layer. The palladium-free nickel plating process for crystalline silicon solar cells provided by the present invention has low process cost and is pollution-free. The formed activation layer not only improves the bonding force between the nickel layer and the silicon substrate, but also makes the nickel layer on the activation layer uniform in thickness and good in density, thereby establishing a good seed layer for the subsequent copper plating layer, thereby ensuring the quality of the solar cell and improving the electrical performance of the crystalline silicon solar cell.

Description

Technical Field

[0001] The invention relates to the technical field of solar cell preparation, in particular to a palladium-free nickel plating process for a crystalline silicon solar cell and a crystalline silicon solar cell. Background Art

[0002] Metallization is one of the key processes in the preparation of silicon solar cells. It is mainly used to make silicon solar cell electrodes, form ohmic contacts at both ends of the PN junction, and achieve current output. Currently, screen printing is the most mature and common metallization process, but the high cost of the silver paste used has become an important factor restricting the promotion of the industry. Therefore, the traditional screen printing process cannot meet the needs of new high-efficiency batteries.

[0003] As a non-contact electrode preparation technology, electroplating technology can completely replace silver paste, and has excellent performance while reducing costs. Electroplating technology usually requires a layer of nickel to be plated on the silicon surface as a seed layer, and then a conductive layer of metal copper is deposited. The presence of the nickel layer can prevent copper ions from diffusing into the silicon, thereby preventing the life of silicon solar cells from being reduced; on the other hand, it can form a nickel-silicon alloy to reduce contact resistance.

[0004] At present, the formation of nickel plating layer usually adopts chemical nickel plating process. Since the silicon substrate itself does not have catalytic activity, it is necessary to activate the silicon substrate first to ensure smooth plating. The traditional activation method uses precious metals such as palladium, gold, and platinum for activation, which is costly and polluting. Moreover, if the precious metals are not cleaned properly, it will not only affect the bonding strength between the subsequent plating layer and the silicon substrate, but also cause overflow plating on the surface of the silicon substrate, resulting in reduced efficiency of solar cells.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] One of the purposes of the present invention is to provide a palladium-free nickel plating process for crystalline silicon solar cells, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0007] A second object of the present invention is to provide a crystalline silicon solar cell.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] A first aspect of the present invention provides a palladium-free nickel plating process for a crystalline silicon solar cell, comprising the following steps:

[0010] A. Printing an activation solution on the surface of a silicon substrate and drying the substrate for activation to obtain a silicon substrate containing an activation layer;

[0011] B. Chemically plating nickel on the silicon substrate containing the activation layer to obtain a nickel layer.

[0012] Furthermore, the activation solution is a nickel-containing sol.

[0013] Preferably, the nickel-containing sol includes at least one of nickel citrate sol, nickel oxalate sol, nickel formate sol and nickel acetate sol.

[0014] Preferably, the nickel-containing sol is obtained by reacting an organic weak acid with basic nickel carbonate.

[0015] Among them, the reaction temperature is 60°C to 70°C; the reaction time is 12h to 24h.

[0016] Preferably, the organic weak acid comprises at least one of oxalic acid, formic acid, acetic acid and citric acid, preferably citric acid.

[0017] Preferably, the mass ratio of the organic weak acid to the basic nickel carbonate is 6-15:8-20.

[0018] Furthermore, in step A, the activation temperature is 40° C. to 80° C., and the activation time is 5 min to 20 min.

[0019] Preferably, the activation method includes laser scanning activation.

[0020] Preferably, the power of the laser scanning activation is 2W to 5W, the spot diameter is 15 μm to 20 μm, and the scanning rate is 100 mm / s to 1000 mm / s.

[0021] Furthermore, the silicon substrate is subjected to film opening and roughening treatments.

[0022] Furthermore, a patterned groove is formed on the silicon substrate by laser film opening to obtain a film-opened silicon substrate.

[0023] Preferably, the width of the patterned groove is 15 μm to 60 μm.

[0024] Furthermore, the silicon substrate after the film opening is placed in a roughening solution for roughening, and then washed and dried to obtain a roughened silicon substrate.

[0025] Preferably, the roughening solution comprises 1 wt.% to 10 wt.% of hydrofluoric acid, 10 wt.% to 30 wt.% of ammonium fluoride, 0.1 wt.% to 0.5 wt.% of a surfactant, and the balance is deionized water.

[0026] Preferably, the surfactant includes at least one of alkyl sulfonates, fatty alcohol sulfates and fatty alcohol polyoxyethylene ether sulfates.

[0027] Furthermore, the roughening temperature is 20°C to 40°C, and the time is 1 min to 5 min.

[0028] Preferably, in step A, the drying temperature is 20° C. to 60° C., and the drying time is 3 min to 15 min.

[0029] Furthermore, in step B, a chemical nickel plating solution is used to perform the chemical nickel plating.

[0030] Preferably, in terms of weight parts, the chemical nickel plating solution comprises 20 to 30 parts of nickel salt, 25 to 43 parts of reducing agent and 10 to 15 parts of complexing agent per unit volume.

[0031] Preferably, the nickel salt includes at least one of nickel sulfamate, nickel sulfate and nickel acetate.

[0032] Preferably, the reducing agent comprises sodium hypophosphite and / or sodium borohydride.

[0033] Preferably, the complexing agent comprises at least one of citrate, pyrophosphate and ammonium salt.

[0034] Furthermore, in step B, the pH of the chemical nickel plating is 7.0-8.0, the temperature is 70° C.-80° C., and the time is 1 min-4 min.

[0035] Furthermore, in step B, the thickness of the nickel layer after nickel plating is 0.4 μm to 1.2 μm.

[0036] A second aspect of the present invention provides a crystalline silicon solar cell produced according to the palladium-free nickel plating process for the crystalline silicon solar cell described in the first aspect.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] The palladium-free nickel plating process for crystalline silicon solar cells provided by the present invention performs laser activation on the silicon substrate after film opening and coarsening, has low process cost and is pollution-free, replaces the traditional palladium activation process, and forms various fine and complex activation layers on the surface of the silicon substrate. The activation layer not only improves the bonding force between the nickel layer and the silicon substrate, but also makes the nickel layer on the activation layer uniform in thickness and good in compactness, and establishes a good seed layer for the subsequent copper plating layer, thereby ensuring the quality of the solar cell and improving the electrical performance of the crystalline silicon solar cell.

[0039] The crystalline silicon solar cell provided by the present invention, in view of the advantages brought by the above-mentioned palladium-free nickel plating process, makes the prepared crystalline silicon solar cell have lower cost and better efficiency, expands the application scenarios of crystalline silicon solar cells, and promotes the development of downstream industries. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0041] Hereinafter, the terms "including", "having" and their cognates, which may be used in various embodiments of the present invention, are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or adding the possibility of one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0042] A first aspect of the present invention provides a palladium-free nickel plating process for a crystalline silicon solar cell, comprising the following steps:

[0043] A. Printing an activation liquid on the surface of a silicon substrate and drying it, and then activating it to obtain a silicon substrate containing an activation layer;

[0044] B. Chemically plating nickel on the silicon substrate containing the activation layer to obtain a nickel layer.

[0045] The palladium-free nickel plating process for crystalline silicon solar cells provided by the present invention performs laser activation on the silicon substrate after film opening and coarsening, has low process cost and is pollution-free, replaces the traditional palladium activation process, and forms various fine and complex activation layers on the surface of the silicon substrate. The activation layer not only improves the bonding force between the nickel layer and the silicon substrate, but also makes the nickel layer on the activation layer uniform in thickness and good in compactness, and establishes a good seed layer for the subsequent copper plating layer, thereby ensuring the quality of the solar cell and improving the electrical performance of the crystalline silicon solar cell.

[0046] Furthermore, the activation solution is a nickel-containing sol.

[0047] Preferably, the nickel-containing sol includes at least one of nickel citrate sol, nickel oxalate sol, nickel formate sol and nickel acetate sol.

[0048] Preferably, the nickel-containing sol is obtained by reacting an organic weak acid with basic nickel carbonate.

[0049] Among them, the reaction temperature is 60°C to 70°C; the reaction time is 12h to 24h.

[0050] Typically but not limiting, the nickel-containing sol is generated at a temperature of, for example, 60° C., 62° C., 64° C., 66° C., 68° C. or 70° C., and for a time of, for example, 12 h, 16 h, 20 h or 24 h.

[0051] Preferably, the organic weak acid comprises at least one of oxalic acid, formic acid, acetic acid and citric acid, preferably citric acid.

[0052] Preferably, the mass ratio of the organic weak acid to the basic nickel carbonate is 6-15:8-20.

[0053] Within the above mass ratio range, the raw materials can generate nickel-containing sol to the maximum extent.

[0054] Typically, but not limiting, the mass ratio of the organic weak acid to the basic nickel carbonate may be, for example, 6:8, 6:14, 6:20, 10:8, 10:14, 10:20, 15:8, 15:14 or 15:20.

[0055] The coating amount of the activation solution is 5-10g / cm 2 .

[0056] Furthermore, in step A, the activation temperature is 40° C. to 80° C., and the activation time is 5 min to 20 min.

[0057] Typically but not limiting, the activation temperature may be, for example, 40°C, 50°C, 60°C, 70°C or 80°C; the activation time may be, for example, 5 min, 8 min, 10 min, 15 min or 20 min.

[0058] Preferably, the activation method includes laser scanning activation, which can produce instant high temperature to activate the nickel-containing gel, and the temperature is easier to control, the activation degree is more uniform, and the activation layer obtained is more precise. The equipment used for laser scanning activation is an infrared laser.

[0059] Preferably, the power of the laser scanning activation is 2W to 5W, the spot diameter is 15 μm to 20 μm, and the scanning rate is 100 mm / s to 1000 mm / s.

[0060] The power of laser scanning activation is lower than 2W, the spot diameter is lower than 15μm, and the scanning rate is lower than 100mm / s, which is equivalent to low laser energy and batch processing volume, which will lead to incomplete reaction of the activated nickel layer and uneven thickness of the nickel layer; the power of laser scanning activation is higher than 5W, the spot diameter is higher than 20μm, and the scanning rate is greater than 1000mm / s, which is equivalent to excessive laser energy, which will cause laser damage to the silicon substrate and affect the open circuit voltage of the battery cell.

[0061] Typically but not limiting, the power of laser scanning activation can be, for example, 2W, 3W, 4W, or 5W; the spot diameter can be, for example, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm; and the scanning rate can be, for example, 100mm / s, 300mm / s, 500mm / s, 700mm / s, 900mm / s, or 1000mm / s.

[0062] Furthermore, the printing method includes screen printing.

[0063] Furthermore, the silicon substrate is subjected to film opening and roughening treatments.

[0064] Preferably, a patterned groove is formed on a silicon substrate by laser film opening to obtain a film-opened silicon substrate.

[0065] Preferably, the width of the patterned groove is 15 μm to 60 μm.

[0066] Furthermore, the silicon substrate after the film opening is placed in a roughening solution for roughening, and then washed and dried to obtain a roughened silicon substrate.

[0067] Preferably, the roughening solution comprises 1 wt.% to 10 wt.% of hydrofluoric acid, 10 wt.% to 30 wt.% of ammonium fluoride, 0.1 wt.% to 0.5 wt.% of a surfactant, and the balance is deionized water.

[0068] Typically but not limiting, the content of hydrofluoric acid in the roughening solution may be, for example, 1wt.%, 3wt.%, 5wt.%, 7wt.%, 9wt.%, 10wt.%; the content of ammonium fluoride may be, for example, 10wt.%, 15wt.%, 20wt.%, 25wt.%, 30wt.%; the content of surfactant may be, for example, 0.1wt.%, 0.2wt.%, 0.3wt.%, 0.4wt.%, 0.5wt.%. Deionized water is used to make up to 100wt.%.

[0069] Preferably, the surfactant includes at least one of alkyl sulfonates, fatty alcohol sulfates and fatty alcohol polyoxyethylene ether sulfates.

[0070] Furthermore, the roughening temperature is 20°C to 40°C, and the time is 1 min to 5 min.

[0071] Typically but not limiting, the roughening temperature may be, for example, 20°C, 25°C, 30°C, 35°C or 40°C; the roughening time may be, for example, 1 min, 2 min, 3 min, 4 min or 5 min.

[0072] Preferably, in step A, the drying temperature is 20° C. to 60° C., and the drying time is 3 min to 15 min.

[0073] Typically but not limiting, the drying temperature may be, for example, 20°C, 30°C, 40°C, 50°C or 60°C; the drying time may be, for example, 3 min, 6 min, 9 min, 12 min or 15 min.

[0074] Furthermore, in step B, a chemical nickel plating solution is used to perform the chemical nickel plating.

[0075] Preferably, in terms of weight parts, the chemical nickel plating solution comprises 20 to 30 parts of nickel salt, 25 to 43 parts of reducing agent and 10 to 15 parts of complexing agent per unit volume.

[0076] Typically but not restrictively, the weight proportion of nickel salt per unit volume of chemical nickel plating solution may be, for example, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts or 30 parts, or any value within the range of 20 to 30 parts; the weight proportion of reducing agent may be, for example, 25 parts, 30 parts, 35 parts, 40 parts or 43 parts, or any value within the range of 25 to 43 parts; the weight proportion of complexing agent may be, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, or any value within the range of 10 to 15 parts.

[0077] Preferably, the nickel salt includes at least one of nickel sulfamate, nickel sulfate and nickel acetate.

[0078] Preferably, the reducing agent comprises sodium hypophosphite and / or sodium borohydride.

[0079] Preferably, the complexing agent comprises at least one of citrate, pyrophosphate and ammonium salt.

[0080] Furthermore, in step B, the pH of the chemical nickel plating is 7.0-8.0, the temperature is 70° C.-80° C., and the time is 1 min-4 min.

[0081] Typically but not limiting, the temperature of chemical nickel plating may be, for example, 70° C., 72° C., 74° C., 76° C., 78° C. or 80° C.; and the time may be, for example, 1 min, 2 min, 3 min or 4 min.

[0082] Furthermore, in step B, the thickness of the nickel layer after nickel plating is 0.4 μm to 1.2 μm.

[0083] Typically but not limiting, the thickness of the nickel plated layer may be, for example, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1.0 μm or 1.2 μm.

[0084] Furthermore, a chemical nickel plating solution is used to form nickel plating layers on both sides of the silicon substrate containing the activation layer.

[0085] A second aspect of the present invention provides a crystalline silicon solar cell produced according to the palladium-free nickel plating process for the crystalline silicon solar cell described in the first aspect.

[0086] The crystalline silicon solar cell provided by the present invention, in view of the advantages brought by the above-mentioned palladium-free nickel plating process, makes the prepared crystalline silicon solar cell have lower cost and better efficiency, expands the application scenarios of crystalline silicon solar cells, and promotes the development of downstream industries.

[0087] In the process of preparing crystalline silicon solar cells, the crystalline silicon solar cell can be obtained by electroplating copper on both sides of the solar cell silicon substrate with a nickel-plated layer.

[0088] The present invention is further described below by specific examples and comparative examples, but it should be understood that these examples are only used for more detailed description and should not be understood as limiting the present invention in any form. The raw materials used in the examples and comparative examples of the present invention, if no specific conditions are specified, are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0089] Example 1

[0090] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells, and the specific preparation process is as follows:

[0091] 1. Laser-opening a silicon substrate to form a patterned groove, wherein the width of the patterned groove is 20 μm, to obtain a silicon substrate after opening the film.

[0092] 2. Place the opened solar cell silicon substrate in a roughening solution containing 5% hydrofluoric acid, 18% ammonium fluoride, 0.3% alkyl sulfonate, and the balance water. The immersion roughening temperature is 30°C, the roughening time is 3 minutes, then take it out, clean it with deionized water and dry it.

[0093] 3. A layer of activation solution was screen-printed on the roughened surface of the solar cell silicon substrate. The activation solution was a nickel citrate sol obtained by water bathing 10 g / L citric acid and 14 g / L basic nickel carbonate in a 60°C reactor for 24 hours. The activation solution was dried at 40°C for 10 minutes, and then the silicon substrate was laser scanned and activated with an infrared laser. The working parameters of the laser activation were: power 4W, spot diameter 18um, scanning rate 500mm / s, and a silicon substrate containing an activation layer was obtained.

[0094] 4. Immerse the silicon substrate containing the activation layer in a chemical nickel plating solution containing 25g / L nickel sulfamate, 20g / L sodium hypophosphite, 13g / L sodium citrate, and 14g / L sodium borohydride. Plate nickel for 3 minutes at a pH of 7.0-8.0 and a temperature of 75°C, then wash with water and dry.

[0095] Example 2

[0096] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells, and the specific preparation process is as follows:

[0097] 1. Laser-opening a silicon substrate to form a patterned groove, wherein the width of the patterned groove is 20 μm, to obtain a silicon substrate after opening the film.

[0098] 2. Place the opened solar cell silicon substrate in a roughening solution containing 1% hydrofluoric acid, 30% ammonium fluoride, 0.3% alkyl sulfonate, and the remainder water. The roughening temperature is 30°C, the roughening time is 3 minutes, then take it out, clean it with deionized water and dry it.

[0099] 3. A layer of activation solution was screen-printed on the roughened surface of the solar cell silicon substrate. The activation solution was a nickel citrate sol obtained by water bathing 6g / L citric acid and 20g / L basic nickel carbonate in a 70°C reactor for 12 hours. The activation solution was dried at 20°C for 15 minutes, and then the silicon substrate was laser scanned and activated with an infrared laser. The working parameters of the laser activation were: power 2W, spot diameter 15um, scanning rate 1000mm / s, and a silicon substrate containing an activation layer was obtained.

[0100] 4. Immerse the silicon substrate containing the activation layer in a chemical nickel plating solution containing 20g / L nickel sulfamate, 15g / L sodium hypophosphite, 10g / L sodium citrate, and 10g / L sodium borohydride. Plate nickel for 1 minute at a pH of 7.0-8.0 and a temperature of 80°C, then wash with water and dry.

[0101] Example 3

[0102] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells, and the specific preparation process is as follows:

[0103] 1. Laser-opening a silicon substrate to form a patterned groove, wherein the width of the patterned groove is 20 μm, to obtain a silicon substrate after opening the film.

[0104] 2. Place the opened solar cell silicon substrate in a roughening solution containing 10% hydrofluoric acid, 10% ammonium fluoride, 0.5% alkyl sulfonate, and the remainder water. The immersion roughening temperature is 40°C, the roughening time is 1 minute, then take it out, clean it with deionized water and dry it.

[0105] 3. A layer of activation liquid was screen-printed on the roughened surface of the solar cell silicon substrate. The activation liquid was a nickel citrate sol obtained by water bathing 15g / L citric acid and 8g / L basic nickel carbonate in a 60°C reactor for 24 hours. After drying the activation liquid at 60°C for 3 minutes, the silicon substrate was laser scanned and activated with an infrared laser. The working parameters of the laser activation were: power 5W, spot diameter 20um, scanning rate 100mm / s, and a silicon substrate containing an activation layer was obtained.

[0106] 4. Immerse the silicon substrate containing the activation layer in a chemical nickel plating solution containing 30 g / L nickel sulfamate, 25 g / L sodium hypophosphite, 15 g / L sodium citrate, and 18 g / L sodium borohydride. Plate nickel for 2 minutes at a pH of 7.0-8.0 and a temperature of 75°C, then wash with water and dry.

[0107] Example 4

[0108] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Embodiment 1 is that the operating parameters of the laser activation in Step 3 are: power 1W, spot diameter 5um, scanning rate 1000mm / s, and the remaining steps and operating parameters are the same as those in Embodiment 1 and will not be repeated here.

[0109] Example 5

[0110] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Embodiment 1 is that the operating parameters of the laser activation in step 3 are: power 8 W, spot diameter 30 um, scanning rate 50 mm / s, and the remaining steps and operating parameters are the same as those in Embodiment 1 and will not be repeated here.

[0111] Example 6

[0112] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that the activation solution is a nickel oxalate sol obtained by bathing 10 g / L oxalic acid and 14 g / L basic nickel carbonate in a 60° C. reactor for 24 hours. The remaining steps and operating parameters are the same as those in Example 1 and will not be repeated here.

[0113] Example 7

[0114] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that the activation solution is a nickel formate sol obtained by bathing 10 g / L formic acid and 14 g / L basic nickel carbonate in a 60° C. reactor for 24 hours. The remaining steps and operating parameters are the same as those in Example 1 and will not be repeated here.

[0115] Example 8

[0116] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that the activation solution is a nickel acetate sol obtained by bathing 10 g / L acetic acid and 14 g / L basic nickel carbonate in a 60° C. reactor for 24 hours. The remaining steps and operating parameters are the same as those in Example 1 and will not be repeated here.

[0117] Example 9

[0118] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that the activation solution is a nickel citrate sol obtained by bathing 20 g / L citric acid and 30 g / L basic nickel carbonate in a 60° C. reactor for 24 hours. The remaining steps and operating parameters are the same as those in Example 1 and will not be repeated here.

[0119] Example 10

[0120] This embodiment provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that the activation solution is a nickel citrate sol obtained by bathing 5 g / L citric acid and 5 g / L basic nickel carbonate in a 60° C. reactor for 24 hours. The remaining steps and operating parameters are the same as those in Example 1 and will not be repeated here.

[0121] Comparative Example 1

[0122] This comparative example provides a palladium-free nickel plating process for a crystalline silicon solar cell. The difference from Example 1 is that step 3 is omitted, and chemical nickel plating is directly performed on the roughened silicon substrate of the solar cell. The remaining raw materials and methods are the same as those in Example 1 and will not be repeated here.

[0123] Comparative Example 2

[0124] This comparative example provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that step 2 and step 3 are omitted, and chemical nickel plating is directly performed on the silicon substrate after film opening. The remaining raw materials and methods are the same as those in Example 1 and will not be repeated here.

[0125] Comparative Example 3

[0126] This comparative example provides a palladium-free nickel plating process for crystalline silicon solar cells. The difference from Example 1 is that step 2 is omitted, and the activation solution is directly screen-printed on the silicon substrate after film opening. The remaining raw materials and methods are the same as those in Example 1 and will not be repeated here.

[0127] Test Case

[0128] The silicon substrate containing the nickel layer obtained in the embodiment and the comparative example was subjected to a nickel layer bonding test, and the test method was as follows:

[0129] 1. The bonding strength between the nickel layer and the silicon substrate: 3M tape test;

[0130] 2. Welding tensile force: The silicon substrate containing the nickel layer enters the electroplating process to form a copper conductive layer with a thickness of 8 to 12 μm. Then, the welding tensile force test is carried out at the PAD point on the copper conductive layer under low temperature conditions (180 to 200°C) (double-sided electroplating involves testing the tensile force on the front and back sides, where the tensile force on both sides is the average value of the 12 test points ≥ 0.8N, and the tensile force on the front side is higher than that on the back side).

[0131] The specific test results are shown in Table 1 (where “ / ” means welding cannot be completed):

[0132] Table 1

[0133]

[0134] As can be seen from Table 1, the present invention uses laser scanning on the surface of the silicon substrate to activate the film-opening area by controlling the laser movement, and deposits a uniform nickel activation layer on the surface, which has a strong catalytic effect on the subsequent chemical nickel plating reaction and can form a complete nickel plating layer in a short time. The surface is uniform and dense and the bonding force is good.

[0135] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A palladium-free nickel plating process for crystalline silicon solar cells, characterized in that: The following steps are involved: A. Printing an activation liquid on the surface of a silicon substrate, drying it, and then activating it to obtain a silicon substrate containing an activation layer; The activation method is laser scanning activation, the power of the laser scanning activation is 2W~5W, the spot diameter is 15μm~20μm, and the scanning rate is 100mm / s~1000mm / s; B, chemically plating nickel on the silicon substrate containing the activation layer to obtain a nickel layer; Wherein, the activation solution is a nickel-containing sol; The nickel-containing sol includes at least one of nickel citrate sol, nickel oxalate sol, nickel formate sol and nickel acetate sol.

2. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: The nickel-containing sol is obtained by reacting an organic weak acid with basic nickel carbonate; Among them, the reaction temperature is 60℃~70℃; the reaction time is 12h~24h.

3. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 2, characterized in that: The organic weak acid includes at least one of oxalic acid, formic acid, acetic acid and citric acid.

4. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 2, characterized in that: The mass ratio of the organic weak acid to the basic nickel carbonate is 6-15:8-20.

5. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: In step A, the activation temperature is 40° C. to 80° C., and the activation time is 5 min to 20 min.

6. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: The silicon substrate is subjected to film opening and roughening treatments.

7. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 6, characterized in that: The silicon substrate after film opening is obtained by forming patterned grooves on the silicon substrate through laser film opening.

8. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 7, characterized in that: The width of the patterned groove is 15 μm to 60 μm.

9. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 6, characterized in that: The opened silicon substrate is placed in a roughening solution for roughening, and then washed and dried to obtain a roughened silicon substrate.

10. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 9, characterized in that: The roughening solution includes 1wt.%~10wt.% of hydrofluoric acid, 10wt.%~30wt.% of ammonium fluoride, 0.1wt.%~0.5wt.% of surfactant, and the balance is deionized water.

11. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 10, characterized in that: The surfactant includes at least one of alkyl sulfonate, fatty alcohol sulfate and fatty alcohol polyoxyethylene ether sulfate.

12. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 9, characterized in that: The roughening temperature is 20°C to 40°C, and the time is 1 min to 5 min.

13. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 9, characterized in that: In step A, the drying temperature is 20°C to 60°C, and the drying time is 3min to 15min.

14. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: In step B, chemical nickel plating is performed using a chemical nickel plating solution.

15. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 14, characterized in that: In terms of weight parts, the chemical nickel plating solution comprises 20 to 30 parts of nickel salt, 25 to 43 parts of reducing agent and 10 to 15 parts of complexing agent per unit volume.

16. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 15, characterized in that: The nickel salt includes at least one of nickel sulfamate, nickel sulfate and nickel acetate.

17. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 15, characterized in that: The reducing agent includes sodium hypophosphite and / or sodium borohydride.

18. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 15, characterized in that: The complexing agent includes at least one of citrate, pyrophosphate and ammonium salt.

19. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: In step B, the pH of the chemical nickel plating is 7.0-8.0, the temperature is 70° C.-80° C., and the time is 1 min-4 min.

20. The palladium-free nickel plating process for crystalline silicon solar cells according to claim 1, characterized in that: In step B, the thickness of the nickel layer after nickel plating is 0.4 μm to 1.2 μm.

21. A crystalline silicon solar cell, characterized in that: The crystalline silicon solar cell is produced by the palladium-free nickel plating process according to any one of claims 1 to 20.

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