Silver-coated nickel paste, its preparation method, and method for metallizing high-temperature sintered crystalline silicon solar cells

Abstract

The present invention belongs to the field of conductive pastes, and discloses a silver-coated nickel paste, a preparation method thereof, and a method for metallizing a high-temperature sintered crystalline silicon solar cell. In the silver-coated nickel paste, the conductive powder accounts for 80-95% by mass of the paste, and the components are silver-coated nickel powder and micron silver powder; the glass powder is 1-6%; the organic resin is 0.1-3%; the thixotropic agent is 0.5-0.8%; other additives are 0-1% and the balance is solvent. Among them, the conductive powder is a mixture of silver-coated nickel powder and silver powder with a mass ratio of 1:(0-50); the resistivity of the used silver-coated nickel powder is ≤96 μΩ·cm, the oxidation-resistant resistivity is ≤205 μΩ·cm, and the titrated nickel content is ≤0.01 mol / L; when using this silver-coated nickel paste to single-backprint crystalline silicon solar cell wafers, compared with pure silver paste, the line resistance is slightly higher, the contact resistance is basically the same, and the printing wet weight is basically the same. After adjustment, the efficiency is 0% to 2% lower than that of pure silver paste, and it can be used to replace the silver paste of crystalline silicon solar cells with pure silver powder. The present invention correspondingly discloses a preparation method of the silver-coated nickel paste and a method for metallizing a high-temperature sintered crystalline silicon solar cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive pastes, and particularly relates to silver-coated nickel paste and its preparation method, and a method for metallizing high-temperature sintered crystalline silicon solar cells. Background Art

[0002] Currently, the metallization of crystalline silicon solar cells mainly adopts processes such as screen printing with silver paste, drying, and then high-temperature sintering. Due to the high silver content in the paste, the metallization process cost of crystalline silicon solar cells is relatively high.

[0003] In order to reduce the silver content in the paste, silver-coated nickel powder is used to partially replace silver powder to make the paste in related technologies. CN118367063A discloses a method for metallizing TOPcon solar cells using silver-coated nickel paste and a solar cell. The silver-coated nickel conductive paste used therein contains 25-95% silver-coated nickel powder, 0-70% silver powder, 1-6% glass powder, 0.1-3% organic resin, 0.1-1% dispersant, 0-5% nickel diffusion regulator, and the balance is solvent. Free nickel will be generated during the metallization process of this kind of paste. Nickel is easily oxidized to nickel oxide during the high-temperature sintering metallization process of TOPcon solar cells, increasing the line resistance of TOPcon solar cells, thereby limiting the improvement of the conversion efficiency of TOPcon solar cells. During the metallization process, it is necessary to rely on a nickel diffusion regulator and secondary laser sintering to form a nano-nickel tunneling layer and prevent the formation of large-size nickel metal particles and nickel "dead layers" from affecting the photoelectric conversion efficiency of the cell.

[0004] However, the amount of free nickel generated during the metallization process is not controllable, and the effect of the nickel diffusion regulator cannot completely prevent / eliminate the negative effects brought by free nickel. Summary of the Invention

[0005] The purpose of the present invention is to provide a silver-coated nickel paste and its preparation method, and a method for metallizing high-temperature sintered crystalline silicon solar cells.

[0006] In the present invention, without special instructions, "antioxidant resistivity" refers to the resistivity obtained by testing the powder after calcination at 180°C for 10 minutes; the "titrated nickel content" is tested according to the method described in CN118961994A. A lower titrated nickel content indicates better compactness of the silver coating layer. The specific testing steps are as follows:

[0007] (1) Accurately weigh 2.00 g (error ≤ 0.001 g) of silver-coated nickel powder and add it to a clean 50 mL centrifuge tube;

[0008] (2) Add 30 g of a 3% dilute sulfuric acid solution and 800 μL of a 20% hydrogen peroxide solution to the above centrifuge tube, cover the lid, and place it on a shaker to shake and mix evenly to obtain a mixed solution; among them, the shaker frequency is 300 r / min, and the shaking time is 5 min;

[0009] (3) After the shaking is completed, quickly take out the centrifuge tube and centrifuge it on a centrifuge (pay attention to balancing). The centrifugation speed reaches 6000 rpm. The above process needs to be completed quickly. After centrifugation, take the supernatant in the centrifuge tube into a new centrifuge tube for standby;

[0010] (4) Accurately measure 20 mL of the supernatant of the above mixed solution with a pipette and add it to a 250 mL conical flask, and add 50 mL of deionized water to the conical flask and shake well; use a burette to add 19 mL of ammonium chloride buffer solution and 0.01 g of murexide indicator to the conical flask and shake well. The solution turns bright yellow to obtain a test solution;

[0011] (5) Pour a 0.05 mol / L disodium ethylenediaminetetraacetate standard solution into the burette to a scale of 10 mL, and titrate the test solution with a 0.05 mol / L disodium ethylenediaminetetraacetate standard solution at a low speed until the test solution turns purple and stop titrating. Shake for 30 s and if it does not turn back to the original color, it is the titration end point. Record the volume of the 0.05 mol / L disodium ethylenediaminetetraacetate standard solution consumed in the titration;

[0012] (6) Calculation of titration result: The calculation formula is c = V1 * C1 / V. In the formula,

[0013] c: Free nickel content, unit: mol / L;

[0014] C1: Concentration of disodium ethylenediaminetetraacetate standard solution, unit: mol / L;

[0015] V1: Volume of disodium ethylenediaminetetraacetate standard solution consumed in the titration, unit: mL;

[0016] V: Volume of the supernatant of the mixed solution taken, unit: mL.

[0017] First aspect, the present invention provides a silver-coated nickel paste, and adopts the following technical solution:

[0018] A silver-coated nickel paste is prepared from the following raw materials by weight percentage,

[0019] Conductive powder 80 - 95%,

[0020] Glass powder 1 - 6%,

[0021] Organic resin 0.1 - 3%,

[0022] Thixotropic agent: 0.5 - 0.8%,

[0023] Other additives: 0 - 1%,

[0024] Solvent: the balance;

[0025] Among them, the conductive powder is a mixture of silver-coated nickel powder and silver powder with a weight ratio of 1:(0 - 50); the resistivity of the used silver-coated nickel powder is ≤96 μΩ·cm, the oxidation-resistant resistivity is ≤205 μΩ·cm, and the titrated nickel content is ≤0.01 mol / L.

[0026] Furthermore, the silver content of the silver-coated nickel powder is 5 wt% - 50 wt%.

[0027] Furthermore, the silver content of the silver-coated nickel powder is 5 wt% - 25 wt%.

[0028] Furthermore, the silver-coated nickel powder is surface-modified, and the specific steps are as follows:

[0029] Using dry modification, 0.05% to 0.5% of the surface modifier based on the mass of the silver-coated nickel powder is mixed evenly with the silver-coated nickel powder to obtain the surface-modified silver-coated nickel powder.

[0030] Furthermore, the surface modifier is selected from one or more of terpineol, fatty acid, and dodecylbenzenesulfonic acid.

[0031] Furthermore, the particle size of the glass powder is 2 - 5 μm.

[0032] Furthermore, the glass powder is prepared from mixed raw materials through melting, cooling, and ball milling; the mixed raw materials are composed of the following components by weight percentage:

[0033] Lead oxide (PbO): 35.3% - 46.31%,

[0034] Silicon dioxide (SiO2): 5.38% - 13.2%,

[0035] Lithium oxide (Li2O): 2.64% - 4.16%,

[0036] Zinc oxide (ZnO): 1.85% - 3.5%,

[0037] Sodium oxide (Na2O): 1.22% - 1.76%,

[0038] Magnesium oxide (MgO): 0.43% - 2.61%,

[0039] Calcium oxide (CaO): 0.35% - 1.57%,

[0040] Tellurium oxide (TeO2): 0 - 30.53%,

[0041] Barium oxide (BaO) 0 - 21.72%,

[0042] Boron oxide (B2O3) 0 - 19.55%,

[0043] Tungsten oxide (WO3) 0 - 9.65%,

[0044] Copper oxide (CuO) 0 - 0.53%.

[0045] Further, the specific preparation steps of the glass powder are as follows: Weigh the raw materials according to the ratio and mix them to obtain a mixture; the mixture is melted at 1250 - 1300 °C for 1.5 h and then quenched to obtain glass fragments; the glass fragments are ground and sieved to obtain glass powder;

[0046] Further, during the preparation of the glass powder, the broken glass pieces are placed in a 20 L vertical ball mill, 15 kg of zirconia balls with a diameter of 5 - 10 mm are added, 2 kg of deionized water and oleic acid are added, and they are stirred at a speed of 250 r / min for 8 h to obtain glass slurry; the glass slurry is sieved and dried to obtain glass powder with a particle size of 2 - 5 μm.

[0047] Further, the organic resin is one or a mixture of more than one of PVB resin, rosin resin, acrylic resin, phenoxy resin, and ethyl cellulose.

[0048] Further, the thixotropic agent is one or a mixture of more than one of polyamide wax, hydrogenated castor oil, and polyethylene glycol.

[0049] Further, the other additives are one or a mixture of more than one of palmitic acid, silane coupling agent, dimethyl silicone oil, oleic acid, and TDO dispersant.

[0050] Further, the solvent is selected from one or more of tripropylene glycol monobutyl ether, dibutyl phthalate, terpineol, tributyl citrate, butyl carbitol, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and benzyl alcohol.

[0051] In a second aspect, the present invention provides a method for preparing silver-coated nickel paste, adopting the following technical solution:

[0052] For the method for preparing silver-coated nickel paste described in any one of the foregoing, weigh each raw material according to the ratio, and after preliminary mixing with a homogenizer, roll it with a three-roll mill to obtain it.

[0053] In a third aspect, the present invention provides a method for metallizing high-temperature sintered crystalline silicon solar cells, adopting the following technical solution:

[0054] A method for metallization of high-temperature fired crystalline silicon solar cells, which is mainly applicable to high-temperature fired crystalline silicon solar cells such as PERC, TOPcon, and BC, and uses the silver-coated nickel paste described in any one of the foregoing. The specific steps are as follows: screen-print the foregoing silver-coated nickel paste on the surface of the high-temperature fired crystalline silicon solar cell wafer, dry it, and sinter it in air at 500-750 °C to complete the metallization of the high-temperature fired crystalline silicon solar cell.

[0055] The present invention has the following beneficial effects:

[0056] The silver-coated nickel conductive paste provided by the present invention contains highly reliable silver-coated nickel powder with a dense coating and does not contain nickel diffusing agents. For single-backside printed high-temperature fired crystalline silicon solar cell wafers, compared with pure silver paste, the line resistance is slightly higher, the contact resistance is basically the same, the printing wet weight is basically the same, and the adjusted photoelectric conversion efficiency is 0% to 2% lower than that of pure silver paste. It can be used to replace the silver paste for high-temperature fired crystalline silicon solar cells made of pure silver powder.

[0057] When the silver-coated nickel conductive paste of the present invention is used in the method for metallization of high-temperature fired crystalline silicon solar cells, expensive silver is replaced by metallic nickel, and the conductive paste effectively reduces costs. Description of the Drawings

[0058] Figure 1 SEM image of the silver-coated nickel powder prepared in the preparation example;

[0059] Figure 2A 、 Figure 2B SEM cross-sectional image of the silver-coated nickel electrode after printing and sintering in Example 2. Detailed Embodiments

[0060] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will further elaborate on the present application.

[0061] Preparation Example

[0062] [Preparation of Silver-Coated Nickel Powder]

[0063] The preparation steps of the silver-coated nickel powder are as follows:

[0064] S1 Surface pretreatment of nickel powder: Add 500 g of micron-sized nickel powder and 2.5 kg of deionized water to a beaker, stir and mix to form a suspension, then add 200 g of sodium bicarbonate while maintaining stirring and place the beaker in an ultrasonic bath to ultrasonically clean the nickel powder. Then, sediment and pour off the supernatant to obtain clean nickel powder, and then add 5 kg of deionized water and 200 g of sodium hydroxide, and stir to obtain an activated nickel powder suspension.

[0065] S2 Dispersion of nickel powder: After step S1 is completed and the supernatant is poured off after sedimentation, the activated nickel powder is obtained. Add 10 kg of deionized water and 200 g of polyethylene glycol 200 to the activated nickel powder, and stir evenly to form a silver-plated nickel powder suspension to be plated.

[0066] Preparation of S3 silver plating solution: Weigh 340 g of silver nitrate and dissolve it in 1 kg of deionized water, and then add 300 mL of concentrated ammonia water to form a complex silver plating solution.

[0067] S4 silver coating process: The prepared silver plating solution is dropped into the nickel powder suspension obtained in step S2 at a rate of 20 mL / min, while keeping stirring. After the dropping is completed, continue stirring and reacting for 30 min to chemically plate silver on the surface of the nickel powder. Then, add 300 g of potassium sodium tartrate to promote the complete reduction and deposition of silver ions on the surface of the nickel powder. After continuing to stir and react for 30 min, the coating process is ended.

[0068] S5 cleaning and drying: After step S4 is completed, the plating solution is allowed to settle and then the supernatant is poured off to obtain silver-coated nickel powder. Each time, 2 kg of deionized water is used for 3 times of stirring, washing, and centrifuging, and then each time 1 kg of absolute ethanol is used for 2 times of stirring, washing, and centrifuging processes to remove the residues adsorbed on the surface of the silver-coated nickel powder, obtaining wet and clean silver-coated nickel powder. The silver-coated nickel powder is put into a blast drying oven and dried at 70 °C for 6 h to obtain about 697 g of clean spherical silver-coated nickel powder.

[0069] S6 surface modification: 2 g of terpineol is evenly sprayed on 697 g of clean silver-coated nickel powder after drying, and then mixed evenly to obtain modified silver-coated nickel powder that can be used for preparing slurry. Figure 1 For preparing the SEM image of the silver-coated nickel powder.

[0070] Referring to the foregoing method, by adjusting the amount of silver nitrate used, several kinds of silver-coated nickel powders shown in Table 1 were respectively prepared, and their resistivity, antioxidant resistivity, and titrated nickel content were respectively measured.

[0071] Table 1. Performance parameter table of silver-coated nickel powder

[0072]

[0073] [Preparation of glass powder]

[0074] Weigh the raw materials according to the ratio shown in Table 2 and mix them to obtain a mixture; the mixture is melted at 1250 - 1300 °C for 1.5 h and then poured into deionized water for quenching to obtain glass fragments; after filtering out the water from the glass fragments, place them in a 20 L vertical ball mill, add 15 kg of zirconia balls with a diameter of 5 - 10 mm, add 2 kg of deionized water and oleic acid, stir at a speed of 250 r / min, and ball mill for 8 h to obtain glass slurry; finally, sieve and dry the glass slurry to obtain glass powder with a particle size of 2 - 5 μm.

[0075] Table 2. Raw material ratio table for preparing glass powder

[0076] Example

[0077] [Examples 1 - 6]

[0078] Weigh the raw materials according to the ratio in Table 3, first mix them preliminarily with a homogenizer, and then roll them with a three - roll mill to obtain silver - coated nickel paste.

[0079] Table 3. Raw material ratio table for Examples 1 - 6

[0080]

[0081] The glass powder used in Examples 1 - 6 was prepared by the method of Preparation Example; the conductive powder used was a mixture of silver powder and silver - coated nickel powder, and the specific composition of the conductive powder is shown in Table 4.

[0082] Table 4. Composition table of conductive powder for Examples 1 - 6

[0083]

[0084] Among them, in Example 4, two kinds of silver - coated nickel powders with silver contents of 50% (Preparation Example 6) and 30% (Preparation Example 2) were used, and the weight ratio of the two kinds of silver - coated nickel powders was 2.4:1. In other examples, self - made or commercially available silver - coated nickel powders of other specifications can be selected as raw materials, and one specification of silver - coated nickel powder can be used alone or multiple specifications of silver - coated nickel powders can be blended.

[0085] Control Example

[0086] [Control Example 1]

[0087] Control Example 1 was based on Example 1, and the difference was that the conductive powder was pure silver powder.

[0088] [Control Example 2]

[0089] Control Example 2 was a commercially available high - temperature sintered crystalline silicon solar cell high - temperature conductive paste from Heraeus, grade SOL3201.

[0090] [Control Examples 3 - 6]

[0091] Control Examples 3 - 6 were all based on Example 1, and the only difference was that the specifications of the silver - coated nickel powder in the conductive powder were different, as shown in Table 5 specifically.

[0092] Table 5. Specification table of silver - coated nickel powder for Control Examples 3 - 5

[0093]

[0094] Application Examples and Comparative Examples Application Examples

[0095] [Application Examples 1 - 6]

[0096] A method for metallization of high-temperature sintered crystalline silicon solar cells, using the silver-coated nickel pastes of Examples 1-6 respectively. The specific steps are as follows: screen-print the aforementioned silver-coated nickel paste on the surface of crystalline silicon solar cell wafers, dry it, and sinter it in air at 500-750 °C to complete the metallization of crystalline silicon solar cells. The SEM cross-sectional view of the silver-coated nickel electrode after printing and sintering with the silver-coated nickel paste of Example 2 is as Figure 2A , Figure 2B shown.

[0097] [Comparative Application Examples 1-5]

[0098] The difference between the comparative application examples and the application examples lies in that the slurries of Control Examples 1-5 are used respectively.

[0099] Performance Detection Test

[0100] For the high-temperature sintered crystalline silicon solar cells prepared by the metallization processes of Application Examples 1-6 and Comparative Application Examples 1-5 of the present invention, electrical performance detection is carried out.

[0101] [Total Wet Weight Detection of Back Auxiliary Grids]

[0102] Detect the weight change of a single 166 silicon wafer before and after printing by the differential method, measure 5 pieces, and take the average value.

[0103] [IV Test]

[0104] Use the commercially available IV tester "YP-CX5000" obtained from Ziyuan Spectrum Intelligence to characterize the solar cells at 25 °C ± 1.0 °C. The stroboscopic pulsed light simulates sunlight, and its AM1.5 intensity on the cell surface is known to be 1000 W / m². To make the simulator have this intensity, the stroboscopic pulsed light flashes several times in a short time until a stable level monitored by the "1.0.0.0" software of the IV tester is reached. The Ziyuan Spectrum IV tester uses the multi-point contact method to measure the current (I) and voltage (V) to determine the IV curve of the cell. All values are automatically determined from this curve by running the software package. As a reference standard sample, a calibrated solar cell obtained from ISE Freiburg with the same area size, the same wafer material, and the same front pattern is tested, and the data is compared with the certified values. Measure at least 20 wafers processed in exactly the same way, and analyze the data by calculating the average value of each value. The software provides the values of conversion efficiency and sheet resistance.

[0105] [Contact Resistance]

[0106] Balance all equipment and materials in an air-conditioned room at a temperature of 22 ± 1 °C before measurement. To measure the contact resistance of the fired electrodes on the doped front layer of a silicon solar cell, use an MLR-5104 on-resistance test system. This device estimates the contact resistance by the transfer length method (TLM) applying the 4-point measurement principle. To measure the contact resistance, cut two strips 1 cm wide from the wafer perpendicular to the printed grid lines of the wafer. Each strip measures its exact width with an accuracy of 0.05 mm. Measure the width of the fired sub-grid lines at 3 different points on each strip using a digital microscope "VHX-970F" equipped with a wide-range zoom lens VH-Z250 from Keyence Corp. Measure the width 10 times at 2-point measurements at each point. The grid line width value is the average of all 30 measurements. The software package calculates the contact resistance using the number of pointers, the strip width, and the distance between the printed sub-grids. Set the measurement current to 14 mA. Install a multi-contact measuring head suitable for contacting 11 adjacent grid lines and make it contact 11 adjacent grid lines. Measure at 10 equally spaced points on each strip. After starting the measurement, the software determines the value (mohm) of the contact resistance at each point on the strip. Take the average of all 20 points as the value of the contact resistance.

[0107] The test results are recorded in Table 6.

[0108] Table 6. Performance Detection Test Results Table

[0109]

[0110] From the data in the above table, it can be seen that: for the silver-coated nickel paste provided by the present invention, for single-back-printed crystalline silicon solar cell wafers, compared with pure silver paste, the line resistance is slightly higher, the contact resistance is basically the same, and the printing wet weight is basically the same. After adjustment, the efficiency is 0.03% - 0.1% lower than that of pure silver paste. That is, the method of replacing pure silver powder in the silver paste of crystalline silicon solar cells with highly reliable silver-coated nickel powder with a dense coating is feasible. When the silver-coated nickel paste of the present invention is used for the metallization of crystalline silicon solar cells, secondary laser sintering is not required.

[0111] The above are all preferred embodiments of this application. It does not limit the protection scope of this application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A method for metallization of a crystalline silicon solar cell, characterized in that, The specific steps are as follows: Screen-print silver-coated nickel paste on the surface of the crystalline silicon solar cell wafer, dry it, and sinter it in air at 500 - 750 °C to complete the metallization of the crystalline silicon solar cell. The silver-coated nickel paste is prepared from the following raw materials by weight percentage: Conductive powder: 80 - 95% Glass powder: 1 - 6% Organic resin: 0.1 - 3% Thixotropic agent: 0.5 - 0.8% Other additives: 0 - 1% Solvent: the balance; Among them, the conductive powder is a mixture of silver-coated nickel powder and silver powder with a weight ratio of 1:(0 - 50); The resistivity of the used silver-coated nickel powder is 30 - 49 μΩ·cm, the oxidation-resistant resistivity is 98 - 189 μΩ·cm, and the titrated nickel content is ≤0.01 mol / L; the silver content of the silver-coated nickel powder is 25 wt% - 50 wt%; The silver-coated nickel powder is subjected to surface modification treatment. The specific steps are as follows: Adopt dry modification. Mix 0.05% - 0.5% of the mass of the silver-coated nickel powder with terpineol and mix them evenly in the silver-coated nickel powder to obtain the surface-modified silver-coated nickel powder. The glass powder is prepared by melting, cooling, and ball milling the mixed raw materials; the mixed raw materials are composed of the following components by weight percentage: Lead oxide: 35.3% - 46.31% Silicon oxide: 5.38% - 13.2% Lithium oxide: 2.64% - 4.16% Zinc oxide: 1.85% - 3.5% Sodium oxide: 1.22% - 1.76% Magnesium oxide: 0.43% - 2.61% Calcium oxide: 0.35% - 1.57% Tellurium oxide: 0 - 30.53% Barium oxide: 0 - 21.72% Boron oxide: 0 - 19.55% Tungsten oxide: 0 - 9.65% Copper oxide: 0 - 0.53%; The specific preparation steps of the glass powder are as follows: Weigh the raw materials according to the ratio and mix them to obtain a mixture; melt the mixture at 1250 - 1300 °C for 1.5 h and then quench it to obtain glass fragments; place the broken glass pieces in a 20 L vertical ball mill, add 15 kg of zirconia balls with a diameter of 5 - 10 mm, add 2 kg of deionized water and oleic acid, stir at a speed of 250 r / min, and ball mill for 8 h to obtain a glass slurry; sieve and dry the glass slurry to obtain glass powder with a particle size of 2 - 5 μm.

2. The method for metallization of a crystalline silicon solar cell according to claim 1, characterized in that: The organic resin is a mixture of one or more of PVB resin, rosin resin, acrylic resin, phenoxy resin, and ethyl cellulose.

3. The method for metallization of a crystalline silicon solar cell according to claim 1, characterized in that: The thixotropic agent is a mixture of one or more of polyamide wax, hydrogenated castor oil, and polyethylene glycol.

4. The method for metallization of a crystalline silicon solar cell according to claim 1, characterized in that: The other additives are a mixture of one or more of palmitic acid, silane coupling agent, dimethyl silicone oil, oleic acid, and TDO dispersant.

5. The method for metallization of a crystalline silicon solar cell according to claim 1, wherein: The solvent is selected from one or more of tripropylene glycol butyl ether, dibutyl phthalate, terpineol, tributyl citrate, butyl carbitol, triethylene glycol butyl ether, diethylene glycol butyl ether, and benzyl alcohol.

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