A nickel-based base metal main grid paste, a preparation method and application thereof

Abstract

The application discloses a nickel-based base metal main grid slurry, which comprises the following components in percentage by mass: 70-85% of a conductive phase, 2-10% of a glass bonding phase, 0.5-5% of a composite solder additive, and 10-25% of an organic carrier; the conductive phase is a nickel-based composite powder with a core-shell-island structure and comprises the following: a core, a nickel-copper pre-alloyed inner core, wherein the mass of copper accounts for 5-30% of the mass of the nickel-copper pre-alloyed inner core; a shell, a silver coating layer, the mass of the silver coating layer being 10-40% of the mass of the nickel-copper pre-alloyed inner core; and islands, metal oxide nano-islands diffusedly distributed on the surface of the core-shell structure powder, the metal oxide nano-islands being one or more of bismuth oxide, zinc oxide and cobalt oxide, the nano-island particle size being 20-200 nm, and the surface coverage being 5-25%. The nickel-based base metal main grid slurry prepared by the application has the advantages of significantly improved tensile property, excellent welding performance, good conductive property and significantly reduced production cost.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic conductive paste technology. More specifically, this invention relates to a nickel-based base metal grid paste, its preparation method, and its application. Background Technology

[0002] With the advent of the era of grid parity for photovoltaic power generation, reducing the cost per kilowatt-hour has become a core demand of the industry. Silver paste used in the electrodes of crystalline silicon solar cells accounts for more than 50% of the non-silicon cost of the cells, and the persistently high price of silver powder has brought enormous cost pressure to cell manufacturers. Using base metals (such as nickel and copper) to replace silver powder in the preparation of conductive paste is the most direct way to reduce electrode costs.

[0003] Nickel powder, due to its high melting point, good anti-electromigration properties, and ability to form silicides with silicon, is considered an ideal base metal material to replace silver powder in the preparation of main grid paste. However, base metal main grid paste still faces three major technical bottlenecks in industrial applications: First, the tensile strength problem, as it is difficult to form ohmic contact between the base metal and the silicon substrate, and oxidation during sintering leads to increased contact resistance and decreased adhesion; second, the welding problem, as an oxide layer easily forms on the surface of the base metal, which is difficult to remove with conventional flux, resulting in poor solderability and insufficient pull-out force of the solder strip; and third, the electrical properties problem, as the intrinsic conductivity of base metal is lower than that of silver, and the density of the sintered film is difficult to control, resulting in a higher bulk resistivity.

[0004] To address the aforementioned issues, existing technologies have made various attempts. CN121237480A discloses a base metal main grid paste that uses surface-modified nickel powder combined with a dual-glass powder system to improve sintering density. CN119811744A improves welding performance by replacing some silver powder with molybdenum and nickel powder, combined with low-softening-temperature glass powder. However, existing solutions mostly focus on optimizing a single property, making it difficult to simultaneously achieve a balance between tensile strength, weldability, and electrical conductivity. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages of the present invention, a nickel-based base metal gate paste is provided, comprising, by mass percentage: 70-85% conductive phase, 2-10% glass binder phase, 0.5-5% composite solder additive, and 10-25% organic carrier; The conductive phase is a nickel-based composite powder with a core-shell-island structure, comprising: Core: Nickel-copper pre-alloyed core, wherein copper accounts for 5-30% of the mass of the nickel-copper pre-alloyed core; Shell: Silver cladding, the mass of which is 10-40% of the mass of the nickel-copper pre-alloyed core; Island: Metal oxide nano-islands dispersed on the surface of core-shell structured powder. The metal oxide nano-islands are one or more of bismuth oxide, zinc oxide, and cobalt oxide. The nano-island particle size is 20~200nm and the surface coverage is 5~25%.

[0007] Preferably, the glass binder phase is a gradient softening point composite glass powder, comprising a first glass powder and a second glass powder, wherein the mass ratio of the first glass powder to the second glass powder is 1~2:1~9; the softening point of the first glass powder is 400~520℃, and by mass percentage comprises: PbO 30~60%, TeO 20~10%, SiO 210~30%, TiO 210~20%, B 2O 35~10%, Al 2O 35~15%; the softening point of the second glass powder is 550~650℃, and by mass percentage comprises: Bi 2O 32~15%, TeO 21~10%, SiO 20~40%, CuO 10~15%, MnO 5~10%, V 2O 52~10%, ZnO 5~15%.

[0008] Preferably, the composite solder additive is a mixture of Sn-Bi alloy powder and Cu3P powder, wherein the weight ratio of Sn-Bi alloy powder to Cu3P powder in the mixture is 2~5:1, and the mass percentage of Bi in the Sn-Bi alloy powder is 30~60%.

[0009] Preferably, the organic carrier comprises, by mass percentage: 10-20% resin, 70-85% organic solvent, 2-5% thixotropic agent and 1-5% dispersant.

[0010] Preferably, the resin is one or two of ethyl cellulose and acrylic resin; the organic solvent is one or two of terpineol and butyl carbitol; the thixotropic agent is hydrogenated castor oil; and the dispersant is triethanolamine.

[0011] A method for preparing the nickel-based base metal gate paste as described above includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix nickel powder and copper powder, and mechanically alloy or atomize and melt under a protective atmosphere to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm. Step 2, Surface coating with silver layer: Add the pre-alloyed powder to the chemical plating solution and stir to react, then filter, wash, and vacuum dry to obtain core-shell structured powder; Step 3: Constructing nanoislands: The core-shell structured powder is added to a metal oxide precursor solution, ultrasonically dispersed, spray-dried, and then subjected to low-temperature heat treatment to obtain a conductive phase; Step 4: Preparation of glass binder phase: Prepare first glass powder and second glass powder separately, then mix them evenly to obtain glass binder phase; Step 5: Preparation of composite solder additive: Mix Sn-Bi alloy powder and Cu3P powder evenly to obtain composite solder additive; Step 6: Preparation of organic carrier: Dissolve the resin in an organic solvent, add thixotropic agent and dispersant, heat and stir to dissolve, filter, and obtain organic carrier; Step 7, Slurry Mixing: The conductive phase, glass binder phase, composite solder additive and organic carrier are put into a planetary mixer and mixed evenly. After being rolled by three rollers and filtered, nickel-based base metal grid slurry is obtained.

[0012] Preferably, in step one, the D50 of the nickel powder is 1~3μm, the D50 of the copper powder is 1~3μm, the protective atmosphere is argon, the mechanical alloying is carried out using a high-energy ball mill, the ball milling speed is 400~500rpm / min, the ball-to-material ratio is 10~30:1, and the ball milling time is 4~8h; in step two, the mass-volume ratio of the pre-alloyed powder and the chemical plating solution is 1g:5~15mL, the concentration of silver nitrate in the chemical plating solution is 20g / L, the concentration of ammonia is 50mL / L, the concentration of potassium sodium tartrate is 0.05~0.2mol / L, the stirring reaction time is 20~40min, the vacuum drying temperature is 50~60℃, and the vacuum drying time is 6~10h; In step three, the mass-to-volume ratio of core-shell structured powder to metal oxide precursor solution is 80-120 g: 500-1000 mL. The metal oxide precursor solution is one of bismuth nitrate-anhydrous ethanol solution, zinc nitrate-anhydrous ethanol solution, or cobalt nitrate-anhydrous ethanol solution. The concentration of bismuth ions, zinc ions, or cobalt ions in the metal oxide precursor solution is 0.01-0.1 mol / L. The ultrasonic dispersion time is 20-40 min. The spray drying gas is nitrogen, and the feed rate is 2-5 mL / min. The low-temperature heat treatment uses a tube furnace, the low-temperature heat treatment temperature is 300-450℃, the low-temperature heat treatment time is 10-30 min, and the heat treatment atmosphere is nitrogen or argon.

[0013] Preferably, in step four, the method for preparing the first and second glass powders is as follows: the metal oxide raw material is melted and quenched at 1100~1300℃ and then ball-milled until D50 < 5μm; in step five, the D50 of the Sn-Bi alloy powder is 2~8μm, the D50 of the Cu3P powder is 1~6μm, and the mass ratio of Sn-Bi alloy powder to Cu3P powder is 1~5:1; in step six, the heating and stirring temperature is 80~90℃, and the heating and stirring time is 1~3h; in step seven, the mixing time is 20~40min, the three-roll milling is performed 3~7 times, and the filtration is done by passing through a 200-mesh sieve.

[0014] A photovoltaic cell, wherein the main grid electrode of the photovoltaic cell is obtained by printing and sintering the nickel-based base metal grid paste described above.

[0015] Preferably, the peak sintering temperature of the photovoltaic cell is 700~800℃, and the sintering time is 1~5s.

[0016] The present invention has at least the following beneficial effects: 1. Significantly improved tensile strength: Through the core-shell-island structure design, the nano-islands induce a uniform distribution of the glass phase, avoiding local stress concentration; the gradient glass powder matches the sintering curve, promoting the full reaction of the nickel-silicon alloy. Tests show that the tensile strength between the main gate and the silicon substrate after sintering of the paste of this invention can reach 3.5-4.2N, comparable to pure silver paste.

[0017] 2. Excellent welding performance: The composite solder additives work synergistically during the welding process to effectively remove the oxide film on the base metal surface, the Sn-Bi alloy melts and spreads, and Cu3P is decomposed and reduced. The pull-out force of the solder strip can reach more than 2.5N, which meets the requirements of the component end.

[0018] 3. Excellent electrical conductivity: The nickel-copper pre-alloyed core improves the intrinsic conductivity of the base metal phase; the silver coating provides a continuous conductive path; the sintered film has high density and the bulk resistivity can be controlled at 5-8 μΩ·cm, which is close to the level of pure silver paste.

[0019] 4. Significantly reduces production costs: The amount of silver used is reduced by more than 50% compared to pure silver paste, greatly reducing the cost of electrode materials.

[0020] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0021] Figure 1 This is a structural diagram of the core-shell-island structured conductive phase prepared in Example 1 of the present invention; Figure 2 This is an image showing the electrode peeling morphology obtained from the nickel-based base metal gate paste prepared in Example 1 of this invention. Figure 3 This is an image showing the electrode peeling morphology obtained from the slurry prepared in Comparative Example 3 of this invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0023] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0024] Example 1 A method for preparing a nickel-based base metal gate paste includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix 90g of nickel powder (D50=1.5μm) with 10g of copper powder (D50=1.2μm), put them into a high-energy ball mill, and ball mill for 6 hours at a speed of 450rpm / min and a ball-to-material ratio of 20:1 under argon atmosphere protection to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm; Step 2: Surface silver coating: 100g of pre-alloyed powder was added to 1L of chemical plating solution (containing 20g / L silver nitrate, 50mL / L ammonia, and 0.1mol / L sodium potassium tartrate), stirred for 30min, filtered, washed, and vacuum dried at 55℃ for 8h to obtain core-shell structured powder; the mass of silver coating determined by the weight gain method was 25% of the mass of the nickel-copper pre-alloyed powder. Step 3: Construction of Nanoislands: 100g of core-shell structured powder was added to 800mL of metal oxide precursor solution (bismuth nitrate-anhydrous ethanol solution, bismuth ion concentration 0.05mol / L), and ultrasonically dispersed for 30min until the suspension was uniform and stable with no obvious sedimentation. Then, it was spray-dried (using nitrogen, with the feed rate controlled at 3mL / min), and then placed in a tube furnace for heat treatment at 350℃ for 20min under a nitrogen atmosphere to obtain a conductive phase with a core-shell-island structure of bismuth oxide nanoislands dispersed on the surface. SEM observation showed that the nanoisland particle size was 50~150nm and the surface coverage was 15%. Step 4: Preparation of the glass binder phase: Preparation of the first glass powder: 45% PbO, 20% SiO2, 15% TiO2, 5% B2O3 and 15% Al2O3 were melted and quenched at 1200℃ and then ball-milled to D50=1.2μm to obtain the first glass powder with a softening point of 480℃. Preparation of the second glass powder: 15% Bi2O3, 7% TeO2, 30% SiO2, 15% CuO, 10% MnO, 8% V2O5 and 15% ZnO were melted and quenched at 1200℃ and then ball-milled to D50=1.0μm to obtain the second glass powder with a softening point of 590℃. The first glass powder and the second glass powder are mixed evenly at a mass ratio of 1:9 to obtain a glass binder phase. Step 5: Preparation of composite solder additive: Sn-Bi alloy powder (D50=5μm, Bi mass percentage is 40%) and Cu3P powder (D50=3μm) are mixed evenly at a mass ratio of 3:1 to obtain composite solder additive; Step 6: Preparation of organic carrier: Dissolve 8% ethyl cellulose and 5% acrylic resin in 75% terpineol and 7% butyl carbitol by mass percentage, add 3% hydrogenated castor oil and 2% triethanolamine, heat and stir at 85°C for 2 hours to dissolve, filter to obtain organic carrier; Step 7: Slurry mixing: According to the mass percentage, add 82% conductive phase, 2.5% glass binder phase, 0.5% composite solder additive and 15% organic carrier into a planetary mixer, mix for 30 minutes, roll five times with three rollers, and filter with 200 mesh to obtain nickel-based base metal grid slurry.

[0025] Example 2 A method for preparing a nickel-based base metal gate paste includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix 80g of nickel powder (D50=1.5μm) with 20g of copper powder (D50=1.2μm), put them into a high-energy ball mill, and ball mill for 6 hours under argon atmosphere protection at a speed of 450rpm / min and a ball-to-material ratio of 20:1 to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm; Step 2: Surface silver coating: Add 100g of pre-alloyed powder to 1L of chemical plating solution (containing 20g / L silver nitrate, 50mL / L ammonia, and 0.08mol / L sodium potassium tartrate), stir for 30min, filter, wash, and vacuum dry at 55℃ for 8h to obtain core-shell structured powder; the mass of silver coating determined by the weight gain method is 15% of the mass of the nickel-copper pre-alloyed powder. Step 3: Construction of Nanoislands: 100g of core-shell structured powder was added to 1000mL of metal oxide precursor solution (zinc nitrate-anhydrous ethanol solution, zinc ion concentration 0.03mol / L). After ultrasonic dispersion for 30min, the suspension was uniform and stable with no obvious sedimentation. Then, it was spray-dried (using nitrogen, with the feed rate controlled at 3mL / min). The solution was then placed in a tube furnace and heat-treated at 350℃ for 20min under a nitrogen atmosphere to obtain a conductive phase with a core-shell-island structure of zinc oxide nanoislands dispersed on the surface. SEM observation showed that the nanoisland particle size was 50~150nm and the surface coverage was 10%. Step 4: Preparation of the glass binder phase: Preparation of the first glass powder: 45% PbO, 20% SiO2, 15% TiO2, 5% B2O3 and 15% Al2O3 were melted and quenched at 1200℃ and then ball-milled to D50=1.2μm to obtain the first glass powder with a softening point of 480℃. Preparation of the second glass powder: 15% Bi2O3, 7% TeO2, 30% SiO2, 15% CuO, 10% MnO, 8% V2O5, and 15% ZnO were melted and quenched at 1200℃ and then ball-milled to D50=1.0μm to obtain the second glass powder with a softening point of 590℃. The first glass powder and the second glass powder are mixed evenly at a mass ratio of 1:1.5 to obtain a glass binder phase; Step 5: Preparation of composite solder additive: Sn-Bi alloy powder (D50=5μm, Bi mass percentage is 50%) and Cu3P powder (D50=3μm) are mixed evenly at a mass ratio of 4:1 to obtain composite solder additive; Step 6: Preparation of organic carrier: Dissolve 8% ethyl cellulose and 5% acrylic resin in 75% terpineol and 7% butyl carbitol by mass percentage, add 3% hydrogenated castor oil and 2% triethanolamine, heat and stir at 85°C for 2 hours to dissolve, filter to obtain organic carrier; Step 7: Slurry mixing: According to the mass percentage, add 82% conductive phase, 2.5% glass binder phase, 0.5% composite solder additive and 15% organic carrier into a planetary mixer, mix for 30 minutes, roll five times with three rollers, and filter with 200 mesh to obtain nickel-based base metal grid slurry.

[0026] Example 3 A method for preparing a nickel-based base metal gate paste includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix 95g of nickel powder (D50=1.5μm) with 5g of copper powder (D50=1.2μm), put them into a high-energy ball mill, and ball mill for 6 hours at a speed of 450rpm / min and a ball-to-material ratio of 20:1 under argon atmosphere protection to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm; Step 2: Surface silver coating: 100g of pre-alloyed powder was added to 1L of chemical plating solution (containing 20g / L silver nitrate, 50mL / L ammonia, and 0.2mol / L sodium potassium tartrate), stirred for 30min, filtered, washed, and vacuum dried at 55℃ for 8h to obtain core-shell structured powder; the mass of silver coating determined by the weight gain method was 35% of the mass of the nickel-copper pre-alloyed powder. Step 3: Construction of Nanoislands: 100g of core-shell structured powder was added to 500mL of metal oxide precursor solution (cobalt nitrate-anhydrous ethanol solution, cobalt ion concentration 0.08mol / L), and ultrasonically dispersed for 30min until the suspension was uniform and stable with no obvious sedimentation. Then, it was spray-dried (using nitrogen, with the feed rate controlled at 3mL / min), and then placed in a tube furnace for heat treatment at 350℃ for 20min under a nitrogen atmosphere to obtain a conductive phase with a core-shell-island structure of cobalt oxide nanoislands dispersed on the surface. SEM observation showed that the nanoisland particle size was 50~150nm and the surface coverage was 20%. Step 4: Preparation of the glass binder phase: Preparation of the first glass powder: 45% PbO, 20% SiO2, 15% TiO2, 5% B2O3 and 15% Al2O3 were melted and quenched at 1200℃ and then ball-milled to D50=1.2μm to obtain the first glass powder with a softening point of 480℃. Preparation of the second glass powder: 15% Bi2O3, 7% TeO2, 30% SiO2, 15% CuO, 10% MnO, 8% V2O5, and 15% ZnO were melted and quenched at 1200℃ and then ball-milled to D50=1.0μm to obtain the second glass powder with a softening point of 590℃. The first glass powder and the second glass powder are mixed evenly at a mass ratio of 1.5:1 to obtain a glass binder phase; Step 5: Preparation of composite solder additive: Sn-Bi alloy powder (D50=5μm, Bi mass percentage is 30%) and Cu3P powder (D50=3μm) are mixed evenly at a mass ratio of 2:1 to obtain composite solder additive; Step 6: Preparation of organic carrier: Dissolve 8% ethyl cellulose and 5% acrylic resin in 75% terpineol and 7% butyl carbitol by mass percentage, add 3% hydrogenated castor oil and 2% triethanolamine, heat and stir at 85°C for 2 hours to dissolve, filter to obtain organic carrier; Step 7: Slurry mixing: According to the mass percentage, add 82% conductive phase, 2.5% glass binder phase, 0.5% composite solder additive and 15% organic carrier into a planetary mixer, mix for 30 minutes, roll five times with three rollers, and filter with 200 mesh to obtain nickel-based base metal grid slurry.

[0027] Comparative Example 1 A method for preparing a slurry includes the following steps: Step 1: Preparation of organic carrier: Dissolve 8% ethyl cellulose and 5% acrylic resin in 75% terpineol and 7% butyl carbitol by mass percentage, add 3% hydrogenated castor oil and 2% triethanolamine, heat and stir at 85°C for 2 hours to dissolve, filter to obtain organic carrier; Step 2, Slurry Mixing: According to the mass percentage, add 82.5% conductive phase (conventional silver-coated nickel powder), 2.5% glass powder (single glass powder with a softening point of 520℃) and 15% organic carrier into a planetary mixer, mix for 30 minutes, roll through three rollers 5 times, and filter through a 200-mesh filter to obtain the slurry.

[0028] Comparative Example 2 A method for preparing a nickel-based base metal gate paste includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix 90g of nickel powder (D50=1.5μm) with 10g of copper powder (D50=1.2μm), put them into a high-energy ball mill, and ball mill for 6 hours at a speed of 450rpm / min and a ball-to-material ratio of 20:1 under argon atmosphere protection to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm; Step 2: Surface silver coating: 100g of pre-alloyed powder was added to 1L of chemical plating solution (containing 20g / L silver nitrate, 50mL / L ammonia, and 0.1mol / L sodium potassium tartrate), stirred for 30min, filtered, washed, and vacuum dried at 55℃ for 8h to obtain a core-shell structured conductive phase; the mass of silver coating determined by the weight gain method was 25% of the mass of the nickel-copper pre-alloyed powder. Step 3: Preparation of the glass binder phase: Preparation of the first glass powder: 45% PbO, 20% SiO2, 15% TiO2, 5% B2O3 and 15% Al2O3 were melted and quenched at 1200℃ and then ball-milled to D50=1.2μm to obtain the first glass powder with a softening point of 480℃. Preparation of the second glass powder: 15% Bi2O3, 7% TeO2, 30% SiO2, 15% CuO, 10% MnO, 8% V2O5, and 15% ZnO were melted and quenched at 1200℃ and then ball-milled to D50=1.0μm to obtain a second glass powder with a softening point of 590℃. The first glass powder and the second glass powder are mixed evenly at a mass ratio of 1:9 to obtain a glass binder phase. Step 4: Preparation of composite solder additive: Sn-Bi alloy powder (D50=5μm, Bi mass percentage is 40%) and Cu3P powder (D50=3μm) are mixed evenly at a mass ratio of 3:1 to obtain composite solder additive; Step 5: Preparation of organic carrier: Dissolve 8% ethyl cellulose and 5% acrylic resin in 75% terpineol and 7% butyl carbitol by mass percentage, add 3% hydrogenated castor oil and 2% triethanolamine, heat and stir at 85°C for 2 hours to dissolve, filter to obtain organic carrier; Step 6, Slurry Mixing: According to the mass percentage, add 82% conductive phase, 2.5% glass binder phase, 0.5% composite solder additive and 15% organic carrier into a planetary mixer, mix for 30 minutes, roll five times with three rollers, and filter with 200 mesh to obtain nickel-based base metal grid slurry.

[0029] Comparative Example 3 The slurry preparation method in this comparative example is exactly the same as the formulation in Example 1 of CN121237480A. The preparation method uses a surface-coated nickel powder and dual glass powder system (without nano-island structure) and does not add composite solder additives.

[0030] Performance testing The slurries prepared in Examples 1-3 and Comparative Examples 1-3 were used to screen print main grid patterns on the same batch of TOPCon monocrystalline silicon wafers. After drying, the wafers were sintered in an infrared sintering furnace at a peak temperature of 760℃ for 3 seconds. The bulk resistivity, tensile strength, tensile strength standard deviation, and welding yield were tested, and the test results are shown in Table 1.

[0031] Table 1 Test results show that the slurries prepared in Examples 1-3 of this invention are significantly superior to those in Comparative Examples 1-3 in terms of conductivity, tensile strength, consistency, and solderability, achieving a breakthrough in the comprehensive performance of base metal grid slurries. A comparison between Examples 1-3 and Comparative Example 1 indicates that the combined use of nickel-based composite powder, glass binder phase, and composite solder additives in the nickel-based base metal grid slurry prepared by this invention is superior to using conventional silver-coated nickel powder and single glass powder. Furthermore, a performance comparison between Example 1 and Comparative Example 2 shows that the innovative design of the "island" in the "core-shell-island" structure significantly improves the various properties of the base metal conductive phase. A comparison between Examples 1-3 and Comparative Example 3 shows that the nickel-based base metal grid slurry prepared by this invention is superior to the preparation method disclosed in CN121237480A in terms of conductivity, weld tensile strength, and reliability, and is superior to existing technologies.

[0032] Figure 1 This is a structural diagram of the core-shell-island structured conductive phase prepared in Example 1 of the present invention.

[0033] Figure 2 This is an image showing the electrode peeling morphology obtained from the nickel-based base metal gate paste prepared in Example 1 of the present invention.

[0034] Figure 3 This is an image showing the electrode peeling morphology obtained from the slurry prepared in Comparative Example 3 of this invention.

[0035] pass Figure 2 and Figure 3The comparison shows that the PAD electrode and the solder strip in Comparative Example 3 are not tightly bonded, and there is obvious incomplete soldering, which poses a risk of tensile failure. In contrast, the solderability of Example 1 is significantly improved.

[0036] Firstly, in terms of conductive phase design, this invention proposes a nickel-based composite powder with a "core-shell-island" structure. The core is pre-alloyed with nickel and copper, utilizing the high conductivity of copper to compensate for the insufficient conductivity of nickel. At the same time, the pre-alloying can suppress the oxidation behavior of nickel during sintering. The middle layer is a silver coating layer, which protects the base metal core on the one hand and provides good sintering activity and weld wettability on the other. The outermost layer consists of dispersed metal oxide nanoislands. These nanoislands can preferentially react with the glass phase in the early stage of sintering, inducing the uniform spread of the glass phase and avoiding stress concentration caused by local aggregation of the glass phase, thereby improving tensile strength consistency.

[0037] Secondly, in the design of the glass binder phase, a gradient softening point composite glass powder is adopted. The low softening point glass powder melts in the early stage of sintering, wetting the surface of the conductive phase particles and promoting particle rearrangement and densification; the high softening point glass powder contains TeO2 and V2O5 components, which can melt and etch the silicon nitride layer on the surface of the silicon wafer in the middle and late stages of sintering, promoting the reaction of nickel-silicon alloy to form ohmic contacts. At the same time, the higher viscosity of the high softening point glass helps to control excessive penetration and avoid leakage.

[0038] Finally, composite solder additives are introduced. Sn-Bi alloy powder melts at the welding temperature, dissolving the oxide layer on the base metal surface and providing a fresh metal surface; Cu3P powder decomposes during the welding process to release phosphorus, which can further reduce residual oxides and form a nickel-phosphorus alloy with nickel, enhancing the strength of the solder joint.

[0039] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A nickel-based base metal gate paste, characterized in that, By mass percentage, it includes the following components: 70-85% conductive phase, 2-10% glass binder phase, 0.5-5% composite solder additive, and 10-25% organic carrier; The conductive phase is a nickel-based composite powder with a core-shell-island structure, comprising: Core: Nickel-copper pre-alloyed core, wherein copper accounts for 5-30% of the mass of the nickel-copper pre-alloyed core; Shell: Silver cladding, the mass of which is 10-40% of the mass of the nickel-copper pre-alloyed core; Island: Metal oxide nano-islands dispersed on the surface of core-shell structured powder. The metal oxide nano-islands are one or more of bismuth oxide, zinc oxide, and cobalt oxide. The nano-island particle size is 20~200nm and the surface coverage is 5~25%.

2. The nickel-based base metal gate paste as described in claim 1, characterized in that, The glass binder phase is a gradient softening point composite glass powder, comprising a first glass powder and a second glass powder, with a mass ratio of the first glass powder to the second glass powder of 1~2:1~9; the softening point of the first glass powder is 400~520℃, and by mass percentage comprises: PbO 30~60%, TeO2 0~10%, SiO2 10~30%, TiO2 10~20%, B2O3 5~10%, Al2O3 5~15%; the softening point of the second glass powder is 550~650℃, and by mass percentage comprises: Bi2O3 2~15%, TeO2 1~10%, SiO2 20~40%, CuO 10~15%, MnO 5~10%, V2O5 2~10%, ZnO 5~15%.

3. The nickel-based base metal gate paste as described in claim 1, characterized in that, The composite solder additive is a mixture of Sn-Bi alloy powder and Cu3P powder. The weight ratio of Sn-Bi alloy powder to Cu3P powder in the mixture is 2~5:1, and the mass percentage of Bi in the Sn-Bi alloy powder is 30~60%.

4. The nickel-based base metal grid paste as described in claim 1, characterized in that, The organic carrier comprises, by mass percentage: 10-20% resin, 70-85% organic solvent, 2-5% thixotropic agent, and 1-5% dispersant.

5. The nickel-based base metal grid paste as described in claim 4, characterized in that, The resin is one or both of ethyl cellulose and acrylic resin; the organic solvent is one or both of terpineol and butyl carbitol; the thixotropic agent is hydrogenated castor oil; and the dispersant is triethanolamine.

6. A method for preparing a nickel-based base metal gate paste as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Preparation of nickel-copper pre-alloyed powder: Mix nickel powder and copper powder, and mechanically alloy or atomize and melt under a protective atmosphere to obtain nickel-copper pre-alloyed powder with D50 of 1~3μm. Step 2, Surface coating with silver layer: Add the pre-alloyed powder to the chemical plating solution and stir to react, then filter, wash, and vacuum dry to obtain core-shell structured powder; Step 3: Constructing nanoislands: The core-shell structured powder is added to a metal oxide precursor solution, ultrasonically dispersed, spray-dried, and then subjected to low-temperature heat treatment to obtain a conductive phase; Step 4: Preparation of glass binder phase: Prepare first glass powder and second glass powder separately, then mix them evenly to obtain glass binder phase; Step 5: Preparation of composite solder additive: Mix Sn-Bi alloy powder and Cu3P powder evenly to obtain composite solder additive; Step 6: Preparation of organic carrier: Dissolve the resin in an organic solvent, add thixotropic agent and dispersant, heat and stir to dissolve, filter, and obtain organic carrier; Step 7, Slurry Mixing: The conductive phase, glass binder phase, composite solder additive and organic carrier are put into a planetary mixer and mixed evenly. After being rolled by three rollers and filtered, nickel-based base metal grid slurry is obtained.

7. The method for preparing the nickel-based base metal gate paste as described in claim 6, characterized in that, In step one, the D50 of the nickel powder is 1~3μm, the D50 of the copper powder is 1~3μm, the protective atmosphere is argon, and mechanical alloying is carried out using a high-energy ball mill at a speed of 400~500 rpm / min, a ball-to-material ratio of 10~30:1, and a milling time of 4~8h. In step two, the mass-to-volume ratio of the pre-alloyed powder and the electroless plating solution is 1g:5~15mL. The concentration of silver nitrate in the electroless plating solution is 20g / L, the concentration of ammonia is 50mL / L, and the concentration of potassium sodium tartrate is 0.05~0.2mol / L. The stirring reaction time is 20~40min, the vacuum drying temperature is 50~60℃, and the vacuum drying time is 6~10h. In step three... In this process, the mass-to-volume ratio of core-shell structured powder to metal oxide precursor solution is 80-120 g: 500-1000 mL. The metal oxide precursor solution is one of bismuth nitrate-anhydrous ethanol solution, zinc nitrate-anhydrous ethanol solution, or cobalt nitrate-anhydrous ethanol solution. The concentration of bismuth ions, zinc ions, or cobalt ions in the metal oxide precursor solution is 0.01-0.1 mol / L. The ultrasonic dispersion time is 20-40 min. The spray drying gas is nitrogen, and the feed rate is 2-5 mL / min. The low-temperature heat treatment uses a tube furnace, the low-temperature heat treatment temperature is 300-450℃, the low-temperature heat treatment time is 10-30 min, and the heat treatment atmosphere is nitrogen or argon.

8. The method for preparing the nickel-based base metal gate paste as described in claim 6, characterized in that, In step four, the method for preparing the first and second glass powders is as follows: the metal oxide raw material is melted and quenched at 1100~1300℃ and then ball-milled until D50 < 5μm; in step five, the D50 of Sn-Bi alloy powder is 2~8μm, the D50 of Cu3P powder is 1~6μm, and the mass ratio of Sn-Bi alloy powder to Cu3P powder is 1~5:1; in step six, the heating and stirring temperature is 80~90℃, and the heating and stirring time is 1~3h; in step seven, the mixing time is 20~40min, the three-roll milling is performed 3~7 times, and the filtration is done by passing through a 200-mesh sieve.

9. A photovoltaic cell, characterized in that, The main grid electrode of the photovoltaic cell is obtained by printing and sintering the nickel-based base metal grid paste as described in any one of claims 1-8.

10. The photovoltaic cell as described in claim 9, characterized in that, The peak sintering temperature of the photovoltaic cell is 700~800℃, and the sintering time is 1~5s.

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