Conductive paste with high base metal addition and method for preparing the same

Abstract

The application discloses a kind of high base metal additive amount conductive paste and preparation method thereof, belong to photovoltaic cell technical field, by mass percentage calculation, including conductive metal powder 88~92%, glass powder 2~6%, organic carrier 6~12%, conductive metal powder includes base metal powder 10~30%, micron grade silver powder 30~70%, high tap density silver powder 20~40%, nano grade silver powder 2~10%, the tap density of high tap density silver powder is greater than 6.3g / cm 3 , the D50 of micron grade silver powder and the D50 ratio of base metal powder is 0.25~0.45.The application uses micron grade silver powder and nano grade silver powder to be used in combination, introduce high tap density silver powder, by optimizing the D50 ratio of micron grade silver powder and base metal powder, different particle size silver powder and base metal powder form good matching and filling relationship, while realizing high base metal additive amount, conductive paste can maintain excellent conductive performance.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell technology, and in particular to a conductive paste with a high amount of base metals and its preparation method. Background Technology

[0002] Photovoltaic power generation, as a crucial component of clean energy, has played an increasingly vital role in the global energy transition in recent years. Crystalline silicon solar cells are currently the mainstream product in the photovoltaic market. Their front-side, which receives light, typically requires metallized electrodes to collect and dissipate photocurrent. Conductive silver paste, with its excellent conductivity, good ohmic contact characteristics, and reliable solderability, has become the preferred material for screen printing the front-side grid electrodes. Typical silver paste consists of silver powder, glass powder, organic carrier, and a small amount of additives. After printing and sintering, it forms dense silver grid lines, maintaining a low line resistance and thus ensuring the photoelectric conversion efficiency of the cell.

[0003] However, silver is a precious metal, with a persistently high and volatile price. The cost of conductive silver paste constitutes a significant proportion of the non-silicon cost of crystalline silicon solar cells. To reduce manufacturing costs, the industry has been seeking technological pathways to decrease silver usage, including fine-line printing, multi-busbar designs, and busbar-less designs. While these methods can reduce silver consumption per cell to some extent, they do not fundamentally eliminate dependence on silver. Against this backdrop, partially replacing silver with base metals such as copper, nickel, and aluminum has become an important research direction. Among these, nickel and nickel alloys are considered promising candidates for achieving higher addition levels in conductive pastes due to their relatively superior conductivity among base metals, good chemical stability, and significantly lower cost than silver.

[0004] Introducing nickel or nickel alloy powder into silver paste to replace part of the silver powder often has limited impact on electrode performance at low addition levels. However, when the addition of base metals is increased to 10%-30% to achieve meaningful cost reduction, conventional silver paste formulations encounter a technical bottleneck of significant battery efficiency degradation. Multiple experiments have shown a strong correlation between this efficiency degradation and the increase in grid line resistance. Using an IV tester to characterize line resistance with the GRF average value, the line resistance of pure silver paste is typically stable in the range of 0.035-0.040 Ω / cm. When the addition of nickel or nickel alloy is around 10%, the line resistance rises to approximately 0.05 Ω / cm, with a corresponding battery efficiency loss exceeding 0.1%. When the addition is further increased to 25%-30%, the line resistance increases sharply to 0.1 Ω / cm or even higher, with an efficiency loss of approximately 0.5%. The increase in line resistance means an increase in series resistance, a decrease in current collection capacity, and directly lowers the battery's fill factor and conversion efficiency.

[0005] The causes of these problems are complex, mainly including: nickel and nickel alloys are more easily oxidized than silver during sintering; the resulting oxide phases not only have poor conductivity but also hinder the sintering connection between silver particles, increasing the porosity and decreasing the density of the electrode; nickel and silver may form high-resistivity alloy phases or intermetallic compounds at the interface; simultaneously, high base metal content alters the sintering characteristics of the paste and the flow and wetting behavior of the glass phase, leading to increased contact resistance between the gate line and the silicon substrate. Conventional silver pastes, with their silver powder types, particle size distributions, surface states, and organic carrier and glass powder systems, are all designed around pure silver or systems with extremely low base metal content, and cannot effectively suppress these deteriorating effects. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a conductive paste with a high base metal content and its preparation method. This involves replacing silver powder with a higher proportion of base metal that has a certain proportional relationship with the D50 particle size of the silver powder. Simultaneously, nano-sized silver powder and silver powder with high tap density are selected to complement the paste, ensuring that the silver powder and base metal particles achieve an ideal downstream state during sintering, thereby improving the performance of the conductive silver paste and battery efficiency.

[0007] To achieve the above objectives, the present invention first provides a conductive paste with a high base metal content, comprising, by mass percentage: 88-92% conductive metal powder, 2-6% glass powder, and 6-12% organic carrier; wherein the conductive metal powder comprises 10-30%, micron-sized silver powder comprises 30-70%, high-tap-density silver powder comprises 18-40%, and nano-sized silver powder comprises 2-10%, wherein the tap density of the high-tap-density silver powder is greater than 6.3 g / cm³. 3 The ratio of the median volume diameter (D50) of the micron-sized silver powder to the median volume diameter (D50) of the base metal powder is in the range of 0.25-0.45. Within this range, the silver powder and base metal particles achieve an ideal state during the sintering process. If the ratio is too large, the silver powder cannot penetrate the gaps in the nickel powder to form a contact with the silicon wafer. If the ratio is too small, the resistivity of the powder body is too large and the continuity between silver films deteriorates, affecting the overall electrical performance.

[0008] In one embodiment of the present invention, the base metal powder includes one or a combination of two or more of nickel powder, copper powder, aluminum powder, tin powder and zinc powder, the combination including physical mixing and / or alloying, the base metal powder having an average particle size of 2-5 μm and a volume median particle size D50 ranging from 2-5 μm.

[0009] In one embodiment of the present invention, the micron-sized silver powder has an average particle size of 1-3 μm, a volume median particle size (D50) ranging from 1-3 μm, and a tap density of 5.5-6.1 g / cm³. 3 .

[0010] In one embodiment of the present invention, the tap density of the high-tap-density silver powder is 6.3-6.8 g / cm³. 3 The average particle size or D50 is 1-3 μm, and the particle size range of the nano-sized silver powder is 500-900 nm.

[0011] In one embodiment of the present invention, the glass powder comprises, by molar percentage, 15-35% PbO, 35-55% B2O3, 2-10% Al2O3, and 15-35% glass powder additives, wherein the glass powder additives are selected from one or more of GaO, ZnO, CaO, Bi2O3, K2O, SiO2, Na2O, Li2O, BaO, and TiO2, or a mixture thereof.

[0012] In one embodiment of the present invention, the glass powder comprises, by molar percentage, 20-25% PbO, 43-46% B2O3, 5-7% Al2O3, and 22-30% glass powder additives, wherein the glass powder additives are selected from one or more of GaO, ZnO, CaO, Bi2O3, K2O, SiO2, Na2O, Li2O, BaO, and TiO2, or a mixture thereof.

[0013] In one embodiment of the present invention, the glass powder has a particle size range of 1.1-2 μm and a melting point of 320-600℃.

[0014] In one embodiment of the present invention, the organic carrier comprises 0.1-30% resin, 60-90% organic solvent, and 0.1-10% additives; the resin may be selected from at least one of acrylic resin, polyurethane resin, rosin resin, ethyl cellulose, styrene-acrylic resin, polyvinyl butyral, polyvinylpyrrolidone, styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-butene-styrene block copolymer (SEBS), poly(α-methylstyrene), epoxy resin, and cellulose acetate butyrate; the organic solvent is selected from diethylene glycol. The additive is selected from at least one of the following: diethyl ether acetate, diethylene glycol butyl ether acetate, diethylene glycol methyl ether acetate, terpineol, oleic acid, diethylene glycol butyl ether, diethylene glycol dibutyl ether, dodecyl alcohol ester, hexadecyl alcohol ester, dimethyl adipate, dioctyl adipate, ethylene glycol butyl ether benzoate, benzyl benzoate, and dimethyl phthalate; the additive is selected from at least one of the following: fumed silica, polyamide wax, hydrogenated castor oil, silicone oil, polyethylene oxide, dodecylaminopropionic acid, benzotriazole, polyethylene glycol, polyhydroxystearic acid, lauric acid, oleic acid, decanoic acid, myristic acid, stearate, and palmitic acid ester.

[0015] In one embodiment of the present invention, the organic carrier, calculated by mass percentage, comprises 0.4-0.6% cellulose acetate butyrate, 0.6-0.8% ethyl cellulose, 6.6-7% styrene-ethylene-propylene-styrene block copolymer, 5.8-6.2% dimethyl adipate, 4.5-5% dodecyl alcohol ester, 23.5-24.1% diethylene glycol butyl ether acetate, 6.0-6.6% hexadecyl alcohol ester, 6.4-7% diethylene glycol dibutyl ether, 10-10.8% ethylene glycol butyl ether benzoate, 25.6-26.6% benzyl benzoate, 7.5-7.8% silicone oil, and 0.3-0.7% polyhydroxystearic acid dispersant.

[0016] The present invention also provides a method for preparing the above-mentioned conductive paste with high base metal content, comprising the following steps: (1) Preparation of glass powder: After thoroughly mixing the analytical grade raw materials and reagents of each component in the glass powder composition, the temperature is raised to 800-1200℃ at a heating rate of 5-10℃ / min, and melted at this temperature for 1-2 hours. The melting atmosphere is air atmosphere or nitrogen protection. During the melting process, a corundum stirring paddle is used for stirring at a speed of 50-100 rpm. Then, the powder is granulated by water quenching or air cooling, and after mechanical crushing, it is ball milled and sieved for classification. (2) Preparation of organic carrier: Weigh the organic solvent, resin and additives according to the mass ratio, stir at 60-80℃ until completely dissolved, keep warm for 1-2 hours and then cool to room temperature to obtain the carrier. First, add the solvent and heat to 60-80℃, then slowly add the resin and stir for 30 minutes until initially dissolved; then add the additive and continue stirring for 30-60 minutes until completely dissolved. After maintaining the temperature, allow it to cool naturally to below 40℃, then force it to cool to room temperature to avoid rapid cooling that could cause the carrier to separate; after cooling, pass it through a 500-mesh sieve to remove undissolved impurities.

[0017] (3) Preparation of conductive paste: Weigh base metal powder, micron-sized silver powder, high tap density silver powder, nano-sized silver powder, glass powder and organic carrier according to the mass ratio, stir using a planetary mixer or centrifuge using a high-speed rotating centrifuge, then grind it to a fineness of <10μm using a three-roll mill, and then filter it to a fineness of <7μm using a 300-500 mesh filter.

[0018] Beneficial effects: 1. This invention employs a combination of micron-sized and nano-sized silver powder, incorporating high-tap-density silver powder. Simultaneously, by optimizing the D50 ratio of micron-sized silver powder to base metal powder, a favorable gradation and space-filling relationship is achieved between silver powders of different particle sizes and morphologies and base metal powders. During sintering, the micron-sized silver powder can fully embed itself into the voids between base metal particles, forming an effective conductive path and contact with the silicon substrate. The nano-sized silver powder further fills the tiny gaps and promotes sintering densification. The high-tap-density silver powder enhances the overall density of the electrode, thus enabling the formation of a continuous and dense conductive network even with a high base metal content. The conductive metal powder provided by this invention significantly suppresses the increase in line resistance caused by base metal oxidation, the formation of high-resistivity interfacial phases, and increased electrode porosity, allowing the slurry to maintain excellent conductivity while achieving a meaningful base metal substitution ratio.

[0019] 2. This invention adjusts the composition of the conductive metal powder so that the conductive paste maintains a high line resistance even with a high base metal powder content, without a significant decrease in battery efficiency. Specifically, when the base metal content reaches 30%, the line resistance (characterized by the average GRF value) of the sintered paste can be controlled at around 0.043 Ω / cm, corresponding to a battery efficiency that is basically the same as or only slightly lower than that of pure silver paste. When the base metal content is around 11%, the line resistance can be as low as around 0.038 Ω / cm, and the battery efficiency can reach a level comparable to or even higher than that of pure silver paste. Compared to conventional silver paste, where the line resistance rises above 0.1 Ω / cm and efficiency drops by 0.5% with the same base metal content, the metal powder compounding scheme of this invention achieves a significant reduction in line resistance over a wide range of addition amounts. This effectively suppresses the increase in series resistance and the decay of the fill factor, enabling the high base metal content paste to have acceptable battery efficiency performance, while also bringing a 10% to 30% cost reduction potential for the paste.

[0020] 3. This invention utilizes a combination of PbO-B2O3-Al2O3 glass powder and conductive metal powder. This glass powder system exhibits suitable softening temperature and flow wetting characteristics during sintering, promoting the rearrangement and densification of metal particles. The conductive metal powder primarily enhances conductivity by reducing electrode bulk resistance, while the introduction of glass powder optimizes interfacial electrical behavior. The synergistic effect of these two components significantly improves both bulk and contact resistance of the grid lines after sintering the high base metal content slurry, thereby further enhancing the photoelectric conversion efficiency of the battery and exceeding the efficiency gains achievable with a simple metal powder blend. Detailed Implementation

[0021] The embodiments of this implementation are described in detail below. These embodiments are only used to explain this implementation and should not be construed as limiting this implementation.

[0022] The components of the organic carrier used in the embodiments and comparative examples of this invention, calculated by mass parts, include: 0.5% cellulose acetate butyrate, 0.7% ethyl cellulose, 6.8% styrene-ethylene-propylene-styrene block copolymer, 6% dimethyl adipate, 4.7% dodecyl alcohol ester, 23.8% diethylene glycol butyl ether acetate, 6.3% hexadecyl alcohol ester, 6.7% diethylene glycol dibutyl ether, 10.4% ethylene glycol butyl ether benzoate, 26.1% benzyl benzoate, 7.5% silicone oil, and 0.5% polyhydroxystearic acid dispersant; wherein, the cellulose acetate butyrate is CAB-1, the ethyl cellulose is Dow Chemical's Ethocel STD-4, the styrene-ethylene-propylene-styrene block copolymer is Kraton 1701 thermoplastic elastomer, the silicone oil is 100 viscosity silicone oil, and the other raw materials are commercially available common raw materials.

[0023] The tap density of the high-tap-density silver powder used in the embodiments and comparative examples of this invention is 6.35 g / cm³. 3 The silver powder has a D50 of 1.54 μm and was purchased from Suzhou Yinrui Optoelectronic Materials Co., Ltd.; its tap density is 6.43 g / cm³. 3 The high tap density silver powder has a D50 of 1.42μm. The raw material was purchased from Ningbo Jingxin Electronic Materials Co., Ltd. The nano silver powder has an average particle size of 800nm.

[0024] Example 1 A conductive paste with a high base metal content, by mass percentage, comprises 90% conductive metal powder, 5% glass powder, and 5% organic carrier. The conductive metal powder includes 11% nickel powder, 62% micron-sized silver powder, 22% high-tap-density silver powder, and 5% nano-sized silver powder. The nickel powder has a D50 of 4.2 μm, the micron-sized silver powder has a D50 of 1.3 μm, and the tap density is 5.8 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.31, and the tap density of high-tap-density silver powder is 6.35 g / cm³. 3 The glass powder, calculated by molar percentage, comprises a mixture of 20% PbO, 40% B2O3, 10% Al2O3, 4% CaO, 18% SiO2, and 8% TiO2.

[0025] A method for preparing a conductive paste with a high amount of base metals includes the following steps: (1) Preparation of glass powder: After the analytical grade raw materials and reagents of each component in the glass powder composition are fully mixed, the temperature is raised to 1000℃ at a heating rate of 8℃ / min, and melted at this temperature for 1.5h. The melting atmosphere is air atmosphere or nitrogen protection. During the melting process, a corundum stirring paddle is used for stirring at a speed of 100rpm. Then, the powder is granulated by water quenching or air cooling, and after mechanical crushing, it is ball milled and sieved for classification. (2) Preparation of organic carrier: Weigh the organic solvent, resin and additives according to the mass ratio, stir at 80℃ until completely dissolved, keep warm for 1 hour and then cool to room temperature to obtain the carrier. First, add the solvent and heat to 80°C. Then, slowly add the resin and stir for 30 minutes until initially dissolved. Next, add the additive and continue stirring for 30 minutes until completely dissolved. After maintaining the temperature, allow it to cool naturally to below 40°C, then force-cool it to room temperature to avoid rapid cooling that could cause the carrier to separate. After cooling, pass it through a 500-mesh sieve to remove undissolved impurities.

[0026] (3) Preparation of conductive paste: Weigh base metal powder, micron-sized silver powder, high tap density silver powder, nano-sized silver powder, glass powder and organic carrier according to the mass ratio, stir using a planetary mixer or centrifuge using a high-speed rotating centrifuge, then grind it to a fineness of <10μm using a three-roll mill, and then filter it to a fineness of <7μm using a 300-mesh filter.

[0027] Example 2 The difference between Example 2 and Example 1 is that, calculated by molar percentage, the glass powder includes 24% PbO, 44% B2O3, 7% Al2O3, 3% ZnO, 2% Bi2O3, 4% Na2O, 14% SiO2 and 2% TiO2.

[0028] Example 3 The difference between Example 3 and Example 1 is that, calculated by molar percentage, the glass powder comprises a mixture of 25% PbO, 44% B2O3, 6% Al2O3, 1.5% GaO, 1.5% ZnO, 1.5% CaO, 0.5% Bi2O3, 1% K2O, 15% SiO2, 1% Na2O, 1% Li2O, 0.5% BaO, and 1.5% TiO2.

[0029] Example 4 The difference between Example 4 and Example 3 is that, by mass percentage, the conductive metal powder comprises 30% nickel powder, 32% micron-sized silver powder, 30% high-tap-density silver powder, and 8% nano-sized silver powder. The nickel powder has a D50 of 4.5 μm, the micron-sized silver powder has a D50 of 1.5 μm, and the tap density is 5.8 g / cm³. 3The D50 ratio of micron-sized silver powder to nickel powder is 0.33, and the tap density of high-tap-density silver powder is 6.43 g / cm³. 3 The formula for the glass powder is the same as in Example 3.

[0030] Example 5 The difference between Example 5 and Example 3 is that the D50 of the nickel powder is 4.5 μm, the D50 of the micron-sized silver powder is 1.5 μm, and the tap density is 5.69 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.33.

[0031] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that, by mass percentage, the conductive metal powder is micron-sized silver powder with a D50 of 1.3 μm and a tap density of 5.8 g / cm³. 3 .

[0032] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that the conductive metal powder does not contain nano-silver powder. By mass percentage, the conductive metal powder comprises 11% nickel powder, 67% micron-sized silver powder, and 22% high-tap-density silver powder. The D50 of the nickel powder is 4.2 μm, the D50 of the micron-sized silver powder is 1.3 μm, and the tap density is 5.8 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.31.

[0033] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that no high-tap-density silver powder was added to the conductive metal powder. By mass percentage, the conductive metal powder comprised 11% nickel powder, 84% micron-sized silver powder, and 5% nano-sized silver powder. The nickel powder had a D50 of 4.2 μm, the micron-sized silver powder had a D50 of 1.3 μm, and the tap density was 5.8 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.31.

[0034] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that only the D50 of the micron-sized silver powder and the D50 of the nickel powder were changed. Calculated by mass percentage, the conductive metal powder comprises 11% nickel powder, 62% micron-sized silver powder, 22% high-tap-density silver powder, and 5% nano-sized silver powder. The D50 of the nickel powder is 4.6 μm, the D50 of the micron-sized silver powder is 1.0 μm, and the tap density is 6.0 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.22.

[0035] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is that only the D50 of the micron-sized silver powder and the D50 of the nickel powder were changed. Calculated by mass percentage, the conductive metal powder comprises 11% nickel powder, 62% micron-sized silver powder, 22% high-tap-density silver powder, and 5% nano-sized silver powder. The D50 of the nickel powder is 2.5 μm, the D50 of the micron-sized silver powder is 1.3 μm, and the tap density is 5.8 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.52.

[0036] Comparative Example 6 The difference between Comparative Example 6 and Example 3 is that the nano-silver powder is omitted, while the D50 of the micron-sized silver powder and the D50 of the nickel powder are changed. Calculated by mass percentage, the conductive metal powder comprises 11% nickel powder, 67% micron-sized silver powder, and 22% high-tap-density silver powder. The nickel powder has a D50 of 2.5 μm, the micron-sized silver powder has a D50 of 1.3 μm, and the tap density is 5.9 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.52.

[0037] Comparative Example 7 The difference between Comparative Example 7 and Example 3 is that, calculated by mass percentage, the conductive metal powder comprises 11% nickel powder, 39% micron-sized silver powder, 45% high-tap-density silver powder, and 5% nano-sized silver powder. The nickel powder has a D50 of 4.2 μm, the micron-sized silver powder has a D50 of 1.3 μm, and the tap density is 5.8 g / cm³. 3 The tap density of high-tap-density silver powder is 6.35 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.31.

[0038] Comparative Example 8 The difference between Comparative Example 8 and Example 3 is that the amount of nano-sized silver powder added is greater than 10%. By mass percentage, the conductive metal powder comprises 11% nickel powder, 55% micron-sized silver powder, 22% high-tap-density silver powder, and 12% nano-sized silver powder. The nickel powder has a D50 of 4.2 μm, the micron-sized silver powder has a D50 of 1.3 μm, and the tap density is 5.8 g / cm³. 3 The tap density of high-tap-density silver powder is 6.35 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.31.

[0039] Comparative Example 9 The difference between Comparative Example 9 and Example 4 is that the conductive metal powder does not contain nano-silver powder or high-tap-density silver powder. By mass percentage, the conductive metal powder comprises 30% nickel powder and 70% micron-sized silver powder. The D50 of the nickel powder is 2.8 μm, the D50 of the micron-sized silver powder is 1.4 μm, and the tap density is 5.8 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.5.

[0040] Comparative Example 10 The difference between Comparative Example 10 and Example 4 is that, calculated by mass percentage, the conductive metal powder comprises 30% nickel powder, 22% high-tap-density silver powder, 40% micron-sized silver powder, and 8% nano-sized silver powder. The nickel powder has a D50 of 4.6 μm, the micron-sized silver powder has a D50 of 1.0 μm, and the tap density is 6.0 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.22, and the tap density of high-tap-density silver powder is 6.43 g / cm³. 3 .

[0041] Comparative Example 11 The difference between Comparative Example 11 and Example 4 is that it lacks high-tap-density silver powder, and the D50 ratio of the micron-sized silver powder to the nickel powder is different. Calculated by mass percentage, the conductive metal powder comprises 30% nickel powder, 62% micron-sized silver powder, and 8% nano-sized silver powder. The D50 of the nickel powder is 4.6 μm, the D50 of the micron-sized silver powder is 1.4 μm, and the tap density is 5.72 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.3.

[0042] Comparative Example 12 The difference between Comparative Example 12 and Example 4 is that Comparative Example 12 does not contain nano-silver powder and the D50 ratio of the micron-sized silver powder to the nickel powder is different. Calculated by mass percentage, the conductive metal powder comprises 30% nickel powder, 48% micron-sized silver powder, and 22% high-tap-density silver powder. The D50 of the nickel powder is 4.6 μm, the D50 of the micron-sized silver powder is 1.0 μm, and the tap density is 6.0 g / cm³. 3 The D50 ratio of micron-sized silver powder to nickel powder is 0.22.

[0043] Comparative Example 13 The difference between Comparative Example 13 and Example 1 is that, calculated by molar percentage, the glass powder comprises 10% PbO, 63% B2O3, 10% Al2O3, 1% CaO, 15% SiO2 and 1% TiO2.

[0044] Comparative Example 14 The difference between Comparative Example 14 and Example 1 is that, calculated by molar percentage, the glass powder comprises a mixture of 29% PbO, 43% B2O3, 1% GaO, 1.5% ZnO, 1% CaO, 0.5% Bi2O3, 2% K2O, 18% SiO2, 1.5% Na2O, 1% Li2O, 1% BaO, and 0.5% TiO2.

[0045] Performance testing: Conductive paste was printed onto the front side of solar cells using screen printing technology. After sintering at suitable temperatures and laser sintering, the photoelectric conversion efficiency of the cells was tested using a HALM IV tester. Test items included line resistance and photoelectric conversion efficiency. The relevant performance test results of the conductive pastes in the examples and comparative cases are shown in Table 1.

[0046] Table 1 Performance test results of the conductive silver pastes prepared in Examples 1-5 and Comparative Examples 1-14

[0047] Note: The change in photoelectric conversion efficiency refers to the change in photoelectric conversion efficiency relative to the battery in Comparative Example 1. Based on the data in the table, it can be seen that this invention uses micron-sized silver powder with a volume median particle size (D50) ratio of 0.25 to 0.45, combined with base metal powder, and simultaneously adds a certain amount of high tap density (tap density > 6.3 g / cm³). 3 The conductive paste prepared by combining silver powder with nano-sized silver powder exhibits low line resistance, while the battery demonstrates high photoelectric conversion efficiency. Using the conductive paste formulation of this invention, even with an addition of up to 30% base metal powder, the battery's photoelectric conversion efficiency remains high, and there is no significant decrease in photoelectric conversion efficiency with the addition of base metal.

[0048] Comparative Examples 1-8 investigated the line resistance of the slurry and the photoelectric conversion efficiency of the battery after changing the slurry formulation when the nickel powder addition was 11%. The results in the table show that if nano-silver powder or high-tap-density silver powder is not added to the conductive metal powder, the line resistance of the conductive slurry increases significantly, leading to a significant decrease in the photoelectric conversion efficiency of the battery. Similarly, improper selection of the D50 of micron-sized silver powder and nickel powder also leads to an increase in the line resistance of the conductive slurry and a decrease in the photoelectric conversion efficiency of the battery. Comparative Examples 7 and 8 added excessive amounts of high-tap-density silver powder and nano-silver powder, respectively. The results show that excessive high-tap-density silver powder resulted in excessively high powder activity, achieving a low line resistance, but causing excessive sintering between the slurry and the silicon wafer, resulting in significant loss of electrical performance. Excessive nano-silver powder led to poor slurry printing quality, resulting in severe grid breakage after printing, thus degrading battery performance. However, the formulation of this invention, even with the addition of 11% nickel, still achieves a significant improvement in battery efficiency, up to 0.05%.

[0049] Besides the fact that conductive metals can cause significant changes in the photoelectric conversion efficiency of batteries, the composition of glass powder also has a significant impact on battery efficiency. Experiments have shown that when the ratio of conductive metal powder is within the range of this invention, if the composition of glass powder is not properly selected, it will also lead to a significant decrease in battery efficiency. For example, Comparative Example 13 reduced the amount of lead oxide, and Comparative Example 14 omitted aluminum oxide, resulting in a significant decrease in the photoelectric conversion efficiency of the battery.

[0050] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A conductive paste with a high content of base metals, characterized in that, The composition, by mass percentage, includes 88-92% conductive metal powder, 2-6% glass powder, and 6-12% organic carrier. The conductive metal powder comprises 10-30% base metal powder, 30-70% micron-sized silver powder, 18-40% high-tap-density silver powder, and 2-10% nano-sized silver powder, wherein the high-tap-density silver powder has a tap density greater than 6.3 g / cm³. 3 The ratio of the median volumetric particle size (D50) of the micron-sized silver powder to the median volumetric particle size (D50) of the base metal powder ranges from 0.25 to 0.

45. The base metal powder comprises one or more of nickel, copper, aluminum, tin, and zinc powders, wherein the combination includes physical mixing and / or alloying. The average particle size of the base metal powder is 2-5 μm, and the median volumetric particle size (D50) ranges from 2-5 μm. The average particle size of the micron-sized silver powder is 1-3 μm, the median volumetric particle size (D50) ranges from 1-3 μm, and the tap density is 5.5-6.1 g / cm³. 3 The high-tap-density silver powder has a tap density of 6.3-6.8 g / cm³. 3 The average particle size or D50 is 1-3 μm, and the particle size range of the nano-sized silver powder is 500-900 nm; calculated by molar percentage, the glass powder includes 15-35% PbO, 35-55% B2O3, 2-10% Al2O3 and 15-35% glass powder additives, wherein the glass powder additives are selected from one or more of GaO, ZnO, CaO, Bi2O3, K2O, SiO2, Na2O, Li2O, BaO and TiO2 and a mixture thereof.

2. The conductive paste according to claim 1, characterized in that, The glass powder comprises, by molar percentage, 20-25% PbO, 43-46% B2O3, 5-7% Al2O3, and 22-30% glass powder additives, wherein the glass powder additives are selected from one or more of GaO, ZnO, CaO, Bi2O3, K2O, SiO2, Na2O, Li2O, BaO, and TiO2, or a mixture thereof.

3. The conductive paste according to claim 1 or 2, characterized in that, The glass powder has a particle size range of 1.1-2 μm and a melting point of 320-600℃.

4. The conductive paste according to claim 1, characterized in that, The organic carrier comprises 0.1-30% resin, 60-90% organic solvent, and 0.1-10% additives; the resin is selected from at least one of acrylic resin, polyurethane resin, rosin resin, ethyl cellulose, styrene-acrylic resin, polyvinyl butyral, polyvinylpyrrolidone, styrene-ethylene-propylene-styrene block copolymer, styrene-ethylene-butene-styrene block copolymer, poly(α-methylstyrene), epoxy resin, and cellulose acetate butyrate; the organic solvent is selected from diethylene glycol ethyl ether acetate and diethylene glycol butyl ether acetate. The additive is selected from at least one of the following: ester, diethylene glycol methyl ether acetate, terpineol, oleic acid, diethylene glycol butyl ether, diethylene glycol dibutyl ether, dodecyl alcohol ester, hexadecyl alcohol ester, dimethyl adipate, dioctyl adipate, ethylene glycol butyl ether benzoate, benzyl benzoate, and dimethyl phthalate; the additive is selected from at least one of the following: fumed silica, polyamide wax, hydrogenated castor oil, silicone oil, polyethylene oxide, dodecylaminopropionic acid, benzotriazole, polyethylene glycol, polyhydroxystearic acid, lauric acid, oleic acid, decanoic acid, myristic acid, stearate, and palmitic acid ester.

5. The conductive paste according to claim 4, characterized in that, The organic carrier, calculated by mass percentage, comprises 0.4-0.6% cellulose acetate butyrate, 0.6-0.8% ethyl cellulose, 6.6-7% styrene-ethylene-propylene-styrene block copolymer, 5.8-6.2% dimethyl adipate, 4.5-5% dodecyl alcohol ester, 23.5-24.1% diethylene glycol butyl ether acetate, 6.0-6.6% hexadecyl alcohol ester, 6.4-7% diethylene glycol dibutyl ether, 10-10.8% ethylene glycol butyl ether benzoate, 25.6-26.6% benzyl benzoate, 7.5-7.8% silicone oil, and 0.3-0.7% polyhydroxystearic acid dispersant.

6. A method for preparing a conductive paste with a high base metal content according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Preparation of glass powder: After thoroughly mixing the analytical grade raw materials and reagents of each component in the glass powder composition, the temperature is raised to 800-1200℃ at a heating rate of 5-10℃ / min, and melted at this temperature for 1-2 hours. The melting atmosphere is air atmosphere or nitrogen protection. During the melting process, a corundum stirring paddle is used for stirring at a speed of 50-100 rpm. Then, the powder is granulated by water quenching or air cooling, and after mechanical crushing, it is ball milled and sieved for classification. (2) Preparation of organic carrier: Weigh the organic solvent, resin and additives according to the mass ratio, stir at 60-80℃ until completely dissolved, keep warm for 1-2 hours and then cool to room temperature to obtain the carrier. First, add the solvent and heat to 60-80℃, then slowly add the resin and stir for 30 minutes until initially dissolved; then add the additive and continue stirring for 30-60 minutes until completely dissolved; after keeping warm, allow it to cool naturally to below 40℃, then force it to cool to room temperature to avoid rapid cooling causing carrier stratification; after cooling, pass it through a 500-mesh sieve to remove undissolved impurities; (3) Preparation of conductive paste: Weigh base metal powder, micron-sized silver powder, high tap density silver powder, nano-sized silver powder, glass powder and organic carrier according to the mass ratio, mix them and then use a planetary mixer or a high-speed centrifuge to mix them. Then grind them to a fineness of <10μm using a three-roll mill, and then filter them to a fineness of <7μm using a 300-500 mesh filter.

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