Modified copper powder, preparation method thereof, conductive copper paste and solar cell

Abstract

This invention provides a modified copper powder, its preparation method, a conductive copper paste, and a solar cell. The modified copper powder comprises copper powder and an organic compound, wherein the organic compound coats the surface of the copper powder to form an organic protective layer, which decomposes during the sintering process of the conductive copper paste. This modified copper powder solves the problems of easy oxidation and poor conductivity of copper paste during sintering in air, and the need for protective atmospheres such as nitrogen and hydrogen, which leads to complex processes and high costs.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a modified copper powder and its preparation method, a conductive copper paste, and a solar cell. Background Technology

[0002] Traditional crystalline silicon solar cells typically use silver paste to make electrodes. In recent years, as crystalline silicon solar cells have developed towards higher efficiency and lower cost, and given the high cost of traditional silver paste, using copper paste to replace silver paste has become an important way to reduce costs.

[0003] Ordinary copper paste is easily oxidized to copper oxide or cuprous oxide during sintering in air, resulting in poor conductivity of the copper electrode. Using protective atmospheres such as nitrogen or hydrogen for sintering complicates the process, increases equipment costs, and significantly raises production costs. Current technologies typically modify copper powder by coating it with inorganic materials; however, the inorganic coating layer cannot be decomposed and removed under low-temperature sintering conditions, remaining as an insulating phase in the copper electrode. This significantly increases the resistivity of the copper electrode and hinders the sintering connectivity between copper particles, affecting the formation of the conductive network.

[0004] Meanwhile, although existing self-reducing copper pastes can be sintered in air, copper atoms tend to diffuse into the silicon substrate and passivation layer during the sintering process, leading to battery leakage and reduced efficiency. Current technologies typically employ the additional deposition of TiO2 and SiN on the passivation layer. X One approach is to use a diffusion barrier layer, but this involves a complicated process and high costs; another approach is to add glass powder to the copper paste and rely on the glass powder to achieve interfacial bonding, but the glass powder will erode and damage the passivation layer, resulting in a significant reduction in the battery open-circuit voltage and damage to battery performance. Summary of the Invention

[0005] The purpose of this invention is to provide a modified copper powder that addresses the problems of copper paste being prone to oxidation and having poor conductivity when sintered in air, and the need for protective atmospheres such as nitrogen and hydrogen, which leads to complex processes and high costs.

[0006] This invention provides a modified copper powder for use in conductive copper paste. The modified copper powder comprises copper powder and organic matter, wherein the organic matter coats the surface of the copper powder to form an organic protective layer; the organic protective layer can decompose during the sintering process of the conductive copper paste.

[0007] In one feasible manner, the organic compound is a long-chain fatty acid or octanoylglutamic acid.

[0008] In one feasible manner, the organic matter in the modified copper powder accounts for 1% to 3% of the mass of the copper powder.

[0009] In one feasible manner, the thermal decomposition temperature of the organic compound is 150°C to 300°C.

[0010] In one feasible embodiment, the copper powder has a particle size D50 of 30 nm to 100 nm and a specific surface area of ​​10 m². 2 / g~25m 2 The tap density of the copper powder is 1.8 g / cm³. 3 ~2.8g / cm 3 .

[0011] The present invention also provides a method for preparing the modified copper powder as described above, comprising the following steps: S1: Add copper powder to the solvent and disperse it evenly to obtain a suspension; S2: Add organic matter to the suspension and stir evenly so that the organic matter coats the surface of the copper powder to form an organic protective layer; S3: Separate, wash and dry the solid products in the suspension in sequence to obtain modified copper powder.

[0012] In one feasible manner, in step S1 above, the primary particle size D50 of the copper powder is 30nm~50nm, and the secondary particle size D50 of the copper powder is 50nm~100nm. And / or, the solvent is anhydrous ethanol or isopropanol.

[0013] In one feasible approach, the stirring conditions in step S2 above are: stirring for 2 to 4 hours under water bath heating conditions of 50°C to 65°C.

[0014] In one feasible manner, in step S3 above, the solid product is subjected to vacuum drying under the following conditions: vacuum degree of -0.08MPa to -0.1MPa, drying temperature of 40℃ to 60℃, and drying time of 6 hours to 12 hours.

[0015] The present invention also provides a conductive copper paste, which, by mass percentage, comprises: 70%~90% modified copper powder, 0.8%~3% in-situ diffusion barrier precursor, 5%~15% organic resin, 5%~20% organic solvent, and 0.1%~1% additives; the in-situ diffusion barrier precursor comprises one or more of nano-TiO2, nano-ZrO2, tetraisopropyl titanate, and zirconium acetylacetonate; the modified copper powder is the modified copper powder as described above or prepared by the preparation method described above.

[0016] In one feasible embodiment, the organic resin comprises one or more of ethyl cellulose and modified acrylic resin; the ethyl cellulose has a viscosity of 5-20 mPa·s and an ethoxy content of 48%-49.5%; the modified acrylic resin comprises one or more of thermoplastic acrylic resin, hydroxyl-modified acrylic resin, carboxyl-modified acrylic resin, and alkyl-modified acrylic resin. And / or, the organic solvent includes one or more of diethylene glycol monobutyl ether, ethylene glycol, isopropanol, glycerol, cyclohexanone, cyclohexanol, terpineol, and diethylene glycol monobutyl ether acetate; And / or, the additives include one or more of the following: ammonium polyacrylate, polyether-modified polydimethylsiloxane, polyamide wax, and hydrogenated castor oil.

[0017] The present invention also provides a solar cell comprising a copper electrode, the copper electrode being obtained by sintering a conductive copper paste as described above.

[0018] The modified copper powder provided by this invention forms an organic protective layer by coating the surface of the copper powder with organic matter. This organic protective layer can inhibit the oxidation of copper powder during the sintering process of conductive copper paste, preventing the copper powder from oxidizing into copper oxide or cuprous oxide during sintering in air, thereby maintaining the good conductivity of the copper powder. Furthermore, the organic protective layer can inhibit the agglomeration of copper powder particles, improving the wettability and dispersion uniformity of the copper powder in the copper paste. Simultaneously, the organic protective layer has a low thermal decomposition temperature, allowing for complete pyrolysis during low-temperature sintering without residual carbon, thus not affecting sintering or conductivity. Therefore, the modified copper powder not only has good dispersibility and strong oxidation resistance, but the organic protective layer can also be completely thermally removed during low-temperature sintering, without affecting the formation of the conductive network. The conductive copper paste using this modified copper powder can be rapidly sintered at low temperatures in an air atmosphere without the need for protective gases such as nitrogen or hydrogen, directly adapting to existing crystalline silicon solar cell screen printing and sintering production lines, exhibiting strong process compatibility and low equipment investment. The copper electrode formed after sintering of the conductive copper paste has low resistivity and excellent conductivity. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in further detail below. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. The terms "first," "second," "third," "fourth," etc. (if present) in the specification and claims of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0020] This invention provides a modified copper powder for use in conductive copper paste. The modified copper powder comprises copper powder and an organic compound, wherein the organic compound coats the surface of the copper powder to form an organic protective layer. This organic protective layer decomposes during the sintering process of the conductive copper paste. By coating the surface of the copper powder with an organic protective layer, the organic protective layer can inhibit the oxidation of the copper powder during the sintering process of the conductive copper paste, preventing the copper powder from oxidizing to copper oxide or cuprous oxide during sintering in air, thereby maintaining good conductivity of the copper powder. Moreover, the organic protective layer can inhibit the agglomeration of copper powder particles, improving the wettability and dispersion uniformity of the copper powder in the copper paste. Simultaneously, the organic protective layer has a low thermal decomposition temperature, allowing it to completely pyrolyze during low-temperature sintering without residual carbon, thus not affecting sintering or conductivity. Therefore, the modified copper powder not only has good dispersibility and strong oxidation resistance, but also the organic protective layer can be completely thermally removed during low-temperature sintering without affecting the formation of the conductive network. The conductive copper paste using this modified copper powder can be sintered rapidly at low temperature in an air atmosphere without the need for protective gases such as nitrogen and hydrogen. It is directly compatible with existing crystalline silicon solar cell screen printing and sintering production lines, with strong process compatibility and low equipment investment. The copper electrode formed after sintering of the conductive copper paste has low resistivity and excellent conductivity.

[0021] Existing technologies typically modify copper powder by coating it with inorganic materials, such as SiO2, Al2O3, TiO2, ZrO2, and phosphates. However, these inorganic coatings cannot be decomposed and removed under low-temperature sintering conditions, remaining as insulating phases in the copper electrode. This significantly increases the resistivity of the copper electrode and hinders the sintering connectivity between copper particles, affecting the formation of the conductive network. Furthermore, in conventional copper paste (where the copper powder surface is not coated with inorganic materials), an in-situ diffusion barrier layer, such as a Cu-Si compound, metal silicide, or oxide, can be formed at the Cu-Si substrate / passivation layer interface. This barrier layer prevents Cu from diffusing into the Si substrate, avoiding Cu contamination that leads to battery efficiency degradation. The presence of an inorganic coating layer directly blocks the contact between Cu and Si, preventing the formation of this in-situ diffusion barrier layer. This allows Cu to diffuse directly into the Si substrate during subsequent high-temperature processes, causing battery leakage and a significant decrease in efficiency. This embodiment uses an organic material as the coating layer, thus avoiding these problems.

[0022] In one embodiment, the thermal decomposition temperature of the organic material (organic protective layer) is 150℃~300℃, specifically 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc., or any combination of the above values. Since the sintering temperature of conductive copper paste is generally 300℃~350℃, and the sintering time is generally 1min~2min, the thermal decomposition temperature of the organic material is less than or equal to the sintering temperature of the conductive copper paste. Therefore, the organic material (organic protective layer) can be completely thermally decomposed during the sintering process of the conductive copper paste.

[0023] In one implementation method, the organic material is a long-chain fatty acid or octanoyl glutamic acid. Using these two organic materials as coating modifiers, they can form stable coordination bonds with the copper powder surface through their carboxyl groups, creating a dense monomolecular organic protective layer on the copper powder surface (this monomolecular organic protective layer is more easily pyrolyzed during sintering, reducing residue). This effectively isolates air, inhibits copper powder oxidation and particle agglomeration, and simultaneously improves the wettability and dispersion uniformity of the copper powder in the copper paste, enhancing the storage stability and printing film performance of the copper paste. Furthermore, both long-chain fatty acids and octanoyl glutamic acid possess excellent low-temperature pyrolysis characteristics, achieving complete pyrolysis and vaporization at 150℃~300℃. The decomposition products leave no residue or carbon slag, and do not introduce non-conductive impurities, ensuring the low resistivity of the copper electrode. Moreover, both are mild in nature, do not corrode the crystalline silicon substrate and passivation film, do not undergo side reactions with the aforementioned in-situ diffusion barrier precursor, and do not interfere with the in-situ formation of the interface ceramic barrier layer, thus maximizing the battery's high open-circuit voltage, high fill factor, and long-term reliability. In one embodiment, the long-chain fatty acid is a long-chain saturated fatty acid or a long-chain unsaturated fatty acid, preferably a long-chain saturated fatty acid. Long-chain saturated fatty acids can form a denser and more complete organic protective layer on the surface of copper powder, thereby achieving a better antioxidant effect.

[0024] In one embodiment, the organic matter in the modified copper powder accounts for 1% to 3% of the mass of the copper powder (i.e., the coating amount of the organic matter is 1% to 3%), specifically 1%, 1.5%, 2%, 2.5%, 3%, etc., or any combination of the above values. This ensures that the organic matter forms a dense and complete organic protective layer on the surface of the copper powder.

[0025] In one embodiment, the copper powder is spherical or near-spherical nano-copper powder, and the particle size D50 of the copper powder is 30nm~100nm, specifically 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc., or any combination of the above values. The specific surface area of ​​the copper powder is 10m². 2 / g~25m 2 / g, specifically 10m 2 / g、12m 2 / g, 15m 2 / g、18m 2 / g、20m 2 / g、22m 2 / g、25m 2 / g, etc., can also be any combination of the above values. The tap density of the copper powder is 1.8 g / cm³. 3 ~2.8g / cm 3 Specifically, it can be 1.8 g / cm³. 3 2.0g / cm 3 2.2g / cm 3 2.5g / cm 3 2.8g / cm 3 "etc." can also be any combination of the above values. Specifically, by limiting the particle size D50 of the copper powder to the above range, the nano-copper powder within this particle size range possesses high surface energy, a high surface atomic ratio, short atomic diffusion paths, a low melting point effect, and a large specific surface area. This allows it to obtain strong atomic diffusion driving force under low-temperature conditions, easily forming sintering necks between particles and rapidly densifying, thereby achieving low-temperature, rapid, and low-resistance sintering. Furthermore, it is easy to perform surface organic coating treatment, which can effectively inhibit copper powder oxidation and agglomeration, improving the storage stability and conductivity reliability of the slurry. If the particle size D50 of the copper powder > 100 nm, the surface energy of the copper powder decreases significantly, atomic diffusion is difficult, sintering activity is insufficient, it is difficult to form a dense conductive layer at low temperatures, and it is easily oxidized to form copper oxide or cuprous oxide, making it difficult to form a conductive network and resulting in high contact resistance.

[0026] In one embodiment, the particle size D50 of the modified copper powder is 30nm~100nm, specifically 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc., or any combination of the above values.

[0027] This invention also provides a method for preparing the above-mentioned modified copper powder, comprising the following steps: S1: Add copper powder to the solvent and disperse it evenly to obtain a suspension; S2: Add organic matter to the suspension and stir evenly to coat the copper powder surface with organic matter to form an organic protective layer; wherein the mass of organic matter is 1% to 3% of the mass of copper powder; S3: Separate, wash and dry the solid products in the suspension in sequence to obtain modified copper powder.

[0028] Specifically, this embodiment uses a liquid-phase adsorption coating method to prepare modified copper powder. This method is not only simple to manufacture and has low cost and high feasibility for mass production, but also allows organic matter to be uniformly adsorbed on the surface of the copper powder, forming a dense and complete organic protective layer on the surface of the copper powder.

[0029] In one embodiment, in step S1 above, the copper powder is spherical or near-spherical nano-copper powder, the primary particle size D50 of the copper powder is 30nm~50nm, and the secondary particle size D50 of the copper powder is 50nm~100nm (wherein, the primary particle size refers to the original single particle size of the copper powder, that is, the original particle size of the copper powder before it is added to the solvent; the secondary particle size refers to the particle size of the agglomerates formed by the copper powder in the dispersion system, that is, the particle size of the copper powder in the suspension).

[0030] In one embodiment, in step S1 above, the solvent is anhydrous ethanol or isopropanol.

[0031] As one implementation method, in step S1 above, copper powder is dispersed by ultrasonic dispersion for 20 min to 30 min.

[0032] In one embodiment, in step S2 above, the organic compound is a long-chain fatty acid or octanoylglutamic acid.

[0033] In one implementation, the stirring conditions in step S2 above are: stirring for 2 to 4 hours under a water bath heating condition of 50°C to 65°C. The water bath heating temperature can be 50°C, 55°C, 60°C, 65°C, or any combination thereof. The stirring time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any combination thereof.

[0034] In one implementation, in step S3 above, the solid products in the suspension are separated by vacuum filtration or centrifugation.

[0035] As one implementation method, in step S3 above, the solid product is washed 2 to 3 times with anhydrous ethanol to remove unadsorbed free modifier (organic matter).

[0036] In one embodiment, in step S3 above, the solid product is vacuum dried under the following conditions: vacuum degree of -0.08MPa to -0.1MPa, drying temperature of 40℃ to 60℃, and drying time of 6 hours to 12 hours.

[0037] In one embodiment, in step S3 above, after drying the solid product, the solid product is also sieved to obtain modified copper powder with the desired particle size range.

[0038] As one implementation method, the specific preparation steps of the modified copper powder are as follows: 1. Add spherical or near-spherical nano-copper powder to anhydrous ethanol or isopropanol, and ultrasonically disperse for 20-30 minutes to form a uniformly dispersed copper powder suspension; 2. Add organic matter, which is long-chain fatty acid or capryloyl glutamic acid, to the suspension at an amount of 1.0~3.0 wt% of the mass of the nano-copper powder. 3. Under water bath conditions of 50℃~65℃, mechanically stir the reaction for 2~4 hours to allow the organic matter to be fully adsorbed on the surface of copper powder and form a dense monomolecular coating layer. 4. Filter or centrifuge the suspension to obtain the solid product; 5. Wash the solid product 2-3 times with anhydrous ethanol to remove unadsorbed free organic matter; 6. Place the washed solid product in a vacuum drying oven and dry it for 6 to 12 hours at 40℃~60℃ and a vacuum of -0.08MPa~-0.1MPa. After cooling to room temperature, sieve to obtain modified copper powder.

[0039] This invention also provides a conductive copper paste, which, by mass percentage, comprises: 70%–90% modified copper powder, 0.8%–3% in-situ diffusion barrier precursor, 5%–15% organic resin, 5%–20% organic solvent, and 0.1%–1% additives. The in-situ diffusion barrier precursor comprises one or more of nano-TiO2, nano-ZrO2, tetraisopropyl titanate, and zirconium acetylacetonate; specifically, nano-TiO2 can be anatase nano-TiO2. The modified copper powder is the modified copper powder described above or prepared using the preparation method described above.

[0040] Specifically, this embodiment adds an in-situ diffusion barrier precursor to the conductive copper paste. During the sintering process, the in-situ diffusion barrier precursor can generate a dense ceramic barrier layer (specifically a TiO2 ceramic barrier layer or a ZrO2 ceramic barrier layer) in situ at the interface between the copper electrode and silicon. This effectively prevents copper atoms from diffusing into the silicon substrate, protects the passivation structure of the battery, and improves the battery's open-circuit voltage, fill factor, and photoelectric conversion efficiency. This solves the problem that copper atoms in existing copper paste easily diffuse into the silicon substrate and passivation layer, causing battery leakage, efficiency degradation, and reduced reliability. It also solves the problems of cumbersome additional diffusion barrier layer preparation process, easy damage to the passivation layer by conventional glass powder, and impact on battery open-circuit voltage.

[0041] The modified copper powder can be 70%, 75%, 80%, 85%, 90% by mass, or any combination thereof. The in-situ diffusion barrier precursor can be 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3% by mass, or any combination thereof. The organic resin can be 5%, 7%, 10%, 12%, 15% by mass, or any combination thereof. The organic solvent can be 5%, 7%, 10%, 12%, 15%, 18%, 20% by mass, or any combination thereof. The additives can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% by mass, or any combination thereof.

[0042] In one implementation method, the particle size D50 of nano-TiO2 is 10nm~20nm, and the particle size D50 of nano-ZrO2 is 10nm~30nm.

[0043] In one embodiment, the organic resin includes one or more of ethyl cellulose and modified acrylic resin. The ethyl cellulose is a low molecular weight, low viscosity thermoplastic ethyl cellulose, with a viscosity of 5-20 mPa·s (preferably 5-10 mPa·s), and an ethoxy content of 48%-49.5%. The ethyl cellulose may contain one type of ethyl cellulose or multiple different types of ethyl cellulose (as long as the above conditions are met). The modified acrylic resin includes one or more of thermoplastic acrylic resin, hydroxyl-modified acrylic resin, carboxyl-modified acrylic resin, and alkyl-modified acrylic resin. Low molecular weight ethyl cellulose, due to its low molecular weight, has moderate viscosity, making it easy to print; furthermore, it readily pyrolyzes at around 300°C, leaving minimal residue. Modified acrylic resin can significantly improve the adhesion, leveling, and dispersion stability of the slurry, and optimize the grid morphology and interfacial bonding.

[0044] In one embodiment, the organic solvent includes one or more of diethylene glycol monobutyl ether, ethylene glycol, isopropanol, glycerol, cyclohexanone, cyclohexanol, terpineol, and diethylene glycol monobutyl ether acetate.

[0045] In one embodiment, the additives include one or more of the following: ammonium polyacrylate, polyether-modified polydimethylsiloxane, polyamide wax, and hydrogenated castor oil.

[0046] As one implementation method, the specific preparation steps of conductive copper paste are as follows: Step 1: Add modified copper powder, in-situ diffusion barrier precursor, organic resin, organic solvent and additives to the reaction apparatus in proportion and mix to obtain a mixture. Step 2: Stir the mixture to ensure that all materials are evenly moistened; Step 3: Grind the mixture using a three-roll mill with a grinding gap of 5μm-120μm and a grinding speed of 50r / min-400r / min to obtain conductive copper paste. The fineness of the conductive copper paste, as measured by an FOG scraper fineness gauge, is less than 2.5μm.

[0047] This invention also provides a solar cell, including a copper electrode, which is obtained by sintering conductive copper paste as described above. Specifically, the conductive copper paste is screen-printed, dried, and sintered on the surface of a silicon wafer to form metal grid lines, thereby forming the desired copper electrode.

[0048] The beneficial effects of this embodiment include: 1. By coating the surface of copper powder with organic matter to form an organic protective layer, the modified copper powder not only has good dispersibility and strong oxidation resistance, but also the organic protective layer can be completely thermally removed during low-temperature sintering without affecting the formation of the conductive network. The conductive copper paste using this modified copper powder can be sintered rapidly at low temperature in an air atmosphere without the need for protective gases such as nitrogen and hydrogen. It can be directly adapted to existing crystalline silicon solar cell screen printing and sintering production lines, with strong process compatibility and low equipment investment. The copper electrode formed after sintering of the conductive copper paste has low resistivity and excellent conductivity.

[0049] 2. By adding an in-situ diffusion barrier precursor to the conductive copper paste, a dense ceramic barrier layer can be generated in-situ at the interface between the copper electrode and silicon during the sintering process. This effectively prevents copper atoms from diffusing into the silicon substrate, protects the passivation structure of the battery, and improves the battery's open-circuit voltage, fill factor, and photoelectric conversion efficiency.

[0050] 3. Replacing silver powder with copper powder as the conductive substrate of the electrode significantly reduces raw material costs, and the process is compatible with existing photovoltaic production lines, which is conducive to promoting the development of silver-free and low-cost solar cells.

[0051] The conductive copper paste in this embodiment, with its core advantages of being able to be sintered rapidly at low temperatures in an air atmosphere, having good oxidation resistance and in-situ diffusion blocking function without damaging the passivation layer, can be widely used in the metallization of crystalline silicon solar cells (including N-type crystalline silicon solar cells such as TOPCon, HJT, IBC, and X-BC), flexible and BIPV photovoltaic modules, as well as electronic devices such as flexible electronics, sensors, and RFID tags. At the same time, it has good expansion potential in power device packaging, transparent conductive films, and other scenarios.

[0052] [Example 1] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 82% In-situ diffusion barrier precursor nano-TiO2: 2% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0053] The preparation methods for modified copper powder and conductive copper paste are described above and will not be repeated here.

[0054] [Example 2] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 82% In-situ diffusion-blocking precursor nano-ZrO2: 2% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0055] [Example 3] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 82% In-situ diffusion-blocking precursor tetraisopropyl titanate: 2% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0056] [Example 4] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 82% In-situ diffusion-blocking precursor zirconium acetylacetonate: 2% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0057] [Comparative Example 1] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 65% In-situ diffusion-blocking precursor zirconium acetylacetonate: 2% Organic resins: 9.6% ethyl cellulose (Dow STD-4), 5% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767) Organic solvents: terpineol 9.5%, diethylene glycol monobutyl ether 8.4% Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0058] [Comparative Example 2] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 93% In-situ diffusion barrier precursor nano-TiO2: 2% Organic resins: 1.3% ethyl cellulose (Dow STD-4), 0.7% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: terpineol 1.3%, diethylene glycol monobutyl ether 1.2% Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0059] [Comparative Example 3] A conductive copper paste, made from the following raw materials in weight percentages: Unmodified copper powder (unmodified copper powder is pure copper powder, with a particle size D50 of 50-80nm): 82% In-situ diffusion barrier precursor nano-TiO2: 2% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0060] [Comparative Example 4] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 84% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0061] [Comparative Example 5] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 83.5% In-situ diffusion-barrier precursor nano-TiO2: 0.5% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0062] [Comparative Example 6] A conductive copper paste, made from the following raw materials in weight percentages: Modified copper powder (particle size D50 of copper powder is 50-80nm, organic coating agent is long-chain saturated fatty acid, coating amount is 1.8%): 80.5% In-situ diffusion-barrier precursor nano-TiO2: 3.5% Organic resins: 4.6% ethyl cellulose (Dow STD-4), 2.4% hydroxyl-modified acrylic resin (Allnex Setalux™ 1767). Organic solvents: 4.5% terpineol, 4% diethylene glycol monobutyl ether Additives: 0.2% ammonium polyacrylate, 0.3% polyether-modified polydimethylsiloxane.

[0063] [Comparative Example 7] Commercially available standard TOPCon fine grid pure silver paste.

[0064] The conductive copper pastes of Examples 1 to 4, Comparative Examples 1 to 6, and the pure silver paste of Comparative Example 7 were used as samples. Each sample was printed on the same substrate and relevant performance tests were conducted. The test process is as follows: 1. Contact Resistance and Photovoltaic Conversion Efficiency: After printing specific patterns onto TOPcon solar cells using a paste (copper / silver paste), the paste is dried and cured. Solar cells of a specified size with the printed pattern area are cut using a laser slicing machine. The contact resistance of each solar cell is measured using a contact resistance meter, specifically the Maiwei IV. The EL tester performs photoelectric conversion efficiency tests on each solar cell.

[0065] 2. Viscosity test: Take a sample of 15~20g of slurry and use a Brookfield DV2 viscometer and a rotor SC-14 to measure the average viscosity of the slurry at 25℃ / 10rpm / 60s.

[0066] 3. Resistivity test: The resistance between the two ends of the electrode is tested using a four-probe ohmmeter.

[0067] 4. 3D morphology image test: The surface grid morphology image of the slurry was tested using Keyence 3D morphology image testing instrument.

[0068] 5. Printability Test: The conductive pastes from the above embodiments and comparative examples were printed onto the back of the silicon wafer using screen printing technology. The screen specifications used for printability testing were a knotless, multi-aperture screen with 500 mesh / 6μm wire diameter / total thickness of 12-13μm / apertures of 11μm, 10μm, and 9μm respectively. The solar cells were dried in an infrared drying oven, and then the printability of the paste was observed with the naked eye and an optical microscope to determine whether there were any broken grids or incomplete prints.

[0069] The performance test data (contact resistance, resistivity, viscosity, photoelectric conversion efficiency, and printability) are shown in the table below:

[0070] As can be seen from the table above: 1. As can be seen from Example 1, Comparative Example 1, and Comparative Example 2, the optimal amount of modified copper powder is 70%-90%. In Comparative Example 1, the amount of modified copper powder added was too low, resulting in low slurry viscosity, poor ink permeability, and insufficient conductive phase, leading to increased volume resistance and contact resistance, and a significant decrease in efficiency. In Comparative Example 2, the amount of modified copper powder added was too high, resulting in insufficient organic carrier ratio, increased internal frictional resistance in the slurry, and a significantly higher viscosity of 75.8 Pa·s, causing severe grid breakage during printing. Furthermore, excessive accumulation of copper powder particles led to agglomeration and porosity, reducing electrode density and resulting in low conductivity and photoelectric conversion efficiency. In Example 1, the modified copper powder content was moderate, the viscosity was within the optimal process window, printability was excellent, and the copper powder was uniformly dispersed in the organic carrier, forming a dense and continuous conductive path.

[0071] 2. As can be seen from Example 1 and Comparative Example 3, the modification treatment of copper powder plays a decisive role in the slurry dispersibility, electrode density, and oxidation resistance. Comparative Example 3 uses unmodified nano-copper powder, which lacks a coating layer on the particle surface, making it prone to agglomeration and oxidation. This results in poor slurry dispersibility, severe grid breakage, and high porosity and thickened oxide layer inside the electrode after sintering, significantly increasing bulk resistance and contact resistance. Example 1 uses modified nano-copper powder, which exhibits excellent particle dispersibility and a surface coating layer that effectively inhibits oxidation. It also produces good printing and forming of a dense and continuous conductive network, effectively reducing resistivity and significantly improving the photoelectric conversion efficiency of the battery.

[0072] 3. As can be seen from Examples 1 and Comparative Examples 4-6, the addition and dosage of the in-situ diffusion barrier precursor are crucial to the electrode interface performance. In Comparative Example 4, no precursor was added, and copper atoms easily diffused to form a high-resistance interface, leading to increased contact resistance and decreased efficiency. In Comparative Example 5, the amount of precursor was insufficient, failing to form a dense barrier layer, resulting in limited improvement in conductivity. In Comparative Example 6, the excessive amount of precursor introduced too much insulating phase and damaged printability, leading to reduced efficiency. In Example 1, the amount of precursor was moderate, forming a continuous and uniform barrier layer, effectively suppressing copper diffusion and maintaining a good conductive network, achieving an optimal balance of various performance characteristics. This indicates that there is a strict optimal range for the amount of precursor added. This invention, through precise control of the dosage, balances diffusion suppression effect and electrode conductivity.

[0073] 4. As can be seen from Example 1 and Comparative Example 7, the copper paste of the present invention is equally competitive with commercially available silver paste. Although the commercially available silver paste used in Comparative Example 7 has excellent conductivity, it is expensive. The copper paste used in Example 1 significantly reduces the cost of electrode materials while ensuring that printability, electrode density, and photoelectric conversion efficiency are close to those of commercially available silver paste. At the same time, it effectively suppresses copper diffusion through an in-situ barrier layer, achieving a balance between low cost and high performance, and has the potential to replace traditional silver paste in industrial applications.

[0074] In summary, this invention achieves synergistic optimization of paste printability, electrode oxidation resistance, interfacial diffusion inhibition, and battery photoelectric performance through precise proportioning of modified nano-copper powder, surface modification treatment, and optimal dosage design of in-situ diffusion-blocking precursors. The electrode surface smoothness and linewidth fidelity prepared in the embodiments of this invention are significantly better than those of the comparative examples. Compared with existing technologies, the copper paste of this invention can achieve low-temperature rapid sintering in an air atmosphere, significantly reducing raw material costs while achieving photoelectric conversion efficiency close to that of commercially available silver paste, thus solving the industry pain points of traditional copper paste such as easy oxidation, severe interfacial diffusion, and poor process adaptability.

[0075] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A modified copper powder for use in conductive copper paste, characterized in that, The modified copper powder includes copper powder and organic matter, wherein the organic matter coats the surface of the copper powder to form an organic protective layer; the organic protective layer can decompose during the sintering process of the conductive copper paste.

2. The modified copper powder as described in claim 1, characterized in that, The organic compound is a long-chain fatty acid or octanoylglutamic acid.

3. The modified copper powder as described in claim 1, characterized in that, In the modified copper powder, the mass of the organic matter is 1% to 3% of the mass of the copper powder.

4. The modified copper powder as described in claim 1, characterized in that, The thermal decomposition temperature of the organic matter is 150℃~300℃.

5. The modified copper powder according to any one of claims 1-4, characterized in that, The copper powder has a particle size D50 of 30nm to 100nm and a specific surface area of ​​10m². 2 / g~25m 2 The tap density of the copper powder is 1.8 g / cm³. 3 ~2.8g / cm 3 .

6. A method for preparing modified copper powder as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Add copper powder to the solvent and disperse it evenly to obtain a suspension; S2: Add organic matter to the suspension and stir evenly so that the organic matter coats the surface of the copper powder to form an organic protective layer; S3: Separate, wash and dry the solid products in the suspension in sequence to obtain modified copper powder.

7. The preparation method according to claim 6, characterized in that, In step S1 above, the primary particle size D50 of the copper powder is 30nm~50nm, and the secondary particle size D50 of the copper powder is 50nm~100nm. And / or, the solvent is anhydrous ethanol or isopropanol.

8. The preparation method according to claim 6, characterized in that, In step S2 above, the stirring conditions are: stirring for 2 to 4 hours under water bath heating conditions of 50℃ to 65℃.

9. The preparation method according to claim 6, characterized in that, In step S3 above, the solid product is vacuum dried under the following conditions: vacuum degree of -0.08MPa to -0.1MPa, drying temperature of 40℃ to 60℃, and drying time of 6 hours to 12 hours.

10. A conductive copper paste, characterized in that, The conductive copper paste, by mass percentage, comprises: 70%–90% modified copper powder, 0.8%–3% in-situ diffusion barrier precursor, 5%–15% organic resin, 5%–20% organic solvent, and 0.1%–1% additives; the in-situ diffusion barrier precursor comprises one or more of nano-TiO2, nano-ZrO2, tetraisopropyl titanate, and zirconium acetylacetonate; the modified copper powder is the modified copper powder as described in any one of claims 1–5 or prepared by the preparation method as described in any one of claims 6–9.

11. The conductive copper paste as described in claim 10, characterized in that, The organic resin includes one or more of ethyl cellulose and modified acrylic resin; the viscosity of the ethyl cellulose is 5~20 mPa·s, and the ethoxy content of the ethyl cellulose is 48%~49.5%; the modified acrylic resin includes one or more of thermoplastic acrylic resin, hydroxyl-modified acrylic resin, carboxyl-modified acrylic resin, and alkyl-modified acrylic resin. And / or, the organic solvent includes one or more of diethylene glycol monobutyl ether, ethylene glycol, isopropanol, glycerol, cyclohexanone, cyclohexanol, terpineol, and diethylene glycol monobutyl ether acetate; And / or, the additives include one or more of the following: ammonium polyacrylate, polyether-modified polydimethylsiloxane, polyamide wax, and hydrogenated castor oil.

12. A solar cell, characterized in that, It includes a copper electrode, which is obtained by sintering a conductive copper paste as described in claim 10 or 11.

Images