Copper slurry and preparation method and application thereof

Abstract

The invention discloses copper paste and a preparation method and application thereof. The copper paste comprises copper powder, resin, a curing agent, a dispersing agent, a reducing copper precursor and a solvent. The reducing copper precursor is a reducing copper complex or a mixture composed of copper salt and a reducing agent; the reductive copper complex is composed of copper ions and reductive ligands; the reducing ligand is selected from one or more than two of organic acid and phenolic compounds containing reducing groups; the reducing agent is selected from one or more than two of organic acid containing reducing groups and phenolic compounds. According to the copper slurry disclosed by the invention, the reducing copper precursor is introduced and is dissolved in the organic phase, and uniform and fine copper nanoparticles are generated in situ in the curing process and are embedded among resin or copper powder particles, so that a conductive path is increased, a tunneling potential barrier among the resin is reduced, and the conductivity is increased.

Description

Technical Field

[0001] This application relates to the field of solar cells, specifically to a copper paste, its preparation method, and its application. Background Technology

[0002] In the 21st century, humanity has become increasingly reliant on electronic information products. These products consist of a variety of components. Currently, electronic pastes are one of the fundamental materials for the development of electronic components towards lightweighting, miniaturization, environmental friendliness, and low cost. Electronic pastes can be used to manufacture electronic components such as electrodes, wires, capacitors, inductors, and resistors, and are widely used in numerous fields including electronic computers, aerospace, automotive, and communications. Conductivity is one of the important parameters for evaluating the quality of electronic pastes. Conductive pastes, as a crucial component of solar cells, play a vital role in improving cell efficiency. Different types of cell structures have different requirements for grid lines. Due to the unique properties of amorphous silicon thin films, such as high hydrogen content, HJT cells require that the production temperature not exceed 250℃. The conductivity of the grid lines has a significant impact on cell efficiency; therefore, the development of high-conductivity cell grid lines is urgently needed. Summary of the Invention

[0003] This application aims to provide a low-temperature curing electronic paste that is resistant to thermal shock. During the curing process, the paste generates uniform and fine copper nanoparticles in situ, which can be distributed to give it low resistivity and contact resistance. Furthermore, the paste exhibits high storage stability, which is beneficial for subsequent processing.

[0004] This application provides a copper paste comprising copper powder, resin, curing agent, reduced copper precursor, solvent, and optional dispersant;

[0005] The reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent;

[0006] The reducing copper complex is composed of copper ions and reducing ligands; the reducing ligands are selected from one or more organic acids and phenolic compounds containing reducing groups.

[0007] The reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups.

[0008] Further, the copper powder comprises 70-95 parts by weight, the resin comprises 2-20 parts by weight, the curing agent comprises 0.1-3 parts by weight, the dispersant comprises 0-10 parts by weight, the reduced copper precursor comprises 0.5-10 parts by weight, and the solvent comprises 5-20 parts by weight.

[0009] Furthermore, the copper salt is an organic copper salt or an inorganic copper salt.

[0010] Furthermore, the organic acid is selected from organic acids containing an aldehyde group, a hydroxyl group, or a double bond;

[0011] The phenolic compounds are selected from aromatic compounds having one or more hydroxyl substitutions or heteroaromatic compounds having hydroxyl substitutions.

[0012] Further, the resin is selected from one or more of epoxy resin, phenolic resin, acrylic resin, polyester resin, polyurethane resin, and aldehyde-ketone resin, preferably epoxy resin; or

[0013] The curing agent is selected from one or more of the following: dicyandiamide curing agents, acid anhydride curing agents, latent imidazole curing agents, blocked amine curing agents, and polysulfide curing agents; or

[0014] The solvent is selected from one or more of diethylene glycol butyl ether acetate, terpineol, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and 2-methyl-2,4-pentanediol; or,

[0015] Optionally, the dispersant is selected from fatty acids, fatty amines, polyethers, aliphatic anionic surfactants, or aliphatic cationic surfactants.

[0016] In this application, "optional" refers to the presence or absence of a dispersant. For example, in one embodiment, the copper paste of this application contains a dispersant; in another embodiment, the copper paste of this application does not contain a dispersant.

[0017] Furthermore, the copper powder includes flake copper powder, the thickness D50 of which is 1-100 nm and the particle size D50 is 100-8000 nm;

[0018] Furthermore, the copper powder also includes spherical copper powder. Based on the mass of 100% copper powder, the mass percentage of the flake copper powder is 40-70%, and the mass percentage of the spherical copper powder is 30-60%; or the particle size D50 of the spherical copper powder is 50-3000 nm.

[0019] This application also provides a method for preparing the aforementioned copper paste, comprising the following steps:

[0020] Copper powder, resin, curing agent, reduced copper precursor, solvent and optional dispersant are mixed and stirred evenly to obtain the copper paste.

[0021] The reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent;

[0022] The reducing copper complex is composed of copper ions and reducing ligands; the reducing ligands are selected from one or more organic acids and phenolic compounds containing reducing groups.

[0023] The reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups.

[0024] This application also provides an electrode, wherein the electrode is prepared by the aforementioned copper paste or the copper paste obtained by the aforementioned preparation method.

[0025] This application also provides a solar cell, including the aforementioned electrodes.

[0026] Furthermore, the electrode contains nano-copper powder.

[0027] This application also provides a solar cell, which includes an electrode comprising nano-copper powder and micron-sized flake copper powder. The electrode has a contact interface with the surface of the solar cell, and the projected area of ​​the nano-copper powder on the contact interface is greater than the projected area of ​​the micron-sized flake copper powder on the contact interface.

[0028] Furthermore, the surface of the aforementioned solar cell has a textured surface, and the electrode is located on the upper part of the textured surface of the solar cell.

[0029] Furthermore, the velvety structure has a recessed structure, and the recessed structure is filled with the nano-copper powder.

[0030] The copper paste described in this application incorporates a reduced copper precursor, which dissolves in the organic phase. During curing, uniform and fine copper nanoparticles are generated in situ and uniformly embedded between the resin or copper powder particles, increasing conductive pathways, reducing the tunneling barrier between resins, and increasing conductivity. Furthermore, this paste exhibits high storage stability, which is beneficial for subsequent processing. Specifically, for textured solar cells, the in-situ generated nano-copper powder can be distributed on the textured surface, improving grid adhesion and the contact resistance between the grid and the TCO. Attached Figure Description

[0031] Figure 1 SEM image of the electrode grid lines provided in this application. Detailed Implementation

[0032] The following description provides exemplary embodiments of this application, including various details to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0033] Existing technologies use copper-amine complexes to prepare in-situ reduced copper paste. The amine reducing agents in these pastes are chemically reactive, generating a large amount of ammonium salts. These ammonium salts act as catalysts for active groups such as epoxy and isocyanate compounds, reducing the stability of the paste and consequently affecting the curing process during grid line fabrication, leading to a decrease in grid line conductivity. This application introduces a reduced copper precursor into the paste, allowing it to dissolve in the organic phase and exhibiting high storage stability, which is beneficial for the screen printing process. During curing, in-situ generated copper nanoparticles are uniformly embedded between resin or powder particles, increasing conductive pathways, reducing the tunneling barrier between resins, and increasing conductivity. Furthermore, the nano-copper powder can be generated in-situ on the TCO surface of the battery, reducing contact resistance. The specific technical solution is as follows:

[0034] This application provides a copper paste comprising copper powder, resin, curing agent, reduced copper precursor, solvent, and optional dispersant;

[0035] In the above copper paste, the reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent;

[0036] In this paper, the reduced copper precursor plays three roles: first, it can reduce copper ions to generate nano-copper powder during the curing of copper paste, thereby increasing the conductive path and improving the conductivity of the grid lines; second, due to its complexation with metals, it can control the particle size and uniformity of the generated nano-copper powder, thereby improving the adhesion of the paste to the battery surface; and third, due to its higher photothermal stability compared to amines and its high compatibility with other components of the paste, it improves the storage stability of the paste.

[0037] The particle size D50 of the further generated nano-copper powder is less than or equal to 200nm, for example, it can be 200nm, 180nm, 160nm, 140nm, 120nm, 100nm, 80nm, 60nm, 50nm, etc.

[0038] In this paper, D50 refers to the particle size at which the cumulative volumetric particle size distribution percentage of a sample reaches 50%. Physically, it means that 50% of the particles are larger than D50, and 50% are smaller. D50 is also called the median particle size or median particle size. The D50 of nano-copper powder was obtained using scanning electron microscopy (SEM). Specifically, more than 10 nano-copper powder particles in the test sample were photographed, and the median particle size was calculated. In copper paste, the D50 values ​​for various copper powder particle sizes were measured using a laser particle size analyzer. In electrodes, the D50 values ​​for various copper powder particle sizes were measured using SEM.

[0039] In some embodiments, the copper paste contains 70-95 parts by weight of copper powder, preferably 85-92 parts by weight; 2-20 parts by weight of resin, preferably 2-5 parts by weight; 0.1-3 parts by weight of curing agent, preferably 0.2-1 parts by weight; 0-10 parts by weight of dispersant, preferably 0.2-2 parts by weight; 0.5-10 parts by weight of reduced copper precursor, preferably 2-5 parts by weight; and 5-20 parts by weight of solvent, preferably 5-7 parts by weight. In some embodiments, the copper powder contains 75-90 parts by weight.

[0040] In some embodiments, the copper powder is in the form of 85 to 92 parts by weight.

[0041] Specifically, in the copper paste, the weight parts of the copper powder can be 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts, 89 parts, 90 parts, 94 parts, 92 parts, 93 parts, 94 parts, 95 parts, etc.

[0042] In some embodiments, the resin is 2-15 parts by weight.

[0043] In some embodiments, the resin is present in 2-5 parts by weight.

[0044] In the copper paste, the weight parts of the resin can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

[0045] In some embodiments, the curing agent is present in 1-3 parts by weight.

[0046] In some embodiments, the curing agent is present in parts by weight of 0.2-1 parts.

[0047] In the copper paste, the curing agent can be present in weight parts of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 parts, etc.

[0048] In some embodiments, the dispersant is present in parts by weight of 1-5 parts.

[0049] In some embodiments, the dispersant is present in a weight fraction of 0.2-2 parts.

[0050] In the copper paste, the weight percentage of the dispersant can be 0 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc. The dispersant can control the particle size of the in-situ generated nano-copper powder and improve the dispersion stability of the copper powder in the paste. Therefore, based on the use of reducing ligands or reducing agents to control the particle size, the dispersant can be further added to the copper paste if necessary to improve the dispersibility of various copper particles in the paste and enhance the stability of the paste. Those skilled in the art can choose whether to add a dispersant as needed.

[0051] In some embodiments, the solvent may be 5-15 parts by weight.

[0052] In some embodiments, the solvent may be 5 to 7 parts by weight.

[0053] In the copper paste, the solvent can be present in weight parts of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

[0054] In some embodiments, the reduced copper precursor may be 1-8 parts by weight.

[0055] In some embodiments, the reduced copper precursor may be 2-5 parts by weight.

[0056] In the copper paste, the weight percentage of the reduced copper precursor can be 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, etc.

[0057] In this application, the reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent.

[0058] When the reducing copper precursor is a reducing copper complex, the reducing copper complex is composed of copper ions and a reducing ligand; the reducing ligand is selected from one or more organic acids and phenolic compounds containing reducing groups; the reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups. The organic acids and phenolic compounds containing reducing groups have oxygen atoms that can complex with copper, which helps disperse copper nanoparticles when copper ions are reduced to copper. In some embodiments, the organic acid containing reducing groups is selected from organic acids containing aldehyde groups, hydroxyl groups, or double bonds; from the perspective of improving low-temperature sintering properties and slurry stability, the number of carbon atoms in the organic acid containing reducing groups is preferably 2-20, and more preferably aliphatic carboxylic acids, such as glyoxylic acid, glycolic acid, oxalic acid, citric acid, succinic acid, maleic acid, tartaric acid, ascorbic acid, lactic acid, methanesulfonic acid, fumaric acid, ricinoleic acid, citric acid, malic acid, oleic acid, etc. The number of carbon atoms is preferably 4-10, such as citric acid, succinic acid, maleic acid, tartaric acid, fumaric acid, malic acid, etc.

[0059] When the reducing ligand is selected from organic acids containing reducing groups, the reducing copper complex is preferably one or more of copper citrate, copper succinate, copper maleate, copper tartrate, copper fumarate, and copper malate; the reducing agent is preferably one or more of citric acid, succinic acid, maleic acid, tartaric acid, fumaric acid, and malic acid.

[0060] The phenolic compounds are selected from aromatic compounds with one or more hydroxyl substitutions or heteroaromatic compounds with hydroxyl substitutions. From the perspective of improving low-temperature sintering performance and slurry stability, the aromatic compounds have 6-18 carbon atoms and are selected from benzene, naphthalene, anthracene, fluorene, etc.; the heteroaromatic compounds have 5-18 carbon atoms and are selected from pyridine, furan, thiophene, imidazole, etc. The aromatic compounds or heteroaromatic compounds can be further substituted with other substituents, such as hydrogen, alkyl, alkenyl, alkynyl, halogen, or cyano. The phenolic compounds are preferably substituted with 1-5 hydroxyl groups. For phenolic compounds with two or more hydroxyl substitutions, examples include catechol, hydroquinone, resorcinol, catechol, and dopamine. For phenolic compounds with one hydroxyl substitution, tert-butylphenol or 2,6-di-tert-butyl-p-methylphenol are preferred.

[0061] Furthermore, reducing organic acids can be added to the reducing copper complex. The copper complex can better control the particle size of the nano-copper and protect it from oxidation, while the reducing organic acid plays a role in in-situ reduction to generate copper. This improves the stability of the slurry, controls the particle size of the in-situ generated particles, and enhances the electrical properties. In the slurry, the amount (molar amount) of reducing organic acid added to the copper complex is 1%-10% relative to the molar amount of the copper complex, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc.

[0062] The reducing copper precursor is a mixture of copper salt and reducing agent. The reducing agent is preferably a phenolic compound.

[0063] Further, the molar ratio of the copper salt to the reducing agent is 1:(0.3-10), for example, it can be 1:0.3, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10, etc.

[0064] By changing the molar ratio of copper salt to reducing agent, the reduction process of copper salt can be controlled. The oxygen atoms on the reducing agent can complex with copper ions. On the one hand, the reducing agent reduces copper ions to copper, and on the other hand, the newly generated nano copper powder is coated by the reducing agent, which prevents the nano copper powder from agglomerating and makes it uniformly dispersed in the slurry system. Therefore, too little reducing agent will make the reduction process slow and leave unreduced copper ions, while too much reducing agent is not conducive to the curing process of the slurry.

[0065] Furthermore, the copper salt is an organic copper salt or an inorganic copper salt.

[0066] Specifically, the organic copper salt is selected from fatty acid copper, such as copper acetate, copper formate, copper propionate, copper stearate, copper oleate, and amino acid copper, preferably copper oleate or copper acetate.

[0067] Specifically, the inorganic copper salt is selected from one of copper chloride, copper sulfate, copper phosphate, copper hydroxide, and basic copper carbonate, preferably copper phosphate.

[0068] In this paper, when the reducing agent or reducing ligand is a reducing organic acid, since reducing organic acids are all weak acids, they have good stability and their stability is even better after salt formation or coordination. The boiling points of carboxyl compounds with the same carbon chain structure are generally higher than those of amines, and their stability is better than that of amine compounds. The range of reducing acid ligands that can be selected is wider, and it is easier to obtain nanopowders with better uniform dispersion.

[0069] In this application, the resin is selected from one or more of epoxy resin, phenolic resin, acrylic resin, polyester resin, polyurethane resin, and aldehyde-ketone resin, preferably epoxy resin. The epoxy resin includes, but is not limited to, bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, etc., forming a strong and tough bonding phase.

[0070] The curing agent is selected from one or more of the following: dicyandiamide curing agents, acid anhydride curing agents, latent imidazole curing agents, blocked amine curing agents, and polysulfide curing agents.

[0071] Optionally, the dispersant is selected from fatty acids, fatty amines, polyethers, aliphatic anionic surfactants, or aliphatic cationic surfactants. The dispersant can control the particle size of the in-situ generated copper nanoparticles.

[0072] The solvent is selected from one or more of diethylene glycol butyl ether acetate, terpineol, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and 2-methyl-2,4-pentanediol.

[0073] The solvent has a boiling point of 170–300°C, for example, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C.

[0074] 290℃, 300℃, etc. When the boiling point of the solvent is between 170 and 300℃, the solvent is not easily volatile during the long-term printing process of the copper paste, thereby avoiding the paste from becoming viscous.

[0075] In this application, the copper powder includes flake copper powder, the thickness D50 of which is 1-100 nm, for example, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, etc., and the particle size D50 of which is 100-8000 nm. m can be, for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm, 3500nm, 4000nm, 4500nm, 5000nm, 5500nm, 6000nm, 6500nm, 7000nm, 7500nm, 8000nm, etc.

[0076] In this application, the copper powder also includes spherical copper powder. Based on the mass of 100% copper powder, the mass percentage of the flake copper powder is 40%-70%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., and the mass percentage of the spherical copper powder is 30%-60%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.

[0077] In this paper, flake-like copper powder refers to copper powder with an aspect ratio (diameter / thickness) greater than or equal to 2 in images observed under a scanning microscope. The ratio of the longest diameter to the shortest diameter of the flake-like copper powder is 1-10. The particle size D50 of the flake-like copper powder refers to the diameter D50. Spherical copper powder refers to copper powder with an aspect ratio (diameter / thickness) less than 2 in images observed under a scanning microscope.

[0078] The particle size D50 of the spherical copper powder is 50-3000nm, for example, it can be 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm, etc.

[0079] In this application, a reducing copper precursor is introduced into the copper paste, dissolving it in the organic phase. During the curing process, the reducing ligand or reducing agent in situ generates copper ions to form nano-copper powder embedded between the resin or powder particles, increasing the conductive pathway, reducing the tunneling barrier between resins, and increasing conductivity. Furthermore, the nano-copper particles can be generated in situ on the TCO surface, reducing contact resistance. In this paper, the reducing agent is a copper ligand. When the reducing agent is a reducing acid, since reducing acids are all weak acids, they inherently possess good stability, and their stability is even better after salt formation or coordination. Carboxyl compounds with the same carbon chain structure generally have higher boiling points than amines, exhibiting superior stability. The range of reducing acid ligands that can be selected is wider, resulting in better dispersibility. Furthermore, choosing a more potent reducing acid makes it easier to obtain uniform nanoparticles. Existing technologies use copper-amine complexes to prepare in-situ reduced copper paste. The amine reducing agents in these pastes are chemically active and generate a large amount of ammonium salts in the paste. Ammonium salts act as catalysts for active groups such as epoxy and isocyanate, reducing the stability of the paste and consequently affecting the curing process during grid line preparation, leading to a decrease in the conductivity of the grid lines.

[0080] This application also provides a method for preparing the aforementioned copper paste, comprising the following steps:

[0081] Copper powder, resin, curing agent, reduced copper precursor, solvent and optional dispersant are mixed and stirred evenly to obtain the copper paste.

[0082] The reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent;

[0083] The reducing copper complex is composed of copper ions and reducing ligands; the reducing ligands are selected from one or more organic acids and phenolic compounds containing reducing groups.

[0084] The reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups, preferably phenolic compounds.

[0085] Furthermore, to prevent the copper powder in the copper paste from being oxidized, an anti-oxidation layer is generally formed on the surface of the copper powder. The method for forming the anti-oxidation layer is a conventional method, for example, by forming the anti-oxidation layer in the following ways:

[0086] Before the copper powder is mixed with the resin, curing agent, reduced copper precursor, solvent, and optional dispersant, a pretreatment process is required. The specific steps are as follows:

[0087] Step a: Place the copper powder in alcohol for ultrasonic cleaning;

[0088] Step b: The copper powder after ultrasonic cleaning is centrifuged and washed for the first time with water and ethanol;

[0089] Step c: Add the washed copper powder to acid for pickling; (the pH of the acid is between 4 and 5, the temperature during the pickling process is 40℃, and the pickling time is 30 min to 2 h)

[0090] Step d: The acid-washed copper powder is centrifuged and washed a second time with water and ethanol (a mixed solvent of water and ethanol in a 1:1 ratio) until the pH reaches 7.

[0091] Step e: The copper powder after the second centrifugal washing is passivated in a passivation solution to obtain pretreated copper powder.

[0092] Specifically: the second dispersant, alcohol solvent and passivation reagent are mixed to prepare a passivation solution. The copper powder obtained after step d is added to the passivation solution and stirred at room temperature for 30 min. The solution is then washed with ethanol until the conductivity is less than 30 μΩ·cm.

[0093] Further, the alcohol is selected from one or more of ethanol, ethylene glycol, methanol, glycerol, tetramethylethylene glycol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, n-pentanol, sec-pentanol, 3-pentanol, tert-pentanol, and n-hexanol, preferably ethanol, methanol, or propanol.

[0094] Furthermore, the acid is selected from one or more of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, perchloric acid, sulfurous acid, phosphoric acid, hydrofluoric acid, acetic acid, carbonic acid, hydrosulfuric acid, and hypochlorous acid, preferably sulfuric acid.

[0095] Furthermore, the second dispersant is selected from one or more of saturated / unsaturated fatty acids containing 8-18 carbons, silane coupling agents, PVP, and thiols, preferably saturated / unsaturated fatty acids, such as oleic acid.

[0096] Furthermore, the passivating agent is selected from one or more of ascorbic acid, glucose, hydrazine hydrate, sodium hypophosphite monohydrate, sodium borohydride, potassium borohydride, and formaldehyde, preferably ascorbic acid.

[0097] This application also provides an electrode, wherein it is prepared by the aforementioned copper paste.

[0098] Pre-prepared copper paste is screen-printed onto solar cells (e.g., HJT / HBC) with grid line widths of 40-120 μm. The cells are then cured in a nitrogen oven at 100-200°C for 10-60 minutes, forming the electrode grid lines. These grid lines can be characterized using SEM (Series Electron Microscopy). Figure 1As shown, the in-situ generated nano-copper powder can be distributed on the surface of the battery cell. Moreover, when the copper paste contains micron-sized flake copper powder, the nano-copper powder occupies a larger area on the contact interface than the micron-sized flake copper powder, thereby improving the adhesion of the grid lines and the contact resistance between the grid lines and the TCO. Furthermore, the nano-copper powder is distributed between the flake copper powder.

[0099] This application also provides a solar cell, which includes the aforementioned electrodes.

[0100] Furthermore, the electrode contains nano-copper powder.

[0101] In this article, nano copper powder refers to copper particles with a particle size distribution of 1-800 nm, and the shape is not limited. It can include nano copper powder prepared in situ and / or spherical copper powder directly added to copper paste.

[0102] This application also provides a solar cell, which includes an electrode comprising nano-copper powder and micron-sized flake copper powder. The electrode has a contact interface with the surface of the solar cell, and the projected area of ​​the nano-copper powder on the contact interface is greater than the projected area of ​​the micron-sized flake copper powder on the contact interface.

[0103] In this application, the nano-copper powder has a larger specific surface area and surface activity than the micron-sized flake copper powder. The in-situ generated nano-copper powder is distributed on the contact interface and can serve as a binder between the electrode and the surface of the solar cell. By controlling the nano-copper powder to occupy a larger area on the contact interface than the micron-sized flake copper powder, the adhesion between the electrode and the surface of the solar cell can be enhanced, the contact resistance of the electrode can be reduced, and the current collection capability of the solar cell can be improved.

[0104] In some embodiments, the nano-copper powder located on the contact interface has a projected area of ​​more than 50% on the contact interface, preferably more than or equal to 70%, for example 70%, 75%, 80%, 85%, 90%, 95%, or 100%.

[0105] Furthermore, the surface of the aforementioned solar cell has a textured surface, and the electrode is located on the upper part of the textured surface of the solar cell.

[0106] In some embodiments, the solar cell has a textured surface structure that traps light to enhance solar radiation collection. The textured surface structure is a surface with a regular or irregular shape, used to scatter incident light and reduce the amount of light reflected back from the solar cell surface; specifically, it can be a pyramidal structure.

[0107] In some embodiments, the textured surface has a recessed structure filled with the nano-copper powder. The in-situ generated nano-copper powder can be distributed on the textured surface of the solar cell, improving grid line adhesion and the contact resistance between the grid line and the TCO.

[0108] Furthermore, the solar cell is selected from one of BC cells, HJT cells, and perovskite / crystalline silicon tandem cells.

[0109] Example

[0110] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0111] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0112] Example 1

[0113] In a slurry tank, 3g of epoxy resin NPEF-170, 0.5g of lauric acid, 5g of diethylene glycol butyl ether acetate, and 0.3g of dicyandiamide were added sequentially. After uniform dispersion using a centrifugal mixer at 1200 rpm, 10g of 1μm spherical copper powder, 80g of 3.5μm flake copper powder, and 1.5g of copper complex copper oleate were added. After uniform dispersion using a centrifugal mixer at 1200 rpm, the slurry was rolled 8 times using a three-roll mill to obtain the slurry. In this embodiment, the spherical and flake copper powders underwent surface pretreatment before addition, resulting in an antioxidant layer on both surfaces. This antioxidant layer was obtained using the following method:

[0114] Copper powder was ultrasonically cleaned in ethanol. The ultrasonically cleaned copper powder was then centrifuged and washed for the first time using water and ethanol. After centrifugation, the copper powder was added to sulfuric acid for acid washing. The pH of the acid was between 4 and 5, the temperature during the acid washing process was 40°C, and the washing time was 30 min to 2 h. The acid-washed copper powder was then centrifuged and washed a second time using water and ethanol until the pH reached 7. After the second centrifugation, the copper powder was passivated in a mixture of ethanol, oleic acid, and ascorbic acid, stirred at room temperature for 30 min, and then washed with ethanol until the conductivity was less than 30 μΩ·cm. The parameters of the slurry in this embodiment are shown in Table 1.

[0115] The only difference between the copper paste of Example 2 and the copper paste of Example 1 is that Catechol is added in Example 2. All other parameters are the same. The parameters of the paste in this example are shown in Table 1.

[0116] The copper pastes of Examples 3 and 4 differ from those of Example 1 only in the type of copper complex; all other parameters are the same. The parameters of the pastes in this example are shown in Table 1.

[0117] The only difference between the copper pastes of Examples 5-10 and the copper paste of Example 1 is that copper salts and reducing agents are used instead of copper complexes in Examples 5-10. All other parameters are the same. The parameters of the pastes in this example are shown in Table 1.

[0118] The only difference between the copper paste of Examples 11-12 and the copper paste of Example 5 is that the types of copper salts used in Examples 11-12 are different. All other parameters are the same. The parameters of the paste in this example are shown in Table 1.

[0119] The only difference between the copper pastes of Examples 13-15 and the copper paste of Example 5 is that the mass ratio of copper salt to reducing agent used in Examples 13-15 is different. All other parameters are the same. The parameters of the pastes in this example are shown in Table 1.

[0120] The copper paste of Comparative Example 1 differs from that of Example 1 only in that copper amine is used instead of copper complex in Comparative Example 1; all other parameters are the same. The copper amine in Comparative Example 1 is obtained as follows: copper formate and diethanolamine are mixed in a 1:1 molar ratio, and the mixture is magnetically stirred at a temperature between 25°C and 80°C for about 20 hours to obtain liquid copper amine. After filtering off excess copper formate, copper amine is obtained. The parameters of the paste in Comparative Example 1 are shown in Table 1.

[0121] Resistivity testing method: Print the paste into 20×20mm sizes. 2 The sheet resistance R□ of the block was measured by a four-probe sheet resistance tester, and its film thickness d was measured by a step tester. The sheet resistivity (ρ) = R□ × d.

[0122] Contact resistance test method: The paste printing area is 20×0.04mm. 2 The contact resistance value of 20 thin wires was tested using a TLM contact resistance tester.

[0123] Adhesion test method: Print the paste onto the main grid of the heterojunction cell, with 9BBs printed and 1mm wide. Weld one end of the solder strip to the surface of the main grid and fix the other end to the tensile testing machine for testing. Record the breaking tensile force when the solder strip or grid line peels off.

[0124] Storage stability: Slurry viscosity stability test: After the slurry is prepared, take 20g and test its viscosity on a Bollerfeld viscometer using a No. 14 rotor. Record the initial viscosity η0. After the test, store the slurry at room temperature and test its viscosity daily, recording η. The viscosity growth rate is calculated using the following formula: dη=(η-η0) / η0. When dη>20%, it is determined that the slurry storage is unqualified for the number of days recorded.

[0125] Slurry electrical performance stability test: Record the initial block resistivity ρ0 of the slurry, track its resistivity ρ daily, and calculate the resistivity growth rate according to the following formula: dρ=(ρ-ρ0) / ρ0. When dρ>20%, it is determined that the slurry storage is unqualified for the number of days.

[0126] Table 1 shows the parameters of the slurry in each embodiment and comparative example.

[0127]

[0128]

[0129] Summary: As shown in the table above, the copper paste described in this application, due to the introduction of a reduced copper precursor, dissolves in the organic phase, and during the curing process, generates uniform and fine copper nanoparticles in situ, which are embedded between the resin or copper powder particles. This increases the conductive pathway, reduces the tunneling barrier between resins, increases conductivity, and reduces resistivity. Furthermore, when the copper paste is applied to solar cells, the in-situ generated nano-copper powder can enhance the adhesion of the grid lines and reduce the contact resistance between the grid lines and the TCO. Moreover, this paste also exhibits high storage stability, which is beneficial for its subsequent processing.

[0130] Although the embodiments of this application have been described above, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of this application, and these are all within the scope of protection of this application.

Claims

1. A copper paste, wherein, Includes copper powder, resin, curing agent, reduced copper precursor, solvent, and optional dispersant; The reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent; The reducing copper complex is composed of copper ions and reducing ligands; the reducing ligands are selected from one or more organic acids and phenolic compounds containing reducing groups. The reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups.

2. The copper paste according to claim 1, wherein, The copper powder comprises 70-95 parts by weight, the resin comprises 2-20 parts by weight, the curing agent comprises 0.1-3 parts by weight, the dispersant comprises 0-10 parts by weight, the reduced copper precursor comprises 0.5-10 parts by weight, and the solvent comprises 5-20 parts by weight.

3. The copper paste according to claim 1 or 2, wherein, The copper salt is an organic copper salt or an inorganic copper salt.

4. The copper paste according to claim 1 or 2, wherein, The organic acid containing a reducing group is selected from organic acids containing an aldehyde group, a hydroxyl group, or a double bond; The phenolic compounds are selected from aromatic compounds having one or more hydroxyl substitutions or heteroaromatic compounds having hydroxyl substitutions.

5. The copper paste according to claim 1 or 2, wherein, The resin is selected from one or more of epoxy resin, phenolic resin, acrylic resin, polyester resin, polyurethane resin, and aldehyde-ketone resin; or The curing agent is selected from one or more of the following: dicyandiamide curing agents, acid anhydride curing agents, latent imidazole curing agents, blocked amine curing agents, and polysulfide curing agents; or The solvent is selected from one or more of diethylene glycol butyl ether acetate, terpineol, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and 2-methyl-2,4-pentanediol; or, optionally, the dispersant is selected from one of fatty acids, fatty amines, polyethers, aliphatic anionic surfactants, or aliphatic cationic surfactants.

6. The copper paste according to claim 1 or 2, wherein, The copper powder includes flake copper powder, the thickness D50 of which is 1-100 nm and the particle size D50 is 100-8000 nm.

7. The copper paste according to claim 6, wherein, The copper powder also includes spherical copper powder. Based on the mass of 100% copper powder, the flake copper powder accounts for 40%-70% of the mass, and the spherical copper powder accounts for 30%-60% of the mass; or, The particle size D50 of the spherical copper powder is 50-3000 nm.

8. A method for preparing copper paste according to any one of claims 1-7, wherein, Includes the following steps: Copper powder, resin, curing agent, reduced copper precursor, solvent and optional dispersant are mixed and stirred evenly to obtain the copper paste. The reducing copper precursor is a reducing copper complex or a mixture of copper salt and reducing agent; The reducing copper complex is composed of copper ions and reducing ligands; the reducing ligands are selected from one or more organic acids and phenolic compounds containing reducing groups. The reducing agent is selected from one or more organic acids and phenolic compounds containing reducing groups.

9. An electrode, wherein, The copper paste is prepared by the copper paste according to any one of claims 1-7 or by the preparation method according to claim 8.

10. A solar cell, wherein, The electrode includes the electrode of claim 9, wherein the electrode comprises nano-copper powder.

11. A solar cell, wherein, The device includes electrodes comprising nano-copper powder and micron-sized flake copper powder. The electrodes have a contact interface with the surface of the solar cell. The projected area of ​​the nano-copper powder on the contact interface is larger than the projected area of ​​the micron-sized flake copper powder on the contact interface.

12. The solar cell according to claim 10 or 11, wherein the surface of the solar cell has a textured surface, and the electrode is located on the upper part of the textured surface of the solar cell.

13. The solar cell according to claim 12, wherein the textured structure has a recessed structure, and the recessed structure is filled with the nano-copper powder.

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