Copper paste, preparation method thereof and application of copper paste in preparation of solar cell

Abstract

The invention provides copper paste, a preparation method thereof and application of the copper paste in preparation of a solar cell, and relates to the technical field of photovoltaic cells, and the copper paste comprises the following components: a conductive material and a conductive reinforcing material; the conductive material comprises at least one of gradient micron-sized nickel-tungsten coated copper powder and micron-sized nickel coated copper powder; the conductive reinforcing material comprises at least one of a nano nickel wire and nano nickel-tungsten coated copper powder. According to the invention, the slurry formula is improved, and the conductivity, the process adaptability and the low-temperature sinterability are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic cell manufacturing, and in particular to a copper slurry, a preparation method thereof, and an application thereof in the preparation of solar cells. Background Art

[0002] The electrode material of photovoltaic cells is a key factor influencing cell efficiency and cost. Traditional processes primarily use silver paste as the electrode material, but the high cost of silver has prompted the industry to turn to copper alternatives. To reduce solar cell costs and improve cell efficiency, copper-in-silver technology offers the greatest potential for cost reduction, as it allows for low or no silver paste consumption.

[0003] In the current copper manufacturing process for photovoltaic cells, a seed layer is usually first plated at the slotted position of the cell with metals such as nickel, titanium, silver, tungsten, and their alloys to prevent the diffusion of copper. Copper and tin are then plated as conductive and protective layers to obtain double-sided electroplated solar cells. On the one hand, although the existing copper electroplating process has the potential to achieve complete silver-free production, the process steps are more complicated, which leads to low yield and production capacity. At the same time, electroplating has problems such as uneven coating thickness and uneven current. This not only affects the conductive efficiency, but also has large internal stress in the coating, resulting in poor bonding between the coating and the silicon substrate. The plating solution has low stability, for example, additives are easily decomposed, and the accumulation of by-products leads to a short plating solution life, requiring frequent replacement and high cost. On the other hand, some researchers have developed copper paste or silver-coated copper paste to prepare front and back electrodes using a screen printing process. However, problems such as seed layer, silver consumption, and easy oxidation of copper still need to be considered.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a copper paste that solves at least one of the technical problems existing in the prior art. The present invention improves the paste formulation to enhance conductivity, process adaptability, and low-temperature sinterability.

[0006] A second object of the present invention is to provide a method for preparing copper slurry.

[0007] A third object of the present invention is to provide a copper paste or an application of the copper paste prepared by the preparation method in the preparation of solar cells.

[0008] A fourth object of the present invention is to provide a solar cell.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0010] In a first aspect, the present invention provides a copper paste comprising the following components: a conductive material and a conductive reinforcing material;

[0011] The conductive material comprises at least one of gradient micron-grade nickel-tungsten coated copper powder and micron-grade nickel-coated copper powder;

[0012] The conductive reinforcement material includes at least one of nano nickel wire and nano nickel tungsten coated copper powder.

[0013] Furthermore, the gradient micron-sized nickel-tungsten-coated copper powder includes micron-sized nickel-tungsten-coated copper powders of several different particle sizes; the particle size of the micron-sized nickel-tungsten-coated copper powder is 0.1-3 μm; the proportion of each particle size of the micron-sized nickel-tungsten-coated copper powder is 15%-50%; the thickness of the nickel-tungsten layer in the micron-sized nickel-tungsten-coated copper powder is 10-50 nm; the content of the copper core in the micron-sized nickel-tungsten-coated copper powder is 75-95 wt%, and the content of the nickel-tungsten layer is 5-25 wt%; the nickel-tungsten mass ratio is 3:1-5:1;

[0014] Preferably, the gradient micron-grade nickel-clad copper powder includes micron-grade nickel-clad copper powders of several different particle sizes; the particle size of the micron-grade nickel-clad copper powder is 0.1-3 μm; the proportion of micron-grade nickel-clad copper powder of each particle size is 15%-50%; in the micron-grade nickel-clad copper powder, the thickness of the nickel layer is 10-50 nm; the content of the copper core is 75-95 wt%, and the content of the nickel-tungsten layer is 5-25 wt%.

[0015] Preferably, the length of the nickel nanowire is 1-2 μm and the diameter is 10-20 nm;

[0016] Preferably, in the nano nickel-tungsten-coated copper powder, the thickness of the nickel-tungsten alloy coating layer is 10-50 nm; in the nano nickel-tungsten-coated copper powder, the content of the copper core is 75-95 wt%, the content of the nickel-tungsten layer is 5-25 wt%; and the nickel-tungsten mass ratio is 3:1-5:1.

[0017] Furthermore, the following components are included: gradient micron-sized tin powder, organic binder, glass powder, multifunctional additive, low-temperature curing aid and strengthening agent;

[0018] Preferably, the gradient micron-sized tin powder comprises micron-sized tin powders of several different particle sizes; the particle size of the micron-sized tin powder is 0.1-3 μm; the proportion of each particle size of the micron-sized tin powder is 15%-50%;

[0019] Preferably, the organic binder comprises one or more of terpineol, ethyl cellulose, dibutyl phthalate, ethylene glycol ethyl ether acetate, tributyl citrate, dibutyl phthalate and hydrogenated castor oil;

[0020] Preferably, the glass powder comprises a PbO-B2O3-SiO2 system; the components of the glass powder include one or more of PbO, B2O3, Li2O, Bi2O3, ZnO, SiO2, CuO, MnO2, TiO2, Cr2O3, NiO, TeO2 and K2O;

[0021] Preferably, the low-temperature curing aid comprises one or more of an acrylic material, a photosensitive resin, and bismuth nanoparticles;

[0022] Preferably, the reinforcing agent includes a coupling agent and / or a corrosion inhibitor;

[0023] Preferably, the coupling agent comprises one or more of aluminum oxide nanoparticles, antimony nanoparticles and graphene quantum dots;

[0024] Preferably, the corrosion inhibitor comprises cerium oxide nanoparticles.

[0025] Furthermore, the copper paste comprises, by mass percentage, 0.5%-1.5% conductive reinforcing material, 5%-10% gradient micron-grade tin powder, 10%-12% organic binder, 1%-5% glass powder, 0.5%-4% multifunctional additive, 3%-5% low-temperature curing aid, 0.5%-1% coupling agent, 0.5%-1% corrosion inhibitor and the balance conductive material;

[0026] Preferably, the conductive reinforcing material comprises, by mass percentage, 30%-50% of nano nickel wires and 50%-70%.

[0027] Furthermore, the raw materials for preparing the multifunctional additive include: dodecafluoroheptyl methacrylate, 2-vinylbenzoxazole and polyethylene glycol methacrylate;

[0028] Preferably, the multifunctional additive comprises, by mass percentage, 40%-60% of dodecafluoroheptyl methacrylate, 25%-35% of 2-vinylbenzoxazole, and 15%-25% of polyethylene glycol methacrylate.

[0029] In a second aspect, the present invention provides a method for preparing a copper paste, comprising: mixing a formulated amount of a conductive material, a conductive reinforcing material, a gradient micron-sized tin powder, an organic adhesive, a glass powder, a multifunctional additive, a low-temperature curing aid and a reinforcing agent to obtain a copper paste.

[0030] Furthermore, the multifunctional additive is prepared by the following method:

[0031] (a) dodecafluoroheptyl methacrylate, a chain transfer agent, and azobisisobutyronitrile are mixed, cooled, and precipitated in cold methanol, and filtered to obtain a solid product;

[0032] (b) mixing the solid product prepared in step (a), 2-vinylbenzoxazole, and a chain transfer agent, and then dialyzing to remove unreacted monomers to obtain a powder product;

[0033] (c) mixing the powder product prepared in step (b) with polyethylene glycol methacrylate to obtain the multifunctional additive;

[0034] Preferably, the chain transfer agent comprises cyanoisopropyl dithiobenzoate;

[0035] Preferably, in step (a), the molar ratio of the chain transfer agent to dodecafluoroheptyl methacrylate is 1-1.5; the molar ratio of azobisisobutyronitrile to the chain transfer agent is 0.1-0.3;

[0036] Preferably, in step (b), the molar ratio of the chain transfer agent to 2-vinylbenzoxazole is 0.5-1.

[0037] In a third aspect, the present invention provides a copper paste or the use of the copper paste prepared by the preparation method in the preparation of solar cells.

[0038] In a fourth aspect, the present invention provides a solar cell, wherein the method for preparing the solar cell comprises: forming patterned grooves on the front and back surfaces of a silicon substrate, and then sequentially forming grid lines in the patterned grooves;

[0039] Wherein, the gate line is prepared by using the copper paste or the copper paste prepared by the preparation method.

[0040] Furthermore, the width of the patterned groove is 10 to 50 μm, and the depth is 80 to 100 nm.

[0041] Preferably, the thickness of the gate line is 8 to 20 μm;

[0042] Preferably, the gate lines are prepared by screen printing; the printed cells are dried and cured; the drying and curing temperature is 200-300°C;

[0043] Preferably, ultraviolet light irradiation is additionally applied to the pre-curing zone; the ultraviolet light irradiation time is 5-10 seconds.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The copper paste provided by the present invention uses at least one of gradient micron-grade nickel-tungsten-coated copper powder and micron-grade nickel-coated copper powder as the main conductive material, which can not only ensure conductivity and good bonding strength, but also prevent the diffusion of copper elements into the silicon substrate, simplifying the traditional copper electroplating process steps of first plating a nickel seed layer and then plating copper; at the same time, at least one of nano nickel wires and nano nickel-tungsten-coated copper powder is used as a conductive reinforcement material to achieve efficient connection of the conductive network and improve printing uniformity; the nano nickel wires also enhance the contact between the gate lines and the silicon substrate and supplement the adhesion. DETAILED DESCRIPTION

[0046] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; however, in the event of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, the use of "or" means "and / or" unless otherwise stated. In addition, the use of the term "including" and other forms is non-limiting.

[0047] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] A first aspect of the present invention provides a copper paste comprising the following components: a conductive material and a conductive reinforcing material;

[0049] The conductive material includes at least one of gradient micron-grade nickel-tungsten-coated copper powder and micron-grade nickel-coated copper powder; using at least one of gradient micron-grade nickel-tungsten-coated copper powder and micron-grade nickel-coated copper powder as the conductive phase, the gradient distribution can effectively alleviate the problem of insufficient mixing, promote stable current transmission, enhance the mechanical bite of the copper slurry and the seed layer through particle size matching, and reduce contact resistance.

[0050] The conductive reinforcement material includes at least one of nano nickel wire and nano nickel tungsten coated copper powder.

[0051] In some preferred embodiments, the gradient micron-grade nickel-tungsten-coated copper powder includes micron-grade nickel-tungsten-coated copper powders of several different particle sizes; the particle size of the micron-grade nickel-tungsten-coated copper powder is 0.1-3μm, for example, it can be 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc.; the proportion of each particle size of micron-grade nickel-tungsten-coated copper powder is 15%-50%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. Among them, the gradient distribution refers to the different particle sizes of micron-grade nickel-tungsten coated copper powder, which can be selected as: the content of micron-grade nickel-tungsten coated copper powder with a particle size of 0.1μm accounts for 15%, the content of micron-grade nickel-tungsten coated copper powder with a particle size of 0.5μm accounts for 15%, the content of micron-grade nickel-tungsten coated copper powder with a particle size of 1μm accounts for 20%, and the content of micron-grade nickel-tungsten coated copper powder with a particle size of 2μm accounts for 50%, forming a gradient distribution, and the total mass of the gradient micron-grade nickel-tungsten coated copper powder is 100%.

[0052] In micron-grade nickel-tungsten-coated copper powder, the core copper powder particle size is generally 50-500nm, and the nickel-tungsten layer thickness is 10-50nm, for example, 10nm, 30nm, 50nm, etc.; in micron-grade nickel-tungsten-coated copper powder, the copper core content is 75-95wt%, and the nickel-tungsten layer content is 5-25wt%; the nickel-tungsten mass ratio is 3:1-5:1;

[0053] In some preferred embodiments, the gradient micron-grade nickel-clad copper powder includes micron-grade nickel-clad copper powders of several different particle sizes; the particle size of the micron-grade nickel-clad copper powder is 0.1-3 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc.; the proportion of micron-grade nickel-clad copper powder of each particle size is 15%-50%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. Among them, the gradient distribution refers to the different particle sizes of micron-grade nickel-clad copper powder, which can be selected as: the content of micron-grade nickel-clad copper powder with a particle size of 0.1μm accounts for 15%, the content of micron-grade nickel-clad copper powder with a particle size of 0.5μm accounts for 15%, the content of micron-grade nickel-clad copper powder with a particle size of 1μm accounts for 20%, and the content of micron-grade nickel-clad copper powder with a particle size of 2μm accounts for 50%, forming a gradient distribution, and the total mass of the gradient micron-grade nickel-tungsten-clad copper powder is 100%.

[0054] In micron-grade nickel-coated copper powder, the core copper powder particle size is usually 50-500nm, the nickel layer thickness is 10-50nm, for example, it can be 10nm, 30nm, 50nm, etc.; the content of the copper core is 75-95wt%, and the content of the nickel-tungsten layer is 5-25wt%.

[0055] In the present invention, gradient micron-sized nickel-tungsten-coated copper powder and gradient micron-sized nickel-coated copper powder can be prepared by common processes, including but not limited to electroplating, chemical plating, physical vapor deposition, chemical vapor deposition, etc. The nickel-tungsten layer can prevent copper oxidation, and at the same time, the nickel-tungsten layer can prevent direct contact between copper and silicon substrate, thereby enhancing the adhesion between the gate line and the substrate; the nickel-tungsten layer is an alloy.

[0056] Preferably, the length of the nickel nanowire is 1-2 μm and the diameter is 10-20 nm.

[0057] Preferably, in the nano nickel-tungsten clad copper powder, the thickness of the nickel-tungsten alloy coating layer is 10-50nm, for example, it can be 10nm, 30nm, 50nm, etc.; in the nano nickel-tungsten clad copper powder, the copper core content is 60-85wt%, for example, it can be 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, etc.; the nickel-tungsten alloy coating layer content is 15-40wt%, for example, it can be 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, etc.; the nickel-tungsten mass ratio is 3:1-5:1, for example, it can be 3:1, 4:1, 5:1, etc.

[0058] Preferably, the nano nickel-tungsten-coated copper powder has a core copper powder particle size of 50-500 nm, a nickel-tungsten coating layer thickness of 10-50 nm, and a final composite particle size of 70-600 nm. The nano nickel-tungsten-coated copper powder can be prepared by chemical reduction, electrochemical replacement, physical vapor deposition, or electroplating or chemical plating.

[0059] In the present invention, nano nickel wires and nano nickel tungsten coated copper powder are used in combination to achieve efficient connection of the conductive network and improve printing uniformity; the nano nickel wires also enhance the contact between the gate line and the silicon substrate and supplement the adhesion.

[0060] In some preferred embodiments, the following components are further included: gradient micron-sized tin powder, organic binder, glass powder, multifunctional additive, low-temperature curing aid and strengthening agent;

[0061] Preferably, the gradient micron-grade tin powder includes micron-grade tin powders of several different particle sizes; the particle size of the micron-grade tin powder is 0.1-3 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc.; the proportion of each particle size of micron-grade tin powder is 15%-50%.

[0062] In the present invention, gradient micron-grade tin powder is added to the copper paste formula, which can achieve sintering at a lower temperature to form a dense conductive layer. At the same time, the addition of tin enhances the oxidation resistance of the grid line and ensures the subsequent weldability; it avoids the complex process of traditional copper plating followed by tin plating, and also avoids the impact of acidic plating solutions such as traditional tin plating on the battery matrix.

[0063] Furthermore, tin powder is added to the copper paste formula of the present invention to enhance solderability and oxidation resistance, avoid the traditional copper electroplating process steps of first copper plating and then tin plating, and achieve complete silver-free.

[0064] Preferably, the organic binder comprises one or more of terpineol, ethyl cellulose, dibutyl phthalate, ethylene glycol ethyl ether acetate, tributyl citrate, dibutyl phthalate and hydrogenated castor oil;

[0065] Preferably, the glass powder includes a PbO-B2O3-SiO2 system; the components of the glass powder include one or more of PbO, B2O3, Li2O, Bi2O3, ZnO, SiO2, CuO, MnO2, TiO2, Cr2O3, NiO, TeO2 and K2O; the preparation of the entire glass powder can be completed by processes such as melting, ball milling, drying and screening.

[0066] Preferably, the glass powder includes the following raw materials in percentage by mass: PbO: 40-60%, B2O3: 15-25%, Li2O: 1-5%, Bi2O3: 0.5-5%, ZnO: 1-8%, SiO2: 10-20%, CuO: 0.1-3%, MnO2: 0.1-2%, TiO2: 0.5-5%, Cr2O3: 0.1-2%, NiO: 0.1-1%, TeO2: 0-3% and K2O: 0.5-4%.

[0067] Optionally, the glass powder is prepared as follows:

[0068] The glass powder is obtained by mixing, melting, ball milling, drying and sieving the glass powder raw materials in the prescribed amount. Preferably, the melting temperature is 900-1400° C. The ball milling is performed using a ball mill for 0.5-5 hours. The drying time is 0.5-2 hours.

[0069] Preferably, the low-temperature curing aid comprises one or more of an acrylic material, a photosensitive resin, and bismuth nanoparticles, wherein the particle size of the bismuth nanoparticles is 10 nm to 30 nm.

[0070] In the present invention, a low-temperature curing aid is an acrylate (or other photosensitive resin) that is combined with nano-nickel wires and nano-nickel-tungsten-coated copper powder. When irradiated with ultraviolet light (wavelength 365nm) for 5-10 seconds, a conductive network is formed, requiring a lower curing temperature. The low-temperature curing aid may also contain bismuth nanoparticles, which have a low melting point. Microwaves selectively heat the metal particles, achieving transient liquid-phase sintering at 150-200°C, forming a dense conductive layer with lower resistivity. The combination of the two creates a low-temperature UV-heat dual-curing system, with light curing forming the initial conductive network and heat curing enhancing interfacial bonding, thus avoiding copper diffusion or oxidation caused by traditional high-temperature sintering.

[0071] Preferably, the reinforcing agent includes a coupling agent and / or a corrosion inhibitor;

[0072] Preferably, the coupling agent includes one or more of aluminum oxide nanoparticles, antimony nanoparticles and graphene quantum dots.

[0073] In the present invention, aluminum oxide nanoparticles (particle size <50nm) + antimony (Sb) nanoparticles (particle size <50nm) or graphene quantum dots (particle size <50nm) are used in the copper slurry formula to improve the adhesion and contact resistance between the slurry and the seed layer.

[0074] Preferably, the corrosion inhibitor comprises cerium oxide nanoparticles having a particle size of 20 nm to 50 nm.

[0075] In the present invention, cerium oxide (CeO2) nanoparticles are used in the copper paste formula to increase the service life in a wet and hot environment and improve the acid resistance and wet and hot resistance of copper.

[0076] In some preferred embodiments, the copper paste comprises, by mass percentage, 0.5%-1.5% conductive reinforcing material, 5%-10% gradient micron-grade tin powder, 10%-12% organic binder, 1%-5% glass powder, 0.5%-4% multifunctional additive, 3%-5% low-temperature curing aid, 0.5%-1% coupling agent, 0.5%-1% corrosion inhibitor and the balance conductive material.

[0077] Based on the total mass of the copper paste as 100%, the amount of conductive reinforcing material added is 0.5%-1.5%, for example, 0.5%, 1%, 1.5%, etc.;

[0078] Based on the total mass of the copper paste as 100%, the addition amount of the gradient micron-grade tin powder is 5%-10%, for example, 5%, 7.5%, 10%, etc.;

[0079] Based on the total mass of the copper paste as 100%, the addition amount of the organic binder is 10%-12%, for example, 10%, 11%, 12%, etc.;

[0080] Based on the total mass of the copper paste as 100%, the amount of glass powder added is 1%-5%, for example, 1%, 3%, 5%, etc.;

[0081] Based on the total mass of the copper paste as 100%, the addition amount of the multifunctional additive is 0.5%-4%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.;

[0082] Based on the total mass of the copper paste as 100%, the addition amount of the low-temperature curing additive is 3%-5%, for example, 3%, 4%, 5%, etc.;

[0083] Based on the total mass of the copper paste as 100%, the addition amount of the coupling agent is 0.5%-1%, for example, 0.5%, 0.75%, 1%, etc.;

[0084] Based on the total mass of the copper slurry as 100%, the amount of the corrosion inhibitor added is 0.5%-1%, for example, 0.5%, 0.75%, 1%, etc.;

[0085] Preferably, the conductive reinforcement material comprises, by mass percentage, 30%-50% of nano nickel wires and 50%-70%;

[0086] Wherein, based on the total mass of the conductive reinforcing material being 100%, the added amount of the nano nickel wire is 30%-50%, for example, 30%, 40%, 50%, etc.

[0087] The second aspect of the present invention provides a method for preparing a copper paste, comprising: mixing a formulated amount of a conductive material, a conductive reinforcing material, a gradient micron-sized tin powder, an organic adhesive, a glass powder, a multifunctional additive, a low-temperature curing aid and a reinforcing agent to obtain a copper paste.

[0088] Specifically, the preparation process of the copper slurry includes the following steps:

[0089] (1) Mixing gradient micron-sized nickel-tungsten-coated copper powder and dilute sulfuric acid (mass fraction of 15%-20%) in a container, stirring thoroughly and letting it stand, filtering out the gradient micron-sized nickel-tungsten-coated copper powder, and stirring, grinding and dispersing the gradient micron-sized nickel-tungsten-coated copper powder, nano nickel wire + nano nickel-tungsten-coated copper powder, gradient micron-sized tin powder, low-temperature curing aid (bismuth nanoparticles), coupling agent, and corrosion inhibitor to obtain a slurry mixture;

[0090] (2) The slurry mixture, the organic binder, the glass powder, the multifunctional additive, and the low-temperature curing aid (acrylate) are mixed and stirred to obtain a copper slurry.

[0091] Preferably, in the present invention, an ultrasonic stirring process is used in the mixing process, which effectively solves the agglomeration problem in the chemical plating process.

[0092] In some preferred embodiments, the multifunctional additive of the present invention is a multifunctional polymer copper paste additive, which can reduce formulation complexity, reduce paste cost, reduce surface tension, reduce shading loss, and has leveling-brightening-wetting effects. The raw materials for preparing the multifunctional additive include: dodecafluoroheptyl methacrylate, 2-vinylbenzoxazole, and polyethylene glycol methacrylate;

[0093] Preferably, the components of the multifunctional additive include, by mass percentage: dodecafluoroheptyl methacrylate (DFMA), 40%-60%, which imparts a leveling function and reduces the jagged edges and roughness of the grid lines; 2-vinylbenzoxazole (VBO), 25%-35%, which improves the surface light reflectivity of the grid lines through a π-π conjugated structure; and polyethylene glycol methacrylate (PEGMA), 15%-25%, which provides wettability and reduces the surface tension of the slurry.

[0094] The multifunctional additive is prepared by a three-step polymerization process under nitrogen protection using the controlled radical polymerization (RAFT) reagent cyanoisopropyl dithiobenzoate (CPDB) as a chain transfer agent, ultimately yielding a multifunctional polymer copper paste additive. The block copolymer is synthesized in a series of steps using reversible addition-fragmentation chain transfer (RAFT) polymerization: 1. Dodecafluoroheptyl methacrylate (other fluorinated acrylate monomers may also be used); 2. 2-vinylbenzoxazole (other benzoxazole monomers may also be used); and 3. Finally, polyethylene glycol methacrylate (PEGMA) is grafted onto the copolymer.

[0095] Preferably, the specific preparation process of the multifunctional additive is as follows:

[0096] Step 1: Synthesis of fluorinated block (PDFMA)

[0097] Reaction system: dodecafluoroheptyl methacrylate DFMA (40-60%, preferably 50%) + cyanoisopropyl dithiobenzoate CPDB (CPDB is 1-1.5 times the molar amount of DFMA) + azobisisobutyronitrile AIBN (AIBN is 0.1-0.3 times the molar amount of CPDB);

[0098] Conditions: 70°C under nitrogen protection for 6 hours.

[0099] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0100] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0101] PDFMA, 2-vinylbenzoxazole VBO (25-35%, preferably 30%), and CPDB (CPDB is 0.5-1 times the molar amount of VBO) are added to the reactor, and azobisisobutyronitrile AIBN (AIBN is 0.1 times the molar amount of CPDB) is added;

[0102] Conditions: 80°C for 8 hours;

[0103] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0104] Step 3: PEGMA Block (Final Triblock Polymer)

[0105] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (15%-25% of the total feed amount, preferably 20%) and a trace amount of AIBN;

[0106] Conditions: 65°C for 4 hours;

[0107] Purification: The solvent was removed by rotary evaporation and vacuum dried for 48 hours (40°C / 10 Pa).

[0108] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 20%-60% stock solution, and ultrasonically dispersed (40 kHz / 30 min).

[0109] In some preferred embodiments, the multifunctional additive is prepared by the following method:

[0110] (a) dodecafluoroheptyl methacrylate, a chain transfer agent, and azobisisobutyronitrile are mixed, cooled, and precipitated in cold methanol, and filtered to obtain a solid product;

[0111] (b) mixing the solid product prepared in step (a), 2-vinylbenzoxazole, and a chain transfer agent, and then dialyzing to remove unreacted monomers to obtain a powder product;

[0112] (c) mixing the powder product prepared in step (b) with polyethylene glycol methacrylate to obtain the multifunctional additive.

[0113] A third aspect of the present invention provides a copper paste or use of the copper paste prepared by the preparation method in preparing solar cells.

[0114] The copper paste provided by the present invention is a copper paste formula for photovoltaic cells that does not require a seed layer. It is used to reduce the cost of traditional silver paste, improve the performance of grid lines, and can enhance conductivity, process adaptability and low-temperature sintering ability.

[0115] A fourth aspect of the present invention provides a solar cell, the preparation method of which includes: preparing patterned grooves on the front and back sides of a silicon substrate, and then sequentially preparing grid lines in the patterned grooves; wherein the grid lines are prepared using the copper paste described or the copper paste prepared using the preparation method described.

[0116] Preferably, the opened film portion of the solar cell is pickled and dried; the pickling solution contains hydrofluoric acid, and the amount of hydrofluoric acid added is 10-20 mL / L; the temperature of the pickling solution is 25-38° C.; and the silicon substrate floats in the pickling solution for 5-50 seconds.

[0117] Preferably, the cell after pickling and drying is subjected to high temperature annealing repair at a temperature of 750-800° C., a conventional sintering furnace conveyor speed of 3-5 m / min, and nitrogen as a protective gas.

[0118] In some preferred embodiments, the width of the patterned groove is 10 to 50 μm, for example, 10 μm, 30 μm, 50 μm, etc.; the depth is 80 to 100 nm, for example, 80 nm, 90 nm, 100 nm, etc.;

[0119] Preferably, the thickness of the gate line is 8 to 20 μm, for example, 8 μm, 14 μm, 20 μm, etc.

[0120] Preferably, the gate lines are prepared by screen printing; the printed cells are dried and cured; the drying and curing temperature is 200-300° C., for example, 200° C., 250° C., 300° C., etc.;

[0121] Preferably, ultraviolet light irradiation is additionally applied to the pre-curing zone; the ultraviolet light irradiation time is 5-10s, for example, 5s, 7.5s, 10s, etc.

[0122] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0123] Example 1

[0124] This embodiment provides a copper paste, which includes the following components by mass percentage:

[0125] 1% conductive reinforcing material (specifically gradient micron-grade nickel-tungsten coated copper powder), 7.5% gradient micron-grade tin powder, 11% organic binder (specifically pineol), 3% glass powder, 2% multifunctional additives, 4% low-temperature curing aids, 0.75% coupling agent, 0.75% corrosion inhibitor (specifically cerium oxide nanoparticles) and the remainder of the conductive material (specifically gradient micron-grade nickel-tungsten coated copper powder).

[0126] The gradient micron-grade nickel-tungsten-coated copper powder includes, by mass percentage, 15% nickel-tungsten-coated copper powder with a particle size of 0.1μm, 15% nickel-tungsten-coated copper powder with a particle size of 0.5μm, 20% nickel-tungsten-coated copper powder with a particle size of 1μm, and 50% nickel-tungsten-coated copper powder with a particle size of 2μm. The thickness of the nickel-tungsten layer in the nickel-tungsten-coated copper powder is 30nm, and the nickel-tungsten mass ratio is 4:1.

[0127] The conductive reinforcement material comprises 40% nano-nickel wires (1.5 μm in length and 15 nm in diameter) and 60% nano-nickel-tungsten-coated copper powder. The size of the nano-nickel-tungsten-coated copper powder is 300 nm. The thickness of the nickel-tungsten alloy coating layer is 30 nm. The copper core content of the nano-nickel-tungsten-coated copper powder is 85 wt%, and the nickel-tungsten alloy coating content is 15 wt%. The nickel-tungsten mass ratio is 4:1.

[0128] The gradient micron-grade tin powder includes, by mass percentage, tin powder with a particle size of 0.1 μm accounting for 15%, tin powder with a particle size of 0.5 μm accounting for 15%, tin powder with a particle size of 1 μm accounting for 20%, and tin powder with a particle size of 2 μm accounting for 50%;

[0129] The glass powder is a PbO-B2O3-SiO2 system, and its specific composition, in terms of mass percentage, includes: B2O3: 20%, Li2O: 3%, Bi2O3: 3%, ZnO: 5%, SiO2: 15%, CuO: 2%, MnO2: 1%, TiO2: 3%, Cr2O3: 1%, NiO: 0.5%, TeO2: 1.5%, K2O: 2% and the balance PbO;

[0130] The low-temperature curing aid comprises an acrylic material (specifically diphenyliodonium hexafluorophosphate) and bismuth nanoparticles (particle size 20 nm) in a mass ratio of 1:1;

[0131] The coupling agent includes aluminum oxide nanoparticles (particle size <50 nm) and antimony (Sb) nanoparticles (particle size <50 nm) in a mass ratio of 1:1;

[0132] The particle size of the cerium oxide nanoparticles is 35 nm.

[0133] The preparation process of the copper slurry comprises the following steps:

[0134] (1) Mixing the gradient micron-sized nickel-tungsten-coated copper powder and dilute sulfuric acid (mass fraction of 18%) in a formulated amount into a container, stirring thoroughly and letting it stand, filtering out the gradient micron-sized nickel-tungsten-coated copper powder, stirring, grinding and dispersing the gradient micron-sized nickel-tungsten-coated copper powder, nano nickel wire + nano nickel-tungsten-coated copper powder, gradient micron-sized tin powder, low-temperature curing aid (bismuth nanoparticles), coupling agent and corrosion inhibitor to obtain a slurry mixture;

[0135] (2) The slurry mixture, the organic binder, the glass powder, the multifunctional additive, and the low-temperature curing aid (acrylate) are mixed and stirred to obtain a copper slurry.

[0136] The specific preparation process of the multifunctional additive is as follows:

[0137] Step 1: Synthesis of fluorinated block (PDFMA)

[0138] Reaction system: dodecafluoroheptyl methacrylate DFMA (50% of the total feed amount) + cyanoisopropyl dithiobenzoate CPDB (CPDB is 1.25 times the molar amount of DFMA) + azobisisobutyronitrile AIBN (AIBN is 0.2 times the molar amount of CPDB);

[0139] Conditions: 70°C under nitrogen protection for 6 hours.

[0140] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0141] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0142] PDFMA, 2-vinylbenzoxazole VBO (30% of the total feed amount), and CPDB (CPDB is 0.75 times the molar amount of VBO) were added to the reactor, and azobisisobutyronitrile AIBN (AIBN is 0.1 times the molar amount of CPDB) was added;

[0143] Conditions: 80°C for 8 hours;

[0144] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0145] Step 3: PEGMA Block (Final Triblock Polymer)

[0146] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (20% of the total feed) and a trace amount (1% of the total feed) of AIBN;

[0147] Conditions: 65°C for 4 hours;

[0148] Purification: remove the solvent by rotary evaporation and vacuum dry for 48 hours (40°C / 10Pa);

[0149] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 40% stock solution, and ultrasonically dispersed (40 kHz / 30 min).

[0150] The glass powder is prepared by the following steps:

[0151] The glass powder raw materials of the formulated amount are sequentially mixed, melted, ball-milled, dried, and sieved to obtain the glass powder; the melting temperature is 1200° C.; the ball milling is performed using a ball mill for 3 hours; and the drying time is 1.5 hours.

[0152] Example 2

[0153] This embodiment provides a copper paste, which differs from Example 1 in that the coupling agent includes aluminum oxide nanoparticles (particle size <50 nm), antimony (Sb) nanoparticles (particle size <50 nm) and graphene quantum dots (particle size <50 nm) in a mass ratio of 1:1:1, and the rest is consistent with Example 1.

[0154] Example 3

[0155] This embodiment provides a copper paste, which differs from the embodiment 1 in that its components, calculated by mass percentage, include the following components:

[0156] 0.5% conductive reinforcing material (specifically gradient micron-grade nickel-tungsten coated copper powder), 10% gradient micron-grade tin powder, 10% organic binder (specifically pineol), 5% glass powder, 0.5% multifunctional additive, 3% low-temperature curing aid, 1% coupling agent, 0.5% corrosion inhibitor (specifically cerium oxide nanoparticles) and the remainder of the conductive material (specifically gradient micron-grade nickel-tungsten coated copper powder).

[0157] The gradient micron-grade nickel-tungsten-coated copper powder includes, by mass percentage, 15% nickel-tungsten-coated copper powder with a particle size of 0.1μm, 20% nickel-tungsten-coated copper powder with a particle size of 0.5μm, 20% nickel-tungsten-coated copper powder with a particle size of 1μm, 25% nickel-tungsten-coated copper powder with a particle size of 2μm, and 20% nickel-tungsten-coated copper powder with a particle size of 3μm. The thickness of the nickel-tungsten layer in the nickel-tungsten-coated copper powder is 10nm, and the nickel-tungsten mass ratio is 3:1.

[0158] The conductive reinforcement material includes 30% nano-nickel wire and 70% nano-nickel-tungsten-coated copper powder; the size of the nano-nickel-tungsten-coated copper powder is 70nm, and the thickness of the nickel-tungsten alloy coating layer is 10nm; the copper core content of the nano-nickel-tungsten-coated copper powder is 75wt%, and the nickel-tungsten alloy coating content is 25wt%; the nickel-tungsten mass ratio is 3:1;

[0159] Among them, the gradient micron-grade tin powder includes, by mass percentage: tin powder with a particle size of 0.1μm accounts for 15%, tin powder with a particle size of 0.5μm accounts for 20%, tin powder with a particle size of 1μm accounts for 20%, tin powder with a particle size of 2μm accounts for 20%, and tin powder with a particle size of 3μm accounts for 25%.

[0160] The preparation process of the copper slurry comprises the following steps:

[0161] (1) Mixing the formulated amount of gradient micron-sized nickel-tungsten-coated copper powder and dilute sulfuric acid (mass fraction of 20%) in a container, stirring thoroughly and letting it stand, filtering out the gradient micron-sized nickel-tungsten-coated copper powder, and stirring, grinding and dispersing the gradient micron-sized nickel-tungsten-coated copper powder, nano nickel wire + nano nickel-tungsten-coated copper powder, gradient micron-sized tin powder, low-temperature curing aid (bismuth nanoparticles), coupling agent and corrosion inhibitor to obtain a slurry mixture;

[0162] (2) The slurry mixture, the organic binder, the glass powder, the multifunctional additive, and the low-temperature curing aid (acrylate) are mixed and stirred to obtain a copper slurry.

[0163] The specific preparation process of the multifunctional additive is as follows:

[0164] Step 1: Synthesis of fluorinated block (PDFMA)

[0165] Reaction system: dodecafluoroheptyl methacrylate DFMA (40% of the total feed amount) + cyanoisopropyl dithiobenzoate CPDB (CPDB is 1.5 times the molar amount of DFMA) + azobisisobutyronitrile AIBN (AIBN is 0.1 times the molar amount of CPDB);

[0166] Conditions: 70°C under nitrogen protection for 6 hours.

[0167] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0168] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0169] PDFMA, 2-vinylbenzoxazole VBO (35% of the total feed amount), and CPDB (CPDB is 1 times the molar amount of VBO) were added to the reactor, and azobisisobutyronitrile AIBN (AIBN is 0.1 times the molar amount of CPDB) was added;

[0170] Conditions: 80°C for 8 hours;

[0171] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0172] Step 3: PEGMA Block (Final Triblock Polymer)

[0173] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (25% of the total feed amount) and a trace amount of AIBN;

[0174] Conditions: 65°C for 4 hours;

[0175] Purification: remove the solvent by rotary evaporation and vacuum dry for 48 hours (40°C / 10Pa);

[0176] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 20% stock solution and ultrasonically dispersed (40 kHz / 30 min).

[0177] The rest of the content is consistent with Example 1.

[0178] Example 4

[0179] This embodiment provides a copper paste, which differs from the embodiment 1 in that its components, calculated by mass percentage, include the following components:

[0180] 1.5% conductive reinforcing material (specifically gradient micron-grade nickel-tungsten coated copper powder), 5% gradient micron-grade tin powder, 12% organic binder (specifically pineol), 1% glass powder, 4% multifunctional additives, 5% low-temperature curing aids, 0.5% coupling agent, 1% corrosion inhibitor (specifically cerium oxide nanoparticles) and the remainder of the conductive material (specifically gradient micron-grade nickel-tungsten coated copper powder).

[0181] The gradient micron-grade nickel-tungsten-coated copper powder includes, by mass percentage, 15% nickel-tungsten-coated copper powder with a particle size of 0.1μm, 15% nickel-tungsten-coated copper powder with a particle size of 0.5μm, 20% nickel-tungsten-coated copper powder with a particle size of 1μm, and 50% nickel-tungsten-coated copper powder with a particle size of 2μm. The thickness of the nickel-tungsten layer in the nickel-tungsten-coated copper powder is 50nm, and the nickel-tungsten mass ratio is 5:1.

[0182] The conductive reinforcement material includes 50% nano-nickel wire and 50% nano-nickel-tungsten-coated copper powder. The size of the nano-nickel-tungsten-coated copper powder is 600nm. The thickness of the nickel-tungsten alloy coating layer in the nano-nickel-tungsten-coated copper powder is 50nm. The copper core content of the nano-nickel-tungsten-coated copper powder is 95wt%, and the nickel-tungsten alloy coating content is 5wt%. The nickel-tungsten mass ratio is 5:1.

[0183] Among them, the gradient micron-grade tin powder includes, by mass percentage: tin powder with a particle size of 0.1μm accounts for 15%, tin powder with a particle size of 0.5μm accounts for 15%, tin powder with a particle size of 1μm accounts for 15%, tin powder with a particle size of 2μm accounts for 15%, tin powder with a particle size of 2.5μm accounts for 20%, and tin powder with a particle size of 3μm accounts for 20%.

[0184] The preparation process of the copper slurry comprises the following steps:

[0185] (1) Mixing the formulated amount of gradient micron-sized nickel-tungsten-coated copper powder and dilute sulfuric acid (mass fraction of 15%) in a container, stirring thoroughly and letting it stand, filtering out the gradient micron-sized nickel-tungsten-coated copper powder, stirring, grinding and dispersing the gradient micron-sized nickel-tungsten-coated copper powder, nano nickel wire + nano nickel-tungsten-coated copper powder, gradient micron-sized tin powder, low-temperature curing aid (bismuth nanoparticles), coupling agent and corrosion inhibitor to obtain a slurry mixture;

[0186] (2) The slurry mixture, the organic binder, the glass powder, the multifunctional additive, and the low-temperature curing aid (acrylate) are mixed and stirred to obtain a copper slurry.

[0187] The specific preparation process of the multifunctional additive is as follows:

[0188] Step 1: Synthesis of fluorinated block (PDFMA)

[0189] Reaction system: dodecafluoroheptyl methacrylate DFMA (60% of the total feed amount) + cyanoisopropyl dithiobenzoate CPDB (CPDB is 1 times the molar amount of DFMA) + azobisisobutyronitrile AIBN (AIBN is 0.3 times the molar amount of CPDB);

[0190] Conditions: 70°C under nitrogen protection for 6 hours.

[0191] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0192] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0193] PDFMA, 2-vinylbenzoxazole VBO (25% of the total feed amount), and CPDB (CPDB is 0.5 times the molar amount of VBO) were added to the reactor, and azobisisobutyronitrile AIBN (AIBN is 0.1 times the molar amount of CPDB) was added;

[0194] Conditions: 80°C for 8 hours;

[0195] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0196] Step 3: PEGMA Block (Final Triblock Polymer)

[0197] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (15% of the total feed amount) and a trace amount of AIBN;

[0198] Conditions: 65°C for 4 hours;

[0199] Purification: remove the solvent by rotary evaporation and vacuum dry for 48 hours (40°C / 10Pa);

[0200] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 60% stock solution, and ultrasonically dispersed (40 kHz / 30 min).

[0201] The rest of the content is consistent with Example 1.

[0202] Example 5

[0203] This embodiment provides a copper paste, which differs from the embodiment 1 in that its components, calculated by mass percentage, include the following components:

[0204] 0.4% conductive reinforcing material, 11% gradient micron-grade tin powder, 9% organic binder, 6% glass powder, 0.3% multifunctional additive, 2% low-temperature curing aid, 1.5% coupling agent, 0.4% corrosion inhibitor and the balance conductive material.

[0205] The gradient micron-grade nickel-tungsten-coated copper powder includes, by mass percentage, 70% nickel-tungsten-coated copper powder with a particle size of 4μm, 10% nickel-tungsten-coated copper powder with a particle size of 5μm, 10% nickel-tungsten-coated copper powder with a particle size of 6μm, and 10% nickel-tungsten-coated copper powder with a particle size of 7μm. In the nickel-tungsten-coated copper powder, the mass ratio of nickel to tungsten is 2:1.

[0206] The conductive reinforcement material includes 60% nano nickel wire and 40% nano nickel tungsten coated copper powder;

[0207] The gradient micron-grade tin powder includes, by mass percentage, tin powder with a particle size of 4 μm accounting for 70%, tin powder with a particle size of 5 μm accounting for 10%, tin powder with a particle size of 6 μm accounting for 10%, and tin powder with a particle size of 7 μm accounting for 10%;

[0208] The specific preparation process of the multifunctional additive is as follows:

[0209] Step 1: Synthesis of fluorinated block (PDFMA)

[0210] Reaction system: dodecafluoroheptyl methacrylate DFMA (30% of the total feed amount) + dithiobenzoic acid cyanoisopropyl ester CPDB + azobisisobutyronitrile AIBN;

[0211] Conditions: 70°C under nitrogen protection for 6 hours.

[0212] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0213] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0214] PDFMA, 2-vinylbenzoxazole VBO (40% of the total amount), and CPDB were added to the reactor, and azobisisobutyronitrile AIBN was added;

[0215] Conditions: 80°C for 8 hours;

[0216] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0217] Step 3: PEGMA Block (Final Triblock Polymer)

[0218] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (30% of the total feed amount) and a trace amount of AIBN;

[0219] Conditions: 65°C for 4 hours;

[0220] Purification: remove the solvent by rotary evaporation and vacuum dry for 48 hours (40°C / 10Pa);

[0221] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 40% stock solution, and ultrasonically dispersed (40 kHz / 30 min).

[0222] Example 6

[0223] This embodiment provides a copper paste, which differs from the embodiment 1 in that its components, calculated by mass percentage, include the following components:

[0224] 2% conductive reinforcing material, 4% gradient micron-grade tin powder, 13% organic binder, 0.5% glass powder, 5% multifunctional additive, 6% low-temperature curing aid, 0.4% coupling agent, 1.5% corrosion inhibitor and the balance conductive material.

[0225] The gradient micron-grade nickel-tungsten-coated copper powder includes, by mass percentage, 70% nickel-tungsten-coated copper powder with a particle size of 4μm, 10% nickel-tungsten-coated copper powder with a particle size of 5μm, 10% nickel-tungsten-coated copper powder with a particle size of 6μm, and 10% nickel-tungsten-coated copper powder with a particle size of 7μm. In the nickel-tungsten-coated copper powder, the mass ratio of nickel to tungsten is 6:1.

[0226] The conductive reinforcement material includes 20% nano nickel wire and 80% nano nickel tungsten coated copper powder;

[0227] The gradient micron-grade tin powder includes, by mass percentage, tin powder with a particle size of 4 μm accounting for 70%, tin powder with a particle size of 5 μm accounting for 10%, tin powder with a particle size of 6 μm accounting for 10%, and tin powder with a particle size of 7 μm accounting for 10%;

[0228] The specific preparation process of the multifunctional additive is as follows:

[0229] Step 1: Synthesis of fluorinated block (PDFMA)

[0230] Reaction system: dodecafluoroheptyl methacrylate DFMA (70% of the total feed amount) + dithiobenzoic acid cyanoisopropyl ester CPDB + azobisisobutyronitrile AIBN;

[0231] Conditions: 70°C under nitrogen protection for 6 hours.

[0232] Product treatment: After cooling, the product was precipitated in cold methanol and filtered to obtain a white solid (PDFMA block).

[0233] Step 2: Grafting of benzoxazole block (PDFMA-PVBO)

[0234] PDFMA, 2-vinylbenzoxazole VBO (20% of the total amount), and CPDB were added to the reactor, and azobisisobutyronitrile AIBN was added;

[0235] Conditions: 80°C for 8 hours;

[0236] Purification: Dialysis was performed to remove unreacted monomers and obtain a powder.

[0237] Step 3: PEGMA Block (Final Triblock Polymer)

[0238] PDFMA-PVBO was mixed with polyethylene glycol methacrylate PEGMA (10% of the total feed amount) and a trace amount of AIBN;

[0239] Conditions: 65°C for 4 hours;

[0240] Purification: remove the solvent by rotary evaporation and vacuum dry for 48 hours (40°C / 10Pa);

[0241] The polymer was dissolved in propylene glycol methyl ether acetate (PGMEA) to prepare a 40% stock solution, and ultrasonically dispersed (40 kHz / 30 min).

[0242] Example 7

[0243] This embodiment provides a copper paste, which is different from Example 1 in that the copper paste formula does not contain gradient micron-grade tin powder; the rest is consistent with Example 1.

[0244] Example 8

[0245] This embodiment provides a copper paste, which is different from Example 1 in that: in the copper paste formula, the low-temperature curing auxiliary agent does not contain bismuth nanoparticles; the rest is consistent with Example 1.

[0246] Example 9

[0247] This embodiment provides a copper paste, which is different from Example 1 in that: in the copper paste formula, the coupling agent does not contain antimony (Sb) nanoparticles; the rest is consistent with Example 1.

[0248] Example 10

[0249] This embodiment provides a copper paste, which is different from Example 1 in that the copper paste formula does not contain a sustained-release agent, and the rest is consistent with Example 1.

[0250] Example 11

[0251] This embodiment provides a copper paste, which is different from Example 1 in that dilute sulfuric acid is not added during the preparation of the copper paste, and the rest is the same as Example 1.

[0252] Example 12

[0253] This embodiment provides a copper paste, which differs from embodiment 1 in that:

[0254] Application Examples 1-11

[0255] Application Examples 1-11 provide a solar cell. Application Examples 1-11 respectively use the copper paste prepared in Examples 1-11. The preparation method of the solar cell includes the following steps:

[0256] Step 1: Providing a solar cell silicon substrate;

[0257] Step 2: Patterned grooves are formed on the front and back sides of the solar cell silicon substrate by laser cutting. The width of the patterned grooves is 30 μm and the depth is 90 nm.

[0258] Step 3: The opened film portion of the solar cell is pickled and dried; the pickling solution contains hydrofluoric acid, and the amount of hydrofluoric acid added is 15 mL / L; the temperature of the pickling solution is 30°C; and the silicon substrate floats in the pickling solution for 30 seconds;

[0259] Step 4: After pickling and drying, the cells are annealed at high temperature at 780°C, with a conveyor speed of 4m / min and nitrogen as the protective gas.

[0260] Step 5: The dried cell is evenly coated with the copper paste by screen printing; the thickness of the grid line is 14 μm;

[0261] Step 6: The printed cell is dried and cured in an annealing furnace (temperature 250°C) to obtain a finished cell. The pre-curing area is additionally irradiated with UV light for 7 seconds.

[0262] Application Example 12

[0263] This application example provides a solar cell, which uses the copper paste prepared in Example 1. The difference from Application Example 1 is that the pre-curing zone is additionally irradiated with ultraviolet light for 5 seconds.

[0264] Application Example 13

[0265] This application example provides a solar cell, which uses the copper paste prepared in Example 1. The difference from Application Example 1 is that the pre-curing zone is additionally irradiated with ultraviolet light for 10 seconds.

[0266] Application Example 14

[0267] This application example provides a solar cell, which uses the copper paste prepared in Example 1. The difference from Application Example 1 is that the pre-curing zone is not irradiated with ultraviolet light.

[0268] Comparative Example 1

[0269] This comparative example provides a copper paste, which differs from Example 1 in that the conductive reinforcement material does not contain nano nickel-tungsten-coated copper powder.

[0270] Comparative Application Example 1

[0271] This comparative example provides a solar cell, which uses the copper paste prepared in comparative example 1, and the preparation method is consistent with that in application example 1.

[0272] Comparative Application Example 2

[0273] This comparative example provides a solar cell, in which copper grid lines are prepared using a conventional process. First, a nickel layer is prepared by electroplating, chemical plating, or vapor deposition, then a copper layer is prepared by electroplating, chemical plating, vapor deposition, or conventional copper paste printing, and finally a tin layer is prepared by electroplating, chemical plating, vapor deposition, or printing.

[0274] Test Case

[0275] Test samples: The solar cells prepared in Application Examples 1-14 and Comparative Application Examples 1-2 were used as samples for testing.

[0276] Test method:

[0277] (1) Electrical performance test: Offline solar IV tester;

[0278] (2) Welding tension under low temperature conditions: tensile force meter;

[0279] (3) Resistivity test: Use a probe resistance tester to test the initial resistance and the resistance after 72 hours at 85°C and 85% RH.

[0280] The test results are shown in Table 1.

[0281] Table 1

[0282]

[0283]

[0284] As can be seen from the data in Table 1, the copper paste provided by the present invention, its preparation method, and its application in the preparation of solar cells can effectively improve the paste formula, enhance conductivity, process adaptability, and low-temperature sintering. It can be seen from Application Example 1 and Application Examples 5-6 that the use of copper paste with components within a specific range to prepare solar cells has better overall product performance; it can be seen from Application Example 1 and Comparative Application Example 1 that the conductive reinforcing material enhances conductivity and reduces resistance, especially the resistance after 72 hours at 85°C and 85% RH is significantly improved, indicating that the new copper paste formula has better stability and its self-repairing performance can be effectively exerted; it can be seen from Application Example 1 and Application Example 11 that the added UV curing step effectively improves the sintering temperature, and the performance of low-temperature sintered batteries under UV curing conditions is more superior; in addition, the grid line preparation process is optimized, which has greater advantages in reducing substrate damage and reducing costs.

[0285] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A copper paste, characterized in that The invention comprises the following components: a conductive material and a conductive reinforcing material; The conductive material comprises at least one of gradient micron-grade nickel-tungsten coated copper powder and micron-grade nickel-coated copper powder; The conductive reinforcement material includes at least one of nano nickel wire and nano nickel tungsten coated copper powder.

2. The copper paste according to claim 1, characterized in that The gradient micron-grade nickel-tungsten-coated copper powder comprises micron-grade nickel-tungsten-coated copper powders of different particle sizes; the particle size of the micron-grade nickel-tungsten-coated copper powder is 0.1-3 μm; the proportion of each particle size of the micron-grade nickel-tungsten-coated copper powder is 15%-50%; the thickness of the nickel-tungsten layer in the micron-grade nickel-tungsten-coated copper powder is 10-50 nm; the content of the copper core in the micron-grade nickel-tungsten-coated copper powder is 75-95 wt%, and the content of the nickel-tungsten layer is 5-25 wt%. The nickel-tungsten mass ratio is 3:1-5:1; Preferably, the gradient micron-sized nickel-coated copper powder comprises micron-sized nickel-coated copper powders of different particle sizes; the particle size of the micron-sized nickel-coated copper powder is 0.1-3 μm; the proportion of each particle size of micron-sized nickel-coated copper powder is 15%-50%; the thickness of the nickel layer in the micron-sized nickel-coated copper powder is 10-50 nm; the content of the copper core is 75-95 wt%, and the content of the nickel-tungsten layer is 5-25 wt%; Preferably, the length of the nickel nanowire is 1-2 μm and the diameter is 10-20 nm; Preferably, in the nano nickel-tungsten-coated copper powder, the thickness of the nickel-tungsten alloy coating layer is 10-50 nm; in the nano nickel-tungsten-coated copper powder, the content of the copper core is 75-95 wt%, and the content of the nickel-tungsten layer is 5-25 wt%. The nickel-tungsten mass ratio is 3:1-5:

1.

3. The copper paste according to claim 1, characterized in that It also includes the following components: gradient micron-sized tin powder, organic binder, glass powder, multifunctional additives, low-temperature curing aids and strengthening agents; Preferably, the gradient micron-sized tin powder comprises micron-sized tin powders of several different particle sizes; the particle size of the micron-sized tin powder is 0.1-3 μm; the proportion of each particle size of the micron-sized tin powder is 15-50%; Preferably, the organic binder comprises one or more of terpineol, ethyl cellulose, dibutyl phthalate, ethylene glycol ethyl ether acetate, tributyl citrate, dibutyl phthalate and hydrogenated castor oil; Preferably, the glass powder comprises a PbO-B2O3-SiO2 system; the components of the glass powder include one or more of PbO, B2O3, Li2O, Bi2O3, ZnO, SiO2, CuO, MnO2, TiO2, Cr2O3, NiO, TeO2 and K2O; Preferably, the low-temperature curing aid comprises one or more of an acrylic material, a photosensitive resin, and bismuth nanoparticles; Preferably, the reinforcing agent includes a coupling agent and / or a corrosion inhibitor; Preferably, the coupling agent comprises one or more of aluminum oxide nanoparticles, antimony nanoparticles and graphene quantum dots; Preferably, the corrosion inhibitor comprises cerium oxide nanoparticles.

4. The copper paste according to claim 3, characterized in that The copper paste comprises, by mass percentage, 0.5%-1.5% of a conductive reinforcing material, 5%-10% of a gradient micron-grade tin powder, 10%-12% of an organic binder, 1%-5% of glass powder, 0.5%-4% of a multifunctional additive, 3%-5% of a low-temperature curing aid, 0.5%-1% of a coupling agent, 0.5%-1% of a corrosion inhibitor, and the remainder of a conductive material; Preferably, the conductive reinforcing material comprises, by mass percentage, 30%-50% of nano nickel wires and 50%-70%.

5. The copper paste according to claim 4, characterized in that The raw materials for preparing the multifunctional additive include: dodecafluoroheptyl methacrylate, 2-vinylbenzoxazole and polyethylene glycol methacrylate; Preferably, the multifunctional additive comprises, by mass percentage, 40%-60% of dodecafluoroheptyl methacrylate, 25%-35% of 2-vinylbenzoxazole, and 15%-25% of polyethylene glycol methacrylate.

6. The method for preparing the copper slurry according to any one of claims 1 to 5, wherein: include: The conductive material, the conductive reinforcing material, the gradient micron-sized tin powder, the organic adhesive, the glass powder, the multifunctional additive, the low-temperature curing auxiliary agent and the reinforcing agent in the formulated amount are mixed to obtain the copper paste.

7. The preparation method according to claim 6, characterized in that The multifunctional additive is prepared by the following method: (a) dodecafluoroheptyl methacrylate, a chain transfer agent, and azobisisobutyronitrile are mixed, cooled, and precipitated in cold methanol, and filtered to obtain a solid product; (b) mixing the solid product prepared in step (a), 2-vinylbenzoxazole, and a chain transfer agent, and then dialyzing to remove unreacted monomers to obtain a powder product; (c) mixing the powder product prepared in step (b) with polyethylene glycol methacrylate to obtain the multifunctional additive; Preferably, the chain transfer agent comprises cyanoisopropyl dithiobenzoate; Preferably, in step (a), the molar ratio of the chain transfer agent to dodecafluoroheptyl methacrylate is 1-1.5; the molar ratio of azobisisobutyronitrile to the chain transfer agent is 0.1-0.3; Preferably, in step (b), the molar ratio of the chain transfer agent to 2-vinylbenzoxazole is 0.5-1.

8. Use of the copper paste according to any one of claims 1 to 5 or the copper paste prepared by the preparation method according to claim 6 or 7 in the preparation of solar cells.

9. A solar cell, characterized in that: The preparation method includes: preparing patterned grooves on the front and back of a silicon substrate, and then sequentially preparing gate lines in the patterned grooves; Wherein, the gate line is prepared by using the copper paste according to any one of claims 1 to 5 or the copper paste prepared by the preparation method according to claim 6 or 7.

10. The solar cell according to claim 9, characterized in that The width of the patterned groove is 10 to 50 μm, and the depth is 80 to 100 nm. Preferably, the thickness of the gate line is 8 to 20 μm; Preferably, the gate lines are prepared by screen printing; the printed cells are dried and cured; the drying and curing temperature is 200-300°C; Preferably, ultraviolet light irradiation is additionally applied to the pre-curing zone; the ultraviolet light irradiation time is 5-10 seconds.

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