Base metal conductive paste for photovoltaic cell, and preparation method, use method and application thereof

Abstract

The invention provides base metal conductive paste for a photovoltaic cell and a preparation method, a use method and application thereof, and the conductive paste comprises the following components in percentage by mass: 5-60wt% of oxide coated base metal powder, 27-77wt% of silver powder, 2-5wt% of glass powder, 0.1-3wt% of an antioxidant aid and the balance of an organic carrier; wherein the base metal powder comprises one or more of copper, tungsten, tin, nickel, aluminum and alloy powder of the copper, the tungsten, the tin, the nickel, the aluminum and the alloy powder of the aluminum, and the oxide comprises one or more of silicon oxide, aluminum oxide, titanium oxide and boric oxide. The base metal powder coated with a specific type and a proper amount of oxide is selected and matched with the oxide and the glass powder which are good in compatibility, the manufacturing cost of the conductive paste and the battery can be effectively reduced, meanwhile, the conductive paste is applied to TOPCon and BC batteries, and the battery conversion efficiency can be kept equivalent to or even superior to that of traditional pure silver conductive paste.

Description

Technical Field

[0001] The present application relates to the technical field of conductive materials, and in particular to base metal conductive paste for photovoltaic cells and its preparation method, use method and application. Background Art

[0002] Tunnel oxide passivating contact (TOPCon) cells and back contact (BC) cells are currently the mainstream photovoltaic cell technologies, offering advantages such as high conversion efficiency, high power generation, and excellent reliability. However, the manufacturing costs of both types of cells are relatively high, with silver paste costs accounting for a significant proportion of the entire cell manufacturing process. Therefore, reducing silver paste costs can effectively reduce overall cell manufacturing costs.

[0003] To address the above issues, existing patents such as CN118367063A provide a low-cost silver-coated nickel powder to replace silver powder for TOPCon solar cell metallization solutions, and CN118609880A provides a TOPCon battery back paste solution, using various types of composite Cu powder and Ag powder as the main conductive phase, and adding an appropriate amount of Cu alloy powder to reduce the amount of Ag, thereby controlling costs. However, while the above technologies effectively reduce the manufacturing costs of conductive pastes and batteries by replacing part of the precious metal silver with base metal copper, nickel or their alloys, due to the high resistivity of copper, nickel or their alloys and their easy oxidation during high-temperature sintering, the resistance of the battery used will increase accordingly, hindering its application in high-temperature environments.

[0004] Therefore, how to provide a solution that reduces the manufacturing cost of the conductive paste while maintaining good battery performance is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a base metal conductive paste for photovoltaic cells. By coating base metal powder with a specific type and appropriate amount of oxide, combined with highly compatible glass powder, this paste effectively avoids the increased resistance caused by base metal oxidation. When applied to TOPCon and BC cells, the resulting cell conversion efficiency is comparable to or even superior to that of traditional pure silver conductive pastes. This solution is applicable to a wide range of base metal powders and their alloys.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions:

[0007] On the one hand, the present application provides a base metal conductive paste for photovoltaic cells, which comprises, by mass percentage, 5-60wt% of oxide-coated base metal powder, 27-77wt% of silver powder, 2-5wt% of glass powder, 0.1-3wt% of antioxidant, and the balance being an organic carrier; wherein the base metal powder comprises one or more of copper, tungsten, tin, nickel, aluminum and alloy powders thereof, and the oxide comprises one or more of silicon oxide, aluminum oxide, titanium oxide and boron oxide.

[0008] In some embodiments, the oxide-coated base metal powder has a particle size D50 of 1-10 μm.

[0009] In some embodiments, the silver powder includes one or more of spherical silver powder, flaky silver powder, and dendritic silver powder.

[0010] In some embodiments, the antioxidant aid includes one or more of nitrogen-containing heterocyclic compounds, inorganic non-metallic materials, carbon-based materials, and transition metals.

[0011] Wherein, the nitrogen-containing heterocyclic compound includes one or more of benzotriazole, 1-phenyl-5-mercaptotetrazolyl and 8-hydroxyquinoline.

[0012] Wherein, the inorganic non-metallic material includes silicon powder and / or boron powder.

[0013] The carbon-based material includes one or more of graphite powder, carbon nanotubes, graphite fibers and graphene powder.

[0014] Wherein, the transition metal includes one or more of zinc powder, chromium powder and yttrium powder.

[0015] On the other hand, the present application also provides a method for preparing the base metal conductive paste for photovoltaic cells as described above, comprising mixing oxide-coated base metal powder, silver powder, glass powder, antioxidant and organic carrier, and grinding and dispersing using a three-roll mill to obtain the base metal conductive paste.

[0016] Among them, the three-roller mill can adopt the EXAKT-80E model.

[0017] In some embodiments, the preparation method of the oxide-coated base metal powder includes a chemical method and a physical method, the chemical method includes any one of atomic layer deposition, chemical vapor deposition, liquid phase reduction co-precipitation and sol-gel method, and the physical method includes any one of physical vapor deposition, water mist method and ball milling method.

[0018] In some embodiments, the sol-gel method includes mixing the precursor with anhydrous ethanol, adding the base metal powder, water, and pH adjuster, heating to 40-60°C, stirring for 4-6 hours, filtering out the supernatant, drying at 100-120°C for 2-3 hours, and then crushing.

[0019] The pH regulator is usually ammonia or citric acid.

[0020] In some embodiments, the atomic layer deposition method includes placing the base metal powder in a chamber at a temperature of 150-200° C., alternately introducing a precursor and ozone with a pulse time of 1-10 s, sweeping for 10-20 s under an inert atmosphere, and cycling for 20-100 times.

[0021] In some embodiments, the aforementioned precursor includes one or more of a silicon-based precursor, an aluminum-based precursor, a titanium-based precursor, and a boron-based precursor.

[0022] In some embodiments, the silicon-based precursor includes one or more of ethyl orthosilicate, tetramethoxysilane, tetraethoxysilane and methyltriethoxysilane; the aluminum-based precursor includes one or more of aluminum nitrate, aluminum isopropoxide and trimethylaluminum; the titanium-based precursor includes one or more of tetrabutyl titanate, ethyl titanate and titanium isopropoxide; the boron-based precursor includes one or more of n-butyl borate, trimethyl borate and triethyl borate.

[0023] In some embodiments, the mass ratio of the precursor to the base metal powder is (0.001-0.5):1.

[0024] In some embodiments, the ball milling method includes mixing the base metal powder and the oxide and ball milling them at a rotation speed of 200-1000 rpm for 30-360 min, and the mass ratio of the oxide to the base metal powder is (0.01-0.5):1.

[0025] In the present application, the ball milling method is used to allow the oxide to be adsorbed on the surface of the base metal powder, thereby achieving a surface coating effect.

[0026] In some embodiments, zirconium balls with a diameter of 2 mm may be used in the ball milling process.

[0027] In some embodiments, the method for preparing the organic carrier comprises mixing the resin and the carrier solvent, heating to 60-80° C., stirring for 2-3 hours, cooling to room temperature, adding silicone oil, and continuing stirring for 1-2 hours.

[0028] The resin includes one or more of ethyl cellulose, polyvinyl butyral and styrene-ethylene-propylene-styrene block copolymer, and the carrier solvent includes one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester and benzyl benzoate.

[0029] The present application also provides a method for using the aforementioned base metal conductive paste for photovoltaic cells, comprising printing the base metal conductive paste for photovoltaic cells on a device, and then sintering at a high temperature to obtain a conductive layer.

[0030] In some embodiments, the high temperature sintering temperature is 600-800°C.

[0031] The present application also provides a use of the aforementioned base metal conductive paste for photovoltaic cells or the base metal conductive paste for photovoltaic cells prepared by the aforementioned preparation method in photovoltaic cells, wherein the photovoltaic cells include TOPCon cells and BC cells.

[0032] Compared with the prior art, this application has the following advantages:

[0033] (1) On the one hand, the present application selects a specific type of oxide-coated base metal powder and combines it with glass powder with good compatibility. During the high-temperature sintering process, the oxide coating layer can effectively inhibit the oxidation of the base metal powder, thereby ensuring better battery performance. It can also replace most of the silver powder in the conductive paste. The weight percentage of silver in the conductive phase component can be as low as 45% or even lower, significantly reducing the manufacturing cost of the conductive paste.

[0034] (2) The preparation method of the base metal conductive paste for photovoltaic cells provided in the present application requires strict control of the amount of oxide coating to ensure that the oxide is coated on the surface of the base metal to form a continuous and dense barrier, thereby preventing the oxidation of the base metal and keeping the electron transmission channel unobstructed. Only then can the electrical performance of the conductive paste obtained be comparable to that of pure silver conductive paste, and it can be compatible with the high-temperature sintering process of 600-800°C, thus overcoming the defect of limited application in high-temperature environments.

[0035] (3) The present application also provides the application of base metal conductive paste in photovoltaic cells, specifically in TOPCon and BC cells, which can achieve a cell conversion efficiency equivalent to that of pure silver conductive paste, and even better than traditional pure silver conductive paste. This also shows that the technical solution of the present application can significantly reduce manufacturing costs while having high reliability and will not affect the conversion efficiency of the cell. It is also applicable to a variety of base metal replacement solutions for silver and has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments of the present application.

[0037] Figure 1 This is a SEM morphology image of the base metal powder of Example 1 of the base metal conductive paste of the present application, magnified 5000 times.

[0038] Figure 2 This is a SEM morphology image of the oxide-coated base metal powder of Example 1 of the base metal conductive paste of the present application, magnified 5000 times. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. It should be understood that the specific embodiments described are only used to explain this application and are not used to limit this application.

[0040] In the description of the embodiments of the present application, it should be noted that all ranges disclosed in this application will be understood to encompass any and all sub-ranges included therein. For example, the stated range "27-77 wt %" should be deemed to include any and all sub-ranges that begin with a minimum of 27 wt % or greater and end with a maximum of 77 wt % or less, for example, 27 wt % to 56 wt %, or 30 wt % to 60 wt %, or 30 wt % to 70 wt %. At the same time, all ranges disclosed in this application are also deemed to include the endpoints of the ranges, unless otherwise expressly stated. For example, the ranges "between 27 wt % and 56 wt %" or "27 wt % to 56 wt %" or "27-56 wt %" should generally be deemed to include the endpoints 27 wt % and 56 wt %.

[0041] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0042] In the field of photovoltaic cells, replacing silver with base metals can reduce costs. However, since base metals, represented by copper, are highly susceptible to oxidation, which affects their conductivity, their application is particularly limited in high-temperature environments. Therefore, overcoming the oxidation problem of base metals during the sintering process is an important research direction for base metal conductive pastes for photovoltaic cells. Based on this, this application explores a technical solution for anti-oxidation suitable for various types of base metals and their alloys, which significantly reduces the cost of conductive pastes and batteries while achieving battery conversion efficiency comparable to that of directly using pure silver paste.

[0043] Based on this, see Figure 1-2 In the first aspect of the present application, a base metal conductive paste for photovoltaic cells is provided, which comprises, by mass percentage, 5-60wt% of oxide-coated base metal powder, 27-77wt% of silver powder, 2-5wt% of glass powder, 0.1-3wt% of antioxidant, and the remainder is an organic carrier; wherein the base metal powder comprises one or more of copper, tungsten, tin, nickel, aluminum and alloy powders thereof; and the oxide comprises one or more of silicon oxide, aluminum oxide, titanium oxide and boron oxide.

[0044] It should be noted that the copper, tungsten, tin, nickel, and aluminum, as well as their alloys, used in this application all have high resistivity and are easily oxidized during high-temperature sintering. This can further increase the resistance of the battery used, which is detrimental to battery performance. To balance manufacturing cost and battery performance, this application uses oxide coating on the surface of these base metal powders to effectively physically isolate oxygen. Compared with conventional organic coatings or antioxidants, the oxides themselves have high melting points and are less prone to decomposition. This effectively prevents oxidation of the base metal powders during high-temperature sintering, thus avoiding the problem of increased resistance caused by oxidation. Furthermore, the specific oxides selected in this application, such as aluminum oxide and silicon oxide, have a small difference in thermal expansion coefficient with the base metal powders selected in this application, which can reduce the problem of cracking of the coating layer caused by thermal stress during subsequent high-temperature sintering. Furthermore, titanium oxide has a low interfacial energy with the base metals selected in this application, enhancing the bonding strength through chemical bonding and preventing detachment. Boron oxide has a low melting temperature and, after melting, adheres to the metal surface to effectively isolate oxygen and prevent oxidation. Furthermore, it can introduce boron vacancy defects, which serve as carrier scattering centers and regulate the conductivity of the metal powder. Furthermore, these specific oxides can also serve as glass components to a certain extent, showing good compatibility with the glass of this application. This shows that this application requires matching specific oxide types suitable for base metal powders. The resulting overall technical solution can be well applied to photovoltaic cell conductive pastes, providing a cost-effective alternative to silver while maintaining comparable cell conversion efficiency to pure silver paste in photovoltaic cells.

[0045] In this application, according to the general explanation in the art, the sum of the components in the conductive paste is calculated as 100%.

[0046] In some embodiments, the particle size of the base metal powder can be 1-10 μm. When the particle size of the base metal powder itself is less than 1 μm, the larger the specific surface area, the more contact points between the particles, and a denser electrode is formed. However, this causes part of the glass to be unable to contact the battery, weakening the effect and significantly reducing the contact resistance. When the particle size is greater than 10 μm, the gaps between the particles increase, and the non-conductive phase will fill the gaps, hindering electron transmission, resulting in increased resistivity, and affecting printing. Therefore, the particle size of the base metal powder also needs to meet an appropriate value.

[0047] In some embodiments, the mass proportion of the oxide-coated base metal powder is 20 wt%-50 wt%, or 25-50 wt%, or 30-50 wt%, or 30-40 wt%.

[0048] In some embodiments, the mass proportion of the silver powder is 30-70 wt %, further 40-65 wt %, and further 45-60 wt %.

[0049] In some embodiments, the glass powder accounts for 2-4 wt %, further 2-3 wt %.

[0050] In some embodiments, the weight percentage of the antioxidant is 0.1-1 wt %, further 0.1-0.5 wt %, and further 0.1-0.2 wt %.

[0051] In the present application, the oxide includes one or more of silicon oxide, aluminum oxide, titanium oxide and boron oxide.

[0052] In some embodiments, the oxide-coated base metal powder has a particle size D50 of 1-10 μm.

[0053] In some embodiments, the oxide-coated base metal powder may be silicon oxide-coated nickel powder, titanium oxide-coated tungsten powder, aluminum oxide-coated tin powder, or aluminum oxide-coated copper powder.

[0054] In some embodiments, the silver powder includes one or more of spherical silver powder, flaky silver powder, and dendritic silver powder.

[0055] In some embodiments, the antioxidant aid includes one or more of nitrogen-containing heterocyclic compounds, inorganic non-metallic materials, carbon-based materials, and transition metals.

[0056] Wherein, the nitrogen-containing heterocyclic compound includes one or more of benzotriazole, 1-phenyl-5-mercaptotetrazolyl and 8-hydroxyquinoline.

[0057] Wherein, the inorganic non-metallic material includes silicon powder and / or boron powder.

[0058] The carbon-based material includes one or more of graphite powder, carbon nanotubes, graphite fibers and graphene powder.

[0059] Wherein, the transition metal includes one or more of zinc powder, chromium powder and yttrium powder.

[0060] Furthermore, the antioxidant auxiliary agent is selected from silicon powder and / or benzotriazole.

[0061] The size of silicon powder is generally selected from 1-2 μm.

[0062] In the present application, the glass powder is generally commercially available glass powder, including glass powder of model FD56 and / or FD61.

[0063] The second aspect of the present application provides a method for preparing the aforementioned base metal conductive paste for photovoltaic cells, comprising mixing oxide-coated base metal powder, silver powder, glass powder, antioxidant and organic carrier, and grinding and dispersing using a three-roll mill to obtain the base metal conductive paste.

[0064] In some embodiments, the preparation method of the oxide-coated base metal powder includes a chemical method and a physical method, the chemical method includes any one of atomic layer deposition ALD, chemical vapor deposition CVD, liquid phase reduction co-precipitation method and sol-gel method, and the physical method includes any one of physical vapor deposition PVD, water mist method and ball milling method.

[0065] In some embodiments, the sol-gel method includes mixing the precursor with anhydrous ethanol, adding the base metal powder, water and pH regulator, heating to 40-60°C, stirring for 4-6 hours, filtering out the supernatant, drying at 100-120°C for 2-3 hours and then crushing.

[0066] The pH regulator is usually ammonia or citric acid.

[0067] In some embodiments, the atomic layer deposition method includes placing the base metal powder in a chamber at a temperature of 150-200° C., alternately introducing a precursor and ozone with a pulse time of 1-10 s, sweeping for 10-20 s under an inert atmosphere, and cycling for 20-100 times.

[0068] In some embodiments, the aforementioned precursor includes one or more of a silicon-based precursor, an aluminum-based precursor, a titanium-based precursor, and a boron-based precursor.

[0069] In some embodiments, the silicon-based precursor includes one or more of ethyl orthosilicate, tetramethoxysilane, tetraethoxysilane and methyltriethoxysilane; the aluminum-based precursor includes one or more of aluminum nitrate, aluminum isopropoxide and trimethylaluminum; the titanium-based precursor includes one or more of tetrabutyl titanate, ethyl titanate and titanium isopropoxide; the boron-based precursor includes one or more of n-butyl borate, trimethyl borate and triethyl borate.

[0070] In some embodiments, the mass ratio of the precursor to the base metal powder is (0.001-0.5):1.

[0071] In some embodiments, the ball milling method includes mixing the base metal powder and the oxide and ball milling them at a rotation speed of 200-1000 rpm for 30-360 min, and the mass ratio of the oxide to the base metal powder is (0.01-0.5):1.

[0072] In some embodiments, the rotation speed is 200-500 rpm, the ball milling time is 60-120 min, and the mass ratio of the oxide to the base metal powder is (0.01-0.1):1, and can further be (0.03-0.08):1, for example, 0.025:1.

[0073] Among them, in this application, the ball milling method is used to allow the oxide to be adsorbed on the surface of the base metal powder, achieving a surface coating effect.

[0074] In some embodiments, zirconium balls with a diameter of 2 mm may be used in the ball milling process.

[0075] It should be noted that the oxide coating of this application needs to form a barrier on the surface of the base metal to prevent the oxidation of the base metal, and at the same time, it is also necessary to ensure the smooth flow of electron transmission channels. Therefore, how to ensure the balance between conductivity and oxidation resistance is crucial. The oxide used in this application is part of the glass powder and is integrated into the glass powder, which may affect the performance of the glass powder. The most important performance of the glass powder is to corrode the passivation film and insulating layer of the battery to form an ohmic contact. Therefore, the amount of the coating oxide layer formed in the final state needs to simultaneously meet the requirements of not oxidizing the base metal or oxidizing as little as possible and avoiding affecting the performance of the glass powder. Therefore, it is necessary to strictly control the amount of precursors and oxides added within an appropriate range.

[0076] In some embodiments, the mass ratio of the precursor to the base metal powder is (0.001-0.1):1, further (0.001-0.05):1, for example, 0.002:1, 0.015:1, 0.02:1.

[0077] In the present application, the preparation method of the organic carrier comprises mixing a resin and a carrier solvent, heating to 60-80° C., stirring at this temperature for 2-3 hours, adding silicone oil after cooling to room temperature, and continuing stirring for 1-2 hours.

[0078] In some embodiments, the silicone oil may be Dow Corning silicone oil.

[0079] The resin includes one or more of ethyl cellulose, polyvinyl butyral and styrene-ethylene-propylene-styrene block copolymer, and the carrier solvent includes one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester and benzyl benzoate.

[0080] In this application, room temperature is generally defined as 25°C according to conventional interpretation.

[0081] The third aspect of the present application also provides a method for using the aforementioned base metal conductive paste for photovoltaic cells, comprising printing the base metal conductive paste for photovoltaic cells on a device, and then sintering at a high temperature to obtain a conductive layer.

[0082] In some embodiments, the high temperature sintering temperature is 600-800°C, further 650-750°C.

[0083] A fourth aspect of the present application also provides the use of the aforementioned base metal conductive paste for photovoltaic cells or the alkali metal conductive paste prepared by the aforementioned preparation method in photovoltaic cells, wherein the photovoltaic cells include TOPCon and BC cells.

[0084] The present application is further explained below with reference to examples.

[0085] Unless otherwise specified, the reagents and materials used in the following examples and comparative examples are commercially available.

[0086] Spherical silver powder with model number 152-16 was purchased from Shandong Jianbang Colloid Materials Co., Ltd., spherical silver powder with model number S700-4 was purchased from Suzhou Yinrui Optoelectronic Materials Co., Ltd., glass powders with models FD56 and FD61 were purchased from Anmi Micronano Co., Ltd., silicon powder and benzotriazole were purchased from MacLean Reagent Co., Ltd., ethyl cellulose model was STD-4, polyvinyl butyral model was PVB-20H, styrene-ethylene-propylene-styrene block copolymer model was G1701, and Dow Corning silicone oil model was PMX200-100.

[0087] Example 1

[0088] This embodiment 1 provides a base metal conductive paste, the raw materials of which include 25.3 wt % of silicon oxide-coated nickel powder, 63.2 wt % of spherical silver powder of model 152-16, 2.5 wt % of glass powder of model FD56, 0.1 wt % of 1 μm silicon powder as an antioxidant, and 8.9 wt % of an organic vehicle.

[0089] The preparation process of the base metal conductive paste is as follows:

[0090] S1. Preparation of silicon oxide-coated nickel powder: 1.5 g of tetraethyl orthosilicate (TEOS) was added to 100 g of anhydrous ethanol solution and stirred for 30 minutes. 100 g of nickel powder with a particle size of 1-10 μm (the mass ratio of tetraethyl orthosilicate to nickel powder was 0.015:1), 5 ml of deionized water, and 1 g of ammonia were added to the solution. The solution was heated to 60° C. and stirred for 6 hours. The surface solution was poured out, dried at 100° C. for 3 hours, and crushed to obtain silicon oxide-coated nickel powder A with a particle size D50 of 1-10 μm.

[0091] S2. Preparation of organic vehicle: 5 g of ethyl cellulose STD-4, 5 g of polyvinyl butyral PVB-20H, 5 g of styrene-ethylene-propylene-styrene block copolymer G1701, 30 g of diethylene glycol butyl ether acetate, 30 g of dodecyl alcohol ester, and 24.5 g of benzyl benzoate were weighed and mixed. The mixture was heated to 80° C. and stirred for 3 hours. After cooling to room temperature, 0.5 g of Dow Corning silicone oil PMX200-100 was added and the mixture was stirred for 1 hour to obtain organic vehicle W.

[0092] S3. Preparation of base metal conductive slurry: Weigh by mass 100 g of the silicon oxide-coated nickel powder A obtained in step S1, 250 g of spherical silver powder of model 152-16, 10 g of glass powder of model FD56, 0.4 g of 1 μm silicon powder of Macklin's reagent as an antioxidant, and 35.20 g of organic vehicle W. After mixing, grind and disperse using an EXAKT-80E three-roll mill to obtain a high-temperature sintered base metal slurry.

[0093] Example 2

[0094] This embodiment 2 provides a base metal conductive paste, the raw materials of which include 30wt% of titanium oxide-coated tungsten powder, 58.6wt% of spherical silver powder of model 152-16, 2.5wt% of glass powder of model FD61, 0.1wt% of benzotriazole as an antioxidant, and 8.8wt% of an organic vehicle.

[0095] The preparation process of the base metal conductive paste is as follows:

[0096] S1. Preparation of titanium oxide-coated tungsten powder: 2 g of tetrabutyl titanate was added to 100 g of anhydrous ethanol solution and stirred for 30 minutes. 100 g of tungsten powder with a particle size of 3-8 μm (the mass ratio of tetrabutyl titanate to tungsten powder was 0.02:1) and 5 g of deionized water were added to the solution. The mixture was heated to 60°C and stirred for 6 hours. The surface solution was poured out and the mixture was dried at 100°C for 3 hours. The powder was crushed to obtain titanium oxide-coated tungsten powder B with a particle size D50 of 3-8 μm.

[0097] S2. Preparation of organic carrier is the same as step S2 in Example 1;

[0098] S3. Preparation of base metal conductive slurry: Weigh 120 g of titanium oxide-coated tungsten powder B obtained in step S1, 234.4 g of spherical silver powder of model 152-16, 10 g of glass powder of model FD61, 0.4 g of benzotriazole as an antioxidant, and 35.20 g of organic vehicle W. After mixing, grind and disperse using an EXAKT-80E three-roll mill to obtain a high-temperature sintered base metal slurry.

[0099] Example 3

[0100] This embodiment 3 provides a base metal conductive paste, the raw materials of which include 48.6 wt % of alumina-coated tin powder, 40 wt % of spherical silver powder of model S700-4, 2.5 wt % of glass powder of model FD61, 0.1 wt % of benzotriazole as an antioxidant, and 8.8 wt % of an organic vehicle.

[0101] The preparation process of the base metal conductive paste is as follows:

[0102] S1. Preparation of alumina-coated tin powder: Weigh 400 g of tin powder with a particle size of 5 μm and 10 g of fumed alumina (mass ratio of fumed alumina to tin powder is 0.025:1). Ball mill 1200 g of 2 mm diameter zirconium balls at 200 rpm for 60 min to obtain alumina-coated tin powder C with a particle size D50 of 5 μm.

[0103] S2. Preparation of organic carrier is the same as step S2 in Example 1;

[0104] S3. Preparation of base metal conductive paste: Weigh 194.4 g of the alumina-coated tin powder C obtained in step S1, 160 g of spherical silver powder of model S700-4, 10 g of glass powder of model FD61, 0.4 g of benzotriazole as an antioxidant, and 35.20 g of organic vehicle W. After mixing, grind and disperse them using an EXAKT-80E three-roll mill to obtain a high-temperature sintered base metal paste.

[0105] Example 4

[0106] This embodiment 4 provides a base metal conductive paste, the raw materials of which include 30wt% of alumina-coated copper powder, 58.6wt% of spherical silver powder of model S700-4, 2.5wt% of glass powder of model FD61, 0.1wt% of benzotriazole as an antioxidant, and 8.8wt% of an organic vehicle.

[0107] The preparation process of the base metal conductive paste is as follows:

[0108] S1. Preparation of alumina-coated copper powder: ALD method, 500g of copper powder is placed in the reaction chamber, the temperature is 150-200℃; 1g of metal precursor trimethylaluminum and 0.5g of ozone O3 (the mass ratio of trimethylaluminum to copper powder is 0.002:1) are alternately introduced, the precursor pulse time is 1-10 seconds, the inert gas argon purge time is 10-20 seconds, the number of cycles is 20-100 times, and the coating thickness is 2-20nm.

[0109] S2. Preparation of organic carrier is the same as step S2 in Example 1;

[0110] S3. Preparation of base metal conductive slurry: Weigh 120 g of alumina-coated copper powder D obtained in step S1, 234.4 g of spherical silver powder model S700-4, 10 g of glass powder model FD61, 0.4 g of benzotriazole as an antioxidant, and 35.20 g of organic vehicle W. After mixing, grind and disperse using an EXAKT-80E three-roll mill to obtain a high-temperature sintered base metal slurry.

[0111] Comparative Example 1

[0112] Comparative Example 1 provides a conductive silver paste, which is weighed by mass: 350 g (88.5 wt%) of spherical silver powder of model 152-16, 10 g (2.5 wt%) of glass powder of model FD56, and 35.60 g (9.0 wt%) of the organic vehicle W prepared in Example 1. After mixing, the mixture is ground and dispersed using an EXAKT-80E three-roll mill to obtain a pure silver conductive paste.

[0113] Comparative Example 2

[0114] Comparative Example 2 provides a conductive paste, which differs from Example 1 only in that untreated pure nickel powder is used instead of silicon oxide-coated nickel powder, and accordingly, step S1 is not included in the preparation process of the base metal conductive paste, and other conditions are the same.

[0115] Comparative Example 3

[0116] Comparative Example 3 provides a conductive paste, which differs from Example 1 only in that an equal mass of magnesium isopropoxide is used instead of ethyl orthosilicate to prepare nickel powder coated with magnesium oxide in step S1, and participates in subsequent steps, and other conditions are the same.

[0117] Comparative Example 4

[0118] Comparative Example 4 provides a conductive paste, which differs from Example 1 only in that 60 grams of tetraethyl orthosilicate (TEOS) and 100 grams of nickel powder with a particle size of 2-10 μm are used in step S1 (the mass ratio of tetraethyl orthosilicate to nickel powder is 0.6:1), and other conditions are the same.

[0119] Effect embodiment

[0120] The conductive pastes obtained in Examples 1-4 and Comparative Examples 1-4 were printed on the back of the TOPCon battery and the N region of the BC battery using a 500-mesh 12-line width screen printing technique. After sintering at 750°C in a sintering furnace, the electrical properties of the TOPCon and BC batteries were tested respectively using the halm solar energy simulation test method. The results are shown in Tables 1 and 2, respectively, where Eta refers to the battery conversion efficiency value, Uoc refers to the open-circuit voltage value, Isc refers to the short-circuit current value, FF refers to the fill factor value, Rs refers to the series resistance value, Rsh refers to the parallel resistance value, and IRev1 and IRev2 respectively represent the reverse current values.

[0121] Table 1

[0122] Electrical properties Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Eta(%) 25.578 25.650 25.615 25.600 25.634 25.4101 25.4045 25.4089 Uoc(mV) 0.7375 0.7374 0.7373 0.7371 0.7378 0.7357 0.7359 0.7359 Isc(mA) 13.859 13.861 13.864 13.868 13.867 13.8519 13.8483 13.8431 FF(%) 83.6914 83.9250 83.7983 83.7485 83.7857 83.39 83.37 83.41 Rs(ohm) 0.000925 0.000900 0.000882 0.000892 0.000921 0.000949 0.000949 0.000979 Rsh(ohm) 2717.4 2909.3 3044.3 2860 2968.4 3020 2909 3174 IRev1(mA) 0.011 0.011 0.011 0.014 0.011 0.011 0.011 0.010 IRev2(mA) 0.010 0.009 0.016 0.019 0.010 0.015 0.014 0013

[0123] Table 2

[0124] Electrical properties Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Eta(%) 26.860 26.883 26.888 26.861 26.859 26.511 26.474 26.499 Uoc(mV) 0.7362 0.7365 0.7367 0.7358 0.7364 0.7331 0.7336 0.7345 Isc(mA) 14.571 14.566 14.560 14.589 14.561 14.5905 14.589 14.590 FF(%) 87.042 87.112 87.136 86.985 87.065 86.15 85.98 85.95 Rs(ohm) 0.000885889 0.0008893 0.0008544 0.0008962 0.000831 0.000916 0.000925 0.000928 Rsh(ohm) 3342.9 3277.5 3202.6 2880 3077.2 2628 2520 2620 IRev1(mA) 0.009 0.012 0.007 0.012 0.010 0.002 0.08 0.09 IRev2(mA) 0.013 0.015 0.012 0.018 0.011 0.009 0.012 0.013

[0125] It can be seen from the example data in Table 1 and Table 2 that the present application only requires a small amount of oxide-coated base metal to replace part of the silver to prepare the conductive silver paste, and the battery conversion efficiency can reach the same level as that of the conductive silver paste prepared under the same conditions in Comparative Example 1 using pure silver. In particular, the solution of Example 2 applied to the TOPCon battery in Table 1 has a filling factor value of 0.17% higher than that of the pure silver paste, and the battery conversion efficiency is also increased by 0.06% compared with the pure silver paste. Similarly, the solution of Example 3 applied to the BC battery in Table 2 has a filling factor value of 0.08% higher than that of the corresponding Comparative Example 1, and the battery conversion efficiency is increased by 0.10%. At the same time, the amount of silver powder used is reduced by more than 40wt%, which significantly reduces the slurry cost and improves economic benefits.

[0126] By comparing Comparative Example 2 in Table 1 with Example 1 and Comparative Example 1, it can be seen that if silver is simply replaced with base metals, the effect is not ideal, and the battery performance is significantly reduced compared to pure silver paste. The same is true for Comparative Example 2 in Table 2 with Example 1 and Comparative Example 1.

[0127] By comparing Example 1 and Comparative Example 3 in Tables 1 and 2, it can be seen that the several types of oxides in the present application are specially selected to match the types of base metal powders, have good bonding strength and can regulate the conductivity of the metal powders. However, other oxides and other antioxidants that are not within the scope of protection of the present application are used for coating. Due to the high reaction activity under high temperature conditions, the integrity of the coating layer will be destroyed, and pulverization will easily occur in an alkaline environment. The corresponding electrical performance will drop sharply, and it is not suitable for use in the conductive paste of photovoltaic cells.

[0128] By comparing Example 1 and Comparative Example 4 in Table 1 and Table 2, it can be seen that the present application only requires a relatively small amount of oxide coating to achieve excellent results. A larger amount of precursor will have a negative impact on the results and is not conducive to maintaining electrical properties.

[0129] In summary, the solution of coating base metals with specific oxides has effectively overcome the defects of base metals that may have limited application in high-temperature environments. It can effectively reduce the cost of conductive paste and battery manufacturing, while also improving battery conversion efficiency to a certain extent. It has high reliability and is suitable for various base metal replacement solutions for silver, and has good universality.

[0130] Although examples of the present embodiment have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and intent of the present embodiment, and the scope of the present embodiment is defined by the claims and their equivalents.

Claims

1. A base metal conductive paste for photovoltaic cells, characterized in that: Calculated by mass percentage, it includes 5-60wt% of oxide-coated base metal powder, 27-77wt% of silver powder, 2-5wt% of glass powder, 0.1-3wt% of antioxidant, and the balance is an organic carrier; The base metal powder includes one or more of copper, tungsten, tin, nickel, aluminum and alloy powders thereof; and the oxide includes one or more of silicon oxide, aluminum oxide, titanium oxide and boron oxide.

2. The base metal conductive paste for photovoltaic cells according to claim 1, characterized in that: The following conditions must be met: a. The particle size D50 of the oxide-coated base metal powder is 1-10 μm; b. The silver powder includes one or more of spherical silver powder, flaky silver powder and dendritic silver powder; c. The antioxidant comprises one or more of nitrogen-containing heterocyclic compounds, inorganic non-metallic materials, carbon-based materials and transition metals.

3. The base metal conductive paste for photovoltaic cells according to claim 2, characterized in that: The following conditions must be met: a. The nitrogen-containing heterocyclic compound includes one or more of benzotriazole, 1-phenyl-5-mercaptotetrazole and 8-hydroxyquinoline; b. The inorganic non-metallic material includes silicon powder and / or boron powder; c. The carbon-based material includes one or more of graphite powder, carbon nanotubes, graphite fibers and graphene powder; d. The transition metal includes one or more of zinc powder, chromium powder and yttrium powder.

4. The method for preparing the base metal conductive paste for photovoltaic cells according to any one of claims 1 to 3, characterized in that: The method comprises the steps of mixing the oxide-coated base metal powder, silver powder, glass powder, an antioxidant and an organic carrier, and grinding and dispersing the mixture using a three-roller mill to obtain a base metal conductive paste.

5. The preparation method according to claim 4, characterized in that The preparation method of the oxide-coated base metal powder includes a chemical method and a physical method. The chemical method includes any one of atomic layer deposition, chemical vapor deposition, liquid phase reduction co-precipitation and sol-gel method. The physical method includes any one of physical vapor deposition, water mist method and ball milling method.

6. The preparation method according to claim 5, characterized in that The sol-gel method includes mixing the precursor with anhydrous ethanol, adding the base metal powder, water and pH regulator, heating to 40-60° C., stirring for 4-6 hours, filtering out the supernatant, drying at 100-120° C. for 2-3 hours and then crushing.

7. The preparation method according to claim 5, characterized in that The atomic layer deposition method includes placing the base metal powder in a chamber at a temperature of 150-200° C., alternately introducing a precursor and ozone with a pulse time of 1-10 seconds, sweeping for 10-20 seconds under an inert atmosphere, and cycling for 20-100 times.

8. The preparation method according to claim 6 or 7, characterized in that The following conditions must be met: a. The precursor includes one or more of a silicon-based precursor, an aluminum-based precursor, a titanium-based precursor and a boron-based precursor, wherein the silicon-based precursor includes one or more of ethyl orthosilicate, tetramethoxysilane, tetraethoxysilane and methyltriethoxysilane; the aluminum-based precursor includes one or more of aluminum nitrate, aluminum isopropoxide and trimethylaluminum; the titanium-based precursor includes one or more of tetrabutyl titanate, ethyl titanate and titanium isopropoxide; the boron-based precursor includes one or more of n-butyl borate, trimethyl borate and triethyl borate; b. The mass ratio of the precursor to the base metal powder is (0.001-0.5):

1.

9. The preparation method according to claim 5, characterized in that The ball milling method includes mixing the base metal powder and the oxide and performing ball milling at a rotation speed of 200-1000 rpm for 30-360 minutes. The mass ratio of the oxide to the base metal powder is (0.01-0.5):

1.

10. The preparation method according to claim 4, characterized in that The preparation method of the organic carrier comprises mixing a resin and a carrier solvent, heating to 60-80° C., stirring at the temperature for 2-3 hours, adding silicone oil after cooling to room temperature, and continuing stirring for 1-2 hours, wherein the resin comprises one or more of ethyl cellulose, polyvinyl butyral, and styrene-ethylene-propylene-styrene block copolymer, and the carrier solvent comprises one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester, and benzyl benzoate.

11. A method for using the base metal conductive paste for photovoltaic cells according to any one of claims 1 to 3, characterized in that: The method comprises printing the base metal conductive paste for photovoltaic cells on a device, and then performing high-temperature sintering to obtain a conductive layer, wherein the temperature of the high-temperature sintering is 600-800°C.

12. Use of the base metal conductive paste for photovoltaic cells according to any one of claims 1 to 3 or the base metal conductive paste for photovoltaic cells prepared by the preparation method according to any one of claims 4 to 10 in photovoltaic cells, wherein the photovoltaic cells include TOPCon cells and BC cells.

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