Conductive paste and preparation method and application thereof

Abstract

The invention provides a conductive paste and a preparation method and application thereof, the conductive paste comprises the following components: 84-90 wt% of a conductive phase, 2-6 wt% of a glass phase, and 8-10 wt% of an organic carrier, the conductive phase comprises silver powder and base metal powder, when the particle size D50 of the base metal powder is less than 2 [mu] m, the mass ratio of the silver powder to the base metal powder is (0.5-2.0): 1, and when the particle size D50 of the base metal powder is less than 2 [mu] m, the mass ratio of the silver powder to the base metal powder is (0.5-2.0): 1. When D50 of the base metal powder is larger than or equal to 2 micrometers and smaller than 10 micrometers, the mass ratio of the silver powder to the base metal powder is (2.5-19): 1. According to the invention, the particle size of the base metal powder is controlled at the same time, the proportion of the silver powder to the base metal powder under the specific particle size is matched, and the composition of the glass powder is matched, so that excellent electrical properties, good printing performance and relatively strong adhesive force of the conductive paste are realized.

Description

Technical Field

[0001] The present application relates to the technical field of conductive materials, and in particular to a conductive paste and a preparation method and application thereof. Background Art

[0002] With the acceleration of the commercialization of TOPCon (tunneling oxide passivation contact) solar cells, its excellent passivation characteristics and high efficiency make it the successor to PERC. However, the traditional TOPCon structure faces a significant challenge in that the amount of silver used is too high, and the manufacturing cost is bound to increase. Therefore, alternative metals such as copper and nickel have application prospects. However, simply replacing silver with copper is easy to diffuse and highly corrosive. Although nickel is stable, it has poor conductivity. In the actual printing process, it has poor adhesion to silicon. During the high-temperature sintering process, the electrode is prone to falling off, and the electrical contact morphology is not good. TOPCon cells have higher requirements for printing performance and adhesion than PERC. Therefore, a simple base metal replacement solution is still difficult to meet the requirements of TOPCon cells for high printability and adhesion of the positive electrode paste.

[0003] Therefore, how to develop a conductive paste that can reduce the manufacturing cost of the conductive paste while ensuring good printing performance and adhesion is an urgent problem to be solved in this field. Summary of the Invention

[0004] Based on the above technical problems, this application achieves excellent electrical properties, good printing performance and strong adhesion of the conductive paste by simultaneously controlling the particle size of the base metal powder, matching the ratio of silver powder to base metal powder at a specific particle size, and coordinating the components of the glass powder.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] On the one hand, the present application provides a conductive paste, which includes the following components: 84-90wt% of a conductive phase, 2-6wt% of a glass phase, and 8-10wt% of an organic vehicle, wherein the conductive phase includes silver powder and base metal powder. When the particle size D50 of the base metal powder is less than 2μm, the mass ratio of the silver powder to the base metal powder is (0.5-2.0):1; when the particle size of the base metal powder is 2μm≤D50<10μm, the mass ratio of the silver powder to the base metal powder is (2.5-19):1.

[0007] In some embodiments, the base metal powder includes one or more of aluminum powder, copper powder, nickel powder, tungsten powder, and tin powder.

[0008] In some embodiments, the base metal powder has a D50 particle size ranging from 0.5 to 9 μm.

[0009] In some embodiments, the purity of the base metal is ≥99.5%, wherein the purity of the aluminum powder is ≥99.5%, the purity of the copper powder is ≥99.6%, the purity of the nickel powder is ≥99.6%, the purity of the tungsten powder is ≥99.6%, and the purity of the tin powder is ≥99.5%.

[0010] In some embodiments, the glass phase includes 0.5-2wt% main glass powder and 0.5-2wt% auxiliary glass powder, and the main glass powder includes the following components by mass percentage: 60-70wt% boron oxide, 5-10wt% aluminum oxide, 10-30wt% bismuth oxide, and 1-20wt% silicon dioxide; the auxiliary glass powder includes the following components by mass percentage: 50-80wt% lead oxide, 5-20wt% silicon dioxide, 10-30wt% boron oxide, and 1-10wt% zinc oxide.

[0011] In some embodiments, the particle size of the main glass powder is in the range of 1-2 μm, and the particle size of the auxiliary glass powder is in the range of 0.8-2 μm.

[0012] In some embodiments, the organic vehicle includes solvents, film-forming agents, and auxiliary agents. By weight, the solvents account for 2-90 wt %, the film-forming agents account for 2-10 wt %, and the auxiliary agents account for 0.1-0.8 wt %.

[0013] In some embodiments, the solvents include one or more of terpineol, butyl carbitol, and ethyl acetate; the film-forming agent includes one or more of ethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose, and sodium carboxymethyl cellulose; and the auxiliary agent includes one or more of hydroxymethyl silicone oil, polydimethylsiloxane, and polyether-modified polydimethylsiloxane.

[0014] The present application also provides a method for preparing the aforementioned conductive paste, comprising the following steps:

[0015] S1. Pretreatment: Mix the base metal powder, the glass powder, and 1-5 wt% of the organic vehicle in proportion, centrifuge at a speed of 800-1200 rpm for 2-8 min, and grind the mixture using a three-roll mill at a speed of 50-120 rpm until the fineness of the base metal glass paste is less than 6 μm.

[0016] S2. Premixing: mixing the silver powder, the base metal glass paste prepared in step S1, and the remaining organic vehicle, and centrifuging at a speed of 800-1200 rpm for 2-8 minutes;

[0017] S3, fineness treatment: transfer the slurry premixed in step S2 to a three-roll mill, control the grinding speed to 80-200 r / min, and grind the slurry to a fineness of less than 6 μm;

[0018] S4, post-processing: centrifuging the ground slurry obtained in step S3 at a rotation speed of 400-600 r / min for 1-2 min, and filtering to obtain the base metal slurry.

[0019] The present application also provides an application of the aforementioned conductive paste or the conductive paste prepared by the aforementioned preparation method in a photovoltaic cell, wherein the photovoltaic cell is a TOPCon cell.

[0020] Compared with the prior art, this application has the following advantages:

[0021] The present application provides a conductive paste, a preparation method thereof, and an application thereof. In a first aspect, by respectively controlling the ratio of silver powder to base metal powder in the small and large particle size ranges of base metal powder, when the particle size of the base metal powder is controlled to be D50 < 2 μm, the base metal powder has a higher specific surface area and surface energy, and is easy to form a dense network during sintering. The corresponding mass ratio of silver powder to base metal powder is (0.5-2.0):1, and a relatively small amount of silver powder can complete the pore filling of the conductive phase to achieve low resistance performance; when the particle size of the base metal powder is 2 μm ≤ D50 < 10 μm, the sintering shrinkage rate of the base metal powder with a larger particle size is higher, so more silver powder is required to compensate for the volume change and maintain the continuity of the conductive path. The corresponding mass ratio of silver powder to base metal powder is (2.5-19):1, and relatively more silver powder is added to compensate for the overall conductivity of the conductive phase; the maximum particle size D50 of the base metal powder is set to no more than 10 μm to prevent excessively large particles from clogging the screen mesh and ensure printing performance. Secondly, through the overall synergistic coordination of the formulation, the conductive paste is applied to photovoltaic cells, especially TOPCon cells, significantly reducing manufacturing costs while ensuring low contact resistance and high photoelectric conversion efficiency, with electrical performance comparable to or even superior to that of pure silver paste in batteries. Thirdly, the present application also provides a simple method for preparing the conductive paste, with easily controllable process parameters, capable of meeting the needs of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Figure 1 Parts (a) to (m) correspond to the frictional powder removal performance diagrams of the products of Examples 1-6 and Comparative Examples 1-3 and 5-8 of the present application, respectively.

[0024] Figure 2Parts (a)-(n) correspond to the EL images of the products of Examples 1-6 and Comparative Examples 1-8 of the present application, respectively. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application. It should be understood that the specific embodiments described are only used to explain the present application and are not used to limit the present application.

[0026] 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 "50-80 wt %" should be deemed to include any and all sub-ranges that begin with a minimum of 50 wt % or greater and end with a maximum of 80 wt % or less, for example, 50 to 60 wt %, or 50 to 70 wt %, or 55 to 65 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 50 wt % and 60 wt %" or "50 wt % to 60 wt %" or "50-60 wt %" should generally be deemed to include the endpoints 50 wt % and 60 wt %.

[0027] 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.

[0028] This application is a technical solution for a base metal paste and a simple preparation method thereof proposed in order to simultaneously meet the high requirements of the existing photovoltaic industry, especially TOPCon batteries, for the conductivity, printing performance and adhesion of the positive electrode paste. This application achieves excellent electrical properties, good printing performance and strong adhesion of the conductive paste by simultaneously controlling the particle size of the base metal powder, matching the ratio of silver powder to base metal powder at a specific particle size, and coordinating the composition of the glass powder.

[0029] Specifically, on the one hand, the present application provides a conductive paste comprising the following components: 84-90 wt % of a conductive phase, 2-6 wt % of a glass phase, and 8-10 wt % of an organic vehicle, wherein the conductive phase comprises silver powder and base metal powder, and when the particle size D50 of the base metal powder is less than 2 μm, the mass ratio of the silver powder to the base metal powder is (0.5-2.0):1; when the particle size of the base metal powder is 2 μm ≤ D50 < 10 μm, the mass ratio of the silver powder to the base metal powder is (2.5-19):1.

[0030] In the present application, the particle size D50 of the silver powder may be 1.0-2.0 μm.

[0031] It should be noted that the inventors discovered that the amount of silver powder added needs to be adjusted for different base metal powder particle sizes. When the base metal powder particle size is controlled within the range of D50 < 2 μm, the base metal powder has a higher specific surface area and surface energy, is more active in sintering, and is more easily fully sintered at lower temperatures or in shorter times, reducing base metal oxidation caused by high sintering temperatures, which in turn leads to increased contact resistance and decreased conductivity. Furthermore, smaller base metal powder particles tend to form a dense network during sintering, and silver powder, as a conductive phase, only needs to fill the pores to achieve low resistance. When the base metal powder particle size is 2 μm ≤ D50 < 10 μm, the larger base metal powder particle size has a higher sintering shrinkage rate, requiring more silver powder to compensate for volume changes and maintain the continuity of the conductive path. Furthermore, base metals within this size range have weak conductivity, requiring silver powder to compensate for this loss in overall conductivity. When the base metal powder particle size D50 is ≥ 10 μm, overly large particles can clog the screen mesh during printing, preventing good printing performance. Therefore, it is very important to comprehensively balance the conductive properties, process stability and printing performance of conductive silver paste containing base metals.

[0032] It can be understood that for base metal powders with a wide range of particle size distribution, the base metal powders can be first subjected to particle size screening to screen out small-particle base metal powders with a particle size D50 < 2 μm and large-particle base metal powders with a particle size of 2 μm ≤ D50 < 10 μm, and the base metal powders with a particle size of D50 ≥ 10 μm are discarded, and then compounded with silver powder to form the conductive phase. Pure small-particle base metal powder can be used to compound silver powder according to the ratio of silver powder: base metal powder = (0.5-2.0): 1, or pure large-particle base metal powder can be used to compound silver powder according to the ratio of silver powder: base metal powder = (2.5-19): 1.

[0033] In some embodiments, the base metal powder includes one or more of aluminum powder, copper powder, nickel powder, tungsten powder, and tin powder.

[0034] In some embodiments, the base metal powder has a particle size range of 0.5-9 μm, for example, any one of 0.5 μm, 1.5 μm, 2 μm, 3.5 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 7 μm, 8 μm and 9 μm, or a range between any two values.

[0035] It should be noted that if the particle size of the base metal powder is too large, its compatibility with other components will be reduced, affecting the overall performance of the slurry. If the particle size is too small, the viscosity of the slurry will increase, the fluidity will deteriorate, and it will be unfavorable for processing.

[0036] In some embodiments, the base metal has a purity of ≥ 99.5%.

[0037] In some embodiments, the purity of the aluminum powder is ≥99.5%, the purity of the copper powder is ≥99.6%, the purity of the nickel powder is ≥99.6%, the purity of the tungsten powder is ≥99.6%, and the purity of the tin powder is ≥99.5%.

[0038] It should be noted that the purity of any base metal in this application must meet ≥99.5%. On the one hand, high-purity metals can minimize the damage of impurities to the conductive network, ensuring that silver and other metals form a continuous and dense conductive path. In addition, for the purpose of optimizing the sintering process, balancing cost and performance, and improving mechanical and chemical stability, it is mainly reflected in the following: tungsten powder itself has a high melting point. When used for high-temperature sintering, high purity can avoid local melting or cracking caused by impurities. Metal powder with a purity of ≥99.6% can better cooperate with silver powder and organic carrier to achieve low-temperature co-firing or high-temperature stability. Since adding base metals to replace part of the silver in the conductive silver paste can reduce costs, it is also necessary to ensure that its conductivity is close to that of pure silver, which requires that the purity of the base metal meet certain requirements. The reason for improving mechanical and chemical stability is that high-purity metal powder can reduce side reactions, enhance coating adhesion and corrosion resistance. For example, the purity of nickel powder needs to meet ≥99.6% to form a dense oxide film to prevent substrate corrosion. Insufficient nickel powder purity is prone to cracking.

[0039] Therefore, strict control of the purity of base metal powder is one of the key means to achieve high performance and low cost of conductive silver paste.

[0040] In some embodiments, the glass phase includes a main glass powder and an auxiliary glass powder. The main glass powder includes the following components by mass percentage: 60-70wt% boron oxide, 5-10wt% aluminum oxide, 10-30wt% bismuth oxide, and 1-20wt% silicon dioxide. The auxiliary glass powder includes the following components by mass percentage: 50-80wt% lead oxide, 5-20wt% silicon dioxide, 10-30wt% boron oxide, and 1-10wt% zinc oxide.

[0041] It should be noted that the main glass powder can effectively promote the bonding of the base metal powder and the silicon wafer during the sintering process, enhancing adhesion. Bismuth oxide acts as a flux, further reducing the sintering temperature. It also forms a Bi-BO glass phase, strengthening the interfacial bonding between the base metal layer and the silicon substrate, thereby enhancing adhesion. During the sintering process, the auxiliary glass powder can fully soften and fill the gaps between the silver powder and the base metal powder, preventing holes and electrode detachment caused by the shrinkage difference between the silver and base metal after sintering. Furthermore, during sintering, the glass undergoes a slight chemical reaction with the silicon nitride anti-reflective layer or silicon substrate on the silicon wafer surface, forming a transition layer that reduces contact resistance. This helps improve the ohmic contact characteristics between the electrode and the silicon wafer and reduces current transmission losses.

[0042] It is further explained that in the above-mentioned main glass powder, a high-boron component with a boron oxide content of up to 60-70wt% is specifically selected. The reason is that boron oxide, as a glass network former, can significantly reduce the softening point of glass, and at the same time improve the fluidity of the molten glass liquid, so that the main glass powder can melt quickly during sintering, effectively corrode the passivation layer on the surface of the silicon wafer, and form a uniform ohmic contact interface, which is more conducive to the performance of electrical properties. At the same time, it cooperates with the high-lead component lead oxide in the auxiliary glass powder. The lead and the boron in the main glass powder form a composite network. When corroding the passivation layer, the lead component may preferentially react with silicon to form a low-resistance lead-silicon compound. At the same time, the boron component in the main glass powder assists the physical bonding of silver powder and silicon, which can enhance the mechanical adhesion of the electrode.

[0043] In some embodiments, the content of the main glass powder in the slurry is 1.5-4 wt %, and the content of the auxiliary glass powder in the slurry is 0.5-2 wt %.

[0044] In some embodiments, the particle size of the main glass powder is in the range of 1-2 μm, and the particle size of the auxiliary glass powder is in the range of 0.8-2 μm.

[0045] In some embodiments, the organic vehicle includes solvents, film-forming agents, and auxiliary agents. By weight, the solvents account for 2-90 wt %, the film-forming agents account for 2-10 wt %, and the auxiliary agents account for 0.1-0.8 wt %.

[0046] In some embodiments, the solvents include one or more of terpineol, butyl carbitol, and ethyl acetate; the film-forming agent includes one or more of ethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose, and sodium carboxymethyl cellulose; and the auxiliary agent includes one or more of hydroxymethyl silicone oil, polydimethylsiloxane, and polyether-modified polydimethylsiloxane.

[0047] In some embodiments, the solvent may be one or more of terpineol, butyl carbitol, and ethyl acetate.

[0048] In some embodiments, the film-forming agent may be ethyl cellulose and / or sodium carboxymethyl cellulose.

[0049] In some embodiments, the auxiliary agent may be hydroxymethyl silicone oil.

[0050] It should be noted that the various components in the organic vehicle cooperate with each other to give the slurry good rheological properties and meet the requirements of the printing process. Among them, the solvent, such as terpineol, can provide good initial fluidity, ensuring that the slurry can easily pass through the mesh during printing. At the same time, its high boiling point slows down volatilization, avoiding mesh blockage or film defects caused by too rapid evaporation of the solvent during printing. Butyl carbitol, also a medium-to-high boiling point solvent, can form a gradient volatilization system with terpineol, initially assisting terpineol in adjusting the viscosity, and gradually volatilizing in the later stage to promote the leveling of the slurry on the substrate surface. Ethyl acetate, as a low-boiling point solvent, can accelerate the surface drying of the slurry, reduce solvent residue after printing, and promote the wetting and bonding of silver powder and substrate, thereby improving the density of the conductive film layer. Ethyl cellulose, as a thickener and film-forming skeleton, imparts thixotropy to the slurry through the entanglement of molecular chains. The viscosity decreases at high shear rates during printing, making it easier to spread. Hydroxymethyl silicone oil, as a thixotropic agent, enhances the anti-settling property of the slurry through the elastic network structure of silicon-oxygen bonds, and forms a hydrophobic interface during the curing process, thereby improving the weather resistance of the silver layer and its adhesion to the substrate.

[0051] On the other hand, the present application further provides a method for preparing the aforementioned conductive paste, characterized in that it comprises the following steps:

[0052] S1. Pretreatment: Mix the base metal powder, the glass powder and 1-5 wt% of the organic carrier in proportion, centrifuge at a speed of 800-1200 r / min for 2-8 minutes, and grind the mixture using a three-roll grinder at a controlled grinding speed of 50-120 r / min until the fineness of the base metal glass slurry is less than 6 μm.

[0053] The gap between the three rollers of the three-roll mill is controlled to be 5-20 microns. Normally, the mill is ground 4-6 times.

[0054] S2. Premixing: mixing the silver powder, the base metal glass paste prepared in step S1 and the remaining organic vehicle, and centrifuging at a speed of 800-1200 r / min for 2-8 minutes.

[0055] S3, fineness treatment: transfer the slurry premixed in step S2 to a three-roll mill, control the grinding speed to 80-200 r / min, and grind the slurry to a fineness of less than 6 μm.

[0056] The gap between the three rollers of the three-roll mill is controlled to be 5-30 microns. Normally, the mill is ground 4-6 times.

[0057] S4, post-processing: centrifuging the ground slurry obtained in step S3 at a rotation speed of 400-600 r / min for 1-2 min, and filtering to obtain the base metal slurry.

[0058] In post-processing, centrifugation is usually performed using a centrifuge to remove bubbles from the slurry.

[0059] The present application also provides an application of the aforementioned conductive paste or the conductive paste prepared by the aforementioned preparation method in a photovoltaic cell, wherein the photovoltaic cell is a TOPCon cell.

[0060] The present application is further explained below with reference to examples.

[0061] The raw materials used in the examples of this application are all commercially available.

[0062] In this application, the test method for particle size D50 is generally obtained according to conventional testing methods in the field, such as dry method testing using a Malvern laser particle size analyzer or an OMEC laser particle size analyzer.

[0063] The components of the main glass powder in the conductive paste of the following embodiments and comparative examples are 65wt% boron oxide, 8wt% aluminum oxide, 22wt% bismuth oxide and 5wt% silicon dioxide, and the particle size of the main glass powder is D50 = 1.5μm; the components of the auxiliary glass powder are 60wt% lead oxide, 7wt% silicon dioxide, 28wt% boron oxide and 5wt% zinc oxide, and the particle size of the auxiliary glass powder is D50 = 1.1μm; the composition of the organic carrier is 55wt% terpineol, 6wt% ethyl cellulose, 4wt% sodium carboxymethyl cellulose, 16.5wt% butyl carbitol, 18wt% ethyl acetate and 0.5wt% hydroxymethyl silicone oil.

[0064] Example 1

[0065] Example 1 provides a TOPCon positive fine conductive paste, which consists of the following components:

[0066] Silver powder 48.3wt%, copper powder and aluminum powder mixture 40wt%, main glass powder 2.0wt%, auxiliary glass powder 0.7wt% and organic carrier 9.0wt%, wherein the mass ratio of silver powder to copper powder and aluminum powder mixture is 1.21, the purity of copper powder is 99.6%, the particle size is D50=1.9, the purity of aluminum powder is 99.8%, the particle size is D50=1.5, and the particle size of silver powder is D50=1.3μm.

[0067] Also provided is a method for preparing the TOPCon positive fine base metal slurry, comprising the following steps:

[0068] S1. Pretreatment: Accurately weigh base metal powder, glass powder, and 3 wt% of an organic vehicle according to the formula ratio and add them to a slurry tank. Centrifuge the mixture at 1000 rpm for 4 minutes. Transfer the mixture to a three-roll mill, control the gap between the three rolls to be 5-20 μm, and grind at 80 rpm for 4-6 times to obtain a base metal glass slurry, wherein the fineness of the base metal glass slurry is less than 6 μm.

[0069] S2. Mixing: adding the pretreated base metal glass slurry and silver powder to the remaining organic carrier, and centrifuging at 1000 rpm for 2-8 minutes to obtain a preliminary mixed slurry;

[0070] S3, grinding and refinement: transfer the preliminary mixed slurry to a three-roll mill, control the gap between the three rollers to be 5-30 microns, grind at a speed of 150 rpm, grind 4-6 times, make the slurry fineness less than 6 microns, and improve the uniformity and fineness of the slurry;

[0071] S4. Post-processing: The ground slurry is centrifuged at 500 rpm for 1-2 minutes to remove bubbles in the slurry, and then filtered to obtain the final TOPCon positive fine metal slurry.

[0072] Example 2

[0073] The only difference between Example 2 and Example 1 is that the slurry components include 58.5wt% silver powder, 30wt% nickel powder, and 0.5wt% auxiliary glass powder, wherein the mass ratio of silver powder to nickel powder is 1.95, the purity of nickel powder is 99.8%, and the particle size is D50=1.8μm. The rest is the same as Example 1.

[0074] Example 3

[0075] The only difference between Example 3 and Example 1 is that: in the slurry components, silver powder is 84.5wt%, nickel powder and tungsten powder mixture is 5wt%, and organic carrier is 8.5wt%, wherein the mass ratio of silver powder to nickel powder and tungsten powder mixture is 16.9, the purity of nickel powder is 99.8%, and the particle size is D50=6μm, the purity of tungsten powder is 99.6%, and the particle size is D50=4.5μm, and the rest are the same as Example 1.

[0076] Example 4

[0077] The only difference between Example 4 and Example 1 is that: in the slurry components, silver powder is 79.3wt%, nickel powder and tin powder mixture is 10wt%, main glass powder is 1.6wt%, and auxiliary glass powder is 0.6wt%, among which the mass ratio of silver powder to nickel powder and tin powder mixture is 7.93, the purity of nickel powder is 99.8%, and the particle size is D50=5.8μm, the purity of tin powder is 99.8%, and the particle size is D50=3.3μm, and the rest are the same as Example 1.

[0078] Example 5

[0079] The only difference between Example 5 and Example 1 is that: in the slurry components, silver powder is 69.1wt%, copper powder and tin powder mixture is 20wt%, main glass powder is 1.8wt%, and auxiliary glass powder is 0.6wt%, among which the mass ratio of silver powder to copper powder and tin powder is 3.46, the purity of copper powder is 99.9%, and the particle size is D50=5.5μm, the purity of tin powder is 99.8%, and the particle size is D50=3.5μm, and the rest are the same as Example 1.

[0080] Example 6

[0081] The only difference between Example 6 and Example 1 is that the slurry components include 63.9wt% silver powder, 25wt% nickel powder, 1.8wt% main glass powder, and 0.8wt% auxiliary glass powder, wherein the mass ratio of silver powder to nickel powder is 2.6, the purity of nickel powder is 99.6%, and the particle size is D50=5.0μm. The rest is the same as Example 1.

[0082] Comparative Example 1

[0083] The only difference between Comparative Example 1 and Example 1 is that the slurry components contain 88.3 wt % silver powder and no base metal powder. Other components are the same as Example 1.

[0084] Comparative Example 2

[0085] The only difference between Comparative Example 2 and Example 1 is that the slurry components include 28.3wt% silver powder and 60wt% mixed powder of copper powder and aluminum powder, wherein the mass ratio of silver powder to the mixed powder of copper powder and aluminum powder is 0.47, and the rest are the same as Example 1.

[0086] Comparative Example 3

[0087] The only difference between Comparative Example 3 and Example 1 is that: in the slurry components, silver powder is 65wt%, nickel powder is 25wt%, and the mass ratio of silver powder to copper powder and aluminum powder mixture is 2.6. Other components are the same as Example 1.

[0088] Comparative Example 4

[0089] The only difference between Comparative Example 4 and Example 1 is that in the slurry component, the particle size of the copper powder is D50=5 μm, and the particle size of the aluminum powder is D50=3 μm. Other differences are the same as Example 1.

[0090] Comparative Example 5

[0091] The only difference between Comparative Example 5 and Example 3 is that the slurry components contain 89.5 wt % silver powder and no base metal powder. Other contents are the same as those in Example 3.

[0092] Comparative Example 6

[0093] The only difference between Comparative Example 6 and Example 3 is that the slurry components include 59.5wt% silver powder and 30wt% mixed powder of nickel powder and tungsten powder, wherein the mass ratio of silver powder to the mixed powder of nickel powder and tungsten powder is 1.98, and the rest are the same as Example 3.

[0094] Comparative Example 7

[0095] The only difference between Comparative Example 7 and Example 3 is that: in the slurry components, silver powder is 86wt%, nickel powder and tungsten powder mixture is 3.5wt%, and the mass ratio of silver powder to nickel powder and tungsten powder mixture is 24.5. The rest is the same as Example 3.

[0096] Comparative Example 8

[0097] The only difference between Comparative Example 8 and Example 3 is that in the slurry component, the particle size of the nickel powder is D50=1.5 μm, and the particle size of the tungsten powder is D50=1.9 μm. The rest are the same as Example 3.

[0098] Some of the corresponding parameters of the corresponding embodiments and comparative examples can be found in Table 1:

[0099] Table 1

[0100]

[0101] Effect embodiment

[0102] Using screen printing technology, the conductive pastes of Examples 1-6 and the conductive pastes of Comparative Examples 1-8 were respectively printed on the front of the TOPCon cell to make the cell. The cell was dried in a belt drying furnace and then sintered at 700-800°C in a chain sintering furnace. After sintering, light injection was completed at 500-550°C through belt light injection, and then LECO treatment was performed to form a TOPCon solar cell.

[0103] For the prepared batteries, the electrical performance of the batteries was tested using an IV tester, and the contact resistance and line resistance were tested using a TLM contact resistance meter. The grid lines of the cells to be tested were stacked normally several times or scraped with a cell to visually observe the grid line shedding to determine the strength of the adhesion. The electroluminescence (EL) of the cells was tested using a Lixit IV-EL all-in-one tester, which is mainly used to detect internal defects in solar cells and modules. Among them, in the electrical performance test: Eta refers to the conversion efficiency value, Voc refers to the open circuit voltage value, Isc refers to the short circuit current value, FF refers to the fill factor value, Rb refers to the line resistance value, and Rc refers to the contact resistance value. The test results are shown in Table 2 below:

[0104] Table 2

[0105]

[0106]

[0107] Combined from Table 2 above Figure 1 and 2 It can be seen that in Comparative Examples 2-4, compared with Example 1, the particle size D50 of the base metal powder in Comparative Example 2 meets the condition of <2μm. At this time, the mass ratio of silver powder and base metal mixed powder is not within the protection range. The electrical performance of Example 1 is significantly better than that of Comparative Example 2, with an Eta improvement of >14.8%, and obvious advantages in contact resistance and line resistance. In Comparative Example 3, the mass ratio of silver powder and base metal mixed powder is also not within the protection range, and the ratio is too large. At this time, small-particle base metals (<2μm) are easy to form a continuous conductive skeleton through "low-temperature sintering" during the sintering process due to their large specific surface area and high surface energy. The conductivity of silver depends on the synergistic effect with this skeleton. As the proportion of small-particle base metal powder decreases, the advantage of "low-temperature sintering" to form a continuous conductive skeleton is lost. Silver powder will also have certain sintering defects at low temperatures. The difference in shrinkage rate will further aggravate the change in the actual amount of glass flow to the interface, resulting in an increase in contact resistance and a deterioration of electrical performance. Figure 1 It can also be seen from parts (h) and (i) of Comparative Example 2 and Comparative Example 3 that the adhesion of the products is better than that of Example 1 ( Figure 1 (a) in the figure all exhibited some degree of powder shedding. In Comparative Example 4, the amount of silver powder added was within the protection range and appropriate, but the base metal powder's particle size was too large, and the proportion of large-size base metal powder was too high. This resulted in increased clogging of the screen mesh during printing and severe screen breakage, making it unsuitable for use. Therefore, the base metal powder's particle size (D50) should be less than 2 μm, and the corresponding silver powder and base metal powder amounts must meet a certain ratio to achieve good electrical performance and adhesion in the battery.

[0108] Similarly, compared with Example 3, Comparative Examples 6-8, the solution of Comparative Example 6 meets the requirement that the base metal powder particle size D50 is greater than 2μm and less than 10μm. When the same base metal conductive phase is introduced, the electrical performance of Example 3 is significantly better than that of Comparative Example 6, with an Eta improvement of >7.9%, and obvious advantages in contact resistance and line resistance. In Comparative Example 7, when the base metal powder particle size is between 2 and 10μm, the "cooperative conductivity" of the base metal and silver depends on a certain proportion of base metal as a "transmission node". When the amount of silver powder added is too much and the base metal ratio is less than 5%, the conductive network breaks and the contact resistance surges, which leads to a decrease in electrical performance. In addition, the silver powder particle size is smaller than the base metal powder. As the silver powder content increases, due to the difference in shrinkage rate, the amount of glass flowing to the interface in the system increases, resulting in excessive corrosion, which leads to a significant deterioration in electrical performance. In Comparative Example 8, due to the smaller base metal powder particle size, deformation and flow occurred earlier during sintering, affecting the shrinkage of the silver powder and the flow of the glass powder, resulting in lower electrical performance and slight powder shedding. This suggests that when the base metal powder particle size is 2μm ≤ D50 < 10μm, the silver powder addition ratio must be strictly controlled to achieve optimal results.

[0109] In addition, through Figure 2 The EL test images of the battery show that the corresponding Figure 2 There is no black or gray defective area in parts (a)-(f), indicating that the conductive paste has good conductive performance and uniformity. Figure 2 As can be seen from (h)-(j) and (l)-(n) in the figure, there are gray shadows or black areas in the EL image, indicating that the electrical performance of the batteries corresponding to comparative examples 2-4 and 6-8 do not meet the standards and have poor reliability.

[0110] It can be seen from the data of Examples 1-6 that, when base metal powder is introduced, the electrical properties are compared with those of Comparative Examples 1 and 5 in which the silver content is as high as 89.5 wt % by adjusting the particle size and ratio. The photoelectric conversion efficiency is still comparable to that of Comparative Examples 1 and 5 in which the silver powder is the conductive phase. At this time, the technical solution corresponding to the embodiment greatly reduces the manufacturing cost of the silver paste due to the reduction in the amount of silver powder added, but does not affect the electrical properties of the conductive silver paste containing base metals at all, and by Figure 1 Parts (a)-(f) show that the adhesion performance can meet the requirements and there is no powdering phenomenon. Figure 2 Parts (a)-(f) illustrate that the conductive paste of the present application has good conductive properties and printing uniformity and high reliability.

[0111] In summary, the present application forms a good conductive network by controlling the proportions of silver powder and base metal powder corresponding to the small particle size and large particle size ranges of the base metal powder respectively, through the overall synergistic coordination of the formula, which is beneficial to improving the conductivity of the slurry. The conductive slurry is applied to photovoltaic cells, especially TOPCon cells, which greatly reduces the manufacturing cost while ensuring low contact resistance and high photoelectric conversion efficiency, and the electrical performance of the paste in the battery is comparable to or even better than that of pure silver paste.

[0112] 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 conductive paste, characterized in that: The conductive paste includes the following components: 84-90wt% of a conductive phase, 2-6wt% of a glass phase, and 8-10wt% of an organic vehicle, wherein the conductive phase includes silver powder and base metal powder. When the particle size D50 of the base metal powder is less than 2μm, the mass ratio of the silver powder to the base metal powder is (0.5-2.0):1; when the particle size of the base metal powder is 2μm≤D50<10μm, the mass ratio of the silver powder to the base metal powder is (2.5-19):

1.

2. The conductive paste according to claim 1, characterized in that The base metal powder includes one or more of aluminum powder, copper powder, nickel powder, tungsten powder and tin powder.

3. The conductive paste according to claim 2, characterized in that The base metal powder has a D50 particle size range of 0.5-9 μm.

4. The conductive paste according to claim 3, characterized in that The purity of the base metal is ≥99.5%, wherein the purity of the aluminum powder is ≥99.5%, the purity of the copper powder is ≥99.6%, the purity of the nickel powder is ≥99.6%, the purity of the tungsten powder is ≥99.6%, and the purity of the tin powder is ≥99.5%.

5. The conductive paste according to claim 1, characterized in that The glass phase includes 1.5-4wt% main glass powder and 0.5-2wt% auxiliary glass powder. The main glass powder includes the following components by mass percentage: 60-70wt% boron oxide, 5-10wt% aluminum oxide, 10-30wt% bismuth oxide, and 1-20wt% silicon dioxide. The auxiliary glass powder includes the following components by mass percentage: 50-80wt% lead oxide, 5-20wt% silicon dioxide, 10-30wt% boron oxide, and 1-10wt% zinc oxide.

6. The conductive paste according to claim 5, characterized in that The particle size of the main glass powder is in the range of 1-2 μm, and the particle size of the auxiliary glass powder is in the range of 0.8-2 μm.

7. The conductive paste according to claim 1, characterized in that: The organic carrier comprises solvents, film-forming agents and auxiliary agents. In terms of mass percentage, the solvents account for 2-90 wt%, the film-forming agents account for 2-10 wt%, and the auxiliary agents account for 0.1-0.8 wt%.

8. The conductive paste according to claim 7, characterized in that: The solvents include one or more of terpineol, butyl carbitol and ethyl acetate, the film-forming agents include one or more of ethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose and sodium carboxymethyl cellulose, and the auxiliary agents include one or more of hydroxymethyl silicone oil, polydimethylsiloxane and polyether-modified polydimethylsiloxane.

9. The method for preparing the conductive paste according to any one of claims 1 to 8, wherein: The steps include: S1. Pretreatment: Mix the base metal powder, the glass powder, and 1-5 wt% of the organic vehicle in proportion, centrifuge at a speed of 800-1200 rpm for 2-8 min, and grind the mixture using a three-roll mill at a speed of 50-120 rpm until the fineness of the base metal glass paste is less than 6 μm. S2. Premixing: mixing the silver powder, the base metal glass paste prepared in step S1, and the remaining organic vehicle, and centrifuging at a speed of 800-1200 rpm for 2-8 minutes; S3, fineness treatment: transfer the slurry premixed in step S2 to a three-roll mill, control the grinding speed to 80-200 r / min, and grind the slurry to a fineness of less than 6 μm; S4, post-processing: centrifuging the ground slurry obtained in step S3 at a rotation speed of 400-600 r / min for 1-2 min, and filtering to obtain the base metal slurry.

10. Use of the conductive paste according to any one of claims 1 to 8 or the conductive paste prepared by the preparation method according to claim 9 in a photovoltaic cell, wherein the photovoltaic cell is a TOPCon cell.

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