Conductive paste for bc battery, method of making, and photovoltaic module

Abstract

This invention relates to a conductive paste, preparation method, and photovoltaic module for BC batteries, belonging to the field of photovoltaic cell technology. It includes: a first conductive phase; a second conductive phase; and an organic carrier. The first conductive phase is flake-shaped tin-coated copper powder with an aspect ratio of 5:1 to 15:1. The second conductive phase is flake-shaped tin-based alloy powder with an aspect ratio of 3:1 to 15:1. The organic carrier is used to adjust the rheological properties of the paste and to achieve printing molding. The melting point of the flake-shaped tin-based alloy powder is lower than that of the flake-shaped tin-coated copper powder. Using flake-shaped tin-coated copper powder as the first conductive phase and flake-shaped tin-based alloy powder as the second conductive phase, the two together constitute a double-flake conductive system. The first conductive phase forms a conductive framework, and the second conductive phase fills the gaps between the first conductive phases, thereby increasing the packing density of conductive particles, reducing the porosity after sintering, and further improving the conductivity of the sintered body.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic cell technology, and in particular relates to conductive paste, preparation method and photovoltaic module for BC cells. Background Technology

[0002] In BC solar cells, conductive paste is used to form the back conductive electrode, and its conductivity, sintering performance, and long-term reliability have a significant impact on the cell performance.

[0003] Currently, the conductive paste used in BC solar cells is mainly silver-containing conductive paste. Replacing some or all of the silver powder with lower-cost metal materials has become an important development direction for conductive pastes.

[0004] The conductive structure formed by existing low-precious metal conductive pastes after sintering still has room for improvement in terms of the connection effect between conductive particles and the density of the conductive network. Meanwhile, some copper-based metal powders are prone to surface oxidation during preparation, storage, and use, which affects the long-term stability of the conductive structure formed by the conductive paste.

[0005] Therefore, the question is how to provide a conductive paste, preparation method, and photovoltaic module for BC cells. Summary of the Invention

[0006] The purpose of this invention is to provide a conductive paste for BC batteries, a preparation method thereof, and a photovoltaic module, thereby improving the electrical performance of the low-precious-metal conductive paste after sintering.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0008] A conductive paste for BC batteries, comprising:

[0009] First conductive phase;

[0010] Second conductive phase;

[0011] Organic carrier;

[0012] in,

[0013] The first conductive phase is a sheet-like tin-coated copper powder, and the aspect ratio of the sheet-like tin-coated copper powder is 5:1 to 15:1.

[0014] The second conductive phase is a sheet-like tin-based alloy powder, wherein the aspect ratio of the sheet-like tin-based alloy powder is 3:1 to 15:1;

[0015] The organic carrier is used to adjust the rheological properties of the slurry and to achieve printing.

[0016] The melting point of the sheet-like tin-based alloy powder is lower than that of the sheet-like tin-coated copper powder.

[0017] On the other hand, a method for preparing a conductive paste for BC batteries is proposed, including the following steps: preparing an organic carrier;

[0018] Flake-shaped tin-coated copper powder and flake-shaped tin-based alloy powder are added to the organic carrier and mixed to obtain a composite conductive paste.

[0019] On the other hand, a BC solar cell is proposed, including a semiconductor substrate and an electrode formed on the back side of the semiconductor substrate, the electrode being formed by sintering a conductive paste for BC cells.

[0020] On the other hand, a BC photovoltaic module is proposed, comprising at least one of the aforementioned BC solar cells.

[0021] Beneficial effects:

[0022] (1) This disclosure uses sheet-like tin-coated copper powder as the first conductive phase and sheet-like tin-based alloy powder as the second conductive phase. The two together constitute a double sheet-like conductive system, wherein the first conductive phase forms a conductive skeleton and the second conductive phase fills the gaps between the first conductive phases, thereby increasing the packing density of conductive particles, reducing the porosity after sintering, and further improving the conductivity of the sintered body.

[0023] (2) The first conductive phase of this disclosure adopts a tin-coated copper core-shell structure, with the tin layer covering the surface of the copper core. While ensuring the conductivity of the copper material and reducing the material cost, it can reduce the contact between copper powder and the external environment, reduce the risk of copper powder oxidation and copper ion migration, thereby improving the long-term stability and reliability of the conductive paste.

[0024] (3) The second conductive phase of this disclosure is a tin-based alloy powder that can preferentially soften or melt at the sintering temperature. During the sintering process, it can form a connecting phase, improve the metallurgical bonding between adjacent conductive particles, improve the continuity of the conductive network, thereby reducing the resistance of the conductive path and improving the conductivity.

[0025] (4) By setting the first conductive phase as a sheet-like tin-coated copper powder with a larger particle size and the second conductive phase as a sheet-like tin-based alloy powder with a smaller particle size, the second conductive phase can fill the gaps formed by the first conductive phase to form a multi-scale gradation stacking structure, which is beneficial to further improve the compactness of the sintered structure and improve the mechanical strength and welding reliability of the grid line after sintering.

[0026] (5) This invention discloses that by combining sheet-like tin-coated copper powder, sheet-like tin-based alloy powder and organic carrier, the amount of silver powder used can be reduced or even silver-free, while taking into account conductivity, sintering performance and long-term reliability, and is suitable for the preparation of conductive electrodes for back contact solar cells.

[0027] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The electrical performance parameters of the batteries in the embodiments and comparative examples of this application;

[0030] Figure 2 The gate line resistivity of the embodiments and comparative examples in this application;

[0031] Figure 3 The porosity of the grid lines in the embodiments and comparative examples of this application;

[0032] Figure 4 The welding tensile force of the embodiments and comparative examples in this application. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To address the technical challenges of high cost, easy oxidation of copper powder, insufficient density of the conductive network after sintering, and easy agglomeration of low-melting-point alloys in existing back-contact solar cells, this application proposes a conductive paste for BC cells and its preparation method, and further provides BC solar cells and BC photovoltaic modules prepared using this composite conductive paste. This application constructs a double-sheet composite conductive system composed of sheet-like tin-coated copper powder and sheet-like tin-based alloy powder, thereby reducing the cost of the conductive paste while improving the conductivity, density, and long-term reliability after sintering.

[0035] On the one hand, a conductive paste for BC batteries is provided.

[0036] The composite conductive paste includes: a first conductive phase 100, a second conductive phase 200, and an organic carrier 300.

[0037] in:

[0038] The first conductive phase 100 is a sheet-like tin-coated copper powder;

[0039] The second conductive phase 200 is a sheet-like tin-based alloy powder;

[0040] Organic carrier 300 is used to adjust the rheological properties of the paste and to achieve printing.

[0041] The melting point of sheet-like tin-based alloy powder is lower than that of sheet-like tin-clad copper powder;

[0042] The specific mass percentages of each component in the composite conductive paste are as follows:

[0043] Flake-shaped tin-coated copper powder, with a mass percentage of 55% to 75%, preferably 60% to 70%.

[0044] Flake tin alloy powder, with a mass ratio of 15% to 35%, preferably 20% to 30%.

[0045] Organic carriers, with a mass percentage of 10% to 30%, and a preferred range of 12% to 20%.

[0046] The sheet-like tin-coated copper powder has a core-shell structure, with a core of metallic copper and a shell of metallic tin or a tin-based alloy, and the whole has a sheet-like morphology.

[0047] The copper core has a copper purity of ≥99.5wt% and an average particle size D50 of 2μm to 10μm, preferably 3μm to 5μm. The copper core can be spherical or near-spherical, and is subsequently shaped into a substrate sheet by mechanical ball milling or air jet milling.

[0048] The tin shell layer has a thickness of 0.2μm to 1.5μm, preferably 0.4μm to 0.8μm. The shell layer is continuous, dense, and free of penetrating pores, with a coverage rate of ≥95%.

[0049] The powder has an overall morphology of flakes, and the aspect ratio is defined as the ratio of the maximum linear size of the flake particles to the minimum thickness, ranging from 5:1 to 15:1, preferably from 5:1 to 10:1.

[0050] The preparation method involves depositing a tin layer on the surface of copper powder using chemical displacement tin plating, electroless tin plating, or electroplating. The powder is then flattened using a planetary ball mill or air jet mill, transforming the spherical core-shell particles into flake-like particles. During the ball milling process, process control agents such as stearic acid can be added to prevent cold soldering.

[0051] In some embodiments, the flake tin alloy powder is a low-melting-point tin-based alloy with a solidus temperature <180°C and a liquidus temperature <220°C, preferably with a melting point range of 130°C to 180°C.

[0052] Applicable alloy systems include, but are not limited to:

[0053] Tin-bismuth (Sn-Bi) alloy, preferably with a eutectic composition of Sn42Bi58 (melting point 138℃);

[0054] Tin-indium (Sn-In) alloy, preferably Sn48In52 (melting point about 118°C);

[0055] Tin-bismuth-silver (Sn-Bi-Ag) ternary alloys, such as Sn42Bi57Ag1 (melting point approximately 140℃);

[0056] Tin-bismuth-copper (Sn-Bi-Cu), etc.

[0057] The average particle size D50 of the flake tin alloy powder is 1μm to 5μm, preferably 1.5μm to 3.5μm; the aspect ratio is 3:1 to 15:1, preferably 6:1 to 10:1.

[0058] Key design: The particle size of the flake tin alloy is significantly smaller than that of the flake tin-coated copper powder, and the aspect ratio is comparable to or higher. This allows it to be uniformly distributed as a "filler phase" in the gaps between the large-sized flake tin-coated copper particles, achieving multi-scale gradation filling.

[0059] Organic carrier:

[0060] Organic carriers are used to disperse metal powders and impart suitable rheological properties to the slurry. Based on the mass percentage of the organic carrier, its formulation mainly includes: organic solvents, thixotropic agents, surfactants, organic acids, corrosion inhibitors, and modified rosin.

[0061] The organic solvent is any one or a combination of at least two of isopropanol, ethylene glycol, methyl silicate, propylene glycol, and terpineol, accounting for 30% to 60% of the organic carrier by weight;

[0062] The thixotropic agent is any one or a combination of at least two of hydrogenated castor oil, polyamide wax, and silica, accounting for 0.5% to 3.5% of the organic carrier by weight;

[0063] The surfactant is one or a combination of at least two of the following: fatty acid esters, polyoxyethylene fatty acid esters, octylphenol polyoxyethylene ether, and hexadecylamine, accounting for 1.5% to 3.5% of the organic carrier by weight;

[0064] The organic acid is one or a combination of at least two of succinic acid, glutaric acid, sebacic acid, and salicylic acid, accounting for 1.5% to 2.5% of the organic carrier by weight;

[0065] The corrosion inhibitor is one or a combination of at least two of benzotriazole, hydroquinone, and methylbenzotriazole, accounting for 0.5% to 2.0% of the organic carrier by weight;

[0066] The modified rosin is one or a combination of at least two of hydrogenated rosin and polymerized rosin, accounting for 34% to 55% of the weight of the organic carrier.

[0067] Preferably, in the embodiments of this application, the flake-shaped tin-coated copper powder accounts for 65% to 75% of the alloy powder mass, the flake-shaped tin-based alloy powder accounts for 25% to 35%, the average particle size of the flake-shaped tin-coated copper powder is 5μm to 7μm, the average particle size of the flake-shaped tin-based alloy powder is 3μm to 5μm, and the sintering temperature is 135℃ to 150℃, which can obtain better electrical conductivity and sintering density.

[0068] On the other hand, this embodiment provides a method for preparing a conductive paste for BC batteries, including the following steps.

[0069] This invention provides a composite conductive paste for back-contact (BC) solar cells, which mainly consists of sheet-like tin-coated copper powder, sheet-like tin-based alloy powder, and an organic carrier. The sheet-like tin-coated copper powder serves as the conductive framework phase, while the sheet-like tin-based alloy powder serves as the filler and connecting phase; together, they construct the conductive network after sintering.

[0070] The sheet-like tin-coated copper powder has a core-shell structure, with copper as the core and tin or tin-based alloy as the outer shell. The melting point of the sheet-like tin-based alloy powder is lower than that of the sheet-like tin-coated copper powder, and it softens or melts preferentially during sintering, thereby promoting interparticle bonding.

[0071] Example 1

[0072] This embodiment provides a composite conductive paste, which is composed of the following components by mass percentage:

[0073] 88% alloy powder and 12% organic carrier;

[0074] The sheet-like tin-coated copper powder accounts for 70% of the total alloy powder by mass, with a tin shell thickness of 0.6 μm, D50 = 6.2 μm, and a diameter-to-thickness ratio of 8:1; the sheet-like tin-bismuth-silver alloy contains 42% Sn, 57% Bi, and 1% Ag, accounting for 30% of the total alloy powder by mass, with a D50 = 4.6 μm and a particle diameter-to-thickness ratio of 5:1.

[0075] The organic carrier is composed of the following components by mass percentage:

[0076]

[0077] Organic solvent, polymerized rosin, and organic acid were placed in a thermostatic magnetic stirrer oil bath and heated for 30–40 minutes at a temperature of 100–130°C. The stirrer was set at 70 rpm and stirred for 10 minutes to ensure uniform mixing. Then, corrosion inhibitor, thixotropic agent, and surfactant were added sequentially and stirred at 50°C for 30 minutes to ensure uniform mixing. Finally, the mixture was ground using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, and ground 5 times to obtain the organic carrier.

[0078] Flake-shaped tin-coated copper alloy powder and flake-shaped tin-bismuth-silver alloy powder were sequentially added to the ground carrier and then stirred in a double planetary stirrer. The stirring was carried out for 10-15 minutes under standard atmospheric pressure and then for 10-15 minutes under vacuum. The stirrer speed was 200 rpm. The composite conductive paste was then prepared. The paste was printed on the back silver of the solar cell using screen printing technology. The back silver grid line width was 10 μm and the height was 6 μm. The composite conductive paste grid line width was 200 μm and the height was 30 μm. The paste was then sintered and cured in a sintering furnace at a temperature of 139℃ for 100-120 seconds.

[0079] Electrical properties such as Figures 1-2 As shown, the grid line resistivity is 41.59 μΩ·cm; Figure 3 As shown, the grid porosity is 7.56%; Figure 4 As shown, the welding tensile force is 3.154 N / mm;

[0080] Example 2

[0081] This embodiment provides a composite conductive paste, which is composed of the following components by mass percentage:

[0082] 85% alloy powder and 15% organic carrier;

[0083] The sheet-like tin-coated copper powder accounts for 70% of the total alloy powder by mass, with a tin shell thickness of 0.6 μm, D50 = 6.2 μm, and a diameter-to-thickness ratio of 8:1; the sheet-like tin-bismuth-silver alloy contains 42% Sn, 57% Bi, and 1% Ag, accounting for 30% of the total alloy powder by mass, with a D50 = 4.6 μm and a particle diameter-to-thickness ratio of 5:1.

[0084] The organic carrier is composed of the following components by mass percentage:

[0085]

[0086] Organic solvent, polymerized rosin, and organic acid were placed in a thermostatic magnetic stirrer oil bath and heated for 30–40 minutes at a temperature of 100–130°C. The stirrer was set at 70 rpm and stirred for 10 minutes to ensure uniform mixing. Then, corrosion inhibitor, thixotropic agent, and surfactant were added sequentially and stirred at 50°C for 30 minutes to ensure uniform mixing. Finally, the mixture was ground using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, and ground 5 times to obtain the organic carrier.

[0087] Flake-shaped tin-coated copper alloy powder and flake-shaped tin-bismuth-silver alloy powder were sequentially added to the ground carrier, and then stirred in a double planetary stirrer. Stirring was carried out first under standard atmospheric pressure for 10–15 minutes, then under vacuum for 10–15 minutes at a stirrer speed of 200 rpm, thus preparing a composite conductive paste. This paste was then screen-printed onto the back silver layer of the solar cell. The back silver grid line width was 10 μm and the height was 6 μm; the composite conductive paste grid line width was 200 μm and the height was 30 μm. The mixture was then sintered and cured in a sintering furnace at 139 °C for 100–120 seconds. Electrical properties are as follows: Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 39.03 μΩ·cm; Figure 3 As shown, the grid porosity is 6.54%; Figure 4 As shown, the welding tensile force is 3.27 N / mm;

[0088] Example 3

[0089] This embodiment provides a composite conductive paste, which is composed of the following components by mass percentage:

[0090] 83% alloy powder and 17% organic carrier;

[0091] The sheet-like tin-coated copper powder accounts for 70% of the total alloy powder by mass, with a tin shell thickness of 0.6 μm, D50 = 6.2 μm, and a diameter-to-thickness ratio of 8:1; the sheet-like tin-bismuth-silver alloy contains 42% Sn, 57% Bi, and 1% Ag, accounting for 30% of the total alloy powder by mass, with a D50 = 4.6 μm and a particle diameter-to-thickness ratio of 5:1.

[0092] The organic carrier is composed of the following components by mass percentage:

[0093]

[0094] Organic solvent, polymerized rosin, and organic acid were placed in a thermostatic magnetic stirrer oil bath and heated for 30–40 minutes at a temperature of 100–130°C. The stirrer was set at 70 rpm and stirred for 10 minutes to ensure uniform mixing. Then, corrosion inhibitor, thixotropic agent, and surfactant were added sequentially and stirred at 50°C for 30 minutes to ensure uniform mixing. Finally, the mixture was ground using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, and ground 5 times to obtain the organic carrier.

[0095] Flake-shaped tin-coated copper alloy powder and flake-shaped tin-bismuth-silver alloy powder were sequentially added to the ground carrier, and then stirred in a double planetary stirrer. Stirring was carried out first under standard atmospheric pressure for 10–15 minutes, then under vacuum for 10–15 minutes at a stirrer speed of 200 rpm, thus preparing a composite conductive paste. This paste was then screen-printed onto the back silver layer of the solar cell. The back silver grid line width was 10 μm and the height was 6 μm; the composite conductive paste grid line width was 200 μm and the height was 30 μm. The mixture was then sintered and cured in a sintering furnace at 139 °C for 100–120 seconds. Electrical properties are as follows: Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 37.42 μΩ·cm; Figure 3 As shown, the grid porosity is 5.81%; Figure 4 As shown, the welding tensile force is 3.19 N / mm;

[0096] Comparative Example 1

[0097] This embodiment provides a composite conductive paste, which is composed of the following components by mass percentage:

[0098] 85% alloy powder and 15% organic carrier;

[0099] The spherical tin-coated copper powder accounts for 70% of the total alloy powder by mass, the thickness of the tin shell layer is 0.6 μm, and D50=6.2 μm; the contents of each element in the spherical tin-bismuth-silver alloy are: 42% Sn, 57% Bi, and 1% Ag, accounting for 30% of the total alloy powder by mass, and D50=4.6 μm.

[0100] The organic carrier is composed of the following components by mass percentage:

[0101]

[0102] Organic solvent, polymerized rosin, and organic acid were placed in a thermostatic magnetic stirrer oil bath and heated for 30–40 minutes at a temperature of 100–130°C. The stirrer was set at 70 rpm and stirred for 10 minutes to ensure uniform mixing. Then, corrosion inhibitor, thixotropic agent, and surfactant were added sequentially and stirred at 50°C for 30 minutes to ensure uniform mixing. Finally, the mixture was ground using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, and ground 5 times to obtain the organic carrier.

[0103] Spherical tin-coated copper alloy powder and spherical tin-bismuth-silver alloy powder were sequentially added to the ground carrier, and then stirred in a double planetary stirrer. The mixture was first stirred for 10–15 minutes under standard atmospheric pressure, and then stirred for 10–15 minutes under vacuum at a speed of 200 rpm. This produced a composite conductive paste. The paste was then screen-printed onto the back silver layer of the solar cell. The back silver grid line width was 10 μm and the height was 6 μm; the composite conductive paste grid line width was 200 μm and the height was 30 μm. The cells were then sintered and cured in a sintering furnace at 139 °C for 100–120 seconds. Electrical properties are as follows: Figure 1 As shown; Figure 2 As shown, the grid resistivity is 50.89 μΩ·cm; Figure 3 As shown, the grid porosity is 11.02%; Figure 4 As shown, the welding tensile force is 3.01 N / mm;

[0104] Comparative Example 2

[0105] This comparative example is basically the same as Example 1, except that:

[0106] The flake-shaped tin-bismuth-silver alloy powder was replaced with spherical tin-bismuth-silver alloy powder.

[0107] Electrical properties such as Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 46.29 μΩ·cm; Figure 3 As shown, the grid porosity is 7.64%; Figure 4 As shown, the welding tensile force was 3.10 N / mm; its resistivity and porosity were both higher than those of Example 1. It can be concluded that the gap-filling ability of spherical low-melting-point alloy powder is relatively weak, which is not conducive to the construction of a dense conductive network.

[0108] Comparative Example 3

[0109] This comparative example is basically the same as Example 1, except that:

[0110] The flake-shaped copper-plated powder was replaced with spherical copper-plated powder.

[0111] Electrical properties such as Figure 1As shown; Figure 2 As shown, the grid line resistivity is 47.48 μΩ·cm; Figure 3 As shown, the grid porosity is 8.24%; Figure 4 As shown, the welding pull force was 3.03 N / mm; the test results indicate that its conductivity is lower than that of Example 1. It can be seen that the sheet-like tin-coated copper particles can form a more continuous conductive framework structure, while the spherical particles mainly form discrete contact points, which is not conducive to electron transport.

[0112] Comparative Example 4

[0113] This comparative example is basically the same as Example 1, except that:

[0114] The particle size D50 of the flake-shaped tin-coated copper powder is 6μm;

[0115] The particle size D50 of the flake tin-bismuth-silver alloy powder is 5.5 μm.

[0116] Both powders have a plate-like structure.

[0117] Electrical properties such as Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 46.91 μΩ·cm; Figure 3 As shown, the grid porosity is 8.04%; Figure 4 As shown, the welding tensile force was 3.08 N / mm; the test results indicate that its porosity is higher than that of Example 1. It can be seen that when the particle sizes of the two powders are similar, the filling effect of small particles on the gaps between large particles is weakened, making it difficult to form an effective graded packing structure.

[0118] Comparative Example 5

[0119] This comparative example is basically the same as Example 1, except that:

[0120] Flake copper powder is used instead of flake tin-coated copper powder.

[0121] Aging tests were conducted. Electrical performance was assessed. Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 45.84 μΩ·cm; Figure 3 As shown, the grid porosity is 7.48%; Figure 4 As shown, the welding pull force was 3.05 N / mm; the test results show that the resistivity increase of Comparative Example 5 is significantly higher than that of Example 1. It can be concluded that the tin coating can effectively block oxygen from contacting the copper substrate and reduce the risk of copper ion migration, thereby improving the long-term stability of the conductive paste.

[0122] Comparative Example 6

[0123] This comparative example is basically the same as Example 1, except that:

[0124] The aspect ratio of the flake-shaped tin-coated copper powder is 16:1; the aspect ratio of the flake-shaped tin-bismuth-silver alloy is 10:1.

[0125] Electrical properties such as Figure 1 As shown; Figure 2 As shown, the grid line resistivity is 46.49 μΩ·cm; Figure 3 As shown, the grid porosity is 7.56%; Figure 4 As shown, the welding pull force was 3.10 N / mm; the test results showed that the welding pull force for conductivity was lower than that in Example 1, indicating that controlling the aspect ratio of the sheet particles within the range defined by this invention is more conducive to forming a dense conductive network.

[0126] Based on the test data of the above comparative examples, the applicant believes that the present invention, by constructing a dual-plate gradation system of "large-size sheet-like tin-clad copper skeleton particles + small-size sheet-like tin-based alloy filler particles", forms a multi-scale dense stacked structure during sintering.

[0127] Large-sized sheet-like tin-coated copper particles form a conductive framework, while small-sized sheet-like tin-based alloy particles fill the gaps in the framework and form a liquid phase connection during sintering, thereby increasing the contact area between particles and the continuity of the conductive network.

[0128] The tin-clad copper core-shell structure can improve the oxidation resistance of copper-based powder and reduce the degradation of conductivity during long-term use.

[0129] Therefore, the present invention can simultaneously achieve low cost, high conductivity, and good long-term reliability.

[0130] On the other hand, this application provides a BC solar cell, which includes a semiconductor substrate and an electrode formed on the back side of the semiconductor substrate, the electrode being formed by sintering the aforementioned composite conductive paste.

[0131] On the other hand, this application provides a BC photovoltaic module, which includes at least one of the above-mentioned BC solar cells.

[0132] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0133] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A conductive paste for BC battery, characterized by, include: First conductive phase; Second conductive phase; Organic carrier; in, The first conductive phase is a sheet-like tin-coated copper powder, and the aspect ratio of the sheet-like tin-coated copper powder is 5:1 to 15:1; The second conductive phase is a sheet-like tin-based alloy powder, wherein the aspect ratio of the sheet-like tin-based alloy powder is 3:1 to 15:1; The organic carrier is used to adjust the rheological properties of the slurry and to achieve printing. The melting point of the sheet-like tin-based alloy powder is lower than that of the sheet-like tin-coated copper powder.

2. The conductive paste for BC batteries according to claim 1, characterized in that, The mass percentage of the flaky tin-coated copper powder is 55% to 75%. The mass percentage of the flaky tin-based alloy powder is 15% to 35%. The organic carrier comprises 10% to 30% by mass.

3. The conductive paste for BC batteries according to claim 1, characterized in that, The sheet-like tin-coated copper powder has a core-shell structure, with a core of metallic copper and a shell of metallic tin or a tin-based alloy, and the whole has a sheet-like morphology.

4. The conductive paste for BC batteries according to claim 3, characterized in that, The copper core has a copper purity of ≥99.5wt% and an average particle size D50 of 2μm to 10μm; The shell thickness is 0.2 μm to 1.5 μm; The shell is continuous, dense, and without penetrating pores, with a coverage rate of ≥95%.

5. The conductive paste for BC batteries according to claim 1, characterized in that, The solidus temperature of the lamellar tin-based alloy powder is less than 180°C, and the liquidus temperature is less than 220°C.

6. The conductive paste for BC batteries according to claim 5, characterized in that, The sheet-like tin-based alloy powder is any one of tin-bismuth alloy, tin-indium alloy, tin-bismuth-silver ternary alloy, or tin-bismuth-copper alloy.

7. The conductive paste for BC batteries according to claim 1, characterized in that, The average particle size D50 of the flake-shaped tin-based alloy powder is 1 μm to 5 μm. The average particle size of the flake-shaped tin-based alloy powder is smaller than the average particle size of the flake-shaped tin-coated copper powder.

8. The method for preparing the conductive paste for the BC battery according to claim 1, characterized in that, The process includes the following steps: preparing an organic carrier; Flake-shaped tin-coated copper powder and flake-shaped tin-based alloy powder are added to the organic carrier and mixed to obtain a composite conductive paste.

9. A BC solar cell, characterized in that, It includes a semiconductor substrate and an electrode formed on the back side of the semiconductor substrate, the electrode being formed by sintering the conductive paste for BC batteries as described in claim 1.

10. A BC photovoltaic module, characterized in that, It includes at least one BC solar cell as described in claim 9.

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