Conductive silver paste for solar cell and preparation method therefor, and solar cell

Abstract

A conductive silver paste for a solar cell and a preparation method therefor, and a solar cell. The conductive silver paste comprises a silver powder, an epoxy resin, a siloxane compound and a solvent, wherein the siloxane compound has a structural formula of R1-R2-[(CH3)2SiO]n-(CH3)2Si-R3-R4, where R 1 and R4 are independently selected from functional groups having reactivity with the epoxy resin, R2 and R3 are independently selected from at least one of alkylene, alkyleneoxy and ether bonds, and n is an integer from 2 to 4. The solar cell comprises a grid electrode formed by curing the conductive silver paste. The conductive silver paste uses a special siloxane compound, which participates in a curing and crosslinking reaction of a resin to become a part of an organic system of the conductive silver paste and also forms a special adhesion unit to achieve a dense contact with a substrate, thereby making a main grid have good welding tension and electrical conductivity after the paste is cured.

Description

Conductive silver paste for solar cell, preparation method thereof, and solar cell

[0001] This application claims priority to Chinese patent application No. 202311135998.1 filed on August 31, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of solar cells, and in particular to a conductive silver paste for solar cells, a preparation method thereof, and a solar cell. Background Art

[0003] Heterojunction solar cells (HJT) are one of the solar cells currently entering mass production due to their higher conversion efficiency and simpler manufacturing process. Conductive silver paste is a key material required for the cell metallization process. This material is used to form the grid electrode on the cell surface. The grid electrode is responsible for conducting photogenerated electrons from the photovoltaic cell and has a significant impact on the solar cell's photoelectric conversion efficiency. The paste is typically printed on the surface of the HJT cell using a step-by-step printing process. The conductive silver paste used for main grid printing is involved in collecting the cell current and subsequent soldering of the photovoltaic module, so it requires both good conductivity and soldering strength.

[0004] Current conductive silver pastes typically incorporate resins and use coupling agents such as silane coupling agents and titanate coupling agents. However, the use of conventional coupling agents often results in low soldering strength and high resistivity after curing the busbar. Some approaches utilize nano-scale silver powder or other alloy powders, but their high surface area increases oil absorption, hindering screen printing. Furthermore, contact between the alloy powder and silver powder increases resistance. Therefore, there is a need for a conductive silver paste for solar cells that achieves excellent conductivity and soldering strength.

[0005] Summary of the Invention

[0006] In order to solve the problems of low welding tensile force and high resistivity of conductive silver paste in conventional solar cells, the present application provides a conductive silver paste for solar cells, a preparation method thereof, and a solar cell. The conductive silver paste adopts a special siloxane compound to participate in the curing and cross-linking reaction of the resin, becoming a part of the organic system of the conductive silver paste. By forming a special adhesion unit, it achieves dense contact with the substrate, so that the main grid has excellent welding tensile force after curing.

[0007] In a first aspect, the present application provides a conductive silver paste for solar cells, comprising silver powder, epoxy resin, a siloxane compound and a solvent, wherein the siloxane compound has a structural formula (I):

[0008] In the structural formula (I), R1 and R4 are independently selected from functional groups that can react with the epoxy resin, R2 and R3 are independently selected from at least one of an alkylene group, an alkyleneoxy group, and an ether bond, and n is an integer from 2 to 4.

[0009] A second aspect of the present application provides a method for preparing a conductive silver paste for a solar cell, comprising the following steps:

[0010] A siloxane compound having structural formula (I), an epoxy resin and a solvent are stirred and mixed to obtain a mixture, and silver powder is added to the mixture, and ground and dispersed to obtain a conductive silver paste.

[0011] In the structural formula (I), R1 and R4 independently include functional groups that can react with the epoxy resin, R2 and R3 independently are at least one selected from an alkylene group, an alkyleneoxy group, and an ether bond, and n is an integer from 2 to 4.

[0012] A third aspect of the present application provides a solar cell comprising a grid line electrode, wherein the grid line electrode is formed by curing the conductive silver paste described in the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG1 is a SEM image of the conductive silver paste prepared according to Example 1 in contact with the textured surface of a cell. DETAILED DESCRIPTION

[0014] The present invention provides a conductive silver paste for solar cells, which includes silver powder, epoxy resin, a siloxane compound and a solvent. The siloxane compound has a structural formula (I):

[0015] In the structural formula (I), R1 and R4 are independently selected from functional groups that can react with the epoxy resin, R2 and R3 are independently selected from at least one of an alkylene group, an alkyleneoxy group, and an ether bond, and n is an integer from 2 to 4.

[0016] The siloxane compound has a linear, straight-chain structure, with silicon and oxygen atoms alternating along the backbone. Multiple siloxane bonds form an adhesion unit, chemically bonding with the substrate to which it is adhered, providing interfacial adhesion. The end-capping groups at both ends of the siloxane compound participate in the epoxy resin's curing and cross-linking reaction, providing more reactive sites, promoting the curing reaction, and forming a tight bond with the epoxy resin. The siloxane compound simultaneously connects the epoxy resin to the substrate through the central adhesion unit and the end-capping groups at both ends, significantly improving the soldering strength of the conductive silver paste.

[0017] In the above formula (I), n is an integer from 2 to 4. When n is within the range of 2-4, the adhesion unit has a more suitable chain length, which can provide better adhesion or cohesion and facilitate subsequent grinding. In a specific embodiment, n can be 3 or 4.

[0018] As end-capping groups, R1 and R4 in the above structural formula (I) can react with the resin, chemically bond with the organic functional groups in the epoxy resin, and promote crosslinking and curing of the resin. In some specific embodiments, R1 and R4 are independently selected from at least one of an amino group, an epoxy group, a phenolic group, and a hydroxyl group. It is understood that R1 and R4 can be the same or different.

[0019] In the above structural formula (I), R2 and R3 are independently selected from at least one of an alkylene group, an alkyleneoxy group and an ether bond. It is understood that R2 and R3 may be the same or different. In some embodiments, R2 and R3 may independently be an alkylene group or an alkyleneoxy group having 1 to 3 carbon atoms. For example, R2 and R3 may independently be -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -O-CH2-, -O-CH2-CH2-, -O-CH2-CH2-CH2-. In some embodiments, R2 and R3 may independently be an ether bond, which may be expressed as -R'-OR"-. In a further embodiment, R' may be selected from an alkylene group having 1 to 3 carbon atoms, and R" may be selected from an alkylene group having 1 to 3 carbon atoms. R' and R" may be the same or different. For example, examples of R2 and R3 include -CH2-O-CH2-, -CH2-CH2-O-CH2-, -CH2-CH2-CH2-O-CH2-, -CH2-O-CH2-CH2-, -CH2-CH2-O-CH2-CH2-, -CH2-O-CH2-CH2-, -CH2-O-CH2-CH2-CH2-.

[0020] In some specific embodiments, the siloxane compound may be:

[0021] CH2(O)CH-CH2-O-(CH2)3-[(CH3)2SiO]3-(CH3)2Si-(CH2)3-O-CH2-CH(O)CH2;

[0022] NH2-(CH2)3-R2-[(CH3)2SiO]4-(CH3)2Si-(CH2)3-NH2;

[0023] C6H5O-(CH2)3-[(CH3)2SiO]3-(CH3)2Si-(CH2)3-C6H5O;

[0024] OH-(CH2)2O(CH2)2-[(CH3)2SiO]4-(CH3)2Si-(CH2)2O(CH2)2-OH.

[0025] In some embodiments of the present application, the weight ratio of the siloxane compound to the epoxy resin is in the range of 1-1.5:2.2. For example, the weight ratio of the siloxane compound to the epoxy resin can be 0.5, 0.55, 0.6, 0.65, or a range consisting of any two of these values. For example, the weight ratio of the siloxane compound to the epoxy resin can be 0.5-0.6 or 0.55-0.65.

[0026] In some embodiments of the present application, the weight fraction of the siloxane compound can be 0.5% to 2.0% based on the total weight of the conductive silver paste. In some specific embodiments, the weight fraction of the siloxane compound can be 1.0% to 1.5%. For example, the weight fraction of the siloxane compound in the conductive silver paste can be 0.5%, 0.6%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.8%, 1.9%, 2.0%, or a range consisting of any two of these values. For example, the weight fraction of the siloxane compound can be 0.9% to 1.2%, 1.4% to 1.8%, or 1% to 1.9%. When the siloxane compound is within an appropriate range, the conductive silver paste can achieve both high soldering strength and low resistivity.

[0027] In some embodiments of the present application, the epoxy resin includes a thermosetting epoxy resin. The thermosetting epoxy resin is cross-linked and cured by heating under the action of a curing agent. The epoxy resin typically contains groups such as epoxy groups, hydroxyl groups, ether bonds, amino groups, and ester groups, which can react with R1 in the above-mentioned siloxane compound. Examples that can be cited include bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, polyester resin, acrylic resin, etc.

[0028] In some embodiments of the present application, the weight fraction of the epoxy resin can be 1.5% to 3.0% based on the total weight of the conductive silver paste. In some specific embodiments, the weight fraction of the epoxy resin can be 2.0% to 2.7%. Exemplarily, the weight fraction of the epoxy resin in the conductive silver paste can be 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0% or a range consisting of any two of these values. For example, the weight fraction of the epoxy resin can be 1.5% to 2.2% or 2.2% to 2.8%. The epoxy resin can be an insulating material, and when the weight fraction of the epoxy resin in the conductive silver paste is within an appropriate range, it will not reduce the conductivity of the grid line.

[0029] In some embodiments of the present application, the silver powder includes one or both of flaky silver powder and spherical silver powder. In a specific embodiment, the particle size D50 of the flaky silver powder is 2 μm to 5 μm. In a specific embodiment, the particle size D50 of the spherical silver powder is 0.2 μm to 1.5 μm. Micron-sized silver powder has a moderate specific surface area, is easy to grind and disperse when mixed with silicone compounds, epoxy resins and solvents, and has low cost. In a specific embodiment, the tap density of the flaky silver powder can be 4.0 to 4.5 g / cm 3 The tap density of spherical silver powder can be 5.5 to 6.5 g / cm 3 .

[0030] In embodiments where the silver powder comprises flake silver powder and spherical silver powder, the weight ratio of the flake silver powder to the spherical silver powder may be 2:8 to 8:2. For example, the weight ratio of the flake silver powder to the spherical silver powder may be 0.25, 0.5, 0.8, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or a range consisting of two of these values. For example, the weight ratio of the flake silver powder to the spherical silver powder may be 2:3 to 3:1, or 0.8 to 1.5.

[0031] In some embodiments of the present application, the weight fraction of silver powder can be 85% to 94% based on the total weight of the conductive silver paste. In some specific embodiments, the weight fraction of silver powder can be 87% to 92%. Exemplarily, the weight fraction of silver powder in the conductive silver paste can be 87.5%, 89%, 90%, 90.5%, 91%, 91.5%, 92%, 93%, 94% or a range consisting of any two of these values. For example, the weight fraction of silver powder can be 89% to 90.5% or 87.5% to 90%. Silver powder is the main component of conductive silver paste. When the weight fraction of silver powder in the conductive silver paste is within an appropriate range, it is beneficial to improve the photoelectric conversion efficiency of solar cells.

[0032] In some specific embodiments, the conductive silver paste includes, by weight, 85% to 94% silver powder, 1.5% to 3.0% epoxy resin, 0.5% to 2.0% siloxane compound, and the balance solvent.

[0033] In a further embodiment of the present application, the conductive silver paste may further include an additive. In a further embodiment, the additive includes any one or more of a reactive diluent, a curing agent, a curing accelerator, a thixotropic agent, a toughening agent, a modifier, and a setting agent. In some specific embodiments of the present application, the conductive silver paste includes a reactive diluent, a curing agent, a curing accelerator, and a thixotropic agent at the same time. These additives can be commercially available products commonly used in the art. The weight fraction of the additive in the conductive silver paste can be 1.9% to 5%. Exemplarily, the weight fraction of the additive can be 1.9%, 2.2%, 2.4%, 3%, 4%, 4.5%, 5%, or a range consisting of any two of these values. For example, the weight fraction of the additive can be 1.9% to 4%.

[0034] In order to improve the process performance of epoxy resin, reduce the viscosity of the curing system and improve the operability, a reactive diluent can be added for adjustment. In some specific embodiments, the weight fraction of the reactive diluent in the conductive silver paste can be 1.3% to 2.0%. For example, the weight fraction of the reactive diluent can be 1.3%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or a range consisting of any two of these values. For example, the weight fraction of the reactive diluent can be 1.5% to 2.0%.

[0035] Reactive diluents known in the art may be used, such as cyclohexane-1,2-dicarboxylic acid diglycidyl ester, 1,4-butanediol diglycidyl ether, phenyl glycidyl ether, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester, 1,2-epoxy-4-vinylcyclohexane, and the like.

[0036] A curing agent and a curing modifier may be added to promote the curing of the epoxy resin. In some specific embodiments, the weight fraction of the curing agent in the conductive silver paste may be 0.2% to 0.6%. For example, the weight fraction of the curing agent may be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or a range consisting of any two of these values. For example, the weight fraction of the curing agent may be 0.3% to 0.5%. Curing agents known in the art may be used, including imidazole curing agents, acid anhydride curing agents, amine curing agents, etc. For example, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, tetrahydrophthalic anhydride, pyromellitic anhydride, maleic anhydride, boron trifluoride monomethylamine, boron trifluoride monoethylamine, boron trifluoride triethanolamine, etc.

[0037] In some specific embodiments, the weight fraction of the curing accelerator in the conductive silver paste can be 0.1% to 0.4%. For example, the weight fraction of the curing accelerator can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, or a range consisting of any two of these values. For example, the weight fraction of the curing accelerator can be 0.2% to 0.3%. Curing agents known in the art can be used, such as benzoyl peroxide, diethylaminopropylamine, 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, 3-(p-chlorophenyl)-1,1-dimethylurea, etc.

[0038] In some specific embodiments, the weight fraction of the thixotropic agent in the conductive silver paste can be 0.3% to 1.0%. Exemplarily, the weight fraction of the thixotropic agent can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range consisting of any two of these values. For example, the weight fraction of the thixotropic agent can be 0.5% to 1.0%. Exemplary thixotropic agents include unsaturated polycarboxylic acid polymer solutions, polycarboxylic acid alkylammonium salt solutions, modified urea solutions, high molecular weight urea-modified non-polar polyamide solutions, and the like.

[0039] In the embodiments of the present application, the conductive silver paste includes a solvent. The solvent is used to dissolve the resin and adjust the viscosity of the slurry. At the same time, it can be volatilized and released smoothly during the curing process of the conductive silver paste. In some specific embodiments, the conductive silver paste includes one or more solvents. A mixed solvent composed of multiple solvents is beneficial to the solubility, boiling point and volatilization rate of the resin, reactive diluent and other additives. In some specific embodiments, the solvent includes any one or more of butyl acetate, diethylene glycol butyl ether acetate, butyl carbitol acetate, propylene glycol methyl ether acetate, diethyl carbonate, diethylene glycol butyl ether, diethylene glycol diethyl ether, propylene glycol ethyl ether and dipropylene glycol butyl ether.

[0040] The conductive silver paste may or may not include low-melting-point glass powder. In order to improve the adhesion between the grid lines and the substrate, the conductive silver paste may further include low-melting-point glass powder.

[0041] Conductive silver paste can be operated in a low temperature environment with a process temperature below 200°C.

[0042] The present invention also provides a method for preparing a conductive silver paste, comprising the following steps:

[0043] A siloxane compound having structural formula (I), an epoxy resin and a solvent are stirred and mixed to obtain a mixture, and silver powder is added to the mixture, and ground and dispersed to obtain a conductive silver paste.

[0044] In the structural formula (I), R1 and R4 independently include functional groups that can react with the epoxy resin, R2 and R3 independently are at least one selected from an alkylene group, an alkyleneoxy group, and an ether bond, and n is an integer from 2 to 4.

[0045] The preparation method has simple steps, strong controllability, high mixing efficiency, and is suitable for large-scale industrial production.

[0046] In some embodiments of the present application, the stirring and mixing step can be performed at a temperature of 20° C. to 30° C. for 30 minutes to 60 minutes.

[0047] In some embodiments of the present application, in order to obtain a conductive silver paste with moderate fineness, a three-roller mill can be used for multi-step grinding and dispersion. In a specific embodiment, the step of grinding and dispersing by a three-roller mill is carried out under the following conditions: the rotation speed is set to 80 rpm to 120 rpm, the rolling temperature is set to 15°C to 25°C, the initial roller gap is set to 10 μm to 80 μm, and the final roller gap is set to 7 μm to 40 μm. Other mixing and dispersion methods known in the art can also be used to make the components in the conductive silver paste reach a uniform mixing state. In some embodiments, before grinding and dispersing, the mixture of silver powder, silicone compound, epoxy resin and solvent can be stirred at a temperature of 3°C to 10°C for 3 to 5 hours.

[0048] In some embodiments, the fineness of the conductive silver paste is 5 μm or less.

[0049] An embodiment of the present application further provides a solar cell, which includes a gate line electrode, and the gate line electrode is formed by curing the above-mentioned conductive silver paste.

[0050] In some embodiments, the volume resistivity of the gate electrode may be 9×10 -6 Ω·cm or less, or 6×10 -6 Ω·cm or less, or 5×10 -6 Ω·cm or less. In some embodiments, the welding tension of the gate electrode can be 1.7-2.3 N / mm, such as 1.9 N / mm, 2.0 N / mm, 2.1 N / mm, 2.2 N / mm or 2.3 N / mm. In some specific embodiments, the volume resistivity of the gate electrode is 5×10 -6 -6×10 -6 Ω·cm, and the welding tension is 1.9-2.2N / mm. The grid line electrode formed by curing the conductive silver paste of the present application has both good conductivity and welding tension, which can meet the performance requirements of the grid line electrode of solar cells.

[0051] The technical solutions of the embodiments of the present application are further described in detail below with multiple embodiments.

[0052] Preparation Example

[0053] (1) The siloxane compound, epoxy resin, auxiliary agent and solvent were stirred and mixed at a temperature of 25° C. and a speed of 100 rpm for 45 minutes to obtain a mixture.

[0054] (2) Add silver powder to the obtained mixture, stir and mix at a temperature of 8°C and a speed of 100 rpm for 3 hours to obtain a preliminarily dispersed slurry, and then pour the slurry onto the initial roller column of a three-roll grinder, set the speed to 100 rpm, and roll at a rolling temperature of 20°C for rolling. The rolling process is as follows: the first step is to mix three times with an initial roller gap of 80 μm and a final roller gap of 40 μm; the second step is to mix three times with an initial roller gap of 40 μm and a final roller gap of 20 μm; the third step is to mix three times with an initial roller gap of 20 μm and a final roller gap of 10 μm; the fourth step is to mix three times with an initial roller gap of 10 μm and a final roller gap of 5 μm, and finally obtain a conductive silver paste.

[0055] Examples 1-10 and Comparative Examples 1-3

[0056] Conductive silver paste was prepared according to the steps described in the preparation example. The components and contents of the conductive silver paste obtained are listed in Table 1 below (data in the table represent weight percentages by wt %).

[0057] Table 1 Components and contents of conductive silver paste

[0058] In Table 1, cyclohexane-1,2-dicarboxylic acid diglycidyl ester, boron trifluoride monoethylamine, 2,4,6-tris(dimethylaminomethyl)phenol and unsaturated polycarboxylic acid polymer solution are used as auxiliary agents, and diethylene glycol butyl ether acetate and diethylene glycol butyl ether are used as solvents.

[0059] Siloxane compound 1 is a diglycidyl ether-terminated polydimethylsiloxane (n=3) having the following structure:

[0060] Siloxane compound 2 is a bis(3-aminopropyl)-terminated polydimethylsiloxane (n=4) having the following structure:

[0061] Siloxane compound 3 is a phenol-terminated polydimethylsiloxane (n=4) having the following structure:

[0062] Siloxane compound 4 is a carbon hydroxyl-terminated polydimethylsiloxane (n=2) having the following structure:

[0063] The siloxane compound 5 is γ-(2,3-epoxypropoxy)propyltrimethoxysilane commonly used in the prior art.

[0064] Effect embodiment

[0065] The conductive silver pastes prepared according to the above Examples 1-10 and Comparative Examples 1-3 were subjected to welding tensile test, volume resistivity test and printability test according to the conventional test methods in the art as described below. The test results are shown in Table 2.

[0066] Soldering tensile test: Conductive silver paste is screen-printed to a fixed pattern, dried at 160°C for 3 minutes, and cured at 200°C for 5 minutes. Using copper-based lead-tin solder tape, soldering is performed at 350°C, and the average tensile strength is tested.

[0067] Volume resistivity test: Use a four-probe ohmmeter to test the resistance of the cured electrode body.

[0068] Printability test:

[0069] (1) Slurry viscosity test: Use a rheometer to test the rheological curve of the slurry after three-roll grinding and dispersion at 25°C;

[0070] (2) Gate line aspect ratio: The slurry is screen-printed on the crystalline silicon cell. After it is completely cured, the gate line aspect ratio is tested using a 3D microscope.

[0071] FIG1 is an SEM image of the conductive silver paste prepared according to Example 1 in contact with the textured surface of the cell, which confirms that the conductive silver paste is effectively attached to the textured surface of the cell.

[0072] Table 2 Conductive silver paste performance test results

[0073] From the performance test results, the examples 1-10 of the present invention achieved a welding tensile force of 1.7-2.3 N / mm, 5×10 -6 -9×10 -6 The siloxane compounds of Examples 1-10, each with a different end-capping structure, each having an epoxy group, an amino group, a phenolic group, or a carbonyl group at each end, produce conductive silver pastes with high adhesion, low volume resistivity, and good printability, as demonstrated by an applicable viscosity range and a high aspect ratio.

[0074] In particular, the content of the siloxane compound in Example 9 is higher than that in Example 1, which achieves better welding tensile strength. In terms of volume resistivity, Examples 1-10 all perform better than Comparative Examples 1-3, especially the volume resistivity of Examples 1-8 and Example 10 can be controlled at a more satisfactory 5×10 -6 -6×10 -6Ω·cm range. Thus, by adjusting the silver powder, epoxy resin, silicone compound, additives, and solvent within appropriate ranges, the conductive silver paste can achieve both high soldering strength and low resistivity. While improving electrode soldering strength, the conductive silver paste also exhibits good volume resistivity and printability, making it suitable for preparing the main grid electrode of heterojunction batteries.

[0075] Comparing the data in Table 2, we can see that in Comparative Example 1, the absence of the siloxane compound resulted in a slightly higher volume resistivity, a lower electrode welding tensile strength after curing, a lower viscosity, and a low aspect ratio for the screen-printed grid lines. In Comparative Example 2, the absence of the siloxane compound and the increased epoxy resin ratio resulted in a significantly higher volume resistivity and poorer conductivity for the main grid electrode after curing. Furthermore, the increased slurry viscosity reduced the smoothness of the conductive silver paste coating and printing.

[0076] Comparative Example 3 uses a general siloxane coupling agent instead of the siloxane compound in Example 1. The main grid electrode welding tensile strength after curing is still significantly lower than that of Example 1. The volume resistivity and printability comprehensive indicators are also inferior to those of Example 1.

[0077] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A conductive silver paste for solar cells, characterized in that: The conductive silver paste comprises silver powder, epoxy resin, siloxane compound and solvent, wherein the siloxane compound has a structural formula (I), In the structural formula (I), R1 and R4 are independently selected from functional groups that can react with the epoxy resin, R2 and R3 are independently selected from at least one of an alkylene group, an alkyleneoxy group and an ether bond, and n is an integer of 2 to 4.

2. The conductive silver paste for solar cells according to claim 1, characterized in that: The R1 and R4 are independently selected from any one of an amino group, an epoxy group, a phenol group and a hydroxyl group.

3. The conductive silver paste for solar cells according to any one of claims 1 to 2, characterized in that: The carbon number of the alkylene group is 1 to 3, and the carbon number of the alkyleneoxy group is 1 to 3; the ether bond is -R'-OR"-, wherein R' and R" are independently selected from alkylene groups having 1 to 3 carbon atoms.

4. The conductive silver paste for solar cells according to any one of claims 1 to 3, characterized in that: R1 and R4 are epoxy groups, and R2 and R3 are -CH2-O-(CH2)2-.

5. The conductive silver paste for solar cells according to any one of claims 1 to 4, characterized in that: Based on the total weight of the conductive silver paste, the weight fraction of the silver powder is 85% to 94%, the weight fraction of the epoxy resin is 1.5% to 3.0%, and the weight fraction of the siloxane compound is 0.5% to 2.0%.

6. The conductive silver paste for solar cells according to any one of claims 1 to 5, characterized in that: The weight ratio of the siloxane compound to the epoxy resin is in the range of 1-1.5:2.

2.

7. The conductive silver paste for solar cells according to any one of claims 1 to 6, characterized in that: The conductive silver paste satisfies at least one of the following conditions: (a) Epoxy resins include thermosetting epoxy resins; (b) the silver powder comprises one or both of flaky silver powder and spherical silver powder, wherein the particle size D50 of the flaky silver powder is 2 μm to 5 μm, and the particle size D50 of the spherical silver powder is 0.2 μm to 1.5 μm; and (c) The conductive silver paste further comprises an auxiliary agent, and the auxiliary agent comprises any one or more of a reactive diluent, a curing agent, a curing accelerator, a thixotropic agent, a toughening agent, a modifier and a setting agent.

8. A method for preparing a conductive silver paste for solar cells, characterized in that: The following steps are involved: A siloxane compound having a structural formula (I), an epoxy resin and a solvent are stirred and mixed to obtain a mixture, and silver powder is added to the mixture, and ground and dispersed to obtain a conductive silver paste. In the structural formula (I), R1 and R4 independently include functional groups that can react with the epoxy resin, R2 and R3 independently are selected from at least one of an alkylene group, an alkyleneoxy group and an ether bond, and n is an integer of 2 to 4.

9. The preparation method according to claim 8, characterized in that: The preparation method satisfies at least one of the following conditions: (a) the stirring and mixing step is performed at a temperature of 20° C. to 30° C. for 30 to 60 minutes; (b) the grinding and dispersing step is carried out using a three-roll mill under the following conditions: the rotation speed is set to 80 rpm to 120 rpm, the rolling temperature is set to 15° C. to 25° C., the initial roll gap is set to 10 μm to 80 μm, and the final roll gap is set to 7 μm to 40 μm; (c) stirring the silver powder and the mixture at a temperature of 3° C. to 10° C. for 3 to 5 hours before grinding and dispersing; and (d) The fineness of the conductive silver paste is less than 5 μm.

10. A solar cell, characterized in that: The invention comprises a gate line electrode, wherein the gate line electrode is formed by curing the conductive silver paste according to any one of claims 1 to 7.

11. The solar cell according to claim 10, characterized in that The volume resistivity of the gate electrode is 9×10 -6 Ω·cm or less.

12. The solar cell according to any one of claims 10 to 11, characterized in that: The welding tension of the gate line electrode is 1.7-2.3 N / mm.

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