CN117854799A - Low-temperature conductive silver paste and preparation method thereof - Google Patents

Abstract

In order to overcome the problem that the rheological property and the conductivity of the low-temperature conductive silver paste are reduced at high solid content, the invention provides the low-temperature conductive silver paste and a preparation method thereof.

Description

Low-temperature conductive silver paste and preparation method thereof

Technical Field

The invention belongs to the technical field of conductive silver paste, and particularly relates to low-temperature conductive silver paste and a preparation method thereof.

Background

The crystalline silicon solar cell is a device for converting light energy into electric energy, and the basic structure is PN junction and electrode. Compared with the main flow PERC battery, the HJT battery is concerned by industry due to the advantages of no light attenuation, simple process flow, low temperature coefficient, high open circuit voltage and the like. The basic principle of HJT battery is that heterojunction is formed on N-type silicon wafer substrate by adopting amorphous silicon deposition mode and is used as passivation layer, and the structure is required to limit the process temperature in low-temperature environment within 200 ℃, so that the traditional high-temperature sintering (700 ℃) production process is not suitable for HJT battery production. This means that the electrode paste of a typical crystalline silicon solar cell cannot be used for HJT cells and low temperature silver paste suitable for HJT cells must be used.

Compared with the traditional high-temperature sintered silver paste, the low-temperature conductive silver paste realizes the binding force among silver particles by means of polymer curing, and simultaneously enables the silver particles to adhere to the surface of the battery and form good contact, so that the silver paste is a key material required in the battery metallization process. In practice, in order to minimize the loss during the cell metallization process, it is desirable to have both extremely low volume resistivity and excellent rheological properties of the slurry. However, as the solid content of the slurry increases, it is often difficult to combine the two. When the solid content of the slurry is increased to more than 90%, a lap joint circuit is formed among silver particles, which is beneficial to reducing the resistance, but at the moment, the silver slurry particles are easy to agglomerate, the rheological property of the slurry is poor, and the slurry is locally even dry and hard.

Disclosure of Invention

Aiming at the problem that the rheological property and the conductivity of the low-temperature conductive silver paste are reduced when the solid content is high, the invention provides the low-temperature conductive silver paste and a preparation method thereof.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the invention provides low-temperature conductive silver paste, which comprises the following components: silver powder and an organic carrier, wherein the organic carrier comprises epoxy resin, polyurethane prepolymer, solvent and controlled flocculation type dispersing agent.

According to the low-temperature conductive silver paste provided by the invention, the rheological property and the conductive requirement of the paste are effectively balanced by adding the controlled flocculation type dispersing agent, and the paste has higher solid content and lower volume resistivity while meeting the high resolution of the paste screen printing grid line. The controlled flocculation type dispersing agent has a weaker network structure and a lower storage modulus in the slurry, so that the printing performance and the welding tension of the slurry are ensured, the solid content of silver powder is improved as much as possible, and the volume resistivity of the slurry is reduced. By adding polyurethane prepolymer, the conductivity, adhesiveness and bending resistance of the slurry are improved.

Optionally, the surface of the silver powder is coated with a silane compound, and the silane compound comprises one or more of glycidyl ether propyl trimethoxysilane and ureido propyl triethoxysilane.

Alternatively, the silver powder includes one or both of plate-like silver powder having a median diameter of 2 μm to 8 μm and spherical silver powder having a median diameter of 0.2 μm to 1.5 μm.

Optionally, the conductive silver paste comprises the following components in parts by weight based on the total mass of the conductive silver paste: 90-95 parts of silver powder and 5.1-10 parts of organic carrier, wherein the organic carrier comprises 0.4-0.7 part of epoxy resin, 0.6-1.1 part of polyurethane prepolymer, 2.5-5.0 parts of solvent and 0.6-1.5 parts of controlled flocculation type dispersing agent.

Optionally, the organic carrier further comprises 0.7-1.5 parts of reactive diluent, 0.1-0.2 parts of curing agent and 0.2-0.4 parts of additive.

Optionally, the reactive diluent comprises one or more of 1, 4-butanediol diglycidyl ether, phenyl glycidyl ether, cyclohexane-1, 2-dicarboxylic acid diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester.

Optionally, the curing agent comprises one or more of dicyandiamide, succinic dihydrazide, tetrahydrophthalic anhydride, boron trifluoride amine complex and 2-ethyl-4-methylimidazole.

Optionally, the additive includes one or more of a thixotropic agent, a toughening agent, and a coupling agent.

Optionally, the controlled flocculation dispersant comprises one or more of an unsaturated polycarboxylic acid polymer solution, a polycarboxylic acid alkyl ammonium salt solution, and a polycarboxylic acid salt solution of a polyamine amide.

Optionally, the epoxy resin includes one or more of bisphenol a type epoxy resin, bisphenol F type epoxy resin, phenolic type epoxy resin, polyurethane resin, and diallyl phthalate resin.

Optionally, the polyurethane prepolymer is an isocyanate-terminated prepolymer, and is prepared from a polyol, isocyanate and a blocking agent, wherein the polyol comprises one or more of polyether glycol, polycaprolactone, polytetrahydrofuran and polyepoxy hexane;

the isocyanate comprises one or more of 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, isophorone diisocyanate and p-phenylene diisocyanate;

the blocking agent comprises one or more of methanol, methyl ethyl ketoxime, diethyl malonate and caprolactam.

Optionally, the solvent comprises one or more of cyclohexanone, butyl acetate, diethylene glycol diethyl ether, diethylene glycol butyl ether acetate, butyl acetate and propylene glycol methyl ether acetate.

On the other hand, the invention also provides a preparation method of the low-temperature conductive silver paste, which comprises the following steps:

uniformly mixing epoxy resin, a solvent, a controlled flocculation dispersing agent and a polyurethane prepolymer, and stirring for 30-50 min at 25-30 ℃ to obtain an organic carrier;

adding the organic carrier into silver powder, uniformly stirring, and grinding to obtain low-temperature conductive silver paste.

Drawings

Fig. 1 is a 3D micrograph of a silk screen grid line of a low temperature conductive silver paste according to example 2 of the present invention.

Fig. 2 is a rheological graph of the low temperature conductive silver paste provided in example 2 of the present invention.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects solved by the invention more clear, the invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

The embodiment of the invention provides low-temperature conductive silver paste, which comprises the following components: silver powder and an organic carrier, wherein the organic carrier comprises epoxy resin, polyurethane prepolymer, solvent and controlled flocculation type dispersing agent.

In the embodiment, the rheological property and the electric conduction requirement of the slurry are effectively balanced by adding the controlled flocculation dispersing agent, and the slurry has higher solid content and lower volume resistivity while meeting the high resolution of the slurry screen printing grid line. The controlled flocculation type dispersing agent has a weaker network structure and a lower storage modulus in the slurry, so that the printing performance and the welding tension of the slurry are ensured, the solid content of silver powder is improved as much as possible, and the volume resistivity of the slurry is reduced. By adding polyurethane prepolymer, the conductivity, adhesiveness and bending resistance of the slurry are improved.

In some embodiments, the silver powder surface is coated with a silane compound comprising one or more of glycidyl ether propyl trimethoxysilane and ureido propyl triethoxysilane. The silane compound is coated on the surface of the silver powder to modify the surface of the silver powder, so that the silver powder and the organic carrier are better soaked, and the dispersibility of the silver powder is improved.

In some embodiments, the silver powder includes one or both of a plate-like silver powder having a median diameter of 2 μm to 8 μm and a spherical silver powder having a median diameter of 0.2 μm to 1.5 μm. By controlling the particle size of the silver powder, the aggregation phenomenon of the silver powder particles in the slurry is improved.

In some embodiments, the mass ratio of the plate-like silver powder to the spherical silver powder is 2:8 to 8:2.

In some preferred embodiments, the mass ratio of the plate-like silver powder to the spherical silver powder is 1:1.

In some embodiments, the conductive silver paste comprises the following components by weight, based on the total mass of the conductive silver paste: 90-95 parts of silver powder and 5.1-10 parts of organic carrier, wherein the organic carrier comprises 0.4-0.7 part of epoxy resin, 0.6-1.1 part of polyurethane prepolymer, 2.5-5.0 parts of solvent and 0.6-1.5 parts of controlled flocculation type dispersing agent.

Specifically, the content of the silver powder may be 91 parts, 92 parts, 93 parts, 94 parts, 95 parts, etc., as long as the silver powder is satisfied in an amount of 90 to 95 parts. The content of the controlled flocculation dispersant may be 0.6 part, 0.7 part, 0.8 part, 0.9 part, 1.0 part, 1.1 part, etc., as long as the controlled flocculation dispersant is satisfied in an amount of 0.6 to 1.5 parts.

In some embodiments, the organic vehicle further comprises 0.7 to 1.5 parts reactive diluent, 0.1 to 0.2 parts curative, and 0.2 to 0.4 parts additive. Under the action of the curing agent, the epoxy resin is crosslinked and cured, and the reactive diluent is added to improve the performance of the epoxy resin and form a part of a crosslinked network structure.

In some embodiments, the controlled flocculation dispersant comprises one or more of an unsaturated polycarboxylic acid polymer solution, a polycarboxylic acid alkyl ammonium salt solution, and a polycarboxylic acid salt solution of a polyamine amide, the controlled flocculation dispersant comprising the polycarboxylic acid salt polymer solution improving the electrical performance of the low temperature conductive silver paste by affecting the polarity and electrolytic properties of the organic carrier. The flocculation-type dispersing agent is formed into a flocculation-type structure in a slurry system, rather than a general hydrogen bond network structure, a weaker internal structure and a lower storage modulus exist in the slurry, silver powder is more easily fully wetted and mixed with an organic carrier in the silver slurry preparation process, and the silver powder is uniformly dispersed in the organic carrier. Therefore, the solid content of silver powder is improved as much as possible while the printing performance and the welding tension are ensured, the improvement of the solid content is beneficial to the formation of a contact path of the conductive filler, and the volume resistivity of the slurry is reduced.

In some embodiments, the epoxy resin includes one or more of bisphenol a type epoxy resin, bisphenol F type epoxy resin, phenolic type epoxy resin, polyurethane resin, and diallyl phthalate resin.

In some embodiments, the reactive diluent comprises one or more of 1, 4-butanediol diglycidyl ether, phenyl glycidyl ether, cyclohexane-1, 2-dicarboxylic acid diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester. The reactive diluent can be used as the supplement of epoxy resin, can be used for adjusting the viscosity of a resin system, improving the process performance, and can react with the epoxy resin and a curing agent in the heating curing process to become a part of a crosslinked network structure, so that the epoxy resin can be modified, and has higher practical value.

In some embodiments, the polyurethane prepolymer is a terminal isocyanate-based prepolymer prepared from a polyol, an isocyanate, and a capping agent, the polyol comprising one or more of a polyether glycol, a polycaprolactone, a polytetrahydrofuran, and a polyepoxide;

the isocyanate comprises one or more of 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, isophorone diisocyanate and p-phenylene diisocyanate;

the blocking agent comprises one or more of methanol, methyl ethyl ketoxime, diethyl malonate and caprolactam, and the isocyanate groups exposed at two ends of the terminal isocyanate groups are blocked by the blocking agent containing active hydride.

In some embodiments, the solvent comprises one or more of cyclohexanone, butyl acetate, diethylene glycol diethyl ether, diethylene glycol butyl ether acetate, butyl acetate, and propylene glycol methyl ether acetate. The solvent plays a role in adjusting the viscosity and adhesion of the paste, and can be volatilized and released smoothly in the silver paste curing process.

In some embodiments, the curing agent includes one or more of dicyandiamide, succinic dihydrazide, tetrahydrophthalic anhydride, boron trifluoride amine complex, and 2-ethyl-4-methylimidazole.

In some embodiments, the additive includes one or more of a thixotropic agent, a toughening agent, and a coupling agent.

Thixotropic agents include, but are not limited to, one or more of hydrogenated castor oil, oxidized polyethylene, polyamide wax, organobentonite, and fumed silica.

The toughening agent includes, but is not limited to, one or more of rubber resins, carboxyl terminated nitrile rubbers, core shell rubbers.

The coupling agent comprises a silane coupling agent selected from one or more of an aminosilane compound, an epoxysilane compound, a vinylsilane compound, an acrylate silane compound, a methacrylate silane compound, and a hydroxysilane compound.

On the other hand, the embodiment of the invention also provides a preparation method of the low-temperature conductive silver paste, which comprises the following steps:

uniformly mixing epoxy resin, a solvent, a controlled flocculation dispersing agent and a polyurethane prepolymer, and stirring for 30-50 min at 25-30 ℃ to obtain an organic carrier;

adding the organic carrier into silver powder, uniformly stirring, and grinding to obtain low-temperature conductive silver paste.

The invention is further illustrated by the following examples.

Example 1

The embodiment is used for explaining the low-temperature conductive silver paste disclosed by the invention, wherein silver powder: 93%. Bisphenol F type epoxy resin: 0.5%; cyclohexane-1, 2-dicarboxylic acid diglycidyl ester (reactive diluent): 1.0%; aromatic polyurethane prepolymers containing butanone oxime-blocked NCO groups: 0.8%; boron trifluoride amine complex (curing agent): 0.1%; polycarboxylate solutions of polyamine amides (controlled flocculation dispersants): 1.5%; diethylene glycol butyl ether acetate (solvent): 3.1%. Wherein the mass ratio of the spherical silver powder to the flake silver powder in the silver powder is 1:1, the spherical silver powder is 0.55-0.61 mu m, and the flake silver powder is 3.7-4.2 mu m.

Example 2

This example is for illustrating the low temperature conductive silver paste disclosed in the present invention, comprising most of the compounds of example 1, except that the surface of the silver powder is coated with glycidol ether propyl trimethoxysilane.

Example 3

This example is intended to illustrate the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, with the difference that the polycarboxylate solution of the polyamine amide: 1.0%; diethylene glycol butyl ether acetate: 3.6%.

Example 4

This example is a comparative illustration of the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, except that the polycarboxylate solution of the polyamine amide (controlled flocculation dispersant): 0.6% diethylene glycol butyl ether acetate (solvent): 4%.

Example 5

This example is for illustrating the low temperature conductive silver paste disclosed in the present invention, and includes most of the compounds of example 2, which is different in that the silver powder: 95%; ethylene glycol butyl ether acetate (solvent): 1.1%

Example 6

This example is for illustrating the low temperature conductive silver paste disclosed in the present invention, and includes most of the compounds of example 2, which is different in that the silver powder: 91%; aromatic polyurethane prepolymers containing butanone oxime-blocked NCO groups: 0.9%; diethylene glycol butyl ether acetate (solvent): 5%.

Example 7

This example is intended to illustrate the low temperature conductive silver paste disclosed herein, including most of the compounds of example 2, except that no reactive diluent is present.

Example 8

This example is a comparative illustration of the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, except that the polycarboxylate solution of the polyamine amide (controlled flocculation dispersant): 0.3%; diethylene glycol butyl ether acetate (solvent): 4.3%.

Example 9

This example is a comparative illustration of the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, except that the polycarboxylate solution of the polyamine amide (controlled flocculation dispersant): 2%; diethylene glycol butyl ether acetate (solvent): 2.6%.

Example 10

This example is a comparative illustration of the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, with the exception that the controlled flocculation dispersing agent is an unsaturated polycarboxylic acid polymer solution.

Example 11

This example is a comparative illustration of the low temperature conductive silver paste disclosed herein, comprising a majority of the compounds of example 2, with the exception that the controlled flocculation dispersing agent is an alkylammonium salt solution of a polycarboxylic acid.

Comparative example 1

This comparative example is used to illustrate the low temperature conductive silver paste disclosed herein, including most of the compounds of example 2, except that no controlled flocculation dispersant, diethylene glycol butyl ether acetate, was included: 4.6%.

Comparative example 2

This comparative example is used to illustrate the low temperature conductive silver paste disclosed herein, including most of the compounds of example 2, except that the controlled flocculation dispersant was replaced with a thixotropic polyamide wax.

Comparative example 3

This comparative example is for illustrating the low temperature conductive silver paste disclosed in the present invention, including most of the compounds in example 2, except that the polyurethane prepolymer is not contained.

The beneficial effects of the invention are further illustrated by the test below.

Performance test method

1. And (3) testing silk screen printing effect: and (3) carrying out screen printing on the slurry on a crystalline silicon battery piece, curing for 30min at 200 ℃, and finally observing the continuity condition of the grid line and testing the height and width of the grid line by using a 3D microscope.

2. Volume resistivity test: the resistance of the cured electrode body was tested using a four-probe ohmmeter.

3. Evaluation and test of slurry formation: and testing the rheological curve of the slurry after three-roller grinding by adopting a rheological tester. The rheological state test standard for better slurry forming refers to the rheological curve of fig. 2, and specifically comprises two aspects, namely slurry viscosity and slurry thixotropic property. At shear rate γ=50s ^-1 Viscosity at the time of using gamma (10 s) ^-1 )/γ(100s ^-1 ) The viscosity ratio at time is thixotropic index and the evaluation of the paste is shown in Table 1:

TABLE 1

The test results are shown in table 2:

TABLE 2

From the test results of examples 1-4, 7 and comparative examples 1 and 2 in Table 2, it is seen that by adding 0.6-1.5 parts of the controlled flocculation type dispersing agent, the slurry can still obtain the rheological property of the slurry suitable for silk screen printing process with the solid content of 93%, including high thixotropic index and viscosity range. The rheological effect of example 2 is as in fig. 2, pseudoplastic, with viscosity decreasing with increasing shear rate. The screen printing effect is as shown in figure 1, no broken grid exists, and the continuity is good. At the same time, a low volume resistivity is maintained.

From the test results of examples 2, 5 and 6, it is understood that the volume resistivity was reduced with the increase of the solid content, but the rheological properties were maintained, and the gate line continuity was good with the aspect ratio of 0.6 or more.

From the test results of examples 2, 8, and 9, it was found that further reduction or increase in the content of the controlled flocculation dispersant affects rheological properties and resistivity, and is characterized by a reduced content of the controlled flocculation dispersant, a thixotropic property, and a reduced aspect ratio. The content of the controlled flocculation type dispersing agent is increased, the overall viscosity of the slurry is too high, the screen printing of the grid line is not facilitated, and the grid breakage occurs.

From example 2 and comparative example 3, it is seen that the volume resistivity of the slurry can be significantly reduced by adding the polyurethane prepolymer. From the test results of example 2 and example 6, it is evident that the volume resistivity of the slurry can be significantly reduced by adding a reactive diluent.

From the test results of examples 2, 10, 11, it was found that the printing performance was maintained well with a slight change in volume resistivity by changing the type of the controlled flocculation type dispersant.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (13)

1. The low-temperature conductive silver paste is characterized by comprising the following components: silver powder and an organic carrier, wherein the organic carrier comprises epoxy resin, polyurethane prepolymer, solvent and controlled flocculation type dispersing agent.

2. The low-temperature conductive silver paste according to claim 1, wherein the silver powder is coated with a silane compound including one or more of glycidyl ether propyl trimethoxysilane and ureido propyl triethoxysilane.

3. The low-temperature conductive silver paste according to claim 2, wherein the silver powder comprises one or both of plate-like silver powder having a median diameter of 2 μm to 8 μm and spherical silver powder having a median diameter of 0.2 μm to 1.5 μm.

4. The low-temperature conductive silver paste according to claim 1, comprising the following components by weight, based on the total mass of the conductive silver paste: 90-95 parts of silver powder and 5.1-10 parts of organic carrier, wherein the organic carrier comprises 0.4-0.7 part of epoxy resin, 0.6-1.1 part of polyurethane prepolymer, 2.5-5.0 parts of solvent and 0.6-1.5 parts of controlled flocculation type dispersing agent.

5. The low temperature conductive silver paste of claim 4, wherein the organic carrier further comprises 0.7 to 1.5 parts of reactive diluent, 0.1 to 0.2 parts of curing agent, and 0.2 to 0.4 parts of additive.

6. The low temperature conductive silver paste of claim 5, wherein the reactive diluent comprises one or more of 1, 4-butanediol diglycidyl ether, phenyl glycidyl ether, cyclohexane-1, 2-dicarboxylic acid diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester.

7. The low temperature conductive silver paste of claim 5, wherein the curing agent comprises one or more of dicyandiamide, succinic dihydrazide, tetrahydrophthalic anhydride, boron trifluoride amine complex and 2-ethyl-4-methylimidazole.

8. The low temperature conductive silver paste of claim 5, wherein the additive comprises one or more of a thixotropic agent, a toughening agent, and a coupling agent.

9. The low temperature conductive silver paste of claim 1, wherein the controlled flocculation dispersant comprises one or more of an unsaturated polycarboxylic acid polymer solution, a polycarboxylic acid alkyl ammonium salt solution, and a polycarboxylic acid salt solution of a polyamine amide.

10. The low temperature conductive silver paste of claim 1, wherein the epoxy resin comprises one or more of bisphenol a type epoxy resin, bisphenol F type epoxy resin, phenolic type epoxy resin, polyurethane resin, and diallyl phthalate resin.

11. The low temperature conductive silver paste of claim 1, wherein the polyurethane prepolymer is an isocyanate-terminated prepolymer, the polyurethane prepolymer being prepared from a polyol, an isocyanate and a capping agent, the polyol comprising one or more of a polyether glycol, a polycaprolactone, a polytetrahydrofuran and a polyepoxide;

the isocyanate comprises one or more of 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, isophorone diisocyanate and p-phenylene diisocyanate;

the blocking agent comprises one or more of methanol, methyl ethyl ketoxime, diethyl malonate and caprolactam.

12. The low temperature conductive silver paste of claim 1, wherein the solvent comprises one or more of cyclohexanone, butyl acetate, diethylene glycol diethyl ether, diethylene glycol butyl ether acetate, butyl acetate, and propylene glycol methyl ether acetate.

13. A method for preparing a low temperature conductive silver paste according to any one of claims 1 to 12, comprising the steps of:

uniformly mixing epoxy resin, a solvent, a controlled flocculation dispersing agent and a polyurethane prepolymer, and stirring for 30-50 min at 25-30 ℃ to obtain an organic carrier;

adding the organic carrier into silver powder, uniformly stirring, and grinding to obtain low-temperature conductive silver paste.