Silver paste and solar cells

Abstract

This application relates to the photovoltaic field, providing a silver paste and a solar cell. By mass fraction, the silver paste comprises: 0.79~7.9 wt% of a first organic carrier, 0.21~2.1 wt% of a second organic carrier, 1~4 wt% of glass powder, and the balance being silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprising block copolymers of C12 and above alkyl-modified propylene polymers, styrene monomers and aliphatic diene monomers, and epoxy resins; the first solvent has a boiling point of 110~260℃; and the second organic carrier comprises cellulose and a second solvent. The silver paste of this application exhibits excellent demolding, inkjet, and shaping capabilities in laser transfer printing, significantly reducing the probability of incomplete printing and broken grids.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a silver paste and a solar cell. Background Technology

[0002] The use of non-contact laser transfer (PTP) technology to improve the fine grid printing process of high-efficiency solar cells not only breaks through the linewidth limitations of traditional screen printing but also enables easy printing of ultra-narrow linewidths. This technology can print ultra-fine grid lines with a larger aspect ratio on the silicon wafer, thus helping the cells reach the standard of ultra-fine dense grid cells, perfectly matching selective emitter technology. This not only improves the efficiency of solar cells but also significantly reduces the amount of paste used, saving more than 20%, thereby reducing the production and power generation costs of the cells. The tunneling oxide passivation contact (TOPCon) process uses N-type double-sided silver paste, which is more sensitive to silver paste consumption. Therefore, laser transfer technology offers even greater savings compared to other technologies. Summary of the Invention

[0003] This application provides a silver paste and a solar cell to solve the problem of high probability of false printing and broken grids in the laser transfer process of silver paste in the prior art.

[0004] To achieve the above objectives, according to one aspect of the present invention, a silver paste is provided, comprising, by mass fraction: 0.79 to 7.9 wt% of a first organic carrier, 0.21 to 2.1 wt% of a second organic carrier, 1 to 4 wt% of glass powder, and the balance being silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprising block copolymers of C12 and above alkyl-modified propylene polymers, styrene monomers and aliphatic diene monomers, and epoxy resins, the first solvent having a boiling point of 110 to 260°C, and the second organic carrier comprising cellulose and a second solvent.

[0005] Furthermore, the mass ratio of the block copolymers of the above-mentioned C12 and above alkyl modified propylene polymers, styrene monomers and aliphatic diene monomers to epoxy resin is (2~8):(7~13):(2~8); and / or, the mass percentage of C12 and above alkyl in the C12 and above alkyl modified propylene polymer is 5~50%.

[0006] Further, the aforementioned C12 and above alkyl-modified propylene polymers are C12 to C22 alkyl-modified propylene polymers; and / or, the propylene polymers in the C12 and above alkyl-modified propylene polymers are selected from any one or more of styrene-acrylic acid copolymers, polymethyl methacrylate, methyl methacrylate-butadiene-styrene copolymers, acrylate-acrylonitrile-styrene copolymers, and acrylonitrile-butadiene-styrene copolymers; and / or, the number average molecular weight of the C12 and above alkyl-modified propylene polymers is 1700 to 50000 g / mol.

[0007] Furthermore, the styrene monomers mentioned above are selected from hydrogenated styrene and / or p-methylstyrene; and / or, the aliphatic diene monomers are selected from any one or more of butadiene, propylene, and pentadiene.

[0008] Furthermore, the block copolymers of styrene monomers and aliphatic diene monomers mentioned above are selected from hydrogenated styrene-butadiene block copolymers and / or p-methylstyrene-butadiene block copolymers; and / or, the weight-average molecular weight of the block copolymers of styrene monomers and aliphatic diene monomers is 50,000 to 400,000 g / mol.

[0009] Furthermore, the epoxy resin is selected from any one or more of bisphenol A type epoxy resin, phenolic polyepoxy resin and glycerol epoxy resin; and / or, the number average molecular weight of the epoxy resin is 300~7000 g / mol.

[0010] Furthermore, the cellulose is selected from any one or more of ethyl cellulose, cellulose acetate butyrate, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; and / or, the number average molecular weight of the cellulose is 7000~300000 g / mol.

[0011] Further, the mass ratio of the resin to the first solvent is (1~3):(7~9), the first solvent is selected from any one or more of butyl acetate, methyl isobutyl ketone and diethylene glycol butyl ether acetate; and / or, the mass ratio of the second solvent to cellulose is (50~80):(20~50), the second solvent is selected from any one or more of terpineol, benzyl alcohol and turpentine; and / or, the silver paste further includes 0.1~0.5% of a dispersant; and / or, the silver paste further includes 0.3~0.7% of a release agent.

[0012] Furthermore, the D50 of the above-mentioned glass powder is 1.0~1.4μm.

[0013] Furthermore, the aforementioned glass powder includes a first glass powder and a second glass powder; by mass percentage, the first glass powder includes 70-80% lead oxide, 2-20% aluminum oxide, 1-10% zinc oxide and 5-20% boron trioxide; by mass percentage, the second glass powder includes 60-70% lead oxide, 15-25% aluminum oxide, 10-20% barium oxide and 1-10% boron trioxide.

[0014] Furthermore, the mass ratio of the first glass powder to the second glass powder is (1~1.5):(0.5~1).

[0015] Furthermore, the silver paste also includes 0.05 to 0.3% silicon carbide; and / or, the silver paste also includes 0.05 to 0.3% titanium nitride.

[0016] Furthermore, the D50 of the aforementioned silicon carbide is 20~50nm; and / or, the D50 of titanium nitride is 20~50nm.

[0017] Furthermore, the silver powder mentioned above includes a first silver powder, a second silver powder, and a third silver powder. The D50 of the first silver powder is 0.5~1μm, the D50 of the second silver powder is 1~1.2μm, and the D50 of the third silver powder is 1.2~1.5μm. The mass ratio of the first silver powder, the second silver powder, and the third silver powder is (10~20):(20~40):(40~60).

[0018] According to another aspect of the present invention, a solar cell is provided, comprising a substrate and grid lines formed on the surface of the substrate, the grid lines being prepared by laser transfer of the aforementioned silver paste.

[0019] The technical solution provided in this application has at least the following advantages:

[0020] This application employs propylene polymers modified with C12 or higher alkyl groups, which have high molecular chain entanglement, helping to improve the cohesiveness and thixotropic properties of the silver paste. The addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear-thinning properties through microphase separation structure, suppressing demolding splashes while maintaining shape stability after demolding. The addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through crosslinking reaction, reducing the risk of demolding deformation. Cellulose can form a three-dimensional network structure in the silver paste, increasing the viscosity of the paste, thereby improving the rheological properties of the silver paste during laser transfer. Controlling the boiling point of the first solvent within the above-mentioned range helps to create a small decomposition temperature difference between the resin and the first solvent, allowing the resin and the first solvent to decompose concentratedly within a smaller temperature range. This promotes the formation of a higher vapor pressure in the film trench in a short time, driving the paste in the trench to demold, improving demolding power, and thus helping to reduce tailing or adhesion phenomena of the silver paste during transfer, improving the demolding ability of the silver paste, and improving the situation of incomplete printing and broken grids. Furthermore, the first solvent, possessing the aforementioned boiling point, exhibits strong polarity. The resin of this application, when used in combination with the first solvent, helps enhance the cohesiveness of the silver paste, resulting in stronger cohesion and thixotropy during the transfer process. This prevents splashing during demolding and reduces deformation after demolding, demonstrating superior shaping ability. Therefore, the silver paste of this application exhibits excellent demolding, inkjet, and shaping capabilities in laser transfer printing, significantly reducing the probability of incomplete printing and broken lines. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0022] As analyzed in the background section of this application, the prior art has a high probability of producing false prints and broken grids in laser transfer using silver paste. In order to solve this problem, this application provides a silver paste and a solar cell.

[0023] In a typical embodiment of this application, a silver paste is provided, comprising, by mass fraction: 0.79-7.9 wt% of a first organic carrier, 0.21-2.1 wt% of a second organic carrier, 1-4 wt% of glass powder, and the balance being silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprising block copolymers of C12 and above alkyl modified propylene polymers, styrene monomers and aliphatic diene monomers, and epoxy resins, the first solvent having a boiling point of 110-260°C, and the second organic carrier comprising cellulose and a second solvent.

[0024] This application employs propylene polymers modified with C12 or higher alkyl groups, which have high molecular chain entanglement, helping to improve the cohesiveness and thixotropic properties of the silver paste. The addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear-thinning properties through microphase separation structure, suppressing demolding splashes while maintaining shape stability after demolding. The addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through crosslinking reaction, reducing the risk of demolding deformation. Cellulose can form a three-dimensional network structure in the silver paste, increasing the viscosity of the paste, thereby improving the rheological properties of the silver paste during laser transfer. Controlling the boiling point of the first solvent within the above-mentioned range helps to create a small decomposition temperature difference between the resin and the first solvent, allowing the resin and the first solvent to decompose concentratedly within a smaller temperature range. This promotes the formation of a higher vapor pressure in the film trench in a short time, driving the paste in the trench to demold, improving demolding power, and thus helping to reduce tailing or adhesion phenomena of the silver paste during transfer, improving the demolding ability of the silver paste, and improving the situation of incomplete printing and broken grids. Furthermore, the first solvent, possessing the aforementioned boiling point, exhibits strong polarity. The resin of this application, when used in combination with the first solvent, helps enhance the cohesiveness of the silver paste, resulting in stronger cohesion and thixotropy during the transfer process. This prevents splashing during demolding and reduces deformation after demolding, demonstrating superior shaping ability. Therefore, the silver paste of this application exhibits excellent demolding, inkjet, and shaping capabilities in laser transfer printing, significantly reducing the probability of incomplete printing and broken lines.

[0025] It should be noted that all components in the silver paste of this application can be obtained by purchasing or by preparing them using existing technologies.

[0026] In one embodiment of this application, the mass ratio of the block copolymer of the C12 and above alkyl modified propylene polymer, styrene monomer and aliphatic diene monomer to epoxy resin is (2~8):(7~13):(2~8); and / or, the mass percentage of C12 and above alkyl in the C12 and above alkyl modified propylene polymer is 5~50%.

[0027] Controlling the mass ratio of C12 and above alkyl-modified propylene polymers, styrene monomers, block copolymers of aliphatic diene monomers, and epoxy resin within the aforementioned range helps improve the synergistic effect between the components, enhances the cohesiveness of the silver paste, and ensures that the silver paste has suitable viscosity and thixotropy during the transfer process, thereby helping to reduce the risk of incomplete printing and grid breakage. Controlling the mass percentage of C12 and above alkyl groups in the C12 and above alkyl-modified propylene polymers within the aforementioned range also helps to form more van der Waals forces and hydrophobic interactions between polymer molecular chains, further enhancing the cohesiveness of the silver paste.

[0028] In one embodiment of this application, the aforementioned C12 and above alkyl-modified propylene polymers are C12 to C22 alkyl-modified propylene polymers; and / or, the propylene polymers in the C12 and above alkyl-modified propylene polymers are selected from any one or more of styrene-acrylic acid copolymers, polymethyl methacrylate, methyl methacrylate-butadiene-styrene copolymers, acrylate-acrylonitrile-styrene copolymers, and acrylonitrile-butadiene-styrene copolymers; and / or, the number average molecular weight of the C12 and above alkyl-modified propylene polymers is 1700 to 50000 g / mol.

[0029] C12-C22 alkyl-modified propylene polymers, with their longer alkyl side chains, enhance intermolecular interactions, thereby improving the overall cohesiveness of the silver paste. These types of propylene polymers exhibit superior silver powder coating ability and dispersion stability, forming a uniform silver powder distribution in the paste, thus contributing to the long-term stability of the paste. Controlling the number-average molecular weight of C12 and higher alkyl-modified propylene polymers within the aforementioned range helps to achieve suitable viscosity and elastic modulus, enabling the formation of a stable molecular network in the paste and enhancing its thixotropic properties.

[0030] In one embodiment of this application, the styrene monomers are selected from hydrogenated styrene and / or p-methylstyrene; and / or, the aliphatic diene monomers are selected from any one or more of butadiene, propylene, and pentadiene.

[0031] Controlling the styrene monomers and aliphatic diene monomers within the aforementioned range helps to enhance the interaction between styrene segments and aliphatic diene segments, thereby contributing to further improving the shear-thinning properties of block copolymers of styrene monomers and aliphatic diene monomers.

[0032] To further enhance the shear-thinning properties of the block copolymers of styrene monomers and aliphatic diene monomers and suppress demolding splashing, in one embodiment of this application, the block copolymers of styrene monomers and aliphatic diene monomers are selected from hydrogenated styrene-butadiene block copolymers and / or p-methylstyrene-butadiene block copolymers; and / or, the weight-average molecular weight of the block copolymers of styrene monomers and aliphatic diene monomers is 50,000 to 400,000 g / mol.

[0033] To further enhance the rigidity of the silver paste network structure and reduce the risk of demolding deformation, in one embodiment of this application, the epoxy resin is selected from any one or more of bisphenol A type epoxy resin, phenolic polyepoxy resin and glycerol epoxy resin; and / or, the number average molecular weight of the epoxy resin is 300~7000g / mol.

[0034] In order to further improve the rheological properties of silver paste in the laser transfer process, in one embodiment of this application, the cellulose is selected from any one or more of ethyl cellulose, cellulose acetate butyrate, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; and / or the number average molecular weight of the cellulose is 7000~300000 g / mol.

[0035] In order to further optimize the rheological properties and printability of silver paste, improve the quality of metallization layer during sintering, reduce organic residues, and enhance the mechanical strength and reliability of metallization layer, in one embodiment of this application, the above-mentioned cellulose is a combination of ethyl cellulose and cellulose acetate butyrate, and the mass ratio of ethyl cellulose to cellulose acetate butyrate is (10~20):(10~20).

[0036] In one embodiment of this application, the mass ratio of the resin to the first solvent is (1~3):(7~9), and the first solvent is selected from any one or more of butyl acetate, methyl isobutyl ketone, and diethylene glycol butyl ether acetate; and / or, the mass ratio of the second solvent to cellulose is (50~80):(20~50), and the second solvent is selected from any one or more of terpineol, benzyl alcohol, and turpentine; and / or, the silver paste further includes 0.1~0.5% of a dispersant; and / or, the silver paste further includes 0.3~0.7% of a release agent.

[0037] Controlling the mass ratio of resin to the first solvent within the aforementioned range helps improve their interaction, enhances the cohesiveness of the silver paste, and gives the silver paste stronger cohesion and thixotropy during the transfer process. Controlling the type of the first solvent within the aforementioned range ensures it has strong polarity, which helps improve the transfer accuracy and internal bonding strength of the silver paste, reducing printing defects caused by phase separation. The addition of the second solvent helps improve the dispersibility of cellulose in the silver paste. Controlling the mass ratio of the second solvent to cellulose and the type of the second solvent within the aforementioned range helps further improve the dispersion stability of cellulose in the silver paste. The addition of dispersants and release agents can further regulate the rheological properties of the paste. Dispersants help ensure uniform distribution of silver powder particles in the paste, reduce agglomeration, and improve the stability and printing consistency of the silver paste. Release agents promote the release of the paste from the mold during printing, further improving tailing and adhesion during the paste transfer process. Controlling the mass ratio of dispersants and release agents within the aforementioned range helps further optimize the printing efficiency and accuracy of the silver paste in the laser transfer process.

[0038] In order to further improve the cohesiveness of the silver paste and make it have strong cohesiveness and thixotropy during the transfer process, in one embodiment of this application, the first solvent is a combination of butyl acetate, methyl isobutyl ketone and diethylene glycol butyl ether acetate, and the mass ratio of butyl acetate, methyl isobutyl ketone and diethylene glycol butyl ether acetate is (25~35):(5~15):(35~45).

[0039] Including but not limited to, the dispersant mentioned above is selected from any one or more of TDO dispersant, Brij-L4 dispersant, lauric acid and polyhydroxystearic acid.

[0040] In one embodiment of this application, the release agent is a combination of dimethyl silicone oil and amino silicone oil, and the mass ratio of dimethyl silicone oil to amino silicone oil is (5~9):(1~5), and the viscosity of the dimethyl silicone oil is 10~100 mm. 2 / s, the viscosity of amino silicone oil is 600~700mm. 2 / s helps enhance the compatibility between the release agent and the silver powder, reduces interfacial delamination, and helps reduce the viscosity of the paste, improves printing fluidity, and also helps form a micron-level isolation layer, reducing release residue.

[0041] In one embodiment of this application, the D50 of the glass powder is 1.0~1.4μm.

[0042] Controlling the D50 of the glass powder within the above range helps to improve the dispersibility of the glass powder in the silver paste, thereby helping to improve the stability of the silver paste.

[0043] In one embodiment of this application, the glass powder includes a first glass powder and a second glass powder; by mass percentage, the first glass powder includes 70-80% lead oxide, 2-20% aluminum oxide, 1-10% zinc oxide and 5-20% boron trioxide; by mass percentage, the second glass powder includes 60-70% lead oxide, 15-25% aluminum oxide, 10-20% barium oxide and 1-10% boron trioxide.

[0044] The first type of glass powder, due to its high lead content and appropriate aluminum, zinc, and boron ratio, can lower the sintering temperature, promote the fusion of silver powder particles, and form a low-resistance conductive path. The low melting point of lead-based glass powder helps form a dense silver layer during sintering, reducing voids and microcracks, thereby lowering contact resistance and improving the battery's conductivity. The second type of glass powder, with its high barium content, optimizes the protection of the passivation layer during sintering. Barium-based glass powder forms a shielding layer during sintering, absorbing and dispersing laser energy, reducing direct thermal damage to the passivation layer on the silicon wafer surface.

[0045] In one embodiment of this application, the mass ratio of the first glass powder and the second glass powder is (1~1.5):(0.5~1).

[0046] Controlling the mass ratio of the first glass powder and the second glass powder within the above range helps to improve the interaction between the two, so that during the sintering process after laser transfer, a metal connection with good conductivity can be formed, and the passivation layer can be gently etched, avoiding damage to the light absorption structure and electrical properties of the silicon wafer surface.

[0047] In one embodiment of this application, the silver paste further includes 0.05-0.3% silicon carbide; and / or, the silver paste further includes 0.05-0.3% titanium nitride.

[0048] Silicon carbide and titanium nitride have high light absorption and thermal conductivity. Adding nano-silicon carbide and titanium nitride to silver paste helps to reduce the direct energy impact of laser on the passivation layer through photothermal conversion, concentrates the laser energy inside the paste, and reduces the risk of thermal damage to the passivation layer interface.

[0049] To further improve the photothermal conversion efficiency, in one embodiment of this application, the D50 of the silicon carbide is 20~50nm; and / or, the D50 of the titanium nitride is 20~50nm.

[0050] In one embodiment of this application, the silver powder includes a first silver powder, a second silver powder, and a third silver powder. The D50 of the first silver powder is 0.5~1μm, the D50 of the second silver powder is 1~1.2μm, and the D50 of the third silver powder is 1.2~1.5μm. The mass ratio of the first silver powder, the second silver powder, and the third silver powder is (10~20):(20~40):(40~60).

[0051] The addition of the first silver powder helps improve the fluidity of the silver paste during the laser transfer process. Small-particle-size silver powder can better penetrate into the laser-transfer film trenches, forming a continuous and clear grid structure, which helps improve the resolution and printing quality of the laser transfer. The presence of the second and third silver powders helps form a denser and smoother metallization layer during sintering. Large-particle-size silver powder can melt and interconnect when heated, forming a stable conductive network, reducing contact resistance, and helping to improve the photoelectric conversion efficiency of solar cells.

[0052] In one embodiment of this application, the method for preparing the above-mentioned silver paste includes:

[0053] (1) Mix the raw materials for the first organic carrier according to the ratio, mix them evenly using a dispersion, emulsification and stirring machine, heat at a constant temperature of 90~110℃, dissolve evenly, and filter after cooling to obtain the first organic carrier.

[0054] (2) Mix the raw materials for the second organic carrier according to the ratio, mix them evenly using a dispersion, emulsification and stirring machine, heat at a constant temperature of 90~110℃, dissolve evenly, and filter after cooling to obtain the second organic carrier.

[0055] (3) Add the second organic carrier, dispersant, silicon carbide, titanium nitride and glass powder to a centrifuge tube and mix evenly. Place the centrifuge tube in a centrifuge and centrifuge 1-2 times at a speed of 700-900 rpm, with each centrifugation time being 1-2 min. After ionization, place the mixture in a three-roll mill for the first three-roll milling treatment. The roller spacing of the three-roll mill is 20-30 μm and the speed is 300-400 rpm to obtain glass slurry.

[0056] (4) Add the first organic carrier, release agent and silver powder to the glass slurry, stir evenly, and centrifuge at 800~900rpm for 2~3 times. After centrifugation, place it in a three-roll mill for a second three-roll milling process. The roller spacing of the three-roll mill is 5~7μm and the speed is 300~400rpm to obtain silver slurry.

[0057] In another typical embodiment of this application, a solar cell is provided, including a substrate and grid lines formed on the surface of the substrate, the grid lines being prepared by laser transfer of the aforementioned silver paste.

[0058] Since the grid lines in the aforementioned solar cell are prepared by laser transfer using the silver paste of this application, the solar cell has a long service life and high photoelectric conversion efficiency.

[0059] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0060] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0061] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0062] The embodiments of this application will now be described in detail. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0063] Example 1

[0064] By mass fraction, the silver paste comprises: 89.5% silver powder, 2.4% glass powder (D50 of 1.2μm), 0.05% silicon carbide (D50 of 30nm), 0.05% titanium nitride (D50 of 30nm), 5.7% first organic carrier, 1.5% second organic carrier, 0.3% dispersant, and 0.5% release agent;

[0065] The silver powder includes first silver powder, second silver powder and third silver powder. The D50 of the first silver powder is 0.8 μm, the D50 of the second silver powder is 1.1 μm and the D50 of the third silver powder is 1.3 μm. The mass ratio of the first silver powder, the second silver powder and the third silver powder is 10:40:40.

[0066] The glass powder includes a first glass powder and a second glass powder, with a mass ratio of 1.3:0.7. By mass percentage, the first glass powder consists of 72% PbO, 10% Al2O3, 4% ZnO, and 14% B2O3; by mass percentage, the second glass powder consists of 60% PbO, 20% Al2O3, 16% BaO, and 4% B2O3.

[0067] Based on the total mass percentage of the first organic carrier being 100%, the first organic carrier comprises 5% of C18 linear alkyl-modified styrene-acrylic acid copolymer (number average molecular weight of 5000 g / mol, with C18 linear alkyl content of 25%), 10% of hydrogenated styrene-butadiene block copolymer (weight average molecular weight of 100000 g / mol), 5% bisphenol A type epoxy resin (number average molecular weight of 5000 g / mol), 30% butyl acetate (boiling point of 126℃), 10% methyl isobutyl ketone (boiling point of 126℃), and 40% diethylene glycol butyl ether acetate (boiling point of 245℃).

[0068] Based on the total mass percentage of the second organic carrier being 100%, the second organic carrier comprises 15% ethyl cellulose (number average molecular weight of 100,000 g / mol), 15% cellulose acetate butyrate (number average molecular weight of 16,000 g / mol), and 70% terpineol.

[0069] The dispersant is Brij-L4 dispersant, and the release agent is dimethyl silicone oil (viscosity 100 mm). 2 / s) and amino silicone oil (viscosity 600 mm) 2 The combination of dimethyl silicone oil and amino silicone oil is 7:3.

[0070] The preparation steps of the conductive paste are as follows:

[0071] (1) The raw materials for the first organic carrier are mixed according to the above ratio, and the mixture is mixed evenly using a dispersion, emulsification and stirring machine. The mixture is heated at a constant temperature of 100°C until it is dissolved evenly. After cooling, the mixture is filtered to obtain the first organic carrier.

[0072] (2) Mix the raw materials for the second organic carrier according to the above ratio, mix them evenly using a dispersion, emulsification and stirring machine, heat at a constant temperature of 100°C until they are evenly dissolved, and filter after cooling to obtain the second organic carrier.

[0073] (3) Add the second organic carrier, dispersant, silicon carbide, titanium nitride and glass powder to a centrifuge tube and mix evenly. Place the centrifuge tube in a centrifuge and centrifuge once at a speed of 800 rpm for 1 min each time. After ionization, place it in a three-roll mill for the first three-roll milling treatment. The roller spacing of the three-roll mill is 20 μm and the speed is 300 rpm to obtain glass slurry.

[0074] (4) Add the first organic carrier, release agent and silver powder to the glass slurry, stir evenly, and centrifuge twice at a speed of 800 rpm. After centrifugation, place it in a three-roll mill for a second three-roll milling process. The roller spacing of the three-roll mill is 5 μm and the speed is 300 rpm to obtain silver slurry.

[0075] Example 2

[0076] The difference from Example 1 is that the total mass of the C18 linear alkyl-modified styrene-acrylic acid copolymer, hydrogenated styrene-butadiene block copolymer and bisphenol A type epoxy resin remains unchanged, and the mass ratio of the C18 linear alkyl-modified styrene-acrylic acid copolymer, hydrogenated styrene-butadiene block copolymer and bisphenol A type epoxy resin is 2:13:2, finally yielding silver paste.

[0077] Example 3

[0078] The difference from Example 1 is that the total mass of the C18 linear alkyl modified styrene-acrylic acid copolymer, hydrogenated styrene-butadiene block copolymer and bisphenol A type epoxy resin remains unchanged, and the mass ratio of the C18 linear alkyl modified styrene-acrylic acid copolymer, hydrogenated styrene-butadiene block copolymer and bisphenol A type epoxy resin is 9:6:9, finally yielding silver paste.

[0079] Example 4

[0080] The difference from Example 1 is that the mass percentage of C18 straight-chain alkyl groups is 40%, resulting in silver paste.

[0081] Example 5

[0082] The difference from Example 1 is that the mass percentage of C18 straight-chain alkyl groups is 3%, resulting in silver paste.

[0083] Example 6

[0084] The difference from Example 1 is that the number average molecular weight of the C18 linear alkyl-modified styrene-acrylic acid copolymer is 2400 g / mol, which ultimately yields the silver paste.

[0085] Example 7

[0086] The difference from Example 1 is that the number average molecular weight of the C18 linear alkyl-modified styrene-acrylic acid copolymer is 1000 g / mol, which ultimately yields the silver paste.

[0087] Example 8

[0088] The difference from Example 1 is that the C18 linear alkyl-modified styrene-acrylic acid copolymer was replaced with a C30 linear alkyl-modified styrene-acrylic acid copolymer, and the final silver paste was obtained.

[0089] Example 9

[0090] The difference from Example 1 is that the weight-average molecular weight of the hydrogenated styrene-butadiene block copolymer is 500,000 g / mol, which ultimately yields the silver paste.

[0091] Example 10

[0092] The difference from Example 1 is that the number average molecular weight of the bisphenol A type epoxy resin is 10000 g / mol, and the final product is silver paste.

[0093] Example 11

[0094] The difference from Example 1 is that cellulose acetate butyrate was completely replaced with ethyl cellulose, resulting in silver paste.

[0095] Example 12

[0096] The difference from Example 1 is that the number average molecular weight of ethyl cellulose is 400,000 g / mol, and the number average molecular weight of cellulose acetate butyrate is 400,000 g / mol, resulting in silver paste.

[0097] Example 13

[0098] The difference from Example 1 is that the second glass is completely replaced with the first glass, and the silver paste is finally obtained.

[0099] Example 14

[0100] The difference from Example 1 is that the addition of silicon carbide and titanium nitride is omitted, and silver paste is finally obtained.

[0101] Example 15

[0102] The difference from Example 1 is that the second and third silver powders are completely replaced with the first silver powder, and the final silver paste is obtained.

[0103] Example 16

[0104] The difference from Example 1 is that, by mass fraction, the silver paste comprises: 87.2% silver powder, 1% glass powder (D50 = 1 μm), 0.3% silicon carbide (D50 = 50 nm), 0.3% titanium nitride (D50 = 50 nm), 7.9% first organic carrier, 2.1% second organic carrier, 0.5% dispersant, and 0.7% release agent;

[0105] The silver powder includes first silver powder, second silver powder and third silver powder. The D50 of the first silver powder is 1 μm, the D50 of the second silver powder is 1.2 μm, and the D50 of the third silver powder is 1.5 μm. The mass ratio of the first silver powder, the second silver powder and the third silver powder is 20:20:60.

[0106] The glass powder includes a first glass powder and a second glass powder, with a mass ratio of 1.5:0.5. By mass percentage, the first glass powder consists of 80% PbO, 5% Al2O3, 10% ZnO, and 5% B2O3; and by mass percentage, the second glass powder consists of 60% PbO, 20% Al2O3, 10% BaO, and 10% B2O3.

[0107] Based on the total mass percentage of the first organic carrier being 100%, the first organic carrier comprises 8% C22 linear alkyl-modified polymethyl methacrylate (number average molecular weight of 5000 g / mol, with C22 linear alkyl groups accounting for 5% by mass), 7% p-methylstyrene-butadiene block copolymer (weight average molecular weight of 170000 g / mol), 5% phenolic epoxy resin (number average molecular weight of 4800 g / mol), 25% butyl acetate (boiling point of 126℃), 15% methyl isobutyl ketone (boiling point of 126℃), and 40% diethylene glycol butyl ether acetate (boiling point of 245℃).

[0108] Based on the total mass percentage of the second organic carrier being 100%, the second organic carrier comprises 10% ethyl cellulose (number average molecular weight of 200,000 g / mol), 20% cellulose acetate butyrate (number average molecular weight of 30,000 g / mol), and 70% benzyl alcohol.

[0109] The dispersant is lauric acid, and the release agent is dimethyl silicone oil (viscosity 50 mm). 2 / s) and amino silicone oil (viscosity 600 mm) 2 The silver paste is obtained by combining dimethyl silicone oil and amino silicone oil in a mass ratio of 5:5.

[0110] Example 17

[0111] The difference from Example 1 is that, by mass fraction, the silver paste comprises: 94.4% silver powder, 4% glass powder (D50 of 1.4 μm), 0.1% silicon carbide (D50 of 20 nm), 0.1% titanium nitride (D50 of 20 nm), 0.79% first organic carrier, 0.21% second organic carrier, 0.1% dispersant, and 0.3% release agent;

[0112] The silver powder includes first silver powder, second silver powder and third silver powder. The D50 of the first silver powder is 0.5μm, the D50 of the second silver powder is 1μm, and the D50 of the third silver powder is 1.2μm. The mass ratio of the first silver powder, the second silver powder and the third silver powder is 15:30:50.

[0113] The glass powder includes a first glass powder and a second glass powder, with a mass ratio of 1:1. By mass percentage, the first glass powder consists of 70% PbO, 20% Al2O3, 1% ZnO, and 9% B2O3; and by mass percentage, the second glass powder consists of 70% PbO, 15% Al2O3, 14% BaO, and 1% B2O3.

[0114] Based on the total mass percentage of the first organic carrier being 100%, the first organic carrier comprises 2% of C12 linear alkyl-modified methyl methacrylate-butadiene-styrene copolymer (number average molecular weight of 50,000 g / mol, with C12 linear alkyl groups accounting for 50% of the mass), 13% of hydrogenated styrene-butadiene block copolymer (weight average molecular weight of 100,000 g / mol), 5% of glycerol epoxy resin (number average molecular weight of 600 g / mol), 35% butyl acetate (boiling point of 126°C), 5% methyl isobutyl ketone (boiling point of 126°C), and 40% diethylene glycol butyl ether acetate (boiling point of 245°C).

[0115] Based on the total mass percentage of the second organic carrier being 100%, the second organic carrier comprises 20% ethyl cellulose (number average molecular weight of 50,000 g / mol), 10% cellulose acetate butyrate (number average molecular weight of 50,000 g / mol), and 70% turpentine oil.

[0116] The dispersant is TDO dispersant, and the release agent is dimethyl silicone oil (viscosity 10 mm). 2 / s) and amino silicone oil (viscosity 600 mm) 2 The silver paste is obtained by combining dimethyl silicone oil and amino silicone oil in a mass ratio of 9:1.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that the addition of C18 linear alkyl-modified styrene-acrylic acid copolymer was omitted, and the final product was silver paste.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the addition of hydrogenated styrene-butadiene block copolymer was omitted, and the final product was silver paste.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that the addition of bisphenol A epoxy resin was omitted, and silver paste was finally obtained.

[0123] Comparative Example 4

[0124] The difference from Example 1 is that the addition of ethyl cellulose and cellulose acetate butyrate was omitted, resulting in silver paste.

[0125] Comparative Example 5

[0126] The difference from Example 1 is that a styrene-acrylic acid copolymer was used instead of the C18 linear alkyl-modified styrene-acrylic acid copolymer, resulting in a silver paste.

[0127] Comparative Example 6

[0128] The difference from Example 1 is that triethylene glycol butyl ether (boiling point 278°C) is used to replace butyl acetate, methyl isobutyl ketone and diethylene glycol butyl ether acetate, and the final silver paste is obtained.

[0129] Comparative Example 7

[0130] The difference from Example 1 is that the silver paste comprises: 87.6% silver powder, 2.4% glass powder (D50 of 1.2 μm), 0.05% silicon carbide (D50 of 30 nm), 0.05% titanium nitride (D50 of 30 nm), 9% first organic carrier, 0.1% second organic carrier, 0.3% dispersant and 0.5% release agent, thus obtaining the final silver paste.

[0131] Electrode sheets were obtained by laser transfer printing of the silver pastes prepared in the examples and comparative examples. The number of electrode sheets with false printing and broken grids in the batch production was observed using screen printing AOI inspection equipment, and the proportion of electrode sheets with false printing and broken grids detected by AOI was recorded. The results are shown in Table 1. The silver pastes prepared in the examples and comparative examples were laser transferred and then sintered on crystalline silicon solar cells to form electrodes, thus obtaining solar cells. The photoelectric conversion efficiency, open circuit voltage, short circuit current and fill factor of the solar cells were tested, and the test results are shown in Table 2.

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0137] This application employs propylene polymers modified with C12 or higher alkyl groups, which have high molecular chain entanglement, helping to improve the cohesiveness and thixotropic properties of the silver paste. The addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear-thinning properties through microphase separation structure, suppressing demolding splashes while maintaining shape stability after demolding. The addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through crosslinking reaction, reducing the risk of demolding deformation. Cellulose can form a three-dimensional network structure in the silver paste, increasing the viscosity of the paste, thereby improving the rheological properties of the silver paste during laser transfer. Controlling the boiling point of the first solvent within the above-mentioned range helps to create a small decomposition temperature difference between the resin and the first solvent, allowing the resin and the first solvent to decompose concentratedly within a smaller temperature range. This promotes the formation of a higher vapor pressure in the film trench in a short time, driving the paste in the trench to demold, improving demolding power, and thus helping to reduce tailing or adhesion phenomena of the silver paste during transfer, improving the demolding ability of the silver paste, and improving the situation of incomplete printing and broken grids. Furthermore, the first solvent, possessing the aforementioned boiling point, exhibits strong polarity. The resin of this application, when used in combination with the first solvent, helps enhance the cohesiveness of the silver paste, resulting in stronger cohesion and thixotropy during the transfer process. This prevents splashing during demolding and reduces deformation after demolding, demonstrating superior shaping ability. Therefore, the silver paste of this application exhibits excellent demolding, inkjet, and shaping capabilities in laser transfer printing, significantly reducing the probability of incomplete printing and broken lines.

[0138] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A silver paste, characterized in that, The silver paste comprises, by mass fraction: 0.79~7.9wt% of the first organic carrier; 0.21~2.1wt% of a second organic carrier; 1~4wt% glass powder; The remainder is silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprising a C12 or higher alkyl-modified propylene polymer, a block copolymer of styrene monomers and aliphatic diene monomers and an epoxy resin, the first solvent having a boiling point of 110~260℃, the second organic carrier comprising cellulose and a second solvent; the mass ratio of the C12 or higher alkyl-modified propylene polymer, the block copolymer of styrene monomers and aliphatic diene monomers and the epoxy resin is (2~8):(7~13):(2~8); the number average molecular weight of the epoxy resin is 300~7000 g / mol.

2. The silver paste according to claim 1, characterized in that, The mass percentage of C12 and above alkyl groups in the propylene polymers modified with C12 and above alkyl groups is 5-50%.

3. The silver paste according to claim 1, characterized in that, The C12 and above alkyl-modified propylene polymers are C12 to C22 alkyl-modified propylene polymers; and / or, the propylene polymers in the C12 and above alkyl-modified propylene polymers are selected from any one or more of styrene-acrylic acid copolymers, polymethyl methacrylate, methyl methacrylate-butadiene-styrene copolymers, acrylate-acrylonitrile-styrene copolymers, and acrylonitrile-butadiene-styrene copolymers; and / or, the number average molecular weight of the C12 and above alkyl-modified propylene polymers is 1700 to 50000 g / mol.

4. The silver paste according to claim 1, characterized in that, The styrene monomers are selected from hydrogenated styrene and / or p-methylstyrene; And / or, the aliphatic diene monomer is selected from any one or more of butadiene, propylene, and pentadiene.

5. The silver paste according to claim 4, characterized in that, The block copolymer of styrene monomers and aliphatic diene monomers is selected from hydrogenated styrene-butadiene block copolymers and / or p-methylstyrene-butadiene block copolymers; and / or, the weight-average molecular weight of the block copolymer of styrene monomers and aliphatic diene monomers is 50,000 to 400,000 g / mol.

6. The silver paste according to any one of claims 1 to 5, characterized in that, The epoxy resin is selected from any one or more of bisphenol A type epoxy resin, phenolic polyepoxy resin, and glycerol epoxy resin.

7. The silver paste according to any one of claims 1 to 5, characterized in that, The cellulose is selected from any one or more of ethyl cellulose, cellulose acetate butyrate, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; and / or the number average molecular weight of the cellulose is 7000~300000 g / mol.

8. The silver paste according to any one of claims 1 to 5, characterized in that, The mass ratio of the resin to the first solvent is (1~3):(7~9), and the first solvent is selected from any one or more of butyl acetate, methyl isobutyl ketone and diethylene glycol butyl ether acetate; And / or, the mass ratio of the second solvent to the cellulose is (50~80):(20~50), and the second solvent is selected from any one or more of terpineol, benzyl alcohol, and turpentine; And / or, the silver paste further includes 0.1-0.5% dispersant; And / or, the silver paste further includes 0.3 to 0.7% of a release agent.

9. The silver paste according to any one of claims 1 to 5, characterized in that, The glass powder has a D50 of 1.0~1.4μm.

10. The silver paste according to any one of claims 1 to 5, characterized in that, The glass powder includes a first glass powder and a second glass powder; The first glass powder comprises, by mass percentage, 70-80% lead oxide, 2-20% aluminum oxide, 1-10% zinc oxide and 5-20% boron trioxide; The second glass powder comprises, by mass percentage, 60-70% lead oxide, 15-25% aluminum oxide, 10-20% barium oxide, and 1-10% boron trioxide.

11. The silver paste according to claim 10, characterized in that, The mass ratio of the first glass powder to the second glass powder is (1~1.5):(0.5~1).

12. The silver paste according to any one of claims 1 to 5, characterized in that, The silver paste further includes 0.05-0.3% silicon carbide; and / or, the silver paste further includes 0.05-0.3% titanium nitride.

13. The silver paste according to claim 12, characterized in that, The silicon carbide has a D50 of 20-50 nm; and / or the titanium nitride has a D50 of 20-50 nm.

14. The silver paste according to any one of claims 1 to 5, characterized in that, The silver powder includes a first silver powder, a second silver powder, and a third silver powder. The first silver powder has a D50 of 0.5~1μm, the second silver powder has a D50 of 1~1.2μm, and the third silver powder has a D50 of 1.2~1.5μm. The mass ratio of the first silver powder, the second silver powder, and the third silver powder is (10~20):(20~40):(40~60).

15. A solar cell, characterized in that, It includes a substrate and grid lines formed on the surface of the substrate, the grid lines being prepared by laser transfer from the silver paste of any one of claims 1 to 14.

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