Silver paste and solar cell

Abstract

The embodiment of the invention relates to the photovoltaic field, and provides silver paste and a solar cell. The silver paste comprises the following components in percentage by mass: 0.79 to 7.9 weight percent of a first organic carrier, 0.21 to 2.1 weight percent of a second organic carrier, 1 to 4 weight percent of glass powder and the balance of silver powder, wherein the first organic carrier comprises resin and a first solvent, the resin comprises a C12 and above alkyl modified propylene polymer, a segmented copolymer of a styrene monomer and an aliphatic diene monomer and epoxy resin, the boiling point of the first solvent is 110-260 DEG C, and the second organic carrier comprises cellulose and a second solvent. The silver paste provided by the invention has excellent demolding, ink jetting and shaping capabilities in laser transfer printing, and the probability of virtual printing and grid breaking is remarkably reduced.

Description

Technical Field

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

[0002] The use of non-contact laser transfer printing (PTP) technology to improve the fine grid printing process of high-efficiency solar cells not only breaks through the line width limitations of traditional screen printing, but also enables easy printing of ultra-narrow line widths. This technology can print ultra-fine grid lines with larger aspect ratios on solar cell silicon wafers, thereby helping the cells meet the standards of ultra-fine dense grid cells and perfectly match the selective emitter technology. This not only improves the efficiency of solar cells, but also significantly reduces the amount of paste used, with paste savings of up to 20% or more, 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, of these two technical routes, laser transfer will save more. Summary of the Invention

[0003] The embodiments of the present application provide a silver paste and a solar cell to solve the problem in the prior art that silver paste has a high probability of false printing and grid breakage during laser transfer.

[0004] To achieve the above-mentioned object, according to one aspect of the present invention, a silver paste is provided, which comprises, 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 of silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprising a C12 or higher alkyl-modified acrylic polymer, a block copolymer of a styrene monomer and an aliphatic diene monomer, and an epoxy resin, the boiling point of the first solvent is 110-260°C, and the second organic carrier comprises cellulose and a second solvent.

[0005] Furthermore, the mass ratio of the above-mentioned C12 or higher alkyl-modified propylene polymer, the block copolymer of styrene monomer and aliphatic diene monomer, and the epoxy resin is (2-8):(7-13):(2-8); and / or, the mass proportion of C12 or higher alkyl groups in the C12 or higher alkyl-modified propylene polymer is 5-50%.

[0006] Furthermore, the above-mentioned C12 and above alkyl-modified propylene polymer is a C12~C22 alkyl-modified propylene polymer; and / or the propylene polymer in the C12 and above alkyl-modified propylene polymer is selected from any one or more of styrene-acrylic acid copolymer, polymethyl methacrylate, methyl methacrylate-butadiene-styrene copolymer, acrylate-acrylonitrile-styrene copolymer, and acrylonitrile-butadiene-styrene copolymer; and / or the number average molecular weight of the C12 and above alkyl-modified propylene polymer is 1700~50000 g / mol.

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

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

[0009] Furthermore, the epoxy resin is selected from any one or more of bisphenol A epoxy resin, novolac 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] Furthermore, the mass ratio of the above-mentioned 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 also includes 0.1~0.5% of a dispersant; and / or, the silver paste also includes 0.3~0.7% of a release agent.

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

[0013] Furthermore, the above-mentioned glass powder includes a first glass powder and a second glass powder; in terms of mass percentage, the first glass powder includes 70~80% lead oxide, 2~20% aluminum oxide, 1~10% zinc oxide and 5~20% boron trioxide; in terms of 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 further includes 0.05-0.3% silicon carbide; and / or the silver paste further includes 0.05-0.3% titanium nitride.

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

[0017] Furthermore, 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 0.5-1 μm, the D50 of the second silver powder is 1-1.2 μm, and the D50 of the third silver powder is 1.2-1.5 μm. 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 a surface of the substrate, wherein the grid lines are prepared by laser transfer of the aforementioned silver paste.

[0019] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0020] This application uses C12 and above alkyl-modified propylene polymers, which have a high degree of molecular chain entanglement, which helps to improve the cohesion of the silver paste and enhance the thixotropy; the addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear thinning properties through microphase separation structure, inhibit demolding splashing, and maintain shape stability after demolding; the addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through cross-linking reaction and reduce the risk of demolding deformation; cellulose can form a three-dimensional network structure in the silver paste, increase the viscosity of the paste, and thus improve the rheological properties of the silver paste during the laser transfer process. Controlling the boiling point of the first solvent within the above range helps to make the decomposition temperature difference between the resin and the first solvent smaller, so that the resin and the first solvent are concentratedly decomposed within a smaller temperature range, promote the formation of a high vapor pressure in the film groove in a short time to promote the demolding of the paste in the groove, and improve the demolding power, thereby helping to reduce the tailing or adhesion of the silver paste during the transfer process, improve the demolding ability of the silver paste, and improve the situation of virtual printing and broken grids. Furthermore, the first solvent having the aforementioned boiling point has a strong polarity. The combination of the resin of the present application and the first solvent helps enhance the cohesive force of the silver paste, giving it strong cohesive force and thixotropy during the transfer process. This prevents splashing during demolding and deformation after demolding, resulting in superior shaping capabilities. Therefore, the silver paste of the present application exhibits excellent demolding, inkjet, and shaping capabilities during laser transfer, significantly reducing the probability of false printing and broken grids. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0022] As analyzed in the background technology of this application, in the prior art, silver paste has a high probability of false printing and broken grid during laser transfer. In order to solve this problem, this application provides a silver paste and a solar cell.

[0023] In a typical embodiment of the present application, a silver paste is provided, which comprises, 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 remainder of silver powder; wherein the first organic carrier comprises a resin and a first solvent, the resin comprises a C12 or higher alkyl-modified acrylic polymer, a block copolymer of a styrene monomer and an aliphatic diene monomer, and an epoxy resin, the boiling point of the first solvent is 110-260° C., and the second organic carrier comprises cellulose and a second solvent.

[0024] This application uses C12 and above alkyl-modified propylene polymers, which have a high degree of molecular chain entanglement, which helps to improve the cohesion of the silver paste and enhance the thixotropy; the addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear thinning properties through microphase separation structure, inhibit demolding splashing, and maintain shape stability after demolding; the addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through cross-linking reaction and reduce the risk of demolding deformation; cellulose can form a three-dimensional network structure in the silver paste, increase the viscosity of the paste, and thus improve the rheological properties of the silver paste during the laser transfer process. Controlling the boiling point of the first solvent within the above range helps to make the decomposition temperature difference between the resin and the first solvent smaller, so that the resin and the first solvent are concentratedly decomposed within a smaller temperature range, promote the formation of a high vapor pressure in the film groove in a short time to promote the demolding of the paste in the groove, and improve the demolding power, thereby helping to reduce the tailing or adhesion of the silver paste during the transfer process, improve the demolding ability of the silver paste, and improve the situation of virtual printing and broken grids. Furthermore, the first solvent having the aforementioned boiling point has a strong polarity. The combination of the resin of the present application and the first solvent helps enhance the cohesive force of the silver paste, giving it strong cohesive force and thixotropy during the transfer process. This prevents splashing during demolding and deformation after demolding, resulting in superior shaping capabilities. Therefore, the silver paste of the present application exhibits excellent demolding, inkjet, and shaping capabilities during laser transfer, significantly reducing the probability of false printing and broken grids.

[0025] It should be noted that each component in the silver paste of the present application can be purchased or prepared using existing technologies.

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

[0027] Controlling the mass ratio of the block copolymer of C12 and higher alkyl-modified propylene polymer, styrene monomer and aliphatic diene monomer, and epoxy resin within the above-mentioned range helps to enhance the synergistic effect between the components, improve the cohesion of the silver paste, and make the silver paste have suitable viscosity and thixotropy during the transfer process, thereby helping to reduce the risk of false printing and broken grids. Controlling the mass ratio of C12 and higher alkyl groups in the propylene polymer modified with C12 and higher alkyl groups within the above-mentioned range helps to form more van der Waals forces and hydrophobic interactions between the polymer molecular chains, thereby enhancing the cohesion of the silver material.

[0028] In one embodiment of the present application, the above-mentioned C12 and above alkyl-modified propylene polymer is a C12~C22 alkyl-modified propylene polymer; and / or, the propylene polymer in the C12 and above alkyl-modified propylene polymer is selected from any one or more of styrene-acrylic acid copolymer, polymethyl methacrylate, methyl methacrylate-butadiene-styrene copolymer, acrylate-acrylonitrile-styrene copolymer, and acrylonitrile-butadiene-styrene copolymer; and / or, the number average molecular weight of the C12 and above alkyl-modified propylene polymer is 1700~50000 g / mol.

[0029] The longer alkyl side chains of C12-C22 alkyl-modified propylene polymers enhance intermolecular interactions, thereby improving the overall cohesion of the silver paste. These propylene polymers possess superior silver powder coating and dispersion stability, enabling a uniform silver powder distribution within 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 achieve an appropriate viscosity and elastic modulus, enabling the formation of a stable molecular network within the paste and enhancing the paste's thixotropy.

[0030] In one embodiment of the present application, the above-mentioned styrene monomer is selected from hydrogenated styrene and / or p-methylstyrene; and / or the aliphatic diene monomer is selected from any one or more of butadiene, propadiene and pentadiene.

[0031] Controlling the content of styrene monomers and aliphatic diene monomers within the above ranges helps to enhance the interaction between the styrene segments and the aliphatic diene segments, thereby helping to further enhance the shear thinning properties of the block copolymer of styrene monomers and aliphatic diene monomers.

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

[0033] In order to further enhance the rigidity of the silver paste network structure and reduce the risk of mold release deformation, in one embodiment of the present application, the above-mentioned epoxy resin is selected from any one or more of bisphenol A 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 during the laser transfer process, in one embodiment of the present application, the above-mentioned 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 printing adaptability of the silver paste, improve the quality of the metallization layer during the sintering process, reduce organic residues, and enhance the mechanical strength and reliability of the metallization layer, in one embodiment of the present 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 the present application, the mass ratio of the above-mentioned 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 the resin to the first solvent within the above range helps improve the interaction between the two, enhancing the cohesion of the silver paste and giving the silver paste stronger cohesion and thixotropy during the transfer process. Controlling the type of the first solvent within the above range, which has strong polarity, 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 above range helps further improve the dispersion stability of cellulose in the silver paste. The addition of dispersants and release agents can further adjust the rheological properties of the paste. Dispersants help evenly distribute silver powder particles in the paste, reduce agglomeration, and improve the stability of the silver paste and printing consistency. Release agents promote the release of the paste from the mold during the printing process, further improving tailing and adhesion during the paste transfer process. Controlling the mass ratio of the dispersant and release agent within the above range helps further optimize the printing efficiency and precision of the silver paste in the laser transfer process.

[0038] In order to further improve the cohesive force of the silver paste and make the silver paste have stronger cohesive force and thixotropy during the transfer process, in one embodiment of the present application, the above-mentioned 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, any one or more of the above dispersants selected from TDO dispersant, Brij-L4 dispersant, lauric acid and polyhydroxystearic acid.

[0040] In one embodiment of the present 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, which helps to enhance the compatibility between the release agent and silver powder, reduce interface stratification problems, and help reduce the viscosity of the slurry, improve printing fluidity, and at the same time help to form a micron-level isolation layer to reduce demolding residue.

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

[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 the present application, the above-mentioned glass powder includes a first glass powder and a second glass powder; in terms of mass percentage, the first glass powder includes 70~80% lead oxide, 2~20% aluminum oxide, 1~10% zinc oxide and 5~20% boron trioxide; in terms of 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 glass powder, due to its high lead content and appropriate ratio of aluminum, zinc, and boron, can reduce the sintering temperature, promote the fusion of silver powder particles, and form a low-resistance conductive path. The low melting point of the lead-based glass powder helps form a dense silver layer during the sintering process, reducing voids and microcracks, thereby reducing contact resistance and improving the battery's conductivity. The high barium content in the second glass powder optimizes the protection of the passivation layer during sintering. During sintering, the barium-based glass powder forms a shielding layer that absorbs and disperses laser energy, reducing direct thermal damage to the passivation layer on the silicon wafer surface.

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

[0046] Controlling the mass ratio of the first glass powder to 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 to avoid damaging the light absorption structure and electrical properties of the silicon wafer surface.

[0047] In one embodiment of the present 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 the silver paste can help reduce the direct energy impact of the laser on the passivation layer through photothermal conversion, concentrate the laser energy inside the paste, and reduce the risk of thermal damage to the passivation layer interface.

[0049] In order to further improve the light-to-heat conversion efficiency, in one embodiment of the present application, the D50 of the silicon carbide is 20-50 nm; and / or the D50 of the titanium nitride is 20-50 nm.

[0050] In one embodiment of the present 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 0.5-1 μm, the D50 of the second silver powder is 1-1.2 μm, and the D50 of the third silver powder is 1.2-1.5 μm. 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 silver powder can better penetrate the laser-transferred film grooves, forming a continuous, clear grid line 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 the sintering process. Large-particle silver powder melts and connects with each other 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 the present application, the method for preparing the silver paste includes:

[0053] (1) The raw materials used for the first organic carrier are mixed according to the proportion, mixed evenly using a dispersing, emulsifying and stirring machine, heated at a constant temperature of 90-110°C, dissolved evenly, and filtered after cooling to obtain the first organic carrier.

[0054] (2) The raw materials used for the second organic carrier are mixed according to the proportion, mixed evenly using a dispersing, emulsifying and stirring machine, heated at a constant temperature of 90-110°C, dissolved evenly, and filtered 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 them evenly. Place the centrifuge tube in a centrifuge and centrifuge it 1-2 times at a speed of 700-900 rpm for 1-2 minutes each time. After the ionization is completed, place it in a three-roll mill for the first three-roll milling process. The roller spacing of the three-roll mill is 20-30 μm and the speed is 300-400 rpm to obtain a glass slurry.

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

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

[0058] Since the grid lines in the solar cell are prepared by laser transfer of the silver paste of the present application, the solar cell has a longer service life and higher photoelectric conversion efficiency.

[0059] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

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

[0061] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0062] The following describes the various embodiments of the present application in detail. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to help readers better understand the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0063] Example 1

[0064] The silver paste consists of 89.5% silver powder, 2.4% glass powder (D50 is 1.2 μm), 0.05% silicon carbide (D50 is 30 nm), 0.05% titanium nitride (D50 is 30 nm), 5.7% first organic vehicle, 1.5% second organic vehicle, 0.3% dispersant, and 0.5% release agent, calculated by mass.

[0065] 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 0.8 μm, the D50 of the second silver powder is 1.1 μm, and the D50 of the third silver powder is 1.3 μm, and 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, the mass ratio of the first glass powder to the second glass powder is 1.3:0.7, and the composition of the first glass powder is 72% PbO, 10% Al2O3, 4% ZnO and 14% B2O3 by mass; the composition of the second glass powder is 60% PbO, 20% Al2O3, 16% BaO and 4% B2O3 by mass;

[0067] Based on the total mass percentage of the first organic carrier as 100%, the first organic carrier includes 5% of a C18 linear alkyl-modified styrene-acrylic acid copolymer (number average molecular weight of 5000 g / mol, and the mass proportion of the C18 linear alkyl group is 25%), 10% of a hydrogenated styrene-butadiene block copolymer (weight average molecular weight of 100,000 g / mol), 5% of a bisphenol A epoxy resin (number average molecular weight of 5000 g / mol), 30% of butyl acetate (boiling point of 126° C.), 10% of methyl isobutyl ketone (boiling point of 126° C.), and 40% of diethylene glycol butyl ether acetate (boiling point of 245° C.);

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

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

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

[0071] (1) The raw materials used for the first organic carrier are mixed according to the above ratio, mixed evenly using a dispersing, emulsifying and stirring machine, heated at a constant temperature of 100° C. to dissolve evenly, and filtered after cooling to obtain the first organic carrier.

[0072] (2) The raw materials used for the second organic carrier are mixed according to the above ratio, mixed evenly using a dispersing, emulsifying and stirring machine, heated at a constant temperature of 100° C. to dissolve evenly, and filtered after cooling to obtain the second organic carrier.

[0073] (3) The second organic carrier, dispersant, silicon carbide, titanium nitride, and glass powder were added to a centrifuge tube and mixed evenly. The centrifuge tube was placed in a centrifuge and centrifuged once at 800 rpm for 1 min. After the ionization, the tube was placed in a three-roll mill for the first three-roll milling process. The roller spacing of the three-roll mill was 20 μm and the speed was 300 rpm to obtain a glass slurry.

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

[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 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 epoxy resin is 2:13:2, and silver paste is finally obtained.

[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 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 epoxy resin is 9:6:9, and silver paste is finally obtained.

[0079] Example 4

[0080] The difference from Example 1 is that the mass proportion of C18 straight-chain alkyl is 40%, and silver paste is finally obtained.

[0081] Example 5

[0082] The difference from Example 1 is that the mass proportion of C18 straight-chain alkyl is 3%, and silver paste is finally obtained.

[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, and a silver paste is finally obtained.

[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, and a silver paste is finally obtained.

[0087] Example 8

[0088] The difference from Example 1 is that a C30 linear alkyl-modified styrene-acrylic acid copolymer is used to replace the C18 linear alkyl-modified styrene-acrylic acid copolymer, and finally a silver paste is 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, and a silver paste is finally obtained.

[0091] Example 10

[0092] The difference from Example 1 is that the number average molecular weight of the bisphenol A epoxy resin is 10,000 g / mol, and a silver paste is finally obtained.

[0093] Example 11

[0094] The difference from Example 1 is that all cellulose acetate butyrate is replaced by ethyl cellulose to finally obtain 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, and finally a silver paste is obtained.

[0097] Example 13

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

[0101] Example 15

[0102] The difference from Example 1 is that the second silver powder and the third silver powder are all replaced by the first silver powder, and finally the 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 vehicle, 2.1% second organic vehicle, 0.5% dispersant, and 0.7% release agent.

[0105] 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 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, and 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, the mass ratio of the first glass powder to the second glass powder is 1.5:0.5, and the composition of the first glass powder is 80% PbO, 5% Al2O3, 10% ZnO and 5% B2O3 by mass percentage; the composition of the second glass powder is 60% PbO, 20% Al2O3, 10% BaO and 10% B2O3 by mass percentage;

[0107] Based on the total mass percentage of the first organic carrier as 100%, the first organic carrier includes 8% of C22 linear alkyl-modified polymethyl methacrylate (number average molecular weight of 5000 g / mol, mass proportion of C22 linear alkyl group is 5%), 7% of p-methylstyrene-butadiene block copolymer (weight average molecular weight of 170000 g / mol), 5% of phenolic polyepoxy resin (number average molecular weight of 4800 g / mol), 25% of butyl acetate (boiling point of 126°C), 15% of methyl isobutyl ketone (boiling point of 126°C), and 40% of diethylene glycol butyl ether acetate (boiling point of 245°C);

[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 50mm 2 / s) and amino silicone oil (viscosity 600mm 2 / s), and the mass ratio of dimethyl silicone oil to amino silicone oil is 5:5, and finally a silver paste is obtained.

[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: 1.4 μm), 0.1% silicon carbide (D50: 20 nm), 0.1% titanium nitride (D50: 20 nm), 0.79% first organic vehicle, 0.21% second organic vehicle, 0.1% dispersant, and 0.3% release agent.

[0112] 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 μm, the D50 of the second silver powder is 1 μm, and the D50 of the third silver powder is 1.2 μm, and 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, the mass ratio of the first glass powder to the second glass powder is 1:1, and the composition of the first glass powder is 70% PbO, 20% Al2O3, 1% ZnO and 9% B2O3 by mass; the composition of the second glass powder is 70% PbO, 15% Al2O3, 14% BaO and 1% B2O3 by mass;

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

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

[0117] Comparative Example 1

[0118] The difference from Example 1 is that the addition of the C18 linear alkyl-modified styrene-acrylic acid copolymer is eliminated, and a silver paste is finally obtained.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the addition of hydrogenated styrene-butadiene block copolymer is eliminated, and a silver paste is finally obtained.

[0121] Comparative Example 3

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

[0123] Comparative Example 4

[0124] The difference from Example 1 is that the addition of ethyl cellulose and cellulose acetate butyrate is eliminated, and a silver paste is finally obtained.

[0125] Comparative Example 5

[0126] The difference from Example 1 is that styrene-acrylic acid copolymer is used to replace the C18 linear alkyl modified styrene-acrylic acid copolymer, and finally the silver paste is obtained.

[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 finally a silver paste is obtained.

[0129] Comparative Example 7

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

[0131] The silver paste prepared in the embodiment and the comparative example was laser transferred and printed to obtain electrode sheets. The number of electrode sheets with virtual printing and broken gates in the batch-produced electrode sheets was observed using a silk screen AOI inspection device, and the proportion of the number of virtual printed electrode sheets and the proportion of the number of broken gate electrode sheets detected by AOI were recorded. The results are shown in Table 1. The silver paste prepared in the embodiment and the comparative example was laser transferred and then sintered on a crystalline silicon cell to form an electrode to obtain a solar cell. The solar cell was tested for photoelectric conversion efficiency, open circuit voltage, short circuit current and fill factor. The test results are shown in Table 2.

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0137] This application uses C12 and above alkyl-modified propylene polymers, which have a high degree of molecular chain entanglement, which helps to improve the cohesion of the silver paste and enhance the thixotropy; the addition of block copolymers of styrene monomers and aliphatic diene monomers helps to provide shear thinning properties through microphase separation structure, inhibit demolding splashing, and maintain shape stability after demolding; the addition of epoxy resin helps to enhance the rigidity of the silver paste network structure through cross-linking reaction and reduce the risk of demolding deformation; cellulose can form a three-dimensional network structure in the silver paste, increase the viscosity of the paste, and thus improve the rheological properties of the silver paste during the laser transfer process. Controlling the boiling point of the first solvent within the above range helps to make the decomposition temperature difference between the resin and the first solvent smaller, so that the resin and the first solvent are concentratedly decomposed within a smaller temperature range, promote the formation of a high vapor pressure in the film groove in a short time to promote the demolding of the paste in the groove, and improve the demolding power, thereby helping to reduce the tailing or adhesion of the silver paste during the transfer process, improve the demolding ability of the silver paste, and improve the situation of virtual printing and broken grids. Furthermore, the first solvent having the aforementioned boiling point has a strong polarity. The combination of the resin of the present application and the first solvent helps enhance the cohesive force of the silver paste, giving it strong cohesive force and thixotropy during the transfer process. This prevents splashing during demolding and deformation after demolding, resulting in superior shaping capabilities. Therefore, the silver paste of the present application exhibits excellent demolding, inkjet, and shaping capabilities during laser transfer, significantly reducing the probability of false printing and broken grids.

[0138] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A silver paste, characterized in that: Measured 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; 1~4wt% glass powder; The balance is silver powder; wherein, the first organic carrier comprises a resin and a first solvent, the resin comprises a C12 and above alkyl-modified acrylic polymer, a block copolymer of a styrene monomer and a fatty diene monomer, and an epoxy resin, the boiling point of the first solvent is 110~260°C, and the second organic carrier comprises cellulose and a second solvent.

2. The silver paste according to claim 1, characterized in that The mass ratio of the C12 and above alkyl-modified propylene polymer, the block copolymer of the styrene monomer and the aliphatic diene monomer, and the epoxy resin is (2-8): (7-13): (2-8); And / or, the mass proportion of C12 and above alkyl groups in the C12 and above alkyl-modified propylene polymer is 5-50%.

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

4. The silver paste according to claim 1, characterized in that The styrene monomer is selected from hydrogenated styrene and / or p-methylstyrene; And / or, the aliphatic diene monomer is selected from any one or more of butadiene, propadiene 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 50,000-400,000 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 epoxy resin, novolac polyepoxy resin and glycerol epoxy resin; and / or the number average molecular weight of the epoxy resin is 300-7000 g / mol.

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 comprises 0.1-0.5% of a dispersant; And / or, the silver paste further comprises 0.3-0.7% of a release agent.

9. The silver paste according to any one of claims 1 to 5, characterized in that The D50 of the glass powder is 1.0-1.4 μm.

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; Measured in mass percentage, the first glass powder comprises 70-80% lead oxide, 2-20% aluminum oxide, 1-10% zinc oxide, and 5-20% boron trioxide; Calculated 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.

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 D50 of the silicon carbide is 20-50 nm; and / or the D50 of the titanium nitride is 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 D50 of the first silver powder is 0.5-1 μm, the D50 of the second silver powder is 1-1.2 μm, the D50 of the third silver powder is 1.2-1.5 μm, and 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: The invention comprises a substrate and grid lines formed on the surface of the substrate, wherein the grid lines are prepared by laser transfer of the silver paste according to any one of claims 1 to 14.

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