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 silver powder, glass powder and an organic carrier, and the glass powder comprises, by mass, 20%-30% of Bi2O3, 30%-40% of TeO2, 8%-18% of H3BO3, 6%-16% of PbO, 1%-10% of SiO2, 1%-5% of ZnO, 0.5%-5% of Al2O3, 0.1%-1% of Ag2O and 1%-10% of alkali metal oxide. The content of each component in the glass powder is controlled within the range, so that the glass powder has higher fluidity and lower etching capability, the silver powder can be well infiltrated in the sintering process, more silver microcrystals can be carried to a grid line interface, and meanwhile, the high-fluidity glass can form a thinner glass layer on a bottom silicon substrate, so that the corrosion resistance of the glass powder is improved, and the service life of the glass powder is prolonged. Therefore, the contact resistance between the grid line and the silicon substrate is reduced, and the photoelectric conversion efficiency of the solar cell is improved.

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] Solar energy, as a clean energy source, is inexhaustible, pollution-free, and environmentally friendly, attracting widespread attention. Surface passivation technology, with its advantages of high efficiency, high bifaciality, and low cost, has become a mainstream product in the photovoltaic industry in recent years.

[0003] The efficiency of N-type Topcon solar cells is closely related to the electrode material. The electrode material consists of three components: conductive metal powder, glass powder, and an organic component. Currently, the glass powder used in the back-grid fine grid paste suffers from insufficient fluidity. The glass lacks good softening fluidity during the interfacial reaction, preventing it from dissolving more liquid silver and reaching the P+ emitter. Subsequently, as the glass cools, nanosilver crystals precipitate, resulting in high contact resistance between the grid line and the silicon wafer, and the cell exhibits a low breakout voltage and low fill. Summary of the Invention

[0004] The main purpose of the present invention is to provide a silver paste and a solar cell to solve the problem of high interface contact resistance between the gate line and the silicon wafer in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a silver paste is provided, which, based on the total mass of the silver paste, comprises 80-93% of silver powder, 0.5-5% of glass powder and 5-15% of an organic vehicle. Based on the total mass of the glass powder, the glass powder comprises: 20-30% of Bi2O3, 30-40% of TeO2, 8-18% of H3BO3, 6-16% of PbO, 1-10% of SiO2, 1-5% of ZnO, 0.5-5% of Al2O3, 0.1-1% of Ag2O and 1-10% of alkali metal oxides.

[0006] Furthermore, the glass powder includes, by mass percentage, 23-27% Bi2O3, 36-40% TeO2, 11-15% H3BO3, 9-13% PbO, 3-7% SiO2, 1-3% ZnO, 1-3% Al2O3, 0.3-0.7% Ag2O and 3-7% alkali metal oxides.

[0007] Furthermore, the mass ratio of the above-mentioned H3BO3 to PbO is (1-1.67):1; and / or the mass ratio of Bi2O3 to TeO2 is (0.65-0.7):1.

[0008] Furthermore, the alkali metal oxide is selected from any one or more of Na2O, Li2O and K2O.

[0009] Furthermore, the alkali metal oxide is a combination of Na2O and Li2O, and the mass ratio of Na2O to Li2O is (0.25-1.5):1.

[0010] Furthermore, the D50 of the glass powder is 0.8 to 1.2 μm.

[0011] Furthermore, the Tg point temperature of the glass powder is 262-287°C; and / or the hemisphere point temperature of the glass powder is 458-549°C.

[0012] Furthermore, the D50 of the silver powder is 1 to 3 μm; and / or the organic carrier comprises a resin, a solvent, a thixotropic agent and a release agent, and the mass ratio of the resin, the solvent, the thixotropic agent and the release agent is (30 to 60): (25 to 40): (35 to 90): (0.5 to 3); the resin is selected from any one or more of PMMA480S resin, ethyl cellulose, diethylene glycol monobutyl ether, diethylene glycol butyl ether acetate, alcohol ester-12, tributyl citrate, polyamide wax, and polyethylene wax; the solvent is selected from any one or more of butyl butyl acetate, tributyl citrate, triethylene glycol butyl ether, butyl acrylate, and benzyl butyl phthalate; the thixotropic agent is selected from any one or more of ThixatrolMAX thixotropic agent, ThixatrolPlus thixotropic agent, ET7020 thixotropic agent, BASF CO40 thixotropic agent, and RS3500 thixotropic agent; and the release agent is selected from methyl silicone oil and / or amino silicone oil.

[0013] Furthermore, the resin is a combination of PMMA480S resin and diethylene glycol butyl ether acetate, and the mass ratio of PMMA480S resin to diethylene glycol butyl ether acetate is (20-35): (10-25).

[0014] According to another aspect of the present invention, a solar cell is provided, comprising a substrate and a grid line formed on a surface of the substrate, wherein the grid line is prepared by the aforementioned silver paste.

[0015] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0016] In this application, the presence of bismuth oxide can help lower the melting point of glass, enhance wettability to silver paste to reduce contact resistance, and protect the passivation layer from metal diffusion through chemical inertness; tellurium oxide, as the main glass network former, can reduce glass viscosity and improve light transmittance after sintering; the presence of H3BO3 can reduce the amount of PbO used, improve the fluidity of glass at high temperatures, and reduce the etching ability of glass, thereby helping to reduce the contact resistance of the grid line; the presence of lead oxide helps to regulate the melting temperature of glass and balance the thermal expansion coefficient with the compatibility of silicon substrate; silicon oxide, as a secondary network former, improves the mechanical strength and high-temperature stability of the glass structure; zinc oxide inhibits interfacial oxidation reaction and enhances the adhesion of glass to silver paste; the presence of Al2O3 helps to strengthen the network structure and improve the chemical stability and high-temperature mechanical strength of glass; the presence of Ag2O facilitates the diffusion of silver and interfacial reaction with silicon, reducing contact resistance; the presence of alkali metal oxides helps to lower the melting point and viscosity of glass, thereby improving the fluidity of glass at high temperatures. Controlling the content of each component in the glass powder within the above range helps the glass powder of the present application have higher fluidity and lower etching ability, can form good infiltration of silver powder during the sintering process, and carry more silver microcrystals to the grid line interface. At the same time, high-fluidity glass can form a thinner glass layer on the bottom silicon base, thereby reducing the contact resistance between the grid line and the silicon substrate and improving the photoelectric conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] One or more embodiments are exemplified by the figures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 The figure shows the deposition of glass powder at the interface between the silicon wafer and the gate line after the glass powder slurry is sintered in Example 1 of the present application;

[0019] Figure 2 The figure shows the deposition of glass powder at the interface between the silicon wafer and the gate line after the slurry prepared by glass powder is sintered in Comparative Example 1 of the present application;

[0020] Figure 3 shows an optical photograph of the glass powder in Example 1 of the present application at 740°C;

[0021] Figure 4 An optical photograph of the glass powder in Comparative Example 1 of the present application at 740° C. is shown. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] Term explanation: The Tg point temperature of glass powder refers to the temperature at which the glass changes from a hard and brittle solid state to a flowable state; the hemisphere point temperature of glass powder refers to the temperature at which the glass powder begins to form hemispherical molten droplets after being heated to a sufficient temperature.

[0024] As analyzed in the background technology of this application, the prior art has the problem of large contact resistance between the gate line and the silicon wafer interface. In order to solve the above problem, this application provides a silver paste and a solar cell.

[0025] In a typical embodiment of the present application, a silver paste is provided, which, based on the total mass of the silver paste, comprises 80-93% silver powder, 0.5-5% glass powder and 5-15% of an organic vehicle. Based on the total mass of the glass powder, the glass powder comprises: 20-30% Bi2O3, 30-40% TeO2, 8-18% H3BO3, 6-16% PbO, 1-10% SiO2, 1-5% ZnO, 0.5-5% Al2O3, 0.1-1% Ag2O and 1-10% alkali metal oxide.

[0026] In this application, the presence of bismuth oxide can help lower the melting point of glass, enhance wettability to silver paste to reduce contact resistance, and protect the passivation layer from metal diffusion through chemical inertness; tellurium oxide, as the main glass network former, can reduce glass viscosity and improve light transmittance after sintering; the presence of H3BO3 can reduce the amount of PbO used, improve the fluidity of glass at high temperatures, and reduce the etching ability of glass, thereby helping to reduce the contact resistance of the grid line; the presence of lead oxide helps to regulate the melting temperature of glass and balance the thermal expansion coefficient with the compatibility of silicon substrate; silicon oxide, as a secondary network former, improves the mechanical strength and high-temperature stability of the glass structure; zinc oxide inhibits interfacial oxidation reaction and enhances the adhesion of glass to silver paste; the presence of Al2O3 helps to strengthen the network structure and improve the chemical stability and high-temperature mechanical strength of glass; the presence of Ag2O facilitates the diffusion of silver and interfacial reaction with silicon, reducing contact resistance; the presence of alkali metal oxides helps to lower the melting point and viscosity of glass, thereby improving the fluidity of glass at high temperatures. Controlling the content of each component in the glass powder within the above range helps the glass powder of the present application have higher fluidity and lower etching ability, can form good infiltration of silver powder during the sintering process, and carry more silver microcrystals to the grid line interface. At the same time, high-fluidity glass can form a thinner glass layer on the bottom silicon base, thereby reducing the contact resistance between the grid line and the silicon substrate and improving the photoelectric conversion efficiency of the solar cell.

[0027] In order to further improve the fluidity of the glass powder at high temperature and reduce the etching ability, in one embodiment of the present application, the glass powder includes, by mass percentage: 23-27% Bi2O3, 36-40% TeO2, 11-15% H3BO3, 9-13% PbO, 3-7% SiO2, 1-3% ZnO, 1-3% Al2O3, 0.3-0.7% Ag2O and 3-7% alkali metal oxides.

[0028] In one embodiment of the present application, the mass ratio of the above-mentioned H3BO3 to PbO is (1-1.67):1, specifically 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.67:1 and a range value between any two ratios; and / or, the mass ratio of Bi2O3 to TeO2 is (0.65-0.7):1, specifically 0.65:1, 0.66:1, 0.67:1, 0.68:1, 0.69:1, 0.7:1 and a range value between any two ratios.

[0029] H3BO3, as a network modifier, increases fluidity in glass, while PbO also lowers the softening point of glass, improving fluidity and sintering performance. Controlling the H3BO3 to PbO mass ratio within the aforementioned range helps improve the fluidity of the glass at high temperatures while reducing SiN etching, thereby boosting the photoelectric conversion efficiency of solar cells. Controlling the Bi2O3 to TeO2 mass ratio within the aforementioned range further lowers the Tg and hemisphere temperatures of the glass frit, improving the fluidity of the glass at high temperatures and thus reducing contact resistance.

[0030] In one embodiment of the present application, the mass ratio of the above-mentioned SiO2 to ZnO is (2-5):1, specifically 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1 and a range value between any two ratios.

[0031] SiO2 acts as a flux during the high-temperature sintering process, which can lower the melting temperature of the glass powder and improve its fluidity, thereby enabling the silver powder to better contact with the silicon substrate; ZnO can form a good interface contact between the silver electrode and the silicon substrate. Controlling the mass ratio of SiO2 to ZnO within the above range helps to improve the mutual synergy between the two, thereby helping to further reduce contact resistance and improve the photoelectric conversion efficiency of solar cells.

[0032] In one embodiment of the present application, the alkali metal oxide is selected from any one or more of Na2O, Li2O and K2O.

[0033] Controlling the type of alkali metal oxide within the above range helps reduce the melting temperature and melt viscosity of the glass powder, promoting its fluidity and diffusion during high-temperature sintering. This helps form a more uniform silver electrode layer on the cell surface, enhancing the effectiveness of the silver-silicon contact, reducing contact resistance, and improving the bonding strength between the electrode and the silicon substrate, thereby improving the overall efficiency of the cell.

[0034] In one embodiment of the present application, the alkali metal oxide is a combination of Na2O and Li2O, and the mass ratio of Na2O to Li2O is (0.25-1.5):1.

[0035] Controlling the mass ratio of Na2O to Li2O within the above range helps to improve the interaction between the two, thereby helping to further reduce the sintering temperature of the glass and improve the fluidity of the glass at high temperatures, thereby helping to further reduce the contact resistance.

[0036] In one embodiment of the present application, the glass powder has a D50 of 0.8 to 1.2 μm and a D100 of less than 4 μm.

[0037] Controlling the D50 of the glass powder within the above range helps to improve the uniformity of the glass powder distribution during the printing process of the silver paste. Controlling the D100 of the glass powder within the above range helps to improve the screen passability of the glass powder under low line width screens.

[0038] In one embodiment of the present application, the Tg point temperature of the glass powder is 262-287°C; and / or the hemisphere point temperature of the glass powder is 458-549°C.

[0039] The glass powder having the above-mentioned Tg point temperature and hemisphere point temperature has a lower sintering temperature, and the silver paste formed therefrom has a better contact interface with the silicon substrate, thereby helping to reduce contact resistance and improve the photoelectric conversion efficiency of solar cells.

[0040] In one embodiment of the present application, the D50 of the silver powder is 1 to 3 μm; and / or the organic carrier includes a resin, a solvent, a thixotropic agent and a release agent, and the mass ratio of the resin, the solvent, the thixotropic agent and the release agent is (30 to 60): (25 to 40): (35 to 90): (0.5 to 3); the resin is selected from any one or more of PMMA480S resin, ethyl cellulose, diethylene glycol monobutyl ether, diethylene glycol butyl ether acetate, alcohol ester-12, tributyl citrate, polyamide wax, and polyethylene wax; the solvent is selected from any one or more of butyl butyl acetate, tributyl citrate, triethylene glycol butyl ether, butyl acrylate, and benzyl butyl phthalate; the thixotropic agent is selected from any one or more of ThixatrolMAX thixotropic agent, ThixatrolPlus thixotropic agent, ET7020 thixotropic agent, BASF CO40 thixotropic agent, and RS3500 thixotropic agent; and the release agent is selected from methyl silicone oil and / or amino silicone oil.

[0041] Controlling the D50 of the silver powder within the above range helps to form a denser silver layer, thereby reducing contact resistance, improving the conductivity of the electrode, and helping to improve the printing performance of the silver paste during screen printing. The presence of resin and solvent gives the silver paste suitable fluidity and viscosity, making it easy to print, while also adhering to the surface of the battery cell to form a uniform coating. The presence of a thixotropic agent helps to regulate the thixotropic properties of the silver paste, allowing the thickness of the printed layer to be precisely controlled during the printing process. The presence of a release agent helps with demolding before sintering, while also reducing the formation of organic residues during the sintering process and reducing the negative impact on electrode performance. Controlling the mass ratio of resin, solvent, thixotropic agent and release agent within the above range is more conducive to the printing of silver paste. Controlling the types of resin, solvent, thixotropic agent and release agent within the above range helps to improve the interaction between the components, thereby helping to further improve the printing efficiency of the silver paste.

[0042] In one embodiment of the present application, the resin is a combination of PMMA480S resin and diethylene glycol butyl ether acetate, and the mass ratio of PMMA480S resin to diethylene glycol butyl ether acetate is (20-35): (10-25).

[0043] Controlling the mass ratio of PMMA480S resin and diethylene glycol butyl ether acetate within the above range helps to improve the film-forming properties, fluidity and controllability of the silver paste during the sintering process, thereby helping to improve the photoelectric conversion efficiency of the cell.

[0044] In one embodiment of the present application, the solvent is a combination of butyl anhydride acetate and butyl acrylate, and the mass ratio of butyl anhydride acetate to butyl acrylate is (20-40):(5-20).

[0045] Controlling the mass ratio of butyl acrylate to butyl anhydride acetate within the above range helps to improve the uniformity and stability of the silver paste.

[0046] In one embodiment of the present application, the thixotropic agent is a combination of Thixatrol MAX thixotropic agent and Thixatrol Plus thixotropic agent, and the mass ratio of Thixatrol MAX thixotropic agent to Thixatrol Plus thixotropic agent is (20-30): (5-10).

[0047] Thixatrol MAX thixotropic agent has good shear thinning properties, making it suitable for high-speed printing. It can quickly respond to the movement of the cutter head, causing the paste to quickly thin during printing and restore viscosity after printing, maintaining the clarity and dimensional stability of the printed pattern. The addition of Thixatrol Plus thixotropic agent helps to enhance the stability of the silver paste. Controlling the mass ratio of Thixatrol MAX thixotropic agent to Thixatrol Plus thixotropic agent within the above range helps to improve the thixotropy and printing performance of the paste, while enhancing the stability of the paste, optimizing the sintering process, and ultimately improving the photoelectric conversion efficiency of solar cells.

[0048] In one embodiment of the present application, the preparation method of the above-mentioned glass powder includes the following steps: fully mixing the raw materials of the glass powder, heating and melting at 900-1100°C for 20-40 minutes; then cooling to obtain glass crushed flakes, and then grinding to obtain glass powder with the desired particle size distribution.

[0049] The raw materials of the glass powder can be selectively added with corresponding metal oxides or compounds that can be heated to form corresponding metal oxides according to the composition of the glass powder. When heating and melting, it can be carried out in a resistance furnace.

[0050] The preparation method of the glass powder of the present invention has no special requirements for the cooling operation, and the cooling can be carried out by water quenching or a stainless steel roller mill.

[0051] In the method for preparing the glass powder of the present invention, the purpose of grinding is to obtain a desired particle size. For example, ball milling can be performed using a planetary ball mill to obtain glass powder with a desired particle size distribution.

[0052] In another typical embodiment of the present application, a solar cell is provided, comprising a substrate and a grid line formed on a surface of the substrate, wherein the grid line is prepared by the aforementioned silver paste.

[0053] Since the grid lines in the solar cell are prepared using the silver paste of the present application, the solar cell has a higher photoelectric conversion efficiency.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of 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.

[0058] Example 1

[0059] TeO2, Bi2O3, H3BO3, PbO, SiO2, ZnO, Al2O3, Na2O, Li2O and Ag2O are fully mixed in a mixer, the mixed materials are heated and melted in a resistance furnace at 1100°C for 40 minutes, and then cooled by water quenching to obtain glass crushed pieces, which are ground by a planetary ball mill to obtain glass powder with D50 of 1 μm and D100 less than 4 μm. In terms of mass percentage, the glass powder includes: 25% Bi2O3, 37% TeO2, 8% H3BO3, 16% PbO, 5% SiO2, 1.5% ZnO, 2% Al2O3, 2% Na2O, 3% Li2O and 0.5% Ag2O.

[0060] In terms of mass percentage, 88% of silver powder (D50 is 2 μm), 2% of the above-mentioned glass powder and 10% of an organic vehicle are mixed and stirred uniformly, and then slurried, filtered and slurried to obtain a silver paste, wherein the organic vehicle includes PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50, and the mass ratio of PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50 is 30:20:25:7:30:10:2.

[0061] Example 2

[0062] The difference from Example 1 is that the mass proportion of H3BO3 in the glass powder is 11%, the mass proportion of PbO is 13%, and the mass ratio of H3BO3 to PbO is 0.85:1, and finally a silver paste is obtained.

[0063] Example 3

[0064] The difference from Example 1 is that the mass proportion of H3BO3 in the glass powder is 15%, the mass proportion of PbO is 9%, and the mass ratio of H3BO3 to PbO is 1.67:1, and finally a silver paste is obtained.

[0065] Example 4

[0066] The difference from Example 1 is that the mass proportion of H3BO3 in the glass powder is 18%, the mass proportion of PbO is 6%, and the mass ratio of H3BO3 to PbO is 3:1, and finally a silver paste is obtained.

[0067] Example 5

[0068] The difference from Example 1 is that the mass proportion of Bi2O3 in the glass powder is 23%, the mass proportion of TeO2 is 39%, and the mass ratio of Bi2O3 to TeO2 is 0.59:1, and finally a silver paste is obtained.

[0069] Example 6

[0070] The difference from Example 1 is that the mass proportion of Bi2O3 in the glass powder is 27%, the mass proportion of TeO2 is 35%, and the mass ratio of Bi2O3 to TeO2 is 0.77:1, and finally a silver paste is obtained.

[0071] Example 7

[0072] The difference from Example 1 is that the mass proportion of Bi2O3 in the glass powder is 30%, the mass proportion of TeO2 is 32%, and the mass ratio of Bi2O3 to TeO2 is 0.94:1, and finally a silver paste is obtained.

[0073] Example 8

[0074] The difference from Example 1 is that the mass proportion of Na2O in the glass powder is 1%, and the mass proportion of Li2O is 4%, and finally a silver paste is obtained.

[0075] Example 9

[0076] The difference from Example 1 is that the mass proportion of Na2O in the glass powder is 3%, and the mass proportion of Li2O is 2%, and finally a silver paste is obtained.

[0077] Example 10

[0078] The difference from Example 1 is that the mass proportion of Na2O in the glass powder is 4%, and the mass proportion of Li2O is 1%, and finally a silver paste is obtained.

[0079] Example 11

[0080] The difference from Example 1 is that, in terms of mass percentage, the glass powder includes: 25% Bi2O3, 37% TeO2, 11% H3BO3, 13% PbO, 6.7% SiO2, 1% ZnO, 1% Al2O3, 2% Na2O, 3% Li2O and 0.3% Ag2O, and finally a silver paste is obtained.

[0081] Example 12

[0082] The difference from Example 1 is that, in terms of mass percentage, the glass powder includes: 25% Bi2O3, 37% TeO2, 11% H3BO3, 13% PbO, 3.3% SiO2, 2% ZnO, 3% Al2O3, 2% Na2O, 3% Li2O and 0.7% Ag2O, and finally a silver paste is obtained.

[0083] Example 13

[0084] The difference from Example 1 is that, in terms of mass percentage, the glass powder includes: 25% Bi2O3, 38% TeO2, 8% H3BO3, 16% PbO, 2.4% SiO2, 5% ZnO, 0.5% Al2O3, 2% Na2O, 3% Li2O and 0.1% Ag2O, and finally a silver paste is obtained.

[0085] Example 14

[0086] The difference from Example 1 is that the organic vehicle includes PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50, and the mass ratio of PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50 is 35:10:30:5:40:20:0.5.

[0087] Example 15

[0088] The difference from Example 1 is that the organic vehicle includes PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50, and the mass ratio of PMMA480S resin, diethylene glycol butyl ether acetate, Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, butyl anhydride acetate, butyl acrylate and silicone oil AK50 is 20:25:20:10:20:5:3.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that, in terms of mass percentage, the glass powder includes: 25% Bi2O3, 37% TeO2, 0% H3BO3, 24% PbO, 5% SiO2, 1.5% ZnO, 2% Al2O3, 2% Na2O, 3% Li2O and 0.5% Ag2O, and finally a silver paste is obtained.

[0091] Comparative Example 2

[0092] The difference from Example 1 is that, in terms of mass percentage, the glass powder includes: 25% Bi2O3, 37% TeO2, 3% H3BO3, 21% PbO, 5% SiO2, 1.5% ZnO, 2% Al2O3, 2% Na2O, 3% Li2O and 0.5% Ag2O, and finally a silver paste is obtained.

[0093] Solar cell preparation

[0094] The silver paste prepared in the examples and comparative examples was printed and then sintered on crystalline silicon cells to form electrodes, and then assembled to obtain solar cells.

[0095] Performance Testing

[0096] The Tg point temperature of the glass powder was detected using a Mettler DsC device (test conditions: Al crucible, sample mass 8 mg, heating rate 10°C / min); the hemisphere point temperature of the glass powder was measured using a high-temperature microscope HM867 instrument (heating rate 23-300°C: 15°C / min; 300-750°C: 5°C / min).

[0097] Contact resistance and contact resistivity test: The test methods and standards are in accordance with the industry standard T / CPIA0051-2023 issued by the Photovoltaic Industry Association.

[0098] The glass powders prepared in the examples and comparative examples were tested for Tg point temperature and hemisphere point temperature. The test results are shown in Table 1.

[0099] The solar cells prepared in the examples and comparative examples were tested for contact resistance and contact resistivity using a solar energy simulation electrical efficiency tester under standard conditions (atmosphere quality AM1.5, light intensity 1000W / m 2 , test temperature 25°C) to conduct photoelectric conversion efficiency, open circuit voltage and fill factor tests. The test results are shown in Table 2.

[0100] Table 1

[0101]

[0102] Table 2

[0103]

[0104]

[0105] Figure 1 This is a diagram of the deposition of glass powder at the interface between the silicon wafer and the gate line after the glass powder slurry is prepared and sintered in Example 1 of this application. Figure 2 This is the deposition diagram of glass powder at the interface between silicon wafer and gate line after sintering the glass powder slurry prepared in comparative example 1 of this application. Figure 1 and Figure 2 By comparison, it can be seen that the glass powder of Comparative Example 1 is unevenly deposited at the interface of the grid line, the glass layer in the middle is thicker, and the glass layer at the edge is less, resulting in less contact between the middle of the grid line and the silicon substrate, a significant increase in contact resistance, and a decrease in cell efficiency; on the contrary, the glass powder of Example 1 is evenly deposited at the interface after sintering is completed, and the glass layer is thin. The above explanation shows that after improving the glass fluidity through this method, the contact resistance between the grid line and the silicon substrate is improved, which is manifested as an increase in the fill factor FF, thereby increasing the efficiency of the cell.

[0106] Figure 3 This is an optical photograph of the glass powder at 740°C in Example 1 of the present application. Figure 4 This is an optical photograph of the glass powder in Comparative Example 1 of this application at 740°C. Figure 3 and Figure 4 By comparison, it can be seen that the glass of comparative example 1 becomes densified after sintering but has poor fluidity and does not wet the silicon wafer. The glass powder improved by this method (Example 1) has significantly improved fluidity, and after sintering, the glass has good wettability to the blue film.

[0107] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0108] In this application, the presence of bismuth oxide can help lower the melting point of glass, enhance wettability to silver paste to reduce contact resistance, and protect the passivation layer from metal diffusion through chemical inertness; tellurium oxide, as the main glass network former, can reduce glass viscosity and improve light transmittance after sintering; the presence of H3BO3 can reduce the amount of PbO used, improve the fluidity of glass at high temperatures, and reduce the etching ability of glass, thereby helping to reduce the contact resistance of the grid line; the presence of lead oxide helps to regulate the melting temperature of glass and balance the thermal expansion coefficient with the compatibility of silicon substrate; silicon oxide, as a secondary network former, improves the mechanical strength and high-temperature stability of the glass structure; zinc oxide inhibits interfacial oxidation reaction and enhances the adhesion of glass to silver paste; the presence of Al2O3 helps to strengthen the network structure and improve the chemical stability and high-temperature mechanical strength of glass; the presence of Ag2O facilitates the diffusion of silver and interfacial reaction with silicon, reducing contact resistance; the presence of alkali metal oxides helps to lower the melting point and viscosity of glass, thereby improving the fluidity of glass at high temperatures. Controlling the content of each component in the glass powder within the above range helps the glass powder of the present application have higher fluidity and lower etching ability, can form good infiltration of silver powder during the sintering process, and carry more silver microcrystals to the grid line interface. At the same time, high-fluidity glass can form a thinner glass layer on the bottom silicon base, thereby reducing the contact resistance between the grid line and the silicon substrate and improving the photoelectric conversion efficiency of the solar cell.

[0109] 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 comprising, based on the total mass of the silver paste, 80-93% silver powder, 0.5-5% glass powder, and 5-15% organic vehicle, characterized in that: Calculated as a percentage of the total mass of the glass powder, the glass powder includes: 20-30% Bi2O3, 30-40% TeO2, 8-18% H3BO3, 6-16% PbO, 1-10% SiO2, 1-5% ZnO, 0.5-5% Al2O3, 0.1-1% Ag2O and 1-10% alkali metal oxides.

2. The silver paste according to claim 1, characterized in that In terms of mass percentage, the glass powder includes: 23-27% of the Bi2O3, 36-40% of the TeO2, 11-15% of the H3BO3, 9-13% of the PbO, 3-7% of the SiO2, 1-3% of the ZnO, 1-3% of the Al2O3, 0.3-0.7% of the Ag2O and 3-7% of the alkali metal oxide.

3. The silver paste according to claim 2, characterized in that The mass ratio of the H3BO3 to the PbO is (1-1.67):1; and / or the mass ratio of the Bi2O3 to the TeO2 is (0.65-0.7):

1.

4. The silver paste according to claim 3, characterized in that The alkali metal oxide is selected from any one or more of Na2O, Li2O and K2O.

5. The silver paste according to claim 4, characterized in that The alkali metal oxide is a combination of the Na2O and the Li2O, and the mass ratio of the Na2O to the Li2O is (0.25-1.5):

1.

6. The silver paste according to any one of claims 1 to 5, characterized in that The D50 of the glass powder is 0.8 to 1.2 μm.

7. The silver paste according to any one of claims 1 to 5, characterized in that The Tg point temperature of the glass powder is 262-287°C; and / or the hemisphere point temperature of the glass powder is 458-549°C.

8. The silver paste according to any one of claims 1 to 5, characterized in that The D50 of the silver powder is 1 to 3 μm; and / or the organic vehicle comprises a resin, a solvent, a thixotropic agent, and a release agent, wherein the mass ratio of the resin, the solvent, the thixotropic agent, and the release agent is (30 to 60): (25 to 40): (35 to 90): (0.5 to 3); The resin is selected from any one or more of PMMA480S resin, ethyl cellulose, diethylene glycol monobutyl ether, diethylene glycol butyl ether acetate, alcohol ester-12, tributyl citrate, polyamide wax, and polyethylene wax; The solvent is selected from any one or more of butyl acetate, tributyl citrate, triethylene glycol butyl ether, butyl acrylate and benzyl butyl phthalate; The thixotropic agent is selected from any one or more of Thixatrol MAX thixotropic agent, Thixatrol Plus thixotropic agent, ET7020 thixotropic agent, BASF CO40 thixotropic agent, and RS3500 thixotropic agent; The release agent is selected from methyl silicone oil and / or amino silicone oil.

9. The silver paste according to claim 8, characterized in that The resin is a combination of the PMMA480S resin and the diethylene glycol butyl ether acetate, and the mass ratio of the PMMA480S resin to the diethylene glycol butyl ether acetate is (20-35):(10-25).

10. A solar cell, characterized in that: The invention comprises a substrate and a grid line formed on the surface of the substrate, wherein the grid line is prepared by the silver paste according to any one of claims 1 to 9.

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