Aluminum paste for overprinting on BC battery silver grid line and preparation method, BC battery grid line

Abstract

The present disclosure proposes an aluminum paste for overprinting on the silver grid lines of BC batteries, a preparation method, and a BC battery grid line, which belongs to the field of BC battery technology. The aluminum paste includes: 65-90 parts by mass of aluminum powder; 2-10 parts by mass of glass powder; 2-5 parts by mass of organic resin; 10-20 parts by mass of solvent; 0-2 parts by mass of additives; wherein the glass powder adopts bismuth-boron glass powder with a softening point of 400-500°C. The present disclosure adopts bismuth-boron glass powder with a low softening point temperature to reduce silver-aluminum alloy during medium-high temperature sintering at 580-630°C, reduce silver-aluminum overlap resistance, ensure low recombination level of grid lines, improve the electrical performance of grid lines, and realize the replacement of aluminum paste for silver paste in BC batteries while achieving high light conversion efficiency, thereby reducing costs.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of BC batteries, and particularly relates to an aluminum paste for overprinting on silver grid lines of BC batteries, a preparation method thereof, and BC battery grid lines. Background Art

[0002] Solar cells are semiconductor devices that convert sunlight into electricity through the photovoltaic effect. Their basic operating principle is that when exposed to sunlight, electrons in a semiconductor material are excited by the energy of photons, generating electron-hole pairs. These pairs then separate and move under the influence of an internal electric field, generating an electric current. Currently, mainstream solar cell structures on the market include PERT, TOPCon, HJT, and BC.

[0003] The BC (Bipolar Junction Cell) is a new type of high-efficiency solar cell structure. It achieves separation and collection of electrons and holes by creating interdigitated P and N regions on the back of the cell, followed by metallized contacts and grid lines. The front side is free of grid lines, enabling higher short-circuit current. The wide metal electrode on the back side reduces series resistance and improves the fill factor (FF). However, when the silver grid lines of a BC cell are located on the back side, the large cross-sectional area of ​​the back grid lines and the high conductivity requirements of the paste lead to high silver paste consumption and high cost. Summary of the Invention

[0004] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and provides an aluminum paste for overprinting on BC battery silver grid lines, a preparation method, and a BC battery grid line.

[0005] In one aspect of the present disclosure, an aluminum paste for overprinting on a silver grid line of a BC battery is provided, the aluminum paste comprising:

[0006] 65-90 parts by mass of aluminum powder;

[0007] 2-10 parts by mass of glass powder;

[0008] 2-5 parts by mass of organic resin;

[0009] 10-20 parts by mass of a solvent;

[0010] 0-2 parts by mass of additives; wherein,

[0011] The glass powder is bismuth-boron glass powder with a softening point of 400-500°C.

[0012] Optionally, the bismuth-boron glass powder includes:

[0013] 40-60 parts by mass of Bi2O3;

[0014] 15-25 parts by mass of B2O3;

[0015] 10-25 parts by mass of BaCO3;

[0016] 2-15 parts by mass of V2O5;

[0017] 2-5 parts by mass of Al2O3;

[0018] 0.01-8 parts by mass of SiO2.

[0019] Optionally, the aluminum powder has a D50 of 5-10 μm, a D90 of ≤25 μm, and an oxygen content of ≤0.3%.

[0020] Optionally, the organic resin includes acrylic resin, PVB resin, or ethyl cellulose.

[0021] Optionally, the mass ratio of the acrylic resin, the PVB resin, and the ethyl cellulose is (2-6):(1-3):1.

[0022] Optionally, the solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate and divalent acid ester.

[0023] Optionally, the mass ratio of the diethylene glycol butyl ether, the diethylene glycol butyl ether acetate and the dibasic acid ester is (1-3):1:(1-3).

[0024] Optionally, the additives include a phosphate dispersant and an organosilicon leveling agent.

[0025] Another aspect of the present disclosure provides a method for preparing the aluminum paste described above, the method comprising:

[0026] Mixing 65-90 parts by mass of aluminum powder, 2-10 parts by mass of glass powder, 2-5 parts by mass of an organic resin, 10-20 parts by mass of a solvent, and 0-2 parts by mass of an additive to obtain a mixed component;

[0027] The mixed components are dispersed and ground to control the fineness of the slurry to be ≤13 μm and the viscosity to be 12-20 Pa·s, thereby obtaining aluminum slurry.

[0028] Another aspect of the present disclosure provides a BC battery grid line, comprising a silver grid line and an aluminum grid line overprinted on at least a portion of the silver grid line; wherein,

[0029] The aluminum grid lines are formed by sintering the aluminum paste described above.

[0030] The present disclosure proposes an aluminum paste for overprinting on the silver grid lines of BC batteries, a preparation method, and BC battery grid lines. The aluminum paste includes: 65-90 parts by mass of aluminum powder; 2-10 parts by mass of glass powder; 2-5 parts by mass of organic resin; 10-20 parts by mass of solvent; 0-2 parts by mass of additives; wherein the glass powder adopts bismuth-boron glass powder with a softening point of 400-500°C. The present disclosure adopts bismuth-boron glass powder with a low softening point temperature, and its thermal expansion coefficient forms a gradient match with the aluminum powder, which helps to reduce the silver-aluminum contact caused by interface stress cracking. At the same time, when the glass powder with a softening point is sintered at a medium-high temperature of 580-630°C, it can reduce the formation of silver-aluminum alloy and reduce the silver-aluminum overlap resistance, thereby meeting the needs of overprinting the aluminum paste on the silver grid lines, reducing the amount of silver paste used, and thus reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flowchart of a method for preparing aluminum paste according to a specific embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present disclosure and are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present disclosure.

[0033] It should be noted that the back grid lines of BC batteries are generally silver grid lines, but due to the large cross-sectional area of ​​the silver grid lines, the amount used is also large and the cost is high. In view of this, the present embodiment innovatively proposes a BC battery aluminum paste, which is used to overprint on at least part of the silver grid lines to replace the use of silver paste. The aluminum grid lines formed after the aluminum paste is sintered are in contact with the silver grid lines to form an electrical connection, which can reduce the amount of silver paste used and thus reduce the cost. However, it should be noted that when the conventional aluminum paste is in contact with the silver paste after sintering, for example, when the conventional aluminum paste is overprinted on the silver grid, the silver grid lines Silver-aluminum alloy will appear at the interface between the silver grid line and the aluminum grid line, which will increase the overlap resistance between the silver grid line part and the aluminum grid line part. At the same time, the aluminum paste will aggravate the composite of the silver grid line, resulting in the deterioration of the overall electrical performance of the grid line. Therefore, in summary, this embodiment proposes an aluminum paste that helps to reduce the overlap resistance between the aluminum grid line and the silver grid line and has good adhesion. It can not only reduce the amount of silver paste used, but also enable the grid line to maintain good conductive properties. The aluminum paste can be sintered at 580-630°C. For the specific components of the aluminum paste, please refer to the following description.

[0034] The present disclosure proposes an aluminum paste for overprinting on the silver grid lines of BC batteries, wherein the aluminum paste comprises: 65-90 parts by mass of aluminum powder; 2-10 parts by mass of glass powder; 2-5 parts by mass of organic resin; 10-20 parts by mass of solvent; and 0-2 parts by mass of additives. The glass powder is bismuth-boron glass powder with a softening point of 400-500°C.

[0035] In this embodiment, the use of bismuth-boron glass frit with a low softening point creates a gradient matching of its thermal expansion coefficient with that of the aluminum powder, helping to reduce interfacial stress cracking leading to silver-aluminum contact. Furthermore, when sintered at a medium-high temperature of 580-630°C, this glass frit with a low softening point can reduce the formation of silver-aluminum alloys and lower the silver-aluminum overlap resistance. Specifically, when the aluminum paste is sintered at 580-630°C to form an electrical connection with the silver busbars, for example, when overprinted onto the silver busbars along the thickness of the silicon wafer, this reduces the busbar overlap resistance and recombination, thereby improving the busbar's electrical conductivity. Furthermore, the bismuth-boron glass frit reduces the fluidity of the glass phase, reducing penetration into the silver layer during the sintering process and further minimizing the formation of silver-aluminum alloys.

[0036] In some preferred embodiments, the content of bismuth-boron glass powder may preferably be 2 parts by mass, 3 parts by mass, 5 parts by mass, 7 parts by mass, 10 parts by mass, etc., and the bismuth-boron glass powder includes: 40-60 parts by mass of Bi2O3; 15-20 parts by mass of B2O3; 10-20 parts by mass of BaCO3; 5-15 parts by mass of V2O5; 2-5 parts by mass of Al2O3; and 0.01-8 parts by mass of SiO2.

[0037] As a further preferred embodiment, the Bi2O3 content can be preferably 40 parts by mass, 45 parts by mass, 48 ​​parts by mass, 50 parts by mass, 53 parts by mass, 55 parts by mass, 57 parts by mass, 60 parts by mass, etc., using Bi2O3 to replace PbO, so that the glass has corrosion resistance, reduces the resistance of the aluminum paste itself, reduces the viscosity of the glass and promotes low-temperature flow, shortens the high-temperature reaction time, and inhibits the diffusion of silver and aluminum. When Bi2O3 is insufficient as a glass network former, the melting temperature of the glass phase increases, making it difficult to fully dissolve the surface oxide layer of the aluminum paste during sintering, resulting in a reduction in metal conductive channels, a significant increase in lap resistance, and reduced adhesion. Excessive Bi2O3 will reduce the viscosity of the glass. During sintering, the glass phase will be too fluid, which may penetrate the passivation layer and excessively corrode the silver grid, causing local fracture of the silver grid and affecting conductivity.

[0038] As a further preferred solution, the content of B2O3 can be preferably 15 parts by mass, 17 parts by mass, 20 parts by mass, 25 parts by mass, etc., with B2O3 as the main network body, so that the glass has a lower softening temperature. B2O3 and Bi2O3 form a composite glass network. By adjusting the ratio of the two, the fluidity is controlled to avoid excessive penetration of the silver layer.

[0039] As a further preferred solution, the content of BaCO3 can be preferably 10 parts by mass, 13 parts by mass, 15 parts by mass, 16 parts by mass, 17 parts by mass, 20 parts by mass, etc. BaCO3 can make the softened glass have a higher viscosity and stronger bonding ability.

[0040] As a further preferred solution, the content of V2O5 can be preferably 2 parts by mass, 5 parts by mass, 10 parts by mass, 15 parts by mass, etc. V2O5 acts as a glass network modifier to further improve the melting characteristics and wettability of the glass powder. At the same time, it can also inhibit the oxidation of aluminum powder and improve the reliability of the grid line.

[0041] As a further preferred solution, the content of Al2O3 can be preferably 2 parts by mass, 3 parts by mass, 4 parts by mass, 5 parts by mass, etc. The Al2O3 component can improve the stability of the glass network, inhibit the migration of aluminum ions at high temperatures, and thus inhibit the combination of silver and aluminum.

[0042] As a further preferred embodiment, the SiO2 content can be preferably 0.01 parts by mass, 0.1 parts by mass, 0.5 parts by mass, 1 part by mass, 3 parts by mass, 5 parts by mass, 8 parts by mass, etc. A trace amount of SiO2 can enhance the density of the glass, reduce the diffusion channels of silver and aluminum at the grain boundaries, and further inhibit the formation of silver-aluminum alloys. As a glass network former, an excessively high SiO2 content can significantly increase the softening point of the glass phase (e.g., exceeding 600°C), resulting in reduced glass fluidity during sintering, hindering the glass phase from effectively dissolving the surface oxide layer of the aluminum paste, and significantly increasing the lap resistance. Furthermore, an excessively high SiO2 glass phase can cause a mismatch in the thermal expansion coefficient and induce aluminum oxidation. Furthermore, the aluminum-silver interface is easily isolated by excess silicon oxide, weakening the interfacial bonding between the aluminum paste and the silver grid.

[0043] In this embodiment, by adjusting the content of each component in the above-mentioned glass powder, the softening temperature and corrosion characteristics of the glass powder are controlled to match the requirements of high temperature sintering of the slurry at 580-630°C, and at the same time, a synergistic effect is exerted to reduce the resistance of the aluminum paste itself, effectively inhibit the formation of silver-aluminum alloy, and thus reduce the overlap resistance between the silver grid line and the aluminum grid line, ensure the low composite level of the grid line, improve the conductive performance, and at the same time, there is good bonding performance between silver and aluminum, and between aluminum and silicon, thereby improving the adhesion strength of the grid line.

[0044] In some preferred embodiments, the weight percentage of aluminum powder is preferably 65-90 parts by weight, further preferably 70-90 parts by weight, and has excellent electrical conductivity. For example, the content of aluminum powder can be preferably 65 parts by weight, 70 parts by weight, 75 parts by weight, 78 parts by weight, 80 parts by weight, 85 parts by weight, 90 parts by weight, etc., and the D50 of the aluminum powder is preferably 5-10 μm, D90 ≤ 25 μm, and the oxygen content is ≤ 0.3%. The above-mentioned aluminum powder particle size distribution can make the conductive network continuous, avoid defects in the conductive network that may form high-resistance nodes at the silver-aluminum overlap, and achieve excellent overlap performance between the aluminum grid line and the silver grid line, reduce the silver-aluminum overlap resistance, and have good electrical conductivity. At the same time, the low oxygen content makes the thickness of the natural oxide layer on the surface of the aluminum powder small, forming a continuous and dense passivation layer, which inhibits the oxidation and release of aluminum during the sintering process.

[0045] In other preferred embodiments, the organic resin content can be preferably 2 parts by mass, 3 parts by mass, 4 parts by mass, 5 parts by mass, etc., and the organic resin includes acrylic resin, PVB resin, and ethyl cellulose. The mass ratio of acrylic resin, PVB resin, and ethyl cellulose can be preferably (2-6):(1-3):1, and more preferably (3-5):2:1. These organic resins can impart good bonding and film-forming properties to the aluminum paste, improving adhesion to the silver grid lines.

[0046] In other preferred embodiments, the content of the solvent may be preferably 10 parts by mass, 15 parts by mass, 17 parts by mass, 20 parts by mass, etc. The solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate and dibasic acid ester, wherein the mass ratio of diethylene glycol butyl ether, the diethylene glycol butyl ether acetate and the dibasic acid ester is preferably (1-3):1:(1-3), and more preferably 2:1:(1-3). The above solvent is conducive to adjusting the viscosity and rheological properties of the aluminum paste to make it have suitable printing adaptability, and the dibasic acid ester plays a plasticizing role, adjusting the grid line width to adapt to the overprinting process.

[0047] In other preferred embodiments, in order to synergistically optimize printability and improve the interfacial bonding force between silver-aluminum and / or aluminum-silicon, additives such as dispersants, leveling agents, thixotropic agents, etc. may be added according to the characteristics of the slurry. The content of the additive may preferably be 0.5 parts by mass, 1 part by mass, 1.5 parts by mass, 2 parts by mass, etc. In some preferred embodiments, the additive includes a phosphate dispersant and an organosilicon leveling agent. Among them, the mass ratio of the phosphate dispersant to the organosilicon leveling agent may preferably be (5~20):1. Of course, in other embodiments, the additive may also include a thixotropic agent, etc., or the additive component may not be added.

[0048] It is worth noting that the aluminum paste proposed in the present disclosure can achieve at least partial replacement of the silver grid lines of BC batteries, and is further preferably a partial replacement of the silver main grid lines of BC batteries. It is further preferred that the aluminum paste is overprinted on the main grid silver paste in the thickness direction of the silicon wafer, and it is further preferred that part of the aluminum paste is in contact with the silicon wafer at the same time. However, it is understandable that the aluminum paste also has a good effect on the silver-aluminum overlap in other directions, such as partially replacing the silver grid lines with aluminum grid lines in the direction perpendicular to the thickness of the silicon wafer. In other words, the present disclosure aims to propose an aluminum paste that can replace the silver grid lines of BC batteries, without limiting the specific overprinting area, overprinting structure, overlapping method, overprinting pattern, overprinting direction, aluminum-silicon contact area, etc. of the silver grid lines and the aluminum grid lines.

[0049] like Figure 1 As shown, another aspect of the present disclosure provides a method S100 for preparing the aluminum paste described above, comprising the following specific steps S110 to S120:

[0050] S110, mixing 65-90 parts by mass of aluminum powder, 2-10 parts by mass of glass powder, 2-5 parts by mass of organic resin, 10-20 parts by mass of solvent, and 0-2 parts by mass of additives to obtain a mixed component.

[0051] In step S110, the aluminum powder may preferably have a D50 of 5-10 μm, a D90 of ≤25 μm, and an oxygen content of ≤0.3%. The aluminum powder may preferably have a weight content of 65-90 parts by weight, more preferably 70-90 parts by weight, and excellent electrical conductivity. For example, the aluminum powder content may preferably be 65 parts by weight, 70 parts by weight, 75 parts by weight, 78 parts by weight, 80 parts by weight, 85 parts by weight, or 90 parts by weight.

[0052] In step S110, the glass frit may be a bismuth-boron glass frit with a softening point of 400-500°C. Its composition includes: 40-60 parts by mass of Bi2O3; 15-25 parts by mass of B2O3; 10-25 parts by mass of BaCO3; 2-15 parts by mass of V2O5; 2-5 parts by mass of Al2O3; and 0.01-8 parts by mass of SiO2. The glass frit content may preferably be 2 parts by mass, 3 parts by mass, 5 parts by mass, 7 parts by mass, or 10 parts by mass.

[0053] It should be noted that the glass powder in step S110 can be homemade bismuth-boron glass powder, which has a softening point of 400-500° C. For example, a melt quenching method can be used.

[0054] In step S110 , the organic resin may preferably be a mixture of acrylic resin, PVB resin, and ethyl cellulose, and the content of the organic resin may preferably be 2 parts by mass, 3 parts by mass, 4 parts by mass, 5 parts by mass, etc.

[0055] In step S110, the solvent may preferably be a mixture of butyl diglycol, butyl diglycol acetate and dibasic acid ester, and the content of the solvent may preferably be 10 parts by mass, 15 parts by mass, 17 parts by mass, 20 parts by mass, etc.

[0056] In step S110, the additives may preferably be phosphate dispersants and silicone leveling agents. Of course, the additives may also include thixotropic agents, etc. The content of the additives may preferably be 0.5 parts by mass, 1 part by mass, 1.5 parts by mass, 2 parts by mass, etc.

[0057] S120, dispersing and grinding the mixed components to control the slurry fineness to ≤13 μm and the viscosity to 12-20 Pa·s to obtain aluminum slurry.

[0058] Specifically, the mixed components of step S110 are placed in a dispersant, dispersed at a speed of 500-2000 rpm for 1 hour, and then ground and dispersed on a three-roll mill to a fineness of ≤13 μm, and the slurry viscosity is controlled at 12-20 Pa·s.

[0059] It should be noted that the slurry viscosity in step S120 is measured using a Brookfield DV2T viscometer at 25° C. and a rotation speed of 10 r / min.

[0060] Another aspect of the present disclosure provides a BC battery grid line, which includes a silver grid line and an aluminum grid line overprinted on at least a portion of the silver grid line. The aluminum paste here should be overprinted on the side of the silver grid line away from the silicon wafer, and the formed aluminum grid line is in contact with at least a portion of the silver grid line, wherein the aluminum grid line is formed by sintering the aluminum paste described above.

[0061] It should be noted that the present disclosure is intended to propose the application of the aforementioned aluminum paste in BC battery grid lines, and does not limit the specific overprinting area, overprinting structure, overlapping method, overprinting pattern, overprinting direction, aluminum-silicon contact area, etc. of the silver grid lines and the aluminum grid lines. For example, when the aluminum grid lines are overprinted on the side of the silver grid lines away from the silicon wafer, the aluminum grid lines can completely wrap the silver grid lines along the length direction of the silver grid lines, or can partially wrap the silver grid lines. Of course, the silver grid lines may be distributed continuously or discontinuously. When the silver grid lines are distributed continuously or discontinuously, the aluminum grid lines can be overprinted continuously or discontinuously on at least part of the silver grid lines. In this way, effective overlapping of the discontinuous silver grid lines can be achieved, thereby reducing the amount of silver paste used. It should be understood that when the aluminum paste is overprinted on the silver grid lines, the corresponding BC battery grid lines formed include silver main grid lines in contact with the silicon wafer and aluminum grid lines overprinted on the silver main grid lines in the thickness direction of the silicon wafer. The aluminum grid lines can partially contact the silicon wafer, and the aluminum grid lines also have good adhesion to the silicon wafer. Of course, the aluminum grid lines in the BC battery grid lines may not be in contact with the silicon wafer, for example, they may be only overprinted on the surface of the silver grid lines that is away from the silicon wafer.

[0062] It should be noted that the sintering temperature of this embodiment is 580-630°C. This medium-high temperature sintering can reduce the silver-aluminum overlap resistance and composite. At the same time, the sintering temperature matches the low softening point glass powder used, which can achieve a lower overlap resistance between the aluminum grid line and the silver grid line, and make the aluminum grid line have good adhesion, thereby ensuring the photoelectric conversion efficiency and reliability of the grid line.

[0063] The following will further explain the aluminum paste overprinted on the silver grid line of BC batteries and its application with reference to specific examples:

[0064] Example 1

[0065] The aluminum paste formula of this example is shown in Table 1, which specifically includes:

[0066] 78 parts by mass of aluminum powder, wherein the aluminum powder has D50 = 9 μm, D90 = 23.5 μm, and an oxygen content = 0.24%.

[0067] 3 parts by mass of glass powder, wherein the glass powder includes 55% Bi2O3, 20% B2O3, 15% BaCO3, 5% V2O5, 4% Al2O3, and 1% SiO2.

[0068] 3 parts by mass of an organic resin, wherein the organic resin comprises acrylic resin: PVB resin: ethyl cellulose = (3-5):2:1.

[0069] 15 parts by mass of a solvent, wherein the solvent comprises butyl diglycol, butyl diglycol acetate, and dibasic acid ester in a ratio of 2:1:(1-3).

[0070] 1 part by mass of additives, wherein the additives include a phosphate dispersant and an organosilicon leveling agent in a ratio of 10:1.

[0071] Furthermore, the aluminum paste was placed in a disperser, dispersed at a speed of 1500 rpm for 1 hour, and then ground and dispersed on a three-roll mill to a fineness of ≤13 μm. The slurry viscosity was controlled at 16 Pa·s to obtain an aluminum paste.

[0072] Furthermore, the obtained aluminum paste is overprinted on the silver main grid in the thickness direction of the silicon wafer and sintered at a high temperature of 600°C to obtain a BC battery grid line, which includes a silver main grid line in contact with the silicon wafer and an aluminum grid line overprinted on part of the silver main grid line in the thickness direction of the silicon wafer, and part of the aluminum grid line is in contact with the silicon wafer.

[0073] As shown in Table 2, the resistivity of the BC battery grid line in this embodiment is 1.62×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.52Ω, and the PL composite is 113 fA / cm 2, 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 26.21%.

[0074] Example 2

[0075] The aluminum paste formula of this example is shown in Table 1. The content and composition of aluminum powder, organic resin, solvent and additives are the same as those in Example 1.

[0076] The glass powder includes 55% Bi2O3, 16% B2O3, 15% BaCO3, 5% V2O5, 4% Al2O3, and 5% SiO2.

[0077] Furthermore, the aluminum paste preparation process, the process of overprinting the obtained aluminum paste on the silver main grid lines, and the obtained BC battery grid line structure of this embodiment 2 are all the same as those of embodiment 1.

[0078] As shown in Table 2, the resistivity of the BC battery grid line in this embodiment is 1.48×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.51Ω, and the PL composite is 98fA / cm 2 , 3M adhesion performance is good, and the photoelectric conversion efficiency is 26.48%.

[0079] Example 3

[0080] The aluminum paste formula of this example is shown in Table 1. The content and composition of aluminum powder, organic resin, solvent and additives are the same as those in Example 1.

[0081] The glass powder includes 45% Bi2O3, 25% B2O3, 20% BaCO3, 5% V2O5, 4% Al2O3, and 1% SiO2.

[0082] Furthermore, the aluminum paste preparation process, the process of overprinting the obtained aluminum paste on the silver main grid lines, and the obtained BC battery grid line structure of this embodiment 2 are all the same as those of embodiment 1.

[0083] As shown in Table 2, the resistivity of the BC battery grid line in this embodiment is 1.89×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.43Ω, and the PL composite is 45fA / cm 2 , 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 26.09%.

[0084] Comparative Example 1

[0085] The aluminum paste formula of this example is shown in Table 1. The content and composition of aluminum powder, organic resin, solvent and additives are the same as those in Example 1.

[0086] The glass powder includes 50% Bi2O3, 15% B2O3, 16% BaCO3, 5% V2O5, 4% Al2O3, and 10% SiO2.

[0087] Furthermore, the aluminum paste preparation process, the process of overprinting the obtained aluminum paste on the silver main grid lines, and the obtained BC battery grid line structure of this embodiment 2 are all the same as those of embodiment 1.

[0088] As shown in Table 2, the PL of the BC battery grid line of this embodiment is 40fA / cm 2 , 3M adhesion performance is poor.

[0089] Comparative Example 2

[0090] The aluminum paste formula of this example is shown in Table 1. The content and composition of aluminum powder, organic resin, solvent and additives are the same as those in Example 1.

[0091] The glass powder includes 38% Bi2O3, 25% B2O3, 20% BaCO3, 12% V2O5, 4% Al2O3, and 10% SiO2.

[0092] Furthermore, the aluminum paste preparation process, the process of overprinting the obtained aluminum paste on the silver main grid lines, and the obtained BC battery grid line structure of this embodiment 2 are all the same as those of embodiment 1.

[0093] As shown in Table 2, the resistivity of the BC battery grid line in this embodiment is 4.47×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.43Ω, and the PL composite is 42fA / cm 2 , 3M adhesion performance is good, and the photoelectric conversion efficiency is 25.13%.

[0094] Comparative Example 3

[0095] The aluminum paste formula of this example is shown in Table 1. The content and composition of glass powder, organic resin, solvent and additives are the same as those in Example 1.

[0096] The D50 of aluminum powder is 4.5 μm, D90 is 19.8 μm, and the oxygen content is 0.29%.

[0097] Furthermore, the aluminum paste preparation process, the process of overprinting the obtained aluminum paste on the silver main grid lines, and the obtained BC battery grid line structure of this embodiment 2 are all the same as those of embodiment 1.

[0098] As shown in Table 2, the resistivity of the BC battery grid line in this embodiment is 1.50×10 -5 Ω·cm, the silver-aluminum lap resistance is 2.55Ω, and the PL composite is 287fA / cm 2, 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 24.88%.

[0099] In summary, according to the results of Examples 1-3 and Comparative Example 1, when the silicon content in the glass powder is high, the high SiO2 glass phase will cause a mismatch in the thermal expansion coefficient and induce aluminum oxidation. At the same time, the aluminum-silver interface is easily isolated by excessive silicon oxide, weakening the interfacial bonding between the aluminum paste and the silver grid, and the bonding between the aluminum grid lines and the silver grid lines is poor. According to the results of Examples 1-3 and Comparative Example 2, when the Bi2O3 content in the glass powder is low, the continuity of the network body decreases, defects increase, and the overlap resistance of the aluminum grid lines and the silver grid lines increases. According to the results of Examples 1-3 and Comparative Example 3, when the particle size of the aluminum powder is too fine, defects in the conductive network are likely to form high-resistance nodes at the silver-aluminum overlap, resulting in a decrease in the interface quality of the silver grid lines and the aluminum grid lines and an increase in resistivity.

[0100] Table 1 Aluminum paste formulations for various examples and comparative examples

[0101]

[0102] Table 2 Performance results of gate lines in various embodiments and comparative examples

[0103]

[0104] The present disclosure provides an aluminum paste for overprinting on a silver grid line of a BC battery, a preparation method thereof, and a BC battery grid line, which has the following beneficial effects compared to the prior art:

[0105] First, the present disclosure optimizes the composition and content of aluminum paste so that it can be sintered at medium to high temperatures and overprinted on silver grid lines, thereby reducing the amount of silver paste used and thus reducing costs. At the same time, the grid lines can maintain reduced overlap resistance and high photoelectric conversion efficiency.

[0106] Second, the present disclosure uses low-softening-point glass powder to match the sintering temperature of the aluminum paste, which is beneficial to reducing the silver-aluminum overlap resistance and composite, and improving the adhesion of the aluminum grid line;

[0107] Third, the present disclosure uses aluminum powder in a specific particle size range to help reduce the silver-aluminum overlap resistance and meet the requirements of overprinting on silver grid lines.

[0108] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. An aluminum paste for overprinting on silver grid lines of BC batteries, characterized in that: The aluminum paste comprises: 65-90 parts by mass of aluminum powder; 2-10 parts by mass of glass powder; 2-5 parts by mass of organic resin; 10-20 parts by mass of a solvent; 0-2 parts by mass of additives; wherein, The glass powder is a bismuth-boron glass powder with a softening point of 400-500° C. The bismuth-boron glass powder includes: 40-60 parts by mass of Bi2O3; 15-25 parts by mass of B2O3; 10-25 parts by mass of BaCO3; 2-15 parts by mass of V2O5; 2-5 parts by mass of Al2O3; 0.01-8 parts by mass of SiO2.

2. The aluminum paste according to claim 1, characterized in that The aluminum powder has a D50 of 5-10 μm, a D90 of ≤25 μm, and an oxygen content of ≤0.3%.

3. The aluminum paste according to claim 1, characterized in that The organic resin includes acrylic resin, PVB resin and ethyl cellulose.

4. The aluminum paste according to claim 3, characterized in that The mass ratio of the acrylic resin, the PVB resin, and the ethyl cellulose is (2-6):(1-3):

1.

5. The aluminum paste according to claim 1, characterized in that The solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate and dibasic acid ester.

6. The aluminum paste according to claim 5, characterized in that The mass ratio of the diethylene glycol butyl ether, the diethylene glycol butyl ether acetate and the dibasic acid ester is (1-3):1:(1-3).

7. The aluminum paste according to claim 1, characterized in that The additives include a phosphate dispersant and an organosilicon leveling agent.

8. A method for preparing the aluminum paste according to any one of claims 1 to 7, characterized in that: The method comprises: Mixing 65-90 parts by mass of aluminum powder, 2-10 parts by mass of glass powder, 2-5 parts by mass of an organic resin, 10-20 parts by mass of a solvent, and 0-2 parts by mass of an additive to obtain a mixed component; The mixed components are dispersed and ground to control the fineness of the slurry to be ≤13 μm and the viscosity to be 12-20 Pa·s, thereby obtaining aluminum slurry.

9. A BC battery grid line, characterized in that: The BC battery grid lines include silver grid lines and aluminum grid lines superimposed on at least part of the silver grid lines; wherein, The aluminum grid lines are formed by sintering the aluminum paste according to any one of claims 1 to 7.

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