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

Abstract

The invention provides aluminum paste overprinted on a BC battery silver grid line, a preparation method of the aluminum paste and the BC battery grid line, and belongs to the technical field of BC batteries. 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 an organic resin; 10-20 parts by mass of a solvent; 0-2 parts by mass of an additive; wherein the glass powder adopts bismuth-boron glass powder with the softening point of 400-500 DEG C. By adopting the bismuth-boron glass powder with low softening point temperature, silver-aluminum alloy is reduced during sintering at the medium-high temperature of 580-630 DEG C, the silver-aluminum lap resistance is reduced, the low composite level of the grid line is ensured, the electrical property of the grid line is improved, the replacement of silver paste by aluminum paste in a BC battery is realized while the light conversion efficiency is high, and the cost is reduced.

Description

Technical Field

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

[0002] A solar cell is a semiconductor device that converts solar energy into electrical energy through the photovoltaic effect. Its basic working principle is that under sunlight irradiation, electrons in the semiconductor material are excited by photon energy to generate electron-hole pairs, which are then separated and move under the action of the built-in electric field to form an electric current. Currently, the mainstream solar cells on the market include various structures such as PERT, TOPCon, HJT, and BC.

[0003] The BC (Bipolar Junction Cell) cell is a new type of high-efficiency solar cell structure. By preparing finger-like spaced P regions and N regions on the back of the cell and forming metallization contacts and grid lines thereon, the separation and collection of electrons and holes are realized. There is no grid line occlusion on its front surface, so a higher short-circuit current can be obtained. The wide metal electrode on the back reduces the series resistance and increases the fill factor FF. However, when the silver grid lines of the BC cell are located on the back of the cell, due to the large cross-sectional area of the back grid lines and the high requirement for the conductivity of the paste, the amount of silver paste used is large and the cost is high. 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 silver grid lines of BC cells, a preparation method thereof, and BC cell grid lines.

[0005] On one hand, the present disclosure provides an aluminum paste for overprinting on silver grid lines of BC cells, and 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 additive; wherein, the glass powder is a bismuth-boron-based glass powder with a softening point of 400 - 500 °C. Optionally, the bismuth-boron-based 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.

[0006] Optionally, the D50 of the aluminum powder is 5-10 μm, D90 ≤ 25 μm, and the oxygen content ≤ 0.3%.

[0007] Optionally, the organic resin includes acrylic resin, PVB resin, and ethyl cellulose.

[0008] Optionally, the mass ratio of the acrylic resin, the PVB resin, and the ethyl cellulose is (2-6):(1-3):1.

[0009] Optionally, the solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibasic acid ester.

[0010] 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).

[0011] Optionally, the additive includes phosphate ester dispersant and silicone leveling agent.

[0012] On the other hand, the present disclosure provides a method for preparing the aluminum paste described above, the method including: 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 additive to obtain a mixed component; Performing dispersion and grinding on the mixed component, controlling the fineness of the slurry ≤ 13 μm and the viscosity to be 12-20 Pa·s to obtain the aluminum paste.

[0013] On the other hand, the present disclosure provides a BC cell grid line, the BC cell grid line including a silver grid line and an aluminum grid line overprinted on at least part of the silver grid line; wherein, The aluminum grid line is formed by sintering the aluminum paste described above.

[0014] The present disclosure provides an aluminum paste for overprinting on a BC cell silver grid line, a preparation method thereof, and a BC cell grid line. 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 additive; wherein, the glass powder is a bismuth borate glass powder with a softening point of 400-500 °C. By using a bismuth borate glass powder with a low softening point temperature, the present disclosure has a gradient match of the thermal expansion coefficient with the aluminum powder, which helps to reduce the silver-aluminum contact caused by interfacial stress cracking. At the same time, when sintering at a medium-high temperature of 580-630 °C, the glass powder with this softening point can reduce the formation of silver-aluminum alloy, lower the silver-aluminum lap resistance, meet the requirement of overprinting the aluminum paste on the silver grid line, reduce the usage amount of silver paste, and thus reduce the cost. Description of the Drawings

[0015] Figure 1 It is a flowchart of the aluminum paste preparation method for the specific implementation manner of the present disclosure. Specific implementation manner

[0016] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below with reference to the accompanying drawings and specific implementation manners. It should be understood that the specific embodiments described herein are only used to explain the present disclosure, which 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 efforts shall fall within the protection scope of the present disclosure.

[0017] It should be noted that the back grid lines of BC cells are generally silver grid lines. However, due to the large cross-sectional area of the silver grid lines, their consumption is also large and the cost is high. In view of this, in this implementation manner, an innovative aluminum paste for BC cells is proposed, which is used to overprint at least part of the silver grid lines to replace the use of silver paste. The aluminum grid lines formed after sintering of this aluminum paste are in electrical connection with the silver grid lines in contact, which can reduce the consumption of silver paste 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, an aluminum-silver alloy will appear at the interface between the silver grid lines and the aluminum grid lines, making the contact resistance between the silver grid line part and the aluminum grid line part larger. At the same time, the aluminum paste will aggravate the recombination of the silver grid lines, resulting in poor electrical performance of the overall grid lines. Therefore, generally speaking, this implementation manner proposes an aluminum paste that helps to reduce the contact resistance between the aluminum grid lines and the silver grid lines and has good adhesion. It can not only reduce the consumption of silver paste but also keep the grid lines in good electrical conductivity. This aluminum paste can be sintered under the condition of 580 - 630 °C. For the specific components of this aluminum paste, please refer to the following description.

[0018] The present disclosure proposes an aluminum paste for overprinting on the silver grid lines of BC cells. This 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 additive; wherein, the glass powder uses a bismuth-boron-based glass powder with a softening point of 400 - 500 °C.

[0019] In this embodiment, by using bismuth borate glass powder with a low softening point temperature, its coefficient of thermal expansion forms a gradient match with that of aluminum powder, which helps to reduce silver-aluminum contact caused by interfacial stress cracking. At the same time, when this 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, lower the silver-aluminum lap resistance. That is to say, when this aluminum paste is sintered at 580-630°C and contacts with the silver grid line to form an electrical connection, for example, when it is overprinted on the silver main grid line in the thickness direction of the silicon wafer, it can reduce the grid line lap resistance and recombination, and improve the conductivity of the grid line. At the same time, the bismuth borate glass powder can reduce the fluidity of the glass phase, reduce the penetration of the silver layer during the sintering process, and further reduce the formation of silver-aluminum alloy.

[0020] In some preferred embodiments, the content of the bismuth borate glass powder can be preferably 2 parts by mass, 3 parts by mass, 5 parts by mass, 7 parts by mass, 10 parts by mass, etc., and this bismuth borate 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; 0.01-8 parts by mass of SiO2.

[0021] As a further preferred scheme, the content of Bi2O3 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. Replacing PbO with Bi2O3 enables the glass to have corrosion resistance, reduces the resistance of the aluminum paste itself, reduces the glass viscosity and promotes low-temperature flow, shortens the high-temperature reaction time, and inhibits silver-aluminum diffusion. As a glass network former, when the content of Bi2O3 is insufficient, the melting temperature of the glass phase increases, and it is difficult to fully dissolve the oxide layer on the surface of the aluminum paste during the sintering process, resulting in a reduction in the metal conductive channels, a significant increase in the lap resistance, and a decrease in the adhesion. Excessive Bi2O3 will reduce the glass viscosity, and the fluidity of the glass phase during sintering is too strong, which may penetrate the passivation layer and erode the silver grid excessively, resulting in local fracture of the silver grid and affecting the conductivity.

[0022] As a further preferred scheme, the content of B2O3 can be preferably 15 parts by mass, 17 parts by mass, 20 parts by mass, 25 parts by mass, etc. Taking B2O3 as the network main body enables the glass to have a lower softening temperature. B2O3 and Bi2O3 form a composite glass network, and the fluidity is controlled by adjusting the ratio of the two to avoid excessive penetration of the silver layer.

[0023] As a further preferred scheme, 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.

[0024] As a further preferred embodiment, 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, as a glass network modifier, further improves the melting characteristics and wettability of the glass powder. At the same time, it can also inhibit the oxidation of aluminum powder, improve the reliability of the grid line.

[0025] As a further preferred embodiment, 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 glass network stability, inhibit the migration of aluminum ions at high temperatures, and thus inhibit the silver-aluminum combination.

[0026] As a further preferred embodiment, the content of SiO2 can be preferably 0.01 part by mass, 0.1 part by mass, 0.5 part by mass, 1 part by mass, 3 parts by mass, 5 parts by mass, 8 parts by mass, etc. Trace amounts of SiO2 can enhance the glass densification, reduce the diffusion channels of silver and aluminum at the grain boundaries, and further inhibit the formation of silver-aluminum alloy. As a glass network former, if the content of SiO2 is too high, it will significantly increase the softening point of the glass phase (such as exceeding 600 °C), resulting in a decrease in the glass fluidity during the sintering process, hindering the effective dissolution of the aluminum paste surface oxide layer by the glass phase, and a significant increase in the lap resistance. At the same time, too high a SiO2 glass phase will cause a mismatch in the thermal expansion coefficient, induce aluminum oxidation, and the aluminum-silver interface is easily isolated by excessive silicon oxides, weakening the interfacial bonding force between the aluminum paste and the silver grid.

[0027] In this embodiment, by adjusting the content of each component in the above glass powder, the softening temperature and corrosion characteristics of the glass powder are controlled to match the requirements of the medium-high temperature sintering of the paste at 580 - 630 °C. At the same time, they play a synergistic role, reduce the resistance of the aluminum paste itself, effectively inhibit the formation of silver-aluminum alloy, and thus reduce the lap resistance between the silver grid line and the aluminum grid line, ensure a low recombination level of the grid line, improve the conductivity. At the same time, there is good bonding performance between silver-aluminum and aluminum-silicon, thereby improving the adhesion strength of the grid line.

[0028] In some preferred embodiments, the mass fraction of the aluminum powder is preferably 65 - 90 parts by mass, more preferably 70 - 90 parts by mass, and has excellent conductivity. For example, the content of the aluminum powder can be preferably 65 parts by mass, 70 parts by mass, 75 parts by mass, 78 parts by mass, 80 parts by mass, 85 parts by mass, 90 parts by mass, etc. And the D50 of the aluminum powder is preferably 5 - 10 μm, D90 ≤ 25 μm, and the oxygen content ≤ 0.3%. The above aluminum powder particle size distribution can make the conductive network continuous, avoid high-resistance nodes that may be formed at the silver-aluminum lap joint due to defects in the conductive network, make the lap performance between the aluminum grid line and the silver grid line excellent, reduce the silver-aluminum lap resistance, and have good conductivity. At the same time, the low oxygen content characteristic makes the thickness of the natural oxide layer on the surface of the aluminum powder small, forming a continuous and dense passivation layer, inhibiting the oxidation release of aluminum during the sintering process.

[0029] In some other preferred embodiments, 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. And the organic resin includes acrylic resin, PVB resin, and ethyl cellulose. Among them, the mass ratio of the acrylic resin, the PVB resin, and the ethyl cellulose may preferably be (2 to 6):(1 to 3):1, and more preferably (3 to 5):2:1. The above-mentioned organic resin can endow the aluminum paste with good adhesion performance and film-forming property, and improve the adhesion to the silver grid line.

[0030] In some other preferred embodiments, 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. And the solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibasic acid ester. Among them, the mass ratio of the diethylene glycol butyl ether, the diethylene glycol butyl ether acetate, and the dibasic acid ester may preferably be (1 to 3):1:(1 to 3), and more preferably 2:1:(1 to 3). The above-mentioned solvent is beneficial to adjusting the viscosity and rheological properties of the aluminum paste, making it have suitable printing adaptability. The dibasic acid ester plays a plasticizing role to adjust the grid line width to adapt to the overprinting process.

[0031] In some other preferred embodiments, in order to synergistically optimize the printability and improve the interfacial bonding force between silver-aluminum and / or aluminum-silicon, additives such as dispersants, leveling agents, thixotropic agents, etc. can be added according to the slurry characteristics. 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. In some preferred embodiments, the additive includes a phosphate ester dispersant and a silicone leveling agent. Among them, the mass ratio of the phosphate ester dispersant and the silicone leveling agent may preferably be (5 to 20):1. Of course, in other embodiments, the additive may also include a thixotropic agent, etc., or the additive component may not be added.

[0032] It should be noted that the aluminum paste proposed in the present disclosure can achieve at least partial replacement of the silver grid line of the BC cell, more preferably partial replacement of the main silver grid line of the BC cell. More preferably, the aluminum paste is overprinted on the main grid silver paste in the thickness direction of the silicon wafer, and more preferably part of the aluminum paste is in contact with the silicon wafer at the same time. However, it can be understood that the aluminum paste also has a good effect on the silver-aluminum lap joint in other directions, such as replacing part of the silver grid line with an aluminum grid line perpendicular to the thickness direction of the silicon wafer. That is to say, the present disclosure aims to propose an aluminum paste for replacing the silver grid line of the BC cell, without limiting the specific overprinting area, overprinting structure, lap joint method, overprinting pattern, overprinting direction, aluminum-silicon contact area, etc. of the silver grid line and the aluminum grid line.

[0033] As Figure 1 shown, on the other hand, the present disclosure proposes a method S100 for preparing the aluminum paste described above, including the following specific steps S110 to S120: S110. Mix 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 additive to obtain a mixed component.

[0034] In step S110, the D50 of the aluminum powder is preferably 5 - 10 μm, D90 ≤ 25 μm, and the oxygen content ≤ 0.3%. The mass fraction of this aluminum powder is preferably 65 - 90 parts by mass, more preferably 70 - 90 parts by mass, and it has excellent electrical conductivity. For example, the content of the aluminum powder can be preferably 65 parts by mass, 70 parts by mass, 75 parts by mass, 78 parts by mass, 80 parts by mass, 85 parts by mass, 90 parts by mass, etc.

[0035] In step S110, the glass powder can be a bismuth - boron - based glass powder with a softening point of 400 - 500 °C, and 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; 0.01 - 8 parts by mass of SiO2. The content of this glass powder can be preferably 2 parts by mass, 3 parts by mass, 5 parts by mass, 7 parts by mass, 10 parts by mass, etc.

[0036] It should be noted that the glass powder in step S110 can be a self - made bismuth - boron - based glass powder with a softening point of 400 - 500 °C. For example, the melting - quenching method can be used, etc.

[0037] In step S110, the organic resin is preferably a mixture of acrylic resin, PVB resin, and ethyl cellulose. The content of this organic resin can be preferably 2 parts by mass, 3 parts by mass, 4 parts by mass, 5 parts by mass, etc.

[0038] In step S110, the solvent is preferably a mixture of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibasic acid ester. The content of this solvent can be preferably 10 parts by mass, 15 parts by mass, 17 parts by mass, 20 parts by mass, etc.

[0039] In step S110, the additive is preferably a phosphate dispersant and an organosilicon leveling agent. Of course, the additive can also include a thixotropic agent, etc. The content of this additive can be preferably 0.5 parts by mass, 1 part by mass, 1.5 parts by mass, 2 parts by mass, etc.

[0040] S120. Perform dispersion and grinding on the mixed component, control the fineness of the slurry ≤ 13 μm and the viscosity to be 12 - 20 Pa·s to obtain aluminum paste.

[0041] Specifically, place the mixed component of step S110 in a dispersant, disperse it at a rotation speed of 500 - 2000 rpm for 1 h, and then grind and disperse it on a three - roll mill until the fineness ≤ 13 μm, and control the slurry viscosity to be 12 - 20 Pa·s.

[0042] It should be noted that the viscosity of the slurry in step S120 was measured at 25 °C and a rotational speed of 10 r / min using a Brookfield DV2T viscometer.

[0043] On the other hand, the present disclosure proposes a BC cell grid line, which includes a silver grid line and an aluminum grid line overprinted on at least part of the silver grid line. Here, the aluminum paste 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 part of the silver grid line. Among them, the aluminum grid line is formed by sintering the aluminum paste described above.

[0044] It should be noted that the present disclosure aims to propose the application of the above-mentioned aluminum paste in the BC cell grid line, and does not limit the specific overprint area, overprint structure, overlapping method, overprint pattern, overprint direction, aluminum-silicon contact area, etc. of the silver grid line and the aluminum grid line. For example, when the aluminum grid line is overprinted on the side of the silver grid line away from the silicon wafer, along the length direction of the silver grid line, the aluminum grid line can completely wrap the silver grid line or partially wrap the silver grid line. Of course, the silver grid line may be continuously distributed or discontinuously distributed. When the silver grid line is continuously distributed or discontinuously distributed, the aluminum grid line can be continuously or discontinuously overprinted on at least part of the silver grid line. In this way, effective overlapping of the discontinuous silver grid line can be achieved, thereby reducing the consumption of silver paste. It should be understood that when the aluminum paste is overprinted on the silver grid line, the corresponding BC cell grid line formed includes a silver main grid line in contact with the silicon wafer and an aluminum grid line overprinted on the silver main grid line in the thickness direction of the silicon wafer. The aluminum grid line can be partially in contact with the silicon wafer, and the aluminum grid line also has good adhesion to the silicon wafer. Of course, the aluminum grid line in the BC cell grid line may not be in contact with the silicon wafer, for example, only overprinted on the surface of the silver grid line away from the silicon wafer.

[0045] 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 overlapping resistance and recombination. At the same time, this sintering temperature matches the low softening point glass powder used, which can achieve a lower overlapping resistance between the aluminum grid line and the silver grid line, and make the aluminum grid line have good adhesion, ensuring the photoelectric conversion efficiency and reliability of the grid line.

[0046] Next, the aluminum paste overprinted on the silver grid line of the BC cell and its application will be further described with specific examples: Example 1 The aluminum paste formulation of this example is shown in Table 1 and specifically includes: 78 parts by mass of aluminum powder, where the D50 of the aluminum powder = 9 μm, D90 = 23.5 μm, and the oxygen content = 0.24%.

[0047] 3 parts by mass of glass powder, wherein the glass powder comprises 55% Bi2O3, 20% B2O3, 15% BaCO3, 5% V2O5, 4% Al2O3, and 1% SiO2.

[0048] 3 parts by mass of organic resin, wherein the organic resin comprises acrylic resin:PVB resin:ethyl cellulose = (3 - 5):2:1.

[0049] 15 parts by mass of solvent, wherein the solvent comprises diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibasic acid ester = 2:1:(1 - 3).

[0050] 1 part by mass of additive, wherein the additive comprises phosphate ester dispersant and silicone leveling agent = 10:1.

[0051] Further, the above aluminum paste is placed in a disperser, dispersed at a rotation speed of 1500 rpm for 1 h, and then ground and dispersed on a three - roll mill until the fineness is ≤13 μm, and the paste viscosity is controlled at 16 Pa·s to obtain the aluminum paste. 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 the BC cell grid line. The BC cell grid line 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.

[0052] As shown in Table 2, the resistivity of the BC cell grid line in this example is 1.62×10 -5 Ω·cm, the silver - aluminum lap resistance is 0.52 Ω, the PL recombination is 113 fA / cm 2 , the 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 26.21%.

[0053] Example 2 The aluminum paste formulation of this example is shown in Table 1, and the contents and compositions of aluminum powder, organic resin, solvent, and additive are the same as those in Example 1.

[0054] The glass powder comprises 55% Bi2O3, 16% B2O3, 15% BaCO3, 5% V2O5, 4% Al2O3, and 5% SiO2.

[0055] Further, the process of preparing the aluminum paste in this Example 2, the process of overprinting the obtained aluminum paste on the silver main grid line, and the structure of the obtained BC cell grid line are the same as those in Example 1.

[0056] As shown in Table 2, the resistivity of the BC cell grid line in this example is 1.48×10 -5 Ω·cm, the silver - aluminum lap resistance is 0.51 Ω, the PL recombination is 98 fA / cm 2, The 3M adhesion performance is good, and the photoelectric conversion efficiency is 26.48%.

[0057] Example 3 The aluminum paste formulation of this example is shown in Table 1, and the contents and compositions of aluminum powder, organic resin, solvent, and additive are the same as those in Example 1.

[0058] The glass powder includes 45% Bi2O3, 25% B2O3, 20% BaCO3, 5% V2O5, 4% Al2O3, and 1% SiO2.

[0059] Furthermore, the process of preparing the aluminum paste in this Example 2, the process of overprinting the obtained aluminum paste on the silver main grid line, and the obtained BC cell grid line structure are all the same as those in Example 1.

[0060] As shown in Table 2, the resistivity of the BC cell grid line in this example is 1.89×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.43Ω, and the PL recombination is 45 fA / cm 2 , The 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 26.09%.

[0061] Comparative Example 1 The aluminum paste formulation of this example is shown in Table 1, and the contents and compositions of aluminum powder, organic resin, solvent, and additive are the same as those in Example 1.

[0062] The glass powder includes 50% Bi2O3, 15% B2O3, 16% BaCO3, 5% V2O5, 4% Al2O3, and 10% SiO2.

[0063] Furthermore, the process of preparing the aluminum paste in this Example 2, the process of overprinting the obtained aluminum paste on the silver main grid line, and the obtained BC cell grid line structure are all the same as those in Example 1.

[0064] As shown in Table 2, the PL recombination of the BC cell grid line in this example is 40 fA / cm 2 , The 3M adhesion performance is poor.

[0065] Comparative Example 2 The aluminum paste formulation of this example is shown in Table 1, and the contents and compositions of aluminum powder, organic resin, solvent, and additive are the same as those in Example 1.

[0066] The glass powder includes 38% Bi2O3, 25% B2O3, 20% BaCO3, 12% V2O5, 4% Al2O3, and 10% SiO2.

[0067] Furthermore, the process of preparing the aluminum paste in Example 2, the process of overprinting the obtained aluminum paste on the silver main grid line, and the obtained BC cell grid line structure are the same as those in Example 1.

[0068] As shown in Table 2, the resistivity of the BC cell grid line in this example is 4.47×10 -5 Ω·cm, the silver-aluminum lap resistance is 0.43 Ω, the PL recombination is 42 fA / cm 2 , the 3M adhesion performance is good, and the photoelectric conversion efficiency is 25.13%.

[0069] Comparative Example 3 The aluminum paste formula of this example is shown in Table 1, and the contents and compositions of the glass powder, organic resin, solvent and additive are the same as those in Example 1.

[0070] The D50 of the aluminum powder is 4.5 μm, the D90 is 19.8 μm, and the oxygen content is 0.29%.

[0071] Furthermore, the process of preparing the aluminum paste in Example 2, the process of overprinting the obtained aluminum paste on the silver main grid line, and the obtained BC cell grid line structure are the same as those in Example 1.

[0072] As shown in Table 2, the resistivity of the BC cell grid line in this example is 1.50×10 -5 Ω·cm, the silver-aluminum lap resistance is 2.55 Ω, the PL recombination is 287 fA / cm 2 , the 3M adhesion performance is excellent, and the photoelectric conversion efficiency is 24.88%.

[0073] In summary, according to the results of Examples 1-3 and Comparative Example 1, when the silicon content in the glass powder is relatively high, the high SiO2 glass phase will cause the mismatch of the thermal expansion coefficient, induce aluminum oxidation at the same time, and the aluminum-silver interface is easily isolated by excessive silicon oxides, weakening the interfacial bonding force between the aluminum paste and the silver grid, and the bonding force between the aluminum grid line and the silver grid line is poor. According to the results of Examples 1-3 and Comparative Example 2, when the Bi2O3 content in the glass powder is relatively low, the continuity of the network main body decreases, the defects increase, and the lap resistance between the aluminum grid line and the silver grid line increases. According to the results of Examples 1-3 and Comparative Example 3, when the particle size of the aluminum powder is too fine, the defects in the conductive network are likely to form high-resistance nodes at the silver-aluminum lap joint, resulting in a decrease in the interfacial quality between the silver grid line and the aluminum grid line and an increase in the resistivity.

[0074] Table 1 Aluminum paste formulas of each example and comparative example

[0075] Table 2 Grid line performance results of each example and comparative example

[0076] The present disclosure provides an aluminum paste for overprinting on the silver grid lines of BC cells, a preparation method thereof, and BC cell grid lines, which have the following beneficial effects compared with the prior art: First, by optimizing the components and contents of the aluminum paste, the present disclosure enables it to be overprinted on the silver grid lines through medium and high temperature sintering, reducing the usage amount of silver paste, thereby reducing costs. At the same time, the grid lines can maintain a reduced contact resistance and a high photoelectric conversion efficiency; Second, by using low softening point glass powder, the present disclosure makes it adaptable to the sintering temperature of the aluminum paste, which is beneficial to reducing the silver-aluminum contact resistance and recombination, and improving the adhesion of the aluminum grid lines; Third, by using aluminum powder within a specific particle size range, the present disclosure helps to reduce the silver-aluminum contact resistance and meet the requirements for overprinting on the silver grid lines.

[0077] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present disclosure. However, the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also considered within the protection scope of the present disclosure.

Claims

1. An aluminum paste for overprinting on the silver grid lines of BC cells, characterized in that, 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 additive; wherein, the glass powder is a bismuth borate glass powder with a softening point of 400 - 500 °C.

2. The aluminum paste according to claim 1, wherein, The bismuth borate 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.

3. The aluminum paste according to claim 1, characterized in that, The D50 of the aluminum powder is 5 - 10 μm, D90 ≤ 25 μm, and the oxygen content ≤ 0.3%.

4. The aluminum paste according to claim 1, wherein, The organic resin includes acrylic resin, PVB resin, and ethyl cellulose.

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

1.

6. The aluminum paste according to claim 1, wherein The solvent includes diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibasic acid ester.

7. The aluminum paste according to claim 6, wherein 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).

8. The aluminum paste according to claim 1, wherein The additive includes phosphate ester dispersant and silicone leveling agent.

9. A method for preparing the aluminum paste according to any one of claims 1-8, characterized in that, The method includes: Mix 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 additive to obtain a mixed component; Perform dispersion and grinding on the mixed component, and control the fineness of the paste ≤ 13 μm and the viscosity to be 12 - 20 Pa·s to obtain the aluminum paste.

10. A BC cell grid line, characterized in that, The BC cell grid line includes a silver grid line and an aluminum grid line overprinted on at least part of the silver grid line; wherein, The aluminum grid line is formed by sintering the aluminum paste according to any one of claims 1 - 8.

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