Conductive silver paste for BC battery, preparation method and BC battery

Abstract

The invention relates to the technical field of electronic materials, in particular to conductive silver paste for a BC battery, a preparation method and the BC battery, and the conductive silver paste comprises the following components in percentage by weight: 88-93 wt% of silver powder, 3-5 wt% of glass powder, 1-3 wt% of organic resin, 6-10 wt% of solvent and 0-1 wt% of other auxiliaries, the sum of the components is 100 wt%, the glass powder comprises an alkali metal ion compound and / or a high-content lead oxide. By adding the rubidium ionic compound, the cesium ionic compound and the high-content lead oxide, the conflict between the softening point and acetic acid resistance of the glass powder can be balanced, so that the problem of high acetic acid attenuation rate of a BC battery is completely or partially solved, and meanwhile, the reliability of the BC battery is improved.

Description

Technical Field

[0001] This application relates to the field of electronic materials technology, particularly to the field of solar cell technology, and especially to a conductive silver paste for BC cells, a preparation method thereof, and the BC cell itself. Background Technology

[0002] A solar cell is a semiconductor device that converts sunlight into electrical energy through the photovoltaic effect. Its basic working principle is that under sunlight, electrons in the semiconductor material are excited by photon energy, generating electron-hole pairs, which then separate and move under the influence of a built-in electric field, forming an electric current.

[0003] Bipolar Junction Cell (BC) cells are a novel type of high-efficiency solar cell structure. They achieve electron and hole separation and collection by fabricating interdigitated P- and N-regions on the back of the cell and mounting ohmic contact grid electrodes on top of them. The absence of grid lines on the front allows for higher short-circuit current. The wide metal electrodes on the back reduce series resistance, resulting in a higher fill factor. Acetic acid degradation is one of the core reliability challenges currently facing the industry in BC cells.

[0004] Therefore, it is necessary to develop a conductive silver paste material for BC batteries that reduces acetic acid degradation rate. Summary of the Invention

[0005] Acetic acid degradation refers to the phenomenon where, under high temperature and humidity conditions, the encapsulation materials of photovoltaic modules readily produce acetic acid during degradation, causing corrosion to the metal parts of the cells and modules, such as grid lines, solder ribbons, and busbars, leading to an irreversible decrease in module power. For conventional modules, acetic acid first corrodes the silver grid lines on the front side. However, BC cells, due to their structure with no grid lines on the front side and a full back electrode, face a more severe reliability challenge from acetic acid degradation. Specifically, the grid lines, especially the silver grid lines, exhibit increased grid contact resistance and increased series resistance between the BC cell and the module.

[0006] In related technologies, the intrinsic resistance of BC batteries to acetic acid corrosion can be improved through optimization of the metallization system, such as using silver paste that is more resistant to acetic acid corrosion. Generally, silver paste includes silver powder, glass powder, organic resin, solvent, and other trace components. The main component, silver powder, acts as the conductive phase after sintering, while the glass powder, which acts as the binder phase, determines whether the silver paste can form excellent ohmic contact with the battery cell and affects the long-term reliability of the electrode.

[0007] The inventors discovered that adding alkali metal ions, such as active ions like Li+ and Na+, to glass powder can provide a lower softening temperature and excellent flowability for BC silver paste glass. However, Li+ and Na+ make the glass powder locally alkaline. Under humid and acidic environments, the glass is prone to acid-base neutralization reactions, leading to a loosened, decomposed, or even ineffective glass powder structure. This ultimately affects the contact resistance between the silicon substrate and the metal grid lines of the BC battery, impacting the acetic acid degradation rate. Therefore, the purpose of this application is to provide a BC silver paste and its preparation method that balances the conflict between the softening point and acetic acid resistance of glass powder, thereby completely or partially solving the problem of high acetic acid degradation rate in BC batteries and improving the reliability of BC batteries.

[0008] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a conductive silver paste for BC batteries, wherein the conductive silver paste comprises the following components by weight percentage: 88-93 wt% silver powder, 3-5 wt% glass powder, 1-3 wt% organic resin, 6-10 wt% solvent, and 0-1 wt% other additives, the sum of the above components being 100 wt%, wherein the glass powder comprises alkali metal ion compounds and / or a high content of lead oxide.

[0009] In the above technical solution, the conductive silver paste mainly comprises silver powder as the conductive phase, low-melting-point glass powder as the binder phase, and the organic resin, solvent, and other additives provide the conductive silver paste with flow properties, viscosity, thixotropy, and other modifiable properties. The glass powder contains lead oxide, which can further reduce the softening point and high-temperature melting viscosity of the glass, making it more suitable for the actual application scenarios of BC silver paste. Additionally, the glass powder contains alkali metal ion compounds, which act as a network disruptor in the glass, providing the glass powder with a lower softening temperature and excellent flowability.

[0010] In conjunction with the first aspect, in one possible implementation, the lead oxide includes PbO, and / or the alkali metal ionic compound includes rubidium ionic compounds and cesium ionic compounds.

[0011] In the above technical solution, the lead oxide includes PbO. PbO is a fluxing agent, mainly used to lower the melting temperature, which can significantly reduce the softening point of conductive silver paste; adjust viscosity to make the molten glass have moderate fluidity; enhance wettability: improve the wetting of silicon and silver by the glass; and provide reactivity to participate in the reaction of etching the silicon nitride layer. In other words, glass containing PbO has a low softening temperature and high fluidity, and can flow smoothly between the silver powder gaps to reach the contact interface. In addition, the high PbO content further reduces the softening point and high-temperature melting viscosity of the glass, making the glass more suitable for the actual application scenarios of BC silver paste. Optionally, the alkali metal ion compound includes rubidium ion compounds and cesium ion compounds. Rb+ and Cs+ are also alkali metal ions with larger atomic radii, which have a stronger ability to break glass networks than Li+. They can also quickly reduce the softening temperature of glass powder and improve the fluidity of glass when used in small quantities. In addition, the basicity (electronegativity) of Rb+ and Cs+ is weaker than that of the active ion Li+, so their acid resistance is stronger than that of Li+.

[0012] In conjunction with the first aspect, in one possible implementation, the rubidium ionic compound includes Rb₂CO₃, and / or the cesium ionic compound includes Cs₂CO₃.

[0013] In conjunction with the first aspect, in one possible implementation, the Rb₂CO₃ content in the glass powder is 0 ≤ y ≤ 2 wt% by weight, and / or the Cs₂CO₃ content is 0 ≤ y ≤ 2 wt%, and / or the PbO content is 35-40 wt%.

[0014] In conjunction with the first aspect, in one possible implementation, the Rb2CO3 content in the glass powder is 1 ≤ y ≤ 1.75 wt% by weight, and / or the Cs2CO3 content is 1 ≤ y ≤ 1.75 wt%, and / or the PbO content is 36-36.5 wt%.

[0015] In conjunction with the first aspect, in one possible implementation, the Rb2CO3 content in the glass powder is 1.5 wt% by weight, and / or the Cs2CO3 content is 1.5 wt%.

[0016] In the above technical solution, by adjusting the content of PbO and rubidium ionic compounds and / or cesium ionic compounds, the softening temperature of the glass can be controlled, while providing highly active ions to strongly corrode silicon nitride and weaken acetic acid decay.

[0017] In conjunction with the first aspect, in one possible implementation, the glass powder is a lead-bismuth-tellurium glass powder, the softening point of which is controlled at 450-600℃. The lead-bismuth-tellurium glass powder comprises a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system comprises 35-40wt% PbO, 30-40wt% Bi2O3, and 20-30wt% TeO2; the second component system comprises 0-5wt% SiO2 and / or 0-3wt% Al2O3 and / or 0-5wt% WO3; and the third component system comprises 0-2wt% Rb2CO3 and / or 0-2wt% Cs2CO3.

[0018] In the above technical solution, the glass powder system is more suitable for BC batteries. While opening the current channel, it constructs a robust conductive electrode bridge, thereby achieving higher battery conversion efficiency and long-term reliability.

[0019] In conjunction with the first aspect, in one possible implementation, the silver powder is spherical with a particle size D50 of 1.4–2.1 μm and a specific surface area of ​​0.25–0.5 m². 2 / g, tap density is 5.5-6.5g / ml, organic coating amount ≤0.7%.

[0020] In conjunction with the first aspect, in one possible implementation, the organic resin includes one or more of SEPS resin, acrylic resin, PVB resin, and CAB resin, wherein the mass ratio of SEPS resin: acrylic resin: PVB resin: CAB resin is (3~5):2:1:1. And / or, the solvent includes one or more of diethylene glycol dibutyl ether, dimethyl phthalate, dodecyl alcohol ester, and diethylene glycol butyl ether acetate, wherein the mass ratio of diethylene glycol dibutyl ether: dimethyl phthalate: dodecyl alcohol ester: diethylene glycol butyl ether acetate is 1:2:1.5:(1~3). And / or, the other additives include one or more of castor oil thixotropic agents and silicone leveling agents, wherein the mass ratio of castor oil thixotropic agent to silicone leveling agent is 5:1.

[0021] In the above technical solution, the SEPS resin imparts good ink permeability to the silver paste, avoiding problems such as incomplete or broken grid lines; the acrylic resin has strong plasticity, giving the silver paste an excellent aspect ratio; the PVB and CAB resins provide sufficient viscosity to the paste, making the silver paste printing more uniform. Optionally, the diethylene glycol dibutyl ether, with its weak polarity and low viscosity, is used to quickly reduce the viscosity of the paste; dimethyl phthalate, with its viscosity-enhancing effect, acts as a plasticizer, which is beneficial for narrowing the line width of the silver paste printing grid; dodecyl alcohol ester and diethylene glycol butyl ether acetate have moderate polarity and are compatible with most resins, serving as stable diluents. Optionally, the castor oil is used to adjust the rheological properties of the paste, which is beneficial for the stability and storage of the paste; silicone oil has the function of lubrication and promoting the differential phase of the organic system, narrowing the grid width while ensuring smooth printing.

[0022] Secondly, this application provides a method for preparing conductive silver paste for BC batteries, comprising the following steps: mixing the silver powder, the glass powder, the organic resin, the solvent, and the other additives, and placing them into a disperser; dispersing the mixture at a speed of 500-2000 rpm for 1 hour, and then grinding and dispersing it on a three-roll mill until the fineness is ≤7 μm, thereby obtaining a conductive paste with a viscosity of 50-70 Pa·S, wherein the viscosity of the paste is measured using a Brookfield DV2T viscometer at 25°C and a speed of 50 rpm.

[0023] Thirdly, this application provides a BC battery, which is prepared by printing and sintering the aforementioned conductive silver paste for BC batteries.

[0024] The first aspect of this application provides a BC silver paste that balances the conflict between glass softening point and acetic acid resistance. By using a high content of PbO, the softening point and high-temperature melt viscosity of the glass are further reduced, making the glass more suitable for the actual application scenarios of BC silver paste. By using rubidium ionic compounds and cesium ionic compounds, Rb+ and Cs+, as alkali metal ions, have larger atomic radii and stronger ability to break up glass networks than Li+. Even when used in small quantities, they can quickly reduce the softening temperature of glass powder and improve the fluidity of the glass. In addition, the basicity (electronegativity) of Rb+ and Cs+ is weaker than that of the active ion Li+, so its acid resistance is stronger than that of Li+.

[0025] The second aspect of this application provides a method for preparing silver paste, which can be used in BC batteries to solve, in whole or in part, the problem of high acetic acid degradation rate in BC batteries, while improving the reliability of BC batteries.

[0026] A third aspect of this application provides a BC battery that exhibits good resistance to acetic acid degradation while ensuring reliability. Detailed Implementation

[0027] To make the technical problems, solutions, and beneficial effects of this application clearer, the following detailed description, in conjunction with embodiments, is provided. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0028] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0029] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items.

[0030] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0031] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0032] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0033] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0034] The term "range" disclosed herein takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0035] Acetic acid degradation refers to the irreversible decrease in photovoltaic (PV) power output caused by the degradation of encapsulation materials, such as the common EVA (ethylene-vinyl acetate copolymer) film, in high-temperature and high-humidity environments. Acetic acid is produced during this degradation process, corroding the metal components of the cells and modules, such as grid lines, solder ribbons, and busbars. EVA undergoes hydrolysis in humid and hot environments, decomposing to produce acetic acid. Higher temperatures, higher humidity, and longer durations accelerate the hydrolysis reaction, resulting in greater acetic acid production. Furthermore, the produced acetic acid lowers the local pH value, which in turn accelerates the hydrolysis of EVA itself, creating a vicious cycle.

[0036] For conventional modules, acetic acid will first corrode the silver grid lines on the front side. However, due to the unique structure of the BC cell, which has a full back contact, it is more sensitive to acetic acid degradation. All electrodes of the BC cell, including the positive and negative grid lines, solder ribbons, and interconnects, are concentrated on the back side. After lamination, the metal electrodes are encapsulated in the same small back cavity environment.

[0037] The encapsulation materials, especially the acetic acid produced by the degradation of EVA on the back, are more likely to accumulate and concentrate in the relatively enclosed space on the back, making it difficult for them to diffuse outwards. High concentrations of acetic acid will simultaneously corrode all metal components of the positive and negative electrodes, including the silver grid lines. Corrosion leads to increased grid line resistance and poor contact. The solder ribbons and interconnects are usually copper-based and tin-plated. Acetic acid will corrode the tin plating layer and further corrode the internal copper. The distance between the positive and negative electrodes is very close in the BC structure. Migrates produced by metal corrosion may bridge between the positive and negative electrodes, leading to leakage or even short circuits, causing battery failure.

[0038] Conventional PERC cells have their positive and negative electrodes on the front and back sides, respectively, resulting in a relatively dispersed acetic acid environment. Furthermore, the silver grid lines on the front side are protected by glass, minimizing corrosion risk. However, BC cells, with their front-side gridless and fully back-electrode structure, offer advantages in high conversion efficiency and aesthetics, but face reliability challenges, particularly acetic acid degradation. This involves increased series resistance in the cell's grid lines, especially the silver grid lines, under the humid and hot conditions of acetic acid, a problem that urgently needs addressing. Optimizing the BC cell structure design and manufacturing process is essential. One approach is to add passivation and protective layers on top of the metal electrodes and semiconductor layer on the back side, forming a denser and more stable passivation layer, such as AlOx or SiNx, to act as a physical and chemical barrier against acetic acid corrosion. Another approach is to optimize the metallization system of the conductive silver paste, using more corrosion-resistant metal pastes, such as conductive silver pastes with higher silver content and more stable glass systems, or improving the welding process to reduce microscopic defects on the metal surface and enhance its intrinsic corrosion resistance.

[0039] This application provides a conductive silver paste for BC batteries, its preparation method, and the battery itself, in order to better reduce the acetic acid degradation rate and improve the reliability of BC batteries. The conductive silver paste for BC batteries in this application reduces the degradation rate and improves battery reliability by adding a large amount of lead oxide and alkali metal ion compounds with large ionic radii to the glass powder.

[0040] The first aspect of this application provides a conductive silver paste for BC batteries, comprising: The conductive silver paste comprises, by weight percentage, the following components: 88-93 wt% silver powder, 3-5 wt% glass powder, 1-3 wt% organic resin, 6-10 wt% solvent, and 0-1 wt% other additives, with the sum of the above components being 100 wt%. The conductive silver paste includes silver powder as the main conductive phase, low-melting-point glass powder as the binder phase, and the organic resin, solvent, and other additives provide the conductive silver paste with flow properties, viscosity, thixotropy, and other modifiable properties.

[0041] The glass powder is a lead-bismuth-tellurium glass powder, the softening point of which is controlled at 450-600℃. The lead-bismuth-tellurium glass powder comprises a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system comprises 35-40wt% PbO, 30-40wt% Bi2O3, and 20-30wt% TeO2; the second component system comprises 0-5wt% SiO2 and / or 0-3wt% Al2O3 and / or 0-5wt% WO3; and the third component system comprises 0-2wt% Rb2CO3 and / or 0-1wt% Li2CO3.

[0042] The glass powder comprises lead oxides and / or alkali metal ion compounds. The lead oxides include PbO, which is a fluxing agent primarily used to lower the melting temperature, significantly reducing the softening point of conductive silver paste; adjusting viscosity to achieve moderate fluidity of the molten glass; enhancing wettability by improving the wetting of silicon and silver; and providing reactivity to participate in the etching reaction of the silicon nitride layer. In other words, glass containing PbO has a low softening temperature and high fluidity, allowing it to flow smoothly between the silver powder particles and reach the contact interface. Furthermore, the high PbO content further reduces the softening point and high-temperature melting viscosity of the glass, making it more suitable for the actual application scenarios of BC silver paste. In this application, the PbO content in the glass powder is 35-40 wt%.

[0043] The Bi₂O₃ exhibits strong corrosive properties, and its ionic characteristics facilitate the dissolution and transport of silver. It can quickly break through the passivation film at the contact site, forming contact points with the poly layer, and can also adjust the coefficient of thermal expansion. The SiO₂, as a network structure, promotes the uniform integration of the glass components, preventing crystallization and inhomogeneity, and providing structural stability, mechanical strength, and chemical durability. The WO₃ reduces the surface tension of the glass after high-temperature melting, making it easier to wet the silver powder surface and contact interface. The TeO₂, being an ultra-low melting point oxide, is used for specific ultra-low temperature sintering requirements.

[0044] The alkali metal ion compounds include rubidium ion compounds and / or cesium ion compounds. Rb+ and Cs+ are also alkali metal ions with larger atomic radii, which have a stronger ability to break glass networks than Li+. They can also quickly reduce the softening temperature of glass powder and improve the fluidity of glass when used in small quantities. In addition, the basicity (electronegativity) of Rb+ and Cs+ is weaker than that of the active ion Li+, so their acid resistance is stronger than that of Li+.

[0045] In some possible embodiments, the rubidium ionic compound is Rb₂CO₃. In some possible embodiments, the Rb₂CO₃ content is 0 ≤ y ≤ 2 wt%. In some possible embodiments, the Rb₂CO₃ content is 1 ≤ y ≤ 1.75 wt%. In other possible embodiments, the Rb₂CO₃ content is 1.5 wt%.

[0046] In some possible embodiments, the rubidium ionic compound is Cs₂CO₃. In some possible embodiments, the Cs₂CO₃ content is 0 ≤ y ≤ 2 wt%. In some possible embodiments, the Cs₂CO₃ content is 1 ≤ y ≤ 1.75 wt%. In other possible embodiments, the Cs₂CO₃ content is 1.5 wt%.

[0047] Optionally, the silver powder is spherical with a particle size D50 of 1.4–2.1 μm and a specific surface area of ​​0.25–0.5 m². 2 / g, tap density is 5.5-6.5g / ml, and organic coating content is ≤0.7%. Among them, the large porosity between medium and large-sized silver powder particles provides ample flow channels for glass; the low organic coating content gives the silver powder high sintering activity and effectively reduces the grid line resistance of silver paste.

[0048] Optionally, the glass powder may contain lead oxide and / or alkali metal ion compounds. The lead oxide in the glass powder can further reduce the softening point and high-temperature melting viscosity of the glass, making it more suitable for the actual application scenarios of BC silver paste.

[0049] Optionally, the glass powder contains alkali metal ion compounds. These alkali metal ions act as a mesh-breaking agent in the glass, providing the glass powder with a lower softening temperature and excellent flowability. The alkali metal ions selected in this application mainly include Rb+ and / or Cs+, using Rb+ and / or Cs+ instead of Li+ used in conventional glass, and increasing the amount of PbO used in the glass.

[0050] According to a second aspect of this application, a method for preparing conductive silver paste for BC batteries is provided, the method comprising the following steps: S01: Prepare the slurry by weighing 88-93 wt% silver powder, 3-5 wt% glass powder, 1-3 wt% organic resin, 6-10 wt% solvent, and 0-1 wt% other additives, with the sum of the above components being 100 wt%. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them into a disperser. S02: Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; S03: Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm to obtain a viscosity of 50-70Pa·S. The viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25°C and 50rpm. Optionally, the roller spacing of the three-roll mill is set to 10-120μm and the grinding speed is 100-200rpm to obtain the conductive slurry. According to a third aspect of this application, a BC battery is provided, wherein the BC battery is prepared by printing and sintering the aforementioned conductive silver paste for BC batteries.

[0051] Specifically, the following steps are included: S10: Front surface and bulk passivation treatment, using N-type silicon wafers, a pyramid-shaped textured surface is formed on the front side through chemical etching to reduce reflection; on the textured surface structure on the front side, an extremely thin, high-quality intrinsic amorphous silicon or aluminum oxide layer is grown through techniques such as atomic layer deposition to achieve excellent chemical passivation; covered with a silicon nitride anti-reflection film. S20: Backside patterning and selective doping: P-type and N-type regions are precisely fabricated on the back of the battery. S30: Backside passivation layer deposition. A high-quality aluminum oxide / silicon nitride stacked passivation film is deposited on the entire backside, including the newly formed P+ and N+ regions, to reduce backside recombination. Using a laser again, micron-sized contact holes are precisely drilled on the passivation layer directly above the P+ and N+ regions on the backside, exposing the heavily doped silicon regions underneath. Using a high-precision screen printing machine, silver paste is printed once or twice to fill the contact holes in the P and N regions, forming the backside gate lines and pads, so that the paste can form good ohmic contact with both P-type and N-type silicon.

[0052] S40: Post-sintering testing, including sintering at high temperature to allow the glass material in the silver paste to form an ohmic contact with the silicon, while simultaneously solidifying the electrode; then testing the battery's electrical performance parameters.

[0053] To achieve better experimental comparison, the slurry in the embodiments and comparative examples of this application was weighed according to the following weight percentages: 88 wt% silver powder, 3.9 wt% glass powder, 2 wt% organic resin, 6 wt% solvent, and 0.1 wt% other additives, with the sum of the above components being 100 wt%. The silver powder used had a particle size D50 of 1.9 μm and a specific surface area of ​​0.5 m². 2 The sample has a tap density of 5.9 g / ml and an organic coating weight of 0.5%. The organic resin comprises a mixture of SEPS resin, acrylic resin, PVB resin, and CAB resin, with a mass ratio of SEPS resin:acrylic resin:PVB resin:CAB resin of (3~5):2:1:1. The solvent comprises a mixture of diethylene glycol dibutyl ether, dimethyl phthalate, dodecyl alcohol ester, and diethylene glycol butyl ether acetate, wherein the mass ratio of diethylene glycol dibutyl ether:dimethyl phthalate:dodecyl alcohol ester:diethylene glycol butyl ether acetate is 1:2:1.5:(1~3). Other additives include a mixture of castor oil thixotropic agent and silicone leveling agent, with a mass ratio of castor oil thixotropic agent:silicone leveling agent of 5:1.

[0054] The differences are explained below with reference to specific embodiments. Table 1 below shows the content of each component of the glass powder in each embodiment and comparative example.

[0055] Table 1

[0056] Example 1 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 7wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 0.5wt% Rb2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 50rpm. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0057] Compared with Comparative Example 1, this demonstrates that by adding 0.5 wt% Rb2CO3, the softening point of BC silver paste glass was lowered while the acetic acid resistance was improved.

[0058] Example 2 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 6.5wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 1wt% Rb2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0059] Compared with Example 1, this demonstrates that increasing the amount of Rb2CO3 added can better reduce the softening point of BC silver paste glass while maintaining good acetic acid resistance.

[0060] Example 3 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 6wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 1.5wt% Rb2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0061] Compared with Examples 1 and 2, it is shown that increasing the amount of Rb2CO3 added can better reduce the softening point of BC silver paste glass while maintaining acetic acid resistance.

[0062] Example 4 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the total weight of the components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 5.75wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 1.75wt% Rb2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0063] Compared with Examples 1 / 2 / 3 and Comparative Example 1, it is further shown that increasing the amount of Rb2CO3 added can better reduce the softening point of BC silver paste glass and improve its acetic acid resistance to a certain extent, but the acetic acid resistance decreases with the increase of the amount added.

[0064] Example 5 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the total weight of the components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 5.5wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 2wt% Rb2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0065] Compared with Examples 1 / 2 / 3 / 4 and Comparative Example 1, it is further shown that increasing the amount of Rb2CO3 added can better reduce the softening point of BC silver paste glass and improve acetic acid resistance to a certain extent, but the acetic acid resistance decreases with the increase of the amount added.

[0066] Comparative Example 1 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 5.5wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 2wt% Li2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0067] Compared to the examples, this comparative example only added 2wt% Li2CO3, and its resistance to acetic acid degradation was relatively weak.

[0068] Comparative Example 2 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 6wt% PbO3, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 3wt% SiO2 and 2.5wt% WO3; and the third component system includes 1wt% Rb2CO3 and 1wt% Li2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0069] Compared to the examples, this comparative example only added 1wt% Rb2CO3 and 1wt% Li2CO3, which has some resistance to acetic acid degradation, but its reliability is not as good as that of the examples.

[0070] Comparative Example 3 A conductive silver paste for BC batteries is prepared by the following steps: (1) Prepare the slurry by weighing 88wt% silver powder, 3.9wt% glass powder, 2wt% organic resin, 6wt% solvent, and 0.1wt% other additives, with the sum of the above components being 100wt%. The glass powder is a lead-bismuth-tellurium glass powder, i.e., a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 30wt% PbO, 33wt% Bi2O3, and 24wt% TeO2; the second component system includes 8.5wt% SiO2 and 2.5wt% WO3; and the third component system includes 1wt% Rb2CO3 and 1wt% Li2CO3. Mix the silver powder, glass powder, organic resin, solvent, and other additives, and place them in a disperser. (2) Disperse using a disperser at a speed of 500-2000 rpm for 1 hour; (3) Grind and disperse the conductive slurry on a three-roll mill until the fineness is ≤7μm, and the viscosity of the conductive slurry is 50-70Pa·S, wherein the viscosity of the slurry is measured by a Brookfield DV2T viscometer at 25℃ and 10r / min. (4) The conductive silver paste prepared above was printed and sintered to prepare a photovoltaic cell for acetic acid degradation test.

[0071] Compared to Comparative Example 2 and the Example 1, this comparative example contains less PbO and has a higher glass softening temperature. The glass softening temperature does not match the actual sintering requirements, resulting in a decrease in photoelectric conversion efficiency.

[0072] Performance testing The conductive silver pastes prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to acetic acid degradation tests. Table 2 shows the results before acetic acid degradation. Table 3 shows the acetic acid degradation rate test results.

[0073] Table 2

[0074] Table 3

[0075] As can be seen from the data in Tables 2 and 3 above, the conductive silver paste of this application contains a high content of PbO in the glass powder, and uses rubidium and cesium ion compounds. Rb+ and Cs+ are also alkali metal ions with larger atomic radii, which have a stronger ability to break up the glass network than Li+. They can also quickly reduce the softening temperature of the glass powder and improve the fluidity of the glass when used in small quantities. In addition, the basicity (electronegativity) of Rb+ and Cs+ is weaker than that of the active ion Li+, so their acid resistance is stronger than that of Li+. This has the best effect on reducing the acetic acid decay rate of BC batteries and improving the reliability of BC batteries.

[0076] It should be noted that, due to space limitations, this application will not elaborate on the experiments involving the addition of Cs+ to glass powder and conductive silver paste. It should also be noted that, during the experimental phase, the effects of adding equal amounts of Cs2CO3 and Rb2CO3 on reducing the acetic acid degradation rate and improving the reliability of BC batteries were essentially similar, therefore, they will not be discussed further here.

[0077] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A conductive silver paste for BC batteries, characterized in that, The conductive silver paste comprises the following components by weight percentage: 88-93 wt% silver powder, 3-5 wt% glass powder, 1-3 wt% organic resin, 6-10 wt% solvent, and 0-1 wt% other additives, with the sum of the above components being 100 wt%. The glass powder contains alkali metal ion compounds and / or a high content of lead oxide.

2. The conductive silver paste for BC batteries as described in claim 1, characterized in that, The lead oxide includes PbO, and / or the alkali metal ionic compound includes rubidium ionic compounds and / or cesium ionic compounds.

3. The conductive silver paste for BC batteries as described in claim 2, characterized in that, The ionic compounds of rubidium include Rb₂CO₃, and / or the ionic compounds of cesium include Cs₂CO₃.

4. The conductive silver paste for BC batteries as described in claim 3, characterized in that, In the glass powder, the Rb2CO3 content is 0≤y≤2wt% by weight, and / or the Cs2CO3 content is 0≤y≤2wt%, and / or the PbO3 content is 5-40wt%.

5. The conductive silver paste for BC batteries as described in claim 4, characterized in that, In the glass powder, the Rb2CO3 content is 1≤y≤1.75wt% by weight, and / or the Cs2CO3 content is 1≤y≤1.75wt%, and / or the PbO3 content is 6-36.5wt%.

6. The conductive silver paste for BC batteries as described in any one of claims 1 to 5, characterized in that, The glass powder is a lead-bismuth-tellurium glass powder, and the softening point of the lead-bismuth-tellurium glass powder is controlled at 450-600℃. The lead-bismuth-tellurium glass powder includes a PbO-Bi2O3-TeO2 system. By weight percentage, the first component system includes 35-40wt% PbO, 30-40wt% Bi2O3, and 20-30wt% TeO2; the second component system includes 0-5wt% SiO2 and / or 0-3wt% Al2O3 and / or 0-5wt% WO3; and the third component system includes 0-2wt% Rb2CO3 and / or 0-2wt% Cs2CO3.

7. The conductive silver paste for BC batteries as described in claim 6, characterized in that, The silver powder is spherical with a particle size D50 of 1.4–2.1 μm and a specific surface area of ​​0.25–0.5 m². 2 / g, tap density is 5.5-6.5g / ml, organic coating amount ≤0.7%.

8. The conductive silver paste for BC batteries as described in claim 7, characterized in that, The organic resin includes one or more of SEPS resin, acrylic resin, PVB resin, and CAB resin, wherein the mass ratio of SEPS resin: acrylic resin: PVB resin: CAB resin is (3~5):2:1:

1. And / or, the solvent includes one or more of diethylene glycol dibutyl ether, dimethyl phthalate, dodecyl alcohol ester, and diethylene glycol butyl ether acetate, wherein the mass ratio of diethylene glycol dibutyl ether: dimethyl phthalate: dodecyl alcohol ester: diethylene glycol butyl ether acetate is 1:2:1.5:(1~3). And / or, the other additives include one or more of castor oil thixotropic agents and silicone leveling agents, wherein the mass ratio of castor oil thixotropic agent to silicone leveling agent is 5:

1.

9. A method for preparing conductive silver paste for BC batteries, comprising the conductive silver paste for BC batteries as described in claims 1-5 and any one of claims 7-8, characterized in that, Includes the following steps: The silver powder, glass powder, organic resin, solvent, and other additives are mixed and placed in a disperser. After dispersing for 1 hour at a speed of 500-2000 rpm, the mixture is ground and dispersed on a three-roll mill until the fineness is ≤7 μm, resulting in a conductive silver paste with a viscosity of 50-70 Pa·S.

10. A BC battery, characterized in that, The BC battery is prepared by printing and sintering the conductive silver paste for BC batteries as described in any one of claims 1 to 5 or 7 to 8, or the conductive silver paste prepared by the method described in claim 9.

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