Organic resin, front silver paste and topcon cell

Abstract

The present application provides an organic resin, a front silver paste and a TOPCon battery, the organic resin comprises, in percentage by mass: a conjugated polymer block copolymer modified resin 40%-45%, a MOF-based crosslinking modified resin 30%-35% and a poly-ionic liquid grafted modified resin 20%-25%. The organic resin not only has good rheological properties, compatibility and sintering adaptability, but also can provide additional conductive channels, thereby adapting the narrow line width printing process of the TOPCon battery.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to an organic resin, a front-side silver paste, and a TOPCon cell. Background Technology

[0002] As TOPCon (Tunnel Oxide Passivated Contact) cells iterate towards higher efficiency and refinement, they have become one of the next generation of mainstream photovoltaic cells due to their higher conversion efficiency. To further improve the photoelectric conversion efficiency of TOPCon cells and reduce the cost per unit power, the electrode printing process for TOPCon cells is developing towards narrower linewidths. The performance of the organic carrier in the front-side silver paste, as a key component of the electrode, directly determines the printing compatibility, rheological properties, and electrode forming quality of the front-side silver paste. Currently, the organic resins in front-side silver pastes are mostly single-system or simple blends, which have two major drawbacks: first, they lack a conjugated conductive structure, only serving a physical bonding function and failing to provide additional conductive channels for ultra-narrow linewidth electrodes, resulting in high silver powder consumption; second, their molecular structure compatibility is poor, either leading to insufficient compatibility causing paste agglomeration or causing problems such as ink overflow, edge collapse, or screen clogging during narrow linewidth printing due to unbalanced rheological properties. Summary of the Invention

[0003] The purpose of this invention is to provide an organic resin that not only has good rheological properties, compatibility and sintering adaptability, but also provides additional conductive channels, thereby adapting to the narrow linewidth printing process of TOPCon batteries.

[0004] This invention provides an organic resin for use in front-side silver paste. By mass percentage, the organic resin comprises: 40%-45% conjugated polymer block copolymer modified resin, 30%-35% MOF-based crosslinked modified resin, and 20%-25% polyionic liquid graft modified resin.

[0005] In one feasible manner, the conjugated polymer block copolymer modified resin is a polythiophene-block-polymethacrylate block copolymer.

[0006] In one feasible manner, the preparation steps of the polythiophene-block-polymethacrylate block copolymer include: Polythiophene initiator was obtained by polymerization using 3-hexylthiophene as a monomer and initiated by ethyl bromide isobutyrate. The polythiophene-block-polymethacrylate block copolymer is obtained by polymerization using methyl methacrylate and hydroxyethyl methacrylate as comonomers and initiated by the polythiophene initiator.

[0007] In one feasible embodiment, the mass ratio of polythiophene segments to polymethacrylate segments in the polythiophene-block-polymethacrylate block copolymer is 3:2, and the PDI of the polythiophene-block-polymethacrylate block copolymer is ≤1.3.

[0008] In one feasible manner, the preparation steps of the MOF-based crosslinked modified resin include: Epoxy-modified polymethacrylate was obtained by polymerization of methyl methacrylate and glycidyl methacrylate as comonomers initiated by azobisisobutyronitrile. The MOF material was mixed with the epoxy-modified polymethyl methacrylate and reacted under the action of a catalyst. The reaction product was then subjected to precipitation, washing and drying to obtain the MOF-based crosslinked modified resin.

[0009] In one feasible manner, the MOF material is HKUST-1, and the preparation steps of HKUST-1 include: reacting copper chloride or copper nitrate with trimesic acid via hydrothermal / solvothermal reaction to synthesize HKUST-1 with carboxyl groups grafted on the surface. Alternatively, the MOF material is Ni-MOF-74, and the preparation steps of Ni-MOF-74 include: reacting nickel chloride or nickel nitrate with 2,5-dihydroxyterephthalic acid via hydrothermal / solvothermal reaction to synthesize Ni-MOF-74 with surface-grafted carboxyl and hydroxyl groups.

[0010] In one feasible manner, the preparation steps of the polyionic liquid grafted modified resin include: The polyionic liquid grafted modified resin is obtained by mixing polymethacrylate or polythiophene as the matrix skeleton with an ionic liquid monomer, adding azobisisobutyronitrile or benzoyl peroxide as an initiator, and then performing free radical graft polymerization; wherein the ionic liquid monomer is an imidazolium-type ionic liquid monomer or a pyridinium-type ionic liquid monomer.

[0011] In one feasible manner, the imidazolium-type ionic liquid monomer comprises 1-vinyl-3-butylimidazolium hexafluorophosphate, and the pyridinium-type ionic liquid monomer comprises 4-vinylpyridine p-toluenesulfonate.

[0012] In one feasible manner, the grafting rate of the ionic liquid monomer is 15%-25%.

[0013] The present invention also provides a front-side silver paste, which, by weight percentage, comprises: 75% silver powder. 90%, glass powder 1.3% 4.1%, organic resin 1%-4%, organic solvent 1%-10% and silicone oil 0.1%-0.5%; the organic resin is the organic resin described above.

[0014] In one feasible embodiment, the silver powder is a highly tapped monodisperse spherical silver powder with a particle size D50 of 0.4 μm-1.5 μm, a particle size D100 < 3.5 μm, and a tap density ≥ 5.5 g / cm³. 3 Loose packing density ≥ 3.0 g / cm³ 3 sphericity ≥ 0.9.

[0015] The present invention also provides a TOPCon battery, including electrodes, which are obtained by sintering front-side silver paste as described above.

[0016] The organic resin provided by this invention employs a synergistic system of three modified resins: a conjugated polymer block copolymer modified resin, a MOF-based crosslinked modified resin, and a polyionic liquid graft modified resin. The mass ratio of these three resins is controlled, allowing for precise division of labor and synergistic effects. The conjugated polymer block copolymer modified resin constructs conductive channels and optimizes printing viscosity through a π-π stacking structure. The MOF-based crosslinked modified resin achieves ultra-narrow linewidth shaping of the silver paste and improves dispersibility through its ultra-high porosity and regular pore structure. The polyionic liquid graft modified resin enhances the anti-settling and long-term printing stability of the silver paste through its unique ionic properties and low volatility. Without the need for special solvents or excessive additives, it achieves significant improvements in linewidth accuracy, anti-settling properties, and conductivity in 3-5μm narrow-aperture printing scenarios, combining innovation, performance advantages, and cost reduction. This organic resin not only possesses excellent rheological properties, compatibility, and sintering suitability but also provides additional conductive channels, thus adapting to the narrow-linewidth printing process of TOPCon batteries. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in further detail below. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. The terms "first," "second," "third," "fourth," etc. (if present) in the specification and claims of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0018] The existing TOPCon front-side silver paste has the following problems in narrow linewidth printing processes: 1. The rheological properties of the organic carrier in traditional front-side silver paste are seriously mismatched with the printing requirements of ultra-narrow linewidths below 5μm, resulting in insufficient printing resolution, ink overflow / jagged edges on the lines, and uncontrolled paste spreading, which in turn leads to poor electrode linewidth consistency and insufficient line height, resulting in increased battery series resistance.

[0019] 2. The organic carrier in traditional front-side silver paste has poor compatibility with silver powder (especially ultrafine silver powder) and glass powder. After high-temperature sintering, it is easy to produce defects such as residual carbon, bubbles, and cracks, which leads to the attenuation of conductivity of ultra-narrow linewidth electrodes, reduced adhesion to the battery surface, and even electrode detachment.

[0020] 3. The resin system, solvent ratio and additive combination of the organic carrier in traditional front-side silver paste cannot meet the precise molding requirements of ultra-narrow linewidth printing below 5μm and the compatibility of TOPCon battery sintering process (rapid heating, low oxygen environment), which restricts the efficiency and long-term stability of ultra-narrow linewidth TOPCon batteries.

[0021] To solve, or at least partially solve, the above-mentioned technical problems, embodiments of the present invention provide a front-side silver paste for TOPCon cells, particularly for TOPCon cells using ultra-narrow linewidth processes. The front-side silver paste comprises, by weight percentage: 75% silver powder. 90%, glass powder 1.3% 4.1%, organic resin 1%-4%, organic solvent 1%-10% and silicone oil 0.1%-0.5%, the sum of the mass percentages of the above components is 100%.

[0022] In the front-side silver paste, the mass percentage of silver powder can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%, or any combination thereof. The mass percentage of glass powder can be 1.3%, 1.5%, 2%, 2.5%, 2.8%, 3%, 3.5%, 4%, or 4.1%, or any combination thereof. The mass percentage of organic resin can be 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%, or any combination thereof. The mass percentage of organic solvent can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or any combination thereof. The mass percentage of silicone oil can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any combination thereof. Organic resin, organic solvent, and silicone oil constitute the organic carrier in the front silver paste.

[0023] As one implementation method, the preparation steps of the front-side silver paste include: Step 1: Add silver powder, glass powder, organic resin, organic solvent and silicone oil to the reaction apparatus in proportion and mix to obtain a mixture. Step 2: Stir the mixture to ensure that all materials are evenly moistened; the stirring time can be, for example, 45 minutes. Step 3: The mixture is milled using a three-roll mill with a milling interval of 10μm - 120μm and a milling speed of 50r / min - 400r / min to obtain the front-side silver paste. The fineness of the front-side silver paste, as measured by an FOG scraper fineness meter, is less than 5μm.

[0024] In one embodiment, the silver powder is a highly tapped monodisperse spherical silver powder with a particle size D50 of 0.4 μm-1.5 μm, a particle size D100 < 3.5 μm, and a tap density ≥ 5.5 g / cm³. 3 Loose packing density ≥ 3.0 g / cm³ 3 The sphericity is ≥0.9. In ultra-narrow linewidth printing, since the opening of the screen is relatively small, the particle size D100 of the silver powder is controlled to prevent the silver powder particle size from being too large, which is not conducive to screen passing. The density of the silver powder is also controlled to be slightly higher, so that the powder is more compact. At the same time, the higher the sphericity of the silver powder, the smoother the powder is, which is more conducive to screen passing and the flowability is also better, thus facilitating ultra-narrow linewidth printing.

[0025] In one embodiment, the glass powder is a commonly used glass powder in the art.

[0026] In one embodiment, the organic solvent includes one or more of tripropylene glycol monomethyl ether, diethylene glycol butyl ether acetate, dodecyl alcohol ester, hexadecyl alcohol ester, benzyl benzoate, butyl carbitol acetate, tripropylene glycol butyl ether, dibutyl phthalate, and dimethyl adipate.

[0027] In one embodiment, the silicone oil includes one or more of polydimethylsiloxane, polymethylhydroxysiloxane, and polymethylethoxysiloxane.

[0028] In one embodiment, the organic resin comprises, by mass percentage: 40%-45% conjugated polymer block copolymer modified resin, 30%-35% MOF (metal-organic framework) based crosslinked modified resin, and 20%-25% polyionic liquid (PIL) graft modified resin, wherein the sum of the mass percentages of the conjugated polymer block copolymer modified resin, MOF-based crosslinked modified resin, and polyionic liquid graft modified resin is 100%; that is, the mass ratio of the conjugated polymer block copolymer modified resin, MOF-based crosslinked modified resin, and polyionic liquid graft modified resin is (40-45): (30-35): (20-25).

[0029] This organic resin employs a synergistic system of three modified resins: conjugated polymer block copolymer modified resin, MOF-based crosslinked modified resin, and polyionic liquid grafted modified resin. By controlling the mass ratio of the three resins, they work precisely and synergistically to enhance the narrow linewidth printing adaptability, anti-settling stability, and conductivity of the TOPCon front-side silver paste. The conjugated polymer block copolymer modified resin constructs conductive channels and optimizes printing viscosity through a π-π stacking structure. The MOF-based crosslinked modified resin achieves ultra-narrow linewidth shaping and improves dispersibility of the silver paste through its ultra-high porosity and regular pore structure. The polyionic liquid grafted modified resin enhances the anti-settling and long-term printing stability of the silver paste through its unique ionic properties and low volatility. Without the need for special solvents or excessive additives, it achieves significant improvements in linewidth accuracy, anti-settling, and conductivity in 3-5μm narrow aperture printing scenarios, combining innovation, performance advantages, and cost reduction. This organic resin not only has good rheological properties, compatibility and sintering compatibility, but also provides additional conductive channels, thus adapting to the narrow linewidth printing process of TOPCon cells.

[0030] The organic resin accounts for 1%-4% of the mass of the front-side silver paste. If the organic resin content is too low, it will not be able to effectively form an encapsulation / dispersion layer, resulting in a lack of interfacial interaction between the silver powder and glass powder. Furthermore, the dilution effect of the organic solvent will damage the thixotropic properties of the paste, leading to insufficient construction of conductive channels and uneven dispersion of glass powder, causing a double failure of the conductivity and adhesion properties of the front-side silver paste. If the organic resin content is too high, it will cause excessive entanglement of resin molecular chains and excessive synergistic cross-linking of ternary resins, resulting in abnormal system viscosity. At the same time, residual resin and glass powder will form a composite insulating layer, damaging the conductive network of silver powder. Phase separation will exacerbate the dispersion imbalance, causing screen clogging during printing and affecting ink application.

[0031] In one embodiment, the mass percentage of the conjugated polymer block copolymer modified resin in the organic resin can be 40%, 41%, 42%, 43%, 44%, or 45%, or any combination thereof. The mass percentage of the MOF-based crosslinked modified resin can be 30%, 31%, 32%, 33%, 34%, or 35%, or any combination thereof. The mass percentage of the polyionic liquid grafted modified resin can be 20%, 21%, 22%, 23%, 24%, or 25%, or any combination thereof.

[0032] In one embodiment, the conjugated polymer block copolymer modified resin is a polythiophene-block-polymethacrylate block copolymer (PTh-b-PMMA), prepared by atom transfer radical polymerization (ATRP). Its molecular structure consists of conjugated conductive segments (polythiophene segments, PTh) and functionally compatible segments (polymethacrylate segments, PMMA), with the following specific structural features: 1. Conjugated conductive segment (polythiophene segment, PTh): 3-hexylthiophene is used as the polymer monomer with a number average molecular weight of 8000-12000 Da, accounting for 60% of the total resin mass; a continuous electron transport channel is formed through the conjugated π electron delocalization effect, and the hydrophobic segment forms van der Waals forces with the silver powder surface, which improves the particle dispersion stability.

[0033] 2. Functional Adaptive Segment (Polymethyl Methacrylate Segment, PMMA): Using methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) as comonomers with a molar ratio of 7:3 and a number average molecular weight of 5000-8000 Da, accounting for 40% of the total resin mass; the hydroxyl groups in the hydroxyethyl ester unit form hydrogen bonds with the hydroxyl groups on the surface of the glass powder, and the methacrylate unit achieves molecular-level compatibility with organic solvents, solving the compatibility problem between organic resin and various components of silver paste.

[0034] 3. Polymerization control parameters: The mass ratio of polythiophene segments to polymethacrylate segments in the polythiophene-block-polymethacrylate block copolymer is 3:2. The degree of polymerization (PDI) of the polythiophene-block-polymethacrylate block copolymer is controlled by the ATRP process, with PDI ≤ 1.3, to ensure the structural uniformity of the resin molecules.

[0035] As one embodiment, the preparation steps of the polythiophene-block-polymethacrylate block copolymer include: Using 3-hexylthiophene as the polymerization monomer, and initiated by ethyl bromide isobutyrate and catalyzed by a first catalyst (which can be CuBr / 2,2'-bipyridine), a polythiophene initiator with bromine-terminated ends (number average molecular weight 8000-12000 Da) is obtained by polymerization. Using methyl methacrylate and hydroxyethyl methacrylate as comonomers (molar ratio 7:3), the copolymers are initiated by the polythiophene initiator and catalyzed by a second catalyst (the second catalyst can be CuBr / 2,2'-bipyridine) to form a block copolymer of methyl methacrylate and hydroxyethyl methacrylate. The reaction product obtained from the polymerization is then purified and dried to obtain a polythiophene-block-polymethyl methacrylate block copolymer.

[0036] The specific preparation steps and reaction mechanism of the polythiophene-block-polymethacrylate block copolymer are as follows: 1. Preparation of polythiophene initiator (PTh-Br): Preparation steps: 3-hexylthiophene, ethyl bromide isobutyrate and anhydrous THF (tetrahydrofuran) are mixed and CuBr / 2,2'-bipyridine is added as a catalyst. The polymerization reaction is carried out under nitrogen atmosphere and 60℃-65℃ to obtain a polythiophene initiator with bromine end groups.

[0037] Main reaction formula:

[0038] Wherein, [-Th-] represents the repeating unit of 3-hexylthiophene. n represents the degree of polymerization (corresponding to a number-average molecular weight of 8000-12000 Da, n≈40-60); the initiator is ethyl bromide isobutyrate. Active bromine atoms are introduced at the ends of polythiophene chains through the ATRP process, providing reaction sites for subsequent block copolymerization.

[0039] 2. Block copolymerization reaction (core reaction for PTh-b-PMMA preparation): Preparation steps: Methyl methacrylate, hydroxyethyl methacrylate, polythiophene initiator and anhydrous DMF (N,N-dimethylformamide) are mixed and CuBr / 2,2'-bipyridine is added as a catalyst. Block copolymerization reaction is carried out in a nitrogen environment at 70℃-75℃ to obtain polythiophene-block-polymethacrylate block copolymer.

[0040] Main reaction formula:

[0041] MMA is methyl methacrylate. HEMA is hydroxyethyl methacrylate. The molar ratio of MMA to HEMA is 7:3, and m is the degree of polymerization of the polymethyl methacrylate segment (corresponding to a number average molecular weight of 5000-8000 Da, m≈50-80).

[0042] Reaction mechanism: The active end groups of the polythiophene macromolecular initiator further initiate the copolymerization of MMA and HEMA. By adjusting the monomer feed ratio and reaction time, the molecular weight and ratio of the two chains (PTh:PMMA=3:2, mass ratio) are precisely controlled, and finally a block copolymer with PDI≤1.3 is obtained.

[0043] 3. Resin post-treatment: The purified block copolymer was vacuum dried at 80℃ for 24h to remove residual solvent and oligomers, resulting in a high-purity polythiophene-block-polymethacrylate block copolymer with a purity ≥99.5% and a thermal decomposition temperature ≥320℃, meeting the requirements of the TOPCon silver paste high-temperature sintering process.

[0044] As one embodiment, the preparation steps of the MOF-based crosslinked modified resin include: Epoxy-modified polymethacrylate was obtained by polymerization of methyl methacrylate and glycidyl methacrylate as comonomers initiated by azobisisobutyronitrile (AIBN). The MOF material was mixed with the epoxy-modified polymethyl methacrylate and reacted under the action of a catalyst (4-dimethylaminopyridine, DMAP). The reaction product was then subjected to precipitation, washing, and drying to obtain the MOF-based crosslinked modified resin. The MOF material was HKUST-1 [corresponding chemical formula: [Cu3(BTC)2(H2O)3]n, with surface-grafted carboxyl groups and / or hydroxyl groups, rich in -COOH] or Ni-MOF-74 [corresponding chemical formula: [Ni2(DOBDC)(H2O)2]n, with surface-rich -OH / -COOH].

[0045] Specifically, the MOF-based crosslinked modified resin uses HKUST-1 or Ni-MOF-74, with surface-grafted carboxyl and / or hydroxyl groups as the crosslinking core (particle size 80-150 nm, metal ion content 15%-20%), and epoxy-modified polymethyl methacrylate (number average molecular weight 30,000-50,000 Da) containing epoxy and ester groups to form a three-dimensional crosslinked network structure through an epoxy ring-opening reaction. The crosslinking degree is 85%-90%, and the porosity is 25%-30%. MOF materials combine the conductivity of metal ions with the compatibility of organic ligands, avoiding the agglomeration problem of traditional conductive fillers. The metal ions in the MOF material (e.g., Cu in HKUST-1) 2+ Ni-MOF-74 contains Ni 2+ Conductivity is achieved through electronic transitions, while the three-dimensional cross-linked network structure enhances the resin's film-forming properties. The amount of MOF material added is 3%-5% of the total mass of the resin system (excessive addition leads to over-crosslinking and brittle slurry; insufficient addition results in insufficient conductivity); the crosslinking reaction temperature is 60℃-70℃, and the reaction time is 2 hours, ensuring a crosslinking degree of 30%-40% (achieving both conductivity and no impact on flowability); after modification, the resin's volume resistivity decreases to 10. 4 -10 5 Ω·cm, with compatibility with silver powder ≥95%.

[0046] The specific preparation steps and reaction mechanism of MOF-based crosslinked modified resin are as follows: 1. Preparation of MOF materials (crosslinked core): Preparation steps: Place copper chloride or copper nitrate (Cu²⁺) into the copper chloride solution. + Source), and pyromellitic acid (1,3,5-phenyltricarboxylic acid, H3BTC, HKUST-1 ligand) are reacted via hydrothermal / solvothermal reaction to synthesize HKUST-1 (chemical formula: Cu3(BTC)2(H2O)3, full name: pyromellitic acid copper(II) metal-organic framework) with surface-grafted carboxyl groups (-COOH). Alternatively, nickel chloride or nickel nitrate (Ni²) + Ni-MOF-74 (chemical formula: Ni2(DOBDC)(H2O)2, full name: 2,5-dihydroxyterephthalic acid nickel(II) metal-organic framework) was synthesized by hydrothermal / solvothermal reaction with 2,5-dihydroxyterephthalic acid (H4DOBDC, Ni-MOF-74 ligand) to graft carboxyl groups (-COOH) and hydroxyl groups (-OH) on the surface.

[0047] Product characteristics: Particle size 80-150 nm, metal ion content 15-20 wt%, providing active reaction sites for subsequent crosslinking.

[0048] 2. Preparation of epoxy-modified polymethyl methacrylate matrix: Preparation steps: Methyl methacrylate (MMA) and glycidyl methacrylate (GMA) are used as comonomers (molar ratio 8:2), and free radical polymerization is carried out under the initiation of azobisisobutyronitrile (AIBN) (reaction temperature 80℃-90℃) to obtain epoxy-modified polymethyl methacrylate containing epoxy groups (number average molecular weight 30000-50000 Da).

[0049] Main reaction formula:

[0050] The product of Poly(MMA-co-GMA) is named poly(methyl methacrylate-co-glycidyl methacrylate), and its full name is epoxy-modified polymethyl methacrylate copolymer.

[0051] Product characteristics: The molecular chain contains epoxy functional groups, which can undergo ring-opening esterification reactions with carboxyl / hydroxyl groups on the MOF surface.

[0052] 3. Crosslinking reaction between MOF and resin matrix: MOF material (30%-35% by mass) was mixed with epoxy-modified polymethyl methacrylate and subjected to esterification / amidation reaction under the action of catalyst (4-dimethylaminopyridine, DMAP) to construct a three-dimensional cross-linked network.

[0053] Main reaction formula:

[0054] The first row of reaction formulas above is the ring-opening esterification reaction of the carboxyl group of MOF with the epoxy group of resin, and the second row of reaction formulas above is the amidation reaction of the carboxyl group of MOF with the amino group of resin (if the resin contains amino groups).

[0055] Reaction conditions: temperature 60-70℃, time 2 h, ensuring a crosslinking degree of 30%-40%.

[0056] 4. Curing and post-treatment: The above reaction products were successively precipitated and washed, and then vacuum dried at 100℃ for 24 h to remove solvent and unreacted monomers, yielding MOF-based crosslinked modified resin (full name: metal-organic framework (MOF) crosslinked modified epoxy polymethyl methacrylate resin; structural essence: MOF particles are covalently grafted onto epoxy modified polymethyl methacrylate molecular chains through ester / amide bonds to form a three-dimensional interpenetrating crosslinked network).

[0057] The structural formula of the final product is: MOF-[COO / CONH]-Poly(MMA-co-GMA) Product characteristics: crosslinking degree 85%-90%, porosity 25%-30%, volume resistivity reduced to 10. 4 -10 5 Ω·cm, compatibility with silver powder ≥95%, thermal decomposition temperature ≥320℃.

[0058] In the above reaction: (1) MOF provides porous conductive cores: metal ions (Cu²⁺) + / Ni² + It achieves electronic conductivity, and the surface carboxyl / hydroxyl groups provide cross-linking sites.

[0059] (2) The resin matrix provides film formation and adhesion: epoxy-modified polymethyl methacrylate ensures film formation and covalently bonds with MOF through epoxy / amino groups.

[0060] (3) Crosslinking reaction to build a stable network: Esterification / amidation reaction firmly binds inorganic MOF to organic resin, avoids agglomeration, and improves resin rigidity and printability.

[0061] As one embodiment, the preparation steps of the polyionic liquid (PIL) grafted modified resin include: The polyionic liquid graft-modified resin is obtained by mixing polymethacrylate or polythiophene as the matrix backbone with ionic liquid monomers and adding azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as initiators, followed by free radical graft polymerization. The ionic liquid monomers are either imidazolium-type or pyridinium-type ionic liquid monomers. Imidazolium-type ionic liquid monomers include 1-vinyl-3-butylimidazolium hexafluorophosphate, and pyridinium-type ionic liquid monomers include 4-vinylpyridine p-toluenesulfonate.

[0062] Specifically, the polyionic liquid graft-modified resin uses polymethacrylate or polythiophene as the matrix backbone (number average molecular weight 20,000-40,000 Da). Functional units of ionic liquid monomers (imidazolium-type or pyridinium-type ionic liquid monomers) are grafted onto the matrix molecular chain via free radical graft polymerization. The grafting rate of the ionic liquid monomers is 15%-25% (too low a grafting rate results in insufficient conductivity, while too high a rate results in excessive hydrophilicity of the resin). The resin's thermal decomposition temperature is ≥330℃. The free radical graft polymerization uses azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as initiators, with the initiator amount being 0.5%-1.0% of the total mass of the ionic liquid monomers. The reaction temperature is 65℃-75℃, and the reaction time is 4-6 hours. This polyionic liquid grafted modified resin improves the paste's anti-settling properties and reduces screen residue by allowing the hydrophobic segments of the ionic liquid functional units to be compatible with the silver paste solvent and the ionic groups to form hydrogen bonds with the hydroxyl groups on the glass powder surface, thus facilitating continuous printing.

[0063] The specific preparation steps and reaction mechanism of the polyionic liquid grafted modified resin are as follows: Preparation steps: Using polymethacrylate or polythiophene as the matrix skeleton, mix with imidazolium-type ionic liquid monomers or pyridinium-type ionic liquid monomers, add 0.5%-1.0% (relative to the total mass of ionic liquid monomers) of azobisisobutyronitrile or benzoyl peroxide as an initiator, and perform free radical grafting polymerization at 65℃-75℃ for 4-6 hours. After precipitation, washing and vacuum drying at 80℃ for 12 hours, a polyionic liquid grafted modified resin with a grafting rate of 15%-25% is obtained.

[0064] Main reaction formula:

[0065] Wherein, EC-CH=CH2 is an ethylene carbonate modified matrix (containing double bonds), [VBIM]Br is 1-vinyl-3-butylimidazolium bromide (PIL monomer), and EC-CH2-CH(-[-VBIM+]-nBr) is an EC-PIL graft copolymer (a copolymer of 1-vinyl-3-butylimidazolium cation grafted onto an ethylene carbonate modified matrix).

[0066] Main reaction mechanism: The vinyl group of PIL monomer undergoes free radical polymerization with the double bond on the EC molecular chain (introduced through pretreatment) to form EC-PIL copolymer.

[0067] Among them, imidazolium cation The EC backbone forms a conductive channel with the migration of bromide (Br) ions, while the EC backbone retains the methoxy group. Its oleophilicity ensures printability.

[0068] This invention also provides a TOPCon battery, including electrodes, which are obtained by sintering front-side silver paste as described above. Specifically, the front-side silver paste is screen-printed, dried, and sintered onto the surface of the battery silicon wafer to form metal grid lines, thereby forming the desired electrodes. For other technical features of this electrode, please refer to the prior art, which will not be repeated here.

[0069] [Example 1] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 0.6% conjugated polymer block copolymer modified resin, 0.45% MOF-based crosslinked modified resin, and 0.3% polyionic liquid grafted modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.85%, Diethylene glycol butyl ether acetate 3.1%, Dodecyl alcohol ester 1.6% The preparation methods for each component in the organic resin and the preparation method for the front silver paste are described above and will not be repeated here.

[0070] [Example 2] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 1% conjugated polymer block copolymer modified resin, 0.75% MOF-based crosslinked modified resin, and 0.5% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.6%, Diethylene glycol butyl ether acetate 3.05%, Dodecyl alcohol ester 1% [Example 3] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 1.4% conjugated polymer block copolymer modified resin, 1.05% MOF-based crosslinked modified resin, and 0.7% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.3%, Diethylene glycol butyl ether acetate 2.45%, Dodecyl alcohol ester 1% [Comparative Example 1] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: Ethyl cellulose (Dow STD-4) 0.5%, acrylic resin (Mitsubishi BR115) 1.5%, SEPS resin (styrene-ethylene / propylene-styrene block copolymer) (Kraton G1726VS) 0.5% Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.6%, Diethylene glycol butyl ether acetate 2.8%, Dodecyl alcohol ester 1% [Comparative Example 2] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 1.2% conjugated polymer block copolymer modified resin, 0.5% MOF-based crosslinked modified resin, and 0.5% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.6%, Diethylene glycol butyl ether acetate 3.1%, Dodecyl alcohol ester 1% [Comparative Example 3] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 0.75% conjugated polymer block copolymer modified resin, 1% MOF-based crosslinked modified resin, and 0.5% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.6%, Diethylene glycol butyl ether acetate 3.05%, Dodecyl alcohol ester 1% [Comparative Example 4] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 1% conjugated polymer block copolymer modified resin, 0.5% MOF-based crosslinked modified resin, and 0.75% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 4.6%, Diethylene glycol butyl ether acetate 3.05%, Dodecyl alcohol ester 1% [Comparative Example 5] A TOPCon front-side silver paste adapted for narrow linewidth processes is made from the following raw materials by weight percentage: Silver powder (D50 0.4-1.5μm): 86% Glass powder: 2.6% Organic resins: 2% conjugated polymer block copolymer modified resin, 1.5% MOF-based crosslinked modified resin, and 1% polyionic liquid graft modified resin. Silicone oil: Polymethylhydroxysiloxane (viscosity 50 mPa·s) 0.5% Solvents: Benzyl benzoate 3.6%, Diethylene glycol butyl ether acetate 1.8%, Dodecyl alcohol ester 1% The performance of the front-side silver paste in Examples 1-3 and Comparative Examples 1-5 was tested, and the test process is as follows: 1. Viscosity test: Take 15-20g of each front-side silver paste and use a Brookfield DV2 viscosity tester and SC-14 rotor to measure the average viscosity of the paste under the conditions of 25℃ / 10rpm / 60 seconds. 2. Photovoltaic Conversion Test: Specific patterns were printed onto the TOPcon solar cells using silver paste on each front side, then dried and cured. Solar cells of a predetermined size with the printed patterns were then cut using a laser slicing machine. The test was conducted using the Maiwei IV... The EL tester performs photoelectric conversion efficiency tests on each solar cell, evaluating the solar cell's photoelectric conversion efficiency (Eta), open-circuit voltage (Voc), fill factor (FF), and short-circuit current (Isc).

[0071] 3. Printability Test: Silver paste from each front side was printed onto the back side of the silicon wafer using screen printing technology. The screen specifications used for printability testing were a knotless, multi-aperture screen with 700 mesh / 4μm wire diameter / total thickness of 16-19μm / apertures of 5μm, 4μm, and 3μm respectively. Each cell was dried in an infrared drying oven, and then the printability of the paste was observed visually and under an optical microscope to determine the presence of broken grids and incomplete printing.

[0072] The test results for each embodiment and comparative example are shown in the table below.

[0073]

[0074] From the table above, we can see that: (1) As can be seen from Examples 1 to 3 and Comparative Example 1, the conversion efficiency was the highest when the total addition amount of the conjugated polymer block copolymer modified resin, MOF-based crosslinked modified resin and polyionic liquid graft modified resin was 2.25% (Example 2), which was 0.4% higher than that of Comparative Example 1. The MOF-based crosslinked modified resin achieved ultra-narrow linewidth plasticity through its ultra-high porosity and regular pore structure. The conjugated polymer block copolymer modified resin constructed a highly efficient conductive channel through the π-π stacking structure. The polyionic liquid graft modified resin improved long-term printing stability through its unique ionic properties and low volatility. The synergistic effect of the three resins produced a significant synergistic effect.

[0075] (2) As can be seen from Examples 1 to 3 and Comparative Example 5, when the total resin content exceeds 4%, grid breakage will occur, which will greatly affect the conversion efficiency. This is because if the resin content is too high, the resin molecular chains will be excessively entangled and the ternary resin will be excessively cross-linked, which will cause abnormal viscosity of the system and affect the ink application of the paste; the excessive resin will form a composite insulating layer with the glass powder, which will destroy the conductive network of the silver powder, and the phase separation will aggravate the dispersion imbalance, causing grid blockage during printing, thereby affecting printability.

[0076] (3) As can be seen from Example 2 and Comparative Example 2, if the proportion of conjugated polymer block copolymer modified resin in the three modified resins is too high, the conversion efficiency will drop sharply. This is because the excessive accumulation of π-π in the conjugated polymer block copolymer modified resin forms a rigid network with the glass powder. After sintering, the conductivity continuity is destroyed, the compatibility with MOF-based resin decreases, and phase separation is triggered, resulting in no glass powder adhering to the lines.

[0077] (4) As can be seen from Example 2 and Comparative Example 3, if the proportion of MOF-based crosslinked modified resin is too high, the conversion efficiency will drop sharply. This is because excessive crosslinking leads to excessive thixotropy of the slurry. During the sintering process, the residual porous structure of MOF forms a composite defect with the glass powder, increasing the brittleness of the system and making the interface between the glass powder and the silver layer easy to peel off.

[0078] (5) As can be seen from Example 2 and Comparative Example 4, if the proportion of polyionic liquid grafted modified resin is too high, the conversion efficiency will drop sharply. This is because the system is too polar, which deteriorates the compatibility with the surface of non-polar silver powder, causing secondary agglomeration. At the same time, it affects the wettability of glass powder, and the residual ionic groups react with glass powder to generate impurities, affecting the contact resistance.

[0079] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An organic resin for use in front-side silver paste, characterized in that, The organic resin comprises, by weight percentage: 40%-45% conjugated polymer block copolymer modified resin, 30%-35% MOF-based crosslinked modified resin, and 20%-25% polyionic liquid graft modified resin.

2. The organic resin according to claim 1, characterized in that, The conjugated polymer block copolymer modified resin is a polythiophene-block-polymethacrylate block copolymer.

3. The organic resin according to claim 2, characterized in that, The preparation steps of the polythiophene-block-polymethacrylate block copolymer include: Polythiophene initiator was obtained by polymerization using 3-hexylthiophene as a monomer and initiated by ethyl bromide isobutyrate. The polythiophene-block-polymethacrylate block copolymer is obtained by polymerization using methyl methacrylate and hydroxyethyl methacrylate as comonomers and initiated by the polythiophene initiator.

4. The organic resin according to claim 2, characterized in that, The mass ratio of polythiophene segments to polymethacrylate segments in the polythiophene-block-polymethacrylate block copolymer is 3:2, and the PDI of the polythiophene-block-polymethacrylate block copolymer is ≤1.

3.

5. The organic resin according to claim 1, characterized in that, The preparation steps of the MOF-based crosslinked modified resin include: Epoxy-modified polymethacrylate was obtained by polymerization of methyl methacrylate and glycidyl methacrylate as comonomers initiated by azobisisobutyronitrile. The MOF material was mixed with the epoxy-modified polymethyl methacrylate and reacted under the action of a catalyst. The reaction product was then subjected to precipitation, washing and drying to obtain the MOF-based crosslinked modified resin.

6. The organic resin according to claim 5, characterized in that, The MOF material is HKUST-1, and the preparation steps of HKUST-1 include: reacting copper chloride or copper nitrate with trimesic acid via hydrothermal / solvothermal reaction to synthesize HKUST-1 with carboxyl groups grafted on the surface. Alternatively, the MOF material is Ni-MOF-74, and the preparation steps of Ni-MOF-74 include: reacting nickel chloride or nickel nitrate with 2,5-dihydroxyterephthalic acid via hydrothermal / solvothermal reaction to synthesize Ni-MOF-74 with surface-grafted carboxyl and hydroxyl groups.

7. The organic resin according to any one of claims 1-6, characterized in that, The preparation steps of the polyionic liquid grafted modified resin include: The polyionic liquid grafted modified resin is obtained by mixing polymethacrylate or polythiophene as the matrix skeleton with an ionic liquid monomer, adding azobisisobutyronitrile or benzoyl peroxide as an initiator, and then performing free radical graft polymerization; wherein the ionic liquid monomer is an imidazolium-type ionic liquid monomer or a pyridinium-type ionic liquid monomer.

8. The organic resin according to claim 7, characterized in that, The imidazolium-type ionic liquid monomer includes 1-vinyl-3-butylimidazolium hexafluorophosphate, and the pyridinium-type ionic liquid monomer includes 4-vinylpyridine p-toluenesulfonate.

9. The organic resin according to claim 7, characterized in that, The grafting rate of the ionic liquid monomer is 15%-25%.

10. A front-side silver paste, characterized in that, By weight percentage, the front-side silver paste comprises: 75% silver powder. 90%, glass powder 1.3% 4.1%, organic resin 1%-4%, organic solvent 1%-10% and silicone oil 0.1%-0.5%; wherein the organic resin is the organic resin as described in any one of claims 1-9.

11. The front-side silver paste as described in claim 10, characterized in that, The silver powder is a highly tapped, monodisperse, spherical silver powder with a particle size D50 of 0.4 μm-1.5 μm, a particle size D100 < 3.5 μm, and a tap density ≥ 5.5 g / cm³. 3 Loose packing density ≥ 3.0 g / cm³ 3 sphericity ≥ 0.

9.

12. A TOPCon battery, characterized in that, Includes an electrode, which is obtained by sintering a front-side silver paste as described in claim 10 or 11.

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