Conductive paste for crystalline silicon heterojunction solar cell and preparation method thereof

Abstract

The invention provides conductive paste for a crystalline silicon heterojunction solar cell and a preparation method of the conductive paste. The conductive paste can be applied to the technical field of electronic material preparation and the technical field of photovoltaic cells. The conductive paste comprises the following components in percentage by mass: 89-94% of composite metal powder, 0.1-10% of semiconductor powder, 1.5-9% of organic composite resin, 0.04-4% of a curing agent, 1-5% of an organic solvent and 0.2-1% of a dispersing agent, the dispersing agent is saturated fatty acid and / or unsaturated fatty acid with the carbon atom number of 8-22. According to the conductive paste for the crystalline silicon heterojunction solar cell and the preparation method thereof, the silk-screen printing adaptability of the conductive paste can be improved, the resistance is reduced, and then the conductivity of the conductive paste is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic material preparation and the technical field of photovoltaic cells, and more particularly to a conductive paste for a crystalline silicon heterojunction solar cell and a preparation method thereof. BACKGROUND

[0002] A solar cell is a kind of photovoltaic semiconductor wafer that directly generates electricity by using sunlight, also known as a "solar chip" or a "photovoltaic cell". It can output voltage and generate current in a loop as long as it is illuminated by light that meets certain illumination conditions. In physics, it is called solar photovoltaic (Photovoltaic, abbreviated as PV) and photovoltaic. The heterojunction (Hereto-junction with Intrinsic Thin-layer, abbreviated as HJT) solar cell is a new type of solar cell based on a thin silicon substrate, which has the advantages of high conversion efficiency, high stability and double-sided power generation.

[0003] In the current HJT solar cell, silver-coated copper paste has become the mainstream and industrialized technical solution to replace pure silver paste. At present, the silver content of silver-coated copper paste is reduced, which reduces the cost of HJT solar cell. However, with the reduction of silver content, the silver-coated copper paste has declined in electrical performance, printing applicability and weather resistance, especially in the case of large particle size of silver-coated copper powder and uneven surface silver shell coating. These problems are particularly prominent, which further affects the conversion efficiency and long-term stability of the HJT solar cell. The main problems currently faced by silver-coated copper paste include: the silver layer is too thin, which easily forms an amorphous structure, causing increased electron scattering and increasing the resistivity of the paste. At the same time, the thin silver layer also increases the risk of copper core exposure. In addition, with the continuous progress of screen printing technology, the grid line width of the screen is increasingly narrowed, the effective contact area between the paste and the substrate is reduced, and the contact resistance of the grid line electrode is further increased, which restricts the improvement of the conversion efficiency of the HJT solar cell. SUMMARY

[0004] In view of the above problems, the present application provides a conductive paste for a crystalline silicon heterojunction solar cell and a preparation method thereof.

[0005] According to a first aspect of the present application, a conductive paste for a crystalline silicon heterojunction solar cell is provided, which comprises, in mass percentage: 89-94% of composite metal powder, 0.1-10% of semiconductor powder, 1.5-9% of organic composite resin, 0.04-4% of curing agent, 1-5% of organic solvent and 0.2-1% of dispersant; the dispersant is a saturated aliphatic acid and / or unsaturated aliphatic acid containing 8-22 carbon atoms.

[0006] According to embodiments of this application, the dispersant includes at least one selected from caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, and linoleic acid.

[0007] According to embodiments of this application, the semiconductor powder is a narrow bandgap semiconductor powder with a bandgap width of 1.2eV to 1.4eV, including at least one of copper indium gallium sulfide powder, copper indium sulfide powder, copper indium tin powder, antimony selenide powder, and antimony sulfide powder.

[0008] According to embodiments of this application, the particle size of the semiconductor powder is less than or equal to 100 nm.

[0009] According to embodiments of this application, the composite metal powder includes 3-5µm silver-coated copper powder and 300-500nm silver powder.

[0010] According to embodiments of this application, the tap density of both the silver-coated copper powder and the silver powder is greater than or equal to 5 g / cm³. 3 Furthermore, the proportion of silver-coated copper powder in composite metal powder is 30-90%.

[0011] According to embodiments of this application, the organic composite resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy-modified acrylic resin, alicyclic epoxy resin, and phenolic epoxy resin.

[0012] According to embodiments of this application, the organic solvent is at least one selected from diethylene glycol butyl ether, diethylene glycol dibutyl ether acetate, diethylene glycol dibutyl ether, diethylene glycol ethyl ether, terpineol, ethylene glycol phenyl ether acetate, divalent ester, and dimethyl malate.

[0013] According to embodiments of this application, the curing agent includes an isocyanate curing agent, a blocked cationic curing agent, and a peroxide thermal initiator.

[0014] The second aspect of this application provides a method for preparing a conductive paste for crystalline silicon heterojunction solar cells, comprising the following steps: mixing composite metal powder, semiconductor powder, organic composite resin, curing agent, organic solvent and dispersant, and grinding them to obtain a conductive paste for crystalline silicon heterojunction solar cells.

[0015] One or more of the above embodiments have the following beneficial effects: Monofunctional fatty acids containing long-chain carbon molecules, as dispersants, can improve the dispersion uniformity of silver-coated copper powder in conductive pastes, enhance the screen printing suitability of conductive pastes, reduce conductive defects caused by agglomeration, and further reduce bulk resistivity. Narrow bandgap semiconductor powders with band gaps close to silicon can promote bridging between metal powders and form conductive channels in the resin phase, making the tunneling effect of current easier to achieve and reducing the bulk resistivity of conductive pastes; in addition, it can increase the contact area between conductive pastes and silicon wafers and prevent the contact interface from shrinking during the curing process, thereby reducing the contact resistivity of conductive pastes. Therefore, by utilizing the special effects of dispersants and semiconductor powders, the bulk resistivity and contact resistivity of conductive pastes can be reduced, further optimizing the electrical properties of the paste and meeting the performance requirements of ultra-narrow linewidth gate lines. In addition, composite metal powder serves as the core conductive substrate, ensuring the basic conductivity of the conductive paste. Organic composite resin provides molding and bonding support for the conductive paste, curing agent helps improve curing stability, and organic solvent optimizes the dispersibility and printing smoothness of the conductive paste, further achieving synergistic optimization of the electrical properties and printability of the conductive paste. Attached Figure Description

[0016] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A flowchart illustrating a method for preparing a conductive paste for a crystalline silicon heterojunction solar cell according to an embodiment of this application is shown. Detailed Implementation

[0018] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0019] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0020] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0021] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0022] In the embodiments of this application, unless otherwise specified, the raw materials used are all commercially available products in the art.

[0023] In an embodiment of this application, a conductive paste for crystalline silicon heterojunction solar cells is provided, comprising, by mass percentage: 89-94% composite metal powder, 0.1-10% semiconductor powder, 1.5-9% organic composite resin, 0.04-4% curing agent, 1-5% organic solvent and 0.2-1% dispersant; the dispersant is a saturated fatty acid and / or an unsaturated fatty acid containing 8-22 carbon atoms.

[0024] In the embodiments of this application, when the composite conductive metal powder consists of multiple conductive metal powders, this application does not have a special limitation on the ratio of different types of conductive metal powders; any ratio is acceptable. For example, the composite metal powder can be silver-coated copper powder and silver powder, silver-coated copper powder and copper powder, silver-coated copper powder and silver-coated tin powder, or silver-palladium alloy coated copper powder and silver powder, etc. When the organic composite resin consists of multiple resins, this application does not have a special limitation on the ratio of different types of resins; any ratio is acceptable. When there are multiple organic solvents, this application does not have a special limitation on the ratio of different organic solvents; any ratio is acceptable.

[0025] In the embodiments of this application, the composite metal powder in the conductive paste is preferably a mixture of silver-coated copper powder and silver powder. The semiconductor powder is preferably a narrow bandgap semiconductor powder with a band gap close to that of silicon, such as copper indium gallium sulfide powder, antimony selenide powder, etc. The organic composite resin is preferably at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy-modified acrylic resin, alicyclic epoxy resin, and phenolic epoxy resin. The curing agent is preferably an isocyanate curing agent, a blocked cationic curing agent, and a peroxide thermal initiator. The organic solvent is preferably at least one of diethylene glycol butyl ether, diethylene glycol dibutyl ether acetate, diethylene glycol dibutyl ether, diethylene glycol ethyl ether, terpineol, ethylene glycol phenyl ether acetate, divalent ester, and dimethyl malate. The dispersant can be a monofunctional fatty acid containing long-chain carbon molecules, i.e., a saturated fatty acid and / or an unsaturated fatty acid containing 8 to 22 carbon atoms.

[0026] According to embodiments of this application, monofunctional fatty acids containing long-chain carbon molecules, used as dispersants, can improve the dispersion uniformity of silver-coated copper powder in conductive pastes, enhance the screen printing suitability of conductive pastes, reduce conductive defects caused by agglomeration, and further reduce bulk resistivity. Narrow bandgap semiconductor powders with band gaps close to silicon can promote bridging between metal powders and form conductive channels in the resin phase, making current tunneling easier to achieve and reducing the bulk resistivity of the conductive paste. Additionally, they can increase the contact area between the conductive paste and the silicon wafer and prevent shrinkage at the contact interface during curing, thereby reducing the contact resistivity of the conductive paste. Therefore, by utilizing the special effects of dispersants and semiconductor powders, the bulk resistivity and contact resistivity of conductive pastes can be reduced, further optimizing the electrical properties of the paste and meeting the performance requirements of ultra-narrow linewidth gate lines. In addition, composite metal powder serves as the core conductive substrate, ensuring the basic conductivity of the conductive paste. Organic composite resin provides molding and bonding support for the conductive paste, curing agent helps improve curing stability, and organic solvent optimizes the dispersibility and printing smoothness of the conductive paste, further achieving synergistic optimization of the electrical properties and printability of the conductive paste.

[0027] In the embodiments of this application, the dispersant includes at least one selected from caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, and linoleic acid.

[0028] In the embodiments of this application, the dispersant may be a saturated fatty acid and / or an unsaturated fatty acid containing 8 to 22 carbon atoms, such as one or more of the following saturated fatty acids: caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and unsaturated fatty acids: oleic acid, linoleic acid.

[0029] Preferably, dispersants with different carbon chain lengths and saturation levels can be adapted to different scenarios. For example, octanoic acid (8 carbons) has good fluidity and is suitable for low-temperature preparation environments; behenic acid (22 carbons) has strong lipophilicity and is suitable for high-proportion silver-coated copper powder systems to reduce copper core exposure; unsaturated oleic acid (18 carbons) has better low-temperature dispersibility due to the presence of carbon-carbon double bonds, further reducing bulk resistivity, etc.

[0030] According to embodiments of this application, monofunctional fatty acids containing long-chain carbon molecules are selected as dispersants for conductive pastes, which helps improve the screen printing performance of the paste. Furthermore, these dispersants have good compatibility with organic composite resins and organic solvents, improving the storage stability of the paste. By optimizing the dispersion effect, the electrical properties and stability of the conductive paste are further enhanced, meeting the requirements of low-temperature curing and narrow grid line printing for HJT solar cells.

[0031] In the embodiments of this application, the semiconductor powder is a narrow bandgap semiconductor powder with a bandgap width of 1.2eV to 1.4eV, including at least one of copper indium gallium sulfide powder, copper indium sulfide powder, copper indium tin powder, antimony selenide powder, and antimony sulfide powder.

[0032] In the embodiments of this application, the bandgap width can refer to the energy difference between the valence band (the energy level where electrons are stably present) and the conduction band (the energy level where electrons can move freely to form current) in a semiconductor material. It is a key parameter determining the conductivity and interface compatibility of a semiconductor. The semiconductor powder is a narrow bandgap semiconductor powder with a bandgap width of 1.2 eV to 1.4 eV, and may include at least one of copper indium gallium sulfide powder, copper indium sulfide powder, copper indium tin powder, antimony selenide powder, and antimony sulfide powder. This application limits the semiconductor powder bandgap to 1.2 eV to 1.4 eV, which is very close to the bandgap of crystalline silicon. This energy level matching helps to reduce the electron transport barrier at the interface between the semiconductor powder and crystalline silicon, thereby reducing contact resistance.

[0033] According to embodiments of this application, narrow bandgap semiconductor powder with a bandgap width of 1.2eV~1.4eV has a certain conductivity and will not cause leakage due to excessively narrow bandgap. It is suitable as a conductive bridging filler to partially replace nano silver powder, thereby reducing costs while improving conductivity.

[0034] In the embodiments of this application, the particle size of the semiconductor powder is less than or equal to 100 nm.

[0035] Composite metal powders may contain gaps at the micrometer and submicrometer scales. Semiconductor powders smaller than 100 nm can fill these gaps like nanobridges, allowing the originally dispersed metal powder to form a continuous conductive network through the semiconductor powder, reducing breakpoints in current transmission and thus lowering bulk resistivity. Nanoscale semiconductor powders have a large specific surface area, which is beneficial for increasing the contact area between the conductive paste and the silicon wafer. Furthermore, when nanoparticles are cured at a low temperature of 200℃, they do not shrink at the contact interface due to differences in thermal expansion coefficients, unlike micrometer particles, thus avoiding increased contact resistance.

[0036] According to embodiments of this application, by limiting the particle size of the semiconductor powder, it is beneficial to reduce the breakpoints in current transmission, reduce the volume resistivity, adapt to screen printing processes, and avoid paste agglomeration.

[0037] In the embodiments of this application, the composite metal powder includes silver-coated copper powder with a particle size of 3~5µm and silver powder with a particle size of 300~500nm.

[0038] In the embodiments of this application, the composite metal powder includes silver-coated copper powder and silver powder. There is no special limitation on the ratio of silver-coated copper powder and silver powder, and any ratio is acceptable.

[0039] Silver-coated copper powder is a core-shell structured powder, meaning it uses low-cost copper as its core and is coated with a layer of silver. Silver-coated copper powder can reduce the silver content from 100% in pure silver paste to 10-15%, and its 3-5µm micron-sized particle size ensures that the powder forms a basic conductive framework in the conductive paste, while avoiding powder agglomeration and increased resistivity caused by excessively small particle sizes (such as nanometers). Because 3-5µm silver-coated copper powder is coarse, micron-sized gaps form between the particles. If only silver-coated copper powder is used, these gaps will be filled by insulating organic resin, causing interruptions in current transmission and increasing volume resistivity. However, 300-500nm silver powder can act as a conductive bridge, embedding itself into these gaps and making close contact with the silver layer of the silver-coated copper powder, forming a continuous conductive path of silver-coated copper powder-silver powder-silver-coated copper powder, reducing current transmission resistance.

[0040] According to the embodiments of this application, a low-cost replacement of pure silver paste is achieved, and a seamless conductive network is constructed through complementary different particle sizes to reduce the bulk resistivity. At the same time, it is compatible with screen printing and low-temperature curing processes to meet the needs of HJT solar cells for cost reduction and efficiency improvement.

[0041] In the embodiments of this application, the tap density of both the silver-coated copper powder and the silver powder is greater than or equal to 5 g / cm³. 3 Furthermore, the proportion of silver-coated copper powder in composite metal powder is 30-90%.

[0042] Tap density refers to the mass per unit volume of powder after it has been vibrated and compacted at a certain frequency. It is a key indicator of the compactness of powder packing. The higher the tap density, the smaller the gaps between powder particles, and the easier it is to form a continuous conductive path. For conductive pastes, the tap density of both silver-coated copper powder and silver powder is greater than or equal to 5 g / cm³. 3 This allows the composite metal powder to be densely packed in the slurry, avoiding increased resistance due to voids. Silver-coated copper powder uses low-cost copper as the core and highly conductive silver as the shell, which can replace some pure silver powder to reduce costs. The preferred proportion of silver-coated copper powder in the composite metal powder is 30-90%, which can balance cost and conductivity.

[0043] According to the embodiments of this application, by optimizing the tap density and the proportion of silver-coated copper powder, the synergistic optimization of cost control, conductivity, and process adaptability is achieved, so that the conductive paste can not only meet the needs of cost reduction and efficiency improvement of HJT solar cells, but also have good printability and stability.

[0044] In the embodiments of this application, the organic composite resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy-modified acrylic resin, alicyclic epoxy resin and phenolic epoxy resin.

[0045] Preferably, the bisphenol A epoxy resin can be bisphenol A diglycidyl ether and its long-chain derivatives, and the bisphenol F epoxy resin can be bisphenol F diglycidyl ether and its long-chain derivatives. The side groups of the bisphenol A epoxy resin and / or the bisphenol F epoxy resin may or may not contain hydroxyl groups, and the functionality can be grade II or higher. Preferably, the epoxy-modified acrylic resin can be an acrylic resin containing bisphenol A or bisphenol F groups, and the functionality can be grade II or higher. Preferably, the alicyclic epoxy resin can be 3,4-epoxycyclohexyl carboxylate and its derivatives, and the functionality can be grade II or higher. Preferably, the molecular weight of the phenolic epoxy resin can be 170-10000, and the epoxy equivalent can be 250-5000.

[0046] According to the embodiments of this application, the organic composite resin is beneficial for firmly bonding conductive powder and is also compatible with low-temperature curing and narrow grid line printing processes, thus meeting the requirements of HJT solar cell structure stability and process compatibility.

[0047] In the embodiments of this application, the organic solvent is at least one selected from diethylene glycol butyl ether, diethylene glycol dibutyl ether acetate, diethylene glycol dibutyl ether, diethylene glycol ethyl ether, terpineol, ethylene glycol phenyl ether acetate, divalent ester and dimethyl malate.

[0048] In the embodiments of this application, when multiple organic solvents are used, there is no special limitation on the ratio of different organic solvents; any ratio is acceptable. Organic composite resins are mostly solids or high-viscosity liquids at room temperature and cannot be directly mixed with composite metal powders or semiconductor powders. Organic solvents need to be dissolved to convert them into low-viscosity fluids (i.e., organic carriers). At the same time, the overall viscosity of the conductive paste is adjusted by its own content and type to avoid the collapse of printed grid lines due to excessively low viscosity, and to prevent the mesh from being blocked due to excessively high viscosity. Furthermore, the boiling points of all listed solvents are above 150°C, allowing them to slowly evaporate at a low temperature (200°C) to avoid the generation of bubbles due to rapid evaporation that could damage the continuity of the electrodes.

[0049] According to the embodiments of this application, different organic solvents can meet the dissolution requirements of different organic composite resins, and are also conducive to adapting to the narrow grid line printing and low-temperature curing process of HJT solar cells.

[0050] In the embodiments of this application, the curing agent includes an isocyanate curing agent, a blocked cationic curing agent, and a peroxide thermal initiator.

[0051] Preferably, the isocyanate curing agent can be a blocked isocyanate, which may include at least one of the following: blocked hexamethyl diisocyanate (HDI), isoflurane diisocyanate (IPDI), and diphenylmethane diisocyanate (MDI). Its advantage is strong adhesion, such as its compatibility with hydroxyl-containing bisphenol A / F epoxy resins.

[0052] Preferably, the blocked cationic curing agent may include at least one of: diphenyl-(4-phenylsulfonium)phenylsulfonium hexafluoroantimonate, bis(4-(diphenylsulfonium)phenyl)sulfide-bis(hexafluorophosphate), triethyloxonium tetrafluoroborate, and tris[4-(diethylamino)phenyl]ammonium hexafluoroantimonate. This type of curing agent is compatible with alicyclic epoxy resins, etc., because alicyclic epoxy resins have high epoxy group activity, react quickly with cationic resins, and can crosslink within 6 minutes. Furthermore, the crosslinked product has strong weather resistance, thus avoiding any impact on the battery's light transmittance.

[0053] Preferably, the peroxide thermal initiator may include at least one of: benzoyl peroxide (BPO), lauroyl peroxide (LPO), tert-amyl peroxide-2-ethylhexanoate (TAPO), tert-butyl peroxide-2-ethylhexanoate (TBPO), di-tert-butyl peroxide (DTBP), and dicumyl peroxide (DCP). Its advantages include rapid reaction speed, compatibility with epoxy-modified acrylic resins containing double bonds, and the ability to compensate for issues such as the insufficient crosslinking efficiency of isocyanates on acrylic resins.

[0054] According to the embodiments of this application, by using three types of complementary curing agents, the crosslinking requirements of different organic composite resins are covered, and the process requirements of low-temperature curing and rapid curing of HJT solar cells are met, thereby further improving the adhesion, weather resistance and stability of the conductive paste.

[0055] Figure 1 A flowchart illustrating a method for preparing a conductive paste for a crystalline silicon heterojunction solar cell according to an embodiment of this application is shown.

[0056] like Figure 1 As shown, a method for preparing a conductive paste for crystalline silicon heterojunction solar cells includes the following steps: In operation S101, composite metal powder, semiconductor powder, organic composite resin, curing agent, organic solvent, and dispersant are mixed to obtain a mixed paste. In operation S102, the mixed paste is ground to obtain a conductive paste for crystalline silicon heterojunction solar cells.

[0057] In the embodiments of this application, the preferred preparation method is:

[0058] Step 1: Weigh the organic resin and organic solvent according to the proportion and put them into a container. Heat the container to 70~100℃ and stir until the organic resin is completely dissolved. After the solution cools to room temperature, add the dispersant and curing agent and stir until the solution is uniform at room temperature to obtain the organic composite carrier.

[0059] Step 2: After loading the silver-coated copper powder, silver powder and semiconductor powder into the powder hopper, mix them evenly using a ball mill (without adding zircon) to obtain composite metal powder;

[0060] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary stirrer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain a preliminary mixed slurry.

[0061] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0062] According to embodiments of this application, monofunctional fatty acids containing long-chain carbon molecules, used as dispersants, can improve the dispersion uniformity of silver-coated copper powder in conductive pastes, enhance the screen printing suitability of conductive pastes, reduce conductive defects caused by agglomeration, and further reduce bulk resistivity. Narrow bandgap semiconductor powders with band gaps close to silicon can promote bridging between metal powders and form conductive channels in the resin phase, making current tunneling easier to achieve and reducing the bulk resistivity of the conductive paste. Additionally, they can increase the contact area between the conductive paste and the silicon wafer and prevent shrinkage at the contact interface during curing, thereby reducing the contact resistivity of the conductive paste. Therefore, by utilizing the special effects of dispersants and semiconductor powders, the bulk resistivity and contact resistivity of conductive pastes can be reduced, further optimizing the electrical properties of the paste and meeting the performance requirements of ultra-narrow linewidth gate lines. In addition, composite metal powder serves as the core conductive substrate, ensuring the basic conductivity of the conductive paste. Organic composite resin provides molding and bonding support for the conductive paste, curing agent helps improve curing stability, and organic solvent optimizes the dispersibility and printing smoothness of the conductive paste, further achieving synergistic optimization of the electrical properties and printability of the conductive paste.

[0063] The technical solutions of this application will be clearly and completely described below with reference to the embodiments in this application, but they should not be construed as limiting the scope of protection of this application.

[0064] Example 1

[0065] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 87% composite metal powder (30% silver-coated copper powder with a particle size of 3-5µm and 57% silver powder with a particle size of 300-500nm), 10% copper indium gallium sulfide powder, 1.5% bisphenol A diglycidyl ether and its long-chain derivatives, 0.05% blocked hexamethyl diisocyanate, 0.05% isoflurane diisocyanate, 0.1% diphenyl-(4-phenylthio)phenylsulfonium hexafluoroantimonate, 0.1% benzoyl peroxide, 0.5% diethylene glycol butyl ether, 0.5% diethylene glycol dibutyl ether acetate, and 0.2% lauric acid.

[0066] Its preparation method includes the following steps:

[0067] Step 1: Weigh bisphenol A diglycidyl ether and its long-chain derivative, diethylene glycol butyl ether, and diethylene glycol dibutyl ether acetate according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add lauric acid, blocked hexamethyl diisocyanate, isoflurane diisocyanate, diphenyl-(4-phenylthio)phenylsulfonium hexafluoroantimonate, and benzoyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0068] Step 2: After loading the silver-coated copper powder, silver powder, and copper indium gallium sulfur powder with a particle size of 100 nm or less into the powder container, mix them evenly using a ball mill to obtain composite metal powder;

[0069] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0070] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0071] The prepared conductive paste was screen-printed onto both sides of the heterojunction solar cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the size required for contact resistivity testing (1×10⁻⁶ cm⁻¹) using the TLM (Transmission Line Model) method. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0072] Example 2

[0073] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 90.5% composite metal powder (45% silver-coated copper powder with a particle size of 3-5µm and 45.5% silver powder with a particle size of 300-500nm), 0.1% copper indium sulfide powder, 3.36% bisphenol F diglycidyl ether and its long-chain derivatives, 0.01% isoflurane diisocyanate, 0.01% bis(4-(diphenylsulfonium)phenyl)sulfide-bis(hexafluorophosphate), 0.02% tert-amyl peroxide 2-ethylhexanoate, 5% diethylene glycol dibutyl ether and 1% n-octanoic acid.

[0074] Its preparation method includes the following steps:

[0075] Step 1: Weigh bisphenol F diglycidyl ether, its long-chain derivative, and diethylene glycol dibutyl ether according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add octanoic acid, isoflurane diisocyanate, bis(4-(diphenylsulfonium)phenyl)sulfide-bis(hexafluorophosphate), and tert-amyl peroxide-2-ethylhexanoate and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0076] Step 2: After loading silver-coated copper powder, silver powder, and copper indium sulfide powder with a particle size of 100 nm or less into the powder hopper, mix them evenly using a ball mill to obtain composite metal powder;

[0077] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0078] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0079] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0080] Example 3

[0081] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 88.5% composite metal powder (60% silver-coated copper powder with a particle size of 3-5µm and 28.5% silver powder with a particle size of 300-500nm), 5.05% copper indium tin powder, 2% bisphenol A diglycidyl ether and its long-chain derivatives, 1% acrylic resin, 0.5% diphenylmethane diisocyanate, 0.5% isoflurane diisocyanate, 0.5% triethyloxonium tetrafluoroborate, 0.5% tert-amyl peroxide, 1% diethylene glycol ethyl ether, 0.3% terpineol, and 0.6% myristic acid.

[0082] Its preparation method includes the following steps:

[0083] Step 1: Weigh bisphenol A diglycidyl ether and its long-chain derivatives, acrylic resin, diethylene glycol ethyl ether, and terpineol according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add myristic acid, diphenylmethane diisocyanate, isoflurane diisocyanate, triethyloxonium tetrafluoroborate, and tert-amyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0084] Step 2: After loading 3~5µm silver-coated copper powder, 300~500 nm silver powder and copper indium tin powder less than or equal to 100 nm into the powder container, mix them evenly through a ball mill to obtain composite metal powder.

[0085] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0086] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0087] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0088] Example 4

[0089] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 94% composite metal powder (90% silver-coated copper powder with a particle size of 3-5µm and 4% silver powder with a particle size of 300-500nm), 1% antimony selenide powder, 2% 3,4-epoxycyclohexylcarboxylate and its derivatives, 0.2% isoflurane diisocyanate, 0.1% diphenylmethane diisocyanate, 0.1% tris[4-(diethylamino)phenyl]ammonium hexafluoroantimonate, 0.1% di-tert-butyl peroxide, 2.3% dimethyl malate and 0.2% oleic acid.

[0090] Its preparation method includes the following steps:

[0091] Step 1: Weigh 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and its derivatives, and dimethyl malate according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add oleic acid, isoflurane diisocyanate, diphenylmethane diisocyanate, tris[4-(diethylamino)phenyl]ammonium hexafluoroantimonate, and di-tert-butyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0092] Step 2: After loading 3~5µm silver-coated copper powder, 300~500 nm silver powder and copper indium antimony powder less than or equal to 100 nm into the powder hopper, mix them evenly through a ball mill to obtain composite metal powder;

[0093] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0094] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0095] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0096] Comparative Example 1

[0097] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 88.5% composite metal powder (60% silver-coated copper powder with a particle size of 3-5µm and 28.5% silver powder with a particle size of 300-500nm), 3% bisphenol A diglycidyl ether and long-chain derivatives, 3% acrylic resin, 0.5% diphenylmethane diisocyanate, 0.5% isoflurane diisocyanate, 0.3% triethyloxonium tetrafluoroborate, 0.2% tert-amyl peroxide, 2% diethylene glycol ethyl ether and 2% terpineol.

[0098] Its preparation method includes the following steps:

[0099] Step 1: Weigh bisphenol A diglycidyl ether and its long-chain derivatives, acrylic resin, diethylene glycol ethyl ether, and terpineol according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add diphenylmethane diisocyanate, isoflurane diisocyanate, triethyloxonium tetrafluoroborate, and tert-amyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0100] Step 2: After loading 3~5µm silver-coated copper powder and 300~500nm silver powder into a powder container, mix them evenly using a ball mill to obtain composite metal powder;

[0101] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0102] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0103] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0104] Comparative Example 2

[0105] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 90.5% composite metal powder (60% silver-coated copper powder with a particle size of 3-5µm and 25.5% silver powder with a particle size of 300-500nm), 3% copper indium tin powder, 1% bisphenol A diglycidyl ether and its long-chain derivatives, 1% acrylic resin, 0.5% diphenylmethane diisocyanate, 0.5% isoflurane diisocyanate, 0.3% triethyloxonium tetrafluoroborate, 0.2% tert-amyl peroxide, 2% diethylene glycol ethyl ether, and 1% terpineol.

[0106] Its preparation method includes the following steps:

[0107] Step 1: Weigh bisphenol A diglycidyl ether and its long-chain derivatives, acrylic resin, diethylene glycol ethyl ether, and terpineol according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add diphenylmethane diisocyanate, isoflurane diisocyanate, triethyloxonium tetrafluoroborate, and tert-amyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0108] Step 2: After loading 3~5µm silver-coated copper powder, 300~500 nm silver powder and copper indium tin powder less than or equal to 100 nm into the powder container, mix them evenly through a ball mill to obtain composite metal powder.

[0109] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0110] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0111] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0112] Comparative Example 3

[0113] In an embodiment of this application, a conductive paste for a crystalline silicon heterojunction solar cell comprises, by weight percentage: 88% composite metal powder (60% silver-coated copper powder with a particle size of 3-5µm and 27% silver powder with a particle size of 300-500nm), 3% bisphenol A diglycidyl ether and long-chain derivatives, 3% acrylic resin, 0.5% diphenylmethane diisocyanate, 0.5% isoflurane diisocyanate, 0.3% triethyloxonium tetrafluoroborate, 0.2% tert-amyl peroxide, 2% diethylene glycol ethyl ether, 2% terpineol, and 0.5% myristic acid.

[0114] Its preparation method includes the following steps:

[0115] Step 1: Weigh bisphenol A diglycidyl ether and its long-chain derivatives, acrylic resin, diethylene glycol ethyl ether, and terpineol according to a predetermined ratio and place them in a container. Heat the container to 70-100°C and stir until the resin is completely dissolved. After the solution cools to room temperature, add myristic acid, diphenylmethane diisocyanate, isoflurane diisocyanate, triethyloxonium tetrafluoroborate, and tert-amyl peroxide and stir until homogeneous at room temperature to obtain an organic composite carrier.

[0116] Step 2: After loading 3~5µm silver-coated copper powder and 300~500 nm silver powder into a powder container, mix them evenly using a ball mill to obtain composite metal powder;

[0117] Step 3: Mix the organic composite carrier obtained in Step 1 with the composite metal powder obtained in Step 2 in a certain proportion and then use a planetary mixer to perform preliminary stirring. After the mixture is evenly mixed, let it stand until it returns to room temperature to obtain the preliminary mixed slurry.

[0118] Step 4: Disperse and mix the preliminary mixed slurry obtained in Step 3 using a three-roll mill. After repeated grinding, the fineness of the slurry reaches below 7 µm. Then, filter it with a 400~600 mesh wire mesh to obtain a conductive slurry.

[0119] The prepared conductive paste was screen-printed onto both sides of the heterojunction cell and then thermo-cured in a constant-temperature oven at 200°C for 6 minutes. After removal, it was laser-cut into the required size (1×10⁻⁶ cm⁻¹) for TLM (Transient Motion Model) contact resistivity testing. 2 Then, contact resistivity tests were performed, and the test results are shown in Table 1. The prepared conductive paste was screen-printed onto a glass slide with a line length of 6 cm. It was cured under the same curing conditions as described above. After removal, the line resistance of the printed line was tested using the four-probe method. The cross-sectional area of ​​the printed line was measured using a 3D confocal microscope, and the volume resistivity of the conductive paste was obtained by conversion. The test results are shown in Table 1.

[0120] Table 1 Comparison of electrical properties of the prepared conductive pastes

[0121]

[0122] Table 1 compares the electrical properties of the prepared conductive pastes. Comparative Example 1 is the conductive paste without added semiconductor powder and dispersant; Comparative Example 2 is the conductive paste without added dispersant; and Comparative Example 3 is the conductive paste without added semiconductor powder. As shown in Table 1, in terms of bulk resistivity, Comparative Examples 1 and 2 (without added dispersant) have the highest bulk resistivity, followed by Comparative Example 3 (without added semiconductor powder). The examples with both added semiconductor powder and dispersant have the lowest bulk resistivity. This indicates that monofunctional fatty acids containing long-chain carbon molecules, as dispersants, can effectively reduce the bulk resistivity of the conductive paste, and semiconductor powder also has the effect of reducing bulk resistivity. In terms of contact resistivity, Comparative Examples 1 and 3 (without added semiconductor powder) have the highest contact resistivity, while Comparative Example 2 (with only added semiconductor powder) has a lower contact resistivity. The examples with both added semiconductor powder and dispersant have the lowest contact resistivity. This indicates that semiconductor powder can reduce not only the bulk resistivity of the conductive paste but also its contact resistivity. This is because nanoscale semiconductor powder can promote bridging between silver-coated copper powder and silver powder, and form conductive channels in the resin phase, making the tunneling effect of current easier to achieve and reducing the bulk resistivity of the conductive paste. In addition, nanoscale semiconductor powder can increase the contact area between the conductive paste and the silicon wafer and prevent the contact interface from shrinking during the curing process, thereby reducing the contact resistivity of the conductive paste. Therefore, by utilizing the special effects of dispersants and semiconductor powder, the bulk resistivity and contact resistivity of the conductive paste can be reduced, further optimizing the electrical properties of the conductive paste and meeting the performance requirements of ultra-narrow linewidth gate lines.

[0123] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

Claims

1. A conductive paste for use in crystalline silicon heterojunction solar cells, characterized in that, By weight percentage, including: 89-94% composite metal powder, 0.1-10% semiconductor powder, 1.5-9% organic composite resin, 0.04-4% curing agent, 1-5% organic solvent and 0.2-1% dispersant; The dispersant is a saturated fatty acid and / or an unsaturated fatty acid containing 8 to 22 carbon atoms.

2. The conductive paste according to claim 1, characterized in that, The dispersant includes at least one of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, and linoleic acid.

3. The conductive paste according to claim 1, characterized in that, The semiconductor powder is a narrow bandgap semiconductor powder with a bandgap width of 1.2eV to 1.4eV, including at least one of copper indium gallium sulfide powder, copper indium sulfide powder, copper indium tin powder, antimony selenide powder, and antimony sulfide powder.

4. The conductive paste according to claim 3, characterized in that, The particle size of the semiconductor powder is less than or equal to 100 nm.

5. The conductive paste according to claim 1, characterized in that, The composite metal powder includes silver-coated copper powder with a particle size of 3~5µm and silver powder with a particle size of 300~500nm.

6. The conductive paste according to claim 5, characterized in that, The tap density of both the silver-coated copper powder and the silver powder is greater than or equal to 5 g / cm³. 3 Furthermore, the silver-coated copper powder accounts for 30-90% of the composite metal powder.

7. The conductive paste according to claim 1, characterized in that, The organic composite resin includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy-modified acrylic resin, alicyclic epoxy resin, and phenolic epoxy resin.

8. The conductive paste according to claim 1, characterized in that, The organic solvent is at least one selected from diethylene glycol butyl ether, diethylene glycol dibutyl ether acetate, diethylene glycol dibutyl ether, diethylene glycol ethyl ether, terpineol, ethylene glycol phenyl ether acetate, divalent ester, and dimethyl malate.

9. The conductive paste according to claim 1, characterized in that, The curing agent includes isocyanate curing agent, blocked cationic curing agent and peroxide thermal initiator.

10. The method for preparing the conductive paste for crystalline silicon heterojunction solar cells according to any one of claims 1 to 9, characterized in that, Includes the following steps: Composite metal powder, semiconductor powder, organic composite resin, curing agent, organic solvent and dispersant are mixed and ground to obtain a conductive paste for crystalline silicon heterojunction solar cells.

Images