Low-temperature silver paste for laser transfer, its preparation method and HJT battery

Abstract

The present invention discloses a low-temperature silver paste for laser transfer, its preparation method and an HJT battery. The low-temperature silver paste comprises the following components in percentage by weight: silver powder 80-97%, thermosetting resin 2-4%, hydroxyl-containing alcohol polymer 0.2-0.5%, blocked isocyanate 0.2-0.8%, latent accelerator 0.1-0.3%, coupling agent 0.1-0.5%, dispersant 0.1-0.3%, and solvent 1-4%. By adding a hydroxyl-containing alcohol polymer to the low-temperature silver paste, the present invention solves the problems of difficult demolding, broken grid lines and peeling during the laser transfer process, enabling the low-temperature silver paste to be applied to the printing of 16μm-18μm grid lines, and having the advantages of easy demolding, not easy to break, excellent heat and cold resistance performance and high photoelectric conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and particularly to a low-temperature silver paste for laser transfer printing, a preparation method thereof, and an HJT cell. Background Art

[0002] With the continuous progress of photovoltaic cell technology, the trend of P-type to N-type iteration has started in 2021, moving towards higher efficiency levels. N-type technology routes represented by TOPcon (Tunnel Oxide Passivating Contacts) tunneling oxide passivating contact cells and HJT (Heterojunction Technology) heterojunction cells have successively made breakthroughs, and the industrialization process is expected to speed up. Compared with TOPcon, HJT has advantages such as better contact resistance and passivation effect, being more suitable for thinning, higher photoelectric conversion efficiency, and being able to meet the requirements of the next-generation tandem cells.

[0003] Currently, the HJT cell mainly uses the screen printing process to form the required electrodes. Due to the presence of flaky silver powder in the low-temperature silver paste, the screen passing property is poor, which is not conducive to finer wire mesh printing; without a thixotropic agent, it is difficult to form a larger aspect ratio; the consumption of single-piece silver paste is large, more than twice that of PERC cells; as the silicon wafer becomes thinner and thinner, the fragmentation rate after screen printing gradually increases.

[0004] Compared with the screen printing technology of mainstream traditional solar cells, the grid lines prepared by the laser transfer printing technology have the following advantages:

[0005] (1) It can significantly reduce the shading area of the grid lines, thereby improving the photoelectric conversion efficiency;

[0006] (2) It can significantly reduce the usage amount of the paste;

[0007] (3) It is a non-contact technology and can effectively reduce the fragmentation rate.

[0008] Therefore, the laser graphic transfer printing technology (PTP) will become one of the main choices for the next-generation metallization process.

[0009] However, in the actual application of HJT low-temperature silver paste in laser transfer printing, there are still the following defects and deficiencies:

[0010] Currently, the grid lines only reach 22μm. When the grid lines are 18μm or even 16μm, it is very difficult to demold smoothly during laser transfer printing. Demolding aids such as dimethyl silicone oil and polyether polysiloxane copolymer are added to the low-temperature paste, and they will remain in the paste after curing, affecting the resistivity of the grid lines, thereby reducing the photoelectric conversion efficiency.

[0011] The laser transfer paste is very sensitive to the powder size. The presence of large particle powders in the paste will affect the filling area of the paste, resulting in very low transfer efficiency. Currently, flaky silver powder is added to the laser transfer paste (Patent: CN115831440A). During the process of filling the paste into the transfer slot, the presence of flakes easily blocks the transfer slot, hinders the filling of spherical powders in the system, making the filling insufficient. The grid lines transferred onto the silicon wafer are not full, there are some gaps between the pastes, affecting the electrical properties of the grid lines, and ultimately reducing the photoelectric conversion efficiency.

[0012] In the laser transfer paste, a toughening agent is usually directly added to solve the problems such as fracture and peeling of the cured grid lines. However, the addition of the toughening agent will affect the electrical properties and printing performance of the grid lines. Summary of the Invention

[0013] In order to overcome the disadvantages and deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature silver paste for laser transfer, its preparation method, and an HJT battery. By adding a hydroxyl group-containing alcohol polymer to the low-temperature silver paste, the problems of difficult demolding, fracture, and peeling of the grid lines during the laser transfer process are solved, enabling the low-temperature silver paste to be applied to the printing of 16μm - 18μm grid lines, and having the advantages of easy demolding, not easy to break, and high photoelectric conversion efficiency.

[0014] The purpose of the present invention is achieved by the following technical solutions:

[0015] A low-temperature silver paste for laser transfer, comprising the following components in weight percentages: silver powder 80 - 97%, thermosetting resin 2 - 4%, hydroxyl group-containing alcohol polymer 0.2 - 0.5%, blocked isocyanate 0.2 - 0.8%, latent accelerator 0.1 - 0.3%, coupling agent 0.1 - 0.5%, dispersant 0.1 - 0.3%, and solvent 1 - 4%.

[0016] In one embodiment, the hydroxyl group-containing alcohol polymer is one or more of polyethylene glycol, polypropylene glycol, and glycerol.

[0017] In one embodiment, the hydroxyl group-containing alcohol polymer is polypropylene glycol.

[0018] In one embodiment, the polypropylene glycol is one or more of PPG1000, PPG2000, PPG - 3000, and PPG - 4000.

[0019] In one embodiment, the silver powder includes micron-sized spherical silver powder, sub-micron-sized spherical silver powder, and nano-sized spherical silver powder, and the weight ratio of the micron-sized spherical silver powder, the sub-micron-sized spherical silver powder, and the nano-sized spherical silver powder is (40 - 60) : (25 - 35) : (5 - 12).

[0020] In one embodiment, the particle size D50 of the micron-sized spherical silver powder is 2-3 μm, and D100 < 10 μm; the particle size D50 of the submicron-sized spherical silver powder is 1-2 μm, and D100 < 4 μm; the particle size D50 of the nano-sized spherical silver powder is 0.3-0.5 nm, and D100 < 2 μm.

[0021] In one embodiment, the thermosetting resin is one or more of bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, alicyclic epoxy resin, and hydantoin epoxy resin.

[0022] In one embodiment, the blocked isocyanate includes one or more of 2,4-toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate;

[0023] The latent accelerator is one or more of urea-modified SH-A100 / A150, EA-3201, N-vinylcarbazole, cyclohexyl vinyl ether, diethylene glycol divinyl ether, 2-ethylhexyl vinyl ether, phenothiazine, anthracene, thioxanthene, benzophenone, 2-ethyl-4-methylimidazole, and 2-methylimidazole;

[0024] The coupling agent is one or more of glycidoxypropyltrimethoxysilane, 3-glycidylpropyltrimethoxysilane, glycidyl ether oxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and methacryloxypropyltrimethoxysilane;

[0025] The dispersant is one or more of KD9, KD13, KD16, KD24, BYK111, and BYK110;

[0026] The solvent is one or more of butyl carbitol, butyl carbitol acetate, terpineol, alcohol ester 12, tributyl citrate, and diethylene glycol butyl ether acetate.

[0027] The present invention also provides a method for preparing the above-mentioned low-temperature silver paste for laser transfer, comprising the following steps:

[0028] S1: Weigh the raw materials with a preset mass for preparing the low-temperature silver paste, add the thermosetting resin, hydroxyl-containing alcohol polymer, blocked isocyanate, latent accelerator, coupling agent, and dispersant into the solvent, and stir and mix evenly to obtain a mixture;

[0029] S2: Add silver powder to the mixture, stir evenly, grind, and filter to obtain the required low-temperature silver paste.

[0030] The present invention also provides an HJT cell, which includes a grid electrode formed by curing the low-temperature silver paste as described above.

[0031] The beneficial effects of the present invention are as follows: By adding a hydroxyl group-containing alcohol polymer to the low-temperature silver paste, the hydroxyl group (-OH) in the hydroxyl group-containing alcohol polymer reacts with the isocyanate group (-NCO) in the blocked isocyanate to form a urethane group, which has good flexibility and plays a good toughening effect, solving the problems of grid line breakage and peeling. Moreover, after curing, it does not affect the resistivity of the grid line, avoiding the problem that the resistivity of the grid line is affected by adding an additional toughening agent, and can maintain excellent photoelectric conversion efficiency; the hydroxyl group has a good lubricating effect, improving the demolding effect of the grid line and solving the problem of difficult demolding during the laser transfer process; and polypropylene glycol has excellent heat and cold resistance performance, which is beneficial to the reliability test of the silver paste. Detailed implementation mode

[0032] The present invention provides a low-temperature silver paste for laser transfer, which includes the following components in weight percentages: silver powder 80 - 97%, thermosetting resin 2 - 4%, hydroxyl group-containing alcohol polymer 0.2 - 0.5%, blocked isocyanate 0.2 - 0.8%, latent accelerator 0.1 - 0.3%, coupling agent 0.1 - 0.5%, dispersant 0.1 - 0.3%, and solvent 1 - 4%. By adding a hydroxyl group-containing alcohol polymer to the low-temperature silver paste in the present invention, the hydroxyl group (-OH) group in the hydroxyl group-containing alcohol polymer reacts with the isocyanate group (-NCO) in the blocked isocyanate to form a urethane group, which has good flexibility and plays a good toughening effect, solving the problems of grid line breakage and peeling. Moreover, after curing, it does not affect the resistivity of the grid line, avoiding the problem that the resistivity of the grid line is affected by adding an additional toughening agent, and can maintain excellent photoelectric conversion efficiency; and the hydroxyl group has a good lubricating effect, improving the demolding effect of the grid line and solving the problem of difficult demolding during the laser transfer process.

[0033] Furthermore, the hydroxyl group-containing alcohol polymer is one or more of polyethylene glycol, polypropylene glycol, and glycerol; polyethylene glycol, polypropylene glycol, and glycerol have good lubricating and dispersing effects, which can improve the demolding effect of the grid line and also help the components disperse more evenly.

[0034] Furthermore, the hydroxyl group-containing alcohol polymer is polypropylene glycol. Polypropylene glycol has excellent heat and cold resistance performance.

[0035] Further, the polypropylene glycol is one or more of PPG1000 (molecular weight 900 - 1100, hydroxyl value 102 - 125 mgKOH / g, acid value ≤ 0.5 mgKOH / g), PPG2000 (molecular weight 1800 - 2200, hydroxyl value 51 - 62 mgKOH / g, acid value ≤ 0.5 mgKOH / g), PPG - 3000 (molecular weight 2700 - 3300, hydroxyl value 34 - 42 mgKOH / g, acid value ≤ 0.5 mgKOH / g), and PPG - 4000 (molecular weight 3700 - 4300, hydroxyl value 26 - 30 mgKOH / g, acid value ≤ 0.5 mgKOH / g).

[0036] Further, the silver powder includes micron - sized spherical silver powder, sub - micron - sized spherical silver powder, and nano - sized spherical silver powder. The weight ratio of the micron - sized spherical silver powder, sub - micron - sized spherical silver powder, and nano - sized spherical silver powder is (40 - 60):(25 - 35):(5 - 12); the D50 of the micron - sized spherical silver powder is 2 - 3 μm, D100 < 10 μm; the D50 of the sub - micron - sized spherical silver powder is 1 - 2 μm, D100 < 4 μm; the D50 of the nano - sized spherical silver powder is 0.3 - 0.5 nm, D100 < 2 μm. This embodiment adopts a spherical powder system with the size controlled within 10 μm. The combination of large - sized and small - sized balls makes the slurry easy to scrape the film, fills the transfer groove more fully, there are no voids between the slurries, and improves the photoelectric conversion efficiency.

[0037] Further, the thermosetting resin is one or more of bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, alicyclic epoxy resin, and hydantoin epoxy resin. After the silver paste is dried, the surface of the silver powder is wrapped by the resin and conducts electricity through the "electronic channel effect" electron transition, and the resin is the transition barrier. The polar groups and conjugated structures contained in the resin induce polarity to electrons and provide electron transport orbits, reducing the resin dielectric property; the main chain of the resin molecule is a straight - chain carbon - carbon single bond with good flexibility, and the resin shrinkage rate is relatively large after the prepared silver paste is cured, the distance between silver powders becomes smaller, and the electron transition distance becomes shorter. Since the thermosetting resin contains more polar groups that form hydrogen bonds, the surface electrostatic attraction and intermolecular force are greater, and the resin has good adhesiveness, making the silver paste have good adhesiveness; and because it contains unsaturated bonds, participates in the epoxy curing reaction, and contains ester - based functional groups with strong polarity and large cohesive force, it can improve the adhesion between the slurry and the battery silicon wafer without increasing the volume resistance, which is beneficial to the elastic fracture of the slurry and the laser transfer template during slurry transfer, and is not easy to generate broken grids, splashes, and grid line collapse or obvious flow, thereby improving the aspect ratio and the ability of thinning of the grid lines.

[0038] Furthermore, the blocked isocyanate includes one or more of 2,4-toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate; the latent accelerator is one or more of urea-modified SH-A100 / A150, EA-3201, N-vinylcarbazole, cyclohexyl vinyl ether, diethylene glycol divinyl ether, 2-ethylhexyl vinyl ether, phenothiazine, anthracene, thioxanthene, benzophenone, 2-ethyl-4-methylimidazole, 2-methylimidazole; the coupling agent is one or more of glycidoxypropyltrimethoxysilane, 3-glycidylpropyltrimethoxysilane, glycidyl ether oxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, methacryloxypropyltrimethoxysilane; the dispersant is one or more of KD9, KD13, KD16, KD24, BYK111, BYK110; the solvent is one or more of butyl carbitol, butyl carbitol acetate, terpineol, alcohol ester 12, tributyl citrate, diethylene glycol monobutyl ether acetate; but not limited thereto.

[0039] The present invention also provides a method for preparing the above-mentioned low-temperature silver paste for laser transfer, comprising the following steps:

[0040] S1: Weigh raw materials with a preset mass for preparing the low-temperature silver paste, add a thermosetting resin, a hydroxyl-containing alcohol polymer, a blocked isocyanate, a latent accelerator, a coupling agent, and a dispersant to a solvent, and stir and mix evenly to obtain a mixture.

[0041] S2: Add silver powder to the mixture, stir evenly, grind, and filter to obtain the required low-temperature silver paste.

[0042] Specifically, at room temperature, a thermosetting resin, a hydroxyl-containing alcohol polymer, a blocked isocyanate, a latent accelerator, a coupling agent, and a dispersant are sequentially and slowly added to a solvent using a constant-temperature stirrer, the rotation speed is set to 300 rpm, and after stirring for 5 minutes, it is mixed evenly to obtain a mixture.

[0043] Micron-sized spherical silver powder, submicron-sized spherical silver powder, and nano-sized spherical silver powder are added to the mixture, stirred evenly, and ground using a three-roll mill to make the dispersion uniform, obtaining a primary silver paste.

[0044] Finally, the primary silver paste is filtered, the filter screen is 400 - 500 meshes, the temperature is 25 °C, and the finished silver paste is obtained after filtration.

[0045] Among them, the grinding gap of the three-roll mill in step S2 includes:

[0046] The first step, the initial roll gap is 80 μm and the final roll gap is 40 μm, and it is mixed 2 times.

[0047] In the second step, the initial roll gap is 40 μm and the final roll gap is 20 μm, and the mixture is carried out twice.

[0048] In the third step, the initial roll gap is 20 μm and the final roll gap is 10 μm, and the mixture is carried out twice.

[0049] In the fourth step, the initial roll gap is 15 μm and the final roll gap is 7 μm, and the mixture is carried out twice.

[0050] The present invention also provides an HJT battery, which includes a grid electrode formed by curing the low-temperature silver paste as described above; through a laser transfer printing technique, the above-mentioned finished silver paste is printed onto a battery silicon wafer substrate with a TCO film, and after curing, a grid electrode is formed.

[0051] The beneficial effects of the present invention are as follows:

[0052] (1) Adding a hydroxyl group-containing alcohol polymer to the laser transfer printing paste of the present invention has a lubricating effect and can play a role in rapid demoulding during laser transfer printing; the hydroxyl group (-OH) in polypropylene glycol can react with the isocyanate (-NCO) group in the system. After curing, it will not only not affect the resistivity of the grid line, but also provide a toughening effect for the entire system.

[0053] (2) The powder system in the laser transfer printing paste of the present invention adopts a ball powder system, and the size is controlled within 10 μm. The combination of large balls and small balls makes the paste easy to scrape the film, fills the transfer groove more fully, and there are no voids between the pastes, improving the photoelectric conversion efficiency.

[0054] (3) Adding a hydroxyl group-containing alcohol polymer to the laser transfer printing paste of the present invention. In the organic system reaction, the hydroxyl group (-OH) in polypropylene glycol can react with the isocyanate (-NCO) group to generate a urethane group, which has good flexibility. There is no need to add an additional toughening agent in the system to reduce the internal stress of the epoxy resin. It will self-react to generate flexible groups, avoiding defects such as fracture and peeling after the grid line is cured.

[0055] (4) Polypropylene glycol has excellent heat and cold resistance, which has a beneficial effect on the reliability test of the silver paste.

[0056] The following further clarifies the present invention in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0057] Examples 1-6

[0058] Example 1:

[0059] A low-temperature silver paste for laser transfer printing is made from the following raw materials in parts by weight:

[0060] Micron-sized spherical silver powder (D50: 2 - 3 μm): 50%

[0061] Sub-micron-sized spherical silver powder (D50: 0.5 - 1 μm): 32%

[0062] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5 μm): 10%

[0063] Thermosetting resin: Bisphenol F epoxy resin, 3.2%

[0064] Polypropylene glycol (PPG - 1000): 0.3%

[0065] Blocked isocyanate: Hexamethylene diisocyanate, 0.6%

[0066] Latent accelerator: 2 - Ethyl - 4 - methylimidazole, 0.2%

[0067] Coupling agent: Epoxypropoxypropyltrimethoxysilane, 0.5%

[0068] Dispersant: BYK110, 0.2%

[0069] Solvent: Diethylene glycol butyl ether acetate, 3%

[0070] Example 2:

[0071] A low-temperature silver paste for laser transfer, made from the following raw materials in parts by weight:

[0072] Micron-sized spherical silver powder (D50: 2 - 3 μm): 50%

[0073] Sub-micron-sized spherical silver powder (D50: 0.5 - 1 μm): 32%

[0074] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5 μm): 10%

[0075] Thermosetting resin: Bisphenol F epoxy resin, 3.2%

[0076] Polypropylene glycol (PPG - 2000): 0.3%

[0077] Blocked isocyanate: Hexamethylene diisocyanate, 0.6%

[0078] Latent accelerator: 2 - Ethyl - 4 - methylimidazole, 0.2%

[0079] Coupling agent: Epoxypropoxypropyltrimethoxysilane, 0.5%

[0080] Dispersant: BYK110, 0.2%

[0081] Solvent: Diethylene glycol butyl ether acetate, 3%

[0082] Example 3:

[0083] A low-temperature silver paste for laser transfer is made from the following raw materials in parts by weight:

[0084] Micron-sized spherical silver powder (D50: 2 - 3 μm): 50%

[0085] Sub-micron-sized spherical silver powder (D50: 0.5 - 1 μm): 32%

[0086] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5 μm): 10%

[0087] Thermosetting resin: Bisphenol F epoxy resin, 3.2%

[0088] Polypropylene glycol (PPG - 3000): 0.3%

[0089] Blocked isocyanate: Hexamethylene diisocyanate, 0.6%

[0090] Latent accelerator: 2 - Ethyl - 4 - methylimidazole, 0.2%

[0091] Coupling agent: Epoxypropoxyltrimethoxysilane, 0.5%

[0092] Dispersant: BYK110, 0.2%

[0093] Solvent: Diethylene glycol butyl ether acetate, 3%

[0094] Example 4:

[0095] A low-temperature silver paste for laser transfer is made from the following raw materials in parts by weight:

[0096] Micron-sized spherical silver powder (D50: 2 - 3 μm): 50%

[0097] Sub-micron-sized spherical silver powder (D50: 0.5 - 1 μm): 32%

[0098] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5 μm): 10%

[0099] Thermosetting resin: Bisphenol F epoxy resin, 3.2%

[0100] Polypropylene glycol (PPG - 4000): 0.3%

[0101] Blocked isocyanate: Hexamethylene diisocyanate, 0.6%

[0102] Latent accelerator: 2 - Ethyl - 4 - methylimidazole, 0.2%

[0103] Coupling agent: Epoxypropyltrimethoxysilane, 0.5%

[0104] Dispersant: BYK110, 0.2%

[0105] Solvent: Diethylene glycol monobutyl ether acetate, 3%

[0106] Example 5:

[0107] A low-temperature silver paste for laser transfer is made from the following raw materials in parts by weight:

[0108] Micron-sized spherical silver powder (D50: 2 - 3μm): 50%

[0109] Sub-micron-sized spherical silver powder (D50: 0.5 - 1μm): 32%

[0110] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5μm): 10%

[0111] Thermosetting resin: Bisphenol A epoxy resin, 3.2%

[0112] Polypropylene glycol (PPG-2000): 0.3%

[0113] Blocked isocyanate: Hexamethylene diisocyanate, 0.6%

[0114] Latent accelerator: 2-Ethyl-4-methylimidazole, 0.2%

[0115] Coupling agent: Epoxypropyltrimethoxysilane, 0.5%

[0116] Dispersant: BYK110, 0.2%

[0117] Solvent: Diethylene glycol monobutyl ether acetate, 3%

[0118] Example 6:

[0119] A low-temperature silver paste for laser transfer is made from the following raw materials in parts by weight:

[0120] Micron-sized spherical silver powder (D50: 2 - 3μm): 50%

[0121] Sub-micron-sized spherical silver powder (D50: 0.5 - 1μm): 32%

[0122] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5μm): 10%

[0123] Thermosetting resin: Phenolic epoxy resin, 3.2%

[0124] Polypropylene glycol (PPG-2000): 0.3%

[0125] Blocked isocyanate: hexamethylene diisocyanate, 0.6%

[0126] Latent accelerator: 2-ethyl-4-methylimidazole, 0.2%

[0127] Coupling agent: glycidoxypropyltrimethoxysilane, 0.5%

[0128] Dispersant: BYK110, 0.2%

[0129] Solvent: diethylene glycol butyl ether acetate, 3%

[0130] Example 7:

[0131] A low-temperature silver paste for laser transfer is made from the following raw materials in parts by weight:

[0132] Micron-sized spherical silver powder (D50: 2 - 3μm): 50%

[0133] Sub-micron-sized spherical silver powder (D50: 0.5 - 1μm): 32%

[0134] Nanometer-sized spherical silver powder (D50: 0.3 - 0.5μm): 10%

[0135] Thermosetting resin: bisphenol F epoxy resin, 3.2%

[0136] Polyethylene glycol (PEG-2000): 0.3%

[0137] Blocked isocyanate: hexamethylene diisocyanate, 0.6%

[0138] Latent accelerator: 2-ethyl-4-methylimidazole, 0.2%

[0139] Coupling agent: glycidoxypropyltrimethoxysilane, 0.5%

[0140] Dispersant: BYK110, 0.2%

[0141] Solvent: diethylene glycol butyl ether acetate, 3%

[0142] Comparative Examples 1 - 3

[0143] Comparative Example 1: In Example 2, polypropylene glycol is not added, and the others are the same;

[0144] Comparative Example 2: In Example 2, polypropylene glycol is replaced with dimethyl silicone oil, and the others are the same;

[0145] Comparative Example 3: In Example 3, the micron-sized spherical silver powder (D50: 2 - 3μm) is replaced with micron-sized flaky silver powder (D50: 2 - 3μm).

[0146] The slurries of the above examples and comparative examples were prepared according to the following steps:

[0147] (1) At room temperature, a thermosetting resin, a hydroxyl-containing alcohol polymer, a blocked isocyanate, a latent accelerator, a coupling agent, and a dispersant were successively and slowly added to a solvent using a constant-temperature stirrer. The rotation speed was set at 300 rpm. After stirring for 5 minutes, the mixture was uniformly mixed to obtain a mixture;

[0148] Among them, in Comparative Example 1, the hydroxyl-containing alcohol polymer was not added, and in Comparative Example 2, the hydroxyl-containing alcohol polymer was replaced with dimethyl silicone oil;

[0149] (2) Micron-sized spherical silver powder, sub-micron-sized spherical silver powder, and nano-sized spherical silver powder were added to the mixture and stirred evenly. Then, it was ground using a three-roll mill to make the dispersion uniform, obtaining a primary silver paste;

[0150] Among them, in Comparative Example 3, the micron-sized spherical silver powder was replaced with micron-sized flaky silver powder;

[0151] (3) Finally, the primary silver paste was filtered through a 400 - 500 mesh filter screen at a temperature of 25°C to obtain the finished silver paste.

[0152] Among them, the grinding gap of the three-roll mill in step (2) included:

[0153] The first step: the initial roll gap was 80 μm and the final roll gap was 40 μm, and it was mixed 2 times;

[0154] The second step: the initial roll gap was 40 μm and the final roll gap was 20 μm, and it was mixed 2 times;

[0155] The third step: the initial roll gap was 20 μm and the final roll gap was 10 μm, and it was mixed 2 times;

[0156] The fourth step: the initial roll gap was 15 μm and the final roll gap was 7 μm, and it was mixed 2 times.

[0157] Test Example

[0158] The above-mentioned finished silver paste was used to prepare the grid electrodes of HJT cells by the method of laser transfer printing. Specifically: Through laser transfer printing technology, the finished silver paste in the above examples and comparative examples was printed onto a silicon wafer substrate with a TCO film (166×166 mm), and the laser irradiation intensity was 400 W. The cell was dried and cured in an infrared curing furnace, and the cured conductive paste was cooled to form grid electrodes.

[0159] Taking the finished silver paste of Examples 1 to 7 and Comparative Examples 1 to 3 as samples, each sample was printed on the same substrate for relevant property tests. The test process was as follows:

[0160] Printing and electrode height-width ratio test: The width, height, and height-width ratio of the electrodes were measured using a 3D optical microscope. Each slurry was tested 6 times, and the average value was taken.

[0161] Viscosity test: The viscosity test was carried out using a Brookfield viscometer at a rotational speed of 10 revolutions per minute to measure the viscosity value when stirring for 4 minutes.

[0162] Resistivity test: A four-probe ohmmeter was used to measure the resistance across the electrodes.

[0163] Electrical performance test (photovoltaic conversion efficiency): It was carried out in a solar simulator under the test conditions of 25 °C, AM1.5 spectrum, and 1.000 kW / m2. Reference standard: "GB / T 6495.1-1996 Photovoltaic devices - Part 1: Measurement of photovoltaic current-voltage characteristics".

[0164] Wet-freeze cycle test: The printed cell wafers were subjected to wet-freeze cycle tests, cycling between (-40 ± 2) °C and (85 ± 2) °C. At the high temperature (85 ± 2) °C, the relative humidity was controlled at (85 ± 5) %, and maintained for 20 hours; at the low temperature (-40 ± 2) °C, the relative humidity was not required and maintained for 4 hours. Between the highest and lowest temperatures, the temperature change rate was 100 °C / hour, and one cycle was completed.

[0165] The results of the printing and height-width ratio test, viscosity test, resistivity test, and electrical performance test are summarized in Table 1.

[0166] Table 1 Test results of printing performance, height-width ratio, viscosity, resistivity, and electrical performance

[0167]

[0168] The results of the wet-freeze cycle test, conversion efficiency comparison, and conversion efficiency change rate comparison are summarized in Table 2.

[0169] Table 2 Test results of wet-freeze cycle

[0170]

[0171] From the test results in Table 1, it can be seen that in Examples 1 to 4, polypropylene glycol with different molecular weights and different hydroxyl values was added to the slurry. Among them, in Example 2, the slurry with PPG-2000 added had the best viscosity, height-width ratio, resistivity, and conversion efficiency. In Example 4, PPG-4000 was added, which had a relatively large molecular weight, resulting in a relatively high viscosity of the prepared slurry, leading to broken grid lines in the laser-printed grid lines and a relatively low conversion efficiency. In Examples 2, 5, and 6, different epoxy resins were respectively added and paired with polypropylene glycol. The results showed that the slurry prepared by pairing bisphenol F epoxy resin with polypropylene glycol (PPG-2000) in Example 2 had the best performance for the low-temperature silver paste used in laser printing.

[0172] In Comparative Example 1, the polypropylene glycol in Example 2 was not added, resulting in a large number of broken grid lines in the laser-printed grid lines and a relatively large resistivity of the paste, making it impossible to test other properties. This shows that the hydroxyl group (-OH) in the polypropylene glycol can react with the isocyanate group (-NCO) to form a urethane group, which has good flexibility. In Comparative Example 2, the polypropylene glycol in Example 2 was replaced with dimethyl silicone oil, resulting in a relatively large resistivity and a low battery conversion efficiency. This shows that dimethyl silicone oil will remain in the paste after curing, affecting the resistivity of the grid lines and thus reducing the photoelectric conversion efficiency. In Comparative Example 3, the micron-sized spherical silver powder was replaced with micron-sized flake silver powder, resulting in broken grid lines during transfer, a poor aspect ratio, and a low conversion efficiency. This shows that the combination of spherical silver powder with large and small balls makes the paste easy to scrape and fill the transfer groove more fully, with no voids between the pastes, improving the photoelectric conversion efficiency and being easy to print.

[0173] As can be seen from Table 2, polypropylene glycol (PPG-2000) has better heat and cold resistance than polyethylene glycol (PEG-2000). When the ambient temperature changes greatly, such as in cold or hot environments, the low-temperature silver paste of the present invention can exhibit more excellent performance and maintain a good photoelectric conversion efficiency.

[0174] It should be noted that each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0175] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above with the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications within the scope of the technical solution of the present invention by using the above-disclosed technical content, which are equivalent embodiments of equivalent changes. However, as long as it does not deviate from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A low-temperature silver paste for laser transfer, characterized in that, Comprising the following components by weight percentage: Micron-sized spherical silver powder, D50: 2 - 3μm: 50% Sub-micron-sized spherical silver powder, D50: 0.5 - 1μm: 32% Nanometer-sized spherical silver powder, D50: 0.3 - 0.5μm: 10% Thermosetting resin: Bisphenol F epoxy resin, 3.2% Polypropylene glycol: PPG - 2000, 0.3% Blocked isocyanate: Hexamethylene diisocyanate, 0.6% Latent accelerator: 2 - Ethyl - 4 - methylimidazole, 0.2% Coupling agent: Epoxypropoxypropyltrimethoxysilane, 0.5% Dispersant: BYK110, 0.2% Solvent: Diethylene glycol butyl ether acetate, 3%.

2. A method for preparing the low-temperature silver paste for laser transfer described in claim 1 above, characterized in that, Comprising the following steps: S1: Weigh the raw materials of a preset mass for preparing the low-temperature silver paste. Add the thermosetting resin, hydroxyl-containing alcohol polymer, blocked isocyanate, latent accelerator, coupling agent, and dispersant into the solvent, and stir and mix evenly to obtain a mixture; S2: Add silver powder to the mixture, stir evenly, grind, and filter to obtain the required low-temperature silver paste.

3. A HJT battery, characterized in that, The HJT battery comprises a grid electrode formed by curing the low-temperature silver paste as described in Claim 1.

Images