Heterojunction silver paste and preparation method and application thereof

Abstract

The invention relates to the technical field of solar cells, and particularly provides heterojunction silver paste and a preparation method and application thereof. In the prior art, a method for improving the welding tension of silver paste by adding flaky silver powder and improving the molecular weight of resin in an organic carrier easily affects the subsequent printing process, the wet weight and the printing linearity. The heterojunction silver paste provided by the invention comprises powder, an organic carrier and an auxiliary agent, and the powder comprises tin powder and silver powder; the organic carrier comprises polyester resin and epoxy resin; the epoxy resin at least comprises bisphenol A epoxy resin. On the basis that good printing performance and electrical performance of the silver paste are guaranteed, the welding tension of the paste is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and specifically provides a heterojunction silver paste, a preparation method and an application thereof. Background Art

[0002] A solar cell is a photovoltaic device that directly converts solar energy into electrical energy through the photovoltaic effect. A heterojunction solar cell is a hybrid solar cell made of a crystalline silicon substrate and an amorphous silicon thin film. Since the upper surface of the heterojunction solar cell is TCO, charges will not be polarized on the TCO on the surface of the cell, and there is no PID phenomenon. The efficiency of the HJT cell is 1-2% higher than that of the P-type monocrystalline silicon cell, and the light-induced attenuation effect common in amorphous silicon solar cells will not occur in HJT solar cells. Therefore, it has become the main development direction of solar cells in recent years.

[0003] However, the heterojunction solar cell contains an amorphous silicon passivation layer, so it cannot withstand high temperatures like a conventional solar cell and must use a low-temperature silver paste cured below 200°C.

[0004] In the low-temperature silver paste, the main functions of welding are the metallization of silver powder and solder and the adhesion of the silver paste itself to the substrate. The metallization of silver powder and solder is related to the contact area between silver powder and solder in the silver paste and the welding process. The adhesion of the silver paste to the substrate is mainly related to the resin in the silver paste. Therefore, currently, manufacturers add flake powder to the silver paste system to increase the specific surface area of the powder so that the solder can form a firm metallization with the silver powder; in terms of the organic carrier, high-molecular-weight epoxy resin is added to improve the adhesion to the substrate, thereby increasing the welding tensile strength of the silver paste.

[0005] In the existing technical solutions, the welding tensile strength of the silver paste is improved by adding flake silver powder and increasing the molecular weight of the resin in the organic carrier. Although the welding tensile strength of the silver paste has been improved, the addition of flake silver powder and high-molecular-weight epoxy resin increases the overall viscosity of the silver paste, which has a great impact on subsequent printing. There will be a large area of broken grid phenomenon, and there will be a sheet-out phenomenon during the dispersion process of the three-roll mill. The overall fineness of the silver paste becomes larger, and the printing process will also have a situation of screen clogging, which has a great impact on the subsequent printing process and the wet weight of printing.

[0006] Correspondingly, the art needs a new technical solution to solve the above technical problems. Summary of the Invention

[0007] The present invention aims to solve the above technical problems, that is, to solve the problem that the method of improving the welding tensile strength of the silver paste by adding flake silver powder and increasing the molecular weight of the resin in the organic carrier in the prior art is likely to affect the subsequent printing process, wet weight and printing linearity.

[0008] In a first aspect, the present invention provides a heterojunction silver paste, comprising a powder, an organic carrier, and an additive. Among them,

[0009] the powder includes tin powder and silver powder;

[0010] the organic carrier includes polyester resin and epoxy resin;

[0011] the epoxy resin includes at least bisphenol A epoxy resin.

[0012] In a preferred technical solution of the above heterojunction silver paste, the mass ratio of the tin powder to the silver powder is (4 - 10):(40 - 46), preferably (5 - 8):(42 - 45);

[0013] and / or, the mass ratio of the polyester resin to the epoxy resin is (0.3 - 1.0):(0.8 - 2.5), preferably (0.5 - 0.8):(1.0 - 2.0).

[0014] In a preferred technical solution of the above heterojunction silver paste, the epoxy resin further includes glycidyl ether and hydrogenated bisphenol A epoxy resin.

[0015] In a further preferred technical solution of the above heterojunction silver paste, the mass ratio of the bisphenol A epoxy resin, glycidyl ether, and hydrogenated bisphenol A epoxy resin is (3 - 10):(2 - 9):(1 - 8).

[0016] In an even more preferred technical solution of the above heterojunction silver paste, the mass ratio of the bisphenol A epoxy resin, glycidyl ether, and hydrogenated bisphenol A epoxy resin is (5 - 8):(3 - 6):(2 - 6).

[0017] In a preferred technical solution of the above heterojunction silver paste, the tin powder is high-purity ultrafine tin powder with a purity of not less than 99.9%.

[0018] In a further preferred technical solution of the above heterojunction silver paste, the particle size D 50 of the high-purity ultrafine tin powder is 100 - 500 nm.

[0019] In an even more preferred technical solution of the above heterojunction silver paste, the particle size D 50 of the high-purity ultrafine tin powder is 100 - 300 nm.

[0020] In a preferred technical solution of the above heterojunction silver paste, the silver powder includes large-particle-size spherical silver powder and nano-scale spherical silver powder, and the mass ratio of the large-particle-size spherical silver powder to the nano-scale spherical silver powder is (15 - 25):(20 - 30), preferably (18 - 22):(23 - 27).

[0021] In the above preferred technical solution of the heterojunction silver paste, the particle size D of the large-particle-size spherical silver powder 50 is 2 - 7 μm; the particle size D of the nano-scale spherical silver powder 50 is 100 - 600 nm.

[0022] In the above preferred technical solution of the heterojunction silver paste, the additives include a curing agent, a solvent, and a coupling agent;

[0023] The dosages of the components in the heterojunction silver paste are as follows:

[0024] In a second aspect, the present invention provides a method for preparing the above heterojunction silver paste, including:

[0025] Mixing an organic carrier, powder, and additives to obtain the product.

[0026] In the above preferred technical solution of the preparation method, the preparation method further includes: before mixing, pretreating the polyester resin in the organic carrier.

[0027] In the above preferred technical solution of the preparation method, the pretreatment of the polyester resin is: dissolving the polyester resin in a solvent and adding a preset dosage of a curing agent during the dissolution process.

[0028] In the above preferred technical solution of the preparation method, the preset dosage is 15 - 25% of the mass of the polyester resin.

[0029] In the above preferred technical solution of the preparation method, the preparation method further includes: before mixing, dissolving the bisphenol A epoxy resin in the organic carrier.

[0030] In a third aspect, the present invention provides an application of the above heterojunction silver paste or the heterojunction silver paste prepared by the above preparation method in a heterojunction solar cell.

[0031] The technical solution of the present invention has the following technical effects:

[0032] The heterojunction silver paste provided by the present invention is improved from two aspects of powder and organic carrier, and they act together on the basis of ensuring good printability and electrical properties of the silver paste to improve the welding tensile strength of the paste. Among them, for the powder part, a method of compounding tin powder and silver powder is adopted. The tin powder provides a supporting effect for the welding tensile strength and forms a good metallization effect with the silver powder, and the silver powder is used to ensure the electrical properties of the paste; for the organic carrier part, polyester resin is added on the basis of epoxy resin as the main resin to enhance the adhesion between the paste and the substrate. Description of the Drawings

[0033] The following describes the preferred embodiments of the present invention with reference to the drawings, in which:

[0034] Figure 1 It is the printing line graph of the heterojunction silver paste of Embodiment 1 of the present invention and Comparative Examples 1 to 3. Detailed implementation manners

[0035] The preferred implementation manners of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these implementation manners are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention.

[0036] In this application, the term "and / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0037] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression means any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0038] It should be understood that in various embodiments of this application, the magnitude of the serial numbers of the above processes does not mean the sequence of execution. Some or all steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic and should not constitute any limitation to the implementation process of the embodiments of this application.

[0039] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms of "a", "the", and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0040] The weight of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between each component. Therefore, as long as the content of the relevant components in the specification of the embodiments of this application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well - known in the chemical engineering field such as μg, mg, g, kg, etc.

[0041] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0042] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments can all be obtained from commercial sources unless otherwise specified.

[0043] Based on the problem in the prior art pointed out in the background art that the method of improving the soldering tensile strength of the silver paste by adding flaky silver powder and increasing the molecular weight of the resin in the organic carrier is likely to affect the subsequent printing process, wet weight and printing linearity. The present invention improves the soldering tensile strength of the paste on the basis of ensuring good printability and electrical properties of the silver paste.

[0044] Specifically, in a first aspect, the present invention provides a heterojunction silver paste, comprising a powder, an organic carrier and an additive, wherein,

[0045] the powder comprises tin powder and silver powder;

[0046] the organic carrier comprises a polyester resin and an epoxy resin;

[0047] the epoxy resin at least comprises bisphenol A epoxy resin.

[0048] The heterojunction silver paste provided by the present invention is improved from two aspects of the powder and the organic carrier, and jointly acts on the basis of ensuring good printability and electrical properties of the silver paste to improve the soldering tensile strength of the paste. Among them, for the powder part, the tin powder and the silver powder are compounded, and the tin powder provides a supporting effect for the soldering tensile strength and forms a good metallization effect with the silver powder, and the silver powder is used to ensure the electrical properties of the paste; for the organic carrier part, the polyester resin is added on the basis of the epoxy resin as the main resin to enhance the adhesion between the paste and the substrate. And the epoxy resin at least comprises bisphenol A epoxy resin, and the bisphenol A epoxy resin mainly provides the bonding and adhesion between the paste and the printing substrate, wraps the surface of the powder in the paste, shrinks after curing to make the powder form a conductive path, and provides a skeleton for the printing and forming of the paste.

[0049] In some specific embodiments, the mass ratio of the tin powder to the silver powder is (4-10):(40-46). For example, it can be 4:46, 10:40, 8:42, 9:41, 6:43, 7:42 or any ratio within the range.

[0050] In some preferred embodiments, the mass ratio of the tin powder to the silver powder is (5 - 8):(42 - 45). For example, it can be 5:45, 6:44, 7:43, 8:42, 6:43, 7:44 or any ratio within the range.

[0051] In some specific embodiments, the mass ratio of the polyester resin to the epoxy resin is (0.3 - 1.0):(0.8 - 2.5). For example, it can be 0.3:2.5, 1.0:0.8, 0.5:2.1, 0.7:1.6, 0.6:1.9 or any ratio within the range.

[0052] In some preferred embodiments, the mass ratio of the polyester resin to the epoxy resin is (0.5 - 0.8):(1.0 - 2.0). For example, it can be 0.5:2.0, 0.8:1.0, 0.7:1.6, 0.6:1.9 or any ratio within the range.

[0053] In some specific embodiments, the epoxy resin further includes glycidyl ether and hydrogenated bisphenol A epoxy resin.

[0054] In some specific embodiments, the mass ratio of bisphenol A epoxy resin, glycidyl ether and hydrogenated bisphenol A epoxy resin is (3 - 10):(2 - 9):(1 - 8). For example, it can be 3:2:1, 10:9:8, 5:4:7 or any ratio within the range.

[0055] In some preferred embodiments, the mass ratio of bisphenol A epoxy resin, glycidyl ether and hydrogenated bisphenol A epoxy resin is (5 - 8):(3 - 6):(2 - 6). For example, it can be 5:3:2, 8:5:3, 5:4:3 or any ratio within the range.

[0056] In the present invention, the polyester resin, bisphenol A epoxy resin, glycidyl ether and hydrogenated bisphenol A epoxy resin are resins commonly used in the art. For example, the polyester resin can be SKES300, ETERKYD 5050 - B - 75; the bisphenol A epoxy resin can be NPES901, YD - 014; the glycidyl ether can be S184; the hydrogenated bisphenol A epoxy resin can be HE2025, EP - 4080.

[0057] In some specific embodiments, the tin powder is high - purity ultrafine tin powder with a purity of not less than 99.9%.

[0058] In some specific embodiments, the particle size D 50 of the high - purity ultrafine tin powder is 100 - 500 nm. For example, it can be 100 nm, 150 nm, 200 nn, 250 nm, 300 nm, 350 nm, 400 nm, 500 nm or any value within the range.

[0059] In some preferred embodiments, the particle size D of the high-purity ultrafine tin powder 50 is 100 - 300 nm. For example, it can be 100 nm, 120 nm, 150 nm, 180 nm, 200 nn, 220 nm, 250 nm, 280 nm, 300 nm or any value within the range.

[0060] In some specific embodiments, the silver powder includes large-particle-size spherical silver powder and nano-scale spherical silver powder, and the mass ratio of the large-particle-size spherical silver powder to the nano-scale spherical silver powder is (15 - 25):(20 - 30). For example, it can be 15:30, 25:20, 16:22, 22:27 or any ratio within the range.

[0061] In some preferred embodiments, the mass ratio of the large-particle-size spherical silver powder to the nano-scale spherical silver powder is (18 - 22):(23 - 27). For example, it can be 18:23, 22:27, 19:25, 20:23 or any ratio within the range.

[0062] In the present invention, the particle size D of the large-particle-size spherical silver powder 50 is 2 - 7 μm. For example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or any value within the range; the particle size D of the nano-scale spherical silver powder 50 is 100 - 600 nm. For example, it can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm or any value within the range.

[0063] It should be noted that in the present invention, the additives are the additives commonly used in the preparation of heterojunction silver paste in the art, such as curing agents, solvents, etc. Those skilled in the art can selectively add them according to actual needs, and the addition amount can also be adjusted according to actual needs.

[0064] However, as a preferred embodiment, the additives include curing agents, solvents and coupling agents.

[0065] In some most preferred embodiments, the amounts of the components in the heterojunction silver paste are as follows:

[0066] The present invention provides, in a second aspect, a method for preparing the above-mentioned heterojunction silver paste, comprising:

[0067] Mixing an organic carrier, powder and additives, and then the heterojunction silver paste is obtained.

[0068] In some specific embodiments, the preparation method further includes pretreating the polyester resin in the organic carrier before mixing.

[0069] In some specific embodiments, the pretreatment of the polyester resin in the organic carrier is as follows: dissolving the polyester resin in a solvent and adding a preset amount of curing agent during the dissolution process.

[0070] In the present invention, the organic carrier includes polyester resin and epoxy resin. If these two resins are first mixed and then the above pretreatment is carried out, since the reactivity, reaction rate, and reaction degree of the two resins with a curing agent such as an imidazole curing agent are different, it cannot be guaranteed that only the polyester resin participates in the reaction. If the epoxy resin also participates in the reaction, the amount of epoxy resin used for the subsequent curing and molding of the slurry in the entire slurry system will decrease, affecting the adhesion and curing degree of the slurry. The polyester resin cannot fully play its role either.

[0071] In the present invention, the polyester resin is pretreated first, that is, by adding a certain preset amount of curing agent during the dissolution process of the polyester resin to increase the crosslinking degree of the polyester resin during the curing process, thereby improving the adhesion between the resin and the substrate.

[0072] In some specific embodiments, the preset amount is 15-25% of the mass of the polyester resin. For example, it can be 15%, 18%, 20%, 22%, 25% or any value within the range.

[0073] In some preferred embodiments, the mass ratio of the polyester resin to the solvent is 1:1 to control the mass percentage of the polyester resin in the total amount of the polyester resin and the solvent to be 50%.

[0074] In some preferred embodiments, the preparation method further includes: dissolving the bisphenol A epoxy resin in the organic carrier before mixing.

[0075] In the present invention, before mixing the organic carrier, powder, and additive, dissolving the bisphenol A epoxy resin in the organic carrier in a solvent can make the bisphenol A epoxy resin better dispersed in the whole system.

[0076] In some preferred embodiments, the mass ratio of the bisphenol A epoxy resin to the solvent is 1:1 to control the mass percentage of the bisphenol A epoxy resin in the total amount of the bisphenol A epoxy resin and the solvent to be 50%.

[0077] In the present invention, the curing agents described in the first aspect and the second aspect are blocked isocyanate curing agents and / or imidazole curing agents; the solvents are one or more of diethylene glycol butyl ether acetate, dibutyl adipate, or diethylene glycol butyl ether; the coupling agents are one or more of KH550, KH560, or phthalate coupling agents.

[0078] In some specific embodiments, the blocked isocyanate curing agent is one or more of Desmodur BL 3370MPA, PT-1080Y, MR-310, PL 350.

[0079] In some specific embodiments, the imidazole curing agent is one or more of 1-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, or 2-phenylimidazole.

[0080] The present invention provides, in a third aspect, the application of the heterojunction silver paste or the heterojunction silver paste prepared by the preparation method in a heterojunction solar cell.

[0081] The following will detail the heterojunction silver paste, preparation method, and application of the present invention through several specific preferred embodiments.

[0082] Example 1

[0083] S1. Pretreatment and dissolution treatment

[0084] Pretreatment of polyester resin: Precisely weigh 100 g of solid particles of polyester resin (SKES300) into a three-necked flask, and then precisely weigh 100 g of solvent (diethylene glycol butyl ether acetate) and 20 g of curing agent (1-methylimidazole) into the same flask. Under heating and rotary stirring with a heating mantle, wait until the polyester resin, solvent, and curing agent are completely dissolved and homogenized to obtain the pretreated polyester resin.

[0085] Dissolution treatment of bisphenol A epoxy resin: Precisely weigh 100 g of solid particles of bisphenol A epoxy resin (NPES901) into a three-necked flask, and then precisely weigh 100 g of solvent (diethylene glycol butyl ether acetate). Under heating and rotary stirring with a heating mantle, wait until the bisphenol A epoxy resin and the solvent are completely dissolved and homogenized to obtain the dissolved bisphenol A epoxy resin.

[0086] S2. Mixing

[0087] After fully mixing the pretreated polyester resin (SKES300), the dissolved bisphenol A epoxy resin (NPES901), glycidyl ether (S184), hydrogenated bisphenol A epoxy resin (HE2025), curing agent (blocked isocyanate curing agent Desmodur BL3370MPA), solvent (diethylene glycol butyl ether acetate), and coupling agent (KH550), add large-particle-size spherical silver powder (average particle size D 50 is 4 μm), nano-scale spherical silver powder (average particle size D 50 is 500 nm), and high-purity ultrafine tin powder (purity 99.99%, average particle size D50 For 200 nm); all components are completely mixed evenly after stirring and three-roll dispersion, and the heterojunction silver paste is obtained; the dosages of each substance are shown in Table 1.

[0088] Table 1. Silver paste components

[0089] Example 2

[0090] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 2 specifically:

[0091] Table 2. Silver paste components

[0092] Example 3

[0093] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 3 specifically:

[0094] Table 3. Silver paste components

[0095] Example 4

[0096] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 4 specifically:

[0097] Table 4. Silver paste components

[0098] Example 5

[0099] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 5 specifically:

[0100] Table 5. Silver paste components

[0101] Example 6

[0102] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 6 specifically:

[0103] Table 6. Silver paste components

[0104] Example 7

[0105] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 7 specifically:

[0106] Table 7. Silver paste components

[0107] Example 8

[0108] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 8 specifically:

[0109] Table 8. Silver paste components

[0110] Example 9

[0111] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 9 specifically:

[0112] Table 9. Silver paste components

[0113] Example 10

[0114] This example refers to Example 1. The difference from Example 1 is that the silver paste components are different, as shown in Table 10 specifically:

[0115] Table 10. Silver paste components

[0116] Example 11

[0117] This example refers to Example 1. The difference from Example 1 is that during the pretreatment process of the polyester resin, the dosage of the curing agent used is 15 g.

[0118] Example 12

[0119] This example refers to Example 1. The difference from Example 1 is that during the pretreatment process of the polyester resin, the dosage of the curing agent used is 25 g.

[0120] Example 13

[0121] This example refers to Example 1. The difference from Example 1 is that during the pretreatment of the polyester resin, the curing agent used is the blocked isocyanate curing agent Desmodur BL 3370MPA.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 1 is that in the silver paste composition, the organic carrier part does not contain polyester resin (SKES300), and the dosage of bisphenol A epoxy resin (NPES901) is 1.2 g; in the powder part, it does not contain high-purity ultrafine tin powder (purity 99.99%, average particle size D 50 is 200 nm), and the dosage of nano-scale spherical silver powder (average particle size D 50 is 500 nm) is 30 g. Specifically, it is shown in Table 11 below:

[0124] Table 11. Silver Paste Composition

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that in the silver paste composition, the powder part does not contain high-purity ultrafine tin powder (purity 99.99%, average particle size D 50 is 200 nm), and the dosage of nano-scale spherical silver powder (average particle size D 50 is 500 nm) is 30 g. Specifically, it is shown in Table 12 below:

[0127] Table 12. Silver Paste Composition

[0128] Comparative Example 3

[0129] The difference between this comparative example and Example 1 is that in the silver paste composition, the organic carrier part does not contain polyester resin (SKES300), and the dosage of bisphenol A epoxy resin (NPES901) is 1.2 g; specifically, it is shown in Table 13 below:

[0130] Table 13. Silver Paste Composition

[0131] Test Example 1

[0132] This test example investigated the influence of the addition or not of tin powder and / or polyester resin in the silver paste composition on the performance of the obtained heterojunction silver paste.

[0133] Electrical performance data and welding tensile strength of the heterojunction silver pastes obtained in Test Example 1, Comparative Example 1 to Comparative Example 3. The specific test methods are as follows:

[0134] Viscosity: Measured using a rotational viscometer (Brookfield viscometer) at room temperature of 25°C.

[0135] Resistivity: The heterojunction silver pastes obtained in Example 1, Comparative Example 1 to Comparative Example 3 were printed using a printing stencil, cured at 200°C for 20 min, the resistance value was measured, and the resistivity was calculated according to the formula R = ρL / S.

[0136] Welding tensile strength: The heterojunction silver pastes obtained in Example 1, Comparative Example 1 to Comparative Example 3 were printed using a printing stencil, cured at 200°C for 20 min, and the welding tensile strength was measured.

[0137] The results of the silver paste performance are shown in Table 14, and the printed line shapes are as Figure 1 shown.

[0138] Table 14. Silver paste performance Number Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Viscosity / mPa·s 110000 90000 95000 100000 Resistivity / Ω·cm <![CDATA[6.5×10 -6 > <![CDATA[6.3×10 -6 > <![CDATA[6.4×10 -6 > <![CDATA[6.7×10 -6 > Welding Tensile Force / N 1.5 0.9 0.9 1.2

[0139] Comparing Example 1 with Comparative Example 1, 2, and 3, it was found that after adding the pretreated polyester resin and high-purity ultrafine tin powder, the viscosity of the paste increased slightly, but it did not affect the printability of the paste. From the Figure 1 printed line shapes, there was no difference compared with the comparative examples, and the printing flatness and width of the line shapes were both good; comparing the change in resistivity, there was no significant change in the resistivity of Example 1 compared with Comparative Example 1, 2, and 3, and it remained at a low level, indicating that the addition of the polyester resin and high-purity ultrafine tin powder did not cause a large change in resistivity; from the tensile strength data, the addition of the polyester resin and high-purity ultrafine tin powder significantly improved the welding tensile strength of the paste, indicating that its help to the tensile strength was particularly obvious.

[0140] From Comparative Example 1, 2, and 3, without adding polyester resin and high-purity ultrafine tin powder, the tensile strength was low; only adding polyester resin, the tensile strength was also low; only adding high-purity ultrafine tin powder, the tensile strength increased, but the increase was still small compared with the example.

[0141] Test Example 2

[0142] This test example investigated the influence of the type of epoxy resin in the organic carrier on the performance of the obtained heterojunction silver paste.

[0143] The test method was the same as that in Test Example 1.

[0144] Test samples: The heterojunction silver paste prepared in Example 1 of the present invention;

[0145] Control sample 1: The components and preparation method refer to Example 1. The difference from Example 1 is that the components do not include bisphenol A epoxy resin.

[0146] Control sample 2: The components and preparation method refer to Example 1. The difference from Example 1 is that the components do not include glycidyl ether.

[0147] Control sample 3: The components and preparation method refer to Example 1. The difference from Example 1 is that the components do not include hydrogenated bisphenol A epoxy resin.

[0148] Control sample 4: The components and preparation method refer to Example 1. The difference from Example 1 is that bisphenol A epoxy resin is replaced by bisphenol F epoxy resin (YDF-161).

[0149] The performance results of the silver paste are shown in Table 15.

[0150] Table 15. Performance of the silver paste Number Test Sample Control Sample 1 Control Sample 2 Control Sample 3 Control Sample 4 Viscosity / mPa·s 110000 181000 115000 115000 87000 Resistivity / Ω·cm <![CDATA[6.5×10 -6 > <![CDATA[14.9×10 -6 > <![CDATA[8.8×10 -6 > <![CDATA[8.8×10 -6 > <![CDATA[6.3×10 -6 > Welding Tensile Force / N 1.5 0.9 1.3 0.8 0.8

[0151] It can be seen from the results in Table 15 that bisphenol A epoxy resin plays a crucial role in the whole system and has a great influence on the welding tensile force, electrical properties and viscosity of the silver paste; glycidyl ether and hydrogenated bisphenol A epoxy resin mainly play an important role in the electrical properties of the silver paste and can effectively reduce the resistivity of the silver paste; after replacing bisphenol A epoxy resin with bisphenol F epoxy resin, since the viscosity of bisphenol F epoxy resin itself is small, the viscosity of the whole system is on the low side, and during the later printing process, the grid lines will show the situation of line expansion and insufficient height, and the initial adhesion of the printing substrate will decrease, resulting in a reduction in the welding tensile force.

[0152] Test Example 3

[0153] This test example investigated the influence of whether to pretreat the polyester resin during the preparation process or to pretreat it after mixing with bisphenol A epoxy resin on the performance of the obtained heterojunction silver paste.

[0154] The test method is the same as that in Test Example 1.

[0155] Test sample: The heterojunction silver paste prepared in Example 1 of the present invention;

[0156] Control sample 5: The components and preparation method refer to Example 1. The difference from Example 1 is that the polyester resin (SKES300) and bisphenol A epoxy resin (NPES901) are first mixed and then pretreated, specifically as follows:

[0157] Accurately weigh 50g of polyester resin (SKES300) solid particles and 50g of bisphenol A epoxy resin (NPES901) in a three-necked flask, and then accurately weigh 100g of solvent (diethylene glycol butyl ether acetate) and 20g of curing agent (1-methylimidazole) in the same flask. Heat and rotate with a heating mantle until the polyester resin and bisphenol A epoxy resin are completely dissolved and evenly dissolved with the solvent and curing agent to obtain a pretreated mixture of polyester resin and bisphenol A epoxy resin.

[0158] The pretreated polyester resin and bisphenol A epoxy resin mixture was then mixed with 0.5 g of glycidyl ether (S184), 0.4 g of hydrogenated bisphenol A epoxy resin (HE2025), 0.8 g of curing agent (blocked isocyanate curing agent Desmodur BL3370MPA), 0.8 g of solvent (butyl diglycol acetate) and 0.1 g of coupling agent (KH550), and then 20 g of large-particle spherical silver powder (average particle size D 50 4μm), 25g nano silver powder (average particle size D 50 500nm) and 5g high-purity ultrafine tin powder (purity 99.99%, average particle size D 50 All components are stirred and dispersed with three rollers and then completely mixed to obtain heterojunction silver paste.

[0159] Control sample 6: Components and preparation method: Refer to Example 1, except that the polyester resin (SKES300) was not pretreated.

[0160] The silver paste performance results are shown in Table 16.

[0161] Table 16, Silver Paste Performance Number Test Sample Control Sample 5 Control Sample 6 Viscosity / mPa·s 110000 110000 95000 Resistivity / Ω·cm <![CDATA[6.5×10 -6 > <![CDATA[8.4×10 -6 > <![CDATA[6.6×10 -6 > Welding Tensile Force / N 1.5 0.5 0.8

[0162] From the results in Table 16, it can be seen that if the two main resins (polyester resin and bisphenol A epoxy resin) are mixed first and then pretreated, the silver paste resistance increases significantly and the welding tension is also reduced by about 3 times, indicating that the silver paste performance obtained by mixing the two resins first and then pretreating is poor; if the polyester resin is not pretreated and directly added to the silver paste system, the electrical properties of the obtained silver paste are not much different, but because the polyester resin is not cross-linked in advance, the overall cross-linking degree is poor during the later curing process of the silver paste, which affects the adhesion and curing degree of the substrate, and reduces the welding tension by about half.

[0163] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A heterojunction silver paste, comprising a powder, an organic carrier, and an additive, wherein the powder comprises tin powder and silver powder; the organic carrier comprises a polyester resin and an epoxy resin; the epoxy resin comprises at least bisphenol A epoxy resin.

2. The heterojunction silver paste according to claim 1, wherein the mass ratio of the tin powder to the silver powder is (4 - 10):(40 - 46), preferably (5 - 8):(42 - 45); and / or, the mass ratio of the polyester resin to the epoxy resin is (0.3 - 1.0):(0.8 - 2.5), preferably (0.5 - 0.8):(1.0 - 2.0).

3. The heterojunction silver paste according to claim 2, wherein the epoxy resin further comprises glycidyl ether and hydrogenated bisphenol A epoxy resin; preferably, the mass ratio of the bisphenol A epoxy resin, glycidyl ether, and hydrogenated bisphenol A epoxy resin is (3 - 10):(2 - 9):(1 - 8); more preferably, the mass ratio of the bisphenol A epoxy resin, glycidyl ether, and hydrogenated bisphenol A epoxy resin is (5 - 8):(3 - 6):(2 - 6).

4. The heterojunction silver paste according to claim 3, wherein the tin powder is high-purity ultrafine tin powder with a purity of not less than 99.9%; Preferably, the particle size D of the high-purity ultrafine tin powder 50 is 100 - 500 nm; More preferably, the particle size D of the high-purity ultrafine tin powder 50 is 100 to 300 nm.

5. The heterojunction silver paste according to claim 4, characterized in that the silver powder comprises large-particle-size spherical silver powder and nano-scale spherical silver powder, and the mass ratio of the large-particle-size spherical silver powder to the nano-scale spherical silver powder is (15 - 25):(20 - 30), preferably (18 - 22):(23 - 27).

6. The heterojunction silver paste according to claim 5, wherein The particle size D of the large-particle-size spherical silver powder 50 is 2 to 7 μm; the particle size D of the nano-scale spherical silver powder 50 is 100 to 600 nm.

7. The heterojunction silver paste according to any one of claims 1 - 6, wherein the additive comprises a curing agent, a solvent, and a coupling agent; preferably, the amounts of each component in the heterojunction silver paste are as follows:

8. A method for preparing the heterojunction silver paste according to any one of claims 1-7, characterized in that, The preparation method comprises: Mixing the organic carrier, the powder, and the additive evenly to obtain the product.

9. The preparation method according to claim 8, characterized in that, The preparation method further comprises: before mixing, pretreating the polyester resin in the organic carrier; preferably, the pretreatment of the polyester resin in the organic carrier is: dissolving the polyester resin in a solvent, and adding a preset amount of curing agent during the dissolution process.

10. The preparation method according to claim 9, wherein the preset amount is 15 - 25% of the mass of the polyester resin.

11. The preparation method according to claim 9 or 10, characterized in that, The preparation method further comprises: before mixing, performing a dissolution treatment on the bisphenol A epoxy resin in the organic carrier. Use of the heterojunction silver paste according to any one of claims 1 - 7 or the heterojunction silver paste prepared by the preparation method according to any one of claims 8 - 11 in a heterojunction solar cell.

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