A conductive silver paste, its preparation method and application

Abstract

The present invention provides a conductive silver paste, a preparation method thereof and an application. The conductive silver paste includes silver powder, photovoltaic glass powder and an organic carrier; wherein, the organic carrier includes component A and component B; wherein, component A includes solvent A and resin A, and solvent A is a hydrocarbon solvent with an oil-water partition coefficient logP > 8; component B includes solvent B and resin B, and solvent B is a polar solvent with logP < 3 and surface tension > 36 dyne / cm. The conductive silver paste of the present invention has excellent photoelectric conversion efficiency, a relatively high short-circuit current, a relatively high grid line welding tensile force and a low grid line shedding rate, and can replace the conductive silver paste containing silicone oil, and is very suitable as the front side metallization silver paste for solar cells.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive silver paste, and in particular to a conductive silver paste, a preparation method and application thereof. Background Art

[0002] The front electrode of a solar cell is a conductive material that forms a tight contact with the PN junction. At present, the entire photovoltaic industry basically uses screen printing to make electrodes. The front metallization silver paste of solar cells is a thick film conductive paste that can be used for screen printing. The front metallization silver paste of solar cells is screen printed onto silicon wafers and then sintered to form the front electrode of solar cells. The morphology, printing quality, and contact degree of the solar cell front electrode of solar cells are the most critical factors in determining the conversion efficiency of solar cells. Therefore, in addition to the advancement of screen printing technology and processes, the continuous optimization of the formula and composition of the front metallization silver paste of solar cells is also an important boost to the advancement of the photovoltaic industry. The basic components of the front metallization silver paste of solar cells are: silver powder, photovoltaic glass powder, organic carrier and other additives. In recent years, almost all the front metallization silver pastes of solar cells produced and used on the market on a large scale use silicone oil as an additive. As an industry consensus, the addition of silicone oil can keep the metallization silver paste relatively thinner in the screen printing process. Finer metallized grid lines mean less shading area, so solar cells can receive more sunlight, generate higher current, and ultimately achieve higher photoelectric conversion efficiency. However, with the photovoltaic industry's continuous pursuit of reducing costs and improving photoelectric conversion efficiency, the screen opening of screen printing has rapidly developed from >30μm a few years ago to ≤15μm. Finer metallized grid lines mean a lower contact area between the paste and the solar cell, and the shedding of the metallized grid lines after sintering has also become an important problem that currently plagues solar cell factories. By tracking and analyzing the corresponding data of the metallized silver paste formula and the frequency of metallized grid line shedding in solar cell factories, it is found that the amount of silicone oil added directly affects the proportion of metallized grid line shedding. In addition, the continuous tracking of the yield and efficiency fluctuations of the client's cells also proves that the addition of silicone oil has a negative impact on the electrode welding tension of the solar cell and the contact performance of the grid lines under the current fine-line screen printing conditions.

[0003] Therefore, it is necessary to invent a conductive silver paste that does not contain silicone oil. Summary of the invention

[0004] The main purpose of the present invention is to provide a conductive silver paste, a preparation method and application thereof, so as to solve the problem that the silver paste containing silicone oil in the prior art has a negative impact in fine line printing.

[0005] To achieve the above object, according to one aspect of the present invention, a conductive silver paste is provided. The conductive silver paste includes: silver powder, photovoltaic glass powder, and an organic carrier; wherein, the organic carrier includes component A and component B; wherein, component A includes solvent A and resin A dissolved in solvent A, and solvent A is a hydrocarbon solvent with an oil-water partition coefficient logP > 8; component B includes solvent B and resin B dissolved in solvent B, and solvent B is a polar solvent with logP < 3 and surface tension > 36 dyne / cm.

[0006] Further, solvent A is one or more of light paraffin oil, heavy paraffin oil, petroleum solvent oil, squalene, squalane, kerosene, diesel oil, petroleum-based lubricating oil, synthetic or semi-synthetic engine oil; preferably, solvent A is one or more of light paraffin oil, heavy paraffin oil, squalane, and kerosene.

[0007] Further, solvent B is one or several of dimethyl phthalate, diethyl phthalate, glycerol diacetate, glycerol triacetate, pentaerythritol triacrylate, propylene glycol phenyl ether, ethyl salicylate, ethyl acetylsalicylate, N-hydroxyethyl-2-pyrrolidone; preferably, solvent B is one or more of dimethyl phthalate, ethyl salicylate, glycerol diacetate, and glycerol triacetate.

[0008] Further, resin A is one or several of terpene resin, polyisobutene with Mw = 400 - 6000, C5 petroleum resin, hydrogenated C5 petroleum resin, C9 petroleum resin, C5 / C9 copolymerized petroleum resin, coumarone resin, SBS resin, SEBS resin, DCPD petroleum resin, hydrogenated DCPD resin; preferably, resin A is one or more of terpene resin, C5 petroleum resin, C9 petroleum resin, and polyisobutene.

[0009] Further, resin B is one or several of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, polymethacrylate, polyvinyl butyral, polyurethane, polycarbonate; preferably, resin B is one or more of hydroxyethyl cellulose, polyvinyl butyral, and polyurethane.

[0010] Further, in the conductive silver paste, the weight ratio of silver powder, photovoltaic glass powder, and organic carrier is (88 - 90):(1.5 - 3):(6.5 - 10); preferably, in the organic carrier, the weight ratio of component A and component B is (10 - 40):(60 - 90); preferably, in component A, the weight ratio of solvent A and resin A is (70 - 95):(5 - 30); preferably, in component B, the weight ratio of solvent B and resin B is (70 - 95):(5 - 30).

[0011] Further, the surface of the silver powder has an organic coating structure.

[0012] Further, the conductive silver paste further includes an additive, and the additive is one or more of a surfactant, a leveling agent, a lubricant, and a filler; preferably, the surfactant is one or more of an anionic surfactant, a cationic surfactant, and a nonionic surfactant; more preferably, the weight ratio of the additive to the silver powder is (0.1~2):(88~90).

[0013] Further, the photovoltaic glass powder is prepared by the following method: melting, quenching, and ball-milling a glass powder precursor to obtain the photovoltaic glass powder; wherein, the glass powder precursor includes lead oxide, bismuth oxide, tellurium oxide, and tungsten oxide; preferably, based on the total weight of the glass powder precursor, the weight content of lead oxide is 0.1~20%, the weight content of bismuth oxide is 30~60%, the weight content of tellurium oxide is 0.1~20%, and the weight content of tungsten oxide is ≥5%; preferably, the weight ratio of tellurium oxide to tungsten oxide is (0.5:1)~(1.75:1); preferably, the glass powder precursor further includes one or more of potassium oxide, sodium oxide, lithium oxide, calcium oxide, magnesium oxide, strontium oxide, barium oxide, nickel oxide, titanium dioxide, boron trioxide, silicon dioxide, zinc oxide, and phosphorus pentoxide.

[0014] According to another aspect of the present invention, there is provided a method for preparing the above conductive silver paste, and the preparation method includes the following steps: S1, mixing resin A with solvent A to obtain component A, and mixing resin B with solvent B to obtain component B; S2, mixing component A and component B, then adding silver powder, photovoltaic glass powder, and an optional additive, and stirring to obtain a paste; S3, grinding the paste to obtain the conductive silver paste.

[0015] According to one aspect of the present invention, there is provided an application of the above conductive silver paste or the conductive silver paste prepared according to the above method in a solar cell chip.

[0016] By applying the technical solution of the present invention, a conductive silver paste that is completely free of silicone oil is obtained. In this conductive silver paste, component A is a non-polar or low-polarity system, which, under the synergistic effect of component B, can adsorb and wrap on the surface of silver powder like silicone oil; while component B has high polarity. Due to the incompatibility between the two components, the silver powder is dispersed in the organic phase while also having a state of local agglomeration, thereby achieving the same grid line shaping effect as the silicone oil-containing system, that is, corresponding to a narrower line width, a higher short-circuit current, and a higher photoelectric conversion efficiency. In addition, because the conductive silver paste product provided by the present invention does not contain silicone oil, it can avoid the defect of poor wettability of the silicone oil-containing paste on the textured surface of the silicon wafer during the printing process, thereby significantly improving the welding tensile strength of the grid line and reducing the grid line shedding rate. In short, the present invention provides a conductive silver paste that can replace the silicone oil-containing paste, which is very suitable as the front surface metallization silver paste for solar cells. Detailed Embodiments

[0017] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] To solve the problems existing in the prior art as described above, according to one aspect of the present invention, a conductive silver paste is provided, which includes: silver powder, photovoltaic glass powder, and an organic carrier; wherein, the organic carrier includes component A and component B; wherein, component A includes solvent A and resin A dissolved in solvent A, and solvent A is a hydrocarbon solvent with an oil-water partition coefficient logP > 8; component B includes solvent B and resin B dissolved in solvent B, and solvent B is a polar solvent with logP < 3 and surface tension > 36 dyne / cm.

[0019] In this conductive silver paste, component A is a non-polar or low-polarity system, which, under the synergistic effect of component B, can adsorb and wrap on the surface of silver powder like silicone oil; while component B has high polarity. Due to the incompatibility between the two components, the silver powder is dispersed in the organic phase while also having a state of local agglomeration, thereby achieving the same grid line shaping effect as the silicone oil-containing system, that is, corresponding to a narrower line width, a higher short-circuit current, and a higher photoelectric conversion efficiency. In addition, because the conductive silver paste product provided by the present invention does not contain silicone oil, it can avoid the defect of poor wettability of the silicone oil-containing paste on the textured surface of the silicon wafer during the printing process, thereby significantly improving the welding tensile strength of the grid line and reducing the grid line shedding rate. In short, the present invention provides a conductive silver paste that can replace the silicone oil-containing paste, which is very suitable as the front surface metallization silver paste for solar cells.

[0020] By selecting solvent A and solvent B according to the above parameter conditions, the hydrophobic solvent A can form a coating on the silver powder, and the solvent B that is immiscible with solvent A acts synergistically with solvent A to "simulate" the grid line shaping effect of the silicone oil-containing system. At the same time, selecting the surface tension of solvent B > 36 dyne / cm can effectively achieve close contact between the printed grid lines and the silicon wafer, thereby reducing the phenomenon of local defects formed between the grid lines and the silicon wafer after drying, further improving the welding tensile force of the grid lines and reducing the grid line dropout rate.

[0021] In actual operation, solvent A is preferably an organic solvent that is immiscible with component B in the long term and can form a phase separation in the organic carrier. For example, solvent A includes, but is not limited to, one or more of light paraffin oil, heavy paraffin oil, petroleum solvent oil, squalene, squalane, kerosene, diesel oil, petroleum-based lubricating oil, synthetic or semi-synthetic engine oil. In this way, it is more beneficial to the stability of the entire conductive silver paste, and can further improve the processability during printing, making the grid lines have better welding tensile force and adhesion ability, fewer grid line defects, and having a better promoting effect on the photoelectric conversion efficiency of the entire solar cell module. More preferably, solvent A is one or more of light paraffin oil, heavy paraffin oil, squalane, and kerosene.

[0022] Similarly, solvent B is preferably an organic solvent that is immiscible with component A in the long term and can form a phase separation in the organic carrier. For example, solvent B includes, but is not limited to, one or more of dimethyl phthalate, diethyl phthalate, glycerol diacetate, glycerol triacetate, pentaerythritol triacrylate, propylene glycol phenyl ether, ethyl salicylate, ethyl acetylsalicylate, N-hydroxyethyl-2-pyrrolidone. More preferably, solvent B is one or more of dimethyl phthalate, ethyl salicylate, glycerol diacetate, and glycerol triacetate.

[0023] Selecting the above solvent A and solvent B is also more conducive to the dissolution of resin A and resin B therein. At the same time, it is more conducive to the formation of a long-term stable heterogeneous organic carrier, and the silver powder realizes more stable microscopic aggregation in the organic carrier, thereby enabling more stable optoelectronic performance.

[0024] In a preferred embodiment, resin A includes one or several of terpene resin, polyisobutene with Mw = 400 - 6000, C5 petroleum resin, hydrogenated C5 petroleum resin, C9 petroleum resin, C5 / C9 copolymerized petroleum resin, coumarone resin, SBS resin, SEBS resin, DCPD petroleum resin, hydrogenated DCPD resin. The above resins are more conducive to increasing the viscosity of component A, enhancing the cohesive force of the silver powder aggregates, improving the grid line shaping, and thus increasing the short-circuit current. Preferred resin A is one or more of terpene resin, C5 petroleum resin, and C9 petroleum resin.

[0025] In a preferred embodiment, the resin B includes one or more of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, polymethacrylate, polyvinyl butyral, polyurethane, and polycarbonate. The above resins are more conducive to improving the adhesion of the slurry to the silicon wafer and improving the printing performance. At the same time, by adjusting the polarity and viscosity of component B, the phase separation state of component A and component B can be made more stable. Preferably, the resin B is one or more of hydroxyethyl cellulose, polyvinyl butyral, and polyurethane.

[0026] Preferably, the above resin A and resin B are more conducive to the dispersion and local aggregation of silver powder in the organic phase, and are more conducive to the long-term stable immiscibility of component A and component B in the present invention, forming a specific heterogeneous organic state. In this state, the conductive silver paste unexpectedly has good plastic forming ability, thereby improving its photoelectric conversion efficiency.

[0027] In actual operation, the resin A and resin B are not limited to the types listed above. As long as the selected ones can be dissolved in solvent A and solvent B respectively, at least some of the beneficial technical effects of the technical solution of the present invention can be achieved.

[0028] In the technical solution provided by the present invention, it does not contain silicone oil. Specifically, it means that the slurry formulation does not contain compounds or polymers with the following structures:

[0029] ;

[0030] In the formula, R is an alkyl group or an aryl group; R' is hydrogen, an alkyl group, an amino group, an aryl group, a polyester or a polyether chain, etc.; X is hydrogen, a hydroxyl group, an amino group, an alkoxy group, an alkyl group, an aryl group, an acetoxy group, a carbon functional group, a polyether or a polyester chain, etc. n , m = 0, 1, 2, 3 …….

[0031] The conductive silver paste formulation provided by the present invention especially does not include methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen-containing silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen-containing silicone oil, hydroxy hydrogen-containing silicone oil, cyanide-containing silicone oil and other modified silicone oils.

[0032] In order to further improve the comprehensive performance of the conductive silver paste, in a preferred embodiment, in the conductive silver paste, the weight ratio of silver powder, photovoltaic glass powder and organic carrier is (88~90):(1.5~3):(6.5~10); preferably, in the organic carrier, the weight ratio of component A and component B is (10~40):(60~90); preferably, in component A, the weight ratio of solvent A and resin A is (70~95):(5~30); preferably, in component B, the ratio of solvent B and resin B is (70~95):(5~30).

[0033] The conductive silver paste prepared according to the above preferred ratio has better performance such as photoelectric conversion efficiency, line width, welding tensile strength, etc.

[0034] In the conductive silver paste, the silver powder mainly plays a conductive role, and the photovoltaic glass powder plays a role in etching the antireflection layer and assisting in melting the silver powder. At the same time, the addition amount of the above organic carrier is more conducive to the formation of an appropriate concentration of silver powder therein, so as to obtain a paste with a viscosity more suitable for the downstream screen printing process. The preferred weight ratio of the solvent and the resin is the above ratio, which is more conducive to having sufficient adhesion between the powders and between the powders and the silicon wafer, and will not make the paste too viscous to be screen printed.

[0035] In a preferred embodiment, the surface of the silver powder has an organic coating structure. In actual operation, preferably, the silver powder can be of common commercially available types. However, in order to make the raw materials more suitable for the technical solution of the present invention, preferably, the particle size D50 of the silver powder is 1~2.5μm, and the specific surface area is 0.35~0.75m 2 / g. The silver powder can have morphological characteristics including spherical, rod-shaped, granular, flaky or amorphous shapes.

[0036] In order to further improve the performance of the conductive silver paste, in a preferred embodiment, the conductive silver paste further includes an additive, and the additive is one or more of a surfactant, a leveling agent, a lubricant, and a filler; preferably, the surfactant is one or more of an anionic surfactant, a cationic surfactant, and a non-ionic surfactant; more preferably, the weight ratio of the additive to the silver powder is (0.1~2):(88~90).

[0037] In actual operation, the anionic surfactant is preferably sodium cocoyl methyl taurate, which plays a role in improving the dispersibility of inorganic powders. The cationic surfactant is preferably cetyl trimethyl ammonium chloride, which plays a role in improving the dispersibility of inorganic powders. The leveling agent is preferably an acrylate leveling agent, which plays a role in improving the leveling property of the printed grid lines and making the grid line morphology more flat. The lubricant is preferably lithium stearate, which plays a role in improving the off-net performance during the grid line printing process and improving the printability of the paste. The filler is preferably carbon black, which plays a role in increasing the solid content of the paste and adjusting the viscosity of the paste.

[0038] In a preferred embodiment, the photovoltaic glass powder is prepared by the following method: melting, quenching, and ball milling the glass powder precursor to obtain the photovoltaic glass powder; wherein, the glass powder precursor includes lead oxide, bismuth oxide, tellurium oxide, and tungsten oxide; preferably, based on the total weight of the glass powder precursor, the weight content of lead oxide is 0.1-20%, the weight content of bismuth oxide is 30-60%, the weight content of tellurium oxide is 0.1-20%, and the weight content of tungsten oxide is ≥5%; preferably, the weight ratio of tellurium oxide to tungsten oxide is (0.5:1)-(1.75:1); preferably, the glass powder precursor further includes one or more of potassium oxide, sodium oxide, lithium oxide, calcium oxide, magnesium oxide, strontium oxide, barium oxide, nickel oxide, titanium dioxide, boron trioxide, silicon dioxide, zinc oxide, and phosphorus pentoxide.

[0039] The photovoltaic glass powder with the above composition is preferred, which can better play the role of etching the antireflection layer and fluxing the silver powder during the sintering stage of the solar cell.

[0040] In this industry, the types and dosages of silver powder and photovoltaic glass powder mainly depend on the different silicon wafers provided by customers.

[0041] According to another aspect of the present invention, there is provided a method for preparing the above conductive silver paste, which includes the following steps: S1, mixing resin A with solvent A to obtain component A, and mixing resin B with solvent B to obtain component B; S2, mixing component A and component B, then adding silver powder, photovoltaic glass powder, and optional additives, and stirring to obtain a paste; S3, grinding the paste to obtain the conductive silver paste.

[0042] The conductive silver paste provided by the present invention prepared by this preparation method has excellent photoelectric conversion efficiency and at the same time avoids the defects of silicone oil-containing conductive silver paste.

[0043] In actual operation, preferably, in order to make the above components mix more fully, technicians can perform operations such as heating, ultrasonic vibration, or stirring on the solution as needed.

[0044] In actual operation, preferably, the grinding treatment in S3 is carried out by a three-roll mill.

[0045] Preferably, the above conductive silver paste is ground to a fineness FOG < 5 μm.

[0046] According to yet another aspect of the present invention, there is provided the application of the above conductive silver paste or the conductive silver paste prepared by the above method in solar cells.

[0047] When this conductive silver paste is applied to solar cells, the obtained solar cells have good photoelectric conversion efficiency, good morphology, and high yield, and are suitable for marketization.

[0048] In actual operation, solar cells can be prepared by conventional techniques well-known to those skilled in the art. Preferably, the prepared silver paste is screen-printed on the front side of a silicon wafer already having a back electrode. The parameters of the screen-printing stencil used are 480 mesh / 11 μm wire diameter / 15 μm yarn thickness / 6 μm film thickness / 12 μm opening. The printed silicon wafer is dried at 200 - 350 °C for 10 - 30 seconds, and then sintered at 400 - 950 °C for 30 - 60 seconds to obtain a solar cell with front and back electrodes.

[0049] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0050] As mentioned above, in actual operation, the dosages of silver powder and photovoltaic glass powder can be adjusted according to actual customer needs. In Examples 1 - 3 and Comparative Examples 1 - 4 of the present invention, in order to compare the effects of the organic carrier and additives on the performance of the battery chip with or without silicone oil, the ratios and components of the silver powder and photovoltaic glass powder used are kept consistent. Specifically, the particle size of the silver powder is D50 = 1.40 μm, the specific surface area is 0.44 m 2 / g, and the morphology is spherical; the composition of the photovoltaic glass powder is PbO - Bi2O3 - TeO2 - WO - Li2O; the silicone oil is Dow Corning PMX - 200.

[0051] The formulations of the conductive silver pastes prepared in Examples 1 - 3 and Comparative Examples 1 - 4 are shown in Table 1; the performance data are shown in Table 2. The formulations of the conductive silver pastes prepared in Examples 4 - 7 are shown in Table 3; the performance data are shown in Table 4.

[0052] The preparation methods of the conductive silver pastes in the examples and comparative examples of the present invention are as follows:

[0053] S1, Mix resin A with solvent A to obtain component A, and mix resin B with solvent B to obtain component B; S2, Mix component A and component B, then add silver powder, photovoltaic glass powder, and additives, and stir to obtain a paste; S3, Grind the paste through a three-roll mill until FOG < 5 μm to obtain the conductive silver paste.

[0054] In the present invention, the performance test methods of the conductive silver pastes prepared in the examples and comparative examples are as follows:

[0055] The photoelectric conversion efficiency, open-circuit voltage, short-circuit current and fill factor are directly read using a MAXWELL printing test all-in-one machine. The test screen has 480 meshes / 11μm wire diameter / 15μm yarn thickness / 6μm film thickness / 12μm opening. The printing speed is 500mm / s, the ink return speed is 1200mm / s. The SP (single printing process) is adopted. For each paste, 100 cell wafers are measured, and the data is averaged.

[0056] The line width is measured using a Keyence VHX-7000H digital microscopy system with a magnification of 200 times. For each paste, four printed and sintered cell wafers are used, and four points are taken from each wafer. The line width is the average value automatically calculated by the microscopy system.

[0057] The welding tensile strength is tested using a Tuobo TOP-8801 full-automatic PV cell stripping testing machine. For each paste, six printed and sintered cell wafers are used. For each wafer, the solder tapes corresponding to the 2nd, 5th, and 8th main grids of the cell are tested. The maximum peeling force in six intervals is measured for each solder tape, and finally the average value of each group of peeling forces is calculated as the welding tensile strength.

[0058] The grid line shedding ratio is sampled. For each paste, 100 printed and sintered cell wafers are randomly selected. An online EL appearance all-in-one machine ZQ500 is used to screen for abnormal wafers. A Keyence VHX-7000H digital microscope is used to observe the abnormal wafers. If local grid line loss is found, it is judged as unqualified. The percentage of unqualified numbers is counted as the grid line shedding ratio.

[0059] Table 1

[0060]

[0061] Table 2

[0062]

[0063] Table 3

[0064]

[0065] Table 4

[0066]

[0067] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0068] 1. Comparative Example 2 and Comparative Example 3 are conventional silicone-containing formulations for solar metallized silver pastes. Comparative Example 1 completely removed silicone. The results showed that when using a traditional single-phase homogeneous organic carrier, the electrical performance of solar cells made from the silver paste would significantly decline without adding silicone. The principle is that the silver powder is coated with organic substances, and its organic coating is various long carbon chain compounds, belonging to a hydrophobic structure. When using a single-phase homogeneous organic carrier, due to the incompatibility between silicone and the organic carrier, silicone tends to adsorb and coat on the surface of the silver powder. Since silicone itself has a certain molecular weight and viscosity, the coating of silicone on the silver powder is not monodisperse. The silver powder and silicone dispersed in the organic carrier are in a microscopic agglomerated state, and this agglomeration effect is the key for the silver paste to maintain good plasticity after printing, that is, corresponding to a narrower line width, higher short-circuit current, and photoelectric conversion efficiency. In Comparative Example 1, under the condition of using the same organic carrier and not adding silicone, the silver powder lost the agglomeration effect of silicone, the printed grid line plasticity collapsed, the line width widened, the short-circuit current decreased, and the photoelectric conversion efficiency decreased.

[0069] 2. Comparing Comparative Example 2 and Comparative Example 3, the silicone content is different. Those skilled in the art can obtain similar photoelectric conversion efficiencies by matching different silicone contents with different organic carriers. However, as the amount of silicone added increases, the welding tensile strength of the paste after printing will decrease, and the proportion of grid line detachment will increase, directly affecting the production yield of downstream solar cell factories.

[0070] 3. Examples 1 to 3 are pastes prepared using the heterogeneous organic carrier described in the present invention without adding silicone. The results showed that the pastes prepared by the combination of non-polar or low-polar component A and high-polar component B can obtain a photoelectric conversion efficiency not lower than that of the silicone-containing paste after printing to obtain solar cells. At the same time, the welding tensile strength of the grid lines is significantly improved, and the grid line detachment rate is significantly reduced. This is because silicone, as a compound with extremely low surface tension, will reduce the wetting effect of the grid lines on the silicon wafer surface during the printing process of the paste. If the printed grid lines cannot form close contact with the silicon wafer before drying, then after drying, the grid lines will form contact defects with the silicon wafer locally. During the subsequent sintering process, the glass powder and silver powder at the defect sites cannot fully infiltrate and etch the silicon wafer, ultimately resulting in grid detachment and reduced tensile strength. The paste prepared by the present invention can completely avoid this problem because it does not contain silicone. The main reasons for the high tensile strength and grid line detachment rate in Comparative Example 1 and Comparative Example 4 are mainly affected by the width of the grid lines. The wider the grid line width, the greater the contact area with the silicon wafer, and the larger the contact area, the more beneficial it is to improve the tensile strength and reduce the grid line detachment rate. However, too wide grid lines will reduce the short-circuit current and affect the photoelectric conversion efficiency.

[0071] 4. When comparing Comparative Example 4 with Example 1, the same proportions of Component A and Component B were used, but the solvent of alcohol ester 12 was additionally added to prove the action mechanism of the present invention. The action mechanism of the silicone-containing silver paste is to utilize the phase separation of silicone oil and organic carrier, so that while the silver powder is dispersed, local agglomeration can also occur, thereby achieving the purpose of improving the shaping of grid lines. The mechanism of the present invention essentially mimics the above-mentioned phase separation and agglomeration phenomenon. The selected Component A of the present invention is a non-polar or low-polarity system, which can adsorb and coat on the surface of silver powder like silicone oil. By adding highly polar Component B, due to the incompatibility of the two components, the silver powder has a state of local agglomeration while being dispersed in the organic phase. Furthermore, the same grid line shaping effect as that of the silicone oil-containing system is achieved. In Comparative Example 4, the alcohol ester 12 solvent is an amphiphilic solvent that can be dissolved in both Component A and Component B at the same time. The results show that when this solvent is added, the phase separation and agglomeration state utilized by the present invention are destroyed, resulting in the loss of good shaping ability of the paste and the subsequent decrease in the photoelectric conversion efficiency. Comparative Example 4 further proves from the opposite side that the present invention can replace the action mechanism of the silicone-containing paste.

[0072] 5. Examples 4 to 7 list conductive silver pastes with other component ratios within the scope of the technical solution of the present invention, all of which have relatively excellent photoelectric conversion efficiency performance. However, the specific ratio of Example 7 is outside the preferred range of the present invention, so its comprehensive performance is slightly worse.

[0073] In summary, the conductive silver paste prepared according to the present invention has a photoelectric conversion efficiency equivalent to or slightly higher than that of the silicone-containing conductive silver paste, and significantly reduced grid line shedding ratio and significantly improved welding tensile strength compared with it, fully meeting the market use requirements.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A conductive silver paste, characterized in that, The conductive silver paste includes: silver powder, photovoltaic glass powder, and an organic carrier; Among them, the organic carrier includes component A and component B; Among them, component A includes solvent A and resin A dissolved in solvent A, and solvent A is a hydrocarbon solvent with an oil-water partition coefficient logP > 8; component B includes solvent B and resin B dissolved in solvent B, and solvent B is a polar solvent with logP < 3 and surface tension > 36 dyne / cm; Solvent A is one or more of light paraffin oil, heavy paraffin oil, petroleum solvent oil, squalene, squalane, kerosene, diesel oil, petroleum-based lubricating oil, synthetic or semi-synthetic engine oil; Solvent B is one or several of dimethyl phthalate, diethyl phthalate, glycerol diacetate, glycerol triacetate, pentaerythritol triacrylate, propylene glycol phenyl ether, ethyl salicylate, ethyl acetylsalicylate, N-hydroxyethyl-2-pyrrolidone; The conductive silver paste does not include an amphiphilic solvent that can be miscible with both component A and component B at the same time.

2. The conductive silver paste according to claim 1, wherein Solvent A is one or more of light paraffin oil, heavy paraffin oil, squalane, kerosene.

3. The electrically conductive silver paste according to claim 1, characterized in that, Solvent B is one or more of dimethyl phthalate, ethyl salicylate, glycerol diacetate, glycerol triacetate.

4. The electrically conductive silver paste according to claim 1, wherein Resin A is one or several of terpene resin, polyisobutene with Mw = 400 - 6000, C5 petroleum resin, hydrogenated C5 petroleum resin, C9 petroleum resin, C5 / C9 copolymerized petroleum resin, coumarone resin, SBS resin, SEBS resin, DCPD petroleum resin, hydrogenated DCPD resin; 5. The conductive silver paste according to claim 4, wherein Resin A is one or more of terpene resin, C5 petroleum resin, C9 petroleum resin, polyisobutene with Mw = 400 - 6000.

6. The conductive silver paste according to claim 1, wherein Resin B is one or several of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, polymethacrylate, polyvinyl butyral, polyurethane, polycarbonate; 7. The electrically conductive silver paste according to claim 6, characterized in that, Resin B is one or more of hydroxyethyl cellulose, polyvinyl butyral, polyurethane.

8. The electrically conductive silver paste according to claim 1, wherein, In the conductive silver paste, the weight ratio of the silver powder, the photovoltaic glass powder, and the organic carrier is (88 - 90):(1.5 - 3):(6.5 - 10).

9. The conductive silver paste according to claim 8, wherein, In the organic carrier, the weight ratio of component A and component B is (10 - 40):(60 - 90).

10. The electrically conductive silver paste according to claim 8, wherein, In component A, the weight ratio of solvent A and resin A is (70 - 95):(5 - 30).

11. The conductive silver paste according to claim 8, characterized in that, In component B, the ratio of solvent B and resin B is (70 - 95):(5 - 30).

12. The conductive silver paste according to claim 1, characterized in that, The surface of the silver powder has an organic coating structure.

13. The conductive silver paste according to claim 1, wherein, The conductive silver paste further includes an additive, and the additive is one or more of a surfactant, a leveling agent, a lubricant, a filler.

14. The electrically conductive silver paste according to claim 13, wherein The surfactant is one or more of an anionic surfactant, a cationic surfactant, a non-ionic surfactant.

15. The conductive silver paste according to claim 14, wherein, The weight ratio of the additive to the silver powder is (0.1 - 2):(88 - 90).

16. The conductive silver paste according to claim 1, characterized in that, The photovoltaic glass powder is prepared by the following method: subjecting a glass powder precursor to melting, quenching, and ball milling to obtain the photovoltaic glass powder; wherein the glass powder precursor includes lead oxide, bismuth oxide, tellurium oxide, and tungsten oxide.

17. The electrically conductive silver paste according to claim 16, wherein, Based on the total weight of the glass powder precursor, the weight content of lead oxide is 0.1 - 20%, the weight content of bismuth oxide is 30 - 60%, the weight content of tellurium oxide is 0.1 - 20%, and the weight content of tungsten oxide is ≥5%.

18. The conductive silver paste according to claim 16, wherein The weight ratio of tellurium oxide to tungsten oxide is (0.5:1) - (1.75:1).

19. The conductive silver paste according to claim 16, wherein The glass powder precursor further includes one or more of potassium oxide, sodium oxide, lithium oxide, calcium oxide, magnesium oxide, strontium oxide, barium oxide, nickel oxide, titanium dioxide, boron trioxide, silicon dioxide, zinc oxide, and phosphorus pentoxide.

20. A method for preparing a conductive silver paste according to any one of claims 1 to 19, characterized in that, The preparation method includes the following steps: S1, mixing resin A with solvent A to obtain component A, and mixing resin B with solvent B to obtain component B; S2, mixing component A and component B, then adding silver powder, photovoltaic glass powder, and optionally an additive, and stirring to obtain a paste; S3, subjecting the paste to grinding treatment to obtain the conductive silver paste.

21. Application of the conductive silver paste according to any one of claims 1 to 19 or the conductive silver paste prepared by the preparation method according to claim 20 in a solar cell chip.

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