Conductive paste for film transfer, preparation method, application, and solar cell

Abstract

The present invention belongs to the technical field of conductive pastes, and provides a conductive paste for film transfer, a preparation method, an application, and a solar cell. The conductive paste includes conductive powder, glass powder, and an organic carrier. Calculated based on the conductive paste, the organic carrier includes 0.1-0.5 wt% of binder, silicone oil, 0.1-2 wt% of elastomer, 0-0.9 wt% of auxiliary agent, 3-7 wt% of solvent, and 2-7 wt% of plasticizer; the elastomer is SEBS or SEBS-modified elastomer or SEPS or SEPS-modified elastomer, the silicone oil is polymethyl silicone oil or other modified silicone oils, and the mass content of the silicone oil is 0.5-0.7%; the binder includes cellulose acetate butyrate, ethyl cellulose, and polyvinyl butyral, and this combination of binders can enable the paste to have good rheology. By adjusting the ratio of the organic carrier of the paste, the present invention obtains good filling ability of the paste, can adapt to a mold with an extremely narrow line width to obtain an excellent aspect ratio of the electrode, and can well overcome the adhesion between the paste and the film, obtain good fluidity and at the same time obtain a clean battery surface.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive pastes, and particularly relates to a conductive paste for film transfer, a preparation method, an application, and a solar cell. Background Art

[0002] With the development of the PV industry, the silver consumption of photovoltaic silver paste has increased rapidly, further driving up the international silver price and restricting the further reduction of LCOE. Patent CN111987175B provides a preparation method for the electrodes of a photovoltaic cell that can effectively reduce silver consumption, that is: fixing the cell on the transfer equipment carrier table, coating a transfer solvent, then starting the electrode grid line mold above the carrier table, and then preparing a film mold for filling silver paste. Then, filling the silver paste into the groove area of the corresponding mold, and during the sintering process, the mold film material decomposes, and then a silver grid line electrode is prepared; Patent CN112018197B only provides a preparation method for the film electrode mold. Considering the differences in electrode construction methods, there will actually be other requirements for this type of silver paste compared to screen-printed electrodes. It can be determined that there will be certain risks in this construction method in practice: one is the risk of silver paste residue in the non-groove area of the mold. The residual silver paste will contaminate the cell surface after sintering, increasing the silver paste consumption, while shading, reducing the photoelectric efficiency of the cell, and increasing the cost per watt of the cell; the second is that in order to meet the requirements of narrow line screen printing, the organic design of the existing silver paste has high thixotropy requirements and has a certain impact on fluidity. The filling rate of the paste for the mold is relatively low, and there is even a risk of broken grids if the filling is not good; the third is that due to the presence of an organic film material between the electrode and the mold, during the sintering process, the decomposition of the film material will deteriorate the adhesion between the silver paste electrode and the textured surface, resulting in grid line shedding.

[0003] Of course, as introduced in previous patents, this construction method of such electrodes can achieve extremely fine grid line electrodes, and it is possible to achieve a sintered electrode line width of less than or equal to 15 μm or less than 10 μm. However, there is currently no conductive silver paste that is particularly suitable for film transfer. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a conductive paste for film transfer, a preparation method, an application, and a solar cell. By adjusting the organic carrier ratio of the paste, the present invention obtains good filling ability of the paste, can adapt to molds with extremely narrow line widths to obtain excellent electrode aspect ratios, and can well overcome the adhesion between the paste and the film material, obtaining good fluidity and a clean cell surface at the same time.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A conductive paste for film transfer, comprising conductive powder, glass powder and an organic carrier. Based on the conductive paste, the organic carrier includes 0.1-0.5 wt% of binder, 0.5-0.7 wt% of silicone oil, 0.1-2 wt% of elastomer, 0-0.5 wt% of auxiliary agent, 3-7 wt% of solvent, and 2-7 wt% of plasticizer;

[0007] The silicone oil is polymethyl silicone oil or other modified silicone oils, and the elastomer is SEBS (hydrogenated styrene-butadiene block copolymer) or SEBS modified elastomer or SEPS (hydrogenated styrene-isoprene block copolymer) or SEPS modified elastomer. Subsequently, SEBS / SEPS or its modified elastomer is referred to as the elastomer;

[0008] The binder includes cellulose acetate butyrate, ethyl cellulose and polyvinyl butyral. This combination of binders can enable the paste to have good rheological properties.

[0009] In the present invention, the mass content of the silicone oil is in the range of 0.5-0.7%. If the amount of silicone oil is too small, the interaction force between the resin and the film is strong, and the risk of paste residue in the non-groove area is high. If the amount of silicone oil is too high, the compatibility of the paste deteriorates, the rigid modulus of the paste increases, the flow deteriorates, and the filling ability decreases; SEBS / SEPS or its copolymer can form a microgel with a suitable solvent. Such elastomers have the characteristics of weak viscosity and strong oil absorption. Compared with the viscous agent, the cohesive force of such elastomers is relatively weak. The gel characteristics are beneficial to the customization and optimization of the rheological properties of the paste. Further, the mass content of SEBS / SEPS and its modified elastomers can be 0.5-1%, and as the solid content of the paste decreases, the mass content is further 1-2%, achieving good rheological characteristics of the paste under low solid content conditions, matching film transfer, and obtaining excellent aspect ratios even under low solid content conditions.

[0010] Preferably, the molecular weight of the cellulose acetate butyrate is 10,000-30,000, the molecular weight of the polyvinyl butyral is 10,000-30,000, and the molecular weight of the ethyl cellulose is 50,000-200,000. In particular, the polyvinyl butyral with such a molecular weight can better disperse silver powder and glass powder, has suitable wetting characteristics with the organic film, reduces the residue of the silver paste on the film in the non-groove area, and at the same time matches the cellulose acetate butyrate with a small molecular weight to improve the fluidity of the paste and the filling ability of the film die; further, a small amount of ethyl cellulose with a high molecular weight can help the silver paste to level and improve the flatness of the silver electrode. In particular, ethyl cellulose with a molecular weight exceeding 100,000 is more suitable.

[0011] Preferably, the content of cellulose acetate butyrate is 0.1 - 0.3 wt%, the content of polyvinyl butyral is 0.1 - 0.2 wt%, and the content of ethyl cellulose is 0.01 - 0.2 wt%. Further preferably, the content of ethyl cellulose is 0.15 - 0.2 wt%. In this range, the binder can obtain excellent viscoelasticity. The content of the overall binder cannot be too low, otherwise the cohesion of the slurry is insufficient and the residual risk is high. However, if the content of the overall binder is too high, the viscosity of the silver paste is high, and the residual risk in the non-filled area of the slurry is also high, and the fluidity is poor and the filling rate is low.

[0012] Preferably, the viscosity of the silicone oil is 5 - 1000 mPaS. The silicone oil in this viscosity range, especially dimethyl silicone oil, has a relatively small molecular weight, a low decomposition temperature, less silicon residue after high-temperature decomposition, and less influence on the sintering of the slurry electrode. At the same time, the silicone oil with a small molecular weight can free between the resin molecules of the binder to reduce the intermolecular force, lubricate to help the slurry flow, and improve the filling ability of the slurry. Further preferably, the viscosity of the silicone oil is 5 - 100 mPaS, and further preferably 20 - 100 mPaS.

[0013] The silicone oil is selected from any one or a mixture of dimethyl silicone oil, hydroxy silicone oil, amino silicone oil, alkyl silicone oil, octyl silicone oil, polyether silicone oil, etc. Further preferably, the silicone oil is selected from the composition of dimethyl silicone oil and amino silicone oil. The combination of dimethyl silicone oil and amino silicone oil can better achieve the balance between the filling ability of the membrane material mold and the flow of the silver paste. On the one hand, the amino group in the amino silicone oil acts with the hydroxyl groups in ethyl cellulose and polyvinyl butyral to reduce the entanglement of the resin and the friction between the resin chains, and improve the flow. On the other hand, during the mold filling process, dimethyl silicone oil frees to the interface, improves the smoothness characteristics of the slurry, and reduces the silver paste residue in the non-groove area.

[0014] Preferably, the solvent is selected from one or a combination of butyl carbitol acetate, diethylene glycol dibutyl ether, diethylene glycol monobutyl ether, or alcohol ester twelve.

[0015] The plasticizer is selected from one or a combination of alcohol ester sixteen, dimethyl adipate, pentaerythritol triacrylate, ethyl 2 - isobutoxybenzoate, dimethyl phthalate, or benzyl benzoate.

[0016] A combination of solvents such as butyl carbitol acetate, diethylene glycol dibutyl ether, diethylene glycol monobutyl ether, plasticizer alcohol ester 16, pentaerythritol triacrylate, ethyl 2-isobutoxybenzoate, and dimethyl phthalate can obtain better slurry rheology; diethylene glycol dibutyl ether and alcohol ester 16 have weak polarity, which can well inhibit the adhesion between the binder and the organic film material and obtain a clean battery surface. At the same time, dimethyl phthalate and ethyl 2-isobutoxybenzoate have good compatibility with SEBS / SEPS, can obtain an ideal gel structure, and have good compatibility with cellulose acetate butyrate, polyvinyl butyral, and ethyl cellulose, thereby obtaining better fluidity. Further preferably, the content of diethylene glycol dibutyl ether is 0.5-1.0 wt%, the content of alcohol ester 16 is 0.2-1 wt%, the content of dimethyl phthalate is 0.5-1.5 wt%, and the content of ethyl 2-isobutoxybenzoate is 0.5-1.0 wt%.

[0017] Preferably, the additives include a dispersant and a thixotropic agent. The dispersant is selected from one or a combination of organic acid dispersants, amine dispersants, acrylic acid dispersants, or silicone dispersants, and the thixotropic agent is selected from one or a mixture of polyamide wax or hydrogenated castor oil.

[0018] Preferably, the dispersant can be used in a combination of one or more of carboxylic acids or amines such as TDO, ED120, ED420, stearic acid, and dodecylamine; the thixotropic agent is polyamide wax;

[0019] Furthermore, the content of the dispersant is 0.05% - 0.4%, and the content of the thixotropic agent is 0.05% - 0.3%.

[0020] Preferably, the mass fraction of the conductive powder in the conductive paste is 85 - 90%, the mass fraction of the glass powder is 1.5 - 5%. The conductive powder is mainly silver powder, and the mass ratio of silver powder is 85 - 90%. The D50 of silver powder is 1 - 2 μm, and the specific surface area of silver powder is 0.3 - 0.7 m 2 / g, and the tapped density is 5.8 - 6.5 g / cm 3 ; the D50 of the glass powder is 1 - 2 μm, and the glass powder can be a mixture of two or more common glass powders such as B-Si-Ba system glass, Pb-Si-B system glass, and Bi-Si-B system glass.

[0021] Based on the same inventive concept, the present invention also provides a preparation method of the above conductive paste for membrane transfer. The conductive powder, glass powder, and organic carrier are fully stirred and mixed to obtain a paste composition; the paste composition is rolled and ground until its fineness is below 7 μm to obtain a slurry precursor; the slurry precursor is filtered and dispersed to obtain a conductive paste for membrane transfer.

[0022] Based on the same inventive concept, the present invention also provides an application of a conductive paste for film transfer in film transfer. A transfer film is coated on a battery substrate, and then a mold with grid lines is placed directly above the battery substrate. After demolding, grid line grooves are left on the transfer film, and then the conductive paste is printed into the grid line grooves on the transfer film. The transfer film is sintered and decomposed to obtain a battery electrode.

[0023] Based on the same inventive concept, the present invention also provides a solar cell, including a substrate and grid lines formed on the surface of the substrate. The grid lines are formed by film transfer of the above-mentioned conductive paste.

[0024] Due to the adoption of the above technical solutions, the present invention has the following advantages and positive effects compared with the prior art:

[0025] By adjusting appropriate binders, silicone oils, and elastomers, the present invention achieves good fluidity, promotes the filling of the paste into the area to be filled of the film, realizes a high paste filling amount in the area to be filled of the grid lines, and further obtains an excellent grid line aspect ratio. Therefore, by adjusting the organic component ratio of the paste, the present invention can obtain good filling ability of the paste and can adapt to molds with extremely narrow line widths to obtain an excellent electrode aspect ratio. On the other hand, by selecting silicone oil and solvents, the adhesion between the paste and the film can be well overcome, good fluidity can be obtained while obtaining a clean battery surface. At the same time, by controlling the residual amount of ash, the bonding performance between the electrode and the silicon wafer is improved. Compared with the existing silver paste, the paste of the present invention can obtain: a) an excellent aspect ratio, with little light shielding of the battery while obtaining a small line resistance; b) a lower PA. Due to the characteristics of film transfer of the film mold, the height-width of the electrode line can be precisely customized. Under the condition of a fine opening, an ideal electrical performance can be obtained with a lower silver consumption; c) a clean battery surface. Through the design of the organic components, the wettability between the paste and the film is appropriate, and there is no silver paste residue in the non-groove area of the transfer film, reducing the consumption of ineffective silver paste; d) by selecting small molecule silicone oil, the residual amount of silicone oil ash is reduced, and the reliability of the sintering connection between the electrode and the textured surface is improved. Description of the Drawings

[0026] Figure 1 It is a schematic process route diagram of film transfer of the present invention. Detailed Embodiments

[0027] The present invention mainly focuses on the technology of film transfer for preparing grid lines of solar cells, which is different from the current screen printing technology. Since the current conductive paste mainly meets the narrow line requirements of screen printing, the organic carrier has high requirements for thixotropy and has a certain impact on fluidity. The filling rate of the paste for the mold is relatively low, and there is even a risk of broken grids if the filling is not good. Moreover, for the film transfer technology, there are also certain requirements for the paste, especially the filling ability and the compatibility with the transfer film.

[0028] Specific analysis: Ideally, the conductive paste for matching film transfer should have the following characteristics:

[0029] (1) Appropriate compatibility between the organic system and the film material. If the compatibility is too good, the silver paste is more likely to remain in the non-mold area of the film material, resulting in more sintered silver debris, deteriorating the appearance and performance of the battery. If the compatibility is too poor, the spreading performance of the silver paste on the film material is not good, and the scraping and filling of the silver paste are blocked.

[0030] (2) The fluidity of the silver paste system needs to be enhanced. The construction method of screen-printed electrodes requires the silver paste to have a certain thixotropy to form a better aspect ratio. The high-thixotropy silver paste system has relatively weak ability to fill grooves, and it is easy to form breakpoints in the mold grooves, manifested as macroscopic battery broken grids or insufficient filling rate of the mold microscopically, increasing the sintering line resistance.

[0031] (3) The organic high-ash content in the silver paste system is low, especially the decomposition temperature of silicone oil should be low enough and the Si residue after heating should be less.

[0032] Therefore, the present invention provides a conductive paste specifically for film transfer technology. By adjusting the organic carrier in the conductive paste, better filling ability can be obtained, adapting to molds with extremely narrow line widths. And through the selection of silicone oil, the adhesion between the paste and the film material can be well overcome, obtaining better fluidity and a clean battery surface at the same time. Meanwhile, by controlling the residual amount of ash, the bonding performance between the electrode and the silicon wafer is improved.

[0033] The following further elaborates in detail on a conductive paste for film transfer, its preparation method, application, and solar cell proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer.

[0034] A conductive paste for film transfer includes conductive powder, glass powder, and an organic carrier. Based on the conductive paste, the organic carrier includes 0.1 - 0.5 wt% binder, 0.5 - 0.7 wt% silicone oil, 0.1 - 2 wt% elastomer, 0 - 0.5 wt% additives, 3 - 7 wt% solvent, and 2 - 7 wt% plasticizer.

[0035] The elastomer is SEBS or SEBS-modified elastomer or SEPS or SEPS-modified elastomer. The silicone oil is polymethyl silicone oil or other modified silicone oils, and the viscosity of the silicone oil is 5 - 1000 mPaS. Further preferably, the viscosity of the silicone oil is 5 - 100 mPaS, and further preferably 20 - 100 mPaS.

[0036] When the mass content of silicone oil is in the range of 0.5 - 0.7%, if the amount of silicone oil is too small, the interaction force between the resin and the film material is strong, and the risk of slurry residue in the non-groove area is high. If the amount of silicone oil is too high, the compatibility of the slurry deteriorates, the rigid modulus of the slurry increases, the fluidity deteriorates, and the filling ability decreases. Moreover, this viscosity of silicone oil, especially dimethyl silicone oil, has a relatively small molecular weight, a low decomposition temperature, less silicon residue after high-temperature decomposition, and less impact on the sintering of the slurry electrode. At the same time, the small-molecular-weight silicone oil can free between resin molecules to reduce the intermolecular force, lubricate to help the slurry flow, and improve the filling ability of the slurry. Further preferably, the silicone oil is selected from the combination of dimethyl silicone oil and amino silicone oil. The combination of dimethyl silicone oil and amino silicone oil can better achieve the balance between the filling ability of the film material mold and the flow of the silver paste. On the one hand, the amino group in the amino silicone oil acts with the hydroxyl groups in ethyl cellulose and polyvinyl butyral to reduce resin entanglement and the friction between resin chains, improving fluidity. On the other hand, during the mold filling process, dimethyl silicone oil frees to the interface, improving the smoothness characteristics of the slurry and reducing the silver paste residue in the non-groove area.

[0037] SEBS / SEPS or its copolymer can form microgels with a suitable solvent. Such elastomers have weak viscosity and strong oil absorption characteristics. Compared with adhesives, the cohesion of such elastomers is relatively weak, and the gel characteristics are conducive to the customized optimization of the rheological properties of the slurry. Further, the mass content of SEBS / SEPS or its modified elastomer can be 0.5 - 1%, and as the solid content of the slurry decreases, the mass content is further 1 - 2% to achieve better rheological characteristics of the slurry under low solid content conditions, matching the film material transfer, and obtaining excellent aspect ratios even under low solid content conditions. Therefore, through the control of the elastomer content and combined with the characteristics of film material transfer, the conductive silver paste has a large customized range of solid content, which can reach 85% - 92%, realizing the customized development of cost and performance.

[0038] The binder includes cellulose acetate butyrate, ethyl cellulose, and polyvinyl butyral. This combination of binders can enable the slurry to have better rheological properties.

[0039] Further preferably, the molecular weight of the cellulose acetate butyrate is 10,000 - 30,000, the molecular weight of the polyvinyl butyral is 10,000 - 30,000, and the molecular weight of the ethyl cellulose is 50,000 - 200,000. In particular, this molecular weight of polyvinyl butyral can better disperse silver powder and glass powder, has suitable wetting characteristics with the organic film material, reduces the silver paste residue of the film material in the non-groove area, and at the same time matches the small-molecular-weight cellulose acetate butyrate to improve the fluidity of the slurry and increase the filling ability of the film material mold. Further, a small amount of high-molecular-weight ethyl cellulose can help the silver paste level off and improve the flatness of the silver electrode. In particular, ethyl cellulose with a molecular weight exceeding 100,000 is more suitable.

[0040] The content of the cellulose acetate butyrate is 0.1 - 0.3 wt%, the content of the polyvinyl butyral is 0.1 - 0.2 wt%, and the content of the ethyl cellulose is 0.01 - 0.15 wt%. An adhesive within this range can achieve excellent viscoelasticity. The content of the overall binder cannot be too low, as otherwise the cohesion of the slurry is insufficient and the residual risk is high; however, if the content of the overall binder is too high, the silver paste has high viscosity, and the residual risk in the non-filled area of the slurry is also high, and the fluidity is poor and the filling rate is low.

[0041] Preferably, the solvent is selected from one or a combination of more of butyl carbitol acetate, diethylene glycol dibutyl ether, diethylene glycol monobutyl ether, or alcohol ester 12;

[0042] The plasticizer is selected from one or a combination of more of alcohol ester 16, dimethyl adipate, pentaerythritol triacrylate, ethyl 2 - isobutoxybenzoate, dimethyl phthalate, or benzyl benzoate.

[0043] A combination of butyl carbitol acetate, diethylene glycol dibutyl ether, diethylene glycol monobutyl ether as the solvent and alcohol ester 16, pentaerythritol triacrylate, ethyl 2 - isobutoxybenzoate as the plasticizer can obtain better slurry rheology; diethylene glycol dibutyl ether and alcohol ester 16 have weak polarity, which can well inhibit the adhesion between the binder and the organic film material to obtain a clean battery surface. At the same time, dimethyl phthalate and ethyl 2 - isobutoxybenzoate have good compatibility with SEBS / SEPS, can obtain an ideal gel structure, and have good compatibility with cellulose acetate butyrate, polyvinyl butyral, and ethyl cellulose, thus obtaining better fluidity. Further preferably, the content of diethylene glycol dibutyl ether is 0.5 - 1.0 wt%, the content of alcohol ester 16 is 0.2 - 1 wt%, the content of dimethyl phthalate is 0.5 - 1.5 wt%, and the content of ethyl 2 - isobutoxybenzoate is 0.5 - 1.0 wt%.

[0044] The conductive paste is prepared according to the mass ratio of the conductive paste listed in Table 1 below according to the preparation method. The specific preparation method is as follows:

[0045] The conductive powder, glass powder, and organic carrier in Table 1 are fully stirred and mixed. After high - shear stirring for 0.5 hours, a paste composition is obtained; the paste composition is repeatedly rolled and ground with different roller spacings of a three - roll mill until its fineness is below 7 μm to obtain a slurry precursor; the slurry precursor is filtered through a sieve and defoamed and dispersed to obtain the conductive paste.

[0046] Table 1 Conductive paste ratios of Examples 1 - 5 and Comparative Examples 1 - 2

[0047]

[0048] Note: In the table, silicone oil 1000 is dimethyl silicone oil with a viscosity of 1000 mPaS, silicone oil 100 is dimethyl silicone oil with a viscosity of 100 mPaS, and silicone oil 10 is dimethyl silicone oil with a viscosity of 10 mPaS.

[0049] The above conductive paste is used to prepare the grid electrodes of solar cells by the method of transferring with the film material as Figure 1 shown. Specifically: an organic material transfer film material is coated on the silicon substrate of the cell, and then a mold with grid lines is placed directly above the cell substrate. After demolding, grid line grooves are left on the transfer film material. Then, the conductive pastes in the above examples and comparative examples are printed into the grid line grooves on the transfer film material. The number of grid lines is 196. Subsequently, it passes through a belt-type firing furnace. During the sintering process, the transfer film material decomposes, and the sintered conductive paste is cooled to form grid electrodes, and then light injection and laser-assisted sintering are carried out. And, the performance tests of the solar cells and their grid lines prepared in each example and comparative example are as follows, and the test results are shown in Table 2.

[0050] Test method:

[0051] (1) Printing and electrode height-width test

[0052] The width, height and height-width ratio of the electrode are measured by an optical microscope and a micro-imaging inspection instrument. Each paste is tested 6 times, and the average value is taken.

[0053] (2) Cell conversion efficiency test

[0054] Under the condition of 1 sun solar irradiance, the formed solar cell is placed in an I-V test to measure its electrical performance, including Voc (open circuit voltage), Isc (short circuit current), FF (fill factor), and Eff (conversion efficiency). Each paste is tested with 12 groups of electrical performance data, and the average value is taken.

[0055] Table 2 Performance tests of solar cells and grid lines prepared in Examples 1-5 and Comparative Examples 1-2

[0056]

[0057] Compared with Examples 1-5, the silicone oil content in Comparative Example 1 exceeds the reasonable range. Compared with other examples, the binder selected in Comparative Example 2 is not appropriate. The binder does not have polyvinyl butyral and cellulose acetate butyrate, and the compatibility of benzyl benzoate with the binder resin is poor; Examples 1-5 can respectively correspond to the differences in silicone oil grades, binder types and ratios.

[0058] Regarding the silicone oil content, compared with Examples 1-5, significant broken grids occurred in the comparative examples. The content and type of dimethyl silicone oil were inappropriate, and the compatibility between silicone oil and diethylene glycol dibutyl ether was poor. Coupled with the poor compatibility between benzyl benzoate and the solvent, the conductive paste had a high rigid modulus, was hard and brittle, had weak filling ability, and was not fully filled locally, resulting in broken grids. Compared with other examples, in Comparative Example 2, the type of binder was unreasonable, the fluidity of the paste deteriorated, and the filling ability was poor. Although no broken grids occurred, the FF was relatively low, the electrical performance was poor, and silver paste debris remained in the non-groove area.

[0059] Comparing Example 1 and Example 2, Example 2 reduced the viscosity of silicone oil and obtained a better film filling effect, and the FF was significantly optimized. Comparing Example 2 and Example 3, in Example 3, by reducing the content of long-chain ethyl cellulose and increasing it to cellulose acetate, compared with ethyl cellulose, cellulose acetate had a shorter resin chain and less entanglement, the fluidity of the paste was enhanced, the filling ability was improved, the electrode sintering was uniform, and the FF was further increased. Comparing Example 3 and Example 4, after replacing dimethyl silicone oil with amino silicone oil in Example 4, the filling ability was further improved and the FF was optimized. Compared with Example 4, in Example 5, the binder was finely adjusted. By reducing the content of polyvinyl butyral and reducing cellulose acetate butyrate in the system, the fluidity of the paste was enhanced, the filling ability was improved, and the FF was increased. Considering the forming mode of the film transfer electrode, even if the viscosity of the paste is reduced, as long as the resin amount is reasonable and the sintering activity of the silver powder matches, the aspect ratio difference of the electrode is not large.

[0060] Therefore, the present invention provides a conductive paste applicable to film transfer. The comprehensive performance of the battery obtained through testing can reach the electrical comprehensive performance obtained by the existing screen printing. Further, using the film transfer method to fabricate the solar cell grid lines can reduce the amount of battery paste used. Compared with the screen printing method, the PA can be reduced by more than 10%, the battery manufacturing cost can be reduced, the actual electrode width is reduced to ≤15um, the aspect ratio exceeds 50%, the electrode collapse and epitaxy are less, and the photoelectric efficiency is increased by more than 0.05%.

[0061] The embodiments of the present invention have been described in detail above with reference to the drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, as long as these changes fall within the scope of the claims of the present invention and their equivalent technologies, they still fall within the protection scope of the present invention.

Claims

1. A conductive paste for film transfer, comprising conductive powder, glass powder and an organic carrier, characterized in that, The organic carrier includes 0.1-0.5wt% of adhesive, 0.5-0.7wt% of silicone oil, 0.1-2wt% of elastomer, 0-0.9wt% of additive, 3-7wt% of solvent, and 2-7wt% of plasticizer based on the conductive paste; The silicone oil is selected from a mixture of dimethyl silicone oil and amino silicone oil, and the elastomer is SEBS or SEBS modified elastomer or SEPS or SEPS modified elastomer; The adhesive comprises cellulose acetate butyrate, ethyl cellulose and polyvinyl butyral, the content of the ethyl cellulose is 0.01-0.2wt%, and the molecular weight of the ethyl cellulose is 10-20w; The viscosity of the silicone oil is 20-100 mPaS; The solvent includes butyl carbitol acetate, diethylene glycol dibutyl ether and diethylene glycol monobutyl ether, and the plasticizer includes alcohol ester hexadecene, ethyl 2-isobutoxybenzoate and dimethyl phthalate; The content of diethylene glycol dibutyl ether is 0.5-1.0wt%, the content of hexadecyl alcohol ester is 0.2-1wt%, the content of dimethyl phthalate is 0.5-1.5wt%, and the content of ethyl 2-isobutoxybenzoate is 0.5-1.0wt%.

2. The conductive paste for film transfer according to claim 1, wherein The content of the cellulose acetate butyrate is 0.1-0.3wt%, and the content of the polyvinyl butyral is 0.1-0.2wt%.

3. The conductive paste for film transfer according to claim 1, wherein The molecular weight of the cellulose acetate butyrate is 1-3w, and the molecular weight of the polyvinyl butyral is 1-3w.

4. The conductive paste for film transfer according to claim 1, characterized in that, The auxiliary agent includes a dispersant and a thixotropic agent. The dispersant is selected from one or more combinations of organic acid dispersants, amine dispersants, acrylic dispersants or silicone dispersants. The thixotropic agent is selected from one or a mixture of polyamide wax or hydrogenated castor oil.

5. The conductive paste for film transfer according to claim 1, wherein, The mass fraction of the conductive powder is 85-90%, and the mass fraction of the glass powder is 1.5-5%.

6. A method for preparing a conductive paste for film transfer as described in any one of claims 1-5, characterized in that, The conductive powder, the glass powder and the organic carrier are fully stirred and mixed to obtain a paste composition; the paste composition is rolled and ground to a fineness of less than 7 μm to obtain a slurry precursor; The slurry precursor is filtered and dispersed to obtain a conductive slurry for film material transfer.

7. Use of a conductive paste for film transfer as described in any one of claims 1-5 in film transfer, characterized in that, A transfer film is coated on a battery substrate, and then a mold with a grid line is placed directly above the battery substrate. After demoulding, a grid line groove is left on the transfer film. Then, the conductive paste described in any one of claims 1 to 5 is printed into the grid line groove on the transfer film, and the transfer film is sintered and decomposed to obtain a battery electrode.

8. A solar cell, characterized in that, It comprises a substrate and a gate line formed on the surface of the substrate, wherein the gate line is formed by transferring the conductive paste according to any one of claims 1 to 5 through a film material.

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