Conductive paste additive, conductive paste and laser transfer printing method

Abstract

The invention discloses a conductive paste additive suitable for laser transfer printing, which is prepared from the following raw materials in percentage by weight: 20 to 30 weight percent of solvent, 5 to 10 weight percent of oligomer, 30 to 50 weight percent of induction reactant, 0 to 10 weight percent of laser absorbent and 20 to 30 weight percent of dispersing agent. The invention further discloses the conductive paste and a laser transfer printing method. According to the invention, the induction reactant and the laser absorbent are combined, and the induction reactant directly absorbs the laser energy after being irradiated by the laser with the wavelength in the set range, and reacts and is decomposed into small molecule gas; or the laser energy is absorbed by the laser absorbent and the induction reactant absorbs the energy transmitted by the laser absorbent for reaction, and the generated small molecule gas pushes the silver paste out of the groove to form the grid line, so that the laser power can be effectively reduced, the sputtering condition can be improved, the line type of the grid line can be optimized, and the phenomenon of grid breakage or uneven thickness and height can be avoided. The conductive paste additive is suitable for both low-temperature silver paste and high-temperature silver paste, has certain universality, and is simple to use and operate.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive silver paste, and particularly relates to a conductive paste additive applicable to laser transfer printing, a conductive paste, and a laser transfer printing method. Background Art

[0002] Conductive silver pastes are classified into two categories according to their binder phases: polymer conductive silver pastes (using organic polymers as the binder phase), also known as low-temperature silver pastes, and sintered conductive silver pastes (using glass powder or oxides as the binder phase), also known as high-temperature silver pastes. Among them, the low-temperature silver paste forms a cross-linking and shrinkage structure through the reaction of an organic resin and a curing agent, making the silver powder more dense, and the electrons undergo a tunneling effect to form a low-resistance conductive path. The high-temperature silver paste corrodes the silicon nitride film layer at high temperature through the glass powder, and the silver powder contacts the crystalline silicon to form a conductive silver-silicon alloy. When printing these two types of conductive silver pastes by traditional screen printing, it is difficult to reduce the grid line width, and the mesh knots of the screen plate will cause uneven heights of the grid lines, affecting the grid line current.

[0003] Laser transfer printing technology (Pattern Transfer Printing, abbreviated as PTP) is a new type of non-contact printing technology. First, the conductive silver paste is filled onto a transparent carrier film, and a high-power laser beam is used for high-speed patterned scanning to transfer the silver paste from the carrier film to the battery surface to form grid lines. This technology can break through the line width limit of traditional screen printing, achieve a line width below 15 μm, reduce the light-shielding area of the grid lines, enable the battery to have a larger light-illuminated area, reach a higher battery efficiency, and save 30 - 40% of the silver paste consumption compared with traditional screen printing under the same efficiency.

[0004] However, when ordinary conductive silver paste is applied to laser transfer printing, it requires a relatively high power for transfer printing, and it is prone to problems such as difficult film removal, broken grids, and easy dispersion of the paste to form sputtering. Therefore, ordinary conductive silver paste applied to screen printing is not suitable for laser transfer printing. Summary of the Invention

[0005] In view of one or more of the above defects or improvement requirements in the prior art, the present invention provides a conductive paste additive applicable to laser transfer printing, a conductive paste, and a laser transfer printing method, which enable ordinary conductive silver paste to be applicable to laser transfer printing, reduce the laser power, improve the sputtering situation, optimize the grid line pattern, have universality, and the addition operation is simple.

[0006] To achieve the above object, according to the first aspect of the present invention, a conductive paste additive applicable to laser transfer printing is provided. By weight percentage, its raw material components include: Solvent 20 - 30 wt%, oligomer 5 - 10 wt%, inducing reactant 30 - 50 wt%, laser absorber 0 - 10 wt%, dispersant 20 - 30 wt%.

[0007] As a further improvement of the present invention, the inducing reactant includes one or more of aromatic or olefin compounds and their derivatives of benzene series, naphthalene series, phenanthrene series, anthracene series, epoxy, pyridine, indole, quinoline heterocyclic compounds; azo, diazo, azide nitrogen-containing compounds and their derivatives, organic acids and their salts, strong oxidizing acids and their salts, ammonium salts, unstable acids and their salts.

[0008] As a further improvement of the present invention, the laser absorber includes wave-absorbing materials and / or ferromagnetic materials; wherein, The wave-absorbing materials include one or more of carbon black, iron powder, copper powder, aluminum powder, and the ferromagnetic materials include one or more of ferrite, nickel-zinc ferrite; The particle size of the laser absorber is preferably less than 500 nm.

[0009] As a further improvement of the present invention, the oligomer includes one or more of polyethylene glycol, polypropylene glycol; and / or, The dispersant includes one or more of ethers, polyethers, ammonium polyacrylate, organosilicons; and / or, The solvent includes one or more of butyl carbitol, alkyl glycidyl ether, cyclohexanol, ethylene glycol, terpineol.

[0010] As a further improvement of the present invention, The boiling point of the oligomer is 150°C to 250°C; and / or, The boiling point of the dispersant is 100°C to 200°C; and / or, The boiling point of the solvent is 100°C to 250°C.

[0011] According to the second aspect of the present invention, a conductive paste is provided, and the conductive paste includes conductive silver paste and the conductive paste additive as described above.

[0012] As a further improvement of the present invention, the conductive silver paste is a low-temperature conductive silver paste or a high-temperature conductive silver paste; For the low-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste, or the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is 0.3 to 1%; For the high-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste, or the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is 0.5 to 1.5%.

[0013] As a further improvement of the present invention, the viscosity range of the conductive paste at 10 RPM is 100 to 500 Pa·s, and its particle size D90 is less than the width of the transparent carrier groove for filling.

[0014] According to the third aspect of the present invention, a laser transfer method is provided, and the conductive paste is used for laser transfer, including the following steps: Fill the conductive paste into the groove of the transparent carrier; Place the battery cell under the transparent carrier, with the groove of the transparent carrier facing the battery cell; Scan the groove of the transparent carrier from the back with a laser, and gas is generated in the gap between the groove of the transparent carrier and the conductive paste, and the conductive paste is pushed out of the groove and falls onto the battery cell to form a grid line.

[0015] As a further improvement of the present invention, the wavelength range of the laser is 500nm~10μm.

[0016] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects are obtained: (1) The conductive paste additive suitable for laser transfer of the present invention combines an inducing reactant and a laser absorber. After being irradiated by a laser with a wavelength within a set range, the inducing reactant directly absorbs the laser energy and decomposes into small molecule gases through a reaction; or simultaneously, the laser absorber absorbs the laser energy, and the inducing reactant absorbs the energy transmitted by the laser absorber for reaction. The generated small molecule gases push the silver paste out of the groove to form a grid line at a certain air pressure, which can effectively reduce the laser power, improve the sputtering situation, optimize the grid line pattern, and avoid the phenomena of broken grids or uneven thickness, height, and width.

[0017] (2) For the conductive paste additive suitable for laser transfer of the present invention, the laser absorber assists in absorbing the laser energy and transfers the energy to the inducing reactant through molecular vibration, heat transfer, etc., so that the inducing reactant has a wider applicable range.

[0018] (3) For the conductive paste additive suitable for laser transfer of the present invention, the boiling points of the solvent, oligomer, and dispersant are all lower than 300°C and can volatilize during the drying process of the conductive silver paste. The inducing reactant finally decomposes into small molecule gases and has less residue in the conductive silver paste. Moreover, the addition amount of the laser absorber is small and mostly conductors, which basically does not affect the electrical properties of the conductive silver paste.

[0019] (4) The conductive paste additive suitable for laser transfer of the present invention is applicable to both low-temperature silver paste and high-temperature silver paste and has a certain generality. It only needs to be added in a certain proportion before using the conductive silver paste and stirred with the conductive silver paste using a blender, and the operation is simple.

[0020] (5) The conductive paste suitable for laser transfer of the present invention can be prepared by mixing the conductive paste additive with the conductive silver paste, or by mixing the raw materials for preparing the conductive paste additive with the conductive silver paste, and can be flexibly selected according to the actual situation. Detailed implementation mode

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] An embodiment of the present invention provides a conductive paste additive suitable for laser transfer. By weight percentage, its raw materials include: 20-30 wt% of solvent, 5-10 wt% of oligomer, 30-50 wt% of inducing reactant, 0-10 wt% of laser absorber, and 20-30 wt% of dispersant.

[0023] Among them, the inducing reactants include aromatic or olefin compounds of benzene series, naphthalene series, phenanthrene series, anthracene series such as triphenylmethane, ethyl anthraquinone, stilbene, and their derivatives; heterocyclic compounds such as epoxy, pyridine, indole, quinoline; nitrogen-containing compounds such as azo, diazo, azide such as azobenzene, triazene, and their derivatives; organic acids and their salts such as oxalic acid, potassium iron oxalate, etc.; strong oxidizing acids and their salts such as silver nitrate, potassium permanganate; ammonium salts such as ammonium chloride, ammonium bicarbonate, ammonium carbonate, etc.; unstable acids and their salts such as sodium bicarbonate, calcium carbonate, magnesium carbonate, basic copper carbonate, etc., one or more compounds that are easily photolyzed or thermally decomposed.

[0024] Among the above-mentioned inducing reactants, the internal carbon atoms of aromatic hydrocarbons, olefins, heterocycles and nitrogen-containing compounds often adopt sp2 hybridization, having rich π bonds and conjugated planes, resulting in high light absorption ability in a relatively wide wavelength range. The light energy is converted into internal energy, making the chemical bonds of the groups more easily broken to form small molecule products such as benzene, nitrogen, ammonia, etc.; organic acids, strong oxidizing acids, unstable acids and their salts, due to their instability, are easily decomposed into small molecule products such as ammonia, carbon dioxide, etc. under the combined action of the laser absorber.

[0025] Further preferably, the laser absorber includes wave-absorbing materials (such as carbon black, iron powder, copper powder, aluminum powder, etc.) and / or ferromagnetic materials (such as ferrites, nickel-zinc ferrites, etc.). The laser absorber uses the high electrical conductivity and porous structure of carbon black and metal powders, or the high magnetic permeability of ferromagnetic materials to guide the light wave to undergo multiple reflections and scatterings, resulting in resonance absorption, coupling the light energy into heat energy, and transferring the light energy to the inducing reactant through resonance or heat transfer. More preferably, the particle size of the laser absorber is less than 500 nm, with a large specific surface area, better contact with the conductive silver paste, and less influence on the resistivity of the conductive silver paste.

[0026] It should be noted that the present invention is applicable to the conductive paste additives for laser transfer. The addition amount of the laser absorber is 0-10%. That is to say, the present invention preferably uses the laser absorber in combination with the induced reactant. However, if the induced reactant has a high absorption rate of laser, the laser absorber can be not added or added less. For example, the internal carbon atoms of aromatics, olefins, heterocycles and nitrogen-containing compounds are sp2 hybridized, with rich π bonds and conjugated planes, making them have high light absorption ability in a relatively wide wavelength range. Such induced reactants have a high absorption rate of laser.

[0027] In a preferred embodiment, the oligomer is one or more low molecular weight polymers such as polyethylene glycol (PEG-200) and polypropylene glycol (PPG-200) to adjust the viscosity of the additive. The oligomer is used to adjust the viscosity of the additive to match the conductive silver paste and reduce the influence on the original conductive silver paste system. For example, if the viscosity is too small, the grid lines will collapse, and if the viscosity is too large, problems such as increased transfer power and broken grids will occur. More preferably, the boiling point of the oligomer is 150°C to 250°C.

[0028] In a preferred embodiment, the dispersant is one or more of ethers or polyethers such as ethylene glycol monoethyl ether and propylene glycol monobutyl ether, ammonium polyacrylate, organosilicon, etc. The dispersant is used to avoid the agglomeration of small-sized particles and make the various components in the additive mix evenly. More preferably, the boiling point of the dispersant is 100°C to 200°C.

[0029] In a preferred embodiment, the solvent is one or more of butyl carbitol, alkyl glycidyl ether, cyclohexanol, ethylene glycol, terpineol, etc. More preferably, the boiling point of the solvent is 100°C to 250°C.

[0030] Furthermore, for the conductive paste additive applicable to laser transfer in the embodiments of the present invention, the preparation method is as follows: first, mix the oligomer, dispersant and solvent; then add the laser absorber, stir by ultrasonic and filter to collect the filtrate; add the induced reactant to the filtrate, stir by ultrasonic in the dark and filter, and collect the filtrate to obtain the conductive paste additive.

[0031] Specifically, the preparation method of the conductive paste additive includes the following steps: Mix the oligomer, dispersant and solvent in a set ratio first, heat and stir at 60-80°C for 5-10 minutes, and slowly add the laser absorber while stirring; stir and disperse by ultrasonic for 5-10 minutes, and filter with a filter screen with a pore size of less than 5 μm to collect the filtrate; add the induced reactant to the filtrate, stir by ultrasonic in the dark for 5-10 minutes, and filter with a filter screen with a pore size of less than 5 μm to collect the filtrate to obtain the conductive paste additive.

[0032] Furthermore, the present invention also provides a conductive paste, which comprises a conductive silver paste and the conductive paste additive prepared as described above. The conductive paste is obtained by mixing the conductive paste additive with the conductive silver paste. The conductive silver paste includes a low-temperature silver paste or a high-temperature silver paste.

[0033] Among them, in the low-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste (i.e., the addition amount of the conductive paste additive) is preferably 0.3-1%. In the high-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste (i.e., the addition amount of the conductive paste additive) is preferably 0.5-1.5%. Since the epoxy resin curing system in the low-temperature silver paste contains amino groups and hydroxyl groups, which is conducive to the laser-induced decomposition reaction, the addition amount of the low-temperature silver paste is preferably lower than that of the high-temperature silver paste.

[0034] Furthermore, the present invention also provides a preparation method of a conductive paste. Add 0.3-1.5% of the conductive paste additive to the conductive silver paste and stir at a speed of 400-1000 RPM for 100-200 seconds to obtain the conductive silver paste.

[0035] However, the present invention is not limited thereto. The conductive paste of the present invention can not only be prepared by first making the conductive paste additive into a finished product and then mixing it with the conductive silver paste according to the above method; it can also be obtained by directly mixing the raw materials for preparing the conductive paste additive with the conductive silver paste during the preparation of the conductive silver paste. Those skilled in the art can make a choice according to the actual situation. Correspondingly, when directly mixing the raw materials for preparing the conductive paste additive with the raw materials of the conductive silver paste, those skilled in the art can mix them according to the prior art experience. Correspondingly, in the low-temperature conductive silver paste, the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is preferably 0.3-1%; in the high-temperature conductive silver paste, the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is preferably 0.5-1.5%.

[0036] Preferably, the viscosity range of the conductive paste at 10 RPM is 100-500 Pa·s, and the particle size D90 is less than the width of the groove of the corresponding filled transparent carrier. The above viscosity requirement is used to ensure that the line type of the printed grid line is within the designed range, and there is no grid line collapse (too low viscosity) or difficulty in printing resulting in broken grids (too high viscosity). The above particle size requirement is used to ensure that the conductive paste can be filled into the groove of the carrier, and there is no situation where the particles are larger than the groove width and cannot be filled into the groove.

[0037] Furthermore, the present invention also provides a laser printing method, which uses the aforementioned conductive paste (the conductive paste obtained by mixing the conductive paste additive with the conductive silver paste or the conductive paste obtained by mixing the raw material components for preparing the conductive paste additive with the conductive silver paste), and includes the following steps: Fill the conductive paste into the groove of the transparent carrier; Place the solar cell under the transparent carrier with the grooves of the transparent carrier facing the solar cell. Scan the grooves from the back with a laser of a set wavelength range and power. Gas is generated in the gap between the grooves and the conductive paste, and the conductive paste is pushed out of the grooves and falls onto the solar cell to form grid lines.

[0038] Specifically, it can be filled into the grooves of the transparent carrier with a squeegee; the shape of the grooves can be adjusted according to the grid line morphology, and multiple grooves form the grid line pattern to be transferred.

[0039] It should be noted that the set wavelength range is determined according to the absorption of the wavelength by the induced reactant, preferably the green wave or the near and mid-infrared bands of 500 nm to 10 μm. In addition, when the power is high, the line type is prone to be wide and short with more sputtering, and when the power is low, the line type is prone to be narrow and high with broken grids. Therefore, within the power range where the line type of the transferred grid line is consistent with the groove type of the carrier, there is no broken grid and less sputtering, and the minimum power is taken.

[0040] The induced reactant of the conductive paste additive of the present invention can directly absorb the laser energy and decompose into small molecule gases after being irradiated by a laser of a set wavelength range, or absorb the laser energy through a laser absorber, and the induced reactant absorbs the energy transferred by the laser absorber to react. Both occur simultaneously, and the generated small molecule gases push the silver paste out of the grooves to form grid lines at a certain air pressure. The conductive paste additive of the present invention can effectively reduce the laser power, improve the sputtering situation, optimize the grid line type, and avoid the phenomena of broken grids or uneven thickness, height, and width.

[0041] The laser absorber of the conductive paste additive of the present invention is to assist in absorbing the laser energy and transfer the energy to the induced reactant through molecular vibration, heat transfer, etc., so that the induced reactant has a larger applicable range.

[0042] The boiling points of the solvent, oligomer, and dispersant of the conductive paste additive of the present invention are all lower than 300 °C and can volatilize during the drying process of the conductive silver paste. The induced reactant finally decomposes to generate small molecule gases, leaving less residue in the conductive silver paste. The addition amount of the laser absorber is small and mostly conductors, which basically does not affect the electrical properties of the conductive silver paste.

[0043] The conductive paste additive of the present invention is applicable to both low-temperature silver paste and high-temperature silver paste, and can be adjusted by adjusting different addition amounts, having a certain generality. And the conductive paste additive of the present invention only needs to be added in a certain proportion before using the conductive silver paste and stirred with the conductive silver paste using a stirrer, and the operation is simple.

[0044] It should be noted that unless otherwise specified, the materials used in the present invention are all obtained commercially.

[0045] The following are specific examples: Example 1 The formulation of the conductive paste additive in this embodiment is as follows: 25 wt% butyl carbitol; 10 wt% PEG-200; 20 wt% azobenzene; 15 wt% potassium ferrioxalate; 5 wt% carbon black; 25 wt% ethylene glycol monoethyl ether; The conductive paste additive is prepared according to the above component ratios, and the preparation process is as follows; First, mix the oligomer, dispersant and solvent according to the above ratios, heat and stir at 60 - 80 °C for 5 - 10 minutes, and slowly add the laser absorber while stirring; use ultrasonic stirring to disperse for 5 - 10 minutes, and filter with a filter screen with a pore size less than 5 μm to collect the filtrate; add the induced reactant to the filtrate, stir ultrasonically in the dark for 5 - 10 minutes, and filter with a filter screen with a pore size less than 5 μm to obtain the conductive paste additive.

[0046] Add it to the low-temperature conductive silver paste and high-temperature conductive silver paste at an addition amount of 1% respectively, mix with a planetary centrifugal mixer at a speed of 500 RPM for 160 seconds, fill the mixed conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, place the side of the transparent carrier groove facing the silicon wafer, scan the groove from the back with the minimum power laser that can be completely transferred, and after scanning, dry and sinter the silicon wafer with the complete grid lines.

[0047] Example 2 A formulation of a conductive paste additive, 20 wt% butyl carbitol; 10 wt% PEG-200; 18 wt% triphenylmethane; 12 wt% silver nitrate; 10 wt% copper powder; 30 wt% ethylene glycol monoethyl ether; The conductive paste additive is prepared according to the above component ratios, and the preparation process is as follows; First, mix the oligomer, dispersant and solvent according to the above ratios, heat and stir at 60 - 80 °C for 5 - 10 minutes, and slowly add the laser absorber while stirring; use ultrasonic stirring to disperse for 5 - 10 minutes, and filter with a filter screen with a pore size less than 5 μm to collect the filtrate; add the induced reactant to the filtrate, stir ultrasonically in the dark for 5 - 10 minutes, and filter with a filter screen with a pore size less than 5 μm to obtain the conductive paste additive.

[0048] Add low-temperature conductive silver paste and high-temperature conductive silver paste respectively with an addition amount of 1%, mix them with a planetary centrifugal mixer at a speed of 500 RPM for 160 seconds, fill the mixed conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, place the transparent carrier groove side facing the silicon wafer, scan the groove from the back with the minimum power laser that can be completely transferred, and after the scanning is completed, dry and sinter and cure the silicon wafer with the complete grid lines printed on it.

[0049] Example 3 20 wt% butyl carbitol; 9 wt% PEG-200; 30 wt% ethyl anthraquinone; 20 wt% ammonium carbonate; 1 wt% aluminum powder; 20 wt% ethylene glycol monoethyl ether; Make a conductive paste additive according to the above component ratios, and its preparation process is as follows; First mix the oligomer, dispersant and solvent according to the above ratio, heat and stir at 60-80 °C for 5-10 minutes, and slowly add the laser absorber while stirring; use ultrasonic stirring to disperse for 5-10 minutes, and filter with a filter screen with a pore size less than 5 μm, and collect the filtrate; add the inducing reactant to the filtrate, stir ultrasonically in the dark for 5-10 minutes, and filter with a filter screen with a pore size less than 5 μm to obtain a conductive paste additive.

[0050] Add high-temperature conductive silver paste respectively with an addition amount of 1%, mix them with a planetary centrifugal mixer at a speed of 500 RPM for 160 seconds, fill the mixed conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, place the transparent carrier groove side facing the silicon wafer, scan the groove from the back with the minimum power laser that can be completely transferred, and after the scanning is completed, dry and sinter and cure the silicon wafer with the complete grid lines printed on it.

[0051] Example 4 30 wt% butyl carbitol; 5 wt% PEG-200; 25 wt% azobenzene; 19 wt% silver nitrate; 1 wt% carbon black; 20 wt% ethylene glycol monoethyl ether; Make a conductive paste additive according to the above component ratios, and its preparation process is as follows; First, mix the oligomer, dispersant, and solvent in the above-mentioned ratio, and heat and stir at 60-80°C for 5-10 minutes. While stirring, slowly add the laser absorbent; disperse by ultrasonic stirring for 5-10 minutes, and filter with a filter screen with a pore size of less than 5μm to collect the filtrate; add the induced reactant to the filtrate, stir ultrasonically in the dark for 5-10 minutes, and filter with a filter screen with a pore size of less than 5μm to obtain the conductive paste additive.

[0052] Add them to the low-temperature conductive silver paste at an addition amount of 1% respectively, mix with a planetary centrifugal mixer at a speed of 500 RPM for 160 seconds, fill the mixed conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, with the side of the transparent carrier groove facing the silicon wafer, and scan the groove from the back with the minimum power laser that can be completely transferred. After scanning, dry and sinter the silicon wafer with the complete grid lines printed on it.

[0053] Comparative Example 1 In this comparative example, the high-temperature conductive silver paste is directly used. Fill the conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, with the side of the transparent carrier groove facing the silicon wafer, and scan the groove from the back with the minimum power laser that can be completely transferred. After scanning, dry and sinter the silicon wafer with the complete grid lines printed on it.

[0054] Comparative Example 2 In this comparative example, the low-temperature conductive silver paste is directly used. Fill the conductive silver paste into the PTP squeegee paste tank, and fill it into the transparent carrier groove with a squeegee. Place the silicon wafer under the transparent carrier, with the side of the transparent carrier groove facing the silicon wafer, and scan the groove from the back with the minimum power laser that can be completely transferred. After scanning, dry and sinter the silicon wafer with the complete grid lines printed on it.

[0055] Take 9 positions in the grid lines after curing in each example and comparative example respectively, measure the line width and line height with a Keyence shape measuring microscope, measure the resistivity of the cured grid lines with a pvtools resistivity measuring instrument, and observe the sputtering situation.

[0056] The test results of each example and comparative example obtained are shown in Table 1: Table 1 Comparison of Test Results of Examples and Comparative Examples

[0057] The results show that the conductive paste additive in Example 1 can significantly reduce the minimum transfer power, reduce sputtering, improve the unevenness of the line thickness and height, and has no obvious effect on the line height, line width, and resistivity.

[0058] In Example 2, compared with Example 1, when the addition amount of the induction reactant is reduced, the transfer power needs to be increased, and there are no obvious changes in the line height, line width, and resistivity.

[0059] In Example 3, compared with the high-temperature conductive silver paste in Example 1, the laser absorber can be added in combination with the induction reactant. Preferably, if the induction reactant has a high laser absorption rate, a small amount of laser absorber can be added. When the addition amount of the induction reactant increases, the transfer power can be reduced, and there are no obvious changes in the line height, line width, and resistivity.

[0060] In Example 4, compared with the low-temperature conductive silver paste in Example 1, the laser absorber can be added in combination with the induction reactant. Preferably, if the induction reactant has a high laser absorption rate, a small amount of laser absorber can be added. When the addition amount of the induction reactant increases, the transfer power can be reduced, and there are no obvious changes in the line height, line width, and resistivity.

[0061] Comparing Comparative Example 1 with the high-temperature conductive silver paste in Examples 1 to 3, it can be seen that for the ordinary high-temperature conductive silver paste without the addition of a conductive paste additive, when applied to laser transfer, a higher transfer power is required, which has a greater impact on the line width difference and line height difference, and is prone to sputtering. Similarly, comparing Comparative Example 2 with the low-temperature conductive silver paste in Examples 1, 2, and 4, it can be seen that for the ordinary low-temperature conductive silver paste without the addition of a conductive paste additive, when applied to laser transfer, a higher transfer power is required, which has a greater impact on the line width difference and line height difference, and is prone to sputtering.

[0062] In addition, the transfer power of the low-temperature silver paste without additives in Comparative Example 2 is lower than that of the high-temperature silver paste without additives in Comparative Example 1, and the sputtering situation is also slightly better because the organic carrier of the low-temperature silver paste contains an epoxy resin system, and its molecular structure is conducive to the laser-induced decomposition reaction, which can reduce the laser transfer power.

[0063] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A conductive paste additive applicable to laser transfer, characterized in that, By weight percentage, its raw materials include: 20 - 30 wt% of solvent, 5 - 10 wt% of oligomer, 30 - 50 wt% of inducing reactant, 0 - 10 wt% of laser absorber, 20 - 30 wt% of dispersant.

2. The conductive paste additive applicable to laser transfer according to claim 1, wherein The inducing reactant includes one or more of aromatic or olefin compounds and their derivatives of benzene series, naphthalene series, phenanthrene series, anthracene series, epoxy, pyridine, indole, quinoline heterocyclic compounds; azo, diazo, azide nitrogen-containing compounds and their derivatives, organic acids and their salts, strong oxidizing acids and their salts, ammonium salts, unstable acids and their salts.

3. The conductive paste additive applicable to laser transfer according to claim 1 or 2, characterized in that, The laser absorber includes wave-absorbing materials and / or ferromagnetic materials; wherein, The wave-absorbing materials include one or more of carbon black, iron powder, copper powder, aluminum powder, and the ferromagnetic materials include one or more of ferrite, nickel-zinc ferrite; The particle size of the laser absorber is preferably less than 500 nm.

4. The conductive paste additive applicable to laser transfer according to claim 1, wherein The oligomer includes one or more of polyethylene glycol, polypropylene glycol; and / or, The dispersant includes one or more of ethers, polyethers, ammonium polyacrylate, silicone; and / or, The solvent includes one or more of butyl carbitol, alkyl glycidyl ether, cyclohexanol, ethylene glycol, terpineol.

5. The conductive paste additive applicable to laser transfer according to claim 1 or 4, wherein, The boiling point of the oligomer is 150°C - 250°C; and / or, The boiling point of the dispersant is 100°C - 200°C; and / or, The boiling point of the solvent is 100°C - 250°C.

6. A conductive paste, characterized in that, The conductive paste includes conductive silver paste and the conductive paste additive according to any one of claims 1 - 5.

7. The conductive paste according to claim 6, wherein The conductive silver paste is low-temperature conductive silver paste or high-temperature conductive silver paste; For the low-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste, or the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is 0.3 - 1%; For the high-temperature conductive silver paste, the ratio of the conductive paste additive to the conductive silver paste, or the ratio of the raw materials of the conductive paste additive to the raw materials of the conductive silver paste is 0.5 - 1.5%.

8. The conductive paste according to claim 6 or 7, characterized in that, The viscosity range of the conductive paste at 10 RPM is 100 - 500 Pa·s, and its particle size D90 is less than the width of the groove of the transparent carrier for filling.

9. A laser transfer method, which uses the conductive paste described in any one of claims 6-8 for laser transfer, is characterized in that, Including the following steps: Filling the conductive paste into the groove of the transparent carrier; Placing the battery cell under the transparent carrier with the groove of the transparent carrier facing the battery cell; Scanning the groove of the transparent carrier from the back with laser, generating gas in the gap between the groove of the transparent carrier and the conductive paste, and pushing the conductive paste out of the groove to fall onto the battery cell to form grid lines.

10. The laser transfer method according to claim 9, wherein The wavelength range of the laser is 500 nm - 10 μm.

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