High-temperature separable conductive adhesives for curing epoxy resins and solar cell modules

Abstract

This invention relates to a high-temperature separable conductive adhesive for curing epoxy resin and a solar cell module using the adhesive. More specifically, this invention relates to a solvent-free conductive adhesive and a solar cell module, the solvent-free conductive adhesive comprising: conductive particles (A); and an adhesive composition (B) comprising modified bisphenol epoxy resin, alicyclic epoxy resin, and a cationic initiator, and being a conductive adhesive for curing epoxy resin. The conductive adhesive is capable of reprocessing due to its high-temperature separability, and in the solar cell module, the conductive adhesive is used to connect the electrodes of the solar cell cells to bonding wires.

Description

Technical Field

[0001] This invention relates to a high-temperature separable conductive adhesive for curing epoxy resin and a solar cell module using the adhesive. More specifically, the invention relates to a conductive adhesive for curing epoxy resin and a solar cell module, wherein the conductive adhesive, by virtue of its high-temperature separability, enables reprocessing, and in the solar cell module, the conductive adhesive for curing epoxy resin is used to connect the electrodes of the solar cell cells to tab wires. Background Technology

[0002] In solar cells, thermosetting conductive adhesives (ECAs) have been used as conductive adhesives to connect the electrodes and bonding wires of each solar cell unit during the manufacture of solar cell modules.

[0003] In general, bonding wires connect individual solar cells in series by connecting one end to the front electrode of one solar cell and the other end to the rear electrode of another adjacent solar cell. When the electrodes are connected to the bonding wires, ECA, acting as a curable adhesive, is processed once and cured.

[0004] Therefore, during the manufacturing of solar cell modules, if the bonding lines connected to the electrodes using ECA are not aligned, the arrangement of the individual solar cell cells in the solar cell module will be inconsistent, which may lead to a poor appearance and low efficiency of the solar cell module. In this case, curable ECA is used for such bonding, so once the adhesive is applied, it is difficult to remove, thus potentially resulting in the solar cell module being discarded or sold in a defective state.

[0005] Furthermore, due to the single-type nature of the solar cell module, its output is only confirmed after dozens of cells have been stacked within the module. In this situation, if defects (microcracks) or incorrect spacing are found in a cell after stacking, the entire string of cells (containing 15 to 21 cells manufactured of the same type) or module should be discarded. However, individual cells that need to be replaced can be replaced after removing the adhesive; that is, if reprocessing is possible, the entire string of cells or module can be reprocessed, significantly reducing cost losses. [Related Literature] [Patent Literature]

[0006] (Patent Document 1) Korean Patent Publication No. 10-2014-0070556 (June 10, 2014) Summary of the Invention [Technical Issues]

[0007] One embodiment of the present invention relates to providing a novel conductive adhesive (ECA) with excellent reworkability and a solar cell module using the adhesive, wherein in the case where the solar cell module is bonded by an ECA adhesive for curing epoxy resin as described above, specifically in the case where each individual cell is misaligned due to adhesion between the bonding wires and electrodes of each cell of the solar cell module, the adhesive enables rework or replacement of the damaged cell by easily removing the adhesive from the erroneous portion.

[0008] In other words, one embodiment of the present invention relates to providing an adhesive that can be easily removed due to increased separability: when electrodes and bonding wires are connected to each other via the curable adhesive, even if the electrodes and bonding wires are misaligned due to curing the curable adhesive, the adhesive can still be easily removed by applying heat to the cured adhesive. Therefore, one embodiment of the present invention relates to providing a novel ECA for curing epoxy resin and a solar cell module using the ECA, the ECA having reworkable properties such that even in misaligned situations, rework can be performed only on defective or problematic portions by easily removing the adhesive.

[0009] Another embodiment of the invention relates to a novel adhesive capable of reprocessing by exhibiting separability that allows for easy removal when heat is applied to the adhesive; that is, it retains reprocessing characteristics even after being cured to perform adhesion and impart strong adhesive properties at the operating temperature of the solar cell. Another embodiment of the invention relates to an adhesive capable of exhibiting separability within 3 minutes at 150°C or greater, preferably 200°C or greater, and more preferably 250°C, and an adhesive for solar cells capable of performing strong adhesion without separability within the operating temperature range of the solar cell, but with the novel function that, when partial replacement is required, the adhesive can be reprocessed due to the increased separability resulting from heating.

[0010] Another embodiment of the invention relates to providing an ECA with excellent reprocessability for curing epoxy resin and a solar cell module using the ECA, which can be easily removed within 3 minutes at 250°C due to the increased separability of the adhesive to perform reprocessing or readjustment, thereby immediately correcting the position.

[0011] Another embodiment of the invention relates to providing an adhesive for solar cells and a solar cell module using the adhesive, wherein the adhesive properties are not problematic at all during normal use of the solar cell. This is because, generally speaking, even in summer, the temperature of the solar cell module only rises to about 60°C to 90°C, and when using the ECA for curing epoxy resin according to the invention, there is absolutely no separability under normal use, and the adhesive adheres firmly. [Technical Solutions]

[0012] As a result of research conducted to solve the above-mentioned problems, the inventors of this invention have completed the invention by discovering that all the above-mentioned objectives can be achieved using a mixture of conductive particles and a specific epoxy resin.

[0013] In one overall embodiment, a solvent-free conductive adhesive is provided, comprising: conductive particles (A); and an adhesive composition (B) comprising a modified bisphenol epoxy resin, an alicyclic epoxy resin, and a cationic initiator.

[0014] The modified bisphenol epoxy resin can be represented by the following formula 1: [Formula 1] R1 to R6 are each independently a hydrogen atom or a C1 to C4 alkyl group, and R7 is selected from C1 to C4. 15 Alkylene*-OR 71 -O-*、 R 71 C1 to C1 are straight or branched chains 15 Alkylene or hydroxyalkylene, and R 72 R 73 R 74 R 75 and R 76 Each can be a straight chain or a branched chain, C1 to C1. 15 Alkylene, a and b are each 1 to 10, p is 0 to 1, q is 1 to 20, and n is 1 to 5.

[0015] The adhesive composition (B) may also contain a reactive diluent with an epoxy equivalent of 200 or less.

[0016] Based on 100 parts by weight of the conductive particles (A), the content of the adhesive composition (B) may be from 10 parts by weight to 100 parts by weight.

[0017] In the adhesive composition (B), the weight ratio of the modified bisphenol epoxy resin to the alicyclic epoxy resin can be from 10:90 to 70:30, and more specifically from 20:80 to 60:40.

[0018] The adhesive composition (B) may also contain 1% to 20% by weight, more specifically 3% to 10% by weight, of a reactive diluent with an epoxy equivalent of 200 or less.

[0019] The cationic initiator may be a cationic thermal polymerization initiator, and the adhesive composition (B) may contain the cationic initiator in an amount of 1% to 10% by weight.

[0020] This solvent-free conductive adhesive can be desorbed by exhibiting separability within 3 minutes at 250°C.

[0021] The solvent-free conductive adhesive can provide an initial bond strength of 1.0 Newton or greater to the ribbon.

[0022] The solvent-free conductive adhesive can provide an initial bond strength of 10 kgf or greater to the wafer.

[0023] This solvent-free conductive adhesive has a pot life of 3 to 10 days at room temperature (25°C).

[0024] The maximum exothermic temperature of this solvent-free conductive adhesive, measured by differential scanning calorimetry (DSC), can be 130°C or less.

[0025] This solvent-free conductive adhesive can have a DSC reaction rate of 35% or greater at 100°C to 130°C.

[0026] In another overall embodiment, a solar cell module is provided in which the front electrode of one solar cell unit and the rear electrode of another solar cell unit adjacent to the solar cell unit are electrically connected to a bonding wire via the solvent-free conductive adhesive, and the solvent-free conductive adhesive is separated within 3 minutes at 250°C.

[0027] The solvent-free conductive adhesive can provide an initial bond strength of 1.0 Newton or greater to the solder ribbon.

[0028] The solvent-free conductive adhesive can provide an initial bond strength of 10 kgf or greater to the wafer.

[0029] The maximum DSC exothermic temperature of this solvent-free conductive adhesive can be 130°C or less. [Beneficial Effects]

[0030] The solvent-free conductive adhesive according to the present invention can be easily separated and desorbed from a cured layer within 3 minutes at a high temperature of 200°C or greater, preferably 250°C or greater, and has excellent separability without leaving any residue, thereby exhibiting excellent reprocessability.

[0031] Furthermore, even if alignment defects occur in the solar cell module, reprocessing or recalibration can be performed without discarding the solar cell module, resulting in extremely high economic efficiency and reprocessability in the manufacture of solar cell modules. Attached Figure Description

[0032] Figure 1 A method for measuring the bond strength between wafers is shown. Detailed Implementation

[0033] The invention will be described in more detail below. The specific examples and embodiments described below are for reference only in describing the invention in detail, and the invention is not limited thereto and can be implemented in various forms.

[0034] Furthermore, all technical and scientific terms have the same meaning as commonly understood by those skilled in the art, unless otherwise defined. The terminology used in the description of this invention is for the purpose of effectively describing certain embodiments only and is not intended to limit the invention.

[0035] Furthermore, the singular forms used in the detailed description and the scope of the patent application are intended to include the plural forms, unless the context otherwise indicates.

[0036] Unless explicitly stated otherwise, “contains” any ingredient will be understood as implying the inclusion of other ingredients, rather than excluding other ingredients.

[0037] The exemplary solutions of the present invention will be described in detail below.

[0038] First, a conductive adhesive according to the present invention for electrically connecting the front or rear electrode of a solar cell to a bonding wire will be described.

[0039] The conductive adhesive according to the present invention is a paste and may be in the form of a film, but the present invention is not limited thereto.

[0040] The conductive adhesive (ECA) according to the present invention is a solvent-free conductive adhesive comprising: conductive particles (A); and an adhesive composition (B) comprising modified bisphenol epoxy resin, alicyclic epoxy resin and a cationic initiator.

[0041] More specifically, based on 100 parts by weight of conductive particles (A), the solvent-free conductive adhesive according to the present invention may contain 10 to 100 parts by weight of adhesive composition (B), which contains modified bisphenol epoxy resin, alicyclic epoxy resin and cationic initiator.

[0042] As a more specific example, based on 100 parts by weight of conductive particles (A), the solvent-free conductive adhesive according to the present invention may contain: 10 to 60 parts by weight of epoxy resin, wherein modified bisphenol epoxy resin and alicyclic epoxy resin are mixed; and 0.1 to 2 parts by weight of cationic initiator.

[0043] As a more specific example, based on 100 parts by weight of conductive particles (A), the solvent-free conductive adhesive according to the present invention may contain: 10 to 60 parts by weight of epoxy resin, wherein the modified bisphenol epoxy resin is mixed with the alicyclic epoxy resin in a weight ratio of 10:90 to 70:30, more specifically 20:80 to 60:40; and 0.1 to 2 parts by weight of cationic initiator.

[0044] In a more specific embodiment, based on 100 parts by weight of conductive particles (A), the solvent-free conductive adhesive according to the present invention may contain 5 to 20 parts by weight of modified bisphenol epoxy resin, 5 to 20 parts by weight of alicyclic epoxy resin and 0.1 to 2 parts by weight of cationic initiator.

[0045] In addition, if necessary, the solventless conductive adhesive according to the present invention may further contain 1 to 10 parts by weight, more specifically 1 to 5 parts by weight, of a reactive diluent with an epoxy equivalent of 200 or less, based on 100 parts by weight of conductive particles (A).

[0046] In addition, when necessary, the solvent-free conductive adhesive according to the present invention may also include inorganic fillers, lubricants, film-forming agents, coupling agents, defoamers, viscosity enhancers and solvents, etc., but the present invention is not limited thereto. [Conductive particles (A)]

[0047] First, the conductive particles (A) will be described.

[0048] In the present invention, conductive particles can be used without limitation, as long as the conductive particles are commonly used in the relevant fields.

[0049] Specific examples of conductive particles include, but are not limited to, silver, nickel, gold, copper, carbon black, graphite, graphene, silver-plated copper, silver-plated graphite, silver-plated polymer, silver-plated aluminum, silver-plated glass, silver-plated carbon, silver-plated boron nitride, silver-plated aluminum oxide, silver-plated aluminum hydroxide, and mixtures thereof, as well as mixtures selected from any one of them or from two or more of them.

[0050] More specifically, the conductive particles can be selected from silver, silver-plated copper, silver-plated graphite, silver-plated polymer, silver-plated aluminum, silver-plated glass, and mixtures thereof.

[0051] The conductive particles can have a flake shape or a granular shape, and their shape is not particularly limited, but a flake shape is preferred.

[0052] The particle size of the conductive particles is not particularly limited, but in terms of connection reliability, they can have sizes ranging from 0.01 micrometers to 30 micrometers, or more specifically from 1 micrometer to 20 micrometers. However, the particle size is not particularly limited, as long as the conductivity is sufficient.

[0053] In one aspect of the invention, the conductive particles are not limited, but specifically, for example, they may be flake-shaped silver particles with an average particle size of 1 to 20 micrometers. [Adhesive Composition (B)]

[0054] The adhesive composition (B) according to the present invention will now be described in more detail.

[0055] Based on 100 parts by weight of conductive particles, the solvent-free conductive adhesive according to the present invention can use 10 to 100 parts by weight, more specifically 10 to 50 parts by weight of adhesive composition. The invention is not limited thereto, but within the above range, mixing can be easy, can impart the desired conductivity, and can exhibit conductivity suitable for the application.

[0056] Adhesive composition (B) contains modified bisphenol epoxy resin, alicyclic epoxy resin, and a cationic initiator. Additionally, if necessary, adhesive composition (B) may also contain a reactive diluent with an epoxy equivalent of 200 or less.

[0057] For example, the epoxy resin in adhesive composition (B) can be used by mixing modified bisphenol epoxy resin and alicyclic epoxy resin. Due to the mixing and use of modified bisphenol epoxy resin and alicyclic epoxy resin, the desired excellent reprocessability can be achieved.

[0058] More specifically, for example, the epoxy resin content in adhesive composition (B) may be from 80% to 99% by weight, but is not limited to this. This provides superior performance because it offers excellent reprocessability within the above range and can be completely removed at high temperatures without leaving any residue.

[0059] In another embodiment, the epoxy resin content can be such that, based on 100 parts by weight of conductive particles (A), the content of the epoxy resin mixed with modified bisphenol epoxy resin and alicyclic epoxy resin can be from 10 parts by weight to 60 parts by weight.

[0060] In one embodiment, the weight ratio of modified bisphenol epoxy resin to alicyclic epoxy resin can be from 10:90 to 70:30, more specifically from 20:80 to 60:40. More preferably, it can be from 30:70 to 55:45 by weight. These ranges are preferred because they provide an adhesive with superior desired reprocessability, and more specifically, the physical property of being desorbable within 3 minutes at 250°C, exhibiting separability, and having an initial bond strength of 1.0 Newton or greater to the solder ribbon and 20 kgf or greater to the wafer.

[0061] Each ingredient will be described in more detail.

[0062] Modified bisphenol epoxy resin can be a polyether-based epoxy resin.

[0063] As a more specific example, modified bisphenol epoxy resins may include bisphenol-based structures and aliphatic structures. More specifically, the aliphatic structure may be alkoxy-based, and even more specifically, alkoxy-based structures such as those of ethylene oxide or propylene oxide, but the invention is not limited thereto.

[0064] As a specific example, the modified bisphenol epoxy resin scheme can be represented by the following formula 1: [Formula 1] R1 to R6 are each independently a hydrogen atom or a C1 to C4 alkyl group, and R7 is selected from C1 to C4. 15 Alkylene, *-OR 71 -O-*、

[0065] R 71 C1 to C1 are straight or branched chains 15 Alkylene or hydroxyalkylene, and R 72 R 73 R 74 R75 and R 76 Each can be a straight chain or a branched chain, C1 to C1. 15 Alkylene, a and b are each 1 to 10, p is 0 to 1, q is 1 to 20, and n is 1 to 5.

[0066] In Formula 1, at least one of R1 to R6 may be a C1 to C4 alkyl group, more specifically a methyl group.

[0067] Furthermore, in Equation 1, R7 can be specifically selected from, for example, C1 to C2. 10 Alkylene Where R 75 It can be a C2 to C4 alkylene group, and a and b can each independently be 1 to 10, and when b is 1, R 75 It can be C2 to C 15 Alkylene.

[0068] Specifically, examples of modified bisphenol epoxy resins include, but are not limited to, commercially available polyether-containing epoxy resins such as KDSF-180 available from Kukdo Chemical Company, EP-4000S, EP-4000L, EP-4003S, EP-4010S and EP-4010L available from ADEKA CORPORATION, and EXA-4850-150 and EXA-4850-1000 available from DIC.

[0069] Alicyclic epoxy resins may be 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylic acid esters, etc. Non-limiting examples of commercially available products include, but are not limited to, ERPL-4221 available from TED PELLA, CELLOXIDE C-2021P and CELLOXIDE C-2081 available from DAICEL, ROYOXY RAR 935 and ROYOXY RAR 936 available from GABRIEL, EPONEX1510 available from MILLER STEPHENSON CHEMICAL, and EPALLOY 5000 and EPALLOY 5200 available from HUNTSMAN, etc.

[0070] Cationic initiators can be cured at low temperatures and exhibit high adhesive strength, but at high temperatures, the adhesive strength decreases and the separability increases, allowing for re-bonding and enabling reprocessing after the adhesive is removed.

[0071] As a cationic initiator, cationic thermal polymerization initiators and cationic photopolymerization initiators can be used, and more preferably, cationic thermal polymerization initiators can be used so as to exhibit separability through heat treatment at high temperature.

[0072] When the cationic initiator is used in the adhesive composition (B) in an amount of 1% to 10% by weight, more specifically 1% to 3% by weight, it exhibits excellent adhesive strength during curing, and the separability of the adhesive is demonstrated within 3 minutes at 250°C.

[0073] Cationic polymerization initiators used to start cationic polymerization include, for example, diazonium salts, iodine salts, sulfonium salts, selenium salts, pyridinium salts, and ferrocenium salts. The initiator may contain salts and thiopyridine salts, and may also contain anions such as PF6, SbF6, AsF6, and BF4. Preferably, the cationic polymerization initiator is a cationic initiator containing SbF6 or B(C6F5)4.

[0074] Examples of cationic initiators include, but are not limited to, CXC-1612, CXC-1614, CX-7231, TAG-2678, TAG-2700, CDI-4302, and CDR-3430, which are commercially available from King Industries. Examples of cationic thermal polymerization initiators include Adeka Optomer CP-66 and Adeka Optomer CP-77, available from Asahi Denka, and D-2238, D-2243, D-2248, D-2503, H-1683, P-1080, P-1081, P-1082, and T-1608, available from Tokyo Chemical Industry Co., Ltd. Furthermore, if the purity of the cationic thermal polymerization initiator is less than 50%, gas release will occur, and the lifespan of the component will be shortened. Therefore, it is preferable to use a cationic thermal polymerization initiator with a purity of 50% to 100%.

[0075] Specific examples of cationic polymerization initiators include, but are not limited to, bis(dodecylphenyl)iodine. Bis(dodecylphenyl)iodonium hexafluoroantimonate, toluene-isopropylphenyl iodide Tetra(pentafluorophenyl)borate, bis(alkyl(C) 10-14 )Phenyl iodine Hexafluoroantimonate (bis(alkyl(C10-14)penyliodonium)hexafluoroantimonate), N-benzylpyridine N-benzylpyridinium hexafluoride arsenate, [4-(octyloxy)phenyl](phenyl)iodine Hexafluoroantimonate (1-)([4-(octyloxy)phenyl](phenyl)iodonium hexafluoroantimonate(1-)), triphenylsulfonium tetrafluoroborate, etc.

[0076] In addition to cationic polymerization initiators, curing accelerators may be used together with cationic polymerization initiators when necessary.

[0077] Specific examples of curing accelerators include: imidazoles, such as 2-methylimidazolium, 2-ethylimidazolium, and 2-ethyl-4-methylimidazolium; tertiary amines, such as 2-(dimethylaminomethyl)phenol and 1,8-diaza-bicyclo(5,4,0)undecene-7; phosphines, such as triphenylphosphine; tertiary ammonium salts, such as tetrabutylammonium salt, triisopropylmethylammonium salt, trimethyldecylammonium salt, and hexadecyltrimethylammonium salt; tertiary... Salts, such as triphenylbenzyl Salt, triphenylethyl Salt and tetrabutyl Salts; and metallic compounds, such as tin octoate.

[0078] If necessary, the present invention may also include a reactive diluent with an epoxy equivalent of 200 or less.

[0079] Examples of reactive diluents include aliphatic diglycidyl ethers, bisphenol-based diglycidyl ethers, and dicyclopentadienyl methacrylate-based epoxy resins.

[0080] Non-limiting examples of aliphatic diglycidyl ethers include, but are not limited to, ED-503, which is available from Adekal Corporation.

[0081] Non-limiting examples of bisphenol-based diglycidyl ethers include, but are not limited to, YDF-170, which is available from Guodu Chemical Company.

[0082] Non-limiting examples of dicyclopentadienyl methacrylate-based epoxy resins include, but are not limited to, KDCP-130, KDCP-150 and KDCP-130EK80 available from Guodu Chemical Company, and EP-4088S and EP-4088L available from Adico Company.

[0083] Based on 100% by weight of the total adhesive composition, it is preferable to use a reactive diluent in an amount of 3% to 20% by weight, more specifically 5% to 20% by weight, because it prevents the adhesive from maintaining separability at high temperatures, i.e., the adhesive strength increases over time.

[0084] The solvent-free conductive adhesive according to the present invention can be desorbed by exhibiting separability within 3 minutes at 250°C. More specifically, the solvent-free conductive adhesive can be desorbed by exhibiting separability within 200 seconds at 250°C. Furthermore, the solvent-free conductive adhesive can be desorbed by exhibiting separability within 150 seconds at 270°C.

[0085] The initial bond strength between the solvent-free conductive adhesive and the solder ribbon according to the present invention can be 1.0 Newton or greater than 1.0 Newton, and more specifically, 1 Newton to 3 Newton.

[0086] The solvent-free conductive adhesive according to the present invention can exhibit an initial bonding strength of 20 kgf or greater than 20 kgf, more specifically 20 kgf to 50 kgf, to the wafer.

[0087] The solvent-free conductive adhesive according to the present invention has a pot life of 3 to 10 days at room temperature (25°C).

[0088] The solvent-free conductive adhesive according to the present invention may have a maximum DSC exothermic temperature of 130°C or less, more specifically 90°C to 130°C.

[0089] The solvent-free conductive adhesive according to the present invention can have a DSC reaction rate of 35% or greater than 35%, more specifically 35% to 100%, at 100°C to 130°C. [Solar Cell Module]

[0090] In a solar cell module according to the present invention, the front electrode of one solar cell unit and the rear electrode of another solar cell unit adjacent to the solar cell unit can be electrically connected to a bonding wire by a solvent-free conductive adhesive according to the present invention, and the solvent-free conductive adhesive can be separated within 3 minutes at 250°C.

[0091] Next, a method for manufacturing a solar cell module using a conductive adhesive according to the present invention will be described.

[0092] Conductive adhesives are typically made into the form of a paste. Alternatively, conductive adhesives can be made into the form of a film. Here, a method for manufacturing modules using adhesives made into paste form will be described.

[0093] The conductive adhesive according to the invention is prepared by mixing components, or preferably mixing the components in a specified ratio, to prepare a paste, applying the paste to the portion where the bonding wire and the back electrode contact each other, and raising the temperature to cure the paste. During the curing process, the conductive adhesive stacked between the bonding wire and the back electrode is cured at a curing temperature typically within 150°C, while pressure is applied to the conductive adhesive to bond the bonding wire and the back electrode together.

[0094] In other words, the method for manufacturing a solar cell module according to the present invention is a method for manufacturing a solar cell module in which the front electrode of a solar cell unit and the rear electrode of another solar cell unit adjacent to the one solar cell unit are electrically connected to bonding wires by means of a conductive adhesive material, wherein the module is manufactured by setting the bonding wires on the front electrode and the rear electrode using the conductive adhesive paste of the present invention, and by curing the conductive adhesive paste by heat and pressure.

[0095] As an example of manufacturing a module according to the present invention, finger electrodes and bus bar electrodes are first formed by coating and firing Ag paste on the surface of the photoelectric conversion element, and an aluminum back electrode is formed on the connection portion of the bonding line on the back surface to manufacture a solar cell unit.

[0096] A solar cell module is manufactured by repeatedly applying the conductive adhesive paste according to the invention to the bus electrode and the aluminum back electrode on the surface of the solar cell unit, setting the bonding wire on the applied adhesive paste, and heating, pressurizing and curing the adhesive paste under a predetermined pressure to electrically connect the bonding wire to the bus electrode and the aluminum back electrode, thereby connecting multiple solar cell units to each other with the adhesive of the invention.

[0097] By using the conductive adhesive of the present invention, even with misalignment and hardening when the electrodes are connected to the bonding wires, the adhesive is relatively easy to remove when heat is applied. Therefore, the module can be reprocessed by reapplying the adhesive; that is, separability is increased at high temperatures, making the adhesive easy to remove. Thus, a novel conductive adhesive that can be reprocessed in cases of misalignment and a solar cell module using this conductive adhesive are provided.

[0098] Furthermore, by allowing the reprocessing characteristics to exhibit separability at 200°C or greater, preferably 250°C or greater, the present invention has the effect of completely preventing such separability from occurring within the temperature range in which the solar cell operates.

[0099] Furthermore, the present invention provides a conductive adhesive with excellent reprocessability and a solar cell module using the conductive adhesive, wherein the separability of the adhesive increases within 3 minutes at 250°C, allowing the adhesive to be easily removed and reprocessed, or readjusted so that the position can be corrected immediately. More preferably, reprocessing is made possible within 2 minutes at 250°C.

[0100] In general, it is known that even in summer, the temperature of solar cell modules only rises to about 60°C to 90°C, and therefore, when using the conductive adhesive according to the invention, no problems will be caused by normal use.

[0101] The present invention will be described in more detail below based on embodiments and comparative examples. However, the following embodiments and comparative examples are merely examples for describing the present invention in a more detailed manner, and the present invention is not limited to the following embodiments and comparative examples. <Reprocessing Characteristics>

[0102] After printing a 5 cm long, 3 mm wide, and 40 ± 5 μm thick back electrode region onto the surface of a solar silicon wafer, another solar silicon wafer's back electrode region was placed on top. A 10 g weight was then applied as pressure, and the wafer was cured at 150°C for 20 seconds in hot air or an infrared (IR) dryer to create a sample for evaluation. The fabricated wafer was placed on a heating plate at 250°C to record the time and location of wafer separation. ×: At 250℃, the wafer cracked but did not separate. ○: Can be separated within 5 minutes ◎: Can be separated within 1 minute <Inter-wafer adhesion strength>

[0103] After printing on the surface of the back Ag electrode of a solar silicon wafer to a length of 5 cm, a line width of 3 mm and a thickness of 40±5 micrometers, place the back electrode region of another solar silicon wafer thereon, then pressurize with a weight of 10 g, and then cure at 150°C for 20 seconds in a hot air or infrared (IR) dryer to prepare a sample for evaluation. A universal testing machine (WL2100) device was used to align with the Figure 1 same direction to measure the adhesive strength of the fabricated wafer. <Initial Adhesion Strength to Ribbon>

[0104] After printing on the surface of the back Ag electrode of a solar silicon wafer to a length of 5 cm, a line width of 3 mm and a thickness of 40±5 micrometers, place a ribbon (material: Sn:Pb=6:4) thereon, then perform curing at 150°C for 2 seconds while applying a weight of 100 g or less. The strength of the cured sample was measured with a multitester available from Mecmesin, and it was observed whether the conductive adhesive remains at the separation region on the wafer and whether the conductive adhesive adheres to the ribbon. <Pot Life>

[0105] After placing the prepared conductive adhesive at room temperature (25±5°C), the viscosity change rate relative to the initial stage is evaluated by measuring the viscosity at the initial stage, after 24 hours and after 48 hours. <DSC Exothermic Temperature>

[0106] The differential scanning calorimetry (DSC) exothermic temperature is measured by using an 823E instrument available from METTLER TOLEDO. Differential scanning calorimetry measures the heat flow generated in a sample during heating, cooling or maintaining isothermal conditions at a constant rate. After weighing 10±2 mg of the prepared conductive adhesive in an analysis pan, it is analyzed from room temperature to 200°C at a heating rate of 5°C / min. At this time, the conductive adhesive exhibits curing behavior through an exothermic reaction, and the temperature of the maximum exothermic peak is measured to compare the reaction temperature of each composition. [Examples and Comparative Examples]

[0107] Except for the conductive particles having the composition shown in Table 1 below, all substances are mixed at room temperature to achieve sufficient and uniform dispersion. Thereafter, by adding silver flakes (average particle diameter: 5.5 micrometers) according to the proportions shown in Table 1, sufficient stirring is performed at room temperature, the mixture is placed in a 3-roll mill and dispersed twice under a pressure condition of 5 bar, so as to prepare a uniform dispersed paste.

[0108] The physical properties are measured as follows using the paste-like conductive adhesive, and these physical properties are listed in Table 3.

[0109] In Tables 1 and 2 below, the content is based on parts by weight. [Table 1] [Table 2]

[0110] In Tables 1 and 2, the average particle size of the silver flakes is 5.5 micrometers.

[0111] In the modified bisphenol A epoxy resin, in Formula 1, R1 and R2 are CH3, R3 to R6 are H, and R7 is... Where b is 5, p is 0.5, n is 1.1, q is 1, and the epoxy equivalent is 400.

[0112] The alicyclic epoxy resin is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylic acid ester.

[0113] Reactive diluent A is an aliphatic diglycidyl ether, Adeka ED-503.

[0114] Reactive diluent B is bisphenol-F diglycidyl ether, YDF-170, which is available from Guodu Chemical Company.

[0115] The reactive diluent C is a DCPD-based epoxy resin, ADEKA EP-4088S.

[0116] Cationic initiator A is [4-(octyloxy)phenyl](phenyl)iodine Hexafluoroantimonate (1-).

[0117] The cationic initiator B is triphenylsulfonium tetrafluoroborate.

[0118] The imidazole-based curing agent is Shikoku 2E4MZ-CN.

[0119] The amine curing agent is Huntsman Jeffamine D-2000. [Table 3]

[0120] Table 3 confirms that high-temperature desorption is possible in Examples 1 to 7, and specifically, the desorption time at 250°C is 150 seconds or less. Furthermore, the separated surfaces were confirmed to be clean and exhibit excellent reprocessability.

[0121] In the foregoing, although the present invention has been described with reference to specific details and limited embodiments, these details and limited embodiments are provided only to aid in a more comprehensive understanding of the invention. Therefore, the present invention is not limited to the exemplary embodiments. Various modifications and changes can be made by those skilled in the art based on this description.

[0122] Therefore, the spirit of this invention should not be limited to the above-described embodiments, and all modifications equal to or equivalent to the scope of the patent application fall within the scope and spirit of this invention.

Claims

1. A solvent-free conductive adhesive, comprising: Conductive particles (A); and The adhesive composition (B) contains modified bisphenol epoxy resin, alicyclic epoxy resin, and a cationic initiator. in, In the adhesive composition (B), the weight ratio of the modified bisphenol epoxy resin to the alicyclic epoxy resin is from 10:90 to 70:30, and The modified bisphenol epoxy resin is represented by the following formula 1: [Formula 1] R1 to R2 are each independently C1 to C4 alkyl groups, R3 to R6 are each independently hydrogen atoms, and R7 is... ,as well as R 74 and R 76 Each branch is independent, consisting of C1 to C2. 15 Alkylene, R 75 For branches C1 to C 15 Alkylene, b is 1 to 10, p is 0 to 1, q is 1 to 20, and n is 1 to 5.

2. The solvent-free conductive adhesive as described in claim 1, wherein: The adhesive composition (B) also contains a reactive diluent with an epoxy equivalent of 200 or less.

3. The solvent-free conductive adhesive as described in claim 1, wherein: The content of the adhesive composition (B) is from 10 parts by weight to 100 parts by weight, based on 100 parts by weight of the conductive particles (A).

4. The solvent-free conductive adhesive as described in claim 3, wherein: The adhesive composition (B) further comprises 1% to 20% by weight of a reactive diluent with an epoxy equivalent of 200 or less.

5. The solvent-free conductive adhesive as described in claim 1, wherein: The cationic initiator is a cationic thermal polymerization initiator, and The adhesive composition (B) contains the cationic initiator in an amount of 1% to 10% by weight.

6. The solvent-free conductive adhesive of claim 1, wherein: The solvent-free conductive adhesive was desorbed by exhibiting separability within 5 minutes at 250°C.

7. The solvent-free conductive adhesive of claim 1, wherein: The solvent-free conductive adhesive has an initial bond strength of 1.0 Newton or greater than 1.0 Newton to the solder ribbon.

8. The solvent-free conductive adhesive as described in claim 1, wherein: The solvent-free conductive adhesive has an initial bonding strength of 10 kgf or greater to the wafer.

9. The solvent-free conductive adhesive as claimed in claim 1, wherein: The solvent-free conductive adhesive has a pot life of 3 to 10 days at room temperature (25°C).

10. The solvent-free conductive adhesive of claim 1, wherein: The maximum differential scanning calorimetry exothermic temperature of the solvent-free conductive adhesive is 130°C or less.

11. The solvent-free conductive adhesive of claim 10, wherein: The solvent-free conductive adhesive has a differential scanning calorimetry reaction rate of 35% or greater at 100°C to 130°C.

12. A solar cell module, wherein, The front electrode of a solar cell unit and the rear electrode of another solar cell unit adjacent to the one solar cell unit are electrically connected to a bonding wire by a solvent-free conductive adhesive as described in any one of claims 1 to 11, and the solvent-free conductive adhesive is separated within 3 minutes at 250°C.

13. The solar cell module as described in claim 12, wherein: The solvent-free conductive adhesive has an initial bond strength of 1.0 Newton or greater than 1.0 Newton to the solder ribbon.

14. The solar cell module as described in claim 12, wherein: The solvent-free conductive adhesive has an initial bonding strength of 10 kgf or greater to the wafer.

15. The solar cell module as described in claim 12, wherein: The maximum differential scanning calorimetry exothermic temperature of the solvent-free conductive adhesive is 130°C or less.

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