Conductive paste composition and solar battery cell

Abstract

Provided is a conductive paste composition that can be cured at a temperature lower than temperatures for conventional products, that can form a cured film having excellent conductivity, and that has excellent printability. A conductive paste composition according to the present invention contains a conductive material (A), an epoxy resin (B), a metal chelate (C), and a polyhydroxy fatty acid (D). The epoxy resin (B) has a weight average molecular weight of 2000-120000. The polyhydroxy fatty acid (D) is represented by general formula (1) (in formula (1), R1 represents an alkylene group or an alkenylene group, R2 and R3 are the same or different from each other and each represent a hydrogen atom, an alkyl group, or an alkenyl group, and n represents the number average degree of polymerization and is an integer of 2-20).

Description

Conductive paste composition and solar cell

[0001] The present invention relates to a conductive paste composition and a solar cell.

[0002] BACKGROUND ART In the field of manufacturing electronic devices or electronic components, a technique using a conductive paste composition has been known as one of methods for forming electrodes, electrical wiring, etc. on a substrate such as a film, a board, or an electronic component.

[0003] The conductive paste composition is a material whose main component is a conductive material made of conductive particles such as silver particles, and can form a cured film having electrical conductivity by thermal curing. For example, the conductive paste composition can be applied to a substrate or pattern-printed, and then heated to dry and cure, thereby forming a cured film. Such a cured film can function as a conductive layer because of the electrical conductivity due to the conductive material. For example, as proposed in Patent Document 1, it is used in electrodes for solar cells, and is therefore extremely useful.

[0004] Japanese Patent Application Laid-Open No. 2020-205245

[0005] Conductive paste compositions are generally cured at a temperature of about 200°C to form a cured film on a substrate. However, it has sometimes been difficult to apply such conductive paste compositions to substrates that are susceptible to heat damage, for example. While it has been conceivable to cure the conductive paste composition at a temperature lower than 200°C, this can result in insufficient formation of a cured film, potentially leading to problems such as high resistance (particularly volume resistivity) of the cured film. Given these circumstances, there has been an urgent need to develop a conductive paste composition that can form a cured film at a lower temperature than conventionally possible. In particular, perovskite solar cells are susceptible to heat damage at about 200°C, and there has been a strong demand for a conductive paste composition that can form a cured film with excellent conductivity at low temperatures.

[0006] The present invention has been made in view of the above, and aims to provide a conductive paste composition that can be cured at a lower temperature than conventional ones, can form a cured film that has excellent conductivity, and also has excellent printability, as well as a solar cell that includes a cured film of the paste composition.

[0007] As a result of extensive research into achieving the above object, the present inventors have discovered that the above object can be achieved by using specific components as essential components, and have thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following items: Item 1: A conductive material (A), an epoxy resin (B), a metal chelate (C), and a polyhydroxy fatty acid (D), wherein the epoxy resin (B) has a weight average molecular weight of 2,000 or more and 120,000 or less, and the polyhydroxy fatty acid (D) is represented by the following general formula (1):

[0009] (In formula (1), R １ represents an alkylene group or an alkenylene group, R ２ and R ３ and n are the same or different and represent a hydrogen atom, an alkyl group, or an alkenyl group, and n is the number average degree of polymerization and is an integer of 2 to 20. Item 2. The conductive paste composition according to Item 1, wherein the number average degree of polymerization is 2 or more and 8 or less. Item 3. The conductive paste composition according to Item 1 or 2, wherein the polyhydroxy fatty acid (D) has a structural unit derived from a hydroxy fatty acid having 12 or more and 22 or less carbon atoms. Item 4. The conductive paste composition according to any one of Items 1 to 3, which is used in a solar cell. Item 5. A solar cell comprising a current collecting electrode on which a cured film of the conductive paste composition according to Item 4 is formed. Item 6. A solar cell module comprising the solar cell according to Item 5. Item 7. A cured film comprising a cured product of the conductive paste composition according to any one of Items 1 to 4.

[0010] The conductive paste composition of the present invention can be cured at a lower temperature than conventional ones, and can form a cured film having excellent conductivity, and also has excellent printability.

[0011]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0012] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. In addition, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits.

[0013] The conductive paste composition of the present invention comprises a conductive material (A), an epoxy resin (B), a metal chelate (C), and a polyhydroxy fatty acid (D), wherein the epoxy resin (B) has a weight-average molecular weight of 2,000 or more and 120,000 or less. The polyhydroxy fatty acid (D) is represented by the following general formula (1):

[0014]

[0015] Here, in formula (1), R １ represents an alkylene group or an alkenylene group, R ２ and R ３ are the same or different and represent a hydrogen atom, an alkyl group, or an alkenyl group; n is the number average degree of polymerization and is an integer of 2 to 20.

[0016] Hereinafter, the conductive material (A), the epoxy resin (B), the metal chelate (C), and the polyhydroxy fatty acid (D) may be referred to as the conductive material, the epoxy resin, the metal chelate, and the polyhydroxy fatty acid, respectively, or may be referred to as the (A) component, the (B) component, the (C) component, and the (D) component, respectively.

[0017] According to such a conductive paste composition, by containing components (A), (B), (C), and (D) as essential components, it is possible to cure at a lower temperature than conventional ones, and it is possible to form a cured film with excellent conductivity. Specifically, even when the conductive paste composition of the present invention is cured at 200°C or less (for example, about 100°C) to form a cured film, such a cured film has a low volume resistivity and excellent conductivity. Furthermore, such a cured film also has a low resistance (hereinafter referred to as "contact resistance") when in contact with ITO or AZO (both of which are transparent conductive films).

[0018] Furthermore, the conductive paste composition of the present invention contains the components (A), (B), (C), and (D) as essential components, and therefore has excellent printability, particularly screen printability. Therefore, the conductive paste composition of the present invention can be suitably used for forming electrodes and wiring for various electronic devices and electronic components. In particular, the conductive paste composition of the present invention is particularly suitable for forming electrodes used in perovskite solar cells.

[0019] Conductive Material (A) The conductive paste composition of the present invention contains a conductive material as component (A). The conductive material serves to impart conductivity to a cured film formed from the conductive paste composition.

[0020] The type of conductive material is not particularly limited, and for example, a wide range of conductive materials contained in known conductive paste compositions used for producing electrodes for solar cells can be used.

[0021] The specific shape of the conductive material is not particularly limited, and may be, for example, particulate, i.e., the conductive material may be conductive particles. Alternatively, the conductive material may be in the form of flakes, such as thin flakes or scales. The conductive particles may be, for example, spherical. Such a spherical shape also means that, even if there are partial irregularities and deformations, when viewed as a whole, it includes a three-dimensional shape that is closer to a cube than a rectangular parallelepiped, and may be substantially spherical or ellipsoidal. Furthermore, the flake shape also includes powder that, even if there are partial irregularities and deformations, when viewed as a whole, is closer to a flat plate or a thin rectangular parallelepiped. The conductive material may be a mixture of conductive particles and flakes.

[0022] Specific examples of conductive materials include conductive particles such as silver powder, copper powder, gold powder, palladium powder, nickel powder, aluminum powder, lead powder, and carbon powder, and the conductive particles may be alloy powders. For example, silver powder includes silver alloy powder, copper powder includes copper alloy powder, and gold powder includes gold alloy powder. The conductive material may also be in the form of flakes, such as silver flakes, copper flakes, and gold flakes.

[0023] Further examples of conductive materials include powders in which a core material is coated with a metal and flakes in which a core material is coated with a metal. Examples of core materials include metals such as silver, copper, gold, palladium, nickel powder, and aluminum, as well as various resins such as polyimide resins and other ceramic materials. Examples of powders in which a core material is coated with a metal include silver-coated copper powder, silver-coated copper alloy powder, silver-coated nickel powder, and silver-coated aluminum powder.

[0024] The conductive material is preferably silver particles, silver flakes, or a powder with a core material coated with silver.

[0025] The average particle size D50 of the conductive material can be, for example, in the range of 0.1 to 10 μm when the conductive material is spherical particles. When the conductive material is in the form of flakes, the average particle size D50 can be, for example, in the range of 2 to 20 μm. The average particle size D50 of the conductive material can be measured by a laser diffraction method using a Microtrac particle size distribution analyzer.

[0026] The method for producing the conductive material is not particularly limited. For example, the conductive material can be obtained by a known production method, or can be obtained from a commercially available product.

[0027] The conductive paste composition of the present invention may contain only one type of conductive material (A), or may contain two or more types of conductive materials (A).

[0028] Epoxy Resin (B) The conductive paste composition of the present invention contains, as component (B), an epoxy resin having a weight-average molecular weight of 2000 or more and 120,000 or less. If the weight-average molecular weight of the epoxy resin is less than 2000, the volume resistivity and contact resistance of the cured film obtained when the conductive paste composition is cured at a low temperature may be high.

[0029] The weight average molecular weight of the epoxy resin is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 20,000 or more, and is preferably 100,000 or less, more preferably 90,000 or less, and even more preferably 80,000 or less.

[0030] The weight average molecular weight of an epoxy resin is the polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC). There are no particular restrictions on the GPC device used in the GPC method, and a commercially available GPC measuring device can be used. Specific measurement conditions are as follows: Column: Shodex OHPak SB-806M HQ Column temperature: 50°C Detector: Differential refractive index detector RID-20A (Shimadzu Corporation) Flow rate: 0.5 ml / min. Note that if the manufacturer's guaranteed or measured value of the weight average molecular weight of the epoxy resin is known, this value can also be used as the weight average molecular weight of the epoxy resin.

[0031] The type of epoxy resin is not limited as long as it has a weight average molecular weight of 2,000 or more and 120,000 or less, and for example, epoxy resins contained in known conductive paste compositions can be widely used.

[0032] The epoxy resin may be a polyhydric epoxy resin having two or more epoxy rings or epoxy groups in one molecule, and the epoxy resin may also have one or more hydroxyl groups.

[0033] Specific examples of epoxy resins include glycidyl epoxy resins, alicyclic epoxy resins such as dicyclopentadiene epoxide, and aliphatic epoxy resins such as butadiene dimer diepoxide. Examples of glycidyl epoxy resins include those obtained by reacting epichlorohydrin or 2-methylepichlorohydrin with a compound having active hydrogen. Examples of compounds having active hydrogen include novolak compounds such as phenol novolak and cresol novolak; polyhydric phenol compounds such as bisphenol, bisphenol A, hydrogenated bisphenol A, bisphenol F, bisphenol S, bisphenol AD, and resorcinol; phenoxy resins; polyhydric alcohol compounds such as ethylene glycol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, triethylene glycol, and polypropylene glycol; polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline; and polyvalent carboxyl compounds such as adipic acid, phthalic acid, and isophthalic acid.

[0034] Among these, the epoxy resin is preferably a polyhydric phenol compound, and particularly preferably a phenoxy resin, which is a bisphenol-type polymeric epoxy resin.

[0035] The epoxy resin contained in the conductive paste composition of the present invention may be one type alone or two or more types.

[0036] The epoxy resin may also contain a blocked polyisocyanate compound. In this case, such a blocked polyisocyanate compound is also considered to be component (B) for convenience. Examples of blocked polyisocyanate compounds include aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, tolidine diisocyanate, xylylene diisocyanate, and naphthalene diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, octamethylene diisocyanate, and trimethylhexamethylene diisocyanate. These polyisocyanate compounds may be used alone or in appropriate combination of two or more. These polyisocyanate compounds may be of the isocyanurate type, adduct type, or biuret type.

[0037] The polyisocyanate compound may be, for example, a compound containing a terminal isocyanate group synthesized by reacting a known polyisocyanate with a known polyol by a known method. Examples of the polyol include polyether polyols, polyester polyols, polycarbonate polyols, and polyalkylene polyols.

[0038] The method for producing the epoxy resin is not particularly limited, and for example, a wide variety of known production methods can be employed. In addition, the epoxy resin can also be obtained from commercial products, etc.

[0039] The epoxy resin (B) contained in the conductive paste composition of the present invention may be one type only, or may be two or more types.

[0040] Metal Chelate (C) The conductive paste composition of the present invention contains a metal chelate as component (C). By including the metal chelate in the conductive paste composition of the present invention, the volume resistivity and contact resistance of the resulting cured film can be reduced even when the conductive paste composition is cured at a low temperature.

[0041] The metal chelate may be capable of so-called pseudo-crosslinking with the epoxy resin, which is the aforementioned component (B), and as a result, even if the conductive paste composition is cured at a low temperature, the volume resistivity and contact resistance of the resulting cured film are likely to be low. In particular, when the epoxy resin has a hydroxyl group, pseudo-crosslinking of the metal chelate to the epoxy resin is likely to occur.

[0042] Examples of metal chelates include chelate compounds obtained by reacting metal alkoxides with chelating agents such as β-diketones, ketoesters (e.g., ethyl acetoacetate), etc. Specific examples of metal chelates include aluminum chelates, zirconium chelates, and titanium chelates, with aluminum chelates being preferred.

[0043] As the aluminum chelate, for example, an aluminum acetylacetonate complex is preferable. The acetylacetonate complex has an acetylacetonate group: —O—C(CH ３ )=CH-CO(CH ３ ) and the methyl acetoacetate group: —O—C(CH ３ )=CH-CO-O-CH ３ and ethyl acetoacetate group: —O—C(CH ３ )=CH-CO-OC ２ H ５ The aluminum chelate preferably has 1 to 3 of these groups in one molecule, and more preferably has 1 to 3 acetylacetonate groups or 1 to 3 ethylacetoacetate groups.

[0044] Further specific examples of aluminum chelates include ethyl acetoacetate aluminum diisopropionate, aluminum tris(ethyl acetoacetate), alkyl acetoacetate aluminum diisopropylate, aluminum tris(acetylacetate), aluminum monoacetylacetate bis(ethyl acetoacetate), aluminum di-n-butoxide monomethyl acetoacetate, aluminum diisobutoxide monomethyl acetoacetate, aluminum dis-sec-butoxide monomethyl acetoacetate, and the like.

[0045] The conductive paste composition of the present invention may contain one type of metal chelate alone or two or more types of metal chelates.

[0046] The method for producing the metal chelate is not particularly limited, and for example, a wide variety of known production methods can be employed. Metal chelates can also be obtained from commercial products, etc.

[0047]

[0033] The conductive paste composition of the present invention contains a polyhydroxy fatty acid as component (D). By including a polyhydroxy fatty acid, the volume resistivity and contact resistance of the cured film obtained from the conductive paste composition can be reduced even when the composition is cured at a low temperature, resulting in excellent conductivity and significantly improved screen printability.

[0048] Polyhydroxy fatty acids are compounds having repeating units derived from hydroxy fatty acids. Specifically, polyhydroxy fatty acids are compounds (oligomers or polymers) represented by the above formula (1).

[0049] In the formula (1), R １ represents an alkylene group or an alkenylene group. From this, it can be said that polyhydroxy fatty acids are compounds having structural units derived from saturated hydroxy fatty acids as repeating units, or compounds having structural units derived from unsaturated hydroxy fatty acids as repeating units. Note that an alkylene group is a divalent group obtained by removing two hydrogen atoms from a straight-chain alkane, and an alkenylene group is a divalent group obtained by removing two hydrogen atoms from a straight-chain alkene.

[0050] R １ When R is an alkylene group, the alkylene group preferably has 4 to 20 carbon atoms (i.e., R １ Ha-(CH ２ ) ｍ Preferably, m is a group represented by the formula - (m is 4 to 20), more preferably 6 to 16, and even more preferably 8 to 12.

[0051] R １When is an alkenylene group, the number of carbon atoms in the alkenylene group is preferably 4 to 20, more preferably 6 to 16, even more preferably 8 to 12, and particularly preferably 9 to 11. In the alkenylene group, the number of double bonds is not particularly limited and may be 1 or 2 or more, but is preferably 3 or less, more preferably 2 or less. Furthermore, in the alkenylene group, the position of the double bond is also not particularly limited.

[0052] The alkylene group and the alkenylene group are preferably linear. The alkylene group and the alkenylene group may or may not have a substituent.

[0053] In the formula (1), R ２ and R ３ are the same or different and represent a hydrogen atom, an alkyl group, or an alkenyl group.

[0054] R ２ and R ３ The number of carbon atoms in the alkyl group in R is preferably 1 to 10, more preferably 2 to 8, even more preferably 3 to 7, and particularly preferably 3 to 6. ２ and R ３ The number of carbon atoms in the alkenyl group in the formula (I) is preferably 1 to 10, more preferably 2 to 8, even more preferably 3 to 7, and particularly preferably 3 to 6. In the alkenyl group, the number of double bonds is not particularly limited and may be 1 or 2 or more, but is preferably 3 or less, more preferably 2 or less. Furthermore, in the alkenylene group, the position of the double bond is also not particularly limited.

[0055] R ２ and R ３ In the formula (I), both the alkyl group and the alkenyl group are preferably linear. In addition, both the alkyl group and the alkenyl group may or may not have a substituent.

[0056] In the formula (1), R ２ and R ３and may both be hydrogen. Preferably, R ２ and R ３ At least one of them is hydrogen, and the other is an alkyl group or an alkenyl group.

[0057] In the formula (1), n ​​represents the number-average degree of polymerization, i.e., the number of repeating units of the compound represented by formula (1). n is an integer from 2 to 20, and preferably 2 or more and 8 or less. That is, the number-average degree of polymerization of the polyhydroxy fatty acid (D) is preferably 2 or more and 8 or less. In this case, even if the conductive paste composition is cured at a low temperature, the volume resistivity and contact resistance of the resulting cured film are smaller, and screen printability is also significantly improved. n is more preferably 3 or more and more preferably 6 or less.

[0058] The polyhydroxy fatty acid (D) preferably has a structural unit derived from a hydroxy fatty acid having 12 or more and 22 or less carbon atoms. In other words, in the formula (1), the total number of carbon atoms present in the structure of the repeating unit is preferably 12 or more and 22 or less. This is one embodiment of the polyhydroxy fatty acid (D). In this case, even if the conductive paste composition is cured at a low temperature, the volume resistivity and contact resistance of the resulting cured film are smaller, and screen printability is also particularly significantly improved. One preferred embodiment of the polyhydroxy fatty acid (D) has a structural unit derived from a hydroxy fatty acid having 12 or more and 22 or less carbon atoms, and the number average degree of polymerization is 2 or more and 8 or less.

[0059] Specific examples of the polyhydroxy fatty acid (D) include polyhydroxystearic acid (i.e., in the formula (1), R １ is an alkylene group having 10 carbon atoms, R ２ is an alkyl group having 6 carbon atoms, R ３ is hydrogen), polyricinoleic acid (i.e., in the formula (1), R １ is an alkenylene group having 10 carbon atoms, R ２ is an alkyl group having 6 carbon atoms, R ３ is hydrogen).

[0060] The polyhydroxy fatty acid (D) contained in the conductive paste composition of the present invention may be one type alone or two or more types.

[0061] The method for producing the polyhydroxy fatty acid (D) is not particularly limited, and for example, a wide variety of known production methods can be employed. Polyhydroxy fatty acids can also be obtained from commercial products, etc.

[0062] Conductive Paste Composition The conductive paste composition of the present invention contains component (A), component (B), component (C), and component (D) as essential components.

[0063] The content of the conductive material (A) is preferably 1,000 parts by mass or more, more preferably 1,250 parts by mass or more, even more preferably 1,300 parts by mass or more, and particularly preferably 1,500 parts by mass or more, relative to 100 parts by mass of the epoxy resin (B), from the viewpoints of easily imparting good conductivity to the cured film and easily improving screen printability, and is preferably 5,000 parts by mass or less, more preferably 4,000 parts by mass or less, even more preferably 3,500 parts by mass or less, and particularly preferably 3,000 parts by mass or less.

[0064] The content of the metal chelate (C) is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more, relative to 100 parts by mass of the epoxy resin (B), because the volume resistivity of the cured film tends to be low. The content is also preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0065] The content of the polyhydroxy fatty acid (D) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 4 parts by mass or more, relative to 100 parts by mass of the epoxy resin (B), from the viewpoints that the volume resistivity of the cured film is likely to be reduced and the screen printability is likely to be improved, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and particularly preferably 10 parts by mass or less.

[0066] The conductive paste composition of the present invention may contain components other than the components (A), (B), (C), and (D) to the extent that the effects of the present invention are not impaired. Examples of other components include a wide range of components contained in conventional conductive paste compositions, particularly components contained in conventional conductive paste compositions used to form electrodes for solar cells.

[0067] Examples of other components include a solvent, as well as a leveling agent, an antioxidant, an ultraviolet absorber, a silane coupling agent, an antifoaming agent, a viscosity modifier, and the like.

[0068] When the conductive paste composition contains a solvent, for example, physical properties such as viscosity or fluidity of the conductive paste composition can be easily adjusted to a desired range. The viscosity of the conductive paste composition is not particularly limited, and can be, for example, within the range of 75 to 100 Pa·s for convenience in forming patterns such as electrodes or wiring, particularly for the efficiency of screen printing. If the viscosity of the conductive paste composition is within this range, pattern formation by screen printing can be carried out satisfactorily.

[0069] The specific type of solvent is not particularly limited, and examples thereof include saturated hydrocarbons such as n-hexane; aromatic hydrocarbons such as toluene; glycol ethers (cellosolves) such as ethyl cellosolve, butyl cellosolve, and butyl cellosolve acetate; glycol ethers such as diethylene glycol diethyl ether and butyl diglycol (butyl carbitol, diethylene glycol monobutyl ether); acetate esters of glycol ethers such as butyl diglycol acetate, butyl carbitol acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate; alcohols such as diacetone alcohol, terpineol, and benzyl alcohol; ketones such as cyclohexanone and methyl ethyl ketone; esters such as DBE, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; etc. These solvents may be used alone or in appropriate combinations of two or more.

[0070] The content of the solvent in the conductive paste composition is not particularly limited, and can be adjusted, for example, so that the viscosity of the conductive paste composition is adjusted within an appropriate range. For example, in terms of readily achieving good printability, the content of the solvent in the entire conductive paste composition is preferably 1 to 40 mass %.

[0071] The content of the components (A), (B), (C), (D), and the solvent relative to the total amount of the conductive paste composition is preferably 80 mass % or more, more preferably 90 mass % or more, and even more preferably 95 mass % or more. The conductive paste composition may consist of only the components (A), (B), (C), and (D) relative to the total amount of the conductive paste composition, or may consist of only the components (A), (B), (C), (D), and the solvent.

[0072] The method for preparing the conductive paste composition of the present invention is not particularly limited. For example, the conductive paste composition can be prepared by mixing the components (A), (B), (C), and (D) and other components, such as a solvent, added as needed, in predetermined amounts.

[0073] By using the conductive paste composition of the present invention, an electrode or electrical wiring can be formed on a substrate. The formation method is not particularly limited, and for example, a wide variety of known methods can be used. A typical example is a method in which a pattern is formed by screen printing, and then the conductive paste composition (the formed pattern) is cured by heat treatment. In addition to screen printing, other printing methods such as gravure printing, offset printing, inkjet printing, dispenser printing, and dipping can also be used.

[0074] The heat treatment conditions can be the same as conventional conditions, but as described above, the conductive paste composition of the present invention can be cured at a lower temperature than conventional conditions. Therefore, the heating temperature is preferably 180°C or lower, more preferably 150°C or lower, even more preferably 130°C or lower, and particularly preferably 120°C or lower. The heating temperature can also be 100°C. The lower limit of the heating temperature is not particularly limited as long as the curing of the conductive paste composition proceeds, and is, for example, 60°C or higher, preferably 80°C or higher. The heat treatment time can be set within an appropriate range depending on the heating temperature and the degree of curing. The heating method in the heat treatment is also not particularly limited, and a wide variety of known heating means can be used.

[0075] As described above, the conductive paste composition of the present invention can be cured at a lower temperature than conventional ones, and can still form a cured film with excellent conductivity. In particular, even when the conductive paste composition of the present invention is cured at 200° C. or lower (for example, about 100° C.) to form a cured film, the cured film has low volume resistivity and excellent conductivity, and furthermore, has low resistance when in contact with a transparent conductive film such as ITO or AZO.

[0076] Therefore, the conductive paste composition of the present invention can be widely used in applications requiring the formation of a cured film at low temperatures, and is particularly suitable for use in forming current collecting electrodes used in heterojunction crystalline silicon solar cells and perovskite solar cells, which require low-temperature processing. In other words, the conductive paste composition of the present invention can be suitably used for solar cells.

[0077] In particular, tandem solar cells consisting of perovskite solar cells and crystalline silicon solar cells, which have attracted attention in recent years, are susceptible to damage from heat, and therefore the conductive paste composition of the present invention, which can form a collecting electrode at low temperatures, can be suitably used.

[0078] The conductive paste composition of the present invention can, of course, be used as a material for forming the collecting electrodes of solar cells other than those mentioned above, and can also be suitably used for other applications, such as external electrodes of chip-type electronic components, electrodes or electrical wiring of components used in RFID, electromagnetic wave shielding, vibrator bonding, membrane switches, electroluminescence, etc. For example, a solar cell is provided with a collecting electrode on which a cured film of the conductive paste composition of the present invention is formed, and therefore is easy to manufacture, and since the collecting electrode is formed by low-temperature treatment in particular, it is less susceptible to damage during the manufacturing process and can have excellent performance.

[0079] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0080] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] (Raw Materials) In each of the Examples and Comparative Examples, the following raw materials were used to prepare the conductive paste compositions. Component (A): Conductive Material Conductive material 1: AG-3-1F (silver, D50: 1.4 μm, spherical) Conductive material 2: AG-5-1F (silver, D50: 2.9 μm, spherical) Conductive material 3: AG-2-8F (silver, D50: 0.9 μm, spherical) Conductive material 4: Mixture of FA-2-3 (silver, D50: 6.0 μm, flakes) and AG-3-1F (silver, D50: 1.4 μm, spherical) Conductive material 5: Toyal Tech Filler TFM-C05P (silver-coated copper, D50: 6 μm, spherical, Toyo Aluminum K.K.)

[0082] Component (B): Epoxy resin Epoxy resin 1: PKHB (weight average molecular weight: 32,000, Tomoe Engineering Co., Ltd.) Epoxy resin 2: jER4007P (weight average molecular weight: 4,000, Mitsubishi Chemical Corporation) Epoxy resin 3: PKFE (weight average molecular weight: 60,000, Tomoe Engineering Co., Ltd.) Epoxy resin 4: YX7553BH30 (weight average molecular weight: 35,000, Mitsubishi Chemical Corporation)

[0083] Component (C): Metal chelates Metal chelate 1: Orgatix AL-3100 (Matsumoto Fine Chemical Co., Ltd.) Metal chelate 2: Orgatix AL-3215 (Matsumoto Fine Chemical Co., Ltd.) Metal chelate 3: Orgatix ZC-150 (Matsumoto Fine Chemical Co., Ltd.)

[0084] Component (D): Polyhydroxy fatty acids Polyhydroxy fatty acid 1: Polyhydroxystearic acid having a number average degree of polymerization of 4 (manufactured by Kokura Synthetic Industries, Ltd.) Polyhydroxy fatty acid 2: Polyhydroxystearic acid having a number average degree of polymerization of 2 (manufactured by Kokura Synthetic Industries, Ltd.) Polyhydroxy fatty acid 3: Polyhydroxystearic acid having a number average degree of polymerization of 6 (manufactured by Kokura Synthetic Industries, Ltd.) Polyhydroxy fatty acid 4: Polyricinoleic acid having a number average degree of polymerization of 4 (manufactured by Kokura Synthetic Industries, Ltd.) Component (D) for comparison Stearic acid solvents Solvent 1: Diethylene glycol monoethyl ether acetate Solvent 2: Diethylene glycol monobutyl ether acetate

[0085] Example 1 A conductive paste composition was prepared by selecting the raw materials and blending amounts shown in Example 1 of the blending conditions in Table 1. Specifically, 2500 parts by mass of conductive material 1 as component (A), 100 parts by mass of epoxy resin 1 as component (B), 20 parts by mass of metal chelate 1 as component (C), 6 parts by mass of polyhydroxy fatty acid 1 as component (D), and 60 parts by mass of solvent 1 as a solvent were prepared and mixed to prepare a conductive paste composition.

[0086] Examples 2 to 15, Comparative Examples 1 to 3 Conductive paste compositions were prepared in the same manner as in Example 1, except that the raw materials and blending amounts were changed as shown in the blending conditions in Table 1.

[0087] (Formation of cured film) An alumina substrate was prepared, and a conductive paste composition was screen-printed on the surface of this substrate to form a conductor pattern. The substrate on which the conductive pattern was formed was heated in a hot air dryer at 120°C for 15 minutes to cure the conductive pattern (conductive paste composition) and form a cured film. Sample 1 for evaluating volume resistivity was thus prepared.

[0088] (Evaluation Method) <Measurement of Volume Resistivity> The volume resistivity was measured using Evaluation Sample 1. First, the film thickness of the conductor pattern (cured film) of Evaluation Sample 1 was measured using a surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., product name Surfcom 480A), and the electrical resistance was measured using a digital multimeter (manufactured by Advantest Corporation, product name R6551). The volume resistivity (μΩ cm) was calculated based on the measured film thickness and electrical resistance.

[0089] <Measurement of Contact Resistance with ITO> A glass substrate coated with ITO was used to measure the contact resistance with ITO. After forming an electrode on the ITO glass substrate using the conductive paste of the example and comparative example, the contact resistance (ITO) was measured by the TLM (Transfer Length Method).

[0090] <Measurement of Contact Resistance with AZO> A glass substrate coated with AZO was used to measure the contact resistance with AZO. After forming an electrode on an ITO glass substrate using the conductive paste of the example and comparative example, the contact resistance (AZO) was measured by the transfer length method (TLM).

[0091] <Screen Printability> The conductor pattern after screen printing performed in the above-mentioned "Formation of a Cured Film" was visually observed, and the screen printability was evaluated based on the following criteria. <Evaluation Criteria> ○: No fading was observed, and printability was good. ×: Fading was observed, and printability was poor.

[0092] Table 1 shows the compounding conditions for the conductive paste compositions prepared in each Example and Comparative Example, the measurement results for the volume resistivity of the resulting cured film, the contact resistance with ITO, and the contact resistance with AZO, and the evaluation results for screen printability. Note that a blank column in the compounding conditions in Table 1 indicates that the raw material was not used.

[0093] It can be seen from Table 1 that the cured films formed from the conductive paste compositions obtained in the Examples all have low volume resistivity, low contact resistance with ITO, and low contact resistance with AZO, and also have excellent screen printability. That is, although the conductive paste compositions obtained in the Examples were cured to form cured films at lower temperatures than conventional ones, the cured films had low volume resistivity and low contact resistance with ITO and AZO, demonstrating excellent screen printability.

[0094]

Claims

1. A conductive paste composition comprising a conductive material (A), an epoxy resin (B), a metal chelate (C), and a polyhydroxy fatty acid (D), wherein the epoxy resin (B) has a weight average molecular weight of 2000 or more and 120,000 or less, and the polyhydroxy fatty acid (D) is represented by the following general formula (1): (In formula (1), R １ represents an alkylene group or an alkenylene group, R ２ and R ３ are the same or different and each represents a hydrogen atom, an alkyl group or an alkenyl group, and n is the number average degree of polymerization and is an integer of 2 to 20).

2. The number average degree of polymerization is 2 or more and 8 or less, and the conductive paste composition according to claim 1.

3. The conductive paste composition according to claim 1, wherein the polyhydroxy fatty acid (D) has a structural unit derived from a hydroxy fatty acid having 12 or more and 22 or less carbon atoms.

4. The conductive paste composition according to any one of claims 1 to 3, which is used for a solar cell.

5. A solar cell including a current collecting electrode on which a cured film of the conductive paste composition according to claim 4 is formed.

6. A solar cell module including the solar cell according to claim 5.

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