Conductive paste, solar cell electrode, and solar cell

Abstract

The present invention provides an electrically conductive paste for solar cell electrode formation that can form an electrode with a low specific resistance, and with a reduced possibility of disconnection.　This electrically conductive paste for solar cell electrode formation includes (A) electrically conductive particles, (B) an epoxy resin, and (C) a curing agent. In the electrically conductive paste, the (A) electrically conductive particles contain an electrically conductive component and two or more types of organic components. The electrically conductive component is silver. The (C) curing agent includes at least one item selected from an imidazole curing agent and a boron trifluoride compound.

Description

[Technical Field]

[0001] The present invention relates to a conductive paste that can obtain a conductive pattern with excellent electrical properties, and more particularly to a conductive paste that can be used to form electrodes for semiconductor devices such as solar cells. [Background technology]

[0002] Conductive pastes containing silver particles are used to form, for example, electrodes and circuit patterns of semiconductor devices and electronic components. Formation of electrodes and circuit patterns using the conductive paste can be achieved by applying the conductive paste in a predetermined pattern onto a substrate or the like by screen printing or the like, and then heating the conductive paste to obtain a conductive film in the predetermined pattern.

[0003] There are two types of conductive paste: high-temperature firing conductive paste and thermosetting conductive paste. High-temperature firing conductive paste is a paste that can form a conductive film by firing at a high temperature of around 550 to 900°C. In the case of high-temperature firing conductive paste, the resin component contained in the conductive paste is burned away during firing. Thermosetting conductive paste is a paste that can form a conductive film by heating at a relatively low temperature of around room temperature (approximately 20°C) to 250°C. In the case of thermosetting conductive paste, the resin component hardens and bonds the silver particles together, forming a conductive film.

[0004] As a high-temperature fired conductive paste, for example, Patent Document 1 describes a conductive paste for forming an electrode of a solar cell, which contains conductive particles, an organic vehicle, and a specific glass frit.

[0005] Furthermore, as a thermosetting conductive paste, Patent Document 2 describes a thermosetting conductive paste composition containing conductive powders in the form of flake powder and spherical powder, a thermosetting component composed of epoxy resins of components A and B, a curing agent, and a solvent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-10628 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-196954 DISCLOSURE OF THE INVENTION

[0007] Thermosetting conductive pastes generally use epoxy resin as a binder, and in order to achieve both good adhesion and good electrical properties (resistivity of 10 μΩ·cm or less), they generally require heat treatment at temperatures above 250°C.

[0008] Thermosetting conductive pastes are sometimes used to form electrodes for solar cells. To obtain solar cells with high conversion efficiency, it is necessary to narrow the width of the electrodes and reduce the electrical resistance of the electrodes. By narrowing the width of the electrodes formed on the surface onto which sunlight is incident, the area onto which sunlight is incident can be increased. Furthermore, by lowering the electrical resistance (resistivity) of the electrodes, it is possible to reduce power loss when the generated current flows through the electrodes.

[0009] Generally, when the conductive particles contained in the conductive paste for forming the electrode are scaly (flake-shaped), the resistivity of the electrode can be lower than when the conductive particles are spherical. However, when scaly (flake-shaped) conductive particles are used, the possibility of the electrode breaking increases. Note that when spherical conductive particles are used, the risk of electrode breakage can be reduced, but as mentioned above, it is known that the resistivity is generally high.

[0010] Therefore, an object of the present invention is to provide a conductive paste for forming solar cell electrodes, which can form electrodes with low resistivity and reduced possibility of breakage.

[0011] In order to solve the above problems, the present invention has the following configuration.

[0012] (Configuration 1) A first aspect of the present invention is a conductive paste for forming an electrode of a solar cell, comprising: (A) conductive particles; (B) an epoxy resin; (C) a curing agent; Including, (A) the conductive particles contain a conductive component and two or more organic components, and the conductive component is silver; (C) A conductive paste in which the curing agent contains at least one selected from an imidazole-based curing agent and a boron trifluoride compound.

[0013] (Configuration 2) A second aspect of the present invention is the conductive paste of the first aspect, wherein the organic component includes a carboxylic acid.

[0014] (Configuration 3) A third aspect of the present invention is the conductive paste of the first aspect, wherein the organic component includes at least one selected from a fatty acid ether or a salt thereof, and a benzotriazole.

[0015] (Configuration 4) A fourth aspect of the present invention is the conductive paste of the first aspect, wherein the organic component includes a carboxylic acid and at least one selected from a fatty acid ether or a salt thereof, and benzotriazole.

[0016] (Configuration 5) In the fifth aspect of the present invention, the organic component comprises one or more organic components α and one or more organic components β, The (A) conductive particles contain an organic component α inside the (A) conductive particles and an organic component β on the surface of the (A) conductive particles, The conductive paste of configuration 1, wherein the organic component α includes at least one selected from a fatty acid ether, a salt of a fatty acid ether, and a benzotriazole.

[0017] (Configuration 6) A sixth aspect of the present invention is the conductive paste of the fifth aspect, wherein the organic component β includes stearic acid or ricinoleic acid.

[0018] (Configuration 7) A seventh aspect of the present invention is the conductive paste of any one of the third to sixth aspects, wherein the fatty acid ether or salt thereof includes at least one selected from palmitic acid ether, myristate ether, and oleic acid ether.

[0019] (Configuration 8) In the eighth aspect of the present invention, the BET specific surface area of ​​the conductive particles (A) is 0.3 to 3.5 m 2 / g The conductive paste according to any one of configurations 1 to 7, wherein:

[0020] (Configuration 9) A ninth aspect of the present invention is the conductive paste of any one of the first to eighth aspects, wherein the (A) conductive particles include spherical conductive particles, and the weight ratio of the spherical conductive particles in the (A) conductive particles is 80% by weight or more.

[0021] (Configuration 10) A tenth aspect of the present invention is the conductive paste of any one of the first to nineteenth aspects, wherein the ratio of the weight of the (A) conductive particles to the total weight of the (B) epoxy resin and the (C) curing agent (weight of the (A) conductive particles:(total weight of the (B) epoxy resin and the (C) curing agent)) is 98.5:1.5 to 93.0:7.0.

[0022] (Configuration 11) An eleventh aspect of the present invention is the conductive paste of any one of the first to tenth aspects, wherein the conductive paste contains 0.1 to 5.0 parts by weight of a curing agent (C) when the total weight of the conductive particles (A) and the epoxy resin (B) is 100 parts by weight.

[0023] (Configuration 12) A twelfth aspect of the present invention is the conductive paste of any one of the first to eleventh aspects, wherein the conductive paste further contains (D) a solvent.

[0024] (Configuration 13) A thirteenth aspect of the present invention is the conductive paste for forming an electrode of a solar cell according to any one of the first to twelfth aspects, wherein the wiring width of the electrode of the solar cell is 20 to 60 μm.

[0025] (Configuration 14) A fourteenth aspect of the present invention is a solar cell electrode, comprising an electrode for a solar cell obtained by heat-treating the conductive paste of any one of the first to thirteenth aspects, the electrode having a wiring width of 20 to 60 μm.

[0026] (Configuration 15) A fifteenth aspect of the present invention is a solar cell, wherein an electrode of the solar cell comprises a cured product obtained by heat-treating the conductive paste of any one of the first to thirteenth aspects.

[0027] According to the present invention, it is possible to provide a conductive paste for forming solar cell electrodes, which can form electrodes with low resistivity and reduced possibility of breakage. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a solar cell having an electrode formed using a conductive paste. [Figure 2] FIG. 2 is a schematic plan view showing a resistivity measurement pattern for an electrode formed using a conductive paste. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are forms for embodying the present invention and are not intended to limit the scope of the present invention.

[0030] The conductive paste of this embodiment is a thermosetting conductive paste. The conductive paste of this embodiment contains predetermined components, and therefore can be thermoset at low temperatures (for example, 250°C or less) to form an electrode. Furthermore, by using the conductive paste of this embodiment, a conductive film (electrode) with low resistivity and reduced possibility of breakage can be formed. The conductive paste of this embodiment can be preferably used as a conductive paste for forming electrodes for solar cells.

[0031] In this specification, the term "conductive film" refers to a thin film pattern formed by printing or the like a conductive paste onto the surface of a predetermined substrate or the like to form a pattern of a predetermined shape, and then curing the printed pattern. The predetermined shape pattern includes any shape, such as a linear, dotted, or planar pattern. The conductive film can be used as an electrode.

[0032] The conductive paste of this embodiment can be used to form electrodes and circuit patterns for semiconductor devices, electronic components, etc. The conductive paste of this embodiment can be used to form electrodes and / or circuit patterns not only on the surfaces of inorganic materials such as semiconductors, oxides, and ceramics, but also on substrates with low heat resistance such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate).

[0033] In this specification, the term "semiconductor device" refers to a device using a semiconductor chip, for example, semiconductor devices such as transistors and integrated circuits, flat panel displays such as liquid crystal displays (LCDs) and plasma display panels (PDPs), and devices using semiconductors such as solar cells. A semiconductor device is a device that utilizes the properties of electrons and holes in a semiconductor, and has electrodes for direct or indirect electrical connection to the semiconductor.

[0034] Electrodes of semiconductor devices may require light transmission. Transparent conductive films are used as materials for such electrodes. Electrodes made of transparent conductive films are called transparent electrodes. Transparent electrodes are used in semiconductor devices such as flat panel displays, such as liquid crystal displays (LCDs) and plasma display panels (PDPs), as well as various solar cells. Examples of solar cells include thin-film solar cells, such as amorphous silicon solar cells and compound semiconductor solar cells (CIS (CuInSe) solar cells, CIGS (Copper Indium Gallium Selenide) solar cells, and CdTe solar cells), heterojunction solar cells, and crystalline silicon solar cells. Transparent electrodes are used, for example, to form electrodes for flat panel displays, thin-film solar cells, and heterojunction solar cells.

[0035] An oxide conductive film can be used as the transparent conductive film, which is the material for the transparent electrode. Examples of oxide conductive films include indium tin oxide (also called "ITO (Indium Tin Oxide)") thin films, tin oxide thin films, and ZnO-based thin films. Currently, ITO thin films are widely used in flat panel displays and various solar cells. A grid-shaped electrode (sometimes simply referred to as "electrode") is formed to electrically connect to the transparent electrode so as not to interfere with the entrance of light to the semiconductor device or the exit of light from the semiconductor device. The conductive paste of this embodiment can be used to form the grid-shaped electrode on the surface of the transparent electrode.

[0036] Depending on the type of semiconductor material of the semiconductor device, the type of material of the electronic components, and the type of non-semiconductor materials that make up the semiconductor device and electronic components, etc., high temperatures, for example, temperatures exceeding 250°C, during the electrode formation process may cause deterioration of the semiconductor chip and / or other materials. By using the conductive paste of this embodiment, it is possible to form electrodes with low resistivity at low temperatures (for example, 250°C or lower). By using the conductive paste of this embodiment, it is possible to form electrodes with a predetermined low resistance without causing deterioration of the semiconductor device due to high temperatures.

[0037] When an electrode is formed on a transparent conductive film using the conductive paste of this embodiment, low contact resistance can be obtained. In particular, when an electrode is formed on an ITO thin film, low contact resistance (for example, 8 mΩ cm 2 Therefore, the conductive paste of this embodiment can be suitably used to form an electrode on a transparent conductive film, particularly an ITO thin film.

[0038] The conductive paste of this embodiment can be preferably used to form an electrode on the surface of a transparent conductive film of a solar cell. Depending on the type of solar cell, a material that is adversely affected by a high-temperature heating process may be used. The conductive paste of this embodiment can be preferably used to form an electrode on the surface of a transparent conductive film of such solar cells with low heat resistance. Amorphous silicon can be cited as an example of a material that is adversely affected by a high-temperature heating process. Examples of solar cells that use amorphous silicon as a material include amorphous silicon solar cells and heterojunction solar cells using amorphous silicon and crystalline silicon (hereinafter simply referred to as "heterojunction solar cells"). The conductive paste of this embodiment can be preferably used to form an electrode on the surface of a transparent conductive film of an amorphous silicon solar cell and a heterojunction solar cell. Furthermore, by using the conductive paste of this embodiment, solar cell electrodes with low resistivity and reduced risk of disconnection can be formed.

[0039] A heterojunction solar cell, which is a preferred application of the conductive paste of this embodiment, will be described with reference to FIG.

[0040] FIG. 1 shows a cross-sectional view of an example of a heterojunction solar cell. The heterojunction solar cell shown in FIG. 1 has an n-type crystalline silicon substrate 10 (e.g., a single-crystal silicon substrate or a polycrystalline silicon substrate) on its light-incident surface, on which an i-type amorphous silicon layer 12 (approximately 10 nm thick) made of intrinsic amorphous silicon and a p-type amorphous silicon layer 14a (approximately 10 nm thick) made of p-type amorphous silicon are stacked in this order. A transparent conductive film, such as a transparent conductive film 16 (approximately 70 nm thick) made of indium tin oxide (ITO), is disposed on the p-type amorphous silicon layer 14a. A grid-shaped light-incident electrode 18a is formed on the surface of the transparent conductive film 16 to obtain a slit-shaped light-incident surface.

[0041] 1, an i-type amorphous silicon layer 12 (thickness: approximately 10 nm) made of intrinsic amorphous silicon and an n-type amorphous silicon layer 14b (thickness: approximately 10 nm) made of highly doped n-type amorphous silicon are stacked in this order on the back surface of the crystalline silicon substrate 10. A transparent conductive film 16 and a lattice-shaped back electrode 18b are formed on the n-type amorphous silicon layer 14b, similar to the light-incident surface.

[0042] In the heterojunction solar cell shown in FIG. 1 , all layers other than the crystalline silicon substrate 10 can be formed at temperatures of approximately 200°C or less using methods such as plasma CVD, sputtering, vapor deposition, or screen printing. Because amorphous silicon is adversely affected by high-temperature heating processes, it is preferable to form the light-incident electrode 18a and the back electrode 18b on the surface of the transparent conductive film 16 at low temperatures (e.g., 250°C or less). By using the conductive paste of this embodiment, the light-incident electrode 18a and the back electrode 18b can be formed at low temperatures (e.g., 250°C or less) with low resistivity and reduced risk of breakage.

[0043] Next, the conductive paste of this embodiment will be described.

[0044] The conductive paste for forming a solar cell electrode of this embodiment contains (A) conductive particles, (B) an epoxy resin, and (C) a curing agent. The conductive paste of this embodiment may further contain (D) a solvent. Each component contained in the conductive paste of this embodiment will be described below.

[0045] <(A) Conductive particles> The conductive paste of this embodiment contains (A) conductive particles, which contain a conductive component and two or more organic components.

[0046] The conductive component contained in the (A) conductive particles can be a metal such as silver, copper, nickel, aluminum, zinc, and / or tin. Because of its relatively low resistivity and ease of availability, the conductive component is preferably silver, and more preferably consists of silver. It is even more preferable that the conductive component consists solely of silver.

[0047] The phrase "the conductive component consists only of silver" means that the conductive component is substantially entirely silver, excluding unavoidably present impurities. In other words, when the conductive component consists only of silver, the conductive component may contain unavoidably present impurities in addition to silver. The same applies to components other than the conductive component.

[0048] The (A) conductive particles contain two or more organic components. The organic components can be contained in the (A) conductive particles together with the conductive components as raw materials when producing the (A) conductive particles. Furthermore, by performing surface treatment using the organic components, the organic components can be contained on the surfaces of particles produced using the (A) conductive particles (and the organic components) as raw materials.

[0049] Any method can be used to produce conductive particles containing two or more organic components, as long as the (A) conductive particles contain a conductive component and two or more organic components. For example, a first method for producing conductive particles containing two or more organic components can involve first producing particles (e.g., silver particles) made of a conductive component, and then surface-treating the surfaces of the particles made of the conductive component with two or more organic components. A second method for producing conductive particles containing two or more organic components can involve producing (A) conductive particles containing two or more organic components using raw materials containing a conductive component and two or more organic components. A third method for producing conductive particles containing two or more organic components can involve first producing (A) conductive particles containing one or more organic components (organic component α) in the same manner as in the second method, and then surface-treating the surfaces of the (A) conductive particles with one or more organic components (organic component β) in the same manner as in the first method. By using the third manufacturing method, it is possible to manufacture (A) conductive particles having a structure in which the organic component α is incorporated into the (A) conductive particles and the organic component β is present on the surface of the (A) conductive particles. Note that, in order for the organic component α to be incorporated into the (A) conductive particles, it is necessary to intentionally add a predetermined amount of the organic component α during the manufacturing of the (A) conductive particles.

[0050] The conductive particles are preferably porous bodies having voids therein. The presence of voids therein allows the organic component (organic component α) to be contained within the conductive particles. The tap density of the conductive particles is 2.0 to 8.0 g / cm. 3 is preferably 2.5 to 7.0 g / cm 3 More preferably, it is 3.0 to 6.0 g / cm 3 When the tap density is in this range, an electrode having sufficient conductivity can be formed.

[0051] In the first method for producing conductive particles containing two or more organic components, the method for producing particles (e.g., silver particles) made of the conductive components is not particularly limited. For example, reduction, pulverization, electrolysis, atomization, heat treatment, or a combination thereof can be used as the production method.

[0052] In the second and third manufacturing methods of conductive particles containing two or more organic components, the following manufacturing method can be used, for example, to manufacture (A) conductive particles containing one or more organic components using raw materials containing a conductive component and an organic component. In the following example, the conductive component is silver, and a manufacturing method for manufacturing silver particles containing an organic component is described. In the following description, the organic component contained inside the (A) conductive particles may be referred to as organic component α, and the organic component contained on the surface of the (A) conductive particles may be referred to as organic component β. It is preferable that the (A) conductive particles contain both organic component α and organic component β.

[0053] The conductive component is silver, and the silver particles containing an organic component can be produced by the following method using a silver ammonia complex salt solution, an additive, and a reducing agent as raw materials.

[0054] First, an aqueous solution containing a silver ammonia complex salt (aqueous silver ammonia complex salt) is prepared. The aqueous silver ammonia complex salt can be produced by adding aqueous ammonia to an aqueous silver nitrate solution. Since the coordination number of ammonia in the silver ammonia complex is 2, it is preferable to add 2 moles or more of ammonia per mole of silver.

[0055] Next, before reducing the silver ammonia complex salt with a reducing agent, an organic component (organic component α) is added to the aqueous solution of the silver ammonia complex. The organic component α can contain at least one selected from fatty acid ethers, salts of fatty acid ethers, and benzotriazole. Adding organic component α before the reduction of silver can suppress aggregation of the silver powder after reduction and also allows the organic component α to be incorporated into the (A) conductive particles.

[0056] The organic component α is not particularly limited and can be appropriately selected depending on the purpose. The organic component can be added directly or as an aqueous solution in water. The amount of organic component α added is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.5% by mass or more and 1.0% by mass or less, based on the amount of silver to be reduced. If the amount of organic component α added is too small, the aggregation suppression effect cannot be obtained, while if the amount added is too large, the reduction of silver is inhibited, making it difficult to efficiently obtain silver particles.

[0057] Next, a reducing agent is added to the aqueous silver ammonia complex solution containing the organic component α to reduce and precipitate silver. The reducing agent is not particularly limited. Examples of reducing agents include formalin and hydrazine. It is preferable to use hydrazine as the reducing agent. By using a reducing agent, spherical silver powder with an appropriate particle size can be efficiently obtained. The amount of reducing agent added is preferably 1 equivalent or more relative to silver.

[0058] The silver powder obtained by reduction precipitation is recovered by filtration and washing. Pure water is preferably used as the washing liquid. There are no particular restrictions on the recovery and washing method. After washing, the silver powder is preferably dried using a hot air dryer or the like.

[0059] In this way, by reducing and precipitating silver from an aqueous solution of a silver ammonia complex containing the organic component α, it is possible to produce silver particles containing the organic component. By incorporating a predetermined amount of the organic component α into the (A) conductive particles, the above-described (A) conductive particles can be preferably used as a raw material for a conductive paste for forming solar cell electrodes. By using a conductive paste containing the above-described (A) conductive particles, it is possible to form an electrode (solar cell electrode) with low resistivity and reduced risk of breakage.

[0060] Next, an example of a method for surface treating the surface of particles (e.g., silver particles) made of a conductive component manufactured by the first manufacturing method, or the surface of conductive particles containing an organic component manufactured by the third manufacturing method, using an organic component (organic component β) will be described.

[0061] As an example of a method for surface treatment using an organic component β, a surface treatment agent containing an organic component is added to a slurry containing conductive particles, and the organic component contained in the surface treatment agent can be adsorbed onto the surfaces of the conductive particles. As described above, when silver is reduced and precipitated from an aqueous solution of a silver ammine complex containing an organic component (first organic component α), if a surface treatment agent containing a second organic component β is added during the reduction and precipitation of silver, the second organic component β is adsorbed onto the surfaces of the silver particles, thereby stopping the particle growth of the silver particles.

[0062] The surface treatment agent containing the organic component β is not particularly limited and can be appropriately selected depending on the purpose. The organic component β for surface treatment is particularly preferably stearic acid or ricinoleic acid.

[0063] The amount of the surface treatment agent containing the organic component β added is preferably 0.05% by weight to 3% by weight, more preferably 0.1% by weight to 1% by weight, based on the weight of the conductive component (for example, silver).

[0064] In this manner, the surface of particles (e.g., silver particles) made of a conductive component produced by the first manufacturing method, or the surface of conductive particles containing an organic component produced by the third manufacturing method, can be surface treated with an organic component.

[0065] The (A) conductive particles contained in the conductive paste of this embodiment contain a conductive component (e.g., silver) and two or more organic components, and when the conductive paste is used to form an electrode, an electrode with low resistivity can be obtained.

[0066] In the conductive paste of this embodiment, the organic component α preferably contains at least one selected from fatty acid ethers or salts thereof, and benzotriazole. These organic components are preferably contained inside the conductive particles manufactured by the above-mentioned first and third manufacturing methods. By using a predetermined organic component as the organic component, it is possible to more reliably obtain an electrode with low specific resistance. The fatty acid ether may be, for example, H 2m+1 C m -O-(CH2-CH2-O) n -H In this compound, "m" represents the number of carbon atoms in the alkyl group (12 to 15), and "n" represents the number of moles of ethylene oxide added.

[0067] In the conductive paste of this embodiment, the organic component β preferably contains a carboxylic acid, which is a compound containing a carboxyl group. The carboxylic acid is preferably at least one selected from the above-mentioned stearic acid and ricinoleic acid. In order to incorporate a carboxylic acid into the (A) conductive particles, it is preferable to use the second or third method for producing conductive particles containing an organic component described above. When the organic component β contains a carboxylic acid, the conductive particles are fused together during heating, thereby reducing the resistivity.

[0068] Examples of fatty acid ethers include palmitic acid ether, myristate ether, and oleic acid ether. The fatty acid ether or a salt thereof preferably contains at least one of palmitic acid ether, myristate ether, and oleic acid ether. The fatty acid ether or a salt thereof may contain multiple components selected from palmitic acid ether, myristate ether, oleic acid ether, and the like. When multiple components are contained, it is preferable that the palmitic acid ether component is present in a larger amount than the other components (for example, myristate ether, oleic acid ether, etc.).

[0069] In the conductive paste of this embodiment, the organic component preferably contains a carboxylic acid and at least one selected from a fatty acid ether or a salt thereof, and benzotriazole.

[0070] As described above, the carboxylic acid of the organic component is preferably at least one selected from stearic acid and ricinoleic acid. Furthermore, in order to incorporate the carboxylic acid into the (A) conductive particles, it is preferable to use the manufacturing method described in the second or third manufacturing method of the conductive particles containing an organic component (a manufacturing method for manufacturing conductive particles containing an organic component using raw materials containing a conductive component and an organic component). Therefore, it is preferable that the carboxylic acid, such as stearic acid or ricinoleic acid, is contained on the surface of the conductive particles.

[0071] As described above, it is preferable that at least one of the organic components selected from fatty acid ether or its salt and benzotriazole is contained inside the conductive particles. This step is included in the first and third manufacturing methods described above. Therefore, by using the third manufacturing method described above, it is more preferable that the (A) conductive particles contain a carboxylic acid, preferably at least one selected from stearic acid and ricinoleic acid, on the surface of the conductive particles, and contain at least one selected from fatty acid ether or its salt and benzotriazole inside the conductive particles. By including such (A) conductive particles in the conductive paste of this embodiment, it is possible to further ensure that an electrode with low specific resistance can be obtained.

[0072] According to this embodiment, a conductive paste can be obtained that has a low resistivity and can form electrodes with a reduced possibility of breakage.

[0073] The conductive particles may be, for example, spherical, flake-like, or needle-like. Conductive particles of different shapes may be mixed and used. Flake-like conductive particles may be produced, for example, by crushing spherical conductive particles using a ball mill or the like.

[0074] In the conductive paste of this embodiment, the (A) conductive particles preferably include spherical conductive particles (conductive particles having a spherical shape). Furthermore, the weight ratio of the spherical conductive particles in the (A) conductive particles is preferably 80 wt % or more, more preferably 90 wt % or more, even more preferably 95 wt % or more, and even more preferably 99 wt % or more. It is particularly preferable that the (A) conductive particles are substantially composed of spherical conductive particles. Compared to the use of scaly (flake) conductive particles, the use of spherical conductive particles can reduce the risk of electrode breakage. However, it is generally known that the use of spherical conductive particles results in high resistivity. As described above, the (A) conductive particles contained in the conductive paste of this embodiment contain a conductive component and two or more organic components. Therefore, despite the spherical shape of the (A) conductive particles contained in the conductive paste of this embodiment, an electrode can be formed that has low resistivity and reduced risk of breakage.

[0075] Furthermore, in the case of a conductive paste for forming an electrode with fine wiring (e.g., a wiring width of 20 to 60 μm), it is particularly preferable that the (A) conductive particles consist essentially of spherical conductive particles. The use of spherical conductive particles is advantageous for forming an electrode with fine wiring because the particle size is easier to control and there are fewer coarse particles than with flake silver.

[0076] The average particle diameter of the (A) conductive particles is preferably 0.05 μm to 15 μm, more preferably 0.1 μm to 5 μm, and even more preferably 0.2 μm to 3 μm. In this specification, the average particle diameter refers to the average particle diameter based on the number standard (average particle diameter at 50% of the cumulative value of all particles: D50) measured by laser diffraction / scattering particle size distribution measurement. When the average particle diameter of the conductive particles is within the above range, the surface condition of the electrodes and circuit patterns obtained by heating the conductive paste is improved. Furthermore, the electrical properties of the electrodes and circuit patterns obtained by heating the conductive paste are improved.

[0077] The conductive paste of this embodiment is characterized in that (A) the BET specific surface area of ​​the conductive particles is 0.3 to 3.5m 2 / g It is preferable that the ratio is 0.3 to 3 m 2 / g More preferably, it is 0.4 to 2.5 m 2 / g It is preferable to be Shii (A) By adjusting the BET specific surface area of ​​the conductive particles to an appropriate range, the electrical properties of the electrodes and circuit patterns obtained by heating the conductive paste are improved.

[0078] The content of the (A) conductive particles contained in the conductive paste of this embodiment is preferably 75 to 99 wt %, more preferably 80 to 96 wt %, and even more preferably 85 to 94 wt %, based on the total weight of the conductive paste.

[0079] <(B) Epoxy resin> The conductive paste of this embodiment contains (B) an epoxy resin.

[0080] Examples of epoxy resins include high molecular weight bisphenol A type epoxy resins, branched polyfunctional bisphenol A type epoxy resins such as p-glycidyloxyphenyldimethyltrisbisphenol A diglycidyl ether, bisphenol F type epoxy resins, biphenyl type epoxy resins such as diglycidylbiphenyl, novolac type epoxy resins, tetrabromobisphenol A type epoxy resins, tris(hydroxylphenyl)methane type epoxy resins, vinyl(3,4-cyclohexene) dioxide, 3,4-epoxycyclohexyl(3,4-epoxycyclohexyl)methyl carboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, 2-(3,4-epoxycyclohexyl)5,1-spiro(3,4-epoxycyclohexyl) Examples of epoxy resins include alicyclic epoxy resins such as 1,3-bis(3-glycidoxypropyl)-m-dioxane, glycidyl ester-type epoxy resins such as diglycidyl hexahydrophthalate, diglycidyl 3-methylhexahydrophthalate, and diglycidyl hexahydroterephthalate, glycidyl amine-type epoxy resins such as diglycidylaniline, diglycidyltoluidine, triglycidyl-p-aminophenol, tetraglycidyl-m-xylylenediamine, and tetraglycidylbis(aminomethyl)cyclohexane, hydantoin-type epoxy resins such as 1,3-diglycidyl-5-methyl-5-ethylhydantoin, and epoxy resins having a silicone skeleton such as 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane.

[0081] The (B) epoxy resin contained in the conductive paste of this embodiment preferably contains at least one selected from phenol novolac epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, and bisphenol A epoxy resins. The (B) epoxy resin preferably consists essentially of at least one selected from phenol novolac epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, and bisphenol A epoxy resins. By using a predetermined epoxy resin as the (B) epoxy resin, the thermosetting resin can be thermally cured at low temperatures (for example, 250°C or lower).

[0082] <(C) Hardener> The conductive paste of this embodiment includes a curing agent (C). The curing agent (C) preferably includes at least one selected from an imidazole-based curing agent and a boron trifluoride compound. Examples of the boron trifluoride compound include boron trifluoride monoethylamine, boron trifluoride piperidine, and boron trifluoride diethyl ether. In terms of resistivity and adhesive strength, it is particularly preferable to use boron trifluoride monoethylamine.

[0083] The (C) curing agent contained in the conductive paste of this embodiment preferably contains at least one selected from the group consisting of imidazoles of formula (1), formula (2), and formula (3). Formula (1) [ka] Formula (2) [ka] Formula (3) [ka]

[0084] The conductive paste of the present embodiment contains a curing agent (C) containing at least one imidazole selected from the group consisting of imidazoles of formula (1), formula (2), and formula (3), thereby making it possible to further reduce the resistivity of the resulting conductive film (e.g., an electrode for a solar cell).

[0085] The conductive paste of this embodiment preferably further contains a phenolic resin as a curing agent (C). By containing a phenolic resin in addition to the imidazole, the conductive paste of the present invention can be more reliably thermally cured at low temperatures (for example, 250°C or lower).

[0086] The phenolic resin is not particularly limited, but it is preferable to use, for example, a phenolic resin such as a resol type phenolic resin, an alkyl resol type phenolic resin, a novolac type phenolic resin, an alkyl novolac type phenolic resin, and / or an aralkyl novolac type phenolic resin.

[0087] In the conductive paste of this embodiment, the ratio of the weight of the (A) conductive particles to the total weight of the (B) epoxy resin and the (C) curing agent (weight of the (A) conductive particles:(total weight of the (B) epoxy resin and the (C) curing agent)) is preferably 98.5:1.5 to 93.0:7.0, and more preferably 98.4:1.6 to 93.5:6.5. By appropriately controlling the ratio of the weight of the (A) conductive particles to the total weight of the (B) epoxy resin and the (C) curing agent, it is possible to form an electrode with low resistivity and reduced possibility of disconnection.

[0088] The conductive paste of this embodiment preferably contains 0.1 to 5.0 parts by weight, more preferably 0.15 to 4.0 parts by weight, and even more preferably 0.2 to 3.5 parts by weight of (C) curing agent, when the total weight of (A) conductive particles and (B) epoxy resin is taken as 100 parts by weight. By setting the weight ratio of (C) curing agent within a predetermined range, (B) epoxy resin can be properly cured, and an electrode of the desired shape can be obtained.

[0089] <(D) Solvent> The conductive paste of this embodiment preferably further contains a solvent (D). By containing a solvent, the viscosity of the conductive paste can be set within an appropriate range, thereby improving screen printing performance.

[0090] Examples of solvents contained in the conductive paste of this embodiment include aromatic hydrocarbons such as toluene, xylene, mesitylene, and tetralin; ethers such as tetrahydrofuran; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; lactams such as 2-pyrrolidone and 1-methyl-2-pyrrolidone; ether alcohols such as ethyl glycol monophenyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether (butyl carbitol), and their corresponding propylene glycol derivatives; esters such as corresponding acetates (e.g., butyl carbitol acetate); and diesters such as methyl esters or ethyl esters of dicarboxylic acids such as malonic acid and succinic acid. Among these, at least one selected from ethylene glycol monophenyl ether and butyl carbitol acetate is preferably used.

[0091] In the conductive paste of this embodiment, the solvent (D) preferably contains ethylene glycol monophenyl ether or butyl carbitol acetate.

[0092] (D) By including ethylene glycol monophenyl ether or butyl carbitol acetate in the solvent, it is possible to more reliably obtain a conductive film (e.g., a solar cell electrode) with low resistivity. Furthermore, by using a specific solvent, the viscosity of the conductive paste can be more appropriately adjusted, thereby improving the printing characteristics of the printed conductive film. Specifically, when the conductive film pattern has a fine line shape, the line width can be made thin and uniform, the film thickness can be made uniform, and a shape with a high aspect ratio can be obtained.

[0093] When the conductive paste of this embodiment is applied to the surface of a transparent conductive film or the like by screen printing, the apparent viscosity of the conductive paste at room temperature is preferably 100 to 1000 Pa·s, more preferably 200 to 900 Pa·s, and even more preferably 300 to 800 Pa·s. The viscosity is measured using a Brookfield viscometer: HBD type (manufactured by Brookfield) at a rotation speed of 5 rpm (shear rate: 2 sec -1 ) and a value measured at a temperature of 25°C can be used. The viscosity of the conductive paste can be adjusted to a predetermined range by adjusting the amount of solvent (D) in the conductive paste.

[0094] <Other ingredients> The conductive paste of this embodiment may contain the following components in addition to the above-mentioned components (A), (B), (C), and (D).

[0095] The conductive paste of this embodiment may contain a thermosetting resin other than an epoxy resin. Examples of such thermosetting resins include amino resins such as urea resins, melamine resins, and guanamine resins; oxetane resins; phenolic resins such as resol-type phenolic resins, alkyl resol-type phenolic resins, novolac-type phenolic resins, alkyl novolac-type phenolic resins, and aralkyl novolac-type phenolic resins; silicone-modified resins such as silicone epoxy and silicone polyester; bismaleimide and polyimide resins.

[0096] The conductive paste of this embodiment may contain a thermoplastic resin, examples of which include novolac phenolic resin, allylphenolic resin, phenoxy resin, butyral resin, cellulose resin, acrylic resin, methacrylic resin, polyester resin, polyurethane resin, polyamide resin, thermoplastic xylene resin, hydroxystyrene polymer, cellulose derivative, and a mixture of two or more of these.

[0097] The conductive paste of this embodiment may further contain a phenolic resin as the thermosetting resin or thermoplastic resin. By further containing a phenolic resin, the conductive paste of this embodiment can more reliably thermally cure the thermosetting resin at low temperatures (for example, 250°C or lower).

[0098] The conductive paste of this embodiment preferably further contains a coupling agent (F), which improves the adhesion between the inorganic components, such as conductive particles, and the thermosetting resin.

[0099] The conductive paste of this embodiment may further contain at least one selected from the group consisting of an inorganic pigment, an organic pigment, a leveling agent, a thixotropic agent, and an antifoaming agent.

[0100] <Method of manufacturing conductive paste> The method for producing the conductive paste of this embodiment is not particularly limited. The conductive paste of this embodiment can be produced by adding the components in a predetermined ratio to a mixer such as a mixing machine, a propeller mixer, a kneader, a three-roll mill, or a pot mill, and mixing them.

[0101] The conductive paste of this embodiment can be applied to the surface of a transparent electrode, etc., by a known method such as screen printing. After the conductive paste is applied to the surface of a transparent electrode, etc., the conductive paste is heated to a predetermined temperature and cured, thereby forming a conductive film.

[0102] The heating temperature for thermally curing the conductive paste is preferably 250° C. or less, more preferably 200° C. or less, during electrode formation. Specifically, the heating temperature for thermally curing the conductive paste is preferably 100 to 250° C., more preferably 120 to 200° C., and even more preferably 150 to 200° C.

[0103] The thickness of the conductive paste applied to the surface of the transparent electrode or the like is preferably 5 to 40 μm, more preferably 10 to 30 μm, and even more preferably 15 to 20 μm.

[0104] The conductive paste of this embodiment can be preferably used to form solar cell electrodes with a wiring width of 20 to 60 μm. Therefore, solar cell electrodes obtained by heat-treating the conductive paste of this embodiment can include electrodes with a wiring width of 20 to 60 μm. The width (wiring width) of the conductive paste applied to the surface of a transparent electrode or the like is preferably 20 to 60 μm, more preferably 20 to 50 μm, and even more preferably 20 to 40 μm.

[0105] The conductive film obtained by heating the conductive paste of this embodiment has the characteristics of high adhesion strength to the substrate, low resistivity (high conductivity), and low contact resistance. Therefore, by using the thermosetting conductive paste of this embodiment, it is possible to form good electrodes for semiconductor devices and the like without the semiconductor devices and the like being deteriorated by high temperatures.

[0106] The conductive paste of this embodiment can be used to form electrodes and circuit patterns of semiconductor devices and electronic components, etc. The conductive paste of this embodiment can be used to form circuit patterns and electrodes not only on semiconductor substrates and ceramic substrates, but also on substrates with low heat resistance, such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate).

[0107] When an electrode is formed on the surface of a transparent conductive film such as an ITO thin film using the thermosetting conductive paste of this embodiment, low contact resistance can be obtained. In particular, when an electrode is formed on an ITO thin film, low contact resistance (for example, 8 mΩ cm 2 Therefore, the thermosetting conductive paste of this embodiment can be suitably used to form an electrode on the surface of a transparent conductive film, particularly a transparent electrode made of an ITO thin film.

[0108] The conductive paste of this embodiment can be preferably used as a conductive paste for forming solar cell electrodes. The conductive paste of this embodiment can be particularly preferably used as a conductive paste for forming electrodes for solar cells using thin-film materials such as amorphous silicon, for example, amorphous silicon solar cells, heterojunction solar cells, and compound semiconductor solar cells (CIS solar cells, CIGS solar cells, CdTe solar cells, etc.). Thin-film materials such as amorphous silicon are vulnerable to high temperatures. By using the conductive paste of this embodiment, electrodes can be formed at relatively low temperatures with low resistivity and reduced risk of breakage. The conductive paste of this embodiment can be particularly preferably used for forming electrodes for heterojunction solar cells with relatively high conversion efficiency, as shown in FIG. 1.

[0109] The conductive paste for forming solar cell electrodes of this embodiment is preferably heated at a temperature of 250°C or less, more preferably 200°C or less, during electrode formation. Forming the electrode at such a heat treatment temperature can suppress adverse effects on thin film materials that are susceptible to high temperatures. A cured product can be formed by heating the conductive paste. The solar cell electrode preferably contains a cured product of the conductive paste of this embodiment. According to this embodiment, a solar cell can be obtained that has an electrode with low resistivity and reduced risk of breakage. This can increase the conversion efficiency of the solar cell. [Example]

[0110] Examples and comparative examples of this embodiment will be described below.

[0111] [Conductive paste preparation] As examples and comparative examples, conductive pastes containing (A) conductive particles, (B) epoxy resin, (C) curing agent, and (D) solvent were produced. Tables 1 to 4 show the formulations of Examples 1 to 25 and Comparative Examples 1 to 6. The formulation ratios shown in Tables 1 to 4 are shown in parts by weight when the weight of the (A) conductive particles is taken as 100 parts by weight.

[0112] (A) Conductive particles As the conductive particles, conductive particles A to J shown in Table 5 were used in the formulations shown in Tables 1 to 4. The conductive component of all of the conductive particles A to J was silver.

[0113] For conductive particles A to D, a salt of fatty acid ether (organic component α) was incorporated into the silver particles during production, and spherical silver powder was used in which the surface of the silver particles was treated with stearic acid (organic component β).

[0114] Conductive particles E were similar to conductive particles A to D, but benzotriazole (organic component α) was used instead of the fatty acid ether salt, and ricinoleic acid (organic component β) was used instead of stearic acid.

[0115] The silver particles of the conductive particles F were spherical silver powders that did not contain any organic components inside and were not surface-treated.

[0116] The silver particles of conductive particle G do not contain any organic components inside, but are spherical silver powder whose surfaces have been treated with oleic acid. Therefore, the silver particles of conductive particle G contain one type of organic component.

[0117] Benzotriazole was used in the production of the silver particles of conductive particle H. Therefore, the silver particles of conductive particle H contain one type of organic component.

[0118] The silver particles of conductive particle I were manufactured in-house as flake silver powder, which contained no organic components and had their surfaces treated with oleic acid. Therefore, the silver particles of conductive particle I contained one type of organic component. The flake silver powder was prepared by stirring a mixture of 1,000 g of spherical silver powder, 20 g of oleic acid, and 100 g of ethanol in a pot mill for a specified period of time, and then filtering the mixture under suction with filter paper to remove the ethanol. The mixture was then dried for 24 hours in a dryer maintained at 60°C to produce flake silver powder.

[0119] The silver particles of Conductive Particle J were manufactured in-house using a fatty acid ether, but without surface treatment. Therefore, the silver particles of Conductive Particle J contain one organic component. The spherical silver powder was prepared by dissolving 150 g of silver nitrate in 6 liters of pure water, raising the temperature to 60°C while stirring, and then adding 40 ml of ammonia water to create a clear yellow complex salt solution. A polycarboxylic acid alkylamine salt was added to the complex salt solution, and 30 g of hydrazine was added while stirring to precipitate silver particles. The solution was repeatedly decanted with pure water and suction-filtered with filter paper to thoroughly remove moisture. The solution was then dried for 24 hours in a dryer maintained at 60°C to completely remove moisture, yielding spherical silver powder.

[0120] The type and content of the organic component contained in the conductive particles can be measured using a Fourier transform infrared spectrophotometer (FT-IR) and a gas chromatograph mass spectrometer (GC-MS).

[0121] (B) Epoxy resin As the epoxy resin, the following epoxy resins A and B were used in the formulations shown in Tables 1 to 4. Epoxy resin A: phenol novolac epoxy resin (model number: JER154, manufactured by Mitsubishi Chemical Corporation) Epoxy resin B: Bisphenol F epoxy resin (model number: EXA835LV, manufactured by DIC Corporation)

[0122] (C) Hardener As the curing agent, curing agents A to F shown in Table 6 were used in the formulations shown in Tables 1 to 4. Note that imidazole-based curing agents A to C are curing agents containing imidazole represented by the following chemical formula. Curing agent A (imidazole-based curing agent 1): Imidazole of the following formula (1) Formula (1) [ka] Curing agent B (imidazole-based curing agent 2): imidazole of the following formula (2) Formula (2) [ka] Curing agent C (imidazole-based curing agent 3): imidazole of the following formula (3) Formula (3) [ka] Hardener D: Boron trifluoride monoethylamine complex (hardener model number BF3 manufactured by Fujifilm (Wako)) Curing agent E: Allyl phenol resin (curing agent for model MEH8000H manufactured by Meiwa Kasei Co., Ltd.) Hardener F: Novolac phenolic resin (hardener of Gunei Chemical Industry Co., Ltd. model number PSM4324)

[0123] (D) Solvent As the solvent, the following two types of solvents A and B were used in the formulations shown in Tables 1 to 4. Solvent A: Ethylene glycol monophenyl ether Solvent B: Butyl carbitol acetate

[0124] [Resistivity measurement] The conductive pastes of Examples 1 to 25 and Comparative Examples 1 to 6 were heated to obtain conductive films, and the resistivities of the films were measured.

[0125] The resistivity of the examples and comparative examples was measured by the following procedure. A silicon substrate measuring 15 mm in width, 15 mm in length, and 180 μm in thickness was prepared. A pattern made of conductive paste as shown in Figure 2 was printed on this substrate using a 325-mesh stainless steel screen.

[0126] Next, the patterns made of the conductive pastes of the examples and comparative examples applied onto the substrate were heated at 200° C. for 30 minutes to obtain samples for measuring resistivity.

[0127] The resistivity of the conductive film patterns of the resistivity measurement samples obtained by heating the conductive pastes of the Examples and Comparative Examples was measured. First, the resistance value was measured by the four-terminal method using a Toyo Corporation multimeter model 2001. The cross-sectional area of ​​the pattern was measured using a Lasertec Corporation confocal microscope OPTELICS H1200 and a surface roughness and shape measuring instrument 1500SD2. Measurements were taken at 50 locations over a 1.6 mm range, and the average value was calculated. The resistivity was calculated using the cross-sectional area and the measured resistance value.

[0128] Four samples for measuring resistivity were prepared under the same conditions, and the measured value was calculated as the average value of the four. The measurement results are shown in Tables 1 to 4.

[0129] As is clear from Tables 1 to 4, the resistivity of the conductive films obtained using the conductive pastes of Examples 1 to 25 of this embodiment was 8.8 μΩ·cm (Example 4) or less. Generally, a conductive film with a resistivity of 10 μΩ·cm or less can be said to be suitable for use as an electrode. In contrast, the resistivity of the conductive films obtained using the conductive pastes of Comparative Examples 1 to 6 ranged from 11 μΩ·cm (Comparative Example 6) to 8684 μΩ·cm (Comparative Example 1). Therefore, it was clear that a lower resistivity could be obtained by forming a conductive film using the conductive pastes of Examples 1 to 25 of this embodiment.

[0130] [Evaluation of printing characteristics] The conductive pastes of the examples and comparative examples were printed on a silicon substrate with an ITO thin film formed on its surface using a screen printer to form a pattern with a width of 22 μm and a length of 46 mm. A stainless steel 360 mesh screen with an emulsion thickness of 17 μm was used for printing, and the printing conditions were as follows: clearance 1.5 mm, printing pressure 70 N, squeegee angle 65 degrees, and squeegee speed 250 mm / sec. The printed pattern was cured in a hot air dryer at 200°C for 45 minutes to obtain a printed pattern for shape measurement.

[0131] The printing characteristics were evaluated by measuring the shape of this printed pattern for shape measurement. The shape of the contact resistance measurement pattern was measured using a Lasertec OPTELICS H1200 confocal microscope and a 1500SD2 surface roughness and shape measuring instrument. Measurements were taken at 50 points over a 1.6 mm range, and any measurement point with a minimum film thickness of 3 μm or less was deemed to be a "disconnection."

[0132] As shown as "good" in Tables 1 to 4, the printing characteristics of the conductive pastes of Examples 1 to 25 and Comparative Examples 2 to 5 on the surface of the transparent conductive film (ITO thin film) were good even for fine wiring of 22 μm width and 46 mm length. However, in Comparative Examples 1 and 6, there were measurement points with a minimum film thickness of 3 μm or less, so they were judged to be "disconnected."

[0133] [Table 1]

[0134] [Table 2]

[0135] [Table 3]

[0136] [Table 4]

[0137] [Table 5]

[0138] [Table 6] [Explanation of symbols]

[0139] 10 Crystalline silicon substrate 12 i-type amorphous silicon layer 14a p-type amorphous silicon layer 14b n-type amorphous silicon layer 16 Transparent conductive film 18a Light incident side electrode 18b Back electrode

Claims

1. A conductive paste for forming an electrode of a solar cell, (A) conductive particles; (B) an epoxy resin; (C) a curing agent; Including, (A) The conductive particles contain a conductive component and two or more organic components, and the conductive component is silver; (C) the curing agent includes at least one selected from an imidazole-based curing agent and a boron trifluoride compound, the organic component comprises a fatty acid ether or a salt thereof; The conductive paste, wherein the organic component further comprises a carboxylic acid.

2. A conductive paste for forming an electrode of a solar cell, (A) conductive particles; (B) an epoxy resin; (C) a curing agent; Including, (A) The conductive particles contain a conductive component and two or more organic components, and the conductive component is silver; (C) the curing agent includes at least one selected from an imidazole-based curing agent and a boron trifluoride compound, the organic component includes one or more organic components α and one or more organic components β; The (A) conductive particles contain an organic component α inside the (A) conductive particles and an organic component β on the surface of the (A) conductive particles, the organic component α comprises at least one selected from a fatty acid ether, a salt of a fatty acid ether, and a benzotriazole; A conductive paste, wherein the organic component β includes a carboxylic acid.

3. The conductive paste according to claim 2 , wherein the organic component β comprises stearic acid or ricinoleic acid.

4. 4. The conductive paste according to claim 1, wherein the fatty acid ether or salt thereof comprises at least one selected from palmitic acid ether, myristate ether, and oleic acid ether.

5. The conductive paste according to any one of claims 1 to 4, wherein the conductive particles (A) have a BET specific surface area of ​​0.3 to 3.5 m 2 / g.

6. The conductive paste according to any one of claims 1 to 5, wherein the (A) conductive particles include spherical conductive particles, and the weight ratio of the spherical conductive particles in the (A) conductive particles is 80 wt% or more.

7. 7. The conductive paste according to claim 1, wherein the ratio of the weight of the (A) conductive particles to the total weight of the (B) epoxy resin and the (C) curing agent (weight of the (A) conductive particles:(total weight of the (B) epoxy resin and the (C) curing agent)) is 98.5:1.5 to 93.0:7.

0.

8. 8. The conductive paste according to claim 1, wherein the conductive paste contains 0.1 to 5.0 parts by weight of the curing agent (C) when the total weight of the conductive particles (A) and the epoxy resin (B) is 100 parts by weight.

9. The conductive paste according to any one of claims 1 to 8, further comprising (D) a solvent.

10. The conductive paste according to any one of claims 1 to 9, which is a conductive paste for forming an electrode of a solar cell having a wiring width of 20 to 60 µm.

11. A solar cell electrode comprising an electrode having a wiring width of 20 to 60 μm, the electrode being obtained by heat-treating the conductive paste according to any one of claims 1 to 10.

12. A solar cell, wherein an electrode of the solar cell comprises a cured product obtained by heat-treating the conductive paste according to any one of claims 1 to 10.

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