Conductive composition, conductive paste, cured product and solar cell

Abstract

The present invention provides a conductive composition for forming an electrode, which has a low specific resistance, at low temperatures.　The present invention provides a conducive composition which contains (A) conductive particles, (B) a solvent and (C) an epoxy resin, wherein: the concentration of easily saponifiable chlorine of the epoxy resin (C) is 1,600 ppm or more; and the amount of the epoxy resin (C) is 1.2 to 10 parts by weight relative to 100 parts by weight of the conductive particles (A).

Description

Conductive composition, conductive paste, cured product, and solar cell

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

[0002] Conductive pastes containing conductive particles such as 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 thermosetting conductive paste, Patent Document 1 describes a conductive paste for forming solar cell electrodes, which contains (A) a conductive component, (C) an epoxy resin, (C) imidazole, and (B) a solvent. Patent Document 1 also describes that the amount of imidazole (C) in the conductive paste is 0.1 to 1.0 wt %, where the conductive paste excluding the (B) solvent is 100 wt %.

[0005] As an example of a solar cell, Patent Document 2 describes a perovskite solar cell. The perovskite solar cell of Patent Document 2 comprises, on a substrate, a first electrode, an electron transport layer containing an electron transport compound and provided on the first electrode, a perovskite compound layer containing a perovskite compound and provided on the electron transport layer, a hole transport layer containing a hole transport compound and provided on the perovskite compound layer, and a second electrode provided on the hole transport layer. The perovskite compound included in the perovskite solar cell of Patent Document 2 is represented by the general formula: X α Y β M γ In the general formula, X represents a halogen atom, Y represents an alkylamine compound, M represents a mixture of lead and antimony, and the ratio of α:β:γ is 3:1:1. Patent Document 2 also describes that the metal oxide is any one of zinc oxide, tin oxide, titanium oxide, aluminum oxide, niobium oxide, yttrium oxide, and barium titanate.

[0006] JP 2019-102719 A JP 2015-191913 A

[0007] Thermosetting conductive pastes generally use epoxy resin as a binder, and generally require heat treatment at temperatures above 200°C to achieve both good adhesion and good electrical properties.

[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. By narrowing the width of the electrodes, the electrical resistance of the electrodes increases. Therefore, to obtain solar cells with high conversion efficiency, the specific resistance of the electrodes must be low. Furthermore, by narrowing the width of the electrodes, the contact area between the electrodes and the solar cell body becomes smaller. Therefore, to obtain solar cells with high conversion efficiency, it is necessary to reduce the contact resistance between the electrodes and the solar cell body.

[0009] In recent years, development of perovskite solar cells such as those described in Patent Document 2 has progressed. It is known that perovskite solar cells deteriorate in performance when heated because the perovskite compound layer is vulnerable to high temperatures. In order to suppress performance degradation of perovskite solar cells, the heating temperature during electrode formation must be 150°C or lower. Therefore, in the case of perovskite solar cells, it is necessary to form electrodes at a lower temperature (for example, 150°C or lower) than conventional ones.

[0010] Therefore, an object of the present invention is to provide a conductive composition for forming an electrode having low resistivity at a low temperature. Specifically, an object of the present invention is to provide a conductive composition for forming an electrode having low resistivity at a low temperature for a perovskite solar cell.

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

[0012] (Configuration 1) Configuration 1 is a conductive composition comprising (A) conductive particles, (B) a solvent, and (C) an epoxy resin, wherein the (C) epoxy resin has an easily saponifiable chlorine concentration of 1600 ppm or more, and the (C) epoxy resin is present in an amount of 1.2 to 10 parts by weight per 100 parts by weight of the (A) conductive particles.

[0013] (Configuration 2) Configuration 2 is the conductive composition of Configuration 1, in which the (A) conductive particles include conductive particles A1 and conductive particles A2, and the average particle size of the conductive particles A2 is larger than the average particle size of the conductive particles A1.

[0014] (Configuration 3) Configuration 3 is the conductive composition of configuration 2, in which the conductive particles A2 have an average particle size of 1.5 to 4.5 μm.

[0015] (Configuration 4) Configuration 4 is the conductive composition of configuration 2 or 3, in which the conductive particles A1 have an average particle size of 0.05 to 1.4 μm, and the conductive particles A2 have an average particle size of 2.0 to 3.5 μm.

[0016] (Configuration 5) Configuration 5 is the conductive composition of any one of Configurations 2 to 4, containing 0 to 40 wt % of the conductive particles A1 and 40 to 90 wt % of the conductive particles A2 relative to 100 wt % of the (A) conductive particles.

[0017] (Configuration 6) In Configuration 6, the BET specific surface area of ​​the conductive particles A1 is 0.3 to 3.5 m ２ / g.

[0018] (Configuration 7) In Configuration 7, the BET specific surface area of ​​the conductive particles A2 is 0.1 to 0.4 m ２ / g.

[0019] (Configuration 8) Configuration 8 is the conductive composition of any one of configurations 2 to 7, in which the conductive particles A1 and the conductive particles A2 are spherical conductive particles.

[0020] (Configuration 9) Configuration 8 is the conductive composition of any one of Configurations 1 to 8, wherein the conductive composition further comprises (D) a curing agent.

[0021] (Configuration 10) Configuration 10 is the conductive composition of configuration 9, wherein the (D) curing agent comprises a compound having a structure of formula (a):

[0022] (Configuration 11) Configuration 11 is a conductive paste for forming an electrode of a solar cell, comprising the conductive composition of any one of Configurations 1 to 10.

[0023] (Configuration 12) Configuration 12 is a conductive paste for forming an electrode of a perovskite solar cell, including the conductive paste of configuration 11.

[0024] (Configuration 13) Configuration 13 is a cured product of the conductive composition of any one of Configurations 1 to 10, or the conductive paste of Configuration 11 or 12.

[0025] (Configuration 14) Configuration 14 is a solar cell comprising the cured product of configuration 13.

[0026] According to the present invention, it is possible to provide a conductive composition for forming an electrode having low resistivity at a low temperature. Specifically, according to the present invention, it is possible to provide a conductive composition for forming an electrode having low resistivity at a low temperature for a perovskite solar cell.

[0027] Fig. 1 is a cross-sectional view showing an example of a perovskite solar cell; Fig. 2 is a cross-sectional view showing an example of a tandem solar cell including a perovskite solar cell; Fig. 3 is a plan view showing a resistivity measurement pattern for an electrode formed using a conductive composition (conductive paste); Fig. 4 is a plan view showing a contact resistance measurement pattern for an electrode formed using a conductive composition (conductive paste).

[0028] Hereinafter, embodiments of the present invention will be described in detail. Note that the following embodiments are forms for realizing the present invention, and are not intended to limit the scope of the present invention.

[0029] The conductive composition of this embodiment is a thermosetting conductive composition. The conductive composition of this embodiment contains predetermined components, and therefore can be thermally cured at low temperatures (for example, 150°C or less) to form an electrode. The conductive composition of this embodiment can be used as a conductive paste. By using the conductive composition (conductive paste) of this embodiment, a conductive film (electrode) with low specific resistance can be formed. The conductive composition of this embodiment can be preferably used as a conductive paste for forming electrodes for solar cells. The conductive composition of this embodiment can be preferably used as a conductive paste for forming electrodes for perovskite solar cells in particular.

[0030] In this specification, the term "conductive film" refers to a thin film pattern formed by printing or the like a conductive composition (conductive paste) on the surface of a predetermined substrate or the like to form a pattern of a predetermined shape, followed by curing. The predetermined shape pattern includes any shape, such as a linear, dotted, or planar pattern. The conductive film can be used as an electrode.

[0031] Next, the conductive composition of this embodiment will be described.

[0032] The conductive paste for forming a solar cell electrode of this embodiment contains (A) conductive particles, (B) a solvent, and (C) an epoxy resin. The conductive paste of this embodiment may further contain (D) a curing agent and other additives. Each component contained in the conductive paste of this embodiment will be described below.

[0033] <(A) Conductive Particles> The conductive composition of the present embodiment contains (A) conductive particles.

[0034] 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 easy 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. Therefore, the (A) conductive particles are preferably composed solely of silver particles.

[0035] In the (A) conductive particles, the phrase "the conductive component is composed only of silver" means that the conductive component is substantially entirely composed of silver, excluding unavoidably present impurities. In other words, when the conductive component is composed 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.

[0036] The preferred average particle size of the (A) conductive particles is 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 size refers to the average particle size based on the number standard (D50: average particle size at 50% of the cumulative value of all particles) measured by laser diffraction / scattering particle size distribution measurement. When the average particle size of the conductive particles is within the above range, the surface condition of the electrodes and circuit patterns obtained by heating the conductive composition (conductive paste) is improved. Furthermore, the electrical properties of the electrodes and circuit patterns obtained by heating the conductive composition (conductive paste) can be improved.

[0037] In the conductive composition of this embodiment, the (A) conductive particles preferably include conductive particles A1 and conductive particles A2, and the average particle size of the conductive particles A2 is larger than the average particle size of the conductive particles A1. The (A) conductive particles contained in the conductive composition of this embodiment include two types of conductive particles A1 and A2 having predetermined average particle sizes, so that the conductive composition of this embodiment can be used to form an electrode with low specific resistance. Furthermore, the (A) conductive particles include two types of conductive particles A1 and A2 having predetermined average particle sizes, so that the contact resistance (sometimes simply referred to as "contact resistance") between a conductive film (electrode) formed using the conductive composition and a substrate can be reduced.

[0038] In the conductive composition of this embodiment, the conductive particles A2 preferably have an average particle size of 1.5 to 4.5 μm, and more preferably 2.0 to 3.5 μm. When the average particle size of the conductive particles A2 is within the specified range, a conductive composition for forming an electrode with low specific resistance and contact resistance at low temperatures can be more reliably obtained.

[0039] In the conductive composition of this embodiment, the conductive particles A1 preferably have an average particle size of 0.05 to 1.4 μm, and the conductive particles A2 preferably have an average particle size of 2.0 to 3.5 μm. The average particle size of the conductive particles A1 is more preferably 0.1 to 1.0 μm, and even more preferably 0.2 to 0.8 μm. The average particle size of the conductive particles A2 is more preferably 2.2 to 3.3 μm, and even more preferably 2.4 to 3.0 μm. By having the average particle sizes of the conductive particles A1 and A2 both within the specified ranges, it is possible to more reliably obtain a conductive composition for forming an electrode with low specific resistance and contact resistance at low temperatures.

[0040] The conductive composition of this embodiment may further contain, as the conductive particles (A), conductive particles A3 having an average particle size of 0.6 to 1.4 μm. By including the conductive particles A3 in the conductive composition in addition to the conductive particles A1 and A2, it is possible to further ensure the formation of an electrode having low specific resistance and contact resistance at low temperatures.

[0041] In order to obtain an electrode with a lower specific resistance, it is preferable that the conductive particles A1, A2 and A3 are all silver particles.

[0042] The particle size of conductive particles generally exhibits a distribution similar to a normal distribution. (A) When two types of conductive particles A1 and A2 with different average particle sizes are present among the conductive particles, two normal distributions corresponding to the particle size distributions of the conductive particles A1 and A2 will exist. Therefore, when two types of conductive particles A1 and A2 are mixed, the particle size distribution can be measured using laser diffraction / scattering particle size distribution measurement, and the peaks corresponding to the two types of conductive particles A1 and A2 can be assumed to be normal distributions and separated to measure the average particle size (D50) of the two types of conductive particles A1 and A2. Furthermore, when two types of conductive particles A1 and A2 with different average particle sizes are present, the particle size distribution measured using laser diffraction / scattering particle size distribution measurement can have two peaks that can be separated. Similarly, when three types of conductive particles A1, A2, and A3 are present, the particle size distribution measured using laser diffraction / scattering particle size distribution measurement can have three peaks that can be separated.

[0043] The conductive composition of this embodiment preferably contains 0 to 40 wt %, more preferably 10 to 35 wt %, and even more preferably 15 to 30 wt % of conductive particles A1 per 100 wt % of the (A) conductive particles. Furthermore, the conductive composition of this embodiment preferably contains 40 to 90 wt %, more preferably 50 to 85 wt %, and even more preferably 60 to 80 wt % of conductive particles A2 per 100 wt % of the (A) conductive particles. By ensuring that the contents of conductive particles A1 and A2 in the (A) conductive particles are within the specified ranges, a conductive composition for forming electrodes with low resistivity and contact resistance at low temperatures can be more reliably obtained.

[0044] 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.

[0045] Furthermore, in the case of a conductive composition (conductive paste) for forming an electrode with fine wiring (e.g., a wiring width of 20 to 60 μm), it is preferable that both the conductive particles A1 and A2 are spherical conductive particles, and it is particularly preferable that the (A) conductive particles consist essentially of spherical conductive particles. By using spherical conductive particles with different average particle sizes, it is possible to further ensure the formation of an electrode with low specific resistance and contact resistance at low temperatures. Furthermore, since spherical conductive particles are easier to control the particle size of and contain fewer coarse particles than flake-shaped silver particles, the use of spherical conductive particles makes it possible to advantageously form an electrode with fine wiring.

[0046] The conductive composition of this embodiment is a conductive particle having a BET specific surface area of ​​0.3 to 3.5 m ２ / g, and 0.3 to 3m ２ / g, and more preferably 0.4 to 2.5 m ２ By setting the BET specific surface area of ​​the (A) conductive particles within an appropriate range, the electrical properties of the electrodes and circuit patterns obtained by heating the conductive composition (conductive paste) are improved.

[0047] In the conductive composition of this embodiment, the BET specific surface area of ​​the conductive particles A1 is 0.3 to 3.5 m ２ / g, and 0.5 to 3.0 m ２ / g, and more preferably 1.0 to 2.5m ２ In the conductive composition of this embodiment, the BET specific surface area of ​​the conductive particles A2 is preferably 0.1 to 0.4 m / g. ２ / g, and 0.15 to 0.35 m ２ / g, and more preferably 0.2 to 0.3 m ２ When the BET specific surface areas of the conductive particles A1 and A2 are within the predetermined range, a conductive composition for forming an electrode having low specific resistance and contact resistance at low temperature can be more reliably obtained.

[0048] The tap density of the conductive particles is 2.0 to 8.0 g / cm ３ is preferably 2.5 to 7.0 g / cm３ More preferably, it is 3.0 to 6.5 g / cm ３ When the tap density is in this range, an electrode having sufficient conductivity can be formed.

[0049] The method for producing conductive particles (e.g., silver particles) made of a conductive component is not particularly limited, and examples of the method that can be used include a reduction method, a pulverization method, an electrolysis method, an atomization method, a heat treatment method, and a combination thereof.

[0050] The (A) conductive particles are preferably surface-treated so that the surfaces of the conductive particles contain a carboxylic acid, preferably at least one selected from stearic acid and oleic acid.

[0051] When the (A) conductive particles contain a predetermined organic substance, the conductive composition of this embodiment preferably contains 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 containing an organic component are essentially 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. On the other hand, it is generally known that the use of spherical conductive particles results in a relatively high resistivity. When the (A) conductive particles contain a predetermined organic component due to surface treatment or the like, an electrode can be formed that has low resistivity and a reduced risk of breakage, despite the spherical shape of the (A) conductive particles.

[0052] The content of the (A) conductive particles in the conductive composition of the present embodiment is preferably 75 to 99 wt %, more preferably 80 to 96 wt %, and even more preferably 85 to 95 wt %, based on the total weight of the conductive composition.

[0053] <(B) Solvent> The conductive composition of the present embodiment preferably further contains a solvent (B). By containing a solvent in the conductive composition, the viscosity of the conductive composition (conductive paste) can be set within an appropriate range, and the screen printing performance can be improved.

[0054] Examples of solvents contained in the conductive composition 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 corresponding propylene glycol derivatives; esters such as corresponding acetates (e.g., diethylene glycol monobutyl ether acetate); and diesters such as methyl esters and ethyl esters of dicarboxylic acids such as malonic acid and succinic acid. Among these, at least one selected from ethylene glycol monophenyl ether, diethylene glycol monobutyl ether, and butyl carbitol acetate is preferably used.

[0055] The conductive composition of this embodiment preferably contains ethylene glycol monophenyl ether, diethylene glycol monobutyl ether (butyl carbitol) and / or diethylene glycol monobutyl ether acetate (butyl carbitol acetate) as the solvent (B).

[0056] By including ethylene glycol monophenyl ether, diethylene glycol monobutyl ether (butyl carbitol), and / or diethylene glycol monobutyl ether acetate (butyl carbitol acetate) in the (B) solvent, it is possible to more reliably obtain a conductive film (e.g., a solar cell electrode) with low specific resistance. Furthermore, by using a specific solvent, the viscosity of the conductive composition (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.

[0057] When the conductive composition (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 composition (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. By adjusting the blending amount of the (B) solvent in the conductive composition (conductive paste), the viscosity of the conductive composition (conductive paste) can be adjusted to a predetermined range.

[0058] <(C) Epoxy Resin> The conductive composition of the present embodiment contains (C) an epoxy resin.

[0059] The epoxy resin (C) contained in the conductive composition of this embodiment has an easily saponifiable chlorine concentration of 1600 ppm or more. The conductive composition of this embodiment contains 1.2 to 10 parts by weight of the epoxy resin (C) per 100 parts by weight of the conductive particles (A).

[0060] The present inventors have found that when the epoxy resin (C) contained in the conductive composition of this embodiment has a low easily saponifiable chlorine concentration, when the conductive composition is heat-treated at a low temperature (e.g., 150°C or lower) to form an electrode, the resistivity of the conductive film (electrode) formed using the conductive composition increases. Based on this finding, the present inventors further investigated the relationship between the easily saponifiable chlorine concentration of the epoxy resin (C) and the resistivity of the conductive film (electrode). As a result, they have found that by including a predetermined amount of epoxy resin (C) having an easily saponifiable chlorine concentration of 1600 ppm or more, an electrode having a resistivity suitable for use as an electrode for solar cells (particularly perovskite solar cells) can be formed by heat-treatment at a low temperature (e.g., 150°C or lower).

[0061] Easily saponifiable chlorine is generated as an impurity in the production process of epoxy resins, as described below. Easily saponifiable chlorine is not usually generated in the production processes of thermosetting resins such as (meth)acrylates, bismaleimides, phenolic resins, and silicone resins.

[0062] As described above, the content of the (C) epoxy resin in the conductive composition is 1.2 to 10 parts by weight per 100 parts by weight of the (A) conductive particles. The content of the (C) epoxy resin can be adjusted appropriately depending on the easily saponifiable chlorine concentration of the (C) epoxy resin. The (C) epoxy resin may be any resin as long as it has an easily saponifiable chlorine concentration of 1600 ppm or more. When the conductive composition contains two or more types of (C) epoxy resins, an epoxy resin having an easily saponifiable chlorine concentration of less than 1600 ppm and an epoxy resin having a high easily saponifiable chlorine concentration can be used in combination to adjust the total easily saponifiable chlorine concentration of the (C) epoxy resins to 1600 ppm or more.

[0063] "Readily saponifiable chlorine" refers to "chlorine species that exist as 1,2-chlorohydrin, which is generated when dehydrochlorination is incomplete." Examples of readily saponifiable chlorine include 1,2-chlorohydrin, 1,3-chlorohydrin, and 1-chloromethyl-2-glycidyl ether (chloromethyl) forms. Readily saponifiable chlorine is usually generated as an impurity in the production process of epoxy resins.

[0064] Examples of 1,2-chlorohydrin compounds include compounds represented by general formula (1). Examples of 1,3-chlorohydrin compounds include compounds represented by general formula (2). Examples of chloromethyl compounds include compounds represented by general formula (3). In the following general formulas (1) to (3), R1, R2, R3, and R4 each independently represent a hydrogen atom or a methyl group. n is an integer of 0 to 30, preferably 0 to 20, and more preferably 0 to 10.

[0065]

[0066]

[0067]

[0068] The type of (C) epoxy resin is not particularly limited, and known epoxy resins can be used. Examples of (C) epoxy resins include bisphenol A type, bisphenol F type, biphenyl type, tetramethylbiphenyl type, cresol novolac type, phenol novolac type, bisphenol A novolac type, dicyclopentadiene phenol condensation type, phenol aralkyl condensation type, and glycidylamine type epoxy resins, as well as brominated epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. These epoxy resins can be used alone or in combination of two or more.

[0069] An example of the epoxy resin (C) is "AK-601 (trade name)" manufactured by Nippon Kayaku Co., Ltd. The readily saponifiable chlorine concentration of "AK-601" is about 6000 ppm. The readily saponifiable chlorine concentration mentioned above is an actually measured value, and the measurement method will be described later. These epoxy resins can be used alone or in combination of two or more.

[0070] Although known epoxy resins can be used as the epoxy resin (C), an epoxy resin that is liquid at room temperature is preferred. Furthermore, among epoxy resins that are liquid at room temperature, it is preferred that the epoxy resin (C) contains a compound having the structure of the following formula (4). The compound having the structure of formula (4) is diglycidyl 1,2-cyclohexanedicarboxylate. By containing a compound having the structure of formula (4), it is possible to more reliably form an electrode with low resistivity by heat treatment at a low temperature (for example, 150°C or lower).

[0071] The easily saponifiable chlorine concentration of the (C) epoxy resin is 1600 ppm or more. The easily saponifiable chlorine concentration of the (C) epoxy resin is preferably 2000 to 50,000 ppm, more preferably 2500 to 30,000 ppm, even more preferably 3000 to 25,000 ppm, and particularly preferably 3200 to 23,000 ppm. If the easily saponifiable chlorine concentration is lower than a predetermined concentration, the specific resistance of the conductive film (electrode) formed by heat treatment at a low temperature (e.g., 150°C or less) increases. If the easily saponifiable chlorine concentration is higher than a predetermined concentration, the contact resistance between the conductive film (electrode) formed by heat treatment at a low temperature (e.g., 150°C or less) and the conductive layer of the substrate (e.g., a transparent conductive film such as ITO) increases. Furthermore, from the viewpoint of lowering both the specific resistance and contact resistance by heat treatment at low temperatures, the easily saponifiable chlorine concentration of the epoxy resin is preferably 3,000 to 10,000 ppm, more preferably 4,000 to 9,000 ppm, and even more preferably 5,000 to 8,000 ppm. In particular, in order to form an electrode having a specific resistance and contact resistance suitable for use as an electrode for a solar cell (particularly a perovskite solar cell) at a low temperature (e.g., 150°C or less), the easily saponifiable chlorine concentration of the (C) epoxy resin is preferably within the above-mentioned predetermined range. Furthermore, when the conductive composition contains two or more types of (C) epoxy resins, it is preferable that the total easily saponifiable chlorine concentration of the epoxy resins be within the above-mentioned predetermined range.

[0072] In the conductive composition of this embodiment, the weight ratio of the (C) epoxy resin to 100 parts by weight of the (A) conductive particles is 1.2 to 10 parts by weight. The weight ratio of the (C) epoxy resin to 100 parts by weight of the (A) conductive particles is preferably 1.3 to 9 parts by weight, more preferably 1.4 to 8 parts by weight, and even more preferably 1.5 to 7.5 parts by weight. Note that if the weight ratio of the (C) epoxy resin to 100 parts by weight of the (A) conductive particles exceeds 10 parts by weight, the amount of the (C) epoxy resin relative to the (A) conductive particles becomes too large, which may lead to sintering inhibition. On the other hand, if the mass ratio of the (C) epoxy resin to 100 parts by weight of the (A) conductive particles is less than 1.2 parts by weight, it may be difficult to maintain the strength of the electrode.

[0073] The following method can be used to measure the easily saponifiable chlorine concentration of epoxy resin (C). First, 25 mL of 2-butanone is added to 1 g of epoxy resin (C) to be measured and dissolved. Next, 25 mL of 2-butoxyethanol is further added to the resulting solution. Next, 25 mL of 1 mol / L sodium hydroxide solution is added to the resulting solution and mixed. Next, the resulting solution is left at room temperature (25°C) for 60 minutes. Next, 25 mL of acetic acid is further added to the solution that has been left for 60 minutes and mixed to obtain a sample solution. Then, a silver electrode for measuring potentiometry is immersed in the resulting sample solution, and potentiometric titration is performed with 0.01 mol / L silver nitrate solution to determine the easily saponifiable chlorine concentration of epoxy resin (C) to be measured.

[0074] <(D) Curing Agent> The conductive composition of the present embodiment preferably further contains a (D) curing agent. By containing the (D) curing agent, it is possible to appropriately control the curing of the (C) epoxy resin.

[0075] The curing agent (D) may be a known curing agent. The curing agent (D) preferably includes at least one selected from a phenolic curing agent, a cationic polymerization initiator, an imidazole 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.

[0076] The conductive composition of this embodiment preferably contains a compound having a structure of formula (a) as the curing agent (D). The compound having the structure of formula (a) is a cationic polymerization initiator. When the curing agent (D) is a compound having a structure of formula (a), it is possible to more reliably form an electrode having a low specific resistance by heat treatment at a low temperature (for example, 150°C or less). Formula (a)

[0077] The conductive composition of this embodiment preferably contains a compound having a structure of formula (b) as a curing agent (D). The compound having a structure of formula (b) is a liquid phenolic resin. When the curing agent (D) is a compound having a structure of formula (b), it is possible to more reliably form an electrode having a low specific resistance by heat treatment at a low temperature (for example, 150°C or less). Formula (b) (wherein n is 0 to 3, and R1 to R5 are hydrogen atoms, hydroxyl groups, or allyl groups.)

[0078] In the conductive composition of this embodiment, the ratio of the weight of the (A) conductive particles to the total weight of the (C) epoxy resin and the (D) curing agent (weight of the (A) conductive particles:total weight of the (C) epoxy resin and the (D) curing agent) is preferably 98.5:1.5 to 90.0:10.0, and more preferably 98.0:2.0 to 92.0:8.0. By appropriately controlling the ratio of the weight of the (A) conductive particles to the total weight of the (C) epoxy resin and the (D) curing agent, it is possible to form an electrode with low resistivity and reduced possibility of breakage.

[0079] In the conductive composition of this embodiment, when the total weight of the (A) conductive particles and the (C) epoxy resin is taken as 100 parts by weight, the conductive composition preferably contains 0.1 to 5.0 parts by weight, more preferably 0.15 to 3.5 parts by weight, and even more preferably 0.2 to 2.0 parts by weight of the (D) curing agent. By setting the weight ratio of the (D) curing agent within a predetermined range, the (C) epoxy resin can be appropriately cured, and an electrode of the desired shape can be obtained.

[0080] <Other Components> The conductive composition of the present embodiment may contain the following components in addition to the above-described components (A), (B), (C), and (D).

[0081] The conductive composition 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, alkylresol-type phenolic resins, novolac-type phenolic resins, alkylnovolac-type phenolic resins, and aralkylnovolac-type phenolic resins; silicone-modified resins such as silicone epoxy and silicone polyester; bismaleimide and polyimide resins.

[0082] The conductive composition of this embodiment may contain (C) a thermoplastic resin other than an epoxy resin. Examples of (C) a thermoplastic resin other than an epoxy resin include novolac phenolic resins, allylphenolic resins, phenoxy resins, butyral resins, cellulose resins, acrylic resins, methacrylic resins, polyester resins, polyurethane resins, polyamide resins, thermoplastic xylene resins, hydroxystyrene polymers, cellulose derivatives, and mixtures of two or more of these.

[0083] The conductive composition of the present embodiment preferably further contains (E) a phenoxy resin. By further containing a phenoxy resin, the conductive composition of the present embodiment can more reliably thermally cure the thermosetting resin at low temperatures (for example, 150°C or lower).

[0084] The conductive composition of this embodiment preferably further contains a coupling agent (F). A silane coupling agent can be used as the coupling agent (F). By further containing the coupling agent (F), the conductive composition can improve the adhesion between inorganic components such as conductive particles and the thermosetting resin.

[0085] The conductive composition of the present 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.

[0086] <Conductive Paste> The conductive paste of this embodiment includes the conductive composition of this embodiment described above. The conductive composition of this embodiment can be used as a conductive paste. By using the conductive paste (conductive composition) of this embodiment, an electrode with low resistivity can be formed at a low temperature. Therefore, the conductive composition of this embodiment can be preferably used as a conductive paste (conductive composition) for forming an electrode of a solar cell.

[0087] The conductive paste of this embodiment can be preferably used as a conductive paste for forming electrodes of perovskite solar cells, because electrode formation for perovskite solar cells needs to be carried out at a low temperature (for example, 150°C or lower) to avoid deterioration of the perovskite compound layer due to heating.

[0088] 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 of the conductive composition of this embodiment in a predetermined ratio to a mixer such as a mortar and pestle mixer, a propeller mixer, a kneader, a three-roll mill, or a pot mill, and mixing them.

[0089] 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 (electrode).

[0090] In this specification, the conductive film, electrode, etc. obtained by heating the conductive composition of this embodiment or the conductive paste of this embodiment to a predetermined temperature and curing it is referred to as a "cured product." The cured product of this embodiment is a cured product of the above-mentioned conductive composition or the above-mentioned conductive paste. The cured product of this embodiment can be preferably used as an electrode for a solar cell (e.g., an electrode for a perovskite solar cell).

[0091] The cured product of this embodiment is preferably a cured product obtained by applying a conductive composition or a conductive paste to the surface of a transparent conductive film and curing the composition or paste at 110° C. for 45 minutes. The specific resistance of the solar cell electrode is preferably, for example, 15 μΩ cm or less, more preferably 12 μΩ cm or less, and even more preferably 10 μΩ cm or less. The cured product of this embodiment is preferably a cured product in which the contact resistance between the cured product (e.g., electrode) and the transparent conductive film is, for example, 65 mΩ cm. ２ and 60 mΩ cm or less. ２ Preferably, it is 30 mΩ cm or less. ２ More preferably, it is 20 mΩ cm or less. ２ More preferably, it is 10 mΩ cm or less. ２ It is more preferable that the following conditions are satisfied: Since the electrode that is the cured product of this embodiment has such properties, it can be preferably used as an electrode for a perovskite solar cell.

[0092] The heat treatment temperature for thermally curing the conductive paste (heat treatment temperature when forming an electrode for a solar cell) is preferably 150°C or less, and more preferably 130°C or less, in the case of a conductive paste for forming an electrode for a perovskite solar cell. Specifically, the heat treatment temperature for thermally curing the conductive paste is preferably 100 to 150°C, and more preferably 100 to 130°C. The heat treatment time is preferably 20 to 60 minutes, and more preferably 25 to 45 minutes. A specific example of the heat treatment conditions is 110°C for 45 minutes.

[0093] 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.

[0094] 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 heat-treated with 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.

[0095] 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.

[0096] 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).

[0097] 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 / or holes in a semiconductor, and has electrodes for direct or indirect electrical connection to the semiconductor.

[0098] Electrodes of semiconductor devices may need to transmit light. Transparent conductive films are used as the material for such electrodes. Electrodes made of transparent conductive films are called transparent electrodes. Transparent electrodes are used in flat panel displays such as liquid crystal displays (LCDs) and plasma display panels (PDPs), as well as in semiconductor devices such as various solar cells. Solar cells include perovskite solar cells, amorphous silicon solar cells, and compound semiconductor solar cells (CIS (CuInSe ２ Examples of such solar cells include thin-film solar cells such as perovskite (CIGS) solar cells, copper indium gallium selenide (CIGS) solar cells, and CdTe solar cells, heterojunction solar cells, and crystalline silicon solar cells. Transparent electrodes are used in the formation of electrodes for flat panel displays, thin-film solar cells including perovskite solar cells, and heterojunction solar cells.

[0099] 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 referred to as "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. Finger-shaped or grid-shaped electrodes (sometimes simply referred to as "electrodes") are formed to electrically connect to the transparent electrode so as not to interfere with the incidence of light into or the emission of light from the semiconductor device. The conductive composition (conductive paste) of this embodiment can be used to form finger electrodes (finger-shaped or grid-shaped electrodes) on the surface of the transparent electrode.

[0100] Depending on the type of semiconductor material of the semiconductor device, the type of material of the electronic component, and the type of non-semiconductor materials constituting the semiconductor device and electronic component, etc., high temperatures, for example, temperatures exceeding 150°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 an electrode with low resistivity at low temperatures (for example, 150°C or lower). By using the conductive paste of this embodiment, it is possible to form an electrode with a predetermined low resistance without causing deterioration of the semiconductor device due to high temperatures. Therefore, the conductive composition of this embodiment can be preferably used, particularly as a conductive paste for forming electrodes for perovskite solar cells.

[0101] When an electrode is formed on a transparent conductive film using the conductive composition (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, 70 mΩ cm ２ The conductive paste of this embodiment can be used to form electrodes (particularly finger electrodes) on transparent conductive films, particularly ITO thin films, with relative ease. The conductive paste of this embodiment can be used particularly preferably as a conductive paste for forming electrodes to be placed on the surface of a transparent conductive film of a perovskite solar cell.

[0102] <Solar Cell> This embodiment relates to a solar cell including a cured product of the above-described conductive composition or conductive paste. The cured product can be an electrode of the solar cell. By using the conductive composition or conductive paste of this embodiment, a solar cell electrode with low resistivity can be formed at a low temperature. Therefore, it is possible to suppress adverse effects on the solar cell caused by high temperatures during heat treatment in electrode formation.

[0103] 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. In particular, in order to suppress deterioration of the perovskite compound layer of a perovskite solar cell, the heating temperature during electrode formation must be 150°C or less. The conductive paste of this embodiment can be preferably used to form an electrode on the surface of a transparent conductive film of such a solar cell with low heat resistance. By using the conductive paste of this embodiment, an electrode for a perovskite solar cell with low specific resistance can be formed.

[0104] A perovskite solar cell, which is a preferred application of the conductive paste of this embodiment, will be described with reference to FIG.

[0105] FIG. 1 shows a schematic cross-sectional view of an example of a perovskite solar cell 10. The perovskite solar cell 10 shown in FIG. 1 includes a metal oxide layer 16 serving as an electron transport layer, a perovskite compound layer 15, a hole transport layer 14, and a first electrode 13 stacked in this order on one surface of a second electrode 17. Furthermore, the perovskite solar cell 10 shown in FIG. 1 includes finger electrodes 18 on the surface of the first electrode 13, which is a transparent conductive film. The conductive composition (conductive paste) of this embodiment can be used to form the finger electrodes 18. Because the transparent conductive film has a high resistivity, providing the finger electrodes 18 can reduce electrical loss. Incident light 30 enters the surface of the first electrode 13 on which the finger electrodes 18 are provided and is absorbed by the perovskite compound layer 15, which is a photosensitizing layer, to generate holes and electrons, thereby generating electricity. The metal oxide layer 16 (e.g., a titanium oxide layer) can include a mesoporous metal oxide layer 16a and a compact metal oxide layer 16b. The second electrode 17 can be, for example, a metal flat plate. That is, in the perovskite solar cell 10 shown in FIG. 1 , the second electrode 17 is a metal flat plate having a certain degree of rigidity, thereby enabling the structural strength to be maintained.

[0106] The perovskite solar cell 10 is not limited to the example shown in Figure 1, and may be, for example, a tandem perovskite solar cell (tandem solar cell) using perovskite solar cells 10 as top cells and, for example, silicon heterojunction solar cells 20 as bottom cells, as shown in Figure 2. In this specification, a solar cell including at least a perovskite compound layer 15 may be referred to as a "perovskite solar cell." In a tandem solar cell, a single-crystalline silicon solar cell or a polycrystalline silicon solar cell may be used instead of the silicon heterojunction solar cell 20.

[0107] FIG. 2 shows a cross-sectional schematic diagram of a tandem solar cell consisting of the perovskite solar cell 10 shown in FIG. 1 and a silicon heterojunction solar cell 20 using amorphous silicon and a crystalline silicon substrate (single-crystal silicon substrate or polycrystalline silicon substrate). Because the band gap of silicon is approximately 1.1 eV, crystalline silicon solar cells have high power generation efficiency using relatively long-wavelength sunlight. In contrast, perovskite solar cells 10 generate power using relatively short-wavelength sunlight and transmit relatively long-wavelength sunlight. Therefore, in the tandem solar cell shown in FIG. 2 , the perovskite solar cell 10 absorbs relatively short-wavelength light from incident light 30 to generate power, while the silicon heterojunction solar cell 20 absorbs relatively long-wavelength light that has passed through the perovskite solar cell 10 to generate power. The tandem solar cell shown in FIG. 2 can generate power by effectively utilizing a wider wavelength range of incident light 30, resulting in a solar cell with high conversion efficiency. The conductive composition (conductive paste) of this embodiment can be used to form finger electrodes 18 disposed on the surface of perovskite solar cells 10 of a tandem solar cell.

[0108] The silicon heterojunction solar cell 20 of the tandem solar cell shown in FIG. 2 has a p-type amorphous silicon layer 22 on one surface of an n-type silicon substrate 25 (an n-type single-crystalline silicon substrate or an n-type polycrystalline silicon substrate), and an n-type impurity diffusion layer 26 and a back electrode 27 on the other surface. A conductive interface layer 21 can be disposed between the perovskite solar cell 10 and the silicon heterojunction solar cell 20. For power generation in the silicon heterojunction solar cell 20, the interface layer 21 must transmit relatively long-wavelength light of the incident light 30 that is not absorbed by the perovskite solar cell 10. Therefore, the material of the interface layer 21 is preferably a transparent conductive film (e.g., a tin oxide thin film, an indium tin oxide (ITO) thin film, etc.).

[0109] In the perovskite solar cell 10 shown in FIG. 1 and the perovskite solar cell 10 of the tandem solar cell shown in FIG. 2 , by using the conductive composition (conductive paste) of this embodiment, finger electrodes 18 with low resistivity and low contact resistance can be formed at a relatively low temperature (e.g., 150° C. or less) in a step after forming the perovskite compound layer 15. Therefore, by forming the finger electrodes 18 using the conductive composition (conductive paste) of this embodiment, a high-performance perovskite solar cell 10 and a tandem solar cell including the perovskite solar cell 10 can be obtained. Therefore, a cured product of the conductive composition (conductive paste) of this embodiment can be preferably used as an electrode (particularly an electrode formed on a transparent conductive film such as an ITO thin film) of the perovskite solar cell 10 or a tandem solar cell including the perovskite solar cell 10.

[0110] Examples and comparative examples of this embodiment will be described below, but this embodiment is not limited to the following examples and comparative examples.

[0111] [Preparation of Conductive Paste] In the examples and comparative examples, conductive pastes containing (A) conductive particles, (B) solvent, (C) epoxy resin, and (D) curing agent, and optionally containing (E) phenoxy resin and (F) silane coupling agent, were produced. Tables 1 to 4 show the formulations of Examples 1 to 21 and Comparative Examples 1 to 4. The formulation ratios shown in Tables 1 to 4 are expressed in parts by weight when the weight of the (A) conductive particles is taken as 100 parts by weight.

[0112] (A) As the conductive particles, the following particles A1 and A2 were used. Particle A1: Silver particles manufactured by DOWA Corporation, product name "AG-SNA-458", shape: spherical, particle size (D50): 0.5 μm, tap density: 4.3 g / cm ３ , BET specific surface area 1.6m ２ / g ・Particle A2: Silver particles manufactured by DOWA, product name "AG-SNA-431", shape spherical, particle size (D50) 2.5 μm, TAP density 6.0 g / cm ３ , BET specific surface area 0.3m ２ / g

[0113] As the (B) solvent, the following solvents B1 and B2 were used: Solvent B1: diethylene glycol monobutyl ether Solvent B2: diethylene glycol monobutyl ether acetate

[0114] The following resins C1 to C9 were used as the (C) epoxy resin. Resin C6 is "AK-601 (trade name)" epoxy resin (diglycidyl 1,2-cyclohexanedicarboxylate, see formula (4)) manufactured by Nippon Kayaku Co., Ltd. Resins C1 to C5 are epoxy resins containing low-concentration saponifiable chlorine components obtained by distilling AK-601 (trade name) using an evaporator. Resins C7 and C8 are epoxy resins containing high concentrations of easily saponifiable chlorine components generated as a by-product when AK-601 (trade name) is distilled. In Tables 1 to 4, the easily saponifiable chlorine concentration when multiple (C) epoxy resins are used represents the weighted average easily saponifiable chlorine concentration of the multiple (C) epoxy resins. Resin C1: Easily saponifiable chlorine concentration: 1200 ppm Resin C2: Easily saponifiable chlorine concentration: 1500 ppm Resin C3: Easily saponifiable chlorine concentration: 3500 ppm Resin C4: Easily saponifiable chlorine concentration: 4500 ppm Resin C5: Easily saponifiable chlorine concentration: 5500 ppm Resin C6: Easily saponifiable chlorine concentration: 6000 ppm Resin C7: Easily saponifiable chlorine concentration: 9200 ppm Resin C8: Easily saponifiable chlorine concentration: 22000 ppm Resin C9: Epoxy resin "EXA835LV (trade name)" manufactured by Dainippon Ink Co., Ltd. (a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin), easily saponifiable chlorine concentration: 40 ppm

[0115] The diglycidyl 1,2-cyclohexanedicarboxylate resins C1 to C8 are compounds having the structure of the following formula (4).

[0116] As the (D) curing agents, the following D1 to D3 were used. Note that curing agent D1 is a compound having the structure of formula (b), and curing agent D2 is a compound having the structure of formula (a). Curing agent D1: phenolic resin of formula (b), manufactured by Meiwa Kasei Co., Ltd., product name "MEH-8000H" Formula (b) (wherein n is 0 to 3, and R1 to R5 each represent a hydrogen atom, a hydroxyl group, or an allyl group.) Curing agent D2: a cationic polymerization initiator of formula (a), manufactured by King Industries, Inc., product name "CXC1614" Formula (a) Curing agent D3: Cationic polymerization initiator, King Industries, Inc., product name "CXC1612."

[0117] (E) As the phenoxy resin, a product name "PKHH" manufactured by GABRIEL was used.

[0118] (F) As the silane coupling agent, a product name "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd. was used.

[0119] [Measurement of Resistivity] The resistivity of the conductive films obtained by heating the conductive pastes of the Examples and Comparative Examples was measured.

[0120] The resistivity of the examples and comparative examples was measured by the following procedure. A single-crystal 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 FIG. 3 was printed on the substrate using a 325-mesh stainless steel screen.

[0121] Next, the patterns made of the conductive pastes of the examples and comparative examples applied onto the substrate were heated at 110° C. for 45 minutes to obtain samples for measuring resistivity.

[0122] 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 using a four-terminal method using a Toyo Corporation Model 2001 multimeter. The cross-sectional area of ​​the pattern was measured using a Lasertec Corporation OPTELICS H1200 confocal microscope and a Lasertec Corporation 1500SD2 surface roughness and shape measuring instrument. 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.

[0123] Four samples were prepared under the same conditions for measuring the resistivity, and the measured value was calculated as the average of the four values. The measurement results are shown in Tables 1 to 4.

[0124] As is clear from Tables 1 to 4, the resistivity of the conductive films obtained using the conductive pastes (conductive compositions) of Examples 1 to 21 of this embodiment was 14.8 μΩ cm or less (Examples 11 and 18). Generally, a resistivity of 15 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 4 ranged from 15.7 μΩ cm (Comparative Example 1) to 1960 μΩ cm (Comparative Example 4). Therefore, it was revealed that a lower resistivity could be obtained by forming a conductive film (electrode) using the conductive pastes (conductive compositions) of Examples 1 to 21 of this embodiment.

[0125] [Measurement of Contact Resistance] Using the conductive pastes of Examples and Comparative Examples, electrodes were formed on the surface of a crystalline silicon substrate having a transparent conductive film, and the contact resistance was measured. Specifically, a contact resistance measurement pattern using the conductive pastes of Examples 1 to 21 and Comparative Examples 1 to 4 was screen-printed on the transparent conductive film formed on the surface of the crystalline silicon substrate, and then heated to obtain an electrode for contact resistance measurement.

[0126] An n-type single crystal silicon substrate (substrate thickness: 200 μm) was used as the substrate.

[0127] Next, a transparent conductive film was formed on the surface of the n-type single crystal silicon substrate. Specifically, an indium tin oxide thin film (ITO thin film) was formed by sputtering using a sputtering target containing indium oxide and tin oxide. The sheet resistance of the obtained ITO thin film was 80 Ω / square. The contact resistance measurement substrate thus obtained was used to prepare electrodes for contact resistance measurement.

[0128] The conductive paste was printed onto the contact resistance measurement substrate by screen printing. A contact resistance measurement pattern was printed on the substrate to a film thickness of approximately 30 μm, and then heated at 110°C for 45 minutes to obtain a contact resistance measurement sample. Figure 4 shows a schematic plan view of the contact resistance measurement pattern used for contact resistance measurement. The contact resistance measurement pattern shown in Figure 4 is a pattern in which seven rectangular electrode patterns, each 0.1 mm wide and 13.5 mm long, are arranged at a pitch of 2.05 mm.

[0129] Three samples were prepared under the same conditions for measuring the contact resistance, and the measured value was calculated as the average value of the three samples.

[0130] The contact resistance was determined by measuring the electrical resistance between the predetermined rectangular electrode patterns shown in Figure 4 using a GP 4TEST Pro manufactured by GP Solar by the TLM (Transfer Length Method). ２ When the contact resistance is 60 mΩ cm or less, it can be used as an electrode on a transparent conductive film. ２ When the thickness is less than 100 μm, it can be more preferably used as an electrode on a transparent conductive film.

[0131] As is clear from Tables 1 to 4, the contact resistance of the conductive films obtained using the conductive pastes of Examples 1 to 21 to the transparent conductive film (thin ITO film) was 63.1 mΩ cm ２ Therefore, it can be said that the contact resistance of Examples 1 to 21 is within a range that allows use as an electrode on a transparent conductive film.

[0132] The contact resistance of the conductive films obtained using the conductive pastes of Examples 2 to 21, which used two types of conductive particles A1 and A2, to a transparent conductive film (thin ITO film) was 59.5 mΩ cm ２ (Examples 5 and 8) ２ Therefore, it was found that a lower contact resistance can be obtained by using two types of conductive particles A1 and A2. Therefore, a conductive paste containing two types of conductive particles A1 and A2 can be more preferably used as an electrode on a transparent conductive film.

[0133] On the other hand, the contact resistance of the conductive film (electrode) obtained using the conductive paste of Comparative Example 2, in which the blending amount of (C) epoxy resin was 15 parts by weight per 100 parts by weight of (A) conductive particles, to the transparent conductive film (ITO thin film) was 94 mΩ cm ２ The contact resistance of the conductive film obtained using the conductive paste of Comparative Example 4, in which the readily saponifiable chlorine concentration of the epoxy resin (C) was 1600 ppm, to the transparent conductive film (thin ITO film) was so high that it was impossible to measure. Therefore, the "Contact Resistance" column for Comparative Example 4 in Table 1 is entered as "-".

[0134] The conductive paste of Comparative Example 1, in which the (C) epoxy resin was 1 part by weight per 100 parts by weight of the (A) conductive particles, had a low contact resistance but a high resistivity of 15.7 μΩ·cm. The conductive paste of Comparative Example 3, in which the (C) epoxy resin had an easily saponifiable chlorine concentration of 1200, also had a low contact resistance but a high resistivity of 156 μΩ·cm. Therefore, it can be said that the conductive pastes of Comparative Examples 1 and 3 are also difficult to use as conductive pastes for solar cells.

[0135] From the above, it is clear that by using the conductive paste (conductive composition) of this embodiment, an electrode having low specific resistance and contact resistance for a perovskite solar cell can be formed at a low temperature (for example, 150°C or lower).

[0136]

[0137]

[0138]

[0139]

[0140] REFERENCE SIGNS LIST 10 Perovskite solar cell 12 Glass substrate 13 First electrode (transparent conductive film) 14 Hole transport layer 15 Perovskite compound layer 16 Metal oxide layer 16a Mesoporous metal oxide layer 16b Compact metal oxide layer 17 Second electrode 18 Finger electrode 20 Silicon heterojunction solar cell 21 Interface layer 22 P-type amorphous silicon layer 25 N-type silicon substrate 26 N-type impurity diffusion layer 27 Rear electrode 30 Incident light

Claims

1. (A) conductive particles; (B) a solvent; (C) an epoxy resin; A conductive composition comprising: the (C) epoxy resin has an easily saponifiable chlorine concentration of 1600 ppm or more; The conductive composition, wherein the (C) epoxy resin is contained in an amount of 1.2 to 10 parts by weight per 100 parts by weight of the (A) conductive particles.

2. The conductive composition according to claim 1 , wherein the (A) conductive particles include conductive particles A1 and conductive particles A2, and the average particle size of the conductive particles A2 is larger than the average particle size of the conductive particles A1.

3. 3. The conductive composition according to claim 2, wherein the conductive particles A2 have an average particle size of 1.5 to 4.5 μm.

4. The conductive particles A1 have an average particle size of 0.05 to 1.4 μm, 4. The conductive composition according to claim 2, wherein the conductive particles A2 have an average particle size of 2.0 to 3.5 μm.

5. 4. The conductive composition according to claim 2, wherein the conductive particles A1 are contained in an amount of 0 to 40% by weight and the conductive particles A2 are contained in an amount of 40 to 90% by weight, based on 100% by weight of the conductive particles (A).

6. The BET specific surface area of ​​the conductive particles A1 is 0.3 to 3.5 m ２ The conductive composition according to claim 2 or 3, wherein the solubility is 1 / g.

7. The BET specific surface area of ​​the conductive particles A2 is 0.1 to 0.4 m ２ The conductive composition according to claim 2 or 3, wherein the solubility is 1 / g.

8. The conductive composition according to claim 2 or 3, wherein the conductive particles (A1) and the conductive particles (A2) are spherical conductive particles.

9. The conductive composition according to claim 1 or 2, further comprising (D) a curing agent.

10. The conductive composition of claim 9 , wherein the (D) curing agent comprises a compound having a structure of formula (a): Formula (a) 【Chemistry 11】

11. A conductive paste for forming an electrode of a solar cell, comprising the conductive composition according to claim 1 or 2.

12. A conductive paste for forming an electrode of a perovskite solar cell, comprising the conductive paste according to claim 11.

13. A cured product of the conductive composition according to claim 1 or 2.

14. A solar cell comprising the cured product according to claim 13.

Images