JP2012022795A - Conductive composition and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive composition capable of forming an electrode, etc. with reduced volume resistivity and excellent adhesion to a silicon substrate, and to provide a solar cell with an electrode formed by using the same.SOLUTION: A conductive composition contains silver powder (A), a fatty acid silver salt (B), an epoxy resin (C) and a cationic curing agent (D). The cationic curing agent (D) is preferably a sulfonium salt. More preferably, the fatty acid silver salt (B) is a fatty acid silver salt (B1) having one or more of each of carboxy silver salt groups (-COOAg) and hydroxyl groups (-OH), and/or polycarboxylic acid silver salt (B2) having two or more carboxy silver salt groups (-COOAg).

Description

  The present invention relates to a conductive composition and a solar battery cell in which an electrode is formed using the conductive composition.

  Solar cells that convert light energy such as sunlight into electrical energy have been actively developed in various structures and configurations as interest in global environmental issues increases. Among them, solar cells using a semiconductor substrate such as silicon are most commonly used due to advantages such as conversion efficiency and manufacturing cost.

As a material for forming such an electrode of a solar cell, an epoxy resin-based paste material is known.
For example, Patent Document 1 states that “a silver powder, a thermosetting component, and a solvent are the main components, and the thermosetting component includes an epoxy resin having an epoxy equivalent of 1000 or less, an epoxy resin having an epoxy equivalent of 1500 or more, and a curing agent. (Claim 1) ”, and the curing agent is selected from Lewis acids containing imidazoles, tertiary amines and boron fluoride, and complexes or salts thereof. It is described that it is selected from at least one of the following groups ([Claim 3]).

  On the other hand, in Patent Documents 2 and 3, conductive line pattern formation for flat panel displays such as liquid crystal displays (LCDs) and plasma display panels (PDPs), electrode parts for touch screens, and PAD part electrodes for surface emitting backlights (FFLs). In addition, a silver paste for forming a conductive film used for an antenna of a flexible PCB and an RFID is described. Patent Document 2 describes “0.1 to 60 wt% of fatty acid silver having 0 to 12 carbon atoms; silver powder 1 -80% by weight; 0.1-15% by weight of binder; and a silver paste for forming a conductive film composed of the remaining amount of organic solvent ”([Claim 1]), and imidazole and fatty acid as curing agents. Citric acid is described as silver, plate-type silver powder as silver powder, and epoxy resin binder as binder ([0024] [0027] [0 35]).

JP 2006-40708 A Special table 2010-504612 gazette Special table 2010-505230 gazette

However, the conductive paste composition described in Patent Document 1 does not proceed with the connection of silver powder, and may have a high volume resistivity (specific resistance) of electrodes and wirings. It became clear that the sex was inferior.
In addition, the paste materials described in Patent Documents 2 and 3 have a high volume resistivity (specific resistance) of a conductive film used for forming a conductive line pattern or an electrode depending on the type of curing agent used and the firing temperature. It became clear that there was a case.

  Therefore, the present invention provides a conductive composition capable of forming an electrode / wiring or conductive film (hereinafter referred to as “electrode or the like”) having a low volume resistivity and excellent adhesion to a silicon substrate, and It is an object to provide a solar battery cell in which an electrode is formed using the same.

  As a result of intensive studies to solve the above problems, the present inventor has found that a conductive composition containing a cationic curing agent has a low volume resistivity with respect to silver powder, fatty acid silver salt and epoxy resin, and silicon The inventors have found that an electrode having excellent adhesion to a substrate can be formed and completed the present invention. That is, the present invention provides the following (1) to (16).

  (1) A conductive composition containing silver powder (A), a fatty acid silver salt (B), an epoxy resin (C), and a cationic curing agent (D).

(2) The conductive composition according to (1), wherein the cationic curing agent (D) is a sulfonium salt represented by the following formula (i).
(In formula (i), X represents a hydroxyl group or a group represented by any of the following formulas (a) to (c), and Ar represents an aryl group.)
(In formulas (a) to (c), each R independently represents an aromatic or aliphatic hydrocarbon group which may have a substituent.)

  (3) The fatty acid silver salt (B1) in which the fatty acid silver salt (B) has at least one carboxy silver base (—COOAg) and one hydroxyl group (—OH), and / or a carboxy silver base (—COOAg). The conductive composition according to the above (1) or (2), which is a polycarboxylic acid silver salt (B2) having two or more.

(4) The conductive composition according to (3), wherein the fatty acid silver salt (B1) is a compound represented by any one of the following formulas (I) to (III).
(In formula (I), n represents an integer of 0 to 2, R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² represents an alkylene group having 1 to 6 carbon atoms. When it is 0 or 1, the plurality of R ² may be the same or different, and when n is 2, the plurality of R ¹ may be the same or different.
In formula (II), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and a plurality of R ¹ may be the same or different.
In formula (III), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ³ represents an alkylene group having 1 to 6 carbon atoms. The plurality of R ¹ may be the same or different. )

  (5) The conductive composition according to (3) or (4), wherein the fatty acid silver salt (B1) has the hydroxyl group at a carbon atom at the α-position and / or β-position with respect to the carboxy silver base. .

  (6) The conductive composition according to any one of (3) to (5), wherein the fatty acid silver salt (B1) has one carboxy silver base and one or two hydroxyl groups.

  (7) The conductive composition according to (3), wherein the polycarboxylic acid silver salt (B2) does not have a hydroxyl group.

(8) The conductive composition according to (3) or (7), wherein the polycarboxylic acid silver salt (B2) is a compound represented by the following formula (IV).
(In Formula (IV), m represents an integer of 2 to 6, R ⁴ represents an m-valent saturated aliphatic hydrocarbon group having 1 to 24 carbon atoms, and an m-valent unsaturated fat having 2 to 12 carbon atoms. family hydrocarbon group, m-valent alicyclic hydrocarbon group having 3 to 12 carbon atoms, or, when the carbon number of the .R ⁴ representing the m-valent aromatic hydrocarbon group having 6 to 12 carbon atoms and p, m ≦ 2p + 2.)

  (9) The conductive composition according to any one of (1) to (8), wherein the epoxy resin (C) is an epoxy resin to which ethylene oxide and / or propylene oxide is added.

  (10) The above (3) to (6) and (9), wherein the fatty acid silver salt (B1) is 2,2-bis (hydroxymethyl) -n-butyric acid silver salt and / or 2-hydroxyisobutyric acid silver salt ).

  (11) The electrical conductivity according to any one of (3) and (7) to (9), wherein the polycarboxylic acid silver salt (B2) is 1,2,3,4-butanetetracarboxylic acid silver salt. Composition.

  (12) The conductivity according to any one of (1) to (11), wherein the content of the fatty acid silver salt (B) is 1 to 100 parts by mass with respect to 100 parts by mass of the silver powder (A). Composition.

  (13) The conductive composition according to any one of (1) to (12), wherein the content of the epoxy resin (C) is 1 to 50 parts by mass with respect to 100 parts by mass of the silver powder (A). object.

  (14) The content of the cationic curing agent (D) is 0.1 to 10 parts by mass with respect to 100 parts by mass of the epoxy resin (C). The electroconductive composition as described.

  (15) The conductive composition according to any one of (1) to (14), which is used for a solar cell electrode paste.

(16) It comprises a surface electrode on the light receiving surface side, a semiconductor substrate and a back electrode,
The photovoltaic cell in which the said surface electrode and / or the said back surface electrode are formed using the electrically conductive composition as described in said (15).

As shown below, according to the present invention, a conductive composition capable of forming an electrode or the like having a low volume resistivity and excellent adhesion to a silicon substrate, and an electrode formed using the same A solar battery cell can be provided.
In addition, if the conductive composition of the present invention is used, even when firing at a low temperature (about 150 to 350 ° C.), an electrode or the like can be formed while suppressing the occurrence of disconnection. It has the effect of reducing damage and is very useful.
Furthermore, if the conductive composition of the present invention is used, a circuit such as an electronic circuit or an antenna can be easily and quickly produced not only on a silicon substrate but also on a substrate having low heat resistance. It is.

FIG. 1 is a cross-sectional view showing an example of a preferred embodiment of a solar battery cell. FIG. 2 is a photograph of the silver powder (AgC-103, manufactured by Fukuda Metal Foil Co., Ltd.) used in the examples taken with a scanning electron microscope (SEM). FIG. 3 is a photograph of silver powder (AgC-2011, manufactured by Fukuda Metal Foil Co., Ltd.) used in the examples taken with a scanning electron microscope (SEM).

The conductive composition of the present invention is a conductive composition containing silver powder (A), a fatty acid silver salt (B), an epoxy resin (C), and a cationic curing agent (D).
Moreover, the electrically conductive composition of this invention may contain the solvent (E) as needed from viewpoints of printability etc. so that it may mention later.
Hereinafter, the silver powder (A), the fatty acid silver salt (B), the epoxy resin (C) and the cationic curing agent (D) and the solvent (E) which may be optionally contained will be described in detail.

<Silver powder (A)>
The silver powder (A) used by the electrically conductive composition of this invention is not specifically limited, What is mix | blended with the conventionally well-known electrically conductive paste can be used.

The silver powder (A) is preferably a spherical silver powder having an average particle diameter of 0.5 to 10 μm because the printability is good and an electrode having a smaller volume resistivity can be formed.
Here, the term “spherical” refers to the shape of particles having a major axis / minor axis ratio of 2 or less.
Moreover, an average particle diameter means the average value of the particle diameter of spherical silver powder, and means the 50% volume cumulative diameter (D50) measured using the laser diffraction type particle size distribution measuring apparatus. In addition, when the cross section of the spherical silver powder is elliptical, the particle diameter that is the basis for calculating the average value is the average value obtained by dividing the total value of the major axis and the minor axis by 2, and is a regular circle Refers to its diameter.
For example, what is shown in the photograph (FIG. 2) of silver powder (AgC-103, manufactured by Fukuda Metal Foil Co., Ltd.) used in Examples described later corresponds to spherical silver powder, but silver powder (AgC-2011, Fukuda Metal Foil). The photo shown in FIG. 3 (manufactured by Kogyo Co., Ltd.) does not correspond to the spherical silver powder, but corresponds to the flake (scale) -like silver powder.

  Further, the average particle diameter of the silver powder (A) is preferably 0.7 to 5 μm because the printability is better, and 1 to 3 μm because the sintering speed is appropriate and the workability is excellent. It is more preferable that

  In the present invention, commercially available products can be used as such silver powder (A), and specific examples thereof include AgC-103 (shape: spherical, average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Co., Ltd.), AG4-8F (shape: spherical, average particle size: 2.2 μm, manufactured by DOWA Electronics), AG2-1C (shape: spherical, average particle size: 1.0 μm, manufactured by DOWA Electronics), AG3-11F (shape: Spherical, average particle size: 1.4 μm, DOWA Electronics Co., Ltd.), EHD (shape: spherical, average particle size: 0.5 μm, Mitsui Kinzoku Co., Ltd.), AgC-2011 (shape: flake shape, average particle size: 2) 10 μm, manufactured by Fukuda Metal Foil Co., Ltd.).

  Moreover, in this invention, content of the said silver powder (A) becomes favorable to printability, and since it can form an electrode with a smaller volume resistivity, etc. in 100 mass parts of solvent (E) mentioned later. It is preferable that it is 300-700 mass parts with respect to it, and it is more preferable that it is 400-600 mass parts.

Furthermore, in this invention, as shown also in Example 4 mentioned later, spherical silver powder and flaky silver powder can be used together as said silver powder (A).
Here, the content when the flaky silver powder is used in combination is preferably 50% by mass or less of the total mass of the silver powder (A).

<Fatty acid silver salt (B)>
The fatty acid silver salt (B) used in the conductive composition of the present invention is not particularly limited as long as it is a silver salt of an organic carboxylic acid. However, from the reason that damage to the silicon substrate due to heat can be further reduced, a carboxy silver base (- A fatty acid silver salt (B1) having at least one COOAg) and a hydroxyl group (—OH) and / or a polycarboxylic acid silver salt (B2) having at least two carboxy silver bases (—COOAg). preferable.
Below, fatty acid silver salt (B1) and polycarboxylic acid silver salt (B2) are explained in full detail.

(Fatty acid silver salt (B1))
The fatty acid silver salt (B1) is a fatty acid silver salt having at least one carboxy silver base (—COOAg) and one hydroxyl group (—OH), and specifically, a fatty acid having at least one hydroxyl group shown below. And silver oxide.

  The fatty acid used for the said reaction will not be specifically limited if it is a fatty acid which has 1 or more of hydroxyl groups, For example, the compound represented by following formula (1)-(3) is mentioned.

In formula (1), n represents an integer of 0 to 2, R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² represents an alkylene group having 1 to 6 carbon atoms. When n is 0 or 1, the plurality of R ² may be the same or different from each other. When n is 2, the plurality of R ¹ may be the same or different.
In Formula (2), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and a plurality of R ¹ may be the same or different.
In formula (3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ³ represents an alkylene group having 1 to 6 carbon atoms. The plurality of R ¹ may be the same or different.

In the above formula (1) to (3), the alkyl group having 1 to 10 carbon atoms of R ^1, a methyl group, an ethyl group, n- propyl group, n- butyl group, n- pentyl group, n- hexyl group , N-heptyl group, n-octyl group, n-nonyl group and n-decyl group. R ¹ is preferably a hydrogen atom, a methyl group, or an ethyl group.
Moreover, in said formula (1), as a C1-C6 alkylene group of R < ² >, a methylene group, ethylene group, propane- 1, 3- diyl group, butane- 1, 4- diyl group, heptane-1 , 5-diyl group and hexane-1,6-diyl group. R ² is preferably a methylene group or an ethylene group. In said formula (1), it is preferable that it is 1 or 2 as an integer of 0-2 of n.
Moreover, in said formula (3), as a C1-C6 alkylene group of R <3>, a methylene group, ethylene group, a propane- 1, ^3- diyl group, butane- 1, 4- diyl group, heptane-1 , 5-diyl group and hexane-1,6-diyl group. R ² is preferably a methylene group or an ethylene group.

  Specific examples of the compound represented by the above formula (1) include 2,2-bis (hydroxymethyl) -n-butyric acid represented by the following formula (1a) and the following formula (1b). 2,2-bis (hydroxymethyl) propionic acid, hydroxypivalic acid represented by the following formula (1c), β-hydroxyisobutyric acid represented by the following formula (1d), and the like. You may use independently and may use 2 or more types together.

  Specific examples of the compound represented by the formula (2) include 2-hydroxy-2-methyl-n-butyric acid represented by the following formula (2a) and the following formula (2b). Examples include 2-hydroxyisobutyric acid, glycolic acid represented by the following formula (2c), DL-2-hydroxybutyric acid represented by the following formula (2d), etc., and these may be used alone. More than one species may be used in combination.

  Specific examples of the compound represented by the above formula (3) include, for example, DL-3-hydroxybutyric acid represented by the following formula (3a) and β-hydroxyvaleric acid represented by the following formula (3b). These may be used, and these may be used alone or in combination of two.

Among these, the resulting fatty acid silver salt (B1) is rapidly reduced, and silver particles are easily generated. As a result, formation of an electrode or the like using the conductive composition of the present invention is performed at a lower temperature and in a shorter time. For the reason that it is possible, those having the hydroxyl group at the carbon atom at the α-position and / or β-position with respect to the carboxy silver base are preferred, having one carboxy silver base and one or two hydroxyl groups. Those having the number are more preferable.
In particular, 2,2-bis (hydroxymethyl) -n-butyric acid and / or 2-hydroxyisobutyric acid is 2,2-bis (hydroxymethyl) -n-, which is the resulting fatty acid silver salt (B2). It is preferable because formation of an electrode or the like using the conductive composition of the present invention containing silver butyrate and / or silver 2-hydroxyisobutyrate is possible at a lower temperature and in a shorter time.

On the other hand, the silver oxide used in the above reaction is silver oxide (I), that is, Ag ₂ O.

The fatty acid silver salt (B1) is obtained by reacting a fatty acid having one or more hydroxyl groups described above with silver oxide, and is represented by the following formulas (I) to (III) in the reaction formulas shown below. Is preferred.
For example, when the compounds represented by the above formulas (1) to (3) are used, this reaction is not particularly limited as long as the reaction represented by the following reaction formula proceeds. A method of proceeding while pulverizing and a method of reacting the fatty acid after pulverizing the silver oxide are preferred. Specifically, as the former method, the above silver oxide and a solution obtained by dissolving the above fatty acid with a solvent are kneaded with a ball mill or the like, and the above solid silver oxide is pulverized at room temperature, The reaction is preferably performed for about 24 hours, preferably 2 to 8 hours.

In formula (I), n represents an integer of 0 to 2, R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² represents an alkylene group having 1 to 6 carbon atoms. When n is 0 or 1, the plurality of R ² may be the same or different from each other. When n is 2, the plurality of R ¹ may be the same or different.
In formula (II), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and a plurality of R ¹ may be the same or different.
In formula (III), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ³ represents an alkylene group having 1 to 6 carbon atoms. The plurality of R ¹ may be the same or different.

Specific examples of the solvent for dissolving the fatty acid include butyl carbitol, methyl ethyl ketone, isophorone, α-terpineol, and the like. These may be used alone or in combination of two or more. Good.
Of these, the use of isophorone and / or α-terpineol as a solvent improves the thixotropy of the conductive composition of the present invention containing the fatty acid silver salt (B1) obtained by the above reaction.

(Polycarboxylic acid silver salt (B2))
The polycarboxylic acid silver salt (B2) is a polycarboxylic acid silver salt having two or more carboxy silver bases (—COOAg), specifically, a fatty acid and silver oxide having two or more carboxy groups shown below. It is obtained by reacting.

  Although the fatty acid used for the said reaction will not be specifically limited if it is a fatty acid which has 2 or more of carboxy groups, It is preferable that it is a fatty acid which does not have a hydroxyl group, for example, the compound etc. which are represented by following formula (4) Is mentioned.

In formula (4), m represents an integer of 2 to 6, R ⁴ represents an m-valent saturated aliphatic hydrocarbon group having 1 to 24 carbon atoms, and an m-valent unsaturated aliphatic group having 2 to 12 carbon atoms. It represents a hydrocarbon group, an m-valent alicyclic hydrocarbon group having 3 to 12 carbon atoms, or an m-valent aromatic hydrocarbon group having 6 to 12 carbon atoms. When the carbon number of R ⁴ is p, m ≦ 2p + 2.
In the formula (4), when m is 2 or more, the carbons of R ^{4 to which} the carbon of the carboxy group is bonded may be the same or different.

  In said formula (4), as an integer of 2-6 of m, it is preferable that it is 2-5, and it is more preferable that it is 2-4.

In the formula (4), as a 1 to 24 carbon atoms, saturated aliphatic hydrocarbon radical R ⁴ represents, is preferably from 1 to 12, and more preferably 1-6.
Examples of the saturated aliphatic hydrocarbon group represented by R ⁴ when m is 2 include a methylene group, an ethane-1,1-diyl group, an ethane-1,2-diyl group, and a propane-1,3-diyl group. , Butane-1,4-diyl group, pentane-1,5-diyl group, hexane-1,6-diyl group, heptane-1,7-diyl group, octane-1,8-diyl group and the like.
Examples of the saturated aliphatic hydrocarbon group represented by R ⁴ when m is 3 include methane-triyl group, ethane-1,1,2-triyl group, propane-1,1,3-triyl group, propane- Examples include 1,2,3-triyl group, butane-1,1,3-triyl group, butane-1,1,4-triyl group, butane-1,2,4-triyl group.
Examples of the saturated aliphatic hydrocarbon group represented by R ⁴ when m is 4 include ethane-1,2,2,2-tetrayl group, propane-1,2,2,3-tetrayl group, butane-1 2,3,4-tetrayl group and the like.

In the above formula (4), 2 to 12 carbon atoms of the unsaturated aliphatic hydrocarbon group represented by R ⁴ are preferably 2 to 10, and more preferably 2 to 6.
Examples of the unsaturated aliphatic hydrocarbon group represented by R ⁴ when m is 2 include an ethylene-1,2-diyl group and a propene-1,3-diyl group.
Examples of the unsaturated aliphatic hydrocarbon group represented by R ⁴ when m is 3 include a propene-1,2,3-triyl group and a propene-1,3,3-triyl group.
Examples of the unsaturated aliphatic hydrocarbon group represented by R ⁴ when m is 4 include a propene-1,1,2,3-tetrayl group.

In the formula (4), the 3 to 12 carbon atoms in the alicyclic hydrocarbon group R ⁴ represents, is preferably from 3-10, more preferably 3-6.
Examples of the alicyclic hydrocarbon group represented by R ⁴ when m is 2 include a cyclohexane-1,2-diyl group, a cyclohexane-1,4-diyl group, a cyclohexene-1,2-diyl group, and a cyclohexene- 4,5-diyl group, 1-methylcyclohexene-4,5-diyl group and the like can be mentioned.
Examples of the alicyclic hydrocarbon group represented by R ⁴ when m is 3 include cyclopropane-1,2,3-triyl group, cyclopentane-1,1,2-triyl group, and cyclohexane-1,2. , 4-triyl group and the like.
Examples of the alicyclic hydrocarbon group represented by R ⁴ when m is 4 include cyclobutane-1,2,3,4-tetrayl group, cyclopentane-1,2,3,4-tetrayl group, and cyclopentane. Examples include -1,2,4,5-tetrayl group, cyclohexane-1,2,4,5-tetrayl group, 3,6-dimethylcyclohexane-1,2,4,5-tetrayl group.

In said formula (4), as 6-12 carbon number of the aromatic hydrocarbon group which R < ⁴ > shows, it is preferable that it is 6-10, and it is more preferable that it is 6-8.
As the aromatic hydrocarbon group represented by R ⁴ when m is 2, for example, benzene-1,2-diyl group, benzene-1,3-diyl group, benzene-1,4-diyl group, naphthalene-1 , 4-diyl group, naphthalene-2,3-diyl group, naphthalene-2,6-diyl group and the like.
Examples of the aromatic hydrocarbon group represented by R ⁴ when m is 3 include a benzene-1,2,4-triyl group and a benzene-1,3,5-triyl group.
Examples of the aromatic hydrocarbon group represented by R ⁴ when m is 4 include a benzene-1,2,4,5-tetrayl group, a biphenyl-3,3 ′, 4,4′-tetrayl group, and the like. It is done.

Examples of the compound represented by the formula (4) include aliphatic polycarboxylic acids, alicyclic polycarboxylic acids, and aromatic polycarboxylic acids.
Specific examples of the aliphatic polycarboxylic acid include saturated dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid; unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid; And saturated tricarboxylic acids such as tricarballylic acid; unsaturated tricarboxylic acids such as aconitic acid; saturated tetracarboxylic acids such as 1,2,3,4-butanetetracarboxylic acid; and the like.
Specific examples of the alicyclic polycarboxylic acid include unsaturated alicyclic dicarboxylic acids such as 4-cyclohexene-1,2-dicarboxylic acid and 4-methyl-4-cyclohexene-1,2-dicarboxylic acid. Saturated alicyclic tetracarboxylic acids such as 1,2,3,4-cyclopentanetetracarboxylic acid; and the like.
Specific examples of the aromatic polycarboxylic acid include benzenedicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; tricarboxylic acids such as trimellitic acid and trimesic acid; pyromellitic acid, 3,3 ′, 4 , 4′-biphenyltetracarboxylic acid and the like; 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 2,3-naphthalenedicarboxylic acid and the like; and the like.
These may be used alone or in combination of two or more.

Among these, aliphatic polycarboxylic acid and alicyclic polycarboxylic acid are used from the viewpoint that printability is improved and formation of an electrode or the like using the conductive composition of the present invention is possible at a lower temperature and in a shorter time. Saturated dicarboxylic acid, saturated tetracarboxylic acid, and unsaturated alicyclic dicarboxylic acid are more preferable.
In particular, the present invention contains 1,2,3,4-butanetetracarboxylic acid silver salt, which is 1,2,3,4-butanetetracarboxylic acid, which is the resulting polycarboxylic acid silver salt (B2). It is preferable because formation of an electrode or the like using the conductive composition is possible at a lower temperature and in a shorter time.

On the other hand, silver oxide used in the above reaction is similar to the reaction (synthesis) of the fatty acid silver salt (B1) described above, and Ag ₂ O.

The polycarboxylic acid silver salt (B2) is obtained by reacting the above-described polycarboxylic acid having two or more carboxy groups with silver oxide, and is represented by the following formula (IV) in the reaction formula shown below. Preferably it is a compound.
For example, when the compound represented by the above formula (4) is used, this reaction is not particularly limited as long as the reaction represented by the following reaction formula proceeds. A method similar to that when the compound represented by (3) is used can be mentioned.

In the formula (IV), m represents an integer of 2 to 6, R ⁴ represents an m-valent saturated aliphatic hydrocarbon group having 1 to 24 carbon atoms, and an m-valent unsaturated aliphatic group having 2 to 12 carbon atoms. It represents a hydrocarbon group, an m-valent alicyclic hydrocarbon group having 3 to 12 carbon atoms, or an m-valent aromatic hydrocarbon group having 6 to 12 carbon atoms. When the carbon number of R ⁴ is p, m ≦ 2p + 2.
In the formula (IV), when m is 2 or more, the carbons of R ^{4 to which} the carbon of the carboxy group is bonded may be the same or different.

  In the present invention, the content of the fatty acid silver salt (B) is good for printability, and can form an electrode having a smaller volume resistivity, and therefore, with respect to 100 parts by mass of the silver powder (A). The amount is preferably 1 to 100 parts by mass, and more preferably 5 to 50 parts by mass.

<Epoxy resin (C)>
The epoxy resin (C) used in the conductive composition of the present invention is not particularly limited as long as it is a resin composed of a compound having two or more oxirane rings (epoxy groups) in one molecule. Is 90-2000.
A conventionally well-known epoxy resin can be used as such an epoxy resin.
Specifically, for example, epoxy compounds having a bisphenyl group such as bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AF type, biphenyl type, and polyalkylene Bifunctional glycidyl ether type epoxy resins such as glycol type, alkylene glycol type epoxy compounds, epoxy compounds having a naphthalene ring, and epoxy compounds having a fluorene group;
Polyfunctional glycidyl ether type epoxy resins such as phenol novolac type, orthocresol novolak type, trishydroxyphenylmethane type, tetraphenylolethane type;
Glycidyl ester epoxy resins of synthetic fatty acids such as dimer acid;
N, N, N ′, N′-tetraglycidyldiaminodiphenylmethane (TGDDM), tetraglycidyldiaminodiphenylsulfone (TGDDS), tetraglycidyl-m-xylylenediamine (TGMXDA), triglycidyl-p-aminophenol, triglycidyl- Glycidylamine epoxy resins such as m-aminophenol, N, N-diglycidylaniline, tetraglycidyl 1,3-bisaminomethylcyclohexane (TG1,3-BAC), triglycidyl isocyanurate (TGIC);
Tricyclo [5,2,1,0 ^2,6] epoxy compound having a decane ring, specifically, for example, after polymerizing the cresols or phenols such as dicyclopentadiene and cresol are reacted with epichlorohydrin Epoxy compounds obtainable by known production methods;
Cycloaliphatic epoxy resin; epoxy resin represented by Toraythiol Co., Ltd. Frep 10 epoxy resin main chain having sulfur atom; urethane modified epoxy resin having urethane bond; polybutadiene, liquid polyacrylonitrile-butadiene rubber or acrylonitrile butadiene rubber Examples thereof include a rubber-modified epoxy resin containing (NBR).

These may be used alone or in combination of two or more.
Of these, bisphenol A type epoxy resins and bisphenol F type epoxy resins are preferable from the viewpoints of curability, heat resistance, durability, and cost.

In the present invention, the epoxy resin (C) is added with ethylene oxide and / or propylene oxide because it has a lower volume resistivity and can form an electrode having better adhesion to the silicon substrate. It is preferable to be an epoxy resin.
Here, addition with ethylene oxide and / or propylene oxide is performed by adding ethylene and / or propylene when an epoxy resin is prepared by reacting, for example, bisphenol A, bisphenol F, etc.) with epichlorohydrin. (Denaturation).
Commercially available products can be used as the epoxy resin to which ethylene oxide and / or propylene oxide is added. Specific examples thereof include ethylene oxide-added bisphenol A type epoxy resin (BEO-60E, manufactured by Shin Nippon Rika Co., Ltd.), propylene oxide addition. Bisphenol A type epoxy resin (BPO-20E, manufactured by Shin Nippon Chemical Co., Ltd.), Propylene oxide added bisphenol A type epoxy resin (EP-4010S, manufactured by ADEKA), Propylene oxide added bisphenol A type epoxy resin (EP-4000S, ADEKA) Manufactured) and the like.

  In the present invention, the content of the epoxy resin (C) is such that the volume resistivity is lower and an electrode or the like having better adhesion to the silicon substrate can be formed, so that the silver powder (A) It is preferable that it is 1-100 mass parts with respect to 100 mass parts, and it is more preferable that it is 5-50 mass parts.

<Cationic curing agent (D)>
The cationic curing agent (D) used in the conductive composition of the present invention is not particularly limited, and sulfonium-based, ammonium-based, and phosphonium-based curing agents are preferable.
Specific examples of the cationic curing agent (D) include boron trifluoride amine salt, P-methoxybenzenediazonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, tetraphenylsulfonium, tetra-n. -Butylphosphonium tetraphenylborate, tetra-n-butylphosphonium-o, o-diethyl phosphorodithioate, sulfonium salt represented by the following formula (i), sulfonium salt represented by the following formula (ii) These may be used alone or in combination of two or more.

(In formula (i), X represents a hydroxyl group or a group represented by any of the following formulas (a) to (c), and Ar represents an aryl group.)
(In formulas (a) to (c), each R independently represents an aromatic or aliphatic hydrocarbon group which may have a substituent.)

R in the above formulas (a) to (c) is not particularly limited because various substituents can be selected from the viewpoint of adjusting curability, but examples of the aromatic hydrocarbon group represented by R include: An aryl group having 6 to 18 carbon atoms, an arylalkyl group, and an arylalkenyl group, and specifically, an aryl group such as a phenyl group, a naphthyl group, a biphenylenyl group, a fluorenyl group, an anthryl group, and a p-toluenesulfonyl group; Arylalkyl groups such as benzyl group and phenylethyl group; arylalkenyl groups such as styryl group and cinnamyl group; and the like.
Similarly, examples of the aliphatic hydrocarbon group represented by R include a saturated or unsaturated chain hydrocarbon group having 1 to 12 carbon atoms (for example, an alkyl group, an alkenyl group, an alkynyl group, etc.). Specifically, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, hexyl group, isohexyl group group, 2-ethylhexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, vinyl group, allyl group, isopropenyl _{group, -CH = CH- (CH 2)} 8 - group, ethynyl group Etc.

  Among these, it is preferable to use the sulfonium salt represented by the above formula (i) for the reason that the curing time is short, and X in the above formula (i) is represented by a hydroxyl group or the above formula (c). It is more preferable to use a sulfonium salt represented by a group (particularly a p-toluenesulfonyl group).

In this invention, low temperature (150-350) is used by using the conductive composition which mix | blended the cationic hardening | curing agent (D) with the silver powder (A) mentioned above, fatty acid silver salt (B), and an epoxy resin (C). Even when firing, an electrode or the like having a low volume resistivity and excellent adhesion to a silicon substrate can be formed.
This is because the degree of polymerization of the epoxy resin (C) is higher than that when an imidazole curing agent is used by using a cationic curing agent (D) that exhibits sufficient curability even at low temperatures (about 150 to 350 ° C.). As a result, the contact between the silver powders (A) described above increases, and it is considered that the occurrence of disconnection is suppressed and high conductivity is expressed. In addition, when silver decomposed from the fatty acid silver salt (B) is melted by heat treatment, the silicon substrate is appropriately wetted and spread, so that the adhesion to the silicon substrate is considered to be improved.

  In the present invention, the content of the cationic curing agent (D) is such that the volume resistivity is lower and an electrode or the like having better adhesion to the silicon substrate can be formed. It is preferable that it is 0.1-10 mass parts with respect to 100 mass parts of epoxy resins (C), and it is more preferable that it is 0.1-5 mass parts.

<Solvent (E)>
The conductive composition of the present invention preferably contains a solvent (E) from the viewpoint of workability such as printability.
The solvent (E) is not particularly limited as long as it can apply the conductive composition of the present invention onto a substrate. Specific examples thereof include butyl carbitol, methyl ethyl ketone, isophorone, α-terpineol. These may be used, and these may be used alone or in combination of two or more.

<Silver oxide>
The conductive composition of the present invention suppresses the above-described decomposition of the epoxy resin (C) and can maintain excellent adhesion to the silicon substrate, so the content of silver oxide is 100 mass of the solvent (E) described above. The amount is preferably 5 parts by mass or less, more preferably 1 part by mass or less, and most preferably an embodiment containing substantially no silver oxide.

<Additives>
The electrically conductive composition of this invention may contain additives, such as metal powder other than the silver powder (A) mentioned above, a reducing agent, as needed.
Specific examples of the metal powder include copper and aluminum. Among them, copper is preferable. Moreover, it is preferable that it is a metal powder with a particle size of 0.01-10 micrometers.
Specific examples of the reducing agent include ethylene glycols.

  The method for producing the conductive composition of the present invention is not particularly limited, and the silver powder (A), the fatty acid silver salt (B), the epoxy resin (C), the cationic curing agent (D), and optionally contained. Examples thereof include a method of mixing the solvent (E), additives, and the like, which may be mixed, using a roll, a kneader, an extruder, a universal agitator, or the like.

The solar cell of the present invention comprises a light-receiving surface-side surface electrode, a semiconductor substrate, and a back electrode, and the surface electrode and / or the back electrode is formed using the above-described conductive composition of the present invention. It is a solar battery cell.
Here, the solar battery cell of the present invention can be applied to the formation of the back electrode of the all back electrode type (so-called back contact type) solar battery because the above-described conductive composition of the present invention can be applied to the all back electrode. The present invention can also be applied to a type solar cell.
Below, the structure of the photovoltaic cell of this invention is demonstrated using FIG.

As shown in FIG. 1, a solar cell 1 of the present invention includes a surface electrode 4 on the light-receiving surface side, a pn junction silicon substrate 7 in which a p layer 5 and an n layer 2 are joined, and a back electrode 6. It is.
Further, as shown in FIG. 1, the solar battery cell 1 of the present invention is provided with an antireflection film 3 by, for example, etching the wafer surface to form a pyramidal texture in order to reduce the reflectance. Is preferred.

<Front electrode / Back electrode>
If either one or both of the front electrode and the back electrode included in the solar battery cell of the present invention are formed using the conductive composition of the present invention, the electrode arrangement (pitch), shape, height, The width and the like are not particularly limited. The height of the electrode is usually designed to be several to several tens of μm, but the ratio of the height and width of the cross section of the electrode formed using the conductive composition of the present invention (height / width) (hereinafter referred to as “height / width”) , “Aspect ratio”) can be adjusted to a large value (for example, about 0.4 or more).
Here, as shown in FIG. 1, the front surface electrode and the back surface electrode usually have a plurality, but in the present invention, for example, only a part of the plurality of front surface electrodes is the conductive composition of the present invention. Or a part of the plurality of front surface electrodes and a part of the plurality of back surface electrodes may be formed of the conductive composition of the present invention.

<Antireflection film>
The antireflection film that the solar battery cell of the present invention may have is a film (film thickness: about 0.05 to 0.1 μm) formed on a portion of the light receiving surface where the surface electrode is not formed. For example, a silicon oxide film, a silicon nitride film, a titanium oxide film, or a laminated film thereof.

<Silicon substrate>
The silicon substrate included in the solar battery cell of the present invention is not particularly limited, and a known silicon substrate (plate thickness: about 100 to 450 μm) for forming a solar battery can be used, and a single crystal or polycrystal Any silicon substrate may be used.

The silicon substrate has a pn junction, which means that a second conductivity type light-receiving surface impurity diffusion region is formed on the surface side of the first conductivity type semiconductor substrate. When the first conductivity type is n-type, the second conductivity type is p-type. When the first conductivity type is p-type, the second conductivity type is n-type.
Here, examples of the impurity imparting p-type include boron and aluminum, and examples of the impurity imparting n-type include phosphorus and arsenic.

  In the solar battery cell of the present invention, the front electrode and / or the back electrode are formed using the conductive composition of the present invention, so that the aspect ratio of the electrode is easily increased, and the electromotive force generated by light reception is used as the current. It can be taken out efficiently.

Although the manufacturing method of the photovoltaic cell of the present invention is not particularly limited, a wiring forming step of forming the wiring by applying the conductive composition of the present invention on a silicon substrate, and heat treating the obtained wiring to form an electrode (surface Electrode forming step of forming an electrode and / or a back electrode).
In addition, when the photovoltaic cell of this invention comprises an antireflection layer, an antireflection film can be formed by well-known methods, such as a plasma CVD method.
Below, a wiring formation process and a heat treatment process are explained in full detail.

<Wiring formation process>
The said wiring formation process is a process of apply | coating the electrically conductive composition of this invention on a silicon base material, and forming wiring.
Here, specific examples of the coating method include inkjet, screen printing, gravure printing, offset printing, letterpress printing, and the like.

<Heat treatment process>
The heat treatment step is a step of obtaining a conductive wiring (electrode) by heat-treating the coating film obtained in the wiring forming step.
By heat-treating the wiring, when the silver decomposed from the fatty acid silver salt (B) melts, the silver powder (A) is connected to form an electrode (silver film).

In the present invention, the heat treatment is not particularly limited, but is preferably a treatment of heating (firing) at a relatively low temperature of 150 to 350 ° C. for several seconds to several tens of minutes. When the temperature and time are within this range, even when an antireflection film is formed on the silicon substrate, the electrode can be easily formed by the fire-through method.
In the present invention, since the conductive composition of the present invention is used, good heat treatment (firing) can be performed even at a low temperature (about 150 to 350 ° C.).

  In the present invention, since the wiring obtained in the wiring formation step can form electrodes even by irradiation with ultraviolet rays or infrared rays, the heat treatment step may be performed by irradiation with ultraviolet rays or infrared rays. .

  Hereinafter, the conductive composition of the present invention will be described in detail using examples. However, the present invention is not limited to this.

(Examples 1-5, Comparative Examples 1-2)
To the ball mill, silver powder and the like shown in Table 1 below were added so as to have the composition ratio shown in Table 1 below, and these were mixed to prepare a conductive composition.
Next, the prepared conductive composition was applied on a silicon substrate (single crystal silicon wafer, LS-25TVA, 156 mm × 156 mm × 200 μm, manufactured by Shin-Etsu Chemical Co., Ltd.) by screen printing to form a coating film. And dried at 200 ° C. for 30 minutes to prepare a conductive film.

<Volume resistivity (specific resistance)>
About each formed conductive film, the specific resistance (volume specific resistance value) was measured by the 4-terminal 4 probe method using the low resistivity meter (Lorestar GP, Mitsubishi Chemical Corporation make). The results are shown in Table 1 below.

<Adhesion>
The evaluation of the adhesion of each formed conductive film to the silicon substrate was performed by a grid peel test. The results are shown in Table 1 below.
Specifically, on each of the obtained silicon substrates with a conductive coating, 100 1 mm bases (10 × 10) were made, and cellophane adhesive tape was completely adhered on the bases, and 10 times with the finger pad. After rubbing, one end of the tape was momentarily pulled away while keeping one end of the tape at right angles to the conductive film, and the number of base meshes remaining without being completely peeled was examined. It is most preferable that the number of base meshes remaining without being completely peeled is 100, that is, those having not peeled off at all.

The following were used for each component in Table 1.
Silver powder 1: AgC-103 (shape: spherical, average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Co., Ltd.)
Silver powder 2: AgC-2011 (shape: flake shape, average particle size: 2 to 10 μm, manufactured by Fukuda Metal Foil Co., Ltd.)

2,2-bis (hydroxymethyl) -n-butyric acid silver salt:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 64 g of 2,2-bis (hydroxymethyl) -n-butyric acid (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) are put in a ball mill and stirred at room temperature for 24 hours. It was made to react.
Subsequently, MEK was removed by suction filtration, and the resulting powder was dried to prepare white 2,2-bis (hydroxymethyl) -n-butyric acid silver salt.

-Silver 2-hydroxyisobutyrate:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 45 g of 2-hydroxyisobutyric acid (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) were placed in a ball mill and reacted by stirring at room temperature for 24 hours.
Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare white 2-hydroxyisobutyric acid silver salt.

-1,2,3,4-butanetetracarboxylic acid silver salt:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 25.29 g of 1,2,3,4-butanetetracarboxylic acid (manufactured by Shin Nippon Rika Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) were put into a ball mill, and the mixture was stirred at room temperature. The reaction was allowed to stir for hours.
Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare white 1,2,3,4-butanetetracarboxylic acid silver salt.

PO addition epoxy resin: propylene oxide addition bisphenol A type epoxy resin (EP-4000, manufactured by ADEKA)
Bisphenol A type epoxy resin: EP-4100E (manufactured by ADEKA)
・ Bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel Chemical Co., Ltd.)
Solvent: α-terpineol Cationic curing agent D1: Sulfonium salt represented by the following formula (i-1) Cationic curing agent D2: Sulfonium salt represented by the following formula (i-2) Imidazole curing Agent: Amicure (Ajinomoto Fine Techno Co., Ltd.)

From the results shown in Table 1, it was found that Comparative Examples 1 and 2 prepared using an imidazole curing agent without using a cationic curing agent (D) had a high volume resistivity.
On the other hand, Examples 1 to 5 prepared using the cationic curing agent (D) have low volume resistivity and adhesion to the silicon substrate even under low temperature firing conditions of 200 ° C. for 30 minutes. It turned out that it is excellent also in property.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 N layer 3 Antireflection film 4 Surface electrode 5 P layer 6 Back electrode 7 Silicon substrate

Claims (16)

  A conductive composition containing silver powder (A), a fatty acid silver salt (B), an epoxy resin (C), and a cationic curing agent (D). The conductive composition according to claim 1, wherein the cationic curing agent (D) is a sulfonium salt represented by the following formula (i).
(In formula (i), X represents a hydroxyl group or a group represented by any of the following formulas (a) to (c), and Ar represents an aryl group.)
(In formulas (a) to (c), each R independently represents an aromatic or aliphatic hydrocarbon group which may have a substituent.)   The fatty acid silver salt (B) is a fatty acid silver salt (B1) having at least one carboxy silver base (—COOAg) and one hydroxyl group (—OH) and / or two carboxy silver bases (—COOAg). The conductive composition according to claim 1, which is a polycarboxylic acid silver salt (B2) having the above. The conductive composition according to claim 3, wherein the fatty acid silver salt (B1) is a compound represented by any one of the following formulas (I) to (III).
(In formula (I), n represents an integer of 0 to 2, R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² represents an alkylene group having 1 to 6 carbon atoms. When it is 0 or 1, the plurality of R ² may be the same or different, and when n is 2, the plurality of R ¹ may be the same or different.
In formula (II), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and a plurality of R ¹ may be the same or different.
In formula (III), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ³ represents an alkylene group having 1 to 6 carbon atoms. The plurality of R ¹ may be the same or different. )   The conductive composition according to claim 3 or 4, wherein the fatty acid silver salt (B1) has the hydroxyl group at a carbon atom at the α-position and / or the β-position with respect to the carboxy silver base.   The conductive composition according to any one of claims 3 to 5, wherein the fatty acid silver salt (B1) has one of the carboxy silver bases and one or two of the hydroxyl groups.   The conductive composition according to claim 3, wherein the polycarboxylic acid silver salt (B2) does not have a hydroxyl group. The conductive composition according to claim 3 or 7, wherein the polycarboxylic acid silver salt (B2) is a compound represented by the following formula (IV).
(In Formula (IV), m represents an integer of 2 to 6, R ⁴ represents an m-valent saturated aliphatic hydrocarbon group having 1 to 24 carbon atoms, and an m-valent unsaturated fat having 2 to 12 carbon atoms. family hydrocarbon group, m-valent alicyclic hydrocarbon group having 3 to 12 carbon atoms, or, when the carbon number of the .R ⁴ representing the m-valent aromatic hydrocarbon group having 6 to 12 carbon atoms and p, m ≦ 2p + 2.)   The conductive composition according to any one of claims 1 to 8, wherein the epoxy resin (C) is an epoxy resin to which ethylene oxide and / or propylene oxide is added.   The conductive acid according to claim 3, wherein the fatty acid silver salt (B1) is 2,2-bis (hydroxymethyl) -n-butyric acid silver salt and / or 2-hydroxyisobutyric acid silver salt. Sex composition.   The conductive composition according to any one of claims 3 and 7 to 9, wherein the silver salt of polycarboxylic acid (B2) is 1,2,3,4-butanetetracarboxylic acid silver salt.   The conductive composition according to any one of claims 1 to 11, wherein a content of the fatty acid silver salt (B) is 1 to 100 parts by mass with respect to 100 parts by mass of the silver powder (A).   Content of the said epoxy resin (C) is 1-50 mass parts with respect to 100 mass parts of said silver powder (A), The electroconductive composition in any one of Claims 1-12.   The conductive composition according to any one of claims 1 to 13, wherein a content of the cationic curing agent (D) is 0.1 to 10 parts by mass with respect to 100 parts by mass of the epoxy resin (C). .   The electroconductive composition according to claim 1, which is used for a solar cell electrode paste. It comprises a surface electrode on the light receiving surface side, a semiconductor substrate and a back electrode
The photovoltaic cell in which the said surface electrode and / or the said back surface electrode are formed using the electrically conductive composition of Claim 15.