JP2012022804A - 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); and an epoxy resin (C) with ethylene oxide and/or propylene oxide added.

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. The conductive paste composition characterized by containing. "
Patent Document 2 states that “in a conductive paste composition containing silver powder, a thermosetting component and a solvent, the thermosetting component contains a bisphenol A type epoxy resin having an epoxy equivalent of 2000 to 3500 g / eq. And a polyhydric alcohol-based glycidyl-type epoxy resin having an epoxy equivalent of 1000 g / eq or less and a viscosity of 10 to 100 mPa · s, and a curing agent, wherein the polyhydric alcohol-based glycidyl-type epoxy resin comprises: An alkyldiol system having the structural formula of Chemical Formula 1 or a polyethylene glycol system having the structural formula of Chemical Formula 2 below, wherein n in the structural formula of Chemical Formula 1 and the structural formula of Chemical Formula 2 is 3 to 9, and the bisphenol A type epoxy The weight mixing ratio of the resin to the polyhydric alcohol glycidyl type epoxy resin is 1: 1 to 1: 3. Conductive paste composition and. "Is described.

  On the other hand, Patent Documents 3 and 4 include 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 flexible PCBs and RFID antennas is described, and Patent Document 3 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 citric acid as fatty acid silver, A plate-type silver powder is described as the silver powder, and an epoxy resin binder is described as the binder ([0027] [0035]).

JP 2006-40708 A JP 2009-146588 A Special table 2010-504612 gazette Special table 2010-505230 gazette

However, in the conductive paste compositions described in Patent Documents 1 and 2, the connection of silver powder does not proceed, and the volume resistivity (specific resistance) of electrodes and wirings may increase. It became clear that the adhesiveness of was inferior.
Further, the paste materials described in Patent Documents 3 and 4 have high volume resistivity (specific resistance) of the conductive film used for forming the conductive line pattern and the electrode depending on the type of epoxy resin binder used and the firing temperature. In addition, it became clear that the adhesion to the silicon substrate was inferior.

  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 an epoxy resin in which ethylene oxide and / or propylene oxide is added to silver powder and a fatty acid silver salt has a volume resistivity. The inventors have found that an electrode and the like that are low and have excellent adhesion to a silicon substrate can be formed, and the present invention has been completed. That is, the present invention provides the following (1) to (13).

  (1) A conductive composition containing silver powder (A), a fatty acid silver salt (B), and an epoxy resin (C) to which ethylene oxide and / or propylene oxide is added.

  (2) 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 carboxy silver base (—COOAg) The conductive composition according to (1) above, which is a polycarboxylic acid silver salt (B2) having two or more.

(3) The conductive composition according to (2), 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. )

  (4) The conductive composition according to (2) or (3), 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. .

  (5) The conductive composition according to any one of (2) to (4), wherein the fatty acid silver salt (B1) has one carboxy silver base and one or two hydroxyl groups.

  (6) The conductive composition according to (2), wherein the polycarboxylic acid silver salt (B2) does not have a hydroxyl group.

(7) The conductive composition according to (2) or (6), 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.)

  (8) The fatty acid silver salt (B1) is at least one selected from the group consisting of 2,2-bis (hydroxymethyl) -n-butyric acid silver salt, 2-hydroxyisobutyric acid silver salt and glycolic acid silver salt. The electroconductive composition in any one of said (2)-(5).

  (9) In the above (2), (6) and (7), the polycarboxylic acid silver salt (B2) is a glutaric acid silver salt and / or a 1,2,3,4-butanetetracarboxylic acid silver salt. The electroconductive composition in any one.

  (10) The conductivity according to any one of (1) to (9), 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.

  (11) The conductive composition according to any one of (1) to (10), 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.

  (12) The conductive composition according to any one of (1) to (11), which is used for a solar cell electrode paste.

(13) A surface electrode on the light-receiving surface side, a semiconductor substrate, and a back electrode are provided,
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 (12).

  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.

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), and an epoxy resin (C) to which ethylene oxide and / or propylene oxide is added.
Moreover, the electrically conductive composition of this invention may contain the solvent (D) as needed from viewpoints of printability etc. so that it may mention later.
Below, the silver powder (A), the fatty acid silver salt (B), the resin (C), and the solvent (D) that may be optionally contained are 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. to 100 mass parts of solvent (D) 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, but even when firing at a low temperature (about 150 to 350 ° C.), the occurrence of disconnection is suppressed. In order to form a wiring (electrode) and reduce damage to the silicon substrate due to heat, a fatty acid silver salt having at least one carboxy silver base (—COOAg) and one hydroxyl group (—OH) each ( B1) and / or a polycarboxylic acid silver salt (B2) having two or more carboxy silver bases (—COOAg) is preferred.
By using such a fatty acid silver salt (B1) or polycarboxylic acid silver salt (B2), not only a silicon substrate but also a circuit such as an electronic circuit and an antenna can be easily and quickly formed on a substrate having low heat resistance. It is very useful because it can be made with.
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, the fatty acid silver salt (B2) obtained is at least one selected from the group consisting of 2,2-bis (hydroxymethyl) -n-butyric acid, 2-hydroxyisobutyric acid and glycolic acid. Electrode using the conductive composition of the present invention containing at least one selected from the group consisting of 2-bis (hydroxymethyl) -n-butyric acid silver salt, 2-hydroxyisobutyric acid silver salt and silver glycolate Is preferable because it can be formed 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.

Of these, aliphatic polycarboxylic acids and alicyclic polycarboxylic acids are used because the printability is good and the formation of electrodes and 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, glutaric acid and / or 1,2,3,4-butanetetracarboxylic acid is the resulting polycarboxylic acid silver salt (B2), glutaric acid silver salt and / or 1,2,3,4. -It is preferable from the reason that formation of an electrode or the like using the conductive composition of the present invention containing a silver salt of butanetetracarboxylic acid 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 80 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 an epoxy resin to which ethylene oxide and / or propylene oxide is added.
Here, the addition by ethylene oxide and / or propylene oxide is performed by adding ethylene and / or propylene when preparing an epoxy resin by reacting bisphenol A, bisphenol F or the like with epichlorohydrin ( Denatured).

  Commercially available products can be used as such epoxy resin (C). Specific examples thereof include ethylene oxide-added bisphenol A type epoxy resin (BEO-60E, manufactured by Shin Nippon Rika Co., Ltd.), propylene oxide added bisphenol A type epoxy resin. (BPO-20E, manufactured by Shin Nippon Rika 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, manufactured by ADEKA) and the like. It is done.

In the present invention, by using a conductive composition in which the epoxy resin (C) is blended together with the silver powder (A) and the fatty acid silver salt (B) described above, the volume resistivity is lowered and the adhesion to the silicon substrate is reduced. It is possible to form an electrode having excellent properties.
This is presumably because the epoxy resin (C) has higher flexibility than a normal epoxy resin such as a bisphenol A type epoxy resin, and therefore exhibits high conductivity by suppressing the occurrence of disconnection. In addition, since the epoxy resin (C) spreads moderately on the silicon substrate together with the silver decomposed from the fatty acid silver salt (B) by heat treatment, it is considered that the adhesion with the silicon substrate is improved.

  Further, 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. A) It is preferable that it is 1-50 mass parts with respect to 100 mass parts, and it is more preferable that it is 1-25 mass parts.

<Solvent (D)>
The conductive composition of the present invention preferably contains a solvent (D) from the viewpoint of workability such as printability.
The solvent (D) is not particularly limited as long as the conductive composition of the present invention can be applied 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.

<Curing agent>
The conductive composition of the present invention preferably contains the epoxy resin (C) curing agent described above.
The said hardening | curing agent is not specifically limited, What is mix | blended with the epoxy resin in the conventionally well-known electrically conductive paste can be used.

<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. Therefore, the silver oxide content is 100 masses of the solvent (D) 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.

<Glass frit>
When the conductive composition of the present invention is used in a solar cell electrode paste, it can contain a glass frit as desired because the adhesion between the formed electrode and the silicon substrate becomes better. In addition, when forming an electrode etc. by baking by low temperature (about 150-350 degreeC), especially the temperature of 200 degrees C or less, glass frit is not normally contained.

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 manufacturing method of the electroconductive composition of this invention is not specifically limited, The said silver powder (A), the said fatty acid silver salt (B), the said epoxy resin (C), and the said solvent (D) hardening which may be contained depending on necessity Examples thereof include a method of mixing agents, additives and the like with a roll, a kneader, an extruder, a universal agitator, and 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 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 1-8, 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. Was dried for 30 minutes under two conditions of 200 ° C. and 450 ° C. to produce 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.

・ Silver glycolate:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 32.8 g of glycolic 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 a white silver glycolate.

・ Glutaric acid silver salt:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 57 g of glutaric 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 silver glutarate.

-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.

・ 2-ethylhexanoic acid silver salt:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 62.21 g of 2-ethylhexanoic 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-ethylhexanoic acid silver salt.

・ Neodecanoic acid silver salt:
First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 74.3 g of neodecanoic acid (manufactured by Toyo Gosei Co., Ltd.) and 300 g of MEK were put into a ball mill and reacted by stirring at room temperature for 24 hours.
Next, MEK was removed by suction filtration, and the obtained powder was dried to prepare a silver neodecanoate.

PO addition epoxy resin: propylene oxide addition bisphenol A type epoxy resin (EP-4000, manufactured by ADEKA)
-EO-added epoxy resin: ethylene oxide-added bisphenol A type epoxy resin (BEO-60E, manufactured by Shin Nippon Rika Co., Ltd.)
-Bisphenol A type epoxy resin: EP-4010 (manufactured by ADEKA)
・ Bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel Chemical Co., Ltd.)
・ Solvent: α-Terpinel ・ Curing agent: Aromatic sulfonium salt (Sl-100L, manufactured by Sanshin Chemical Industry Co., Ltd.)

From the results shown in Table 1, Comparative Examples 1 and 2 prepared using an epoxy resin to which ethylene oxide or propylene oxide is not added have high volume resistivity and inferior adhesion to the silicon substrate. I understood.
On the other hand, Examples 1 to 8 prepared using a predetermined epoxy resin (C) are not only medium temperature baking conditions of 450 ° C. for 30 minutes, but also low temperature baking conditions of 200 ° C. for 30 minutes, It was found that the volume resistivity was low and the adhesion to the silicon substrate was excellent. In particular, Examples 1 to 7 prepared using a predetermined fatty acid silver salt (B1) and polycarboxylic acid silver salt (B2) were found to have a lower volume resistivity.

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 (13)

  A conductive composition containing silver powder (A), a fatty acid silver salt (B), and an epoxy resin (C) to which ethylene oxide and / or propylene oxide is added.   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 2, 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. )   4. The conductive composition according to claim 2, wherein the fatty acid silver salt (B1) has the hydroxyl group at the α-position and / or β-position carbon atom with respect to the carboxy silver base.   The conductive composition according to claim 2, wherein the fatty acid silver salt (B1) has one carboxy silver base and one or two hydroxyl groups.   The conductive composition according to claim 2, wherein the polycarboxylic acid silver salt (B2) does not have a hydroxyl group. The conductive composition according to claim 2 or 6, wherein the silver polycarboxylic acid 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 fatty acid silver salt (B1) is at least one selected from the group consisting of 2,2-bis (hydroxymethyl) -n-butyric acid silver salt, 2-hydroxyisobutyric acid silver salt and glycolic acid silver salt. The electrically conductive composition in any one of 2-5.   The electroconductive composition according to any one of claims 2, 6 and 7, wherein the polycarboxylic acid silver salt (B2) is a glutaric acid silver salt and / or a 1,2,3,4-butanetetracarboxylic acid silver salt. object.   The conductive composition according to any one of claims 1 to 9, 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).   The conductive composition according to any one of claims 1 to 10, wherein a 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).   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 12.