JP2012248790A - Conductive composition for forming solar cell collector electrode, and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive composition for forming a solar cell collector electrode, which allows an electrode having a low volume resistivity and a high aspect ratio to be formed, and to provide a solar cell using the same which exhibits a high fill factor.SOLUTION: The conductive composition for forming a solar cell collector electrode contains conductive particles (A), a fatty acid silver salt (B), an organic thixotropic agent (C), glass frit (D), and a solvent (E).

Description

  The present invention relates to a conductive composition for forming a solar battery collecting electrode and a solar battery cell.

  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 an electrode of such a solar cell, for example, Patent Document 1 discloses, by the present applicant, “silver oxide (A), silver carboxylate (B), and an organic compound having a boiling point of 200 ° C. or more. A conductive composition containing a solvent (C) and containing at least 50% by mass of the silver oxide (A) in the composition ”([Claim 3]), and silver powder or glass as an optional component. A mode including frit and the like is described ([claim 6] [claim 7] [0041] [0044] and the like).

  In addition, in Patent Document 2, the present applicant states that “a silver powder (A), a silver oxide (B), and an organic solvent (D) are contained, and the silver powder (A) is contained in the composition. A conductive composition that is 50% by mass or more in a simple substance and a silver compound has been proposed ([Claim 1]), and an embodiment that includes silver carboxylate as an optional component, and other additives such as glass frit. A mode of inclusion is described ([Claim 2] [0030] [0031] [0032] and the like).

JP 2011-35061 A JP 2011-35062 A

  However, the present inventor examined the conductive compositions described in Patent Documents 1 and 2, and when only silver powder was used instead of silver oxide, the volume resistivity of the formed electrode was kept low. However, it has been clarified that the aspect ratio is low and the fill factor (FF) of the obtained solar battery cell may be low.

  Accordingly, the present invention provides a conductive composition for forming a solar battery collecting electrode capable of forming an electrode having a low volume resistivity and a high aspect ratio, and a solar battery cell having a high fill factor using the same. The issue is to provide.

  As a result of intensive studies to solve the above problems, the present inventor has a low volume resistivity and a high aspect ratio by blending an organic thixotropic agent into a conductive composition containing glass frit. The inventors have found that an electrode can be formed and completed the present invention. That is, the present invention provides the following (1) to (11).

  (1) A conductive composition for forming a solar cell collecting electrode, comprising conductive particles (A), fatty acid silver salt (B), organic thixotropic agent (C), glass frit (D) and solvent (E) .

  (2) The conductive composition for forming a solar cell collecting electrode according to (1) above, wherein the pyrolysis temperature of the organic thixotropic agent (C) by thermogravimetry is 300 to 500 ° C.

  (3) The organic thixotropic agent (C) is a hydrogenated castor oil thixotropic agent (C1), a polyethylene oxide thixotropic agent (C2), an amide type thixotropic agent (C3), or a polymerized oil type thixotropic agent. (C4) and for forming a solar cell collecting electrode according to the above (1) or (2), which is at least one thixotropic agent selected from the group consisting of a surfactant thixotropic agent (C5) Conductive composition.

  (4) The solar cell collection according to (3), wherein the organic thixotropic agent (C) is the polyethylene oxide thixotropic agent (C2) and / or the amide type thixotropic agent (C3). A conductive composition for forming an electrode.

  (5) The fatty acid silver salt (B2) in which the fatty acid silver salt (B) has at least one fatty acid silver salt (B1), carboxy silver base (—COOAg) and hydroxyl group (—OH) each having 18 or less carbon atoms. And at least one fatty acid silver salt selected from the group consisting of a polycarboxylic acid silver salt (B3) having two or more carboxy silver bases (—COOAg) without having a hydroxyl group (—OH) (1) -The conductive composition for solar cell current collection electrode formation in any one of (4).

  (6) The above (A) wherein the fatty acid silver salt (B1) is a combined system of a fatty acid silver salt having 1 to 8 carbon atoms (B1-1) and a fatty acid silver salt having 9 to 18 carbon atoms (B1-2). 5) A conductive composition for forming a solar cell collecting electrode.

  (7) The sun according to any one of (1) to (6), wherein the content of the fatty acid silver salt (B) is 1 to 25 parts by mass with respect to 100 parts by mass of the conductive particles (A). A conductive composition for forming a battery current collecting electrode.

  (8) Any of (1) to (7), wherein the content of the organic thixotropic agent (C) is 0.1 to 10 parts by mass with respect to 100 parts by mass of the conductive particles (A). The electrically conductive composition for solar cell current collection electrode formation of description.

  (9) The conductive composition for forming a solar cell collector electrode according to any one of (1) to (8), further comprising a resin binder (F).

  (10) A light-receiving surface side surface electrode, an antireflection film, a semiconductor substrate, and a back surface electrode are provided, and at least the surface electrode is for forming a solar cell collecting electrode according to any one of (1) to (9) above A solar battery cell formed using a conductive composition.

  (11) A solar cell module in which the solar cells according to (10) are wired in series using an interconnector.

  As shown below, according to the present invention, a conductive composition for forming a solar cell collector electrode capable of forming an electrode having a low volume resistivity and a high aspect ratio, and a high fill factor using the same. Can be provided.

FIG. 1 is a cross-sectional view showing an example of a preferred embodiment of a solar battery cell.

[Conductive composition for forming solar cell collector electrode]
The conductive composition for forming a solar cell collecting electrode of the present invention (hereinafter abbreviated as “the conductive composition of the present invention”) is composed of conductive particles (A), fatty acid silver salt (B), and organic system fluctuation. It is an electroconductive composition for solar cell current collection electrode formation containing an agent (C), glass frit (D), and a solvent (E).
Hereinafter, the conductive particles (A), the fatty acid silver salt (B), the organic thixotropic agent (C), the glass frit (D) and the solvent (E), and other components that may be optionally contained, are described in detail. Describe.

<Conductive particles (A)>
The conductive particles (A) used in the conductive composition of the present invention are not particularly limited, and for example, a metal material having an electrical resistivity of 20 × 10 ⁻⁶ Ω · cm or less can be used.
Specific examples of the metal material include gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), and the like. One species may be used alone, or two or more species may be used in combination.
Among these, gold, silver, and copper are preferable, and silver is more preferable because an electrode having a smaller volume resistivity can be formed and a solar battery cell having a higher fill factor can be manufactured. preferable.

In the present invention, it is preferable to use a metal powder having an average particle size of 0.5 to 10 μm for the conductive particles (A) because of good printability.
Of the above metal powders, it is more preferable to use spherical silver powder because an electrode having a smaller volume resistivity can be formed and a solar battery cell having a higher fill factor can be produced.
Here, an average particle diameter means the average value of the particle diameter of a metal 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 metal powder is an ellipse, the particle diameter used as the basis for calculating the average value is an average value obtained by dividing the total value of the major axis and the minor axis by 2, and in the case of a perfect circle, Refers to the diameter.
The spherical shape refers to the shape of particles having a major axis / minor axis ratio of 2 or less.

  Further, in the present invention, the average particle diameter of the conductive particles (A) is preferably 0.7 to 5 μm because the printing property is better, and the sintering speed is appropriate and the workability is improved. From the reason of being excellent, it is more preferable that it is 1-3 micrometers.

  Furthermore, in this invention, a commercial item can be used as said electroconductive particle (A), As the specific example, AgC-102 (shape: spherical shape, average particle diameter: 1.5 micrometers, Fukuda metal foil powder industry) AGC-103 (shape: spherical, average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry 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, manufactured by DOWA Electronics), SPN5J (shape: spherical) , Average particle size: 1.2 μm, manufactured by Mitsui Kinzoku Co., Ltd.), EHD (shape: spherical, average particle size: 0.5 μm, manufactured by Mitsui Kinzoku Co., Ltd.), AgC-2011 (shape: flake shape, average particle size: 2) 10 [mu] m, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), AgC-301K (shape: flaky, average particle size: 3 to 10 [mu] m, Fukuda metal foil Powder Co., Ltd.) and the like.

<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 (fatty acid), and for example, [0063] to [0068] of JP-A-2008-198595. ] Fatty acid metal salts described in paragraph (particularly tertiary fatty acid silver salts), fatty acid silver salts described in paragraph [0030] of Japanese Patent No. 4482930, and [0029] to [0045] of JP 2010-92684 A. ] The fatty acid silver salt having one or more hydroxyl groups described in the paragraph, the secondary fatty acid silver salt described in the paragraphs [0046] to [0056] of the publication, and [0022] to [0022] of JP 2011-35062 A The silver carboxylate described in [0026] can be used.

Among these, since the printability is improved and a solar battery cell having a higher fill factor can be produced, a carboxylic acid silver salt (B1) having 18 or less carbon atoms, a carboxy silver base (—COOAg) and a hydroxyl group (—OH). ) And a polycarboxylic acid silver salt (B3) having at least two carboxy silver bases (—COOAg) without having a hydroxyl group (—OH). It is preferred to use at least one carboxylic acid silver salt selected from the group.
Among them, as the carboxylate silver salt (B1), an electrode having a higher aspect ratio can be formed, so that the fatty acid silver salt (B1-1) having 1 to 8 carbon atoms and the carbon number 9 to 18 are used. It is more preferable to use the fatty acid silver salt (B1-2) in combination, and it is more preferable to use the fatty acid silver salt (B1-2) in such a range that the ratio (B1-1 / B1-2) is 95/5 to 50/50.
Further, as the polycarboxylic acid silver salt (B3), it has 3 or more carboxy silver bases (—COOAg) without having a hydroxyl group (—OH) because a solar cell exhibiting a higher curve factor can be produced. It is more preferable to use a polycarboxylic acid silver salt.

Here, examples of the carboxylic acid silver salt (B1) include compounds represented by the following formula (I).

(In the formula (I), R ¹ represents an alkyl group having 1 to 6 carbon atoms, R ² represents an alkyl group having 1 to 16 carbon atoms, and R ³ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Represents an alkyl group.)

Moreover, as said carboxylate silver salt (B2), the compound represented by either of following formula (II)-(IV) is mentioned, for example.

(In formula (II), n represents an integer of 0 to 2, R ⁴ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁵ represents an alkylene group having 1 to 6 carbon atoms. When 0 or 1, the plurality of R ⁵ may be the same or different, and when n is 2, the plurality of R ⁴ may be the same or different.
In formula (III), R ⁴ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and a plurality of R ⁴ may be the same or different.
In formula (IV), R ⁴ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁶ represents an alkylene group having 1 to ⁶ carbon atoms. A plurality of R ⁴ may be the same or different. )

Examples of the polycarboxylic acid silver salt (B3) include a compound represented by the following formula (V).

(In the formula (V), m represents an integer of 2 to 6, R ⁷ 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 ⁷ representing the m-valent aromatic hydrocarbon group having 6 to 12 carbon atoms and p, m ≦ 2p + 2.)

Specific examples of the carboxylic acid silver salt (B1-1) include 2-methylpropanoic acid silver salt (also known as isobutyric acid silver salt) and 2-methylbutanoic acid silver salt.
Specific examples of the carboxylic acid silver salt (B1-2) include silver laurate and silver stearate.
Specific examples of the carboxylic acid silver salt (B2) include 2-hydroxyisobutyric acid silver salt and 2,2-bis (hydroxymethyl) -n-butyric acid silver salt.
Specific examples of the polycarboxylic acid silver salt (B3) include 1,3,5-pentanetricarboxylic acid silver salt and 1,2,3,4-butanetetracarboxylic acid silver salt. Is done.

  Moreover, in this invention, content of the said fatty acid silver salt (B) is 1 to 100 mass parts of said electroconductive particle (A) from the reason which can produce the photovoltaic cell which shows a higher curve factor. The amount is preferably 25 parts by mass, and more preferably 5 to 15 parts by mass.

<Organic thixotropic agent (C)>
The organic thixotropic agent (C) used in the conductive composition of the present invention is not particularly limited, but is preferably one that thermally decomposes at a firing temperature (for example, high temperature firing at 700 to 800 ° C.) during electrode formation, It is more preferable to use one having a thermal decomposition temperature of 300 to 500 ° C. according to a measuring method.

Examples of the organic thixotropic agent (C) include hydrogenated castor oil thixotropic agent (C1), oxidized polyethylene thixotropic agent (C2), amide type thixotropic agent (C3), and polymerized oil type thixotropic agent. (C4), surfactant thixotropic agent (C5), and the like, and these may be used alone or in combination of two or more.
Of these, the polyethylene oxide thixotropic agent (C2) and / or the amide type thixotropic agent (C3) are used because they are excellent in dispersibility and facilitate the preparation of the conductive composition of the present invention. Is preferred.

The hydrogenated castor oil thixotropic agent (C1) is a wax-like thixotropic agent obtained by adding hydrogen to castor oil (non-drying oil whose main component is ricinoleic acid) and is also called castor oil wax. .
In the present invention, as the hydrogenated castor oil-based thixotropic agent (C1), for example, commercially available products such as ADVITROL100 (manufactured by Zude Chemie Catalysts Co., Ltd.), DISPARLON 305 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON 4300 (manufactured by Enomoto Kasei Co., Ltd.) Can be used.

The polyethylene oxide thixotropic agent (C2) is a wax obtained by oxidizing polyethylene and introducing a polar group.
In the present invention, as the oxidized polyethylene thixotropic agent (C2), for example, DISPARLON 4200-10 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON 4200-20 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON 4401-25M (manufactured by Enomoto Kasei Co., Ltd.) ) Etc. can be used.

The amide thixotropic agent (C3) is a wax that is synthesized from vegetable oil fatty acid and an amine and has an amide bond.
In the present invention, examples of the amide thixotropic agent (C3) include DISPARLON PFA-231 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON 6650 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON 6900-20X (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON Commercial products such as A650-20X (Enomoto Kasei Co., Ltd.), DISPARLON A670-20M (Enomoto Kasei Co., Ltd.), DISPARLON F-9030 (Enomoto Kasei Co., Ltd.) and the like can be used.

Specific examples of the polymer oil-based thixotropic agent (C4) include polymerized linseed oil known as a body agent.
Specific examples of the surfactant-based thixotropic agent (C5) include diamic acid esters and sulfuric acid compound amine salts.

  In the present invention, as a composite thixotropic agent using the polyethylene oxide thixotropic agent (C2) and the amide thixotropic agent (C3) in combination, for example, DISPARLON NS-30 (manufactured by Enomoto Kasei Co., Ltd.), DISPARLON NS Commercially available products such as -5210 (Enomoto Kasei Co., Ltd.), DISPARLON F-9010 (Enomoto Kasei Co., Ltd.), and DISPARLON F-9050 (Enomoto Kasei Co., Ltd.) can be used.

By using the conductive composition of the present invention containing such an organic thixotropic agent (C), the volume resistivity of the formed electrode is low and the aspect ratio is high, and the solar battery cell obtained The curve factor becomes higher.
Here, the reason why the volume resistivity is low is that the organic thixotropic agent is thermally decomposed at the firing temperature at the time of electrode formation, considering that it is lower than when an inorganic thixotropic agent is used. This is probably because it does not remain in the (coating film).
The reason why the aspect ratio becomes high is considered that the organic thixotropic agent is more dispersible than the inorganic thixotropic agent and has a great effect of increasing thixotropy.
Moreover, the reason why the fill factor of the solar battery cell is high is that an electrode with a high aspect ratio can be formed, so that a current collecting area is increased, and an electrode with a narrow line width can be formed, so that a wide light receiving area is secured. It is thought that it is possible.

  In the present invention, the content of the organic thixotropic agent (C) is 0 with respect to 100 parts by mass of the conductive particles (A) because an electrode having a higher aspect ratio can be formed. It is preferable that it is 1-10 mass parts, and it is more preferable that it is 1-5 mass parts.

<Glass frit (D)>
The glass frit (D) used in the conductive composition of the present invention is not particularly limited, and it is preferable to use one having a softening temperature of 300 ° C. or higher and a firing temperature (heat treatment temperature) or lower.
Specific examples of the glass frit (D) include a borosilicate glass frit having a softening temperature of 300 to 800 ° C.
The shape of the glass frit (D) is not particularly limited, and may be spherical or crushed powder. The average particle diameter (D50) of the spherical glass frit is preferably 0.1 to 20 μm, and more preferably 1 to 10 μm. Furthermore, it is preferable to use a glass frit having a sharp particle size distribution from which particles of 15 μm or more are removed.
The content of the glass frit (D) is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the conductive particles (A).

<Solvent (E)>
The solvent (E) used in the conductive composition of the present invention is not particularly limited as long as it can apply the conductive composition of the present invention onto a substrate.
Specific examples of the solvent (E) include butyl carbitol, butyl carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, diethylene glycol dibutyl ether, methyl ethyl ketone, isophorone, (alpha)-terpineol etc. are mentioned, These may be used individually by 1 type, or may use 2 or more types together.
Moreover, it is preferable that it is 2-30 mass parts with respect to 100 mass parts of said electroconductive particle (A), and, as for content of the said solvent (E), it is more preferable that it is 5-20 weight part.

<Resin binder (F)>
The electrically conductive composition of this invention may contain the resin binder (F) as needed from a printable viewpoint.
The resin binder is obtained by dissolving a resin having a binder function (excluding a thermosetting resin) in a solvent.
Specific examples of the resin include ethyl cellulose resin, nitrocellulose resin, alkyd resin, and styrene resin. These may be used alone or in combination of two or more. Among these, it is preferable to use ethyl cellulose resin from the viewpoint of thermal decomposability.
Specific examples of the solvent include α-terpineol, butyl carbitol, butyl carbitol acetate, diacetone alcohol, methyl isobutyl ketone, and the like. You may use the above together. In the present invention, the solvent may be a part of the solvent (E) described above.

<Metal oxide>
In order to improve the photoelectric conversion efficiency, the conductive composition of the present invention may contain a metal oxide.
Specific examples of the metal oxide include zinc oxide, silicon oxide, cerium oxide, bismuth oxide, tin oxide, and ABO ₃ (wherein A is at least selected from the group consisting of Ba, Ca, and Sr). 1 represents one element, and B represents at least one element selected from the group consisting of Ti, Zr, and Hf and represents Ti). One species may be used alone, or two or more species may be used in combination.
In the present invention, since an electrode having a higher aspect ratio can be formed, the content of silver oxide that can correspond to the metal oxide is 5 with respect to 100 parts by mass of the solvent (E). It is preferably at most 1 part by mass, more preferably at most 1 part by mass, and most preferably an embodiment containing substantially no silver oxide.

  The method for producing the conductive composition of the present invention is not particularly limited, and the conductive particles (A), the fatty acid silver salt (B), the organic thixotropic agent (C), the glass frit (D), and the above Examples thereof include a method of mixing the solvent (E) and the resin binder (F) which may be optionally contained and the metal oxide by a roll, a kneader, an extruder, a universal agitator or the like.

[Solar cells]
The solar cell of the present invention comprises a surface electrode on the light-receiving surface side, an antireflection film, a semiconductor substrate, and a back electrode, and at least the surface electrode is formed by using the above-described conductive composition of the present invention. It is a battery cell.
In addition, since the conductive composition of the present invention described above can also be applied to the formation of the back electrode of an all back electrode type (so-called back contact type) solar battery cell, it is also applicable to an all back electrode type solar cell. can do.
Below, the structure of the photovoltaic cell of this invention is demonstrated using FIG. In FIG. 1, the solar cell of the present invention will be described by taking a crystalline silicon solar cell as an example. However, the present invention is not limited to this. For example, a thin film amorphous silicon solar cell, a hybrid type (HIT) It may be a solar cell or the like.

As shown in FIG. 1, a solar cell 10 of the present invention includes a surface electrode (finger electrode) 1 on the light receiving surface side, an antireflection film 2, a pn junction silicon substrate 4 in which an n layer 3 and a p layer 5 are joined. (Hereinafter, these are also referred to as “crystalline silicon substrate 7”.) And a back electrode (full-surface electrode) 6 are provided.
Moreover, as shown in FIG. 1, it is preferable that the photovoltaic cell 10 of this invention forms a pyramid-like texture by, for example, etching the wafer surface in order to reduce reflectivity.

<Front electrode / Back electrode>
The surface electrode and the back electrode provided in the solar battery cell of the present invention are arranged (pitch), shape, height, width, etc. of the electrode as long as at least the surface electrode is formed using the conductive composition of the present invention. Is not particularly limited.
Here, a plurality of surface electrodes are usually provided, but in the present invention, only a part of the plurality of surface electrodes may be formed of the conductive composition of the present invention.

<Antireflection film>
The antireflection film included in the solar battery cell of the present invention is a 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. It is composed of an oxide film, a silicon nitride film, a titanium oxide film, a laminated film of these, and the like.

<Crystal silicon substrate>
The crystalline 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. Any polycrystalline silicon substrate may be used.

The crystalline 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.

  The solar cell of the present invention exhibits a high fill factor because at least the surface electrode is formed of the conductive composition of the present invention.

Although the manufacturing method of the photovoltaic cell of the present invention is not particularly limited, an antireflection film forming step of forming an antireflection film on a crystalline silicon substrate, and applying the conductive composition of the present invention on the antireflection film. There is a method including a wiring forming step for forming a wiring and a heat treatment step for heat-treating the obtained wiring to form an electrode (front electrode and / or back electrode).
Hereinafter, the antireflection film forming step, the wiring forming step, and the heat treatment step will be described in detail.

<Antireflection film formation process>
The antireflection film forming step is a step of forming an antireflection film on the crystalline silicon substrate.
Here, the formation method of the antireflection film is not particularly limited, and can be formed by a known method such as a plasma CVD method.

<Wiring formation process>
The said wiring formation process is a process of apply | coating the electrically conductive composition of this invention on an antireflection film, and forming a 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 wiring obtained in the wiring forming step.
Here, although the said heat processing is not specifically limited, It is preferable that it is the process heated (baking) for several seconds-several tens of minutes at the temperature of 700-800 degreeC. When the temperature and time are within this range, the wiring applied on the antireflection film is fire-through (fired through), whereby an electrode in contact with the crystalline silicon substrate can be formed.
In addition, since the wiring obtained by the wiring formation process described above can form electrodes even by irradiation with ultraviolet rays or infrared rays, the heat treatment step in the present invention may be performed by irradiation with ultraviolet rays or infrared rays.

[Solar cell module]
The solar cell module of the present invention is a solar cell module in which the solar cells of the present invention are wired in series using an interconnector.
Here, as the interconnector, a connector used in a conventionally known solar cell module can be used. Specifically, for example, a copper ribbon coated with solder or a conductive adhesive is preferably used. it can.

  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)
<Preparation of conductive composition>
To the ball mill, conductive particles shown in Table 1 below were added so as to have the composition ratio (mass ratio) shown in Table 1 below, and these were mixed to prepare a conductive composition.

<Production of solar cells>
A single crystal silicon wafer subjected to an alkali texture treatment was prepared, and an aluminum paste was applied to the entire back surface (the surface opposite to the light receiving surface) by screen printing, followed by drying at 150 ° C. for 15 minutes.
Next, after forming a silicon nitride film as an antireflection film on the surface by plasma CVD, each prepared conductive composition was applied by screen printing (290 mesh, emulsion thickness: 30 μm) to form a wiring pattern. .
Then, it baked for 30 seconds in two conditions of peak temperature 720 degreeC and 800 degreeC with an infrared baking furnace, and produced the sample of the photovoltaic cell in which the conductive wiring (electrode) was formed.

<Volume resistivity (specific resistance)>
About the sample of the photovoltaic cell produced by firing at 800 ° C., the volume resistivity of the electrode was measured by a four-terminal four-probe method using a resistivity meter (Lorestar GP, manufactured by Mitsubishi Chemical Corporation). The results are shown in Table 1 below.

<Aspect ratio>
About the sample of the photovoltaic cell produced by baking at 800 degreeC, the electrode was observed with the laser microscope, height and width were measured, and the aspect ratio (height / width) was calculated | required. The results are shown in Table 1 below.

<Curve factor>
About the sample of the produced photovoltaic cell, the fill factor was measured using a cell tester (manufactured by Yamashita Denso Co., Ltd.). The relative evaluation based on the measurement result of Comparative Example 1 is shown in Table 1 below.

The following were used for each component in Table 1.
Silver powder: AG2-1C (shape: spherical, average particle size: 1.0 μm, manufactured by DOWA Electronics)
Silver salt of isobutyrate: First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 38 g of isobutyric acid (manufactured by Kanto Chemical Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) are put into a ball mill and reacted by stirring at room temperature for 24 hours. It was. Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare white silver isobutyrate.
Silver salt of 1,3,5-pentanetricarboxylic acid: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 30 g of 1,3,5-pentanetricarboxylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) are ball milled. 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 white 1,3,5-pentanetricarboxylic acid silver salt.
Silver stearate: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 123 g of stearic acid (manufactured by Kanto Chemical Co., Ltd.) and 300 g of 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 stearate salt.

Amide thixotropic agent 1: DISPARLON PFA-231 (thermal decomposition temperature: 414 ° C., manufactured by Enomoto Kasei Co., Ltd.)
Amide thixotropic agent 2: DISPARLON 6900-20X (thermal decomposition temperature: 406 ° C., manufactured by Enomoto Kasei Co., Ltd.)
-Composite thixotropic agent 1: DISPARLON NS-30 (thermal decomposition temperature: 452 ° C, manufactured by Enomoto Kasei Co., Ltd.)
-Composite thixotropic agent 2: DISPARLON NS-5210 (thermal decomposition temperature: 394 ° C., manufactured by Enomoto Kasei Co., Ltd.)
・ Polyethylene oxide thixotropic agent: DISPARLON 4200-10 (thermal decomposition temperature: 385 ° C., manufactured by Enomoto Kasei Co., Ltd.)
-Fumed silica: Aerosil 202 (manufactured by Nippon Aerosil Co., Ltd.)

Glass frit: Pb glass frit Solvent: α-terpineol Resin binder: EC-100 FTP (ethyl cellulose resin solid content: 9%, manufactured by Nisshin Kasei Co., Ltd.)

From the results shown in Table 1, the conductive composition of Comparative Example 2 prepared by blending an inorganic thixotropic agent can form an electrode having a higher aspect ratio than Comparative Example 1, but is sufficiently high. However, it was found that the volume resistivity was higher than that of Comparative Example 1, and the effect of improving the fill factor was not sufficient.
In contrast, the conductive compositions of Examples 1 to 8 prepared by blending an organic thixotropic agent had a volume resistivity lower than that of Comparative Example 1 and an aspect ratio higher than that of Comparative Example 1. It has been found that a sufficiently high electrode can be formed, and that a solar battery cell having a high fill factor of about 40% in a wide firing temperature range (720 to 800 ° C.) is formed.
In addition, the conductive composition of Example 8 prepared by using silver isobutyrate and silver stearate together can form an electrode having a higher aspect ratio, and was prepared in Examples 1-7. It has been found to form solar cells that exhibit a fill factor as high as the conductive composition.

DESCRIPTION OF SYMBOLS 1 Front electrode 2 Antireflection film 3 N layer 4 pn junction silicon substrate 5 P layer 6 Back electrode 7 Crystalline silicon substrate 10 Solar cell

Claims (11)

  A conductive composition for forming a solar cell collecting electrode, comprising conductive particles (A), a fatty acid silver salt (B), an organic thixotropic agent (C), a glass frit (D) and a solvent (E).   The conductive composition for forming a solar cell collector electrode according to claim 1, wherein a thermal decomposition temperature of the organic thixotropic agent (C) measured by a thermogravimetric method is 300 to 500 ° C.   The organic thixotropic agent (C) is a hydrogenated castor oil thixotropic agent (C1), a polyethylene oxide thixotropic agent (C2), an amide type thixotropic agent (C3), or a polymerized oil type thixotropic agent (C4). And at least one thixotropic agent selected from the group consisting of a surfactant-based thixotropic agent (C5).   The said organic thixotropic agent (C) is the said oxidation polyethylene type thixotropic agent (C2) and / or the said amide type thixotropic agent (C3). Conductive composition.   The fatty acid silver salt (B) is a fatty acid silver salt (B2) having 18 or less carbon atoms, a fatty acid silver salt (B2) having at least one carboxy silver base (—COOAg) and one hydroxyl group (—OH), and A fatty acid silver salt selected from the group consisting of a polycarboxylic acid silver salt (B3) having two or more carboxy silver bases (-COOAg) without having a hydroxyl group (-OH). 4. The conductive composition for forming a solar cell collecting electrode according to any one of 4 above.   6. The fatty acid silver salt (B1) is a combined system of a fatty acid silver salt (B1-1) having 1 to 8 carbon atoms and a fatty acid silver salt (B1-2) having 9 to 18 carbon atoms. A conductive composition for forming a solar cell collector electrode.   Content of the said fatty-acid silver salt (B) is 1-25 mass parts with respect to 100 mass parts of said electroconductive particle (A), For solar cell current collection electrode formation in any one of Claims 1-6 Conductive composition.   Content of the said organic thixotropic agent (C) is 0.1-10 mass parts with respect to 100 mass parts of said electroconductive particle (A), The solar cell collection in any one of Claims 1-7. A conductive composition for forming an electrode.   Furthermore, the electrically conductive composition for solar cell current collection electrode formation in any one of Claims 1-8 containing a resin binder (F).   A light-receiving surface side surface electrode, an antireflection film, a semiconductor substrate, and a back surface electrode are provided, and at least the surface electrode uses the conductive composition for forming a solar cell collector electrode according to any one of claims 1 to 9. A solar battery cell formed.   The solar cell module which wired the solar cell of Claim 10 in series using the interconnector.