JP4743350B1 - Solar cell electrode paste and solar cell - Google Patents

Abstract

An object of the present invention is to form an electrode that can have a low volume resistivity and a high aspect ratio, has excellent adhesion to a silicon substrate, and does not break when formed as a wiring. It is providing the solar cell electrode paste which can carry out, and a solar cell using the same. The solar cell electrode paste of the present invention is a solar cell electrode paste containing spherical silver powder having a predetermined average particle diameter, a fatty acid silver salt represented by a predetermined formula, and a solvent.
[Selection figure] None

Description

  The present invention relates to a solar battery electrode paste 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 such an electrode of a solar cell, a resin-based paste material is known.
For example, Patent Document 1 discloses that “a silver electrode paste comprising at least silver powder, glass frit, a resin and an organic solvent, wherein the glass frit is a residue classified by a sieve having an opening diameter of 24 to 100 μm. Is described.
Patent Document 2 discloses that “a first silver powder having a crystallite diameter of 58 nm or more, a second silver powder having a crystallite diameter different from that of the silver powder, a glass frit, and a resin binder, and a solar cell electrode paste. Is described.
Patent Document 3 describes “a paste for solar cell light-receiving surface electrode containing silver particles having a specific surface area of 0.20 to 0.60 m ² / g, glass frit, a resin binder, and thinner.” Has been.

JP 2004-146154 A JP 2007-194581 A JP 2007-235082 A

  However, when an electrode is formed using a resin-based paste material as described in Patent Documents 1 to 3, the volume resistivity (specific resistance) of the electrode itself may increase, and the cross-section of the electrode It became clear that the ratio of height to width (height / width) (hereinafter referred to as “aspect ratio”) was small, and the adhesion between the electrode and the silicon substrate was poor.

  In addition, the present inventor, instead of the resin-based conductive paste described in Patent Documents 1 to 3, proposes “silver oxide (A) proposed by the present applicant and a secondary fatty acid having a boiling point of 200 ° C. or less. A conductive composition containing a secondary fatty acid silver salt (B) obtained by using a conductive composition containing silver oxide (A) and a fatty acid silver salt (B) having one or more hydroxyl groups. As a result of applying a conductive composition (for example, see Japanese Patent No. 3990712, Japanese Patent Application Laid-Open No. 2009-105034, etc.), a wire formed as an electrode may be disconnected. It became clear.

  Therefore, the present invention is to form an electrode that can have a low volume resistivity and a high aspect ratio, has excellent adhesion to a silicon substrate, and does not break when formed as a wiring. It is an object of the present invention to provide a solar cell electrode paste and a solar cell using the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a paste for a solar cell electrode using a silver powder having a specific particle size and shape with respect to a fatty acid silver salt represented by a predetermined formula has a volume resistivity. And an aspect ratio can be made high, and it has excellent adhesiveness with a silicon substrate, and an electrode that does not break when formed as a wiring can be formed, and the present invention is completed. I let you. That is, the present invention provides the following (1) to (4).

(1) Silver powder (A), fatty acid silver salt (B) represented by the following formula (I), and solvent (C) are contained,
The solar cell electrode paste, wherein the silver powder (A) is a spherical silver powder having an average particle diameter of 0.5 to 5 µm.
(In formula (I), R ¹ and R ² both represent a methyl group, and R ³ represents a hydrogen atom.)

  (2) The paste for solar cell electrodes according to (1), 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).

  (3) The solar cell electrode paste according to (1) or (2), further comprising glass frit.

(4) It comprises a surface electrode on the light receiving surface side, a semiconductor substrate and a back electrode,
The solar cell in which the surface electrode and / or the back electrode are formed using the solar cell electrode paste according to any one of (1) to (3).

As shown below, according to the present invention, a solar cell electrode paste capable of forming an electrode having a low volume resistivity, a high aspect ratio, and excellent adhesion to a silicon substrate, and The used solar battery cell can be provided.
Moreover, if the solar cell electrode paste of the present invention is used, it is very useful because wiring (electrode) can be formed while suppressing occurrence of disconnection.

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 comparative example, taken with a scanning electron microscope (SEM).

The solar cell electrode paste of the present invention contains silver powder (A), a fatty acid silver salt (B) represented by the above formula (1), and a solvent (C), and the silver powder (A) is an average. It is a paste for solar cell electrodes which is a spherical silver powder having a particle diameter of 0.5 to 5 μm.
Below, silver powder (A), fatty-acid silver salt (B), and a solvent (C) are explained in full detail.

<Silver powder (A)>
The silver powder (A) used in the solar cell electrode paste of the present invention is a spherical silver powder having an average particle diameter of 0.5 to 5 μm.
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 (produced by Fukuda Metal Foil Co., Ltd.) (FIG. 3) does not correspond to spherical silver powder, but corresponds to flake (scalar) silver powder.

In the present invention, the average particle diameter of the silver powder (A) is preferably 0.7 to 5 μm because the printability is good, and the reason is that the sintering speed is appropriate and the workability is excellent. More preferably, it is ˜3 μm.
Further, the content of the silver powder (A) is 300 to 700 parts by mass with respect to 100 parts by mass of the solvent (C) described later, because the printability is improved and an electrode having a smaller specific resistance can be formed. It is preferable that it is 400-600 mass parts.

  Moreover, in this invention, a commercial item can be used as said silver powder (A), As a specific example, AgC-102 (average particle diameter: 1.5 micrometer, Fukuda metal foil powder industry company make), AgC- 103 (average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Co., Ltd.), AG4-8F (average particle size: 2.2 μm, manufactured by DOWA Electronics), AG2-1C (average particle size: 1.0 μm, DOWA Electronics Co., Ltd.) Manufactured), AG3-11F (average particle size: 1.4 μm, manufactured by DOWA Electronics), EHD (shape: spherical, average particle size: 0.5 μm, manufactured by Mitsui Kinzoku Co., Ltd.), and the like.

Furthermore, in this invention, as shown also in Example 4 mentioned later, flaky silver powder can be used together with the said silver powder (A).
Here, it is preferable that content when using together flaky silver powder is 50 mass% or less with respect to the total mass with the said silver powder (A).
In addition, when using together flaky silver powder, the description regarding content of the said silver powder (A) mentioned other than this paragraph is the total content of the said silver powder (A) and flaky silver powder. Say.

<Fatty acid silver salt (B)>
The fatty acid silver salt (B) used in the solar cell electrode paste of the present invention is not particularly limited as long as it is a compound represented by the above formula (1), and specifically, the following fatty acid and silver oxide are reacted. Can be obtained.

  In the present invention, the fatty acid used in the reaction of the fatty acid silver salt (B) is a fatty acid represented by the following formula (1), that is, 2-methylpropanoic acid (also known as isobutyric acid). When such a fatty acid is used, the fluidity and thixotropy of the solar cell electrode paste of the present invention containing the resulting fatty acid silver salt (B) are improved, so that the printability is improved, and the release property is also improved. As a result, the electrode (printing pattern) is less likely to be broken or blurred, and clogging due to screen printing is less likely to occur.

(In the formula, each of R ¹ and R ² represents a methyl group, and R ³ represents a hydrogen atom.)

In the present invention, from the viewpoint of thixotropy, it is preferable to use an aliphatic monocarboxylic acid having 8 or more carbon atoms or a tertiary fatty acid silver salt together with the fatty acid represented by the above formula (1).
Specific examples of the aliphatic monocarboxylic acid include capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid.
Specific examples of the tertiary fatty acid silver salt include neodecanoic acid.
Here, the content in the case of using an aliphatic monocarboxylic acid or a tertiary fatty acid silver salt in combination is preferably 50% by mass or less based on the total mass with the fatty acid silver salt (B).

On the other hand, the silver oxide used for the reaction of the fatty acid silver salt (B) is silver (I), that is, Ag ₂ O.

The fatty acid silver salt (B) used in the solar cell electrode paste of the present invention is obtained by reacting the above-described fatty acid and silver oxide, and is a compound represented by the following formula (I) in the reaction formula shown below. is there.
This reaction is not particularly limited as long as the reaction represented by the following reaction formula proceeds, for example, a method of proceeding while pulverizing the silver oxide, or the fatty acid after pulverizing the silver oxide. A reaction method is 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), R ¹ and R ² both represent a methyl group, and R ³ represents a hydrogen atom.)

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.
When the fatty acid silver salt (B) is prepared using these solvents, the fatty acid silver salt (B) is preferably taken out as crystals and then dissolved in the solvent (C) described later.

  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) because the printability is good and an electrode having a smaller specific resistance can be formed. It is preferable that it is 5 to 80 parts by mass.

In the present invention, by using the solar cell electrode paste containing the silver powder (A) and the fatty acid silver salt (B) described above, the volume resistivity can be lowered and the aspect ratio can be increased, An electrode that is excellent in adhesiveness with a silicon substrate and does not cause disconnection when formed as a wiring can be formed.
It is considered that this is because the silver powder (A) is connected when the silver decomposed from the fatty acid silver salt (B) is melted by heat treatment, thereby suppressing the occurrence of disconnection and expressing high conductivity. 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. Furthermore, since the fatty acid silver salt (B) imparts an appropriate thixotropy to the solar cell electrode paste and can suppress the spread of the coated surface while ensuring fluidity during printing, the aspect ratio can be increased. Conceivable.

  In the present invention, the thixotropy of the solar cell electrode paste becomes better and the aspect ratio can be increased, so that the silver oxide content is 10 with respect to 100 parts by mass of the solvent (C) described later. It is preferably no greater than 5 parts by mass, more preferably no greater than 5 parts by mass, even more preferably no greater than 1 part by mass, and most preferably an embodiment containing substantially no silver oxide.

<Solvent (C)>
The solvent (C) used in the solar cell electrode paste of the present invention is not particularly limited as long as the solar cell electrode paste of the present invention can be applied onto a substrate.
Specific examples of the solvent (C) include butyl carbitol, methyl ethyl ketone, isophorone, α-terpineol, and the like. These may be used alone or in combination of two or more.

<Glass frit>
The solar cell electrode paste of the present invention preferably contains glass frit because the adhesion between the electrode to be formed and the silicon substrate becomes better.

In the present invention, when blending the glass frit, 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 such a glass frit include a borosilicate glass frit having a softening temperature of 300 to 800 ° C.

In the present invention, the shape of the glass frit is not particularly limited, and may be spherical or crushed powder.
Moreover, it is preferable that the average particle diameter (D50) of a spherical glass frit is 0.1-20 micrometers, and it is more preferable that it is 1-3 micrometers.
Furthermore, it is preferable to use a glass frit having a sharp particle size distribution from which particles of 10 μm or more are removed.

  In this invention, when mix | blending the said glass frit, it is preferable that the content is 0.1-10 mass parts with respect to 100 mass parts of said silver powder (A), and is 1-5 mass parts. Is more preferable.

<Vehicle>
The solar cell electrode paste of the present invention may contain a vehicle in which a resin having a binder function is dissolved in an organic solvent, if necessary.
Specific examples of the resin include ethyl cellulose resin, nitrocellulose resin, alkyd resin, acrylic resin, styrene resin, phenol resin and the like, and these may be used alone or in combination of two or more. May be. Among these, it is preferable to use ethyl cellulose resin from the viewpoint of thermal decomposability.
Specific examples of the organic solvent include α-terpineol, butyl carbitol, butyl carbitol acetate, diacetone alcohol, methyl isobutyl ketone, and the like. More than one species may be used in combination.

The solar cell electrode paste of the present invention may contain additives such as a metal powder other than the above-described silver powder (A) and a reducing agent, if necessary.
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 solar cell electrode paste of the present invention is not particularly limited, and the silver powder (A), the fatty acid silver salt (B), the solvent (C), and an additive (glass frit which may be optionally contained). , Including a vehicle) by 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 solar cell electrode paste of the present invention described above. It is a solar battery cell.
Here, since the solar cell electrode of the present invention described above can be applied to the formation of the back electrode of the all back electrode type (so-called back contact type) solar cell, The present invention can also be applied to an electrode 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 provided in the solar battery cell of the present invention are formed using the solar cell electrode paste of the present invention, the arrangement (pitch), shape, and height of the electrodes The width and the like are not particularly limited. In addition, although the height of an electrode is normally designed by several to several dozen micrometer, the aspect ratio of the electrode formed using the solar cell electrode paste of this invention will be 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 for the solar cell electrode of the present invention. It may be formed of a paste, or part of the plurality of front surface electrodes and part of the plurality of back surface electrodes may be formed of the solar cell electrode paste 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 cell of the present invention, since the front electrode and / or the back electrode is formed using the solar cell electrode paste of the present invention, the electrode has an aspect ratio of 0.4 or more, and the electromotive force generated by light reception Can be efficiently extracted as a current.

Although the manufacturing method of the photovoltaic cell of this invention is not specifically limited, The wiring formation process which apply | coats the solar cell electrode paste of this invention on a silicon substrate, and forms wiring, heat-treats the obtained wiring, and an electrode ( And an electrode forming step of forming a front 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 paste for solar cell electrodes 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 temperature of 500 to 850 ° 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 solar cell electrode paste of the present invention will be described in detail with reference to Examples. However, the present invention is not limited to this.

(Examples 1-6, Comparative Examples 1-6)
The silver powder shown in the following Table 1 was added to the ball mill so as to have the composition ratio shown in the following Table 1, and these were mixed to prepare a solar cell electrode paste.
The prepared solar cell electrode paste 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 wiring.
Then, it dried for 10 minutes at 700 degreeC in oven, and produced the sample of the photovoltaic cell in which the electroconductive wiring (electrode) was formed.

<Disconnection>
Wiring before drying (firing) formed by screen printing was observed with an optical microscope to confirm the presence or absence of disconnection. The results are shown in Table 1 below.

<Aspect ratio (before firing)>
The wiring before drying (firing) formed by screen printing was observed with a confocal microscope, the height and width were measured, and the aspect ratio (height / width) was determined.
An aspect ratio of 0.6 or more is evaluated as “◎” as the aspect ratio is sufficiently high (sufficiently satisfactory), and an aspect ratio of 0.4 or more and less than 0.6 is evaluated as “◯” as the aspect ratio is high (satisfied). Evaluation was evaluated as “x” as the aspect ratio was low (unsatisfactory) when less than 0.4.
These results are shown in Table 1 below.

<Volume resistivity (specific resistance)>
About the sample of each produced photovoltaic cell, the volume resistivity of the electrode was measured by a 4-terminal 4-probe method using a resistivity meter (Lorestar GP, manufactured by Mitsubishi Chemical Corporation). The results are shown in Table 1 below.

<Adhesion>
After the cellophane adhesive tape (width 18 mm) is completely attached on the surface of each solar cell sample produced, immediately hold one end of the tape at a right angle and pull it away instantaneously to see if the electrode (print pattern) is peeled off I investigated.
The case where peeling was confirmed on the electrode was evaluated as “x” as being poor in adhesion, and the case where peeling was not confirmed on the electrode was evaluated as “◯” as being excellent in adhesion. The results are shown in Table 1 below.

<Aspect ratio (after firing)>
About the sample of each produced photovoltaic cell, the electrode was observed with the laser microscope, height and width were measured, and the aspect ratio (height / width) was calculated | required.
An aspect ratio of 0.6 or more is evaluated as “◎” as the aspect ratio is sufficiently high (sufficiently satisfactory), and an aspect ratio of 0.4 or more and less than 0.6 is evaluated as “◯” as the aspect ratio is high (satisfied). Evaluation was evaluated as “x” as the aspect ratio was low (unsatisfactory) when less than 0.4.
These results are shown in Table 1 below.

<Photoelectric conversion efficiency>
Among the produced solar cells, for Example 2 and Comparative Example 6, a solar simulator was used as a light source, and AM1.5 pseudo-sunlight was irradiated from the photoelectrode side with a light intensity of 100 mW / cm ^2. Conversion efficiency was determined using a measuring device (Digital Source Meter 2400 manufactured by Keithley Instruments). The results are shown in Table 1 below.

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: Ag-4-8F (shape: spherical, average particle size: 2.2 μm, manufactured by DOWA Electronics)
Silver powder 3: AgC-2011 (shape: flake shape, average particle size: 2 to 10 μm, manufactured by Fukuda Metal Foil Co., Ltd.)

-Silver salt of 2-methylpropanoic acid: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 38 g of 2-methylpropanoic acid (manufactured by Kanto Chemical Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) are put into a ball mill, and are kept at room temperature for 24 hours. The reaction was allowed to stir. Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare silver 2-methylpropanoate.
Silver 2-methylbutanoate: First, 50 g of silver oxide (manufactured by Toyo Kagaku Kogyo Co., Ltd.), 44 g of 2-methylbutanoic acid (manufactured by Kanto Chemical Co., Ltd.) and 300 g of MEK were 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 silver 2-methylbutanoate.
-Silver 2-ethylbutyrate: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 50.2 g of 2-ethylbutyric acid (manufactured by Kanto Chemical Co., Ltd.) and 300 g of MEK are put into a ball mill and stirred at room temperature for 24 hours. Reacted. Subsequently, MEK was removed by suction filtration, and the obtained powder was dried to prepare silver 2-ethylbutyrate.
-Neodecanoic acid silver salt: First, 50 g of silver oxide (manufactured by Toyo Kagaku Co., Ltd.), 74.3 g of neodecanoic acid (manufactured by Toyo Gosei Co., Ltd.) and 300 g of MEK were charged 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.
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 silver stearate salt.

Silver oxide: Silver oxide (I) (manufactured by Toyo Chemical Industry Co., Ltd.)
Α-terpineol: solvent glass frit: lead borosilicate glass powder silver paste: resin-based silver paste (DWP-025, manufactured by Toyobo Co., Ltd.)

From the results shown in Table 1, in Comparative Example 1 prepared with a conventionally known resin-based silver paste, there was no disconnection, but the volume resistivity of the electrode was slightly high and the adhesion to the silicon substrate was poor, It was found that the aspect ratio was low both before and after firing.
Further, Comparative Example 2 prepared with a paste containing silver oxide instead of silver powder has a disconnection, the electrode has a high volume resistivity, is inferior in adhesion to the silicon substrate, and before and after firing. In both cases, the aspect ratio was found to be low.
Further, Comparative Example 3 prepared using flaky silver powder not corresponding to silver powder (A) has a disconnection, the electrode has a high volume resistivity, is inferior in adhesion to the silicon substrate, and is further fired. It was found that the aspect ratio was low before and after.
Further, Comparative Examples 4 and 6 prepared using a fatty acid silver salt not corresponding to the fatty acid silver salt (B) have no disconnection, the volume resistivity of the electrode is sufficiently low, and the adhesion to the silicon substrate is also good. Although it was excellent, it was found that the aspect ratio after firing was low.
Further, Comparative Example 5 prepared using a fatty acid silver salt not corresponding to the fatty acid silver salt (B) had a sufficiently low volume resistivity of the electrode and excellent adhesion to the silicon substrate. It was found that the aspect ratio after firing was low.

On the other hand, Examples 1-6 using silver powder (A) and fatty acid silver salt (B) have no disconnection, the volume resistivity of an electrode is low enough, and is excellent in adhesiveness with a silicon substrate, Further, it was found that the aspect ratio was high both before and after firing.
Moreover, it turned out that the secondary fatty acid silver salt is more suitable for a solar cell electrode use than the tertiary fatty acid silver salt from the result of the photoelectric conversion efficiency of Example 2 and Comparative Example 6. In addition, the difference between the photoelectric conversion efficiency (14.01) of Example 2 and the photoelectric conversion efficiency (13.20) of Comparative Example 6 is remarkable as a difference that appears as a difference of only the electrode material.

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 (4)

Silver powder (A), fatty acid silver salt (B) represented by the following formula (I), and solvent (C),
The solar cell electrode paste, wherein the silver powder (A) is a spherical silver powder having an average particle diameter of 0.5 to 5 µm.
(In formula (I), R ¹ and R ² both represent a methyl group, and R ³ represents a hydrogen atom.)   The solar cell electrode paste according to claim 1, 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).   Furthermore, the solar cell electrode paste of Claim 1 or 2 containing a glass frit. 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 paste for solar cell electrodes in any one of Claims 1-3.