JP5527901B2 - Conductive composition for forming solar battery collecting electrode and solar battery cell - Google Patents

Description

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

  Conventionally, conductive particles such as silver particles, a binder made of a thermoplastic resin (eg, acrylic resin, vinyl acetate resin, etc.) or a thermosetting resin (eg, epoxy resin, unsaturated polyester resin, etc.), organic solvent, cured Silver paste (conductive composition) obtained by adding and mixing agents, catalysts, etc., is printed on a synthetic resin substrate (for example, a polyester film) so as to have a predetermined circuit pattern, and these are heated. There is known a method of manufacturing a circuit board by forming a conductive wiring forming a conductor circuit.

For example, Patent Document 1 states that “Laser diffraction method 50% particle size is ³ to 8 μm, apparent density is 0.4 to 1.1 / cm ³ , and BET specific surface area value is 1.5. A conductive paste comprising flaky silver powder having a viscosity of ˜4.0 m ² / g and a resin, wherein the conductive paste has a peak of electric resistance between 150 and 200 ° C. Is described ([Claim 5]).

Patent Document 2 discloses that “flaky silver powder A having an average particle diameter of 3 to 8 μm, a specific surface area of 1.5 to 4.0 m ² / g and an apparent density of 0.4 to 1.1 g / cm ^3. Conductive paste containing flaky silver powder B having a mean particle diameter of 3 to 10 μm, a specific surface area of 0.6 to 1.2 m ² / g and an apparent density of 1.5 to 2.1 g / cm ³ and a resin A composition comprising flaky silver powder A in a proportion of 30 to 95 parts by weight with respect to 100 parts by weight of the total weight of flaky silver powder A and flaky silver powder B, and flaky silver powder A and flaky silver powder The conductive paste composition containing 35 to 85% by weight of the total amount of B with respect to the solid content of the conductive paste "is described ([Claim 3]).

Further, Patent Document 3 states that “a metal material (A) having an electrical resistivity of 20 × 10 ⁻⁶ Ω · cm or less, a fatty acid silver salt (B) having one or more hydroxyl groups, and a boiling point of 200 ° C. or less. And a secondary fatty acid silver salt (C) obtained by using a secondary fatty acid ”([Claim 1]), and a film-forming property such as an epoxy resin as an optional component. Resin is described ([0061]), and silver powder is used as the metal material (A) in the examples ([0071]).

JP 2003-55701 A Japanese Patent No. 3955805 JP 2010-92684 A

However, when the present inventor examined the paste materials described in Patent Documents 1 to 3, when a solar cell collecting electrode having many circuit patterns with a narrow line width is formed, disconnection, meandering, bleeding, and the like are caused. It was found that the printability was inferior and the ratio of the height and width of the cross section of the electrode (height / width) (hereinafter referred to as “aspect ratio”) was also reduced.
In particular, a pyramidal fine texture structure is formed on the surface of the silicon wafer of a silicon solar cell, but depending on the shape of the texture, the phenomenon that the printed paste material spreads along the texture groove (brightening) may occur. It turns out that it may be easy to occur.

  Then, this invention makes it a subject to provide the electrically conductive composition for solar cell current collection electrode formation which is excellent in printability, and can form an electrode with a high aspect ratio, and a photovoltaic cell using the same.

As a result of diligent studies to solve the above problems, the present inventor prepared by using spherical silver powder having a predetermined average particle diameter and flaky silver powder having a predetermined average thickness and apparent density in combination at a specific ratio. The present invention was completed by finding that the obtained composition can form an electrode having good printability and a high aspect ratio. That is, the present invention provides the following (1) to ( 9 ).

(1) a spherical silver powder (A) having an average particle size of 0.5 to 5.0 μm;
A flaky silver powder (B) having an average thickness of 0.05 to 0.2 μm and an apparent density of 0.4 to 1.1 g / cm ³ ,
The conductive composition for forming a solar cell collector electrode, wherein the content of the flaky silver powder (B) is 10 % by mass or less based on the total mass of the spherical silver powder (A) and the flaky silver powder (B). .

( 2 ) Furthermore, the electroconductive composition for solar cell current collection electrode formation as described in said (1 ) containing an epoxy resin (C).

( 3 ) The conductive composition for forming a solar cell collector electrode according to (1) or (2) , further comprising a fatty acid silver salt (D).

( 4 ) The epoxy resin (C) is at least a bisphenol A type epoxy resin (C1) having an epoxy equivalent of 1500 to 4000 g / eq and a polyhydric alcohol glycidyl type epoxy resin (C2) having an epoxy equivalent of 1000 g / eq or less. The conductive composition for forming a solar cell collector electrode according to ( 2 ) or ( 3 ) above.

(5) the fatty acid silver salt (D) is, mosquitoes Rubokishi silver base (3) is a polycarboxylic silver (D2) having three or more (-COOAg) or solar collector according to (4) Electroconductive composition for electrode formation.

( 6 ) The conductive composition for forming a solar cell collecting electrode according to ( 5 ), wherein the polycarboxylic acid silver salt (D2) is 1,2,3,4-butanetetracarboxylic acid silver salt.

( 7 ) The said ( 2 )-( 6 ) content of the said epoxy resin (C) is 2-20 mass parts with respect to a total of 100 mass parts of the said spherical silver powder (A) and the said flaky silver powder (B). ) The conductive composition for forming a solar cell collecting electrode according to any one of 1).

(8) The content of the fatty acid silver salt (D) is, the (3) is 0.1 to 10 parts by weight per 100 parts by weight of the spherical silver powder (A) and the flaky silver powder (B) The electrically conductive composition for solar cell current collection electrode formation in any one of-( 7 ).

( 9 ) 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 for solar cell current collection electrode formation in any one of said (1)-( 8 ).

As shown below, according to the present invention, there are provided a conductive composition for forming a solar battery collecting electrode, which is excellent in printability and capable of forming an electrode having a high aspect ratio, and a solar battery cell using the same. be able to.
In particular, the conductive composition for forming a solar cell collector electrode of the present invention (hereinafter referred to as “the conductive composition of the present invention”) is excellent in the printability of a fine line portion (line width: about 50 to 100 μm). Therefore, it can be suitably used for screen printing.
In addition, if the conductive composition of the present invention is used, an electrode can be formed even when firing at a low temperature (about 150 to 500 ° C.) while suppressing the occurrence of disconnection and blemishes. For example, it has an effect of reducing damage to a silicon substrate or the like by heat, which is very useful.

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 spherical silver powder (AgC-103, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) used in the examples, taken with a scanning electron microscope (SEM). FIG. 3 is a photograph taken with a scanning electron microscope (SEM) of the flaky silver powder (Ag-XF301K, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) used in the examples. FIG. 4 is a photograph taken with a scanning electron microscope (SEM) of the flaky silver powder (AgC-A, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) used in the comparative example.

[Conductive composition for forming solar cell collector electrode]
The conductive composition of the present invention has a spherical silver powder (A) having an average particle diameter of 0.5 to 5.0 μm, an average thickness of 0.05 to 0.2 μm, and an apparent density of 0.4. It is an electroconductive composition for solar cell current collection electrode containing -1.1g / cm < ³ > flaky silver powder (B).
Hereinafter, the spherical silver powder (A), the flaky silver powder (B), and other components that may be optionally contained are described in detail.

<Spherical silver powder (A)>
The spherical silver powder (A) used in the conductive composition of the present invention is a silver powder having an average particle diameter of 0.5 to 5 μm.
Here, the term “spherical” refers to the shape of a particle 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 Powder Industry Co., Ltd.) used in the examples described later corresponds to the spherical silver powder, but is used in the examples described later. What is shown by the photograph (FIG. 3) of silver powder (Ag-XF301K, made by Fukuda Metal Foil Powder Industry Co., Ltd.) and the photograph (FIG. 4) of silver powder (AgC-A, made by Fukuda Metal Foil Powder Industry Co., Ltd.) used together in the comparative example. Does not correspond to spherical silver powder, but corresponds to flake-shaped silver powder.

  Further, the average particle diameter of the spherical silver powder (A) is preferably 0.7 to 5 μm from the reason that the printability is better, and from the reason that the sintering speed is appropriate and the workability is excellent, 1 to More preferably, it is 3 μm.

  In the present invention, a commercially available product can be used as the spherical silver powder (A). Specific examples thereof include AgC-102 (average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.), AgC-103. (Average particle diameter: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.), AG4-8F (average particle diameter: 2.2 μm, manufactured by DOWA Electronics), AG2-1C (average particle diameter: 1.0 μm, DOWA electronics) AG3-11F (average particle size: 1.4 μm, manufactured by DOWA Electronics), EHD (average particle size: 0.5 μm, manufactured by Mitsui Kinzoku Co., Ltd.), and the like.

<Flake silver powder (B)>
The flaky silver powder (B) used in the conductive composition of the present invention is a silver powder having an average thickness of 0.05 to 0.2 μm and an apparent density of 0.4 to 1.1 g / cm ^3. is there.
Here, the flake shape means a shape having a ratio of major axis / minor axis of more than 2, and as described above, for example, the silver powder shown in FIG. 3 and FIG. Silver powder corresponds to flaky silver powder (B).
The average thickness (d) is a value calculated from the following formula (i), where S (m ² / g) is the specific surface area of silver powder measured by the BET method (gas adsorption method).
d = 0.19 / S (i)
The apparent density means a value measured by the method described in “Metal powder—apparent density measuring method” of JIS Z2504: 2000.

The average thickness of the flaky silver powder (B) is preferably 0.05 to 0.1 μm because the printability becomes better and the paste is easily formed.
Similarly, the apparent density of the flaky silver powder (B) is preferably from 0.4~1.1g / cm ^3, and more preferably 0.5 to 1.0 g / cm ^3.

In the present invention, the method for preparing the flaky silver powder (B) is not particularly limited. For example, it can be prepared by the method described in paragraphs [0007] to [0015] of Patent Document 1.
Moreover, a commercial item can be used as said flaky silver powder (B), As the specific example, Ag-XF301K (average thickness: 0.1 micrometer, apparent density: 0.82 g / cm < ³ >, Fukuda metal foil) Powder industry)).

In the present invention, by using the above-mentioned spherical silver powder (A) and flaky silver powder (B) in combination, the printability of the resulting conductive composition of the present invention is improved, and an electrode having a high aspect ratio is formed. be able to.
Although this is not clear in detail, the inventor presumes as follows.
First, in general paste materials, it is considered that the thixotropy improves as the surface area of the inherent powder increases. And since the flaky silver powder (B) used by this invention has a very large surface area compared with normal flaky silver powder and the effect which provides thixotropy is high, it is thought that printability becomes favorable. Further, by using the spherical silver powder (A) and the flaky silver powder (B) in combination, the spherical silver powder (A) is sandwiched between the flaky silver powder (B) and is difficult to move. , Fatty acid silver salt, solvent, etc.) are included between the flaky silver powders (B), and thus it is considered that an electrode having excellent shape retention after printing and a high aspect ratio can be formed.

In the present invention, the thixotropy and viscosity are appropriate, and the printability is better, so that the content of the flaky silver powder (B) is such that the spherical silver powder (A) and the flaky silver powder (B ) or less 10% by weight relative to the total weight of, more preferably from 1 to 10 wt%, 5 and even more preferably from 10% by mass.

<Epoxy resin (C)>
The conductive composition of the present invention preferably further contains an epoxy resin (C) as a film-forming resin, if necessary.

As the epoxy resin (C), a conventionally known epoxy resin can be used.
Specifically, for example, bisphenol type epoxy resins such as bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AF type;
Ethylene glycol glycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polyneopentyl glycol Diglycidyl ether, 1,4-butanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyglycerin polyglycidyl ether , Polyoxyethylene Glycol diglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, polytetramethylene glycol diglycidyl ether, pentaerythritol diglycidyl ether, pentaerythritol triglycidyl ether, polypentaerythritol polyglycidyl ether, trimethyl Polyhydric alcohol-based glycidyl type epoxy resins such as propanediglycidyl ether, tetrakis (glycidyloxyphenyl) ethane, tris (glycidyloxy) methane;
Glycidyl ester epoxy resins of synthetic fatty acids such as dimer acid;
N, N, N ′, N′-tetraglycidyldiaminodiphenylmethane (TGDDM), tetraglycidyldiaminodiphenylsulfone (TGDDS), tetraglycidyl-m-xylylenediamine (TGMXDA), triglycidyl-p-aminophenol, triglycidyl- glycidylamine epoxy resins such as m-aminophenol, N, N-diglycidylaniline, tetraglycidyl 1,3-bisaminomethylcyclohexane (TG1,3-BAC), triglycidyl isocyanurate (TGIC); These may be used alone or in combination of two or more.

  In the present invention, since the epoxy resin (C) can form an electrode with good solderability, the bisphenol A type epoxy resin (C1) having an epoxy equivalent of 1500 to 4000 g / eq and an epoxy equivalent of It is preferable to use a polyhydric alcohol glycidyl type epoxy resin (C2) of 1000 g / eq or less in combination.

(Bisphenol A type epoxy resin (C1))
The bisphenol A type epoxy resin (C1) is a bisphenol A type epoxy resin having an epoxy equivalent of 1500 to 4000 g / eq.
When the epoxy equivalent of the bisphenol A type epoxy resin (C1) is in the above range, the hardness of the conductive composition of the present invention after curing becomes good, and excellent solderability to the cured product (electrode) is maintained. Can do.
Moreover, the epoxy equivalent of the said bisphenol A type epoxy resin (C1) becomes the solderability with respect to an electrode more favorable, and since the ratio of hardening shrinkage is small and can suppress the curvature of a photovoltaic cell board | substrate, it is 2000-4000 g / It is preferably eq, more preferably 2000 to 3500 g / eq.

(Polyhydric alcohol glycidyl type epoxy resin (C2))
The polyhydric alcohol glycidyl epoxy resin (C2) is a polyhydric alcohol glycidyl epoxy resin having an epoxy equivalent of 1000 g / eq or less.
When the epoxy equivalent of the polyhydric alcohol glycidyl type epoxy resin (C2) is within the above range, the viscosity of the conductive composition of the present invention becomes good, and the printability becomes better.
The epoxy equivalent of the polyhydric alcohol-based glycidyl type epoxy resin (C2) is preferably 100 to 400 g / eq, and preferably 100 to 300 g / eq, because the viscosity at the time of screen printing becomes appropriate. More preferably.

In the present invention, the epoxy resin (C) is an epoxy resin (C3) to which ethylene oxide and / or propylene oxide is added because it can form an electrode having good adhesion to the solar cell substrate. ) Is preferred.
Here, addition with ethylene oxide and / or propylene oxide is performed by adding ethylene and / or propylene when an epoxy resin is prepared by reacting, for example, bisphenol A, bisphenol F, etc.) with epichlorohydrin. (Denaturation).
Commercially available products can be used as the epoxy resin (C3). 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. .

  In the present invention, the content in the case of containing the epoxy resin (C) is that the spherical silver powder (A) and the above can be formed because an electrode having better adhesion to the solar cell substrate can be formed. It is preferable that it is 2-20 mass parts with respect to a total of 100 mass parts of flaky silver powder (B), and it is more preferable that it is 2-10 mass parts.

<Fatty acid silver salt (D)>
The conductive composition of the present invention can form an electrode even when fired at a lower temperature (about 150 to 200 ° C.), and can further reduce damage to the solar cell substrate due to heat. It is preferable to contain a silver salt (D).

The fatty acid silver salt (D) is not particularly limited as long as it is a silver salt of an organic carboxylic acid. For example, the fatty acid metal salt described in paragraphs [0063] to [0068] of JP-A-2008-198595 (particularly, Tertiary fatty acid silver salt), fatty acid silver described in paragraph [0030] of Japanese Patent No. 4482930, and one or more hydroxyl groups described in paragraphs [0029] to [0045] of JP 2010-92684 A Fatty acid silver salts, secondary fatty acid silver salts described in paragraphs [0046] to [0056] of the same publication, and the like can be used.
Among these, a polycarboxylic acid having at least three carboxy silver bases (-COOAg) and / or a fatty acid silver salt (D1) having at least one carboxy silver base (-COOAg) and at least one hydroxyl group (-OH). It is preferable to use a silver salt (D2).
Specifically, for example, as the fatty acid silver salt (D1), 2,2-bis (hydroxymethyl) -n-butyric acid silver salt and 2-hydroxyisobutyric acid silver salt can be suitably used. As the carboxylic acid silver salt (D2), 1,2,3,4-butanetetracarboxylic acid silver salt can be preferably used.

  In the present invention, the content of the fatty acid silver salt (D) is based on 100 parts by mass of the total of the spherical silver powder (A) and the flaky silver powder (B) because the printability is better. The amount is preferably 0.1 to 10 parts by mass, and more preferably 1 to 10 parts by mass.

<Cationic curing agent (E)>
When the conductive composition of the present invention optionally contains the epoxy resin (C), it preferably contains a cationic curing agent (E) as a curing agent for the epoxy resin.
The cationic curing agent (E) is not particularly limited, and amine-based, sulfonium-based, ammonium-based, and phosphonium-based curing agents are preferable.
Specific examples of the cationic curing agent (E) include boron trifluoride ethylamine, boron trifluoride piperidine, boron trifluoride phenol, p-methoxybenzenediazonium hexafluorophosphate, diphenyliodonium hexa Fluorophosphate, tetraphenylsulfonium, tetra-n-butylphosphonium tetraphenylborate, tetra-n-butylphosphonium-o, o-diethylphosphorodithioate, sulfonium salts represented by the following formula (I), and the like. These may be used alone or in combination of two or more.
Among these, it is preferable to use a sulfonium salt represented by the following formula (I) because the curing time is shortened.

(In the formula, R ¹ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and R ² is substituted with an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms. R ³ represents an alkyl group having 1 to 4 carbon atoms, and Q is represented by any one of the following formulas (a) to (c). X represents SbF ₆ , PF ₆ , CF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ N, BF ₄ , B (C ₆ F ₅ ) ₄ or Al (CF ₃ SO ₃ ) ₄ . )
(In the formula (a), R represents a hydrogen atom, an acetyl group, a methoxycarbonyl group or a benzyloxycarbonyl group.)

Among the sulfonium salts represented by the above formula (I), X in the above formula (I) is a sulfonium salt represented by SbF ₆ because an electrode having good solderability can be formed. Are preferred, and specific examples thereof include compounds represented by the following formulas (1) and (2).

  In the present invention, since the content of the cationic curing agent (E) can be activated by heat to sufficiently proceed with the ring-opening reaction of the epoxy group, the epoxy resin (C) 100 is used. It is preferably 1 to 10 parts by mass, more preferably 1 to 5 parts by mass with respect to parts by mass.

<Solvent (F)>
The conductive composition of the present invention preferably further contains a solvent (F) from the viewpoint of workability such as printability.
The solvent (F) 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.
Moreover, it is preferable that content in the case of containing the said solvent (F) is 2-20 mass parts with respect to a total of 100 mass parts of the said spherical silver powder (A) and the said flaky silver powder (B), It is more preferably 5 to 15 parts by mass.

<Additives>
The electrically conductive composition of this invention may contain additives, such as metal powder other than the spherical silver powder (A) mentioned above and flaky silver powder (B), and 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.
On the other hand, since the aspect ratio can be further increased and the decomposition of the epoxy resin (C) described above is suppressed, the content of silver oxide is 5 parts by mass with respect to 100 parts by mass of the solvent (F) described above. It is preferably the following, more preferably 1 part by mass or less, and most preferably an embodiment containing substantially no silver oxide.

  The manufacturing method of the electroconductive composition of this invention is not specifically limited, The said spherical silver powder (A) and the said flaky silver powder (B), the said epoxy resin (C) which may be contained depending on necessity, the said fatty acid silver salt ( D), the said cationic hardening | curing agent (E), the said solvent (F), and an additive are mixed with a roll, a kneader, an extruder, a universal stirrer, etc. are mentioned.

[Solar cells]
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 aspect ratio of the electrode formed using the conductive composition of the present invention can be adjusted to 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 cell of the present invention, since the front electrode and / or the back electrode is formed using the conductive composition of the present invention, the aspect ratio of the electrode is 0.4 or more, and the electromotive force generated by light reception is reduced. It can be taken out efficiently as a current.

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 A heat treatment 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 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 150-800 degreeC. When the temperature and time are within this range, even when an antireflection film is formed on the silicon substrate, the electrode can be easily formed by the fire-through method.
In the present invention, since the conductive composition of the present invention is used, favorable heat treatment (firing) can be performed even at a low temperature (about 150 to 500 ° C.).
In the present invention, since the wiring obtained in the wiring formation step can form electrodes even by irradiation with ultraviolet rays or infrared rays, the heat treatment step may be performed by irradiation with ultraviolet rays or infrared rays. .

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

(Reference Example 1-8, Example 9, Reference Example 10, Example 11-15, Comparative Examples 1-3)
To the stirrer, spherical silver powder shown in Table 1 below was added so as to have the composition ratio shown in Table 1 below, and these were mixed to prepare a conductive composition.

<Screen printability>
The prepared conductive composition is 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 and wiring (line width: 80 μm, length) : 5 cm).
Wiring before drying (firing) formed by screen printing was observed with an optical microscope.
As a result, when none of the disconnection, meandering, bleeding and mesh marks is confirmed, the printability is evaluated as “良好”, and no disconnection is confirmed, but any one of meandering, bleeding and mesh marks is When confirmed, the printability is evaluated as “good”, and disconnection is not confirmed. However, when any two or more of meandering, bleeding, and mesh marks are confirmed, the printability is inferior. The case where disconnection was confirmed was evaluated as “x” because the printability was extremely inferior. These results are shown in Table 1 below.

<Volume resistivity (specific resistance)>
After forming the wiring by screen printing, it was dried in an oven at 200 ° C. for 30 minutes to produce a solar cell sample on which conductive wiring (electrode) was formed.
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.

<Aspect ratio (after firing)>
About the sample of each photovoltaic cell produced similarly to the above, the electrode was observed with the laser microscope, height and width were measured, and the aspect ratio (height / width) was calculated | required.
A sample having an aspect ratio of 0.4 or more and less than 0.8 is evaluated as “◯” with a high aspect ratio (satisfactory), and a sample with a aspect ratio of 0.4 or less is evaluated as “x” with a low aspect ratio (not satisfactory). evaluated. These results are shown in Table 1 below.

The following were used for each component in Table 1.
-Spherical silver powder A-1: Ag2-1C (average particle size: 1.0 μm, manufactured by DOWA Electronics)
Spherical silver powder A-2: AgC-103 (average particle diameter: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)
・ Flake silver powder B-1: Ag-XF301K (average thickness: 0.1 μm, apparent density: 0.82 g / cm ³ , manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)
・ Flake silver powder X: AgC-A (average thickness: 0.3 μm, apparent density: 1.82 g / cm ³ , manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

Bisphenol A type epoxy resin C1-1: YD-019 (epoxy equivalent: 2400-3300 g / eq, manufactured by Nippon Steel Chemical Co., Ltd.)
Polyhydric alcohol glycidyl type epoxy resin C2-1: Polyethylene glycol diglycidyl ether (EX-821, epoxy equivalent: 185 g / eq, manufactured by Nagase ChemteX Corporation)
PO addition epoxy resin C3-1: propylene oxide addition bisphenol A type epoxy resin (epoxy equivalent: 260 g / eq, EP-4000S, manufactured by ADEKA)
PO addition epoxy resin C3-2: 350 g / eq, propylene oxide addition bisphenol A type epoxy resin (EP-4010S, manufactured by ADEKA)

  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.

  ・ 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 methyl ethyl ketone (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 a white silver neodecanoate.

  Silver salt of 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) are put in a ball mill and are allowed to stand 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 white 2-hydroxyisobutyric acid silver salt.

  ・ 2,2-bis (hydroxymethyl) -n-butyric acid silver salt: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 64 g of 2,2-bis (hydroxymethyl) -n-butyric acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Then, 300 g of methyl ethyl ketone (MEK) was put into a ball mill and reacted by stirring at room temperature for 24 hours. 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.

  -1,2,3,4-butanetetracarboxylic acid silver salt: First, 50 g of silver oxide (manufactured by Toyo Chemical Co., Ltd.), 1,2,3,4-butanetetracarboxylic acid (manufactured by Shin Nippon Rika Co., Ltd.) 29 g 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 1,2,3,4-butanetetracarboxylic acid silver salt.

Curing agent: aromatic sulfonium salt represented by the above formula (1) (Sl-100L, manufactured by Sanshin Chemical Industry Co., Ltd.)
・ Solvent: α-Terpinel

From the results shown in Table 1, Comparative Example 1 prepared using only the flaky silver powder (B) is very poor in printability because of the disconnection, the aspect ratio is too small to be measured, and the volume resistivity is also low. It turned out to be high.
Moreover, although the comparative example 2 which used spherical silver powder (A) and the flaky silver powder which does not correspond to flaky silver powder (B) is improving rather than the comparative example 1, it is still inferior to printability, It was found that the aspect ratio was low and the volume resistivity was high.
Moreover, it turned out that the comparative example 3 prepared using only spherical silver powder (A) has good printability and low volume resistivity but low aspect ratio.

On the other hand, Reference Examples 1 to 8, Example 9, Reference Example 10, and Examples 11 to 15 prepared by using the spherical silver powder (A) and the flaky silver powder (B) in combination have good printability. It was found that the aspect ratio was high and the volume resistivity was low.
In addition, Reference Examples 4 to 8, Example 9, Reference Example 10, and Examples 11 to 15 prepared by adding a fatty acid silver salt have a lower volume resistivity than that of Reference Example 1, and are slightly higher. It was found that the aspect ratio also increased.

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 (9)

Spherical silver powder (A) having an average particle size of 0.5 to 5.0 μm,
A flaky silver powder (B) having an average thickness of 0.05 to 0.2 μm and an apparent density of 0.4 to 1.1 g / cm ³ ,
The conductive composition for forming a solar cell collecting electrode, wherein the content of the flaky silver powder (B) is 10 % by mass or less based on the total mass of the spherical silver powder (A) and the flaky silver powder (B). .   Furthermore, the electroconductive composition for solar cell current collection electrode formation of Claim 1 containing an epoxy resin (C).   Furthermore, the electrically conductive composition for solar cell current collection electrode formation of Claim 1 or 2 containing fatty-acid silver salt (D).   The epoxy resin (C) is at least a bisphenol A type epoxy resin (C1) having an epoxy equivalent of 1500 to 4000 g / eq and a polyhydric alcohol glycidyl type epoxy resin (C2) having an epoxy equivalent of 1000 g / eq or less. Item 4. A conductive composition for forming a solar cell collecting electrode according to Item 2 or 3.   The conductive composition for forming a solar cell collector electrode according to claim 3 or 4, wherein the fatty acid silver salt (D) is a polycarboxylic acid silver salt (D2) having three or more carboxy silver bases (-COOAg). .   The conductive composition for forming a solar cell collector electrode according to claim 5, wherein the silver salt of polycarboxylic acid (D2) is 1,2,3,4-butanetetracarboxylic acid silver salt.   The content of the epoxy resin (C) is 2 to 20 parts by mass with respect to a total of 100 parts by mass of the spherical silver powder (A) and the flaky silver powder (B). A conductive composition for forming a solar cell collector electrode.   The content of the fatty acid silver salt (D) is 0.1 to 10 parts by mass with respect to 100 parts by mass in total of the spherical silver powder (A) and the flaky silver powder (B). A conductive composition for forming a solar cell collecting electrode according to claim 1. 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 for solar cell current collection electrode formation in any one of Claims 1-8.