TWI673306B - Electroconductive composition, solar cell, and solar cell module - Google Patents

Abstract

An object of the present invention is to provide a conductive composition capable of forming an electrode having a low contact resistance with respect to a transparent conductive layer and the like while maintaining a low volume resistivity, and a solar cell unit having a collector electrode formed using the same. And solar cell modules. The conductive composition of the present invention contains metal powder (A), epoxy resin (B), and phenoxy resin (C). The epoxy resin (B) is larger than the epoxy resin (B). For the total mass, the content of the urethane-modified epoxy resin (B1) is 5 to 50% by mass, and the content of the phenoxy resin (C) is 5 with respect to 100 parts by mass of the above-mentioned epoxy resin (B). ~ 50 parts by mass.

Description

Conductive composition, solar cell, and solar cell module

The invention relates to a conductive composition, a solar cell and a solar cell module.

As people's concerns about global environmental issues increase, industry is actively developing solar cells with various structures and structures that can convert light energy such as sunlight into electrical energy. Among them, solar cells using semiconductor substrates such as silicon are most commonly used due to their advantages in conversion efficiency and manufacturing cost.

As a material for forming an electrode of such a solar cell, an epoxy-based paste material is well known.

For example, Patent Document 1 discloses "a conductive composition containing silver powder (A), a fatty acid silver salt (B), an epoxy resin (C), a core-shell type particle (D), and / or benzene "Ethoxy resin (E)" ([Applicable Patent Scope 1]), Examples 2 and 3 disclose a conductive composition ([0121]) containing an epoxy resin and a phenoxy resin.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2012-023096

However, the present inventors have studied the conductive composition described in Patent Document 1 and found that although the volume resistivity of the formed electrode or wiring (hereinafter also referred to as "electrode" etc.) is sufficiently low, it is transparent. When an electrode or the like is formed on a conductive layer (for example, a transparent conductive oxide layer (TCO)), the contact resistance increases.

Therefore, an object of the present invention is to provide a conductive composition capable of forming an electrode having a low contact resistance with respect to a transparent conductive layer and the like while maintaining a low volume resistivity, and a solar energy having a collector electrode formed using the same. Battery cell and solar cell module.

The present inventors made intensive studies to solve the above-mentioned problems, and found that by blending a urethane-modified epoxy resin and a phenoxy resin in a specific amount as an epoxy resin added together with metal powder, it is possible to maintain low At the same time as the volume resistivity, an electrode or the like having a lower contact resistance to the transparent conductive layer or the like is formed, and the present invention is completed.

That is, the present inventors have found that the above problems can be solved by the following configuration.

[1] A conductive composition containing a metal powder (A), an epoxy resin (B), and a phenoxy resin (C). The epoxy resin (B) is larger than the epoxy resin (B). ), The content of the urethane-modified epoxy resin (B1) is 5-50% by mass, and the content of the phenoxy resin (C) is 100 parts by mass relative to the above-mentioned epoxy resin (B). 5 to 50 parts by mass.

[2] The conductive composition according to [1], further containing a fatty acid metal salt (D).

[3] The conductive composition according to [1] or [2], further comprising a cationic hardener (E).

[4] A solar cell unit having a current collecting electrode formed using the conductive composition according to any one of [1] to [3].

[5] The solar cell unit according to the above [4], further comprising a transparent conductive layer as a base layer of the current collecting electrode.

[6] A solar cell module using a solar cell unit such as [4] or [5].

As described below, according to the present invention, it is possible to provide a conductive composition capable of forming an electrode having a low contact resistance with respect to a transparent conductive layer and the like while maintaining a low volume resistivity, and a conductive electrode having a collector electrode formed using the same. Solar cell unit and solar cell module.

In addition, if the conductive composition of the present invention is used, Low temperature to medium temperature (less than 450 ° C), especially low temperature (about 150 to 350 ° C) heat treatment (drying or sintering), can also maintain low volume resistivity while forming contact resistance for transparent conductive layers, etc. Low electrodes and the like are also very useful because they have the effect of reducing thermal damage to the solar cell (especially the second embodiment described below).

Furthermore, after using the conductive composition of the present invention, not only high-heat-resistant materials such as indium tin oxide (ITO) or silicon, but also low-heat-resistant materials such as PET films, electronic circuits and antennas can be easily manufactured in a short time. Circuit, very useful.

1, 100‧‧‧ solar cell

2‧‧‧n floor

3‧‧‧Anti-reflection film

4‧‧‧ surface electrode

5‧‧‧p layer

6‧‧‧ back electrode

7‧‧‧ silicon substrate

11‧‧‧n-type single crystal silicon substrate

12a, 12b‧‧‧i type amorphous silicon layer

13a‧‧‧p-type amorphous silicon layer

13b‧‧‧n-type amorphous silicon layer

14a, 14b ‧‧‧ transparent conductive layer

15a, 15b ‧‧‧ collector electrode

FIG. 1 is a cross-sectional view showing a first embodiment of a solar cell.

Fig. 2 is a sectional view showing a second embodiment of a solar cell;

Hereinafter, the conductive composition of the present invention, a solar cell and a solar cell module having a current collecting electrode formed using the same will be described.

The numerical range indicated by "~" in this specification is a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[Conductive composition]

The conductive composition of the present invention contains a metal powder (A), and The total mass of the epoxy resin (B), the phenoxy resin (C), and the epoxy resin (B) with respect to the total mass of the epoxy resin (B), the urethane-modified epoxy resin (B1) The content is 5 to 50 mass%, and the content of the phenoxy resin (C) is 5 to 50 parts by mass relative to 100 parts by mass of the epoxy resin (B).

The conductive composition of the present invention is as described below, and may contain a fatty acid metal salt (D), a cationic hardener (E), a solvent (F), and the like as necessary.

In the present invention, as described above, the urethane-modified epoxy resin (B1) is blended in a specific amount as the epoxy resin (B), and benzene is blended in a specific amount with respect to the epoxy resin (B). The oxyresin (C) forms a conductive composition capable of forming an electrode having a low contact resistance to a transparent conductive layer and the like while maintaining a low volume resistivity.

Although the detailed reason is not clear, it can be roughly estimated as follows.

That is, considering the viewpoint of reduction in reflectivity and the like, a texture (concavo-convex) structure is generally provided on the surface of a silicon substrate (silicon wafer) generally used as a substrate of a solar cell.

Therefore, we believe that by blending the urethane-modified epoxy resin (B1) and phenoxy resin (C) in a specific amount, it is possible to impart appropriate fluidity to the conductive composition. The undulations of the transparent conductive layer and the like generated by the uneven structure can improve the followability, so that electrodes with low contact resistance can be formed.

As shown in the following comparative example, one or both of the urethane-modified epoxy resin (B1) and the phenoxy resin (C) are not blended. In the example, as a result of the increase in contact resistance, the above conclusion can also be reached.

Hereinafter, the metal powder (A), the epoxy resin (B), and the phenoxy resin (C) contained in the conductive composition of the present invention, and other components that may be contained as necessary will be described in detail.

<Metal powder (A)>

The metal powder (A) contained in the conductive composition of the present invention is not particularly limited, and for example, a resistivity of 20 × 10 ^-6 Ω can be used. Metal materials below cm.

Specific examples of the metal material include gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), and nickel (Ni). These may be used alone, Two or more of them may be used in combination.

Among them, in consideration of the reason that a collector electrode having a low contact resistance can be formed, silver powder or a silver coating on at least a part of the surface of a metal powder (for example, nickel powder, copper powder, etc.) other than silver is preferred. Silver metal powder.

In the present invention, for reasons of good printability (especially screen printing), the metal powder (A) is preferably a spherical metal powder (A1), and more preferably used together with the spherical metal powder (A1). The sheet (scale) metal powder (A2) is used in combination, and the mass ratio (A1: A2) is preferably 70:30 to 30:70, and the spherical metal powder (A1) and the sheet metal powder (A2) ).

Here, the spherical shape refers to a particle shape in which the ratio of the major diameter to the short diameter is 2 or less, and the flake shape refers to a particle shape in which the ratio of the major diameter to the short diameter is greater than 2. shape.

In consideration of the reason that the printability is better, the average particle diameter of the spherical metal powder (A1) as the metal powder (A) is preferably 0.5 to 10 μm, and more preferably 0.5 to 5.0 μm.

Here, the average particle diameter of the spherical metal powder (A1) refers to the average particle diameter of the spherical metal powder, and it is a 50% volume cumulative diameter (D50) measured using a laser diffraction particle size distribution measuring device. In addition, regarding the particle size used as the basis for calculating the average value, when the cross section of the metal powder is oval, it means the average value of the total value of its long and short diameters divided by 2, and when it is a perfect circle, it means its diameter.

In consideration of the reason that the printability is better and the paste becomes easier, the average thickness of the flake metal powder (A2) of the metal powder (A) is preferably 0.05 to 2.0 μm, and more preferably 0.05 to 1.0 μm.

Here, the average thickness of the flaky metal powder (A2) refers to a value in which the specific surface area of the flaky metal powder is measured by the BET method (gas adsorption method) as S (m ² / g), and is expressed by the following formula ( i) Calculated value.

The average thickness = 0.19 / S. ． ． (i)

In the present invention, a commercially available product can be used as the metal powder (A).

Specific examples of commercially available products of spherical silver powder include AG2-1C (average particle diameter: 1.0 μm, manufactured by DOWA Electronics), AG4-8F (average particle diameter: 2.2 μm, manufactured by DOWA Electronics), and AG3 -11F (average particle diameter: 1.4 μm, manufactured by DOWA Electronics), AgC-102 (average particle diameter: 1.5 μm, Fukuda metal foil Powder Industry Co., Ltd.), AgC-103 (average particle size: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.), EHD (average particle size: 0.5 μm, manufactured by Mitsui Metals Co., Ltd.), and the like.

In addition, as a specific example of a commercially available product of the flaky silver powder, Ag-XF301K (average thickness: 0.1 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) and the like are mentioned.

<Epoxy resin (B)>

The content of the urethane-modified epoxy resin (B1) in the epoxy resin (B) contained in the conductive composition of the present invention is 5 to 50% by mass.

Here, "urethane-modified epoxy resin" refers to a product formed by introducing a urethane bond into an epoxy resin, as long as it has a urethane bond and two or more epoxy groups in the molecule , There are no special restrictions.

The epoxy equivalent of the epoxy resin (B) is preferably 50 to 10,000 g / eq, and more preferably 90 to 5000 g / eq.

The urethane-modified epoxy resin (B1) is preferably, for example, a resin obtained by reacting a compound (b1) containing a urethane bond with an epoxy compound (b2) containing a hydroxyl group, The urethane-bonded compound (b1) has an isocyanate group obtained by reacting a polyhydroxy compound with a polyisocyanate compound.

Here, examples of the polyhydroxy compound include a polyether polyol, a polyester polyol, an adduct of a hydroxycarboxylic acid and an alkylene oxide, a polybutadiene polyol, a polyolefin polyol, and the like.

The polyisocyanate compound is not particularly limited as long as it has two or more isocyanate groups. Specific examples thereof include aliphatic polyisocyanates, aromatic polyisocyanates, and polyisocyanates having aromatic hydrocarbon groups. Among them, aromatic polyisocyanates are preferred.

Examples of the aromatic polyisocyanate include toluene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate.

By reacting the above-mentioned polyhydroxy compound with a polyisocyanate compound, a urethane prepolymer having a free isocyanate group at the terminal can be obtained.

Furthermore, the obtained urethane prepolymer and an epoxy resin having at least one hydroxyl group in one molecule (for example, diglycidyl ether of bisphenol A type epoxy resin, bisphenol F type epoxy resin) The diglycidyl ether of the resin, the diglycidyl ether of the aliphatic polyhydric alcohol, and the glycidol are reacted to obtain a urethane-modified epoxy resin (B1).

The epoxy equivalent of the urethane-modified epoxy resin (B1) is preferably 100 to 400 g / eq, and more preferably 200 to 350 g / eq.

The urethane-modified epoxy resin (B1) may be used alone or in combination of two or more.

In the present invention, as described above, by blending the urethane-modified epoxy resin (B1) with the content of 5 to 50 mass percent of the epoxy resin (B), a conductive composition can be formed. While maintaining a low volume resistivity, an electrode or the like having a low contact resistance with respect to a transparent conductive layer or the like can be formed.

Furthermore, considering the reason that an electrode having a lower contact resistance can be formed, the content of the urethane-modified epoxy resin (B1) contained in the epoxy resin (B) is preferably 5 to 45 mass%.

On the other hand, as the epoxy resin (hereinafter also referred to as "other epoxy resin") other than the urethane-modified epoxy resin (B1) contained in the epoxy resin (B), only one molecule is required. The resin composed of a compound having two or more ethylene oxide rings (epoxy groups) is not particularly limited. Generally, the epoxy equivalent is 50 to 10,000 g / eq, preferably 90 to 5000 g / eq.

As such another epoxy resin, a conventionally well-known epoxy resin can be used.

Specific examples include bisphenol A, bisphenol F, brominated bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol AF, and biphenyl. Epoxy compounds, or polyalkylene glycol-type, alkanediol-type epoxy compounds, and epoxy compounds with naphthalene rings, or epoxy compounds with fluorenyl groups, etc., bifunctional glycidyl ether epoxy resins; Polyfunctional glycidyl ether epoxy resins such as phenol novolac type, o-cresol novolac type, trihydroxyphenylmethane type, and tetraphenolyl ethane type; glycidyl ester type epoxy resins of synthetic fatty acids such as dimer acid ; N, N, N ', N'-tetraglycidyl diamino diphenylmethane (TGDDM), tetraglycidyl diamino diphenyl hydrazone (TGDDS), tetraglycidyl metaxylylenediamine (TGMXDA), triglycidyl p-aminophenol, triglycidyl-m-aminophenol, N, N-diglycidyl aniline, tetraglycidyl 1,3-cyclohexanedimethylamine (TG1, 3- BAC), glycidylamine epoxy resin such as triglycidyl isocyanurate (TGIC); epoxy compounds with tricyclic [5.2.1.0 ^2.6 ] decane ring, with Specifically, for example, an epoxy compound obtained by polymerizing dicyclopentadiene with cresols or phenols such as m-cresol and then reacting epichlorohydrin can be obtained by this well-known manufacturing method; Cyclic epoxy resin; epoxy resin with sulfur atom in the epoxy resin main chain represented by Toray Thiokol company FLEP10; polyurethane modified epoxy resin with polyurethane bond; containing polybutadiene, liquid polypropylene Nitrile-butadiene rubber or acrylonitrile-butadiene rubber (NBR) rubber modified epoxy resin.

These other epoxy resins may be used alone or in combination of two or more.

Among these, in view of hardenability, heat resistance, durability, and cost, bisphenol A-type epoxy resin and bisphenol F-type epoxy resin are preferred.

In the present invention, other epoxy resins are preferably epoxy resins with less curing shrinkage. Since the silicon wafer used as the substrate is easily damaged, if an epoxy resin with a large hardening shrinkage is used, the wafer may be cracked or damaged. Recently, in order to reduce costs, silicon wafers have been continuously thinned, and epoxy resins with less hardening shrinkage also have the effect of suppressing wafer bending.

Considering the reason of reducing the hardening shrinkage, and reducing the contact resistance of the formed collector electrode, and further the better adhesion with the transparent conductive layer, it is preferable to add a ring with ethylene oxide and / or propylene oxide. Oxygen resin.

Here, regarding the epoxy resin to which ethylene oxide and / or propylene oxide are added, for example, when bisphenol A, bisphenol F, etc. react with epichlorohydrin to prepare the epoxy resin, ethylene and / Or obtained by addition (modification) of propylene.

As the epoxy resin to which ethylene oxide and / or propylene oxide is added, a commercially available product can be used. As a specific example, bisphenol A type epoxy resin (BPO-60E to which ethylene oxide is added) can be cited. , Manufactured by Shin Nihon Chemical Co., Ltd.), bisphenol A epoxy resin with added propylene oxide (BPO-20E, manufactured by Shin Nihon Chemical Co., Ltd.), bisphenol A epoxy resin with added propylene oxide (EP-4010S , Made by ADEKA), bisphenol A epoxy resin (EP-4000S, made by ADEKA) with propylene oxide addition, etc.

In the present invention, in order to reduce the hardening shrinkage and reduce the contact resistance of the formed collector electrode, and further the adhesion with the transparent conductive layer is better, it is preferable to use the urethane-modified epoxy resin ( B1) Simultaneously use bisphenol A epoxy resin (B2) with epoxy equivalent of 1500 ~ 4000g / eq and polyol glycidyl epoxy resin (B3) with epoxy equivalent of 1000g / eq or less or 1000g / eq Diluted bisphenol A epoxy resin (B4).

In addition, the urethane-modified epoxy resin (B1) and the bisphenol A-type epoxy resin (B2), the polyol-based glycidol-type epoxy resin (B3), and the bisphenol A-type epoxy resin The total content of (B4) is preferably 55 to 95 mass percent, and more preferably 60 to 95 mass percent.

(Bisphenol A epoxy resin (B2))

The bisphenol A type epoxy resin (B2) is a bisphenol A type epoxy resin having an epoxy equivalent of 1500 to 4000 g / eq.

Since the epoxy equivalent of the bisphenol A-type epoxy resin (B2) is within the above range, as described above, if the bisphenol A-type epoxy resin (B2) is used in combination, the conductive composition of the present invention can harden and shrink. It is suppressed, and the adhesiveness with respect to a board | substrate or a transparent conductive layer is also favorable. Considering the reason for the lower volume resistivity, the epoxy equivalent is preferably 2000 to 4000 g / eq, and more preferably 2000 to 3500 g / eq.

(Polyol-based glycidyl epoxy resin (B3))

The polyol-based glycidyl epoxy resin (B3) is a polyol-based glycidyl epoxy resin having an epoxy equivalent of 1,000 g / eq or less.

Since the above-mentioned polyol-based glycidyl epoxy resin (B3) has an epoxy equivalent in the above range, as described above, when the polyol-based glycidyl epoxy resin (B3) is used in combination, the conductive composition of the present invention Good viscosity and good printability.

In addition, considering the reason that the viscosity is appropriate during screen printing, the epoxy equivalent of the polyhydric alcohol glycidyl epoxy resin (B3) is preferably 100 to 400 g / eq, and more preferably 100 to 300 g / eq.

(Diluted bisphenol A epoxy resin (B4))

The diluted bisphenol A type epoxy resin (B4) is a bisphenol A type epoxy resin having an epoxy equivalent of 1,000 g / eq or less. In the case of not impairing the characteristics of the epoxy resin, a low viscosity treatment has been performed using a reactive diluent.

Since the above-mentioned diluted bisphenol A type epoxy resin (B4) has an epoxy equivalent in the above range, as described above, if the diluted bisphenol A type epoxy resin (B4) is used in combination, the conductive composition of the present invention Good viscosity and good printability.

In addition, considering the reason that the viscosity is appropriate during screen printing, the epoxy equivalent of the above-mentioned dilute bisphenol A epoxy resin (B4) is preferably 100 to 400 g / eq, and more preferably 100 to 300 g / eq.

In the present invention, in order to reduce the hardening shrinkage, reduce the contact resistance of the formed collector electrode, and further improve the adhesion with the transparent conductive layer, it is preferable to use the urethane-modified epoxy resin ( B1) A trifunctional epoxy resin (B5) and / or a bisphenol E-type epoxy resin (B6) having a structural formula represented by the following formula (1) are used together.

In addition, the content of the urethane-modified epoxy resin (B1), the trifunctional epoxy resin (B5), and the bisphenol E-type epoxy resin (B6) (any one of which is used in combination) The content of one) is preferably 20 to 80% by mass.

In the present invention, considering the reason that the formed collector electrode has lower contact resistance and better adhesion with the transparent conductive layer, the epoxy resin (B) is 100 parts by mass of the metal powder (A). The content is preferably 2 to 20 parts by mass, more preferably 2 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass.

<Phenoxy resin (C)>

The phenoxy resin (C) contained in the conductive composition of the present invention is not particularly limited, and conventionally known phenoxy resins can be used. Phenoxy resin is a polyhydroxy polyether (thermoplastic resin) synthesized from bisphenols and epichlorohydrin. Since it is a thermoplastic resin, it does not substantially have an epoxy group and generally has a molecular weight to some extent (weight average molecular weight (Mw) is tens of thousands or more).

The weight average molecular weight of the phenoxy resin (C) is preferably 10,000 or more, more preferably 20,000 or more, particularly preferably 30,000 or more, and more preferably 120,000 or less, more preferably 100,000 or less, and particularly preferably 90,000 or less.

The reason why the phenoxy resin (C) is compatible with the epoxy resin (B) and a stable paste state is considered. Specifically, for example, bisphenol A type phenoxy resin, bis Phenol F-type phenoxy resin.

In the present invention, a commercially available product can be used as the phenoxy resin (C), and specific examples thereof include a bisphenol A type phenoxy resin (1256, manufactured by Japan Epoxy Resin Company), and a bisphenol A type benzene. Oxyresin (YP-50, manufactured by Toto Kasei Co., Ltd.), bisphenol F type phenoxy resin (FX-316, manufactured by Toto Kasei Co., Ltd.), copolymer type of bisphenol A type and bisphenol F type (YP-70, Toto Kasei Co., Ltd.) and so on.

Moreover, in this invention, content of the said phenoxy resin (C) is 5-50 mass parts with respect to 100 mass parts of said epoxy resin (B), Preferably it is 10-40 mass parts.

Furthermore, considering the reasons that the formed collector electrode has lower contact resistance and better adhesion to the transparent conductive layer, the phenoxy resin (C) is 100 parts by mass of the metal powder (A). The content is preferably 0.1 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass.

<Fatty acid metal salt (D)>

In consideration of the reason that the contact resistance of the formed electrode or the like is lower, the conductive composition of the present invention preferably contains a fatty acid metal salt (D).

The fatty acid metal salt (D) may be a metal salt of an organic carboxylic acid, Although it does not specifically limit, For example, the carboxylic acid metal salt of at least 1 sort (s) of metal selected from the group which consists of silver, magnesium, nickel, copper, zinc, yttrium, zirconium, tin, and lead can be used.

Among these, a metal salt of a carboxylic acid silver (hereinafter also referred to as "silver carboxylate") is preferably used.

Here, the silver salt of a carboxylic acid is not particularly limited as long as it is a silver salt of an organic carboxylic acid (fatty acid). Fatty acid metal salts (especially grade 3 fatty acid silver salts), fatty acid silver salts described in paragraph [0030] of Japanese Patent No. 4482930, and described in paragraphs [0029] to [0045] of Japanese Patent Laid-Open No. 2010-92684 Silver salts of fatty acids having one or more hydroxyl groups, silver salts of secondary fatty acids described in paragraphs [0046] to [0056] of this bulletin, and paragraphs [0022] to [0026] of Japanese Patent Laid-Open No. 2011-35062 Of silver carboxylate.

In the present invention, in consideration of the reason that the contact resistance of the formed collector electrode is lower, the content when the fatty acid metal salt (D) is contained is preferably 0.1 to 10 parts by mass relative to 100 parts by mass of the metal powder (A). , More preferably 0.5 to 5 parts by mass.

<Cationic hardener (E)>

The conductive composition of the present invention preferably contains a cationic curing agent (E) as a curing agent for the epoxy resin (B).

The above-mentioned cationic hardener (E) is not particularly limited, but is preferably an amine-based, arsine-based, ammonium-based, or arsine-based hardener.

Specific examples of the cationic hardener (E) include boron trifluoride ethylamine, boron trifluoride piperidine, boron trifluoride phenol, p-methoxyphenyldiazonium hexafluorophosphate, and diphenyl. Iodonium hexafluorophosphate, tetraphenylphosphonium, tetrabutyltetraphenylborate, tetrabutylphosphonium-O, O-diethylphosphinophosphate, phosphonium salts represented by the following formula (I), etc., These can be used alone or in combination of two or more.

In consideration of the reason for shortening the curing time, a sulfonium salt represented by the following formula (I) is preferably used among these.

(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 represents a benzyl group which may be substituted by an alkyl group having 1 to 4 carbon atoms and an alkyl group having 1 to 4 carbon atoms. Or α-naphthylmethyl, R ³ represents an alkyl group having 1 to 4 carbon atoms, and Q represents a group represented by any one of the following formulae (a) to (c), and 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 formula (a), R represents a hydrogen atom, an ethylfluorenyl group, a methoxycarbonyl group, or a fluorenyloxycarbonyl group)

In consideration of the reason that an electrode having good solderability can be formed, among the sulfonium salts represented by the above formula (I), X in the above formula (I) is preferably a sulfonium salt represented by SbF ₆ , and specific examples thereof include: Compounds represented by the following formulae (1) and (2).

In the present invention, in consideration of the reason that the ring-opening reaction of the epoxy group can be sufficiently performed after thermal activation, the content when the cationic hardener (E) is contained with respect to 100 parts by mass of the epoxy resin (B) is preferably 1 to 10 parts by mass, more preferably 1 to 5 parts by mass.

<Solvent (F)>

The conductive composition of the present invention preferably contains a solvent (F) in view of workability such as printability.

The solvent (F) is not particularly limited as long as it can coat the conductive composition of the present invention on a substrate, and specific examples thereof include butylcarbitol, methyl ethyl ketone, and isophor Ketone, α-terpineol, etc. may be used alone or in combination of two or more.

<Additives>

The conductive composition of the present invention may contain additives such as a reducing agent as necessary.

Specific examples of the reducing agent include ethylene glycols.

In addition, the conductive composition of the present invention does not require glass frit that is generally used as a high-temperature (700-800 ° C) sintered conductive adhesive, and it is relatively larger than 100 parts by mass of the metal powder (A). It is preferably less than 0.1 parts by mass, and preferably not substantially contained.

The method for producing the conductive composition of the present invention is not particularly limited, and examples thereof include a method of mixing the aforementioned components using a drum, a kneader, an extruder, a universal mixer, or the like.

[Solar cell unit]

The solar cell unit of the present invention is a solar cell unit that uses the conductive composition of the present invention as a collector electrode.

<First Embodiment of Solar Cells>

As a first embodiment of the solar cell unit of the present invention, a solar cell unit is provided, which includes a surface electrode on a light-receiving surface side, a semiconductor substrate, and a back electrode, and is formed using the conductive composition of the present invention. The front surface electrode and / or the back surface electrode.

Hereinafter, a first embodiment of a solar cell unit according to the present invention will be described using FIG. 1.

As shown in FIG. 1, the solar cell 1 includes a surface electrode 4 on the light-receiving surface side, a pn-bonded silicon substrate 7 formed by bonding the p-layer 5 and the n-layer 2, and a back-surface electrode 6.

In addition, as shown in FIG. 1, in order to reduce the reflectivity, the solar cell unit 1 teaches, for example, Jia Jia to perform etching on the wafer surface to form a pyramid-shaped texture, and includes an anti-reflection film 3.

Hereinafter, the above-mentioned surface electrode, back electrode, silicon substrate and the anti-reflection film which may be provided in the first embodiment of the solar cell unit of the present invention will be described in detail.

<Front electrode / back electrode>

Any one or both of the front electrode and the back electrode may be formed using the conductive composition of the present invention, and the arrangement (pitch), shape, height, width, and the like of the electrodes are not particularly limited. In addition, the electrode height is usually designed to be several μm to several tens μm. However, an electrode formed using the conductive composition of the present invention has a ratio of a cross-sectional height to a width (height / width) (hereinafter referred to as ("Aspect ratio") can be adjusted to a larger value (for example, about 0.4 or more).

Here, as shown in FIG. 1, there are usually a plurality of surface electrodes and back electrodes, but for example, only a part of the plurality of surface electrodes may be formed of the conductive composition of the present invention, or a part of the plurality of surface electrodes and a plurality of back electrodes Part of the electrode is formed of the conductive composition of the present invention.

<Anti-reflection film>

The anti-reflection film is a film (film thickness: about 0.05 to 0.1 μm) formed on the light-receiving surface where the surface electrode is not formed, such as a silicon oxide film, a silicon nitride film, a titanium oxide film, a laminated film of these, etc. Make up.

In addition, the above-mentioned silicon substrate has a pn junction, which means that the light-receiving surface impurity diffusion region of the second conductivity type is formed on the surface side of the first conductivity type semiconductor substrate. When the first conductivity type is an n-type, the second conductivity type is a p-type, and when the first conductivity type is a p-type, the second conductivity type is an n-type.

Here, examples of the p-type impurity include boron and aluminum, and examples of the n-type impurity include phosphorus and arsenic.

(Si substrate)

The silicon substrate is not particularly limited, and a silicon substrate (plate thickness: about 80 to 450 μm), which is well-known for forming solar cells, can be used, and it may be a single crystal or polycrystalline silicon substrate.

In the first embodiment of the solar cell unit of the present invention, the solar cell unit uses the conductive composition of the present invention to form a surface. The electrode and / or the back electrode, so it is easy to increase the electrode aspect ratio, and the electromotive force generated by the light can be effectively taken out as a current.

In addition, the conductive composition of the present invention described above is also suitable for forming a back electrode of a full-back electrode type (so-called full-back electrode) solar cell. Therefore, it can also be applied to a full-back electrode type solar cell.

<Manufacturing Method of Solar Cell (First Embodiment)>

The manufacturing method of the above-mentioned solar cell (first embodiment) is not particularly limited, and examples thereof include a method having the following process: a conductive forming composition of the present invention is coated on a silicon substrate, a wiring forming process for forming wiring, and A heat treatment process is performed on the formed wiring to form electrodes (front electrode and back electrode).

In addition, when the solar cell is provided with an antireflection layer, the antireflection film can be formed by a well-known method such as a plasma CVD method.

Hereinafter, the wiring formation process and the heat treatment process will be described in detail.

(Wiring formation process)

The above-mentioned wiring formation process is a process in which the conductive composition of the present invention is coated on a silicon substrate to form a wiring.

Specific examples of the coating method include inkjet, screen printing, gravure printing, offset printing, and letterpress printing.

(Heat treatment process)

The heat treatment process refers to the coating formed in the wiring forming process. The film is subjected to a heat treatment (drying or sintering) to form a conductive wiring (electrode).

The above heat treatment is not particularly limited, and a heat treatment (sintering) at a relatively low temperature of 150 to 350 ° C. for several seconds to several tens of minutes is preferred. When the temperature and time are within this range, even if an antireflection film is formed on the silicon substrate, an electrode can be easily formed.

In addition, in the first embodiment of the solar cell unit of the present invention, since the conductive composition of the present invention is used, good heat treatment (sintering) can be performed even at a low temperature of 150 to 350 ° C.

In the present invention, since the wiring formed in the wiring forming process can be formed by irradiation of ultraviolet or infrared rays, the heat treatment process can also be performed by ultraviolet or infrared rays.

<Second Embodiment of Solar Cells>

As a second embodiment of the solar cell unit of the present invention, a unit cell of a solar cell (for example, a heterojunction solar cell) can be cited. The n-type single crystal silicon substrate is used as the center, and an amorphous silicon layer and a transparent conductive layer are provided on the top and bottom. (For example, TCO), and uses the transparent conductive layer as a base layer, and uses the conductive composition of the present invention to form a collector electrode on the transparent conductive layer. The above-mentioned solar cell unit (second embodiment) is a monocrystalline silicon and amorphous silicon hybrid cell unit, and has high photoelectric conversion efficiency.

Hereinafter, a second embodiment of the solar cell unit of the present invention will be described using FIG. 2.

As shown in FIG. 2, the solar cell 100 is an n-type unit. The crystalline silicon substrate 11 is centered, and includes i-type amorphous silicon layers 12a and 12b, p-type amorphous silicon layers 13a and n-type amorphous silicon layers 13b, transparent conductive layers 14a and 14b, and the conductivity using the above-mentioned present invention The collector electrodes 15a and 15b formed of the composition.

The n-type single crystal silicon substrate is a single crystal silicon layer doped with an n-type impurity. The n-type impurities are generated as described above.

The i-type amorphous silicon layer is an undoped amorphous silicon layer.

The p-type amorphous silicon is an amorphous silicon layer doped with impurities that generate p-type. The p-type impurities are generated as described above.

The n-type amorphous silicon is an amorphous silicon layer doped with an n-type impurity. The n-type impurities are generated as described above.

The current collecting electrode is a current collecting electrode formed using the conductive composition of the present invention. The specific form of the current collecting electrode is the same as the above-mentioned surface electrode or back electrode.

(Transparent conductive layer)

As specific examples of the above-mentioned transparent conductive layer materials, single metal oxides such as zinc oxide, tin oxide, indium oxide, and titanium oxide, indium tin oxide (ITO), indium zinc oxide, indium titanium oxide, and cadmium tin oxide can be listed. Various metal oxides, cadmium-added zinc oxide, aluminum-added zinc oxide, boron-added zinc oxide, titanium-added zinc oxide, titanium-added indium oxide, zirconium-added indium oxide, fluorine-added tin oxide, etc.

<Manufacturing Method of Solar Cell (Second Embodiment)>

The manufacturing method of the said solar cell (2nd Embodiment) is not specifically limited, For example, it can manufacture by the method described in Unexamined-Japanese-Patent No. 2010-34162.

Specifically, an i-type amorphous silicon layer 12a can be formed on one main surface of one side of the n-type single crystal silicon substrate 11 by a method such as plasma enhanced chemical vapor deposition (PECVD). Further, a p-type amorphous silicon layer 13a is formed on the formed i-type amorphous silicon layer 12a by a method such as a plasma-assisted chemical vapor deposition method.

Next, an i-type amorphous silicon layer 12b is formed on the other main surface of the other side of the n-type single crystal silicon substrate 11 by a method such as plasma-assisted chemical vapor deposition. Furthermore, an n-type amorphous silicon layer 13b is formed on the formed i-type amorphous silicon layer 12b by a method such as a plasma-assisted chemical vapor deposition method.

Next, transparent conductive layers 14a and 14b such as indium tin oxide are formed on the p-type amorphous silicon layer 13a and the n-type amorphous silicon layer 13b by a method such as sputtering.

Next, the conductive composition of the present invention is coated on the formed transparent conductive layers 14a and 14b to form wirings, and the formed wirings are further heat-treated to form current collecting electrodes 15a and 15b.

The method of forming the wiring is the same as the method described in the wiring forming process of the above-mentioned solar cell (first embodiment).

The method of heat-treating the wiring is the same as the method described in the heat-treatment process of the above-mentioned solar cell (first embodiment), but the heat-treatment temperature (sintering temperature) is preferably 150 to 200 ° C.

[Example]

Hereinafter, the electroconductive composition of this invention is demonstrated in detail using an Example. However, the present invention is not limited to this.

[Examples 1 to 5, Comparative Examples 1 to 3]

Metal powders and the like shown in Table 1 below were added to a ball mill so that the composition ratio (mass ratio) shown in Table 1 below was achieved, and these were mixed to prepare a conductive composition.

<Volume resistivity (specific resistance)>

Each of the prepared conductive compositions was coated by a screen printing method on a TCO, that is, an indium tin oxide vapor-deposited glass substrate, to form a test pattern of 25 mm × 25 mm coating on the entire surface. Then, it was dried in an oven at 150 ° C. for 30 minutes or 200 ° C. for 30 minutes to prepare a conductive film.

With respect to each of the produced conductive films, the volume resistivity was evaluated by a resistivity meter (Loresta-GP, manufactured by Mitsubishi Chemical Corporation) by the 4-terminal 4-probe method. The results are shown in Table 1.

<Contact resistance>

On the surface of soda lime glass, ITO (Sn-doped indium oxide) is made into a film as a transparent conductive layer.

Next, each of the produced conductive compositions was coated on a transparent conductive layer by a screen printing method to form six thin linear test patterns having a width of 0.08 mm and a length of 15 mm, and arranged at 1.8 mm intervals.

Dry in an oven at 200 ° C. for 30 minutes to form a thin linear conductive film (thin wire electrode) to prepare a solar cell unit cell sample.

For the prepared solar cell cell sample, a digital multimeter (3541 RESISTANCE HiTESTER, manufactured by HIOKI) was used to measure the resistance value between the thin wire electrodes, and then the contact resistance was calculated by the Transfer Length Method (TLM, transmission line model method). The results are shown in Table 1 below.

The following substances are used for each component in Table 1.

˙Spherical metal powder A1-1: AgC-103 (shape: spherical, average particle diameter: 1.5 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

˙Flake metal powder A2-1: AgC-224 (shape: flake, average thickness: 0.7 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

˙ Urethane modified epoxy resin B1-1: EPU-1395 (epoxy equivalent: 215 g / eq, manufactured by ADEKA Corporation)

˙ Urethane modified epoxy resin B1-2: EPU-11F (epoxy equivalent: 320g / eq, manufactured by ADEKA)

˙ Urethane modified epoxy resin B1-3: EPU-78-11 (epoxy equivalent: 230g / eq, manufactured by ADEKA)

˙Bisphenol A epoxy resin B4-1: EP-4100E (epoxy equivalent: 190 g / eq, manufactured by ADEKA)

˙Bisphenol A epoxy resin B2-1: YD-019 (epoxy equivalent: 2400 ~ 3300g / eq, manufactured by Nippon Steel & Sumikin Co., Ltd.)

˙Polyol-based glycidyl epoxy resin B3-1: EX-850 (epoxy equivalent: 122 g / eq, manufactured by Nagase ChemteX)

˙Bisphenol A phenoxy resin C-1: YP-50 (weight average molecular weight: 70,000, manufactured by Tohto Kasei Co., Ltd.)

˙Copolymer phenoxy resin C-2: ZX-1356-2 (weight average molecular weight: 70,000, manufactured by Nippon Steel & Sumitomo Chemical Co., Ltd.)

˙Bisphenol F-type phenoxy resin C-3: FX-316 (weight average molecular weight: 50,000, manufactured by Toto Kasei Co., Ltd.)

˙Bisphenol A phenoxy resin C-4: PKHB (weight average molecular weight: 37,000, manufactured by InChem)

˙Bisphenol A phenoxy resin C-5: PKHJ (weight average molecular weight: 57,000, manufactured by InChem)

银 Silver 2-methylpropionate: First put 50 g of silver oxide (manufactured by Toyo Chemical Industry Co., Ltd.), 38 g of 2-methyl propionate (manufactured by Kanto Chemical Co., Ltd.) and 300 g of methyl ethyl ketone (MEK) into a ball mill. The reaction was stirred at room temperature for 24 hours.

Next, MEK was removed by suction filtration, and the obtained powder was dried to prepare silver 2-methylpropionate.

银 Silver 2-hydroxyisobutyrate:

˙ Put 50 g of silver oxide (manufactured by Toyo Chemical Industry Co., Ltd.), 45 g of 2-hydroxyisobutyric acid (manufactured by Tokyo Chemical Industry Co., Ltd.), and 300 g of methyl ethyl ketone (MEK) into a ball mill, and stir at room temperature for 24 hours. Make it react.

Next, MEK was removed by suction filtration, and the obtained powder was dried to prepare a silver salt of 2-hydroxyisobutyrate.

˙Silver salt of 1,2,3,4-butanetetracarboxylic acid: 50 g of silver oxide (manufactured by Toyo Chemical Industry Co., Ltd.) g and methyl ethyl 300 g of ketone (MEK) was put into a ball mill, and stirred at room temperature for 24 hours to react.

Next, MEK was removed by suction filtration, and the obtained powder was dried to prepare a white silver salt of 1, 2, 3, and 4-butanetetracarboxylic acid.

˙Cationic hardener: boron trifluoride ethylamine (manufactured by Stella-Chemifa)

˙Solvent: terpineol: terpineol (manufactured by Yasuhara Chemical)

From the results shown in Table 1, it can be seen that in the conductive composition in which either or both of the urethane-modified epoxy resin (B1) and the phenoxy resin (C) were not blended, High contact resistance (Comparative Examples 1 to 3).

In contrast, in the conductive compositions of Examples 1 to 5 in which the urethane-modified epoxy resin (B1) and the phenoxy resin (C) were blended in a predetermined amount during the preparation, the volume resistivity was relatively small. Low and low contact resistance to the transparent conductive layer.

Claims (6)

A conductive composition comprising a metal powder (A), an epoxy resin (B), and a phenoxy resin (C). The epoxy resin (B) is larger than the epoxy resin (B). ), The content of the urethane-modified epoxy resin (B1) is 5-50% by mass, and the content of the phenoxy resin (C) is 100 parts by mass relative to the aforementioned epoxy resin (B). 5 to 50 parts by mass, the content of the phenoxy resin (C) is 0.1 to 10 parts by mass based on 100 parts by mass of the metal powder (A). The conductive composition according to claim 1, further comprising a fatty acid metal salt (D). The conductive composition according to claim 1 or 2, further comprising a cationic curing agent (E). A solar cell is provided with a current collecting electrode formed using the conductive composition according to any one of claims 1 to 3. The solar cell of claim 4, wherein a transparent conductive layer is provided as a base layer of the aforementioned collector electrode. A solar cell module is characterized by using a solar cell unit as claimed in claim 4 or 5.