JP6065049B2 - Electrode paste composition and solar cell - Google Patents

Description

  The present invention relates to an electrode paste composition and a solar cell.

  Generally, a crystalline silicon solar cell is provided with a surface electrode. The wiring resistance and contact resistance of the surface electrode are related to voltage loss related to conversion efficiency, and the wiring width and shape affect the amount of incident sunlight. (For example, refer nonpatent literature 1).

  The surface electrode of a solar cell is usually formed as follows. That is, a conductive composition is applied by screen printing or the like onto an n-type semiconductor layer formed by thermally diffusing phosphorus or the like at a high temperature on the light-receiving surface side of a p-type silicon substrate, and this is applied to 800 to 900. A surface electrode is formed by baking at ° C. The conductive composition forming the surface electrode includes conductive metal powder, glass particles, various additives, and the like.

  As the conductive metal powder, silver powder is generally used. However, use of metal powders other than silver powder has been studied for various reasons. For example, a conductive composition capable of forming a solar cell electrode containing silver and aluminum is disclosed (for example, see Patent Document 1). Moreover, the composition for electrode formation containing the metal nanoparticle containing silver and metal particles other than silver is disclosed (for example, refer patent document 2).

JP 2006-313744 A JP 2008-226816 A

Akihiro Tsujikawa, “Latest Photovoltaic Power Generation Technology and System”, CMC Publishing Company, 2001, p26-27

  In general, silver used for electrode formation is a noble metal, and due to the problem of resources, and the metal itself is expensive, a proposal of a paste material to replace the silver-containing conductive composition (silver-containing paste) is desired. . A promising material that can replace silver is copper that is applied to semiconductor wiring materials. Copper is abundant in terms of resources, and the cost of bullion is as low as about 1/100 of silver. However, copper is a material that is easily oxidized at a high temperature of 200 ° C. or higher. For example, in the composition for forming an electrode described in Patent Document 2, when copper is contained as a conductive metal, this is baked to form an electrode. Therefore, a special process of baking in an atmosphere of nitrogen or the like is necessary.

  The present invention provides a paste composition for an electrode capable of forming an electrode having low resistivity with suppressed oxidation of copper during firing, and a solar cell having an electrode formed using the paste composition for electrode. The task is to do.

In the first aspect of the present invention, copper-containing particles having a peak temperature of an exothermic peak having a maximum area in differential thermal-thermogravimetric simultaneous measurement (TG-DTA) of 280 ° C. or more, carbon particles, and a glass softening point It is the paste composition for electrodes containing the glass particle which is 600 degrees C or less, a solvent, and resin.

  The copper-containing particles are preferably at least one selected from phosphorus-containing copper alloy particles and silver-coated copper particles.

  The carbon particles are preferably at least one particle selected from the group consisting of amorphous carbon, graphite, fullerene, and carbon nanotubes.

  The electrode paste composition preferably further includes silver particles, and the content of the copper-containing particles is 9% by mass to 88% by mass when the total amount of the copper-containing particles and the silver particles is 100% by mass. The following is more preferable. The total content of the copper-containing particles and the silver particles is 60% by mass or more and 94% by mass or less, and the carbon particle content is 0.1% by mass or more and 35% by mass with respect to the entire electrode paste composition. And the glass particle content is 0.1% by mass or more and 10% by mass or less, and the total content of the solvent and the resin is 3% by mass or more and 30% by mass or less. preferable.

A second aspect of the present invention is an electrode paste composition comprising phosphorus-containing copper alloy particles, carbon particles, glass particles having a glass softening point of 600 ° C. or less, a solvent, and a resin.

  The glass particles preferably have a glass softening point of 600 ° C. or lower and a crystallization start temperature exceeding 600 ° C.

  The electrode paste composition preferably further includes silver particles, and the content of the copper-containing particles is 9% by mass to 88% by mass when the total amount of the copper-containing particles and the silver particles is 100% by mass. The following is more preferable. The total content of the copper-containing particles and the silver particles is 60% by mass or more and 94% by mass or less, and the carbon particle content is 0.1% by mass or more and 35% by mass with respect to the entire electrode paste composition. And the glass particle content is 0.1% by mass or more and 10% by mass or less, and the total content of the solvent and the resin is 3% by mass or more and 30% by mass or less. preferable.

The third aspect of the present invention is an electrode paste composition comprising silver-coated copper particles, carbon particles, glass particles having a glass softening point of 600 ° C. or lower, a solvent, and a resin.

  The 4th aspect of this invention is a solar cell which has an electrode formed by baking the said paste composition for electrodes provided on the silicon substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the oxidation of copper at the time of baking is suppressed, the paste composition for electrodes which can form an electrode with low resistivity, and the solar cell which has an electrode formed using this paste composition for electrodes Can be provided.

It is sectional drawing of the solar cell concerning this invention. It is a top view which shows the light-receiving surface side of the solar cell concerning this invention. It is a top view which shows the back surface side of the solar cell concerning this invention. (A) It is a perspective view which shows the AA cross-section structure of the back contact type solar cell concerning this invention. (B) It is a top view which shows the back surface side electrode structure of the back contact type solar cell concerning this invention.

  In the present specification, “to” indicates a range including numerical values described before and after that as a minimum value and a maximum value, respectively.

<Paste composition for electrodes>
The electrode paste composition of the present invention comprises at least one copper-containing particle having a peak temperature of an exothermic peak having a maximum area in differential thermal-thermogravimetric simultaneous measurement of 280 ° C. or more, at least one carbon particle, It contains at least one kind of glass particles, at least one kind of solvent, and at least one kind of resin.
With such a configuration, oxidation of copper during firing is suppressed, and an electrode with low resistivity can be formed.

(Copper-containing particles)
In the copper-containing particles of the present invention, the peak temperature of the exothermic peak showing the maximum area in differential thermal-thermogravimetric simultaneous measurement (TG-DTA) is 280 ° C. or higher. By using such copper-containing particles imparted with oxidation resistance, oxidation of metallic copper during firing is suppressed, and an electrode with low resistivity can be formed. In addition, simultaneous measurement of differential heat-thermogravimetry is performed in a normal atmosphere using a measurement device: differential heat-thermogravimetric analyzer (manufactured by SII Nanotechnology, TG / DTA-6200), for example, measurement temperature Range: room temperature to 1000 ° C., temperature rising rate: 40 ° C./min, atmospheric flow rate: 200 ml / min.
In general, when differential thermal-thermogravimetric simultaneous measurement is performed on pure copper (metallic copper), the peak temperature at the exothermic peak showing the maximum area is around 200 ° C., but in the copper-containing particles used in the present invention, the peak temperature is 280. It is above ℃. Furthermore, in this invention, it is preferable that it is 280-800 degreeC from a viewpoint of the low resistivity as an electrode, and it is more preferable that it is 350-750 degreeC.

Copper-containing particles having a peak temperature of 280 ° C. or higher at the exothermic peak showing the maximum area can be constituted by imparting oxidation resistance to the copper particles.
Specifically, for example, it is preferable to use at least one selected from phosphorus-containing copper alloy particles and silver-coated copper particles. The copper-containing particles may be used alone or in combination of two or more.

Although there is no restriction | limiting in particular as a particle diameter of the said copper containing particle | grains, It is 0.4-10 micrometers as a particle diameter (Hereinafter, it may abbreviate as "D50%.") When the integrated weight is 50%. Is preferable, and it is more preferable that it is 1-7 micrometers. When the thickness is 0.4 μm or more, the oxidation resistance is more effectively improved. Moreover, the contact area of the copper containing particles in an electrode becomes large because it is 10 micrometers or less, and a resistivity falls more effectively. The particle diameter of the copper-containing particles is measured by a microtrack particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., MT3300 type).
Further, the shape of the copper-containing particles is not particularly limited, and may be any of a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like, from the viewpoint of oxidation resistance and low resistivity, It is preferably substantially spherical, flat, or plate-shaped.

As the content ratio of the copper-containing particles contained in the electrode paste composition of the present invention, or the total content of the copper-containing particles and silver particles in the case of containing silver particles described later, the entire paste composition for electrodes, For example, it can be set to 60 to 94% by mass, preferably 70 to 94% by mass, more preferably 72 to 90% by mass, and 74 to 88% from the viewpoint of oxidation resistance and low resistivity. More preferably, it is mass%.
In the present invention, conductive particles other than the copper-containing particles may be used in combination.

-Phosphorus-containing copper alloy particles-
As a phosphorus-containing copper alloy, a brazing material called phosphorus copper brazing (phosphorus concentration: about 7% by mass or less) is known. Phosphorus copper brazing is also used as a bonding agent between copper and copper, but by using phosphorous-containing copper alloy particles as copper-containing particles contained in the electrode paste composition of the present invention, oxidation resistance is improved. An electrode having excellent and low resistivity can be formed. Further, the electrode can be fired at a low temperature, and the effect that the process cost can be reduced can be obtained.

The phosphorus content contained in the phosphorus-containing copper alloy in the present invention is not limited as long as the peak temperature of the exothermic peak showing the maximum area is 280 ° C. or higher in simultaneous differential heat-thermogravimetric measurement. Specifically, it is 0.01% by mass or more based on the total mass of the phosphorus-containing copper alloy particles. In the present invention, from the viewpoint of oxidation resistance and low resistivity, it is preferably 0.01% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 7.8% by mass or less. More preferably, it is 1 mass% or more and 7.5 mass% or less.
When the phosphorus content contained in the phosphorus-containing copper alloy is 8% by mass or less, a lower resistivity can be achieved, and the productivity of the phosphorus-containing copper alloy is excellent. Moreover, the more outstanding oxidation resistance can be achieved because it is 0.01 mass% or more.

  The phosphorus-containing copper alloy particles are an alloy containing copper and phosphorus, but may further contain other atoms inevitably mixed therein. As other atoms inevitably mixed, for example, Sb, Si, K, Na, Li, Ba, Sr, Ca, Mg, Be, Zn, Pb, Cd, Tl, V, Sn, Al, Zr, W , Mo, Ti, Co, Ni, Au, and the like.

The particle diameter of the phosphorus-containing copper alloy particles is not particularly limited, but the particle diameter when the accumulated weight is 50% (hereinafter sometimes abbreviated as “D50%”) is 0.4 to 10 μm. It is preferably 1 to 7 μm. When the thickness is 0.4 μm or more, the oxidation resistance is more effectively improved. Moreover, the contact area of the phosphorus containing copper alloy particles in an electrode becomes large because it is 10 micrometers or less, and a resistivity falls more effectively.
The shape of the phosphorus-containing copper alloy particles is not particularly limited, and may be any of a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like, but from the viewpoint of oxidation resistance and low resistivity. Therefore, it is preferably substantially spherical, flat, or plate-shaped.

The phosphorous copper alloy can be produced by a commonly used method. Also, the phosphorus-containing copper alloy particles can be prepared using a normal method of preparing metal powder using a phosphorus-containing copper alloy prepared so as to have a desired phosphorus content, for example, a water atomization method Can be produced by a conventional method. The water atomization method is described in Metal Handbook (Maruzen).
Specifically, for example, after phosphorus-containing copper alloy is dissolved and powdered by nozzle spray, the obtained powder is dried and classified, whereby desired phosphorus-containing copper alloy particles can be produced. Moreover, the phosphorus containing copper alloy particle | grains which have a desired particle diameter can be manufactured by selecting classification conditions suitably.

The content of the phosphorus-containing copper alloy particles contained in the electrode paste composition of the present invention, or the total content of the phosphorus-containing copper alloy particles and silver particles in the case of containing silver particles to be described later, For example, it can be 60 to 94% by mass with respect to the whole, and is preferably 70 to 94% by mass and more preferably 72 to 90% by mass from the viewpoint of oxidation resistance and low resistivity. It is more preferable that it is 74-88 mass%.
In the present invention, the phosphorus-containing copper alloy particles may be used singly or in combination of two or more. Furthermore, it may be used in combination with copper-containing particles other than phosphor copper alloy particles, the peak temperature of the exothermic peak showing the maximum area being 280 ° C. or higher.

Furthermore, in this invention, from a viewpoint of oxidation resistance and the low resistivity of an electrode, phosphorus containing copper alloy particle | grains whose phosphorus content rate is 0.01 mass% or more and 8 mass% or less are made with respect to the paste composition for electrodes. 60 to 94% by mass (when silver particles described later are included, the total content of silver-coated phosphorus-containing copper alloy particles and silver particles) is preferably included, and the phosphorus content is 1 to 7.5% by mass. More preferably, the copper alloy particles are contained in an amount of 74 to 88% by mass (the total content of silver-coated phosphorus-containing copper alloy particles and silver particles when silver particles described later are included) with respect to the electrode paste composition.
In the present invention, conductive particles other than the phosphorus-containing copper alloy particles may be used in combination.

-Silver-coated copper particles-
As the silver-coated copper particles in the present invention, it is sufficient that at least a part of the surface of the copper particles is coated with silver. By using silver-coated copper particles as the copper-containing particles contained in the electrode paste composition of the present invention, an electrode having excellent oxidation resistance and low resistivity can be formed. Furthermore, since the copper particles are coated with silver, the interface resistance between the silver-coated copper particles and the silver particles is reduced, and an electrode with a lower resistivity can be formed. Furthermore, when it is set as a paste composition, when a water | moisture content mixes, the effect that the oxidation of copper at room temperature can be suppressed and the pot life can be improved can be obtained by using silver-coated copper particles.

  As the silver coating amount (silver content) in the silver-coated copper particles, the coating amount (silver content) such that the peak temperature of the exothermic peak showing the maximum area in differential thermal-thermogravimetric simultaneous measurement is 280 ° C. or more. If there is no limit. Specifically, it is 1% by mass or more with respect to the total mass of the silver-coated copper particles, but from the viewpoint of oxidation resistance and low resistivity of the electrode, 1 to 88% by mass with respect to the total mass of the silver-coated copper particles. It is preferable that it is 3-80 mass%, and it is further more preferable that it is 5-75 mass%.

The particle diameter of the silver-coated copper particles is not particularly limited, but the particle diameter when the accumulated weight is 50% (hereinafter sometimes abbreviated as “D50%”) is 0.4 μm to 10 μm. It is preferable that it is 1-7 micrometers. When the thickness is 0.4 μm or more, the oxidation resistance is more effectively improved. Moreover, the contact area of the silver covering copper particle in an electrode becomes large because it is 10 micrometers or less, and a resistivity falls more effectively.
Further, the shape of the silver-coated copper particles is not particularly limited and may be any of a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like, from the viewpoint of oxidation resistance and low resistivity. It is preferably substantially spherical, flat or plate-like.

  Copper constituting the silver-coated copper particles may contain other atoms inevitably mixed. As other atoms inevitably mixed, for example, Sb, Si, K, Na, Li, Ba, Sr, Ca, Mg, Be, Zn, Pb, Cd, Tl, V, Sn, Al, Zr, W , Mo, Ti, Co, Ni, Au, and the like.

Moreover, it is also preferable that the silver-coated copper particles are those in which the above-described phosphorus-containing copper alloy is silver-coated. As a result, the oxidation resistance is further improved, and the resistivity of the formed electrode is further reduced.
About the detail of the phosphorus containing alloy in a silver covering copper particle, it is synonymous with the above-mentioned phosphorus containing copper alloy, and its preferable aspect is also the same.

The method for preparing the silver-coated copper particles is not particularly limited as long as at least a part of the surface of the copper particles (preferably phosphorus-containing copper alloy particles) can be coated with silver. For example, copper powder (or phosphorus-containing copper alloy powder) is dispersed in an acidic solution such as sulfuric acid, hydrochloric acid, and phosphoric acid, and a chelating agent is added to the copper powder dispersion to prepare a copper powder slurry. By adding a silver ion solution to the obtained copper powder slurry, a silver layer can be formed on the surface of the copper powder by a substitution reaction.
Although there is no restriction | limiting in particular as said chelating agent, For example, ethylenediaminetetraacetic acid salt, triethylenediamine, diethylenetriaminepentaacetic acid, iminodiacetic acid, etc. can be used. Moreover, as a silver ion solution, a silver nitrate solution etc. can be used, for example.

As a content rate of the said silver covering copper particle contained in the paste composition for electrodes of this invention, or a silver covering copper particle in the case of containing the silver particle mentioned later, as a total content rate of a silver covering copper particle and silver particle, for example, 60-94 mass% From the viewpoint of oxidation resistance and low resistivity, the content is preferably 72 to 90% by mass, and more preferably 74 to 88% by mass.
In the present invention, the silver-coated copper particles may be used singly or in combination of two or more. Moreover, you may use in combination with the copper containing particle | grains other than silver covering copper particle | grains, Comprising: The peak temperature in the exothermic peak which shows the maximum area is 280 degreeC or more.

In the present invention, from the viewpoint of oxidation resistance and low resistivity of the electrode, the silver-coated copper particles having a silver content of 1 to 88% by mass relative to the total mass of the silver-coated copper particles are compared with the electrode paste composition. 60 to 94% by mass (when silver particles described later are included, the total content of silver-coated copper particles and silver particles) is preferably included, and the silver-coated copper particles having a silver content of 5 to 75% by mass Is more preferably 74 to 88% by mass with respect to the electrode paste composition (when silver particles described later are included, the total content of silver-coated copper particles and silver particles).
Further, the silver-coated phosphorus-containing copper alloy particles having a silver content of 1 to 88% by mass and a phosphorus content of 0.01 to 8% by mass are used in an amount of 60 to 94% by mass (based on the electrode paste composition). When silver particles described later are included, it is preferable to include silver coated phosphorus-containing copper alloy particles and silver particles), the silver content is 5 to 75% by mass, and the phosphorus content is 1 to 7%. The silver-coated phosphorus-containing copper alloy particles, which are 5% by mass or less, are 74 to 88% by mass with respect to the electrode paste composition (when silver particles described later are included, the total of silver-coated phosphorus-containing copper alloy particles and silver particles It is more preferable to include the content).
In the present invention, conductive particles other than the silver-coated copper particles may be used in combination.

(Carbon particles)
As described above, the electrode paste composition of the present invention includes carbon particles in addition to the copper-containing particles. When the electrode paste composition of the present invention contains carbon particles, oxidation of the copper-containing particles when the electrode paste composition is sintered is suppressed. The reason is not clear, but the carbon particles actively capture oxygen molecules during sintering, and the trapped oxygen molecules combine with carbon to form carbon dioxide, so that the copper contained in the copper-containing particles is reduced. It is presumed to suppress oxidation by oxygen molecules.

The carbon particles are preferably at least one particle selected from the group consisting of amorphous carbon, graphite, fullerene, and carbon nanotubes, for example.
Specific examples of amorphous carbon include carbon black, coke, charcoal, animal charcoal, soot, and carbon fiber.
Carbon black, graphite, and carbon nanotube are preferable as the component of the carbon particle from the viewpoint that the carbon particle easily captures oxygen molecules and oxidation of the copper-containing particle is suppressed, and among these, carbon black is more preferable.
The addition amount of the carbon particles with respect to 100 parts by mass of the copper-containing particles is preferably 10 parts by mass or more and 80 parts by mass or less, and more preferably 15 parts by mass or more and 50 parts by mass or less from the viewpoint of suppressing oxidation of the copper-containing particles.

The carbon particles preferably have a specific surface area of 10 m ² / g or more, more preferably 100 m ² / g or more from the viewpoint of efficiently capturing oxygen molecules that oxidize copper-containing particles during heating. Desirably, it is more desirable to have 1000 m < ² > / g or more.

  Moreover, it is preferable that the said carbon particle is a fine particle from a viewpoint of the handleability at the time of patterning by screen printing etc. as an electrode paste composition. Specifically, the fine particles of the carbon particles preferably have a particle diameter (D50%) of 100 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. When the particle diameter (D50%) of the carbon particles is smaller than 100 μm, it becomes difficult to clog the screen plate mesh during screen printing. The particle diameter (D50%) is measured in the same manner as the particle diameter (D50%) of the copper-containing particles.

(Glass particles)
The electrode paste composition of the present invention contains at least one kind of glass particles. When the electrode paste composition contains glass particles, the silicon nitride film as the antireflection film is removed by so-called fire-through at the electrode formation temperature, and an ohmic contact between the electrode and the silicon substrate is formed.

The glass particles are usually used in the technical field as long as they can soften and melt at the electrode formation temperature, oxidize the contacted silicon nitride film, and take the oxidized silicon dioxide to remove the antireflection film. The glass particles used can be used without particular limitation.
In the present invention, glass particles containing glass having a glass softening point of 600 ° C. or lower and a crystallization start temperature exceeding 600 ° C. are preferable from the viewpoint of oxidation resistance and low resistivity of the electrode. The glass softening point is measured by a normal method using a thermomechanical analyzer (TMA), and the crystallization start temperature is measured using a differential thermal-thermogravimetric analyzer (TG / DTA). Measured by method.

Generally, the glass particles contained in the electrode paste composition are composed of glass containing lead because silicon dioxide can be efficiently taken up. Examples of such lead-containing glass include those described in Japanese Patent No. 03050064, and these can also be suitably used in the present invention.
In the present invention, it is preferable to use lead-free glass that does not substantially contain lead in consideration of the influence on the environment. Examples of the lead-free glass include lead-free glass described in paragraph numbers 0024 to 0025 of JP-A-2006-313744, and lead-free glass described in JP-A 2009-188281, and the like. It is also preferable to select from free glass as appropriate and apply it to the present invention.

Examples of the glass component used in the electrode paste composition of the present invention include silicon dioxide (SiO ₂ ), phosphorus oxide (P ₂ O ₅ ), aluminum oxide (Al ₂ O ₃ ), and boron oxide (B ₂ O _3). ), Vanadium oxide (V ₂ O ₅ ), potassium oxide (K ₂ O), bismuth oxide (Bi ₂ O ₃ ), sodium oxide (Na ₂ O), lithium oxide (Li ₂ O), barium oxide (BaO) Strontium oxide (SrO), calcium oxide (CaO), magnesium oxide (MgO), beryllium oxide (BeO), zinc oxide (ZnO), lead oxide (PbO), cadmium oxide (CdO), tin oxide (SnO), oxide zirconium _(ZrO 2), tungsten oxide _(WO 3), molybdenum oxide _(MoO 3), lanthanum oxide _{(La 2 O} 3), acid Niobium _{(Nb 2 O} 5), tantalum oxide _{(Ta 2 O} 5), yttrium oxide _{(Y 2 O} 3), titanium oxide _(TiO 2), germanium oxide _(GeO 2), tellurium oxide _(TeO 2), lutetium oxide ( Examples include Lu ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), copper oxide (CuO), iron oxide (FeO), silver oxide (AgO), and manganese oxide (MnO). Among these, it is preferable to use at least one selected from SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ , B ₂ O ₃ , V ₂ O ₅ , Bi ₂ O ₃ , ZnO, and PbO.

  As a content rate of the said glass particle, it is preferable that it is 0.1-10 mass% with respect to the total mass of the paste composition for electrodes, It is more preferable that it is 0.5-8 mass%, 1-7 More preferably, it is mass%. By including glass particles with a content in such a range, oxidation resistance, low resistivity of the electrode, and low contact resistance can be achieved more effectively.

(Solvent and resin)
The electrode paste composition of the present invention contains at least one solvent and at least one resin. Thereby, the liquid physical property (for example, a viscosity, surface tension, etc.) of the paste composition for electrodes of this invention can be adjusted to the required liquid physical property according to the provision method at the time of providing to a silicon substrate.

  There is no restriction | limiting in particular as said solvent. For example, hydrocarbon solvents such as hexane, cyclohexane and toluene; chlorinated hydrocarbon solvents such as dichloroethylene, dichloroethane and dichlorobenzene; cyclics such as tetrahydrofuran, furan, tetrahydropyran, pyran, dioxane, 1,3-dioxolane and trioxane Ether solvents; amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide; sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone and cyclohexanone; ethanol; Alcohol compounds such as 2-propanol, 1-butanol, diacetone alcohol; 2,2,4-trimethyl-1,3-pentanediol monoacetate, 2,2,4- Limethyl-1,3-pentanediol monopropionate, 2,2,4-trimethyl-1,3-pentanediol monobutyrate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, Ester solvents of polyhydric alcohols such as 2,2,4-triethyl-1,3-pentanediol monoacetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate; ethers of polyhydric alcohols such as butyl cellosolve and diethylene glycol diethyl ether Terpene solvents such as α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, oximene, ferrandrene, and the like A mixture is mentioned.

As the solvent in the present invention, a polyhydric alcohol ester solvent, a terpene solvent, and a polyhydric alcohol ether solvent from the viewpoints of coatability and printability when the electrode paste composition is formed on a silicon substrate. Is preferably at least one selected from the group consisting of an ester solvent of a polyhydric alcohol and a terpene solvent.
In this invention, the said solvent may be used individually by 1 type or in combination of 2 or more types.

  As the resin, any resin that is usually used in the technical field can be used without particular limitation as long as it can be thermally decomposed by firing. Specifically, for example, cellulose resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and nitrocellulose; polyvinyl alcohols; polyvinyl pyrrolidones; acrylic resins; vinyl acetate-acrylic acid ester copolymers; butyral resins such as polyvinyl butyral; phenol Examples thereof include alkyd resins such as modified alkyd resins and castor oil fatty acid modified alkyd resins; epoxy resins; phenol resins; rosin ester resins.

The resin in the present invention is preferably at least one selected from cellulosic resins and acrylic resins, more preferably at least one selected from cellulosic resins, from the viewpoint of disappearance during firing. preferable.
In this invention, the said resin may be used individually by 1 type or in combination of 2 or more types.

In the electrode paste composition of the present invention, the content of the solvent and the resin can be appropriately selected according to the desired liquid properties and the type of solvent and resin used. For example, the total content of the solvent and the resin is preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 25% by mass or less with respect to the total mass of the electrode paste composition. More preferably, the content is 7% by mass or more and 20% by mass or less.
When the total content of the solvent and the resin is within the above range, the application suitability when applying the electrode paste composition to the silicon substrate is improved, and an electrode having a desired width and height is more easily formed. can do.

In the electrode paste composition of the present invention, when the silver particles described later are not used, the content of the copper-containing particles is from 60% by mass to 94% by mass from the viewpoint of oxidation resistance and low resistivity of the electrode. The content of the carbon particles is 0.1% by mass or more and 35% by mass or less, and the content of the glass particles is 0.1% by mass or more and 10% by mass or less, and the solvent and the resin The total content of is preferably 3% by mass or more and 30% by mass or less.
Moreover, when not using the silver particle mentioned later, the content rate of the said copper containing particle is 74 mass% or more and 88 mass% or less, Comprising: The content rate of the said carbon particle is 1 mass% or more and 18 mass% or less, More preferably, the glass particle content is 0.5% by mass or more and 8% by mass or less, and the total content of the solvent and the resin is 7% by mass or more and 20% by mass or less.
Furthermore, when not using the silver particle mentioned later, the total content rate of the said copper containing particle and the said silver particle is 74 mass% or more and 88 mass% or less, Comprising: The content rate of the said carbon particle is 3 mass% or more and 17 mass%. More preferably, the content of the glass particles is 1% by mass or more and 7% by mass or less, and the total content of the solvent and the resin is 7% by mass or more and 20% by mass or less.

(Silver particles)
The electrode paste composition of the present invention preferably further contains at least one silver particle. By containing silver particles, the oxidation resistance is further improved, and the resistivity as an electrode is further reduced. Furthermore, the effect that the solder connection property at the time of setting it as a solar cell module improves is also acquired. This can be considered as follows, for example.

  In general, in a temperature range of 600 ° C. to 900 ° C., which is an electrode formation temperature range, a small amount of silver is dissolved in copper and a small amount of copper is dissolved in silver, and copper is formed at the interface between copper and silver. -A silver solid solution layer (solid solution region) is formed. When a mixture of copper-containing particles and silver particles is heated to a high temperature and then slowly cooled to room temperature, it is considered that a solid solution region does not occur, but at the time of electrode formation, it is cooled from the high temperature region to room temperature in a few seconds. It is thought that the solid solution layer in FIG. 4 covers the surface of the silver particles and the copper-containing particles as a non-equilibrium solid solution phase or a eutectic structure of copper and silver. Such a copper-silver solid solution layer can be considered to contribute to the oxidation resistance of the copper-containing particles at the electrode formation temperature.

  The copper-silver solid solution layer starts to be formed at a temperature of 300 ° C. to 500 ° C. or higher. Therefore, by using silver particles together with copper-containing particles having a peak temperature of an exothermic peak showing a maximum area in differential thermal-thermogravimetric simultaneous measurement of 280 ° C. or more, the oxidation resistance of the copper-containing particles is more effectively improved. It can be considered that the resistivity of the formed electrode is further reduced.

  The silver which comprises the said silver particle may contain the other atom mixed unavoidable. As other atoms inevitably mixed, for example, Sb, Si, K, Na, Li, Ba, Sr, Ca, Mg, Be, Zn, Pb, Cd, Tl, V, Sn, Al, Zr, W , Mo, Ti, Co, Ni, Au, and the like.

  The particle diameter of the silver particles in the present invention is not particularly limited, but the particle diameter (D50%) when the accumulated weight is 50% is preferably 0.4 μm or more and 10 μm or less, and 1 μm or more and 7 μm or less. It is more preferable that When the thickness is 0.4 μm or more, the oxidation resistance is more effectively improved. Moreover, the contact area of metal particles, such as a silver particle and copper containing particle | grains in an electrode, becomes large because it is 10 micrometers or less, and resistivity falls more effectively.

  In the electrode paste composition of the present invention, the relationship between the particle diameter of the copper-containing particles (D50%) and the particle diameter of the silver particles (D50%) is not particularly limited, but either one of the particle diameters (D50 %) Is preferably smaller than the other particle diameter (D50%), and the ratio of the other particle diameter to any one particle diameter is more preferably 1 to 10. Thereby, the resistivity of an electrode falls more effectively. This can be attributed to, for example, an increase in contact area between metal particles such as copper-containing particles and silver particles in the electrode.

Moreover, as content rate of the silver particle in the paste composition for electrodes of this invention, it is 8.4-85.5 mass% with respect to the paste composition for electrodes from a viewpoint of oxidation resistance and the low resistivity of an electrode. It is preferable that it is 8.9-80.1 mass%.
Furthermore, in the present invention, from the viewpoint of oxidation resistance and low resistivity of the electrode, the content of the copper-containing particles is 9 to 88% by mass when the total amount of the copper-containing particles and the silver particles is 100% by mass. It is preferable to become 17 to 77% by mass.
When the content of the copper-containing particles is 9% by mass or more, for example, when the glass particles contain divanadium pentoxide, the reaction between silver and vanadium is suppressed, and the volume resistance of the electrode is further reduced. In addition, in the hydrofluoric acid aqueous solution treatment of the electrode-formed silicon substrate for the purpose of improving the energy conversion efficiency of a solar cell, the electrode material is resistant to hydrofluoric acid (the property that the electrode material does not peel off from the silicon substrate by the hydrofluoric acid aqueous solution) Will improve.
Moreover, it becomes more suppressed that the content rate of the said copper containing particle | grain becomes 88 mass% or less, and the copper contained in a copper containing particle | grain contacts a silicon substrate, and the contact resistance of an electrode falls more.

  Moreover, in the electrode paste composition of the present invention, the total content of the copper-containing particles and the silver particles is 70% by mass or more and 94 from the viewpoint of oxidation resistance, low resistivity of the electrode, and applicability to a silicon substrate. It is preferable that it is mass% or less, and it is more preferable that it is 74 mass% or more and 88 mass% or less. When the total content of the copper-containing particles and the silver particles is 70% by mass or more, a suitable viscosity can be easily achieved when the electrode paste composition is applied. Moreover, generation | occurrence | production of the blurring at the time of providing the paste composition for electrodes can be suppressed more effectively because the total content of the said copper containing particle | grains and the said silver particle is 94 mass% or less.

Furthermore, in the electrode paste composition of the present invention, from the viewpoint of oxidation resistance and low resistivity of the electrode, the total content of the copper-containing particles and the silver particles is 60% by mass or more and 94% by mass or less, The content of the carbon particles is 0.1% by mass or more and 35% by mass or less, the content of the glass particles is 0.1% by mass or more and 10% by mass or less, and the total content of the solvent and the resin The rate is preferably 3% by mass or more and 30% by mass or less.
The total content of the copper-containing particles and the silver particles is 74% by mass or more and 88% by mass or less, and the content of the carbon particles is 1% by mass or more and 18% by mass or less. More preferably, the content is 0.5% by mass or more and 8% by mass or less, and the total content of the solvent and the resin is 7% by mass or more and 20% by mass or less.
Furthermore, the total content of the copper-containing particles and the silver particles is 74% by mass or more and 88% by mass or less, and the content of the carbon particles is 3% by mass or more and 17% by mass or less. More preferably, the content is 1% by mass or more and 7% by mass or less, and the total content of the solvent and the resin is 7% by mass or more and 20% by mass or less.

(flux)
The electrode paste composition may further include at least one flux. By containing the flux, the oxidation resistance is further improved, and the resistivity of the formed electrode is further reduced. Furthermore, the effect that the adhesiveness of an electrode material and a silicon substrate improves is also acquired.

  The flux in the present invention is not particularly limited as long as the oxide film formed on the surface of the copper-containing particles can be removed. Specifically, for example, fatty acids, boric acid compounds, fluorinated compounds, borofluorinated compounds and the like can be mentioned as preferred fluxes.

More specifically, lauric acid, myristic acid, palmitic acid, stearic acid, sorbic acid, stearic acid, boron oxide, potassium borate, sodium borate, lithium borate, potassium borofluoride, sodium borofluoride, borofluoride Examples include lithium, acidic potassium fluoride, acidic sodium fluoride, acidic lithium fluoride, potassium fluoride, sodium fluoride, and lithium fluoride.
Among these, potassium borate and potassium borofluoride are particularly preferable fluxes from the viewpoints of heat resistance at the time of firing the electrode material (characteristic that the flux does not volatilize at a low temperature during firing) and supplementing the oxidation resistance of the copper-containing particles.
In the present invention, each of these fluxes may be used alone or in combination of two or more.

  Moreover, as the content rate of the flux when the electrode paste composition of the present invention contains a flux, the viewpoint of effectively expressing the oxidation resistance of the copper-containing particles and the portion where the flux is removed at the completion of the firing of the electrode material From the viewpoint of reducing the porosity, it is preferably 0.1 to 5% by mass, more preferably 0.3 to 4% by mass, and more preferably 0.5 to 4% by mass with respect to the total mass of the electrode paste composition. It is further preferably 3.5% by mass, particularly preferably 0.7 to 3% by mass, and extremely preferably 1 to 2.5% by mass.

(Other ingredients)
Furthermore, the electrode paste composition of the present invention can further contain other components usually used in the technical field, if necessary, in addition to the components described above. Examples of other components include a plasticizer, a dispersant, a surfactant, an inorganic binder, a metal oxide, a ceramic, and an organometallic compound.

  There is no restriction | limiting in particular as a manufacturing method of the paste composition for electrodes of this invention. The copper-containing particles, the carbon particles, the glass particles, the solvent, the resin, and the silver particles contained as necessary can be produced by dispersing and mixing them using a commonly used dispersion and mixing method.

The electrode paste composition of the present invention can be applied on a silicon substrate, dried, and then fired in the presence of oxygen (for example, in the air) to form an electrode with low resistivity.
Examples of the method for applying the electrode paste composition onto the silicon substrate include screen printing, an ink jet method, a dispenser method, and the like. From the viewpoint of productivity, application by screen printing is preferable.

  When the electrode paste composition of the present invention is applied by screen printing, it preferably has a viscosity in the range of 80 to 1000 Pa · s. The viscosity of the electrode paste composition is measured at 25 ° C. using a Brookfield HBT viscometer.

In addition, as heat treatment conditions (firing conditions) when forming an electrode using the electrode paste composition of the present invention, heat treatment conditions usually used in the technical field can be applied.
Generally, the heat treatment temperature (baking temperature) is 800 to 900 ° C., but when the electrode paste composition of the present invention is used, heat treatment conditions at a lower temperature can be applied, for example, 600 to 850. An electrode having good characteristics can be formed at a heat treatment temperature of ° C.
The heat treatment time can be appropriately selected according to the heat treatment temperature or the like, and can be set to, for example, 1 second to 20 seconds.

<Solar cell>
The solar cell of this invention has the electrode formed by baking the said paste composition for electrodes provided on the silicon substrate. Thereby, the solar cell which has a favorable characteristic is obtained, and it is excellent in the productivity of this solar cell.

Hereinafter, although the specific example of the solar cell of this invention is demonstrated, referring drawings, this invention is not limited to this.
A sectional view showing an example of a typical solar cell element, and outlines of a light receiving surface and a back surface are shown in FIGS.
Usually, single crystal or polycrystalline Si is used for the semiconductor substrate 130 of the solar cell element. The semiconductor substrate 130 contains boron or the like and constitutes a p-type semiconductor. On the light receiving surface side, unevenness (texture, not shown) is formed by etching in order to suppress reflection of sunlight. The light receiving surface side is doped with phosphorus or the like, an n-type semiconductor diffusion layer 131 is provided with a thickness of submicron order, and a pn junction is formed at the boundary with the p-type bulk portion. Further, on the light receiving surface side, an antireflection layer 132 such as silicon nitride is provided on the diffusion layer 131 with a film thickness of about 100 nm by vapor deposition or the like.

Next, the light receiving surface electrode 133 provided on the light receiving surface side, and the current collecting electrode 134 and the output extraction electrode 135 formed on the back surface will be described. The light-receiving surface electrode 133 and the output extraction electrode 135 are formed from the electrode paste composition. The collecting electrode 134 is formed from an aluminum electrode paste composition containing glass powder. These electrodes are formed by applying the paste composition to a desired pattern by screen printing or the like, and then baking the paste composition at about 600 to 850 ° C. in the atmosphere.
In the present invention, by using the electrode paste composition, an electrode having excellent resistivity and contact resistivity can be formed even when fired at a relatively low temperature.

At that time, on the light receiving surface side, the glass particles contained in the electrode paste composition forming the light receiving surface electrode 133 react with the antireflection layer 132 (fire-through), and the light receiving surface electrode 133 and the diffusion layer are reacted. 131 is electrically connected (ohmic contact).
In the present invention, the light-receiving surface electrode 133 is formed using the electrode paste composition, so that copper is suppressed as a conductive metal, and the oxidation of copper is suppressed. , Formed with good productivity.

  On the back surface side, aluminum in the aluminum electrode paste composition that forms the collecting electrode 134 during firing diffuses to the back surface of the semiconductor substrate 130 to form the electrode component diffusion layer 136, thereby forming the semiconductor substrate 130. Ohmic contact can be obtained between the current collector electrode 134 and the output extraction electrode 135.

FIG. 4 shows a perspective view (a) of a light receiving surface and an AA cross-sectional structure as an example of a solar cell element according to another aspect of the present invention, and a plan view (b) of a back surface side electrode structure.
As shown in the perspective view of FIG. 4A, the cell wafer 1 made of a p-type semiconductor silicon substrate is formed with through holes penetrating both the light receiving surface side and the back surface side by laser drilling or etching. . Further, a texture (not shown) for improving the light incident efficiency is formed on the light receiving surface side. Further, on the light receiving surface side, an n-type semiconductor layer 3 by n-type diffusion treatment and an antireflection film (not shown) are formed on the n-type semiconductor layer 3. These are manufactured by the same process as a conventional crystalline Si type solar cell element.

Next, the electrode paste composition of the present invention is filled into the previously formed through-holes by a printing method or an ink jet method, and the electrode paste composition of the present invention is also formed in a grid on the light receiving surface side. The composition layer which is printed and forms the through-hole electrode 4 and the current collecting grid electrode 2 is formed.
Here, in the paste used for filling and printing, it is desirable to use a paste having an optimum composition for each process including viscosity, but filling and printing may be performed collectively with the paste having the same composition. .

  On the other hand, a heavily doped layer 5 for preventing carrier recombination is formed on the opposite side (back side) of the light receiving surface. Here, boron (B) or aluminum (Al) is used as an impurity element for forming the heavily doped layer 5, and a p + layer is formed. The high-concentration doped layer 5 may be formed by performing a thermal diffusion process using, for example, B as a diffusion source in the solar cell element manufacturing process before forming the antireflection film, or using Al. In this case, in the printing step, the Al paste may be printed on the opposite surface side.

  Thereafter, the electrode paste composition fired at 650 to 850 ° C., filled in and printed on the antireflection film formed in the through hole and on the light receiving surface side, has a lower n-type layer due to the fire through effect. Ohmic contact is achieved.

  On the opposite surface side, as shown in the plan view of FIG. 4 (b), the electrode paste composition according to the present invention is printed and fired in stripes on the n side and the p side, respectively. 7 is formed.

In the present invention, the through-hole electrode 4, the current collecting grid electrode 2, the back electrode 6 and the back electrode 7 are formed by using the electrode paste composition, so as to contain copper as a conductive metal, Copper oxidation is suppressed, and the low resistivity through-hole electrode 4, current collecting grid electrode 2, back electrode 6 and back electrode 7 are formed with excellent productivity.
The electrode paste composition of the present invention is not limited to the use of solar cell electrodes. For example, electrode wiring and shield wiring of plasma displays, ceramic capacitors, antenna circuits, various sensor circuits, and heat dissipation of semiconductor devices. It can be suitably used for applications such as materials.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

<Example 1>
(A) Preparation of electrode paste composition A phosphorus-containing copper alloy containing 1% by mass of phosphorus was prepared, dissolved and powdered by the water atomization method, and then dried and classified. The classified powders were blended and subjected to deoxygenation / dehydration treatment to produce phosphorus-containing copper alloy particles containing 1% by mass of phosphorus. The particle diameter (D50%) of the phosphorus-containing copper alloy particles was 1.5 μm. Moreover, about the obtained phosphorus containing copper alloy particle | grains, the result of having measured the peak temperature of the exothermic peak which shows the maximum area in the differential thermal-thermogravimetric simultaneous measurement (TG-DTA) by the said method is shown in Table 1.

32 parts of vanadium oxide (V ₂ O ₅ ), 26 parts of phosphorus oxide (P ₂ O ₅ ), 10 parts of barium oxide (BaO), 10 parts of tungsten oxide (WO ₃ ), 1 part of sodium oxide (Na ₂ O), oxidation A glass composed of 3 parts of potassium (K ₂ O), 10 parts of zinc oxide (ZnO), and 8 parts of manganese oxide (MnO) (hereinafter sometimes abbreviated as “G19”) was prepared. The obtained glass G19 had a softening point of 447 ° C. and a crystallization temperature of over 600 ° C.
By using the obtained glass G19, glass particles having a particle diameter (D50%) of 1.7 μm were obtained.

31.8 parts of the phosphorus-containing copper alloy particles obtained above, 38.2 parts of silver particles (particle size (D50%) 3 μm, high-purity chemical product manufactured by Aldrich), 1.7 parts of glass particles, 4 parts % Butyl carbitol acetate (BCA, diethylene glycol monobutyl ether acetate) solution containing ethyl cellulose (EC) 13.2 parts, and carbon black (particle diameter 17 μm, Mitsubishi Chemical Corporation, Mitsubishi Carbon Black # 850, ratio) 15.1 parts of a surface area of 220 m ^{2 /} g) were mixed and stirred in an agate mortar for 20 minutes to prepare an electrode paste composition 1.

(B) Fabrication of solar cell element A p-type semiconductor substrate having a thickness of 190 μm having an n-type semiconductor layer, a texture, and an antireflection film (silicon nitride film) formed on the light receiving surface is prepared and cut into a size of 125 mm × 125 mm. It was. Using the screen printing method on the light receiving surface, the electrode paste composition 1 obtained above was printed so as to have an electrode pattern as shown in FIG. The electrode pattern was composed of a finger line with a width of 150 μm and a bus bar with a width of 1.1 mm, and the printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the film thickness after firing was 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

Subsequently, an aluminum electrode paste was similarly printed on the back surface by screen printing. The printing conditions were appropriately adjusted so that the film thickness after firing was 40 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.
Subsequently, a heat treatment (firing) was performed at 850 ° C. for 2 seconds in an infrared rapid heating furnace in an air atmosphere to produce a solar cell element 1 on which a desired electrode was formed.

<Example 2>
A solar cell element 2 was produced in the same manner as in Example 1 except that the addition amounts of phosphorus-containing copper alloy particles, silver particles, and carbon black were changed as shown in Table 1.

<Example 3>
In Example 1, carbon nanotubes instead of carbon black (having a nano-carbon Technology Co., MWNT, a specific surface area of ^{25m 2 / g~30m 2 / g)} , in the same manner as in Example 1, the solar cell element 3 was produced.

<Comparative Example 1>
A solar cell element C1 was produced in the same manner as in Example 1 except that the carbon particles were not added and the amounts of phosphorus-containing copper alloy particles and silver particles were changed as shown in Table 1.

<Evaluation>
Evaluation of the produced solar cell element is as follows: WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as pseudo-sunlight, and I-V CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT Co., Ltd.) as a current-voltage (IV) evaluation measuring instrument. ) Was combined with the measuring device. Eff (conversion efficiency), FF (fill factor), Voc (open circuit voltage), and Jsc (short circuit current) indicating the power generation performance as a solar cell are JIS-C-8912, JIS-C-8913 and JIS-C-, respectively. It is obtained by performing measurement according to 8914. The obtained measured values are converted into relative values with the measured value of Comparative Example 1 as 100.0, and are shown in Table 2.

<Example 4>
Using the electrode paste composition 1 obtained above, a solar cell element 4 having a structure as shown in FIG. 4 was produced. The heat treatment was performed at 850 ° C. for 2 seconds.
When the obtained solar cell element was evaluated in the same manner as described above, it was found that good characteristics were exhibited as described above.

<Example 5>
(A) Preparation of electrode paste composition 30.8 parts of silver-coated copper particles (manufactured by Hitachi Chemical Co., Ltd., silver coverage 25% by mass, particle size 5 μm), silver particles (particle size (D50%) 1 μm) , 39.2 parts of Aldrich high-purity chemical), 1.7 parts of glass particles (glass G19 obtained in Example 1), and butyl carbitol acetate (BCA, 4% ethyl cellulose (EC)). 13.2 parts of diethylene glycol monobutyl ether acetate) solution and 15.1 parts of carbon black (particle diameter 17 μm, Mitsubishi Chemical Black, Mitsubishi Carbon Black # 850, specific surface area 220 m ^{2 /} g) as carbon particles were mixed together. The electrode paste composition 5 was prepared by stirring in a mortar for 20 minutes. In addition, about the used silver covering copper particle, the result of having measured the peak temperature of the exothermic peak which shows the maximum area in the differential thermal-thermogravimetric simultaneous measurement (TG-DTA) by the said method is shown in Table 3.

(B) Fabrication of solar cell element A p-type semiconductor substrate having a film thickness of 190 μm having an n-type semiconductor layer, texture, and antireflection film (silicon nitride film) formed on the light-receiving surface is prepared and cut into a size of 125 mm × 125 mm It was. Using the screen printing method on the light receiving surface, the electrode paste composition 5 obtained above was printed so as to have an electrode pattern as shown in FIG. The electrode pattern was composed of a finger line with a width of 150 μm and a bus bar with a width of 1.1 mm, and the printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the film thickness after firing was 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

Subsequently, an aluminum electrode paste was similarly printed on the back surface by screen printing. The printing conditions were appropriately adjusted so that the film thickness after firing was 40 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.
Subsequently, a heat treatment (baking) was performed at 850 ° C. for 2 seconds in an infrared rapid heating furnace in an air atmosphere to produce a solar cell element 5 on which a desired electrode was formed.

<Example 6>
A solar cell element 6 was produced in the same manner as in Example 5 except that the amount of silver-coated copper particles, silver particles, and carbon black added was changed as shown in Table 3 in Example 5.

<Example 7>
In Example 5, the carbon nanotubes instead of carbon black used (nanocarbon Technologies Inc., MWNT, a specific surface area of ^{25m 2 / g~30m 2 / g)} , silver-coated copper particles, silver particles, and the amount of carbon nanotubes Was changed as shown in Table 3, and a solar cell element 7 was produced in the same manner as in Example 5.

<Comparative example 2>
A solar cell element C2 was produced in the same manner as in Example 5 except that the addition amount of silver-coated copper particles, the addition amount of silver particles, and the particle diameter were changed as shown in Table 3 without adding carbon particles. did.

<Evaluation>
Evaluation of the produced solar cell element is as follows: WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as pseudo-sunlight, and I-V CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT Co., Ltd.) as a current-voltage (IV) evaluation measuring instrument. ) Was combined with the measuring device. Eff (conversion efficiency), FF (fill factor), Voc (open circuit voltage), and Jsc (short circuit current) indicating the power generation performance as a solar cell are JIS-C-8912, JIS-C-8913 and JIS-C-, respectively. It is obtained by performing measurement according to 8914. The obtained measured values were converted into relative values with the measured value of Comparative Example 2 as 100.0, and are shown in Table 4.

<Example 8>
Using the electrode paste composition 5 obtained above, a solar cell element 8 having a structure as shown in FIG. 4 was produced. The heat treatment was performed at 750 ° C. for 10 seconds.
When the obtained solar cell element was evaluated in the same manner as described above, it was found that good characteristics were exhibited as described above.

From the above results, in the examples using the electrode paste composition of the present invention, compared with the comparative example not containing carbon particles, the increase in the Jsc value accompanying the decrease in the resistance value of the electrode and the increase in the conversion efficiency. It can be seen that even when copper is used as the conductive metal of the electrode, an electrode with low resistivity can be formed, and a solar cell exhibiting excellent characteristics can be constructed.
It can also be seen that the examples showed better performance than the comparative examples at the processing temperatures (calcination temperatures) of 750 ° C. and 850 ° C.

130 Semiconductor substrate 131 Diffusion layer 132 Antireflection layer 133 Light receiving surface electrode 134 Current collecting electrode 135 Output extraction electrode 136 Electrode component diffusion layer 1 Cell wafer made of p-type silicon substrate 2 Current collecting grid electrode 3 N-type semiconductor layer 4 Through-hole electrode 5 Highly doped layer 6 Back electrode 7 Back electrode

Claims (7)

Copper-containing particles having a peak temperature of 280 ° C. or higher, carbon particles, glass particles having a glass softening point of 600 ° C. or lower, a solvent, and a resin. An electrode paste composition comprising:   The electrode paste composition according to claim 1, wherein the copper-containing particles are at least one selected from phosphorus-containing copper alloy particles and silver-coated copper particles.   The electrode paste composition according to claim 1 or 2, wherein the carbon particles are at least one particle selected from the group consisting of amorphous carbon, graphite, fullerene, and carbon nanotubes.   The paste composition for an electrode according to any one of claims 1 to 3, further comprising silver particles.   The paste composition for an electrode according to claim 4, wherein the content of the copper-containing particles is 9% by mass or more and 88% by mass or less when the total amount of the copper-containing particles and the silver particles is 100% by mass.   The total content of the copper-containing particles and the silver particles is 60% by mass or more and 94% by mass or less, and the content of the carbon particles is 0.1% by mass or more and 35% by mass with respect to the entire electrode paste composition. The content ratio of the glass particles is 0.1% by mass or more and 10% by mass or less, and the total content of the solvent and the resin is 3% by mass or more and 30% by mass or less. The electrode paste composition according to claim 5.   The solar cell which has an electrode formed by baking the paste composition for electrodes of any one of Claims 1-6 provided on the silicon substrate.