WO2012140787A1

WO2012140787A1 - Electrode paste composition, solar-cell element, and solar cell

Info

Publication number: WO2012140787A1
Application number: PCT/JP2011/060472
Authority: WO
Inventors: 修一郎足立; 吉田　誠人; 野尻　剛; 岩室　光則; 木沢　桂子; 拓也青柳; 山本　浩貴; 内藤　孝; 隆彦加藤
Original assignee: 日立化成工業株式会社
Priority date: 2011-04-14
Filing date: 2011-04-28
Publication date: 2012-10-18
Also published as: TW201246231A; JP2012227183A; CN103503079A; CN103503079B

Abstract

An electrode paste composition comprising phosphorus/tin-containing copper alloy particles, glass particles, a solvent, and a resin. Also, a solar-cell element, and a solar cell, having an electrode formed using said electrode paste composition.

Description

Electrode paste composition, solar cell element and solar cell

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

Generally, electrodes are formed on the light receiving surface and the back surface of a silicon-based solar cell. In order to efficiently extract the electrical energy converted in the solar cell by the incidence of light to the outside, it is necessary that the volume resistivity of the electrode is sufficiently low and that a good ohmic contact is formed with the Si substrate. is there. In particular, the electrode on the light receiving surface tends to have a small wiring width and a high aspect ratio in order to minimize the amount of incident light loss of sunlight.

The electrode used for the light receiving surface of the solar cell is usually formed as follows. That is, a texture (unevenness) is formed on the light-receiving surface side of a p-type silicon substrate, and then a conductive composition is screen-printed on an n-type silicon layer formed by thermally diffusing phosphorus or the like at a high temperature. The light-receiving surface electrode is formed by applying and baking at 800 ° C. to 900 ° C. in the atmosphere. The conductive composition forming the light-receiving surface electrode includes conductive metal powder, glass particles, various additives, and the like.

As the conductive metal powder, silver powder is generally used. This is because the volume resistivity of the silver particles is as low as 1.6 × 10 ⁻⁶ Ω · cm, the silver particles are self-reduced and sintered under the above firing conditions, and a good ohmic contact is formed with the silicon substrate. In addition, the tab material for electrically connecting the solar cell elements is preferably used in so-called modularization in which the solder material has excellent wettability with respect to the electrode made of silver particles and the solar cell element is sealed with a glass substrate or the like. The reason is that it can be bonded.

As described above, the conductive composition containing silver particles exhibits excellent characteristics as an electrode of a solar cell. On the other hand, since silver is a noble metal and the bullion itself is expensive, and also from the problem of resources, a proposal of a paste material that replaces the silver-containing conductive composition 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 in the atmosphere, and it is difficult to form an electrode in the above process.

In order to solve the above-mentioned problems of copper, for example, Japanese Patent Application Laid-Open Nos. 2005-314755 and 2004-217952 use various methods to impart oxidation resistance to copper and oxidize even at high temperature firing. Copper particles that have not been reported have been reported.

However, even the above copper particles have oxidation resistance up to 300 ° C. and are almost oxidized at a high temperature of 800 ° C. to 900 ° C., so that they have not been put into practical use as solar cell electrodes. Furthermore, the additive applied in order to provide oxidation resistance inhibits sintering of the copper particles during firing, and as a result, there is a problem that a low resistance electrode such as silver cannot be obtained.

Also, as another method for suppressing copper oxidation, there is a special process in which a conductive composition using copper as a conductive metal powder is fired in an atmosphere of nitrogen or the like.

However, when the above method is used, an environment completely sealed with the above atmospheric gas is required in order to completely suppress the oxidation of copper particles, which is not suitable for mass production of solar cell elements in terms of process costs.

Another problem for applying copper to solar cell electrodes is ohmic contact with a silicon substrate. That is, even if an electrode made of copper can be formed without being oxidized during high-temperature firing, copper and silicon are in direct contact with each other, thereby causing mutual diffusion of copper and silicon, and copper at the interface between the electrode and the silicon substrate. In some cases, a reactant phase (Cu ₃ Si) composed of silicon and silicon is formed.

The formation of Cu ₃ Si may extend to several μm from the interface of the silicon substrate, and may crack on the Si substrate side. In some cases, the semiconductor performance (pn junction characteristics) of the solar cell is deteriorated by penetrating an n-type silicon layer formed in advance on the silicon substrate. In addition, the formed Cu ₃ Si lifts the electrode made of copper, which may hinder the adhesion with the silicon substrate and cause a decrease in the mechanical strength of the electrode.

The present invention has been made in view of the above-described problems, and can suppress the oxidation of copper during firing, can form an electrode with low resistivity, and can further suppress the formation of a reactant phase between copper and a silicon substrate. It is an object to provide an electrode paste composition capable of forming a copper-containing electrode having an ohmic contact, and a solar cell element and a solar cell having an electrode formed using the electrode paste composition.

The inventors of the present invention have completed the present invention as a result of diligent research to solve the above problems. That is, the present invention includes the following aspects.

A first aspect of the present invention is an electrode paste composition containing phosphorus-tin-containing copper alloy particles, glass particles, a solvent, and a resin.

The phosphorus-tin-containing copper alloy particles preferably have a phosphorus content of 2% by mass to 15% by mass and a tin content of 5% by mass to 30% by mass.

The glass particles preferably have a glass softening point of 650 ° C. or lower and a crystallization start temperature exceeding 650 ° C.

The phosphorus-tin-containing copper alloy particles preferably further contain at least one metal atom selected from the group consisting of silver, manganese and cobalt, and the content of the metal atoms in the phosphorus-tin-containing copper alloy particles Is more preferably 0.1% by mass or more and 10% by mass or less.

The paste composition for an electrode preferably further contains silver particles, and the content of the silver particles when the total content of the phosphorus-tin-containing copper alloy particles and the silver particles is 100% by mass is 0.1. More preferably, the content is from 10% by mass to 10% by mass.

The electrode paste composition has a total content of the phosphorus-tin-containing copper alloy particles and silver particles of 70% by mass to 94% by mass, and a content of the glass particles of 0.1% by mass to 10% by mass. It is preferable that the total content of the solvent and the resin is 3% by mass or more and 29.9% by mass or less.

The second aspect of the present invention is a solar cell element having an electrode formed on the silicon substrate by baking the electrode paste composition applied on the silicon substrate.

The electrode preferably includes a Cu—Sn alloy phase and a Sn—PO glass phase, and the Sn—PO glass phase is disposed between the Cu—Sn alloy phase and a silicon substrate. It is more preferable.

A third aspect of the present invention is a solar cell having the solar cell element and a tab wire disposed on an electrode of the solar cell element.

According to the present invention, a copper-containing electrode having a good ohmic contact in which oxidation of copper during firing is suppressed and an electrode having a low resistivity can be formed, and formation of a reactant phase between copper and a silicon substrate is suppressed. An electrode paste composition that can be formed, and a solar cell element and a solar cell having electrodes formed using the electrode paste composition can be provided.

It is a schematic sectional drawing which shows an example of the silicon type solar cell element concerning this invention. It is a schematic plan view which shows an example of the light-receiving surface of the silicon type solar cell element concerning this invention. It is a schematic plan view which shows an example of the back surface of the silicon type solar cell element concerning this invention. It is a schematic plan view which shows an example of the back surface side electrode structure of the back contact type solar cell element concerning this invention. It is a schematic perspective view which shows an example of AA cross-section structure in FIG. 4 of the back contact type solar cell element concerning this invention. It is a schematic perspective view which shows an example of AA cross-section structure in FIG. 4 of the back contact type solar cell element concerning this invention. It is a schematic perspective view which shows an example of AA cross-section structure in FIG. 4 of the back contact type solar cell element concerning this invention.

In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes. .
In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
Further, when referring to the amount of each component in the composition in the present specification, when there are a plurality of substances corresponding to each component in the composition, the plurality of the components present in the composition unless otherwise specified. It means the total amount of substance.

<Paste composition for electrodes>
The electrode paste composition of the present invention contains at least one phosphor-tin-containing copper alloy particle, at least one glass particle, at least one solvent, and at least one resin. With such a configuration, oxidation of copper during firing in the atmosphere is suppressed, and an electrode with low resistivity can be formed. Furthermore, the formation of a reactant phase between copper and the silicon substrate is suppressed, and a good ohmic contact can be formed between the formed electrode and the silicon substrate.

(Phosphorus particles containing phosphorus-tin)
The electrode paste composition includes at least one type of phosphorus-tin-containing copper alloy particles. In general, as a copper alloy containing phosphorus, 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 copper alloy particles containing phosphorus in the electrode paste composition of the present invention, the reducibility of phosphorus to copper oxide is improved. It is possible to form an electrode having excellent oxidation resistance and low volume resistivity. 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-tin-containing copper alloy particles in the present invention are particles made of a copper alloy further containing tin in addition to phosphorus. When the copper alloy particles contain tin, an electrode having a low resistivity and excellent adhesion can be formed in the firing step described later.
This can be considered as follows, for example. Since the copper alloy particles contain phosphorus and tin, phosphorus, tin, and copper react with each other in a firing step described later to form an electrode composed of a Cu—Sn alloy phase and a Sn—PO glass phase. Here, it is considered that the Cu—Sn alloy phase forms a dense bulk body in the electrode and functions as a conductive layer, thereby forming an electrode with low resistivity.
Here, the dense bulk body means that the massive Cu—Sn alloy phases are in close contact with each other to form a three-dimensional continuous structure.

Further, when an electrode is formed on a substrate containing silicon (hereinafter, also simply referred to as “silicon substrate”) using the electrode paste composition of the present invention, an electrode having high adhesion to the silicon substrate can be formed, Furthermore, good ohmic contact between the electrode and the silicon substrate can be achieved.
This can be considered as follows, for example. Phosphorus, tin, and copper contained in the copper alloy particles react with each other in the firing step to form an electrode composed of a Cu—Sn alloy phase and a Sn—PO glass phase. Since the Cu—Sn alloy phase is a dense bulk body, the Sn—PO glass phase is formed between the Cu—Sn alloy phase and the silicon substrate. This can be considered to improve the adhesion of the Cu—Sn alloy phase to the silicon substrate. In addition, when the Sn—PO glass phase functions as a barrier layer for preventing mutual diffusion between copper and silicon, a good ohmic contact between the electrode formed by firing and the silicon substrate can be achieved. Can think. In other words, the formation of a reaction phase (Cu ₃ Si) formed when an electrode containing copper and silicon are directly contacted and heated is suppressed, and the silicon substrate and the silicon substrate are not degraded without deteriorating semiconductor performance (for example, pn junction characteristics) It is considered that a good ohmic contact can be expressed while maintaining the adhesiveness.

Such an effect is generally manifested when an electrode is formed on a substrate containing silicon using the electrode paste composition of the present invention, and the type of substrate containing silicon is particularly limited. Is not to be done. As a board | substrate containing silicon, the silicon substrate used for manufacture of the silicon substrate for solar cell formation, semiconductor devices other than a solar cell etc. can be mentioned, for example.

That is, in the present invention, by including the phosphorus-tin-containing copper alloy particles in the electrode paste composition, first, by utilizing the reducibility of the phosphorus atoms in the phosphorus-tin-containing copper alloy particles to the copper oxide, oxidation resistance An electrode having excellent properties and low volume resistivity is formed. Next, a reaction with tin in the phosphorus-tin-containing copper alloy particles forms a conductive layer composed of a Cu—Sn alloy phase and a Sn—PO glass phase while keeping the volume resistivity low. For example, the Sn—PO glass phase functions as a barrier layer for preventing mutual diffusion of copper and silicon, so that a reactant phase is formed between the electrode containing copper and the silicon substrate. It can be considered that two characteristic mechanisms of suppressing and forming a good ohmic contact between the electrode containing copper and the silicon substrate can be realized simultaneously in the firing step.

The phosphorus content contained in the phosphorus-tin-containing copper alloy in the present invention is not particularly limited. From the viewpoint of oxidation resistance and low resistivity, the phosphorus content is preferably 2% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 12% by mass or less, and more preferably 4% by mass or more and 10% by mass. % Or less is more preferable. When the phosphorus content contained in the phosphorus-tin-containing copper alloy is 15% by mass or less, a lower resistivity can be achieved, and the productivity of the phosphorus-tin-containing copper alloy particles is excellent. Moreover, the more outstanding oxidation resistance can be achieved because it is 2 mass% or more.

Further, the tin content contained in the phosphorus-tin-containing copper alloy is not particularly limited. From the viewpoint of oxidation resistance and reactivity with copper and phosphorus, it is preferably 5% by mass or more and 30% by mass or less, more preferably 6% by mass or more and 25% by mass or less, and 7% by mass or more and 20% by mass. More preferably, it is% or less. When the tin content in the phosphorus-tin-containing copper alloy particles is 30% by mass or less, a sufficient volume of the Cu—Sn alloy phase can be formed, and the volume resistivity of the electrode is lowered. Moreover, reaction with copper and phosphorus can be more uniformly produced by making tin into 5 mass% or more.

Furthermore, as a combination of the phosphorus content and the tin content contained in the phosphorus-tin-containing copper alloy, the phosphorus content is 2% by mass or more and 15% from the viewpoint of oxidation resistance, low resistance and reactivity with copper and phosphorus. Preferably, the tin content is 5% by mass or more and 30% by mass or less, the phosphorus content is 3% by mass or more and 12% by mass or less, and the tin content is 6% by mass or more and 25% by mass or less. More preferably, the phosphorus content is 4% by mass or more and 10% by mass or less, and the tin content is 7% by mass or more and 20% by mass or less.

In addition to phosphorus and tin, the phosphorus-tin-containing copper alloy in the present invention is also preferably a copper alloy further containing at least one other metal atom selected from the group consisting of silver, manganese and cobalt. By further including other metal atoms, a lower resistance electrode can be formed.
The content of other metal atoms in the copper alloy containing phosphorus, tin, and other metal atoms can be appropriately selected according to the type and purpose of the other metal atoms. For example, it can be 0.05 to 20% by mass, preferably 0.1 to 15% by mass, more preferably 1 to 10% by mass. When the content of other metal atoms is 0.05% by mass or more, the melting point of the alloy particles can be further reduced, and the sintering reaction of the alloy particles proceeds in the firing step. Moreover, oxidation resistance improves and the low resistance electrode is formed because the content rate of another metal atom is 20 mass% or less.

The phosphorus-tin-containing copper alloy particles are a copper alloy containing phosphorus and tin, but may further contain other atoms. Examples of other atoms include Sb, Si, K, Na, Li, Ba, Sr, Ca, Mg, Be, Zn, Pb, Cd, Tl, V, Al, Zr, W, Mo, Ti, Ni, And Au.
The content of other atoms contained in the phosphorus-tin-containing copper alloy particles can be, for example, 3% by mass or less in the phosphorus-tin-containing copper alloy particles, and the oxidation resistance and low resistivity can be reduced. From the viewpoint, it is preferably 1% by mass or less.

In the present invention, the phosphorus-tin-containing copper alloy particles may be used singly or in combination of two or more.

The particle diameter of the phosphorus-tin-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 μm to The thickness is preferably 10 μm, more preferably 1 μm to 7 μm. When the thickness is 0.4 μm or more, the oxidation resistance is more effectively improved. When the thickness is 10 μm or less, the contact area between the phosphorus-tin-containing copper alloy particles in the electrode is increased, and the resistivity is more effectively reduced. The particle diameter (D50%) of the phosphorus-tin-containing copper alloy particles is measured with a microtrack particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., MT3300 type).
Further, the shape of the phosphorus-tin-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 the oxidation resistance and the low resistivity. From this point of view, it is preferably substantially spherical, flat or plate-like.

The content of the phosphorus-tin-containing copper alloy particles in the electrode paste composition is not particularly limited, but from the viewpoint of oxidation resistance and low electrode resistivity, the electrode paste composition contains 70% by mass to 94% by mass. Or less, more preferably 74 mass% or more and 88 mass% or less.

The phosphorus-tin-containing copper alloy can be produced by a commonly used method. Also, the phosphorus-tin-containing copper alloy particles should be prepared using a normal method of preparing metal powder using a phosphorus-tin-containing copper alloy prepared so as to have a desired phosphorus content and tin content. Can do. For example, it can be manufactured by a conventional method using a water atomizing method. For details of the water atomization method, the description of Metal Handbook (Maruzen Co., Ltd. Publishing Division) can be referred to.
Specifically, a desired phosphorus-tin-containing copper alloy particle is produced by dissolving a phosphorus-tin-containing copper alloy, pulverizing this by nozzle spraying, and drying and classifying the obtained powder. Can do. In addition, phosphorus-tin-containing copper alloy particles having a desired particle size can be produced by appropriately selecting the classification conditions.

(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 adhesion between the electrode portion and the substrate is improved during firing. Also. In particular, in forming the electrode on the light-receiving surface side of the solar cell, the silicon nitride film as the antireflection film is removed by so-called fire-through during firing, and an ohmic contact between the electrode and the silicon substrate is formed.

The glass particles are glass particles containing glass having a glass softening point of 650 ° C. or lower and a crystallization start temperature exceeding 650 ° C. from the viewpoint of adhesion to the substrate and reduction in resistivity of the electrode. preferable.
The glass softening point is measured by a usual method using a thermomechanical analyzer (TMA), and the crystallization start temperature is measured using a differential heat-thermogravimetric analyzer (TG-DTA). Measured by method.

When the paste composition for an electrode of the present invention is used as an electrode on the light-receiving surface side of a solar cell, the glass particles are softened and melted at an electrode formation temperature to oxidize a contacted silicon nitride film, and oxidized silicon dioxide As long as the antireflection film can be removed by incorporating, glass particles usually used in the technical field can be used without particular limitation.

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 glass containing lead 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. It is also preferable that the lead-free glass is appropriately selected and applied to the present invention.

In addition, when the electrode paste composition of the present invention is used as, for example, a back surface extraction electrode, a through-hole electrode or a back surface electrode in a back contact solar cell element other than the electrode on the light receiving surface side of the solar cell, the glass softening point is 650 ° C. If it is the following and it is a glass particle containing the glass whose crystallization start temperature exceeds 650 degreeC, it can use without including a component required for fire through like the said lead.

As the glass component constituting the glass particles used in the electrode paste composition of the present invention, silicon dioxide _(SiO 2), phosphorus oxide _(P _{2 O} 5), aluminum oxide _(Al _{2 O} 3), 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) , zirconium oxide _(ZrO 2), tungsten oxide _(WO 3), molybdenum oxide _(MoO 3), lanthanum oxide (La ₂ _3), niobium oxide _(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 (Lu ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), copper oxide (CuO), iron oxide (FeO), silver oxide (AgO), and manganese oxide (MnO).

Among them, as the glass component, at least one selected from the group consisting of 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 is used. It is preferable to use at least one selected from the group consisting of SiO ₂ , PbO, B ₂ O ₃ , Bi ₂ O ₃ and Al ₂ O ₃ . In the case of such glass particles, the softening point is more effectively lowered. Furthermore, since the wettability with the phosphorus-tin-containing copper alloy particles and the silver particles contained as necessary is improved, sintering between the particles proceeds in the firing process, and an electrode with lower resistivity can be formed. it can.

On the other hand, from the viewpoint of low contact resistivity, glass particles containing phosphorous pentoxide (phosphate glass, P ₂ O ₅ glass particles) are preferable. In addition to diphosphorus pentoxide, divanadium pentoxide is used. Furthermore, it is more preferable to include glass particles (P ₂ O ₅ —V ₂ O ₅ glass particles). By further containing divanadium pentoxide, the oxidation resistance is further improved, and the resistivity of the electrode is further reduced. This can be attributed to, for example, that the softening point of the glass is lowered by further containing divanadium pentoxide. When diphosphorus pentoxide-divanadium pentoxide glass particles (P ₂ O ₅ —V ₂ O ₅ glass particles) are used, the content of divanadium pentoxide is 1% by mass or more based on the total mass of the glass. It is preferably 1% by mass to 70% by mass.

The particle diameter of the glass particles in the present invention is not particularly limited, but the particle diameter (D50%) when the integrated weight is 50% is preferably 0.5 μm or more and 10 μm or less, and 0.8 μm or more. It is more preferably 8 μm or less, and further preferably 1 μm or more and 5 μm or less.
When the thickness is 0.5 μm or more, workability at the time of preparing the electrode paste composition is improved. Moreover, when it is 10 μm or less, it can be uniformly dispersed in the electrode paste composition, fire-through can be efficiently generated in the firing step, and adhesion to the silicon substrate is also improved. The particle size (D50%) of the glass particles is measured with a Microtrac particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., MT3300 type).
Further, the shape of the glass 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. A spherical shape, a flat shape, or a plate shape is preferable.

The content of the glass particles is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass, based on the total mass of the electrode paste composition. More preferably, the content is 8% by mass to 8% by mass. By including glass particles in such a content ratio, oxidation resistance, lower electrode resistivity, and lower contact resistance can be achieved more effectively, and phosphorus contained in the phosphorus-tin-containing copper alloy particles can be achieved. The reaction of tin and copper can be promoted.

(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 etc.

The solvent is not particularly limited. 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 and diacetone alcohol; 2,2,4-trimethyl-1,3-pentanediol monoacetate, 2,2,4- Limethyl-1,3-pentanediol monopropiolate, 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; butyl cellosolve, diethylene glycol monobutyl ether, diethylene glycol diethyl ether Dihydric alcohol ether solvents: α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, osimene, ferrand And terpene solvents such as len and mixtures thereof.

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 polyhydric alcohol ester solvents and terpene solvents.
In the present invention, the solvents may be used singly or in combination of two or more.

In addition, as the resin, any resin that is usually used in the technical field can be used 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 a cellulose resin and an acrylic resin from the viewpoint of disappearance at the time of firing.
In the present invention, the resins may be used alone or in combination of two or more.

Moreover, the weight average molecular weight of the resin in the present invention is not particularly limited. Among these, the weight average molecular weight is preferably from 5,000 to 500,000, and more preferably from 10,000 to 300,000. It can suppress that the viscosity of the paste composition for electrodes increases that the weight average molecular weight of the said resin is 5000 or more. This can be considered to be because, for example, the three-dimensional repulsive action when adsorbed on phosphorus-tin-containing copper alloy particles is insufficient, and the particles aggregate. On the other hand, when the weight average molecular weight of the resin is 500000 or less, aggregation of the resins in the solvent is suppressed, and increase in the viscosity of the electrode paste composition can be suppressed.
In addition, if the weight average molecular weight of the resin is 500,000 or less, it is suppressed that the resin combustion temperature becomes high, and the resin is not completely burned when the electrode paste composition is fired, and remains as a foreign substance. Is suppressed, and the electrode can be configured to have a lower resistance.

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 29.9% by mass or less, and more preferably 5% by mass or more and 25% by mass or less, based on the total mass of the electrode paste composition. Preferably, it is 7 mass% or more and 20 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.

Furthermore, in the electrode paste composition of the present invention, the content of the phosphorus-tin-containing copper alloy particles is 70% by mass or more and 94% by mass or less from the viewpoint of oxidation resistance and the low resistivity of the electrode. The content is preferably 0.1% by mass or more and 10% by mass or less, and the total content of the solvent and the resin is preferably 3% by mass or more and 29.9% by mass or less. The content of the phosphorus-tin-containing copper alloy particles Is 74 mass% or more and 88 mass% or less, the glass particle content is 0.5 mass% or more and 8 mass% or less, and the total content of solvent and resin is 7 mass% or more and 20 mass% or less. More preferably, the content of the phosphorus-tin-containing copper alloy particles is 74% by mass or more and 88% by mass or less, the content of the glass particles is 1% by mass or more and 8% by mass or less, and the total content of the solvent and the resin 7 mass% or more and 20 mass% or less A further preferred.

(Silver particles)
The electrode paste composition of the present invention preferably further contains silver particles. By containing silver particles, the oxidation resistance is further improved, and the resistivity as an electrode is further reduced. Further, the Ag particles are precipitated in the Sn—PO glass phase formed by the reaction of the phosphorus-tin-containing copper alloy particles, so that the ohmic contact between the Cu—Sn alloy phase in the electrode layer and the silicon substrate is achieved. More improved. Furthermore, the effect that the solder connection property at the time of setting it as a solar cell module improves is also acquired.

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.
Moreover, the content rate of the other atom contained in the said silver particle can be 3 mass% or less in a silver particle, for example, and it is 1 mass% or less from a viewpoint of melting | fusing point and the low resistivity of an electrode. preferable.

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. When the thickness is 10 μm or less, the contact area between the silver particles and the phosphorus-tin-containing copper alloy particles in the electrode is increased, and the resistivity is more effectively reduced.
The particle diameter (D50%) of the silver particles is measured by a microtrack particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., MT3300 type).
Further, the shape of the silver 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. A spherical shape, a flat shape, or a plate shape is preferable.

When the electrode paste composition of the present invention contains silver particles, the content of silver particles is 100% by mass as the total content of the phosphorus-tin-containing copper alloy particles, the tin-containing particles, and the silver particles. The content of the silver particles is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less.

In addition, in the electrode paste composition of the present invention, from the viewpoint of oxidation resistance, electrode resistivity reduction, and coating properties on a silicon substrate, the electrode paste composition is composed of phosphorus-tin-containing copper alloy particles and silver particles. The total content of is preferably 70% by mass or more and 94% by mass or less, and more preferably 74% by mass or more and 88% by mass or less. When the total content of the phosphorus-tin-containing copper alloy 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. Further, when the total content of the phosphorus-tin-containing copper alloy particles and the silver particles is 94% by mass or less, it is possible to more effectively suppress the occurrence of blurring when the electrode paste composition is applied.

Further, when the electrode paste composition of the present invention further contains silver particles, the total content of the phosphorus-tin-containing copper alloy particles and silver particles is 70% by mass from the viewpoint of oxidation resistance and low resistivity of the electrode. It is preferably 94% by mass or less, the glass particle content is 0.1% by mass or more and 10% by mass or less, and the total content of solvent and resin is preferably 3% by mass or more and 29.9% by mass or less. The total content of the phosphorus-tin-containing copper alloy particles and the silver particles is 74 to 88% by mass, the glass particle content is 0.5 to 8% by mass, and the solvent and the resin The total content is more preferably 7% by mass or more and 20% by mass or less, and the total content of the phosphorus-tin-containing copper alloy particles and the silver particles is 74% by mass or more and 88% by mass or less, The rate is 1 mass% or more and 8 mass% or less, It is more preferable that the total content of the solvent and the resin is 20 mass% or less 7 mass% or more.

(flux)
The electrode paste composition may further include at least one flux. By containing the flux, the oxide film formed on the surface of the phosphorus-tin-containing copper alloy particles can be removed, and the reduction reaction of the phosphorus-tin-containing copper alloy particles during firing can be promoted. Further, since the melting of the tin-containing particles during firing proceeds, the reaction with the phosphorus-tin-containing copper alloy particles proceeds, and as a result, the oxidation resistance is further improved and the resistivity of the formed electrode is further decreased. 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 it can remove the oxide film formed on the surface of the phosphorus-tin-containing copper alloy particles and promote the melting of the tin-containing particles. Specifically, for example, fatty acids, boric acid compounds, fluorinated compounds, borofluorinated compounds and the like can be mentioned as preferred fluxes.

More specifically, the flux includes lauric acid, myristic acid, palmitic acid, stearic acid, sorbic acid, stearic acid, propionic acid, boron oxide, potassium borate, sodium borate, lithium borate, potassium borofluoride, borofluoride. Sodium fluoride, lithium borofluoride, acidic potassium fluoride, acidic sodium fluoride, acidic lithium fluoride, potassium fluoride, sodium fluoride, lithium fluoride and the like can be mentioned.
Of these, potassium borate and potassium borofluoride are particularly preferable fluxes from the viewpoint of heat resistance during electrode material firing (the property that the flux does not volatilize at low temperatures during firing) and supplementing the oxidation resistance of the phosphorus-tin-containing copper alloy particles. It is done.
In the present invention, each of these fluxes may be used alone or in combination of two or more.

In the case where the electrode paste composition of the present invention contains a flux, the flux content is such that the oxidation resistance of the phosphorus-tin-containing copper alloy particles is effectively expressed and the melting of the tin-containing particles is promoted and the electrode From the viewpoint of reducing the porosity of the part from which the flux has been removed when the firing of the material is completed, it is preferably 0.1% by mass to 5% by mass, and 0.3% by mass in the total mass of the electrode paste composition Is more preferably 4 to 4% by mass, further preferably 0.5 to 3.5% by mass, particularly preferably 0.7 to 3% by mass, and 1 to 2.5% by mass. It is very preferable that it is mass%.

(Other ingredients)
In addition to the components described above, the electrode paste composition of the present invention can further contain other components that are usually used in the technical field, if necessary. 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. By dispersing / mixing the phosphorus-tin-containing copper alloy particles, the tin-containing particles, the glass particles, the solvent, the resin, and the silver particles contained as necessary, using a commonly used dispersion / mixing method. Can be manufactured.
The dispersion / mixing method is not particularly limited, and can be appropriately selected and applied from commonly used dispersion / mixing methods.

The electrode paste composition contains phosphorus-tin-containing copper alloy particles, glass particles, a solvent and a resin from the viewpoint of providing the composition, and has a viscosity at 25 ° C. in the range of 20 Pa · s to 1000 Pa · s. The viscosity is more preferably in the range of 25 Pa · s to 800 Pa · s, and still more preferably in the range of 30 Pa · s to 600 Pa · s.
The viscosity of the electrode paste composition is measured at 25 ° C. using a Brookfield HBT viscometer.

The electrode paste composition includes phosphorus-tin-containing copper alloy particles, glass particles, a solvent and a resin, and preferably has a solid content concentration in the range of 70% by mass to 98% by mass. The range is more preferably 75% by mass to 96% by mass, and still more preferably 80% by mass to 95% by mass.
In addition, solid content concentration of the paste composition for electrodes means the residue which remove | excluded the volatile component from the component which comprises the paste composition for electrodes. Specifically, the measurement is performed on the basis of the residue after the electrode paste composition is left in an environment of 25 ° C. and 1 atm for 10 hours to remove volatile components.

<Method for Producing Electrode Using Electrode Paste Composition>
As a method for producing an electrode using the electrode paste composition of the present invention, the electrode paste composition is applied to a region where an electrode is to be formed, dried and then fired to form an electrode in a desired region. can do. By using the paste composition for an electrode, an electrode having a low resistivity can be formed even when a baking treatment is performed in the presence of oxygen (for example, in the air).

Specifically, for example, when a solar cell electrode is formed using the electrode paste composition, the electrode paste composition is applied on a silicon substrate so as to have a desired shape, and dried and fired. Thereby, a solar cell electrode with low resistivity can be formed in a desired shape. Further, by using the electrode paste composition, an electrode having a low resistivity can be formed even when a baking treatment is performed in the presence of oxygen (for example, in the air). Furthermore, the electrode formed on the silicon substrate has excellent adhesion to the silicon substrate, and can achieve a good ohmic contact.

Examples of the method for applying the electrode paste composition 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, the electrode paste composition preferably has a viscosity in the range of 20 Pa · s to 1000 Pa · s. The viscosity of the electrode paste composition is measured at 25 ° C. using a Brookfield HBT viscometer.

The application amount of the electrode paste composition can be appropriately selected according to the size of the electrode to be formed. For example, the application amount of the electrode paste composition can be 2 g / m ² to 10 g / m ^2, and preferably 4 g / m ² to 8 g / m ² .

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 (firing temperature) is 800 ° C. to 900 ° C. However, when the electrode paste composition of the present invention is used, heat treatment conditions at a lower temperature can be applied, for example, 450 ° C. An electrode having good characteristics can be formed at a heat treatment temperature of ˜850 ° C.
The heat treatment time can be appropriately selected according to the heat treatment temperature and the like, and can be, for example, 1 second to 20 seconds.

As the heat treatment apparatus, any apparatus that can be heated to the above temperature can be used as appropriate, and examples thereof include an infrared heating furnace and a tunnel furnace. An infrared heating furnace is highly efficient because electric energy is directly input to a heating material in the form of electromagnetic waves and is converted into heat energy, and rapid heating is possible in a short time. Further, since there is no product due to combustion and non-contact heating, it is possible to suppress contamination of the generated electrode. Since the tunnel furnace automatically and continuously conveys the sample from the entrance to the exit and fires it, it can be fired uniformly by dividing the furnace body and controlling the transport speed. From the viewpoint of the power generation performance of the solar cell element, it is preferable to perform heat treatment with a tunnel furnace.

The volume resistivity of the electrode is not particularly limited. From the viewpoint of the power generation performance of the solar cell element, it is preferably 1 × 10 ⁻⁴ Ω · cm or less, more preferably 8 × 10 ⁻⁵ Ω · cm or less, and 6 × 10 ⁻⁶ Ω · cm or less. More preferably.
The volume resistivity of the electrode is measured as follows.
The electrode paste composition of the present invention is applied on a desired substrate and fired under predetermined conditions to obtain a fired product. Next, the volume resistivity of the obtained fired product is measured by a resistivity meter using a four-probe, four-terminal method (for example, Loresta-EP MCP-T360 type resistivity meter manufactured by Mitsubishi Chemical Corporation).

<Solar cell element and manufacturing method thereof>
The solar cell element of this invention has the electrode formed by baking the said paste composition for electrodes provided on the silicon substrate. Thereby, the solar cell element which has a favorable characteristic is obtained, and it is excellent in productivity of this solar cell element.
In this specification, the solar cell element means one having a silicon substrate on which a pn junction is formed and an electrode formed on the silicon substrate. In addition, the solar cell is a state in which a tab wire is provided on the electrode of the solar cell element, and a plurality of solar cell elements are connected via the tab line as necessary and sealed with a sealing resin or the like. Means things.

Hereinafter, although the specific example of the solar cell element 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.
As schematically shown in FIG. 1, single crystal or polycrystalline silicon is usually used for the semiconductor substrate 1 of the solar cell element. The semiconductor substrate 1 contains boron and constitutes a p-type semiconductor. In order to suppress reflection of sunlight on the light receiving surface side, irregularities (also referred to as texture, not shown) are formed by an etching solution made of NaOH and IPA (isopropyl alcohol). Phosphorus or the like is doped on the light receiving surface side, the n ⁺ -type diffusion layer 2 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 film 3 such as silicon nitride is provided on the n ⁺ type diffusion layer 2 with a film thickness of about 90 nm by PECVD or the like.

Next, a method of forming the light receiving surface electrode 4 provided on the light receiving surface side schematically shown in FIG. 2, and the current collecting electrode 5 and the output extraction electrode 6 formed on the back surface schematically shown in FIG.
The light-receiving surface electrode 4 and the back surface output extraction electrode 6 are formed from the electrode paste composition of the present invention. The back current collecting electrode 5 is formed of an aluminum electrode paste composition containing glass powder. As a first method for forming the light-receiving surface electrode 4, the back surface collecting electrode 5 and the back surface output extraction electrode 6, the paste composition is applied to a desired pattern by screen printing or the like, then dried, and then in the atmosphere. It may be formed by firing at about 450 ° C. to 850 ° C. at the same time. 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 4 react with the antireflection layer 3 (fire-through), and the light receiving surface electrode 4 and the n ⁺ The mold diffusion layer 2 is electrically connected (ohmic contact).
In the present invention, the light-receiving surface electrode 4 is formed using the electrode paste composition, so that copper is suppressed as a conductive metal, and copper oxidation is suppressed. , Formed with good productivity.
Further, in the present invention, it is preferable that the formed electrode includes a Cu—Sn alloy phase and a Sn—PO glass phase, and the Sn—PO glass phase includes a Cu—Sn alloy phase and a silicon substrate. (Not shown) is more preferable. As a result, the reaction between copper and the silicon substrate is suppressed, and an electrode having low resistance and excellent adhesion can be formed.

On the back surface side, aluminum in the aluminum electrode paste composition that forms the back current collecting electrode 5 during firing diffuses to the back surface of the p-type silicon substrate 1 to form the p ⁺ -type diffusion layer 7. Thus, an ohmic contact can be obtained between the p-type silicon substrate 1, the back surface collecting electrode 5, and the back surface output extraction electrode 6.

As a second method for forming the light-receiving surface electrode 4, the back surface collecting electrode 5 and the back surface output extraction electrode 6, the aluminum electrode paste composition for forming the back surface collecting electrode 5 is first printed, and after drying, the atmosphere After baking at about 750 ° C. to 850 ° C. to form the back surface collecting electrode 5, the electrode paste composition of the present invention is printed on the light receiving surface side and the back surface side, and after drying, 450 ° C. to 650 ° C. in the atmosphere. A method of forming the light-receiving surface electrode 4 and the back surface output extraction electrode 6 by firing at a degree is mentioned.

This method is effective in the following cases, for example. That is, when the aluminum electrode paste forming the back surface collecting electrode 5 is fired, at a firing temperature of 650 ° C. or less, depending on the composition of the aluminum paste, the aluminum particles may be sintered and diffused into the p-type silicon substrate 1. In some cases, the amount of the p ⁺ -type diffusion layer cannot be sufficiently formed due to an insufficient amount. In this state, a sufficient ohmic contact cannot be formed between the p-type silicon substrate 1 on the back surface, the back surface collecting electrode 5 and the back surface output extraction electrode 6, and the power generation performance as a solar cell element may be reduced. Therefore, after forming the back current collecting electrode 5 at an optimum firing temperature (for example, 750 ° C. to 850 ° C.) for the aluminum electrode paste composition, the electrode paste composition of the present invention is printed and dried at a relatively low temperature ( Preferably, the light-receiving surface electrode 4 and the back surface output extraction electrode 6 are formed by baking at 450 ° C. to 650 ° C.

FIG. 4 is a schematic plan view of a back-side electrode structure common to a so-called back contact solar cell element according to another embodiment of the present invention, and FIG. 4 shows an outline of a solar cell element which is a back contact solar cell element according to another embodiment. The perspective view which shows a structure is shown in FIG.5, FIG6 and FIG.7, respectively. 5, 6, and 7 are perspective views taken along a section AA in FIG. 4.

In the solar cell element having the structure shown in the perspective view of FIG. 5, the p-type silicon substrate 1 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 diffusion layer 2 by n-type diffusion treatment and an antireflection film (not shown) are formed on the n ⁺ -type diffusion layer 2. 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 9 and the light receiving surface collecting electrode 8 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, an n ⁺ -type diffusion layer 2 and a p ⁺ -type diffusion layer 7 for preventing carrier recombination are formed on the back surface side. Here, boron (B) or aluminum (Al) is used as an impurity element for forming the p ⁺ -type diffusion layer 7. The p ⁺ -type diffusion layer 7 may be formed, for example, by performing a thermal diffusion process using B as a diffusion source in the solar cell element manufacturing process before the formation of the antireflection film, or by using Al. When using, in the said printing process, you may form by printing and baking an aluminum paste on the opposite surface side.

On the back side, as shown in the plan view of FIG. 4, the electrode paste composition of the present invention is printed on the n ⁺ -type diffusion layer 2 and the p ⁺ -type diffusion layer 7 in stripes, thereby forming the back electrode. 10 and 11 are formed. Here, when the p ⁺ type diffusion layer 7 is formed using an aluminum paste, the back electrode may be formed using the electrode paste composition of the present invention only on the n ⁺ type diffusion layer 2 side.

Thereafter, it is dried and baked at about 450 ° C. to 850 ° C. in the atmosphere to form the light receiving surface collecting electrode 8, the through hole electrode 9, and the

back electrodes

10 and 11. As described above, when an aluminum electrode is used for one of the back electrodes, aluminum paste is first printed and fired from the viewpoint of aluminum sinterability and ohmic contact between the back electrode and the p ⁺ -type diffusion layer 7. Then, one of the back electrodes is formed, and then the electrode paste composition of the present invention is printed, filled, and baked to form the light receiving surface collecting electrode 8 and the through-hole electrode 9 and the other of the back electrodes. You may do it.

Further, the solar cell element having the structure shown in the perspective view of FIG. 6 can be manufactured in the same manner as the solar cell element having the structure shown in the perspective view of FIG. 5 except that the light receiving surface collecting electrode is not formed. it can. That is, in the solar cell element having the structure shown in the perspective view of FIG. 6, the electrode paste composition of the present invention can be used for the through-hole electrode 9 and the

back electrodes

10 and 11.

Further, the solar cell element having the structure shown in the perspective view of FIG. 7 has the structure shown in the perspective view of FIG. 5 except that the n-type silicon substrate 12 is used as a base substrate and no through hole is formed. It can be manufactured in the same manner as a solar cell element having That is, in the solar cell element having the structure shown in the perspective view of FIG. 7, the electrode paste composition of the present invention can be used for the

back electrodes

10 and 11.

The electrode paste composition of the present invention is not limited to the use of the solar cell electrode as described above. For example, electrode wiring and shield wiring of a plasma display, ceramic capacitor, antenna circuit, various sensor circuits, It can also be suitably used for applications such as heat dissipation materials for semiconductor devices.
Among these, it can be suitably used particularly when an electrode is formed on a substrate containing silicon.

<Solar cell>
The solar cell of the present invention includes at least one of the solar cell elements, and is configured by arranging tab wires on the electrodes of the solar cell element. If necessary, the solar cell may be configured by connecting a plurality of solar cell elements via tab wires and further sealing with a sealing material.
The tab wire and the sealing material are not particularly limited, and can be appropriately selected from those usually used in the art.

The disclosure of Japanese application 2011-090519 is incorporated herein in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples, and “parts” and “%” are based on mass unless otherwise specified. . In addition, as a method of expressing the composition of the phosphorus-tin-containing copper alloy particles, for example, in the case of Cu-AX-BY-CZ, in the copper alloy, element X is A mass%, element Y is B mass%, and element Z is It shows that C mass% is contained.

<Example 1>
(A) Preparation of electrode paste composition A phosphorus-tin-containing copper alloy containing 6% by mass of phosphorus and 10% by mass of tin was prepared, dissolved and powdered by the water atomization method, and then dried and classified. did. The classified powders were blended and subjected to deoxygenation / dehydration treatment to produce phosphorus-tin-containing copper alloy particles containing 6% by mass phosphorus and 10% by mass tin. The particle diameter (D50%) of the phosphorus-tin-containing copper alloy particles was 5.0 μm, and the shape thereof was substantially spherical.

3 parts of silicon dioxide (SiO ₂ ), 60 parts of lead oxide (PbO), 18 parts of boron oxide (B ₂ O ₃ ), 5 parts of bismuth oxide (Bi ₂ O ₃ ), 5 parts of aluminum oxide (Al ₂ O ₃ ), A glass composed of 9 parts of zinc oxide (ZnO) (hereinafter sometimes abbreviated as “G01”) was prepared. The obtained glass G01 had a softening point of 420 ° C. and a crystallization temperature of over 650 ° C.
By using the obtained glass G01, glass G01 particles having a particle diameter (D50%) of 2.5 μm were obtained. The shape was substantially spherical.

81.4 parts of the phosphorus-tin-containing copper alloy particles obtained above, 4.1 parts of glass G01 particles, 14.1 parts of terpineol (Ter), and 0.4 parts of ethyl cellulose (EC) were mixed together. The electrode paste composition 1 was prepared by stirring in a mortar for 20 minutes.

(B) Fabrication of solar cell element A p-type semiconductor substrate having a thickness of 190 μm having an n ⁺ -type diffusion layer, a texture, and an antireflection film (silicon nitride film) formed on the light receiving surface is prepared, and the size is 125 mm × 125 mm. Cut out. 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 1.5 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, the electrode paste composition 1 and the aluminum electrode paste were printed by screen printing in the same manner as described above so as to have an electrode pattern as shown in FIG.
The pattern of the back surface output extraction electrode made of the electrode paste composition 1 was 123 mm × 5 mm, and was printed in two places in total. The printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the back surface output extraction electrode had a film thickness after firing of 20 μm. Also, an aluminum electrode paste was printed on the entire surface other than the back surface output extraction electrode to form a back surface current collecting electrode pattern. Moreover, the printing conditions of the aluminum electrode paste were appropriately adjusted so that the film thickness of the back surface collecting electrode after firing was 30 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

Subsequently, using a tunnel furnace (manufactured by Noritake Co., Ltd., one-row transport W / B tunnel furnace), a heat treatment (firing) is performed at a firing maximum temperature of 800 ° C. and a holding time of 10 seconds in an air atmosphere to form a desired electrode. The produced solar cell element 1 was produced.

<Example 2>
In Example 1, a solar cell element 2 was produced in the same manner as in Example 1 except that the firing condition at the time of electrode formation was changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 850 ° C. for 8 seconds.

<Example 3>
Example 1 except that the phosphorus content of the phosphorus-tin-containing copper alloy particles was changed from 6% by mass to 5% by mass and the tin content was changed from 10% by mass to 15% by mass in Example 1. In the same manner as above, an electrode paste composition 3 was prepared, and a solar cell element 3 was produced.

<Example 4>
In Example 3, a solar cell element 4 was produced in the same manner as in Example 3 except that the firing condition at the time of electrode formation was changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 850 ° C. for 8 seconds.

<Example 5>
A paste composition for an electrode was prepared in the same manner as in Example 1, except that silver was further added to the phosphor-tin-containing copper alloy particles and the composition was changed to Cu-6P-15Sn-1Ag. 5 was prepared and the solar cell element 5 was produced.

<Example 6>
In Example 1, except that silver was added to the phosphorus-tin-containing copper alloy particles and the composition was changed to Cu-6P-15Sn-5Ag, the electrode paste composition 6 was prepared in the same manner as in Example 1. The solar cell element 6 was prepared.

<Example 7>
In Example 1, except that silver was added to the phosphor-tin-containing copper alloy particles and the composition was changed to Cu-6P-15Sn-10Ag, an electrode paste composition 7 was prepared in the same manner as in Example 1. The solar cell element 7 was prepared.

<Example 8>
In Example 1, except that manganese was added to the phosphorus-tin-containing copper alloy particles and the composition was changed to Cu-6P-15Sn-2Mn, the electrode paste composition 8 was prepared in the same manner as in Example 1. The solar cell element 8 was prepared.

<Example 9>
In Example 1, except that cobalt was added to the phosphorus-tin-containing copper alloy particles and the composition was changed to Cu-6P-15Sn-2Co, the electrode paste composition 9 was prepared in the same manner as in Example 1. The solar cell element 9 was prepared.

<Example 10>
A paste composition 10 for an electrode was prepared in the same manner as in Example 1 except that the particle diameter of the phosphorus-tin-containing copper alloy particles was changed from 5.0 μm to 1.5 μm in Example 1, and the solar cell Element 10 was produced.

<Example 11>
In Example 1, silver particles (particle diameter (D50%) 3.0 μm; purity 99.5%) were added to the electrode paste composition, and the content of each component was 77.3% of phosphorus-tin-containing copper alloy particles. Example 1 except that 4 parts, 4.0 parts of silver particles, 4.1 parts of glass particles, 14.1 parts of solvent, and 0.4 parts of resin were respectively changed. The electrode paste composition 11 was prepared, and the solar cell element 11 was produced.

<Example 12>
In Example 1, silver particles (particle size (D50%) 3.0 μm; purity 99.5%) were added to the electrode paste composition, and the content of each component was 73.3% of phosphorus-tin-containing copper alloy particles. Example 1 except that the amount was changed to 4 parts, 8.0 parts of silver particles, 4.1 parts of glass particles, 14.1 parts of solvent, and 0.4 parts of resin. The electrode paste composition 12 was prepared, and the solar cell element 12 was produced.

<Example 13>
Example 1 except that the phosphorus content of the phosphorus-tin-containing copper alloy particles was changed from 6% by mass to 10% by mass and the tin content was changed from 10% by mass to 20% by mass in Example 1. In the same manner as above, an electrode paste composition 13 was prepared, and a solar cell element 13 was produced.

<Example 14>
In Example 13, the solar cell element 14 was produced in the same manner as in Example 13, except that the firing condition at the time of electrode formation was changed from the maximum temperature of 800 ° C. for 10 seconds to the maximum temperature of 850 ° C. for 8 seconds. .

<Example 15>
In Example 13, a solar cell element 15 was produced in the same manner as in Example 13 except that the firing condition at the time of electrode formation was changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 750 ° C. for 12 seconds.

<Example 16>
In Example 1, except that the composition of the glass particles was changed from the glass G01 to the glass G02 shown below, the electrode paste composition 16 was prepared in the same manner as in Example 1 to produce the solar cell element 16. did.
Glass G02 is composed of 45 parts of vanadium oxide (V ₂ O ₅ ), 24.2 parts of phosphorus oxide (P ₂ O ₅ ), 20.8 parts of barium oxide (BaO), 5 parts of antimony oxide (Sb ₂ O ₃ ), oxidation It was prepared to consist of 5 parts of tungsten (WO ₃ ). Further, the softening point of the glass G02 was 492 ° C., and the crystallization start temperature exceeded 650 ° C.
By using the obtained glass G02, glass G02 particles having a particle diameter (D50%) of 2.5 μm were obtained. The shape was substantially spherical.

<Example 17>
In Example 16, the content of the phosphorus-tin-containing copper alloy particles was changed from 81.4% by mass to 79.0% by mass, and the content of the glass G02 particles was changed from 4.1% by mass to 6.5% by mass. Except that it was changed to, in the same manner as in Example 16, an electrode paste composition 17 was prepared, and a solar cell element 17 was produced.

<Example 18>
In Example 1, the resin was changed from terpineol to diethylene glycol monobutyl ether (BC), and the resin was changed from ethyl cellulose to polyethyl acrylate (EPA). Specifically, the content of each component is 81.4 parts of phosphorus-tin-containing copper alloy particles, 4.1 parts of glass G01 particles, 12.3 parts of diethylene glycol monobutyl ether, and 2.2 parts of polyethyl acrylate. Except having changed into the part, it carried out similarly to Example 1, and prepared the paste composition 18 for electrodes, and produced the solar cell element 18. FIG.

<Examples 19 to 23>
In Example 1, the phosphorus content, the tin content, the silver content, the manganese content, the cobalt content, the particle diameter (D50%) and the content thereof, the silver particle content, A paste composition for an electrode in the same manner as in Example 1 except that the type and content of glass particles, the type and content of solvent, the type and content of resin were changed as shown in Table 1. 19-23 were prepared respectively.

Next, a desired electrode was formed in the same manner as in Example 1 except that the obtained electrode paste compositions 19 to 23 were used, respectively, and the heat treatment temperature and treatment time were changed as shown in Table 1. The solar cell elements 19 to 23 thus prepared were respectively produced.

<Example 24>
A p-type semiconductor substrate having a film thickness of 190 μm having an n ⁺ -type diffusion layer, a texture, and an antireflection film (silicon nitride film) formed on the light receiving surface was prepared and cut into a size of 125 mm × 125 mm. Thereafter, an aluminum electrode paste was printed on the back surface to form a back surface collecting electrode pattern. The back surface collecting electrode pattern was printed on the entire surface other than the back surface output extraction electrode as shown in FIG. Moreover, the printing conditions of the aluminum electrode paste were appropriately adjusted so that the film thickness of the back surface collecting electrode after firing was 30 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.
Subsequently, using a tunnel furnace (manufactured by Noritake Co., Ltd., single-row transport W / B tunnel furnace), heat treatment (baking) for 10 seconds at a maximum firing temperature of 800 ° C. is performed in the air atmosphere for current collection on the back surface. An electrode and a p ⁺ type diffusion layer were formed.

Thereafter, the electrode paste composition 1 was printed so as to have an electrode pattern as shown in FIGS. The electrode pattern on the light-receiving surface is composed of 150 μm wide finger lines and 1.5 mm wide bus bars, and printing conditions (screen plate mesh, printing speed, printing pressure) are appropriately set so that the film thickness after firing is 20 μm. It was adjusted. The back electrode pattern was 123 mm × 5 mm, and was printed in two places 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.

Using a tunnel furnace (manufactured by Noritake, one-row transport W / B tunnel furnace), heat treatment (firing) is performed in an air atmosphere at a firing maximum temperature of 650 ° C. and a holding time of 10 seconds to form a desired electrode. The solar cell element 24 thus manufactured was produced.

<Example 25>
In Example 24, a solar cell element 25 was produced in the same manner as in Example 24 except that the electrode paste composition 7 obtained above was used to produce the light-receiving surface electrode and the back surface output extraction electrode.

<Example 26>
In Example 24, a solar cell element 26 was produced in the same manner as in Example 24 except that the electrode paste composition 11 obtained above was used to produce the light receiving surface electrode and the back surface output extraction electrode.

<Example 27>
Using the electrode paste composition 1 obtained above, a solar cell element 27 having a structure as shown in FIG. 5 was produced. A specific manufacturing method is described below. First, with respect to the p-type silicon substrate, a through hole having a diameter of 100 μm penetrating both the light receiving surface side and the back surface side was formed by a laser drill. Further, a texture, an n ⁺ -type diffusion layer, and an antireflection film were sequentially formed on the light receiving surface side. The n ⁺ -type diffusion layer was also formed inside the through hole and part of the back surface. Next, the previously formed through-hole internal electrode paste composition 1 was filled by an inkjet method, and further printed on the light-receiving surface side in a grid.

On the other hand, on the back surface side, the electrode paste composition 1 and the aluminum electrode paste were used to print in stripes in a pattern as shown in FIG. 4, and the electrode paste composition 1 was printed under the through holes. Formed as follows. This was subjected to heat treatment using a tunnel furnace (manufactured by Noritake Co., Ltd., single-row transport W / B tunnel furnace) in an air atmosphere at a firing maximum temperature of 800 ° C. for a holding time of 10 seconds, and the sun on which the desired electrode was formed A battery element 27 was produced.
At this time, with respect to the part where the aluminum electrode paste was formed, Al diffused into the p-type silicon substrate by firing, whereby a p ⁺ -type diffusion layer was formed.

<Example 28>
In Example 27, a solar cell element 28 was produced in the same manner as in Example 27, except that the firing conditions at the time of electrode formation were changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 850 ° C. for 8 seconds. .

<Example 29>
In Example 27, except that the electrode paste composition 1 was changed to the electrode paste composition 12 obtained above, and a light receiving surface collecting electrode, a through-hole electrode, and a back electrode were formed, Example In the same manner as in Example 27, a solar cell element 29 was produced.

<Example 30>
In Example 1, the electrode paste composition 30 was prepared in the same manner as in Example 1 except that the glass particles were changed from the glass G01 particles to the glass G03 particles.
Glass G03 is composed of 13 parts of silicon dioxide (SiO ₂ ), 58 parts of boron oxide (B ₂ O ₃ ), 38 parts of zinc oxide (ZnO), 12 parts of aluminum oxide (Al ₂ O ₃ ), and barium oxide (BaO). Prepared to consist of 12 parts. The obtained glass G03 had a softening point of 583 ° C. and a crystallization temperature of over 650 ° C.
By using the obtained glass G03, glass G03 particles having a particle diameter (D50%) of 2.5 μm were obtained. The shape was substantially spherical.

Next, using the electrode paste composition 30 obtained above, a solar cell element 30 having a structure as shown in FIG. 6 was produced. The manufacturing method is the same as in Examples 27 to 29 except that the light receiving surface electrode is not formed. The firing conditions were a maximum temperature of 800 ° C. and a holding time of 10 seconds.

<Example 31>
In Example 28, a solar cell element 31 was produced in the same manner as in Example 30 except that the firing condition at the time of electrode formation was changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 850 ° C. for 8 seconds.

<Example 32>
In Example 13, an electrode paste composition 32 was prepared in the same manner as in Example 13 except that the glass composition was changed from glass G01 to glass G03. Except having used this, it carried out similarly to Example 30, and produced the solar cell element 32 which has a structure as shown in FIG.

<Example 33>
Using the electrode paste composition 30 obtained above, a solar cell element 33 having a structure as shown in FIG. 7 was produced. The manufacturing method is the same as that in Example 27 except that an n-type silicon substrate is used as the base substrate and that the light receiving surface electrode, the through hole, and the through hole electrode are not formed. The firing conditions were a maximum temperature of 800 ° C. and a holding time of 10 seconds.

<Example 34>
In Example 33, a solar cell element 34 was produced in the same manner as in Example 33 except that the firing condition at the time of electrode formation was changed from a maximum temperature of 800 ° C. for 10 seconds to a maximum temperature of 850 ° C. for 8 seconds.

<Example 35>
In Example 13, the electrode paste composition 35 was prepared in the same manner as in Example 13 except that the glass particles were changed from the glass G01 particles to the glass G03 particles. Using this, a solar cell element 35 having a structure as shown in FIG.

<Comparative Example 1>
The preparation of the electrode paste composition in Example 1 was carried out in the same manner as in Example 1 except that each component was changed to the composition shown in Table 1 without using the phosphorus-tin-containing copper alloy particles. Thus, electrode paste composition C1 was prepared.
A solar cell element C1 was produced in the same manner as in Example 1 except that the electrode paste composition C1 containing no phosphorus-bell-containing copper alloy particles was used.

<Comparative Examples 2 to 4>
Instead of the phosphorus-tin-containing copper alloy particles, copper particles (purity 99.5%), phosphorus-containing copper alloy particles and tin-containing copper alloy particles were used, respectively, and electrode paste compositions C2 to C4 having the compositions shown in Table 1 were used. Were prepared respectively.
Solar cell elements C2 to C4 were respectively produced in the same manner as in Comparative Example 1 except that the electrode paste compositions C2 to C4 were used.

<Comparative Example 5>
In Example 27, except that the electrode paste composition 1 was changed from the electrode paste composition 1 to the electrode paste composition C1 obtained above, the light receiving surface collecting electrode, the through-hole electrode, and the back electrode were formed. In the same manner as in Example 27, a solar cell element C5 was produced.

<Comparative Example 6>
In Example 30, a solar cell element C6 was produced in the same manner as in Example 30, except that the electrode paste composition 30 was changed to the electrode paste composition C1 obtained above.

<Comparative Example 7>
In Example 33, a solar cell element C7 was produced in the same manner as in Example 33 except that the electrode paste composition 33 was changed to the electrode paste composition C1 obtained above.

<Evaluation>
Evaluation of the produced solar cell element was performed by using WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as pseudo-sunlight, and IV CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT Co., Ltd.) as a current-voltage (IV) evaluation measuring instrument. ) Was combined with the measuring device. Jsc (short-circuit current), Voc (open circuit voltage), FF (fill factor), and Eff (conversion efficiency) 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. In the solar cell element having a double-sided electrode structure, the obtained measured values are converted into relative values with the measured value of Comparative Example 1 (solar cell element C1) as 100.0, and are shown in Table 2. In Comparative Example 2, the resistivity of the electrode increased due to oxidation of the copper particles, and evaluation was impossible.
Furthermore, the cross section of the light-receiving surface electrode formed by firing the prepared electrode paste composition was observed with a scanning electron microscope Miniscope TM-1000 (manufactured by Hitachi, Ltd.) at an acceleration voltage of 15 kV. The presence or absence of the Cu—Sn alloy phase, Sn—PO glass phase, and the formation site of the Sn—PO glass phase were investigated. The results are also shown in Table 2.

From Table 2, the power generation performance deteriorated in Comparative Example 3 and Comparative Example 4 as compared with Comparative Example 1. In Comparative Example 3, although the phosphorus content in the copper alloy particles is 6% by mass, since tin is not included, the silicon substrate and copper are interdiffused during firing, and the pn junction characteristics in the substrate It is conceivable that has deteriorated. In Comparative Example 5, since copper alloy particles not containing phosphorus and containing tin were used, it is considered that the alloy particles were oxidized during firing and the resistance of the electrode was increased without forming a Cu—Sn alloy phase.

On the other hand, the power generation performance of the solar cell elements produced in Examples 1 to 26 was almost the same as the measured value of Comparative Example 1. In particular, the solar cell elements 24 to 26 exhibited high power generation performance even though the electrode paste composition was fired at a relatively low temperature (650 ° C.). Further, as a result of the structure observation, a Cu—Sn alloy phase and a Sn—PO glass phase are present in the light receiving surface electrode, and a Sn—PO glass phase is formed between the Cu—Sn alloy phase and the silicon substrate. It had been.

Subsequently, for each of the back contact solar cell elements having the structure of FIG. 5, the obtained measured values are converted into relative values with the measured value of Comparative Example 5 as 100.0, and Table 3 It was shown to. Further, the results of observation of the cross section of the light-receiving surface electrode are also shown in Table 3.

From Table 3, it can be seen that the solar cell elements produced in Examples 27 to 29 exhibited almost the same power generation performance as the solar cell element of Comparative Example 5. Further, as a result of the structure observation, a Cu—Sn alloy phase and a Sn—PO glass phase are present in the light receiving surface electrode, and a Sn—PO glass phase is formed between the Cu—Sn alloy phase and the silicon substrate. It had been.

Subsequently, for each of the back contact solar cell elements having the structure of FIG. 6, the obtained measured values were converted into relative values with the measured value of Comparative Example 6 as 100.0. It was shown to. Further, the results of observation of the cross section of the light-receiving surface electrode are also shown in Table 4.

From Table 4, it can be seen that the solar cell elements produced in Examples 30 to 32 exhibited almost the same power generation performance as the solar cell element of Comparative Example 6. Further, as a result of the structure observation, the Cu—Sn alloy phase and the Sn—PO glass phase exist in the electrode formed by firing the prepared electrode paste composition among the back electrodes, and Sn—PO A glass phase was formed between the Cu—Sn alloy phase and the silicon substrate.

Subsequently, for each of the back contact solar cell elements having the structure of FIG. 7, the obtained measured values were converted into relative values with the measured value of Comparative Example 7 as 100.0, and Table 5 It was shown to. Further, the results of observation of the cross section of the light-receiving surface electrode are also shown in Table 5.

It can be seen that the solar cell elements produced in Examples 33 to 35 exhibited almost the same power generation performance as the solar cell element of Comparative Example 7. Further, as a result of the structure observation, the Cu—Sn alloy phase and the Sn—PO glass phase exist in the electrode formed by firing the prepared electrode paste composition among the back electrodes, and Sn—PO A glass phase was formed between the Cu—Sn alloy phase and the silicon substrate.

Claims

An electrode paste composition comprising phosphorus-tin-containing copper alloy particles, glass particles, a solvent, and a resin.
The electrode paste composition according to claim 1, wherein the phosphorus-tin-containing copper alloy particles have a phosphorus content of 2% by mass to 15% by mass and a tin content of 5% by mass to 30% by mass. .
The electrode paste composition according to claim 1 or 2, wherein the glass particles have a glass softening point of 650 ° C or lower and a crystallization start temperature exceeding 650 ° C.
The electrode paste composition according to any one of claims 1 to 3, wherein the phosphorus-tin-containing copper alloy particles further include at least one metal atom selected from the group consisting of silver, manganese, and cobalt. .
The electrode paste composition according to claim 4, wherein the phosphorus-tin-containing copper alloy particles have a metal atom content of 0.1 mass% or more and 10 mass% or less.
The electrode paste composition according to any one of claims 1 to 5, further comprising silver particles.
7. The electrode according to claim 6, wherein the content of the silver particles is 0.1% by mass to 10% by mass when the total content of the phosphorus-tin-containing copper alloy particles and the silver particles is 100% by mass. Paste composition.
The total content of the phosphorus-tin-containing copper alloy particles and silver particles is 70% by mass or more and 94% by mass or less, the content of the glass particles is 0.1% by mass or more and 10% by mass or less, the solvent and The electrode paste composition according to claim 6 or 7, wherein a total content of the resin is 3% by mass or more and 29.9% by mass or less.
A solar cell element having an electrode formed by firing the electrode paste composition according to any one of claims 1 to 8 applied on a silicon substrate.
10. The solar cell element according to claim 9, wherein the electrode includes a Cu—Sn alloy phase and a Sn—P—O glass phase.
The solar cell element according to claim 10, wherein the Sn-PO glass phase is disposed between the Cu-Sn alloy phase and the silicon substrate.
A solar cell comprising the solar cell element according to any one of claims 9 to 11 and a tab wire disposed on an electrode of the solar cell element.