WO2022176519A1

WO2022176519A1 - Composition for forming electrode, solar cell element, and aluminum/silver stacked electrode

Info

Publication number: WO2022176519A1
Application number: PCT/JP2022/002478
Authority: WO
Inventors: 剛早坂; 剛野尻; 修一郎足立; 研耶守谷
Original assignee: 昭和電工マテリアルズ株式会社
Priority date: 2021-02-16
Filing date: 2022-01-24
Publication date: 2022-08-25
Also published as: JPWO2022176519A1; TW202244944A

Abstract

This composition for forming electrodes comprises silver-containing particles, bismuth-containing particles, and glass particles that include glass particles containing vanadium and tellurium.

Description

Electrode-forming composition, solar cell element, and aluminum/silver laminated electrode

The present disclosure relates to electrode-forming compositions, solar cell elements, and aluminum/silver laminated electrodes.

In recent years, there has been growing interest in environmental issues such as global warming and air pollution. Above all, as a countermeasure against the problem of global warming, there is an increasing demand for renewable energy to replace fossil fuels. Renewable energy includes solar, geothermal, wind, wave, tidal, and biomass. In particular, photovoltaic power generation, which utilizes inexhaustible solar energy, is attracting attention as a clean natural energy that does not emit carbon dioxide during power generation, and is expected to be an effective solution to the increasingly serious energy problem.

As a solar cell, a crystalline silicon solar cell using a silicon (Si) substrate as a semiconductor substrate is common. On each of the light receiving surface and the back surface (the surface opposite to the light receiving surface) of a solar cell (solar cell element) using a Si substrate, there are current collecting electrodes for recovering carriers and an electrode for extracting carriers as an output. Output extraction electrodes (busbar electrodes) are formed. The current-collecting electrodes on the light-receiving surface are particularly called finger electrodes. A silver (Ag) electrode-forming composition is used to form the light-receiving surface electrodes, and the finger electrodes and busbar electrode portions are printed individually or collectively. As for the back surface, a silver electrode-forming composition is used to form the busbar electrodes, and an aluminum (Al) electrode-forming composition is used to form the current-collecting electrodes. Each electrode-forming composition contains conductive metal particles, glass particles, various additives, and the like.

Silver particles are generally used as the conductive metal particles in a silver electrode-forming composition for forming light-receiving surface electrodes and back surface bus bar electrodes. The reasons for this are that the volume resistivity of silver is low (1.47×10 ⁻⁶ Ωcm), that the silver particles are self-reduced and sintered under the above heat treatment conditions, and that the silver particles and the silicon substrate are in good ohmic contact. and that the electrode formed from silver particles has excellent wettability with a solder material, and can preferably adhere wiring materials (such as tab wires) that electrically connect solar cell elements.

When the aluminum electrode-forming composition is used to form the current-collecting electrode on the back surface, aluminum in the aluminum electrode-forming composition undergoes a eutectic reaction with silicon to form a high-concentration diffusion layer (p ⁺ - forming a Si layer, Back Surface Field (BSF); Thereby, a structure is provided in which electrons, which are minority carriers in the p-type silicon substrate, are repelled to the light receiving surface side, and the probability of carrier recombination can be reduced.
However, in the back electrode/BSF structure using a conventional composition for forming an aluminum electrode, the minority carrier recombination rate on the back surface is as high as about 3×10 ³ cm/s, which is a factor in lowering the power generation performance of the solar cell element. can be.

A PERC (Passivated Emitter, Rear Cell) structure is attracting attention as a measure for reducing backside recombination loss (see, for example, Patent Document 1). The PERC structure is characterized by limiting the ohmic contact portion between the back electrode and the Si substrate, which is one of the causes of back recombination, in a point or line shape. It is Backside passivation films that can be used in PERC structures include amorphous aluminum oxide (AlO _x ) films by Atomic Layer Deposition (ALD) or CVD (Chemical Vapor Deposition). An AlO _X film formed by the ALD method or the CVD method is known to have a large negative fixed charge, and a PERC structure solar cell element to which this film is applied is known to exhibit high power generation performance.

In the PERC structure, since the contact portion between the back electrode and the silicon substrate is limited, a bifacial solar cell element can be realized. Advantages of the bifacial-PERC structure include the ability to utilize the light that enters the rear surface.

In the above PERC structure including the bifacial-PERC structure, MBB (Multi Busbar)-bifacial-PERC structure, etc., when forming the back electrode, generally an electrode-forming composition containing silver and an electrode containing aluminum are used. Each of the forming compositions is printed on a predetermined region of the substrate, dried, and then subjected to a heat treatment at once.
In the above structure, the wettability between the aluminum oxide (Al ₂ O ₃ ) film formed on the surface of the aluminum electrode and the solder coating the wiring material is poor, so the wiring material cannot be directly bonded to the aluminum electrode. On the back surface, as with the light-receiving surface side, it is necessary to form a silver electrode as an output extraction electrode at the location where the wiring material is connected. A composition for forming a silver electrode is applied. At this time, with the backside electrode formed by the conventional process, the step (difference in thickness) between the aluminum electrode and the silver electrode as the backside output extraction electrode causes poor connection of the wiring material and reduces the reliability of the solar cell. sexuality may be compromised.

This can be considered, for example, as follows. Of the backside electrodes, the silver electrode as an output extraction electrode is not formed continuously along the connection direction of the wiring material, but is formed in the connection direction of the wiring material from the viewpoint of reducing the amount of the silver electrode-forming composition used. Along the way, an aluminum electrode may be formed between the silver electrodes. The thickness of the aluminum electrode after heat treatment (after baking) is generally 20 μm to 40 μm, and the thickness of the silver electrode as the rear output extraction electrode is generally 2 μm to 5 μm. In such a case, part of the wiring material is placed on the aluminum electrode. It is conceivable that the connection of the wiring material becomes insufficient. Moreover, even if the wiring material can be connected to the silver electrode, the wiring material is deformed while forming irregularities according to the steps, so stress other than the internal stress due to heat is thought to be applied. Under such circumstances, during a test or an environment (for example, a temperature cycle test) in which temperature changes are applied to solar cell members, cracks or the like occur in the joints, resulting in a large decrease in power generation performance. .

As a method for solving the above-described problems, instead of forming an aluminum electrode and a silver electrode on a substrate, an aluminum electrode formed on a substrate and a silver electrode formed thereon are laminated. (hereinafter also referred to as an aluminum/silver laminated electrode).
As a method for forming an aluminum/silver laminated electrode, for example, an electrode-forming composition containing aluminum particles is applied to the back surface of a substrate in a desired pattern to form an aluminum particle-containing film, and then an electrode-forming composition containing silver is applied. It is conceivable to print the composition in a desired pattern on the aluminum particle-containing film and heat-treat it all at once.

Japanese Patent No. 6203990

When forming the aluminum/silver laminated electrode, the passivation film may be etched, and the power generation performance of the PERC structure solar cell element may be lowered. Therefore, there is a demand for an electrode-forming composition that suppresses etching of a passivation film when forming an aluminum/silver laminated electrode.
The present disclosure has been made in view of the above-described conventional circumstances, and an embodiment of the present disclosure provides an electrode-forming composition that suppresses etching of a passivation film, and an electrode-forming composition obtained using this electrode-forming composition. An object of the present invention is to provide a solar cell element and an aluminum/silver laminated electrode.

Specific means for achieving the above object are as follows.
<1> containing silver-containing particles, bismuth-containing particles, and glass particles,
The composition for forming an electrode, wherein the glass particles contain glass particles containing vanadium and tellurium.
<2> The electrode-forming material according to <1>, wherein in the composition of the glass constituting the glass particles containing vanadium and tellurium, the content of vanadium oxide is 20.0% by mass to 50.0% by mass. Composition.
<3> According to <1> or <2>, the content of tellurium oxide in the composition of the glass constituting the glass particles containing vanadium and tellurium is 35.0% by mass to 65.0% by mass. Composition for electrode formation of.
<4> Any one of <1> to <3>, wherein the proportion of the glass particles containing vanadium and tellurium in the total glass particles is 50.0% by mass to 100.0% by mass. Composition for electrode formation of.
<5> The electrode-forming composition according to any one of <1> to <4>, wherein the glass particles further contain phosphorus-containing glass particles.
<6> The electrode-forming composition according to <5>, wherein in the composition of the glass constituting the phosphorus-containing glass particles, the content of phosphorus oxide is 20.0% by mass to 50.0% by mass.
<7> The electrode-forming composition according to <5> or <6>, wherein the phosphorus-containing glass particles account for 40.0% by mass or less of the entire glass particles.
<8> The electrode-forming material according to any one of <1> to <7>, wherein the bismuth-containing particles include at least one selected from the group consisting of metal bismuth particles, bismuth alloy particles, and bismuth oxide particles. Composition.
<9> Any one of <1> to <8>, wherein the mass ratio of the content of the bismuth-containing particles to the content of the silver-containing particles (Bi/Ag ratio) is 0.30 to 1.40 The electrode-forming composition according to 1.
<10> Any one of <1> to <9>, wherein the mass ratio of the content of the bismuth-containing particles to the content of the glass particles (Bi/G ratio) is 0.5 to 15.0 The electrode-forming composition as described.
<11> The electrode-forming composition according to any one of <1> to <10>, wherein the content of the glass particles is 1.0% by mass to 15.0% by mass of the entire electrode-forming composition. Composition.
<12> The electrode-forming composition according to any one of <1> to <11>, further comprising at least one selected from the group consisting of a solvent and a resin.
<13> The electrode-forming composition according to any one of <1> to <12>, for forming an aluminum/silver laminated electrode.
<14> A semiconductor substrate, a passivation film provided on the semiconductor substrate, and a heat-treated product of the electrode-forming composition according to any one of <1> to <13> provided on the passivation film. and an aluminum/silver laminated electrode.
<15> An aluminum/silver laminated electrode containing the heat-treated electrode-forming composition according to any one of <1> to <13>,
An aluminum/silver laminated electrode comprising a first electrode comprising aluminum and a second electrode comprising silver disposed over said first electrode, said first electrode further comprising a bismuth oxide phase and a glass phase.

According to one embodiment of the present disclosure, an electrode-forming composition in which etching of a passivation film is suppressed, and a solar cell element and an aluminum/silver laminated electrode obtained using this electrode-forming composition are provided. .

FIG. 2 is a diagram showing an example of a cross section of an aluminum electrode and an aluminum/silver laminated electrode on the back surface of a solar cell element; It is a cross-sectional schematic diagram which shows an example of the manufacturing method of an aluminum/silver laminated electrode. It is a cross-sectional schematic diagram which shows an example of the manufacturing method of an aluminum/silver laminated electrode. It is a cross-sectional schematic diagram which shows an example of the manufacturing method of an aluminum/silver laminated electrode. It is a cross-sectional schematic diagram of an aluminum/silver laminated electrode. FIG. 2 is a schematic plan view showing an example of a light receiving surface of a solar cell element; FIG. 2 is a schematic plan view showing an example of the back surface of a solar cell element; FIG. 2 is a schematic plan view showing an example of the back surface of a solar cell element; FIG. 5B is a schematic cross-sectional view showing an example of a solar cell element (a cross-sectional view taken along line A-A' in FIG. 5A). FIG. 5B is a schematic cross-sectional view showing an example of a solar cell element (a cross-sectional view taken along the line B-B' in FIG. 5B). FIG. 5B is a schematic cross-sectional view showing an example of a solar cell element (a cross-sectional view taken along line C-C' in FIG. 5B).

A detailed description will be given below of the embodiment for implementing the present disclosure. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
In the present disclosure, the particles corresponding to each component may include multiple types of particles. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In the present disclosure, the term “layer” or “film” refers to the case where the layer or film is formed in the entire region when observing the region where the layer or film is present, and only a part of the region. It also includes the case where it is formed.
In the present disclosure, the term "laminate" indicates stacking layers, and two or more layers may be bonded, or two or more layers may be detachable.
In the present disclosure, the average thickness of a layer or film is a value obtained by measuring the thickness of the target layer or film at five points and giving the arithmetic mean value.
In the present disclosure, the term “cross section” means a plane obtained by cutting the solar cell element perpendicularly to the surface direction of the semiconductor substrate.
In the present disclosure, the term "heat treatment" includes heating (firing, etc.) under conditions that sinter or melt the particles contained in the subject of the heat treatment.
The thickness of a layer or film can be measured using a micrometer or the like. In this disclosure, when the thickness of a layer or film can be measured directly, it is measured using a micrometer. On the other hand, when measuring the thickness of one layer or the total thickness of a plurality of layers, the thickness may be measured by observing the cross section of the object to be measured using an electron microscope.

<Composition for electrode formation>
The electrode-forming composition of the present disclosure contains silver-containing particles, bismuth-containing particles, and glass particles, wherein the glass particles contain vanadium and tellurium. Hereinafter, glass particles containing vanadium and tellurium are sometimes referred to as vanadium-tellurium-containing glass particles.
An electrode-forming composition containing silver-containing particles, bismuth-containing particles, and vanadium-tellurium-containing glass particles as glass particles is an electrode that contains silver-containing particles and bismuth-containing particles but does not contain vanadium-tellurium-containing glass particles as glass particles. Etching of the passivation film is suppressed compared to the forming composition. The reason for this is not necessarily clear, but is presumed as follows.

An electrode-forming composition containing silver-containing particles and bismuth-containing particles is applied to a desired region on an aluminum particle-containing film formed on a substrate, dried as necessary, and then heat-treated. Thereby, a silver electrode is formed on the aluminum electrode.
By heat treatment, the silver-containing particles contained in the electrode-forming composition are sintered to form a silver electrode, and the aluminum particles contained in the aluminum particle-containing film are sintered to form an aluminum electrode. At this time, the bismuth oxide phase formed by oxidizing the bismuth contained in the bismuth-containing particles develops a property (hereinafter also referred to as a diffusion barrier property) to suppress interdiffusion at the interface between the silver electrode and the aluminum electrode. On the other hand, bismuth has the property of etching the passivation film.
When the electrode-forming composition is heat-treated, the molten vanadium-tellurium-containing glass particles have a property of being difficult to permeate between the aluminum particles contained in the aluminum particle-containing film. Therefore, the use of the vanadium-tellurium-containing glass particles prevents bismuth from reaching the passivation film through the aluminum particle-containing film as the molten glass particle component permeates between the aluminum particles. There is a tendency. Also, the vanadium-tellurium-containing glass particles hardly etch the passivation film. Therefore, even if some of the molten vanadium-tellurium-containing glass particles penetrate between the aluminum particles and reach the passivation film, the passivation film is hardly etched.
From the above, it is inferred that the electrode-forming composition of the present disclosure suppresses etching of the passivation film.

Each component contained in the electrode-forming composition of the present disclosure will be described below. The electrode-forming composition of the present disclosure contains silver-containing particles, bismuth-containing particles, and glass particles, and may contain other components. In addition, the electrode-forming composition of the present disclosure contains vanadium-tellurium-containing glass particles as glass particles, and may contain other glass particles.

(Silver-containing particles)
The electrode-forming composition contains silver-containing particles. The silver-containing particles contained in the electrode-forming composition may be of one type or two or more types.

The silver-containing particles are not particularly limited as long as they contain silver. Among them, it is preferably at least one selected from the group consisting of silver particles and silver alloy particles, and at least one selected from the group consisting of silver particles and silver alloy particles having a silver content of 50.0% by mass or more. One type is more preferable.

The content of silver in silver particles is not particularly limited. For example, it can be 95.0% by mass or more, preferably 97.0% by mass or more, more preferably 99.0% by mass or more, of the entire silver particles.

The silver alloy particles are not particularly limited as long as they are alloy particles containing silver. Above all, from the viewpoint of the melting point and sinterability of the silver alloy particles, the silver content is preferably 50.0% by mass or more, more preferably 60.0% by mass or more, based on the total amount of the particles. It is more preferably 0% by mass or more, and particularly preferably 80.0% by mass or more. The content may be 95.0% by mass or less.

Ag-Pd-based alloys, Ag-Pd-Au-based alloys, Ag-Pd-Cu-based alloys, Ag-Pd-In-based alloys, Ag-In-based alloys, Ag-Sn-based alloys, Ag-Zn system alloys, Ag--Sn--Zn system alloys, and the like.
The silver-containing particles may or may not contain components not applicable to silver and silver alloys.
When the silver-containing particles contain a component that does not correspond to silver or a silver alloy, the content of the silver-containing particles can be 3.0% by mass or less, preferably 1.0% by mass or less. .

The particle diameter of the silver-containing particles is not particularly limited, but in the volume-based particle size distribution obtained by the laser diffraction/scattering method, the particle diameter (volume average particle diameter) when the accumulation from the small diameter side is 50% is 0.1 μm. It is preferably up to 50.0 μm, more preferably 0.15 μm to 40.0 μm, even more preferably 0.2 μm to 30.0 μm. When the volume average particle diameter of the silver-containing particles is 0.1 μm or more, the concentration of silver on the surface of the aluminum/silver laminated electrode can be sufficiently increased, and the connection strength of the wiring material is improved. When the volume average particle size of the silver-containing particles is 50.0 μm or less, the resistance in the aluminum/silver laminated electrode tends to decrease.

The particle size of the silver-containing particles is measured by a laser diffraction particle size distribution analyzer (for example, Beckman Coulter, Inc., LS 13 320 laser scattering diffraction particle size distribution measuring device). Specifically, silver-containing particles are added to 125 g of a solvent (terpineol) within a range of 0.01% by mass to 0.3% by mass to prepare a dispersion. About 100 ml of this dispersion is injected into the cell and measured at 25°C. Particle size distribution is measured assuming the refractive index of the solvent to be 1.48.

The shape of the silver-containing particles is not particularly limited, and may be approximately spherical, flat, block-shaped, plate-shaped, scale-shaped, or the like. From the viewpoint of sinterability between the silver-containing particles, it is preferably substantially spherical, flat, or tabular.

(Bismuth-containing particles)
The electrode-forming composition includes bismuth-containing particles. The bismuth-containing particles contained in the electrode-forming composition may be of one type or two or more types.

The bismuth-containing particles are not particularly limited as long as they contain bismuth. Among them, at least one selected from the group consisting of metal bismuth particles, bismuth alloy particles and bismuth oxide particles is preferable, and metal bismuth particles, bismuth alloy particles having a bismuth content of 40.0% by mass or more and oxide More preferably, it is at least one selected from the group consisting of bismuth particles.
In the present disclosure, when the bismuth-containing particles are glassy (glass particles containing bismuth), they do not correspond to bismuth-containing particles.

The content of bismuth in the metal bismuth particles is not particularly limited. For example, it can be 95.0% by mass or more, preferably 97.0% by mass or more, and more preferably 99.0% by mass or more of the entire metal bismuth particles.

The bismuth alloy particles are not particularly limited as long as they are alloy particles containing bismuth. Above all, from the viewpoint of the melting point and diffusion barrier properties of the bismuth alloy particles, the bismuth content of the bismuth alloy particles is preferably 40.0% by mass or more, more preferably 50.0% by mass or more. It is preferably 60.0% by mass or more, and particularly preferably 70.0% by mass or more. The bismuth content of the bismuth alloy particles may be 95.0% by mass or less.

Bismuth alloys include Bi-Sn alloys, Bi-Sn-Cu alloys, Bi-Pb-Sn alloys, and Bi-Cd alloys.

Bismuth oxide particles include particles of bismuth trioxide (Bi ₂ O ₃ ). Bismuth oxide particles are preferably used in combination with metal bismuth particles from the viewpoint of exhibiting sufficient diffusion barrier properties and low resistance of the aluminum/silver laminated electrode itself.
The bismuth-containing particles may or may not contain components that are not metal bismuth, bismuth alloys, and bismuth oxide.
When the bismuth-containing particles contain components that do not correspond to metal bismuth, bismuth alloys, and bismuth oxide, the content is 3.0% by mass or less in the bismuth-containing particles from the viewpoint of formation of the bismuth oxide phase and diffusion barrier properties. and preferably 1.0% by mass or less.

The particle diameter of the bismuth-containing particles is not particularly limited, but the volume average particle diameter is preferably 0.1 μm to 50.0 μm, more preferably 0.15 μm to 40.0 μm, and more preferably 0.2 μm to 30.0 μm. 0 μm is even more preferable. When the particle diameter of the bismuth-containing particles is 0.1 μm or more, the transition to the aluminum particle-containing film and the formation of the bismuth oxide phase are promoted. When the particle diameter of the bismuth-containing particles is 50.0 μm or less, diffusion barrier properties are effectively exhibited.
The volume average particle size of the bismuth-containing particles is measured in the same manner as the volume average particle size of the silver-containing particles.

The shape of the bismuth-containing particles is not particularly limited, and may be approximately spherical, flat, block-shaped, plate-shaped, scale-shaped, or the like. From the viewpoint of diffusion barrier properties, it is preferably substantially spherical, flat or plate-shaped.

The mass ratio of the content of bismuth-containing particles to the content of silver-containing particles in the electrode-forming composition (Bi/Ag ratio) is preferably 0.30 to 1.40, more preferably 0.35 to 1.30. is more preferably 0.40 to 1.20, and particularly preferably 0.45 to 1.10. A Bi/Ag ratio of 0.30 or more tends to effectively suppress interdiffusion between aluminum and silver. By setting the Bi/Ag ratio to 1.40 or less, a sufficient silver concentration is ensured on the surface of the aluminum/silver laminated electrode, and the connection strength (solder wettability) of the connection material tends to be maintained satisfactorily.

(glass particles)
The electrode-forming composition contains glass particles, and the glass particles contain vanadium-tellurium-containing glass particles. Vanadium-tellurium containing glass particles include glass particles comprising vanadium oxide (V ₂ O ₅ ) and tellurium oxide (TeO ₂ ).

In the composition of the glass constituting the vanadium-tellurium-containing glass particles, the content of vanadium oxide is preferably 20.0% by mass to 50.0% by mass, more preferably 25.0% by mass to 45.0% by mass. more preferably 30.0% by mass to 40.0% by mass.
In the composition of the glass constituting the vanadium-tellurium-containing glass particles, the content of tellurium oxide is preferably 35.0% by mass to 65.0% by mass, more preferably 40.0% by mass to 60.0% by mass. more preferably 45.0% by mass to 55.0% by mass.
The mass-based ratio of vanadium oxide to tellurium oxide (vanadium oxide/tellurium oxide) constituting the vanadium-tellurium-containing glass particles is preferably 20/80 to 60/40, and preferably 25/75 to 55/45. more preferably 30/70 to 50/50.

The vanadium-tellurium-containing glass particles may include vanadium oxide, tellurium oxide, and oxides other than vanadium oxide and tellurium oxide.
Other oxides contained in the glass constituting the vanadium-tellurium-containing glass particles include, for example, silicon dioxide (SiO ₂ ), phosphorus oxide (P ₂ O ₅ ), aluminum oxide (Al ₂ O ₃ ), boron oxide ( _B2O3 ), potassium oxide ₍ K2O), bismuth oxide (Bi2O3), sodium oxide ₍ _Na2O ) _, lithium oxide ₍ Li2O), barium oxide ₍ BaO), strontium oxide (SrO) , calcium oxide (CaO), magnesium oxide (MgO), beryllium oxide (BeO), zinc oxide (ZnO), cadmium oxide (CdO), tin oxide (SnO), zirconium oxide ₍ ZrO2), tungsten oxide ₍ WO3) , molybdenum oxide ( _MoO3 ), lanthanum oxide (La2O3) _, niobium oxide ₍ _Nb2O3 ) _, tantalum oxide ₍ Ta2O5) _, yttrium oxide ₍ _Y2O3 ), titanium oxide ( _TiO2 ) , germanium oxide ( _GeO2 ), lutetium oxide ( _Lu2O3 ), antimony oxide (Sb2O3), copper oxide ( _CuO ), iron oxide ₍ _Fe2O3 ) _, silver oxide ₍ _Ag2O ) and oxide Manganese (MnO) is included.
Among these, other oxides include zinc oxide (ZnO), copper oxide (CuO), lithium oxide (Li ₂ O), and the like.
The proportion of other oxides in the entire glass constituting the vanadium-tellurium-containing glass particles is preferably 5.0% by mass to 25.0% by mass, more preferably 7.0% by mass to 23.0% by mass. more preferably 10.0% by mass to 20.0% by mass.

The number of glass particles contained in the electrode-forming composition may be one or two or more.

The electrode-forming composition may contain only vanadium-tellurium-containing glass particles as glass particles, or may contain glass particles other than vanadium-tellurium-containing glass particles. Other glass particles contain at least one selected from the group consisting of SiO ₂ , Al ₂ O ₃ , ZnO, B ₂ O ₃ , Bi ₂ O ₃ , CuO, SnO, Li ₂ O and P ₂ O ₅ It may be something to do.
The proportion of vanadium-tellurium-containing glass particles in the total glass particles is preferably 50.0% by mass to 100.0% by mass, more preferably 60.0% by mass to 90.0% by mass. is more preferable, and 70.0% by mass to 85.0% by mass is even more preferable. In other aspects, it is preferably 60.0% by mass to 100.0% by mass, more preferably 65.0% by mass to 100.0% by mass, and 70.0% by mass to 100.0% by mass. % is more preferred.

Glass particles containing phosphorus are preferable as other glass particles. Hereinafter, glass particles containing phosphorus may be referred to as phosphorus-containing glass particles. Glass containing phosphorus includes glass containing phosphorus oxide (P ₂ O ₅ ), and phosphate glass is preferred.
Phosphate glass in the present disclosure means glass containing phosphorus oxide ₍ P2O5) as a network _- forming oxide.

In the composition of the glass constituting the phosphorus-containing glass particles, the content of phosphorus oxide is preferably 20.0% by mass to 50.0% by mass, more preferably 30.0% by mass to 50.0% by mass, from the viewpoint of the functionality of the glass. It is more preferably 45.0% by mass, and even more preferably 35.0% to 40.0% by mass.

The phosphorus-containing glass particles may contain phosphorus oxide and oxides other than phosphorus oxide. Specific examples of other oxides include the oxides mentioned as other oxides contained in the glass constituting the vanadium-tellurium-containing glass particles.
The phosphorus-containing glass particles preferably contain at least one selected from the group consisting of aluminum oxide, tin oxide and zinc oxide. The use of glass with such a composition tends to further improve the reliability of the aluminum/silver laminated electrode in a high-temperature, high-humidity environment.

When the glass constituting the phosphorus-containing glass particles contains tin oxide, the tin oxide content is preferably 20.0% by mass to 80.0% by mass, more preferably 30.0% by mass to 70.0% by mass. and more preferably 40.0% by mass to 60.0% by mass.
Preferably, the phosphorus-containing glass particles do not contain boron oxide or contain less boron oxide than phosphorus oxide.

The proportion of phosphorus-containing glass particles in the total glass particles may be 40.0% by mass or less, preferably 0.0% by mass to 40.0% by mass, and more preferably 0.0% by mass to 35.0% by mass. It is more preferably 0% by mass, and even more preferably 0.0% by mass to 30.0% by mass.

When forming an aluminum/silver laminated electrode on a SiN _X film, it is preferable to use lead-free glass that does not substantially contain lead. Examples of lead-free glass include lead-free glasses described in paragraphs 0024 to 0025 of JP-A-2006-313744, lead-free glasses described in JP-A-2009-188281, and the like.

The softening point of the glass constituting each glass particle is not particularly limited, but is preferably 650°C or lower, more preferably 500°C or lower. The softening point of the glass can be obtained from a differential thermal (DTA) curve measured using a simultaneous differential thermal/thermogravimetric analyzer.

The shape of the glass particles is not particularly limited, and may be approximately spherical, flat, block-shaped, plate-shaped, scale-shaped, or the like. From the viewpoint of wettability with silver-containing particles and bismuth-containing particles, the shape of the glass particles is preferably substantially spherical, flat, or plate-like.

The volume average particle diameter of each glass particle is preferably 0.5 μm to 15.0 μm, more preferably 0.7 μm to 12.0 μm, and further preferably 0.9 μm to 10.0 μm. preferable.
When the volume-average particle size of the glass particles is 0.5 μm or more, unevenness due to the glass particles tends to be formed on the surface of the silver electrode obtained by heat-treating the electrode-forming composition. As a result, since the contact between the wiring material and the silver electrode becomes a point contact, the stress is relieved, and the reliability tends to be improved in a high-temperature and high-humidity environment.
When the volume average particle diameter of the glass particles is 15.0 μm or less, the dispersibility of the glass particles in the electrode-forming composition is good, and uneven distribution of the irregularities formed on the surface of the silver electrode is minimized. tend to be suppressed.
The volume average particle size of the glass particles is measured in the same manner as the volume average particle size of the silver-containing particles.

The content of the glass particles contained in the electrode-forming composition is preferably 1.0% by mass to 15.0% by mass, more preferably 3.5% by mass to 14.0% by mass, based on the entire electrode-forming composition. and more preferably 4.0% by mass to 12.0% by mass.
By setting the content of the glass particles to 1.0% by mass or more, good reliability tends to be maintained in a high-temperature, high-humidity environment. By setting the glass particle content to 15.0% by mass or less, the silver concentration on the surface of the silver electrode formed on the aluminum electrode is sufficiently ensured, and the connection strength (solder wettability) of the connection material is improved. It tends to be well maintained.

The mass ratio of the content of the bismuth-containing particles to the content of the glass particles contained in the electrode-forming composition (Bi/G ratio) is preferably 0.5 to 15.0, more preferably 1.0 to 12.0. It is more preferably 0, more preferably 1.5 to 10.0. By setting the Bi/G ratio to 0.5 or more, the diffusion barrier property of the bismuth oxide phase tends to be effectively exhibited. By setting the Bi/G ratio to 15.0 or less, the reliability tends to be effectively improved in a high temperature and high humidity environment.

(solvent and resin)
The electrode-forming composition may contain at least one selected from the group consisting of solvents and resins.
A method for imparting the liquid properties (viscosity, surface tension, etc.) of the electrode-forming composition to a substrate or the like by including at least one selected from the group consisting of a solvent and a resin in the electrode-forming composition. can be adjusted within a suitable range.
The solvent or resin contained in the electrode-forming composition may be of one type or two or more types.

Solvents include hydrocarbon solvents such as hexane, cyclohexane and toluene; halogenated hydrocarbon solvents such as dichloroethylene, dichloroethane and dichlorobenzene; Ether solvents, amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide, sulfoxide solvents such as dimethylsulfoxide and diethylsulfoxide, ketone solvents such as acetone, methylethylketone, diethylketone and cyclohexanone, ethanol, 2-propanol, 1-butanol, alcohol solvents such as diacetone alcohol, 2,2,4-trimethyl-1,3-pentanediol monoacetate, 2,2,4-trimethyl-1,3-pentanediol monopropionate, 2, Ester solvents of polyhydric alcohols such as 2,4-trimethyl-1,3-pentanediol monobutyrate, ethylene glycol monobutyl ether acetate and diethylene glycol monobutyl ether acetate, polyvalent solvents such as butyl cellosolve, diethylene glycol monobutyl ether and diethylene glycol diethyl ether Ether solvents of alcohols, and terpene solvents such as α-terpinene, terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, carvone, ocimene, and phellandrene.

The solvent is at least one solvent selected from the group consisting of polyhydric alcohol ester solvents, terpene solvents, and polyhydric alcohol ether solvents, from the viewpoint of imparting properties (e.g., coatability or printability) of the electrode-forming composition. It preferably contains seeds, and more preferably contains at least one selected from the group consisting of polyhydric alcohol ester solvents and terpene solvents.

The resin is not particularly limited as long as it can be thermally decomposed by heat treatment, and may be a natural polymer or a synthetic polymer. Specifically, cellulose resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and nitrocellulose, polyvinyl alcohol compounds, polyvinylpyrrolidone compounds, acrylic resins, vinyl acetate-acrylic acid ester copolymers, butyral resins such as polyvinyl butyral, and phenol-modified alkyds. Resins, alkyd resins such as castor oil fatty acid-modified alkyd resins, epoxy resins, phenol resins, rosin ester resins, and the like.

From the viewpoint of thermal decomposition by heat treatment, the resin preferably contains at least one selected from the group consisting of cellulose resins and acrylic resins.

The weight average molecular weight of the resin is not particularly limited. Among them, the weight average molecular weight of the resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000. When the weight-average molecular weight of the resin is 5,000 or more, the increase in the viscosity of the electrode-forming composition tends to be suppressed. It can be considered that this is because, for example, when the resin is adsorbed to the particles, the steric repulsive action becomes sufficient, and the cohesion of these resins is suppressed. On the other hand, when the weight-average molecular weight of the resin is 500,000 or less, aggregation of the resins in the solvent is suppressed, and an increase in the viscosity of the electrode-forming composition tends to be suppressed. When the weight-average molecular weight of the resin is 500,000 or less, the combustion temperature of the resin is too high and the electrode-forming composition is not burned and remains as a foreign matter during the heat treatment, which results in a lower resistivity. electrode can be formed.

The weight-average molecular weight is obtained by converting the molecular weight distribution measured by GPC (gel permeation chromatography) using a standard polystyrene calibration curve. A standard curve is approximated in three dimensions using a set of 5 standard polystyrene samples (PStQuick MP-H, PStQuick B, Tosoh Corporation). The measurement conditions of GPC are as follows.
・ Apparatus: (Pump: L-2130 [Hitachi High-Technologies Co., Ltd.]), (Detector: L-2490 RI [Hitachi High-Technologies Co., Ltd.]), (Column Oven: L-2350 [Co., Ltd. Hitachi High Technologies])
・ Column: Gelpack GL-R440 + Gelpack GL-R450 + Gelpack GL-R400M (3 in total) (Showa Denko Materials Co., Ltd.)
・Column size: 10.7 mm × 300 mm (inner diameter)
・ Eluent: Tetrahydrofuran ・ Sample concentration: 10 mg/2 mL
・Injection volume: 200 μL
・Flow rate: 2.05 mL/min ・Measurement temperature: 25°C

When the electrode-forming composition contains a solvent and a resin, the contents of the solvent and the resin can be selected depending on the desired liquid properties of the electrode-forming composition, the types of the solvent and the resin used, and the like.
For example, the total content of the solvent and the resin is preferably 3.0% by mass to 70.0% by mass, more preferably 20.0% by mass to 55.0% by mass, of the entire electrode-forming composition. More preferably, it is 30.0% by mass to 50.0% by mass.
When the total content of the solvent and the resin is within the above range, the application aptitude of the electrode-forming composition to the substrate is improved, and an electrode having a desired width and height can be formed more easily. tend to be able to
When the electrode-forming composition contains a solvent and a resin, the content ratio of the solvent and the resin should be appropriately selected according to the types of the solvent and resin used so that the electrode-forming composition has desired liquid physical properties. can be done.

The electrode-forming composition contains silver-containing particles, bismuth-containing particles and glass from the viewpoint of the sinterability of silver-containing particles, the diffusion barrier properties of bismuth-containing particles, and the effect of improving the strength and adhesion of aluminum electrodes by glass particles. The total content of particles is preferably 30.0% by mass to 97.0% by mass, more preferably 45.0% by mass to 80.0% by mass, based on the entire electrode-forming composition. It is more preferably 0.0% by mass to 70.0% by mass.

(other ingredients)
In addition to the components described above, the electrode-forming composition may further contain other components commonly used in the art. Other components include plasticizers, dispersants, surfactants, thickeners, inorganic binders, metal oxides (except bismuth oxide), ceramics, organometallic compounds, and the like.

(Method for producing electrode-forming composition)
The method for producing the electrode-forming composition is not particularly limited. For example, it can be produced by dispersing and mixing silver-containing particles, bismuth-containing particles, glass particles, and optionally other components. Dispersion and mixing methods are not particularly limited, and can be applied by selecting from commonly used methods.

<Aluminum/silver laminated electrode>
The aluminum/silver laminated electrode of the present disclosure includes a heat-treated product of the electrode-forming composition of the present disclosure described above, and includes a first electrode containing aluminum and silver disposed on the first electrode. and a second electrode comprising: the first electrode further comprising a bismuth oxide phase and a glass phase.

Whether or not the first electrode contains the bismuth oxide phase and the glass phase can be confirmed using a transmission electron microscope. Specifically, the existence of a bismuth oxide phase can be confirmed by the presence of lattice fringes (atomic arrangement) of crystalline Bi ₂ O ₃ , and the existence of a glass phase can be confirmed by the existence of a structure peculiar to amorphous. The magnification of the transmission electron microscope is set, for example, at several hundred thousand times.

The aluminum/silver laminated electrode having the above structure is preferably arranged on the substrate constituting the solar cell element, and more preferably arranged on the side corresponding to the back surface of the solar cell element.
In the present disclosure, "on the substrate" includes a film formed on the surface of the substrate, such as a passivation film and a protective film for the passivation film.

The thickness (minimum thickness if the thickness is not uniform) of the first electrode containing aluminum may be, for example, in the range of 0.5 μm to 50.0 μm.
The thickness (minimum thickness if the thickness is not uniform) of the second electrode containing silver may range, for example, from 0.5 μm to 30.0 μm.

The aluminum/silver laminated electrode having the above structure can be produced, for example, using the electrode-forming composition described above.
An example of the structure of an aluminum/silver laminated electrode manufactured using the electrode-forming composition and a solar cell element including the same will be described with reference to FIG. However, the embodiment of the aluminum/silver laminated electrode is not limited to this.
In addition, the sizes of the members in each drawing are conceptual, and the relative relationship between the sizes of the members is not limited to this. Note that members having substantially the same functions are given the same reference numerals throughout the drawings, and redundant description may be omitted.
FIG. 1 is a schematic cross-sectional view of a back electrode of a solar cell element having a PERC structure produced using an electrode-forming composition. As shown in FIG. 1, a passivation film 18 and a protective film 19 (SiN _x ) are formed in this order on the surface of a semiconductor substrate 1, and an aluminum electrode (also referred to as an aluminum particle sintered portion) 5 and an aluminum electrode are formed thereon. /A silver laminated electrode 8 is formed.
The aluminum/silver laminated electrode 8 includes a portion where an aluminum electrode and a silver electrode (also referred to as a silver particle sintered portion) are laminated. For example, a silver particle sintered portion may be formed on the outermost surface of the aluminum/silver laminated electrode 8 . Moreover, the aluminum electrode 5 and the aluminum electrode constituting the aluminum/silver laminated electrode 8 may be formed at the same time.

(Manufacturing method of aluminum/silver laminated electrode)
There is no particular limitation on the method of producing the aluminum/silver laminated electrode using the electrode-forming composition.
For example, a step of forming an aluminum particle-containing film on a semiconductor substrate, a step of applying an electrode-forming composition onto the aluminum particle-containing film and drying if necessary, and a step of forming the aluminum particle-containing film and the electrode. and a step of heat-treating the composition for use in this order.

The aluminum particle-containing film may be formed on a semiconductor substrate on which a passivation film and a protective film (SiN _x ) are formed. Also, the aluminum particle-containing film may be formed by drying the aluminum electrode-forming composition that has been applied onto the semiconductor substrate. The semiconductor substrate may be a silicon (Si) substrate. When forming an aluminum particle-containing film on a semiconductor substrate using the composition for forming an aluminum electrode, the method for applying the composition for forming an aluminum electrode includes a screen printing method, an inkjet method, a dispenser method, and the like. screen printing method is preferable from the viewpoint of productivity. As drying conditions after application of the composition for forming an aluminum electrode, heat treatment conditions commonly used in the technical field can be applied.

Examples of the method for applying the electrode-forming composition onto the aluminum particle-containing film include a screen printing method, an inkjet method, a dispenser method, and the like, and the screen printing method is preferable from the viewpoint of productivity.

When the electrode-forming composition is applied onto the aluminum particle-containing film by screen printing, the electrode-forming composition is preferably in the form of a paste. The paste-like electrode-forming composition preferably has a viscosity in the range of 20 Pa·s to 1000 Pa·s. The viscosity of the electrode-forming composition is measured at 25° C. using a Brookfield HBT viscometer.

The amount of the electrode-forming composition to be applied to the aluminum particle-containing film can be appropriately selected according to the size of the electrode to be formed. For example, the amount of the electrode-forming composition applied can be 1.0 mg/cm ² to 20.0 mg/cm ² , preferably 2.0 mg/cm ² to 15.0 mg/cm ² . .

As the heat treatment conditions for forming the aluminum/silver laminated electrode using the electrode-forming composition, heat treatment conditions that are commonly used in the relevant technical field can be applied. As the heat treatment temperature, a range of 700° C. to 900° C., which is used when manufacturing a general crystalline silicon solar cell element, can be suitably used.
Also, the heat treatment time can be appropriately selected according to the heat treatment temperature, and can be, for example, 1 second to 20 seconds.

As the heat treatment device, any device capable of heating to the above temperature can be appropriately adopted, and examples thereof include infrared heating furnaces and tunnel furnaces. An infrared heating furnace is highly efficient because electric energy is applied to the heating material in the form of electromagnetic waves and converted into thermal energy, and rapid heating in a shorter time is possible. Furthermore, since there are few combustion products and non-contact heating, it is possible to suppress contamination of the generated electrodes. Since the tunnel furnace automatically and continuously transports the sample from the entrance to the exit for heat treatment, more uniform heat treatment is possible by dividing the furnace body and controlling the transport speed. From the viewpoint of the power generation performance of the solar cell element, heat treatment in a tunnel furnace is preferable.

A specific example of the method for manufacturing the aluminum/silver laminated electrode will be described below with reference to the drawings. However, the present disclosure is not limited to this. An example of a method of manufacturing a typical aluminum/silver laminated electrode is shown in FIGS. 2A-2C.

First, as shown in FIG. 2A, a paste-like aluminum electrode forming composition 2 is applied by screen printing to one surface of a semiconductor substrate 1 on which a passivation film 18 and a protective film (SiN _x ) 19 are formed. do. This is heated at a temperature of about 150° C. to remove the solvent in the aluminum electrode forming composition 2 . Thereby, as shown in FIG. 2B, the aluminum particle-containing film 3 is formed on the semiconductor substrate 1 on which the passivation film 18 and the protective film (SiN _x ) 19 are formed.
Next, the electrode-forming composition 4 is applied to a desired region on the aluminum particle-containing film 3, and is dried by heating at a temperature of about 150°C. When the electrode-forming composition 4 is in the form of a paste, it is applied by screen printing as in the case of the aluminum electrode-forming composition 2 . After that, it is heat-treated under the conditions described above. Thereby, as shown in FIG. 2C, the aluminum/silver laminated electrode 8 is formed on the semiconductor substrate 1 on which the passivation film 18 and the protective film (SiN _x ) 19 are formed.
The aluminum/silver layered electrode 8 has a silver particle sintered portion 7 disposed on the outermost surface, and a space between the silver particle sintered portion 7 and the semiconductor substrate 1 on which a passivation film 18 and a protective film (SiN _x ) 19 are formed. , an aluminum particle sintered portion/bismuth oxide phase mixed portion 6 is arranged.

FIG. 3 is an enlarged view of the portion where the aluminum/silver laminated electrode is formed in FIG. 2C. As shown in FIG. 3 , the aluminum particle sintered portion/bismuth oxide phase mixed portion 6 includes the aluminum particle sintered portion 5 and the bismuth oxide phase 9 filled in the voids of the aluminum particle sintered portion 5 . The aluminum particle sintered portion/bismuth oxide phase mixed portion 6 has such a configuration because, as described above, part or all of the bismuth-containing particles in the electrode-forming composition 4 are heat-treated to form an aluminum particle-containing film. This is for transitioning to 3.

The bismuth oxide phase 9 may be arranged so as to separate the silver particle sintered portion 7 and the aluminum particle sintered portion 5, and the aluminum particles in the aluminum particle sintered portion 5 and the silver particle sintered portion 7 may be partially formed. In this case, the bismuth oxide phase 9 is arranged so as to separate the silver particle sintered portion 7 and the aluminum particle sintered portion 5 to the extent that excessive mutual diffusion between the aluminum particles and the silver particles is suppressed. preferable.
In FIG. 3, the aluminum particle sintered portion/bismuth oxide phase mixed portion 6 corresponds to the first electrode containing aluminum, and the silver particle sintered portion 7 corresponds to the second electrode containing silver. The bismuth oxide phase 9 also includes a glass phase.

<Solar cell element>
A solar cell element of the present disclosure includes a semiconductor substrate, a passivation film provided on the semiconductor substrate, and an aluminum/silver laminated electrode comprising a heat-treated product of the electrode-forming composition of the present disclosure provided on the passivation film. and

If necessary, the solar cell element may include a protective film for protecting a passivation film provided on the semiconductor substrate. A specific example of the passivation film is an aluminum oxide film (AlO _x ). A specific example of the protective film is a silicon nitride film (SiN _x ).
The aluminum/silver laminated electrode of the solar cell element may be provided on the back surface of the semiconductor substrate. Moreover, the solar cell element may have a PERC structure.

A specific example of the configuration of the solar cell element will be described below with reference to the drawings, but the present disclosure is not limited to this. An example of a typical solar cell element is shown in FIGS. 4, 5A, 5B, 6A, 6B and 6C.

FIG. 4 is a schematic plan view of the light receiving surface side of the solar cell element. The light-receiving surface electrode 14 shown in FIG. 4 is generally formed using a silver electrode paste. Specifically, a silver electrode paste is applied in a desired pattern on the antireflection film 13, dried, and then heat treated at about 700° C. to 900° C. in the atmosphere to form the light receiving surface electrode 14.

FIG. 5A is a schematic plan view of the back surface of the solar cell element. An aluminum electrode 5 is formed on the entire back surface of the solar cell element shown in FIG. 5A. FIG. 5B is a schematic plan view when the aluminum finger electrodes 20 and the aluminum busbar electrodes 21 are formed on part of the back surface of the solar cell element.
After applying and drying the aluminum electrode-forming composition on the rear surface of the solar cell element, the electrode-forming composition of the present disclosure is applied in a desired pattern and dried. Next, this is heat-treated in the air at about 700° C. to 900° C. to form an aluminum/silver laminated electrode. The heat treatment may be performed together with the heat treatment for forming the light-receiving surface electrode 14 described above.

As shown in the schematic cross-sectional views of FIGS. 6A to 6C, an n ⁺ -type diffusion layer 12 is formed near the surface of one surface of the semiconductor substrate 1, and an output extraction electrode 14 and a reflector are formed on the n ⁺ -type diffusion layer 12. A protective film 13 is formed.

FIG. 6A is a cross section along A-A' in FIG. 5A. If the A-A' section does not cross the opening of the backside passivation film, the backside has the structure shown in FIG. 6A. FIG. 6B is a cross section along line B-B' in FIG. 5B. If the BB' section does not cross the opening of the backside passivation film, the backside has the structure shown in FIG. 6B. FIG. 6C is a cross section along line C-C' in FIG. 5B. When the C-C' cross section crosses the openings (aluminum finger electrodes 20) of the back surface passivation film, the back surface has the structure shown in FIG. 6C.

As shown in FIGS. 6A to 6C, on the light-receiving surface side, the glass particles contained in the silver electrode paste forming the light-receiving surface electrode 14 react (fire through) with the antireflection film 13 by heat treatment, and the light-receiving surface The electrode 14 and the n ⁺ -type diffusion layer 12 are electrically connected (ohmic contact).
On the back side, heat treatment causes the aluminum in the aluminum electrodes 5, the aluminum finger electrodes 20, or the aluminum bus bar electrodes 21 to diffuse into a portion of the back surface of the semiconductor substrate 1 (the portion where the back surface passivation film is removed by laser or the like). , p ⁺ -type diffusion layers 15 partially form an ohmic contact between the semiconductor substrate 1 and the aluminum electrode 5 .

The contents of the present disclosure will be described in more detail below using examples and comparative examples, but the scope of the present disclosure is not limited to the following examples.

In the following examples, the shape of the glass particles was observed and determined using a scanning electron microscope (Hitachi High-Technologies Corporation, TM-1000). The volume average particle diameter of the glass particles was calculated using a laser scattering diffraction method particle size distribution analyzer (Beckman Coulter, LS 13 320 type, measurement wavelength: 632 nm). The softening point of the glass particles was obtained from a differential thermal (DTA) curve measured using a simultaneous differential thermal/thermogravimetric analyzer (Shimadzu Corporation, DT-60H). Specifically, the softening point can be estimated from the endothermic part in the DTA curve.

(Preparation of boron-containing glass particles)
Silicon dioxide ( _SiO2 ) 1.6% by mass, boron oxide ₍ _B2O3 ) 13.4% by mass, bismuth oxide ₍ Bi2O3) 84.1% by mass and lithium oxide ₍ _Li2O ) 0.9% A boron-containing glass consisting of % by weight was obtained. The softening point of the obtained boron-containing glass was 440°C.
Using the obtained boron-containing glass, boron-containing glass particles having a volume average particle size of 1.1 μm were obtained. The shape of the particles was approximately spherical.
(Preparation of phosphorus-containing glass particles)
from 38.0% by weight phosphorus oxide ₍ P2O5), 57.0% by weight tin oxide (SnO), _3.5 % by weight zinc oxide (ZnO) and 1.5% by weight aluminum oxide ₍ _Al2O3 ) A phosphorus-containing glass was obtained. The obtained phosphorus-containing glass had a softening point of 340°C. Using phosphorus-containing glass, phosphorus-containing glass particles having a volume average particle size of 8.0 μm were obtained. The shape of the particles was approximately spherical.
(Preparation of vanadium-tellurium-containing glass particles)
Vanadium consisting of 13.2% by mass of zinc oxide (ZnO), 1.9% by mass of copper oxide (CuO), 35.6% by mass of vanadium oxide ₍ _V2O5 ) and 49.3% by mass of tellurium oxide ( _TeO2 ) - A tellurium-containing glass was obtained. The softening point of the resulting vanadium-tellurium-containing glass was 290°C. Vanadium-tellurium-containing glass was used to obtain vanadium-tellurium-containing glass particles having a volume average particle size of 1.4 μm. The shape of the particles was approximately spherical.

(Preparation of electrode-forming composition)
The components shown in Table 1 were blended in the amounts shown in Table 1, and mixed using a roll mill (BR-150HCV, Imex Co., Ltd.) to obtain pasty electrode-forming compositions of Examples 1 to 4 and Comparative Examples. prepared. Details of the components listed in Table 1 are as follows. The numerical values in Table 1 are parts by mass.

Ag: silver particles (volume average particle size: 0.6 μm, silver content: 99.9% by mass)
Bi: metal bismuth particles (volume average particle size: 1.5 μm, bismuth content: 99.5% by mass)
Bi ₂ O ₃ : Bismuth oxide particles (volume average particle size: 2.2 μm)
B glass: Boron-containing glass particles as described above V-Te glass: Vanadium-tellurium-containing glass particles as described above P glass: Phosphorus-containing glass particles as described above TPO: Terpineol Ethyl cellulose: Nisshin Kasei Co., Ltd., STD-10

Using the electrode-forming composition obtained above, a solar cell element was produced by the following method.
An n ⁺ -type diffusion layer, a texture and an antireflection (SiN _x ) film are formed on the light receiving surface, and aluminum oxide (AlO _x ) as a passivation film is formed on the surface opposite to the light receiving surface (hereinafter also referred to as “back surface”). A p-type silicon single crystal substrate having a thickness of 160 μm, on which a film and a protective film (SiN _x ) were formed in this order, was prepared and cut into a size of 158.75 mm×158.75 mm. Next, as shown in FIG. 5B, portions of the passivation film/protective film on the back surface were removed by laser at portions where aluminum finger electrodes were to be formed, exposing the silicon substrate. A composition for forming a silver electrode (PV20, manufactured by DuPont) containing silver particles and lead glass particles was applied to the light-receiving surface by screen printing so as to form an electrode pattern as shown in FIG. Actually, the number of the light-receiving surface output extraction electrodes 14 is nine. This was heated in a heated tunnel furnace (Despatch Co.) at a set temperature of 250° C. and a conveying speed of 240 inches/minute to remove the solvent by evaporation.

Subsequently, an aluminum electrode-forming composition (RX8401 by Ruxing) and the electrode-forming composition obtained above were applied to the back surface of the silicon substrate by screen printing to form an electrode pattern as shown in FIG. 5B. given the shape. In practice, the number of aluminum busbar electrodes 21 was set to nine, and the number of aluminum/silver laminated electrodes formed on each aluminum busbar electrode 21 was set to six.
Specifically, the composition for forming an aluminum electrode was printed in the shape of fine line patterns of the aluminum finger electrodes 20 and the aluminum busbar electrodes 21, and dried to form an aluminum particle-containing film. Thereafter, an electrode-forming composition was printed on the aluminum particle-containing film.
The positions where the aluminum finger electrodes were formed were aligned with the exposed portions of the silicon substrate. The conditions for printing the aluminum electrode-forming composition were adjusted so that the thickness of the aluminum electrode after heat treatment was 30 μm. The electrode-forming composition was printed using a pattern in which pad shapes each having a size of 1.6 mm×8.0 mm were arranged so that the coating amount was 8.0 mg/cm ² .
After printing the aluminum electrode-forming composition and the electrode-forming composition, respectively, they are heated in a tunnel furnace (Despatch) under the conditions of a set temperature of 250° C. and a conveying speed of 240 inches/minute to evaporate the solvent. Removed.

Subsequently, heat treatment was performed using a tunnel furnace (Despatch Co.) in an air atmosphere at a maximum temperature of 870° C. and a conveying speed of 240 inches/minute to form an aluminum/silver laminated electrode as a rear output extraction electrode. A formed solar cell element was produced.

- Observation of the surface of the back side electrode -
When the surface state of the aluminum/silver laminated electrode on the back side of the obtained solar cell element was visually observed, all the solar cell elements exhibited a silvery white color and were in a state capable of functioning as an electrode.

-PL contrast ratio-
The defect of the obtained solar cell element was mapped by the photoluminescence method and numerically processed to calculate the PL contrast ratio. Specifically, a PL image was photographed using an EL/PL image observation system (manufactured by Aites PVX100 and optional unit POPLI V2R) with the light-receiving surface side of the solar cell element as the upper surface. In the PL image, 28 arbitrarily selected positions of aluminum/silver laminated electrode formation and non-electrode formation were derived using image processing software (Developed by National Institutes of Health, ImageJ). The value obtained from the following formula (A) was taken as the PL contrast ratio of each solar cell element.
(Average value of shading values at 28 locations where aluminum/silver laminated electrodes are formed)/(Average value of shading values at 28 locations where electrodes are not formed) Formula (A)
The value of the PL contrast ratio obtained in the solar cell element of the comparative example was used as a reference (1.00), and the value of the PL contrast ratio obtained in the solar cell element of each example was calculated in the solar cell element of the comparative example. Table 1 shows the value (PL ratio) divided by the PL light-dark ratio.

As shown in Table 1, the PL ratio of the solar cell element of each example is improved with respect to the solar cell element of the comparative example. The results of the PL ratio suggest that the etching of the passivation layer provided on the back surface of the solar cell element of each example is suppressed compared to the solar cell element of the comparative example.

REFERENCE SIGNS LIST 1 semiconductor substrate 2 aluminum electrode-forming composition (paste) 3 aluminum particle-containing film 4 electrode-forming composition (before and after drying) 5 aluminum particle sintered portion, aluminum electrode 6 Aluminum particle sintered portion/bismuth oxide phase mixed portion 7 Silver particle sintered portion 8 Aluminum/silver laminated electrode 9 Bismuth oxide phase 12 n ⁺ type diffusion layer 13 Antireflection film 14 Light-receiving surface electrode and output extraction electrode, 15: p ⁺ -type diffusion layer, 18: passivation film, 19: protective film (SiN _x ), 20: aluminum finger electrode, 21: aluminum busbar electrode

The disclosure of Japanese Patent Application No. 2021-022877 filed on February 16, 2021 is incorporated herein by reference in its entirety.
All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated herein by reference.

Claims

comprising silver-containing particles, bismuth-containing particles, and glass particles;
The composition for forming an electrode, wherein the glass particles contain glass particles containing vanadium and tellurium.
The electrode-forming composition according to claim 1, wherein the content of vanadium oxide in the composition of the glass constituting the glass particles containing vanadium and tellurium is 20.0% by mass to 50.0% by mass.
3. The electrode formation according to claim 1, wherein the content of tellurium oxide in the composition of the glass constituting the glass particles containing vanadium and tellurium is 35.0% by mass to 65.0% by mass. composition.
The electrode formation according to any one of claims 1 to 3, wherein the proportion of the glass particles containing vanadium and tellurium in the total glass particles is 50.0% by mass to 100.0% by mass. composition.
The electrode-forming composition according to any one of claims 1 to 4, wherein the glass particles further contain phosphorus-containing glass particles.
The electrode-forming composition according to claim 5, wherein the content of phosphorus oxide is 20.0% by mass to 50.0% by mass in the composition of the glass constituting the glass particles containing phosphorus.
The electrode-forming composition according to claim 5 or 6, wherein the proportion of the phosphorus-containing glass particles in the entire glass particles is 40.0% by mass or less.
The electrode-forming composition according to any one of claims 1 to 7, wherein the bismuth-containing particles include at least one selected from the group consisting of metal bismuth particles, bismuth alloy particles and bismuth oxide particles.
The mass ratio (Bi/Ag ratio) of the content of the bismuth-containing particles to the content of the silver-containing particles is 0.30 to 1.40, according to any one of claims 1 to 8. A composition for forming an electrode.
The electrode according to any one of claims 1 to 9, wherein the mass ratio (Bi/G ratio) of the content of the bismuth-containing particles to the content of the glass particles is 0.5 to 15.0. Forming composition.
The electrode-forming composition according to any one of claims 1 to 10, wherein the content of the glass particles is 1.0% by mass to 15.0% by mass of the entire electrode-forming composition.
The electrode-forming composition according to any one of claims 1 to 11, further comprising at least one selected from the group consisting of solvents and resins.
The electrode-forming composition according to any one of claims 1 to 12, for forming an aluminum/silver laminated electrode.
Aluminum/silver comprising a semiconductor substrate, a passivation film provided on the semiconductor substrate, and a heat-treated product of the electrode-forming composition according to any one of claims 1 to 13 provided on the passivation film. A solar cell element having a laminated electrode.
An aluminum/silver laminated electrode comprising a heat-treated product of the electrode-forming composition according to any one of claims 1 to 13,
An aluminum/silver laminated electrode comprising a first electrode comprising aluminum and a second electrode comprising silver disposed over said first electrode, said first electrode further comprising a bismuth oxide phase and a glass phase.