WO2022181730A1

WO2022181730A1 - Solar cell element and solar cell

Info

Publication number: WO2022181730A1
Application number: PCT/JP2022/007754
Authority: WO
Inventors: 修一郎足立; 剛野尻; 剛早坂; 研耶守谷; クレイグエイチ．ピーターズ; ブライアンイー．ハーディン
Original assignee: 昭和電工マテリアルズ株式会社
Priority date: 2021-02-24
Filing date: 2022-02-24
Publication date: 2022-09-01
Also published as: JPWO2022181730A1

Abstract

Provided is a solar cell element comprising a semiconductor substrate, a passivation film provided upon the semiconductor substrate, and a layered aluminum/silver electrode provided upon the passivation film, wherein the layered aluminum/silver electrode includes a bismuth oxide–containing phase, and the surface concentration of silver measured through energy-dispersive X-ray spectroscopy at an accelerating voltage of 5 kV is 55.0 at% or higher.

Description

Solar cell element and solar cell

The present invention relates to solar cell elements and solar cells.

In recent years, there has been an increasing interest in environmental problems 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). AlO _X films produced by ALD or CVD are known to have large negative fixed charges, and PERC structure solar cell elements to which this is applied are known to exhibit high power generation performance.

In the PERC structure, the contact portion between the back electrode and the Si substrate is limited, so 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 PERC structure (including the bifacial-PERC and MBB-bifacial-PERC structures) described above, when forming the back electrode, generally an electrode-forming composition containing silver and an electrode-forming composition containing aluminum are used. are printed on predetermined regions of the substrate, dried, and heat-treated all at once. In the above structure, the wiring material cannot be directly bonded to the aluminum electrode because the aluminum electrode (Al ₂ O ₃ ) film formed on the surface of the aluminum electrode has poor wettability with the solder covering the wiring material.
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, in the rear surface electrode formed by the conventional process, a step (difference in thickness) between the aluminum electrode and the silver electrode as the rear surface output extraction electrode causes connection failure of the wiring material, and the solar cell cannot be used. Reliability 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 (burning) is generally 20 μm to 40 μm, and the thickness of the silver electrode as the rear output extraction electrode may be 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 the aluminum/silver laminated electrode is formed by the above-described method, the contact area between the aluminum electrode and the silver electrode is large, so interdiffusion between aluminum and silver may proceed excessively during heat treatment (firing). As a result, there is a possibility that the function (for example, the connectivity of the wiring material) as the back surface output extraction electrode will be impaired.

In view of the above circumstances, one embodiment of the present disclosure provides a solar cell element and a solar cell with a PERC structure that has excellent connectivity of wiring materials to the back electrode.

Means for carrying out the above tasks include the following embodiments.
<1> A semiconductor substrate, a passivation film provided on the semiconductor substrate, and an aluminum/silver laminated electrode provided on the passivation film,
A solar cell element, wherein the aluminum/silver laminated electrode contains a bismuth oxide-containing phase and has a surface silver concentration of 55.0 atomic % or more as measured by energy dispersive X-ray analysis at an accelerating voltage of 5 kV.
<2> The solar cell element according to <1>, wherein the aluminum/silver laminated electrode has a silver particle sintered portion on its surface.
<3> The solar cell element according to <1> or <2>, wherein the bismuth oxide-containing phase contains boron.
<4> The solar cell element according to any one of <1> to <3>, wherein the bismuth oxide-containing phase contains phosphorus.
<5> The solar cell according to any one of <1> to <4>, wherein the aluminum/silver laminated electrode comprises a heat-treated electrode-forming composition containing silver-containing particles and bismuth-containing particles. element.
<6> The solar cell according to <5>, wherein the bismuth-containing particles include at least one selected from the group consisting of bismuth particles, bismuth alloy particles having a bismuth content of 40.0% by mass or more, and bismuth oxide particles. element.
<7> The solar cell element according to <5> or <6>, wherein the electrode-forming composition contains glass particles.
<8> The solar cell element according to <7>, wherein the glass particles contain boron.
<9> The solar cell element according to <7> or <8>, wherein the glass particles contain phosphorus.
<10> A solar cell comprising the solar cell element according to any one of <1> to <9> and a wiring material provided on the aluminum/silver laminated electrode of the solar cell element.

According to one embodiment of the present disclosure, a solar cell element and a solar cell with a PERC structure that have excellent connectivity of wiring materials to the back electrode are provided.

FIG. 4 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 according to one embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the manufacturing method of the aluminum/silver laminated electrode which concerns on one Embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the manufacturing method of the aluminum/silver laminated electrode which concerns on one Embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the manufacturing method of the aluminum/silver laminated electrode which concerns on one Embodiment. 1 is a schematic cross-sectional view of an aluminum/silver laminated electrode according to one embodiment; FIG. 1 is a schematic plan view showing an example of a light receiving surface of a solar cell element according to one embodiment; FIG. 1 is a schematic plan view showing an example of the back surface of a solar cell element according to one embodiment; FIG. 1 is a schematic plan view showing an example of the back surface of a solar cell element according to one embodiment; FIG. FIG. 5B is a schematic cross-sectional view (cut along line AA' in FIG. 5A) showing an example of a solar cell element according to an embodiment. FIG. 5B is a schematic cross-sectional view (cut along BB' in FIG. 5B) showing an example of a solar cell element according to an embodiment. FIG. 5B is a schematic cross-sectional view (a cross-sectional view taken along line CC′ in FIG. 5B) showing an example of a solar cell element according to an embodiment. It is an image taken with a scanning electron microscope (SEM), showing a surface texture of an aluminum/silver laminated electrode according to an example.

Hereinafter, embodiments of the present disclosure will be described in detail. However, the present invention is not limited to the following embodiments. In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the purpose of the process is achieved.
In the present disclosure, a numerical range indicated using "to" indicates a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, when there are multiple substances corresponding to each component in the composition, the content of each component in the composition is the total of the multiple substances present in the composition unless otherwise specified. means quantity.
In this disclosure, the term "laminate" refers to stacking two or more layers.
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.
In the drawings, the same reference numerals are given to the same components.

In the present disclosure, "solar cell element" means one having a semiconductor substrate formed with a pn junction and an electrode formed on the semiconductor substrate. In the present disclosure, “a solar cell element having a PERC structure” means a solar cell element having a passivation film on the back surface thereof.

<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 provided on the passivation film, wherein the aluminum/silver laminated electrode is oxidized. The solar cell element contains a bismuth-containing phase and has a surface silver concentration of 55.0 atomic % or more as measured by energy dispersive X-ray analysis at an acceleration voltage of 5 kV.

In the solar cell element of the present disclosure, the aluminum/silver laminated electrode contains a bismuth oxide-containing phase. In the aluminum/silver laminated electrode having such a structure, the silver particle sintered portion is sufficiently formed on the surface. The reason is considered as follows.

In the case of forming an aluminum/silver laminated electrode by performing heat treatment in a state in which a layer is formed using an electrode-forming composition containing silver particles on a layer formed using an electrode-forming composition containing aluminum particles, Mutual diffusion of aluminum and silver occurs at the interface between the aluminum electrode (aluminum sintered portion) and the silver electrode (silver particle sintered portion) formed by heat treatment, and part of the aluminum migrates to the silver electrode side.
Interdiffusion between aluminum and silver contributes to the formation of a conductive path between the aluminum electrode and the silver electrode, while excessive interdiffusion reduces the silver concentration on the surface of the silver electrode, resulting in the sintering of silver particles. It can be a cause of difficulty in forming.
When the aluminum/silver laminated electrode contains the bismuth oxide-containing phase, the bismuth oxide-containing phase develops the property of suppressing excessive interdiffusion between silver and aluminum (hereinafter also referred to as diffusion barrier property). For this reason, the aluminum concentration in the silver electrode is kept low, and an aluminum/silver laminated electrode in which silver particle sintered portions are sufficiently formed on the surface can be obtained.

Furthermore, in the solar cell element of the present disclosure, the silver concentration on the surface of the aluminum/silver laminated electrode is 55.0 atomic % or more. When the silver concentration on the surface of the aluminum/silver laminated electrode is 55.0 atomic % or more, the area ratio of the silver particle sintered portion on the surface of the aluminum/silver laminated electrode is increased, and the connectivity of the wiring material is improved. . Specifically, the adhesion of the wiring material to the aluminum/silver laminated electrode is improved, and the contact resistance between the wiring material and the aluminum/silver laminated electrode is reduced.

From the viewpoint of the connection strength of the wiring material, the silver concentration on the surface of the aluminum/silver laminated electrode is preferably 57.0 atomic % or more, more preferably 59.0 atomic % or more, and more preferably 60.0 atomic % or more. It is more preferably at least atomic %.
The upper limit of the silver concentration on the surface of the aluminum/silver laminated electrode is not particularly limited, but from the viewpoint of the formation process of the aluminum/silver laminated electrode, economic efficiency, etc., it may be 80.0 atomic % or less, and may be 75.0 atomic % or less. It may be atomic % or less, or may be 70.0 atomic % or less.

In the present disclosure, the silver concentration on the surface of the aluminum/silver laminate electrode is measured using Energy Dispersive X-ray Analysis (EDX). The EDX measurement conditions are as follows. The measurement is performed using, for example, a Schottky scanning electron microscope "SU5000, Hitachi High-Technologies Corporation" and an attached EDX detector.
・Acceleration voltage: 5 kV
・Measurement magnification: 100 times ・Analysis area: 1250 μm×860 μm
・Analysis mode: Analyzer mode

The aluminum/silver laminated electrode containing the bismuth oxide-containing phase can be formed using, for example, an electrode-forming composition containing bismuth.
In addition to the diffusion barrier effect described above, the bismuth oxide-containing phase contained in the aluminum/silver laminated electrode improves the strength of the electrode by filling the gaps between the aluminum particles contained in the aluminum electrode, and improves the adhesion to the semiconductor substrate. It is considered to be effective.

The bismuth oxide-containing phase contained in the aluminum/silver laminated electrode may contain an amorphous phase. When the bismuth oxide-containing phase contains an amorphous phase, the phenomenon that bismuth oxide reaching the passivation film on the semiconductor substrate etches the passivation film tends to be suppressed. In addition, there is a tendency for the adhesion of the aluminum/silver laminated electrode to the semiconductor substrate to improve.

An aluminum/silver laminated electrode in which the bismuth oxide-containing phase contains an amorphous phase can be formed, for example, using an electrode-forming composition containing glass particles. When the electrode-forming composition containing glass particles is heat-treated, the melt of the glass particles melts into the bismuth oxide-containing phase, forming a state in which the bismuth oxide-containing phase contains an amorphous phase.

Whether or not the aluminum/silver laminated electrode contains a bismuth oxide phase can be confirmed by performing energy dispersive X-ray analysis (EDX) on the cross section of the aluminum/silver laminated electrode. Confirmation is performed, for example, under the conditions described in Examples.

Whether or not the bismuth oxide-containing phase of the aluminum/silver laminated electrode contains an amorphous phase can be confirmed using a transmission electron microscope (TEM). Specifically, when the bismuth oxide-containing phase is observed at a high magnification, the existence of the amorphous phase can be confirmed by observing whether or not a structure peculiar to amorphous without crystal lattice fringes is observed. Observation is performed, for example, under the conditions described in Examples.

The bismuth oxide-containing phase contained in the aluminum/silver laminate electrode may contain boron.
When the bismuth oxide-containing phase contains boron, the power generation performance of the solar cell element tends to be maintained well. The reason for this is not necessarily clear, but is considered as follows.
The bismuth oxide contained in the bismuth oxide-containing phase may dissolve the SiN _X film, which is the protective film of the passivation film, and reduce the passivation effect of the passivation film. When the bismuth oxide-containing phase contains boron, the bismuth oxide concentration in the bismuth oxide-containing phase near the semiconductor substrate decreases, thereby suppressing dissolution of the SiN _X film. As a result, it is considered that the power generation performance of the solar cell element is favorably maintained.

The bismuth oxide-containing phase contained in the aluminum/silver laminate electrode may contain phosphorus.
When the bismuth oxide-containing phase contains phosphorus, the reliability of the aluminum/silver laminated electrode tends to improve in a high-temperature, high-humidity environment. The reason for this is not necessarily clear, but is considered as follows.
When the aluminum/silver laminated electrode is placed in a high-temperature and high-humidity environment, part of the bismuth oxide contained in the bismuth oxide-containing phase is reduced to metallic bismuth at the interface between the aluminum electrode and the silver electrode, causing a volume change. Cracks or the like are generated at the interface between the aluminum electrode and the silver electrode, which causes deterioration of the reliability of the electrode. When the bismuth oxide-containing phase contains phosphorus, the phosphorus acts to suppress the reduction of bismuth oxide. As a result, it is believed that the state of the interface between the aluminum electrode and the silver electrode is maintained in good condition, improving the reliability in a high-temperature and high-humidity environment.

An aluminum/silver laminated electrode in which the bismuth oxide-containing phase contains boron or phosphorus can be formed, for example, using an electrode-forming composition containing glass particles containing boron or phosphorus.

The concentration of atoms other than silver on the surface of the aluminum/silver laminated electrode is not particularly limited. For example, the concentrations of bismuth, aluminum, oxygen, silicon, boron and phosphorus may each be within the following ranges. The concentration of atoms other than silver is measured in the same manner as the silver concentration.

Bismuth: 2.0 atomic % to 10.0 atomic %
Aluminum: 2.0 atomic % to 10.0 atomic %
Oxygen: 10.0 atomic % to 35.0 atomic %
Silicon: 0.0 atomic % to 5.0 atomic %
Boron: 0.0 atomic % to 1.0 atomic %
Phosphorus: 0.0 atomic % to 1.0 atomic %

The thickness of the aluminum/silver laminated electrode is not particularly limited. For example, the thickness (minimum thickness if the thickness is not uniform) of the aluminum/silver laminated electrode may be selected from the range of 1.0 μm to 80.0 μm.
The thickness of the aluminum electrode in the aluminum/silver laminated electrode is not particularly limited. For example, the thickness of the aluminum electrode (minimum thickness if the thickness is not constant) may be selected from the range of 0.5 μm to 50.0 μm.
The thickness of the silver electrode in the aluminum/silver laminated electrode is not particularly limited. For example, the thickness of the silver electrode (minimum thickness if the thickness is not constant) may be selected from the range of 0.5 μm to 30.0 μm.

A protective film for protecting the passivation film may be formed on the 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 ).

An example of the structure of an aluminum/silver laminated electrode and a solar cell element including the same will be described with reference to FIG.
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 thereon an aluminum electrode (also called an aluminum particle sintered portion) 5 and an aluminum /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 . The aluminum electrode 5 and the aluminum electrode forming the aluminum/silver laminated electrode 8 may be formed at the same time.

The aluminum/silver laminated electrode may include a heat-treated electrode-forming composition containing silver-containing particles and bismuth-containing particles.
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 semiconductor substrate, dried as necessary, and then heat-treated to form an electrode. The silver-containing particles contained in the composition for use are sintered to form a silver electrode. On the other hand, the aluminum particles contained in the aluminum particle-containing film are sintered to form an aluminum electrode. As a result, an aluminum/silver laminated electrode in which the silver electrode is arranged on the aluminum electrode is formed.

The bismuth-containing particles contained in the electrode-forming composition turn into a bismuth oxide-containing phase by heat treatment, exhibiting a property (also referred to as a diffusion barrier property) of suppressing interdiffusion at the interface between the silver electrode and the aluminum electrode.
At this time, part of the bismuth-containing particles contained in the electrode-forming composition migrates to the aluminum particle-containing film to form a bismuth oxide-containing phase between the aluminum particles or between the aluminum particles and the semiconductor substrate. This improves the bulk strength of the formed aluminum electrode and the adhesion to the substrate.

(Silver-containing particles)
The silver-containing particles contained in the electrode-forming composition are not particularly limited as long as they contain silver. Among them, at least one selected from silver particles and silver alloy particles is preferable, and at least one selected from silver particles and silver alloy particles having a silver content of 50.0% by mass or more is preferable. The silver-containing particles contained in the electrode-forming composition may be of one type or two or more types.

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 size of the silver-containing particles is not particularly limited, but the particle size (volume average particle size, hereinafter “D50% ”) is preferably 0.1 μm 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 bismuth-containing particles contained in the electrode-forming composition are not particularly limited as long as they contain bismuth. Among them, it is preferably at least one selected from metal bismuth particles, bismuth alloy particles and bismuth oxide particles, and is selected from metal bismuth particles, bismuth alloy particles having a bismuth content of 40.0% by mass or more, and bismuth oxide particles. It is preferable that it is at least one kind. The bismuth-containing particles contained in the electrode-forming composition may be of one type or two or more types.

In the present disclosure, when the bismuth-containing particles are vitreous (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/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, from the viewpoint of the formation of the bismuth oxide-containing phase and the aluminum/silver barrier property, the content of the bismuth-containing particles is 3. It can be 0% by mass or less, 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-containing 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 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. It is more preferably 0.35 to 1.30, even more preferably 0.40 to 1.20, even more 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, the silver concentration on the surface of the aluminum/silver laminated electrode is sufficiently ensured, and the connection strength (solder wettability) of the connection material tends to be maintained satisfactorily. .

(glass particles)
The electrode-forming composition may contain glass particles. When the electrode-forming composition contains glass particles, the glass particles melted by the heat treatment are mixed with bismuth oxide to form a state in which the bismuth oxide-containing phase contains an amorphous phase.

The electrode-forming composition may contain glass particles containing boron (hereinafter also referred to as boron-containing glass particles). When the electrode-forming composition contains boron-containing glass, it is possible to form an aluminum/silver laminated electrode in which the bismuth oxide-containing phase contains an amorphous phase and contains boron.

Glass containing boron includes glass particles containing boron oxide (B ₂ O ₃ ), more preferably borate glass.
In the present disclosure, borate glass means a glass containing boron oxide ₍ _B2O3 ) as a network-forming oxide.

As for the composition of the glass that constitutes the boron-containing glass particles, from the viewpoint of the function of the glass, the content of boron oxide as an oxide is preferably 3.0% by mass or more, preferably 5.0% by mass. It is more preferably 10.0% by mass or more, and more preferably 10.0% by mass or more. The content of boron oxide is preferably 25.0% by mass or less, more preferably 20.0% by mass or less, and even more preferably 15.0% by mass or less.

The boron-containing glass particles may contain boron oxide and oxides other than boron oxide.
Examples of oxides other than boron oxide contained in the glass constituting the boron-containing glass particles include silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), phosphorus oxide (P ₂ O ₅ ), vanadium oxide ( _V2O5 ), 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 (GeO ₂ ), tellurium oxide (TeO ₂ ), lutetium oxide (Lu ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ), copper oxide (CuO), iron oxide (Fe ₂ O ₃ ), silver oxide (AgO) and manganese oxide (MnO).
Preferably, the boron-containing glass particles do not contain phosphorus oxide or contain phosphorus oxide less than boron oxide.

The boron-containing glass particles preferably contain at least one selected from silicon oxide, aluminum oxide, zinc oxide, bismuth oxide, copper oxide and lithium oxide, more preferably bismuth oxide, and bismuth-containing borate glass. (B ₂ O ₃ -Bi ₂ O ₃ system) and the like are preferred examples. A glass with such a composition has a low softening point, and tends to further improve the adhesion of the electrode to the substrate after heat treatment.

When the boron-containing glass particles contain bismuth oxide, the content of bismuth oxide is preferably 50.0% by mass or more, more preferably 60.0% by mass or more, and 70.0% by mass or more. is more preferable. The content of bismuth oxide is preferably 95.0% by mass or less, more preferably 90.0% by mass or less, and even more preferably 85.0% by mass or less.

The electrode-forming composition may contain phosphorus-containing glass particles (hereinafter also referred to as phosphorus-containing glass particles). By including phosphorus-containing glass in the electrode-forming composition, it is possible to form an aluminum/silver laminated electrode in which the bismuth oxide-containing phase contains an amorphous phase and contains phosphorus.

Phosphorus-containing glasses include glass particles containing phosphorus oxide (P ₂ O ₅ ), and phosphate glasses are preferred.
Phosphate glass in the present disclosure means glass containing phosphorus oxide ₍ P2O5) as a network _- forming oxide.

As for the composition of the glass that constitutes the phosphorus-containing glass particles, the content of phosphorus oxide is preferably 20.0% by mass or more, more preferably 30.0% by mass or more, from the viewpoint of the functionality of the glass. is more preferable, and 35.0% by mass or more is even more preferable. The content of phosphorus oxide (P ₂ O ₅ ) is preferably 50.0% by mass or less, more preferably 45.0% by mass or less, and further preferably 40.0% by mass or less. preferable.

The phosphorus-containing glass particles may contain phosphorus oxide and oxides other than phosphorus oxide.
Examples of oxides other than phosphorus oxide contained in the glass constituting the phosphorus-containing glass particles include the oxides exemplified as the oxides that may be contained in the glass constituting the boron-containing glass particles.
Preferably, the phosphorus-containing glass particles do not contain boron oxide or contain less boron oxide than phosphorus oxide.

The phosphorus-containing glass particles preferably contain at least one selected from vanadium oxide, aluminum oxide, tin oxide and zinc oxide, more preferably tin oxide, and tin-containing phosphate glass (P ₂ O ₅ - SnO-based) and the like are preferred examples. 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 phosphorus-containing glass particles contain tin oxide, the content of tin oxide is preferably 20.0% by mass or more, more preferably 30.0% by mass or more, and 40.0% by mass or more. is more preferable. The tin oxide content is preferably 80.0% by mass or less, more preferably 70.0% by mass or less, and even more preferably 60.0% by mass or less.

From the viewpoint of achieving both improved reliability and maintenance of power generation performance in a high-temperature and high-humidity environment, the electrode-forming composition preferably contains boron-containing glass particles and phosphorus-containing glass particles.

When the electrode-forming composition contains boron-containing glass particles and phosphorus-containing glass particles, the content of the phosphorus-containing glass particles with respect to the sum of the boron-containing glass particles and the phosphorus-containing glass particles is 3.0% by mass to 50.0% by mass. % by mass is preferable, 3.5% by mass to 45.0% by mass is more preferable, and 4.0% by mass to 40.0% by mass is even more preferable.
By setting the content of the phosphorus-containing glass particles to 3.0% by mass or more with respect to the total of the boron-containing glass particles and the phosphorus-containing glass particles, the reliability of the aluminum/silver laminated electrode in a high-temperature and high-humidity environment is more effective. tend to improve. Further, by setting the content of the phosphorus-containing glass particles to 50.0% by mass or less, the dissolution of the SiN _X film due to the bismuth oxide-containing phase is more effectively suppressed, and the power generation performance is maintained satisfactorily.

The glass particles contained in the electrode-forming composition may be of one type or two or more types.
When the electrode-forming composition contains two or more types of glass particles, all of the glass particles may contain phosphorus, or at least one of the glass particles may contain phosphorus.

When forming the aluminum/silver laminated electrode on the protective film (SiN _x ) of the passivation 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.

Although the softening point of the glass particles is not particularly limited, it is preferably 650°C or lower, more preferably 500°C or lower. The softening point of glass particles is measured by conventional methods using a thermomechanical analyzer (TMA).

The particle size of the glass particles is not particularly limited, but the volume average particle size is preferably 0.2 μm to 10.0 μm, more preferably 0.5 μm to 8.0 μm, more preferably 2.0 μm to 5.0 μm. 0 μm is even more preferable.
When the volume average particle size of the glass particles is 0.2 μm or more, the workability during the production of the electrode-forming composition is improved. When the volume average particle diameter of the glass particles is 10 µm or less, the dispersibility of the glass particles in the electrode-forming composition is improved, and the uniformity of the composition of the aluminum/silver laminated electrode is also improved.
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 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, it is preferably substantially spherical, flat, or plate-like.

The content of the glass particles contained in the electrode-forming composition (when the glass particles containing boron or phosphorus and the glass particles not containing boron or phosphorus are included, the total content) is the total content of the electrode-forming composition. It is preferably 3.0% by mass to 15.0% by mass, more preferably 3.5% by mass to 14.0% by mass, and 4.0% by mass to 12.0% by mass is more preferred.
By setting the content of the glass particles to 3.0% 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 is sufficiently ensured, and the connection strength (solder wettability) of the connection material tends to be maintained satisfactorily. .

The 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. is 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-containing phase tends to be effectively exhibited. Also, by setting the Bi/G ratio to 15.0 or less, there is a tendency to effectively improve reliability in a high-temperature and high-humidity environment and maintain good battery performance.

(molybdenum-containing particles)
The electrode-forming composition may contain molybdenum-containing particles. Molybdenum contained in the molybdenum-containing particles reacts with the aluminum oxide (Al ₂ O ₃ ) film formed on the surface of the aluminum electrode during the heat treatment. At this time, part of the aluminum oxide film is destroyed, and the molten aluminum inside flows out of the particles, thereby promoting interdiffusion between aluminum and silver.
As a result, a good conductive path is formed between the aluminum electrode and the silver electrode, and the resistance value of the aluminum/silver laminated electrode is reduced. In addition, excessive generation of the bismuth oxide phase between the silver electrode and the aluminum electrode is suppressed, improving reliability in a high-temperature and high-humidity environment.

The molybdenum-containing particles are not particularly limited as long as they contain molybdenum. In the present disclosure, when the molybdenum-containing particles are vitreous (glass particles containing molybdenum), they are not regarded as molybdenum-containing particles.

The content of molybdenum in the molybdenum-containing particles is not particularly limited. For example, the content of molybdenum may be 70.0% by mass or more, 80.0% by mass or more, or 90.0% by mass or more of the entire particles.

Although the particle size of the molybdenum-containing particles is not particularly limited, the volume average particle size 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 molybdenum-containing particles is 0.1 μm or more, the reaction between molybdenum and the aluminum oxide film can be effectively promoted. When the particle diameter of the molybdenum-containing particles is 50.0 μm or less, the surface silver concentration of the aluminum/silver laminated electrode after heat treatment can be kept high.
The volume average particle size of the molybdenum-containing particles is measured in the same manner as the volume average particle size of the silver-containing particles.

The shape of the molybdenum-containing particles is not particularly limited, and may be approximately spherical, flat, block-shaped, plate-shaped, scale-shaped, or the like.

The content of molybdenum-containing particles contained in the electrode-forming composition is preferably 0.1% by mass to 5.0% by mass, more preferably 0.2% by mass to 2.0% by mass, based on the total electrode-forming composition. %, more preferably 0.5 mass % to 1.0 mass %.
By setting the content of the molybdenum-containing particles to 0.1% by mass or more, the reaction between the molybdenum and the aluminum oxide film can be effectively promoted. By setting the content of the molybdenum-containing particles to 5.0% by mass or less, the surface silver concentration of the aluminum/silver laminated electrode after heat treatment can be kept high.

(solvent and resin)
The electrode-forming composition may contain at least one of a solvent and a resin.
By including at least one of a solvent and a resin in the electrode-forming composition, the liquid properties (viscosity, surface tension, etc.) of the electrode-forming composition are adjusted within a range suitable for the application method when applied to a substrate or the like. can do.
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, Alcohol solvents such as 1-butanol and diacetone alcohol, 2,2,4-trimethyl-1,3-pentanediol monoacetate, 2,2,4-trimethyl-1,3-pentanediol monopropionate, 2,2 Ester solvents of polyhydric alcohols such as ,4-trimethyl-1,3-pentanediol monobutyrate, ethylene glycol monobutyl ether acetate and diethylene glycol monobutyl ether acetate, polyhydric alcohols such as butyl cellosolve, diethylene glycol monobutyl ether and diethylene glycol diethyl ether , terpineols such as α-terpineol, α-terpinene, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, carvone, ocimene, and terpene solvents such as phellandrene.

The solvent is selected from the group consisting of a polyhydric alcohol ester solvent, a terpene solvent, and a polyhydric alcohol ether solvent, from the viewpoint of imparting properties (e.g., coatability or printability) of the electrode-forming composition. It preferably contains at least one, 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, so that the electrode-forming composition is not burned and remains as a foreign substance during the heat treatment. tend to be able to form electrodes.

The weight-average molecular weight of the resin 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) (Hitachi Chemical 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 at least one of a solvent and a resin, the total content can be selected depending on the desired liquid properties of the electrode-forming composition, the types of the solvent and 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 at least one of a solvent and a resin, the content ratio of the solvent and the resin is appropriately determined according to the types of the solvent and resin used so that the electrode-forming composition has desired liquid properties. can be selected.

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 or more and 97.0% by mass or less, more preferably 45.0% by mass or more and 80.0% by mass or less, of the entire electrode-forming composition. , 50.0% by mass or more and 70.0% by mass or less.

(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, and optionally glass particles and other components. Dispersion and kneading methods are not particularly limited, and can be applied by selecting from commonly used methods.

(Manufacturing method of aluminum/silver laminated electrode)
A method for producing an aluminum/silver laminated electrode using the electrode-forming composition is not particularly limited.
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 applied to the aluminum particle-containing film may be adjusted 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 . .
From the viewpoint of sufficiently forming silver particle sintered portions on the surface, the amount of the electrode-forming composition applied to the aluminum particle-containing film is preferably 5.0 mg/cm ² or more.

The heat treatment for forming the aluminum/silver laminated electrode using the electrode-forming composition can be carried out under the conditions commonly used in the technical field. The heat treatment temperature may be in the range of 700° C. to 900° C., which is used when manufacturing a general crystalline silicon solar cell element. The heat treatment time can be adjusted 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-containing 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-containing phase mixed portion 6 includes the aluminum particle sintered portion 5 and the bismuth oxide-containing phase 9 filled in the voids of the aluminum particle sintered portion 5. include. The aluminum particle sintered portion/bismuth oxide-containing 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 contain aluminum particles. This is because it migrates to the membrane 3 .

The bismuth oxide-containing 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-containing 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. is preferred.

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, silver electrode paste is applied on the antireflection film 13 in a desired pattern, dried, and then heat-treated at about 700° C. to 900° C. in the atmosphere.

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 to the rear surface of the solar cell element, the electrode-forming composition 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 line AA' in FIG. 5A. If the AA' 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 BB' 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-sectional view taken along line CC' in FIG. 5B. When the CC' 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 of the solar cell element, 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. Thus, the light-receiving surface electrode 14 and the n ⁺ -type diffusion layer 12 are electrically connected (ohmic contact).
On the back side of the solar cell element, the heat treatment causes the aluminum in the aluminum electrodes 5, the aluminum finger electrodes 20, or the aluminum bus bar electrodes 21 to be part of the back side of the semiconductor substrate 1 (the part where the back side passivation film is removed by laser or the like). An ohmic contact is partially formed between the semiconductor substrate 1 and the aluminum electrode 5 by diffusing to form the p ⁺ -type diffusion layer 15 .

<Solar cell>
A solar cell according to an embodiment of the present disclosure is a solar cell having the solar cell element described above and a wiring material provided on the aluminum/silver laminated electrode of the solar cell element.

In the present disclosure, the term “solar cell” refers to a structure in which a wiring material such as a tab wire is provided on the electrodes of a solar cell element, and a plurality of solar cell elements are connected via the wiring material as necessary, and a sealing resin or the like is used. means a state sealed with
The solar cell of the present disclosure includes at least one solar cell element, and may be configured by arranging a wiring material on the electrode of the solar cell element. If necessary, the solar cell may be configured by connecting a plurality of solar cell elements via a wiring material and further sealing with a sealing material.
The types of wiring material and sealing material are not particularly limited, and can be selected from those commonly used in the industry.

Hereinafter, the present disclosure will be described in more detail using examples and comparative examples, but the present disclosure is not limited to the following examples. be.

In the following examples, the shape of the glass particles was observed and determined using a scanning electron microscope (Hitachi High-Technologies Corporation, Model TM-1000). The volume average particle diameter (D50%) of the glass particles was calculated using a laser scattering diffraction method particle size distribution analyzer (Beckman Coulter, Inc., LS 13 320 type) at a measurement wavelength of 632 nm. The softening point of the glass particles was obtained from a differential thermal (DTA) curve obtained 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.

<Example 1>
(a) Preparation of electrode-forming composition 1 Silicon dioxide (SiO ₂ ) 1.3% by mass, boron oxide (B ₂ O ₃ ) 6.0% by mass, bismuth oxide (Bi ₂ O ₃ ) 75.0% by mass , 13.5% by mass of zinc oxide (ZnO) and 4.2% by mass of copper oxide (CuO) to obtain a borate glass (hereinafter sometimes abbreviated as “GB01”). The softening point of the obtained glass GB01 was 380°C.
Using the obtained glass GB01, glass GB01 particles having a particle size (D50%) of 3.9 μm were obtained. The shape of the glass GB01 particles was approximately spherical.

A pasty electrode-forming composition 1 was prepared by mixing the following materials using a roll mill (BR-150HCV, Imex Co., Ltd.).

Silver particles (Ag; D50% is 0.6 μm, silver content is 99.9% by mass): 34.8 parts by mass Metal bismuth particles (Bi; D50% is 2.5 μm, bismuth content is 99.5% by mass ) 22.7 parts by mass Glass GB01 particles: 6.5 parts by mass Terpineol (TPO): 30.9 parts by mass Ethyl cellulose (EC; Nisshin Kasei Co., Ltd., STD-10): 5.1 parts by mass

(b) Fabrication of solar cell element 1 An n ⁺ -type diffusion layer, a texture, and an antireflection film (SiN _x ) are formed in this order on the light receiving surface, and 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 an aluminum oxide film (AlO _x ) as a passivation 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. rice field. 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 is applied on the light-receiving surface so as to form an electrode pattern as shown in FIG. (the number of lines was set to 9)) was applied by screen printing. This was heated in a sintering furnace (tunnel furnace manufactured by Despatch Co.) at a set temperature of 250° C. and a conveying speed of 240 inches/minute to remove the solvent by evaporation.

Subsequently, on the back side of the silicon substrate, an aluminum electrode-forming composition (RX8401, manufactured by Ruxing) and the electrode-forming composition 1 obtained above were applied in this order by screen printing to obtain a composition as shown in FIG. 5B. It was applied to the shape of an electrode pattern (actually, the number of aluminum busbar electrodes 21 was 9, and the number of aluminum/silver laminated electrodes 21 was 6 for each aluminum busbar electrode 21).
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. After that, the electrode-forming composition 1 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 composition for forming an aluminum electrode were adjusted so that the thickness of the aluminum electrode after heat treatment was 30 μm. The electrode-forming composition 1 was printed using a pattern in which pad shapes each having a size of 1.6 mm×8.0 mm were arranged, and the coating amount was 8.0 mg/cm ² .
After printing the aluminum electrode-forming composition and the electrode-forming composition 1, respectively, they were heated in a firing furnace (a tunnel furnace manufactured by Despatch) at a set temperature of 250° C. and a conveying speed of 240 inches/minute. , the solvent was removed by evaporation.

Subsequently, using a firing furnace (tunnel furnace manufactured by Despatch Co.), heat treatment was performed under the conditions of a maximum temperature of 870°C and a conveying speed of 240 inches/minute in an air atmosphere, and the desired electrode was formed. A battery element 1 was produced.

<Example 2>
Silicon dioxide (SiO ₂ ) 1.6% by mass, boron oxide (B ₂ O ₃ ) 13.4% by mass, bismuth oxide particles (Bi ₂ O ₃ ) 84.1% by mass and lithium oxide (Li ₂ O) 0.2% by mass. A borate glass containing 9% by mass (hereinafter sometimes abbreviated as “GB02”) was obtained. The softening point of the resulting glass GB02 was 440°C.
Using the obtained glass GB02, glass GB02 particles having a volume average particle size (D50%) of 1.1 μm were obtained. The shape of the glass GB02 particles was approximately spherical.

A pasty electrode-forming composition 2 was prepared by mixing the following materials using a roll mill (BR-150HCV, Imex Co., Ltd.). A solar cell element 2 was produced in the same manner as in Example 1 using the electrode-forming composition 2 thus obtained.

Silver particles (Ag; D50% is 0.6 μm, silver content is 99.9% by mass): 30.4 parts by mass Metal bismuth particles (Bi; D50% is 1.5 μm, bismuth content is 99.5% by mass ): 19.8 parts by mass Bismuth oxide particles ₍ Bi2O3; D50% is _2.2 µm, bismuth oxide content is 99.9% by mass): 10.0 parts by mass Glass GB02 particles: 3.3 parts by mass Molybdenum Particles (Mo; Shin Nippon Metal Co., Ltd. "Mo-1K", D50% is 1.5 μm, molybdenum content is 99.8% by mass): 0.5 parts by mass Terpineol (TPO): 30.9 parts by mass Ethyl cellulose (EC; Nisshin Kasei Co., Ltd. "STD-10"): 5.1 parts by mass

<Example 3>
from 38.0% by weight phosphorus oxide ₍ P2O5), 57.9% by weight tin oxide (SnO), _3.5 % by weight zinc oxide (ZnO) and 1.5% by weight aluminum oxide ₍ _Al2O3 ) A phosphate glass (hereinafter sometimes abbreviated as "GP01") was obtained. The softening point of the obtained glass GP01 was 340°C.
Using the obtained glass GP01, glass GP01 particles having a volume average particle diameter (D50%) of 8.0 μm were obtained. The shape of the glass GP01 particles was approximately spherical.

A pasty electrode-forming composition 3 was prepared by mixing the following materials using a roll mill (BR-150HCV, Imex Co., Ltd.). A solar cell element 3 was produced in the same manner as in Example 1 using the electrode-forming composition 3 thus obtained.

Silver particles (Ag; D50% is 0.6 μm, silver content is 99.9% by mass): 31.9 parts by mass Metal bismuth particles (Bi; D50% is 1.5 μm, bismuth content is 99.5% by mass ): 19.6 parts by mass Bismuth oxide particles ₍ Bi2O3; D50% is _2.2 µm, bismuth oxide content is 99.9% by mass): 5.0 parts by mass Glass GB02 particles: 5.6 parts by mass Glass GP01 particles: 1.4 parts by mass Molybdenum particles (Mo; Shin Nippon Metal Co., Ltd. "Mo-1K", D50% is 1.5 μm, molybdenum content is 99.8% by mass): 0.5 parts by mass Terpineol (TPO ): 30.9 parts by mass Ethyl cellulose (EC; Nisshin Kasei Co., Ltd. "STD-10"): 5.1 parts by mass

<Example 4>
A pasty electrode-forming composition 4 was prepared by mixing the following materials using a roll mill (BR-150HCV, Imex Co., Ltd.). A solar cell element 4 was produced in the same manner as in Example 1 using the electrode-forming composition 4 thus obtained.

Silver particles (Ag; D50% is 0.6 μm, silver content is 99.9% by mass): 35.6 parts by mass Metal bismuth particles (Bi; D50% is 1.5 μm, bismuth content is 99.5% by mass ): 21.4 parts by mass Bismuth oxide particles (Bi ₂ O ₃ ; D50% is 2.2 μm, bismuth oxide content is 99.9% by mass): 3.0 parts by mass Glass GB02 particles: 5.6 parts by mass Glass GP01 particles: 1.4 parts by weight terpineol (TPO): 28.3 parts by weight ethyl cellulose (EC; Nisshin Kasei Co., Ltd. "STD-10"): 4.7 parts by weight

<Comparative Example 1>
In Example 1, a commercial silver paste for solar cells (manufactured by DuPont, PV51M) was used in forming the back electrode. Specifically, a silver paste was first printed on the back surface and then dried. The pattern of the rear surface output extraction electrode formed using silver paste was configured to have a size of 1.8 mm×8.0 mm, and was printed in the same arrangement as in Example 1. The printing conditions (mesh of screen plate, printing speed and printing pressure) were adjusted so that the thickness of the rear surface output extraction electrode after heat treatment was 5 μm. After that, the composition for forming an aluminum electrode (RX8401) was printed on the pattern described in Example 1, except for the areas where the silver paste was printed and dried, and dried.
After that, heat treatment was performed in the same manner as in Example 1 to produce a solar cell element C1.

<Comparative Example 2>
A solar cell element C2 was produced in the same manner as in Example 1, except that the electrode-forming composition 1 was not used and a commercially available solar cell silver paste (PV51M) was used.

<Comparative Example 3> A solar cell was fabricated in the same manner as in Example 1, except that the coating amount of the electrode-forming composition 1 was changed from 8.0 mg/cm ² to 3.8 mg/cm ² . A device C3 was produced.

<Comparative Example 4>
In Example 1, except that the content of silver particles was changed from 34.8 parts by mass to 50.3 parts by mass, and the content of metal bismuth particles was changed from 22.7 parts by mass to 7.2 parts by mass. An electrode-forming composition C4 was prepared in the same manner as in Example 1, and a solar cell element C4 was produced.

<Comparative Example 5>
In Example 3, the content of silver particles was changed from 31.9 parts by mass to 31.2 parts by mass, the content of metal bismuth particles was changed from 19.6 parts by mass to 18.5 parts by mass, and glass GP01 An electrode-forming composition C5 was prepared and a solar cell element C5 was produced in the same manner as in Example 3, except that the content of the particles was changed from 1.4 parts by mass to 3.2 parts by mass.

Table 1 shows the compositions of the electrode-forming compositions used in Examples 1-4 and Comparative Examples 1-5.

(1) Measurement of Element Concentration on Surface of Aluminum/Silver Laminated Electrode (manufactured by SU5000) and EDX analysis attached to the device. In Comparative Example 1, the element concentration on the surface of the electrode formed using silver paste instead of the aluminum/silver laminated electrode was measured. Table 2 shows the results. The EDX measurement conditions are as follows.
・Acceleration voltage: 5 kV
・Measurement magnification: 100 times ・Analysis area: 1250 μm×860 μm
・Analysis mode: Analyzer mode

(2) Observation of Cross-Sectional Structure of Aluminum/Silver Laminated Electrode A cross-section of the aluminum/silver laminated electrode serving as the backside output extraction electrode of the fabricated solar cell element was observed using a scanning electron microscope (SU5000, manufactured by Hitachi High-Tech Co., Ltd.) under an accelerating voltage. Observed at 15 kV. In addition, EDX analysis attached to the device was also performed to determine the presence or absence of the formation of a silver particle sintered portion on the surface of the aluminum / silver laminated electrode, the presence or absence of the formation of a bismuth oxide-containing phase inside the aluminum / silver laminated electrode, and the presence of bismuth oxide. The coverage of phases on silicon substrates was investigated. In Comparative Example 1, since no aluminum/silver laminated electrode was formed, the cross-sectional structure was not observed. Table 3 shows the results. The EDX measurement conditions in the cross-sectional structure analysis of the aluminum/silver laminated electrode are as follows.
・Acceleration voltage: 15 kV
・Measurement magnification: 2000 to 8000 times (arbitrary)
・ Analysis area: 20 μm × 15 μm to 80 μm × 60 μm (optional)
・Analysis mode: mapping mode, point analysis mode

(3) Microstructure Observation in Bismuth Oxide-Containing Phase Cross sections of the aluminum/silver laminated electrodes of the solar cell elements produced in Examples 1 and 3 were observed using a transmission electron microscope (TEM) under the following conditions. , investigated whether the bismuth oxide-containing phase of the aluminum/silver laminated electrode contains an amorphous phase.
・ Apparatus: Transmission electron microscope (TITAN G2 60-300, manufactured by FEI)
・Acceleration voltage: 300 kV
・Measurement magnification: 500,000 times to 910,000 times ・Analysis area: 20 nm × 20 nm to 50 nm × 50 nm
・Observation mode: High resolution TEM (HRTEM) mode

(4) Measurement of power generation performance of solar cell element Evaluation of the fabricated solar cell element was performed by WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as simulated sunlight, and I as a current-voltage (IV) evaluation measuring instrument. -V CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT) was used in combination. J _SC (short-circuit current), V _OC (open-circuit voltage), FF (form factor) and η (conversion efficiency), which indicate power generation performance as a solar cell element, are JIS-C-8912: 2011 and JIS-C-8913, respectively. : 2005 and JIS-C-8914:2005. Table 3 shows the obtained measured values converted into relative values with the measured value of Comparative Example 1 (solar cell element C1) set to 100.0.

(5) Measurement of Connection Strength of Wiring Material A wiring material was connected to the rear surface output extraction electrode of the fabricated solar cell element, and the connection strength of the wiring material was measured by a peel test.
Specifically, a wiring material (Ulbrich Co., Multi-Tabbing wire, Sn--Pb-based eutectic solder coating, Cu core material with a diameter of 0.4 mm) is placed on the rear surface output extraction electrode, and is placed on the wiring material. The connection was made by pressing a soldering iron and melting the solder. Next, using a desktop peel tester (Shimadzu Corporation, EZ-S), the pulling speed of the wiring material was set to 300 mm/min, and the strength when the wiring material was peeled off from the rear output extraction electrode in a direction of 180° was measured. It was defined as connection strength (N). Table 3 shows the results.

(6) Measurement of Solder Contact Angle The solder contact angle was measured in order to evaluate the connectivity (wettability) of the solder to the surface of the back output extraction electrode. Specifically, a commercially available solder ball (Senju Metal Industry Co., Ltd., ECO Solder BALL (Pb-free), diameter: 0.76 mm) was placed on the back output extraction electrode, and this was placed on a hot plate at a temperature of 250°C. for 30 seconds to melt the solder on the back surface output extraction electrode. Next, the solder-connected rear surface output extraction electrode was observed from the side, and the contact angle between the solder and the rear surface output extraction electrode interface was calculated using image processing software (ImageJ). Table 3 shows the results.

The power generation performance of the solar cell elements produced in Examples 1 to 4 showed almost the same value as the measured value of the solar cell element of Comparative Example 1.

As a result of structural analysis, an aluminum/silver laminated electrode was formed on the back surface of the solar cell elements produced in Examples 1-4. As a result of EDX analysis, a silver particle sintered portion was formed on the outermost surface of the electrode, and a bismuth oxide-containing phase was formed in the void portion of the aluminum electrode. Furthermore, part of the bismuth oxide-containing phase reached the surface of the substrate in contact with the aluminum/silver laminated electrode.
As a result of the TEM observation performed for Examples 1 and 3, an amorphous phase was included in the bismuth oxide-containing phase.

The surface silver concentration of the back surface output extraction electrode (aluminum/silver laminated electrode) of the solar cell elements produced in Examples 1 to 4 was 55.0 atomic % or more. When the surfaces of the aluminum/silver laminated electrodes of the solar cell elements produced in Examples 1 to 4 were observed with an SEM, it was found that silver particle sintered portions were sufficiently formed on the surfaces of the aluminum/silver laminated electrodes. . FIG. 7 shows an observed image of the surface of the aluminum/silver laminated electrode of the solar cell element produced in Example 1. As shown in FIG.

As a result of the peel test, the connection strength of the wiring material in the back surface output extraction electrode of the solar cells produced in Examples 1 to 4 showed a high value of 2N or more. The reason for this is that the surface silver concentration of the aluminum/silver laminated electrode, which is the rear output extraction electrode, is high, so that the wettability of the solder is good, and part of the bismuth oxide-containing phase reaches the silicon substrate. It is conceivable that the bulk strength of the aluminum electrode and the adhesion to the substrate (passivation protective film formation surface) are good due to the close contact and melting of the glass particles into the bismuth oxide-containing phase.

The solder contact angles on the aluminum/silver laminated electrodes of the solar cell elements produced in Examples 1 to 4 were all 90° or less, indicating that the molten solder spread well on the surface of the aluminum/silver laminated electrodes. Do you get it. From this, it can be considered that the electrical connectivity between the aluminum/silver laminated electrode and the wiring material is also good, the series resistance as a solar cell can be reduced, and sufficient power generation performance can be secured.

The aluminum/silver laminated electrode of Comparative Example 2 formed using the electrode-forming composition containing no bismuth-containing particles had a blackened surface, and no silver particle sintered portion was observed. Moreover, it was not possible to connect the wiring material to the electrode surface using the solder material.
The aluminum/silver laminated electrodes of the solar cell elements produced in Comparative Example 3, in which the coating amount of the electrode-forming composition was reduced, and in Comparative Example 4, in which the amount of bismuth-containing particles in the electrode-forming composition was reduced, were coated with silver particles. Although joints were observed, the surface was partially blackened, and the silver concentration on the surface was less than 55.0 atomic %. Moreover, the connection strength when the wiring material was connected to the electrode surface using the solder material was lower than that of the example.
The reason why the surfaces of the aluminum/silver laminated electrodes produced in Comparative Examples 2 to 4 turned black is that the interdiffusion of aluminum and silver proceeded excessively during the heat treatment, inhibiting the sintering of the silver particles, and the silver, aluminum and This is considered to be due to the formation of a composite oxide composed of bismuth. This point can also be inferred from the measurement result of the surface element concentration by EDX (oxygen concentration is high).

The aluminum/silver laminated electrode prepared in Comparative Example 5, in which the amount of glass GP01 particles contained in the electrode-forming composition used in Comparative Example 3 was increased, had a lower connection strength of the wiring material than in Comparative Example 3. This is because the electrode-forming composition used in Comparative Example 5 contains a large amount of phosphate glass particles (GP01), and a composite oxide other than the silver particle sintered portion is formed on the surface of the aluminum/silver laminated electrode. It is conceivable that the wettability of the solder of the wiring material was lowered because the wiring material became more susceptible to soldering. This point can also be inferred from the measurement result of the surface element concentration by EDX (the phosphorus concentration is high).

The solder contact angles on the aluminum/silver laminated electrodes of the solar cell elements produced in Comparative Examples 2 to 5 were all as high as 100° or more, and it was found that solder connection to the aluminum/silver laminated electrode surface was difficult. This point can also be inferred from the measurement result of the surface element concentration by EDX (silver concentration is low).

The disclosure of US patent application Ser. No. 63/152,847 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

A semiconductor substrate, a passivation film provided on the semiconductor substrate, and an aluminum/silver laminated electrode provided on the passivation film,
A solar cell element, wherein the aluminum/silver laminated electrode contains a bismuth oxide-containing phase and has a surface silver concentration of 55.0 atomic % or more as measured by energy dispersive X-ray analysis at an acceleration voltage of 5 kV.
The solar cell element according to claim 1, wherein the aluminum/silver laminated electrode has a silver particle sintered portion on its surface.
The solar cell element according to claim 1 or 2, wherein the bismuth oxide-containing phase contains boron.
The solar cell element according to any one of claims 1 to 3, wherein the bismuth oxide-containing phase contains phosphorus.
The solar cell element according to any one of claims 1 to 4, wherein the aluminum/silver laminated electrode comprises a heat-treated electrode-forming composition containing silver-containing particles and bismuth-containing particles.
The solar cell element according to claim 5, wherein the bismuth-containing particles include at least one selected from the group consisting of bismuth particles, bismuth alloy particles having a bismuth content of 40.0% by mass or more, and bismuth oxide particles.
The solar cell element according to claim 5 or 6, wherein the electrode-forming composition contains glass particles.
The solar cell element according to claim 7, wherein the glass particles contain boron.
The solar cell element according to claim 7 or 8, wherein the glass particles contain phosphorus.
A solar cell comprising the solar cell element according to any one of claims 1 to 9 and a wiring material provided on the aluminum/silver laminated electrode of the solar cell element.