JP2020071997A - Conductive paste and solar battery - Google Patents

Abstract

To provide a conductive paste which causes less damage to a passivation film and has excellent adhesion to a passivation film when formed into an electrode and to provide a solar battery.SOLUTION: There are provided: a conductive paste which contains conductive particles, an organic vehicle, a glass frit, a copper oxide and a metal compound having at least one metal selected from the group consisting of titanium, zirconium and hafnium, wherein the metal compound is at least one selected from the group consisting of an alkoxide, an acetylacetonate complex and a halide of the above metal; and a solar battery having an electrode formed using the conductive paste.SELECTED DRAWING: Figure 1

Description

  The present invention relates to conductive pastes and solar cells.

BACKGROUND ART Conventionally, a conductive paste or the like has been used to form an electrode included in a semiconductor device such as a solar cell.
The conductive paste is generally a paste-like composition containing conductive particles, an organic vehicle (the organic vehicle usually contains a binder resin and a solvent), and a glass frit.
When the electrode on the light receiving surface side of the solar cell (also referred to as the surface electrode or the light incident side electrode) is formed using the conductive paste, the antireflection film (for example, silicon nitride) is formed by the fire through by the action of the glass frit. The membrane) can be dissolved and removed, and electrical contact between the surface electrode and the diffusion layer can be achieved.
On the other hand, on the back surface side of the solar cell, it has been attempted to form an electrode (back surface electrode) on the back surface passivation film using the conductive paste.
For example, a conductive paste for forming an electrode formed on a passivation film of a solar cell,
(A) conductive particles,
(B) an organic vehicle, and (C) a specific glass frit,
A conductive paste containing 0.3 to 2 parts by weight of glass frit per 100 parts by weight of conductive particles has been proposed (Patent Documents 1 and 2).

Further, Patent Document 3 aims to provide a conductive composition for forming an electrode, which has a wide choice of glass frits and metal compounds to be used, and which can further suppress the resistance between the electrode and the substrate. ) A conductive powder, (b) glass frit, (c) CuO, Y ₂ O ₃ , and at least one metal oxide selected from La ₂ O ₃ , and (c ′) titanium black, and Disclosed is a conductive composition for forming an electrode, in which the component (b) contains an oxide of a group III element and / or an oxide of a group V element.

JP, 2018-6064, A JP, 2008-32491, A Japanese Patent No. 5757977

Generally, the back surface passivation film of the solar cell is a silicon nitride film, and the material of the film is the same as that of the antireflection film. For this reason, when the conductive paste that has been conventionally used for the antireflection film is used on the back surface passivation film and is baked, the conductive paste (rear surface electrode) fire-throughs the back surface passivation film, or Since the back surface passivation film is removed by the paste and a large number of surface defects are generated on the substrate (crystalline silicon substrate), there is a problem that the performance of the solar cell is reduced as a result.
Under these circumstances, the present inventors prepared a conductive paste with reference to Patent Document 1 and the like and evaluated it. Such a conductive paste still damages the passivation film with respect to the above problems. It has been clarified that (for example, surface defects are generated on the substrate, fire-through occurs, etc.), or the adhesion to the passivation film may be low.
Therefore, it is an object of the present invention to provide a conductive paste that is less likely to damage the passivation film when it becomes an electrode and has excellent adhesion to the passivation film.
As a result of less damage to the passivation film as described above, the power generation efficiency of the solar cell can be increased.
Another object of the present invention is to provide a solar cell.

As a result of intensive studies to solve the above problems, the present inventors have found that a desired effect can be obtained by using copper oxide and a predetermined metal compound for conductive particles, an organic vehicle and a glass frit. The present invention has been reached.
The present invention is based on the above findings and the like, and specifically solves the above problems by the following configurations.

[1] conductive particles,
Organic vehicle,
Glass frit,
Copper oxide, and
Containing a metal compound having at least one metal selected from the group consisting of titanium, zirconium and hafnium,
A conductive paste in which the metal compound is at least one selected from the group consisting of alkoxides, acetylacetonato complexes, and halides of the above metals.
[2] The conductive paste according to [1], wherein the copper oxide has an average particle diameter (D50) of 1.0 μm or less.
[3] The conductive paste according to [1] or [2], wherein the content of the metal compound is 0.01 to 2.0 parts by mass with respect to 100 parts by mass of the conductive particles.
[4] The conductive paste according to any one of [1] to [3], wherein the conductive particles have an average particle diameter (D50) of 2.0 μm or less.
[5] The electroconductivity according to any one of [1] to [4], wherein the organic vehicle contains at least one selected from the group consisting of a cellulosic polymer, a (meth) acrylic polymer, and a rosin resin. Sex paste.
[6] The conductive paste according to any one of [1] to [5], wherein the glass frit has a glass transition temperature of 500 ° C. or lower.
[7] The conductive paste according to any one of [1] to [6], wherein the glass frit contains ZnO and / or PbO.
[8] The conductive paste according to any one of [1] to [7], wherein the content of the glass frit is 0.1 to 10 parts by mass with respect to 100 parts by mass of the conductive particles.
[9] The conductive paste according to any one of [1] to [8], wherein the copper oxide contains copper (I) oxide and / or copper (II) oxide.
[10] The conductive paste according to any one of [1] to [9], wherein the content of the copper oxide is 0.01 to 2.0 parts by mass with respect to 100 parts by mass of the conductive particles.
[11] The conductive paste according to any one of [1] to [10], further containing tellurium or a tellurium compound.
[12] The conductive paste according to [11], wherein the tellurium compound contains at least one selected from the group consisting of tellurium oxide, telluric acid, and tellurium alkoxide.
[13] A solar cell having an electrode formed using the conductive paste according to any one of [1] to [12].
[14] The solar cell according to [13], wherein the electrode constitutes at least a part of a back electrode.
[15] The solar cell according to [14], wherein the back electrode has the electrode and an aluminum electrode.
[16] Further, having a back surface passivation film,
The solar cell according to any one of [13] to [15], wherein on the back surface side of the solar cell, the back surface passivation film is provided between the substrate and the electrode forming the solar cell.
[17] The solar cell according to [16], wherein the electrode is in direct contact with the back surface passivation film.

The conductive paste of the present invention is less likely to damage the passivation film when it becomes an electrode, and has excellent adhesion to the passivation film.
Further, the solar cell of the present invention has less damage to the passivation film and has excellent adhesion to the passivation film.

FIG. 1 is a cross-sectional view schematically showing one embodiment of the solar cell of the present invention.

The present invention will be described in detail below.
In addition, in this specification, (meth) acrylate represents acrylate or methacrylate, (meth) acryloyl represents acryloyl or methacryloyl, and (meth) acryl represents acryl or methacryl.
Further, in the present specification, the numerical range represented by using "to" means a range including the numerical values before and after "to" as the lower limit value and the upper limit value.
In the present specification, unless otherwise specified, each of the components used may be a substance corresponding to the component alone or in combination of two or more kinds. When a component contains two or more substances, the content of the component means the total content of the two or more substances.
In the present specification, the fact that the conductive paste of the present invention has little damage to the passivation film when it becomes an electrode is simply referred to as "less damage". The adhesion may be simply referred to as "adhesion".
In the present specification, the fact that at least one of the above-mentioned less damage and excellent adhesion is more excellent may mean that the effect of the present invention is more excellent.

  As used herein, "crystalline silicon" includes single crystal and polycrystalline silicon. The “crystalline silicon substrate” refers to a material obtained by molding crystalline silicon into a shape suitable for element formation, such as a flat plate shape, for forming a semiconductor device such as an electric element or an electronic element. Any method may be used as the method for producing crystalline silicon. For example, the Czochralski method can be used in the case of single crystal silicon, and the casting method can be used in the case of polycrystalline silicon. Further, other manufacturing methods, for example, a polycrystalline silicon ribbon manufactured by a ribbon pulling method, polycrystalline silicon formed on a heterogeneous substrate such as glass, or the like can also be used as the crystalline silicon substrate. In addition, the “crystalline silicon solar cell” refers to a solar cell manufactured using a crystalline silicon substrate.

[Conductive paste]
The conductive paste of the present invention contains conductive particles, an organic vehicle, a glass frit, copper oxide, and a metal compound having at least one metal selected from the group consisting of titanium, zirconium and hafnium,
The above metal compound is a conductive paste, which is at least one selected from the group consisting of alkoxides, acetylacetonato complexes, and halides of the above metals.

Since the conductive paste of the present invention has such a structure, it is considered that the desired effect can be obtained. The reason for this is not clear, but it is presumed to be approximately as follows.
When a conductive paste is used on the back surface passivation film or antireflection film of the solar cell and is baked, the glass frit contained in the conductive paste acts on the back surface passivation film and the like (for example, erosion due to reaction). It is known that a conductive paste (electrode) dissolves and removes a back surface passivation film and the like, and fires through. If a fire-through occurs in the back surface passivation film, the frequency of carrier recombination due to back surface defects increases, resulting in a decrease in power generation efficiency.

On the other hand, the conductive paste of the present invention contains copper oxide.
Copper oxide is a compound of copper and oxygen, and the oxidation number of copper in copper oxide is, for example, monovalent or divalent.
Therefore, when the conductive paste of the present invention is applied onto the back surface passivation film or the like and fired, the glass frit contained in the conductive paste of the present invention acts on the back surface passivation film or the like. The present inventors presume that it reacts with copper oxide first and can alleviate the action of the glass frit on the back surface passivation film.
In addition, the conductive paste of the present invention, by containing copper oxide and a predetermined metal compound, an electrode formed using the conductive paste of the present invention, and a solder used for connection to other members, etc. The present inventors presume that it is possible to appropriately control the alloying of and to improve the adhesion between the electrode and the solder.
Hereinafter, each component contained in the conductive paste of the present invention will be described in detail.

<Conductive particles>
The conductive paste of the present invention contains conductive particles.
The conductive particles contained in the conductive paste of the present invention are not particularly limited as long as they are granular substances having conductivity.
Examples of the conductive particles include particles of gold (Au), silver (Ag), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), or the like.
Among them, the conductive particles are preferably silver particles or silver-coated copper particles (hereinafter, these may be referred to as “silver particles and the like”) from the viewpoint of being excellent in the effect of the present invention.
The silver particles are metal silver particles.

-Shape of conductive particles (for example, silver particles) The shape of the conductive particles (for example, silver particles) is not particularly limited. For example, a spherical shape and a flake (scale) shape may be mentioned.
The conductive particles (for example, silver particles) are preferably spherical from the viewpoint of being excellent in the effect of the present invention and being excellent in the strength of the obtained (silver) electrode itself.
Here, the term “spherical” means the shape of particles having a ratio of major axis / minor axis of 2 or less. The flake shape means a shape in which the ratio of major axis / minor axis is more than 2.
The major axis and the minor axis of the conductive particles (for example, silver particles) can be determined based on an image obtained from a scanning electron microscope (SEM). The “major axis” refers to the longest line segment among the line segments that pass through the approximate center of gravity of the conductive particles (for example, silver particles) in the particle image obtained by SEM. “Short axis” refers to the shortest line segment among the line segments passing through substantially the center of gravity of conductive particles (for example, silver particles) in a particle image obtained by SEM.
In addition, 100 conductive particles (for example, silver particles) are arbitrarily selected in the above image, the major axis of the 100 conductive particles (for example, silver particles) is measured, and the 100 conductive particles (for example, silver particles) are measured. The average value calculated from the long diameters of (), etc.) is the average (average value) of the long diameters of the conductive particles (eg, silver particles). The same applies to the average of the short diameters of the conductive particles (eg, silver particles).

-Average particle diameter of conductive particles (for example, silver particles) The average particle diameter (D50) of the conductive particles (for example, silver particles) is excellent due to the effects of the present invention, and the strength of the obtained (silver) electrode itself is excellent. From the viewpoint, it is preferably 2.0 μm or less, and more preferably 1.0 μm or less.
In addition, as the conductive particles, for example, silver particles having an average particle diameter (D50) of several tens of nanometers, which is called nano silver, can be used. The shape of the nano silver is not particularly limited, but specific examples thereof include spherical shapes.
The shape of the conductive particles (for example, silver particles) having the above-mentioned average particle diameter is not particularly limited, but for example, the particle diameter of spherical conductive particles (for example, spherical silver particles) is defined by the above-mentioned average particle diameter (D50). You can

  The average particle size of the conductive particles (for example, silver particles) is obtained by measuring the volume-based particle size distribution using a laser diffraction particle size distribution measuring device, and the particle size at a cumulative 50% (50% cumulative volume size). Also referred to as "average particle diameter (D50)". As such a laser diffraction type particle size distribution measuring device, for example, a device conforming to LA-500 (trade name) manufactured by Horiba Ltd. can be mentioned.

・ Spherical conductive particles (eg spherical silver particles)
The spherical conductive particles that can be used as the conductive particles are not particularly limited. For example, conventionally known ones (for example, spherical silver particles) can be mentioned.
..Average particle diameter (D50) of spherical conductive particles (eg, spherical silver particles)
The average particle diameter (D50) of the spherical conductive particles (for example, spherical silver particles) is preferably 2.0 μm or less from the viewpoint that the effect of the present invention is excellent and the strength of the obtained (silver) electrode itself is excellent. , 1.0 μm or less is more preferable.

.Flake-shaped conductive particles (for example, flake-shaped silver particles)
The flaky conductive particles that can be used as the flaky conductive particles are not particularly limited. For example, conventionally known particles (for example, flake-shaped silver particles) can be mentioned.
.. Major axis and minor axis of flake-shaped conductive particles (for example, flake-shaped silver particles) The major axis (width) of the flake-shaped conductive particles (for example, flake-shaped silver particles) is excellent due to the effects of the present invention (silver) electrode From the viewpoint of excellent strength, the average particle size is preferably 2.0 μm or less, and more preferably 1.0 μm or less.
The minor axis (thickness) of the flaky conductive particles (for example, flake silver particles) is less than 1.0 μm on average from the viewpoint that the effect of the present invention is excellent and the strength of the obtained (silver) electrode itself is excellent. Is preferable, and 0.1 μm or less is more preferable.
The average of the major axis and the minor axis of the flaky conductive particles (for example, flake silver particles) can be obtained as described above.

As the flake-shaped conductive particles, for example, silver having an average (average value) of minor axis (thickness) of several tens nm (for example, 10 to 90 nm) and an average major axis (width) of 0.3 to 6 μm. Particles are preferred.
Examples of commercial products of the above flake-shaped silver particles include trade name N300 marketed by Toxen Industry Co., Ltd.

<Organic vehicle>
The conductive paste of the present invention contains an organic vehicle.
The organic vehicle may include an organic binder.
The organic vehicle may include an organic binder and a solvent. In the present invention, an organic vehicle having a solvent added thereto may be used as the organic vehicle.

Examples of organic binders include cellulose-based polymers, (meth) acrylic-based polymers, and rosin-based resins.
The organic vehicle is at least one kind (organic binder) selected from the group consisting of a cellulosic polymer, a (meth) acrylic polymer and a rosin resin, from the viewpoint of being excellent in the effect of the present invention and being excellent in printability. It is preferable to include.

Examples of the cellulose-based resin include ethyl cellulose and nitrocellulose.
Examples of the (meth) acrylic resin include polymethyl acrylate and polymethyl methacrylate.
Examples of the rosin-based resin include rosin ester.

  The organic vehicle preferably contains an organic binder and a solvent.

  Examples of the solvent that can be contained in the organic vehicle include alcohols (for example, terpineol, α-terpineol, β-terpineol, butyl carbitol, etc.), esters (for example, hydroxy group-containing esters, 2,2,4-trimethyl). -1,3-pentanediol monoisobutyrate, butyl carbitol acetate and the like).

-Concentration of Organic Binder When the above organic vehicle contains an organic binder and a solvent, the concentration of the organic binder with respect to the total amount of the organic vehicle is 2 to 15% by mass from the viewpoint of being excellent in the effect of the present invention and being easy to handle. Is preferred and 3 to 10% by mass is more preferred.

-Content of organic vehicle The content of the organic vehicle (including the case where the organic vehicle contains an organic binder and a solvent) is excellent in the effect of the present invention, and from the viewpoint of excellent printability, the conductive particles (for example, silver). (Particle etc.) 100 parts by mass is preferably 1 to 150 parts by mass, more preferably 30 to 150 parts by mass, further preferably 50 to 100 parts by mass.
Content of Organic Binder The content of the organic binder is 1 to 25 parts by mass with respect to 100 parts by mass of the conductive particles (for example, silver particles) from the viewpoint of being excellent in the effect of the present invention and being excellent in printability. Is preferred.

<Glass frit>
The conductive paste of the present invention contains glass frit.
The glass frit is mainly composed of a plurality of types of oxides, for example, metal oxides, and is generally in the form of glassy particles.

The oxide that constitutes the glass frit is not particularly limited. For example, ZnO, PbO, is _{B 2 O 3, SiO 2,} Al 2 O 3 and the like.
The glass frit preferably contains ZnO and / or PbO, and more preferably contains PbO, from the viewpoints of being excellent in the effects of the present invention and being easily available.
When the glass frit contains ZnO and / or PbO, it is preferable that the glass frit further contains B ₂ O ₃ and / or SiO ₂ .
When the glass frit contains PbO, it is preferable that the glass frit further contains SiO ₂ .

-Glass transition temperature of glass frit The glass transition temperature of the above glass frit is 550 ° C or lower from the viewpoint of being excellent in the effect of the present invention, being easy to soften, and being excellent in the fill factor when used as a solar cell. The temperature is preferably 500 ° C or lower, more preferably 500 ° C or lower, and further preferably lower than 460 ° C.
The average glass transition temperature of the glass frit used is preferably 520 ° C. or lower from the viewpoints of being excellent in the effect of the present invention, being easy to soften, and being excellent in fill factor when used as a solar cell. ..

Regarding the glass transition temperature of the glass frit, a differential scanning calorimeter DSC-50 manufactured by SHIMADZU was used to raise the temperature to 3780 ° C. at a temperature rising rate of 15 ° C./min, and a DSC in a temperature range of about 50 ° C. to about 370 ° C. The curve was measured. The temperature of the first inflection point of the DSC curve was taken as the glass transition temperature of the glass frit.
The average glass transition temperature of the glass frit used can be calculated from the glass transition temperature measured as described above and the amount used.

Content of glass frit The content of the glass frit is 0.1 to 10 parts by mass with respect to 100 parts by mass of the conductive particles (for example, silver particles) from the viewpoint of being excellent in the effect of the present invention. Is preferred, and more preferably 0.5 to 5.0 parts by mass.

<Copper oxide>
The conductive paste of the present invention contains copper oxide.
Copper that constitutes copper oxide has an oxidation number (for example, monovalent or divalent).
By containing copper oxide, the conductive paste of the present invention is less likely to damage the passivation film when it becomes an electrode, and has excellent adhesion to the passivation film. Since the passivation film is less damaged as described above, the solar cell having an electrode obtained by using the conductive paste of the present invention has high power generation efficiency.
In addition, the electrode formed using the conductive paste of the present invention has excellent adhesion to solder (which can be used for connection with other members).

Examples of the copper oxide include copper (I) oxide and copper (II) oxide.
The copper oxide preferably contains copper (I) oxide and / or copper (II) oxide, and more preferably copper (II) oxide, from the viewpoint of being more excellent in the effect of the present invention.

(Average particle diameter of copper oxide (D50))
The average particle diameter (D50) of the copper oxide is preferably 1.0 μm or less, and more preferably 20 to 200 nm, from the viewpoint of being more excellent in the effects of the present invention.

  The average particle diameter of the copper oxide is obtained by measuring a volume-based particle size distribution using a laser diffraction particle size distribution measuring device (particle diameter at a cumulative 50% (50% volume cumulative diameter. “Average particle diameter (D50 ) ".). As such a laser diffraction type particle size distribution measuring device, for example, a device conforming to LA-500 (trade name) manufactured by Horiba Ltd. can be mentioned.

(Copper oxide content)
The content of the copper oxide is preferably 0.01 to 2.0 parts by mass, and 0.1 to 1.0 parts by mass with respect to 100 parts by mass of the particles, from the viewpoint of being more excellent in the effect of the present invention. Parts are more preferred.

(Metal compound)
The conductive paste of the present invention contains a metal compound having at least one metal selected from the group consisting of titanium, zirconium and hafnium,
The metal compound is at least one selected from the group consisting of alkoxides, acetylacetonato complexes and halides of the above metals.

-Metal The metal contained in the above metal compound is preferably titanium, zirconium or hafnium, and more preferably titanium, from the viewpoint of being excellent in the effect of the present invention.
In addition, it is mentioned as one of the preferable aspects that one molecule of the metal compound has one metal.

Metal compound In the present invention, the metal compound is at least one selected from the group consisting of alkoxides, acetylacetonato complexes and halides of the above metals.

Examples of the metal compound include titanium alkoxide, acetylacetonate complex or halide;
Alkoxide, acetylacetonate complex or halide of zirconium;
Hafnium alkoxides, acetylacetonate complexes or halides are mentioned.

It is preferable that the metal compound contains an alkoxide of the metal from the viewpoint of being excellent in the effect of the present invention and / or being excellent in adhesiveness to solder.
The metal compound preferably contains a titanium alkoxide from the viewpoint of being more excellent in the effect of the present invention.
Further, it is more preferable that the metal compound contains titanium tetraalkoxide from the viewpoints of excellent effects of the present invention and high power generation efficiency.

  Examples of the combination of the above metal compounds include a combination of titanium alkoxide and zirconium or hafnium alkoxide, and a combination of a titanium alkoxide and a hafnium alkoxide is excellent in the effect of the present invention and has high power generation efficiency. Is preferred.

The metal compound is a titanium alkoxide (for example, titanium tetraalkoxide, titanium trialkoxide, titanium dialkoxide, titanium monoalkoxide, from the viewpoint of being excellent in the effect of the present invention (particularly the adhesiveness) or being excellent in the adhesiveness with solder. ), Zirconium alkoxide and hafnium alkoxide are preferably contained at least one kind, more preferably titanium alkoxide, more preferably titanium tetraalkoxide, and titanium tetrabutoxide (titanium tetrabutoxide). Is particularly preferable.
When the titanium alkoxide is titanium trialkoxide, titanium dialkoxide or titanium monoalkoxide, the functional group other than the alkoxy group contained in the titanium alkoxide is not particularly limited. Examples include acetylacetonates and halogens. The same applies to zirconium alkoxide and hafnium alkoxide. The functional groups contained in the metal compound will be described later.

Examples of the titanium alkoxide include titanium tetraalkoxides such as titanium tetrapropoxide and titanium tetrabutoxide;
Titanium trialkoxides such as titanium tripropoxycyclolide;
Mention may be made of titanium dialkoxides such as titanium dipropoxy bis (ethyl acetoacetate).

Examples of the zirconium alkoxide include titanium tetraalkoxides such as zirconium tetrapropoxide and zirconium tetrabutoxide.
Examples of the above hafnium alkoxide include hafnium butoxide and hafnium 2-ethylhexoxide.

-Functional group The above metal can have one or more functional groups selected from the group consisting of alkoxy groups, acetylacetonates and halogens.
.. Alkoxy group The alkoxy group as the functional group is not particularly limited. For example, the alkoxy group which has a C1-C10 alkyl group is mentioned. The alkyl group contained in the alkoxy group may be linear, branched, cyclic, or a combination thereof.
When the metal alkoxide has a plurality of alkoxy groups, the plurality of alkoxide groups may be the same or different. The same applies to acetylacetonates and halogens described below.
Examples of the alkoxy group include a methoxy group, an ethoxy group and a butoxy group. The alkoxy group is preferably a butoxy group from the viewpoint of being more excellent in the effects of the present invention.

-Acetylacetonates Examples of the acetylacetonates as the functional group include acetylacetonate and alkylacetoacetates such as ethylacetoacetate.

.. Halogen Examples of the halogen as the functional group include chlorine and bromine.

-Combination of functional groups Examples of the combination of the above functional groups include a combination of an alkoxy group and a halogen, and a combination of an alkoxy group and an acetylacetonate.

  In the present invention, when the metal compound has an alkoxy group, the metal compound is referred to as a metal alkoxide. Examples of the above metal alkoxides include those in which all functional groups are alkoxy groups, those having an alkoxy group and halogen as functional groups, and those having an alkoxy group and acetylacetonates as functional groups.

  Further, in the present invention, when the metal compound has acetylacetonates, the metal compound is referred to as a metal acetylacetonate complex. The metal acetylacetonate complex conceptually includes, in addition to acetylacetonates as functional groups, those having, for example, an alkoxy group. On the other hand, in the present specification, as described above, the alkoxide of the metal includes one having an alkoxy group and acetylacetonates as a functional group. Therefore, from the relationship with the above description, in classifying both of them in the present specification, those having an alkoxide are excluded from the metal acetylacetonato complexes.

  Further, in the present invention, when the metal compound has halogen, the metal compound is referred to as a metal halide. The metal halides conceptually include those having, for example, an alkoxy group in addition to halogen as a functional group. On the other hand, in the present specification, as described above, the metal alkoxide includes one having an alkoxy group and a halogen as functional groups. Therefore, from the relationship with the above description, in classifying both of them in the present specification, those having an alkoxide are excluded from the metal halides.

Content of Metal Compound The content of the metal compound is 100 masses of the conductive particles (for example, silver particles) from the viewpoint of being excellent in the effect (particularly the adhesion) of the present invention or being excellent in the adhesion to solder. It is preferably 0.01 to 2.0 parts by mass, and more preferably 0.05 to 1.0 parts by mass with respect to parts.

(Tellurium or tellurium compound)
The conductive paste of the present invention may further contain tellurium or a tellurium compound.
The conductive paste of the present invention preferably further contains a tellurium compound from the viewpoint of being excellent in the effect of the present invention (particularly the adhesiveness) and being excellent in power generation efficiency.
Further, the tellurium compound is selected from the group consisting of tellurium oxide, telluric acid (Te (OH) ₆ ) and tellurium alkoxide from the viewpoint of being excellent in the effect of the present invention (particularly adhesion) and being excellent in power generation efficiency. It is preferable to contain at least one kind.

Tellurium alkoxide ... Alkoxy group The alkoxy group of tellurium alkoxide is not particularly limited. For example, the alkoxy group which has a C1-C10 alkyl group is mentioned. The alkyl group contained in the alkoxy group may be linear, branched, cyclic, or a combination thereof.
When the tellurium alkoxide has a plurality of alkoxy groups, the plurality of alkoxide groups may be the same or different.
Examples of the alkoxy group include a methoxy group, an ethoxy group and a butoxy group. The alkoxy group is preferably an ethoxy group from the viewpoint of being excellent in the effects of the present invention.

  Tellurium alkoxide may have a functional group other than an alkoxy group.

  In the present invention, when the tellurium alkoxide has an alkoxy group, the tellurium compound is referred to as the tellurium alkoxyside.

  Examples of the tellurium alkoxide include tellurium (IV) ethoxide.

  The tellurium compound preferably contains the above tellurium alkoxyside, more preferably contains tellurium tetraalkoxide, and more preferably tellurium, from the viewpoint of being excellent in the effect of the present invention and / or being excellent in adhesiveness to solder. It is further preferable that (IV) ethoxide is included.

-Content of tellurium or tellurium compound The content of the tellurium compound is superior to the effect (especially adhesion) of the present invention, or from the viewpoint of excellent adhesion to solder, with respect to 100 parts by mass of the conductive particles. , 0.01 to 2.0 parts by mass, more preferably 0.05 to 1.0 parts by mass.
The content of tellurium is the same as the content of the tellurium compound.

(Additive)
The conductive paste of the present invention may further contain an additive such as a reducing agent, if necessary.
Specific examples of the reducing agent include ethylene glycols and the like.

  The method for producing the conductive paste of the present invention is not particularly limited, the conductive particles, the organic vehicle, the glass frit, the copper oxide and the metal compound, and optionally the additive may be contained, a roll, The method of mixing with a kneader, an extruder, a universal stirrer, etc. is mentioned.

Applications of the conductive paste of the present invention include, for example, solar cell electrodes.
As an electrode of a solar cell to which the conductive paste of the present invention can be applied, for example, a bus bar electrode on the light receiving surface side; a back surface electrode occupying a part of the back surface side or the entire surface can be cited.

When the conductive paste of the present invention is applied to a solar cell, the position in the solar cell to which the conductive paste of the present invention is applied is not particularly limited.
When the conductive paste of the present invention is applied to the back surface side of the solar cell to form the electrode, the conductive paste of the present invention may be directly applied to the back surface of the substrate, for example.
When the substrate has a back surface passivation film on the back surface, the conductive paste of the present invention may be applied to at least a part of the back surface passivation film.

  An electrode can be formed by firing the conductive paste of the present invention under conditions of 700 to 900 ° C., for example.

  An interconnector (metal wire coated with solder) can be connected to the electrode formed of the conductive paste of the present invention.

[Solar cell]
The solar cell of the present invention is a solar cell having an electrode formed using the conductive paste of the present invention.
The solar cell of the present invention is not particularly limited except that it has an electrode formed using the conductive paste of the present invention.

  An electrode formed using the conductive paste of the present invention may be hereinafter referred to as a "predetermined electrode".

  Examples of the predetermined electrode include a bus bar electrode on the light receiving surface side (light incident side) and an electrode on the back surface side (a part or the entire surface of the back surface electrode). The predetermined electrode is preferably an electrode on the back surface side, and more preferably constitutes at least a part of the back surface electrode.

  When the predetermined electrode constitutes a part of the back electrode, the back electrode preferably includes the predetermined electrode and the aluminum electrode.

The solar cell of the present invention can further have a back surface passivation film (back surface passivation solar cell).
In this case, on the back surface side of the solar cell, it is preferable that the back surface passivation film is provided between the substrate forming the solar cell and the predetermined electrode. The predetermined electrode may be in direct contact with the back surface passivation film.

  The solar cell of the present invention further has a back surface passivation film, and on the back surface side of the solar cell, there is the back surface passivation film between the substrate and the predetermined electrode of the solar cell, and the predetermined It is preferable that the electrode is in direct contact with the back surface passivation film, and the back surface electrode has the predetermined electrode and the aluminum electrode.

The solar cell of the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the attached drawings.
FIG. 1 is a cross-sectional view schematically showing one embodiment of the solar cell of the present invention.
The solar cell shown in FIG. 1 is a backside passivation solar cell.
The back surface passivation type solar cell shown in FIG. 1 has a light incident side bus bar electrode 20a formed on the light incident side, an antireflection film 2, an n type impurity diffusion layer (n type silicon layer) 4, a p type crystal system. The silicon substrate 1 has a back surface passivation film 14 and a back surface electrode 15 on the back surface. The back surface electrode 15 has a back surface electrode 15b and a back surface electrode 15a. Due to the dot-shaped opening formed in the back surface passivation film 14, the substrate 1 (crystalline silicon substrate) and the back surface electrode 15b have electrical contact. An impurity diffusion portion 18 (p-type impurity diffusion portion) is arranged at a portion where the substrate 1 and the back surface electrode 15b are in contact with each other. The impurity diffusion portion 18 has a BSF (Back Surface Field) layer 18a and an Al-Si alloy layer 18b.

  In FIG. 1, the back surface electrode 15a is formed using the conductive paste of the present invention.

In FIG. 1, there is a back surface passivation film 14 between the substrate 1 and the back surface electrode 15a, the back surface electrode 15a is in direct contact with the back surface passivation film 14, and the back surface electrode 15 has a back surface electrode 15a and a back surface electrode 15b. The conductive paste that can form the back electrode 15b can be the conductive paste of the present invention or a conductive paste other than this. Examples of the conductive paste other than the conductive paste of the present invention include a conductive paste capable of forming an aluminum electrode (a conductive paste containing aluminum).
In FIG. 1, the back surface passivation film 14 between the substrate 1 and the back surface electrode 15a is not fired through.

In FIG. 1, the light incident side bus bar electrode 20a is fire-through the antireflection film 2. As the conductive paste used for forming the light incident side bus bar electrode 20a, there can be mentioned, for example, a publicly known conductive paste which can pass through an antireflection film by fire.
When the conductive paste of the present invention is applied to the light incident side bus bar electrode 20a, the obtained light incident side bus bar electrode does not fire through the antireflection film 2.

(Production method)
Next, a method for manufacturing the solar cell of the present invention will be described. The method for manufacturing the solar cell of the present invention is not particularly limited except that it has an electrode formed using the conductive paste of the present invention. The following manufacturing method is an example of the method for manufacturing the solar cell of the present invention.

-Substrate The method for manufacturing a solar cell of the present invention includes a step of preparing a (crystalline silicon) substrate 1 of one conductivity type (p-type or n-type conductivity type). As the (crystalline silicon) substrate 1, for example, a p-type crystalline silicon substrate, specifically, for example, a p-type single crystal silicon substrate can be used.
From the viewpoint of obtaining high conversion efficiency, it is preferable that the surface of the (crystalline silicon) substrate 1 on the light incident side has a pyramidal texture structure.

-Formation of Impurity Diffusion Layer 4 Next, in the method for manufacturing a solar cell of the present invention, another conductivity type impurity diffusion layer 4 is formed on one surface of the (crystalline silicon) substrate 1 prepared in the above step. Including the step of For example, when the p-type crystalline silicon substrate 1 is used as the (crystalline silicon) substrate 1, an n-type impurity diffusion layer in which P (phosphorus) that is an n-type impurity is diffused is formed as the impurity diffusion layer 4. be able to. It is also possible to manufacture a crystalline silicon solar cell using an n-type crystalline silicon substrate. In that case, a p-type impurity diffusion layer is formed as the impurity diffusion layer.

-Formation of Antireflection Film 2 and Backside Passivation 14 Next, in the method for manufacturing a solar cell according to the present invention, the antireflection film 2 is formed on the surface of the impurity diffusion layer 4 formed in the above step, and the backside of the substrate 1 is formed. And the step of forming the back surface passivation film 14 is included.

  As the antireflection film 2, a silicon nitride film (SiN film) can be formed. When the silicon nitride film is used as the antireflection film 2, the layer of the silicon nitride film also has a function as a surface passivation film. Therefore, when a silicon nitride film is used as the antireflection film 2, a high performance crystalline silicon solar cell can be obtained. Further, since the antireflection film 2 is a silicon nitride film (silicon nitride film), it can exhibit an antireflection function with respect to incident light. The silicon nitride film can be formed by a PECVD (Plasma Enhanced Chemical Vapor Deposition) method or the like.

  Further, in this step, a back surface passivation film 14 such as a silicon nitride film is formed on the back surface of the substrate 1. On the back surface passivation film 14, a dot-shaped opening for making electrical contact between the (crystalline silicon) substrate 1 and the back surface electrode 15b can be formed by patterning or the like.

-Formation of light incident side electrode and back surface electrode The method for manufacturing a solar cell of the present invention includes a step of forming a light incident side electrode by printing a conductive paste on the surface of the antireflection film 2 and baking it.
Further, the method for manufacturing a solar cell of the present invention further includes a step of forming a back electrode 15 by printing a conductive paste on the other surface (back surface) of the (crystalline silicon) substrate 1 and baking the paste. ..

  Specifically, first, a pattern of the light-incident-side electrodes (light-incident-side finger electrodes and / or light-incident-side bus bar electrodes) printed using a conductive paste is kept at a temperature of about 100 to 150 ° C. for several minutes (for example, Dry for 0.5-5 minutes). At this time, of the light incident side electrode patterns, the light incident side bus bar electrode 20a can be formed using the conductive paste of the present invention or another conductive paste. This is because when the light-incident-side bus bar electrode 20a is formed using the conductive paste of the present invention, it does not adversely affect the antireflection film 2 that is a passivation film. A known conductive paste for forming the light incident side electrode can be used for forming the light incident side finger electrode.

  Following the printing and drying of the pattern of the light incident side electrode, the conductive paste of the present invention for forming the back surface electrode 15a and the back surface electrode 15b are formed on the back surface passivation film for forming the back surface electrode 15. The conductive paste for printing is printed.

  The method of printing the conductive paste of the present invention for forming the back surface electrode 15 or the back surface electrode 15a on the back surface passivation film is not particularly limited. Further, when the conductive paste for forming the back surface electrode 15b is different from the conductive paste of the present invention, the method of printing the conductive paste for forming the back surface electrode 15b is not particularly limited. All of them include, for example, conventionally known ones.

  The conductive paste used to form the back surface electrode 15a is not particularly limited as long as it is the conductive paste of the present invention.

..Conductive paste for forming back electrode 15b The conductive paste for forming back electrode 15b may be the same as or different from the conductive paste of the present invention.
When the conductive paste for forming the back surface electrode 15b is different from the conductive paste of the present invention, examples of the conductive paste for forming the back surface electrode 15b include aluminum paste.
The aluminum paste is not particularly limited. For example, an aluminum paste containing aluminum powder, glass powder and an organic vehicle can be mentioned.

(Aluminum powder)
The aluminum powder preferably has an average particle size of 1 to 10 μm. The average particle size of the aluminum powder can be measured using a laser diffraction particle size distribution meter.
The aluminum powder can be mentioned as one of the preferred embodiments that it is spherical.

(Glass powder)
The glass powder is said to have a function of assisting the reaction between the aluminum powder and silicon and the sintering of the aluminum powder itself. The glass powder may contain one kind or two or more kinds selected from the group consisting of Pb, Bi, V, B, Si, Sn, P and Zn. Further, a lead-containing glass powder or a lead-free glass powder such as a bismuth-based, vanadium-based, tin-phosphorus-based, zinc borosilicate-based, or alkali borosilicate-based glass powder can be used. Particularly, in view of the influence on the human body, it is desirable to use lead-free glass powder. The glass powder preferably has a softening point of 750 ° C. or lower. Glass powder having a softening point of higher than 750 ° C. may significantly impair the adhesion to the back surface passivation film when the back surface passivation film is used. The average particle diameter of the glass powder is preferably 1 μm or more and 3 μm or less. The content of the glass powder contained in the aluminum paste is not particularly limited, but it is preferably 0.5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the aluminum powder. If the content of the glass powder in the conductive aluminum paste is less than 0.5 parts by mass, the adhesion with the wafer and the passivation film may be reduced, and if it exceeds 40 parts by mass, the electrical resistance as an electrode may increase. This is because.

(Organic vehicle)
As the organic vehicle, for example, a solvent in which an organic binder (resin) is dissolved can be used. If desired, various additives may be added.
Known solvents can be used as the solvent. For example, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether and the like can be mentioned.
As the above-mentioned various additives, for example, an antioxidant, a corrosion inhibitor, an antifoaming agent, a thickener, a tackfire, a coupling agent, an electrostatic imparting agent, a polymerization inhibitor, a thixotropic agent, an anti-settling agent, etc. are used. can do. Specifically, for example, polyethylene glycol ester compound, polyethylene glycol ether compound, polyoxyethylene sorbitan ester compound, sorbitan alkyl ester compound, aliphatic polyvalent carboxylic acid compound, phosphoric acid ester compound, amide amine salt of polyester acid, polyethylene oxide. A system compound, a fatty acid amide wax, etc. can be used.
As the organic binder (resin), known ones can be used, such as ethyl cellulose, nitrocellulose, polyvinyl butyral, phenol resin, melanin resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic resin, polyimide. Thermosetting resin such as resin, furan resin, urethane resin, isocyanate compound, cyanate compound, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, Polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene oxide, polysulfone, polyimide, polyether sulfone, polyarylate, Riete ether ketone, polyethylene tetrafluoride, can be used in combination of two or more kinds of such as silicon resin.
The content of the organic vehicle contained in the aluminum paste is not particularly limited, but it is preferably 70 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the aluminum powder. This is because if the content of the organic vehicle is less than 70 parts by mass or exceeds 200 parts by mass, the printability of the paste may deteriorate.

  Examples of the method for producing the aluminum paste include a method for producing the aluminum paste by mixing the aluminum powder, the glass powder, and the organic vehicle with a well-known mixer.

..Drying As described above, the conductive paste of the present invention for forming the back electrode 15 or the conductive paste and the back electrode 15b of the present invention for forming the back electrode 15a are formed on the back passivation film. After printing the conductive paste for forming, it can be dried.
-Firing The dried conductive paste can be fired under a predetermined firing condition in the air using a firing furnace such as a tubular furnace. As the firing conditions, the firing atmosphere is in the air, and the firing temperature is 500 to 1000 ° C, more preferably 600 to 1000 ° C, further preferably 500 to 900 ° C, and particularly preferably 700 to 900 ° C. The firing is preferably performed in a short time, and the temperature profile (temperature-time curve) during the firing is preferably peaked. For example, with the above temperature as the peak temperature, the in-out time of the firing furnace is preferably 10 to 60 seconds, and more preferably 20 to 40 seconds.

  At the time of firing, it is preferable to simultaneously fire the conductive paste for forming the light incident side electrode and the back surface electrode 15 to form both electrodes at the same time. In this case, since the firing for forming the electrodes can be performed only once, the solar cell can be manufactured at low cost.

  The solar cell of the present invention can be manufactured as described above.

  In the method for manufacturing a solar cell according to the present invention, when the conductive paste printed on the light-incident-side surface of the substrate 1 for forming the light-incident-side electrode is fired, the light-incident-side finger electrode and / or the light-incident-side bus bar is formed. It is preferable that the conductive paste for forming the electrodes fire-through the antireflection film 2. Thereby, the light incident side electrode can be formed so that the light incident side electrode is in contact with the impurity diffusion layer 4. As a result, the contact resistance between the light incident side electrode and the impurity diffusion layer 4 can be reduced. The conductive paste for forming the light incident side electrode that can be used for making the antireflection film 2 fire through is not particularly limited. For example, conventionally known ones can be mentioned.

A solar cell module can be obtained by electrically connecting the solar cells of the present invention obtained as described above with a metal ribbon for interconnects and laminating with a glass plate, a sealing material, a protective sheet, and the like. it can. As the metal ribbon for the interconnect, a metal ribbon whose periphery is covered with solder (for example, a ribbon made of copper) can be used. As the solder, those having tin as a main component, specifically, lead-containing solder containing lead, lead-free solder, and the like, which are commercially available, can be used.
In the solar cell of the present invention, the metal ribbon can be connected to the light incident side bus bar electrode by, for example, soldering.
Further, in the solar cell of the present invention, the metal ribbon can be connected to a predetermined electrode (for example, a part or the entire surface of the back surface electrode) with, for example, solder.

  The solar cell of the present invention can provide a high performance solar cell by having a predetermined electrode formed using the conductive paste of the present invention.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

<Production of conductive paste>
The components shown in Table 1 below were used in the composition (parts by mass) shown in the same table, and these were mixed with a stirrer to produce a conductive paste.
The organic binder and the solvent shown in the column "Organic vehicle" of Table 1 were used in advance in the amounts shown in Table 1, and the obtained mixture was used as the organic vehicle.

<Evaluation>
The following evaluation was performed using the conductive paste manufactured as described above. The results are shown in Table 1.

(Damage to passivation film)
Damage to the passivation film due to the conductive paste was evaluated by a photoluminescence imaging method (referred to as “PL method”).
The PL method is a method of irradiating a substance with light and observing the light generated when excited electrons return to a ground state. By using this, it is possible to evaluate the damage (reactivity) to the passivation film due to the conductive paste in a non-destructive, non-contact and short time.
Specifically, the sample is irradiated with light having an energy larger than the forbidden band to emit light, and the state of the light emission is used to evaluate the state of defects in the crystal and the surface and interface defects. When the sample has defects in the crystalline silicon substrate and surface and interface defects, the defects act as the centers of recombination of electron-hole pairs generated by light irradiation, and correspondingly the emission intensity by photoluminescence. Is reduced. That is, when the passivation film is eroded by the electrode formed by printing and firing the conductive paste, and a surface defect is formed on the surface of the crystalline silicon substrate from which the passivation film is removed, a portion where the surface defect is formed ( That is, the emission intensity of photoluminescence of the electrode portion formed on the sample) decreases. The reactivity of the trial paste with passivation can be evaluated based on the intensity of the photoluminescence emission intensity.

  For evaluation by the PL method, a substrate with a back electrode was prepared in the same manner as the substrate for adhesion evaluation prepared in the evaluation of “adhesion to passivation film” described later.

-Measurement by PL method The measurement by PL method was performed using a Photoluminescence Imaging System apparatus (model number LIS-R2) manufactured by BT Imaging.
The substrate with the back electrode was irradiated with light from an excitation light source (wavelength 650 nm, output 3 mW) to obtain an image of photoluminescence emission intensity and visually observed.

-Evaluation criteria In the image of the emission intensity of photoluminescence obtained as described above, when the emission intensity of the electrode printed part is equal to the emission intensity of the part where the electrode is not printed, there is little damage to the passivation film. Was evaluated, and this was displayed as "○".
In the above image, when the light emission intensity of the electrode printed part is weaker than the light emission intensity of the part where the electrode is not printed (the electrode formation part is darker than the part where the electrode is not printed), the damage to the passivation film is large. Was evaluated, and this was displayed as “x”.

(Adhesion to passivation film)
An adhesiveness evaluation substrate simulating a solar cell was prototyped using the conductive paste produced as described above, and an adhesiveness test to a passivation film was performed. In the above adhesion test, it means that both the adhesion strength between the passivation film and the predetermined electrode and the adhesion strength between the metal ribbon and the predetermined electrode are measured. Since the conductive particles (metal particles) contained are silver particles, the adhesive strength between the metal ribbon and the predetermined electrode is relatively high. Therefore, the above test can evaluate the adhesion between the passivation film and the predetermined electrode.

Preparation of Adhesion Evaluation Substrate As a substrate, a p-type single crystal silicon substrate (substrate: vertical and horizontal 6 inches, thickness 200 μm) was used.
First, a silicon oxide layer of about 20 μm was formed on the above substrate (the substrate 1 in FIG. 1 and the following reference numerals are the same as those in FIG. 1) by dry oxidation, and then a solution of hydrogen fluoride, pure water and ammonium fluoride was mixed. Etching was performed to remove damage on the substrate surface. Further, heavy metal cleaning was performed with an aqueous solution containing hydrochloric acid and hydrogen peroxide.
The adhesion evaluation substrate does not have the light incident side electrode, the light incident side surface texture structure, the n-type impurity diffusion layer 4, and the antireflection film 2.

Next, a silicon nitride film having a thickness of about 60 nm was formed as the back surface passivation film 14 on the entire back surface of the substrate 1 by using a silane gas and an ammonia gas by a plasma CVD method. Specifically, a silicon nitride film (rear surface passivation film 14) having a film thickness of about 60 nm was formed by plasma CVD method by glow discharge decomposition of a mixed gas of NH ₃ / SiH ₄ = 0.5 1 Torr (133 Pa). ..

Each conductive paste manufactured as described above was printed on the back surface passivation film 14 of the substrate with the back surface passivation film by a screen printing method to form five back surface electrodes 15a at intervals of 30 mm.
Each back electrode 15a had a film thickness of about 10 μm, a length of 100 mm, and a width of 2 mm.
Then, the conductive paste-applied substrate was dried at 150 ° C. for about 1 minute.

  Each dried conductive paste-applied substrate was fired under predetermined conditions in the atmosphere using a near-infrared firing furnace (high-speed firing test furnace for solar cells manufactured by NGK Insulators) using a halogen lamp as a heating source. The baking conditions were set to a peak temperature of 775 ° C., and baking was performed in the air in and out of the baking furnace for 30 seconds to prepare a substrate with a back electrode.

Next, a copper ribbon (width 1.5 mm × total thickness 0.16 mm, eutectic solder [tin: lead = 64: 36 weight ratio] is coated with a film thickness of about 40 μm) which is a metal ribbon for interconnects, Five substrates were prepared for each substrate with a back electrode.
In the substrate with back electrode manufactured as described above, one metal ribbon is arranged on each back electrode 15a so as to cover each back electrode 15a, and a temperature of 250 ° C. is applied onto the soldering pad using flux. The substrate for adhesion evaluation was obtained by soldering for 3 seconds. The substrate for adhesion evaluation obtained as described above has five back surface electrodes 15a each having one metal ribbon soldered to each back surface electrode 15a.

-Tensile test The ring-shaped part provided at one end of the metal ribbon soldered as described above was connected to a digital tensile gauge (Digital Force Gauge AD-4932-50N manufactured by A & D Corporation), and the metal was attached to the substrate 1. The adhesion strength was measured by pulling the ribbon in the direction of 180 degrees and measuring the breaking strength with the above digital tensile gauge.
Three substrates for adhesion evaluation were prepared for each example, and the adhesion strengths of 15 back electrodes 15a soldered as described above were measured as described above, and the measured values of the adhesion strength obtained by the above measurement were measured. I calculated the average.

-Evaluation Criteria In the present invention, when the adhesion strength (the average value of the adhesion strengths obtained as described above; the same applies hereinafter) is greater than 1 N / mm, the adhesion to the passivation film is considered to be excellent.
The adhesion strength is greater than 1 N / mm, the better the adhesion.

(Power generation efficiency)
Regarding solar cells, a p-type single crystal silicon substrate (substrate: 6 inches in length and width, 200 μm in thickness) is provided with a linear opening in advance using a laser or the like, and a back surface passivation type single crystal silicon substrate having a resistance value of 3 Ω · cm. Was used.
On the back surface passivation film of the back surface passivation type single crystal silicon substrate, each conductive paste prepared as described above was applied in a line shape so as to be 0.02 to 0.03 g per solar cell, and the back surface electrode 15a. (5 lines, 30 mm apart. Each back electrode 15a has a film thickness of about 10 μm, a length of 100 mm, and a width of 2 mm).
Then, an aluminum paste produced by a known technique is applied to the entire remaining portion of the back surface of the back surface passivation type single crystal silicon substrate so that the weight of each solar cell is 0.9 to 1.0 g, and the back surface electrode 15b ( Line) was printed.
Further, an Ag paste prepared by a known technique was printed on the light receiving surface for a surface electrode.
The substrate on which each electrode was printed as described above was baked at 800 ° C. for 3 seconds to obtain a substrate for power generation efficiency evaluation.

-Power generation efficiency of a solar cell About the power generation efficiency evaluation board obtained as described above, using a Wacom Denso Co., Ltd. solar simulator: WXS-156S-10, IV measuring device: IV15040-10, I-V The measurement was performed and the conversion efficiency (Eff, unit%) of the solar cell was calculated. The power generation efficiency of the solar cell was evaluated based on the result of the conversion efficiency.
In the present invention, the power generation efficiency is preferably 20.0% or more, more preferably 20.3% or more.

Details of each component shown in Table 1 are as follows.
<Conductive particles (silver particles)>
-Spherical silver particles: Spherical silver particles. Average particle size (D50) 0.8 μm
-Flake silver particles: Flake silver particles. Product name N300 (manufactured by Toksen Kogyo Co., Ltd., long diameter (width) average 0.3 μm, short diameter (thickness) average 0.05 μm).

<Organic vehicle>
-Organic binder: ethyl cellulose. Product name STD300, made by Nikkei Seisha.
-Solvent: terpineol. Made by Yasuhara Chemical

<Metal compound>
-Titanium acetylacetonate: manufactured by Tokyo Chemical Industry Co., Ltd. The following structure. Titanium (IV) acetylacetonate.

・ Titanium tetrabutoxide: Ti (OBu) ₄ , manufactured by Tokyo Chemical Industry Co., Ltd.

・ Titanium triisopropoxycyclolide: TiCl (OC ₃ H ₇ ) ₃ , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

-Titanium diisopropoxy bis (ethyl acetoacetate): manufactured by Gelest. The following structure.

Zirconium (IV) butoxide: Zr (OBu) ₄ , manufactured by Gelest

Hafnium butoxide: Hf (OBu) ₄ , manufactured by Gelest

<Copper oxide>
-Copper (II) oxide: CuO. Made by CIK Nanotech. Average particle size (D50) 48 nm

(Copper compound (comparison))
-Copper acetylacetonate: manufactured by Tokyo Chemical Industry Co., Ltd. The following structure. Copper (II) acetylacetonate.

(Tellurium compound)
Tellurium (IV) ethoxide: Te (OEt) ₄ , manufactured by Gelest

(Glass frit)
_{· ZnO · B 2 O 3 ·} SiO 2: Glass transition temperature 490 ° C..
_{· PbO · B 2 O 3 ·} SiO 2: Glass transition temperature 460 ° C..
· PbO · B ₂ O _3: Glass transition temperature 380 ° C..
PbO.SiO ₂ : glass transition temperature 430 ° C.
PbO.SiO ₂ : glass transition temperature 550 ° C.
· PbO · SiO _2: glass transition temperature of 470 ℃.

-Titanium black (comparison): Product name Titanium black 13M-C, manufactured by Mitsubishi Materials Electronic Chemicals. Black Titanium Oxide.

As is clear from the results shown in Table 1, Comparative Example 1 containing no copper oxide had low adhesion to the passivation film.
Comparative Example 2 containing no copper oxide and containing copper acetylacetonate instead had low adhesion to the passivation film.
Comparative Example 3, which did not contain the predetermined metal compound but contained titanium black instead, had low adhesion to the passivation film.
Comparative Example 2 containing no predetermined metal compound had a large damage to the passivation film.

On the other hand, the conductive paste of the present invention has less damage to the passivation film when it becomes an electrode, and has excellent adhesion to the passivation film.
In addition, the conductive paste of the present invention was excellent in power generation efficiency because the damage to the passivation film was small.

1 p-type crystalline silicon substrate 2 antireflection film 4 n-type impurity diffusion layer (n-type silicon layer)
14 Backside Passivation Film 15 Backside Electrode 15a Backside Electrode 15b Backside Electrode 18 Impurity Diffusion Part (p-type Impurity Diffusion Part)
18a BSF (Back Surface Field) layer 18b Al-Si alloy layer 20a Light incident side bus bar electrode

Claims (17)

Conductive particles,
Organic vehicle,
Glass frit,
Copper oxide, and
Containing a metal compound having at least one metal selected from the group consisting of titanium, zirconium and hafnium,
A conductive paste, wherein the metal compound is at least one selected from the group consisting of an alkoxide, an acetylacetonato complex, and a halide of the metal.   The conductive paste according to claim 1, wherein the average particle diameter (D50) of the copper oxide is 1.0 µm or less.   The conductive paste according to claim 1 or 2, wherein the content of the metal compound is 0.01 to 2.0 parts by mass with respect to 100 parts by mass of the conductive particles.   The conductive paste according to claim 1, wherein the average particle diameter (D50) of the conductive particles is 2.0 μm or less.   The conductive paste according to claim 1, wherein the organic vehicle contains at least one selected from the group consisting of a cellulosic polymer, a (meth) acrylic polymer, and a rosin resin.   The conductive paste according to claim 1, wherein the glass transition temperature of the glass frit is 500 ° C. or lower.   The conductive paste according to any one of claims 1 to 6, wherein the glass frit contains ZnO and / or PbO.   The conductive paste according to claim 1, wherein the content of the glass frit is 0.1 to 10 parts by mass with respect to 100 parts by mass of the conductive particles.   The conductive paste according to any one of claims 1 to 8, wherein the copper oxide contains copper (I) oxide and / or copper (II) oxide.   The conductive paste according to claim 1, wherein the content of the copper oxide is 0.01 to 2.0 parts by mass with respect to 100 parts by mass of the conductive particles.   Further, the conductive paste according to claim 1, further comprising tellurium or a tellurium compound.   The conductive paste according to claim 11, wherein the tellurium compound contains at least one selected from the group consisting of tellurium oxide, telluric acid, and tellurium alkoxide.   A solar cell having an electrode formed by using the conductive paste according to claim 1.   The solar cell according to claim 13, wherein the electrode constitutes at least a part of a back electrode.   The solar cell according to claim 14, wherein the back electrode has the electrode and an aluminum electrode. Furthermore, having a back surface passivation film,
The solar cell according to any one of claims 13 to 15, wherein on the back surface side of the solar cell, the back surface passivation film is provided between a substrate that constitutes the solar cell and the electrode.   The solar cell according to claim 16, wherein the electrode is in direct contact with the back surface passivation film.