JP2020075843A - Glass, glass powder, electroconductive paste, and solar battery - Google Patents

Abstract

To provide a glass capable of making appearance of an electrode good to keep reliability of the product by suppressing generation of a particulate matter in the electrode when forming the electrode through an insulation film on a semiconductor substrate such as a solar battery, and improving conversion efficiency of the solar battery, a glass powder composed of the glass, an electroconductive paste containing the glass powder, and a solar battery having an improved conversion efficiency using the electroconductive paste.SOLUTION: The glass contains 40-60% of BO, 5-25% of BiO, 20-30% of ZnO, 2-7% of SiO, 1-10% of SbO, and 0-10% of BaO by mol% expressed in terms of oxide. The glass powder is composed of the glass, and has a Dof 0.5-6.0 μm when a 50% particle size of a volume reference in a cumulative particle size distribution is D.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to glass, glass powder, a conductive paste and a solar cell, and particularly has glass suitable for forming an electrode of a solar cell, glass powder, a conductive paste using the same, and an electrode formed by the conductive paste. It concerns solar cells.

  Conventionally, electronic devices in which a conductive layer to be an electrode is formed on a semiconductor substrate such as silicon (Si) have been used for various purposes. The conductive layer to be the electrode is formed by applying a conductive paste obtained by dispersing a conductive metal powder such as aluminum (Al), silver (Ag), or copper (Cu) and glass powder in an organic vehicle onto a semiconductor substrate, It is formed by firing at a temperature required for electrode formation.

  When the electrodes are formed on the semiconductor substrate in this manner, the insulating film is formed on the entire surface of the semiconductor substrate on which the electrodes are formed, and the patterned electrodes partially penetrate the insulating film to the semiconductor substrate. It may be formed in contact. For example, in a solar cell, an antireflection film is provided on a semiconductor substrate that serves as a light receiving surface, and electrodes are provided in a pattern on the antireflection film. The antireflection film is for reducing the surface reflectance and improving the light receiving efficiency while maintaining a sufficient visible light transmittance, and is usually made of an insulating material such as silicon nitride, titanium dioxide, silicon dioxide or aluminum oxide. Composed. In a solar cell such as PERC (Passivated Emitter and Rear Contact), a passivation film made of an insulating material similar to the antireflection film is also provided on the entire back surface, and electrodes are partially formed on the semiconductor substrate on the passivation film. It is formed in contact with each other.

  Here, in the formation of the electrode, it is essential to form the electrode so as to be in contact with the semiconductor substrate. On the light-receiving surface, the insulating film has a portion corresponding to the pattern of the electrode removed, and the insulating film has a portion removed. An electrode is formed on. Further, on the back surface of the PERC solar cell or the like, the insulating film is partially removed within the range where electrical contact is possible, and the electrode is formed on the entire back surface.

  As a method of partially removing the insulating film, the insulating film is physically removed by a laser or the like, and an electrode is formed at the portion where the insulating film is removed, so that the semiconductor is brought into contact with the semiconductor and operates as a solar cell. .. In the conventional solar cell structure, when the back surface electrode is in direct contact with the semiconductor substrate such as Si on the entire surface to form an electrode, the entire surface of the back surface operates as a solar cell. On the other hand, in the case of a structure such as a PERC solar cell, the area of the portion where the insulating film is removed is about 1 to 3% of the entire back surface, and most of the back surface electrode is formed on the insulating film.

The above technique of forming electrodes on a semiconductor substrate is also applied to the formation of electrodes on a pn junction type semiconductor substrate in a solar cell. As such a conductive paste containing glass powder, for example, Patent Document 1 describes a conductive paste used for forming an electrode of a semiconductor device or the like, and a specific glass composition is B in terms of oxide. the ₂ O ₃ 29.0 mol%, the ZnO 33.8 mol%, the _Bi 2 _{O 3} 30.4 mol%, the _Al 2 _{O 3} 6.0 mole%, containing SiO ₂ 0.8 mol% Glass is disclosed. However, the glass described in Patent Document 1 does not sufficiently contain B ₂ O ₃ , and particularly when the back electrode of the solar cell in the p-type semiconductor substrate is formed, boron, which is a majority carrier, is sufficiently contained in the Si substrate. There is a problem that electrical characteristics are deteriorated because diffusion is not possible.

Patent Document 2, as glass for forming electrodes of a solar cell, a _B 2 _{O 3} 66.7 mol% in terms of oxide, glass containing _Bi 2 _{O 3} 33.3 mol% is disclosed. However, in the glass described in Patent Document 2, if the total content of B ₂ O ₃ and Bi ₂ O ₃ is excessively large, for example, when aluminum is used for the back electrode, aluminum or aluminum-silicon during firing is used. There is a problem in that a granular material having an alloy composition is generated and protrudes on the surface of the back electrode after firing, resulting in poor appearance. Further, there is a problem that when the solar battery cell is modularized, the cell is cracked starting from the protruding portion of the particulate matter.

JP, 2018-6064, A JP, 2017-222543, A

Regarding B ₂ O ₃ —Bi ₂ O ₃ based glass used for forming electrodes of solar cells, many techniques for improving the electrode formability have been developed as in Patent Document 1 and Patent Document 2. However, particularly in a solar cell such as PERC, even if the composition of the glass of the glass powder used for forming the electrode or the particle size distribution of the powder is adjusted, the above-mentioned aluminum or aluminum-silicon alloy in the electrode accompanying the formation of the electrode is currently used. It is difficult to reduce the electrical resistance between the electrode and the semiconductor substrate and improve the conversion efficiency of the solar cell while suppressing the generation of the particulate matter derived from the metal for forming an electrode, which is represented by the above. That is, a technique for improving the conversion efficiency of the solar cell and suppressing the generation of particulate matter in the electrode during electrode formation to maintain a good appearance and maintain the reliability of the product is under development.

  The present invention, in the glass used for electrode formation, improves the appearance of the electrode obtained by suppressing the generation of particulate matter in the electrode when the electrode is formed on a semiconductor substrate such as a solar cell via an insulating film. Therefore, it is an object of the present invention to provide a glass which can maintain the reliability of the product and can improve the conversion efficiency of the solar cell. A further object of the present invention is to provide a glass powder made of the glass, a conductive paste containing the glass powder, and a solar cell having improved product reliability and conversion efficiency by using the conductive paste.

The present invention provides glass, glass powder, a conductive paste and a solar cell having the following constitutions.
[1] B ₂ O ₃ is 40% or more and 60% or less, Bi ₂ O ₃ is 5% or more and 25% or less, ZnO is 20% or more and 30% or less, and SiO ₂ is 2% in mol% in terms of oxide. Glass containing 7% or more, Sb ₂ O ₃ of 1% or more and 10% or less, and BaO of 0% or more and 10% or less.
[2] 50% particle diameter based on volume in a cumulative particle size distribution is taken as _{D 50, D 50} is 0.5μm or more 6.0μm or less [1] glass powder comprising glass according.
[3] A conductive paste containing the glass powder according to [2], a conductive metal powder, and an organic vehicle.

[4] A solar cell comprising an electrode formed using the conductive paste according to [3].
[5] A conductive paste containing a metal, glass, and an organic vehicle, wherein the metal is contained in an amount of 63.0 mass% or more and 97.9 mass% or less based on the total mass of the conductive paste, and Al, Ag, It contains at least one selected from the group consisting of Cu, Au, Pd and Pt, and the glass contains 0.1 part by mass or more and 9.8 parts by mass or less based on 100 parts by mass of the metal, and is converted into oxide. In mol% display, B ₂ O ₃ is 40% or more and 60% or less, Bi ₂ O ₃ is 5% or more and 25% or less, ZnO is 20% or more and 30% or less, SiO ₂ is 2% or more and 7% or less, and Sb ₂ 1% or more and 10% or less of O ₃ and 0% or more and 10% or less of BaO are included, and the organic vehicle is contained in an amount of 2% by mass or more and 30% by mass or less based on the total mass of the conductive paste. Conductive paste.

[6] The glass is a 50% particle diameter on a volume basis when the _{D 50} in a cumulative particle size _{distribution, D 50} is 6.0μm or less of the glass powder above 0.5 [mu] m [5], wherein the conductive paste.
[7] The conductive paste according to [5] or [6], wherein the metal contains Al.
[8] The organic vehicle is an organic resin binder solution in which an organic resin binder is dissolved in a solvent, and the organic resin binder is methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate, and 2- At least one selected from the group consisting of an acrylic resin obtained by polymerizing one or more selected from the group consisting of hydroxyethyl acrylate, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose. And the solvent comprises at least one selected from the group consisting of diethylene glycol monobutyl ether, terpineol, butyl diglycol acetate, ethyl diglycol acetate, propylene glycol diacetate, and methyl ethyl ketone [5] to [7] The conductive paste as described in Crab.

[9] A silicon substrate having a sunlight receiving surface, a first insulating film provided on the sunlight receiving surface side of the silicon substrate, and a surface of the silicon substrate opposite to the sunlight receiving surface. A second insulating film having at least one opening provided, a second electrode partially contacting the silicon substrate through the opening of the second insulating film; A solar cell comprising: a first electrode penetrating a part of an insulating film and contacting the silicon substrate, wherein the second electrode is a group consisting of Al, Ag, Cu, Au, Pd and Pt. A metal containing at least one selected, and in terms of mol% in terms of oxide, B ₂ O ₃ is 40% or more and 60% or less, Bi ₂ O ₃ is 5% or more and 25% or less, and ZnO is 20% or more 30. %, SiO ₂ of 2% or more and 7% or less, Sb ₂ O ₃ of 1% or more and 10% or less, and BaO of 0% or more and 10% or less, a solar cell.

[10] The solar cell according to [9], wherein the second electrode contains 90% by mass or more and 99.9% by mass or less of the metal and 0.1% by mass or more and 10% by mass or less of the glass.
[11] The solar cell according to [9] or [10], wherein the metal contained in the second electrode contains at least Al.
[12] The solar cell according to any one of [9] to [11], wherein the first electrode contains a metal containing at least Ag.
[13] The solar cell according to any one of [9] to [12], wherein the first insulating film is made of silicon nitride.
[14] A metal oxide film made of aluminum oxide or silicon oxide, in which the second insulating film is in contact with a surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film is further formed on the metal oxide film. The solar cell according to any one of [9] to [13].

  The glass of the present invention, and the glass powder made of the glass, when used in a conductive paste together with a conductive component, are granular in the electrode when the electrode is formed on a semiconductor substrate such as a solar cell via an insulating film. It is possible to maintain the reliability of the product by improving the appearance of the electrode obtained by suppressing the generation of substances and sufficiently ensuring the contact with the insulating film and the semiconductor substrate. Further, the glass of the present invention and the glass powder made of the glass contain boron, and it is possible to diffuse the boron contained in the glass during formation of an electrode into, for example, a p-type layer of a semiconductor substrate. Therefore, a good p + layer can be formed to improve the conversion efficiency of the solar cell.

  In particular, it is known that a particulate material having an aluminum or aluminum-silicon alloy composition is generated during firing in a back electrode using Al such as a PERC solar cell. In forming such an electrode, the effect of suppressing generation of the particulate matter by the glass of the present invention is remarkable. As a result, it is possible to suppress damage to the solar cells and the like when the solar cells are modularized due to the protruding portions of the generated particulate matter, and it is possible to improve the productivity.

  In the present invention, by containing the glass powder, a conductive paste that can improve the conversion efficiency of the solar cell with the formation of an electrode using the glass powder, and a solar cell that has the conversion efficiency improved by using the conductive paste. Batteries can be provided.

It is the figure which showed typically the cross section of an example of the p-type Si substrate single-sided light receiving solar cell in which the electrode was formed using the electrically conductive paste of this invention.

Hereinafter, embodiments of the present invention will be described.
<Glass>
The glass of the present invention is represented by mol% of oxide _equivalent, B 2 _{O 3} 40 to 60%, a _Bi 2 _{O 3} 5 to 25%, the ZnO 20 to 30%, the SiO ₂ 2 to 7%, sb ₂ O ₃ and 1-10%, and BaO 0%. In the following description, unless otherwise specified, the indication of "%" in the content of each component of glass is the indication of mol% in terms of oxide. In the present specification, “to” representing a numerical range includes upper and lower limits.

  The content of each component in the glass of the present invention is the result of inductively coupled plasma (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectroscopy) analysis or electron beam microanalyzer (EPMA: Electron Probe Micro Analyzer) analysis. Required from.

B ₂ O ₃ is an essential component in the glass of the present invention. B ₂ O ₃ has a function of improving softening fluidity of glass and improving contactability with an insulating film and a semiconductor substrate in an electrode obtained by using a conductive paste containing the glass. B ₂ O ₃ is a component that stabilizes glass. Hereinafter, in the description of the glass component, "conductive paste" is "conductive paste containing the glass of the present invention", "electrode""electrode obtained using the conductive paste containing the glass of the present invention" Means

Further, B ₂ O ₃ can promote the direct reaction between the semiconductor substrate and the glass in the conductive paste by causing the glass to flow. Thereby, for example, when the semiconductor substrate is a pn junction type Si semiconductor substrate, the glass can form ap ⁺ layer or an n ⁺ layer in contact with the electrode. For example, when forming the electrode in contact with the p ⁺ layer can promote the diffusion of the p ⁺ layer of B ₂ O ₃ is a component that glass contains as B, to form a better p ⁺ layer be able to.

The glass of the present invention contains B ₂ O ₃ in a proportion of 40% or more and 60% or less. If the content of B ₂ O ₃ is less than 40%, B cannot be sufficiently diffused into the Si semiconductor substrate during electrode formation, and thus conversion efficiency in a solar cell, for example, may not be improved. Further, B ₂ O ₃ is a glass network structure forming component, and if it is less than 40%, vitrification cannot be performed. The content of B ₂ O ₃ is preferably 45% or more. On the other hand, when the content of B ₂ O ₃ exceeds 60%, the glass reacts too much with the semiconductor substrate during the formation of the electrode, and particulate matter is generated in the electrode. The content of B ₂ O ₃ is preferably 59% or less.

Bi ₂ O ₃ is an essential component in the glass of the present invention. Bi ₂ O ₃ has a function of improving the softening fluidity of glass and improving the contact property between the electrode and the insulating film and the semiconductor substrate. Further, the metal Bi particles produced by reducing Bi ₂ O ₃ in the glass lower the melting temperature of the particles of the conductive metal by the eutectic reaction. As a result, particles of the conductive metal is diffused into the semiconductor substrate, forming a p ⁺ layer, or further enhanced the performance of the p ⁺ layer, which contributes to the conversion efficiency of the solar cell. The effect is particularly high when the conductive metal is Al.

Bi ₂ O ₃ further has a function of promoting the direct reaction between the semiconductor substrate and the glass by causing the glass to flow. As a result, it is possible to promote the diffusion of B ₂ O ₃ in the glass as B into the p ⁺ layer of the semiconductor substrate, and to form a better p ⁺ layer. The glass of the present invention contains Bi ₂ O ₃ in a proportion of 5% or more and 25% or less. When the content of Bi ₂ O ₃ is less than 5%, the softening point of glass becomes high, so that the fluidity is lowered and the reaction with the semiconductor substrate is not sufficient. The content of Bi ₂ O ₃ is preferably 7% or more, and more preferably 10% or more. On the other hand, if the Bi ₂ O ₃ content exceeds 25%, glass cannot be obtained due to crystallization. The content of Bi ₂ O ₃ is preferably 22% or less, more preferably 20% or less.

  ZnO is an essential component in the glass of the present invention. ZnO is a component that can suppress the crystallization of glass and improve the reactivity between the glass and the insulating film on the semiconductor substrate such as the Si substrate or the Si substrate. The glass of the present invention contains ZnO in a proportion of 20% or more and 30% or less. When the content of ZnO is less than 20%, the reactivity between the glass and the insulating film on the semiconductor substrate such as the Si substrate or the Si substrate is deteriorated, and the bonding strength is weakened, or the electrode and the semiconductor substrate are separated from each other. The electrical resistance will become high. The ZnO content is preferably 22% or more. When the content of ZnO exceeds 30%, the glass reacts too much with the semiconductor substrate at the time of forming the electrode, and particulate matter is generated in the electrode. The ZnO content is preferably 29% or less.

SiO ₂ is an essential component in the glass of the present invention. The glass can be stabilized by containing SiO ₂ . The glass of the present invention contains SiO ₂ in a proportion of 2% or more and 7% or less. When the content of SiO ₂ is less than 2%, it is difficult to obtain glass due to crystallization, and it becomes impossible to obtain long-term reliability of the characteristics of the solar cell. The content of SiO ₂ is preferably 3% or more, more preferably 5% or more. If the content of SiO ₂ exceeds 7%, the glass transition point increases, and the glass cannot flow during sintering. The content of SiO ₂ is preferably 6% or less.

Sb ₂ O ₃ is an essential component in the glass of the present invention. The glass can be stabilized by containing Sb ₂ O ₃ . The glass of the present invention contains Sb ₂ O ₃ in a ratio of 1% or more and 10% or less. When the content of Sb ₂ O ₃ is less than 1%, it is difficult to obtain glass due to crystallization, and it becomes impossible to obtain long-term reliability as the characteristics of the solar cell. The content of Sb ₂ O ₃ is preferably 2% or more, more preferably 3% or more. If the content of Sb ₂ O ₃ exceeds 10%, the glass transition point increases, and the glass cannot flow during sintering. The content of Sb ₂ O ₃ is preferably 8% or less, more preferably 5% or less.

  In the glass of the present invention, BaO is a component that lowers the contact resistance component between the electrode and the semiconductor substrate. Further, BaO can be stabilized as a glass component and also as a modified oxide. The content of BaO in the glass of the present invention is 0% or more and 10% or less. The content of BaO is preferably 1% or more. If the content of BaO exceeds 10%, glass cannot be obtained due to crystallization. The content of BaO is preferably 5% or less.

The glass of the present invention may contain other optional components other than these. Other optional ingredients, _{specifically, PbO, P 2 O 5,} V 2 O 5, Sb 2 O 5, As 2 O 5, Li 2 O, Na 2 O, K 2 O, ZrO 2, Fe 2 Examples thereof include various oxide components such as O ₃ , CuO, SnO ₂ , MgO, CaO, SrO, Al ₂ O ₃ , MnO, MnO ₂ , CeO ₂ , TiO ₂ , MoO ₃ , and WO _{3, which} are commonly used in glass. These other optional components may be used alone or in combination of two or more depending on the purpose. The total content of other optional components is preferably 5% or less in total.

  The method for producing the glass of the present invention is not particularly limited. For example, it can be manufactured by the following method.

  First, a raw material mixture is prepared. The raw material is not particularly limited as long as it is a raw material used for producing a usual oxide glass, and an oxide, a carbonate or the like can be used. In the obtained glass, the kind and ratio of the raw materials are appropriately adjusted so as to be within the above composition range to obtain a raw material mixture.

  Next, the raw material mixture is heated by a known method to obtain a melt. The temperature of melting by heating (melting temperature) is preferably 800 to 1400 ° C, more preferably 900 to 1300 ° C. The heating and melting time is preferably 30 to 300 minutes.

  Then, the glass of the present invention can be obtained by cooling and solidifying the melt. The cooling method is not particularly limited. A method of quenching by a roll-out machine, a press machine, dropping on a cooling liquid, or the like can also be used. The glass obtained is preferably completely amorphous, ie it has a crystallinity of 0%. However, a crystallized portion may be included as long as the effect of the present invention is not impaired.

  The glass of the present invention thus obtained may have any form. For example, it may have a block shape, a plate shape, a thin plate shape (flake shape), a powder shape, or the like.

  The glass of the present invention has a function as a binder and is preferably used for a conductive paste. The conductive paste containing the glass of the present invention is suitably used, for example, for forming electrodes of solar cells. When the glass of the present invention is contained in the conductive paste, the glass is preferably powder.

<Glass powder>
The glass powder of the present invention is made of the glass of the present invention and preferably has a D ₅₀ of 0.5 μm or more and 6.0 μm or less. This D ₅₀ range is a particularly preferable range for use in a conductive paste. When D ₅₀ is 0.5 μm or more, the dispersibility in the conductive paste is further improved. Further, when D ₅₀ is 6.0 μm or less, a portion where the glass powder does not exist around the conductive metal powder is less likely to occur, and thus the adhesiveness between the electrode and the semiconductor substrate or the like is further improved. In this case, D ₅₀ is more preferably 0.8 μm or more. D ₅₀ is more preferably 5.0 μm or less.

In the present specification, “D ₅₀ ” denotes a volume-based 50% particle size in the cumulative particle size distribution, and specifically, of the particle size distribution measured using a laser diffraction / scattering particle size distribution measuring device. In the cumulative particle size curve, it represents the particle size when the integrated amount occupies 50% by volume.

  The glass powder of the present invention can be obtained by pulverizing the glass produced as described above, for example, by a dry pulverizing method or a wet pulverizing method so as to have the above-mentioned specific particle size distribution.

  As a glass pulverizing method for obtaining the glass powder of the present invention, for example, a method of dry pulverizing a glass having an appropriate shape and then wet pulverizing is preferable. The dry pulverization and the wet pulverization can be performed using a pulverizer such as a roll mill, a ball mill, a jet mill. The particle size distribution can be adjusted, for example, by adjusting the crushing time in each crushing process, the size of the balls in the ball mill, and the like. In the case of the wet pulverization method, it is preferable to use water as the solvent. After wet pulverization, water content is removed by drying or the like to obtain glass powder. In order to adjust the particle size of the glass powder, in addition to crushing the glass, classification may be carried out if necessary.

<Conductive paste>
The glass of the present invention can be applied to a conductive paste as glass powder, for example. The conductive paste made of the glass of the present invention contains the above-mentioned glass powder of the present invention, a conductive metal powder and an organic vehicle.

  As the conductive metal powder contained in the conductive paste of the present invention, a metal powder usually used for an electrode formed on a circuit board (including a laminated electronic component) such as a semiconductor substrate or an insulating substrate is used without particular limitation. .. Specific examples of the conductive metal powder include powders of Al, Ag, Cu, Au, Pd, Pt and the like. Among these, Al powder is preferable from the viewpoint of productivity. When the conductive metal powder is Al powder, the effect of the glass of the present invention to improve the appearance of the obtained electrode by suppressing the generation of particulate matter in the electrode when forming the electrode is remarkable.

From the viewpoint of suppressing aggregation and obtaining uniform dispersibility, the conductive metal powder preferably has a particle diameter D ₅₀ of 0.3 μm or more and 10 μm or less.

  The content of the conductive metal powder in the conductive paste is preferably 63.0 mass% or more and 97.9 mass% or less with respect to the total mass of the conductive paste. When the content of the conductive metal powder is less than 63.0% by mass, the conductive metal powder is more sintered and glass float or the like is likely to occur. On the other hand, when the content of the conductive metal powder exceeds 97.9 mass%, it may not be possible to cover the periphery of the conductive metal powder with the glass deposit. In addition, the adhesion between the electrode and the circuit board such as the semiconductor substrate or the insulating substrate may deteriorate. The content of the conductive metal powder relative to the total mass of the conductive paste is more preferably 75.0% by mass or more and 95.0% by mass or less.

  The content of the glass powder in the conductive paste is, for example, preferably 0.1 part by mass or more and 9.8 parts by mass or less with respect to 100 parts by mass of the conductive metal powder. If the content of the glass powder is less than 0.1 parts by mass, the periphery of the conductive metal powder may not be covered with the glass precipitate. In addition, the adhesion between the electrode and the circuit board such as a semiconductor substrate or an insulating substrate may deteriorate. On the other hand, when the content of the glass powder exceeds 9.8 parts by mass, the conductive metal powder is more sintered and the glass float easily occurs. The content of the glass powder with respect to 100 parts by mass of the conductive metal powder is more preferably 0.5 parts by mass or more and 5 parts by mass or less.

  As the organic vehicle contained in the conductive paste, an organic resin binder solution obtained by dissolving an organic resin binder in a solvent can be used.

  Examples of the organic resin binder used in the organic vehicle include cellulosic resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, An organic resin such as an acrylic resin obtained by polymerizing one or more kinds of acrylic monomers such as butyl acrylate and 2-hydroxyethyl acrylate is used.

  As the solvent used for the organic vehicle, solvents such as diethylene glycol monobutyl ether, terpineol, butyl diglycol acetate, ethyl diglycol acetate, propylene glycol diacetate in the case of a cellulose resin, methyl ethyl ketone, terpineol, butyl in the case of an acrylic resin. Solvents such as diglycol acetate, ethyl diglycol acetate and propylene glycol diacetate are preferably used.

  The ratio of the organic resin binder and the solvent in the organic vehicle is not particularly limited, but it is selected so that the obtained organic resin binder solution has a viscosity capable of adjusting the viscosity of the conductive paste. Specifically, the mass ratio of organic resin binder: solvent is preferably about 3:97 to 15:85.

  The content of the organic vehicle in the conductive paste is preferably 2% by mass or more and 30% by mass or less based on the total amount of the conductive paste. When the content of the organic vehicle is less than 2% by mass, the viscosity of the conductive paste increases, so that the coating property of the conductive paste such as printing is deteriorated, and it becomes difficult to form a good conductive layer (electrode). Further, when the content of the organic vehicle exceeds 30% by mass, the content ratio of the solid content of the conductive paste becomes low, and it becomes difficult to obtain a sufficient coating film thickness.

As one mode of the conductive paste of the present invention, a metal containing at least one selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt is used in an amount of 63.0 to 97.9 mass based on the total mass of the conductive paste. % wherein, _B 2 _{O 3} 40 to 60% in mol% of the oxide equivalent, the _{Bi 2 O 3 5~25%, 20~30} % of ZnO, the _{SiO 2 2~7%, Sb 2 O} 3 1 to 10% and glass containing 0 to 10% of BaO in an amount of 0.1 to 9.8 parts by mass relative to 100 parts by mass of the metal, and an organic vehicle in an amount of 2 to 30 parts by mass with respect to the total mass of the conductive paste. % Of the conductive paste. The glass in this aspect is the glass of the present invention. With respect to the glass, metal and organic vehicle contained in the conductive paste of the present aspect, preferable aspects such as composition, type, form and content can be the same as described above.

  In the conductive paste of the present invention, in addition to the above-mentioned glass powder, conductive metal powder, and organic vehicle, known additives can be added as necessary and to the extent not deviating from the object of the present invention. ..

Examples of such additives include various inorganic oxides. Specific examples of the inorganic oxide include B ₂ O ₃ , ZnO, SiO ₂ , Al ₂ O ₃ , TiO ₂ , MgO, ZrO ₂ , Sb ₂ O ₃ , and complex oxides thereof. These inorganic oxides have the effect of softening the sintering of the conductive metal powder when firing the conductive paste, and thus have the effect of adjusting the bonding strength after firing. The size of the additive made of these inorganic oxides is not particularly limited, but for example, those having D ₅₀ of 10 μm or less can be suitably used.

  The content of the inorganic oxide in the conductive paste is appropriately set according to the purpose, but is preferably 10% by mass or less, and more preferably 7% by mass or less based on the glass powder. If the content of the inorganic oxide with respect to the glass powder exceeds 10% by mass, the fluidity of the conductive paste at the time of forming the electrode may decrease, and the adhesive strength between the electrode and the circuit board such as the semiconductor substrate or the insulating substrate may decrease. There is. Further, in order to obtain a practical compounding effect (adjustment of bonding strength after firing), the lower limit of the above content is preferably 0.5% by mass, more preferably 1.0% by mass.

  Additives known in the conductive paste, such as a defoaming agent and a dispersant, may be added to the conductive paste. The organic vehicle and these additives are components that usually disappear during the process of forming an electrode. A known method using a rotary mixer equipped with a stirring blade, a crusher, a roll mill, a ball mill, or the like can be applied to the preparation of the conductive paste.

  The application and firing of the conductive paste on a circuit board such as a semiconductor substrate or an insulating substrate can be performed by the same method as the coating and firing in the conventional electrode formation. Examples of the coating method include screen printing and dispensing method. The firing temperature depends on the type of the conductive metal powder contained, the surface state, etc., but a temperature of about 500 to 1000 ° C. can be exemplified. The firing time is appropriately adjusted according to the shape and thickness of the electrode to be formed. Further, a drying process at about 80 to 200 ° C. may be provided between the application and firing of the conductive paste.

<Solar cell>
The solar cell of the present invention includes an electrode formed using such a conductive paste of the present invention, specifically, an electrode baked on a semiconductor substrate. The solar cell of the present invention preferably comprises an electrode formed using the conductive paste of the present invention as a back electrode of a single-sided light receiving solar cell such as a PERC solar cell. A PERC solar cell usually has an antireflection film made of an insulating material on the light receiving surface, and also has an insulating film made of the same insulating material as the antireflection film on the entire back surface except a part thereof.

  The solar cell of the present invention is a PERC solar cell or the like in which an electrode formed by using the conductive paste of the present invention is used as an electrode formed on the insulating film provided on the back surface so as to partially contact the semiconductor substrate. It is preferably provided. This electrode is formed on the entire surface of the insulating film so as to come into contact with the semiconductor substrate in the opening formed as described below, for example. When the conductive paste of the present invention is used, when forming an electrode on a semiconductor substrate via an insulating film, it is an electrode in which the contact with the semiconductor substrate at the portion where the insulating film is removed is sufficiently secured. The generation of the particulate matter is suppressed and the flatness of the obtained electrode surface is secured, so that the electrode having high reliability can be obtained.

  As described above, the conductive paste of the present invention preferably contains Al powder as the conductive metal powder. That is, the conductive paste of the present invention is preferably used for forming an Al electrode. More preferably, the insulating film is formed on the semiconductor substrate, and a part of the insulating film is removed by, for example, a laser to form an insulating film having an opening, and then the semiconductor film is provided on the insulating film through the opening. The conductive paste of the present invention is used to form Al electrodes in a partially contacting form.

The Al electrode provided on the insulating film having the opening so as to be in contact with the semiconductor substrate through the opening may be, for example, a back electrode of a PERC solar cell using a p-type Si substrate, an n-type Si substrate. Back electrode of a PERT (Passivated Emitter, Rear Totally diffused) solar cell using the above, an electrode provided on the p layer or p ⁺ layer side of a double-sided light receiving solar cell using an n-type Si substrate or a p-type Si substrate, a back electrode One electrode of a contact solar cell and the like can be mentioned.

As an embodiment of the solar cell of the present invention, a silicon substrate having a sunlight receiving surface, a first insulating film provided on the sunlight receiving surface side of the silicon substrate, and a sunlight receiving surface of the silicon substrate are opposite to each other. A second insulating film having at least one opening provided on the side surface, a second electrode partially contacting the silicon substrate through the opening of the second insulating film, a first insulating film A solar cell comprising a first electrode penetrating a part of an insulating film and contacting a silicon substrate, wherein the second electrode is selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt. A metal containing at least one of the following, and B ₂ O ₃ is 40 to 60%, Bi ₂ O ₃ is 5 to 25%, ZnO is 20 to 30%, and SiO ₂ is 2 to 2 in terms of mol% in terms of oxide. A solar cell made of 7%, glass containing 1 to 10% of Sb ₂ O ₃ and 0 to 10% of BaO can be mentioned.

  Note that the opening of the second insulating film refers to a portion provided so as to penetrate from the surface of the second insulating film to the surface of the silicon substrate opposite to the solar light receiving surface. In the following description, the term "opening" is used in the same meaning as above.

  The shape of the opening is not particularly limited, but may be linear or circular. When the shape is linear, the line width is preferably 30 to 100 μm, and when the shape is circular, the diameter is preferably 30 to 100 μm. The area of the opening is preferably 1 to 3% with respect to the total area of the surface of the silicon substrate opposite to the solar light receiving surface.

  The first electrode preferably contains a metal containing at least one selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt, and the metal preferably contains at least Ag. The first insulating film is made of an insulating material such as silicon nitride, titanium dioxide, silicon oxide, or aluminum oxide, and is preferably made of silicon nitride.

  The second electrode preferably contains 90 to 99.9 mass% of the above metal and 0.1 to 10 mass% of the above glass. The glass contained in the second electrode is the glass of the present invention, and the preferable composition is as described above. The metal contained in the second electrode preferably contains at least Al. When the metal contains Al, the glass of the present invention has a remarkable effect of suppressing the generation of particulate matter in the electrode when forming the electrode and improving the appearance of the electrode.

  The second insulating film is preferably a multilayer film, and a metal oxide film made of aluminum oxide or silicon oxide is in contact with the surface of the silicon substrate opposite to the solar light receiving surface, and the metal oxide film is further nitrided. A multilayer film structure including a silicon film is preferable.

  Hereinafter, a case where the electrodes of the p-type Si substrate single-sided light receiving solar cell are formed of the conductive paste of the present invention will be described as an example. FIG. 1 is a diagram schematically showing a cross section of an example of a p-type Si substrate single-sided solar cell in which electrodes are formed using the conductive paste of the present invention.

  The solar cell 10 shown in FIG. 1 has a p-type Si substrate 1, an insulating film 2A provided on the upper surface thereof, and an insulating film 2B having an opening 7 provided on the lower surface thereof, and the insulating film 2B is provided on the entire surface thereof. It has an Al electrode 4 which is formed and partially contacts the p-type Si substrate through the opening 7, and an Ag electrode 3 which penetrates part of the insulating film 2A and contacts the p-type Si substrate 1. The upper surface of the p-type Si substrate 1 has, for example, a concave-convex structure formed by using a wet etching method so as to reduce the light reflectance. In addition, the upper and lower sides of the drawings do not necessarily indicate the upper and lower sides in use. Moreover, both surfaces of the p-type Si substrate may have an uneven structure, if necessary.

The p-type Si substrate 1 is composed of an n ⁺ layer 1a and a p layer 1b in order from the top, and the Al electrode 4 is in contact with the p layer 1b and the Ag electrode 3 is in contact with the n ⁺ layer 1a. Here, the n ⁺ layer 1a can be formed by, for example, doping P, Sb, As or the like on the surface on which the uneven structure is formed.

  The Al electrode 4 and the Ag electrode 3 are formed as follows by using an Al electrode forming conductive paste containing glass powder and Al powder, and an Ag electrode forming conductive paste containing glass powder and Ag powder, respectively. It

  That is, the insulating film 2A provided on the upper surface of the p-type Si substrate 1 exists on the entire surface before forming the Ag electrode 3 without any gap, and the above-mentioned Ag electrode forming conductive paste for forming the Ag electrode 3 is applied. By melting only the portion where the conductive paste is baked, the Ag electrode 3 that penetrates the insulating film 2A and contacts the p-type Si substrate 1 is formed.

  On the other hand, the insulating film 2B is provided on the entire lower surface of the p-type Si substrate 1 without any gap, and then a part thereof is physically removed by a laser to form the Al electrode 4 and has an opening 7. It is composed. The conductive paste for forming an Al electrode described above is applied to the entire surface of the insulating film 2B having the opening 7 and baked to cover the entire surface of the insulating film 2B and the Al partially contacted with the semiconductor at the opening 7 is formed. The electrode 4 is formed.

When the Al electrode 4 is formed, the conductive paste for forming the Al electrode is brought into contact with the p layer 1b of the p-type Si substrate 1 in the opening 7 and then melted during firing, so that the Al from the Al electrode enters the p layer 1b. The Al-Si alloy layer 5 is diffused to form the Al-Si alloy layer 5 directly on the Al electrode. Further, a BSF (Back Surface Field) layer 6 is obtained as ap ⁺ layer immediately above the Al-Si alloy layer 5.

  In the above, the conductive paste of the present invention can be used as the Ag electrode forming conductive paste and the Al electrode forming conductive paste, but as described above, it is particularly preferable to use the Al electrode forming conductive paste.

  By using the glass powder of the present invention and the conductive paste of the present invention containing Al powder as the conductive paste for forming an Al electrode, the electrode, the insulating film, and the semiconductor substrate are formed when the electrode is formed through the insulating film. A sufficient contact with the p-type Si substrate 1 is ensured, and the Al electrode 4 that is in sufficient contact with the p-type Si substrate 1 is obtained. In addition, generation of particulate matter in the electrode is suppressed during electrode formation, and the appearance of the obtained electrode can be improved.

  Note that the insulating film included in the solar cell has a function of preventing reflection and can suppress recombination of semiconductor carriers. As the insulating material forming the film, the insulating materials listed above can be used. The insulating film may be a single layer film or a multilayer film. The conductive paste of the present invention is particularly useful for forming an electrode through an insulating film having a layer made of silicon nitride and a layer made of aluminum oxide or silicon oxide, and the semiconductor substrate partially formed on the electrode and the insulating film. It has sufficient solar cell characteristics by ensuring sufficient contact with.

  In the solar cell of the present invention, particularly in the PERC solar cell, the insulating film is partially removed on the back surface within the range where electrical contact is possible, and the entire surface of the insulating film is formed when the electrode containing the glass powder of the present invention is formed. A portion where the electrode is formed and the insulating film is partially removed at the same time can form an electrode structure in which contact with the semiconductor substrate is secured. By using the conductive paste, it was possible to suppress the generation of particulate matter in the electrode when forming the electrode, and to form the electrode with a good appearance, and to realize high reliability and high battery characteristics. A solar cell can be provided.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples. Examples 1 to 8 are examples, and Examples 9 and 10 are comparative examples.

(Examples 1 to 10)
Glass was manufactured as a thin glass by the following method, and glass powder was manufactured from the thin glass.

<Production of glass (thin plate glass)>
Raw material powders were mixed and mixed so as to have the composition shown in Table 1, and melted for 30 minutes to 2 hours using a crucible in an electric furnace at 800 to 1400 ° C. to obtain a thin glass sheet made of glass having the composition shown in Table 1. Molded.

<Production of glass powder>
In each example, the obtained thin glass plate was pulverized as follows by combining dry pulverization and wet pulverization to adjust the particle size distribution.

First, the glass was dry-milled with a ball mill, and then the glass powder from which coarse particles were removed was further wet-milled with water with a ball mill to obtain a glass slurry. In order to obtain a predetermined D ₅₀ during this wet pulverization, the balls were made of alumina having a diameter of 5 mm, and the D ₅₀ was adjusted by the pulverization time. After that, the slurry obtained by the wet pulverization was filtered to remove most of the water content, and then dried at 130 ° C. by a dryer to adjust the water content to produce a glass powder.

<Evaluation>
With respect to the glass of each example, the D ₅₀ of the glass powder was evaluated by the following method. The results are shown in Table 1 together with the composition. In addition, the blank column in the column of each component of the glass composition indicates the content “0%”.

_{(D 50)}
With respect to the glass of each example, 0.02 g of glass powder was mixed with 20 cc of water, and ultrasonically dispersed for 1 minute to prepare a sample. The sample was put into a Microtrac measuring device (laser diffraction / scattering type particle size distribution measuring device) to obtain a value of D ₅₀ .

<Production of conductive paste>
The conductive paste for Al electrode formation containing the glass powder of each example produced above was produced by the following method.

First, 100 parts by mass of an aluminum powder having a D ₅₀ of 6.0 μm generated by a gas atomization method and 1.5 parts by mass of a glass powder of each example were dispersed in 35 parts by mass of a resin liquid obtained by dissolving ethyl cellulose in butyl diglycol. It was made into a paste using (dispar). As a result, a conductive paste for forming an Al electrode was obtained.

<Production of Al electrode in solar cell and evaluation of appearance and cell characteristics>
(Manufacture of solar cells)
A solar cell 10 having the configuration shown in FIG. 1 was manufactured using the conductive paste for forming an Al electrode and the commercially available conductive paste for forming an Ag electrode produced in each example as described below, and the obtained solar cell was obtained. The appearance and battery characteristics of the Al electrode in Example 1 were evaluated. The solar cell 10 has a non-light-receiving surface on the p-type Si semiconductor substrate 1 with an Al electrode 4 as a back surface electrode and a light-receiving surface nitrided via an insulating film 2B made of a two-layer film of an aluminum oxide layer and a silicon nitride layer. In this structure, the Ag electrode 3 as a surface electrode is provided via the insulating film 2A made of a silicon layer.

  First, an insulating film 2A made of a silicon nitride layer is formed on each of the light-receiving surface side and the non-light-receiving surface side of a Si semiconductor substrate, and an insulating film made of a two-layer film of an aluminum oxide layer and a silicon nitride layer in order from the non-light-receiving surface side of the substrate. 2B was formed. Further, the insulating film 2B was formed with an opening 7 at a predetermined position by a laser. Next, the glass powder of each of the above examples is used on the entire surface on the non-light-receiving surface side, that is, on the surface of the insulating film 2B and the surface of the semiconductor substrate which faces the opening 7 where the insulating film 2B is partially removed by a laser. The Al electrode-forming conductive paste thus obtained was applied by screen printing and dried at 100 ° C.

  Next, the Ag electrode-forming conductive paste was applied to the entire surface of the insulating film 2A of the Si semiconductor substrate 1 by screen printing in a line shape. After that, baking was performed at a peak temperature of 800 ° C. for 60 seconds using an infrared heating belt furnace to form the front surface Ag electrode 3 and the rear surface Al electrode 4, thereby completing the solar cell 10. The front surface Ag electrode 3 was formed so as to penetrate the insulating film 2A.

(1) Appearance evaluation The appearance of the back surface Al electrode 4 obtained above was visually evaluated by the following criteria from the viewpoint of whether or not an electrode can be formed as an Al electrode without the generation of particulate matter. The results are shown in Table 1.

◯: No particulate matter is generated on the Al electrode.
X: A granular substance is generated on the Al electrode.
The granular material on the Al electrode can be visually recognized if the particle diameter is about 20 μm or more.

(2) Measurement of conversion efficiency of solar cell The conversion efficiency of the solar cell manufactured using the conductive paste for Al electrode formation containing the glass powder of each said example was measured using the solar simulator. Specifically, a solar cell was installed in a solar simulator, and the current-voltage characteristic was measured in accordance with JIS C8912 by a standard sun ray having a spectral characteristic AM1.5G to derive the conversion efficiency of each solar cell. Table 1 shows the obtained conversion efficiency results.

The symbols in Table 1 have the following meanings.
Isc (A); short-circuit current Voc (mV) in short-circuit state; open-circuit voltage FF (%) in open state; fill factor Eff (%); conversion efficiency

From the results of Table 1, in the case of solar cells having electrodes formed by using the paste compositions of Examples 1 to 8 which are examples using the glass frit of the present invention, high conversion efficiency can be obtained. It can be seen that generation of particulate matter on the electrode surface is suppressed. On the other hand, when the paste compositions of Examples 9 and 10 which are comparative examples not using the glass frit of the present invention are used, the paste compositions of Examples 1 to 8 which are Examples in terms of conversion efficiency or firing appearance are obtained. It turns out to be inferior. In Example 9 having a Bi ₂ O ₃ content of more than 25 mol% in the glass, a granular substance was generated on the electrode surface, and in Example 10 not containing Bi ₂ O ₃ , the conversion efficiency (Eff (%)) was 21.0. It was well below%.

10 ... Solar cell, 1 ... P-type Si semiconductor substrate, 1a ... N ⁺ layer, 1b ... P layer, 2A, 2B ... Insulating film, 3 ... Ag electrode, 4 ... Al electrode, 5 ... Al-Si alloy layer, 6 ... BSF layer, 7 ... opening.

Claims (14)

In terms of oxide equivalent mol%,
40% or more and 60% or less of B ₂ O ₃ ,
Bi ₂ O ₃ is 5% or more and 25% or less,
ZnO is 20% or more and 30% or less,
SiO ₂ is 2% or more and 7% or less,
A glass containing 1% or more and 10% or less of Sb ₂ O ₃ and 0% or more and 10% or less of BaO. 50% particle diameter based on volume in a cumulative particle size distribution is taken as _{D 50,} glass powder comprising glass according to claim 1, wherein _{D 50} is 0.5μm or more 6.0μm or less.   A conductive paste containing the glass powder according to claim 2, a conductive metal powder, and an organic vehicle.   A solar cell comprising an electrode formed using the conductive paste according to claim 3. A conductive paste comprising metal, glass, and an organic vehicle,
The metal is contained in an amount of 63.0% by mass or more and 97.9% by mass or less based on the total mass of the conductive paste, and includes at least one selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt. ,
The glass, the included 9.8 parts by mass 0.1 parts by mass with respect to the metal 100 parts by weight, as represented by mol% of oxide _equivalent, B 2 _{O 3} 40% to 60% or less, Bi ₂ O ₃ is 5% or more and 25% or less, ZnO is 20% or more and 30% or less, SiO ₂ is 2% or more and 7% or less, Sb ₂ O ₃ is 1% or more and 10% or less, and BaO is 0% or more and 10% or less. The conductive paste contains the organic vehicle in an amount of 2% by mass or more and 30% by mass or less based on the total mass of the conductive paste. The glass is a 50% particle diameter on a volume basis when the _{D 50} in a cumulative particle size _{distribution,} according to claim 5, wherein the conductive paste _{D 50} is 6.0μm or less of the glass powder above 0.5 [mu] m.   The conductive paste according to claim 5, wherein the metal contains Al. The organic vehicle is an organic resin binder solution prepared by dissolving an organic resin binder in a solvent,
The organic resin binder is an acrylic resin obtained by polymerizing one or more selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate, and 2-hydroxyethyl acrylate, methyl cellulose. , Ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and at least one selected from the group consisting of nitrocellulose,
The conductive material according to any one of claims 5 to 7, wherein the solvent contains at least one selected from the group consisting of diethylene glycol monobutyl ether, terpineol, butyl diglycol acetate, ethyl diglycol acetate, propylene glycol diacetate, and methyl ethyl ketone. paste. A silicon substrate having a sunlight receiving surface,
A first insulating film provided on the solar light receiving surface side of the silicon substrate;
A second insulating film having at least one opening provided on the surface of the silicon substrate opposite to the solar light receiving surface;
A second electrode that partially contacts the silicon substrate through the opening of the second insulating film;
A first electrode penetrating a part of the first insulating film and contacting the silicon substrate,
The second electrode is a metal containing at least one selected from the group consisting of Al, Ag, Cu, Au, Pd, and Pt, and has a B ₂ O ₃ content of 40% or more in terms of oxide mol%. 60% or less, Bi ₂ O ₃ 5% or more and 25% or less, ZnO 20% or more and 30% or less, SiO ₂ 2% or more and 7% or less, Sb ₂ O ₃ 1% or more and 10% or less, and BaO A solar cell comprising a glass containing 0% or more and 10% or less.   The solar cell according to claim 9, wherein the second electrode contains 90 mass% or more and 99.9 mass% or less of the metal and 0.1 mass% or more and 10 mass% or less of the glass.   The solar cell according to claim 9, wherein the metal contained in the second electrode contains at least Al.   The solar cell according to claim 9, wherein the first electrode contains a metal containing at least Ag.   The solar cell according to claim 9, wherein the first insulating film is made of silicon nitride.   The second insulating film further includes a metal oxide film made of aluminum oxide or silicon oxide, which is in contact with a surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film is further provided on the metal oxide film. Item 14. The solar cell according to any one of Items 9 to 13.

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