TWI841623B - Glass, glass powder, conductive paste and solar cell - Google Patents

Abstract

The present invention provides a glass which can suppress the generation of granular substances in an electrode when an electrode is formed on a semiconductor substrate of a solar cell through an insulating film, thereby making the obtained electrode have a good appearance, ensuring the reliability of the product, and improving the conversion efficiency of the solar cell, as well as a glass powder containing the glass, a conductive paste containing the glass powder, and a solar cell with improved conversion efficiency by using the conductive paste. The glass is characterized in that, when expressed in mole % converted to oxides, it contains 40-60% _{B2O3 ,} 5-25% _Bi2O3 , 20-30% ZnO, 2-7% _SiO2 , 1-10% _Sb2O3 , and 0-10% BaO; and the glass powder contains the glass, and when the 50% particle size based on volume in the cumulative _particle size distribution is set _{as D50} , _D50 is 0.5-6.0 μm.

Description

Glass, glass powder, conductive paste and solar cell

The present invention relates to a glass, a glass powder, a conductive paste and a solar cell, and more particularly to a glass suitable for forming an electrode of a solar cell, a glass powder, a conductive paste using the glass powder, and a solar cell having an electrode formed by the conductive paste.

Electronic devices that have a conductive layer serving as an electrode formed on a semiconductor substrate such as silicon (Si) have been used in various applications. The conductive layer serving as the electrode is formed by applying a conductive paste in which conductive metal powder such as aluminum (Al), silver (Ag), copper (Cu), and glass powder are dispersed in an organic carrier on the semiconductor substrate and baking it at a temperature required for forming an electrode.

When forming electrodes on a semiconductor substrate in this way, there is a case where an insulating film is formed on the entire surface of the semiconductor substrate on which the electrodes are formed, and the patterned electrodes are formed in a manner that partially penetrates the insulating film and contacts the semiconductor substrate. For example, in a solar cell, an anti-reflection film is provided on the semiconductor substrate that becomes the light-receiving surface, and the electrodes are provided thereon in a pattern. The anti-reflection film is used to maintain sufficient visible light transmittance and reduce surface reflectivity to improve light receiving efficiency, and usually includes insulating materials such as silicon nitride, titanium dioxide, silicon dioxide, and aluminum oxide. In solar cells such as PERC (Passivated Emitter and Rear Contact), a passivation film containing the same insulating material as the anti-reflection film is also provided on the entire back side, and an electrode is formed on the passivation film in a form of partially contacting the semiconductor substrate.

Here, when forming the above-mentioned electrode, it is necessary to form it in a manner that the electrode contacts the semiconductor substrate. In the light-receiving surface, the insulating film is removed from the portion corresponding to the electrode pattern, and the electrode is formed in the portion where the insulating film has been removed. In addition, in the back side of the PERC solar cell, the insulating film is partially removed within the range that can be electrically contacted, and the electrode is formed on the entire back side.

As a method of partially removing the insulating film, the insulating film is physically removed by laser or the like, and an electrode is formed on the portion where the insulating film has been removed to contact the semiconductor, thereby operating as a solar cell. In the previous solar cell structure, if a semiconductor substrate such as Si is directly in contact with the entire surface of the back electrode to form an electrode, the entire back surface is contacted to operate as a solar cell. On the other hand, if a structure such as a PERC solar cell is used, the area of the portion where the insulating film is removed becomes about 1 to 3% of the entire back surface, and most of the back electrode is formed on the insulating film.

The above-mentioned technique for forming an electrode on a semiconductor substrate is also applied to forming an electrode 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 when forming an electrode in a semiconductor element, and discloses the following glass: as a specific glass composition, _it contains 29.0 mol% _{B2O3 ,} 33.8 mol% ZnO, 30.4 mol% _Bi2O3 , 6.0 mol% _Al2O3 , and 0.8 mol% _SiO2 in terms of _oxides . However, the glass described in Patent Document 1 does not contain sufficient B ₂ O ₃ . In particular, when forming the back electrode of a solar cell in a p-type semiconductor substrate, boron, which is a carrier, cannot be sufficiently diffused into the Si substrate, resulting in a problem of deterioration of electrical characteristics.

Patent Document 2 discloses a glass containing 66.7 mol% _B2O3 and 33.3 mol% _Bi2O3 in terms of oxides as glass for forming electrodes of solar cells. However, in the glass described in Patent Document 2, when the combined content of _B2O3 and _Bi2O3 is too high, for example, when _aluminum is used in the back electrode, there is _a problem _of poor appearance due to the generation _of granular materials composed of aluminum or aluminum-silicon alloy during baking and the granular materials protruding from the surface of the back electrode after baking. In addition, there is a problem of damage to the cell due to the protruding parts of the granular materials when the solar cell cell is modularized. [Prior Art Document] [Patent Document]

[Patent document 1] Japanese Patent Publication No. 2018-6064 [Patent document 2] Japanese Patent Publication No. 2017-222543

[The problem the invention is trying to solve]

Regarding _{B2O3 - Bi2O3} glass used _in forming the electrodes of solar cells, a large number of technologies for improving the formability of electrodes have been developed, such as Patent Document 1 or Patent Document 2. However, in particular in PERC solar cells, even if the glass composition or the particle size distribution of the glass powder used in forming the electrodes is adjusted, it is not easy to simultaneously suppress the generation of granular materials from the electrode forming metal represented by the aluminum or aluminum-silicon alloy mentioned above in the electrodes during the formation of the electrodes and reduce the resistance between the electrodes and the semiconductor substrate to improve the conversion efficiency of the solar cells. That is, the technology that can both improve the conversion efficiency of solar cells and suppress the generation of particulate matter in the electrode during electrode formation so as to maintain a good appearance and ensure the reliability of the product is still under development.

The purpose of the present invention is to provide a glass used in forming electrodes, which can suppress the generation of granular materials in the electrode when the electrode is formed on a semiconductor substrate such as a solar cell through an insulating film, so that the obtained electrode has a good appearance, can ensure the reliability of the product, and can improve the conversion efficiency of the solar cell. The purpose of the present invention is to further provide a glass powder containing the glass, a conductive paste containing the glass powder, and a solar cell that improves the reliability and conversion efficiency of the product by using the conductive paste. [Technical means for solving the problem]

The present invention provides glass, glass powder, conductive paste and solar cell having the following compositions. [1] A glass characterized by comprising, in terms of mole % _{of oxides, 40% to 60% B2O3, 5% to 25% Bi2O3 , 20 %} to 30% ZnO, 2% to ₇ % SiO2, 1% to 10% _Sb2O3 and 0% to 10% _BaO . [2] A glass powder comprising the glass described in [1], wherein _D50 is 0.5 μm to 6.0 μm when the 50% particle size based on volume in the cumulative particle size distribution is defined as _D50 . [3] A conductive paste comprising the glass powder described in [2], conductive metal powder and an organic carrier.

[4] A solar cell having electrodes formed using the conductive paste as described in [3]. [5] A conductive paste comprising a metal, a glass, and an organic carrier, wherein: the conductive paste comprises 63.0 mass % to 97.9 mass % of the metal, the metal comprising at least one selected from the group consisting of Al, Ag, Cu, Au, Pd, and Pt, the glass comprising 0.1 mass % to 9.8 mass % of the glass, relative to 100 mass % of the metal, and the glass comprising, in terms of mole % converted to oxides, 40 mass % to 60 mass % of _B2O3 , 5 mass % to 25 mass % of _Bi2O3 , 20 mass % to 30 mass % of ZnO, 2 mass % to 7 _mass % of _SiO2 , and _{1 mass} % to 10 mass % of _Sb2O3 , and BaO in an amount of not less than 0% and not more than 10%, and the conductive paste contains not less than 2% by mass and not more than 30% by mass of the organic carrier relative to the total mass of the conductive paste.

[6] The conductive paste as described in [5], wherein the glass is a glass powder having a _D50 of 0.5 μm or more and 6.0 μm or less when the 50% particle size based on volume in the cumulative particle size distribution is set as _D50 . [7] The conductive paste as described in [5] or [6], wherein the metal comprises Al. [8] The conductive paste as described in any one of [5] to [7], wherein the organic carrier is an organic resin binder solution in which an organic resin binder is dissolved in a solvent, and the organic resin binder comprises one or more selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate, and 2-hydroxyethyl acrylate. The present invention relates to an acrylic resin obtained by polymerization, 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, diethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, propylene glycol diacetate, and methyl ethyl ketone.

[9] A solar cell comprising: a silicon substrate having a solar light receiving surface; a first insulating film disposed on the solar light receiving surface side of the silicon substrate; a second insulating film having at least one opening disposed on the surface of the silicon substrate opposite to the solar light receiving surface; and a first insulating film disposed on the surface of the silicon substrate opposite to the solar light receiving surface. The second electrode in contact with the silicon substrate and the first electrode penetrating a portion of the first insulating film and in contact with the silicon substrate are characterized in that the second electrode comprises a glass containing at least one metal selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt _, and, when expressed in mole % converted to oxides, comprises 40% to 60% of _B2O3 , 5% to 25% of _{Bi2O3 ,} 20% to 30% of ZnO, 2% to 7% of _SiO2 , ₁ % to 10% of _Sb2O3 , and 0% to 10% of BaO.

[10] The solar cell described in [9], wherein the second electrode contains 90 mass % to 99.9 mass % of the metal and 0.1 mass % to 10 mass % of the glass. [11] The solar cell described in [9] or [10], wherein the metal contained in the second electrode contains at least Al. [12] The solar cell described in any one of [9] to [11], wherein the first electrode contains a metal containing at least Ag. [13] The solar cell described in any one of [9] to [12], wherein the first insulating film contains silicon nitride. [14] A solar cell as described in any one of [9] to [13], wherein the second insulating film comprises a metal oxide film comprising aluminum oxide or silicon oxide in contact with the surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film located on the metal oxide film. [Effect of the invention]

If the glass of the present invention and the glass powder containing the glass are used together with a conductive component in a conductive paste, when forming an electrode through an insulating film on a semiconductor substrate of a solar cell, the generation of granular materials in the electrode can be suppressed, so that the appearance of the obtained electrode is good, and the reliability of the product can be guaranteed by fully ensuring the contact with the insulating film and the semiconductor substrate. In addition, the glass of the present invention and the glass powder containing the glass contain boron, and when forming an electrode, the boron contained in the glass can be diffused into, for example, a p-type layer of the semiconductor substrate, thereby forming a good p+ layer and improving the conversion efficiency of the solar cell.

In particular, it is known that in the back electrode using Al in PERC solar cells, granular materials having an aluminum or aluminum-silicon alloy composition are generated during firing. When forming such an electrode, the glass of the present invention has a significant effect in suppressing the generation of the granular materials. Thus, when modularizing solar cell units, damage to the unit due to the protruding parts of the generated granular materials can be suppressed, and productivity can be improved.

The present invention can provide a conductive paste containing the glass powder, thereby improving the conversion efficiency of a solar cell when an electrode is formed using the glass powder, and a solar cell having improved conversion efficiency by using the conductive paste.

The _following is a description of the embodiments of the present invention. <Glass> The glass of the present invention contains 40-60% _B2O3 , 5-25% _Bi2O3 , 20-30% _ZnO , 2-7% _SiO2 , 1-10% _Sb2O3 , and 0-10% BaO when expressed in mole % in terms of oxide conversion. In the following description, unless otherwise stated, "%" in the content of each component of the glass is expressed in mole % in terms of _oxide conversion. In this specification, "~" indicating a numerical range includes both upper and lower limits.

The content of each component in the glass of the present invention is obtained based on the results of inductively coupled plasma (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectroscopy) analysis or electron probe micro analyzer (EPMA: Electron Probe Micro Analyzer) analysis of the obtained glass.

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

Furthermore _{, B2O3} can promote direct reaction between the semiconductor substrate and the glass in the conductive paste by making the glass flow. Thus, for example, when the semiconductor substrate is a pn junction type Si semiconductor substrate, the glass can form a p ⁺ layer or n ⁺ layer in contact with the electrode. For example, when forming an electrode in contact with the p ⁺ layer, _{B2O3 ,} which is a component contained in the glass, can be promoted to diffuse into the p ⁺ layer as B, and a better p ⁺ layer can be formed.

The glass of the present invention contains B ₂ O ₃ at a ratio of not less than 40% and not more than 60%. If the content of B ₂ O ₃ is less than 40%, B cannot be sufficiently diffused into the Si semiconductor substrate when forming an electrode, so, for example, there is a situation where the conversion efficiency in a solar cell cannot be improved. Furthermore, B ₂ O ₃ is a component that forms the network structure of the glass, and if it does not reach 40%, vitrification cannot be performed. The content of B ₂ O ₃ is preferably not less than 45%. On the other hand, if the content of B ₂ O ₃ exceeds 60%, the glass and the semiconductor substrate over-react when forming an electrode to produce granular substances in the electrode. The content of B ₂ O ₃ is preferably not more than 59%.

In the glass of the present invention, _Bi2O3 is _an essential component. _Bi2O3 has the function of _improving the softening fluidity of the glass and improving the contact between the electrode and the insulating film and the semiconductor substrate. In addition, the metal Bi particles generated by the reduction _{of Bi2O3} in the glass reduce the melting temperature of the conductive metal particles through the eutectic reaction. As a result, the conductive metal particles diffuse toward the semiconductor substrate to form a p ⁺ layer, or further improve the performance of the p ⁺ layer, which helps to improve the conversion efficiency in the solar cell. When the conductive metal is Al, the effect is particularly high.

Bi ₂ O ₃ further has the function of promoting the direct reaction between the semiconductor substrate and the glass by making the glass flow. In this way, the diffusion of B ₂ O ₃ in the glass as B to the p ⁺ layer of the semiconductor substrate can be promoted, and a better p ⁺ layer can be formed. The glass of the present invention contains Bi ₂ O ₃ at a ratio of not less than 5% and not more than 25%. If the content of Bi ₂ O ₃ is less than 5%, the softening point of the glass becomes higher, so the fluidity decreases and the reaction with the semiconductor substrate becomes insufficient. The content of Bi ₂ O ₃ is preferably not less than 7%, and more preferably not less than 10%. On the other hand, if the content of Bi ₂ O ₃ exceeds 25%, glass cannot be obtained by crystallization. The content of Bi ₂ O ₃ is preferably not more than 22%, and more preferably not more than 20%.

In the glass of the present invention, ZnO is an essential component. ZnO is a component that can inhibit the crystallization of glass and enhance the reactivity of glass with insulating films or Si substrates on semiconductor substrates such as Si substrates. The glass of the present invention contains ZnO at a ratio of 20% to 30%. If the ZnO content is less than 20%, the reactivity of glass with insulating films or Si substrates on semiconductor substrates such as Si substrates will deteriorate, the bonding strength will weaken, and the resistance between the electrode and the semiconductor substrate will increase. The ZnO content is preferably 22% or more. If the ZnO content exceeds 30%, the glass and the semiconductor substrate will over-react when the electrode is formed, and granular substances will be generated in the electrode. The ZnO content is preferably 29% or less.

In the glass of the present invention, SiO ₂ is an essential component. By containing SiO ₂ , the glass can be stabilized. The glass of the present invention contains SiO ₂ at a ratio of 2% to 7%. If the content of SiO ₂ is less than 2%, it is difficult to obtain glass by crystallization, and long-term reliability as a characteristic of solar cells cannot be obtained. The content of SiO ₂ is preferably 3% or more, and more preferably 5% or more. If the content of SiO ₂ exceeds 7%, the glass transition point rises, so the glass becomes unable to flow during sintering. The content of SiO ₂ is preferably 6% or less.

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

In the glass of the present invention, BaO is a component that reduces the contact resistance between the electrode and the semiconductor substrate. Moreover, even if BaO is a glass component, it can also be stabilized as a modified oxide. The content of BaO in the glass of the present invention is 0% to 10%. The content of BaO is preferably 1% or more. If the content of BaO exceeds 10%, it is impossible to obtain glass by crystallization. The content of BaO is preferably 5% or less.

The glass of the present invention may also contain other optional components in addition to the above. Specifically, the other optional components include: PbO, _P2O5 , _{V2O5 , Sb2O5 , As2O5} , Li2O _{, Na2O , K2O} , _ZrO2 , _Fe2O3 , _CuO , _SnO2 , MgO, CaO, SrO, _Al2O3 , MnO _{, MnO2} , _CeO2 , _TiO2 , _MoO3 , _WO3 and other oxide components commonly used in glass. These other optional components may be used alone or in combination of two or more depending on the purpose. The content of the other optional components is preferably 5 _% or less in total.

The manufacturing method of the glass of the present invention is not particularly limited. For example, it can be manufactured by the method shown below.

First, a raw material mixture is prepared. The raw materials are not particularly limited as long as they are raw materials used in the production of ordinary oxide-based glass. Oxides or carbonates can be used. In the obtained glass, the types and ratios of the raw materials are appropriately adjusted so as to obtain a raw material mixture within the above-mentioned composition range.

Next, the raw material mixture is heated by a known method to obtain a melt. The heating and melting temperature (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.

Thereafter, the molten material is cooled and solidified to obtain the glass of the present invention. The cooling method is not particularly limited. A method of rapid cooling by a rolling press, a pressurizing machine, or dripping into a cooling liquid may also be selected. It is preferred that the obtained glass is completely amorphous, that is, the degree of crystallization is 0%. However, as long as it does not impair the effect of the present invention, a crystallized portion may be included.

The glass of the present invention obtained in this way can be in any form, such as block, plate, thin plate (sheet), powder, etc.

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

<Glass Powder> The glass powder of the present invention includes 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 particularly suitable for use in conductive pastes. By having a D ₅₀ of 0.5 μm or more, the dispersibility when making a conductive paste is further improved. In addition, by having a D ₅₀ of 6.0 μm or less, it is less likely that a location without glass powder will be generated around the conductive metal powder, so the adhesion between the electrode and the semiconductor substrate is further improved. D ₅₀ is more preferably 0.8 μm or more. D ₅₀ is more preferably 5.0 μm or less.

In this specification, " _D50 " means the 50% particle size based on volume in the cumulative particle size distribution. Specifically, it means the particle size at which the cumulative amount accounts for 50% based on volume in the cumulative particle size curve of the particle size distribution measured using a laser diffraction/scattering particle size distribution measuring device.

The glass powder of the present invention can be obtained, for example, by pulverizing the glass produced as described above in a manner having the above-mentioned specific particle size distribution by dry pulverization or wet pulverization.

The method for pulverizing glass used to obtain the glass powder of the present invention is preferably a method of dry pulverizing glass of an appropriate shape and then wet pulverizing it. Dry pulverization and wet pulverization can be performed using a pulverizer such as a roller mill, a ball mill, or a jet mill. The particle size distribution can be adjusted by adjusting the pulverization time at each pulverization or the size of the balls of the ball mill, for example. In the case of the wet pulverization method, it is preferred to use water as a solvent. After the wet pulverization, the water is removed by drying, etc. to obtain a glass powder. In order to adjust the particle size of the glass powder, in addition to pulverizing the glass, classification can be performed as needed.

<Conductive paste> The glass of the present invention can be used as glass powder for conductive paste. The conductive paste obtained by using the glass of the present invention contains the glass powder of the present invention, conductive metal powder and an organic carrier.

The conductive metal powder contained in the conductive paste of the present invention can be used as a metal powder commonly used in electrodes formed on circuit substrates such as semiconductor substrates or insulating substrates (including laminated electronic components) without any particular limitation. Specifically, the conductive metal powder includes powders such as Al, Ag, Cu, Au, Pd, and Pt. Among them, Al powder is preferred in terms of productivity. When the conductive metal powder is Al powder, the glass of the present invention can significantly suppress the generation of granular materials in the electrode when the electrode is formed, and improve the appearance of the obtained electrode.

From the viewpoint of suppressing aggregation and obtaining uniform dispersion, the particle size of the conductive metal powder is preferably 0.3 μm or more and 10 μm or less in D ₅₀ .

The content of the conductive metal powder in the conductive paste is preferably set to 63.0 mass % or more and 97.9 mass % or less relative to the total mass of the conductive paste. If the content of the conductive metal powder is less than 63.0 mass %, the conductive metal powder is further sintered and glass ridges are easily generated. On the other hand, if the content of the conductive metal powder exceeds 97.9 mass %, there is a risk that the conductive metal powder cannot be covered with glass precipitates. In addition, there is a risk that the adhesion between the electrode and the circuit substrate such as a semiconductor substrate or an insulating substrate will deteriorate. The content of the conductive metal powder is more preferably 75.0 mass % or more and 95.0 mass % or less relative to the total mass of the conductive paste.

The content of the glass powder in the conductive paste is preferably set to, for example, 0.1 to 9.8 parts by mass relative 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, there is a risk that the conductive metal powder cannot be covered with glass precipitates. In addition, there is a risk that the adhesion between the electrode and the circuit substrate such as a semiconductor substrate or an insulating substrate will deteriorate. On the other hand, if the content of the glass powder exceeds 9.8 parts by mass, the conductive metal powder is further sintered, and glass ridges are likely to occur. The content of the glass powder is more preferably 0.5 to 5 parts by mass relative to 100 parts by mass of the conductive metal powder.

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

As the organic resin binder used for the organic carrier, for example, cellulose resins such as methylcellulose, ethylcellulose, carboxymethylcellulose, oxyethylcellulose, benzylcellulose, propylcellulose, and nitrocellulose, and acrylic resins obtained by polymerizing one or more acrylic monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate, and 2-hydroxyethyl acrylate can be used.

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

The ratio of the organic resin binder to the solvent in the organic carrier is not particularly limited, and the obtained organic resin binder solution is selected so as to have a viscosity that can adjust the viscosity of the conductive paste. Specifically, the organic resin binder:solvent ratio is preferably about 3:97 to 15:85 in terms of the mass ratio shown.

The content of the organic carrier in the conductive paste is preferably 2% by mass or more and 30% by mass or less relative to the total amount of the conductive paste. If the content of the organic carrier is less than 2% by mass, the viscosity of the conductive paste increases, so the coating properties of the conductive paste such as printing decrease, and it becomes difficult to form a good conductive layer (electrode). In addition, if the content of the organic carrier exceeds 30% by mass, the content ratio of the solid components of the conductive paste becomes low, and it is difficult to obtain a sufficient coating film thickness.

As one aspect of the conductive paste of the present invention, the following conductive paste can be cited: the conductive paste contains 63.0-97.9 mass % of at least one metal selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt, and 0.1-9.8 mass % of glass containing 40-60% _B2O3 , _5-25 % _Bi2O3 , 20-30% ZnO, 2-7% _SiO2 , 1-10% Sb2O3, and 0-10 _% BaO, expressed as mol% of oxide conversion, relative to 100 mass % of _the above metals, and contains 2-30 mass % of an organic carrier relative to the total mass of the conductive paste. The glass in _this aspect is the glass of the present invention. The preferred aspects of the glass, metal and organic carrier contained in the conductive paste of this aspect, such as composition, type, form, content, etc., can be the same as those mentioned above.

In the conductive paste of the present invention, in addition to the above-mentioned glass powder, conductive metal powder, and organic carrier, known additives may be mixed as needed within the limits that do not violate the purpose of the present invention.

As such additives, for example, various inorganic oxides can be cited. Specifically _, inorganic oxides include _B2O3 , _ZnO , _SiO2 , _Al2O3 , _TiO2 , MgO, _ZrO2 , _Sb2O3 , and composite oxides thereof. These inorganic oxides have the effect of slowing down the sintering of the conductive metal powder when the conductive paste is _baked , thereby having the function of adjusting the bonding strength after baking. The size of the additives including these inorganic oxides is not particularly limited, and for example, those with a _D50 of 10 μm or less can be preferably used.

The content of inorganic oxide in the conductive paste is appropriately set according to different purposes, but is preferably 10% by mass or less, and more preferably 7% by mass or less relative to the glass powder. If the content of inorganic oxide exceeds 10% by mass relative to the glass powder, there is a risk that the fluidity of the conductive paste will decrease when forming an electrode and the bonding strength between the electrode and a circuit substrate such as a semiconductor substrate or an insulating substrate will decrease. In addition, in order to obtain a practical formulation effect (adjustment of the bonding strength after baking), the lower limit of the above content is preferably 0.5% by mass, and more preferably 1.0% by mass.

In the conductive paste, known additives such as defoamers or dispersants may be added. Furthermore, the organic carrier and the additives are usually components that disappear during the electrode formation process. For the preparation of the conductive paste, a known method using a rotary mixer with a stirring blade, a grinder, a roller mill, a ball mill, etc. may be applied.

The conductive paste can be applied and baked on a circuit substrate such as a semiconductor substrate or an insulating substrate by the same method as the application and baking for forming the electrode. Screen printing and dispensing can be cited as the application method. The baking temperature depends on the type of conductive metal powder contained, the surface state, etc., and can be exemplified by a temperature of about 500 to 1000°C. The baking time can be appropriately adjusted according to the shape and thickness of the electrode to be formed. In addition, a drying treatment at about 80 to 200°C can be provided between the application and baking of the conductive paste.

<Solar cell> The solar cell of the present invention has an electrode formed using the conductive paste of the present invention, specifically, an electrode sintered onto a semiconductor substrate. The solar cell of the present invention preferably has 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. PERC solar cells usually have an anti-reflection film containing an insulating material on the light-receiving surface, and an insulating film containing the same insulating material as the anti-reflection film on the entire back surface except for a portion.

In PERC solar cells and the like, the solar cell of the present invention is preferably provided with an electrode formed using the conductive paste of the present invention as an electrode formed on an insulating film provided on the back surface in a form of partially contacting a semiconductor substrate. The electrode is formed on the entire surface of the insulating film in a form of contacting the semiconductor substrate in an opening formed as follows. If the conductive paste of the present invention is used, an electrode can be obtained that fully ensures contact with the portion of the semiconductor substrate from which the insulating film has been removed when the electrode is formed on the semiconductor substrate via the insulating film, and an electrode having higher reliability by suppressing the generation of granular substances in the electrode and ensuring the flatness of the obtained electrode surface.

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 conductive paste of the present invention is used to form an insulating film on a semiconductor substrate, for example, after removing a portion of the insulating film by laser to form an insulating film having an opening, and then forming an Al electrode on the insulating film in a form that is in contact with the semiconductor substrate through the opening.

Examples of Al electrodes disposed on an insulating film having an opening in contact with a semiconductor substrate via the opening include: a back electrode of a PERC solar cell using a p-type Si substrate, a back electrode of a PERT (Passivated Emitter, Rear Totally Diffused) solar cell using an n-type Si substrate, an electrode disposed 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, and one electrode of a rear contact solar cell.

As an embodiment of the solar cell of the present invention, the following solar cell can be cited, which comprises: a silicon substrate having a solar light receiving surface, a first insulating film provided on the solar light receiving surface side of the silicon substrate, a second insulating film provided on the surface of the silicon substrate opposite to the solar light receiving surface and having at least one opening, and a second insulating film extending through the opening of the second insulating film. A second electrode partially contacts the silicon substrate, and a first electrode penetrates a portion of the first insulating film and contacts the silicon substrate; and the second electrode of the solar cell comprises a glass containing at least one metal selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt, and containing 40-60% of _B2O3 , 5-25% of _Bi2O3 , 20-30% of _ZnO , 2-7% of _SiO2 , 1-10% of _Sb2O3 , and 0-10% of _BaO when _expressed in mole % converted to oxides.

Furthermore, the opening of the second insulating film refers to a portion extending 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 with the same meaning as above.

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

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

The second electrode preferably contains 90-99.9 mass % of the above metal and 0.1-10 mass % of the above glass. The glass contained in the second electrode is the glass of the present invention, and the preferred composition is as described above. The metal contained in the second electrode preferably contains at least Al. When the metal contains Al, the effect brought by the use of the glass of the present invention is significantly obtained, that is, when the electrode is formed, the generation of granular materials in the electrode is suppressed, so that the appearance of the obtained electrode is good.

The second insulating film is preferably a multi-layer film, and preferably has a multi-layer film structure including a metal oxide film containing aluminum oxide or silicon oxide in contact with the surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film further located on the metal oxide film.

The following is an example of using the conductive paste of the present invention to form electrodes of a p-type Si substrate single-sided light-receiving type solar cell. FIG1 is a schematic cross-sectional view of an example of a p-type Si substrate single-sided light-receiving type solar cell with electrodes 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 disposed on the upper surface thereof; an insulating film 2B disposed on the lower surface and having an opening 7; an Al electrode 4 formed on the entire surface of the insulating film 2B and partially in contact with the p-type Si substrate via the opening 7; and an Ag electrode 3 penetrating a portion of the insulating film 2A and in contact with the p-type Si substrate 1. The upper surface of the p-type Si substrate 1 has a concave-convex structure formed, for example, by wet etching to reduce light reflectivity. Furthermore, the up and down of the figure does not necessarily represent the up and down during use. Also, if necessary, both surfaces of the p-type Si substrate may have a concave-convex structure.

The p-type Si substrate 1 includes an n ⁺ layer 1a and a p layer 1b in order from the top, an Al electrode 4 contacts the p layer 1b, and an Ag electrode 3 contacts the n ⁺ layer 1a. Here, the n ⁺ layer 1a can be formed by doping the surface of the above-mentioned concavo-convex structure with P, Sb, As, etc.

The Al electrode 4 and the Ag electrode 3 are formed in the following manner using a conductive paste for forming an Al electrode containing glass powder and Al powder and a conductive paste for forming an Ag electrode containing glass powder and Ag powder, respectively.

That is, the insulating film 2A provided on the upper surface of the p-type Si substrate 1 exists on the entire surface without gaps before the Ag electrode 3 is formed, and by melting only a portion of the conductive paste for forming the Ag electrode 3 applied when the conductive paste is baked, the Ag electrode 3 is formed which penetrates the insulating film 2A and contacts the p-type Si substrate 1.

On the other hand, after the insulating film 2B is provided without gaps on the entire lower surface of the p-type Si substrate 1, a portion of it is physically removed by laser to form the Al electrode 4, thereby forming a structure having an opening 7. By applying the above-mentioned conductive paste for forming the Al electrode on the entire surface of the insulating film 2B having the opening 7 and baking it, the Al electrode 4 covering the entire surface of the insulating film 2B and contacting the semiconductor part through the opening 7 is formed.

Furthermore, when forming the Al electrode 4, the conductive paste for forming the Al electrode is brought into contact with the p-layer 1b of the p-type Si substrate 1 by utilizing the opening 7, and melts during sintering, thereby causing Al to diffuse from the Al electrode into the p-layer 1b, and forming an Al-Si alloy layer 5 directly above the Al electrode. Furthermore, a BSF (Back Surface Field) layer 6 as a p ⁺ layer is obtained directly above the Al-Si alloy layer 5.

In the above, the conductive paste of the present invention can be used as a conductive paste for forming an Ag electrode and a conductive paste for forming an Al electrode, but as mentioned above, it is particularly preferably used as a conductive paste for forming an Al electrode.

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

Furthermore, the insulating film of the solar cell has an anti-reflection function and can suppress the recombination of the semiconductor carrier. As the insulating material constituting the insulating film, the insulating materials listed above can be used. The insulating film can be a single-layer film or a multi-layer film. The conductive paste of the present invention, in particular, can fully ensure the contact between the electrode and the insulating film and the partially formed semiconductor substrate when forming an electrode through an insulating film having a layer containing silicon nitride and a layer containing aluminum oxide or silicon oxide, thereby having higher solar cell characteristics.

In the solar cell of the present invention, especially in the PERC solar cell, when the insulating film is partially removed on the back side within the range of electrical contact to form an electrode containing the glass powder of the present invention, the following electrode structure can be formed: the electrode is formed on the entire insulating film, and at the same time, the portion after the insulating film is partially removed can ensure contact with the semiconductor substrate. By using the conductive paste, a solar cell can be provided that can suppress the generation of granular materials in the electrode when forming the electrode, can form the electrode with good appearance, and can achieve high reliability and high battery characteristics. [Example]

The present invention is further described in detail below with reference to the embodiments, but the present invention is not limited to the embodiments. Examples 1 to 8 are embodiments, and Examples 9 and 10 are comparative examples.

(Examples 1 to 10) Glass is manufactured into thin plate-shaped glass by the following method, and glass powder is manufactured from the thin plate-shaped glass.

<Manufacturing of glass (thin plate glass)> Raw material powders are prepared and mixed in a manner to obtain the composition shown in Table 1, and melted in a crucible in an electric furnace at 800 to 1400°C for 30 minutes to 2 hours to form a thin plate glass containing the glass composition shown in Table 1.

<Production of glass powder> In each example, the obtained thin plate-shaped glass was pulverized and the particle size distribution was adjusted in the following manner using a combination of dry pulverization and wet pulverization.

First, the glass is dry-pulverized using a ball mill, and then the coarse particles are removed and wet-pulverized using water in a ball mill to obtain glass slurry. During the wet pulverization, aluminum balls with a diameter of 5 mm are used to obtain a specific D ₅₀ , and the D ₅₀ is adjusted by the pulverization time. After that, the slurry obtained by wet pulverization is filtered to remove most of the water, and then it is dried at 130°C in a dryer to adjust the water content to produce glass powder.

<Evaluation> The D ₅₀ of the glass powder of each example 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 ) For each glass example, 0.02 g of glass powder was mixed into 20 cc of water and dispersed by ultrasonic dispersion for 1 minute to prepare a sample. The sample was placed in a Microtrac measuring machine (laser diffraction, scattering type particle size distribution measuring device) to obtain the D ₅₀ value.

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

First, 100 parts by mass of aluminum powder with a _D50 of 6.0 μm produced by gas atomization and 1.5 parts by mass of the glass powder of each example were paste-formed in 35 parts by mass of a resin solution prepared by dissolving ethyl cellulose in diethylene glycol butyl ether acetate using a dispersing device (disperser). Thus, a conductive paste for forming an Al electrode was prepared.

<Production of Al electrodes in solar cells and evaluation of appearance and battery characteristics> (Production of solar cells) The Al electrode-forming conductive pastes of the above-described examples and the commercially available Ag electrode-forming conductive pastes were used to produce solar cells 10 having the structure shown in FIG. 1 in the following manner, and the appearance and battery characteristics of the Al electrodes in the obtained solar cells were evaluated. The solar cell 10 is constructed as follows: an Al electrode 4 as a back electrode is provided on a non-light-receiving surface on a p-type Si semiconductor substrate 1 via an insulating film 2B including two layers of aluminum oxide and silicon nitride, and an Ag electrode 3 as a surface electrode is provided on a light-receiving surface via an insulating film 2A including a silicon nitride layer.

First, an insulating film 2A including a silicon nitride layer and an insulating film 2B including the two layers of aluminum oxide and silicon nitride in order from the non-light-receiving side of the Si semiconductor substrate are formed on the light-receiving side and the non-light-receiving side, respectively. Furthermore, an opening 7 is formed in a specific position in the insulating film 2B by laser. Next, a conductive paste for forming an Al electrode obtained by using the glass powder of each of the above examples is applied by screen printing to the entire surface of the non-light-receiving side, that is, the surface of the insulating film 2B and the surface of the semiconductor substrate facing the opening 7 of the insulating film 2B partially removed by laser, and dried at 100°C.

Next, a conductive paste for forming an Ag electrode is applied in lines on the entire surface of the insulating film 2A of the Si semiconductor substrate 1 by screen printing. Then, an infrared light heating belt furnace is used to bake at a peak temperature of 800°C for 60 seconds to form a surface Ag electrode 3 and a back Al electrode 4, thereby completing the solar cell 10. Furthermore, the surface Ag electrode 3 is formed through the insulating film 2A.

(1) Appearance Evaluation The appearance of the back Al electrode 4 obtained above was evaluated visually based on the following criteria from the perspective of whether the Al electrode can be formed without generating granular materials. The results are shown in Table 1.

○; No granular material is generated on the Al electrode. ×; Granular material is generated on the Al electrode. Furthermore, if the particle size of the granular material on the Al electrode is approximately 20 μm or more, it can be identified with the naked eye.

(2) Determination of conversion efficiency of solar cells The conversion efficiency of solar cells made of conductive paste for forming Al electrodes containing the glass powder of each example above was measured using a solar simulator. Specifically, a solar cell was placed on the solar simulator, and the current-voltage characteristics were measured in accordance with JIS C8912:2011 using reference solar light with spectral characteristics of AM1.5G, and the conversion efficiency of each solar cell was derived. The obtained conversion efficiency results are shown in Table 1.

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

[Table 1] example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Glass composition (mol%) _{B2O3 ​} 59.0 47.6 53.7 53.2 52.7 52.2 52.0 52.1 66.7 19.0 _{Bi2O3 ​} 10.2 17.9 10.3 10.2 10.1 10.0 10.0 10.0 33.3 _{Sb2O3 ​} 3.0 2.7 2.0 3.0 3.0 2.9 5.0 7.8 Al ₂ O ₃ 7.3 ZnO 22.0 24.9 28.1 27.8 27.5 27.3 27.3 27.2 24.3 BaO 1.8 1.0 2.0 17.3 SiO ₂ 5.8 5.2 5.9 5.8 5.7 5.7 5.7 2.9 V ₂ O ₅ 21.7 _{P2O5 ​} 4.6 WO ₃ 5.7 D ₅₀ (μm) 1.0 0.8 1.1 1.0 1.1 1.1 1.0 0.9 1.5 2.7 Solar Battery Reviews Baking appearance ○ ○ ○ ○ ○ ○ ○ ○ × ○ Isc[A] 9.88 9.86 9.87 9.87 9.87 9.86 9.85 9.86 9.79 9.69 Voc[mV] 661 660 661 661 661 661 657 656 661 647 FF[%] 79.3 79.8 79.4 79.7 79.3 79.4 79.4 79.5 79.6 79.5 Eff[%] 21.2 21.3 21.2 21.3 21.2 21.2 21.0 21.0 21.1 20.3

According to the results in Table 1, in the case of a solar cell having an electrode formed by using the paste composition of Examples 1 to 8 as embodiments using the specific glass of the present invention, a higher conversion efficiency is obtained and the generation of granular substances on the electrode surface is suppressed. On the other hand, in the case of using the paste composition of Examples 9 and 10 as comparative examples without using the specific glass of the present invention, it is known that the conversion efficiency and firing appearance are inferior to the paste composition of Examples 1 to 8 as embodiments. In Example 9, in which the Bi ₂ O ₃ content in the glass exceeds 25 mol%, granular substances are generated on the electrode surface, and in Example 10, which does not contain Bi ₂ O ₃ , the conversion efficiency (Eff(%)) is much lower than 21.0%.

Although the present invention has been described in detail with reference to specific embodiments, the industry recognizes that various changes or modifications may be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2018-211600 filed on November 9, 2018, and its contents are cited here for reference.

1: p-type Si semiconductor substrate 1a: n ⁺ layer 1b: p layer 2A: insulating film 2B: insulating film 3: Ag electrode 4: Al electrode 5: Al-Si alloy layer 6: BSF layer 7: opening 10: solar cell

FIG. 1 is a schematic cross-sectional view of an example of a p-type Si substrate single-sided light-receiving type solar cell in which electrodes are formed using the conductive paste of the present invention.

1: p-type Si semiconductor substrate

1a:n ⁺ layer

1b: p layer

2A: Insulation film

2B: Insulation film

3: Ag electrode

4:Al electrode

5: Al-Si alloy layer

6:BSF layer

7: Opening

10: Solar cells

Claims (15)

A glass characterized by comprising, expressed in mole % in terms of oxide conversion, 40% to 60% of _{B2O3 ,} 5% to 25% of _{Bi2O3 ,} 20% to 30% of ZnO, 2% to 7% of _SiO2 , 1% to 10% of _Sb2O3 , and 0% to 10% of _BaO . A glass powder comprising the glass of claim 1, wherein when _D50 is a 50% particle size based on volume in a cumulative particle size distribution, _D50 is 0.5 μm or more and 6.0 μm or less. A conductive paste comprising the glass powder as claimed in claim 2, conductive metal powder, and an organic carrier. A solar cell having an electrode formed using the conductive paste as claimed in claim 3. A conductive paste comprising a metal, a glass, and an organic carrier, wherein the conductive paste comprises 63.0 mass % to 97.9 mass % of the metal relative to the total mass of the conductive paste, wherein the metal comprises at least one selected from the group consisting of Al, Ag, Cu, Au, Pd, and Pt, and the glass comprises 0.1 mass % to 9.8 mass % relative to 100 mass % of the metal, wherein the glass comprises 40 mass % to 60 mass % of _B2O3 , 5 mass % to 25 mass % of _Bi2O3 , 20 mass % to 30 _mass % of _ZnO , 2 mass % to 7 mass % of _SiO2 , and 1 mass % to 10 mass % of _{Sb2O3 ,} in terms of mole % converted to oxides. , and BaO in an amount of not less than 0% and not more than 10%, and the conductive paste contains not less than 2% by mass and not more than 30% by mass of the organic carrier relative to the total mass of the conductive paste. The conductive paste of claim 5, wherein when the 50% particle size based on volume in the cumulative particle size distribution is set as _D50 , the glass is a glass powder having a _D50 of not less than 0.5 μm and not more than 6.0 μm. The conductive paste of claim 5 or 6, wherein the metal mentioned above includes Al. The conductive paste of claim 5 or 6, wherein the organic carrier is an organic resin binder solution in which an organic resin binder is dissolved in a solvent, and the organic resin binder comprises an acrylate 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. At least one selected from the group consisting of acrylic resin, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose, and the above-mentioned solvent includes at least one selected from the group consisting of diethylene glycol monobutyl ether, terpineol, diethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, propylene glycol diacetate, and methyl ethyl ketone. A solar cell comprises: a silicon substrate having a solar light receiving surface, a first insulating film provided on the solar light receiving surface side of the silicon substrate, a second insulating film provided on the surface of the silicon substrate opposite to the solar light receiving surface and having at least one opening, a second electrode contacting part of the silicon substrate through the opening of the second insulating film, and a first electrode contacting the silicon substrate through a part of the first insulating film, wherein the second electrode comprises at least one metal selected from the group consisting of Al, Ag, Cu, Au, Pd and Pt, and comprises 40% to 60% of _B2O in terms of mole % converted to oxide. _3. Glass containing not less than 5% but not more than 25% Bi ₂ O ₃ , not less than 20% but not more than 30% ZnO, not less than 2% but not more than 7% SiO ₂ , not less than 1% but not more than 10% Sb ₂ O ₃ , and not less than 0% but not more than 10% BaO. As in claim 9, the solar cell, 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. As in claim 9 or 10, the metal contained in the second electrode contains at least Al. A solar cell as claimed in claim 9 or 10, wherein the first electrode comprises a metal containing at least Ag. A solar cell as claimed in claim 9 or 10, wherein the first insulating film comprises silicon nitride. A solar cell as claimed in claim 9 or 10, wherein the second insulating film comprises a metal oxide film containing aluminum oxide in contact with the surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film located on the metal oxide film. A solar cell as claimed in claim 9 or 10, wherein the second insulating film comprises a silicon oxide film in contact with the surface of the silicon substrate opposite to the solar light receiving surface, and a silicon nitride film located on the silicon oxide film.