JP2017218335A - Glass, conductive paste and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead-free glass capable of forming an electrode which can sufficiently secure contact with a semiconductor substrate by penetrating an insulation film at low cost with good production efficiency during forming an electrode via the insulation film on the semiconductor substrate of a solar battery or the like in a glass used for electrode formation, a conductive paste containing a powder of the glass and capable of forming the electrode which sufficiently secures contact with the semiconductor substrate by penetrating the insulation film at low cost with good production efficiency during forming an electrode and a solar battery having enhanced reliability and productivity by using the conductive paste.SOLUTION: There are provided a glass containing, by cation%, Vof 15 to 55% and Biof 1 to 85% and practically no Pb, a powder of the glass, a conductive paste containing a conductive metal powder and an organic vehicle, and a solar battery having an electrode formed by using the conductive paste.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, an electronic device in which a conductive layer serving as an electrode is formed on a semiconductor substrate such as silicon (Si) has been used for various applications. For the conductive layer to be the electrode, a conductive paste in which conductive metal powder such as aluminum (Al), silver (Ag), copper (Cu), and glass powder is dispersed in an organic vehicle is applied on a semiconductor substrate, It is formed by firing at a temperature equal to or higher than the melting point of the conductive metal powder.

  Thus, when forming an electrode on a semiconductor substrate, an insulating film is formed on the entire surface of the semiconductor substrate on which the electrode is formed, and the patterned electrode partially penetrates the insulating film to form the semiconductor substrate. It may be formed to contact. For example, in a solar cell, an antireflection film is provided on a semiconductor substrate serving as a light receiving surface, and electrodes are provided in a pattern on the semiconductor substrate. The antireflection film is for reducing the surface reflectance while increasing the visible light transmittance while increasing the light receiving efficiency, and is usually made of an insulating material such as silicon nitride, titanium dioxide, silicon dioxide, or aluminum oxide. Composed. Moreover, in solar cells such as PERC (Passivated Emitter and Rear Contact), a passivation film made of the same insulating material as the antireflection film is provided on the entire back surface, and electrodes are partially formed on the semiconductor substrate on the passivation film. It is formed in contact shape.

  Here, in the formation of the electrode, it is essential to form the electrode in contact with the semiconductor substrate. The insulating film is removed from the light-receiving surface in a portion corresponding to the electrode pattern, and the insulating film is removed. An electrode is formed on the substrate. In addition, the insulating film is partially removed on the back surface of the PERC solar cell or the like as long as electrical contact is possible, and an electrode is formed on the entire back surface.

  As a method of partially removing the insulating layer, there is a method of physically removing it with a laser or the like. However, since the manufacturing process is increased and the cost of introducing the device is increased, glass powder is included in the electrode formation in recent years. A method is used in which a conductive paste (a paste-like electrode material) is used to penetrate an insulating film through the conductive paste by fire-through. In this method, for example, after an insulating film is provided on the entire surface of the semiconductor substrate, a conductive paste is applied on the insulating film in an appropriate shape and subjected to a baking treatment. As a result, the electrode material is heated and melted, and at the same time, the insulating film in contact with the glass reacts and melts with the glass, so that the electrode penetrates the insulating film and comes into contact with the semiconductor substrate. In a back electrode of a PERC solar cell or the like, a conductive paste that penetrates the insulating film and a conductive paste that does not penetrate the insulating film are used in combination, so that it is formed on the entire back surface and partially penetrates the insulating film and contacts the semiconductor substrate An electrode is obtained.

  As such a conductive paste containing glass powder that penetrates the insulating film by fire-through, for example, Patent Document 1 describes a solar cell electrode paste. In patent document 1, as glass which comprises the said glass powder, it contains Te, Bi, Li, and Zn as an essential main component in a specific ratio, respectively, in terms of oxide, and Mg, Ti, V, Cr, Mn, Lead-free glass containing 5 mol% or less of Fe, Co, Ni, Cu, and W is optionally used.

  Moreover, although the usage method as an electrically conductive paste which penetrates an insulating film is not described, the conductive material for electrode formation using the glass powder containing V and Bi, and the composite material using the glass containing V and Bi It has been known. For example, Patent Document 2 describes a glass containing 50% by mass of V and 5% by mass of Bi in terms of oxide in glass used for glass fiber reinforced plastic. Patent Document 3 describes a glass containing 0.5 to 10 mol% of V in terms of oxide and Bi as glass used for an antenna conductive paste provided on a window glass of an automobile or the like. Yes. Furthermore, Patent Document 4 describes a glass powder for forming a solar cell electrode that contains Bi, Zn, and Al as essential components, and optionally contains V in an amount of 15% by mass or less in terms of oxide.

Patent No. 5856277 WO2013 / 099469 WO2016 / 017240 JP2015-41741A

  The present invention relates to a glass used for forming an electrode, and when forming an electrode on a semiconductor substrate such as a solar cell via an insulating film, an electrode that penetrates the insulating film and can sufficiently ensure contact with the semiconductor substrate is provided. The purpose is to provide lead-free glass that can be formed at low cost and with high production efficiency. The present invention uses a conductive paste containing the glass powder, which can form an electrode penetrating an insulating film at the time of electrode formation and ensuring contact with a semiconductor substrate at low cost and with high production efficiency, and the conductive paste. The purpose is to provide a solar cell with improved reliability and productivity.

The present invention provides a glass, a conductive paste and a solar cell having the following constitution.
[1] A glass containing 15 to 55% of V ⁵⁺ and 1 to 85% of Bi ³⁺ and substantially free of Pb ²⁺ in terms of cation%.
[2] The glass according to [1], which is used for forming an electrode of a solar cell.
[3] The glass according to [2], wherein the electrode is an aluminum electrode.
[4] The basicity of the glass calculated using the ionic radius of atoms contained in the glass is 0.01 to 0.50, according to any one of [1] to [3] Glass.
[5] Furthermore, it contains 10 to 80% of B ³⁺ in terms of cation%, and the content of Bi ³⁺ is 1 to 75%, according to any one of [1] to [4] Glass.
[6] The glass according to any one of [1] to [5], further containing 0 to 70% of Zn ²⁺ in terms of cation%.
[7] The glass according to any one of [1] to [6], further containing 0 to 70% of Al ³⁺ in terms of cation%.
[8] the form of the glass is a powder, glass according to any one of the 50% particle size _{D 50} based on volume in a cumulative particle size distribution of the powder is 0.5 to 10 [mu] m [1] ~ [7] .
[9] A conductive paste containing the glass powder, conductive metal powder and organic vehicle according to any one of [1] to [7].
[10] The conductive paste according to [9], wherein a volume-based 50% particle size D ₅₀ in the cumulative particle size distribution of the glass powder is 0.5 to 10 μm.
[11] A solar cell comprising an electrode formed using the conductive paste according to [9] or [10].

  The glass of the present invention is a glass used for electrode formation, and when an electrode is formed on a semiconductor substrate such as a solar cell via an insulating film, sufficient contact with the semiconductor substrate can be ensured through the insulating film. Lead-free glass that can form electrodes at low cost and with high production efficiency. In the present invention, a conductive paste containing the glass powder and capable of forming an electrode penetrating an insulating film at the time of electrode formation and ensuring contact with a semiconductor substrate at low cost and using the conductive paste is used. Thus, it is possible to provide a solar cell with improved reliability and productivity.

It is the figure which showed typically the cross section of an example of the n-type Si substrate double-sided light reception type solar cell by which the electrode was formed using the electrically conductive paste of this invention. It is a photograph which shows the evaluation result of the insulating-film penetration of the electrically conductive paste containing the glass of an Example (Example 3). It is a photograph which shows the evaluation result of the insulating-film penetration of the electrically conductive paste containing the glass of a comparative example (Example 17).

Hereinafter, embodiments of the present invention will be described.
<Glass>
The glass of the present invention is characterized by containing, in terms of cation%, 15 to 55% of V ⁵⁺ and 1 to 85% of Bi ³⁺ and substantially not containing Pb ²⁺ .

The glass of the present invention is represented by cation% and contains V ⁵⁺ and Bi ³⁺ in the specified amounts, respectively, so that a fire-through is performed using a conductive paste containing the glass and conductive metal powder on a semiconductor substrate via an insulating film. When the electrode is formed by the process, the glass component reacts with the component of the insulating film at the time of firing, so that the conductive paste penetrates the insulating film, thereby forming a highly reliable insulating film through electrode having sufficient contact with the semiconductor substrate. It becomes possible. When the glass of the present invention is used, the insulating film through electrode can be formed at a low cost with higher production efficiency than the method of physically removing the insulating film with a laser or the like. Moreover, since the glass of this invention does not contain Pb2 ⁺ substantially, there is little load with respect to an environment.

  Here, the valence of the cation in the glass may vary depending on the state, but the description of the valence in the ion notation of the element symbol of the cation of the present invention is typically expressed by a possible valence. ing.

  In the present specification, “cation%” is a unit as follows. First, the constituent components of glass are divided into a cation component and an anion component. “Cation%” is a unit in which the content of each cation component is expressed as a percentage when the total content of all the cation components contained in the glass is 100 mol%. Hereinafter, the content of the cation component of the glass is cation% unless otherwise specified, and is simply referred to as “%”.

  The content of each cation component in the glass of the present invention is determined from the results of inductively coupled plasma-inductively coupled plasma (ICP-AES) analysis of the obtained glass.

  Further, in the present specification, substantially not containing means that it is not actively contained, but is allowed to be mixed due to inevitable impurities.

Hereinafter, the cation component of the glass of the present invention will be described. The anion component of the glass of the present invention is only O ²⁻ . The glass of the present invention can exhibit the above-described effects when an electrode is formed by fire-through using a conductive paste containing the glass and conductive metal powder on a semiconductor substrate via an insulating film. In the following description, “when forming an electrode” refers to a case where an electrode is formed by fire-through using a conductive paste containing glass and conductive metal powder on a semiconductor substrate via an insulating film unless otherwise specified. This refers to the time of electrode formation.

V ⁵⁺ is an essential component in the glass of the present invention. V ⁵⁺ has a function of improving the softening fluidity of the glass and improving the bonding strength between the semiconductor substrate and the electrode. V ⁵⁺ is a component that reduces the basicity of the glass, thereby suppressing oxygen in the glass from diffusing into the conductive metal powder during electrode formation, and can contribute to the improvement of the insulating film penetration of the conductive paste. . That is, V ⁵⁺ is a component that contributes to forming the electrode so as to penetrate the insulating film and contact the semiconductor substrate.

Further, V ⁵⁺ can promote direct reaction between the semiconductor substrate and the glass by flowing the glass. Thereby, for example, when the semiconductor substrate is a pn junction type Si semiconductor substrate and the glass contains a cation component that forms a p ⁺ layer or an n ⁺ layer in contact with the electrode or enhances its performance. , It is possible to promote the diffusion of the cation component into the p ⁺ layer and the n ⁺ layer. For example, when forming an electrode in contact with the p ⁺ layer, it is possible to promote diffusion of B ³⁺ , which is a preferable cation component, into the p ⁺ layer as B, thereby forming a better p ⁺ layer. it can.

The glass of the present invention contains V ⁵⁺ in a proportion of 15% to 55%. When the content of V ⁵⁺ is less than 15%, the glass softening point is increased, so that the fluidity is lowered, the bonding strength between the semiconductor substrate and the electrode is not sufficient, and the conductive paste at the time of electrode formation Insulating film penetration is insufficient. The content of V ⁵⁺ is preferably 18% or more, more preferably 20% or more. On the other hand, if the content of V ⁵⁺ exceeds 55%, glass may not be obtained due to crystallization, and weather resistance becomes poor, so that the wet pulverization process becomes difficult. The content of V ⁵⁺ is preferably 50% or less, and more preferably 45% or less.

In the glass of the present invention, Bi ³⁺ is an essential component that improves the softening fluidity of the glass and improves the bonding strength between the semiconductor substrate and the electrode. Moreover, the metal Bi particle produced | generated by reducing Bi3 ⁺ in glass reduces the melting temperature of the particle | grains of an electroconductive metal by a eutectic reaction. As a result, for example, when the semiconductor substrate is a pn junction type Si semiconductor substrate, the conductive metal particles are diffused into the Si semiconductor substrate to form a p ⁺ layer or an n ⁺ layer, or to further improve its performance. Thus, for example, it contributes to improving the conversion efficiency in solar cells. For example, if the conductive metal of Al, Al particles are sufficiently diffused into the Si semiconductor substrate to form a p ⁺ layer, or it is possible to enhance the performance of the p ⁺ layer.

Furthermore, it is possible to promote direct reaction between the semiconductor substrate and the glass by flowing the glass. Thereby, for example, when the semiconductor substrate is a pn junction type Si semiconductor substrate and the glass contains a cation component that forms a p ⁺ layer or an n ⁺ layer in contact with the electrode or enhances its performance. , It is possible to promote the diffusion of the cation component into the p ⁺ layer and the n ⁺ layer. For example, when forming the electrode in contact with the p ⁺ layer may be preferably B ³⁺ is a component containing can promote the diffusion of the p ⁺ layer as B, to form a better p ⁺ layer .

The glass of the present invention contains Bi ³⁺ in a proportion of 1% to 85%. When the content of Bi ³⁺ is less than 1%, the glass softening point is increased, so that the fluidity is lowered and the bonding strength between the semiconductor substrate and the electrode is not sufficient. The content of Bi ³⁺ is preferably 3% or more, more preferably 5% or more. On the other hand, if the content of Bi ³⁺ exceeds 85%, glass cannot be obtained due to crystallization. The content of Bi ³⁺ is preferably 80% or less, more preferably 75% or less, and still more preferably 70% or less.

In the glass of the present invention, the cation component may be composed only of V ⁵⁺ and Bi ³⁺ , and if necessary, any other cation component other than V ⁵⁺ , Bi ³⁺ and Pb ²⁺ (hereinafter referred to as “other cation component”). May be included). The kind of other cation component will not be restrict | limited especially if it is a cation component which does not impair the effect of the glass of this invention. Specifically, the glass of the present invention may have a composition containing 15 to 55% of V ^{5+, 1} to 85% of Bi ^3+, and 0 to 84% in total of other cation components in terms of cation%. . However, content of another cation component is content which does not impair the effect of the glass of this invention about each cation component.

As other cation components, specifically, P ⁵⁺ , As ⁵⁺ , Sb ⁵⁺ , Te ⁴⁺ , B ³⁺ , Al ³⁺ , Ga ³⁺ , In ³⁺ , Zn ²⁺ , Si ⁴⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ , Na ⁺ , K ⁺ , Zr ⁴⁺ , Fe ³⁺ , Cu ²⁺ , Sb ³⁺ , Sn ²⁺ , Sn ⁴⁺ , Mo ⁶⁺ , W ⁶⁺ , Mn ²⁺ , Mn ⁴⁺ , Ce ⁴⁺ , Ti ^4+, etc. Examples include various cationic components used for glass. These cationic components are used singly or in combination of two or more depending on the purpose.

For example, when the glass of the present invention is used for forming an electrode in contact with the n ⁺ layer of the Si semiconductor substrate, as other cation components, the performance of the n ⁺ layer such as P ⁵⁺ , As ⁵⁺ , Sb ⁵⁺ is improved. A cationic component capable of forming is preferable. For example, when the glass of the present invention is used for forming an electrode in contact with the p ⁺ layer of the Si semiconductor substrate, other cation components include p ⁺ layers such as B ³⁺ , Al ³⁺ , Ga ³⁺ , and In ³⁺ . Cationic components that can enhance performance are preferred.

When the glass of the present invention contains a cation component that contributes to the performance of the n ⁺ layer or p ⁺ layer, the lower limit of the content is appropriately adjusted according to the type of the cation component. In that case, for example, it is preferable to adjust the composition by lowering the upper limit of the content of Bi ³⁺ without changing the content of V ⁵⁺ . The upper limit of each cation component is appropriately adjusted within a range not impairing the effects of the present invention.

The glass of the present invention preferably contains B ³⁺ which is a cation component contributing to the performance of the p ⁺ layer as other cation component in addition to V ⁵⁺ and Bi ³⁺ . In that case, by ^cationic%, the ^{V 5+} 15 to 55%, the ^{Bi 3+} 1 to ^75%, the composition containing ^{B 3+} 10 to 80% are preferred.

In the glass of the present invention, B ³⁺ diffuses in the Si semiconductor substrate as B, thereby forming a p ⁺ layer or improving its performance, for example, having a function of improving conversion efficiency in a solar cell. It is also a glass forming component. The content of B ^{3+ in} the glass is preferably 10% or more and 80% or less. If the content of B ³⁺ is less than 10%, B cannot be sufficiently diffused into the Si semiconductor substrate at the time of electrode formation. For example, conversion efficiency in a solar cell may not be increased. The content of B ³⁺ is more preferably 15% or more, and further preferably 20% or more. If the content of B ³⁺ exceeds 80%, the stability of the glass may be reduced. The content of B ³⁺ is more preferably 75% or less, and still more preferably 70% or less.

The glass of the present invention preferably contains Zn ²⁺ from the viewpoint of stabilizing the glass as another cation component. Zn ²⁺ is also a component that increases the water resistance of the electrode, and can be contained in the glass in a proportion of 0% to 70%. When Zn ²⁺ is contained, the content is preferably 3% or more, and more preferably 5% or more. When the content of Zn ²⁺ exceeds 70%, the stability of the glass is deteriorated and the glass tends to be devitrified, so that the productivity may be deteriorated. The content of Zn ²⁺ is more preferably 60% or less, and further preferably 50% or less.

The glass of the present invention preferably contains Al ³⁺ from the viewpoint of stabilizing the glass as another cation component. Al ³⁺ can be contained in the glass in a proportion of 0% to 70%. In the glass of the present invention, Al ³⁺ has a function of improving the conversion efficiency by forming a p ⁺ layer or improving its performance by diffusing into the Si semiconductor substrate as Al. When Al ³⁺ is contained, the content is preferably 2% or more, and more preferably 4% or more. If the content of Al ³⁺ exceeds 70%, the glass tends to be devitrified, and the electrode may not be stably produced. The content of Al ³⁺ is more preferably 60% or less, and further preferably 50% or less.

The glass of the present invention can contain, for example, Ce ⁴⁺ from the viewpoint of productivity. Ce ⁴⁺ has, for example, a function of suppressing erosion of the device by metal Bi generated by reducing Bi ³⁺ during glass production. Ce ⁴⁺ can be contained in the glass in a proportion of 0% to 10%. The Ce ⁴⁺ content is preferably 0.3% or more, and more preferably 0.5% or more. When the content of Ce ⁴⁺ exceeds 10%, the glass tends to be devitrified, and there is a possibility that the electrode cannot be stably produced. The Ce ⁴⁺ content is preferably 5% or less, more preferably 3% or less.

  In the glass of the present invention, the basicity of the glass calculated using the ionic radius of atoms contained in the glass is preferably 0.01 or more and 0.50 or less.

  The basicity of glass represents the ability to donate oxygen, and the larger the value, the easier it is to donate oxygen and the easier transfer of oxygen with other metal oxides. Basicity can be obtained by calculation, but there are two types of calculation methods, including a calculation method using electronegativity and a calculation method using the ionic radius of atoms. In the calculation using the electronegativity, no distinction is made by the valence, so in the present invention, the basicity is calculated using the ionic radius of the atom in consideration of the valence. In addition, the method of calculating the basicity of glass using the ionic radius of an atom is specifically as follows.

Ｘ_ｉ；陽イオン−酸素間引力
Ｚ_ｉ；陽イオンの電荷
ｒ_ｉ；陽イオンのイオン半径（Å）
２；酸素イオンの電荷
１．４０；酸素イオンのイオン半径（Å） Bonding force between M _i -O oxide M _{i O} cation - is given by the following equation (1) as the oxygen attraction between.

X _i ; cation-oxygen attractive force Z _i ; cation charge r _i ; cation radius (Å)
2; Charge of oxygen ion 1.40; Ion radius of oxygen ion (Å)

このＹ_ｉ値を以下のとおり規格すると、各単成分酸化物のＹ_ｉ値は表１のようになる。

Here, as shown by the following equation (2), and _{X i} of the reciprocal _{Y i} ie 1 / _{X i} a single-component oxide _{M i} O oxygen donating ability.

When this Y _i value is standardized as follows, the Y _i value of each single component oxide is as shown in Table 1.

Basicity Y of the glass, and Y _i for each oxide component of the glass contains, from the content n _i of cationic components of the oxide in the glass is determined by the equation (3). In the present specification, the basicity of glass refers to the basicity Y determined in this manner using the ionic radius of atoms unless otherwise specified.

  In the present invention, it was confirmed that the basicity of the glass is related to the insulating film penetration of the conductive paste during electrode formation. When the basicity of the glass of the present invention is 0.01 or more and 0.50 or less, the glass and the insulating film are suppressed while suppressing the oxidation of the conductive metal contained in the conductive paste together with the glass, particularly Al, during the electrode formation. Since the reaction with the component is sufficiently performed, the insulating film penetrability of the conductive paste becomes better.

  The lower the basicity value of the glass, the less the conductive metal introduced tends to be oxidized, so that the diffusion of oxygen in the glass to the conductive metal powder can be suppressed during electrode formation. It can contribute only to the reaction with the components. On the other hand, if the basicity is too low, the reaction between the glass and the insulating film component may be insufficient during electrode formation. Thus, in the glass of the present invention, by adjusting the basicity, the insulating film penetrability of the conductive paste during electrode formation can be improved, and as a result, an electrode that easily penetrates the insulating film can be obtained. It can be formed so as to be in direct contact with the semiconductor substrate.

  If the basicity of the glass is less than 0.01, the reactivity between the glass and the insulating film component becomes poor during electrode formation, and the conductive paste may not be able to penetrate the insulating film. The basicity of the glass is preferably 0.03 or more, more preferably 0.05 or more. Further, since the oxygen in the glass is diffused into the conductive metal powder as the basicity of the glass is increased, sufficient penetration of the insulating film at the time of electrode formation cannot be obtained. Therefore, if the basicity of the glass exceeds 0.50, there is a possibility that the electrode cannot be directly contacted with the semiconductor substrate after the electrode is formed. The basicity of the glass is preferably 0.45 or less, more preferably 0.40 or less.

  In addition, the preferable range of the basicity of the glass is a range that works effectively particularly when Al is used as the conductive metal. Since there is a difference in the degree of oxidization depending on the type of the conductive metal, the preferable range of the basicity of the glass is preferably adjusted as appropriate depending on the type of the conductive metal. Further, the preferable range of the basicity of the glass depends on the insulating material constituting the insulating film. In the case of silicon nitride, titanium dioxide, silicon dioxide, aluminum oxide, etc., which are typical materials constituting the insulating film, the basicity range of the glass is preferably applicable.

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

  First, a raw material mixture is prepared. A raw material will not be specifically limited if it is a raw material used for manufacture of normal oxide type glass, An oxide, carbonate, etc. can be used. In the obtained glass, the kind and ratio of the raw materials are appropriately adjusted so as to be in the above composition range to obtain a raw material composition.

  Next, the raw material mixture is heated by a known method to obtain a melt. 1000-1400 degreeC is preferable and, as for the temperature (melting temperature) which heat-melts, 1200-1300 degreeC is more preferable. 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, dripping into a cooling liquid, or the like can also be used. The resulting glass is preferably completely amorphous, i.e. having a crystallinity of 0%. However, as long as the effect of the present invention is not impaired, a crystallized portion may be included.

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

  The glass of this invention is used suitably for electrode formation on a semiconductor substrate, for example, electrode formation of a solar cell. The glass of the present invention is particularly effective when an electrode penetrating the insulating film is formed by fire-through using a conductive paste containing the glass and conductive metal powder on the semiconductor substrate via the insulating film. Can demonstrate. Furthermore, a remarkable effect can be exhibited when the electrode in the electrode formation is an aluminum electrode. When forming an electrode using the electrically conductive paste containing the glass of this invention, it is preferable that glass is a powder.

  The glass powder can be obtained by pulverizing the glass produced as described above by a dry pulverization method or a wet pulverization method. In the case of the wet pulverization method, it is preferable to use water as a solvent. The pulverization can be performed using a pulverizer such as a roll mill, a ball mill, or a jet mill.

The glass powder of the present invention preferably has a volume-based 50% particle size D ₅₀ in the cumulative particle size distribution of the powder of from 0.5 μm to 10 μm. If D ₅₀ of the glass powder is less than 0.5 [mu] m, it may be dispersed when the paste is difficult. Further, D ₅₀ of the glass powder is more than 10.0 [mu] m, since the point where there is no glass around the conductive metal powder occurs, there is a case adhesion between the electrode and the semiconductor substrate is not sufficient. The D ₅₀ of the glass powder is more preferably 7.0 μm or less. Adjustment of the particle size of the glass powder can be performed, for example, by classification as necessary after pulverization.

Incidentally, D ₅₀ as described herein, in cumulative particle size curve of the particle size distribution measured using a laser diffraction / scattering particle size distribution measuring apparatus, the particle diameter when the cumulative volume accounts for 50% by volume Represents.

<Conductive paste>
The conductive paste of the present invention contains the glass powder of the present invention, a conductive metal powder, and an organic vehicle. The glass powder is preferably a glass powder having a D ₅₀ of 0.5 μm or more and 10 μm or less.

  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 semiconductor substrate is used without particular limitation. Specific examples of the conductive metal powder include powders such as Al, Ag, Cu, Au, Pd, and Pt. Among these, Al powder is preferable. Since Al is easily oxidized, when the Al powder is used as a conductive metal powder, the diffusion of oxygen to the conductive metal powder is suppressed, and the insulating film penetration of the conductive paste can be improved. The effect is remarkable.

D ₅₀ of the conductive metal powder, aggregation is suppressed, and, 2 to 15 [mu] m is preferable from the viewpoint of uniform dispersion is obtained. For example, the content of the glass powder in the conductive paste is preferably 0.1 parts by mass or more and 10 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 conductive metal powder may not be covered with the glass deposit. Moreover, there exists a possibility that the adhesiveness of an electrode and a semiconductor substrate may worsen. On the other hand, when the content of the glass powder exceeds 10 parts by mass, the conductive metal powder is more sintered and blisters and the like are easily generated. 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 cellulose 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 acrylic monomers such as butyl acrylate and 2-hydroxyethyl acrylate is used.

  Solvents used for organic vehicles include terpineol, butyl diglycol acetate, ethyl diglycol acetate, propylene glycol diacetate in the case of cellulose resins, and methyl ethyl ketone, terpineol, butyl diglycol acetate, in the case of acrylic resins, A solvent such as ethyl diglycol acetate or propylene glycol diacetate is preferably used.

  The ratio of the organic resin binder and the solvent in the organic vehicle is not particularly limited, but 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 indicated by the organic resin binder: solvent is preferably about 3:97 to 15:85.

  The content of the organic vehicle in the conductive paste is preferably 5% by mass or more and 30% by mass or less with respect to the total amount of the conductive paste. When the content of the organic vehicle is less than 5% by mass, the viscosity of the conductive paste increases, so that coating properties such as printing of the conductive paste decrease, and it becomes difficult to form a good conductive layer (electrode). Moreover, when content of an organic vehicle exceeds 30 mass%, the content rate of the solid content of an electrically conductive paste will become low, and it will become difficult to obtain sufficient coating film thickness.

  In addition to the glass powder, conductive metal powder, and organic vehicle described above, the conductive paste of the present invention may be blended with known additives as necessary and within the limits that do not contradict the purpose of the present invention. it can.

Examples of such additives include various inorganic oxides. Specific examples of the inorganic oxide include B ₂ O ₃ , SiO ₂ , Al ₂ O _3, TiO ₂ , MgO, ZrO ₂ , Sb ₂ O ₃ , and composite oxides thereof. These inorganic oxides have an effect of reducing the sintering of the conductive metal powder when the conductive paste is fired, and thereby have an effect of adjusting the bonding strength after firing. The size of the additives consisting of inorganic oxides is not particularly limited, for example, can be suitably used D ₅₀ is 10μm or less.

  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, 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 inorganic oxide at the time of electrode formation may be reduced, and the adhesive strength between the electrode and the semiconductor substrate may be reduced. In order to obtain a practical blending effect (adjustment of bonding strength after firing), the lower limit of the content is preferably 3% by mass or more, more preferably 5% by mass or more.

  You may add a well-known additive with an electrically conductive paste like an antifoamer and a dispersing agent to an electrically conductive paste. The organic vehicle and these additives are components that usually disappear during the electrode formation process. For the preparation of the conductive paste, 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.

  The conductive paste of the present invention is suitable for electrode formation by firing on a semiconductor substrate, particularly for electrode formation performed by fire-through by partially applying the conductive paste on an insulating film provided on the semiconductor substrate. Used. When the conductive paste of the present invention is used, the glass is an insulating film material while suppressing diffusion of oxygen in the glass contained in the conductive paste to the conductive metal powder at the portion where the conductive paste is applied during firing. As a result of the reaction, the insulating film is melted to obtain an electrode penetrating the insulating film and sufficiently contacting the semiconductor substrate.

  The application and baking of the conductive paste on the insulating film can be performed by the same method as the application and baking in electrode formation performed by conventional fire-through. Examples of the coating method include screen printing and dispensing method. The firing temperature depends on the type of conductive metal powder contained, the surface condition, and the like, but a temperature of about 500 to 1000 ° C. can be exemplified. The firing time is appropriately adjusted depending on the thickness of the insulating film to be penetrated, the kind of the insulating film, and the like. Moreover, you may provide the drying process at about 80-200 degreeC between application | coating and baking of an electrically 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. In the solar cell of the present invention, at least one of the electrodes is an electrode provided in such a manner as to partially penetrate the insulating film and contact the semiconductor substrate by fire-through using the conductive paste of the present invention. Is preferred.

  As an electrode that penetrates such an insulating film of a solar cell, for example, a semiconductor that partially penetrates an insulating film that is an antireflection film as an electrode of a light receiving surface of a solar cell using a pn junction type semiconductor substrate The electrode provided in the form which contacts a board | substrate is mentioned. In this case, the light receiving surface may be one side or both sides of the semiconductor substrate, and the semiconductor substrate may be either n-type or p-type. The electrode provided on the light receiving surface of such a solar cell can be formed by fire-through using the conductive paste of the present invention.

  In solar cells such as PERC, a passivation film made of the same insulating material as that of the antireflection film is also provided on the entire back surface, and electrodes are formed on the passivation film so as to partially contact the semiconductor substrate. . Such a back electrode of a PERC solar cell is also an electrode that can be formed by fire-through using the conductive paste of the present invention.

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. As an Al electrode provided in such a manner as to partially penetrate the insulating film and contact the semiconductor substrate by fire-through, for example, a back electrode of a PERC solar cell using a p-type Si substrate, an n-type Si substrate is used. Back electrode of PERRT (Passivated Emitter, Rear Totally diffused) solar cell, electrode provided on the p-type layer or p ⁺ layer side of double-sided solar cell using n-type Si substrate or p-type Si substrate, back contact One electrode of the solar cell and the like.

  Hereinafter, the case where the electrode of the n-type Si substrate double-sided solar cell is formed with 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 an n-type Si substrate double-sided solar cell on which an electrode is formed using the conductive paste of the present invention.

  A solar cell 10 shown in FIG. 1 has an n-type Si substrate 1, an insulating film 2A provided on the upper surface thereof, and an insulating film 2B provided on the lower surface, and penetrates a part of the insulating film 2A to form an n-type. An Al electrode 3 that contacts the Si substrate 1 and an Ag electrode 4 that penetrates a part of the insulating film 2B and contacts the n-type Si substrate 1 are provided. Both surfaces of the n-type Si substrate 1 have a concavo-convex structure formed by using, for example, 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.

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

  The Al electrode 3 and the Ag electrode 4 are formed as follows using an Al electrode forming conductive paste containing glass and Al powder and an Ag electrode forming conductive paste containing glass and Ag powder, respectively. That is, the insulating film 2A and the insulating film 2B provided on both surfaces of the n-type Si substrate 1 exist on the entire surface before the formation of the Al electrode 3 and the Ag electrode 4, and form the Al electrode 3 and the Ag electrode 4. Only the portions where the conductive paste is applied are melted when the conductive paste is fired, so that the Al electrode 3 and the Ag electrode 4 that penetrate the insulating film 2A and the insulating film 2B and contact the n-type Si substrate 1 respectively. It is formed.

  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 it is particularly preferable to use it as a conductive paste for forming an Al electrode as described above.

By using the glass powder of the present invention containing the above specific amounts of V ⁵⁺ and Bi ³⁺ and the conductive paste of the present invention containing Al powder as the Al electrode forming conductive paste, The diffusion of oxygen into the Al powder is suppressed, and the glass sufficiently reacts with the insulating material constituting the insulating film, so that the Al electrode forming conductive paste penetrates the insulating film, and the p of the n-type Si substrate 1 An Al electrode 3 in sufficient contact with the ⁺ layer 1a is obtained.

Further, the glass of the present invention using the Al electrode formation conductive ^pastes, and other cationic components in addition to the ^{V 5+} and ^{Bi 3+,} the use of the glass containing ^{B 3+,} the n-type Si substrate 1 ^{p +} layer 1a The glass in the conductive paste that has reached the P ⁺ layer reacts directly with the B ⁺ and diffuses into the p ⁺ layer 1a as B ³⁺ is reduced, thereby improving its performance.

  The insulating film 2A and the insulating film 2B included in the solar cell 10 are antireflection films, and the insulating materials listed above can be used as the insulating materials constituting the films. The antireflection film may be a single layer film or a multilayer film. The conductive paste of the present invention has a high penetrability particularly for an insulating film having a layer made of silicon nitride.

  In the solar cell of the present invention, the electrode is formed using a conductive paste that can easily form an electrode that penetrates the insulating film and ensures contact with the semiconductor substrate when forming the electrode containing the glass powder of the present invention. As a result, the solar cell has improved reliability and productivity.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail with reference to an Example, this invention is not limited to an Example. Examples 1 to 15 are examples, and examples 16 to 18 are comparative examples.

[Examples 1 to 18]
Glass was manufactured by the following method, and the insulating film penetrability at the time of forming an electrode by fire through was evaluated about the conductive paste for electrode formation containing this glass.

<Manufacture of glass powder>
As the glass used for the conductive paste for electrode formation, glass powders having the compositions and characteristics shown in Tables 2 and 3 were produced. That is, raw material powders were blended and mixed so as to have the compositions shown in Tables 2 and 3, and melted in a 1000 to 1300 ° C. electric furnace using a platinum crucible for 30 minutes to 1 hour to form a sheet glass. after this the thin plate glass dry milled to _{D 50} with a ball mill is a predetermined range (0.5 to 10 [mu] m), to remove coarse particles at 150 mesh sieve. For Examples 2, 3, 5, 6, 8, 9, 11, 12, 14, and 15, the glass powder obtained by removing coarse particles after dry grinding was used as the glass powder as it was.

For the glasses of Examples 1, 4, 7, 10, 13, 16 to 18, in order to make D ₅₀ smaller within the above predetermined range, the glass powder from which coarse particles were removed after the dry pulverization was further ball milled. Glass powder obtained by wet pulverization using water was used as glass powder. In order to obtain a predetermined D ₅₀ during the wet pulverization, the balls were made of alumina having a diameter of 5 mm, and D ₅₀ was adjusted by the pulverization time. Thereafter, the slurry obtained by wet pulverization was filtered to remove most of the water, and then dried at 130 ° C. with a dryer to adjust the amount of water to produce a glass powder.

The glass powder Examples 1 to 18 obtained above, together with measuring the D ₅₀ as follows, were calculated basicity. Moreover, the conductive paste for Al electrode formation was manufactured using the glass powder of Examples 1-18, and the silicon nitride film penetrability at the time of electrode formation was evaluated. The results are shown in Tables 2 and 3.

_{(D 50)}
In the glass powders of Examples 1 to 15, 0.02 g of glass powder was mixed with 60 cc of water and dispersed by ultrasonic dispersion for 1 minute. And the sample placed in a Microtrac measuring machine, to obtain a value of D ₅₀ is 50% particle diameter on a volume basis. The glass powders of Examples 16 to 18 were mixed with 0.02 g of glass powder in 60 cc of isopropyl alcohol and dispersed for 1 minute by ultrasonic dispersion. And the sample placed in a Microtrac measuring machine, to obtain a value of D ₅₀ is 50% particle diameter on a volume basis in a cumulative particle size distribution.

(Basicity)
The basicity of the glasses of Examples 1 to 18 was calculated by a method using the ionic radius of atoms contained in each glass. That is, it calculated by Formula (3) using the _Yi value of the single-component oxide of Table 1 and the compositions shown in Tables 2 and 3.

(Silicon nitride film penetration)
(1) Preparation of Al electrode forming conductive paste Al electrode forming conductive pastes 1 to 18 each containing the glass powders of Examples 1 to 18 were prepared by the following method.

  First, 90 parts by mass of butyl diglycol acetate was mixed with 10 parts by mass of ethyl cellulose and stirred at 85 ° C. for 2 hours to prepare an organic vehicle. Next, 21 parts by mass of the organic vehicle thus obtained was mixed with 79 parts by mass of Al powder (manufactured by Minalco, sprayed aluminum powder: # 800F), and then kneaded for 10 minutes by a crusher. Then, glass powder was mix | blended in the ratio of 4 mass parts with respect to 100 mass parts of Al powder, and also knead | mixed for 60 minutes with the crusher, and it was set as the electrically conductive paste for Al electrode formation.

(2) Production of Al electrode and evaluation of silicon nitride film penetrability Using the Al electrode-forming conductive pastes 1 to 18 produced above, an insulating film (silicon nitride film) was formed on the semiconductor substrate as follows. Then, an Al electrode was formed, and the silicon nitride film penetrability at that time was evaluated.

  Using an n-type crystalline Si semiconductor substrate sliced to a thickness of 160 μm, the surface was first etched with a very small amount of hydrofluoric acid in order to clean the sliced surface of the substrate. Thereafter, a concavo-convex structure for reducing the light reflectance was formed on the surface of the crystalline Si semiconductor substrate on the light receiving surface side by using a wet etching method. Next, a p-type layer is formed by diffusion on the light receiving surface of the semiconductor substrate. B was used as a p-type doping element. Next, an antireflection film was formed on the light receiving surface (surface of the p-type layer) of the semiconductor substrate. As a material for the antireflection film, silicon nitride was mainly used, and it was formed to a thickness of 80 nm by plasma CVD. Next, the Al electrode-forming conductive paste obtained above was applied in a line shape of 500 μm in width by 200-mesh screen printing on the antireflection film (silicon nitride film) on the light receiving surface. Thereafter, baking was performed at a peak temperature of 800 ° C. for 100 seconds using an infrared light heating batch furnace to form an Al electrode.

  The n-type Si semiconductor substrate having the Al electrode formed on the p-type layer side through the antireflection film (silicon nitride film) obtained above is mixed with hydrochloric acid (35 to 38% aqueous solution of hydrogen chloride) and water. The Al electrode was removed from the substrate by immersion in an aqueous solution mixed at a mass ratio of 1: 1 for 24 hours. Thereafter, whether or not the antireflection film (silicon nitride film) was removed by an optical microscope (100 times) was evaluated according to the following criteria.

A: The antireflection film (silicon nitride film) is removed in a line shape having a width of 200 to 600 μm.
X: The location where the antireflection film (silicon nitride film) is removed cannot be confirmed.

  The evaluation results are shown in Table 2 and Table 3. Further, in FIG. 2, after forming the Al electrode as described above using the Al electrode forming conductive paste 3 containing the glass of Example 3 (Example), the p-type electrode of the n-type Si semiconductor substrate from which the Al electrode was removed. An optical microscope (100 times) photograph of the mold layer side surface is shown. According to the photograph in FIG. 2, it can be seen that, when the Al electrode is formed, the silicon nitride constituting the antireflection film reacts with the glass powder of Example 3, and the obtained Al electrode reaches the Si semiconductor substrate. . FIG. 3 shows the p-type layer of the n-type Si semiconductor substrate from which the Al electrode was formed after the Al electrode was formed as described above using the Al electrode-forming conductive paste 17 containing the glass of Example 17 (Comparative Example). An optical microscope (100 times) photograph of the side surface is shown. According to the photograph of FIG. 3, when forming the Al electrode, the glass powder of Example 17 has poor reactivity with silicon nitride constituting the antireflection film, and the obtained Al electrode does not reach the Si semiconductor substrate. I understand that.

  As is apparent from Tables 2 and 3, the glass powders of Examples 1 to 15 as examples are suitable for forming an Al electrode of a solar cell.

  According to the present invention, in glass used for electrode formation, when an electrode is formed on a semiconductor substrate such as a solar cell via an insulating film, sufficient contact with the semiconductor substrate can be ensured through the insulating film. A lead-free glass capable of forming electrodes at low cost with high production efficiency is obtained. Further, in the present invention, an electrically conductive paste containing the glass powder and capable of forming an electrode penetrating an insulating film and ensuring contact with a semiconductor substrate at the time of electrode formation at low cost and with high production efficiency, and the electrically conductive paste It is possible to provide a solar cell with improved reliability and productivity.

DESCRIPTION OF SYMBOLS 10 ... Solar cell, 1 ... n-type Si semiconductor substrate, 1a ... p ⁺ layer, 1b ... n layer, 1c ... n ⁺ layer, 2A, 2B ... insulating film, 3 ... Al electrode, 4 ... Ag electrode.

Claims (11)

In cation% display,
V ⁵⁺ 15-55%,
1 to 85% of Bi ³⁺ is contained,
A glass characterized by substantially not containing Pb2 ⁺ .   The glass of Claim 1 used for formation of the electrode of a solar cell.   The glass according to claim 2, wherein the electrode is an aluminum electrode.   The glass according to any one of claims 1 to 3, wherein the basicity of the glass calculated using the ionic radius of atoms contained in the glass is 0.01 to 0.50. Furthermore, the ^{B 3+} by cationic% and containing 10% to 80%, the glass according to any one of claims 1 to 4, the content of the ^{Bi 3+} is characterized in that 1 to 75%. Furthermore, 0-70% of Zn2 ⁺ is contained by cation% display, The glass of any one of Claims 1-5 characterized by the above-mentioned. Furthermore, it contains 0 to 70% of Al ³⁺ in terms of cation%, and the glass according to any one of claims 1 to 6. The form of glass is a powder, glass according to any one of claims 1 to 7 in 50% particle diameter D ₅₀ on a volume basis is 0.5~10μm in a cumulative particle size distribution of the powder.   The electrically conductive paste containing the glass powder of any one of Claims 1-7, electroconductive metal powder, and an organic vehicle. 10. The conductive paste according to claim 9, wherein a volume-based 50% particle size D ₅₀ in the cumulative particle size distribution of the glass powder is 0.5 to 10 μm.   A solar cell comprising an electrode formed using the conductive paste according to claim 9.

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