JP2017222542A - Glass powder, conductive paste, and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass powder, a conductive paste, and a solar battery, which enable elements contained in glass to be diffused in a semiconductor substrate when an electrode is formed, thereby enabling the conversion efficiency of the solar battery to be improved.SOLUTION: The glass powder includes 25 to 80% Band 20 to 75% Pb, expressed in cationic percentage. In the glass powder, D/Dis 2.0 to 4.5 and D/Dis 1.5 to 3.4 on the assumption that a 10% particle size on a volumetric basis is D, a 50% particle size on a volumetric basis is D, a 90% particle size on a volumetric basis is Din a cumulative particle size distribution.SELECTED DRAWING: Figure 1

Description

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

  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.

The above-described technique for forming an electrode on a semiconductor substrate is also applied to the formation of an electrode on a pn junction type semiconductor substrate in a solar cell. For example, Patent Document 1 discloses that glass used for an electrode formed by penetrating an antireflection film on a light receiving surface of a solar cell has good penetrability of the antireflection film, and conversion efficiency of the solar cell at the time of electrode formation. It describes a lead-based glass that is difficult to lower the temperature. Patent Document 1 discloses, as a specific glass composition, a composition containing 60 to 95% of PbO, 0 to 10% of B ₂ O ₅ and 1 to 30% of SiO ₂ + Al ₂ O ₃ by mass%. Has been.

International Publication No. 2013/103087

  As for the glass used for forming the electrode of the solar cell, as in Patent Document 1, many techniques for improving the electrode formability have been developed. However, in a glass powder used for electrode formation, particularly a lead-based glass powder, by adjusting the glass composition and the particle size distribution of the powder, an element that can contribute to the performance of the semiconductor substrate along with the electrode formation may be a p-type layer or A technique for improving the conversion efficiency of the solar cell by diffusing into the n-type layer is under development.

  In the present invention, glass powder used for electrode formation on a semiconductor substrate can diffuse elements contained in the glass into the semiconductor substrate during electrode formation, thereby improving the conversion efficiency of the solar cell. An object of the present invention is to provide a glass powder, a conductive paste, and a solar cell that can be used.

The present invention provides a glass powder, a conductive paste and a solar cell having the following constitution.
[1] In terms of cation%, B ³⁺ is contained in 25 to 80% and Pb ²⁺ is contained in 20 to 75%. A volume-based 10% particle diameter in the cumulative particle size distribution is D ₁₀ , and a volume-based 50% particle diameter is D _50. A glass powder having a D ₅₀ / D ₁₀ of 2.0 to 4.5 and a D ₉₀ / D ₅₀ of 1.5 to 3.4 when the volume-based 90% particle size is D ₉₀ .
[2] The glass powder of [1] used for forming an electrode of a solar cell.
[3] The glass powder of [2], wherein the electrode is an aluminum electrode.
[4] The glass powder of any one of [1] to [3], wherein the D ₅₀ is 0.5 to 5.0 μm.
[5] The glass powder according to any one of [1] to [4], which has a water content of 0.2 to 1.0% by mass.
[6] A conductive paste containing the glass powder of any one of [1] to [5], a conductive metal powder, and an organic vehicle.
[7] A solar cell comprising an electrode formed using the conductive paste according to [6].

  According to the glass powder, the conductive paste, and the solar cell of the present invention, it is possible to diffuse an element contained in the glass at the time of electrode formation, for example, B into the semiconductor substrate, thereby improving the conversion efficiency of the solar cell. be able to.

It is a figure which shows typically the cross section of an example of the solar cell by which the electrode formation was carried out using the glass powder of this invention. It is a graph which shows the measurement result of the boron (B) average density | concentration in Si semiconductor substrate in the electrode formation surface of the solar cell of an Example and a comparative example.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

<Glass powder>
The glass powder of the present invention comprises a glass powder having a composition containing 25 to 80% B ³⁺ and 20 to 75% Pb ²⁺ in terms of cation%. Then, the powder of the glass, _{D 10} 10% particle diameter on a volume basis in a cumulative particle size distribution, _{D 50} 50% particle diameter on a volume basis, 90% particle diameter on a volume basis when the _{D 90,} D ₅₀ / _{D 10} is 2.0 to 4.5, _and, D 90 _{/ D 50} is 1.5 to 3.4.

In the glass powder of the present invention, the glass containing B ³⁺ and Pb ²⁺ in the above-mentioned predetermined amounts, expressed as cation%, is used as the glass powder having the specific particle size distribution, so that the glass is formed on the semiconductor substrate. When an electrode is formed by applying and baking a conductive paste containing powder and a conductive metal powder, the dispersion state of the glass powder in the conductive paste and the contact state with the semiconductor substrate become high density and uniform, and glass The high fluidity of the glass itself allows sufficient contact between the glass and the semiconductor substrate and reaction. As a result, it is possible to improve the bonding strength between the electrode and the semiconductor substrate, and to diffuse B ³⁺ contained in the glass as B in the semiconductor substrate, for example, in the p-type layer, thereby improving the p ⁺ layer. And the conversion efficiency of the solar cell can be improved.

  The glass powder of the present invention can exhibit the above-described effect when, for example, an electrode is formed on a semiconductor substrate using a conductive paste containing the glass powder and a conductive metal powder. In the following description, unless otherwise specified, a case where an electrode is formed by applying and baking a conductive paste containing the glass powder and conductive metal powder on a semiconductor substrate, particularly a pn junction type Si semiconductor substrate. This is simply referred to as “electrode formation”.

  Here, in the glass powder, 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 a typical valence. Expressed in numbers.

  In the present specification, “cation%” is a unit as follows. First, the constituent components in the glass composition 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 powder of the present invention is determined by inductively coupled plasma-inductively coupled plasma (ICP-AES) analysis or electron probe microanalyzer (EPMA) of the obtained glass powder. ) It is obtained from the result of analysis.

In the present specification, “D ₁₀ ”, “D ₅₀ ”, and “D ₉₀ ” indicate a 10% particle size, a 50% particle size, and a 90% particle size, respectively, on a volume basis in the cumulative particle size distribution. Specifically, in the cumulative particle size curve of the particle size distribution measured using a laser diffraction / scattering type particle size distribution measuring device, when the integrated amount occupies 10%, 50%, and 90% on a volume basis, respectively. Represents particle size.

Hereinafter, the cation component of glass in the glass powder of the present invention will be described. Incidentally, the glass powder of the present invention, the anionic component of the glass is O ^2- only.

In the glass powder of the present invention, Pb ²⁺ in the glass is an essential component. Pb ²⁺ improves the softening fluidity of the glass and improves the bonding strength between the semiconductor substrate and the electrode. When the glass contains Al ³⁺ as a cation component, metal Pb particles generated by reducing Pb ^{2+ in} the glass and metal Al particles generated by reducing Al ³⁺ in the glass at the time of electrode formation. Eutectic reaction causes the melting temperature of the Al particles to decrease. As a result, the conversion efficiency of the solar cell can be improved by diffusing Al particles into the semiconductor substrate to form a good P ⁺ layer.

Further, Pb ²⁺ can promote direct reaction between the semiconductor substrate and the glass by flowing the glass. Thereby, it is possible to promote the diffusion of B ³⁺ in the glass as B into the semiconductor substrate, and a better p ⁺ layer can be formed.

In the glass powder of the present invention, the glass contains Pb ²⁺ in an amount of 20% to 75%. When the content of Pb ²⁺ is less than 20%, 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 Pb ²⁺ is preferably 25% or more, and more preferably 30% or more. On the other hand, if the content of Pb ²⁺ exceeds 75%, glass cannot be obtained by crystallization. The content of Pb ²⁺ is preferably 73% or less, and more preferably 70% or less.

B ³⁺ in the glass is an essential component. B ³⁺ is a component that improves the conversion efficiency of the solar cell by forming a p ⁺ layer in the semiconductor substrate. B ³⁺ is also a glass forming component. When B ³⁺ in the glass diffuses as B in the semiconductor substrate, the semiconductor substrate can be operated as a p-type similarly to the above-described Al.

In the present invention, the glass contains B ³⁺ in an amount of 25% to 80%. When the content of B ³⁺ is less than 25%, B cannot be sufficiently diffused into the semiconductor substrate at the time of electrode formation, and thus the conversion efficiency of the solar cell is not improved. The content of B ³⁺ is preferably 27% or more, more preferably 30% or more. When the content of B ³⁺ exceeds 80%, the stability of the glass is lowered. The content of B ³⁺ is preferably 75% or less, more preferably 70% or less.

Cationic component of glass, may consist only ^{Pb 2+} and ^{B 3+,} any other cationic components other than ^{Pb 2+} and ^{B 3+} (hereinafter, referred to as "other cationic components.") May contain. 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 in this invention. Moreover, content of another cation component is content which does not impair the effect of the glass in this invention about each cation component.

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

The glass preferably contains Zn ²⁺ as another cation component. Zn ²⁺ is a component that stabilizes the glass and is a component that increases the water resistance of the electrode. When glass contains Zn < ²⁺ >, it is preferable that the content is 5% or more and 30% or less. When the Zn ²⁺ content is 5% or more, the water resistance of an electrode, particularly an Al electrode, is improved, and long-term reliability is easily obtained. The Zn ²⁺ content is more preferably 10% or more, and still more preferably 13% or more. On the other hand, when the content of Zn ²⁺ is 30% or less, the stability of the glass is hardly deteriorated and devitrification can be suppressed, so that a reduction in productivity can be suppressed. The Zn ²⁺ content is more preferably 28% or less, and even more preferably 25% or less.

Powder of the glass of the present invention, for a 10% particle diameter _{D 10} on a volume basis in a cumulative particle size distribution, the ratio of the 50% particle size _{D 50} of the volume-based _(D 50 _{/ D 10)} is 2.0 to 4.5 , and the relative 50% particle diameter _{D 50} on a volume basis, the ratio of 90% particle diameter _{D 90} on a volume basis _(D 90 _{/ D 50)} is 1.5 or more 3.4 or less. Since the glass powder of the present invention has the above specific narrow particle size distribution, the glass powder can be uniformly contacted with the semiconductor substrate together with the conductive metal powder. The dispersed state and the contact state with the semiconductor substrate can be made high density and uniform. Thereby, the characteristics of the glass composition are fully exhibited, that is, the bonding strength between the electrode and the semiconductor substrate is improved, and B ³⁺ contained in the glass is diffused as B in the p-type layer of the semiconductor substrate, for example. As a result, the conversion efficiency of the solar cell can be improved by forming a good p ⁺ layer.

When D ₅₀ / D ₁₀ is less than 2.0, it becomes difficult to close-pack the glass powder in the conductive paste. D ₅₀ / D ₁₀ is preferably 2.3 or more, and more preferably 2.5 or more. On the other hand, if D ₅₀ / D ₁₀ exceeds 4.5, the contact state between the glass powder and the semiconductor substrate changes during electrode formation, and the diffusion state of B into the p ⁺ layer becomes not constant. As a result, the characteristics of the solar cell become unstable. D ₅₀ / D ₁₀ is preferably 4.0 or less, and more preferably 3.5 or less.

Further, when D _{90 /} D ₅₀ is less than 1.5, closest packing of the glass powder in the conductive paste becomes difficult. D ₉₀ / D ₅₀ is preferably 1.6 or more, and more preferably 1.8 or more. On the other hand, if D ₉₀ / D ₅₀ exceeds 3.4, the contact state between the glass powder and the semiconductor substrate changes during electrode formation, and the diffusion state of B into the p ⁺ layer becomes not constant. As a result, the characteristics of the solar cell become unstable. D ₉₀ / _{D 50} is preferably 3.0 or less, more preferably 2.5 or less.

The glass powder of the present invention, _{D 50} of the powder of the glass of the above composition is preferably 0.5μm or more 5.0μm or less. By D ₅₀ is 0.5μm or more, dispersibility when used as a conductive paste is improved. Further, D ₅₀ is that it is less 5.0 .mu.m, for places not glass present around the conductive metal powder is less likely to occur, thereby improving the adhesion between the electrode and the semiconductor substrate. D ₅₀ is more preferably 2.0 μm or less.

  The glass powder of the present invention may contain moisture. Moisture has the effect of oxidizing the conductive metal powder during electrode formation. For example, when the conductive metal is aluminum, when the surface of the aluminum powder is oxidized, it becomes aluminum oxide and becomes an oxide similar to the component of the glass powder. Thereby, the water | moisture content in glass powder has an effect which improves the fluidity | liquidity of glass at the time of electrode formation.

  When the glass powder of this invention contains a water | moisture content, it is preferable that the water | moisture content with respect to glass powder whole quantity is 0.2 to 1.0 mass%. When the water content is 0.2% by mass or more, the fluidity of the glass is improved during electrode formation. The water content is more preferably 0.24% by mass or more, and further preferably 0.25% by mass or more. On the other hand, when the water content is 1.0% by mass or less, the glass powder is less likely to aggregate, and the dispersibility of the conductive paste is improved. The water content is more preferably 0.93% by mass or less, and still more preferably 0.90% by mass or less. In addition, the water content described in the present specification represents a value measured when heated to 300 ° C. using the Karl Fischer method.

  The manufacturing method of the glass powder of this invention is not specifically limited as long as the glass of the said composition is obtained as a glass powder which has the said specific particle size distribution. 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 powder, the raw material composition is prepared by appropriately adjusting the type and amount of the raw material so as to be within the above composition range.

  Next, the raw material mixture is heated by a known method to obtain a melt. 900-1300 degreeC is preferable and, as for the temperature (melting temperature) which heat-melts, 1000-1200 degreeC is more preferable. The heating and melting time is preferably 30 to 200 minutes.

  Then, the glass of the said composition based on the glass powder of this invention can be obtained by cooling and solidifying a 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 powder of the present invention can be obtained by pulverizing the glass produced as described above to have the specific particle size distribution by, for example, a dry pulverization method or a wet pulverization method. In order to adjust the particle size of the glass powder, classification may be performed as necessary in addition to pulverization of the glass.

  The glass pulverization method for obtaining the glass powder of the present invention is preferably, for example, a method of dry pulverizing glass having an appropriate shape and then performing wet pulverization. Dry pulverization and wet pulverization can be performed using a pulverizer such as a roll mill, a ball mill, or a jet mill. The particle size distribution can be adjusted, for example, by adjusting the pulverizer such as the pulverization time in each pulverization and the ball size of the ball mill. In the case of the wet pulverization method, it is preferable to use water as a solvent. After the wet pulverization, water is removed by drying or the like to obtain glass powder.

  Moreover, the water content of the glass powder of this invention can be adjusted with the heating temperature and heating time at the time of the drying after the wet grinding | pulverization of the said glass.

  The glass powder of this invention is used suitably for electrode formation on a semiconductor substrate, for example, electrode formation of a solar cell. The glass powder of the present invention can exert a remarkable effect particularly when the electrode in forming the electrode is an aluminum electrode.

<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.

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 from the viewpoint of productivity. Aggregation is suppressed, and the particle diameter of the conductive metal powder from the viewpoint of uniform dispersibility is obtained D ₅₀ is, 2 to 15 [mu] m is preferred.

  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 conductive metal powder, glass powder, and organic vehicle described above, the conductive paste of the present invention can be blended with known additives as necessary and within the limits not departing from the object of the present invention. .

Examples of such additives include various inorganic oxides. Specific examples of the inorganic oxide include SiO ₂ , Al ₂ O _3, TiO ₂ , MgO, ZrO ₂ , and composite oxides thereof. These inorganic oxides have an effect of reducing the sintering of the conductive metal powder during firing of the conductive paste, and can suppress the generation of blisters on the electrode surface 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 with respect to the glass powder. When content of an inorganic oxide exceeds 10 mass%, there exists a possibility that the fluidity | liquidity of the inorganic oxide at the time of electrode formation may fall, and adhesive strength may fall. In order to obtain a practical blending effect (suppression of blister generation on the electrode surface), 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 electrically conductive paste of this invention is used suitably for electrode formation by baking on a semiconductor substrate, especially a pn junction type Si semiconductor substrate. The conductive paste of the present invention contains the glass powder of the present invention, so that it is possible to improve the bonding strength between the electrode and the semiconductor substrate when forming the electrode, and the B ³⁺ contained in the glass powder contains, for example, p-type of the semiconductor substrate. It can be diffused as B in the layer, thereby forming a good p ⁺ layer. Therefore, if the electrically conductive paste of this invention is used for electrode formation on the semiconductor substrate in a solar cell, the conversion efficiency can be improved.

  The application and baking of the conductive paste on the semiconductor substrate can be performed by the same method as the application and baking in conventional electrode formation. 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 shape and thickness of the electrode. 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, particularly an electrode baked on a pn junction type Si semiconductor substrate. The electrode formed using the conductive paste of the present invention can be applied to an electrode provided to be in contact with a p-type layer, a p ⁺ layer, an n-type layer, or an n ⁺ layer of a semiconductor substrate of a solar cell. It is preferably used for an electrode provided so as to be in contact with the mold layer or the p ⁺ layer.

The electrode provided as to contact the p-type layer or p ⁺ layer semiconductor substrate having a solar cell, for example, formed on the p-type layer or p ⁺ layer serving as a non-light-receiving surface of the p-type Si semiconductor substrate (back surface) And a surface electrode provided on a p-type layer serving as a light-receiving surface (front surface) of an n-type Si semiconductor substrate. An Al electrode is preferably used as the electrode provided so as to be in contact with the p-type layer or the p ⁺ layer.

In addition, in a PERC (Passivated Emitter and Rear Contact) type solar cell, a passivation film made of an insulating material is provided on the entire non-light-receiving surface (back surface), and the back electrode partially contacts the semiconductor substrate on the passivation film. To form. Such a back electrode of a PERC type solar cell can also be formed using the conductive paste of the present invention. In this case, for example, the non-light-receiving surface is a p-type layer or a p ⁺ layer, and an Al electrode is preferably used as the back electrode.

  Hereinafter, a case where a back electrode is formed of the conductive paste of the present invention in a solar cell using a pn junction type p-type Si semiconductor substrate will be described as an example. FIG. 1 is a diagram schematically showing a cross section of an example of a solar cell using a p-type Si semiconductor substrate on which a back electrode is formed using the conductive paste of the present invention.

  The solar cell 10 shown in FIG. 1 is in contact with the p-type Si semiconductor substrate 1 through the p-type Si semiconductor substrate 1, the antireflection film 2 provided on the light receiving surface S1, and a part of the antireflection film 2. And an Al electrode 4 as a back electrode provided in contact with the entire surface of the non-light-receiving surface S2 of the p-type Si semiconductor substrate 1. The light-receiving surface S1 of the p-type Si semiconductor substrate 1 has a concavo-convex structure (not shown) that is formed using, for example, a wet etching method and reduces the light reflectance.

The p-type Si semiconductor substrate 1 is composed of an n-type layer 1a, a p-type layer 1b, and a p ⁺ layer 1c in this order from the light-receiving surface S1 side. The Ag electrode 3 is partially on the n-type layer 1a, and the Al electrode 4 is p. Each of the ⁺ layers 1c is in contact with the entire surface. The n-type layer 1a of the p-type Si semiconductor substrate 1 can be formed by doping P, Sb, As or the like on the light receiving surface S1 on which the concavo-convex structure is formed. Further, regarding the p ⁺ layer 1c, when the Al electrode 4 is formed using the conductive paste of the present invention, B ³⁺ contained in the glass powder in the conductive paste is diffused and formed as B in the p-type layer. Layer.

  The Al electrode 4 is the conductive paste of the present invention containing the glass powder of the present invention and Al powder, and the Ag electrode 3 is the conductive material for forming an Ag electrode containing the glass powder and Ag powder having good penetrability of the antireflection film. Each paste is used to form as follows. That is, the conductive paste for forming the Ag electrode 3 for forming the Ag electrode 3 on the antireflection film 2 provided on the light receiving surface S1 of the p-type Si semiconductor substrate 1 in a predetermined pattern and the p-type Si semiconductor substrate 1 The above-described conductive paste for forming the Al electrode 4 is applied to the entire surface of the non-light-receiving surface S2 and baked, whereby the Ag electrode 3 and the Al electrode 4 are formed. The Ag electrode 3 is formed in contact with the n-type layer 1a of the p-type Si semiconductor substrate 1 when the Ag electrode-forming conductive paste penetrates the antireflection film during firing.

As described above, when the Al electrode 4 is formed using the conductive paste of the present invention, the dispersion state of the glass powder in the conductive paste and the contact state with the p-type layer of the p-type Si semiconductor substrate 1 are formed during electrode formation. The glass and the p-type layer of the p-type Si semiconductor substrate 1 can sufficiently contact and react with each other due to the high fluidity of the glass itself. As a result, it is possible to improve the bonding strength between the Al electrode 4 and the p-type Si semiconductor substrate 1 and to diffuse B ³⁺ contained in the glass as B in the p-type layer of the p-type Si semiconductor substrate 1. Thereby, a favorable p ⁺ layer 1c can be formed, and the conversion efficiency of the solar cell can be improved.

  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 5 are examples, and examples 6 to 8 are comparative examples.

(Examples 1-8)
The glass powder was manufactured by the following method, and the electrically conductive paste for electrode formation containing this glass powder was manufactured. When the obtained conductive paste was used to form a solar cell having the same configuration as in FIG. 1, the B average concentration at a depth of 1 to 5 μm from the surface of the p ⁺ layer in the Si semiconductor substrate was measured. The conversion efficiency was evaluated.

  As a glass powder used for electrode formation, a glass powder having the composition, particle size distribution, and water content shown in Table 1 was produced. That is, raw material powders were blended and mixed so as to have the composition shown in Table 1, and melted in a 1000 to 1300 ° C. electric furnace using a platinum crucible for 30 minutes to 1 hour to form a thin glass sheet. Thereafter, the glass sheet was dry pulverized with a ball mill for 2 hours, and coarse particles were removed with a 150 mesh sieve.

Next, dry crushed glass so that D ₁₀ which is 10% particle size based on volume, D ₅₀ which is 50% particle size based on volume, and D ₉₀ which is 90% particle size based on volume are within a predetermined range. Glass powder was manufactured by wet-pulverizing the powder with water using a ball mill. For the glass powders of Examples 1 to 5, in this wet pulverization, in order to obtain predetermined D ₁₀ , D ₅₀ , and D ₉₀ , using an alumina ball having a diameter of 5 mm, the respective pulverization times shown in Table 1 were used. By grinding, D ₁₀ , D ₅₀ , and D ₉₀ were adjusted.

  Thereafter, the slurry containing the glass powder obtained by wet pulverization was filtered to remove most of the water, and then dried at 130 ° C. with a dryer to adjust the water content to produce a glass powder.

  The glass powders of Examples 6 and 7 were produced by dry pulverizing the thin glass obtained above with a ball mill for 24 hours. The glass powder of Example 8 was produced by subjecting the thin glass obtained above to dry pulverization with a ball mill for 24 hours, and then classification by airflow classification.

The glass powder of the Examples 1-8, the particle size was determined _{D 10, D 50, D 90} and water content as follows. The results are shown in Table 1.

(Particle size _{D 10, D} 50 _{D 90)}
A sample was prepared by mixing 0.02 g of the glass powder of Examples 1 to 8 with 60 cc of isopropyl alcohol and dispersing for 1 minute by ultrasonic dispersion. Each sample obtained above was put into the microtrack measuring machine, and the values of D ₁₀ , D ₅₀ and D ₉₀ were obtained.

(Moisture content)
The water content of the glass powders of Examples 1 to 8 obtained above was measured by the Karl Fischer method. The measurement condition is 300 ° C. The measurement results are shown in Table 1.

<Manufacture of conductive paste>
A conductive paste for forming an Al electrode containing each of the glass powders of Examples 1 to 8 prepared above was prepared by the following method. As the conductive paste for forming an Ag electrode, a commercially available product (manufactured by DuPont, trade name: Solarmet PV18A) was prepared.

  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 1.3 mass part 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.

<Manufacture of solar cells>
Using the Al electrode forming conductive paste and the Ag electrode forming conductive paste obtained above, a back electrode is formed on the non-light-receiving surface S2 on the p-type Si semiconductor substrate 1 having the same configuration as that shown in FIG. As a surface electrode, an Ag electrode 3 was formed on the Al electrode 4 and the light receiving surface S1, and a solar cell 10 was manufactured.

  Using a p-type crystalline Si semiconductor substrate sliced to a thickness of 160 μm, first, in order to clean the sliced surface of the Si semiconductor substrate, the light-receiving surface and the non-light-receiving surface were etched by a very small amount with hydrofluoric acid. 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, an n-type layer is formed by diffusion on the light receiving surface of the Si semiconductor substrate. P (phosphorus) was used as an n-type doping element. Next, an antireflection film was formed on the light receiving surface (the surface of the n-type layer) of the Si 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, an Ag electrode and an Al electrode were formed on the light-receiving surface side and the non-light-receiving surface side of the obtained Si semiconductor substrate with an antireflection film, respectively. First, Ag paste was applied to the surface on the light receiving surface side, that is, the surface of the antireflection film by screen printing in a line shape and dried at 120 ° C.

Next, the Al electrode-forming conductive paste obtained using the glass powders of Examples 1 to 8 was applied to the entire surface of the non-light-receiving surface of the Si semiconductor substrate by screen printing. Thereafter, firing was performed at a peak temperature of 800 ° C. for 100 seconds using an infrared light heating belt furnace to form a front surface Ag electrode and a rear surface Al electrode, thereby completing a solar cell. The Ag electrode is formed by firing so as to penetrate the antireflection film and come into contact with the n-type layer of the Si semiconductor substrate. In addition, on the non-light-receiving surface side of the Si semiconductor substrate, B ³⁺ contained in the glass in the conductive paste was diffused as B to form a p ⁺ layer.

(Evaluation)
(1) B (boron) average concentration at a depth of 1 to 5 μm from the surface of the p ⁺ layer in the Si semiconductor substrate A solar cell produced using the Al electrode-forming conductive paste containing each of the glass powders in the above examples was hydrochloric acid. (35 to 38% aqueous solution of hydrogen chloride): immersed in an aqueous solution mixed with water = 1: 1 for 24 hours, and the Al electrode on the back surface was removed to prepare a sample to be measured.

Thereafter, the B concentration determination standard sample and the measurement target sample are simultaneously introduced into the secondary ion mass spectrometer and analyzed, and the Si semiconductor substrate in a region of 10 μm or more in depth from the back surface (p ⁺ layer surface) of the measurement target sample. A concentration profile of B was obtained. Note that a Si semiconductor substrate (B injection amount: 1.3 × 10 ¹⁴ ions / cm ² , energy: 130 keV) into which B ions were implanted at a known concentration was used as a standard sample for determining the B concentration. The analysis conditions for secondary ion mass spectrometry were as follows.

Measuring device: ADEPT1010 manufactured by ULVAC-PHI
Primary ion species: O _x ⁺
Primary acceleration voltage: 5.0 kV
Primary ion current: 1μA
Primary ion incidence angle: 45 ° from the sample surface vertical direction
Raster size: 200 × 200 μm ²
Detection area: 40 × 40 μm ²
Sputtering rate: The depth of the analysis crater formed by secondary ion mass spectrometry was measured with a stylus type surface shape measuring device (Dektak 150 manufactured by Veeco) to determine the sputtering rate.
Secondary ion polarity: plus Neutralization electron gun used: Yes

B concentration from the surface of the p ⁺ layer to a depth of 10 μm obtained by the secondary ion mass spectrometry of the solar cell produced using the conductive paste for forming an Al electrode containing each of the glass powders of Examples 4 and 7. [Number of atoms / cm ³ ] is shown in FIG. In FIG. 2, the numerical value “1E + 15” on the vertical axis indicates “1 × 10 ¹⁵ ”, and the other numerical values are the same.

Using the B concentration [number of atoms / cm ³ ] in the p ⁺ layer surface layer measured above, the B average concentration at a depth of 1 to 5 μm from the p ⁺ layer surface was calculated as follows. That is, the B average concentration is obtained by integrating the measured value of the B concentration [number of atoms / cm ³ ] from the position of 1 μm depth to the position of 5 μm depth from the p ⁺ layer surface, and then dividing by the integration range width of 4 μm. It was calculated by doing. The results are shown in Table 1.

(2) Measurement of conversion efficiency of solar cell Conversion efficiency of a solar cell manufactured using an Al electrode forming conductive paste containing the glass powder of each of the above examples was measured using a solar simulator (YSS-180S, manufactured by Yamashita Denso Co., Ltd.). It measured using. Specifically, the solar cell was installed in the solar simulator, the current-voltage characteristic was measured based on JIS C8912 with the reference solar beam having the spectral characteristic AM1.5G, and the conversion efficiency of each solar cell was derived. The obtained conversion efficiency results are shown in Table 1.

From Table 1, in the solar cell using the glass powder of Examples 1 to 5, B is sufficiently diffused on the non-light-receiving surface (back surface) side of the Si semiconductor substrate as compared with the case of using the glass powder of Examples 6 to 8. It can be seen that a good p ⁺ layer is formed. Moreover, from Table 1, when using the glass powder of Examples 1-5, it turns out that conversion efficiency was able to obtain 18% or more. On the other hand, when using the glass powder of Examples 6-8, it turns out that conversion efficiency was less than 18%.

  As is clear from the above, the glass powders of Examples 1 to 5 are suitable for forming solar cell electrodes.

ADVANTAGE OF THE INVENTION According to this invention, the glass powder suitable for forming the electrode of a solar cell can be provided. Using such a glass powder, an electrically conductive paste capable of diffusing the elements contained in the glass during the formation of the electrode into the semiconductor substrate, in particular, boron can be diffused into the p-type layer of the Si semiconductor substrate and forming a good p ⁺ layer, and By using the conductive paste, it is possible to provide a solar cell with improved reliability and productivity.

DESCRIPTION OF SYMBOLS 10 ... Solar cell, 1 ... p-type Si semiconductor substrate, 1a ... n-type layer, 1b ... p-type layer, 1c ... p ⁺ layer, 2 ... Antireflection film, 3 ... Ag electrode, 4 ... Al electrode, S1 ... Light reception Surface, S2 ... non-light-receiving surface.

Claims (7)

In cation% display,
25-80% B ³⁺ ,
Containing 20-75% Pb2 ⁺ ,
_{D 10} 10% particle diameter on a volume basis in a cumulative particle size distribution, _{D 50} 50% particle diameter on a volume basis, 90% particle diameter on a volume basis when the _{D 90,}
D ₅₀ / _{D 10} is 2.0 to 4.5 and,
_{D 90} / D ₅₀ is 1.5 to 3.4
Glass powder.   The glass powder of Claim 1 used for formation of the electrode of a solar cell.   The glass powder according to claim 2, wherein the electrode is an aluminum electrode. Glass powder according to any one of claims 1-3 wherein _{D 50} is 0.5 to 5.0 .mu.m.   Water content is 0.2-1.0 mass%, Glass powder of any one of Claims 1-4.   The electrically conductive paste containing the glass powder of any one of Claims 1-5, electroconductive metal powder, and an organic vehicle.   A solar cell comprising an electrode formed using the conductive paste according to claim 6.

Images