TW201440077A - Electrode forming paste - Google Patents

Abstract

The present invention provides an electrode forming paste which can refine an electrode pattern during printing and suppress an increase in electrical resistance due to disconnection of an electrode pattern and unexpected shrinkage. The paste for electrode formation provided by the present invention is used for forming a paste of an electrode, and comprises an electrically conductive powder, resin particles, and an organic vehicle component which can disperse the conductive powder and the resin particles. When the volume of the conductive powder is 100% by volume, the resin particles preferably contain more than 0% by volume and 8% by volume or less.

Description

Electrode forming paste Technical field

The present invention relates to an electrode forming paste used in forming an electrode pattern.

In addition, the present application claims priority based on Japanese Patent Application No. 2012-281547, the entire entire disclosure of which is hereby incorporated by reference.

Background technique

Heretofore, in forming an electrode such as a semiconductor element or an electronic circuit, a method of forming an electrode pattern by various printing methods on the surface of a semiconductor substrate or an unfired ceramic substrate or the like has been widely used. The electrode can be formed by, for example, preparing an electrode forming paste in which an electrically conductive powder is dispersed in an organic vehicle component, and screen-printing the surface of the substrate or the like according to a desired electrode pattern, and then It is carried out by calcining in a temperature range of about 300 ° C to 1500 ° C to densify the conductive powders.

In the meantime, in recent years, the electrode elements have been required to be thinned (thinned) with high integration and high performance of semiconductor devices and electronic circuits. The degree of refinement required varies depending on the components and circuits of the object to be manufactured, but the size of a multilayer ceramic capacitor (MLCC) has been ultra-small and will be 1005 feet. The size of the inch is reduced to 0402 size (outer size: 0.4mm × 0.2mm × 0.2mm), and the solar cell element also has a need to further increase the light-receiving area per unit area of each cell, so it is more compact than ever. The electrode pattern avoids the increase in resistance due to the above refinement, and there is a need to increase the thickness of the electrode (increasing the film thickness of the electrode film). Moreover, the wire breakage of the electrode pattern and the unexpected shrinkage of the electrode pattern directly result in an increase in the resistance of the formed electrode, so there is also a need to improve the printing accuracy of the electrode pattern. Next, as an example, Patent Document 1 proposes a conductive paste (electrode forming paste) which can refine the electrode and suppress an increase in electric resistance.

[First technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2007-095663

[Patent Document 2] Japanese Patent Application Publication No. 2004-355862

Summary of invention

The conductive paste disclosed in Document 1 contains a sulfide particle having a layered structure or a spherical particle such as fullerene 60 as an additive. Therefore, the improvement of the shaking property of the above-mentioned conductive paste has been disclosed, and as a result, the conductive paste which is printed by printing can be prevented from diffusing in the lateral direction.

However, since the electrode patterns formed on various semiconductor elements, electronic circuits, and the like are different depending on the application, the composition of the electrode forming paste and the required physical properties may be various. Therefore, I look forward to more The form provides a paste for electrode formation which can refine the electrode pattern formed by printing and suppress an increase in electric resistance.

Therefore, the present invention has been made in view of the above circumstances, and a main object thereof is to provide an electrode forming paste which can achieve refinement of an electrode pattern during printing and suppress an increase in electric resistance due to disconnection and unexpected shrinkage of an electrode pattern. . Further, other objects are to provide a semiconductor element, such as a solar cell element, which can be improved by the above-described electrode forming paste.

In order to achieve the above object, the present invention can provide an electrode forming paste which can be applied to an electrode (electrode pattern) by various printing methods known in the art.

That is, the paste for electrode formation provided by the present invention is characterized by comprising a conductive powder, resin particles, and an organic vehicle component which can disperse the conductive powder and the resin particles.

In the electrode-forming paste having the above-described structure, the resin particles having a smaller specific gravity than the conductive powder or the like are contained. Therefore, when the paste is printed in a predetermined volume, the weight of the printed body and the amount of the conductive powder contained in the printed body are reduced, which may increase. The probability of wire breakage and shrinkage of the printed electrode pattern. Further, unlike the conductive paste disclosed in Patent Document 1, the electrode-forming paste disclosed herein has almost no improvement in the shakeability due to the inclusion of the resin particles. However, by using the paste for electrode formation disclosed herein and forming an electrode pattern by a known printing technique, it is actually confirmed that the printability is improved. That is, the ratio of the number of broken lines of the electrode pattern and the thinning of the pattern thin line is reduced, and a high-quality electrode pattern can be obtained.

In a preferred embodiment of the electrode-forming paste disclosed herein, when the volume of the conductive powder is 100% by volume, the resin particles contain more than 0% by volume and 8% by volume or less.

In the paste for electrode formation, typically, the resin pellets are burned together with the organic vehicle component when calcined for sintering the conductive powder. Further, the disappearance of the resin particles causes voids to be formed at positions where the resin particles originally exist in the electrode pattern after firing, and the electrode pattern has a porous structure. The voids in the electrode pattern hinder the formation of the conduction path of the conductive powder and cause an increase in the resistance value. Therefore, the content of the resin particles with respect to the conductive powder is preferably in the above ratio.

In a preferred embodiment of the electrode-forming paste, the resin particles are contained in an amount of more than 0% by mass and not more than 1% by mass, based on the weight of the conductive powder.

In the paste for electrode formation, typically, the resin pellets are burned together with the organic vehicle component when calcined for sintering the conductive powder. Further, the disappearance of the resin particles causes voids to be formed at positions where the resin particles originally exist in the electrode pattern after firing, and the electrode pattern has a porous structure. The voids in the electrode pattern hinder the formation of the conduction path of the conductive powder and cause an increase in the resistance value. Therefore, the content of the resin particles with respect to the conductive powder is preferably in the above ratio. The content of the resin particles is more than 0% by mass and not more than 0.5% by mass, and more preferably from 0.1% by mass to 0.3% by mass.

In the present specification, the description of the range of the physical quantity or the like is described by the symbol "~" such as "A mass% to B mass%", but the above description means "A mass% or more and B mass%". the following".

A preferred aspect of the paste for electrode formation disclosed in the present invention is characterized in that the particle diameter of the resin particles is equal to or smaller than a minimum dimension of a cross section of the printed body after the paste for electrode formation is printed.

Since the resin particles are generally composed of an insulating material, the particle diameter of the resin particles used for the electrode-forming paste may be such that the printed matter such as the electrode thin wires formed without causing the paste for forming the electrode electrode is broken. That is, it may be below the minimum dimension of any cross section of the printed body. Therefore, the particle diameter of the resin particles varies depending on the fineness (thinness) of the target printing body. However, the average particle diameter of the resin particles is preferably 10 μm or less, and may be, for example, about 5 μm or less.

A preferred aspect of the electrode-forming paste disclosed herein is characterized in that the resin particles are burned out at a temperature of 600 ° C or less in an oxidizing gas atmosphere.

In the above, when the electrode pattern is formed by the electrode formation paste, the resin particles are eliminated, and the conductive powder is densified, and the adjacent conductive powders are firmly bonded (sintered) to each other, so that, for example, Side effects such as an increase in line resistance caused by resin particles composed of an insulating material are reduced.

A preferred aspect of the electrode forming paste disclosed in the present invention is characterized in that the resin constituting the resin particles is selected from the group consisting of a phenol resin, an alkyd resin, a melamine urea resin, an epoxy resin, a polyurethane resin, Any one or two or more of the group consisting of a ruthenium resin, a chlorinated rubber resin, an acrylic resin, a vinyl chloride resin, a fluororesin, and a cellulose resin.

The material of the resin particles used for the above electrode forming paste is not particularly Further, for example, particles composed of the above-mentioned general-purpose resin can be suitably used. It is preferred to use a phenol resin, an acrylic resin, a vinyl chloride resin or the like.

A preferred aspect of the paste for electrode formation disclosed in the present invention is characterized in that the metal species constituting the conductive powder contains any one or two selected from the group consisting of nickel, platinum, palladium, silver, and copper. More than one species.

The composition and the like of the conductive powder to be used in the electrode-forming paste are not particularly limited. For example, various metal materials and alloys thereof having a suitable melting point and excellent electrical conductivity can be suitably used. It is preferred to use silver, platinum and nickel.

A preferred aspect of the paste for electrode formation disclosed in the present invention is characterized in that it further contains a glass powder in a proportion of not more than 5% by mass based on the entire paste.

According to the above composition, for example, the adhesion to the substrate on which the electrode is formed can be improved, and an electrode having better mechanical strength can be formed. In addition, in the case where the above-described electrode-forming paste is used in forming the light-receiving surface electrode of the solar cell element, a paste capable of exhibiting a fire through effect can be obtained.

A preferred aspect of the electrode forming paste disclosed in the present invention is characterized in that it can be used in any one selected from the group consisting of screen printing, gravure printing, lithography, and inkjet printing. .

When the electrode for forming an electrode is suitable for forming an electrode by printing, in particular, it is excellent in separation from a printing plate, passage of an opening of a printing plate, and flowability from a nozzle, and thus can be suitably applied to the above printing method. . It is better for screen printing that can be printed at a lower cost and that requires higher printing accuracy, and can fully exert its effects.

The present invention also provides a semiconductor element provided with an electrode formed using the paste for electrode formation disclosed in any of the above aspects, in order to achieve the above object. Typically, the semiconductor element may be a solar cell element provided with a light-receiving surface electrode formed using the electrode-forming paste.

For example, when the electrode forming paste of the present invention is supplied to the light-receiving surface of the semiconductor substrate through the opening of the printing plate for screen printing by the screen printing method, the film passes through the opening. Good in properties, which can greatly improve the effluent and transferability. Therefore, it is possible to suppress the occurrence of the printed ruthenium portion which is evaluated as being broken or the electrode pattern is reduced. Therefore, even when it is used for printing such as an electrode pattern having a finer line width, printing defects are less likely to occur, and can be suitably used.

Therefore, for example, it is possible to realize finer wiring for the printing of the electrode patterns of various semiconductor elements, and to realize a high-performance semiconductor element in which the semiconductor element is further miniaturized and integrated.

Moreover, for example, once the light-receiving surface electrode of the solar cell element is made thinner, the amount of light received per unit area of the light-receiving surface can be increased, and more power can be generated, so that a higher performance solar cell element can be realized. .

In addition, the "screen printing" of the present invention is exemplified by the above-mentioned opening portion through a mask in which an opening portion is formed in accordance with a pattern of a target pattern such as a corresponding electrode pattern, and is printed on a substrate such as a substrate. The term "printing technique" for supplying the paste for forming an electrode for the target pattern is not limited as to the precision of the material and pattern of the mask to be used. Screen printing (mesh) made of synthetic resin (such as polyester), screen printing screen made of metal (such as stainless steel wire mesh), processing of metal materials by etching and laser processing The printing (patterning) of various masks, such as a metal mask having an opening, is an electrode pattern forming technique covered by "screen printing" in the present specification.

10‧‧‧Solar battery components (cells)

11‧‧‧Semiconductor substrate (矽 substrate)

11A‧‧‧Glossy surface

11B‧‧‧Back

12‧‧‧ Busbar electrode (light-receiving electrode)

13‧‧‧Finger type electrode (light receiving surface electrode)

14‧‧‧Anti-reflective film

16‧‧‧n-Si layer

18‧‧‧p-Si layer

20‧‧‧Back aluminum electrode

22‧‧‧Electrode for external connection on the back side

24‧‧‧p+ layer

Fig. 1 is a cross-sectional view schematically showing an example of a solar cell structure.

Fig. 2 is a plan view schematically showing an electrode pattern formed on a light receiving surface of a solar cell.

3A is a scanning electron microscope (SEM) image illustrating a cross-sectional observation result of a printed body obtained by screen printing using a conventional electrode forming paste.

3B is a scanning electron microscope (SEM) image illustrating a cross-sectional observation result of a printed matter obtained by screen printing using the paste for electrode formation of the present invention.

4A is a scanning electron microscope (SEM) image illustrating a cross-sectional observation result of an electrode body obtained by screen printing and baking of a conventional electrode forming paste.

4B is a scanning electron microscope (SEM) image illustrating a cross-sectional observation result of an electrode body obtained by screen printing and baking of the paste for electrode formation of the present invention.

Fig. 5 is a graph showing the relationship between the amount of phenol particle preparation of each paste prepared in the examples and the printability evaluation result of the light-receiving surface electrode formed using the paste.

Fig. 6 is a graph showing the relationship between the blending amount of the acrylic particles of each paste produced in the examples and the printability evaluation results of the light-receiving surface electrode formed using the paste.

Fig. 7 is a graph showing the results of the evaluation of the printability of the phenol particles of each paste produced in the examples and the light-receiving surface electrode formed by using the paste and the printing plate 1. The chart of the department.

Fig. 8 is a graph showing the relationship between the particle diameter of the phenol particles of each paste produced in the examples and the printability evaluation results of the light-receiving surface electrode formed by using the paste and the printing plate 2.

Fig. 9 is a graph showing the relationship between the particle diameter of the phenol particles of each paste produced in the examples and the printability evaluation results of the light-receiving surface electrode formed by using the paste and the printing plate 3.

Form for implementing the invention

Hereinafter, preferred embodiments of the present invention will be described. In addition, the technical content other than the content specifically mentioned in the present specification is the content required for the implementation of the present invention, and can be understood as the design content of practitioners in the technical field based on the prior art. The present invention can be implemented based on the technical contents disclosed in the present specification and the technical knowledge of the technical scope of the present technology.

The electrode-forming paste disclosed in the above is the same as the conventional electrode-forming paste (also referred to as a conductor paste), and constitutes an organic powder component containing a conductive powder and dispersing the powder, and further contains the electrode. Resin particles not present in the paste are used as the main body.

The paste for electrode formation of the above composition contains resin particles having a specific gravity smaller than that of the conductive powder or the like. Therefore, when the electrode forming paste is printed in a predetermined volume, the weight of the printed body (the amount of adhesion) and the amount of the conductive powder contained in the printed body are reduced, so that the printed electrode pattern is broken. And the probability of shrinking is high, and the conductivity of the electrode may be lowered. Moreover, it can be inferred that the printed body formed by using the above electrode forming paste will be caused by containing resin particles. The resistance increases. However, contrary to these predictions, the separation of the electrode for forming an electrode of the present invention, the separation of the printing plate or the like, the opening of the outlet, the screen, and the like are excellent, and the formation of the printing body which is not inferior to the conventional paste can be realized. . Further, in the case of printing using the electrode-forming paste, in addition to the improvement of the breakage of the thin wire electrode, the shrinkage of the printed fine wire can be greatly improved. In other words, when the paste for electrode formation of the present invention is printed at a fine (high-precision), the printability (i.e., transfer property) can be remarkably improved. Therefore, the electrode pattern refined by using the paste for electrode formation can be stably printed to suppress the occurrence of wire breakage and shrinkage, and to compensate for the increase in resistance caused by the resin particles, thereby obtaining an additional effect (such as an electrode). The line resistance of the overall pattern is reduced).

The "conductive powder" which is a main body of the solid matter of the paste can be used as a powder composed of various metals or alloys thereof having conductivity and other physical properties required for the purpose of use. Examples of the material constituting the conductive powder may be exemplified by gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), ruthenium (Rh). Metals such as Ir), ruthenium (Os), nickel (Ni), and aluminum (Al) and alloys thereof, carbonaceous materials such as carbon black, LaSrCoFeO ₃ -based oxides (such as LaSrCoFeO ₃ ), and LaMnO ₃ -based oxides (such as A conductive ceramic represented by a transition metal perovskite structure oxide represented by LaSrGaMgO ₃ ), a LaFeO ₃ -based oxide (such as LaSrFeO ₃ ), a LaCoO ₃ -based oxide (such as LaSrCoO ₃ ), or the like. Among them, monomers of noble metals such as silver (Ag), platinum (Pt), palladium (Pd), and gold (Au), and alloys thereof (Ag-Pd alloy, Pt-Pd alloy, etc.) and nickel (Ni) may be mentioned. The material composed of the alloy and the like is a typical material constituting the conductive powder. Further, in terms of low cost and high electrical conductivity, it is preferable to use a powder composed of silver and an alloy thereof (hereinafter referred to as "Ag powder"). Hereinafter, the paste for electrode formation of the present invention will be described by taking Ag powder as a conductive powder as an example.

The particle diameter of the Ag powder and other conductive powders is not particularly limited, and powders of various particle sizes suitable for the use can be used. Typically, a powder having an average particle diameter of 5 μm or less based on a laser diffraction method (light scattering method) is appropriately sized, and a powder having an average particle diameter of 3 μm or less (typically 1 to 3 μm, such as 1 to 2 μm) is preferably used. .

The shape of the particles constituting the conductive powder is not particularly limited, and typically spherical, scaly, conical, or rod-shaped particles or the like can be suitably used. Since it is easy to form a dense light-receiving electrode or the like because of the good filling property, it is preferable to use spherical or scaly particles. The conductive powder to be used is preferably a powder having a relatively large particle size distribution (small particle size range). For example, it is preferable to use a conductive powder having a particle size distribution which is substantially free of particles having a particle diameter of 10 μm or more. As the index, the ratio (D10/D90) of the particle diameter (D10) at a cumulative volume of 10% of the particle size distribution based on the laser scattering diffraction method to the particle diameter (D90) at the cumulative volume of 90% can be used. When the particle diameters of the constituent powders are all equal, the value of D10/D90 is 1, and conversely, the larger the particle size distribution range, the closer the value of D10/D90 is to 0. It is preferable to use a powder having a particle size distribution in which the particle diameter range of D10/D90 is 0.2 or more (such as 0.2 to 0.5).

The conductive powder using the electrode for forming an electrode having the above-described average particle diameter and particle shape is excellent in filling property, and a dense electrode can be formed. This is advantageous in forming a fine electrode pattern with high shape accuracy.

The method of producing the conductive powder such as the above Ag powder is not particularly limited. For example, if you need to use it, you can use the well-known wet type. A conductive powder (typically Ag powder) prepared by a primary method, a gas phase reaction method, a gas reduction method, or the like. The above classification can be carried out using, for example, a classification machine using a centrifugal separation method.

Further, the "organic vehicle component" in which the above-mentioned conductive powder is dispersed is not particularly limited, and various components which have hitherto been used for such electrode-forming paste can be used for the purpose desired. Typically, the vehicle is composed of an organic binder of various compositions and an organic solvent. In the organic vehicle component, the organic binder may be completely dissolved in the organic solvent or partially dissolved (may be an emulsion type organic vehicle component).

As the organic binder, a cellulose-based polymer such as ethyl cellulose or hydroxyethyl cellulose, an acrylic resin such as polybutyl methacrylate, polymethyl methacrylate or polyethyl methacrylate can be suitably used. An organic binder based on epoxy resin, phenol resin, alkyd resin, polyvinyl alcohol, polyvinyl butyral or the like. It is particularly preferable to use a cellulose-based polymer such as ethyl cellulose to achieve particularly good viscosity characteristics required for screen printing.

Further, as the organic solvent, an ester solvent such as butyl succinate or diethylene glycol butyl ether acetate (BCA: diethylene glycol monobutyl ether) or butyl carbitol (BC: diethylene glycol monobutyl) can be suitably used. An ether solvent such as an ether solvent, an ethylene glycol and a diethylene glycol derivative, an organic solvent such as toluene, xylene, mineral spirits, terpineol or menthol.

The solvent constituting the organic vehicle liquid is preferably an organic solvent having a boiling point of about 200 ° C or higher (typically about 200 to 260 ° C). It is more preferred to use an organic solvent having a boiling point of about 230 ° C or higher (typically about 230 to 260 ° C). The solvent component of Optima is butyl carbitol (BC), diethylene glycol butyl ether acetate (BCA), 2, 2, 4- Trimethyl-1,3 pentanediol monoisobutyrate or the like.

The resin particles which are characteristic of the essential components contained in the paste for electrode formation of the present invention are not particularly limited, and spherical particles composed of various resin materials can be used. Although the spherical particles may be suitably used as particles having a nearly spherical shape, they are not limited to the so-called geometrically identifiable particles of a true spherical shape, and substantially spherical particles can be suitably used. Further, the resin particles may be so-called hollow particles having a hollow structure in which voids are provided, or so-called solid particles having no voids inside. That is, various commercially available substantially spherical various resin particles can be used.

The resin material constituting the resin particles is not particularly limited. For example, various resins which do not have solubility when mixed with the organic solvent contained in the organic vehicle component can be used. An example of the above resin material may be used, for example, from a phenol resin, an alkyd resin, a melamine urea resin, an epoxy resin, a polyurethane resin, a enamel resin, a chlorinated rubber resin, an acrylic resin, a vinyl chloride resin, or a fluororesin. A single one or a mixture of two or more selected from the group consisting of cellulose resins and the like.

The resin particles are not particularly limited, but are preferably characterized in that they have a property of being burned under the firing conditions of the paste for forming an electrode. The above conditions are such as in an oxidizing gas environment, which is preferably burned out at a temperature below 600 °C. That is, it is preferable to have a thermal decomposition property of 600 ° C or less (preferably 100 ° C or more and 400 ° C or less, such as 100 ° C or more and 300 ° C or less). With the above configuration, the densification of the electrode (conductive powder) by baking can be achieved, and the conduction path can be more reliably formed, and the increase in resistance can be suppressed.

The particle size of the resin particles is substantially accommodating in the formed The particle size of the size and shape of the electrode pattern is not particularly limited. For example, a particle size of a size smaller than the smallest dimension of the cross section of the printed body after the electrode forming paste is applied can be used. However, in the case of forming an electrode by printing using the electrode forming paste, it is preferable to use particles having a particle diameter which satisfies the characteristics of a printing machine or the like applied to the printing method. For example, when the screen printing method is employed, it is preferable to use a resin particle which can appropriately pass through the mesh size of the screen printing net used for the printing (less than the mesh of the screen printing screen). Further, in the case of the ink jet printing method, it is preferable to use resin particles which can appropriately pass through the size of the outlet of the ink jet nozzle (less than the outlet of the ink jet nozzle). In view of the above, in general, the average particle diameter of the resin particles is preferably 10 μm or less, and more preferably 5 μ or less.

The blending ratio of each component contained in the electrode-forming paste differs depending on the method of forming the electrode, and typically varies depending on the printing method. Therefore, it cannot be generalized, but it is possible to add a paste for electrode formation substantially to the composition used so far. The proportion of the form in which the resin particles are added is added. As an example, the ratio of each component can be determined by the following formulation.

In other words, when the proportion of the content of the conductive powder in the electrode-forming paste is 100% by mass or less, the total amount of the paste is about 70% by mass or more (typically 70% by mass to 95% by mass), and the ratio is 80% by mass. The degree of ~90 is better, and is preferably about 85 mass%. Increasing the content ratio of the conductive powder is suitable from the viewpoint of forming a pattern of an electrode having a good shape accuracy and a dense electrode. On the other hand, if the content ratio is too high, the workability of the paste and the suitability for various printability are lowered, which is not applicable.

Further, the content ratio of the resin particles is such that, for example, the specific gravity of the hollow particles and the resin exemplified above cannot be significantly different, and therefore it is preferably determined based on the weight of the conductive powder based on the weight. That is, when the content ratio of the above resin particles is 100% by volume based on the total volume of the conductive powder, the blending ratio is preferably more than 0% by volume and 8% by volume or less. Even if a small amount of the resin particles are blended, the effect of improving the printability of the paste for electrode formation can be obtained. However, too much blending will cause the resistance of the formed electrode to increase excessively, which is not applicable. The content ratio of the resin particles can be adjusted, for example, in excess of 0% by volume and 8% by volume or less. An amount of 1% by volume or more and 5% by volume or less is more preferable.

Further, as a standard, when Ag powder is used as the conductive powder and solid particles composed of a general resin are used as the resin particles, the content ratio of the resin particles is set so that the total mass of the conductive powder is 100% by mass. In the case of more than 0% by mass and 1.2% by mass or less, more preferably 0% by mass and 1% by mass or less, and even more preferably 0.1% by mass to 0.6% by mass or less.

When the total mass of the conductive powder is 100% by mass, the organic binder in the organic vehicle component is preferably contained in an amount of about 15% by mass or less, and typically about 1% by mass to 10% by mass. The ratio of 2% by mass to 6% by mass based on 100% by mass of the conductive powder is particularly preferable. Further, the above organic binder may also contain an organic binder component such as dissolved in an organic solvent, and an organic binder component which is not dissolved in an organic solvent. When the organic binder component which has been dissolved in the organic solvent and the undissolved organic binder component are contained, the ratio thereof is not particularly limited, but In other words, the organic binder component dissolved in the organic solvent can be used (40% to 10%).

In addition, the content ratio of the entire organic vehicle liquid may be changed according to the properties of the obtained paste. As a general standard, when the entire paste is 100% by mass, the amount is, for example, 5% by mass to 20% by mass, and the appropriate ratio is It is preferably in an amount of 5 mass% to 15 mass% (especially 7 mass% to 12 mass%).

In addition, the above numerical range of the content ratio of each component should not be strictly interpreted, and may be slightly deviated from the above range within the limits of the purpose of the invention.

In addition to the above-mentioned conductive powder, resin particles and organic vehicle components, various inorganic additives and/or organic additives may be contained within the limits of the purpose of the invention. Suitable examples of the inorganic additive include glass powder and other ceramic powders (ZnO ₂ , Al ₂ O ₃ , SiO _{2 ,} etc.), and various other fillers. Among them, ceramic powder, especially glass powder (glass frit), should be added. Typically, the average particle diameter of the powder (filler) is preferably adjusted to be the same as or smaller than the conductive powder. The filler having an average particle diameter of, for example, a laser scattering diffraction method of 3 μm or less is preferably 2 μm or less, and typically a glass powder, ceramic powder or other powder having an average particle diameter of about 0.1 μm to 2 μm can be used. Wait.

Further, the glass component to be added is not particularly limited, and various glasses can be used. For example, in addition to the usual amorphous glass, it may be a crystallized glass. Further, the glass component is not particularly limited, and examples thereof include lead-based glass, lead-lithium-based glass, zinc-based glass, borosilicate glass, alkali-based glass, lead-free glass, and cerium oxide or cerium oxide. Glass and so on. And, These glasses may be used alone or in combination of two or more. Typically, a glass frit can be used for the above glass powder. More specifically, for example, glass A to C having a representative composition (the oxide-converted composition; the entire glass is set to 100 mol%) shown below can be exemplified as a preferable composition.

[A: lead glass]

SiO ₂ : 38 mol% or more and 53 mol% or less

B ₂ O ₃ : 1 mol% or more and 7 mol% or less

PbO: 46 mol% or more and 57 mol% or less

[B: Lead lithium glass]

SiO ₂ : 20 mol% or more and 65 mol% or less

B ₂ O ₃ : 1 mol% or more and 18 mol% or less

PbO: 20 mol% or more and 65 mol% or less

Li ₂ O: 0.6 mol% or more and 18 mol% or less

[C: Lead-free glass (lead-free glass)]

Bi ₂ O ₃ : 10 mol% or more and 29 mol% or less

B ₂ O ₃ : 20 mol% or more and 33 mol% or less

SiO ₂ : 0 mol% or more and 20 mol% or less

ZnO: 15 mol% or more and 30 mol% or less

Li ₂ O, Na ₂ O, and K ₂ O total: 8 mol% or more and 21 mol% or less

Although the glass softening point is not particularly limited, it is preferably about 300 to 600 ° C (such as 400 to 500 ° C). The softening of the glass A~C has been specifically shown above. The point may be in the range of 300 ° C or more and 600 ° C or less as an example. When the paste for electrode formation containing the glass powder having the softening point is used for forming a light-receiving surface electrode such as a solar cell element, when the paste coating material (which can be a printing body) is fired, the glass component and the substrate (typically In order to weld the tantalum substrate, an electrode having good adhesion to the electrode can be formed. Further, in the formation of the above-mentioned light-receiving surface electrode, electrode formation can be performed by a burn-through method.

In addition, the content ratio of the glass powder and the other ceramic powder is appropriately 10% by mass or less, and is usually 5% by mass or less (for example, about 1 to 5% by mass). The composition example of the paste for electrode formation in the case of containing a glass component can be specifically exemplified as a conductive powder: 85% by mass to 90% by mass, resin particles: 0.1% by mass to 1.2% by mass, and an organic vehicle liquid component: 5% by mass. 12% by mass, etc.

In addition to the above components, the electrode forming paste disclosed herein may be added with various additives as needed. For example, additives such as a surfactant, an antifoaming agent, an antioxidant, a dispersing agent, and a polymerization inhibitor may be mentioned.

The above electrode-forming paste has a property of being excellent in releasability or passability as described above, and thus, for example, it can be suitably used for printing for screen printing, gravure printing, lithography, inkjet printing, and the like. Pastes (which may also be slurries or inks, etc.), for example, are particularly useful for forming electrode patterns that require more refinement. In the present invention, the absolute value of the fine line size of the electrode pattern that can be achieved is not problematic. For example, by adding resin particles to the conventional electrode-forming paste, it is possible to print a finer electrode pattern with high quality. Focus.

Therefore, for example, solar power will be used as an example of a semiconductor component. The pool element is exemplified, and an example in which a comb-shaped electrode pattern including a finer finger electrode on a light-receiving surface is formed by screen printing, and a solar cell element as a semiconductor element of the present invention is described. Further, the solar cell element is the same as the conventional solar cell except for the structure of the light-receiving electrode in which the features of the present invention are located, and the above-mentioned structure and the use of the same materials as those of the conventional ones are not The features of the present invention are omitted, and detailed descriptions are omitted.

1 and 2 schematically illustrate an example of a solar cell element (cell sheet) 10 which can be suitably produced by the practice of the present invention, that is, using a single crystal or polycrystalline or amorphous type of germanium (Si). The wafer formed is a so-called 太阳-type solar cell element 10 of the semiconductor substrate 11. The battery sheet 10 shown in Fig. 1 is a general single-sided light receiving type solar cell element 10.

Specifically, the solar cell element 10 includes an n-Si layer 16 formed on the light-receiving surface side of the p-Si layer (p-type crystalline germanium) 18 of the tantalum substrate (Si wafer) 11 by pn bonding. The surface of the surface is provided with an antireflection film 14 made of titanium oxide or tantalum nitride formed by CVD or the like, and light-receiving surface electrodes 12 and 13 formed of a paste for electrode formation containing Ag powder or the like.

On the back side of the p-Si layer 18, a backside external connection electrode formed by a predetermined electrode formation paste (typically, a conductive paste of a conductive powder of Ag powder) is provided on the back side of the light-receiving surface electrode 12. 22, and a back aluminum electrode 20 which can exhibit the effect of a back surface field (BSF). The aluminum electrode 20 is formed on the entire surface of the back surface by printing or baking an aluminum paste mainly composed of aluminum powder. At the time of the above-mentioned baking, an Al-Si alloy layer (not shown) is formed, and aluminum is diffused to the p-Si layer 18 to form the p ⁺ layer 24. The formation of the p ⁺ layer 24, that is, the BSF layer, prevents the light-generating carriers from recombining in the vicinity of the back electrode, thereby achieving an increase such as a short-circuit current and an open circuit voltage (Voc).

As shown in FIG. 2, on the light-receiving surface 11A side of the substrate 11 of the solar cell element 10, a plurality of (for example, one to three) linear parallel bus bars (connection) electrodes 12 are formed, and the foregoing The bus bar electrodes 12 intersect and are connected in parallel with each other (for example, about 60 to 90) strip-shaped finger-type (collection) electrodes 13 as the light-receiving surface electrodes 12 and 13.

The finger electrodes 13 are formed in a plurality of pieces to collect light-generating carriers (holes and electrons) generated by light. The bus bar electrode 12 is a connection electrode for concentrating the carrier collected by the finger electrode 13. A portion where the light-receiving surface electrodes 12 and 13 are formed forms a non-light-receiving portion (light blocking portion) on the light-receiving surface 11A of the solar cell element. Therefore, as far as possible, the bus bar electrode 12 and the finger electrode 13 (especially the finger electrode 13 having a large number) provided on the light-receiving surface 11A side are thinned, and the corresponding amount of the non-light-receiving portion (light blocking portion) can be reduced. And expand the light receiving area per unit area of each cell. This makes it possible to extremely easily increase the output per unit area of the solar cell element 10.

At this time, the line width of the refining electrode is uniform, that is, there is no problem, but for example, if the portion is shrunk, the resistance of the portion where the shrinkage is caused increases, and the loss of current collection occurs. In addition, if a part of the electrode that has been refined is broken, the current of the generated current cannot be collected through the above-mentioned disconnected portion (the current flowing through the substrate of the high resistance will be collected in a state in which the collector loss has occurred. Electricity). Therefore, the formation of the light-receiving surface electrode of the solar cell element requires a high-quality printing technique and an electrode forming paste which is excellent in printability.

The solar cell element 10 described above is roughly produced by the following processes.

That is, the appropriate germanium wafer is prepared, and predetermined impurities are doped by a general technique such as thermal diffusion or ion implantation to form the p-Si layer 18 and the n-Si layer 16 described above, thereby forming the germanium substrate ( Semiconductor substrate) 11. Next, an anti-reflection film 14 made of tantalum nitride or the like is formed by a technique such as plasma CVD.

Then, on the back surface 11B side of the semiconductor substrate 11, a predetermined electrode forming paste (typically, a conductive powder is a conductive paste of Ag powder) is screen-printed into a predetermined pattern, and then dried to form a film. After the baking, the back side conductor paste coated article of the back side external connection electrode 22 (see FIG. 1) is formed. Next, a paste containing aluminum powder as a conductor component is applied (supplied) by a screen printing method or the like on the entire back surface side, and dried to form an aluminum film.

Next, on the anti-reflection film 14 formed on the light-receiving surface 11A side of the ruthenium substrate 11, the electrode formation paste of the present invention is typically printed (supplied) by the screen printing method according to the wiring pattern shown in FIG. The line width to be printed is not particularly limited, but the electrode for forming an electrode of the present invention can be formed to have a line width of about 70 μm or less (preferably in the range of 50 μm to 60 μm, and in the range of 40 μm to 50 μm). More preferably, the coating film (printed body) of the electrode pattern of the finger electrode. The substrate is then dried in a suitable temperature range (typically from 100 ° C to 200 ° C, such as from about 120 ° C to 150 ° C). The content of the more suitable screen printing method will be described later.

As described above, in a roasting furnace such as a near-infrared high-speed calciner in an atmospheric environment, a paste coating is formed on both sides by baking at a suitable baking temperature (such as 700 to 900 ° C) (dry film coating) Object) Then the substrate 11 is turned on.

By the above calcination, the light-receiving surface electrodes (typically Ag electrodes) 12 and 13 and the back side external connection electrodes (typically Ag electrodes) 22, and the calcined aluminum electrode 20 can be formed together, and can be simultaneously formed. The Al-Si alloy layer is made to diffuse aluminum to the p-Si layer 18 to form the above p ⁺ layer (BSF layer) 24 to fabricate the solar cell element 10.

Further, as described above, in addition to the simultaneous firing, firing such as a light-receiving surface electrode (typically an Ag electrode) 12, 13 for forming the light-receiving surface 11A side, and an aluminum electrode for forming the back surface 11B side may be separately performed. 20 and baking of the external connection electrode 22.

In the above-described formation process of the light-receiving electrode, the method of screen printing is not particularly limited, but for example, an opening portion having a corresponding wiring pattern formed by etching or laser processing in accordance with a correct shape may be used. A general screen printing is performed with a metal mask as a preferred example.

Specifically, a predetermined metal mask is placed on the light receiving surface 11A of the semiconductor substrate (矽 substrate) 11, and an electrode forming paste of a desired composition is supplied onto the surface of the metal mask disposed as described above. Secondly, it is preferable to move the rubber roller of a suitable shape at a high speed of 100 to 300 mm/sec (such as 150 to 250 mm/sec) on the surface of the metal mask, so that the paste for electrode formation has a moderate filling effect, and the metal can be directed toward the metal. The opening of the mask is filled with paste.

The printing pressure of the rubber roller (the pressure applied by the rubber roller) should be appropriately changed according to the material and structure of the rubber roller itself, so it is not particularly limited, but it is usually 0.05 to 0.3 MPa, and typically 0.1 to 0.1. 0.2MPa level.

The opening width of the opening of the metal mask to be used is preferably a size that can achieve thinning of the light-receiving surface electrode. For example, when a finger electrode having a line width of 70 μm or less is to be formed, a metal mask having a width corresponding to the opening of the size may be used, and typically 60 μm or less (such as 30 to 60 μm) or 50 μm or less (such as 30 μm to 40 μm) may be used. Metal cover. It also varies depending on the line width of the target, and although it is not particularly limited, for example, a mask having a width wider than the target finger electrode width of 5 to 30% can be used (if the target is For an electrode having a line width of about 60 μm, a mask having an opening width of about 45 ± 5 μm is used. Further, the metal mask to be used may be a mask in which both the opening for forming the finger electrode line and the opening for forming the bus electrode line are formed, or only the opening for the finger electrode line is formed. Mask. When a metal mask in which only the opening for forming the finger electrode line is formed is used, the other electrode screen printing plate can be used to form the bus bar electrode.

According to the electrode forming paste (that is, the electrode forming paste containing the resin particles) disclosed above, for example, the paste filled in the opening of the metal mask does not remain in the opening, and can be smoothly detached from the opening. It is supplied (printed) onto the substrate 11 . The paste for forming an electrode has good passability to the fine opening portion. Therefore, in a state in which the shrinkage of the wire and the occurrence of the wire breakage are greatly reduced, a line width of 75 μm or less is formed (for example, 70 μm or less). Preferably, the finger electrode 13 is preferably 65 μm or less. Since the bus bar electrode is hardly affected by the shrinkage of the wire and the wire breakage, it is not necessary to use the electrode forming paste, but it is also possible to form a high-quality bus bar electrode having a line width of about 1000 to 3000 μm.

When screen printing is performed using a conventional electrode forming paste, it is difficult to predict The pattern is formed into a fine current collecting electrode (finger type electrode) having a line width (line width) of 70 μm or less and avoids occurrence of breakage and line width narrowing. In particular, when screen printing is performed using a general screen printing screen (screen printing screen), there is a high possibility of shrinkage and disconnection at the intersection of the screen, and metal must be used to avoid the risk of the above-mentioned disconnection. The mask is used for screen printing of the light-receiving surface electrode. Since there is no screen in the opening of the mask of the metal mask, the resistance of the electrode forming paste is small, and the clogging condition is also small, so that the occurrence of disconnection can be avoided. However, in general, a metal mask is subjected to a processing procedure of an opening such as a laser or a plating, so that the manufacturing cost is high, and there is also a disadvantage that durability against deformation or the like is poor.

According to the electrode forming paste disclosed above, since the passability to the fine opening portion is good as described above, even when a metal mask is used, the thinning of the thin line can be suppressed and the thin screen can be suppressed. High quality printing that occurs when a wire break occurs. For example, a finger electrode having a line width of 70 μm or less (typically 60 μm or less, such as 50 μm or less, more preferably 40 μm ± 5 μm) can be formed even in screen printing. Thus, the occurrence of the narrowing of the electrode lines and the occurrence of the disconnection are greatly suppressed, and when the resistance value of each of the finger electrodes is slightly increased, the line resistance value of the entire electrode pattern is also lowered. Therefore, the width and the number of the fingers 13 are optimally combined to provide a solar cell element having a high photoelectric conversion efficiency.

In the following, several embodiments of the invention are described, but it is not intended that the invention be limited by the disclosure of the embodiments.

(First embodiment) [Preparation of paste for electrode formation]

A total of seven kinds of pastes for electrode formation shown in Table 1 below were prepared.

As the conductive powder, Ag powder having an average particle diameter of 2 μm was used. As the organic vehicle component, a vehicle containing ethyl cellulose as a resin component is used. Further, as the glass frit, a general lead borosilicate glass powder (average particle diameter: 0.5 to 1.6 μm) which is commonly used in the preparation of an electrode forming paste in the field of electronic materials is used. Next, in the present embodiment, the resin particles used were phenol particles having an average particle diameter of 1.5 μm. The preparation of these materials is as follows. That is, it is first formulated in accordance with the ratio of 85 mass% of Ag powder, 3 mass% of glass frit, and 12 mass% of organic vehicle. Further, as shown in Table 1, the resin particles were blended by changing the ratio in the range of 0 to 1.26 mass% (about 0 to 10% by volume) based on the mass of the Ag powder. These materials were thoroughly mixed using a three-roller to prepare pastes for electrode formation of samples 1 to 7.

[Production of solar cell element (light-receiving electrode) for test]

The electrode forming pastes of the samples 1 to 7 obtained as described above were used, and the light-receiving surface electrode of the solar cell element (that is, the comb-shaped electrode composed of the finger electrode and the bus bar electrode) was formed by the screen printing method.

That is, a commercially available 156 mm square (6 吋 square) solar cell p-type single crystal germanium wafer (thickness: 200 μm) was prepared, and the surface (light-receiving surface) was subjected to alkali etching treatment with an aqueous solution of NaOH to remove the damaged layer. Forming a textured structure of the unevenness, and then applying a phosphorus-containing solution to the texture structural surface and performing thermal diffusion treatment to form an n-Si layer having a thickness of about 0.3 μm to 0.4 μm on the light-receiving surface of the germanium wafer (n ⁺ Floor). Then, a tantalum nitride film having a thickness of about 50 nm to 100 nm is formed on the n-Si layer by a plasma CVD (PECVD) method to form an anti-reflection film.

Then, use the pastes of samples 1-7, and in the atmosphere, An electrode pattern for a light-receiving surface electrode (Ag electrode) is printed on the anti-reflection film by screen printing under room temperature conditions.

Specifically, as shown in FIG. 2, an electrode pattern composed of three linear bus bar electrodes parallel to each other and 67 finger electrodes parallel to the bus bar electrodes and formed parallel to each other is formed by printing. The target finger electrode has a line width of about 60 μm to 70 μm. Moreover, the line width of the bus bar electrode was set to 1.5 mm.

In the above printing, a screen printing mask (screen printing plate) for screen printing on which the opening portion of the electrode pattern is formed is formed on the screen printing screen. The screen printing plate is placed on the light-receiving surface of the substrate, and the electrode forming paste is supplied onto the screen printing plate, and then a rubber roller (or a hardness of 70 degrees) made of a silicone rubber (or urethane rubber or the like) is used. Depending on the angle of attack of 45 degrees and the printing pressure of 0.2 MPa, the screen printing plate is contacted and directly moved to the plate at a speed of 200 mm/sec, and the electrode forming paste is received by the opening of the screen printing plate. On the face side, a printed body is produced. The printing conditions are general, excluding special conditions and operations.

After the screen printing was carried out, the substrate was dried at 120 ° C, and then the substrate was fired in a firing temperature range of 700 to 800 ° C in a near-infrared high-speed baking furnace in an atmosphere to form a light-receiving surface electrode.

[Evaluation]

First, an electrode pattern formed by using a paste 1 in which phenol particles are not formulated and a paste 7 in which 10% by volume of phenol particles are prepared is used, and a cross-sectional structure before and after baking is observed by a scanning electron microscope (SEM: Scanning Electron Microscope). . The results are shown in Figures 3A to 4B.

Figure 3A shows the drying of the electrode pattern (printed body) prepared by paste 1 after drying. The cross-sectional state of the film, FIG. 3B shows the cross-sectional state of the dried film after the electrode pattern (printed body) of the paste 7 is dried. The spheroids which are clearly visible in Figs. 3A and 3B are Ag powders, and the globules which are surrounded by Ag powder in Fig. 3B and which are dark in appearance are resin granules. In the state of the dried film, there is no significant difference between the dried film of the paste 1 in which the resin particles are not blended and the dried film of the paste 7 in which the resin particles are blended, except that the Ag powder is replaced with the resin particles.

4A and 4B show the cross-sectional state of the electrode film after the electrode pattern (printed body) made of the paste 1 and the paste 7 is fired, respectively. As shown in FIG. 4A, it is understood that the electrode film obtained by the paste 1 in which the resin particles are not prepared has a small gap formed between the Ag powders, and the adjacent Ag powders are bonded to each other to form an electrode film. However, it is understood that the Ag powder which has been largely accumulated before the firing is randomly disintegrated due to the above sintering, and unevenness is generated on the surface of the electrode film. On the other hand, as shown in FIG. 4B, it has been found that in the electrode film prepared by disposing the resin particles, it is possible to clearly confirm the void formed between the large void formed by the burnt out of the resin particles and the Ag powder, and the volume of the void. It is larger than the electrode film prepared from the paste 1, but the Ag powder and the resin particles which have been piled up before the firing are maintained in an accumulated state and sintered. Further, it was confirmed that no significant unevenness occurred on the surface of the electrode film.

Next, the following evaluation items were investigated on the pattern of the light-receiving surface electrode (finger electrode, bus bar electrode) formed as described above: (a) the number of broken portions of the finger electrode, and (b) the number of narrowed portions of the finger electrode, ( c) the amount of adhesion of the paste for electrode formation, (d) the width of the finger electrode, and (e) the thickness of the finger electrode. Among these evaluation items, the measurement of (a), (b), and (d) uses a solar cell inspection device (GP Solar GmbH, in-line visual inspection system for solar cell electrode defects detection GP PRINT-Q FS. Cam) Automated image processing Analytical results of pattern observation. In the above (c), a digital scale (manufactured by Sartorius Co., Ltd., CPA224S) was used, and the above (e) was measured using a surface roughness measuring machine (Mitutoyo Co., Ltd., SURFTEST SV-3100).

Further, the measurement of the (f) line resistance of the obtained electrode has also been carried out. For the line resistance value, a resistance value (Ω) at an arbitrary interval (24 mm) of the surface of the finger electrode was measured using a resistance meter (DIGITAL HiTESTER, manufactured by Hioki Electric Co., Ltd.).

Further, in the evaluation results, the evaluation results of the above (a) to (c) are shown in Fig. 5 . As is apparent from Fig. 5, the phenol particles are blended in the paste for electrode formation, and the amount (weight) of the paste printed on the substrate tends to decrease, and the amount of the conductive powder in the paste is substantially reduced. However, for example, it has been confirmed that, as with the paste 2, only a small amount of the resin particles is added, the number of the broken portions of the finger electrodes and the shrinkage phenomenon can be greatly reduced, and the printability can be improved by stability. However, it is known that, as with the paste 7, if the amount of the resin particles added exceeds a certain value, the above-mentioned effect of improving the printability cannot be obtained.

From the above, in the screen printing, the passability of the paste through the screen printing plate is poor, and the amount of paste adhesion on the substrate is reduced, which results in the influence on the number of the broken portions and the number of the broken portions of the finger electrodes. . However, since the opening portion of the paste in which the phenol particles are formulated has good passability, it is inferred that the amount of the paste (weight) corresponding to the amount of the phenol particles is not reduced. As described above, according to the electrode forming pastes 2 to 6 of the present invention, it has been found that high-quality printing can be performed. In addition, although the paste for electrode formation of paste 2 to 6 has been found to have a certain deviation from the printability of the phenol particle blending amount, it is inferred that the quality deviation between batches of other materials such as conductive powder is relatively related. .

In the evaluation results, the evaluation results of the above (d) to (f) have been combined and shown in Table 1 below. In addition, these results are average values of the complex (n=6 or more) secondary measurement values. (4) The width of the finger electrode is a conventional paste 1 which is not formulated with phenol particles, and the paste 2~6 of the present invention which is formulated with phenol particles forms a line width by the same mask, and the former has a narrow line width. . However, a large difference in line width was not found between the pastes 2 and 6, and the deviation of the measured values was substantially the same between the pastes 1 to 7. (5) Regarding the film thickness of the finger electrode, compared with the conventional paste 1 in which the phenol particles were not formulated, it was found that the pastes 2 to 6 of the present invention in which the phenol particles were formulated had a slight tendency to be thinned. However, no significant difference in film thickness was observed between the pastes 2 and 6, and the deviation of the measured values was substantially the same between the pastes 1 to 7.

In addition, (6) regarding the line resistance, it has been confirmed that between the pastes 2 to 7 in which the phenol particles are formulated, the line resistance value slightly increases as the amount of the phenol particles is increased. However, as a result, the wiring resistance of the pastes 2 and 3 in which 1% by volume and 2% by volume of the phenol particles were formulated was lower than the paste 1 in which the phenol particles were not formulated. If the cross-sectional area of the finger electrode is reduced or a void is formed in the electrode structure due to the mixing of the phenol particles, the result is surprising, but it can be inferred that the electrode pattern as a whole is reduced by the disconnection and the shrinkage. . Further, the variation of the measured value of the line resistance of the paste 1 is the largest, and the paste 3 is the least. Therefore, it can be confirmed that the phenol particles are blended in an appropriate amount for the electrode formation paste, whereby the printability can be improved and the quality can be improved.

(Second embodiment) [Preparation of paste for electrode formation]

A total of 5 kinds of pastes shown in Table 2 below have been prepared.

In other words, the resin particles of the first embodiment were changed to acrylic particles having an average particle diameter of 2 μm, and the acrylic particles were blended in the proportions shown in Table 2 below. Other conditions were the same as in the first embodiment described above, and a sample 8 was prepared. 12 electrode forming paste.

Next, using the obtained electrode for forming an electrode of Samples 8 to 12, the light-receiving surface electrode of the solar cell element was formed by the screen printing method under the same conditions as in the above-described first embodiment.

【Table 2】

[Evaluation]

In the same manner as in the first embodiment, the pattern of the light-receiving surface electrode (finger electrode, bus bar electrode) formed as described above was analyzed by the image analyzing device to evaluate the printability.

Items to be evaluated by pattern observation by automatic image processing are mainly classified into (a) the number of broken portions of the finger electrodes, (b) the number of reduced portions, and (c) the amount of adhesion of the paste for electrode formation, (d) The width of the finger electrode and (e) the film thickness of the finger electrode. Further, in the same manner as in the first embodiment, the measurement of the line resistance of (f) of the obtained electrode was carried out.

Among the evaluation results, the evaluation results of the above (a) to (c) are shown in Fig. 6. For comparison, the results of the electrode prepared from the paste 1 which was not prepared with acrylic particles were also shown. It can be seen from Fig. 6 that changing the kind of the resin particles from the phenol particles to the acrylic particles can further reduce (a) the number of broken portions of the finger electrodes and (b) the number of the reduced portions, and it is confirmed that the obtained particles can be better. Improvement in printability and print quality.

However, it is understood that when the acrylic granules are added, the blending amount is preferably about 8% by volume or less.

In the evaluation results, the evaluation results of the above (d) to (f) were not specifically shown, but the results were substantially similar to those of the first embodiment. That is, the (d) width of the finger electrode and the (e) film thickness are the same as those of the paste 8-12 of the present invention prepared with acrylic particles under the same printing conditions, and as a result, the conventional paste 1 in which the phenol particles are not formulated is formed. Thinner and more generous line width. However, in essence, no significant difference was found between the pastes 1, 8 and 12, and the deviations of the measured values were also substantially the same.

Further, (6) regarding the line resistance, it has been confirmed that the line resistance value increases as the amount of the acrylic particles is increased between the finger electrodes made of the pastes 1, 8 to 12. The above line resistance is increased more than when the phenol particles are used in the same amount. It has been confirmed that the deviation of the measured value of the line resistance is not particularly different between the finger electrodes made of the pastes 1, 8 to 12.

(Third embodiment) [Preparation of paste for electrode formation]

A total of 3 kinds of pastes shown in Table 3 below have been prepared.

In other words, the paste for electrode formation of samples 1 and 4 which is the same as the paste prepared in the first embodiment, and the sample 13 prepared by using the same phenol pellets having an average particle diameter of 5 μm and the other conditions for electrode formation paste 4 were prepared. The electrode forming paste.

[Production of solar cell element (light-receiving electrode) for test]

Next, the prepared electrode forming pastes of the samples 1, 4, and 13 were used to form the light-receiving surface electrode of the solar cell element. That is, an electrode pattern composed of three mutually parallel linear bus bar electrodes and 67 finger electrodes parallel to the bus bar electrodes and parallel to each other as shown in FIG. 2 is formed by a screen printing method. Further, in the present embodiment, three types of screen printing plates used for screen printing have been prepared. Specifically, the printing plate 1 was a plate of ST325 screen, and the line width (design line width) of the target finger electrode was 45 μm. The printing plate 2 uses the ST400 screen design with a line width of 45 μm, and the printing plate 3 uses the ST400 screen design with a line width of 40 μm. Moreover, the line width of the bus bar electrode was set to 1.5 mm.

In the above printing, a screen printing mask for screen printing in which an opening portion corresponding to the electrode pattern is formed is used. The screen printing mask is placed on the light receiving surface of the substrate, and the electrode forming paste is supplied onto the screen printing mask, and then a rubber roller (hardness 70) made of a silicone rubber (or urethane rubber or the like) is used. Degree) The metal mask is contacted at a 45-degree angle of attack and a printing pressure of 0.2 MPa, and is directly moved at a high speed of 200 mm/sec on the mask, and the electrode-forming paste passes through the light-receiving side of the opening of the mask. That is, a printed body is produced.

After the screen printing was carried out, the substrate was dried at 120 ° C, and then the substrate was fired in a firing temperature range of 700 to 800 ° C using a near-infrared high-speed baking furnace in an air atmosphere to form a light-receiving surface electrode.

[Evaluation]

In the same manner as in the first embodiment, the pattern of the light-receiving surface electrode (finger electrode, bus bar electrode) formed as described above was analyzed by the image analyzing device to evaluate the printability.

Items to be evaluated by pattern observation by automatic image processing are mainly classified into (a) the number of broken portions of the finger electrodes, (b) the number of reduced portions, and (c) the amount of adhesion of the paste for electrode formation, (d) The width of the finger electrode and (e) the film thickness of the finger electrode. Further, in the same manner as in the first embodiment, the measurement of the line resistance of (f) of the obtained electrode was carried out.

Among the evaluation results, the evaluation results of the above (a) to (c) are shown in Figs. 7 to 9. Fig. 7 shows the results of the electrode pattern printed using the plate 1, Fig. 8 shows the result of the electrode pattern printed using the plate 2, and Fig. 9 shows the result of the electrode pattern printed using the plate 3. As shown in FIGS. 7 to 9, it has been confirmed that printing using any of the plates 1 to 3 can reduce the number of printing turns by adding resin particles to improve printability. The size of the resin particles is known to be an appropriate particle diameter depending on the line width and film thickness of the target, but it is confirmed that when any resin particle of the particle size is used, the printing property can be obtained as compared with the case where the resin particles are not contained. Improve the effect. In particular, when the plate 2 and the plate 3 for fine line printing are used, the effect of improving the above printability is clearly confirmed. Specifically, although the paste 1 containing no resin particles can be used for printing with a line width of 45 μm, it is found to be difficult to use for printing having a line width of 40 μm. On the other hand, it is understood that the pastes 4 and 13 containing the resin particles can be suitably applied to printing having a line width of 45 μm, and can also be applied to printing having a line width of 40 μm.

The evaluation results of the above (d) to (f) are shown in Table 4 below. The values shown in Table 4 are the average of the complex values (n = 6 or more). In the present embodiment, as a result of the (4) width, the (5) film thickness, and the (6) line resistance of the finger electrodes, the paste 1 was slightly superior to the pastes 4 and 13, but no significant difference was observed.

The present invention has been described with reference to the preferred embodiments. However, the invention is not intended to limit the invention.

Claims (12)

A paste for forming an electrode, which is used for forming an electrode paste, comprising: a conductive powder; a resin particle; and an organic vehicle component for dispersing the conductive powder and the resin particle. In the electrode forming paste of claim 1, when the volume of the conductive powder is 100% by volume, the resin particles contain more than 0% by volume and 8% by volume or less. In the case of the electrode-forming paste according to claim 1 or 2, when the weight of the conductive powder is 100% by mass, the resin particles are contained in an amount of more than 0% by mass and not more than 1% by mass. The paste for electrode formation according to any one of claims 1 to 3, wherein the particle diameter of the resin particles is equal to or smaller than a minimum dimension of a cross section of the printed body after the paste for electrode formation is printed. The paste for electrode formation according to any one of claims 1 to 4, wherein the resin particles have an average particle diameter of 10 μm or less. The electrode forming paste according to any one of claims 1 to 5, wherein the resin particles are burned out at a temperature of 600 ° C or lower in an oxidizing gas atmosphere. The electrode forming paste according to any one of claims 1 to 6, wherein the resin constituting the resin particles is selected from the group consisting of a phenol resin, an alkyd resin, a melamine urea resin, an epoxy resin, a polyurethane resin, Neodymium resin, chlorinated rubber resin, acrylic resin, vinyl chloride resin, fluororesin and fiber Any one or two or more of the group consisting of the resin. The electrode-forming paste according to any one of claims 1 to 7, wherein the metal species constituting the conductive powder is selected from the group consisting of nickel, platinum, palladium, silver, and copper. More than one species. The paste for electrode formation according to any one of claims 1 to 8, which further contains a glass powder in a proportion of not more than 5% by mass of the entire paste. The electrode forming paste according to any one of claims 1 to 9, which is prepared by using any one of printing methods selected from the group consisting of screen printing, gravure printing, lithography, and inkjet printing. A semiconductor element provided with an electrode formed using the paste for electrode formation according to any one of claims 1 to 10. A solar cell element comprising a light-receiving surface electrode formed using the electrode-forming paste according to any one of claims 1 to 10.