KR100955496B1 - Conductive composition for forming electrode of solar cell - Google Patents

Abstract

PURPOSE: A conductive composition for forming an electrode of solar cell is provided to ensure high coating adhesive strength with a substrate and excellent weldability with solder ribbon, and to obtain excellent electrical specific-resistivity property at a low temperature. CONSTITUTION: A conductive composition for forming an electrode of solar cell comprises 30-95 weight% conductive powder, 0.1-20 weight% water glass, 0.5-50 weight% binder, and the remaining amount of a solvent with a boiling point of 80-300 °C. The conductive powder is at least one selected from the group consisting of silver powder, gold powder, platinum powder, palladium powder, indium powder, copper powder, nickel powder, silver-plated nickel powder, silver-plated copper powder, and silver-plated tin powder.

Description

Conductive composition for solar cell electrode formation {CONDUCTIVE COMPOSITION FOR FORMING ELECTRODE OF SOLAR CELL}

The present invention relates to a conductive composition for forming a solar cell, and more particularly, has a high coating film adhesion strength with a substrate, and excellent electrical resistivity characteristics can be obtained even in a low temperature region of 300 ° C. or lower, and when applied to a solar cell, a solder ribbon The present invention relates to a conductive composition for forming a solar cell electrode, which has excellent weldability and excellent printing characteristics, and can realize an electrode pattern with high resolution, and further, having high rheological characteristics, thereby achieving a high aspect ratio.

Conventional electronic devices, for example, solar cells, display devices, low-temperature electrode technology applied to products such as RFID devices (RFID), conductive powder, thermosetting resins (epoxy, silicon, etc.), curing agents, solvents, etc. Techniques for mixing pastes have been used. However, such a conductive paste is a chemical bonding method for securing a bonding force with a substrate by a compound produced by curing upon heating, and has a disadvantage in that the coating film strength is weak, and the adhesion between the conductive powders is reduced, thereby making it difficult to obtain excellent electrical conductivity. For example, in the case of solar cells, the weldability of the electrode and the solder ribbon is required, but the epoxy cured product causes a problem that the solder hardenability is deteriorated due to the thermal deformation of the resin already cured due to the temperature (150-450 ° C.) applied during welding. .

Therefore, the object of the present invention is high coating film adhesion strength with the substrate, it is possible to obtain excellent electrical resistivity characteristics even in the low temperature region below 300 ℃, when applied to the solar cell is very excellent weldability with the solder ribbon, excellent printing characteristics It is possible to implement a high-resolution electrode pattern, and further to provide a conductive composition for forming a solar cell electrode that can implement a high aspect ratio by excellent rheological properties.

The present invention to achieve the above object,

At least one selected from the group consisting of silver powder, gold powder, platinum powder, palladium powder, indium powder, copper powder, nickel powder, nickel powder coated with silver, copper powder coated with silver, and tin powder coated with silver 30 to 95% by weight of the conductive powder;

Water glass from 0.1 to 20% by weight;

0.5 to 50% by weight of a binder selected from the group consisting of cellulose resins, acrylic resins or copolymers thereof, alkyd resins, butyral resins and polyvinyl alcohols; And

Residual solvent with boiling point of 80-300 ℃

It provides a conductive composition for forming a solar cell electrode comprising a.

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According to the present invention, the coating film adhesion strength with the substrate is high, excellent electrical resistivity characteristics can be obtained even in a low temperature region of 300 ° C. or less, and when applied to a solar cell, the weldability with the solder ribbon is very excellent and the printing characteristics are excellent. It is possible to provide a high-resolution electrode pattern, and furthermore, to provide a conductive composition for forming a solar cell electrode capable of realizing a high aspect ratio due to excellent rheological properties of the paste.

The conductive composition for forming a solar cell electrode of the present invention is a conductive metal powder; water glass; bookbinder; And a solvent.

In the present invention, the "composition for forming an electrode" includes a composition used as a circuit forming material such as an electronic device made of a laminated structure or a wiring board made of a single layer or a multilayer. Therefore, not only the electrodes used for solar cells, display elements, RFID elements, etc. but also the electric wirings used for these apparatuses are applicable.

The conductive composition for forming a solar cell electrode of the present invention may be prepared in paste or ink form. The properties of the composition can be obtained by adjusting the weight ratio of the kind of conductive powder used and the organic matter (binder, solvent).

Metal, alloy or metal oxide powder may be used as the conductive powder in the composition for forming a conductive electrode of the present invention. The metal is 1 from the group consisting of silver powder, gold powder, platinum powder, palladium powder, indium powder, copper powder, nickel powder, nickel powder coated with silver, copper powder coated with silver, and tin powder coated with silver. It may be a conductive powder selected from species or more. Preferably, silver powder or metal powder coated with silver may be mentioned. The metal powder coated with silver may include nickel powder, copper powder, tin powder, or an alloy powder thereof.

These shapes may be spherical, plate-like, needle-like, indefinite, or the like, and the average particle diameter of the particles is preferably 0.01 to 30 m. If the average particle diameter is smaller than 0.01 μm, the powders are agglomerated with each other and high dispersion is difficult, and the paste may be difficult to form due to high viscosity. If the average particle diameter exceeds 30 μm, there may be a problem that it is difficult to form a fine pattern when the conductor pattern is formed. Can be.

The conductive powder may be included in the solid content of 30 to 95% by weight, and when added to less than 30% by weight, the contact density of the conductive powder is small, the pattern height is low when the fine pattern is implemented, the wire resistance characteristics are insufficient, the viscosity of the paste Low can result in pattern spreading. In addition, when the content exceeds 95% by weight, it is difficult to uniformly disperse the conductive powder and the coating property may be reduced, thereby forming a conductor having a non-uniform pattern.

Water glass used as the inorganic adhesive includes a material represented by the following formula.

M ₂ O-nSiO ₂ -H ₂ O (M is an alkali metal, n is a number from 1-8)

The water glass is an alkali silicate salt obtained by melting silicon dioxide and an alkali or an aqueous solution thereof, and examples of more specific materials include SiO ₂ K ₂ O, SiO ₂ Li ₂ O, SiO ₂ Na ₂ O, and the like. It can be illustrated. The content of the water glass is not particularly limited as long as it is an amount capable of achieving the object of the present invention, and is 0.1 to 20% by weight, preferably 1.0 to 10% by weight, depending on the weight of the conductive paste. If the content of the water glass is less than 0.1% by weight, there is a fear that the adhesive strength is insufficient, if the content of the water glass exceeds 20% by weight it is difficult to expect excellent electrical properties.

As the binder used in the conductive composition for forming a solar cell electrode of the present invention, those known in the art may be used. For example, Cellulose resins, such as methyl cellulose, ethyl cellulose, nitrocellulose, hydroxy cellulose, and hydroxypropyl cellulose; Acrylic resins such as methyl methacrylate, n-butyl methacrylate, ethyl methacrylate, isobutyl methacrylate or copolymers thereof, alkyd resin, saturated polyester resin, butyral resin, polyvinyl alcohol, etc. Can be mentioned. A binder can be used individually or in mixture of 2 or more. The content of the binder is 0.5 to 50% by weight, preferably 1 to 30% by weight, based on the weight of the conductive composition.

The solvent that can be used in the present invention is not particularly limited, and the boiling point is preferably 80 ° C. or higher, more preferably 150 ° C. or higher. The boiling point here is a boiling point in normal pressure. By using the thing whose boiling point is 80 degreeC or more as a solvent, it can prevent that the drying speed of a composition becomes excessively fast. This is advantageous in that a problem can be prevented from forming in the coating film of the composition, and furthermore, a conductive thin film having desired characteristics can be obtained. Although there is no restriction | limiting in particular in the upper limit of the boiling point of a solvent, When considering the drying speed of a coating film, Preferably it is 350 degrees C or less, More preferably, it is 100-300 degreeC.

As a solvent, both an aqueous and non-aqueous are used. For example, water, polyhydric alcohol, polyhydric alcohol alkyl ether, polyhydric alcohol aryl ether, ester, nitrogen-containing heterocyclic compound, amide, amine, long chain alkanes, cyclic alkanes, aromatic hydrocarbons, monoalcohols and the like can be used. These solvents can be used individually or in combination of 2 or more types.

As the polyhydric alcohol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, dipropylene glycol, triethylene glycol and the like can be used.

As polyhydric alcohol alkyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl Ether, triethylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether and the like can be used.

Ethylene glycol monophenyl ether etc. can be used as polyhydric alcohol aryl ether.

As acetate, ethyl cellosolve acetate, butyl cellosolve acetate, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, (gamma)-butyrolactone, etc. can be used.

As the nitrogen-containing heterocyclic compound, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be used.

As the amide, formamide, N-methylformamide, N, N-dimethylformamide, or the like can be used.

As the amine, monoethanolamine, diethanolamine, triethanolamine, tripropylamine, tributylamine and the like can be used.

As the long chain alkanes, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane and the like can be used.

Cyclohexane, decalin, etc. can be used as cyclic alkane.

Benzene, toluene, xylene, dodecylbenzene, trimethylbenzene, etc. can be used as an aromatic hydrocarbon.

Monoalcohols include propanol, butanol, pentanol, hexanol, heptanol, octanol, decanol, cyclohexanol, terpineol, benzyl alcohol, 2-propanol, sec-butanol, t-butanol, 2-pentanol, 3-pentanol, 2-ethyl-1-butanol, 2-heptanol, 3-heptanol, 2-octanol, 3-octanol, 4-octanol, 2-ethylhexanol, nonanol and the like can be used. have.

In addition, the conductive composition for forming a solar cell electrode of the present invention may further include additives that may be conventionally included as needed. Examples of the additives include thickeners, stabilizers, dispersants, surfactants, plasticizers, leveling agents, leveling agents, antifoaming agents, and the like, with respect to the weight of the conductive composition for forming a solar cell electrode of the present invention. It is recommended to use within the range.

In addition, an organic solvent may be further blended to adjust the appropriate viscosity of the conductive composition for forming a solar cell electrode of the present invention. Examples of the organic solvent include aromatic hydrocarbons such as toluene, xylene, mesityrene and tetramine; Ethers such as tetrahydrofuran; Ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isoboron; Lactams such as 2-pyrrolidone, 1-methyl-2-pyrrolidone; Ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, or propylene glycol derivatives corresponding thereto Alcohols; Esters such as acetic acid esters corresponding thereto; And diesters such as methyl esters of dicarboxylic acids such as malonic acid and succinic acid and ethyl esters. The amount of the organic solvent to be used may be appropriately selected depending on the type and content of the conductive particles used, the printing of the conductive composition, or the method of coating.

When preparing the conductive composition for forming a solar cell electrode of the present invention as a paste, the above-mentioned essential components and optional components may be blended according to a predetermined ratio and uniformly dispersed in a kneader such as a blender or a triaxial roll. Can be. Preferably, the conductive paste of the present invention has a Brookfield HBT viscometer at 1 to 300 Pa when measured at a shear rate of 3.84 sec ⁻¹ at 25 ° C. as a # 51 spindle ^. It may have a viscosity of S.

When preparing the electroconductive composition for solar cell electrode formation of this invention with ink, the electroconductive ink of this invention can set the viscosity extensively. Specifically, the viscosity of the conductive ink of the present invention is preferably 100 mPa · s or less, particularly 50 mPa · s or less at 20 ° C. What is necessary is just to adjust the compounding quantity of the above-mentioned each component mix | blended with the viscosity of ink suitably. In this case, the viscosity can be measured by a vibratory viscometer (VM-100A manufactured by Yamaichi Denki Co., Ltd.) or a viscoelasticity measuring device (RS-1 manufactured by Hake Corporation).

In particular, when the conductive ink of the present invention is applied to an inkjet printing method as described below, the viscosity (20 ° C) is preferably set to 50 mPa · s or less, particularly 30 mPa · s or less.

The electroconductive composition for solar cell electrode formation of this invention is prepared, for example by the method described below. The conductive metal powder is dispersed in a solvent to obtain a slurry. Water glass as an inorganic adhesive is added to the slurry thus obtained, followed by stirring and mixing. In this way, the target ink is obtained.

When preparing a conductive composition for forming a solar cell electrode according to the present invention in the form of a paste, the compounding component is printed or coated on the metal layer formed by sputtering, spraying, sintering, etc. by any method such as screen printing, transfer, immersion cloth, etc. It can be used to form electrodes used in various electronic components (solar cell, display, RFID device, etc.) by a method of curing by heating at 150 to 200 ° C for 10 to 30 minutes.

The present invention provides a method for forming an electrode of a solar cell and a solar cell electrode manufactured by the method, wherein the conductive paste is printed on a substrate, dried, cured or fired. Except for using the conductive paste according to the present invention in the method of forming a solar cell electrode of the present invention, the substrate, printing, drying and curing or firing can be used as a method commonly used in the manufacture of solar cells, of course to be. For example, the substrate may be a Si substrate, the electrode may be a front electrode of a silicon solar cell, the printing may be screen printing, the drying for 3 to 30 minutes at 60-150 ℃, and curing or Firing can be carried out at 150-300 ° C. for 5 to 60 minutes. In addition, drying and firing are performed at the same time at a low temperature of 100-300 ℃. It may be performed for 5 to 60 minutes. The printing is preferably printed in a thickness of 15 to 50 ㎛. As a specific example, in the structure of the solar cell described in Japanese Patent Laid-Open No. 2005-268239 and its production, the electrode of the solar cell can be formed using the paste for forming a solar cell electrode of the present invention.

The electrically conductive electrode formation paste composition of this invention is used suitably as an electronic device which consists of a laminated structure, and the circuit formation material, such as the wiring board which consists of a single | mono layer or a multilayer. It is particularly suitable for solar cells, display devices and RFID devices. Specifically, a known printing method is used to print the paste of the present invention on a substrate made of various materials such as glass, ceramics, metal, plastic, etc., with a predetermined printing pattern. Subsequently, when the formed printing pattern is fired in the atmosphere, in an inert atmosphere or in vacuum, a target conductive thin film is formed.

The electrode obtained from the conductive paste according to the present invention has a high coating film adhesion strength with the substrate, excellent electrical resistivity characteristics can be obtained even in a low temperature region of 300 ° C. or lower, and has excellent weldability with a solder ribbon when applied to a solar cell. Excellent printing characteristics can realize a high-resolution electrode pattern. In addition, the rheological properties of the paste are excellent, resulting in high aspect ratios.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

35% by weight of a spherical silver powder with an average particle diameter of 0.1 μm, 1% by weight of potassium silicate, 11% by weight of hydroxycellulose as a binder, 12% by weight of isobutyl methacrylate, 30% by weight of ethylene glycol as a solvent, and 10 parts of butyl cellulsolve The conductive paste was prepared by mixing and dispersing the wt% and 1 wt% of the dispersant with a three roll kneader.

Example 2

In Example 1 70% by weight of the spherical silver powder having an average particle diameter of 2.5 ㎛, 3% by weight of potassium silicate, 3% by weight of hydroxycellulose as a binder, 3% by weight of isobutyl methacrylate, 15% by weight of ethylene glycol as a solvent A conductive paste was prepared in the same manner as in Example 1, except that 5 wt% of butyl cellussolve and 1 wt% of a dispersant were used.

Example 3

In Example 1, 82 wt% of the spherical silver powder having an average particle diameter of 2.5 μm, 3 wt% of potassium silicate, 2 wt% of hydroxycellulose as a binder, 0.5 wt% of isobutyl methacrylate, and 8 wt% of ethylene glycol as a solvent A conductive paste was prepared in the same manner as in Example 1, except that 4 wt% of butyl cellussolve and 0.5 wt% of a dispersant were used.

Example 4

A conductive paste was prepared in the same manner as in Example 1, except that 3 wt% of sodium silicate was used as the water glass in Example 3.

Example 5

A conductive paste was prepared in the same manner as in Example 1, except that 3% by weight of lithium silicate was used as the water glass in Example 3.

Example 6

A conductive paste was prepared in the same manner as in Example 1, except that 82 wt% of silver coated copper powder was used as the conductive powder in Example 3.

Comparative Example 1

In Example 1 70% by weight of the spherical silver powder having an average particle diameter of 2.5 ㎛, 10% by weight of bisphenol A resin as epoxy resin, 1% by weight of amine-based curing agent, 13% by weight of ethylene glycol as solvent, 5% by weight of butyl cellsolve Conductive pastes were prepared in the same manner as in Example 1, except that%, and 1 wt% of a dispersant were used.

Comparative Example 2

In Example 1, 85 wt% of the spherical silver powder having an average particle diameter of 2.5 μm, 5 wt% of a bisphenol A resin as an epoxy resin, 0.5 wt% of an amine curing agent, 5 wt% of ethylene glycol as a solvent, and 4 wt% of butylcellulose solution Conductive paste was prepared in the same manner as in Example 1, except that%, and 0.5 wt% of a dispersant were used.

[Experimental Example]

Specific resistance, coating film strength, substrate adhesion, welding strength, resolution, and aspect ratio of the conductive pastes prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were measured, as shown in Table 1 below.

The resistivity was calculated by printing the electrode paste on an alumina substrate, firing at 250 ° C. for 30 minutes, measuring the sheet resistance using a 4 point probe, and measuring the height using a scanning electron microscope (SEM). The coating film strength was measured for the scratch hardness using a pencil lead of 4B ~ 4H on the fired specimen. The evaluation of substrate adhesion was performed by lattice adhesion evaluation (ASTM D3359), and the number of grids torn after the adhesion evaluation was recorded using 3M tape # 610 for 100 lattice. The welding strength was measured by tearing strength of the electrode and the solder ribbon by using an adhesion tester (SESIN Corporation SS30WD). In the resolution evaluation, the case where the line width change rate of the pattern was 10% or less after printing, drying, and firing with a resolution mask having a 60-120 μm pattern was recorded as the resolution. The aspect ratio is expressed as the ratio of height / line width × 100 of the pattern.

TABLE 1

As can be seen in Table 1, the substrate adhesion is excellent, and even when the substrate material is metal, ceramic, or glass, the adhesion strength is excellent, and thus it can be widely used in electronic devices such as solar cells, displays including PDP, and RFID. In addition, the conductive paste according to the present invention has excellent electrical resistivity in the low temperature region (below 300 ℃), so it is used for low temperature process and low temperature such as heterojunction solar cell (HIT Cell), thin film solar cell, polymer solar cell, etc. It is applicable to the field where an electrode is required. In addition, the conductive paste according to the present invention has a high pull adhesive strength of 200 gf or more after solder ribbon welding, which is excellent in welding strength, and excellent in rheological properties of the paste. In addition, the conductive paste according to the present invention has a higher aspect ratio than the conventional paste, so that the screen mesh is eliminated during printing, so that a pattern having a high aspect ratio can be realized, thereby obtaining excellent line resistance characteristics even at high resolution.

Claims (13)

At least one selected from the group consisting of silver powder, gold powder, platinum powder, palladium powder, indium powder, copper powder, nickel powder, nickel powder coated with silver, copper powder coated with silver, and tin powder coated with silver 30 to 95% by weight of the conductive powder; Water glass from 0.1 to 20% by weight; 0.5 to 50% by weight of a binder selected from the group consisting of cellulose resins, acrylic resins or copolymers thereof, alkyd resins, butyral resins and polyvinyl alcohols; And Residual solvent with boiling point of 80-300 ℃ Conductive composition for forming a solar cell electrode comprising a. delete The method of claim 1, The water glass is a conductive composition for forming a solar cell electrode, characterized in that the water glass containing at least one material selected from the group consisting of potassium silicate, sodium silicate and lithium silicate. The method of claim 1, The water glass is a conductive composition for forming a solar cell electrode, characterized in that selected from the material represented by the following formula: M ₂ O-nSiO ₂ -H ₂ O (M is an alkali metal, n is a number from 1-8) delete delete delete An ink composition comprising a conductive composition for forming a solar cell electrode according to claim 1, 3, or 4. delete delete delete delete delete