KR102040302B1 - Composition for forming solar cell and electrode prepared using the same - Google Patents

Abstract

The present invention includes a conductive powder, a glass frit, an organic vehicle and a surface tension modifier, the surface tension of the surface tension modifier is 40 to 65 mN / m, for forming a solar cell electrode, characterized in that It relates to a composition.
[Equation 1]

Description

A composition for forming a solar cell electrode and an electrode manufactured therefrom {COMPOSITION FOR FORMING SOLAR CELL AND ELECTRODE PREPARED USING THE SAME}

The present invention relates to a composition for forming a solar cell electrode and an electrode prepared therefrom. More particularly, the present invention relates to a composition for forming a solar cell electrode and an electrode manufactured therefrom, which are capable of printing a fine line width when printing on a substrate by a screen printing method and having excellent conversion efficiency.

Solar cells generate electrical energy using the photoelectric effect of pn junctions that convert photons of sunlight into electricity. In the solar cell, front and rear electrodes are formed on the upper and lower surfaces of the semiconductor wafer or substrate on which the pn junction is formed. The photovoltaic effect of the pn junction is induced by solar light incident on the semiconductor wafer, and electrons generated therefrom provide a current flowing through the electrode to the outside. Electrodes of such solar cells may be formed on the wafer surface by coating, patterning, and firing the composition for forming an electrode.

Methods for printing the composition for forming a solar cell electrode on a substrate can be largely divided into gravure offset printing method and screen printing method. In particular, it is important to use a composition for forming an electrode that can have a high aspect ratio while printing at a fine line width when the composition for forming an electrode is printed on a substrate. In the case of gravure offset printing, the viscosity, dryness, and tackiness requirements of the composition have a significant influence. In the case of screen printing, the rheological properties or thixotrophy of the composition have a significant influence.

In the case of Korean Patent Laid-Open No. 2011-0040713, the leveling and thixotropic properties of the composition were adjusted with a plasticizer in order to realize a narrow line width and a high aspect ratio. In the case of Korean Patent Publication No. 2010-0069950, in order to realize a high aspect ratio, a gravure offset printing method using a binder having a high glass transition temperature (Tg) as a two-layer electrode was used. Korean Patent Publication No. 2007-0055489 attempts to solve the control of thixotropy (TI) by the particle size of silver (Ag) powder, but there are still limitations in implementing a printing pattern having a fine line width and a high aspect ratio.

An object of the present invention is to provide a composition for forming a solar cell electrode that can implement a fine line width during printing.

Another object of the present invention is to provide a composition for forming a solar cell electrode excellent in conversion efficiency.

The above objects of the present invention can be achieved by the present invention described below.

One aspect of the invention comprises a conductive powder, a glass frit, an organic vehicle and a surface tension regulator, the surface tension of the surface tension regulator is 40 to 65 mN / m, the composition for forming a solar cell electrode that satisfies the following formula 1 It is about:

[Equation 1]

 In Equation 1, the thixotropic index (TI) is a value calculated by substituting the viscosity measured at each rotation speed (rpm) with a spindle 14 using a rotational viscometer at 23 ° C.

The surface tension modifiers ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, propylene carbonate, formamide, glycerol And at least one compound selected from the group consisting of furfural.

The composition comprises 50 to 90% by weight of the conductive powder; 1 to 15% by weight of the glass frit; 5 to 40% by weight of the organic vehicle; And it may include 0.1 to 40% by weight of the surface tension regulator.

The conductive powder is silver (Ag), gold (Au), palladium (Pd), platinum (Pt), copper (Cu), chromium (Cr), cobalt (Co), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), iron (Fe), iridium (Ir), osmium (Os), rhodium (Rh), tungsten (W), molybdenum (Mo), nickel (Nickel) and ITO (indium tin oxide) It may include one or more metal powder selected from the group consisting of.

The glass frit may comprise leaded glass frit, lead-free glass frit or mixtures thereof.

The glass frit may have an average particle diameter (D50) of 0.1 μm to 5 μm.

The composition may further comprise at least one additive selected from the group consisting of dispersants, plasticizers, viscosity stabilizers, antifoams, pigments, ultraviolet stabilizers, antioxidants and coupling agents.

Another aspect of the invention relates to a solar cell electrode prepared from the composition for forming a solar cell electrode.

The composition for forming a solar cell electrode of the present invention can implement a printed pattern of fine line width, it is excellent in conversion efficiency.

1 is a conceptual diagram schematically showing the structure of a solar cell according to an embodiment of the present invention.

Composition for forming solar cell electrode

The composition for forming a solar cell electrode of the present invention includes a conductive powder (A), a glass frit (B), an organic vehicle (C) and a surface tension modifier (D), and fine line widths when printed on a wafer substrate by screen printing. It is possible to implement, the solar cell electrode prepared with the composition is excellent in conversion efficiency.

Hereinafter, the present invention will be described in detail.

(A) conductive powder

As the conductive powder used in the present invention, both organic or inorganic materials having conductivity may be used. Preferably silver (Ag), gold (Au), palladium (Pd), platinum (Pt), copper (Cu), chromium (Cr), cobalt (Co), aluminum (Al), tin (Sn), lead ( Pb), zinc (Zn), iron (Fe), iridium (Ir), osmium (Os), rhodium (Rh), tungsten (W), molybdenum (Mo), nickel (Nickel) or ITO (indium tin oxide) Can be used. Such conductive powder can be used 1 type or in mixture of 2 or more types. Preferably, the conductive powder includes silver (Ag) particles, and nickel (Ni), cobalt (Co), iron (Fe), zinc (Zn) or copper (Cu) particles may be further added in addition to the silver particles. .

The conductive powder may be used having an average particle diameter (D50) having an average particle diameter of 0.1 to 10㎛. Preferably it is 0.2-7 micrometers, More preferably, it is 0.5-5 micrometers.

The conductive powder may be included in 50 to 90% by weight relative to the total weight of the composition, preferably from 70 to 90% by weight. In this range, it is possible to prevent the conversion efficiency from being lowered due to the increase of the resistance, to prevent the difficulty of pasting due to the relative decrease in the amount of the organic vehicle, and to have appropriate dispersibility, flowability, and printability.

(B) glass frit

The glass frit etches the anti-reflection film during the firing process of the electrode paste, generates silver crystal grains in the emitter region to melt the silver particles to lower the resistance, and the adhesion between the conductive powder and the wafer And soften during sintering to induce an effect of lowering the firing temperature.

Increasing the area of the solar cell in order to increase the efficiency of the solar cell can increase the contact resistance of the solar cell to minimize damage to the pn junction (pn junction) and at the same time minimize the series resistance. In addition, since the fluctuation range of the firing temperature increases with the increase of wafers with various sheet resistances, it is preferable to use a glass frit that can sufficiently secure thermal stability even at a wide firing temperature.

The glass frit may be any one or more of a flexible glass frit or a lead-free glass frit typically used in a composition for forming a solar cell electrode.

The glass frit may include solely or a mixture of metal oxides selected from lead oxide, silicon oxide, tellurium oxide, bismuth oxide, zinc oxide, boron oxide, aluminum oxide, tungsten oxide, and the like. For example, zinc oxide-silicon oxide type (ZnO-SiO2), zinc oxide-boron oxide-silicon oxide type (ZnO-B2O3-SiO2), zinc oxide-boron oxide-silicon oxide-aluminum oxide type (ZnO-B2O3- SiO2-Al2O3), bismuth oxide-silicon oxide based (Bi2O3-SiO2), bismuth oxide-boron oxide-silicon oxide based (Bi2O3-B2O3-SiO2), bismuth oxide-boron oxide-silicon oxide-aluminum oxide-based (Bi2O3-B2O3 -SiO2-Al2O3), bismuth oxide-zinc oxide-boron oxide-silicon oxide system (Bi2O3-ZnO-B2O3-SiO2) or bismuth oxide-zinc oxide-boron oxide-silicon oxide-aluminum oxide system (Bi2O3-ZnO-B2O3 -SiO2-Al2O3) glass frit and the like can be used.

Glass frits can be prepared from the metal oxides described above using conventional methods. For example, it mixes with the composition of the metal oxide described above. Mixing can be performed using a ball mill or planetary mill. The mixed composition is melted at conditions of 900 ° C.-1300 ° C. and quenched at 25 ° C. The obtained result can be pulverized by a disk mill, planetary mill or the like to obtain a glass frit.

The shape of the glass frit may be spherical or indefinite.

The glass frit may have an average particle diameter (D50) of 0.1 μm to 5 μm.

The glass frit is used to purchase a commercial product or to obtain a desired composition, for example, silicon dioxide (SiO 2), aluminum oxide (Al 2 O 3), boron oxide (B 2 O 3), bismuth oxide (Bi 2 O 3), sodium oxide (Na 2 O). Zinc oxide (ZnO) or the like may be selectively melted to prepare.

The glass frit may be included in an amount of 1 to 15% by weight, and preferably 2 to 10% by weight, based on the total weight of the composition. It may have a suitable dispersibility, flowability and printability in the above range.

(C) organic vehicle

The organic vehicle imparts suitable viscosity and rheological properties to the composition through mechanical mixing with the inorganic component of the composition for forming a solar cell electrode.

The organic vehicle may be an organic vehicle that is typically used in a composition for forming a solar cell electrode, and may include a conventional binder resin, a solvent, and the like.

As the binder resin, an acrylate-based or cellulose-based resin may be used, and ethyl cellulose is generally used. However, ethyl hydroxyethyl cellulose, nitro cellulose, a mixture of ethyl cellulose and phenol resin, alkyd resin, phenol resin, acrylic ester resin, xylene resin, polybutene resin, polyester resin, urea resin, melamine Resins, vinyl acetate-based resins, wood rosins, or polymethacrylates of alcohols;

As the solvent, for example, hexane, toluene, ethyl cellosolve, cyclohexanone, butyl centrosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) Butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma butyrolactone or ethyl lactate alone or the like It can mix and use 2 or more types.

The organic vehicle may be included in 5 to 40% by weight based on the total weight of the composition for forming a solar cell electrode. It is possible to secure sufficient adhesive strength and excellent printability in the above range.

(D) surface tension modifier

The composition of the present invention may comprise a surface tension modifier. In the present invention, the surface tension modifier means a co-solvent having a surface tension of 40 mN / m or more, for example, 40 to 65 mN / m.

As an example, the surface tension modifier may be ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, propylene carbonate, One or more compounds selected from the group consisting of formamide, glycerol, and furfural.

The surface tension modifier may be included in 0.1 to 40% by weight, preferably 0.1 to 25% by weight relative to the total weight of the composition for forming a solar cell electrode. It can have a suitable fluidity and printability in the above range.

(E) other additives

The composition for forming a solar cell electrode of the present invention may further include a conventional additive as needed to improve the flow characteristics, process characteristics and stability in addition to the components described above. The additive may be used alone or in combination of two or more of a dispersant, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, an ultraviolet stabilizer, an antioxidant, a coupling agent and the like. These may be included in 0.1 to 5% by weight relative to the total weight of the composition for forming a solar cell electrode, but may be changed in content as necessary.

The composition for forming a solar cell electrode of the present invention is a composition applied to screen printing that satisfies Equation 1 below, and printing of fine patterns is possible and may exhibit excellent conversion efficiency.

[Equation 1]

In Equation 1, the thixotropic index (TI) is a value calculated by substituting the viscosity measured at each rotation speed (rpm) with a spindle 14 using a rotational viscometer at 23 ° C.

Specifically, the thixotropic index (TI) of Equation 1 may be defined as the ratio of the viscosity values measured by varying the number of revolutions (rpm) of the rotational viscometer. As an example, the thixotropic index (TI 10) means a viscosity ratio measured at a rotational speed of 100 rpm using a rotational viscometer at 23 ° C. at 14 rpm. Examples of the rotational viscometer include Brookfield's HBDV-II + Pro.

Moreover, it is preferable that the composition for solar cell electrode formation has a viscosity range of 200-600 Pa.s from a printing workability viewpoint. The said viscosity is a value when it measures at the rotation speed of 10 rpm at 23 degreeC using a rotational viscometer.

When printing on a substrate with the composition for forming a solar cell electrode of the present invention, in particular, when printing by the screen printing method, the line width of the printed pattern is 65 to 90㎛, the line thickness may be 15 to 20㎛. In addition, the aspect ratio (line thickness / line width), which is the ratio of the line thickness to the line width of the printed pattern, may be 0.15 or more, preferably 0.15 to 0.50, more preferably 0.20 to 0.30. It may have excellent printability in the range of the aspect ratio.

Solar cell electrode and solar cell comprising same

Another aspect of the invention relates to an electrode formed from the composition for forming a solar cell electrode and a solar cell comprising the same. 1 illustrates a structure of a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a composition for forming an electrode is printed and baked on a wafer 100 or a substrate including a p layer (or n layer) 101 and an n layer (or p layer) 102 as an emitter. Thus, the rear electrode 210 and the front electrode 230 may be formed. For example, the electrode forming composition may be printed on the back side of the wafer and then dried at a temperature of about 200 ° C. to 400 ° C. for about 10 to 60 seconds to perform a preliminary preparation step for the back electrode. In addition, the composition for forming an electrode on the front surface of the wafer may be printed and dried to perform a preliminary preparation step for the front electrode. Thereafter, a firing process may be performed at 400 ° C. to 950 ° C., preferably 750 ° C. to 950 ° C., for about 30 seconds to 50 seconds to form a front electrode and a rear electrode.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Examples 1-14 and Comparative Examples 1-3

Example 1

6.4% by weight of ethyl cellulose (Dow Chemical Company, STD4, SDT200) as an organic binder was sufficiently dissolved in 5% by weight of butyl carbitol (Dow Chem.) At 60 ° C to prepare an organic vehicle, and an average particle diameter of the organic vehicle. 85 wt% of this 2.0 μm spherical silver powder (Dowa Hightech CO. LTD, AG-4-8), 3 wt% of glass frit (Particleage, CI-124) having an average particle diameter of 1.0 μm, surface tension Mix evenly by adding 0.1% by weight of tetraethylene glycol (Sigma Aldrich), 0.2% by weight of dispersant (BYK102, BYK-chemie), and 0.3% by weight of thixotropic agent (Thixatrol ST, Elementis co.) As a regulator. After mixing and dispersing with a three-roll kneader to prepare a composition for forming a solar cell electrode.

The composition for forming a solar cell electrode was printed by screen printing a predetermined pattern on the entire surface of a wafer. After measuring the physical properties according to the following physical property measurement method is shown in Table 2 below.

Example  2-13 and Comparative example  1-3

Except that each component is included in the composition of Table 2 and Table 3 to prepare a composition for forming a solar cell electrode in the same manner as in Example 1 and then printed the pattern by screen printing.

Property measurement method

o Determination of thixotropic index (TI):

The rotational viscometer was used to calculate the ratio of the viscosity measured at 23 ° C. using Spindle 14 with HBDV-II + Pro of Brookfield. After the sample was completely filled in the sample cup, the spindle was mounted to stabilize the temperature for 5 minutes, and the viscosity was measured after the retention time shown in Table 1 below.

TABLE 1

After calculating the TI index of the formula 1 based on the measured viscosity is shown in Table 2 and Table 3, respectively.

Property evaluation method

Short circuit current and conversion efficiency measurement

The composition for forming a solar cell electrode prepared in Examples and Comparative Examples was printed by screen printing in a predetermined pattern on the entire surface of a crystalline mono wafer (Wafer), and dried using an infrared drying furnace. The cell formed by the above process was fired for 60 seconds to 210 seconds between 600 and 900 ° C. using a belt type kiln, and the cell thus manufactured was manufactured using a solar cell efficiency measuring device (Pasan, CT-801). The short circuit current (Isc) and conversion efficiency (%) of were measured.

o Line width measurement:

A composition for forming a solar cell electrode was prepared and printed by screen printing in a predetermined pattern on the entire surface of a wafer using a screen mask designed with a line width of 40 μm. After drying and baking the printed wafer, the line width of the pattern was measured with a three-dimensional measuring microscope.

TABLE 2

TABLE 3

Referring to the results of Table 2 and Table 3, the composition for forming a solar cell electrode of Examples 1 to 13 using the surface tension regulator having a surface tension of 40 to 65 mN / m satisfying the formula 1 is fine pattern printing It is excellent in the properties, it can be seen that the solar cell electrode manufactured therefrom is excellent in conversion efficiency.

Simple modifications and variations of the present invention can be easily made by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (6)

50 to 90 weight percent conductive powder, 1 to 15 weight percent glass frit, 5 to 40 weight percent organic vehicle, and 0.1 to 40 weight percent surface tension modifier,
The organic vehicle comprises a binder resin and a solvent,
The solvent is hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol, dibutyl carbitol, butyl carbitol acetate, propylene glycol monomethyl ether, hexylene glycol, terpinol, methylethyl Ketones, benzyl alcohol, gamma butyrolactone, ethyl lactate or combinations thereof,
The surface tension of the surface tension regulator is 40 to 65 mN / m,
The surface tension modifier 1 selected from the group consisting of ethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, propylene carbonate and formamide Includes at least one compound,
Composition for forming a solar cell electrode, characterized in that to satisfy the following formula 1:
[Equation 1]

In Equation 1, the thixotropic index (TI) is a value calculated by substituting the viscosity measured at each rotation speed (rpm) with a spindle 14 using a rotational viscometer at 23 ° C.
The method of claim 1,
The conductive powder is silver (Ag), gold (Au), palladium (Pd), platinum (Pt), copper (Cu), chromium (Cr), cobalt (Co), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), iron (Fe), iridium (Ir), osmium (Os), rhodium (Rh), tungsten (W), molybdenum (Mo), nickel (Nickel) and ITO (indium tin oxide) Composition for forming a solar cell electrode comprising at least one metal powder selected from the group consisting of.
The method of claim 1,
The glass frit is a composition for forming a solar cell electrode comprising a flexible glass frit, lead-free glass frit or a mixture thereof.
The method of claim 1,
The glass frit has a composition for forming a solar cell electrode, characterized in that the average particle diameter (D50) is 0.1㎛ to 5㎛.
The method of claim 1,
The composition is a composition for forming a solar cell electrode, characterized in that it further comprises at least one additive selected from the group consisting of dispersants, plasticizers, viscosity stabilizers, antifoams, pigments, ultraviolet stabilizers, antioxidants and coupling agents.
A solar cell electrode prepared from the composition for forming a solar cell electrode according to any one of claims 1 to 5.

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