KR20110024655A - Composition for foarming solar-cell electrode characterized by low bowing - Google Patents

Abstract

PURPOSE: Paste for forming a solar cell electrode is provided to ensure excellent mechanical strength of an electrode and adhesion to a substrate, to achieve back surface field effects, and to enhance the efficiency of a solar cell. CONSTITUTION: Paste for forming a solar cell electrode comprises aluminum powder, glass frit, and organic vehicles, and further inorganic filler. The inorganic filler is included in the amount of 1~10 weight%. The aluminum powder is a mixed powder of spherical aluminum powder with a grain size of 0.1~2 micron and spherical aluminum powder with a grain size of 0.5 ~ 20 micron, or a mixture of plate-like aluminum powder with an average length of 20 ~ 50 micron with the mixed powder.

Description

COMPOSITION FOR FOARMING SOLAR-CELL ELECTRODE CHARACTERIZED BY LOW BOWING}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste for forming a solar cell electrode, and in particular, has excellent mechanical strength of the electrode and adhesion to the substrate, and can sufficiently achieve the BSF (back surface field) effect required by the solar cell. The present invention relates to a solar cell electrode forming paste capable of suppressing the phenomenon.

Recently, the spread of solar cells is rapidly spreading due to various reasons such as pollution-free, convenience of equipment, and durability improvement. Accordingly, solar cell efficiency can be improved, and various methods of manufacturing solar cells with excellent mass production are being studied. have.

Among the solar cells currently produced, crystalline silicon solar cells using silicon wafers are most commonly used due to their high power generation efficiency.

On the other hand, the manufacturing method of the crystalline solar cell is as follows.

A P-N junction is formed on a thin wafer of silicon, and one side of it is coated with an antireflection coating to prevent sunlight reflection loss. Thereafter, the front electrode, the rear electrode, and a tapping electrode for soldering tabs for electrically connecting each cell in the solar cell module are formed by screen printing, and finally, the solar cell is manufactured by heat treatment at 900 to 1000 ° C.

In particular, an electrode of a solar cell is formed by printing, drying and firing a paste comprising a conductive metal powder, a glass frit and an organic vehicle on a silicon substrate. In this process, the aluminum paste used for forming the electrode diffuses Group 3 aluminum into the silicon wafer during the heat treatment to form a BSF layer, which is a P layer, and makes electrical contact with the silicon wafer. The formed aluminum electrode plays a role of improving an internal electric field, preventing electron recombination, collecting holes as a plurality of carriers, reflector reflecting long wavelength light of sunlight, and adjusting bending characteristics. .

In particular, it is important to adjust the bending characteristics among them. If the bending characteristic is 2 mm or more, the battery itself is easily damaged by heat during the manufacture of the module assembly. In addition, the adhesion between the mechanical strength and the substrate at the time of firing is inferior, and warpage of the substrate may occur after the firing.

In order to improve such bending characteristics, the Al thickness needs to be lowered, which causes a decrease in BSF layer properties and lowers the electrical conductivity, thereby lowering the open voltage, thereby reducing the light conversion change efficiency.

Therefore, there is a need to develop a rear electrode having good bending characteristics while maintaining an appropriate thickness of the rear electrode.

In order to solve the problems of the prior art as described above, the present invention can sufficiently achieve the BSF (back surface field) effect required by the solar cell even when forming a thin electrode layer with excellent adhesion between the electrode and the mechanical strength of the electrode. It is possible to suppress the warpage of the substrate after firing and to increase the efficiency of the solar cell. Especially, it is suitable for high temperature / high speed firing and is excellent in mass production. The purpose is to provide.

The present invention has been made to solve the above problems of the prior art,

In the paste composition for forming a solar cell electrode including an aluminum powder, a glass frit, and an organic vehicle, the paste composition for forming a solar cell electrode is characterized by further comprising an inorganic filler.

In the paste composition of the present invention, the inorganic filler is one selected from FeCr, CoAl, CoAlTi, CoCrAl, CoAl, MnSbTi, FeZnTi, and CoNiZnTi, or a combination of two or more thereof. Provided is a paste composition for formation.

In addition, in the paste composition of the present invention, the inorganic filler provides a paste composition for forming a solar cell electrode, characterized in that contained 1 to 10% by weight relative to the total composition.

In addition, in the paste composition of the present invention, the aluminum powder is a mixture of spherical aluminum powder having a particle diameter of 0.1 to 2 µm and spherical aluminum powder having a particle diameter of 0.5 to 20 µm; Or it provides a paste composition for forming a solar cell electrode, characterized in that the plate-shaped aluminum powder having an average length of 20 to 50 ㎛ in both sides of the mixed powder is selectively further mixed.

In addition, in the paste composition of the present invention, the aluminum powder, the spherical aluminum powder having a particle diameter of 0.1 ~ 2 ㎛ 40 to 50% by weight relative to the total aluminum powder; 20 to 30% by weight of the spherical aluminum powder having a particle diameter of 0.5 to 20 μm relative to the total aluminum powder; And it provides a paste composition for forming a solar cell electrode, characterized in that the plate-shaped aluminum powder having an average length of 20 to 50 ㎛ of both sides, 0 to 10% by weight compared to the total aluminum powder.

In addition, in the paste composition of the present invention, the glass frit is PbO-SiO _{2 type} , PbO-SiO ₂ -B ₂ O _{3 type} , ZnO-SiO _{2 type} , ZnO-B ₂ O ₃ -SiO _{2 type} , and Bi _It provides a paste composition for forming a solar cell electrode, characterized in that at least one selected from ₂ O ₃ -B ₂ O ₃ -ZnO-SiO ₂ system.

In addition, in the paste composition of the present invention, the glass frit provides a paste composition for forming a solar cell electrode, characterized in that contained 1 to 20% by weight relative to the total composition.

In addition, in the paste composition of the present invention, the organic vehicle provides a paste composition for forming a solar cell electrode, characterized in that contained 20 to 50% by weight relative to the total composition.

In addition, there is provided a solar cell electrode prepared using the paste composition of the present invention.

In addition, in the solar cell electrode of the present invention, the electrode provides a solar cell electrode, characterized in that the back electrode.

The paste for forming a solar cell electrode and the electrode forming method of the solar cell according to the present invention have excellent BSF (back surface field) effects required by the solar cell even when the electrode layer is thinly formed while having excellent adhesion between the electrode and the mechanical strength of the electrode. It can be sufficiently achieved, can suppress the warpage phenomenon of the substrate after aqueous, there is an advantage that can increase the efficiency of the solar cell.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

TECHNICAL FIELD This invention relates to the paste composition for solar cell electrode formation containing aluminum powder, glass frit, an organic vehicle, and an inorganic filler.

In the present invention, the inorganic filler may be one selected from FeCr, CoAl, CoAlTi, CoCrAl, CoAl, MnSbTi, FeZnTi, and CoNiZnTi, or a combination of two or more thereof.

The inorganic filler is preferably included 1 to 10% by weight relative to the total composition. The inorganic filler can reduce the bending property after firing by adjusting the thermal expansion coefficient of the aluminum paste and the silicon wafer by adjusting the thermal expansion coefficient in the whole paste composition, improves the conductivity of the metal electrode by excellent conductivity properties compared to other oxides To improve efficiency.

In the present invention, the aluminum powder is a mixture of spherical aluminum powder having a particle diameter of 0.1 ~ 2 ㎛, and spherical aluminum powder having a particle diameter of 0.5 ~ 20 ㎛; Alternatively, it is preferable that the plate-shaped aluminum powder having an average length of 20 to 50 μm in both sides of the mixed powder is further mixed selectively. Forming a structure in which the aluminum powder forming the electrode paste in the present invention is mixed using three kinds of powders increases the diffusion area by increasing the contact area with the silicon wafer, thereby increasing the back surface field layer (BSF). ) To efficiently form particles, and to increase the packing density in the aluminum powder by mixing particles with different particle sizes, thereby improving electrical properties and minimizing thermal expansion of metal components during heat treatment, thereby minimizing shrinkage of the particles. To do this. In addition, due to the mixing of three or more kinds of aluminum powder in the present invention, it is possible to minimize the index of the surface resistance value and the bending characteristic, and to significantly lower the small-the-better characteristics in the solar cell. do. That is, in the case of the bending characteristic, when the module assembly is formed after cell fabrication, it is easy to be damaged if it is 1 mm or more. For this purpose, it is desirable to have the mesh resistance in terms of solar cell efficiency and surface resistance value. In the present invention, the improvement of the mesh characteristics can be formed by mixing three kinds of aluminum powder.

The aluminum powder, the spherical aluminum powder having a particle diameter of 0.1 ~ 2 ㎛ 34 ~ 50% by weight compared to the total aluminum powder; Spherical aluminum powder having a particle diameter of 0.5 to 20 µm is 17 to 30% by weight relative to the total aluminum powder; And a plate-shaped aluminum powder having an average length of 20 to 50 μm on both sides of the horizontal and vertical sides is preferably 0 to 10 wt% of the total aluminum powder.

In the present invention, the glass frit is PbO-SiO ₂ system, PbO-SiO ₂ -B ₂ O ₃ system, ZnO-SiO ₂ system, ZnO-B ₂ O ₃ -SiO ₂ system, and Bi ₂ O ₃ -B ₂ O ₃ may be selected from at least one is selected from -ZnO-SiO ₂ system.

The glass frit is preferably contained 1 to 20% by weight, more preferably 1 to 10% by weight relative to the total composition. When the glass frit is less than 1wt%, the adhesion and warpage characteristics are inhibited, and when the glass frit is more than 20wt%, the electrical properties are not good, which affects the efficiency characteristics.

The glass frit has a softening point of 300 to 600 ° C. and an average particle diameter of 1 to 10 μm. In the average particle diameter of this range, the advantage of maximizing the filling and sintering density is realized, especially when the softening point is lowered below 1 μm, the problem of etching too much with the anti-reflection film occurs. A problem arises in that the antireflection film is etched too little.

In the present invention, the organic vehicle, through mechanical mixing with the inorganic component of the solar cell electrode forming paste, imparts consistency characteristics and rheological properties so that the paste is suitable for printing.

The organic vehicle may be an organic vehicle that is commonly used in solar cell electrode pastes, and may be, for example, a mixture of a polymer and a solvent.

As the polymer, an acrylate resin, ethyl cellulose, nitrocellulose, a polymer of ethyl cellulose and a phenol resin, a wood rosin, or a polymethacrylate of alcohol may be used. Preferably, ethyl cellulose is preferable.

As the solvent, butyl carbitol acetate, butyl carbitol, butyl cellsolve, butyl cellulsolve acetate, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether propionate, ethyl ether propio Nate, terpineol, propylene glycol monomethyl ether acetate, dimethylamino formaldehyde, methyl ethyl ketone, gamma butyrolactone, ethyl lactate, and texanol alone or in combination of two or more thereof. Can be. Preferably, butyl carbitol acetate is used.

In addition, the organic vehicle may include the phosphorus-based dispersant, thixotropic agent, leveling agent, antifoaming agent, and the like.

The thixotropic agent may be a polymer / organic material such as urea-based, amide-based, urethane-based, or inorganic silica.

The organic vehicle is preferably contained 20 to 50% by weight, more preferably 20 to 30% by weight relative to the total composition. If it is less than 20% by weight, the organic matter content is too small, the printability is worse, and if the amount exceeds 50% by weight, the film is collapsed after printing due to the viscosity decrease.

The manufacturing method of the said solar cell electrode formation paste composition is demonstrated.

First, an organic vehicle is prepared by dissolving a polymer resin such as acrylate resin, ethyl cellulose, nitrocellulose, ethyl cellulose, and the like in a solvent such as butyl carbitol acetate and then premixing.

Thereafter, the organic vehicle, three kinds of aluminum powder having different powder shapes, and an inorganic filler are premixed. After premixing, it is effective to incorporate amine-based, acid-based, and bipolar dispersion additives to increase particle dispersibility.

The mixture is preferably aged for 1-12 hours for proper dispersion. The aged mixture is subjected to the second mixing and dispersing process through a paste mixer, planetary mill, and 3 roll mill, and the aluminum is processed through the final process of filtering and degassing. It is made into a paste.

In addition, the present invention provides a solar cell electrode produced by printing, drying and baking the paste composition for forming a solar cell electrode on a substrate.

Except for using the solar cell electrode forming paste in the method for forming a solar cell electrode of the present invention, the substrate, printing, drying and firing is a matter of course can be used commonly used in the manufacture of solar cells. In the present invention, the electrode may be a back electrode of a silicon solar cell, the printing may be screen printing, the drying may be made at 90 to 250 ℃, the firing may be made at 600 to 950 ℃. Preferably, the high-temperature / high speed firing is performed at 800 to 950 ° C., more preferably at 850 to 900 ° C. for 5 seconds to 1 minute, and the printing is preferably performed at a thickness of 20 to 60 μm. . As a specific example, the content of Unexamined-Japanese-Patent No. 10-2006-0108550, 10-2006-0127813, Unexamined-Japanese-Patent No. 2001-202822, and 2003-133567 can be illustrated, and this is the said patent document. All content disclosed in is cited as the content of the specification of this invention.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. Since the embodiments herein are only for the detailed description of the invention, it is clear that there is no intention to limit the scope by this.

Example 1

A paste composition was prepared using 65 g (65 wt%) of aluminum powder, 5 g (5 wt%) of inorganic filler CoNiTiZn oxide, and 26 g (26 wt%) of organic vehicle.

Example 2

A paste composition was prepared in the same manner as in Example 1, except that 2 g (2 wt%) of CoNiTiZn-based oxide inorganic filler was used.

Example 3

A paste composition was prepared in the same manner as in Example 1, except that 3 g (3 wt%) of CoNiTiZn-based oxide inorganic filler was used.

Example 4

A paste composition was prepared in the same manner as in Example 1 except that 1 g (1 wt%) of CoNiTiZn-based oxide inorganic filler was used.

Example 5

A paste composition was prepared in the same manner as in Example 1 except that 2 g (2 wt%) of CoAlTi-based oxide inorganic filler was used.

Example 6

A paste composition was prepared in the same manner as in Example 1 except that 3 g (3 wt%) of CoAlTi-based oxide inorganic filler was used.

Example 7

A paste composition was prepared in the same manner as in Example 1 except that 1 g (1 wt%) of Fe-based oxide inorganic filler was used.

Example 8

A paste composition was prepared in the same manner as in Example 1 except that 2 g (2 wt%) of Fe-based oxide inorganic filler was used.

Example 9

A paste composition was prepared in the same manner as in Example 1 except that 3 g (3 wt%) of an Fe-based oxide inorganic filler was used.

Comparative example

Except not using an inorganic filler, all of the paste composition was prepared in the same manner as in Example 1.

Experimental Example

The paste compositions of Examples 1 to 9 and Comparative Examples were screen printed on a silicon wafer, dried at about 160 ° C., and then rapidly heated to about 850 ° C. with IR rapid heat treatment to prepare a solar cell back electrode.

The produced solar cell back electrode was tested for performance and efficiency, and the results were shown in Tables 1 and 2 below.

The efficiency characteristic refers to the light conversion efficiency after fabricating the cell. The short current (ISC) is a current flowing in the absence of resistance, and the short circuit current, Voc, is an open voltage measured by opening the electrode terminal, Fill factor (FF) is the fill factor, which is the ratio of the actual output value to the maximum solar cell output.

The light conversion efficiency described above was measured using a solar simulator, and surface resistance and BSF resistance were measured using a 4-point probe. In addition, in case of whip characteristics, the bending characteristics of the center of dial gauge were measured.

As shown in Table 1, in the case of the bending property, it can be seen that the embodiments of the present invention exhibited more improved properties than the comparative example without the addition of the metal oxide inorganic filler, and the increase in the content of each inorganic filler further improved the bending property. Can be.

The conductivity characteristics were all satisfactory at the baseline value of 15 mΩ / sq or more.

As a result of measuring the final efficiency, when the 1 wt% of CoNiTiZn-based oxide was added, it was found that the efficiency characteristic was increased by 1.02 times than that of the other case.

In addition, the examples in which the inorganic filler was added had better BSF characteristics than those in the comparative example. The thicker BSF layer prevents electron recombination and the BSF layer acts as a reflector to enhance photoelectric efficiency.

Claims (10)

A paste composition for forming a solar cell electrode comprising aluminum powder, glass frit, and an organic vehicle, the paste composition for forming a solar cell electrode further comprising an inorganic filler. The paste composition of claim 1, wherein the inorganic filler is one selected from FeCr, CoAl, CoAlTi, CoCrAl, CoAl, MnSbTi, FeZnTi, and CoNiZnTi, or a combination of two or more thereof. . The paste composition of claim 1, wherein the inorganic filler is included in an amount of 1 to 10 wt% based on the total composition. The method of claim 1, wherein the aluminum powder, the spherical aluminum powder having a particle diameter of 0.1 ~ 2 ㎛, and the spherical aluminum powder having a particle diameter of 0.5 ~ 20 ㎛ mixed; Or the paste composition for forming a solar cell electrode, characterized in that the plate-shaped aluminum powder having an average length of 20 to 50 ㎛ in both sides of the mixed powder selectively mixed. According to claim 1, wherein the aluminum powder, the spherical aluminum powder having a particle size of 0.1 ~ 2 ㎛ 34 ~ 50% by weight relative to the total aluminum powder; Spherical aluminum powder having a particle diameter of 0.5 to 20 µm is 17 to 50% by weight relative to the total aluminum powder; And a plate-shaped aluminum powder having an average length of 20 to 50 μm on both sides of the horizontal and vertical sides is 0 to 10 wt% of the paste composition for forming a solar cell electrode. The glass frit according to claim 1, wherein the glass frit is PbO-SiO ₂ -based, PbO-SiO ₂ -B ₂ O ₃ -based, ZnO-SiO ₂ -based, ZnO-B ₂ O ₃ -SiO ₂ -based, and Bi ₂ O _3- Paste composition for forming a solar cell electrode, characterized in that at least one selected from the B ₂ O ₃ -ZnO-SiO ₂ system. The paste composition of claim 1, wherein the glass frit is included in an amount of 1 to 10 wt% based on the total composition. The paste composition of claim 1, wherein the organic vehicle contains 20 to 30 wt% of the total composition. The solar cell electrode manufactured using the paste composition of any one of Claims 1-8. The solar cell electrode of claim 9, wherein the electrode is a back electrode.