KR20130043263A - Aluminium paste composition and solar cell device using the same - Google Patents

Abstract

The present invention relates to an aluminum paste composition and a solar cell device using the same, and more particularly, an aluminum powder having an average particle diameter of 3 to 6 μm; PbO-based glass frits containing BaO; And an organic vehicle, which minimizes the gap between the aluminum paste layer and the silicon wafer substrate after printing and drying, increases the filling rate, suppresses the occurrence of bumps on the surface during firing, and has excellent appearance and warpage phenomenon of the silicon wafer substrate. The present invention relates to an aluminum paste composition capable of increasing the maximum output current (Isc) of the solar cell device and securing improved efficiency as well as the solar cell device using the same.

Description

Aluminum paste composition and solar cell device using same {ALUMINIUM PASTE COMPOSITION AND SOLAR CELL DEVICE USING THE SAME}

The present invention relates to an aluminum paste composition and a solar cell device using the same, which can produce an electrode having excellent appearance and improved efficiency by suppressing occurrence of bumps on a surface during firing.

Solar cells, which are rapidly spreading in recent years, are electronic devices that directly convert solar energy, which is clean energy, into electricity as a next generation energy source.

In the solar cell element, as shown in FIG. 1, the N + layer 20, the antireflection film 30, and the front electrode 40 are formed on the light receiving surface side of the silicon wafer substrate 10, and the light receiving of the substrate 10 is performed. The P + layer 50 and the back electrode 60 are formed on the opposite side of the surface side. When sunlight shines on a solar cell device having such a structure, electrons (-) and holes (+) are generated inside, and the generated electrons (-) are N + layers 20 and holes (+) are P + layers 50. Will move to each. Due to this phenomenon, a potential difference is generated between the P + layer 50 and the N + layer 20. At this time, the solar energy is converted into electrical energy on the principle that a current is generated when the load is connected.

The back electrode 60 is formed by applying an aluminum paste composition on a silicon wafer substrate 10 having a fine pyramid formed on the surface thereof by screen printing, drying, and baking. As the aluminum is diffused into the silicon wafer substrate 10 during firing, an Al—Si alloy layer is formed between the back electrode 60 and the substrate 10 and a P + layer 50 is formed by diffusion of aluminum atoms. . The P + layer 50 acts as a back surface field (BSF) that prevents recombination of electrons and improves the collection efficiency of product carriers, and also serves as a reflector reflecting long wavelength light of sunlight.

The aluminum paste composition for forming the back electrode 60 includes aluminum powder, glass frit, and an organic vehicle. Of these, when the particle size of the aluminum powder, which is a main component, is not controlled, voids are formed between the aluminum paste layer and the substrate, and the filling rate is low, thereby causing bumps and bubbles. In addition, glass frit, which is a component for further strengthening the bond with the silicon wafer substrate 10, is usually composed of PbO-B ₂ O ₃ -SiO ₂ based, PbO-B ₂ O ₃ -Al ₂ O ₃ based, and PbO as main components. Those containing -B ₂ O ₃ -ZnO-based oxides were mainly used. However, even when the above glass frit is used, bumps tend to occur on the surface after firing, and it is difficult to obtain an electrode having excellent appearance. Accordingly, there is a disadvantage that the efficiency of the solar cell is also reduced.

An object of the present invention is to provide an aluminum paste composition that can suppress the occurrence of bumps on the surface during firing and ensure improved efficiency.

Another object of the present invention is to provide an electrode formed from the aluminum paste composition.

In addition, another object of the present invention is to provide a solar cell device provided with the electrode.

1. aluminum powder with an average particle diameter of 3 to 6 mu m; PbO-based glass frits containing BaO; And an organic vehicle.

2. In the above 1, the aluminum powder is aluminum paste composition containing 60 to 78% by weight.

3. In the above 1, BaO is aluminum paste composition containing 0.1 to 10 mol% in PbO-based glass frit.

4. In the above 1, the PbO-based glass frit is aluminum paste composition PbO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ -TiO ₂ -BaO-based glass frit.

5. In the above 4, PbO-based glass frit is PbO 30 to 60 mol%, Al ₂ O ₃ 1 to 15 mol%, SiO ₂ 20 to 40 mol%, B ₂ O ₃ 10 to 30 mol%, TiO ₂ 0.5 Aluminum paste composition comprising from 5 to 5 mol% and BaO 0.1 to 10 mol%.

6. In the above 1, PbO-based glass frit is contained in aluminum paste composition 0.01 to 5% by weight.

7. The aluminum paste composition of 1 above, wherein the organic vehicle is contained in 20 to 35% by weight.

8. The aluminum paste composition of 1 above, wherein the organic vehicle is a mixture of 1 to 25% by weight of the polymer resin and 75 to 99% by weight of the organic solvent.

9. The electrode formed of the aluminum paste composition of any one of the above 1 to 8.

10. Solar cell device provided with the electrode of the above 9.

The aluminum paste composition according to the present invention minimizes the voids between the aluminum paste layer and the silicon wafer substrate after printing and drying, increases the filling rate, suppresses the occurrence of bumps on the surface during firing, and has excellent appearance and warpage of the silicon wafer substrate. Even fewer electrodes can be provided. Through this, it is possible to increase the maximum output current (Isc) of the solar cell element and also to improve the efficiency.

1 is a diagram schematically illustrating a cross-sectional view of a solar cell element.

The present invention relates to an aluminum paste composition and a solar cell device using the same.

Hereinafter, the present invention will be described in detail.

Aluminum paste composition of the present invention is an aluminum powder having an average particle diameter of 3 to 6㎛; PbO-based glass frits containing BaO; And an organic vehicle.

Aluminum powder is a conductive metal that is the main component of the paste composition for forming the back electrode.

The silicon wafer substrate for forming the back electrode has a structure in which fine pyramids are formed on the surface by texturing both surfaces to increase the light receiving area of sunlight. Normally formed fine pyramids have a height of 2-15 μm and a width of 2-20 μm, and have an irregular maze shape. On the silicon wafer substrate having such a surface structure, the aluminum paste composition is printed by a method such as screen printing, gravure printing, or offset printing, dried, and then baked to form a back electrode. At this time, when the particle size of the aluminum powder is too large, the aluminum paste composition and the silicon wafer substrate are not in contact well, and voids are formed between them after printing and drying. These pores are ejected to the surface through the aluminum paste layer during the firing process, which results in aluminum bumps and bubbles. In consideration of this point, the present invention is characterized by selectively using an average particle size of 3 to 6㎛ as aluminum powder. If the average particle size is less than 3㎛ the thermal stability during firing may cause bumps and warp of the substrate, if the average particle size is more than 6㎛ may reduce the filling rate between the aluminum layer and the substrate to reduce the efficiency of the solar cell device Can be.

Aluminum powder is preferably included in 60 to 78% by weight in 100% by weight of the total amount of aluminum paste composition. If the content is less than 60% by weight, the thickness of the printed aluminum rear electrode after firing becomes thin so that the back field (BSF) may not be sufficiently formed and the efficiency may be lowered. When the content is more than 78% by weight, the thickness of the silicon wafer substrate is too thick. May cause warpage.

In the present invention, the glass frit is characterized by using a PbO-based oxide containing a BaO component. This glass frit has the advantages of easy melting point control and low coefficient of thermal expansion. In particular, the glass frit suppresses the occurrence of bumps on the surface during firing, thereby improving the appearance and minimizing the warpage of the silicon wafer substrate.

The glass frit may contain 0.1 to 10 mol% of BaO component, preferably 0.5 to 7 mol%, more preferably 1 to 5 mol%. If the content is less than 0.5 mol%, it is difficult to sufficiently suppress the generation of bumps on the electrode surface after firing, and if the content is more than 10 mol%, the thermal expansion coefficient may be large to cause warpage of the silicon wafer substrate.

The glass frit is preferably a PbO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ -TiO ₂ -BaO-based oxide, more preferably 30 to 60 mol% of PbO, 1 to 15 mol% of Al ₂ O ₃ , 20 to 40 mol% of SiO ₂ , 10 to 30 mol% of B ₂ O ₃ , 0.5 to 5 mol% of TiO ₂ , and 0.1 to 10 mol% of BaO may be included.

Further, the glass frit may contain 0 to 10 mol% of alkali metal oxides such as K ₂ O, Na ₂ O, Li ₂ O, and the like; 0-10 mol% of alkaline earth metal oxides, such as MgO, CaO, and SrO; ZnO 0-15 mol%; V ₂ O ₅ 0-10 mole%; P ₂ O ₅ 0 To 10 mol% may be further included.

The glass transition temperature (Tg) of the glass frit is adjustable according to the type of the constituents and their content, and may be, for example, 350 to 500 ° C.

The glass frit is preferably contained in an amount of 0.01 to 5% by weight, more preferably 0.05 to 4% by weight in 100% by weight of the total content of the aluminum paste composition. If the content is less than 0.01% by weight, the adhesion between the aluminum back electrode and the silicon wafer substrate may be reduced after firing. If the content is more than 5% by weight, the warpage of the silicon wafer substrate may increase and the resistance may increase, thereby reducing the efficiency of the solar cell device. Can be.

The organic vehicle is a component for imparting consistency and rheological properties suitable for printing to the aluminum paste composition, and may be a solution in which a polymer resin and various additives are dissolved in an organic solvent as necessary.

The organic vehicle may be a mixture of 75 to 99% by weight of the organic solvent and 1 to 25% by weight of the polymer resin, and may be a mixture of 1 to 10% by weight of the additive.

As the organic solvent, a known one may be used, and a solvent having a boiling point of 150 to 300 ° C. may be used to prevent drying of the paste composition and control fluidity during the printing process. Specifically, tripropylene glycol methyl ether, tripropylene glycol n-butyl ether, dipropylene glycol n-propyl ether, dipropylene glycol n-butyl ether, propylene glycol phenyl ether, diethylene glycol ethyl ether, diethylene glycol n-butyl Ether, diethylene glycol hexyl ether, ethylene glycol hexyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol n-butyl ether, ethylene glycol phenyl ether, ethylene glycol, terpineol, butyl carbitol, butyl Carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (texanol), and the like, and these may be used alone or in combination of two or more thereof.

The organic solvent is preferably included in 75 to 99% by weight relative to 100% by weight of the total amount of the organic vehicle. In this content range, optimum fluidity can be imparted to the paste composition.

As the polymer resin, known ones can be used, for example ethyl cellulose, nitrocellulose, hydroxypropyl cellulose, phenol, acryl, rosin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyvinyl butyral, urea, xyl Ethylene, alkyd, unsaturated polyester, polyimide, furan, urethane, isocyanate, cyanate, polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene (ABS), polymethylmethacrylate, polyvinyl chloride, polychloride Vinylidene, polyvinylacetate, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene oxide, polysulfone, polyimide, polyether sulfone, polyarylate, polyether ether ketone, silicone Resin, such as these, can be mentioned. These can be used individually or in mixture of 2 or more types.

The polymer resin may be included in an amount of 1 to 25% by weight, preferably 5 to 25% by weight, based on 100% by weight of the total amount of the organic vehicle. When the content is less than 1% by weight, the printability and dispersion stability of the paste composition may be lowered, and when the content is more than 25% by weight, the paste composition may not be printed.

The organic vehicle may further comprise a dispersant as an additive together with the above components.

As the dispersant, a known surfactant can be used, for example, polyoxyethylene alkyl ether having 6 to 30 carbon atoms in the alkyl group, polyoxyethylene alkyl aryl ether having 6 to 30 carbon atoms in the alkyl group, and 6 to 30 carbon atoms in the alkyl group. Ethers such as polyoxyethylene-polyoxypropylene alkyl ether; Ester ethers such as glycerin ester addition polyoxyethylene ether, sorbitan ester addition polyoxyethylene ether, and sorbitol ester addition polyoxyethylene ether; Esters such as polyethylene glycol fatty acid ester, glycerin ester, sorbitan ester, propylene glycol ester, sugar ester and alkyl polyglucoside; Nitrogen-containing systems such as fatty acid alkanolamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine having 6 to 30 carbon atoms of an alkyl group, and amine oxide; And high molecular compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylic acid-maleic acid copolymer, and poly12-hydroxystearic acid. Commercially available products include Hypermer KD (Uniqema), AKM 0531 (Japan Oil Holding Co., Ltd.), KP (Shin-Etsu Chemical Co., Ltd.), POLYFLOW (Kyoeisha Chemical Co., Ltd.), EFTOP (Tochem Products), Asahi guard (Asahi Glass, Inc.), Suflon (Asahi Glass, Inc.), SOLSPERSE (Genekka), EFKA (EFKA Chemicals, Inc.) ), PB 821 (Ajinomoto Co., Ltd.), BYK-184, BYK-185, BYK-2160, Anti-Terra U (manufactured by BYK), and the like can also be used. These can be used individually or in mixture of 2 or more types.

The dispersant may be included in an amount of 1 to 10% by weight, preferably 1 to 5% by weight, based on 100% by weight of the total amount of the organic vehicle.

The organic vehicle may further include additives such as thixotropic agents, wetting agents, antioxidants, corrosion inhibitors, antifoaming agents, thickeners, dispersants, tackifiers, coupling agents, antistatic agents, polymerization inhibitors, and antisettling agents.

The organic vehicle is preferably included in 20 to 35% by weight relative to the total content of aluminum paste composition 100% by weight. If the content is less than 20% by weight, the viscosity of the aluminum paste composition may be too high to reduce fluidity and printability.When the content is more than 35% by weight, it is difficult to secure a sufficient thickness of the paste layer due to the relatively low content of aluminum powder. .

The aluminum paste composition including the components as described above may minimize the voids between the aluminum paste layer and the silicon wafer substrate and increase the filling rate after printing and drying, and may suppress the occurrence of bumps on the surface during firing.

The present invention provides an electrode formed from the aluminum paste composition.

The electrode is formed through a process of printing, drying, and firing an aluminum paste composition on a substrate such as a silicon wafer substrate on which an Ag front electrode is formed. The printing method is not particularly limited, and for example, screen printing, gravure printing, offset printing or the like can be used. Drying may be carried out at 60 to 300 ° C. for several seconds to several minutes, and firing may be performed at 600 to 950 ° C. for several seconds.

The electrode formed as described above is applied to the rear electrode of the solar cell element, thereby increasing the maximum output current Isc of the solar cell element and securing improved efficiency.

The present invention provides a solar cell device provided with an electrode formed from the aluminum paste composition.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but these examples are merely illustrative of the present invention and are not intended to limit the scope of the appended claims. It is apparent to those skilled in the art that various changes and modifications can be made to the present invention, and such modifications and changes belong to the appended claims.

Example

Manufacturing example  1-3. Glass Frit Preparation of I-III

Glass frit was prepared with the components and contents shown in Table 1 below.

division designation Component (mol%) Coefficient of thermal expansion
(10 ^-7 / ℃) Tg
(℃) PbO Al ₂ O ₃ SiO ₂ B ₂ O ₃ TiO ₂ BaO Preparation Example 1 I 46 3.3 25.3 22.4 1.5 1.5 76 406

Example  One

74 weight% of aluminum powder having an average particle size of 3.2 μm, 3 weight% of glass frit I of Preparation Example 1, 23 weight% of an organic vehicle in which hydroxypropyl cellulose resin was dissolved in butyl carbitol were added, followed by simultaneous rotation and revolution. An aluminum paste composition was prepared by stirring at 1,000 rpm for 3 minutes using a mixer.

Example  2-3, Comparative example  1-5

The same procedure as in Example 1, except that the ingredients and contents as shown in Table 2 were used. At this time, the content represents weight%.

division Aluminum powder Glass frit Organic vehicle Average particle size (㎛) content Kinds content Example 1 3.2 74 I 3 23 Example 2 4.6 74 I 3 23 Example 3 5.8 74 I 3 23 Comparative Example 1 0.9 74 I 3 23 Comparative Example 2 1.5 74 I 3 23 Comparative Example 3 9.3 74 I 3 23 Comparative Example 4 2.6 74 I 3 23 Comparative Example 5 6.5 74 I 3 23

Test Example

The physical properties of the aluminum paste compositions prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 3 below.

Print and dry bus bars with silver paste composition on the back side of single crystal silicon wafer substrates with a size of 156 mm x 156 mm, thickness 200 m and pyramid structure of about 4-6 m in height by texturing process I was. Thereafter, the prepared aluminum paste composition was applied and dried using a 250 mesh screen printing plate. At this time, the coating amount was set to 1.5 ± 0.1g before drying. The finger lines were then printed and dried using silver paste on the front SiNx side. The substrate subjected to the above process was fired for about 10 seconds in an infrared continuous kiln having a temperature of 720-900 ° C. The firing process is carried out by simultaneous firing front and back while passing the silicon wafer substrate into a belt furnace comprising a burn-out section of about 600 ° C. and a firing section of 800-950 ° C. After removing the organic material in the paste, the aluminum was melted to form an electrode, thereby manufacturing a solar cell device.

(One) Bump  Count

Bumps and aluminum bubbles generated on the rear aluminum electrode portions of the manufactured solar cell elements were visually observed and the number thereof was measured.

(2) deflection (mm)

The manufactured solar cell device was placed on a flat bottom and four corners were aligned with the bottom, and then the degree of lifting of the center part was measured. Usually, when warping is 1.50 mm or less, it is regarded as a good level.

(3) Efficiency (%)

The efficiency of the manufactured solar cell device was evaluated using an evaluation device (SCM-1000, FitTech).

division Number of bumps () Deflection (mm) efficiency(%) Example 1 0 1.30 17.45 Example 2 0 1.25 17.53 Example 3 0 1.37 17.51 Comparative Example 1 8-13 1.80 17.39 Comparative Example 2 5-9 1.76 17.40 Comparative Example 3 2-5 1.45 17.46 Comparative Example 4 1-3 1.49 17.47 Comparative Example 5 1-2 1.51 17.49

As shown in Table 3, the electrode formed by using the aluminum paste composition of Examples 1 to 3 containing a PbO-based glass frit containing BaO and using an aluminum powder having an average particle diameter of 3 to 6㎛ according to the present invention is The occurrence of bumps on the surface is suppressed and the amount of warpage is small, so that the appearance is excellent and the efficiency is high when applied to solar cell devices.

On the other hand, the electrode formed by using the aluminum paste composition of Comparative Examples 1 to 5 using an aluminum powder whose average particle diameter does not fall within the scope of the present invention was difficult to generate bumps and to satisfy both warpage and efficiency characteristics. In particular, the smaller the average particle diameter, the more bumps occurred and the larger the warpage phenomenon.

10: silicon wafer substrate 20: N + layer
30: antireflection film 40: front electrode
50: P + layer 60: rear electrode

Claims (10)

Aluminum powder having an average particle diameter of 3 to 6 µm;
PbO-based glass frits containing BaO; And
An aluminum paste composition comprising an organic vehicle.
The aluminum paste composition of claim 1, wherein the aluminum powder is included in an amount of 60 to 78 wt%.
The aluminum paste composition of claim 1, wherein BaO is included in an amount of 0.1 to 10 mol% in the PbO-based glass frit.
The aluminum paste composition of claim 1, wherein the PbO-based glass frit is PbO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ -TiO ₂ -BaO-based glass frit.
The method according to claim 4, PbO-based glass frit is 30 to 60 mol% PbO, 1 to 15 mol% Al ₂ O ₃ , 20 to 40 mol% SiO ₂ , 10 to 30 mol% B ₂ O ₃ , 0.5 to 5 TiO ₂ An aluminum paste composition comprising mol% and 0.1-10 mol% BaO.
The aluminum paste composition of claim 1, wherein the PbO-based glass frit is included in an amount of 0.01 to 5 wt%.
The aluminum paste composition of claim 1, wherein the organic vehicle is included in an amount of 20 to 35 wt%.
The aluminum paste composition of claim 1, wherein the organic vehicle is a mixture of 1 to 25% by weight of the polymer resin and 75 to 99% by weight of the organic solvent.
Electrode formed from the aluminum paste composition of any one of Claims 1-8.
Solar cell device provided with an electrode of claim 9.

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