KR101711149B1 - Aluminium paste composition and solar cell device using the same - Google Patents

Abstract

The present invention is an aluminum paste composition and as it relates to a solar cell element using the same, more particularly to prevent the reaction with the moisture by being optimized to a content of _{Bi 2 O 3, B 2 O} 3, ZnO and SiO ₂ satisfies a specific condition To an environmentally friendly aluminum paste composition and a solar cell device using the same.

Description

TECHNICAL FIELD [0001] The present invention relates to an aluminum paste composition, and a solar cell device using the same. BACKGROUND ART [0002]

The present invention relates to an aluminum paste composition which is environmentally friendly and excellent in water resistance to improve durability of a solar cell element and to suppress damage to an electrode, and a solar cell element using the same.

Solar cells, which are rapidly spreading in recent years, are next-generation energy sources, and are electronic devices that convert solar energy, which is clean energy, directly to electricity.

1, an N + layer 20, an antireflection film 30, and a front electrode 40 are formed on the light receiving surface side of the silicon wafer substrate 10, and the opposite side of the substrate 10 And a P + layer 50 and a rear electrode 60 are formed on the surface. When electrons (-) and electrons (-) are generated in the inside of the solar cell element having such a structure, the N + layer 20 and the P + layer 50 are generated. Respectively. Due to this phenomenon, a potential difference occurs between the P + layer 50 and the N + layer 20. At this time, when the load is connected, a current is generated, and solar energy is converted into electric energy.

The rear electrode 60 is formed by applying an aluminum paste composition by screen printing or the like, and drying and firing the aluminum paste composition. When aluminum is diffused into the silicon wafer substrate 10 during firing, the rear electrode 60 and the substrate 10, An Al-Si alloy layer is formed and a P + layer 50 is formed by diffusion of aluminum atoms. The P + layer 50 not only functions as a back surface field (BSF) for preventing recombination of electrons and improving the collection efficiency of generated carriers, but also serves as a reflector for reflecting long wavelength light of sunlight.

The aluminum paste composition for forming such a backside electrode 60 comprises aluminum powder, glass frit and an organic vehicle. Among these, glass frit is a component for further strengthening bonding with the silicon wafer substrate 10, and is usually composed mainly of PbO-B ₂ O ₃ -SiO ₂ system, PbO-B ₂ O ₃ -Al ₂ O ₃ system, PbO- B ₂ O ₃ -ZnO-based oxide.

In recent years, it has been proposed that Bi ₂ O ₃ -based oxides having properties similar to those of the PbO-based oxide are included without containing PbO components due to environmental problems (Korean Patent Publication No. 2008-0104179, Korean Patent No. 0890866 ). However, the glass frit contains the Bi ₂ O ₃ component when the flew the softening point is low, less than 500 ℃ contains the Bi ₂ O ₃ component is too much by thermal etching of the aluminum powder, the surface of the layer of aluminum oxide to increase the moisture and reactive and , Which causes a disadvantage that the durability of the solar cell element itself is significantly lowered. Accordingly, the reactivity between the Bi ₂ O ₃ component and the aluminum oxide film can be lowered by forming the softening point at 500 ° C. or higher. However, since the work is performed at various process temperatures, it is inevitable to use a glass frit having a low softening point.

The present invention relates to an aluminum paste composition which does not contain a PbO component and is eco-friendly and at the same time can optimize the content ratio of Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ components to prevent reaction with moisture by thermal etching The purpose is to provide.

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

It is another object of the present invention to provide a solar cell element having the electrode.

1. An aluminum paste composition comprising glass frit which satisfies the following equations (1) and (2):

2. The aluminum paste composition according to 1 above, wherein the glass frit contains 1-40 mol% of Bi ₂ O ₃ , 1-50 mol% of B ₂ O ₃ , 0-70 mol% of ZnO and 0.1-45 mol% of SiO ₂ .

3. The aluminum paste composition according to 2 above, wherein the glass frit further contains at least one selected from the group consisting of Al ₂ O ₃ , an alkali metal oxide and an alkaline earth metal oxide.

4. The aluminum paste composition of 3 above, wherein the glass frit has a softening point of at least 300 캜 and less than 500 캜.

5. The composition of claim 1, wherein the aluminum powder is 65-75 wt%; 0.01-5% by weight of glass frit; And 20-34.9% by weight of an organic vehicle.

6. The aluminum paste composition of claim 5, wherein the aluminum powder is a mixture of 60-95 wt.% Powder having an average particle size of 4-6 μm and 5-40 wt.% Powder having an average particle size of 2-4 μm.

7. The aluminum paste composition according to 5 above, wherein the organic vehicle is a mixture of 1-25% by weight of a polymer resin and 75-99% by weight of an organic solvent.

8. An electrode formed from an aluminum paste composition according to any one of claims 1 to 7.

9. A solar cell element comprising the above eight electrodes.

The aluminum paste composition according to the present invention is eco-friendly because it contains no PbO component which is restricted by its use due to environmental problems, and contains Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ at an optimum content ratio, The thermal etchability is lowered and the reaction with moisture can be prevented. Through this, it is possible to enhance the durability of the solar cell element itself, suppress damage of the electrode, increase the maximum output current Isc, and improve the efficiency.

1 is a diagram schematically showing a sectional view of a solar cell element,
2 is a graph showing the water resistance of the solar cell element manufactured in Example 1 of the present invention,
3 is a graph showing the water resistance of the solar cell element manufactured in Comparative Example 1,
4 is a graph showing the efficiency measurement result of the solar cell device manufactured in Example 1 of the present invention.

The present invention relates to an aluminum paste composition which is environmentally friendly and excellent in water resistance, and a solar cell device using the same.

Hereinafter, the present invention will be described in detail.

The aluminum paste composition of the present invention comprises aluminum powder; Glass frit; And an organic vehicle, in particular, for optimizing the content of constituents of the glass frit.

More specifically, the glass frit is characterized by simultaneously satisfying the following conditions (1) and (2):

[Equation 1]

&Quot; (2) "

.

The aluminum powder is preferably a conductive metal as a main component of the paste composition for forming the rear electrode, and it is preferable to use two kinds of mixed powders having different average particle sizes.

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 in order to increase the light receiving area of sunlight. Usually, the height of the fine pyramid formed is 2-15 탆, the width is 2-20 탆, and it shows an irregular maze shape. The aluminum paste composition is printed on a silicon wafer substrate having such a surface structure by a method such as screen printing, gravure printing, or offset printing, followed by drying and baking to form a rear 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 with each other, and voids are formed between the aluminum paste composition and the silicon wafer substrate after printing and drying. These voids are ejected through the aluminum paste layer during the firing process, resulting in aluminum bumps and bubbles. Therefore, it is preferable to minimize the size of the pores by mixing two kinds of aluminum powders having different average particle sizes.

The aluminum powder is preferably a mixture of 60-95 wt% powder having an average particle size of 4-6 탆 and 5-40 wt% powder having an average particle size of 2-4 탆. Powders having an average particle size of 4-6 μm suppress the shrinkage of the silicon wafer substrate after firing to enable the formation of a high-density low-shrinkable electrode. Powders having an average particle size of 2-4 μm serve as a binder between aluminum powders Allowing the paste to penetrate deeply and evenly onto the textured surface of the substrate. In this case, the porosity between the substrate and the paste is reduced, the rear electric field (BSF) is uniformly formed, the resistance of the rear electrode is lowered, and the warpage of the substrate is also suppressed. Therefore, the maximum output current Isc of the solar cell device can be increased and the efficiency can be increased, and the yellowing phenomenon occurring in the rear electrode after the firing process can be prevented.

The aluminum powder is preferably contained in an amount of 65 to 75% by weight based on 100% by weight of the aluminum paste composition. When the content is less than 65 wt%, the thickness of the aluminum back electrode printed after baking becomes thin, the back electric field (BSF) is not sufficiently formed and the efficiency may be lowered. When the content exceeds 75 wt%, the printing thickness becomes too thick, Which may result in warpage.

In the present invention, glass frit containing Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ is used, and its content is optimized so as to satisfy the following equations (1) and (2) simultaneously:

[Equation 1]

&Quot; (2) "

.

In general, glass frit containing a PbO component is easy to control the melting point and has a low thermal expansion coefficient. However, its use is limited due to environmental problems, and a glass frit containing a Bi ₂ O ₃ component having similar properties has a softening point of 500 ° C., the reactivity of the glass frit component melted in the liquid firing process becomes excessively large, so that the aluminum powder reacts with the aluminum oxide layer on the surface of the aluminum powder to lower the water resistance of the aluminum electrode, and as a result, the durability of the solar cell element tends to be deteriorated. As a result, the reactivity between the Bi ₂ O ₃ component and the aluminum oxide layer can be lowered by setting the softening point to be 500 ° C. or higher. However, since the work is performed at various process temperatures, it is inevitable to use a glass frit having a low softening point .

In consideration of this point, the present invention is characterized in that the content of Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ components contained in the glass frit is optimized to control the reactivity of the aluminum powder with the oxide film. The Bi ₂ O ₃ component should be contained in a content which satisfies the formula (1) with respect to the total content of the B ₂ O ₃ , ZnO and SiO ₂ components which are the network forming agents as the components which have the greatest influence on the etching of the aluminum oxide. At the same time, the total content of the B ₂ O ₃ and ZnO components, which are stabilizers among the network forming agents B ₂ O ₃ , ZnO and SiO ₂ , should be contained in an amount satisfying the formula (2) with respect to the content of the SiO ₂ component.

The range of the content of Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ components contained in the glass frit is not particularly limited as long as it satisfies the conditions of the formulas (1) and (2) simultaneously. For example, it may be contained in an amount of 1-40 mol% of Bi ₂ O ₃ , 1-50 mol% of B ₂ O ₃ , 0-70 mol% of ZnO and 0.1-45 mol% of SiO ₂ based on 100 mol% of the total glass frit.

The glass frit is made of Al ₂ O ₃ ; At least one alkali metal oxide selected from the group consisting of K ₂ O, Na ₂ O, and Li ₂ O; MgO, CaO, SrO, and BaO, and the like, and they may be contained alone or in a mixture of two or more. At this time, Al ₂ O ₃ may be contained in an amount of from ₁ to 20 mol%, alkali metal oxide in an amount of from ₂ to 10 mol%, and alkaline earth metal oxide in an amount of from ₂ to 10 mol% based on 100 mol% of the total glass frit.

The glass frit has a softening point of less than 500 캜, preferably 300 캜 Or more and less than 500 ° C.

The glass frit is preferably contained in an amount of 0.01-5% by weight, more preferably 0.5-5% by weight, based on 100% by weight of the total content of the aluminum paste composition. If the content is less than 0.01% by weight, adhesion between the aluminum back electrode and the silicon wafer substrate may be deteriorated after firing. If the content is more than 5% by weight, the resistance may increase and the efficiency of the solar cell device may be deteriorated.

The glass frit containing such a component does not contain a PbO component and is eco-friendly, and at the same time, the content of Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ components is optimized and the softening point is less than 500 ° C., Lt; 0 > C, it is possible to effectively prevent deterioration of the water resistance by thermal etching.

The organic vehicle may be a solution for imparting viscoelasticity and rheological properties suitable for printing on an aluminum paste composition, and may be a solution in which a polymer resin and various additives are dissolved in an organic solvent.

The organic vehicle may be a mixture of 75-99% by weight of an organic solvent and 1-25% by weight of a polymer resin, and may further contain 1-15% by weight of an additive.

As the organic solvent, a known solvent may be used, and a solvent having a boiling point of 150-300 DEG C may be used so as to prevent the paste composition from drying and control the flowability during the printing process. Specific examples thereof include 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- But are not limited to, 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, Carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (texanol), etc. These may be used alone or in admixture of two or more.

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

As the polymer resin, those known can be used, and examples thereof include ethylcellulose, nitrocellulose, phenol, acrylic, rosin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyvinylbutyral, urea, xylene, alkyd, unsaturated Butadiene-styrene (ABS), polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinylidene chloride, polyvinylidene chloride, polyvinylidene chloride, polyvinylidene chloride, A resin such as acetates, polyacetals, polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyphenylene oxides, polysulfones, polyimides, polyether sulfone, polyarylates, polyether ether ketones, . These may be used alone or in combination of two or more.

The polymer resin may be contained in an amount of 1-25% by weight, preferably 5-25% by weight based on 100% by weight of the total amount of the organic vehicle. If the content is less than 1% by weight, the printing property and dispersion stability of the paste composition may be deteriorated, and if more than 25% by weight, the paste composition may not be printed.

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

As the dispersing agent, known surfactants can be used. Examples thereof include polyoxyethylene alkyl ethers having 6 to 30 carbon atoms in the alkyl group, polyoxyethylene alkylaryl ethers having 6 to 30 carbon atoms in the alkyl group, Ether type such as polyoxyethylene-polyoxypropylene alkyl ether; Ester ethers such as glycerin ester addition type polyoxyethylene ether, sorbitan ester addition type polyoxyethylene ether and sorbitol ester addition type polyoxyethylene ether; Esters such as polyethylene glycol fatty acid esters, glycerin esters, sorbitan esters, propylene glycol esters, sugar esters and alkylpolyglucosides; Nitrogen-containing systems such as fatty acid alkanolamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine having 6 to 30 carbon atoms in the alkyl group, and amine oxide; And polymeric compounds such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, polyacrylic acid-maleic acid copolymer, and poly 12-hydroxystearic acid. Also, commercially available products such as hypermer KD (Uniqema), AKM 0531 (Nippon Kayaku Co., Ltd.), KP (Shinetsugaku Kagaku Co., Ltd.), POLYFLOW (Kyoeisha Chemical Co., Ltd.) Asahi guard (Asahi Glass Co.), Surflon (Asahi Glass Co., Ltd.), SOLSPERSE (Geneka Co., Ltd.), EFKA (EFKA Chemical Co., Ltd.) ), PB 821 (Ajinomoto Co., Ltd.), BYK-184, BYK-185, BYK-2160 and Anti-Terra U (manufactured by BYK). These may be used alone or in combination of two or more.

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

The organic vehicle may further contain additives such as a thixotropic agent, a humectant, an antioxidant, a corrosion inhibitor, a defoamer, a thickener, a dispersant, a tackifier, a coupling agent, an antistatic agent, a polymerization inhibitor and a sedimentation inhibitor.

The organic vehicle is preferably included in an amount of 20-34.9% by weight based on 100% by weight of the total content of the aluminum paste composition. When the content is less than 20% by weight, the viscosity of the aluminum paste composition becomes too high, and the fluidity is deteriorated and the printing property may be deteriorated. When the content exceeds 34.9% by weight, the content of aluminum powder is relatively decreased, it's difficult.

The aluminum paste composition containing the above components is not only environmentally friendly because it does not contain a PbO ingredient that is restricted by its use due to environmental problems, but also optimizes the content of Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ And deterioration of the water resistance can be prevented.

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

The electrode is formed through a process of printing and drying and firing an aluminum paste composition on a substrate, for example, 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, and the like can be used. Drying is carried out at 60-300 ° C for a few seconds and firing can be carried out at 600-950 ° C for several seconds.

The electrode thus formed is applied to the back electrode of the solar cell element, thereby improving the durability of the solar cell element, increasing the maximum output current Isc of the solar cell element and increasing the efficiency.

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

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the invention and are not intended to limit the scope of the claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

Example

Production Example 1-6. Preparation of glass frit Ⅰ-Ⅵ

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

division Kinds Component (mol%) Softening point
(° C) Al ₂ O ₃ B ₂ O ₃ BaO Bi ₂ O ₃ CaO SiO ₂ SrO ZnO Production Example 1 Ⅰ 4 42 - 15 8 22 9 - 480 ± 10 Production Example 2 Ⅱ - 34 - 10 - 6 - 50 470 ± 10 Production Example 3 Ⅲ 9 21 - 25 - 30 15 - 470 ± 10 Production Example 4 IV 6 39 - 30 - 20 5 - 460 ± 10 Production Example 5 V 8 35 - 19 - 31 7 - 460 ± 10 Production Example 6 VI 9 15 4 15 - 45 - 12 510 ± 10

Example  One

Aluminum powder having an average particle size of 4-6 占 퐉 and aluminum powder having an average particle size of 2-4 占 퐉 were mixed in a weight ratio of 90:10 by mixing 74 weight% of the mixed powder, 0.5 weight% of the glass frit I of Preparation Example 1, 25.5% by weight of an organic vehicle in which ethylcellulose resin was dissolved in propylene glycol methyl ether was added, and the mixture was stirred at 1,000 rpm for 3 minutes using a mixer that simultaneously performs rotation and revolution to prepare an aluminum paste composition.

Example 2

The same procedure as in Example 1 was carried out except that the glass frit II of Production Example 2 was used.

Comparative Example 1

The same procedure as in Example 1 was carried out except that the glass frit III of Production Example 3 was used.

Comparative Example 2

The glass frit IV of Production Example 4 was used in the same manner as in Example 1 above.

Comparative Example 3

The glass frit V of Production Example 5 was used in the same manner as in Example 1.

Reference Example 1

The same procedure as in Example 1 was carried out except that the glass frit VI of Production Example 6 was used.

Test Example

The 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 2 below.

- Aluminum paste composition on the backside of a monocrystalline silicon wafer substrate having a size of 156 mm x 156 mm and a thickness of 200 microns and a pyramid structure having a height of about 4-6 microns formed by a texturing process was applied to a 250 mesh screen Using a printing plate. At this time, the coating amount was adjusted to 1.4 ± 0.1 g before drying. The coated paste was dried at 200 캜 and then fired in an infrared continuous firing furnace having a temperature of 720 - 900 캜 for about 10 seconds. The firing process is performed by front and back co-firing while passing the silicon wafer substrate through a belt furnace including a burn-out zone at about 600 ° C and a firing zone at 800-950 ° C , Organic materials in the paste were burned off, and aluminum was melted to form an electrode, thereby manufacturing a solar cell device.

(1) Water resistance

The manufactured solar cell element was placed in a thermostatic chamber filled with distilled water at 80 캜 and left for 10 minutes. Whether or not the hydrogen gas was generated by the reaction of the aluminum electrode formed in the thermostatic chamber with water was visually observed and then evaluated based on the following criteria.

<Evaluation Criteria>

○: No bubbles were generated (good).

×: bubble occurred (poor).

(2) Electrode damage

The photovoltaic devices tested in (1) above were visually observed for any phenomena such as peeling or brittleness, and evaluated based on the following criteria.

<Evaluation Criteria>

?: No peeling and no flaking (Good).

X: peeling or blemish (poor).

(3) Efficiency (%)

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

division Equation 1 Equation 2 Water resistance Electrode damage efficiency(%) Example 1 23 ○ 191 ○ ○ ○ 17.8 ± 0.3 Example 2 11 ○ 1400 ○ ○ ○ 17.8 ± 0.3 Comparative Example 1 49 × 70 × × × 17.8 ± 0.3 Comparative Example 2 51 × 195 ○ × × 17.8 ± 0.3 Comparative Example 3 29 ○ 113 × × × 17.8 ± 0.3 Reference Example 1 21 ○ 60 × ○ ○ 17.8 ± 0.3 Formula 1:? When the value is less than 30?,?
(2): &amp; cir &amp; over 150, x

As shown in the above Table 2 and Figs. 2 to 4, according to the present invention, it is possible to use a composition containing Bi ₂ O ₃ , B ₂ O ₃ , ZnO and SiO ₂ components The solar cell device using the aluminum paste composition of Examples 1 and 2 including the glass frit having optimized contents is environmentally friendly and has excellent water resistance even though the softening point is less than 500 ° C. As shown in FIG. 2, There is no reaction such as generation of air bubbles at the interface and there is no peeling or shattering even after the reaction, so that the durability of the solar cell device can be improved. In addition, as shown in FIG. 4, the low Rs value and the stable Rsh value are shown, and the high efficiency of the solar cell is obtained because the high Isc and Voc values have high FF. This shows that the same effect as that in Reference Example 1 in which the softening point is higher than 500 占 폚 is exhibited.

On the other hand, the solar cell devices using the aluminum paste compositions of Comparative Examples 1 to 3 do not satisfy the conditions of Equations 1 and 2 at the same time, and as shown in FIG. 3, by the reaction of moisture and moisture at the interface between the solar cell devices Bubbles were generated and the durability was degraded.

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

Claims (9)

An aluminum paste composition comprising glass frit which satisfies the following equations (1) and (2):
[Equation 1]

&Quot; (2) &quot;

(Bi ₂ O ₃ , B ₂ O ₃ , ZnO, and SiO ₂ in the formulas (1) and (2) represent mol%, respectively). The aluminum paste composition according to claim 1, wherein the glass frit contains 1-40 mol% of Bi ₂ O ₃ , 1-50 mol% of B ₂ O ₃ , 0-70 mol% of ZnO and 0.1-45 mol% of SiO ₂ .
The aluminum paste composition according to claim 2, wherein the glass frit further contains at least one selected from the group consisting of Al ₂ O ₃ , an alkali metal oxide, and an alkaline earth metal oxide.
The aluminum paste composition according to claim 3, wherein the glass frit has a softening point of 300 ° C or more and less than 500 ° C.
The method of claim 1, further comprising: 65-75 wt% aluminum powder; 0.01-5% by weight of glass frit; And 20-34.9% by weight of an organic vehicle.
The aluminum paste composition according to claim 5, wherein the aluminum powder is a mixture of 60-95 wt% powder having an average particle size of 4-6 탆 and 5-40 wt% powder having an average particle size of 2-4 탆.
The aluminum paste composition according to claim 5, wherein the organic vehicle is a mixture of 1-25% by weight of a polymer resin and 75-99% by weight of an organic solvent.
The aluminum paste composition of claim 1, wherein the composition is used to form a backside electrode in contact with a P + layer of a solar cell element.
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