WO2017074149A1 - Electrode paste for solar cell and solar cell prepared by means of same - Google Patents

Abstract

The present invention provides a paste composition, for a solar cell electrode, comprising conductive metal powder, glass frit and an organic vehicle, wherein the glass transition temperature (Tg) of the glass frit is equal to or higher than 200℃ and lower than 300℃.

Description

Electrode paste for solar cell and solar cell manufactured using same

The present invention relates to an electrode paste composition for a solar cell and a solar cell manufactured using the same.

A solar cell is a semiconductor device that converts solar energy into electrical energy and generally has a p-n junction. The basic structure is the same as that of a diode.

8 is a structure of a general solar cell device, and the solar cell device is generally configured using a p-type silicon semiconductor substrate having a thickness of 180 to 250 μm. On the light-receiving surface side of the silicon semiconductor substrate, an n-type impurity layer having a thickness of 0.3 to 0.6 µm, an antireflection film and a front electrode are formed thereon. A back electrode is formed on the back side of the p-type silicon semiconductor substrate. The front electrode is formed by screen printing or the like using a conductive paste containing conductive particles containing silver as a main component, glass frit, and an organic vehicle, and the back electrode is formed of aluminum powder, glass frit, and organic vehicle. The aluminum paste composition which consists of (organic vehicle) is apply | coated by screen printing etc., and dried, and it forms by baking at the temperature more than 660 degreeC (melting point of aluminum). During the firing, aluminum diffuses into the p-type silicon semiconductor substrate, whereby an Al-Si alloy layer is formed between the back electrode and the p-type silicon semiconductor substrate, and a p + layer is formed as an impurity layer by diffusion of aluminum atoms. do. The presence of such a p + layer results in a back surface field (BSF) effect that prevents electron recombination and improves the collection efficiency of product carriers.

On the other hand, during firing, the anti-reflection film is eroded by the redox reaction of the glass frit powder, and the conductive metal crystals are precipitated in the form of the conductive powder crystals in the glass frit powder at the substrate interface. In addition to acting as a crosslinking of the bulk front electrode and the silicon substrate, it is known to exhibit contact by tunneling effect or direct adhesion with the bulk electrode depending on the thickness of the glass frit powder.

Conventional crystalline solar cells have a high temperature firing process with an actual temperature of more than 750 ℃ due to the composition of the back Al, the back Ag, and the front Ag, but in the case of passivated emitter structured solar cells (PESC, PERC, PERL), which are being actively studied recently, Lower firing temperatures or rapid firing are required. So, the initial research used the method of depositing the electrode itself by plating, but the investment cost is high, and the process is complicated. Recently, the research to introduce the electrode into the printing process is actively underway. However, the conventional electrode paste composition is unstable in contact with the emitter under the firing conditions of 750 ° C or less, poor contact resistance at the surface resistance (100 kPa / sq or more), and uneven melting of the glass frit. There is a need for an electrode paste composition suitable for this.

The present invention can increase the melt uniformity, improve the uniformity of the cell characteristics, ensure excellent contact characteristics even at low temperature / rapid firing, and can be applied to high-resistance solar cell electrode paste composition and high efficiency It is an object to provide a solar cell.

As a means for solving the above problems,

The present invention provides a paste composition for a solar cell electrode comprising a conductive metal powder, a glass frit, and an organic vehicle, wherein the glass transition temperature (Tg) of the glass frit is in a range of 200 ° C. or more and less than 300 ° C. Provided is a paste composition for a solar cell electrode.

In addition, there is provided a paste composition for a solar cell electrode, characterized in that two or more crystallization peaks on the DSC data of the glass frit.

In addition, there is provided a paste composition for a solar cell electrode, characterized in that a crystallization peak occurs on the DSC data of the glass frit below 500 ° C.

In addition, the first crystallization peak on the DSC data of the glass frit provides a paste composition for a solar cell electrode, characterized in that occurring below 400 ℃.

In addition, the average particle diameter (D50) of the glass frit provides a solar cell electrode paste composition, characterized in that in the range of 0.5 ~ 10㎛.

In addition, the PbO content of the glass frit provides a paste composition for a solar cell electrode, characterized in that in the range of 10 to 29 mol% relative to the entire glass frit.

In addition, in the solar cell having a front electrode on the upper substrate, and a back electrode on the lower substrate, the front electrode is manufactured by applying the solar cell electrode paste composition and baking To provide.

The present invention having the above-described structural characteristics can increase the melt uniformity of the glass frit, and can improve the cell property uniformity. In addition, it is possible to ensure excellent contact characteristics even at low temperature / rapid firing, it can be applied particularly well to high surface resistance (90 ~ 120 Ω / sq) solar cells.

1 is a conceptual diagram of differential scanning calorimetry (DSC) data showing thermal behavior of a glass frit.

2 to 4 are glass frit DSC data of Preparation Example and Comparative Preparation Example,

5 to 7 are performance evaluation data of Examples and Comparative Examples,

8 is a schematic cross-sectional view of a general solar cell element.

Hereinafter, the present invention will be described in more detail with reference to the drawings and embodiments. The following descriptions are for specific examples of the present invention, but are not intended to limit the scope of the rights set forth in the claims, even if there is an assertive or limited expression.

The present invention provides a paste composition for a solar cell electrode comprising a conductive metal powder, a glass frit, and an organic vehicle, wherein the glass frit has a special thermal behavior.

Each component is demonstrated concretely below.

<Conductive Metal Powder>

As the conductive metal powder, silver powder, copper powder, nickel powder, aluminum powder, or the like may be used. For the front electrode, silver powder is mainly used, and for the back electrode, aluminum powder is mainly used. For convenience, the conductive metal material will be described using silver powder as an example. The following description is equally applicable to other metal powders.

The silver powder is preferably a pure silver powder. In addition, a silver-coated composite powder having at least a surface of a silver layer, an alloy containing silver as a main component, and the like can be used. In addition, other metal powders may be mixed and used. For example, aluminum, gold, palladium, copper, nickel, etc. are mentioned. The average particle diameter of the silver powder may be 0.1 to 10 μm, and 0.5 to 5 μm is preferable in consideration of the ease of pasting and the density at the time of baking, and the shape may be at least one of spherical, needle, plate and amorphous. have. Silver powder may mix and use 2 or more types of powder from which an average particle diameter, particle size distribution, shape, etc. differ. The content of the silver powder is preferably 60 to 98% by weight based on the total weight of the electrode paste composition in consideration of the electrode thickness formed during printing and the wire resistance of the electrode.

<Organic vehicle>

The organic vehicle is not limited but may include an organic binder and a solvent. Sometimes the solvent can be omitted. The organic vehicle is not limited but is preferably 1 to 10% by weight based on the total weight of the electrode paste composition.

The organic vehicle is required to maintain a uniformly mixed state of metal powder and glass frit. For example, when the conductive paste is applied to a substrate by screen printing, the conductive paste is made homogeneous and the printed pattern is blurred. And properties for suppressing flow and improving the dischargeability and plate separation property of the conductive paste from the screen plate.

Although the binder used in the electrode paste composition according to the embodiment of the present invention is not limited, examples of the cellulose ester-based compound include cellulose acetate and cellulose acetate butylate, and the cellulose ether compound includes ethyl cellulose, methyl cellulose, and hydride. Roxy flophyll cellulose, hydroxy ethyl cellulose, hydroxy propyl methyl cellulose, hydroxy ethyl methyl cellulose, and the like, and examples of the acryl-based compound include poly acrylamide, poly methacrylate, poly methyl methacrylate, and polyethyl meta An acrylate etc. can be mentioned, For example, polyvinyl butyral, polyvinyl acetate, a polyvinyl alcohol, etc. are mentioned as a vinyl type. At least one or more of the binders may be selected and used.

Solvents used for dilution of the composition include alpha-terpineol, texanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol mono butyl ether, ethylene At least one compound selected from the group consisting of glycol mono butyl ether acetate, diethylene glycol mono butyl ether, diethylene glycol mono butyl ether acetate and the like is preferably used.

<Glass frit>

The glass frit used is not limited. Lead-free glass frits can be used as well as leaded glass frits.

Glass transition temperature (Tg) of the glass frit is not limited, but may be 200 ~ 600 ℃, preferably the glass transition temperature is in the range of 200 ℃ to less than 300 ℃. By using a glass frit with a low glass transition temperature of less than 300 ° C., melt uniformity can be increased and cell uniformity can be improved. In addition, it is possible to secure excellent contact characteristics even at low temperature / rapid firing, it can be optimized for high surface resistance (90 ~ 120 Ω / sq) solar cells.

In addition, the crystallization properties of the glass frit can be treated as an important factor.

1 is DSC data showing the thermal behavior of the glass frit, the glass transition temperature (Tg), softening point (Ts), crystallization peak can be observed.

In the conventional glass frit, the initial crystallization temperature is generally higher than 550 ° C. during DSC measurement. In the present invention, the crystallization occurs more quickly when firing by allowing the initial crystallization peak in the DSC measurement data of the glass frit to be less than 400 ° C. The electrical characteristics can be excellent by significantly reducing the breakdown of the emitter and the increase in the line width of the electrode. There may be more than one crystallization peak, in which case it is preferred that the crystallization peak first occur on the DSC data below 400 ° C., and the secondary crystallization peak occur above 400 ° C. and below 500 ° C. More preferably, all of the crystallization peaks occur below 500 ° C., in particular below 400 ° C., on the DSC data.

In addition, there is no restriction | limiting in particular in the composition, particle diameter, and shape of a glass frit. Preferably, as a component and content of the glass frit, PbO is 10 to 29 mol%, TeO2 is 20 to 34 mol%, Bi2O3 is 3 to 20 mol%, SiO2 is 20 mol% or less and B2O3 is 10 mol% or less , Alkali metals (Li, Na, K, etc.) and alkaline earth metals (Ca, Mg, etc.) may contain 10 to 20 mol%. By combining the organic content of the above components, it is possible to prevent the increase of the electrode line width, to improve the contact resistance at the sheet resistance, and to improve the short-circuit current characteristics.

In particular, if the content of PbO is too high, it is not environmentally friendly, there is a problem that the viscosity of the electrode is too low to melt the line width of the electrode during firing, so PbO is preferably included within the above range in the glass frit. Furthermore, when PbO exceeds 30 mol% and the content of alkali metals and alkaline earth metals falls below the above range, the Al2O3 layer removal performance in the insulating layer is not preferable, which is not preferable.

On the other hand, the average particle diameter of the glass frit is not limited, but may have a particle diameter within the range of 0.5 ~ 10㎛, it is also possible to use a mixture of different paper particles having a different average particle diameter. Preferably, at least one glass frit has a mean particle size (D50) of 3 µm or more and 10 µm or less. Through this, the reactivity is excellent during firing, and the damage of the n-layer can be minimized, especially at high temperatures, and the adhesion can be improved and the open voltage (Voc) can be excellent. In addition, it is possible to reduce the increase in the line width of the electrode during firing. In addition, it is preferable that the glass transition temperature (Tg) of the glass frit whose average particle diameter is 3 micrometers or more and 10 micrometers or less is less than 300 degreeC. Since particles having a relatively large particle size are used, problems such as uneven melting during firing can be prevented by lowering the glass transition temperature.

The content of the glass frit is preferably 1 to 15% by weight based on the total weight of the conductive paste composition. If the content is less than 1% by weight, incomplete firing may occur to increase the electrical resistivity. There are too many components, and there exists a possibility that an electrical resistivity may also become high.

<Other additives>

The paste composition for electrodes according to the present invention may further include additives commonly known as necessary, for example, a dispersant, a plasticizer, a viscosity modifier, a surfactant, an oxidant, a metal oxide, a metal organic compound, and the like.

The present invention also provides a method for forming an electrode of a solar cell and a solar cell electrode manufactured by the method, characterized in that the paste for the solar cell electrode is applied on a substrate, dried and baked. Except for using the solar cell electrode forming paste in the method of forming a solar cell electrode of the present invention, the substrate, printing, drying and firing is a general method that can be used for the manufacture of a solar cell, of course. For example, the substrate may be a silicon wafer, and the electrode made of the paste of the present invention may be a finger electrode or a busbar electrode on the front surface, and the printing may be screen printing or offset printing, and the drying may be 90 to 250. It may be made at ℃, 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 structure of the solar cell described in Korean Unexamined-Japanese-Patent No. 10-2006-0108550, 10-2006-0127813, Unexamined-Japanese-Patent No. 2001-202822, and 2003-133567, and its manufacturing method are mentioned. have.

It will be described in more detail through the following examples.

<Example>

Preparation of Glass Frit

A glass frit was prepared with the composition as shown in Table 1 below, and the DSC data thereof was measured and shown in FIGS. 2 (Preparation Example 1) and 3 (Preparation Example 2). On the other hand, Viox glass frit was prepared as a glass frit of Comparative Preparation Example, the DSC data was measured and shown in Figure 4 (Comparative Preparation Example 1).

Component Preparation Example 1 (mol%) Preparation Example 2 (mol%) PbO 29 25 TeO2 34 34 Bi2O3 10 15 SiO2 10 5 Li2O 5 7 Na2O 5 5 K2O 5 5 ZnO One 2 Al2O3 2 TIO2 One

Preparation of Paste Composition

Binders, solvents, additives, glass frit and the like as shown in Table 2 below, dispersed using a three-bone mill, and then mixed with silver powder (spherical, average particle diameter 1 ~ 2㎛) and further using a three-bone mill Dispersed. Thereafter, vacuum / pressure defoaming was carried out to prepare a conductive paste.

division Example 1 Example 2 Comparative Example 1 Ethyl Cellulose 0.5 0.5 0.5 Texanol 2.4 2.4 2.4 DBA 2 2 2 DB 1.8 1.8 1.8 BYK-108 0.5 0.5 0.5 Amide wax 0.5 0.5 0.5 DPGDB 0.2 0.2 0.2 Silver powder 90 90 90 Glass frit (production example 1) (Tg 265 degrees Celsius) 2.1 Glass frit (production example 2) (Tg 255 degrees Celsius) 2.1 Glass frit (Comparative Production Example 1) (Tg 340 ° C) 2.1

Experimental Example Preparation and Characterization of Cell

The paste compositions prepared in Examples 1 and 2 and Comparative Example 1 were printed with Al paste by screen printing on the back of the wafer, and dried at 200-300 ° C. for 20 seconds using an IR drying furnace. Thereafter, a pattern of 40 μm line width was printed on the front surface of the wafer by screen printing, and dried in the same manner. The cell formed by the above process was calcined for 20 seconds to 30 seconds using a belt-type kiln for 20 to 30 seconds, and the firing was performed at a maximum peak temperature of 740 ° C., 770 ° C., and 800 ° C., respectively. Using a solar cell efficiency measuring equipment (Halm, Cetis PV-celltester3), Isc, Voc, Rs, Fill Factor, the efficiency of observing the performance shown in Table 3 and Figures 5 to 7 below.

Firing temperature Isc Voc Eff FF Rs 740 ℃ Comparative Example 1 9.29 0.64 19.28 76.95 0.00215 Example 1 9.35 0.65 19.59 77.64 0.00203 Example 2 9.32 0.65 19.60 77.87 0.00198 770 ℃ Comparative Example 1 9.32 0.65 19.62 77.98 0.00189 Example 1 9.33 0.65 19.70 78.23 0.00177 Example 2 9.35 0.65 19.74 78.20 0.00181 800 ℃ Comparative Example 1 9.30 0.64 19.57 78.05 0.00187 Example 1 9.30 0.65 19.67 78.38 0.00175 Example 2 9.32 0.64 19.58 78.08 0.00179

As shown in Table 3 and Figures 5 to 7, it can be seen that the embodiments of the present invention have improved several electrical properties, compared to the comparative example. In particular, it can be seen that the performance is excellent at low temperature firing.

Since the above description is an example for better understanding of the present invention, modifications, substitutions, modifications, omissions, and the like which can be added within the scope of the technical idea of the present invention are within the scope of the present invention defined by the claims. Included.

[Description of the code]

10: P-type silicon semiconductor substrate

20: N-type impurity layer

30: antireflection film

40: P + layer (BSF: back surface field)

50: back aluminum electrode

60: back silver electrode

100: front electrode

Claims (7)

A paste composition for solar cell electrodes comprising a conductive metal powder, a glass frit, and an organic vehicle, The glass transition temperature (Tg) of the glass frit is a solar cell electrode paste composition, characterized in that within the range of 200 ℃ or less. The method of claim 1, Paste composition for a solar cell electrode, characterized in that more than one crystallization peak on the DSC data of the glass frit. The method of claim 1, The paste composition for solar cell electrodes, characterized in that a crystallization peak occurs below 500 ° C. on the DSC data of the glass frit. The method of claim 1, Paste composition for a solar cell electrode, characterized in that the first crystallization peak occurs below 400 ℃ on the DSC data of the glass frit. The method of claim 1, Paste composition for a solar cell electrode, characterized in that the average particle diameter (D50) of the glass frit is in the range of 0.5 ~ 10㎛. The method of claim 1, PbO content of the glass frit is a paste composition for a solar cell electrode, characterized in that in the range of 10 to 29 mol% compared to the entire glass frit. In a solar cell having a front electrode on the upper substrate, and a back electrode on the lower substrate, The front electrode is manufactured by applying a paste composition for solar cell electrodes of any one of claims 1 to 6 and then firing.

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