KR101733161B1 - Electrode Paste Composition For Solar Cell's Electrode And Solar Cell - Google Patents

Abstract

The present invention relates to a paste composition for a solar cell electrode which is composed of conductive metal powder, glass frit, and an organic vehicle. The paste composition for a solar cell electrode can reduce a line width of an electrode even in the same printing condition and the same heat treatment process, and can reduce an increase in the line width of the electrode after sintering by additionally including a polyether modified silicon-based additive.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode paste composition for a solar cell and a solar cell manufactured using the composition.

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

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

Fig. 4 shows a structure of a general solar cell element. The solar cell element is generally constituted by using a p-type silicon semiconductor substrate having a thickness of 180 to 250 mu m. 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 占 퐉 is formed, and 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. An electrode is formed by a method such as screen printing using a conductive paste in which conductive particles containing silver as a main component, glass frit, organic vehicle and the like are mixed, and the back electrode is made of aluminum powder, glass frit and organic vehicle an aluminum paste composition comprising an organic vehicle is applied by screen printing or the like and dried, followed by firing at a temperature of 660? (melting point of aluminum) or higher. Aluminum is diffused into the p-type silicon semiconductor substrate at the time of firing, so that 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 existence of such a p + layer prevents the recombination of electrons and improves the collection efficiency of the generated carriers, thereby obtaining a BSF (Back Surface Field) effect.

On the other hand, when the firing is performed, the antireflection film is eroded through the oxidation-reduction reaction of the glass frit powder, conductive metal crystal grains are precipitated in the form of the conductive powder crystal in the glass frit powder precipitated on the substrate interface, It is known that it not only serves as a bridge between the bulk front electrode and the silicon substrate but also exhibits a tunneling effect or contact by direct adhesion to the bulk electrode depending on the thickness of the glass frit powder.

The line width of the metal pattern at the front electrode of the solar cell must be reduced because the loss due to light absorption or reflection to the metal electrode must be minimized and the height of the pattern must be increased for electrode resistance. In general, the aspect ratio of the electrode height / line width has been increased in such a manner that the printing method is changed or the screen mesh design is changed. In the case of the paste composition, a method of increasing the viscosity by merely taking rheological characteristics into account is applied Has attempted to reduce the line width.

An object of the present invention is to provide an electrode paste composition for a solar cell and a high-efficiency solar cell that can reduce the line width of an electrode even under the same printing conditions and heat treatment process, and can reduce an increase in the line width of the electrode after firing.

As means for solving the above problem,

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 paste composition further comprises a polyether-modified silicone additive.

The present invention also provides a paste composition for a solar cell electrode, wherein the polyether-modified silicone additive is represented by the following general formula (1).

≪ Formula 1 >

Wherein R1 and R2 are independently selected from a hydrogen and a methyl group, R1 may be a hydrogen and a methyl group together in one molecule, m is an integer of 5 to 100, n is an integer of 1 to 10, x is An integer of 1 to 300, and y is an integer of 1 to 100)

When R 1 is independently selected from hydrogen and a methyl group and the ethylene oxide group (when R 1 is hydrogen) and the propylene oxide group (when R 1 is a methyl group) coexist in one molecule, the molar ratio of the ethylene oxide group to the propylene oxide group Is in the range of 6: 4 to 8: 2.

In the above formula (1), x: y is in the range of 10: 1 to 100: 1.

Also, the content of the polyether-modified silicone additive is within the range of 0.01 wt% to 0.3 wt% based on the total paste composition.

The paste composition for a solar cell electrode was applied to a solar cell silicon substrate through a screen printing with a mesh size of 50 탆 or less on the surface of the solar cell, and then heated to 500 to 900 캜 using a belt-type firing furnace to perform firing for 25 seconds. Wherein an increase in an electrode bleeding line width after firing against an electrode line width before pre-firing is within an average of 12 占 퐉.

The present invention also provides a solar cell having a front electrode on a substrate and a back electrode on the bottom of the substrate, wherein the front electrode is formed by applying the paste composition for a solar cell electrode, Lt; / RTI >

In the present invention having the above-described constitutional features, the line width of the electrode can be reduced by using the high-polarity modified silicone additive even in the same printing conditions and the heat treatment step, and the increase in line width of the electrode after firing can be remarkably reduced.

Figs. 1 to 3 are photographs of linewidths of the paste compositions of Examples and Comparative Examples before and after firing,
4 is a schematic cross-sectional view of a general solar cell element.

Hereinafter, the present invention will be described in detail with reference to the drawings and examples. Although the following description relates to a specific example of the present invention, even if there is a definite and definite expression, the scope of the right defined by the claims is not limited.

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 paste composition further comprises a polyether-modified silicone additive.

Each component will be described in detail below.

≪ Polyether-modified silicone additive >

In the present invention, special additives may be added to reduce the increase in the line width of the electrode during firing. That is, a polyether-modified silicone-based additive may be incorporated, and preferably a polyether-modified silicone-based additive may be added. When such an additive is added, the increase in line width during firing can be remarkably reduced. The content of the polyether-modified silicone additive is preferably in the range of 0.01 wt% to 0.3 wt% based on the entire paste composition. Below the above range, the effect of decreasing the line width is insignificant. If the range is exceeded, the electrical characteristics of the solar cell electrode may be disadvantageous or the adhesion of the electrode and the silicon substrate may be deteriorated and the contact may be interfered.

As an example of the polyether-modified polydimethylsiloxane, a polyether-modified polydimethylsiloxane having the following general formula (1) can be used.

≪ Formula 1 >

Here, R1 and R2 are independently selected from hydrogen and a methyl group. R1 may be a hydrogen and a methyl group in one molecule. When ethylene oxide (EO) group and propylene oxide (PO) group coexist, an ethylene oxide group and a propylene oxide group The molar ratio may be from 2: 8 to 8: 2. It is predicted that the high polarity property is obtained through the polyether modification to reduce the surface tension during firing, thereby reducing the line width increase during firing. Since the ethylene oxide group is higher in polarity than the propylene oxide group, the molar ratio of the ethylene oxide group to the propylene oxide group is preferably from 6: 4 to 8: 2. Wherein m is an integer of 5 to 100, n is an integer of 1 to 10, x is an integer of 1 to 300, y is an integer of 1 to 100, x: y is 10: 1 to 100: .

≪ Conductive metal powder &

As the conductive metal powder, silver powder, copper powder, nickel powder, and aluminum powder can be used. In the case of the front electrode, powder is mainly used, and the back electrode is mainly made of aluminum powder. Hereinafter, the conductive metal material will be described for convenience 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 silver layer on its surface, or an alloy containing silver as a main component may be used. Further, other metal powders may be mixed and used. For example, aluminum, gold, palladium, copper, and nickel. The average particle diameter of the silver powder may be 0.1 to 10 탆. The average particle diameter of the silver powder is preferably 0.5 to 5 탆 in consideration of ease of paste formation and denseness in firing. The shape of the powder is spherical, acicular, Plate type) and amorphous type (at least one type or more). The silver powder may be a mixture of powders of two or more kinds having different average particle diameter, particle size distribution and shape. The content of the silver powder is preferably 60 to 98% by weight based on the total weight of the electrode paste composition, considering the thickness of the electrode formed at the time of printing and the line resistance of the electrode.

<Organic Vehicle>

The organic vehicle is not limited, but organic binders, solvents, and the like may be included. Solvents may sometimes 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 have a property of keeping the metal powder and the glass frit uniformly mixed. For example, when the conductive paste is applied to the substrate by screen printing, the conductive paste becomes homogeneous, And a property to suppress the flow and to improve the discharging property and the plate separability of the conductive paste from the screen plate.

The binder used in the electrode paste composition according to an embodiment of the present invention is not limited. Examples of the cellulose ester compound include cellulose acetate and cellulose acetate butyrate. Examples of the cellulose ether compound include ethylcellulose, methylcellulose, Hydroxypropylmethylcellulose, hydroxyethylmethylcellulose and the like. Examples of the acrylic compound include polyacrylamide, polymethacrylate, polymethylmethacrylate, polyethylmethacrylate, polymethylmethacrylate, polymethylmethacrylate, Acrylate, and examples of the vinyl-based resin include polyvinyl butyral, polyvinyl acetate, polyvinyl alcohol, and the like. At least one or more kinds of the binders may be selected and used.

Examples of the solvent used for diluting the composition include alpha-terpineol, texanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene Glycol monobutyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and the like.

<Glass frit>

The glass frit used is not limited. It is possible to use not only flexible glass frit but also lead-free glass frit. And there is no particular limitation on the composition, particle size and shape thereof. Preferably, the glass frit contains 10 to 29 mol% of PbO, 20 to 34 mol% of TeO 2, 3 to 20 mol% of Bi 2 O 3, 20 mol% or less of SiO 2, 10 mol% or less of B 2 O 3 , An alkali metal (Li, Na, K, etc.) and an alkaline earth metal (Ca, Mg, etc.) in an amount of 10 to 20 mol%. By combining the organic components of the above components, it is possible to prevent an increase in the line width of the electrode, to improve the contact resistance in the high-surface resistance, and to improve the short-circuit current characteristic.

Particularly, when the content of PbO is too high, it is not environmentally friendly, and the viscosity during melting is too low, so that there is a problem that the line width of the electrode increases during firing, and therefore PbO is preferably contained within the above range within the glass frit. Furthermore, when the content of PbO exceeds 30 mol% and the contents of alkali metals and alkaline earth metals fall within the above range, the Al 2 O 3 layer removal performance of the insulating layer deteriorates.

On the other hand, the mean particle size of the glass frit is not limited, but it may have a particle size within a range of 0.5 to 5 mu m, and may be used by mixing various particles having different average particle sizes. Preferably, at least one kind of glass frit has an average particle diameter (D50) of not less than 3 mu m and not more than 10 mu m. As a result, it is possible to improve the reactivity during firing, minimize the damage of the n-layer at a high temperature, improve the adhesion and improve the open-circuit voltage (Voc). Also, the increase in the line width of the electrode during firing can be reduced. It is preferable that the glass transition temperature (Tg) of the glass frit having an average particle diameter of 3 占 퐉 or more and 10 占 퐉 or less is less than 300 占 폚. Particles having a relatively large particle diameter are used, so that it is possible to prevent problems such as non-uniform melting at the time of firing 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 less than 1% by weight, incomplete firing may occur to increase the electrical resistivity. If the amount exceeds 15% by weight, There is a possibility that the electrical resistivity becomes too high due to too much component.

The glass transition temperature (Tg) of the glass frit is not limited, but may be 200 to 600 ° C, and preferably the glass transition temperature is in the range of 200 ° C or more and less than 300 ° C. By using a glass frit having a glass transition temperature of less than 300 DEG C, melt uniformity can be increased and cell property uniformity can be improved. In addition, excellent contact characteristics can be secured even at a low temperature / rapid firing, and can be optimized for a high-surface-resistance (90 to 120? / Sq) solar cell.

Crystallization properties of glass frit can be treated as an important factor. In the case of the conventional glass frit, the initial crystallization temperature at the time of DSC measurement is generally 550 ° C or higher. In the present invention, the crystallization peak occurs at a temperature lower than 400 ° C on the DSC measurement data of the glass frit, The electrical characteristics can be improved by significantly reducing the line width of the electrode during the process. Preferably, the crystallization peak appears on the DSC data at a temperature lower than 400 ° C., and the secondary crystallization peak occurs at a temperature higher than 400 ° C. and lower than 500 ° C. It is more preferable that all of the crystallization peaks occur at less than 400 DEG C on the DSC data.

<Other additives>

The paste composition for an electrode according to the present invention may further contain commonly known additives such as a dispersant, a plasticizer, a viscosity adjusting agent, a surfactant, an oxidizing agent, a metal oxide, a metal organic compound and the like.

The present invention also provides a method of forming an electrode of a solar cell and a solar cell electrode produced by the method, wherein the paste for solar cell electrode is applied on a substrate, followed by drying and firing. It is needless to say that the methods used in the production of solar cells, such as substrate, printing, drying and firing, except that the paste for forming the solar cell electrode is used in the method for forming a solar cell electrode of the present invention. For example, the substrate may be a silicon wafer, and the electrode made of the paste of the present invention may be a front finger electrode, a bus bar electrode, and the printing may be screen printing, offset printing, Lt; 0 &gt; C, and the calcination may be performed at 600 to 950 &lt; 0 &gt; C. Preferably, the firing is performed at a high temperature / high-speed firing at 800 to 950 ° C, more preferably 850 to 900 ° C for 5 seconds to 1 minute, and the printing is preferably performed at a thickness of 20 to 60 μm . Specific examples of the structure of the solar cell described in Korean Patent Laid-Open Nos. 10-2006-0108550, 10-2006-0127813, 2001-202822 and 2003-133567, have.

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Examples>

Preparation of paste composition

A binder, a dispersing agent, a leveling agent, a glass frit (average particle size: 1 m) and the like were put in a composition shown in the following Table 1, and the mixture was dispersed using a triple mill and then silver powder (spherical, And dispersed using a triple mill. Thereafter, vacuum degassing was conducted to prepare a conductive paste.

division Example 1 Example 2 Comparative Example 1 EC 0.5 0.5 0.5 EFKA-4330 0.5 0.5 0.5 BYK180 0.7 0.7 0.7 Texanol 2.5 2.5 2.7 Butyl cellosolve 2.5 2.5 2.6 Thixatrol ST 0.5 0.5 0.5 Dimethyl adipate 1.5 1.5 1.5 Silver Powder 89.5 89.5 89.5 Glass frit 1.5 1.5 1.5 Silicone additive Additive 1 Additive 2 0.3 0.3

&Lt; Experimental Example >

The paste composition prepared in Examples 1 to 2 and Comparative Example 1 was pattern printed on the entire surface of the wafer by a screen printing method using a 50 μm mesh and dried at 200 to 350 ° C. for 20 seconds to 30 seconds using a belt- . Then, Al paste was printed on the back side of the wafer and dried by the same method. The cells thus formed were fired at 500 to 900 ° C. for 20 seconds to 30 seconds using a belt-type firing furnace. The cells thus manufactured were subjected to measurement using a solar cell efficiency measuring instrument (Halm, cetis PV-Celltest 3) Isc, Voc, Rseries, Rshadow, and relative performance based on the value of 100 in the comparative example are shown in Table 2 below. The linewidths of the front electrodes before and after firing were measured and are shown in Table 2 and Figs. 1 to 3, respectively. Here, the electrode bleeding line width is defined as the outermost reference line width of the electrode, which is caused by a phenomenon that glass frit or the like appears on the outermost side of the electrode as the electrode spreads after firing.

division Example 1 Example 2 Comparative Example 1 Bark line width 50.152 49.540 50.152 After firing
Bleeding
Line width 61.161 56.268 66.665 Isc 100.21 100.43 100.0 Rseries 100.58 101.22 100.0 Rshadow 96.18 91.98 100.0 Voc 100.0 100.0 100.0 efficiency 100.23 100.49 100.0

As shown in Table 2, in the examples of the present invention, the increase in the line width of the electrode after firing was within 12 占 퐉, and the increase in the line width was significantly reduced, and the Isc was improved. It can be seen that the total resistance is reduced due to the reduction of the shadow resistance compared with the increase of the resistance, and the efficiency is improved.

Therefore, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. * * * * * Recently Added Patents .

10: P-type silicon semiconductor substrate
20: N-type impurity layer
30: antireflection film
40: P + layer (BSF: back surface field)
50: rear aluminum electrode
60: rear silver electrode
100: front electrode

Claims (7)

1. A paste composition for a solar cell electrode comprising a conductive metal powder, glass frit, and an organic vehicle,
A polyether-modified silicone additive represented by the following formula (1)
In the formula (1), x: y is in the range of 10: 1 to 100: 1, R1 is independently selected from hydrogen and methyl groups, and ethylene oxide groups (when R1 is hydrogen) and propylene oxide groups Methyl group) coexist, the molar ratio of the ethylene oxide group to the propylene oxide group is in the range of 6: 4 to 8: 2.

&Lt; Formula 1 >

Wherein R1 and R2 are independently selected from a hydrogen and a methyl group, R1 may be a hydrogen and a methyl group together in one molecule, m is an integer of 5 to 100, n is an integer of 1 to 10, x is An integer of 1 to 300, and y is an integer of 1 to 100.)
delete delete delete The method according to claim 1,
Wherein the content of the polyether-modified silicone additive is in the range of 0.01 wt% to 0.3 wt% based on the total paste composition.
The method according to claim 1,
A paste composition for a solar cell electrode is applied to a solar cell silicon substrate through a screen printing with a mesh size of 50 탆 or less on the surface thereof and fired for 25 seconds using a belt type firing furnace at a temperature of 500 to 900 캜, Wherein an increase in an electrode bleeding line width after firing with respect to a total electrode line width is within an average of 12 占 퐉.
1. A solar cell having a front electrode on a substrate and a back electrode on a bottom of the substrate,
Wherein the front electrode is manufactured by applying the paste composition for a solar cell electrode according to any one of claims 1 to 5 and then baking.

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