KR20130067693A - Ag paste composition for forming electrode and silicon solar cell using the same - Google Patents

Abstract

PURPOSE: A silver paste composition for forming an electrode is provided to facilitate the separation of screen masks, thereby improving electric performance. CONSTITUTION: A silver paste composition for forming an electrode comprises a silver powder, glass frit powder, and organic binder, includes at least one or more hydroxy groups, and includes a low molecular weight additive represented by chemical formula 1: R1COOH or chemical formula 2: R2-OH. In the chemical formula, R1 is C1-20 alkyl group or alkenyl group, having at least one or more hydroxyl group, and can be substituted or unsubstituted by C1-5 carboxyl group; R2 is C1-20 alkyl group, and can be substituted by a hydroxyl group. [Reference numerals] (AA) Line width & line height(um); (BB) Comparative example 1; (CC) Example 1; (DD) Example 2; (EE) Example 3; (FF) Example 4; (GG) Example 5

Description

Ag paste composition for forming electrode and Silicon solar cell using the same}

The present invention relates to a silver paste composition for forming an electrode and a silicon solar cell using the same, and more particularly, using an additive having at least one or more hydroxyl groups capable of realizing a high aspect ratio and having a low molecular weight of 1000 or less. The present invention relates to a silver paste composition for forming an electrode capable of improving printability when forming an electrode pattern and improving electrical characteristics of a solar cell, and a silicon solar cell using the same.

Recently, as electronic industry has developed, miniaturization and high reliability of electronic products and devices have been demanded. Various methods have been tried to form circuit patterns and electrodes of electronic products requiring high integration. Among them, the use of conductive metal pastes is of interest because of less generation of by-products or contaminants during the process.

The metal paste generally used includes a conductive metal, a glass frit, and an organic binder. As the conductive metal, silver, aluminum, or the like is used. Among them, silver is mainly used. At present, conductive metal paste is mainly used for hybrid IC, semiconductor IC mounting and various capacitors and electrodes. Recently, it is widely used in high-tech electronic products such as PCB, EL, touch panel, RFID, LCD, PDP, As the related industries are expanded and developed, the demand is also increasing.

For example, in the case of photovoltaic cells, there is a growing interest in alternative energy sources, as existing energy resources such as oil and coal are expected to be depleted. Among them, solar cells are rich in energy resources and have no problems with environmental pollution Especially noteworthy.

Solar cells are classified into solar cells that generate steam required to rotate turbines using solar heat, and solar cells that convert photons into electrical energy using the properties of semiconductors. It refers to a solar cell (hereinafter referred to as a solar cell).

Solar cells are divided into silicon solar cell, compound semiconductor solar cell and tandem solar cell according to raw materials. Of these three types of solar cells, silicon solar cells are the mainstream in the solar cell market.

1 is a cross-sectional view showing a basic structure of a silicon solar cell. Referring to the drawings, a silicon solar cell includes a substrate 101 made of a p-type silicon semiconductor and an emitter layer 102 made of an n-type silicon semiconductor, and a diode 101 is formed at the interface between the substrate 101 and the emitter layer 102. [ A pn junction is formed.

When sunlight is incident on a solar cell having the above structure, electrons and holes are generated in a silicon semiconductor doped with impurities by a photovoltaic effect. For reference, electrons are generated in a majority carrier in the emitter layer 102 made of an n-type silicon semiconductor, and holes are generated in a majority carrier in the substrate 101 made of a p-type silicon semiconductor. Electrons and electrons generated by the photovoltaic effect are attracted toward the n-type silicon semiconductor and the p-type silicon semiconductor, respectively, and are electrically connected to the front and back electrodes 103 and 104 bonded to the bottom of the substrate 101 and the top of the emitter layer 102, When the electrodes 103 and 104 are connected by a wire, a current flows.

The conductive metal paste is used for manufacturing the front electrode or the back electrode in the solar cell, and as described above, is used for manufacturing various electrodes in other electronic products.

In addition, in order to increase the efficiency of solar cells, cells have recently been developed in a direction in which the shadow area is reduced.

However, the conventional silver paste containing the conductive metal has a lot of stickiness and high viscosity, so that printing is not desired in the process of forming an electrode pattern, thereby limiting the efficiency of the solar cell.

For example, in the conventional method, a fatty acid or an amine additive has been used to improve printability, but in this case, although the effect of lowering the viscosity of the paste does not reduce stickiness, the paste is coated on a substrate. It was difficult to implement narrow line width and high sentence.

An object of the present invention is to improve the printability when forming the front electrode pattern by using an additive having at least one or more hydroxyl groups capable of high aspect ratio and having a low molecular weight of less than 1000, and improve the electrical characteristics of the solar cell. It is to provide a silver paste composition for forming electrodes and a silicon solar cell using the same.

The present invention includes silver powder, glass frit powder, organic binder,

It provides a silver paste composition for forming an electrode having at least one or more hydroxyl groups and containing a low molecular weight additive represented by the following formula (1) or (2) having a molecular weight of 1,000 or less.

[Formula 1]

R ₁ COOH

[Formula 2]

R ₂ -OH

Where

R ₁ is an alkyl or alkenyl group having 1 to 20 carbon atoms having at least one hydroxyl group, which may be substituted or unsubstituted with a carboxyl group having 1 to 5 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms, which may be unsubstituted or substituted with a hydroxyl group.

Also in accordance with the present invention, a silicon semiconductor substrate;

An emitter layer formed on the substrate;

An antireflection film formed on the emitter layer;

A front electrode penetrating the antireflection film and connected to the emitter layer; And

Is a silicon solar cell comprising a back electrode connected to the back of the substrate,

The front electrode provides a silicon solar cell formed by applying and firing the silver paste composition on the anti-reflection film in a predetermined pattern.

The silver paste composition for forming an electrode of the present invention uses an additive having at least one or more hydroxyl groups in a molecule and a low molecular weight of 1000 or less, thereby reducing stickiness while decreasing the viscosity of the paste to form a front electrode on a substrate. Since the printability of the paste can be greatly improved, a high aspect ratio can be realized, thereby improving the electrical characteristics of the solar cell.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the detailed description of the present invention serve to further understand the technical spirit of the present invention, the present invention includes matters described in such drawings. It should not be construed as limited to.
1 is a cross-sectional view showing a schematic structure of a conventional silicon solar cell.
2 is a schematic diagram of a solar cell manufactured according to an embodiment of the invention.
Figure 3 shows a comparison of the line width and line height of the pattern for the silicon solar cell using the paste prepared in Examples 1 to 5 and Comparative Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In the case of silver paste containing no hydroxyl group, the line width is spread while increasing the stickiness of the paste, while the additive containing hydroxyl group can improve the line spread and stickiness. If more is increased, the line height can be improved, so that the high aspect ratio can be realized to increase the efficiency of the solar cell.

Therefore, the shadow area can be reduced due to the reduction of the electrode line width and the texturing of the substrate, so that the present invention can form a contact well after the paste is printed on the textured substrate while implementing a narrow line width and a high line height. It is about a method.

Accordingly, the present invention is to provide a silver paste composition for forming an electrode using a low molecular weight additive having at least one hydroxyl group and a silicon solar cell using the same.

The silver paste composition for forming an electrode of the present invention includes a silver powder, a glass frit, and an organic binder, and is characterized by including the low molecular weight additive for increasing the efficiency of the solar cell. The silver paste composition for forming an electrode may be used to form a front electrode.

The low molecular weight additive used in the present invention has a low molecular weight even if there is only one hydroxyl group in the compound, or the more hydroxyl group, the viscosity decreases and the sticky (tacky) of the paste is reduced, so that the separation between the paste and the screen mask during printing. Can be made smoothly. In addition, the additives with hydroxyl groups can enter the matrix of the binder in the paste and interfere with the intermolecular bonding of the binder while reducing the binder's sticky, thereby improving the printability of the paste. Accordingly, the present invention can form an electrode pattern having a high line height and a line width similar to the pattern size.

In addition, the more hydroxyl groups in the compound of the low molecular weight additive, the higher the line width accuracy as well as the line height of the pattern, thereby improving aspect ratio (aspect ratio to line width, aspect ratio). Accordingly, the present invention can narrow the line width of the pattern of the electrode and increase the line height, thereby increasing the light incident amount of the solar cell, thereby improving battery characteristics.

Preferably, the present invention can implement a narrow line width and a high sentence by using the low molecular weight additive. For example, the present invention can adjust the ratio of the line width (height) and the height (height) in the ratio of 100㎛: 10-50㎛ to 60㎛: 10-40㎛. More preferably, the ratio of line width and height may be 60 µm: 20 µm.

The low molecular weight additive having at least one or more hydroxyl groups used in the present invention is a compound represented by the following formula (1) or (2), preferably having a molecular weight of 1,000 or less, and more preferably an intramolecular hydroxyl (-OH) group. It is good that it is one or more and molecular weight is 100-1,000.

[Formula 1]

R ₁ COOH

[Formula 2]

R ₂ -OH

Where

R ₁ is an alkyl or alkenyl group having 1 to 20 carbon atoms having at least one hydroxyl group, which may be substituted or unsubstituted with a carboxyl group having 1 to 5 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms, which may be unsubstituted or substituted with a hydroxyl group.

In the low molecular weight additive of Formula 1 or 2, even if the molecular weight of the hydroxyl group is one or more, if the molecular weight exceeds 1,000, the stickiness of the binder in the paste is increased to reduce the printability of the paste. As a result, desired line widths cannot be obtained during substrate printing and separation between screen masks cannot be performed smoothly.

In addition, the lower molecular weight additive of Formula 1 or 2 is advantageous in printability, shape retention characteristics, etc., the lower the boiling point. For example, the low molecular weight additive is preferably boiling point 100 to 400 ℃.

Preferred examples of the low molecular weight additives of Formula 1 or 2 include stearic acid, oleic acid, maleic acid, citric acid and hydrogenated caster oil Use a compound selected from the group.

In addition, the content of the low molecular weight additive of Formula 1 or Formula 2 is preferably used in an amount of 0.1 to 5% by weight, more preferably 0.1 to 3% by weight, most preferably 0.1 to 1% by weight based on the total silver paste composition. It is good to be%. When the content of the low molecular weight additive of Formula 1 or Formula 2 is less than 0.1% by weight, there is no effect of adding the additive, and when the content of the low molecular weight additive is more than 5% by weight, the viscosity of the paste decreases and printability may be rather deteriorated.

The Ag particles of the silver powder included in the silver paste composition of the present invention can be used without limitation as long as they are commonly used silver particles. For example, an average particle diameter of 0.3 to 7 μm may be used, but is not limited thereto.

The content of the silver powder is preferably 60 to 90% by weight based on the total silver paste composition, more preferably 70 to 85% by weight, most preferably 80 to 85% by weight. If the content of the silver powder is less than 60% by weight, there is a problem that the viscosity decreases while the specific resistance falls, and when the content of the silver powder exceeds 90% by weight, the viscosity rises excessively, resulting in a poor printability. In this case, the content of silver powder is most preferably 80 to 85% by weight in the material for the front Ag electrode, and the content of silver powder is 60 to 70 in the material for the back Ag electrode. Weight percent is preferred.

Glass frit powder that can be used in the present invention may be used without limitation so long as the glass frit used in the art. Examples of such glass frit powders may include lead oxides and / or bismuth oxides. Specifically, SiO ₂ -PbO system, SiO ₂ -PbO-B ₂ O ₃ system, Bi ₂ O ₃ -B ₂ O ₃ -SiO ₂ system, or PbO-Bi ₂ O ₃ -B ₂ O ₃ -SiO ₂ system Powders and the like may be used alone or in combination of two or more, but is not limited thereto.

The organic binder is used to prepare silver powder, glass frit and baking aid in paste form, and the organic binder used in the present invention may be used without limitation as long as it is an organic binder used in the art for preparing a paste composition. For example, the organic binder may be any one or a mixture of two or more selected from the group consisting of cellulose resins, acrylic resins, butylcarbitol, and terpineol, but is not limited thereto. Preferably, ethyl cellulose or acryl Rate-based polymer resins can be used.

In addition, the content of the glass frit and the organic binder is easy to form the electrode, has a very easy viscosity for screen printing, and if the range that can exhibit a suitable aspect ratio by preventing the paste from flowing down after screen printing, The range is not particularly limited.

For example, the content of the glass frit is preferably 0.5 to 8% by weight, more preferably 1 to 6% by weight, most preferably 2 to 4% by weight based on the total silver paste composition. If the content of the glass frit is less than 0.5% by weight, there is a problem that the electrode adhesion is weak, and if it exceeds 8% by weight, there may be a problem that the specific resistance is increased by forming an insulating layer by the glass frit.

In addition, the content of the organic binder is preferably 1 to 20% by weight based on the total silver paste composition, more preferably 5 to 12% by weight. If the content of the organic binder is less than 1% by weight, there is a problem in printability. If the content of the organic binder exceeds 20% by weight, the printed pattern may be spread or a stickiness of the paste may cause problems in printability.

The silver paste composition of the present invention can be obtained by mixing by various methods known in the art so that the above components are uniformly dispersed.

Optionally, the silver paste composition of the present invention may further include additional additives without departing from the scope of the present invention. For example, conductive metal particles, antifoaming agents, dispersants, plasticizers and the like can be further added to the composition of the present invention as needed.

The manufacturing method of the silver paste composition of this invention is as follows. Basically, a paste can be manufactured using the method of simultaneously adding and mixing silver powder, glass frit powder, a binder, and the said low molecular weight additive which has the said at least 1 or more hydroxyl group. Mixing of each component can be mixed uniformly using a 3 roll mill or the like. The silver paste composition of the present invention prepared by this method preferably has a viscosity of 150 to 250 Ps on the basis of 1 rpm.

On the other hand, the present invention provides a solar cell comprising a front electrode prepared using the silver paste composition. The solar cell may be a silicon solar cell.

According to a preferred embodiment, the present invention is a silicon semiconductor substrate; An emitter layer formed on the substrate; An antireflection film formed on the emitter layer; A front electrode penetrating the antireflection film and connected to the emitter layer; And a back electrode connected to a rear surface of the substrate, wherein the front electrode is coated with the silver paste composition according to any one of claims 1 to 7 on the anti-reflection film in a predetermined pattern. It provides a silicon solar cell formed by firing.

Hereinafter, a silicon solar cell using the silver paste composition of the present invention will be described with reference to FIG. 2 as an example. However, the embodiments described in the specification and the drawings shown below are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, which can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

2, the silicon solar cell according to the present invention includes a silicon semiconductor substrate 201, an emitter layer 202 formed on the substrate 201, and an anti-reflection film formed on the emitter layer 202. 203, a front electrode 204 penetrating the antireflection film 203 and connected to the upper surface of the emitter layer 202, and a rear electrode 205 connected to the rear surface of the substrate 201.

As the p-type impurity, B, Ga, In or the like as a Group 3 element can be doped as an impurity into the substrate 201, and P, As, Sb or the like as an n-type impurity as an n-type impurity is doped into the emitter layer 202 as an impurity Lt; / RTI > When the substrate 201 and the emitter layer 202 are doped with an impurity of the opposite conductivity type, a p-n junction is formed at the interface between the substrate 201 and the emitter layer 202. On the other hand, the p-n junction may be formed by doping the substrate 201 with an n-type impurity and doping the emitter layer 202 with a p-type impurity.

The antireflection film 203 immobilizes defects (e.g., dangling bonds) existing in the surface or bulk of the emitter layer 202 and reduces the reflectance of sunlight incident on the front surface of the substrate 201. When defects existing in the emitter layer 202 are passivated, the recombination sites of the minority carriers are removed and the open circuit voltage of the solar cell is increased. When the reflectance of the solar light is reduced, the amount of light reaching the p-n junction is increased to increase the short circuit current of the solar cell. When the open-circuit voltage and the short-circuit current of the solar cell are increased by the antireflection film 203, the conversion efficiency of the solar cell is improved accordingly.

The antireflection film 203 may be a single film selected from the group consisting of a silicon nitride film, a silicon nitride film containing hydrogen, a silicon oxide film, a silicon oxynitride film, MgF ₂ , ZnS, MgF ₂ , TiO ₂ and CeO ₂ , But not limited to, a multi-film structure in which two or more material films are combined. The anti-reflection film 203 may be formed by vacuum deposition, chemical vapor deposition, spin coating, screen printing, or spray coating. However, the method of forming the anti-reflection film 203 according to the present invention is not limited thereto.

The front electrode 204 and the rear electrode 205 are metal electrodes made of silver and aluminum, respectively. The front electrode 204 may be manufactured using the silver paste composition of the present invention and the back electrode 205 is manufactured using a conventional aluminum paste composition. The silver electrode is excellent in electrical conductivity, and the aluminum electrode is not only excellent in electrical conductivity but also excellent in affinity with the substrate 201 made of a silicon semiconductor, and thus has an advantage of good bonding.

The front electrode 204 and the rear electrode 205 can be manufactured by various known techniques, but are preferably formed by a screen printing method. That is, the front electrode 204 is formed by screen printing the silver paste composition of the present invention described above on the front electrode formation point and then performing heat treatment. When the heat treatment is performed, the front electrode penetrates the antireflection film 203 and is connected to the emitter layer 202 by a punch through phenomenon.

Similarly, the back electrode 205 is formed by printing on the back surface of the substrate 201 using a conventional aluminum paste for back electrode to which aluminum, quartz silica, binder, etc. are added, and then performing heat treatment. Aluminum may be diffused through the rear surface of the substrate 201 to form a back surface field layer (not shown) at the interface between the rear electrode 205 and the substrate 201 during the heat treatment of the rear electrode have. When the rear whole layer is formed, the carrier can be prevented from moving to the rear surface of the substrate 201 and recombining. When the recombination of the carriers is prevented, the open voltage and the fidelity are increased and the conversion efficiency of the solar cell is improved.

At this time, in the present invention, in the formation of the front electrode and the rear electrode, in addition to the screen printing method described above, conventional methods such as doctor blade, inkjet printing, and gravure printing may be used.

Best Mode for Carrying Out the Invention Hereinafter, the function and effect of the present invention will be described in more detail through a specific embodiment of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

< Comparative example  1 to 3 and Example  1 to 3>

To the silver paste composition was prepared by mixing each component in the composition and content of Table 1 (unit: wt%).

Silver powder was used as particles having an average particle diameter of 3μ, glass frit was used as the average particle diameter of 2μ containing bismuth oxide, and the organic binder was ethyl cellulose. In this case, the "μ" unit is the same as "μm" as is well known. In addition, the physical properties of each additive used in the examples are shown in Table 2.

Silver powder
(weight%) Glass frit
(weight%) abandonment
bookbinder
(weight%) additive ingredient content
(weight%) Example 1 84 4 11.5 Stearic acid 0.5 Example 2 84 4 11.5 Oleic acid 0.5 Example 3 84 4 11.5 Maleic acid 0.5 Example 4 84 4 11.5 H.C.O 0.5 Example 5 84 4 11.5 Citric acid 0.5 Comparative Example 1 84 4 12 - 0

Note) In Table 1, H.C.O is hydrogenated castor oil of Formula 3

(3)

Stearic acid H.C.O Oleic acid Maleic acid Citric acid -OH count One 4 One 2 4 Molecular Weight 284 934 282 116 192 Melting point (℃) 69.6 14 131 153 Boiling point (℃) 383 360 135 174

< Experimental Example >

In a conventional manner, the silicon semiconductor substrate 201 shown in FIG. 2, the emitter layer 202 formed on the substrate 201, the antireflection film 203 formed on the emitter layer 202, and the antireflection film A silicon solar cell having a structure including a front electrode 204 connected to an upper surface of the emitter layer 202 and a rear electrode 205 connected to a rear surface of the substrate 201 through 203 was manufactured. .

Subsequently, the line widths and line heights of the patterns of the silicon solar cells using the pastes prepared in Examples 1 to 5 and Comparative Example 1 were measured, and the results are shown in FIG. 3.

In the results of FIG. 3, Comparative Example 1 without adding a low molecular weight additive having at least one hydroxyl group showed a result of spreading the pattern line width.

On the other hand, in Examples 1 to 5 to which the low molecular weight additive having at least one hydroxyl group was added, it can be seen that the line width is clearly narrower than that of Comparative Example 1 (mask line width of 100 μm). In addition, the more hydroxyl groups, the higher the width accuracy as well as the line height of the pattern, and the aspect ratio is increased.

The narrower the line width and the higher the line height, the higher the light incident amount of the solar cell and the higher the Jsc value, which may have the effect of improving efficiency.

101: substrate
102: emitter layer
103: front electrode
104: rear electrode
201: substrate 202: emitter layer
203: antireflection film
204: front electrode 205: rear electrode

Claims (8)

Silver powder, glass frit powder, organic binder,
Low molecular weight additives having at least one hydroxyl group and represented by the following general formula (1) or (2) having a molecular weight of 1,000 or less
Silver paste composition for forming an electrode comprising:
[Formula 1]
R ₁ COOH
(2)
R ₂ -OH
In this formula,
R ₁ is an alkyl or alkenyl group having 1 to 20 carbon atoms having at least one hydroxyl group, which may be substituted or unsubstituted with a carboxyl group having 1 to 5 carbon atoms,
R ₂ is an alkyl group having 1 to 20 carbon atoms, which may be unsubstituted or substituted with a hydroxyl group. The silver paste composition of claim 1, wherein the low molecular weight additive of Formula 1 or 2 has a boiling point of 100 to 400 ° C. The silver paste composition of claim 1, wherein the low molecular weight additive of Formula 1 or 2 is a compound selected from the group consisting of stearic acid, oleic acid, maleic acid, citric acid, and hydrogenated castor oil. The silver paste composition of claim 1, wherein the low molecular weight additive of Formula 1 or 2 is present in an amount of 0.1 to 5 wt% based on the total silver paste composition. The silver paste composition of claim 1, wherein the silver powder has an average particle diameter of 0.3 μm to 7 μm. The silver paste composition of claim 1, wherein the glass frit powder comprises lead oxide or bismuth oxide. The metal paste composition of claim 1, wherein the organic binder is any one selected from the group consisting of cellulose resins, acrylic resins, butylcarbitol, and terpineol. Silicon semiconductor substrates;
An emitter layer formed on the substrate;
An anti-reflection film formed on the emitter layer;
A front electrode penetrating the antireflection film and connected to the emitter layer; And
Is a silicon solar cell comprising a back electrode connected to the back of the substrate,
The front electrode is formed by applying the silver paste composition according to any one of claims 1 to 7 on the antireflection film in a predetermined pattern and firing.

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