WO2018084464A1 - Conductive paste for solar cell electrode and solar cell manufactured using same - Google Patents

Abstract

The present invention relates to a conductive paste for a solar cell electrode comprising a metal powder, a glass frit, an organic binder, and a solvent. By mixing at least two or more kinds of solvents including a first solvent and a second solvent as the solvent to adjust a surface tension and a boiling point of the solvent, it is possible to enhance conductivity by improving an aspect ratio, i.e., a line width and line pitch, of an electrode which is formed using the conductive paste according to the present invention. In addition, as the line width of the electrode decreases, a light receiving surface increases to provide a solar cell having high generation efficiency.

Description

Conductive paste for solar cell electrodes and solar cell manufactured using same

The present invention relates to a conductive paste used for forming an electrode of 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. 1 is a structure of a general solar cell device, and the solar cell device is generally configured using a p-type silicon semiconductor substrate 10 having a thickness of 180 to 250 μm. On the light-receiving surface side of the silicon semiconductor substrate, an n-type impurity layer 20 having a thickness of 0.3 to 0.6 µm, an antireflection film 30 and a front electrode 100 are formed thereon. In addition, the back electrode 50 is formed on the back side of the p-type silicon semiconductor substrate. The front electrode 100 is formed by applying a conductive paste mixed with silver powder, glass frit, organic vehicle solvent, and additives containing silver as a main component on the anti-reflection film 30. After baking, the electrode is formed, and the back electrode 50 is coated with an aluminum paste composition composed of aluminum powder, glass frit, organic vehicle, and additives by screen printing and dried, and then dried at 660 ° C. (melting point of aluminum). It is formed by baking at the temperature above. 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 the p + layer 40 is formed as an impurity layer by diffusion of aluminum atoms. ) Is formed. 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. The rear silver electrode 60 may be further positioned below the rear aluminum electrode 50.

Since the front electrode of the solar cell is mainly formed through a screen printing process, the front and rear electrode paste compositions are also manufactured in consideration of the printability of the screen printing process. In most conventional compositions, a high boiling point solvent suitable for screen printing is used or In consideration of storage stability and compatibility of the paste, a polar solvent is used, but in particular, the front electrode is difficult to realize a good resolution by reproducing a desired line width. For example, the conventional method uses a silver conductive paste composition for the front electrode, and even if the line width of the screen printing mask for the front electrode is 80 μm, the line width of the front electrode is 10 to 20 μm wider after actual printing. many. As a result, the light receiving surface of the cell is reduced, and as a result, a problem of deterioration of battery characteristics occurs.

In addition, Korean Patent Publication No. 2013-0139022 (December 20, 2013) uses a hydrophobic binder and a hydrophobic solvent when the hydrophilic conductive metal is included in the conductive paste composition, and a hydrophobic binder and a hydrophobic solvent when the hydrophobic conductive metal is included. To provide an excellent aspect ratio and improve electrical properties. However, when the solvent is used by controlling the properties (hydrophilicity and hydrophobicity) of the solvent according to the properties of the conductive metal used as described above, the selection of the binder or powder is restricted, and particularly when the hydrophilic solvent is used This weakness has a problem of poor storage stability.

An object of the present invention is to improve the efficiency of a solar cell including an electrode formed using the prepared conductive paste by adjusting the composition of the solvent in the composition of the conductive paste for solar cell electrodes.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention comprises a metal powder, a glass frit, an organic binder and a solvent, wherein the solvent is characterized by controlling the surface tension and boiling point by using a mixture of at least two or more solvents including a first solvent and a second solvent. It provides a conductive paste for a solar cell electrode.

In addition, the solvent is ethyl acetate, butyl carbitol acetate, ethyl carbitol acetate, ethyl carbitol acetate, texanol, diethylene glycol monobutyl ether, It is characterized in that it comprises a first solvent and a second solvent selected from the group consisting of propylene glycol monophenyl ether (Propylene glycol butyl ether) and diethylene glycol monophenyl Ether (Diethylene Glycol Monophenyl Ether).

The solvent is a solvent having a surface tension of 20 to 60mN / m by mixing at least two or more solvents comprising a first solvent 20 to 30m / Nm and a second solvent having a surface tension of 40 to 50m / Nm It features.

In addition, the solvent is a solvent having a boiling point of 150 to 300 ℃ by mixing at least two or more solvents including a first solvent having a boiling point of 150 to 220 ℃ and a second solvent having a boiling point of 190 to 300 ℃.

In addition, the mixing ratio of the first solvent and the second solvent is characterized in that 8: 2 to 5: 5 by weight.

In addition, the conductive paste for the solar cell electrode further comprises a dispersant, the dispersant is characterized in that it comprises any one or more of vegetable oil and animal oil.

In another aspect of the present invention, there is provided a solar cell including a front electrode on an upper substrate and a back electrode on a lower substrate, wherein the front electrode is manufactured by coating and firing the conductive paste for the solar cell electrode. Provide a battery.

The present invention can improve the conductivity by controlling the surface tension of the solvent used in the conductive paste for solar cell electrodes, thereby improving the aspect ratio, that is, the line width and line height of the electrode formed using the prepared conductive paste. As the line width of the electrode decreases, the light receiving surface increases, thereby providing a solar cell having high power generation efficiency.

In addition, a solvent having different boiling points is mixed with a conductive paste for solar cell electrodes, and pin-holes, cracks, etc. of electrodes formed by gradually evaporating the solvent during electrode formation using the prepared conductive paste. By preventing the defects of the solar cell efficiency characteristics such as leakage current can be minimized.

In addition, since the solvent composition according to the present invention does not depend on the kind or characteristics of other components (conductive metal powder and binder) used in the conductive paste, it is limited to the kind or characteristics of the conductive metal powder and binder when manufacturing the conductive paste for solar cell electrodes. It doesn't work.

1 is a schematic cross-sectional view of a general solar cell device.

Prior to describing the present invention in detail below, it is understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention, which is limited only by the scope of the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise indicated.

Throughout this specification and claims, unless otherwise indicated, the termcomprise, constitutes, and configure means to include the referenced article, step, or group of articles, and step, and any other article It is not intended to exclude a stage or group of things or groups of stages.

On the other hand, various embodiments of the present invention can be combined with any other embodiment unless clearly indicated to the contrary. Any feature indicated as particularly preferred or advantageous may be combined with any other feature and features indicated as preferred or advantageous. Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention and the effects thereof.

The paste according to an embodiment of the present invention is a paste suitable for use in forming a solar cell electrode, and provides a conductive paste for a solar cell electrode including two or more solvents in order to control surface tension and boiling point. More specifically, the conductive paste according to the present invention comprises a metal powder, a glass frit, a binder, a solvent and other additives.

As the metal powder, silver (Ag) powder, gold (Au) powder, platinum (Pt) powder, nickel (Ni) powder, copper (Cu) powder, or the like may be used. It may be used as, the alloy of the above-described metal may be used, or at least two of the above-described powder may be used as a mixed powder. In addition, the surface of the metal powder can be used as a surface-treated metal powder such as hydrophilic treatment can be used regardless of the surface properties such as hydrophobicity, hydrophilicity of the metal powder.

Among them, it is preferable to use silver (Ag) powder which has excellent electrical conductivity and is mainly used for front electrodes. 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 content of the metal powder is preferably 40 to 95% by weight based on the total weight of the conductive paste composition in consideration of the electrode thickness formed during printing and the wire resistance of the electrode. If less than 40% by weight may be a high specific resistance of the electrode formed, when more than 95% by weight there is a problem that the metal powder is not uniformly dispersed due to insufficient content of other components. More preferably included in 70 to 90% by weight.

The average particle diameter of the silver powder may be 0.1 to 10 μm, and 0.1 to 3 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.

There is no restriction | limiting in particular in the composition, particle diameter, and shape of the said glass frit. Lead-free glass frits can be used as well as leaded glass frits. Preferably, the glass frit component may include at least one selected from the group consisting of Bi ₂ O ₃ , Si-B-Pb, Si-Bi-Zn and Si-Pb-Al-Zn. By combining the organic content of each component of the glass frit, it is possible to prevent an increase in the electrode line width and to improve the contact resistance at the sheet resistance, and to improve the short-circuit current characteristics.

The average particle diameter of the glass frit is not limited, but may have a particle diameter within the range of 0.1 to 10 μm, and may be used by mixing multi-sheet particles having different average particle diameters. Preferably, at least 1 type of glass frit uses that whose average particle diameter (D50) is 0.1 micrometer or more and 5 micrometers or less. Through this, the reactivity is excellent during firing, and the damage of the n-layer can be minimized, especially at high temperature, and the adhesion can be improved and the open-circuit voltage (Voc) can be excellent. In addition, it is possible to reduce the increase in the line width of the electrode during firing.

The content of the glass frit is preferably 1 to 10% 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.

The organic vehicle including the organic binder and the solvent is required to maintain a uniformly mixed state of the metal powder and the glass frit. For example, when the conductive paste is applied to the substrate by screen printing, the conductive paste is used. It is required to have a property of making it homogeneous, suppressing the blurring and flow of the printing pattern, and improving the dischargeability and plate separation property of the conductive paste from the screen plate.

The organic binder may be a cellulose compound, an acrylic compound, an epoxy compound, a polyester compound, a polyvinyl compound, or the like. Examples of the cellulose compounds include cellulose acetate, cellulose acetate butylate, ethyl cellulose, methyl cellulose, hydroxy flophyll cellulose, hydroxy ethyl cellulose, hydroxy propyl methyl cellulose, hydroxy ethyl methyl cellulose, and the like. Examples thereof include poly acrylamide, poly methacrylate, poly methyl methacrylate, polyethyl methacrylate, and the like, and epoxy compounds include bisphenol-A type, bisphenol-F type, bromine type, and novolac. Type, alcohol type, and the like, and examples of the polyvinyl compound include polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol. At least one organic binder may be selected and used.

The organic binder is not limited but is preferably 1 to 15% by weight based on the total weight of the conductive paste composition. When the content of the organic binder is less than 1% by weight, the viscosity of the composition and the adhesion of the formed electrode pattern may be lowered. When the content of the organic binder exceeds 15% by weight, the amount of the metal powder, the solvent, and the dispersant may not be sufficient.

The solvent may control the surface tension and the boiling point by using a mixture of at least two or more solvents including a first solvent and a second solvent. More specifically, the solvent included in the conductive paste according to the present invention is ethyl acetate, butyl carbitol acetate, ethyl carbitol acetate, texanol, texanol, diethylene glycol At least two solvents selected from the group consisting of mono ethylene ether (Diethylene glycol monobutyl ether), propylene glycol monophenyl ether (Propylene glycol butyl ether) and diethylene glycol monophenyl Ether (Diethylene Glycol Monophenyl Ether).

A solvent having a surface tension of 20 to 60 mN / m is used by mixing the first and second solvents selected from the above solvents. For example, a solvent in which a first solvent having a surface tension of 20 to 30 m / Nm and a second solvent having a surface tension of 40 to 50 m / Nm is used. In this case, a butyl carbitol acetate, texanol, and the like may be used as the first solvent, and diethylene glycol monobutyl ether, propylene glycol monophenyl, and the like may be used as the second solvent. Ether (Propylene glycol butyl ether), diethylene glycol monophenyl ether (Diethylene Glycol Monophenyl Ether) and the like can be used. In addition, the mixing ratio of the first solvent and the second solvent is preferably 8: 2 to 5: 5.

By controlling the surface tension of the solvent, the conductivity can be improved by improving the aspect ratio, that is, the line width and line height, of the electrode formed using the prepared conductive paste, and the light receiving surface increases as the line width of the electrode decreases. It is possible to provide a solar cell having a high power generation efficiency.

In addition, a solvent having a boiling point of 150 to 300 ° C. is used by mixing the first and second solvents selected from the above solvents. For example, the solvent which mixed the 1st solvent whose boiling point is 150-220 degreeC, and the 2nd solvent whose boiling point is 190-300 degreeC is used. In this case, ethyl carbitol acetate, propylene glycol monobutyl ether, and the like may be used as the first solvent, and butyl carbitol acetate, and tex may be used as the second solvent. Sanol (Texanol), diethylene glycol monobutyl ether (Diethylene glycol monobutyl ether) Diethylene glycol monophenyl ether (Diethylene Glycol Monophenyl Ether) and the like can be used. In addition, the mixing ratio of the first solvent and the second solvent is preferably 8: 2 to 5: 5.

By mixing solvents with different boiling points, using a conductive paste prepared to prevent the defects such as pin-holes, cracks, etc. of the electrodes formed by gradually evaporating the solvent during electrode formation. It can minimize the part that disturbs solar cell efficiency characteristics such as leakage current.

Most preferably, butyl carbitol acetate and diethylene glycol monophenyl ether are mixed at a 7: 3 (weight) ratio to use a solvent having a surface tension of 35 mN / m and a boiling point of 250 ° C.

The content of the solvent is preferably 5 to 15% by weight based on the total weight of the conductive paste composition. If the content is less than 5% by weight, the electrode may break due to rapid drying during printing. If the content exceeds 15% by weight, the solvent may not be suitable for printing. There is a problem that is formed.

Since the solvent composition according to the present invention does not depend on the kind or properties of other components (conductive metal powder and binder) used in the conductive paste, the solvent composition is not limited to the kind or properties of the conductive metal powder and the binder when manufacturing the conductive paste for solar cell electrodes. Do not.

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

The dispersant may be a vegetable oil, an animal oil, or the like. The dispersant may be included in an amount of 0.1 to 5 wt% based on the total weight of the conductive paste composition. When included in less than 0.1% by weight, there is a problem that the dispersibility is lowered due to insufficient dispersion effect, when included in excess of 5% by weight, the viscosity is lowered due to overdispersion, and stability problems due to paste phase separation during long-term storage Can cause. More preferably included in 0.1 to 3% by weight.

The above-mentioned conductive paste composition for a solar cell electrode may be prepared by mixing and dispersing a metal powder, a glass frit, an organic binder, a solvent and an additive, and then filtering and defoaming.

The present invention also provides a method for forming an electrode of a solar cell and a solar cell electrode produced by the method, wherein the conductive paste is coated on a substrate, dried and baked. Except for using the conductive paste containing the silver powder of the above characteristics in the method of forming a solar cell electrode of the present invention, the substrate, printing, drying and firing can be used as the method commonly used in the manufacture of solar cells as well to be. For example, the substrate may be a silicon wafer.

Examples and Comparative Examples

Metal powder, glass frit, organic binder, solvent and dispersant were added in a composition as shown in Table 1 below, and dispersed using a three-bone mill, followed by mixing silver powder (spherical, average particle diameter of 1 μm) and further using a three-bone mill. And dispersed. After that, degassed under reduced pressure to prepare a conductive paste. The composition of the solvent is shown separately in Table 2 below.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Silver powder 85 85 85 85 Surface Hydrophilized Silver Powder 85 85 85 Glass frit 5 5 5 5 5 5 5 bookbinder 2 2 2 2 2 2 2 Solvent A 7 Solvent B 7 Solvent C 7 Solvent D 7 Solvent E 7 Solvent F 7 Solvent G 7 Dispersant One One One One One One One

Solvent A Solvent B Solvent C Solvent D Solvent E Solvent F Solvent G Furtherance Butyl Carbitol Acetate 5 2 4 Texanol 4 Diethylene Glycol Monophenyl Ether 2 5 3 3 3 2 One Propylene glycol butyl ether 4 5 6 Surface tension (mN / m) 35 40 30 31 28 25 22 Boiling point (℃) 250 250 250 240 240 240 220

Experimental Example

(1) line width and sentence

Line width (μm) Sentence Aspect ratio Example 1 44 21 0.47 Example 2 43 21 0.49 Comparative Example 1 47 19 0.4 Comparative Example 2 46 17 0.37 Comparative Example 3 47 18 0.38 Comparative Example 4 49 15 0.31 Comparative Example 5 51 14 0.27

As shown in Table 3, it can be seen that the line width of the electrode formed of the conductive paste according to the embodiment of the present invention is narrow, the line height is high, and the aspect ratio is high, and thus the electrical conductivity of the solar cell manufactured is excellent. Can be.

(2) Conversion efficiency and electrical conductivity measurement

The obtained conductive paste was pattern printed on the front surface of the wafer by a 40 μm mesh screen printing technique, and dried at 200 to 350 ° C. for 40 to 50 seconds using a belt type drying furnace. After printing the Al paste on the back of the wafer and dried in the same way. The cell formed by the above process was fired for 60 seconds to 80 seconds between 500 to 900 ° C. using a belt type kiln to manufacture solar cells.

The manufactured cell is analyzed by the conversion efficiency (Eff), short circuit current (Isc), open circuit voltage (Voc), curve factor (FF) using a solar cell efficiency measurement equipment (Halm, cetisPV-Celltest 3) It is shown in Table 4, it was shown in Table 4 to measure the line resistance of the electrode pattern.

Isc (A) Voc (V) Eff (%) FF (%) Rs (ohm) Example 1 9.491 0.6386 19.746 77.74 0.00168 Example 2 9.4918 0.6393 19.767 77.749 0.00177 Comparative Example 1 9.472 0.6384 19.651 77.7 0.00198 Comparative Example 2 9.477 0.6371 19.619 77.05 0.00211 Comparative Example 3 9.459 0.6378 19.589 77.75 0.00173 Comparative Example 4 9.4266 0.6379 19.524 78.21 0.00156 Comparative Example 5 9.4116 0.6393 19.518 76.957 0.00207

In general, a solar cell divides efficiency into 0.2% units, and considering that the 0.2% efficiency increase is a value having a very large meaning, an electrode made of a conductive paste containing a solvent according to the present invention as shown in Table 3 above is shown. In the case of a solar cell including a high conversion efficiency compared to the comparative example it can be seen that the power generation efficiency of the solar cell is improved.

Features, structures, effects, and the like illustrated in the above-described embodiments may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, contents related to such combinations and modifications should be construed as being included in the scope of the present invention.

Claims (13)

Metal powder, glass frit, organic binder and solvent, The solvent is a conductive paste for a solar cell electrode, characterized in that to adjust the surface tension and boiling point by using a mixture of at least two or more solvents including a first solvent and a second solvent. The method of claim 1, The solvent is ethyl acetate, butyl carbitol acetate, ethyl carbitol acetate, texanol, diethylene glycol monobutyl ether, propylene A conductive paste for solar cell electrodes comprising a first solvent and a second solvent selected from the group consisting of glycol monobutyl ether and diethylene glycol monophenyl ether. . The method of claim 1, The solvent is a conductive paste for a solar cell electrode, characterized in that the solvent having a surface tension of 20 to 60mN / m by mixing at least two or more solvents including the first solvent and the second solvent. The method of claim 3, The first solvent is a solvent having a surface tension of 20 to 30m / Nm, The second solvent is a conductive paste for a solar cell electrode, characterized in that the solvent having a surface tension of 40 to 50m / Nm. The method of claim 4, wherein The mixing ratio of the first solvent and the second solvent is a conductive paste for a solar cell electrode, characterized in that 8: 8 to 5: 5 by weight. The method of claim 1, The solvent is a conductive paste for a solar cell electrode, characterized in that the boiling point is 150 to 300 ℃ by mixing at least two or more solvents including the first solvent and the second solvent. The method of claim 6, The first solvent is a solvent having a boiling point of 150 to 220 ℃, The second solvent is a conductive paste for a solar cell electrode, characterized in that the boiling point is a solvent having a 190 to 300 ℃. The method of claim 7, wherein The mixing ratio of the first solvent and the second solvent is a conductive paste for a solar cell electrode, characterized in that 8: 8 to 5: 5 by weight. The method of claim 1, The metal powder is a powder having an average particle diameter of 0.1 to 10㎛, selected from the group consisting of silver (Ag) powder, gold (Au) powder, platinum (Pt) powder, nickel (Ni) powder and copper (Cu) powder. Conductive paste for solar cell electrodes comprising any one or more. The method of claim 1, The glass frit has an average particle diameter of 0.1 to 10 μm and includes at least one selected from the group consisting of Bi ₂ O ₃ based, Si-B-Pb based, Si-Bi-Zn based and Si-Pb-Al-Zn based Electroconductive paste for solar cell electrodes characterized by the above-mentioned. The method of claim 1, The organic binder comprises any one or more selected from the group consisting of cellulose compounds, acrylic compounds, epoxy compounds, polyester compounds, and polyvinyl compounds, the conductive paste for solar cell electrodes. The method of claim 1, The conductive paste for solar cell electrodes further comprises a dispersant, The dispersant is a conductive paste for a solar cell electrode, characterized in that it comprises any one or more of vegetable oil and animal oil. 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 conductive paste for solar cell electrode of any one of claims 1 to 12 and then firing.

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