TWI621600B - Paste composition for solar cell front electrode and solar cell using thereof - Google Patents

Abstract

The present invention provides a paste composition for a front electrode of a solar cell, and a solar cell manufactured using the paste composition. The paste composition for a solar cell front electrode according to the present invention can be used for manufacturing a solar cell front electrode, and the content of lead oxide in the paste composition is low, so that the paste composition has an ecological environment Friendly advantage. Furthermore, the paste composition for a front electrode of a solar cell according to the present invention can have low contact resistance to an antireflection film while having excellent etching ability, so that a solar cell using the front electrode of the solar cell can have high energy Conversion efficiency, the solar cell front electrode is formed using the paste composition.

Description

Paste composition for solar cell front electrode and solar cell using same [Priority statement]

The priority and the right of the Korean Patent Application No. 10-2015-0139737, filed on October 5, 2015, in the Korean Intellectual Property Office, is hereby incorporated by reference. reference.

The following disclosure relates to a paste composition for a solar cell front electrode, and a solar cell manufactured using the paste composition.

A solar cell is a semiconductor device for converting solar energy into electrical energy, and is composed of a semiconductor wafer, an anti-reflection film, a front electrode, and a rear electrode. In a solar cell, a P-N junction photoelectric effect of a semiconductor wafer is induced by incident sunlight, and an electron generated by a photoelectric effect supplies current through the electrode to the outside.

Wherein the front electrode is applied to one of the wafers by applying a metal paste Formed on the surface. A paste composition containing a metal, a glass frit or the like is applied to a substrate by using a usual screen printing method or the like to form a circuit of a specific shape, and dried and sintered. The applied paste composition imparts conductivity.

In particular, since the front electrode is located at the topmost portion of the solar cell, it is necessary to increase the conductivity while minimizing the light shading loss, so that an excellent adhesive force and a low contact resistance should be developed ( Contact resistance) Metal paste. Among them, the research on glass frit has been actively implemented, and glass frit is one of the important components in metal paste.

The glass frit causes an interface reaction with the antireflection film to etch the antireflection film, wherein the interfacial reaction is a redox reaction, causing some of the elements to be reduced, thereby producing by-products. However, in the glass frit according to the prior art, the content of lead oxide (PbO) is high, causing lead to be reduced after the interface reaction, thereby causing environmental problems.

Therefore, compared to the prior art, there is a continuing need for an eco-friendly paste for solar cell front electrodes that can provide more excellent conversion efficiency and resistance characteristics.

[Previous Technical Document] [Patent Document]

Korean Patent Application No. 10-2011-0074392

An embodiment of the present invention provides an ability to have an excellent conversion A paste composition for solar cell front electrodes that simultaneously reduces the lead oxide content.

Another embodiment of the present invention provides a solar cell fabricated using the paste composition for a front electrode of a solar cell according to the present invention.

This invention relates to a paste composition for a high efficiency solar cell front electrode.

In a general aspect, a paste composition for a solar cell front electrode comprises: a conductive metal powder; a glass frit containing 20 to 60% by weight of TeO ₂ , 1 to 30% by weight PbO, 1 to 20% by weight of ZnO, and 1 to 30% by weight of Bi ₂ O ₃ ; and an organic vehicle.

The glass frit may further comprise one or more selected from the group consisting of SiO ₂ , Li ₂ O, B ₂ O ₃ , Al ₂ O ₃ , CuO, Na ₂ O, ZrO ₂ , MgO, P ₂ O ₅ , CaO, BaO, SnO, SrO, K ₂ O, TiO ₂ , and MnO ₂ .

The glass frit may contain 20 to 60% by weight of TeO ₂ , 1 to 30% by weight of PbO, 1 to 20% by weight of ZnO, 1 to 30% by weight of Bi ₂ O ₃ , and 0.1 to 5% by weight of Li ₂ O, 0.1 to 15% by weight of SiO ₂ , and 0.1 to 10% by weight of B ₂ O ₃ .

The glass frit may be contained in the paste composition in an amount of from 0.1 to 15% by weight.

The conductive metal powder may contain one or more selected from the group consisting of silver, Gold, copper, nickel, aluminum, palladium, chromium, cobalt, tin, lead, zinc, iron, tungsten, magnesium, and alloys thereof. The conductive metal powder may be contained in the paste composition in an amount of 60 to 99.5% by weight.

The organic vehicle may be a binder solution in which an organic binder is dissolved in a solvent and is contained in the paste composition in an amount of 0.1 to 35% by weight. The organic binder may include one or more selected from the group consisting of a cellulose based resin, an acrylic resin, and a polyvinyl based resin.

In another general aspect, there is provided a solar cell front electrode fabricated using the paste composition for a solar cell front electrode as described above, and a solar cell including the paste composition.

Hereinafter, a paste composition for a front electrode of a solar cell according to the present invention will be described in detail. Here, unless otherwise defined, the technical terms and scientific terms used in the specification have the ordinary meaning understood by those skilled in the art to which the invention belongs, and in the following description, the subject matter of the present invention is unnecessarily obscured. Known functions and constructions will be omitted.

In the present invention, a solar cell is a semiconductor component that converts solar energy into electrical energy, and is composed of a semiconductor wafer, an anti-reflection film, a front electrode, and a back electrode.

The present invention relates to a paste composition for a solar cell front electrode, the paste composition comprising: a conductive metal powder; a glass frit containing 20 to 60% by weight of TeO ₂ , 1 to 30% by weight of PbO, 1 to 20% by weight of ZnO, and 1 to 30% by weight of Bi ₂ O ₃ ; and an organic carrier.

The glass frit contained in the paste composition for solar cell front electrode according to the present invention can induce the effect of etching the anti-reflection film in the sintering process, improve the adhesion between the conductive metal powder and the wafer, and further reduce Sintering temperature.

The glass frit causes an interface reaction with the antireflection film to etch the antireflection film, wherein the interfacial reaction is a redox reaction, causing some of the elements to be reduced, thereby producing by-products. However, in the glass frit according to the prior art, the content of lead oxide (PbO) is high, causing lead to be reduced after the interface reaction, thereby causing environmental problems.

Therefore, the paste composition for a front electrode according to the present invention can be environmentally friendly and has excellent etching by reducing the amount of existing lead oxide used in the prior art and increasing the content of ZnO and Bi ₂ O ₃ . ability.

Furthermore, the paste composition for a front electrode according to the present invention can further improve the etching ability and reduce the contact resistance with the antireflection film by containing TeO ₂ while increasing the adhesion between the substrate and the front electrode. This makes it possible to increase the open-circuit voltage.

The glass frit according to the invention may comprise from 20 to 60% by weight of TeO ₂ , from 1 to 30% by weight of PbO, from 1 to 20% by weight of ZnO, and from 1 to 30% by weight, relative to the total content of the glass frit. Bi ₂ O ₃ , thereby improving the light efficiency of the solar cell, but is not limited thereto.

In order to improve the excitation voltage effect, the glass frit according to the present invention may further contain one or more selected from the group consisting of SiO ₂ , Li ₂ O, B ₂ O ₃ , Al ₂ O ₃ , CuO. , Na ₂ O, ZrO ₂ , MgO, P ₂ O ₅ , CaO, BaO, SnO, SrO, K ₂ O, TiO ₂ , and MnO ₂ , and preferably, the glass frit may further contain Li ₂ O, SiO ₂ , with B ₂ O ₃ .

The excitation voltage, which is a required voltage to provide the minimum energy required to cause an atom or molecule to collide to excite an atom or molecule, is indicative of an effect of improving solar cell efficiency.

The content of Li ₂ O, SiO ₂ , and B ₂ O ₃ is not limited, but the glass frit may preferably contain 0.1 to 5% by weight of Li ₂ O, 0.1 to 15% by weight of SiO ₂ , and 0.1 to 10 parts by weight. % of B ₂ O ₃ . The glass frit according to the present invention may preferably contain 20 to 60% by weight of TeO ₂ , 1 to 30% by weight of PbO, 1 to 20% by weight of ZnO, 1 to 30% by weight of Bi ₂ O ₃ , 0.1 to 5 Lithium by weight of Li ₂ O, 0.1 to 15% by weight of SiO ₂ , and 0.1 to 10% by weight of B ₂ O ₃ .

The glass frit according to the present invention may have a network structure containing oxygen, and more specifically, may be composed of an oxygen polyhedron having a random network structure. Preferably, the softening point of the glass frit is from 300 to 500 °C. The viscosity of the glass frit in the above range is suitable, and it is preferable in view of electrode formation, but the glass frit is not limited thereto.

The glass frit according to the present invention may be contained in an amount of 0.1 to 15% by weight. It is contained in the paste composition, thereby having excellent conversion efficiency and preventing an increase in electrical resistance and a decline in solderability, but is not limited thereto.

The glass frit can be produced using a conventional method. For example, the components as described above may be added in the above combination ratio, melted at 900 to 1300 ° C, and then quenched. The glass frit can be obtained by grinding a mixed composition using a ball mill, a disk mill, a planetary mill or the like.

The glass frit may have an average particle size D50 of 0.1 to 5 μm, preferably 0.5 to 3 μm, but is not limited thereto.

The conductive metal powder according to the present invention may be a metal powder generally used for the production of solar cell electrodes. For example, the conductive metal powder may contain one or more selected from the group consisting of silver, gold, copper, nickel, aluminum, palladium, chromium, cobalt, tin, lead, zinc, iron, tungsten, magnesium, and alloys thereof. Preferably, the conductive metal powder may be a silver powder having excellent conductivity and forming strong interfacial adhesion with a crystalline inorganic semiconductor such as ruthenium.

The conductive metal powder, preferably silver powder, may have a purity of 80% or more, preferably 95% or more, but is not particularly limited as long as it satisfies the conditions generally required as an electrode.

The shape of the conductive metal powder is not particularly limited as long as the shape is known in the technical field to which the present invention pertains. For example, the conductive metal powder may have a spherical shape, a flake shape, or a combination thereof, but is not limited thereto.

In addition, the particle size of the conductive metal powder can be sintered in consideration of The rate is adjusted within the appropriate range in the case of the effect of forming the electrode process. According to the present invention, the conductive metal powder may have an average particle size of about 0.1 to 5 μm, thereby reducing contact resistance, but is not limited thereto.

In the paste composition for a solar cell front electrode according to the present invention, the conductive metal powder may be contained in an amount of 60 to 99.5% by weight in view of prevention of viscosity reduction or phase separation of the paste and economic efficiency, preferably It is contained in an amount of 70 to 99.5% by weight, and more preferably, it is contained in an amount of 80 to 99.5% by weight.

The paste composition for a front electrode of a solar cell according to the present invention may contain an organic carrier for adjusting the viscosity and serving as a dispersion medium of a solid phase particle. The organic carrier can be a binder solution in which the organic binder is dissolved in a solvent.

Regarding the organic binder according to the present invention, any organic binder may be used as long as it is generally used, and the organic binder may include one or more selected from the group consisting of cellulose resins, acrylic resins, and poly Vinyl resin.

Specific examples of one of the organic binders may include one or more materials selected from the group consisting of methylcellulose, ethylcellulose, carboxymethylcellulose, nitrocellulose, hydroxycellulose, ethylhydroxyethylcellulose ( Ethylhydroxyethyl cellulose), polymethacrylate, acrylate, butyl acrylate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, and the like.

The solvent of the organic vehicle may be an organic solvent that dissolves the organic binder. A specific example thereof may include one or more solvents selected from the group consisting of pine oil, diethyleneglycol monoethylacetate, diethylene glycol monobutyl Diethyleneglycol monobutylether, diethyleneglycol monobutyletheracetate, ethyleneglycol monobutylether, ethylene glycol monobutyl ether acetate, terpineol, armor Methylglutaric acid, di(2-ethylhexyl)phthalate, diethyl phthalate, diisononyl adipic acid, Dibasic ester, etc.

The content of the organic binder contained in the organic vehicle according to the present invention may be 10 to 30% by weight based on the organic carrier, but is not limited thereto.

The organic vehicle according to the present invention may be contained in an amount of 0.1 to 35% by weight, preferably 10 to 25% by weight, relative to the paste composition for the solar cell front electrode, thereby easily dispersing the conductive metal powder and maintaining it. The efficiency of solar cells is high, but not limited to this.

If desired, the paste composition for a front electrode of a solar cell according to the present invention may further contain a generally known additive. An example of one of the additives may include one or more materials selected from the group consisting of: a thickener, a thixotropic agent, a stabilizer, a dispersing agent, a leveling agent, and a defoaming agent. )Wait. The amount of the additive may be from about 0.1 to 10% by weight with respect to the paste composition, but may be determined depending on the characteristics of the finally obtained paste composition for the front electrode of the solar cell.

Further, the present invention can provide a solar cell front electrode formed using the paste composition.

The electrode can be used in a printing paste composition according to the present invention. The wafer substrate is formed by drying and sintering the applied paste composition. Regarding the printing method, a screen printing method, a gravure printing method, an offset printing method, a roll-to-roll printing method, an aerosol printing method (aerosol) can be used. Printing method), jet printing method, etc., but the printing method is not particularly limited thereto.

Furthermore, the present invention can provide a solar cell including the front electrode of the solar cell. The solar cell according to the present invention can have excellent conversion efficiency and resistance characteristics, thereby making it possible to remarkably improve the power generation efficiency of the solar cell.

A solar cell according to an exemplary embodiment of the present invention is as follows.

The solar cell system includes a first semiconductor layer; a second semiconductor layer formed on the first semiconductor layer; an anti-reflection film formed on the second semiconductor layer; and a front electrode penetrating the anti-reflective film Connected to the second semiconductor layer; and a back electrode formed on a back surface of one of the semiconductor layers.

Specifically, one of the semiconductor materials used in the semiconductor layer may be a crystalline germanium. For example, a stack of wafers can be used. One of the first and second semiconductor layers may be a semiconductor layer doped with a p-type impurity, and the other may be a semiconductor layer doped with an n-type impurity. Regarding the p-type impurity, a group 3 element (B, Ga, In, etc.) may be doped, and with respect to the n-type impurity, a group 5 element (P, As, Sb, etc.) may be doped.

The P-N junction may be formed in an interface between the semiconductor layers, and The P-N junction is a portion that receives solar light to generate a current by the photoelectric effect. The electrons and holes generated by the photoelectric effect can be pulled to the P and N layers, respectively, to thereby move to the electrodes connected to the upper and lower portions thereof, respectively, and the electric power generated in the electrodes can be used by It is applied to the load applied to the electrode.

An anti-reflection film may be formed on the second semiconductor layer. The anti-reflection film can reduce the reflectance of solar light incident on one of the front surfaces of the solar cell. When the reflectance of the solar light is lowered, the amount of light reaching the P-N junction can be increased, so that the short-circuit current of the solar cell can be reduced, and the conversion efficiency of the solar cell can be improved.

The antireflection film can be made of a material that absorbs less light and has insulating properties. For example, an antireflection film can be produced by: tantalum nitride (SiN _x ), yttrium oxide (SiO ₂ ), titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), oxidation. Cerium (CeO ₂ ), or a combination thereof, and the antireflection film may be formed of a single layer or a plurality of layers.

The front electrode may be formed on the anti-reflection film, and the back electrode may be formed on the back surface of the semiconductor layer. The electrode can be formed by printing a paste composition containing a conductive metal powder on a semiconductor wafer and then performing heat treatment thereon.

The antireflection film can be partially removed by chemical treatment. The antireflection film can be deposited by a chemical vapor deposition (CVD) method, a plasma enhanced chemical vapor deposition (PECVD) method, a sputtering method, or the like. The electrical contact between a semiconductor layer and one of the conductors of the paste composition can be improved by partially removing the anti-reflective film. The paste composition can be printed as a pattern On the anti-reflection film, the pattern is, for example, a bus bar having a connection line. The paste composition can be printed by a screen printing method, a plating method, an extrusion method, a forming or multiple printing method, or a ribbon method.

In the process of forming an electrode, the conductive metal powder can be sintered by heating the paste composition. Typically, the sintering temperature can be set such that any other organic materials and organic materials present in the paste composition can be burned out. According to an exemplary embodiment, the sintering temperature may be 750 to 950 °C.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are only intended to specifically explain the present invention. Therefore, the invention is not limited thereto.

[Examples 1 to 6]

1. Preparation of glass frit

After mixing the content ratios (% by weight) described in Table 1 below in the following Table 1 with each other, the mixture was melted at 1100 ° C for 30 minutes, and then quenched by pure water (H ₂ O). The mixture is rapidly cooled. The rapidly cooled glass frit was ground using an Attrition-mill grinder, thereby preparing a glass frit having an average particle size of 1.5 μm.

The components and contents of the glass frit corresponding to the respective examples are described in Table 1 below.

2. Preparation of paste composition

Each paste composition was prepared using the glass frit produced. Regarding the conductive metal powder, it is used at a content of 90% by weight and has an average particle size of 2 micron silver powder. The glass frit was used in an amount of 2% by weight. Regarding the organic binder, cellulose ester (EASTMAN, CAB) and ethyl cellulose resin (AQUALON, ECN) were each used in an amount of 1% by weight.

Regarding the organic solvent, 2% by weight of trimethyl pentanyl diisobutylate (TXIB), 3% by weight of a dibasic ester (dimethyl adipate / dimethyl glutarate) / dimethyl adipate / dimethyl glutarate / dimethyl succinate mixture, TCI), and 1% by weight of butyl carbitol (BC).

3. Manufacturing of solar cells

To fabricate a solar cell, a semiconductor layer having a sheet resistance of 90 ohms/square (Ω/sq) is used at 810 ° C in a tube furnace using a 156 mm single crystal germanium wafer. It is formed by doping phosphorus (P) with POCl ₃ through a diffusion process, and a tantalum nitride film is used by chemical vapor deposition (PECVD) using SiH ₄ and NH ₃ precursors at 70 nm. The thickness is deposited on the semiconductor layer, thereby forming an anti-reflection film.

In order to manufacture the back electrode, an electrode paste composition containing aluminum powder (instead of silver powder) was applied to a back surface by a screen printing method at a thickness of 30 μm, followed by drying at 250 ° C in a drying oven. second. In order to manufacture the front electrode, the paste composition prepared according to the examples of the present invention and the paste composition prepared in the comparative example were each applied by a screen printing method at a thickness of 20 μm, followed by drying. The oven was dried at 200 ° C for 60 seconds. The solar cell printed thereon is carried out at 820 ° C in a belt firing furnace. The sintering process was carried out for 1 minute, thereby producing a solar cell. The results obtained by evaluating the characteristics of the manufactured solar cells are described in Table 2 below.

[Comparative Examples 1 to 3]

A solar cell was fabricated using the same methods and conditions as in Example 1, except that the composition of the glass frit described in Table 1 below was different. The results obtained by evaluating the characteristics of the manufactured solar cells are described in Table 2 below.

[Feature evaluation]

1. Manufacturing a solar cell that is printed/sintered to have a 3 bus bar structure, a 50 micron finger width, and a pattern of 105 finger lines, and its characteristics are Evaluation. The electro-optical characteristic of the fabricated solar cell was measured, and the current density-voltage characteristic (JV) was measured at 100 mW/cm 2 by the Oriel 1000W solar simulator. (mW/cm ² ) measured under light (AM 1.5G). The energy conversion efficiency (%) was obtained using the measured value and the following formula I. Conversion efficiency means the ratio of the output power of a solar cell to the incident light energy per unit area.

The series resistance is calculated after measuring the J-V characteristics of the simulator and is used to understand the correlation with the fill factor (FF).

V _oc refers to the open circuit voltage (V), J _sc refers to the short circuit current (milliamps per square centimeter (mA/cm ² )), FF refers to the fill factor (%), and the incident light intensity Pin is 100 mW/square. Centimeters.

2. The ribbon adhesive force was evaluated using a solder ribbon used to fabricate a module having a width of 1.2 mm. The solder ribbon is composed of Pb and Sn (ratio: 60/40 (Pb/Sn)), and the surface of the solder ribbon coated with KESTER 955 flux is soldered. Attached to the upper end of the busbar of the manufactured solar cell.

A ribbon which was cut at a length of 200 mm was immersed in a Kester 955 flux solution for 1 minute and dried at 100 ° C for 10 minutes, thereby being prepared. The welding tape system uses SCB-130B manual soldering equipment. (SEMTEK) is attached to the solar cell. The soldering is performed by placing a flux-coated solder ribbon on the upper end of the busbar of the solar cell and heating the ribbon at 300 ° C for 1 minute.

The adhesion of the attached solder ribbon was measured using a DS2-20N device (IMADA). In this case, the angle between the ribbon and the solar cell is maintained at 180 degrees.

As shown in Table 2, it can be seen that, in comparison with the comparative examples, in the solar cell manufactured in the embodiment using the paste composition for solar cell front electrode according to the present invention, the electrode and a solar substrate Series resistance between less. Therefore, the open circuit voltage and the fill factor characteristics are improved, and therefore, it can be observed that the solar cell has excellent energy conversion efficiency.

Further, as a result of confirming the adhesion of the solder ribbon, it was confirmed that the solar cell system according to the embodiment of the present invention has strong adhesion as compared with the comparative embodiment. Since the solar cell could not be modularized in the case where the adhesion of the solder ribbon was weak, it was confirmed that the solar cell module using the paste composition according to the present invention has excellent safety.

The paste composition for a solar cell front electrode according to the present invention can be used to manufacture a solar cell front electrode, and the lead content in the paste composition is low, so that the paste composition has an eco-friendly advantage.

Furthermore, the paste composition for a front electrode of a solar cell according to the present invention can have low contact resistance to an antireflection film while having excellent etching ability, resulting in use of the front electrode of the solar cell (using a paste composition) The formed solar cell can have high energy conversion efficiency.

The present invention has been described above by way of exemplary embodiments, and such embodiments are only provided to assist in the understanding of the invention. Accordingly, the invention is not limited to such exemplary embodiments. Various modifications and changes can be made by those skilled in the art from this disclosure.

Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the scope of the following claims and the modifications and equivalents of the claims are intended to fall within the scope and spirit of the invention.

Claims (9)

A paste composition for a solar cell front electrode, the paste composition comprising: a conductive metal powder; a glass frit, containing 20 to 60% by weight of TeO ₂ , 1 to 30% by weight of PbO, 1 to 20% by weight of ZnO, 1 to 30% by weight of Bi ₂ O ₃ , 0.1 to 5% by weight of Li ₂ O, 0.1 to 15 by weight % SiO ₂ , and 0.1 to 10% by weight of B ₂ O ₃ ; and an organic vehicle. The paste composition of claim 1, wherein the glass frit further comprises one or more selected from the group consisting of Al ₂ O ₃ , CuO, Na ₂ O, ZrO ₂ , MgO, P ₂ O ₅ , CaO , BaO, SnO, SrO, K ₂ O, TiO ₂ , and MnO ₂ . The paste composition of claim 1, wherein the glass frit is contained in the paste composition in an amount of from 0.1 to 15% by weight. The paste composition of claim 1, wherein the conductive metal powder contains one or more selected from the group consisting of silver, gold, copper, nickel, aluminum, palladium, chromium, cobalt, tin, lead, zinc, iron, tungsten. , magnesium, and alloys thereof. The paste composition of claim 1, wherein the conductive metal powder is contained in the paste composition in an amount of from 60 to 99.5% by weight. The paste composition of claim 1, wherein the organic vehicle is contained in the paste composition in an amount of from 0.1 to 35% by weight. The paste composition of claim 1, wherein the organic carrier is a binder solution A binder solution in which an organic binder is dissolved in a solvent. The paste composition of claim 7, wherein the organic binder comprises one or more selected from the group consisting of a cellulose based resin, an acrylic resin, and a polyethylene resin. Based resin). A solar cell manufactured by using the paste composition according to any one of claims 1 to 8.