KR20150019404A - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

The present invention relates to a composition for forming a solar cell electrode, wherein the composition comprises: a silver (Ag) powder; a glass frit including neodymium oxide (Nd2O3) and tellurium oxide (TeO2); and an organic vehicle. The neodymium oxide and the tellurium oxide are included at a mole ratio of 1:3 to 1:100. The composition has improved contact with an electrode and a wafer by introducing neodymium oxide. A solar cell electrode produced using the composition has a low leakage current value, a high open voltage, and an excellent conversion effect.

Description

TECHNICAL FIELD [0001] The present invention relates to a composition for forming a solar cell electrode, and an electrode made therefrom. BACKGROUND ART [0002]

The present invention relates to a composition for forming a solar cell electrode and an electrode made therefrom.

Solar cells generate electrical energy by using the photoelectric effect of pn junction that converts photon of sunlight into electricity. The solar cell is formed with a front electrode and a rear electrode on a semiconductor wafer or a substrate on which a pn junction is formed. The photovoltaic effect of the pn junction is induced in the solar cell by the sunlight incident on the semiconductor wafer, and the electrons generated from the pn junction provide a current flowing to the outside through the electrode. The electrode of such a solar cell can be formed on the surface of the wafer by applying, patterning and firing the composition for electrode formation.

Recently, as the thickness of the emitter is continuously thinned to increase the efficiency of the solar cell, it is possible to cause a shunting phenomenon which may degrade the performance of the solar cell. In order to increase the conversion efficiency The area of the solar cell is gradually increasing, which can reduce the efficiency of the solar cell by increasing the contact resistance of the solar cell.

Accordingly, it is urgently required to develop a composition capable of producing a solar cell electrode having excellent conversion efficiency by improving the contact property with a wafer.

It is an object of the present invention to provide a composition for forming a solar cell electrode that is excellent in contact properties between an electrode and a wafer surface.

Another object of the present invention is to provide a composition for forming a solar cell electrode capable of minimizing leakage current.

It is still another object of the present invention to provide a solar cell electrode having excellent open circuit voltage and conversion efficiency.

It is still another object of the present invention to provide a solar cell electrode made of the above composition.

The above and other objects of the present invention can be achieved by the present invention described below.

As one aspect of the present invention, a composition for forming a solar cell electrode comprises a silver (Ag) powder; Glass frit including neodymium oxide (Nd2O3) and tellurium oxide (TeO2); And an organic vehicle, wherein the neodymium oxide and the tellurium oxide may be contained in a molar ratio of 1: 3 to 1: 100.

The glass frit may be formed of at least one selected from the group consisting of lead (Pb), bismuth (Bi), tellurium (Te), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Se) (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (V), Ru, Ba, Ni, Cu, Na, K, As, Manganese (Mn), and aluminum (Al) oxides.

The glass frit may contain 0.5 to 30% by weight of neodymium oxide based on the total weight of the glass frit.

Wherein the composition for forming the solar cell electrode comprises 60 to 95% by weight of silver (Ag) powder; 0.1 to 20% by weight of glass frit comprising neodymium oxide and tellurium oxide; And 1 to 30% by weight of the organic vehicle.

The glass frit may have an average particle diameter (D50) of 0.1 占 퐉 to 10 占 퐉.

The composition may further include at least one additive selected from the group consisting of a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoamer, a pigment, a UV stabilizer, an antioxidant and a coupling agent.

A solar cell electrode, which is another aspect of the present invention, may be formed from the composition for forming the solar cell electrode.

The composition for forming a solar cell electrode of the present invention improves the contact between the electrode and the wafer by introducing neodymium oxide. The solar cell electrode made of the composition has low leakage current, high open circuit voltage, high conversion efficiency Do.

1 is a schematic view briefly showing a structure of a solar cell according to an embodiment of the present invention.

Composition for forming solar cell electrode

The composition for forming a solar cell electrode of the present invention comprises silver (Ag) powder (A); Glass frit (B); And an organic vehicle (D). Hereinafter, the present invention will be described in detail.

(A) is powder

The composition for forming a solar cell electrode of the present invention uses silver (Ag) powder which is a conductive powder as a first metal powder. The silver powder may be a nano-sized or micro-sized powder, for example, a silver powder having a size of several tens to several hundreds of nanometers, a silver powder of several to several tens of micrometers, Silver powder may be mixed and used.

The silver powder may have a spherical shape, a plate shape, and an amorphous shape as the particle shape

The average particle diameter (D50) of the silver powder is preferably 0.1 to 10 mu m, more preferably 0.5 to 5 mu m. The average particle diameter was measured using a 1064 LD model manufactured by CILAS after dispersing the conductive powder in isopropyl alcohol (IPA) by ultrasonication at 25 캜 for 3 minutes. Within this range, the contact resistance and line resistance can be lowered.

The silver powder may be included in an amount of 60 to 95% by weight based on the total weight of the composition. In the above range, it is possible to prevent the conversion efficiency from being lowered by increasing the resistance. Preferably 70 to 90% by weight.

(B) Glass Frit

The glass frit is produced by etching an antireflection film during a sintering process of a composition for forming a solar cell electrode, melting silver particles to produce silver crystal grains in the emitter region so that resistance can be lowered, The adhesion between the wafers is improved and softening at the time of sintering induces an effect of lowering the firing temperature.

Increasing the area of the solar cell in order to increase the efficiency of the solar cell may increase the contact resistance of the solar cell. Therefore, the damage to the pn junction should be minimized and the series resistance should be minimized. In addition, it is preferable to use a glass frit which can sufficiently secure thermal stability even at a wide firing temperature because the range of variation in firing temperature becomes large as wafers of various sheet resistances increase.

In one embodiment, the glass frit comprises neodymium oxide (Nd2O3) and tellurium oxide (TeO2), wherein the neodymium oxide and tellurium oxide are present in a molar ratio of 1: 3 to 1: 100. It is possible to sufficiently secure the mobility of the silver particles upon firing the composition for forming a solar cell electrode within the range of the mole ratio, thereby minimizing the leakage current (Jo2), thereby improving the open-circuit voltage (Voc) Can be obtained.

The glass frit may contain 0.5 to 30% by weight of neodymium oxide based on the total weight of the glass frit.

As yet another embodiment. The glass frit may be formed of at least one selected from the group consisting of lead (Pb), bismuth (Bi), tellurium (Te), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Se) (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (V), Ru, Ba, Ni, Cu, Na, K, As, Manganese (Mn), and aluminum (Al) oxides.

The glass frit may be at least one of a flexible glass frit or a lead-free glass frit, but may be preferably a flexible glass frit.

The glass frit can be prepared from the metal oxides described above using conventional methods. For example, in the composition of the metal oxide described above. The blend can be mixed using a ball mill or a planetary mill. The mixed composition is melted at 700 ° C to 1300 ° C and quenched at 25 ° C. The resulting product is pulverized by a disk mill, a planetary mill or the like to obtain a glass frit.

The glass frit may have an average particle diameter (D50) of 0.1 to 10 mu m and may be contained in an amount of 0.5 to 20 wt% based on the total weight of the composition.

The shape of the glass frit may be spherical or irregular. In a specific example, two kinds of glass frit having different transition points may be used. For example, a first glass frit having a transition temperature of 200 ° C or higher and 350 ° C or lower and a second glass frit having a transition point of 350 ° C or higher and 550 ° C or lower may be mixed at a weight ratio of 1: 0.2 to 1: 1.

(C) Organic Vehicle

The organic vehicle imparts viscosity and rheological properties suitable for printing to a composition for forming a solar cell electrode through mechanical mixing with an inorganic component.

The organic vehicle may be an organic vehicle commonly used in a composition for forming a solar cell electrode, and may generally include a binder resin, a solvent, and the like.

As the binder resin, an acrylate-based or cellulose-based resin can be used, and ethylcellulose is generally used. However, it is preferable to use a mixture of ethylhydroxyethylcellulose, nitrocellulose, a mixture of ethylcellulose and phenol resin, an alkyd resin, a phenol resin, an acrylic ester resin, a xylene resin, a polybutene resin, a polyester resin, Based resin, a rosin of wood, or a polymethacrylate of alcohol may be used.

Examples of the solvent include hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) , Butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma butyrolactone or ethyl lactate, Two or more of them may be used in combination.

The blending amount of the organic vehicle may be 1 to 30% by weight based on the total weight of the composition. Within this range, sufficient adhesive strength and excellent printability can be ensured.

(D) Additive

The composition for forming a solar cell electrode of the present invention may further include conventional additives as needed in order to improve flow characteristics, process characteristics, and stability in addition to the above-described components. The additive may be used alone or as a mixture of two or more of a dispersing agent, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoaming agent, a pigment, an ultraviolet stabilizer, an antioxidant and a coupling agent. These may be added in an amount of 0.1 to 5% by weight based on the total weight of the composition, and may be changed as necessary.

Solar cell electrode and solar cell comprising same

Another aspect of the present invention relates to an electrode formed from the composition for forming a solar cell electrode and a solar cell including the same. 2 shows a structure of a solar cell according to one embodiment of the present invention.

1, a composition for electrode formation is printed on a wafer 100 or a substrate including a p-layer (or n-layer) 101 and an n-layer (or p-layer) So that the rear electrode 210 and the front electrode 230 can be formed. For example, the electrode forming composition may be applied to the rear surface of the wafer by printing and then dried at a temperature of about 200 캜 to 400 캜 for about 10 to 60 seconds to perform a preliminary preparation step for the rear electrode. In addition, a preparation step for the front electrode can be performed by printing a composition for electrode formation on the entire surface of the wafer and then drying it. Thereafter, the front electrode and the rear electrode may be formed by performing a firing process at 400 ° C. to 950 ° C., preferably 750 ° C. to 950 ° C., for 30 seconds to 180 seconds.

Hereinafter, the present invention will be described in more detail by way of examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Example

Example  One

3% by weight of ethyl cellulose (STD4) as an organic binder was sufficiently dissolved in 6.5% by weight of butylcarbitol as a solvent at 60 占 폚, and spherical silver powder having an average particle diameter of 2.0 占 퐉 (Dowa High Tech CO. (BYK-chemie) 0.2% by weight as an additive and 0.3% by weight of Thixatrol ST (Elementis co.) As an additive. %, And the mixture was evenly mixed and then mixed and dispersed with a three-roll kneader to prepare a composition for forming a solar cell electrode.

Example  2-4 and Comparative Example  1 - 3

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except that glass frit having the composition shown in the following Table 1 was used.

Property evaluation method

The composition for forming a solar cell electrode according to the above-described Examples and Comparative Examples was screen-printed on a crystal mono wafer in a predetermined pattern, and dried using an infrared drying furnace. Thereafter, a composition for forming an electrode containing aluminum was printed on the rear surface of the wafer by back printing and then dried by the same method. The cells thus formed were fired at 600 to 900 ° C for 60 seconds to 210 seconds using a belt-type sintering furnace. The cells thus manufactured were measured for solar cell efficiency (Pasan Co., CT-801) (Leakage Current, Jo2), Open Voltage (Voc), and Conversion Efficiency (%) were measured and shown in Table 2 below.

[Table 1]

[Table 2]

As shown in the results of Table 2, the electrode made of the composition for forming a solar cell electrode including the glass frit of Example 1-4 had the glass frit of Comparative Examples 1 and 2 containing no neodymium oxide, The open-circuit voltage and the conversion efficiency are superior to those of the electrode made of the glass frit of Comparative Example 3 in which the mole ratio of tellurium and tellurium oxide is outside the range defined in the present invention.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

Silver (Ag) powder;
Glass frit including neodymium oxide (Nd2O3) and tellurium oxide (TeO2); And
An organic vehicle;
Wherein the composition comprises neodymium oxide and tellurium oxide in a molar ratio of 1: 3 to 1: 100.
The method according to claim 1,
The glass frit may be formed of at least one selected from the group consisting of lead (Pb), bismuth (Bi), tellurium (Te), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Se) (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (V), Ru, Ba, Ni, Cu, Na, K, As, Manganese (Mn), and aluminum (Al) oxides.
The method according to claim 1,
Wherein the glass frit comprises 0.5 to 30% by weight of neodymium oxide based on the total weight of the glass frit.
The method according to claim 1,
From 60 to 95% by weight of silver (Ag) powder;
0.1 to 20% by weight of glass frit comprising neodymium oxide and tellurium oxide; And
And 1 to 30% by weight of the organic vehicle.
The composition for forming a solar cell electrode according to claim 1, wherein the glass frit has an average particle diameter (D50) of 0.1 to 10 mu m.
The method according to claim 1,
Wherein the composition further comprises at least one additive selected from the group consisting of dispersing agents, thixotropic agents, plasticizers, viscosity stabilizers, defoamers, pigments, ultraviolet stabilizers, antioxidants and coupling agents .
A solar cell electrode made of the composition for forming a solar cell electrode according to any one of claims 1 to 6.

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