KR20160075422A - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

The present invention relates to silver powder; A glass frit comprising from 0.1 to 5% by weight of at least two alkali metal oxides and from 95 to 99.9% by weight of at least one non-alkali metal oxide; And an organic vehicle, wherein the electrode made of the composition minimizes the damage to the emitter by alkali ions, so that the open-circuit voltage is high, and when the series resistance is low, the conversion efficiency is excellent Do.

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. Such an electrode of the solar cell can be formed on the surface of the wafer by applying, patterning and firing the electrode paste composition.

Recently, as the thickness of the emitter is continuously thinned to increase the efficiency of the solar cell, the shunting phenomenon which can degrade the performance of the solar cell can be caused. Further, the area of the solar cell is gradually increased to increase the efficiency of the solar cell, which can reduce the efficiency of the solar cell by increasing the contact resistance of the solar cell.

In general, when the alkali metal oxide is included in the glass frit, the alkali ions in the glass frit are diffused into the wafer, thereby damaging the emitter layer of the wafer. You can give. Such a damage lowers the open-circuit voltage (Voc) of the manufactured solar cell electrode, and consequently, the conversion efficiency may be lowered. The present inventors have completed the present invention in order to minimize the damage of the emitter layer by the alkali metal oxide and to improve the conversion efficiency without lowering the open-circuit voltage.

An object of the present invention is to provide a composition for forming a solar cell electrode capable of minimizing the damage of an alkali ion to an emitter.

Another object of the present invention is to provide a composition for forming a solar cell electrode having high open-circuit voltage and excellent conversion efficiency.

It is another object of the present invention to provide an electrode made from the composition.

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

One aspect of the present invention relates to a silver powder; A glass frit comprising from 0.1 to 5% by weight of at least two alkali metal oxides and from 95 to 99.9% by weight of at least one non-alkali metal oxide; And an organic vehicle. The present invention also relates to a composition for forming a solar cell electrode.

The alkali metal oxide may be a metal oxide selected from the group consisting of lithium oxide, potassium oxide, sodium oxide, cesium oxide, and rubidium oxide.

The alkali metal oxide may include a first alkali metal oxide and a second alkali metal oxide, and the first alkali metal oxide and the second alkali metal oxide may be contained in a weight ratio of 1: 1.5 to 1.5: 1.

Wherein the alkali metal oxide comprises a first alkali metal oxide, a second alkali metal oxide and a third alkali metal oxide, wherein the first alkali metal oxide, the second alkali metal oxide and the third alkali metal oxide have a ratio of 1: 1.2 : 0.4 to 1: 0.8: 0.6.

The non-alkali metal oxide is lead oxide (PbO), bismuth oxide (Bi ₂ O _3), oxide tellurium (TeO _2), silicon oxide (SiO _2), barium (BaO), vanadium oxide (V ₂ O ₅₎ , a (P ₂ O _5), magnesium oxide (MgO), cerium oxide (CeO _2), boron oxide (B ₂ O _3), strontium (SrO), molybdenum oxide (MoO _3), titanium oxide (TiO ₂ ), tin oxide (SnO), indium oxide (In ₂ O _3), nickel (NiO), copper oxide (Cu ₂ O or CuO), antimony oxide _{(Sb 2 O 3, Sb 2} O 4 or Sb ₂ O ₅ ), germanium oxide (GeO _2), gallium (Ga ₂ O _3), calcium oxide (CaO), the oxidation of arsenic (As ₂ O _3), cobalt oxide (CoO or Co ₂ O _3), zirconium oxide (ZrO ₂₎ and it may be at least one selected from the group consisting of manganese oxide _{(MnO, Mn 2 O 3 or} Mn 3 O 4) , and aluminum (Al ₂ O ₃₎ oxide.

The non-alkali metal oxide comprises 20 to 50 wt% of tellurium oxide; 20 to 70% by weight of lead oxide; And 1 to 30% by weight of bismuth oxide.

Said composition comprising 60 to 95% by weight silver powder; 0.5 to 20% by weight of the glass frit; 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 solar cell electrode made of the composition for forming a solar cell electrode of the present invention can have a high open-circuit voltage (Voc), a low series resistance (Rs) and an excellent conversion efficiency by minimizing the damage of the alkali ion to the emitter.

1 (a) is a graph showing the mobility of alkali ions according to the total amount of alkali metal oxides. FIG. 1 (b) is a graph showing the mobility of alkali ions according to the mixing ratio when two kinds of alkali metal oxides are mixed and used Fig.
2 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 powder; A glass frit comprising at least two alkali metal oxides and at least one non-alkali metal oxide; And an organic vehicle. The solar cell electrode made of the composition has a high open-circuit voltage and excellent conversion efficiency because damage of the alkali ion to the emitter is minimized.

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 as the conductive 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 distributing the conductive powder to 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 this range, it is possible to prevent the conversion efficiency from being lowered by increasing the resistance. Preferably 70 to 90% by weight.

(B) a glass frit comprising two or more alkali metal oxides and one or more non-alkali metal oxides

The glass frit is formed by etching the antireflection film during the firing process of the electrode paste, melting the silver particles to produce silver grains in the emitter region so that the resistance can be lowered, and the adhesion between the conductive powder and the wafer And softening at sintering to lower the firing temperature.

Increasing the area of the solar cell to increase the efficiency or the fill factor of the solar cell may increase the contact resistance of the solar cell and minimize the damage to the pn junction and minimize the series resistance. 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.

Generally, when a composition including a glass frit containing an alkali metal oxide is subjected to a firing process for producing an electrode, alkali ions in the glass frit are diffused into the wafer, thereby damaging the emitter layer . Such a damage lowers the open-circuit voltage (Voc) of the manufactured solar cell electrode, and consequently, the conversion efficiency may be lowered. On the other hand, when the alkali metal oxide is excluded from the glass frit composition in order to prevent the damage of the emitter layer, the passivation SiNx layer is not etched on the surface of the Si wafer in order to protect the emitter layer, ) May be increased, and the efficiency of the solar cell thus manufactured may be lowered.

The present invention introduces a heterogeneous alkali metal oxide and reduces the diffusion rate or mobility of the alkali ion by mutual interference of these alkali metal oxides to minimize the damage of the alkali ion on the emitter. to be.

1 (a) is a graph showing the mobility of alkali ions according to the total amount of alkali metal oxides. FIG. 1 (b) is a graph showing the mobility of alkali ions according to the mixing ratio when two kinds of alkali metal oxides are mixed and used Fig. As shown in FIG. 1 (a), when the total amount of the alkali metal oxides is increased, the glass structure is loosened and the mobility of the alkali ions is increased. However, in the case of using glass frit containing two or more kinds of alkali metal oxides, as shown in the graph of FIG. 1 (b), there is an optimum mixing ratio in which the mobility of alkali ions has the minimum value according to the mixing ratio of alkali metal oxides .

The glass frit of the present invention comprises two or more alkali metal oxides and may include one or more non-alkali metal oxides.

The alkali metal oxide may be a metal oxide selected from the group consisting of lithium oxide, potassium oxide, sodium oxide, cesium oxide, and rubidium oxide. The alkali metal oxide may be included in an amount of 0.1 to 5% by weight based on the total weight of the glass frit. Minimization of the mobility of the alkali ion in the above range can minimize the damage of the alkali ion to the emitter.

In one embodiment, when the alkali metal oxide is composed of two kinds of alkali metal oxides including a first alkali metal oxide and a second alkali metal oxide, the first alkali metal oxide and the second alkali metal oxide are preferably 1: 1.5 To 1.5: 1 by weight.

In another embodiment, when the alkali metal oxide is composed of three types of alkali metal oxides including a first alkali metal oxide, a second alkali metal oxide, and a third alkali metal oxide, the first alkali metal oxide, the second alkali metal oxide, The alkali metal oxide and the third alkali metal oxide are preferably contained in a weight ratio of 1: 1.2: 0.4 to 1: 0.8: 0.6.

The non-alkali metal oxide is lead oxide (PbO), bismuth oxide (Bi ₂ O _3), oxide tellurium (TeO _2), silicon oxide (SiO _2), barium (BaO), vanadium oxide (V ₂ O ₅₎ , a (P ₂ O _5), magnesium oxide (MgO), cerium oxide (CeO _2), boron oxide (B ₂ O _3), strontium (SrO), molybdenum oxide (MoO _3), titanium oxide (TiO ₂ ), tin oxide (SnO), indium oxide (In ₂ O _3), nickel (NiO), copper oxide (Cu ₂ O or CuO), antimony oxide _{(Sb 2 O 3, Sb 2} O 4 or Sb ₂ O ₅ ), germanium oxide (GeO _2), gallium (Ga ₂ O _3), calcium oxide (CaO), the oxidation of arsenic (As ₂ O _3), cobalt oxide (CoO or Co ₂ O _3), zirconium oxide (ZrO ₂₎ , it may be at least one member selected from the group consisting of manganese oxide _{(MnO, Mn 2 O 3 or} Mn 3 O 4) , and aluminum (Al ₂ O ₃₎ oxide. The non-alkali metal oxide may be contained in an amount of 95 to 99.9% by weight based on the total weight of the glass frit, and may exhibit a high open-circuit voltage and thus excellent conversion efficiency.

In one embodiment, the non-alkali metal oxide comprises 20 to 50 wt% of tellurium oxide relative to the total weight of the glass frit; 20 to 70% by weight of lead oxide; And 1 to 30% by weight of bismuth oxide. A low series resistance Rs and a high open-circuit voltage Voc in the above range can be ensured.

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 a temperature of 900 ° C to 1300 ° C and quenched at 25 ° C. The resulting product is pulverized by a disk mill, a planetary mill, a jet 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.

(C) Organic vehicle

The organic vehicle imparts suitable viscosity and rheological properties to the paste composition through mechanical mixing with inorganic components of the composition for forming the solar cell electrode.

The organic vehicle may be an organic vehicle usually 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 are added in an amount of 0.1 to 5% by weight based on the total weight of the composition, but they can be changed as needed.

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 illustrates a structure of a solar cell according to an embodiment of the present invention.

2, the composition for forming a solar cell electrode is printed and fired on a wafer 100 or a substrate including a p-layer 101 and an n-layer 102 as an emitter to form the rear electrode 210 and / The front electrode 230 may be formed. For example, a composition for forming a solar cell electrode may be printed on the rear surface of a wafer, and then dried at a temperature of about 200 to 400 캜 for about 10 to 60 seconds to perform a preliminary preparation step for the rear electrode. In addition, a preparation for the front electrode can be performed by printing a composition for forming a solar cell electrode on the entire surface of the wafer and then drying the same. Thereafter, the front electrode and the rear electrode can be formed by performing a sintering process in which sintering is performed at 400 ° C to 950 ° C, preferably 850 ° C to 950 ° C, for 30 seconds to 50 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 1

The metal oxides were mixed with the composition shown in Table 1 below, and the glass frit having an average particle diameter (D50) of 2.0 占 퐉 was prepared by melting and sintering at 900 to 1400 占 폚.

20% by weight of ethyl cellulose (STD4) as an organic binder was sufficiently dissolved in 80% by weight of butylcarbitol as a solvent at 60 DEG C, and spherical silver powder having an average particle diameter of 2.0 mu m (Dowa Hightech CO. 88.5% by weight of the above prepared glass frit, 0.3% by weight of dispersant BYK-102 (BYK-chemie) as an additive and 0.4% by weight of Thixatrol ST (Elementis Co.) as additives, Mixed and dispersed with a three roll kneader to prepare a composition for forming a solar cell electrode.

Aluminum paste was printed on the back side of the wafer and dried in the same manner. Then, the composition for forming the solar cell electrode was screen-printed on the entire surface of a wafer having a sheet resistance of 80? / Sq. By a predetermined pattern, and dried using a drying furnace. The cells thus formed were sintered at a temperature of 980 ° C. for 30 seconds to 50 seconds using a belt-type sintering furnace. The thus-prepared cells were subjected to conversion efficiency (%) using solar cell efficiency measuring equipment (Pasan Co., ), The open-circuit voltage Voc (mV), and the series resistance Rs (Ω) are shown together in Table 1 below.

Examples 2 to 8 and Comparative Examples 1 to 4

The composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except that glass frit was prepared in the contents shown in the following Table 1, and physical properties thereof were measured and shown in Table 1 below.

Composition of glass frit (unit: wt%) Eff (%) Voc
(mV) Rs
(Ω) PbO Bi ₂ O ₃ TeO ₂ Li ₂ O Na ² O K ₂ O Example 1 45.0 6.5 48.0 0.1 0.4 0.0 16.08 615.7 5.2 Example 2 45.0 6.5 48.0 0.2 0.3 0.0 16.14 616.9 5.1 Example 3 45.0 6.5 48.0 0.25 0.25 0.0 16.26 618.6 5.2 Example 4 45.0 6.5 48.0 0.3 0.2 0.0 16.16 617.1 5.2 Example 5 45.0 6.5 48.0 0.4 0.1 0.0 16.08 616.1 5.3 Example 6 45.0 6.5 48.0 0.25 0.0 0.25 16.11 617.0 5.1 Example 7 45.0 6.5 48.0 0.0 0.25 0.25 16.03 615.9 5.3 Example 8 45.0 6.5 48.0 0.2 0.2 0.1 16.01 615.2 5.2 Comparative Example 1 45.0 6.5 48.0 0.5 0.0 0.0 15.74 614.2 5.3 Comparative Example 2 45.0 6.5 48.0 0.0 0.5 0.0 15.71 614.1 5.2 Comparative Example 3 45.0 6.5 48.0 0.0 0.0 0.5 15.66 612.8 5.3 Comparative Example 4 45.0 7.0 48.0 0.0 0.0 0.0 15.71 616.3 7.1

As shown in the above Table 1, the solar cell electrode made of the composition for forming a solar cell electrode using the glass frit of Examples 1 to 8 containing two or more types of alkali metal oxides was comparable to Comparative Example 1 using only one kind of alkali metal oxide To 3 and the comparative example 4 in which the alkali metal oxide was excluded from the glass frit composition, the open-circuit voltage was high, and when the series resistance was low, the conversion efficiency was excellent.

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 (8)

Silver powder;
A glass frit comprising from 0.1 to 5% by weight of at least two alkali metal oxides and from 95 to 99.9% by weight of at least one non-alkali metal oxide; And
An organic vehicle;
Wherein the alkali metal oxide comprises a first alkali metal oxide and a second alkali metal oxide, the first alkali metal oxide and the second alkali metal oxide are contained in a weight ratio of 1: 1.5 to 1.5: 1,
The non-alkali metal oxide comprises 20 to 50 wt% of tellurium oxide; 20 to 70% by weight of lead oxide; And 1 to 30% by weight of bismuth oxide.
The method according to claim 1,
Wherein the alkali metal oxide is a metal oxide selected from the group consisting of lithium oxide, potassium oxide, sodium oxide, cesium oxide, and rubidium oxide. The method according to claim 1,
Wherein the alkali metal oxide further comprises a third alkali metal oxide, and the first alkali metal oxide, the second alkali metal oxide and the third alkali metal oxide are mixed in a weight ratio of 1: 1.2: 0.4 to 1: 0.8: 0.6 Wherein the composition for forming a photovoltaic cell electrode is a photocatalyst. The method according to claim 1,
The non-alkali metal oxide is a silicon oxide (SiO _2), barium (BaO), vanadium oxide (V ₂ O _5), oxidation of (P ₂ O _5), magnesium (MgO), cerium oxide (CeO _2), (B ₂ O ₃ ), strontium oxide (SrO), molybdenum oxide (MoO ₃ ), titanium oxide (TiO ₂ ), tin oxide (SnO), indium oxide (In ₂ O ₃ ) copper (Cu ₂ O or CuO) oxide, antimony oxide _{(Sb 2 O 3, Sb 2} O 4 or Sb ₂ O _5), germanium oxide (GeO _2), gallium oxide (Ga ₂ O _3), calcium oxide (CaO) oxide, arsenic (As ₂ O _3), cobalt oxide _{(CoO or Co 2 O 3)} , zirconium oxide (ZrO _2), manganese oxide _{(MnO, Mn 2 O 3 or} Mn 3 O 4) , and aluminum (Al ₂ O oxide ₃ ). ≪ Desc / Clms Page number 13 > The method according to claim 1,
60 to 95 wt% of the silver powder; 0.5 to 20% by weight of the glass frit; And 1 to 30% by weight of the organic vehicle. The method according to claim 1,
Wherein the glass frit has an average particle diameter (D50) of 0.1 占 퐉 to 10 占 퐉. 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 7.

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