KR20190010343A - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

A composition for forming a solar cell electrode having excellent adhesion includes conductive powder, glass frit, and an organic vehicle. The glass frit is formed from a metallic compound containing 10 to 50 wt% of bismuth oxide, more than 10 wt% and less than 55 wt% of tellurium oxide, 1 to 20 wt% of lithium oxide, 1 to 20 wt% of zinc oxide, and 5 to 50 wt% of selenium oxide.

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 a composition for forming a solar cell electrode.

As the composition for forming a solar cell electrode, a conductive paste composition including conductive powder, glass frit and organic vehicle is used. Among them, the glass frit dissolves an antireflection film formed on a semiconductor wafer, So as to be brought into contact with each other.

In order to increase the efficiency of the solar cell, the series resistance (Rs) must be lowered or the open-circuit voltage (Voc) or the short-circuit current (Isc) must be increased. In general, since they are in a trade off relationship, .

On the other hand, when the ribbon connecting the cells of the solar cell is poor in adhesion with the electrode, the series resistance Rs is large and conversion efficiency is reduced.

Therefore, a solar cell electrode that not only improves the series resistance Rs and the open-circuit voltage Voc at the same time, but also has excellent adhesion to the ribbon is required.

Prior art related to this is disclosed in Japanese Laid-Open Patent Publication No. 2012-84585.

An object of the present invention is to provide a composition for forming a solar cell electrode capable of simultaneously improving the series resistance (Rs) and the open-circuit voltage (Voc) and having excellent adhesion, and an electrode made therefrom.

Another object of the present invention is to provide a composition for forming a solar cell electrode having excellent conversion efficiency and fill factor of a solar cell and an electrode made therefrom.

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 composition for forming a solar cell electrode.

In one embodiment, the composition for forming a solar cell electrode comprises conductive powder, glass frit and organic vehicle, wherein the glass frit comprises 10 wt% to 50 wt% of bismuth oxide, 10 wt% to 55 wt% of tellurium oxide, From 1 to 20% by weight of a lithium compound, from 1 to 20% by weight of zinc oxide, and from 5 to 50% by weight of selenium oxide.

The metal compound may include the tellurium oxide and the selenium oxide in a weight ratio of 2: 1 to 6: 1.

The metal compound may include the tellurium oxide and the selenium oxide in a total amount of 50 to 90% by weight.

The content of tellurium oxide and the content of selenium oxide may satisfy the following formula (1).

[Formula 1]

900? M (Te) M (Se)? 2,000

(Where M (Te) is the weight percent of tellurium oxide and M (Se) is the weight percent of selenium oxide).

The selenium oxide may be included in the metal compound in an amount of 15 to 45% by weight.

The metal compound may be at least one selected from the group consisting of PbO, Na, P, Ge, Ga, Ce, Fe, Si, (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni) (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn), and aluminum (Al).

The composition for forming a solar cell electrode may include 60 to 95% by weight of the conductive powder, 0.1 to 20% by weight of the glass frit, and 1 to 30% by weight of the organic vehicle.

The composition may further comprise at least one of a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoamer, a pigment, a UV stabilizer, a reducing agent, an antioxidant and a coupling agent.

Another aspect of the present invention relates to a solar cell electrode.

In one embodiment, the solar cell electrode may be made of the composition for forming the solar cell electrode.

The present invention provides a composition for forming a solar cell electrode capable of simultaneously improving a series resistance (Rs) and an open-circuit voltage (Voc), exhibiting excellent adhesive force, and having excellent conversion efficiency and fill factor of a solar cell and an electrode .

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

Hereinafter, the present invention will be described in more detail.

In the following description of the present invention, detailed description of known related arts will be omitted when it is determined that the gist of the present invention may be unnecessarily obscured by the present invention.

In the case where the word 'includes', 'having', 'done', etc. are used in this specification, other parts can be added unless '~ only' is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

Also, in interpreting the constituent elements, even if there is no separate description, it is interpreted as including the error range.

As used herein, the 'metal compound' may include at least one of metal oxides, metal nitrides, metal sulfides, and metal carbonates.

In the present specification, 'X to Y' representing the range means 'X or more and Y or less'.

Composition for forming solar cell electrode

The composition for forming a solar cell electrode of the present invention comprises a conductive powder, a glass frit and an organic vehicle, wherein the glass frit comprises 10 wt% to 50 wt% of bismuth oxide, 10 wt% to less than 55 wt% of tellurium oxide, 1 to 20 wt% of at least one of oxide and lithium carbonate, 1 to 20 wt% of zinc oxide, and 5 to 50 wt% of selenium oxide.

Hereinafter, each component of the composition of the present invention will be described in detail.

Conductive powder

The conductive powder is for imparting electrical conductivity. The composition for forming a solar cell electrode of the present invention may use a metal powder such as silver (Ag) or aluminum (Al) as the conductive powder, and for example, silver powder may be used. The conductive powder may be a powder having a nano-sized or micro-sized particle size, for example, a silver powder having a size of tens to hundreds of nanometers, or a powder having a particle size of several to several tens of micrometers. In addition, silver powder having two or more different sizes may be mixed with the conductive powder.

The shape of the conductive powder is not particularly limited, and particles having various shapes, for example, spherical, plate-like or amorphous shapes may be used without limitation.

The average particle diameter (D50) of the conductive powder may be 0.1 占 퐉 to 10 占 퐉, and specifically 0.5 占 퐉 to 5 占 퐉. 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 conductive powder may be contained in the composition for forming a solar cell electrode in an amount of 60 to 95% by weight, specifically 70 to 90% by weight. When the content of the conductive powder satisfies the above range, the conversion efficiency of the solar cell is excellent, and the paste can be smoothly formed.

Glass frit

The glass frit is for etching the antireflection film during the firing process of the composition for forming the solar cell electrode and melting the conductive powder to produce metal crystal grains in the emitter region. Further, the glass frit improves the adhesive force between the conductive powder and the wafer, softens at the time of sintering, and induces an effect of lowering the firing temperature.

The glass frit of the present invention comprises 10 to 50 wt% of bismuth oxide, 10 to 55 wt% of tellurium oxide, 1 to 20 wt% of lithium compound, 1 to 20 wt% of zinc oxide and 5 to 50 wt% of selenium oxide %. ≪ / RTI > In this content range, the series resistance (Rs) and the open-circuit voltage (Voc) of the solar cell electrode can be improved at the same time, the adhesion to the ribbon is excellent, and the solar cell conversion efficiency and fill factor are excellent. The lithium compound may include at least one of lithium oxide and lithium carbonate.

The metal compound may include the tellurium oxide and the selenium oxide in a weight ratio of 2: 1 to 6: 1, specifically 2: 1 to 5: 1, more specifically 2: 1 to 4: 1. In the weight ratio range, conversion efficiency and fill factor of the solar cell are improved.

The metal compound may include the tellurium oxide and the selenium oxide in a total amount of 50 to 90% by weight, specifically 55 to 85% by weight. Within this range, the balance of the electrical characteristics of the solar cell is excellent.

The content of tellurium oxide and the content of selenium oxide may satisfy the following formula (1). In this case, the series resistance (Rs) and the open-circuit voltage (Voc) of the electrode can be improved at the same time, and the adhesive strength to the ribbon is excellent.

[Formula 1]

900? M (Te) M (Se)? 2,000

(Where M (Te) is the weight percent of tellurium oxide and M (Se) is the weight percent of selenium oxide).

The selenium oxide may be specifically included in the metal compound in an amount of 10 to 45% by weight, specifically 15 to 45% by weight, more specifically 15 to 40% by weight. In the above content range, the series resistance Rs can be minimized and the open-circuit voltage Voc can be maximized.

The metal compound may be at least one selected from the group consisting of PbO, Na, P, Ge, Ga, Ce, Fe, Si, (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni) (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn), and aluminum (Al).

The glass frit can be produced by a conventional method used in the art, and is not particularly limited. For example, the glass frit may be prepared by mixing the above-described composition using a ball mill or a planetary mill, melting the mixed composition at a temperature of 900 ° C to 1300 ° C, Followed by quenching at 25 ° C, and then pulverizing the obtained product by a disk mill, a planetary mill or the like.

On the other hand, the glass frit may be contained in the composition for forming a solar cell electrode in an amount of 0.1 to 20% by weight, specifically 0.5 to 10% by weight. When it is contained in the above range, stability of pn junction can be ensured under various sheet resistance, resistance can be minimized, and the efficiency of the solar cell can be ultimately improved.

abandonment Vehicle

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

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 organic vehicle may include 1 to 30% by weight of the composition for forming a solar cell electrode. Within this range, sufficient adhesive strength and excellent printability can be ensured.

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 dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoamer, a pigment, a UV stabilizer, a reducing agent, an antioxidant and a coupling agent. These may be contained in an amount of 0.1 to 5% by weight based on the total weight of the composition for forming a solar cell electrode, but the content can 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. 1 shows a structure of a solar cell according to an embodiment of the present invention.

1, a solar cell 100 according to one embodiment of the present invention includes a substrate 10, a front electrode 23 formed on the front surface of the substrate 10, And a rear electrode 21.

The substrate 10 of one embodiment may be a substrate on which a PN junction is formed. Specifically, the substrate 10 may include a semiconductor substrate 11 and an emitter 12. More specifically, the substrate 10 can be a substrate on which an N-type emitter 12 is formed by doping an N-type dopant on one surface of the P-type semiconductor substrate 11. [ Alternatively, the substrate 10 may be a substrate on which a P-type emitter 12 is formed by doping a P-type dopant on the N-type semiconductor substrate 11. At this time, the semiconductor substrate 11 means either a P-type substrate or an N-type substrate. The P-type substrate may be a semiconductor substrate 11 doped with a P-type dopant, and the N-type substrate may be a semiconductor substrate 11 doped with an N-type dopant.

In describing the substrate 10, the semiconductor substrate 11, and the like in this specification, the surface on the side where light is incident is referred to as a front surface (light receiving surface). The surface on the side opposite to the front surface is referred to as the rear surface.

In one embodiment, the semiconductor substrate 11 may be made of crystalline silicon or compound semiconductor. At this time, the crystalline silicon may be single crystalline or polycrystalline. As the crystalline silicon, for example, a silicon wafer can be used.

In this case, the P-type dopant may be a material containing Group III elements of the periodic table such as boron, aluminum, and gallium. In addition, the N-type dopant may be a material containing elements in the group V of the periodic table such as phosphorus, arsenic, and antimony.

The front electrode 23 and / or the rear electrode 21 may be formed using the electrode forming composition according to the present invention. Specifically, the front electrode 23 may be manufactured using a composition using silver powder as the conductive powder, and the rear electrode 21 may be manufactured using a composition using aluminum powder as the conductive powder. The front electrode 23 may be formed by printing and firing an electrode forming composition on the emitter 12 and the rear electrode 21 may be formed on the rear surface of the semiconductor substrate 11 And then firing it.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Manufacturing example  1 to 12

The metal compounds having the compositions shown in Table 1 were melted and sintered at 900 ° C to 1400 ° C to prepare glass frits 1 to 12 having an average particle diameter (D50) dl of 1.7 μm.

weight% TeO ₂ Bi ₂ O ₃ ZnO Li ₂ CO ₃ SeO ₂ MgO MgO ₂ WO ₃ B ₂ O ₃ Glass frit 1 54.0 14.0 7.0 7.0 18.0 - - - - Glass frit 2 32.0 29.0 20.0 14.0 5.0 - - - - Glass frit 3 40.0 20.0 15.0 15.0 10.0 - - - - Glass frit 4 50.0 21.0 7.0 7.0 15.0 - - - - Glass frit 5 36.0 12.0 10.0 12.0 15.0 5.0 - 5.0 5.0 Glass frit 6 40.0 10.0 5.0 20.0 10.0 - 10.0 - 5.0 Glass frit 7 69.0 14.6 7.0 7.0 - 2.4 - - - Glass frit 8 65.0 21.0 7.0 7.0 - - - - - Glass frit 9 48.0 29.0 10.0 10.0 3.0 - - - - Glass frit 10 60.0 12.0 5.0 5.0 18.0 - - - - Glass frit 11 48.0 12.0 10.0 12.0 3.0 5.0 - 5.0 5.0 Glass frit 12 50.0 - 5.0 10.0 20.0 - 10.0 - 5.0

Example  One

2.5% by weight of ethyl cellulose (STD4) as an organic binder was sufficiently dissolved in 7.5% by weight of solvent Nippon Terpene at 60 DEG C, and spherical silver powder having an average particle diameter of 2.8 mu m (Dowa Hightech CO. LTD (Dowa Hightech CO. LTD., 3-11F), glass frit 1 having an average particle diameter of 2.0 탆, 2 wt% %, 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 to 6 and Comparative Example  1 to 6

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that the glass frit was applied as shown in Table 2 below.

Applied glass frit Applied glass frit Example 1 Glass frit 1 Comparative Example 1 Glass frit 7 Example 2 Glass frit 2 Comparative Example 2 Glass frit 8 Example 3 Glass frit 3 Comparative Example 3 Glass frit 9 Example 4 Glass frit 4 Comparative Example 4 Glass frit 10 Example 5 Glass frit 5 Comparative Example 5 Glass frit 11 Example 6 Glass frit 6 Comparative Example 6 Glass frit 12

Example  7

2.0% by weight of ethyl cellulose (STD4) as an organic binder was sufficiently dissolved in 7.2% by weight of solvent Nippon Terpene at 60 DEG C, and spherical silver powder having an average particle diameter of 2.8 mu m (Dowa Hightech CO. LTD , 26 wt% of a spherical silver powder (Dowa Hightech CO. LTD., AG-3-11F) having an average particle size of 1.4 탆, 2.3 wt% of glass frit 1 having an average particle diameter of 2.0 탆 %, And 0.5 wt% of Thixatrol ST (Elementis co.) Were mixed and mixed by a 3 roll kneader to prepare a composition for forming a solar cell electrode.

Comparative Example  7

A composition for forming a solar cell electrode was prepared in the same manner as in Example 8, except that glass frit 8 was used instead of glass frit 1 in Example 8.

How to measure property

(1) A short circuit current (Isc, A), an open circuit voltage (Voc, mV), and a series resistance (Rs, m?) The solar cell electrode forming paste prepared in the above- Printed by screen printing, and dried using an infrared drying furnace. The cell formed by the above process was fired at 600 to 900 ° C. for 60 seconds to 210 seconds using a belt type firing furnace. The thus-prepared cell was subjected to a short-circuit current (hereinafter referred to as " Isc), open-circuit voltage (Voc) and series resistance (Rs) are shown in Table 3 below.

(2) Fill Factor (%) and Efficiency (%): The paste for forming a solar cell electrode prepared in the above Examples and Comparative Examples was screen-printed on the entire surface of the wafer in a predetermined pattern and dried using an infrared drying furnace . Thereafter, aluminum paste was printed on the rear side of the wafer and then dried in the same manner. The cell thus formed was fired at 400 to 900 ° C. for 30 seconds to 180 seconds using a belt-type sintering furnace. The cell thus manufactured was subjected to a solar cell efficiency measurement (Pasan Co., CT-801) The Fill Factor (FF,%) and the conversion efficiency (Eff.,%) Of the battery were measured and are shown in Table 3 below.

(3) Bond Strength (N / mm): The composition for forming a solar cell electrode prepared in the above Examples and Comparative Examples was screen-printed on the entire surface of 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 formed in the above process were fired at 910 for 40 seconds using a belt-type firing furnace. Flux was applied to the electrodes of the thus fabricated cells, and then bonded to the ribbon at 300-400 using an iron soldering machine (HAKKO) . The adhesive strength was measured at an elongation rate of 50 mm / min using a tensile tester (Tinius olsen) at a peeling angle of 180 °, and is shown in Table 3 below.

Short-circuit current
(A) Open-circuit voltage
(V) Series resistance
(mΩ) FF
(%) Eff.
(%) Adhesive strength
(N / mm) Example 1 9.145 638.6 4.2 78.40 19.01 3.41 Example 2 9.133 639.5 4.5 77.76 18.89 3.50 Example 3 9.143 637.5 4.3 77.80 19.02 3.82 Example 4 9.144 638.2 5.1 77.76 18.96 3.3 Example 5 9.122 642.2 5.4 77.41 18.84 4.01 Example 6 9.155 642.1 5.5 76.35 18.82 4.50 Example 7 9.150 641.1 5.3 77.50 18.89 3.51 Comparative Example 1 9.150 638.2 4.5 78.12 18.95 2.15 Comparative Example 2 9.146 637.8 4.8 77.85 18.90 2.65 Comparative Example 3 9.151 636.7 5.2 77.67 18.68 3.22 Comparative Example 4 9.142 636.1 5.7 76.30 18.70 2.98 Comparative Example 5 9.148 632.1 5.6 77.51 18.65 4.01 Comparative Example 6 9.144 635.8 5.7 77.05 18.94 3.05 Comparative Example 7 9.155 636.5 5.1 77.24 18.75 3.11

As shown in Table 3, the solar cell electrode manufactured by using the glass frit to which the specific components and contents of the present invention were applied had both the series resistance Rs and the open-circuit voltage Voc improved at the same time, It can be seen that not only the factor is excellent but also the adhesive strength is excellent.

On the other hand, Comparative Examples 1, 2, 3 and 5, which do not contain selenium oxide or are out of the scope of the present invention, exhibit poor bonding strength, poor balance of short-circuit current, open- In Comparative Example 4 in which the tellurium oxide exceeded the scope of the present invention, the resistance was high and the bonding strength was low. In Comparative Example 6 which did not contain bismuth oxide, Comparative Example 7 in which the open voltage was low and Comparative Example 7 which did not include selenium oxide It can be seen that the adhesive strength is lower than that of Example 7.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are in all respects illustrative and not restrictive.

10: substrate
11: semiconductor substrate
12: Emitter
21: Rear electrode
23: front electrode

Claims (9)

Conductive powder, glass frit and organic vehicle,
The glass frit,
10 wt% to 50 wt% of bismuth oxide;
From 10 wt% to less than 55 wt% of tellurium oxide;
1 to 20% by weight of a lithium compound;
1 to 20% by weight of zinc oxide; And
And 5 to 50% by weight of selenium oxide.
The method according to claim 1,
Wherein the metal compound comprises the tellurium oxide and the selenium oxide in a weight ratio of 2: 1 to 6: 1.
The method according to claim 1,
Wherein the metal compound comprises the tellurium oxide and the selenium oxide in a total amount of 50 to 90% by weight.
The method according to claim 1,
Wherein the tellurium oxide and the selenium oxide satisfy the following formula 1:
[Formula 1]
900? M (Te) M (Se)? 2,000
(Where M (Te) is the weight percent of tellurium oxide and M (Se) is the weight percent of selenium oxide).
The method according to claim 1,
Wherein the selenium oxide is contained in the metal compound in an amount of 15 to 45% by weight.
The method according to claim 1,
The metal compound may be at least one selected from the group consisting of PbO, Na, P, Ge, Ga, Ce, Fe, Si, (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni) Further comprising at least one of oxide (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn), and aluminum (Al).
The method according to claim 1,
60 to 95% by weight of the conductive powder;
0.1 to 20% by weight of the glass frit; And
And 1 to 30% by weight of the organic vehicle.
The method according to claim 1,
Wherein the composition further comprises at least one of a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoamer, a pigment, an ultraviolet stabilizer, a reducing agent, an antioxidant and a coupling agent.
9. A solar cell electrode made of the composition for forming a solar cell electrode according to any one of claims 1 to 8.

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