KR20220006374A - Composition for forming solar cell electrode and solar cell electrode prepared using the same - Google Patents

Abstract

Disclosed are: a composition for forming a solar cell electrode, which comprises a conductive powder, a glass frit, and an organic vehicle, wherein the glass frit includes lead (Pb), tellurium (Te), lithium (Li), copper (Cu), and a first element, wherein the first element is at least one of indium (In), aluminum (Al), gallium (Ga), and thallium (Tl), and a molar ratio of copper (Cu) to the first element is 1 : 0.5 to 1 : 15, and a total mol% of copper (Cu) and the first element is 0.5 to 5 mol%; and the solar cell electrode formed from the same.

Description

A composition for forming a solar cell electrode and a solar cell electrode formed therefrom

It relates to a composition for forming a solar cell electrode and a solar cell electrode formed therefrom, and more particularly, a solar cell electrode having a fine line width and a high aspect ratio, and excellent conversion efficiency by minimizing a rise in series resistance along with improvement of short-circuit current and open-circuit voltage It relates to a composition for forming and a solar cell electrode formed therefrom.

A solar cell generates electrical energy by using the photoelectric effect of a p-n junction that converts photons of sunlight into electricity. In a solar cell, a front electrode and a rear electrode are respectively formed on the upper and lower surfaces of a semiconductor wafer or substrate on which a p-n junction is formed. In a solar cell, a photoelectric effect of a p-n junction is induced by sunlight incident on a semiconductor wafer, and electrons generated therefrom provide a current flowing to the outside through an electrode. The electrode of such a solar cell may be formed on the wafer surface by applying, patterning, and firing a paste composition for an electrode.

In recent years, as the thickness of an emitter is continuously reduced in order to increase the efficiency of a solar cell, a shunting phenomenon that may deteriorate the performance of the solar cell may be induced. In addition, in order to increase the efficiency of the solar cell, the area of the solar cell is gradually increased, which may increase the contact resistance of the solar cell and decrease the efficiency of the solar cell.

Therefore, by minimizing damage to the bonding of the emitter layer under various sheet resistances and improving the conductivity at the interface between the wafer and the electrode, it is possible to improve the contact resistance and series resistance, and to develop a paste composition for an electrode that can increase solar cell efficiency. There is a need.

An object of the present invention is to provide a composition for forming a solar cell electrode having a fine line width and a high aspect ratio.

Another object of the present invention is to provide a composition for forming a solar cell electrode having excellent conversion efficiency by minimizing the increase in series resistance along with improvement of short-circuit current and open-circuit voltage.

Another object of the present invention is to provide a solar cell electrode formed from the composition.

1. According to one aspect, a composition for forming a solar cell electrode is provided. The composition includes a conductive powder, a glass frit, and an organic vehicle, wherein the glass frit includes lead (Pb), tellurium (Te), lithium (Li), copper (Cu) and a first element, wherein the first The element is at least one of indium (In), aluminum (Al), gallium (Ga), and thallium (Tl), and the molar ratio of copper (Cu) to the first element is 1:0.5 to 1:15, and copper (Cu) ) and the total mol% of the first element may be 0.5 to 5 mol%.

2. In 1 above, the glass frit may contain 5 to 50 mol% of lead (Pb).

3. In 1 or 2 above, the glass frit may contain tellurium (Te) in an amount of 15 to 70 mol%.

4. In any one of 1 to 3, the glass frit may contain lithium (Li) in an amount of 0.1 to 30 mol%.

5. The glass frit according to any one of 1 to 4, wherein the glass frit further comprises a second element, wherein the second element is bismuth (Bi), zinc (Zn), phosphorus (P), germanium (Ge), silver ( Ag), iron (Fe), silicon (Si), tungsten (W), magnesium (Mg), molybdenum (Mo), cesium (Cs), niobium (Nb), strontium (Sr), titanium (Ti), tin ( Sn), vanadium (V), barium (Ba), nickel (Ni), sodium (Na), potassium (K), calcium (Ca), arsenic (As), selenium (Se), cobalt (Co), zirconium ( Zr), manganese (Mn), calcium (Ca), tantalum (Ta), cerium (Ce), and may include one or more of boron (B).

6. In any one of 1 to 5, the glass frit may further contain 1 to 20 mol% of bismuth (Bi).

7. In any one of 1 to 6, the glass frit may further contain 0.1 to 15 mol% of zinc (Zn).

8. The composition for forming a solar cell electrode according to any one of 1 to 7 above, further comprising at least one of a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, a UV stabilizer, an antioxidant, and a coupling agent can

9. In any one of 1 to 8, the composition for forming a solar cell electrode comprises 60 to 95 wt% of the conductive powder; 0.1 to 20% by weight of the glass frit; and 1 to 30% by weight of the organic vehicle; may include

10. According to another aspect, a solar cell electrode is provided. The electrode may be formed from the composition of any one of 1 to 9 above.

The present invention has the effect of providing a composition for forming a solar cell electrode having a fine line width and a high aspect ratio, and excellent conversion efficiency by minimizing a rise in series resistance along with improvement of short circuit current and open circuit voltage, and a solar cell electrode formed therefrom.

1 schematically shows a solar cell according to an embodiment of the present invention.

In the present specification, the singular expression includes the plural expression unless the context clearly dictates otherwise.

In this specification, terms such as include or have means that the features or components described in the specification exist, and the possibility that one or more other features or components will be added is not excluded in advance.

The terms first, second, etc. used herein may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

Unless otherwise indicated herein, the content of each component of the glass frit is based on the total number of moles of the glass frit, and is based on oxide conversion.

In the present specification, "to" in "a to b" representing a numerical range is defined as ≥a and ≤b.

Composition for forming a solar cell electrode

According to one aspect, the composition for forming a solar cell electrode includes a conductive powder, a glass frit, and an organic vehicle, and the glass frit includes lead (Pb), tellurium (Te), lithium (Li), copper (Cu) and a contains one element, wherein the first element is at least one of indium (In), aluminum (Al), gallium (Ga), and thallium (Tl), and the molar ratio of copper (Cu) to the first element is 1: 0.5 to 1:15, and the total mol% of copper (Cu) and the first element may be 0.5 to 5 mol%.

Hereinafter, each component of the composition for forming a solar cell electrode will be described in more detail.

conductive powder

The conductive powder may include, for example, one or more metal powders of silver (Ag), gold (Au), platinum (Pt), palladium (Pd), aluminum (Al), and nickel (Ni), but is not limited thereto. it is not According to one embodiment, the conductive powder may include silver powder.

The particle shape of the conductive powder is not particularly limited, and particles of various shapes, for example, spherical, plate-like, or amorphous particles may be used.

The conductive powder may be a powder having a particle size of a nano size or a micro size, for example, a conductive powder having a size of several tens to several hundreds of nanometers, or a conductive powder having a size of several to several tens of micrometers. In addition, as the conductive powder, two or more conductive powders having different sizes may be mixed and used.

The average particle diameter (D ₅₀ ) of the conductive powder may be 0.1 to 10 µm (eg, 0.5 to 5 µm), and contact resistance and series resistance may be lowered in the above range, but is not limited thereto. Here, the average particle diameter (D ₅₀ ) may be measured using a 1064LD model manufactured by CILAS, after ultrasonically dispersing the conductive powder in isopropyl alcohol (IPA) at 25° C. for 3 minutes.

The amount of the conductive powder used is not particularly limited, but, for example, the conductive powder may be included in an amount of 60 to 95% by weight (eg, 70 to 90% by weight) of the total weight of the composition for forming a solar cell electrode. In the above range, the conversion efficiency of the solar cell is excellent, and the pasting can be performed smoothly.

glass frit

The glass frit is for generating crystal particles of the conductive powder in the emitter region by etching the antireflection film during the firing process of the composition for forming the solar cell electrode and melting the conductive powder. In addition, the glass frit improves adhesion between the conductive powder and the wafer and softens during sintering to induce the effect of lowering the sintering temperature.

The glass frit includes lead (Pb), tellurium (Te), lithium (Li), copper (Cu) and a first element, wherein the first element is indium (In), aluminum (Al), gallium (Ga) and at least one of thallium (Tl), a molar ratio of copper (Cu) to the first element is 1:0.5 to 1:15, and a total mol% of copper (Cu) and the first element is 0.5 to 5 mol%. can In this case, the conversion efficiency may be excellent by having a fine line width and a high aspect ratio, and minimizing the increase in series resistance along with improvement of short circuit current and open circuit voltage. For example, a molar ratio of copper (Cu) to the first element in the glass frit may be 1:0.5 to 1:10, for example, 1:1 to 1:8, but is not limited thereto. For example, the total mol% of copper (Cu) and the first element in the glass frit may be 0.5 to 4.5 mol%, for example 1 to 4.5 mol%, for another example, 1 to 4 mol%, The present invention is not limited thereto.

According to one embodiment, the glass frit may contain 5 to 50 mol% of lead (Pb). In the above range, the contact resistance may be improved and the conversion efficiency may be excellent. For example, the glass frit may include 10 to 50 mol% of lead (Pb), for example, from 10 to 45 mol%, for another example, from 15 to 45 mol%, but is not limited thereto.

According to one embodiment, the glass frit may include tellurium (Te) in an amount of 15 to 70 mol%. In the above range, the contact resistance may be improved and the conversion efficiency may be excellent. For example, the glass frit may include tellurium (Te) in an amount of 15 to 60 mol%, for example 15 to 55 mol%, for another example, 15 to 50 mol%, but is not limited thereto. .

According to one embodiment, the glass frit may include lithium (Li) in an amount of 0.1 to 30 mol%. In the above range, the contact resistance may be improved and the conversion efficiency may be excellent. For example, the glass frit may include lithium (Li) in an amount of 1 to 30 mol%, for example, 5 to 25 mol%, for another example, 5 to 20 mol%, but is not limited thereto.

According to one embodiment, a molar ratio of copper (Cu) to lithium (Li) in the glass frit is 1: 2 to 1: 65 (eg, 1: 5 to 1: 50, for another example, 1: 10 to 1) : 45), in which contact resistance is improved and conversion efficiency is excellent in the above range, but is not limited thereto.

According to one embodiment, the molar ratio of the first element (eg, indium (In)) to lithium (Li) in the glass frit is 1:1 to 1:30 (eg, 1:1 to 1:20, Another example may be 1:1 to 1:15), and contact resistance may be improved in the above range, and conversion efficiency may be excellent, but is not limited thereto.

According to one embodiment, the glass frit may further include a second element different from the first element. Examples of the second element include bismuth (Bi), zinc (Zn), phosphorus (P), germanium (Ge), silver (Ag), iron (Fe), silicon (Si), tungsten (W), and magnesium (Mg). , molybdenum (Mo), cesium (Cs), niobium (Nb), strontium (Sr), titanium (Ti), tin (Sn), vanadium (V), barium (Ba), nickel (Ni), sodium (Na) , potassium (K), calcium (Ca), arsenic (As), selenium (Se), cobalt (Co), zirconium (Zr), manganese (Mn), calcium (Ca), tantalum (Ta), cerium (Ce) , boron (B), and the like, but is not limited thereto. When the glass frit further includes the second element, contact resistance may be improved, and conversion efficiency may be excellent.

According to one embodiment, the glass frit may further include bismuth (Bi) in an amount of 1 to 20 mol%. In the above range, the contact resistance may be improved and the conversion efficiency may be excellent. For example, the glass frit may include bismuth (Bi) in an amount of 1 to 15 mol%, for example 3 to 15 mol%, and for another example, 5 to 15 mol%, but is not limited thereto.

According to one embodiment, the glass frit may further include 0.1 to 15 mol% of zinc (Zn). In the above range, the contact resistance may be improved and the conversion efficiency may be excellent. For example, the glass frit may contain 1 to 15 mol% of zinc (Zn), for example, 1 to 10 mol%, but is not limited thereto.

The shape and size of the glass frit are not particularly limited. For example, the shape of the glass frit may be spherical or irregular, and the average particle diameter (D ₅₀ ) of the glass frit may be 0.1 to 10 μm. Here, the average particle diameter (D ₅₀ ) may be measured using a 1064LD model manufactured by CILAS after ultrasonically dispersing the glass frit in isopropyl alcohol (IPA) at 25° C. for 3 minutes.

Glass frits may be prepared from the elements and/or element oxides described above using conventional methods. For example, after mixing the above-described elements and/or element oxides using a ball mill or a planetary mill, the mixed composition is melted at 800 to 1,300°C, and 25°C After quenching in the , the obtained result can be obtained by pulverizing by a disk mill, a planetary mill, or the like.

The amount of the glass frit used is not particularly limited, but, for example, the glass frit may be included in an amount of 0.1 to 20% by weight (eg, 0.1 to 10% by weight) of the total weight of the composition for forming a solar cell electrode. In the above range, p-n junction stability can be secured under various sheet resistances, resistance can be minimized, and ultimately, the efficiency of the solar cell can be improved.

organic vehicle

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

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

As the binder resin, an acrylate-based resin or a cellulose-based resin may be used. For example, ethyl cellulose may be used as the binder resin. In another example, as the binder resin, hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and phenol resin, alkyd resin, phenol-based resin, acrylic acid ester-based resin, xylene-based resin, polybutene-based resin, polyester-based resin, Urea-based resin, melamine-based resin, vinyl acetate-based resin, wood rosin, polymethacrylate of alcohol, etc. may be used alone or in combination.

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, ethyl lactate, 2,2, 4-trimethyl-1,3-pentanediol monoisobutyrate (eg, Texanol) may be used alone or in combination.

The amount of the organic vehicle used is not particularly limited, but, for example, the organic vehicle may be included in an amount of 1 to 30% by weight (eg, 3 to 20% by weight) of the total weight of the composition for forming a solar cell electrode. Within the above range, sufficient adhesive strength and excellent printability can be ensured.

additive

In addition to the above components, the composition for forming a solar cell electrode contains a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, a UV stabilizer, an antioxidant, a coupling agent, etc. It may further include alone or two or more types. These may be included 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 may be changed as needed.

Solar cell electrode and solar cell including same

According to another aspect, a solar cell electrode formed from the composition for forming a solar cell electrode and a solar cell including the same are provided. 1 schematically shows the structure of a solar cell 100 according to an embodiment of the present invention.

Referring to FIG. 1 , on a wafer or substrate 10 including a p-layer (or n-layer) 11 and an n-layer (or p-layer) 12 as an emitter, a composition for forming a solar cell electrode is printed and firing to form the rear electrode 21 and the front electrode 23 . For example, after the composition for forming a solar cell electrode is printed and applied to the rear surface of the wafer, it is dried at 200 to 400° C. for 10 to 60 seconds to perform a pre-preparation step for the rear electrode. In addition, the composition for forming a solar cell electrode may be printed on the front surface of the wafer and dried to perform a pre-preparation step for the front electrode. Thereafter, a firing process of firing at 400 to 950° C. for 30 to 210 seconds may be performed to form the front electrode and the rear electrode.

Hereinafter, for example, the composition for forming a solar cell electrode according to an embodiment of the present invention will be described in more detail. However, this is presented as a preferred example of the present invention, and it cannot be construed as limiting the present invention in any sense.

Example

Example 1

After sufficiently dissolving 2 parts by weight of ethyl cellulose (STD4, Dow chemical) as a binder resin with 6.5 parts by weight of terpinol (Nippon Terpine) as a solvent at 60° C., spherical silver powder (4-8F, Dowa) having an average particle diameter of 2.0 μm Company) 90 parts by weight, 1.5 parts by weight of the glass frit A of Table 1 below having an average particle diameter of 1.0 μm, mixed evenly, and mixed and dispersed with a 3-roll kneader to prepare a composition for forming a solar cell electrode.

Examples 2 to 6 and Comparative Examples 1 to 7

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that glass frits B to F of Table 1 were used instead of glass frit A.

glass frit PbO
(mole%) TeO ₂
(mole%) Li ₂ O
(mole%) CuO
(mole%) In ₂ O ₃
(mole%) Tl ₂ O ₃
(mole%) Bi ₂ O ₃
(mole%) ZnO
(mole%) Cu: first element
(molar ratio) Cu + first element
(mole%) Example 1 A 27 42.5 13.6 0.4 2.1 - 8.3 6.1 1:5.3 2.5 Example 2 B 26.6 42 13.4 0.4 3.4 - 8.2 6 1:8.5 3.8 Example 3 C 30.8 42.6 9.8 0.6 1.2 - 8.3 6.7 1: 2 1.8 Example 4 D 27 42.6 13.6 0.4 - 2 8.3 6.1 1: 5 2.4 Example 5 E 30.8 42.6 9.8 0.6 - 1.2 8.3 6.7 1: 2 1.8 Example 6 F 31.6 41 12.8 0.6 0.5 - 9.4 4.1 1: 0.8 1.1 Comparative Example 1 G 27.6 43.7 13.9 - - - 8.5 6.3 - 0 Comparative Example 2 H 27.1 42.8 13.6 - 2.1 - 8.3 6.1 - 2.1 Comparative Example 3 I 27.5 43.5 13.9 0.4 - - 8.5 6.2 - 0.4 Comparative Example 4 J 31.7 41.1 12.9 0.6 0.2 - 9.4 4.1 1: 0.3 0.8 Comparative Example 5 K 26 41.1 13.1 0.3 5.6 - 8 5.9 1:18.7 5.9 Comparative Example 6 L 27.6 43.6 13.9 0.07 0.13 - 8.5 6.2 1: 1.9 0.2 Comparative Example 7 M 25.6 40.5 12.9 1.2 6.1 - 7.9 5.8 1:5.1 7.3

Evaluation Example 1: Electrical properties

Wafer (single crystal wafer in which an n ⁺ _{layer is formed with POCl 3} and silicon nitride (SiNx:H) is formed as an anti-reflection film after texturing the entire surface of the p-type wafer doped with boron) After printing the aluminum paste on the back side of the plate, it was dried at 300°C for 30 seconds. Then, the composition for forming a solar cell electrode prepared in Examples and Comparative Examples was screen-printed on the entire surface of the wafer and dried at 300° C. for 30 seconds. The cell formed by the above process was fired at 940° C. for 70 seconds using a belt-type firing furnace to prepare a solar cell. Short-circuit current (Isc, unit: A), open circuit voltage (Voc, unit: mV), series resistance (Rs, unit : mΩ) and conversion efficiency (Eff., unit: %) were measured, and the results are shown in Table 2 below.

Evaluation Example 2: Aspect Ratio

The compositions for forming solar cell electrodes prepared in Examples and Comparative Examples were screen-printed (screen mask: 360 mesh, emulsion 15, width 35 μm) in a uniform pattern on the entire surface of a crystalline silicon mono wafer. The shape of the electrode was trapezoidal, and the maximum width was 75 µm and the maximum height was 17 µm. Using a belt-type firing furnace, the electrode obtained by drying at 375° C. for 30 to 60 seconds and firing at 600 to 900° C. for 60 to 210 seconds was observed with a 3D laser microscope (KEYENCE, VK-9700), After measuring the thickness (unit: μm) and line width (unit: μm), the aspect ratio (thickness/line width) of the electrode was calculated, and the results are shown in Table 2.

short circuit current open voltage series resistance conversion efficiency line width thickness aspect ratio Example 1 10.179 676.2 1.83 22.11 51.3 17.63 0.34 Example 2 10.179 673.9 1.91 21.98 53.35 18.31 0.34 Example 3 10.202 675.4 1.87 22.09 51.32 18.15 0.35 Example 4 10.223 675.1 1.92 22.02 50.85 18.23 0.36 Example 5 10.171 675.5 1.82 22.00 52.97 16.99 0.32 Example 6 10.182 673.8 1.79 21.97 50.65 17.47 0.34 Comparative Example 1 10.122 671.8 2.16 21.71 65.79 16.89 0.26 Comparative Example 2 10.157 673.3 2.41 21.67 55.78 16.31 0.29 Comparative Example 3 10.152 668.1 2.10 21.65 53.2 15.55 0.29 Comparative Example 4 10.142 669.1 1.95 21.78 64.71 18.55 0.29 Comparative Example 5 10.132 675.4 4.01 21.14 64.84 18.2 0.28 Comparative Example 6 10.156 670.7 1.92 21.66 53.92 16.36 0.30 Comparative Example 7 10.183 676.1 4.30 21.16 52.97 16.99 0.32

As can be seen from Table 2, the solar cells formed from the compositions for forming solar cell electrodes of Examples 1 to 6 including the glass frit of the present invention have fine line width and high aspect ratio compared to Comparative Examples 1 to 7, which is not. It can be seen that the short-circuit current, open-circuit voltage, series resistance and conversion efficiency are excellent.

Up to now, the present invention has been looked at focusing on examples. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

Claims (10)

a conductive powder, a glass frit and an organic vehicle;
The glass frit includes lead (Pb), tellurium (Te), lithium (Li), copper (Cu) and a first element,
The first element is at least one of indium (In), aluminum (Al), gallium (Ga), and thallium (Tl);
The molar ratio of copper (Cu) to the first element is 1:0.5 to 1:15,
The total mol% of copper (Cu) and the first element is 0.5 to 5 mol%, a composition for forming a solar cell electrode.
According to claim 1,
The glass frit comprises lead (Pb) in an amount of 5 to 50 mol%, a composition for forming a solar cell electrode.
According to claim 1,
The glass frit comprises tellurium (Te) in an amount of 15 to 70 mol%, a composition for forming a solar cell electrode.
According to claim 1,
The glass frit comprises lithium (Li) in an amount of 0.1 to 30 mol%, a composition for forming a solar cell electrode.
According to claim 1,
The glass frit further comprises a second element,
The second element is bismuth (Bi), zinc (Zn), phosphorus (P), germanium (Ge), silver (Ag), iron (Fe), silicon (Si), tungsten (W), magnesium (Mg), Molybdenum (Mo), cesium (Cs), niobium (Nb), strontium (Sr), titanium (Ti), tin (Sn), vanadium (V), barium (Ba), nickel (Ni), sodium (Na), Potassium (K), Calcium (Ca), Arsenic (As), Selenium (Se), Cobalt (Co), Zirconium (Zr), Manganese (Mn), Calcium (Ca), Tantalum (Ta), Cerium (Ce) and A composition for forming a solar cell electrode, comprising at least one of boron (B).
According to claim 1,
The glass frit further comprises 1 to 20 mol% of bismuth (Bi), the composition for forming a solar cell electrode.
According to claim 1,
The glass frit further comprises 0.1 to 15 mol% of zinc (Zn), a composition for forming a solar cell electrode.
According to claim 1,
The composition for forming a solar cell electrode further comprises at least one of a dispersing agent, a thixotropic agent, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, an ultraviolet stabilizer, an antioxidant, and a coupling agent.
According to claim 1,
The composition for forming the solar cell electrode,
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; A composition for forming a solar cell electrode comprising a.
A solar cell electrode formed from the composition of any one of claims 1 to 9.

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