KR20190073210A - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

An objective of the present invention is to provide a composition for forming an electrode of a solar cell with the excellent printability and reliability and an electrode manufactured therefrom. The composition for forming an electrode of a solar cell of the present invention comprises: conductive powder; glass frit; an organic binder; and a solvent.

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 the solar cell electrode, a conductive paste composition including conductive powder, glass frit, binder and solvent is used. Among them, the solvent has viscosity and rheological properties suitable for printing through mixing of composition components for forming a solar cell electrode .

In particular, the solvent is involved in the printability and plasticity of the composition, and thus affects the reliability of the solar cell electrode, the open circuit voltage and the conversion efficiency.

Prior art related to this is disclosed in Japanese Laid-Open Patent Publication No. 2012-084585.

An object of the present invention is to provide a composition for forming a solar cell electrode having excellent printability and reliability and an electrode made therefrom.

Another object of the present invention is to provide a composition for forming a solar cell electrode having improved electrical characteristics such as open-circuit voltage and conversion efficiency 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.

The composition for forming a solar cell electrode according to an embodiment includes a conductive powder, a glass frit, an organic binder and a solvent, and the solvent has a flash point of 140 to 180 ° C.

The solvent may have a boiling point of 257 캜 to 300 캜.

The solvent may have an FB index of 36,000 or more as calculated by the following formula (1).

[Formula 1]

FB index = boiling point of solvent in ° C × flash point value of solvent in ° C.

In one embodiment, the solvent is 2- (1-methyl-1- (4-methylcyclohexyl) ethoxy) ethanol and diethyl phthalate ≪ / RTI >

In another embodiment, the solvent is selected from the group consisting of hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) , At least one of butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma butyrolactone and ethyl lactate .

Wherein the glass frit is formed from a metal oxide and the metal oxide is selected from the group consisting of tellurium (Te), lithium (Li), zinc (Zn), bismuth (Bi), lead (Pb), sodium (Na) (Ga), Ce, Fe, Si, W, Mg, Mo, Cs, Sr, The metal layer may include at least one selected from the group consisting of titanium, tin, indium, vanadium, barium, nickel, copper, potassium, arsenic, And may include at least one oxide of zirconium (Zr), manganese (Mn), aluminum (Al), and boron (B).

The organic binder may be selected from the group consisting of ethylhydroxyethylcellulose, nitrocellulose, a mixture of ethylcellulose and a phenol resin, an alkyd resin, a phenol resin, an acrylate resin, a xylene resin, a polybutene resin, , Melamine resins, vinyl acetate resins, wood rosin, and polymethacrylates of alcohols.

The composition may include 60 to 95 wt% of the conductive powder, 0.1 to 20 wt% of the glass frit, 0.1 to 15 wt% of the organic binder, and 0.1 to 20 wt% of the solvent.

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, 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.

INDUSTRIAL APPLICABILITY The present invention has an effect of providing a composition for forming a solar cell electrode having excellent printability and reliability and improved electrical characteristics such as open-circuit voltage and conversion efficiency, and an electrode made therefrom.

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.

In this specification, 'metal oxide' may mean one metal oxide and may refer to a plurality of metal oxides.

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 includes a conductive powder, a glass frit, an organic binder and a solvent, and the solvent has a flash point of 140 to 180 캜.

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 may be formed from a metal oxide and the metal oxide may be selected from the group consisting of tellurium (Te), lithium (Li), zinc (Zn), bismuth (Bi), lead (Pb), sodium (Na) , Ge, Ga, Cd, Fe, Si, W, Mg, Mo, ), Tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), potassium (K), arsenic ), Zirconium (Zr), manganese (Mn), aluminum (Al), and boron (B).

For example, the glass frit may be a Bi-Te-O glass frit, a Bi-Te-Li-O glass frit, a Bi-Te-Li-Zn glass frit, a Pb- A glass frit of Pb-Bi-Te-Li-O system glass frit, a glass frit of Pb-Bi-Te-Li-Zn system And may include any one or more of them. In this case, there is an advantage that the balance of the electrical characteristics of the solar cell electrode is excellent.

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.

Organic binder

The organic binder may be an acrylate-based or cellulose-based resin, and ethylcellulose is a commonly used resin. 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.

The organic binder may be contained in the composition for forming a solar cell electrode in an amount of 0.1 to 15% by weight, specifically 0.1 to 10% by weight. Within the above range, sufficient adhesion strength of the solar cell electrode can be ensured.

menstruum

The solvent of the present invention has a flash point of 140 캜 to 180 캜. The composition for forming the solar cell electrode in the above-described range of the flash point is advantageous in that the continuous printing property is excellent and the conversion efficiency is improved because it is advantageous for high temperature firing.

In embodiments, the solvent may have a boiling point of from 257 캜 to 300 캜. Since the drying of the composition during the printing process can be minimized in the above-mentioned boiling range, the continuous printing property is further improved, and the open circuit voltage is excellent while retarding the firing in the firing process.

The solvent may have an FB index of 36,000 or more, for example, 36,000 to 90,000 as calculated by Formula 1 below. There is an advantage that the balance between printability and electrical characteristics is excellent in the FB index range.

[Formula 1]

FB index = boiling point of solvent in ° C × flash point value of solvent in ° C.

In one embodiment, the solvent may comprise at least one of 2- (1-methyl-1- (4-methylcyclohexyl) ethoxy) ethanol and diethyl phthalate.

In another embodiment, the solvent is selected from the group consisting of hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) , At least one of butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma butyrolactone and ethyl lactate And the content thereof may be appropriately mixed according to purposes and other components as long as it satisfies the flash point range, boiling point range or FB index range of the present invention.

The solvent may be contained in the composition for forming a solar cell electrode in an amount of 0.1 to 20% by weight, specifically 0.1 to 15% by weight. Within the above range, excellent printability of the composition for forming a solar cell electrode 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 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 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 one surface of 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.

Example  One

0.7 wt% of ethyl cellulose (STD4) as an organic binder was sufficiently dissolved in 10 wt% of solvent diethyl phthalate (flash point: 161.1 DEG C, boiling point 295 DEG C) at 60 DEG C, and spherical silver powder having an average particle diameter of 2.0 mu m 2% by weight of Bi-Te-O glass frit (BT-653, AGC Co.) having an average particle diameter of 1.0 탆, 86.8% by weight of a dispersant (Dowa Hightech CO. 0.2% by weight of tin, and 0.3% by weight of Thiamatrol ST, Elementis co.) were mixed and dispersed by a three roll kneader to prepare a composition for forming a solar cell electrode.

Example  2

The same procedure as in Example 1 was conducted except that 2- (1-methyl-1- (4-methylcyclohexyl) ethoxy) ethanol (flash point: 142 ° C, boiling point 259 ° C) A composition was prepared.

Example  3

(Boiling point: 142 占 폚, boiling point 259 占 폚) of diethyl phthalate (flash point: 161.1 占 폚, boiling point: 295 占 폚) and 7 The composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that the weight% was used.

Comparative Example  One

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except that butyl carbitol (a flash point: 93 ° C, a boiling point of 231 ° C) was used as a solvent.

Comparative Example  2

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that? -Terpineol (flash point: 82 占 폚, boiling point: 217 占 폚) was used as a solvent.

Comparative Example  3

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that Tecanol (a flash point: 122 ° C, boiling point: 254 ° C) was used as a solvent.

Comparative Example  4

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that dibutylcarbitol was used as a solvent (flash point: 118 캜, boiling point: 256 캜).

How to measure property

(1) Series Resistance (Rs, m?), Open Voltage (Voc, mV): The paste for forming the solar cell electrode prepared in the above Examples and Comparative Examples was screen printed on the entire surface of the wafer by a predetermined pattern, ≪ / RTI > The cells formed by the above process were fired at 600 to 900 ° C. for 60 seconds to 210 seconds using a belt type firing furnace. The thus-prepared cells were measured for contact resistance of the solar cell using a TLM (Tranfer Length Method) Rc), series resistance (Rs) and open-circuit voltage (Voc) are shown in Table 1 below.

(2) 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) Fill Factor (FF,%) and conversion efficiency (Eff.,%) Of the battery were measured and are shown in Table 1 below.

(3) Printability (Number of Short Circuits / Cell): After printing 100 lines of finger electrodes having a line width of 32 m using the paste for forming a solar cell electrode prepared in the above Examples and Comparative Examples, Broken number) were measured and the results are shown in Table 1 below.

When the short circuit number is 2 or more, it is not suitable for application as a solar cell electrode.

Series resistance
(mΩ) Open-circuit voltage
(mV) Eff. (%) Number of Circuits / Cell Example 1 25.23 640 17.925 One Example 2 25.16 641 17.910 One Example 3 25.18 640 17.919 One Comparative Example 1 27.31 638.6 17.796 6 Comparative Example 2 28.5 638 17.758 8 Comparative Example 3 27.6 639 17.800 6 Comparative Example 4 28.1 638.2 17.788 7

As shown in Table 1, Examples 1 to 3 satisfying the flash point range of the present invention have not only excellent electrical properties such as series resistance, open-circuit voltage and conversion efficiency, but also excellent reliability.

On the other hand, Comparative Examples 1 to 4, in which a solvent having a flash point outside the range of the present invention, is applied, reveals that electrical characteristics and reliability are degraded.

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 (10)

Conductive powder, glass frit, organic binder and solvent,
Wherein the solvent has a flash point of 140 캜 to 180 캜.
The method according to claim 1,
Wherein the solvent has a boiling point of 257 캜 to 300 캜.
The method according to claim 1,
Wherein the solvent has an FB index of 36,000 or more calculated by the following formula 1:
[Formula 1]
FB index = boiling point of solvent in ° C × flash point value of solvent in ° C.
The method according to claim 1,
Wherein the solvent comprises at least one of 2- (1-methyl-1- (4-methylcyclohexyl) ethoxy) ethanol and diethyl phthalate.
5. The method of claim 4,
The solvent is selected from the group consisting of 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 and ethyl lactate. (2).
The method of claim 1, wherein the glass frit is formed from a metal oxide,
The metal oxide may be at least one selected from the group consisting of tellurium (Te), lithium (Li), zinc (Zn), bismuth (Bi), lead (Pb), sodium (Na), phosphorus (P), germanium (Ge) (Ce), iron (Fe), silicon (Si), tungsten (W), magnesium (Mg), molybdenum (Mo), cesium (Cs), strontium (Sr), titanium (Ti) (In), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), potassium (K), arsenic (As), cobalt (Co), zirconium (Zr) A composition for forming a solar cell electrode comprising at least one oxide of aluminum (Al) and boron (B).
The method according to claim 1,
The organic binder may be selected from the group consisting of ethylhydroxyethylcellulose, nitrocellulose, a mixture of ethylcellulose and a phenol resin, an alkyd resin, a phenol resin, an acrylate resin, a xylene resin, a polybutene resin, , A melamine-based resin, a vinyl acetate-based resin, a rosin of wood, and a polymethacrylate of alcohol.
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;
0.1 to 15% by weight of an organic binder; And
And 0.1 to 20% by weight of a solvent.
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, an antioxidant and a coupling agent.
A solar cell electrode made of the composition for forming a solar cell electrode according to any one of claims 1 to 9.

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