KR101748006B1 - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

(상기 화학식 1에서, R1, R2 및 R4는 명세서 중에 정의된 내용과 동일하다)The present invention relates to a composition for forming a solar cell electrode comprising a silver (Ag) powder, a glass frit, an organic binder and a solvent, wherein the organic binder contains a repeating unit represented by the following formula (1). The composition for forming a solar cell electrode is excellent in dispersibility and storage stability, capable of forming a fine pattern, and excellent in printing property.
[Chemical Formula 1]

(Wherein R1, R2 and R4 are the same as defined in the specification)

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.

In order to improve the conversion efficiency of the solar cell electrode, the contact resistance (Rc) and the series resistance (Rs) can be minimized by improving the contact with the wafer, or the line width of the screen mask There is a prior art related to a composition for forming a solar cell electrode which improves the efficiency by increasing the short circuit current Isc by forming a fine line, but a method of reducing the electrode line width using a screen mask is a method of decreasing the line resistance Rs And there is a problem that the continuous printing property of a fine pattern can be lowered.

The composition for forming a solar cell electrode uses an organic vehicle to impart viscosity and rheological properties suitable for printing, and the organic vehicle may typically include an organic binder, a solvent, and the like. Cellulosic and acrylic binder resins are used as the organic binder, and ethyl cellulose resin is used in particular. However, organic binders have limitations in the selection of organic binders in that solvent solubility must be considered.

In order to improve dispersibility and storage stability, various additives may be used, the content of the organic binder may be increased, or a high molecular weight organic binder may be used. However, when the additive is used or the content of the organic binder is increased, the resistance of the electrode may be increased. When a high molecular weight organic binder is used, the viscosity is increased even at a high shear rate, And a printing failure may occur.

The object of the present invention is to provide a composition for forming a solar cell electrode which is excellent in dispersibility and storage stability.

Another object of the present invention is to provide a composition for forming a solar cell electrode capable of forming a fine pattern and having excellent printability.

Another object of the present invention is to provide an electrode made of the composition.

One aspect of the present invention is a composition for forming a solar cell electrode comprising a silver (Ag) powder, a glass frit, an organic binder and a solvent, wherein the organic binder includes a compound containing a repeating unit represented by the following formula Lt; / RTI >

[Chemical Formula 1]

Wherein R 1 and R 2 are each independently a hydrogen atom, a hydroxy group, an acetyl group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a nitro group, n is an integer from 5 to 1,000;

(2)

In the above formula (2), R 3 is an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 5, and * is a bonding site.

Said composition comprising 60 to 95 wt% silver (Ag) powder; 0.5 to 20% by weight of glass frit; 1 to 30% by weight of an organic binder; And 1 to 30% by weight of a solvent.

The glass frit may be made of at least one selected from the group consisting of Pb, Tell, Bi, P, Ge, Ga, (Si), Zn (Zn), W, Mg, Cs, Sr, Mo, Ti, (V), barium, nickel, copper, sodium, potassium, arsenic, cobalt, zirconium, manganese and aluminum And aluminum (Al).

The solvent may be selected from the group consisting of methyl cellosolve, ethyl cellosolve, butyl cellosolve, alcohols, alpha-terpineol, beta-terpineol, dihydro Selected from the group consisting of Dihydro-terpineol, Ethylene Grycol, Ethylene glycol mono butyl ether, Butyl Cellosolve acetate and Texanol. And may include one or more species.

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.

Another aspect of the present invention relates to a solar cell electrode made of the composition for forming a solar cell electrode.

The composition for forming a solar cell electrode of the present invention is excellent in dispersibility and storage stability, capable of forming a fine pattern, and excellent in printing property.

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

Composition for forming solar cell electrode

The composition for forming a solar cell electrode according to the present invention comprises silver (Ag) powder; Glass frit; Organic binders; And a solvent. 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 dispersing the conductive powder in isopropyl alcohol (IPA) by ultrasonication at 25 캜 for 3 minutes. Within this range, the contact resistance and line resistance can be lowered.

The silver powder may be included in an amount of 60 to 95% by weight based on the total weight of the composition. In this range, it is possible to prevent the conversion efficiency from being lowered by increasing the resistance, and to prevent the paste from becoming difficult due to the relative reduction in the amount of the organic vehicle. Preferably 70 to 90% by weight.

(B) glass frit

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

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

The glass frit may be typically at least one of a flexible glass frit or a lead-free glass frit used in a composition for forming a solar cell electrode.

The glass frit may be made of at least one selected from the group consisting of Pb, Tell, Bi, P, Ge, Ga, (Si), Zn (Zn), W, Mg, Cs, Sr, Mo, Ti, (V), barium, nickel, copper, sodium, potassium, arsenic, cobalt, zirconium, manganese and aluminum And aluminum (Al).

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

The glass frit may have an average particle diameter (D50) of 0.1 to 10 mu m and may be contained in an amount of 0.5 to 20 wt% based on the total weight of the composition. The shape of the glass frit may be spherical or irregular. In a specific example, two kinds of glass frit having different transition points may be used. For example, a first glass frit having a transition temperature of 200 ° C or higher and 350 ° C or lower and a second glass frit having a transition point of 350 ° C or higher and 550 ° C or lower may be mixed at a weight ratio of 1: 0.2 to 1: 1.

(C) Organic binder

The organic binder of the present invention may contain a compound containing a repeating unit represented by the following formula (1) and a derivative thereof to improve dispersibility and storage stability of the composition for forming a solar cell electrode.

[Chemical Formula 1]

Wherein R 1 and R 2 are each independently a hydrogen atom, a hydroxy group, an acetyl group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a nitro group, n is an integer from 5 to 1,000,

(2)

In the above formula (2), R3 is an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 5, and * indicates a bonding site.

The compound containing the repeating unit represented by the formula (1) forms a side chain in the chemical structure of cellulose originally, thereby maintaining a high viscosity at a low shear rate and a low viscosity at a high shear rate It is possible to improve the shear thinning which indicates the viscosity, thereby enabling the implementation of a fine pattern and improving the printing property.

The compound represented by the formula (1) is a graft copolymer of a cellulose polymer represented by the following formula (3) and a monomer represented by the following formula (4), and the reaction mechanism can be represented by the following chemical reaction formula (1).

(3)

Wherein R 1 and R 2 are each independently a hydrogen atom, a hydroxy group, an acetyl group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group or a nitro group having 2 to 6 carbon atoms, and n is an integer of 5 to 1,000.

[Chemical Formula 4]

In Formula 4, R 3 is an alkyl group having 1 to 6 carbon atoms, and m is an integer of 2 to 5.

[Chemical reaction formula 1]

The monomer represented by the general formula (4) can be obtained by reacting 2- [2- (2-alkoxyethoxy) ethoxy] acetic acid (2- [ (2-alkoxyethoxy) ethoxy] acetic acid), it is possible to induce electrical bonding of the surface charge of the oxygen (O) and silver (Ag) particles of the carbotol group to ensure better dispersion and storage stability.

[Chemical Formula 5]

The weight average molecular weight (Mw) of the compound represented by Formula 1 may be 3,000 to 200,000 g / mol.

The organic binder may be contained in an amount of 1 to 30 wt%, preferably 5 to 15 wt%, based on the total weight of the composition for forming a solar cell electrode. If the content of the organic binder is less than 1% by weight, the viscosity of the composition may become too low or the adhesive force with the substrate may deteriorate. If the content of the organic binder exceeds 20% by weight, Decomposition of the organic binder is not smoothly performed, resistance is increased, and problems such as cracking, opening, and pinhole generation may occur during the firing process.

(D) Solvent

The solvent may be selected from the group consisting of methyl cellosolve, ethyl cellosolve, butyl cellosolve, aliphatic alcohol, alpha-terpineol, ,? -terpineol, dihydro-terpineol, ethylene glycol, ethylene glycol mono butyl ether, butyl cellosolve acetate, or Texanol, etc. may be used alone or in combination of two or more.

The organic solvent may be contained in an amount of 1 to 30% by weight based on the total weight of the composition for forming a solar cell electrode. Within this range, sufficient adhesive strength and excellent printability can be ensured.

(E) 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 one embodiment of the present invention.

1, a composition for electrode formation is printed on a wafer 100 or a substrate including a p-layer (or n-layer) 101 and an n-layer (or p-layer) So that the rear electrode 210 and the front electrode 230 can be formed. For example, the electrode forming composition may be applied to the rear surface of the wafer by printing and then dried at a temperature of about 200 캜 to 400 캜 for about 10 to 60 seconds to perform a preliminary preparation step for the rear electrode. In addition, a preparation step for the front electrode can be performed by printing a composition for electrode formation on the entire surface of the wafer and then drying it. Thereafter, the front electrode and the rear electrode can be formed by performing a sintering process by sintering at 400 to 980 ° C, preferably 700 to 980 ° C for about 30 seconds to 210 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.

Synthesis Example 1

300 ml of 1,4-dioxane and 1.5 eq of 2,2- (methoxyethoxy) acetic acid were added to a 1 L round-bottomed flask and slowly added to 50 After 1.5 eq. Of trifluoroacetic anhydride (TFAA) was added, the same temperature was maintained for 30 minutes, and 1 equivalent of ethyl cellulose (Dow chemical, STD4) was added. After the reaction, the precipitate was re-precipitated in ultrapure water, filtered and washed several times with ultrapure water. The resulting product was vacuum dried to finally obtain ethylcellulose methoxyethoxy acetate (CMA-1) with a replacement ratio of 10%.

Synthesis Example 2

Except that the usage equivalents (eq) of 2,2- (methoxyethoxy) acetic acid and trifluoroacetic anhydride were changed as shown in Table 1 below, except that ethylcellulose Ethylcellulose methoxyethoxy acetate (CMA-2) was obtained.

Synthesis Example 3

Except that 2,2- (2- (methoxyethoxy) ethoxy) acetic acid was used instead of 2,2- (methoxyethoxy) acetic acid as shown in the following Table 1, substitution ratio 10 % Of ethylcellulose (methoxyethoxy) ethoxyacetate (CMEA-1) was obtained.

Synthesis Example 4

Except that 2,2- (2- (methoxyethoxy) ethoxy) acetic acid was used instead of 2,2- (methoxyethoxy) acetic acid as shown in the following Table 1, substitution ratio 30 % Of ethylcellulose (methoxyethoxy) ethoxyacetate (CMEA-2) was obtained.

STD-45 (eq) 2-2- (methoxyethoxy) acetic acid (eq) 2-2- (2- (methoxyethoxy) ethoxy) acetic acid (eq) TFAA (eq) 1,4-dioxane (ml) Replacement ratio (%) Synthesis Example 1 CMA-1 One 1.1 - 1.1 300 10 Synthesis Example 2 CMA-2 One 1.5 - 1.5 300 30 Synthesis Example 3 CMEA-1 One - 1.1 1.1 300 10 Synthesis Example 4 CMEA-2 One - 1.5 1.5 300 30

Examples 1-4 and Comparative Example 1

Example 1

3.0% by weight of CMA-1 prepared in Synthesis Example 1 was dissolved in 6.5% by weight of butylcarbitol as a solvent at 60 占 폚 as an organic binder, and spherical silver powder having an average particle size of 2.0 占 퐉 (Dowa Highech CO (Flexible glass, particle size: CI-124) having an average particle diameter of 1.0 占 퐉 and a transition point of 341 占 폚, dispersant BYK102 (BYK-chemie ) And 0.3 wt% of Thixatrol ST (Elementis co.) As a thixotropic agent were mixed and dispersed by a three roll kneader to prepare a composition for forming a solar cell electrode.

Examples 2-4

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

Comparative Example 1

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that ethyl cellulose (Dow chemical, STD4) was used instead of CMA-1 as an organic binder.

Property evaluation method

(1) Storage stability (%) : The storage stability was evaluated by the rate of change in viscosity (? F) before and after storage of the electrode-forming composition prepared according to the following formula 1. The results are shown in Table 2.

[Formula 1]

(F0: composition for electrode formation was stored for 1 day at 25 DEG C and 50 +/- 5% relative humidity,

    Viscosity value measured at room temperature

 F1: After the composition for electrode formation was stored for 30 days at 25 占 폚 and 50? 5% relative humidity,

    Viscosity value measured at room temperature)

* Viscosity measurement: Using a Brookfield viscometer (HBDV-2 + pro), a SC4-14 spindle and an SC4-6RP chamber were mounted, and the preshear was applied for 30 seconds at 25 ° C at 10 rpm.

(2) Evaluation of fine pattern : The prepared composition for forming a solar cell electrode was screen-printed on the entire surface of a polyP type silicon wafer having a surface resistance of 90? Using a screen mask to print an electrode pattern (finger bar) ≪ / RTI > Thereafter, a composition for forming an electrode containing aluminum was printed on the rear surface of the wafer by back printing and then dried by the same method. The cells thus formed were fired at 400 to 950 DEG C for 30 seconds to 50 seconds using a belt-type firing furnace. An EL tester (MV tech) was used to confirm whether or not the finger bar was cut off. The line width and thickness of the electrode line were measured using a VK instrument (KEYENCE VK9710). The results are shown in Table 2 below.

* Screen mask: SUS325 type / Emulsion thickness 15㎛ / Finger bar line width 45㎛, Finger bar number 80

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 article
castle

(wt%) Silver powder 87 87 87 87 87 Glass frit 2 2 2 2 2 Organic binder 3
(CMA-1) 3
(CMA-2) 3
(CMEA-1) 3
(CMEA-2) 3
(STD4) Organic solvent 4 4 4 4 4 additive 4 4 4 4 4 water
castle Storage stability (%) 4.5 3.2 3.9 2.1 7 Line width after printing L1 (占 퐉) 58 57 59 56 62 Line width after drying L2 (占 퐉) 72 66 72 61 76 Line width after firing L3 (占 퐉) 91 75 84 68 95 Thickness after firing D1 (占 퐉) 16.3 16.8 16.4 17.1 16 Line width? (L1-L2) (占 퐉) -14 -9 -13 -5 -14 Aspect ratio (D1 / L3) 0.179 0.224 0.195 0.251 0.168 Line open () 0 0 0 0 0

As shown in the results of Table 2, the composition for forming a solar cell electrode of Example 1-4 using the compound represented by Formula 1 of the present invention as an organic binder has excellent storage stability compared to Comparative Example 1 using ethylcellulose It can be seen that the fine line width can be realized because the aspect ratio is 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 (7)

Silver (Ag) powder, glass frit, organic binder and solvent,
Wherein the organic binder comprises a compound containing a repeating unit represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

Wherein R 1 and R 2 are each independently a hydrogen atom, a hydroxy group, an acetyl group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a nitro group, n is an integer from 5 to 1,000;
(2)

In the above formula (2), R 3 is an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 5, and * is a bonding site.
The method according to claim 1,
60 to 95 wt% of the silver (Ag) powder;
0.5 to 20% by weight of the glass frit;
1 to 30% by weight of the organic binder; And
And 1 to 30% by weight of the solvent.
The method according to claim 1,
The glass frit may be made of at least one selected from the group consisting of Pb, Tell, Bi, P, Ge, Ga, (Si), Zn (Zn), W, Mg, Cs, Sr, Mo, Ti, (V), barium, nickel, copper, sodium, potassium, arsenic, cobalt, zirconium, manganese and aluminum And at least one metal element selected from the group consisting of aluminum (Al).
The method according to claim 1,
The solvent may be selected from the group consisting of methyl cellosolve, ethyl cellosolve, butyl cellosolve, alcohols, alpha-terpineol, beta-terpineol, dihydro Selected from the group consisting of Dihydro-terpineol, Ethylene Grycol, Ethylene glycol mono butyl ether, Butyl Cellosolve acetate and Texanol. Wherein the composition comprises at least one member selected from the group consisting of a metal oxide and a metal oxide.
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 6.

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