KR101930286B1 - Electrode Paste For Solar Cell's Electrode And Solar Cell using the same - Google Patents

Abstract

The present invention relates to a conductive paste for a solar cell electrode, which comprises a metal powder, a glass frit, an organic vehicle and a dispersant, wherein the dispersant is a low-molecular dispersant having a molecular weight of 100 to 1000 g / Which can shorten the dispersion step and time, exhibit a low viscosity and can be easily controlled in content, and the stability of the conductive paste produced by maximizing the dispersion effect can be ensured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for a solar cell electrode,

The present invention relates to a conductive paste used for forming an electrode of a solar cell and a solar cell manufactured using the conductive paste.

A solar cell is a semiconductor device that converts solar energy into electrical energy. It has a p-n junction type and its basic structure is the same as a diode. FIG. 1 shows a structure of a general solar cell element. The solar cell element is generally constituted by using a p-type silicon semiconductor substrate 10 having a thickness of 180 to 250 .mu.m. On the light receiving surface side of the silicon semiconductor substrate, an n-type impurity layer 20 having a thickness of 0.3 to 0.6 占 퐉, an anti-reflection film 30 and a front electrode 100 are formed thereon. A back electrode 50 is formed on the back side of the p-type silicon semiconductor substrate. The front electrode 100 is formed by applying a conductive paste, which is a mixture of silver powder, glass frit, organic vehicle, and additives, which are mainly composed of silver, on the antireflection coating 30 The back electrode 50 is formed by applying an aluminum paste composition composed of aluminum powder, glass frit, organic vehicle and additives to the substrate by screen printing or the like, drying the substrate, Or more. Aluminum is diffused into the p-type silicon semiconductor substrate at the time of firing, so that an Al-Si alloy layer is formed between the back electrode and the p-type silicon semiconductor substrate, and the p + layer 40 Is formed. The existence of such a p + layer prevents the recombination of electrons and improves the collection efficiency of the generated carriers, thereby obtaining a BSF (Back Surface Field) effect. A rear silver electrode 60 may be further disposed under the rear aluminum electrode 50.

The dispersing agent is essentially used for dispersing the conductive paste. Since the metal powder contained in the conductive paste contains nano-sized metal particles, coagulation phenomenon may occur between the nano-particles in the paste, and therefore it is inevitable to use the metal powder for uniform dispersion of the metal powder.

Generally, the dispersing agents used are divided into a water base, a non-aqueous base, an anion base, a cation base, a polar base, a non-polar base, an amine base and an acid base by using a polymer of 5,000 to 30,000 g / mol in the range of 0.1 to 1% .

However, since there is a problem that the viscosity of the paste increases due to the use of the polymer, there is a limitation in the amount of use, and as the content of the polymer dispersant increases, the finger disconnection increases and the resistance increases.

1. Korean Patent Publication No. 2013-0090276 (2013.08.13) 2. Korean Patent Publication No. 2013-0104614 (2013.09.25)

The present invention aims to improve the stability of the paste by maximizing the dispersing effect by using a dispersing agent in the composition of the conductive paste for a solar cell electrode by using a low molecular dispersing agent to shorten the dispersing step and time and by using a dispersant having an acid value and an amine value .

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

The present invention provides a conductive paste for a solar cell electrode, which comprises a metal powder, a glass frit, an organic vehicle and a dispersant, wherein the dispersant is a low molecular weight dispersant having a molecular weight of 100 to 1000 g / mol.

The dispersant may be present in an amount of 0.1 to 5 wt% based on the total weight of the conductive paste.

In addition, the dispersal agent R1-COONa, R1-CH ( SO 3 Na) COOCH 3, R1- (C 6 H 4) SO 3 Na, R1-OSO 3 Na, R1-O (CH 2 CH 2 O) n SO 3 _{Na, R1-OSO 3 -.} + NH (CH 2 CH 2 OH) 3, R1-R2-COO -. + PO (OH) m -R2-R1 consisting of (R1 = alkyl group, R2 = ether group) And at least one selected from the group consisting of

Further, the dispersant is characterized by being a dispersant having an acid value and an amine value.

Also, the dispersant has an acid value and an amine value in the range of 20 mg KOH / g to 80 mg KOH / g, and the difference between the acid value and the amine value is 10 mg KOH / g or less.

The dispersant may be a dispersant having a solid content of 30 to 70%.

The conductive paste has a viscosity of 40 to 60 Pa · s at 25 ° C.

The present invention also provides a solar cell having a front electrode on a substrate and a back electrode on the bottom of the substrate, wherein the front electrode is formed by applying the conductive paste for the solar cell electrode and then firing Thereby providing a battery.

According to the present invention, it is possible to use a low-molecular dispersant of 100 to 1000 g / mol as a dispersant contained in the conductive paste to shorten the dispersion process and time, exhibit low viscosity and easy control of the content, The stability of the paste can be secured.

The solar cell including the electrode formed using the conductive paste according to the present invention exhibits excellent conversion efficiency and provides an effect of securing a certain level of resistance even when the content of the low molecular dispersant is increased to improve the solar cell power generation efficiency .

1 is a schematic cross-sectional view of a general solar cell element.
2 is a graph showing viscosity measurement results of the conductive paste according to an embodiment of the present invention.
FIGS. 3 to 7 show electroluminescence measurement images of electrodes formed using conductive pastes according to Examples and Comparative Examples of the present invention.

Before describing the present invention in detail, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention, which is defined solely by the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise stated.

Throughout this specification and claims, the word "comprise", "comprises", "comprising" means including a stated article, step or group of articles, and steps, , Step, or group of objects, or a group of steps.

On the contrary, the various embodiments of the present invention can be combined with any other embodiments as long as there is no clear counterpoint. Any feature that is specifically or advantageously indicated as being advantageous may be combined with any other feature or feature that is indicated as being preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

The paste according to an embodiment of the present invention is a paste suitable for forming a solar cell electrode, and provides a conductive paste containing a low molecular dispersant. More specifically, the conductive paste according to the present invention comprises a metal powder, a glass frit organic vehicle, and a low-molecular dispersant.

As the metal powder, silver powder, copper powder, nickel powder, aluminum powder, etc. may be used. In the case of the front electrode, powder is mainly used, and in the case of the rear electrode, aluminum powder is mainly used. Hereinafter, the metal powder will be described as an example for convenience. The following description is equally applicable to other metal powders.

The content of the metal powder is preferably 40 to 95% by weight based on the total weight of the conductive paste composition, taking into consideration the electrode thickness formed at the time of printing and the line resistance of the electrode.

The silver powder is preferably a pure silver powder. In addition, a silver-coated composite powder having at least a silver layer on its surface, or an alloy containing silver as a main component may be used. Further, other metal powders may be mixed and used. For example, aluminum, gold, palladium, copper, and nickel.

The average particle diameter of the silver powder may be 0.1 to 10 탆. The average particle diameter of the silver powder is preferably 0.5 to 5 탆 in consideration of ease of paste formation and denseness in firing, and the shape thereof may be spherical, acicular, Plate type) and amorphous type (at least one type or more). The silver powder may be a mixture of powders of two or more kinds having different average particle diameter, particle size distribution and shape.

The composition, particle diameter and shape of the glass frit are not particularly limited. It is possible to use not only flexible glass frit but also lead-free glass frit. Preferably, the content and content of the glass frit are 5 to 29 mol% of PbO, 20 to 34 mol% of TeO ₂ , 3 to 20 mol% of Bi ₂ O ₃ , 20 mol% or less of SiO ₂ , 10 mol% or less of B ₂ O ₃ , 10 to 20 mol% of an alkali metal (Li, Na, K, etc.) and an alkaline earth metal (Ca, Mg, etc.) By combining the organic components of the above components, it is possible to prevent an increase in the line width of the electrode, to improve the contact resistance in the high-surface resistance, and to improve the short-circuit current characteristic.

The average particle diameter of the glass frit is not limited, but it may have a particle diameter in the range of 0.5 to 10 mu m, and a mixture of various particles having different average particle diameters may be used. Preferably, at least one kind of glass frit has an average particle diameter (D50) of not less than 2 mu m and not more than 10 mu m. As a result, the reactivity at the time of firing can be improved, the damage of the n-layer at the high temperature can be minimized, the adhesion can be improved, and the open-circuit voltage (Voc) can be improved. Also, the increase in the line width of the electrode during firing can be reduced.

The content of the glass frit is preferably 1 to 10% by weight based on the total weight of the conductive paste composition. If the content is less than 1% by weight, incomplete firing may occur to increase the electrical resistivity. If more than 10% by weight, There is a possibility that the electrical resistivity becomes too high due to too much component.

The organic vehicle is not limited, but organic binders, solvents, and the like may be included. Solvents may sometimes be omitted. The organic vehicle is not limited, but is preferably 1 to 30% by weight based on the total weight of the conductive paste composition.

The organic vehicle is required to have a property of keeping the metal powder and the glass frit uniformly mixed. For example, when the conductive paste is applied to the substrate by screen printing, the conductive paste becomes homogeneous, And a property to suppress the flow and to improve the discharging property and the plate separability of the conductive paste from the screen plate.

The organic binder contained in the organic vehicle is not limited, but examples of the cellulose ester compound include cellulose acetate and cellulose acetate butyrate. Examples of the cellulose ether compound include ethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose Examples of the acrylic compound include polyacrylamide, polymethacrylate, polymethylmethacrylate, and polyethylmethacrylate, and the like. Examples of the acrylic compound include polyacrylamide, polymethacrylate, polymethylmethacrylate, and polyethylmethacrylate And examples of vinyl based ones include polyvinyl butyral, polyvinyl acetate, polyvinyl alcohol, and the like. At least one or more organic binders may be selected and used.

Examples of the solvent used for diluting the composition include alpha-terpineol, texanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene Glycol monobutyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and the like.

A low-molecular dispersant of 100 to 1000 g / mol is used as the dispersing agent. Low-molecular-weight dispersant is R1-COONa, R1-CH ( SO 3 Na) COOCH 3, R1- (C 6 H 4) SO 3 Na, R1-OSO 3 Na, R1-O (CH 2 CH 2 O) n SO 3 Na _{, R1-OSO 3 -. +} NH (CH 2 CH 2 OH) 3, R1-R2-COO -. + PO (OH) n -R2-R1 group consisting of (R1 = alkyl group, R2 = ether group) May be used. It is preferable to use R1-R2-COO-. + PO (OH) _m -R2-R1 having a molecular weight of preferably 100 to 1000 g / mol. The dispersing agent may be a single component dispersing agent or a dispersing agent containing plural components.

The dispersant is contained in an amount of 0.1 to 5% by weight based on the total weight of the conductive paste composition. If it is contained in an amount of less than 0.1% by weight, there is a problem that the dispersing effect is insufficient and the dispersibility is poor. When the content is more than 5% by weight, the viscosity becomes low due to dispersion and the stability problem due to paste phase separation . More preferably 0.1 to 3% by weight.

The dispersant has an acid value and an amine value. The dispersant has an acid value, which improves the dispersibility and the control of the electric charge. Therefore, it is advantageous to lower the resistance characteristic of the electrode. By having the amine value, dispersibility can be improved to increase the density of the electrode and delay agglomeration and sedimentation Thereby enhancing the stability of the paste.

More preferably, a dispersant having an acid value and an amine value is used. Here, the acid value and the amine value are similar, which means that the difference between the acid value and the amine value is 10 mg KOH / g or less. The dispersant preferably has an acid value and an amine value within a range of 20 mg KOH / g to 80 mg KOH / g, more preferably a dispersant having an acid value and an amine value. When the acid value and the amine value are less than 20 mg KOH / g, there is a problem in flocculation due to the lowering of the dispersibility. When the acid value and the amine value are more than 80 mg KOH / g, there is a problem in re- It is more preferable that the difference in acid value and amine value is within a range of 40 mg KOH / g to 70 mg KOH / g of 5 mg KOH / g or less.

The dispersant uses a dispersant having a solid content of 30 to 70%. The solid content means a value obtained by converting the weight of the solid matter remaining by evaporating water into a percentage in terms of the total weight of the dispersing agent. When the solid content is less than 30%, there is a problem of long-term storage stability, particularly sedimentation. When the solid content is more than 70%, there is a problem in formation of a low-molecular dispersant. And more preferably 40 to 60%.

The conductive paste composition according to the present invention may further contain commonly known additives such as plasticizers, viscosity regulators, surfactants, oxidizing agents, metal oxides, metal organic compounds, and the like, if necessary.

The viscosity of the conductive paste composition according to the present invention has a low viscosity of 40 to 60 Pa · s at 25 ° C to easily control the content of the composition and provide an excellent stability.

The present invention also provides a method of forming an electrode of a solar cell and a solar cell electrode produced by the method, wherein the conductive paste is applied on a substrate, followed by drying and firing. In the method for forming a solar cell electrode of the present invention, the methods used for producing substrates, printing, drying, and firing can be generally those used for manufacturing solar cells, except that conductive pastes containing silver powder having the above- to be. For example, the substrate may be a silicon wafer.

Examples and Comparative Examples

The glass frit, the organic vehicle and the dispersing agent were put in a composition as shown in Table 1 below, dispersed using a triple mill, and then mixed with a silver powder (spherical, average particle diameter 1 탆). Thereafter, vacuum degassing was conducted to prepare a conductive paste. The properties of the dispersant are shown in Table 2 below.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Ethyl Cellulose 0.4 0.4 0.4 0.4 0.4 Texanol 2.3 2.3 2.3 2.3 2.3 DBA 2.0 2.0 2.0 2.0 2.0 DB 1.8 1.8 1.8 1.8 1.8 Amide Wax 0.3 0.3 0.3 0.3 0.3 DPGDB 0.2 0.2 0.2 0.2 0.2 Silver Powder 89.5 89.5 89.5 89.5 89.5 Glass frit 2.0 2.0 2.0 2.0 2.0 Dispersant 1 1.5 Dispersant 2 1.5 Dispersant 3 1.5 Dispersant 4 1.5 Dispersant 5 1.5

division Dispersant 1 Dispersant 2 Dispersant 3 Dispersant 4 Dispersant 5 ingredient Fatty acid & amine mixture Fatty acid & amine mixture Acrylic block copolymer Alkylol ammonium salt Carboxylic acid salts Molecular Weight 500 g / mol 600 g / mol 12,000 g / mol 8,000 g / mol 5,000 g / mol Acid value 50 60 19 94 51 Amine 50 60 - 94 53 Solid content (%) 50 60 50 81 48

Experimental Example

(1) Viscosity measurement

The viscosity of the conductive paste prepared above was measured using a RV1 rheometer (HAAKE) under the conditions of P35 Ti L spindle, 30 RPM, and 25 ° C. The results are shown in FIG. As shown in FIG. 2, the viscosity of the conductive paste according to the embodiment of the present invention is 47.959 Pa · s and 57.101 Pa · s, respectively, and it is easy to control the content because the viscosity is low even if the dispersant is included in the same amount as the comparative example have.

(2) Analysis of conversion efficiency

The obtained conductive paste was pattern-printed on the entire surface of the wafer by a screen printing technique with a mesh size of 40 mu m and dried at 200 to 350 DEG C for 20 seconds using a belt type drying furnace for 30 seconds. Then, Al paste was printed on the back side of the wafer and dried by the same method. The cells thus formed were fired at 500 to 900 ° C for 20 seconds to 30 seconds using a belt-type firing furnace to produce a solar cell.

The manufactured cell was analyzed for conversion efficiency Eff, short-circuit current Isc, open-circuit voltage Voc and curve factor FF using a solar cell efficiency measuring device (Halm, cetis PV-Celltest 3) Table 3 shows the results.

Isc (A) Voc (V) Eff (%) FF (%) Example 1 9.4217 0.6385 19.810 78.755 Example 2 9.4367 0.6388 19.840 78.711 Comparative Example 1 9.4273 0.6381 19.541 77.692 Comparative Example 2 9.3922 0.6392 17.946 71.492 Comparative Example 3 9.3914 0.6377 19.699 78.671

Considering that the efficiency of a solar cell is generally divided by 0.2% and the 0.2% efficiency increase is a very significant value, as shown in Table 3, the electrode made of the conductive paste containing the low molecular dispersant of the present invention It is found that the conversion efficiency is higher than that of the comparative example, and the power generation efficiency of the solar cell is improved.

(3) Electroluminescence measurement

3 to 7 show images obtained by measuring electroluminescence (EL) with respect to the prepared cells using a K3300 ELX instrument manufactured by Mac Science. Fig. 3 is an electroluminescent image of a cell prepared using conductive pastes of Example 1, Fig. 4, Example 2, Fig. 5, Comparative Example 1, Fig. 6, and Comparative Example 2, and Comparative Example 3, respectively.

The electroluminescent images show brighter light with better cell characteristics in the cell characteristic part of the solar cell when the same voltage or current is applied, and the part with the shorted line becomes black. In the case of Examples, electroluminescence was brighter than Comparative Example, and it was confirmed that it is superior in electrical characteristics such as contact resistance and can have higher cell efficiency.

The features, structures, effects, and the like illustrated in the above-described embodiments can be combined and modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

10: P-type silicon semiconductor substrate
20: N-type impurity layer
30: antireflection film
40: P + layer (BSF: back surface field)
50: rear aluminum electrode
60: rear silver electrode
100: front electrode

Claims (8)

Metal powders, glass frit, organic vehicles and dispersants,
The dispersant is a low-molecular dispersant having a molecular weight of 100 to 1000 g / mol,
0.1 to 5% by weight based on the total weight of the conductive paste,
R1-COONa, R1-CH ( SO 3 Na) COOCH 3, R1- (C 6 H 4) SO 3 Na, R1-OSO 3 Na, R1-O (CH 2 CH 2 O) n SO 3 Na (n = 1-15 integer) and R1-OSO ₃ between - includes any one or more selected from the group consisting of _{+ NH (CH 2 CH 2 OH} ) 3 (R1 = alkyl group) having a carbon number of 15 or less, and
An acid value and an amine value, and the difference between the acid value and the amine value in the range of 20 mg KOH / g to 80 mg KOH / g is 10 mg KOH / g or less.
delete delete delete delete The method according to claim 1,
Wherein the dispersant is a dispersant having a solid content of 30 to 70%.
The method according to claim 1,
Wherein the conductive paste has a viscosity of 40 to 60 Pa · s at 25 ° C.
1. A solar cell having a front electrode on a substrate and a back electrode on a bottom of the substrate,
Wherein the front electrode is manufactured by applying the conductive paste for a solar cell electrode according to any one of claims 1, 6, and 7, followed by firing.

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