KR102340931B1 - Parameters for improving the printing characteristics of the conductive paste satisfying the parameters - Google Patents

Abstract

The present invention relates to a conductive paste comprising a metal powder, a solvent, an organic binder, and a glass frit, wherein the value of A in the following formula 1 is 2 to 7, and the conductive paste satisfying the above parameters has the effect of realizing good printability without disconnection even when applying a screen mask with high mesh and narrow finger openings.
[Equation 1]
A=T100/(Slip velocity/Minimum shear stress)

Description

Parameters for improving the printing characteristics of the conductive paste satisfying the parameters

The present invention relates to a parameter for improving the printing properties of a conductive paste and a conductive paste satisfying the same, and is applied to conductive paste for forming electrodes in electronic components such as solar cells, internal electrodes of multilayer capacitors, and conductor patterns of circuit boards It is about possible parameters.

Conductive paste is a paste that has application ability to form a coating film and conducts electricity to a dried or fired coating film. It is a fluid composition dispersed with a conductive filler (metal filler) alone or together with a glass frit in a vehicle consisting of a resin-based binder and a solvent, It is widely used in the formation of circuits and the formation of external electrodes of ceramic capacitors.

In particular, silver paste is the most chemically stable and excellent in conductivity among composite conductive pastes, so its application range is quite wide in various fields, such as for conductive adhesion and coating, and for forming micro-circuits. In electronic components that place special importance on reliability, such as printed circuit boards (PCBs), silver paste is used as an adhesive or coating material for STH (Silver Through Hole), for internal electrodes in multilayer capacitors, and recently for silicon-based solar cells. It is widely used as an electrode material in

The rheology of the conductive paste is a major factor that determines the printing properties (application aptitude). In order to cope with the miniaturization of electronic parts and the densification or fine patterning of electrode patterns, the conductive paste affects the printing properties. The rheological properties of the conductive paste are important, especially since the screen-printed electrode for solar cells requires a narrow line width and high thickness of the electrode, that is, an increase in the aspect ratio.

In addition, as an electrode paste for solar cells, when printing for a long time, the viscosity of the paste changes due to internal friction, heat, solvent absorption, and solvent evaporation due to the squeegee and plate making.

On the other hand, most of the parameters proposed in the prior art are for implementing a narrow line width, and research on solutions to problems that may occur during long-time printing is insufficient.
<Prior art literature>
<Patent Literature>

Korean Patent Registration No. 1733161 (August 8, 2017 Announced)

An object of the present invention is to provide a conductive paste with improved long-term printability by satisfying the viscosity and shear stress-related parameters of the conductive paste that can solve the above problems during long-time printing.

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

The present invention provides a conductive paste comprising a metal powder, a solvent, an organic binder, and a glass frit, wherein the value of A in Equation 1 is 2 to 7.

[Equation 1]

A=T100/(Slip velocity/Minimum shear stress)

(Here, T100 is the ratio of the viscosities measured at 10 rpm and 100 rpm, respectively, with spindle 14 using a rotational viscometer at 25 ° C., and the minimum shear stress is laminated at Gap 1.0 mm with a PP50 spindle using an Antonpar rheometer at 25 ° C. It is the minimum shear stress required for desorption after desorption, and it is a value measured at -500um/s speed. It is the value calculated by the following formula for rotational speed.

Slip velocity=2Х3.14Х50Х(Rotational Speed)/60)

In addition, the value A in Formula 1 is characterized in that 3 to 6.

In addition, the conductive paste is characterized in that it contains silicone oil.

In addition, the molecular weight of the silicone oil is characterized in that 1 ~ 100,000cs.

In addition, the silicone oil is characterized in that it contains a linear molecule, a branched molecule, a cyclic molecule, or a mixture thereof.

In addition, the linear molecule is characterized in that it comprises at least one selected from decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, and hexadecamethylheptasiloxane. do.

In addition, the cyclic molecule is characterized in that it comprises at least one selected from decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane.

In addition, the present invention provides a solar cell including an electrode formed by using the solar cell electrode paste.

When an electrode is formed using the conductive paste satisfying the parameters according to the present invention, there is little change in characteristics even in a long-term process, so that process defects such as disconnection and printing defects occurring during long-time printing can be reduced. Thus, it is possible to increase the production yield through stable process progress.

Specifically, even when a screen mask having a high mesh and a narrow finger opening is applied, good printability can be realized without disconnection, thereby providing a solar cell with excellent conversion efficiency.

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

Throughout this specification and claims, unless stated otherwise, the term comprise, comprises, comprising is meant to include the stated object, step or group of objects, and steps, and any other object. It is not used in the sense of excluding a step or a group of objects or groups of steps.

On the other hand, various embodiments of the present invention may be combined with any other embodiments unless clearly indicated to the contrary. Any feature indicated as particularly preferred or advantageous may be combined with any other feature and features indicated as preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

The conductive paste according to an embodiment of the present invention is a paste comprising metal powder, a solvent, an organic binder, and a glass frit, and the parameters according to the present invention can be particularly suitably applied to a conductive paste for forming a solar cell electrode.

Parameters for improving the printing properties of the conductive paste according to the present invention are parameters related to viscosity and shear stress. In particular, the viscosity of the conductive paste during screen printing is correlated with the line width of the pattern. Under the same screen printing conditions, as the conductive paste viscosity decreases, the line width increases, thereby reducing the solar cell electrode efficiency. Conversely, if the viscosity of the conductive paste becomes too high, the probability of disconnection increases, which increases the line resistance, thereby reducing the solar cell electrode efficiency. Therefore, it is necessary to have an appropriate viscosity value and to determine to what extent it is advantageous to maintain it even after time has elapsed.

When an electrode is formed using the conductive paste satisfying the parameters according to the present invention, there is little change in characteristics even in a long-term process, so that process defects such as disconnection and printing defects occurring during long-time printing can be reduced. Thus, it is possible to increase the production yield through stable process progress.

Specifically, even when a screen mask having a high mesh and a narrow finger opening is applied, good printability can be realized without disconnection, thereby improving the conversion efficiency of the manufactured solar cell.

The present invention provides parameters that can serve as criteria as described above. The measured viscosity value of the conductive paste is required for parameter calculation according to the present invention, and the viscosity value is measured at 25° C. using a rotational viscometer at each rotation speed (rpm) with the 14th spindle. Specific viscosity value measurement conditions are shown in Table 1 below.

division How to measure
10rpm* Stabilization (0rpm) 1rpm 10rpm 100rpm Analysis conditions 30 seconds (1 min) 30 seconds 30 seconds 30 seconds

The parameter is characterized in that it includes the first parameter with the condition that the value A calculated by the following Equation 1 is within the range of 2 to 7.

[Equation 1]

A=T100/(Slip velocity/Minimum shear stress)

(Here, T100 is the ratio of viscosities measured at 10 rpm and 100 rpm, respectively, with spindle 14 using a rotational viscometer at 25 ° C. The minimum shear stress is laminated with a PP50 spindle at a gap of 1.0 mm using an Antonpar rheometer at 25 ° C. This is the minimum shear stress required for desorption after desorption, and it is a value measured at a speed of -500um/s The slip velocity was measured at 20~800Pa at a gap of 0.6mm with a PP50 spindle at 25℃ using an Antonpar rheometer at 800Pa. It is the value calculated by the following formula for rotational speed.

Slip velocity=2×3.14×50×(Rotational Speed)/60)

The conductive paste satisfying the above parameters does not cause disconnection during long-term printing, and thus has excellent printing characteristics.

In addition, the paste prepared by the parameters according to the present invention may contain silicone oil.

The type of the silicone oil is not limited, but it is preferable to use a linear molecule, a branched molecule, a cyclic molecule, or a mixture thereof.

Specifically, the silicone oil is a linear molecule and includes decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, hexadecamethylheptasiloxane, and the like. , as a cyclic molecule, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, tetradecamethylcycloheptasiloxane, and the like can be exemplified. At least one of the silicone oils may be selected and used. In addition, the silicone oil is at least one selected from the group consisting of phenyl trimethione, dimethicone, cyclomethicone, polydimethylsiloxane, and silicone gum. may be included, and a modified silicone oil may also be used. Preferably, it may be polysiloxane such as polydimethylsiloxane, and it is preferable to use unmodified polysiloxane oil in consideration of slip properties.

In addition, it is preferable that the molecular weight of the silicone oil is 1-100,000cs. When the molecular weight of the silicone oil exceeds 100,000cs, the viscosity is too high, and the fluidity of the paste is lowered, resulting in more disconnection and difficult manufacturing.

The silicone oil is included in an amount of 0.1 to 5% by weight based on the total weight of the conductive paste composition. When silicone oil is added in an amount of less than 0.1% by weight, there is a slight problem in improving the slip property, and when it is added in excess of 5% by weight, there are many silicone components in the material remaining after firing the paste, which adversely affects resistance, etc. there is In addition, there is a problem in that silicon evaporated from the kiln during sintering sticks.

Paste manufacturing

Hereinafter, with respect to the conductive paste that satisfies the above parameters, the improvement in printing characteristics during long-time printing will be described through specific examples and comparative examples.

First, a silver paste including silver powder as the conductive paste is mixed and dispersed in the composition shown in Tables 2 and 3 below, followed by filtration and defoaming.

Category [wt%] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 ethyl
Cellulose resin STD4 0.4 0.4 0.4 0.4 0.4 0.6 0.4 STD100 0.4 STD200 Diethylene glycol butyl ether acetate 6.7 6.7 6.7 6.7 5.9 5 5.7 4.8 wax One One One One One One One One silver powder 88.5 88.5 88.5 88.5 88.5 88.5 88.5 88.5 glass frit 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 additive 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 PDMS 50cs 0.2 PDMS 100cs 0.2 0.2 One 2 One 2.2 PDMS 1000cs 0.2

Category [wt%] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 STD4 0.8 0.4 0.4 STD100 STD200 0.4 Diethylene glycol butyl ether acetate 5.5 6.7 6.9 4.0 wax One One One One silver powder 88.5 88.5 88.5 88.5 glass frit 3.1 3.1 3.1 3.1 additive 0.1 0.1 0.1 0.1 PDMS 50cs PDMS 100cs One 0.2 3

Experimental Example - Viscosity Measurement and Parameter Calculation

Viscosity was measured for each of Examples 1 to 8 and Comparative Examples 1 to 4 prepared above. Viscosity was measured at each rotation speed (rpm) with spindle 14 using a rotational viscometer at 25 ° C., and T100, the ratio of the viscosity value at 10 rpm to the viscosity value at 100 rpm, minimum shear stress, slip velocity, and The values calculated using these are shown in Tables 4 and 5 below.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 10rpm Viscosity 380,000 442,000 362,000 452,000 364,000 374,000 394,000 381,000 100rpm Viscosity 62,000 63,100 57,000 66,200 59,000 62,000 60,000 64,000 T100 [a] 6.13 7.00 6.35 6.83 6.17 6.03 6.57 5.95 Minimum shear stress 37.71 40.21 38.36 37.92 35.36 30.25 55.46 26.32 slip velocity 16.23 12.32 14.24 19.38 26.32 28.23 22.74 30.23 Slip velocity / minimum shear stress [b] 2.32 3.26 2.69 1.96 1.34 1.07 2.44 0.87 A([a] / [b] 2.64 2.15 2.36 3.49 4.59 5.63 2.69 6.84

division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 10rpm Viscosity 475,000 497,000 430,000 550,00 100rpm Viscosity 64,000 63,300 65,000 92,000 T100 [a] 7.42 7.85 6.62 5.99 Minimum shear stress 57.25 45.42 49.24 24.32 slip velocity 13.11 7.29 14.82 32.19 Slip velocity / minimum shear stress [b] 4.37 6.23 3.32 0.76 A([a] / [b]) 1.26 1.70 1.99 7.88

Experimental Example - Measurement of Conversion Efficiency and Resistance

The conductive paste prepared according to the above Examples and Preparation Examples was pattern-printed on the entire surface of the wafer by a screen printing technique of 40 μm mesh, and dried at 200 to 350° C. for 20 to 30 seconds using a belt-type drying furnace. After that, Al paste was printed on the back side of the wafer and dried in the same way. A solar cell was manufactured by firing the cell formed by the above process at a temperature between 500 and 900° C. for 20 to 30 seconds using a belt-type firing furnace.

The prepared cell uses a solar cell efficiency measuring device (Halm, cetisPV-Celltest 3), short-circuit current (Isc), open-circuit voltage (Voc), conversion efficiency (Eff), curve factor (FF), series resistance ( Rs) and grid resistance were measured and shown in Table 6 below, and line width, height and aspect ratio were measured and shown in Table 7 below.

IV DATA Isc (A) Voc (V) Eff (%) FF (%) Rser(Ω) Rsht(Ω) grid resistance
(1-2) grid resistance
(2-3) Example 1 9.8319 0.6651 21.68 80.85 0.00022 81.0 27.5 26.5 Example 2 9.8402 0.6658 21.67 80.65 0.00019 103.0 31.0 29.7 Example 3 9.8322 0.6649 21.67 80.84 0.00022 89.3 27.1 26.4 Example 4 9.8442 0.6651 21.73 80.97 0.00021 236.1 27.7 26.6 Example 5 9.8447 0.6658 21.75 81.05 0.00014 186.8 28.8 27.8 Example 6 9.8449 0.6654 21.72 80.95 0.00019 81.0 27.5 26.5 Example 7 9.8418 0.6658 21.66 80.66 0.00027 93.8 31.3 32.8 Example 8 9.8428 0.6652 21.70 80.88 0.00021 92.0 28.5 27.9 Comparative Example 1 9.8184 0.6624 21.42 78.78 0.00042 125.4 37.6 36.3 Comparative Example 2 9.8082 0.6629 21.39 78.21 0.00049 103.7 38.6 37.4 Comparative Example 3 9.8288 0.6644 21.60 80.78 0.00021 120.4 26.6 26.5 Comparative Example 4 9.8432 0.6649 21.51 78.91 0.00045 113.3 32.1 30.8

line width Height aspect ratio Example 1 32.23 15.58 0.48 Example 2 31.52 15.23 0.48 Example 3 32.79 15.32 0.47 Example 4 31.13 15.98 0.51 Example 5 28.17 16.8 0.60 Example 6 29.51 16.82 0.57 Example 7 30.23 16.42 0.54 Example 8 29.31 16.72 0.57 Comparative Example 1 33.21 13.24 0.40 Comparative Example 2 32.32 13.97 0.43 Comparative Example 3 34.12 14.59 0.43 Comparative Example 4 29.32 15.62 0.53

As shown in Tables 4 to 6, it can be seen that the conversion efficiency of Examples 4, 5, and 6, in which the value A obtained by dividing T100 by (slip velocity/minimum shear stress) corresponds to 3 to 6, is the best. On the other hand, it can be seen that Comparative Examples 1 to 4 in which A is less than 2 or more than 7 have lower conversion efficiency than Examples in which A is 2 to 7. In addition, as shown in Tables 4, 5, and 7, it can be seen that the embodiment in which A is 2 to 7 has a better aspect ratio compared to the comparative example in which A is less than 2 or more than 7.

Features, structures, effects, etc. exemplified in each of the above-described embodiments may be combined or modified for other embodiments by those of ordinary skill in the art to which the embodiments belong. Accordingly, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

Claims (8)

A conductive paste comprising a metal powder, a solvent, an organic binder, and a glass frit,
A value of Formula 1 below is a conductive paste, characterized in that 2 to 7.
[Equation 1]
A=T100/(Slip velocity/Minimum shear stress)
(Here, T100 is the ratio of the viscosities measured at 10 rpm and 100 rpm, respectively, with spindle 14 using a rotational viscometer at 25 ° C., and the minimum shear stress is laminated at Gap 1.0 mm with a PP50 spindle using an Antonpar rheometer at 25 ° C. It is the minimum shear stress required for desorption after desorption, and it is a value measured at -500um/s speed. The slip velocity was measured at 20~800Pa at a gap of 0.6mm with a PP50 spindle at 25℃ using an Antonpar rheometer at 800Pa. It is the value calculated by the following formula for rotational speed.
Slip velocity=2Х×3.14Х×50Х(Rotational Speed)/60)
According to claim 1,
The value A of Equation 1 is 3 to 6. Conductive paste, characterized in that.
According to claim 1,
The conductive paste is a conductive paste, characterized in that it contains silicone oil.
4. The method of claim 3,
The molecular weight of the silicone oil is 1-100,000cs, the conductive paste.
4. The method of claim 3,
The silicone oil contains a linear molecule, a branched molecule, a cyclic molecule, or a mixture thereof, the conductive paste.
6. The method of claim 5,
The linear molecule is characterized by comprising at least one selected from decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, and hexadecamethylheptasiloxane conductive paste.
6. The method of claim 5,
The cyclic molecule is a conductive paste comprising at least one selected from decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane.
A solar cell comprising an electrode formed using the conductive paste of any one of claims 1 to 7.