KR20110125849A - Electrode material composition, preparation method thereof and solar cell manufactured using same - Google Patents

Abstract

The present invention relates to a composition for a solar cell electrode material comprising a polyacrylate-carbon nanotube composite, a method for preparing the composition, and a solar cell including a counter electrode formed from the composition. Using carbon nanotube electrode material as a binder, at a lower cost than Pt or Ag used as a counter electrode of a fuel-sensitized solar cell, while taking advantage of the low sheet resistance and large surface area of the carbon nanotube electrode. It is possible to provide an electrode material which exhibits excellent photoelectric conversion at low intensity and exhibits efficiency or long-term stability equal to or higher than that of the Pt counter electrode.

Description

A composition for an electrode material, a method of manufacturing the same, and a solar cell manufactured using the same {A Composition for an Electrode, Preparation Method for the Same, and the Solar Cell Prepared Thereby}

The present invention relates to a composition for a solar cell electrode material comprising a polyacrylate-carbon nanotube composite, a method for preparing the composition, and a solar cell including a counter electrode formed from the composition.

CO ₂ due to environmental pollution In order to reduce the occurrence, the strengthening trade and customs regulations around the world are strengthened, so that the developed countries that use large amounts of energy, developed new materials for energy saving, environmentally friendly energy source technology, artificial materials to replace limited resources, In order to maximize energy efficiency, we are developing technology by encouraging enormous manpower and funds for energy use technology. As a feature of environmentally friendly energy materials, it is desirable to be able to utilize the input energy without loss as much as possible, so that raw materials can be infinitely supplied from nature, and at the same time, it is desirable to secure economical efficiency in the manufacturing process and use.

Electrode materials are mainly used in solar cells, transparent electrodes, displays, and sensors. Due to the development of the electronics industry and short and thin products, there is an urgent need to develop materials having better economics and quality than before. Conventional electrode materials may be classified into metals such as platinum (Pt) and silver (Ag) and metal oxides such as indium-tin oxide (ITO) and fluorine coated tin oxide (FTO). Precious metals such as platinum (Pt) and silver (Ag) are widely used in counter electrodes and connecting electrodes of solar cells, antistatic and electromagnetic shielding materials, catalysts in secondary and fuel cells, RFID, electronic ink, and despite their high price Usage is increasing. Silver (Ag) is currently used as a counter electrode material by sputtering onto a substrate on an initial paste as a counter electrode material in the solar cell field, which is currently being spotlighted as a renewable energy source (see FIGS. 1 and 2).

However, the development of new electrode materials that can solve these problems is urgent because most of these silver-paste electrode materials are imported, finite resources, and expensive and limited in use.

Carbon nanotubes form a continuous network in the base matrix, enabling electron hopping between carbon nanotubes at the junctions of elongated nanotube networks, which greatly improves electrical conductivity. In addition to improving the mechanical properties such as strength, stiffness, thermal conductivity, stability, and wear resistance. Highly conductive carbon nanocomposites can be used by coating, coating, and bonding in the fields of conductive fibers, thin films, thick paper, tubes, shielding large structures, electrostatic painting of panels, electrostatic discharge and optoelectronic devices. Carbon nanotubes can be manufactured almost infinitely by properly synthesizing them using infinitely high hydrocarbon gas and natural oxides. Advantages in terms of ease of raw material acquisition, low price compared to conventional electrode materials, multifunctionality, It is an ideal material that can be used in various fields such as retaining catalytic properties, excellent electrical conductivity and heat dissipation characteristics. In addition, carbon nanotubes have a linear structure with an aspect ratio of 1,000 or more, and thus, when properly dispersed, carbon nanotubes can form a conductive network having a high surface density even with a small amount, so that they can be used as conductive materials and electrode materials. It is more suitable than any material.

Currently, there is an acceleration in the development of thin-film solar cells (second generation), which are cheaper to produce than crystalline solar cells (first generation) utilizing polysilicon. Second generation solar cells using carbon nanotubes are attracting attention because they are known to exhibit excellent catalytic properties with low cost and excellent chemical stability. Although much research has been conducted in the meantime, to this day, only the technology of the laboratory stage is maintained, and the problem of efficiency reduction in large-area applications and materials such as platinum and silver, which are used as counter electrodes, are not only difficult to obtain a large amount of production, but also strong There is a problem in that there is a limit in securing a large surface area necessary for obtaining a catalysis.

Accordingly, an object of the present invention is to provide a composition for an electrode material comprising a polyacrylate-carbon nanotube mixture, which can replace the platinum counter electrode at low cost while exhibiting the same efficiency as the platinum counter electrode.

In addition, another object of the present invention, a step of mixing a polyacrylate and a solvent, adding and mixing carbon nanotubes to the mixture, dispersing the polyacrylate and carbon nanotubes using a roll mill (roll mill) It provides a method for producing a composition for an electrode material comprising a polyacrylate-carbon nanotube composite comprising the steps of, and removing bubbles from the polyacrylate / carbon nanotube composite paste in a vacuum oven.

Another object of the present invention is to provide a solar cell including a counter electrode made of a mixture of polyacrylate and carbon nanotubes.

The inventors of the present invention show that carbon nanotubes are used as fillers, and polyacrylates are used as binders to produce composites, and the carbon nanotubes exhibit at least the same efficiency and long-term stability as compared to platinum counter electrodes. The present invention has been completed based on the fact that it can take advantage of the low sheet resistance and the large surface area of the tube electrode, and can exhibit excellent photoelectric conversion at low intensity.

Accordingly, the present invention provides a composition for electrode materials in which carbon nanotubes are dispersed using polyacrylate as a binder.

Polyacrylates usable in the present invention may be selected from a variety of polymers having a monomer structure of formula (1), preferably those having a molecular weight of about 873,200 and a viscosity of about 13,500 cps.

Specifically, examples of the polyacrylates usable in the present invention and their glass transition temperatures (° C.) are shown in Table 1.

polymer Glass transition temperature (℃) Methyl acrylate 6 Ethyl acrylate -24 Propyl acrylate -45 Isopropyl acrylate -3 n-butyl acrylate -55 sec-butyl acrylate -20 Isobutyl acrylate -43 tert-butyl acrylate 43 Cyclohexyl acrylate 16 2-ethyl hexyl acrylate -70 Vinyl acetate 28

The use of polyacrylate in the composition for electrode materials of the present invention has advantages in terms of good adhesion, abrasion resistance, low temperature properties, crosslinking function, mixing with other polymer emulsions, ease of viscosity adjustment, safety and ease of handling, and the like.

On the other hand, the carbon nanotubes that can be used in the electrode material composition according to the invention as a single-walled carbon nanotube (Single-walled carbon nanotube), double walled carbon nanotube (double walled carbon nanotube), multi-walled carbon nanotubes (multi -walled carbon nanotubes, and single-walled carbon nanotubes have better electrical characteristics than multi-walled carbon nanotubes, but solar cell electrode materials use a large area, so the cost aspect of using large area is considered. If so, it is preferable to use multi-walled carbon nanotubes as shown in FIG.

The multi-walled carbon nanotubes usable in the present invention may preferably have a diameter of 50 nm or less and a length of 100 μm or less, and preferably have a diameter of 5-20 nm and a length of 10 μm or less.

According to the present invention, polyacrylate and carbon nanotubes preferably form a complex using methyl ethyl ketone as a solvent, but solvents such as ethyl acetate, toluene and methyl isobutyl ketone may also be used.

The electrode material composition according to the present invention comprises 100 parts by weight of polyacrylate, 7 to 23 parts by weight of carbon nanotubes and 60 to 100 parts by weight of solvent, the solvent is 100% volatilized after drying, polyacrylate of the raw material components It is concentrated by drying the island, leaving only about 23% solids as compared to before drying. Therefore, the counter electrode formed by the composition for electrode material according to the present invention is composed of a mixture of about 30 to 50% by weight of carbon nanotubes and about 50 to 70% by weight of polyacrylate, more preferably about 45 to 50 wt% carbon nanotubes.

In addition, according to the present invention, a step of mixing a polyacrylate and a solvent, adding and mixing carbon nanotubes to the mixture, dispersing the polyacrylate and carbon nanotubes using a roll mill And, and a method for producing a composition for an electrode material comprising a polyacrylate-carbon nanotube composite comprising the step of removing bubbles from the polyacrylate / carbon nanotube composite paste in a vacuum oven.

Methods of dispersing carbon nanotubes include ball mills, ultrasonic sonification, and 3-roll mills, among which polyacrylates are used by using 3-roll mills. And carbon nanotubes are preferably dispersed.

3-roll-mill is a device that can achieve the effect of milling and mixing. Dispersion and grinding using fine gap by passing the high viscosity paste through the gap between rollers rotating at three different speeds Can be performed simultaneously. Each roller is inefficiently operated at different rotation speeds, and thus serves to uniformly process the injected paste by shearing force. In a three-roll mill, the sample enters the hopper and is rolled into the feeder and the central roller, where the once dispersed mixture is attached to the bottom of the central roller and then sent between the second barrels, where the mixture is at the desired granularity. The dispersed, scraper system removes the finished product from the April roller.

The main advantage of the three-roll mill is that the size of the particles is reduced and the aggregates are dispersed due to the shearing force due to the compaction force of the roller and the speed difference of the rollers. It also has advantages in terms of excellent temperature control, contamination prevention, easy volume control, predictable process control, reduced raw material loss, ease of cleaning, and strong cutting forces. And narrow particles can be sized and dispersed. It can also handle products with various viscosities from 200cPoise to 1,000,000cPoise.

In particular, carbon nanotubes have a very large surface area and are very difficult to disperse in a resin, but 3 roll-mill can be used to maintain a high length-to-diameter ratio without damaging the carbon nanotubes.

Specifically, according to the present invention, it is preferable to put the pre-mixed polyacrylate / carbon nanotubes in the beaker between the gaps, and repeat this operation about 10 times at room temperature so that the paste is easily dispersed between the rolls and the rolls. Do.

The mixture paste of polyacrylate and carbon nanotubes dispersed as described above is used to remove bubbles at about 30 ° C. for about 20 minutes using a vacuum oven. In addition to the vacuum oven, various bubble removing methods known in the art may be used. .

The electrode material composition prepared according to the above method can be used to form a counter electrode in a solar cell. Electrode material composition according to the present invention is a composition that can replace Ag or Pt for solar cell electrode material, in order to form an electrode, FTO or TiO ₂ and The composition prepared by screen printing is placed on the glass sprayed with the same conductive material, and then a pattern of electrode material is floated to replace the solar cell electrode material. Thereby, the solar cell in which the counter electrode was formed with the composition for electrode materials of this invention by replacing Ag or Pt can be manufactured.

According to the present invention, by providing a carbon nanotube electrode material using a polyacrylate as a binder, the low sheet resistance of the carbon nanotube electrode and low cost compared to Pt or Ag used as a counter electrode of a fuel-sensitized solar cell Taking advantage of the large surface area, an electrode material which exhibits excellent photoelectric conversion at low intensity and exhibits efficiency or long-term stability equal to or higher than that of the Pt counter electrode can be provided.

1 and 2 illustrate an example of using an Ag counter electrode in a crystalline silicon solar cell.
3 is a simulation picture of multi-walled carbon nanotubes (MWNT),
Figure 4 schematically shows a method for producing a polyacrylate / carbon nanotube composite sheet according to the present invention,
5 is a FE-SEM measurement picture of measuring the thickness of the composite made of 1 sheet, 2 sheets and 4 sheets using a carbon nanotube solution of 30wt%,
6 to 8 show 1 sheet (FIG. 6), 2 sheets (FIG. 7) and 4 sheets (FIG. 8) using 30 wt%, 35 wt%, 40 wt%, 45 wt% and 50 wt% carbon nanotube solutions, respectively. After manufacturing the composite sheet, the fracture surface is a photograph measured by FE-SEM,
9 shows the change of the surface resistance value according to the thickness of the composite,
10 is a result of measuring the change in thermal properties of the composite sheet according to the content of carbon nanotubes by TGA,
11 and 12 show the results of measuring the change in the thermal properties of the composite sheet according to the content of the carbon nanotubes by DMA.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to Examples.

Example  One: Polyacrylate Of carbon / carbon nanotube composite sheet

100 g of polyacrylate was prepared and placed in a beaker to release polyacrylate using approximately 60-100 g of methyl ethyl ketone. Polyacrylate was a polyacrylate SEN-3100 of Geomyung Tech Co., Ltd., having a molecular weight of 873,200 g / ml and a solution viscosity of 13,500 cps. As methyl ethyl ketone, methyl ethyl ketone (2-butanol) was used in a large tablet. As multi-walled carbon nanotubes, multi-walled carbon nanotubes having a diameter of 5 to 20 nm and a length of 10 μm manufactured by Applied Carbon Nano Co., Ltd. were purchased and used.

After 10 minutes of loosening, multi-walled carbon nanotubes (MWNT) are weighed and weighed about 7-23 g in polyacrylates, then mixed for another 10 minutes, 30wt%, 35wt%, 40wt% , 45 wt%, 50 wt% MWNT solution was prepared.

Subsequently, the polyacrylate and MWNTs were dispersed using a 3 roll mill (model name EXAKT 50 (length 320 X width 280 X thickness 320)), and the pre-mixed polyacrylate / MWNT was gapped in the beaker. To this end, this operation was repeated about 10 times at room temperature so that the paste was easily dispersed between the rolls and the rolls.

Bubbles of polyacrylate / MWNT prepared at 30 ° C. for 20 minutes were removed using a vacuum oven.

The paste was thus cast on a film with a constant thickness using a doctor blade having a thickness of about 200 μm on a release film. It was dried for about 24 hours in an 80 ℃ drying oven. Samples of 1 sheet, 2 sheets, and 4 sheets were prepared using a hot press under conditions of a temperature of 110 ° C., a duration of about 1-5 minutes, and a pressure of 1,500 psi.

Example  2: measurement of thermal and electrical properties

(1) FE-SEM measurement

FE-SEM scans the surface of the sample by the accelerated electron beam in the field emission electron gun, and the secondary electron, back scatter electron, and X-ray are generated by the interaction with the sample. It is a high resolution scanning electron microscope that detects (X-ray) signals, observes the shape of the sample surface, and measures qualitative, quantitative analysis and crystal structure of the elements constituting the sample.

Specifically, FE-SEM measurement was performed using the JSM-6500F with a resolution of 1.5 nm, x10 to x300,000, and a schottky field emission electron gun. The results are shown in FIGS. 5 to 8.

Figure 5 shows the thickness by measuring the fracture surface for each thickness of the sheet produced at x120 magnification, Figures 6 to 8 is an image measured at x5,000 magnification.

As a result of the measurement, as shown in FIG. 5, when the 30 wt% carbon nanotube solution was used, the thicknesses of the composites prepared from 1 sheet, 2 sheets and 4 sheets were 95.3 μm to 121.9 μm, 197.7 μm to 219.6 μm, and 438.3, respectively. It was found that the m ~ 446.1μm. As the thickness increases as the electrode material is used, the resistance value is lowered. However, in view of the case where the Ag electrode is combined with the solar cell, the thickness of about 100 μm is also preferable in the present invention.

In addition, as a result of measuring the fracture surface by FE-SEM, it was confirmed that the carbon nanotubes were evenly dispersed as the content of the carbon nanotubes increased (FIGS. 6 to 8).

(2) measurement of surface resistance

The dried paste film was measured for surface resistance with a 4-point probe.

The four-point probe measurement method measures the surface resistance by bringing four chips into contact with a sample. Both chips have current and the middle two chips have voltage. In this case, the resistance is measured as the current and voltage flow. will be. Surface resistance is expressed in ohms / sq, where sq is also represented by □, and is a separate unit rather than a metric (such as cm ² ), interpreted as an infinite area. Wire resistance measures resistance over any distance with two probes, but in the case of surface resistance, four probes of equal spacing are measured.

The probe used is a 4 point probe, and the probe uses probes arranged in 1mm intervals.The current and voltage are measured by four probes.Then, the resistance value is obtained, and the probe is calibrated to calculate the surface resistance in ohm / sq. Apply the coefficient CF. Surface resistance values of the polyacrylate / MWNT sheet measured based on the above are shown in FIG. 9. When the content in the sheet was low 30wt%, the surface resistance value was lower than 10 ¹ dl / sq, and at 50wt%, the surface resistance value was lower. Therefore, as a result of measuring the electrical properties of the composite sheet, it was found that the thicker the composite, the higher the content of carbon nanotubes, the lower the surface resistance, indicating high electrical conductivity (FIG. 9).

(3) TGA measurement

The TGA is a device that measures the weight change of a sample by applying a temperature program to the sample. The TGA knows the heat state of the sample from the curve of temperature-weight change and enables qualitative and quantitative analysis. In addition, this temperature-weight change curve indicates the thermal stability of the sample used, the composition ratio of the materials, the thermal properties of the intermediates generated during heating, and the amount of residue left after heating.

In this experiment, TGA measurement was performed using the equipment name TA-Q500 (temperature range: ~ 1000 degrees, temperature rising rate: 0.01 degrees ~ 100 degrees per minute).

As a result, as shown in Figure 10, as the content of carbon nanotubes increased, the Td (pyrolysis temperature) of the composite was found to increase about 14 ~ 16 ℃ (Fig. 10). Specifically, the results of FIG. 10 are 10 degrees per minute, and the temperature is measured at room temperature to 600 degrees. When the polyacrylate / MWNT content is prepared at 30, 35, 40, 45, and 50 wt%, 50 wt% is contained. When the pyrolysis temperature was 95%, it was confirmed that the pyrolysis temperature was about 13 degrees higher than that of the polyacrylate at 361.43 degrees, and thus the interfacial adhesion between the polyacrylate polymer resin and the MWNT was increased.

(4) DMA measurement

The instrument name of the DMA (dynamic mechanical analysis) is TA-Q800, which measures the mechanical properties of the sample as a function of time, temperature and frequency. Q800 DMA devices offer performance, usability and ease of use. Extremely sensitive optical sensor technology precisely measures strain, air bearing technology realizes almost frictionless movement, operates over a wide temperature range of -150 to 600 degrees, and a measuring range of modulus is ~ pa The frequency ranges from 0.01 to 200 Hz and can be measured using three-point bending, tension, compression, and various variations of shear. Temperature measurements from -70 degrees to 100 degrees and frequency measurements at 2 degrees per minute (HZ) (Figs. 11 and 12) showed a loss modulus at -20 degrees, with storage modulus at 50 wt%. As a result, it was found that the tan δ value decreased as the content increased, which is thought to be due to the increase in the damping effect as the number of knitted polyacrylates increased. That is, as the content of the composite carbon nanotubes increased, the storage modulus (E ') increased (FIG. 11), but there was little change in the tanδ value (FIG. 12).

Claims (3)

Electrode material composition comprising 100 parts by weight of polyacrylate, 7 to 23 parts by weight of carbon nanotubes and 60 to 100 parts by weight of solvent. (1) mixing a polyacrylate with a solvent;
(2) adding and mixing carbon nanotubes to the mixture obtained in step (1);
(3) dispersing polyacrylate and carbon nanotubes using a roll mill; And
(4) removing bubbles from the polyacrylate / carbon nanotube composite paste prepared in step (3) in a vacuum oven
Method for producing a composition for electrode material according to claim 1 comprising a. A solar cell comprising a counter electrode consisting of a mixture of 30 to 50% by weight of carbon nanotubes and 50 to 70% by weight of polyacrylate.

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