The present invention relates to the technical field of organic electroluminescence devices, in particular to a transparent carbon nano-tube (CNT) polymer compound conductive ink for transparent electrodes and the preparation method thereof.
In such display devices and photovoltaic devices as liquid crystal panel, OLED panel, touch screen, electronic paper and solar cell, transparent electrodes are indispensable components. Indium tin oxide (ITO) forms ITO films on glass substrate, exhibiting excellent transparence and conductivity, so it possesses leading position in application fields of commercial transparent electrodes. With development of science and technology and diversification of application fields of transparent electrodes, however, transparent electrodes must meet requirements such as low square resistance, good transmittance within visible light, flexibility and simple operation technology capable of realizing large area fine coating and filming, which makes that problems which can not be overcome technologically exist in expanded application of ITO films. Indium (In) is a rare element with low reserves in the world and content of In2O3 in films is high, so the production cost is high; ITO films are brittle and are easy to generate cracks after many times of periodic bending or compression, causing invalidity of conductivity. When ITO films deposit on matching plastic substrates at low temperature, the film layer exhibits relatively high surface resistance and degree of roughness. Therefore, it is a technical difficulty which must be solved in electronic display fields and application fields of photovoltaic to develop novel flexible transparent electrode materials for replacement of ITO electrodes.
CNT is a kind of carbon materials with typical lamellar hollow structures and body of the CNT consists of hexagonal graphite carbon ring structure units. It is a one-dimensional quantum material with special structures (the radial dimension is in nanometer scale and axial dimension is in micrometer scale). Tube wall consists of several or dozens of layers of coaxial circular pipes. Fixed distance is kept between different layers and it is about 0.34 nm, with diameter at 2˜20 nm. P electrons of carbon atoms on CNT form large range delocalized π-bond. Due to obvious conjugative effect, CNT has some special electrical properties. Because structure of CNT is identical to the lamellar structure of graphite, CNT has very good electrical properties. Due to high electron transfer rate, low resistivity and high transparency, CNT materials have been considered by the field of scientific research and industry to replace ITO transparent electrodes.
Combination of CNT and conducting materials into a compound layer can improve conducting properties of transparent electrodes. In present methods, CNT together with conducting materials is generally manufactured into a mixing solution and then spin coating is carried out or the mixing solution is printed on an electrode. Due to specificity of structure of CNT and bad compatibility with other substances, however, dispersion of CNT in the mixing solution is bad and the mixing solution is unstable and easy to deposit.
The present invention provides a novel transparent CNT polymer conductive ink is disclosed. In preparation of the ink, modified CNT and conductive polymer are used as raw materials and special cosolvent is adopted. Moreover, the blend technology of solution is adopted to realize uniform dispersion of CNT and conductive polymer solution and the obtained ink has good stability and re-dispersibility.
The present invention also provides preparation method of the transparent CNT polymer conductive ink.
A transparent CNT polymer conductive ink, comprising the following components in the following weight parts:
The said modified CNT is prepared by the following method: add 30% HNO3 aqueous solution into CNT, after dispersion by ultrasonic wave for 40 min, stir at 50-70° C. for 30 min, filter with a 200 μm porous membrane, rinse to neutrality, and dry at 100° C. to obtain the modified CNT after purification.
The said CNT is single-wall CNT (SWCNT), double-wall CNT (DWCNT) or multi-wall CNT (MWCNT) powders.
The said conductive polymer is selected from polyaniline, poly(3,4-ethylenedioxythiophene), polyacetylene or polypyrrole.
The said corresponding polymer cosolvent is selected from polystyrene sulfonate, camphorsulfonic acid, dodecyl benzene sulfonic acid, hexadecyl benzene sulfonic acid or naphthalene sulfonic acid.
The said polymer modification additive is one or more selected from propylene glycol, glycerin, ethylene glycol monobutyl ether, sorbitol, dimethyl sulfoxide and N,N-dimethyl formamide.
The said surfactant is sodium dodecyl benzene sulfonate or polyvinylpyrrolidone.
The said conductive polymer is poly(3,4-ethylenedioxythiophene), the said conductive polymer cosolvent is sodium polystyrene sulfonate, and the said surfactant is polyvinylpyrrolidone
The preparation method of the transparent CNT polymer conductive ink, comprises the following steps:
The said conductive polymer: conductive polymer cosolvent is poly(3,4-ethylenedioxythiophene) (PEDOT): Sodium polystyrene sulfonate (PSS).
In formation of the present invention, except for basic modified CNT, conductive polymer and deionized water, conductive polymer cosolvent and polymer modification additive and surfactant are also added, so that dispersibility of CNT is improved obviously and stability and re-dispersibility of the obtained ink are good.
CNT being conducting transmission materials of conducting film, its dispersion in conductive polymer system is very important. However, surface tension of CNT is large and CNT is easy to agglomerate into particles. Therefore, uniform dispersion of CNT in the ink system is very important. In the present invention, amorphous carbon on surfaces of CNT is removed by adopting the method of acidifying. At the same time, such functional groups as OH and COOH are grafted on surfaces of CNT, reducing agglomeration and CNT and increasing solubility of CNT in water. In addition, stable dispersion of CNT in the ink system can be improved under adjustment effects of surfactants on surface tension of CNT.
The conductive polymer itself is difficult to be soluble in water and it can form a water-soluble solution system under bonding action of polymer cosolvent. In order to adjust its conducting characteristics, some substances with high melting point can be added to improve the conducting properties and these substances are called as conducting additives.
The present invention provides a novel transparent CNT polymer conductive ink is disclosed. In preparation of the ink, modified CNT and conductive polymer are used as raw materials and special cosolvent is adopted. Moreover, the blend technology of solution is adopted to realize uniform dispersion of CNT and conductive polymer solution and the obtained ink has good stability and re-dispersibility. The transparent CNT polymer conductive ink can be used for preparing fine electrode patterns under room temperature by adopting such devices as spin coating and ink jet printing. It can realize preparation of fine electrode patterns through photo-resisting technology and can also be prepared into photoresist type conductive ink to realize one-off preparation of electrode patterns with fine structures.
The transparent CNT ink can be applied for very transparent electrode materials in such devices as flexible OLED display, solar cell, liquid crystal display and panel of touch screen. It has such advantages as good compatibility with transparent polymer matrix and strong adhesion to ensure use life of the flexible electrode.
The present invention will be further described in details hereinafter with reference to specific embodiments.
Preparation Method:
Technological Processes:
The preparation method is the same as that in Embodiment 1.
The transparent CNT polymer conductive ink can be used for preparing fine electrode patterns under room temperature by adopting such devices as spin coating and ink jet printing. It can realize preparation of fine electrode patterns through photo-resisting technology and can also be prepared into photoresist type conductive ink to realize one-off preparation of electrode patterns with fine structures.
Example: the conductive ink in Embodiment 1 is coated on electronic glass substrate by spin coating. Implementation technology: rotation speed 3000 rpm, time 30 s, drying temperature 120° C., and drying time 20 min.
Single layer thickness of the obtained film is 19-23 nm and thickness of three layers of film is 55-60 nm. Within the wave length range of 300-600 nm, the optical transmittance (with respect to the substrate) is larger than 90% and the square resistance of three layers of films reaches up to 150-200Ω/□, as shown in Table 1 and
Number | Date | Country | Kind |
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201310089765.2 | Mar 2013 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2014/072623 | 2/27/2014 | WO | 00 |