KR20060061810A - Light-emitting diode - Google Patents

Abstract

The invention pertains to a light- emitting diode (LED) comprising layers of an anode, an acidic hole conducting-injecting material, a light-emitting polymer, and a cathode, characterized in that the hole conducting-injecting material comprises a poly(3,4-ethylenedioxythiophene poly(styrenesulfonate) (PEDOT), which is obtainable by at least partially neutralizing the PEDOT with an anion that is comprised or formed from a sodium or potassium compound, and the light-emitting material comprises a light-emitting p-arylene-vinylene polymer (PAV). The invention further relates to a method for increasing the efficiency of said light-emitting diode.

Description

Light Emitting Diodes {LIGHT-EMITTING DIODE}

The present invention relates to a light emitting diode comprising a layer of an anode, an acidic hole conduction-injecting material, a light emitting polymer and a cathode.

Most poly-LEDs (polymer based light emitting diodes) have two electrode materials, a hole conducting-injecting material and two polymer layers interposed between the light emitting diodes. It consists of. The light emitting polymer may be made of a type of P-arylene-vinylene polymer (poly (p-arylene vinylene): PAV). For the first function, poly (3,4-ethylenedioxythiophene): PEDT} obtainable by dispersing in water together with polystyrene sulfonic acid (PSS) may be used. The dispersion is called PEDOT and is commercially available as BAYTRON®P VP CH8000 (high resistance) or BAYTRON®P VP AI 4083 (low resistance) sold by HC Starck, due to the acidity of PSS, it has a 2.5% solids content. The pH of the phosphorus PEDOT solution is below pH 2. The function of the PSS is to maintain the PEDT so that it can be dissolved in the solution and stable in the solution In practice, the PEDT is polymerized in the presence of the PSS. It is doped at the same time, which creates a charged polymer and can conduct the hole into the charged polymer.The negatively charged sulfonate functional group is intended for incorporation into a positively charged PEDT unit. Acts as a counter ion balance (usually one of the three to four units in the PEDT is incorporated in an amount grades).

Such light emitting diodes are incorporated by reference and are known in US 2003/0011306.

There is a continuing need to increase the efficiency of light emitting diodes, in particular to improve the brightness of displays comprising light emitting diodes. US Patent No. US 6,284,435 proposes to improve quantum efficiency by adding high polar organic anionic surfactant additives such as lithium salts of ether sulfate anionic surfactants.

The inventors have found that the efficiency of light-emitting diodes comprising PEDOT as a hole conduction-injecting material and P-arylene-vinylene polymer (PAV) as a light emitting polymer can be used with expensive surfactants or other organic materials. It has been found that it can be significantly improved in a simple and inexpensive way that does not need to. When at least partially neutralized PEDOT according to the invention is used in combination with PAV, increased brightness levels can be obtained under high voltage (at least 10V, preferably at least 15V) in a pulsed driving mode. have. The invention therefore also relates to a light emitting diode comprising vibration driving means suitable for supplying a voltage of at least 10V, preferably at least 15V. Neutralization can be carried out by the removal of protons in PEDOT and by the addition of bases such as, for example, metal hydroxides, by substitution of metal ions or by other substances capable of removing protons from PEDOT. Equation 1 is an example of neutralization using sodium hydroxides and the structure of the polymer is represented by the following formula.

[Formula]

In the present invention, the hole conduction-injection material includes poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonate) (PEDOT), and includes an anion formed by sodium or potassium compounds or formed from sodium or potassium compounds. Obtained by at least partially neutralizing with the poly (3,4-ethylenedioxythiophene) (PEDOT), the light-emitting material comprising a luminescent p-arylene-vinylene polymer (PAV) It relates to the light emitting diode described.

The sodium or potassium compound is preferably sodium or potassium hydroxide, nitrate, carbonate or hydrogen carbonate, more preferably sodium hydroxide. The best results are obtained when PEDOT is neutralized to at least pH 3. Preferably the pH is 3-7, more preferably 5.5-6.5. Neutralization of PEDOT is a common acid-base reaction, e.g. under these conditions, since sodium nitrate forms nitrate anions that capture protons in the PEDOT leaving the solution as gaseous nitric acid. For example, it can be obtained by capturing protons in PEDOT under acid-base reactions with sodium hydroxide or under conditions for removing the aqueous solvent in situ.

The present invention also provides a method of increasing the efficiency of a light emitting diode comprising a layer of an anode, an acidic hole conduction-injection material, a light emitting polymer and a cathode, wherein the hole conduction-injection material is poly (3,4-ethylenedioxythiophene) / Poly (styrenesulfonate (PEDOT), the light emitting material relates to a method of increasing the efficiency of a light emitting diode comprising poly (p-arylene vinylene) (PAV), the method is acidic hole conduction The injection material is at least partially neutralized with anions comprising or forming from sodium or potassium compounds.

1 is a cross-sectional view schematically showing an embodiment of a light emitting diode according to the present invention.

1 is a schematic diagram of a light emitting diode, a substrate (1) which is generally glass, an anode (2) which may be indium-tin oxide (ITO), a layer (3) comprising PEDOT, p-phenylene A light emitting diode composed of a layer 4 and a cathode 5 containing p-penylene vinylene (PPV) is shown.

In particular, reference is made to patent application WO 96/08047, which discloses a variety of materials and methods for producing a variety of materials, the contents of which are incorporated herein by reference. The material for use as a conductive transparent polymer (CTP) is a mixture of poly-3,4-ethylenedioxythiophene and polystyrene sulfonic acid.

The active layer is located between two electrode layers of conductive material. At least one of the electrode layers should be transparent or translucent to the light emitted from the active layer. One of the electrode layers serves as a (positive) electrode for injecting holes into the active layer. The material of this electrode layer has a high work function and is generally formed by an indium oxide layer or an indium-tin oxide (ITO) layer. The layer is also transparent to light emitted on the active layer. Indium-tin oxide (ITO) is particularly suitable due to its sufficient electrical conductivity and high transparency. The other electrode layer serves as a (negative) electrode for injecting electrons into the active layer.

The material for the electrode layer has a low work function and is generally formed of a layer of, for example, indium, calcium, barium or magnesium.

The electrode layer of indium-tin oxide (ITO) is made by vacuum evaporation, sputtering or chemical vapor deposition (CVD). Such electrode layers and sometimes negative electrode layers, for example calcium electrode layers, are obtained by partially covering the electrode layer with a mask in a general photolithographic process or during a vacuum deposition process. As a pattern it is constructed according to a pattern that matches a desired pattern for display. As a general example of the display, the electrodes of the first electrode layer and the second electrode layer have a linear structure and cross each other at right angles, thereby forming a matrix of rectangular LEDs that can be driven separately.

A rectangular light emitting diode constitutes a pixel, i.e., a pixel, of a display. When the electrodes of the first electrode layer and the second electrode layer are connected to an electrical source, light-emitting pixels are formed at the intersections of the electrodes. As such, the display can be formed in a simple manner. The structure of the pixel is not limited to a particular form. Basically all the shapes of the pixels can be in the form of pieces, for example icons or simple forms. In accordance with the present invention, it should be noted that an active matrix structure can be used, independent of the passive matrix structure.

Light-emitting polymers, including homopolymers, terpolymers, copolymers, block copolymers, oligomers (including low molecular weight compounds) and other similar materials ( Light-emitting polymers include poly (p-phenylene vinylene: PPV}, such as poly (p-phenylene vinylene: PPV), in which a phenylene group may be substituted, as disclosed in WO98 / 27136. p-arylene vinylene) {poly (p-arylene vinylene): PAV} electroluminescent material (poly-p-phenylene vinylene) {poly (p-phenylene vinylene): PPV} Phenyl-substituted PPV (PPV), more particularly substituted with phenyl groups, is a preferred polymer type that may be used PAV-type polymers include at least two arylene-vinylene components, the same or different. Therefore, the copolymers according to the invention and other similar materials are fluorescent. It may further include other light emitting components such as ene) component or spirofluorene component.

Preferably, a soluble conjugated polymer is used because it can be easily applied in a spin-coating process or by ink jetting. Preferred solubility is improved by substituting a PPV derivative conjugated with alkyl and / or alkoxy or phenyl groups. The luminescent material may also be a doped low molecular material, which is treated with a dye such as quinacridone deposited in a vacuum process, 8-hydroxyquinolin-aluminum (8-hydroxyquinolin). -aluminum).

Depending on the method of making the conjugated polymer, the conjugated polymer may comprise 5-10% unconjugated unit. The non-bonded unit increases the electroluminescence efficiency and is limited by the number of photons per injected electron on the active layer.

The conjugated PAV derivatives described above can be dissolved in common organic solvents such as halogenated hydrocarbons such as chloroform, toluene, xylenes, anisoles. It can be dissolved in optionally substituted aromatic hydrocarbons such as chlorobenzene and mesitylene. In addition, methylbenzoate and tetrahydrofurane may be used as the solvent.

The degree of polymerization of the conjugated polymer is in the range of 10 to 100,000.

The thickness of the light emitting layer of the conjugated polymer is in the range of 10 to 250 nm, and more specifically in the range of 50 to 130 nm.

The light emitting structure is placed on a substrate made of glass, quartz glass, ceramic or synthetic material. Transistors or other electronic means will be placed between the substrate and the transparent electrode forming a so-called active matrix substrate. Preferably a translucent substrate or a transparent substrate is used. If a flexible electroluminescent device is desired, a transparent foil of synthetic resin is used. Examples of suitable transparent and flexible synthetic resins are polyamide, polyethylene, terephthalate, polycarbonate, polyethene and polyvinyl chloride.

The invention is illustrated by the following examples.

The efficiency of the device in candela (cd / A: unit of brightness) at the set brightness

BAYTRON®P VP CH8000 is neutralized with hydroxides of cesium (Cs) (comparative) or sodium (Na). Cesium hydroxide (CsOH) does not show a beneficial effect on the efficiency of the light emitting diodes. It was found that brightness above 100.000 cd / m 2 could not be obtained in the range of pH 1-7.

In contrast, sodium hydroxide (NaOH) has a significant effect in terms of efficiency. It was found that the higher the pH, the higher the efficiency. The use of sodium hydroxide (NaOH) as the base makes it possible to obtain light emitting diodes with brightness above 100.000 mW / m 2. Above pH 4 even brightness above 200.000 mW / m 2 was possible.

The apparatus used to obtain the data in the table below has standard device configurations of Indium-Tin Oxides (ITO), 200 nm PEDOT, 80 nm SY-LEP, and Ba / Al anodes. The device is operated in vibration mode with a 1% vibration duty cycle at 200 Hz with the voltage indicated in parentheses in the table below.

SY-LEP was obtained commercially from Covion, Germany, and is a copolymer of at least a building block structure, as shown in the following structural formula.

[constitutional formula]

compound pH Efficiency at 20.000 ㏅ / m2 {Eff. (㏅ / A)} Efficiency at 60.000 ㏅ / m2 {Eff. (㏅ / A)} Efficiency at 200.000 ㏅ / m2 {Eff. (㏅ / A)} Ref. One 10 (8.3) 9 (12.0) - Cesium hydroxide 2 9 (9.0) 8.5 (13.0) - Cesium hydroxide 3 7 (11.5) 6.5 (16.0) - Cesium hydroxide 4 2.5-3.5 (16.0) - - Cesium hydroxide 5 2.5-3.5 (16.0) - - Cesium hydroxide 6 2.5-3.5 (16.5) - - Sodium hydroxide 2 9.5-11 (10.0) 8-9 (13.5) - Sodium hydroxide 3 11-13 (10.3) 13-15 (14.0) - Sodium hydroxide 4 9-10 (12.5) 15-17 (14.5) 17-23 (17.5) Sodium hydroxide 5 7.5-10 (11.5) 11-16 (13.0) 15-20 (16.2) Sodium hydroxide 6 16-17 (10.5) 20-25 (12.0) 28-40 (15.0) Ref .: Neutralizer-free Eff .: Efficiency

The voltage at which the indicated brightness level was obtained is indicated in parentheses.

The present invention can be used for a light emitting diode.

Claims (9)

A light emitting diode comprising a layer of an anode, an acidic hole conduction-injecting material, a light emitting polymer, and a cathode, the light emitting diode comprising: The hole conduction-injection material comprises poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonate) (PEDOT) and includes an anion comprising sodium or potassium compounds or formed from sodium or potassium compounds and the Obtained by at least partially neutralizing poly (3,4-ethylenedioxythiophene) (PEDOT), The light emitting material of claim 1, wherein the light emitting diode comprises p-arylene-vinylene polymer (PAV). The light emitting diode of claim 1, wherein the compound is sodium, potassium hydroxide, nitrate, carbonate, or sodium bicarbonate. The light emitting diode of claim 2, wherein the compound is sodium hydroxide. The light emitting diode according to any one of claims 1 to 3, wherein the pH is 3 or more. The light emitting diode according to any one of claims 1 to 4, wherein the pH is 3-7, more preferably 5.5-6.5. The light emitting diode according to any one of claims 1 to 5, wherein the p-arylene-vinylene polymer (PAV) is poly (p-phenylene vinylene). 7. Vibration mode drive means according to any one of the preceding claims, characterized in that it comprises vibration mode driving means adapted to impart a voltage of at least 10 volts (V), more preferably at least 15 volts (V). Light emitting diode. In the method of driving the light emitting diode of claim 7, And the light emitting diode is driven in a vibration mode at a voltage of at least 10 volts (V), more preferably at least 15 volts (V). A method of increasing the efficiency of a light emitting diode comprising a layer of an anode, an acidic hole conduction-injecting material, a light emitting polymer, and a cathode, The hole conduction-injection material includes poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonate (PEDOT), and the light emitting material includes poly (p-arylene vinylene). In the method of increasing the efficiency, 20. A method of increasing the efficiency of a light emitting diode, wherein the acidic hole conduction-injecting material is at least partially neutralized with anions comprising or formed from sodium or potassium compounds.

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