JP2003036975A - Organic electric field light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electric field light-emitting element in which color purity is improved by improving element constitution of the organic electric field light-emitting element. SOLUTION: The organic electric field light-emitting element has a pair of electrodes and a layer composed of an organic substance of at least one layer or more sandwiched between them, and a light-emitting color adjusting layer is inserted between the organic layer and the electrode. By this, to improve the color purity becomes possible. Further, it is also enabled that the light- emitting color adjusting layer is made to have an absorbance in wavelength regions in addition to the desired emitting wavelength region, and by this, suppression of deteriorating the color purity becomes possible by absorbing unnecessary light emissions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent element which is widely used as various display devices and has excellent color purity.

[0002]

2. Description of the Related Art An electroluminescent device is brighter and clearer than a liquid crystal device due to self-luminous display.
It has been studied by many researchers since ancient times. As an electroluminescent device that has reached a practical level, Z, which is an inorganic material, is currently used.
There is an element using nS. However, such an inorganic electroluminescent device requires a driving voltage of 50 V or higher for light emission, and thus has not been widely used.

On the other hand, an electroluminescent element using an organic material
The organic electroluminescent device, which is a child
It was far from, but in 1987 Eastman
・ CW Tan of Kodak Company
g) The characteristics of the laminated structure element developed by
Has made great strides. They have a stable vapor-deposited film structure
Layer consisting of a phosphor that can transport
Light emitting layer) and an organic substance capable of transporting holes.
Layer (hole-transporting layer) to stack holes and electrons in the phosphor.
It was succeeded in injecting into and making it emit light. By this
The luminous efficiency of the electroluminescent device is improved and the voltage is 10 V or less.
1000 cd / m²The above light emission can be obtained
It was After that, the electron-transporting light-emitting layer was formed into a light-emitting layer and an electron-transporting layer.
The functional separation of the layers that make up the device was promoted.
As a result, at present 10,000 cd / m ²The above emission characteristics
Has been obtained.

Since such an organic electroluminescent device can make the emission colors of red, blue and green uniform by changing the material of the light emitting layer, its application to a full color display is under study.

[0005]

In order to realize a full-color display having a higher display quality for use in electronic devices and the like, it is necessary to increase the color purity of each luminescent color. Since an organic electroluminescent element often uses a light emitting material having a fluorescence spectrum with a wide half-value width, many of the obtained elements have low color purity.

The present invention has been made in view of such conventional problems, and an object thereof is to realize an organic electroluminescent device having improved color purity by improving the device structure of the organic electroluminescent device. Especially.

[0007]

The organic electroluminescence device of the present invention has a pair of electrodes and at least one layer made of an organic material sandwiched between the electrodes, and the luminescent color is provided between the organic layer and the electrodes. It is characterized in that an adjustment layer is inserted.

The invention according to claim 1 includes a pair of electrodes,
An organic electroluminescent device characterized by having at least one layer made of an organic substance sandwiched between them, and having an emission color adjusting layer inserted between the organic layer and an electrode, which has an effect of improving color purity. Have.

The invention according to claim 2 is characterized in that the emission color adjusting layer has an absorbance in a wavelength range other than a desired emission wavelength range, and it absorbs unnecessary emission. It has an effect of suppressing a decrease in purity.

The invention according to claim 3 is characterized in that the emission color adjusting layer is adjusted to have a film thickness capable of strengthening a desired emission wavelength region, and thereby the desired emission color adjusting layer is obtained. It has an effect of realizing an organic electroluminescence device having an emission peak in the wavelength range.

The invention according to claim 4 is characterized in that the emission color adjusting layer comprises a mixed layer of a charge transport material and a metal, whereby the charge transporting property of the emission color adjusting layer is improved. It has an effect that an element having improved and high efficiency and good color purity can be realized.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic configuration of an organic electroluminescence device according to an embodiment of the present invention. In this organic electroluminescence device, an anode 2 which is an electrode is formed on a glass substrate 1 which is a base, and on the anode 2,
From the side of the glass substrate 1 and the anode 2, the hole transport layer 3,
The light emitting layer 4, the electron transport layer 5, the emission color adjusting layer 6, and the cathode 7 are formed. The organic electroluminescent element according to this embodiment is characterized in that the emission color adjusting layer 6 according to the present invention is formed between the electron transport layer 5 and the cathode 7.

For the anode 2, indium tin oxide (ITO) as a transparent electrode or a gold thin film as a semitransparent electrode can be used.

The charge transport layer is roughly classified into a hole transport layer 3 and an electron transport layer 5. Each of them has a function of facilitating the injection of charges from the electrodes and transporting the injected charges to the light emitting region. A charge injection layer may be provided between the charge transport layer and the electrode. As a material for the hole injection layer, a material having a low HOMO level is used in order to facilitate injection of holes from the anode 2. Specifically, copper phthalocyanine (CuPc) and tris {4-[(3-methylphenyl) phenylamino] phenyl} amine (m-MTDA
TA) and the like. Further, as the hole transport layer 3,
A material having a strong hole transporting property is used. Specifically, N, N
'-Diphenyl-N, N'-bis (3-methylphenyl)
1,1'-biphenyl-4,4'-diamine (TPD)
A triphenylamine derivative or the like can be used.

On the other hand, a material having a strong electron-transporting property can be used for the electron-transporting layer 5, and specific examples thereof include a phenanthroline derivative, an oxadiazole derivative and tris (8-hydroxyquinolinol) aluminum (Alq). The use of quinolinol metal complexes and the like is being investigated. Furthermore, it has been studied to use a porphyrin derivative or a mixed film of the above-mentioned electron transport material and a metal as the electron injection layer.

A large number of compounds have been studied as the light emitting layer 4, but basically any substance capable of injecting electrons / holes and having fluorescence / phosphorescence can be used. Further, by using a film in which a small amount of a dye is dispersed in a material having excellent film-forming property as the light emitting layer 4, it is considered to improve the efficiency and the life of the organic electroluminescent device and adjust the emission color. Has been done. This method is very effective for fluorescent dyes and phosphorescent dyes that are easily crystallized or cause concentration quenching by themselves.

The cathode 7 needs to be capable of injecting electrons into the organic film, and an alkali metal, an alkaline earth metal or a compound thereof is often used as one of the constituent materials. Specifically, lithium, magnesium and calcium,
Alternatively, these metals and compounds can be used in combination with other metals.

According to the present invention, by providing the luminescent color adjusting layer 6 between the electron transport layer 5 and the cathode 7, it becomes possible to extract only the light in the desired luminescent area to the outside of the device. The color purity of the electroluminescent element can be improved. For the emission color adjusting layer 6, a material having an absorbance outside the desired emission wavelength range is used. By combining an appropriate luminescent material and the luminescent color adjusting layer 6, part of the light from the luminescent layer 4 can be absorbed and the color purity can be increased. For example, when a blue light emitting material is used, by using an organic material having absorption in a wavelength region longer than 500 nm for the emission color adjusting layer 6, light of 500 nm or more is absorbed and a green light emitting component is cut off. This improves the color purity. Further, when the film thickness between the light emitting region and the electrode is changed, the spectrum changes due to the interference effect. Therefore, the emission color can be changed by setting the light emission color adjusting layer 6 to an appropriate film thickness.

It is important that the luminescent color adjusting layer 6 also has a charge transporting property. For that purpose, it is effective to use a mixed layer of a charge transport material and a metal as the emission color adjusting layer 6.

In the above description, the case where the emission color adjusting layer 6 is provided between the cathode 7 and the electron transporting layer 5 which is an organic layer has been described, but the anode 2 and the hole transporting layer which is an organic layer. The same idea can be applied to the case where the emission color adjusting layer 6 is provided between the light emitting element 3 and the light emitting element 3.

[0021]

EXAMPLES Next, specific examples of the present invention will be described.

(Example 1) As a substrate, an indium tin oxide film (ITO) was previously formed on a glass as a transparent anode and patterned into an electrode shape. After thoroughly cleaning the glass substrate 1, the glass substrate 1 was set in a vacuum apparatus together with the material to be vapor-deposited, and vacuum exhausted to 10 ⁻⁴ Pa.
After that, as the hole transport layer 3, N, N′-bis [4 ′-(N, N-diphenylamino) -4-biphenylyl] -N, N′-diphenylbenzidine (TPT) was deposited to a thickness of 50 nm. Then, the light emitting layer 4
Alq was formed into a film of 50 nm as the electron-transporting layer 5. Then, copper phthalocyanine (CuP) is used as the emission color adjusting layer 6.
A co-deposited film of c) and lithium metal was formed to a thickness of 140 nm.
The mixing ratio of CuPc and lithium metal was 1: 1 in terms of molar ratio. After that, an Al / Li mixed film as a cathode 7 is formed to a thickness of 150 n.
A film having a thickness of m was formed to prepare an organic electroluminescence device. Cu
The Pc / Li mixed film and the Al / Li mixed film were produced by a co-evaporation method in which two kinds of materials are evaporated from independent evaporation sources. These film formations were continuously performed without breaking the vacuum even once. The film thickness was monitored by a crystal oscillator. Immediately after manufacturing the organic electroluminescent device, the electrode was taken out in dry nitrogen, and the characteristics were measured. When a voltage was applied to the obtained organic electroluminescence device, uniform green light emission was obtained. Emission spectrum is 5
There is a peak at 20 nm, and the spectral half width is 81 n.
m, chromaticity coordinates in the XYZ color system are x = 0.27y =
It was 0.58.

Example 2 As a substrate, an indium tin oxide film (ITO) was previously formed as a transparent anode on glass and patterned into an electrode shape. After thoroughly cleaning the glass substrate 1, the glass substrate 1 was set in a vacuum apparatus together with the material to be vapor-deposited, and vacuum exhausted to 10 ⁻⁴ Pa.
After that, TPT having a thickness of 50 nm was formed as the hole transport layer 3. Then, 25 nm of the compound (1) shown in Chemical formula 1 was formed as the light emitting layer 4, and 25 nm of Alq was formed as the electron transporting layer 5.

[Chemical 1] ... (Chemical formula 1)

After that, a co-evaporated film of quinacridone (Qd) and lithium metal was formed to a thickness of 125 nm as the emission color adjusting layer 6. The content of lithium metal in Qd was 1: 1 in molar ratio. After that, an Al / Li mixed film is formed as the cathode 7 by 150
A film having a thickness of nm was formed to produce an organic electroluminescence device. Q
The d / Li mixed film and the Al / Li mixed film were produced by a co-evaporation method in which two kinds of materials are evaporated from independent evaporation sources. These film formations never break the vacuum,
It went continuously. The film thickness was monitored by a crystal oscillator. Immediately after manufacturing the organic electroluminescent device, the electrode was taken out in dry nitrogen, and the characteristics were measured.
When a voltage was applied to the obtained organic electroluminescent element,
A uniform green emission was obtained. The emission spectrum is 470
There is a peak at nm, the spectral half width is 69 nm, X
The chromaticity coordinate in the YZ color system is x = 0.15y = 0.1
It was 6.

(Comparative Example 1) As Comparative Example 1, except that the emission color adjusting layer 6 is not provided and the Al / Li mixed layer of the cathode 7 is directly laminated on Alq which is the light emitting layer 4 and the electron transport layer 5. An organic electroluminescence device was produced in the same manner as in Example 1. When a voltage was applied to this organic electroluminescent device, uniform yellow-green light emission was obtained. The emission spectrum had a peak at 526 nm, the spectrum half width was 100 nm, and the chromaticity coordinate in the XYZ color system was x = 0.32y = 0.56.

Comparative Example 2 As Comparative Example 2, the same as Example 2 except that the emission color adjusting layer 6 was not provided and the Al / Li mixed layer of the cathode 7 was directly laminated on the electron transport layer 5 of Alq. Similarly, an organic electroluminescent device was produced. When a voltage was applied to this organic electroluminescent device, uniform yellow-green light emission was obtained. The emission spectrum has a peak at 477 nm,
The spectrum half width was 75 nm, and the chromaticity coordinate in the XYZ color system was x = 0.15y = 0.20.

From the results shown in Examples 1 and 2 and Comparative Examples 1 and 2, the organic electroluminescent elements obtained in this Example have a narrow half-width of emission spectrum and improved color purity. It became clear.

[0028]

As described above, according to the present invention, a pair of electrodes and at least one layer made of an organic material sandwiched between the electrodes are provided, and an emission color adjusting layer is inserted between the organic layer and the electrodes. Therefore, the effect that the color purity can be improved can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a structure of an electroluminescent device according to the present invention.

[Explanation of symbols]

1 glass substrate 2 anode 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Emission color adjustment layer 7 cathode

Claims (4)

[Claims] 1. An organic electroluminescence device having a pair of electrodes and at least one layer made of an organic material sandwiched between the electrodes, wherein an emission color adjusting layer is inserted between the organic layer and the electrodes. Organic electroluminescent device. 2. The organic electroluminescent element according to claim 1, wherein the emission color adjusting layer has an absorbance in a wavelength range other than a desired emission wavelength range. 3. The organic electroluminescent element according to claim 1, wherein the emission color adjusting layer is adjusted to have a film thickness that enhances a desired emission wavelength range. 4. The emission color adjusting layer comprises a mixed layer of a charge transport material and a metal.
The organic electroluminescent element as described in 1.