JPH11260554A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EL element having practical, high luminescence and sufficient durability by doping a substance formed from a terthiophene derivative in a luminescent layer that is formed from an organic compound and located between a pair of electrodes. SOLUTION: In this organic EL element, a luminescent layer formed from an organic compound is formed between a pair of electrodes at least one of which is transparent. A substance formed from a terthiophene derivative expressed by formula I into the luminescent layer. In the formula I, each group represented by R1 and R2 is a group arbitrarily selected from a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group and groups represented by formula II through formula XI. The doping ratio in the range of 0.5-5 mol.% is preferable and the ratio of 1 mol.% is most suitable. If the terthiophene derivative is used for the organic luminescent layer, the luminescence of the EL element is improved and continuous light emission that is stable for more than 1000 hours can be provided. In addition, luminous colors can be varied by changing substitutional groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device having an organic light emitting layer (hereinafter referred to as an organic EL device).
Element). In particular, the present invention relates to an organic EL device that achieves practically high luminance and sufficient durability.

[0002]

2. Description of the Related Art An organic EL device has a structure in which a thin film containing a fluorescent organic compound is sandwiched between an electron injecting electrode and a hole injecting electrode, and electrons and holes are injected into the thin film and recombined. This is a display element that generates excitons (excitons) and emits light (fluorescence / phosphorescence) when the excitons are deactivated. As described above, at least a light emitting layer which is a thin film containing a fluorescent organic compound is provided between the electron injecting electrode and the hole injecting electrode. Each layer such as a layer, an electron transport layer, and an electron injection layer is formed as necessary.

One of the basic structures of the organic EL device is shown in FIG.
It was shown to. This organic EL element is made of a glass substrate 100.
ITO (Indium Tin Oxide) on the hole injection electrode 101 above,
A triphenylamine derivative (Dia
mine), tris (8-quinolilite) aluminum (III) (Alq ₃ ) as the organic light emitting layer 103, the electron injection electrode 104
As an alloy of magnesium and silver. The thickness of each organic layer is about 50 nm. Each layer is formed by vacuum evaporation. In this organic EL element, green light emission of about 1000 cd / m ² can be obtained by applying a DC voltage of 10 V with the electron injection electrode being negative and the hole injection electrode being positive.

[0004]

SUMMARY OF THE INVENTION The above-mentioned conventional organic E
According to the L element, sufficient luminance was not obtained. Also,
This organic EL element has a short luminance half-life and has a problem in durability.

An object of the present invention is to provide an organic EL device having practically high luminance and sufficient durability.

[0006]

The organic electroluminescence device according to the present invention has a basic structure in which at least one of the transparent electrodes is provided with at least a light-emitting layer made of an organic compound between a pair of transparent electrodes. ing. The present invention is characterized in that the light emitting layer is doped with a substance represented by the chemical formula (Formula 1). Note that (Chemical Formula 1) is a general formula of a terthiophene derivative, and in this formula, the groups represented by R1 and R2 are a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, and the chemical formula (Chemical Formula 2). And arbitrarily selected from the group consisting of the groups represented by the chemical formula (Chem. 11).

[0007]

Embodiment 1) Embodiment 1 The structure and manufacturing method of the organic EL of this embodiment will be described with reference to FIG. An ITO film 2 which is a transparent conductive film is formed on an anode substrate 1. On the cleaned substrate with ITO, m-MTDATA having a starburst molecular structure represented by the chemical formula (Formula 12) is formed as the hole injection layer 3.

[0008]

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On the hole injection layer 3, a thin film of α-NPD is formed as a hole transport layer 4 by vacuum evaporation. α-N
PD is represented by the chemical formula (Formula 13).

[0010]

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A light emitting layer 5 is formed on the hole transport layer 4. Using tris (8-quinolilite) aluminum (III) (Alq ₃ ) represented by the chemical formula (Formula 14) as a base,
It was formed by co-evaporation at a rate of 1 mol% using a substance represented by the chemical formula (Formula 15), which is an example of the terthiophene derivative represented by the chemical formula (Formula 1), as a dopant.

[0012]

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[0013]

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In the terthiophene derivative represented by the chemical formula (1), R ₁ is a hydrogen atom, R
_This is the case where ₂ is a formyl group.

Although the ratio of the dopant was 1 mol%, according to experiments, the ratio of the dope was 0.5 to 5 mol%.
% Is preferable, and the 1 mol% is an example of an optimum value within the range. Below this range, Alq ₃
The light itself glows and the color turns green. If it is larger than this range, the color is orange, but the brightness is reduced, which is below the practical limit.

[0016] The co-evaporation is a technique in which two evaporation materials are provided in one evaporation apparatus and are evaporated simultaneously on a common object. In this example, a base material and a dopant were co-evaporated to form an organic light emitting layer.

Further, an alloy of Al and Li was deposited as a cathode 6 on the light emitting layer 5. On the cathode 6 of this element, a glass case 7 coated with an ultraviolet curable resin on the edge in a dry air atmosphere was fixed to the anode substrate 1, cured with ultraviolet light, and the envelope was sealed.

The dry air is air having a low water content such as a dew point of, for example, -60 ° C. Since the organic EL generates heat at the time of driving, it is preferable that the inside of the element is not a vacuum but contains air for transmitting the released heat to the outside. However, since the organic EL is very weak against moisture, it is preferable that the air sealed in the element is particularly low in moisture.

Each of the layers constituting the organic EL device is 1 ×
It was formed by vapor deposition under a vacuum of 10 ^-6 Torr. The film thickness is as follows. Cathode 6: 200 nm, Emission layer 5: 50 nm Hole transport layer 4: 10 nm Hole injection layer 3: 40 nm

As shown in FIG. 1, an ITO film 2 serving as an anode
And the cathode 6 are led out of the envelope of the device, and a DC voltage is applied between the two electrodes. This organic EL element emitted light of 7,000 cd / m ² at a DC voltage of 16 V. (A) in FIG.
As shown by, the emission peak wavelength was 511 nm.
When the organic EL device was continuously illuminated by driving at a constant current of 10 mA / cm ² , stable luminescence was observed for 1000 hours or more.

2) Example 2 A device was produced in the same manner as in Example 1 except that the compound represented by the chemical formula (Formula 16) was used as a dopant.

[0022]

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The chemical formula (Formula 16) is a case where, in the terthiophene derivative represented by the chemical formula (Formula 1), R ₁ is a hydrogen atom (not shown) and R ₂ is a group represented by the chemical formula (Formula 12).

This organic EL device has a DC voltage of
Light emission of 00 cd / m ² was obtained. As shown by (b) in FIG. 2, the emission peak wavelength was 536 nm. When the device was continuously driven at a constant current of 10 mA / cm ² , stable light emission was observed for 1000 hours or more.

4) Other Examples In the present invention, in an organic EL device, an organic light emitting layer is doped with a specific substance. The substance is a terthiophene derivative represented by the chemical formula (Formula 1). In this formula, the groups represented by R1 and R2 are a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, It is a group arbitrarily selected from the groups represented by the chemical formula (Formula 2) to the chemical formula (Formula 11). Accordingly, there are many types of substances applicable to the present invention, which are summarized in Tables 1 to 7 below.
It was shown to.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

[Table 5]

[0031]

[Table 6]

[0032]

[Table 7]

In each of the above tables, 64 types of compounds indicated by numbers 1 to 64 shown in the “compound” column on the left are shown. The substance of Example 1 corresponds to the substance of No. 1 (Table 1), the substance of Example 2 corresponds to the substance of No. 11 (Table 2), and the substance of Example 3 corresponds to the substance of No. 16 (Table 2).
No. (Table 2).

Even with the substances other than the examples 1 to 3 shown in the table, performances similar to those of the examples 1 to 3 and superior to the related art can be obtained.

[0035]

According to the present invention, since a terthiophene derivative is used as a dopant in an organic light emitting layer, the luminance is improved as compared with a conventional organic EL device. In addition, stable continuous light emission for 1000 hours or more could be obtained. As a result, practical use of the organic EL element as a display can be expected. Further, the emission color can be changed by changing the substituent.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of an embodiment of the present invention.

FIG. 2 is an emission spectrum of the organic EL device according to the first and second embodiments of the present invention.

FIG. 3 is a cross-sectional view schematically showing a structure of a conventional organic EL element.

[Explanation of symbols]

 2 ITO film as anode 6 Cathode 5 Light emitting layer

Claims (1)

[Claims] 1. An organic electroluminescence device in which at least one light emitting layer made of an organic compound is provided between a pair of electrodes, at least one of which is transparent, wherein the substance represented by the following chemical formula (Chem. 1) is used for the light emission. An organic electroluminescent device characterized in that the layer is doped. Embedded image However, in the chemical formula (Chemical formula 1), the groups represented by R1 to R4 are a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, and a group represented by the following chemical formula (Chemical formula 2). Is a group arbitrarily selected from Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image