JPH06240243A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To provide an organic electroluminescent element which emits light at a high efficiency. CONSTITUTION:A coumarin compd. of formula I or II is used as an org. guest compd. in producing the element which comprises an anode, a hole transport layer consisting of an org. compd., a luminescent layer consisting of an org. host compd. and the org. guest compd., and a cathode laminated subsequently in this order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device provided with a light emitting layer in which such a substance is formed into a layer by utilizing the electroluminescence of a substance which emits light when an electric current is injected, and particularly the light emitting layer emits an organic compound. The present invention relates to an organic electroluminescence element configured as a body (hereinafter referred to as an organic EL element).

[0002]

2. Description of the Related Art As an organic EL device of this type, as shown in FIG. 1, a light emitting layer 3 composed of an organic host material and a fluorescent guest material and a hole transport layer are provided between a metal cathode 1 and a transparent anode 2. A two-layer structure in which the layer 4 is arranged (Japanese Patent Laid-Open No. 63-2
64692) and, as shown in FIG.
There is known a three-layer structure in which an electron transport layer 5, which is made of an organic compound, a light emitting layer 3 and a hole transport layer 4, which are laminated between a transparent anode 2 and a transparent anode 2, are arranged (Japanese Patent Laid-Open No. 2-2167).
No. 90).

Here, the hole transport layer 4 has the function of facilitating the injection of holes from the anode and the function of blocking the electrons, and the electron transport layer 5 has the function of facilitating the injection of electrons from the cathode. ing. In these organic EL devices, a glass substrate 6 is arranged outside the transparent anode 2 and excited by recombination of electrons injected from the metal cathode 1 and holes injected from the transparent anode 2 into the light emitting layer 3. The excitons emit light in the process of radiative deactivation, and this light emits light.
And is emitted to the outside through the glass substrate 6.

[0004]

[Problems to be Solved by the Invention] However, organic E
In the L element, practically, there is not yet a combination of organic functional materials that form a light emitting layer sufficient to emit light with good light emitting efficiency, and an element having higher light emitting efficiency is desired. Therefore, an object of the present invention is to provide an organic EL device that emits light with high luminous efficiency.

[0005]

The organic EL device of the present invention is an organic electroluminescent device in which an anode, a hole transport layer made of an organic compound, a light emitting layer made of an organic host compound and an organic guest compound, and a cathode are sequentially laminated. In the luminescence device, the organic guest compound is a coumarin compound represented by the following chemical formula 1 or chemical formula 2.

[0006]

[Chemical 1]

[0007]

[Chemical 2]

It is characterized in that

[0009]

According to the present invention, an organic EL device having high luminous efficiency which emits light with high brightness at a low applied voltage is obtained.

[0010]

The present invention will be described below with reference to the drawings. The organic EL device of the present invention, as shown in FIG.
It has a structure in which a hole transport layer 4 made of an organic compound, a light emitting layer 3 made of an organic host substance and a fluorescent organic guest substance, and a metal cathode 1 are sequentially stacked. Also, FIG.
As shown in FIG. 3, an organic EL having a three-layer structure in which an electron transport layer 5 made of an organic compound is laminated between the light emitting layer 3 and the metal cathode 1.
It may be an element. In either case, one of the electrodes 1 and 2 may be transparent. For example, the cathode 1 may be made of a metal having a small work function, such as aluminum, magnesium, indium, silver, or an alloy of each, and having a thickness of about 100 to 5000 angstroms. Further, for example, the anode 2 is made of a conductive material having a large work function such as indium tin oxide (hereinafter referred to as ITO) and has a thickness of 10
About 00 to 3000 angstroms or 800 with gold
A material having a size of about 1500 Å can be used. In addition,
When gold is used as the electrode material, the electrode becomes semitransparent.

The light emitting layer 3 has an organic host material capable of transporting holes and electrons, that is, having a bipolar transport ability, but lower than the electron transport layer and the hole transport layer, and a hole. And an organic guest material capable of emitting light in response to recombination of electrons or in response to excitation energy from an organic host material. As the host substance, CV (cyclic voltammetry) having a large absolute value of potential on both the oxidation side and the reduction side is used. Therefore, as the guest substance of the light emitting layer 3, those having an absolute potential value smaller than that of the host substance on both the oxidation side and the reduction side in CV are preferably used. The larger the overlapping portion between the excitation wavelength spectrum distribution of the guest substance and the fluorescence wavelength spectrum distribution of the host substance, the more efficiently the light emission occurs. Here, the guest substance is selected from fluorescent dyes having a high fluorescence quantum yield, and is 0.01% in the light emitting layer of the host substance.
wt. % To 10 wt. It is preferably contained at a concentration of%. This is because light emission with high brightness can be obtained with a low applied voltage.

Specifically, the organic guest substance is a coumarin compound represented by the chemical formula 1.

[0013]

[Chemical 1]

Coumarin compound represented by Chemical Formula 2 (hereinafter referred to as C525)

[0015]

[Chemical 2]

(Hereinafter referred to as C545) is used.
The compound represented by Chemical Formula 3 is used as the organic host substance.

[0017]

[Chemical 3]

(In the above formula, M is Al, Zn, Ga, I
n, La, Zr, Y, Cd, Lu, Sc, Be or Mg
R _{1 to} R ₃ each independently represent an alkyl group (having 1 to 6 carbon atoms), a haloalkyl group, a carboxy group, an alkaloyl group, an alkoxycarbonyl group, a cyano group or a halogen atom, and n 1 Represents an integer of 2 to 3) and is specifically a tris (8-quinolinol) aluminum compound represented by Chemical Formula 4, for example.

[0019]

[Chemical 4]

(Hereinafter referred to as Alq ₃ ) is used.
Next, in the hole transport layer 4, for example, N, N'-diphenyl-N, N'-bis (3methylphenyl) -1,1'-biphenyl-4,4'-diamine represented by the following chemical formula 5 is shown. (Hereinafter referred to as TPD) is preferably used.

[0021]

[Chemical 5]

As the organic electron transport layer 5, for example, the above A
lq ₃ can be used. Further, as the electron transport layer 5, a Bu-PBD [2- (4'-tert-But] represented by the following chemical formula 6 is used.
[ylphenyl) -5- (biphenyl) -1,3,4-oxadiazole] is preferably used, and compounds represented by the following chemical formulas 7 to 12 can also be used.

[0023]

[Chemical 6]

[0024]

[Chemical 7]

[0025]

[Chemical 8]

[0026]

[Chemical 9]

[0027]

[Chemical 10]

[0028]

[Chemical 11]

[0029]

[Chemical 12]

Example 1 On a glass substrate on which an anode made of ITO having a film thickness of 2000 angstrom was formed,
Each thin film was vacuum-deposited to a vacuum degree of 1.0 × 10 ⁻⁵ Torr.
It was laminated below. First, the above TPD was formed as a hole transport layer on ITO at a deposition rate of 3.5 angstrom / sec. To a thickness of 500 angstrom. Next, the Alq _{3 as a} host material and the C525 as a guest material were formed on a TPD as a light emitting layer from different evaporation sources in a volume ratio Alq 3.
₃ : C525 = 100: 2 and co-deposited to a thickness of 500 Å. Next, the atomic ratio Mg: Ag = of magnesium and silver as cathodes on the light emitting layer from different vapor deposition sources.
Co-deposited 10: 1 to a thickness of 1500 Å.

The EL device having a two-layer structure as shown in FIG. 3 thus produced has a luminance of 94 at a current density of 7.5 mA / cm ^2.
The emission peak wavelength was ² cd / m ² , and the emission peak wavelength was 515 nm. Also,
The quantum yield was 4.1%. (Comparative Example 1) An EL device was manufactured in the same manner as in Example 1 except that a light emitting layer having a thickness of 500 angstroms, which was made of only Alq _{3 as} a host material, was formed without including the C525 as a guest material in the light emitting layer. It was created.

[0032] The EL element, the luminance 306cd / m ² o'clock current density 7.5 mA / cm ^2, showed a peak emission wavelength 530 nm. The quantum yield was 1.3%. (Example 2) In place of the above-mentioned guest material C525, a light-emitting layer containing the above-mentioned C545 guest material was formed.
An EL device was prepared in the same manner as in Example 1.

[0033] The EL element has brightness 750 cd / m ² o'clock current density 7.5 mA / cm ^2, showed a peak emission wavelength 530 nm. The quantum yield was 3.2%. (Comparative Example 2) An EL was prepared in the same manner as in Example 1 except that a light emitting layer containing a coumarin compound represented by the following chemical formula 13 as a guest substance was formed in place of the above C525 of the guest substance.
A device was created.

[0034]

[Chemical 13]

[0035] The EL element, the luminance of at a current density of 7.5 mA / cm ² is 452cd / m ^2, showing a light emitting peak wavelength of 520 nm. The quantum yield was 1.83%. (Comparative Example 3) An EL device was prepared in the same manner as in Example 1 except that a light emitting layer containing a coumarin compound represented by the following chemical formula 14 as a guest substance was formed in place of the above C525 of the guest substance.
A device was created.

[0036]

[Chemical 14]

[0037] The EL element, the luminance of at a current density of 7.5 mA / cm ² is 568cd / m ^2, showing a light emitting peak wavelength of 520 nm. The quantum yield was 2.3%.

[0038]

As described above, according to the present invention, the anode,
In an organic EL device in which a hole transport layer made of an organic compound, a light emitting layer made of an organic compound, an electron transport layer made of an organic compound, and a cathode are laminated in this order, the light emitting layer is an organic host compound, and holes and electrons are regenerated. The guest compound represented by the above Chemical Formula 1 or Chemical Formula 2, which has the ability to emit light in response to a bond, emits high brightness at a low applied voltage,
Luminous efficiency is improved.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an organic EL device having a two-layer structure.

FIG. 2 is a structural diagram showing an organic EL device having a three-layer structure.

FIG. 3 is a structural diagram showing a guest-host type organic EL device having a two-layer structure according to an example of the present invention.

FIG. 4 is a structural diagram showing a guest-host type organic EL device having a three-layer structure according to an example of the present invention.

[Explanation of symbols for main parts]

 1 Metal Electrode (Cathode) 2 Transparent Electrode (Anode) 3 Light Emitting Layer 4 Organic Hole Transport Layer 5 Electron Transport Layer 6 Glass Substrate

Claims (2)

[Claims] 1. A positive electrode, a hole transport layer comprising an organic compound,
What is claimed is: 1. An organic electroluminescent device comprising a light emitting layer comprising an organic host compound and an organic guest compound, and a cathode, which are sequentially laminated, wherein the organic guest compound is a coumarin compound represented by the following chemical formula 1 or chemical formula 2. [Chemical 2] An organic electroluminescence device comprising: 2. The organic host compound is a compound represented by the following chemical formula 3. embedded image (In the above formula, M is Al, Zn, Ga, In, La, Z
represents a metal atom of r, Y, Cd, Lu, Sc, Be, or Mg, and R _{1 to} R ₃ are each independently an alkyl group (having a carbon number of 1 to 1).
6), a haloalkyl group, a carboxy group, an alkaloyl group, an alkoxycarbonyl group, a cyano group or a halogen atom, and n is an integer of 2 to 3). Luminescence element.