JPH06306357A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To provide the title element which can luminesce at high luminance and high luminous efficiency under a low applied voltage by forming an organic electroluminescent element prepared by laying a luminescent layer, a hole transport layer and an electron transport layer as thin films between a metallic cathode and a transparent anode, wherein a specified tetradiphenylaminopyrimidopyrimidine derivative as the luminescent layer. CONSTITUTION:A compound of the general formula wherein Rs are each H, halogen, alkyl or aryl is used as the luminescent layer of an organic electroluminescent element. Fig. shows an organic electroluminescent element, wherein an electron transport layer 5, a luminescent layer 3 and a hole transport layer 4 as thin films are laid between a metallic cathode 1 and a transparent anode 2 on a glass base 6. As the cathode an alkaline earth metal, an alkali metal or an alloy thereof is used. As the anode 2, an indium tin oxide or the like is used. As the luminescent layer 3, the above compound is used. As the hole transport layer 4, a tetraphenylene derivative or the like is used. As the electron transport layer 5, a quinone derivative having a high electron transport property or the like is used.

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 formed by layering such a substance by utilizing 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 phosphor thin film 3 made of an organic compound, that is, a light emitting layer and a positive electrode, are laminated between a metal cathode 1 and a transparent anode 2. A two-layer structure in which the hole transport layer 4 is arranged, or an electron transport layer 5 made of an organic compound laminated between the metal cathode 1 and the transparent anode 2 as shown in FIG.
A three-layer structure in which the light emitting layer 3 and the hole transport layer 4 are arranged is known. Here, the hole transport layer 4 has a function of facilitating injection of holes from the anode and a function of blocking electrons, and the electron transport layer 5 has a function of facilitating injection of electrons from the cathode.

In these organic EL devices, the transparent anode 2
A glass substrate 6 is disposed on the outer side of, and excitons are generated by recombination of electrons injected from the metal cathode 1 and holes injected from the transparent anode 2 to the light emitting layer 3, and the excitons emit Light is emitted in the process of deactivation, and this light is emitted to the outside through the transparent anode 2 and the glass substrate 6. Furthermore, FIG.
An organic EL device having a two-layer structure shown in (3), in which the light emitting layer 3 is formed from an organic host material having an electron transporting property and a fluorescent guest material and which emits stable light, has also been developed.

[0004]

However, in the conventional organic EL element of the organic compound having the above-mentioned structure, an organic EL element which emits blue light with higher brightness is desired. An object of the present invention is to provide an organic EL device that can emit light with high brightness.

[0005]

The organic EL device according to the present invention comprises:
An anode, a hole transport layer made of an organic compound, a light emitting layer made of an organic compound, and a cathode are laminated in this order, and the light emitting layer is a tetradiphenylaminopyrimidopyrimidine derivative represented by Chemical Formula 1.

[0006]

[Chemical 1]

[In the chemical formula 1, each R independently represents a hydrogen atom, a halogen atom, an alkyl group, or an aryl group].

[0008]

According to the present invention, it is possible to emit light with high luminance and high luminous efficiency at a low applied voltage.

[0009]

The present invention will be described below with reference to the drawings. The organic EL element of the present invention is similar to the organic EL element having the structure shown in FIGS. 1 and 2, and as shown in FIG. 1, a light emitting layer 3 and a light emitting layer 3 are provided between a pair of metal cathode 1 and transparent anode 2. The hole transport layer 4 is laminated and formed as a thin film, or, as shown in FIG. 2, an electron transport layer 5, a light emitting layer 3 and a hole transport layer between a pair of metal cathode 1 and transparent anode 2. A structure in which 4 is formed may be used. In either case, one of the electrodes 1 and 2 may be transparent. For example, for the cathode 1, aluminum,
Alkaline earth metals such as magnesium, indium, silver,
It is possible to use an alkali metal such as lithium or a metal having a small work function such as an alloy of each and having a thickness of about 100 to 5000 Å. 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 about 1000 to 3000Å, or gold with a thickness of about 800 to 1500Å. Can be used. When gold is used as the electrode material, the electrode becomes semitransparent.

The light-emitting layer 3 has a pyrimido [5,4-d] pyrimidine (Pyrimido [5,4]
-d] Pyrimidine) having a skeleton of tetradiphenylaminopyrimidopyrimidine derivative. Specific examples of the tetradiphenylaminopyrimidopyrimidine derivative include 2,4,6,8-tetradiphenylaminopyrimido [5,4-d] pyrimidine (2,4,6,8-Tetradipheny) represented by the chemical formula 2.
lamino pyrimido [5,4-d] pyrimidine).

[0011]

[Chemical 2]

By using only the above-mentioned tetradiphenylaminopyrimidopyrimidine derivative for the light emitting layer 3, an organic EL device having a two-layer or three-layer structure can be formed. The light emitting layer 3 may be formed by mixing tetradiphenylaminopyrimidopyrimidine derivative with a small amount of a fluorescent guest substance and an organic host substance having a high electron transporting property. Examples of the host material of the light emitting layer 3 include t-Bu-PBD described later.
{2- (4'-tert-Butylphenyl) -5- (biphenyl) -1,3,4-oxad
iazole} and tris (8-quinolinol) aluminum of the following chemical formula 3

[0013]

[Chemical 3]

It is preferable to use the quinoline derivative of. Other quinoline derivatives include, for example, bis (8-quinolinol) magnesium, bis (benzo {f} -8-
Quinolinol) zinc, bis (2-methyl-8-quinolinol) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8-). Quinolinol) gallium, bis (5-chloro-8-quinolinol) calcium, and poly [zinc (II) -bis (8-hydroxy-5-).
Quinolinyl) methane].

As described above, the above-mentioned tetradiphenylaminopyrimidopyrimidine derivative is used as the guest material of the light emitting layer. In this case, it is preferable that the atomic ratio of the electron-transporting organic host substance is higher than the atomic ratio of the tetradiphenylaminopyrimidopyrimidine derivative as the fluorescent guest substance. Here, it is preferable that the tetradiphenylaminopyrimidopyrimidine derivative as the guest substance is contained at a concentration or atomic ratio of 1% or less in the light emitting layer of the host substance, for example, t-Bu-PBD. This is because light emission with high brightness can be obtained with a low applied voltage.

Next, in the hole transport layer 4, for example, N, N'-diphenyl-N, N'-bis (3methylphenyl) -1,1'-biphenyl-4, represented by the following chemical formula 4,
Tetraphenyldiamine derivatives such as 4'-diamine (hereinafter referred to as TPD) are preferably used, and further, CTM (Carrier Transporting Materials) of the following chemical formulas 5 and 6 are used.
The compounds known as) can be used alone or as a mixture.

[0017]

[Chemical 4]

[0018]

[Chemical 5]

[0019]

[Chemical 6]

Further, in the above embodiment, the light emitting layer 3 and the organic hole transport layer 4 are arranged between the cathode 1 and the anode 2 to have a two-layer structure, but as shown in FIG. The same effect can be obtained even with a three-layer organic EL device having the electron transport layer 5. Further, the electron transport layer 5 includes 1,1,4,4-tetraphenyl represented by the following chemical formulas 7 and 8 in addition to the quinoline derivative of the above chemical formula 3 having a high electron transporting property.
-1,2-Butadiene (TPB) and t-Bu-PBD are preferably used.

[0021]

[Chemical 7]

[0022]

[Chemical 8]

Specifically, an EL device having a light emitting layer containing only a tetradiphenylaminopyrimidopyrimidine derivative was prepared. (Specific Example) First, a glass substrate with ITO, in which a plurality of ITO thin films were formed in a band shape (2 mm width) on a glass substrate, was prepared, ultrasonically cleaned, and dried. Using the 2,4,6,8-tetradiphenylaminopyrimido [5,4-d] pyrimidine represented by the chemical formula 2 by continuous vapor deposition in vacuum by a resistance heating method on the cleaned ITO substrate. , A hole transport layer, a light emitting layer, and an electron transport layer (three-layer structure) corresponding to device numbers 1 to 9 shown in Table 1 below, and a hole transport layer and a light emitting layer (2
The layer structure) was sequentially laminated to form an EL device. The cathode was prepared by co-evaporation so that the volume ratio of Mg and Ag was 10: 1.

The response characteristics (IV-L characteristics) of current and luminance with respect to voltage of the obtained EL element were measured, and the emission spectrum of the light emitted from the EL element cell was measured with a photometer. The emission characteristics of these EL devices were measured, and the results shown in Tables 2 and 3 were obtained.

[0025]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Device number Hole transport layer (Å) / Emitting layer (Å ) / Electron transport layer (Å) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1 TPD (500) / TPB (150) / TDPHPYPY (372) / MGAG (900) 2 TPD (500) / TDPHPYPY (265) / MGAG (883) 3 TDPHPYPY (372) / TPD (300) / ALQ (500) / MGAG (885) 4 TPD (300) / TDPHPYPY (186) / ALQ (200) / MGAG (1000) 5 TPD (300) / TDPHPYPY (186) / ALQ (500) / MGAG (950) 6 TDPHPYPY (124) / TPD (300) / ALQ (500) / MGAG (882) 7 TPD (500) / TDPHPYPY (188) / ALQ (500) / MGAG (882) 8 TPD (500) / TDPHPYPY (434) / MGAG (868) 9 TDPHPYPY (434) / t-Bu- PBD (500) / MGAG (900) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ TPD = Tetraphenyldiamine TPB = Tetraphenylbutadiene MGAG = MgAg alloy ALQ = Aluminium quinoline TDPHPYPY = 2,4,6,8-Tetradiphenylamino pyrimido [5,4-
d] pyrimidine () shows the thickness of each layer. The unit is Å.

[0026]

[Table 2]

[0027]

[Table 3] With the exception of the element numbers 1 and 6, all the electroluminescence spectra were obtained in which the peak around 550 nm, which is the fluorescence spectrum peak of the TDPHPYPY thin film, was obtained.
It was estimated that the recombination of electrons and holes occurred in TDPHPYPY.

Comparing the current-voltage characteristics of the element numbers 8 and 9, it was found that the element number 8 was more likely to flow a current than the element number 9. From the comparison of the current-luminance characteristics, it was found that the element number 9 was easier to emit light than the element number 8. This is considered to indicate that TDPHPYPY is hole transporting. Also, the current of each element −
Since the voltage characteristics are good, it is considered that this hole transport property is very high.

When a current of I = 242.9 (microampere / 4 mm ² ) was applied to the element number 7, the luminance L = 264 (n
It) and the voltage V was 7.29 (V). The current was kept flowing as it was, and when measured again about 63 hours later, it was L = 190 (nit).
As a two-layer organic electroluminescent device, TPD (500Å) / ALQ (500
Å) / MGAG (1000Å) type element with luminous efficiency at 300 (nit)
The highest value is 1.99 (1m / W). This time, a value of 2.38 (1 m / W), which is higher than that of element number 7, was obtained.

[0030]

INDUSTRIAL APPLICABILITY As described above, in the organic EL device in which the anode, the hole transport layer made of an organic compound, the light emitting layer made of an organic compound and the cathode according to the present invention are laminated in this order, the tetradiphenylaminopyrrole represented by the above chemical formula 1 is used. Since it has a light emitting layer containing a midopyrimidine derivative, it is possible to emit light with high brightness and high light emission efficiency at a low applied voltage.

[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.

[Explanation of symbols]

 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 (3)

[Claims] 1. A positive electrode, a hole transport layer comprising an organic compound,
A light emitting layer made of an organic compound and a cathode are laminated in this order, and the light emitting layer is a tetradiphenylaminopyrimidopyrimidine derivative represented by Chemical Formula 1. An organic electroluminescence device comprising: {in Chemical Formula 1, each R independently represents a hydrogen atom, a halogen atom, an alkyl group, or an aryl group}. 2. The light emitting layer contains an electron-transporting organic host material, and the atomic ratio of the electron-transporting organic host material is higher than the atomic ratio of the tetradiphenylaminopyrimidopyrimidine derivative. The organic electroluminescence device according to claim 1, which is characterized in that. 3. The organic electroluminescence device according to claim 1, further comprising an organic electron transport layer disposed between the cathode and the light emitting layer.