JP3241484B2 - Organic electroluminescence device - Google Patents

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 having a light-emitting layer in which a substance that emits light by current injection is formed by utilizing the electroluminescence of the substance, and in particular, the light-emitting layer emits an organic compound. The present invention relates to an organic electroluminescent element (hereinafter, referred to as an organic EL element) configured as a body.

[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, which is made of an organic compound, is laminated between a metal cathode 1 and a transparent anode 2, that is, a light emitting layer and a positive electrode. A two-layer structure in which a hole transport layer 4 is disposed, or an electron transport layer 5 made of an organic compound laminated between a metal cathode 1 and a transparent anode 2 as shown in FIG.
A three-layer structure in which a light emitting layer 3 and a 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, a transparent anode 2
A glass substrate 6 is disposed outside the substrate, and excitons are generated by recombination of electrons injected from the metal cathode 1 and holes injected from the transparent anode 2 into the light emitting layer 3, and the excitons are radiated. Light is emitted in the process of deactivation, and this light is emitted outside through the transparent anode 2 and the glass substrate 6. Further, FIG.
An organic EL device having a two-layer structure shown in FIG. 1 and in which the light emitting layer 3 is formed from an organic host material having an electron transporting property and a fluorescent guest material to emit light stably has been developed.

[0004]

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

[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 sequentially laminated, and the light emitting layer is a tetradiphenylaminopyrimidopyrimidine derivative represented by Chemical Formula 1.

[0006]

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[0007] 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, light can be emitted with high luminance and high luminous efficiency at a low applied voltage.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. The organic EL device of the present invention is the same as the organic EL device having the structure shown in FIGS. 1 and 2, and as shown in FIG. 1, a light emitting layer 3 and a transparent anode 2 are provided between a pair of metal cathodes 1 and a transparent anode 2. The electron transport layer 5, the light emitting layer 3, and the hole transport layer between the metal cathode 1 and the transparent anode 2, as shown in FIG. 4 may be used. In any case, one of the electrodes 1 and 2 only needs to be transparent. For example, the cathode 1 has aluminum,
Alkaline earth metals such as magnesium, indium, silver,
An alkali metal such as lithium or a metal having a small work function such as an alloy thereof and having a thickness of about 100 to 5000 ° can be used. 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 3000 mm, or gold and has a thickness of about 800 to 1500 mm. Can be used. When gold is used as an electrode material, the electrode is in a translucent state.

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

[0011]

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An organic EL device having a two-layer or three-layer structure can be formed by using only the above-mentioned tetradiphenylaminopyrimidopyrimidine derivative in the light-emitting layer 3. Further, the light emitting layer 3 may be formed by mixing tetradiphenylaminopyrimidopyrimidine derivative with a small amount of fluorescent guest substance and an organic host substance having high electron transporting property. As a host material of the light emitting layer 3, t-Bu-PBD described later is used.
｛2- (4´-tert-Butylphenyl) -5- (biphenyl) -1,3,4-oxad
iazole｝ or tris (8-quinolinol) aluminum of the following chemical formula 3

[0013]

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It is preferable to use the quinoline derivative of the present invention. 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-quinolinollithium, 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 substance of the light emitting layer. In this case, it is preferable that the atomic ratio of the organic host substance having an electron transporting property is larger than the atomic ratio of the tetradiphenylaminopyrimidopyrimidine derivative as the fluorescent guest substance. Here, it is preferable that the tetradiphenylaminopyrimidopyrimidine derivative of the guest substance is contained at a concentration or an 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 luminance can be obtained with a low applied voltage.

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

[0017]

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[0018]

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[0019]

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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 in a two-layer structure. However, as shown in FIG. The same effect can be obtained with an organic EL element having a three-layer structure in which the electron transport layer 5 is provided. Further, as the electron transporting layer 5, in addition to the quinoline derivative of the above chemical formula 3 having a high electron transporting property, 1,1,4,4-tetraphenyl represented by the following chemical formulas 7 and 8 can be used.
-1,2-Butadiene (TPB) and t-Bu-PBD are preferably used.

[0021]

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[0022]

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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, and this was ultrasonically cleaned and dried. Using 2,4,6,8-tetradiphenylaminopyrimido [5,4-d] pyrimidine represented by Chemical Formula 2 by continuous evaporation in vacuum by resistance heating on an ITO substrate having been subjected to predetermined washing. The hole transport layer, the light emitting layer, and the electron transport layer (three-layer structure) and the hole transport layer and the light emitting layer (2) corresponding to the device numbers 1 to 9 shown in Table 1 below.
To form an EL element. The cathode was prepared by co-evaporation of Mg and Ag at a volume ratio of 10: 1.

The response characteristics (IVL characteristics) of current and luminance to voltage were measured for the obtained EL device, and the emission spectrum of the emitted light from the EL device 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) / light-emitting layer (Å ) / Electron transport layer (Å) １ 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 () indicates the thickness of each layer. The unit is Å.

[0026]

[Table 2]

[0027]

[Table 3] Except for device numbers 1 and 6, electroluminescence spectra were obtained such that the peak was around 550 nm, which is the fluorescence spectrum peak of the TDPHPYPY thin film.
In TDPHPYPY, it was estimated that the recombination of electrons and holes occurred.

Comparing the current-voltage characteristics of the element numbers 8 and 9, it was found that the element number 8 was easier for the current to flow than the element number 9. In addition, from the comparison of the current-luminance characteristics, the result that the element number 9 emits light more easily than the element number 8 was obtained. This is considered to indicate that TDPHPYPY is hole transportable. Also, the current of each element-
It is considered that the hole transportability is very high because of the good voltage characteristics.

When a current of I = 242.9 (microampere / 4 mm ² ) was applied to element number 7, the luminance L = 264 (n
it), and the voltage V was 7.29 (V). When the current was continued to flow and the measurement was performed again after about 63 hours, L = 190 (nit).
TPD (500 型) / ALQ (500
発 光) / MGAG (1000)) type device has higher luminous efficiency at 300 (nit).
The value of 1.99 (1m / W) is the highest. This time, a value of 2.38 (1 m / W), which is a higher value, was obtained for element number 7.

[0030]

As described above, in the organic EL device in which the anode according to the present invention, the hole transport layer made of an organic compound, the light emitting layer made of an organic compound, and the cathode are sequentially laminated, the tetradiphenylaminopyridyl compound of the above formula (1) is used. Since the light-emitting layer contains a midpyrimidine derivative, light can be emitted with high luminance and high luminous efficiency at a low applied voltage.

[Brief description of the 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]

 Reference Signs List 1 metal electrode (cathode) 2 transparent electrode (anode) 3 light emitting layer 4 organic hole transport layer 5 electron transport layer 6 glass substrate

Continuation of front page (56) References JP-A-4-226918 (JP, A) JP-A-63-23813 (JP, A) JP-A-61-43117 (JP, A) JP-A-58-170715 (JP, A) JP-A-58-67620 (JP, A) JP-A-52-59192 (JP, A) JP-A-48-97509 (JP, A) JP-A-4-110390 (JP, A) 3-37292 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/14 C09K 11/06 REGISTRY (STN) CA (STN)

Claims (3)

(57) [Claims] 1. An anode, a hole transport layer comprising an organic compound,
A light emitting layer made of an organic compound and a cathode are sequentially laminated, and the light emitting layer is a tetradiphenylaminopyrimidopyrimidine derivative represented by Chemical Formula 1. An organic electroluminescent device comprising: {wherein R in Formula 1 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 substance, and the atomic ratio of the electron-transporting organic host substance is larger than the atomic ratio of the tetradiphenylaminopyrimidopyrimidine derivative. The organic electroluminescence device according to claim 1, wherein: 3. The organic electroluminescence device according to claim 1, wherein an organic electron transport layer is provided between the cathode and the light emitting layer.