JP2003272869A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element that has a high luminous efficiency and small degradation of luminance during the drive life. <P>SOLUTION: This is an organic electroluminescent element that has organic layers between a pair of electrodes. As a buffer layer 5 that is provided in contact with the negative electrode 6 in the pair of electrodes, a layer is used in which at least an aromatic amine compound and a metal having a work function of 4.0 eV or less are mixed. For the negative electrode 6, a metal which is not contained in the buffer layer 5 is used. Thereby, an organic electroluminescent element having a high luminous efficiency and small degradation of luminance during the drive life can be provided. <P>COPYRIGHT: (C)2003,JPO

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 which is widely used as various display devices, and more particularly to an organic electroluminescent device which is excellent in low driving voltage, high brightness and stability.

[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. Currently, as an electroluminescent element that has reached a practical level and is commercialized,
There is an element using ZnS which is an inorganic material. However, such an inorganic electroluminescent device has a driving voltage of 2
Since it requires about 00V, it has not been widely used.

On the other hand, an organic electroluminescence device, which is an electroluminescence device using an organic material, has hitherto been far from a practical level, but in 1987, a C.D. W. The laminated structure element developed by Tang et al. Has dramatically improved its characteristics (Non-Patent Document 1).
reference. ). They deposited a phosphor that has a stable vapor-deposited film structure that can transport electrons and an organic material that can transport holes, and inject both carriers into the phosphor to emit light. succeeded in.

As a result, the luminous efficiency of the organic electroluminescent device is improved, and it is possible to obtain light emission of 1000 cd / m ² or more at a voltage of 10 V or less. Such an organic electroluminescent device has very excellent basic light emitting characteristics, and one of the biggest problems currently hindering its practical use is lack of stability. Specifically, the emission brightness decreases, a non-emission area called a dark spot occurs,
The short circuit of the element causes destruction. One of the causes of such characteristic deterioration is the problem of the interface between the cathode and the organic layer, and in order to solve the problem, improvement of the organic layer in contact with the cathode has been studied.

Specifically, an interface layer made of an aromatic amine compound is provided between the organic light emitting layer and the cathode (see Patent Document 1), or an electron injection layer containing an alkali metal compound is provided (see Patent Document 2). , Etc. are disclosed, but these are still insufficient.

[0006]

[Non-Patent Document 1] Appl. Phys. Lett. , 5
Volume 1, Page 913, 1987

[Patent Document 1] JP-A-6-267658

[Patent Document 2] Japanese Patent Laid-Open No. 9-17574

[0007]

In the above-mentioned conventional techniques, there is a major problem that the stability is insufficient due to a decrease in light emission luminance or the occurrence of a dark spot region called no light emission. is there.

It is an object of the present invention to provide an organic electroluminescent device which has a high luminous efficiency and a small decrease in luminance during the driving life.

[0009]

In order to solve this problem, the present invention is an organic electroluminescent device having an organic layer between a pair of electrodes, which is provided in contact with the cathode of the pair of electrodes. The buffer layer is a mixture of at least an aromatic amine compound and a metal having a work function of 4.0 eV or less, and a metal not contained in the buffer layer is used for the cathode. It is an electroluminescent device.

According to such a structure, an organic electroluminescence device having a high luminous efficiency and a small decrease in luminance during the driving life is provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The first invention of the present invention is an organic electroluminescent device having an organic layer between a pair of electrodes, wherein the buffer layer is provided in contact with the cathode of the pair of electrodes. , At least the work function of the porphyrin compound and 4.
An organic electroluminescent device characterized by using a mixture of a metal of 0 eV or less and using a metal not contained in the buffer layer for the cathode. A porphyrin compound is usually considered as a hole transport material. However, the use of the above structure improves the injection of electrons from the cathode, and thus has the effect of increasing the luminous efficiency and prolonging the driving life.

A second invention is a porphyrin compound represented by the general formula (1).

[0013]

[Chemical 1]

(Wherein R1 to R8 represent the same or different hydrogen atom, halogen or a monovalent organic residue, R1 and R2, R3 and R4, R5 and R6, R7 and R8.
May together form a ring, and A1 is -N = or-.
CR9 =, R9 is a hydrogen atom, a halogen or a monovalent organic residue, and M1 is a hydrogen atom, a metal atom, a metal oxide, a metal halide or a metal having a monovalent organic residue. ) Thereby, as the monovalent organic residue of R1 to R9, an alkyl group which may or may not be branched, a substituted or unsubstituted aryl group, an unsaturated hydrocarbon group such as a vinyl group or an allyl group, a carboxyl group Group, carboxyalkyl group, hydroxyl group, alkoxyl group, acyl group, alkyloxy group, aryloxy group, alkylthio group, arylthio group, nitro group, amino group, aminoalkyl group, cyano group, cyanoalkyl group, substituted or unsubstituted And a heterocyclic ring having 3 or more members can be used. Also, R1 and R
2, R3 and R4, R5 and R6, and R7 and R8 may jointly form a ring, and particularly when a benzene ring or a naphthalene ring of an aromatic ring is formed, a benzoporphyrin compound, a phthalocyanine compound, a naphthalene compound, It becomes a group of compounds called phthalocyanine compounds. Such a compound has a function of obtaining a compound with improved stability.

M1 is 2 hydrogen atoms, 1 or 2 metal atoms, metal oxide, metal halide or 1
It is a metal having a valent organic residue, and L is a metal atom.
i, Na, K, Rb, Cs, Be, Sr, Ba, Ca,
Mg, Fe, Co, Ni, Cu, Zn, Mn, Cr, A
l, Ga, Sn, Si, Ge, Sc, Ti, Pb, V,
Pt, Pd, Cd, etc. can be used. Further, as the monovalent organic residue, an alkyl group which may or may not be branched, a substituted or unsubstituted aryl group, an unsaturated hydrocarbon group such as a vinyl group or an allyl group, a carboxyl group, a carboxyalkyl group, Hydroxyl group, alkoxyl group, acyl group, alkyloxy group, aryloxy group, alkylthio group,
An arylthio group, a nitro group, an amino group, an aminoalkyl group, a cyano group, a cyanoalkyl group, a substituted or unsubstituted heterocyclic ring having three or more members, or the like can be used.

Specifically, porphine, ethioporphine, mesoporphine, protoporphine, protoporphine zinc, 2,3,7,8,12,13,17,18-
Octaethylporphine, 2,3,7,8,12,1
3,17,18-octaethylporphine copper, 2,3
7,8,12,13,17,18-octaethylporphine magnesium, 5,10,15,20-tetraphenylporphine, 5,10,15,20-tetraphenylporphine copper, 5,10,15,20- Tetrapyridylporphine, tetrabenzoporphine, 5,10,1
5,20-tetraazaporphyrin, 2,3,7,8,
12,13,17,18-octaethyl-5,10,1
5,20-Tetraazaporphyrin, 2,7,12,1
7-tetra-t-butyl-5,10,15,20-tetraazaporphyrin, 5,10,15,20-tetraphenyl-5,10,15,20-tetraazaporphyrin,
5,10,15,20-tetraphenyl-5,10,1
5,20-Tetraazaporphyrin copper, metal-free phthalocyanine, copper phthalocyanine, lead phthalocyanine, zinc phthalocyanine, magnesium phthalocyanine, cobalt phthalocyanine, tin phthalocyanine, tin phthalocyanine chloride, aluminum phthalocyanine, titanyl phthalocyanine, naphthalocyanine, copper naphthalocyanine copper, Cobalt naphthalocyanine, copper-4,4 ', 4'',
4 ′ ″ tetraazaphthalocyanine and the like can be mentioned.

A third invention of the present invention is an organic electroluminescent device having an organic layer between a pair of electrodes, wherein at least an aromatic compound is used as a buffer layer provided in contact with the cathode of the pair of electrodes. An organic electroluminescent device characterized by using a mixture of an amine compound and a metal having a work function of 4.0 eV or less, and using a metal not contained in the buffer layer for the cathode. Amine compounds are usually considered as hole transport materials, but when used in the above configuration, electron injection from the cathode easily occurs and the luminous efficiency increases significantly, which reduces the decrease in luminance during driving. It has an effect that it becomes possible to do.

The above-mentioned aromatic amine compounds may be those usually used in organic electroluminescent devices, and aromatic tertiary amine compounds, starburst amines, aromatic amine oligomers and the like are preferable. In particular, JP-A-7-12661
No. 5, JP-A-7-331238, and JP-A-8-
The aromatic amine compound disclosed in Japanese Patent No. 100172 has improved heat resistance and is optimal. In addition, as a metal having a work function of 4.0 eV or less, an alkali metal,
Examples include alkaline earth metals, rare earth metals, scandium, yttrium, and the like.

According to a fourth aspect of the present invention, the work function is 4.0.
The metal having eV or less may be an alkali metal or an alkaline earth metal, and Li, Mg, Ca, Sr and the like are particularly preferable. As a method for forming the buffer layer, a method of vapor-depositing the porphyrin compound or the aromatic amine compound and a metal having a work function of 4.0 eV or less from different vapor deposition sources by a vacuum vapor deposition method is preferable, but other thin films are preferable. A forming method may be used. The thickness of the buffer layer may be 0.5 nm or more, and the characteristic change is small even if the thickness is increased.

A fifth aspect of the present invention is an organic electroluminescent device having an organic layer between a pair of electrodes, wherein the buffer layer provided in contact with the cathode of the pair of electrodes has the general formula ( An organic electroluminescent device containing the porphyrin compound described in 2).

[0021]

[Chemical 2]

(Wherein R10 to R17 represent the same or different hydrogen atom, halogen or a monovalent organic residue, A2 represents -N = or -CR18 =, and R18 represents a hydrogen atom, halogen or 1). M1 is a hydrogen atom, a metal atom, a metal oxide, a metal halide, or a metal having a monovalent organic residue.) Also, R10 to R10
As the monovalent organic residue of 18, an alkyl group which may be branched or not, a substituted or unsubstituted aryl group, an unsaturated hydrocarbon group such as a vinyl group or an allyl group, a carboxyl group,
Carboxyalkyl group, hydroxyl group, alkoxyl group, acyl group, alkyloxy group, aryloxy group,
Alkylthio group, arylthio group, nitro group, amino group, aminoalkyl group, cyano group, cyanoalkyl group,
A substituted or unsubstituted heterocyclic ring having 3 or more membered rings can be used.

M1 is 2 hydrogen atoms, 1 or 2 metal atoms, metal oxide, metal halide or 1
It is a metal having a valent organic residue, and L is a metal atom.
i, Na, K, Rb, Cs, Be, Sr, Ba, Ca,
Mg, Fe, Co, Ni, Cu, Zn, Mn, Cr, A
l, Ga, Sn, Si, Ge, Sc, Ti, Pb, V,
Pt, Pd, Cd, etc. can be used. Further, as the monovalent organic residue, an alkyl group which may or may not be branched, a substituted or unsubstituted aryl group, an unsaturated hydrocarbon group such as a vinyl group or an allyl group, a carboxyl group, a carboxyalkyl group, Hydroxyl group, alkoxyl group, acyl group, alkyloxy group, aryloxy group, alkylthio group,
An arylthio group, a nitro group, an amino group, an aminoalkyl group, a cyano group, a cyanoalkyl group, a substituted or unsubstituted heterocyclic ring having three or more members, or the like can be used.

Specifically, porphine, ethioporphine, mesoporphine, protoporphine, protoporphine zinc, 2,3,7,8,12,13,17,18-
Octaethylporphine, 2,3,7,8,12,1
3,17,18-octaethylporphine copper, 2,3
7,8,12,13,17,18-octaethylporphine magnesium, 5,10,15,20-tetraphenylporphine, 5,10,15,20-tetraphenylporphine copper, 5,10,15,20- Tetrapyridylporphine, 5,10,15,20-tetraazaporphyrin, 2,3,7,8,12,13,17,18-
Octaethyl-5,10,15,20-tetraazaporphyrin, 2,7,12,17-tetra-t-butyl-5,5
10,15,20-Tetraazaporphyrin, 5,1
0,15,20-tetraphenyl-5,10,15,2
0-tetraazaporphyrin, 5,10,15,20-
Examples thereof include tetraphenyl-5,10,15,20-tetraazaporphyrin copper and the like.

A sixth invention is the organic electroluminescent device according to any one of the first to fifth inventions, wherein the cathode is an organic electroluminescent device comprising a metal having a work function of 4.0 eV or more, high luminous efficiency, and driving life. Has the action of enabling a long device. Specifically, aluminum, silver, copper, gold, tin, indium, manganese, nickel, platinum and the like are preferable.
Note that various fluorescent materials such as various fluorescent metal complex compounds, fluorescent organic dye compounds such as oxazole derivatives and styryl derivatives, and fluorescent polymer compounds such as polyparaphenylene vinylene can be used as the light emitting material.
Further, by adding various fluorescent materials such as quinacridone, coumarin, rubrene, and perylene as dopants to the light emitting layer, an organic electroluminescent device having higher efficiency, higher brightness and higher reliability can be manufactured.

The device structure of the present invention includes the following, but any structure may be used as long as the buffer layer is provided in contact with the cathode. Further, usually, the layers are laminated on the substrate in the order from the anode to the cathode, but conversely, the layers may be laminated on the substrate in the order from the cathode to the anode.

Anode / light emitting layer / buffer layer / cathode anode / hole transport layer / light emitting layer / buffer layer / cathode anode / hole injection layer / hole transport layer / light emitting layer / buffer layer / cathode anode / hole transport Layer / light emitting layer / electron transport layer / buffer layer / cathode anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer /
Buffer layer / cathode.

[0028]

EXAMPLES Specific examples of the present invention will be described below.

In the following examples, an unsubstituted triphenylamine tetramer (TPT) represented by (Chemical Formula 3) is used as a hole transport material.
Using tris (8-quinolinol) aluminum (hereinafter referred to as Alq) as the light emitting material and aluminum as the cathode, the anode, the hole transport layer, the light emitting layer, the buffer layer,
Although the structure of the element in which the cathode is laminated in order is shown as a representative, the present invention is not limited to this structure.

[0030]

[Chemical 3]

Example 1 The electroluminescent device of this example is
As shown in FIG. 1, a structure in which a hole transport layer 3, a light emitting layer 4, a buffer layer 5, and a cathode 6 are vapor-deposited in this order on a glass substrate 1 on which an ITO electrode has been previously formed as a transparent electrode 2. Have.

First, a thoroughly washed glass substrate (ITO
The electrode was formed into a film), TPT, Alq, copper phthalocyanine, aluminum and lithium were set in the vapor deposition apparatus. Then, after evacuation to 2 × 10 -6 torr, 0.
TPT set at a rate of 1 nm / sec was vapor-deposited to form a hole transport layer having a thickness of 50 nm. Next, the light emitting material A that was set
lq was vapor-deposited at a rate of 0.1 nm / sec to form a light emitting layer having a film thickness of 25 nm.

Next, copper phthalocyanine and lithium were vapor-deposited from different vapor deposition sources, and a buffer layer composed of copper phthalocyanine and lithium was laminated to a thickness of 25 nm. Then, aluminum was vapor-deposited at a rate of 0.5 nm / sec to a thickness of 150 nm. All of these vapor depositions were continuously performed without breaking the vacuum, and the film thickness was monitored by a crystal oscillator.

Immediately after the device was manufactured, the electrode was taken out in dry nitrogen, and the characteristics were continuously measured. Here, the luminous efficiency of the obtained device is as follows: luminous luminance of 500 cd /
It was defined by the value in the case of m ² . Further, the driving life is 1000 cd / m ² as the initial luminance, and when driven with a constant current,
It was defined as the time during which the luminance reached half of the initial value, 500 cd / m ² .

As a result, in this example, the light emission characteristic was 3.1 cd / A and the driving life was 510 hours.

On the other hand, for comparison, an organic electroluminescence device was prepared in the same manner except that the buffer layer was not provided, and the characteristics were examined. As a result, the luminous efficiency was 0.7 cd / A and the driving life was 1 hour or less.

From the above, it was confirmed that the organic electroluminescent device of the present example has significantly improved luminous efficiency and driving life.

Example 2 In this example, an organic electroluminescent device was prepared in the same manner as in Example 1 except that the mixed film of the porphyrin compound and lithium shown in (Table 1) was used as the buffer layer. Its characteristics were evaluated.

The results are shown in (Table 1) below.

[0040]

[Table 1]

From Table 1, it was confirmed that the organic electroluminescent device of this example had a significantly improved luminous efficiency and driving life.

(Example 3) In this example, an organic electroluminescent device was prepared in the same manner as in Example 1 except that a mixed film of copper phthalocyanine and the metals shown in Table 2 was used as the buffer layer, and its characteristics. Was evaluated.

The results are shown in (Table 2) below.

[0044]

[Table 2]

From Table 2, it was confirmed that the organic electroluminescent device of this example had a significantly improved luminous efficiency and driving life.

(Example 4) In this example, an organic electroluminescent device was prepared in the same manner as in Example 1 except that a mixed film of an aromatic amine compound and lithium was used as the buffer layer.
Its characteristics were evaluated. Examples of the aromatic amine compound include TPT, N, N′-diphenyl-N, and
N'bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine TPD, and 4,4 ',
MTDATA, which is 4 ″ -tris (N- (3-methylphenyl) -N-phenylamino) triphenylamine
Was used.

The results are shown in (Table 3) below.

[0048]

[Table 3]

From Table 3, it was confirmed that the organic electroluminescent device of this example had a significantly improved luminous efficiency and driving life.

Example 5 In this example, an organic electroluminescent device was prepared in the same manner as in Example 1 except that only the porphyrin compound shown in (Table 4) was used as the buffer layer, and the characteristics were evaluated. did.

The results are shown in (Table 4) below.

[0052]

[Table 4]

From Table 4, it was confirmed that the organic electroluminescent device of this example had a significantly improved luminous efficiency and driving life.

[0054]

As described above, according to the present invention, the buffer layer provided in contact with the cathode of the pair of electrodes contains at least a porphyrin compound and a metal having a work function of 4.0 eV or less. The advantageous effect is obtained that an organic electroluminescent device having high luminous efficiency and a small decrease in luminance during driving life can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an organic electroluminescent device according to an embodiment of the present invention.

[Explanation of symbols]

1 glass substrate 2 transparent electrode 3 Hole transport layer 4 Light emitting layer 5 buffer layers 6 cathode

Continued front page    (72) Inventor Akito Miyamoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 3K007 AB03 AB08 AB11 CC00 DB03

Claims (3)

[Claims] 1. An organic electroluminescent device having an organic layer between a pair of electrodes, wherein the buffer layer provided in contact with the cathode of the pair of electrodes has a work function of at least 4 with an aromatic amine compound. An organic electroluminescent device, characterized in that a metal mixed with a metal of 0.0 eV or less is used and a metal not contained in the buffer layer is used for the cathode. 2. The organic electroluminescent device according to claim 1, wherein the metal having a work function of 4.0 eV or less is an alkali metal or an alkaline earth metal. 3. The organic electroluminescent device according to claim 1, wherein the cathode is made of a metal having a work function of 4.0 eV or more.