JP2004047493A - Organic light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic light emitting element forming an organic luminescent layer of high reproducibility in process while providing new luminescent colors with high luminance by taking out luminescence from an exciplex. <P>SOLUTION: In this organic light emitting element having at least an organic luminescent layer between a positive electrode and a negative electrode, the organic luminescent layer comprises at least two kinds of organic substance to form the exciplex. An organic polynuclear metal complex formed of an electron-deficient compound is applied as a new electron transport material, and the exciplex is formed to realize luminescence of high luminance while providing various luminescent colors. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an organic light-emitting device used as a light-emitting display or a backlight for a liquid crystal display.

Electroluminescence (EL) panels are characterized by high visibility, excellent display capability, and high-speed response. In recent years, an organic light-emitting device using an organic compound as a constituent material has been reported (for example, Non-Patent Document 1). This report describes an organic light emitting device having a structure in which an organic light emitting layer and a charge transport layer are laminated.

The organic light emitting device is divided into three types of laminated structures shown in FIGS. 1 are generally referred to as SH-A type, FIG. 2 is referred to as SH-B type, and FIG. 3 is referred to as DH type.

報告 The report of Tang et al. In Non-Patent Document 1 has a configuration called the SH-A type in FIG. As a light-emitting material, a tris (8-quinolinol) aluminum complex (hereinafter, Alq) is used, which is an excellent light-emitting substance having both high luminous efficiency and electron transport.

非 Also, in the non-patent literature, a device was prepared in which Alq for forming an organic light emitting layer was doped with a coumarin derivative or a fluorescent dye such as DCM1, and it was found that the emission color was changed by appropriate selection of the dye. Furthermore, it was clarified that the luminous efficiency was higher than that of the undoped one. In this case, the DH type shown in FIG. 3 can be realized by doping only the recombination region of carriers in addition to the SH-A type shown in FIG. 1 and separating the functions of light emission and electron transport.

On the other hand, the SH-B type in FIG. 2 is an oxadiazole derivative represented by 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole (PBD) Is often used as an electron transport material. However, oxadiazole derivatives such as PBD easily cause crystallization and are not suitable for practical use.

Therefore, research and development has been focused on the SH-A type shown in FIG. 1 or the DH shown in FIG. 3, and new device materials corresponding to the functions of electron transport, hole transport and fluorescence have been developed and studied. ing. In particular, a large number of materials having a basic skeleton of triphenylamine as a hole transporting organic molecule have been developed, and fluorescent pigments, laser dyes, and the like have been actively applied and modified for fluorescent organic molecules.
Applied Physics Letters, 51, 1987 (Applied Physics Letters, 51, 1987, P. 913.) 2 Journal of Applied Physics, 65, 3610, 1989 (Journal of Applied Physics, 65, 1989, p. 3610.)

However, on the other hand, the number of electron transporting organic molecules is very small, and only electron transporting light-emitting materials such as Alq, Alq derivatives, and chelate metal complexes of beryllium benzoquinoline are mentioned. Therefore, there is a problem that there is very little room for material selection.

In addition, these complexes have been developed based on the element structure of the SH-A type or the DH type, and the emission color of the complex is from green to yellow. Emission color cannot be obtained in principle.

The organic light emitting layer is generally formed by doping the above-mentioned fluorescent pigment or laser dye as a guest material. In the doping method, since the doping concentration and the luminous efficiency are in inverse proportion, the efficiency is high when the doping concentration is low, and the efficiency decreases due to the concentration quenching as the doping concentration increases. Usually, the optimum concentration is in the range of 0.1 to 1%, so it is difficult to control.

Further, the magnitude of the overlap between the absorption spectrum of the fluorescent dye as a dopant and the emission spectrum of the host material is a deciding factor of the luminous efficiency. However, as described above, the choice of the electron transporting luminescent material that can be the host material is narrow, There arises a problem that the range for selecting the dopant becomes narrow.

In addition, the doping method has a problem that light emission on the short wavelength side cannot be obtained because the wavelength is shifted longer than the light emission of the host material.

Furthermore, red light emission is a problem for organic light emitting devices. To obtain red color, a compound having a narrow energy gap is required, but such a compound has a large spread of the pi-electron system and requires further consideration to concentration quenching.

Therefore, the present inventors have provided a novel electron-transporting organic material, and have realized a stable organic light-emitting device by using the same. In addition, by extracting light emitted from the exciplex, a high-luminance and novel light-emitting color can be given, and an organic light-emitting layer having high reproducibility can be formed even in terms of process. .

Specifically, the organic light-emitting device of the present invention is an organic light-emitting device having at least an organic light-emitting layer between a positive electrode and a negative electrode, wherein the organic light-emitting layer contains two or more kinds of organic substances and forms an exciplex. It is characterized by becoming.

It is preferable that at least one kind of the organic substance contained in the organic light emitting layer is an organic polynuclear metal complex compound.

The organic polynuclear metal complex compound preferably has a pyrazaball structure.

Preferably, the organic polynuclear metal complex compound is 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyraza ball.

According to the present invention, a stable organic light-emitting device can be realized by proposing and applying an organic polynuclear metal complex compound composed of an electron-deficient compound as a novel electron transport material. Further, by forming the exciplex, various emission colors can be achieved, and high-luminance emission can be realized at the same time.

に お い て In the present invention, an organic light emitting device material composed of an organic polynuclear metal complex compound may be an electron-deficient compound represented by the following general formula (Formula 1).

(However, R ₁ and R ₂ are a bridging ligand having a nitrogen-containing aromatic ring or a nitrogen-containing aromatic ring derivative containing at least two nitrogen atoms or a bridging ligand having a halogen or an alkyl having 1 to 3 carbon atoms. R ₃ , R ₄ , R ₅ and R ₆ are each a hydrogen, alkyl, aryl or aryl derivative and a nitrogen-containing aromatic ring containing at least one nitrogen atom or a nitrogen-containing aromatic ring containing at least one nitrogen atom. It is one selected from a nitrogen aromatic ring derivative, and M represents a central metal.)
Further, in the present invention, an organic light-emitting device having at least an organic light-emitting layer and an organic electron-transporting layer between a positive electrode and a negative electrode, wherein at least the organic electron-transporting layer comprises the organic light-emitting device material of the above formula (1) May be included.

The organic polynuclear metal complex compound contained in the organic electron transport layer of the organic light emitting device may have a pyrazaball structure.

The organic polynuclear metal complex compound contained in the organic electron transport layer of the organic light emitting device may be composed of 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyraza ball.

According to the present invention, in an organic light emitting device comprising a positive electrode, an organic light emitting layer, an organic electron transporting layer and a negative electrode, at least the organic electron transporting layer may contain the organic light emitting device material of the above formula (1).

According to the present invention, in an organic light emitting device having at least an organic light emitting layer between a positive electrode and a negative electrode, the organic light emitting layer may contain two or more kinds of organic substances to form an exciplex.

The organic light emitting device is formed of a positive electrode, an organic light emitting layer, an organic electron transporting layer, and a negative electrode sequentially, and at least the organic electron transporting layer contains the organic light emitting device material of the formula (1), and the organic light emitting layer May contain two or more organic substances to form an exciplex.

In an organic light emitting device having an organic light emitting layer made of an organic boron complex compound between the positive electrode and the negative electrode, the organic light emitting layer may contain an aromatic substituted amine derivative.

In an organic light emitting device having an organic light emitting layer made of an organic boron complex compound between the positive electrode and the negative electrode, the organic light emitting layer may contain a pyrene derivative.

The organic boron complex compound may be 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyraza ball.

Hereinafter, embodiments of the present invention will be described.

The electron-deficient compound of the present invention is a compound that has a smaller number of valence electrons than the number of valence orbitals and does not follow the octet rule. As a result of investigations by the present inventors, an organic polynuclear metal complex compound, which is an electron-deficient compound having a three-center two-electron bond, as shown in the general formula (Chemical Formula 1) of claim 1, is suitable as an organic light emitting device material. I found that. As elements constituting the electron-deficient compound, Li, Be, Mg, B, and Al are well known. These compounds are stabilized by gaining electrons because they are literally short of electrons. In particular, it has excellent thermal and film properties as an electron transport layer that transmits electrons by forming anion radicals. Examples of useful compounds include:
A-1 Pilaza ball A-2 1,3,5,7-Tetramethyl pyraza ball A-3 4,4,8,8-Tetraethyl pyraza ball A-4 4,4,8,8-Tetrakis (1H- Pyrazol-1-yl) pyrazaball Among the compounds represented by the general formula (Chemical Formula 1), organic polynuclear metal complex compounds having a pyrazaball structure including A-1 to A-4 have a thickness of 400 nm to 420 nm in a solution or in a thin film state. It has purple emission. This means that the band gap is wide and the ionization potential is large. At the same time, since it has an excellent electron transporting ability as described above, when it is used as an organic electron transporting layer, the energy moves to a lower side, that is, a light emission color on a longer wavelength side than purple becomes possible.

(4) The thin film composed of the organic polynuclear metal complex is very stable, does not crystallize unlike the PBD thin film, and does not crystallize even when left in the air. Therefore, a stable SH-B type device configuration can be realized by placing not only the SH-A type and DH type but also a hole transporting light emitting layer or a light emitting site composed of an exciplex on the layer on the anode side. Can be.

エ The exciplex formed in the organic light emitting layer is realized by an exciplex formed of a combination of different organic molecules.

In this case, neither organic molecule is required to emit light necessary for itself, unlike ordinary dopants, so that the overlapping of spectra necessary for energy transfer, the interaction due to the spread of the pi-electron system, or the concentration quenching are caused. There is no danger.

For example, in JP-A-10-159076, the wavelength of the dopant in the electron transport layer shifts from the emission color of the original dopant due to the interaction with the hole transport material. Although a blocking layer is provided in the present invention, in the present invention, such a complicated process is not required, a completely different molecule is formed in the light emitting layer, and light emission from the exciplex can be obtained.

That is, even if each organic molecule has a weak fluorescence intensity, the formation of an exciplex generates a new electronic state, and it is possible to realize strong fluorescence emission.

Exciplexes are formed not only when the whole molecule interacts with each other, but also when a part of the molecule interacts with each other due to electron accepting or electron donating properties. There is also.

Therefore, by finding the combination, high-luminance light emission and various color tones can be easily obtained.

内 At least one of the organic molecules contained in the organic light emitting layer is preferably an organometallic complex compound. Further, it preferably has a pyrazaball structure, particularly preferably 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyrazorball. 2,4-bis (5,6-diphenyl-1,2,4-triazin-3-yl) pyridine, 3- (2-pyridyl) -5,6-diphenyl-1,2,4-triazine, 5,6-di Heteroaromatics such as 2-furyl 3- (2-pyridyl) -1,2,4-triazine, 3- (4-biphenylyl) 4-phenyl-5- (4-tert-butylphenyl) 1,2,4-triazole The organic molecule having a ring alone emits weak fluorescence in a blue region in a solution or in a vapor-deposited film, and forms an exciplex in combination with the organic molecule having a pyrazaball structure, and has a high luminance in an orange to red region. Enables light emission.

(4) An organic boron complex compound represented by A-1 to A-4 forms an organic light emitting layer together with an aromatic substituted amine derivative. The following general formulas (Chemical Formula 2) and (Chemical Formula 3) can be given as the aromatic substituted amine derivatives.

(However, n is an integer of 1 to 6. R ₁ , R ₂ , and R ₃ may be the same or different in any of benzene, naphthalene, anthracene, and phenanthrene. In addition, an alkyl group, an amino group, and a phenyl group may be used. May be substituted.)

(However, at least one of R ₁ , R ₂ , and R ₃ comprises styryl, phenylstyryl, and naphthylstyryl, and may be substituted with an alkyl group, an amino group, or a phenyl group, respectively. Examples of the constituents of R ₁ , R ₂ , and R ₃ include an alkyl group, an amino group, a phenyl group, an alkyl-substituted benzene, and an amino-substituted benzene.)
Specific examples of (Chemical Formula 2) include N, N'-diphenyl-N. N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, N, N'-diphenyl-N. N'-binaphthyl-1,1'-biphenyl-4,4'-diamine; N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine;

Specific examples of (Chemical Formula 3) include 4-N, N′-diphenylamino-α-phenylstilbene, 4-N, N′-bis (p-methylphenyl) amino-α-phenylstilbene, 4-N , N′-diphenylamino-α-naphthylstilbene, 4,4′-bis (α-phenylstyryl) triphenylamine, 4,4 ′, 4 ″ -tri (α-phenylstyryl) triphenylamine, 4,4 '-Bis (3-methylphenylstyryl) triphenylamine, 4,4'-bis (2,4-dimethylphenylstyryl) triphenylamine, 4,4'-bis (α-biphenylstyryl) triphenylamine and the like No.

These compounds emit blue light with a maximum emission wavelength of 430 nm to 490 nm in a solution or in a thin film state. The mixing ratio of the organic boron complex compound and the aromatic substituted amine derivative is preferably such that the aromatic substituted amine derivative is contained at 1 to 50% by weight.

The organic boron complex compound represented by A-1 to A-4 forms an organic light emitting layer together with a pyrene derivative. Specific examples of the pyrene derivative include pyrene, 1-pyrenemethylamine, phenylstyrylpyrene, N- (1-pyrenyl) maleimide, and the like.

The pyrene derivative has a bluish green emission near a maximum emission wavelength of 500 nm in a solution or in a thin film state, but when coexisting with an organic boron complex compound, the emission color of the pyrene derivative is not observed.

(4) Rather, it was found that an exciplex was formed in the organic boron complex, and the organic boron complex emitted blue light having a maximum emission wavelength of about 460 nm.

Furthermore, the luminous efficiency is extremely high, up to 10 times as high as when the luminescent layer is formed with the organic boron complex compound alone. As for the pyrene derivative, the performance as a light emitting material could not be sufficiently brought out because there was no suitable host material in the conventional doping method.

In the present invention, the discovery of a combination of an organoboron complex compound and a pyrene derivative has led to emission from an exciplex. The mixing ratio of the organoboron complex compound and the pyrene derivative is preferably such that the pyrene derivative is contained at 1 to 50 wt%.

膜厚 The thickness of the organic electron transport layer is preferably 10 to 1000 nm.

The thickness of the organic light-emitting layer may be a thickness sufficient for the dye to emit light, and is preferably 1 to 100 nm, more preferably 5 to 50 nm.

Next, regarding the hole transport layer in the present invention, a derivative having triphenylamine as a basic skeleton is preferable as a constituent material.

Examples include a tetraphenylbenzidine compound, triphenylamine trimer and benzidine dimer described in JP-A-7-126615.

Also, various triphenyldiamine derivatives described in JP-A-8-48656 or MTPD (commonly known as TPD) described in JP-A-7-65958 may be used. In particular, a triphenylamine tetramer described in Japanese Patent Application No. 9-341238 is preferred.

各 It is preferable that the organic light emitting layer, the electron transporting layer, and the hole transporting layer are each formed as a homogeneous film in an amorphous state, and is preferably formed by a vacuum deposition method.

Furthermore, by forming each layer continuously in a vacuum, by preventing impurities from adhering to the interface between each layer, it is possible to improve characteristics such as lowering of operating voltage, higher efficiency, and longer life. it can.

Further, when forming each of these layers by a vacuum deposition method, when a plurality of compounds are contained in one layer, it is preferable to individually co-deposit each boat containing the compounds by controlling the temperature individually, but it is preferable to deposit a mixture in advance. You may.

Further, as other film forming methods, a solution coating method, a Langmuir-Blodgett (LB) method, or the like can be used. In the solution coating method, each compound may be dispersed in a matrix material such as a polymer.

The organic light-emitting element can emit surface light by making at least one electrode transparent or translucent. Usually, an ITO (indium tin oxide) film is often used for the anode as a hole injection electrode.

In addition, tin oxide, Ni, Au, Pt, Pd and the like can be mentioned.

(4) In order to improve the transparency or reduce the resistivity of the ITO film, a film forming method such as sputtering, electron beam evaporation, or ion plating is employed. The film thickness is determined from the required sheet resistance value and visible light transmittance. However, since the driving current density of the organic light emitting element is relatively high, the organic light emitting element is used at a thickness of 100 nm or more to reduce the sheet resistance value. Is often done.

For the cathode as the electron injection electrode, an alloy of a metal having a low work function and a low electron injection barrier, such as a MgAg alloy or an AlLi alloy proposed by Tang et al., And a metal having a relatively large work function and being stable may be used. Many.

Further, a metal having a low work function may be formed on the organic layer side, and a metal having a large work function may be thickly laminated for the purpose of protecting the metal having a low work function, such as Li / Al or LiF / Al. Stacked electrodes can be used. For forming these cathodes, a vapor deposition method or a sputtering method is preferable.

The substrate may be any as long as it can support the organic light-emitting element in which the above-described thin films are stacked, and may be a transparent or translucent material so as to extract light emitted in the organic layer. Or a polyester or other resin film.

Next, a more detailed description will be given based on specific examples.

(Example 1)
A 50 nm-thick hole transport layer made of N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine is formed on a glass substrate on which ITO is formed.

{Circle over (2)} After depositing Alq to a thickness of 20 nm as an organic light emitting layer, A-4 was deposited to a thickness of 40 nm as an organic electron transporting layer. Finally, a negative electrode made of an AlLi alloy was formed.

直流 When a DC voltage was applied to the device and evaluated, green light emission from Alq having a maximum emission wavelength of 520 nm was obtained. The efficiency was 4.0 cd / A, and the light continued to glow stably.

同 様 Similar results were obtained when A-1 to A-3 were used instead of A-4.

(Example 2)
A 50 nm-thick hole transport layer made of N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine is formed on a glass substrate on which ITO is formed.

(4) A-4 was deposited as an organic electron transporting layer to a thickness of 40 nm. Finally, a negative electrode made of an AlLi alloy was formed.

(4) When a DC voltage was applied to this device and evaluated, blue-violet emission from A-4 having a maximum emission wavelength of 420 nm was obtained. The efficiency was 0.5 cd / A due to low visibility. Similar results were obtained when A-1 to A-3 were used instead of A-4.

(Example 3)
An organic light emitting layer made of A-2 and 10 wt% of phenylstyrylpyrene was formed to a thickness of 50 nm on a glass substrate on which an ITO film was formed, and then an organic electron transporting layer made of A-4 was deposited to a thickness of 50 nm. Finally, a negative electrode made of an AlLi alloy was formed. When a DC voltage was applied to the device and evaluated, blue-green light emission having a maximum emission wavelength of 470 nm was obtained. The efficiency was 2.0 cd / A, and the light continued to glow stably.

(Example 4)
A 50 nm-thick hole transport layer made of N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine is formed on a glass substrate on which ITO is formed.

(5) A 50-nm co-evaporation film of A-4 and 20% by weight of 4-N, N'-bis (p-methylphenyl) amino-α-phenylstilbene was deposited as an organic light emitting layer.

(5) Finally, a negative electrode made of an AlLi alloy was formed. When a DC voltage was applied to the device for evaluation, blue light emission having a maximum emission wavelength of 460 nm was obtained. The efficiency was 2.8 cd / A, and it continued to glow stably.

(Example 5)
In forming the organic light emitting layer of Example 4, 20 wt% of 4,4′-bis (α-phenyl) was used instead of 20 wt% of 4-N, N′-bis (p-methylphenyl) amino-α-phenylstilbene. An organic light-emitting device was produced in the same manner as in Example 4 except that (styryl) triphenylamine was used. When a DC voltage was applied to this device and evaluated, blue light emission having a maximum emission wavelength of 460 nm, which was light emission from the organic light emitting layer, was obtained. The efficiency was 3.4 cd / A, and it continued to glow stably.

(Example 6)
Example 4 Except that 20 wt% of phenylstyrylpyrene was used instead of 20 wt% of 4-N, N′-bis (p-methylphenyl) amino-α-phenylstilbene in forming the organic light emitting layer of Example 4. An organic light-emitting device was produced in the same manner as in No. 4. When a DC voltage was applied to the device and evaluated, light blue emission having a maximum emission wavelength of 480 nm, which was emission from the organic light emitting layer, was obtained. The efficiency was 5.2 cd / A, and it continued to glow stably.

(Comparative Example 1)
A 50 nm-thick hole transport layer made of N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine is formed on a glass substrate on which ITO is formed.

(5) Alq was subsequently evaporated to a thickness of 50 nm as an organic electron transporting layer. Finally, a negative electrode made of an AlLi alloy was formed. When a DC voltage was applied to the device for evaluation, green light emission from Alq having a maximum emission wavelength of 520 nm was obtained. The efficiency was 3.3 cd / A.

(Comparative Example 2)
An organic light-emitting device was manufactured in the same manner as in Comparative Example 1, except that PBD was used instead of Alq in forming the organic electron transport layer of Comparative Example 1. When a DC voltage was applied to the device for evaluation, blue light emission from the TPD having a maximum emission wavelength of 460 nm was obtained. The efficiency was 0.8 cd / A, and almost no light was emitted after about 1 hour.

Sectional drawing of the conventional general SH-A type organic light emitting element. Sectional drawing of the conventional general SH-B type organic light emitting element. Sectional drawing of the conventional general DH type organic light emitting element.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Anode 2 Hole transport layer 3 Organic light emitting layer 4 Electron transport layer 5 Cathode

Claims (4)

(4) An organic light-emitting device having at least an organic light-emitting layer between a positive electrode and a negative electrode, wherein the organic light-emitting layer contains two or more kinds of organic substances and forms an exciplex. The organic light emitting device according to claim 1, wherein at least one of the organic substances contained in the organic light emitting layer is an organic polynuclear metal complex compound. 3. The organic light emitting device according to claim 2, wherein the organic polynuclear metal complex compound has a pyrazaball structure. The organic light-emitting device according to claim 2, wherein the organic polynuclear metal complex compound is 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyrazaball.

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