JPH09272863A - Organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an organic EL element enabling red-color luminescence, and useful in e.g. a flat panel-type color display with three-primary-colors- luminescent elements arranged in a two-dimensional way, by sandwichedly providing an organic EL thin film layer containing a specific compound-contg. layer between electrodes. SOLUTION: This organic EL element is obtained by constituting (A) a transference electrode layer as anode, (B) an organic EL thin film layer made up from an organic thin film layer and (C) a metallic electrode layer as cathode on a light-transmitting substrate in this order. The component B comprises a layer containing a compound of the formula (X is a halogen, NO2 or H; R2 is H or an alkyl; R1 is an acyl or the same as R2 ; R3 is the same as R2 , or allyl, an alkoxy or halogen) e.g. 2-[4-(N,N-dimethylamino)phenly]azo-6- nitrobenzothiazole}.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic EL device utilizing an electroluminescence (EL) phenomenon, and more particularly,
The present invention relates to an organic EL device using a novel red light emitting material.

[0002]

2. Description of the Related Art A conventional EL using an organic compound has been researched from the discovery of an EL emission phenomenon due to carrier injection in a single crystal of a compound having a strong fluorescence such as anthracene, to a thin film stack type organic EL device. Developed, 1000
High-luminance light emission of cd / m ² or more and operation at a driving voltage of 10 V or less have been reported.

Applications of organic EL devices include red (R),
A flat panel type color display in which light emitting elements of three primary colors of green (G) and blue (B) are two-dimensionally arranged and an optical printer head in which light emitting elements are one-dimensionally arranged are considered.

[0004]

In order to use it for a flat panel type color display, it is necessary to develop a light emitting element of three primary colors of red, green and blue. However, materials having sufficient emission brightness have not been developed for red and blue other than green. Further, as described in Japanese Patent Application No. 6-187090, which has already been proposed by the inventor of the present application, an optical printer head using an organic EL element is
Suitable for high speed, small size, and low cost. Therefore, it can be expected to develop an optical printer of lower cost and higher function by combining it with a photoconductor drum which is currently mass-produced and whose price has been reduced.

However, the photoconductor drums used in the currently produced optical printers have a history of being developed for optical printers using a semiconductor laser element for emitting near infrared light as a light source. Infrared (approximately 600 nm
It is designed to have high sensitivity to the above wavelengths). Therefore, when an optical printer head using an organic EL element is combined with a conventional photosensitive drum to form an optical printer, it is necessary to develop an organic EL element that emits red light.

The present invention eliminates the above-mentioned problems and uses a novel light emitting material, so that an organic EL device capable of emitting red light can be obtained.
It is intended to provide an element.

[0007]

In order to achieve the above object, the present invention provides:

[0008]

Embedded image

A nitrobenzothiazolylazo compound represented by the above chemical formula [1] is used as an organic EL light emitting material. Here, X in the chemical formula [1] represents NO ₂ , a halogen atom, or H, R ₁ represents H, an alkyl group, or an acyl group, R ₂ represents H, or an alkyl group, R ₃ is H, an alkyl group, an allyl group, an alkoxy group,
Or a halogen atom.

The structure of the organic EL element is of the following two types. (A) A transparent positive electrode layer, a hole transporting organic thin film layer, a thin film layer made of the compound represented by the chemical formula [1], an electron transporting organic thin film layer, and a metal negative electrode on a transparent substrate. A structure in which layers are sequentially formed. (B) A transparent positive electrode layer, a hole-transporting organic thin film layer, a co-deposited thin film layer of an electron-transporting organic compound and the compound represented by the chemical formula [1], and a metal shadow on a transparent substrate. A structure in which electrode layers are sequentially formed.

As described above, by using the novel light emitting material, it is possible to provide an organic EL element capable of emitting red light. In particular, the novel light emitting material has a wavelength of 700 to
Near-infrared light emission having a peak in the 800 nm band was obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A first embodiment of the present invention will be described.

[0013]

Embedded image

As an example of the organic EL light emitting material of the first embodiment of the present invention, X in the chemical formula [1] is H and R ₁
And R ₂ are ethyl groups C ₂ H ₅ and R ₃ are H, respectively, 4-diethylaminophenyl-azo-6-nitrobenzothiazole (hereinafter referred to as DEP) represented by the above formula [2].
An example of a method of synthesizing ABT) will be described. First, 6 g of sodium nitrite is added to 100 ml of concentrated sulfuric acid to generate nitrosyl sulfuric acid. Next, this is 15 ℃
To this is added 100 ml of a 1: 1 volume ratio of glacial acetic acid-propionic acid mixture, keeping it at the following temperature, then it is cooled to a temperature of -5 ° C.

Next, 10 g of 6-nitro-2-aminobenzothiazole is added to this, and the mixture is reacted at a temperature of -5 ° C for 5 hours with stirring. Next, urea is added to this to decompose excess sodium nitrite, and then 15 g of a mixture of glacial acetic acid-propionic acid-water in which diethylaniline is dissolved is added and the mixture is allowed to stand at a temperature of 0 ° C.

After standing, the reaction solution is neutralized with sodium acetate, and the precipitated crystals are collected by filtration. The filtrate is purified by a recrystallization method using alcohol. The material thus obtained was red-black crystals. The DEPABT thus obtained was vacuum deposited on a synthetic quartz glass substrate to a thickness of 100 nm. The vapor deposition was carried out by placing the compound in a quartz crucible and heating the crucible with a resistance wire.

An argon laser (514.
FIG. 1 shows the result of measuring the fluorescence spectrum by irradiating with light of 5 nm). In FIG. 1, the vertical axis represents fluorescence intensity (arbitrary unit), and the horizontal axis represents wavelength (nm). As is clear from this figure, near-infrared light emission having a peak at a wavelength of 720 nm was obtained.

Next, the results of measuring the absorption spectrum of DEPABT are shown in FIG. In FIG. 2, the vertical axis represents the absorbance (arbitrary unit) and the horizontal axis represents the wavelength (nm). As shown in FIG. 2, it was found that the absorbance around the wavelength of 500 nm was large. FIG. 3 is a schematic cross-sectional view of an organic EL device manufactured according to the first embodiment of the present invention.

As shown in this figure, a transparent electrode layer (ITO thin film) 12 as a positive electrode, an organic hole transport layer 13, a DEPABT layer 14, an organic electron transport layer 15, and a negative electrode are provided on a glass substrate 11. The metal electrode layer 16 is sequentially laminated by a vacuum vapor deposition method or the like. More specifically, first, an ITO thin film having a thickness of 200 nm is sputtered on a glass substrate 11 that has been sufficiently washed.
Formed to a thickness of The sheet resistance of the formed ITO thin film was 10 Ω / □. Further, this ITO film was processed into a stripe shape having a width of 2 mm by a photolithography etching method to obtain an ITO thin film 12.

Next, this substrate was ultrasonically cleaned using acetone and isopropyl alcohol, dried, and transferred to a vacuum deposition apparatus for forming an organic film. First, TPD [N, N′-diphenyl-N, purified as a hole transport material,
N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine] is vapor-deposited to a thickness of 40 nm to form the organic hole transport layer 13. The evaporation was performed by placing the sample in a quartz crucible and heating the crucible with a resistance wire to evaporate the sample. By adjusting the temperature of the crucible, the vapor deposition rate is controlled to be 0.3 nm / sec.

Next, as a light emitting material, DEPABT placed in another crucible in the same vacuum apparatus was evaporated at a deposition rate of 0.01 n.
Evaporated to a thickness of 2 nm at m / sec to form the DEPABT layer 1
4 is formed. Furthermore, subsequently, sublimation-purified Alq [Tris (8-
Hydroxyquinolinol) aluminum] was similarly formed to a vapor deposition rate of 0.3 nm / sec and a film thickness of 40 nm to obtain an organic electron transport layer 15.

Next, this substrate was transferred to a vacuum apparatus for metal deposition, and magnesium (Mg) was deposited at a deposition rate of 1.5 nm.
/ Sec to vapor-deposit a thickness of 150 nm to form a metal electrode layer 16 to be a negative electrode. This is performed by covering the substrate with a metal mask provided with a slit having a width of 2 nm to form a stripe having a width of 2 nm. The positive electrode I
The TO stripe and the negative electrode stripe are formed so as to be orthogonal to each other.

The film thickness, vapor deposition rate, etc. described here are not limited to the numerical values of the embodiment, and are optimized so that the light emission is the strongest or the light emission efficiency is the best. It is something. Further, the hole transport material and the electron transport material used are not limited, and as described in the literature, the hole transport layer includes triphenylamine-based, triphenylmethane-based, pyrazoline-based, Materials such as hydrazone type and polyvinylcarbazole type can be applied. As the organic material used for the electron transport layer, a quinolinol-based or porphyrin-based metal complex, a perylene derivative, an oxadiazole derivative, or the like can be used.

Furthermore, regarding the substrate on which the element is formed,
The material is not limited to glass, and transparent plastic or the like can be used. Although not shown in the process, in order to prevent the organic material from being deteriorated due to exposure to an atmosphere containing humidity and the electron injecting electrode and the like from being oxidized and deteriorated, a protection having a moisture-proof and deoxidizing function is provided. It is desirable to seal the device with layers. The moisture-proof material is a resin such as polyimide or epoxy, and the deoxidizing material is G
Getter materials such as eO and BaO can be used.

In addition to ITO, the hole injection electrode material used for the positive electrode has a large work function (approximately 4e).
A metal or an electrically conductive material (V or more) can be used.
Specifically, a transparent conductive oxide material such as SnO ₂ or ZnO, or a metal such as Au (gold) can be used. A
When u is used, it is desirable that the film thickness is 10 to 40 nm and the film is a semitransparent thin film in order to improve the transmission of EL light.

Further, as the electron injection electrode material used for the negative electrode, a work function other than Mg is small (generally 4 eV).
The following metals, alloys, etc. can be used. Specifically, metals such as In and Al, MgAg, MgIn, and AlLi
Alloys such as can be used. When a voltage was applied between both electrodes of the element thus formed, light emission was generated from a crossed portion (a region of 2 mm × 2 mm) of both electrodes, which was observed from the glass substrate side. The emitted light was red light having a peak at a wavelength of 630 nm.

As described above, the novel light emitting material DEPABT
Was found to be a material that emits fluorescence having a peak at a wavelength of 720 nm. In the organic EL device formed by laminating DEPABT between the hole transport layer and the electron transport layer, red light emission having a peak at a wavelength of 630 nm was obtained. This is because the holes injected from the positive electrode and conducted in the hole transport layer and the electrons injected from the negative electrode and conducted in the electron transport layer are recombined, and the energy thereof causes DEPA.
It is considered that BT was excited to emit light.

Next, a second embodiment of the present invention will be described. FIG. 4 is a schematic cross-sectional view of an organic EL device showing a second embodiment of the present invention. In this figure, 11 is a glass substrate, 12 is a transparent electrode layer (ITO thin film) as a positive electrode,
13 is an organic hole transport layer, 16 is a metal electrode layer as a negative electrode, and these have the same structure as in the first embodiment,
It is laminated by a vacuum deposition method or the like.

The second embodiment is characterized in that the thin film layer 20 formed by co-evaporation of the light emitting material DEPABT and the electron transporting material Alp is formed on the organic hole transporting layer 13. First, in the same manner as in the first embodiment, I is formed on the glass substrate 11.
The TO thin film 12 and the organic hole transport layer 13 are formed. next,
The crucible containing DEPABT and the crucible containing Alp were temperature-controlled independently, and the deposition rate of DEPABT was 0.
01 nm / sec, Alp deposition rate is 0.3 nm / s
When ec becomes constant, a shutter arranged between the substrate and the crucible is opened and co-evaporation is performed to form a thin film layer 20 having a thickness of 40 nm. Next, as in the first embodiment, M
A metal electrode layer 16 of g is formed as a negative electrode.

When a voltage was applied between both electrodes of the organic EL element thus constructed and completed, red light emission was observed from the glass substrate 11 side. FIG. 5 shows the result of measurement of the relationship between the applied voltage and the emission luminance of this organic EL element. In FIG. 5, the vertical axis represents luminance (cd / m ² ) and the horizontal axis represents voltage (V). As is clear from this figure, about 8V
Therefore, the characteristics that the light emission sharply rises were obtained.

As described above, in the organic EL device in which the co-deposited film of the novel light emitting material DEPABT and the electron transporting material was formed on the hole transporting layer, red light emission having a peak at a wavelength of 630 nm was obtained. Next, a third embodiment of the present invention will be described.

[0032]

[Chemical 6]

As an example of the organic EL light emitting material of the present invention represented by the chemical formula [1], X in the chemical formula [1] is H, and R ₁ and R ₂ are each a methyl group CH ₃ ,
An example of a method for synthesizing 4-dimethylaminophenyl-azo-6-nitrobenzothiazole (hereinafter, abbreviated as DMPABT) represented by the above formula [3] in which R ₃ is H will be described.

First, 6 g of sodium nitrite is added to 100 ml of concentrated sulfuric acid to generate nitrosyl sulfuric acid. Then 100 ml of a 1: 1 volume ratio of glacial acetic acid-propionic acid mixture is added to this, keeping it at a temperature below 15 ° C, then it is cooled to a temperature of -5 ° C. Next, 10 g of 6-nitro-2-aminobenzothiazole is added thereto, and the mixture is reacted at a temperature of -5 ° C for 5 hours with stirring.

Next, urea was added to this to decompose excess sodium nitrite, and then 15 g of a mixture of glacial acetic acid-propionic acid-water in which dimethylaniline was dissolved was added to a temperature of 0 ° C. put. After standing, the reaction solution is neutralized with sodium acetate, and the precipitated crystals are collected by filtration. Then, the filtrate is purified by a recrystallization method using alcohol. The material thus obtained was red-black crystals.

In order to confirm the emission characteristics, DMPAB
T was vacuum-deposited on a synthetic quartz glass substrate to a thickness of 100 nm. The vapor deposition was carried out by placing the compound in a quartz crucible and heating the crucible with a resistance wire. FIG. 6 shows the result of measuring the fluorescence spectrum by irradiating the produced sample with light having a wavelength of 355 nm that was dispersed by a spectroscope. In this figure, the vertical axis represents fluorescence intensity (arbitrary unit) and the horizontal axis represents wavelength (nm). As is clear from this figure, near-infrared light emission having a peak at a wavelength of 790 nm was obtained.

Explaining in the same way as in the first embodiment, the organic EL device produced has the same schematic structure as that of the first embodiment shown in FIG. 3 and will be described with reference to FIG. On the glass substrate 11 under the same method and conditions as in the first embodiment,
A stripe made of the ITO thin film 12 is formed. next,
The glass substrate was ultrasonically cleaned using acetone and isopropyl alcohol, dried, and transferred to a vacuum deposition device for forming an organic film. First, α-NPD [N, N′-diphenyl-N, N′-bis (naphthyl) -1,1′-biphenyl-4,4′-diamine] purified by a recrystallization method as a hole-transporting material has a thickness of 35 nm. To form an organic hole transport layer 13 by vapor deposition at a vapor deposition rate of 0.2 nm / sec.

Next, DMPABT placed in another crucible in the same vacuum apparatus as a light emitting material was vapor-deposited at a rate of 0.01 n.
Evaporated to a thickness of 3 nm at m / sec to form the DEPABT layer 1
4 is formed. Further subsequently, purified PBD [2- (4-biphenylyl) -5- (4-tert-butylphenyl)-was placed in another crucible as an electron transport material.
1,3,4-oxadiazole] in the same manner with a vapor deposition rate of 0.
An organic electron transport layer 15 was obtained by forming the film with a thickness of 40 nm at 3 nm / sec. Next, this substrate was transferred to a vacuum apparatus for metal vapor deposition, and magnesium (Mg) and silver (Ag) were co-deposited at a vapor deposition rate ratio of 10: 1 to obtain a thickness of 100 n.
A metal electrode layer 16 as a negative electrode of m is formed.

When a voltage was applied between both electrodes of the organic EL element thus formed, light emission was generated from the crossed portion (2 mm × 2 mm area) of both electrodes, and the light emission observed from the glass substrate 11 side was obtained. The emission was near infrared light having a peak at a wavelength of 700 nm. It was found that the novel light emitting material DMPABT thus configured is a material that emits fluorescence having a peak at a wavelength of 790 nm. DMPA
In the organic EL device formed by laminating BT between the hole transport layer and the electron transport layer, near infrared light emission having a peak at a wavelength of 700 nm was obtained. This is because the holes injected from the positive electrode and conducted in the hole transport layer are recombined with the electrons injected from the negative electrode and conducted in the electron transport layer, and the energy excites the DMPABT to generate light emission. It is considered to be a thing.

Next, a fourth embodiment of the present invention will be described. An organic EL device was produced by the same method and conditions as in Example 2 except that DMPABT was used as the light emitting material. Therefore, the manufactured laminated structure has an ITO electrode, a TPD thin film layer that is a hole transport layer, DMPABT and A
The order is the co-deposited thin film layer with lp and the Mg electrode.

A voltage was applied between both electrodes of the organic EL device thus constituted and the emission spectrum was measured. As a result, near infrared emission having a peak at a wavelength of 700 nm was obtained. Further, when the applied voltage-luminance luminance characteristic was measured, a characteristic curve similar to that in the case of the second example in which the light emission sharply rises from around 8 V was obtained. As described above, in the organic EL device in which the co-evaporated film of the novel light emitting material DMPABT and the electron transport material is formed on the hole transport layer, the wavelength of 70
Near-infrared emission having a peak at 0 nm was obtained. In addition,
The present invention is not limited to the above embodiments, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, an organic EL element capable of emitting red light can be provided by using a novel light emitting material. Especially,
Near-infrared light emission having a peak in the wavelength range of 600 to 800 nm was obtained from the novel light emitting material.

[Brief description of drawings]

FIG. 1 is a diagram showing a light emitting characteristic of a material of an organic EL device showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an absorption spectrum of a material of the organic EL element showing the first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional configuration diagram of an organic EL element showing a first embodiment and a third embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of an organic EL device showing a second embodiment of the present invention.

FIG. 5 is a diagram showing characteristics of an organic EL element showing a second embodiment of the present invention.

FIG. 6 is a diagram showing the light emission characteristics of the material of the organic EL device showing the third embodiment of the present invention.

[Explanation of symbols]

11 Glass Substrate 12 Transparent Electrode Layer (ITO Thin Film) as Positive Electrode 13 Organic Hole Transport Layer 14 DEPABT Layer 15 Organic Electron Transport Layer 16 Metal Electrode Layer as Negative Electrode 20 Coevaporation of Light Emitting Material DEPABT and Electron Transport Material Alp Thin film layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Saito 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (7)

[Claims] 1. An organic EL device formed on a transparent substrate in the order of at least a transparent electrode layer serving as an anode, an organic EL thin film layer composed of one or more organic thin film layers, and a metal electrode layer serving as a cathode. Wherein the organic EL thin film layer includes at least one layer containing a nitrobenzothiazolylazo compound represented by the following chemical formula [1]. Embedded image 2. The organic EL device according to claim 1, wherein
The organic EL thin film layer has a three-layer structure in which a hole transporting thin film layer, a thin film layer made of the compound represented by the chemical formula [1], and an electron transporting thin film layer are laminated in this order. element. 3. The organic EL element according to claim 1,
The organic EL thin film layer has a two-layer structure in which a hole transporting thin film layer and a co-deposited film of the compound represented by the chemical formula [1] and an electron transporting compound are laminated in this order. element. 4. In an organic EL device, the organic EL thin film layer is a three-layer structure in which a hole transporting thin film layer, a thin film layer made of a compound represented by the following chemical formula [2], and an electron transporting thin film layer are laminated in this order. An organic EL device having a structure. Embedded image 5. In an organic EL device, the organic EL thin film layer is a two-layer structure in which a hole transporting thin film layer and a co-evaporated film of a compound represented by the chemical formula [2] and an electron transporting compound are laminated in this order. An organic EL device having a structure. 6. In an organic EL device, the organic EL thin film layer is a three-layer structure in which a hole transporting thin film layer, a thin film layer made of a compound represented by the following chemical formula [3], and an electron transporting thin film layer are laminated in this order. An organic EL device having a structure. Embedded image 7. In an organic EL device, the organic EL thin film layer is formed by laminating a hole transporting thin film layer and a co-deposited film of a compound represented by the formula [3] and an electron transporting compound in this order.
An organic EL device having a layered structure.