JPH1036831A - EL device - Google Patents

Abstract

[PROBLEMS] To easily obtain an organic electroluminescent device having a thermally stable thin film structure and excellent characteristics. A transparent first electrode, an organic layer mainly containing an organic compound which emits light by application of a voltage, are provided on a transparent substrate;
In an electroluminescent element formed by sequentially laminating a second electrode and a second electrode,
The organic layer includes an aromatic compound molecule containing at least one oxadiazole ring, and the aromatic compound molecule has a branched structure and / or a non-planar structure in the molecule. The aromatic compound molecule has a structure in which an aromatic compound is bonded across an oxadiazole ring. Therefore, crystallization of the organic layer is prevented and an amorphous phase is formed, so that a stable and uniform thin film can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electroluminescent device having an organic layer. Since the electroluminescent element is a planar light emitting body capable of electrically emitting light, it can be used as a display device such as a front display of an automobile or a backlight of a liquid crystal display.

[0002]

2. Description of the Related Art An electroluminescent device has a pair of electrodes attached to a solid organic compound having strong fluorescence, and emits light by applying a voltage. In general, an electroluminescent device includes a transparent electrode (ITO), an organic layer as a light emitting layer made of a solid organic compound having strong fluorescence, and a metal (M) on a transparent glass substrate.
g) electrodes are sequentially stacked. The principle of light emission of this electroluminescent device is as follows. When holes are injected from the anode and electrons are injected from the cathode, the injected holes and electrons move through the solid, collide and recombine, and disappear. The energy generated by the recombination is used to generate the excited state of the light-emitting molecule and emits fluorescence.

[0003] Such an electroluminescent device has no limitation on the viewing angle, can operate at a low voltage and can respond at high speed, and has a higher display performance than other display devices such as a liquid crystal, a plasma display, and an inorganic electroluminescent device. Has excellent characteristics as. However, it has been pointed out that the electroluminescent device in which the light emitting portion is formed of an organic layer has a short life. One of the reasons why the life of the electroluminescent device is short is that there is a problem of deterioration and deterioration due to crystallization of organic substances (hole transporting molecules).
That is, peeling occurs at the junction interface of the element due to heat generation of the element at the time of driving, the crystal structure of the organic substance in the organic layer changes due to heat, and the organic substance itself deteriorates,
The organic layer may be thermally degraded.

In order for an organic electroluminescent device to emit light efficiently, molecules having a hole transporting function, a light emitting function, and an electron transporting function are indispensable. These are used for the organic EL element in a form of a single substance or dispersed in a matrix. In order to extend the life of the organic EL element and improve heat resistance, these molecules must form a stable amorphous film. . A molecule used as a hole transport material has a stable amorphous layer as seen in TPD (N, N'-diphenyl-N, N'-ditolylbenzidine) which is a material typically used for an organic EL device. Excellent materials to form are known.

On the other hand, molecules used for an electron transporting material of an organic electroluminescence device are mainly found in Alq3 (a kind of aluminoquinol) (Tang et, al., Appl. Phys. Let.
t., 51, 913 (1987)) Metal complex materials and oxadiazole materials proposed by Tsutsui et al. (Tsutsui et al., Nikka Kagaku., 11, 1540 (1991)) . These materials are
It is deposited as an electron transporting layer on the hole transporting layer formed on the ITO substrate, and is used as an element constituting an organic electroluminescent device. Since an evaporation process is applied to fabricate an organic EL device, molecules that can be used are necessarily limited to low molecules.

[0006] Among metal complex-based materials, there are materials having an extremely high electron transport function such as Alq3 and are stable, but the number of metal complex materials that can be used practically is small.
On the other hand, various derivatives of oxadiazole-based compounds have been synthesized and their properties have been examined as seen in the examples of Tsutsui et al. It has been clarified that all of these compounds have an electron transport function. However, oxadiazole-based compounds tend to crystallize, for example,
PBD (2- (4
-Biphenylyl) -5- (4-t-butylphenyl)-
When an organic EL device is manufactured by an evaporation method using (1,3,4-oxadiazole), PBD is crystallized immediately after the evaporation, and the smoothness of the evaporated film is impaired. Therefore, there is a problem that stability is low in using the PBD as the electron transport layer.

[0007] One of the means for producing a thin film which is so low in crystallinity that it can be used as an electron transporting layer of an organic electroluminescent device is to polymerize the electron transporting molecule of interest. . Such an example is often found in a polymerized hole transport function molecule. For example, a polymer-dispersed electroluminescent device using polyvinylcarbazole as a matrix (Applied Physics 61 (10), 1044 (1992)) or a polymer containing triphenylamine or TPD in the side chain (Polymer Papers, 52, ( 4) 216 (1995)), and a material in which a hole transporting function molecule is introduced into the main chain of polycarbonate (Japanese Patent Laid-Open No. 5-205).
247458) is known.

However, the polymer type organic EL device manufactured in this manner is difficult to remove impurities (for example, inorganic salts, solvents, etc.) mixed during the polymerization, Since it is impossible or difficult to remove a chemical defect incorporated in the polymer chain, there is a problem that the properties and the life are adversely affected.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to suppress crystallization in a low molecular state without polymerizing an electron transporting molecule. An object of the present invention is to easily obtain an organic electroluminescent device having a thin film structure and excellent characteristics.

[0010]

According to the electroluminescent device of the present invention, a transparent first electrode, an organic layer mainly composed of an organic compound which emits light by applying a voltage, and a second electrode are formed on a transparent substrate. In the electroluminescent device formed by sequentially stacking, the organic layer includes an aromatic compound molecule containing at least one oxadiazole ring, and the aromatic compound molecule has a branched structure and / or a non-planar structure in the molecule. It is characterized by the following.

It is desirable that the aromatic compound molecule has a structure in which an aromatic compound is bonded with an oxadiazole ring interposed therebetween. The non-planar structure of the aromatic compound molecule is a compound in which triphenylamine, biphenyl, and aromatic rings are connected to each other, and the aromatic ring has a substituent at an ortho position of the connecting portion and the aromatic rings cannot maintain a planar structure. Desirably.

The aromatic compounds include aromatic hydrocarbons such as phenyl group, naphthyl group, anthranyl group and biphenyl group, nitrogen-containing aromatic compounds such as triphenylamine, oxygen-containing aromatic compounds such as diphenyl ether, pyridine and bipyridine. And heterocyclic compounds such as indole, quinoline, thiophene and furan.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The electroluminescent device of the present invention comprises a transparent first substrate, a transparent first electrode, an organic layer, and a second electrode, which are laminated in this order. is there. The aromatic compound molecule contained in the organic layer has two aromatic groups, A, on the oxadiazole ring represented by the general formula (1).
The compound has a structure in which r ₁ and Ar ₂ are bonded, and at least one of Ar ₁ and Ar ₂ has a non-planar or branched structure.

[0014]

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In the formula, Ar ₁ and Ar ₂ are, for example, aromatic compounds such as phenyl, naphthyl, anthranyl and biphenyl; oxygen-containing aromatic compounds such as diphenyl ether; and nitrogen-containing compounds such as triphenylamine. Examples include aromatic compounds, oxygen-containing aromatic compounds such as diphenyl ether, and heterocyclic compounds such as pyridine, bipyridine, indole, quinoline, thiophene, and furan.

Further, a compound in which these are linked or a compound in which they are condensed may be used. Examples of a unit for introducing a non-planar structure into an aromatic compound include triphenylamine, biphenyl, and a structural unit in which aromatic rings are connected to each other and an ortho position of a connecting portion is substituted by a substituent (methyl, phenyl, or the like) (for example, 2,2'-dimethylbiphenyl). These are molecular structures in which aromatic rings cannot maintain the same plane due to the presence of the ortho-position substituent. For example, triphenylamine represented by the formulas (2) and (3),
When a methyl group at the ortho-position of biphenyl and an oxadiazole ring represented by the formulas and formulas (5) and (6) are present, a compound in which a phenanthrene ring is bonded to the oxadiazole ring as shown in the formula (6) is exemplified.

[0017]

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[0018]

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[0019]

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[0020]

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[0021]

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The unit for introducing a branched structure into the aromatic compound may be a polysubstituted aromatic compound, for example, an aromatic hydrocarbon such as phenyl, naphthyl, anthranyl or biphenyl, or a nitrogen-containing aromatic compound such as triphenylamine. Group-containing compounds, oxygen-containing aromatic compounds such as diphenyl ether, and compounds having a structure in which three or more heterocyclic compounds such as pyridine, bipyridine, indole, quinoline, thiophene, and furan are substituted. Further, a compound in which these are linked or a compound in which they are condensed may be used. For example, a compound having a structure in which a phenyl group trisubstituted as shown in Chemical Formula 7, and a biphenyl group represented by Chemical Formula 8 or Chemical Formula 9 is substituted by 4 is given.

[0023]

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[0024]

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[0025]

Embedded image A substituent may be introduced into the electron transporting molecule, for example, an alkyl group, an allyl group, an aryl group, an amino group, an alkoxy group, an allyloxy group, an aryloxy group,
And substituents such as a thioalkyl group, a thioallyl group, a sulfone group, a phosphoryl group, a carboxyl group, a carbonyl group, a thiocarbonyl group, an imino group, a hydroxy group, an amide group, an alkoxysilyl group, and a cyano group.

An object of the present invention is to suppress crystallization in a low molecular state without increasing the molecular weight of the electron transporting molecule.
For this purpose, an aromatic compound molecule bonded to an oxadiazole ring, which has been conventionally planar and linear, has a branched or non-planar structure. It is considered that by forming the aromatic compound molecule into a branched structure, crystallization is less likely to occur as the symmetry of the molecule is reduced. Further, it is considered that the non-planar shape suppresses the overlapping of molecular planes required in the process of crystal formation, thereby suppressing crystallization. As a result, even when applied to a polymer-dispersed EL device, a stable organic EL device that does not precipitate crystals even when dispersed at a high concentration in a polymer matrix can be manufactured.

Alternatively, a mixture obtained by dispersing a molecule having a hole transporting function, an electron transporting function, and a luminescent function in the above-mentioned electron transporting molecule may be included. Here, the dispersed molecules are not limited to low molecules and may be high molecules. The organic layer constituting the organic layer of the electroluminescent element may be a single layer, but it is a laminated film of a thin film formed by a coating method or an evaporation method and a thin film containing the polymer. Is also good.

The organic layer containing the polymer may be formed by a coating method such as a spin coating method or a dip coating method, or may be formed by a vacuum evaporation method.

[0029]

Embodiments will be described below with reference to embodiments. (Example 1) Synthesis of OXD1 (Formula 7) Synthesis of t-butyl benzoic acid hydrazide 120.55 g of t-butyl benzoic acid ethyl ester, 207 g of hydrazine hydrate, and 320 g of dry ethanol were mixed, and 100 ° C. under a nitrogen atmosphere. For 6 hours. The mixture was concentrated to dryness, dissolved in 200 ml of ethyl ether, and washed twice with 100 ml of water. After removing the ethyl ether, the residue was recrystallized from benzene and dried in vacuo to obtain 91.37 g (yield 81%) of t-butylbenzoic acid hydrazide.

2.0 g of t-butylbenzoic hydrazide,
1.11 g of sodium carbonate and 8 g of dioxane are mixed,
The mixture was stirred under a nitrogen atmosphere. Under stirring, a solution of trimesic acid trichloride (0.92 g) in dioxane (5 g) was added for about 10 minutes.
Dropped over minutes. After heating at 90 ° C for 3 hours,
0 ml of water was added, and the precipitate was separated by filtration and washed with water. 6 products
Vacuum drying was performed at 0 ° C. to obtain 2.4 g of the condensed compound 1.

A mixture of 2.2 g of the condensed compound 1, 6.6 g of thionyl chloride and 0.13 g of pyridine was stirred and refluxed for 3.5 hours under a nitrogen atmosphere. The mixture was allowed to cool and concentrated, and the precipitate was separated by filtration, washed with water and dried in vacuo. The product was purified by silica gel column chromatography to obtain 800 mg of OXD1 of the formula (7). (Example 2) Synthesis of OXD2 (Formula 8) 66.2 g of 5-aminoisophthalic acid, 110 ml of 48% hydrobromic acid, and 100 ml of water were mixed and mechanically stirred at 4 ° C. 26.35 g of sodium nitrite in water (3
(50 ml) solution was added dropwise over 1.5 hours and then stirred for 28 hours. This suspension was mixed with 62.8 g of copper (I) bromide and 4
1. To a suspension of 30 ml of 8% hydrobromic acid at 4 ° C. under stirring.
It was added dropwise over 5 hours. After stirring for 30 minutes, a further 80
Stirred at 30 ° C for 30 minutes. After cooling, the precipitate was separated by filtration, washed with water, vacuum-dried at 50 ° C for impurity analysis, further washed with hot dilute hydrochloric acid to remove impurities, filtered, washed with water, and vacuum-dried to give 76 g of 5-bromoisophthalic acid. I got

14.37 g of 5-bromoisophthalic acid and 9.38 g of sodium hydroxide were mixed and dissolved in 45 g of water. This PdCl ₂ · 2NaCl palladium chloride (I
I) 0.11 g of sodium was suspended. A mixture of 16.9 g of water, 3.76 g of methanol, and 5.4 g of formic acid was added dropwise with stirring while the suspension was heated from room temperature to 90 ° C. over 20 minutes. The mixture was heated and stirred at 90 ° C. for 3 hours. The crystals precipitated after standing for 2 days were collected by filtration. This was dissolved in an aqueous sodium hydroxide solution, the solution was filtered, and the filtrate was adjusted to pH 1 by adding concentrated hydrochloric acid. The solution was cooled to 5 ° C., left for 30 minutes, and the precipitate was collected by filtration. 8 products
Vacuum dried at 0 ° C. and 0.61 g of biphenyl-3,5,5
3 ′, 5′-Tetracarboxylic acid was obtained.

0.61 g of biphenyl-3,5,3 ', 5'-tetracarboxylic acid was suspended in 5 g of thionyl chloride and 0.05 g of DMF (dimethylformamide), and the mixture was stirred and refluxed under a nitrogen atmosphere for 3.5 hours. After allowing to cool, evaporate, and vacuum dry at room temperature, biphenyl-3,5,3 ',
5′-Tetracarbonyl chloride was obtained. Subsequently, 1.42 g of t-butylbezoylhydrazide were added to the above product.
And 0.88 g of sodium carbonate and 10 g of dioxane were added, and the mixture was stirred with a mechanical stirrer at 90 ° C. for 6 hours under a nitrogen atmosphere. After standing to cool, wash with water, vacuum dry at 50 ° C,
3.01 g of the condensed compound 2 was obtained.

3.01 g of this condensed compound 2 was suspended in 10 g of thionyl chloride and 0.2 g of pyridine, and heated and stirred at 80 ° C. under a nitrogen atmosphere. Five hours later, the mixture was poured into ice water, and the precipitate was filtered and washed with water. Vacuum dried at 50 ° C and purified by silica gel column chromatography to give 750m
g of OXD2 (formula 8) was obtained. Example 3 Synthesis of OXD3 (Formula 2) Synthesis of tri (4-ethoxycarbonylphenyl) amine 7.48 g of ethyl 4-aminobenzoate, 25.2 g of ethyl 4-iodobenzoate, potassium carbonate 1
3.8 g, copper 0.5 g, copper oxide (I) 0.5 g, 18 crown 0.4 g, and xylene 40 g were put in a flask equipped with a reflux tube and a dehydration tube, and heated at 190 ° C. for 40 hours under a nitrogen atmosphere. . After cooling, the mixture was filtered and the residue was washed with chloroform. The filtrate and the washing solution were mixed, washed with water, dried over sodium sulfate, and then evaporated. The product is recrystallized from ethanol and dried under vacuum to 16.79 g
To give tri (4-ethoxycarbonylphenyl) amine.

Synthesis of tri (4-hydroxycarbonylphenyl) amine Tri (4-ethoxycarbonylphenyl) amine
02 g, 15 g of potassium hydroxide, 80 g of water and 130 g of ethanol were mixed and heated and stirred at 100 ° C. for 10 hours.
After standing to cool, the mixture was filtered and washed with water.
Was set to 1. After standing for 1 hour, the precipitate was filtered and washed with water.
Vacuum dried at ℃ to obtain 9.01 g of tri (4-hydroxycarbonylphenyl) amine. 1. Synthesis of tri (4-chlorocarbonylphenyl) amine tri (4-hydroxycarbonylphenyl) amine
0 g, 14 g of thionyl chloride and 0.05 g of DMF were mixed, and the mixture was refluxed and stirred under a nitrogen atmosphere for 3 hours. After evaporating the reaction solution, it was dried under vacuum to obtain tri (4-chlorocarbonylphenyl) amine. This product and t-
3.06 g of butyl benzoic acid hydrazide, 1.8 g of sodium carbonate and 20 g of dioxane were mixed, and the mixture was stirred at 110 ° C. for 5 hours under a nitrogen stream. 400 ml of water was added to the reaction solution, and the precipitate was filtered and washed with water. 3. Vacuum dry at 80 ° C.
56 g of the condensed compound 3 was obtained.

4.5 g of this condensed compound 3, 20 g of thionyl chloride and 0.4 g of pyridine were mixed, and mixed under nitrogen atmosphere.
The mixture was stirred under reflux for an hour. After cooling, the mixture was poured into 50 ml of ice water. The precipitate was filtered, washed with water, dried and purified by silica gel column chromatography to obtain 4.18 g of OXD3.
(Formula 2) was obtained. Example 4 Synthesis of OXD4 (Formula 3) Synthesis of Naphthalic Acid Methyl Ester 11.4 g of pyridine and 40 g of methanol were mixed and cooled with ice. To this, 25 g of naphthalic acid chloride was added dropwise over 15 minutes. After stirring at room temperature for 2 hours, the mixture was heated at 50 ° C. for 1 hour. Subsequently, 1 ml of concentrated hydrochloric acid and 100 ml of ice water were added, and the mixture was extracted twice with 100 ml of chloroform. The chloroform layer was washed twice with 100 ml of water, dried over sodium sulfate, evaporated and dried under vacuum to obtain 26.4 g of naphthaleic acid methyl ester.

26.4 g of methyl naphthalate,
47.1 g of hydrazine / hydrate and 66 g of ethanol were mixed and heated and stirred at 100 ° C. for 5 hours under a nitrogen atmosphere. The reaction solution was evaporated, the precipitate was filtered, washed with water and washed with water.
Vacuum dried at 0 ° C. Recrystallize from ethanol 19.
5 g of naphthaic hydrazide were obtained. 2.0 g of tri (4-hydroxycarbonylphenyl) amine, 14 g of thionyl chloride and 0.05 g of DMF were mixed, and the mixture was refluxed and stirred under a nitrogen atmosphere for 3 hours. The reaction solution was evaporated and dried under vacuum to synthesize tri (4-chlorocarbonylphenyl) amine. This product was combined with 2.97 g of naphthaic acid hydrazide, 1.8 g of sodium carbonate and 20 of dioxane.
g were mixed and stirred at 110 ° C. for 5 hours under a nitrogen stream.
400 ml of water was added, and the precipitate was filtered and washed with water. 80
Vacuum drying was performed at 4.degree. C. to obtain 4.47 g of the condensed compound 4.
A mixture of 4.5 g of the condensed compound 4, 20 g of thionyl chloride and 0.4 g of pyridine was refluxed and stirred under a nitrogen atmosphere for 4 hours. After cooling, the reaction solution was poured into 50 ml of ice water. The precipitate was filtered, washed with water, dried in vacuo, and then purified by silica gel column chromatography to obtain 4.23 g of OXD4 (Chemical Formula 3).
Formula) was obtained.

Example 5 Measurement of DSC For measurement of DSC, TAC7 / D manufactured by PerkinElmer Co. was used.
The temperature was raised at 10 ° C./min using X. Table 1 shows the measurement results of OXDs 1 to 4. All show no melting point of crystal and high T
It is an amorphous material having a g (transition temperature) and can be used as an electron transporting material having excellent heat resistance of an EL element.

[0039]

[Table 1] (Comparative Example) Measurement of DSC As a comparative sample, BND (bisnaphthyloxadiazole), which is a planar and linear molecule, was similarly subjected to DSC measurement. As a result, the melting point peak (240 ° C). That is, it was found that, unlike the compounds of Examples OXD1 to OX4, the simple substance could not be used for the electron transporting material of the organic EL device.

Example 6 Production of Polymer-Dispersed EL Element This polymer-dispersed EL element was composed of a glass substrate 1 on which an ITO film 2 of a transparent electrode was formed as shown in a schematic sectional view of FIG.
The organic layer 3 is formed on the ITO film 2, and the Mg: Ag electrode 4 is formed on the upper surface of the organic layer 3.

The organic layer 3 was produced as follows.
Matrix and hole transport molecule PVK (polyvinyl carbazole) 130 mg, electron transport molecule (OXD1-4)
130 mg and 2.7 mg of luminescent molecule coumarin 6 were dissolved in 7.6 g of dichloroethane. Using this solution, the organic layer 3 was formed by applying a film to a thickness of about 100 nm on the glass substrate 1 on which the ITO film 2 was formed by dip coating. Subsequently, M
The g: Ag electrode 4 was formed at a ratio of Mg: Ag = 10: 1 to a thickness of 180 nm by a binary vapor deposition method.

Appearance of Device In each organic layer 3 of the formed device, OXD1 was slightly clouded, but OXD2 to OXD4 did not show such clouding. It is believed that such an improvement in the dispersion stability of the electron transport molecule is due to the introduction of a branched, non-planar aromatic compound into the oxadiazole ring.

Comparative Example 2 As a comparative example, when BND (bisnaphthyloxadiazole) was used as the electron transporting material in the above polymer dispersed EL device, the device was prepared by adding 50% by weight of the electron transporting molecule. Upon fabrication, the organic layer was clouded by the electron transport material. (Example 7) Evaluation of device The evaluation of the polymer-dispersed EL device manufactured in Example 6 was performed in a nitrogen atmosphere. The initial characteristics were obtained by increasing the voltage of each element by 1 V about every 5 seconds and measuring the luminance and current density at each voltage. Brightness is Minolta nt
Measured using -1 °.

FIG. 2 is a graph showing the relationship between current density and luminance, and FIG. 3 is a graph showing the relationship between voltage and current density. The maximum luminance (the maximum value of each data series in FIG. 2) is OXD4 (104
0 cd / m ² ), OXD3 (420 cd / m ² ), OX
D2 (320 cd / m ² ), OXD1 (330 cd / m ² )
² ) The order was as follows. As can be seen from the luminance plot at the current density of 10 ² , the luminance is O
XD4>OXD3>OXD2> OXD1.
Luminous efficiency (/ lm / w) = π × (brightness) ÷ [(voltage) ×
(Current density)] in the same order. The driving voltage is shown in FIG.
As can be seen from the graph, OXD4 was the lowest, followed by OXD1, OXD2 and OXD3. As a result, OXD4 has the best element characteristics, and then OXD2
OXD3 and OXD1.

(Comparative Example 3) When the electron transporting material is polymerized Hole transporting molecule (polyvinyl carbazole (PVK))
Of copolymer (50:50 molar ratio) of styrene and PPBD 660 mg of vinyl PBD, 34 of 9-vinylcarbazole
0 mg and 3 mg of a polymerization initiator AIBN (azobisisobutyronitrile) were dissolved in 15 g of benzene, and the reaction vessel was degassed and sealed, followed by heat polymerization at 60 ° C. for 40 hours. After cooling, reprecipitation was performed 5 times with benzene-methanol,
Lyophilization from benzene gave a PVK-PPBD copolymer.

Preparation and Evaluation of Device (Polyvinylcarbazole (PVK)) PVK-PPB
Dissolve 250 mg of D copolymer and 2.5 mg of coumarin 6 in 7.6 g of dichloroethane and put 100 n on the ITO electrode.
m to dip coat. Metal electrodes are Mg and Ag
Was manufactured by a binary co-evaporation method. Metal composition is Mg: A
g = 10: 1, deposition rate was 150 ° / min. At 150
nm. This element is 31 V, 45 mA / cm ²
In this case, light was emitted at a luminance of 19 cd / m ² . As shown in Table 2, the luminance was not sufficient as compared with the device prepared in Example 7.

[0047]

[Table 2] (Example 8) Fabrication of vapor deposition laminated type element TPD (N, N'-diphenyl-) was formed on an ITO glass substrate.
Tolyl-benzidine) 70 nm, OXD1 70 nm
Evaporated. Subsequently, a Mg: Ag electrode was formed in a thickness of 180 nm by a binary deposition method at a ratio of 10: 1.

Evaluation of device The device was evaluated in a nitrogen atmosphere. The initial characteristics were obtained by increasing the voltage of the device by 1 V every about 5 seconds and measuring the luminance and current density at each voltage. Luminance was measured using Minolta nt-1 °. This vapor deposition lamination type element showed a luminance of 414 cd / m ^{2 at} 22v.

(Comparative Example 4) Fabrication of vapor deposition laminated device Fabrication of device using PBD which is a planar aromatic compound instead of OXD1 of Example 8 TPD (N, N'-diphenyl) was formed on an ITO glass substrate. −
70 nm of tolyl-benzidine) and PBD (2- (4-
Biphenylyl) -5- (4-t-butylphenyl)-
1,3,4-oxadiazole) was deposited to a thickness of 70 nm.
Subsequently, a Mg: Ag electrode was formed in a thickness of 180 nm by a binary deposition method at a ratio of 10: 1.

Evaluation of Device The device was evaluated in a nitrogen atmosphere. The initial characteristics were obtained by increasing the voltage of the vapor-deposited laminated device by 1 V approximately every 5 seconds and measuring the luminance and current density at each voltage. Luminance was measured using Minolta nt-1 °. This vapor-deposited laminated element did not emit light due to dielectric breakdown.

[0051]

According to the present invention, when a low molecular weight compound is used, purification of the electron transporting compound is easier than in the method of polymerizing the electron transporting molecule. It is possible to obtain an organic EL device which is less affected by an object, has excellent characteristics, and has excellent durability.

In addition, compared to conventional electron transport molecules, the aromatic compound bonded to oxadiazole has a branched or non-planar structure, which causes deterioration of the organic EL device such as crystallization or precipitation in a matrix. Problem is less likely to occur. On the other hand, a thin film of PBD, which is a flat, linear low-molecular-weight electron transport material, crystallizes in a few days, and cannot retain the film form.
No crystallization is observed after several months. Therefore, according to the present invention, an organic electroluminescent device having excellent durability and excellent light emitting characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an electroluminescent device used for evaluation in this example.

FIG. 2 is a graph showing a relationship between current density and luminance of the organic EL device manufactured in this example.

FIG. 3 is a graph showing a relationship between current density and voltage of the organic EL device manufactured in this example.

[Explanation of symbols]

1. 1. glass substrate, 2. transparent electrode; 3. organic layer;
Mg-Ag electrode,

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Shizuto Tokito, Inventor 41, Chukoku Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 Toyota Toyota Central R & D Laboratories Co., Ltd. No. 41, Changchun Yokomichi 1 Toyota Central Research Laboratory Co., Ltd.

Claims (4)

[Claims] 1. An electroluminescent device comprising a transparent substrate and a transparent first electrode, an organic layer mainly composed of an organic compound emitting light by application of a voltage, and a second electrode laminated in this order on the transparent substrate. An electroluminescent device, wherein the layer includes an aromatic compound molecule containing at least one oxadiazole ring, and the aromatic compound molecule has a branched structure and / or a non-planar structure in the molecule. 2. The electroluminescent device according to claim 1, wherein the aromatic compound molecule has a structure in which an aromatic compound is bonded with an oxadiazole ring interposed therebetween. 3. The non-planar structure of the aromatic compound molecule is such that triphenylamine, biphenyl, or aromatic rings are connected to each other, and the aromatic ring has a substituent at an ortho-position. 3. The electroluminescent device according to claim 1, wherein the electroluminescent device is caused by any one of the compounds which cannot maintain a planar structure. 4. The aromatic compound molecule includes a phenyl group, a naphthyl group, an anthranyl group, a biphenyl group, triphenylamine, diphenyl ether, pyridine, bipyridine,
The electroluminescent device according to any one of claims 1 to 3, wherein the device is selected from indole, quinoline, thiophene, and furan.