JPH1154284A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an element having an output of high luminance by containing at least one kind selected from among specific compounds in at least one layer of layers formed of one or a plurality of organic compounds which are held between a pair of electrodes. SOLUTION: A compound is expressed by a formula, where R<1> -R<16> each independently represents a hydrogen atom, a halogen atom, a cyano group, a nitro group, a substituted or unsubstituted amino group, alkyl group, alkoxy group, ester group, aryl group, or heterocyclic group. As a specific example of substituents, there are a halogen atom, a cyano group and a nitro group. A fluorine atom is used as a halogen atom. A substitutional amino group such as an amino group and a dimethylamine group is used as the substituted or unsubstituted amino group. A methyl group and an ethyl group are used as the substituted or unsubstituted alkyl group. A methoxy group and an ethoxy group are used as the substituted or unsubstituted alkoxy group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device having a light-emitting layer made of a light-emitting substance and capable of directly converting electric field applied energy to light energy by applying an electric field.

More specifically, unlike conventional incandescent lamps, fluorescent lamps, light-emitting diodes, etc., they have the features of large area, high resolution, thin, lightweight, high-speed operation, and complete solid-state devices.
The present invention relates to an electroluminescent device used for an electroluminescence (EL) panel which may satisfy a high demand.

[0003]

2. Description of the Related Art An electroluminescent phenomenon of an organic material was observed in an anthracene single crystal by Pope et al. In 1963 (J. Chem. Phys. 38 (1963) 2).
042), followed by Helfrich (He) in 1965.
lfinch) and Schneider
Has succeeded in observing a relatively strong injection type EL by using a solution electrode system having high injection efficiency (Phys. Re.
v. Lett. 14 (1965) 229).

Since then, US Pat. No. 3,172,862
No. 3,173,050, U.S. Pat.
0,167, J.M. Chem. Phys. 44 (196
6) 2902; Chem. Phys. 50 (196
9) 14364; Chem. Phys. 58 (19
73) 1542, or Chem. Phys. Let
t. 36 (1975) 345 etc.
Studies have been conducted on the formation of an organic luminescent material with a conjugated organic host material and a conjugated organic activator having a fused benzene ring. Naphthalene, anthracene, phenanthrene, tetracene, pyrene, benzopyrene, chrysene, picene, carbazole, fluorene, biphenyl, terphenyl,
Triphenylene oxide, dihalobiphenyl, trans-stilbene, 1,4-diphenylbutadiene and the like are shown as examples of organic host materials, and anthracene, tetracene, pentacene and the like are mentioned as examples of activators. However, each of these organic luminescent substances is 1 μm
It existed as a single layer having a thickness exceeding the above, and a high electric field was required for light emission. For this reason, research on a thin film element by a vacuum deposition method has been advanced (for example, Thin Solid).
Films 94 (1982) 171, Polyme
r 24 (1983) 748, Jpn. J. Appl.
Phys. 25 (1986) L773). However, although thinning was effective in reducing the driving voltage, it did not lead to obtaining a high-brightness element on a practical level.

However, in recent years Tang et al. (App
l. Phys. Lett. 51 (1987) 913 or U.S. Pat. No. 4,356,429), devising an EL element in which two extremely thin layers (a charge transport layer and a light emitting layer) are stacked by vacuum deposition between an anode and a cathode, and low driving is performed. High brightness was achieved with voltage. This type of stacked organic EL device has been actively studied thereafter, and is disclosed in, for example, JP-A-59-194393.
No. 4,539,507, Japanese Unexamined Patent Publication No.
194393, U.S. Pat. No. 4,720,432,
JP-A-63-264692, Appl. Phys
s. Lett. 55 (1989) 1467;
163188.

Further, Jpn. J. Appl. Phys
s. 27 (1988) L269. L713 reports a three-layered EL device in which the functions of carrier transport and light emission are separated from each other. In selecting a dye for the light-emitting layer that determines the emission color, the restrictions on carrier transport performance are relaxed, and the degree of freedom in selection is increased. It is also suggested that there is a possibility of improving the light emission by effectively confining holes and electrons (or excitons) in the central light emitting layer.

Although a vacuum evaporation method is generally used for producing a stacked organic EL device, it has been reported that a device having a considerably high brightness can be obtained by a casting method (for example, the 50th application). Proceedings of academic conference
006 (1989) and Proceedings of the 50th Annual Meeting of the Japan Society for Materials Science 1041 (1990)).

Further, even a mixed single-layer EL device formed by a dip coating method from a solution in which polyvinyl carbazole as a hole transporting compound, an oxadiazole derivative as an electron transporting compound, and coumarin 6 as a luminescent material has a considerably high luminous efficiency. Has been reported (eg,
Proceedings of the 38th Annual Conference of the Famous Relationships of the Lectures 1086 (19
91)). As noted above, recent advances in organic EL devices have shown remarkably widespread application possibilities.

[0009] However, the history of these researches is still short, and research on materials and devices has not yet been sufficiently performed. At present, there is still a problem in terms of durability, such as light output with higher luminance, a change over time due to long-term use, and deterioration due to an atmospheric gas containing oxygen or moisture. In addition, when considering application to full color display, etc., blue, green,
Problems such as diversification of emission wavelengths for accurately selecting a red emission hue have not yet been sufficiently solved.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art.
First, it is an object of the present invention to provide an electroluminescent device having an extremely high luminance light output. Secondly, it is an object of the present invention to provide an electroluminescent device having various emission wavelengths, exhibiting various emission hues, and being extremely durable. Third, it is an object of the present invention to provide an electroluminescent device which can be easily manufactured and can be provided at relatively low cost.

[0011]

That is, the present invention relates to an electroluminescent device having at least a pair of electrodes and one or more layers of an organic compound sandwiched between the pair of electrodes. At least one of the layers comprises at least one selected from compounds represented by the following general formula [1].

[0012]

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(Wherein R ^{1 to} R ¹⁶ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, a substituted or unsubstituted amino group, an alkyl group, an alkoxy group, an ester group, an aryl group, a heterocyclic ring, Represents a group.)

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An electroluminescent device according to the present invention is an electroluminescent device having at least a pair of electrodes comprising an anode and a cathode, and at least one organic compound layer sandwiched between the pair of electrodes. At least one of the layers comprising the organic compound contains at least one selected from compounds represented by the following general formula [1].

[0015]

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In the general formula [1], R ^{1 to} R ¹⁶ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, a substituted or unsubstituted amino group, an alkyl group, an alkoxy group, an ester group, and an aryl group. , Represents a heterocyclic group.

Specific examples of the above substituents are shown below.
Hydrogen, cyano, and nitro groups. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the substituted or unsubstituted amino group include an amino group and a substituted amino group such as a dimethylamino group, a dibenzylamino group, a diphenylamino group, and a morpholino group. Examples of the substituted or unsubstituted alkyl group include a methyl group, an ethyl group, an n-propyl group, and an iso group.
-Propyl group, phenethyl group, benzyl group and the like.

Examples of the substituted or unsubstituted alkoxy group include a methoxy group, an ethoxy group, a phenoxy group, a phenylmethoxy group and a phenylethoxy group. Examples of the substituted or unsubstituted ester group include a methyl ester group, an ethyl ester group, a phenyl ester group, a methyl phenyl ester group, and a nitrophenyl ester group.

Examples of the substituted or unsubstituted aryl group include a phenyl group, a toluyl group, a biphenyl group, a naphthyl group, an anthryl group, a pyrenyl group, an aminophenyl group and a dimethylphenyl group. Examples of the substituted or unsubstituted heterocyclic group include a heterocyclic group such as a pyridyl group, a thienyl group, a furyl group, a quinolyl group, a carbazolyl group, a methylpyridyl group, a propylthienyl group, and a cyanoquinolyl group.

Each of R ^{1 to} R ¹⁶ may be the same or different.

Next, typical examples of the compound represented by the general formula [1] will be given below. However, it is not limited to these compounds.

[0022]

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[0023]

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[0024]

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[0025]

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[0026]

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[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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[0033]

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[0034]

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[0035]

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[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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The electroluminescent device of the present invention has one or more organic compound layers sandwiched between an anode and a cathode, and at least one of the organic compound layers has the general formula [1] At least one compound selected from the group consisting of:

In the electroluminescent device of the present invention, the compound represented by the above general formula [1] is formed between the anode and the cathode by a vacuum deposition method, a solution coating method or the like. The thickness of the organic layer is thinner than 2 μm, preferably 0.5 μm or less, more preferably 0.05 to 0.5 μm.

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a sectional view showing an example of the electroluminescent device of the present invention. FIG. 1 shows a structure in which an anode 2, a light emitting layer 3 and a cathode 4 are sequentially provided on a substrate 1. The electroluminescent device used here is useful when it has a single hole transporting ability, electron transporting ability, and luminous performance, or when it is used by mixing compounds having the respective properties.

FIG. 2 is a sectional view showing another example of the electroluminescent device of the present invention. FIG. 2 shows a configuration in which an anode 2, a hole transport layer 5, an electron transport layer 6, and a cathode 4 are sequentially provided on a substrate 1. In this case, the light-emitting substance is a material having either a hole-transporting property or an electron-transporting property or both, and is used in combination with a simple hole-transporting substance or an electron-transporting substance having no light-emitting property. Useful in cases. In this case, the light emitting layer 3 is composed of the hole transport layer 5 and the electron transport layer 6.

FIG. 3 is a sectional view showing another example of the electroluminescent device of the present invention. FIG. 3 shows a structure in which an anode 2, a hole transport layer 5, a light emitting layer 3, an electron transport layer 6, and a cathode 4 are sequentially provided on a substrate 1. It separates the functions of carrier transport and luminescence, and is used in a timely combination with a compound having each of hole transport, electron transport, and luminescent properties. Since various compounds having different wavelengths can be used, the emission hue can be diversified. Further, it is also possible to effectively confine holes and electrons (or excitons) in the central light emitting layer to improve the light emission efficiency.

The compound represented by the general formula [1] used in the present invention is a compound having extremely excellent luminous characteristics as compared with the conventional compound, and may have any of the forms shown in FIGS. An electroluminescent element can also be used.

The compound represented by the general formula [1] used in the present invention has one or both of a hole transport property and an electron transport property depending on the structure.
In any of the embodiments shown in FIG. 3, two or more compounds represented by the general formula [1] may be used as necessary.

In the present invention, the compound represented by the general formula [1] is used as a component of the light-emitting layer. If necessary, a hole-transporting compound which has been studied in the electrophotographic photoreceptor field or the like may be used. Hitherto known hole-transporting luminescent compounds (for example, compounds shown in Tables 1 to 5)
Alternatively, an electron transporting compound or a conventionally known electron transporting luminescent compound (for example, compounds listed in Tables 6 to 9) can be used together.

Table 10 shows examples of dopant dyes. These dyes are capable of significantly improving the luminous efficiency and changing the luminescent color by doping a small amount of the dye into the light emitting layer. Used as 3

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

[0055]

[Table 7]

[0056]

[Table 8]

[0057]

[Table 9]

[0058]

[Table 10]

In the electroluminescent device of the present invention, the layer containing the compound represented by the general formula [1] and the layer made of another organic compound are generally formed into a thin film by vacuum deposition or by combining with an appropriate binder resin. Form.

The binder can be selected from a wide range of binder resins, for example, polyvinyl carbazole resin, polycarbonate resin, polyester resin, polyarylate resin, butyral resin, polystyrene resin, polyvinyl acetal resin, diallyl phthalate resin, acrylic resin , Methacrylic resin, phenolic resin, epoxy resin,
Examples include, but are not limited to, silicone resins, polysulfone resins, urea resins, and the like. These may be used alone or as a copolymer in one kind or as a mixture of two or more kinds.

The anode material preferably has a work function as large as possible. For example, nickel, gold, platinum, palladium, selenium, rhenium, iridium and alloys thereof, or tin oxide, indium tin oxide (ITO), copper iodide Is preferred. Further, a conductive polymer such as poly (3-methylthiophene), polyphenylene sulfide, or polypyrrole can also be used.

On the other hand, as a cathode material, silver, lead, tin, magnesium, aluminum, calcium, manganese, indium, chromium, or an alloy thereof having a small work function is used.

At least one of the materials used for the anode and the cathode is 50% in the emission wavelength region of the device.
Preferably, more than% of light is transmitted. Further, as the transparent substrate used in the present invention, glass, plastic film, or the like is used.

[0064]

The present invention will be described below in detail with reference to examples.

Example 1 A transparent support substrate was prepared by forming tin oxide-indium (ITO) on a glass substrate to a thickness of 100 nm by a sputtering method. After washing the transparent support substrate, a hole transport compound (TPD) represented by the following structural formula

[0066]

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Was formed to a thickness of 65 nm, and the above-mentioned Compound No. was formed thereon. No. 17 was formed to a thickness of 65 nm, and a metal electrode having an atomic ratio of Mg: Ag of 10: 1 was formed by vacuum evaporation to produce an organic electroluminescent device. The degree of vacuum at the time of vapor deposition was 3 to 4 × 10 ⁻⁶ torr, the film formation rate was 0.2 to 0.3 nm / sec for the organic layer, and 2 nm / sec for the metal electrode.

When a direct current is applied to the device thus obtained using the ITO electrode as the anode and the Mg / Ag electrode as the cathode, a current flows at a current density of 34 mA / cm ² at an applied voltage of 12 V, Blue light emission was observed at a luminance of 2500 cd / m ² .

In a nitrogen atmosphere, the current density was set to 5 mA /
When a voltage was applied for 100 hours kept in cm ^2, deterioration of the initial luminance 110 cd / ^{m 2} to 100 hours after 100 cd / ^{m 2} next luminance was very small.

Examples 2 to 6 Exemplified compound Nos. In place of Ex. Elements were prepared in the same manner as in Example 1 except that 15, 24, 31, 48, and 61 were used. The performance results of the device are shown in Table 11 below.

[0071]

[Table 11]

Comparative Example 1 Exemplified Compound No. used in Example 1 above A device was prepared in the same manner as in Example 1, except that a compound having the following structural formula was used instead of 17.

[0073]

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When a direct current is applied to the device thus obtained using the ITO electrode as an anode and the Mg / Ag electrode as a cathode, a current flows at a current density of 27 mA / cm ² at an applied voltage of 15 V, Blue light emission was observed at a luminance of 35 cd / m ² .

In a nitrogen atmosphere, the current density is set to 10 mA.
/ Cm ² , when the voltage was applied for 100 hours, the initial luminance was changed from 8 cd / m ² to 0 cd / m ² after 100 hours. As is clear from Examples 1 to 6 and Comparative Example 1,
It can be seen that the compound of the present invention is extremely superior in luminance and lifetime as compared with the comparative compound.

Example 7 A transparent support substrate was prepared by forming tin-indium oxide (ITO) on a glass substrate to a thickness of 100 nm by a sputtering method. After washing the transparent support substrate, a hole transporting compound (TPD) was formed into a film having a thickness of 50 nm. 40 was formed to a thickness of 20 nm, and an electron transporting compound (Alq3) was
The film was formed with the following film thickness. A metal electrode made of aluminum was formed thereon to a thickness of 150 nm, thereby producing an element as shown in FIG.

[0077]

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When a direct current is applied to the device thus obtained with the ITO electrode serving as the anode and the Al electrode serving as the cathode, a current flows through the device at a current density of 76 mA / cm ² at an applied voltage of 15 V, and 6270 cd / cm ^2. Blue-green light emission was observed at a luminance of m ² .

In a nitrogen atmosphere, the current density was set to 10 mA.
/ Cm ² , and when a voltage is applied for 100 hours, the initial luminance is 230 cd / m ^2, and after 100 hours, 215 cd / m ^2.
And the deterioration of luminance was not very small.

Example 8 A transparent support substrate was prepared by forming tin oxide-indium (ITO) on a glass substrate to a thickness of 100 nm by a sputtering method. After washing the transparent support substrate, a hole transporting compound (TPD) was formed into a film having a thickness of 60 nm, and a fluorescent dye (DCM) and the exemplified compound N were formed thereon.
o. 58 was formed into a film with a thickness of 10 nm by co-evaporation, and further, an electron transporting compound (Alq3) was formed with a film thickness of 65 nm. A metal electrode made of aluminum is placed on the
An element having a film thickness of 0 nm was formed as shown in FIG.

[0081]

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When a direct current is applied to the device thus obtained with the ITO electrode serving as the anode and the Al electrode serving as the cathode, a current flows at a current density of 35 mA / cm ² at an applied voltage of 11 V, and 1850 cd / cm ² orange light emission was observed at a luminance of m ^2.

The current density was set to 10 mA in a nitrogen atmosphere.
/ Cm ² and applying a voltage for 100 hours, from an initial luminance of 150 cd / m ² to 140 cd / m ² after 100 hours.
And the deterioration of luminance was not very small.

Example 9 A transparent support substrate was prepared by forming tin oxide-indium (ITO) on a glass substrate to a thickness of 100 nm by a sputtering method. After washing the transparent support substrate, the above-mentioned exemplary compound No. 45 0.10 g, a hole transport compound (TPD) 0.10 g, and a coating solution prepared by dissolving 0.30 g of a polycarbonate resin (weight average molecular weight 35,000) in 50 ml of tetrahydrofuran were prepared, and the coating solution was coated on a substrate. It was applied by dip coating to form a film having a thickness of 120 nm. A metal electrode made of Mg / In was formed thereon to a thickness of 150 nm, thereby producing an element as shown in FIG.

When a direct current is applied to the device thus obtained using the ITO electrode as an anode and the Mg / In electrode as a cathode, a current flows at a current density of 50 mA / cm ² at an applied voltage of 18 V, Orange light emission was observed at a luminance of 630 cd / m ² .

The current density was set to 15 mA in a nitrogen atmosphere.
/ Cm ² , and when a voltage was applied for 100 hours, the initial luminance was changed from 105 cd / m ² to 85 cd / m ² after 100 hours, and the luminance was not significantly deteriorated.

[0087]

As described above, the electroluminescent device using the compound represented by the general formula [1] of the present invention can obtain extremely high-luminance luminescence with a low applied voltage and have high durability. Is also very good. Also, the device can be prepared by a vacuum deposition method or a casting method, and a relatively inexpensive and large-area device can be easily prepared.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of the electroluminescent device of the present invention.

FIG. 2 is a sectional view showing another example of the electroluminescent device of the present invention.

FIG. 3 is a sectional view showing another example of the electroluminescent device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Light emitting layer 4 Cathode 5 Hole transport layer 6 Electron transport layer 7 Hole injection transport layer

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Mashimo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (1)

[Claims] 1. An electroluminescent device having at least a pair of electrodes and one or more organic compound layers sandwiched between the pair of electrodes, wherein at least one of the organic compound layers has the following general formula: An electroluminescent device comprising at least one selected from the compounds represented by [1]. Embedded image (Wherein, R ^{1 to} R ¹⁶ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, a substituted or unsubstituted amino group, an alkyl group, an alkoxy group, an ester group, an aryl group, and a heterocyclic group. .)