JP2000021574A - Light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diversify a light emitting wave length in high luminance and to provide various light emitting hues by including an organic compound having an aryl group at least in one layer of layers composed of an organic compound of a light emitting element. SOLUTION: At least one kind of compounds expressed by formula I is included at least in one layer of a light emitting element composed of an organic compound sandwiched between a pair of electrodes. In formula I, R1 and R2 are each a substituted or an unsubstituted aryl group or substituted or unsubstituted heterocyclic group; and R1 and R2 may be the same or may be different. R1 and R2 are selected from groups having a structure expressed by formula II or formula III. R3 to R15 in formula II and formula III are each a hydrogen atom, halogen atom, alkyl group, aryl group, heterocyclic group, aralkyl group, aroyl group, a formyle group, a nitrile group, a nitro group or an amino group. The compound is formed by a vacuum deposition method and the application of a solution, and the thickness of an organic layer is desirably thinned than 2 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting element having a light-emitting layer made of a light-emitting substance and capable of easily extracting energy by injecting electric charge.

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 organic light-emitting diode (organic LED) used for an electroluminescence (EL) panel which may satisfy high requirements.

[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.

[0005] However, 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 LED device has been actively studied thereafter, for example, see Japanese Patent Application Laid-Open No. 59-19439.
3, U.S. Pat. No. 4,539,507,
No. 194393, U.S. Pat. No. 4,720,432
No., JP-A-63-264692, Appl. Ph
ys. Lett. 55 (1989) 1467;
163188 and the like.

Also, see <Jpn. J. Appl. Phys
s. 27 (1988) L269. L713 reports an organic LED device having a three-layer structure in which the functions of carrier transport and light emission are separated. In selecting a dye of a light-emitting layer that determines a light emission color, restrictions on carrier transport performance are relaxed, and the degree of freedom of selection is reduced. It is suggested that holes and electrons (or excitons) may be effectively confined in the central light emitting layer to improve light emission.

In general, a vacuum evaporation method is used to produce a stacked organic LED element. However, it has been reported that an element having a considerably high brightness can be obtained by a casting method (for example, the 50th application). Proceedings of the Academic Lecture Meeting of the Society of Japan 1006 (1989) and Proceedings of the 50th Academic Lecture 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 transport compound, an oxadiazole derivative as an electron transport compound, and coumarin 6 as a luminous body 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.
The first object is to provide a light emitting device having an extremely high luminance light output. Secondly, it is an object of the present invention to provide a light-emitting element that has various emission wavelengths, exhibits various light-emitting hues, and is extremely durable. Third, it is an object of the present invention to provide a light-emitting element which can be easily manufactured and can be provided at relatively low cost.

[0011]

That is, the present invention relates to a light-emitting element having at least a pair of electrodes and one or more layers of an organic compound sandwiched between the pair of electrodes. A light-emitting element, wherein at least one of the layers contains at least one selected from compounds represented by the following general formula [1].

[0012]

Embedded image (Wherein, R ₁ and R ₂ represent a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group. R ₁ , R ₂
May be the same or different. )

[0013]

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

[0014]

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In the general formula [1], R ₁ and R ₂ represent a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group. R ₁ and R ₂ may be the same or different.

Examples of the aryl group include a single ring and a condensed ring such as a phenyl group, a naphthyl group and an anthranyl group. Examples of the heterocyclic group include a pyrrolyl group, a thienyl group,
Examples thereof include a 5-membered ring, a 6-membered heterocyclic group, a 5-, 6-membered condensed ring, a 6, and a 6-membered condensed ring such as a pyridyl group, a quinolyl group, an acrylidyl group, a phenadyl group, and a dihydrophenazine group.

Examples of R ₁ and R ₂ are shown below, but are not limited thereto.

[0018]

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[0019]

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[0020]

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[0021]

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In the above formula, the substituents R ₃ -R
₃₀ represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a heterocyclic group, an aralkyl group, an aroyl group, a formyl group, a nitrile group, a nitro group or an amino group. Further, R _{3 to} R ₃₀ may be the same or different.

Examples of the alkyl group include a linear alkyl group such as methyl, ethyl, n-propyl and n-octyl, and a branched alkyl group such as isopropyl, isobutyl and 3-methylhexyl.

Examples of the aryl group include a substituted or unsubstituted phenyl group such as a phenyl group, a tolyl group, a chlorophenyl group and a nitrophenyl group, and a substituted or unsubstituted polycyclic fused aromatic ring such as a naphthyl group and an anthranyl group. Is mentioned.

Examples of the heterocyclic group include a 5-membered heterocyclic group such as a substituted or unsubstituted thienyl group, a pyrrolyl group and a furyl group, and a 6-membered heterocyclic group such as a substituted or unsubstituted pyridyl group and a pyridazyl group. Examples include a ring group, a substituted or unsubstituted quinolyl group, a condensed polycyclic heterocyclic group such as a phenadyl group and an acrylidyl group.

Examples of the aralkyl group include a substituted or unsubstituted benzyl group and a phenethyl group. Examples of the aroyl group include a substituted or unsubstituted benzoyl group and a naphthoyl group. The amino group may be primary or secondary, for example, an anilino group, aromatic amino group such as diphenylamino group, methylamino group, ethylamino group, diisopropylamino group, benzylamino group,
Examples include an alkylamino group such as a methylbenzylamino group.

M and n are integers of 1 or more, and m and n
May be the same or different integers. Preferably, m and n are in the range of 1 to 10.

Representative examples of the compound represented by the general formula [1] will be given below, but it should not be construed that the invention is limited thereto.

[0029]

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[0030]

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The light emitting device of the present invention has one or a plurality of 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 selected from the compounds represented by

In the light emitting 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 light emitting 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 light-emitting element used here is useful when it has a single hole-transporting ability, electron-transporting ability, and light-emitting performance, or when a mixture of compounds having the respective properties is used.

FIG. 2 is a sectional view showing another example of the light emitting 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 light emitting 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 properties as compared with the conventional compound, and may have any of the forms shown in FIGS. Light emitting elements can also be used.

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

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 field of electrophotographic photoreceptors, or the like, may be used. Hitherto known hole-transporting luminescent compounds (for example, compounds shown in Tables 1 to 4)
Alternatively, an electron transporting compound or a conventionally known electron transporting luminescent compound (for example, the compounds listed in Tables 5 to 6) can be used together if necessary.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

In the light emitting device of the present invention, the general formula [1]
The layer containing the compound represented by the formula (1) and the layer composed of another organic compound are generally formed into a thin film by vacuum deposition or in combination with an appropriate binder resin.

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.

As the anode material, one having a work function as large as possible is preferable. 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.

The light emitting device of the present invention has a large area, high resolution,
It has features of being thin, lightweight, high-speed operation, and a completely solid-state device, and is useful as a light-emitting element that may satisfy high requirements.

[0051]

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 substrate, N, N'-bis (3-methylphenyl) -N, N'-diphenyl-
(1,1′-biphenyl) 4,4′-diamine (TP
D) having a film thickness of 65 nm and the exemplified compound No. A light emitting device was prepared by sequentially vacuum-depositing 1-7 with a film thickness of 65 nm and further Mg / Ag alloy in a ratio of 10/1 to a film thickness of 150 nm. The degree of vacuum at the time of vapor deposition is 3 to 5 × 10 ⁻⁶ t.
orr, the film formation speed of the organic layer is 0.2 to 0.3 nm /
sec, and 1 nm / sec for the metal electrode.

When a DC voltage was applied to the device thus obtained using the ITO electrode as the anode and the Mg / Ag electrode as the cathode, a current density of 8.3 mA / cm was obtained at an applied voltage of 12 V.
² passed through the device, and yellow-green light was emitted at a luminance of 130 cd / m ² . When a voltage is applied for 100 hours while maintaining the current density at 5 mA / cm ² under a nitrogen atmosphere,
Initial luminance 50 cd / m ² to 35 cd / m after 100 hours
² , the luminance degradation was small.

Examples 2 to 4 Exemplified compound Nos. In place of the above-mentioned compound No. 1-7, A device was prepared in the same manner as in Example 1, except that 1-1, 1-2 and 1-4 were used. Then, a current having a current density of 12 mA / cm ² was passed through the obtained devices for 100 hours. The results at that time are shown in Table 7 below.

[0055]

[Table 7]

Comparative Examples 1 to 3 Exemplified Compound Nos. An element was formed in the same manner as in Example 1 except that a compound having the following structural formula was used instead of 1-7.

[0057]

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The anode and cathode of each element thus formed were connected by a lead wire, a DC power supply was connected, and the result of the current density and light output flowing to the element when a voltage of 10 V was applied in the same manner as in Example 1 Is shown in Table 8 below.

[0059]

[Table 8]

As is clear from Tables 7 and 8, the light emitting device using the compound according to the present invention is extremely superior in luminance as compared with the light emitting device using the comparative compound.

Example 5 The above-mentioned Compound No. 0.06 g of 1-6 and 0.10 g of polyvinyl carbazole (PVK) were added to chloroform 1
The solution was dissolved in 0 ml to prepare a coating solution. This coating solution was applied on a transparent electrode of a glass substrate on which a tin oxide-indium (ITO) coating (film thickness: 100 nm) was formed as a transparent electrode by a spin coating method (2,000 rpm) to obtain a 125 nm thick film. A layer was formed. An Mg / In alloy was vacuum-deposited thereon at a ratio of 5/1 to form a 150 nm-thick metal electrode.

When a DC voltage is applied to the device thus fabricated using the ITO electrode as the anode and the Mg / In electrode as the cathode, a current of 7.8 mA / cm ² flows at an applied voltage of 10 V, and 150 cd / m ^2. Blue-green light was emitted at a luminance of. When the applied voltage is further increased to 20 V, 95 mA
/ Cm ² and a luminance of 1800 cd / m ² was exhibited.

Example 6 On the transparent electrode of a glass substrate on which a tin oxide-indium (ITO) coating (film thickness: 100 nm) was formed as a transparent electrode, the above-mentioned compound No. 1 was used as a hole transport compound. 1-
8 as a hole transport layer (film thickness 50 nm) and a light emitting layer as described in the above-mentioned Compound No. 1-5 (thickness 15 nm), an electron transport compound represented by the following electron transport layer made of (Alq ₃₎ (thickness 50 nm), followed by Mg / Ag (10/1)
A cathode (thickness: 150 nm) made of an alloy was sequentially formed by vacuum evaporation to produce a device as shown in FIG.

[0064]

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A DC voltage of 7 V was applied to the device thus prepared by using the ITO electrode as an anode and the Mg / Ag electrode as a cathode.
, A current of 18 mA / cm ² flows,
Blue-green light emission was observed at a luminance of 000 cd / m ² .

Example 7 A hole transport layer made of a hole transport compound (TPD) was formed to a thickness of 65 nm on a transparent electrode of a glass substrate on which a tin oxide-indium (ITO) film (film thickness: 100 nm) was formed as a transparent electrode. The exemplified compound No. An electron transporting and emitting layer having a weight ratio of 1:20 of 1-6 and an electron transporting compound (Alq ₃ ) was formed to a thickness of 65 nm, and a cathode made of Al was formed to a thickness of 150 nm by vacuum deposition. An element as shown was prepared.

[0067]

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When a DC voltage is applied to the device thus prepared using the ITO electrode as the anode and the Al electrode as the cathode, a current of 7.2 mA / cm ² flows at an applied voltage of 10 V, and 23,000 cd / m ^2. Blue-green light was emitted at a luminance of.

Example 8 The above-mentioned Compound No. 0.08 g of 1-8, 0.10 g of a hole transport compound (TPD), and an electron transport compound (Al
0.10 g of q ₃ ) and 0.30 g of a polycarbonate resin (weight average molecular weight: 35,000) were dissolved in 50 ml of tetrahydrofuran to prepare a coating solution. This coating solution was applied by a dip coating method on a transparent anode of a glass substrate on which a tin oxide-indium (ITO) coating (film thickness: 100 nm) was formed as a transparent anode to form a layer having a thickness of 150 nm. Then, aluminum is vacuum-deposited thereon to a thickness of 15 mm.
A 0 nm cathode was formed to produce a device.

When an anode and a cathode of the device thus prepared were connected with a lead wire, a DC power supply was connected, and a voltage of 3 V was applied, a current having a current density of 30 mA / cm ² flowed through the device.
An optical output of 90 cd / m ² was confirmed.

[0071]

As described above, the light-emitting device using the compound represented by the general formula [1] of the present invention can obtain extremely high-luminance light emission at a low applied voltage, and has high durability. 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 a light emitting device of the present invention.

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

FIG. 3 is a sectional view showing another example of the light emitting 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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Seiji Mashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Non-corporation F term (reference) 3K007 AB02 AB04 AB11 AB18 CA01 CB01 CC00 DA01 DB03 EB00 FA01 FA03

Claims (2)

[Claims] 1. A light-emitting element having at least a pair of electrodes and one or more layers of an organic compound sandwiched between the pair of electrodes, wherein at least one of the layers of the organic compound has the following general formula [ [1] A light emitting device comprising at least one compound selected from the group consisting of: Embedded image (Wherein, R ₁ and R ₂ represent a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group. R ₁ , R ₂
May be the same or different. ) 2. The light emitting device according to claim ₁ , wherein said R ₁ and R ₂ are selected from groups having the following structures. Embedded image Embedded image Embedded image Embedded image (Wherein, R ₃ to R ₃₀ is a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a heterocyclic group, an aralkyl group, an aroyl group, formyl group, a nitrile group, .R ₃ a nitro group or an amino group; R ₃₀ may be the same or different, and m and n each represent an integer of 1 or more.)