JPH05239455A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To provide an electroluminescent element which is excellent in durability and emits light with a high luminance over a long term even at a low driving voltage by using a layer contg. a specific org. compd. as an org. hole transport layer. CONSTITUTION:A layer contg. a triamine compd. of the formula [wherein B<1>n and B<2>n are each (substd.)arylene; (n) is 1-4; and Ar<1> to Ar<5> are each H, (substd.) alkyl, or aryl] is used as an org. hole transport layer of this element, which has, between a hole injection electrode and an electron injection electrode, an org. bilayer structure consisting of the org. hole transport layer and an org. luminescent layer formed in this order from the side of the hole injection electrode or an org. trilayer structure consisting of the org. hole transport layer, the org. luminescent layer, and an org. electron transport layer formed in this order from the side of the hole injection electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an organic electroluminescent device using a novel organic material having high durability in a hole transport layer.

[0002]

2. Description of the Related Art An electroluminescence device has an intrinsic electroluminescence device which emits light only in an alternating electric field by (1) exciting a light emitter by local movement of electrons and holes in a light emitting layer due to a difference in emission excitation mechanism. The element is divided into (2) a carrier injection type electroluminescent element that operates by a DC electric field by injecting electrons and holes from an electrode and recombining the electrons and holes in the light emitting layer to excite a luminescent body. The intrinsic electroluminescence type light emitting device of (1) is generally ZnS.
An inorganic compound added with Mn, Cu, etc. is used as a light emitting body, but it requires a high AC voltage of 200 V or more for driving, high manufacturing cost, insufficient brightness and durability, etc. Has many problems.

In the carrier injection type electroluminescent device (2), a thin film organic compound has been used as a light emitting layer, and a high brightness device has been obtained. For example, JP-A-59-194393, U.S. Pat. No. 4,539,507,
Japanese Patent Laid-Open No. 63-2956695, US Pat. No. 4,720,4
32 and JP-A-63-264692 disclose an electroluminescent device comprising an anode, an organic hole injecting and transporting material, an organic electron injecting luminescent material and a cathode.

In these organic electroluminescent devices, 1
It has a light emission luminance of 1000 cd / m ² or more at a current density of 00 mA / cm ² , and initially has sufficient light emission characteristics. And, as the hole transport layer material, 1,1-
Bis (4-di-tolylaminophenyl) -cyclohexane and N, N, N ', N'-
Triphenylamine-based materials such as Tetra-p-tolyl-4,4'-diaminobiphenyl have been used. However, when these conventional hole transport materials are used, a decrease in light output and an increase in driving voltage are observed within a few hours, and there is a problem in durability of the electroluminescent device.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art, and it is an object of the present invention to provide an organic electroluminescent device having excellent durability.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive studies on the constituent elements of the hole transport layer, and as a result,
An organic two-layer structure in which an organic hole transporting layer and an organic light emitting layer are sequentially formed from the hole injecting electrode side, or an organic two-layer structure in which an organic hole transporting layer, an organic light emitting layer, and an organic electron transporting layer are sequentially formed from the hole injecting electrode side. In the electroluminescent device having a three-layer structure, it was found that the organic hole transporting layer is a layer containing a specific triamine compound as a constituent, and the electroluminescent device is effective for the above problems, and the present invention is completed. Came to.

That is, according to the present invention, an organic two-layer structure in which an organic hole transport layer and an organic light emitting layer are sequentially formed from the hole injection electrode side between the hole injection electrode and the electron injection electrode, or an organic hole transport layer is formed. In an electroluminescent device having an organic three-layer structure in which a layer, an organic light emitting layer, and an organic electron transport layer are sequentially formed from the hole injecting electrode side, the organic hole transport layer is a triamine compound represented by the following general formula 1. There is provided an organic electroluminescent device characterized by being a layer containing as a structural component.

[Chemical 1] (In the formula, B ¹ n and B ² n are each independently a substituted or unsubstituted arylene group, n is an integer of 1 to 4, and Ar ¹ , Ar ² , Ar ³ , Ar ⁴ , and Ar ⁵ are respectively Represents an independently selected hydrogen atom, substituted or unsubstituted alkyl group or aryl group.)

B in the general formula 1¹n and B²as n
Is, for example, phenylene group, biphenylene group,
Examples thereof include a nylene group. And these arylene groups are
Having a plurality of substituents (1) to (9) defined below
be able to. (1) Halogen atom, trifluoromethyl group, cyano
Group, nitro group. (2) Alkyl group: preferably C₁~ C₂₀Especially C₁
~ C₁₂A linear or branched alkyl group of
The alkyl group of is further hydroxyl group, cyano group, phenyl group or
Is a halogen atom, C₁~ C₁₂Alkoxy group, alkyl
Group or C₁~ C₁₂Substituted with an alkoxy group of
It may have a phenyl group. (3) Alkoxy group (-OR¹): R¹Is defined in (2)
Represents an alkyl group. (4) Aryloxy group: phenyl as an aryl group
Group, naphthyl group, and these are C₁~ C₁₂The al
Coxy group, C₁~ C₁₂Alkyl group or halogen atom
May be contained as a substituent. (5) Alkylthio group (-SR¹): R¹Is defined in (2)
Represents an alkyl group.Acyl such as alkyl group, acetyl group, benzoyl group
Group or an aryl group, and as the aryl group,
For example, phenyl group, biphenylyl group, or naphthyl
Groups, which are C₁~ C₁₂Alkoxy group of C₁
~ C₁₂Alkyl group or halogen atom as a substituent
May be included. In addition, piperidyl group, morpholyl group
Like R¹And R²May form a ring in cooperation with the nitrogen atom
Yes. In addition, aryl-based carbon sources such as urolysyl
You may form a ring with a child. (7) Alkoxycarbonyl group (-COOR^Four): R^FourIs
The alkyl group defined in (2) or defined in (4)
Represents an aryl group. (8) Acyl group, (-COR^Four), Sulfonyl group, cal
Vamoyl group : In the formula, R², R³And R^FourIs the meaning defined above
You However, R²And R³At the carbon atom on the aryl group
Except when forming a ring jointly with. (9) such as methylenedioxy group or methylenedithio group
An alkylenedioxy group or an alkylenedithio group.

Ar ¹ , Ar ² , A in the general formula 1
When r ³ , Ar ⁴ and Ar ⁵ are aryl groups, they are carbocyclic aromatic groups or heterocyclic aromatic groups, and examples of the former include phenyl group, biphenylyl group,
Non-condensed carbocyclic aromatic groups such as terphenylyl groups and condensed polycyclic hydrocarbon groups can be mentioned. The fused polycyclic hydrocarbon group preferably has 1 ring carbon atom (s).
Examples include eight or less. For example, pentalenyl group, indenyl group, naphthyl group, azulenyl group, heptanenyl group, s-indacenyl group, acenaphthylenyl group,
Preyadenyl group, acenaphthenyl group, phenalenyl group, phenanthryl group, anthryl group, fluoranthenyl group, acephenanthrylenyl group, aceanthrylenyl group, triphenylenyl group, pyrenyl group, chrysenyl group,
Examples thereof include biphenylenyl group, as-indacenyl group, fluorenyl group and naphthacenyl group.

Examples of heterocyclic aromatic groups in which Ar ¹ , Ar ² , Ar ³ , Ar ⁴ and Ar ⁵ are the following groups. Pyridyl group, pyrimidyl group, pyrazinyl group, triazinyl group, furanyl group, pyrrolyl group, thiophenyl group, quinolyl group, coumarinyl group, benzofuranyl group, benzimidazolyl group, benzoxazolyl group, dibenzofuranyl group, benzothiophenyl group, Dibenzothiophenyl group, indolyl group, carbazolyl group, pyrazolyl group, imidazolyl group, oxazolyl group, isoxazolyl group, thiazolyl group, indazolyl group, benzothiazolyl group, pyridazinyl group, cinnolyl group, quinazolyl group,
Quinoxalyl group, phthalazinyl group, phthalazine dionyl group, phthalamidyl group, chromonyl group, naphtholactamyl group, quinononyl group, o-sulfobenzoic acid imidyl group,
Imidyl maleate group, naphthalidinyl group, benzimidazolonyl group, benzoxazolonyl group, benzothiazolonyl group, benzothiazothionyl group, quinazolonyl group,
Quinoxalonyl group, phthalazonyl group, dioxopyrimidinyl group, pyridonyl group, isoquinononyl group, isoquinolinyl group, isothiazolyl group, benzisoxazolyl group,
A benzisothiazolyl group, an indazironyl group, an acridinyl group, an acridonyl group, a quinazoline dionyl group, a quinoxaline dionyl group, a benzoxazine dionyl group, a benzoxazinonyl group, and a naphthalimidyl group. Also,
These aryl groups are the substituents (1) to
(9) can be included.

Next, specific examples of the compound represented by the generalized formula 1 used in the present invention are shown in Table 1, but the present invention is not limited thereto.

[Table 1- (1)]

[Table 1- (2)]

[Table 1- (3)]

In Table 1, D _{1 to} D ₉ mean the following groups.

[Table 2]

In the electroluminescent device of the present invention, the organic compound described above is formed to a thickness of less than 2 μm, more preferably 0.05 μm to 0.5 μm, by the vacuum evaporation method, solution coating or the like. It is constituted by forming an organic compound layer by thinning it and sandwiching it with an anode and a cathode.

The present invention will be described in more detail below with reference to the drawings. FIG. 1 is a typical example of the electroluminescent device of the present invention, which has a structure in which a hole injection electrode (anode), a light emitting layer and an electron injection electrode (cathode) are sequentially provided on a substrate. The electroluminescent device according to FIG. 1 is particularly useful when a single compound has a hole transporting property, an electron transporting property and a light emitting property, or when a compound having each property is mixed and used.

FIG. 2 shows a light emitting layer formed by combining a hole transporting compound and an electron transporting compound. This structure is a combination of the preferable characteristics of organic compounds. By combining compounds having excellent hole transporting properties or electron transporting properties, it is possible to smoothly inject holes or electrons from the electrodes and obtain an element having excellent light emitting properties. Is to In addition, in the case of this type of electroluminescent element, since the light emitting substance varies depending on the organic compound to be combined, it is not possible to unambiguously determine which compound emits light.

FIG. 3 shows that a light emitting layer is formed by a combination of a hole transporting compound, a light emitting compound, and an electron transporting compound, which is considered to be a type which further advances the above idea of functional separation. You can

This type of electroluminescent device can be obtained by appropriately combining compounds having hole transporting properties, electron transporting properties and light emitting properties.
Since the target range of the compound becomes extremely wide, the selection thereof becomes easy.

The electroluminescent device of the present invention electrically biases the light emitting layer to emit light. However, since a short circuit may occur due to a slight pinhole, the device may not function as an element. It is desirable to use a compound having excellent film-forming property in combination. Further, such a compound having an excellent film forming property may be combined with, for example, a polymer binder to form a light emitting layer. Examples of the polymer binder that can be used in this case include polystyrene, polyvinyltoluene, poly-N-vinylcarbazole, polymethylmethacrylate, polymethylacrylate, polyester, polycarbonate and polyamide. Further, in order to improve the efficiency of charge injection from the electrode, a charge injection / transport layer can be separately provided between the electrode and the electrode.

As the material for the hole injecting electrode (anode), nickel, gold, platinum, palladium, alloys thereof, tin oxide (SnO ₂ ), indium tin oxide (ITO), copper iodide, or other metals having a large work function, and those Alloys, compounds,
Furthermore, conductive polymers such as poly (3-methylthiophene) and polypyrrole can be used.

On the other hand, as the material of the electron injection electrode (cathode), silver, tin, lead, magnesium, manganese, aluminum or an alloy thereof having a small work function is used. Hole injection electrode (anode) and electron injection electrode (cathode)
At least one of the materials used as is preferably sufficiently transparent in the emission wavelength region of the device. Specifically, it is desirable to have a light transmittance of 80% or more.

In the present invention, it is preferable that a transparent hole injecting electrode (anode) is formed on a transparent substrate to have a structure as shown in FIGS. 1 to 3, but the reverse structure may be adopted in some cases. .. As the transparent substrate, glass, plastic film or the like can be used.

Further, in the present invention, in order to improve the stability of the electroluminescent device thus obtained, especially to protect it against atmospheric moisture, a separate protective layer may be provided or the entire device may be provided in a cell. It may be filled with silicone oil or the like.

[0023]

【Example】

Hereinafter, the present invention will be described more specifically based on Examples. Example 1 ITO (indium tin oxide: sheet resistance 20Ω / □)
The substrate was sequentially ultrasonically cleaned with a neutral detergent, acetone and isopropyl alcohol. Then, the ITO substrate was immersed in boiled isopropyl alcohol for 5 minutes and dried. Compound No. as hole transport material Using 21 compounds 10
- was formed by depositing a hole transport layer of 500Å by heating an alumina crucible under a vacuum of ⁶ torr. Next, a light emitting layer material represented by the following chemical formula 2 was vapor-deposited by 500Å. In addition, 200 MgAg electrodes with an atomic ratio of 10: 1 are formed on the light emitting layer.
0Å vapor deposition. The electroluminescent device initially exhibited a luminescence intensity of 740 cd / m ² at a current density of 30 mA / cm ² . Then, after 100 hours, maintaining high luminance of 400 cd / m ² even after lapse of 400 cd / m ^2, 500 hours. 30m below
7 shows changes in emission luminance and changes in drive voltage with time under a constant current of A / cm ² .

[Chemical 2]

[0024]

[Table 3]

Comparative Example 1 An electroluminescent device was prepared in the same manner as in Example 1 except that triphenyldiamine represented by the following chemical formula 3 was used for the hole transport layer. This device initially has a current density of 20 mA / cm ² and 750 cd
The emission brightness was / m ² , but it was 4 after only 10 hours.
It only showed an emission brightness of 0 cd / m ² . The results are shown below.

[Chemical 3]

[0026]

[Table 4]

[0027]

Since the electroluminescent device of the present invention uses the compound represented by the general formula 1 as a constituent material of the organic compound layer, it is possible to obtain high-luminance light emission over a long period of time even at a low driving voltage. It is also excellent in durability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electroluminescent device according to the present invention.

FIG. 2 is a schematic cross-sectional view of another electroluminescent device according to the present invention.

FIG. 3 is a schematic cross-sectional view of still another electroluminescent device according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Takahashi 1-3-3 Nakamagome, Ota-ku, Tokyo Stock company Ricoh (72) Inventor Tomoyuki Shimada 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Company Ricoh

Claims (3)

[Claims] 1. Between the hole injecting electrode and the electron injecting electrode,
An organic two-layer structure in which an organic hole transporting layer and an organic light emitting layer are sequentially formed from the hole injecting electrode side, or an organic two-layer structure in which an organic hole transporting layer, an organic light emitting layer, and an organic electron transporting layer are sequentially formed from the hole injecting electrode side. In the electroluminescent device having a three-layer structure, the organic hole transport layer is a layer containing a triamine compound represented by the following general formula 1 as a structural component. [Chemical 1] (In the formula, B ¹ n and B ² n are each independently a substituted or unsubstituted arylene group, n is an integer of 1 to 4, and Ar ¹ , Ar ² , Ar ³ , Ar ⁴ , and Ar ⁵ are respectively Represents an independently selected hydrogen atom, substituted or unsubstituted alkyl group or aryl group.) 2. The organic electroluminescent device according to claim 1, wherein B ¹ and B ² in the triamine compound are phenylene groups, biphenylene groups, or terphenylene groups, which are independently selected. 3. The organic electroluminescent device according to claim 1, wherein either Ar ¹ or Ar ² and Ar ³ or Ar ^{4 in} the triamine compound are aryl groups.