JPH06145658A - Electroluminescent element - Google Patents

Abstract

(57) [Summary] [Structure] At least one of the organic compound layers contains an oxadiazole compound having a plurality of aryl oxadiazole structures represented by the following general formula (I) (Chemical formula 1) as a constituent component. An electroluminescent device characterized by being a layer. [Chemical 1] (In the formula, R ₁ and R ₂ each independently represent a hydrogen atom, a halogen atom, an alkyl group or the like, and Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic group. It represents a heterocyclic group.) [Effect] The electroluminescent device of the present invention can obtain high-luminance light emission for a long period of time even with a low driving voltage, and can exhibit various color tones, and also can be manufactured as a device. Since it can be easily performed, it has an advantage that an inexpensive and large-area element can be efficiently produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device using a light emitting material which is excellent in film forming property and can exhibit sufficient brightness.

[0002]

2. Description of the Related Art In recent years, with the diversification of information equipment, CR
There is an increasing need for a flat panel display device that consumes less power and occupies less space than T. Liquid crystal, plasma display, and the like are available as such flat display elements. Recently, electroluminescent elements (EL elements), which are luminescent type and have a clear display, have recently been developed.
Is attracting attention.

Here, the above EL elements can be roughly classified into inorganic EL elements and organic EL elements depending on the constituent materials, and the inorganic EL elements have already been put to practical use. However, the driving method of the above-mentioned inorganic EL is so-called collision excitation type light emission in which electrons accelerated by application of a high electric field collide and excite light emission centers to emit light, and therefore, it is necessary to drive at a high voltage. Therefore, there is a problem that the cost of the peripheral device is increased.

On the other hand, the above-mentioned organic EL device has a structure in which opposing electrodes having different work functions are arranged across the organic light emitting layer, and holes injected from the anode and electrons injected from the cathode are the light emitting layer. This is so-called injection type light emission in which light having the same wavelength as the fluorescent light of the light emitting layer is recombined in the inside. Therefore, it is possible to drive at a low voltage, and it is possible to obtain an arbitrary emission color by changing the material of the light emitting layer.

In addition, since the organic compound used in the organic EL element has different properties by changing the substituents, the degree of freedom in material design is higher than that of the inorganic compound. Therefore, it is considered that an arbitrary light emitting material can be obtained by changing the molecular structure of the organic compound while considering the electronic state of the molecule. Therefore, in theory,
It is possible to emit all colors from blue to red, and in fact, various stable light emitting materials that emit green, yellow and orange have been proposed.

As the organic electroluminescent device structure, a two-layer structure (a structure in which a hole transport layer and a light emitting layer are formed between a hole injection electrode and an electron injection electrode (SH-A
Structure) (JP-A-59-194393, Appl. Phy
s. Lett. 51,913 (1987)), or
A structure in which a light emitting layer and an electron transport layer are formed between a hole injecting electrode and an electron injecting electrode (SH-B structure) (USP No.
5,085947, JP-A-2-25092, Appl.
Phys. Lett. 55, 1489 (1989)),
Alternatively, a three-layer structure (a structure in which a hole transport layer, a light emitting layer, and an electron transport layer are formed between a hole injection electrode and an electron injection electrode (DH structure) (Appl. Phys. Lett. 57,
531 (1990)) has been reported.

As the hole injecting electrode, Au or IT
An electrode material having a large work function such as O (indium-tin-oxide) is used, and an electrode material having a small work function such as Ca, Mg, Al and their alloys is used as the electron injection electrode. In addition, until now, various organic compounds have been reported as materials that can be used for the hole transport layer, the light emitting layer, and the compound transport layer. Examples of the organic material used in these materials include aromatic tertiary amines for the hole transport layer, and aluminum trisoxine for the light emitting layer material (JP-A-59-194393 and JP-A-63).
-295695), styrylamine derivatives, styrylbenzene derivatives and the like (JP-A-2-209988),
As the electron transport layer, oxadiazole derivatives and the like (Journal of the Chemical Society of Japan, No. 11, p1540 (1990), JP-A-4-212286, JP-A-4-308688, JP-A-4308688)
-363891, JP-A-4-363894)

Up to now, by using various element structures and organic materials, an element with a high-luminance light emission of 1000 cd / m ² or more and a driving voltage of about 10 V was initially obtained, but continuous driving was performed. In this case, in the conventional organic material, a decrease in light output and an increase in driving voltage are observed in several hours, and there is a big problem in long-term durability of the EL element. Particularly in blue light emitting devices, the search for materials has not been sufficiently conducted, and many problems such as improvement in light emission efficiency remain.
Carrier injection type electroluminescent devices using organic compounds as light emitters, including these examples, have a short history of research and development, and it cannot be said that research into materials and devices has been sufficiently conducted. There are many problems such as further improvement of brightness, control of emission wavelength, and improvement of durability.

A light-emitting material that emits blue light stably and with high brightness has not yet been developed, regardless of whether it is an inorganic EL element or an organic EL element. For example, 1,1,4,4-tetraphenyl-1,3-butadiene derivatives and styrylbenzene derivatives have been proposed as blue light emitting materials in organic EL devices, but they are all inferior in film formability and satisfactory. It is not possible to obtain high brightness and stability.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art, and an object thereof is to have sufficient brightness and light emitting performance, which is excellent in durability for a long time. It is to provide an electroluminescent device.

[0011]

Means for Solving the Problems The inventors of the present invention have diligently studied the constituent elements of a light emitting layer for solving the above problems, and as a result, have made a positive electrode and a negative electrode and one or a plurality of layers sandwiched between them. An electroluminescent device comprising an organic compound layer, wherein at least one of the organic compound layers is a layer containing an oxadiazole compound having a specific plurality of aryl oxadiazole structures as a constituent component. The inventors have found that they are effective against the above problems, and have completed the present invention.

That is, according to the present invention, the anode and the cathode and at least one of the one or more organic compound layers sandwiched between the anode and the cathode are represented by the following general formula (I) An electroluminescent device comprising a layer containing at least one oxadiazole-based compound having a plurality of aryl oxadiazole structures selected from the formula (VI) (formula 6) as a constituent component. It

[Chemical 1] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

[Chemical 2] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

[Chemical 3] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

[Chemical 4] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

[Chemical 5] (In the formula, R ₁ represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ , Ar ₂ each independently represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

[Chemical 6] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)

R ₁ in the general formulas (I) to (VI),
Specific examples of R ₂ include the following groups.

(1) Hydrogen atom, halogen atom, trifru
Oromethyl group, cyano group, nitro group. (2) Alkyl group; preferably C₁~ C₂₀Especially C₁~
C₁₂A straight or branched chain alkyl group of
Alkyl groups are further hydroxyl groups, cyano groups, C₁~ C₁₂The al
Coxy group, phenyl group, or halogen atom, C₁~ C
₁₂Alkyl group of or C₁~ C₁₂With the alkoxy group of
It may contain a substituted phenyl group. (3) Aryl group; carbocyclic or heterocyclic aromatic ring
Yes, phenyl, naphthyl, anthryl, acenaphthenic
Le, fluorenyl, phenanthryl, indenyl, pyret
Nyl, pyridyl, pyrimidyl, furanyl, pyronyl, thiyl
Ophenyl, quinolyl, benzofuranyl, benzothiof
Phenyl, indolyl, carbazolyl, benzoxazoli
, Quinoxalyl, benzimidazolyl, pyrazolyl,
Dibenzofuranyl, dibenzdithiophenyl, etc.
These aryl groups also include halogen atoms, hydroxyl groups, and cyano groups.
Group, nitro group, alkyl group, alkoxy group, amino group,
It may be substituted with a styryl group or the like. (4) Alkoxy group (-OR³): R³Is defined in (2)
Represents an alkyl group. (5) 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. (6) Alkylthio group (-SR³): R³Is defined in (2)
Represents an alkyl group. Acyl group such as alkyl group, acetyl group, benzoyl group,
Or an aryl group.
Phenyl, biphenylyl, or naphthyl groups.
And these are C₁~ C₁₂Alkoxy group of C₁~ C₁₂A
Even if it contains a alkyl group or a halogen atom as a substituent,
good. In addition, like a piperidyl group and a morpholyl group, R^Four
And R^FiveMay form a ring in cooperation with the nitrogen atom. See you
A ring in cooperation with a carbon atom on an aryl group, such as a lorisyl group.
May be formed. (8) Alkoxycarbonyl group (-COOR⁶): R⁶Is
Alkyl group defined in (2) or defined in (3)
Represents an aryl group. (9) Acyl group (-COR⁶), A sulfonyl group (-SO₂
R⁶), Carbamoyl group And R⁶Represents the meaning defined above. However, R^FourAnd R
^FiveForm a ring with a carbon atom on the aryl group in
Except when (10) Methylenedioxy group or methylenedithio group, etc.
An alkylenedioxy group or an alkylenedithio group. Well
Also, Ar in the general formulas (I) to (VI)₁, Ar₂Is good
It is an aromatic hydrocarbon group or an aromatic heterocyclic group.
Specific examples include styryl, phenyl, and biphenyl.
Le, terphenyl, naphthyl, anthryl, acenaphthe
Nil, fluorenyl, phenanthryl, indenyl, pi
Renyl, pyridyl, pyrimidyl, furanyl, pyronyl,
Thiophenyl, quinolyl, benzofuranyl, benzothio
Phenyl, indolyl, carbazolyl, benzoxazo
Ril, quinoxalyl, benzimidazolyl, pyrazoli
Group, dibenzofuranyl, dibenzothiophenyl, etc.
However, these aryl groups may also contain one or more halogen radicals.
Child, hydroxyl group, cyano group, nitro group, alkyl group, alcohol
Xy, amino, trifluoromethyl, phenyl
Group, tolyl group, naphthyl group, aralkyl group, etc.
May be.

Next, specific examples of the compounds represented by the general formula (I) (formula 1) to the general formula (VI) (formula 6) used in the present invention are shown in Table 1, but the present invention is not limited thereto. It is not something that will be done.

[0016]

[Table 1- (1)]

[Chemical 1]

[0017]

[Table 1- (2)]

[Chemical 2]

[0018]

[Table 1- (3)]

[Chemical 3]

[0019]

[Table 1- (4)]

[Chemical 4]

[0020]

[Table 1- (5)]

[Chemical 5]

[0021]

[Table 1- (6)]

[Chemical 5]

[0022]

[Table 1- (7)]

[Chemical 6]

[0023]

[Table 1- (8)]

[Chemical 6]

The electroluminescent device in the present invention is constituted by thinning the compound described above by a vacuum vapor deposition method, a solution coating method or the like and sandwiching it with an anode and a cathode. At that time, plural kinds of other substances may be added to the compound as additives. Further, a charge injection / transport layer may be separately provided between the electrode and the electrode in order to improve the efficiency of charge injection from the electrode.

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

On the other hand, as the cathode material, silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof having a small work function is used. At least one of the materials used as the anode and the cathode 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.

FIG. 1 shows a typical configuration example of the electroluminescent device according to the present invention. In FIG. 1, 1 is a substrate, 2 and 4 are electrodes, 3a is a light emitting layer, 3b is an electron transport layer, and 3c is a hole transport layer. FIG. 1 shows a structure in which an electrode 2 is provided on a substrate 1, a light emitting layer 3a is independently provided on the electrode 2, and an electrode is provided thereon. 2 shows an electrode 2 and a light emitting layer 3 in FIG.
The hole transport layer 3c is provided between a and
In FIG. 1, the electron transport layer 3b is provided between the light emitting layer 3a and the electrode 4.
Is provided. FIG. 4 shows a structure in which the hole transport layer 3c is provided between the electrode 2 and the light emitting layer 3a in FIG.

The electroluminescent device of the present invention is constructed as a device by sequentially laminating the above layers on a transparent substrate such as glass. However, it is possible to improve the stability of the device, particularly to protect it from moisture in the atmosphere. Therefore, a protective layer may be separately provided, or the entire device may be put in a cell and silicon oil or the like may be sealed therein.

[0029]

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

Example 1 On a glass substrate having an ITO anode having a surface resistance of 20 Ω / □, a hole-transporting layer having a thickness of 500 Å made of a triphenylamine derivative represented by the following structural formula (Formula 7), and the compound N
o. An EL device as shown in FIG. 2 was manufactured by sequentially stacking a light emitting layer of 2 having a thickness of 500Å and a cathode of a thickness of 2000Å made of a MgAg alloy having an atomic ratio of 10: 1 by vacuum deposition. Substrate temperature at the time of device fabrication is room temperature, vacuum degree is 1
It was x10 ^-6 torr. The light emitting surface of the EL element is 2x
It has a size of 2 mm. The EL device thus obtained showed clear blue light emission at a drive voltage of 20 V or less.

[Chemical 7]

Examples 2 to 5 EL devices were prepared in the same manner as in Example 1 except that the compounds shown in Table 2 below were used as the light emitting layer. The EL device thus obtained showed clear blue light emission at a driving voltage of 20 V or less, as in Example 1. The emission color is blue, bluish purple, or green-blue as shown in Table 2 below.

[0032]

[Table 2]

Example 6 On the same glass substrate as in Example 1, a hole-transporting light-emitting layer having a thickness of 500 Å and made of a stilbene derivative represented by the following formula (Formula 8) was prepared. Thickness consisting of 25 500
Å electron transport layer, atomic ratio 10: 1 thickness 2000
The MgAg cathode of Å was sequentially laminated by vacuum vapor deposition to fabricate an EL device as shown in FIG. The device thus obtained has an emission luminance of 23 at a current density of 30 mA / cm ^2.
The driving voltage was 0 cd / cm ² and the driving voltage was 11.2V. The emission spectrum showed a green emission centered at 520 nm.

[Chemical 8]

Comparative Example 1 On the same glass substrate as in Example 1, 500 Å of the hole transporting light emitting layer represented by the above structural formula (Chemical formula 8) and an electron transporting layer made of the compound represented by the following structural formula (Chemical formula 9) 500
Å, a cathode was formed by vacuum evaporation from MgAg having an atomic ratio of 10: 1 to 2000Å to prepare an EL device. When a direct current power supply was connected to the anode and cathode of the device thus manufactured through lead wires, clear green light emission was observed. The light emission at this time had a peak at 520 nm.
When this device was continuously driven under a constant current with a current density of 30 mA / cm ² , EL emission was not observed at all after 1 hour.

[Chemical 9]

Comparative Example 2 An EL device was prepared in the same manner as in Comparative Example 1. However, a compound represented by the following structural formula (Formula 10) was used as the electron transport layer. When a direct current power supply was connected to the anode and cathode of the device thus manufactured through lead wires, clear green light emission was observed. The light emission at this time had a peak at 522 nm. When this device was continuously driven under a constant current with a current density of 30 mA / cm ² , the EL emission intensity after one hour was 50 cd / m ² or less.

[Chemical 10]

Comparative Example 3 On the same ITO substrate as in Example 1, 400 Å of the compound (Chemical formula 7) as a hole transport layer, 150 Å of the following compound (Chemical formula 11) as a light emitting layer, and the structural formula (Chemical formula: The compound shown in 9) is vapor-deposited by 500Å and EL
A device was produced. When a direct current power supply was connected to the anode and cathode of the device thus produced through lead wires, clear blue-green light emission was observed. Light emission at this time is 458n
It had a peak at m. This device has a current density of 30 mA
When continuously driven under a constant current of / cm ² , EL emission was 20 cd / m ² or less after 1 hour.

[Chemical 11]

Comparative Example 4 An EL device was prepared in the same manner as Comparative Example 3. However, the compound represented by the structural formula (Formula 10) was used as the electron transport layer. When a direct current power supply was connected to the anode and cathode of the device thus produced through lead wires, clear blue-green light emission was observed. The light emission at this time had a peak at 483 nm. When this device was continuously driven under a constant current with a current density of 30 mA / cm ² , the EL emission intensity after one hour was 60 cd / m ² or less.

Comparative Example 5 An EL device was prepared in the same manner as Comparative Example 3. However, a compound represented by the following structural formula (Formula 12) was used as the electron transport layer. When a direct current power supply was connected to the anode and cathode of the device thus produced through a lead wire, green light emission having a peak at 499 nm was observed, unlike in the case of Example 1. The current density of this device is 30 mA / cm.
^When continuously driven under a constant current of ² , 105 cd
No emission was obtained with an emission luminance of / m ² . A decrease in EL emission efficiency was observed as compared to the case where 66 was used for the electron transport layer.

[Chemical 12]

Examples 7 to 17 On the same ITO substrate as in Example 1, 400 Å of the compound (Chemical Formula 7) as a hole transport layer, 150 Å of the compounds shown in the following Tables 3 and 4 as a light emitting layer, and further an electron transport layer. As the compound No. 66 was vapor-deposited in an amount of 500Å to prepare an EL device. When the EL device thus manufactured was driven by applying a direct current voltage, the device characteristics shown in Table 4 were exhibited.

Examples 18 to 21 On the same ITO substrate as in Example 1, 400 Å of the compound (Chemical formula 7) was used as a hole transport layer, and 150 Å of the compound represented by the structural formula (Chemical formula 11) was used as a light emitting layer. Compounds shown in Table 5 are vapor-deposited by 500Å and EL
A device was produced. When a direct current voltage was applied to the EL device thus manufactured and the device was driven, the device characteristics shown in Table 5 were exhibited.

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

Since the electroluminescent device of the present invention uses the above-mentioned specific oxadiazole compound as the 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. With it, it becomes possible to exhibit various color tones. Further, since such an oxadiazole-based compound is a compound that is excellent in film-forming property and is stable over time, it also has an advantage that an electroluminescent device can be obtained by a simple method.

[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 another electroluminescent device according to the present invention.

FIG. 4 is a schematic cross-sectional view of still another electroluminescent device according to the present invention.

FIG. 5 shows No. 1 in Table 1- (3) of the present invention. 25 of the oxadiazole compound R. Spectrum (KBr tablet method).

FIG. 6 shows No. 1 in Table 1- (3) of the present invention. 26 of the oxadiazole compound. R. Spectrum (KBr tablet method).

FIG. 7 shows No. 1 in Table 1- (3) of the present invention. I. of the oxadiazole compound of 27. R. Spectrum (KBr tablet method).

FIG. 8 shows No. 1 in Table 1- (3) of the present invention. 22 of the oxadiazole compound. R. Spectrum (KBr tablet method).

FIG. 9 shows No. 1 in Table 1- (3) of the present invention. Of the oxadiazole compound of 23. R. Spectrum (KBr tablet method).

[Explanation of symbols]

1 ... Substrate, 2, 4 ... Electrode, 3a ... Light emitting layer, 3b ... Electron transport layer, 3c ... Hole transport layer.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Chihaya Adachi 1-3-3 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. An anode and a cathode, and at least one layer of one or a plurality of organic compound layers sandwiched between the anode and the cathode are represented by the following general formula (I) (formula 1) to the following general formula (VI).
An electroluminescent element comprising a layer containing at least one oxadiazole-based compound having a plurality of aryl oxadiazole structures selected from the chemical formula (6) as a constituent component. [Chemical 1] [Chemical 2] [Chemical 3] [Chemical 4] [Chemical 5] [Chemical 6] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, an alkoxy group, a substituted or unsubstituted amino group, a cyano group or the like. Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group.)