JP3146619B2 - Organic electroluminescent device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to a thin film type device which emits light by applying an electric field by a combination of a hole transport layer and an electron transport layer made of an organic compound. It is about devices.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent device,
ZnS, Ca, which are II-VI compound semiconductors of inorganic materials
In S, SrS, etc., Mn as a luminescence center and rare earth elements (E
u, Ce, Tb, Sm, etc.) are generally used. However, electroluminescent devices made from the above inorganic materials require: 1) AC drive (50 to 1000 Hz); 2) High drive voltage (Up to 200 V), 3) it is difficult to achieve full color (particularly, blue is a problem), and 4) the cost of peripheral driving circuits is high.

However, in recent years, in order to improve the above problems,
Electroluminescent devices using organic materials have been developed. As the light emitting layer material, in addition to anthracene and pyrene which have been known for a long time, a cyanine dye (J. Chem. S)
oc., Chem. Commun., 557, 1985), pyrazoline (Mol. Crys. Liq. Cryst., 135, 355,
1986), perylene (Jpn. J. Appl. Phys., 25).
Vol. L773, 1986) or a coumarin compound or tetraphenylbutadiene (JP-A-57-5178).
No. 1) has been reported.

Further, in order to improve the efficiency of injecting carriers from the electrodes in order to increase the luminous efficiency, the type of the electrodes is optimized, and a device for providing a luminescent layer composed of a hole transport layer and an organic phosphor is disclosed (Japanese Patent Application Laid-open No. Sho. No. 57-51781, JP-A-59
194393, JP-A-63-29569, Appl. Phys. Lett., 51, 913, 1987.
Year). Further, for the purpose of improving the luminous efficiency of the device and changing the luminescent color, doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl.
hys., 65, 3610, 1989).

[0005]

As described above, the organic electroluminescent devices disclosed so far are still insufficient in luminous performance, particularly luminous efficiency and stability of luminous characteristics over a long period of time. Was desired. In view of the above situation, the present inventors have conducted intensive studies with the aim of providing an organic electroluminescent device that can be stably driven for a long time with high luminous efficiency. The present invention has been completed by finding that it is suitable for the organic electron transporting layer to be contained.

[0006]

That is, the gist of the present invention is as follows.
In an organic electroluminescent device in which an anode, an organic hole transport layer, an organic electron transport layer, and a cathode are sequentially laminated, the organic hole transport layer and / or the organic electron transport layer are represented by the following general formula (I)
And / or an organic electroluminescent device containing the compound represented by (I ′).

[0007]

Embedded image

(Wherein R ¹ represents a hydrogen atom, an alkyl group, an alkoxycarbonyl group, an alkoxycarbonylalkyl group, an aralkyl group or a phenyl group, and R ² represents an alkoxycarbonyl group, an alkoxyalkoxycarbonyl group, an acyl group, a cyano group Or a carbamoyl group which may have a substituent, and R ³ represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a nitro group, a cyano group,
It represents an alkoxycarbonyl group, a carbamoyl group which may have a substituent, a sulfamoyl group which may have a substituent or a dialkylamino group. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view schematically showing an example of the structure of an organic electroluminescent device of the present invention, wherein 1 is a substrate, 2a and 2b are conductive layers, 3 is an organic hole transport layer, and 4 is an organic electron transport. Each layer is represented. The substrate 1 serves as a support for the organic electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, or the like. Transparent synthetic resin substrates such as polymethacrylate, polycarbonate, and polysulfone are preferred.

A conductive layer 2a is provided on the substrate 1,
The conductive layer 2a is usually made of a metal such as aluminum, gold, silver, nickel, palladium, and tellurium, a metal oxide such as an oxide of indium and / or tin, copper iodide, carbon black, or poly (3-methylthiophene). )
And the like. The formation of the conductive layer 2a is usually performed by a sputtering method, a vacuum deposition method, or the like, but metal fine particles such as silver or copper iodide, carbon black, conductive metal oxide fine particles,
In the case of a conductive resin fine powder or the like, it can also be formed by dispersing in an appropriate binder resin solution and applying it on a substrate. Further, in the case of a conductive resin, a thin film can be formed directly on a substrate by electrolytic polymerization. Conductive layer 2
a can also be formed by laminating different substances.

The thickness of the conductive layer 2a varies depending on the required transparency. If transparency is required, the visible light transmittance is desirably 60% or more, preferably 80% or more. In this case, the thickness is usually 50 to 1000
0 °, preferably about 100 to 5000 °. If opaque, the conductive layer 2a may be the same as the substrate 1. Further, the conductive layer 2a can be stacked with a different material.

In the example shown in FIG. 1, the conductive layer 2a functions as an anode (anode) for injecting holes. on the other hand,
The conductive layer 2b serves as a cathode (cathode) as the organic electron transport layer 4
Plays the role of injecting electrons into As the material used for the conductive layer 2b, the material for the conductive layer 2a can be used. However, for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium,
A metal such as indium, aluminum, silver, or an alloy thereof is used. The thickness of the conductive layer 2b is generally the same as that of the conductive layer 2a, and can be formed by the same method as the conductive layer 2a.

Although not shown in FIG. 1, a substrate similar to substrate 1 can be further provided on conductive layer 2b. However, as the electroluminescent element, at least one of the conductive layer 2a and the conductive layer 2b needs to have good transparency. From this, one of the conductive layers 2a and 2b
The thickness is preferably 100 to 5000 °, and good transparency is desired.

An organic hole transport layer 3 is provided on the conductive layer 2a. The organic hole transport layer 3 efficiently transports holes from the anode between the electrodes to which an electric field is applied. Formed from compounds that can be transported in the direction of The organic hole transport compound needs to be a compound having a high hole injection efficiency from the conductive layer 2a and capable of efficiently transporting the injected holes. For this purpose, it is required that the compound has a small ionization potential, a large hole mobility, and a trap which is excellent in stability and positive and hardly occurs during production or use.

Examples of such hole transport compounds include those described on pages 5 to 6 of JP-A-59-194393 and columns 13 and 14 of US Pat. No. 4,175,960. Can be Preferred specific examples of these compounds include N, N'-diphenyl-N, N'-
(3-methylphenyl) -1,1′-biphenyl-4,
Aromatic amine compounds such as 4'-diamine, 1,1'-bis (4-di-p-tolylaminophenyl) cyclohexane, and 4,4'-bis (diphenylamino) quadrophenyl. Other than the aromatic amine compounds,
Hydrazone compounds disclosed in JP-A-2-311591 can be mentioned. These aromatic amine compounds or hydrazone compounds may be used alone or, if necessary, as a mixture.

The organic hole transport layer 3 is formed by laminating on the conductive layer 2a by a coating method or a vacuum evaporation method. For example, in the case of a coating method, one or more organic hole transporting compounds are added and dissolved by adding additives such as a binder resin which does not trap holes as required and a coating property improving agent such as a leveling agent. The applied coating solution is adjusted, applied to the conductive layer 2a by a method such as spin coating, and dried to form the organic hole transporting layer 3. Examples of the binder resin include polycarbonate, polyacrylate, and polyester. Since a large amount of the binder resin decreases the hole mobility, a small amount is desirable, and the amount is preferably 50% by weight or less.

In the case of the vacuum evaporation method, the organic hole transporting material is put in a crucible provided in a vacuum vessel, and the inside of the vacuum vessel is evacuated to 10 ^-6 Torr by a suitable vacuum pump. Is heated to evaporate the hole transport material and form a layer on the substrate placed opposite the crucible. The thickness of the organic hole transport layer 3 is usually 100 to 3000 °, preferably 300 to 1000 °. In order to uniformly form such a thin film, a vacuum deposition method is often used.

An organic electron transporting layer 4 is provided on the organic hole transporting layer 3. The organic electron transporting layer 4 efficiently transfers electrons from a cathode between electrodes to which an electric field is applied. It is formed from a compound that can be transported in three directions. The organic electron transport compound needs to be a compound having high electron injection efficiency from the conductive layer 2b and capable of efficiently transporting injected electrons. For this purpose, it is required that the compound has a high electron affinity, a high electron mobility, a high stability, and hardly generates impurities serving as traps during production or use.

Materials satisfying such conditions include aromatic compounds such as tetraphenylbutadiene (Japanese Patent Laid-Open No.
No. 51781) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP-A-59-194393).
), Cyclopentadiene derivatives (JP-A-2-28)
9675), perinone derivatives (JP-A-2-289)
676), oxadiazole derivatives (Japanese Unexamined Patent Publication No.
No. 216791), bisstyrylbenzene derivatives (Japanese Patent Laid-Open Nos. 1-245087 and 2-222484).
Japanese Patent Application Laid-Open Nos. 2-189890 and 3-7991, coumarin compounds (Japanese Patent Laid-Open Nos. 2-191694 and 3-792), and rare earth complexes (Japanese Patent Laid-Open No. 1-256884). Japanese Patent Application Laid-Open No. 3-252292), distyrylpyrazine derivatives (JP-A-2-252793), thiadiazolopyridine derivatives (JP-A-3-37292), pyrrolopyridine derivatives (JP-A-3-37293), and naphthyridine derivatives (JP-A-3-37293). Kaihei 3-2033982
Publication). When these compounds are used, the organic electron transport layer 4 simultaneously plays the role of transporting electrons and the role of emitting light when holes and electrons recombine.

The thickness of the organic electron transporting layer 4 is usually 100
Å2000Å, preferably 300〜1000Å.
The organic electron transporting layer 4 can be formed in the same manner as the organic hole transporting layer 3, but usually, a vacuum evaporation method is used. Further, in order to further improve the luminous efficiency of the organic electroluminescent element, another organic electron transport layer 5 can be further laminated on the organic electron transport layer 4 as shown in FIG. The compound used for the organic electron transport layer 5 is required to be capable of easily injecting electrons from the cathode and to have a higher electron transport ability. Examples of such an organic electron transporting compound include diphenylquinone derivatives such as a compound represented by the following structural formula (D11), and perylenetetracarboxylic acid derivatives such as a compound represented by the following structural formula (D12) (Jp
n. J. Appl. Phys. 27, L269, 1988
Oxadiazole derivatives such as a compound represented by the following structural formula (D13) (Appl. Phys. Lett. 55, 1
489, 1989).

[0021]

Embedded image

[0022]

Embedded image

[0023]

Embedded image

The thickness of the organic electron transport layer 5 is as follows.
Usually 100 to 2000 °, preferably 300 to 100
0 °. In addition, it is also possible to stack the conductive layer 2b, the organic electron transport layer 4, the organic hole transport layer 3, and the conductive layer 2a in this order on the substrate, that is, at least as described above. It is also possible to provide the electroluminescent element of the present invention between two substrates, one of which is highly transparent. Also,
Similarly, the structure may be reversed from that of FIG.

Conventionally, various fluorescent dyes have been doped with an 8-hydroxyquinoline aluminum complex as a host material for the purpose of improving the luminous efficiency of an organic light emitting device and changing the luminescent color (US). Japanese Patent No. 4,769,292) has the advantages of this doping method that the luminous efficiency is improved by using a high-efficiency fluorescent dye, the emission wavelength is checked by selecting the fluorescent dye, and a fluorescent dye that causes concentration quenching can also be used. Fluorescent dyes having poor film properties can also be used.

In the present invention, when the organic electron transporting layer plays a role, the host material includes the above-mentioned organic electron transporting compound. When the organic hole transporting layer plays the role, the host material includes And the aforementioned aromatic amine compounds and hydrazone compounds. In the present invention, the region doped with the compound represented by the general formula (I) and / or (I ′) is the entire organic hole transport layer 3 and / or the organic electron transport layer 4, It may be a part of it. The amount of the compound represented by the general formula (I) doped with respect to the host material is preferably 10 ⁻³ to 10 mol%.

The compound represented by the general formula (I) and / or (I ') shows strong fluorescence in a dispersed state, and when doped with a host material, the luminous efficiency of the device is improved. Further, the thin film state of the host material can be structurally stabilized, and the organic electroluminescent device can be provided with long-term stability. The compound represented by the general formula (I) and / or (I ′) is converted into an organic hole transport layer 3 and / or
Alternatively, as a method of doping the organic electron transporting layer 4, for example, in the case of a coating method, an organic hole transporting compound or an organic electron transporting compound and the general formula (I) and / or (I ′)
In addition, if necessary, a coating solution prepared by adding and dissolving a binder resin which does not trap holes or electrons as necessary, or an additive such as a coating property improving agent such as a leveling agent, if necessary, is adjusted by spinning. It is formed by applying by a coating method or the like and drying. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the mobility of holes or electrons is reduced. In the case of the vacuum evaporation method, an organic hole transporting compound or an organic electron transporting compound is put into a crucible placed in a vacuum vessel, and the compound represented by the general formula (I) and / or (I ′) is separated. And put the inside of the vacuum vessel with a suitable vacuum pump to 10 ^-6 To
After evacuation to about rr, each crucible is heated and evaporated simultaneously to form a layer on the substrate placed facing the crucible. As another method, a mixture of the above materials at a predetermined ratio may be evaporated using the same crucible.

In the above general formulas (I) and (I '),
Preferably, R ¹ is a hydrogen atom; an alkyl group such as a methyl group and an ethyl group; an alkoxycarbonyl group such as a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group and a butoxycarbonyl group; a methoxycarbonylmethyl group, an ethoxycarbonylmethyl group, and a propoxy group. An alkoxycarbonylalkyl group such as a carbonylmethyl group or a butoxycarbonylmethyl group; an aralkyl group such as a benzyl group or a phenethyl group; a phenyl group; and R ² represents a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, a butoxycarbonyl group, or the like. An alkoxycarbonyl group; an alkoxyalkoxycarbonyl group such as a methoxyethoxycarbonyl group and an ethoxyethoxycarbonyl group; an acyl group such as an acetyl group and a benzoyl group; a cyano group; a carbamoyl group; A substituted carbamoyl group such as phenylcarbamoyl group, methylcarbamoyl group, ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group, dimethylcarbamoyl group, diethylcarbamoyl group, morpholinocarbamoyl group; R ³ represents a hydrogen atom; Atom; methyl group, ethyl group,
Alkyl groups such as propyl group and butyl group; alkoxy groups such as methoxy group, ethoxy group, propoxy group and butoxy group; nitro group; cyano group; alkoxy groups such as methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group and butoxycarbonyl group Carbonyl group; carbamoyl group; phenylcarbamoyl group, methylcarbamoyl group, ethylcarbamoyl group, propylcarbamoyl group,
A substituted carbamoyl group such as a butylcarbamoyl group, a dimethylcarbamoyl group, a diethylcarbamoyl group, and a morpholinocarbamoyl group; a sulfamoyl group; a substituted sulfamoyl group such as a phenylsulfamoyl group, a methylsulfamoyl group and a dimethylfamoyl group; a dimethylamino group;
And a dialkylamino group such as a diethylamino group and a dipropylamino group.

These compounds can be synthesized by the following method. For example, first, Japanese Patent Publication No. 53-40
According to the method shown in JP-A-212, a compound represented by the following general formula (II) is synthesized according to the following reaction formula.

[0030]

Embedded image

(Wherein R ¹ and R ² are those of the above-mentioned general formula (I)
Has the same meaning as in That is, the hydrazone compound obtained by imidizing 4,5-dichloronaphthalic anhydride with hydrazine and then reacting with a carbonyl compound is cyclized in the presence of a basic condensing agent to obtain the compound represented by the general formula (II). The compound represented by is obtained. next,
For example, EC Horning, "Organic Syntheses", 3
Volume, 475, John Wiley & Sons., (1967), according to the following reaction formula:
A compound represented by the following general formula (III) is synthesized.

[0032]

Embedded image

(Wherein R ³ has the same meaning as in the above formula (I)), ie, hydrazinobenzoic acid obtained by diazotizing an anthranilic acid derivative with sodium nitrite and then reacting with concentrated hydrochloric acid The 3-hydroxyindazole derivative represented by the general formula (III) can be obtained by boiling the hydrochloride in an aqueous hydrochloric acid solution and neutralizing with sodium carbonate. The compound represented by the above general formula (II), the 3-hydroxyindazole derivative represented by the above general formula (III) and potassium carbonate obtained as described above are dissolved in N-methylpyrrolidone at 150 ° C. To react. After the reaction, methanol is added after cooling.
The precipitate is filtered and then recrystallized from N-methylpyrrolidone to obtain the compound represented by the general formula (I) and / or (I ').

As described above, the heterocyclic compounds thus produced may be of two types, and in some cases four or eight types, as represented by the general formulas (I) and / or (I '). There are isomers. In the present invention, any one of these isomers can be used, but it is convenient to use it as a mixture without separating the isomers. Specific examples of the compounds thus obtained are shown in Table 1, but are not limited thereto. These compounds have a high fluorescence intensity in a dispersed state, and have good light resistance and heat resistance.

[0035]

[Table 1]

[0036]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. Example 1 An organic electroluminescent device having the structure shown in FIG. 1 was produced by the following method.

A transparent conductive film of indium tin oxide (ITO) deposited on a glass substrate at 1200.degree. Is subjected to ultrasonic cleaning with an organic alkali, water cleaning, and ultrasonic cleaning with isopropyl alcohol, and then placed in a vacuum evaporation apparatus. Then, air was evacuated using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less. As an organic hole transport layer material, hydrazone compounds represented by the following structural formulas (H1) and (H2) were mixed at a molar ratio of 1: 0.3.

[0038]

Embedded image

This was placed in a ceramic crucible and heated by a tantalum wire heater around the crucible to evaporate in a vacuum vessel. The temperature of the crucible was in the range of 150 to 175 ° C., and the degree of vacuum during evaporation was 7 × 10 ⁻⁷ Torr. Thus, an organic hole transport layer having a thickness of 510 ° was formed. The deposition time was 3 minutes. Next, an 8-hydroxyquinoline complex of aluminum represented by the following structural formula (E1) is used as a material for the organic electron transport layer.

[0040]

Embedded image

Table 1 shows the compounds to be doped.
The compounds (4) shown in (1) and (2) were simultaneously heated and vapor-deposited in separate crucibles. At this time, the temperature of each crucible was 200 to 250 ° C. for the 8-hydroxyquinoline complex of aluminum, and 1 ° for the compound (4).
It controlled at 80-200 degreeC. Vacuum degree during evaporation is 9 × 10
^{At -7} Torr, the deposition time was 3 minutes. as a result,
There was obtained an organic electron transporting layer having a thickness of 770 ° in which the compound (4) was doped at 1.5 mol% with respect to the above complex.

Finally, as a cathode, an alloy electrode of magnesium and silver was vapor-deposited to a thickness of 1200 ° by a binary simultaneous vapor deposition method. The vapor deposition was performed using a molybdenum boat, the degree of vacuum was 5 to 6 × 10 ⁻⁶ Torr, and the vapor deposition time was 6 minutes.
A glossy film was obtained. The atomic ratio of magnesium to silver was 10: 3.2. Table 2 shows the results of the emission characteristics measured by applying a positive DC voltage to the ITO electrode (anode) and applying a negative DC voltage to the magnesium / silver electrode (cathode) of the organic electroluminescent device thus manufactured.

This device exhibited yellow uniform light emission, and the peak wavelength of the light emission was 575 nm, which almost coincided with the fluorescence wavelength of the solution shown in Reference Example 3 below. FIG. 3 shows the relationship between the luminous efficiency and the voltage characteristics of this device. Comparative Example 1 An organic electroluminescent device was produced in the same manner as in Example 1, except that the compound (4) was not doped into the organic electron transporting layer. Table 2 shows the measurement results of the light emission characteristics of this device. This device exhibited uniform green emission having a peak emission wavelength at 530 nm. FIG. 3 shows the relationship between the luminous efficiency and the voltage characteristics of this device.

[0044]

[Table 2] Vth: voltage at which the luminance becomes 1 cd / m ² Luminous efficiency: luminous efficiency at practical luminance (100 cd / m ² ) Example 2 The device produced in Example 1 was stored in a vacuum for 30 days, and then the luminous characteristics were measured. As a result, reductions in light emission luminance and light emission efficiency did not pose any practical problems, and showed long-term stability. Comparative Example 2 After the device manufactured in Comparative Example 1 was stored in a vacuum, the light emission characteristics were measured. As a result, after 30 days, the drive voltage was significantly increased and the luminance was significantly reduced.

REFERENCE EXAMPLE A solution prepared by dissolving the compounds (1) and (7) shown in Table 1 at a concentration of 1 mmol / liter in chloroform was excited with a mercury lamp (wavelength 350 nm) and measured. Table 3 shows the results of the fluorescence measurement. The standard of the relative fluorescence intensity was a chloroform solution of aluminum 8-hydroxyquinoline complex (E1) (abbreviated as Al (ox) _{3 in the} table).

[0046]

[Table 3]

[0047]

According to the organic electroluminescent device of the present invention, an anode, an organic hole transporting layer, an organic electron transporting layer and a cathode are sequentially provided on a substrate, and the organic hole transporting layer and / or the organic electron transporting layer are provided. Alternatively, since a specific compound is doped in a part thereof, when a voltage is applied using both conductive layers as electrodes, light emission with practically sufficient luminance can be obtained at a low driving voltage, and after storage for a long time. Can maintain the initial light emission characteristics.

Accordingly, the electroluminescent device of the present invention is a light source (for example, a light source of a copier, a liquid crystal display or an instrument) utilizing the features of the field of flat panel displays (for example, OA computers and wall-mounted televisions) and surface illuminators. It can be applied to various types of backlight sources, display boards, and marker lights, and its technical value is great.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of the organic electroluminescent device of the present invention.

FIG. 2 is a schematic sectional view of another embodiment of the organic electroluminescent device of the present invention.

FIG. 3 is a diagram showing a relationship between luminous efficiency and voltage characteristics of the organic electroluminescent devices manufactured in Example 1 and Comparative Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2a, 2b Conductive layer 3 Organic hole transport layer 4 Organic electron transport layer 4a Organic electron transport layer doped with fluorescent dye 5 Organic electron transport layer composed of a compound different from 4a

Claims (1)

(57) [Claims] 1. An organic electroluminescent device comprising an anode, an organic hole transporting layer, an organic electron transporting layer, and a cathode sequentially laminated, wherein the organic hole transporting layer and / or the organic electron transporting layer has the following general formula: An organic electroluminescent device comprising the compound represented by (I) and / or (I ′). Embedded image (Wherein, R ¹ represents a hydrogen atom, an alkyl group, an alkoxycarbonyl group, an alkoxycarbonylalkyl group, an aralkyl group or a phenyl group, and R ² represents an alkoxycarbonyl group, an alkoxyalkoxycarbonyl group, an acyl group,
A cyano group or a carbamoyl group which may have a substituent, wherein R ³ is a hydrogen atom, a halogen atom, an alkyl group,
It represents an alkoxy group, a nitro group, a cyano group, an alkoxycarbonyl group, a carbamoyl group which may have a substituent, a sulfamoyl group which may have a substituent or a dialkylamino group. )