JPH05295362A - Organic electroluminescent element - Google Patents

Abstract

(57) [Summary] [Object] To provide an organic electroluminescent device which can be stably driven over a long period of time. [Structure] An organic electroluminescent device comprising an anode, a hole transport layer, an organic electron transport layer and a cathode, which are sequentially laminated,
The organic electron transport layer contains a hydrazone compound. [Effect] It is possible to obtain light emission with practically sufficient brightness at a low driving voltage, and exhibit stable light emission performance for a long period of time.

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 specifically, it is a thin film type device which emits light by applying an electric field by a combination of a hole transporting layer and an electron transporting 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 group compound semiconductors of inorganic materials
In S, SrS, etc., Mn, which is the emission center, and rare earth elements (E
(u, Ce, Tb, Sm, etc.) is generally doped, but the electroluminescent device made of the above inorganic material is: 1) AC drive is required (50 to 1000 Hz), 2) High drive voltage (Up to 200 V), 3) full colorization is difficult (especially blue color is a problem), and 4) peripheral drive circuit cost is high.

However, in recent years, in order to improve the above problems,
Development of electroluminescent devices using organic materials has started. In addition to the previously known anthracene and pyrene as the light emitting layer material, cyanine dyes (J. Chem. S
oc., Chem. Commun., 557, p. 1985, pyrazoline (Mol. Crys. Liq. Cryst., 135, 355,
1986), Perylene (Jpn. J. Appl. Phys., 25)
Vol., L773, 1986) or coumarin compounds and tetraphenyl butadiene (JP-A-57-5178).
No. 1) has been reported.

Further, in order to improve the efficiency of carrier injection from the electrode in order to increase the luminous efficiency, the kind of the electrode is optimized and a light emitting layer comprising a hole transport layer and an organic phosphor is provided. 57-51781, JP-A-59-59
-194393, JP-A-63-295695, Appl. Phys. Lett., 51, 913, 1987.
Years) etc. Furthermore, for the purpose of improving the light emission efficiency of the device and changing the light emission color, dope a fluorescent dye for laser such as coumarin using aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. P.
hys., 65, 3610, 1989).

[0005]

In the organic electroluminescence device as described above, an electrode material having a low work function for injecting electrons from the cathode into the electron transport layer, for example, Japanese Patent Laid-Open No. HEI-2.
The magnesium-based alloy disclosed in Japanese Patent Publication No. -15595 is used, but the efficiency of electron injection is still insufficient.

In Japanese Unexamined Patent Publication No. 2-213088, an organic compound having a porphyrin ring or a phthalocyanine skeleton is used as an organic electron transport layer, and an electron-donating organic compound such as tetrathiofulvalene (TTF) or tetrathiotetracene ( It has been disclosed to mix TTT) and the like in a ratio of 5: 1. However, since all of these compounds have a quenching effect, it is conceivable that the emission brightness will be significantly reduced when they come into contact with the light emitting layer. Further, since these compounds have large absorption in the visible light region, it is considered that the emission spectrum itself is changed,
Considering the application of the organic electroluminescent device to full-color display, the above method is not preferable.

In addition, in the organic electroluminescent devices disclosed so far, electroluminescence is brought about by recombination of injected holes and electrons. However, in general, injection of carriers, for example, injection of holes must be carried out by overcoming the injection barrier at the interface between the anode and the organic hole transport layer, and injection of electrons by overcoming injection barrier at the interface between the cathode and the light emitting layer. I won't. In particular, a high electric field is required due to the barrier of electron injection, and as a result, the driving voltage of the device becomes high, resulting in insufficient light emission performance, particularly light emission efficiency, and instability of operation due to interface instability. Therefore, further improvement studies are desired.

In view of the above situation, the inventors of the present invention have made earnest studies for the purpose of providing an organic electroluminescent device which can be driven at a low voltage, and as a result, the electron transport layer preferably contains a hydrazone compound. Therefore, the present invention has been completed.

[0009]

The organic electroluminescent device of the present invention is an organic electroluminescent device in which an anode, a hole transporting layer, an organic electron transporting layer and a cathode are sequentially laminated, and the organic electron transporting layer is It is characterized by containing a hydrazone compound. In addition, in the present invention, the organic electron transport layer is particularly preferably one of the hydrazone compounds represented by the following general formula (I).
It is preferable to contain one kind or a mixture of two or more kinds.

[0010]

[Chemical 2]

In the above general formula (I), A is monovalent or divalent containing at least one aromatic hydrocarbon ring or aromatic heterocycle.
Shows a valent organic group, and these rings may have a substituent. R ¹ , R ² , R ³ , R ⁴ and R ⁵ represent a hydrogen atom or an alkyl group which may have a substituent, an aralkyl group, an aromatic hydrocarbon group or a heterocyclic group, and R ⁶ and R ⁷ Is an optionally substituted alkyl group, aralkyl group, allyl group, aromatic hydrocarbon group or heterocyclic group, and l is 0
Alternatively, 1 and m are 0, 1 or 2, and n is an integer of 1 or 2. However, A, R ¹ and the carbon atom to which R ¹ is bonded may be bonded to each other to form a ring, and R ⁶ and R ⁷ and the nitrogen atom to which they are bonded are bonded to each other to form a ring. May be formed.

Hereinafter, the organic electroluminescent device of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a structural example of the organic electroluminescent element of the present invention.
Is a substrate, 2a and 2b are conductive layers, 3 is a hole transport layer, and 4 is an organic electron transport layer. The substrate 1 serves as a support for the organic electroluminescent element of the present invention, and a plate of quartz or glass, a metal plate or metal foil, a plastic film or sheet, or the like can be used, but a glass plate, polyester,
A transparent synthetic resin substrate such as polymethacrylate, polycarbonate or polysulfone is preferable.

A conductive layer 2a is provided on the substrate 1,
This conductive layer 2a is usually a metal such as aluminum, gold, silver, nickel, palladium, tellurium, indium and / or
Alternatively, a metal oxide such as tin oxide, a conductive resin such as copper iodide, carbon black, or poly (3-methylthiophene) is used. The conductive layer 2a is usually formed 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, conductive resin fine powder, etc. In this case, it can also be formed by dispersing it 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 directly formed on the substrate by electrolytic polymerization. Conductive layer 2a
Can be formed by stacking different materials.

The thickness of the conductive layer 2a varies depending on the required transparency, but when the transparency is required, it is desirable that the visible light transmittance is 60% or more, preferably 80% or more, In this case, the thickness is usually 50 to 1000.
It is 0Å, preferably about 100 to 5000Å. The conductive layer 2a may be the same as the substrate 1 if it is opaque. Further, the conductive layer 2a can be laminated with different materials.

In the example of FIG. 1, the conductive layer 2a plays a role of injecting holes as an anode. On the other hand, the conductive layer 2b plays a role of injecting electrons into the organic electron transport layer 4 as a cathode. The material used for the conductive layer 2b can be the material for the conductive layer 2a, but a metal having a low work function is preferable for efficient electron injection, and tin,
Metals such as magnesium, indium, aluminum and silver or alloys thereof are used. The thickness of the conductive layer 2b is usually about the same as that of the conductive layer 2a, and the conductive layer 2b can be formed by the same method.

Although not shown in FIG. 1, a substrate similar to the substrate 1 may be further provided on the conductive layer 2b. However, in 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 is
A film thickness of 100 to 5000Å is preferable, and good transparency is desired.

The hole transport layer 3 is provided on the conductive layer 2a. The hole transport layer 3 efficiently directs holes from the anode between the electrodes to which an electric field is applied to the organic electron transport layer 4. Formed from a compound that can be transported to. The hole transport material 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 that purpose, it is required that the compound has a small ionization potential, a large hole mobility, and a stable and excellent trapping impurity that does not easily occur during manufacturing or use.

Examples of such hole-transporting materials include organic materials described in JP-A-59-194393, pages 5 to 6 and US Pat. No. 4,175,960, columns 13 to 14 and the like. Can be mentioned. Specific preferred examples of these compounds include N, N'-diphenyl-N,
N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, 1,1'-bis (4-di-p-
Examples thereof include aromatic amine compounds such as tolylaminophenyl) cyclohexane and 4,4′-bis (diphenylamino) quadrophenyl. Other than aromatic amine compounds, hydrazone compounds disclosed in JP-A-2-311591, silazane compounds disclosed in US Pat. No. 4,950,950 and the like can be mentioned. These compounds are
They may be used alone or as a mixture as required. In addition to the above compounds, polyvinylcarbazole and Appl. Phys. Lett. Volume 59, page 2760 (1991)
Polymer compounds such as polysilanes shown in 1).

The organic hole transport layer 3 is formed by laminating on the conductive layer 2a by a coating method or a vacuum deposition method. For example, in the case of a coating method, one or more organic hole transport compounds are added and dissolved by adding a binder resin that does not become a hole trap if necessary and an additive such as a coating property improving agent such as a leveling agent. The coating solution thus prepared is prepared, coated on the conductive layer 2a by a method such as spin coating, and dried to form the organic hole transport layer 3. Examples of the binder resin include polycarbonate, polyacrylate, polyester and the like. If the addition amount of the binder resin is large, the hole mobility is lowered.

In the case of the vacuum deposition method, the organic hole transporting material is placed in a crucible installed in a vacuum container, the interior of the vacuum container is evacuated to 10 ^-6 Torr by a suitable vacuum pump, and then the crucible is placed. Is heated to evaporate the organic hole transport material and form a layer on the substrate placed facing the crucible. An inorganic material can also be used as the hole transport material. Examples of the inorganic material include p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, p-type hydrogenated microcrystalline silicon carbide, p-type zinc sulfide, and p-type zinc selenide. Such an inorganic hole transport layer 3 is formed by CVD.
Method, plasma CVD method, vacuum deposition method, sputtering method, or the like.

The thickness of the hole transport layer 3 is usually 100-3.
It is 000Å, preferably 300 to 1000Å. In order to uniformly form such a thin film, the vacuum evaporation method is often used. An organic electron transport layer 4 is provided on the hole transport layer 3, and the organic electron transport layer 4 efficiently transfers electrons from the cathode between the electrodes to which an electric field is applied in the direction of the organic hole transport layer 3. Formed from a compound that can be transported.

As the organic electron transport compound, the conductive layer 2b is used.
It is necessary for the compound to have a high electron injection efficiency and to efficiently transport the injected electrons. For that purpose, it is required that the compound has a high electron affinity, a high electron mobility, excellent stability, and an impurity that becomes a trap and is unlikely to be generated at the time of production or use.

As a material satisfying such a condition, an aromatic compound such as tetraphenyl butadiene (see JP-A-57 / 57)
No. 51781), aluminum complexes of 8-hydroxyquinoline, and other metal complexes (JP-A-59-194393).
JP-A-2-28).
9675), perinone derivatives (JP-A-2-289)
676), an oxadiazole derivative (JP-A-2-
No. 216791), and bisstyrylbenzene derivatives (JP-A Nos. 1-245087 and 2-222484).
No.), perylene derivatives (JP-A-2-189890 and JP-A-3-791), coumarin compounds (JP-A-2-191694 and JP-A-3-792), and rare earth complexes (JP-A-1-256584). No.), a distyrylpyrazine derivative (JP-A-2-252793), a thiadiazolopyridine derivative (JP-A-3-37292), a pyrrolopyridine derivative (JP-A-3-37293), a naphthyridine derivative (special Kaihei 3-203982
Gazette) and the like. When these compounds are used, the organic electron transport layer 4 simultaneously plays a role of transporting electrons and a role of causing light emission upon recombination of holes and electrons.

The thickness of the organic electron transport layer 4 is usually 100.
˜2000 Å, preferably 300 to 1000 Å.
The organic electron transport layer 4 can also be formed by the same method as that of the hole transport layer 3, but a vacuum deposition method is usually used.
In order to further improve the light emission efficiency of the organic electroluminescent device, as shown in FIG. 3, an anode, a hole transport layer, an organic light emitting layer, an organic electron transport layer doped with a hydrazine compound,
It may be a cathode or a laminated device structure. In this case, the organic light-emitting material includes the organic electron-transporting material, and the hydrazine compound-doped organic electron-transporting material is selected from materials different from the organic light-emitting layer, and is selected from the organic electron-transporting materials. Alternatively, it is required that the electron injection from the cathode be easy and the electron transporting capacity be even greater. Examples of such an organic electron transport compound include diphenylquinone derivatives such as the compound represented by the following structural formula (D11) and perylene tetracarboxylic acid derivatives (Jpn. J. A.) such as the compound represented by the following structural formula (D12).
ppl. Phys. 27, L269, 1988), oxadiazole derivatives such as compounds represented by the following structural formula (D13) (Appl. Phys. Lett. 55, 1489).
Page, 1989).

[0025]

[Chemical 3]

The film thickness of such an organic electron transport layer 5 is
Usually, 100 to 2000Å, preferably 300 to 100
It is 0Å. In addition, it is also possible to stack the conductive layer 2b, the organic electron transporting layer 4, the hole transporting layer 3, and the conductive layer 2a in this order on the substrate in the reverse structure to that of FIG. It is also possible to provide the electroluminescent device of the present invention between two highly transparent substrates. Similarly, the structure opposite to that shown in FIG. 2 can be adopted. In the present invention, the region doped with the compound represented by the general formula (I) is the entire organic electron transport layer 4,
It may be a part thereof. The amount of the compound represented by the general formula (I) doped with respect to the host material is 1
0 ^-3 to 10 mol% are preferred.

The compound represented by the general formula (I) exhibits strong fluorescence in a dispersed state, and when doped in the host material, the luminous efficiency of the device is improved. Furthermore, the thin film state of the host material can be structurally stabilized, and the organic electroluminescent device can be provided with long-term stability. As a method for doping the organic electron transporting layer 4 with the compound represented by the general formula (I), for example, in the case of a coating method, the organic electron transporting compound and the compound represented by the general formula (I) are used. Further, if necessary, a binder resin that does not become a trap of holes or electrons is added if necessary, and an additive such as a leveling agent or other coating improver is added to prepare a dissolved coating solution. The method is applied and dried to form. As a binder resin,
Examples thereof include polycarbonate, polyarylate, polyester and the like. The binder resin lowers the mobility of holes or electrons when it is added in a large amount, and therefore it is preferable that the binder resin be added in a small amount, preferably 50% by weight or less. In the case of the vacuum deposition method, the organic electron transporting compound is put in a crucible installed in a vacuum container, the compound represented by the general formula (I) is put in another crucible, and the inside of the vacuum container is put into an appropriate vacuum pump. At 10 ^-6 T
After exhausting to about orr, each crucible is simultaneously heated and evaporated to form a layer on the substrate placed facing the crucible. Further, as another method, a mixture of the above materials in a predetermined ratio may be evaporated using the same crucible.

In the organic electroluminescent device of the present invention, the hole injecting and transporting layer 3 is a hydrazone, preferably one or a mixture of two or more selected from the hydrazone compounds represented by the general formula (I). Is included. In the general formula (I), A represents a monovalent or divalent organic group containing at least one aromatic hydrocarbon ring or aromatic heterocycle, and these groups have a plurality of respective rings. Of course, it includes the case of forming a condensed polycycle. As an example of such an organic group, a group formed from a hydrocarbon is derived from benzene, naphthalene, anthracene, pyrene, perylene, phenanthrene, fluoranthene, acenaphthene, acenaphthylene, azulene, fluorene, indene, tetralin, naphthacene and the like. Monovalent or divalent aromatic hydrocarbon group; monovalent or divalent aromatic heterocycle derived from pyrrole, thiophene, furan, indole, carbazole, pyrazole, pyridine, acridine, phenazine, benzothiophene, benzofuran, etc. Group; further, condensed polycyclic compounds such as xanthene, thioxanthene, indoline, and phenothiazine. Further, as a group to which these are directly bonded, the following monovalent or divalent groups, namely, biphenyl, terphenyl, phenylanthracene, bithiophene, terthiophene, bifuran, thienylbenzene, thienylnaphthalene, pyrrolylthiophene, A monovalent or divalent group derived from N-phenylcarbazole and the like can be mentioned.

The group formed by combining the above-mentioned rings with a bonding group includes, as the bonding group, —CH ₂ —, —CH ₂ —CH ₂ —, —C (CH ₃ ) ₂ —,

[0030]

[Chemical 4]

An alkylene group which may have a substituent such as --CH ₂ CH ₂ CH _2- , --CHCH--, --C (CH
_{3) = CH -, - CH} 2 -CH = CH-CH 2 -, - CH
═CH—CH═CH— and other optionally substituted alkenylene groups, —C≡C—, —O—, —OCH ₂ CH ₂ O
-, -CO-, -CO-O-, -CO-CO-, -CO
_{-CH 2 -CH 2 -CO -, -} CS -, - S -, - S-S
-, - SO -, - SO 2 -, - N (CH 3) -, - CO-
NH-, -N = N-,

[0032]

[Chemical 5]

The monovalent or divalent group derived from the compound formed by using the above-mentioned bonding groups alone or in combination of two or more kinds. Examples of the compound formed using a bonding group, by these bonding groups, the aromatic ring or the heterocycle forms a condensed ring, for example, diphenylmethane, stilbene, tolan, 1,4-diphenylphthaldiene, diphenyl ether, Diphenyl sulfide, N-
Examples thereof include methyldiphenylamine, triphenylamine, azobenzene, and the like, and compounds in which the aromatic hydrocarbon or the heterocycle is combined using a bonding group instead of the phenyl group in the above examples. These aromatic hydrocarbon ring groups,
The aromatic heterocyclic group and the group derived from the compound formed by using the above-mentioned direct or bonding group may have a substituent. Examples of such a substituent include a lower alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group and a hexyl group; a lower alkoxy group such as a methoxy group, an ethoxy group and a butoxy group; an allyl group; a benzyl group and naphthylmethyl. Group, aralkyl group such as phenethyl group; aryloxy group such as phenoxy group, tolyloxy group; arylalkoxy group such as benzyloxy group, phenethyloxy group; aryl group such as phenyl group, naphthyl group; styryl group, naphthylvinyl group, etc. Aryl vinyl group; and dialkylamino groups such as dimethylamino group and diethylamino group. Further, the alkyl component in the above substituents may be substituted with an ether group, an ester group, a cyano group, a sulfide group or the like.

In the general formula (I), R ¹ , R ² , R ³ ,
R ⁴ and R ⁵ are each a hydrogen atom or a lower alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group or a hexyl group which may have a substituent; an aralkyl group such as a benzyl group or a phenethyl group; phenyl Group, naphthyl group, acenaphthyl group, anthryl group, pyrenyl group and the like aromatic hydrocarbon group similar to the above A; thienyl group, bithienyl group, carbazole group, indolyl group, furyl group, indoline group and the like in the above A The same heterocyclic group is shown. Substituents substituted with these include lower alkyl groups such as methyl group, ethyl group, propyl group, butyl group and hexyl group; lower alkoxy groups such as methoxy group, ethoxy group, butoxy group; aryl such as phenoxy group and tolyloxy group. Oxy groups; arylalkoxy groups such as benzyloxy group and phenethyloxy group; aryl groups such as phenyl group and naphthyl group; substituted amino groups such as dimethylamino group, diethylamino group, phenylmethylamino group, diphenylamino group, etc. .. However, R ¹ may form a ring together with A and the carbon atom to which R ¹ is bonded. Examples of such a case include the following.

[0035]

[Chemical 6]

R ⁶ and R ⁷ are optionally substituted lower alkyl groups such as methyl group, ethyl group, propyl group and butyl group; aralkyl groups such as benzyl group, phenethyl group and naphthylmethyl group; allyl Groups, aromatic hydrocarbon groups such as phenyl group and naphthyl group; and heterocyclic groups such as pyridyl group, thienyl group, furyl group and pyrrolyl group. Examples of the substituents substituting for these are the same as those for R ¹ , R ² , R ³ , R ⁴ and R ⁵ . However, R ⁶ and R ⁷
And a nitrogen atom to which these are bonded may be combined to form a ring, and examples of such a ring include the following.

[0037]

[Chemical 7]

In the general formula (I), n is A = 1.
In the case of a divalent group, 1 is represented, and in the case of a divalent group, 2 is represented.
The hydrazone compound represented by the general formula (I) can be easily produced, for example, by the method described in JP-A-2-311591. Main specific examples of the hydrazone compound thus obtained and the value of the ionization potential of each hydrazone compound (measured in a thin film state using an ultraviolet photoelectron analyzer (AC-1 type) manufactured by Riken Keiki Co., Ltd.). However, the present invention is not limited to these.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

In general, the organic electron transport material is an insulator itself without injection of carriers from the electrodes, and it is considered that it has almost no carriers. Generally, there is an electron injection barrier between the conductive layer 2b and the organic electron transport layer 4, and it is considered that this injection barrier is the difference between the work function of the conductive layer 2b and the electron affinity of the organic electron transport layer 4. You can Conductive layer 2
As the material of b, an electrode material having a low work function, for example, a magnesium-based alloy disclosed in JP-A-2-15595 is used, but the atomic ratio of magnesium to silver is 1
The work function of the alloy film of 0: 0.2 was 3.6 eV (the work function was measured by an ultraviolet photoelectron analyzer (AC-1 type) manufactured by Riken Keiki Co., Ltd.).

On the other hand, 8-hydroquinoline aluminum complex (J.P.
hys. Lett., 51, 913, 1987) A value of K reduction potential of -1.8 eV has been reported (US Pat. No. 4,769,292, IEICE Research Report OME9).
0-41, 1991), the electron affinity obtained from the values of these oxidation potentials is 2.5 eV by the following formula.

Electron affinity = reduction potential + 4.3 (J. Simon and J. J, Andre, Moleculer Semiconducto
rs, Springer-Verlag, 1985, p. 24) Based on the work function of the above magnesium alloy and the electron affinity of the aluminum complex of 8-hydroquinoline, in this case, the conductive layer 2b (cathode) and the organic electron transport layer 4 The electron injection barrier existing between is estimated to be 1.1 eV.

Similarly, the conductive layer 2a and the organic hole transport layer 3 are formed.
There is a hole injection barrier between and, and this injection barrier can be considered to be the difference between the ionization potential of the organic hole transport layer 3 and the work function of the conductive layer 2a. Indium tin oxide (hereinafter abbreviated as "ITO") is used for the conductive layer 2a.
Is usually used, but commercially available ITO glass (HO
YA Co., Ltd., glass is NA-40, ITO film thickness is 12
The work function of 00Å) is about 4.70 eV.

Further, as the organic hole transport layer, for example, the above-mentioned N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1' which is a conventionally used aromatic diamine is used.
-Biphenyl-4,4'-diamine (Jpn. J. Ap
pl. Phys. , 27, L269, 1988)
Was formed by vacuum vapor deposition, and its ionization potential was similarly measured with AC-1 and found to be 5.23 eV. Therefore, the hole injection barrier in this case is 0.5.
It is estimated to be 3 eV.

From the above results, the electron injection barrier from the conductive layer 2b to the organic electron transport layer 4 is about twice as large as the hole injection barrier, and therefore a high electric field is required to cross the electron injection barrier. In addition, since a voltage drop occurs at the interface between the anode and the organic electron transport layer, Joule heat is concentrated on the interface when the device is driven, which causes instability and deterioration of the device operation.

In the present invention, the compound represented by the general formula (I) has a small ionization potential, and when it is doped into the organic electron transport layer, it ionizes itself to give an electron to the organic electron transport material. As a result, electron generation as carriers occurs in the organic electron transport layer without depending on electron injection from the cathode, and as a result, excellent light emission characteristics, particularly a reduction in driving voltage can be achieved.

[0049]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative 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 to a thickness of 1200 Å was ultrasonically washed with an organic alkali, washed with water, and further with isopropyl alcohol, and then in a vacuum vapor deposition apparatus. And was evacuated using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less. As the organic hole injection layer material, hydrazone compounds represented by the following structural formulas (H1) and (H2) were mixed at a molar ratio of 1: 0.3.

[0051]

[Chemical 8]

This was placed in a ceramic crucible, heated with a tantalum wire heater around the crucible and evaporated in a vacuum vessel. The temperature of the crucible was in the range of 130 to 155 ° C., and the degree of vacuum during evaporation was 7 to 8 × 10 ⁻⁷ Torr. Thus, an organic hole transport layer having a film thickness of 525 Å was formed. The vapor deposition time was 1 minute. Next, as a material for the organic electron transport layer, an aluminum 8-hydroxyquinoline complex represented by the following structural formula (E1)

[0053]

[Chemical 9]

The hydrazone compound (18) shown in Table 1 as a compound to be doped was vapor-deposited by simultaneously heating each using a different crucible. The temperature of each crucible at this time was 210 to 250 ° C. for the aluminum 8-hydroxyquinoline complex, and the hydrazone compound (1
For 8), it was controlled at 155 ° C. The degree of vacuum during vapor deposition was 6 × 10 ⁻⁷ Torr, and the vapor deposition time was 1 minute and 30 seconds. As a result, an organic electron transport layer having a film thickness of 775 Å in which the hydrazone compound (18) was doped at 6.0 mol% with respect to the above complex was obtained.

Finally, as a cathode, a combination of magnesium and silver
Gold electrode is vapor-deposited to a film thickness of 1200Å by the two-source simultaneous vapor deposition method.
did. Vapor deposition uses a molybdenum boat and the degree of vacuum is 1 ×
10 ^-FiveThe deposition time was 3 minutes and 20 seconds at Torr. light
A rich film was obtained. The atomic ratio of magnesium to silver is 1
It was 0: 2.3. Organic electric field produced in this way
Plus to the ITO electrode (anode) of the light emitting element, magnesium
・ Measure by applying a negative DC voltage to the silver electrode (cathode)
The results of the emission characteristics are shown in the table.

This device shows a uniform emission of yellow-green,
The peak wavelength of light emission is 565 nm. The light emission luminance-voltage characteristic of this element is shown in FIG. Comparative Example 1 An organic electroluminescence device was produced in the same manner as in Example 1 except that the hydrazone compound (18) was not doped in the organic electron transport layer. Table 4 shows the measurement results of the emission characteristics of this device.
Shown in. This device had a peak wavelength of light emission at 530 nm and showed uniform green light emission. Moreover, the light emission luminance-voltage characteristic of this element is shown in FIG.

[0057]

[Table 4]

Example 2 An organic electroluminescent device having the structure shown in FIG. 2 was produced by the following method. In the same manner as in Example 1, an organic hole transport layer made of the hydrazone compound represented by the structural formulas (H1) and (H2) was formed on the ITO glass substrate to have a film thickness of 520Å. Next, the aluminum 8-hydroxyquinoline complex represented by the above structural formula (E1) was singly laminated as an organic electron transport layer on the organic hole transport layer to a thickness of 360 Å. Further, in the same manner as in Example 1, the structural formula (E1)
An aluminum-hydroxyquinoline complex represented by the following formula was laminated with an organic electron transport layer doped with a hydrazone compound (18) to a film thickness of 410 Å. At this time, the dope concentration was 0.8 mol%.

Finally, in the same manner as in Example 1, a magnesium-silver alloy electrode was formed into a film having a thickness of 120 by a two-source simultaneous vapor deposition method.
It was vapor-deposited to 0Å. Table 5 shows the results of the emission characteristics measured by applying a positive DC voltage to the ITO electrode (anode) and a negative DC voltage to the magnesium-silver electrode (cathode) of the organic electroluminescent device thus produced.

This device showed uniform green light emission, and the emission peak wavelength was 530 nm. Examples 3 and 4 In the same manner as in Example 2 except that the hydrazone compound (5) shown in the above table was doped to the cathode side of the organic electron transport layer instead of the hydrazone compound (18), the structure shown in FIG. An organic electroluminescent device was produced. The dope concentration at this time was 2.0 mol% (Example 3) and 7.7 mol% (Example 4).
Met.

Table 5 shows the measurement results of the emission characteristics of the obtained device.
Shown in. These devices showed uniform green light emission, and the peak wavelength of light emission was 530 nm. Example 2
The relationship between the ionization potential of the hydrazone compound used in Examples 4 to 4 and the luminous efficiency of the obtained device is shown in FIG. Examples 5 to 9 Instead of the hydrazone compound (18), the hydrazone compound (4) shown in the above table was doped at a concentration of 6.2 mol% (Example 5), and the hydrazone compound (8) was doped at a concentration of 1.8.
Mol% (Example 6), hydrazone compound (10) dope concentration 1.2 mol% (Example 7), hydrazone compound (12) dope concentration 2.9 mol% (Example 8), hydrazone compound (13 ) Was doped on the cathode side of the organic electron transport layer at a dope concentration of 4.1 mol% (Example 9) to prepare an organic electroluminescent device having the structure shown in FIG.

Table 2 shows the measurement results of the emission characteristics of the obtained device.
Shown in. These devices showed uniform green light emission, and the peak wavelength of light emission was 530 nm.

[0063]

[Table 5]

Example 10 The device produced in Example 1 was stored in a vacuum for 30 days, and then the emission characteristics were measured. The results are shown in Table 6. The decrease in light emission brightness and light emission efficiency did not pose any practical problems, and stability was exhibited for a long period of time. Example 11 The device manufactured in Example 8 was stored in a vacuum for 30 days, and then the emission characteristics were measured. The results are shown in Table 6. The decrease in light emission brightness and light emission efficiency did not pose any practical problems, and stability was exhibited for a long period of time.

[0065]

[Table 6]

Comparative Example 2 The device prepared in Comparative Example 1 was stored in a vacuum and the light emission characteristics were measured. As a result, after 30 days, the driving voltage was remarkably increased and at the same time the luminance was significantly decreased.

[0067]

The organic electroluminescent device of the present invention comprises a conductive layer (anode), a positive transport layer, an organic electron transport layer, and a conductive layer (cathode).
Are sequentially provided on the substrate, and since the organic electron transport layer is doped with a hydrazone compound, when a voltage is applied with both conductive layers as electrodes, light emission of practically sufficient brightness can be obtained with a low driving voltage. Thus, an element exhibiting stable light emission performance for a long period of time can be obtained.

The organic electroluminescent device of the present invention is a light source (for example, a light source for a copying machine, a liquid crystal display or a meter) which makes the most of the field of flat panel displays (for OA computers or wall-mounted televisions) and the characteristics as a surface light emitter. Is considered to be industrially useful.

[Brief description of drawings]

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

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

FIG. 3 is a cross-sectional view of another embodiment of the organic electroluminescent device of the present invention.

FIG. 4 is a diagram showing emission luminance-voltage characteristics of the organic electroluminescent elements produced in Example 1 and Comparative Example 1.

FIG. 5 is a diagram showing the relationship between the ionization potential of the hydrazone compound doped in the organic electron transport layer and the luminous efficiency of the obtained organic electroluminescence device.

[Explanation of symbols]

1 Substrate 2a, 2b Conductive Layer 3 Hole Transport Layer 4, 4b Organic Electron Transport Layer Doped with Hydrazine Compound 4a Organic Electron Transport Layer Not Doped with Hydrazine Compound 4 ′ Organic Light Emitting Layer 5 Doped organic electron transport layer

Claims (2)

[Claims] 1. An organic electroluminescent device comprising an anode, a hole transporting layer, an organic electron transporting layer and a cathode, which are successively laminated, wherein the organic electron transporting layer contains a hydrazone compound. element. 2. The organic electroluminescent device according to claim 1, wherein the organic electron transport layer contains one kind or a mixture of two or more kinds of hydrazone compounds represented by the following general formula (I). [Chemical 1] (In the general formula (I), A represents a monovalent or divalent organic group containing at least one aromatic hydrocarbon ring or aromatic heterocycle, and these rings may have a substituent. . R ¹ ,
R ² , R ³ , R ⁴ and R ⁵ represent a hydrogen atom or an alkyl group which may have a substituent, an aralkyl group, an aromatic hydrocarbon group or a heterocyclic group, and R ⁶ and R ⁷ represent a substituent. Represents an alkyl group, an aralkyl group, an allyl group, an aromatic hydrocarbon group or a heterocyclic group which may have, 1 is 0 or 1, m is 0, 1 or 2, and n is an integer of 1 or 2. is there. However, A, R ¹ and the carbon atom to which R ¹ is bonded may be bonded to each other to form a ring, and R ⁶ and R ⁷ and the nitrogen atom to which they are bonded are bonded to each other to form a ring. May be formed. )