JP2001102175A - Organic electroluminescent device, organic electroluminescent device group and method of controlling its emission spectrum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL device, which enables a reduction in drive power and also a control in emission spectrum. SOLUTION: A layer 5 adjacent to a negative electrode 5 is doped with an organic metal compound as a doner dopant. A change in a thickness of the metal-doped layer 5 produces a change in an optical path length between the negative electrode 6 and an emission layer 4. Also, the metal-doped layer 5 inhibits a spectrum of light emitted from a device. Thus, the metal-doped layer 5 serves as an emission spectrum-controlling layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an organic electroluminescent device (hereinafter, referred to as an organic EL device) used for a flat light source or a display device.

[0002]

2. Description of the Related Art An organic EL device in which a light-emitting layer is made of an organic compound has attracted attention as a device for realizing a low-voltage driven large-area display device. Tang and colleagues stacked organic compounds with different carrier transport properties to increase the efficiency of the device, and made a structure in which holes and electrons were injected in a balanced manner from the anode and cathode, respectively.
Å or less, 1000 cd / m ² at an applied voltage of 10 V or less
And an external quantum efficiency of 1% have been successfully obtained with high brightness and high efficiency (Appl. Phys. Lett., 51, 913 (19
87).). In this high-efficiency device, Tang et al. Reduced the work function of Mg (magnesium), which lowers the energy barrier, which is a problem when injecting electrons from a metal electrode, into an organic compound that is basically regarded as an insulator. It was used. At that time, Mg is easily oxidized and unstable,
Since it has poor adhesion to the organic surface, it is relatively stable, and is alloyed with Ag (silver) having good adhesion to the organic surface by co-evaporation.

A group of Toppan Printing Co., Ltd. (The 51st Annual Meeting of the Japan Society of Applied Physics, Proceedings 28a-PB-4, p.1040)
And Pioneer Corporation's group (The 54th Annual Conference of the Japan Society of Applied Physics, Proceedings 29p-ZC-15, p.1127)
Uses Li (lithium) which has a smaller work function than Mg
By stabilizing by alloying with Al (aluminum) and using it as a cathode, a lower driving voltage and higher luminous brightness than the element using Mg alloy are achieved. In addition, the present inventors have reported that Li is independently deposited on the organic compound layer in an extremely thin thickness of about 10 °, and that a two-layer cathode in which silver is laminated thereon is effective for realizing a low driving voltage. Yes (IEEE T
rans. Electron Devices., 40, 1342 (1993)).

[0004] These devices are disclosed in Japanese Patent Application Laid-Open No. 63-264892.
As described in Japanese Patent Application Laid-Open Publication No. H10-209, by setting the thickness of the organic layer to 1 μm or less (substantially 0.2 μm or less), even if an organic material, which is basically an insulator, can be used practically, It enables driving with voltage.

As disclosed in Japanese Patent Application Laid-Open No. 10-270171, the present applicant co-deposits a low work function metal such as an alkali metal, an alkaline earth metal, or a transition metal containing a rare earth metal and an electron accepting organic material. A low-voltage driving independent of the work function of the cathode was realized by mixing a predetermined amount by the method described above and forming an electron injection layer. In this device, a metal which is a donor (electron-donating) dopant substance that can serve as a reducing agent for an organic compound is doped in the organic compound layer in contact with the cathode in advance, so that the organic compound is in a reduced state (that is, an electron is reduced). (Electrons are injected and electrons are injected), so that the electron injection energy barrier can be reduced, and the driving voltage can be further reduced as compared with the conventional organic EL device. Moreover, a metal such as stable Al generally used as a wiring material can be used for the cathode. In such a metal-doped layer, if an appropriate combination of an organic compound and a metal is selected, the drive voltage is observed to increase even if the layer thickness is increased to the order of μm, unlike a conventional layer composed of only an organic substance. However, the dependence of the driving voltage on the layer thickness disappears.

On the other hand, the emission spectrum of an organic EL device utilizes the fluorescence of an organic dye, and therefore, the half width of the spectrum is generally wide, and is not always satisfactory from the viewpoint of color purity. Some ingenuity has been made so far.

[0007] Nakayama, et al., Hitachi, Ltd.
As shown in JP-A-174, a translucent reflective layer is provided between a glass substrate and an ITO (indium-tin oxide) transparent electrode, and an optical distance (optical path length) between the light emitting layer and the back electrode (cathode). By adjusting, the effect of an optical resonator is provided and the color purity is improved.

[0008] Tokito et al. Of the Toyota Central R & D Laboratories also set the optical path length using almost the same structure as Nakayama et al. And set the element light emission mode to a single mode, as disclosed in Japanese Patent Application Laid-Open No. 9-180883. It achieves monochromaticity and strong forward directivity.

In these device structures, thin films having different refractive indexes such as TiO ₂ and SiO ₂ formed by a technique such as sputtering are alternately laminated between a transparent conductive film as an anode and a transparent glass substrate. A translucent reflective film is formed, and an optical resonator structure is formed between the cathode and the cathode as a reflecting mirror.However, when a charge injection layer is to be formed only by an organic substance like a conventional organic EL device, In order to obtain an effective resonance length in order to utilize the interference effect of light, the translucent reflection layer must be provided outside the organic layer in this way.

[0010] Matsumura et al. Of Osaka University deliberately set the layer thickness of the aluminum quinoline complex (Alq3), which is both an electron injection layer and a light emitting layer, to be 3000 mm or more thicker than a normal element, and to interfere with light reflected by the cathode. By creating phenomena and analyzing their spectra, we discuss the dependence of the emission region on the cathode material, device degradation, and voltage (thin solid films33
1 (1998) 96-100, Synthetic Metals 91 (1997) 197-198, IEE
E TRANSACTION ON ELECTRON DEVICES, VOL.44, NO.8, AUGU
ST 1997). Although this can be said to be a useful method as one of the analysis methods, an increase in drive voltage cannot be avoided.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention not only to reduce the driving voltage of the device but also to make the electron injection layer in contact with the cathode a metal doping layer. Another object of the present invention is to provide an organic EL device that also functions as an emission spectrum control layer by utilizing that a driving voltage does not depend on the thickness of the metal doping layer.

[0012]

SUMMARY OF THE INVENTION According to the present invention, when an organic compound layer in contact with a cathode is doped with a metal functioning as a donor (electron-donating) dopant, an electron injection barrier from the cathode to the organic compound layer is reduced. Have been completed by finding that the drive voltage does not increase even if the layer thickness is increased.

That is, according to the present invention, in an organic EL device, an organic EL device having at least one light-emitting layer composed of an organic compound between opposing anode and cathode electrodes, wherein Having an organic compound layer doped with a metal functioning as a donor dopant as a metal doping layer, and the emission spectrum of light emitted by the organic electroluminescent device is controlled by the thickness of the metal doping layer. It is characterized by.

When the layer thickness of the metal doping layer is changed in this manner, the optical layer thickness (optical path length of the layer thickness; layer thickness × refractive index) between the cathode acting as a reflecting mirror and the light emitting layer changes. Therefore, the emission spectrum of light emitted from the element due to the light interference effect can be controlled. In other words, if a metal doping layer is used as the electron injection layer in contact with the cathode, the driving voltage of the device does not depend on the thickness of the metal doping layer, and the light interference effect is used without sacrificing device characteristics. As a result, not only the improvement of the color purity but also the light of various colors can be obtained by adjusting the thickness of the metal doping layer.
That is, even if the thickness of the metal doping layer is increased, the color purity can be improved and the color tone can be changed without increasing the driving voltage.

The metal functioning as a donor dopant is
More specifically, it can be composed of one or more of transition metals including an alkali metal, an alkaline earth metal, and a rare earth metal having a work function of 4.2 eV or less.

Further, the molar ratio of the metal in the metal doping layer to the organic compound is preferably in the range of 0.1 to 10, and the thickness of the metal doping layer is not particularly limited, but is not less than 500 °. By doing so, it becomes possible to express a light interference effect. There is basically no limitation on the layer thickness, and there is no problem even if it exceeds 1 μm.

Further, the organic compound of the metal doping layer includes
If a molecule having a function as a ligand for a metal ion to be doped (a function capable of coordinating with the metal ion) is used, the above-described reduction reaction occurs more effectively,
In addition, since it can exist in a stable state, it can be used particularly preferably.

In the organic EL device according to the present invention, divided areas having different layer thicknesses in each area can be provided as metal doping layers. By providing such divided areas, an organic EL device having a different emission spectrum for each divided area can be obtained. The layer thickness of each divided area is controlled so that a specific emission spectrum is obtained in each divided area. Such a divided area can be, for example, a large number of pixel groups arranged in a matrix.

Further, according to the present invention, in an embodiment of a plurality of organic EL element groups, an organic electroluminescent element group having at least one light emitting layer composed of an organic compound between opposed anode and cathode electrodes. , Each organic electroluminescent element has, at the interface with the cathode electrode, an organic compound layer doped with a metal functioning as a donor (electron donating) dopant as a metal doping layer. The thickness of the metal doping layer of the device is controlled so that the emission spectrum of light emitted from each organic electroluminescent device is different.

Further, according to the present invention, in an aspect of a method for controlling an emission spectrum of an organic EL device, at least one light-emitting layer composed of an organic compound is provided between an opposed anode electrode and a cathode electrode. At the interface on the light emitting layer side of
In an organic electroluminescent device having an organic compound layer doped with a metal functioning as a donor (electron donating) dopant as a metal doping layer, by changing the thickness of the metal doping layer, the present organic electroluminescent device Is characterized by controlling the emission spectrum of the light emitted from it. A plurality of organic electroluminescent devices in which the emission spectrum is changed by changing the layer thickness of the metal doping layer can be driven at substantially the same drive voltage regardless of the layer thickness.

[0021]

FIG. 1 is a schematic view showing an embodiment of an organic EL device according to the present invention. On a glass substrate (transparent substrate) 1, a transparent electrode 2 constituting an anode electrode,
A hole transporting layer 3 having a hole transporting property, a light emitting layer 4, a metal doping layer 5, and a cathode electrode 6 are laminated. Among these elements (layers), a glass substrate (transparent substrate) 1
The transparent electrode 2, the hole transport layer 3, the light emitting layer 4, and the cathode electrode 6 are well-known elements, and the metal doping layer 5 is an element (layer) proposed in the present invention. Specific examples of the laminated structure of the organic EL device include anode / light-emitting layer / metal-doped layer / cathode, anode / hole-transport layer / light-emitting layer / metal-doped layer / cathode, anode / hole-transport layer / light emission Layer / electron transport layer / metal doping layer / cathode, anode / hole injection layer / emission layer / metal doping layer / cathode, anode / hole injection layer / hole transport layer / emission layer / metal doping layer / cathode, anode / Hole injection layer / hole transport layer / emission layer / electron transport layer / metal doping layer / cathode, and the like. In the organic EL device according to the present invention, the metal doping layer 5 is provided at the interface with the cathode electrode 6. Any element configuration may be used as long as it has the same.

In the organic EL device, the process of injecting electrons from the cathode into the organic compound layer, which is basically an insulator, is reduction of the organic compound on the surface of the cathode, that is, formation of a radical anion state (Phys. Rev. Lett.). ., 14, 229 (1965)). In the organic EL device of the present invention, a metal that is a donor (electron-donating) dopant substance that can be a reducing agent for an organic compound is doped in the organic compound layer in contact with the cathode in advance, so that electrons can be injected from the cathode electrode. Energy barrier can be reduced. Metal doping layer 5
Is an organic compound layer doped with a metal that functions as a donor dopant in this manner. In the metal doping layer, molecules already reduced by the dopant (that is, electrons are received and electrons are injected) are present, so the electron injection energy barrier is small, and compared with the conventional organic EL device. The drive voltage can be reduced. Moreover, a metal such as stable Al generally used as a wiring material can be used for the cathode. In this case, the donor dopant is an alkali metal such as Li capable of reducing an organic compound,
There is no particular limitation as long as it is a transition metal containing an alkaline earth metal such as Mg or a rare earth metal. In particular, metals having a work function of 4.2 eV or less can be suitably used, and specific examples thereof include Li, Na, K, Rb, and C.
s, Be, Mg, Ca, Sr, Ba, Y, La, Mg, Sm, Eu, Gd, Yb and the like.

The dopant concentration in the metal doping layer is:
It is preferable that the molar ratio of the donor dopant in the metal doping layer is 0.1 to 10 with respect to the organic compound.
If it is less than 0.1, the concentration of the molecule reduced by the dopant (hereinafter referred to as “reduced molecule”) is too low, and the doping effect is small. If it exceeds 10, the metal concentration in the film far exceeds the organic molecule concentration, Because the concentration of
The effect of doping is also reduced. The thickness of the metal doping layer has basically no upper limit.

The metal doping layer 5 may be formed by any thin film forming method, for example, a vapor deposition method or a sputtering method. When a thin film can be formed by application from a solution, an application method from a solution such as spin coating or dip coating can be used. In this case, the organic compound to be doped and the dopant may be dispersed and used in an inert polymer.

The organic compound which can be used as the light emitting layer, the electron transporting layer and the metal doping layer is not particularly limited, but includes polycyclic compounds such as p-terphenyl and quaterphenyl and derivatives thereof, naphthalene, tetracene and pyrene. , Coronene, chrysene, anthracene, diphenylanthracene, naphthacene, condensed polycyclic hydrocarbon compounds such as phenanthrene and derivatives thereof, phenanthroline, bathophenanthroline, bathocuproine, phenanthridine, acridine, quinoline, quinoxaline, condensed heterocyclic compounds such as phenazine And their derivatives, fluorescein, perylene, phthaloperylene, naphthalopallylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene, tetraphenylbutadiene, oxadiazo Le, aldazine, bisbenzoxazoline, bisstyryl, pyrazine, cyclopentadiene, oxine, aminoquinoline, imine, diphenylethylene, vinyl anthracene, diaminocarbazole,
Examples include pyran, thiopyran, polymethine, merocyanine, quinacridone, rubrene, and derivatives thereof.

Further, JP-A-63-295695, JP-A-8-2
No. 2557, JP-A-8-81472, JP-A-5-9470, and JP-A-5-17764, tris (8-quinolinolato) is a metal chelate complex compound, particularly a metal chelated oxanoid compound. ) Aluminum, bis (8-quinolinolato) magnesium, bis [benzo (f)-
8-quinolinolato] zinc, bis (2-methyl-8-quinolinolato) aluminum, tris (8-quinolinolato) indium, tris (5-methyl-8-quinolinolato) aluminum, 8-quinolinolatolithium, tris (5-chloro) A metal complex having at least one of 8-quinolinolato or a derivative thereof such as -8-quinolinolato) gallium and bis (5-chloro-8-quinolinolato) calcium as a ligand is preferably used.

Oxadiazoles disclosed in JP-A-5-202011, JP-A-7-179394, JP-A-7-278124, JP-A-7-228579, JP-A-7-157473 JP-A-6-32080 and JP-A-6-320396, the triazines disclosed in JP-A-6-203963, the stilbene derivatives and distyrylarylene derivatives disclosed in JP-A-6-203963
Styryl derivatives disclosed in 88072, JP-A-6
The diolefin derivatives disclosed in JP-A-100857 and JP-A-6-207170 are also preferable as the light emitting layer, the electron transport layer, and the metal doping layer.

Further, fluorescent brighteners such as benzoxazole, benzothiazole, and benzimidazole can be used, and examples thereof include those disclosed in JP-A-59-194393. As a typical example, 2,5-bis (5,7-di-t-bentyl-2-benzoxazolyl) -1,3,4
-Thiadiazole, 4,4'-bis (5,7-t-pentyl-2-benzooxazolyl) stilbene, 4,4'-bis [5,7-di- (2-
Methyl-2-butyl) -2-benzoxazolyl] stilbene, 2,5-bis (5.7-di-t-pentyl-2-benzoxazolyl) thiophene, 2,5-bis [5- (α, α-Dimethylbenzyl) -2-benzoxazolyl] thiophene, 2,5-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl] -3,4-diphenyl Thiophene, 2,5-bis (5-methyl-
2-benzoxazolyl) thiophene, 4,4'-bis (2-benzoxazolyl) biphenyl, 5-methyl-2- {2- [4-
(5-methyl-2-benzoxazolyl) phenyl] vinyl} benzoxazole, 2- [2- (4-chlorophenyl)
Benzoxazoles such as vinyl] naphtho (1,2-d) oxazole, benzothiazoles such as 2,2 '-(p-phenylenedipinylene) -bisbenzothiazole, 2- {2- [4-
(2-benzimidazolyl) phenyl] vinyl} benzimidazole, 2- [2- (4-carboxyphenyl) vinyl]
Fluorescent whitening agents such as benzimidazoles such as benzimidazole are exemplified.

As the distyrylbenzene compound, for example, those disclosed in European Patent No. 0 375 382 can be used. Typical examples are 1,4-bis (2-methylstyryl) benzene, 1,4-bis (3-methylstyryl) benzene, 1,4-bis (4-methylstyryl) benzene, distyrylbenzene, 1,4-bis (2-ethylstyryl) benzene, 1,4-bis (3-ethylstyryl) benzene, 1,4-bis (2-methylstyryl) -2-methylbenzene, 1,4-bis (2- Methylstyryl) -2-ethylbenzene and the like.

Further, a distyrylpyrazine derivative disclosed in JP-A-2-252793 is also used as a light emitting layer, an electron transport layer,
It can be used as a metal doping layer. Typical examples are 2,5-bis (4-methylstyryl) pyrazine,
2,5-bis (4-ethylstyryl) pyrazine, 2,5-bis [2-
(1-Naphthyl) vinyl] pyrazine, 2,5-bis (4-methoxystyryl) pyrazine, 2,5-bis [2- (4-biphenyl)
Vinyl] pyrazine, 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine and the like.

In addition, dimethylidin derivatives disclosed in European Patent No. 388768 and JP-A-3-231970 can be used as a material for a light emitting layer, an electron transport layer and a metal doping layer. Typical examples are 1,4-phenylenedimethylidin, 4,4'-phenylenedimethylidin, 2,5-xylylenedimethylidin, 2,6-naphthylenedimethylidin, 1,4-biphenylene Dimethylidin, 1,4-
p-Telephenylenedimethylidin, 9,10-anthracenediyldimethylidin, 4,4 '-(2,2-di-t-butylphenylvinyl) biphenyl, 4,4'-(2,2-diphenylvinyl )
Biphenyl and the like and derivatives thereof, and JP-A-6-4907
No. 9, JP-A-6-293778, silanamin derivatives disclosed in JP-A-6-279322, JP-A-6-279323
Patent Application Publication No.
Oxadiazole derivatives disclosed in JP-A-6-107648 and JP-A-6-92947, anthracene compounds disclosed in JP-A-6-206865, and disclosed in JP-A-6-145146 Oxynate derivatives, JP-A-4-9699
0, a triphenylbutadiene compound disclosed in JP-A-3-296595, and a coumarin derivative disclosed in JP-A-2-191694, 2-196885, perylene derivatives disclosed in JP-A-2-255789, naphthalene derivatives disclosed in JP-A-2-289676, JP-A-2-289676 and
Examples thereof include a phthaloperinone derivative disclosed in JP-A-2-88689 and a styrylamine derivative disclosed in JP-A-2-250292. Further, a known device conventionally used for manufacturing an organic EL device can be appropriately used.

The arylamine compounds used as the hole injecting layer, the hole transporting layer, and the hole transporting light emitting layer include:
Although not particularly limited, JP-A-6-25659, JP-A-6-203
No. 963, JP-A-6-215874, JP-A-7-145116, JP-A-7-224012, JP-A-7-157473,
JP-A-8-48656, JP-A-7-126226, JP-A-7
-188130, JP-A-8-40995, JP-A-8-40996
Publication, JP-A-8-40997, JP-A-7-122225, JP-A-7-101911, and arylamine compounds disclosed in JP-A-7-97355 are preferable, for example, N, N, N ', N'-tetraphenyl-4,4'-diaminophenyl, N, N'-diphenyl-N, N'-di (3-methylphenyl) -4,
4'-diaminobiphenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane, N, N, N ', N'-tetra-p-tolyl-4,
4'-diaminobiphenyl, bis (4-di-p-tolylaminophenyl) phenylmethane, N, N'-diphenyl-N, N'-di (4
-Methoxyphenyl) -4,4'-diaminobiphenyl, N, N,
N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether, 4,4'-bis (diphenylamino) quadriphenyl, 4-N, N-diphenylamino- (2-diphenylvinyl)
Benzene, 3-methoxy-4'-N, N-diphenylaminostilbenzene, N-phenylcarbazole, 1,1-bis (4-di-
p-triaminophenyl) -cyclohexane, 1,1-bis (4
-Di-p-triaminophenyl) -4-phenylcyclohexane, bis (4-dimethylamino-2-methylphenyl) -phenylmethane, N, N, N-tri (p-tolyl) amine, 4- (di- p
-Tolylamino) -4 '-[4 (di-p-tolylamino) styryl] stilbene, N, N, N', N'-tetraphenyl-4,4'-diamino-biphenylN-phenylcarbazole, 4,4 ' -Bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl,
4,4 ''-bis [N- (1-naphthyl) -N-phenyl-amino] p-
Terphenyl, 4,4'-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (3-acenaphthenyl) -N-phenyl-amino] biphenyl, 1 , 5-bis [N-
(1-Naphthyl) -N-phenyl-amino] naphthalene, 4,4 '
-Bis [N- (9-anthryl) -N-phenyl-amino] biphenyl, 4,4 ''-bis [N- (1-anthryl) -N-phenyl-
Amino] p-terphenyl, 4,4'-bis [N- (2-phenanthryl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (8-fluoranthenyl) -phenyl-amino ] Biphenyl, 4,4'-bis [N- (2-pyrenyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (2-perylenyl) -N-phenyl-amino] biphenyl, 4 , 4'-Bis [N- (1-coronenyl) -N-phenyl-amino] biphenyl, 2,6-bis (di-p-tolylamino) naphthalene, 2,6-bis [di- (1-
Naphthyl) amino] naphthalene, 2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene, 4.4 ''-
Bis [N, N-di (2-naphthyl) amino] terphenyl, 4.
4'-bis ｛N-phenyl-N- [4- (1-naphthyl) phenyl]
Amino dibiphenyl, 4,4'-bis [N-phenyl-N- (2-pyrenyl) -amino] biphenyl, 2,6-bis [N, N-di (2-
Naphthyl) amino] fluorene, 4,4 ''-bis (N, N-di-p
-Tolylamino) terphenyl, bis (N-1-naphthyl)
(N-2-naphthyl) amine and the like. In addition, conventional organic
A known device used for manufacturing an EL element can be used as appropriate.

Further, as the hole injecting layer, the hole transporting layer, and the hole transporting light emitting layer, those in which the above-mentioned organic compound is dispersed in a polymer or those in which a polymer is formed can be used. So-called π such as polyparaphenylene vinylene and its derivatives
Conjugated polymers, hole-transporting non-conjugated polymers represented by poly (N-vinylcarbazole), and sigma-conjugated polymers such as polysilanes can also be used.

The hole injection layer formed on the ITO electrode is not particularly limited, but metal phthalocyanines such as copper phthalocyanine and non-metal phthalocyanines, carbon films, and conductive polymers such as polyaniline can be suitably used. Further, the arylamines described above can be reacted with a Lewis acid as an oxidizing agent to form radical cations and be used as a hole injection layer.

The cathode electrode is not limited as long as it is a metal that can be used stably in the air. In particular, aluminum, which is generally widely used as a wiring electrode, is preferable.

[Examples] The present invention will be described below with reference to examples, but the present invention is not limited thereto. In addition, VPC-400 vacuum vapor deposition machine manufactured by Vacuum Kiko Co., Ltd. was used for vapor deposition of the organic compound and metal, and DekTak3ST stylus type step meter manufactured by Sloan Co., Ltd. was used for measuring the layer thickness. For element characteristics evaluation, Keithley SourceMeter 2400, Topcon BM-8
A luminance meter was used. DC voltage is applied stepwise at a rate of 1 V / 2 seconds with ITO as the anode and Al as the cathode, and the voltage rises 1
After 2 seconds, the luminance and the current value were measured. The EL spectrum was measured with a constant current drive using a Hamamatsu Photonics PMA-11 optical multichannel analyzer.

Example 1 The present invention is applied to the organic EL device having the laminated structure shown in FIG. A glass substrate 1 is coated with ITO (indium-tin oxide, sputter deposited by Sanyo Vacuum Co., Ltd.) having a sheet resistance of 20Ω / □ as an anode transparent electrode 2. The following formula (1) having a hole transport property thereon:

Embedded image Was formed at a deposition rate of 2 ° / sec to a thickness of 500 ° at 10 ^-6 torr to form a hole transport layer 3. Next, the following formula (2) having green light emission as the light emitting layer 4 on the hole transport layer 3:

Embedded image A tris (8-quinolinolato) aluminum complex layer (hereinafter referred to as “Alq”) 4 represented by the following formula was formed by vacuum evaporation to a thickness of 400 ° under the same conditions as the hole transport layer 3. Next, as a metal doping layer 5 on the light emitting layer 4, the following formula (3):

Embedded image 1: 1 molar ratio of bathophenanthroline and Li represented by
The deposition rate was adjusted so as to obtain a film of 300 °. Finally, a cathode electrode 6 is formed on the metal doping layer 5.
Was deposited at a deposition rate of 10 ° / sec to 1000 °. The light emitting region was a square having a length of 0.5 cm and a width of 0.5 cm. The above organic EL
In the device, ITO as the anode electrode and Al as the cathode electrode
6, a DC voltage was applied, and the luminance of green light emission from the light emitting layer Alq4 was measured. The circle plots in FIGS. 2 and 3 show the luminance-voltage characteristics and the luminance-current density characteristics, in which a high luminance of 28000 cd / m ² at the maximum is shown at 11V. The current density at this time was 600 mA / cm ² . Also, 100
A luminance of 0 cd / m ² was obtained at 7V. Observation of the emission spectrum was consistent with the fluorescence spectrum of Alq (solid line in FIG. 4).

Comparative Example 1 As in Example 1, αNPD was first formed on ITO as a hole transport layer.
Is formed to a thickness of 500 °, and Al is formed thereon as a light emitting layer.
q was formed by vacuum evaporation to a thickness of 700 mm under the same conditions as the hole transport layer. Then, Al is used as a cathode from above
Evaporated. The triangle plots in FIGS. 2 and 3 show the luminance of this element.
-Indicates voltage characteristics, luminance-current density characteristics, 15V
Gave a maximum brightness of 4700 cd / m ² . Also, 1
13 V had to be applied to obtain a luminance of 000 cd / m ² . This experiment shows that the metal doping layer 5 is effective in lowering the driving voltage.

Example 2 In the same manner as in Example 1, αNPD was formed as a hole transport layer 3 on ITO.
Is vacuum-deposited at 500 ° and Alq is deposited at 400 ° as the light-emitting layer 4, and the respective deposition rates are adjusted so that the molar ratio of bathophenanthroline and Li is 1: 1 to 1900 ° and 480.
Metal doping layers having three different thicknesses of 0 ° and 10000 ° (1 μm) were formed. From above, Al was vapor-deposited on the three types of devices as the cathode electrode 6 at 1000 ° to produce devices. FIG. 5 shows the voltage-current characteristics of these devices. In the figure, A, B, and C indicate the thickness of the metal doping layer,
It is a plot which shows the device characteristic of 1900 degrees, 4800 degrees, and 10000 degrees (1 micrometer), respectively.

According to this experiment, in the embodiment in which bathophenanthroline having a function as a ligand for the ion of the metal to be doped is used as the organic substance of the metal doping layer 5, even if the layer thickness is increased, the driving voltage of the device is increased. Did not rise at all. Observation of the emission spectrum showed that the emission spectrum from Alq changed due to the interference effect with the reflected light at the cathode, and that the color purity and color tone could be controlled. The dotted line in FIG. 4 shows an emission spectrum when the metal doping layer is 1900 °, and the color purity is improved as compared with 300 °. The dotted and solid lines in the spectrum of FIG. 6 indicate that the thickness of the metal doping layer is 4800 ° and 10000 °, respectively.
This shows that the color tone can be largely changed by the interference effect with the reflected light from the cathode.

Example 3 As in Example 2, αNPD was formed as a hole transport layer 3 on ITO.
After vacuum-depositing 500 mm of Alq and 400 mm of Alq as the light-emitting layer 4,
The following equation (4):

Embedded image The evaporation rates were adjusted so that the molar ratio of bathocuproine and Li represented by 1 was 1: 1 and 19001, 4800Å, 10
Metal doping layers having three types of thicknesses of 000 ° (1 μm) were formed. From above, Al was vapor-deposited on the three types of devices as the cathode electrode 6 at 1000 ° to produce devices. The voltage-current characteristics of these devices are shown in FIGS. From this experiment, even if the metal doping layer is formed using bathocuproine having a function as a ligand for ions of the metal to be doped, and the layer thickness is increased,
As in the case of Example 2 using bathophenanthroline, it was found that the driving voltage of the device was not increased at all. Observation of the emission spectrum showed that the emission spectrum from Alq changed due to the effect of interference with the reflected light from the cathode as in the case of Example 2, and that the color purity and color tone could be controlled.

Comparative Example 1 As in Examples 2 and 3, a hole transport layer 3 was formed on ITO.
After vacuum-depositing αNPD at 500 ° and Alq at 400 ° as the light emitting layer 4, adjust the respective deposition rates so that the molar ratio of Alq and Li is 1: 1. Doping layers were each formed. From above,
Al was vapor-deposited on the two types of elements as the cathode electrode 6 at 1000 ° to produce the elements. The voltage-current characteristics of these devices are shown in FIG.
G and H of FIG. Organic material in metal doping layer is Alq
In this case, as compared with bathophenanthroline and bathocuproine, the drive voltage gradually shifted to a higher voltage as the layer thickness was increased, and the voltage dependence of the layer thickness was observed.

As described above, when a compound such as bathophenanthroline or bathocuproine, which functions as a ligand for ions of the metal to be doped, is used as the organic substance in the metal doping layer, the organic substance is effectively reduced and radicals are reduced. It was found that since anions can be generated, the dependence of the driving voltage on the layer thickness disappears, and the emission spectrum can be controlled freely.

As described above, according to the organic EL device of the present invention, by changing the thickness of the metal doping layer,
The emission spectrum of light emitted from the element can be controlled. Therefore, in the organic EL device of the present invention, by setting divided areas having different layer thicknesses in each area in the metal doping layer, an element having a different emission color for each divided area can be obtained. Furthermore, color display is possible by dividing the divided areas into a large number of pixels arranged in a matrix and changing the emission color by varying the layer thickness for each pixel. For example,
As shown in FIG. 7, three pixels 1 each having a layer thickness set to emit R (red), G (green), and B (blue) light are emitted.
1, 12, 13 are arranged vertically and horizontally. And color C
By selectively applying a drive voltage to these pixels by a well-known color display method used in an RT display, a color liquid crystal display, or the like, a color image or a color image can be displayed.

[0045]

According to the present invention, it is possible to provide an organic EL device in which the driving voltage of the device can be reduced and the emission spectrum can be controlled by using the metal injection layer as the electron injection layer in contact with the cathode. it can.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a laminated structure of an organic EL device of the present invention.

FIG. 2 is a graph showing luminance-voltage characteristics of the organic EL device of the present invention and a comparative example.

FIG. 3 is a graph showing luminance-current density characteristics of the organic EL device of the present invention and a comparative example.

FIG. 4 is a graph showing an emission spectrum of the organic EL device of the present invention.

FIG. 5 is a graph showing voltage-current characteristics of the organic EL device of the present invention and a comparative example.

FIG. 6 is a graph showing an emission spectrum of the organic EL device of the present invention.

FIG. 7 is a schematic diagram showing pixels of a color display.

[Explanation of symbols]

 Reference Signs List 1 transparent substrate 2 anode transparent electrode (ITO) 3 hole transport layer 4 light emitting layer 5 metal doping layer (electron injection layer) 6 cathode electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Yokoi 3 Kirihara-cho, Fujisawa-shi, Kanagawa F-term in Aimes Corporation (reference) 3K007 AB00 AB04 AB06 CA01 CB01 DA00 DB03 EB00 FA01

Claims (15)

[Claims] An organic electroluminescent device having at least one light-emitting layer composed of an organic compound between an anode electrode and a cathode electrode facing each other, wherein a donor (electron donating property) is provided at an interface with the cathode electrode. A) an organic compound layer doped with a metal that functions as a dopant is provided as a metal doping layer, and the emission spectrum of light emitted from the organic electroluminescent device is controlled by the thickness of the metal doping layer. Characteristic organic electroluminescent element. 2. The organic electroluminescent device according to claim 1, wherein the metal in the metal doping layer is a transition metal containing an alkali metal, an alkaline earth metal, and a rare earth metal having a work function of 4.2 eV or less. An organic electroluminescent device comprising at least one metal selected from the group consisting of: 3. The organic electroluminescent device according to claim 1, wherein the molar ratio of the metal in the metal doping layer is 0.1 to 10 with respect to the organic compound. 4. The organic electroluminescent device according to claim 1, wherein the thickness of the metal doping layer is 500 ° or more. 5. The organic electroluminescent device according to claim 1, wherein the organic compound in the metal doping layer has a function as a ligand for ions of the metal. Electroluminescent element. 6. The organic electroluminescent device according to claim 1, wherein the metal doping layer has divided areas having different thicknesses in each area. Cent element. 7. The organic electroluminescent device according to claim 6, wherein the divided area is a group of a large number of pixels arranged in a matrix. 8. The organic electroluminescent device according to claim 6, wherein a layer thickness of the divided area is controlled so that a specific emission spectrum is obtained in each divided area. element. 9. An organic electroluminescent device group having at least one light-emitting layer composed of an organic compound between opposing anode and cathode electrodes, wherein each of the organic electroluminescent devices is a cathode. An organic compound layer doped with a metal that functions as a donor (electron-donating) dopant is provided as a metal doping layer at the interface with the electrode, and the thickness of the metal doping layer of each organic electroluminescent element is An organic electroluminescent device group, wherein the emission spectra of light emitted from the luminescent devices are controlled to be different from each other. 10. The organic electroluminescent device group according to claim 9, wherein the metal in the metal doping layer is a transition including an alkali metal, an alkaline earth metal, and a rare earth metal having a work function of 4.2 eV or less. An organic electroluminescent device group comprising one or more metals selected from metals. 11. The organic electroluminescent device group according to claim 9, wherein the molar ratio of the metal in the metal doping layer is 0.1 to 0.1 with respect to the organic compound.
10. An organic electroluminescent device group of No. 10. 12. The organic electroluminescent element group according to claim 9, wherein the metal doping layer has a thickness of 500 ° or more. 13. The organic electroluminescent device group according to claim 9, wherein the organic compound in the metal doping layer has a function as a ligand for ions of the metal. Organic electroluminescent device group. 14. An anode and a cathode, which are opposed to each other,
An organic compound layer doped with a metal that functions as a donor (electron-donating) dopant as a metal-doped layer at an interface of the cathode electrode on the light-emitting layer side, which has at least one light-emitting layer composed of an organic compound; In the organic electroluminescent device, by changing the thickness of the metal doping layer,
A method for controlling an emission spectrum of an organic electroluminescent device, comprising controlling an emission spectrum of light emitted from the present organic electroluminescent device. 15. The control method according to claim 14, wherein
A plurality of organic electroluminescent devices in which the emission spectrum is changed by changing the layer thickness of the metal doping layer,
A method for controlling an emission spectrum of an organic electroluminescent device driven at substantially the same drive voltage regardless of the layer thickness.