JPH03114197A - Organic thin-film el element - Google Patents

Abstract

PURPOSE:To provide an EL element having high brightness with low voltage and an excellent light emission efficiency by interposing a layer as a mixture of electric charge implanting material and an organic fluorescent substance between an electric charge implant layer and a light emitting layer. CONSTITUTION:A clear electrode 2 consisting of ITO is formed on a glass plate 1, which is followed by formation of three layers one after another-i.e., a pos. hole implant layer 3 consisting of N,N,N',N'-tetraphenyl-4,4'- diaminobyphenyl, a layer 4 as mixture of diamine and tris (8-hydroxyquinoline) aluminum as organic fluorescent substance in the proportion of 1:1, and a light emitting layer 5 using almi-quinoline. Finally a metal electrode 6 is formed by the electron beam evaporation method, and thus an organic thin film light emitting element is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an organic thin film light emitting device used for flat light sources and displays.

[Conventional technology]

EL (electroluminescent) devices made from organic materials are attracting attention as a means of realizing inexpensive large-area film-like full-color display devices due to their abundant materials and molecular-level synthesis technology6.For example, anthracene DC-driven organic thin-film light-emitting devices have been produced using cotton-polymerized polycyclic aromatic materials such as perylene and perylene as raw materials and made into thin films by the LB method, vacuum evaporation method, etc., and their light-emitting characteristics have been studied. Furthermore, a new type of organic thin film light emitting device with a two-layer organic thin film structure has recently been reported and is attracting strong interest (Applied Physics Letters, Vol. 51, p. 913, 1987), as shown in Figure 4. As shown in Fig. 2, it was reported that bright green light emission could be obtained by using a metal Kir-1 compound that emits strong fluorescence in the light-emitting layer 44 and an amine material in the hole-injection layer 43 of a hole-conducting organic material. There is. Approximately 100 cd with 6 to 7 cm of DC applied
/rr? The brightness is obtained. 41 is a glass plate, 42 is a transparent electrode, and 45 is a metal electrode.

Furthermore, in order to promote electron injection into the light-emitting layer, a three-layer structure element in which an electron injection layer is added has been proposed.

[Problem to be solved by the invention]

The light emitting region of the organic thin film EL device having the structure shown in FIG.
It is said to be about the size of a human. Other regions are not thought to be directly involved in light emission.

Moreover, since this non-light-emitting region acts as a high-resistance layer, it increases the on-sale voltage and, as a result, lowers the luminous efficiency. Furthermore, if the resistance value of this region not involved in light emission is high, it has the effect of accelerating the luminance saturation phenomenon in the high luminance region.

However, if the light-emitting layer 44 is as thin as 500 Å or less, the number of pinholes in the device increases significantly, resulting in a significant loss of characteristics as a display device. Therefore, the light emitting layer 44 needs to have a certain thickness in order to improve the applicability.

In order to put organic thin-film EL devices into practical use, it is necessary to improve luminous efficiency and luminance while ensuring the same level of reliability as conventional devices. To achieve this, it is necessary to expand the light emitting area beyond that of conventional elements, but conventional techniques have not been able to solve this problem.

An object of the present invention is to provide an organic thin film El-element that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, the organic thin film EL device according to the present invention has at least one charge injection layer and at least one light emitting layer made of an organic phosphor laminated between a pair of electrodes, at least one of which is transparent. In the organic thin [F, L] element, a mixed layer made of a mixture of a charge injection material and an organic phosphor is inserted between the charge injection layer and the emission layer.

[Effect]

The light emitting mechanism of this organic thin film EL element is considered as follows. That is, in FIG. 4, holes flow into the hole injection layer 43 from an electric current 42 such as TTO, but the holes do not enter the light emitting layer 44, and the hole concentration decreases near the interface with the light emitting layer 44. becomes higher. On the other hand, electrons enter the light emitting layer 44 from the metal electrode 45, are conducted therein, and reach the interface with the hole injection layer 43. As a result, the hole injection layer 43 and the light emitting layer 4
At the interface of 4, electrons and holes recombine to generate -heavy ring excitons, which are thought to be the source of light emission. Recent research has revealed that in conventional organic thin-film EL devices, the recombination region is extremely narrow due to the low mobility of electrons and holes, resulting in a small light-emitting region of about 200. .

In the case of organic thin film EL devices, even if a mixed layer consisting of a hole injection layer and a light emitting layer is inserted at the interface between the hole injection layer and the light emitting layer, charge transport by hopping is still possible, although the mobility decreases slightly. Ta. During this charge transport process, the opportunity for electron/hole recombination increases compared to when the hole injection layer and light emitting layer are completely separated, and the recombination area is substantially larger than in conventional devices.0 Luminous efficiency/brightness Improvement was observed.

The hole injection layer is made of organic low-molecular materials used in electrophotography, such as hydrazone derivatives, ofsazole derivatives,
Amine derivatives, triphenylmethane derivatives, etc. can be used. As the organic phosphor, one that exhibits strong fluorescence in a solid state such as tris(8-hydroxyquinoline)aluminum, anthracene, perylene, naphthalimide, phthaloperinone, triphenylcyclopentadiene, and stilbene can be used. In so-called three-layer elliptical devices, in which an electron injection layer is inserted between the emissive layer and the metal electrode in order to promote electron injection into the emissive layer, a mixed layer is inserted between the electron injection layer and the emissive layer. However, the same effect of improving the light emission characteristics was obtained.

〔Example〕

The present invention will be explained in detail below with reference to Examples.

(Example 1) As shown in FIG. 1, after forming a transparent electrode 2 made of ITO or the like on a glass plate 1, N, N was applied.

Hole injection layer 3 made of N', N'-tetraphenyl-4,4'-diaminobiphenyl (hereinafter abbreviated as diamine)
300 people, mixed layer 4 consisting of a 1:1 mixture of tris(8-hydroxyquinoline) aluminum (hereinafter abbreviated as aluminum quinoline) and diamine as an organic phosphor, 500 people, and finally aluminum quinoline. The light emitting layer 5 was formed one by one by 300 people. I & then Mg and In 10:1
An organic thin film EL device is completed by forming 1,500 metal-type TIF16 alloys mixed with the above by electron beam evaporation.

When the luminescent properties of this device were measured in dry nitrogen, it was found that when a DC voltage of approximately 5V was applied, the luminescence characteristics were 300 cd/rr? Green luminescence was obtained. Emission brightness and efficiency are 2 times lower than conventional elements.
It can be seen that this is a 5 times improvement.

When this organic thin film light emitting device was subjected to an aging test at a current density of 0.51 A/-, the luminance half-life was over 100 hours. The reliability of this device is significantly improved compared to 10 to 50 hours for conventional devices.

Furthermore, the shift in electrical properties was about 5 layers, which was significantly lower than before.

The present invention relates not only to tris(8-hydroxyquinoline)aluminum organic phosphors but also to anthracene derivatives, pyrene derivatives, tetracene derivatives, stilbene derivatives, perylene derivatives, quinone derivatives, phenanthrene derivatives,
Similar effects were observed even when naphthane derivatives, naphthalimide derivatives, phthaloperinone derivatives, cyclopentadiene derivatives, cyanine derivatives, and other organic substances that emit strong fluorescence in the visible region were used as materials for the light-emitting layer 5.

In addition, the emission wavelength can be changed by further adding other highly fluorescent organic molecules such as rhodamine, cyanine, pyran, coumarin, fluorene, POPOP, PBBO, etc. of about 10-5 to 1O-2no1 to this organic phosphor. can. The transparent electrode 2 is made of ZnO:AQR? Sn
02: Any conductive material having a work function of 4.5 cV or more may be used, such as S b , I n20s , or Au.

(Example 2) In this example, from 610nn to 630r+n in FIG.
A perylene derivative that emits strong fluorescence is used for the light-emitting layer 5,
This is an organic thin film EL device using a triphenylmethane derivative as the hole injection layer 3. As shown in FIG. 2, the mixed layer 4 gradually changes from 100% triphenylmethane derivative to 100% perylene derivative. The thickness of this mixed layer 4 is 600. Luminescent layer 5 made of perylene derivative
The film thickness is 400 people. Further, the film thickness of the triphenylmethane derivative is 100 people. Finally, Mg and In are 10=
A metal electrode 6 of the alloy mixed in step 1 is formed by electron beam evaporation to complete an organic thin film light emitting device.

The effect was recognized even though the concentration distribution of the mixed layer 4 in FIG. 2 was step-like.

(Example 3) In this example, as shown in Fig. 3, from 610r+n to 630
This is an organic thin film EL device using a phthaloperinone derivative that emits strong fluorescence in nm wavelength for the light emitting layer 33 and aluminum quinoline for the electron injection layer 35. 31 is a glass plate, 32
is a transparent electrode. Mixed layer 34 is aluminum quinoline 100
% to 100% phthaloperinone derivative. II of this mixed layer 34! The thickness is 700 people. The thickness of the light-emitting layer 33 made of a phthaloperinone derivative is 400 mm.
It's a person. Furthermore, the film thickness of aluminum quinoline is 300 mm. Finally, 1,500 back metal electrodes 36 made of an alloy of Mg and In mixed at a ratio of 10:1 are formed by electron beam evaporation to complete the organic thin film light emitting device.

Anthracene, tetracene, etc. may be used as the material for the electron injection layer 35, and similar effects were also obtained with an element having a four-layer or five-layer structure in which a hole injection layer was added.

〔Effect of the invention〕

As described above, the present invention has made it possible to provide an element that has high luminance and high luminous efficiency at a lower voltage than conventional organic thin film EL elements. Furthermore, because it emits brighter light at a lower voltage than conventional devices, the device can be driven with less input power.

As a result, element deterioration is less than that of conventional elements, and 100%
There is little increase in drive voltage or decrease in brightness over time.

In this way, the present invention contributes to the industrialization of organic thin films EL and devices.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an organic thin film EL device according to Example 1 and Example 2 of the present invention, and FIG. 2 shows the concentration distribution of the organic thin film EL device used in Example 2 of the present invention. FIG. 3 is a diagram showing an organic thin [EL element] according to Example 3 of the present invention.
FIG. 4 is a diagram showing a conventional organic thin film EL element. 1, 31.41... Glass plate 2, 32.42...
・Transparent electrode 3.43...Hole injection layer 5.33.4
4... Luminous layer 35... Electron injection layer 4, 34
...Mixed layer 6, 36.45...Metal electrode

Claims (1)

[Claims] (1) In an organic thin film EL device in which at least one charge injection layer and a light emitting layer made of at least one organic phosphor are laminated between a pair of electrodes, at least one of which is transparent, the charge injection layer and the light emitting layer are stacked. An organic thin film EL device characterized in that a mixed layer made of a mixture of a charge injection material and an organic phosphor is inserted between the layers.