JP3028530B2 - Organic thin film EL device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an organic thin-film EL device used for a flat light source or a display.

[Prior Art] An EL (electroluminescence) element using an organic substance as a raw material has attracted attention as an inexpensive large-area full-color display element. For example, a direct current driven organic thin film EL device thinned by an LB method or a vacuum evaporation method using a condensed polycyclic aromatic system such as anthracene or perylene as a raw material has been manufactured, and the light emission characteristics thereof have been studied. However, the driving voltage of the conventional organic thin-film EL device is high, and the emission luminance and efficiency are lower than those of the inorganic thin-film EL device. In addition, the light emission characteristics were significantly deteriorated, and a practical level was not obtained.

However, recently, a new type of organic thin film EL device having an organic thin film having a two-layer structure has been reported and has attracted a great deal of interest (Applied Physics Letters, Vol. 51, 913).
1987). According to reports, this organic thin film EL
As shown in FIG. 2, the device has a two-layer structure using a metal chelate complex emitting strong fluorescence for the organic phosphor thin film layer 24 and an amine-based organic material for the hole conductive thin film layer 23.
It is disclosed that bright green light emission was obtained by sandwiching these between the transparent electrode 22 and the back electrode 25.
A luminance of several hundred cd / m ² is obtained by applying a DC voltage of 7V. The maximum luminous efficiency is 1.5lm / W, which is close to the practical level.

[Problems to be Solved by the Invention] As described above, a new organic thin film EL device having a structure in which an organic phosphor thin film and an organic hole conductive thin film are laminated in two layers has a maximum emission luminance of 1000 cd / m ² or more. Shows bright green light emission. Since this element is of a current-driven type, a current of 100 mA / cm ² or more must be passed to obtain the above luminance.

However, in the conventional organic hole conductive thin film layer, a sufficient current could not be supplied stably. This is because the hole-conducting thin film layer is degraded with energization, and as a result, holes are less likely to be injected into the organic phosphor thin film layer. In addition, an increase in power loss (Joule heat) has led to a decrease in luminous efficiency of the device. Furthermore, the Joule heat of the organic thin-film EL element accelerated the degradation rate of the emission luminance.

The present invention has been made in view of the above-described conventional circumstances, and an object of the present invention is to provide an organic thin-film EL device in which the device luminous efficiency is further improved and the luminous luminance is deteriorated at a reduced rate.

[Means for Solving the Problems] In the present invention, at least one of the transparent electrodes is provided between a pair of electrodes.
In an organic EL device in which an organic hole conductive thin film and an organic phosphor thin film are laminated, the main component of the organic hole conductive thin film is a general formula; (Wherein, R represents a hydrogen atom or a phenyl group, m is a positive integer, n is 0 or a positive integer, and represents the number of monomer units in the total polymer compound). An organic thin film EL device characterized by having a polystyrene derivative.

As shown in FIG. 1, the organic thin film EL device of the present invention has a hole conductive compound in a side chain as a hole conductive thin film layer on a transparent electrode 12 which is a transparent and hole injecting electrode. In addition to the structure using the polymer compound thin film layer 13 to increase the hole injection efficiency from the transparent electrode 12 and the transport efficiency in the hole conductive thin film layer, as shown in FIG. An organic electron conductive thin film layer 36 was installed between 34 and the back electrode 35,
An organic thin film EL device having a so-called three-layer structure is also included. The effect is recognized when the thickness of the polymer compound thin film layer is 100 mm or more. Incidentally, as the transparent electrode, any may be used as long as it is usually used, for example, ITO, SnO ₂ : Sb, ZnO: Al, Au
Etc. are raised. In, Mg: Ag or the like is used for the back electrode.

Examples of the polymer compound used in the present invention include a polystyrene hole-conductive compound, and specific examples thereof include poly [4- (N, N-diphenylhydrazonomethyl) styrene] and poly [4 -(N, N-diphenylhydrazonomethyl) styrenecostyrene] and the like,
These compounds were prepared according to Example 1 of JP-A-60-63212.
And 5 can be manufactured. These polystyrene derivatives include, for example, 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, 4,4′-bis (diphenylamino) quadriphenyl, N, N, N-tris (p
-Tolyl) amine, oxadiazole and the like may be mixed at an appropriate ratio.

Specific examples of the organic phosphor used in the present invention include tris (8-hydroxyquinoline) aluminum, 12-phthaloperinone, 8,9,10,11-tetrachloro-1
2-phthaloperinone, 1,2,3,4-tetraphenylcyclopentadiene, naphthalimide, 4-aminonaphthalimide, N-methyl-4-aminonaphthalimide, N-ethyl-4-aminonaphthalimide, N-propyl- 4-aminonaphthalimide, N-n-butyl-4-aminonaphthalimide, 4-acetylaminonaphthalimide, N-methyl-4-acetylaminonaphthalimide, N-ethyl-4-acetylaminonaphthalimide, N-n -Butyl-4-acetylaminonaphthalimide, N-methyl-4
-Methoxynaphthalimide, N-ethyl-4-methoxynaphthalimide, N-propyl-4-methoxynaphthalimide, Nn-butyl-4-methoxynaphthalimide, N-methyl-4-ethoxynaphthalimide, N-ethyl -4-ethoxynaphthalimide, N-propyl-4
-Ethoxynaphthalimide, N-n-butyl-4-ethoxynaphthalimide, N- (2,4-xylyl) -4-aminonaphthalimide, N-butyl-4-butylaminonaphthalimide, etc. Absent.

The luminous efficiency of the organic thin film EL device according to the present invention is improved by a factor of 2 to 3 compared to the conventional organic thin film EL device. Further, since the luminous efficiency is improved as compared with the conventional case, the amount of generated Joule heat is reduced, and as a result, the deterioration of the luminescent characteristics due to the heat generation of the element is also reduced.

As described above, an important point of the present invention is an organic thin film EL device characterized in that the main component of the material used for the hole conductive thin film layer is a polymer compound having a hole conductive compound in a side chain. In addition, the material constituting the element other than the hole conductive thin film layer is not limited.

[Effect] The light emission mechanism of the organic thin film EL device having the two-layer structure is considered to be as follows. That is, holes are injected from a hole injection electrode such as ITO into the hole conductive thin film layer, and are conducted through the layer to inject holes into the organic phosphor thin film layer. on the other hand,
Electrons are injected into the organic phosphor thin film layer from an electron injection electrode mainly composed of a metal having a low work function. The injected electrons conduct through the organic phosphor thin film layer, and recombine with holes at the interface with the hole conductive thin film layer to generate singlet excitons. As a result,
Light is emitted from the organic phosphor layer.

In order to improve the luminous efficiency of the organic thin film EL device, it is important to increase the charge injection efficiency, the charge transport efficiency, the exciton generation and the luminescence transition probability. In particular, when the voltage applied to the device increases, recombination at the interface between the organic phosphor thin film layer and the hole conductive thin film layer, that is, the exciton generation efficiency decreases, so that the hole injection and transport efficiency is improved at a low voltage. It is important that A particular problem with the conventional device is that the organic hole conductive thin film layer deteriorates with the passage of current, and as a result, hole injection and transport efficiency decreases. as a result,
The resistance of the hole conductive thin film layer has increased, causing problems such as an increase in drive voltage and an increase in Joule heat.

The present inventors have conducted intensive studies to solve the problems of the conventional organic hole conductive thin film layer, and found that a polymer compound having a hole conductive compound in a side chain, particularly a polystyrene having a hydrazone compound in a side chain. Showed excellent characteristics. That is, when these compounds are used for the organic hole conductive thin film layer, the layer hardly deteriorates due to energization, so that an organic thin film EL device having excellent characteristics can be obtained.

EXAMPLES Examples of the present invention will be described below in detail.

Tris (8-hydroxyquinoline) aluminum was used as the organic phosphor.

As shown in FIG. 1, an ITO transparent electrode 1 was placed on a glass substrate 11.
After forming 2, the polymer compound thin film layer 13 made of poly [N, N-diphenylhydrazonomethyl) styrene]
And a dip coating method using a tetrahydrofuran solvent. Then, the organic phosphor thin film layer
14 was formed at a film thickness of 500 ° by vapor deposition in a vacuum of 10 ^-6 Torr. Finally, a back metal electrode 15 of an alloy in which Mg and Ag are mixed at a ratio of 10: 1 is formed by electron beam evaporation at a thickness of 1500 Å to complete the organic thin film EL device.

When the light emission characteristics of this device were measured in dry nitrogen,
When a DC voltage of about 8 V was applied, light emission of 300 cd / m ² was obtained. The emission luminance and efficiency are improved by a factor of 2 to 3 as compared with the conventional device. When an aging test was performed on this organic thin film EL device at a current density of 0.5 mA / cm ² , the luminance half-life was 500
It was more than an hour. In the conventional device, it took 100 to 300 hours.

[Effects of the Invention] As described above, according to the present invention, an organic thin-film EL device having significantly improved light-emitting characteristics and reliability is provided.

As described above, the present invention makes it possible to raise the organic thin film EL element to a practical level, and its industrial value is high.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of the organic thin film EL device of the present invention,
FIG. 2 is a schematic sectional view of an example of a conventional organic thin film EL device, and FIG. 3 is a schematic sectional view of another example of the organic thin film EL device of the present invention. 11,21,31… Glass substrate 12,22,32… Transparent electrode 13,33… Polymer thin film 14,24,34… Organic phosphor thin film 15,25,35… Back electrode 23 …… Organic hole conductive thin film layer 36 …… Organic electron conductive thin film layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-264692 (JP, A) JP-A-60-63212 (JP, A) JP-B-6-25230 (JP, B2) U.S. Pat. , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/00-33/28 CAPLUS (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein at least one of the electrodes is transparent.
In an organic EL device in which an organic hole conductive thin film and an organic phosphor thin film are laminated, the main component of the organic hole conductive thin film is a general formula; (Wherein, R represents a hydrogen atom or a phenyl group, m is a positive integer, n is 0 or a positive integer, and represents the number of monomer units in the total polymer compound). An organic thin film EL device characterized by being a polystyrene derivative having the same.