Organic electroluminescent device and preparation thereof

Details Organic electroluminescent device and preparation thereof Organic electroluminescent device and preparation thereof

2001-12-28

2004-10-19

Yamnitzky, Marie (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000

Reexamination Certificate

active

06805976

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an organic electroluminescent (EL) device and a preparation thereof; and, more particularly, to an organic EL device and a preparation thereof, in which a new bis-condensed DCM (4-(dicyanomethylene)-2-methyl-6-(para-(dimethylaminostyryl)-4H-pyran) derivative is used as an electroluminescence material.
PRIOR ART OF THE INVENTION
An organic emitting layer is gained by recombining electron and hole, and contains an emitting material representing electroluminescence, as a most simple structure, and also this emitting layer (EML) is provided as a single layer representing a high fluorescent quantum yield such as tris-(8-hydroxyquinoline) aluminum (hereinafter, referred to as Alq
3
).
Organic EL devices (OELDS) have been much researched for an application to a flat plate display which has a high efficiency, full color and a low voltage driving, since Tang's publication (Appl. Phys. Lett. 51, 913 (1987)). However, a red (R), green (G) or blue (B) EML, which has a high luminescent efficiency and color coordinates based on a high purity and is stable in heat, is required to get full color EL display.
In a red emitting layer of a conventional technique to obtain red color, there is a method of doping, by a number of wt% and below, derivative of DCM represented in the following chemical formula 1 as a guest, or a fluorescent material of red color such as porphyrin, on a host such as a Alq3, or of using metal complex for EML (Appl. Phys. Lett. 69, 2959 (1996), ibid, 65, 2124 (1994)).
Y. Hamada et al. attempted to obtain pure red having a narrow width of spectrum by using Rubrene with emitting assist dopant (EA) which serves as an energy transfer role from the host to the dopant though itself does not emit light, in order to complement the shortcoming mentioned above in the device using a DCJ represented in the following chemical formula 2, but did not yet obtain high purity red color (red color coordinates on NTSC: 0.67, 0.33).
Among methods to gain red OELDs, in a general phenomenon occurring when a red emitting material such as DCM is doped as a guest on a host such as Alq
3
, there are shortcomings that emission spectrum is shifted to long wavelength in a range of 590 nm-650 nm according to a concentration increase of dopant, and that a luminous efficiency becomes lower.
V. Bulovic et al. had reported that a shift phenomenon of an emission wavelength is caused by polarization effects of a red fluorescent material such as DCJ (Chem. Phys. Lett., 287(1998)455), and that the emission wavelength becomes a red shift according that the polarization phenomenon is getting increased, namely, a dipole moment value is getting large.
The red shift of the spectrum based on a concentration change of the DCM dopant and a reduction of the luminous efficiency are caused by an interaction between the dopant in a high concentration thereof, which is well-known as a concentration quenching. Therefore, in order to reduce such concentration quenching, a methyl group is induced into a julolidin ring, to then compose DCJT represented in the following chemical formula 3 (Proc. 2
nd
Internat. Sym. Chem. Functional Dyes, 1992, 536).
C. H. Chen et al. introduced substituents such as phenyl (DCJP), ethyl (DCJTE), t-butyl (DCJPB), and mesityl (DCJTM) groups as shown in the following chemical formula 4, instead of a methyl group of an activated pyran ring. Among them, the DCJTB most prominent in an aspect of luminescent efficiency reduced the phenomenon of the concentration quenching, but the emission spectrum gained 615 nm (Macromol. Symp. 125, 49(1997), U.S. Pat. No. 5,908,581).
Further, C. H. Chen et al. introduced an isopropyl group instead of the t-butyl group, to compose DCJTI represented in the following chemical formula 5 through a simple synthesis process than DCTJB so as to obtain a red electroluminescence material at a lower price. The DCJTI obtained the emission spectrum of 615 nm such as DCJTB, but did not yet obtain red color based on the high purity (Reference to Thin Solid Films 363, 327(2000)).
As above-described, in the red organic electroluminescence most well-known until now, there is the method of doping the DCM derivative on the Alq
3
host, but there is still a shortcoming that luminescence of Alq
3
itself as peak: 524 nm is reduced in the concentration increase of the dopant and luminescence of the red dopant is increased, to thus cause a shift to the long wavelength in the range of 600-650 nm.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide organic electroluminescence devices and a preparation thereof, in which bis-condensed DCM derivative based on a new concept is used as a red electroluminescent material so as to gain high purity red color (CIE: 0.67,0.33) luminescence of NTSC (National Television System Committee) with smaller concentration than red color dopant known up to now.
Another object of the present invention is to provide OELD, which is thermally stable and simple in synthesis, and represents a red color based on high purity, and a preparation thereof.
To achieve these and other advantages, and in accordance with the purpose of the present invention, it is provided OELDs composed of an organic emitting layer containing a compound which has a structure of the following chemical formula 6.
In the formula 6, X is O, S, CH
2
or NR, R is a lower alkyl group; and R
1
and R
2
are either fused ring structures having a ring-contained tertiary amine or 2-(dialkylamino) thienyl rings.
The compound having the structure of the chemical formula 6 contains compound represented in the following chemical formulas 7 through 10.
In the above chemical formulas 7 through 10, it has no problem that X is O, S, CH
2
or NR, R being a lower alkyl group; Y
1
, Y
2
, Y
3
and Y
4
individually indicate H or OH; and m, n, o and p individually represent an integer between 1 and 20.
Or, in the chemical formulas 7 and 10, it has no problem that, Y
1
and Y
3
are cyclic amine types in which the sum of —CH
2
CH
2
—, m+0 is an integer from 0 to 2, and that Y
2
and Y
4
taken together are —CH
2
CH
2
—, forming a cyclic amine wherein in sum of n+p is an integer from 0 to 2.
The OELDs have a structure that an anode
120
, an organic medium layer
150
and a cathode
190
are sequentially multilayered, and it can be also constructed by a structure that a dielectric layer
160
is formed between the anode and the cathode.
The inventive method of manufacturing the OELDs includes the steps of: forming the anode
120
on a device substrate
110
; forming the organic medium layer
150
containing a compound having the structure of the chemical formula 6; and forming the cathode on top of the organic medium layer
150
. Herewith, it is desirable that the compound of the chemical formula 6 is contained by a concentration of 20 weight % and below based on the host organic emitting layer. It is also desirable that the compound of the chemical formula 6 is uniformly mixed and doped in polymers matrix in the forming step of the organic medium layer.
In the invention, further, a self-emitting display containing the inventive OELDs is provided.
Doping one or two or more dopants on the host material provides the afore-described red emitting material, and the EL device based on a high efficiency is constructed by using such method. Color of the EL device can be also obtained by using fluorescent materials having mutually different luminescent wavelength with a general host material. The structure of the dopant in which the Alq
3
is provided as the host, in the EL device, was described in detail by Tang (J. Appl. Phys., 75, 3610(1989); U.S. Pat. No. 4,769,292).
The most important relation to select the red fluorescent materials as the dopant is to energy transfer of a host corresponding to a band gap as an energy difference between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) to the dopant. That is, a requisite condition in an occurrence of an efficient energy tra

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