Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-02-01
2002-05-21
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C428S704000, C313S504000, C313S506000, C252S301160, C252S301260, C257S040000, C257S103000
Reexamination Certificate
active
06391482
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic material for an electroluminescent device and an electroluminescent (EL) device using the same.
BACKGROUND OF THE INVENTION
An electroluminescence panel is characterized by high visibility, excellent display performance and a high-speed response. Recently, an organic electroluminescent device (hereinafter referred to also as EL device) using organic compounds is reported (see, for example, relevant document in “Applied Physics Letters,” Vol. 51, p913, 1987). This document describes an organic EL device having a structure in which a hole transport layer and an organic light emitting layer are laminated.
The structure of conventional organic EL devices is explained with reference to
FIGS. 11
to
14
.
An organic EL device
1
of
FIG. 11
includes a glass substrate
2
, an anode
3
laminated on the glass substrate
2
, an organic light emitting layer
4
and a cathode
5
. The anode
3
is a transparent electrode.
An organic EL device
1
a
of
FIG. 12
is called an SH-A type device. The organic EL device
1
a
includes a glass substrate
2
, an anode
3
laminated on the glass substrate
2
, a hole transport layer
6
, an organic light emitting layer
4
and a cathode
5
. The above-mentioned report by Tang et al. relates to the organic EL device
1
a,
which uses a tris (8-quinolinolato) aluminum (hereinafter, referred to also as Alq) for the organic light emitting layer
4
. This Alq is an excellent light emitting material having both high luminous efficiency and high electron transporting property. Another type of the organic EL device
1
a
is a device in which Alq, which forms the organic light emitting layer
4
, is doped with a fluorescent dye such as a coumarin derivative or DCM1, etc. (see Journal of Applied Physics, Vol. 65, p3610, 1989). According to the organic EL device
1
a,
the luminescent colors can be varied and the luminous efficiency can also be improved by selecting appropriate dyes.
An organic EL device
1
b
of
FIG. 13
is called an SH-B type device. The organic EL device
1
b
includes a glass substrate
2
, an anode
3
laminated on the glass substrate
2
, an organic light emitting layer
4
, an electron transport layer
7
and a cathode
5
. For the electron transport layer
7
, an oxadiazole derivative, typically 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (hereinafter, referred to also as PBD), is often used. However, the oxadiazole derivative such as PBD etc. tends to be crystallized and is not suitable for practical use.
An organic EL device
1
c
of
FIG. 14
is called a DH type device. The organic EL device
1
c
includes a glass substrate
2
, an anode
3
laminated on the glass substrate
2
, a hole transport layer
6
, an organic light emitting layer
4
, an electron transport layer
7
and a cathode
5
.
At present, the SH-A type devices of
FIG. 12
or the DH type devices of
FIG. 14
are mainly studied and developed. As to the electron transport layer, the hole transport layer and the light emitting layer, new materials suitable for each layer's function have been developed and studied. In particular, as a hole transporting organic molecule used for the hole transport layer, a large number of materials derived from triphenylamine have been developed. Furthermore, for a fluorescent organic molecule used for the light emitting layer, a fluorescent pigment, a laser dye, etc. can be used.
Furthermore, the cathode
5
is stable and can easily inject electrons when the cathode
5
is made of an alloy of an alkali metal or an alkaline-earth metal having a low work function and a stable metal such as aluminum or silver, etc. According to one report, for example, by controlling a Li concentration contained in the alloy to be such a slight amount as 0.01 wt. % or more and 0.1 wt. % or less, an EL device can exhibit a high luminous efficiency and high stability (see, for example, Publication of Japanese Patent Application No. Hei 5-121172 A). Furthermore, according to another report, a cathode in which a thin film made of a metal having a low work function is formed as an electron injection electrode on the side of an organic compound layer, and a thin film made of a stable metal is formed thereon as a protective electrode. With such a cathode structure, since it is not necessary to control the concentration of an alkaline metal such as Li, etc. having a high reactivity with water, a cathode that easily can be manufactured can be obtained.
Furthermore, an organic EL device in which an electron injection layer is placed on the cathode at the side of the organic layer is also reported. For example, the organic EL device using an alkaline metal compound for the electron injection layer and optimizing the thickness of this electron injection layer is disclosed (see Publication of Japanese Patent Application No. Hei 9-17574A). Furthermore, the relationship between the thickness of these electron injection layers and a dark spot is reported in detail (T. Wakimoto, Y. Fukuda, K. Nagayama, A. Yokoi, H. Nakada and M. Tsuchida, IEEE Transactions on Electron Devices, Vol. 44, No. 8, p1245, 1997).
As mentioned above, in the organic EL device, the electron injection layer has been studied as an important factor for determining the luminous efficiency and lifetime.
However, conventional organic EL devices do not have satisfactory luminous efficiency, selectivity of emission wavelength and lifetime.
In particular, when the light emitting layer is formed by a doping method, it is difficult to control the concentration of a dopant. Furthermore, guest materials for emitting red light have a wide range of &pgr; electron system, so that they tend to be interacted with each other and are easily subjected to concentration quenching.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a organic material suitable for an electroluminescent device and an electroluminescent device using the same.
In order to achieve the above-mentioned object, a first organic material for an EL device of the present invention is a complex compound expressed by the following formula (F1):
wherein R1 and R2, which can be same or different, respectively denote one selected from the group consisting of halogen, alkyl having 1 to 3 carbon atoms, and a bridging ligand having a nitrogen-containing aromatic ring containing at least two nitrogen atoms, and when R1 or R2 is a bridging ligand having a nitrogen-containing aromatic ring, nitrogen in the nitrogen-containing aromatic ring is a coordinating atom; R3, R4, R5 and R6, which can be same or different, respectively denote one member selected from the group consisting of hydrogen, alkyl, aryl, an aryl derivative, a nitrogen-containing aromatic ring and a derivative of a nitrogen-containing aromatic ring; and M is a central metal. The above-mentioned organic material is suitable for the EL device.
It is preferable in the above-mentioned first organic material for an EL device that the complex compound has a pyrazabole structure.
It is preferable in the above-mentioned organic material for an EL device that the complex compound is 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyrazabole.
Furthermore, a second organic material for an EL device of the present invention is an organic boron complex compound having an electron accepting phenyl group as a ligand.
It is preferable in the above-mentioned second organic material for an EL device that the boron organic complex compound is expressed by the formula (F2):
wherein R7 to R9, which can be same or different, respectively denote an electron accepting phenyl group.
Furthermore, an EL device of the present invention includes an anode, a cathode and an organic compound layer placed between the anode and the cathode, and the organic compound layer includes the above-mentioned first organic material for the EL device. Thus, an EL device having an excellent property can be obtained.
It is preferable in the above-mentioned EL device that the organic material has a pyrazabole structure.
It is prefera
Hisada Hitoshi
Kishimoto Yoshio
Matsuo Mikiko
Satou Tetsuya
Sugiura Hisanori
Kelly Cynthia H.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P,C,
Xu Ling
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