Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-09-24
2004-11-23
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S504000, C544S225000, C546S004000, C549S003000
Reexamination Certificate
active
06821646
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a luminescence device, a display apparatus and a metal coordination compound therefor. More specifically, the present invention relates to a luminescence device employing an organic metal coordination compound having a formula (1) appearing hereinafter as a luminescence material so as to allow stable luminescence efficiency, a display apparatus including the luminescence device and the metal coordination compound adapted for use in the luminescence device.
An organic electroluminescence (EL) device has been extensively studied as a luminescence device with a high responsiveness and high efficiency.
The organic EL device generally has a sectional structure as shown in
FIG. 1A
or
1
B (e.g., as described in “Macromol. Symp.”, 125, pp. 1-48 (1997)).
Referring to the figures, the EL device generally has a structure including a transparent substrate
15
, a transparent electrode
14
disposed on the transparent substrate
15
, a metal electrode
11
disposed opposite to the transparent electrode
14
, and a plurality of organic (compound) layers disposed between the transparent electrode
14
and the metal electrode
11
.
Referring to
FIG. 1
, the EL device in this embodiment has two organic layers including a luminescence layer
12
and a hole transport layer
13
.
The transparent electrode
14
may be formed of a film of ITO (indium tin oxide) having a larger work function to ensure a good hole injection performance into the hole transport layer. On the other hand, the metal electrode
11
may be formed of a layer of aluminum, magnesium, alloys thereof, etc., having a smaller work function to ensure a good electron injection performance into the organic layer(s).
These (transparent and metal) electrodes
14
and
11
may be formed in a thickness of 50-200 nm.
The luminescence layer
12
may be formed of, e.g., aluminum quinolinol complex (representative example thereof may include Alq3 described hereinafter) having an electron transporting characteristic and a luminescent characteristic. The hole transport layer
13
may be formed of, e.g., triphenyldiamine derivative (representative example thereof may include &agr;-NPD described hereinafter) having an electron donating characteristic.
The above-described EL device exhibits a rectification characteristic, so that when an electric field is applied between the metal electrode
11
as a cathode and the transparent electrode
14
as an anode, electrons are injected from the metal electrode
11
into the luminescence layer
12
and holes are injected from the transparent electrodes
14
.
The thus-injected holes and electrons are recombined within the luminescence layer
12
to produce excitons, thus causing luminescence. At that time, the hole transport layer
13
functions as an electron-blocking layer to increase a recombination efficiency at the boundary between the luminescence layer
12
and the hole transport layer
13
, thus enhancing a luminescence efficiency.
Referring to
FIG. 1B
, in addition to the layers shown in
FIG. 1A
, an electron transport layer
16
is disposed between the metal electrode
11
and the luminescence layer
12
, whereby an effective carrier blocking performance can be ensured by separating functions of luminescence, electron transport and hole transport, thus allowing effective luminescence.
The electron transport layer
16
may be formed of, e.g., oxadiazole derivatives.
In ordinary organic EL devices, fluorescence caused during a transition of luminescent center molecule from a singlet excited state to a ground state is used as luminescence.
On the other hand, not the above fluorescence (luminescence) via singlet exciton, phosphorescence (luminescence) via triplet exciton has been studied for use in organic EL device as described in, e.g., “Improved energy transfer in electrophosphorescent device” (D. F. O'Brien et al., Applied Physics Letters, Vol. 74, No. 3, pp. 442-444 (1999)) and “Very high-efficiency green organic light-emitting devices based on electrophosphorescence” (M. A. Baldo et al., Applied Physics Letters, Vol. 75, No. 1, pp. 4-6 (1999)).
The EL devices shown in these documents may generally have a sectional structure shown in FIG.
1
C.
Referring to
FIG. 1C
, four organic layers including a hole transfer layer
13
, a luminescence layer
12
, an exciton diffusion-prevention layer
17
, and an electron transport layer
16
are successively formed in this order on the transparent electrode (anode)
14
.
In the above documents, higher efficiencies have been achieved by using four organic layers including a hole transport layer
13
of &agr;-NPD (shown below), an electron transport layer
16
of Alq3 (shown below), an exciton diffusion-prevention layer
17
of BPC (shown below), and a luminescence layer
12
of a mixture of CPB (shown below) as a host material with Ir(ppy)
3
(shown below) or PtOEP (shown below) as a guest phosphorescence material doped into CBP at a concentration of ca. 6 wt. %.
Alq3: tris(8-hydroxyquinoline) aluminum (aluminum-quinolinol complex),
&agr;-NPD: N4,N4′-di-naphthalene-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine (4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl),
CBP: 4,4′-N,N′-dicarbazole-biphenyl,
BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenan-throline,
Ir(ppy)
3
: fac tris(2-phenylpyridine)iridium (iridium-phenylpyridine complex), and
PtEOP: 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (platinum-octaethyl porphine complex).
The phosphorescence (luminescence) material used in the luminescence layer
12
has attracted notice. This is because the phosphorescence material is expected to provide a higher luminescence efficiency in principle.
More specifically, in the case of the phosphorescence material, excitons produced by recombination of carriers comprise singlet excitons and triplet excitons presented in a ratio of 1:3. For this reason, when fluorescence caused during the transition from the singlet excited state to the ground state is utilized, a resultant luminescence efficiency is 25% (as upper limit) based on all the produced excitons in principle.
On the other hand, in the case of utilizing phosphorescence caused during transition from the triplet excited state, a resultant luminescence efficiency is expected to be at least three times that of the case of fluorescence in principle. In addition thereto, if intersystem crossing from the singlet excited state (higher energy level) to the triplet excited state is taken into consideration, the luminescence efficiency of phosphorescence can be expected to be 100% (four times that of fluorescence) in principle.
The use of phosphorescence based on transition from the triplet excited state has also been proposed in, e.g., Japanese Laid-Open Patent Application (JP-A) 11-329739, JP-A 11-256148 and JP-A 8-319482.
However, the above-mentioned organic EL devices utilizing phosphorescence have accompanied with a problem of luminescent deterioration particularly in an energized state.
The reason for luminescent deterioration has not been clarified as yet but may be attributable to such a phenomenon that the life of triplet exciton is generally longer than that of singlet exciton by at least three digits, so that molecule is placed in a higher-energy state for a long period to cause reaction with ambient substance, formation of exciplex or excimer, change in minute molecular structure, structural change of ambient substance, etc.
Accordingly, the (electro)phosphorescence EL device is expected to provide a higher luminescence efficiency as described above, while the EL device is required to suppress or minimize the luminescent deterioration in energized state.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a luminescence device capable of providing a high-efficiency luminescent state at a high brightness (or luminance) for a long period while minimizing the deterioration in luminescence in energized state.
Another object of the present invention is to provide a
Furugori Manabu
Igawa Satoshi
Kamatani Jun
Miura Seishi
Mizutani Hidemasa
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Yamnitzky Marie
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