Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
2001-12-21
2004-02-17
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S103000, C313S504000
Reexamination Certificate
active
06693295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light-emitting device utilizable in the fields of back light, flat panel display, illumination light source, display device, electrophotography, organic semiconductor laser, recording light source, exposure light source, read light source, sign, signboard, optical communication device, etc.
BACKGROUND OF THE INVENTION
Among various light-emitting devices, organic electroluminescent (EL) devices have been actively investigated and developed in recent years, since they can emit luminescence of high luminance at a low driving voltage. In general, the organic electrolight-emitting device is composed of a light-emitting layer and a pair of counter electrodes between which the light-emitting layer is interposed, and electrons injected from the cathode and holes injected from the anode are recombined in the light-emitting layer to generate excitons luminescence from which is utilized.
At present an organic electrolight-emitting device which emits luminescence of high luminance at a low driving voltage has a stratified structure as described in Tang et al,
Applied Physics Letters,
Vol. 51, page 913 (1987). The organic electrolight-emitting device can emit green luminescence of high luminance by laminating an electron-transporting and luminescent material and a hole-transporting material, and the luminance reaches to several thousands of candelas per square meter at a direct current voltage of 6 to 7 V. However, from the standpoint of practical use, it has been desired to develop a light-emitting device having higher luminance and higher luminous efficiency.
Recently, in order to develop light-emitting devices having higher luminous efficiency, light-emitting devices employing various transition metal complexes as luminescent materials have been investigated. As an light-emitting device which emits in particularly high luminous efficiency, an light-emitting device using an ortho-metalated complex of iridium (tris-orthoiridated complex with 2-phenylpyridine (Ir(ppy)
3
)) as a luminescent material is reported in
Applied Physics Letters,
Vol. 75, page 4 (1999). The light-emitting device has an external quantum yield of 8.3%. This value exceeds an external quantum yield of 5% which has been regarded as the limit value. However, since it is restricted to a green light-emitting device, development of other color light-emitting devices having higher luminous efficiency is necessary in order to apply to a full-color display or a white light-emitting device.
On the other hand, the organic light-emitting devices which provide luminescence of high luminance are those having a stratified structure of organic substance formed by vacuum deposition. While the production of devices using a coating technique is desirable from the standpoints of simplification of production process, processability, increase in size, etc., the devices produced using any conventional coating technique are inferior to the devices produced by using vacuum deposition in view of the luminance and luminous efficiency. Accordingly, an important subject has been to increase the luminance and luminous efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a material for light-emitting device which can emit luminescence of high luminance in high luminous efficiency, has excellent stability in repetitions of use at high temperature and enables to homogeneous planer emission, and an light-emitting device employing the same.
Another object of the present invention is to provide a material for light-emitting device which can emit blue luminescence of good color purity in a high luminous efficiency, and an light-emitting device employing the same.
A further object of the present invention is to provide a host material which can emit luminescence of high luminance in high luminous efficiency by doping a transition metal complex having a high quantum yield.
A still further object of the present invention is to provide a material for light-emitting device which can emit luminescence of high luminance in high luminous efficiency and be prepared by a coating technique.
Other objects of the present invention will become apparent from the following description and examples.
The above described objects of the present invention are accomplished by the following items (1) to (14).
(1) A light-emitting device comprising: a pair of electrodes formed on a substrate; and at least one organic compound layer containing a light-emitting layer provided between the electrodes, wherein the at least one organic compound layer comprises a host material, a layer of the host material has an energy gap of from 3.6 eV to 5.2 eV and an ionization potential of the host material is from 5.4 eV to 6.3 eV.
(2) The light-emitting device as described in (1) above, wherein the at least one organic compound layer comprises a compound comprising a partial structure represented by the following formula (I):
wherein X represents one of a nitrogen atom and C—R
12
; L
11
represents one of a n
1
-valent connecting group having a heteroaryl group and a n
1
-valent connecting group comprising a non-conjugate connecting group having an arylene group; R
12
R
13
, R
14
and R
15
each independently represents one of a hydrogen atom and a substituent; one of the combinations of R
12
and R
13
, R
13
and R
14
and R
14
and R
15
may be combined with each other to form a condensed ring; and n
1
represents an integer of 2 or more.
(3) The light-emitting device as described in (1) or (2) above, wherein the single layer of the host material has an absorption spectrum having a maximum absorption wavelength of not more than 340 nm.
(4) The light-emitting device as described in any one of (1) to (3) above, wherein the host material comprises a compound comprising a partial structure represented by the following formula (I):
wherein X represents one of a nitrogen atom and C—R
12
; L
11
represents one of a n
1
-valent connecting group having a heteroaryl group and a n
1
-valent connecting group comprising a non-conjugate connecting group having an arylene group; R
12
, R
13
, R
14
and R
15
each independently represents one of a hydrogen atom and a substituent; one of the combinations of R
12
and R
13
, R
13
and R
14
and R
14
and R
15
may be combined with each other to form a condensed ring; and n
1
represents an integer of 2 or more.
(5) The light-emitting device as described in any one of (1) to (4) above, wherein the host material comprises a compound comprising a partial structure represented by the following formula (II):
wherein L
12
represents one of a from 2- to 6-valent connecting group having a heteroaryl group and a from 2- to 6-valent connecting group comprising a non-conjugate connecting group having an arylene group; n
2
represents an integer of from 2 to 6; R represents one of an alkyl group having from 1 to 20 carbon atoms, an aryl group having from 6 to 20 carbon atoms, a heteroaryl group having from 2 to 20 carbon atoms and a silyl group having from 3 to 20 carbon atoms; and m represents an integer of from 0 to 6.
(6) The light-emitting device as described in any one of (1) to (5) above, wherein the light-emitting layer comprises at least one luminescent material.
(7) The light-emitting device as described in (6) above, wherein the luminescent material is a transition metal complex.
(8) The light-emitting device as described in (7) above, wherein the transition metal complex is capable of generating luminescence by a transition from a triplet excitation state thereof.
(9) The light-emitting device as described in any one of (1) to (8) above, wherein the light-emitting layer comprises a high molecular compound.
(10) The light-emitting device as described in any one of (1) to (9) above, wherein the light-emitting layer has a thickness of from 1 nm to 5 &mgr;m.
(11) The light-emitting device as described in (2) above, wherein the substituent represented by R
12
, R
13
, R
14
or R
15
is selected from an alkyl group, an alkenyl group, an alkynyl group, an aralkyl gro
Crane Sara
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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