U.S. patent application number 12/662520 was filed with the patent office on 2010-08-12 for organic electroluminescence device.
This patent application is currently assigned to Idemitsu Kosan Co., Ltd.. Invention is credited to Takashi Arakane, Kenichi Fukuoka, Hisahiro Higashi, Chishio Hosokawa, Hidetsugu Ikeda.
Application Number | 20100201255 12/662520 |
Document ID | / |
Family ID | 18859823 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100201255 |
Kind Code |
A1 |
Hosokawa; Chishio ; et
al. |
August 12, 2010 |
Organic electroluminescence device
Abstract
An organic electroluminescence device comprising a pair of
electrodes and a layer of an organic light emitting medium disposed
between the pair of electrodes, wherein the layer of an organic
light emitting medium comprises a mixed layer comprising (A) at
least one hole transporting compound and (B) at least one electron
transporting compound, an energy gap of the hole transporting
compound represented by Eg1 and an energy gap of the electron
transporting compound represented by Eg2 satisfy a relation:
Eg1<Eg2. Electrons and holes are recombined in the layer of an
organic light emitting medium and light is emitted. The organic
electroluminescence device has a long life and emits light at a
high efficiency.
Inventors: |
Hosokawa; Chishio;
(Sodegaura-shi, JP) ; Higashi; Hisahiro;
(Sodegaura-shi, JP) ; Fukuoka; Kenichi;
(Sodegaura-shi, JP) ; Ikeda; Hidetsugu;
(Sodegaura-shi, JP) ; Arakane; Takashi;
(Sodegaura-shi, JP) |
Correspondence
Address: |
STEPTOE & JOHNSON LLP
1330 CONNECTICUT AVENUE, N.W.
WASHINGTON
DC
20036
US
|
Assignee: |
Idemitsu Kosan Co., Ltd.
Chiyoda-ku
JP
|
Family ID: |
18859823 |
Appl. No.: |
12/662520 |
Filed: |
April 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11169792 |
Jun 30, 2005 |
7709102 |
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12662520 |
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10870997 |
Jun 21, 2004 |
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11169792 |
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10025634 |
Dec 26, 2001 |
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10870997 |
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Current U.S.
Class: |
313/504 |
Current CPC
Class: |
C09K 2211/186 20130101;
H01L 51/506 20130101; C09K 2211/1011 20130101; H01L 51/0081
20130101; H01L 51/5008 20130101; H01L 51/5036 20130101; H05B 33/14
20130101; C09K 2211/1014 20130101; H01L 2251/308 20130101; H01L
51/006 20130101; H01L 51/5012 20130101; C09K 2211/188 20130101;
H01L 51/0058 20130101; H01L 51/0052 20130101; Y10T 428/24942
20150115; C09K 2211/1029 20130101; Y10S 428/917 20130101; H01L
51/0055 20130101; C09K 11/06 20130101; H01L 51/5076 20130101; H01L
51/0056 20130101 |
Class at
Publication: |
313/504 |
International
Class: |
H01L 51/54 20060101
H01L051/54 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2000 |
JP |
2000-394152 |
Claims
1. An organic electroluminescence device comprising a pair of
electrodes and a layer of an organic light emitting medium disposed
between the pair of electrodes, wherein the layer of an organic
light emitting medium comprises a mixed layer consisting
essentially of (A) at least one compound selected from hole
transporting compounds and (B) at least one compound selected from
electron transporting compounds in amounts such that a ratio of an
amount of component (A) to an amount of component (B) is in a range
of 8:92 to 92:8; an energy gap of the hole transporting compound
represented by Eg1 and an energy gap of the electron transporting
compound represented by Eg2 satisfy a relation: Eg1<Eg2; and the
electron transporting compound is represented by the following
general formula (5) or the following general formula (6):
A.sup.1-L-A.sup.2 (5) wherein A.sup.1 and A.sup.2 may be the same
or different from each other and each independently represents a
substituted or unsubstituted monophenylanthryl group or a
substituted or unsubstituted diphenylanthryl group, and L
represents a single bond or a divalent bonding group;
A.sup.3-An-A.sup.4 (6) wherein An represents a substituted or
unsubstituted anthracene residue group, and A.sup.3 and A.sup.4 may
be the same or different from each other and each independently
represents a substituted or unsubstituted monovalent condensed
aromatic cyclic group having 10 to 40 carbon atoms or a substituted
or unsubstituted aryl group having no condensed cyclic structures
and having 12 to 40 carbon atoms.
2. The organic electroluminescence device according to claim 1,
wherein an ionization energy of the hole transporting compound
represented by IP1 and an ionization energy of the electron
transporting compound represented by IP2 satisfy a relation:
IP1<IP2.
3. The organic electroluminescence device according to claim 2,
wherein an electron affinity of the hole transporting compound
represented by Af1 and an electron affinity of the electron
transporting compound represented by Af2 satisfy a relation:
Af1.ltoreq.Af2 and .DELTA.Ev given by .DELTA.Ev=IP2-IP1 and
.DELTA.Ec given by .DELTA.Ec=Af2-AF1 satisfy a relation:
.DELTA.Ev.gtoreq.Ec.
4. The organic electroluminescence device according to claim 2,
wherein an electron affinity of the hole transporting compound
represented by Af1 and an electron affinity of the electron
transporting compound represented by Af2 satisfy a relation:
Af1>Af2 and .DELTA.Ev given by .DELTA.Ev=IP2-IP1 and .DELTA.Ec
given by .DELTA.Ec'=Af1-AF2 satisfy a relation:
.DELTA.Ev.gtoreq.Ec'.
5. The organic electroluminescence device according to claim 1,
wherein the hole transporting compound is an aromatic amine having
condensed cyclic structures.
6. The organic electroluminescence device according to claim 5,
wherein the aromatic amine is represented by following general
formula (1): ##STR00017## wherein Ar.sup.1 to Ar.sup.4 each
independently represents a substituted or unsubstituted aromatic
hydrocarbon group having 6 to 40 carbon atoms or a substituted or
unsubstituted aromatic heterocyclic group having 3 to 40 carbon
atoms, Y represents a substituted or unsubstituted aromatic residue
group having 2 to 60 carbon atoms, at least one of the groups
represented by Ar.sup.1 to Ar.sup.4 and Y has a condensed cyclic
group having 3 or more rings, and a substituent in the groups
represented by Ar.sup.1 to Ar.sup.4 and Y may form a ring with two
groups selected from the groups represented by Ar.sup.1 to Ar.sup.4
and Y.
7. The organic electroluminescence device according to claim 5,
wherein the aromatic amine is represented by following general
formula (2): ##STR00018## wherein Ar.sup.1 to Ar.sup.6 each
independently represents a substituted or unsubstituted aromatic
hydrocarbon group having 6 to 40 carbon atoms or a substituted or
unsubstituted aromatic heterocyclic group having 3 to 40 carbon
atoms, Z represents a substituted or unsubstituted aromatic residue
group having 3 to 60 carbon atoms, at least one of the groups
represented by Ar.sup.1 to Ar.sup.6 and Z has a condensed cyclic
group having 3 or more rings, and a substituent in the groups
represented by Ar.sup.1 to Ar.sup.6 and Z may form a ring with two
groups selected from the groups represented by Ar.sup.1 to Ar.sup.6
and Z.
8.-12. (canceled)
13. The organic electroluminescence device according to claim 1,
wherein the mixed layer in the layer of an organic light emitting
medium further comprises (C) a fluorescent compound.
14. The organic electroluminescence device according to claim 13,
wherein the layer of an organic light emitting medium comprises
component (A), component (B) and component (C) in amounts such that
a ratio of a total amount by weight of component (A) and component
(B) to an amount by weight of component (C) is in a range of 100:1
to 10:1.
15. The organic electroluminescence device according to claim 1,
wherein a layer of a chalcogenide, a metal halide or a metal oxide
is disposed on a surface of at least one of the pair of
electrodes.
16. The organic electroluminescence device according to claim 1,
wherein a mixed region of a reducing dopant and the electron
transporting compound or a mixed region of an oxidizing dopant and
the hole transporting compound is disposed on a surface of at least
one of the pair of electrodes.
17. The organic electroluminescence device according to claim 1,
wherein a work function WF of an anode which injects holes into the
layer of an organic light emitting medium and an ionization energy
of the hole transporting compound IP1 satisfy a relation:
IP1-WF.ltoreq.0.2eV.
18. An organic electroluminescence device comprising a pair of
electrodes and a layer of an organic light emitting medium disposed
between the pair of electrodes, wherein the layer of an organic
light emitting medium comprises a mixed layer comprising (A) at
least one compound selected from hole transporting compounds and
(B) at least one compound selected from electron transporting
compounds; an energy gap of the hole transporting compound
represented by Eg1 and an energy gap of the electron transporting
compound represented by Eg2 satisfy a relation: Eg1<Eg2 and
holes are transported in the layer of an organic light emitting
medium with the hole transporting compound; and the electron
transporting compound is represented by the following general
formula (5) or the following general formula (6): A.sup.1-L-A.sup.2
(5) wherein A.sup.1 and A.sup.2 may be the same or different from
each other and each independently represents a substituted or
unsubstituted monophenylanthryl group or a substituted or
unsubstituted diphenylanthryl group, and L represents a single bond
or a divalent bonding group; A.sup.3-An-A.sup.4 (6) wherein An
represents a substituted or unsubstituted anthracene residue group,
and A.sup.3 and A.sup.4 may be the same or different from each
other and each independently represents a substituted or
unsubstituted monovalent condensed aromatic cyclic group having 10
to 40 carbon atoms or a substituted or unsubstituted aryl group
having no condensed cyclic structures and having 12 to 40 carbon
atoms.
Description
TECHNICAL FIELD
[0001] The present invention relates to an organic
electroluminescence device (hereinafter, "electroluminescence" will
be referred to as EL) and, more particularly, to an organic EL
device having a long life and emitting light at a high
efficiency.
BACKGROUND ART
[0002] EL devices which utilize light emission under application of
an electric field show high self-distinguishability due to the
self-emission and exhibit excellent impact resistance since they
are completely solid devices. Therefore, EL devices have been
attracting attention for application as light emitting devices in
various types of display apparatus.
[0003] The EL devices include inorganic EL devices in which an
inorganic compound is used as the light emitting material and
organic EL devices in which an organic compound is used as the
light emitting material. Organic EL devices have been extensively
studied for practical application as a light emitting device of the
next generation because the applied voltage can be decreased to a
great extent, the size of the device can be reduced easily,
consumption of electric power is small, planar light emission is
possible and three primary colors are easily emitted.
[0004] As for the construction of the organic EL device, the basic
construction comprises an anode/an organic light emitting layer/a
cathode. Constructions having a hole injecting and transporting
layer or an electron injecting layer suitably added to the basic
construction are known. Examples of such constructions include the
construction of an anode/a hole injecting and transporting layer/an
organic light emitting layer/a cathode and the construction of an
anode/a hole injecting and transporting layer/an organic light
emitting layer/an electron injecting layer/a cathode.
[0005] In the development of organic EL devices which can be
practically applied, various studies to obtain a light emitting
element having a long life and emits light at a high efficiency
have been conducted. However, an element having a longer life and
emits light at a higher efficiency is desired so that consumption
of electric power can be further reduced.
[0006] For example, in International Patent Application Laid-Open
No. 98/08360 and U.S. Pat. No. 5,853,905, elements in which a mixed
layer of an amine derivative having the electron transporting
property and an energy gap of 3 eV or greater and an aluminum
complex of 8-hydroxyquinoline (Alq) as an electron transporting
compound is used as the light emitting medium are disclosed. Since
the energy gap of Alq is 2.7 eV, holes and electrons are recombined
in Alq having a lower energy gap and light is emitted in this light
emitting medium. Since Alq itself has a small quantum yield of
fluorescence, the efficiency is enhanced by adding a light emitting
dopant such as coumarine and rubrene.
[0007] However, the technology disclosed in the above references
has a drawback in that the life of the device cannot be increased
to the desired value. In other words, in general, few organic
materials which simultaneously achieve excellent transportation of
electrons and excellent durability under an electric current can be
found. It is confirmed that Alq is degraded when holes are injected
into Alq although Alq exhibits excellent durability in
transportation of electrons. In the case of the above light
emitting medium, the energy gap of the hole transporting compound
Eg1 and the energy gap of the electron transporting compound Eg2
has the relation: Eg1>Eg2. Therefore, holes tend to be injected
into Alq having a smaller energy gap and the life of the device
cannot be increased to the desired value. Although it is known that
durability of Alq can be improved by addition of a light emitting
dopant such as coumarine and rubrene, further improvement has been
desired.
DISCLOSURE OF THE INVENTION
[0008] Under the above circumstances, the present invention has an
object of providing an organic EL device which has a longer life
and emits light at a higher efficiency than those of conventional
organic EL devices.
[0009] As the result of intensive studies by the present inventors
to achieve the above object, it was found that an organic EL device
having a longer life and emitting light at a higher efficiency than
those of conventional organic EL devices could be obtained when an
organic electroluminescence device comprising a layer of an organic
light emitting medium comprised a mixed layer comprising (A) at
least one hole transporting compound and (B) at least one electron
transporting compound and an energy gap of the hole transporting
compound represented by Eg1 was smaller than an energy gap of the
electron transporting compound represented by Eg2. The present
invention has been completed based on the knowledge.
[0010] The present invention provides an organic
electroluminescence device comprising a pair of electrodes and a
layer of an organic light emitting medium disposed between the pair
of electrodes, wherein the layer of an organic light emitting
medium comprises a mixed layer comprising (A) at least one compound
selected from hole transporting compounds and (B) at least one
compound selected from electron transporting compounds and an
energy gap of the hole transporting compound represented by Eg1 and
an energy gap of the electron transporting compound represented by
Eg2 satisfy a relation: Eg1<Eg2.
THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION
[0011] The present invention provides an organic
electroluminescence device comprising a pair of electrodes and a
layer of an organic light emitting medium disposed between the pair
of electrodes, wherein the layer of an organic light emitting
medium comprises a mixed layer comprising (A) at least one compound
selected from hole transporting compounds and (B) at least one
compound selected from electron transporting compounds and an
energy gap of the hole transporting compound represented by Eg1 and
an energy gap of the electron transporting compound represented by
Eg2 satisfy a relation: Eg1<Eg2.
[0012] Due to this relation in the layer of an organic light
emitting medium, holes are transported with the hole transporting
compound and electrons are injected into the hole transporting
compound in the area of recombination. Light is emitted by
recombination of the holes and the electrons. Since injection of
holes into the electron transporting compound is suppressed,
degradation of the electron transporting compound is suppressed and
the life of the device is extended. The hole transporting compound
can also provide durability to the electron injection.
[0013] It is preferable that the ionization energy of the hole
transporting compound represented by IP1 and the ionization energy
of the electron transporting compound represented by IP2 satisfy
the relation: IP1.ltoreq.IP2.
[0014] Due to this relation, holes are more easily injected into
the lowest occupied orbital of the hole transporting compound from
an outer layer of the light emitting medium. The outer layer means
a layer other than the layer of the light emitting medium such as
the anode, a hole injecting layer, a hole transporting layer and a
buffer layer.
[0015] It is preferable that the electron affinity of the hole
transporting compound represented by Af1 and the electron affinity
of the electron transporting compound represented by Af2 satisfy a
relation: Af1.ltoreq.Af2. The electron affinities represented by
Af1 and Af2 are values of the energies of the lowest vacant
orbitals based on the energy level of an electron in the vacuum as
the reference. Due to this relation, electrons are more easily
injected into the lowest vacant orbital of the electron
transporting compound from an outer layer of the layer of the light
emitting medium. The outer layer means a layer other than the layer
of the light emitting medium such as the cathode, an electron
injecting layer, an electron transporting layer, a hole arresting
layer or a buffer layer. In this case, it is preferable that
.DELTA.Ev given by .DELTA.Ev=IP2-IP1 and ac given by
.DELTA.Ec=Af2-AF1 satisfy a relation: .DELTA.Ev.gtoreq..DELTA.Ec.
Due to this relation, electrons are more easily injected into the
lowest vacant orbital of the hole transporting compound through the
electron transporting compound. On the other hand, injection of
holes into the lowest vacant orbital of the electron injecting
compound is suppressed.
[0016] The electron affinity of the hole transporting compound
represented by Af1 and the electron affinity of the electron
transporting compound represented by Af2 may satisfy a relation:
Af1>Af2. In this case, the hole transporting compound does not
substantially transport electrons or the mobility of electrons with
the hole transporting compound is smaller than the mobility of
electrons with the electron transporting compound. In this the
mobility of electrons with the electron transporting compound. In
this case, it is preferable that .DELTA.Ev given by
.DELTA.Ev=IP2-IP1 and .DELTA.Ec' given by .DELTA.Ec'=Af1-AF2
satisfy a relation: .DELTA.Ev.gtoreq..DELTA.Ec'. Due to this
relation, the trapping effect of the hole transporting compound
decreases and electrons transported with the electron transporting
compound can more easily reach the area of recombination.
[0017] It is preferable that the hole transporting compound used in
the organic EL device of the present invention is an aromatic amine
having a condensed cyclic structure.
[0018] It is preferable that the aromatic amine is represented by
the following general formula (1):
##STR00001##
wherein Ar.sup.1 to Ar.sup.4 each independently represent a
substituted or unsubstituted aromatic hydrocarbon group having 6 to
40 carbon atoms or a substituted or unsubstituted aromatic
heterocyclic group having 3 to 40 carbon atoms, Y represents a
substituted or unsubstituted aromatic residue group having 2 to 60
carbon atoms, at least one of the groups represented by Ar.sup.1 to
Ar.sup.4 and Y has a condensed cyclic group having 3 or more rings
and a substituent in the groups represented by Ar.sup.1 to Ar.sup.4
and Y may form a ring with two groups selected from the groups
represented by Ar.sup.1 to Ar.sup.4 and Y; or by the following
general formula (2):
##STR00002##
wherein Ar.sup.1 to Ar.sup.6 each independently represent a
substituted or unsubstituted aromatic hydrocarbon group having 6 to
40 carbon atoms or a substituted or unsubstituted aromatic
heterocyclic group having 3 to 40 carbon atoms, Z represents a
substituted or unsubstituted aromatic residue group having 3 to 60
carbon atoms, at least one of the groups represented by Ar.sup.1 to
Ar.sup.6 and Z has a condensed cyclic group having 3 or more rings
and a substituent in the groups represented by Ar.sup.1 to Ar.sup.6
and Z may form a ring with two groups selected from the groups
represented by Ar.sup.1 to Ar.sup.6 and Z.
[0019] In the above general formulae (1) and (2), examples of the
groups represented by Ar.sup.1 to Ar.sup.6, Y and Z include
aromatic residue groups derived from anthracene, chrysene,
fluorene, pyrene, perylene, naphthalene, pentacene, coronene,
fluoranthene, pycene, rubicene and acenaphtho-fluoranthene.
[0020] It is preferable that the compounds represented by general
formulae (1) and (2) are compounds represented by any of the
following general formulae (7) to (11).
##STR00003##
[0021] In the above general formula (7), R.sup.8 to R.sup.19 each
independently represent hydrogen atom, a halogen atom, hydroxyl
group, a substituted or unsubstituted amino group, nitro group,
cyano group, a substituted or unsubstituted alkyl group having 1 to
30 carbon atoms, a substituted or unsubstituted alkenyl group
having 2 to 30 carbon atoms, a substituted or unsubstituted
cycloalkyl group having 5 to 30 carbon atoms, a substituted or
unsubstituted alkoxyl group having 1 to 30 carbon atoms, a
substituted or unsubstituted aromatic hydrocarbon group having 6 to
40 carbon atoms, a substituted or unsubstituted aromatic
heterocyclic group having 3 to 40 carbon atoms, a substituted or
unsubstituted aralkyl group having 7 to 40 carbon atoms, a
substituted or unsubstituted aryloxyl group having 6 to 40 carbon
atoms, a substituted or unsubstituted alkoxycarbonyl group having 2
to 40 carbon atoms or carboxyl group. Two groups selected from the
groups represented by R.sup.8 to R.sup.19 may form a ring and at
least one of the groups represented by R.sup.8 to R.sup.19 is a
diarylamino group represented by --NAr.sup.7Ar.sup.8. Ar.sup.7 and
Ar.sup.8 each independently represent a substituted or
unsubstituted aryl group having 6 to 20 carbon atoms.
##STR00004##
[0022] In the above general formula (8), R.sup.21 to R.sup.38 each
independently represent hydrogen atom, a halogen atom, hydroxyl
group, a substituted or unsubstituted amino group, nitro group,
cyano group, a substituted or unsubstituted alkyl group having 1 to
30 carbon atoms, a substituted or unsubstituted alkenyl group
having 2 to 30 carbon atoms, a substituted or unsubstituted
cycloalkyl group having 5 to 30 carbon atoms, a substituted or
unsubstituted alkoxyl group having 1 to 30 carbon atoms, a
substituted or unsubstituted aromatic hydrocarbon group having 6 to
40 carbon atoms, a substituted or unsubstituted aromatic
heterocyclic group having 3 to 40 carbon atoms, a substituted or
unsubstituted aralkyl group having 7 to 40 carbon atoms, a
substituted or unsubstituted aryloxyl group having 6 to 40 carbon
atoms, a substituted or unsubstituted alkoxycarbonyl group having 2
to 40 carbon atoms or carboxyl group. Two groups selected from the
groups represented by R.sup.21 to R.sup.38 may form a ring and at
least one of the groups represented by R.sup.21 to R.sup.38 is a
diarylamino group represented by --NAr.sup.7Ar.sup.8. Ar.sup.7 and
Ar.sup.8 each independently represent a substituted or
unsubstituted aryl group having 6 to 20 carbon atoms.
##STR00005##
[0023] In the above general formula (9), Te represents a terylene
residue group, Ar.sup.9 and Ar.sup.10 each independently represent
a substituted or unsubstituted alkyl group having 1 to 30 carbon
atoms, a substituted or unsubstituted monocyclic group or a
substituted or unsubstituted condensed polycyclic group having 6 to
40 carbon atoms and r represents an integer of 1 to 6.
##STR00006##
[0024] In the above general formula (10), Ar.sup.11 to Ar.sup.14
each independently represent a substituted or unsubstituted aryl
group having 6 to 16 carbon atoms and R.sup.41 to R.sup.48 each
independently represent hydrogen atom, a halogen atom, hydroxyl
group, a substituted or unsubstituted amino group, nitro group,
cyano group, a substituted or unsubstituted alkyl group having 1 to
30 carbon atoms, a substituted or unsubstituted alkenyl group
having 2 to 30 carbon atoms, a substituted or unsubstituted
cycloalkyl group having 5 to 30 carbon atoms, a substituted or
unsubstituted alkoxyl group having 1 to 30 carbon atoms, a
substituted or unsubstituted aromatic hydrocarbon group having 6 to
40 carbon atoms, a substituted or unsubstituted aromatic
heterocyclic group having 3 to 40 carbon atoms, a substituted or
unsubstituted aralkyl group having 7 to 40 carbon atoms, a
substituted or unsubstituted aryloxyl group having 6 to 40 carbon
atoms, a substituted or unsubstituted alkoxycarbonyl group having 2
to 40 carbon atoms or carboxyl group and two groups selected from
the groups represented by R.sup.41 to R.sup.48 may form a ring.
##STR00007##
[0025] In the above general formula (11), Ar.sup.15 to Ar.sup.18
each independently represent a substituted or unsubstituted alkyl
group having 1 to 30 carbon atoms, a substituted or unsubstituted
monocyclic group, a substituted or unsubstituted condensed
polycyclic group having 8 to 40 carbon atoms; an integral
combination of Ar.sup.15 and Ar.sup.16 and an integral combination
of Ar.sup.17 and Ar.sup.18 each represent a condensed polycyclic
group having a nitrogen atom as a bonding atom; Q represents a
divalent bonding group bonding a cyclic group or a plurality of
cyclic groups and may be substituted or unsubstituted; R.sup.51 to
R.sup.66 each independently represent hydrogen atom, a halogen
atom, hydroxyl group, a substituted or unsubstituted amino group,
nitro group, cyano group, a substituted or unsubstituted alkyl
group having 1 to 30 carbon atoms, a substituted or unsubstituted
alkenyl group having 2 to 30 carbon atoms, a substituted or
unsubstituted cycloalkyl group having 5 to 30 carbon atoms, a
substituted or unsubstituted alkoxyl group having 1 to 30 carbon
atoms, a substituted or unsubstituted aromatic hydrocarbon group
having 6 to 40 carbon atoms, a substituted or unsubstituted
aromatic heterocyclic group having 3 to 40 carbon atoms, a
substituted or unsubstituted aralkyl group having 7 to 40 carbon
atoms, a substituted or unsubstituted aryloxyl group having 6 to 40
carbon atoms, a substituted or unsubstituted alkoxycarbonyl group
having 2 to 40 carbon atoms or carboxyl group; and two groups
selected from the groups represented by R.sup.51 to R.sup.66 may
form a ring.
[0026] The aromatic amine compound, the aromatic diamine compound
and the aromatic triamine compound used in the present invention
are compounds having structures represented by the above general
formulae (1), (2) and (7) to (11). In each general formula,
preferable examples of the substituent include halogen atoms,
hydroxyl group, substituted and unsubstituted amino groups, nitro
group, cyano group, substituted and unsubstituted alkyl groups,
substituted and unsubstituted alkenyl groups, substituted and
unsubstituted cycloalkyl groups, substituted and unsubstituted
alkoxyl groups, substituted and unsubstituted aromatic hydrocarbon
groups, substituted and unsubstituted aromatic heterocyclic groups,
substituted and unsubstituted aralkyl groups, substituted and
unsubstituted aryl groups, substituted and unsubstituted aryloxyl
groups, substituted or unsubstituted alkoxycarbonyl groups and
carboxyl group.
[0027] Examples of the substituted and unsubstituted alkyl groups
include methyl group, ethyl group, propyl group, isopropyl group,
n-butyl group, s-butyl group, isobutyl group, t-butyl group,
n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group,
hydroxymethyl group, 1-hydroxyethyl group, 2-hydroxyethyl group,
2-hydroxyisobutyl group, 1,2-dihydroxyethyl group,
1,3-dihydroxyisopropyl group, 2,3-dihydroxy-t-butyl group,
1,2,3-trihydroxypropyl group, chloromethyl group, 1-chloroethyl
group, 2-chloroethyl group, 2-chloroisobutyl group,
1,2-dichloroethyl group, 1,3-dichloroisopropyl group,
2,3-dichloro-t-butyl group, 1,2,3-trichloropropyl group,
bromomethyl group, 1-bromoethyl group, 2-bromoethyl group,
2-bromoisobutyl group, 1,2-dibromoethyl group, 1,3-dibromoisopropyl
group, 2,3-dibromo-t-butyl group, 1,2,3-tribromopropyl group,
iodomethyl group, 1-iodoethyl group, 2-iodoethyl group,
2-iodoisobutyl group, 1,2-diiodoethyl group, 1,3-diiodoisopropyl
group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropyl group,
aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,
2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropyl
group, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,
cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,
2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropyl
group, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,
nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,
2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropyl
group, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl
group.
[0028] Examples of the substituted and unsubstituted alkenyl groups
include vinyl group, allyl group, 1-butenyl group, 2-butenyl group,
3-butenyl group, 1,3-butadienyl group, 1-methylvinyl group, styryl
group, 2,2-diphenylvinyl group, 1,2-diphenylvinyl group,
1-methylallyl group, 1,1-dimethylallyl group, 2-methylallyl group,
1-phenylallyl group, 2-phenylallyl group, 3-phenylallyl group,
3,3-diphenylallyl group, 1,2-dimethylallyl group,
1-phenyl-1-butenyl group and 3-phenyl-1-butenyl group.
[0029] Examples of the substituted and unsubstituted cycloalkyl
groups include cyclopropyl group, cyclobutyl group, cyclopentyl
group, cyclohexyl group and 4-methylcyclohexyl group.
[0030] The substituted and unsubstituted alkoxyl groups are
represented by --OY.sup.1. Examples of the group represented by
Y.sup.1 include methyl group, ethyl group, propyl group, isopropyl
group, n-butyl group, s-butyl group, isobutyl group, t-butyl group,
n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group,
hydroxymethyl group, 1-hydroxyethyl group, 2-hydroxyethyl group,
2-hydroxyisobutyl group, 1,2-dihydroxyethyl group,
1,3-dihydroxy-isopropyl group, 2,3-dihydroxy-t-butyl group,
1,2,3-trihydroxypropyl group, chloromethyl group, 1-chloroethyl
group, 2-chloroethyl group, 2-chloroisobutyl group,
1,2-dichloroethyl group, 1,3-dichloroisopropyl group,
2,3-dichloro-t-butyl group, 1,2,3-trichloropropyl group,
bromomethyl group, 1-bromoethyl group, 2-bromoethyl group,
2-bromoisobutyl group, 1,2-dibromoethyl group, 1,3-dibromoisopropyl
group, 2,3-dibromo-t-butyl group, 1,2,3-tribromopropyl group,
iodomethyl group, 1-iodoethyl group, 2-iodoethyl group,
2-iodoisobutyl group, 1,2-diiodoethyl group, 1,3-diiodoisopropyl
group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropyl group,
aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,
2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropyl
group, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,
cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,
2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropyl
group, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,
nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,
2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropyl
group, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl
group.
[0031] Examples of the substituted and unsubstituted aromatic
hydrocarbon groups include phenyl group, 1-naphthyl group,
2-naphthyl group, 1-anthryl group, 2-anthryl group, 9-anthryl
group, 1-phenanthryl group, 2-phenanthryl group, 3-phenanthryl
group, 4-phenanthryl group, 9-phenanthryl group, 1-naphthacenyl
group, 2-naphthacenyl group, 9-naphthacenyl group, 1-pyrenyl group,
2-pyrenyl group, 4-pyrenyl group, 2-biphenylyl group, 3-biphenylyl
group, 4-biphenylyl group, p-terphenyl-4-yl group, p-terphenyl-3-yl
group, p-terphenyl-2-yl group, m-terphenyl-4-yl group,
m-terphenyl-3-yl group, m-terphenyl-2-yl group, o-tolyl group,
m-tolyl group, p-tolyl group, p-t-butylpheny group,
p-(2-phenylpropyl)phenyl group, 3-methyl-2-naphthyl group,
4-methyl-1-naphthyl group, 4-methyl-1-anthryl group,
4'-methylbiphenylyl group and 4''-t-butyl-p-terphenyl-4-yl
group.
[0032] Examples of the substituted and unsubstituted aromatic
heterocyclic groups include 1-pyrrolyl group, 2-pyrrolyl group,
3-pyrrolyl group, pyradinyl group, 2-pyridinyl group, 3-pyridinyl
group, 4-pyridinyl group, 1-indolyl group, 2-indolyl group,
3-indolyl group, 4-indolyl group, 5-indolyl group, 6-indolyl group,
7-indolyl group, 1-isoindolyl group, 2-isoindolyl group,
3-isoindolyl group, 4-isoindolyl group, 5-isoindolyl group,
6-isoindolyl group, 7-isoindolyl group, 2-furyl group, 3-furyl
group, 2-benzofuranyl group, 3-benzofuranyl group, 4-benzofuranyl
group, 5-benzofuranyl group, 6-benzofuranyl group, 7-benzofuranyl
group, 1-isobenzofuranyl group, 3-isobenzofuranyl group,
4-isobenzofuranyl group, 5-isobenzofuranyl group, 6-isobenzofuranyl
group, 7-isobenzofuranyl group, 2-quinolyl group, 3-quinolyl group,
4-quinolyl group, 5-quinolyl group, 6-quinolyl group, 7-quinolyl
group, 8-quinolyl group, 1-isoquinolyl group, 3-isoquinolyl group,
4-isoquinolyl group, 5-isoquinolyl group, 6-isoquinolyl group,
7-isoquinolyl group, 8-isoquinolyl group, 2-quinoxanyl group,
5-quinoxanyl group, 6-quinoxanyl group, 1-carbazolyl group,
2-carbazolyl group, 3-carbazolyl group, 4-carbazolyl group,
9-carbazolyl group, 1-phenanthridinyl group, 2-phenanthridinyl
group, 3-phenanthridinyl group, 4-phenanthridinyl group,
6-phenanthridinyl group, 7-phenanthridinyl group, 8-phenanthridinyl
group, 9-phenanthridinyl group, 10-phenanthridinyl group,
1-acridinyl group, 2-acridinyl group, 3-acridinyl group,
4-acridinyl group, 9-acridinyl group, phenanthrolyl group,
2-thienyl group, 3-thienyl group, 2-methylpyrrol-1-yl group,
2-methylpyrrol-3-yl group, 2-methylpyrrol-4-yl group,
2-methylpyrrol-5-yl group, 3-methylpyrrol-1-yl group,
3-methylpyrrol-2-yl group, 3-methylpyrrol-4-yl group,
3-methyl-pyrrol-5-yl group, 2-t-butylpyrrol-4-yl group,
3-(2-phenylpropyl)pyrrol-1-yl group, 2-methyl-1-indolyl group,
4-methyl-1-indolyl group, 2-methyl-3-indolyl group,
4-methyl-3-indolyl group, 2-t-butyl-1-indolyl group,
4-t-butyl-1-indolyl group, 2-t-butyl-3-indolyl group and
4-t-butyl-3-indolyl group.
[0033] Examples of the substituted and unsubstituted aralkyl groups
include benzyl group, 1-phenylethyl group, 2-phenylethyl group,
1-phenylisopropyl group, 2-phenylisopropyl group, phenyl-t-butyl
group, .alpha.-naphthylmethyl group, 1-.alpha.-naphthylethyl group,
2-.alpha.-naphthylethyl group, 1-.alpha.-naphthyl-isopropyl group,
2-.alpha.-naphthylisopropyl group, .beta.-naphthylmethyl group,
1-.beta.-naphthylethyl group, 2-.beta.-naphthylethyl group,
1-.beta.-naphthylisopropyl group, 2-.beta.-naphthylisopropyl group,
1-pyrrolylmethyl group, 2-(1-pyrrolyl)ethyl group, p-methylbenzyl
group, m-methylbenzyl group, o-methylbenzyl group, p-chlorobenzyl
group, m-chlorobenzyl group, o-chlorobenzyl group, p-bromobenzyl
group, m-bromobenzyl group, o-bromobenzyl group, p-iodobenzyl
group, m-iodobenzyl group, o-iodobenzyl group, p-hydroxybenzyl
group, m-hydroxybenzyl group, o-hydroxybenzyl group, p-aminobenzyl
group, m-aminobenzyl group, o-aminobenzyl group, p-nitrobenzyl
group, m-nitrobenzyl group, o-nitrobenzyl group, p-cyanobenzyl
group, m-cyanobenzyl group, o-cyanobenzyl group,
1-hydroxy-2-phenylisopropyl group and 1-chloro-2-phenylisopropyl
group.
[0034] Examples of the substituted and unsubstituted aryl groups
include phenyl group, 1-naphthyl group, 2-naphthyl group, 1-anthryl
group, 2-anthryl group, 9-anthryl group, 1-phenanthryl group,
2-phenanthryl group, 3-phenanthryl group, 4-phenanthryl group,
9-phenanthryl group, 1-naphthacenyl group, 2-naphthacenyl group,
9-naphthacenyl group, 1-pyrenyl group, 2-pyrenyl group, 4-pyrenyl
group, 2-biphenylyl group, 3-biphenylyl group, 4-biphenylyl group,
p-terphenyl-4-yl group, p-terphenyl-3-yl group, p-terphenyl-2-yl
group, m-terphenyl-4-yl group, m-terphenyl-3-yl group,
m-terphenyl-2-yl group, o-tolyl group, m-tolyl group, p-tolyl
group, p-t-butylpheny group, p-(2-phenylpropyl)phenyl group,
3-methyl-2-naphthyl group, 4-methyl-1-naphthyl group,
4-methyl-1-anthryl group, 4'-methylbiphenyl group,
4''-t-butyl-p-terphenyl-4-yl group, 2-pyrrolyl group, 3-pyrrolyl
group, pyradinyl group, 2-pyridinyl group, 3-pyridinyl group,
4-pyridinyl group, 2-indolyl group, 3-indolyl group, 4-indolyl
group, 5-indolyl group, 6-indolyl group, 7-indolyl group,
1-isoindolyl group, 3-isoindolyl group, 4-isoindolyl group,
5-isoindolyl group, 6-isoindolyl group, 7-isoindolyl group, 2-furyl
group, 3-furyl group, 2-benzofuranyl group, 3-benzofuranyl group,
4-benzofuranyl group, 5-benzofuranyl group, 6-benzofuranyl group,
7-benzofuranyl group, 1-isobenzofuranyl group, 3-isobenzofuranyl
group, 4-isobenzofuranyl group, 5-isobenzofuranyl group,
6-isobenzofuranyl group, 7-isobenzofuranyl group, 2-quinolyl group,
3-quinolyl group, 4-quinolyl group, 5-quinolyl group, 6-quinolyl
group, 7-quinolyl group, 8-quinolyl group, 1-isoquinolyl group,
3-isoquinolyl group, 4-isoquinolyl group, 5-isoquinolyl group,
6-isoquinolyl group, 7-isoquinolyl group, 8-isoquinolyl group,
2-quinoxanyl group, 5-quinoxanyl group, 6-quinoxanyl group,
1-carbazolyl group, 2-carbazolyl group, 3-carbazolyl group,
4-carbazolyl group, 1-phenanthridinyl group, 2-phenanthridinyl
group, 3-phenanthridinyl group, 4-phenanthridinyl group,
6-phenanthridinyl group, 7-phenanthridinyl group, 8-phenanthridinyl
group, 9-phenanthridinyl group, 1-acridinyl group, 2-acridinyl
group, 3-acridinyl group, 4-acridinyl group, 9-acridinyl group,
phenanthrolyl group, 2-thienyl group, 3-thienyl group,
2-methylpyrrol-1-yl group, 2-methylpyrrol-3-yl group,
2-methylpyrrol-4-yl group, 2-methyl-pyrrol-5-yl group,
3-methylpyrrol-1-yl group, 3-methylpyrrol-2-yl group,
3-methylpyrrol-4-yl group, 3-methylpyrrol-5-yl group,
2-t-butylpyrrol-4-yl group, 3-(2-phenylpropyl)pyrrol-1-yl group,
2-methyl-1-indolyl group, 4-methyl-1-indolyl group,
2-methyl-3-indolyl group, 4-methyl-3-indolyl group,
2-t-butyl-1-indolyl group, 4-t-butyl-1-indolyl group,
2-t-butyl-3-indolyl group and 4-t-butyl-3-indolyl group.
[0035] The substituted and unsubstituted aryloxy groups are
represented by --OZ.sup.1. Examples of the group represented by
Z.sup.1 include phenyl group, 1-naphthyl group, 2-naphthyl group,
1-anthryl group, 2-anthryl group, 9-anthryl group, 1-phenanthryl
group, 2-phenanthryl group, 3-phenanthryl group, 4-phenanthryl
group, 9-phenanthryl group, 1-naphthacenyl group, 2-naphthacenyl
group, 9-naphthacenyl group, 1-pyrenyl group, 2-pyrenyl group,
4-pyrenyl group, 2-biphenylyl group, 3-biphenylyl group,
4-biphenylyl group, p-terphenyl-4-yl group, p-terphenyl-3-yl group,
p-terphenyl-2-yl group, m-terphenyl-4-yl group, m-terphenyl-3-yl
group, m-terphenyl-2-yl group, o-tolyl group, m-tolyl group,
p-tolyl group, p-t-butylpheny group, p-(2-phenylpropyl)phenyl
group, 3-methyl-2-naphthyl group, 4-methyl-1-naphthyl group,
4-methyl-1-anthryl group, 4'-methylbiphenylyl group,
4''-t-butyl-p-terphenyl-4-yl group, 2-pyrrolyl group, 3-pyrrolyl
group, pyradinyl group, 2-pyridinyl group, 3-pyridinyl group,
4-pyridinyl group, 2-indolyl group, 3-indolyl group, 4-indolyl
group, 5-indolyl group, 6-indolyl group, 7-indolyl group,
1-isoindolyl group, 3-isoindolyl group, 4-isoindolyl group,
5-isoindolyl group, 6-isoindolyl group, 7-isoindolyl group, 2-furyl
group, 3-furyl group, 2-benzofuranyl group, 3-benzofuranyl group,
4-benzofuranyl group, 5-benzofuranyl group, 6-benzofuranyl group,
7-benzofuranyl group, 1-isobenzofuranyl group, 3-isobenzofuranyl
group, 4-isobenzofuranyl group, 5-isobenzofuranyl group,
6-isobenzofuranyl group, 7-isobenzofuranyl group, 2-quinolyl group,
3-quinolyl group, 4-quinolyl group, 5-quinolyl group, 6-quinolyl
group, 7-quinolyl group, 8-quinolyl group, 1-isoquinolyl group,
3-isoquinolyl group, 4-isoquinolyl group, 5-isoquinolyl group,
6-isoquinolyl group, 7-isoquinolyl group, 8-isoquinolyl group,
2-quinoxanyl group, 5-quinoxanyl group, 6-quinoxanyl group,
1-carbazolyl group, 2-carbazolyl group, 3-carbazolyl group,
4-carbazolyl group, 1-phenanthridinyl group, 2-phenanthridinyl
group, 3-phenanthridinyl group, 4-phenanthridinyl group,
6-phenanthridinyl group, 7-phenanthridinyl group, 8-phenanthridinyl
group, 9-phenanthridinyl group, 1-acridinyl group, 2-acridinyl
group, 3-acridinyl group, 4-acridinyl group, 9-acridinyl group,
phenanthrolyl group, 2-thienyl group, 3-thienyl group,
2-methylpyrrol-1-yl group, 2-methylpyrrol-3-yl group,
2-methylpyrrol-4-yl group, 2-methylpyrrol-5-yl group,
3-methylpyrrol-1-yl group, 3-methylpyrrol-2-yl group,
3-methylpyrrol-4-yl group, 3-methyl-pyrrol-5-yl group,
2-t-butylpyrrol-4-yl group, 3-(2-phenylpropyl)pyrrol-1-yl group,
2-methyl-1-indolyl group, 4-methyl-1-indolyl group,
2-methyl-3-indolyl group, 4-methyl-3-indolyl group,
2-t-butyl-1-indolyl group, 4-t-butyl-1-indolyl group,
2-t-butyl-3-indolyl group and 4-t-butyl-3-indolyl group.
[0036] The substituted and unsubstituted alkoxycarbonyl groups are
represented by --COOY.sup.2. Examples of the group represented by
Y.sup.2 include methyl group, ethyl group, propyl group, isopropyl
group, n-butyl group, s-butyl group, isobutyl group, t-butyl group,
n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group,
hydroxymethyl group, 1-hydroxyethyl group, 2-hydroxyethyl group,
2-hydroxyisobutyl group, 1,2-dihydroxyethyl group,
1,3-dihydroxyisopropyl group, 2,3-dihydroxy-t-butyl group,
1,2,3-trihydroxypropyl group, chloromethyl group, 1-chloroethyl
group, 2-chloroethyl group, 2-chloroisobutyl group,
1,2-dichloroethyl group, 1,3-dichloroisopropyl group,
2,3-dichloro-t-butyl group, 1,2,3-trichloropropyl group,
bromomethyl group, 1-bromoethyl group, 2-bromoethyl group,
2-bromoisobutyl group, 1,2-dibromoethyl group, 1,3-dibromoisopropyl
group, 2,3-dibromo-t-butyl group, 1,2,3-tribromopropyl group,
iodomethyl group, 1-iodoethyl group, 2-iodoethyl group,
2-iodoisobutyl group, 1,2-diiodoethyl group, 1,3-diiodoisopropyl
group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropyl group,
aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,
2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropyl
group, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,
cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,
2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropyl
group, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,
nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,
2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropyl
group, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl
group.
[0037] It is preferable that the electron transporting compound
used in the organic EL device of the present invention is a
heterocyclic compound having a nitrogen atom or a complex having a
nitrogen atom and more preferably a complex having a nitrogen atom.
The heterocyclic compound having a nitrogen atom and the complex
having a nitrogen atom are preferable since these compounds have
electron affinities as great as 2.7 eV or greater and mobilities of
electrons as great as 1.times.10.sup.-6 cm.sup.2/VS or greater.
[0038] Examples of the heterocyclic compound having a nitrogen atom
include oxadiazole derivatives such as
2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole and
bis[2-(4-tert-butyl-phenyl)-1,3,4-oxadiazole]-m-phenylene, triazole
derivatives and quinoxalinequinoline derivatives.
[0039] It is preferable that the complex having a nitrogen atom is
represented by the following general formula (3):
M-A.sub.mB.sub.n (3)
[0040] wherein M represents a monovalent to trivalent metal, A
represents a ligand having a nitrogen atom, B represents a ligand
having no nitrogen atoms, m represents an integer of 1 to 4, n
represents an integer of 0 to 2 and integers represented by m and n
satisfy m+n.ltoreq.4.
[0041] Examples of the metal represented by M include Li, Na, Cs,
Be, Mg, Ca, Ba, Zn, Cd, Al, Ga, In and Yb. Among these metals, Al,
Be and Ga are preferable.
[0042] Examples of the ligand represented by A include ligands
based on quinolinol and ligands based on benzoquinolinol.
[0043] Examples of the complex having a nitrogen atom include
complexes represented by the following general formulae (i) to
(iii):
M+A or M+A' (M+representing a monovalent metal ion) (i)
M.sup.2+A.sub.2, M.sup.2+AA' or M.sup.2+A'.sub.2 (M.sup.2+
representing a divalent metal ion) (ii)
M.sup.3+A.sub.3, M.sup.3+A.sub.2A', M.sup.3+AA'.sub.2 or
M.sup.3+A'.sub.3 (M.sup.3+ representing a trivalent metal ion)
(ii)
[0044] Examples of the ligands represented by A and A' include
ligands represented by the following general formula (iv). The
ligands represented by A and A' may the same with or different from
each other. Substituents in the ligands represented by A and A' may
be the same with or different from each other. Examples of the
substituent include alkyl groups, alkoxyl groups, aryloxyl groups
and aryl groups.
##STR00008##
[0045] In the above general formula (iv), A.sup.1 and A.sup.2 each
independently represent a substituted or unsubstituted aromatic
cyclic structure and may represent the same structure or different
structures.
[0046] Further examples of the ligands represented by A and A'
include ligands represented by the following general formulae:
##STR00009##
[0047] In the above formulae, D represents an atom selected from
Si, Ge and Sn and Ar.sup.21 to Ar.sup.25 each independently
represent an aromatic hydrocarbon group or an aromatic heterocyclic
group which may have substituents.
[0048] Further examples of the ligands represented by A and A'
include benzoazoles such as derivatives of benzimidazole,
benzothiazole and benzoxazole.
[0049] Among the above ligands having a nitrogen atom which are
represented by A and A', ligands represented by the following
general formula (4) are preferable:
##STR00010##
wherein R.sup.2 to R.sup.7 each independently represent hydrogen
atom, a halogen atom, hydroxyl group, a substituted or
unsubstituted amino group, nitro group, cyano group, a substituted
or unsubstituted alkyl group having 1 to 30 carbon atoms, a
substituted or unsubstituted alkenyl group having 2 to 30 carbon
atoms, a substituted or unsubstituted cycloalkyl group having 5 to
30 carbon atoms, a substituted or unsubstituted alkoxyl group
having 1 to 30 carbon atoms, a substituted or unsubstituted
aromatic hydrocarbon group having 6 to 40 carbon atoms, a
substituted or unsubstituted aromatic heterocyclic group having 3
to 40 carbon atoms, a substituted or unsubstituted aralkyl group
having 7 to 40 carbon atoms, a substituted or unsubstituted
aryloxyl group having 6 to 40 carbon atoms, a substituted or
unsubstituted alkoxycarbonyl group having 2 to 40 carbon atoms or
carboxyl group and two groups selected from the groups represented
by R.sup.2 to R.sup.7 may form a ring.
[0050] Examples of the complex having ligands having a nitrogen
atom as the complex having a nitrogen atom include complexes having
ligands having a nitrogen atom which are derived from 8-quinolinol
or derivative thereof such as tris(8-quinolinolato)aluminum,
bis(8-quinolinolato)magnesium, bis-(benzo(f)-8-quinolinolato)zinc,
bis(2-methyl-8-quinolinolato)aluminum oxide,
tris(8-quinolinolato)indium,
tris(5-methyl-8-quinolinolato)aluminum, 8-quinolinolatolithium,
tris(5-methyl-8-quinolinolato)gallium,
bis(5-chloro-8-quinolinolato)calcium,
5,7-dichloro-8-8-quinilinolatoaluminum,
tris(5,7-dibromo-8-hydroxyquinolinolato)aluminum and
poly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane].
[0051] Examples of the complex having a ligand having a nitrogen
atom and a ligand having no nitrogen atoms include
bis(2-methyl-8-quinolinolato)(phenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(ortho-cresolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(metacresolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(para-cresolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,3-dimethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,6-dimethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(3,4-dimethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,6-diphenylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,4,6-triphenylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,3,6-trimethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2,3,5,6-tetramethylphenolato)aluminum(III),
bis(2-methyl-8-quinolinolato)(1-naphtholato)aluminum(III),
bis(2-methyl-8-quinolinolato)(2-naphtholato)aluminum(III),
bis(2,4-dimethyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III),
bis(2,4-dimethyl-8-quinolinolato)(para-phenylphenolato)aluminum
bis(2,4-dimethyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),
bis(2,4-dimethyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),
bis(2,4-dimethyl-8-quinolinolato)(3,5-di-tent-butylphenolato)aluminum(III-
),
bis(2-methyl-4-ethyl-8-quinolinolato)(para-cresolato)aluminum(III),
bis(2-methyl-4-methoxy-8-quinolinolato)(para-phenylphenolato)aluminum(III-
),
bis(2-methyl-5-cyano-8-quinolinolato)(ortho-cresolato)aluminum(III),
bis(2-methyl-6-trifluoromethyl-8-quinolinolato)(2-naphtholato)aluminum(II-
I),
bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8-qui-
nolinolato)-aluminum(III),
bis(2,4-dimethyl-8-quinolinolato)-aluminum(III)-.mu.-oxo-bis(2,4-dimethyl-
-8-quinolinolato)aluminum(III),
bis(4-ethyl-2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(4-ethyl-2-
-methyl-8-quinolinolato)-aluminum(III),
bis(2-methyl-4-mothoxyquinolinolato)-aluminum(III)-.mu.-oxo-bis(2-methyl--
4-methoxyquinolinolato)aluminum(III),
bis(5-cyano-2-methyl-8-quinolinolato)aluminum
(5-cyano-2-methyl-8-quinolinolato)aluminum(III) and
bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis-
(2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum(III).
[0052] The electron transporting compound used in the organic EL
device of the present invention may be an anthracene derivative
represented by the following general formula (5):
A.sup.1-L-A.sup.2 (5)
[0053] wherein A.sup.1 and A.sup.2 each independently represent a
substituted or unsubstituted monophenylanthryl group or a
substituted or unsubstituted diphenylanthryl group and may
represent the same group or different groups and L represents a
single bond or a divalent bonding group; or by the following
general formula (6):
A.sup.3-An-A.sup.4 (6)
[0054] wherein An represents a substituted or unsubstituted
anthracene residue group and A.sup.3 and A.sup.4 each independently
represent a substituted or unsubstituted monovalent condensed
aromatic cyclic group having 10 to 40 carbon atoms or a substituted
or unsubstituted aryl group having no condensed cyclic structures
and having 12 to 40 carbon atoms and may represent the same group
or different groups.
[0055] Examples of the substituent in general formulae (5) and (6)
include alkyl groups having 1 to 6 carbon atoms, cycloalkyl groups
having 3 to 6 carbon atoms, alkoxyl groups having 1 to 6 carbon
atoms, aryloxyl groups having 5 to 18 carbon atoms, aralkyloxyl
groups having 7 to 18 carbon atoms, amino groups substituted with
aryl groups having 5 to 16 carbon atoms, nitro group, cyano group,
ester groups having 1 to 6 carbon atoms, halogen atoms and alkenyl
groups.
[0056] Examples of the alkyl group having 1 to 6 carbon atoms
include methyl group, ethyl group, propyl group, isopropyl group,
butyl group, isobutyl group, sec-butyl group, tert-butyl group,
various types of pentyl groups and various types of hexyl
groups.
[0057] Examples of the cycloalkyl group having 3 to 6 carbon atoms
include cyclopropyl group, cyclobutyl group, cyclopentyl group and
cyclohexyl group.
[0058] Examples of the alkoxyl group having 1 to 6 carbon atoms
include methoxyl group, ethoxyl group, propoxyl group, isopropoxyl
group, butoxyl group, isobutoxyl group, sec-butoxyl group,
tert-butoxyl group, various types of pentyloxyl groups and various
types of hexyloxyl groups.
[0059] Examples of the aryloxyl group having 5 to 18 carbon atoms
include phenoxyl group, tolyloxyl group and naphthyloxyl group.
[0060] Examples of the aralkyloxyl group having 7 to 18 carbon
atoms include benzyloxyl group, phenetyloxyl group and
naphthylmethoxyl group.
[0061] Examples of the amino group substituted with an aryl group
having 5 to 16 carbon atoms include diphenylamino group,
ditolylamino group, dinaphthylamino group and naphthylphenylamino
group.
[0062] Examples of the ester group having 1 to 6 carbon atoms
include methoxycarbonyl group, ethoxycarbonyl group,
propoxycarbonyl group and isopropoxycarbonyl group.
[0063] Examples of the halogen atom include fluorine atom, chlorine
atom and bromine atom.
[0064] Examples of the aryl group include styrylphenyl group,
styrylbiphenyl group and styrylnaphthyl group.
[0065] Preferable examples of the anthracene derivative represented
by general formula (5) include anthracene derivatives represented
by general formula (5-a):
##STR00011##
wherein R.sup.71 to R.sup.76 each independently represent an alkyl
group, a cycloalkyl group, an alkenyl group, a substituted or
unsubstituted aryl group, an alkoxyl group, an aryloxyl group, an
alkylamino group, an arylamino group or a substituted or
unsubstituted heterocyclic group; a and b each represent an integer
of 0 to 5; c, d, e and f each represent an integer of 0 to 4; when
any of a to f represents an integer of 2 or greater, a plurality of
groups represented by the corresponding R.sup.71, R.sup.72,
R.sup.73, R.sup.74, R.sup.75 or R.sup.76 may be the same with or
different from each other and may form a ring by forming a bond
between each other; and L.sup.1 represents a single bond, --O--,
--S--, --N(R)-- or an arylene group, R representing an alkyl group
or a substituted or unsubstituted aryl group; and anthracene
derivatives represented by general formula (5-b):
##STR00012##
wherein R.sup.77 to R.sup.84 each independently represent an alkyl
group, a cycloalkyl group, an alkenyl group, a substituted or
unsubstituted aryl group, an alkoxyl group, an aryloxyl group, an
alkylamino group, an arylamino group or a substituted or
unsubstituted heterocyclic group; g and h each represent an integer
of 0 to 4; i, j, k and l each represent an integer of 0 to 5; p and
q each represent an integer of 0 to 3; when any of g to l
represents an integer of 2 or greater, a plurality of groups
represented by corresponding R.sup.77, R.sup.78, R.sup.79,
R.sup.80, R.sup.81 or R.sup.82 may be the same with or different
from each other and may form a ring by forming a bond between each
other; and L.sup.2 represents a single bond, --O--, --S--, --N(R)--
or an arylene group, R representing an alkyl group or a substituted
or unsubstituted aryl group.
[0066] In the above general formulae (5-a) and (5-b), preferable
examples of the groups represented by R.sup.71 to R.sup.84 include
alkyl groups having 1 to 6 carbon atoms, cycloalkyl groups having 3
to 6 carbon atoms, aryl groups having 5 to 18 carbon atoms, alkoxyl
groups having 1 to 6 carbon atoms, aryloxy groups having 5 to 18
carbon atoms, amino groups substituted with an aryl group having 5
to 16 carbon atoms and heterocyclic groups such as triazole group,
oxadiazole group, quinoxaline group, furanyl group and thienyl
group.
[0067] In the group represented by --N(R)-- which is represented by
L.sup.1 or L.sup.2, preferable examples of the group represented by
R include alkyl groups having 1 to 6 carbon atoms and aryl groups
having 5 to 18 carbon atoms.
[0068] Preferable examples of the anthracene derivative represented
by general formula (6) include anthracene derivatives represented
by general formula (6-a):
A.sup.3'-An-A.sup.4' (6-a)
[0069] wherein An represents a substituted or unsubstituted
divalent anthracene residue group and A.sup.3' and A.sup.4' each
independently represent a monovalent residue group derived from
biphenyl, fluoranthene, naphthalene, phenanthrene, anthracene,
pyrene, perylene, coronene, chrysene, picene, fluorene, terphenyl,
diphenylanthracene, biphenyl, an N-alkylcarbazole, an
N-arylcarbazole, triphenylene, rubicene, benzoanthracene or
dibenzo-anthracene, which may be substituted or unsubstituted; or a
group represented by general formula (6-b):
##STR00013##
wherein B.sup.1 and B.sup.2 each represent a substituted or
unsubstituted phenyl group, naphthyl group, biphenyl group,
terphenyl group or anthryl group.
[0070] Examples of the substituent in the groups represented by An,
A.sup.3' and A.sup.4' include the groups described as the examples
of the substituents in general formulae (5) and (6).
[0071] In the present invention, the anthracene derivative may be
used singly or in combination of two or more.
[0072] The electron transporting compound used in the organic EL
device of the present invention may be a cyclic derivative having
Si such as silacyclopentadiene derivatives.
[0073] In the organic EL device of the present invention, it is
preferable that the thickness of the layer of the organic light
emitting medium is in the range of 5 to 200 nm and more preferably
in the range of 10 to 100 nm since the voltage applied to the
device can be remarkably decreased.
[0074] By using the combination of component (A) and component (B)
for the layer of the organic light emitting medium, crystallization
in the layer of the organic light emitting medium is suppressed and
the layer of the organic light emitting medium becomes more
amorphous. Therefore, stability is enhanced and heat resistance is
improved. As the compound of component (B), compounds having a
glass transition temperature of 110.degree. C. or higher are
preferable. By mixing the compound having a glass transition
temperature of 110.degree. C. or higher, the glass transition
temperature of the layer of the organic light emitting medium can
be raised to 110.degree. C. or higher and a heat resistance in
storage of 500 hours or longer at 85.degree. C. can be
obtained.
[0075] The chromaticity and the peak wavelength in the spectrum of
the emitted light can be controlled by adjusting the relative
amounts of component (A) and component (B). By increasing the
relative amount of component (A), the peak wavelength in the
spectrum of the emitted light shifts to longer wavelengths and the
x-coordinate of the chromaticity coordinates increases. This
phenomenon takes place because the peak wavelength in the spectrum
of emitted light due to component (A) is in the region of longer
wave lengths.
[0076] It is preferable that component (A) and component (B) are
mixed in amounts such that the ratio of the amount by weight of
component (A) to the amount by weight of component (B) is in the
range of 8:92 to 92:8. When the amount of component (A) is less
than 8% by weight, it becomes difficult that holes are transported
to the area of recombination through the lowest occupied orbital of
the hole transporting compound. This phenomenon can be found from
the increase in the voltage applied to the device when the amount
of component (A) is less than 8%. When the amount of component (A)
exceeds 92% by weight, it becomes difficult that electrons are
transported to the area of recombination through the lowest
unoccupied orbital of the electron transporting compound. It is
preferable that the ratio of the amount by weight of component (A)
to the amount by weight of component (B) is in the range of 15:60
to 85:40 since the device has a longer life.
[0077] In the organic EL device of the present invention, it is
preferable that the mixed layer in the layer of the organic light
emitting medium further comprises (C) a fluorescent compound since
heat resistance and the efficiency of light emission are further
improved. It is preferable that the mixed layer of the organic
light emitting medium comprises components (A), (B) and (C) in
amounts such that a ratio of a total amount by weight of component
(A) and component (B) to an amount by weight of component (C) is in
the range of 100:1 to 10:1.
[0078] In the organic EL device of the present invention, it is
preferable that various intermediate layers are disposed between
the electrodes and the layer of the organic light emitting medium.
Examples of the intermediate layer include a hole injecting layer,
a hole transporting layer, an electron injecting layer and an
electron transporting layer. It is known that various organic and
inorganic compounds can be used for these layers.
[0079] Typical examples of the construction of the organic EL
device include: [0080] An anode/a layer of an organic light
emitting medium/a cathode; [0081] An anode/a hole injecting layer/a
layer of an organic light emitting medium/a cathode; [0082] An
anode/a layer of an organic light emitting medium/an electron
injecting layer/a cathode; [0083] An anode/a hole injecting layer/a
layer of an organic light emitting medium/an electron injecting
layer/a cathode; [0084] An anode/an organic semiconductor layer/a
layer of an organic light emitting medium/a cathode; [0085] An
anode/an organic semiconductor layer/an electron barrier layer/a
layer of an organic light emitting medium/a cathode; [0086] An
anode/an organic semiconductor layer/a layer of an organic light
emitting medium/an adhesion improving layer/a cathode; and [0087]
An anode/a hole injecting layer/a hole transporting layer/a layer
of an organic light emitting medium/an electron injecting layer/a
cathode.
[0088] However, the construction of the organic EL device is not
limited to the above examples.
[0089] In general, the organic EL device is prepared on a substrate
which transmits light. The substrate which transmits light is the
substrate which supports the organic EL device. It is preferable
that the substrate which transmits light has a transmittance of
light of 50% or greater and more preferably 80% or greater in the
visible region of 400 to 700 nm. It is also preferable that a flat
and smooth substrate is used.
[0090] As the substrate which transmits light, for example, glass
plates and synthetic resin plates are advantageously used. Specific
examples of the glass plates include plates made of soda ash glass,
glass containing barium and strontium, lead glass, aluminosilicate
glass, borosilicate glass, barium borosilicate glass and quartz.
Specific examples of the synthetic resin plates include plates made
of polycarbonate resins, acrylic resins, polyethylene terephthalate
resins, polyether sulfide resins and polysulfone resins.
[0091] As the anode, an electrode made of a material such as a
metal, an alloy, a conductive compound and a mixture of these
materials which has a great work function (4 eV or more) is
preferably used. Specific examples of the material for the anode
include metals such as Au and conductive materials such as CuI, ITO
(indium tin oxide), SnO.sub.2, ZnO and In--Zn--O. The anode can be
prepared by forming a thin film of the electrode material described
above in accordance with a process such as the vapor deposition
process and the sputtering process. When the light emitted from the
light emitting layer is obtained through the anode, it is
preferable that the anode has a transmittance of the emitted light
greater than 10%. It is also preferable that the sheet resistivity
of the anode is several hundred .OMEGA./.quadrature. or smaller.
The thickness of the anode is, in general, selected in the range of
10 nm to 1 .mu.m and preferably in the range of 10 to 200 nm
although the preferable range may be different depending on the
used material.
[0092] As the cathode, an electrode made of a material such as a
metal, an alloy, a conductive compound and a mixture of these
materials which has a small work function (4 eV or smaller) is
used. Specific examples of the material for the cathode include
sodium, sodium-potassium alloys, magnesium, lithium,
magnesium-silver alloys, aluminum/aluminum oxide, Al/Li.sub.2O,
Al/LiO.sub.2, Al/LiF, aluminum-lithium alloys, indium and rare
earth metals. The cathode can be prepared by forming a thin film of
the material described above in accordance with a process such as
the vapor deposition process and the sputtering process. When the
light emitted from the layer of the organic light emitting medium
is obtained through the cathode, it is preferable that the cathode
has a transmittance of the emitted light greater than 10%. It is
also preferable that the sheet resistivity of the cathode is
several hundred .OMEGA./.quadrature. or smaller. The thickness of
the cathode is, in general, selected in the range of 10 nm to 1
.mu.m and preferably in the range of 50 to 200 nm although the
preferable range may be different depending on the used
material.
[0093] In the organic EL device of the present invention, it is
preferable that a layer of a chalcogenide, a metal halide or a
metal oxide (this layer may occasionally be referred to as a
surface layer) is disposed on the surface of at least one of the
pair of electrodes prepared as described above. Specifically, it is
preferable that a layer of a chalcogenide (including an oxide) of a
metal such as silicon and aluminum is disposed on the surface of
the anode at the side of the layer of the organic light emitting
medium and a layer of a metal halide or a metal oxide is disposed
on the surface of the cathode at the side of the layer of the
organic light emitting medium. Due to the above layers, holes or
electrons are more easily injected into the light emitting medium
and the device can be driven at a lower voltage.
[0094] Preferable examples of the chalcogenide include SiO.sub.x
(1.ltoreq.x.ltoreq.2), AlO.sub.x (1.ltoreq.x.ltoreq.1.5), SiON and
SiAlON. Preferable examples of the metal halide include LiF,
MgF.sub.2, CaF.sub.2 and fluorides of rare earth metals. Preferable
examples of the metal oxide include Cs.sub.2O, Li.sub.2O, MgO, SrO,
BaO and CaO.
[0095] In the organic EL device of the present invention, the
electron transporting property and the hole transporting property
of the layer of the organic light emitting medium are
simultaneously improved by suitably adjusting the relative amounts
of component (A) and component (B) described above and the above
intermediate layers such as the hole injecting layer, the hole
transporting layer and the electron injecting layer can be omitted.
In this case, it is preferable that the surface layer described
above is disposed.
[0096] In the organic EL device of the present invention, it is
preferable that a mixed region of an electron transfer compound and
a reducing dopant or a mixed region of a hole transfer compound and
an oxidizing dopant is disposed on the surface of at least one of
the pair of electrodes prepared as described above. Due to the
mixed region disposed on the surface of the pair of electrodes, the
electron transfer compound is reduced to form an anion. Injection
and transportation of electrons from the mixed region into the
light emitting medium can be facilitated and the device can be
driven at a lower voltage. The hole transfer compound is oxidized
to form a cation and injection and transportation of holes from the
mixed region into the light emitting medium is facilitated.
Preferable examples of the oxidizing dopant include various types
of Lewis acid and acceptor compounds. Preferable examples of the
reducing dopant include alkali metals, compounds of alkali metals,
alkaline earth metals, rare earth metals and compounds of these
metals.
[0097] In the organic EL device of the present invention, the layer
of the organic light emitting medium has the following
functions:
(1) The injecting function: the function of injecting holes from
the anode or the hole injecting layer and injecting electrons from
the cathode or the electron injecting layer when an electric field
is applied; (2) The transporting function: the function of
transporting injected charges (electrons and holes) by the force of
the electric field; and (3) The light emitting function: the
function of providing the field for recombination of electrons and
holes and leading the recombination to the emission of light.
[0098] In the organic EL device of the present invention, it is
preferable that the work function WF of the anode which injects
holes into the layer of the organic light emitting medium and the
ionization energy of the hole transporting compound IP1 satisfy a
relation: IP1-WF.ltoreq.0.2 eV. When the above relation is
satisfied, hole injection from the anode into the light emitting
medium is increased and the hole injection layer can be omitted.
Therefore, the device can be simplified and the production cost of
the device can be reduced.
[0099] As the process for forming the layer of the organic light
emitting medium, a conventional process such as the vapor
deposition process, the spin coating process and the
Langmuir-Blodgett process (the LB process) can be used. It is
particularly preferable that the layer of the organic light
emitting medium is a molecular deposit film. The molecular deposit
film is a thin film formed by deposition of a material compound in
the gas phase or a thin film formed by solidification of a material
compound in a solution or in the liquid phase. In general, the
molecular deposit film can be distinguished from the thin film
formed in accordance with the LB process (the molecular
accumulation film) based on the differences in the aggregation
structure and higher order structures and functional differences
caused by these structural differences.
[0100] As disclosed in Japanese Patent Application Laid-Open No.
Showa 67 (1982)-51781, the layer of the organic light emitting
medium can also be formed by dissolving a binder such as a resin
and the material compounds into a solvent to prepare a solution,
followed by forming a thin film from the prepared solution in
accordance with the spin coating process or the like.
[0101] In the present invention, where desired, conventional light
emitting media other than component (A), component (B) and
component (C) described above may be comprised in the layer of the
organic light emitting medium or a layer of an organic light
emitting medium comprising other conventional light emitting media
may be laminated to the layer of the organic light emitting medium
comprising the compounds described in the present invention as long
as the object of the present invention is not adversely
affected.
[0102] The hole injecting layer and the hole transporting layer are
layers which help injection of holes into the layer of the organic
light emitting medium and transport the holes to the light emitting
region. The layers exhibit a great mobility of holes and, in
general, have an ionization energy as small as 5.5 eV or smaller.
For the hole injecting layer and the hole transporting layer, a
material which transports holes to the layer of the organic light
emitting medium at a small electric field strength is preferable. A
material which exhibits, for example, a mobility of holes of at
least 10.sup.-6 cm.sup.2/Vsec under application of an electric
field of 10.sup.4 to 10.sup.6 V/cm is more preferable. A material
can be selected from materials which are conventionally used as the
charge transporting material of holes in photoconductive materials
and conventional materials which are used for the hole injecting
layer in organic EL devices.
[0103] To form the hole injecting layer or the hole transporting
layer, a thin film may be formed from a material substance for the
hole injecting layer or the hole transporting layer, respectively,
in accordance with a conventional process such as the vacuum vapor
deposition process, the spin coating process, the casting process
and the LB process. The thickness of the hole injecting layer and
the hole transporting layer is not particularly limited. In
general, the thickness is 5 nm to 5 .mu.m.
[0104] The electron injection layer is a layer which helps
injection of electrons into the layer of the organic light emitting
medium and exhibits a great mobility of electrons. The adhesion
improving layer is a layer made of a material exhibiting excellent
adhesion with the cathode in the electron injecting layer. As the
material for the electron injecting layer, metal complexes of
8-hydroxyquinoline and derivatives thereof are preferably used.
Specific examples of the metal complex of 8-hydroxyquinoline and
derivatives thereof include metal chelates of oxinoid compounds
including chelates of oxine (in general, 8-quinolinol or
8-hydroxyquinoline). For example, tris(8-quinolinol)aluminum can be
used as the electron injecting material.
[0105] To prepare the organic EL device of the present invention,
for example, the anode, the layer of the organic light emitting
medium and, where necessary, the hole injecting layer and the
electron injecting layer are formed in accordance with the above
process using the above materials and the cathode is formed in the
last step. The organic EL device may be prepared by forming the
above layers in the order reverse to that described above, i.e.,
the cathode being formed in the first step and the anode in the
last step.
[0106] An embodiment of the process for preparing an organic EL
device having a construction in which an anode, a hole injecting
layer, a layer of the organic light emitting medium, an electron
injecting layer and a cathode are disposed successively on a
substrate which transmits light will be described in the
following.
[0107] On a suitable substrate which transmits light, a thin film
made of a material for the anode is formed in accordance with the
vapor deposition process or the sputtering process so that the
thickness of the formed thin film is 1 .mu.m, or smaller and
preferably in the range of 10 to 200 nm. The formed thin film is
used as the anode. Then, a hole injecting layer is formed on the
anode. The hole injecting layer can be formed in accordance with
the vacuum vapor deposition process, the spin coating process, the
casting process or the LB process, as described above. The vacuum
vapor deposition process is preferable because a uniform film can
be easily obtained and the possibility of formation of pin holes is
small. When the hole injecting layer is formed in accordance with
the vacuum vapor deposition process, in general, it is preferable
that the conditions are suitably selected in the following ranges:
the temperature of the source of the deposition: 50 to 450.degree.
C.; the vacuum: 10.sup.-7 to 10.sup.-3 Torr; the rate of
deposition: 0.01 to 50 nm/second; the temperature of the substrate:
-50 to 300.degree. C. and the thickness of the film: 5 nm to 5
.mu.m; although the conditions of the vacuum vapor deposition are
different depending on the used compound (the material for the hole
injecting layer) and the crystal structure and the recombination
structure of the hole injecting layer to be formed.
[0108] Then, the layer of the organic light emitting medium is
formed on the hole injecting layer formed above. Using the organic
light emitting medium described in the present invention, a thin
film of the organic light emitting medium can be formed in
accordance with the vacuum vapor deposition process, the sputtering
process, the spin coating process or the casting process and the
formed thin film is used as the layer of the organic light emitting
medium. The vacuum vapor deposition process is preferable because a
uniform film can be easily obtained and the possibility of
formation of pin holes is small. When the layer of the organic
light emitting medium is formed in accordance with the vacuum vapor
deposition process, in general, the conditions of the vacuum vapor
deposition process can be selected in the same ranges as those
described for the vacuum vapor deposition of the hole injecting
layer although the conditions are different depending on the used
compound. It is preferable that the thickness is in the range of 10
to 40 nm.
[0109] An electron injecting layer is formed on the layer of the
organic light emitting medium formed above. Similarly to the hole
injecting layer and the layer of the organic light emitting medium,
it is preferable that the electron injecting layer is formed in
accordance with the vacuum vapor deposition process since a uniform
film must be obtained. The conditions of the vacuum vapor
deposition can be selected in the same ranges as those described
for the vacuum vapor deposition of the hole injecting layer and the
layer of the organic light emitting medium.
[0110] A cathode is formed on the electron injecting layer formed
above in the last step and an organic EL device can be obtained.
The cathode is made of a metal and can be formed in accordance with
the vacuum vapor deposition process or the sputtering process. It
is preferable that the vacuum vapor deposition process is used in
order to prevent formation of damages on the lower organic layers
during the formation of the film.
[0111] In the above preparation of the organic EL device, it is
preferable that the above layers from the anode to the cathode are
formed successively while the preparation system is kept in a
vacuum after being evacuated.
[0112] The organic EL device which can be prepared as described
above emits light when a direct voltage of 3 to 40 V is applied in
the condition that the anode is connected to a positive electrode
(+) and the cathode is connected to a negative electrode (-). When
the connection is reversed, no electric current is observed and no
light is emitted at all. When an alternating voltage is applied to
the organic EL device, light emission is observed only in the
condition that the polarity of the anode is positive and the
polarity of the cathode is negative. When an alternating voltage is
applied to the organic EL device, any type of wave shape can be
used.
[0113] The present invention will be described more specifically
with reference to examples in the following. However, the present
invention is not limited to the examples.
Example 1
The Ratio of Amounts by Weight: 40:20
[0114] On a glass plate having a size of 25.times.75.times.1.1 mm,
a transparent electrode made of indium tin oxide and having a
thickness of 120 nm was formed. After the glass substrate was
cleaned by irradiation with ultraviolet light and exposure to
ozone, the glass substrate was placed in a vacuum vapor deposition
apparatus.
[0115] In the first step, TPD106 expressed by the following
formula:
##STR00014##
was vapor deposited so that a layer having a thickness of 60 nm was
formed. Then, TPD78 expressed by the following formula:
##STR00015##
was vapor deposited on the formed layer so that a hole transporting
layer having a thickness of 20 nm was formed on the layer of
TPD106. Then, DC5 expressed by the following formula:
##STR00016##
as the hole transporting compound and Alq (an Al complex of
8-hydroxyquinoline) as the electron transporting compound were
simultaneously vapor deposited on the formed layers in amounts such
that the ratio of the amount by weight of DC5 to the amount by
weight of Alq was 67.7:32.3 and a layer of an organic light
emitting medium having a thickness of 40 nm was formed. Then, Alq
was vapor deposited so that a layer having a thickness of 20 nm was
formed on the layer formed above as the electron injecting
layer.
[0116] The energy gap of DC5 (Eg1) is 2.57 eV and smaller than the
energy gap (Eg2) of Alq which is 2.7 eV. The ionization energy of
DC5 (IP1) is 5.6 eV and smaller than the ionization energy (IP2) of
Alq which is 5.7 eV. The electron affinity of DC5 (Af1) is 3.0 eV
and the same as the electron affinity (Af2) of Alq which is 3.0
eV.
[0117] Then, LiF which was an alkali metal halide was vapor
deposited so that a layer having a thickness of 0.3 nm was formed
on the above layers and aluminum was vapor deposited so that a
layer having a thickness of 100 nm was formed on the layer of LiF.
The layers of LiF and Al worked as the cathode. An organic EL
device was prepared as described above.
[0118] The prepared organic EL device was tested by passing an
electric current. Reddish orange light emission having a luminance
of 110 cd/m.sup.2 was obtained at a voltage of 4.5 V and a current
density of 2.46 mA/cm.sup.2. The chromaticity coordinates were
(0.6039, 0.3931) and the efficiency of light emission was 4.47
cd/A. The device was tested by continuously passing a current
constantly at an initial luminance of 500 cd/m.sup.2 and the
half-life time was found to be as long as 3,120 hours.
Example 2
[0119] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 44.4:55.6.
[0120] The prepared organic EL device was tested by passing an
electric current. Red light emission having a luminance of 109
cd/m.sup.2 was obtained at a voltage of 4.0 V and a current density
of 2.71 mA/cm.sup.2. The chromaticity coordinates were (0.5886,
0.4072) and the efficiency of light emission was 4.02 cd/A. The
device was tested by continuously passing a current constantly at
an initial luminance of 500 cd/m.sup.2 and the half-life time was
found to be as long as 3,760 hours.
Example 3
[0121] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 28.6:71.4.
[0122] The prepared organic EL device was tested by passing an
electric current. Red light emission having a luminance of 124
cd/m.sup.2 was obtained at a voltage of 4.0 V and a current density
of 2.96 mA/cm.sup.2. The chromaticity coordinates were (0.5741,
0.4228) and the efficiency of light emission was 4.19 cd/A. The
device was tested by continuously passing a current constantly at
an initial luminance of 500 cd/m.sup.2 and the half-life time was
found to be as long as 4,100 hours.
Example 4
[0123] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 12:88.
[0124] The prepared organic EL device was tested by passing an
electric current. Red light emission having a luminance of 135
cd/m.sup.2 was obtained at a voltage of 4.5 V and a current density
of 3.0 mA/cm.sup.2. The chromaticity coordinates were (0.5652,
0.4352) and the efficiency of light emission was 4.50 cd/A. The
device was tested by continuously passing a current constantly at
an initial luminance of 500 cd/m.sup.2 and the half-life time was
found to be as long as 2,900 hours.
Comparative Example 1
[0125] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 2.4:97.6.
[0126] The prepared organic EL device was tested by passing an
electric current. A current of 1.30 mA/cm.sup.2 was observed at a
voltage of 6 V. The applied voltage was higher than those for the
organic EL devices of Examples 1 to 4. The luminance was 173
cd/m.sup.2, the chromaticity coordinates were (0.5416, 0.4550) and
the efficiency of light emission was 8.78 cd/A. The purity of red
light was insufficient in comparison with those in Examples 1 to 4.
The device was tested by continuously passing a current constantly
at an initial luminance of 500 cd/m.sup.2 and the half-life time
was found to be 970 hours. The half-life was much shorter than
those in Examples 1 to 4.
Comparative Example 2
[0127] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 4.8:95.2.
[0128] Using the prepared organic EL device, the voltage showing
the same luminance as that of the device of Comparative Example 1
was measured and found to be 7.3 V. The voltage was higher than
that of the device of Comparative Example 1.
Comparative Example 3
[0129] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that DC5 and
Alq were used for forming the layer of an organic light emitting
medium in amounts such that the ratio of the amount by weight of
DC5 to the amount by weight of Alq was 9.1:90.9.
[0130] Using the prepared organic EL device, the voltage showing
the same luminance as that of the device of Comparative Example 1
was measured and found to be 7.1 V. The voltage was higher than
that of the device of Comparative Example 1.
[0131] It can be concluded from the results in Comparative Examples
2 and 3 that Alq worked as the trap for holes transported from DC5
and the applied voltage increased. In contrast, devices in which
DC5 was added in an amount exceeding 10% by weight showed a
remarkable decrease in the voltage. It can be concluded that the
voltage decreased since DC5 worked as a compound having the hole
transporting property and holes could be transported at a high
efficiency.
Comparative Example 4
[0132] An organic EL device was prepared in accordance with the
same procedures as those conducted in Example 1 except that TPD
(N,N'-bis(m-methylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine)
having an energy gap (Eg1) of 3.0 eV was used in place of DC5.
[0133] The prepared organic EL device was tested by passing an
electric current. Green light emission having a luminance of 56
cd/m.sup.2 was obtained at a voltage of 5.6 V and a current density
of 2.8 mA/cm.sup.2. The efficiency of light emission was 2.0 cd/A.
The device was tested by continuously passing a current constantly
at an initial luminance of 500 cd/m.sup.2 and the half-life time
was found to be as short as 130 hours. Therefore, the device in
Example 1 was superior to the device in Comparative Example 4 with
respect to both of the efficiency of light emission and the life.
Thus, it is shown that an organic EL device in the condition of
Eg1.gtoreq.Eg2 has a problem in practical applications.
INDUSTRIAL APPLICABILITY
[0134] As described in detail in the above, in accordance with the
present invention, the organic EL device having a longer life and
emitting light at a higher efficiency than those of conventional EL
devices can be obtained. The organic EL device of the present
invention can be advantageously used, for example, for displays of
information instruments.
* * * * *