U.S. patent application number 09/969758 was filed with the patent office on 2002-09-12 for organic electroluminescent device.
This patent application is currently assigned to Mitsubishi Chemical Corporation. Invention is credited to Fugono, Masayo, Sato, Hideki, Sato, Yoshiharu.
Application Number | 20020125818 09/969758 |
Document ID | / |
Family ID | 27344858 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020125818 |
Kind Code |
A1 |
Sato, Hideki ; et
al. |
September 12, 2002 |
Organic electroluminescent device
Abstract
An organic electroluminescent device is disclosed, comprising a
substrate having thereon a light-emitting layer sandwiched by an
anode and a cathode, wherein the light-emitting layer comprises at
least: (1) a host material having electron-transporting or
hole-transporting property, (2) Compound A capable of
phosphorescence emission at room temperature, and (3) Compound B
capable of phosphorescence emission or fluorescence emission at
room temperature and having the maximum light emission wavelength
longer than the maximum light emission wavelength of Compound A,
and the maximum light emission wavelength of said device is
attributable to said (3). The light emission attributable to (3) is
intensified by (2) to elevate the light emission efficiency and by
selecting a fluorescent compound as (3), the device can be
prevented from aging deterioration of the luminance.
Inventors: |
Sato, Hideki; (Kanagawa,
JP) ; Sato, Yoshiharu; (Kanagawa, JP) ;
Fugono, Masayo; (Kanagawa, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Mitsubishi Chemical
Corporation
Tokyo
JP
|
Family ID: |
27344858 |
Appl. No.: |
09/969758 |
Filed: |
October 4, 2001 |
Current U.S.
Class: |
313/504 ;
428/690 |
Current CPC
Class: |
H01L 51/009 20130101;
H01L 51/0052 20130101; H01L 51/0077 20130101; H01L 51/0059
20130101; H01L 51/0084 20130101; H01L 51/0071 20130101; H01L
51/0072 20130101; H01L 51/006 20130101; H01L 51/0085 20130101; H01L
51/0065 20130101; H01L 51/0081 20130101; H01L 51/5016 20130101;
H01L 51/0068 20130101; Y10S 428/917 20130101 |
Class at
Publication: |
313/504 ;
428/690 |
International
Class: |
H05B 033/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2000 |
JP |
2000-304655 |
Oct 4, 2000 |
JP |
2000-304656 |
Jun 21, 2001 |
JP |
2001-188392 |
Claims
What is claimed is:
1. An organic electroluminescent device comprising a substrate
having thereon a light-emitting layer sandwiched by an anode and a
cathode, wherein said light-emitting layer comprises at least: (1)
a host material having electron-transporting or hole-transporting
property, (2) Compound A capable of phosphorescence emission at
room temperature, and (3) Compound B capable of phosphorescence
emission or fluorescence emission at room temperature and having
the maximum light emission wavelength longer than the maximum light
emission wavelength of Compound A, and the maximum light emission
wavelength of said device is attributable to said (3).
2. The organic electroluminescent device as claimed in claim 1,
wherein Compound A is an organic metal complex containing a metal
selected from Groups 7 to 11 of the periodic table.
3. The organic electroluminescent device as claimed in claim 1,
wherein Compound B is an organic metal complex of presenting
phosphorescence emission at room temperature and containing a metal
selected from Groups 7 to 11 of the periodic table.
4. The organic electroluminescent device as claimed in claim 2 or
3, wherein the metal of Groups 7 to 11 of the periodic table is
selected from ruthenium, rhodium, palladium, silver, rhenium,
osmium, iridium, platinum and gold.
5. The organic electroluminescent device as claimed in claim 2 or
3, wherein the organic metal complex is a compound represented by
the following formula (IV): 42wherein the ring D represents an
aromatic hydrocarbon ring which may have a substituent or an
aromatic heterocyclic ring which may have a substituent, the ring E
represents a nitrogen-containing aromatic heterocyclic ring which
may have a substituent, a group on the ring D and a group on the
ring E may combine to form a ring condensed to these rings, M.sup.4
represents a metal selected from Groups 7 to 11 of the periodic
table, L.sup.2 represents an arbitrary bidentate ligand, m
represents a valence number of M.sup.4, and k represents an integer
satisfying 0.multidot.k<m.
6. The organic electroluminescent device as claimed in claim 2 or
3, wherein the organic metal complex is selected from the compounds
represented by the following formula (IV-1) or (IV-2): 43wherein
M.sup.5 and M.sup.6 each represents a metal selected from Groups 7
to 11 of the periodic table, m represents a valence number of said
metal, the rings D.sup.1 and D.sup.2 each represents an aromatic
hydrocarbon ring or aromatic heterocyclic ring which may have a
substituent, the rings E.sup.1 and E.sup.2 each represents a
nitrogen-containing aromatic heterocyclic ring which may have a
substituent, a substituent on the ring D.sup.1 and a substituent on
the ring E.sup.1 may combine to form a ring condensed to these
rings, or a substituent on the ring D.sup.2 and a substituent on
the ring E.sup.2 may combine to form a ring condensed to these
rings.
7. The organic electroluminescent device as claimed in claim 2 or
3, wherein the organic metal complex is selected from the compounds
represented by the following formula (V): 44wherein R.sup.81 to
R.sup.92 each represents a hydrogen atom, a halogen atom, an alkyl
group, an aralkyl group, an alkenyl group, a cyano group, an amino
group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an
alkoxy group, an alkylamino group, an aralkylamino group, a
haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent, each of the pairs R.sup.81 and R.sup.82,
R.sup.84 and R.sup.85, R.sup.87 and R.sup.88, and R.sup.90 and
R.sup.91 may combine with each other to form a ring, M.sup.7
represents a metal selected from Groups 7 to 11 of the periodic
table, X.sup.9 to X.sup.12 each represents carbon or nitrogen,
provided that when any one of X.sup.9 to X.sup.12 is a nitrogen
atom, R.sup.83, R.sup.86, R.sup.89 or R.sup.92 bonded to said
nitrogen atom is absent.
8. The organic electroluminescent device as claimed in claim 1,
which contains an iridium complex as Compound A and/or Compound
B.
9. The organic electroluminescent device as claimed in claim 1,
which contains at least one iridium complex and at least one
platinum complex, one as Compound A and the other as Compound
B.
10. The organic electroluminescent device as claimed in claim 1,
which contains one iridium complex as Compound A and one iridium
complex as Compound B.
11. The organic electroluminescent device as claimed in claim 1,
wherein the host material is a compound represented by the
following formula (I): 45wherein the carbazolyl group and the
phenylene group each may have an arbitrary substituent, and Z.sup.1
represents a direct bond or a divalent linking group.
12. The organic electroluminescent device as claimed in claim 10,
wherein the compound represented by formula (I) is represented by
the following formula (I-1): 46wherein R.sup.1 to R.sup.16 each
independently represents a hydrogen atom, a halogen atom, an alkyl
group, an aralkyl group, an alkenyl group, a cyano group, an amino
group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an
alkoxy group, an alkylamino group, an aralkylamino group, a
haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent, each of the adjacent substituents R.sup.1 and
R.sup.2, R.sup.3 and R.sup.4, R.sup.5 and R.sup.6, R.sup.7 and
R.sup.8, R.sup.9 and R.sup.10, R.sup.11 and R.sup.12, R.sup.13 and
R.sup.14, and R.sup.15 and R.sup.16 may combine to form a ring, and
Z.sup.1 represents a direct bond or a divalent linking group.
13. The organic electroluminescent device as claimed in claim 10,
wherein in formula (I), Z.sup.1 is a direct bond, an oxygen atom, a
sulfur atom, a linking group shown below: 47a divalent aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent, or any one of the following linking groups:
48any benzene ring moiety in the each structure may have an
arbitrary substituent, and Ar.sup.1 to Ar.sup.6 each represents an
aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent or a group represented by the
following formula (I-2): 49wherein the carbazolyl group and the
phenylene group each may have an arbitrary substituent.
14. The organic electroluminescent device as claimed in claim 12,
wherein the group represented by formula (1-2) is a group
represented by the following formula (1-3): 50wherein R.sup.17 to
R.sup.24 each independently represents a hydrogen atom, a halogen
atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano
group, an amino group which may have a substituent, an acyl group,
an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group, a
hydroxyl group, an aryloxy group, or an aromatic hydrocarbon ring
group or aromatic heterocyclic group which may have a substituent,
each of the pairs R.sup.17 and R.sup.18, R.sup.19 and R.sup.20,
R.sup.21 and R.sup.22, and R.sup.23 and R.sup.24 may combine with
each other to form a ring.
15. The organic electroluminescent device as claimed in claim 1,
wherein the host material is a compound represented by the
following formula (II): 51wherein M represents a metal selected
from Groups 1, 2, 3, 12 and 13 of the periodic table, n represents
a valence number of said metal, L represents an arbitrary
substituent, j represents a number of the substituent L and is 0 or
1, X.sup.2 represents a carbon atom or a nitrogen atom, the ring A
represents a nitrogen-containing heterocyclic ring and may have a
substituent, and the ring B represents an aromatic hydrocarbon ring
group or an aromatic heterocyclic group and may have a
substituent.
16. The organic electroluminescent device as claimed in claim 14,
wherein the compound represented by formula (IT) is represented by
any one of the following formulae (II-1), (II-2) and (II-3):
[Organic Metal Complex] 52wherein M.sup.1 is a mono-, di- or
trivalent metal, n, X.sup.2 and the rings A and B have the same
meanings as in formula (II); [Mixed Ligand Complex] 53wherein
M.sup.2 represents a trivalent metal, X.sup.2 and the rings A and B
have the same meanings as in formula (II), and L.sup.1 represents
the following formula (II-2a), (II-2b) or (II-2c): 54wherein
Ar.sup.11 to Ar.sup.15 each represents an aromatic hydrocarbon ring
group which may have a substituent or an aromatic heterocyclic
group which may have a substituent, and Z.sup.2 represents silicon
or germanium; [Binuclear Metal Complex] 55wherein M.sup.3 and
M.sup.3, each represents a trivalent metal, X.sup.2 and the rings A
and B have the same meanings as in formula (II), X.sup.2' and the
rings A' and B' have the same meanings as X.sup.2 and the rings A
and B, respectively.
17. The organic electroluminescent device as claimed 3in claim 1,
wherein a host material is a compound having a group represented by
the following formula (III): 56wherein R.sup.51 to R.sup.54 each
independently represents a hydrogen atom or an arbitrary
substituent, each of the pairs R.sup.51 and R.sup.52, and R.sup.53
and R.sup.54 may combine to form a ring, and X.sup.3 represents an
oxygen atom or a sulfur atom.
18. The organic electroluminescent device as claimed in claim 16,
wherein the compound having a group represented by formula (III)
has a molecular weight of approximately from 400 to 1,200.
19. The organic electroluminescent device as claimed in claim 16,
wherein the compound represented by formula (III) is represented by
the following formula (III-1) or (III-2): 57wherein R.sup.55 to
R.sup.62 each independently represents a hydrogen atom, a halogen
atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl
group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an .alpha.-haloalkyl group, a hydroxyl group, or
an aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent, each of the pairs R.sup.55 and
R.sup.56, R.sup.57 and R.sup.58, R.sup.59 and R.sup.60, and
R.sup.61 and R.sup.62 may combine with each other to form a ring,
X.sup.4 and X.sup.5 each independently represents an oxygen group
or a sulfur group, and Q.sup.1 represents a divalent linking group
comprising an aromatic hydrocarbon ring group or aromatic
heterocyclic group which may have a substituent; 58wherein R.sup.63
to R.sup.74 each independently represents a hydrogen atom, a
halogen atom, an alkyl group, an aralkyl group, an alkenyl group,
an allyl group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an .alpha.-haloalkyl group, a hydroxyl group, or
an aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent, each of the adjacent substituents
R.sup.63 and R.sup.64, R.sup.65 and R.sup.66, R.sup.67 and
R.sup.68, R.sup.69 and R.sup.70, R.sup.71 and R.sup.72, R.sup.73and
R.sup.74 may combine to form a ring, X.sup.6 to X.sup.8 each
independently represents an oxygen atom or a sulfur atom, and
Q.sup.2 represents a trivalent linking group comprising an aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent.
20. The organic electroluminescent device as claimed in claim 1,
wherein Compound B is a fluorescent compound of presenting green
light emission, yellow light emission or red light emission.
21. The organic electroluminescent device as claimed in claim 1,
which has a hole-blocking layer between said light-emitting layer
and a cathode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an organic
electroluminescent device. More specifically, the present invention
relates to a thin film-type device which emits light upon
application of an electric field to a light-emitting layer
comprising an organic compound.
BACKGROUND OF THE INVENTION
[0002] In conventional thin film-type electroluminescent (EL)
devices, an inorganic material group II-VI compound semiconductor
such as ZnS, CaS and SrS is generally doped with Mn or a rare earth
element (e.g., Eu, Ce, Tb, Sm) as a emission center. However, the
EL device fabricated from the above-described inorganic material
has problems such that:
[0003] 1) a.c. (alternating current) driving is necessary (from 50
to 1,000 Hz),
[0004] 2) the driving voltage is high (up to 200 V),
[0005] 3) full color emission is difficult (particularly blue)
and
[0006] 4) the peripheral driving circuit costs highly.
[0007] In recent years, however, for the purpose of improving the
above-described problems, studies have been made to develop an EL
device using an organic thin film. In order to elevate the light
emission efficiency, an organic electroluminescent device has been
developed, where the kind of electrode is optimized for the purpose
of improving the efficiency of carrier injection from an electrode
and a hole-transporting layer comprising an aromatic diamine and a
light-emitting layer comprising an aluminum complex of
8-hydroxyquinoline are provide (see, Appl. Phys. Lett., Vol. 51,
page 913 (1987)). By this technique, the light emission efficiency
is greatly improved as compared with conventional EL devices using
a single crystal such as anthracene. Furthermore, for example, an
aluminum complex of 8-hydroxyquinoline as a host material is doped
with a fluorescence dye for laser, such as coumarin (see, J. Appl.
Phys., Vol. 65, page 3610 (1989)), with an attempt to improve the
light emission efficiency, convert the light emission wavelength or
the like. The devices are coming to have practically usable
properties.
[0008] In addition to these electroluminescent devices using a
low-molecule-weight material, studies are being made to develop an
electroluminescent device using a polymer material such as
poly(p-phenylenevinylene),
poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenyle- nevinylene] or
poly(3-alkylthiophene) for the light-emitting layer material or to
develop a device using a low molecule light-emitting material and
an electron-transfer material by mixing these with a polymer such
as polyvinylcarbazole.
[0009] Also, use of not only fluorescence but also phosphorescence
is being studied with an attempt to elevate the light emission
efficiency. If phosphorescence is used, that is, light emission
from the triplet excitation state is utilized, an improvement of
about three times higher efficiency can be expected as compared
with conventional devices using fluorescence (singlet). For this
purpose, it has been proposed to form the light-emitting layer
using a coumarin derivative or a benzophenone derivative (see, The
51th Autumn Meeting. 1990; The Japan Society of Applied Physics,
28a-PB-7 (1990)). However, only an extremely low luminance could be
obtained. Thereafter, use of an europium complex is studied with an
attempt to utilize the triplet excitation state, however, high
light emission efficiency could not be attained either by this
use.
[0010] Recently, it has been reported that red light emission with
high efficiency can be attained by using a platinum complex (T-1)
shown below (see, Nature, Vol. 395, page 151 (1998)). Thereafter,
the efficiency in green light emission is further greatly improved
by doping an iridium complex (T-2) shown below to the
light-emitting layer (see, Appl. Phys. Lett., Vol. 75, page 4
(1999)). 1
[0011] For applying the organic electroluminescent device as a
display device such as flat panel display, further, as a light
source for fluorescent lamp or marker lamp, the light emission
efficiency of the device must be more improved.
[0012] The organic electroluminescent device using the
phosphorescence molecule (T-2) described in the above-described
publication emits light with relatively high efficiency, however,
the organic electroluminescent device using (T-1) is low in the
light emission efficiency as compared with devices using (T-2). The
main cause of this is presumed to reside in the relationship
between the host material in the light-emitting layer and the
phosphorescent substance.
[0013] The formation probability of triplet exciton is three times
higher than that of singlet exciton and therefore, if light
emission from the triplet exciton (namely, phosphorescence) is
used, the light emission efficiency is elevated. However, use of a
phosphorescent substance alone suffers from bad stability of film
and low mobility of electric charge (hole or electron) injected
from electrodes and accordingly, the light emission efficiency is
not elevated. On the other hand, use of a host material alone
cannot provide light emission from a triplet exciton and the
material uses its energy mostly for heat and is deactivated, as a
result, the light emission efficiency is not elevated. For
overcoming this problem, a method of forming a light-emitting layer
by dispersing a phosphorescent substance in a host material which
exhibits fluorescent property is employed.
[0014] According to this method, triplet excitons generated from
the host material are used as triplet excitons for the
phosphorescent substance to cause light emission therefrom.
However, this method involves energy transfer and unless the
excited triplet level in the host material is close to the excited
triplet level of the phosphorescent substance, the probability of
energy transfer decreases and the triplet excitons cannot
contribute to the light emission. In the case of the
above-described device using (T-1) and (T-2), the excited triplet
level of the host material used is considered close to the excited
triplet level of (T-2).
[0015] Under these circumstances, the present inventors have made
investigations on the method for, in an organic electroluminescent
device using a phosphorescent emission, attaining high-luminance
and high-efficiency light emission from a phosphorescent material
which by itself does not emit light with high efficiency.
[0016] In order to apply an organic electroluminescent device to a
display device such as flat panel display, the device must be
ensured with sufficiently high stability at the driving in addition
to the improvement of light emission efficiency. However, the
organic electroluminescent device using the phosphorescence
molecule (T-2) described in the above-described publication, which
ensures high-efficiency light emission, is insufficient in the
driving stability for practical use (see, Jpn. J. Appl. Phys., Vol.
38, page L1502 (1999)). Thus, a high-efficiency display device
cannot be realized.
[0017] This driving deterioration is presumed to arise mainly
because of deterioration of the light-emitting layer.
[0018] Electric charges injected from electrodes form electron-hole
pairs (excitons) at a certain probability. In general, the light
emission (phosphorescence) by triplet excitons has a longer
lifetime as compared with the light emission (fluorescence) by
singlet excitons but, on the contrary, the singlet exciton has
higher thermal stability than triplet exciton.
[0019] With increase of a current applied to a device, electric
charges injected to the light-emitting layer increase and
accompanying this, the amount of electric charges not participating
in the generation of excitons also increase. Also, the amount of
excitons which are generated but not contribute to the light
emission in the light-emitting layer and are thermally deactivated
increases and this causes elevation of the temperature of the
light-emitting layer.
[0020] At this time, the device is considered to deteriorate
because the triple exciton is inferior in the thermal stability as
compared with singlet exciton. This can be also verified from the
fact that the light emission efficiency of the organic
electroluminescent device using the phosphorescence molecule (T-2)
greatly decreases with the increase of injected current (see, Appl.
Phys. Lett., Vol. 75, page 4 (1999)).
[0021] As such, organic electroluminescent devices using a
phosphorescence molecule have a serious problem in the device
driving stability for the practical use at present.
[0022] For applying an organic electroluminescent device to a
display device such as flat panel display, polychromatic display
must be realized. In recent years, compact display devices such as
portable telephone, which are a promising use of the organic
electroluminescent device, are also required to have polychromatic
display.
[0023] For realizing polychromatic display such as multicolor
display and full color display by using an organic
electroluminescent device, the following methods have been
heretofore proposed:
[0024] 1) a method of providing light emission sub pixel for
desired colors such as red (R), green (G) and blue (B),
[0025] 2) a method of disposing a color filter on a white
light-emission layer and coloring the emitted light, and
[0026] 3) a method of disposing a fluorescence converting layer on
a blue light-emitting layer and converting the color of emitted
light.
[0027] Among these, the method 1) uses no layer of absorbing
emitted light, such as color filter, and ensures high use
efficiency of light and therefore, this method is ideal for
high-efficiency self-light emission-type polychromatic display
devices. However, in this method, the materials suitable for
respective emitted light colors must be prepared.
[0028] For this purpose, as described above, for example, a
fluorescence dye for laser, such as coumarin, is doped into an
aluminum complex of 8-hydroxyquinoline used as a host material to
convert the light emission wavelength (see, J. Appl. Phys., Vol.
65, page 3610 (1989)).
[0029] However, since conventionally proposed methods of doping a
fluorescence dye all utilize the light emission by singlet
excitons, the probability of generating excitons is theoretically
low as described above and a sufficiently high light emission
efficiency cannot be attained. Furthermore, the method of using a
phosphorescence molecule such as (T-1) or (T-2) has a problem in
that the number of molecules known to emit phosphorescence at room
temperature is very small and desired colors cannot be
afforded.
[0030] By taking account of these circumstances, the present
inventors have studied on the method for attaining high efficiency,
high driving stability and capability of polychromatic display, and
succeeded in reaching the present invention.
SUMMARY OF THE INVENTION
[0031] The organic electroluminescent device of the present
invention is characterized by that in an organic electroluminescent
device comprising a substrate having thereon a light-emitting layer
sandwiched by an anode and a cathode, the light-emitting layer
comprises at least
[0032] (1) a host material having electron-transporting and/or
hole-transporting property,
[0033] (2) Compound A capable of phosphorescence emission at room
temperature, and
[0034] (3) Compound B capable of phosphorescence emission or
fluorescence emission at room temperature and having the maximum
light emission wavelength longer than the maximum light
emission-wavelength of Compound A, and the maximum light emission
wavelength of the device is attributable to (3).
[0035] More specifically, the present inventors have found that
when the constituent element (2), namely, Compound A capable of
phosphorescence emission at room temperature is used in combination
with the constituent element (3), namely, Compound B which is (a) a
phosphorescent compound of not emitting light with high efficiency
by itself or (b) a fluorescent compound of emitting light in
various colors but incapable of ensuring light emission efficiency
as high as that of the phosphorescent compound for any of those
colors, Compound A plays a role of sensitizer and the light
emission of Compound B is intensified.
[0036] As a result, a device capable of emitting light in various
colors can be obtained and accordingly, this is very useful in
realizing a flat panel display of multi-color display or full-color
display using an organic electroluminescent device.
[0037] In the case where Compound B is a compound capable of
fluorescence emission at room temperature, an effect of inhibiting
the deterioration of luminance and the decrease in a light emission
efficiency can also be provided and this is preferred. By the
combination use with the phosphorescence emission Compound A, a
light emission color attributable to the fluorescent Compound B and
light emission efficiency close to the phosphorescence emission can
be realized and at the same time, the aging deterioration of
luminance and the decrease in the light emission efficiency when
the device emits light at a high luminance, which occurs very often
in phosphorescence emission devices, can be inhibited to elevate
the driving stability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a schematic sectional view showing one example of
the organic electroluminescent device according to the present
invention.
[0039] FIG. 2 is a schematic sectional view showing another example
of the organic electroluminescent device according to the present
invention.
[0040] FIG. 3 is a schematic sectional view showing another example
of the organic electroluminescent device according to the present
invention.
[0041] FIG. 4 is a graph showing the change in a luminance when the
devices fabricated in Example 4 or Comparative Example 5 emitted
light at a high luminance.
[0042] FIG. 5 is a graph showing the change in a luminance when the
devices fabricated in Example 5 or Comparative Example 5 emitted
light at a high luminance.
[0043] FIG. 6 is a graph showing the change in a luminance when the
devices fabricated in Example 6 or Comparative Example 5 emitted
light at a high luminance.
[0044] FIG. 7 is a graph showing the change in a luminance when the
devices fabricated in Example 4 or Comparative Example 5 were
driven continuously.
[0045] FIG. 8 is a graph showing the change in a luminance when the
devices fabricated in Example 5 or Comparative Example 5 were
driven continuously.
[0046] FIG. 9 is a graph showing the change in a luminance when the
devices fabricated in Example 6 or Comparative Example 5 were
driven continuously.
DETAILED DESCRIPTION OF THE INVENTION
[0047] The present invention relates to an organic
electroluminescent device containing a host material, Compound A
capable of phosphorescence emission at room temperature and
Compound B capable of phosphorescence emission or fluorescence
emission at room temperature in the light-emitting layer, and
having a maximum light emission wavelength attributable to Compound
B. In the organic electroluminescent device, the light-emitting
layer preferably contains the host material as a main component and
Compound A and Compound B as sub-components.
[0048] The term "main component" as used herein means a material
occupying 50% by weight or more in the materials constituting the
layer and the term "sub-component" means a material occupying less
than 50% by weight in the materials constituting the layer. That
is, the term "contains Compounds A and B as sub-components" means
that the total amount of Compound A and Compound B is less than 50%
by weight based on the materials for forming the light-emitting
layer.
[0049] The host material preferably has an excited triplet level in
an energy state higher than the excited triplet level of Compound A
and the excited triplet level (when Compound B is a phosphorescent
compound) or excited singlet level (when Compound B is a
fluorescent compound) of Compound B, contained in the
light-emitting layer.
[0050] Also, the host material must be a compound ensuring a stable
thin film shape, having a high glass transition temperature (Tg)
and being capable of efficiently transporting holes and/or
electrons.
[0051] Furthermore, the host material must be a compound which is
electrochemically and chemically stable and does not easily allow
the generation of impurities working out to a trap or quenching the
emitted light during the production or use.
[0052] Examples of the host material satisfying these requirements
include the compounds represented by the following formula (I) or
(II), or the compounds having the group represented by the
following formula (III): 2
[0053] (wherein the carbazolyl group and the phenylene group each
may have an arbitrary substituent, and Z.sup.1 represents a direct
bond or a divalent linking group). 3
[0054] (wherein M represents a metal selected from Groups 1, 2, 3,
12 and 13 of the periodic table, n represents a valence number of
the metal, L represents an arbitrary substituent, j represents a
number of the substituent L and is 0 or 1, X.sup.2 represents a
carbon atom or a nitrogen atom, the ring A represents a
nitrogen-containing heterocyclic ring and may have a substituent,
and the ring B represents an aromatic hydrocarbon ring group or an
aromatic heterocyclic group and may have a substituent). 4
[0055] (wherein R.sup.51 to R.sup.54 each independently represents
a hydrogen atom or an arbitrary substituent, each of the pairs
R.sup.51 and R.sup.52, and R.sup.53 and R.sup.54 may combine to
form a ring, and X.sup.3 represents an oxygen atom or a sulfur
atom).
[0056] Preferred examples of the compound having an
N-phenylcarbazole skeleton, represented by formula (I) include the
compounds represented by the following formula (I-1): 5
[0057] (wherein R.sup.1 to R.sup.16 each independently represents a
hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an
alkenyl group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group, a
hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring
group or aromatic heterocyclic group which may have a substituent,
each of the adjacent substituents R.sup.1 and R.sup.2, R.sup.3 and
R.sup.4, R.sup.5 and R.sup.6, R.sup.7 and R.sup.8, R.sup.9 and
R.sup.10, R.sup.11 and R.sup.12, R.sup.13 and R.sup.14, and
R.sup.15 and R.sup.16 may combine to form a ring, and z.sup.1
represents a direct bond or a divalent linking group).
[0058] Specific examples of R.sup.1 to R.sup.16 in formula (I-1)
include a hydrogen atom; a halogen atom such as chlorine atom and
fluorine atom; an alkyl group having from 1 to 6 carbon atoms such
as methyl group and ethyl group; an aralkyl group such as benzyl
group; an alkenyl group having from 2 to 6 carbon atoms such as
vinyl group; a cyano group; an amino group; an acyl group; an
alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; a carboxyl group;
an alkoxy group having from 1 to 6 carbon atoms such as methoxy
group and ethoxy group; an alkylamino group such as diethylamino
group and diisopropylamino group; an aralkylamino group such as
dibenzylamino group and diphenethylamino group; a haloalkyl group
such as trifluoromethyl group; a hydroxyl group; an aryloxy group
such as phenoxy group and benzyloxy group; an aromatic hydrocarbon
ring group such as phenyl group or naphthyl group, which may have a
substituent; and an aromatic heterocyclic group such as thienyl
group and pyridyl group, which may have a substituent.
[0059] Examples of the substituent which the aromatic hydrocarbon
ring group and the aromatic heterocyclic group each can have
include a halogen atom such as fluorine atom; an alkyl group having
from 1 to 6 carbon atoms such as methyl group and ethyl group; an
alkenyl group having from 2 to 6 carbon atoms such as vinyl group;
an alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
an alkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group.
[0060] Each pair of the adjacent substituents R.sup.1 and R.sup.2,
R.sup.3 and R.sup.4, R.sup.5 and R.sup.6, R.sup.7 and R.sup.8,
R.sup.9 and R.sup.10, R.sup.11 and R.sup.12, R.sup.13 and R.sup.14,
and R.sup.15 and R.sup.16 may be combine to form a 5-, 6- or
7-membered ring such as benzene ring or cyclohexane ring.
[0061] R.sup.1 to R.sup.16 each is particularly preferably a
hydrogen atom, an alkyl group or a cyano group.
[0062] Z.sup.1 in formula (I) or (I-1) is preferably a direct bond,
an oxygen atom, a sulfur atom, a linking group shown below: 6
[0063] a divalent aromatic hydrocarbon ring group or aromatic
heterocyclic group which may have a substituent, or any one of the
following linking groups: 7
[0064] (any benzene ring moiety in the each structure may have an
arbitrary substituent, and Ar.sup.1 to Ar.sup.6 each represents an
aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent or a group represented by the
following formula (I-2): 8
[0065] wherein the carbazolyl group and the phenylene group each
may have an arbitrary substituent).
[0066] Among the preferred linking groups for Z.sup.1 in formula
(I) or (I-1), examples of the aromatic hydrocarbon ring group
include a 5- or 6-membered monocyclic ring and a 2-, 3- or
4-condensed ring, such as phenylene group, naphthylene group,
anthranyl group and naphthacene, and examples of the aromatic
heterocyclic group include a 5- or 6-membered monocyclic ring and a
2- or 3-condensed ring, such as divalent thiophene ring residue,
furan ring residue, pyridine ring residue, pyrimidine ring residue
and quinoline ring residue.
[0067] These aromatic hydrocarbon ring group and aromatic
heterocyclic group may have a substituent such as an alkyl group
having from 1 to 6 carbon atoms (e.g. methyl, ethyl), a halogen
group (e.g. fluorine) or an a-haloalkyl group (e.g.
trifluoromethyl).
[0068] Examples of Ar.sup.1 to Ar.sup.6 include an aromatic
hydrocarbon ring group which is a 5- or 6-membered monocyclic ring
or a 2-, 3- or 4-condensed ring, such as phenylene group,
naphthylene group, anthranyl group and naphthacene, and an aromatic
heterocyclic ring which is a 5- to 6-membered monocyclic ring or a
2- or 3-condensed ring, such as thienyl group, furan group, pyridyl
group, pyrimidinyl group and quinolyl group. These aromatic
hydrocarbon ring group and aromatic heterocyclic group may have a
substituent such as an alkyl group (e.g. methyl, ethyl), a halogen
group (e.g. fluorine) or an .alpha.-haloalkyl group (e.g.
trifluoromethyl).
[0069] The structure represented by formula (I-2) is preferably
represented by the following formula (I-3): 9
[0070] (wherein R.sup.17 to R.sup.24 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, a cyano group, an amino group which may have a
substituent, an acyl group, an alkoxycarbonyl group, a carboxyl
group, an alkoxy group, an alkylamino group, an aralkylamino group,
a haloalkyl group, a hydroxyl group, an aryloxy group, or an
aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent, each of the pairs R.sup.17 and
R.sup.18, R.sup.19 and R.sup.20, R.sup.21 and R.sup.22, and
R.sup.23 and R.sup.24 may combine with each other to form a
ring).
[0071] Specific examples of R.sup.17 to R.sup.24 in formula (I-3)
include a hydrogen atom; a halogen atom; an alkyl group having from
1 to 6 carbon atoms such as methyl group and ethyl group; an
aralkyl group such as benzyl group; an alkenyl group having from 2
to 6 carbon atoms such as vinyl group; a cyano group; an amino
group; an acyl group; an alkoxycarbonyl group having from 2 to 6
carbon atoms such as methoxycarbonyl group and ethoxycarbonyl
group; a carboxyl group; an alkoxy group having from 1 to 6 carbon
atoms such as methoxy group and ethoxy group; an alkylamino group
such as diethylamino group and diisopropylamino group; an
aralkylamino group such as dibenzylamino group and diphenethylamino
group; a haloalkyl group such as trifluoromethyl group; a hydroxyl
group; an aryloxy group such as phenoxy group and benzyloxy group;
an aromatic hydrocarbon ring group such as phenyl group and
naphthyl group, which may have a substituent; and an aromatic
heterocyclic group such as thienyl group and pyridyl group, which
may have a substituent.
[0072] Examples of the substituent which the aromatic hydrocarbon
ring group and the aromatic heterocyclic group each can have
include a halogen atom such as fluorine atom; an alkyl group having
from 1 to 6 carbon atoms such as methyl group and ethyl group; an
alkenyl group having from 2 to 6 carbon atoms such as vinyl group;
an alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
a dialkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group.
[0073] Each pair of the adjacent substituents R.sup.17 and
R.sup.18, R.sup.19 and R.sup.20, R.sup.21 and R.sup.22, and
R.sup.23 and R.sup.24 may combine to form a 5-, 6- or 7-membered
ring such as benzene ring or cyclohexane ring.
[0074] Specific preferred examples of the compound represented by
formula (I) are set forth below, however, the present invention is
not limited thereto. 10
[0075] In the light-emitting layer, these compounds may be used
individually or, if desired, in combination of two or more
thereof.
[0076] In the organic electroluminescent device of the present
invention, an organic metal complex compound represented by formula
(II) may be used as the host material of the light-emitting layer.
An organic metal complex represented by the following formula
(II-1), a mixed ligand complex represented by the following formula
(II-2) and a binuclear metal complex represented by the following
formula (II-3) are particularly preferred.
[0077] [Organic Metal Complex] 11
[0078] (wherein M.sup.1 is a mono-, di- or trivalent metal, n,
X.sup.2 and the rings A and B have the same meanings as in formula
(II));
[0079] [Mixed Ligand Complex] 12
[0080] (wherein M.sup.2 represents a trivalent metal, X.sup.2 and
the rings A and B have the same meanings as in formula (II), and
L.sup.1 represents the following formula (II-2a), (II-2b) or
(II-2c)): 13
[0081] (wherein Ar.sup.11 to Ar.sup.15 each represents an aromatic
hydrocarbon ring group which may have a substituent or an aromatic
heterocyclic group which may have a substituent, and Z.sup.2
represents silicon or germanium); [Binuclear Metal Complex] 14
[0082] (wherein M.sup.3 and M.sup.3' each represents a trivalent
metal, X.sup.2 and the rings A and B have the same meanings as in
formula (II), X.sup.2' rings A' and B' have the same meanings as
X.sup.2 and the rings A and B, respectively).
[0083] A plurality of the following structural moieties: 15
[0084] (in formula (II-3), the following structural moieties each
present in a couple in one compound: 16
[0085] namely, the rings A, the rings B and X.sup.2s (in the case
of formula (II-3), the rings A, the rings A', the rings B, the
rings B', X.sup.2s and X.sup.2's), contained in one molecule of the
compound represented by formula (II), (II-1), (II-2) or (II-3) may
be the same or different. From the standpoint that the synthesis is
facilitated, all of these are preferably the same.
[0086] Similarly, M.sup.3 and M.sup.3' in the compound represented
by formula (II-3) may be the same or different and from the
standpoint that the synthesis is facilitated, both of these are
preferably the same.
[0087] The ring A, the ring A', the ring B and the ring B' in the
compounds represented by formula (II), (II-1), (II-2) or (II-3)
each is preferably selected from the following rings.
[0088] [Ring A and Ring A']
[0089] 5-Membered or 6-membered nitrogen-containing aromatic
heterocyclic rings which may have a substituent. One or two 5- or
6-membered aromatic hydrocarbon ring or aromatic heterocyclic ring
may be condensed to the ring to form a condensed ring.
[0090] [Ring B and ring B']
[0091] 6-Membered aromatic hydrocarbon rings or aromatic
heterocyclic rings, which may have a substituent. One or two 5- or
6-membered aromatic hydrocarbon ring or aromatic heterocyclic ring
may be condensed to the ring to form a condensed ring.
[0092] The ring A, the ring A', the ring B and the ring B' in the
compounds represented by formula (II), (II-1), (II-2) or (II-3)
each is more preferably a monocyclic ring and particularly
preferably a ring selected from the following rings.
[0093] [Ring A and Ring A']
[0094] Diazole ring, thiazole ring, oxazole ring, thiadiazole ring,
oxadiazole ring, triazole ring, pyridine ring, diazine ring and
triazine ring, which may have a substituent. [Ring B and Ring
B']
[0095] Benzene ring, pyridine ring, diazine ring and triazine ring,
which may have a substituent.
[0096] The ring A, the ring A', the ring B and the ring B' in the
compounds represented by the formula (II), (II-1), (II-2) or (II-3)
each is most preferably a ring selected from the following
structural formulae:
[0097] [Ring A and Ring A'] 17
[0098] (wherein R.sup.31 to R.sup.37 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group, a
hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring
group or aromatic heterocyclic group which may have a substituent,
or each of the pairs R.sup.31 and R.sup.32, R.sup.31 and R.sup.33,
R.sup.34 and R.sup.35, R.sup.35 and R.sup.36, and R.sup.36 and
R.sup.37 may combine with each other to form a ring).
[0099] [Ring B and Ring B'] 18
[0100] (wherein R.sup.38 to R.sup.41 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group, a
hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring
group which may have a substituent or an aromatic heterocyclic
group that may have a substituent, or each of the pairs R.sup.38
and R.sup.39, R.sup.39 and R.sup.40, and R.sup.40 and R.sup.41 may
combine with each other to form a ring).
[0101] In each structure of [Ring B and Ring B'] shown above, two
bonds either may be bonded to either the oxygen atom or the atom X
on the ring A or the ring A' insofar as the definitions of the ring
B and ring B' structures in formulae (II) and (II-1) to (II-3) are
satisfied.
[0102] R.sup.31 to R.sup.41 each specifically represents a hydrogen
atom; a halogen atom; an alkyl group having from 1 to 6 carbon
atoms such as methyl group or ethyl group; an aralkyl group such as
benzyl group; an alkenyl group having from 2 to 6 carbon atoms such
as vinyl group; a cyano group; an amino group; an acyl group; a
carboxyl group; an alkoxy group having from 1 to 6 carbon atoms
such as methoxy group or ethoxy group; an alkoxycarbonyl group
having from 2 to 6 carbon atoms such as methoxycarbonyl group or
ethoxycarbonyl group; an aryloxy group such as phenoxy group or
benzyloxy group; a dialkylamino group such as diethylamino group or
diisopropylamino group; a diaralkylamino group such as
dibenzylamino group or diphenethylamino group; an .alpha.-haloalkyl
group such as trifluoromethyl group; a hydroxyl group; an aromatic
hydrocarbon ring group such as phenyl group or naphthyl group,
which may have a substituent; or an aromatic heterocyclic group
such as thienyl group or pyridyl group, which may have a
substituent.
[0103] Examples of the substituent which the aromatic hydrocarbon
ring group and the aromatic heterocyclic group each can have
include a halogen atom such as fluorine atom; an alkyl group having
from 1 to 6 carbon atoms such as methyl group and ethyl group; an
alkenyl group having from 2 to 6 carbon atoms such as vinyl group;
an alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
a dialkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group.
[0104] Examples of the ring formed by combining each pair of the
adjacent substituents R.sup.31 and R.sup.32, R.sup.31 and R.sup.33,
R.sup.34 and R.sup.35, R.sup.35 and R.sup.36, R.sup.36 and
R.sup.37, R.sup.38 and R.sup.39, R.sup.39 and R.sup.40, and
R.sup.40 and R.sup.41 include a benzene ring and a cyclohexane
ring.
[0105] R.sup.31 to R.sup.41 each is preferably a hydrogen atom, a
halogen atom, an alkyl group, an alkoxy group, a haloalkyl group or
an aromatic hydrocarbon group which may have a substituent, or each
combine with the adjacent substituent to form a ring.
[0106] The metal M (M.sup.1, M.sup.2, M.sup.3 and M.sup.3') in the
compounds represented by formula (II), (II-1), (II-2) or (II-3) is
not particularly limited insofar as the metal is selected from
Groups 1, 2, 3, 12 and 13 of the periodic table, however, preferred
examples thereof include zinc, aluminum, gallium, beryllium and
magnesium.
[0107] Specific examples of the compounds represented by formula
(II), (II-1), (II-2) or (II-3) are set forth below, however, the
present invention is not limited thereto. 19
[0108] In the light-emitting layer, these compounds may be used
individually as a main component or, if desired, may be used in
combination.
[0109] In the organic electroluminescent device of the present
invention, the host material used in the light-emitting layer may
be a compound having a group represented by formula (III)
(structural formula shown below): 20
[0110] (wherein R.sup.51 to R.sup.54 each independently represents
a hydrogen atom or an arbitrary substituent, each of the pairs
R.sup.51 and R.sup.52, and R.sup.53 and R.sup.54 may combine to
form a ring, and X.sup.3 represents an oxygen atom or a sulfur
atom).
[0111] Examples of the ring formed by combining each of the pairs
R.sup.51 and R.sup.52, and R.sup.53 and R.sup.54 include a benzene
ring and a cyclohexane ring.
[0112] R.sup.51 to R.sup.54 each specifically represents a hydrogen
atom; a halogen atom; an alkyl group having from 1 to 6 carbon
atoms such as methyl group or ethyl group; an aralkyl group such as
benzyl group; an alkenyl group such as vinyl group; a cyano group;
an amino group; an acyl group; an alkoxy group having from 1 to 6
carbon atoms such as methoxy group or ethoxy group; an
alkoxycarbonyl group having from 1 to 6 carbon atoms such as
methoxycarbonyl group or ethoxycarbonyl group; an aryloxy group
such as phenoxy group or benzyloxy group; a dialkylamino group such
as diethylamino group or diisopropylamino group; a diaralkylamino
group such as dibenzylamino group or diphenethylamino group; an
a-haloalkyl group such as trifluoromethyl group; a hydroxyl group;
an aromatic hydrocarbon ring group such as phenyl group or naphthyl
group, which may have a substituent; or an aromatic heterocyclic
group such as thienyl group or pyridyl group, which may have a
substituent. Examples of the substituent include a halogen atom
such as fluorine atom; an alkyl group having from 1 to 6 carbon
atoms such as methyl group and ethyl group; an alkenyl group such
as vinyl group; an alkoxycarbonyl group having from 1 to 6 carbon
atoms such as methoxycarbonyl group and ethoxycarbonyl group; an
alkoxy group having from 1 to 6 carbon atoms such as methoxy group
and ethoxy group; an aryloxy group such as phenoxy group and
benzyloxy group; a dialkylamino group such as dimethylamino group
and diethylamino group; an acyl group such as acetyl group; a
haloalkyl group such as trifluoromethyl group; and a cyano group.
Among these substituents, the alkyl, alkoxy or alkoxycarbonyl group
having from 1 to 6 carbon atoms may be liner and branched. The same
applies to the substituents exemplified below.
[0113] Specific preferred examples of the group represented by
formula (III) are set forth below, however, the present invention
is not limited thereto. 21
[0114] The compound having a group represented by formula (III) may
be a low molecular compound or a polymer compound. In the case of a
polymer compound, the group may be contained in the main chain or
may be contained as a side chain.
[0115] This compound is preferably a low molecular compound having
a molecular weight of approximately from 400 to 1,200. In the
compound having a group represented by formula (III), the total
number of rings as the entire compound is preferably from 6 to 20,
more preferably from 7 to 18. The compound having a group
represented by formula (III) is preferably a compound having from 2
to 3 units represented by formula (III) within the molecule.
[0116] In particular, the group represented by formula (III) is
preferably (S-1) or (S-2).
[0117] The compound having a group represented by formula (III) is
preferably a compound represented by the following formula (III-1)
or (III-2): 22
[0118] (wherein R.sup.55 to R.sup.62 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, an allyl group, a cyano group, an amino group, an
acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy
group, an alkylamino group, an .alpha.-haloalkyl group, a hydroxyl
group, or an aromatic hydrocarbon ring group or aromatic
heterocyclic group which may have a substituent, each of the pairs
R.sup.55 and R.sup.56, R.sup.57 and R.sup.58, R.sup.59 and
R.sup.60, and R.sup.61 and R.sup.62 may combine with each other to
form a ring, X.sup.4 and X.sup.5 each independently represents an
oxygen group or a sulfur group, and Q.sup.1 represents a divalent
linking group comprising an aromatic hydrocarbon ring group or
aromatic heterocyclic group which may have a substituent); 23
[0119] (wherein R.sup.63 to R.sup.74 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, an allyl group, a cyano group, an amino group, an
acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy
group, an alkylamino group, an .alpha.-haloalkyl group, a hydroxyl
group, or an aromatic hydrocarbon ring group or aromatic
heterocyclic group which may have a substituent, each of the
adjacent substituents R.sup.63 and R.sup.64, R.sup.65 and R.sup.66,
R.sup.67 and R.sup.68, R.sup.69 and R.sup.70, R.sup.71 and
R.sup.72, R.sup.73 and R.sup.74 may combine to form a ring, X.sup.6
to X.sup.8 each independently represents an oxygen atom or a sulfur
atom, and Q.sup.2 represents a trivalent linking group comprising
an aromatic hydrocarbon ring group or aromatic heterocyclic group
which may have a substituent).
[0120] In formula (III-1), R.sup.55 to R.sup.62 each independently
represents a hydrogen atom; a halogen atom; an alkyl group having
from 1 to 6 carbon atoms such as methyl group or ethyl group; an
aralkyl group such as benzyl group; an alkenyl group such as vinyl
group; a cyano group; an amino group; an acyl group; an alkoxy
group having from 1 to 6 carbon atoms such as methoxy group or
ethoxy group; an alkoxycarbonyl group having from 1 to 6 carbon
atoms such as methoxycarbonyl group or ethoxycarbonyl group; an
aryloxy group such as phenoxy group or benzyloxy group; a
dialkylamino group such as diethylamino group or diisopropylamino
group; a diaralkylamino group such as dibenzylamino group or
diphenethylamino group; an .alpha.-haloalkyl group such as
trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon
ring group such as phenyl group or naphthyl group, which may have a
substituent; or an aromatic heterocyclic group such as thienyl
group or pyridyl group, which may have a substituent. Examples of
the substituent include a halogen atom such as fluorine atom; an
alkyl group having from 1 to 6 carbon atoms such as methyl group
and ethyl group; an alkenyl group such as vinyl group; an
alkoxycarbonyl group having from 1 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
a dialkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group. Each of the pairs
R.sup.55 and R.sup.56, R.sup.57 and R.sup.58, R.sup.59 and R.sup.60
and R.sup.61 and R.sup.62 may combine with each other to form a
benzene ring or a cyclohexane group. X.sup.4 and X.sup.5 each
independently represents an oxygen group or a sulfur group. Q.sup.1
represents a divalent linking group comprising an aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent. Preferred examples of the linking group Q.sup.1
are set forth below. 24
[0121] Among these, the linking group Q.sup.1 is preferably (A-2),
(A-6), (A-8), (A-10) or (A-12). The compound is most preferably a
compound having this linking group Q.sup.1 and having the ring
structure (S-1) or (S-2).
[0122] Specific preferred examples of the compound represented by
formula (III-1) are shown in Table 1, however, the present
invention is not limited thereto.
1TABLE 1 25 Compound R.sup.55-R.sup.58, R.sup.59-R.sup.62, Linking
Number Substituted Moiety Substituted Moiety group Q.sup.1 (H-101)
(S-1) (S-1) (A-1) (H-102) (S-2) (S-2) (A-1) (H-103) (S-1) (S-1)
(A-2) (H-104) (S-2) (S-2) (A-2) (H-105) (S-3) (S-3) (A-2) (H-106)
(S-1) (S-2) (A-2) (H-107) (S-4) (S-4) (A-2) (H-108) (S-5) (S-5)
(A-2) (H-109) (S-6) (S-6) (A-2) (H-110) (S-7) (S-7) (A-2) (H-111)
(S-8) (S-8) (A-2) (H-112) (S-2) (S-9) (A-2) (H-113) (S-10) (S-10)
(A-2) (H-114) (S-11) (S-11) (A-2) (H-115) (S-12) (S-12) (A-2)
(H-116) (S-13) (S-13) (A-2) (H-117) (S-13) (S-2) (A-2) (H-118)
(S-14) (S-14) (A-2) (H-119) (S-13) (S-14) (A-2) (H-120) (S-15)
(S-15) (A-2) (H-121) (S-2) (S-16) (A-2) (H-122) (S-16) (S-16) (A-2)
(H-123) (S-1) (S-1) (A-3) (H-124) (S-2) (S-2) (A-3) (H-125) (S-1)
(S-1) (A-4) (H-126) (S-2) (S-2) (A-4) (H-127) (S-2) (S-2) (A-5)
(H-128) (S-1) (S-1) (A-6) (H-129) (S-2) (S-2) (A-6) (H-130) (S-3)
(S-3) (A-6) (H-131) (S-1) (S-1) (A-7) (H-132) (S-2) (S-2) (A-7)
(H-133) (S-1) (S-1) (A-8) (H-134) (S-2) (S-2) (A-8) (H-135) (S-3)
(S-3) (A-8) (H-136) (S-1) (S-1) (A-9) (H-137) (S-2) (S-2) (A-9)
(H-138) (S-1) (S-1) (A-10) (H-139) (S-2) (S-2) (A-10) (H-140) (S-1)
(S-2) (A-10) (H-141) (S-3) (S-3) (A-10) (H-142) (S-4) (S-4) (A-10)
(H-143) (S-7) (S-7) (A-10) (H-144) (S-10) (S-10) (A-10) (H-145)
(S-13) (S-13) (A-10) (H-146) (S-14) (S-14) (A-10) (H-147) (S-1)
(S-2) (A-11) (H-148) (S-2) (S-2) (A-11) (H-149) (S-1) (S-1) (A-12)
(H-150) (S-2) (S-2) (A-12) (H-151) (S-2) (S-2) (A-13) (H-152) (S-2)
(S-2) (A-14) (H-153) (S-2) (S-2) (A-15) (H-154) (S-1) (S-1) (A-16)
(H-155) (S-2) (S-2) (A-17)
[0123] In formula (III-2), R.sup.63 to R.sup.74 each independently
represents a hydrogen atom; a halogen atom; an alkyl group having
from 1 to 6 carbon atoms such as methyl group or ethyl group; an
aralkyl group such as benzyl group; an alkenyl group such as vinyl
group; a cyano group; an amino group; an acyl group; an alkoxy
group having from 1 to 6 carbon atoms such as methoxy group or
ethoxy group; an alkoxycarbonyl group having from 1 to 6 carbon
atoms such as methoxycarbonyl group or ethoxycarbonyl group; an
aryloxy group such as phenoxy group or benzyloxy group; a
dialkylamino group such as diethylamino group or diisopropylamino
group; a diaralkylamino group such as dibenzylamino group or
diphenethylamino group; an .alpha.-haloalkyl group such as
trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon
ring group such as phenyl group or naphthyl group, which may have a
substituent; or an aromatic heterocyclic group such as thienyl
group or pyridyl group, which may have a substituent. Examples of
the substituent include a halogen atom such as fluorine atom; an
alkyl group having from 1 to 6 carbon atoms such as methyl group
and ethyl group; an alkenyl group such as vinyl group; an
alkoxycarbonyl group having from 1 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
a dialkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group. Each of the pairs
R.sup.63 and R.sup.64, R.sup.65 and R.sup.66, R.sup.67 and
R.sup.68, R.sup.69 and R.sup.70, R.sup.71 and R.sup.72, and
R.sup.73 and R.sup.74 may combine with each other to form a benzene
ring or a cyclohexane group. X.sup.6 to X.sup.8 each independently
represents an oxygen group or a sulfur group, and Q.sup.2
represents a trivalent linking group comprising an aromatic
hydrocarbon ring group or aromatic heterocyclic group which may
have a substituent. Preferred examples of the linking group Q are
set forth below. 26
[0124] Among these, the linking group Q.sup.2 is preferably (B-1),
(B-2) or (B-7). The compound is most preferably a compound having
this linking group and having the ring structure (S-1) or
(S-2).
[0125] Specific preferred examples of the compound represented by
formula (III-2) are shown in Table 2, however, the present
invention is not limited thereto.
2TABLE 2 27 R.sup.63-R.sup.66, R.sup.67-R.sup.70,
R.sup.71-R.sup.74, Compound Substituted Substituted Substituted
Linking No. Moiety Moiety Moiety Group Q.sup.2 (H-201) (S-1) (S-1)
(S-1) (B-1) (H-202) (S-2) (S-2) (S-2) (B-1) (H-203) (S-1) (S-1)
(S-1) (B-2) (H-204) (S-2) (S-2) (S-2) (B-2) (H-205) (S-3) (S-3)
(S-3) (B-2) (H-206) (S-1) (S-1) (S-2) (B-2) (H-207) (S-4) (S-4)
(S-4) (B-2) (H-208) (S-13) (S-13) (S-13) (B-2) (H-209) (S-14)
(S-14) (S-14) (B-2) (H-210) (S-15) (S-15) (S-15) (B-2) (H-211)
(S-16) (S-16) (S-16) (B-2) (H-212) (S-1) (S-1) (S-1) (B-3) (H-213)
(S-2) (S-2) (S-2) (B-3) (H-214) (S-1) (S-1) (S-1) (B-4) (H-215)
(S-13) (S-13) (S-13) (B-4) (H-216) (S-1) (S-1) (S-1) (B-5) (H-217)
(S-2) (S-2) (S-2) (B-5) (H-218) (S-2) (S-2) (S-2) (B-6) (H-219)
(S-4) (S-4) (S-4) (B-6) (H-220) (S-1) (S-1) (S-1) (B-7) (H-221)
(S-2) (S-2) (S-2) (B-7) (H-222) (S-3) (S-3) (S-3) (B-7) (H-223)
(S-7) (S-7) (S-7) (B-7) (H-224) (S-1) (S-2) (S-2) (B-7) (H-225)
(S-10) (S-10) (S-10) (B-7) (H-226) (S-13) (S-13) (S-13) (B-7)
(H-227) (S-14) (S-14) (S-14) (B-7) (H-228) (S-15) (S-15) (S-15)
(B-7) (H-229) (S-16) (S-16) (S-16) (B-7) (H-230) (S-1) (S-1) (S-1)
(B-8) (H-231) (S-2) (S-2) (S-2) (B-8) (H-232) (S-1) (S-1) (S-1)
(B-9) (H-233) (S-2) (S-2) (S-2) (B-9) (H-234) (S-1) (S-1) (S-1)
(B-10) (H-235) (S-2) (S-2) (S-2) (B-10) (H-236) (S-13) (S-13)
(S-13) (B-10) (H-237) (S-14) (S-14) (S-14) (B-10)
[0126] In the light-emitting layer, only one compound having a
group represented by formula (III) may be contained or two or more
thereof may be contained.
[0127] In addition to formulae (I) to (III), the host material
which can be used includes the following compounds. 28
[0128] For the host material, a plurality of compounds which can be
represented by the same formula may be used in combination as
described above, or compounds which cannot be represented by the
same formula may also be used in combination.
[0129] In the organic electroluminescent device of the present
invention, the host material of the light-emitting layer is most
preferably the compound represented by formula (I).
[0130] The constituent element (2) of the present invention,
namely, Compound A capable of phosphorescence emission at room
temperature is described below.
[0131] Compound A preferably has an excited triplet level lying
between the excited triplet level of the host material and the
excited triplet level (when Compound B is a phosphorescent
compound) or excited singlet level (when Compound B is a
fluorescent compound) of Compound B which is described later.
[0132] In view of the structure, an organic metal complex
containing a metal selected from Groups 7 to 11 of the periodic
table is preferred.
[0133] From the standpoint that the charge transfer between the
center metal and the ligand readily occurs, the metal is preferably
a metal of the fifth or sixth period of the periodic table.
Specific examples thereof include ruthenium, rhodium, palladium,
silver, rhenium, osmium, iridium, platinum and gold.
[0134] Examples of the complex thereof include the compounds
represented by the following formula (IV): 29
[0135] (wherein the ring D represents an aromatic hydrocarbon ring
which may have a substituent or an aromatic heterocyclic ring which
may have a substituent, the ring E represents a nitrogen-containing
aromatic heterocyclic ring which may have a substituent, a group on
the ring D and a group on the ring E may combine to form a ring
condensed to these rings, M.sup.4 represents a metal selected from
Groups 7 to 11 of the periodic table, L.sup.2 represents an
arbitrary bidentate ligand, m represents a valence number of
M.sup.4, and k represents an integer satisfying
0.ltoreq.k<m).
[0136] In the ligand 30
[0137] the ring D represents an aromatic hydrocarbon ring or
aromatic heterocyclic ring which may have a substituent, preferably
a phenyl group, a naphthyl group, an anthryl group, a thienyl
group, a pyridyl group, a furyl group, a benzothienyl group, a
benzofuryl group, a quinolyl group or an isoquinolyl group.
[0138] Examples of the substituent which these aromatic hydrocarbon
ring group and aromatic heterocyclic group may have include a
halogen atom such as fluorine atom; an alkyl group having from 1 to
6 carbon atoms such as methyl group and ethyl group; an alkenyl
group having from 2 to 6 carbon atoms such as vinyl group; an
alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aromatic hydrocarbon ring group such as phenyl group and
naphthyl group; an aryloxy group such as phenoxy group and
benzyloxy group; a dialkylamino group such as dimethylamino group
and diethylamino group; an acyl group such as acetyl group; a
haloalkyl group such as trifluoromethyl group; and a cyano
group.
[0139] The ring E represents a nitrogen-containing aromatic
heterocyclic group, preferably a pyridyl group, a pyrimidyl group,
a pyrazine group, a triazine group, a benzothiazole group, a
benzoxazole group, a benzimidazole, a quinolyl group, an
isoquinolyl group, a quinoxaline group or phenanthridine group,
which may have a substituent.
[0140] Examples of the substituent which this aromatic heterocyclic
group may have include a halogen atom such as fluorine atom; an
alkyl group having from 1 to 6 carbon atoms such as methyl group
and ethyl group; an alkenyl group having from 2 to 6 carbon atoms
such as vinyl group; an alkoxycarbonyl group having from 2 to 6
carbon atoms such as methoxycarbonyl group and ethoxycarbonyl
group; an alkoxy group having from 1 to 6 carbon atoms such as
methoxy group and ethoxy group; an aromatic hydrocarbon ring group
such as phenyl group and naphthyl group; an aryloxy group such as
phenoxy group and benzyloxy group; a dialkylamino group such as
dimethylamino group and diethylamino group; an acyl group such as
acetyl group; a haloalkyl group such as trifluoromethyl group; and
a cyano group.
[0141] The substituent of the ring D and the substituent of the
ring E may combine to form one condensed ring as a whole. Examples
of the condensed ring include 7,8-benzoquinoline.
[0142] More preferred examples of the substituent of the ring D and
the ring E include an alkyl group, an alkoxy group, an aromatic
hydrocarbon ring group and a cyano group.
[0143] Examples of the ligand 31
[0144] include the following structures, however, the present
invention is not limited thereto. In the following examples, the
substituents in the ring D and the ring E are omitted but, as
described above, these rings each may have a substituent. 32
[0145] The arbitrary bidentate ligand L.sup.2 in formula (IV) is
not particularly limited insofar as it is a monovalent bidentate
ligand, however, when the steric hindrance is considered, the
ligand is preferably not so bulky and examples thereof include the
following ligands. 33
[0146] (wherein R, R', R" and R'" each independently represents an
alkyl group having from 1 to 4 carbon atoms or a haloalkyl group
having from 1 to 4 carbon atoms, and the substituents in the
aromatic hydrocarbon ring and the aromatic heterocyclic ring are
omitted.)
[0147] Among the ligands L.sup.2, the following ligands are
particularly preferred. 34
[0148] As long as the valence number of the center metal M.sup.4 in
formula (IV) is satisfied, any combination of the ligand containing
the ring D and the ring E with the arbitrary ligand L.sup.2 may be
used and how many ligands may be coordinated, however, the compound
represented by the following formula (IV-1) or (IV-2) is preferred:
35
[0149] (wherein the rings D.sup.1 and D.sup.2 have the same
meanings as the ring D in formula (IV), the rings E.sup.1 and
E.sup.2 have the same meanings as the ring E in formula (IV),
M.sup.5 and M.sup.6 have the same meanings as M.sup.4 in formula
(IV) and m has the same meaning as in formula (IV)).
[0150] Specific examples of the phosphorescent Compound A
represented by formula (IV) are set forth below, however, the
present invention is not limited thereto. 36
[0151] For Compound B, an organic metal complex represented by the
following formula (V) can be used in addition to the organic metal
complex represented by formula (IV). 37
[0152] (wherein R.sup.81 to R.sup.92 each independently represents
a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group,
an alkenyl group, a cyano group, an amino group, an acyl group, an
alkoxycarbonyl group, a carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group, a
hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring
group or aromatic heterocyclic group which may have a substituent,
each of the pairs R.sup.81 and R.sup.82, R.sup.84 and R.sup.85,
R.sup.87 and R.sup.88, and R.sup.90 and R.sup.91 may combine with
each other to form a ring, M.sup.7 represents a metal selected from
Groups 7 to 11 of the periodic table, X.sup.9 to X.sup.12 each
represents carbon or nitrogen, provided that when any one of
X.sup.9 to X.sup.12 is a nitrogen atom, R.sup.83, R.sup.86,
R.sup.89 or R.sup.92 bonded to the nitrogen atom is absent).
[0153] Similarly to M.sup.5 and M.sup.6 in formulae (IV-1) and
(IV-2), M.sup.7 in formula (V) is preferably a metal of the fifth
or sixth period of the periodic table. Specific examples thereof
include ruthenium, rhodium, palladium, silver, rhenium, osmium,
iridium, platinum and gold. Among these, preferred are divalent
metals such as platinum and palladium.
[0154] Specific examples of the organic metal complex represented
by formula (V) are set forth below, however, the present invention
is not limited thereto. 38
[0155] The constituent element (3) of the present invention, that
is, Compound B capable of phosphorescence emission or fluorescence
emission at room temperature is described below.
[0156] The case where Compound B is a phosphorescent compound is
described below.
[0157] The organic electroluminescent device of the present
invention is characterized in that Compound A fills the role of
sensitizer in the light-emitting layer and therefore, the light
emission attributable to Compound B is intensified. Accordingly, it
is important that the phosphorescent Compound B has an excited
triplet level in the energy state lower than the excited triplet
level of the phosphorescent Compound A.
[0158] Examples of the phosphorescent Compound B include the same
compounds as described above for Compound A. Among those, a
compound having an energy level satisfying the above-described
relationship with Compound A is preferably selected.
[0159] In view of the energy transfer, at least one complex
containing iridium is preferably contained as Compound A or B. In
particular, it is preferred to contain at least one iridium complex
as Compound A and also at least one iridium complex as Compound B
or to contain at least one iridium complex as either one of
Compound A and Compound B and contain at least one platinum complex
as the other compound.
[0160] As described above, in order to realize the smooth energy
transfer from Compound A to Compound B, it is important that the
maximum light emission wavelength of Compound B is longer than the
maximum light emission wavelength of Compound A. The term "the
maximum light emission wavelength of Compound A" means the maximum
light emission wavelength at a phosphorescence emission spectrum of
Compound A. The term "the maximum light emission wavelength of
Compound B" means the maximum light emission wavelength at a
phosphorescence emission spectrum when Compound B is a
phosphorescent compound, and the maximum light emission wavelength
at a fluorescence emission spectrum when Compound B is a
fluorescent compound.
[0161] The conditions for measuring the maximum emission wavelength
of Compound A or Compound B are not particularly limited, the
maximum emission wavelength of Compound A and Compound B may be
measured under the same conditions and the thus obtained value for
Compound A may be compared with that for Compound B. For example,
Compound A is compared with Compound B with respect to light
emission spectra of solutions dissolving Compound A or B in the
same solvent, single-layer films made from each compound alone,
organic electroluminescent devices having the same structure except
for doping each compound to the light-emitting layer, or the
like.
[0162] The case where Compound B is a fluorescent compound is
described below.
[0163] In the organic electroluminescent device of the present
invention, for letting Compound A to fill the role of sensitizer in
the light-emitting layer, it is important, as described above, that
the fluorescent Compound B has an excited singlet level in the
energy state lower than the excited triplet level of Compound A.
Examples of the fluorescent Compound B include compounds which
present blue light emission, such as perylene, pyrene, anthracene
and derivatives thereof; compounds which present green light
emission, such as quinacridone derivatives and coumarin
derivatives; compounds which present yellow light emission, such as
rubrene and perimidone derivatives; and compounds which present red
light emission, such as coumarin derivatives, benzopyran
derivatives, rhodamine derivatives, phenoxazone derivatives,
benzothioxanthene derivatives and azabenzothioxanthene.
[0164] In addition to these fluorescent compounds, the fluorescent
compounds described in Laser Kenkyu (Laser Research), Vol. 8, pages
694, 803 and 958 (1980); and ibid., Vol. 9, page 85 (1981) can be
used as the fluorescent Compound B according to host material and
the phosphorescent Compound A.
[0165] Among these, the fluorescent compounds of presenting green
light emission, yellow light emission or red light emission are
preferred.
[0166] The construction of the organic electroluminescent device of
the present invention is described below by referring to the
drawings, however, the present invention is not limited
thereto.
[0167] FIGS. 1 to 3 each is a sectional view schematically showing
an embodiment of the organic electroluminescent device of the
present invention, where 1 denotes a substrate, 2 denotes an anode,
3 denotes an anode buffer layer, 4 denotes a hole-transporting
layer, 5 denotes a light-emitting layer, 6 denotes a hole-blocking
layer, 7 denotes an electron-transporting layer and 8 denotes a
cathode. The construction is described mainly by referring to the
device shown in FIG. 1.
[0168] The substrate 1 works out to a support of the organic
electroluminescent device and for example, a plate of quartz or
glass, a metal sheet or foil, or a plastic film or sheet is used
therefor. Particularly, a glass plate or a transparent synthetic
resin plate such as polyester, polymethacrylate, polycarbonate or
polysulfone is preferred. In the case of using a synthetic resin
substrate, it is necessary to take notice of the gas-barrier
property. If the substrate has excessively low gas-barrier
property, the organic electroluminescent device may
disadvantageously deteriorate due to outside air passing through
the substrate. Accordingly, a dense silicon oxide film or the like
is provided at least on one surface of the synthetic resin
substrate to ensure the gas-barrier property and this is one of the
preferred methods.
[0169] On the substrate 1, an anode 2 is provided. The anode 2
fills the role of injecting holes into the hole-transporting layer
4. This anode 2 is generally composed of a metal such as aluminum,
gold, silver, nickel, palladium or platinum, a metal oxide such as
indium oxide and/or tin oxide, a metal halide such as copper
iodide, a carbon black or an electrically conductive polymer such
as poly(3-methyl thiophene), polypyrrole or polyaniline. The anode
2 is usually formed by sputtering or vacuum vapor deposition. In
the case where a metal fine particle of silver, a fine particle of
copper iodide, carbon black, an electrically conductive metal oxide
fine particle or an electrically conductive polymer fine particle
is used, the anode 2 can be formed by dispersing this in an
appropriate binder resin solution and applying the dispersion
solution on the substrate 1. Furthermore, in the case of using an
electrically conductive polymer, the anode 2 can be provided by
forming a thin film directly on the substrate 1 using electrolytic
polymerization or by coating the electrically conductive polymer on
the substrate 1 (see, Appl. Phys. Lett., Vol. 60, page 2711
(1992)).
[0170] The anode 2 may also be a stacked layer structure formed by
stacking layers comprising different materials.
[0171] The thickness of the anode 2 varies depending on the
required transparency. In the case where the transparency is
necessary, the transmittance of visible ray is usually set to 60%
or more, preferably 80% or more, and in this case, the thickness is
usually from 5 to 1,000 nm, preferably on the order of 10 to 500
nm. In the case where the transparency is not required, the anode 2
may have substantially the same thickness as the substrate 1. On
this anode 2, a different electrically conductive material can also
be further stacked.
[0172] On the anode 2, a hole-transporting layer 4 is provided. The
material for the hole-transporting layer 4 is required to ensure
high efficiency in the hole injection from the anode 2 and
efficient transportation of the injected holes. To satisfy these
requirements, the material is required to have a small ionization
potential, a high transparency to visible ray, a high hole
mobility, excellent stability and difficulty of generating
impurities serving as a trap during the production or use. Since
the hole-transporting layer 4 contacts with the light-emitting
layer 5, the material is also required not to quench the light
emission from the light-emitting layer 5 or not to form an exciplex
between the hole-transporting layer 4 and the light-emitting layer
5 and thereby reduce the efficiency. In addition to these general
requirements, when an application to a display for the mounting on
vehicles is considered, since the device is further required to
have heat resistance, the material preferably has a Tg of
75.degree. C. or more, more preferably 85.degree. C. or more.
[0173] Examples of the hole-transporting material include aromatic
diamines containing two or more tertiary amines and having two or
more condensed aromatic rings substituted to nitrogen atoms,
represented by 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (see,
JP-A-5-234681); aromatic amine compounds having a star burst
structure, such as
4,4',4"-tris(1-naphthylphenylamino)triphenylamine (see, J. Lumin.,
Vol. 72-74, page 985 (1997)); aromatic amine compounds comprising a
tetramer of triphenylamine (see, Chem. Commun., page 2175 (1996));
and spiro compounds such as
2,2',7,7'-tetrakis(diphenylamino)-9,9'-spirobifluorene (see, Synth.
Metals, Vol. 91, page 209 (1997)). These compounds may be used
individually or, if desired, in combination.
[0174] In addition to the above-described compounds, examples of
the material for the hole-transporting layer 4 include polymer
materials such as polyvinylcarbazole, polyvinyltriphenylamine (see,
JP-A-7-53953), polyarylene ether sulfone containing
tetraphenylbenzidine (see, Polym. Adv. Tech., Vol. 7, page 33
(1996)).
[0175] In the case of forming the hole-transporting layer 4 by the
coating method, one or more hole-transporting material is, if
desired, after adding additives which do not become a trap for the
holes, such as binder resin and coatability improving agent,
dissolved to prepare a coating solution and the coating solution is
coated on the anode 2 by spin coating or the like and dried to form
the hole-transporting layer 4. Examples of the binder resin include
polycarbonate, polyarylate and polyester. If the amount of the
binder resin added is large, the hole mobility is reduced.
Therefore, the amount added thereof is preferably as low as
possible and in terms of the content in the hole-transporting layer
4, preferably 50% by weight or less.
[0176] In the case of forming the hole-transporting layer 4 by the
vacuum vapor deposition method, the hole-transport material is
placed in a crucible disposed within a vacuum container, the inside
of the vacuum chamber is evacuated to about 10.sup.-4 Pa by an
appropriate vacuum pump and then the crucible is heated to
evaporate the hole-transport material, whereby the
hole-transporting layer 4 is formed on the substrate 1 having
formed thereon the anode 2 and being disposed to face the
crucible.
[0177] The thickness of the hole-transporting layer 4 is usually
from 5 to 300 nm, preferably from 10 to 100 nm. In order to
uniformly form such a thin film, the vacuum vapor deposition method
is generally used in many cases.
[0178] On the hole-transporting layer 4, the light-emitting layer 5
is provided. The light-emitting layer 5 comprises at least (1) a
host material having electron-transporting property or
hole-transporting property, (2) Compound A capable of
phosphorescence emission at room temperature and (3) Compound B
capable of phosphorescence emission or fluorescence emission at
room temperature. Between the electrodes applied with an electric
field, a hole injected from the anode 2 and transferring through
the hole-transporting layer 4 and an electron injected from the
cathode 8 and transferring through the hole-blocking layer 6 are
recombined and thereby the light-emitting layer is excited and
emits strong light. The maximum light emission wavelength in the
light emission spectrum is attributable to the above-described
Compound B.
[0179] The light-emitting layer 5 may contain components other than
the above-described (1) to (3) within the range of not impairing
the performance of the present invention.
[0180] The content of Compound A capable of phosphorescence
emission is preferably from 0.1 to 30% by weight based on the
entire light-emitting layer. If the content is less than 0.1% by
weight, Compound A may fail in sufficiently contributing to the
improvement of light emission efficiency of the device, whereas if
it exceeds 30% by weight, concentration quenching may occur to
cause reduction of the light emission efficiency.
[0181] In the case of using a compound capable of phosphorescence
emission as Compound B, the content thereof is also preferably from
0.1 to 30% by weight based on the entire light-emitting layer but
more preferably, the total amount of Compounds A and B is from 0.1
to 30% by weight based on the entire light-emitting layer. In view
of the energy transfer, the ratio of Compound B to Compound A
(compound B)/(compound A) is preferably from 0.3 to 3 (molar
ratio).
[0182] In the case of using a compound capable of fluorescence
emission as Compound B, the content thereof is preferably from 0.05
to 10% by weight, more preferably from 0.05 to 2% by weight, based
on the entire light-emitting layer.
[0183] Compound A and Compound B may be uniformly distributed
within the light-emitting layer or may be non-uniformly present by
having a distribution in the film thickness direction.
[0184] The thickness of the light-emitting layer 5 is usually from
10 to 200 nm, preferably from 20 to 100 nm. This thin film is
formed by the same method as the hole-transporting layer 4.
[0185] The hole-blocking layer 6 is stacked on the light-emitting
layer 5 to come into contact with the interface of the
light-emitting layer 5 in the cathode side and fills the role of
inhibiting the holes transferring from the hole-transporting layer
4, from reaching the cathode 8. The hole-blocking layer 6 is formed
of a compound capable of transporting the electrons injected from
the cathode 8 toward the direction of the light-emitting layer 5
with good efficiency. The material constituting the hole-blocking
layer 6 is required to have high electron mobility and low hole
mobility. The hole-blocking layer 6 has a function of enclosing
holes and electrons within the light-emitting layer 5 and thereby
improving the light emission efficiency.
[0186] Preferred examples of the hole-blocking material satisfying
these requirements include mixed ligand complexes represented by
the following formula (VI): 39
[0187] (wherein R.sup.101 to R.sup.106 each represents a hydrogen
atoms or an arbitrary substituent, Q.sup.3 represents a metal atom
selected from aluminum, gallium and indium, and Y.sup.1 is
represented by any one of the following formulae (VI-1), (VI-2) and
(VI-3): 40
[0188] (wherein Ar.sup.21 to Ar.sup.25 each represents an aromatic
hydrocarbon ring group which may have a substituent or an aromatic
heterocyclic group which may have a substituent, and Y.sup.2
represents silicon or germanium).
[0189] In formula (VI), R.sup.101 to R.sup.106 each independently
represents a hydrogen atom or an arbitrary substituent, preferably
a hydrogen atom; a halogen atom such as chlorine or bromine; an
alkyl group having from 1 to 6 carbon atoms such as methyl group or
ethyl group; an aralkyl group such as benzyl group; an alkenyl
group having from 2 to 6 carbon atoms such as vinyl group; a cyano
group; an amino group; an acyl group; an alkoxy group having from 1
to 6 carbon atoms such as methoxy group or ethoxy group; an
alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group or ethoxycarbonyl group; a carboxyl group; an
aryloxy group such as phenoxy group or benzyloxy group; an
alkylamino group such as diethylamino group or diisopropylamino
group; an aralkylamino group such as dibenzylamino group or
diphenethylamino group; a haloalkyl group such as trifluoromethyl
group; a hydroxyl group; an aromatic hydrocarbon ring group such as
phenyl group or naphthyl group, which may have a substituent; or an
aromatic heterocyclic group such as thienyl group or pyridyl group,
which may have a substituent.
[0190] Examples of the substituent which these aromatic hydrocarbon
ring group and aromatic heterocyclic group can have include a
halogen atom such as fluorine atom; an alkyl group having from 1 to
6 carbon atoms such as methyl group and ethyl group; an alkenyl
group having from 2 to 6 carbon atoms such as vinyl group; an
alkoxycarbonyl group having from 2 to 6 carbon atoms such as
methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group
having from 1 to 6 carbon atoms such as methoxy group and ethoxy
group; an aryloxy group such as phenoxy group and benzyloxy group;
an alkylamino group such as dimethylamino group and diethylamino
group; an acyl group such as acetyl group; a haloalkyl group such
as trifluoromethyl group; and a cyano group.
[0191] R.sup.101 to R.sup.106 each is more preferably a hydrogen
atom, an alkyl group, a halogen atom or a cyano group. R.sup.104 is
particularly preferably a cyano group.
[0192] Specific examples of Ar.sup.21 to Ar.sup.25 in formula (VI)
include an aromatic hydrocarbon ring group such as phenyl group,
biphenyl group and naphthyl group, which may have a substituent,
and an aromatic heterocyclic group such as thienyl group and
pyridyl group. Among these, preferred are those resulting from
condensation of two or three 5-membered rings, 6-membered rings or
5-membered and/or 6-membered rings, or those resulting from direct
bonding of two or more of these rings. Between the aromatic
hydrocarbon ring group and the aromatic heterocyclic group, the
aromatic hydrocarbon ring group is preferred.
[0193] Examples of the substituent which Ar to Ar can have include
the same groups as described above for the substituent of the
aromatic hydrocarbon ring group or aromatic heterocyclic group
represented by, for example, R.sup.101 to R.sup.106.
[0194] Specific preferred examples of the compound represented by
formula (VI) are set forth below, however, the present invention is
not limited thereto. 41
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