U.S. patent application number 10/856043 was filed with the patent office on 2007-07-05 for organic electroluminescence device.
Invention is credited to Mari Ichimura, Mitsuhiro Kashiwabara, Yukinari Sakamoto, Shinichiro Tamura.
Application Number | 20070152566 10/856043 |
Document ID | / |
Family ID | 33128267 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070152566 |
Kind Code |
A1 |
Sakamoto; Yukinari ; et
al. |
July 5, 2007 |
ORGANIC ELECTROLUMINESCENCE DEVICE
Abstract
An organic electroluminescence device including an organic layer
having a light emission region and being disposed between an anode
and a cathode is provided. The organic layer contains, as an
organic light-emitting material, a compound represented by the
following formula (1): ##STR1## wherein each of R.sub.1 to R.sub.26
represents a substituents, such as a hydrogen atom, a halogen atom,
a hydroxyl group, a mercapto group, a nitro group, an amino group,
a cyano group, an alkyl group, an alkenyl group, a cycloalkyl
group, an alkoxy group, an alkylthio group, a silyl group, an
alkylsilyl group, a siloxanyl group, an aralkyl group, an aromatic
hydrocarbon group, an aromatic heterocyclic group, an ester group,
an aryloxy group, a formyl group, an alkoxycarbonyl group, and a
carboxyl group, and n.sub.1 is a numeric value from 1 to 3.
Inventors: |
Sakamoto; Yukinari;
(Kanagawa, JP) ; Ichimura; Mari; (Kanagawa,
JP) ; Kashiwabara; Mitsuhiro; (Kanagawa, JP) ;
Tamura; Shinichiro; (Kanagawa, JP) |
Correspondence
Address: |
BELL, BOYD & LLOYD, LLP
P. O. BOX 1135
CHICAGO
IL
60690
US
|
Family ID: |
33128267 |
Appl. No.: |
10/856043 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
313/504 ;
257/E51.049; 428/690; 428/917 |
Current CPC
Class: |
Y10S 428/917 20130101;
H01L 51/0054 20130101; H01L 51/0059 20130101; H01L 51/5036
20130101; H01L 51/0081 20130101; H01L 51/0058 20130101; H01L 51/006
20130101 |
Class at
Publication: |
313/504 ;
428/690; 428/917; 257/E51.049 |
International
Class: |
H01L 51/54 20060101
H01L051/54 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2003 |
JP |
P2003-152189 |
Claims
1. An organic electroluminescence device comprising: an organic
layer having a light emission region that emits white light and
being disposed between an anode and a cathode, wherein the organic
layer contains, as an organic light-emitting material, a compound
represented by a following formula (1): ##STR27## where each of
R.sub.1 to R.sub.26 represents a substituent selected from the
group consisting of a hydrogen atom, a halogen atom, a hydroxyl
group, a mercapto group, a nitro group, an amino group, a cyano
group, an alkyl group, an alkenyl group, a cycloalkyl group, an
alkoxy group, an alkylthio group, a silyl group, an alkylsilyl
group, a siloxanyl group, an aralkyl group, an aromatic hydrocarbon
group, an aromatic heterocyclic group, an ester group, an aryloxy
group, a formyl group, an alkoxycarbonyl group, and a carboxyl
group, and n.sub.1 is a numeric value ranging from 1 to 3, wherein
the compound emits white light or substantially white light.
2. The organic electroluminescence device according to claim 1,
wherein each of R.sub.1 to R.sub.26 represents a substituent
selected from the group consisting of a hydrogen atom, an alkyl
group, an alkoxy group, an aromatic hydrocarbon group, and an
aromatic heterocyclic group.
3. The organic electroluminescence device according to claim 2,
wherein the organic electroluminescence device emits white
light.
4. An organic electroluminescence device comprising: an organic
layer having a light emission region that emits white light and
being disposed between an anode and a cathode, wherein the organic
layer contains, as an organic light-emitting material, a compound
represented by a following formula (2): ##STR28## where each of
R.sub.1 to R.sub.26 represents a substituent selected from the
group consisting of a hydrogen atom, a halogen atom, a hydroxyl
group, a mercapto group, a nitro group, an amino group, a cyano
group, an alkyl group, an alkenyl group, a cycloalkyl group, an
alkoxy group, an alkylthio group, a silyl group, an alkylsilyl
group, a siloxanyl group, an aralkyl group, an aromatic hydrocarbon
group, an aromatic heterocyclic group, an ester group, an aryloxy
group, a formyl group, an alkoxycarbonyl group, and a carboxyl
group, wherein the compound emits white light or substantially
white light.
5. The organic electroluminescence device according to claim 4,
wherein each of R.sub.1 to R.sub.26 represents a substituent
selected from the group consisting of a hydrogen atom, an alkyl
group, an alkoxy group, an aromatic hydrocarbon group, and an
aromatic heterocyclic group.
6. The organic electroluminescence device according to claim 5,
wherein the organic electroluminescence emits white light.
7. The organic electroluminescence device according to claim 4,
wherein the compound has a following structural formula (3):
##STR29##
8. The organic electroluminescence device according to claim 4,
wherein the compound has a following structural formula (4):
##STR30##
9. The organic electroluminescence device according to claim 4,
wherein the compound has a following structural formula (5):
##STR31##
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. P2003-152189, filed on May 29, 2003, the disclosure
of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to an organic
electroluminescence device. More specifically, the present
invention relates to an organic electroluminescence device having a
layered structure and emitting white or substantially white
light.
[0003] An organic electroluminescence device is a device which
itself emits light, and has features such that it can emit light
with wide viewing angle and high luminance and can be reduced in
thickness, and therefore, application of the device to
next-generation flat display or its flat light source has attracted
attention. The method for achieving full-color display using the
organic electroluminescence device may be roughly classified into
the following three methods.
[0004] The first one is a method in which light emitting portions
respectively for red (R), green (G), and blue (B) are formed on a
flat surface, for example, by a resistance heating deposition
method using a metal mask. In the manufacturing process for this
display, RGB, i.e., three types of elements (subpixels) are
individually formed on the same substrate and combined to form one
pixel. Therefore, there is a need to prepare a deposition mask
having a fine pattern for pixels and align it on the substrate with
high accuracy. This can be problematic in that the productivity is
low and the cost is high in the manufacturing process.
[0005] The second one is a method in which full-color display is
made using an organic light-emitting layer which emits
monochromatic light, for example, blue light, and a color changing
layer, provided on the forward side as viewed in the light emitting
direction, for changing the blue light to red or green light.
[0006] The third one is a method in which light emitted from an
organic electroluminescence device emitting white light is divided
into RGB using a color filter. In the method of obtaining arbitrary
light by using the white-light emitting layer and the color filter
in combination, there is no need to align a deposition mask to
produce individual colors of light, and therefore the number of
manufacturing steps may be reduced, making it possible to improve
the productivity in the manufacturing process and suppress the
cost.
[0007] Examples of methods for obtaining white light emission
include: (1) a method using RGB light emitting layers in
combination; (2) a method for allowing a single or a plurality of
light emitting layers to emit light having two wavelengths which
have the relationship of complementary colors, such as, bluish
green and red light, or blue and yellow to orange light; and (3) a
method utilizing exciplex emission. As the method (1) above, a
method in which blue-, green-, and red-light emitting layers are
stacked on one another to obtain white light has been proposed
(see, Japanese Patent Application Publication No. 07-142169). The
method (2) above includes a method in which two light-emitting
layers for individual colors are stacked (see, Japanese Patent
Application Publication No. 06-158038 and 07-65958), a method in
which emission of two colors of light is obtained from a single
light emitting layer (see, Japanese Patent Application Publication
No. 09-208946), and the like. As the method (3) above, a
white-light device using a boron-hydroxyphenylpyridine complex
(see, Angew. Chem. Int. Ed. 2002, 41, No. 1) and the like have been
reported.
SUMMARY OF THE INVENTION
[0008] The present invention generally relates to an organic
electroluminescence device. More specifically, the present
invention relates to an organic electroluminescence device having a
layered structure and emitting white or substantially white
light.
[0009] It is desirable to provide an organic electroluminescence
device whose productivity is higher and which has a layered
structure that can emits white or substantially white light and is
less complex in structure pursuant to an embodiment of the present
invention.
[0010] According to an embodiment of the present invention, there
is provided an organic electroluminescence device which includes an
organic layer having a light emission region and being disposed
between an anode and a cathode. The organic layer contains, as an
organic light-emitting material, a compound represented by the
following formula (1) in an embodiment: ##STR2##
[0011] where each of R.sub.1 to R.sub.26 independently represents a
substituents, such as a hydrogen atom, a halogen atom, a hydroxyl
group, a mercapto group, a nitro group, an amino group, a cyano
group, an alkyl group, an alkenyl group, a cycloalkyl group, an
alkoxy group, an alkylthio group, a silyl group, an alkylsilyl
group, a siloxanyl group, an aralkyl group, an aromatic hydrocarbon
group, an aromatic heterocyclic group, an ester group, an aryloxy
group, a formyl group, an alkoxycarbonyl group, a carboxyl group,
and the like and n.sub.1 is a numeric value from 1 to 3.
[0012] According to another embodiment of the present invention,
there is provided an organic electroluminescence device, wherein,
in the formula (1) discussed above for the compound, each of
R.sub.1 to R.sub.26 independently represents a substituent, such as
a hydrogen atom, an alkyl group, an alkoxy group, an aromatic
hydrocarbon group, an aromatic heterocyclic group and the like.
[0013] In an embodiment, the organic electroluminescence device
emits white light.
[0014] In yet another embodiment of the present invention, there is
provided an organic electroluminescence device which includes an
organic layer having a light emission region and being disposed
between an anode and a cathode. The organic layer contains, as an
organic light-emitting material, a compound represented by the
following formula (2): ##STR3##
[0015] where each of R.sub.1 to R.sub.26 independently represents a
substituents, such as a hydrogen atom, a halogen atom, a hydroxyl
group, a mercapto group, a nitro group, an amino group, a cyano
group, an alkyl group, an alkenyl group, a cycloalkyl group, an
alkoxy group, an alkylthio group, a silyl group, an alkylsilyl
group, a siloxanyl group, an aralkyl group, an aromatic hydrocarbon
group, an aromatic heterocyclic group, an ester group, an aryloxy
group, a formyl group, an alkoxycarbonyl group, a carboxyl group
and the like.
[0016] In still yet another embodiment of the present invention,
there is provided an organic electroluminescence device, wherein,
in the formula (2) discussed above for the compound, each of
R.sub.1 to R.sub.26 represents a substituent, such as a hydrogen
atom, an alkyl group, an alkoxy group, an aromatic hydrocarbon
group, an aromatic heterocyclic group and the like. In an
embodiment, the organic electroluminescence device emits white
light.
[0017] In a further embodiment of the present invention, there is
provided an organic electroluminescence device, wherein, as the
compound represented by the formula (2) above, a compound
represented by the following structural formula (3) is used:
##STR4##
[0018] According to yet a further embodiment of the present
invention, there is provided an organic electroluminescence device,
wherein, as the compound represented by the formula (2) above, a
compound represented by the following structural formula (4) is
used: ##STR5##
[0019] According to still yet a further embodiment of the present
invention, there is provided an organic electroluminescence device,
wherein, as the compound represented by the formula (2) above, a
compound represented by the following structural formula (5) is
used: ##STR6##
[0020] The compound represented by the formula (1) described an
above in embodiment is a compound which itself emits white or
substantially white light, namely, a single compound having
respective peak tops in the RGB regions. Therefore, by passing
light emitted from a light emitting material containing this
compound through a color filter, the light may be divided into RGB
individual pixels. Thus, an organic electroluminescence device
having a simple layered structure can be prepared pursuant to an
embodiment of the present invention.
[0021] Further, if an appropriate blue-light material is used as a
host and the above light emitting material is used as a dopant to
correct the B (blue) region, more complete white light may be
obtained according to an embodiment.
[0022] According to an embodiment of the present invention, there
may be provided an organic electroluminescence device whose
productivity is higher and which has a simpler layered structure
that can emits white or substantially white light.
[0023] Additional features and advantages of the present invention
are described in, and will be apparent from, the following Detailed
Description of the Invention and the figures.
BRIEF DESCRIPTION OF THE FIGURES
[0024] FIG. 1 is a diagram showing a fluorescence spectrum of the
compound of the structural formula (3) used in an organic
electroluminescence device according to an embodiment of the
present invention.
[0025] FIG. 2 is a diagrammatic cross-sectional view of one example
of an organic electroluminescence device according to an embodiment
of the present invention.
[0026] FIG. 3 is a diagrammatic cross-sectional view of another
example of an organic electroluminescence device according to an
embodiment of the present invention.
[0027] FIG. 4 is a diagram showing an emission spectrum of the
organic electroluminescence device prepared in Example 1.
[0028] FIG. 5 is a diagram showing the result of a
voltage-luminance measurement with respect to one example of an
organic electroluminescence device according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention generally relates to an organic
electroluminescence device. More specifically, the present
invention relates to an organic electroluminescence device having a
layered structure and emitting white or substantially white
light.
[0030] Various embodiments of the present invention will be
described below in greater detail.
[0031] In an embodiment of the present invention, examples of an
"organic layer having a light emission region" can include a
two-layer type including a hole transport layer and a light
emitting layer; a three-layer type including a hole transport
layer, a light emitting layer, and an electron transport layer; a
five-layer type including a hole injection layer, a hole transport
layer, a light emitting layer, an electron transport layer, and an
electron injection layer, and the like.
[0032] The phrase "the organic layer contains, as an organic
light-emitting material, a compound" or other like terms means that
the compound of the formula (1) is contained in at least one layer
of the above-mentioned layers and contributes to the light
emission. With respect to the use of the compound in an embodiment
of the present invention in the organic layer, either the compound
of the formula (1) may be solely used, or the compound of the
formula (1) as a dopant and a host material may used in
combination.
[0033] The compound used as an organic light-emitting material in
an embodiment of the present invention is represented by the
formula (1) wherein each of R.sub.1 to R.sub.26 independently
represents a substituent, for example, a hydrogen atom, a halogen
atom, a hydroxyl group, a mercapto group, a nitro group, an amino
group, a cyano group, an alkyl group, an alkenyl group, a
cycloalkyl group, an alkoxy group, an alkylthio group, a silyl
group, an alkylsilyl group, a siloxanyl group, an aralkyl group, an
aromatic hydrocarbon group, an aromatic heterocyclic group, an
ester group, an aryloxy group, a formyl group, an alkoxycarbonyl
group, a carboxyl group, and the like and n.sub.1 is a numeric
value from 1 to 3. Preferably, each of R.sub.1 to R.sub.26
represents a substituent, such as a hydrogen atom, an alkyl group,
an alkoxy group, an aromatic hydrocarbon group, an aromatic
heterocyclic group and the like.
[0034] Further, in the formula (1) above, it is preferred that
n.sub.1 is 1. Corresponding to the formula (2) above, and, in this
case, in the formula, each of R.sub.1 to R.sub.26 independently
represents a substituent, such as a hydrogen atom, a halogen atom,
a hydroxyl group, a mercapto group, a nitro group, an amino group,
a cyano group, an alkyl group, an alkenyl group, a cycloalkyl
group, an alkoxy group, an alkylthio group, a silyl group, an
alkylsilyl group, a siloxanyl group, an aralkyl group, an aromatic
hydrocarbon group, an aromatic heterocyclic group, an ester group,
an aryloxy group, a formyl group, an alkoxycarbonyl group, a
carboxyl group and the like. It is preferred that each of R.sub.1
to R.sub.26 independently represents a substituent, such as a
hydrogen atom, an alkyl group, an alkoxy group, an aromatic
hydrocarbon group, an aromatic heterocyclic group and the like.
[0035] The number of carbon atoms contained in each of the alkyl
group and the alkoxy group are 20 or less in an embodiment. The
number of carbon atoms contained in each of the aromatic
hydrocarbon group and the aromatic heterocyclic group are 30 or
less in an embodiment. For example, the following compound
represented by structural formulae (1-1) to (1-4) can be used for
the alkoxy group, structural formulae (1-5) to (1-6) can be used
for the aromatic hydrocarbon group (aryl group), and structural
formulae (1-7) to (1-8) for the aromatic heterocyclic group
according to an embodiment. ##STR7## ##STR8## ##STR9##
##STR10##
[0036] Further, in addition to the compounds represented by the
structural formulae (3) to (5) discussed above, as examples of the
compounds of the formula (2), compounds represented by the
following structural formulae (6) to (30) can be used in an
embodiment: ##STR11## ##STR12## ##STR13## ##STR14## ##STR15##
##STR16## ##STR17## ##STR18## ##STR19## ##STR20## ##STR21##
##STR22##
[0037] There is correlation between an emission spectrum of the
organic electroluminescence device and a fluorescence spectrum of
the organic light-emitting material. The compound represented by
the formula (1) or (2), especially the group of compounds
represented by the structural formulae (3) to (30) has
characteristic fluorescence wavelengths having respective peak tops
in the RGB regions. For example, a fluorescence spectrum of the
compound of the structural formula (3) as a representative compound
is shown in FIG. 1. As can be seen in FIG. 1, the compound has
respective peak tops near the RGB regions, although the intensity
in the B region is slightly low.
[0038] By passing light emitted from the organic light-emitting
material through a color filter, the light can be divided into RGB.
For example, by effecting a color filter on the organic
electroluminescence device which includes the organic layer having
a light emission region and being disposed between an anode and a
cathode, wherein the light emitting layer contains, as the organic
light-emitting material, at least one compound such as compounds
represented by the formulae (1) and (2), especially the compounds
represented by the structural formulae (3) and (6) to (16) wherein
the light emitted from the device can be divided into RGB
individual pixels.
[0039] Further, by effecting a color filter on the organic
electroluminescence device which includes the organic layer having
a light emission region and being disposed between an anode and a
cathode, wherein the light emitting layer contains, as the organic
light-emitting material, at least one compound, such as compounds
represented by the formulae (1) and (2), especially the compounds
represented by the structural formulae (3) and (6) to (16), wherein
the intensities of RGB can be made at the same level in order to
obtain white light.
[0040] The organic light-emitting material in an embodiment can be
either solely used in the light emitting layer or used in
combination with a blue-light emitting layer made of a blue-light
material, which appropriately corrects the spectrum in the B (blue)
region, to form a layered structure. Alternatively, the organic
light-emitting material can be the combination of a host material
and a dopant. In this case, a light emitting material emitting blue
light as a host and at least one light emitting material
represented by the formula (1) as a dopant are used in combination
in the light emitting layer to obtain white light. The light
emitting layer can be of either a single layer or a layered
structure having two or more layers.
[0041] The compound in an embodiment of the present invention is
generally contained in the light emitting layer as mentioned above,
but it may be contained in another layer in the organic layer
having a light emission region.
[0042] According to the embodiment of the present invention, RGB
light emission can be obtained from a single chemical species.
Therefore, there is provided a light emitting device which stably
emits light without causing color drift, resulting in remarkable
advantages from the viewpoint of the technique and cost in the
manufacturing process. Further, white light can be obtained from
the device having a considerably simple layered structure.
[0043] Another embodiment of the present invention will be
described below with reference to the drawings.
[0044] FIG. 2 is a diagrammatic cross-sectional view of one example
of an organic electroluminescence device according to the present
embodiment. The organic electroluminescence device includes an
anode 2, an organic layer 3 having a light emission region, and a
cathode 4, which are formed on a substrate 1 in this order from
bottom. This organic electroluminescence device is a top emission
type organic electroluminescence device which emits light from the
side of the cathode.
[0045] In the substrate 1, glass, a plastic, or another material
may be used if it is applicable. When the organic
electroluminescence device and another display device are used in
combination, the substrate 1 may be shared by them. As the anode 2,
one having a layered structure including an indium tin oxide (ITO)
layer can be used.
[0046] The organic layer 3 contains an organic light-emitting
material represented by the formula (1) above. With respect to the
organic layer 3, as the construction of layers for obtaining
organic electroluminescence, various types of constructions
conventionally known can be employed. For example, if the material
constituting any one of the hole transport layer and the electron
transport layer has light emission properties, a structure obtained
by stacking thin films of the hole transport layer and electron
transport layer may be used.
[0047] For improving the charge transport performance to an extent
such that the effect addressed in the present invention is not
sacrificed, in any one of or both of the hole transport layer and
the electron transport layer, a structure obtained by stacking thin
films of a plurality of materials, or a thin film made of a mixture
of a plurality of materials may be used. For improving the light
emission performance, a structure including a thin film of at least
one fluorescent material disposed between the hole transport layer
and the electron transport layer, or the above structure in which
any one of or both of the hole transport layer and the electron
transport layer contain at least one fluorescent material can be
used. In the above cases, for improving the light emission
efficiency, a thin film for controlling the hole or electron
transport can be further incorporated into the construction of
layers in an embodiment.
[0048] As the electrode material for the cathode 4, an alloy of an
active metal, such as Li, Mg, Ca, or the like and a metal, such as
Ag, Al, In, and the like or a structure obtained by staking these
metals on one another may be used. In the organic
electroluminescence device which emits light from the side of the
cathode, by selecting the thickness of the cathode, a light
transmittance suitable for the desired application can be
obtained.
[0049] FIG. 3 is a diagrammatic cross-sectional view of an organic
electroluminescence device having a construction such that a color
filter 5 is provided on a cathode 4 to divide white light emitted
from an organic layer 3 into RGB pixels as described below. In this
case, by passing the white light emitted from the organic layer 3
through the color filter 5 which passes only light having a
specific wavelength in RGB to cut off other wavelengths, the white
light can be divided into RGB pixels.
[0050] In the above embodiment, an explanation is made on the
so-called top emission type organic electroluminescence device
which emits light from the side of the electrode on top, but the
present invention is not limited to this type and may also be
applied to a so-called bottom emission type organic
electroluminescence device which emits light from the side of the
electrode on bottom. The bottom emission type organic
electroluminescence device includes, for example, a light
transmitting anode made of an ITO or the like formed on a glass
substrate, an organic layer having a light emission region formed
on the anode, and a light reflecting cathode formed on the organic
layer.
EXAMPLES
[0051] The organic electroluminescence device according to an
embodiment of the present invention will be described below with
reference to the following Examples, which are illustrative of the
present invention and thus should not be construed as limiting the
scope thereof.
Synthesis Example
[0052] A compound represented by the structural formula (3) above
was synthesized by a Suzuki coupling method using 2,6-dibromopyrene
and 1-Pyrene boronic acid in toluene-water in the presence of
Pd(PPh.sub.3).sub.4 (tetrakis (triphenylphosphine) palladium) and
Na.sub.2CO.sub.3. The reaction formula for the synthesis is as
follows. ##STR23##
[0053] The resultant product was identified by a molecular ion peak
(m/z 602) in a mass spectrum. A fluorescence spectrum of this
compound in the form of thin film is shown in FIG. 1. Compounds
represented by the structural formulae (4) and (5) were
individually synthesized in the same manner and used in the
following Examples.
Example 1
[0054] The present Example is an example in which an organic
electroluminescence device having a layered structure including a
blue-light emitting layer made of a blue-light material and the
compound represented by the structural formula (4) above was
prepared.
[0055] First, a 30 mm.times.30 mm substrate having formed on one
surface an anode made of a stacked film including an ITO layer was
set in a vacuum deposition machine. The anode had the total
thickness of 130 nm including layers of ITO of 20 nm, Ag alloy of
100 nm and ITO of 10 nm, starting from a side of the substrate. The
substrate was a TFT substrate, which contain TFTs (Thin Film
Transistors) for driving, covered with a planarized insulation
film. On the anode, as a hole injection layer, m-MIDATA
(4,4',4''-tris (3-methylphenylphenyl-amino) triphenylamine)
represented by the structural formula below was deposited by a
vacuum deposition method in a vacuum at 10.sup.-4 Pa or less so
that the thickness of the resultant film was 10 nm. On the hole
injection layer, .alpha.-NPD
(N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl4,4'-diamine)
represented by the structural formula below was deposited as a hole
transport layer material directly on the hole injection layer so
that the thickness of the resultant film was 100 nm. The deposition
rate was 0. 1 nm/second. ##STR24##
[0056] Subsequently, as a light emitting layer, DPVBi (4,4'-Bis
(2,2-diphenyl-ethen-1-yl) -diphenyl) (emitting blue light)
represented by the structural formula below was deposited directly
on the hole transport layer so that the thickness of the resultant
film was 10 nm. ##STR25##
[0057] Then, the compound of the structural formula (4) was
deposited directly on the DPVBi so that the thickness of the
resultant film became 25 nm.
[0058] Next, Alq.sub.3 {tris(8-hydroxyquinolinato)aluminum} of the
structural formula below was deposited as an electron transport
layer material at a deposition rate of 0.2 nm/second so that the
thickness of the resultant film became 30 nm. ##STR26##
[0059] As materials for a cathode, Mg and Ag were used with a ratio
of Mg:Ag=9:1, and they were co-deposited at a deposition rate of 1
nm/second so that the resultant film had such a thickness that it
was able to transmit light, for example, 70 nm. On the cathode, a
passivation film made of SiNx was formed. Furthermore, on the
passivation layer, thermosetting resin was applied and a glass
substrate was placed thereon. The cathode with these structures
described above is heated for curing the thermosetting resin to
complete sealing. As described above, an example of the organic
electroluminescence device shown in FIG. 2 was prepared.
[0060] A forward bias direct voltage was applied to the thus
prepared organic electroluminescence device in Example 1 in a
nitrogen gas atmosphere to evaluate the light emission properties.
The light emitted was white, and a spectrophotometry measurement
offered a spectrum having emission peaks around 460 nm, 560 nm, and
600 nm shown in FIG. 4. In the spectrophotometry measurement, a
spectrophotometer using a photodiode array, manufactured and sold
by Otsuka Electronics Co., Ltd., as a detector was used.
[0061] In addition, a voltage-luminance measurement was carried
out. The result shown in FIG. 5 was obtained, and a luminance of
1,000 cd/m.sup.2 was obtained at 8 V. The emission efficiency was 6
cd/A.
[0062] The organic electroluminescence device prepared was allowed
to stand in a nitrogen gas atmosphere for one month, but no
deterioration was observed in the device. Further, a fixed current
was permitted to flow through the organic electroluminescence
device at an initial luminance of 500 cd/m.sup.2 so that the device
continuously emitted light and suffered forced deterioration. As a
result, it was found that a 1,000-hour period of time was required
until the luminance reduced by half.
[0063] Example 2
[0064] The present Example is an example in which an organic
electroluminescence device using the compound represented by the
structural formula (3) above as a dopant material was prepared. The
doping concentration of the light emitting layer is not limited to
that in the present Example.
[0065] First, a 30 mm.times.30 mm glass substrate having formed on
one surface an anode made of a stacked film including an ITO layer
and having a thickness of 100 nm was set in a vacuum deposition
machine. On the anode, as a hole injection layer, the above
m-MTDATA was deposited by a vacuum deposition method in a vacuum at
10.sup.-4 Pa or less so that the thickness of the resultant film
became 10 nm. On the hole injection layer, the above .alpha.-NPD
was deposited as a hole transport layer material directly on the
hole injection layer so that the thickness of the resultant film
became 100 nm. The deposition rate was 0.1 nm/second.
[0066] Subsequently, as a light emitting layer, the compound
represented by the structural formula (3) above and the above DPVBi
were co-deposited at, respectively, 0.02 nm/second and 0.2
nm/second directly on the hole transport layer so that the
thickness of the resultant film was 40 nm.
[0067] Then, Alq.sub.3 {tris(8-hydroxyquinolinato)aluminum} of the
structural formula above was deposited as an electron transport
layer material so that the thickness of the resultant film was 15
nm to form an electron transport layer. The deposition rate was 0.2
nm/second.
[0068] As materials for a cathode, Mg and Ag were used, and they
were co-deposited at a deposition rate of 1 nm/second so that the
thickness of the resultant film became 5 to 50 nm, thus preparing
an organic electroluminescence device shown in FIG. 2.
[0069] A forward bias direct voltage was applied to the thus
prepared organic electroluminescence device in Example 2 in a
nitrogen gas atmosphere to evaluate the light emission properties.
The light emitted was white, and a spectrophotometry measurement
offered a spectrum having emission peaks around 470 nm, 550 nm, and
600 nm. In the spectrophotometry measurement, a spectrophotometer
using a photodiode array, manufactured and sold by Otsuka
Electronics Co., Ltd., as a detector was used. In addition, a
voltage-luminance measurement was carried out. As a result, a
luminance of 900 cd/m.sup.2 was obtained at 8 V. The emission
efficiency was 5 cd/A.
[0070] The organic electroluminescence device prepared was allowed
to stand in a nitrogen gas atmosphere for one month, but no
deterioration was observed in the device. Further, a fixed current
was permitted to flow through the organic electroluminescence
device at an initial luminance of 500 cd/m.sup.2 so that the device
continuously emitted light and suffered forced deterioration. As a
result, it was found that a 1,300-hour period of time was required
until the luminance reduced by half.
[0071] Example 3
[0072] The present Example is an example in which an organic
electroluminescence device using a single film made of the compound
represented by the structural formula (5) in the light emitting
layer was prepared.
[0073] First, a 30 mm.times.30 mm glass substrate having formed on
one surface an anode made of a stacked film including an ITO layer
and having a thickness of 100 nm was set in a vacuum deposition
machine. On the anode, as a hole injection layer, the above
m-MTDATA was deposited by a vacuum deposition method in a vacuum at
10.sup.-4 Pa or less so that the thickness of the resultant film
was 50 nm. On the hole injection layer, the above .alpha.-NPD was
deposited as a hole transport layer material directly on the hole
injection layer. The thickness of the hole transport layer made of
.alpha.-NPD was 45 nm, and the deposition rate was 0.1
nm/second.
[0074] Then, as a light emitting layer, the compound represented by
the structural formula (5) was deposited directly on the hole
transport layer so that the thickness of the resultant film was 30
nm. Then, Alq.sub.3 (tris(8-hydroxyquinolinato)aluminum) of the
structural formula above was deposited as an electron transport
layer material. The thickness of the electron transport layer made
of Alq.sub.3 was 35 nm, and the deposition rate was 0.2
nm/second.
[0075] As materials for a cathode, Mg and Ag were used, and they
were co-deposited at a deposition rate of 1 nm/second so that the
thickness of the resultant film about 5 nm to about 50 nm, thus
preparing an organic electroluminescence device shown in FIG.
2.
[0076] A forward bias direct voltage was applied to the thus
prepared organic electroluminescence device in a nitrogen gas
atmosphere to evaluate the light emission properties. The light
emitted was yellowish white, and a spectrophotometry measurement
offered a spectrum having emission peaks around 450 nm, 550 nm, and
600 nm. In the spectrophotometry measurement, a spectrophotometer
using a photodiode array, manufactured and sold by Otsuka
Electronics Co., Ltd., as a detector was used. In addition, a
voltage-luminance measurement was carried out. As a result, a
luminance of 900 cd/m.sup.2 was obtained at 8 V. The emission
efficiency was 4 cd/A.
[0077] The organic electroluminescence device prepared was allowed
to stand in a nitrogen gas atmosphere for one month, but no
deterioration was observed in the device. Further, a fixed current
was permitted to flow through the organic electroluminescence
device at an initial luminance of 500 cd/m.sup.2 so that the device
continuously emitted light and suffered forced deterioration. As a
result, it was found that a 700-hour period of time was required
until the luminance reduced by half.
[0078] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present invention and without diminishing its intended
advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *