U.S. patent application number 14/532458 was filed with the patent office on 2015-03-05 for organic electroluminescence device.
The applicant listed for this patent is Sony Corporation. Invention is credited to Yasunori Kijima, Eisuke Matsuda, Shigeyuki Matsunami, Hirofumi Nakamura, Tetsuo Shibanuma.
Application Number | 20150060837 14/532458 |
Document ID | / |
Family ID | 37069537 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150060837 |
Kind Code |
A1 |
Shibanuma; Tetsuo ; et
al. |
March 5, 2015 |
ORGANIC ELECTROLUMINESCENCE DEVICE
Abstract
An organic electroluminescence device including a lower
electrode disposed on a substrate, an organic layer having at least
a light emission layer and disposed above the lower electrode, and
upper electrode having a transparent conductive film and disposed
above the organic layer, in which the device has an electron
injecting layer between the organic layer and the upper electrode.
The electron injecting layer has a buffer layer comprising an
insulative material and a mixed layer comprising an organic
material that has an electron transporting property and a metal
material that has an electron injecting property.
Inventors: |
Shibanuma; Tetsuo;
(Kanagawa, JP) ; Matsuda; Eisuke; (Kanagawa,
JP) ; Kijima; Yasunori; (Tokyo, JP) ;
Nakamura; Hirofumi; (Kanagawa, JP) ; Matsunami;
Shigeyuki; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sony Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
37069537 |
Appl. No.: |
14/532458 |
Filed: |
November 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11278456 |
Apr 3, 2006 |
8906517 |
|
|
14532458 |
|
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Current U.S.
Class: |
257/40 |
Current CPC
Class: |
H01L 51/0059 20130101;
H05B 33/22 20130101; H01L 51/5092 20130101; Y10S 428/917 20130101;
H01L 51/5278 20130101; H01L 27/3209 20130101; H05B 33/28 20130101;
H01L 51/5072 20130101; H01L 51/0081 20130101; H01L 2251/5315
20130101; H01L 51/5234 20130101; H01L 51/5056 20130101 |
Class at
Publication: |
257/40 |
International
Class: |
H01L 27/32 20060101
H01L027/32; H01L 51/50 20060101 H01L051/50 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2005 |
JP |
2005-107036 |
Jun 17, 2005 |
JP |
2005-177215 |
Claims
1. A display device comprising: a plurality of light emission units
laminated between a lower electrode and an upper electrode, where
each light emission unit comprises at least an organic light
emission layer; and a connection layer is between the respective
light emission units, wherein, the organic light emission layer in
each light emission unit includes a hole injection layer, a hole
transporting layer, a light emission layer, an electron
transporting layer in direct succession in the recited order,
beginning on the lower electrode, the connection layer having a
laminate part comprising (1) a buffer layer of a thickness of 1 nm
or less in contact with the organic light emission layer, the
buffer layer (a) employing an oxide which contains at least one of
an alkali metal and an alkaline-earth metal, and (b) the buffer
layer having a hole blocking property resulting from disposing the
buffer layer in contact with the organic light emission layer, (2)
a mixed layer employing a charge transporting organic material
having an electron transporting property and a metal material
having an electron injecting property, the mixed layer being
composed of the same material as the electron transporting layer in
the organic light emission layer, the metal material reacts while
reducing the charge transporting organic material to become
transparent to ensure the electron injecting property, and (3) a
protective layer employing at least one of triphenylene derivatives
and azatriphenylene derivatives, the protective layer is oxidized
to become light permeable to prevent oxidation of the mixed layer,
are successively laminated from the lower electrode side in direct
succession.
2. The display device according to claim 1, wherein the charge
transporting organic material constituting the connection layer is
an electron transporting organic material.
3. The display device according to claim 2, wherein the mixed layer
employing a charge transporting organic material comprises only an
electron transporting organic material.
4. The display device according to claim 1, wherein the charge
transporting organic material within the connection layer is a hole
transporting organic material.
5. The display device according to claim 4, wherein the buffer
layer, the mixed layer, and the protective layer were deposited
successively utilizing vapor deposition.
6. The display device according to claim 1, wherein the buffer
layer confines holes to the organic light emission layer.
7. The display device according to claim 1, wherein the layer
employing an oxide constitutes a boundary layer on the lower
electrode side in the connection layer.
8. The display device according to claim 1, wherein the oxide is at
least one selected from the group consisting of Li.sub.2Si0.sub.3,
Li.sub.2C0.sub.3, Cs.sub.2C0.sub.3, Li.sub.2W0.sub.4 and SrO.
9. A display device comprising in order a lower electrode, a light
emission layer, a buffer layer, and an upper electrode, wherein the
buffer layer includes ytterbium (Yb).
10. The light emission layer according to any one of claim 1,
wherein the light emission layer is also configured to be an
electron transporting light emission layer.
11. The light emission layer according to any one of claim 1,
wherein the light emission layer is also configured to be a hole
transporting light emission layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/278,456 filed Apr. 3, 2006, the entirety of
which is incorporated herein by reference to the extent permitted
by law. The present invention contains subject matter related to
Japanese Patent Application JP 2005-107036 filed on Apr. 4, 2005
and JP 2005-177215 filed on Jun. 17, 2005 in the Japanese Patent
Office, the entire contents of which are being incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention concerns an organic
electroluminescence device.
[0004] 2. Description of the Related Art
[0005] Organic electroluminescence devices are light emitting
devices capable of operating at low voltage and suitable to saving
of power consumption. Accordingly, they have now been used
generally as light emitting devices for use in display devices and
illumination devices. The organic electroluminescence device
usually has a structure in which a lower electrode, an organic
layer formed by laminating an organic hole transporting layer and
an organic light emitting layer, and an upper electrode in this
order above a substrate. Further, one of the lower electrode and
the upper electrode sandwiching the organic layer is used as an
anode and the other of them is used as a cathode.
[0006] A structure in which the upper electrode is formed as a
transparent electrode and emission light caused in the device is
taken out on the side of the upper electrode is referred to as a
top emission organic electroluminescence device. There is also a
structure of using a semi-transparent upper electrode thereby
resonating emission light generated in the device. Further, there
is also a structure of taking out light from both of the upper
electrode and the lower electrode.
[0007] In a structure using the upper electrode as a transparent
electrode, in a case of using the upper electrode as a cathode
(that is, transparent cathode), a portion in contact with the
organic layer has an electron injecting layer particularly formed
of a material having high light transmittance selected from
materials having low work function. However, it may be difficult to
find materials of sufficiently high light transmittance among the
materials having low work function.
[0008] Then, it has been proposed a first structure having an
electron injecting layer of a super thin film comprising a metal
material having low work function disposed to a portion on the side
of a cathode in contact with an organic layer, and a transparent
conductive layer comprising an Indium-Tin-Oxide (ITO),
Indium-Zinc-Oxide (IZO), etc. disposed further thereon (refer to JP
No. 3560375 and JP-A No. 10-162959).
[0009] Further, it has been proposed a second structure having the
electron injecting layer as a mixed layer comprising a metal
material having low work function and an electron transporting
organic material (refer to JP-A No. 10-162959).
[0010] Further, it has been proposed a third structure having an
electron injecting layer of a laminate structure. In this case, the
electron injecting layer is formed by laminating a metal layer
comprising a metal material having low work function, and a mixed
layer comprising a metal material having low work function and an
electron transporting organic material orderly from the side of the
organic layer. The electron injecting layer is disposed directly on
the light emission layer (refer to JP-A 2004-296410).
SUMMARY OF THE INVENTION
[0011] However, in the first structure and the second structure
described above, since the transparent conductive film comprising
ITO, etc. disposed on the electron injecting layer is usually
formed by a sputtering method in an oxygen atmosphere, a metal
material having low work function such as an alkali metal or an
alkaline earth metal forming the electron injecting layer is
oxidized upon formation of the transparent conductive layer. This
can no more ensure a sufficient electron injecting efficiency from
the electron injecting layer to the organic layer and no sufficient
life can be obtained compared with a device of using a
not-transparent cathode (for example, Mg--Ag alloy, Al, etc. of a
thick film of about 100 nm).
[0012] Further, in the third structure, the electron injecting
layer has a two-layered structure. Accordingly, during formation of
the transparent conductive film, the mixed layer that forms the
upper layer of the electron injecting layer serves as an oxidation
protective film to prevent oxidation of the metal layer disposed in
adjacent with the organic layer. Accordingly, the electron
injecting efficiency is not impaired. However, since the metal
layer is not oxidized as a result, light absorption inherent to the
metal remains and possibly making it difficult to ensure light
transmittance.
[0013] Further, in JP-A No. 2004-296410 that discloses the third
structure, the metal layer (electron injecting layer) is disposed
in contact with the light emission layer that forms the organic
layer. In this case, the electron injecting layer can not provide a
hole blocking property as a function inherent to the layer. Then,
holes can not be confined sufficiently in the light emission layer
to decrease the probability of re-combination between holes and
electrons in the light emission layer. Accordingly, light emission
efficiency is lowered. Further, since the metal layer (electron
injection layer) is disposed in contact with the light emission
layer that forms the organic layer, the electron transportability
increases excessively in the device. Accordingly, balance between
the holes and the electrons is worsened giving rise to a problem
that no sufficient luminance half-decay life can be obtained.
[0014] In view of the above, the present invention intends to
provide an organic electroluminescence device having a structure of
taking out emitted light on the side of an upper electrode used as
a cathode, in which the upper electrode of the organic layer has a
sufficient transmittance to the emission light, an appropriate
electron injecting efficiency and a hole blocking property from the
upper electrode to the organic layer are ensured properly thereby
capable of improving the light emission intensity and the light
emission life.
[0015] According to an embodiment of the invention, there is
provided an electroluminescence device including a lower electrode
disposed on a substrate, an organic layer having at least a light
emission layer and disposed above the lower electrode, and an upper
electrode having a transparent conductive film and disposed on the
organic layer. Particularly, a buffer layer formed of an insulative
material, and an electron injecting layer are laminated orderly
from the side of the organic layer between the organic layer and
the upper electrode. The electron injecting layer has a mixed layer
comprising an organic material that has an electron transporting
property and a metal material that has an electron injecting
property.
[0016] Since the buffer layer comprising the insulative material,
it can easily ensure the light transmittance. Further, since the
mixed layer comprises the organic material and the metal material,
the metal material reacts while reducing the organic material and
becomes transparent while ensuring the electron injecting property.
Accordingly, the light transmittance on the side of the upper
electrode of the organic layer is ensured sufficiently.
[0017] Further, due to the structure of disposing the buffer layer
comprising the insulating material in contact with the organic
layer, the buffer layer has the hole blocking property to the
organic layer. Accordingly, holes can be confined to the organic
layer. Further, since the electron injecting layer having a mixed
layer is disposed above the buffer layer, an appropriate electron
injecting property to the organic layer can be ensured by the
electron injecting layer.
[0018] According to the organic electroluminescence device as
described above, since the light transmittance is ensured on the
side of the upper electrode of the organic layer, the intensity of
light emission from the side of the upper electrode used as the
cathode can be improved. Further, since the appropriate electron
injecting efficiency from the upper electrode to the organic layer
can be ensured and the hole blocking property to the organic layer
can also be ensured, the light emission intensity and the light
emission life can be improved.
DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0019] FIG. 1 is a schematic cross sectional view showing the
structure of an organic electroluminescence device according to an
embodiment of the invention;
[0020] FIG. 2 is a graph showing a relation between an operating
time and an operating voltage in an organic electroluminescence
device of Examples 1, 2 and Comparative Example 1;
[0021] FIG. 3 is a graph showing a relation between an operating
time and a relative luminance in an organic electroluminescence
device of each of examples and comparative examples;
[0022] FIG. 4 is a schematic cross sectional view showing the
structure of an organic electroluminescence device according to
another embodiment of the invention;
[0023] FIG. 5 is a graph showing change with time of a relative
luminance (life curve) in display devices of Example 1' and
Comparative Examples 1' to 3';
[0024] FIG. 6 is a graph showing change with time of a relative
luminance (life curve) in display devices of Example 13' and
Comparative Examples 1' to 3';
[0025] FIG. 7 is a graph showing change with time of a relative
voltage in display devices of Example 1' and Comparative Examples
1' to 3'; and
[0026] FIG. 8 is a graph showing change with time of a relative
voltage in display devices of Example 13' and Comparative Examples
1' to 3'.
PREFERRED EMBODIMENTS OF THE INVENTION
[0027] An organic electroluminescence device and a display device
according to preferred embodiments of the present invention are to
be described specifically with reference to the drawings. FIG. 1 is
a cross sectional view schematically showing an organic
electroluminescence device of an embodiment according to the
invention.
[0028] An organic electroluminescence device 11 shown in the
drawing is disposed above a substrate 10. That is, in the organic
electroluminescence device 11, a lower electrode 13, an organic
layer 14, an electron injecting layer 15, and an upper electrode 16
are laminated successively above a substrate 10 and is adapted to
take out light emission on the side of the upper electrode 16. In a
display device using the organic electroluminescence device 11, a
plurality of organic electroluminescence devices 11 are formed
being arranged on every pixel on one identical substrate 10.
[0029] Detailed structures for the portions in the organic
electroluminescence device 11 are to be described from the side of
the substrate 10 successively.
[0030] At first, the substrate 10 is properly selected for use from
transparent substrates such as made of glass, silicon substrates,
and film-like flexible substrates. In a case where the operation
system of a display device using the organic electroluminescence
device 11 is an active matrix system, a TFT substrate in which
TFT(s) are disposed on every pixels is used as the substrate 10. In
this case, it is advantageous to use a display device of a top
emission organic electroluminescence device 11 of taking out
emission light only on the side opposite to the substrate 10 in
view of the rate of opening for pixels. Further, each of the
organic electroluminescence devices 11 has a structure of operating
by using TFT in this case. In a case where the organic
electroluminescence device 11 is a both side light emission type of
taking out emission light also on the side of the substrate 10, the
substrate 10 is formed of a material having light
transmittance.
[0031] Then, for the lower electrode 13 used as an anode on the
substrate 10, those having a high work function from the vacuum
level of the electrode material, for example, chromium (Cr), gold
(Au), alloy of tin oxide (SnO.sub.2) and antimony (Sb), alloy of
zinc oxide (ZnO) and aluminum (Al), as well as oxides of such
metals or alloys can be used each alone or in admixture in order to
efficiently inject holes.
[0032] Particularly, in a case where the organic
electroluminescence device 11 is of a top emission type, it is
possible to improve the efficiency of taking out light to the
outside by high reflectance effect by forming the lower electrode
13 of a high reflectance material. As the electrode material, for
example, an electrode mainly comprising Al, Ag, etc. is used
preferably. It is also possible to enhance the charge injecting
efficiency by disposing a transparent electrode material layer
having high work function, for example, ITO on the high reflectance
material layer.
[0033] In a case where the operation system for the display device
using the organic electroluminescence device 11 is of an active
matrix system, the lower electrode 13 is patterned on every pixels
to which TFTs are disposed. Then, a not illustrated insulative film
is disposed over the lower electrode 13 and the surface of the
anode 13 for each of the pixels is exposed through the openings in
the insulative film.
[0034] On the other hand, in a case where the organic
electroluminescence device 11 is of a both side light emission
type, the lower electrode 13 may be formed, for example, of a
transparent electrode material such as ITO.
[0035] The organic layer 14 disposed above the lower electrode 13
described above is formed by laminating a hole injecting layer 14a,
a hole transporting layer 14b, a light emission layer 14c, and an
electron transporting layer 14d successively from the side of the
lower electrode 13. There is no particular restriction on the
materials for forming each of the layers and those materials used
generally as the material for constituting each of the layers may
be used.
[0036] For example, hole transporting materials such as benzidine
derivatives, styrylamine derivatives, triphenylmethane derivatives,
and hydrazone derivatives can be used for the hole transporting
layer 14b. Further, organic materials such as perylene derivatives,
coumalin derivatives, pyran dyes, and triphenylamine derivatives
may be doped by a slight amount to the host material of the light
emission layer 14c. Further, electron transporting materials such
as Alq (quinolinol aluminum complex), phenanthroline derivatives,
Anthraquinodimethane derivatives, diphenylquinone derivatives,
oxadiazole derivatives, and perylene tetracarboxylic acid
derivatives can be used for the electron transporting layer
14d.
[0037] Each of the layers 14a to 14d described above may also have
other constituent factors. For example, the light emission layer
14d may also be an electron transporting light emission layer or a
hole transporting light emission layer. In this case, the layer
structure may be simplified by saving the electron transporting
layer 14d or the hole transporting layer 14b particularly. Further,
it is also possible to adopt a laminate structure for each of the
layers 14a to 14d. For example, the light emission layer 14c may be
a white light emission device formed of a blue light emission
portion, a green light emission portion, and a red light emission
portion. Further, it may adopt also a laminate structure in which
each of the hole injecting layer 14a and the hole transporting
layer 14b may have plural layers.
[0038] Each of the layers 14a to 14d forming the organic layer 14
described above can be prepared, for example, by a vacuum vapor
deposition method or other method, for example, a spin coating
method.
[0039] The buffer layer 15a disposed above the organic layer 14
comprises an insulative material. The buffer layer 15a has an
electron injecting property. As the insulative material, oxides,
composite oxides, silicates, carbonates, composite oxides, or
halides of metal materials having electron charging property are
used as the insulative material and, further, they may be used also
as a mixture with enhanced stability. Then, it is important to
select and use those materials of favorable light transmittance
from such insulative materials.
[0040] As the metal material having the electron injecting property
described above, metals having high electron injecting property
(that is, low work function), for example, metals having a work
function of 4.2 V or less are suitable and specific examples
include, preferably, alkali metals such as lithium (Li), sodium
(Na), potassium (K), and cesium (Cs), alkaline earth metals such as
barium (Ba), calcium (Ca), strontium (Sr), beryllium (Be), and
magnesium (Mg). In addition, they also include yttrium (Y),
lanthanum (La), samarium (Sm), gadolinium (Gd), ytterbium (Yb),
silver (Ag), aluminum (Al), indium (In), etc.
[0041] Specific examples of the insulative materials that form the
buffer layer 15a described above include, for example, Li.sub.2O as
lithium (Li) oxide and Cs.sub.20 as cesium (Cs) oxide and, further,
mixtures of such oxides. In addition, they also include, for
example, alkaline earth metals such as calcium (Ca) and barium (Ba)
and alkali metals such as lithium (Li) and cesium (Cs) and,
further, those metals having low work function such as indium (In),
magnesium (Mg), and silver (Ag), as well as fluorides, oxides, and
composite oxides of such metals, for example, oxysilicides and
oxycarbides. Among them, LiF is used preferably since the electron
injecting property is favorable and light transmittance is also
high.
[0042] Since the buffer layer 15a gives a favorable electron
injecting property in spite of the inherent insulative property
when it is formed as a super thin film using an insulative
material, the thickness thereof is preferably from 1 nm or
less.
[0043] A mixed layer 15b and the protective layer 15c are laminated
above the buffer layer 15a.
[0044] Among them, the mixed layer 15b comprises an organic
material having an electron transporting property and a metal
material having an electron injection property. For the organic
material having the electron transporting property, the same
material as that forming the electron transporting layer 14d in the
organic layer 14 is used. Particularly, for a combination having an
appropriate electron injecting property and capable of obtaining a
sufficient light emission efficiency and a luminance half-decay
life, it is preferred to use Alq as the organic material for the
electron transporting layer 14d and the mixed layer 15b described
above. Further, as the metal material having the electron injecting
property, at least one of the metal materials having low work
function described above is used suitably.
[0045] In the mixed layer 15b, the concentration of the metal
material is, preferably, about from 0.1 to 10% by weight and by
restricting the concentration of the metal material lower relative
to the concentration of the organic molecule, a high light emission
efficiency can be obtained while suppressing the light absorption
or light reflection inherent to the metal and increasing the
transmittance of the entire device.
[0046] Further, the protective layer 15c comprises a material
having the charge transporting property. The protective layer 15c
is formed by using at least one of metal materials having the
electron charging property described above (particularly, metal
materials having low work function described above) for forming the
electron charging layer 15. Among them, since Mg is inexpensive and
easy to handle with, it is used particularly preferably.
[0047] For the protective layer 15c, the metal materials described
above may be used as an element, or may be used also as an alloy.
Further, the layer may be formed of an oxide or halide of the metal
material described above. Further, the layer may also be formed as
a mixed layer by using an organic material together with at least
one of the metal materials having low work function.
[0048] For example, in a case of the protective layer 15c
comprising an alloy of metal materials, MgAg can be used. However,
in a case of forming the protective layer 15c with an element of
each of the metal materials or the alloys thereof, it is important
to form the layer as such a super thin film as capable of ensuring
the light transmittance. For example, in a case of forming the
protective layer 15c by using MgAg exemplified above, the thickness
of the protective layer 15c is restricted to about 3 nm or less,
preferably, 2 nm. This ensures the light transmittance in the
protective layer 15c. It is preferred that the metal material of
low work function described above is contained by 95% by weight or
more in the protective layer 15c. This is because the metal
material such as Mg having low work function is liable to be
oxidized and oxidized after film formation and, as a result, can
ensure the light transmittance easily. Accordingly, in a case of
using MgAg, a protective layer 15c of higher light transmittance
can be obtained by incorporating 95% or more of Mg to Ag.
[0049] Further, in a case where the protective film 15c is a mixed
layer of a metal material with low work function and an organic
material, the metal material with low work function may be used as
the element, alloy, oxide, or halide as described above. However,
since the protective layer 15c also constitutes an electron
injecting layer 15 as described above, it is preferred to ensure
the electron injecting property to some extent. Accordingly, a
metal material having an electron injecting property of about 10%
or less is doped.
[0050] The organic material used for the protective layer 15c is
not restricted to those having electron transporting property. That
is, in the organic electroluminescence device 11, a main component
for electron injection to the light emission layer 14c in the
organic layer 14 is the electron transporting layer 14d of the
organic layer 14 and the mixed layer 15b. Accordingly, the organic
material used in the protective layer 15c may have either a hole
transporting or electron transporting property.
[0051] In a case the organic material constituting the protective
layer 15c has the electron transporting property, a material with
high electron transporting property is preferably used in view of
lower voltage of the organic electroluminescence device 11. That
is, since the mixed layer 15b is not the main component for
electron injection to the light emission layer 14c as described
above, even in case the mixed layer 15b comprises an organic
material with high electron transportability, the injection balance
between the holes and the electrons to the light emission layer 14c
is not lost. Accordingly, a material of higher electron moveability
than that of the electron transporting layer 14d can be used as the
organic material that forms the protective layer 15c, by which the
voltage for the organic electroluminescence device 11 can be
lowered.
[0052] As the organic material having such high electron
transportability, a phenanthroline derivative is used suitably.
Since the phenanthroline derivative has a high electron
transportability, in a case of using the same for the electron
transporting layer, the injection balance described above is lost
to result in remarkable lowering in the luminance half-decay
life.
[0053] Further, as the organic material forming the protective
layer 15c, general host materials and hole transporting materials
for the light emission layer 14c are used. An example of the host
material is ADN (Anthracene Dinaphthyl). Further, an example of the
hole transporting material is .alpha.-NPD (.alpha.-naphthyl phenyl
diamine). Also in a case of using such materials, the organic
electroluminescence device 11 can be provided with a sufficient
light emitting efficiency and a luminance half-decay life.
[0054] In case the organic material constituting the protective
layer 15c has a hole transporting property, the material of the
following formula (1) and derivatives thereof are preferably
used.
##STR00001##
[0055] In the formula (1), R.sup.1 to R.sup.6 each represents
independently a hydrogen, halogen, hydroxyl group, amino group,
arylamino group, substituted or not-substituted carbonyl group of
20 or less carbon atoms, substituted or not-substituted carbonyl
ester group of 20 or less carbon atoms, substituted or
not-substituted alkyl group of 20 or less carbon atoms, substituted
or not-substituted alkenyl group of 20 or less carbon atoms,
substituted or not-substituted alkoxyl group of 20 or less carbon
atoms, substituted or not-substituted aryl group of 30 or less
carbon atoms, substituted or not-substituted heterocyclic group of
30 or less carbon atoms, or substituent selected from nitrile
group, cyano group, nitro group, or silyl group. Adjacent R.sup.m
(m=1 to 6) may join to each other by way of a cyclic structure.
Further, X.sup.1 to X.sup.6 in the formula (1) each represents
independently a carbon or nitrogen atom.
[0056] One of specific examples of the organic materials
represented by the formula (1) described above is, for example, a
material of the following formula (2).
##STR00002##
[0057] By forming the protective layer 15c using the mixed layer
comprising the organic material of the formula (1) or usual host
material or hole transporting material for the light emission layer
14c, and the metal material of low work function, the light
emission efficiency of the organic electroluminescence device is
improved and long life can be obtained particularly.
[0058] In the electron injection layer 15, the thickness for each
of the layers is set such that the transmittance at a wavelength
region of from 440 to 700 nm is 85% or more.
[0059] Then, the upper electrode 16 disposed above the electron
injection layer 15 is formed, for example, of a so-called
transparent conductive film. The transparent conductive film is a
transparent conductive film typically represented by
Indium-Tin-Oxide and a mixture of indium oxide (In.sub.20.sub.3)
and zinc oxide (ZnO), that is, Indium-Zinc-Oxide (IZO: trade mark
of Idemitsu Kosan Co.) and it is formed, for example, of IZO at a
film thickness of about 50 nm.
[0060] The upper electrode 16 having such a transparent conductive
film is formed by a sputtering method in an oxygen atmosphere.
[0061] The organic electroluminescence device 11 of this embodiment
as has been described above has a structure in which a buffer layer
15a made of an insulative material, a mixed layer 15b, and a
protective layer 15c are laminated in this order between the
organic layer 14 and the upper electrode 16.
[0062] Among them, since the buffer layer 15a comprises an
insulative material, a light transmittance can be ensured easily.
Further, since the mixed layer 15b comprises an organic material
and a metal material, the metal material reacts while reducing an
organic material and becomes transparent while ensuring the
electron injecting property. Further, in a case where the
protective layer 15c consists only of a super thin film of the
metal material, this is oxidized to become light permeable upon
forming the upper electrode 16. On the other hand, in a case where
the protective film 15c comprises an organic material and a metal
material, the light transmittance is ensured inherently like the
mixed layer 15b and, further, this is oxidized upon film formation
of the upper electrode 16 to improve the light transmittance.
[0063] Accordingly, light transmittance of the organic layer 14 on
the side of the upper electrode 16 can be ensured sufficiently.
Further, since the buffer layer 15a comprising the insulative
material is disposed in contact with the organic layer 14, the
buffer layer 15a has a hole blocking property to the organic layer
14. Accordingly, holes can be confined to the organic layer 14.
[0064] Further, since the mixed layer 15b disposed on the buffer
layer 15a is formed by using the metal material having the electron
injection property, this serves as a main component for electron
injection. A protective layer 15c having a charge transporting
property is disposed on the mixed layer 15b. Thus, in an oxidative
atmosphere upon forming the film of the upper electrode 16 having
the transparent conductive film on the protective layer, the
protective layer 15c functions as a protective film for preventing
oxidation of the mixed layer 15b as a main component for electron
injection. Accordingly, lowering of the electron injection
efficiency by the oxidation of the mixed layer 15b is
prevented.
[0065] From the foregoings, the electron injection efficiency from
the electron injection layer 15 to the organic layer 14 can be
maintained at an appropriate value.
[0066] As a result, according to the organic electroluminescence
device 11 having the constitution as described above, since the
light transmittance of the organic layer 14 on the side of the
upper electrode 16 is ensured, the light emission intensity from
the side of the upper electrode used as the cathode can be
improved. In addition, since an appropriate electron injection
efficiency from the upper electrode 16 to the organic layer 14 can
be ensured and since the hole blocking property to the organic
layer 14 can also be ensured, the light emission intensity and the
emission life can be improved.
[0067] In the organic electroluminescence device 11 constructed as
described above, in a case where the protective layer 15c is a
mixed layer comprising the metal material and the organic material,
the range for selecting the organic material to be used can be
extended. That is, since it is necessary for the protective layer
15c to ensure the electron injection property to some extent, it is
necessary to dope a metal material having an electron injection
property of about 10% or less. However, the mixed layer 15b below
the protective layer 15c mainly conducts electron injection to the
light emission layer 14c. Accordingly, the organic material as the
medium may be either hole transporting or electron transporting or
may transport both of the charge. Accordingly, it is possible to
form the protective layer 15c using an organic material having high
electron transportability as the medium without considering the
injection balance between electrons and holes to the organic layer
14, thereby obtaining an effect of lowering the operating
voltage.
[0068] Then, since the protective layer 15c is constituted as
described above, an organic material selected optimally can be used
for the mixed layer 15b disposed therebelow while only considering
to properly determine the amount of electrons to be injected into
the light emission layer 14.
[0069] This enables to optimize the device property such that the
operating voltage is decreased by using the protective layer 15c of
high electron transportability while ensuring sufficient light
emission efficiency and luminance half-decay life by properly
selecting the organic material used for the mixed layer 15b and the
protective layer 15c within a range of selection at high degree of
freedom. In addition, the light transmittance of the device itself
is not impaired.
[0070] The organic electroluminescence device 11 as has been
described in the preferred embodiment can also be applied to a
tandem organic electroluminescence device formed by laminating a
unit (light emission unit) of the organic layer 14 having the light
emission layer 14c.
In this structure, the upper electrode 16 formed of the transparent
conductive film is disposed as a cathode by way of the electron
injection layer 15 above the uppermost light emission unit.
[0071] Further, in the embodiment described above, the structure of
the organic electroluminescence device 11 having the electron
injection layer 15 of the three-layered structure has been
explained. However, the organic electroluminescence device of the
invention may also adopt a structure not provided with the
protective layer 15c. Also in such a case, since the buffer layer
15a below the mixed layer 15b is formed by using a metal having the
electron injection property and can provide the function of
injecting electrons, the electron injection efficiency can be
ensured to some extent. Further, the light transmittance and the
hole blocking property can also be ensured.
Example
In a Case of Single Light Emission Unit
[0072] Then, description is to be made for the procedures of
manufacturing organic electroluminescence devices of actual
Examples 1 to 6 of the invention and Comparative Examples 1 and 2
with reference to FIG. 1 and then the result of evaluation for them
is to be described.
Example 1
[0073] In this example, an organic electroluminescence device in
which the electron injection layer 15 has a two-layered structure
was manufactured.
[0074] At first, an Ag--Pd--Cu layer was formed on a substrate of a
glass plate sized 30 mm.times.30 mm and an ITO layer was formed
thereon to form a lower electrode 13 of a two-layered structure as
an anode. Subsequently, a film of SiO.sub.2 was formed by
sputtering and patterned by lithography to manufacture a cell for
use in an organic electroluminescence device masked for a portion
other than a 2 mm.times.2 mm light emission region with an
insulative film (not illustrated).
[0075] Then, as the hole injection layer 14a, 2-TNATA
(4,4',4''-tris(2-naphtylphenylamino)triphenylamine] was vapor
deposited at a film thickness of 15 nm (vapor deposition rate: 0.2
to 0.4 mm/sec).
[0076] Then, an .alpha.-NPD (.alpha.-naphthyl phenyl diamine) was
formed by vapor deposition at film thickness of 15 nm (vapor
deposition rate: 0.2 to 0.4 nm/sec) as the hole transporting
layer.
[0077] Then, the light emission layer 14c was vapor deposited at a
film thickness of 32 nm in total using ADN (anthracene dinaphthyl)
as a host material and BD-052x (manufactured by Idemitsu Kosan Co.)
as a dopant such that the dopant concentration was 5.0% by
weight.
[0078] Finally, Alq3 (8-hydroxy quinoline aluminum) was vapor
deposited at a film thickness of 10 nm as the electron transporting
layer 14d. Then, LiF was vapor deposited at a film thickness of 0.1
nm as the buffer layer 15a.
[0079] Successively, Alq and Mg at 100:5 weight ratio were formed
at a 5 nm film thickness by co-vapor deposition as the mixed layer
15b. Further, as the protective layer 15c, the material represented
by the following formula (2) and Mg were formed at a film thickness
of 5 nm at 100:5 weight ratio by co-vapor deposition by a vacuum
vapor deposition method. Thus, the electron injection layer 15
having two layers of the mixed layer 15b and the protective layer
15c was formed.
##STR00003##
[0080] Then, IZO was formed at a film thickness of 50 nm as the
upper electrode 16 by a sputtering method.
[0081] With the procedures described above, the top emission
organic electroluminescence device having the transparent
conductive film as the upper electrode 16 of the cathode was
manufactured.
Example 2
[0082] An organic electroluminescence device was manufactured in
the same manufacturing procedures as those in Example 1 except for
forming the protective layer 15c with an Mg--Ag alloy. In the
formation of the protective layer 15c, the Mg--Ag alloy was
co-vapor deposited to a film thickness of 2 nm at a weight ratio of
Mg:Ag=100:5.
Example 3
[0083] An organic electroluminescence device was manufactured in
the same manufacturing procedures as those in Example 1 except for
forming the protective layer 15c as the mixed layer comprising
.alpha.-NPD and Mg as the hole transporting material. In the
formation of the protective layer 15c, the .alpha.-NPD-Mg alloy was
co-vapor deposited at a film thickness of 5 nm at a weight ratio of
.alpha.-NPD:Mg=100:5.
Example 4
[0084] An organic electroluminescence device was manufactured in
the same manufacturing procedures as those in Example 1 except for
forming the protective layer 15c as the mixed layer comprising ADN
and Mg used usually as the host material for the light emission
layer. In the formation of the protective layer 15c, ADN and Mg
were co-vapor deposited at a film thickness of 5 nm at a weight
ratio of ADN:Mg=100:5.
Example 5
[0085] An organic electroluminescence device was manufactured in
the same manufacturing procedures as those in Example 1 except for
forming the protective layer 15c as the mixed layer comprising BCP
(basocuproin) as one of phenanthroline derivatives having extremely
high electron transportability. In the formation of the protective
layer 15c, the BCP and Mg were co-vapor deposited to a film
thickness of 5 nm at a weight ratio of BCP:Mg=100:5.
Example 6
[0086] An organic electroluminescence device was manufactured in
the same procedures as those in Example 1 except for forming the
electron injection layer 15 with a mono-layered structure
consisting only of the mixed layer 15b in the manufacturing
procedures of Example 1. That is, in the manufacturing procedures
in Example 1, after forming the mixed layer 15b, the upper
electrode 16 was formed without forming the protective layer
15c.
Comparative Example 1
[0087] A top emission organic electroluminescence device was
manufactured in the same manufacturing procedures as those in
Example 6 except for saving the formation of the buffer layer 15a
in Example 6.
Comparative Example 2
[0088] An organic electroluminescence device was manufactured in
the same manufacturing procedures as those in Example except for
using BCP instead of Alq as the organic material forming the mixed
layer 15b in the manufacturing procedure in Example 6. That is,
this is an example in which the organic material forming the mixed
layer 15b had a higher electron transportability than the electron
transporting layer 14d (Alq) in the organic layer 14. In the
formation of the mixed layer 15b, BCP and Mg were co-vapor
deposited at a film thickness of 5 nm at a weight ratio of
BCP:Mg=100:5.
Result of Evaluation
[0089] For the organic electroluminescence devices of Examples 1 to
6 and Comparative Examples 1 and 2 manufactured as described above,
light emission efficiency, operating voltage, and transmittance
were measured. The following Table 1 shows the result of the
evaluation together with the layer structure of the electron
injecting layer in the organic electroluminescence devices. The
light emission efficiency (cd/A) of the organic electroluminescence
device was a value measured upon application of a current at a
density of 10 mA/cm.sup.2.
TABLE-US-00001 TABLE 1 Light Electron injecting layer 15 emitting
Operating Buffer Mixed layer Protective efficiency voltage
Transmittance layer 15a 15b layer 15c (cd/A) (V) (%) Example 1 LiF
Alq-Mg Formula 3.7 5.67 85 or higher (2)-Mg Example 2 '' '' Mg--Ag
3.4 6.02 90 or higher Example 3 '' '' .alpha. NPD-Mg 3.7 6.97 90 or
higher Example 4 '' '' ADN-Mg 3.7 5.96 90 or higher Example 5 '' ''
BCP-Mg 3.9 5.26 90 or higher Example 6 '' '' -- 2.9 7.85 90 or
higher Comp. -- '' -- 2.2 9.65 90 or higher Example 1 Comp. LiF
BCP-Mg -- 3.9 5.02 90 or higher Example 2 *: Light emission
efficiency and operating voltage are those under operation at 10
mA/cm.
[0090] From the result shown in Table 1, it was confirmed that the
light emission efficiency was improved and the operating voltage
was lowered in the organic electroluminescence devices of Examples
1 to 6 having the laminate structure of the buffer layer 15a and
the mixed layer 15b when compared with the organic
electroluminescence device of Comparative Example 1 not having the
electron injecting layer of such a laminate structure. Further, it
was confirmed also for the light transmittance that a sufficient
value as 85% or more could be ensured in Examples 1 to 6 with all
the provision of the buffer layer 15a.
[0091] FIG. 2 shows the result of measuring the operating
time-operating voltage for the organic electroluminescence devices
of Examples 1 and 2, and Comparative Example 1. It can be seen also
from the result that the operating voltage was lowered in the
organic electroluminescence devices having the structure of
Examples 1 and 2 as a preferred embodiment of the invention
compared with the organic electroluminescence device of Comparative
Example 1.
[0092] Further, it was confirmed for the organic
electroluminescence devices of Example 1 to Example 5 provided with
the protective layer 15c that the light emission efficiency could
be improved and the operating voltage could be lowered when
compared with the organic electroluminescence device of Example 6
not provided with the protective layer 15c. Thus, by providing the
protective layer 15c it was confirmed that the effect capable of
preventing the oxidation of the mixed layer 15b and keeping the
electron injecting property in the mixed layer 15b.
[0093] Then, FIG. 3 shows the result of measuring the relation for
the operating time--relative luminance of the organic
electroluminescence devices of Examples 1 to 6 and Comparative
Examples 1, 2. From the result, it was confirmed that the light
emission life was improved in the organic electroluminescence
devices of Examples 1 to 6 having the laminate structure of the
buffer layer 15a and the mixed layer 15b compared with the organic
electroluminescence device of Comparative Example 1 not having such
a laminate structure.
[0094] Further, it was confirmed for the organic
electroluminescence devices of Examples 1 to 5 provided with the
protective layer 15c on the mixed layer 15b that the light emission
life was improved compared with the organic electroluminescence
device of Example 6 not provided with the protective layer 15c.
Also in view of the above, it was confirmed the effect capable of
preventing the oxidation of the mixed layer 15b and maintaining the
electron charging property in the mixed layer 15b by the provision
of the protective layer 15c.
[0095] Further, as shown in FIG. 3, in the organic
electroluminescence devices of Examples 1 to 5 in which the
protective layers 15c were formed of respective materials, the rate
of lowering the relative luminance was substantially identical. It
can be seen from the foregoings that the kind of the organic
materials used for the protective layer 15c gives scarce effects on
the light emission life and the effect of prolonging the life by
preventing oxidation of the electron injecting layer was
predominant. On the contrary, Example 6 not provided with the
protective film 15c showed the result that the life was remarkably
shortened compared with Examples 1 to 5 by the effect of direct
exposure of the Alq-Mg mixed alloy layer 15b having relatively
lower electron transportability to the oxygen atmosphere.
[0096] Then, for the organic electroluminescence device shown in
Comparative Example 2, it was confirmed from the result shown in
Table 1 that the most advantageous effect was obtained for the
light emission efficiency and the operating voltage, as well as a
sufficient transmittance was obtained. Referring to the
transmittance, this is because the transmittance was improved as a
result of exposure of the upper electrode to an oxygen atmosphere
during film formation by sputtering. However, no sufficient light
emission life was obtained for Comparative Example 2. This is
because appropriate balance between the hole and the electrons was
lost by disposing BCP-Mg of extremely high electron
transportability as the mixed layer 15b near the electron
transporting layer 14d which greatly worsened the device life.
[0097] Then, with the foregoing results, it was confirmed that all
of the device property required for the organic electroluminescence
device 11, that is, the light emission efficiency, the operating
voltage, and the light emission life could be ensured sufficiently
by properly combining the mixed layer 15b for predominantly
controlling the electron injecting property and the protective
layer 15c for preventing the mixed layer 15b from being oxidized
during film formation by sputtering of the upper electrode 16.
[0098] It was confirmed that a favorable organic
electroluminescence device 11 can be obtained concerning all of the
initial efficiency, the operating voltage, and the light emission
life particularly by adopting the structure, for the electron
injecting layer 15 disposed above the electron transporting layer
14d, that is, as a structure of laminating the mixed layer 15b
having the same extent of electron transportability as that of the
electron transporting layer 14d and the protective film 16b of
higher electron transportability.
In a Case of Plural Light Emission Units
[0099] Then, procedures for manufacturing tandem display devices
including plural light emission units and the result of evaluation
for them are to be explained. In the tandem display devices in
another embodiment of the invention, a connection layer 115
disposed between the light emission units had an identical
structure with that of the electron injecting layer 15 as described
previously. Specifically, the connection layer had a laminate
structure including a metal oxide layer, a charge transporting
material layer, and a triphenylene layer. In Examples 1' to 24', a
display device 110 shown in FIG. 4 was manufactured. In this case,
the constitution of the connection layers 115 were respectively
shown in the following Table 2. Examples of electron transporting
materials in the charge transporting materials 115b forming the
connection layer are shown by the formulae (1)-1 to (1)-42 in Table
2. Examples of the hole transporting materials are shown by the
formulae (2)-1 to (2)-95 in Table 3.
TABLE-US-00002 TABLE 2 ##STR00004## (1)-1 ##STR00005## (1)-2
##STR00006## (1)-3 ##STR00007## (1)-4 ##STR00008## (1)-5
##STR00009## (1)-6 ##STR00010## (1)-7 ##STR00011## (1)-8
##STR00012## (1)-9 ##STR00013## (1)-10 ##STR00014## (1)-11
##STR00015## (1)-12 ##STR00016## (1)-13 ##STR00017## (1)-14
##STR00018## (1)-15 ##STR00019## (1)-16 ##STR00020## (1)-17
##STR00021## (1)-18 ##STR00022## (1)-19 ##STR00023## (1)-20
##STR00024## (1)-21 ##STR00025## (1)-22 ##STR00026## (1)-23
##STR00027## (1)-24 ##STR00028## (1)-25 ##STR00029## (1)-26
##STR00030## (1)-27 ##STR00031## (1)-28 ##STR00032## (1)-29
##STR00033## (1)-30 ##STR00034## (1)-31 ##STR00035## (1)-32
##STR00036## (1)-33 ##STR00037## (1)-34 ##STR00038## (1)-35
##STR00039## (1)-36 ##STR00040## (1)-37 ##STR00041## (1)-38
##STR00042## (1)-39 ##STR00043## (1)-40 ##STR00044## (1)-41
##STR00045## (1)-42
TABLE-US-00003 TABLE 3 ##STR00046## (2)-1 ##STR00047## (2)-2
##STR00048## (2)-3 ##STR00049## (2)-4 ##STR00050## (2)-5
##STR00051## (2)-6 ##STR00052## (2)-7 ##STR00053## (2)-8
##STR00054## (2)-9 ##STR00055## (2)-10 ##STR00056## (2)-11
##STR00057## (2)-12 ##STR00058## (2)-13 ##STR00059## (2)-14
##STR00060## (2)-15 ##STR00061## (2)-16 ##STR00062## (2)-17
##STR00063## (2)-18 ##STR00064## (2)-19 ##STR00065## (2)-20
##STR00066## (2)-21 ##STR00067## (2)-22 ##STR00068## (2)-23
##STR00069## (2)-24 ##STR00070## (2)-25 ##STR00071## (2)-26
##STR00072## (2)-27 ##STR00073## (2)-28 ##STR00074## (2)-29
##STR00075## (2)-30 ##STR00076## (2)-31 ##STR00077## (2)-32
##STR00078## (2)-33 ##STR00079## (2)-34 ##STR00080## (2)-35
##STR00081## (2)-36 ##STR00082## (2)-37 ##STR00083## (2)-38
##STR00084## (2)-39 ##STR00085## (2)-40 ##STR00086## (2)-41
##STR00087## (2)-42 ##STR00088## (2)-43 ##STR00089## (2)-44
##STR00090## (2)-45 ##STR00091## (2)-46 ##STR00092## (2)-47
##STR00093## (2)-48 ##STR00094## (2)-49 ##STR00095## (2)-50
##STR00096## (2)-51 ##STR00097## (2)-52 ##STR00098## (2)-53
##STR00099## (2)-54 ##STR00100## (2)-55 ##STR00101## (2)-56
##STR00102## (2)-57 ##STR00103## (2)-58 ##STR00104## (2)-59
##STR00105## (2)-60 ##STR00106## (2)-61 ##STR00107## (2)-62
##STR00108## (2)-63 ##STR00109## (2)-64 ##STR00110## (2)-65
##STR00111## (2)-66 ##STR00112## (2)-67 ##STR00113## (2)-68
##STR00114## (2)-69 ##STR00115## (2)-70 ##STR00116## (2)-71
##STR00117## (2)-72 ##STR00118## (2)-73 ##STR00119## (2)-74
##STR00120## (2)-75 ##STR00121## (2)-76 ##STR00122## (2)-77
##STR00123## (2)-78 ##STR00124## (2)-79 ##STR00125## (2)-80
##STR00126## (2)-81 ##STR00127## (2)-82 ##STR00128## (2)-83
##STR00129## (2)-84 ##STR00130## (2)-85 ##STR00131## (2)-86
##STR00132## (2)-87 ##STR00133## (2)-88 ##STR00134## (2)-89
##STR00135## (2)-90 ##STR00136## (2)-91 ##STR00137## (2)-92
##STR00138## (2)-93 ##STR00139## (2)-94 ##STR00140## (2)-95
[0100] Procedures for manufacturing the display devices of Examples
1' to 24' are to be described below.
Examples 1' to 10'
[0101] Substrates used for the evaluation of top emission organic
electroluminescence devices were manufactured each by forming
silver alloy as an anode 113 above a substrate 112 made of a glass
plate sized 30 mm.times.30 mm, forming ITO (film thickness: about
10 nm) as a protective layer and hole injecting electrode and,
further, masking regions other than the 2 mm.times.2 mm light
emission region with an insulative film (not illustrated) by
SiO.sub.2 vapor deposition.
[0102] Then, a hole injecting material comprising a triphenylene
derivative: compound (3)-10 was formed at a film thickness of 11 nm
by a vacuum vapor deposition method (vapor deposition rate: 0.2 to
0.4 nm/sec) as a hole injecting layer 114a constituting the light
emission unit 114-1 at the first layer (vapor deposition rate: 0.2
to 0.4 nm/sec).
[0103] Then, .alpha.-NPD (Bis[N-(1-naphthyl)-N-phenyl]bendizine)
was formed at a film thickness of 11 nm by a vacuum vapor
deposition method (vapor deposition rate: 0.2 to 0.4 nm/sec) as a
hole transporting layer 114b.
[0104] Further, as a light emission layer 114c, ADN was used as a
host material and BD-052x (trade name of products manufactured by
Idemitsu Kosan Co.) was used as a dopant and the materials were
formed to a film at a thickness of 28 nm in total such that the
film thickness ratio was 5% by a vacuum vapor deposition
method.
[0105] Finally, as the electron transporting layer 114d Alq3
[Tris(8-hydroxyquinolinato)aluminum (III)] was formed to a film at
a thickness of 10 nm by a vacuum vapor deposition method.
[0106] After forming the light emission unit 114-1 at the first
layer as described above, the materials shown in the following
Table 4 were vapor deposited successively as an oxide containing
layer 115a, a charge transporting organic material layer 115b, and
a triphenylene layer 115c thereby forming the connection layer
115.
TABLE-US-00004 TABLE 4 Oxide Charge transporting containing organic
material Triphenylene Light emission layer 115a layer 115b layer
115c efficiency (Electron transportability) [cd/A] Example 1'
Li.sub.2CO.sub.3 Compound (1)-1 Compound (3)-10 6.2 Example 2'
Compound (1)-2 Compound (3)-10 6.1 Example 3' Compound (1)-3
Compound (3)-10 6.2 Example 4' Compound (1)-20 Compound (3)-10 6.0
Example 5' Compound (1)-1 Compound (3)-34 5.9 Example 6' Compound
(1)-1 Compound (3)-66 6.0 Example 7' Li.sub.2SiO.sub.3 Compound
(1)-1 Compound (3)-10 6.1 Example 8' Compound (1)-2 Compound (3)-10
6.0 Example 9' Compound (1)-3 Compound (3)-10 6.1 Example 10'
Compound (1)-4 Compound (3)-10 5.8 Example 11' Li.sub.2CO.sub.3 +
Compound (1)-1 Compound (3)-10 6.0 Compound (1)-1 Example 12'
Li.sub.2CO.sub.3 Compound (1)-1/ Compound (3)-10 5.9 Compound (1)-1
+ Compound (3)-10 (Hole transportability) Example 13'
Li.sub.2CO.sub.3 Compound (2)-34 Compound (3)-10 6.0 Example 14'
Compound (2)-35 Compound (3)-10 6.0 Example 15' Compound (2)-42
Compound (3)-10 5.9 Example 16' Compound (2)-46 Compound (3)-10 6.0
Example 17' Compound (2)-34 Compound (3)-34 5.9 Example 18'
Compound (2)-34 Compound (3)-66 6.0 Example 19' Li.sub.2SiO.sub.3
Compound (2)-34 Compound (3)-10 6.1 Example 20' Compound (2)-35
Compound (3)-10 6.0 Example 21' Li.sub.2CO.sub.3 Compound (2)-57
Compound (3)-10 6.0 Example 22' Compound (2)-83 Compound (3)-10 5.7
Example 23' Li.sub.2CO.sub.3 + Compound (2)-34 Compound (3)-10 5.8
Compound (2)- 34 Example 24' Li.sub.2CO.sub.3 Compound (2)-34/
Compound (3)-10 5.7 Compound (2)-34 + Compound (3)-10 Comp.
Li.sub.2CO.sub.3 -- Compound (3)-10 6.3 Example 1' Comp. LiF/Alq3 +
Mg/Compound (3)-10 6.2 Example 2' Comp. -- -- -- 3.0 Example 3'
[0107] For example, in Example 1', Li.sub.2CO.sub.3 was formed to a
film at 0.3 nm thickness as the oxide containing layer 115a, the
compound (1)-1 was formed to a film at 5 nm thickness as the charge
transporting organic material layer 115b having an electron
transporting property and, finally, the compound (3)-10 was formed
to a film at 60 nm thickness as the triphenylene layer 115c.
Further, also in Examples 2' to 10', materials shown in Table 4
were formed at the same film thickness as in Example 1' by vapor
deposition.
[0108] After the procedures as described above, a light emission
unit 114-2 was formed in the same manner as the light emission unit
114-1 at the first layer.
[0109] Then, LiF was formed to a film at about 0.3 nm thickness as
a first layer 116a of a cathode 116 by a vacuum vapor deposition
method (vapor deposition rate: 0.01 nm/sec or less) and then MgAg
was formed to a film of 10 nm thickness as a second layer 116b to
form the cathode 116 of a two-layered structure. Thus, a top
emission display device 110 was manufactured.
Example 11'
[0110] The manufacturing procedures were conducted in the same
manner as those in Example 1' except for co-vapor depositing
Li.sub.2CO.sub.3 and the compound (1)-1 as the oxide-containing
layer 115a to form the oxide containing layer 115a of the mixed
layer in Example 1'. The oxide layer 115a had a compositional ratio
of Li.sub.2CO.sub.3:compound (1)-1=4:1 (ratio of film thickness)
and was formed to a film at nm thickness. Further, the charge
transporting organic material layer 115b comprising the compound
(1)-1 was formed to a film at a thickness of 2 nm.
Example 12'
[0111] The manufacturing procedures were conducted in the same
manner as those in Example 1' except for forming the compound (1)-1
to a film at 3 nm thickness as the charge transporting organic
material layer 115b and then, forming a mixed layer of the compound
(1)-1 and the compound (3)-10 to a film at a thickness of 2 nm to
form a charge transporting organic material layer 115b of a
two-layered structure. The compositional ratio of the compound
(1)-1 and the compound (3)-10 in the mixed layer was 1:1 (ratio of
film thickness).
Examples 13' to 22'
[0112] In the formation of the connection layer 115 in the
manufacturing procedures of Example 1', the materials shown in the
Table 4 were vapor deposited successively as the oxide containing
layer 115a, the charge transporting organic material layer 115b and
the triphenylene layer 115c thereby forming the connection layer
115. Other procedures than those described above were conducted in
the same manner as in Example 1'.
[0113] For example, in Example 13', Li.sub.2CO.sub.3 was formed to
a film at 0.3 nm thickness as the oxide containing layer 115a,
then, the compound (2)-34 was formed to a film at a thickness of
2.5 nm as the charge transporting organic material layer 115b
having a hole transporting property and, finally, the compound
(3)-10 was formed to a film at 62.5 nm thickness as the
triphenylene layer 115c. Further, also in Examples 14' to 22', the
materials shown in Table 4 were formed to films of the same
thickness as in Example 13' by vapor deposition.
Example 23'
[0114] The manufacturing procedures were conducted in the same
manner as in Example 13' except for co-vapor depositing
Li.sub.2CO.sub.3 and the compound (2)-34 as the oxide containing
layer 115a, to form the oxide containing layer 115a of the mixed
layer in Example 13'. The oxide containing layer 115a of the mixed
layer had a compositional ratio of Li.sub.2CO.sub.3:compound
(2)-34=4:1 (ratio of film thickness) and was formed to a film at 3
nm thickness. Further, the charge transporting organic material
layer 115b comprising the compound (2)-34 was formed to a film at a
thickness of 2 nm.
Example 24'
[0115] The manufacturing procedures were conducted in the same
manner as those in Example 13' except for forming the compound
(2)-34 to a film at 3 nm thickness as the charge transporting
organic material 115b and then forming a mixed layer of the
compound (2)-34 and the compound (3)-10 to a film at 2 nm thickness
to form a charge transporting organic material layer 115b of a
two-layered structure in Example 13'. The compositional ratio of
the compound (2)-34 and the compound (3)-10 in the mixed layer was
1:1 (ratio of film thickness).
Comparative Example 1'
[0116] The manufacturing procedures were conducted in the same
manner as in Example 1' except for forming the connection layer 115
of a laminate structure of the oxide containing layer 115a and the
triphenylene layer 115c without forming the charge transporting
organic material layer 115b in the formation of the connection
layer 115 in Example 1'.
Comparative Example 2'
[0117] In the manufacturing procedures of Example 1', a connection
layer having a structure in which an LiF layer, the mixed layer of
Alq3 and Mg described above, and the layer comprising the compound
(3)-10 were laminated in this order was formed in the formation of
the connection layer 115.
Comparative Example 3'
[0118] In Comparative Example 3' the cathode 116 was formed
directly on the light emission unit 114-1 at the first layer to
manufacture a not tandem one-unit display device in the
manufacturing procedures of Example 1'.
Result of Evaluation
[0119] Table 4 shows the light emission efficiency (Quantum Yield:
Q/Y) of the display devices manufactured in Example 1' to 12', 13'
to 24', and Comparative Examples 1' to 3'. It was confirmed from
the result that the light emission efficiency in the display
devices of Examples 1' to 24' was about twice the efficiency of the
display device of the one-unit structure of Comparative Example 3'
and the effect due to the tandem structure formed by laminating the
light emission units in two layers was obtained. In the tandem
device, it was expected that the light emission efficiency was
doubled by stacking the light emission units in two stages in an
ideal device, and it was confirmed almost ideal elements could be
obtained in Examples 1 to 24. The emission efficiency was increased
to about twice also in Comparative Examples and 2 and the effect
due to the tandem structure was obtained.
[0120] (a)-(h) in the following Table 5 show the relative luminance
and the operating voltage after operation for initial 100 hours
(100 h) and for 800 hours (800 h) normally at a room temperature
(30.degree. C.) and at a high temperature (60.degree. C.) of
Examples 1', 13' and Comparative Examples 1' to 3' manufactured as
described above. As the operating condition, operation at a room
temperature was conducted as the constant current operation at
mA/cm.sup.2 and operation at a high temperature was conducted as
constant current operation at 20 mA/cm.sup.2.
TABLE-US-00005 TABLE 5 Comp. Comp. Comp. Example Example Example
Example Example 1' 13' 1' 2' 3' (a) Relative luminance - 100 h 0.93
0.87 0.85 0.91 0.96 (30.degree. C.) (b) Relative luminance - 800 h
0.69 0.67 0.64 0.60 0.76 (30.degree. C.) (c) Operating voltage
(initial 0.60 1.01 1.00 0.10 -0.20 .DELTA.V) - 100 h (30.degree.
C.) (V) (d) Operating voltage (.DELTA.V) - 1.30 1.45 1.60 0.90 0.00
800 h (30.degree. C.) (V) (e) Relative luminance - 0.94 0.93 0.86
0.91 0.97 100 h (60.degree. C.) (f) Relative luminance - 0.85 0.85
0.77 0.78 0.95 800 h (60.degree. C.) (g) Operating voltage (initial
0.30 1.15 1.00 0.40 0.10 .DELTA.V) - 100 h (60.degree. C.) (V) (h)
Operating voltage (.DELTA.V) - 0.20 1.32 1.30 0.70 0.10 800 h
(60.degree. C.) (V)
(a) Relative Luminance (30.degree. C., 100 h)
[0121] In Examples 1' and 13' having the connection layer 115 of
the laminate structure as another embodiment of the invention, it
was confirmed that lowering of the luminance of the initial stage
(100 h) was distinctly improved compared with Comparative Example 1
not having the connection layer of such a laminate structure and
that the performance approached to that of Comparative Example 3'
of at one unit structure. Particularly, in Example 1' of using the
electron transporting material as the charge transporting organic
material layer 115b in the connection layer 115, lowering of the
initial stage luminance was improved even compared with Comparative
Example 2 and the effect of using the electron transporting
material as the charge transporting organic material layer 115b was
confirmed.
(b) Relative Luminance (30.degree. C., 800 h)
[0122] In view of the result of Example 1' and Example 13' having
the connection layer 115 of the laminate structure as the
embodiment of the invention, deterioration was distinctly
suppressed compared with Comparative Examples 1' and 2' not having
such a connection layer of the laminate structure and the effect of
improving the long time reliability according to the embodiment of
the invention was confirmed. Further, since Comparative Example 2'
showing relatively less degradation during the initial 100 h stage
deteriorated most after 800 h, this suggested that the stationary
degradation rate was high in the structure of Comparative Example
2'. On the other hand, Example 1' and Example 13' showed low
stationary degradation rate and were excellent in the long time
reliability.
(c), (d) (Operating Voltage (30.degree. C., 100 h, 800 h)
[0123] The change with time of the operating voltage in Example 1'
and Example 13' having the connection layer 115 as a laminate
structure as another embodiment of the invention was large compared
with Comparative Example 3' of the one-unit structure. However, it
was confirmed that increase in the operating voltage was suppressed
distinctly compared with Comparative Example 1'.
(e), (f) Relative Luminance (60.degree. C., 100 h, 800 h)
[0124] It was confirmed that degradation of the luminance at the
high temperature in Example 1' and Example 13' according to the
embodiment of the invention was suppressed distinctly compared with
Comparative Example 1' and Comparative Example 2'.
(g) (h) Operating Voltage (60.degree. C., 100 h, 800 h)
[0125] Increase in the voltage at high temperature in Example 1'
having the connection layer 115 as the laminate structure according
to the embodiment of the invention showed apparently smaller value
compared with Comparative Example 1', Comparative Example 2', and
Comparative Example 3'. This suggested that the structure is
excellent in the operating stability at high temperature. On the
contrary, while increase in the voltage at the room temperature and
at the high temperature in Example 13' showed larger values
compared with Comparative Example 1', Comparative Example 2', and
Comparative Example 3', suppression for the degradation of the
luminance which is considered most important could be obtained.
[0126] Also in Examples 2' to 12', change of the relative luminance
or increase in the operating voltage at the room temperature and at
the high temperature showed similar trend as in Example 1' both for
100 h and 800 h, and the effect of providing the connection layer
having the structure according to the embodiment of the invention
was apparent.
[0127] Further, also in Examples 14' to 24', change of the relative
luminance or increase in the operating voltage at room temperature
and at the high temperature showed similar trend as in Example 13'
both for 100 h and 800 h.
[0128] FIG. 5 shows the life curve for Example 1' together with
life curves for Comparative Examples 1' to 3'. Further, FIG. 6
shows the life curve for Example 13' together with life curves for
Comparative Examples 1' to 3'. Also in view of the results, it can
be seen that degradation in the initial stage of the relative
luminance was large in Comparative Example 1', which was improved
in Example 1' and Example 13'.
[0129] FIG. 7 shows the relative change of voltage in Example 1'
together with relative change of voltage in Comparative Examples 1'
to 3'. FIG. 8 shows the relative change of voltage in Example 13'
together with the relative change of voltage in Comparative
Examples 1' to 3'. From the results, it can be seen that the
increase in voltage was improved particularly in Example 1' using
the electron transporting material as the charge transporting
organic material layer in the connection layer 115 compared with
Comparative Example 1'.
[0130] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *