U.S. patent application number 11/072392 was filed with the patent office on 2005-07-07 for organic electroluminescent device.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Hamada, Yuji, Matsusue, Noriyuki.
Application Number | 20050147848 11/072392 |
Document ID | / |
Family ID | 19114455 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050147848 |
Kind Code |
A1 |
Hamada, Yuji ; et
al. |
July 7, 2005 |
Organic electroluminescent device
Abstract
In an organic EL device, a hole injection electrode is formed on
a glass substrate, and a hole transport layer, a luminescent layer,
a hole blocking layer, an electron transport layer, and an electron
injection electrode are formed in this order on the glass
substrate. The hole blocking layer includes a ternary complex
compound including two quinolinol derivatives, a group IIIB
element, and a halogen element or a phenol derivative.
Inventors: |
Hamada, Yuji; (Ikoma-gun,
JP) ; Matsusue, Noriyuki; (Osaka, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Osaka
JP
|
Family ID: |
19114455 |
Appl. No.: |
11/072392 |
Filed: |
March 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11072392 |
Mar 7, 2005 |
|
|
|
10252014 |
Sep 23, 2002 |
|
|
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Current U.S.
Class: |
428/690 ;
313/504; 313/506; 428/917 |
Current CPC
Class: |
H01L 51/0077 20130101;
H01L 51/0081 20130101; H01L 51/0085 20130101; H01L 51/0062
20130101; H01L 51/0059 20130101; Y10S 428/917 20130101; H01L
51/5048 20130101; H01L 51/5096 20130101; H01L 51/005 20130101 |
Class at
Publication: |
428/690 ;
428/917; 313/504; 313/506 |
International
Class: |
H05B 033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2001 |
JP |
2001-292500 |
Claims
1-6. (canceled)
7. An organic electroluminescent device comprising in the following
order: a hole injection electrode, a luminescent layer, a hole
blocking layer; and an electron injection electrode said hole
blocking layer including a ternary complex compound that is a
bis-(2-methyl-8-quinolinolato)-4-(tert- -butyl-phenolato)aluminum
having a molecular structure represented by the following formula
(5): 15
8. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to organic electroluminescent
devices.
[0003] 2. Description of the Background Art
[0004] Organic electroluminescence devices (hereinafter referred to
as organic EL devices) are expected as new self-light emitting
devices. An organic EL device has a stacked layered structure that
a carrier transport layer (an electron transport layer or a hole
transport layer) and a luminescent layer are formed between a hole
injection electrode and an electron injection electrode.
[0005] Electrode materials having a large work function such as
gold or ITO (indium-tin oxide) are employed for the hole injection
electrode, while those having a small work function such as Mg
(magnesium) or Li (lithium) are employed for the electron injection
electrode.
[0006] Organic materials are employed for the hole transport layer,
the luminescent layer and the electron transport layer. Materials
having the property of a p-type semiconductor are employed for the
hole transport layer, while those having the property of an n-type
semiconductor are employed for the electron transport layer. The
luminescent layer is also composed of organic materials that have
carrier transportability such as electron transportability or hole
transportability and emit fluorescence or phosphorescence.
[0007] These hole injection electrode, hole transport layer,
luminescent layer, electron transport layer and electron injection
electrode are stacked in turn to form the organic EL device.
[0008] Each function layer such as the hole transport layer, the
electron transport layer and the luminescent layer is constituted
by a plurality of layers or omitted depending on the organic
materials to be used.
[0009] In such an elementary structure as shown in Appl. Phys.
Lett., Vol. 55, pp. 1489-1491 by Chihaya Adachi et al., for
example, only two organic layers, which are a luminescent layer and
an electron transport layer exist between a hole injection
electrode and an electron injection electrode. This is because the
luminescent layer composed of luminescent materials called NSD has
excellent hole transportability and hence serves also as a hole
transport layer.
[0010] Further, the elementary structure shown in Appl. Phys.
Lett., Vol. 51, pp. 913-915 (1987) by C. W. Tang et al. is
constituted by two organic layers, which are a hole transport layer
and a luminescent layer. In this case,
tris(8-hydroxyquinolinato)aluminum (hereinafter referred to as Alq)
contained in the luminescent layer serves to both emit light and
transport electrons.
[0011] On the other hand, the elementary structure shown in Appl.
Phys. Lett., Vol. 69, pp. 2160-2162(1996) by S. A. Van Slyke et al.
is constituted by three organic layers, which are a hole injection
layer, a hole transport layer and a luminescent layer. In this
case, the hole injection layer is composed of copper
phthalocyanine, serving for the same function as the hole transport
layer, which results in two hole transport layers existing in the
entire device.
[0012] Thus, the number of the electron transport layer, hole
transport layer and luminescent layer can freely be adjusted
depending on the organic materials to be used.
[0013] A triplet luminescent material is considered as a promising
material for a luminescent layer having high luminescent
efficiency. The triplet luminescent material transits from a
triplet excited state to a ground state to generate
phosphorescence. An organic EL device including a luminescent layer
of a triplet luminescent material has a device structure as
follows.
[0014] A hole injection electrode (anode), a hole transport layer,
a luminescent layer, a hole blocking layer, an electron transport
layer and an electron injection electrode (cathode) are stacked in
this order on a glass substrate. The luminescent layer includes
4,4'-bis(carbazol-9-yl)-b- iphenyl (hereinafter referred to as
"CBP") as a host material, and a triplet luminescent material as a
luminescent dopant.
[0015] In this device structure, the hole blocking layer is used to
prevent the electron transport layer from emitting light. More
specifically, electrons are injected from the electron injection
electrode into the electron transport layer, passed through the
hole blocking layer, then injected into the luminescent layer and
recombined with holes. Meanwhile, holes are injected from the hole
injection electrode, passed through the hole transport layer, then
injected into the luminescent layer, and recombined with electrons.
In order to improve the recombination probability between holes and
electrons in the luminescent layer, the holes must be prevented
from penetrating through the hole blocking layer and being injected
into the electron transport layer. Therefore, a highly stable hole
blocking material having a high hole blocking characteristic is
necessary as a material for the hole blocking layer.
[0016] As a conventional example, the use of Bathocuproine
(hereinafter referred to as "BCP") as a hole blocking material is
suggested in M. A. Baldo, et al., Appl. Phys. Lett., 75. 4, 1999.
The material has a molecular structure expressed by the following
formula (6). Note that the formal name of BCP is
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. 1
[0017] The BCP is however prone to crystallization with time after
it is formed into a film. Therefore, the organic EL device produced
using the BCP tends to suffer from current leakage, and stable
light emission is not provided.
SUMMARY OF THE INVENTION
[0018] It is an object of the present invention to provide an
organic electroluminescent device capable of stably emitting light
with high luminance and high luminescent efficiency.
[0019] An organic electroluminescent device according to one aspect
of the present invention comprises a hole injection electrode, a
luminescent layer, a hole blocking layer, and an electron injection
electrode in this order. The hole blocking layer includes a ternary
complex compound composed of two quinolinol derivatives, a group
IIIB element, and a halogen element or a phenol derivative.
[0020] In the organic electroluminescent device according to the
invention, the hole blocking layer includes a ternary complex
compound composed of two quinolinol derivatives, a group IIIB
element, and a halogen element or a phenol derivative.
[0021] The presence of the hole blocking layer increases the energy
barrier between the luminescent layer and the hole blocking layer.
Therefore, holes can be prevented from being injected into the
electron injection electrode side from the luminescent layer, so
that electrons and holes can efficiently be recombined in the
luminescent layer. Thus, the luminance and the luminescent
efficiency of the organic electroluminescent device can be
improved.
[0022] Since the above ternary complex compound is stable, the
organic electroluminescent device can stably emit light.
[0023] The ternary complex compound may have a molecular structure
represented by the following formula (1) where R1 and R2 may be
identical to or different from one another each representing a
hydrogen atom or a substituent. A maybe a halogen element or
phenol, and M may be a group IIIB element. 2
[0024] The group IIIB element may be gallium, indium or aluminum.
This permits light to be more stably emitted.
[0025] The ternary complex compound may be
bis-(2-methyl-8-quinolinolato)-- chloro-gallium (hereinafter
referred to as "GaMq2Cl") having a molecular structure represented
by the following formula (2): 3
[0026] The ternary complex compound may be
bis-(2-methyl-8-quinolinolato)-- chloro-indium (hereinafter
referred to as "InMq2Cl") having a molecular structure represented
by the following formula (3): 4
[0027] The ternary complex-compound-may be
bis-(2-methyl-8-quinolinolato)-- phenolato-aluminum (hereinafter
referred to as "PhOAlq") having a molecular structure represented
by the following formula (4): 5
[0028] The ternary complex compound may be
bis-(2-methyl-8-quinolinolato)-- 4-(tert-butyl-phenolato)-aluminum
(hereinafter referred to as "tBuPhOAlq") having a molecular
structure represented by the following formula (5): 6
[0029] Preferably, the organic electroluminescent device further
includes an electron transport layer provided between the hole
blocking layer and the electron injection electrode, and the hole
blocking layer has greater ionization potential than that of the
electron transport layer.
[0030] In this way, holes can be prevented from being injected into
the electron transport layer from the luminescent layer, so that
electrons and holes can efficiently be recombined at the
luminescent layer. Therefore, the luminescent efficiency of the
organic electroluminescent device can be improved.
[0031] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic diagram of an organic EL device
according to one embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] FIG. 1 is a schematic diagram of an organic
electroluminescent device (hereinafter referred to as "organic EL
device") according to an embodiment of the present invention.
[0034] As shown in FIG. 1, in an organic EL device 100, a hole
injection electrode (anode) 2 composed of a transparent electrode
film is formed on a glass substrate 1. A hole transport layer 3 of
an organic material and a luminescent layer 4 composed of an
organic material are formed in this order on the hole injection
electrode 2. A hole blocking layer 5 composed of an organic
material is formed on the luminescent layer 4, an electron
transport layer 6 is formed on the hole blocking layer 5, and an
electron injection electrode (cathode) 7 is formed thereon.
[0035] The hole blocking layer 5 includes a ternary complex
compound composed of two quinolinol derivatives, a group IIIB
element, and a halogen element or a phenol derivative. The hole
blocking layer 5 has ionization potential greater than that of the
electron transport layer 6.
[0036] The ternary complex compound has a molecular structure
represented by the following formula (1): 7
[0037] In the above formula (1), R1 and R2 may be identical to or
different from one another each representing a hydrogen atom or a
substituent, A represents a halogen element or a phenol derivative,
and M represents a group IIIB element.
[0038] For example, R1 and R2 are --C.sub.nH.sub.2n+1(n=0 to 5),
--CN, --Cl, --Br, --OCH.sub.3, --OC.sub.2H.sub.5,
--N(CH.sub.3).sub.2, --N(C.sub.2H.sub.5).sub.2, a phenyl group, or
a thiophene group.
[0039] In the above formula (1), M represents gallium (Ga), indium
(In), aluminum (Al) or the like.
[0040] The ternacy complex compound represented by the above
formula (1) is manufactured by reacting a quinolinol derivative, a
group IIIB element compound, and a hologen element or a phenol
derivative to coordinate or chelate the quinolinol derivative and
the halogen element or the phenol derivative with the group IIIB
element. In this case, 1.5 to 2.5 mole of the quinolinol derivative
and 0.5 to 1.5 mole of the halogen element or the phenol derivative
are reacted with 1 mole of the group IIIB element compound. As the
group IIIB element compond, a chloride of Al, Ga or In or the like
can be used.
[0041] In particular, the above ternary complex compound is
preferably GaMq2Cl having a molecular structure represented by the
following formula (2): 8
[0042] The above ternary complex compound may be InMq2Cl having a
molecular structure represented by the following formula (3): 9
[0043] The above ternary complex compound may also be PhOAlq having
a molecular structure represented by the following formula (4):
10
[0044] The above ternary complex compound may also be tBuPhOAlq
having a molecular structure represented by the following formula
(5): 11
[0045] In the above described organic EL device 100, voltage is
applied across the hole injection electrode 2 and the electron
injection electrode 7, which causes the luminescent layer 4 to
generate light, and the light is emitted from the back surface of
the glass substrate 1.
[0046] In the organic EL device according to the embodiment, the
hole blocking layer 5 includes a ternary complex compound composed
of two quinolinol derivatives, a group IIIB element, and a halogen
element or a phenol derivative.
[0047] The presence of the hole blocking layer 5 increases the
energy barrier between the luminescent layer 4 and the hole
blocking layer 5. Therefore, holes can be prevented from being
injected into the electron transport layer 6 on the side of the
electron injection electrode 7 from the luminescent layer 4, so
that electrons and holes can efficiently be recombined at the
luminescent layer 4. In this way, the luminance and luminescent
efficiency of the organic EL device can be improved.
[0048] Since the above ternary complex compound is stable, the
organic EL device can stably emit light.
[0049] Note that the organic EL device according to the invention
is not limited to the above structure, and various other structures
can be employed. For example, there may be three layers, i.e., a
luminescent layer 4, a hole blocking layer 5 and an electron
transport layer 6 between the hole injection electrode 2 and the
electron injection electrode 7.
EXAMPLES
[0050] Organic EL devices according to Inventive Examples 1 to 4
and Comparative Example 1 were manufactured and measured for their
luminescent characteristics.
Inventive Examples 1 to 4
[0051] In Inventive Examples 1 to 4, such an organic EL device was
used that a hole injection electrode (anode) 2, a hole transport
layer 3, a luminescent layer 4, a hole blocking layer 5, an
electron transport layer 6 and an electron injection electrode
(cathode) 7 was stacked in this order on a glass substrate 1.
[0052] In this case, the hole injection electrode 2 in the organic
EL device is as thick as 1000 .ANG. and composed of indium-tin
oxide (ITO). The hole transport layer 3 is as thick as 500 .ANG.
and composed of N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine)
(hereinafter referred to as "NPB") having a molecular structure
represented by the following formula (7): 12
[0053] The luminescent layer 4 is as thick as 100 .ANG. and it
contains 4,4'-bis(carbazol-9-yl)-biphenyl (hereinafter referred to
as "CBP") having a molecular structure represented by the following
formula (8) as a host material and tris(2-phenylpyridine)iridium
(hereinafter referred to as "Ir(ppy)3") having a molecular
structure represented by the following formula (9) as a luminescent
dopant. 13
[0054] Note that in this case, the luminescent layer 4 includes 6
wt % Ir(ppy)3 relative to the CBP as the host material. The
ionization potential of the CBP as the host material is 5.9 eV.
[0055] The hole blocking layer 5 is as thick as 100 .ANG. and
composed of a ternary complex compound having a molecular structure
represented by the formula (1). In Inventive Example 1, as a
material for the hole blocking layer 5, GaMq2Cl having a molecular
structure represented by the formula (2) was used. In Inventive
Example 2, as a material for the hole blocking layer 5, InMq2Cl
having a molecular structure represented by the formula (3) was
used. In Inventive Example 3, as a material for the hole blocking
layer 5, PhOAlq having a molecular structure represented by the
formula (4) was used. In Inventive Example 4, as a material for the
hole blocking layer 5, tBuPhOAlq having a molecular structure
represented by the formula (5) was used.
[0056] The electron transport layer 6 is as thick as 200 .ANG., and
composed of tris (8-hydroxyquinolinato) aluminum (hereinafter
referred to as "Alq") having a molecular structure represented by
the following formula (10). The ionization potential of the
electron transport layer 6 of the Alq is 5.5 eV. 14
[0057] The electron injection electrode 7 is composed of a MgIn
alloy (in the ratio of 10:1) having a thickness of 2000 .ANG..
[0058] The organic EL devices having the above structure were
manufactured by the following method.
[0059] A hole injection electrode 2 made of indium-tin oxide (ITO)
was formed on a glass substrate 1. Then, the glass substrate 1 thus
having the hole injection electrode 2 thereon was cleaned with a
neutral detergent and was then subjected to ultrasonic-cleaning in
acetone for 10 minutes and in ethanol for 10 minutes. The surface
of the glass substrate 1 was then further cleaned using an ozone
cleaner.
[0060] Then, a hole transport layer 3, a luminescent layer 4, a
hole blocking layer 5, an electron transport layer 6 and an
electron injection electrode 7 were formed in this order on the
hole injection electrode 2 of ITO by vacuum vapor deposition. They
were all deposited at ordinary temperature at a vacuum degree of
1.times.10.sup.-6 Torr without controlling the substrate
temperature.
Comparative Example
[0061] The organic EL device according to Comparative Example 1 has
the same structure as those of the organic EL devices according to
Inventive Examples 1 to 4 except that BCP having a molecular
structure represented by the formula (6) is used as a material for
the hole blocking layer 5. The organic EL device according to
Comparative Example 1 was manufactured by the same method as that
for manufacturing the organic EL devices according to Embodiments 1
to 4.
[0062] Evaluation
[0063] The organic EL devices according to Inventive Examples 1 to
4 and Comparative Example 1 were measured for the luminescent
characteristics and tested for the luminescence in continuous use
with constant current. In the test, the organic EL devices were
driven with DC current while the initial luminance was set to 500
cd/cm.sup.2, and the retention rate of the initial luminance of 500
cd/cm.sup.2 after 300 hours was measured.
[0064] The measured results about the luminescent efficiency, the
luminescent wavelength, the maximum luminance and the retention
rate of the initial luminance of 500 cd/cm.sup.2 are given in Table
1.
1 TABLE 1 material luminescent retention rate of for hole
efficiency luminescent maximum initial luminance blocking (cd/A)
wavelength luminance 500 cd/m.sup.2 after 300 layer at10
mA/cm.sup.2 (nm) (cd/m.sup.2) hours Inventive GaMq2Cl 20.0 540
35,700 66% example 1 Inventive InMq2Cl 17.0 541 21,000 50% example
2 Inventive PhOAlq 25.0 540 45,000 70% example 3 Inventive
tBuPhOAlq 26.0 540 46,000 72% example 4 Comparative BCP 19.0 541
30,100 35% example 1
[0065] As shown in Table 1, the organic EL devices according to
Inventive Examples 1, 3, and 4 showed higher luminescent efficiency
and greater maximum luminance than the organic EL device according
to Comparative Example 1. Based on the result of the constant
current continues luminescence test, it was found that the organic
EL devices according to Inventive Examples 1 to 4 each provided a
retention rate of the initial luminance higher than that of the
organic EL device according to Comparative Example 1, and the
luminescence was stable. This is probably because in the organic EL
devices according to Inventive Examples 1 to 4, the ternary complex
compound used as a material for the hole blocking layer 5 was
stabler after the film was formed than the BCP used as a material
for the hole blocking layer in Comparative Example 1.
[0066] As in the foregoing and as can be understood from the
results by Inventive Examples 1 to 4 and Comparative Example 1,
using the ternary complex compound as a material for the hole
blocking layer 5, an organic EL device capable of stably emitting
light with high luminance and high luminescent efficiency can be
provided.
[0067] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *