U.S. patent application number 13/108484 was filed with the patent office on 2011-09-08 for organic electric field light emitting element and production therefor.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Koichiro IIDA, Hironori ISHIKAWA, Yuichiro KAWAMURA, Tomoyuki OGATA, Kazuki OKABE, Hideki SATO, Asato TANAKA, Mitsuru TANAMURA, Masayoshi YABE.
Application Number | 20110215312 13/108484 |
Document ID | / |
Family ID | 36953141 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110215312 |
Kind Code |
A1 |
YABE; Masayoshi ; et
al. |
September 8, 2011 |
ORGANIC ELECTRIC FIELD LIGHT EMITTING ELEMENT AND PRODUCTION
THEREFOR
Abstract
A composition for an organic electroluminescent device is a
composition for forming an organic light emitting layer of an
organic electroluminescent device by wet coating process. The
composition contains a phosphorescent material, a charge transport
material, and a solvent, in which the phosphorescent material and
the charge transport material are each an unpolymerized organic
compound, and the first oxidation potential of the phosphorescent
material E.sub.D.sup.+, the first reduction potential of the
phosphorescent material E.sub.D.sup.-, the first oxidation
potential of the charge transporting material E.sub.T.sup.+, and
the first reduction potential of the charge transporting material
E.sub.T.sup.- satisfy the following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.s-
up.+-0.1 or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1.
Inventors: |
YABE; Masayoshi; (Kanagawa,
JP) ; OGATA; Tomoyuki; (Kanagawa, JP) ; SATO;
Hideki; (Kanagawa, JP) ; IIDA; Koichiro;
(Kanagawa, JP) ; TANAKA; Asato; (Kanagawa, JP)
; TANAMURA; Mitsuru; (Kanagawa, JP) ; KAWAMURA;
Yuichiro; (US) ; ISHIKAWA; Hironori;
(Kanagawa, JP) ; OKABE; Kazuki; (Kanagawa,
JP) |
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Minato-ku
JP
|
Family ID: |
36953141 |
Appl. No.: |
13/108484 |
Filed: |
May 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11816672 |
Aug 20, 2007 |
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PCT/JP2006/302502 |
Feb 14, 2006 |
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13108484 |
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Current U.S.
Class: |
257/40 ;
252/301.16; 257/E51.018 |
Current CPC
Class: |
H01L 51/5088 20130101;
H01L 51/0081 20130101; H01L 51/0052 20130101; H01L 51/0059
20130101; H01L 51/0072 20130101; H01L 51/0058 20130101; C09K 11/025
20130101; H01L 51/5072 20130101; H01L 51/0007 20130101; H01L 51/008
20130101; H05B 33/14 20130101; H01L 51/0085 20130101; H01L 51/005
20130101; C09K 11/06 20130101; H01L 51/5048 20130101; H01L 51/0067
20130101; H01L 51/0061 20130101; H01L 51/5096 20130101; C09K
2211/1029 20130101; H01L 51/5016 20130101; H01L 51/0035 20130101;
C09K 2211/185 20130101; C09K 2211/1007 20130101 |
Class at
Publication: |
257/40 ;
252/301.16; 257/E51.018 |
International
Class: |
H01L 51/52 20060101
H01L051/52; C09K 11/06 20060101 C09K011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2005 |
JP |
2005-044250 |
Claims
1. A composition for an organic electroluminescent device,
comprising a phosphorescent material, a charge transport material,
and a solvent, wherein each of the phosphorescent material and the
charge transport material is independently an unpolymerized organic
compound, and wherein the first oxidation potential of the
phosphorescent material ED.sup.+, the first reduction potential of
the phosphorescent material ED.sup.-, the first oxidation potential
of the charge transport material ET.sup.+, and the first reduction
potential of the charge transport material ET.sup.- satisfy the
following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1 (1) or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1 (2).
2. The composition for an organic electroluminescent device
according to claim 1, wherein said condition
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1 is satisfied, and an absolute value of the difference
between E.sub.D.sup.+ and
E.sub.T.sup.+|E.sub.D.sup.+-E.sub.T.sup.+| is 0.1 V or more.
3. The composition for an organic electroluminescent device
according to claim 1, wherein said condition
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1 is satisfied, an absolute value of the difference between
E.sub.D.sup.+ and E.sub.T.sup.- |E.sub.D.sup.+-E.sub.T.sup.-| is
1.0 V or more.
4. The composition for an organic electroluminescent device
according to claim 1, wherein said condition
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1 is satisfied, an absolute value of the difference between
E.sub.D.sup.- and E.sub.T.sup.- |E.sub.D.sup.--E.sub.T.sup.-| is
0.10 V or more.
5. The composition for an organic electroluminescent device
according to claim 1, wherein said condition
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1 is satisfied, an absolute value of the difference between
E.sub.T.sup.+ and E.sub.D.sup.- |E.sub.T.sup.+-E.sub.D.sup.-| is
1.5 V or more.
6. The composition for an organic electroluminescent device
according to claim 1, wherein the condition
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1 is satisfied, and an absolute value of the difference
between E.sub.D.sup.- and E.sub.T.sup.-
|E.sub.D.sup.--E.sub.T.sup.-| is 0.1 V or more.
7. The composition for an organic electroluminescent device
according to claim 1, wherein the condition
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1 is satisfied, and an absolute value of the difference
between E.sub.T.sup.+ and E.sub.D.sup.-
|E.sub.T.sup.+-E.sub.D.sup.-| is 1.0 V or more.
8. The composition for an organic electroluminescent device
according to claim 1, wherein the condition
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1 is satisfied, and an absolute value of the difference
between E.sub.D.sup.+ and E.sub.T.sup.+
|E.sub.D.sup.+-E.sub.T.sup.+| is 0.1 V or more.
9. The composition for an organic electroluminescent device
according to claim 1, wherein the condition
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1 is satisfied, and an absolute value of the difference
between E.sub.T.sup.- and E.sub.D.sup.+
|E.sub.T.sup.--E.sub.D.sup.+| is 1.5 V or more.
10. A thin film for an organic electroluminescent device formed
from the composition for an organic electroluminescent device of
claim 1 by a wet coating process.
11. The thin film for an organic electroluminescent device
according to claim 10, wherein the thin film has a refractive index
of 1.78 or less with respect to light having a wavelength of 500 nm
to 600 nm.
12. A transfer member for a thin film for an organic
electroluminescent device, comprising a base material and a thin
film arranged on the base material, wherein the thin film is formed
from the composition for an organic electroluminescent device of
claim 1 by a wet coating process.
13. An organic electroluminescent device comprising a substrate
bearing an anode, a cathode, and an organic light emitting layer
arranged between the two electrodes, wherein the organic light
emitting layer is a layer formed by using the transfer member for a
thin film for an organic electroluminescent device of claim 12.
14. An organic electroluminescent device comprising a substrate
bearing an anode, a cathode, and an organic light emitting layer
arranged between the anode and cathode, wherein the organic light
emitting layer is a layer formed from the composition for an
organic electroluminescent device of claim 1 by a wet coating
process.
15. The organic electroluminescent device according to claim 13,
further comprising a hole injection layer between the organic light
emitting layer and the anode.
16. The organic electroluminescent device according to claim 14,
further comprising a hole injection layer between the organic light
emitting layer and the anode.
17. The organic electroluminescent device according to claim 13,
further comprising an electron injection layer between the organic
light emitting layer and the cathode.
18. The organic electroluminescent device according to claim 14,
further comprising an electron injection layer between the organic
light emitting layer and the cathode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a composition for an
organic electroluminescent device which can easily yield an organic
electroluminescent device through wet coating process, and the
resulting organic electroluminescent device has an excellent
luminous efficiency and a satisfactory operating life. It also
relates to a thin film for an organic electroluminescent device, a
transfer member for a thin film for an organic electroluminescent
device, and an organic electroluminescent device, each of which is
formed by using the composition for an organic electroluminescent
device. In addition, it relates to a method of manufacturing the
organic electroluminescent device.
BACKGROUND OF THE INVENTION
[0002] There have been developed electroluminescent devices using
organic thin films (organic electroluminescent devices). Materials
for organic electroluminescent devices can be roughly classified
into low molecular weight materials and high molecular weight
materials.
[0003] There have been developed organic electroluminescent devices
using low molecular weight materials. Examples of such devices
include an organic electroluminescent device having a hole
transport layer formed from an aromatic diamine, and a light
emitting layer formed from aluminum 8-hydroxyquinoline complex; and
an organic electroluminescent device using aluminum
8-hydroxyquinoline complex as a host material, doped with a
fluorescent dye for laser, such as coumarin. Low molecular weight
materials such as the following platinum complex and iridium
complex are also used as materials for light emitting layers.
##STR00001##
[0004] There have also been developed organic electroluminescent
devices using high molecular weight materials such as
poly(p-phenylenevinylene)s,
poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]s, and
poly(3-alkylthiophene)s; and devices using high molecular weight
materials such as polyvinylcarbazoles, in combination with low
molecular weight luminescent materials and electron transfer
materials. Most of such devices using high molecular weight
materials are manufactured by wet coating process such as spin
coating or an ink jet process, in consideration of properties of
the materials.
[0005] Focusing attention on processes for forming thin films,
films of most low molecular weight materials have been formed by
vacuum deposition, and films of most high molecular weight
materials have been formed by wet coating process. The vacuum
deposition is advantageous typically in that a film with good
quality can be uniformly formed on a substrate, that a multilayer
film can be easily formed to yield a device having excellent
properties easily, and that contamination of impurities derived
from the manufacturing process is very little. Accordingly, most of
organic electroluminescent devices currently used in practice are
formed by vacuum deposition using low molecular weight
materials.
[0006] In contrast, the wet coating process is advantageous
typically in that no vacuum process is required, that a film with a
larger area can be easily obtained, and that one layer (coating
composition) can contain plural materials having different
functions. The wet coating process, however, has following
problems, and most devices formed by wet coating process are not
developed to a practical level, except for those using some high
molecular weight materials.
[0007] It is difficult to control the degrees of polymerization and
the molecular weight distributions of high molecular weight
materials (polymerized organic compounds).
[0008] When devices are operated continuously, terminal residues
cause deterioration of the devices.
[0009] It is difficult to purify high molecular weight materials
highly, and the resulting materials may contain impurities.
[0010] As an attempt to solve these problems, following Patent
Document 1 and Patent Document 2 each disclose the use of low
molecular weight materials (unpolymerized organic compounds) each
containing a fluorescent substance, a hole transport material, and
an electron transport material, instead of high molecular weight
materials (polymerized organic compounds). This attempt is intended
to reduce the drive voltage by allowing the hole transport material
and the electron transport material to transport holes and
electrons injected from an anode and a cathode, respectively. The
resulting devices, however, operate at high drive voltages and have
insufficient luminous efficiencies, because holes and electrons are
not sufficiently injected from the anode and cathode, respectively.
Oxadiazole derivatives used as the electron transport material are
insufficient in drive stability (operation stability) and thereby
insufficient in operating life. In addition, it is difficult to
adopt a phosphorescent material or a blue-emitting material as a
luminescent material, because the resulting luminescent material
has a large energy gap. [0011] Patent Document 1: Japanese Patent
No. 3069139 [0012] Patent Document 2: Japanese Unexamined Patent
Application Publication No. 11-273859
DISCLOSURE OF INVENTION
[0013] An object of the present invention is to provide an organic
electroluminescent device which has an organic light emitting layer
formed by wet coating process, enables charges to be injected from
electrodes into the organic light emitting layer satisfactorily,
and shows an excellent luminous efficiency and a satisfactory
operating life.
[0014] According to a first aspect of the present invention, there
is provided a composition for an organic electroluminescent device,
including a phosphorescent material, a charge transport material,
and a solvent. Each of the phosphorescent material and the charge
transport material is independently an unpolymerized organic
compound.
[0015] In the composition, the first oxidation potential of the
phosphorescent material E.sub.D.sup.+,
[0016] the first reduction potential of the phosphorescent material
E.sub.D.sup.-,
[0017] the first oxidation potential of the charge transporting
material E.sub.T.sup.+, and
[0018] the first reduction potential of the charge transporting
material E.sub.T.sup.-
satisfy the following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.s-
up.+-0.1
or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.s-
up.+-0.1
[0019] According to a second aspect, there is provided a thin film
for an organic electroluminescent device, which is a thin film
formed from the composition for an organic electroluminescent
device according to the first aspect through wet coating
process.
[0020] According to a third aspect, there is provided a transfer
member for a thin film for an organic electroluminescent device,
which includes a base material and a thin film arranged on the base
material, in which the thin film is formed from the composition for
an organic electroluminescent device according to the first aspect
through wet film-formation.
[0021] According to a fourth aspect, there is provided an organic
electroluminescent device including a substrate bearing an anode, a
cathode, and an organic light emitting layer arranged between the
two electrodes, in which the organic light emitting layer is a
layer formed by using the transfer member for a thin film for an
organic electroluminescent device according to the third
aspect.
[0022] According to a fifth aspect, there is provided an organic
electroluminescent device including a substrate bearing an anode, a
cathode, and an organic light emitting layer arranged between the
two electrodes, in which the organic light emitting layer is a
layer formed from the composition for an organic electroluminescent
device according to the first aspect through wet
film-formation.
[0023] According to a six aspect, there is provided a method of
manufacturing an organic electroluminescent device including a
substrate bearing an anode, a cathode, and an organic light
emitting layer arranged between the two electrodes. The method
includes the step of forming the organic light emitting layer by
wet film-formation using the composition for an organic
electroluminescent device according to the first aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic cross-sectional view illustrating an
embodiment of a transfer member for a thin film for an organic
electroluminescent device.
[0025] FIG. 2 is a schematic cross-sectional view illustrating an
embodiment of an organic electroluminescent device.
[0026] FIG. 3 is a schematic cross-sectional view illustrating
another embodiment of the organic electroluminescent device.
[0027] FIG. 4 is a schematic cross-sectional view illustrating yet
another embodiment of the organic electroluminescent device.
[0028] FIG. 5 is a schematic cross-sectional view illustrating
another embodiment of the organic electroluminescent device.
[0029] FIG. 6 is a schematic cross-sectional view illustrating
another embodiment of the organic electroluminescent device.
[0030] FIG. 7 is a schematic cross-sectional view illustrating
another embodiment of the organic electroluminescent device.
[0031] FIG. 8 is a graph showing an electroluminescence spectrum of
a device prepared according to Example 1.
DETAILED DESCRIPTION
[0032] A composition for an organic electroluminescent device
according to the present invention has a long pot life, excellent
heat resistance, and a low viscosity, and is satisfactorily
homogenous. In addition, the thickness of a film of the composition
upon film-formation can be easily adjusted. By using the
composition for an organic electroluminescent device, an organic
electroluminescent device can be easily obtained through wet
film-formation, and the resulting device enables charges to be
satisfactorily injected from electrodes into an organic light
emitting layer and has an excellent luminous efficiency and a
satisfactory operating life.
[0033] Known organic electroluminescent devices prepared through
wet film-formation fail to enable charges to be satisfactorily
injected from electrodes into an organic light emitting layer. They
also operate at high drive voltages and have insufficient luminous
efficiencies, unsatisfactory drive stability and operating lives.
In addition, they have such energy gaps in their luminescent
materials as to inhibit practical use of such devices. In contrast,
the composition for an organic electroluminescent device according
to the present invention solves these problems in related art. The
reason for this has not yet been clarified but is supposed as
follows.
[0034] It has been considered that wide-gap charge transporting
materials (host materials) are required for light emission of
wide-gap devices typically including phosphorescent materials and
blue-emitting materials. A phosphorescent material and a charge
transporting material can be significantly involved in injection of
either one of hole and electron, and as a result the device can be
driven at low voltage, when:
[0035] the first oxidation potential of the phosphorescent material
E.sub.D.sup.+,
[0036] the first reduction potential of the phosphorescent material
E.sub.D.sup.-,
[0037] the first oxidation potential of the charge transporting
material E.sub.T.sup.+, and
[0038] the first reduction potential of the charge transporting
material E.sub.T.sup.-
satisfy the following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.s-
up.+-0.1
or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.s-
up.+-0.1
When one of the charges (hole or electron) is trapped by the
highest occupied molecular orbital (HOMO) or lowest unoccupied
molecular orbital (LUMO) of the phosphorescent material, the
phosphorescent material has an increased lowest unoccupied
molecular orbital (LUMO) or a decreased highest occupied molecular
orbital (HOMO) to such a level as to easily receive a charge from
the lowest unoccupied molecular orbital (LUMO) or the highest
occupied molecular orbital (HOMO) of the charge transporting
material. Thus, the phosphorescent material can emit light with a
high efficiency.
[0039] When materials satisfy the above-mentioned condition,
satisfactory advantages are obtained in an organic
electroluminescent device having a light emitting layer formed
through wet coating process. When the light emitting layer is
formed by vapor deposition, there is generally no difference
between a device which satisfies the condition and a device which
does not.
[0040] A thin film for an organic electroluminescent device
according to the present invention is formed from the composition
for an organic electroluminescent device according to the present
invention through wet coating process. The thin film has excellent
light-emitting properties, good quality, and excellent heat
resistance and is resistant to deterioration even when being
electrified over a long time.
[0041] A transfer member for a thin film for an organic
electroluminescent device according to the present invention
includes a base material and a thin film formed on the base
material through wet coating process using the composition for an
organic electroluminescent device according to the present
invention. By using the transfer member, an organic thin film can
be easily and conveniently obtained, and the organic thin film has
excellent light-emitting properties, good quality, and excellent
heat resistance and is resistant to deterioration even when being
electrified over a long time.
[0042] An organic electroluminescent device according to the
present invention includes an organic light emitting layer formed
through wet coating process using the composition for an organic
electroluminescent device according to the present invention. A
method for manufacturing the organic electroluminescent device
according to the present invention manufactures the organic
electroluminescent device by forming an organic light emitting
layer formed through wet coating process using the composition for
an organic electroluminescent device according to the present
invention. According to the organic electroluminescent device and
the manufacturing method thereof, an organic electroluminescent
device having high practicality can be easily manufactured through
easy and convenient steps.
[0043] Accordingly, organic electroluminescent devices according to
the present invention can supposedly be applied to flat panel
displays such as those for office automation (OA) computers and
those as wall-hanging televisions; onboard display devices;
displays for cellular phones; light sources utilizing the
characteristics as flat light-emitting devices, such as light
sources for copying machines and backlight sources for liquid
crystal displays or meters; indication panels; and marker
lamps.
[0044] Some embodiments of the present invention will be
illustrated in detail below. It should be noted, however, that
following description on components is illustrated only as examples
(representative examples) of embodiments according to the present
invention, and they are not limitative at all unless departing from
the scope and spirit of the present invention.
[Composition for Organic Electroluminescent Device]
[0045] A composition for an organic electroluminescent device
according to the present invention includes a phosphorescent
material, a charge transporting material, and a solvent. Each of
the phosphorescent material and the charge transporting material is
independently an unpolymerized organic compound.
[0046] The first oxidation potential of the phosphorescent material
E.sub.D.sup.+,
[0047] the first reduction potential of the phosphorescent material
E.sub.D.sup.-,
[0048] the first oxidation potential of the charge transporting
material E.sub.T.sup.+, and
[0049] the first reduction potential of the charge transporting
material E.sub.T.sup.-
satisfy the following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.s-
up.+-0.1
or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.s-
up.+-0.1
[0050] The terms "unpolymerized organic compound", "phosphorescent
material", and "charge transporting material" herein are defined as
follows.
[0051] Unpolymerized Organic Compound
[0052] The term "unpolymerized organic compound" as used herein
refers to an organic compound other than a compound generally
called polymer (polymerized organic compound). Namely, it refers to
a substance other than a substance containing a high molecular
weight polymer or a condensation product formed as a result of
chain-like repetitions of the same or similar reactions of a low
molecular weight compound. More specifically, it refers to a
compound which has a substantially single molecular weight and
differs from a high molecular weight organic compound formed as a
result of regular or random polymerization of one or more
polymerizable monomers, oligomers, or polymers, according to any
process. The "unpolymerized organic compound" has a molecular
structure that can be uniquely and quantitatively defined by a
chemical formula.
[0053] Phosphorescent Material
[0054] The term "phosphorescent material" as used herein refers to
a component which mainly acts to emit light and corresponds to a
dopant component in an organic electroluminescent device according
to the present invention. A component or material is defined as the
luminescent material when generally 10% to 100%, preferably 20% to
100%, more preferably 50% to 100%, and most preferably 80% to 100%
of light (unit: cd/m.sup.2) emitted from the organic
electroluminescent device is identified to be from the component or
material.
[0055] However, the phosphorescent material may have charge
transporting ability, as long as its light emitting function is not
impaired. The phosphorescent material may include one compound
alone or two or more different compounds in arbitrary combinations
and proportions.
[0056] Hereinafter the "phosphorescent material" is also simply
referred as "luminescent material".
[0057] Charge Transport Material
[0058] The term "charge transport material" refers to a material
that can transfer a given charge (namely, electron or hole). The
charge transporting material is not specifically limited, as long
as it satisfy this condition, and can include any materials. Each
of these charge transporting materials can be used alone or used in
arbitrary combinations and proportions.
[0059] Methods of Measuring Oxidation Potentials and Reduction
Potentials
[0060] The first oxidation potential and the first reduction
potential can be determined according to the following
electrochemical measurement (cyclic voltammetry). A supporting
electrolyte, a solvent, and electrodes for use in the measurement
are not limited to those described below, and any supporting
electrolyte, solvent, and electrodes will do, as long as a similar
measurement can be conducted.
[0061] Initially, a tested material (a luminescent material or
charge transport material relating to the present invention) is
dissolved in an organic solvent containing about 0.1 mol/L of a
supporting electrolyte such as tetrabutylammonium perchlorate or
tetrabutylammonium hexafluorophosphate, to yield about 0.1 to 2 mM
solution. After removing oxygen from the solution by procedures
such as bubbling of dry nitrogen, degassing under reduced pressure,
or application of ultrasound, the solution in an electrically
neutral state is subjected to electrolytic oxidation (or reduction)
using a working electrode such as a glassy carbon electrode, and a
counter electrode such as a platinum electrode at a sweep rate of
100 mV/sec. The potential of a first peak detected in electrolytic
oxidation (or reduction) is compared with the oxidation/reduction
potential of a reference material such as ferrocene, to thereby
determine the oxidation (or reduction) potential of the tested
material. The oxidation (or reduction) potential thus determined is
further converted into a value versus saturated calomel electrode
(SCE) as the reference electrode, and the converted value is
defined as the first oxidation (or reduction) potential in the
present invention.
[0062] An organic solvent for use in the measurement should be one
having a sufficiently low water content. The organic solvent may be
one that can satisfactorily dissolve a luminescent material or
charge transport material relating to the present invention
therein, is resistant to electrolytic oxidation (or reduction), and
ensures a wide potential window. Examples of such organic solvents
include acetonitrile, methylene chloride, N,N-dimethylformamide,
and tetrahydrofuran.
[0063] Individual components constituting a composition for an
organic electroluminescent device according to the present
invention, and the conditions for their oxidation/reduction
potentials, for example, will be described below.
[0064] <Phosphorescent Material>
[0065] Any known materials are applicable as the phosphorescent
material, and each of such phosphorescent materials can be used
alone or in combination. Phosphorescent materials are excellent
from the viewpoint of internal quantum efficiency. If a fluorescent
material is used herein instead of a phosphorescent material, the
resulting device does not effectively have an improved efficiency
or a prolonged life, even the condition between the charge
transport material and the luminescent material is satisfied.
[0066] It is important to reduce the molecular symmetry or rigidity
of the luminescent material and/or to introduce a lipophilic
substituent such as an alkyl group into the luminescent material,
in order to improve the solubility in a solvent.
[0067] Preferred examples of phosphorescent materials include
organometallic complexes each containing a metal selected from
transition metals belonging to Group 7 to Group 11 of the periodic
table (periodic table of elements: IUPAC Periodic Table of the
Elements, 2004).
[0068] Preferred metals in phosphorescent organometallic complexes
each containing a metal selected from transition metals belonging
to Group 7 to Group 11 of the periodic table include ruthenium,
rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and
gold. Preferred examples of these organometallic complexes include
compounds represented by following Formulae (4) and (5), and
compounds described in PCT International Publication Numbers WO
2005/011370 and WO 2005/019373.
MG.sub.(q-j)G'.sub.j (4)
[0069] In Formula (4), M represents a metal; "q" represents the
valency of the metal M; G and G' each represent a bidentate ligand;
and "j" represents 0, 1, or 2.
##STR00002##
[0070] In Formula (5), M.sup.5 represents a metal; T represents
carbon or nitrogen; and R.sup.92 to R.sup.95 each independently
represent a substituent, wherein R.sup.94 and R.sup.95 are absent
when T is nitrogen.
[0071] Initially, compounds represented by Formula (4) will be
illustrated below.
[0072] In Formula (4), M represents any metal. Preferred examples
thereof include the metals listed as the metals selected from Group
7 to Group 11 of the periodic table.
[0073] The bidentate ligands G and G' in Formula (4) each
independently represent a ligand having the following partial
structure:
##STR00003## ##STR00004##
[0074] From the viewpoint of stability of the complex, G' is
especially preferably:
##STR00005##
[0075] In the partial structures in G and G', Ring Q1 represents an
aromatic hydrocarbon group or an aromatic heterocyclic group, each
of which may have a substituent; and Ring Q2 represents a
nitrogen-containing aromatic heterocyclic group which may have a
substituent.
[0076] The phrase "which may have a substituent" as used herein
means "which may have one or more substituents".
[0077] Preferred substituents on Rings Q1 and Q2 include halogen
atoms such as fluorine atom; alkyl groups such as methyl group and
ethyl group; alkenyl groups such as vinyl group; alkoxycarbonyl
groups such as methoxycarbonyl group and ethoxycarbonyl group;
alkoxy groups such as methoxy group and ethoxy group; aryloxy
groups such as phenoxy group and benzyloxy group; dialkylamino
groups such as dimethylamino group and diethylamino group;
diarylamino groups such as diphenylamino group; carbazolyl group;
acyl groups such as acetyl group; haloalkyl groups such as
trifluoromethyl group; cyano group; and aromatic hydrocarbon groups
such as phenyl group, naphthyl group, and phenantrhyl group.
[0078] More preferred examples of compounds represented by Formula
(4) include compounds represented by following Formulae (4a), (4b),
and (4c):
##STR00006##
[0079] In Formula (4a), M.sup.a represents a metal as with M;
q.sup.a represents the valency of the metal M.sup.a; Ring Q1
represents an aromatic hydrocarbon group or an aromatic
heterocyclic group, each of which may have a substituent; and Ring
Q2 represents a nitrogen-containing aromatic heterocyclic group
which may have a substituent.
##STR00007##
[0080] In Formula (4b), M.sup.b represents a metal as with M;
q.sup.b represents the valency of the metal M.sup.b; Ring Q1
represents an aromatic hydrocarbon group or an aromatic
heterocyclic group, each of which may have a substituent; and Ring
Q2 represents a nitrogen-containing aromatic heterocyclic group
which may have a substituent.
##STR00008##
[0081] In Formula (4c), M.sup.c represents a metal as with M;
q.sup.c represents the valency of the metal M.sup.c; "j" represents
0, 1, or 2; Ring Q1 and Ring Q1' each independently represent an
aromatic hydrocarbon group or an aromatic heterocyclic group, each
of which may have a substituent; and Ring Q2 and Ring Q2' each
independently represent a nitrogen-containing aromatic heterocyclic
group which may have a substituent.
[0082] Preferred examples as Ring Q1 and Ring Q1' in Formulae (4a),
(4b), and (4c) include phenyl group, biphenyl group, naphthyl
group, anthryl.quadrature.group, thienyl group, furyl group,
benzothienyl group, benzofuryl group, pyridyl group, quinolyl
group, isoquinolyl group, and carbazolyl group.
[0083] Preferred examples as Ring Q2 and Ring Q2' include pyridyl
group, pyrimidyl group, pyrazyl group, triazyl group,
benzothiazolyl group, benzoxazolyl group, benzimidazolyl group,
quinolyl group, isoquinolyl group, quinoxalyl group, and
phenanthrydyl group.
[0084] Examples of substituents which compounds represented by
Formulae (4a), (4b), and (4c) may have include halogen atoms such
as fluorine atom; alkyl groups such as methyl group and ethyl
group; alkenyl groups such as vinyl group; alkoxycarbonyl groups
such as methoxycarbonyl group and ethoxycarbonyl group; alkoxy
groups such as methoxy group and ethoxy group; aryloxy groups such
as phenoxy group and benzyloxy group; dialkylamino groups such as
dimethylamino group and diethylamino group; diarylamino groups such
as diphenylamino group; carbazolyl group; acyl groups such as
acetyl group; haloalkyl groups such as trifluoromethyl group; and
cyano group.
[0085] When the substituent is an alkyl group, it may generally
have one or more and six or less carbon atoms. When the substituent
is an alkenyl group, it may generally have two or more and six or
less carbon atoms. When the substituent is an alkoxycarbonyl group,
it may generally have two or more and six or less carbon atoms.
When the substituent is an alkoxy group, it may generally have one
or more and six or less carbon atoms. When the substituent is an
aryloxy group, it may generally have six or more and fourteen or
less carbon atoms. When the substituent is a dialkylamino group, it
may generally have two or more and twenty-four or less carbon
atoms. When the substituent is a diarylamino group, it may
generally have twelve or more and twenty-eight or less carbon
atoms. When the substituent is an acyl group, it may generally have
one or more and fourteen or less carbon atoms. When the substituent
is a haloalkyl group, it may generally have one or more and twelve
or less carbon atoms.
[0086] These substituents may be combined to form a ring. More
specifically, for example, a substituent of Ring Q1 and a
substituent of Ring Q2 may be combined to form one condensed ring,
or a substituent of Ring Q1' and a substituent of Ring Q2' may be
combined to form one condensed ring. An example of the condensed
ring includes 7,8-benzoquinoline group.
[0087] More preferred substituents on Ring Q1, Ring Q1', Ring Q2,
and Ring Q2' include alkyl groups, alkoxy groups, aromatic
hydrocarbon groups, cyano group, halogen atoms, haloalkyl groups,
diarylamino groups, and carbazolyl group.
[0088] Preferred examples of M.sup.a, M.sup.b, and M.sup.c in
Formulae (4a), (4b), and (4c) include ruthenium, rhodium,
palladium, silver, rhenium, osmium, iridium, platinum, and
gold.
[0089] Specific examples of organometallic complexes represented by
Formulae (4), (4a), (4b), and (4c) are illustrated below, which,
however, are not limitative at all. In the following formulae, Ph
represents phenyl group.
##STR00009## ##STR00010## ##STR00011## ##STR00012##
##STR00013##
[0090] Of organometallic complexes represented by Formulae (4),
(4a), (4b), and (4c), typically preferred are compounds each
having, as ligand G and/or G', a 2-arylpyridine ligand such as an
2-arylpyridine, an 2-arylpyridine derivative having any
substituent, or an 2-arylpyridine derivative condensed with any
group.
[0091] Next, compounds represented by Formula (5) will be
illustrated.
[0092] In Formula (5), M.sup.5 represents a metal, and specific
examples thereof include the metals listed as the metal selected
from metals belonging to Group 7 to Group 11 of the periodic table.
Among them, preferred are ruthenium, rhodium, palladium, silver,
rhenium, osmium, iridium, platinum, and gold, of which bivalent
metals such as platinum and palladium are more preferred.
[0093] In Formula (5), R.sup.92 and R.sup.93 each independently
represent hydrogen atom, a halogen atom, an alkyl group, an aralkyl
group, an alkenyl group, cyano group, an amino group, an acyl
group, an alkoxycarbonyl group, carboxyl group, an alkoxy group, an
alkylamino group, an aralkylamino group, a haloalkyl group,
hydroxyl group, an aryloxy group, an aromatic hydrocarbon group, or
an aromatic heterocyclic group.
[0094] When T is carbon, R.sup.94 and R.sup.95 each independently
represent a substituent exemplified as with R.sup.92 and R.sup.93.
When T is nitrogen, R.sup.94 and R.sup.95 are absent.
[0095] R.sup.92 to R.sup.95 may each further have a substituent.
There is no limitation on substituents which these groups may
further have, and any groups can be employed as the
substituents.
[0096] Adjacent two of R.sup.92 to R.sup.95 may be combined to form
a ring.
[0097] Specific examples (5-a, 5-b, 5-c, 5-d, 5-e, 5-f, and 5-g) of
organometallic complexes represented by Formula (5) are illustrated
below, which, however, are not limitative at all. In the following
formulae, Me represents methyl group, and Et represents ethyl
group.
##STR00014## ##STR00015##
[0098] The molecular weight of a compound for use as a luminescent
material in the present invention is generally 10000 or less,
preferably 5000 or less, more preferably 4000 or less, and further
preferably 3000 or less, and is generally 100 or more, preferably
200 or more, more preferably 300 or more, and further preferably
400 or more. If the molecular weight is less than 100, there may
result in significant decrease of heat resistance, may cause gas
generation, may invite decreased quality of a film formed from the
composition, or may cause morphological change of the resulting
organic electroluminescent device due typically to migration. If
the molecular weight exceeds 10000, it may be difficult to purify
the organic compound or it may possibly take a long time to
dissolve the organic compound in a solvent.
[0099] The first oxidation potential E.sub.D.sup.+ of a luminescent
material for use in the present invention is generally 0.1 V or
more, preferably 0.2 V or more, more preferably 0.3 V or more,
further preferably 0.4 V or more, and most preferably 0.5 V or
more, and is generally 2.0 V or less, preferably 1.6 V or less,
more preferably 1.4 V or less, further preferably 1.2 V or less,
and most preferably 1.0 V or less.
[0100] If the first oxidation potential of the luminescent material
E.sub.D.sup.+ is less than 0.1 V, the first reduction potential of
the luminescent material E.sub.D.sup.- must be set at a very low
value. When this luminescent material is used in an organic
electroluminescent device, there may result in significant
imbalance between positive and negative charges, or there may cause
decreased durability of the luminescent material against reduction,
and the device may highly possibly fail to have a sufficient
luminance and/or a satisfactory life. In contrast, if the first
oxidation potential of the luminescent material E.sub.D.sup.+
exceeds 2.0 V, there may invite decreased durability of the
luminescent material against oxidation, and the device may highly
possibly fail to have a sufficient luminance and/or a satisfactory
life.
[0101] The first reduction potential of the luminescent material
E.sub.D.sup.- for use in the present invention is generally -3.0 V
or more, preferably -2.8 V or more, more preferably -2.7 V or more,
further preferably -2.6 V or more, and most preferably -2.5 V or
more, and is -1.0 V or less, preferably -1.2 V or less, more
preferably -1.4 V or less, further preferably -1.6 V or less, and
most preferably -1.8 V or less.
[0102] If a luminescent material having a first reduction potential
E.sub.D.sup.- less than -3.0 V is used in an organic
electroluminescent device, there may result in significant
imbalance between positive and negative charges, or there may cause
decreased durability of the luminescent material against reduction,
and the device may highly possibly fail to have a sufficient
luminance and/or a satisfactory life. In contrast, if a luminescent
material having a first reduction potential E.sub.D.sup.- exceeding
-1.0 V is used in an organic electroluminescent device, the first
oxidation potential E.sub.D.sup.+ of the luminescent material must
be set at a very high value, and there may invite decreased
durability of the luminescent material against oxidation, and the
device may highly possibly fail to have a sufficient luminance
and/or a satisfactory life.
[0103] <Charge Transport Material>
[0104] A charge transport material for use in the present invention
desirably has at least one of the following functions:
[0105] (i) Injection function: the function of receiving a hole
from an anode or a hole injection layer when an electric field is
applied, and/or the function of receiving an electron from a
cathode or an electron injection layer when an electric field is
applied.
[0106] (ii) Transporting function: the function of transporting
injected charges by the action of an electric field.
[0107] (iii) Light emitting function: the function of providing a
field for the recombination between an electron and a hole and
using this for the light emission.
[0108] (iv) Blocking function: the function of controlling the
transfer of charges so as to enable transportation and
recombination of the charges in good balance.
[0109] There may be a difference in easiness between the hole
injection and the electron injection, and there may be a difference
in transportability as represented by mobility between hole and
electron. However, a charge transport material for use herein
should essentially be capable of efficiently transporting at least
one of the two charges (hole and electron).
[0110] From these viewpoints, the compound for use as a charge
transport material is typically preferably an organic compound
represented by following Formula (1):
(A)n-Z (1)
[0111] In Formula (1), "A" represents an aromatic hydrocarbon group
or an aromatic heterocyclic group;
[0112] "n" represents an integer of 1 or more and 10 or less;
[0113] "Z" represents a hydrogen atom or a substituent when "n" is
1, and "Z" represents a direct bond or a linkage group having a
valency of "n" when "n" is 2 or more; and
[0114] when "n" is 2 or more, plural "A"s may be the same as or
different from each other, and wherein "A" and "Z" may each further
have a substituent.
[0115] Compounds represented by Formula (1) will be illustrated in
detail below.
[0116] In Formula (1), "n" represents an integer which is generally
1 or more, and preferably 2 or more, and is generally 10 or less,
and preferably 6 or less. If the number "n" exceeds this range, it
may be difficult to reduce impurities sufficiently through
purification procedures. If "n" is less than this range, the charge
injecting/transporting ability may be significantly reduced.
[0117] When "n" is 1, "Z" is hydrogen atom or any substituent in
Formula (1). When "Z" is a substituent, specific examples thereof
include alkyl groups, alkenyl groups, alkynyl groups, amino groups,
alkoxycarbonylamino groups, aryloxycarbonylamino groups,
heterocyclic oxycarbonylamino groups, sulfonylamino groups, alkoxy
groups, aryloxy groups, heterocyclic oxy groups, acyl groups,
alkoxycarbonyl groups, aryloxycarbonyl groups, heterocyclic
oxycarbonyl groups, acyloxy groups, sulfamoyl groups, carbamoyl
groups, alkylthio groups, arylthio groups, heterocyclic thio
groups, sulfonyl groups, sulfenyl groups, ureido groups,
phosphoramido groups, hydroxyl group, mercapto group, cyano group,
sulfo group, carboxyl group, nitro group, hydroxamate group,
sulfino group, hydrazino group, silyl groups, boryl groups,
phosphino groups, aromatic hydrocarbon groups, aromatic
heterocyclic groups, groups represented by following Formula (2),
and groups represented by following Formula (3):
##STR00016##
[0118] In Formula (2), R.sup.a represents any substituent. The
substituent R.sup.a is generally a substituent having one or more
and ten or less carbon atoms, and is preferably one having six or
less carbon atoms. Specific examples of R.sup.a include alkyl
groups, aralkyl groups, and aromatic hydrocarbon groups.
[0119] In Formulae (2) and (3), R.sup.b, R.sup.c, and R.sup.d each
independently represent hydrogen atom or any substituent. When
R.sup.b, R.sup.c, and R.sup.d are arbitrary substituents, their
carbon numbers and specific examples are independently as with the
carbon number and specific examples of R.sup.a.
[0120] When Z is an alkyl group, it is a linear or branched alkyl
group which preferably has one or more and thirty or less carbon
atoms, and more preferably has one or more and twelve or less
carbon atoms. Examples thereof include methyl, ethyl, n-propyl,
2-propyl, n-butyl, isobutyl, tert-butyl, and n-octyl groups.
[0121] When Z is an alkenyl group, it preferably has two or more
carbon atoms and preferably has thirty or less, and further
preferably twelve or less carbon atoms. Examples thereof include
vinyl, allyl, and 1-butenyl groups.
[0122] When Z is an alkynyl group, it preferably has two or more
and thirty or less carbon atoms, and further preferably has twelve
or less carbon atoms. Example thereof include ethynyl and propargyl
groups.
[0123] When Z is an amino group, it can also be an amino group
substituted with a hydrocarbon group such as an alkyl group or an
aromatic hydrocarbon group. The amino group generally has zero or
more and thirty-six or less carbon atoms, and preferably has twenty
or less, and more preferably twelve or less carbon atoms. Specific
examples of such amino groups include amino group, methylamino
group, dimethylamino group, ethylamino group, diethylamino group,
phenylamino group, diphenylamino group, dibenzylamino group,
thienylamino group, dithienylamino group, pyridylamino group, and
dipyridylamino group.
[0124] When Z is an alkoxycarbonylamino group, it generally has two
or more and twenty or less carbon atoms, and preferably has sixteen
or less, and more preferably twelve or less carbon atoms. Specific
examples thereof include methoxycarbonylamino group.
[0125] When Z is an aryloxycarbonylamino group, it generally has
seven or more and twenty or less carbon atoms, and preferably has
sixteen or less, and more preferably twelve or less carbon atoms.
Specific examples thereof include phenoxycarbonyl group.
[0126] When Z is a heterocyclic oxycarbonylamino group, it
generally has two or more, preferably five or more carbon atoms,
and generally has twenty-one or less, preferably fifteen or less,
and more preferably eleven or less carbon atoms. Specific examples
thereof include thienyloxycarbonylamino group.
[0127] When Z is a sulfonylamino group, it generally has one or
more carbon atoms and generally has twenty or less, preferably
sixteen or less, and more preferably twelve or less carbon atoms.
Specific examples thereof include methanesulfonylamino group,
benzenesulfonylamino group, and thiophenesulfonylamino group.
[0128] When Z is an alkoxy group, it generally has one or more
carbon atoms, and generally has twenty or less, preferably twelve
or less, and more preferably eight or less carbon atoms. Specific
examples thereof include methoxy group, ethoxy group, isopropoxy
group, n-butoxy group, and t-butoxy group.
[0129] When Z is an aryloxy group, it generally has six or more
carbon atoms, and generally has ten or less, preferably eight or
less, and more preferably six carbon atoms. Specific examples
thereof include phenoxy group.
[0130] When Z is a heterocyclic oxy group, it generally has one or
more, preferably two or more, and more preferably four or more
carbon atoms, and generally has ten or less, preferably eight or
less, and more preferably five or less carbon atoms. Specific
examples thereof include thienyloxy group and pyridyloxy group.
[0131] When Z is an acyl group, it generally has one or more carbon
atoms, and generally has twenty or less, preferably sixteen or
less, and more preferably twelve or less carbon atoms. Specific
examples thereof include acetyl group, benzoyl group, formyl group,
pivaloyl group, thenoyl group, and nicotinoyl group.
[0132] When Z is an alkoxycarbonyl group, it generally has two or
more carbon atoms and generally has twenty or less, preferably
sixteen or less, and more preferably twelve or less carbon atoms.
Specific examples thereof include methoxycarbonyl group and
ethoxycarbonyl group.
[0133] When Z is an aryloxycarbonyl group, it generally has seven
or more carbon atoms, and generally has twenty or less, preferably
sixteen or less, and more preferably seven carbon atoms. Specific
examples thereof include phenoxycarbonyl group.
[0134] When Z is a heterocyclic oxycarbonyl group, it generally has
two or more, and preferably five or more carbon atoms, and
generally has twenty or less, preferably twelve or less, and more
preferably six or less carbon atoms. Specific examples thereof
include thienyloxycarbonyl group and pyridyloxycarbonyl group.
[0135] When Z is an acyloxy group, it generally has two or more
carbon atoms, and generally has twenty or less, preferably sixteen
or less, and more preferably twelve or less carbon atoms. Specific
examples thereof include acetoxy group, ethylcarbonyloxy group,
benzoyloxy group, pivaloyloxy group, thenoyloxy group, and
nicotinoyloxy group.
[0136] When Z is a sulfamoyl group, it can also be a sulfamoyl
group substituted with a hydrocarbon group such as an alkyl group
or an aromatic hydrocarbon group. The sulfamoyl group generally has
zero or more carbon atom, and generally has twenty or less, and
preferably twelve or less carbon atoms. Specific examples thereof
include sulfamoyl group, methylsulfamoyl group, dimethylsulfamoyl
group, phenylsulfamoyl group, and thienylsulfamoyl group.
[0137] When Z is a carbamoyl group, it can also be a carbamoyl
group substituted with a hydrocarbon group such as an alkyl group
or an aromatic hydrocarbon group. The carbamoyl group generally has
one or more carbon atoms, and generally has twenty or less,
preferably sixteen or less, and more preferably twelve or less
carbon atom. Specific examples thereof include carbamoyl group,
methylcarbamoyl group, diethylcarbamoyl group, and phenylcarbamoyl
group.
[0138] When Z is an alkylthio group, it generally has one or more
carbon atoms, and generally has twenty or less, preferably sixteen
or less, and more preferably twelve or less carbon atoms. Specific
examples thereof include methylthio group, ethylthio group, and
n-butylthio group.
[0139] When Z is an arylthio group, it generally has six or more
carbon atoms, and generally has twenty-six or less, preferably
twenty or less, and more preferably twelve or less carbon atoms.
Specific examples thereof include phenylthio.
[0140] When Z is a heterocyclic thio group, it generally has one or
more, preferably two or more, and more preferably five or more
carbon atoms, and generally has twenty-five or less, preferably
nineteen or less, and more preferably eleven or less carbon atoms.
Specific examples thereof include thienylthio group and pyridylthio
group.
[0141] When Z is a sulfonyl group, such sulfonyl groups further
include a sulfonyl group substituted with a hydrocarbon group such
as an alkyl group or an aromatic hydrocarbon group. The sulfamoyl
group generally has one or more carbon atoms, and generally has
twenty or less, preferably sixteen or less, and more preferably
twelve or less carbon atoms. Specific examples thereof include
tosyl group and mesyl group.
[0142] When Z is a sulfinyl group, it can also be a sulfinyl group
substituted with a hydrocarbon group such as an alkyl group or an
aromatic hydrocarbon group. The sulfinyl group has one or more
carbon atoms, and generally has twenty or less, preferably sixteen
or less, and more preferably twelve or less carbon atoms. Specific
examples thereof include methylsulfinyl group and phenylsulfinyl
group.
[0143] When Z is a ureido group, it can also be a ureido group
substituted with a hydrocarbon group such as an alkyl group or an
aromatic hydrocarbon group. The ureido group generally has one or
more carbon atoms, and generally has twenty or less, preferably
sixteen or less, and more preferably twelve or less carbon atoms.
Specific examples thereof include ureido group, methylureido group,
and phenylureido group.
[0144] When Z is a phosphoramido group, it can also be a
phosphoramido group substituted with a hydrocarbon group such as an
alkyl group or an aromatic hydrocarbon group. The phosphoramido
group generally has one or more carbon atoms, and generally has
twenty or less, preferably sixteen or less, and more preferably
twelve or less carbon atoms. Specific examples thereof include
diethylphosphoramido group and phenylphosphoramido group.
[0145] When Z is a silyl group, it can also be a silyl group
substituted with a hydrocarbon group such as an alkyl group or an
aromatic hydrocarbon group. The silyl group generally has one or
more carbon atoms, and generally has ten or less, and preferably
six or less carbon atoms. Specific examples thereof include
trimethylsilyl group and triphenylsilyl group.
[0146] When Z is a boryl group, it can also be a boryl group
substituted with a hydrocarbon group such as an alkyl group or an
aromatic hydrocarbon group. The boryl group generally has one or
more carbon atoms, and generally has ten or less, and preferably
six or less carbon atoms. Specific examples thereof include
dimesitylboryl group.
[0147] When Z is a phosphino group, it can also be a phosphino
group substituted with a hydrocarbon group such as an alkyl group
or an aromatic hydrocarbon group. The phosphino group generally has
one or more carbon atoms, and generally has ten or less, and
preferably six or less carbon atoms. Specific examples thereof
include diphenylphosphino group.
[0148] When Z is an aromatic hydrocarbon group, it generally has
six or more carbon atoms, and generally has twenty or less, and
preferably fourteen or less carbon atoms. Specific examples thereof
include groups derived from six-membered monocyclic rings, or
bicyclic, tricyclic, tetracyclic or pentacyclic condensed rings
containing such six-membered rings, such as benzene ring,
naphthalene ring, anthracene ring, phenanthrene ring, perylene
ring, tetracene ring, pyrene ring, benzopyrene ring, chrysene ring,
triphenylene ring, and fluoranthene ring.
[0149] When Z is an aromatic heterocyclic group, constitutive
hetero atoms thereof include nitrogen atom, oxygen atom, and sulfur
atom. In this case, Z generally has one or more, preferably three
or more carbon atoms, and generally has nineteen or less, and
preferably thirteen or less carbon atoms. Specific examples thereof
include groups derived from five-membered or six-membered
monocyclic rings, or bicyclic, tricyclic, or tetracyclic condensed
rings containing such five-membered or six-membered rings, such as
furan ring, benzofuran ring, thiophene ring, benzothiophene ring,
pyrrole ring, pyrazole ring, oxazole ring, imidazole ring,
oxadiazole ring, indole ring, carbazole ring, pyrroloimidazole
ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole
ring, thienothiophene ring, furopyrrole ring, furofuran ring,
thienofuran ring, benzisoxazole ring, benzisothiazole ring,
benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring,
pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring,
cinnoline ring, quinoxaline ring, benzimidazole ring, perimidine
ring, quinazoline ring, quinazolinone ring, and azulene ring.
[0150] When "n" is two or more, Z represents a direct bond or a
linkage group having a valency of "n".
[0151] When Z is a linkage group having a valency of "n", specific
examples thereof include a group represented by the following
formula:
##STR00017##
[0152] When Z is a linkage group having a valency of "n", specific
examples of Z further include groups corresponding to the groups
listed as the specific examples of Z when Z is a substituent,
except for removing (n-1) hydrogen atom(s) therefrom.
[0153] When Z is an alkynyl group, it generally has two or more
carbon atoms, and generally has eight or less, and preferably four
or less carbon atoms. Specific examples thereof include ethynyl
group and propargyl group.
[0154] Among them, Z is preferably an aromatic hydrocarbon group or
an aromatic heterocyclic group, from the viewpoints of improving
durability against electric oxidation/reduction and improving heat
resistance.
[0155] Z may further have a substituent and/or may be condensed
with another group. When Z has two or more substituents, they may
be the same as or different from each other. If possible, these
substituents may be combined with each other to form a ring.
[0156] Z may have any substituent(s) such as alkyl groups, alkenyl
groups, alkynyl groups, aromatic hydrocarbon groups, acyl groups,
alkoxy groups, aryloxy groups, alkylthio groups, arylthio groups,
alkoxycarbonyl groups, aryloxycarbonyl groups, arylamino groups,
alkylamino groups, and aromatic heterocyclic groups. Among them,
alkyl groups, aromatic hydrocarbon groups, and aromatic
heterocyclic groups are preferred, of which aromatic hydrocarbon
groups are more preferred. Specific examples of the substituents
listed herein are as with the specific examples of Z when Z is a
substituent.
[0157] Z may have any molecular weight. When Z is a substituent or
a linkage group, the molecular weight thereof is generally 5000 or
less, and preferably 2000 or less.
[0158] In Formula (1), "A" represents any aromatic hydrocarbon
group or any aromatic heterocyclic group.
[0159] When "A" is an aromatic hydrocarbon group, it generally has
six or more carbon atoms, and generally has thirty or less, and
preferably twenty or less carbon atoms. Specific examples thereof
include groups derived from six-membered monocyclic rings, or
bicyclic, tricyclic, tetracyclic, or pentacyclic fused rings
containing such six-membered rings, such as benzene ring,
naphthalene ring, anthracene ring, phenanthrene ring, perylene
ring, tetracene ring, pyrene ring, benzopyrene ring, chrysene ring,
triphenylene ring, and fluoranthene ring.
[0160] When "A" is an aromatic heterocyclic group, it generally has
one or more, and preferably three or more carbon atoms, and
generally has twenty-nine or less, and preferably nineteen or less
carbon atoms. Specific examples thereof include groups derived from
five-membered or six-membered monocyclic rings, or bicyclic,
tricyclic, or tetracyclic fused rings containing such five-membered
or six-membered rings, such as furan ring, benzofuran ring,
thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring,
oxazole ring, imidazole ring, oxadiazole ring, indole ring,
carbazole ring, pyrroloimidazole ring, pyrrolopyrazole ring,
pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring,
furopyrrole ring, furofuran ring, thienofuran ring, benzisoxazole
ring, benzisothiazole ring, benzimidazole ring, pyridine ring,
pyrazine ring, pyridazine ring, pyrimidine ring, triazine ring,
quinoline ring, isoquinoline ring, cinnoline ring, quinoxaline
ring, benzimidazole ring, perimidine ring, quinazoline ring,
quinazolinone ring, azulene ring, tetrazole ring, and
imidazopyridine ring.
[0161] Of the above listed groups, "A" is preferably a group
derived from benzene ring, naphthalene ring, pyridine ring,
pyrimidine ring, pyrazine ring, triazine ring, quinoline ring,
isoquinoline ring, thiazole ring, oxazole ring, imidazole ring,
indole ring, benzimidazole ring, imidazopyridine ring, or carbazole
ring. This is from the points of durability against electric
oxidation/reduction, and a wide band gap between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO).
[0162] Of these, "A" is more preferably a group derived from
benzene ring, naphthalene ring, pyridine ring, triazine ring,
oxazole ring, thiazole ring, imidazole ring, quinoline ring,
isoquinoline ring, benzimidazole ring, imidazopyridine ring, or
carbazole ring, and is further more preferably a group derived from
benzene ring, pyridine ring, quinoline ring, isoquinoline ring,
benzimidazole ring, imidazopyridine ring, or carbazole ring.
[0163] "A" is especially preferably a group derived from pyridine
ring or carbazole ring.
[0164] Of such groups derived from pyridine ring, bipyridyl group
or a group derived from a pyridine ring having substituent(s) at
the 2-, 4-, and/or 6-position of pyridine ring is preferred for
more satisfactory stability against electric reduction. A
substituent to be combined with the bipyridyl group or the group
derived from a pyridine ring having substituent(s) at the 2-, 4-,
and/or 6-position of pyridine ring is arbitrary, but it is
preferably an aromatic hydrocarbon group or an aromatic
heterocyclic group.
[0165] In Formula (1), "A" may have a substituent. "A" may have any
substituent, and specific examples of such substituents are as with
the above-listed substituents which Z may have. When "A" has two or
more substituents, they may be the same as or different from each
other. If possible, these substituents may be combined with each
other to form a ring.
[0166] The molecular weight of "A" including its substituent(s) is
generally 5000 or less, and preferably 2000 or less.
[0167] Specific examples of "A" and Z will be illustrated
below.
[0168] Initially, specific examples of "A" and Z when "n" is 1
include the following groups R-1 to R-99. In the following specific
examples, L.sup.1, L.sup.2, and L.sup.3 each independently
represent hydrogen atom or any substituent. They are each
independently preferably an alkyl group, an aromatic hydrocarbon
group, or an aromatic heterocyclic group and most preferably phenyl
group, from the viewpoint of electric durability. The groups listed
herein may each further have a substituent, in addition to L.sup.1,
L.sup.2, and L.sup.3.
##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022##
##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027##
##STR00028## ##STR00029## ##STR00030## ##STR00031##
[0169] Specific examples of Z when "n" is 2 or more include
following bonds and linkage groups, and each of these can be
adopted alone, or two or more of the same or different bonds or
linkage groups can be combined to be adopted. In the following
formulae, Z-1 represents a direct bond, and Z-2 to Z-187 each
represent a linkage group. In the following specific examples,
L.sup.1, L.sup.2, and L.sup.3 each independently represent hydrogen
atom or any substituent. They are each independently preferably an
alkyl group, an aromatic hydrocarbon group, or an aromatic
heterocyclic group, and are each most preferably phenyl group, from
the viewpoint of electric durability. The groups listed herein may
each further have a substituent, in addition to L.sup.1, L.sup.2,
and L.sup.3.
##STR00032## ##STR00033## ##STR00034## ##STR00035## ##STR00036##
##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041##
##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046##
##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051##
##STR00052## ##STR00053##
[0170] Specific examples of compounds represented by Formula (1)
are illustrated below.
[0171] Examples as carbazole compounds (including triarylamine
compounds) include compounds described as charge transport
materials typically in Japanese Unexamined Patent Application
Publications No. 63-235946, No. 2-285357, No. 2-261889, No.
3-230584, No. 3-232856, No. 5-263073, No. 6-312979, No. 7-053950,
No. 8-003547, No. 9-157643, No. 9-268283, No. 9-165573, No.
9-249876, No. 9-310066, No. 10-041069, and No. 10-168447; EP Patent
No. 847228; Japanese Unexamined Patent Application Publications No.
10-208880, No. 10-226785, No. 10-312073, No. 10-316658, No.
10-330361, No. 11-144866, No. 11-144867, No. 11-144873, No.
11-149987, No. 11-167990, No. 11-233260, and No. 11-241062; PCT
International Publication Number WO-00/70655; U.S. Pat. No.
6,562,982; Japanese Unexamined Patent Application Publications No.
2003-040844, No. 2001-313179, No. 2001-257076, and No. 2005-47811;
Japanese Patent Application No. 2003-204940; and Japanese
Unexamined Patent Application Publication No. 2005-068068.
[0172] Examples as phenylanthracene derivatives include compounds
described as charge transport materials typically in Japanese
Unexamined Patent Application Publication No. 2000-344691.
[0173] Examples as fused arylene star-burst compounds include
compounds described as charge transport materials typically in
Japanese Unexamined Patent Application Publications No. 2001-192651
and No. 2002-324677.
[0174] Examples as fused imidazole compounds include compounds
described as charge transport materials typically in "Appl. Phys.
Lett., vol. 78, p. 1622, 2001", Japanese Unexamined Patent
Application Publication No. 2001-335776, No. 2002-338579, No.
2002-319491, No. 2002-367785, and No. 2002-367786.
[0175] Examples as azepine compounds include compounds described as
charge transport materials typically in Japanese Unexamined Patent
Application Publication No. 2002-235075.
[0176] Examples as fused triazole compounds include compounds
described as charge transport materials typically in Japanese
Unexamined Patent Application Publication No. 2002-356489.
[0177] Examples as propeller-like arylene compounds include
compounds described as charge transport materials typically in
Japanese Unexamined Patent Application Publication No.
2003-027048.
[0178] Examples as monotriarylamine compounds include compounds
described as charge transport materials typically in Japanese
Unexamined Patent Application Publications No. 2002-175883, No.
2002-249765, and No. 2002-324676.
[0179] In addition, examples as arylbenzidine compounds include
compounds described as charge transport materials typically in
Japanese Unexamined Patent Application Publication No.
2002-329577.
[0180] Examples as triarylboron compounds include compounds
described as charge transport materials typically in Japanese
Unexamined Patent Application Publications No. 2003-031367 and No.
2003-031368.
[0181] Examples as indole compounds include compounds described as
charge transport materials typically in Japanese Unexamined Patent
Application Publications No. 2002-305084, No. 2003-008866, and No.
2002-015871.
[0182] Examples as indolizine compounds include compounds described
as charge transport materials typically in Japanese Unexamined
Patent Application Publication No. 2000-311787.
[0183] Examples as pyrene compounds include compounds described as
charge transport materials typically in Japanese Unexamined Patent
Application Publication No. 2001-118682.
[0184] Examples as dibenzoxazole (or dibenzothiazole) compounds
include compounds described as charge transport materials typically
in Japanese Unexamined Patent Application Publication No.
2002-231453.
[0185] Examples as bipyridyl compounds include compounds described
as charge transport materials typically in Japanese Unexamined
Patent Application Publication No. 2003-123983.
[0186] Examples as pyridine compounds include compounds described
as charge transport materials typically in Japanese Unexamined
Patent Application Publications No. 2005-276801 and No.
2005-268199.
[0187] Of these, preferred examples are carbazole compounds
(including triarylamine compounds), fused arylene star-burst
compounds, fused imidazole compounds, propeller-like arylene
compounds, monotriarylamine compounds, indole compounds, indolizine
compounds, bipyridyl compounds, and pyridine compounds, from the
point of excellent light emission properties when used in organic
electroluminescent devices.
[0188] Among them, carbazole compounds, bipyridyl compounds, and
pyridine compounds are more preferred, and the combination use of a
carbazole compound with a bipyridyl compound or the combination use
of a carbazole compound and a pyridine compound is most preferred.
This is because, when they are used in organic electroluminescent
devices, the devices can have further satisfactory operating lives.
Likewise, compounds having both a carbazolyl group and a pyridyl
group are preferably used. For example, the charge transport
materials described in Japanese Patent Applications No. 2004-358592
and No. 2004-373981 are preferred.
[0189] It is also important to reduce the molecular symmetry or
rigidity of these materials and/or to introduce a lipophilic
substituent such as an alkyl group into the materials, in order to
improve the solubility in a solvent.
[0190] Specific examples of especially preferred compounds as the
charge transport material are illustrated below. In the following
illustrated structural formulae, --N-Cz represents N-carbazolyl
group.
##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058##
##STR00059## ##STR00060## ##STR00061## ##STR00062## ##STR00063##
##STR00064## ##STR00065## ##STR00066## ##STR00067##
[0191] The glass transition point of a compound for use as the
charge transporting material is generally 70.degree. C. or higher,
preferably 100.degree. C. or higher, more preferably 120.degree. C.
or higher, further preferably 130.degree. C. or higher, and most
preferably 150.degree. C. or higher. If a compound having an
excessively low glass transition point is used in an organic
electroluminescent device, the device may have reduced heat
resistance and may possibly have a short operating life.
[0192] The molecular weight of a compound for use as the charge
transporting material in the present invention is generally 10000
or less, preferably 5000 or less, more preferably 3000 or less, and
is generally 100 or more, preferably 300 or more, and more
preferably 500 or more. If the molecular weight is less than 100,
there may result in significant decrease of heat resistance, may
cause gas generation, may invite decreased quality of a film formed
from the composition, or may cause morphological change of the
resulting organic electroluminescent device due typically to
migration. If the molecular weight exceeds 10000, it may be
difficult to purify the organic compound or it may possibly take a
long time to dissolve the organic compound in a solvent.
[0193] The band gap of a compound for use as the charge transport
material in the present invention is generally 3.0 V or more,
preferably 3.2 V or more, and more preferably 3.5 V or more.
Blue-emitting fluorescent materials and phosphorescent materials
typified by green to blue-emitting materials have large band gaps.
When an organic electroluminescent device is manufactured by using
a phosphorescent material of this type, a charge transporting
material to be arranged surrounding the phosphorescent material
preferably has a band gap equal to or larger than the band gap of
the phosphorescent material, from the points of the luminous
efficiency and life as an organic electroluminescent device.
[0194] The first oxidation potential of a charge transporting
material E.sub.T.sup.+ for use in the present invention is
generally 0.0 V or more, preferably 0.1 V or more, more preferably
0.2 V or more, further preferably 0.3 V or more, and most
preferably 0.9 V or more, and is generally 2.1 V or less,
preferably 1.7 V or less, more preferably 1.6 V or less, further
preferably 1.5 V or less, and most preferably 1.4 V or less.
[0195] If the first oxidation potential of the charge transporting
material E.sub.T.sup.+ is less than 0.0 V, the first reduction
potential E.sub.T.sup.- of the charge transport material must be
set at a very low value. When this material is used in an organic
electroluminescent device, there may result in significant
imbalance between positive and negative charges, or there may cause
decreased durability of the charge transport material against
reduction, and the device may highly possibly fail to have a
sufficient luminance and/or a satisfactory life. In contrast, if
the first oxidation potential of the charge transport material
E.sub.T.sup.+ exceeds 2.1 V, there may invite decreased durability
of the luminescent material against oxidation, and the device may
highly possibly fail to have a sufficient luminance and/or a
satisfactory life.
[0196] The first reduction potential of the charge transport
material E.sub.T.sup.- as described in the present invention is
generally -3.1 V or more, preferably -2.9 V or more, more
preferably -2.8 V or more, further preferably -2.7 V or more, and
most preferably -2.1 V or more and is generally -0.9 V or less,
preferably -1.1 V or less, more preferably -1.3 V or less, further
preferably -1.5 V or less, and most preferably -1.7 V or less.
[0197] If a charge transport material having a first reduction
potential E.sub.T.sup.- less than -3.1 V is used in an organic
electroluminescent device, there may result in significant
imbalance between positive and negative charges, or there may cause
decreased durability of the charge transport material against
reduction, and the device may highly possibly fail to have a
sufficient luminance and/or a satisfactory life. In contrast, if a
charge transport material having a first reduction potential
E.sub.T.sup.- exceeding -0.9 V is used in an organic
electroluminescent device, the first oxidation potential of the
charge transport material E.sub.T.sup.+ must be set at a very high
value, and there may invite decreased durability of the charge
transport material against oxidation, and the device may highly
possibly fail to have a sufficient luminance and/or a satisfactory
life.
[0198] <First Oxidation Potential E.sub.D.sup.+ and First
Reduction Potential E.sub.D.sup.- of Luminescent Material, and
First Oxidation Potential E.sub.T.sup.+ and First Reduction
Potential E.sub.T.sup.- of Charge Transport Material>
[0199] A layer referred to as a light emitting layer in an organic
electroluminescent device mainly contains a mixture of a
luminescent material called "dopant" and a charge transport
material called "host". In this case, the following pathway is
regarded as a likely major light emission mechanism.
[0200] Specifically, holes travel through the highest occupied
molecular orbital (HOMO) of the charge transport material and come
into the highest occupied molecular orbital (HOMO) of the
luminescent material. Electrons travel through the lowest
unoccupied molecular orbital (LUMO) of the charge transporting
material and come into the lowest unoccupied molecular orbital
(LUMO) of the luminescent material. The holes and electrons are
then recombined as charges, to make the luminescent material
excited. At the time when the luminescent material undergoes
transition from its excited state to its ground state, the
luminescent material emits electromagnetic waves (light)
corresponding to the energy difference between the two states.
[0201] The "HOMO level" herein corresponds to the first oxidation
potential of each material, and the "LUMO level" corresponds to the
first reduction potential of each material.
[0202] Accordingly, it has been believed in related art that a
luminescent material in an electrically neutral state is preferably
more susceptible to electron donation (oxidation) and electron
acceptation (reduction) than a charge transport material.
Specifically, the first oxidation potential of the luminescent
material E.sub.D.sup.+, the first reduction potential of the
luminescent material E.sub.D.sup.-, the first oxidation potential
of the charge transport material E.sub.T.sup.+, and the first
reduction potential of the charge transporting material
E.sub.T.sup.- in related art generally satisfy the following
condition:
E.sub.T.sup.-<E.sub.D.sup.-<E.sub.D.sup.+<E.sub.T.sup.+
[0203] However, according to the present invention, a luminescent
material and a charge transport material are selected so as to
allow the first oxidation potential of the luminescent material
E.sub.D.sup.+, the first reduction potential of the luminescent
material E.sub.D.sup.-, the first oxidation potential of the charge
transport material E.sub.T.sup.+, and the first reduction potential
of the charge transport material E.sub.T.sup.- to satisfy the
following condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.s-
up.+-0.1
or
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.s-
up.+-0.1
[0204] (1) In the case when the parameters satisfy the condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1
[0205] A possible mechanism in this case is as follows. Electrons
travel through the charge transport material to the luminescent
material in an electrically neutral state earlier than holes do,
and the electrons are trapped in the lowest unoccupied molecular
orbital (LUMO) of the luminescent material; and thereafter holes
are injected into a bonding orbital having the highest energy level
in the resulting luminescent material in an anionic state. The
bonding orbital corresponds to the highest occupied molecular
orbital (HOMO) of the luminescent material in a neutral state.
[0206] Specifically, it is primarily important that the first
reduction potential of the luminescent material E.sub.D.sup.- is
necessarily and sufficiently larger than the first reduction
potential of the charge transport material E.sub.T.sup.-. In other
words, it is important that the luminescent material is necessarily
and sufficiently more susceptible to electron acceptation but more
resistant to electron donation than the charge transport material.
In addition, it is also important that the first oxidation
potential of the luminescent material E.sub.D.sup.+ is moderately
larger than the first oxidation potential of the charge transport
material E.sub.T.sup.+. Namely, it is important that the charge
transport material is more likely to accept and transport
holes.
[0207] Based on the above description, the absolute value of the
difference between E.sub.D.sup.- and E.sub.T.sup.-
|E.sub.D.sup.--E.sub.T.sup.-| is preferably 0.1 V or more, more
preferably 0.15 V or more, and most preferably 0.2 V or more. The
absolute value |E.sub.D.sup.--E.sub.T.sup.-| is preferably 1.5 V or
less, more preferably 1.0 V or less, and most preferably 0.5 V or
less. If the absolute value |E.sub.D.sup.--E.sub.T.sup.-| is lower
than the lower limit, the electron may not be firmly trapped by the
luminescent material in an electrically neutral state, there may
occur a decreased probability of charge recombination on the
luminescent material, and this may cause decreased luminous
efficiency of the organic electroluminescent device. If the
absolute value |E.sub.D.sup.--E.sub.T.sup.-| exceeds the upper
limit, the drive voltage of the device may significantly increase
due to increased voltage loss.
[0208] The absolute value of the deference between E.sub.T.sup.+
and E.sub.D.sup.- |E.sub.T.sup.+-E.sub.D.sup.-| is preferably 1.0 V
or more, more preferably 1.5 V or more, and most preferably 2.0 V
or more. The absolute value |E.sub.T.sup.+-E.sub.D.sup.-| is
preferably 4.5 V or less, more preferably 3.5 V or less, and most
preferably 3.0 V or less. If the absolute value
|E.sub.T.sup.+-E.sub.D.sup.-| is less than the lower limit, the
device may show a decreased luminous efficiency, or may operate at
a significantly increased drive voltage due to increased voltage
loss. If the absolute value |E.sub.T.sup.+-E.sub.D.sup.-| exceeds
the upper limit, the device may operate a significantly increased
drive voltage.
[0209] The absolute value of the difference between E.sub.D.sup.+
and E.sub.T.sup.+ |E.sub.D.sup.+-E.sub.T.sup.+| is preferably 0.1 V
or more, more preferably 0.15 V or more, and most preferably 0.2 V
or more. The absolute value |E.sub.D.sup.+-E.sub.T.sup.+| is
preferably 1.5 V or less, more preferably 1.0 V or less, and most
preferably 0.5 V or less. If the absolute value
|E.sub.D.sup.+-E.sub.T.sup.+| is less than the lower limit, holes
can be easily injected not only into the highest occupied molecular
orbital (HOMO) of the charge transporting material in an
electrically neutral state but also into the highest occupied
molecular orbital (HOMO) of the luminescent material in an
electrically neutral state, and this may cause a decreased
probability of charge recombination to thereby cause a decreased
luminous efficiency of the organic electroluminescent device. If
the absolute value |E.sub.D.sup.+-E.sub.T.sup.+| exceeds the upper
limit, this may seriously hinder the charge recombination on the
luminescent material to thereby cause a decreased luminous
efficiency of the device.
[0210] The absolute value of the difference between E.sub.T.sup.-
and E.sub.D.sup.+ |E.sub.T.sup.--E.sub.D.sup.+| is preferably 1.5 V
or more, more preferably 2.5 V or more, and most preferably 3.0 V
or more. The absolute value |E.sub.T.sup.--E.sub.D.sup.+| is
preferably 5.5 V or less, more preferably 4.5 V or less, and most
preferably 4.0 V or less. If the absolute value
|E.sub.T.sup.--E.sub.D.sup.+| is less than the lower limit, there
may fail to provide a device that efficiently emit light in the
visible ray region. If the absolute value
|E.sub.T.sup.--E.sub.D.sup.+| exceeds the upper limit, the drive
voltage of the device may significantly increase.
[0211] (2) In the case when the parameters satisfy the condition:
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1
[0212] A possible mechanism in this case is as follows. Holes
travel through the charge transport material to the luminescent
material in an electrically neutral state earlier than electrons
do, and the holes are trapped in the highest occupied molecular
orbital (HOMO) of the luminescent material; and thereafter holes
are injected into an anti-bonding orbital having the lowest energy
level in the resulting luminescent material in a cationic state.
The anti-bonding orbital corresponds to the lowest unoccupied
molecular orbital (LUMO) of the luminescent material in a neutral
state.
[0213] Specifically, it is primarily important that the first
oxidation potential of the luminescent material E.sub.D.sup.+ is
necessarily and sufficiently smaller than the first oxidation
potential of the charge transport material E.sub.T.sup.+. In other
words, it is important that the luminescent material is more
susceptible to hole acceptation but more resistant to hole donation
(hole release) than the charge transport material. In addition, it
is also important that the first reduction potential of the
luminescent material E.sub.D.sup.- is moderately smaller than the
first reduction potential of the charge transport material
E.sub.T.sup.-. Namely, it is important that the charge transport
material is more likely to accept and transport electrons.
[0214] Based on the above description, the absolute value of the
difference between E.sub.D.sup.+ and E.sub.T.sup.+
|E.sub.D.sup.+-E.sub.T.sup.+| is preferably 0.1 V or more, more
preferably 0.15 V or more, and most preferably 0.2 V or more. The
absolute value |E.sub.D.sup.+-E.sub.T.sup.+| is also preferably 1.5
V or less, more preferably 1.2 V or less, and most preferably 0.9 V
or less. If the absolute value |E.sub.D.sup.+-E.sub.T.sup.+| is
less than the lower limit, the hole may not firmly trapped by the
luminescent material in an electrically neutral state, there may
occur a decreased probability of charge recombination on the
luminescent material, and this may cause decreased luminous
efficiency of the organic electroluminescent device. If the
absolute value |E.sub.D.sup.+-E.sub.T.sup.+| exceeds the upper
limit, the drive voltage of the device may significantly increase
due to increased voltage loss.
[0215] The absolute value of the difference between E.sub.D.sup.+
and E.sub.T.sup.- |E.sub.D.sup.+-E.sub.T.sup.-| is preferably 1.0 V
or more, more preferably 1.5 or more, and most preferably 2.0 V or
more. The absolute value |E.sub.D.sup.+-E.sub.T.sup.-| is also
preferably 4.5 V or less, more preferably 3.5 V or less, and most
preferably 3.0 or less. If the absolute value
|E.sub.D.sup.+-E.sub.T.sup.-| is less than the lower limit, the
luminous efficiency of the device may decrease, or the drive
voltage of the device may significantly increase due to increased
voltage loss. If the absolute value |E.sub.D.sup.+-E.sub.T.sup.-|
exceeds the upper limit, the drive voltage of the device may
significantly increase.
[0216] The absolute value of the difference between E.sub.D.sup.-
and E.sub.T.sup.- |E.sub.D.sup.--E.sub.T.sup.-| is preferably 0.10
V or more, more preferably 0.15 V or more, and most preferably 0.20
V or more. The absolute value |E.sub.D.sup.--E.sub.T.sup.-| is also
preferably 1.5 V or less, more preferably 1.0 V or less, and most
preferably 0.5 V or less. If the absolute value
|E.sub.D.sup.--E.sub.T.sup.-| is less than the lower limit,
electrons can be easily injected not only into the charge
transporting material in an electrically neutral state but also
into the luminescent material in an electrically neutral state, and
this may cause a decreased probability of charge recombination to
thereby cause a decreased luminous efficiency of the organic
electroluminescent device. If the absolute value
|E.sub.D.sup.--E.sub.T.sup.-| exceeds the upper limit, this may
seriously hinder the charge recombination on the luminescent
material to thereby cause a decreased luminous efficiency of the
device.
[0217] The absolute value of the difference between E.sub.T.sup.+
and E.sub.D.sup.- |E.sub.T.sup.+-E.sub.D.sup.-| is preferably 1.5 V
or more, more preferably 2.5 V or more, and most preferably 3.0 V
or more. The absolute value |E.sub.T.sup.+-E.sub.D.sup.-| is also
preferably 5.5 V or less, more preferably 4.5 V or less, and most
preferably 4.0 V or less. If the absolute value
|E.sub.T.sup.+-E.sub.D.sup.-| is less than the lower limit, there
may fail to provide a device that efficiently emit light in the
visible ray region. If the absolute value
|E.sub.T.sup.+-E.sub.D.sup.-| exceeds the upper limit, the drive
voltage of the device may significantly increase.
[0218] [Comparison in Voltage when Composition for Organic
Electroluminescent Device Contains Two or More Diffident
Luminescent Materials and Charge Transport Materials]
[0219] <In the Case when Composition for Organic
Electroluminescent Device According to the Present Invention
Contains Two or More Different Charge Transport Materials>
[0220] When the parameters satisfy the condition:
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1, the "first oxidation potential of the charge transport
material E.sub.T.sup.+" refers to the first oxidation potential of
a charge transport material which has the smallest first oxidation
potential (namely, a material which is most susceptible to
oxidation). The "first reduction potential of the charge transport
material E.sub.T.sup.-" refers to the first reduction potential of
a charge transport material which has the largest first reduction
potential (namely, a material which is most susceptible to
reduction). When the parameters satisfy the condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1, the "first oxidation potential of the charge transport
material E.sub.T.sup.+" to the first oxidation potential of a
charge transport material which has the smallest first oxidation
potential (namely, a material which is most susceptible to
oxidation). The "first reduction potential of the charge transport
material E.sub.T.sup.-" refers to the first reduction potential of
a charge transport material which has the largest first reduction
potential (namely, a material which is most susceptible to
reduction).
[0221] <In the Case when Composition for Organic
Electroluminescent Device According to the Present Invention
Contains Two or More Different Luminescent Materials>
[0222] When the parameters satisfy the condition:
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1, the "first oxidation potential of the luminescent material
E.sub.D.sup.+" refers to the first oxidation potential of a
luminescent material which has the smallest first oxidation
potential (namely, a material which is most susceptible to
oxidation), and the "first reduction potential of the luminescent
material E.sub.D.sup.-" refers to the first reduction potential of
a luminescent material which has the largest first reduction
potential (namely, a material which is most susceptible to
reduction).
[0223] When the parameters satisfy the condition:
E.sub.D.sup.-+0.1.ltoreq.E.sub.1.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1, the "first oxidation potential of the luminescent material
E.sub.D.sup.+" refers to the first oxidation potential of a
luminescent material which has the smallest first oxidation
potential (namely, a material which is most susceptible to
oxidation), and the "first reduction potential of the luminescent
material" refers to the first reduction potential of a luminescent
material E.sub.D.sup.- which has the largest first reduction
potential (namely, a material which is most susceptible to
reduction).
[0224] <Solvent>
[0225] Solvents to be contained in a composition for an organic
electroluminescent device according to the present invention are
not specifically limited, as long as the solutes can be
satisfactorily dissolved therein. However, since most of materials
for organic electroluminescent devices generally have aromatic
rings, typical examples of solvents for use herein include aromatic
hydrocarbons such as toluene, xylenes, mesitylene,
cyclohexylbenzene, and tetralin; halogenated aromatic hydrocarbons
such as chlorobenzene, dichlorobenzene, and trichlorobenzene;
aromatic ethers such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene,
anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene,
4-methoxytoluene, 2,3-dimethylanisole, 2,4-dimethylanisole, and
diphenyl ether; aromatic esters such as phenyl acetate, phenyl
propionate, methyl benzoate, ethyl benzoate, ethyl benzoate, propyl
benzoate, and n-butyl benzoate; alicyclic ketones such as
cyclohexanone and cyclooctanone; and alicyclic alcohols such as
cyclohexanol and cyclooctanol.
[0226] When the solute molecule has a suitable substituent such as
an ester group or an ether group, examples of solvents for use
herein also include, in addition to the above-listed solvents,
aliphatic ketones such as methyl ethyl ketone and dibutyl ketone;
aliphatic alcohols such as butanol and hexanol; aliphatic ethers
such as ethylene glycol dimethyl ether, ethylene glycol diethyl
ether, and propylene glycol-1-monomethyl ether acetate (PGMEA); and
aliphatic esters such as ethyl acetate, n-butyl acetate, ethyl
lactate, and n-butyl lactate.
[0227] When a solvent excessively evaporates from a composition for
an organic electroluminescent device during wet coating process,
the stability in film-formation may deteriorate. To avoid this,
solvents each having a boiling point of 100.degree. C. or higher,
preferably a boiling point of 150.degree. C. or higher, and more
preferably a boiling point of 200.degree. C. or higher are
effective. In addition, a solvent must evaporate at a suitable rate
from a liquid film immediately after film-formation in order to
yield a more homogenous film. For this purpose, the solvent
generally has a boiling point of 80.degree. C. or higher,
preferably a boiling point of 100.degree. C. or higher, more
preferably a boiling point of 120.degree. C. or higher and
generally has a boiling point of lower than 270.degree. C.,
preferably a boiling point of lower than 250.degree. C., and more
preferably a boiling point of lower than 230.degree. C.
[0228] If the composition contains water, the water may remain in a
film after drying to thereby adversely affect the properties of an
organic electroluminescent device, because most of materials
typically in a cathode of such an organic electroluminescent device
significantly deteriorate due to water. Examples of a procedure for
reducing the water content in the solution (composition) include
sealing with nitrogen gas, the use of a drying agent,
predehydration of a solvent, and the use of a solvent having a low
water solubility. Among them, the use of a solvent having a low
water solubility is preferred, because this prevents whitening of a
film of the solution due to absorption of water from the atmosphere
during a wet film-formation step. From these viewpoints, a
composition for an organic electroluminescent device according to
this embodiment preferably contains 10 percent by weight or more of
a solvent having a solubility in water at 25.degree. C. of 1
percent by weight or less, preferably 0.1 percent by weight or
less.
[0229] When a solvent satisfies all these requirements, i.e., the
solubility of the solute, the evaporation rate, and water
solubility, it may be used alone. When, however, it is difficult to
select such a solvent satisfying all the requirements, two or more
different solvents may be used in combination.
[0230] <Other Components>
[0231] A composition for an organic electroluminescent device
according to the present invention may further contain other
solvents in addition to the solvents as listed above. Examples of
such other solvents include amides such as N,N-dimethylformamide
and N,N-dimethylacetamide; and dimethyl sulfoxide.
[0232] The composition may further contain various additives such
as leveling agents and antifoaming agents.
[0233] When two or more layers are laminated through wet coating
process, these layers may be dissolved in each other. To avoid
this, the composition may contain a photo-curable resin and/or a
thermosetting resin, so as to cure the composition after coating to
be insoluble. The resin for use herein such as a photo-curable
resin and/or a thermosetting resin is generally a resin having a
first oxidation potential E.sub.x.sup.+ and a first reduction
potential E.sub.x.sup.- and satisfying the following
conditions:
E.sub.x.sup.-<E.sub.T.sup.- and E.sub.D.sup.+<E.sub.x.sup.+
when
E.sub.T.sup.-+0.1.ltoreq.E.sub.D.sup.-<E.sub.T.sup.+.ltoreq.E.sub.D.su-
p.+-0.1;
or a resin having a first oxidation potential E.sub.x.sup.+ and a
first reduction potential E.sub.x.sup.- and satisfying the
following conditions:
E.sub.x.sup.-<E.sub.D.sup.- and E.sub.T.sup.+<E.sub.x.sup.+
when
E.sub.D.sup.-+0.1.ltoreq.E.sub.T.sup.-<E.sub.D.sup.+.ltoreq.E.sub.T.su-
p.+-0.1.
[0234] <Contents and Proportions of Materials in Composition for
Organic Electroluminescent Device>
[0235] The solid content including a luminescent material, a charge
transport material, and an additional component to be added
according to necessity, such as a leveling agent, in a composition
for an organic electroluminescent device is generally 0.01 percent
by weight or more, preferably 0.05 percent by weight or more, more
preferably 0.1 percent by weight or more, further preferably 0.5
percent by weight or more, and most preferably 1 percent by weight
or more, and is generally 80 percent by weight or less, preferably
50 percent by weight or less, more preferably 40 percent by weight
or less, further preferably 30 percent by weight or less, and most
preferably 20 percent by weight or less. If the content is less
than 0.01 percent by weight, it may be difficult to form a thick
film from the composition. If the content exceeds 80 percent by
weight, it may be difficult to form a thin film from the
composition.
[0236] The weight ratio of a luminescent material to a charge
transporting material in a composition for an organic
electroluminescent device according to the present invention is
generally 0.1/99.9 or more, more preferably 0.5/99.5 or more,
further preferably 1/99 or more, and most preferably 2/98 or more,
and is generally 50/50 or less, more preferably 40/60 or less,
further preferably 30/70 or less, and most preferably 20/80 or
less. If the ratio is less than 0.1/99.9 or exceeds 50/50, the
luminous efficiency may seriously decrease.
[0237] <Preparation Method of Composition for Organic
Electroluminescent Device>
[0238] A composition for an organic electroluminescent device
according to the present invention may be prepared by dissolving
solutes such as a luminescent material and a charge transporting
material, and additives such as a leveling agent and an
anti-foaming agent added according to necessity, in a suitable
solvent. The solutes are generally dissolved with stirring the
mixture so as to shorten the time necessary for the dissolving step
and to uniformize the concentrations of solutes in the composition.
The dissolving step may be carried out at ordinary temperature, or
carried out with heating so as to accelerate dissolution when the
dissolution rate is low. After the completion of the dissolving
step, the composition may be subjected to a filtrating step such as
filtering according to necessity.
[0239] <Properties and Physical Properties of Composition for
Organic Electroluminescent Device>
[0240] Water Content
[0241] The water content of the composition as a solution is
preferably minimized, because, if the composition contains water
upon wet film-formation for forming a film in an organic
electroluminescent device, water migrates into the formed film to
thereby impair the uniformity of the film. In addition, generally
most of materials typically in a cathode of an organic
electroluminescent device may deteriorate due to water.
Accordingly, if the composition contains water, water may remain in
a film after drying and may possibly impair the properties of the
device.
[0242] Specifically, the water content of a composition for an
organic electroluminescent device according to the present
invention is generally 1 percent by weight or less, preferably 0.1%
or less, and more preferably 0.01% or less.
[0243] The water content of the composition is preferably analyzed
according to the method specified in Japanese Industrial Standards
(JIS) "Test methods for water content of chemical products" (JIS
K0068:2001). It can be analyzed typically by Karl-Fischer reagent
method (JIS K0211-1348).
[0244] Concentration of Primary Amine- and Secondary
Amine-Containing Compounds
[0245] A composition for an organic electroluminescent device
according to the present invention preferably has a low
concentration of a primary amine- and secondary amine-containing
compounds, because such primary amine- and secondary
amine-containing compounds have lower charge transporting ability,
are more likely to act as a charge trap, and are more susceptible
to decomposition reaction such as proton detachment than tertiary
amine compounds.
[0246] More specifically, the concentration of nitrogen atoms
derived from primary amino group (--NH.sub.2) and secondary amino
group (>NH) is preferably 100 ppm (.mu.g/g) or less, and more
preferably 10 ppm (.mu.g/g) or less, based on the total weight of
materials other than solvents.
[0247] The "primary amine-containing compound" in a composition for
an organic electroluminescent device refers to a compound which
contains one or more nitrogen atoms, in which at least one of the
nitrogen atom(s) is combined with two hydrogen atoms and one atom
other than hydrogen. Namely, the primary amine-containing compound
is a compound represented by RNH.sub.2, wherein R represents any
group other than hydrogen atom.
[0248] The "secondary amine-containing compound" refers to a
compound which contains one or more nitrogen atoms, in which at
least one of the nitrogen atom(s) is combined with one hydrogen
atom and two atoms other than hydrogen. Namely, the secondary
amine-containing compound is a compound represented by RR'NH,
wherein R and R' each independently represent any group other than
hydrogen atom, or R and R' may be combined to form a ring.
[0249] Examples of procedures for identifying primary amine- and
secondary amine-containing compounds include processes using
magnetic resonance systems (NMR (.sup.1H-NMR and .sup.13C-NMR)) and
Fourier transform infrared spectrophotometers (FT-IR), as well as
mass spectrometry (MS, LC/MS, GC/MS, and MS/MS). Where necessary,
other apparatuses can be used in combination. Examples of such
apparatuses include gas chromatographs (GC), high-performance
liquid chromatographs (HPLC), high-performance amino acid analyzers
(AAA), capillary electrophoresis measurement systems (CE), size
exclusion chromatographs (SEC), gel permeation chromatographs
(GPC), cross fractionation chromatographs (CFC),
ultraviolet-visible ray-near infrared spectrophotometers (UV.VIS,
NIR), and electron spin resonance spectrometers (ESR).
[0250] Known techniques can be applied to the separation of primary
amine- and secondary amine-containing compounds. Examples of such
techniques include the techniques described in "Handbook of
Separation/Purification Technology" (1993, edited by the Chemical
Society of Japan), "High-purity Separation of Trace Components and
Difficult-to-Separate Substances by Chemical Conversion" (1988,
published by IPC Co., Ltd.), and "Experimental Chemistry (Fourth
Ed.) Vol. 1; Section: Separation and Purification" (1990, edited by
the Chemical Society of Japan).
[0251] Specific examples of purification procedures include various
chromatography techniques, extraction, adsorption, occlusion,
melting or fusion, crystallization, distillation, evaporation,
sublimation, ion exchange, dialysis, filtration, ultrafiltration,
reverse osmosis, pressurized osmosis, zone melting,
electrophoresis, centrifugation, floatation separation,
sedimentation, and magnetic separation. Such chromatography
techniques are classified by shape into column, paper, thin-layer,
and capillary chromatography; by mobile phase into gas, liquid,
micelle, and supercritical fluid chromatography; and by separation
mechanism into adsorption, partition, ion-exchange, molecular
sieve, chelate, gel filtration, exclusion, and affinity
chromatography.
[0252] Examples of processes for detecting/determining primary
amine- and secondary amine-containing compounds include:
[0253] i) a process of subjecting a sample with concentrated
sulfuric acid to ignition decomposition to thereby convert them
into ammonium sulfate, adjusting the decomposition mixture to be
strongly basic, distilling ammonia through steam distillation, and
trapping ammonia in a sulfuric acid or boric acid solution having a
known concentration;
[0254] ii) a process of oxidatively decomposing a sample with basic
potassium peroxodisulfate into nitric acid ion, adjusting the pH of
the resulting solution to 2 to 3, and determining absorbance of
nitric acid ion at a wavelength of 220 nm to thereby determine the
nitrogen concentration (ultraviolet absorptiometry);
[0255] iii) a process for the detection by using an
electrogenerated chemiluminescence reaction with Ru(II) bipyridine
complex as a detection reagent, described in Japanese Unexamined
Patent Application Publication No. 4-315048; and
[0256] iv) a process for the detection using a surface ionization
detector (SID), described in Japanese Unexamined Patent Application
Publication No. 10-115606.
[0257] Uniformity
[0258] A composition for an organic electroluminescent device
according to the present invention is preferably a homogenous
liquid at ordinary temperature. Thus, the stability increases in
wet film-formation. For example, when the composition is discharged
from a nozzle according to an ink-jet process, the discharge
stability increases. The phrase "homogenous liquid at ordinary
temperature" means that the composition is a liquid of a homogenous
phase and does not contain particle components having a size of 0.1
.mu.m or more.
[0259] Physical Properties
[0260] If a composition for an organic electroluminescent device
according to the present invention has an extremely low viscosity,
a film of the composition formed in a film-formation step, for
example, may have excessively high flowability to thereby cause an
uneven film surface, or the composition may not be satisfactorily
discharged from a nozzle in ink-jet film-formation. In contrast, if
the composition has an extremely high viscosity, it may often cause
plugging of a nozzle in ink-jet film-formation. Consequently, the
viscosity of a composition according to the present invention at
25.degree. C. is generally 2 mPas or more, preferably 3 mPas or
more, and more preferably 5 mPas or more, and is generally 1000
mPas or less, preferably 100 mPas or less, and more preferably 50
mPas or less.
[0261] The surface tension at 20.degree. C. of a composition for an
organic electroluminescent device according to the present
invention is generally less than 50 mN/m, and preferably less than
40 mN/m. This is because, if the composition has a high surface
tension and is used as a composition for film-formation on a
substrate, the composition may have poor wettability, and a film
formed from the composition may have poor leveling property to
thereby often cause an uneven surface of the film after drying.
[0262] The vapor pressure at 25.degree. C. of a composition for an
organic electroluminescent device according to the present
invention is generally 50 mmHg or less, preferably 10 mmHg or less,
and more preferably 1 mmHg or less. This is because, if the
composition has a high vapor pressure, for example, the composition
may often undergo change in concentrations of the solutes due to
evaporation of the solvent.
[0263] <Storage of Composition for Organic Electroluminescent
Device>
[0264] A composition for an organic electroluminescent device
according to the present invention is preferably stored by placing
in a vessel that blocks ultraviolet transmission, such as a brown
glass bottle, and hermetically sealing the vessel. The storage
temperature is generally -30.degree. C. or higher, and preferably
0.degree. C. or higher, and is generally 35.degree. C. or lower,
and preferably 25.degree. C. or lower.
[Thin Film for Organic Electroluminescent Device]
[0265] A thin film for an organic electroluminescent device
according to the present invention is generally used as an organic
light emitting layer of an organic electroluminescent device.
[0266] The refractive index of a thin film for an organic
electroluminescent device according to the present invention is
preferably 1.78 or less with respect to light with a wavelength of
500 nm to 600 nm.
[0267] The refractive index of the film is determined, for example,
by spectroscopic ellipsometry or prism coupling. The spectroscopic
ellipsometry for use in determination of the refractive index in
the present invention will be illustrated in detail below.
[0268] In the spectroscopic ellipsometry, a change in polarization
of light reflected from the surface of a sample. Optical constants
are determined by optimizing parameters of a suitable model
function indicating the optical constants so as to reproduce
actually measured values of .PSI. and .DELTA..
[0269] Such optical constants are generally in the form of smooth
functions with respect to wavelengths, and their real part and
imaginary part have a causal relation called Kramers-Kronig
relation. Accordingly, the optical constants of most materials can
be modeled as functions.
[0270] Representative model functions for use in analyses by
spectroscopic ellipsometry are as follows:
[0271] Cauchy model typically for a transparent body or a
transparent film;
[0272] Lorentz model typically for a metal film or a transparent
conductive film; and
[0273] Parameterized Semiconductor model typically for a
semiconductor material or a transparent film.
[0274] According to the spectroscopic ellipsometry, optical
constants (refractive index n and extinction coefficient k) as bulk
or as a thin film can be determined at wavelengths in the near
ultraviolet, visible, and near infrared regions (300 to 1700 nm),
and the thickness (d) of a single layer or a multilayer film can be
determined in the range of, for example, several nanometers to
several micrometers.
[0275] The values .PSI. and .DELTA. can be determined with high
precision and high reproducibility according to spectroscopic
ellipsometry, because ratios are measured in the spectroscopic
ellipsometric determination.
[0276] Wet film-formation is desirable as a film-formation process
for yielding a thin film for an organic electroluminescent device
having a refractive index within the preferred range.
[0277] The film-formation of a thin film for an organic
electroluminescent device (hereinafter also referred to as "organic
layer") using a composition for an organic electroluminescent
device according to the present invention is preferably carried out
through wet film-formation. Such a wet film-formation process can
be selected according to the properties of materials to be
contained in the composition and of a substrate as a base material
from among, for example, spin coating, spray coating, an ink-jet
process, flexographic printing, and screen printing. A film formed
by such a film-formation process is preferably dried through
heating so as to reduce water and residual solvent contained in the
film. The drying through heating is carried out by using a heating
device or procedure such as a hot plate or an oven, or by induction
heating. The heating treatment is preferably carried out at
60.degree. C. or higher for sufficient effects, and is more
preferably carried out at 100.degree. C. or higher for reducing the
content of residual water. The heating time is generally about one
minute to about eight hours.
[0278] When an organic layer is formed through wet film-formation
on an anode typically of indium tin oxide (ITO), the anode may be
treated with a specific halogen compound, such as
4-trifluoromethylbenzoyl chloride shown below, immediately before
the film-formation as disclosed in Japanese Unexamined Patent
Application Publication No. 2002-270369. This treatment enables
easy injection of holes from the anode. Specifically, when ITO is
treated with an acid chloride having an electron withdrawing group,
such as the following compound, the anode surface is modified with
the compound having an electron withdrawing group to thereby form
an electric double layer on the anode surface. An electric field
generated by the action of the electric double layer increases the
work function of the anode and hence enables easy injection of
holes from the anode.
##STR00068##
[0279] The film may be subjected to a surface treatment typically
for improving the leveling property of the film and for improving
the coatability typically through reduction of crawling. Examples
of such surface treatments include UV/ozone treatment, oxygen
plasma treatment, hydrogen plasma treatment, and
hexamethyldisilazane (HMDS) treatment. Each of these surface
treatments can be used in combination.
[0280] Residual water, if contained in an organic layer thus
formed, is not desirable, because the residual water may adversely
affect the properties of the device, as described above. More
specifically, the water content in the resulting organic layer is
1000 ppm by weight or less, preferably 100 ppm by weight or less,
and more preferably 10 ppm by weight or less. A residual solvent
derived from the composition, if remains in the organic layer, is
also not desirable. This is because the residual solvent may often
cause migration of materials constituting the organic layer, due to
heat generated upon energizing of the organic electroluminescent
device or due to elevated temperatures in the environment where the
device is used. Specifically, the content of residual solvent in
the organic layer is 1000 ppm by weight or less, preferably 100 ppm
by weight or less, and more preferably 10 ppm by weight or
less.
[0281] The contents of water and residual solvent in the organic
layer can be analyzed typically by programmed thermal
desorption-mass spectrometry (TPD-MS).
[0282] [Transfer Member for Thin Film for Organic
Electroluminescent Device]
[0283] Such a transfer member is a member used as an
image-imparting element for transferring an image pattern to an
image-receiving element according to laser induced thermal imaging
process (LITI process). This technique is widely used in the fields
typically of printing, composition (typesetting), and
photography.
[0284] FIG. 1 illustrates a typical configuration of a transfer
member for a thin film for an organic electroluminescent device
according to the present invention. With reference to FIG. 1, a
transfer member 11 includes a base material 12, and a photothermal
conversion layer 13, an intermediate layer 14, and a transfer layer
15 arranged sequentially on the base material 12. The transfer
layer 15 is melted as a result of heating by the action of the
photothermal conversion layer 13 and is transferred as a pattern
onto an image-receiving element (not shown). A transfer member for
a thin film for an organic electroluminescent device according to
the present invention may further arbitrarily include one or more
additional layers according to necessity.
[0285] The base material 12 in a transfer member for a thin film
for an organic electroluminescent device according to the present
invention can be formed from any natural or synthetic material, as
long as it satisfies requirements for a transfer member for a thin
film for an organic electroluminescent device. Requirements for the
base material include, for example, transparency to laser light and
heat resistance, because heating for transfer of an image component
is carried out by the application of laser light. The requirements
also include moderate flexibility, lightness, handleability, and
mechanical strength, because the transfer member is applied to an
image-receiving element upon use and removed therefrom after use. A
transparent polymer is preferably used as the base material.
Examples thereof include polyesters such as poly(ethylene
terephthalate)s; acrylic resins; polyepoxys (epoxy resins);
polyethylenes; and polystyrenes, of which poly(ethylene
terephthalate)s are more preferably used. The thickness of the base
material can be arbitrarily adjusted according typically to the
specifications of a desired transfer member for a thin film for an
organic electroluminescent device, and is generally within a range
of 0.01 to 1 mm.
[0286] The photothermal conversion layer 13 supported by the base
material 12 acts to receive applied laser light, convert the
optical energy into thermal energy, melt the image component in the
transfer layer 15 facing the photothermal conversion layer 13 with
the interposition of the intermediate layer 14, and transfer and
solidify the molten image component to the surface of the image
receiving element. Consequently, the photothermal conversion layer
13 preferably includes a light-absorptive material such as a metal
layer (film) composed of aluminum, oxide and/or sulfide thereof;
carbon black; graphite; or an infrared dye, or includes a layer
containing a dispersed light-absorptive material. The photothermal
conversion layer 13 preferably contains a photo-induced
polymerizable component for curing the layer. When a photothermal
conversion layer 13 is formed as the metal layer (film) as the
light-absorptive layer, it is suitably formed to a thickness of 100
to 5000 angstroms by vacuum deposition, electron beam deposition,
or sputtering.
[0287] Preferred examples of the photothermal conversion layer 13
also include a layer containing a carbon black, a photo-induced
polymerizable monomer or oligomer, and/or photopolymerization
initiator dispersed in a binder resin. Such a photothermal
conversion layer 13 of components dispersed in a binder resin can
be generally formed, for example, by applying a resin composition
having a predetermined composition to a surface of the base
material 12 according to a known coating process such as spin
coating, gravure printing, or die coating, and drying the applied
film. The thickness of the photothermal conversion layer 13 of
components dispersed in a binder resin can be set within a wide
range depending typically on the specifications and advantages of a
desired transfer member for a thin film for an organic
electroluminescent device. The thickness is generally within a
range of 0.001 to 10 .mu.m.
[0288] The intermediate layer 14 arranged between the photothermal
conversion layer 13 and the transfer layer 15 especially acts to
uniformize the photothermal conversion action of the photothermal
conversion layer 13. The layer can be generally formed from a resin
material satisfying the above-mentioned requirements. The
intermediate layer 14 can be generally formed, for example, by
applying a resin composition having a predetermined composition to
a surface of the photothermal conversion layer 13 according to a
known coating process such as spin coating, gravure printing, or
die coating, and drying the applied film, in the same manner as the
photothermal conversion layer 13. The thickness of the intermediate
layer 14 can be set within a wide range depending typically on
desired effects and is generally within a range of 0.05 to 10
.mu.m.
[0289] The structure of a transfer member for a thin film for an
organic electroluminescent device can be modified according to its
use. For example, the transfer member for a thin film for an
organic electroluminescent device may have an antireflection
coating so as to prevent the properties of the transfer layer 15
from decreasing due to reflection, and/or it may have a gas
generation layer instead of the intermediate layer 14, so as to
improve the sensitivity of the transfer member.
[0290] When the gas generation layer absorbs light or heat, it
decomposes to discharge nitrogen gas or hydrogen gas to thereby
provide transferring energy. Examples of the gas generation layer
include at least one material selected from pentaerythritol
tetranitrate (PETN) and trinitrotoluene (TNT).
[0291] The transfer layer 15 is arranged as a topmost layer of the
transfer member 11 for a thin film for an organic
electroluminescent device according to the present invention. This
layer is an electroluminescent thin film which is melted by the
action of the photothermal conversion layer 13 or is delaminated by
the action of a vaporized gas generation layer and is transferred
as a pattern to an image-receiving element, as is described above.
It corresponds to a thin film for an organic electroluminescent
device according to the present invention and can be formed as a
film by the above-mentioned process.
[Organic Electroluminescent Device]
[0292] An organic electroluminescent device according to the
present invention is an organic electroluminescent device including
a substrate bearing an anode, a cathode, and an organic light
emitting layer arranged between the two electrodes, in which the
organic light emitting layer is a layer formed through wet
film-formation using the composition for an organic
electroluminescent device according to the present invention, or is
a layer formed by using the transfer member for a thin film for an
organic electroluminescent device according to the present
invention.
[0293] FIG. 2 is a cross-sectional view schematically illustrating
a structure of a general organic electroluminescent device for use
in the present invention. FIG. 2 shows a substrate 1, an anode 2, a
hole injection layer 3, an organic light emitting layer 4, an
electron injection layer 5, and a cathode 6.
[0294] <Substrate>
[0295] The substrate 1 functions as a support in the organic
electroluminescent device and includes a plate of quartz or glass,
a metal plate or metal foil, or a plastic film or sheet. In
particular, a glass plate and a plate or film of transparent
synthetic resin such as a polyester, a polymethacrylate, a
polycarbonate or a polysulfone are preferred. When a synthetic
resin substrate is used, its gas barrier properties are important.
If the gas barrier properties are too poor, the organic
electroluminescent device may deteriorate due to the air outside
having passed through the substrate, thus poor gas barrier
properties not being preferred. To avoid this, for example, a dense
silicon oxide film may be preferably arranged on at least one side
of the synthetic resin substrate to thereby ensure sufficient gas
barrier properties.
[0296] <Anode>
[0297] An anode 2 is arranged on the substrate 1. The anode 2
serves to inject holes into a hole transport layer 4. The anode 2
generally includes a metal such as aluminum, gold, silver, nickel,
palladium or platinum; a metal oxide such as indium oxide and/or
tin oxide; a metal halide such as copper iodide; carbon black; or a
conductive polymer such as poly(3-methylthiophene), polypyrrole or
polyaniline. The anode 2 is generally formed by sputtering or
vacuum deposition. When the anode 2 is formed from fine particles
of a metal such as silver, fine particles of copper iodide, carbon
black, fine particles of a conductive metal oxide, or fine
particles of a conductive polymer, it can also be formed by
dispersing such particles in a suitable binder resin solution to
yield a dispersion, and coating the dispersion on the substrate 1.
Further, when the anode 2 is formed from an electroconductive
polymer, the anode 2 can also be directly formed as a polymerized
thin film on the substrate 1 through electrolytic polymerization or
formed by applying an electroconductive polymer to the substrate 1
(App. Phys. Lett., vol. 60, p. 2711, 1992). The anode 2 may be of a
multilayer structure made from two or more different materials.
[0298] The thickness of the anode 2 varies depending upon required
transparency. When some transparency is required, the transmittance
for visible light is adjusted to be usually 60% or more, and
preferably 80% or more. In this case, the thickness of the anode is
usually 5 nm or more, and preferably 10 nm or more, and is usually
1,000 nm or less, and preferably 500 nm or less. When the anode may
be opaque, the anode 2 may also function as the substrate 1. In
addition, a layer of another electroconductive material may be
arranged on the anode 2.
[0299] The surface of the anode is preferably subjected to an
ultraviolet ray (UV)/ozone treatment or a treatment with oxygen
plasma or argon plasma to remove impurities deposited on the anode
and to adjust ionization potential to thereby carry out hole
injection more satisfactorily.
[0300] <Hole Injection Layer>
[0301] An organic electroluminescent device according to the
present invention preferably further includes a hole injection
layer between the organic light emitting layer and the anode.
[0302] Since the hole injection layer 3 is a layer which functions
to transport holes from the anode 2 to the organic light emitting
layer 4, the hole injection layer 3 preferably contains a
hole-transporting compound.
[0303] A hole is transported in such a manner that one electron is
removed from an electrically neutral compound to yield a cation
radical, and the cation radical receives one electron from a
neighboring electrically neutral compound. If the hole injection
layer does not contain a cation radical compound when the device is
not energized, a hole-transporting compound gives an electron to
the anode to thereby form a cation radical of the hole-transporting
compound, and the cation radical receives an electron from another
electrically neutral hole-transporting compound to thereby
transport a hole.
[0304] The hole injection layer preferably contains a cation
radical compound. This is because, when the hole injection layer 3
contains a cation radical compound, a cation radical necessary for
hole transportation is present in a concentration equal to or
higher than the concentration thereof formed as a result of the
oxidation of the anode 2, and this improves the hole-transporting
ability. The hole injection layer more preferably contains both a
cation radical compound and a hole-transporting compound, because
an electron can be smoothly received/given when an electrically
neutral hole-transporting compound is present in the vicinity of a
cation radical compound.
[0305] The "cation radical compound" herein is an ionic compound
containing a cation radical and a counter anion, which cation
radical is a chemical species corresponding to a hole-transporting
compound, except for removing one electron therefrom. The cation
radical compound already has an easy-to-move hole (free
carrier).
[0306] The hole injection layer 3 also preferably contains a
hole-transporting compound and an electron-accepting compound. This
is because the cation radical compound is formed by mixing a
hole-transporting compound with an electron-accepting compound to
thereby cause one electron to transfer from the hole-transporting
compound to the electron-accepting compound.
[0307] Summarizing preferred materials as mentioned above, the hole
injection layer 3 preferably contains a hole-transporting compound
and more preferably contains both a hole-transporting compound and
an electron-accepting compound. The hole injection layer 3 also
preferably contains a cation radical compound and more preferably
contains both a cation radical compound and a hole-transporting
compound.
[0308] Where necessary, the hole injection layer 3 further contains
a coatability improver and/or a binder resin that hardly acts as a
charge trap.
[0309] It is also possible, however, that an electron-accepting
compound alone is applied as the hole injection layer 3 to the
anode 2 by wet film-formation, and a composition for an organic
electroluminescent device according to the present invention is
directly applied to the hole injection layer 3. In this case, part
of the composition for an organic electroluminescent device
according to the present invention interacts with the
electron-accepting compound to thereby constitute a layer having
excellent hole injection ability.
[0310] Hole-Transporting Compound
[0311] The hole-transporting compound is preferably a compound
having an ionization potential between those of the anode 2 and the
organic light emitting layer 4. More specifically, the
hole-transporting compound is preferably a compound having an
ionization potential of 4.5 eV to 6.0 eV.
[0312] Examples thereof include aromatic amine compounds,
phthalocyanine derivatives or porphyrin derivatives, oligothiophene
derivatives, and polythiophene derivatives, of which aromatic amine
compounds are preferred for their non-crystallinity and
transmittance to visible rays.
[0313] Of aromatic amine compounds, aromatic tertiary amine
compounds are more preferred. The "aromatic tertiary amine
compounds" herein refer to compounds having aromatic tertiary amine
structures and also include compounds each having a group derived
from an aromatic tertiary amine.
[0314] While types of such aromatic tertiary amine compounds are
not specifically limited, more preferred are polymeric compounds
(polymerized organic compounds having sequential repeating units)
each having a weight-average molecular weight of 1000 or more and
1000000 or less, from the point of effectively smoothing the
surface of the layer.
[0315] Preferred examples of such polymeric aromatic tertiary amine
compounds include polymeric compounds each having a repeating unit
represented by following General Formula (6):
##STR00069##
[0316] In General Formula (6), Ar.sup.21 and Ar.sup.22 each
independently represent an aromatic hydrocarbon group which may
have a substituent, or an aromatic heterocyclic group which may
have a substituent; Ar.sup.23 to Ar.sup.25 each independently
represent a bivalent aromatic hydrocarbon group which may have a
substituent, or a bivalent aromatic heterocyclic group which may
have a substituent; and Y represents a linkage group selected from
the following Group Y1 of linkage groups, where two groups of
Ar.sup.21 to Ar.sup.25 bound to the same nitrogen atom may be
combined to form a ring.
##STR00070##
[0317] In the above formulae, Ar.sup.31 to Ar.sup.41 each
independently represent a monovalent or bivalent group which may
have a substituent and is derived from an aromatic hydrocarbon ring
or an aromatic heterocyclic ring; and R.sup.31 and R.sup.32 each
independently represent hydrogen atom or any substituent.
[0318] The groups Ar.sup.21 to Ar.sup.25 and Ar.sup.31 to Ar.sup.41
can each be a monovalent or bivalent group derived from any
aromatic hydrocarbon ring or any aromatic heterocyclic ring. These
may be different from or the same with one another. They may each
have any substituent.
[0319] Examples of such aromatic hydrocarbon rings include five- or
six-membered monocyclic rings, or bicyclic, tricyclic, tetracyclic,
or pentacyclic condensed rings containing such five- or
six-membered rings. Specific examples thereof include benzene ring,
naphthalene ring, anthracene ring, phenanthrene ring, perylene
ring, tetracene ring, pyrene ring, benzopyrene ring, chrysene ring,
triphenylene ring, acenaphthene ring, fluoranthene ring, and
fluorene ring.
[0320] Examples of aromatic heterocyclic rings include five- or
six-membered monocyclic rings, or bicyclic, tricyclic, or
tetracyclic condensed rings containing such five- or six-membered
rings. Specific examples thereof include furan ring, benzofuran
ring, thiophene ring, benzothiophene ring, pyrrole ring, pyrazole
ring, imidazole ring, oxadiazole ring, indole ring, carbazole ring,
pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring,
thienopyrrole ring, thienothiophene ring, furopyrrole ring,
furofuran ring, thienofuran ring, benzisoxazole ring,
benzisothiazole ring, benzimidazole ring, pyridine ring, pyrazine
ring, pyridazine ring, pyrimidine ring, triazine ring, quinoline
ring, isoquinoline ring, cinnoline ring, quinoxaline ring,
phenanthridine ring, benzimidazole ring, perimidine ring,
quinazoline ring, quinazolinone ring, and azulene ring.
[0321] The groups Ar.sup.23 to Ar.sup.25, Ar.sup.31 to Ar.sup.35,
and Ar.sup.37 to Ar.sup.40 can also be groups each containing two
or more groups combined with each other, the groups being selected
from one or more of bivalent groups derived from the
above-illustrated aromatic hydrocarbon rings and/or aromatic
heterocyclic rings.
[0322] The groups as Ar.sup.21 to Ar.sup.41 derived from aromatic
hydrocarbon rings and/or aromatic heterocyclic rings may each
further have a substituent. The molecular weight of the substituent
is generally about 400 or less, and is preferably about 250 or
less. The substituent is not specifically limited in its type and
can be, for example, one or more substituents selected from
following Group W of Substituents.
[Group W of Substituents]
[0323] Group W of Substituents includes methyl group, ethyl group,
and other alkyl groups generally having one or more carbon atoms,
and generally ten or less, and preferably eight or less carbon
atoms; vinyl group and other alkenyl groups generally having two or
more carbon atoms, and generally having eleven or less, and
preferably five or less carbon atoms; ethynyl group and other
alkynyl groups generally having two or more carbon atoms, and
generally having eleven or less, and preferably five or less carbon
atoms; methoxy group, ethoxy group, and other alkoxy groups
generally having one or more carbon atoms, and generally having ten
or less, and preferably six or less carbon atoms; phenoxy group,
naphthoxy group, pyridyloxy group, and other aryloxy groups
generally having four or more, and preferably five or more carbon
atoms, and generally having twenty-five or less, and preferably
fourteen or less carbon atoms; methoxycarbonyl group,
ethoxycarbonyl group, and other alkoxycarbonyl groups generally
having two or more carbon atoms, and generally having eleven or
less, and preferably seven or less carbon atoms; dimethylamino
group, diethylamino group, and other dialkylamino groups generally
having two or more carbon atoms, and generally having twenty or
less, and preferably twelve or less carbon atoms; diphenylamino
group, ditolylamino group, N-carbazolyl group, and other
diarylamino groups generally having ten or more, preferably twelve
or more carbon atoms, and generally having thirty or less, and
preferably twenty-two or less carbon atoms; phenylmethylamino group
and other arylalkylamino groups generally having six or more,
preferably seven or more carbon atoms, and generally having
twenty-five or less, and preferably seventeen or less carbon atoms;
acetyl group, benzoyl group, and other acyl groups generally having
two or more carbon atoms, and generally having ten or less, and
preferably seven or less carbon atoms; fluorine atom, chlorine
atom, and other halogen atoms; trifluoromethyl group and other
haloalkyl groups generally having one or more carbon atoms, and
generally having eight or less, and preferably four or less carbon
atoms; methylthio group, ethylthio group, and other alkylthio
groups generally having one or more carbon atoms, and generally
having ten or less, and preferably six or less carbon atoms;
phenylthio group, naphthylthio group, pyridylthio group, and other
arylthio groups generally having four or more, preferably five or
more carbon atoms, and generally having twenty-five or less, and
preferably fourteen or less carbon atoms; trimethylsilyl group,
triphenylsilyl group, and other silyl groups generally having two
or more, preferably three or more carbon atoms, and generally
having thirty-three or less, and preferably twenty-six or less
carbon atoms; trimethylsiloxy group, triphenylsiloxy group, and
other siloxy groups generally having two or more, preferably three
or more carbon atoms, and generally having thirty-three or less,
and preferably twenty-six or less carbon atoms; cyano group; phenyl
group, naphthyl group, and other aromatic hydrocarbon cyclic groups
generally having six or more carbon atoms, and generally having
thirty or less, and preferably eighteen or less carbon atoms; and
thienyl group, pyridyl group, and other aromatic heterocyclic
groups generally having three or more, preferably four or more
carbon atoms, and generally having twenty-eight or less, and
preferably seventeen or less carbon atoms.
[0324] Preferred as the groups Ar.sup.21 and Ar.sup.22 are
monovalent groups derived from benzene ring, naphthalene ring,
phenanthrene ring, thiophene ring, and pyridine ring, of which
monovalent groups derived from phenyl group and naphthyl group are
more preferred, from the points of the solubility, heat resistance,
and hole injection/transporting ability of the polymeric
compounds.
[0325] Preferred as the groups Ar.sup.23 to Ar.sup.25 are bivalent
groups derived from benzene ring, naphthalene ring, anthracene
ring, and phenanthrene ring, of which bivalent groups derived from
phenylene group, biphenylene group, and naphthylene group are more
preferred, from the points of the heat resistance and the hole
injection/transporting ability including oxidation/reduction
potentials.
[0326] The groups R.sup.31 and R.sup.32 may be the same as or
different from each other and can each be hydrogen atom or any
substituent. The substituents herein are not specifically limited
in their types, and applicable substituents include alkyl groups,
alkenyl groups, alkynyl groups, alkoxy groups, silyl groups, siloxy
groups, aromatic hydrocarbon groups, aromatic heterocyclic groups,
and halogen atoms. Specific examples thereof include the groups as
listed in Group W of Substituents.
[0327] Specific examples and preferred examples of polymeric
aromatic tertiary amine compounds each having a repeating unit
represented by General Formula (6) include, but are not limited to,
those described in PCT International Publication Number WO
2005/089024.
[0328] Preferred examples of polymeric aromatic tertiary amine
compounds further include polymeric compounds containing repeating
units represented by following General Formula (7) and/or (8):
##STR00071##
[0329] In General Formulae (7) and (8), Ar.sup.45, Ar.sup.47 and
Ar.sup.48 each independently represent an aromatic hydrocarbon
group which may have a substituent, or an aromatic heterocyclic
group which may have a substituent; Ar.sup.44 and Ar.sup.46 each
independently represent a bivalent aromatic hydrocarbon group which
may have a substituent, or a bivalent aromatic heterocyclic group
which may have a substituent, wherein two groups of Ar.sup.45 to
Ar.sup.48 bound to the same nitrogen atom may be combined to form a
ring; and R.sup.41 to R.sup.43 each independently represent
hydrogen atom or any substituent.
[0330] Specific examples, preferred examples, examples of
substituents which they may have, and examples of preferred
substituents of Ar.sup.45, Ar.sup.47, and Ar.sup.48, and Ar.sup.44
and Ar.sup.46 are as with those of Ar.sup.21 and Ar.sup.22, and
Ar.sup.23 to Ar.sup.25, respectively. The groups R.sup.41 to
R.sup.43 are preferably hydrogen atoms or substituents listed in
[Group W of Substituents], of which hydrogen atoms, alkyl groups,
alkoxy groups, amino groups, aromatic hydrocarbon groups, and
aromatic hydrocarbon groups are more preferred.
[0331] Specific examples and preferred examples of polymeric
aromatic tertiary amine compounds each containing repeating units
represented by General Formula (7) and/or (8) include, but are not
limited to, those described in PCT International Publication Number
WO 2005/089024.
[0332] When the hole injection layer is formed through wet
film-formation, a hole-transporting compound that is highly soluble
in various solvents is preferably used. From this viewpoint,
preferred examples of aromatic tertiary amine compounds include
binaphthyl compounds represented by following General Formula (9)
(Japanese Unexamined Patent Application Publication No.
2004-014187) and unsymmetrical 1,4-phenylenediamine compounds
represented by following General Formula (10) (Japanese Unexamined
Patent Application Publication No. 2004-026732). The material for
use herein can also be selected as a compound that is highly
soluble in various solvents, from among compounds used as materials
for forming thin films having hole injection/transporting ability
in known organic electroluminescent devices.
##STR00072##
[0333] In General Formula (9), Ar.sup.51 to Ar.sup.54 each
independently represent an aromatic hydrocarbon group which may
have a substituent, or an aromatic heterocyclic group which may
have a substituent; two groups of Ar.sup.51 to Ar.sup.54 bound to
the same nitrogen atom may be combined to form a ring; X.sup.1 and
X.sup.2 each independently represent a direct bond or a bivalent
linkage group; "u" and "v" each independently represent an integer
of 0 or more and 4 or less, wherein "u" and "v" satisfy the
condition: u+v.gtoreq.1, and wherein the naphthalene rings in
General Formula (9) may each have a substituent, in addition to
--X.sup.1NAr.sup.5lAr.sup.52 and --X.sup.2NAr.sup.53Ar.sup.54.
##STR00073##
[0334] In General Formula (10), Ar.sup.55, Ar.sup.56, and Ar.sup.57
each independently represent an aromatic hydrocarbon group which
may have a substituent, or an aromatic heterocyclic group which may
have a substituent, and each of these has a total of ten or more
carbon atoms, in which Ar.sup.56 and Ar.sup.57 bound to the same
nitrogen atom may be combined to form a ring.
[0335] Specific examples, preferred examples, examples of
substituents which they may have, and examples of preferred
substituents of Ar.sup.51 to Ar.sup.57 are as with those of
Ar.sup.21 and Ar.sup.22, respectively. The groups Ar.sup.51 and
Ar.sup.53 are typically preferably aromatic hydrocarbon groups
having a diarylamino group substituted at the para-position, such
as 4-(diphenylamino)phenyl group.
[0336] The numbers "u" and "v" are preferably both 1.
[0337] X.sup.1 and X.sup.2 are each preferably a direct bond or a
bivalent linkage group derived from an aromatic hydrocarbon ring
and are most preferably both direct bonds.
[0338] The naphthalene rings in General Formula (9) may each have
any substituent, in addition to --X.sup.1NAr.sup.51Ar.sup.52 and
--X.sup.2NAr.sup.53Ar.sup.54. The substituents
--X.sup.1NAr.sup.51Ar.sup.52 and --X.sup.2NAr.sup.53Ar.sup.54 may
be substituted at any positions of the naphthalene rings but are
preferably substituted at the 4- and 4'-positions of the
naphthalene rings in binaphthyl compounds represented by General
Formula (9).
[0339] The binaphthylene structures in compounds represented by
General Formula (9) preferably have substituents at the 2- and/or
2'-position. Examples of such substituents at the 2- and/or
2'-position include alkyl groups, alkoxy groups, alkenyl groups,
and alkoxycarbonyl groups, each of which may have a
substituent.
[0340] The binaphthylene structures in compounds represented by
General Formula (9) may have any substituents in addition to those
at the 2- and 2'-positions. Examples of the substituents include
the groups listed as the substituents at the 2- and 2'-positions.
Compounds represented by General Formula (9) are supposed to have
high solubility, because the two naphthalene rings are distorted
with respect to each other. The compounds, if having substituents
at the 2- and 2'-positions, are supposed to have further higher
solubility, because the two naphthalene rings are further distorted
with respected to each other.
[0341] The compounds represented by General Formula (10) are
supposed to have high solubility in solvents, because they do not
have symmetry of C2 or higher. Unsymmetrical diamine compounds
represented by following General Formula (11) are also preferred,
because they are supposed to be highly soluble in various solvents
for the same reason as above.
##STR00074##
[0342] In General Formula (11), Ar.sup.58 to Ar.sup.61 each
independently represent an aromatic hydrocarbon group which may
have a substituent, or an aromatic heterocyclic group which may
have a substituent; Ar.sup.62 represents a bivalent aromatic
hydrocarbon group which may have a substituent, or a bivalent
aromatic heterocyclic group which may have a substituent, wherein
two of Ar.sup.58 to Ar.sup.61 bound to the same nitrogen atom may
be combined to form a ring, and wherein Ar.sup.58 is a group
different from any of Ar.sup.59 to Ar.sup.61.
[0343] Specific examples, preferred examples, examples of
substituents which they may have, and examples of preferred
substituents of Ar.sup.58 to Ar.sup.61 are as with those of
Ar.sup.21 and Ar.sup.22. Specific examples, preferred examples,
examples of substituents which they may have, and examples of
preferred substituents of Ar.sup.62 are as with those of Ar.sup.23
to Ar.sup.25.
[0344] The molecular weights of the compounds represented by
General Formulae (9), (10), and (11) are each generally less than
5000, preferably less than 2500 and are generally 200 or more,
preferably 400 or more.
[0345] Specific examples and preferred examples of the compounds
represented by General Formulae (9), (10), and (11) include, but
are not limited to, those described in Japanese Patent Application
No. 2005-21983.
[0346] Such aromatic amine compounds usable as the
hole-transporting compound in the hole injection layer further
include known compounds used as materials for forming layers having
hole injection/transporting ability in organic electroluminescent
devices. Examples thereof include aromatic diamine compounds each
including a series of aromatic tertiary amine units, such as
1,1-bis(4-di-p-tolylaminophenyl)cyclohexane (Japanese Unexamined
Patent Application Publication No. 59-194393); aromatic amine
compounds containing two or more tertiary amines and having two or
more condensed aromatic rings substituted on nitrogen atom,
typified by 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl
(Japanese Unexamined Patent Application Publication No. 5-234681);
aromatic triamine compounds as triphenylbenzene derivatives having
a starburst structure (U.S. Pat. No. 4,923,774); aromatic diamine
compounds such as
N,N'-diphenyl-N,N'-bis(3-methylphenyl)biphenyl-4,4'-diamine (U.S.
Pat. No. 4,764,625);
.alpha.,.alpha.,.alpha.',.alpha.-'tetramethyl-.alpha.,.alpha.'-bis(4-di(p-
-tolyl)aminophenyl)-p-xylene (Japanese Unexamined Patent
Application Publication No. 3-269084); triphenylamine derivatives
which are three-dimensionally unsymmetrical as the whole molecules
(Japanese Unexamined Patent Application Publication No. 4-129271);
compounds each containing a pyrenyl group substituted with two or
more aromatic diamino groups (Japanese Unexamined Patent
Application Publication No. 4-175395); aromatic diamine compounds
each containing tertiary aromatic amine units combined with each
other through ethylene group (Japanese Unexamined Patent
Application Publication No. 4-264189); aromatic diamines having
styryl structures (Japanese Unexamined Patent Application
Publication No. 4-290851); compounds each containing aromatic
tertiary amine units combined with each other through thiophene
group (Japanese Unexamined Patent Application Publication No.
4-304466); star-burst aromatic triamine compounds (Japanese
Unexamined Patent Application Publication No. 4-308688);
benzylphenyl compounds (Japanese Unexamined Patent Application
Publication No. 4-364153); compounds each containing tertiary
amines combined with each other through fluorene group (Japanese
Unexamined Patent Application Publication No. 5-25473); triamine
compounds (Japanese Unexamined Patent Application Publication No.
5-239455); bisdipyridylaminobiphenyl (Japanese Unexamined Patent
Application Publication No. 5-320634); N,N,N-triphenylamine
derivatives (Japanese Unexamined Patent Application Publication No.
6-1972); aromatic diamines having phenoxazine structures (Japanese
Unexamined Patent Application Publication No. 7-138562);
diaminophenylphenanthridine derivatives (Japanese Unexamined Patent
Application Publication No. 7-252474); hydrazone compounds
(Japanese Unexamined Patent Application Publication No. 2-311591);
silazane compounds (U.S. Pat. No. 4,950,950); silanamine
derivatives (Japanese Unexamined Patent Application Publication No.
6-49079); phosphamine derivatives (Japanese Unexamined Patent
Application Publication No. 6-25659); and quinacridone compounds.
Where necessary, each of these aromatic amine compounds may be used
in combination.
[0347] Preferred examples of phthalocyanine derivatives or
porphyrin derivatives usable as the hole-transporting compound in
the hole injection layer include porphyrin,
5,10,15,20-tetraphenyl-21H,23H-porphyrin,
5,10,15,20-tetraphenyl-21H,23H-porphyrin cobalt(II),
5,10,15,20-tetraphenyl-21H,23H-porphyrin copper(II),
5,10,15,20-tetraphenyl-21H,23H-porphyrin zinc(II),
5,10,15,20-tetraphenyl-21H,23H-porphyrin vanadium(IV) oxide,
5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin, copper(II)
29H,31H-phthalocyanine, zinc(II) phthalocyanine, titanium
phthalocyanine, magnesium phthalocyanine oxide, lead
phthalocyanine, copper(II) phthalocyanine, and
4,4',4'',4'''-tetraaza-29H,31H-phthalocyanine.
[0348] Preferred examples of oligothiophene derivatives usable as
the hole-transporting compound in the hole injection layer include
.alpha.-terthiophene and derivatives thereof, .alpha.-sexithiophene
and derivatives thereof, and oligothiophene derivatives each
containing naphthalene ring (Japanese Unexamined Patent Application
Publication No. 6-256341).
[0349] Preferred examples of polythiophene derivatives usable as
the hole-transporting compound in the present invention include
poly(3,4-ethylenedioxythiophene)s (PEDOT) and
poly(3-hexylthiophene)s.
[0350] The molecular weights of these hole-transporting compounds,
except for polymeric compounds (polymerized compounds having a
series of repeating units), are each generally 9000 or less,
preferably 5000 or less, and are generally 200 or more, and
preferably 400 or more. A hole-transporting compound having an
excessively high molecular weight may be difficult to synthesize
and purify. In contrast, a hole-transporting compound having an
excessively low molecular weight may have poor heat resistance.
[0351] The material for the hole injection layer may contain each
of such hole-transporting compounds alone or in combination. When
the material contains two or more different hole-transporting
compounds, one or more polymeric aromatic tertiary amine compounds
and one or more other hole-transporting compounds are preferably
used in combination.
[0352] Electron-Accepting Compound
[0353] Preferred as the electron-accepting compound are compounds
having oxidizing power and capability of accepting one electron
from the hole-transporting compound. More specifically, compounds
having an electron affinity of 4 eV or more are preferred, of which
compounds having an electron affinity of 5 eV or more are more
preferred.
[0354] Examples of such compounds include onium salts substituted
with organic group(s), such as
4-isopropyl-4'-methyldiphenyliodonium
tetrakis(pentafluorophenyl)borate; high-valence inorganic compounds
such as iron(III) chloride (Japanese Unexamined Patent Application
Publication No. 11-251067) and ammonium peroxodisulfate; cyano
compounds such as tetracyanoethylene; aromatic boron compounds such
as tris(pentafluorophenyl)borane (Japanese Unexamined Patent
Application Publication No. 2003-31365); fullerene derivatives; and
iodine.
[0355] Of these compounds, onium salts substituted with organic
group(s), and high-valence inorganic compounds are preferred for
their high oxidizing power, and onium salts substituted with
organic group(s), cyano compounds, and aromatic boron compounds are
preferred for their solubility in various solvents and
applicability to wet coating.
[0356] Specific examples and preferred examples of such onium salts
substituted with organic group(s), cyano compounds, and aromatic
boron compounds as preferred electron-accepting compounds include,
but are not limited to, those described in PCT International
Publication Number WO 2005/089024.
[0357] Cation Radical Compound
[0358] The "cation radical compound" refers to an ion compound
containing a cation radical and a counter anion, in which the
cation radical is a chemical species corresponding to a
hole-transporting compound except for removing one electron
therefrom. However, when the cation radical is derived from a
hole-transporting polymeric compound, the cation radical has a
structure corresponding to the polymeric compound, except for
removing one electron from its repeating unit.
[0359] The cation radical is preferably a chemical species
corresponding to one of the above-listed hole-transporting
compounds, except for removing one electron therefrom, and is more
preferably one of the above-listed preferred hole-transporting
compounds, except for removing one electron therefrom. This is
because these cation radicals provide further satisfactory
non-crystallinity, transmittance to visible light, heat resistance,
and solubility.
[0360] Such a cation radical compound can be formed by mixing the
hole-transporting compound and the electron-accepting compound.
Specifically, by mixing the hole-transporting compound and the
electron-accepting compound, an electron travels from the
hole-transporting compound to the electron-accepting compound to
thereby yield a cation radical compound containing a cation radical
of the hole-transporting compound, and a counter anion.
[0361] Cation radical compounds derived from polymeric compounds,
such as poly(ethylene dioxythiophene) doped with polystyrene
sulfonic acid (PEDOT/PSS) (Adv. Mater., 2000, vol. 12, p. 481) and
emeraldine hydrochloride (J. Phys. Chem., 1990, vol. 94, p. 7716)
can also be formed through oxidative polymerization
(dehydrogenative polymerization). Namely, they can be formed by
chemically or electrochemically oxidizing one or more monomers
typically with a peroxodisulfate in an acidic solution. In the
oxidative polymerization (dehydrogenative polymerization), the
monomer is polymerized and a cation radical corresponding to the
polymer, except for removing one electron from its repeating unit,
is formed as a result of oxidation. An anion derived from the
acidic solution serves as a counter anion with respect to the
cation radical.
[0362] The hole injection layer 3 is formed on or above the anode 2
through wet film-formation or vacuum deposition.
[0363] Indium thin oxide (ITO) generally used as the anode 2 has a
surface roughness (Ra) of about 10 nm, often has local projections,
and is thereby liable to cause bridging faults. The hole injection
layer 3 is advantageously formed on or above the anode 2 through
wet film-formation rather than vacuum deposition, so as to reduce
defects of the device caused by the unevenness of the anode
surface.
[0364] When the hole injection layer 3 is formed through wet
film-formation, the layer may be formed by dissolving predetermined
amounts of one or more of the respective materials including the
hole-transporting compounds, the electron-accepting compounds, and
the cation radical compounds, and where necessary a coatability
improver and a binder resin that does not act as a charge trap, in
a solvent to yield a coating solution, applying the coating
solution to the anode through wet film-formation, and drying the
applied film. Examples of processes for the wet film-formation
include spin coating, spray coating, dip coating, die coating,
flexographic printing, screen printing, and an ink-jet process.
[0365] Solvents for use in the formation of the layer through wet
film-formation are not specifically limited in their types, as long
as they are solvents that can dissolve the respective materials
including the hole-transporting compounds, the electron-accepting
compounds, and the cation radical compounds therein. They
preferably contain neither deactivating substances nor substances
forming such deactivating substances. The deactivating substances
herein are substances that may deactivate the respective materials
for the hole injection layer, including the hole-transporting
compounds, the electron-accepting compounds, and the cation radical
compounds.
[0366] Examples of preferred solvents satisfying these conditions
include ether solvents and ester solvents. Specific examples of
ether solvents include aliphatic ethers such as ethylene glycol
dimethyl ether, ethylene glycol diethyl ether, and propylene
glycol-1-monomethyl ether acetate (PGMEA); and aromatic ethers such
as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole,
2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene,
2,3-dimethylanisole, and 2,4-dimethylanisole. Specific examples of
ester solvents include aliphatic esters such as ethyl acetate,
n-butyl acetate, ethyl lactate, and n-butyl lactate; and aromatic
esters such as phenyl acetate, phenyl propionate, methyl benzoate,
ethyl benzoate, propyl benzoate, and n-butyl benzoate. Each of
these can be used alone or used in any combinations and
proportions.
[0367] In addition to the ether solvents and ester solvents,
solvents usable herein also include aromatic hydrocarbon solvents
such as benzene, toluene, and xylenes; amide solvents such as
N,N-dimethylformamide and N,N-dimethylacetamide; and dimethyl
sulfoxide. Each of these can be used alone or used in any
combinations and proportions. It is acceptable to use one or more
of these solvents in combination with one or more of the ether
solvents and ester solvents. In particular, aromatic hydrocarbon
solvents, such as benzene, toluene, and xylenes, are preferably
used in combination with one or more of the ether solvents and
ester solvents, because they have low capability of dissolving
electron-accepting compounds and cation radical compounds.
[0368] Solvents containing deactivating substances that may
deactivate the respective materials for the hole injection layer
including the hole-transporting compounds, the electron-accepting
compounds, and the cation radical compounds, or solvents containing
substances forming such deactivating substances include aldehyde
solvents such as benzaldehyde; and ketone solvents having hydrogen
atom at the alpha position, such as methylethyl ketone,
cyclohexanone, and acetophenone. These aldehyde solvents and ketone
solvents are undesirable, because they may cause condensation
reaction between solvent molecules or may react with the respective
materials including the hole-transporting compounds,
electron-accepting compounds, and cation radical compounds to yield
impurities.
[0369] The concentration of the solvent in the coating solution is
generally 10 percent by weight or more, preferably 30 percent by
weight or more, more preferably 50 percent by weight or more, and
is generally 99.999 percent by weight or less, preferably 99.99
percent by weight or less, and further preferably 99.9 percent by
weight or less. When two or more different solvents are used as the
solvent, the total concentration of these solvents may be set
within this range.
[0370] When the hole injection layer is formed through vacuum
deposition, the layer may be formed in the following manner. One of
the respective materials including the hole-transporting compounds,
the electron-accepting compounds, or the cation radical compounds,
when used alone, is placed in a crucible disposed in a vacuum
chamber, the vacuum chamber is evacuated using a proper vacuum pump
to a pressure of about 10.sup.-4 Pa, the crucible is heated to
vaporize the material to thereby form a hole injection layer on the
anode on a substrate placed facing the crucible, while controlling
the amount of evaporation. When two or more of the materials are
used, the above procedure is repeated, except that the materials
are placed in different crucibles disposed in a vacuum chamber,
respectively, the crucibles are heated respectively, and the
amounts of the evaporated materials are controlled independently.
When two or more of the materials are used, the hole injection
layer can also be formed by placing a mixture of these materials in
a crucible, and heating the crucible to evaporate the mixture.
[0371] The thickness of the hole injection layer 3 which may be
formed in the above manner is generally 5 nm or more, preferably 10
nm or more, and is generally 1000 nm or less, and preferably 500 nm
or less.
[0372] <Organic Light Emitting Layer>
[0373] An organic light emitting layer 4 is arranged on the hole
injection layer 3. The organic light emitting layer 4 is a layer
formed by using the composition for an organic electroluminescent
device according to the present invention containing a luminescent
material, a charge transporting material, and a solvent. The
organic light emitting layer can mainly emit light when strongly
excited in a space between energized electrodes. The excitation is
caused by recombination of holes injected from the anode 2 via the
hole injection layer 3 with electrons injected from the cathode 6
via the electron injection layer 5. The organic light emitting
layer 4 may further contain any other materials and components,
within ranges not adversely affecting the performance obtained
according to the present invention. A device according to the
present invention is preferably prepared using a method including
the step of forming the organic light emitting layer through wet
film-formation using the composition. The wet film-formation herein
is as described in the thin film for an organic electroluminescent
device according to the present invention.
[0374] Provided that the same material is used, an organic
electroluminescent device generally operates at a decreasing drive
voltage with a decreasing thickness of a layer between the
electrodes, because the effective electric field increases and
thereby the injected current increases with a decreasing thickness.
Accordingly, the organic electroluminescent device operates at a
decreasing drive voltage with a decreasing thickness of layers
between the electrodes. The total thickness of the layers, however,
should be a certain level or more, because an excessively small
total thickness may cause short circuit due to projections
typically caused by the electrodes made typically of ITO.
[0375] When a device according to the present invention further
includes a hole injection layer and an electron injection layer in
addition to the organic light emitting layer, the total thickness
of the organic light emitting layer 4 and other organic layers such
as the hole injection layer 3 and the electron injection layer 5 is
generally 30 nm or more, preferably 50 nm or more, and further
preferably 100 nm or more, and is generally 1000 nm or less,
preferably 500 nm or less, and further preferably 300 nm or less.
When the hole injection layer 3 and/or the electron injection layer
5 other than the organic light emitting layer 4 has a high
electroconductivity, the amount of charges to be injected to the
organic light emitting layer 4 increases. In this case, the drive
voltage can be reduced while maintaining the total thickness to a
certain level by increasing the thickness of, for example, the hole
injection layer 3 and decreasing the thickness of the organic light
emitting layer 4.
[0376] Accordingly, the thickness of the organic light emitting
layer 4 in this case is generally 10 nm or more, preferably 20 nm
or more, and is generally 300 nm or less, and preferably 200 nm or
less. When a device according to the present invention includes the
organic light emitting layer alone between the anode and the
cathode, the thickness of the organic light emitting layer 4 is
generally 30 nm or more, preferably 50 nm or more, and is generally
500 nm or less, preferably 300 nm or less.
[0377] A thin film as the organic light emitting layer 4 is formed
according to the wet film-formation process described in the thin
film for an organic electroluminescent device according to the
present invention.
[0378] <Electron Injection Layer>
[0379] The electron injection layer 5 functions to inject electrons
injected from the cathode 6 into the organic light emitting layer 4
efficiently. To conduct electron injection efficiently, materials
for constituting the electron injection layer 5 are preferably
metals having low work functions, including alkali metals such as
sodium and cesium; and alkaline earth metals such as barium and
calcium. The thickness of this layer is preferably 0.1 to 5 nm.
[0380] Further, in order to improve efficiency of the device, it is
also an effective technique to arrange an extremely thin insulating
film typically of LiF, MgF.sub.2, or Li.sub.2O at the interface
between the cathode 6 and the light-emitting layer 4 or the
after-mentioned electron transport layer 8 (Appl. Phys. Lett., vol.
70, p. 152, 1997; Japanese Unexamined Patent Application
Publication No. 10-74586; IEEE Trans. Electron. Devices, vol. 44,
p. 1245, 1997; and SID 04 Digest, p. 154).
[0381] It is preferred to dope an organic electron transporting
material with an alkali metal such as sodium, potassium, cesium,
lithium, or rubidium (described typically in Japanese Unexamined
Patent Application Publications No. 10-270171, No. 2002-100478, and
No. 2002-100482), because this serves to improve the electron
injection/transporting ability and to provide excellent film
quality. The organic electron transporting material is typified by
nitrogen-containing heterocyclic compounds such as
bathophenanthroline; and metal complexes such as aluminum
8-hydroxyquinoline complex. The thickness of this layer is
generally 5 nm or more, preferably 10 nm or more, and is generally
200 nm or less, and preferably 100 nm or less.
[0382] The electron injection layer 5 may be formed by forming a
film on the organic light emitting layer 4 by a coating process as
in the organic light emitting layer 4 or by vacuum deposition. When
vacuum deposition is employed, the electron injection layer may be
formed by placing an evaporation source in a crucible or metal boat
disposed in a vacuum chamber, evacuating the vacuum chamber to a
pressure of about 10.sup.-4 Pa using a proper vacuum pump, heating
the crucible or metal boat to evaporate the evaporation source, and
thereby forming a film as the electron injection layer on a
substrate placed facing the crucible or metal boat.
[0383] The evaporation of the alkaline metal is usually carried out
using an alkaline metal dispenser containing an alkaline metal salt
of chromic acid and a reducing agent packed in a Ni--Cr alloy
(nichrome). By heating this dispenser in a vacuum chamber, the
alkaline metal salt of chromic acid is reduced so that the alkaline
metal is evaporated. When an organic electron transporting material
and an alkali metal are co-evaporated, the organic electron
transporting material is put in a crucible placed in the vacuum
chamber. The vacuum chamber is then evacuated to a pressure of
about 10.sup.-4 Torr by a proper vacuum pump. The crucible and the
dispenser are then simultaneously heated to evaporate the materials
so that an electron injection/transport layer is formed on a
substrate disposed facing the crucible and the dispenser.
[0384] In this case, the materials are co-deposited homogenously in
a thickness direction of the electron injection layer. However,
there may be distribution in concentrations of the materials in a
thickness direction.
[0385] <Cathode>
[0386] The cathode 6 serves to inject electrons into the organic
light emitting layer 4, or a layer arranged between the cathode and
the organic light emitting layer, such as the electron injection
layer 5. As materials for the cathode 6, those materials which are
used for the anode 2 may be employed but, in order to inject
electrons highly efficiently, metals having low work functions are
preferred. Thus, suitable metals such as tin, magnesium, indium,
calcium, aluminum and silver or alloys thereof are used. Specific
examples of the cathode include electrodes of alloys having a low
work function, such as a magnesium-silver alloy, a magnesium-indium
alloy and a aluminum-lithium alloy. The thickness of the cathode 6
is generally as with that of the anode 2. A metal layer having a
high work function and stable in the atmosphere may be arranged on
the cathode in order to protect the cathode formed from such a
metal having a low work function. This improves the stability of
the device. For this purpose, metals such as aluminum, silver,
copper, nickel, chromium, gold, and platinum are used.
[0387] <Other Constitutive Layers>
[0388] While there has been mainly described a device having the
layer configuration shown in FIG. 2, an organic electroluminescent
device according to the present invention may further include any
other layers between the anode 2 and the organic light emitting
layer 4 and between the cathode 6 and the organic light emitting
layer 4 in addition to the above-illustrated layers, as long as not
adversely affecting the performance of the device. Any layer
between the cathode 6 and the anode 2, except for the organic light
emitting layer 4, may be omitted.
[0389] An example of the layers which the device may further
include is an electron blocking layer 7 arranged between the hole
injection layer 3 and the organic light emitting layer 4 (refer to
FIGS. 3, 4, and 5). The electron blocking layer 7 serves to block
electrons having migrated from the organic light emitting layer 4
from reaching the hole injection layer 3, to thereby increase the
recombination probability between electrons and holes in the
organic light emitting layer 4, and to confine resulting exitons
within the light emitting layer 4. It also serves to transport
holes injected from the hole injection layer 3 toward the organic
light emitting layer 4 efficiently. This layer is particularly
effective when a phosphorescent material or a blue-emitting
material is used as a luminescent material. Properties required for
the electron blocking layer 7 are high hole transporting ability, a
large energy gap (difference between the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)),
and a high excited triplet level (T1). In addition, the electron
blocking layer 7 should be applicable to wet film-formation,
because the organic light emitting layer 4 in a device according to
the present invention is formed through wet film-formation, and the
device is thereby easily manufactured. Examples of materials for
the electron blocking layer 7 include copolymers of dioctylfluorene
and triphenylamine, typified by F8-TFB (described in PCT
International Publication Number WO 2004/084260).
[0390] The layers which the device may further have also include an
electron transport layer 8. The electron transport layer 8 is
arranged between the organic light emitting layer 4 and the
electron injection layer 5 in order to further improve the luminous
efficiency of the device (FIGS. 4, 5, 6, and 7).
[0391] The electron transport layer 8 is formed from a compound
which can efficiently transport electrons injected from the cathode
6 toward the organic light emitting layer 4 between the energized
electrodes. Electron transporting compounds for use in the electron
transport layer 8 must be compounds that efficiently inject
electrons from the cathode 6 or the electron injection layer 5 and
have high electron mobility to thereby efficiently transport the
injected electrons.
[0392] Examples of materials satisfying such conditions include
metal complexes such as aluminum complex of 8-hydroxyquinoline
(Japanese Unexamined Patent Application Publication No. 59-194393);
metal complexes of 10-hydroxybenzo[h]quinoline; oxadiazole
derivatives; distyrylbiphenyl derivatives; silole derivatives;
metal complexes of 3- or 5-hydroxyflavone; metal complexes of
benzoxazole; metal complexes of benzothiazole;
trisbenzimidazolylbenzene (U.S. Pat. No. 5,645,948); quinoxaline
compounds (Japanese Unexamined Patent Application Publication No.
6-207169); phenanthroline derivatives (Japanese Unexamined Patent
Application Publication No. 5-331459);
2-t-butyl-9,10-N,N'-dicyanoanthraquinonediimine; n-type
hydrogenated amorphous silicon carbide; n-type zinc sulfide; and
n-type zinc selenide.
[0393] The lower limit of the thickness of the electron transport
layer 8 is generally about 1 nm, and preferably about 5 nm, and its
upper limit is generally about 300 nm, and preferably about 100
nm.
[0394] The electron transport layer 8 may be formed on the organic
light emitting layer 4 by coating or vacuum deposition in the same
manner as with the hole injection layer 3, but this layer is
generally formed by vacuum deposition.
[0395] It is also effective to provide a hole blocking layer 9
(refer to FIGS. 5 and 7), for the same purpose as with the electron
blocking layer 7. The hole blocking layer 9 is arranged on the
organic light emitting layer 4 at an interface of the organic light
emitting layer 4 facing the cathode 6. This layer is formed by a
compound which serves to prevent holes migrating form the anode 2
from reaching the cathode 6 and can efficiently transport electrons
injected from the cathode 6 toward the organic light emitting layer
4. Required properties for the material constituting the hole
blocking layer 9 include a high electron mobility and a low hole
mobility, a large energy gap (difference between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO)), and a high excited triplet level (T1).
The hole blocking layer 9 has the function of confining holes and
electrons within the organic light emitting layer 4 to thereby
improve the luminous efficiency.
[0396] Examples of materials for the hole blocking layer satisfying
these conditions include mixed ligand complexes such as
bis(2-methyl-8-quinolinolato)(phenolato)aluminum and
bis(2-methyl-8-quinolinolato)(triphenylsilanolato)aluminum; metal
complexes such as
bis(2-methyl-8-quinolato)aluminum-.mu.-oxo-bis-(2-methyl-8-quinolylato)al-
uminum binuclear metal complex; styryl compounds such as
distyrylbiphenyl derivatives (Japanese Unexamined Patent
Application Publication No. 11-242996); triazole derivatives such
as 3-(4-biphenylyl)-4-phenyl-5(4-tert-butylphenyl)-1,2,4-triazole
(Japanese Unexamined Patent Application Publication No. 7-41759);
and phenanthroline derivatives such as bathocupuroine (Japanese
Unexamined Patent Application Publication No. 10-79297).
[0397] Preferred hole blocking materials further include compounds
having at least one pyridine ring substituted on the 2-, 4-, and/or
6-position, represented by following General Formula (12):
##STR00075##
[0398] In General Formula (12), R.sup.51, R.sup.52, and R.sup.53
each independently represent hydrogen atom or any substituent;
linkage group G represents a linkage group having a valency of "m",
where the linkage group G is directly bound to the pyridine ring at
any one of the 2-, 3-, 4-, 5-, and 6-positions; and "m" represents
an integer of 1 to 8.
[0399] Specific examples of the compounds having at least one
pyridine ring substituted at 2-, 4-, and/or 6-position, represented
by the structural formula are illustrated below, which, however,
are not limitative at all.
##STR00076## ##STR00077##
[0400] The thickness of the hole blocking layer 9 is generally 0.3
nm or more, preferably 0.5 nm or more, and is generally 100 nm or
less, and preferably 50 nm or less. The hole blocking layer 9 can
be formed in the same manner as with the hole injection layer 3,
but it is generally formed by vacuum deposition.
[0401] The electron transport layer 8 and the hole blocking layer 9
may be arranged as appropriate according to necessity. A device may
have, for example, 1) the electron transport layer alone, 2) the
hole blocking layer alone, 3) a multilayer of the hole blocking
layer and the electron transport layer, or 4) none of the two
layers.
[0402] A reverse layer structure to that in FIG. 2 is also
possible. In the reversed structure, on a substrate 1, there are
sequentially arranged a cathode 6, an electron injection layer 5,
an organic light emitting layer 4, a hole injection layer 3, and an
anode 2 in this order. As is described above, an organic
electroluminescent device according to the present invention may be
arranged between two substrates, at least one of which is highly
transparent. Likewise, reverse layer structures to those shown in
FIGS. 3 to 7, respectively, are also possible.
[0403] It is also possible to employ a layer structure in which a
plurality of the layer structures shown in FIGS. 2 to 7 are stacked
(a structure including a plurality of the light-emitting units as
stacked). In this case, V.sub.2O.sub.5, for example, is preferably
used as a charge generating layer (CGL) instead of the interface
layers (when ITO and aluminum (Al) are used as the anode and the
cathode, respectively, the two layers of the anode and the cathode)
between the units (light-emitting units). This serves to reduce
barrier between the units, thus being more preferred in view of
luminous efficiency and drive voltage.
[0404] The present invention can be applied to any of structures of
organic luminescent devices, such as a structure in which the
organic electroluminescent device includes a single device, a
structure which includes devices arranged in an array form, and a
structure wherein the anode and the cathode are arranged in an X-Y
matrix pattern.
[0405] An organic electroluminescent device according to the
present invention uses a composition for an organic
electroluminescent device according to the present invention which
contains a luminescent material and a charge transporting material
having a specific relationship in oxidation/reduction potentials,
and a solvent. The device can thereby be easily manufactured, has a
high luminous efficiency, and shows significantly improved drive
stability. The device can thereby exhibit excellent performance
when applied to large-area display devices or lightning.
EXAMPLES
[0406] Next, the present invention will be illustrated in further
detail with reference to a measurement example, several examples
and comparative examples below, which, however, are not limitative
at all, as long as not exceeding the scope and the spirit of the
present invention.
Measurement Example 1
Determination of Oxidation/Reduction Potentials of Compounds
[0407] The oxidation/reduction potentials of following Compounds T1
to T4 and D4 were determined by cyclic voltammetry.
##STR00078##
[0408] A series of sample solutions to be measured was prepared by
dissolving tetrabutylammonium perchlorate in each analysis solvent
in Table 1 to yield 0.1 mol/L solutions and further dissolving one
of the compounds in the solutions to a concentration of 1 mmol/L.
The measurement was conducted at a sweep rate of 100 mV/s using
glassy carbon (supplied from BAS Inc.) as a working electrode, a
platinum wire as a counter electrode, and a silver wire as a
reference electrode. The oxidation/reduction potentials were
determined by using ferrocene/ferrocenium (Fc/Fc.sup.+) as an
internal standard and converting the measured potentials of samples
into potentials versus a saturated calomel electrode (SCE),
provided that the internal standard has a potential of +0.41 V vs.
SCE. The determined first oxidation potentials and first reduction
potentials of the compounds are shown in Table 1.
TABLE-US-00001 TABLE 1 Oxidation Potential Reduction Potential
Compound [V vs. SCE] [V vs. SCE] Analysis Solvent T1 +1.34 -2.10
1:1 by volume (25.degree. C.) mixture of acetonitrile and
tetrahydrofuran T2 +1.76 -2.03 Oxidation potential: methylene
chloride Reduction potential: acetonitrile T3 +0.99 -2.10 1:1 by
volume (25.degree. C.) mixture of acetonitrile and tetrahydrofuran
T4 +1.29 -2.05 N,N-dimethylformamide D1 +0.72 -2.30 1:1 by volume
(25.degree. C.) mixture of acetonitrile and tetrahydrofuran
Example 1
Device Preparation 1
[0409] An indium-tin oxide (ITO) transparent electroconductive film
deposited to a thickness of 150 nm on a glass substrate (supplied
from Sanyo Vacuum Industries Co., Ltd., sputtered film) was
patterned in a 2-mm width stripe pattern using a common
photolithography technique and etching with hydrochloric acid-iron
chloride solution thereby forming an anode. The patterned ITO
substrate was rinsed by sequentially carrying out ultrasonic
cleaning in an aqueous surfactant solution and rinsing with pure
water, followed by drying in dried nitrogen gas, and UV/ozone
cleaning. In addition, a composition for an organic
electroluminescent device was prepared by mixing 90 mg of the
compound (T1), 90 mg of the compound (T2), and 9 mg of the compound
(D1), each represented by the structural formula, and 2.8 g of
chlorobenzene as a solvent, and removing insoluble matter by
filtration through a PTFE membrane filter having a pore size of 0.2
.mu.m. The composition was applied to the ITO substrate by spin
coating under the following conditions to thereby form a uniform
thin film having a thickness of 160 nm.
[0410] Revolution number of spinner: 1500 rpm
[0411] Revolution time of spinner: 30 seconds
[0412] Spinning atmosphere: in the atmosphere at a temperature of
23.degree. C. and relative humidity of 30%
[0413] Drying condition: drying by heating in an oven at
140.degree. C. for 15 minutes
[0414] When Compound D1 has a first reduction potential of
E.sub.D1.sup.- [V vs. SCE] and a first oxidation potential of
E.sub.D1.sup.+ [V vs. SCE], and
[0415] Compound T1 has a first reduction potential of
E.sub.T1.sup.- [V vs. SCE] and a first oxidation potential of
E.sub.T1.sup.+ [V vs. SCE], the first oxidation potentials and
first reduction potentials in this composition satisfy the
following condition:
E.sub.D1.sup.-(-2.30)+0.1<E.sub.T1.sup.-(-2.03)<E.sub.D1.sup.+(+0.-
72)<E.sub.T1.sup.+(+1.34)-0.1
[0416] Next, a 2-mm width striped shadow mask as a mask for the
vacuum deposition of a cathode was brought into intimate contact
with the substrate bearing the coated film perpendicular to the ITO
stripe of the anode, and the device was then placed in a vacuum
deposition apparatus. After roughly evacuating the apparatus using
an oil rotary pump, the apparatus was evacuated to a vacuum degree
of 3.times.10.sup.-4 Pa or less. As a cathode, an alloy electrode
of magnesium and silver was deposited in vacuo to a thickness of
110 nm through co-evaporation, in which magnesium and silver were
placed in different molybdenum boats and heated simultaneously. The
vacuum deposition of magnesium was conducted at a deposition rate
of 0.4 to 0.5 nm per second and a degree of vacuum of
5.times.10.sup.-4 Pa, and the atomic ratio of magnesium to silver
was set at 10:1.4. The temperature of the substrate upon vacuum
deposition of the cathode was kept to room temperature.
[0417] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared.
[0418] The light emitting properties of the device are shown in
Table 2.
[0419] This device emitted green light with a luminance of 30
cd/m.sup.2 upon application of a voltage of 55 V at a flowing
current density of 120 mA/cm.sup.2 and a luminous efficiency of 0.1
lm/W. The electro-emission spectrum of the device is shown in FIG.
8. The dimensions of the emission spectrum demonstrate that the
light is emitted from Compound D1.
Example 2
Device Preparation 2
[0420] A composition for an organic electroluminescent device was
prepared by mixing 90 mg of the compound (T3), 90 mg of the
compound (T4), and 9 mg of the compound (D1), each represented by
the structural formula, and 2.8 g of o-dichlorobenzene as a
solvent, and removing insoluble matter by filtration through a PTFE
membrane filter having a pore size of 0.2 .mu.m. In addition, an
ITO substrate was patterned and rinsed in the same manner as with
Example 1. The composition was applied to the resulting ITO
substrate by spin coating under the following conditions to thereby
form a uniform thin film having a thickness of 160 nm.
[0421] Revolution number of spinner: 1500 rpm
[0422] Revolution time of spinner: 30 seconds
[0423] Spinning atmosphere: spinning was conducted in the
atmosphere at a temperature of 23.degree. C. and relative humidity
of 30%
[0424] Drying condition: drying by heating on a hot plate at
80.degree. C. for 1 minutes and further drying by heating in an
oven at 140.degree. C. for 15 minutes
[0425] When Compound D1 has a first reduction potential of
E.sub.D1.sup.- [V vs. SCE] and a first oxidation potential of
E.sub.D1.sup.+ [V vs. SCE], and
[0426] Compound T3 has a first reduction potential of
E.sub.T3.sup.- [V vs. SCE] and a first oxidation potential of
E.sub.T3.sup.+ [V vs. SCE], the first oxidation potentials and
first reduction potentials in this composition satisfy the
following condition:
E.sub.D1.sup.-(-2.30)+0.1<E.sub.T3.sup.-(-2.05)<E.sub.D1.sup.+(+0.-
72)<E.sub.T3.sup.+(+0.99)-0.1
[0427] Next, the substrate bearing the coated film was placed in a
vacuum deposition apparatus, and the apparatus was evacuated in the
same manner as with Example 1. A film of sodium was applied by
vapor deposition to a thickness of 0.5 nm. The vapor deposition of
sodium was conducted by heating a sodium dispenser (supplied from
SAES Getters) containing sodium chromate. The vapor deposition was
conducted at an average deposition rate of 0.01 nm per second and a
degree of vacuum of 8.times.10.sup.-5 Pa. Subsequently, aluminum
was deposited using a molybdenum boat at a deposition rate of 0.4
to 0.6 nm per second and a degree of vacuum of 5.times.10.sup.-4 Pa
to yield an aluminum film 80 nm thick. The temperature of the
substrate upon vapor deposition of sodium and aluminum was kept to
room temperature.
[0428] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared.
[0429] The light emitting properties of this device, namely, the
emission luminance (in unit of cd/m.sup.2) at a flowing current
density of 250 mA/cm.sup.2, the luminous efficiency (in unit of
lm/W) at an emission luminance of 100 cd/m.sup.2, and the drive
voltage (in unit of V) are shown in Table 2.
[0430] The results in Table 2 demonstrate that a device that emits
light with a high luminance was obtained by using a multilayer
electrode of sodium and aluminum as the cathode.
Example 3
Device Preparation 3
[0431] Initially, an ITO substrate was patterned and rinsed in the
same manner as with Example 2 and was immersed in a solution for
five minutes. The solution was a 5 mM solution of the compound
(ST1) represented by the following structural formula in
dichloromethane. The substrate was then taken out from the
solution, rinsed with dichloromethane for one minute, and was dried
using a nitrogen blow. Thus, surface treatment of the ITO anode was
conducted.
##STR00079##
[0432] A composition for an organic electroluminescent device was
prepared by mixing 60 mg of the compound (T3), 10 mg of the
compound (T4), 4 mg of the compound (D1), and 2 g of
o-dichlorobenzene as a solvent, and removing insoluble matter by
filtration through a PTFE membrane filter having a pore size of 0.2
.mu.m. The composition was applied to the surface treated ITO
substrate by spin coating under the condition as with Example 2 to
form a uniform thin film having a thickness of 160 nm.
[0433] Next, sodium was deposited on the substrate bearing the
coated film to form a film 0.5 nm thick, and aluminum was deposited
thereon to form a film 80 nm thick in the same manner as with
Example 2.
[0434] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared.
[0435] The light emitting properties of this device, namely, the
emission luminance (in unit of cd/m.sup.2) at a flowing current
density of 250 mA/cm.sup.2, the luminous efficiency (in unit of
lm/W) at an emission luminance of 100 cd/m.sup.2, and the drive
voltage (in unit of V), are shown in Table 2.
[0436] The results in Table 2 demonstrate that a device that emits
light with a further higher luminance was obtained by subjecting
the ITO anode to surface treatment.
TABLE-US-00002 TABLE 2 Measuring Condition Flowing Current Density
Luminance 250[mA/cm.sup.2] 100 [cd/m.sup.2] Measured Data Luminance
[cd/m.sup.2] Luminous Efficiency [lm/W] Drive Voltage [V] Example 1
.sup. 30.sup.1) .sup. 0.1.sup.2) 55.sup.3) Example 2 2050 0.2 12.3
Example 3 3040 0.4 9.2 .sup.1)The luminance of the device prepared
according to Example 1 was measured at a flowing current density of
120 mA/cm.sup.2. .sup.2)The luminous efficiency of the device
prepared according to Example 1 was measured at a luminance of 30
cd/m.sup.2. .sup.3)The drive voltage of the device prepared
according to Example 1 was measured at a luminance of 30
cd/m.sup.2.
Example 4
Device Preparation 4
[0437] An organic electroluminescent device having the structure
shown in FIG. 6 was prepared in the following manner.
[0438] An indium-tin oxide (ITO) transparent electroconductive film
deposited to a thickness of 150 nm on a glass substrate 1
(sputtered film; sheet resistance: 15.OMEGA.) was patterned in a
2-mm width striped pattern using a common photolithography
technique and etching with hydrochloric acid, thereby forming an
anode 2. The patterned ITO substrate was rinsed by sequentially
carrying out ultrasonic cleaning in acetone, rinsing with pure
water, and rinsed by sequentially carrying out ultrasonic cleaning
in isopropyl alcohol, followed by drying in a nitrogen blow and
UV/ozone cleaning.
[0439] Next, a hole injection layer 3 was formed by wet coating in
the following manner. As materials for the hole injection layer 3,
a polymeric compound (PB-1) having a weight-average molecular
weight of 26500 and a number-average molecular weight of 12000 and
containing an aromatic amino group of the following structural
formula, and an electron-acceptor (A-2) of the following structural
formula were applied by spin coating under the following
conditions.
##STR00080##
[0440] <Conditions of Spin Coating>
[0441] Solvent: anisole
[0442] Concentrations in coating composition: 2.0 percent by weight
of PB-1, and [0443] 0.4 percent by weight of A-2
[0444] Revolution number of spinner: 2000 rpm
[0445] Revolution time of spinner: 30 seconds
[0446] Drying condition: drying at 230.degree. C. for 5.5 hours
[0447] A uniform thin film 30 nm thick was formed by the spin
coating.
[0448] Subsequently, an organic light emitting layer 4 was formed
by wet coating in the following manner. A composition for an
organic electroluminescent device was prepared by dissolving the
compounds (T5) and (D2) as materials for the light emitting layer 4
in concentrations in a solvent shown below. The composition was
applied by spin coating under the following conditions, to thereby
yield the organic light emitting layer 4.
##STR00081##
[0449] <Conditions of Spin Coating>
[0450] Solvent: xylene
[0451] Concentrations in coating composition: 2.5 percent by weight
of T5 [0452] 0.13 percent by weight of D2
[0453] Revolution number of spinner: 1500 rpm
[0454] Revolution time of spinner: 30 seconds
[0455] Drying condition: drying at 130.degree. C. under reduced
pressure for 60 minutes
[0456] A uniform thin film 45 nm thick was formed by the spin
coating.
[0457] Next, following aluminum 8-hydroxyquinoline complex (ET-1)
was deposited as an electron transport layer 8. The temperature of
the crucible of aluminum 8-hydroxyquinoline complex in this
procedure was controlled within the range of from 321.degree. C. to
311.degree. C. The vacuum deposition was conducted at a degree of
vacuum of 1.3 to 1.5.times.10.sup.-4 Pa (about 1.1 to
1.0.times.10.sup.-6 Torr) and a deposition rate of 0.08 to 0.16 nm
per second to yield a film 30 nm thick.
##STR00082##
[0458] The temperature of the substrate upon vacuum deposition of
the electron transport layer 8 was kept to room temperature.
[0459] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 1.8.times.10.sup.-6 Torr (about
2.4.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0460] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of 0.01
to 0.06 nm per second and a degree of vacuum of 2.0.times.10.sup.-6
Torr (about 2.6.times.10.sup.-4 Pa) using a molybdenum boat.
[0461] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.1 to
0.3 nm per second and a degree of vacuum of 3.0 to
6.8.times.10.sup.-6 Torr (about 4.0 to 9.0.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0462] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0463] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 515 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.310, 0.626).
Example 5
Device Preparation 5
[0464] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0465] Film-formation up to the organic light emitting layer 4 was
conducted in the same manner as with Example 4, except that the
hole injection layer 3 was dried at 230.degree. C. for three hours.
Thereafter, the following pyridine derivative (HB-1) was deposited
as a hole blocking layer 9 to a thickness of 5 nm. The vacuum
deposition was conducted at a crucible temperature of 230.degree.
C. to 238.degree. C., a deposition rate of 0.07 to 0.11 nm per
second, and a degree of vacuum of 1.9.times.10.sup.-4 Pa (about
1.4.times.10.sup.-6 Torr).
##STR00083##
[0466] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 352.degree. C. to 338.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 2.0
to 1.9.times.10.sup.-4 Pa (about 1.5 to 1.4.times.10.sup.-6 Torr)
and a deposition rate of 0.07 to 0.13 nm per second to yield a film
30 nm thick.
[0467] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0468] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 2.0.times.10.sup.-6 Torr (about
2.6.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0469] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of 0.01
to 0.06 nm per second and a degree of vacuum of 2.1.times.10.sup.-6
Torr (about 2.8.times.10.sup.-4 Pa) using a molybdenum boat.
[0470] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.2 to
0.6 nm per second and a degree of vacuum of 3.8 to
6.8.times.10.sup.-6 Torr (about 5.0 to 9.0.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0471] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0472] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 515 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.315, 0.623).
Example 6
Device Preparation 6
[0473] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0474] After conducting film-formation up to the hole injection
layer 3 in the same manner as with Example 5, an organic light
emitting layer 4 was formed by wet coating in the following manner.
A composition for an organic electroluminescent device was prepared
by dissolving the following compounds (T6) and (D2) as materials
for the light emitting layer 4 in concentrations in a solvent
mentioned below. The composition was applied by spin coating under
the following conditions, to thereby yield the organic light
emitting layer 4.
##STR00084##
[0475] <Conditions of Spin Coating>
[0476] Solvent: xylene
[0477] Concentrations in coating composition: 3.0 percent by weight
of T6 [0478] 0.15 percent by weight of D2
[0479] Revolution number of spinner: 1000 rpm
[0480] Revolution time of spinner: 30 seconds
[0481] Drying condition: drying at 80.degree. C. under reduced
pressure for 60 minutes
[0482] A uniform thin film 60 nm thick was formed by the spin
coating.
[0483] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5.1 nm. The vacuum deposition
was conducted at a crucible temperature of 284.degree. C. to
289.degree. C., a deposition rate of 0.09 to 0.13 nm per second,
and a degree of vacuum of 2.8.times.10.sup.-4 Pa (about
2.1.times.10.sup.-6 Torr).
[0484] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 in the same manner. The
temperature of the crucible for the aluminum 8-hydroxyquinoline
complex in this procedure was controlled within the range of from
349.degree. C. to 340.degree. C. The vacuum deposition was
conducted at a degree of vacuum of 2.9 to 4.3.times.10.sup.-4 Pa
(about 2.2 to 3.2.times.10.sup.-6 Torr) and a deposition rate of
0.08 to 0.12 nm per second to yield a film 30 nm thick.
[0485] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0486] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 2.3.times.10.sup.-6 Torr (about
3.1.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0487] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.005 to 0.04 nm per second and a degree of vacuum of
2.6.times.10.sup.-6 Torr (about 3.42 to 3.47.times.10.sup.-4 Pa)
using a molybdenum boat.
[0488] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.04 to
0.4 nm per second and a degree of vacuum of 3.5 to
7.8.times.10.sup.-6 Torr (about 4.6 to 10.4.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0489] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0490] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 514 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.324, 0.615).
Example 7
Device Preparation 7
[0491] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0492] After conducting film-formation up to the hole injection
layer 3 in the same manner as with Example 5, an organic light
emitting layer 4 was formed by wet coating in the following manner.
A composition for an organic electroluminescent device was prepared
by dissolving the following compounds (T6) and (D3) as materials
for a light emitting layer 4 in concentrations in a solvent
mentioned below. The composition was applied by spin coating under
the following conditions, to thereby yield the organic light
emitting layer 4.
##STR00085##
[0493] <Conditions of Spin Coating>
[0494] Solvent: xylene
[0495] Concentrations in coating composition: 2.0 percent by weight
of T6 [0496] 0.1 percent by weight of D3
[0497] Revolution number of spinner: 1500 rpm
[0498] Revolution time of spinner: 30 seconds
[0499] Drying condition: drying at 130.degree. C. under reduced
pressure for 60 minutes
[0500] A uniform thin film 60 nm thick was formed by the spin
coating.
[0501] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5 nm. The vacuum deposition was
conducted at a crucible temperature of 277.degree. C. to
280.degree. C., a deposition rate of 0.11 to 0.13 nm per second,
and a degree of vacuum of 2.9 to 3.2.times.10.sup.-4 Pa (about 2.2
to 2.4.times.10.sup.-6 Torr).
[0502] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 in the same manner. The
temperature of the crucible for the aluminum 8-hydroxyquinoline
complex in this procedure was controlled within the range of from
372.degree. C. to 362.degree. C. The vacuum deposition was
conducted at a degree of vacuum of 3.7 to 4.3.times.10.sup.-4 Pa
(about 2.8 to 3.2.times.10.sup.-6 Torr) and a deposition rate of
0.1 nm per second to yield a film 30 nm thick.
[0503] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0504] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 1.5.times.10.sup.-6 Torr (about
3.1.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0505] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of 0.01
to 0.03 nm per second and a degree of vacuum of 2.3 to
2.5.times.10.sup.-6 Torr (about 3.1 to 3.3.times.10.sup.-4 Pa)
using a molybdenum boat.
[0506] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.3 to
0.5 nm per second and a degree of vacuum of 2.9 to
6.6.times.10.sup.-6 Torr (about 3.8 to 8.8.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0507] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0508] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 513 nm,
which was identified as being from the iridium complex (D3). The
chromaticity in terms of CIE (x, y) was (0.303, 0.625).
Example 8
Device Preparation 8
[0509] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0510] After conducting film-formation up to the hole injection
layer 3 in the same manner as with Example 5, an organic light
emitting layer 4 was formed by wet coating in the following manner.
A composition for an organic electroluminescent device was prepared
by dissolving the following compounds (T7) and (D2) as materials
for a light emitting layer 4 in concentrations in a solvent
mentioned below. The composition was applied by spin coating under
the following conditions, to thereby yield the organic light
emitting layer 4.
##STR00086##
[0511] <Conditions of Spin Coating>
[0512] Solvent: 1,4-dioxane
[0513] Concentrations in coating composition: 2.0 percent by weight
of T7 [0514] 0.1 percent by weight of D2
[0515] Revolution number of spinner: 1500 rpm
[0516] Revolution time of spinner: 30 seconds
[0517] Drying condition: drying at 130.degree. C. under reduced
pressure for 60 minutes
[0518] A uniform thin film 60 nm thick was formed by the spin
coating.
[0519] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5 nm. The vacuum deposition was
conducted at a crucible temperature of 237.degree. C. to
238.degree. C., a deposition rate of 0.1 nm per second, and a
degree of vacuum of 9.3 to 9.2.times.10.sup.-5 Pa (about 7.0 to
6.9.times.10.sup.-6 Torr).
[0520] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 in the same manner. The
temperature of the crucible for the aluminum 8-hydroxyquinoline
complex in this procedure was controlled within the range of from
294.degree. C. to 288.degree. C. The vacuum deposition was
conducted at a degree of vacuum of 9.1 to 8.5.times.10.sup.-5 Pa
(about 6.8 to 6.4.times.10.sup.-6 Torr) and a deposition rate of
0.11 to 0.12 nm per second to yield a film 30 nm thick.
[0521] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0522] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 2.0.times.10.sup.-6 Torr (about
2.6.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0523] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of 0.02
nm per second and a degree of vacuum of 2.0.times.10.sup.-6 Torr
(about 2.6.times.10.sup.-4 Pa) using a molybdenum boat.
[0524] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.2 nm
per second and a degree of vacuum of 3.2.times.10.sup.-6 Torr
(about 4.2.times.10.sup.-4 Pa) to yield an aluminum layer 80 nm
thick. A cathode 6 was thus completed.
[0525] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0526] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 519 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.365, 0.591).
Example 9
Device Preparation 9
[0527] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0528] After conducting film-formation up to the hole injection
layer 3 in the same manner as with Example 5, an organic light
emitting layer 4 was formed by wet coating in the following manner.
A composition for an organic electroluminescent device was prepared
by dissolving the following compounds (T8) and (D2) as materials
for a light emitting layer 4 in concentrations in a solvent
mentioned below. The composition was applied by spin coating under
the following conditions, to thereby yield the organic light
emitting layer 4.
##STR00087##
[0529] <Conditions of Spin Coating>
[0530] Solvent: xylene
[0531] Concentrations in coating composition: 2.0 percent by weight
of T8 [0532] 0.1 percent by weight of D2
[0533] Revolution number of spinner: 1500 rpm
[0534] Revolution time of spinner: 30 seconds
[0535] Drying condition: drying at 130.degree. C. under reduced
pressure for 60 minutes
[0536] A uniform thin film 60 nm thick was formed by the spin
coating.
[0537] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5.1 nm. The vacuum deposition
was conducted at a crucible temperature of 273.degree. C., a
deposition rate of 0.1 nm per second, and a degree of vacuum of
3.3.times.10.sup.-4 Pa (about 2.5.times.10.sup.-6 Torr).
[0538] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 in the same manner. The
temperature of the crucible for the aluminum 8-hydroxyquinoline
complex in this procedure was controlled within the range of from
376.degree. C. to 371.degree. C. The vacuum deposition was
conducted at a degree of vacuum of 3.1.times.10.sup.-4 Pa (about
2.3.times.10.sup.-6 Torr) and a deposition rate of 0.11 to 0.12 nm
per second to yield a film 30 nm thick.
[0539] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0540] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 2.5.times.10.sup.-6 Torr (about
3.3.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0541] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.006 nm per second and a degree of vacuum of 2.6.times.10.sup.-6
Torr (about 3.5.times.10.sup.-4 Pa).
[0542] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.1 to
0.35 nm per second and a degree of vacuum of 3.4 to
4.5.times.10.sup.-6 Torr (about 4.5 to 6.0.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0543] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0544] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 513 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.311, 0.622).
Example 10
Device Preparation 10
[0545] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0546] An anode 2 was formed on a glass substrate 1, and rinsing
was conducted in the same manner as with Example 4. Thereafter, a
hole injection layer 3 was formed by wet coating in the following
manner. As materials for the hole injection layer 3, a polymeric
compound (PB-3) having a weight-average molecular weight of 29400
and a number-average molecular weight of 12600 and containing an
aromatic amino group of the following structural formula, and an
electron-acceptor (A-2) of the following structural formula were
applied by spin coating under the following conditions.
##STR00088##
[0547] <Conditions of Spin Coating>
[0548] Solvent: ethyl benzoate
[0549] Concentrations in coating composition: 2.0 percent by weight
of PB-3 [0550] 0.8 percent by weight of A-2
[0551] Revolution number of spinner: 1500 rpm
[0552] Revolution time of spinner: 30 seconds
[0553] Drying condition: drying at 230.degree. C. for 3 hours
[0554] A uniform thin film 30 nm thick was formed by the spin
coating.
[0555] Subsequently, an organic light emitting layer 4 was formed
by wet coating in the following manner. A composition for an
organic electroluminescent device was prepared by dissolving the
following compounds (T6), (T9) and (D2) in concentrations in a
solvent mentioned below. The composition was applied by spin
coating under the following conditions, to thereby yield the
organic light emitting layer 4.
[0556] The term "Ink Storage" in the following conditions for spin
coating refers to the condition and time period of storage of the
composition for an organic electroluminescent device between its
preparation and use in spin coating.
##STR00089##
[0557] <Conditions of Spin Coating>
[0558] Ink storage: storage at 4.degree. C. in a dark place for 18
days
[0559] Solvent: toluene
[0560] Concentrations in coating composition: 1.0 percent by weight
of T6 [0561] 1.0 percent by weight of T9 [0562] 0.1 percent by
weight of D2
[0563] Revolution number of spinner: 1500 rpm
[0564] Revolution time of spinner: 30 seconds
[0565] Drying condition: drying at 80.degree. C. under reduced
pressure for 60 minutes
[0566] A uniform thin film 60 nm thick was formed by the spin
coating.
[0567] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5.1 nm. The vacuum deposition
was conducted at a crucible temperature of 307.degree. C. to
312.degree. C., a deposition rate of 0.07 to 0.13 nm per second,
and a degree of vacuum of 2.7.times.10.sup.-4 Pa (about
2.0.times.10.sup.-6 Torr).
[0568] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 469.degree. C. to 444.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 6.0
to 3.3.times.10.sup.-4 Pa (about 4.5 to 2.5.times.10.sup.-6 Torr)
and a deposition rate of 0.07 to 0.13 nm per second to yield a film
30 nm thick.
[0569] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0570] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 1.5.times.10.sup.-6 Torr (about
3.0.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0571] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.007 to 0.01 nm per second and a degree of vacuum of 2.2 to
2.3.times.10.sup.-6 Torr (about 2.9 to 3.0.times.10.sup.-4 Pa).
[0572] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.08 to
0.35 nm per second and a degree of vacuum of 3.8 to
6.5.times.10.sup.-6 Torr (about 5.1 to 8.7.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0573] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0574] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 512 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.309, 0.619).
Example 11
Device Preparation 11
[0575] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the same manner as with Example 10,
except for carrying out the ink storage in "Conditions of spin
coating" at a temperature of 20.degree. C. in the formation of the
organic light emitting layer 4.
[0576] The maximal wavelength in emission spectrum of the device
was 513 nm, which was identified as being from the iridium complex
(D2). The chromaticity in terms of CIE (x, y) was (0.314,
0.617).
Example 12
Device Preparation 12
[0577] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0578] Film-formation up to the organic light emitting layer 4 was
conducted in the same manner as with Example 10, except for
carrying out the ink storage for a time period of 7 days before
spin coating in the formation of the light emitting layer 4.
Thereafter, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5 nm. The vacuum deposition was
conducted at a crucible temperature of 327.degree. C. to
332.degree. C., a deposition rate of 0.08 nm per second, and a
degree of vacuum of 1.7.times.10.sup.-4 Pa (about
1.3.times.10.sup.-6 Torr).
[0579] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 440.degree. C. to 425.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 1.7
to 1.6.times.10.sup.-4 Pa (about 1.3 to 1.2.times.10.sup.-6 Torr)
and a deposition rate of 0.1 to 0.14 nm per second to yield a film
30 nm thick.
[0580] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0581] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 1.5.times.10.sup.-6 Torr (about
1.96.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0582] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.008 to 0.013 nm per second and a degree of vacuum of 1.5 to
1.6.times.10.sup.-6 Torr (about 2.0 to 2.1.times.10.sup.-4 Pa)
using a molybdenum boat.
[0583] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.05 to
0.42 nm per second and a degree of vacuum of 2.5 to
7.0.times.10.sup.-6 Torr (about 3.3 to 9.3.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0584] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0585] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 513 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.315, 0.617).
Example 13
Device Preparation 13
[0586] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the same manner as with Example 12,
except for carrying out the ink storage at a temperature of
20.degree. C. before spin coating in the formation of the organic
light emitting layer 4.
[0587] The maximal wavelength in emission spectrum of the device
was 513 nm, which was identified as being from the iridium complex
(D2). The chromaticity in terms of CIE (x, y) was (0.314,
0.617).
Example 14
Device Preparation 14
[0588] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0589] Film-formation up to the organic light emitting layer 4 was
conducted in the same manner as with Example 10, except for using
the ink (composition) in spin coating immediately after its
preparation without storage in the formation of the light emitting
layer 4. Thereafter, the pyridine derivative (HB-1) was deposited
as a hole blocking layer 9 to a thickness of 5.1 nm. The vacuum
deposition was conducted at a crucible temperature of 315.degree.
C. to 319.degree. C., a deposition rate of 0.07 to 0.094 nm per
second, and a degree of vacuum of 3.1 to 2.7.times.10.sup.-4 Pa
(about 2.3 to 2.0.times.10.sup.-6 Torr).
[0590] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 481.degree. C. to 391.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 2.7
to 3.6.times.10.sup.-4 Pa (about 2.0 to 2.7.times.10.sup.-6 Torr)
and a deposition rate of 0.11 to 0.18 nm per second to yield a film
30 nm thick.
[0591] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0592] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 3.1.times.10.sup.-6 Torr (about
4.1.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0593] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.007 to 0.012 nm per second and a degree of vacuum of 3.2 to
3.3.times.10.sup.-6 Torr (about 4.3 to 4.4.times.10.sup.-4 Pa)
using a molybdenum boat. Next, aluminum was heated in the same
manner using a molybdenum boat and was deposited at a deposition
rate of 0.05 to 0.47 nm per second and a degree of vacuum of 4.0 to
7.4.times.10.sup.-6 Torr (about 5.3 to 9.8.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0594] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0595] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 512 nm,
which was identified as being from the iridium complex (D2). The
chromaticity in terms of CIE (x, y) was (0.303, 0.622).
Example 15
Device Preparation 15
[0596] An organic electroluminescent device having the structure
shown in FIG. 7 was prepared in the following manner.
[0597] Film-formation up to the hole injection layer 3 was
conducted in the same manner as with Example 10, except that the
concentration of the compound (A-2) was 0.4 percent by weight and
drying was carried out at 230.degree. C. for 15 minutes in the spin
coating in the formation of the hole injection layer 3. Thereafter,
an organic light emitting layer 4 was formed by wet coating in the
following manner. A composition for an organic electroluminescent
device was prepared by dissolving the following compounds (T6),
(T12) and (D4) as materials for the light emitting layer 4 in
concentrations in a solvent mentioned below. The composition was
applied by spin coating under the following conditions, to thereby
yield the organic light emitting layer 4.
##STR00090##
[0598] <Conditions of Spin Coating>
[0599] Solvent: toluene
[0600] Concentrations in coating composition: 1.0 percent by weight
of T6 [0601] 1.0 percent by weight of T12 [0602] 0.1 percent by
weight of D4
[0603] Revolution number of spinner: 1500 rpm
[0604] Revolution time of spinner: 30 seconds
[0605] Drying condition: drying at 80.degree. C. under reduced
pressure for 60 minutes
[0606] A uniform thin film 60 nm thick was formed by the spin
coating.
[0607] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5 nm. The vacuum deposition was
conducted at a crucible temperature of 238.degree. C. to
249.degree. C., a deposition rate of 0.014 to 0.024 nm per second,
and a degree of vacuum of 3.5 to 3.7.times.10.sup.-4 Pa (about 2.6
to 2.8.times.10.sup.-6 Torr).
[0608] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 240.degree. C. to 247.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 3.7
to 3.3.times.10.sup.-4 Pa (about 2.8 to 2.5.times.10.sup.-6 Torr)
and a deposition rate of 0.1 to 0.11 nm per second to yield a film
30 nm thick.
[0609] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0610] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 2.1.times.10.sup.-6 Torr (about
2.2.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0611] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of
0.006 to 0.008 nm per second and a degree of vacuum of 2.3 to
2.4.times.10.sup.-6 Torr (about 3.1 to 3.2.times.10.sup.-4 Pa)
using a molybdenum boat.
[0612] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.25 to
0.41 nm per second and a degree of vacuum of 2.5 to
7.4.times.10.sup.-6 Torr (about 3.3 to 9.8.times.10.sup.-4 Pa) to
yield an aluminum layer 80 nm thick. A cathode 6 was thus
completed.
[0613] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0614] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. A peak
of 474 nm was observed in emission spectrum of the device, which
was identified as being from the iridium complex (D4).
Comparative Example 1
[0615] An organic electroluminescent device having the structure
shown in FIG. 6 was prepared in the following manner.
[0616] Film-formation up to the hole injection layer 3 was
conducted in the same manner as with Example 10, except that the
concentration of the compound (A-2) was 0.4 percent by weight in
spin coating in the formation of the hole injection layer 3.
Thereafter, an organic light emitting layer 4 was formed by wet
coating in the following manner. As materials for the light
emitting layer 4, the following compounds (T10), (T11) and (D3)
were dissolved in concentrations in a solvent mentioned below to
yield a composition for an organic electroluminescent device. The
composition was applied by spin coating under the following
conditions, to thereby yield the organic light emitting layer
4.
##STR00091##
[0617] <Conditions of Spin Coating>
[0618] Solvent: chloroform
[0619] Concentrations in coating composition: 1.0 percent by weight
of T10 [0620] 1.0 percent by weight of T11 [0621] 0.1 percent by
weight of D3
[0622] Revolution number of spinner: 1500 rpm
[0623] Revolution time of spinner: 30 seconds
[0624] Drying condition: drying at 80.degree. C. under reduced
pressure for 60 minutes
[0625] A uniform thin film 100 nm thick was formed by the spin
coating.
[0626] Next, the following compound (ET-2) was deposited as an
electron transport layer 8. The vacuum deposition herein was
conducted at a degree of vacuum of 1.79 to 1.71.times.10.sup.-4 Pa
(about 1.3.times.10.sup.-6 Torr) and a deposition rate of 0.09 to
0.1 nm per second, to thereby yield a film 20 nm thick.
##STR00092##
[0627] Next, as an electron injection layer 5, lithium fluoride
(LiF) was deposited to a thickness of 0.5 nm on the electron
transport layer 8. The vacuum deposition was conducted at a
deposition rate of 0.009 to 0.013 nm per second and a degree of
vacuum of 1.3.times.10.sup.-6 Torr (about 1.76.times.10.sup.-4 Pa)
using a molybdenum boat.
[0628] Next, aluminum was heated in the same manner using a
molybdenum boat and was deposited at a deposition rate of 0.06 to
0.19 nm per second and a degree of vacuum of 2.1.times.10.sup.-6
Torr (about 3.15 to 10.0.times.10.sup.-4 Pa) to yield an aluminum
layer 80 nm thick. A cathode 6 was thus completed.
[0629] The temperature of the substrate upon vapor deposition of
these layers was kept to room temperature.
[0630] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 514 nm,
which was identified as being from the iridium complex (D3). The
chromaticity in terms of CIE (x, y) was (0.308, 0.621).
[0631] The oxidation/reduction potentials of host materials and
dopant materials used in the formation of the organic light
emitting layer 4 in Examples 4 to 15 and Comparative Example 1 are
shown in Table 3.
[0632] The normalized luminance half-lives and initial luminance
when driven at a constant current, and the current efficiencies and
drive voltages upon light emission at a luminance of 100 cd/m.sup.2
are shown in Table 4.
TABLE-US-00003 TABLE 3 Oxidation Potential Reduction Potential (V
vs. SCE) (V vs. SCE) T5 1.20 -2.02 T6 1.30 -2.09 T7 1.24 -1.95 T8
1.34 -1.99 T9 0.89 -2.56 T10 1.27 -2.40 T11 0.78 -2.41 T12 0.94
-2.48 D2 0.64 -2.44 D3 0.65 -2.48 D4 1.29 -1.88
TABLE-US-00004 TABLE 4 Life Initial Current Drive Normalized
Converted Lumi- Effi- Volt- Host Dopant Luminance at 1000 nance
ciency age Material Material Half-life cd/m2 * (cd/m2) (cd/A) (V)
T5 D2 2.70 9.7 2500 22.4 6.0 T5 D2 5.41 19.5 2500 26.4 6.3 T6 D2
10.81 38.9 2500 -- -- T6 D3 20.27 16.4 857 16.7 7.2 T7 D2 21.62 8.4
508 -- -- T8 D2 10.81 10.8 1000 11.0 9.1 T6/T9 D2 3.78 3.8 1000
19.3 8.6 T6/T9 D2 3.78 3.8 1000 19.7 9.0 T6/T9 D2 4.05 4.1 1000
15.1 8.3 T6/T9 D2 4.05 4.1 1000 15.7 8.8 T6/T9 D2 1.62 1.6 1000
21.9 7.2 T10/T11 D3 1.00 1.0 1000 9.1 7.2 * Data with initial
luminance other than 1000 cd/m.sup.2 are converted with an
accelerating factor of the 1.4th power of the luminance. This is
defined as the "Life converted at 1000 cd/m.sup.2"
[0633] Of the data in Table 4, Table 5 shows the current
efficiencies and drive voltages of devices, and the normalized
luminance half-lives and initial luminance of the devices when
compositions for organic electroluminescent devices were stored at
4.degree. C. or 20.degree. C. in the atmosphere (air) in a dark
place.
TABLE-US-00005 TABLE 5 Normal- Storage Condition Current Drive ized
Initial Temper- Effi- Volt- Lumi- Lumi- ature Time ciency age nance
nance (.degree. C.) (day) (cd/A) (V) Half-life (cd/m.sup.2)
Example10 4 18 19.3 8.6 2.5 1000 Example11 20 18 19.7 9.0 2.5 1000
Example12 4 7 15.1 8.3 2.33 1000 Example13 20 7 15.7 8.8 2.33 1000
Example14 -- 0 21.9 7.2 1 1000
[0634] These results demonstrate that compositions for organic
electroluminescent devices according to the present invention have
long pot lives, and devices prepared using the compositions have
high luminous efficiencies and long lives.
Referential Example 1
[0635] An organic electroluminescent device was prepared in the
following manner, in which a light emitting layer was formed by
vapor deposition. The resulting organic electroluminescent device
has a layer structure as with the organic electroluminescent device
shown in FIG. 7, except for having a hole transport layer instead
of the hole injection layer 3.
[0636] An indium-tin oxide (ITO) transparent electroconductive film
deposited to a thickness of 150 nm on a glass substrate 1
(sputtered film; sheet resistance: 15.OMEGA.) was patterned in a
2-mm width striped pattern using a common photolithography
technique and etching with hydrochloric acid, thereby forming an
anode 2. The patterned ITO substrate was rinsed by sequentially
carrying out ultrasonic cleaning in acetone, rinsing with pure
water, and ultrasonic cleaning in isopropyl alcohol, followed by
drying in a nitrogen blow and UV/ozone cleaning.
[0637] Next, a hole injection layer 3 was formed by wet coating in
the following manner. As materials for the hole injection layer 3,
a polymeric compound (PB-2) having a weight-average molecular
weight of 29400 and a number-average molecular weight of 12600 and
containing an aromatic amino group of the following structural
formula, and an electron-acceptor (A-2) of the following structural
formula were applied by spin coating under the following
conditions.
##STR00093##
[0638] <Conditions of Spin Coating>
[0639] Solvent: ethyl benzoate
[0640] Concentrations in coating composition: 2.0 percent by weight
of PB-2 [0641] 0.4 percent by weight of A-2
[0642] Revolution number of spinner: 1500 rpm
[0643] Revolution time of spinner: 30 seconds
[0644] Drying condition: drying at 230.degree. C. for 15
minutes
[0645] A uniform thin film 30 nm thick was formed by the spin
coating.
[0646] Subsequently, the following amine derivative (T11) was
deposited as a hole transport layer at a crucible temperature of
254.degree. C. to 274.degree. C. and a deposition rate of 0.09 to
0.13 nm per second to a thickness of 40 nm. The vacuum deposition
was conducted at a degree of vacuum of 5.2 to 5.3.times.10.sup.-5
Pa (about 3.9 to 4.0.times.10.sup.-7 Torr).
##STR00094##
[0647] Next, the following compound (T10) together with an iridium
complex (D5) of the following structural formula was deposited as
an organic light emitting layer 4 by vacuum deposition. The vacuum
deposition was carried out at a crucible temperature of 288.degree.
C. to 293.degree. C. and a deposition rate of 0.08 to 0.09 nm per
second for the compound (T10), and at a crucible temperature of
247.degree. C. to 248.degree. C. and a deposition rate of 0.005 nm
per second for the compound (D5), to thereby yield a film 30 nm
thick. The vacuum deposition was conducted at a degree of vacuum of
5.4 to 5.5.times.10.sup.-5 Pa (about 4.1.times.10.sup.-7 Torr). The
compound (D5) has an oxidation potential of +0.71 V and a reduction
potential of -2.3 V.
##STR00095##
[0648] Next, the pyridine derivative (HB-1) was deposited as a hole
blocking layer 9 to a thickness of 5 nm. The vacuum deposition was
conducted at a crucible temperature of 230.degree. C. to
233.degree. C., a deposition rate of 0.09 to 0.11 nm per second,
and a degree of vacuum of 5.3 to 5.1.times.10.sup.-5 Pa (about 4.0
to 3.8.times.10.sup.-7 Torr).
[0649] Next, the aluminum 8-hydroxyquinoline complex (ET-1) was
deposited as an electron transport layer 8 on the hole blocking
layer 9 in the same manner. The temperature of the crucible for the
aluminum 8-hydroxyquinoline complex in this procedure was
controlled within the range of from 263.degree. C. to 259.degree.
C. The vacuum deposition was conducted at a degree of vacuum of 5.3
to 5.2.times.10.sup.-5 Pa (about 4.0 to 3.9.times.10.sup.-6 Torr)
and a deposition rate of 0.1 to 0.13 nm per second to yield a film
30 nm thick.
[0650] The temperature of the substrate upon vacuum deposition of
the hole blocking layer 9 and the electron transport layer 8 was
kept to room temperature.
[0651] The device which had been subjected to vacuum deposition up
to the electron transport layer 8 was once taken out of the vacuum
deposition apparatus into the atmosphere. A 2-mm width striped
shadow mask as a mask for vacuum deposition of a cathode was
brought into intimate contact with the device perpendicularly to
the ITO stripe of the anode 2, and the device was placed in another
vacuum deposition apparatus. The apparatus was evacuated to a
degree of vacuum of 1.4.times.10.sup.-6 Torr (about
1.9.times.10.sup.-4 Pa) or less in the same manner as with the
organic layers.
[0652] As an electron injection layer 5, lithium fluoride (LiF) was
deposited to a thickness of 0.5 nm on the electron transport layer
8. The vacuum deposition was conducted at a deposition rate of 0.6
nm per second and a degree of vacuum of 2.2.times.10.sup.-6 Torr
(about 2.9.times.10.sup.-4 Pa) using a molybdenum boat. Next,
aluminum was heated in the same manner using a molybdenum boat and
was deposited at a deposition rate of 0.1 to 0.5 nm per second and
a degree of vacuum of 4.8 to 10.0.times.10.sup.-6 Torr (about 6.4
to 13.3.times.10.sup.-4 Pa) to yield an aluminum layer 80 nm thick.
A cathode 6 was thus completed.
[0653] The temperature of the substrate upon vacuum deposition of
the two-layered cathode 6 was kept to room temperature.
[0654] Thus, an organic electroluminescent device having a
light-emitting area of 2 mm wide and 2 mm long was prepared. The
maximal wavelength in emission spectrum of the device was 512 nm,
which was identified as being from the iridium complex (D5). The
chromaticity in terms of CIE (x, y) was (0.294, 0.588).
Referential Example 2
[0655] An organic electroluminescent device was prepared in the
same manner as with Referential Example 1, except for forming an
organic light emitting layer 4 by vacuum deposition under the
following conditions using the following compound (T5) and an
iridium complex (D5) of the following structural formula.
[0656] The vacuum deposition was conducted at a crucible
temperature of 428.degree. C. to 425.degree. C. and a deposition
rate of 0.09 to 0.08 nm per second for the compound (T5), and at a
crucible temperature of 251.degree. C. to 254.degree. C. and a
deposition rate of 0.005 nm per second for the compound (D5), to
yield a film 30 nm thick. The vacuum deposition was conducted at a
degree of vacuum of 6.0 to 6.1.times.10.sup.-5 Pa (about 4.5 to
4.6.times.10.sup.-7 Torr).
##STR00096##
[0657] The maximal wavelength in emission spectrum of the device
was 513 nm, which was identified as being from the iridium complex
(D5). The chromaticity in terms of CIE (x, y) was (0.301,
0.597).
[0658] Table 6 shows, of the devices produced by vacuum deposition,
the current efficiencies and drive voltages at a luminance of 100
cd/m.sup.2, and the normalized luminance half-lives when driven at
a constant current provided that the initial luminance is 2500
cd/m.sup.2.
TABLE-US-00006 TABLE 6 Current Drive Normalized Initial Efficiency
Voltage Luminance Luminance (cd/A) (V) Half-life (cd/m.sup.2)
Referential Example 1 28.8 5.0 1 2500 Referential Example 2 22.4
6.1 0.64 2500
[0659] The results in Table 6 demonstrate that there is not so much
difference between effects of the devices prepared according to
vacuum deposition, regardless of whether or not the condition as
specified in the present invention is satisfied.
[0660] While the present invention has been shown and described in
detail with reference to specific embodiments thereof, it will be
understood by those skilled in the art that various changes and
modifications may be made without departing from the spirit and
scope of the present invention.
[0661] The present application is based on Japanese Patent
Application No. 2005-044250 filed on Feb. 21, 2005, the entire
contents of which being incorporated herein by reference.
* * * * *