U.S. patent application number 15/797463 was filed with the patent office on 2018-02-15 for organic compound, light-emitting element, display module, lighting module, light-emitting device, display device, lighting device, and electronic device.
This patent application is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Takao HAMADA, Hiroshi KADOMA, Yuko KAWATA, Satomi MITSUMORI, Satoshi SEO.
Application Number | 20180047911 15/797463 |
Document ID | / |
Family ID | 52131571 |
Filed Date | 2018-02-15 |
United States Patent
Application |
20180047911 |
Kind Code |
A1 |
KADOMA; Hiroshi ; et
al. |
February 15, 2018 |
Organic Compound, Light-Emitting Element, Display Module, Lighting
Module, Light-Emitting Device, Display Device, Lighting Device, and
Electronic Device
Abstract
A novel organic compound that can be used as a carrier-transport
material, a host material, or a light-emitting material in a
light-emitting element is provided. Specifically, an organic
compound that can give a light-emitting element having favorable
characteristics even when the organic compound is used in a
light-emitting element emitting phosphorescence is provided. The
organic compound has a bipyridine skeleton formed by two pyridine
skeletons to each of which a dibenzothiophenyl group or a
dibenzofuranyl group is bonded via an arylene group.
Inventors: |
KADOMA; Hiroshi;
(Sagamihara, JP) ; MITSUMORI; Satomi; (Atsugi,
JP) ; KAWATA; Yuko; (Atsugi, JP) ; HAMADA;
Takao; (Atsugi, JP) ; SEO; Satoshi;
(Sagamihara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Kanagawa-ken |
|
JP |
|
|
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd.
Kanagawa-ken
JP
|
Family ID: |
52131571 |
Appl. No.: |
15/797463 |
Filed: |
October 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14333061 |
Jul 16, 2014 |
9825235 |
|
|
15797463 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/0072 20130101;
H01L 51/5092 20130101; H01L 51/5088 20130101; H01L 51/5072
20130101; C09K 11/06 20130101; H01L 51/5056 20130101; H01L 51/0073
20130101; H01L 51/0067 20130101; H01L 51/0074 20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00; C09K 11/06 20060101 C09K011/06; H01L 51/50 20060101
H01L051/50 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2013 |
JP |
2013-150305 |
Claims
1. (canceled)
2. An organic compound represented by General Formula (G6),
##STR00075## wherein Ar.sup.1 is bonded to a pyridine skeleton at 3
position, wherein Ar.sup.2 is bonded to the pyridine skeleton at 5
position, wherein A.sup.1 and A.sup.2 separately represent any one
of a dibenzofuranyl group and a dibenzothiophenyl group, wherein
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms, wherein the pyridine skeleton comprises n
substituents, wherein the n substituents include Ar.sup.1 and
A.sup.2, and wherein n is 2 or 4.
3. The organic compound according to claim 2, wherein the organic
compound is represented by General Formula (G7), ##STR00076##
wherein Ar.sup.1 and Ar.sup.2 separately represent an arylene group
having 6 to 13 carbon atoms, and wherein Z represents any one of an
oxygen atom and a sulfur atom.
4. The organic compound according to claim 2, wherein the organic
compound is represented by Structural Formula (300),
##STR00077##
5. The organic compound according to claim 2, wherein the organic
compound is represented by Structural Formula (400),
##STR00078##
6. A light-emitting element comprising: a pair of electrodes; and a
layer comprising the organic compound according to claim 2 between
the pair of electrodes.
7. The light-emitting element according to claim 6, wherein the
layer comprises at least a light-emitting layer, and wherein the
light-emitting layer comprises the organic compound.
8. A display module comprising the light-emitting element according
to claim 6.
9. A lighting module comprising the light-emitting element
according to claim 6.
10. An electronic device comprising the light-emitting element
according to claim 6.
11. A light-emitting device comprising: the light-emitting element
according to claim 6; and a unit for controlling the light-emitting
element.
12. A display device comprising: the light-emitting element
according to claim 6 in a display portion; and a unit for
controlling the light-emitting element.
13. A lighting device comprising: the light-emitting element
according to claim 6 in a lighting portion; and a unit for
controlling the light-emitting element.
14. An organic compound represented by General Formula (G8),
##STR00079## wherein R.sup.41 is a group represented by General
Formula (A-1), wherein R.sup.43 is a group represented by General
Formula (A-2), wherein R.sup.40, R.sup.42 and R.sup.44 separately
represent any one of hydrogen, an alkyl group having 1 to 6 carbon
atoms, and an aryl group having 6 to 13 carbon atoms, ##STR00080##
wherein R.sup.10 to R.sup.16 and R.sup.20 to R.sup.26 separately
represent any one of hydrogen, an alkyl group having 1 to 6 carbon
atoms, and an aryl group having 6 to 13 carbon atoms, wherein
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms, and wherein Z represents any one of an oxygen
atom and a sulfur atom.
15. The organic compound according to claim 14, wherein the organic
compound is represented by General Formula (G10), ##STR00081##
wherein R.sup.40, R.sup.42, R.sup.44, R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately represent
any one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and
an aryl group having 6 to 13 carbon atoms, and wherein Z represents
any one of an oxygen atom and a sulfur atom.
16. A light-emitting element comprising: a pair of electrodes; and
a layer comprising the organic compound according to claim 14
between the pair of electrodes.
17. A light-emitting device comprising: the light-emitting element
according to claim 16; and a unit for controlling the
light-emitting element.
18. A display device comprising: the light-emitting element
according to claim 16 in a display portion; and a unit for
controlling the light-emitting element.
19. A lighting device comprising: the light-emitting element
according to claim 16 in a lighting portion; and a unit for
controlling the light-emitting element.
Description
[0001] This application is a continuation of copending U.S.
application Ser. No. 14/333,061, filed on Jul. 16, 2014 which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to an organic compound that
can be used as a light-emitting element material. The present
invention relates to a light-emitting element, a display module, a
lighting module, a light-emitting device, a display device, a
lighting device, and an electronic device each using the organic
compound.
2. Description of the Related Art
[0003] As next generation lighting devices or display devices,
display devices using light-emitting elements (organic EL elements)
in which organic compounds are used as light-emitting substances
have been rapidly developed because of their potential for
thinness, lightness, high speed response to input signals, low
power consumption, and the like.
[0004] In an organic EL element, voltage application between
electrodes, between which a light-emitting layer is interposed,
causes recombination of electrons and holes injected from the
electrodes, which brings a light-emitting substance into an excited
state, and the return from the excited state to the ground state is
accompanied by light emission. Since the wavelength of light
emitted from a light-emitting substance depends on the
light-emitting substance, use of different types of organic
compounds as light-emitting substances makes it possible to obtain
light-emitting elements which exhibit various wavelengths, i.e.,
various colors.
[0005] In the case of display devices which are used to display
images, such as displays, at least three-color light, i.e., red
light, green light, and blue light is necessary for reproduction of
full-color images. Furthermore, in application to lighting devices,
it is ideal to obtain light having wavelength components evenly
spreading in the visible light region for obtaining a high color
rendering property, but in reality, light obtained by mixing two or
more kinds of light having different wavelengths is used for
lighting application in many cases. It is known that, with a
mixture of three-color light, i.e., red light, green light, and
blue light, white light having a high color rendering property can
be obtained.
[0006] Light emitted from a light-emitting substance is peculiar to
the substance as described above. However, important performances
as a light-emitting element, such as a lifetime, power consumption,
and even emission efficiency, are not only dependent on the
light-emitting substance but also greatly dependent on layers other
than the light-emitting layer, an element structure, properties of
an emission center substance and a host material, compatibility
between them, carrier balance, and the like. Therefore, there is no
doubt that many kinds of light-emitting element materials are
necessary for a growth in this field. For the above-described
reasons, light-emitting element materials with a variety of
molecular structures have been suggested (e.g., see Patent Document
1).
[0007] As is generally known, the generation ratio of a singlet
excited state to a triplet excited state in a light-emitting
element using electroluminescence is 1:3. Therefore, a
light-emitting element in which a phosphorescent material capable
of converting the triplet excited state to light emission is used
as an emission center substance can theoretically obtain higher
emission efficiency than a light-emitting element in which a
fluorescent material capable of converting the singlet excited
state to light emission is used as an emission center
substance.
[0008] As a host material in a host-guest type light-emitting layer
or a substance contained in each transport layer in contact with a
light-emitting layer, a substance having a wider band gap or a
higher triplet level (T.sub.1, a larger energy difference between a
triplet excited state and a singlet ground state) than an emission
center substance is used for efficient conversion of excitation
energy into light emission from the emission center substance.
[0009] However, most substances that are used as a host material of
the light-emitting element are fluorescent materials, in which
electron transition between different states is forbidden. The
triplet excited state of the material is at a lower energy level
than the singlet excited state of the material, which means that a
host material for obtaining phosphorescence needs to have a wider
band gap than a host material for obtaining fluorescence of the
same wavelength.
[0010] Therefore, a host material and a carrier-transport material
each having a further wider band gap are necessary in order to
efficiently obtain phosphorescence. However, it is extremely
difficult to develop a substance to be a light-emitting element
material which has such a wide band gap while enabling a balance
between important characteristics of a light-emitting element, such
as low driving voltage and high emission efficiency.
REFERENCE
Patent Document
[Patent Document 1] Japanese Published Patent Application No.
2007-15933
SUMMARY OF THE INVENTION
[0011] In view of the above, another object of one embodiment of
the present invention is to provide a novel organic compound that
can be used as a carrier-transport material, a host material, or a
light-emitting material in a light-emitting element. Specifically,
an object of one embodiment of the present invention is to provide
an organic compound that can give a light-emitting element having
favorable characteristics even when the organic compound is used in
a light-emitting element emitting phosphorescence.
[0012] Another object of one embodiment of the present invention is
to provide an organic compound which has a high T.sub.1 level.
[0013] Another object of one embodiment of the present invention is
to provide an organic compound having a high carrier-transport
property.
[0014] Another object of one embodiment of the present invention is
to provide a light-emitting element containing the organic
compound.
[0015] Another object of one embodiment of the present invention is
to provide a display module, a lighting module, a light-emitting
device, a lighting device, a display device, and an electronic
device each using the organic compound and achieving low power
consumption.
[0016] It is only necessary that at least one of the
above-described objects be achieved in the present invention.
[0017] In one embodiment of the present invention, an organic
compound is provided in which two aryl groups are bonded to a
pyridine skeleton or a bipyridine skeleton and a dibenzothiophenyl
group or a dibenzofuranyl group is bonded to each of the aryl
groups.
[0018] That is, one embodiment of the present invention is an
organic compound represented by General Formula (G0).
##STR00001##
[0019] In the formula, A.sup.1 and A.sup.2 separately represent any
one of a dibenzofuranyl group and a dibenzothiophenyl group, and
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms. Furthermore, n is 1 or 2.
[0020] In the organic compound represented by General Formula (G0),
n is preferably 2, in which case the organic compound enables a
light-emitting element to have low driving voltage. That is,
another embodiment of the present invention is an organic compound
represented by General Formula (G1).
##STR00002##
[0021] In the formula, A.sup.1 and A.sup.2 separately represent any
one of a dibenzothiophenyl group and a dibenzofuranyl group, and
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms. Note that the organic compound represented by
General Formula (G1) may have a substituent other than that
illustrated in General Formula (G1). Specifically, A.sup.1 and
A.sup.2 may separately represent any one of a substituted
dibenzothiophenyl group and a substituted dibenzofuranyl group, and
Ar.sup.1 and Ar.sup.2 may separately represent a substituted
arylene group having 6 to 13 carbon atoms. Furthermore, the
bipyridine skeleton in General Formula (G1) may have a substituent.
Examples of the substituent include an alkyl group having 1 to 6
carbon atoms and an aryl group having 6 to 13 carbon atoms.
[0022] Furthermore, in the organic compound represented by General
Formula (G1), the arylene groups are preferably bonded to the
4-positions of the dibenzofuranyl and/or dibenzothiophenyl groups.
That is, another embodiment of the present invention is an organic
compound represented by General Formula (G2).
##STR00003##
[0023] In the formula, Ar.sup.1 and Ar.sup.2 separately represent
an arylene group having 6 to 13 carbon atoms, and Z represents any
one of an oxygen atom and a sulfur atom. Note that the organic
compound represented by General Formula (G2) may have a substituent
other than that illustrated in General Formula (G2). Examples of
the substituent include an alkyl group having 1 to 6 carbon atoms
and an aryl group having 6 to 13 carbon atoms.
[0024] Furthermore, in the organic compound represented by General
Formula (G2), the bipyridine skeleton is preferably a
2,2'-bipyridine skeleton. That is, another embodiment of the
present invention is an organic compound represented by General
Formula (G3).
##STR00004##
[0025] In the formula, one of R.sup.1 to R.sup.4 is a group
represented by General Formula (A-1) and the others of R.sup.1 to
R.sup.4 separately represent any one of hydrogen, an alkyl group
having 1 to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms; and one of R.sup.5 to R.sup.8 is a group represented by
General Formula (A-2) and the others of R.sup.5 to R.sup.8
separately represent any one of hydrogen, an alkyl group having 1
to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms.
##STR00005##
[0026] In General Formulae (A-1) and (A-2), R.sup.10 to R.sup.16
and R.sup.20 to R.sup.26 separately represent any one of hydrogen,
an alkyl group having 1 to 6 carbon atoms, and an aryl group having
6 to 13 carbon atoms. Furthermore, Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms, and Z
represents any one of an oxygen atom and a sulfur atom.
[0027] In the organic compound represented by General Formula (G3),
it is preferable that Ar.sup.1 and Ar.sup.2 be each an m-phenylene
group. That is, another embodiment of the present invention is an
organic compound represented by General Formula (G4).
##STR00006##
[0028] In the formula, one of R.sup.1 to R.sup.4 is a group
represented by General Formula (A-3) and the others of R.sup.1 to
R.sup.4 separately represent any one of hydrogen, an alkyl group
having 1 to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms; and one of R.sup.5 to R.sup.8 is a group represented by
General Formula (A-4) and the others of R.sup.5 to R.sup.8
separately represent any one of hydrogen, an alkyl group having 1
to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms.
##STR00007##
[0029] In General Formulae (A-3) and (A-4), R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately represent
any one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and
an aryl group having 6 to 13 carbon atoms. Furthermore, Z
represents any one of an oxygen atom and a sulfur atom.
[0030] In General Formula (G4), it is preferable that the groups
represented by General Formulae (A-3) and (A-4) be bonded to the
4-position and the 4'-position of the bipyridine skeleton. That is,
another embodiment of the present invention is an organic compound
represented by General Formula (G5).
##STR00008##
[0031] In General Formula (G5), R.sup.1, R.sup.2, R.sup.4, R.sup.5,
R.sup.7, R.sup.8, R.sup.10 to R.sup.16, R.sup.20 to R.sup.26, and
R.sup.30 to R.sup.37 separately represent any one of hydrogen, an
alkyl group having 1 to 6 carbon atoms, and an aryl group having 6
to 13 carbon atoms. Furthermore, Z represents any one of an oxygen
atom and a sulfur atom.
[0032] An organic compound represented by General Formula (G0) in
which n is 1 can be represented by General Formula (G6).
##STR00009##
[0033] In the formula, A.sup.1 and A.sup.2 separately represent any
one of a dibenzofuranyl group and a dibenzothiophenyl group, and
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms. Note that the organic compound represented by
General Formula (G6) may have a substituent other than that
illustrated in General Formula (G6). Examples of the substituent
include an alkyl group having 1 to 6 carbon atoms and an aryl group
having 6 to 13 carbon atoms.
[0034] Furthermore, in the organic compound represented by General
Formula (G6), the arylene groups are preferably bonded to the
4-positions of the dibenzofuranyl and/or dibenzothiophenyl groups.
That is, another embodiment of the present invention is an organic
compound represented by General Formula (G7).
##STR00010##
[0035] In the formula, Ar.sup.1 and Ar.sup.2 separately represent
an arylene group having 6 to 13 carbon atoms, and Z represents any
one of an oxygen atom and a sulfur atom. Note that the organic
compound represented by General Formula (G7) may have a substituent
other than that illustrated in General Formula (G7). Examples of
the substituent include an alkyl group having 1 to 6 carbon atoms
and an aryl group having 6 to 13 carbon atoms.
[0036] The organic compound represented by General Formula (G7) can
also be represented by General Formula (G8).
##STR00011##
[0037] In the formula, one of R.sup.40 to R.sup.44 is a group
represented by General Formula (A-1), another of R.sup.40 to
R.sup.44 is a group represented by General Formula (A-2), and the
others of R.sup.40 to R.sup.44 separately represent any one of
hydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl
group having 6 to 13 carbon atoms.
##STR00012##
[0038] In General Formulae (A-1) and (A-2), R.sup.10 to R.sup.16
and R.sup.20 to R.sup.26 separately represent any one of hydrogen,
an alkyl group having 1 to 6 carbon atoms, and an aryl group having
6 to 13 carbon atoms. Furthermore, Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms, and Z
represents any one of an oxygen atom and a sulfur atom.
[0039] In the organic compound represented by General Formula (G8),
it is preferable that Ar.sup.1 and Ar.sup.2 be each an m-phenylene
group. That is, another embodiment of the present invention is an
organic compound represented by General Formula (G9).
##STR00013##
[0040] In the formula, one of R.sup.40 to R.sup.44 is a group
represented by General Formula (A-3), another of R.sup.40 to
R.sup.44 is a group represented by General Formula (A-4), and the
others of R.sup.40 to R.sup.44 separately represent any one of
hydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl
group having 6 to 13 carbon atoms.
##STR00014##
[0041] In General Formulae (A-3) and (A-4), R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately represent
any one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and
an aryl group having 6 to 13 carbon atoms. Furthermore, Z
represents any one of an oxygen atom and a sulfur atom.
[0042] In General Formula (G9), it is preferable that the group
represented by General Formula (A-3) and the group represented by
General Formula (A-4) be bonded to the 3-position and the
5-position of the pyridine at the center. That is, another
embodiment of the present invention is an organic compound
represented by General Formula (G10).
##STR00015##
[0043] In the formula, R.sup.40, R.sup.42, R.sup.44, R.sup.10 to
R.sup.16, R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately
represent any one of hydrogen, an alkyl group having 1 to 6 carbon
atoms, and an aryl group having 6 to 13 carbon atoms. Furthermore,
Z represents any one of an oxygen atom and a sulfur atom.
[0044] Another embodiment of the present invention is an organic
compound represented by Structural Formula (100).
##STR00016##
[0045] Another embodiment of the present invention is an organic
compound represented by Structural Formula (200).
##STR00017##
[0046] Another embodiment of the present invention is an organic
compound represented by Structural Formula (300).
##STR00018##
[0047] Another embodiment of the present invention is an organic
compound represented by Structural Formula (400).
##STR00019##
[0048] Another embodiment of the present invention is a
light-emitting element that includes a pair of electrodes and a
layer containing an organic compound between the pair of
electrodes. The layer containing the organic compound contains any
one of the above organic compounds.
[0049] Another embodiment of the present invention is a
light-emitting element that includes a pair of electrodes and a
layer containing an organic compound between the pair of
electrodes. The layer containing the organic compound includes at
least a light-emitting layer. The light-emitting layer contains any
one of the above organic compounds.
[0050] Another embodiment of the present invention is a display
module including the light-emitting element with any one of the
above structures.
[0051] Another embodiment of the present invention is a lighting
module including the light-emitting element with any one of the
above structures.
[0052] Another embodiment of the present invention is a
light-emitting device including the light-emitting element with any
one of the above structures and a unit for controlling the
light-emitting element.
[0053] Another embodiment of the present invention is a display
device including the light-emitting element with any one of the
above structures in a display portion, and a unit for controlling
the light-emitting element.
[0054] Another embodiment of the present invention is a lighting
device including the light-emitting element with any one of the
above structures in a lighting portion, and a unit for controlling
the light-emitting element.
[0055] Another embodiment of the present invention is an electronic
device including the light-emitting element with any one of the
above structures.
[0056] A light-emitting element of the present invention has high
emission efficiency.
[0057] The organic compound of the present invention has a wide
band gap. Furthermore, the organic compound has a high
carrier-transport property. Accordingly, the organic compound can
be suitably used in a light-emitting element, as a material of a
transport layer, a host material in a light-emitting layer, or an
emission center substance in the light-emitting layer.
[0058] Another embodiment of the present invention can provide a
display module, a lighting module, a light-emitting device, a
lighting device, a display device, and an electronic device each
using the organic compound and achieving low power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIGS. 1A and 1B are conceptual diagrams of light-emitting
elements.
[0060] FIG. 2 is a conceptual diagram of an organic semiconductor
element.
[0061] FIGS. 3A and 3B are conceptual diagrams of an active matrix
light-emitting device.
[0062] FIGS. 4A and 4B are conceptual diagrams of an active matrix
light-emitting device.
[0063] FIG. 5 is a conceptual diagram of an active matrix
light-emitting device.
[0064] FIGS. 6A and 6B are conceptual diagrams of a passive matrix
light-emitting device.
[0065] FIGS. 7A to 7D illustrate electronic devices.
[0066] FIG. 8 illustrates a light source device.
[0067] FIG. 9 illustrates a lighting device.
[0068] FIG. 10 illustrates a lighting device.
[0069] FIG. 11 illustrates in-vehicle display devices and lighting
devices.
[0070] FIGS. 12A to 12C illustrate an electronic device.
[0071] FIGS. 13A and 13B are NMR charts of 4,4'mDBTP2BPy-II.
[0072] FIGS. 14A and 14B show absorption spectra and emission
spectra of 4,4'mDBTP2BPy-II.
[0073] FIG. 15 shows results of LC/MS analysis of
4,4'mDBTP2BPy-II.
[0074] FIGS. 16A and 16B are NMR charts of 4,4'DBfP2BPy.
[0075] FIGS. 17A and 17B show absorption spectra and emission
spectra of 4,4'DBfP2BPy.
[0076] FIG. 18 shows results of LC/MS analysis of 4,4'DBfP2BPy.
[0077] FIG. 19 shows luminance-current density characteristics of a
light-emitting element 1, a light-emitting element 2, and a
comparative light-emitting element 1.
[0078] FIG. 20 shows current efficiency-luminance characteristics
of a light-emitting element 1, a light-emitting element 2, and a
comparative light-emitting element 1.
[0079] FIG. 21 shows luminance-voltage characteristics of a
light-emitting element 1, a light-emitting element 2, and a
comparative light-emitting element 1.
[0080] FIG. 22 shows external quantum efficiency-luminance
characteristics of a light-emitting element 1, a light-emitting
element 2, and a comparative light-emitting element 1.
[0081] FIG. 23 shows emission spectra of a light-emitting element
1, a light-emitting element 2, and a comparative light-emitting
element 1.
[0082] FIG. 24 shows time dependence of normalized luminance of a
light-emitting element 1, a light-emitting element 2, and a
comparative light-emitting element 1.
[0083] FIG. 25 shows luminance-current density characteristics of a
light-emitting element 3 and a light-emitting element 4.
[0084] FIG. 26 shows current efficiency-luminance characteristics
of a light-emitting element 3 and a light-emitting element 4.
[0085] FIG. 27 shows luminance-voltage characteristics of a
light-emitting element 3 and a light-emitting element 4.
[0086] FIG. 28 shows external quantum efficiency-luminance
characteristics of a light-emitting element 3 and a light-emitting
element 4.
[0087] FIG. 29 shows emission spectra of a light-emitting element 3
and a light-emitting element 4.
[0088] FIGS. 30A and 30B are NMR charts of 3,5mDBTP2Py.
[0089] FIGS. 31A and 31B show absorption spectra and emission
spectra of 3,5mDBTP2Py.
[0090] FIGS. 32A and 32B are NMR charts of 3,5mDBFP2Py.
[0091] FIGS. 33A and 33B show absorption spectra and emission
spectra of 3,5mDBFP2Py.
[0092] FIG. 34 shows luminance-current density characteristics of a
light-emitting element 5 and a light-emitting element 6.
[0093] FIG. 35 shows current efficiency-luminance characteristics
of a light-emitting element 5 and a light-emitting element 6.
[0094] FIG. 36 shows luminance-voltage characteristics of a
light-emitting element 5 and a light-emitting element 6.
[0095] FIG. 37 shows external quantum efficiency-luminance
characteristics of a light-emitting element 5 and a light-emitting
element 6.
[0096] FIG. 38 shows emission spectra of a light-emitting element 5
and a light-emitting element 6.
[0097] FIG. 39 shows luminance-current density characteristics of a
light-emitting element 7 and a light-emitting element 8.
[0098] FIG. 40 shows current efficiency-luminance characteristics
of a light-emitting element 7 and a light-emitting element 8.
[0099] FIG. 41 shows luminance-voltage characteristics of a
light-emitting element 7 and a light-emitting element 8.
[0100] FIG. 42 shows external quantum efficiency-luminance
characteristics of a light-emitting element 7 and a light-emitting
element 8.
[0101] FIG. 43 shows emission spectra of a light-emitting element 7
and a light-emitting element 8.
[0102] FIG. 44 shows time dependence of normalized luminance of a
light-emitting element 7 and a light-emitting element 8.
[0103] FIG. 45 shows time dependence of normalized luminance of
light-emitting elements 9 to 12 and comparative light-emitting
elements 3 and 4.
DETAILED DESCRIPTION OF THE INVENTION
[0104] Embodiments of the present invention will be described
below. It is easily understood by those skilled in the art that
modes and details disclosed herein can be modified in various ways
without departing from the spirit and the scope of the present
invention. Therefore, the present invention is not interpreted as
being limited to the description of the following embodiments.
Embodiment 1
[0105] In an organic compound in this embodiment, two aryl groups
are bonded to a pyridine skeleton or a bipyridine skeleton and a
dibenzothiophenyl group or a dibenzofuranyl group is bonded to each
of the aryl groups. The organic compound has a wide band gap and a
high triplet level. Moreover, the organic compound has a high
carrier-transport property. Note that this organic compound can be
regarded as an organic compound in which two dibenzothiophenyl
groups, two dibenzofuranyl groups, or a dibenzothiophenyl group and
a dibenzofuranyl group are bonded to a pyridine skeleton or a
bipyridine skeleton via arylene groups.
[0106] Therefore, a light-emitting element containing the organic
compound can have a high emission efficiency.
[0107] The arylene group of the above organic compound is
preferably an arylene group having 6 to 13 carbon atoms. Examples
of the arylene group having 6 to 13 carbon atoms include a
phenylene group, a naphthalenediyl group, a biphenyldiyl group, and
a fluorenediyl group, and in particular, a phenylene group, a
biphenyldiyl group, and a fluorenediyl group are preferable to give
a high triplet level. Among these groups, a phenylene group,
specifically, an in-phenylene group is favorable.
[0108] When the central skeleton is a bipyridine skeleton, it is
preferably a 2,2'-bipyridine skeleton.
[0109] In the organic compound of one embodiment of the present
invention in which the central skeleton is a 2,2'-bipyridine
skeleton, the arylene groups to each of which a dibenzothiophenyl
group or a dibenzofuranyl group is bonded are preferably bonded to
the 4-position and the 4'-position of the 2,2'-bipyridine
skeleton.
[0110] When the central skeleton is a pyridine skeleton, the
arylene groups to each of which a dibenzothiophenyl group or a
dibenzofuranyl group is bonded are preferably bonded to the
3-position and the 5-position of the pyridine skeleton, in which
case the use of the organic compound as a material of a
light-emitting element leads to a reduction in driving voltage.
[0111] In the organic compound, the arylene groups are preferably
bonded to the 4-positions of the dibenzothiophenyl and/or
dibenzofuranyl groups.
[0112] Note that each of these organic compounds may have a
substituent, and the substituent can be an alkyl group having 1 to
6 carbon atoms, an aryl group having 6 to 13 carbon atoms, or the
like.
[0113] Since the organic compound with such a structure has a wide
band gap, in a light-emitting element, the organic compound can be
suitably used as a host material in a light-emitting layer whose
emission center substance emits blue fluorescence or fluorescence
having a shorter wavelength than blue fluorescence, or can be
suitably used for a carrier-transport layer that is adjacent to the
light-emitting layer. Since the organic compound also has a high
triplet level, the organic compound can be suitably used as a host
material in a light-emitting layer whose emission center substance
emits phosphorescence, or can be suitably used for a
carrier-transport layer that is adjacent to the light-emitting
layer. The organic compound has a wide band gap or a high triplet
level (T.sub.1 level), so that the energy of carriers that
recombine at a host material can be effectively transferred to an
emission center substance. Thus, a light-emitting element having a
high emission efficiency can be manufactured.
[0114] The organic compound can be suitably used as a host material
or for a carrier-transport layer in a light-emitting element due to
its high carrier-transport property. Since the organic compound has
a high carrier-transport property, a light-emitting element with
low driving voltage can be manufactured. Furthermore, in the case
where the organic compound is used for a carrier-transport layer
closer to a light-emitting region in a light-emitting layer, loss
of excitation energy of an emission center substance can be
suppressed because of a wide band gap or a high triplet level of
the organic compound, so that a light-emitting element having a
high emission efficiency can be obtained.
[0115] The above organic compound of one embodiment of the present
invention can also be represented by General Formula (G0).
##STR00020##
[0116] In the formula, A.sup.1 and A.sup.2 separately represent any
one of a dibenzofuranyl group and a dibenzothiophenyl group, and
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms. Furthermore, n is 1 or 2. Note that the
organic compound represented by General Formula (G0) may be
substituted or unsubstituted; when the organic compound has a
substituent, the substituent is an alkyl group having 1 to 6 carbon
atoms or an aryl group having 6 to 13 carbon atoms.
[0117] In the organic compound represented by General Formula (G0),
n is preferably 2, in which case the organic compound enables a
light-emitting element to have low driving voltage. This organic
compound can be represented by General Formula (G1).
##STR00021##
[0118] In the formula, A.sup.1 and A.sup.2 separately represent any
one of a dibenzothiophenyl group and a dibenzofuranyl group, and
Ar.sup.1 and Ar.sup.2 separately represent an arylene group having
6 to 13 carbon atoms. Note that the organic compound represented by
General Formula (G1) may be substituted or unsubstituted; when the
organic compound has a substituent, the substituent is an alkyl
group having 1 to 6 carbon atoms or an aryl group having 6 to 13
carbon atoms.
[0119] In the organic compound represented by General Formula (G1),
Ar.sup.1 and Ar.sup.2 are preferably bonded to the 4-positions of
the dibenzothiophenyl and/or dibenzofuranyl groups, and an organic
compound having such a structure can be represented by General
Formula (G2).
##STR00022##
[0120] In the formula, Ar.sup.1 and Ar.sup.2 separately represent
an arylene group having 6 to 13 carbon atoms. Furthermore, Z
represents any one of an oxygen atom and a sulfur atom. Note that
the organic compound represented by General Formula (G2) may be
substituted or unsubstituted; when the organic compound has a
substituent, the substituent is an alkyl group having 1 to 6 carbon
atoms or an aryl group having 6 to 13 carbon atoms.
[0121] In the organic compound represented by General Formula (G2),
Ar.sup.1 and Ar.sup.2 are bonded to the 4-positions of the
dibenzofuranyl and/or dibenzothiophenyl groups. By having this
structure, the organic compound represented by General Formula (G2)
can be easily synthesized and highly cost-effective.
[0122] The above organic compound can also be represented by
General Formula (G3).
##STR00023##
[0123] In General Formula (G3), one of R.sup.1 to R.sup.4 is a
group represented by General Formula (A-1) and the others of
R.sup.1 to R.sup.4 separately represent any one of hydrogen, an
alkyl group having 1 to 6 carbon atoms, and an aryl group having 6
to 13 carbon atoms. Moreover, one of R.sup.5 to R.sup.8 is a group
represented by General Formula (A-2) and the others of R.sup.5 to
R.sup.8 separately represent any one of hydrogen, an alkyl group
having 1 to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms.
##STR00024##
[0124] In General Formulae (A-1) and (A-2), R.sup.10 to R.sup.16
and R.sup.20 to R.sup.26 separately represent any one of hydrogen,
an alkyl group having 1 to 6 carbon atoms, and an aryl group having
6 to 13 carbon atoms. Furthermore, Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms, and Z
represents any one of an oxygen atom and a sulfur atom.
[0125] In the organic compound of one embodiment of the present
invention described in this embodiment, the arylene group is
preferably any of a phenylene group and a biphenyldiyl group, and
in particular, the phenylene group is further preferable.
[0126] It is preferable that the bipyridine skeleton and the
dibenzofuranyl and/or dibenzothiophenyl groups be bonded by
Ar.sup.1 and Ar.sup.2 not linearly to each other but bonded to each
other so as to form a folded structure. This is because an
interaction between orbits of the two skeletons can be decreased,
the band gap width can be increased, and the triplet level can be
increased. For example, when Ar.sup.1 and Ar.sup.2 are each a
phenylene group, an m-phenylene group is preferred to a p-phenylene
group. When Ar.sup.1 and Ar.sup.2 are each a biphenyldiyl group, a
1,1'-biphenyl-3,3'-diyl group is preferable.
[0127] That is, the above organic compound can be represented by
General Formula (G4).
##STR00025##
[0128] In General Formula (G4), one of R.sup.1 to R.sup.4 is a
group represented by General Formula (A-3) and the others of
R.sup.1 to R.sup.4 separately represent any one of hydrogen, an
alkyl group having 1 to 6 carbon atoms, and an aryl group having 6
to 13 carbon atoms; and one of R.sup.5 to R.sup.8 is a group
represented by General Formula (A-4) and the others of R.sup.5 to
R.sup.8 separately represent any one of hydrogen, an alkyl group
having 1 to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms.
##STR00026##
[0129] In General Formulae (A-3) and (A-4), R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately represent
any one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and
an aryl group having 6 to 13 carbon atoms. Furthermore, Z
represents any one of an oxygen atom and a sulfur atom.
[0130] In the organic compound represented by General Formula (G4),
it is preferable that the group represented by General Formula
(A-3) and the group represented by General Formula (A-4) be bonded
to the 4-position and the 4'-position of the bipyridine skeleton.
That is, an organic compound represented by General Formula (G5) is
preferable.
##STR00027##
[0131] In General Formula (G5), R.sup.1, R.sup.2, R.sup.4, R.sup.5,
R.sup.7, R.sup.8, R.sup.10 to R.sup.16, R.sup.20 to R.sup.26, and
R.sup.30 to R.sup.37 separately represent any one of hydrogen, an
alkyl group having 1 to 6 carbon atoms, and an aryl group having 6
to 13 carbon atoms. Furthermore, Z represents any one of an oxygen
atom and a sulfur atom.
[0132] In the organic compound represented by General Formula (G5),
the phenyl groups to which the dibenzofuranyl and/or
dibenzothiophenyl groups are bonded are bonded to the 4-position
and the 4'-position of the 2,2'-bipyridine skeleton.
[0133] Note that each of R.sup.1 to R.sup.8, R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 is preferably
hydrogen, because synthesis can be carried out at low cost due to
the easiness in synthesis and availability of a raw material.
[0134] An organic compound represented by General Formula (G0) in
which n is 1 can also be represented by General Formula (G6).
##STR00028##
[0135] In the general formula, A.sup.1 and A.sup.2 separately
represent any one of a dibenzofuranyl group and a dibenzothiophenyl
group, and Ar.sup.1 and Ar.sup.2 separately represent an arylene
group having 6 to 13 carbon atoms. Note that the organic compound
represented by General Formula (G6) may have a substituent other
than that illustrated in General Formula (G6). Examples of the
substituent include an alkyl group having 1 to 6 carbon atoms and
an aryl group having 6 to 13 carbon atoms.
[0136] In the above organic compound, Ar.sup.1 and Ar.sup.2 are
preferably bonded to the 4-positions of the dibenzothiophenyl
and/or dibenzofuranyl groups, and an organic compound having such a
structure can be represented by General Formula (G7).
##STR00029##
[0137] In the general formula, Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms, and Z
represents any one of an oxygen atom and a sulfur atom. Note that
the organic compound represented by General Formula (G7) may have a
substituent other than that illustrated in General Formula (G7).
Examples of the substituent include an alkyl group having 1 to 6
carbon atoms and an aryl group having 6 to 13 carbon atoms.
[0138] The organic compound represented by General Formula (G7) can
also be represented by General Formula (G8).
##STR00030##
[0139] In General Formula (G8), one of R.sup.40 to R.sup.44 is a
group represented by General Formula (A-1), another of R.sup.40 to
R.sup.44 is a group represented by General Formula (A-2), and the
others of R.sup.40 to R.sup.44 separately represent any one of
hydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl
group having 6 to 13 carbon atoms.
##STR00031##
[0140] In General Formulae (A-1) and (A-2), R.sup.10 to R.sup.16
and R.sup.20 to R.sup.26 separately represent any one of hydrogen,
an alkyl group having 1 to 6 carbon atoms, and an aryl group having
6 to 13 carbon atoms. Furthermore, Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms, and Z
represents any one of an oxygen atom and a sulfur atom.
[0141] In the organic compound represented by General Formula (G8),
it is preferable that Ar.sup.1 and Ar.sup.2 be each an m-phenylene
group because a triplet level is not easily reduced. That is, an
organic compound represented by General Formula (G9) is
preferable.
##STR00032##
[0142] In the general formula, one of R.sup.40 to R.sup.44 is a
group represented by General Formula (A-3), another of R.sup.40 to
R.sup.44 is a group represented by General Formula (A-4), and the
others of R.sup.40 to R.sup.44 separately represent any one of
hydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl
group having 6 to 13 carbon atoms.
##STR00033##
[0143] In General Formulae (A-3) and (A-4), R.sup.10 to R.sup.16,
R.sup.20 to R.sup.26, and R.sup.30 to R.sup.37 separately represent
any one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and
an aryl group having 6 to 13 carbon atoms. Furthermore, Z
represents any one of an oxygen atom and a sulfur atom.
[0144] In General Formula (G9), it is preferable that the group
represented by General Formula (A-3) and the group represented by
General Formula (A-4) be bonded to the 3-position and the
5-position of the pyridine skeleton. That is, an organic compound
represented by General Formula (G10) is preferable.
##STR00034##
[0145] In General Formula (G10), R.sup.40, R.sup.42, R.sup.44,
R.sup.10 to R.sup.16, R.sup.20 to R.sup.26, and R.sup.30 to
R.sup.37 separately represent any one of hydrogen, an alkyl group
having 1 to 6 carbon atoms, and an aryl group having 6 to 13 carbon
atoms. Furthermore, Z represents any one of an oxygen atom and a
sulfur atom.
[0146] Note that in the explanation of the organic compounds
represented by General Formulae (G0) to (G10), specific examples of
the alkyl group having 1 to 6 carbon atoms include a methyl group,
an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl
group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a
pentyl group, a hexyl group, and a cyclohexyl group. Specific
examples of the aryl group having 6 to 13 carbon atoms include a
phenyl group, a biphenyl group, a fluorenyl group, and a naphthyl
group. Note that such substituents may be bonded to each other and
form a ring. As an example of such a case, a spirofluorene skeleton
is formed in such a manner that a carbon atom at the 9-position of
a fluorenyl group has two phenyl groups as substituents and these
phenyl groups are bonded to each other.
[0147] Specific examples of the arylene groups having 6 to 13
carbon atoms that are represented by Ar.sup.1 and Ar.sup.2 include
a phenylene group, a naphthalenediyl group, a biphenyldiyl group,
and a fluorenediyl group, and in particular, a phenylene group, a
biphenyldiyl group, and a fluorenediyl group are preferable to give
a high triplet level.
[0148] Specific examples of structures of the organic compounds
represented by General Formulae (G0) to (G10) are represented by
Structural Formulae (100) to (127), (200) to (227), (300) to (327),
and (400) to (427).
##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039##
##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044##
##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049##
##STR00050## ##STR00051## ##STR00052##
[0149] Furthermore, because of their high triplet level, the above
organic compounds allow a phosphorescent light-emitting element to
have high emission efficiency. Specifically, the organic compounds
allow even a light-emitting element emitting green or blue
phosphorescence, which has a short wavelength, to have favorable
characteristics without reducing the emission efficiency. Moreover,
the high triplet level means that the organic compounds have a wide
band gap, which allows a blue-emissive fluorescent light-emitting
element to emit light efficiently.
[0150] Furthermore, the organic compound of this embodiment can be
used as a light-emitting material that emits blue to ultraviolet
light.
[0151] Subsequently, a method for synthesizing these organic
compounds is described. As shown in Synthesis Scheme (A-1), a
halide of a pyridine derivative or a pyridine derivative that has a
triflate group as a substituent (compound 1) may be coupled with an
organoboron compound or a boronic acid (compound 2) of a pyridine
derivative by the Suzuki-Miyaura reaction, whereby the organic
compound represented by General Formula (G1) can be provided.
Synthesis Scheme (A-1) is shown below.
##STR00053##
[0152] In Synthesis Scheme (A-1), A.sup.1 and A.sup.2 separately
represent any one of a dibenzofuranyl group and a dibenzothiophenyl
group, and Ar.sup.1 and Ar.sup.2 separately represent an arylene
group having 6 to 13 carbon atoms. R.sup.50 and R.sup.51 separately
represent any one of hydrogen and an alkyl group having 1 to 6
carbon atoms. In Synthesis Scheme (A-1), R.sup.50 and R.sup.51 may
be bonded to each other to form a ring. Furthermore, X.sup.1
represents any one of a halogen and a triflate group.
[0153] Alternatively, the organic compound represented by General
Formula (G1) can be provided through the reaction represented by
Synthesis Scheme (B-1), in which a halide of a bipyridine
derivative or a bipyridine derivative that has a triflate group as
a substituent (compound 3) may be coupled with organoboron
compounds or boronic acids (compounds 4 and 5) of dibenzofuran
and/or dibenzothiophene derivatives by the Suzuki-Miyaura reaction.
Synthesis Scheme (B-1) is shown below.
##STR00054##
[0154] In Synthesis Scheme (B-1), A.sup.1 and A.sup.2 separately
represent any one of a dibenzofuranyl group and a dibenzothiophenyl
group, and Ar.sup.1 and Ar.sup.2 separately represent an arylene
group having 6 to 13 carbon atoms. R.sup.52 to R.sup.55 separately
represent any one of hydrogen and an alkyl group having 1 to 6
carbon atoms. In Synthesis Scheme (B-1), R.sup.52 and R.sup.53, and
R.sup.54 and R.sup.55 may be bonded to each other to form a ring.
Furthermore, X.sup.2 and X.sup.3 separately represent any one of a
halogen and a triflate group.
[0155] Examples of the palladium catalyst that can be used in
Synthesis Schemes (A-1) and (B-1) include, but are not limited to,
palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0),
and bis(triphenylphosphine)palladium(II) dichloride. Examples of
ligands of the palladium catalyst that can be used in Synthesis
Scheme (B-1) include tri(ortho-tolyl)phosphine, triphenylphosphine,
and tricyclohexylphosphine. Note that the ligand of the palladium
catalyst that can be used is not limited to these ligands. Examples
of a base that can be used in Synthesis Schemes (A-1) and (B-1)
include, but are not limited to, organic bases such as sodium
tert-butoxide and inorganic bases such as potassium carbonate and
sodium carbonate. Examples of a solvent that can be used in
Synthesis Schemes (A-1) and (B-1) include, but not limited to, a
mixed solvent of toluene and water; a mixed solvent of toluene,
alcohol such as ethanol, and water; a mixed solvent of xylene and
water; a mixed solvent of xylene, alcohol such as ethanol, and
water; a mixed solvent of benzene and water; a mixed solvent of
benzene, alcohol such as ethanol, and water; and a mixed solvent of
water and an ether such as ethylene glycol dimethyl ether. Further,
a mixed solvent of toluene and water, a mixed solvent of toluene,
ethanol, and water, or a mixed solvent of an ether such as ethylene
glycol dimethyl ether and water is more preferable.
[0156] To synthesize the objective substance, although the compound
2, the compound 4, and the compound 5 are separately any one of an
organoboron compound and a boronic acid and the Suzuki-Miyaura
coupling reaction is caused in Synthesis Scheme (A-1) and Synthesis
Scheme (B-1), the compound 2, the compound 4, and the compound 5
may be separately any one of an organoaluminum compound, an
organozirconium compound, an organozinc compound, an organotin
compound, and the like and a cross coupling reaction may be caused.
However, one embodiment of the present invention is not limited
thereto.
[0157] Further, in the Suzuki-Miyaura coupling reaction shown in
Synthesis Scheme (B-1), an organoboron compound or a boronic acid
of a bipyridine derivative may be reacted with a halide of a
dibenzofuran derivative, a halide of a dibenzothiophene derivative,
a dibenzofuran derivative having a triflate group as a substituent,
or a dibenzothiophene derivative having a triflate group as a
substituent.
[0158] The organic compound represented by General Formula (G6) can
be provided through the reaction represented by Synthesis Scheme
(C-1), in which a halide of a pyridine derivative or a pyridine
derivative that has a triflate group as a substituent (compound 6)
may be coupled with organoboron compounds or boronic acids
(compounds 7 and 8) of dibenzofuran and/or dibenzothiophene
derivatives by the Suzuki-Miyaura reaction. Synthesis Scheme (C-1)
is shown below.
##STR00055##
[0159] In Synthesis Scheme (C-1), A.sup.1 and A.sup.2 separately
represent any one of a dibenzofuranyl group and a dibenzothiophenyl
group, and Ar.sup.1 and Ar.sup.2 separately represent an arylene
group having 6 to 13 carbon atoms. R.sup.57 to R.sup.60 separately
represent any one of hydrogen and an alkyl group having 1 to 6
carbon atoms. In Synthesis Scheme (C-1), R.sup.57 and R.sup.58, and
R.sup.59 and R.sup.60 may be bonded to each other to form a ring.
Furthermore, X.sup.4 and X.sup.5 separately represent any one of a
halogen and a triflate group.
[0160] Examples of the palladium catalyst that can be used in
Synthesis Scheme (C-1) include, but are not limited to,
palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0),
and bis(triphenylphosphine)palladium(II) dichloride. Examples of
ligands of the palladium catalyst that can be used in Synthesis
Scheme (C-1) include tri(ortho-tolyl)phosphine, triphenylphosphine,
and tricyclohexylphosphine. Note that the ligand of the palladium
catalyst that can be used is not limited to these ligands. Examples
of a base that can be used in Synthesis Scheme (C-1) include, but
are not limited to, organic bases such as sodium tert-butoxide and
inorganic bases such as potassium carbonate and sodium carbonate.
Examples of a solvent that can be used in Synthesis Scheme (C-1)
include, but not limited to, a mixed solvent of toluene and water;
a mixed solvent of toluene, alcohol such as ethanol, and water; a
mixed solvent of xylene and water; a mixed solvent of xylene,
alcohol such as ethanol, and water; a mixed solvent of benzene and
water; a mixed solvent of benzene, alcohol such as ethanol, and
water; and a mixed solvent of water and an ether such as ethylene
glycol dimethyl ether. Further, a mixed solvent of toluene and
water, a mixed solvent of toluene, ethanol, and water, or a mixed
solvent of an ether such as ethylene glycol dimethyl ether and
water is more preferable.
[0161] To synthesize the objective substance, although the compound
7 and the compound 8 are separately any one of an organoboron
compound and a boronic acid and the Suzuki-Miyaura coupling
reaction is caused in Synthesis Scheme (C-1), the compound 7 and
the compound 8 may be separately any one of an organoaluminum
compound, an organozirconium compound, an organozinc compound, an
organotin compound, and the like and a cross coupling reaction may
be caused. However, one embodiment of the present invention is not
limited thereto.
[0162] Further, in the Suzuki-Miyaura coupling reaction shown in
Synthesis Scheme (C-1), an organoboron compound or a boronic acid
of a pyridine derivative may be reacted with a halide of a
dibenzofuran derivative, a halide of a dibenzothiophene derivative,
a dibenzofuran derivative having a triflate group as a substituent,
or a dibenzothiophene derivative having a triflate group as a
substituent.
[0163] Through the above-described steps, the organic compounds
described in this embodiment can be synthesized.
Embodiment 2
[0164] In this embodiment, an example will be described in which
the organic compound represented by General Formula (G0) described
in Embodiment 1 is used for an active layer of a vertical
transistor (static induction transistor (SIT)), which is a kind of
an organic semiconductor element. In General Formula (G0), A.sup.1
and A.sup.2 separately represent any one of a dibenzofuranyl group
and a dibenzothiophenyl group, and Ar.sup.1 and Ar.sup.2 separately
represent an arylene group having 6 to 13 carbon atoms.
Furthermore, n is 1 or 2.
##STR00056##
[0165] The element has a structure in which a thin-film active
layer 1202 containing the organic compound represented by General
Formula (G0) is interposed between a source electrode 1201 and a
drain electrode 1203, and a gate electrode 1204 is embedded in the
active layer 1202, as illustrated in FIG. 2. The gate electrode
1204 is electrically connected to a unit for applying gate voltage,
and the source electrode 1201 and the drain electrode 1203 are
electrically connected to a unit for controlling the voltage
between a source and a drain.
[0166] In such an element structure, when voltage is applied
between the source and the drain under the condition that gate
voltage is not applied, a current flows (an ON state). Then, when
gate voltage is applied in this state, a depletion layer is
generated in the periphery of the gate electrode 1204, and thus a
current does not flow (an OFF state). With such a mechanism, the
element operates as a transistor.
[0167] In a vertical transistor, a material which has both a
carrier-transport property and favorable film quality are required
for an active layer like in a light-emitting element. Any of the
organic compounds represented by General Formula (G0) can be
suitably used because it sufficiently meets these requirements.
Embodiment 3
[0168] In this embodiment, one mode of a light-emitting element
that includes an organic compound of one embodiment of the present
invention disclosed in Embodiment 1 will be described with
reference to FIG. 1A.
[0169] The light-emitting element of this embodiment has a
plurality of layers between a pair of electrodes. In this
embodiment, the light-emitting element includes a first electrode
101, a second electrode 102, and an EL layer 103 provided between
the first electrode 101 and the second electrode 102. Note that in
FIG. 1A, the first electrode 101 functions as an anode and the
second electrode 102 functions as a cathode. In other words, when
voltage is applied between the first electrode 101 and the second
electrode 102 such that the potential of the first electrode 101 is
higher than that of the second electrode 102, light emission is
obtained. Of course, a structure in which the first electrode
functions as a cathode and the second electrode functions as an
anode can be employed. In that case, the stacking order of layers
in the EL layer is reversed from the stacking order described
below. Note that in the light-emitting element of this embodiment,
at least one of layers in the EL layer 103 contains the organic
compound of one embodiment of the present invention described in
Embodiment 1. Note that a layer that contains the organic compound
is preferably a light-emitting layer or an electron-transport layer
because the characteristics of the organic compound can be utilized
and a light-emitting element having favorable characteristics can
be obtained.
[0170] For the electrode functioning as an anode, any of metals,
alloys, electrically conductive compounds, and mixtures thereof
which have a high work function (specifically, a work function of
4.0 eV or more) or the like is preferably used. Specific examples
are indium oxide-tin oxide (ITO: indium tin oxide), indium
oxide-tin oxide containing silicon or silicon oxide, indium
oxide-zinc oxide, indium oxide containing tungsten oxide and zinc
oxide (IWZO), and the like. Films of these electrically conductive
metal oxides are usually formed by sputtering but may be formed by
a sol-gel method or the like. For example, indium oxide-zinc oxide
can be formed by a sputtering method using a target in which zinc
oxide is added to indium oxide at 1 wt % to 20 wt %. Moreover,
indium oxide containing tungsten oxide and zinc oxide (IWZO) can be
formed by a sputtering method using a target in which tungsten
oxide is added to indium oxide at 0.5 wt % to 5 wt % and zinc oxide
is added to indium oxide at 0.1 wt % to 1 wt %. Other examples are
gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),
molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium
(Pd), a nitride of a metal material (such as titanium nitride), and
the like. Graphene may also be used.
[0171] There is no particular limitation on the stacked structure
of the EL layer 103. The EL layer 103 can be formed by combining a
layer containing a substance having a high electron-transport
property, a layer containing a substance having a high
hole-transport property, a layer containing a substance having a
high electron-injection property, a layer containing a substance
having a high hole-injection property, a layer containing a bipolar
substance (a substance having a high electron-transport and
hole-transport property), a layer having a carrier-blocking
property, and the like as appropriate. In this embodiment, the EL
layer 103 has a structure in which a hole-injection layer 111, a
hole-transport layer 112, a light-emitting layer 113, an
electron-transport layer 114, and an electron-injection layer 115
are stacked in this order over the electrode functioning as an
anode. Materials contained in the layers are specifically given
below.
[0172] The hole-injection layer 111 is a layer containing a
substance having a hole-injection property. The hole-injection
layer 111 can be formed using molybdenum oxide, vanadium oxide,
ruthenium oxide, tungsten oxide, manganese oxide, or the like. The
hole-injection layer 111 can also be formed using a
phthalocyanine-based compound such as phthalocyanine (abbreviation:
H.sub.2Pc) or copper phthalocyanine (abbreviation: CuPc); an
aromatic amine compound such as
4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl
(abbreviation: DPAB) or
N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-
-biphenyl)-4,4'-diamine (abbreviation: DNTPD); a high molecule
compound such as
poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)
(PEDOT/PSS), or the like.
[0173] The hole-injection layer 111 can be formed using a composite
material in which a substance exhibiting an electron-accepting
property (hereinafter, simply referred to as "electron-accepting
substance") with respect to a substance having a hole-transport
property is contained in the substance having a hole-transport
property. In this specification, the composite material refers to
not a material in which two materials are simply mixed but a
material in the state where charge transfer between the materials
can be caused by a mixture of a plurality of materials. This charge
transfer includes the charge transfer that occurs only when an
electric field exists.
[0174] Note that by using the composite material in which the
electron-accepting substance is contained in the substance having a
hole-transport property, a material used for forming the electrode
can be selected regardless of the work function of the material. In
other words, besides a material having a high work function, a
material having a low work function can be used for the electrode
functioning as an anode. Examples of the electron-accepting
substance are 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane
(abbreviation: F.sub.4-TCNQ), chloranil, and the like. A transition
metal oxide can also be used. In particular, an oxide of a metal
belonging to any of Groups 4 to 8 of the periodic table can be
suitably used. Specifically, vanadium oxide, niobium oxide,
tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,
manganese oxide, and rhenium oxide are preferable because of their
high electron-accepting properties. Among these, molybdenum oxide
is especially preferable as the electron-accepting substance
because it is stable in the air, has a low hygroscopic property,
and is easily handled.
[0175] As the substance with a hole-transport property used for the
composite material, any of a variety of organic compounds such as
an aromatic amine compound, a carbazole compound, an aromatic
hydrocarbon, and a high molecular compound (such as an oligomer, a
dendrimer, or a polymer) can be used. The organic compound used for
the composite material is preferably an organic compound having a
high hole-transport property. Specifically, a substance having a
hole mobility of 1.times.10.sup.-6 cm.sup.2/Vs or higher is
preferably used. Note that any other substance may be used as long
as the substance has a hole-transport property higher than an
electron-transport property. Specific examples of the organic
compound that can be used as a substance having a hole-transport
property in the composite material are given below.
[0176] Examples of the aromatic amine compound are
N,N'-di(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (abbreviation:
DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl
(abbreviation: DPAB),
N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-b-
iphenyl)-4,4'-diamine (abbreviation: DNTPD),
1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene
(abbreviation: DPA3B), and the like.
[0177] Specific examples of the carbazole compound that can be used
for the composite material are
3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole
(abbreviation: PCzPCA1),
3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole
(abbreviation: PCzPCA2),
3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole
(abbreviation: PCzPCN1), and the like.
[0178] Other examples of the carbazole compound that can be used
for the composite material are 4,4'-di(N-carbazolyl)biphenyl
(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene
(abbreviation: TCPB),
9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:
CzPA), 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene,
and the like.
[0179] Examples of the aromatic hydrocarbon that can be used for
the composite material are
2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),
2-tert-butyl-9,10-di(1-naphthyl)anthracene,
9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),
2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation:
t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),
9,10-diphenylanthracene (abbreviation: DPAnth),
2-tert-butylanthracene (abbreviation: t-BuAnth),
9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA),
2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,
9,10-bis[2-(1-naphthyl)phenyl]anthracene,
2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,
2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthryl,
10,10'-diphenyl-9,9'-bianthryl,
10,10'-bis(2-phenylphenyl)-9,9'-bianthryl,
10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl,
anthracene, tetracene, rubrene, perylene,
2,5,8,11-tetra(tert-butyl)perylene, and the like. Other examples
are pentacene, coronene, and the like. The aromatic hydrocarbon
having a hole mobility of 1.times.10.sup.-6 cm.sup.2/Vs or more and
having 14 to 42 carbon atoms is particularly preferable.
[0180] The aromatic hydrocarbon that can be used for the composite
material may have a vinyl skeleton. Examples of the aromatic
hydrocarbon having a vinyl group are
4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi),
9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation:
DPVPA), and the like.
[0181] Other examples are high molecular compounds such as
poly(N-vinylcarbazole) (abbreviation: PVK),
poly(4-vinyltriphenylamine) (abbreviation: PVTPA),
poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N-phenylamino}phenyl)metha-
crylamide] (abbreviation: PTPDMA), and
poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine]
(abbreviation: poly-TPD).
[0182] The hole-transport layer 112 is a layer containing a
substance having a hole-transport property. As the substance having
a hole-transport property, those given above as the substances
having hole-transport properties, which can be used for the above
composite material, can be used. Note that detailed description is
omitted to avoid repetition. Refer to the description of the
composite material.
[0183] The light-emitting layer 113 is a layer containing a
light-emitting substance. The light-emitting layer 113 may be
formed using a film containing only a light-emitting substance or a
film in which an emission center substance is dispersed in a host
material.
[0184] There is no particular limitation on a material that can be
used as the light-emitting substance or the emission center
substance in the light-emitting layer 113, and light emitted from
the material may be either fluorescence or phosphorescence.
Examples of the above light-emitting substance or the emission
center substance are fluorescent substances and phosphorescent
substances. Examples of the fluorescent substance are
N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N'-diphenylpyrene-1,6-diam-
ine (abbreviation: 1,6FLPAPrn),
N,N'-bis[4-(9H-carbazol-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine
(abbreviation: YGA2S),
4-(9H-carbazol-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine
(abbreviation: YGAPA),
4-(9H-carbazol-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine
(abbreviation: 2YGAPPA),
N,N'-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine
(abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene
(abbreviation: TBP),
4-(10-phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBAPA),
N,N'-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphe-
nyl-1,4-phenylenediamine] (abbreviation: DPABPA),
N,N'-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine
(abbreviation: 2PCAPPA),
N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediam-
ine (abbreviation: 2DPAPPA),
N,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetr-
aamine (abbreviation: DBC1), coumarin 30,
N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine
(abbreviation: 2PCAPA),
N-[9,10-bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-ami-
ne (abbreviation: 2PCABPhA),
N-(9,10-diphenyl-2-anthryl)-N,N',N'-triphenyl-1,4-phenylenediamine
(abbreviation: 2DPAPA),
N-[9,10-bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,N',N'-triphenyl-1,4-phenylen-
ediamine (abbreviation: 2DPABPhA),
9,10-bis(1,1'-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthr-
acen-2-amine (abbreviation: 2YGABPhA),
N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA), coumarin
545T, N,N'-diphenylquinacridone (abbreviation: DPQd), rubrene,
5,12-bis(1,1'-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation:
BPT),
2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)pro-
panedinitrile (abbreviation: DCM1),
2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethen-
yl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2),
N,N,N',N'-tetrakis(4-methylphenyl)tetracene-5,11-diamine
(abbreviation: p-mPhTD),
7,14-diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2--
a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD),
2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[i-
j]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile
(abbreviation: DCJTI),
2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[-
ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile
(abbreviation: DCJTB),
2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propane-
dinitrile (abbreviation: BisDCM),
2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benz-
o[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile
(abbreviation: BisDCJTM),
N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N'-diphenylpyrene-1,6-diam-
ine (abbreviation: 1,6FLPAPrn), and the like. Examples of
blue-emissive phosphorescent substances include an organometallic
iridium complex having a 4H-triazole skeleton, such as tris
{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-.kapp-
a.N2]phenyl-.kappa.C}iridium(III) (abbreviation:
[Ir(mpptz-dmp).sub.3]),
tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)
(abbreviation: [Ir(Mptz).sub.3]), or
tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium
(III) (abbreviation: [Ir(iPrptz-3b).sub.3]); an organometallic
iridium complex having a 1H-triazole skeleton, such as
tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III-
) (abbreviation: [Ir(Mptz1-mp).sub.3]) or
tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)
(abbreviation: [Ir(Prptz1-Me).sub.3]); an organometallic iridium
complex having an imidazole skeleton, such as
fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)
(abbreviation: [Ir(iPrpmi).sub.3]) or
tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridiu-
m(III) (abbreviation: Ir(dmpimpt-Me).sub.3); and an organometallic
iridium complex in which a phenylpyridine derivative having an
electron-withdrawing group is a ligand, such as
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium (III)
tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium(III)
picolinate (abbreviation: FIrpic),
bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C.sup.2'}iridium(III-
) picolinate (abbreviation: [Ir(CF.sub.3ppy).sub.2(pic)]), or
bis[2-(4',6'-difluorophenyl)pyridinato-N,C.sup.2']iridium(III)
acetylacetonate (abbreviation: FIr(acac)). Note that an
organometallic iridium complex having a 4H-triazole skeleton has
excellent reliability and emission efficiency and thus is
especially preferable. Examples of green-emissive phosphorescent
substances include an organometallic iridium complex having a
pyrimidine skeleton, such as
tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:
[Ir(mppm).sub.3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(tBuppm).sub.3)),
(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(mppm).sub.2(acac)]),
(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)
(abbreviation: [Ir(tBuppm).sub.2(acac)]),
(acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium
(III) (abbreviation: [Ir(nbppm).sub.2(acac)]),
(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iri-
dium(III) (abbreviation: [Ir(mpmppm).sub.2(acac)]), or
(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)
(abbreviation: [Ir(dppm).sub.2(acac)]); an organometallic iridium
complex having a pyrazine skeleton, such as
(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)
(abbreviation: [Ir(mppr-Me).sub.2(acac)]) or
(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)
(abbreviation: [Ir(mppr-iPr).sub.2(acac)]); an organometallic
iridium complex having a pyridine skeleton, such as
fac-tris(2-phenylpyridine)iridium (abbreviation: [Ir(ppy).sub.3]),
bis(2-phenylpyridinato-N,C.sup.2')iridium (III) acetylacetonate
(abbreviation: [Ir(ppy).sub.2(acac)]),
bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation:
[Ir(bzq).sub.2(acac)]), tris(benzo[h]quinolinato)iridium(III)
(abbreviation: [Ir(bzq).sub.3]),
tris(2-phenylquinolinato-N,C.sup.2')iridium (III) (abbreviation:
[Ir(pq).sub.3]), or bis(2-phenylquinolinato-N,C.sup.2')iridium(III)
acetylacetonate (abbreviation: [Ir(pq).sub.2(acac)]); and a rare
earth metal complex such as
tris(acetylacetonato)(monophenanthroline)terbium(III)
(abbreviation: Tb(acac).sub.3(Phen)). Note that an organometallic
iridium complex having a pyrimidine skeleton has distinctively high
reliability and emission efficiency and thus is especially
preferable. Examples of red-emissive phosphorescent substances
include an organometallic iridium complex having a pyrimidine
skeleton, such as
(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium
(III) (abbreviation: [Ir(5mdppm).sub.2(dibm)]),
bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)
(abbreviation: [Ir(5mdppm).sub.2(dpm)]), or
bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)
(abbreviation: [Ir(d1npm).sub.2(dpm)]); an organometallic iridium
complex having a pyrazine skeleton, such as
(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)
(abbreviation: [Ir(tppr).sub.2(acac)]),
bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium (III)
(abbreviation: [Ir(tppr).sub.2(dpm)]), or
(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)
(abbreviation: [Ir(Fdpq).sub.2(acac)]); an organometallic iridium
complex having a pyridine skeleton, such as
tris(1-phenylisoquinolinato-N,C.sup.2')iridium(III) (abbreviation:
[Ir(piq).sub.3]) or
bis(1-phenylisoquinolinato-N,C.sup.2')iridium(III)acetylacetonate
(abbreviation: [Ir(piq).sub.2(acac)]); a platinum complex such as
2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II)
(abbreviation: PtOEP);
[0185] and a rare earth metal complex such as
tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium
(III) (abbreviation: [Eu(DBM).sub.3(Phen)]) or
tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(-
III) (abbreviation: [Eu(TTA).sub.3(Phen)]). Note that an
organometallic iridium complex having a pyrimidine skeleton has
distinctively high reliability and emission efficiency and thus is
especially preferable. Further, because an organometallic iridium
complex having a pyrazine skeleton can provide red light emission
with favorable chromaticity, the use of the organometallic iridium
complex in a white light-emitting element improves a color
rendering property of the white light-emitting element. Note that
the organic compound of one embodiment of the present invention
described in Embodiment 1 exhibits light in blue to ultraviolet
regions, and thus can be used as an emission center substance.
[0186] The material that can be used as the light-emitting
substance or the emission center substance may be selected from
known substances as well as from the substances given above.
[0187] As a host material in which the emission center substance is
dispersed, the organic compound of one embodiment of the present
invention described in Embodiment 1 is preferably used.
[0188] Since the organic compound has a wide band gap and a high
triplet level, the organic compound can be suitably used as a host
material in which an emission center substance having a high-energy
excited state is dispersed, such as an emission center substance
emitting blue fluorescence or an emission center substance emitting
green phosphorescence. Needless to say, the organic compound can
also be used as a host material in which an emission center
substance emitting fluorescence of a wavelength longer than that of
blue light or an emission center substance emitting phosphorescence
of a wavelength longer than that of green light is dispersed. In
addition, it is effective to use the organic compound as a material
of a carrier-transport layer (preferably an electron-transport
layer) adjacent to a light-emitting layer. Since the organic
compound has a wide band gap or a high triplet level, even when the
emission center substance is a material emitting high-energy light,
such as a material emitting blue fluorescence or a material
emitting green phosphorescence, the energy of carriers that have
recombined in a host material can be effectively transferred to the
emission center substance. Thus, a light-emitting element having
high emission efficiency can be fabricated. Note that in the case
where the organic compound is used as a host material or a material
of a carrier-transport layer, the emission center substance is
preferably, but not limited to, a substance having a narrower band
gap than the organic compound or a substance having a lower singlet
level (S.sub.1 level) or a lower triplet level than the organic
compound.
[0189] In the case where the organic compound of one embodiment of
the present invention described in Embodiment 1 is not used for the
host material, a known material can be used for the host
material.
[0190] Examples of materials which can be used as the above host
material are given below. The following are examples of materials
having an electron-transport property: a metal complex such as
bis(10-hydroxybenzo[h]quinolinato)beryllium (II) (abbreviation:
BeBq.sub.2),
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)
(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation:
Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation:
ZnPBO), or bis[2-(2-benzothiazolyl)phenolato]zinc(II)
(abbreviation: ZnBTZ); a heterocyclic compound having a polyazole
skeleton such as
2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
(abbreviation: PBD),
3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole
(abbreviation: TAZ),
1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene
(abbreviation: OXD-7),
9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole
(abbreviation: CO11),
2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)
(abbreviation: TPBI), or
2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole
(abbreviation: mDBTBIm-II); a heterocyclic compound having a
diazine skeleton such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo
quinoxaline (abbreviation: 2mDBTPDBq-II),
2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline
(abbreviation: 2mDBTBPDBq-II),
2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline
(abbreviation: 2mCzBPDBq),
4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:
4,6mPnP2Pm), or 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine
(abbreviation: 4,6mDBTP2Pm-II); and a heterocyclic compound having
a pyridine skeleton such as
3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:
35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation:
TmPyPB). Among the above materials, a heterocyclic compound having
a diazine skeleton and a heterocyclic compound having a pyridine
skeleton have high reliability and are thus preferable.
Specifically, a heterocyclic compound having a diazine (pyrimidine
or pyrazine) skeleton has a high electron-transport property to
contribute to a reduction in driving voltage.
[0191] The following are examples of materials which have a
hole-transport property and can be used as the host material: a
compound having an aromatic amine skeleton such as
4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),
N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine
(abbreviation: TPD),
4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl
(abbreviation: BSPB),
4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:
BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine
(abbreviation: mBPAFLP),
4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBA1BP),
4,4'-diphenyl-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBBi1BP),
4-(1-naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBANB),
4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine
(abbreviation: PCBNBB),
9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-am-
ine (abbreviation: PCBAF), or
N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluoren-2-am-
ine (abbreviation: PCBASF); a compound having a carbazole skeleton
such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),
4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP),
3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP),
or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound
having a thiophene skeleton such as
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II), 2,
8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene
(abbreviation: DBTFLP-III), or
4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene
(abbreviation: DBTFLP-IV); and a compound having a furan skeleton
such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran)
(abbreviation: DBF3P-II) or
4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran
(abbreviation: mmDBFFLBi-II). Among the above materials, a compound
having an aromatic amine skeleton and a compound having a carbazole
skeleton are preferable because these compounds are highly reliable
and have high carrier-transport properties to contribute to a
reduction in driving voltage.
[0192] Note that a substance having a higher triplet level and a
wider band gap than the emission center substance is preferably
selected as the host material. The light-emitting layer may contain
a third substance in addition to the host material and the
phosphorescent substance.
[0193] Here, to achieve high emission efficiency of a
light-emitting element that uses a phosphorescent substance, energy
transfer between the host material and the phosphorescent substance
will be considered. Carrier recombination occurs in both the host
material and the phosphorescent substance; thus, efficient energy
transfer from the host material to the phosphorescent substance is
necessary to increase emission efficiency. Note that in this
explanation of energy transfer, a molecule providing excitation
energy is referred to as a host molecule, while a molecule
receiving the excitation energy is referred to as a guest
molecule.
[0194] When a phosphorescent compound is used as the guest
material, in an absorption spectrum of the phosphorescent compound,
an absorption band that is considered to contribute to light
emission most greatly is at an absorption wavelength corresponding
to direct transition from a ground state to a triplet excited state
and a vicinity of the absorption wavelength, which is on the
longest wavelength side. Therefore, it is considered preferable
that the emission spectrum (a fluorescence spectrum and a
phosphorescence spectrum) of the host material overlap with the
absorption band on the longest wavelength side in the absorption
spectrum of the phosphorescent compound.
[0195] Here, first, energy transfer from a host material in a
triplet excited state will be considered. It is preferable that, in
energy transfer from a triplet excited state, the phosphorescence
spectrum of the host material and the absorption band on the
longest wavelength side of the guest material have a large
overlap.
[0196] However, a question here is energy transfer from the host
molecule in the singlet excited state. In order to efficiently
perform not only energy transfer from the triplet excited state but
also energy transfer from the singlet excited state, it is clear
from the above-described discussion that the host material needs to
be designed such that not only its phosphorescence spectrum but
also its fluorescence spectrum overlaps with the absorption band on
the longest wavelength side of the guest material. In other words,
unless the host material is designed so as to have its fluorescence
spectrum in a position similar to that of its phosphorescence
spectrum, it is not possible to achieve efficient energy transfer
from the host material in both the singlet excited state and the
triplet excited state.
[0197] However, in general, the S.sub.1 level differs greatly from
the T.sub.1 level (S.sub.1 level >T.sub.1 level); therefore, the
fluorescence emission wavelength also differs greatly from the
phosphorescence emission wavelength (fluorescence emission
wavelength <phosphorescence emission wavelength). Accordingly,
it is extremely difficult to design a host material so as to have
its fluorescence spectrum in a position similar to that of its
phosphorescence spectrum.
[0198] Fluorescence is emitted from an energy level higher than
that of phosphorescence, and the T.sub.1 level of a host material
whose fluorescence spectrum corresponds to a wavelength close to an
absorption spectrum of a guest material on the longest wavelength
side is lower than the T.sub.1 level of the guest material.
[0199] Thus, in the case where a phosphorescent substance is used
as the emission center substance in the light-emitting element of
one embodiment of the present invention, it is preferable that the
light-emitting layer include a third substance in addition to the
host material and the emission center substance and that the host
material foul' an excited complex (also referred to as an exciplex)
in combination with the third substance.
[0200] In that case, at the time of recombination of carriers
(electrons and holes) in the light-emitting layer, the host
material and the third substance form an exciplex. A fluorescence
spectrum of the exciplex is on a longer wavelength side than a
fluorescence spectrum of the host material alone or the third
substance alone. Therefore, energy transfer from a singlet excited
state can be maximized while the T.sub.1 levels of the host
material and the third substance are kept higher than the T.sub.1
level of the guest material. In addition, the exciplex is in a
state where the T.sub.1 level and the S.sub.1 level are close to
each other; therefore, the fluorescence spectrum and the
phosphorescence spectrum exist at substantially the same position.
Accordingly, both the fluorescence spectrum and the phosphorescence
spectrum of the exciplex can have a large overlap with an
absorption corresponding to transition of the guest molecule from
the singlet ground state to the triplet excited state (a broad
absorption band of the guest molecule existing on the longest
wavelength side in the absorption spectrum), and thus a
light-emitting element having high energy transfer efficiency can
be obtained.
[0201] As the third substance, the above material which can be used
as the host material or additives can be used. There is no
particular limitation on the host materials and the third substance
as long as they can form an exciplex; a combination of a compound
which readily accepts electrons (a compound having an
electron-transport property) and a compound which readily accepts
holes (a compound having a hole-transport property) is preferably
employed.
[0202] In the case where a compound having an electron-transport
property and a compound having a hole-transport property are used
for the host material and the third substance, carrier balance can
be controlled by the mixture ratio of the compounds. Specifically,
the ratio of the host material to the third substance (or additive)
is preferably from 1:9 to 9:1. Note that in that case, the
following structure may be employed: a light-emitting layer in
which one kind of an emission center substance is dispersed is
divided into two layers, and the two layers have different mixture
ratios of the host material to the third substance. With this
structure, the carrier balance of the light-emitting element can be
optimized, so that the lifetime of the light-emitting element can
be improved. Furthermore, one of the light-emitting layers may be a
hole-transport layer and the other of the light-emitting layers may
be an electron-transport layer.
[0203] In the case where the light-emitting layer having the
above-described structure is formed using a plurality of materials,
the light-emitting layer can be formed using co-evaporation by a
vacuum evaporation method; or an inkjet method, a spin coating
method, a dip coating method, or the like with a solution of the
materials.
[0204] The electron-transport layer 114 is a layer containing a
substance having an electron-transport property. For example, the
electron-transport layer 114 is formed using a metal complex having
a quinoline skeleton or a benzoquinoline skeleton, such as
tris(8-quinolinolato)aluminum (abbreviation: Alq),
tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq.sub.3),
bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation:
BeBq.sub.2), or
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum
(abbreviation: BAlq), or the like. A metal complex having an
oxazole-based or thiazole-based ligand, such as
bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation:
Zn(BOX).sub.2) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc
(abbreviation: Zn(BTZ).sub.2), or the like can also be used. Other
than the metal complexes,
2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
(abbreviation: PBD),
1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene
(abbreviation: OXD-7),
3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole
(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),
bathocuproine (abbreviation: BCP), or the like can also be used.
The substances given here are mainly ones having an electron
mobility of 10.sup.-6 cm.sup.2/Vs or higher. Note that any
substance other than the above substances may be used for the
electron-transport layer as long as the substance has an
electron-transport property higher than a hole-transport
property.
[0205] The organic compound of one embodiment of the present
invention described in Embodiment 1 may also be used as a material
contained in the electron-transport layer 114. The organic compound
has a wide band gap and a high T.sub.1 level and thus can
effectively prevent transfer of excitation energy in the
light-emitting layer to the electron-transport layer 114 to inhibit
a reduction in emission efficiency due to the excitation energy
transfer, and allow a light-emitting element having high emission
efficiency to be fabricated. Moreover, the organic compound has a
high carrier-transport property; thus, a light-emitting element
having low driving voltage can be provided.
[0206] The electron-transport layer is not limited to a single
layer, and may be a stack including two or more layers containing
any of the above substances.
[0207] Between the electron-transport layer and the light-emitting
layer, a layer that controls transport of electron carriers may be
provided. This is a layer formed by addition of a small amount of a
substance having a high electron-trapping property to the
aforementioned materials having a high electron-transport property,
and the layer is capable of adjusting carrier balance by retarding
transport of electron carriers. Such a structure is very effective
in preventing a problem (such as a reduction in element lifetime)
caused when electrons pass through the light-emitting layer.
[0208] It is preferable that the host material in the
light-emitting layer and a material of the electron-transport layer
have the same skeleton, in which case transfer of carriers can be
smooth and thus the driving voltage can be reduced. Moreover, it is
effective that the host material and the material of the
electron-transport layer be the same material.
[0209] The electron-injection layer 115 may be provided in contact
with the second electrode 102 between the electron-transport layer
114 and the second electrode 102. For the electron-injection layer
115, lithium, calcium, lithium fluoride (LiF), cesium fluoride
(CsF), calcium fluoride (CaF.sub.2), or the like can be used. A
composite material of a substance having an electron-transport
property and a substance exhibiting an electron-donating property
(hereinafter, simply referred to as electron-donating substance)
with respect to the substance having an electron-transport property
can also be used. Examples of the electron-donating substance
include an alkali metal, an alkaline earth metal, and compounds
thereof. Note that such a composite material is preferably used for
the electron-injection layer 115, in which case electrons are
injected efficiently from the second electrode 102. With this
structure, a conductive material as well as a material having a low
work function can be used for the cathode.
[0210] For the electrode functioning as a cathode, any of metals,
alloys, electrically conductive compounds, and mixtures thereof
which have a low work function (specifically, a work function of
3.8 eV or less) or the like can be used. Specific examples of such
a cathode material are elements belonging to Groups 1 and 2 of the
periodic table, such as lithium (Li), cesium (Cs), magnesium (Mg),
calcium (Ca), and strontium (Sr), alloys thereof (e.g., MgAg and
AlLi), rare earth metals such as europium (Eu) and ytterbium (Yb),
alloys thereof, and the like. However, when the electron-injection
layer is provided between the second electrode 102 and the
electron-transport layer, for the second electrode 102, any of a
variety of conductive materials such as Al, Ag, ITO, or indium
oxide-tin oxide containing silicon or silicon oxide can be used
regardless of the work function. Films of these electrically
conductive materials can be formed by a sputtering method, an
inkjet method, a spin coating method, or the like.
[0211] Any of a variety of methods can be used to form the EL layer
103 regardless whether it is a dry process or a wet process. For
example, a vacuum evaporation method, an inkjet method, a spin
coating method, or the like may be used. Different formation
methods may be used for the electrodes or the layers.
[0212] In addition, the electrode may be formed by a wet method
using a sol-gel method, or by a wet method using paste of a metal
material. Alternatively, the electrode may be formed by a dry
method such as a sputtering method or a vacuum evaporation
method.
[0213] Note that the structure of the EL layer provided between the
first electrode 101 and the second electrode 102 is not limited to
the above structure. However, it is preferable that a
light-emitting region where holes and electrons recombine be
positioned away from the first electrode 101 and the second
electrode 102 so as to prevent quenching due to the proximity of
the light-emitting region and a metal used for an electrode or a
carrier-injection layer.
[0214] Further, in order that transfer of energy from an exciton
generated in the light-emitting layer can be inhibited, preferably,
the hole-transport layer and the electron-transport layer which are
in direct contact with the light-emitting layer, particularly a
carrier-transport layer in contact with a side closer to the
light-emitting region in the light-emitting layer 113 is formed
with a substance having a wider band gap than the emission center
substance of the light-emitting layer or the light-emitting
substance included in the light-emitting layer.
[0215] In the light-emitting element having the above-described
structure, current flows due to a potential difference between the
first electrode 101 and the second electrode 102, and holes and
electrons recombine in the light-emitting layer 113 which contains
a substance having a high light-emitting property, so that light is
emitted. In other words, a light-emitting region is formed in the
light-emitting layer 113.
[0216] Light is extracted out through one or both of the first
electrode 101 and the second electrode 102. Therefore, one or both
of the first electrode 101 and the second electrode 102 are
light-transmitting electrodes. In the case where only the first
electrode 101 is a light-transmitting electrode, light is extracted
from the substrate side through the first electrode 101. In
contrast, when only the second electrode 102 is a
light-transmitting electrode, light is extracted from the side
opposite to the substrate side through the second electrode 102. In
the case where both the first electrode 101 and the second
electrode 102 are light-transmitting electrodes, light is extracted
from both the substrate side and the side opposite to the substrate
side through the first electrode 101 and the second electrode
102.
[0217] Since the light-emitting element of this embodiment is
formed using the organic compound of one embodiment of the present
invention having a wide band gap, efficient light emission can be
obtained even if the emission center substance is a substance that
emits blue fluorescence or green phosphorescence, and the
light-emitting element can have a high emission efficiency. Thus, a
light-emitting element with lower power consumption can be
provided. Further, the organic compound has a high
carrier-transport property; thus, a light-emitting element having
low driving voltage can be provided.
[0218] Such a light-emitting element may be fabricated using a
substrate made of glass, plastic, or the like as a support. A
plurality of such light-emitting elements are formed over one
substrate, thereby forming a passive matrix light-emitting device.
Alternatively, a transistor may be formed over a substrate made of
glass, plastic, or the like, and the light-emitting element may be
fabricated over an electrode electrically connected to the
transistor. In this manner, an active matrix light-emitting device
in which the driving of the light-emitting element is controlled by
the transistor can be fabricated.
Embodiment 4
[0219] In this embodiment is described one mode of a light-emitting
element having a structure in which a plurality of light-emitting
units are stacked (hereinafter, also referred to as stacked-type
element), with reference to FIG. 1B. This light-emitting element
includes a plurality of light-emitting units between a first
electrode and a second electrode. Each light-emitting unit can have
the same structure as the EL layer 103 which is described in
Embodiment 3. In other words, the light-emitting element described
in Embodiment 3 is a light-emitting element having one
light-emitting unit while the light-emitting element described in
this embodiment is a light-emitting element having a plurality of
light-emitting units.
[0220] In FIG. 1B, a first light-emitting unit 511 and a second
light-emitting unit 512 are stacked between a first electrode 501
and a second electrode 502, and a charge generation layer 513 is
provided between the first light-emitting unit 511 and the second
light-emitting unit 512. The first electrode 501 and the second
electrode 502 respectively correspond to the first electrode 101
and the second electrode 102 in Embodiment 3, and materials
described in Embodiment 3 can be used. Further, the structures of
the first light-emitting unit 511 and the second light-emitting
unit 512 may be the same or different.
[0221] The charge generation layer 513 includes a composite
material of an organic compound and a metal oxide. As this
composite material of an organic compound and a metal oxide, the
composite material that can be used for the hole-injection layer
and described in Embodiment 3 can be used. As the organic compound,
any of a variety of compounds such as aromatic amine compounds,
carbazole compounds, aromatic hydrocarbons, and high molecular
compounds (oligomers, dendrimers, polymers, or the like) can be
used. Note that the organic compound preferably has a hole mobility
of 1.times.10.sup.-6 cm.sup.2/Vs or more. However, any other
substance may be used as long as the substance has a hole-transport
property higher than an electron-transport property. Since a
composite material of an organic compound and a metal oxide is
excellent in carrier-injection property and carrier-transport
property, low voltage driving and low current driving can be
achieved. Note that in the light-emitting unit whose anode side
surface is in contact with the charge generation layer, a
hole-injection layer is not necessarily provided because the charge
generation layer can also function as the hole-injection layer.
[0222] The charge generation layer 513 may have a stacked-layer
structure of a layer containing the composite material of an
organic compound and a metal oxide and a layer containing another
material. For example, a layer containing the composite material of
an organic compound and a metal oxide may be combined with a layer
containing a compound of a substance selected from
electron-donating substances and a compound having a high
electron-transport property. Moreover, the charge generation layer
513 may be formed by combining a layer containing the composite
material of an organic compound and a metal oxide with a
transparent conductive film.
[0223] The charge generation layer 513 provided between the first
light-emitting unit 511 and the second light-emitting unit 512 may
have any structure as long as electrons can be injected to a
light-emitting unit on one side and holes can be injected to a
light-emitting unit on the other side when voltage is applied
between the first electrode 501 and the second electrode 502. For
example, in FIG. 1B, any layer can be used as the charge generation
layer 513 as long as the layer injects electrons into the first
light-emitting unit 511 and holes into the second light-emitting
unit 512 when voltage is applied such that the potential of the
first electrode is higher than that of the second electrode.
[0224] Although the light-emitting element having two
light-emitting units is described in this embodiment, the present
invention can be similarly applied to a light-emitting element in
which three or more light-emitting units are stacked. With a
plurality of light-emitting units partitioned by the charge
generation layer between a pair of electrodes, as in the
light-emitting element according to this embodiment, light with
high luminance can be obtained while current density is kept low;
thus, a light-emitting element having a long lifetime can be
obtained. In addition, a low power consumption light-emitting
device which can be driven at low voltage can be achieved.
[0225] By making the light-emitting units emit light of different
colors from each other, the light-emitting element can provide
light emission of a desired color as a whole. For example, by
forming a light-emitting element having two light-emitting units
such that the emission color of the first light-emitting unit and
the emission color of the second light-emitting unit are
complementary colors, the light-emitting element can provide white
light emission as a whole. Note that the word "complementary" means
color relationship in which an achromatic color is obtained when
colors are mixed. In other words, when light obtained from
substances which emit light of complementary colors are mixed,
white light emission can be obtained. Further, the same can be
applied to a light-emitting element having three light-emitting
units. For example, the light-emitting element as a whole can
provide white light emission when the emission color of the first
light-emitting unit is red, the emission color of the second
light-emitting unit is green, and the emission color of the third
light-emitting unit is blue. Alternatively, in the case of
employing a light-emitting element in which a phosphorescent
emission center substance is used for a light-emitting layer of one
light-emitting unit and a fluorescent emission center substance is
used for a light-emitting layer of the other light-emitting unit,
both fluorescence and phosphorescence can be efficiently emitted
from the light-emitting element. For example, when red
phosphorescence and green phosphorescence are obtained from one
light-emitting unit and blue fluorescence is obtained from the
other light-emitting unit, white light with high emission
efficiency can be obtained.
[0226] Since the light-emitting element of this embodiment contains
the organic compound of one embodiment of the present invention,
the light-emitting element can have high emission efficiency or
operate at low driving voltage. In addition, since light emission
with high color purity which is derived from the emission center
substance can be obtained from the light-emitting unit including
the organic compound, color adjustment of the light-emitting
element as a whole is easy.
[0227] Note that this embodiment can be combined with any of other
embodiments as appropriate.
Embodiment 5
[0228] In this embodiment, explanation will be given with reference
to FIGS. 3A and 3B of an example of the light-emitting device
fabricated using a light-emitting element including the organic
compound of one embodiment of the present invention. Note that FIG.
3A is a top view of the light-emitting device and FIG. 3B is a
cross-sectional view taken along the lines A-B and C-D in FIG. 3A.
This light-emitting device includes a driver circuit portion
(source side driver circuit) 601, a pixel portion 602, and a driver
circuit portion (gate side driver circuit) 603, which control light
emission of a light-emitting element 618 and denoted by dotted
lines. A reference numeral 604 denotes a sealing substrate; 605, a
sealing material; and 607, a space surrounded by the sealing
material 605.
[0229] Reference numeral 608 denotes a wiring for transmitting
signals to be input to the source side driver circuit 601 and the
gate side driver circuit 603 and receiving signals such as a video
signal, a clock signal, a start signal, and a reset signal from a
flexible printed circuit (FPC) 609 serving as an external input
terminal. Although only the FPC is illustrated here, a printed
wiring board (PWB) may be attached to the FPC. The light-emitting
device in the present specification includes, in its category, not
only the light-emitting device itself but also the light-emitting
device provided with the FPC or the PWB.
[0230] Next, a cross-sectional structure is explained with
reference to FIG. 3B. The driver circuit portion and the pixel
portion are formed over an element substrate 610; here, the source
side driver circuit 601, which is a driver circuit portion, and one
of the pixels in the pixel portion 602 are shown.
[0231] As the source side driver circuit 601, a CMOS circuit in
which an n-channel TFT 623 and a p-channel TFT 624 are combined is
formed. In addition, the driver circuit may be formed with any of a
variety of circuits such as a CMOS circuit, a PMOS circuit, and an
NMOS circuit. Although a driver integrated type in which the driver
circuit is formed over the substrate is illustrated in this
embodiment, the driver circuit is not necessarily formed over the
substrate, and the driver circuit can be formed outside, not over
the substrate.
[0232] The pixel portion 602 includes a plurality of pixels
including a switching TFT 611, a current controlling TFT 612, and a
first electrode 613 electrically connected to a drain of the
current controlling TFT 612. Note that to cover an end portion of
the first electrode 613, an insulator 614 is formed, for which a
positive photosensitive resin film is used here.
[0233] Note that a structure of the transistor is not particularly
limited. Either a staggered TFT or an inverted staggered TFT may be
employed. In addition, the crystallinity of a semiconductor used
for the TFT is not particularly limited. In addition, a driver
circuit formed in a TFT substrate may be formed with n-type TFTs
and p-type TFTs, or with either n-type TFTs or p-type TFTs. The
semiconductor layer for forming the TFTs may be formed using any
material as long as the material exhibits semiconductor
characteristics; for example, an element belonging to Group 14 of
the periodic table such as silicon (Si) and germanium (Ge), a
compound such as gallium arsenide and indium phosphide, an oxide
such as zinc oxide and tin oxide, and the like can be given. For
the oxide exhibiting semiconductor characteristics (oxide
semiconductor), composite oxide of an element selected from indium,
gallium, aluminum, zinc, and tin can be used. Examples thereof are
zinc oxide (ZnO), indium oxide containing zinc oxide (indium zinc
oxide), and oxide containing indium oxide, gallium oxide, and zinc
oxide (IGZO: indium gallium zinc oxide). An organic semiconductor
may also be used. The semiconductor layer may have either a
crystalline structure or an amorphous structure. Specific examples
of the crystalline semiconductor layer are a single crystal
semiconductor, a polycrystalline semiconductor, and a
microcrystalline semiconductor.
[0234] In order to improve coverage with a film formed over the
insulator 614, the insulator 614 is formed to have a curved surface
with curvature at its upper or lower end portion. For example, in
the case where a positive photosensitive acrylic resin is used for
a material of the insulator 614, only the upper end portion of the
insulator 614 preferably has a surface with a curvature radius (0.2
.mu.m to 3 .mu.m). As the insulator 614, either a negative
photosensitive material or a positive photosensitive material can
be used.
[0235] An EL layer 616 and a second electrode 617 are formed over
the first electrode 613. As a material used for the first electrode
613 which functions as an anode, a material having a high work
function is preferably used. For example, a single-layer film of an
ITO film, an indium tin oxide film containing silicon, an indium
oxide film containing zinc oxide at 2 wt % to 20 wt %, a titanium
nitride film, a chromium film, a tungsten film, a zinc film, a
platinum film, or the like, a stack including a titanium nitride
film and a film containing aluminum as its main component, a stack
including three layers of a titanium nitride film, a film
containing aluminum as its main component, and a titanium nitride
film, or the like can be used. The stacked structure achieves low
wiring resistance, a favorable ohmic contact, and a function as an
anode.
[0236] The EL layer 616 is formed by any of a variety of methods
such as an evaporation method using an evaporation mask, an inkjet
method, and a spin coating method. The EL layer 616 contains the
organic compound of one embodiment of the present invention.
Further, for another material included in the EL layer 616, any of
low molecular-weight compounds and polymeric compounds (including
oligomers and dendrimers) may be used.
[0237] As a material used for the second electrode 617, which is
formed over the EL layer 616 and functions as a cathode, a material
having a low work function (e.g., Al, Mg, Li, Ca, or an alloy or
compound thereof, such as MgAg, MgIn, or AlLi) is preferably used.
In the case where light generated in the EL layer 616 passes
through the second electrode 617, a stack including a thin metal
film and a transparent conductive film (e.g., ITO, indium oxide
containing zinc oxide at 2 wt % to 20 wt %, indium tin oxide
containing silicon, or zinc oxide (ZnO)) is preferably used for the
second electrode 617.
[0238] Note that the light-emitting element is formed with the
first electrode 613, the EL layer 616, and the second electrode
617. The light-emitting element has the structure described in
Embodiment 3 or 4. In the light-emitting device of this embodiment,
the pixel portion, which includes a plurality of light-emitting
elements, may include both the light-emitting element with the
structure described in Embodiment 3 or 4 and a light-emitting
element with a structure other than those.
[0239] The sealing substrate 604 is attached to the element
substrate 610 with the sealing material 605, so that the
light-emitting element 618 is provided in the space 607 surrounded
by the element substrate 610, the sealing substrate 604, and the
sealing material 605. The space 607 is filled with filler. The
filler may be an inert gas (such as nitrogen or argon), or a resin
and/or a desiccant.
[0240] An epoxy-based resin or glass frit is preferably used for
the sealing material 605. It is preferable that such a material do
not transmit moisture or oxygen as much as possible. As the sealing
substrate 604, a glass substrate, a quartz substrate, or a plastic
substrate formed of fiber reinforced plastic (FRP), poly(vinyl
fluoride) (PVF), a polyester, an acrylic resin, or the like can be
used.
[0241] As described above, the light-emitting device fabricated by
using the light-emitting element that contains the organic compound
of one embodiment of the present invention can be obtained.
[0242] FIGS. 4A and 4B illustrate examples of light-emitting
devices in which full color display is achieved by forming a
light-emitting element exhibiting white light emission and
providing a coloring layer (a color filter) and the like. In FIG.
4A, a substrate 1001, a base insulating film 1002, a gate
insulating film 1003, gate electrodes 1006, 1007, and 1008, a first
interlayer insulating film 1020, a second interlayer insulating
film 1021, a peripheral portion 1042, a pixel portion 1040, a
driver circuit portion 1041, first electrodes 1024W, 1024R, 1024G,
and 1024B of light-emitting elements, a partition wall 1025, an EL
layer 1028, a second electrode 1029 of the light-emitting elements,
a sealing substrate 1031, a sealant 1032, and the like are
illustrated.
[0243] In FIG. 4A, coloring layers (a red coloring layer 1034R, a
green coloring layer 1034G, and a blue coloring layer 1034B) are
provided on a transparent base material 1033. Further, a black
layer (a black matrix) 1035 may be additionally provided. The
transparent base material 1033 provided with the coloring layers
and the black layer is positioned and fixed to the substrate 1001.
Note that the coloring layers and the black layer are covered with
an overcoat layer 1036. In FIG. 4A, light emitted from some of the
light-emitting layers does not pass through the coloring layers,
while light emitted from the others of the light-emitting layers
passes through the coloring layers. Since light which does not pass
through the coloring layers is white and light which passes through
any one of the coloring layers is red, blue, or green, an image can
be displayed using pixels of the four colors.
[0244] FIG. 4B illustrates an example in which coloring layers (a
red coloring layer 1034R, a green coloring layer 1034G, and a blue
coloring layer 1034B) are formed between the gate insulating film
1003 and the first interlayer insulating film 1020. As shown in
FIG. 4B, the coloring layers may be provided between the substrate
1001 and the sealing substrate 1031.
[0245] The above-described light-emitting device has a structure in
which light is extracted from the substrate 1001 side where the
TFTs are formed (a bottom emission structure), but may have a
structure in which light is extracted from the sealing substrate
1031 side (a top emission structure). FIG. 5 is a cross-sectional
view of a light-emitting device having a top emission structure. In
this case, a substrate which does not transmit light can be used as
the substrate 1001. The process up to the step of forming a
connection electrode which connects the TFT and the anode of the
light-emitting element is performed in a manner similar to that of
the light-emitting device having a bottom emission structure. Then,
a third interlayer insulating film 1037 is formed to cover an
electrode 1022. This insulating film may have a planarization
function. The third interlayer insulating film 1037 can be formed
using a material similar to that of the second interlayer
insulating film, and can alternatively be formed using any other
known material.
[0246] The first electrodes 1024W, 1024R, 1024G, and 1024B of the
light-emitting elements each serve as an anode here, but may serve
as a cathode. Further, in the case of a light-emitting device
having a top emission structure as illustrated in FIG. 5, the first
electrodes are preferably reflective electrodes. The EL layer 1028
is formed to have a structure similar to the structure described in
Embodiment 3 or 4, with which white light emission can be
obtained.
[0247] In FIGS. 4A and 4B and FIG. 5, the structure of the EL layer
for providing white light emission can be achieved by, for example,
using a plurality of light-emitting layers or using a plurality of
light-emitting units. Note that the structure to provide white
light emission is not limited to the above.
[0248] In the case of a top emission structure as illustrated in
FIG. 5, sealing can be performed with the sealing substrate 1031 on
which the coloring layers (the red coloring layer 1034R, the green
coloring layer 1034G, and the blue coloring layer 1034B) are
provided. The sealing substrate 1031 may be provided with the black
layer (the black matrix) 1035 which is positioned between pixels.
The coloring layers (the red coloring layer 1034R, the green
coloring layer 1034G, and the blue coloring layer 1034B) and the
black layer (the black matrix) may be covered with the overcoat
layer. Note that a light-transmitting substrate is used as the
sealing substrate 1031.
[0249] Although an example in which full color display is performed
using four colors of red, green, blue, and white is shown here,
there is no particular limitation and full color display using
three colors of red, green, and blue may be performed.
[0250] Since the light-emitting device of this embodiment uses the
light-emitting element described in Embodiment 3 or 4 (the
light-emitting element including the organic compound of one
embodiment of the present invention), the light-emitting device can
have favorable characteristics. Specifically, the organic compound
of one embodiment of the present invention has a wide band gap and
a high triplet level and can inhibit energy transfer from a
light-emitting substance; thus, a light-emitting element having
high emission efficiency can be provided, leading to a
light-emitting device having reduced power consumption.
Furthermore, the organic compound of one embodiment of the present
invention has a high carrier-transport property, so that a
light-emitting element with low driving voltage can be provided,
leading to a light-emitting device with low driving voltage.
[0251] An active matrix light-emitting device is described above,
whereas a passive matrix light-emitting device is described below.
FIGS. 6A and 6B illustrate a passive matrix light-emitting device
fabricated by application of the present invention. FIG. 6A is a
perspective view of the light-emitting device, and FIG. 6B is a
cross-sectional view of FIG. 6A taken along line X-Y. In FIGS. 6A
and 6B, over a substrate 951, an EL layer 955 is provided between
an electrode 952 and an electrode 956. An edge portion of the
electrode 952 is covered with an insulating layer 953. A partition
layer 954 is provided over the insulating layer 953. The sidewalls
of the partition layer 954 slope so that the distance between one
sidewall and the other sidewall gradually decreases toward the
surface of the substrate. In other words, a cross section taken
along the direction of the short side of the partition layer 954 is
trapezoidal, and the base (a side which is in the same direction as
a plane direction of the insulating layer 953 and in contact with
the insulating layer 953) is shorter than the upper side (a side
which is in the same direction as the plane direction of the
insulating layer 953 and not in contact with the insulating layer
953). By providing the partition layer 954 in such a manner, a
defect of the light-emitting element due to static electricity or
the like can be prevented. The passive matrix light-emitting device
can also be driven with low power consumption, by including the
light-emitting element described in Embodiment 3 or 4 (the
light-emitting element including the organic compound of one
embodiment of the present invention) capable of operating at low
driving voltage. Furthermore, the passive matrix light-emitting
device can be driven with low power consumption by including the
light-emitting element using the organic compound of one embodiment
of the present invention and having a high emission efficiency (the
light-emitting element described in Embodiment 3 or 4).
[0252] Since many minute light-emitting elements arranged in a
matrix in the light-emitting device described above can each be
controlled, the light-emitting device can be suitably used as a
display device for displaying images.
Embodiment 6
[0253] In this embodiment, electronic devices each including the
light-emitting element described in Embodiment 3 or 4 will be
described. The light-emitting element described in Embodiment 3 or
4 includes the organic compound of one embodiment of the present
invention and thus has reduced power consumption; as a result, the
electronic devices described in this embodiment can each include a
display portion having reduced power consumption. In addition, the
electronic devices can have low driving voltage since the
light-emitting element described in Embodiment 3 or 4 has low
driving voltage.
[0254] Examples of the electronic device to which the above
light-emitting element is applied include television devices (also
referred to as TV or television receivers), monitors for computers
and the like, cameras such as digital cameras and digital video
cameras, digital photo frames, mobile phones (also referred to as
cellular phones or cellular phone devices), portable game machines,
portable information terminals, audio playback devices, large game
machines such as pachinko machines, and the like. Specific examples
of these electronic devices are given below.
[0255] FIG. 7A illustrates an example of a television device. In
the television device, a display portion 7103 is incorporated in a
housing 7101. In addition, here, the housing 7101 is supported by a
stand 7105. The display portion 7103 enables display of images and
includes light-emitting elements which are the same as the
light-emitting element described in Embodiment 3 or 4 and arranged
in a matrix.
[0256] The television device can be operated with an operation
switch of the housing 7101 or a separate remote controller 7110.
With operation keys 7109 of the remote controller 7110, channels
and volume can be controlled and images displayed on the display
portion 7103 can be controlled. Furthermore, the remote controller
7110 may be provided with a display portion 7107 for displaying
data output from the remote controller 7110.
[0257] Note that the television device is provided with a receiver,
a modem, and the like. With the use of the receiver, general
television broadcasting can be received. Moreover, when the
television device is connected to a communication network with or
without wires via the modem, one-way (from a sender to a receiver)
or two-way (between a sender and a receiver or between receivers)
information communication can be performed.
[0258] FIG. 7B illustrates a computer, which includes a main body
7201, a housing 7202, a display portion 7203, a keyboard 7204, an
external connection port 7205, a pointing device 7206, and the
like. Note that this computer is fabricated by using light-emitting
elements arranged in a matrix in the display portion 7203, which
are the same as that described in Embodiment 3 or 4.
[0259] FIG. 7C illustrates a portable game machine having two
housings, a housing 7301 and a housing 7302, which are connected
with a joint portion 7303 so that the portable game machine can be
opened or folded. A display portion 7304 including light-emitting
elements which are the same as that described in Embodiment 3 or 4
and arranged in a matrix is incorporated in the housing 7301, and a
display portion 7305 is incorporated in the housing 7302. In
addition, the portable game machine illustrated in FIG. 7C includes
a speaker portion 7306, a recording medium insertion portion 7307,
an LED lamp 7308, an input unit (an operation key 7309, a
connection terminal 7310, a sensor 7311 (a sensor having a function
of measuring force, displacement, position, speed, acceleration,
angular velocity, rotational frequency, distance, light, liquid,
magnetism, temperature, chemical substance, sound, time, hardness,
electric field, current, voltage, electric power, radiation, flow
rate, humidity, gradient, oscillation, odor, or infrared rays), and
a microphone 7312), and the like. Needless to say, the structure of
the portable game machine is not limited to the above as far as the
display portion including light-emitting elements which are the
same as that described in Embodiment 3 or 4 and arranged in a
matrix is used as at least either the display portion 7304 or the
display portion 7305, or both, and the structure can include other
accessories as appropriate. The portable game machine illustrated
in FIG. 7C has a function of reading out a program or data stored
in a storage medium to display it on the display portion, and a
function of sharing information with another portable game machine
by wireless communication. The portable game machine illustrated in
FIG. 7C can have a variety of functions without limitation to the
above.
[0260] FIG. 7D illustrates an example of a mobile phone. A mobile
phone is provided with a display portion 7402 incorporated in a
housing 7401, operation buttons 7403, an external connection port
7404, a speaker 7405, a microphone 7406, and the like. Note that
the mobile phone has the display portion 7402 including
light-emitting elements which are the same as that described in
Embodiment 3 or 4 and arranged in a matrix.
[0261] When the display portion 7402 of the mobile phone
illustrated in FIG. 7D is touched with a finger or the like, data
can be input into the mobile phone. In this case, operations such
as making a call and creating e-mail can be performed by touching
the display portion 7402 with a finger or the like.
[0262] There are mainly three screen modes of the display portion
7402. The first mode is a display mode mainly for displaying an
image. The second mode is an input mode mainly for inputting
information such as characters. The third mode is a
display-and-input mode in which two modes of the display mode and
the input mode are combined.
[0263] For example, in the case of making a call or creating
e-mail, a character input mode mainly for inputting characters is
selected for the display portion 7402 so that characters displayed
on a screen can be input. In this case, it is preferable to display
a keyboard or number buttons on almost the entire screen of the
display portion 7402.
[0264] When a detection device including a sensor for detecting
inclination, such as a gyroscope or an acceleration sensor, is
provided inside the mobile phone, display on the screen of the
display portion 7402 can be automatically changed by determining
the orientation of the mobile phone (whether the mobile phone is
placed horizontally or vertically for a landscape mode or a
portrait mode).
[0265] The screen modes are switched by touch on the display
portion 7402 or operation with the operation buttons 7403 of the
housing 7401. The screen modes can be switched depending on the
kind of images displayed on the display portion 7402. For example,
when a signal of an image displayed on the display portion is a
signal of moving image data, the screen mode is switched to the
display mode. When the signal is a signal of text data, the screen
mode is switched to the input mode.
[0266] Moreover, in the input mode, when input by touching the
display portion 7402 is not performed for a certain period while a
signal detected by an optical sensor in the display portion 7402 is
detected, the screen mode may be controlled so as to be switched
from the input mode to the display mode.
[0267] The display portion 7402 may function as an image sensor.
For example, an image of a palm print, a fingerprint, or the like
is taken by touch on the display portion 7402 with the palm or the
finger, whereby personal authentication can be performed. Further,
by providing a backlight or a sensing light source which emits
near-infrared light in the display portion, an image of a finger
vein, a palm vein, or the like can be taken.
[0268] Note that the structure described in this embodiment can be
combined with any of the structures described in Embodiments 1 to 5
as appropriate.
[0269] As described above, the application range of the
light-emitting device having the light-emitting element described
in Embodiment 3 or 4 which includes the organic compound of one
embodiment of the present invention is wide so that this
light-emitting device can be applied to electronic devices in a
variety of fields. By using the organic compound of one embodiment
of the present invention, an electronic device having reduced power
consumption and low driving voltage can be obtained.
[0270] The light-emitting element including the organic compound of
one embodiment of the present invention can also be used for a
light source device. One mode of application of the light-emitting
element including the organic compound of one embodiment of the
present invention to a light source device is described with
reference to FIG. 8. Note that the light source device includes a
light-emitting element including the organic compound of one
embodiment of the present invention as a light irradiation unit and
at least includes an input-output terminal portion which supplies
current to the light-emitting element. Further, the light-emitting
element is preferably shielded from the outside atmosphere by
sealing.
[0271] FIG. 8 illustrates an example of a liquid crystal display
device using the light-emitting elements including the organic
compound of one embodiment of the present invention for a
backlight. The liquid crystal display device illustrated in FIG. 8
includes a housing 901, a liquid crystal layer 902, a backlight
903, and a housing 904. The liquid crystal layer 902 is connected
to a driver IC 905. The light-emitting element including the above
organic compound is used in the backlight 903, to which current is
supplied through a terminal 906.
[0272] The light-emitting element including the above organic
compound is used for the backlight of the liquid crystal display
device; thus, the backlight can have reduced power consumption. In
addition, the use of the light-emitting element including the above
organic compound enables fabrication of a planar-emission lighting
device and further a larger-area planar-emission lighting device;
therefore, the backlight can be a larger-area backlight, and the
liquid crystal display device can also be a larger-area device.
Furthermore, the backlight using the light-emitting element
including the above organic compound can be thinner than a
conventional one; accordingly, the display device can also be
thinner.
[0273] FIG. 9 illustrates an example in which the light-emitting
element including the organic compound of one embodiment of the
present invention is used for a table lamp which is a lighting
device. The table lamp illustrated in FIG. 9 includes a housing
2001 and a light source 2002, and the light-emitting element
including the above organic compound is used for the light source
2002.
[0274] FIG. 10 illustrates an example in which the light-emitting
element including the organic compound of one embodiment of the
present invention is used for an indoor lighting device 3001. Since
the light-emitting element including the above organic compound has
reduced power consumption, a lighting device that has reduced power
consumption can be obtained. Further, since the light-emitting
element including the above organic compound can have a large area,
the light-emitting element can be used for a large-area lighting
device. Furthermore, since the light-emitting element including the
above organic compound is thin, a lighting device having a reduced
thickness can be fabricated.
[0275] The light-emitting element including the organic compound of
one embodiment of the present invention can also be used for an
automobile windshield or an automobile dashboard. FIG. 11
illustrates one mode in which the light-emitting elements including
the above organic compound are used for an automobile windshield
and an automobile dashboard. Display regions 5000 to 5005 each
include the light-emitting element that contains the above organic
compound.
[0276] The display region 5000 and the display region 5001 are
provided in an automobile windshield. The light-emitting element
including the above organic compound can be formed into a so-called
see-through display device, through which the opposite side can be
seen, by including a first electrode and a second electrode formed
of electrodes having light-transmitting properties. Such
see-through display devices can be provided even in the windshield
of the car, without hindering the vision. Note that in the case
where a transistor for driving the light-emitting element is
provided, a transistor having a light-transmitting property, such
as an organic transistor using an organic semiconductor material or
a transistor using an oxide semiconductor, is preferably used.
[0277] A display region 5002 is provided in a pillar portion. The
display region 5002 can compensate for the view hindered by the
pillar portion by showing an image taken by an imaging unit
provided in the car body. Similarly, the display region 5003
provided in the dashboard can compensate for the view hindered by
the car body by showing an image taken by an imaging unit provided
in the outside of the car body, which leads to elimination of blind
areas and enhancement of safety. Showing an image so as to
compensate for the area which a driver cannot see makes it possible
for the driver to confirm safety easily and comfortably.
[0278] The display region 5004 and the display region 5005 can
provide a variety of information by displaying navigation data,
speed, the number of revolutions, a mileage, a fuel level, a
gearshift state, and air-condition setting. The content or layout
of the display can be changed freely by a user as appropriate. Note
that such information can also be shown by the display regions 5000
to 5003. The display regions 5000 to 5005 can also be used as
lighting devices.
[0279] By including the organic compound of one embodiment of the
present invention, the light-emitting element including the above
compound has low driving voltage and low power consumption.
Therefore, load on a battery is small even when a number of large
screens such as the display regions 5000 to 5005 are provided,
which provides comfortable use. For that reason, the light-emitting
device and the lighting device each of which includes the
light-emitting element including the above organic compound can be
suitably used as an in-vehicle light-emitting device and lighting
device.
[0280] FIGS. 12A and 12B illustrate an example of a foldable tablet
terminal. FIG. 12A illustrates the tablet terminal which is
unfolded. The tablet terminal includes a housing 9630, a display
portion 9631a, a display portion 9631b, a display mode switch 9034,
a power switch 9035, a power-saving mode switch 9036, a clasp 9033,
and an operation switch 9038. Note that in the tablet terminal, one
or both of the display portion 9631a and the display portion 9631b
is/are formed using a light-emitting device which includes a
light-emitting element including the above organic compound.
[0281] Part of the display portion 9631a can be a touchscreen
region 9632a and data can be input when a displayed operation key
9637 is touched. Although half of the display portion 9631a has
only a display function and the other half has a touchscreen
function, one embodiment of the present invention is not limited to
the structure. The whole display portion 9631a may have a
touchscreen function. For example, a keyboard is displayed on the
entire region of the display portion 9631a so that the display
portion 9631a is used as a touchscreen; thus, the display portion
9631b can be used as a display screen.
[0282] Like the display portion 9631a, part of the display portion
9631b can be a touchscreen region 9632b. When a keyboard display
switching button 9639 displayed on the touchscreen is touched with
a finger, a stylus, or the like, the keyboard can be displayed on
the display portion 9631b.
[0283] Touch input can be performed in the touchscreen region 9632a
and the touchscreen region 9632b at the same time.
[0284] The display mode switch 9034 can switch the display between
portrait mode, landscape mode, and the like, and between monochrome
display and color display, for example. The power-saving switch
9036 can control display luminance in accordance with the amount of
external light in use of the tablet terminal detected by an optical
sensor incorporated in the tablet terminal. Another detection
device including a sensor for detecting inclination, such as a
gyroscope or an acceleration sensor, may be incorporated in the
tablet terminal, in addition to the optical sensor.
[0285] Although FIG. 12A illustrates an example in which the
display portion 9631a and the display portion 9631b have the same
display area, one embodiment of the present invention is not
limited to the example. The display portion 9631a and the display
portion 9631b may have different display areas and different
display quality. For example, one display panel may be capable of
higher-resolution display than the other display panel.
[0286] FIG. 12B illustrates the tablet terminal which is folded.
The tablet terminal includes the housing 9630, a solar cell 9633, a
charge and discharge control circuit 9634, a battery 9635, and a
DC-to-DC converter 9636. As an example, FIG. 12B illustrates the
charge and discharge control circuit 9634 including the battery
9635 and the DC-to-DC converter 9636.
[0287] Since the tablet terminal is foldable, the housing 9630 can
be closed when the tablet terminal is not in use. As a result, the
display portion 9631a and the display portion 9631b can be
protected, which offers a tablet terminal having excellent
durability and high reliability in terms of long-term use.
[0288] The tablet terminal illustrated in FIGS. 12A and 12B can
have other functions such as a function of displaying various kinds
of data (e.g., a still image, a moving image, and a text image), a
function of displaying a calendar, a date, the time, or the like on
the display portion, a touch-input function of operating or editing
the data displayed on the display portion by touch input, and a
function of controlling processing by various kinds of software
(programs).
[0289] The solar cell 9633 provided on a surface of the tablet
terminal can supply power to the touchscreen, the display portion,
a video signal processing portion, or the like. Note that the solar
cell 9633 is preferably provided on one or two surfaces of the
housing 9630, in which case the battery 9635 can be charged
efficiently.
[0290] The structure and operation of the charge and discharge
control circuit 9634 illustrated in FIG. 12B will be described with
reference to a block diagram of FIG. 12C. FIG. 12C illustrates the
solar cell 9633, the battery 9635, the DC-to-DC converter 9636, a
converter 9638, switches SW1 to SW3, and the display portion 9631.
The battery 9635, the DC-to-DC converter 9636, the converter 9638,
and the switches SW1 to SW3 correspond to the charge and discharge
control circuit 9634 illustrated in FIG. 12B.
[0291] First, description is made of an example of the operation in
the case where power is generated by the solar cell 9633 with the
use of external light. The voltage of the power generated by the
solar cell 9633 is raised or lowered by the DC-to-DC converter 9636
so as to be voltage for charging the battery 9635. Then, when power
supplied from the battery 9635 charged by the solar cell 9633 is
used for the operation of the display portion 9631, the switch SW1
is turned on and the voltage of the power is raised or lowered by
the converter 9638 so as to be voltage needed for the display
portion 9631. When images are not displayed on the display portion
9631, the switch SW1 is turned off and the switch SW2 is turned on
so that the battery 9635 is charged.
[0292] Although the solar cell 9633 is described as an example of a
power generation unit, the power generation unit is not
particularly limited, and the battery 9635 may be charged by
another power generation unit such as a piezoelectric element or a
thermoelectric conversion element (Peltier element). The battery
9635 may be charged by a non-contact power transmission module
which is capable of charging by transmitting and receiving power by
wireless (without contact), or another charge unit used in
combination, and the power generation unit is not necessarily
provided.
[0293] One embodiment of the present invention is not limited to
the electronic device having the shape illustrated in FIGS. 12A to
12C as long as the display portion 9631 is included.
Example 1
[0294] In this example, a synthesis method and properties of
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'mDBTP2BPy-II) represented by Structural Formula
(200), which is one of organic compounds represented by General
Formula (G1), will be described.
##STR00057##
<Synthesis Method>
[0295] Into a 500-mL three-neck flask were put 3.1 g (10 mmol) of
4,4'-dibromo-2,2'-bipyridine, 6.7 g (22 mmol) of
3-(dibenzothiophen-4-yl)phenylboronic acid, 100 mL of toluene, 15
mL of ethanol, and 15 mL of a 2M aqueous solution of sodium
carbonate. The mixture was degassed by being stirred under reduced
pressure, and the air in the flask was replaced with nitrogen.
Then, 0.43 g (0.37 mmol) of
tetrakis(triphenylphosphine)palladium(0) was added to the mixture,
and the mixture was stirred at 100.degree. C. under a nitrogen
stream for 3.5 hours. After the predetermined time elapsed, this
mixture was cooled to 60.degree. C., 100 mL of toluene and 15 mL of
water were added to the mixture, and a solid was collected by
suction filtration. A methanol suspension of this solid was
irradiated with ultrasonic waves, and a solid was collected by
suction filtration. The obtained solid was dissolved in toluene,
and the toluene solution was suction filtered through Celite
(produced by Wako Pure Chemical Industries, Ltd., Catalog No.
531-16855, the same shall apply hereinafter) and alumina, and the
filtrate was concentrated. An obtained solid was recrystallized
with toluene, so that 2.2 g of a target white powder was obtained
in a yield of 32%. The synthesis scheme of this reaction is shown
below.
##STR00058##
[0296] By a train sublimation method, 2.2 g of the obtained powder
of 4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine was
purified by sublimation. The purification by sublimation was
carried out by heating
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine at
340.degree. C. under a pressure of 3.1 Pa with an argon flow rate
of 5.0 mL/min. After the purification by sublimation, 2.0 g of a
white powder of 4,4'mDBTP2BPy-II was obtained at a collection rate
of 91%.
[0297] The .sup.1H NMR data of the obtained compound are as
follows: .sup.1H NMR (CDCl.sub.3, 300 MHz): .delta.=7.47-7.50 (m,
4H), 7.56-7.70 (m, 8H), 7.83-7.90 (m, 6H), 8.15 (s, 2H), 8.19-8.23
(m, 4H), 8.78 (d, J=5.4 Hz, 2H), 8.82 (s, 2H).
[0298] FIGS. 13A and 13B show .sup.1H NMR charts. Note that FIG.
13B is a chart showing an enlarged part of FIG. 13A in the range of
7.00 ppm to 9.0 ppm. The measurement results show that
4,4'mDBTP2BPy-II, which was the target substance, was obtained.
<<Properties of 4,4'mDBTP2BPy-II>>
[0299] FIG. 14A shows an absorption spectrum and an emission
spectrum of a toluene solution of 4,4'mDBTP2BPy-II, and FIG. 14B
shows an absorption spectrum and an emission spectrum of a thin
film of 4,4'mDBTP2BPy-II. The spectra were measured with a
UV-visible spectrophotometer (V550, produced by JASCO Corporation).
The spectra of the toluene solution were obtained with the toluene
solution of 4,4'mDBTP2BPy-II put in a quartz cell. The spectra of
the thin film were measured with a sample prepared by deposition of
4,4'mDBTP2BPy-II on a quartz substrate by evaporation. Note that in
the case of the absorption spectrum of the toluene solution of
4,4'mDBTP2BPy-II, the absorption spectrum obtained by subtraction
of the absorption spectra of the quartz cell and toluene from the
raw spectra is illustrated. In the case of the absorption spectrum
of the thin film of 4,4'mDBTP2BPy-II, the absorption spectrum
obtained by subtraction of the absorption spectrum of the quartz
substrate from the raw spectra is illustrated.
[0300] As shown in FIG. 14A, in the case of 4,4'mDBTP2BPy-II in the
toluene solution, absorption peaks were observed at approximately
332 nm and 282 nm, and an emission peak was observed at
approximately 351 nm (excitation wavelength: 333 nm). As shown in
FIG. 14B, in the case of the thin film of 4,4'mDBTP2BPy-II,
absorption peaks were observed at approximately 336 nm, 318 nm, 288
nm, and 246 nm, and an emission peak was observed at approximately
371 nm (excitation wavelength: 274 nm). Thus, it was found that
absorption and emission of 4,4'mDBTP2BPy-II occur in extremely
short wavelength regions.
[0301] The ionization potential of 4,4'mDBTP2BPy-II in a thin film
state was measured by a photoelectron spectrometer (AC-3,
manufactured by Riken Keiki, Co., Ltd.) in the air. The obtained
value of the ionization potential was converted into a negative
value, so that the HOMO level of 4,4'mDBTP2BPy-II was -6.38 eV.
From the data of the absorption spectrum of the thin film in FIG.
14B, the absorption edge of 4,4'mDBTP2BPy-II, which was obtained
from Tauc plot with an assumption of direct transition, was 3.48
eV. Therefore, the optical band gap of 4,4'mDBTP2BPy-II in a solid
state was estimated to be 3.48 eV; from the values of the HOMO
level obtained above and this band gap, the LUMO level of
4,4'mDBTP2BPy-II was estimated to be -2.90 eV. The above results
show that 4,4'mDBTP2BPy-II in the solid state has a band gap as
wide as 3.48 eV.
[0302] Phosphorescence of 4,4'mDBTP2BPy-II was measured. The
measurement was performed by using a PL microscope, LabRAM HR-PL,
produced by HORIBA, Ltd., a He--Cd laser (325 nm) as excitation
light, and a CCD detector at a measurement temperature of 10 K. For
the measurement, a thin film as a sample was formed over a quartz
substrate to a thickness of approximately 50 nm and another quartz
substrate was attached to the deposition surface in a nitrogen
atmosphere. The results showed that the peak on the shortest
wavelength side of a phosphorescence spectrum of 4,4'mDBTP2BPy-II
is at 470 nm, which means that 4,4'mDBTP2BPy-II has a high T.sub.1
level.
[0303] Next, 4,4'mDBTP2BPy-II was analyzed by liquid chromatography
mass spectrometry (LC/MS).
[0304] The analysis by LC/MS was carried out with Acquity UPLC
(produced by Waters Corporation) and Xevo G2 Tof MS (produced by
Waters Corporation).
[0305] In the MS analysis, ionization was carried out by an
electrospray ionization (ESI) method. Capillary voltage and sample
cone voltage were set to 3.0 kV and 30 V, respectively. Detection
was performed in a positive mode. A component which underwent the
ionization under the above-described conditions was collided with
an argon gas in a collision cell to dissociate into product ions.
Energy (collision energy) for the collision with argon was 70 eV. A
mass range for the measurement was m/z=100 to 1200. FIG. 15 shows
the results.
Example 2
[0306] In this example, a synthesis method and properties of
4,4'-bis[3-(dibenzofuran-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'DBfP2BPy) represented by Structural Formula
(100), which is one of organic compounds represented by General
Formula (G1), will be described.
##STR00059##
<Synthesis Method>
[0307] Into a 500-mL three-neck flask were put 3.1 g (10 mmol) of
4,4'-dibromo-2,2'-bipyridine, 6.4 g (22 mmol) of
3-(dibenzofuran-4-yl)phenylboronic acid, 120 mL of toluene, 15 mL
of ethanol, and an aqueous solution in which 3.2 g (30 mmol) of
sodium carbonate was dissolved in 15 mL of water. The mixture was
degassed by being stirred under reduced pressure, and the air in
the flask was replaced with nitrogen. Then, 0.48 g (0.42 mmol) of
tetrakis(triphenylphosphine)palladium(0) was added to the mixture,
and the mixture was stirred at 100.degree. C. under a nitrogen
stream for 13 hours. After the predetermined time elapsed, 120 mL
of toluene and 15 mL of water were added to this mixture and
stirring was performed at 60.degree. C. for 3 hours. After the
predetermined time elapsed, this mixture was suction filtered to
give a solid. A methanol suspension of this solid was irradiated
with ultrasonic waves, and a solid was collected by suction
filtration. The obtained solid was dissolved in hot toluene, and
the toluene solution was suction filtered through Celite (produced
by Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855, the
same shall apply hereinafter) and alumina, and the filtrate was
concentrated. An obtained solid was recrystallized with toluene, so
that 3.7 g of a target white powder was obtained in a yield of 58%.
The synthesis scheme of this reaction is shown below.
##STR00060##
[0308] By a train sublimation method, 3.7 g of the obtained powder
of 4,4'DBfP2BPy was purified by sublimation. The purification by
sublimation was carried out by heating 4,4'DBfP2BPy at 335.degree.
C. under a pressure of 3.5 Pa with an argon flow rate of 5.0
mL/min. After the purification by sublimation, 2.4 g of a white
powder of 4,4'DBfP2BPy was obtained at a collection rate of
65%.
[0309] The .sup.1H NMR data of the obtained compound are as
follows: .sup.1H NMR (CDCl.sub.3, 300 MHz): .delta.=7.38 (t, J=7.2
Hz, 2H), 7.46-7.51 (m, 4H), 7.61-7.72 (m, 8H), 7.87 (d, J=7.2 Hz,
2H), 7.99-8.04 (m, 6H), 8.31 (s, 2H), 8.81 (d, J=4.8 Hz, 2H), 8.86
(s, 2H).
[0310] FIGS. 16A and 16B show .sup.1H NMR charts. Note that FIG.
16B is a chart showing an enlarged part of FIG. 16A in the range of
7.00 ppm to 9.0 ppm. The measurement results show that
4,4'DBfP2BPy, which was the target substance, was obtained.
<<Properties of 4,4'DBfP2BPy>>
[0311] FIG. 17A shows an absorption spectrum and an emission
spectrum of a toluene solution of 4,4'DBfP2BPy, and FIG. 17B shows
an absorption spectrum and an emission spectrum of a thin film of
4,4'DBfP2BPy. The spectra were measured with a ITV-visible
spectrophotometer (V550, produced by JASCO Corporation). The
spectra of the toluene solution were obtained with the toluene
solution of 4,4'DBfP2BPy put in a quartz cell. The spectra of the
thin film were measured with a sample prepared by deposition of
4,4'DBfP2BPy on a quartz substrate by evaporation. Note that in the
case of the absorption spectrum of the toluene solution of
4,4'DBfP2BPy, the absorption spectrum obtained by subtraction of
the absorption spectra of the quartz cell and toluene from the raw
spectra is illustrated. In the case of the absorption spectrum of
the thin film of 4,4'DBfP2BPy, the absorption spectrum obtained by
subtraction of the absorption spectrum of the quartz substrate from
the raw spectra is illustrated.
[0312] As shown in FIG. 17A, in the case of 4,4'DBfP2BPy in the
toluene solution, absorption peaks were observed at approximately
287 nm, 300 nm, and 314 nm, and an emission peak was observed at
approximately 344 nm (excitation wavelength: 289 nm). As shown in
FIG. 17B, in the case of the thin film of 4,4'DBfP2BPy, absorption
peaks were observed at approximately 314 nm, 301 nm, 291 nm, 254
nm, and 206 nm, and an emission peak was observed at approximately
366 nm (excitation wavelength: 305 nm). Thus, it was found that
absorption and emission of 4,4'DBfP2BPy occur in extremely short
wavelength regions.
[0313] The ionization potential of 4,4'DBfP2BPy in a thin film
state was measured by a photoelectron spectrometer (AC-3,
manufactured by Riken Keiki, Co., Ltd.) in the air. The obtained
value of the ionization potential was converted into a negative
value, so that the HOMO level of 4,4'DBfP2BPy was -6.47 eV. From
the data of the absorption spectrum of the thin film in FIG. 17B,
the absorption edge of 4,4'DBfP2BPy, which was obtained from Tauc
plot with an assumption of direct transition, was 3.73 eV.
Therefore, the optical band gap of 4,4'DBfP2BPy in a solid state
was estimated to be 3.73 eV; from the values of the HOMO level
obtained above and this band gap, the LUMO level of 4,4'DBfP2BPy
was estimated to be -2.74 eV. The above results show that
4,4'DBfP2BPy in the solid state has a band gap as wide as 3.73
eV.
[0314] Phosphorescence of 4,4'DBfP2BPy was measured. The
measurement was performed by using a PL microscope, LabRAM HR-PL,
produced by HORIBA, Ltd., a He--Cd laser (325 nm) as excitation
light, and a CCD detector at a measurement temperature of 10 K. For
the measurement, a thin film as a sample was formed over a quartz
substrate to a thickness of approximately 50 nm and another quartz
substrate was attached to the deposition surface in a nitrogen
atmosphere. The results showed that the peak on the shortest
wavelength side of a phosphorescence spectrum of 4,4'DBfP2BPy is at
467 nm, which means that 4,4'DBfP2BPy has a high T.sub.1 level.
[0315] Next, 4,4'DBfP2BPy was analyzed by liquid chromatography
mass spectrometry (LC/MS).
[0316] The analysis by LC/MS was carried out with Acquity UPLC
(produced by Waters Corporation) and Xevo G2 Tof MS (produced by
Waters Corporation).
[0317] In the MS analysis, ionization was carried out by an
electrospray ionization (ESI) method. Capillary voltage and sample
cone voltage were set to 3.0 kV and 30 V, respectively. Detection
was performed in a positive mode. A component which underwent the
ionization under the above-described conditions was collided with
an argon gas in a collision cell to dissociate into product ions.
Energy (collision energy) for the collision with argon was 70 eV. A
mass range for the measurement was m/z=100 to 1200. FIG. 18 shows
the results.
Example 3
[0318] This example will describe green-emissive phosphorescent
light-emitting elements in which
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'mDBTP2BPy-II) or
4,4'-bis[3-(dibenzofuran-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'DBfP2BPy) was used as a host material and an
electron-transport material (a light-emitting element 1 and a
light-emitting element 2) and a green-emissive phosphorescent
light-emitting element in which
4,4'-bis[3-(9H-carbazol-9-yl)phenyl]-2,2'-bipyridine (abbreviation:
4,4'mCzP2BPy) was used as a host material and an electron-transport
material (a comparative light-emitting element 1).
[0319] Molecular structures of organic compounds that were used in
this example are shown by Structural Formulae (i) to (vii) below.
The element structure in FIG. 1A was employed.
##STR00061## ##STR00062##
<<Fabrication of Light-Emitting Element 1>>
[0320] First, a glass substrate, over which a film of indium tin
oxide containing silicon (ITSO) was formed to a thickness of 110 nm
as the first electrode 101, was prepared. A surface of the ITSO
film was covered with a polyimide film so that an area of 2
mm.times.2 mm of the surface was exposed. The electrode area was 2
mm.times.2 mm. As pretreatment for forming the light-emitting
element over the substrate, the surface of the substrate was washed
with water and baked at 200.degree. C. for 1 hour, and then
UV-ozone treatment was performed for 370 seconds. After that, the
substrate was transferred into a vacuum evaporation apparatus where
the pressure had been reduced to approximately 10.sup.-4 Pa, and
was subjected to vacuum baking at 170.degree. C. for 30 minutes in
a heating chamber of the vacuum evaporation apparatus, and then the
substrate was cooled down for approximately 30 minutes.
[0321] Then, the substrate was fixed to a holder provided in the
vacuum evaporation apparatus so that the surface provided with ITSO
faced downward.
[0322] The pressure in the vacuum evaporation apparatus was reduced
to 10.sup.-4 Pa. Then,
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II) represented by Structural Formula (i) and molybdenum(VI)
oxide were deposited by co-evaporation so that the weight ratio of
DBT3P-II to molybdenum oxide was 4:2, whereby the hole-injection
layer 111 was formed. The thickness was set to 60 nm. Note that
co-evaporation is an evaporation method in which a plurality of
different substances are concurrently vaporized from respective
different evaporation sources.
[0323] Next, 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP)
represented by Structural Formula (ii) was deposited by evaporation
to a thickness of 20 nm, whereby the hole-transport layer 112 was
formed.
[0324] Moreover,
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'mDBTP2BPy-II) represented by Structural Formula
(iii), PCCP, and fac-tris(2-phenylpyridine)iridium (abbreviation:
[Ir(ppy).sub.3]) represented by Structural Formula (iv) were
co-deposited by evaporation to a thickness of 20 nm on the
hole-transport layer 112 so that
4,4'mDBTP2BPy-II:PCCP:[Ir(ppy).sub.3]=1:0.3:0.06 (weight ratio),
and then, 4,4'mDBTP2BPy-II and [Ir(ppy).sub.3] were co-deposited by
evaporation to a thickness of 20 nm so that
4,4'mDBTP2BPy-II:[Ir(ppy).sub.3]=1:0.06 (weight ratio), whereby the
light-emitting layer 113 was formed.
[0325] Next, 4,4'mDBTP2BPy-II was deposited by evaporation to a
thickness of 10 nm, and then bathophenanthroline (abbreviation:
BPhen) represented by Structural Formula (v) was deposited by
evaporation to a thickness of 20 nm, whereby the electron-transport
layer 114 was formed.
[0326] Then, lithium fluoride was deposited by evaporation to a
thickness of 1 nm on the electron-transport layer 114, whereby the
electron-injection layer 115 was formed. Lastly, a film of aluminum
was formed to a thickness of 200 nm as the second electrode 102
which serves as a cathode. Thus, the light-emitting element 1 was
completed. Note that in all the above evaporation steps,
evaporation was performed by a resistance-heating method.
<<Fabrication of Light-Emitting Element 2>>
[0327] The light-emitting element 2 was fabricated in a manner
similar to that of the light-emitting element 1 except that
4,4'-bis[3-(dibenzofuran-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'DBfP2BPy) represented by Structural Formula (vi)
was used instead of 4,4'mDBTP2BPy-II.
<<Fabrication of Comparative Light-Emitting Element
1>>
[0328] The comparative light-emitting element 1 was fabricated in a
manner similar to that of the light-emitting element 1 except that
4,4'-bis[3-(9H-carbazol-9-yl)phenyl]-2,2'-bipyridine (abbreviation:
4,4'mCzP2BPy) represented by Structural Formula (vii) was used
instead of 4,4'mDBTP2BPy-II.
<<Operation Characteristics of Light-Emitting Element 1,
Light-Emitting Element 2, and Comparative Light-Emitting Element
1>>
[0329] The light-emitting element 1, the light-emitting element 2,
and the comparative light-emitting element 1 obtained as described
above were sealed in a glove box containing a nitrogen atmosphere
so as not to be exposed to the air (specifically, a sealant was
applied onto an outer edge of each element, and heat treatment at
80.degree. C. for 1 hour and UV treatment were performed at the
time of sealing). Then, the operating characteristics of the
light-emitting elements were measured. Note that the measurement
was carried out at room temperature (in an atmosphere kept at
25.degree. C.).
[0330] FIG. 19 shows the luminance-current density characteristics
of the light-emitting element 1, the light-emitting element 2, and
the comparative light-emitting element 1; FIG. 20 shows the current
efficiency-luminance characteristics thereof; FIG. 21 shows the
luminance-voltage characteristics thereof; and FIG. 22 shows the
external quantum efficiency-luminance characteristics thereof.
[0331] FIG. 20 shows that the light-emitting element 1 and the
light-emitting element 2 have favorable current
efficiency-luminance characteristics and thus have a high emission
efficiency. Accordingly, 4,4'mDBTP2BPy-II and 4,4'DBfP2BPy have a
high triplet level and a wide band gap, and allow even a
light-emitting substance emitting green phosphorescence to be
effectively excited. Similarly, as shown in FIG. 22, the
light-emitting element 1 and the light-emitting element 2 have
favorable external quantum efficiency-luminance characteristics.
Moreover, FIG. 21 shows that the light-emitting element 1 and the
light-emitting element 2 have favorable luminance-voltage
characteristics and thus have low driving voltage. This means that
4,4'mDBTP2BPy-II and 4,4'DBfP2BPy have a high carrier-transport
property. FIG. 19 also shows that the light-emitting element 1 and
the light-emitting element 2 have favorable luminance-current
density characteristics.
[0332] The above results show that the light-emitting element 1
that contains 4,4'mDBTP2BPy-II and the light-emitting element 2
that contains 4,4'DBfP2BPy have favorable characteristics including
a distinctively high emission efficiency as compared to the
comparative light-emitting element 1 which was formed in a similar
manner using 4,4'mCzP2BPy.
[0333] FIG. 23 shows emission spectra at the time when a current of
0.1 mA was made to flow in the fabricated light-emitting elements.
FIG. 23 shows that the light-emitting element 1, the light-emitting
element 2, and the comparative light-emitting element 1 emit green
light originating from [Ir(ppy).sub.3], which is the emission
center substance.
[0334] Next, these light-emitting elements were subjected to
reliability tests. In the reliability tests, a change in luminance
(normalized luminance) over driving time was measured with an
initial luminance taken as 100% under the conditions where the
initial luminance was 1000 cd/m.sup.2 and the current density was
constant. FIG. 24 shows the results. The above results show that
the light-emitting element 1 and the light-emitting element 2 have
high reliability as compared to the comparative light-emitting
element 1.
Example 4
[0335] This example will describe blue-emissive phosphorescent
light-emitting elements in which
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'mDBTP2BPy-II) or
4,4'-bis[3-(dibenzofuran-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'DBfP2BPy) was used as a host material and an
electron-transport material (a light-emitting element 3 and a
light-emitting element 4).
[0336] Molecular structures of organic compounds that were used in
this example are shown by Structural Formulae (i) to (iii), (v),
(vi), and (viii). The element structure in FIG. 1A was
employed.
##STR00063## ##STR00064##
<<Fabrication of Light-Emitting Element 3>>
[0337] First, a glass substrate, over which a film of indium tin
oxide containing silicon (ITSO) was formed to a thickness of 110 nm
as the first electrode 101, was prepared. A surface of the ITSO
film was covered with a polyimide film so that an area of 2
mm.times.2 mm of the surface was exposed. The electrode area was 2
mm.times.2 mm. As pretreatment for forming the light-emitting
element over the substrate, the surface of the substrate was washed
with water and baked at 200.degree. C. for 1 hour, and then
UV-ozone treatment was performed for 370 seconds. After that, the
substrate was transferred into a vacuum evaporation apparatus where
the pressure had been reduced to approximately 10.sup.-4 Pa, and
was subjected to vacuum baking at 170.degree. C. for 30 minutes in
a heating chamber of the vacuum evaporation apparatus, and then the
substrate was cooled down for approximately 30 minutes.
[0338] Then, the substrate was fixed to a holder provided in the
vacuum evaporation apparatus so that the surface provided with ITSO
faced downward.
[0339] The pressure in the vacuum evaporation apparatus was reduced
to 10.sup.-4 Pa. Then,
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II) represented by Structural Formula (i) and molybdenum(VI)
oxide were deposited by co-evaporation so that the weight ratio of
DBT3P-II to molybdenum oxide was 4:2, whereby the hole-injection
layer 111 was formed. The thickness was set to 60 nm. Note that
co-evaporation is an evaporation method in which a plurality of
different substances are concurrently vaporized from respective
different evaporation sources.
[0340] Next, 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP)
represented by Structural Formula (ii) was deposited by evaporation
to a thickness of 20 nm, whereby the hole-transport layer 112 was
formed.
[0341] Moreover,
4,4'-bis[3-(dibenzothiophen-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'mDBTP2BPy-II) represented by Structural Formula
(iii), PCCP, and tris
{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-.kapp-
a.N2]phenyl-.kappa.C}iridium(III) (abbreviation:
[Ir(mpptz-dmp).sub.3]) represented by Structural Formula (viii)
were co-deposited by evaporation to a thickness of 30 nm on the
hole-transport layer 112 so that PCCP:4,4'mDBTP2BPy-II:
[Ir(mpptz-dmp).sub.3]=1:0.3:0.06 (weight ratio), and then,
4,4'mDBTP2BPy-II and [Ir(mpptz-dmp).sub.3] were co-deposited by
evaporation to a thickness of 10 nm so that
4,4'mDBTP2BPy-II:[Ir(mpptz-dmp).sub.3]=1:0.06 (weight ratio),
whereby the light-emitting layer 113 was formed.
[0342] Next, 4,4'mDBTP2BPy-II was deposited by evaporation to a
thickness of 10 nm, and then bathophenanthroline (abbreviation:
BPhen) represented by Structural Formula (v) was deposited by
evaporation to a thickness of 15 nm, whereby the electron-transport
layer 114 was formed.
[0343] Then, lithium fluoride was deposited by evaporation to a
thickness of 1 nm on the electron-transport layer 114, whereby the
electron-injection layer 115 was formed. Lastly, a film of aluminum
was formed to a thickness of 200 nm as the second electrode 102
which serves as a cathode. Thus, the light-emitting element 3 was
completed. Note that in all the above evaporation steps,
evaporation was performed by a resistance-heating method.
<<Fabrication of Light-Emitting Element 4>>
[0344] The light-emitting element 4 was fabricated in a manner
similar to that of the light-emitting element 3 except that
4,4'-bis[3-(dibenzofuran-4-yl)phenyl]-2,2'-bipyridine
(abbreviation: 4,4'DBfP2BPy) represented by Structural Formula (vi)
was used instead of 4,4'mDBTP2BPy-II.
<<Operation Characteristics of Light-Emitting Element 3 and
Light-Emitting Element 4>>
[0345] The light-emitting element 3 and the light-emitting element
4 obtained as described above were sealed in a glove box containing
a nitrogen atmosphere so as not to be exposed to the air
(specifically, a sealant was applied onto an outer edge of each
element, and heat treatment at 80.degree. C. for 1 hour and UV
treatment were performed at the time of sealing). Then, the
operating characteristics of the light-emitting elements were
measured. Note that the measurement was carried out at room
temperature (in an atmosphere kept at 25.degree. C.).
[0346] FIG. 25 shows the luminance-current density characteristics
of the light-emitting element 3 and the light-emitting element 4;
FIG. 26 shows the current efficiency-luminance characteristics
thereof; FIG. 27 shows the luminance-voltage characteristics
thereof; and FIG. 28 shows the external quantum
efficiency-luminance characteristics thereof.
[0347] FIG. 26 shows that the light-emitting element 3 and the
light-emitting element 4 have favorable current
efficiency-luminance characteristics and thus have a high emission
efficiency. Accordingly, 4,4'mDBTP2BPy-II and 4,4'DBfP2BPy have a
high triplet level and a wide band gap, and allow even a
light-emitting substance emitting blue phosphorescence to be
effectively excited. Similarly, as shown in FIG. 28, the
light-emitting element 3 and the light-emitting element 4 have
favorable external quantum efficiency-luminance characteristics.
Moreover, FIG. 27 shows that the light-emitting element 3 and the
light-emitting element 4 have favorable luminance-voltage
characteristics and thus have low driving voltage. This means that
4,4'mDBTP2BPy-II and 4,4'DBfP2BPy have a high carrier-transport
property. FIG. 25 also shows that the light-emitting element 3 and
the light-emitting element 4 have favorable luminance-current
density characteristics.
[0348] FIG. 29 shows emission spectra at the time when a current of
0.1 mA was made to flow in the light-emitting element 3 and the
light-emitting element 4. FIG. 29 shows that the light-emitting
element 3 and the light-emitting element 4 emit blue light
originating from [Ir(mpptz-dmp).sub.3], which is the emission
center substance.
Example 5
[0349] In this example, a synthesis method and properties of
3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine (abbreviation:
3,5mDBTP2Py) represented by Structural Formula (400), which is one
of organic compounds represented by General Formula (G0), will be
described.
##STR00065##
<Synthesis Method>
[0350] Into a 200-mL three-neck flask were put 1.6 g (6.8 mmol) of
3,5-dibromopyridine, 4.5 g (15 mmol) of
3-(dibenzothiophen-4-yl)phenylboronic acid, and 0.20 g (0.66 mmol)
of tris(2-methylphenyl)phosphine, and the air in the flask was
replaced with nitrogen. To this mixture were added 15 mL of a 2M
aqueous solution of potassium carbonate, 25 mL of toluene, and 8.5
mL of ethanol, and the mixture was degassed by being stirred under
reduced pressure. Then, 30 mg (0.13 mmol) of palladium(II) acetate
was added to this mixture, and the mixture was stirred at
90.degree. C. for 6 hours under a nitrogen stream. After the
predetermined time elapsed, the organic layer and the aqueous layer
of this mixture were separated and the aqueous layer was subjected
to extraction using chloroform. The obtained solution of the
extract and the organic layer were combined, and the mixture was
washed with water and a saturated aqueous solution of sodium
chloride, and dried with magnesium sulfate. This mixture was
separated by gravity filtration, and the filtrate was concentrated
to give an oily brown substance. This oily substance was purified
by silica gel column chromatography (as a developing solvent,
first, toluene was used, and then toluene and ethyl acetate
(toluene:ethyl acetate=20:1) was used). The obtained fraction was
concentrated to give a white solid. This solid was recrystallized
from toluene, whereby a white solid was obtained. This white solid
was purified by high performance liquid column chromatography
(HPLC) (the developing solvent was chloroform). The obtained
fraction was concentrated to give a white solid. To this solid was
added hexane, followed by irradiation with ultrasonic waves. A
solid was collected by suction filtration to give 2.0 g of a white
solid, which was a target substance, in a yield of 50%. The
synthesis scheme of this reaction is shown below.
##STR00066##
[0351] The obtained white solid was purified by sublimation using a
train sublimation method. In the purification by sublimation, the
white solid was heated at 310.degree. C. under a pressure of 3.2 Pa
with an argon flow rate of 5 mL/min. After the purification by
sublimation, 1.6 g of a white solid was obtained at a collection
rate of 85%.
[0352] The .sup.1H NMR data of the obtained compound are as
follows: .sup.1H NMR (CDCl.sub.3, 300 MHz): .delta.=7.41-7.52 (m,
4H), 7.56-7.69 (m, 6H), 7.72-7.82 (m, 6H), 8.07-8.08 (m, 2H),
8.17-8.21 (m, 4H), 8.23-8.25 (m, 1H), 8.97 (d, J=2.1 Hz, 2H).
[0353] FIGS. 30A and 30B show .sup.1H NMR charts. Note that FIG.
30B is a chart showing an enlarged part of FIG. 30A in the range of
7.00 ppm to 9.5 ppm. The measurement results show that 3,5mDBTP2Py,
which was the target substance, was obtained.
<<Properties of 3,5mDBTP2Py>>
[0354] FIG. 31A shows an absorption spectrum and an emission
spectrum of a toluene solution of 3,5mDBTP2Py, and FIG. 31B shows
an absorption spectrum and an emission spectrum of a thin film of
3,5mDBTP2Py. The spectra were measured with a UV-visible
spectrophotometer (V550, produced by JASCO Corporation). The
spectra of the toluene solution were obtained with the toluene
solution of 3,5mDBTP2Py put in a quartz cell. The spectra of the
thin film were measured with a sample prepared by deposition of
3,5mDBTP2Py on a quartz substrate by evaporation. Note that in the
case of the absorption spectrum of the toluene solution of
3,5mDBTP2Py, the absorption spectrum obtained by subtraction of the
absorption spectra of the quartz cell and toluene from the raw
spectra is illustrated. In the case of the absorption spectrum of
the thin film of 3,5mDBTP2Py, the absorption spectrum obtained by
subtraction of the absorption spectrum of the quartz substrate from
the raw spectra is illustrated.
[0355] As shown in FIG. 31A, in the case of 3,5mDBTP2Py in the
toluene solution, absorption peaks were observed at approximately
331 nm, 319 nm, and 283 nm, and an emission peak was observed at
approximately 352 nm (excitation wavelength: 289 nm). As shown in
FIG. 31B, in the case of the thin film of 3,5mDBTP2Py, absorption
peaks were observed at approximately 332 nm, 315 nm, 284 nm, 272
nm, 240 nm, and 220 nm, and an emission peak was observed at
approximately 369 nm (excitation wavelength: 274 nm). Thus, it was
found that absorption and emission of 3,5mDBTP2Py occur in
extremely short wavelength regions.
[0356] The ionization potential of 3,5mDBTP2Py in a thin film state
was measured by a photoelectron spectrometer (AC-3, manufactured by
Riken Keiki, Co., Ltd.) in the air. The obtained value of the
ionization potential was converted into a negative value, so that
the HOMO level of 3,5mDBTP2Py was -6.42 eV. From the data of the
absorption spectrum of the thin film in FIG. 31B, the absorption
edge of 3,5mDBTP2Py, which was obtained from Tauc plot with an
assumption of direct transition, was 3.49 eV. Therefore, the
optical band gap of 3,5mDBTP2Py in a solid state was estimated to
be 3.49 eV; from the values of the HOMO level obtained above and
this band gap, the LUMO level of 3,5mDBTP2Py was estimated to be
-2.93 eV. The above results show that 3,5mDBTP2Py in the solid
state has a band gap as wide as 3.49 eV.
[0357] Phosphorescence of 3,5mDBTP2Py was measured. The measurement
was performed by using a PL microscope, LabRAM HR-PL, produced by
HORIBA, Ltd., a He--Cd laser (325 nm) as excitation light, and a
CCD detector at a measurement temperature of 10 K. For the
measurement, a thin film as a sample was formed over a quartz
substrate to a thickness of approximately 50 nm and another quartz
substrate was attached to the deposition surface in a nitrogen
atmosphere. The results showed that the peak on the shortest
wavelength side of a phosphorescence spectrum of 3,5mDBTP2Py is at
472 nm, which means that 3,5mDBTP2Py has a high T.sub.1 level.
Example 6
[0358] In this example, a synthesis method and properties of
3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine (abbreviation:
3,5mDBFP2Py) represented by Structural Formula (300), which is one
of organic compounds represented by General Formula (G0), will be
described.
##STR00067##
<Synthesis Method>
[0359] Into a 200-mL three-neck flask were put 1.7 g (7.2 mmol) of
3,5-dibromopyridine, 4.5 g (16 mmol) of
3-(dibenzofuran-4-yl)phenylboronic acid, and 0.22 g (0.72 mmol) of
tris(2-methylphenyl)phosphine, and the air in the flask was
replaced with nitrogen. To this mixture were added 16 mL of a 2M
aqueous solution of potassium carbonate, 27 mL of toluene, and 9.0
mL of ethanol, and the mixture was degassed by being stirred under
reduced pressure. Then, 32 mg (0.14 mmol) of palladium(II) acetate
was added to this mixture, and the mixture was stirred at
90.degree. C. for 6 hours under a nitrogen stream. After the
predetermined time elapsed, this mixture was separated into the
organic layer and the aqueous layer and the aqueous layer was
subjected to extraction using chloroform. The obtained solution of
the extract and the organic layer were combined, and the mixture
was washed with water and a saturated aqueous solution of sodium
chloride, and dried with magnesium sulfate. This mixture was
separated by gravity filtration, and the filtrate was concentrated
to give a brown solid. This solid was purified by silica gel column
chromatography (as a developing solvent, first, toluene was used,
and then toluene and ethyl acetate (toluene:ethyl acetate=20:1) was
used). The obtained fraction was concentrated to give a white
solid. This white solid was purified by high performance liquid
column chromatography (HPLC) (the developing solvent was
chloroform). The obtained fraction was concentrated to give a white
solid. To this solid was added hexane, followed by irradiation with
ultrasonic waves. A solid was collected by suction filtration to
give 1.6 g of a white solid, which was a target substance, in a
yield of 40%.
##STR00068##
[0360] The 1.6 g of 3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBFP2Py) was purified by sublimation using a
train sublimation method. In the purification by sublimation, the
white solid was heated at 280.degree. C. under a pressure of 3.6 Pa
with an argon flow rate of 5 mL/min. After the purification by
sublimation, 1.4 g of a white solid was obtained at a collection
rate of 88%.
[0361] The .sup.1H NMR data of the obtained compound are as
follows: .sup.1H NMR (CDCl.sub.3, 300 MHz): .delta.=7.34-7.49 (m,
6H), 7.58 (d, J=7.8 Hz, 2H), 7.66-7.77 (m, 6H), 7.97-8.02 (m, 6H),
8.21-8.22 (m, 2H), 8.27-8.28 (m, 1H), 8.99 (d, J=2.4 Hz, 2H).
[0362] FIGS. 32A and 32B show .sup.1H NMR charts. Note that FIG.
32B is a chart showing an enlarged part of FIG. 32A in the range of
7.00 ppm to 9.5 ppm. The measurement results show that 3,5mDBFP2Py,
which was the target substance, was obtained.
<<Properties of 3,5mDBFP2Py>>
[0363] FIG. 33A shows an absorption spectrum and an emission
spectrum of a toluene solution of 3,5mDBFP2Py, and FIG. 33B shows
an absorption spectrum and an emission spectrum of a thin film of
3,5mDBFP2Py. The spectra were measured with a UV-visible
spectrophotometer (V550, produced by JASCO Corporation). The
spectra of the toluene solution were obtained with the toluene
solution of 3,5mDBFP2Py put in a quartz cell. The spectra of the
thin film were measured with a sample prepared by deposition of
3,5mDBFP2Py on a quartz substrate by evaporation. Note that in the
case of the absorption spectrum of the toluene solution of
3,5mDBFP2Py, the absorption spectrum obtained by subtraction of the
absorption spectra of the quartz cell and toluene from the raw
spectra is illustrated. In the case of the absorption spectrum of
the thin film of 3,5mDBFP2Py, the absorption spectrum obtained by
subtraction of the absorption spectrum of the quartz substrate from
the raw spectra is illustrated.
[0364] As shown in FIG. 33A, in the case of 3,5mDBFP2Py in the
toluene solution, absorption peaks were observed at approximately
314 nm and 288 nm, and emission peaks were observed at
approximately 342 nm and 332 nm (excitation wavelength: 292 nm). As
shown in FIG. 33B, in the case of the thin film of 3,5mDBFP2Py,
absorption peaks were observed at approximately 316 nm, 304 nm, 293
nm, 272 nm, 250 nm, and 206 nm, and emission peaks were observed at
approximately 356 nm and 341 nm (excitation wavelength: 305 nm).
Thus, it was found that absorption and emission of 3,5mDBFP2Py
occur in extremely short wavelength regions.
[0365] The ionization potential of 3,5mDBFP2Py in a thin film state
was measured by a photoelectron spectrometer (AC-3, manufactured by
Riken Keiki, Co., Ltd.) in the air. The obtained value of the
ionization potential was converted into a negative value, so that
the HOMO level of 3,5mDBFP2Py was -6.49 eV. From the data of the
absorption spectrum of the thin film in FIG. 33B, the absorption
edge of 3,5mDBFP2Py, which was obtained from Tauc plot with an
assumption of direct transition, was 3.69 eV. Therefore, the
optical band gap of 3,5mDBFP2Py in a solid state was estimated to
be 3.69 eV; from the values of the HOMO level obtained above and
this band gap, the LUMO level of 3,5mDBFP2Py was estimated to be
-2.80 eV. The above results show that 3,5mDBFP2Py in the solid
state has a band gap as wide as 3.69 eV.
[0366] Phosphorescence of 3,5mDBFP2Py was measured. The measurement
was performed by using a PL microscope, LabRAM HR-PL, produced by
HORIBA, Ltd., a He--Cd laser (325 nm) as excitation light, and a
CCD detector at a measurement temperature of 10 K. For the
measurement, a thin film as a sample was formed over a quartz
substrate to a thickness of approximately 50 nm and another quartz
substrate was attached to the deposition surface in a nitrogen
atmosphere. The results showed that the peak on the shortest
wavelength side of a phosphorescence spectrum of 3,5mDBFP2Py is at
467 nm, which means that 3,5mDBFP2Py has a high T.sub.1 level.
Example 7
[0367] This example will describe blue-emissive phosphorescent
light-emitting elements in which
3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine (abbreviation:
3,5mDBTP2Py) or 3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBFP2Py) was used as a host material and an
electron-transport material (a light-emitting element 5 and a
light-emitting element 6).
[0368] Molecular structures of organic compounds that were used in
this example are shown by Structural Formulae (i), (ii), (v),
(viii), (ix), and (x). The element structure in FIG. 1A was
employed.
##STR00069## ##STR00070##
<<Fabrication of Light-Emitting Element 5>>
[0369] First, a glass substrate, over which a film of indium tin
oxide containing silicon (ITSO) was formed to a thickness of 110 nm
as the first electrode 101, was prepared. A surface of the ITSO
film was covered with a polyimide film so that an area of 2
mm.times.2 mm of the surface was exposed. The electrode area was 2
mm.times.2 mm. As pretreatment for forming the light-emitting
element over the substrate, the surface of the substrate was washed
with water and baked at 200.degree. C. for 1 hour, and then
UV-ozone treatment was performed for 370 seconds. After that, the
substrate was transferred into a vacuum evaporation apparatus where
the pressure had been reduced to approximately 10.sup.-4 Pa, and
was subjected to vacuum baking at 170.degree. C. for 30 minutes in
a heating chamber of the vacuum evaporation apparatus, and then the
substrate was cooled down for approximately 30 minutes.
[0370] Then, the substrate was fixed to a holder provided in the
vacuum evaporation apparatus so that the surface provided with ITSO
faced downward.
[0371] The pressure in the vacuum evaporation apparatus was reduced
to 10.sup.-4 Pa. Then,
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II) represented by Structural Formula (i) and molybdenum(VI)
oxide were deposited by co-evaporation so that the weight ratio of
DBT3P-II to molybdenum oxide was 4:2, whereby the hole-injection
layer 111 was formed. The thickness was set to 60 nm. Note that
co-evaporation is an evaporation method in which a plurality of
different substances are concurrently vaporized from respective
different evaporation sources.
[0372] Next, 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP)
represented by Structural Formula (ii) was deposited by evaporation
to a thickness of 20 nm, whereby the hole-transport layer 112 was
formed.
[0373] Moreover, 3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBTP2Py) represented by Structural Formula (ix),
PCCP, and tris
{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-
-yl-.kappa.N2]phenyl-.kappa.C}iridium(III) (abbreviation:
[Ir(mpptz-dmp).sub.3]) represented by Structural Formula (viii)
were co-deposited by evaporation to a thickness of 30 nm on the
hole-transport layer 112 so that
PCCP:3,5mDBTP2Py:[Ir(mpptz-dmp).sub.3]=1:0.3:0.06 (weight ratio),
and then, 3,5mDBTP2Py and [Ir(mpptz-dmp).sub.3] were co-deposited
by evaporation to a thickness of 10 nm so that
3,5mDBTP2Py:[Ir(mpptz-dmp).sub.3]=1:0.06 (weight ratio), whereby
the light-emitting layer 113 was formed.
[0374] Next, 3,5mDBTP2Py was deposited by evaporation to a
thickness of 10 nm, and then bathophenanthroline (abbreviation:
BPhen) represented by Structural Formula (v) was deposited by
evaporation to a thickness of 15 nm, whereby the electron-transport
layer 114 was formed.
[0375] Then, lithium fluoride was deposited by evaporation to a
thickness of 1 nm on the electron-transport layer 114, whereby the
electron-injection layer 115 was formed. Lastly, a film of aluminum
was formed to a thickness of 200 nm as the second electrode 102
which serves as a cathode. Thus, the light-emitting element 5 was
completed. Note that in all the above evaporation steps,
evaporation was performed by a resistance-heating method.
<<Fabrication of Light-Emitting Element 6>>
[0376] The light-emitting element 6 was fabricated in a manner
similar to that of the light-emitting element 5 except that
3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine (abbreviation:
3,5mDBFP2Py) represented by Structural Formula (x) was used instead
of 3,5mDBTP2Py.
<<Operation Characteristics of Light-Emitting Element 5 and
Light-Emitting Element 6>>
[0377] The light-emitting element 5 and the light-emitting element
6 obtained as described above were sealed in a glove box containing
a nitrogen atmosphere so as not to be exposed to the air
(specifically, a sealant was applied onto an outer edge of each
element, and heat treatment at 80.degree. C. for 1 hour and UV
treatment were performed at the time of sealing). Then, the
operating characteristics of the light-emitting elements were
measured. Note that the measurement was carried out at room
temperature (in an atmosphere kept at 25.degree. C.).
[0378] FIG. 34 shows the luminance-current density characteristics
of the light-emitting element 5 and the light-emitting element 6;
FIG. 35 shows the current efficiency-luminance characteristics
thereof; FIG. 36 shows the luminance-voltage characteristics
thereof; and FIG. 37 shows the external quantum
efficiency-luminance characteristics thereof.
[0379] FIG. 35 shows that the light-emitting element 5 and the
light-emitting element 6 have favorable current
efficiency-luminance characteristics and thus have a high emission
efficiency. Accordingly, 3,5mDBTP2Py and 3,5mDBFP2Py have a high
triplet level and a wide band gap, and allow even a light-emitting
substance emitting blue phosphorescence to be effectively excited.
Similarly, as shown in FIG. 37, the light-emitting element 5 and
the light-emitting element 6 have favorable external quantum
efficiency-luminance characteristics. Moreover, FIG. 36 shows that
the light-emitting element 5 and the light-emitting element 6 have
favorable luminance-voltage characteristics and thus have low
driving voltage. This means that 3,5mDBTP2Py and 3,5mDBFP2Py have a
high carrier-transport property. FIG. 34 also shows that the
light-emitting element 5 and the light-emitting element 6 have
favorable luminance-current density characteristics.
[0380] FIG. 38 shows emission spectra at the time when a current of
0.1 mA was made to flow in the light-emitting element 5 and the
light-emitting element 6. FIG. 38 shows that the light-emitting
element 5 and the light-emitting element 6 emit blue light
originating from [Ir(mpptz-dmp).sub.3], which is the emission
center substance.
[0381] A comparative light-emitting element 2 was also fabricated
in which 3,5mDBTP2Py in the light-emitting element 5 was replaced
with an organic compound having the same structure as 3,5mDBTP2Py
except that it has a pyrimidine skeleton instead of a pyridine
skeleton. The external quantum efficiency of the light-emitting
element 5 was higher than that of the comparative light-emitting
element 2. The light-emitting element 5 also exhibited a sharp
spectrum, which means that it has high color purity.
Example 8
[0382] This example will describe green-emissive phosphorescent
light-emitting elements in which
3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine (abbreviation:
3,5mDBTP2Py) or 3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBFP2Py) was used as a host material and an
electron-transport material (a light-emitting element 7 and a
light-emitting element 8).
[0383] Molecular structures of organic compounds that were used in
this example are shown by Structural Formulae (i), (ii), (iv), (v),
(ix), (x), and (xii). The element structure in FIG. 1A was
employed.
##STR00071## ##STR00072##
<<Fabrication of Light-Emitting Element 7>>
[0384] First, a glass substrate, over which a film of indium tin
oxide containing silicon (ITSO) was formed to a thickness of 110 nm
as the first electrode 101, was prepared. A surface of the ITSO
film was covered with a polyimide film so that an area of 2
mm.times.2 mm of the surface was exposed. The electrode area was 2
mm.times.2 mm. As pretreatment for forming the light-emitting
element over the substrate, the surface of the substrate was washed
with water and baked at 200.degree. C. for 1 hour, and then
UV-ozone treatment was performed for 370 seconds. After that, the
substrate was transferred into a vacuum evaporation apparatus where
the pressure had been reduced to approximately 10.sup.-4 Pa, and
was subjected to vacuum baking at 170.degree. C. for 30 minutes in
a heating chamber of the vacuum evaporation apparatus, and then the
substrate was cooled down for approximately 30 minutes.
[0385] Then, the substrate was fixed to a holder provided in the
vacuum evaporation apparatus so that the surface provided with ITSO
faced downward.
[0386] The pressure in the vacuum evaporation apparatus was reduced
to 10.sup.-4 Pa. Then,
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II) represented by Structural Formula (i) and molybdenum(VI)
oxide were deposited by co-evaporation so that the weight ratio of
DBT3P-II to molybdenum oxide was 4:2, whereby the hole-injection
layer 111 was formed. The thickness was set to 60 nm.
[0387] Next, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine
(abbreviation: BPAFLP) represented by Structural Formula (xii) was
deposited by evaporation to a thickness of 20 nm, whereby the
hole-transport layer 112 was formed.
[0388] Moreover, 3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBTP2Py) represented by Structural Formula (ix),
3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP) represented by
Structural Formula (ii), and fac-tris(2-phenylpyridine)iridium
(abbreviation: [Ir(ppy).sub.3]) represented by Structural Formula
(iv) were co-deposited by evaporation to a thickness of 40 nm on
the hole-transport layer 112 so that
3,5mDBTP2Py:PCCP:[Ir(ppy).sub.3]=0.8:0.2:0.06 (weight ratio),
whereby the light-emitting layer 113 was formed.
[0389] Next, 3,5mDBTP2Py was deposited by evaporation to a
thickness of 10 nm, and then bathophenanthroline (abbreviation:
BPhen) represented by Structural Formula (v) was deposited by
evaporation to a thickness of 15 nm, whereby the electron-transport
layer 114 was formed.
[0390] Then, lithium fluoride was deposited by evaporation to a
thickness of 1 nm on the electron-transport layer 114, whereby the
electron-injection layer 115 was formed. Lastly, a film of aluminum
was formed to a thickness of 200 nm as the second electrode 102
which serves as a cathode. Thus, the light-emitting element 7 was
completed. Note that in all the above evaporation steps,
evaporation was performed by a resistance-heating method.
<<Fabrication of Light-Emitting Element 8>>
[0391] The light-emitting element 8 was fabricated in a manner
similar to that of the light-emitting element 7 except that
3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine (abbreviation:
3,5mDBFP2Py) represented by Structural Formula (x) was used instead
of 3,5mDBTP2Py.
<<Operation Characteristics of Light-Emitting Element 7 and
Light-Emitting Element 8>>
[0392] The light-emitting element 7 and the light-emitting element
8 obtained as described above were sealed in a glove box containing
a nitrogen atmosphere so as not to be exposed to the air
(specifically, a sealant was applied onto an outer edge of each
element, and heat treatment at 80.degree. C. for 1 hour and UV
treatment were performed at the time of sealing). Then, the
operating characteristics of the light-emitting elements were
measured. Note that the measurement was carried out at room
temperature (in an atmosphere kept at 25.degree. C.).
[0393] FIG. 39 shows the luminance-current density characteristics
of the light-emitting element 7 and the light-emitting element 8;
FIG. 40 shows the current efficiency-luminance characteristics
thereof; FIG. 41 shows the luminance-voltage characteristics
thereof; and FIG. 42 shows the external quantum
efficiency-luminance characteristics thereof.
[0394] FIG. 40 shows that the light-emitting element 7 and the
light-emitting element 8 have favorable current
efficiency-luminance characteristics and thus have a high emission
efficiency. Accordingly, 3,5mDBTP2Py and 3,5mDBFP2Py have a high
triplet level and a wide band gap, and allow even a light-emitting
substance emitting green phosphorescence to be effectively excited.
Similarly, as shown in FIG. 42, the light-emitting element 7 and
the light-emitting element 8 have favorable external quantum
efficiency-luminance characteristics. Moreover, FIG. 41 shows that
the light-emitting element 7 and the light-emitting element 8 have
favorable luminance-voltage characteristics and thus have low
driving voltage. This means that 3,5mDBTP2Py and 3,5mDBFP2Py have a
high carrier-transport property. FIG. 39 also shows that the
light-emitting element 7 and the light-emitting element 8 have
favorable luminance-current density characteristics.
[0395] The above results show that the light-emitting element 7
that contains 3,5mDBTP2Py and the light-emitting element 8 that
contains 3,5mDBFP2Py have favorable characteristics including a
high emission efficiency.
[0396] FIG. 43 shows emission spectra at the time when a current
was made to flow in the fabricated light-emitting elements at a
current density of 2.5 mA/cm.sup.2. FIG. 43 shows that the
light-emitting element 7 and the light-emitting element 8 emit
green light originating from [Ir(ppy).sub.3], which is the emission
center substance.
[0397] Next, these light-emitting elements were subjected to
reliability tests. In the reliability tests, a change in luminance
(normalized luminance) over driving time was measured with an
initial luminance taken as 100% under the conditions where the
initial luminance was 5000 cd/m.sup.2 and the current density was
constant. FIG. 44 shows the results. The above results show that
the light-emitting element 7 and the light-emitting element 8 have
high reliability.
Example 9
[0398] This example will describe the reliability of light-emitting
elements (light-emitting elements 9 to 13 and comparative
light-emitting elements 3 and 4), which are different in a material
of a hole-transport layer, a host material of a light-emitting
layer, and a material of an electron-transport layer.
[0399] Molecular structures of organic compounds that were used in
this example are shown by Structural Formulae (i), (ii), (iv), (v),
(ix), (x), (xii), and (xiii). The element structure in FIG. 1A was
employed.
##STR00073## ##STR00074##
<<Fabrication of Light-Emitting Element 9>>
[0400] First, a glass substrate, over which a film of indium tin
oxide containing silicon (ITSO) was formed to a thickness of 110 nm
as the first electrode 101, was prepared. A surface of the ITSO
film was covered with a polyimide film so that an area of 2
mm.times.2 mm of the surface was exposed. The electrode area was 2
mm.times.2 mm. As pretreatment for forming the light-emitting
element over the substrate, the surface of the substrate was washed
with water and baked at 200.degree. C. for 1 hour, and then
UV-ozone treatment was performed for 370 seconds. After that, the
substrate was transferred into a vacuum evaporation apparatus where
the pressure had been reduced to approximately 10.sup.-4 Pa, and
was subjected to vacuum baking at 170.degree. C. for 30 minutes in
a heating chamber of the vacuum evaporation apparatus, and then the
substrate was cooled down for approximately 30 minutes.
[0401] Then, the substrate was fixed to a holder provided in the
vacuum evaporation apparatus so that the surface provided with ITSO
faced downward.
[0402] The pressure in the vacuum evaporation apparatus was reduced
to 10.sup.-4 Pa. Then,
4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:
DBT3P-II) represented by Structural Formula (i) and molybdenum(VI)
oxide were deposited by co-evaporation so that the weight ratio of
DBT3P-II to molybdenum oxide was 4:2, whereby the hole-injection
layer 111 was formed. The thickness was set to 60 nm.
[0403] Next, 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP)
represented by Structural Formula (ii) was deposited by evaporation
to a thickness of 20 nm, whereby the hole-transport layer 112 was
formed.
[0404] Moreover, 3,5-bis[3-(dibenzothiophen-4-yl)phenyl]pyridine
(abbreviation: 3,5mDBTP2Py) represented by Structural Formula (ix),
PCCP, and fac-tris(2-phenylpyridine)iridium (abbreviation:
[Ir(ppy).sub.3]) represented by Structural Formula (iv) were
co-deposited by evaporation to a thickness of 40 nm on the
hole-transport layer 112 so that
3,5mDBTP2Py:PCCP:[Ir(ppy).sub.3]=0.8:0.2:0.06 (weight ratio),
whereby the light-emitting layer 113 was formed.
[0405] Next, 3,5mDBTP2Py was deposited by evaporation to a
thickness of 10 nm, and then bathophenanthroline (abbreviation:
BPhen) represented by Structural Formula (v) was deposited by
evaporation to a thickness of 15 nm, whereby the electron-transport
layer 114 was formed.
[0406] Then, lithium fluoride was deposited by evaporation to a
thickness of 1 nm on the electron-transport layer 114, whereby the
electron-injection layer 115 was formed. Lastly, a film of aluminum
was formed to a thickness of 200 nm as the second electrode 102
which serves as a cathode. Thus, the light-emitting element 9 was
completed. Note that in all the above evaporation steps,
evaporation was performed by a resistance-heating method.
<<Fabrication of Light-Emitting Element 10>>
[0407] The light-emitting element 10 was fabricated in a manner
similar to that of the light-emitting element 9 except that in the
hole-transport layer,
4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:
BPAFLP) represented by Structural Formula (xii) was used instead of
PCCP.
<<Fabrication of Light-Emitting Element 11>>
[0408] The light-emitting element 11 was fabricated in a manner
similar to that of the light-emitting element 9 except that
3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine (abbreviation:
3,5mDBFP2Py) represented by Structural Formula (x) was used instead
of 3,5mDBTP2Py.
<<Fabrication of Light-Emitting Element 12>>
[0409] The light-emitting element 12 was fabricated in a manner
similar to that of the light-emitting element 10 except that
3,5-bis[3-(dibenzofuran-4-yl)phenyl]pyridine (abbreviation:
3,5mDBFP2Py) represented by Structural Formula (x) was used instead
of 3,5mDBTP2Py.
<<Fabrication of Comparative Light-Emitting Element
3>>
[0410] The comparative light-emitting element 3 was fabricated in a
manner similar to that of the light-emitting element 9 except that
3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:
35DCzPPy) represented by Structural Formula (xiii) was used instead
of 3,5mDBTP2Py.
<<Fabrication of Comparative Light-Emitting Element
4>>
[0411] The comparative light-emitting element 4 was fabricated in a
manner similar to that of the light-emitting element 10 except that
3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:
35DCzPPy) represented by Structural Formula (xiii) was used instead
of 3,5mDBTP2Py.
[0412] The table below lists the materials used in the
hole-transport layers of the light-emitting elements 9 to 12 and
the comparative light-emitting elements 3 and 4, the host materials
used in the light-emitting layers thereof, and the materials used
in the electron-transport layers thereof.
TABLE-US-00001 TABLE 1 Host Material and Hole-transport
Electron-transport Layer Layer Light-emitting Element 9 PCCP
3,5mDBTP2Py Light-emitting Element 10 BPAFLP 3,5mDBTP2Py
Light-emitting Element 11 PCCP 3,5mDBFP2Py Light-emitting Element
12 BPAFLP 3,5mDBFP2Py Comparative Light-emitting PCCP 35DCzPPy
Element 3 Comparative Light-emitting BPAFLP 35DCzPPy Element 4
[0413] Next, these light-emitting elements were subjected to
reliability tests. In the reliability tests, a change in luminance
(normalized luminance) over driving time was measured with an
initial luminance taken as 100% under the conditions where the
initial luminance was 5000 cd/m.sup.2 and the current density was
constant. FIG. 45 shows the results.
[0414] The luminance of the comparative light-emitting elements 3
and 4 decreased to 50% of the initial luminance in 190 hours and
150 hours, respectively. Meanwhile, the light-emitting elements 9
and 10 respectively kept 61% and 60% of the initial luminance after
370 hours elapsed, and the light-emitting elements 11 and 12
respectively kept 51% and 53% of the initial luminance after 340
hours elapsed. The results revealed that a light-emitting element
that uses the organic compound of one embodiment of the present
invention is highly reliable.
[0415] This application is based on Japanese Patent Application
serial no. 2013-150305 filed with Japan Patent Office on Jul. 19,
2013, the entire contents of which are hereby incorporated by
reference.
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