# Patent

## Title
Electroconductive device, organic electroluminescence device using the device and process for producing the electroconductive device

## Abstract

An electroconductive device includes a pair of oppositely disposed electrodes, a luminescence layer and an electroconductive layer disposed between the electrodes. The electroconductive layer includes a mixture of a plurality of organic compounds which are mutually structural isomers and include a major component and a minor component. The mixture contains the major and minor components in a (major component/minor component) ratio of 1/1 to 9/1. When the electroconductive layer is used as a carrier injection or transport layer, preferably an electron injection layer, a resultant electroluminescence (EL) device exhibits a high luminescence efficiency.

## Background
FIELD OF THE INVENTION AND RELATED ARAT
The present invention relates to an organic electroluminescence (EL) device for use in, e.g., flat panel displays, projection displays, and printers; an electroconductive device used for the EL device; and a process for producing the electroconductive device.
Since C. W. Tang et al substantiated in 1987 that it is possible to effect high-brightness luminescence under application of a low DC voltage by utilizing a lamination structure comprising a film of fluorescent metal chelate complex and a diamine-based molecular film, an applied study on an organic electroluminescence (EL) device as a luminescence device with high-speed responsiveness and high efficiency has been extensively conducted. The organic EL device is a self-light emitting device of a carrier injection type using luminescence occurring at the time of re-combination of electrons and holes reached to a luminescent layer.
FIG. 6 shows a structure of an ordinary organic EL device.
Referring to FIG. 6, the EL device includes a transparent substrate 21, and thereon layers of a transparent electrode 22, a hole transporting layer 23, a luminescent layer 24 and a metal electrode 25 are successively disposed in this order. Between the metal electrode 25 (as a cathode) and the transparent electrode 22 (as an anode) for taking out emitted light, organic compound layers 20 comprising the luminescence layer 24 and the hole transporting layer 23 are formed and disposed each in a thickness of ca. several hundred Å. Examples of the cathode metal electrode 25 may include a metal or an alloy having a smaller work function, such as aluminum, aluminum-lithium alloy and magnesium-silver alloy. Examples of the anode transparent electrode 22 may include an electroconductive material having a larger work function, such as ITO (indium tin oxide). The organic compound layer 20 in this structure (FIG. 6) has a two-layer structure comprising the luminescence layer 24 and the hole transporting layer 23.
FIG. 7 shows another structure of an ordinary organic EL device.
Referring to FIG. 7, the EL device includes a transparent substrate 21 on which a transparent electrode 22 (anode), a hole transporting layer 23, a luminescence layer 24, an electron transporting layer 31 and a metal electrode 25 (cathode) are sequentially disposed in this order. In this case, an organic compound layer 20 has a three-layer structure comprising the hole transporting layer 23, the luminescence layer 24 and the electron transporting layer 31.
Generally, the hole transporting layer (23 in FIGS. 6 and 7) has a function of efficiently injecting holes from the anode (transparent electrode 22) into the luminescence layer (24). On the other hand, the electron transporting layer (31 in FIG. 7) generally has a function of efficiently injecting electrons from the cathode (metal electrode 25) into the luminescence layer (24).
These hole transporting and electron transporting layers (23 and 31) also have an electron (carrier) blocking function and a hole (carrier) blocking function, respectively, thus enhancing a resultant luminescence efficiency.
For these carrier (hole and electron) transporting layers (23 and 31), it is important to exhibit a sufficient charge (carrier) transporting ability, particularly a carrier mobility.
Accordingly, if the carrier mobility in the carrier transporting layer is increased, more carriers can be injected into the luminescence layer 24 to enhance the luminescence efficiency. In addition, the higher mobility is also effective in increasing a thickness (e.g., ca. 1 μm) of the carrier transporting layer (generally, several hundred Å-thick). As a result, it becomes possible to prevent an occurrence of short circuit between the pair of electrodes (anode and cathode) and improve a productivity.
For this reason, at present, a compound (material) for the carrier transport layer has been extensively developed in order to achieve a high luminescence efficiency of the organic EL device.
In order to obtain a high electroconductivity by applying an electric field to a pair of electrodes between which an organic compound layer is disposed, it is necessary to provide a good carrier (electron/hole) injection performance from the electrodes and a high carrier mobility.
Incidentally, although hole injection/transport materials exhibiting relatively good performances have been proposed, an electron injection/transport material exhibiting a sufficient characteristic has not been found as yet.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem, an object of the present invention is to provide an electroconductive device using a carrier injection and/or transport layer comprising a material suitable for efficiently injecting and/or transporting carriers (holes or electrons).
Another object of the present invention is to provide an organic electroluminescence (EL) device including the electroconductive device and having a high luminescence efficiency and a high reliability.
A further object of the present invention is to provide a process for producing the electroconductive device.
According to the present invention, there is provided an electroconductive device, comprising: a pair of oppositely disposed electrodes, and a luminescence layer and an electroconductive layer disposed between the electrodes, wherein

    
    
        the electroconductive layer comprises a mixture of a plurality of organic compounds which are mutually structural isomers and include a major component and a minor component, the mixture comprising the major and minor components in a (major component)/(minor component) ratio of 1/1 to 9/1.
    
    


According to the present invention, there is also provided an electroluminescence (EL) device including the above-mentioned electroconductive device wherein the electroconductive layer is used as a carrier injection layer and/or a carrier transport layer.
According to the present invention, there is further provided a process for producing the above-mentioned electroconductive device, comprising:

    
    
        a step of forming the above-mentioned electroconductive layer between the pair of electrodes.
    
    


These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view of an embodiment of an electroconductive device (organic EL device) prepared in Example 2 (appearing hereinafter) according to the present invention.
FIGS. 2 and 3 are respectively a graph showing a current (density)-voltage characteristic of an organic EL device prepared in Example 2 (FIG. 2) and Comparative Example 1 (FIG. 3), respectively.
FIGS. 4 and 5 are respectively a graph showing a luminescence efficiency of an organic EL device prepared in Example 2 (FIG. 4) and Comparative Example 1 (FIG. 5), respectively.
FIGS. 6 and 7 are respectively a schematic sectional view of an embodiment of an organic EL device.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The electroconductive device according to the present invention is characterized in that an electroconductive layer disposed between a pair of electrodes is formed by using a mixture of a plurality of organic compounds which are mutually structural isomers and include a major component and a minor component (hereinafter, referred to as a “structural isomer mixture”). The structural isomer mixture comprises the major and minor component in (major component)/(minor component) ratio of 1/1 to 9/1, preferably 1/1 to 5/1.
The organic EL device according to the present invention using the electroconductive layer as a carrier injection layer and/or a carrier transport layer, preferably as an electron injection layer and/or an electron transport layer.
Herein, the structural isomers refer to compounds having an identical ring structure and an identical rational formula but having (molecular) structures different in the manner in which their atoms are linked.
A compound molecule having at least one ring structure has a planar molecular structure by nature, thus being liable to be crystallized in the case of a single compound (free from structural isomer).
On the other hand, we have found that it is possible to stably form an amorphous structure by using a structural isomer mixture, particularly a mixture of low-molecular compounds each having such a ring structure that a plurality of rings are connected via a single bond.
In the present invention, by using the structural isomer mixture having such a stabilized amorphous structure, it becomes possible to form an electroconductive layer exhibiting a high carrier injection and/or transport performance. Further, by using the electroconductive layer as a charge injection and/or transport layer, it is possible to provide an organic EL device with a high luminescence efficiency.
Incidentally, with respect to a luminescent layer, it has been suggested that the luminescent layer containing an aminoquinoline complex having a facial-rich stereostructure provides better performances (Japanese Laid-Open Patent Application (JP-A) No. 4-85388).
According to the present invention, by using the structural isomer mixture in the electroconductive layer (as the carrier injection and/or transfer layer), the resultant EL device exhibits an excellent luminescent characteristic.
In the present invention, the organic compounds constituting the structural isomer mixture may preferably be represented by the following formula (1):

(R—X)n—Ar—(X′—R′)m  (1),

wherein Ar denotes a connected ring structure comprising two single rings connected with each other via a single bond or two fused rings connected with each other via a single bond; X and X′ independently denote a single bond, —O—, —S—, —OOC— or —COO—; R and R′ independently denote —H, —F or a linear or branched alkyl group having 1-20 carbon atoms capable of including one methylene group which can be replaced with —O—, —S—, —CH═CH— or —C≡C—; and m and n are an integer of 1-8, with the proviso that R and R′ cannot be —H at the same time when X and X′ are a single bond.

In the formula (1), Ar may preferably be a connected ring structure comprising two fused rings connected with each other via a single bond, wherein each of said two fused rings comprises 2-5 rings. Further, Ar in the formula (1) may preferably be a connected ring structure represented by any one of the following formulas (a) to (n): 







wherein CH is optionally substituted with N or NH, and CH2 is optionally substituted with S or O.

Ar in the formula (1) may preferably be a connected ring structure represented by the following formula (2):

A—B  (2),

wherein A and B independently denote any one of phenyl-diyl, pyridine-diyl, pyrazine-diyl, pyrimidine-diyl, pyridazine-diyl, indene-diyl, indolizine-diyl, isoindole-diyl, indole-diyl, purine-diyl, naphthalene-diyl, quinoline-diyl, isoquinoline-diyl, quinoxaline-diyl, 1,5-naphthyridine-diyl, 1,6-naphthyridine-diyl, 1,7-naphtharidine-diyl, 1,8-naphthyridine-diyl, quinazoline-diyl, cinnoline-diyl, pyrido[2,3-b]pyrazine-diyl, pyrazino[2,3-b]pyrazine-diyl, pteridine-diyl, biphenylene-diyl, fluorene-diyl, carbazole-diyl, thianthrene-diyl, phenalene-diyl, phenanthridine-diyl, phenanthrene-diyl, anthracene-diyl, chrysene-diyl, acridine-diyl, perimidine-diyl, phenanthroline-diyl, phenazine-diyl, phenothiazine-diyl, phenoxathin-diyl, indan-diyl, coumaran-diyl, phthalan-diyl, chroman-diyl, isochroman-diyl, thiachroman-diyl, isothiachroman-diyl, and thiaxanthene-diyl.

In the formula (2), A may preferably be quinoxaline-diyl.
In the formula (1) and (2), R═R′, X═X′, m=n=1 are satisfied in the formula (1), and A═B may preferably be satisfied to form a symmetric structure having a center of symmetry.
The organic compounds used for constituting the structural isomer mixture in the present invention may desirably be selected based on the following molecular design factors (1) to (3).
(1) Lowering in LUMO (Lowest Unoccupied Molecular Orbital) Level
An electron transport is effected by hopping conduction on LUMO of organic compound molecules. Accordingly, it is important to improve electron injection from an electrode to LUMO. Generally, in view of chemical stability of the electrode, it is difficult to decrease a work function of the electrode. As a result, a key feature for the improved electron injection is how to lower the LUMO level of organic compounds used.
From the above viewpoint, we have calculated HOMO (highest occupied molecular orbital) levels and LUMO levels of several ring structures (capable of constituting the organic compounds used in the present invention) according to molecular orbital method in order to expect the LUMO level of the organic compounds. As the molecular orbital method, in the present invention, a semiempirical molecular orbital method (the AM1 method) is used.
The results are as follows.















HOMO
LUMO























quinoline
−9.2
−0.47







isoquinoline
−9.0
−0.56







quinoxaline
−9.6
−0.68







[1,5]naphthyridine
−9.7
−0.67







[1,6]naphthyridine
−9.5
−0.77







[1,7]naphthyridine
−9.5
−0.76







[1,8]naphthyridine
−9.8
−0.71







quinazoline
−9.5
−0.77







pyrido[2,3-b]pyrazine
−10.0
−0.93







pyradino[2,3-b]pyrazine
−9.9
−1.21







naphtyalene
−8.7
−0.27









As shown above, compared with naphthalene, naphthalene skeleton having 1-4 nitrogen atoms (substituted for corresponding CH group(s) of naphthalene) can lower the LUMO level of naphthalene.
Accordingly, by using such heterocyclic fused ring structure as a skeleton of organic compound, a resultant electron injection performance from an electrode is expected to be improved based on lowering in LUMO level.
(2) Symmetry of Molecular Structure
As described in (1), the electroconductivity of liquid crystal compound is based on the hopping conduction, which varies largely depending on a magnitude of overlap integral of π electron cloud between adjacent molecules. It is important to increase the overlap integral of the π electron cloud in order to improve an electron conductivity. For the electron conduction, it is effective to impart a (molecular-structural) symmetry to the organic compound molecules so as to dispose their π electron skeletons close to each other, thus increasing the overlap integral of π electron cloud. As a result, a mobility of electron is improved to provide an enhanced electroconductivity.
Even if a complete symmetry of molecular structure is not ensured, the above advantages are retained as far as organic compound molecules have a similar skeleton structure such that both of terminal chains have an almost equal carbon number.
Accordingly, in the present invention, the organic compounds may preferably have a symmetric structure having a center of symmetry by designing molecular structure so as to satisfy R═R′, X═X′, m=n=1 and A═B (in A—B as Ar) in the above-mentioned formulas (1) and (2).
(3) Suppression of Crystallization in the Presence of Structural Isomers
The increase in overlap integral of π electron cloud between adjacent molecules leads to an increase in regularity of mutually adjacent molecules, thus resulting in a high crystallinity thereof.
In order to prevent an occurrence of such a crystallization, it is expected that the crystallinity of the structural isomer mixture can be lowered by mixing a plurality of organic compounds having different substituents outside the π electron clouds, thus providing an amorphous property to increase an electroconductivity.
Accordingly, the structural isomer mixture constituting the electroconductive layer used in the present invention may desirably be placed in an amorphous state.
In the present invention, the above-described three molecular design factors (1), (2) and (3) are not necessarily fulfilled at the same time.
Based on the above molecular design factors, we have found that it is possible to realize a luminescence device with a high luminescence efficiency by using the structural isomer mixture comprising a plurality of organic compounds of the formula (1) (preferably formula (2)) in a carrier injection and/or transport layer of an organic EL device.
Particularly, when an electron injection layer is formed by using the structural isomer mixture comprising such organic compounds based on the above molecular design factors, it becomes possible to considerably improve an electron injection performance.
The luminescence device (electroconductive device) with a high luminescence efficiency can be applied to products required to effect energy saving or provide a high luminance (brightness), such as a display apparatus, an illumination apparatus, a light source for a printer, and a backlight for a liquid crystal display apparatus. More specifically, as the display apparatus, it is possible to provide a flat panel display excellent in energy saving performance, visibility and weight reduction. As the light source for a printer, it is possible to replace a laser light source of a laser beam printer widely used at present with the electroconductive device of the present invention. Image formation may be performed by disposing independently addressable devices in array and subjecting a photosensitive drum to a desired exposure to light. By using the electroconductive device of the present invention, it is possible to remarkably reduce an apparatus size (volume). With respect to the illumination apparatus and the backlight, it is possible to expect an energy saving performance by the use of the electroconductive device of the present invention.
Hereinbelow, specific but non-exhaustive examples of the organic compounds of the formula (2) constituting the structural isomer mixture used in the electroconductive device (or EL device) of the present invention will be enumerated in the following Tables 5-15. Symbols a1 to a33 used for specifying a ring structure for liquid crystal compounds shown in Tables 5-15 have specific skeletons (ring structures) shown in the following Tables 1-4.











TABLE 1







Symbol
Name
Formula









a1
quinoxaline-diyl








a2









a3
quinoline-diyl








a4









a5
isoquinoline-diyl








a6









a7
quinoline-diyl








a8



























TABLE 2







Symbol
Name
Formula









a9
[1,5]naphthyridine-diyl








a10
[1,6]naphthyridine-diyl








a11









a12
[1,7]naphthyridine-diyl








a13









a14
[1,8]naphthyridine-diyl








a15
quinazoline-diyl








a16









a17
cinnoline-diyl
























TABLE 3





Symbol
Name
Formula







a18
cinnoline-diyl







a19
pyrido[2,3-b]pyridine-diyl







a20








a21
pyrido[2,3-b]pyrazine-diyl







a22








a23
pyrazino[2,3-b]pyrazine-diyl







a24
pteridine-diyl







a25
























TABLE 4





Symbol
Name
Formula







a26
naphthalene-2,6-diyl







a27
chrycene-2,6-diyl







a28
phenazine-diyl







a29
isochroman-diyl







a30
phenoxathiin-diyl







a31
phenanthroline-diyl







a32
pyrazine-diyl







a33
[1,8]naphthyridine-diyl



























TABLE 5





No.
R
X
A
B
X′
R′





















1
CH3
O
a1
a1
—
C7H15


2
C8H17
—
a1
a1
—
C11H23


3
F
—
a1
a1
—
C20H41


4
H
—
a1
a1
O
OC9H19


5
C4H9
O
a1
a1
—
C8H17


6
C12H25
O
a1
a1
—
C10H21


7
C6H13
O
a1
a1
O
C6H13


8
C8H17
O
a1
a1
O
C8H17


9
C11H23
O
a1
a1
O
C11H23


10
C4H9OCH(CH3)CH2(CH2)4
O
a1
a1
O
(CH2)4CH2CH(CH3)OC4H9


11
C9H19
O
a1
a1
O
(CH2)5OC3H7


12
C5H11OCH23
O
a1
a1
O
(CH2)3OC5H11


13
C5H11
O
a1
a1
O
C≡CC6H13


14
C5H11CH═CH
O
a1
a1
O
CH═CHC5H11


15
C10H21
S
a1
a1
S
C10H21


16
C3H7
—
a1
a1
—
C3H7


17
C4H9
—
a1
a1
—
C4H9


18
C5H11
—
a1
a1
—
C5H11


19
C6H13
—
a1
a1
—
C6H13


20
C7H15
—
a1
a1
—
C7H15






















TABLE 6





No.
R
X
A
B
X′
R′







21
C8H17 
—
a1
a1
—
C8H17


22
C9H19 
—
a1
a1
—
C9H19


23
C10H21
—
a1 
a1
—
C10H21


24
C11H23
—
a1
a1
—
C11H23


25
C12H25
—
a1
a1
—
C12H25


26
C18H37
—
a1
a1
—
C18H37


27
C6H13
—
a1
a1
—
C8H17


28
C11H23
—
a1
a1
—
C3H7


29
C6H13
COO
a1
a1
OOC
C6H13


30
C5H11
COO
a1
a1
COO
C11H23


31
C2H5CH(CH3)CH2(CH2)4
OOC
a1
a1
COO
(CH2)5CH(CH3)C2H5


32
H
—
a1
a26
O
C4H9


33
C8H17
—
a1
a26
O
C5H11


34
C11H23
—
a1
a26
O
C10H21 


35
C9H19
O
a1
a26
O
C9H19


36
C15H31
O
a1
a26
O
C7H15


37
C13H27 
—
a1
a26
—
C3H7


38
C6H13 
—
a1
a26
—
C6H13


39
C9H19
—
a1
a26
—
C9H19


40
C3H7
O
a2
a2
O
C14H29






















TABLE 7





No.
R
X
A
B
X′
R′







41
C7H15
—
a2
a2
—
C7H15


42
C12H25
—
a2
a2
—
C18H37


43
H
—
a2
a26
O
C4H9


44
C8H17
—
a2
a26
—
C11H23 


45
C5H11
—
a2
a26
O
(CH2)5OC6H13


46
C2H5
O
a3
a3
—
C8H17


47
C6H13
—
a3
a3
—
C6H13


48
C7H15
—
a3
a3
—
C7H15 


49
C8H17
—
a3
a3
—
C8H17


50
C12H25
—
a3
a3
—
C12H25


51
C9H19
O
a3
a3
O
C5H11


52
C10H21
—
a3
a26
O
C4H9


53
C5H11
—
a3
a26
—
C5H11


54
C8H17
—
a4
a4
—
C8H17


55
C3H7
—
a4
a26
O
C10H21


56
C7H15
—
a5
a5
—
C6H13


57
C5H11
O
a5
a5
—
C5H11


58
C3H7
O
a5
a5
—
C11H23


59
H
—
a5
a5
O
C16H33


60
C9H19
O
a5
a5
O
C7H15






















TABLE 8





No.
R
X
A
B
X′
R′







61
C6H13
—
a5
a5
—
C6H13


62
C7H15
—
a5
a5
—
C7H15


63
C8H17 
—
a5
a5
—
C8H17


64
C13H27
—
a5
a5
—
C5H11


65
C10H21
—
a5
a26
O
(CH2)5C≡CCH3


66
C4H9
—
a5
a26
—
C9H19


67
C5H11
—
a5
a26
—
C5H11


68
C6H13
—
a6
a6
—
C6H13


69
C12H25
—
a6
a6
—
C12H25


70
C9H19
—
a6
a26
O
C3H7


71
C10H21
—
a6
a26
—
C10H21


72
C3H7
—
a7
a7
—
C3H7


73
C10H21
—
a7
a7
—
C4H9


74
C11H23
—
a7
a7
O
(CH2)7CH(CH3)2


75
C17H35
O
a7
a7
—
C8H17


76
C7H15
—
a7
a7
—
C7H15


77
C8H17
—
a7
a7
—
C8H17


78
C9H19
—
a7
a7
—
C9H19


79
C10H21
—
a7
a7
—
C10H21


80
C11H23
—
a7
a7
—
C3H7






















TABLE 9





No.
R
X
A
B
X′
R′







81
C7H15
—
a7
a26
O
CH3


82
C7H15
—
a7
a26
OOC
C4H9


83
C8H17
—
a7
a26
—
C8H17


84
C7H15
—
a8
a8
—
C7H15


85
C8H17
—
a8
a8
—
C8H17


86
C12H25
—
a8
a26
O
C5H11


87
C18H37
—
a8
a26
—
C4H9


88
C7H15 
—
a9
a9
—
C7H15


89
C8H17
—
a9
a9
—
C8H17


90
C9H19
—
a9
a9
—
C9H19


91
C4H9
—
a9
a9
—
C4H9


92
C15H31
—
a9
a9
—
C15H31


93
C5H11
—
a9
a9
—
C8H17


94
C10H21
—
a9
a9
—
C6H13


95
C6H13
—
a9
a26
COO
(CH2)3OC3H7


96
C9H19
—
a9
a26
—
C9H19


97
C7H15
—
a10
a10
O
C6H13


98
C7H15
—
a10
a10
—
C7H15


99
C10H21
—
a10
a10
—
C10H21


100 
C5H11
—
a10
a26
O
C11H23






















TABLE 10





No.
R
X
A
B
X′
R′







101
C8H17
—
a10
a26
—
C12H25


102
C8H17
—
a11
a11
—
C8H17


103
C9H19
—
a11
a11
—
C9H19


104
C3H7
O
a11
a11
—
C8H17


105
C18H37
O
a11
a26
O
C2H5


106
C6H13
—
a12
a12
—
C6H13


107
C9H19
—
a12
a12
—
C9H19


108
C10H21
—
a12
a12
—
C10H21


109
C11H23
—
a12
a12
—
C11H23


110
C12H25
—
a12
a12
—
C12H25


111
C7H15
—
a12
a26
O
C5H11


112
C13H27
—
a12
a26
—
C10H21


113
C4H9
—
a13
a13
—
C4H9


114
C9H19
—
a13
a13
S
C8H17


115
C5H11
—
a14
a14
—
C5H11


116
C7H15
O
a14
a14
—
C9H19


117
C10H21
—
a14
a33
O
(CH2)3OC5H11


118
C7H15
—
a14
a33
—
C7H15


119
C12H25
—
a14
a33
—
C12H25


120
C8H17
—
a14
a26
—
C4H9






















TABLE 11





No.
R
X
A
B
X′
R′







121
C6H13
—
a14
a26
—
C6H13


122
C3H7
—
a33
a14
—
C15H31


123
C8H17
—
a33
a26
O
C8H17


124
C3H7
O
a15
a15
—
C10H21


125
C7H15
—
a15
a15
—
C7H15


126
C5H11
—
a15
a15
O
C7H15


127
C4H9
—
a15
a15
—
C4H9


128
C5H11
—
a15
a15
—
C5H11


129
C6H13
—
a15
a15
—
C6H13


130
C7H15
—
a15
a15
—
C7H15


131
C8H17
—
a15
a15
—
C8H17


132
C12H25
—
a15
a15
—
C3H7


133
H
—
a15
a26
O
C16H33


134
C10H21
—
a15
a26
—
C10H21


135
C8H17
—
a16
a16
—
C8H17


136
C18H37
—
a16
a16
—
C18H37


137
C6H13
—
a16
a26
—
C6H13


138
C11H23
—
a16
a26
O
C2H5


139
C8H17C≡C
O
a17
a17
—
C10H21


140
C9H19
—
a17
a18
O
C3H7






















TABLE 12





No.
R
X
A
B
X′
R′







141
C7H15
—
a17
a17
—
 C7H15


142
C8H17
—
a17
a17
—
C8H17


143
C9H19
—
a17
a17
—
C9H19


144
C10H21
—
a17
a26
—
C10H21


145
C5H11
—
a18
a18
—
C5H11


146
C7H15
—
a18
a26
O
C12H25


147
C8H17
—
a19
a19
—
C8H17


148
C4H9
—
a19
a19
—
C4H9


149
C7H15
—
a19
a19
—
C7H15


150
C10H21
—
a19 
a19 
—
C10H21


151
C8H17
—
a19
a26
O
C10H21


152
C7H15
—
a 19
a 26
—
C7H15


153
C9H19
—
a20
a20
—
C9H19


154
C12H25
—
a20
a20
—
C5H11


155
C8H17
—
a21
a21
—
C8H17


156
C6H13
O
a21
a21
—
C11H23


157
C10H21
—
a21
a21
O
C4H9


158
C5H11
—
a21
a21
—
C5H11


159
C11H23
—
a21
a21
—
C11H23


160
C4H9
—
a21
a26
O
C12H25






















TABLE 13





No.
R
X
A
B
X′
R′







161
C19H39
—
a21
a26
—
H


162
C13H27
—
a22
a26
—
C3H7


163
C7H15
—
a22
a20 
—
C7H15


164
C5H11
—
a23
a23
—
C5H11


165
C7H15
—
a23
a23
—
C7H15


166
C10H21
—
a23
a23
—
C10H21


167
C4H9
—
a23
a23
—
C9H19


168
C12H25
—
a23
a26
O
(CH2)7CH(CH3)OC2H5


169
C3H7
—
a24
a24
—
C3H7


170
C6H13
—
a24
a24
—
C6H13


171
C7H15
—
a24
a24
—
C7H15


172
C8H17
—
a24
a24
—
C8H17


173
C11H23
—
a24
a24
—
C11H23


174
C9H19
—
a24
a26
O
C5H11


175
C6H13
—
a25
a24
—
C4H9


176
C17H35
—
a25
a25
—
C17H35


177
C7H15
O
a27
a27
—
C7H15


178
C8H17
—
a28
a26
—
C9H19


179
CH3
—
a29
a4
—
C10H21


180
C9H19
O
a30
a30
—
C11H23






















TABLE 14





No.
R
X
A
B
X′
R′







181
C4H9
—
a31
a25
—
C12H25


182
C15H31
—
a32
a26
—
C15H31


183
C8H17
—
a1
a4
—
C8H17


184
C5H11
—
a1
a6
—
C5H11


185
C12H25
—
a1
a6
—
C12H25


186
C7H15
—
a1
a7
—
C7H15


187
C5H11
—
a1
a8
—
C11H23


188
C9H19
—
a1
a9
—
C9H19


189
C6H13
—
a1
a10
—
C6H13


190
C4H9
—
a1
a14
—
C4H9


191
C7H15
—
a1
a16
—
C7H15


192
C11H23
—
a1
a18
—
C11H23


193
C8H17
—
a1
a25
—
C9H19


194
C5H11
—
a3
a6
—
C5H11


195
C10H21
—
a7
a10
—
C3H7


196
C6H13
—
a7
a22
—
C6H13


197
C7H15
—
a14
a18
—
C10H21


198
C4H9
—
a15
a25
—
C4H9


199
C6H13
—
a1
a25
—
C5H11


200
C8H17
—
a24
a26
—
C8H17






















TABLE 15





No.
R
X
A
B
X′
R′







201
C2H5OC3H6
—
a1
a1
—
C2H5OC3H6


202
C3H7OC3H6
—
a1
a1
—
C3H7OC3H6


203
C4H9OC3H6
—
a1
a1
—
C4H9OC3H6


204
(CH3)2CHCH2CH2CH2
—
a1
a1
—
CH2CH2CH2CH(CH3)2


205
(CH3)2CHCH2CH2CH2CH2
—
a1
a1
—
CH2CH2CH2CH2CH(CH3)2


206





—
a1
a1
—














In a preferred embodiment, the structural isomer mixture (comprising a plurality of organic compounds) used in the present invention may suitably be prepared by reacting two mono-substituted cyclic compounds (monomers) each having a plurality of reaction sites (positions) with each other or by effecting dimerization of one mono-substituted cyclic compound having a plurality of reaction sites.
The thus-prepared structural isomer mixture includes a major component (structural-isomer) and a minor component (structural isomer) in a (major component)/(minor component) ratio of 1/1 to 9/1, particularly 1/1 to 5/1.
In the electroconductive device of the present invention, the electroconductive layer comprising the above-mentioned structural isomer mixture is disposed between a pair of oppositely disposed electrodes, thus improving current and device characteristics. The electroconductive layer allows a high joint efficiency with metal and a high (carrier) mobility, so that the resultant electroconductive device is applicable to various semiconductor devices. The structure of the pair of electrodes may appropriately be changed depending on characteristics and structures of the semiconductor devices used.
In the EL device of the present invention, the electroconductive layer of structural isomer mixture is used as a carrier injection layer and/or a carrier transport layer, thus improving carrier injection and/or transport performances from the electrodes to ensure a good luminescent characteristic.
The EL device according to the present invention has a principal structure wherein a luminescence layer and the electroconductive layer of structural isomer mixture (as the carrier injection layer and/or the carrier transport layer as described above) are disposed between a pair of oppositely disposed electrodes as shown in FIGS. 6 and 7.
Referring to FIGS. 6 and 7, materials for the transparent substrate 21, anode (transparent electrode) 22, luminescence layer 24 and cathode (metal electrode) 25 may be known ones.
More specifically, the anode 22 may be formed of a transparent conductive material having a larger work function, preferably ITO (indium tin oxide) or IZO (indium zinc oxide). ITO may preferably contain 1-30 wt. % of SnO2 per In2O3, and IZO may preferably contain 5-30 wt. % of ZnO per In2O3, so as to provide a lower electric resistance. The anode 22 may also be formed of other materials, such as indium oxide, tin oxide, Cd2SnO4, zinc oxide, copper iodide, gold and platinum.
The cathode 25 may be formed of a material (metal, alloy or compound) having a smaller work function by (vacuum) vapor deposition or sputtering. Examples of the material for the cathode 25 may include i metals, such as K, Li, Na, Mg, Ka, Ce, Ca, Cr and Ba; compounds, such as BaO, BaS, CaO, HfC, LaB6 MgO, MoC, NbC, PbS and SiO; and alloys of Al—Ca (Ca=1-30 wt. %) and Al—Li (Li=0.5-10 wt. %), in order to improve stability.
The luminescence layer 24 may be formed of Alq 3 (tris(8-quinolinato)aluminum), BeBq (bis(benzoquinolinolato)beryllium complex), DTVBi (4,4′-bis-(2,2-di-p-tolyl-vinyl)-biphenyl), Eu (DBM)3 (Phen) (tris(1,3-diphenyl-1,3-propanediono) (mono-phenanthroline) Eu (III), diphenylethylene derivatives, triphenylamine derivatives, diaminocarbazole derivatives, bisstyryl derivatives, benzothiazole derivatives, benzoxazole derivatives, aromatic diamine derivatives, quinacridone compounds, perylene compounds, oxadiazole compounds, coumarin compounds, and anthraquinone compounds. These materials may preferably be formed in a layer in an amorphous state by vacuum (vapor) deposition.
The electroconductive layer formed of the above-mentioned structural isomer mixture is used as at least one layer of a hole transfer layer 23 (shown in FIGS. 6 and 7), an electron transport layer 31 (shown in FIGS. 6 and 7), a hole injection layer (not shown) and an electron injection layer (not shown). These carrier injection and transport layers other than the electroconductive layer may be formed of known materials.
In the EL device of the present invention, the electroconductive layer of a structural isomer mixture may particularly preferably be used as the electron injection layer. More specifically, in an ordinary EL device, it is generally difficult to effect injection of electrons from the cathode into the organic compound layer(s) compared with injection of holes from the anode into the organic compound layer(s). This may be attributable to difficulty of decreasing a work function of a metal (used for the metal (cathode) electrode) compared with LUMO level of the organic material used, due to lower stability of the metal material. Accordingly, in the EL device having such a structure that one or plural organic compound layers (films) are disposed between the cathode and the anode, the electroconductive layer of structural isomer mixture may effectively be used as the electron injection layer, thus allowing use of a material having a molecular structure with a high planarity (which cannot be conventionally used due to crystallization of its deposited film) to give more latitude in selection of material used.
The hole transport layer may be formed of an electron-donating material, such as triphenyldiamine derivatives (a representative example thereof may include α-NPD (bis[N-(1-naphthyl)-N-phenyl]benzidine) shown hereinafter). Examples of the hole injection layer material may include tetraarylbenzidine compounds (triphenyldiamine), hydrazone derivatives, carbazole derivatives, triazole derivatives, imidazole derivatives, oxadiazole derivatives and polythiophene.
In the case of forming the electron injection layer, a material therefor may include quinoline derivatives (such as Alq3 described above), oxadiazole derivatives and perylene derivatives.
Hereinbelow, the present invention will be described more specifically based on Examples.
EXAMPLE 1
Synthesis of Ex. Comp. No. 19





In a 2 liter-round bottomed flask, 64 g (371.1 mM) of 1,2-diamino-4-hexylbenzene (a) and 49.5 g (412.1 mM) of 1,4-dioxane-2,3-diol (b) were placed and dissolved in 793 ml of ethanol, followed by stirring overnight at room temperature.
After the reaction, the reaction mixture was subjected to distilling-off of the solvent under reduced pressure and purified by silica gel column chromatography (eluent: toluene/ethyl acetate=1/4), followed by distilling-off of the solvent under reduced pressure to obtain 53.3 g of 6-hexyl-quinoxaline (e). 




In a 200 ml-round bottomed flask, 53.3 g (248.7 mM) of 6-hexylquinoxaline (c), 31 g (258.8 mM) of pyridine-1-oxide and 20 g of palladium-carbon were placed and heat-refluxing overnight under stirring. After cooling, the reaction mixture was subjected to filtration, followed by distilling-off of the solvent under reduced pressure to obtain a residue. The residue was washed with ethanol and subjected to filtration, followed by recrystallization from pyridine to obtain a crude product. The crude product was dissolved in chloroform and filtered with alumina. The filtrate was recrystallized from toluene to obtain 10.4 g of structural isomer mixture (2,2′-bihexyl-quinoxaline ((d1)/(d2)/(d3)=1/2/1); Ex. Comp. No. 19).
The structural isomer mixture showed the following phase transition series.
Phase Transition Temperatures (° C.) 




The above-prepared structural isomer mixture (Ex. Comp. No. 19) and two comparative compounds (Comparative Compounds 1 and 2) were evaluated in terms of crystallization characteristic in the following manner.
Each compound was formed in a 20 nm-thick film by vacuum (vapor) deposition and observed at 30° C., thus determining a time required to cause crystallization.
The results are shown in Table 16.









TABLE 16





Ex.

Crystallization


Comp. No.
Formula
(Hr at 30° C.)















19





>72










Comparative compound 1





12


Comparative compound 2





0









As shown in Table 16, compared with monomolecular compounds (Comparative Compounds 1 and 2), the structural isomer mixture (Ex. Comp. No. 19) provided a stable amorphous structure.
EXAMPLE 2
An organic EL device (electroconductive device) having a sectional structure as shown in FIG. 1 was prepared by using the structural isomer mixture (Ex. Comp. No. 19) prepared in Example 1 in the following manner.
On a 1 mm-thick glass substrate 11, a 70 nm-thick ITO (indium tin oxide) film was formed as an anode (ITO electrode) 12 by sputtering and ultraviolet-light irradiation for surface treatment (cleaning).
The above-treated substrate 11 having the ITO film (anode) 12 was placed in a vacuum chamber held at a pressure of ca. 1.33×10−3 Pa (ca. 1×10−5 Torr), and a 50 nm-thick layer of α-NPD (bis[N-(1-naphthyl)-N-phenyl]benzidine) represented by a formula shown below was formed on the ITO film 12 as a hole (carrier) transporting layer 13 by (resistance heating) vacuum deposition at a rate of 0.1 nm/sec. 




Under similar vacuum deposition conditions, three organic layer segments (luminescence layer segments) 14 exhibiting different luminescent wavelengths were respectively formed in a thickness of 50 nm on the hole transporting layer 13 by vacuum deposition. The three organic layer (luminescence layers) 14a-14c were respectively formed of (95 wt. % of) Alq3 of a formula (a) shown below doped with 5 wt. % of perylene of a formula (b) shown below for shifting the luminescence wavelength to a shorter wavelength side, (95 wt. % of) Alq3 of the formula (a) doped with 5 wt. % of DCM (a styryl dye) of a formula (c) shown below for shifting the luminescence wavelength to a longer wavelength side, and Alq3 alone (providing a center luminescence wavelength).
On each of the luminescence layers 14a-14c, a 20 nm-thick layer of a structural isomer mixture (Ex. Comp. No. 19) was formed as an electron (carrier) injection layer 16 by vacuum deposition.
The thus-formed electron injection layer (structural isomer mixture layer) 16 was coated with a lamination-type cathode metal layer as a cathode electrode 15 each comprising a 10 nm-thick layer of Al—Li alloy (Al/Li=98.2/1.8 by weight) and a 150 nm-thick Al layer, respectively, formed by vacuum deposition to prepare an organic EL device as shown in FIG. 1. 




The thus-prepared EL device was subjected to measurement of a current-voltage characteristic and a luminescence efficiency at room temperature at a portion containing the luminescence layer 14c comprising Alq3 alone (i.e., free from the dopants of the formulas (b) and (c)) by using a microammeter (“4140B”, mfd. by Hewlett-Packard Co.) and a luminance meter (“BM7”, mfd. by Topcon K.K.), respectively.
The results are shown in FIGS. 2 and 4, respectively.
Referring to FIG. 2, the resultant current-voltage curve showed that the EL device provided a good rectifying performance and a higher current density with respect to an applied electric field. Further, as shown in FIG. 4, it was also confirmed that the EL device provided a higher luminescence efficiency in proportion to the current density.
The higher current density may be attributable to improvement in electron injection efficiency (performance) by the use of the structural isomer mixture (Ex. Comp. No. 19 in this example) since the EL device provided the higher current density compared with that in Comparative Example 1 below although the EL device had a lower electric field intensity.
Comparative Example 1
An organic EL device was prepared and evaluated in the same manner as in Example 2 except that the electron injection layer 16 (of the structural isomer mixture (Ex. Comp. No. 19) was not formed.
The results (current-voltage characteristic and luminescence efficiency) are shown in FIGS. 3 and 5, respectively.
Compared with FIG. 2 (Example 2), although a higher electric field strength (a smaller organic compound layer thickness) was applied, the EL device (of Comparative Example 1) provided smaller current density values as shown in FIG. 3, thus resulting in an inferior electron injection performance.
As described hereinabove, according to the present invention, by using the electroconductive layer formed of structural isomer mixture excellent in carrier injection and/or transport characteristics, it is possible to apply the resultant electroconductive device to various devices including semiconductor devices, thus improving their characteristics. Particularly, the organic EL device according to the present invention wherein the electroconductive layer is used as a carrier injection layer and/or a carrier transport layer provides improved luminescence efficiency and current-voltage characteristic, so that it is also possible to employ a thicker organic compound layer thereby to improve reliability (e.g., prevention of occurrence of short-circuit between a pair of electrodes).

## Claims

1. An electroconductive device, comprising:
a pair of oppositely disposed electrodes, and a luminescence layer and an electroconductive layer disposed between the electrodes, wherein 
the electroconductive layer comprises a mixture of a plurality of organic compounds which are mutually intermolecularly structural isomers having an identical ring structure and an identical rational formula but having structures different in the manner in which their atoms are linked, and said plurality of organic compounds include a major component and a minor component, the mixture comprising the major and minor components in a (major component)/(minor component) ratio of 1/1 to 9/1, and 
wherein the organic compounds are represented by the following formula (1): 


(R—X)n—Ar—(X′—R′)m  (1), 



wherein Ar denotes a connected ring structure comprising two single rings connected with each other via a single bond or two fused rings connected with each other via a single bond; X and X′ independently denote a single bond, —O—, —S—, —OOC— or —COO—; R and R′ independently denote —H, —F or a linear or branched alkyl group having 1-20 carbon atoms capable of including one methylene group which can be replaced with —O—, —S—, —CH═CH— or —C≡C; and m and n are an integer of 1-8, with the proviso that R and R′ cannot be —H at the same time when X and X′ are a single bond.

2. A device according to claim 1, wherein Ar in the formula (1) is a connecting ring structure comprising two fused rings connected with each other via a single bond, each of said two fused rings comprising 2-5 rings.

3. A device according to claim 2, wherein Ar in the formula (1) is a connected ring structure represented by any one of the following formulas (a) to (n): 







wherein CH is optionally substituted with N or NH, and CH2 is optionally substituted with S or O.

4. A device according to claim 1, wherein Ar in the formula (1) is a connecting ring structure represented by the following formula (2):


A—B  (2), 


wherein A and B independently denote any one of phenyl-diyl, pyridine-diyl, pyrazine-diyl, pyrimidine-diyl, pyridazine-diyl, indene-diyl, indolizine-diyl, isoindole-diyl, indole-diyl, purine-diyl, naphthalene-diyl, quinoline-diyl, isoquinoline-diyl, quinoxaline-diyl, 1,5-naphthyridine-diyl, 1,6-naphthyridine-diyl, 1,7-naphtharidine-diyl, 1,8-naphthyridine-diyl, quinazoline-diyl, cinnoline-diyl, pyrido[2,3-b]pyrazine-diyl, pyrazino[2, 3]b]pyrazine-diyl, pteridine-diyl, biphenylene-diyl, fluorene-diyl, carbazole-diyl, thianthrene-diyl, phenalene-diyl, phenanthridine-diyl, phenanthrene-diyl, anthracene-diyl, chrysene-diyl, acridine-diyl, perimidine-diyl, phenanthroline-diyl, phenazine-diyl, phenothiazine-diyl, phenoxathin-diyl, indan-diyl, coumaran-diyl, phthalan-diyl, chroman-diyl, isochroman-diyl, thiachroman-diyl, isothiachroman-diyl, and thiaxanthene-diyl.

5. A device according to claim 4, wherein A in the formula (2) is quinoxaline-diyl.

6. A device according to claim 1, wherein R═R′, X═X7 and m=n=1 are satisfied in the formula (1), and A═B is satisfied in the formula (2) to form a symmetric structure having a center of symmetry.

7. A device according to claim 1, wherein the mixture of a plurality of organic compounds is in an amorphous state.

8. An electroluminescence device, comprising:
a pair of oppositely disposed electrodes, and a luminescence layer and a carrier injection layer and/or a carrier transport layer disposed between the electrodes, wherein 
the carrier injection layer and/or the carrier transport layer comprises the electroconductive layer of the electroconductive device according to claim 1.

9. A device according to claim 8, wherein the device comprises the luminescence layer and the carrier injection layer disposed between the electrodes, the carrier injection layer being an electron injection layer.