U.S. patent application number 11/065940 was filed with the patent office on 2005-11-10 for organic electroluminescent element.
Invention is credited to Kido, Junji, Mori, Toshitaka, Ohyagi, Yasuyuki.
Application Number | 20050249974 11/065940 |
Document ID | / |
Family ID | 34431652 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050249974 |
Kind Code |
A1 |
Mori, Toshitaka ; et
al. |
November 10, 2005 |
Organic electroluminescent element
Abstract
A main object of the present invention is to provide an organic
EL element which can ease damages of an organic EL layer upon
formation of an electrode layer, and enables display of a high
quality image. The present invention attains the above object by
providing an organic electroluminescent element comprising: a
substrate; a first electrode layer formed on the substrate; an
organic electroluminescent layer which is formed on the first
electrode layer, and has at least a light emitting layer; a
semiconductor buffer layer which is formed on the organic
electroluminescent layer, and contains an inorganic compound having
a band gap of 2.0 eV or more and a metal; and a second electrode
layer formed on the semiconductor buffer layer.
Inventors: |
Mori, Toshitaka; (Tokyo,
JP) ; Ohyagi, Yasuyuki; (Tokyo, JP) ; Kido,
Junji; (Yonezawa, JP) |
Correspondence
Address: |
SEYFARTH SHAW LLP
55 EAST MONROE STREET
SUITE 4200
CHICAGO
IL
60603-5803
US
|
Family ID: |
34431652 |
Appl. No.: |
11/065940 |
Filed: |
February 25, 2005 |
Current U.S.
Class: |
428/690 ;
257/103; 313/504; 313/506; 428/917 |
Current CPC
Class: |
H01L 51/5221 20130101;
Y10S 428/917 20130101; H01L 51/5088 20130101; H01L 51/5206
20130101; H01L 51/5092 20130101; H01L 51/5215 20130101 |
Class at
Publication: |
428/690 ;
428/917; 313/504; 313/506; 257/103 |
International
Class: |
H05B 033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2004 |
JP |
2004-051288 |
Claims
What is claimed is:
1. An organic electroluminescent element comprising: a substrate; a
first electrode layer formed on the substrate; an organic
electroluminescent layer which is formed on the first electrode
layer, and has at least a light emitting layer; a semiconductor
buffer layer which is formed on the organic electroluminescent
layer, and contains an inorganic compound having a band gap of 2.0
eV or more and a metal; and a second electrode layer formed on the
semiconductor buffer layer.
2. An organic electroluminescent element comprising: a substrate;
an electrode layer formed on the substrate; an organic
electroluminescent layer which is formed on the electrode layer and
has at least a light emitting layer; and a semiconductor electrode
layer which is formed on the organic electroluminescent layer and
contains an organic compound having a band gap of 2.0 eV or more
and a metal.
3. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer or the semiconductor
electrode layer is a mixed semiconductor layer in which the metal
is dispersed in the inorganic compound.
4. The organic electroluminescent element according to claim 2,
wherein the semiconductor buffer layer or the semiconductor
electrode layer is a mixed semiconductor layer in which the metal
is dispersed in the inorganic compound.
5. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer comprises: an inorganic
layer comprising the inorganic compound; and a metal layer
comprising the metal, and the metal layer is formed in the
inorganic layer, or between the inorganic layer and the second
electrode layer.
6. The organic electroluminescent element according to claim 2,
wherein the semiconductor electrode layer comprises: an inorganic
layer comprising the inorganic compound; and a metal layer
comprising he metal, and the metal layer is formed in the inorganic
layer, or on an opposite side to a side on which the organic
electroluminescent layer is formed.
7. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer or the semiconductor
electrode layer comprises: a mixed semiconductor layer in which the
metal is dispersed in the inorganic compound; and an inorganic
layer comprising the inorganic compound.
8. The organic electroluminescent element according to claim 2,
wherein the semiconductor buffer layer or the semiconductor
electrode layer comprises: a mixed semiconductor layer in which the
metal is dispersed in the inorganic compound; and an inorganic
layer comprising the inorganic compound.
9. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer or the semiconductor
electrode layer comprises: a mixed semiconductor layer in which the
metal is dispersed in the inorganic compound; and a metal layer
comprising the metal.
10. The organic electroluminescent element according to claim 2,
wherein the semiconductor buffer layer or the semiconductor
electrode layer comprises: a mixed semiconductor layer in which the
metal is dispersed in the inorganic compound; and a metal layer
comprising the metal.
11. The organic electroluminescent element according to claim 1,
wherein an electric resistivity .rho. of the metal is less than
1.times.10.sup.-5 .OMEGA..multidot.cm.
12. The organic electroluminescent element according to claim 2,
wherein work function of a metal contained in the semiconductor
electrode layer is 4.2 eV or more.
13. The organic electroluminescent element according to claim 1,
wherein the inorganic compound is an inorganic semiconductor
compound.
14. The organic electroluminescent element according to claim 13,
wherein the inorganic semiconductor compound is a compound
containing at least one kind of element selected from elements of
Group 12 to Group 16 in 18 Group-type Element Periodic Table.
15. The organic electroluminescent element according to claim 1,
wherein the inorganic compound is a metal compound containing at
least one kind of element selected from elements of Group 17 in 18
Group-type Element Periodic Table.
16. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer or the semiconductor
electrode layer has a thickness in a range of 1 nm to 500 nm, and
an average light transmittance in a visible region is 30% or
more.
17. The organic electroluminescent element according to claim 1,
wherein a content of the metal in the semiconductor buffer layer or
the semiconductor electrode layer is in a range of 0.0001% by
volume to 90% by volume.
18. The organic electroluminescent element according to claim 1,
wherein the metal is contained in the semiconductor buffer layer or
the semiconductor electrode layer so that, when a metal contained
in the semiconductor buffer layer or the semiconductor electrode
layer is formed into a layer consisting only of the metal, a
thickness of the layer consisting only of the metal is 100 nm or
less.
19. The organic electroluminescent element according to claim 1,
wherein the semiconductor buffer layer or the semiconductor
electrode layer is formed into a film by a vacuum deposition
method.
20. The organic electroluminescent element according to claim 1,
wherein a charge injecting/transporting layer is formed between the
light emitting layer, and the semiconductor buffer layer or the
semiconductor electrode layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the invention
[0002] The present invention relates to an organic
electroluminescent (hereinafter, may be abbreviated as organic EL)
element.
[0003] 2. Description of the related art
[0004] The organic EL element has an advantage that visibility is
high due to self light emission, impact resistance is excellent,
different from a liquid crystal d splay, due to a wholly solid
display, a response rate is rapid, scarcely influenced by a
temperature change, and a visual angle is large. Utility as a light
emitting element in an image displaying apparatus attracts
attention.
[0005] The organic EL element has a fundamental construction of a
laminated structure of anode/light emitting layer/cathode, and a
construction in which an anode as a transparent electrode is formed
on a substrate such as a glass substrate is usually adopted. In
this case, emitted light is taken out from the substrate side
(anode side).
[0006] On the other hand, in recent years, an attempt has been made
to take out emitted light from the cathode side by using a
transparent electrode as the cathode, that is, to perform top side
light emission. By realizing this top side light emission, when
both of the cathode and the anode are transparent electrodes, it
enables to form a transparent light emitting element as a whole,
and double side light emission can be realized. In such the
transparent light emitting element, since an arbitrary color can be
adopted as a background color, a colored display, even when light
is not emitted, becomes possible, and ornamentality is improved. In
addition, when a color filter layer or a color converting layer is
formed on a light emitting element, the color filter layer or the
color converting layer can be arranged and laminated on the light
emitting layer, as in conventional light emitting element of bottom
side light emission, in the light emitting element capable of
performing top side light emission. Further, in the light emitting
element capable of performing top side light emission, light
emission is not shielded by TFT (thin film transistor) of an active
driving display, and a display having a high opening rate becomes
possible.
[0007] As an example of an organic EL element in which top side
light emission is made possible by adopting a transparent electrode
as the cathode, Japanese Patent Application Laid-Open (JP-A)
No.10-162959 discloses an organic EL element in which an organic EL
layer containing a light emitting layer)lies between an anode and a
cathode, the cathode consists of an electron injecting layer and a
transparent electrode layer, and this electron injecting layer is
arranged to be contact with the organic EL layer.
[0008] However, in the conventional organic EL element in which top
side light emission or double side light emission is possible, the
transparent electrode such as ITO is generally formed into a film
by a sputtering method. And there arises a problem that, upon
formation of the transparent electrode, the organic EL layer
containing the light emitting layer, and the electron injecting
layer or the hole injecting layer are shocked by sputtered
particles, Ar.sup.+ at sputtering, and an ionized electron, so that
the light emitting property is deteriorated (reduction in current
density, reduction in light emitting efficiency, leakage of
current). Further, there is also a problem that, upon formation of
the transparent electrode as the cathode, a highly reactive metal
contained in the electron injecting layer is oxidized due to oxygen
introduction or release of oxygen from a target, and deterioration
in property of the organic EL layer and the electron injecting
layer (reduction in current density property, reduction in light
emitting efficiency, increase in dark spot) is caused. When there
are these problems, a high quality image display cannot be
obtained.
[0009] Therefore, in order to improve deterioration in light
emitting property or deterioration in property of he organic EL
layer or the electron injecting layer due to impact at formation of
the cathode film, an attempt has been made to form a buffer layer
or a barrier layer between the cathode and the organic EL layer.
For example, JP-A No.2002-75658 discloses an organic EL element
using CuPu as a buffer layer for the purpose of preventing damage
of an organic EL layer due to sputtering upon formation of a
cathode film. In addition, JP-A No.10-144957 discloses a method for
preventing a short circuit of an organic EL element and
deterioration in property by providing a Ca diffusion barrier layer
between a cathode and an organic EL layer or preventing diffusion
of materials constituting the cathode into the organic EL layer
containing the light emitting layer. Further, JP-A No.10-223377 and
JP-A No.2000-215984 disclose an organic EL element in which a
semiconductor such as ZnSe, ZnS and CdS intervenes between a
cathode and an organic EL layer to improve electron transport from
the cathode. In addition, JP-A No.10-125469 discloses an organic EL
element in which an conductive material layer such as Ag, Mg and
TiN intervenes between a cathode and an organic EL layer containing
a light emitting layer to reduce a resistance of the cathode.
[0010] However, when the aforementioned buffer layer or barrier
layer (organic substance, semiconductor etc.) is inserted, in
particular, in an organic EL element which is driven under a high
current density (organic EL element using a conductive polymer),
there is a problem that current density-voltage property is
deteriorated as compared with the conventional organic EL element
which takes emitted light out from the bottom side.
SUMMARY OF THE INVENTION
[0011] The present invention was done in view of the aforementioned
problems, and a main object of the present invention is to provide
an organic EL element which can ease damages of an organic EL layer
upon formation of an electrode layer, and enables display of a high
quality image.
[0012] In order to attain the aforementioned object, the present
invention provides an organic electroluminescent element
comprising: a substrate; a first electrode layer formed on the
substrate; an organic electroluminescent layer which is formed on
the first electrode layer, and has at least a light emitting layer;
a semiconductor buffer layer which is formed on the organic
electroluminescent layer, and contains an inorganic compound having
a band gap of 2.0 eV or more and a metal; and a second electrode
layer formed on the semiconductor buffer layer.
[0013] In the present invention, since the semiconductor buffer
layer is formed between the organic EL layer and the second
electrode layer, impact due to a sputtered particle, a plasma gas
ion at sputtering, and an ionized electron at formation of the
second electrode layer can be alleviated, and property
deterioration of the organic EL layer and light emitting property
deterioration of the organic EL element can be prevented. In
addition, since the semiconductor buffer layer contains an
inorganic compound and a metal, and an electric resistivity of this
metal is lower as compared with the inorganic compound,
deterioration in current density-voltage property can be prevented.
Thereby, an organic EL element which enables high quality image
display can be obtained.
[0014] Also, the present invention provides an organic
electroluminescent element comprising: a substrate; an electrode
layer formed on the substrate; an organic electroluminescent layer
which is formed on the electrode layer and has at least a light
emitting layer; and a semiconductor electrode layer which is formed
on the organic electroluminescent layer and contains an organic
compound having a band gap of 2.0 eV or more and a metal.
[0015] In the present invention, since the semiconductor electrode
layer is formed into a film, for example, by a vacuum deposition
method, the organic EL layer does not undergo impact at formation
of the semiconductor electrode layer, and light emitting property
deterioration of the organic EL element can be avoided. In
addition, in the vacuum deposition method, since oxygen is not
usually introduced, for example, even when an electron injecting
layer is formed between the light emitting layer and the
semiconductor electrode layer, oxidation of the metal contained in
this electron injecting layer can be avoided.
[0016] In addition, in the present invention, the semiconductor
buffer layer or the semiconductor electrode layer may be a mixed
semiconductor layer in which the metal is dispersed in the
inorganic compound.
[0017] Further, in the present invention, the semiconductor buffer
layer comprises: an inorganic layer comprising the inorganic
compound; and a metal layer comprising the metal, and the metal
layer may be formed in the inorganic layer, or between the
inorganic layer and the second electrode layer. On the other hand,
the semiconductor electrode layer comprises: an inorganic layer
comprising the inorganic compound; and a metal layer comprising the
metal, and the metal layer may be formed in the inorganic layer, or
on an opposite side to a side on which the organic
electroluminescent layer is formed.
[0018] In addition, in the present invention, the semiconductor
buffer layer or the semiconductor electrode layer may comprise: a
mixed semiconductor layer in which the metal is dispersed in the
inorganic compound; and an inorganic layer comprising the inorganic
compound. In addition, the semiconductor buffer layer or the
semiconductor electrode layer may comprise: a mixed semiconductor
layer in which the metal is dispersed in the inorganic compound;
and a metal layer comprising the metal.
[0019] Further, in the present invention, it is preferable that an
electric resistivity p of the metal is less than 1.times.10.sup.-5
.OMEGA..multidot.cm. This is because an electrical conductivity of
the semiconductor buffer layer or the semiconductor electrode layer
can be enhanced when the electric resistivity of the metal is in
the aforementioned range.
[0020] In addition, in the present invention, it is preferable that
work function of a metal contained in the semiconductor electrode
layer is 4.2 eV or more.
[0021] Further, in the present invention, the inorganic compound
may be an inorganic semiconductor compound. Thereupon, it is
preferable that the inorganic semiconductor compound is a compound
containing at least one kind of element selected from elements of
Group 12 to Group 16 in 18 Group-type Element Periodic Table. This
is because such the compound has a great band gap and is
transparent.
[0022] In addition, in the present invention, the inorganic
compound may be a metal compound containing at least one kind of
element selected from elements of Group 17 in 18 Group-type Element
Periodic Table.
[0023] Further, in the present invention, it is preferable that the
semiconductor buffer layer or the semiconductor electrode layer has
a thickness in a range of 1 nm to 500 nm, and an average light
transmittance in a visible region is 30% or more. This is because
there is a possibility that the light transmittance is lowered when
the thickness of the semiconductor buffer layer or the
semiconductor electrode layer is too thick. Conversely, when the
thickness of the semiconductor buffer layer is too thin, there is a
possibility that effect of protecting the organic EL layer from
impact, at formation of the second electrode layer, is not
obtained. And also, when the thickness of the semiconductor
electrode layer is too thin, there is a possibility that the layer
does not perform a function as an electrode.
[0024] In addition, in the present invention, it is preferable that
a content of the metal in the semiconductor buffer layer or the
semiconductor electrode layer is in a range of 0.0001% by volume to
90% by volume. When the content of the metal is too much, there is
a possibility that the light transmittance of the semiconductor
buffer layer or the semiconductor electrode layer is lowered.
Conversely, when the content of the metal is too little, there is a
possibility that effect of enhancing electrical conductivity of the
semiconductor buffer layer or the semiconductor electrode layer is
not obtained.
[0025] Further, in the present invention, it is preferable that,
the metal is contained in the semiconductor buffer layer or the
semiconductor electrode layer so that, when a metal contained in
the semiconductor buffer layer or the semiconductor electrode layer
is formed into a layer consisting only of the metal, a thickness of
the layer consisting only of the metal is 100 nm or less. When the
thickness of the layer consisting only of the metal is zoo thick,
there is a possibility that the light transmittance of the
semiconductor buffer layer or the semiconductor electrode layer is
reduced.
[0026] In addition, in the present invention, it is preferable the
semiconductor buffer layer or the semiconductor electrode layer is
formed into a film by a vacuum deposition method. In the vacuum
deposition method, since oxygen is not usually introduced, for
example, even when the electron injecting layer is formed between
the light emitting layer and the semiconductor buffer layer or the
semiconductor electrode layer, oxidation of the metal contained in
this electron injecting layer can be avoided.
[0027] Further, in the present invention, a charge
injecting/transporting layer may be formed between the light
emitting layer, and the semiconductor buffer layer or the
semiconductor electrode layer. This is because this can stabilize
injection of a charge into the light emitting layer, and enhance
the light emitting efficiency.
[0028] In the present invention, since the semiconductor buffer
layer is formed between the organic EL layer and the second
electrode layer, damage of the organic EL layer due to impact at
formation of the second electrode layer can be alleviated. In
addition, for example, even when the electron injecting layer is
formed between the light emitting layer and the semiconductor
buffer layer, oxidation of the metal contained in this electron
injecting layer can be prevented. As described above, in the
present invention, such effect can be exerted that property
deterioration of the organic EL layer and light emitting property
deterioration of the organic EL element can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic cross-sectional view showing one
example of the organic EL element of the present invention.
[0030] FIG. 2 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0031] FIG. 3 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0032] FIG. 4 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0033] FIG. 5 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0034] FIG. 6 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0035] FIG. 7 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
[0036] FIG. 8 is a schematic cross-sectional view showing other
example of the organic EL element of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The organic EL element of the present invention will be
explained in detail below.
[0038] The organic EL element of the present invention can be
classified into two embodiments based on a construction of the
organic EL element, A first embodiment of the organic EL element of
the present invention is characterized in comprising: a substrate;
a first electrode layer formed on the substrate; an organic
electroluminescent layer which is formed on the first electrode
layer, and has at least a light emitting layer; a semiconductor
buffer layer which is formed on the organic electroluminescent
layer, and contains an inorganic compound having a band gap of 2.0
eV or more and a metal; and a second electrode layer formed on the
semiconductor buffer layer. In addition, a second embodiment of the
organic EL element of the present invention is characterized in
comprising: a substrate; an electrode layer formed on the
substrate; an organic electroluminescent layer which is formed on
the electrode layer and has at least a light emitting layer; and a
semiconductor electrode layer which is formed on the organic
electroluminescent layer and contains an organic compound having a
band gap of 2.0 eV or more and a metal. Each embodiment will be
explained below.
1. First Embodiment
[0039] The first embodiment of the organic EL element of the
present invention is characterized in comprising: a substrate; a
first electrode layer formed on the substrate; an organic
electroluminescent layer which is formed on the first electrode
layer, and has at least a light emitting layer; a semiconductor
buffer layer which is formed on the organic electroluminescent
layer, and contains an inorganic compound having a band gap of 2.0
eV or more and a metal; and a second electrode layer formed on the
semiconductor buffer layer.
[0040] The organic EL element of the present embodiment will be
explained by referring to the drawings. FIG. 1 is a schematic
cross-sectional view showing one example of the organic EL element
of the present embodiment. In FIG. 1, an organic EL element
comprises: a substrate 1; a first electrode layer 2 formed on the
substrate 1; an organic EL layer 3 which is formed on the first
electrode layer 2 and has at least a light emitting layer; an
electron injecting layer 6 formed on the organic EL layer 3; a
semiconductor buffer layer 4 formed on the electron injecting layer
6; and a second electrode layer 5 formed on the semiconductor
buffer layer 4.
[0041] Conventionally, for example, the electrode layer is formed
into a film on the organic EL layer by sputtering and, since the
organic EL layer undergoes impact due to Ar.sup.+, a sputtered
particle and an ionized electron having a high energy amount at a
few hundred volt, there is a disadvantage that a structure of the
organic EL layer is changed, and radiationless quenching is caused
at an interface between the organic EL layer and the electrode
layer at charge injection, leading to light emitting property
deterioration. In addition, for example, when the electron
injecting layer containing an alkali metal or an alkaline earth
metal is formed between the light emitting layer and the
semiconductor buffer layer, since these metals are easily oxidized,
there is a possibility that the metal is oxidized by oxygen
introduction or release of oxygen from a target, at sputtering in
formation of the electrode layer, and charge injecting function is
lost. On the other hand, in the present embodiment, since the
semiconductor buffer layer is formed between the organic EL layer
and the second electrode layer, even when the second electrode
layer is formed into a film by sputtering, impact to the organic EL
layer due to plasma gas ions, the sputtered particles and the
ionized electrons at sputtering can be alleviated. Therefore,
property deterioration of the organic EL layer and light emitting
property deterioration of the organic EL element can be prevented.
In addition, for example, when the electron injecting layer is
formed between the light emitting layer and the semiconductor
buffer layer, since the electron injecting layer is protected by
the semiconductor buffer layer, oxidation of the metal contained in
the electron injecting layer can be prevented. Thereby, the light
emitting efficiency and durability of the organic EL element can be
improved, and the organic EL element capable of performing display
of a high quality image can be obtained.
[0042] In addition, since the inorganic compound is generally of
not low in electric resistivity, when a layer consisting only of
the inorganic compound is formed between the organic EL layer and
the second electrode layer, there is a disadvantage that a current
density under high voltage (high current density region) is not
increased, and a brightness is not improved. On the other hand,
since the semiconductor buffer layer used in the present embodiment
contains the inorganic compound and the metal, and the electric
resistivity of this metal is lower as compared with the inorganic
compound, reduction in current density-voltage property can be
prevented. Thereby, for example, it can be suitably used in the
organic EL element which is driven under high current density
(organic EL element using an electrically conductive polymer).
[0043] Each essential component of such the organic EL element will
be explained below.
[0044] (1) Semiconductor Buffer Layer
[0045] First, the semiconductor buffer layer used in the present
embodiment will be explained. The semiconductor buffer layer used
in the present embodiment is formed between the organic EL layer
and the second electrode layer, and contains an inorganic compound
having a band gap of 2.0 eV or more and the metal.
[0046] A semiconductor buffer layer in the present embodiment has
two functions of function of protecting the organic EL layer at
formation of the second electrode layer, and function of
transporting and injecting a charge into the organic EL layer as
described above. In addition, when a charge injecting/transporting
layer is formed between the semiconductor buffer layer and the
light emitting layer, the semiconductor buffer layer also has
function of protecting the charge injecting/transporting layer, and
function of transporting and injecting a charge to the charge
injecting/transporting layer. In the present embodiment, by forming
the semiconductor buffer layer between the organic EL layer and the
second electrode layer, impact to the organic EL layer at formation
of the second electrode layer can be alleviated. In addition, when
the electron injecting layer is formed between the light emitting
layer and the semiconductor buffer layer, oxidation of the metal
contained in this electron injecting layer can be prevented.
Further, by inclusion of the metal in the semiconductor buffer
layer, reduction in current density-voltage property can be
suppressed. Thereby, the light emitting efficiency and durability
of the organic EL element can be improved.
[0047] The semiconductor buffer layer used in the present
embodiment can be classified into four aspects based on a
construction of this semiconductor buffer layer. That is, they are:
the case where the semiconductor buffer layer is a mixed
semiconductor layer in which the metal is dispersed in the
inorganic compound (first aspect); the case where the semiconductor
buffer layer comprises an inorganic layer comprising an inorganic
compound and a metal layer comprising a metal, and this metal layer
is formed in the inorganic layer or between the inorganic layer and
the second electrode layer (second aspect); the case where the
semiconductor buffer layer comprises a mixed semiconductor layer in
which a metal is dispersed in an inorganic compound, and an
inorganic layer comprising an inorganic compound (third aspect);
and the case where the semiconductor buffer layer comprises a mixed
semiconductor layer in which a metal is dispersed in an inorganic
compound, and a metal layer comprising a metal (forth aspect).
[0048] Each aspect of such the semiconductor buffer layer will be
explained below.
[0049] (i) First Aspect
[0050] The first aspect of the semiconductor buffer layer used in
the present embodiment is a mixed semiconductor layer in which a
metal is dispersed in an inorganic compound. In the present aspect,
since the metal is dispersed in the mixed semiconductor layer, an
electric resistivity of the mixed semiconductor layer can be
reduced, and reduction in current density-voltage property can be
suppressed.
[0051] Materials constituting such the mixed semiconductor layer
will be explained below.
[0052] (Inorganic Compound)
[0053] The inorganic compound used in the present aspect has its
band gap of 2.0 eV or more. The inorganic compound used in the
present aspect is not particularly limited as long as it can be
formed into a layer having protecting function of alleviating
impact to the organic EL layer or the charge injecting/transporting
layer at formation of the second electrode layer as described
above. In addition, the band gap of the inorganic compound may be
2.0 eV or more, preferably 2.4 eV or more, particularly preferably
2.6 eV or more. When the band gap of the inorganic compound is in
the aforementioned range, the light transmittance, in a visual
region, of the mixed semiconductor layer can be enhanced. In
addition, when the band gap is too small, there is a possibility
that a mixed semiconductor layer is colored, and the light
transmittance in the visible region is reduced. On the other hand,
an upper limit value of the band gap of the inorganic compound is
not particularly limited because as the band gap gets larger, the
light transmittance is increased. However, the value is usually 30
eV or less.
[0054] Examples of such the inorganic compound include an inorganic
semiconductor compound having a prescribed band gap and an
insulating compound having light permeability. In the present
embodiment, among the above, it is preferable to use the inorganic
semiconductor compound.
[0055] The inorganic semiconductor compound is not particularly
limited as long as it can be formed into a layer having protecting
function of alleviating impact to the organic EL layer or the
charge injecting/transporting layer at formation of the second
electrode layer as described above. In addition, the band gap of
the inorganic semiconductor compound may be 2.0 eV or more,
preferably 2.4 eV or more, particularly preferably 2.6 eV or more.
When the band gap of the inorganic semiconductor compound is in the
aforementioned range, the light transmittance of the mixed
semiconductor layer in the visible region can be enhanced. In
addition, when the band gap is too small, there is a possibility
that the mixed semiconductor layer is colored, and the light
transmittance in the visible region is lowered. On the other hand,
an upper limit value of the band gap of the inorganic semiconductor
compound is not particularly limited because as the band gap gets
larger, light permeability is increased as described above.
However, the value is usually 8 eV or less.
[0056] Examples of such the inorganic semiconductor compound
include compounds containing at least one kind of element selected
from elements of Group 12 to Group 16 in 18 Group-type Element
Periodic Table. Specific examples include ZnS, ZnSe, ZnTe, GaN,
GaS, Ga.sub.2S.sub.3, GaP, GaSe, AlN, AlP, AlAs, AlSb,
Al.sub.2Se.sub.3, BN, BP, BAs, CdS, HgS, SiC and the like. These
compounds may be used alone, or two Or more kinds may be used by
mixing. In the present aspect, among the aforementioned compounds,
it is preferable to use at least one kind of a compound selected
from ZnS, ZnSe, GaN and GaS, and particularly, ZnS and ZnSe are
preferable. This is because the aforementioned compounds have a
large band gap, and are transparent.
[0057] In addition, the insulating compound having light
permeability is not particularly limited as long as it can be
formed into a layer having protecting function of alleviating
impact to the organic EL layer or the charge injecting/transporting
layer at formation of the second electrode layer. In addition, the
band gap of the insulating compound may be 2.0 eV or more and,
since insulating property is exhibited, 8 eV or more is usually
used. An upper limit value of the band gap of the insulating
compound is not particularly limited because as the band gap gets
larger, light permeability is increased as described above.
However, the values is usually 30 eV or smaller. When the band gap
of the insulating compound is in the aforementioned range, the
light transmittance of the mixed semiconductor layer in the visible
region can be enhanced.
[0058] Examples of such the insulating compound include metal
compounds containing at least one kind of element selected from
elements of Group 17 in 18 Group-type Element Periodic Table.
Specific examples include fluoride, chloride, bromide and iodide of
an alkali metal, an alkaline earth metal, a rare earth element and
a transition element and the like. Further specific examples
include LiF, NaF, KE, MgF.sub.2, CaF.sub.2, BaF.sub.2, LaF.sub.3,
AlF.sub.3, ZnF.sub.2, CuF.sub.2, LiCl, RbCl, MgCl.sub.2,
BeCl.sub.2, NaBr, GeBr, NaI, KI and the like. These compounds may
be used alone, or two or more kinds may be used by mixing. In the
present embodiment, among the above, it is preferable to use
fluoride of an alkali metal, an alkaline earth metal, a rare earth
element and a transition element, and it is particularly preferable
to use LiF, MgF.sub.2 or CaF.sub.2.
[0059] (Metal)
[0060] The metal used in the present aspect is not particularly
limited as long as it has function of transporting and injecting
the charge to the organic EL layer as described above, and the
electric resistivity .rho. is preferably less than
1.times.10.sup.-5 .OMEGA..multidot.cm, among the above,
3.times.10.sup.-6 .OMEGA..multidot.cm or less, particularly
preferably 1.times.10.sup.-6 .OMEGA..multidot.cm. When the electric
resistivity of the metal is in the aforementioned range, electric
conductivity of the mixed semiconductor layer can be enhanced.
[0061] Examples of such the metal include, for example, an alkali
metal (Li, Na, K, Rb, Cs, Fr), an alkaline earth metal (Be, Mg, Ca,
Sr, Ba, Ra), a transition metal (Cu, Ag, Au, Cr, Fe, Mo, Mn, Ni,
Ta, W, Pt, Ti, Os), a rare earth metal (Sc, Y, Au, Er, Yb), and Al,
Ga, In, Zn and the like. These metals may be used alone, or two or
more kinds may be used jointly. In the present aspect, among the
above metals, it is preferable to use an alkali metal, an alkaline
earth metal, Cu, Ag, Au or Al, and it is particularly preferable to
use an alkali metal or an alkaline earth metal. If the alkali metal
or the alkaline earth metal is used as the metal, for example, as
described layer, since when the electron injecting layer is formed
between the light emitting layer and the mixed semiconductor layer,
this electron injecting layer is generally formed using the alkali
metal or the alkaline earth metal, types of the material to be used
for manufacturing the organic EL element can be decreased, and a
manufacturing process becomes simple. In addition, for example,
when the second electrode layer is a cathode, since the alkali
metal or the alkaline earth metal has a small work function value,
better electron injection can be performed by direct contact of
these metals with the organic EL layer. On the other hand, when Cu,
Ag, Au or Al is used as the metal, since these metals have a large
work function such as 4.0 eV or more, when the second electrode
layer is an anode, a hole injected from this second electrode layer
can be stably injected into the light emitting layer.
[0062] In addition, in the present aspect, the metal is not
particularly limited as long as it is dispersed in the mixed
semiconductor layer, and the metal may be dispersed uniformly, or
may be dispersed ununiformly In particular, when the metal is an
alkali metal or an alkaline earth metal, it is preferable that the
metal is present on the organic EL layer side at a large amount,
and little metal is present on the second electrode layer side.
Since the alkali metal and the alkaline earth metal are the metal
having high reactivity, they are easily oxidized and, when the
alkai metal and the alkaline earth metal are present on the second
electrode layer side in a large amount, there is a possibility that
the metal is easily oxidized by oxygen introduction or release of
an oxygen from a target at formation of the second electrode layer,
and a current density or brightness property of the organic EL
element is deteriorated.
[0063] A content of the metal, in the mixed semiconductor layer,
can be set in a range of usually 0.0001% by volume to 90% by
volume, preferably 0.01% by volume to 60% by volume, among the
above, 0.1% by volume to 50% by volume, particularly preferably 1%
by volume to 20% by volume. When the content of the metal is too
large, there is a possibility that the light transmittance of the
mixed semiconductor layer is reduced. Conversely, when the content
of the metal is too small, there is a possibility that effect of
enhancing electric conductivity of the mixed semiconductor layer is
not obtained.
[0064] The content of the metal can be measured using an X-ray
photoelectron spectrometry (XPS) or Rutherford back scattering
analysis method (RBS).
[0065] In addition, when a metal contained in the mixed
semiconductor layer is formed into a layer consisting only of the
metal, a thickness of the layer containing only of this metal is
preferably 100 nm or less, among the above, in a range of 1 nm to
30 nm, further 1 nm to 20 nm, particularly preferably 1 nm to 10
nm. When the thickness of the layer consisting only of the metal is
too thick, there is a possibility that the light transmittance of
the mixed semiconductor layer is reduced. Conversely, when the
thickness of the layer consisting only of the metal is too thin,
there is a possibility that electric conductivity of the
semiconductor buffer layer is reduced.
[0066] The thickness of the layer consisting only of the metal can
be calculated from a content of the metal in the mixed
semiconductor layer, and a volume and an area of the mixed
semiconductor layer. In this case, the formula is as follows:
(thickness of the layer consisting only of the metal)=(volume of
the mixed semiconductor layer).times.(content of the
metal).div.(area of the mixed semiconductor layer)
[0067] The thickness of the layer consisting only of the metal can
be also calculated from a deposition rate and a deposition time
upon deposition of a mixed semiconductor layer. For example, when
the mixed semiconductor layer is co-deposited, the formula is as
follows:
(thickness of the layer consisting only of the metal)=(deposition
rate of the metal).times.(deposition time)
[0068] (Semiconductor Buffer Layer)
[0069] As the semiconductor buffer layer in the present aspect, it
is preferable that an average light transmittance in a visible
region 380 to 780 nm is 30% or more, among the above, more
preferably 50% or more. Thereby, even when light is taken out from
the second electrode layer side, light is not shielded. The average
light transmittance is a value measured by using an ultraviolet and
visible spectrophotometer (UV-2200A, manufactured by Shimadzu
Corporation), at room temperature in the atmosphere.
[0070] In addition, it is preferable that the electric resistivity
of the semiconductor buffer layer is a value between an electric
resistivity of the second electrode layer and the electric
resistivity of an El layer. Thereby, a charge injected from the
second electrode layer can be effectively injected into the organic
EL layer. Specifically, it is preferable that the electric
resistivity of the semiconductor buffer layer is in a range of
1.times.10.sup.-4 .OMEGA..multidot.cm to 1.times.10.sup.3
.OMEGA..multidot.cm, among the above, 1.times.10.sup.-4
.OMEGA..multidot.cm to 1.times.10.sup.2 .OMEGA..multidot.cm,
particularly 1.times.10.sup.-4 .OMEGA..multidot.cm to 10
.OMEGA..multidot.cm. The electric resistivity is a value measured
by a four probe method using Dia Instruments Loresta-GP
(MCP-T600).
[0071] A thickness of the semiconductor buffer layer is not
particularly limited as long as it is such a thickness that the
average light transmittance and the electric resistivity are
satisfied, specifically the thickness is preferably in a range of 1
nm to 500 nm, among the above, 1 nm to 100 nm, particularly
preferably in a range of 10 nm to 50 nm. When the thickness of the
semiconductor buffer layer is too thick, there is a possibility
that the light transmittance is reduced. Conversely, when the
thickness of the semiconductor buffer layer is too thin, there is a
possibility that effect of protecting the organic EL layer or the
charge injecting/transporting layer from impact at formation of tie
second electrode layer.
[0072] A method for forming the semiconductor buffer layer in the
present aspect is not particularly limited as long as it is a
method which does not influence the organic EL layer. For example,
a vacuum deposition method, a high frequency sputtering method, a
magnetron sputtering method, an ion beam sputtering method, an ion
plating method and the like can be used and, among the above, it is
preferable to use a vacuum deposition method. For example, even
when the electron injecting layer is formed between the
semiconductor buffer layer and the light emitting layer, since
oxygen is not usually introduced in the vacuum deposition method,
there is no possibility that the metal contained in the electron
injecting layer is oxidized at formation of the semiconductor
buffer layer. Examples of such the vacuum deposition method include
a resistance heating deposition method, an electron beam deposition
method, a flash deposition method and the like. In particular, a
one source deposition method, a two sources deposition method or a
three sources deposition method using the resistance heating
deposition method or the electron beam deposition method is
preferable. On the other hand, when a high frequency sputtering
method, a magnetron sputtering method, an ion beam sputtering
method, or ion plating method is used, it is preferable that oxygen
is not introduced based on the aforementioned reasons. Thereupon,
not oxygen, but a rare gas such as argon, or nitrogen and the like
may be introduced, among the above, argon is preferably
introduced.
[0073] (ii) Second Aspect
[0074] The second aspect of the semiconductor buffer layer used in
the present embodiment comprises: an inorganic layer comprising the
inorganic compound; and a metal layer comprising the metal, and
this metal layer is formed in the inorganic layer, or between the
inorganic layer and the second electrode layer. For example, in
FIG. 2, a semiconductor buffer layer 4 has a construction that an
inorganic layer 14a, a metal layer 14b and an inorganic layer 14a
are laminated in this order. In the present aspect, because the
semiconductor buffer layer comprises the metal layer comprising the
metal, an electric resistivity of the semiconductor buffer layer,
as a whole, can be reduced, and it becomes possible to suppress
reduction in current density-voltage property.
[0075] As the forming position of the inorganic layer and the metal
layer in the present aspect, for example, as shown in FIG. 2, a
metal layer 14b is formed so as to be held by inorganic layers 14a
and, as shown in FIG. 3, a metal layer 14b may be formed between an
inorganic layer 14a and a second electrode layer 5. In addition, it
is acceptable as long as the metal layer is not in contact with the
organic EL layer. A plurality of metal layers and a plurality of
inorganic layers may be laminated.
[0076] Each essential component of such the semiconductor buffer
layer will be explained below.
[0077] (Inorganic Layer)
[0078] The inorganic layer used in the present aspect is a layer
comprising the inorganic compound. In the present aspect, as the
inorganic compound, an inorganic semiconductor compound having a
prescribed band gap can be used. Since the inorganic semiconductor
compound is the same as that described in the first aspect, the
explanation is omitted herein.
[0079] A thickness of the inorganic layer is not particularly
limited as long as it is such a thickness that, as the while
semiconductor buffer layer, the organic EL layer can be protected
from impact at formation of the second electrode layer. For
example, when the metal layer 14b is held between inorganic layers
14a as shown in FIG. 2, since the metal layer 14b is formed so as
not to be in contact with an organic EL layer 3 in the present
aspect, the thickness of the inorganic layer 14a provided on the
organic EL layer 3 side can be set at around 1 nm to 500 nm.
[0080] A method for forming the inorganic layer is not particularly
limited as long as it is a method with does not influence the
organic EL layer. For example, a vacuum deposition method, a high
frequency sputtering method, a magnetron sputtering method, an ion
beam sputtering method, an ion plating method and the like can be
used. Among the above, it is preferable to use a vacuum deposition
method. For example, even when the electron injecting layer is
formed between the semiconductor buffer layer and the light
emitting layer, since oxygen is not usually introduced in the
vacuum deposition method, there is no possibility that a metal
contained in an electron injecting layer is oxidized at formation
of the inorganic layer. Examples of such the vacuum deposition
method include a resistance heating deposition method, an electron
beam deposition method, and an ion beam deposition method and the
like. In particular, a one source deposition method, a two sources
deposition method or a three sources deposition method using a
resistance heating deposition method or an electron beam deposition
method is preferable. On the other hand, when a high frequency
sputtering method, a magnetron sputtering method, an ion beam
sputtering method, or an ion plating method is used, it is
preferable that oxygen is not introduced for the aforementioned
reason. Thereupon, not oxygen, but a rare gas such as argon, or
nitrogen and the like may be introduced, among the above, argon is
preferably introduced.
[0081] (Metal Layer)
[0082] The metal layer used in the present aspect is a layer
comprising the metal. The metal used in the metal layer is not
particularly limited as long as it can reduce the electric
resistivity of the semiconductor buffer layer as a whole, and it is
preferable that the metal has an electric resistivity described in
the first aspect.
[0083] In the present aspect, for example, when the metal layer 14b
is held between the inorganic layers 14a as shown in FIG. 2,
examples of the metal to be used include an alkali metal (Li, Na,
K, Rb, Cs, Fr), an alkaline earth metal (Be, Mg, Ca, Sr, Ba, Ra), a
transition metal (Cu, Ag, Au, Cr, Fe, Mo, Mn, Ni, Ta, W, Pt, Ti,
Os), and a rate earth metal (Sc, Y, Eu, Er, Yb), and Al, Ga, In, Zn
and the like. These metals may be used alone, or two or more kinds
may be used jointly.
[0084] In addition, for example, when the metal layer 14b is formed
between the inorganic layer 14a and the second electrode layer 5,
as shown in FIG. 3, examples of a metal to be used include the
aforementioned metals. Among the above, it is preferable to use the
metal having work function of around 4.0 to 5.5 eV. Examples of
such the metal include Ag, Au, Al, Cr, Cu, Fe, Mo, Mn, Ni, Ta, W
and the like. These metals may be used alone, or two or more kinds
may be used jointly. Since these metals have low reactivity, and
are not likely to be oxidized by oxygen introduction or release of
oxygen from a target at formation of the second electrode layer,
durability of the organic EL element can be enhanced.
[0085] A thickness of the metal layer is preferably 100 nm or less,
among the above, in a range of 1 nm to 30 nm, further 1 nm to 20
nm, particularly preferably 1 nm to 10 nm. When the thickness of
the metal layer is too thick, there is a possibility that the light
transmittance of the semiconductor buffer layer is reduced.
Conversely, when the thickness of the metal layer is too thin,
there is a possibility that electrical conductivity of the
semiconductor buffer layer is reduced.
[0086] In addition, method for forming the metal layer is not
particularly limited as long as it is a method which does not
influence the organic EL layer. For example, a vacuum deposition
method, a high frequency sputtering method, a magnetron sputtering
method, an ion beam sputtering method, an ion plating method and
the like can be used. Among the above, it is preferable to use a
vacuum deposition method. For example, even when the electron
injecting layer is formed between the semiconductor buffer layer
and the light emitting layer, since oxygen is not usually
introduced in the vacuum deposition method, there is no possibility
that the metal contained in the electron injecting layer is
oxidized at formation of the metal layer. Examples of such the
vacuum deposition method include a resistance heating deposition
method, an electron beam deposition method, an ion beam deposition
method and the like. In particular, a one source deposition method,
a two sources deposition method or a three sources deposition
method using a resistance heating deposition method or an electron
beam deposition method is preferable. When a high frequency
sputtering method, a magnetron sputtering method, an ion beam
sputtering method or an ion plating method is used, it is
preferable that oxygen introduction is not performed for the
aforementioned reason. Thereupon, not oxygen, but a rare gas such
as argon, or nitrogen and the like may be introduced. Among the
above, it is preferable to introduce argon.
[0087] Since other respects of the semiconductor buffer layer are
the same as those described for the first aspect, explanation is
not repeated herein.
[0088] (iii) Third Aspect
[0089] The third aspect of the semiconductor buffer layer used in
the present embodiment comprises: a mixed semiconductor layer in
which the metal is dispersed in the inorganic compound; and an
inorganic layer comprising the inorganic compound. In the present
aspect, since the mixed semiconductor layer constituting the
semiconductor buffer layer is such than the metal is dispersed in
the inorganic compound, it becomes possible to suppress reduction
in current density-voltage property.
[0090] A forming position of the mixed semiconductor layer and the
inorganic layer in the present aspect is not particularly limited.
The mixed semiconductor layer and the inorganic layer mat be
laminated in this order from the organic EL layer side, or the
inorganic layer and the mixed semiconductor layer may be laminated
in this order. Alternatively, a plurality of mixed semiconductor
layers and a plurality of inorganic layers may be laminated.
[0091] Since other respects of the mixed semiconductor layer and
the semiconductor buffer layer are the same as those described for
the first aspect, and the inorganic layer is the same as that
described for the second aspect, explanation is not repeated
herein.
[0092] (iv) Forth Aspect
[0093] The forth aspect of the semiconductor buffer layer used in
the present embodiment comprises: a mixed semiconductor layer in
which the metal is dispersed in the inorganic compound; and a metal
layer comprising the metal. In the present aspect, the mixed
semiconductor layer constituting the semiconductor buffer layer is
such that the metal is dispersed in the inorganic compound and,
because the semiconductor buffer layer has the metal layer
comprising the metal, the electric resistivity of the semiconductor
buffer layer, as a whole, can be reduced, and it becomes possible
to suppress reduction in current density-voltage property.
[0094] A forming position of the mixed semiconductor layer and the
metal layer in the present aspect is not particularly limited. The
mixed semiconductor layer and the metal layer may be laminated in
this order from the organic EL layer side, or the metal layer and
the mixed semiconductor layer may be laminated in this order.
Alternatively, a plurality of mixed semiconductor layers and a
plurality of metal layers may be laminated.
[0095] Each component of such the semiconductor buffer layer will
be explained below. Since a mixed semiconductor layer is the same
as that described for the first aspect, explanation is not repeated
herein.
[0096] (Metal Layer)
[0097] The metal layer used in the present aspect is a layer
comprising the metal. The metal used in the metal layer is not
particularly limited as long as an electric resistivity of the
semiconductor buffer layer as a whole can be reduced, and it is
preferable that the metal layer has the electric resistivity
described in the first aspect.
[0098] Examples of the metal used in the metal layer in the present
aspect include an alkali metal (Li, Na, K, Rb, Cs, Fr), an alkaline
earth metal (Be, Mg, Ca, Sr, Ba, Ra), a transition metal (Cu, Ag,
Au, Cr, Fe, Mo, Mn, Ni, Ta, W, Pt, Ti, Os), a rare earth metal (Sc,
Y, Eu, Er, Yb), and Al, Ga, In, Zn and the like. These metals maybe
used alone, or two or more kinds may be used jointly.
[0099] For example, when the metal layer is formed so as to be held
by mixed semiconductor layers, the metal is preferably an alkali
metal or an alkaline earth metal. For example, when the electron
injecting layer is formed between the organic EL layer and the
semiconductor buffer layer as described later, since his electron
injecting layer is generally formed using an alkali metal or an
alkaline earth metal, types of the materials to be used for
manufacturing an organic EL element can be decreased, and a
manufacturing process becomes simple.
[0100] In addition, for example, when a metal layer is formed so as
to be in contact with the second electrode layer, it is preferable
that, as the metal, a metal having work function of around 4.0 to
5.5 eV is used. Examples of such the metal include Ag, Au, Al, Cr,
Cu, Fe, Mo, Mn, Ni, Ta, W and the like. These metals maybe used
alone, or two or more kinds maybe used jointly. Since these metals
have low reactivity, and they are less likely to be oxidized by
oxygen introduction or release of oxygen from a target at formation
of the second electrode layer, durability of the organic EL element
can be enhanced.
[0101] Further, for example, when the metal layer is formed so as
to be in contact with the organic EL layer, the preferable metal is
different depending on a kind of the second electrode layer (anode,
cathode) described later. When the second electrode layer is a
cathode, it is preferable that the metal is an alkali metal or an
alkaline earth metal. Thereby, the electron can be injected into
the organic EL layer stably. In addition, when the electron
injecting layer is formed between the organic EL layer and the
semiconductor buffer layer as described above, since this electron
injecting layer is generally formed using an alkali metal or an
alkaline earth metal, types of materials used for manufacturing the
organic EL element can be decreased, and a manufacturing process
becomes simple. On the other hand, when the second electrode layer
is an anode, it is preferable that the metal has work function of
around 4.0 to 5.5 eV, and specifically, it is preferable to use Ag,
Au, Al, Cr, Cu, Fe, Mo, Mn, Ni, Ta, W and the like. Thereby, a hole
can be stably injected into the organic EL layer.
[0102] Since other respects of the metal layer are the same as
those described in the second aspect, explanation is not repeated
herein. Since other respects of the semiconductor buffer layer are
the same as those described in the first aspect, explanation is not
repeated here.
[0103] (v) Others
[0104] The semiconductor buffer layer in the present embodiment may
be such that, in addition to the aforementioned components, the
mixed semiconductor layer, the metal layer and the inorganic layer
are laminated. In this case, a forming position of the mixed
semiconductor layer, the metal layer and the inorganic layer is not
particularly limited. Examples include the case where a mixed
semiconductor layer, the metal layer and the inorganic layer are
laminated in this order from the organic EL layer side, and the
case where the inorganic layer, the mixed semiconductor layer and
the metal layer are laminated in this order.
[0105] In addition, in the semiconductor buffer layer used in the
present embodiment, those with the mixed semiconductor layer
laminated thereon has higher electrical conductivity than those
with the inorganic layer and the metal layer are laminated thereon,
because the metal is diffused (present) throughout the
semiconductor buffer layer.
[0106] (2) Organic EL layer
[0107] Next, the organic EL layer used in the present embodiment
will be explained. The organic EL layer used in the present
embodiment is formed between the semiconductor buffer layer and the
first electrode layer described later.
[0108] The organic EL layer in the present embodiment is
constructed of the organic layer of one layer or a plurality of
layers containing at least the light emitting layer. That is, the
organic EL layer is a layer containing at least the light emitting
layer, and refers to a Layer construction of one or more organic
layers. Usually, when the organic EL layer is formed by a wet
method by coating, since it is difficult to laminate many layers
concerning solvents, the organic EL layer is formed of one layer or
two layers of organic layers in many cases, an organic material is
devised so that solubility into a solvent is different, or further
many layers may be formed by combining a vacuum deposition
method.
[0109] Examples of the organic layer formed in the organic EL
layer, other than the light emitting layer, include the charge
injecting layer such as the hole injecting layer and the electron
injecting layer. Further, examples of other organic layer include
the charge transporting layer such as the hole transporting layer
for transporting the hole to the light emitting layer, and the
electron transporting layer for transporting the electron to the
light emitting layer. Usually, they are formed by integration with
the charge injecting layer in many cases, by imparting function of
charge transportation to the charge injecting layer. Examples of
other organic layer formed in the organic EL layer include a layer
for enhancing a recombining efficiency, such as a career blocking
layer, by preventing the hole or the electron from going through,
and by preventing diffusion of an exciton to confine an exciton in
the light emitting layer.
[0110] In such the organic EL layer, the light emitting layer which
is an essential component will be explained below.
[0111] (i) Light Emitting Layer
[0112] The light emitting layer used in the present embodiment has
function of emitting light by offering a place for the electron and
the hole to be recombined. Examples of the material for forming the
light emitting layer usually include a pigment-based light emitting
material, a metal complex-based light emitting material, and a
polymer-based light emitting material.
[0113] Examples of the pigment-based light emitting material
include a cyclopentadiene derivative, a tetraphenylbutaciene
derivative, a triphenylamine derivative, an oxadiazole derivative,
a pyrazoloquinoline derivative, a distyrylbenzene derivative, a
distyrylarylene derivative, a silole derivative, a thiophene ring
compound, a pyridine ring compound, a perynone derivative, a
perylene derivative, an oligothiophene derivative, a
trifumanylamine derivative, a coumarin derivative, an oxadiazole
dimer, and pyrazoline dimer.
[0114] In addition, examples of the metal complex-based light
emitting material include a metal complex having Al, Zn, Be, Ir, Pt
and the like, or a rare earth metal such as Tb, Eu and Dy in a
central metal and having oxadiazole, thiaziazole, phenylpyridine,
phenylbenzoimidazole or quinoline structure, in a legend, such as
an aluminumquinolinol complex, a benzoquinolinolberyllium complex,
a benzooxazole zinc complex, a benzothiazole zinc complex, an
azomethyl zinc complex, a porphyrin zinc complex, europium complex,
an iridium metal complex, a platinum metal complex and the like.
Specifically, a tris(8-quinolinolato)aluminum complex (Alq3) can be
used.
[0115] Further, examples of the polymer-based light emitting
material include a polyparaphenylenevinylene derivative, a
polythiophene derivative, a poylparaphenylene derivative, a
polysilane derivative, a polyacetylene derivative,
polyvinylcarbazole, a polyfluorenone derivative, a polyfluorene
derivative, a polyquinoxaline derivative, a polydialkylfluorene
derivative, and a copolymer thereof. In addition, examples include
a polymer of the pigment-based light emitting material and the
metal complex-based light emitting material.
[0116] Among the aforementioned materials, the light emitting
material used in the present embodiment is preferably a metal
complex-based light emitting material or a polymer-based light
emitting material, further preferably a polymer-based light
emitting material. Among polymer-based light emitting materials, an
electrically conductive polymer having a .pi. conjugated structure
is preferable. Examples of such the electrically conductive polymer
having a .pi. conjugated structure include the aforementioned a
polyparaphenylenevinylene derivative, a polythiophenel derivative,
a polyparaphenylene derivative, a polysilane derivative, a
polyacetylene derivative, a polyfluorenone derivative, a
polyfluorene derivative, a polyquinoxaline derivative, a
polydialkylfluorene compound, and a copolymer thereof.
[0117] A thickness of the light emitting layer is not particularly
limited as long as it is such the thickness that can provide a
place for the electron and the hole to be recombined, and can
exhibit function of light emission. However, for example, the
thickness can be around 1 nm to 200 nm.
[0118] In addition, a dopant which emits fluorescent light or
phosphorescent light may be added to the light emitting layer for
the purpose of improving a light emitting efficiency or changing a
light emitting wavelength. Examples of such the dopant include a
perylene derivative, a coumarin derivative, a rubrene derivative, a
quinacridone derivative, a squarylium derivative, a porphyrin
derivative, a styryl pigment, a tetracene derivative, a pyrazoline
derivative, decacyclene, phenoxazone, a quinoxaline derivative, a
carbazole derivative, and a fluorene derivative.
[0119] In the present embodiment, light emitting layers emitting
different colors can be combined and, when a full color and multi
color display is manufactured, patterning is necessary.
[0120] A method for forming the light emitting layer is not
particularly limited as long as it is a method which enables highly
precise patterning. Examples include a deposition method, a
printing method, an ink jet method, a spin-coating method, a
casting method, a dipping method, a bar coating method, a blade
coating method, a roll coating method, a gravure coating method, a
flexographic printing method, a spray coating method, and a
self-assembling method (a layer-by-layerself-assemb- ling method,
self-assembling monolayer method). Among the above, it is
preferable to use a deposition method, a spin-coating method, and
an ink jet method. In addition, when the light emitting layer is
subjected to patterning, separate coating or deposition maybe
performed by a method of masking a pixel having a different
emitting color, or a partition may be formed between light emitting
layers. As a material for forming such the partition, a
photocuring-type resin such as a photosensitive polyimide resin and
an acryl-based resin, or a thermally curing-type resin, and an
inorganic material can be used. Further, a material forming the
partition may be treated so that surface energy (wettability) is
changed.
[0121] (3) First Electrode Layer
[0122] Next, the first electrode layer used in the present
embodiment will be explained. The first electrode layer used in the
present embodiment is formed between the organic EL layer and a
substrate described layer, and is formed as an electrode which is
opposite to the below-described second electrode layer. The first
electrode layer may be an anode or a cathode, and may be
transparent or translucent, or may not be transparent or
translucent. For example, when light is taken out from a substrate
side, it is required that the first electrode layer is transparent
or translucent and, when light is taken out from the second
electrode layer side, the first electrode layer may not be
transparent or translucent. In addition, when light is taken out
from both sides of the substrate side and the second electrode
layer side, it is required that both of the first electrode layer
and the second electrode layer are transparent or translucent.
[0123] A material for forming the first electrode layer is not
particularly limited as long as it is an electrically conductive
material. Example of the material includes Au, Ta, W, Pt, Ni, Pd,
Cr, Cu, Mo, a metal such as an alkali metal and an alkaline earth
metal, oxide of these metals, and alloy such as an Al alloy such as
AlLi, AlCa and AlMg, a Mg alloy such as MgAg, a Ni alloy, a
Cralloy, an alloy of an alkali metal, and an alloy of an alkaline
earth metal. These electrically conductive materials may be used
alone, two or more kinds may be used by combining them, or two or
more kinds may be used to laminate them. Further, as the
electrically conductive material; an electrically conductive
inorganic oxide such as In--Sn--O, In--Zn--O, In--O, Zn--O,
Zn--O--Al, Zn--Sn--O and the like; an electrically conductive
polymer such as polythiophene, polyanililne, polyacetylene,
polyalkylthiophene derivative and polysilane derivative doped with
a metal; .alpha.-Si; .alpha.-Sic and the like may be also used.
[0124] In the present embodiment, the first electrode layer may be
an anode or a cathode and, usually, the first electrode layer is
formed as an anode. When the first electrode layer is formed as an
anode, it is preferable to use an electrically conductive material
having a large work function value so that the hole is easily
injected. Among the above, it is preferable to use at least one
kind selected from the group consisting of the metal having work
function of 4.5 eV or more, an alloy of such the metal, and the
aforementioned electrically conductive inorganic oxide. When work
function of the metal is less than 4.5 eV, a hole injecting
efficiency is reduced in some cases.
[0125] In addition, in order to increase a value of work function
of the first electrode layer, UV ozone treatment, oxygen plasma
treatment, argon plasma treatment and the like may be performed.
For example, when the first electrode layer consisting of the metal
is subjected to oxygen plasma treatment, and only the metal on a
superficial surface is oxidized, since the value of work function
is increased, the hole injecting efficiency can be improved. In
this case, oxygen plasma treatment is performed only on a
superficial surface of the first electrode layer, because as the
thickness of a layer consisting only of the oxidized metal grows
larger, insulating property is manifested. Alternatively, when the
metal used in the first electrode layer is naturally oxidized,
since the oxidized metal present on the surface can be removed by
argon plasma treatment, the hole injecting efficiency can be
improved.
[0126] Further, in order to prevent a short circuit or a leak
current of the organic EL element, the first electrode layer may be
subjected to mirror polishing treatment. In mirror polishing
treatment, since the first electrode layer can be flattened, a
short circuit or a leak current of the organic EL element can be
prevented.
[0127] In addition, when the first electrode layer is formed as a
cathode, it is preferable to use an electrically conductive
material having a small value of work function so that an electron
is easily injected. As the electrically conductive material having
a small value of work function, it is acceptable as long as the
value of the work function of the electrically conductive material
is smaller than that of the electrically conductive material used
in the anode. As when work function of the metal is less than 4.5
eV, the metal is easily oxidized as described above, it is
preferable to use at least one kind selected from the group
consisting of a metal having work function of 4.2 eV or more, an
alloy of such the metal, and the aforementioned electrically
conductive inorganic oxide.
[0128] A specific resistance value of the first electrode layer is
preferably 1.times.10.sup.-2 .OMEGA..multidot.cm or less, further
preferably 5.times.10 .OMEGA..multidot.cm or less. When a specific
resistance value of the first electrode layer is in the
aforementioned range, circuit loss of electric power due to an
electrode resistance can be prevented. The specific resistance
value is a value measured by a four probing method using Dia
Instruments Loresta-GP (MCP-T600).
[0129] In the present embodiment, when light is taken out from the
substrate side, it is required that the first electrode layer is
transparent or translucent and, as a specific light transmittance,
it is preferable that an average light transmittance at a visible
region of 380 to 780 nm is preferably 50% or more, among the above
80% or more, particularly 85% or more.
[0130] In addition, a thickness of the first electrode layer is not
particularly limited as long as it is such a thickness that the
specific resistance value and the average light transmittance are
satisfied, and the thickness is different depending on the
electrically conductive material to be used, and is preferably in a
range of 40 nm to 500 nm. When the thickness of the first electrode
layer is too thin, the resistance is increased in some cases, and
when the thickness of the first electrode layer is too thick, there
is a possibility that, due to a step difference present at an end
part of the first electrode layer which is formed in a pattern
manner, cutting or breaking of wire occurs in an organic EL layer,
the semiconductor buffer layer or the second electrode layer, or
the short circuit between the first electrode layer and the second
electrode layer occurs.
[0131] Examples of a method for forming the first electrode layer
include a sputtering method, a vacuum heating deposition method, an
EB deposition method, and an ion plating method.
[0132] (4) Second Electrode Layer
[0133] Next, the second electrode layer used in the present
embodiment will be explained. The second electrode layer used in
the present embodiment is formed on the semiconductor buffer layer,
and is formed as an electrode opposite to the first electrode
layer.
[0134] The second electrode layer used in the present embodiment
may be an anode or a cathode. In addition, the second electrode
layer may be transparent or translucent, or may not be transparent
or translucent. For example, when light is taken out from the
second electrode layer side, it is required that the second
electrode layer is transparent or translucent, but when light is
taken out from the substrate side, the second electrode layer may
not be transparent or translucent. In addition, when light is taken
out from both sides of the substrate side and the second electrode
layer side, it is required that both of the first electrode layer
and the second electrode layer are transparent or translucent.
[0135] Since a forming material, a specific resistance value and an
average light transmittance of the second electrode layer are the
same as those described in a column of the first electrode layer,
explanation is not repeated herein.
[0136] A thickness of the second electrode layer is not
particularly limited as long as it is such a thickness that the
specific resistance value and the average light transmittance are
satisfied, and the thickness is different depending on the
electrically conductive material to be used, and is preferably in a
range of 10 nm to 500 nm. When the thickness of the second
electrode layer is too thin, there is a possibility that electrical
conductivity is insufficient. Conversely, when the thickness of the
second electrode layer is too thick, there is a possibility that
light permeability becomes insufficient, and a defect such as crack
easily occurs when the organic EL element is deformed during or
after a process for manufacturing the organic EL element.
[0137] Examples of a method for forming the second electrode layer
include a vacuum film making method such a sputtering method, an
ion plating method, and an electron beam method. In the present
embodiment, since the semiconductor buffer layer is formed between
the organic EL layer and the second electrode layer, the organic EL
layer can be protected from impact at formation of the second
electrode layer. In addition, even when the organic EL layer
contains the metal having high reactivity, since oxidation of the
metal due to oxygen introduction or release of oxygen from a target
at formation of the second electrode layer is prevented by the
semiconductor buffer layer, deterioration in property of injecting
a charge into the light emitting layer in the organic EL layer can
be prevented.
[0138] (5) Substrate
[0139] Next, substrate used in the present embodiment will be
explained. A material for forming the substrate used in the present
embodiment is not particularly limited, as long as it is the
material having self supporting ability. When light is taken out
from the substrate side, it is required that the substrate is
transparent, but when light is taken out from the second electrode
layer side, it is not necessary for the substrate to have
transparency.
[0140] Examples of the material used for such the substrate
include: the inorganic material such as quartz, glass, silicon
wafer, and glass on which TFT (thin film transistor) is formed; and
a polymer material such as polycarbonate (PC), polyethylene
terephthalate (TET), polybutylene terephthalate (PBT),
polyphenylene sulfide (PPS), polyimide (PI), polyamidoimide (PAI),
polyethersultone (PES), polyetherimide (PEI), polyether ether
ketone (PEEK) and the like. Among them, it is preferable to use
quawrz, glass, silicon wafer, or polyimide (PI), polyamidoimide
(PAI), polyethersulfone (PES), polyetherimide (PEI), or polyether
ether ketone (PEEK) which is a superengineering plastic. These
materials have heat resistance of 200.degree. C. or higher, and a
substrate temperature in a manufacturing process can be elevated.
In particular, when an active driving display using TFT is
manufactured, since a temperature is high during the manufacturing
process, the aforementioned materials can be suitably used.
[0141] In addition, when the aforementioned polymer material is
used in the substrate, since there is a possibility that the
organic EL layer is deteriorated by a gas generated from this
polymer material, it is preferable to provide a gas barrier layer
between the substrate and the first electrode layer. Examples of
such the gas barrier layer include silicon oxide and silicon
nitride.
[0142] Further, a substrate whose surface has been subjected to
microlens processing, which enhances a light taking out efficiency,
may be used. In this case, the first electrode layer and the
organic EL layer are formed on the opposite side of the side which
has been subjected to microlens processing.
[0143] A thickness of the substrate is appropriately selected
depending on utility of the material and the organic EL element to
be used, and can be, for example, around 0.005 mm to 5 mm.
[0144] (6) Charge Injecting/Transporting Layer
[0145] In the present embodiment, for example, as shown in FIG. 4,
a charge injecting/transporting layer 6 may be formed between a
light emitting layer in the organic EL layer 3 and a first
electrode layer 2, or between a light emitting layer in the organic
EL layer 3 and a semiconductor buffer layer 4. As used herein, a
charge injecting/transporting layer has function of stably
transporting the charge from the first electrode layer or the
second electrode layer to the light emitting layer and, by
providing such the charge injecting/transporting layer between the
light emitting layer and the first electrode layer, or between the
light emitting layer and the semiconductor buffer layer, injection
of the charge into the light emitting layer is stabilized, and the
light emitting efficiency can be enhanced.
[0146] Examples of such the charge injecting/transporting layer
include the hole injecting/transporting layer for transporting the
hole injected from the anode into the light emitting layer, and the
electron injecting/transporting layer for transporting an electron
injected from the cathode into the light emitting layer similarly.
The hole injecting/transporting layer and an electron
injecting/transporting layer will be explained below.
[0147] (i) Hole Injecting/Transporting Layer
[0148] The hole injecting/transporting layer used in the present
embodiment is not particularly limited as long as it is a layer
which can transport the hole injected from an anode into the light
emitting Layer. For example, the layer may have either one of: the
hole injecting layer having function of stably injecting the hole
injected from an anode into the light emitting layer; and the hole
transporting layer having function of transporting the hole
injected from the anode into the light emitting layer. The layer
may have both of the hole injecting layer and the hole transporting
layer, or may be a single layer having both functions of hole
injecting function and hole transporting function.
[0149] In addition, in the present embodiment, the hole
injecting/transporting layer is formed on the side of the electrode
layer which is to be an anode. For example, when the first
electrode layer is an anode, a hole injecting/transporting layer is
formed between the light emitting layer and the first electrode
layer, and when the second electrode layer is an anode, the hole
injecting/transporting layer is formed between the light emitting
layer and the semiconductor buffer layer.
[0150] A material for forming such the hole injecting/transporting
layer is not particularly limited as long as it is the material
which can stably transport the hole injected from the anode into
the light emitting layer. Examples include, in addition to
compounds exemplified for the aforementioned light emitting
material of the light emitting layer; oxide such as phenylamine
based, starburst-type amine, phthalocyanine based, vanadium oxide,
molybdenum oxide, ruthenium oxide and aluminum oxide; and
derivatives such as amorphous carbon, polyaniline, polythiophene,
polyphenylenevinylene and the like. Specifically,
bis(N-(1-naphthyl-N-phe- nyl)benzidine (.alpha.-NPD),
4,4,4-tris(3-methylphenylphenylamino)tripheny- lamine (NTCATA),
poly3,4ethylenedioxythiophene-polystyrenesulfonic acid (PEDOT-PSS),
and polyvinylcarbazole (PVCz) can be used.
[0151] A thickness of the hole injecting layer is not particularly
limited as long as it is such a thickness that function, of
injecting the hole from the first electrode layer or the second
electrode layer and transporting the hole to the light emitting
layer, is sufficiently exerted. Specifically, the thickness is
preferably in a range of 0.5 nm to 300 nm, among the above in a
range of 10 nm to 100 nm.
[0152] (ii) Electron Injecting/Transporting Layer
[0153] Next, electron injecting/transporting layer used in the
present embodiment will be explained. The electron
injecting/transporting layer used in the present embodiment is not
particularly limited as long as it is a layer which can transport
electron injected from a cathode into light emitting layer. For
example, the layer may have either one of: electron injecting layer
having function of stably injecting the electron injected from
cathode into light emitting layer; and electron transporting layer
having function of transporting the electron into light emitting
layer. The layer may have both of electron injecting layer and
electron transporting layer, or may be a single layer having both
functions of electron injecting function and electron transporting
function.
[0154] In addition, in the present embodiment, the electron
injecting/transporting layer is formed on the side of the electrode
layer which is to be the cathode. For example, when the first
electrode layer is the cathode, the electron injecting and
transporting layer is formed between the light emitting layer and
the first electrode layer, or when the second electrode layer is
the cathode, the electron injecting/transporting layer is formed
between the light emitting layer and the semiconductor buffer
layer.
[0155] A material for forming the electron injecting layer used in
the present embodiment is not particularly limited as long as it is
the material which can stabilize injection of the electron into the
light emitting layer. Examples include, in addition to compounds
exemplified in the aforementioned light emitting material of the
light emitting layer, an alkali metal or an alkaline earth metal,
oxide of an alkali metal or an alkaline earth metal, fluoride of an
alkali metal or an alkaline earth metal, and an organic complex of
an alkali metal, such as aluminum, strontium, potassium, lithium,
cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium
oxide, lithium fluoride, magnesium fluoride, strontium fluoride,
potassium fluoride, barium fluoride, cesium fluoride, and sodium
polymethyl methacrylate polystyrene sulfonate. Among the above, it
is preferable to use fluoride of an alkaline earth metal, because
fluoride of an alkaline earth metal can improve stability and
lifetime of the organic EL layer. The reason is as follows:
fluoride of an alkaline earth metal has low reactivity with water
as compared with the aforementioned alkali metal compounds and
oxide of alkaline earth metal, and water absorption is small during
or after the formation of the electrode injecting layer. Further,
fluoride of an alkaline earth metal has a higher melting point, and
is excellent in heat resistance stability as compared with the
aforementioned alkali metal compounds.
[0156] Conventionally, for example, when an alkali metal, an
alkaline earth metal or a rare earth metal is used as the electron
injecting layer, and the electron injecting layer is formed between
the light emitting layer and the second electrode layer, since the
metal is easily oxidized, the metal used in an electron injecting
layer is oxidized due to oxygen introduction or release of oxygen
from a target at formation of the second electrode layer, and the
electron injection function is lost in some cases. On the other
hand, in the present embodiment, since the semiconductor buffer
layer is formed between the light emitting layer and the second
electrode layer, even when the electron injecting layer is formed
between the light emitting layer and the semiconductor buffer
layer, oxidation of the metal used in the electron injecting layer
can be prevented since the electron injecting layer is protected by
the semiconductor buffer layer at formation of the second electrode
layer.
[0157] A thickness of the electron injecting layer is preferably in
a range of around 0.2 nm to 10 nm since the aforementioned compound
and like of alkali metal or alkaline earth metal has insulating
property.
[0158] In addition, when a transparent electrically conductive
material such as In--Zn--O is used as the cathode, since work
function thereof is 4.6 eV or more, it is preferable to form the
electron injecting layer using a material having work function of
4.0 eV or less. Although it is difficult to inject the electron
from the cathode consisting of In--Zn--O having work function of
4.6 eV or more directly into the light emitting layer under a low
driving voltage, injection of the electron becomes easy by
providing the electron injecting layer having work function of 4.0
eV or less between the cathode and the light emitting layer.
Examples of such the material having work function of 4.0 eV or
less include Ba, Ca, Li, Cs, Mg and the like. When the electron
injecting layer is formed of such the material, it is preferable
that a thickness of the electron injecting layer is in a range of
0.2 nm to 50 nm, among the above 0.2 nm to 20 nm. In this case,
since the transparent electrically conductive material is used as
the cathode, light can be taken out from the cathode side, and when
light is taken out from the cathode side, it is required that the
electron injecting layer also has transparency. When the thickness
of the electron injecting layer is too thick, there is a
possibility that transparency is reduced.
[0159] A material for forming the electron transporting layer used
in the present embodiment is not particularly limited as long as it
is a material which can transport an electron injected from the
cathode or the electron injecting layer into the light emitting
layer. Examples of an electron transporting organic material
include BCP (bathocuproine), Bpehn (bathophenanthroline),
phenanthroline derivative, tris(8-quinolinolato)al- uminum complex
(Alq3) and the like.
[0160] In addition, when an electron injecting/transporting layer
used in the present embodiment consists of a single layer having
both functions of electron injecting function and electron
transporting function, a metal-doped layer, of which an electron
transporting organic material is doped with an alkali metal or an
alkaline earth metal, can be used. Examples of the electron
transporting organic material include bathocuproine (BCP),
bathophenanthroline (Bphen) and the like. Examples of a doping
metal include Li, Cs, Ba and Sr. It is Preferable that a mole ratio
of the electron transporting organic material and the metal in the
metal-doped layer is in a range of 1:1 to 3, among the above, in a
range of 1:1 to 2. It is preferable that a thickness of such the
metal-doped layer is in a range of 5 nm to 500 nm, among the above,
in a range of 10 nm to 100 nm. Since the metal-doped layer has a
large electron mobility, and higher light permeability as compared
with the metal simple substance, the thickness can be increased as
compared with the electron injecting layer.
[0161] (iii) Others
[0162] In the present embodiment, in some cases, it is preferable
to form the electron injecting/transporting layer, depending on the
aforementioned aspect of the semiconductor buffer layer (first
aspect to fourth aspect), the types of the metal contained in the
semiconductor buffer layer, and the types of the second electrode
layer (anode, cathode). Hereinafter, each aspect of the
semiconductor buffer layer will be explained.
[0163] (When the Semiconductor Buffer Layer is the First
Aspect)
[0164] The present aspect is the case where the semiconductor
buffer layer is the mixed semiconductor layer.
[0165] In the present aspect, when the second electrode layer is
the cathode, if Cu, Ag, Au, Al and the like having work function of
4.0 eV or more is used as a metal contained in the mixed
semiconductor, an energy barrier at an interface between the mixed
semiconductor layer and the light emitting layer becomes high, and
it becomes difficult so inject the electron from the mixed
semiconductor layer directly into the light emitting layer under a
low voltage, in some cases. For this reason, where the second
electrode layer is the cathode, and work function of the metal
contained in the mixed semiconductor layer is 4.0 eV or more, it is
preferable to provide the electron injecting/transporting layer
between the mixed semiconductor layer and the light emitting layer.
Thereupon, when light is taken out from the second electrode side,
it is preferable that the electron injecting/transporting layer has
sufficient light permeability.
[0166] On the other hand, when an alkali metal or an alkaline earth
metal is used as the metal contained in the mixed semiconductor,
since these metals have small work function of 4.0 eV or less, the
electron injected from the second electrode layer can be stably
injected into the light emitting layer. For this reason, when the
second electrode layer is a cathode, and the metal contained in the
mixed semiconductor layer is an alkali metal or an alkaline earth
metal, it is not necessary that the electron injecting/transporting
layer is provided between the mixed semiconductor layer and the
light emitting layer.
[0167] In addition, in the present aspect, when the second
electrode layer is the anode, if an alkali metal or an alkaline
earth metal is used as the metal contained in the mixed
semiconductor layer, since these metals have small work function of
4.0 eV or less, an energy barrier at an interface between the mixed
semiconductor layer and the light emitting layer becomes high, and
it becomes difficult to inject the hole from the mixed
semiconductor layer directly into the light emitting layer under a
low voltage, in some cases. For this reason, when the second
electrode layer is the anode, and the metal contained in the mixed
semiconductor layer is an alkali metal or an alkaline earth metal,
it is preferable that the hole injecting/transporting layer is
provided between the mixed semiconductor layer and the light
emitting layer. Thereupon, when light is taken out from the second
electrode layer side, it is preferable that the hole
injecting/transporting layer has sufficient light permeability.
[0168] On the other hand, when Cu, Ag, Au, Al and the like having
work function of 4.0 eV or more is used as the metal contained in
the mixed semiconductor layer, the hole injected from the second
electrode layer can be stably injected into the light emitting
layer. For this reason, when the second electrode layer is the
anode, and the metal contained in the mixed semiconductor layer has
work function of 4.0 eV or more, it is not necessary to provide the
hole injecting/transporting layer between the mixed semiconductor
layer and the light emitting layer.
[0169] (When the Semiconductor Buffer Layer is the Second
Aspect)
[0170] The present aspect is the case where the semiconductor
buffer layer comprises the inorganic layer and the metal layer. In
the present aspect, it is preferable to provide the charge
injecting layer between the light emitting layer and the
semiconductor buffer layer. In this case, since the metal layer is
formed so as not to be in contact with the organic EL layer, there
is a possibility that injection of the charge is insufficient.
However, by providing the charge injecting layer between the light
emitting layer and the semiconductor buffer layer, the charge can
be effectively injected into the light emitting layer. Thereupon,
when light is taken out from the second electrode layer side, it is
preferable that the charge injecting/transporting layer has
sufficient light permeability.
[0171] (When the Semiconductor Buffer Layer is the Third
Aspect)
[0172] The present aspect is the case where the semiconductor
buffer layer comprises the mixed semiconductor layer and the
inorganic layer.
[0173] In the present aspect, when the inorganic layer is formed so
as to be in contact with the organic EL layer, it is preferable to
provide the charge injecting layer between the light emitting layer
and the inorganic layer. In this case, since the metal contained in
the mixed semiconductor layer is not brought into contact with the
organic EL layer, there is a possibility that injection of the
charge is insufficient. However, by providing the charge injecting
layer between the light emitting layer and the inorganic layer, the
charge can be effectively injected into the light emitting layer.
Thereupon, when light is taken cut from the second electrode layer
side, it is preferable that the charge injecting/transporting layer
has sufficient light permeability.
[0174] In addition, in the present aspect, when the mixed
semiconductor layer is formed so as to be in contact with the
organic EL layer, the second electrode layer is the cathode and the
metal contained in the mixed semiconductor layer is an alkali metal
or an alkaline earth metal, it is not necessary to provide the
electron injecting/transporting layer between the mixed
semiconductor layer and the light emitting layer. Since these
metals have small work function of 4.0 eV or less, the electron
injected from the second electrode layer can be stably injected
into the light emitting layer.
[0175] Further, in the present aspect, when the mixed semiconductor
layer is formed so as to be in contact with the organic EL layer,
the second electrode layer is the anode, and the metal contained in
the mixed semiconductor layer is Cu, Ag, Au, Al and the like as
described above, it is not necessary to provide the hole
injecting/transporting layer between the mixed semiconductor layer
and the light emitting layer. Since these metals have a large work
function of 4.0 eV or more, the hole injected from the second
electrode layer can be stably injected into the light emitting
layer.
[0176] (When the Semiconductor Buffer Layer is the Fourth
Aspect)
[0177] The present aspect is the case where the semiconductor
buffer layer comprises the mixed semiconductor layer and the metal
layer.
[0178] In the present aspect, when the second electrode layer is
the cathode, and the metal contained in a layer which is in contact
with the organic EL layer, among the mixed semiconductor layer and
the metal layer, is an alkali metal or an alkaline earth metal, it
is not necessary that the electron injecting/transporting layer is
provided between the semiconductor buffer layer and the light
emitting layer. Since these metals have small work function of 4.0
eV or less, the electron injected from the second electrode layer
can be stably injected into the organic EL layer.
[0179] Further, in the present aspect, when the second electrode
layer is the anode, and the metal contained in a layer which is in
contact with the organic EL layer, among the mixed semiconductor
layer and the metal layer, is Cu, Ag, Au, Al and the like having
work function of 4.0 eV or more, it is not necessary that the hole
injecting/transporting layer is provided between the semiconductor
buffer layer and the light emitting layer. The hole injected from
the second electrode layer can be stably injected into the organic
El layer.
[0180] (7) Others
[0181] In the present embodiment, a color filter layer and/or a
color converting layer may be formed on the second electrode layer.
Thereby, light of each color of the light emitting layer in the
organic EL layer can be color corrected to enhance color
purity.
[0182] The color filter layer may be, for example, a red-colored
layer, a green-colored layer or a blue-colored layer, and each
color filter layer can be formed using a photosensitive resin
composition prepared by dispersing one or two or more kinds of a
pigment, such as an azo based, a phthalocyanine based, and an
anthraquinone based, in a photosensitive resin.
[0183] In addition, the color converting layer can be, for example,
a red converting layer, a green converting layer or a blue
converting layer. Each color converting layer can be formed by a
method of coating a coating solution, obtained by dispersing or
solubilizing a desired fluorescent pigment and resin, by a
spin-coating method, a roll-coating method, a casting method and
the like to form a film, and pattering this by a photolithography
method.
2. Second Embodiment
[0184] Next, the second embodiment of the organic EL element of the
present invention will be explained. The second embodiment of the
organic EL element of the present invention is characterized in
comprising: a substrate; an electrode layer formed on the
substrate; an organic electroluminescent layer which is formed on
the electrode layer and has at least a light emitting layer; and a
semiconductor electrode layer which is formed on the organic
electroluminescent layer and contains an organic compound having a
band gap of 2.0 eV or more and a metal.
[0185] The organic EL element of the present embodiment will be
explained by referring to the drawings. FIG. 5 is a schematic
cross-sectional view showing one example of the organic EL element
of the present embodiment. In FIG. 5, an organic EL element
comprises: a substrate 21; an electrode layer 22 formed on the
substrate 21; an organic EL layer 23 which is formed on the
electrode layer 22 and has at least a light emitting layer; an
electron injecting layer 26 formed on the organic EL layer 23; and
a semiconductor electrode layer 24 formed on the electron injecting
layer 26.
[0186] In the present embodiment, since the semiconductor electrode
layer is formed into a film, for example, by the vacuum deposition
method, the organic EL Layer does not undergo the impact at
formation of the semiconductor electrode layer, and light emitting
property deterioration of the organic EL element can be avoided. In
addition, even when the electron injecting layer is formed between
the light emitting layer and the semiconductor electrode layer,
since oxygen is not usually introduced in the vacuum deposition
method, oxidation of the metal contained in the electron injecting
layer can be avoided.
[0187] Each component of such the organic EL element will be
explained below. Since the organic EL layer and the substrate are
the same as those described in the first embodiment, and the
electrode layer is the same as the first electrode layer described
in the first embodiment, explanation will be omitted herein.
[0188] (1) Semiconductor Electrode Layer
[0189] First, the semiconductor electrode layer used in the present
embodiment will be explained. The semiconductor electrode layer
used in the present embodiment is formed on the organic EL layer,
and contains the inorganic compound having the band gap of 2.0 eV
or more and the metal. The semiconductor electrode layer is formed
as an electrode opposite to the electrode layer. The semiconductor
electrode layer used in the present embodiment may be an anode or a
cathode, and may be transparent or translucent, or may not be
transparent or translucent. For example, when light is taken out
from the semiconductor electrode layer side, it is required that
the semiconductor electrode layer is transparent or translucent.
And when light is taken out from the substrate side, the
semiconductor electrode layer may not be transparent or
translucent. In addition, when light is taken out from both sides
of the substrate side and the semiconductor electrode layer side,
it is required that both of the semiconductor electrode layer and
the electrode layer are transparent or translucent.
[0190] The semiconductor electrode layer used in the present
embodiment can be classified into four aspects depending on a
construction of this semiconductor electrode layer. They are: the
case where the semiconductor electrode layer is the mixed
semiconductor layer in which the metal is dispersed in the
inorganic compound (fifth aspect); the case where the semiconductor
electrode layer comprises an inorganic layer comprising the
inorganic compound and a metal layer comprising the metal, and this
metal layer is formed in the inorganic layer, or on the opposite
side of the side on which the organic EL layer is formed (sixth
aspect); the case where the semiconductor electrode layer comprises
a mixed semiconductor layer in which the metal is dispersed in the
inorganic compound, and an inorganic layer comprising the inorganic
compound (seventh aspect); and the case where the semiconductor
electrode layer comprises a mixed semiconductor layer in which the
metal is dispersed in the inorganic compound, and a metal layer
comprising the metal (eighth aspect).
[0191] Each aspect of such the semiconductor electrode layer will
be explained below.
[0192] (i) Fifth Aspect
[0193] The fifth aspect of the semiconductor electrode layer used
in the present embodiment is the mixed semiconductor layer in which
the metal is dispersed in the inorganic compound.
[0194] The material constituting such the mixed semiconductor layer
will be explained below.
[0195] (Inorganic Compound)
[0196] The inorganic compound used in the present aspect has its
band gap of 2.0 eV or more. The inorganic compound used in the
present aspect is not particularly limited as long as it can be
formed into a layer having function as the electrode, and the same
inorganic compounds as those described in the column of the first
aspect of the aforementioned "1. First aspect (1) Semiconductor
buffer layer" can be used. In addition, in the present aspect,
among the above, it is preferable to use at least one kind of
inorganic semiconductor compound selected from ZnS, ZnSe, GaN and
GaS.
[0197] (Metal)
[0198] The metal used in the present aspect is not particularly
limited as long as it can be formed into a layer having function as
the electrode, and it is preferable to use the metal which is less
likely to be oxidized, and has work function of 4.0 eV or more.
Examples of such the metal include Ag, Al, Au, Be, Co, Cr, Cu, Ga,
Fe, In, Ir, Mn, Mo, Nb, Ni, Os, Pb, Pt, Re, Ru, Sbr Sn, Ta, Ti and
W. These metals may be used alone, or two or more kinds may be used
jointly. In the present aspect, among the above, it is preferable
to use a metal having work function of 4.2 eV or more,
specifically, Ag, Al, Au, Be, Co, Cr, Cu, Ga, Fe, Ir, Mo, Nb, Ni,
Os, Pb, Pt, Re, Ru, Sb, Sn and W are preferably used.
[0199] In addition, when the metal contained in the mixed
semiconductor layer is made into a layer consisting only of the
metal, a thickness of this layer consisting only of the metal is
preferably 100 nm or less, among the above in a range of 1 nm to 50
nm, further 1 nm to 30 nm, particularly 1 nm to 20 nm. When the
thickness of the layer consisting only of the metal is too thick,
there is a possibility that the light transmittance of the mixed
semiconductor layer is reduced. Conversely, when the thickness of
the layer consisting only of the metal is too thin, there is a
possibility that electrically conductivity of the semiconductor
buffer layer is reduced. The thickness of the layer consisting only
of the metal can be calculated by the aforementioned method
described in the first embodiment.
[0200] (Semiconductor Electrode Layer)
[0201] The thickness of the semiconductor electrode layer in the
present aspect is not particularly limited as long as it is such a
thickness that a prescribed average light transmittance and
electric resistivity are satisfied. Specifically, the thickness is
preferably in a range of 1 nm to 500 nm, among the above 10 nm to
200 nm, particularly 10 nm to 100 nm. When a thickness of the
semiconductor electrode layer is too thick, there is a possibility
that the light transmittance is reduced. Conversely, when the
thickness of a semiconductor electrode layer is too thin, there is
a possibility that function as the electrode is not obtained.
[0202] Since an average light transmittance, an electric
resistivity and a forming method of the semiconductor electrode
layer are the same as those of the semiconductor buffer layer
described in the column of the first aspect of the aforementioned
"1. First aspect (1) Semiconductor buffer layer", explanation will
be omitted herein.
[0203] (ii) Sixth Aspect
[0204] The sixth aspect of the semiconductor electrode layer used
in the present aspect comprises: an inorganic layer comprising the
inorganic compound; and a metal layer comprising the metal, and
this metal layer is formed in the inorganic layer, or on an
opposite side to a side on which the organic EL layer is
formed.
[0205] A forming position of the inorganic layer and the metal
layer in the present aspect may be such that the metal layer 34b is
formed so as to be held by inorganic layers 34a as shown in FIG. 6,
or a metal layer 34b is formed on the inorganic layer 34a, that is,
formed on the opposite side to the side on which the organic EL
layer 23 is formed, as shown in FIG. 7. In addition, since a
construction is acceptable that the metal layer is not in contact
with the organic EL layer, a plurality of metal layers and a
plurality of inorganic layers may be laminated.
[0206] In addition, a thickness of the metal layer in the present
aspect is preferably 100 nm or less, among the above, in a range of
1 nm to 50 nm, further 1 nm to 30 nm, particularly preferably 1 nm
to 20 nm. When the thickness of the metal layer is too thick, there
is a possibility that a light transmittance of the semiconductor
electrode layer is reduced. Conversely, when the thickness of the
metal layer is too thin, there is a possibility that electrically
conductivity of the semiconductor electrode layer is reduced.
[0207] Since other respects of the metal layer, and the inorganic
layer are the same as those described in the column of the
aforementioned second aspect of "1. First embodiment (1)
Semiconductor buffer layer", and since an average light
transmittance and an electric resistivity of a semiconductor
electrode layer are the same as those of the semiconductor buffer
layer described in a column of the first aspect of "1. First
embodiment (1) Semiconductor buffer layer", explanation will be
omitted herein. Further, a thickness of the semiconductor electrode
layer, and the inorganic compound and the metal which are
preferably used are the same as those of the fifth aspect.
[0208] (iii) Seventh Aspect
[0209] The seventh aspect of the semiconductor electrode layer used
in the present embodiment comprises: a mixed semiconductor layer in
which the metal is dispersed in the inorganic compound; and an
inorganic layer comprising the inorganic compound.
[0210] A forming position of the mixed semiconductor layer and he
inorganic layer in the present aspect is not particularly limited,
and the mixed semiconductor layer and he inorganic layer may be
laminated in this order from the organic EL layer side, or the
inorganic layer and the mixed semiconductor layer may be laminated
in this order. Alternatively, a plurality of mixed semiconductor
layers and a plurality of inorganic layers may be laminated.
[0211] Since the mixed semiconductor layer is the same as that
described in the column of the aforementioned first aspect of "1.
First embodiment (1) Semiconductor buffer layer", and the inorganic
layer is the same as that described in a column of the
aforementioned second aspect of "1. First embodiment (1)
Semiconductor buffer layer", explanation will be omitted herein. In
addition, since an average light transmittance and an electric
resistivity of the semiconductor electrode layer are the same as
those of the semiconductor buffer layer described in the column of
the aforementioned first aspect of "1. First embodiment (1)
Semiconductor buffer layer", explanation will be omitted herein.
Further, a thickness of the semiconductor electrode layer, and the
inorganic compound and the metal which are preferably used are the
same as those of the aforementioned fifth aspect.
[0212] (iv) Eighth Aspect
[0213] The eighth aspect of the semiconductor electrode layer used
in the present embodiment comprises: a mixed semiconductor layer in
which the metal is dispersed in the inorganic compound; and a metal
layer comprising the metal.
[0214] A forming position of the mixed semiconductor layer and the
metal layer in the present aspect is not particularly limited. The
mixed semiconductor layer and the metal layer maybe laminated in
this order from the organic EL layer side, or the metal layer and
the mixed semiconductor layer may be laminated in this order.
Alternatively, a plurality of mixed semiconductor layers and a
plurality of metal layers may be laminated.
[0215] Since the mixed semiconductor layer is the same as that
described in the column of the aforementioned first aspect of "1.
First embodiment (1) Semiconductor buffer layer", a metal layer is
the same as that described in a column of the aforementioned fourth
aspect of "1. First embodiment (1) Semiconductor buffer layer", and
the light transmittance, an electric resistivity and the like of
the semiconductor electrode layer are the same as those of the
semiconductor buffer layer described in the column of the first
aspect of "1. First embodiment (1) Semiconductor buffer layer",
explanation will be omitted herein. Further, a thickness of the
semiconductor electrode layer, the thickness of the metal layer,
and the inorganic compound and the metal which are preferably used
are the same as those of the fifth aspect.
[0216] (v) Others
[0217] The semiconductor electrode layer in the present embodiment,
the mixed semiconductor layer, the metal layer and the inorganic
layer may be laminated, in addition to the aforementioned
components. In this case, a forming position of the mixed
semiconductor layer, the metal layer and the inorganic layer is not
particularly limited. Examples include: the case where the mixed
semiconductor layer, the metal layer and the inorganic layer are
laminated in this order from the organic EL layer side; and the
case where the inorganic layer, the mixed semiconductor layer and
the metal layer are laminated in this order.
[0218] (6) Charge Injecting/Transporting Layer
[0219] In the present embodiment, for example, as shown in FIG. 8,
a charge injecting/transporting layer 26 may be formed between a
light emitting layer in the organic EL layer 23 and an electrode
layer 22, or between a light emitting layer in the organic EL layer
23 and a semiconductor electrode layer 24. The charge
injecting/transporting layer has function of stably transporting
the charge from the electrode layer or the semiconductor electrode
layer to the light emitting layer. And by providing such the charge
injecting/transporting layer between the light emitting layer and
the electrode layer, or between the light emitting layer and the
semiconductor electrode layer, injection of the charge into the
light emitting layer can be stabilized, and the light emitting
efficiency can be enhanced.
[0220] Since the charge injecting/transporting layer is the same as
that described in the aforementioned first embodiment, explanation
will be omitted herein.
[0221] In the present embodiment, it is preferable to form the
charge injecting/transporting layer, in some cases, depending on
the aforementioned aspect of the semiconductor electrode layer
(fifth aspect to eighth aspect), a kind of the metal contained in
the semiconductor electrode layer, and a kind of the semiconductor
electrode layer (anode, cathode). Each aspect of the semiconductor
electrode layer will be explained below.
[0222] (When the Semiconductor Electrode Layer is the Fifth
Aspect)
[0223] The present aspect is the case where the semiconductor
electrode layer is the mixed semiconductor layer.
[0224] In the present aspect, when the semiconductor electrode
layer is the cathode, and work function of the metal contained in
the mixed semiconductor layer, which is the semiconductor electrode
layer, is 4.0 eV or more, it is preferable to provide the electron
injecting/transporting layer between the mixed semiconductor layer
and the light emitting layer. When a value of work function of the
metal is large, an energy barrier at an interface between the mixed
semiconductor layer and the light emitting layer will be high, and
it becomes difficult to inject the electron from the mixed
semiconductor layer directly into the light emitting layer under a
low voltage, in some cases. However, by providing the electron
injecting/transporting layer between the mixed semiconductor layer
and the light emitting layer, the electron can be effectively
injected into he light emitting layer. Thereupon, when light is
taken out from the mixed semiconductor layer side, it is preferable
that the electron injecting/transporting layer has sufficient light
permeability.
[0225] Further, when the semiconductor electrode layer is the
anode, and work function of the metal contained in the mixed
semiconductor layer, which is the semiconductor electrode layer, is
4.0 eV or more, it is not necessary to provide the hole
injecting/transporting layer between the mixed semiconductor layer
and the light emitting layer. This is because since the value of
work function of the metal is large, the hole can be stably
injected into the light emitting layer.
[0226] (When the Semiconductor Electrode Layer is the Sixth
Aspect)
[0227] The present aspect is the case where the semiconductor
electrode layer comprises the in organic layer and the metal layer.
In the present aspect, it is preferable to provide the charge
injecting/transporting layer between the light emitting layer and
the semiconductor electrode layer. In this case, since the metal
layer is formed so as not to be in contact with the organic EL
layer, there is a possibility that injection of the charge is
insufficient. However, by providing the charge
injecting/transporting layer between the light emitting layer and
the semiconductor electrode layer, the charge can be effectively
injected into the light emitting layer. Thereupon, when light is
taken out from the semiconductor electrode layer side, it is
preferable that the charge injecting/transporting layer has
sufficient light permeability.
[0228] (When the Semiconductor Electrode Layer is the Seventh
Aspect)
[0229] The present aspect is the case where the semiconductor
electrode layer comprises the mixed semiconductor layer and the
inorganic layer.
[0230] In the present aspect, when the inorganic layer is formed so
as to be in contact with the organic EL layer, it is preferable to
provide the charge injecting/transporting layer between the light
emitting layer and the inorganic layer. In this case, since the
metal contained in the mixed semiconductor layer is not brought
into contact with the organic EL layer, there is a possibility that
injection of the charge is insufficient. However, by providing the
charge injecting/transporting layer between the light emitting
layer and the inorganic layer, the charge can be effectively
injected into the light emitting layer. Thereupon, when light is
taken out from the semiconductor electrode layer side, it is
preferable that the charge injecting/transporting layer has
sufficient light permeability.
[0231] Further, in the present aspect, when the mixed semiconductor
layer is formed so as to be in contact with the organic EL layer,
the semiconductor electrode layer is the anode, and work function
of the metal contained in the mixed semiconductor layer is 4.0 eV
or more, it is not necessary to provide the hole
injecting/transporting layer between the mixed semiconductor layer
and the light emitting layer. This is because since the value of
work function of the metal is large, the hole can be stably
injected into the light emitting layer.
[0232] (When the Semiconductor Electrode Layer is the Eighth
Aspect)
[0233] The present aspect is the case where the semiconductor
electrode layer has the mixed semiconductor layer and the metal
layer.
[0234] In the present aspect, when the semiconductor electrode
layer is the anode, and work function of the metal contained in a
layer which contacts with the organic EL layer, among the mixed
semiconductor layer and the metal layer, is 4.0 eV or more, it is
not necessary to provide the hole injecting/transporting layer
between the semiconductor electrode layer and the light emitting
layer. This is because since a value of work function of the metal
is large, the hole can be stably injected into the light emitting
layer.
[0235] Since other respects of the organic EL element are the same
as those described in the first embodiment, explanation will be
omitted herein.
[0236] The present invention is not limited to the aforementioned
embodiments. The aforementioned embodiments are examples, and any
embodiments having substantially the same constitution as the
technical idea described in claims of the present invention, and
exerting the same function and effect are included in the technical
scope of the present invention.
EXAMPLES
[0237] The present invention will be specifically explained below
using Examples and Comparative Examples.
Example 1
[0238] (Formation of First Electrode Layer)
[0239] As a substrate, a transparent glass substrate having a size
of 40 mm.times.40 mm and a thickness of 0.7 mm (alkaliless glass
NA35 manufactured by NH Technoglass) was prepared, this transparent
glass substrate was cleaned according to a conventional method, and
a thin film of an indium zinc oxide compound (IZO) (thickness 130
nm) was formed as an anode on the transparent glass substrate by a
sputtering method. Upon formation of the IZO thin film, a mixed gas
of Ar and O.sub.2 (volume ratio Ar:O.sub.2=100:1) was used as a
sputtering gas, and a pressure of 0.1 Pa and a DC output of 150 W
were used. Further, a photosensitive resist (OFPR-800 manufactured
by Tokyo Ohka Kogyo Co., Ltd.) was coated on the IZO thin film
(anode), and mask exposure, development (using NMD3 manufactured by
Tokyo Ohka Kogyo Co., Ltd.) and etching were performed to pattern
an IZO thin film (anode).
[0240] (Formation of Hole Injecting/Transporting Layer)
[0241] The aforementioned transparent glass substrate provided with
the IZO thin film (anode) was cleaned, subjected to UV ozone
treatment, and the transparent glass substrate was coated with
polyethylenedioxythiophen- e-polystyrenesulfonate (PEDOT-PSS)
represented by the following chemical formula (1), in the
atmosphere, by a spin-coating method so as to cover the IZO thin
film (anode). The above was dried to form a hole
injecting/transporting layer (thickness 80 nm). 1
[0242] Wherein, in the formula (1), n is 10,000 to 500,000.
[0243] (Formation of Light Emitting Layer)
[0244] In a glove box in a low oxygen (oxygen concentration 1 ppm
or lower) and low humidity (water steam concentration 1 ppm or
lower) state, polymer (5BTF8) formed of
poly(9,9dioctylfluorene-co-benzothiazole) (F8BT) and
poly(9,9dioctylfluorene) (PFB) represented by the following
chemical formula (2) was coated on the aforementioned hole
injecting/transporting layer by a spin-coating method, and this was
dried to form a light emitting layer (thickness 80 nm). The polymer
(5BTF8) is a light emitting material obtained by blending F8BT and
PF8 at a weight ratio 5:95. 2
[0245] Wherein, in the formula (2), n is 100,000 to 1,000,000.
[0246] (Formation of Electron Injecting Layer)
[0247] Ca was deposited on the light emitting layer at a thickness
of 3 nm to form an electron injecting layer. Deposition conditions
were; a vacuum degree of 5.times.10.sup.-5 Pa; and a film making
rate of 1 .ANG./sec.
[0248] (Formation of Semiconductor Buffer Layer)
[0249] ZnSe and Ca were co-deposited on the electron injecting
layer to form a semiconductor buffer layer having a thickness of 30
nm. Deposition conditions were: a volume ratio of ZnSe and Ca of
10:1; a vacuum degree of 5.times.10.sup.-5 Pa; a rate of making a
film of ZnSe of 1 .ANG./sec; and a rate of making a film of Ca of
0.1 .ANG./sec.
[0250] (Formation of Second Electrode Layer)
[0251] Further, to form a cathode, an IZO thin film (thickness 100
nm) was formed on the semiconductor buffer layer, by a counter
target sputtering method. Upon formation of the IZO thin film, Ar
was used as a sputtering gas, and a pressure of 7.0.times.10.sup.-2
Pa, a DC output of 150 W, and a RF output of 100 W were used.
[0252] (Manufacture of Organic EL Element)
[0253] After the second electrode layer was formed, in a glove box
in a low oxygen (oxygen concentration 1 ppm or lower) and low
humidity (water steam concentration 1 ppm or lower), sealing was
performed with an alkaliless glass. By the aforementioned series of
procedures, an organic EL element having four places of light
emitting areas (area 4 mm.sup.2) was manufactured. The organic EL
element comprises: an anode which was patterned in a form of lines
with a width of 2 mm; an electron injecting layer which is
patterned in a form of lines having a width of 2 mm so as to cross
with the pattern of the anode perpendicularly; a semiconductor
buffer layer; and a cathode.
[0254] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 215
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4000 cd/m.sup.2.
From this result, it was confirmed that, in the light emitting
area, because the semiconductor buffer layer, which is a mixed
semiconductor layer of ZnSe and Ca, exists, oxidation of the light
emitting layer and the electron injecting layer at formation of a
cathode, and damage at spattering are prevented.
[0255] (Evaluation of Light Transmittance and Specific
Resistance)
[0256] In addition, an electron injecting layer, a semiconductor
buffer layer and a second electrode layer were successively formed
in this order on a transparent glass substrate by the
aforementioned forming method to prepare a laminate. Regarding this
laminate, a specific resistance value and a light transmittance in
a visible region of 380 to 780 nm were measured under the following
conditions. As a result, an average light transmittance in a
visible region was about 60%, and a light transmittance at a
wavelength of 500 nm was about 70%. Further, an average specific
resistance value of the laminate (thickness 130 nm) was
8.times.10.sup.-3 .OMEGA..multidot.cm.
[0257] <Measurement of Film Thickness>
[0258] For a film thickness, a cross-section of a film was measured
by using Nanopics 1000 manufactured by Seiko Instruments.
[0259] <Measurement of Light Transmittance>
[0260] A light transmittance was measured at room temperature in
the atmosphere, by using an ultraviolet and visible
spectrophotometer UV-2200A manufactured by Shimadzu Corporation
[0261] <Measurement of Specific Resistance Value>
[0262] A specific resistance value was measured by a four probing
method using Dia Instruments Loresta-GP (MCP-T600)
Example 2
[0263] An organic EL element was manufactured by the same manner as
that of Example 1, except that, as the semiconductor buffer layer,
ZnS and Ca were co-deposited to form a semiconductor buffer layer
having a thickness of 30 nm. Deposition conditions upon formation
of the semiconductor buffer layer were: a volume ratio of ZnS and
Ca of 10:1; a vacuum degree of 5.times.10.sup.-5 Pa; a rate of
forming a film of ZnS of 1 .ANG./sec; and a rate of forming a film
of Ca of 0.1 .ANG./sec.
[0264] When a voltage of 6V was applied to the anode and the
cathode of the organic EL element, a current density was about 230
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4500 cd/m.sup.2.
From this result, it was confirmed that, because the semiconductor
buffer Layer, which is the mixed semiconductor layer of ZnS and Ca,
exists, oxidation of the light emitting layer and the electron
injecting layer at formation of the cathode, and damage due to
sputtering were prevented.
Example 3
[0265] (Formation of First Electrode Layer)
[0266] As a substrate, a transparent glass substrate having a size
of 40 mm.times.40 mm and a thickness of 0.7 mm (alkaliless glass
NA35 manufactured by NH Technoglass) was prepared, this transparent
glass substrate was cleaned by a conventional method, and a thin
film composed of chromium having a thickness of 150 nm was formed
as an anode, on the transparent glass substrate, by a magnetron
sputtering method. Upon formation of the chromium thin film, Ar was
used as a sputtering gas, and a pressure of 0.3 Pa, and a DC output
of 200 W were used. There after, patterning of the chromium thin
film (anode) was performed by a photolithography method (resist:
OFPR-800 manufactured by Tokyo Ohka Kogyo Co., Ltd., etchant:
Cr-01N manufactured by KANTO KAGAKU) so that a pattern of 2 mm
width line.times.2 was obtained.
[0267] Further, the transparent glass substrate provided with the
chromium thin film (anode) was subjected to plasma treatment.
Initially, Ar was used as a sputtering gas, and a pressure of 1.0
Pa and a RF output of 100 W were used. After removing an oxidized
layer at a surface of the chromium thin film, which had been
naturally oxidized, plasma treatment was performed for 1 minute
using Ar and O.sub.2 as sputtering gas, at a gas partial pressure
of Ar:O.sub.2=1:1, a pressure of 1.0 Pa and a RF output of 100
W.
[0268] (Formation of a Hole Injecting/Transporting Layer, Light
Emitting Layer, Electron Injecting Layer, and Semiconductor Buffer
Layer)
[0269] By the same manner as that of Example 1, a hole
injecting/transporting layer, a light emitting layer, an electron
injecting layer, and a semiconductor buffer layer were successively
formed on the chromium thin film (anode).
[0270] (Formation of Second Electrode Layer)
[0271] Further, an IZO thin film (thickness 100 nm) was formed as
the cathode on the semiconductor buffer layer by a counter target
sputtering method. Upon formation of the IZO thin film, Ar was used
as a sputtering gas, and a pressure of 0.07 Pa, RF output of 100 W
and a DC output of 5 W were used.
[0272] (Manufacturing of Organic EL Element)
[0273] By the same manner as that of Example 1, sealing was
performed to manufacture an organic EL element.
[0274] When a voltage of 6 W was applied to the anode and the
cathode of the organic EL element, a current density was about 220
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 9000 cd/m.sup.2.
From this result, it was confirmed that, because the semiconductor
buffer layer, which is the mixed semiconductor layer of ZnSe and
Ca, exists, oxidation of the light emitting layer and the electron
injecting layer at formation of the cathode, and damage at
sputtering were prevented.
Comparative Example 13
[0275] An organic EL element was manufactured by the same manner as
that o- Example 1, except that the IZO thin film as a cathode was
formed on the electron injecting layer, without forming the
semiconductor buffer layer.
[0276] When a voltage of 6 V was applied to the anode and the
cathode of the organic EL display, a current density was about 0.18
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 0.2 cd/m.sup.2. From
this result, it was confirmed that, in an organic EL element in
which the semiconductor buffer layer is not formed, light emitting
property is deteriorated due to oxidation of the electron injecting
layer by oxygen at formation of the cathode.
Comparative Example 2
[0277] An organic EL element was manufactured by the same manner as
that of Example 1, except that, as the semiconductor buffer layer,
only ZnSe was used to form a 30 nm semiconductor buffer layer.
[0278] When a voltage of 6 V was applied to the anode and the
cathode of the organic EL element, a current density was about 19
mA/cm.sup.2, and a brightness of the light emitting area measured
from upper surface (cathode) side was about 1000 cd/m.sup.2. From
his result, it was confirmed that, in an organic EL element in
which the metal is not contained in the semiconductor buffer layer,
charge transporting function in the semiconductor buffer layer is
reduced, and light emitting property is deteriorated.
Comparative Example 3
[0279] An organic EL element was manufactured by the same manner as
that of Example 1, except that, as the semiconductor buffer layer,
only ZnS was used to form a 30 nm semiconductor buffer layer.
[0280] When a voltage of 6 V was applied to the anode and the
cathode of the organic EL element, a current density was about 50
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 1480 cd/m.sup.2.
From this result, it was confirmed that, in an organic EL element
in which the metal is not contained in the semiconductor buffer
layer, charge transporting function of the semiconductor buffer
layer is deteriorated, and light emitting property is
deteriorated.
Example 4
[0281] (Formation of First Electrode Layer)
[0282] By the same manner as that of Example 1, an IZO thin film as
an anode was formed on a transparent glass substrate. (Formation of
hole injecting layer and hole transporting layer) The transparent
glass substrate provided with the IZO thin film (anode) was exposed
to oxygen plasma. Thereafter, a hole injecting layer (thickness 30
nm) formed of tris(naphthyl(phenyl)amino]triphenylamine (1-TNATA),
represented by the following chemical formula (3), was formed on
the transparent glass substrate, by a vacuum heating deposition
method, so as to cover the IZO thin film (anode) Conditions for
forming a film of this hole injecting layer were: a vacuum degree
of 5.times.10.sup.-5 Pa; a rate of forming a film of 2 .ANG./sec;
and a heating temperature of 350.degree. C. 3
[0283] Further, a hole transporting layer (thickness 30 nm) formed
of bis (N-naphtyl) -N-phenylbenzidine (.alpha.-NPD), represented by
the following chemical formula (4), was formed on the hole
injecting layer by a vacuum deposition method. Conditions for
forming a film of this hole transporting layer were: a vacuum
degree of 5.times.10.sup.-5 Pa; a rate of forming a film of 2
.ANG./sec; and a heating temperature of 350.degree. C. 4
[0284] (Formation of Light Emitting Layer)
[0285] A tris(8-quinolinolato)aluminum complex (Alq3) represented
by the following chemical formula (5) and coumarin 6 (C6)
represented by the following chemical formula (6) were formed into
a film, on the hole transporting layer, by co-deposition, to form a
light emitting layer (thickness 40 nm) Conditions for forming the
film of this light emitting layer were: C6 was doped so that C6
will be contained in Alq3 by a weight ratio of 1%; a vacuum degree
of 5.times.10.sup.-5 Pa; and a rate of forming a Alq3 film of 2
.ANG./sec. 5
[0286] (Formation of Electron Transporting Layer and Electron
Injecting Layer)
[0287] An electron transporting layer (thickness 20 nm) formed of
bathocuproin (BCP) represented by the following chemical formula
(7) was formed on the light emitting layer by a vacuum deposition
method. Conditions for forming the film of this electron
transporting layer were: a vacuum degree of 5.times.10.sup.-5 Pa;
and a rate of forming a film of 2 .ANG./sec. 6
[0288] Further, an electron injecting layer (thickness 3 nm) formed
of Li was formed on the electron transporting layer by a vacuum
deposition method. Conditions for forming a film of this electron
injecting layer were: a vacuum degree of 5.times.10.sup.-5 Pa; and
a rate of forming a film of 0.2 .ANG.A/sec.
[0289] (Formation of Semiconductor Buffer Layer and Second
Electrode Layer)
[0290] An organic EL element was manufactured by forming the
semiconductor buffer layer and the second electrode layer, and
sealing by the same manner as that of Example 2.
[0291] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 150
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 3300 cd/m.sup.2.
From this result, it was confirmed that, because the semiconductor
buffer layer, which is the mixed semiconductor layer of ZnS and Ca,
exists, oxidation of the electron injecting layer at formation of
the cathode, and damage of the light emitting layer and the
electron injecting layer in sputtering were prevented.
Example 5
[0292] (Formation of First Electrode Layer)
[0293] By the sane manner as that of Example 1, an IZO thin film as
a cathode was formed on a transparent glass substrate.
[0294] (Formation of Electron Injecting Layer and Electron
Transporting Layer)
[0295] The transparent glass substrate provided with the IZO thin
film (cathode) was exposed to argon plasma. Thereafter, BCP and Li
were co-deposited on the transparent glass substrate by a vacuum
heating deposition method so as to cover the IZO thin film
(cathode), to form an electron injecting layer (thickness 20 nm).
Conditions for forming the film of this electron injecting layer
were: a vacuum degree of 5.times.10.sup.-5 Pa; a rate of forming a
BCP film of 2 .ANG./sec; and co-deposition at a mole ratio of BCP
and Li of 1:2.
[0296] Further, by the same manner as that of Example4, an electron
transporting layer (thickness 20 nm) formed of BCP was formed on
the electron injecting layer.
[0297] (Formation of Light Emitting Layer)
[0298] By the same manner as that of Example 4, a light emitting
layer (thickness 40 nm) formed of Alq3 and C6 was formed on the
electron transporting layer.
[0299] (Formation of Hole Transporting Layer and Hole Injecting
Layer)
[0300] By the same manner as that of Example 4, a hole transporting
layer (thickness 30 nm) formed of .alpha.-NPD and a hole injecting
layer (thickness 30 nm) formed of 1-TNATA were successively formed
on the light emitting layer.
[0301] (Formation of Semiconductor Buffer Layer)
[0302] ZnS and Au were co-deposited on the hole injecting layer to
form a semiconductor buffer layer having a thickness of 30 nm.
Conditions for forming a film of this semiconductor buffer layer
were: a volume ratio of ZnS and Au of 10:1; a vacuum degree of
5.times.10.sup.-5 Pa; a rate of forming a ZnS film of 1 .ANG./sec;
and a rate of forming an Au film of 0.1 .ANG./sec.
[0303] (Formation of Second Electrode Layer)
[0304] An IZO thin film (thickness 100 nm), as an anode, was formed
on the semiconductor buffer layer, and sealing was performed to
manufacture an organic EL element.
[0305] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 101
mA/Cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (anode) side was about 2800 cd/m.sup.2. From
this result, it was confirmed that, because the semiconductor
buffer layer, which is brightness mixed semiconductor layer of ZnS
and Au, exists, damage of the light emitting layer, the hole
transporting layer and the hole injecting layer due to sputtering
at formation of the anode was prevented.
Comparative Example 4
[0306] An organic EL element was manufactured by the same manner as
that of Example 4, except that the IZO thin film as a cathode was
formed on the electron injecting layer without forming a
semiconductor buffer layer.
[0307] When a voltage of 6 V was applied to the anode and the
cathode of the organic EL element, a current density was about 1.2
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4.6 cd/m.sup.2. From
this result, it was confirmed that, in an organic EL element in
which the semiconductor buffer layer is not formed, due to
oxidation of the electron injecting layer at formation of the
cathode, and damage of the light emitting layer and the electron
transporting layer by sputtering, leak current is often caused so
that light emitting property is deteriorated.
Comparative Example 5
[0308] An organic EL element was manufactured by the same manner as
that of Example 4, except that, as the semiconductor buffer layer,
a semiconductor buffer layer (thickness 30 nm) consisting only of
ZnS was formed.
[0309] When a voltage of 6 V was applied to the anode and the
cathode of the organic EL element, a current density was about 80
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4100 cd/m.sup.2.
From this result, it was confirmed that, in an organic EL element
in which the metal is not contained in the semiconductor buffer
layer, charge transporting function of the semiconductor buffer
layer is deteriorated, and light emitting property is
deteriorated.
Example 6
[0310] An organic EL element was manufactured by the same manner as
that of Example 1, except that, as the semiconductor buffer layer,
ZnS was deposited at a thickness of 30 nm, thereafter, Au was
deposited to be 5 nm, and further, ZnS was deposited at 30 m to
form the semiconductor buffer layer formed of the organic layer
(ZnS), the metal layer (Au) and the inorganic layer (ZnS).
[0311] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 190
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4000 cd/m.sup.2.
From this result, it was confirmed that, because the semiconductor
buffer layer having a laminated construction of ZnS/Au/ZnS exists,
oxidation of the light emitting layer and the electron injecting
layer at formation of the cathode, and damage due to sputtering
were prevented.
Example 7
[0312] By the same manner as that of Example 1, an IZO thin film
(cathode), a hole injecting/transporting layer, a light emitting
layer, and an electron injection layer were successively formed on
a transparent glass substrate. Thereafter, ZnSe and Au were
co-deposited on the electron injecting layer to form a
semiconductor electrode layer (anode) having a thickness of 100 nm,
thereby, an organic EL element was manufactured. Conditions for
forming the film of the semiconductor electrode layer were: a
volume ratio of ZnSe and Au of 10:1; a vacuum degree of
5.times.10.sup.-5 Pa; a rate of forming a ZnSe film of 1 .ANG./sec;
and rate of forming an Au film of 0.1 .ANG./sec.
[0313] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 210
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 4300 cd/m.sup.2.
From this result, it was confirmed that, since the anode can be
formed into a film without performing sputtering by forming the
semiconductor electrode layer, which is the mixed semiconductor
layer of ZnSe and Au, oxidation of the light emitting layer and the
electron injecting layer, and damage due to sputtering can be
avoided, and better property can be obtained.
Example 8
[0314] An organic EL element was manufactured by the same manner as
that of Example 1, except that, as the semiconductor buffer layer,
CaF.sub.2 and Au were co-deposited to form the semiconductor buffer
layer having a thickness of 30 nm. Deposition conditions were: a
volume ratio of CaF.sub.2 and Au of 2:1; a vacuum degree of
5.times.10.sup.-5 Pa; a rate of forming a CaF.sub.2 film of 1
.ANG./sec; and a rate of forming an Au film of 0.5 .ANG./sec. A
light transmittance of only the semiconductor buffer layer having a
thickness of 30 nm was about 65% at a wavelength of 510 nm.
[0315] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 190
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 3500 cd/m.sup.2.
From this result, it was confirmed that, because the semiconductor
buffer layer, which is the mixed semiconductor layer of CaF.sub.2
and Au, exists, oxidation of the light emitting layer and the
electron injecting layer at formation of the cathode, and damage
due to sputtering are prevented.
Example 9
[0316] By the same manner as that of Example 1, an anode, a hole
injecting/transporting layer, a light emitting layer and an
electron injecting layer were formed on a transparent glass
substrate. CaF.sub.2 and Au were co-deposited on this electron
injecting layer to form a semiconductor electrode layer having a
thickness of 50 nm. Deposition conditions were; volume ratio of
CaF.sub.2 and Au of 2:1; a vacuum degree of 5.times.10.sup.-5 Pa; a
rate of forming a CaF.sub.2 film of 1 .ANG./sec; and a rate of
forming an Au film of 0.5 .ANG./sec. A light transmittance of only
the semiconductor electrode layer having a thickness of 50 nm was
about 52% at a wavelength of 510 nm.
[0317] When a voltage of 6 V was applied to the anode and the
cathode of this organic EL element, a current density was about 160
mA/cm.sup.2, and a brightness of the light emitting area measured
from an upper surface (cathode) side was about 3000 cd/m.sup.2.
From this result, it was confirmed that, by forming the
semiconductor electrode layer, which is a mixed semiconductor layer
of CaF.sub.2 and Au, using a vacuum deposition method, a cathode
can be formed without damaging the light emitting layer, and
oxidation of the electron injecting layer is prevented.
* * * * *