WO 2005/025276 PCT/KR2004/002261
HIGHLY RFFICIENT ORGANIC LIGHT EMITING DEVICE USING
SUBSTRATE HAVING NANOSIZED HEMISPHERICAL RECESSES
AND METHOD FOR PREPARING THE SAME
5 Technical Field
The present invention relates to an organic light
emitting device, and particularly to an organic light
emitting device having layers including a substrate in the
form of a non-planar structure. Moire particularly, the
10 present invention relates to a highly efficient organic light
emitting device using a substrate formed with a nano-sizsd
hemispherical recess.
Background Art
15 Organic electroluminascence means to convert electrical
energy into light energy by vising organic materials. That is,
when voltage is applied between an anode and a cathode while
aligning an organic material layer between the anode and the
cathode, holes are injected into the organic material layer
20 from the anode and elections are injected: into the organic
material layer from the cathode. When the holes meet the
electrons, excitons may be formed and such excitons generate
light when they fall to the ground state.
Recently, research and studies are being actively
25 carried out for fabricating displays ox illumination units by
using the electroluminescent phenomenon. In addition,
techniques for depositing organic material layers in the form
of a single layer or multi-layers are being actively studied
in order to achieve effective organic light emitting devices.
30 Most of currently available organic light emitting devices
1:

WO 2005/025276 PCT/KR2004/002261
include art electrode layer and an organic material layer
deposited in the form of a planar structure. Among those
organic light emitting devices, an organic light, emmitting;
device having a planar multi-layer structure including an
5 electrode layer and four organic material layers, such as a
hole injection layer, a hole transport layer, a light
emitting layer, and an electron -transport layer as shown in
Fig. 1, has been widely used.
Referring to the organic light emitting device having a
10 planar structure shown in FIG. 1, if an anode is a
transparent anode and a substrate is a glass substrate, light
generated from an organic material. layer may pass through "the
transparent anode and the glass substrate. At this time, the
light generated from a light emitting layer may travel
15 through two different paths. Firstly, the light can be
emitted out of the organic light emitting device. Secondly,
the light may remain in the organic light emmiting device
while being reflected totally from the glass substrate or a
surface of the anode, among light generated from the light
20 emitting layer, about l/2n2 of the light can be emitted out of
the organic light, emiting device wherein, n is a refractive
index- of the organic material layer) . If the refractive index
of the organic material layer of the device is 1.7, less than
17% of the light generated from the device can be emitted out
25 of the organic light emitting device.
To solve, "the. above problem. are emit a large amount of
light out of the organic light emitting device, an organic
light emitting device structure including non-planar layer,
i.e. non-planar structure has been suggested. The organic
30 light emitting device having a structure a non-planar
2

WO 2005/025276 PCT/KR2004/002261
structure, can be fabricated through the following two
methods.
According to a first method, a photonic crystal having a
gravure pattern is formed on a glass substrate through a
5 photolithography process before a transparent anode is
deposited on the glass substrate (See, U.S. Publication No.
2003/0057417 and a document Appl. Phys. Lett. 82, 3779 issued
on 2003 toy Y. Lee et al.), or a corrugated pattern is formed
on the glass substrate by using an. interference of light (see,
10 WO 2000/70691 and a document Adv. Mater. 13, 123 issued on
2001 by By J. Matterson et al. ) , so as to improve light
emitting efficiency. In detail, the former deposits an anode
layer on the glass substrate, after farming the photonic
crystal on the glass substrate and planarizing a surface of
15 the glass substrate by using SiN8. The latter deposits an
electrode layer and an organic Material layer on the glass
substrate while maintaining a corrugated pattern, after
forming the corrugated, pattern, of transparent polymer on the
glass substrate- by -using photoresist materials and an
20 interference of light.
According to a second method, after fabricating an
oxganic light emitting device having a planar structure as
shown in FIG. 1, a micro-sized lens structure (see, WO
2003/007653 and a document J. Appl. Phys. 91, 3324 issued on
25 2000 by S. Moller et- al,) or a millimetre-sized: lens
structure (see, WO 2001/33593) is attached to a surface, of a
glass substrate of the organic light emitting device, thereby
improving Light emtting efficiency of the device
The above two methods can improve the light emitting
30 efficiency of the light emitting device. However, the above
3

WO 2005/025276 PCT/KR2004/002261
two methods do not suggest a hemispherical recess structure
formed on a substrate having high reflectance in order to
effectively emit light. in addition, the above two inethods
represent problems when. they are. applied to an available
5 light, emitting device.
That is, the first method uses the photolithography
process, so it is impossible to form the photonic crystal
structure ox the corrugated struct ore over a large-sized
area. That is, in order to fabricate the light end tt ing
10 device using the photonic crystal structure, it is necessary
to sequentially Carry out a deposition process, a
photolithography process, and. an etching process, At this
time, the substrate must, be processed, at least two times
under a vacuum state- In addition, in order to fabricate the
15 light emitting device using the corrugated structure, it is
necessary to perform the photolithography process by using an
interference of light. However, the photolithography process
is not- adaptable for forming a uniform corrugated structure
over a substrate having an area more, than a few cm2.
20 The second method represents limitations when it is
applied to display ,because the lens structure has a sire
within a range of about a few micrometers to a few
millimeters. In addition, the second method is not adaptable
for a. large-sized area due to preparation work thereof.
25 According to the lens structure disclosed In WO 2003/007663,
a minimum surface size of the lens structure is defined as a
few pan such that minimum surface size of the lens structure
must toe larger than a maximum wavelength of visible ray
emitted from the organic light emitting device. In addition,
30 accordingly to the lens structure disclosed in, WQ 2001/39598.,
4

WO 2005/025276 PCT/KR2004/002261
the size of the lens structure must be larger than a size of
one unit of an organic light emitting device,
Disclosure of the Invention
5 Inventors of the present invention have found that light
genarated from an organic "material layer can be efficiently
emitted out of a light emitting device when a substrate
and/or an electrode of the organic light emitting device is
formed with hemispherical recessesr particularly nano-sized
10 hemispherical recesses continuously- In addition, when an
electrode has above structure,. a surface area of the
electrode becomes enlarged so that an amount of current
applied to the organic light emitting device may increase
under the. same voltage. condition, thereby improving
15 brightness of the organic light emitting device. Moreover,
the substrate, of above structure can be fabricated through a
porous aluminum oxide layer forming process, so that it is
possible to fabricate a large-sized organic light emitting
device having the substrate of the above structure at. a low
20 cost.
Accordingly, it is an object of the present invention to
provide an organic light emitting device having a substrate
formed with a plurality of head spherical recesses,
preferably, a plurality of hemispherical recesses
25 continuously formed in the substrate, and a method for
fabricating the same.
In order to accomplish the above object, accordingly to
one aspect of the present invention, there is provided an
organic light emitting device comprising a substrate, a first
30 electrode, an organic material layer and a second electrode
5

WO 2005/025276 PCT/KR2004/002261
RO/KR 13.10.2004
in sequentially laminated form; wherin. a plurality of
continued hemispherical recesses are formed on an upper
surface of the substrate aligned adjacent to the first
electrode.
5 In order to accomplish the above object, according to
another aspect of the present invention, there is provided a
method for fabricating an organic light emitting device.,
comprising the steps of: a) dipping a substrate having at
least one aluminum surface in an acid solution, and applying
10 oxidation voltage of 10 to. 400 V to the substrate so as to
form an aluminum oxide layer on the aluminum surface of the
substrate, in such a manner that a plurality of continued
recesses are formed on the aluminum oxide layer, and a
plurality of continued recesses having curvature, in identical
15 direction to that of the recesses on the aluminum oxide layer
are formed on an interface between the aluminum oxide layer
and the substrate; b) removing the aluminum oxide layer from
the substrate, thereby forming a. plurality of continued
hemispherical recesses on one surface of the substrate; and
20 c) forming an organic material layer and an electrode on one
surface of the substrate formed with the hemispherical
recesses -
Brief Description of the Drawings
25 The foregoing and other objects, features and advantages
of the present invention will become more apparent from the
following detailed description when taken in conjunction with
the accompanying drawings in which i
FIG, 1 shows a conventional organic light emitting
30 device having a planar structure;
6

WO 2005/025276 PCT/KR2004/002261
FIG. 2 shows one embodiment of an organic light emitting
device according to the present invention;
FIG. 3 shows a plan. view and a cross sectional -view of
a substrate formed with a plurality. of continued
5 hemispherical recesses;
FIG. A shows a light route in an organic light emitting
device having a substrate of a planar structure and in an
organic light emiting device, having a substrats formed with
a plurality of hemispherical recesses;
10 FIG. 5 shows an organic light- emitting device having a
transparent thin film layer laminated between a substrate and
a- first electrode according to. one embodiment .of the present
invention;
PIG. 6 shows an organic light emitting device having a
15 transparent thin film layer laminated between a substrate and
a first electrode according to another embodiment of the
present invention;
FIG. 7 shows a manufacturing process- for a substrate
having a plurality of continued hemispherical recesses;
20 FIG. 8 is an electron microphotograph (x 5,000) showing
a surface of a substrate having a plurality of hemispherical
recesses according to Example 1 of the present invention;
FIG. 9 is an electron microphotograph(x 60,000) showing
a surface of a substrate having a plurality of hemispherical
25 recesses according to Example 1 of the present invention;
FIGS. 10 and 11,. respectively, represent measurement
results for a surface structure and a cross sectional
structure of a substrate having a plurality of heroispherical
recesses taken by an atomic force microscope according to
30 Example 1 of the present invention;
7

WO 2005/025276 PCT/KR2004/002261
FIG. 12 is an electron microphotograph(x. .25,000)
showing a cross sectional structure of a substrate after an
oxide layer is formed, on the substrate before the oxide layer
is removed from "the substrate according to Example 2 of the
5 present invention;
FIG- 13 is an electron miccophotograph (x 50,000)
showing a surface srxucture of s substrate having a plurality
of hemispherical recesses according to Example 2 of the
present, invention;
10 FIGS. 14 and 15, respectively, represent measurement
results for a surface structure and a cross sectional
structure of a cathode of an organic light emitting device
taken by an atomic force microscops according to Example 2 of
the present invention
15 FIG- 3.6 is an electron microphotograph (x 30,000)
showing surface structures of substrates having a plurality
of hemispherical recesses according to Example 3 of the
present invention; and
FIG. 17 shows reflectance of light obtained at a planar
20 aluminum substrate and substrates having a plurality of
hemispherical recesses of different sizes respectively
according to Example 3 of the present invention.
Best Mode for carrying out the Invantion
25 Hereinafter, a preferred embodiment of the present
invention will be described, with reference to accompanying
drawings.
There are no cases in a field of organic light emitting
devices of forming a "hemispherical recess" in a substrste of
30 a light emitting device in order to fabricate the substrate
8

WO 2005/025276 PCT/KR2004/002261
having a non-planar structure. In addition, there are also no
cases of using a "nano-sized structure" in order to fabricate
a substrate of an organic light emitting device-having a non-
planar structure- Inventors of the present invention have
5 found that the following advantages can be achieved when a
plurality of nano-sized "hemispherical recesses are
continuously formed on an upper surface of a substrate-
aligned adjacent to a first electrode and preferably, on an
upper surface of a first electrode aligned adjacent to the
10 organic material layer of an organic light emitting device
(see, FIG. 2).
The organic light emitting device may have a laminated
structure comprising two electrodes having a high refractive
index, that, is, a transparent electrode through which light
15 is outputted and an opaque electrode having high reflectance ,-
and an organic material layer interposed, between -two
electrodes so as to emit light, as charges are injected
thereto, A. conventional organic light emitting device, as
shown in FIG- 4 {a) , includes two electrodes having a planar
20 structure so that a total internal reflection, may occur at a
transparent electron havinig a high refractive index when
light passes through the transparent electrode so as to be
emitted to an atmosphere. Thus, the light -may remain within
the organic light emitting device- However, as shown in FIG.
25 4 (b) , in an organic light -emitting device including an
opaque electrode having high reflectance with a plurality of
continued hemispherical recesses, light can be easily emitted
to the atmosphere by reflecting from a substrate having, a
high reflectivity by several times, preferably one or two
30 times.
9

WO 2005/025276 PCT/KR2004/002261
In. addition, as shown in FIG. 2, when an electrode and
an organic material layer are deposited on a substrate having
a plurality of continued hemispherical recesses, a surface
area of the electrode aligned adjacent to the hemispherical
5 recesses becomes increased as compared with a surface area of
an electrode of the conventional organic light emitting
device, having the planar structure, so that an amount of
current injected to the device may increase under the same
voltage condition, thereby improving brightness of the
10 device.
In addition, since hemispherical recesses formed on the
substrate are nano-sized, the brightness of the. organic light
emitting device can be further inproved due to a wave
character of light when light is emitted out of the organic
15 light emitting device. For instance, when a diameter of the
hemispherical recess is identical to or shorter than a
wavelength of a visible ray, the hemispherical recess may
convert a route of light by a diffused reflection or a
scattering phenomenon, of light. Therefore the organic light
20 emitting device of the present invention roay relieve the
total internal reflection condition of light occurring at the
transparent electrode as compared with the conventional
organic light emitting device having the planar structure.
Thus, a larger amount of light can be emitted out of the
25 organic light emitting device. Such effect may be maximized
when the diameter of the hemispherical recesses is set within
a range "between a half-wavelength and one wavelength of the
visible ray.
According to the present invention, since the
30 wavelength of the light is very short, in order to realize
10

WO 2005/025276 PCT/KR2004/002261
the non-planar structure in relation to the wavelength of the
light, it is preferred for the hemispherical recess to have a
diameter identical- to as less than. 10 times of thicness of
an organic material layer of the organic light shutting
5 device. That is, since generally the thickness of the organic
material layer of the organic light emitting device is about
100 to 500 nm, the diameter pf the hemispherical recess is
preferably less than or identical to 5 um. In addition, in
order to achieve the aibove mentioned effect of the present
10 invention, it is more preferred for the hemispherical recess
to have a- diameter within a range between a half-wavelength
and one wavelength of the visible ray, that is,200 to 800
nm. The hemispherical recesses are uniformly distributed on
the substrater and preferably on the electrode of the organic
15 light emitting device. FIG- 3 illustrates the hemispherical
recess structure formed on the substrate, and preferably on
the electrode of the organic light emitting device.
According to the present invention/ the substrate
having a plurality of continued, hemispherical recesses, is
20 characterized by being fabricated through a porous aluminum
oxide layer forming process. The porous aluminum oxide layer
forming process is generally known, However:, there are no
cases of using the porous aluminum oxide layer forming
process to fabricate the organic light emitting device.
25 Inventors of the present invention have found for the first
time that an organic light emitting device having a non-
plartar structure with a large size can be fabricated at a low
cost through the porous aluminum oxide layer forming process.
The porous aluminum oxide layer forming process has
30 been disclosed in a document [A.P. Li et al. J. Appl. Phys.,
11

WO 2005/025276 PCT/KR2004/002261
84, 6023 (1998)], etc. In detail, a substrate having at least
one aluminum, surface is dipped in an acid solution, such as a
sulfuric acid solution, a phosphoric acid solution, an oxalic
acid solution or a chromic acid solution. Then, appropriate
5 oxidation voltage, for example 10 to 400 V is applied to the
substrate so that an oxide layer, in which recesses having a
diameter of about 25 to 10D0 am, preferably 200 to 800 ran,
and a depth of about a few hundreds of nm to few fm axe
uniformly distributed, can be formed at the aluminum surface
10 of the substrate. The depth of the recess may increase
proportional to a process time. At this time, at an interface
between the oxide layer and the substrate, recesses having
curvature in identical direction to curvature of the
hemisphferical recesses are formed on the oxide layer.
- 15 FIG. 7 shows a forming process for an aluminium oxide
layer through the above method. In. FIG. 1, steps a) to d)
represent shape-variation of the oxide layer as a function of
process time. In an initial stage, a thin, and uniform oxide
layer is formed on an aluminum substrate (see, (a) in FIG.
20 7) Then, as a voluioe of the oxide layer is expanded, a
surface of true oxide layer is irregularly deformed (see, (b)
in FIG. 7) . Such, an irregular surface of the oxide layer may
cause an uneven current density. That is, the current density
may increase at 3 recess section of the oxide layer and may
25 decrease at a protrusion section of the oxide layer. Then,
hemispherical recesses are formed at the recess section
having a nigh current density due to an operation of an
electric field and an electrolyte of the acid solution. The
diameter of the hemispherical recesses does not further
30 increase after a predetermined time lapses (see, (c) in FIG.
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WO 2005/025276 PCT/KR2004/002261
7) . In addition, the depth of the hemispherical recesses may
rapidly increase in a vertical direction with respect to the
surface of the oxide layer while constantly maintaining the
number of hemispherical recesses (see, (d) in FIG- 7). As the
5 depth, of the hemispherical recesses increases, recesses
having curvature in identical direction to curvature of the
hemispherical recesses on the aluminum oxide layer are formed
at an interface of the aluminium oxide layer and the aluminum,
substrate (see, (c) and (d) in FIG. 7) .
10 The aluminum oxide layer formed on the substrate is
then removed,, thereby obtaining the substrate having a
plurality of continued hemispherical recesses (see, (e) in
FIG. 7). The aluminum oxide layer can be removed through a
chemical etching process, an electrochemical etching process
15 or an electrical shock process. However, the present
invention does not limit the process for removing the
aluminium oxide layer.
According to the chemical etching process, the oxide
layer is etched toy using an acid solution. Herein, the
20 example of the acid solution includes a mixture of a
phosphoric acid solution and a chromic acid solution,
according to the electrochemical etching process, a substrate
formed with the oxide layer is used as an electrode and the
substrate is dipped in this acid solution so that the oxide
25 layer is removed from the substrate through an
electrochemical reaction between the oxide layer and the acid
solution. Herein,, the example of the acid solution includes a
mixture of ethanol and HClO4. According to the electrical
shock process, electric shock is applied to. the substrate by
30 electrochemically adjusting voltage, thereby removing the
13

WO 2005/025276 PCT/KR2004/002261
oxide layer from the aluminum substrate.
After fabricating the substrate, formed with a plurality
of continued, hemispherical recesses through the above
process, sharp edge portions on the substrate are smoothly
5 treated for preventing s short circuit of the organic light
emitting device. For instance:, the sharp edge portions of the
substrate can be changed into smoothly curved surfaces
through an electric etching process, a chemical etching
process using Hgcl2, etc., or a spin coating process using
10 polyimide-based polymer., photoaccyl-based polymer or BCB
(benzo cylo butens) , etc.
The present invention does not limit a material for the
substrate if the substrate includes at least one aluminum
surface. For instance, as the substrate of the present
15 invention, a substrate consisting of aluminum can .be used,
acid a substrate consisting of a glass substrate and an
aluminum layer laminated, on the glass substrate also can be
used. When the aluminum substrate is Used, aluminum having
purity above 99% and ,a thickness above 200 run is preferably
20 used. When the glass substrate is used, the aluminum layer is
laminated bn the glass substrate through process such as a
sputtering process . At this time, in order to reinforce
adhesive force between the glass substrate and "the aluminum
layer, a chrome layer or a titanium layer having a thickness
25 above 2 nm can be formed on the glass substrate before the
alominum is laminated on the glass substrate.
According to a method of the present invention, when
the substrate has at lesst two aluminum surfaces, an aluminum
oxide layer can be fomed. on only one of aluminium surfaces by
30 protecting remaining surface, Or dipping only one aluminum
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WO 2005/025276 PCT/KR2004/002261
surface into the acid solution.
According to the present invention, it is passible to
fabricate the organic light emitting device by using a
substrate formed with a plurality of continued hemispherical
5 recesses.
The organic light emitting device of the present
invention can be fabricated by laminating sequentially a
first electrode, an organic material layer and a second
electrode on the substrates. When, the substrate including the
10 hemispherical recesses has electric conductivity, the
substrate may act as a first electrode, so it is not
necessary to form the first electrode between the substrate
and the organic material layer.
According to tha preferred embodiment of "the present.
15 invention, the organic light emitting device has a structure
as shown in FIG. 2. The organic light emitting device shown
in FIG. 2, can. be fabricated by depositing an anode on the
substrate having a plurality of continued hemispherical
recesses, usinig a metal, an metal oxide having conductivity,
20 or an alloy thereof used for an anode, while maintaining the
hemispherical recess structure of the substrate, and then
depositing an organic material layer and a transparent
material used for a cathode on the anode, by a sputtering
process or a physical vapor deposition process, such as an E-
25 beam evaporation process, etc.
According to another embodiment of the piesent
invention,- an organic light emitting device can be fabricated
by sequentially depositing a cathode material, an organic
roaterial layer, and an anode material on the substrate having
30 a plurality of continued hemispherical recesses (see,. WO
15

WO 2005/025276 PCT/KR2004/002261
2003/012890) . In most cases of organic materials used for the
organic light emitting device, mobility of holes is faster
than .mobility of electrons. As a result, density of holes is
higher than density of electrons in most cases of organic
5 Light emitting devices. Accordingly, when "the cathode is
formed. on the substrate having the hemispherical recesses,. a
surface area of the cathode becomes larger tiian a surface
area of the anode., so that an amount of electrons injected
into, the organic light emitting device may increase as
10 compared with an amount of electrons injected into the
conventional organic light emitting device having the planar
structure- Thus, the light emitting efficiency can be
improved if the density of holes is formed identically the
density of ale^tcoiis in THE- organic light emitting device by
15 said process.
The organic light emitting device of the present
indention may includes an organic material layer in the form
of a single layer structure or a multi-layer structure. The
organic material layer of the multi-layer structure includes
20 a hole injection layer, a hole transport layer, a light
emitting layer and an electron transport layer, etc. The
organic material layer may be formed in a smaller number of
layers through a solution process , such as a spin coating
process, a screen printing process or an ink jet process,
25 instead of a physical vapor deposition process.
According to the present invention, materials used for
fabricating the anode, the organic material layer and the
cathode of the organic light emitting device are generally
known in the art. For exanple, the following materials can be
30 used far the above elements.
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WO 2005/025276 PCT/KR2004/002261
The. anode, is fabricated by using a material having a
nigh work function in order to allow holes to be easily
injected into the organic material layer. Particularly, the
material for the anode includes metals, such as "vanadiumm,
5 chrome, copper, zinc, gold, or an alloy thereof; metal-
oxides, such as a. zinc oxide, an indium oxicte, an indium-tin-
oxide (ITO), or an indium zinc oxide (IZO) ; a mixture of a
metal and an oxide, such as 2nO:Al or sno2:sb and conductive
polymers, such as poly (3-methylthiophene), poly [3, 4-
10 [ethylene-l,2-dioxy) thiophene (PEDT), polypyrrdle, or
palyaniline, etc:. However, the present invention does not
limit the material for the anode. Among those- elements,
material having high reflectance (>50%) or a high trarnsparent
degree (>50%) is selectively used as a material for the anode
15 in order to relieve a total internal reflection condition by
a recesses structure formed at a lower portion of the organic
light emitting device, In particular, according to this.
present invention, materials having high reflectance, such as
Ag, Al, Ni, Cr, Au or an alloy including the same, are
20 preferably used as materials for the anode.
in addition, the cathode is fabricated by using a
material having a low work -function in order to allow
electrons to be easily injected into the organic material
layer. In detail, the material for the cathode includes
25 metals, such as Mg, Ca, Na, K, Ti, In, yt, Li, Gd, Al, Ag,
Sn, pb, or an alloy of the same; said metals doped with
electron transport materials; and multilayer materials such
as liF/Al ox LiO2/Al. However, the present invention does not
limit the material for the cathode. According to the present
30 invention, in order to prepare the cathode, it is more
17

WO 2005/025276 PCT/KR2004/002261
preferred that a mixture of Mg and Ag, or Al is formed as a
transparent thin film, and then a transparent conductive
material, such as an ITO or ah IZO, is deposited on the
transparent thin film.
5 The hole injectiotion layers is fabricated by using a
material capable of allowing holes to be injected from the
anode at a low voltage condition. It is preferred that the
material for the hole injection layer has an HOMO (highest
occupied molecular orbital) between the work function of the
10 anode, material and the HOMO of a peripheral organic material
layer. Iii detail, the material for the hole injection layer
includes metal porphyrine, oligothiophene, arylamine-based
organic materials, hexanitrile hexaazatriphenylene,
quinacridone-based organic materials, perylene-based organic
15 toaterials., anthraguinone-based conductive. polymer,
polyaniline and polythiophene-based conductive polymer or
conductive polymer, such as a dopant. However, the present
indention does not limit the material for the hole injection
layer.
20 The hole transport layer is fabricated by using a
material capable of transporting holes from the anode or the
hole injection layer to the light emitting layer. It is
preferred, that the material for the hole transport layer has
high hole mobility . In detail, the material for the hole
25 transport layer includes arylamine-based organic materials,
conductive polymers and block copolymers including a
conjugate section and a non-conjugate section, etc However,
the present invention does not limit the material for the
hole transport layer.
30 The light einitting layer is fabricated by using a
18

WO 2005/025276 PCT/KR2004/002261
material capable of generating light of a visible ray range
by confining hales with electrons transferred from the hole
transport layer and the electron transport layer,
respectively. It is preferred that the material for the light
5 emitting layer represents superior quantum efficiency with
respect to fluorescnce or phosphorescence. In. detail, the
material for the light emitting layer includes 8-hydroxy-
quinolina aluminum complex: (Al03) , carbazole-based compounds,
climerized styryl compounds, BAlq, 10—hydroxybenzo quinoline—
10 metal compounds,. compounds based on benzoxazole,
benztiazole, and benzimidazole, poly (p-phenylenevinylene ) -
based polymers, poly phenylene- vinyine(PPV)-based polymers.,
spiro compounds, polyflurone, rubrene, etc. However , the
present invention does not limit the material for the light
15 emitting layer.
The electron transport layer is fabricated by using a
material capable of transporting electrons from the cathode
to the light emitting layer. It is prefer red that the
materiel for the electron transport layer has high electron
20 mobility. In detail, the material for the electron transport
layer includes .8-hydroxy-quinoline aluminum complex,
complexes including Alqs, organic radical compounds, and
hydroxyflavone-metal complexes/ etc. However, the present
invention does not limit "the material for the electron
25 transport layer.
According to the preferred embodiment of the present
invention, the organic light emitting device may include a
transparent thin film aligned between the substrate and. the
first electrode . At this time, the transparent thin film
30 preferably has trarsmittance above 50%, more preferably above
19

WO 2005/025276 PCT/KR2004/002261
80% with respect to a visible ray. According to the present
invention, the transmittance of the transparent, thin film can
be adjust ad by selecting the propex natexial or thickness of
the material fonaing the transparent thin film. This can be
5 performed easily toy one skilled in the art.
The transparent thin film may include a transparent
inorganic material layer obtained by using a sol-gel reaction
or an organic material layer, such as parylene, obtained.
through a chemical vapor deposition process. In addition, it
10 is preferred that the "transparent thin film is "fabricated by
using a heat resistant material having superior endurance
against a deposition process for the ITO or IZO. In detail,
the material for the transparent thin film includes
polyimide, photoacryl, or BCB(benzo cyclo butene), etc.
15 However, the present invention does not limit the material
for the transparent thin film. when the first electrode is a
transparent electrode., the transparent thin "film can be
formed by using the material forming the first electrode.
When forming the transparent thin film, the ITO or 120 is
20 preferably used for the anode, and copper phthalocyanine or
hexanitrile hexaazatriphenylene is used for the hole
injection layer-
A surface of the transparent thin film aligned adjacent
to the. first electrode can be formed with hemispherical
25 recesses in match with the hemispherical recesses formed in
the substrate or can be formed in a planar structure without
the hemispherical recesses- Hereinafter, the transparent thin
film will be described in detail with reference to FIGS. 5
and 6-
30 Referring to FIG. 5, a transparent thin film is
20

WO 2005/025276 PCT/KR2004/002261
laminated between a substrate and a transparent anode. The
transparent thin film can be obtained by coating insulation
material on the substrate having hemispherical recesses while
remaining hemispherical recesses of the substrate. The
5 transparent thin film way surround sharp portions of the
substrate having the hemispherical recesses,, so the safety of
the organic light emitting device may be improved. In
addition, -the. transparent thirv film allows- an electrode
farmed at an upper portion thereof to have the hemispherical
10 recesses. Thus, a surface area of the electrode may become
increased so that a greater amount of current can be injected
to the electrode under a law voltage condition..
Referring to FIG. 6, a transparent thin 'film is
laminated between a substrate and an anode. However
15 differently from the organic light emitting device shown in
FIG. 5, a surface of the transparent thin, film aligned
adjacent to a first electrode has a planar structure.. Thus,
the transparent thin film can prevent short circuit of the
organic light emitting device caused by sharp portions of the
20 . aluminium substrate. In addition, devices., such as thin film
transistors, can be formed on. the- transparent thin filmr so
it is possible.to fabricate various electronic devices-
Example 1
25 Fabrication of Substrate having a plurality of continued
Hemispherical recesses
After dipping an aluminum substrate (100x100 mm,
thickness: 0.7 mm, purity :99.7%) in a phosphoric acid
solution, oxidation voltage of 150 V was applied to the
30 aluminum substrate, thereby forming an aluminum oxide layer
21

WO 2005/025276 PCT/KR2004/002261
formed with xecesses having a diameter of about 200 to 400 run
and 3 thickness of about a few um on the aluminum, substrate.
At this time, the aluminum substrate was used as a working
electrode and a copper substrate was used as a counter
5 electrode.
Then, the aluminum oxide layer was removed from the
aluminum substrate by performing a chemical etching process
using a mixture of the phosphoric acid solution and a qhromic
acid solution, thereby obtaining an aluminum'substrate having
10 a plurality of continued hemispherical recesses.
FIGS. 8: and & show a surface structure of the aluminum
substrate fabricated through the above process, in which FIG.
8 was taken by an electron microscope (x 5,000) and FIG. 9
was taken by an electron microscope (x 60,000)- As shown in
15 FIGS. 8 and 9, a plurality of hemispheirical recesses was
uniformly formed on a large area through the above. process.
According to the present Example 1, the aluminum substrate
has a size of 100x100 nm. However, the size of the aluminium
substrate depends on a size of a counter electrode and a
20 reaction chamber. Accordingly, the aluminum substrate can be
fabricated with a. size larger than l00xl00 nm by adjusting
the size of the counter electrode and the reaction chamber.
But it cannot be easy to fabricate a substrate having a size
of 100x100 mm with the non-planar structure by a conventional
25 method-
FIGS. 10 and 11 represent measurement results for a
surface structure and a cross sectional structure of a
substrate taken by an atomic force microscope, respectively.
As shown in EIGS. 10 and 11, recesses having a substantially
30 hemispherical structure axe continuously and uniformly formed

WO 2005/025276 PCT/KR2004/002261
on the aluminum substrate.
Fabrication of Organic Light Emitting Device
As mentioned above, the aluminum substrate having the
5 b.hemiapherical lecesaes was used as a substrate and an anode.
In addtion, hexanitrile hexaazatriphenylene {500 A), 4,4'-
bis[N-(l-naphthyl)-N-phenylamnijbiphenyl (NPB) (400 A),
Alq3.(500 A), and compounds represented as the following
chemical! formula 1 were sequentially deposited on the
10 aluminum substrate through a thermal vacuum deposition
process, thereby forming a hole injection layer, a hole
transport layer and a light emitting/electron transport layer
on the aluminum, substrate- Tbsn, lithium fluoride (LiF)
having a thicKness. of 12 A and aluminium having a thicness of
15 100 A are seqentially deposited oh the light
emiting ing/electron transport layer so as to form a cathode of
an organic light emitting device. Since the cathode has a
translucent property, light emission may be observed through
the cathode.
20
[Chemical Formula 1]

23

WO 2005/025276 PCT/KR2004/002261
In the process of fabricating the organic light
emitting device, a deposition rate of the organic material
was maintained at 0.4 to 0.7 A/sec, a deposition rate of the
LiF of the cathode was maintained at 0.3 A/sec, a deposition
5 rate of aluminum was maintained, at 2 A/sec, and a vacuum
degree was maintained at 2x10-7 to 5x10-8torr during the
deposition process.
When a forward electric field of 7.5 V was applied to
the organic light emitting device fabricated -through the
10 above process, current of 50 mA/cm2 was injected into organic
light emitting device. At this time, green emission was
observed from. Alq3 representing a peak at 555 nm.
Example 2
15 Fabrication of Substrate having a plurality of continued
Hemispherical recesses
An aluminum layer having a thickness of 1.5 nm was
formed on a glass substrate (100x100 nm, thickness: 0.7 nm)
through a sputtering process. Then, after dipping the glass
20 substrate formed with the aluminum layer in. a phosphoric acid
solution, oxidation voltage of 195 V was applied to the
substrate, thereby uniformly forming an aluminum oxide layer
having a diameter of about 200 to 500 nm on the aluminum
layer. FIG. 12 is an electron microphotograph showing a cross
25 sectional structure of the oxide layer formed, on the aluminum
layer (x 25,000). As shown in FIG. 12, the oxide layer has a
thickness of about 1 nm.
Then, the oxide layer was removed from the aluminum
layer by performing a chemical etching process using a
30 mixture of the phosphoric acid solution and a chromic acid
24

WO 2005/025276 PCT/KR2004/002261
solution. FIG. 13 is an electron microphotogaraph showing a
surface structure of the aluminum layer, in which the oxide
layer has been removed (x 50,000). As shown in FIG, 13, the
hemispherical recesses were -uniformly formed on the aluminum
5 layer-
Fabrication of Organic light Emitting Device
The substrate having hemispherical recesses prepared as
the above, was used as a substrate and an. anode. Then, with
10 the same manner as Example 1, a hole injection layer, a hole
transport layer, a light emitting/electron transport layer,
and a cathode are sequentially formed on the substrate.
In this state, when a forward electric field of 7,4 V
was applied to the organic light emitting device fabricated
15 through the above process., current of 50 mA/cm2- was
represented. At this time, green emission was observed from
Alg3 representing a peak at 536 nm. The green emission did not
vary depending on a viewing angle.
FIGS. 14 and 15 represent measurement results for a
20 surface structure and a sectional structure of the cathode of
the organic light emitting device taken by an atomic force
microscope, respectively. It is understood from FIGS. 14 and
15 that nano-sized. hemispherical recesses were partially
maintained at the surface of the cathode of the organic light
25 emitting device.
Example 3
Three substrates (first to third substrates) having
hemispherical racesses were fabricated in the same manner as
30 Example 2, except that oxidation voltages of 130 V, 195 V and
25

WO 2005/025276 PCT/KR2004/002261
220 v were applied to the first to third substrates,
respectively. According to the inspection for the first to
third substrates by means of an electron microscope,, an
average value of the diameters of the hemispherical recesses
5 increased in proportional to oxidation voltages applied to
the substrates (Fig 16) , Besides the first to third
substrates, s fourth substrate was further fabricated through
the above method without forming the hemispherical- recesses
in the fourth substrate.
10 After that, reflectance of the first to fourth
substrates was measured by means of an n & k Analyzer (n & k
Technology) while setting an incident angle of the n & k
analyzer to 3°. The reflectance of the first to fourth
substrates was obtained by measuring an amount of. light
15 reflected at a reflection angle of 3°. The substrates reflect
or scatter the visible ray. At this time, absorption or
transmission of the visible xay toy the substrates can be
disregarded. Thus, the lower value of the reflectance of
substrates means that a larger amount of visible rays is
20 scattered by substrates.
Aluminum layers of the substrates were formed through
the sputtering process before oxide aluminum layers have been,
formed. It had been observed that a large domain was formed
on. the aluminum layer during the sputtering process. As a
25 result, the fourth substrate had reflectance below 80% at a
visible ray area.
FIG. 17 is a graph showing a test result for
reflectance of the substrates. As shown in FIG. 17 , the
substrate having the hemispherical recess represents
30 reflectance lower than reflectance of the substrate without
26

WO 2005/025276 PCT/KR2004/002261
the hemispherical recess at the visible ray area. in
addition, as oxidation voltage applied to the substrate
during the fabrication of the substrate increases,
reflectance at the visible ray area of the substrate becomes
5 reduced.
Accordingly, it is understood from the above result
that the nano-sized hemispherical recesses may interact with
the visible ray so that the reflectance of the substrate can
be reduced. Therefore, if the substrate having the nano-sized
10 hemispherical recesses is employed for the organic light
emitting device, that it is possible to reduce confinement, of
light, by total reflection at the transparent electrode by a
scattering effect of light. Thus, it is possible to fabricate
the high efficient organic light emitting device,
15
Example 4
Fabrication of _Organic_Liight _Emitting_ Device
The substrate having hemispherical recesses was
fabricated in the same manner: as Example 2. Then,
20 Aluminum (500 A) and LiF (15A) were sequentially deposited by
thermal evaporation process on the substrats and used as a
cathode. Then, compounds represented as the following
chemical formula 1(200 A). Alg3(300 A), 4,4'-bis[N- (1-
naphthyl)-N-phanylamino] biphenyl (KPB) (400 A), and
25 nexanitrile hexaazatri-phenyiene (700 A) were sequentially
deposited on the cathode through a thermal, vacuum deposition
process, thereby forming an electron, transport layer, a light
emitting layer, a hole transport layer, and .a hole injection
layer. Then IZO (Indium Zinc Oxide, 1500 A) was deposited by
30 sputteriing process and used as an anode. Since tho IZO anode
27

WO 2005/025276 PCT/KR2004/002261
has a transparent property, light emission may be observed
through the anode.
When a forward electric field of 6.7 v was applied to the
organic light emitting device fabricated through the above
5 process, current of 100 mA/cm2 was observed- AC this time,
green emission vas observed from Alq3 and the luminance was
5 230 cd/m2.
Comparative Example
10 The organic light emitting device was fabricated using
the same process as Example 4, except for using aluminum
substrate without hemispherical recess.
When 3 forward electric field of 6.9 V was. applied to
the organic light emitting dtevice fabricated through the
15 above process, current of 100 mA/cm2 was observed. At this
time, green emission was observed from Alq3 and the luminance
was 3340 cd/m2.
By comparing results from Example 4 and Comparative
example the organic light emitting device with, hemispherica1
20 recesses on the substrate needs less voltage for the same
current infection and shows the better luminance than the
organic light emitting device without hemispnerical recesses
on the substrate.
25 Industrial applicablity
As can be seen from the foregoing, the organic light
emitting- device having a plurality of hemispherical recessed,
which are continuously formed on the substrate, and
preferably on. the electrode of the organic light emitting
30 device can maximally emit light generated from the organic
28-

WO 2005/025276 PCT/KR2004/002261
material layer out. of the organic light emitting device by
the hemispherical recesses. In acidities, since a surface, area
of the electrode becomes enlarged, an amount of current
applied to the organic light emitting device may increase
5 under the safce voltage condition, thereby improving
brightness of the organic light emitting device- In addition,
the substrate having the above-mentioned structure can be
fabricated with a large size at a low cost through a porous
aluminium oxide layer foming process. Thus, the organic light
10 emitting device according to the present invention is
adaptable for use in a large area economically.
While this invention has been described in connection
with what is presently considered to be the most practical
and preferred embodiment, it is to be understood that the
15 invention is not limited to the disclosed etnbodiment and the
drawings, but, on the contrary, it is intended to cover
various modifications and variations within the spirit and
scope of the appended claims.
29

WO 2005/025276 PCT/KR2004/002261
Claims
1. An organic light emitting device comprising a
substrate, a first electrode, an organic material layer,, and
a second electrode in sequentially laminated form; wherein,
5 on an upper surface of the substrate aligned adjacent to the
first electrode, a plurality of continued hemispherical
recesses are formed.
2. The organic light emitting device as claimed in
10 claim 1, wherein each of the hemispherical recesses has a
diameter of 25 to 1000 nm.
3. The organic light emitting device as claimed in
claim 1, wherein the upper surface of the substrate aligned.
15 adjacent to the first electrode is formed with aluminum.
4. The organic light emitting device as claimed in
claim 1, wherein the substrate is made from aluminum.
20 5. The organic light emitting device as claimed in
claim 1, wherein the substrate includes a glass layer and an
aluminium layer laminated. on the glass layer-
6 The organic light emitting device as claimed in
25 claim 1, wherein the substrate has a function identical to
that of the first electrode so that the first electrode is
replaced with the substrate.
7. The organic light emitting device as claimed in
30 claim 1, further comprising a transparent thin film
30

WO 2005/025276 PCT/KR2004/002261
laminated between the substrate and tne first electrode.
8. The organic light emitting device as claimed in
claim 7, wherein the transparent thin film, which is aligned
5 adjacent to the first electrode, is formed at an upper
surface thereof with corresponding' hemispherical recesses in
match with a plurality of continued- hemispherical recesses
formed on the suhstrate-
10 9. The organic light emitting device as claimed in
claim 7, wherein an upper surface of the transparent thin
film, which is aligned adjacent to the first electrode, has
a planar structure-
15 10. The organic light emitting device as claimed in
claim l, wherein the substrate is fabricated through a
method comprising the steps of:
a) dipping a substrate having, at least one aluminum
surface in an acid solution, and applying oxidation voltage
20 of 10 to 400 V to the substrate so as to form an aluminum
oxide layer on the aluminium.- surface of the substrate, in
such a manner that a plurality of continued recesses are
formed on toe aluminum oxide layer, and a plurality of
continued. recesses having curvature in identical direction,
25 to that of the recesses on the aluminum oxide layer axe
formed on an interface between the aluminum oxide layer and
the substrate; and
b) removing the aluminum oxide layer from the
substrate, thereby forming a plurality of continued
30 hemispherical recesses on one surface Of the substrate-
31

WO 2005/025276 PCT/KR2004/002261
11. The organic light emitting device as claimed in
claim 1, wherein the. organic material layer includes a
single layer or at least two layers.
5
12. The organic light emitting device as claimed in
claim 11, wherein the organic material layer includes a hole,
injection layer, a hole transport layer, a light emitting
layer and an electron transport layer.
10
13. A method for fabricating an organic light
ertdtting device, comprising the steps of:
a) dipping a substrate having at least one aluminum
surface in an acid solution, and applying oxidation voltage
15 of 10 to 400 v to the substrate so as to form an aluminum
oxide layer on the aluminum surface of the substrate in such
a manner that a plurality of continued recesses are formed
on the aluminum oxide layer, and a plurality of continued
recesses having curvature in identical direction to that of
20 the recesses on the aluminum oxide layer are formed on an
interface between the aluminum oxide layer and the
substrate
b) removing the aluminum oxide layer from the
substrate, thereby forming a plurality of continued
25 hemispherical recesses on the surface of the substrate? and
c) forming an organic material layer and an electrode
on one surface of the substrate formed with the
hemispherical recesses.
30 14. The method as claimed in claim 13, wherein, in
32

WO 2005/025276 PCT/KR2004/002261
step b) , the aluminum oxide layer is removed from the
substrate through one selected from the group consisting of
a chemical etching process, an electrochemical etching
process and an electric shock process.
5
15. The method as claimed in claim 13, wherein, in
step c) , the organic material layer and the electrode are
formed on the substrate through a physical vapor deposition
process.
10
16. The method as claimed in claim 13, wherein, in
step c), the organic material layer is formed on the
substrate through a solution process.
15
33

The present invention provides an organic light emiting device comprising a substrate, a first elecirode, an organic
material layer and a second elcctrode in sequentialy maintained form, wherein a plurality of continued hemisiphcjical recesses are
formed on an upper surface of the substrate digned adjacent to the; first electrode. In-addition the present invention provides a method
comprising the steps of a dipping a substrate having at least one aluminium surface in an acid solution,and applying oxidation voltage
of 10 to 100 V to the substrate as to form an aluminium oxidelayer on the aluminium-surface of of the substrate in such a. manner that
a plurality of continued recesses art formed on the aluminum, oxide layer. and-a plurality of continued recesses having curveture in
identical direction to dial of the recesses on the aluminum oxide layer are formed on an interface between the aluminum oxide layer
And the-substrate; b) removing the aluminium oxide layer from the substrate, thereby forming 3 plurality of continued hemispherical
recesses- and t) forming an organic material layer and an electrode on the surface ofthe substrate fromed with the hemispherical
recesses.