U.S. patent application number 14/408154 was filed with the patent office on 2015-05-28 for layered structure for oled device, method for manufacturing the same, and oled device having the same.
This patent application is currently assigned to SAINT-GOBAIN GLASS FRANCE. The applicant listed for this patent is SAINT-GOBAIN GLASS FRANCE. Invention is credited to Ji Woong Baek, Jin Woo Han, Young Seong Lee.
Application Number | 20150144900 14/408154 |
Document ID | / |
Family ID | 49758491 |
Filed Date | 2015-05-28 |
United States Patent
Application |
20150144900 |
Kind Code |
A1 |
Lee; Young Seong ; et
al. |
May 28, 2015 |
LAYERED STRUCTURE FOR OLED DEVICE, METHOD FOR MANUFACTURING THE
SAME, AND OLED DEVICE HAVING THE SAME
Abstract
A layered structure for an organic light-emitting diode (OLED)
device, the layered structure including a light-transmissive
substrate and an internal extraction layer formed on one side of
the light-transmissive substrate, in which the internal extraction
layer includes (1) a scattering area containing scattering elements
composed of solid particles and pores, the solid particles having a
density that decreases as it goes away from the interface with the
light-transmissive substrate, and the pores having a density that
increases as it goes away from the interface with the
light-transmissive substrate, and (2) a free area where no
scattering elements are present, formed from the surface of the
internal extraction layer, which is opposite to the interface, to a
predetermined depth.
Inventors: |
Lee; Young Seong; (Seoul,
KR) ; Han; Jin Woo; (Seoul, KR) ; Baek; Ji
Woong; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAINT-GOBAIN GLASS FRANCE |
Seoul |
|
KR |
|
|
Assignee: |
SAINT-GOBAIN GLASS FRANCE
Seoul
KR
|
Family ID: |
49758491 |
Appl. No.: |
14/408154 |
Filed: |
June 14, 2013 |
PCT Filed: |
June 14, 2013 |
PCT NO: |
PCT/KR13/05290 |
371 Date: |
December 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61659597 |
Jun 14, 2012 |
|
|
|
Current U.S.
Class: |
257/40 ; 428/158;
428/310.5; 428/426 |
Current CPC
Class: |
C03C 2217/48 20130101;
H01L 2251/5346 20130101; C03C 2217/70 20130101; H01L 51/5262
20130101; H01L 2251/5369 20130101; H01L 51/5221 20130101; C03C
2217/475 20130101; H01L 2251/558 20130101; H01L 51/0096 20130101;
C03C 2217/948 20130101; C03C 3/068 20130101; C03C 2217/477
20130101; C03C 8/04 20130101; H01L 51/0081 20130101; C03C 17/007
20130101; H01L 51/0077 20130101; H01L 51/56 20130101; H01L 51/5215
20130101; H01L 51/5092 20130101; H01L 51/0072 20130101; C03C
17/3411 20130101; H01L 51/5268 20130101; C03C 2217/91 20130101;
C03C 2217/452 20130101; C03C 8/20 20130101; H01L 51/0055 20130101;
H01L 51/5056 20130101; C03C 3/066 20130101; C03C 2218/32 20130101;
H01L 51/5072 20130101; Y10T 428/249961 20150401; C03C 17/42
20130101; H01L 51/5088 20130101; C03C 2217/478 20130101; H01L
51/005 20130101; H01L 51/5206 20130101; H01L 51/5012 20130101; Y10T
428/24496 20150115; H01L 51/0058 20130101; C03C 17/002 20130101;
C03C 17/3435 20130101 |
Class at
Publication: |
257/40 ;
428/310.5; 428/158; 428/426 |
International
Class: |
H01L 51/52 20060101
H01L051/52; H01L 51/00 20060101 H01L051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2012 |
KR |
10-2012-0063851 |
Claims
1. A layered structure for an organic light-emitting diode (OLED)
device, the layered structure comprising: a light-transmissive
substrate, and an internal extraction layer formed on one side of
the light-transmissive substrate, wherein the internal extraction
layer comprises a scattering area containing scattering elements
composed of solid particles and pores, the solid particles having a
density that decreases as it goes away from an interface with the
light-transmissive substrate, and the pores having a density that
increases as it goes away from the interface with the
light-transmissive substrate, and a free area where no scattering
elements are present, formed from a surface of the internal
extraction layer, which is opposite to the interface, to a
predetermined depth.
2. The layered substrate for the OLED device of claim 1, wherein
more than about 90% of all solid particles are present in a first
area corresponding to one-half or two-thirds of an entire thickness
of the internal extraction layer from the interface.
3. The layered substrate for the OLED device of claim 2, wherein
the density of the pores in a second area is higher than that of
the pores in the first area, the second area being defined between
the boundary of the first area and the boundary of the free
area.
4. The layered substrate for the OLED device of claim 3, wherein
the first area has a thickness of about 5 to 15 .mu.m, the second
area has a thickness of about 3 to 10 .mu.m, and the entire
thickness of the internal extraction layer is about 8 to 25
.mu.m.
5. The layered substrate for the OLED device of claim 4, wherein
the free area has a thickness of about 0.5 to 2.0 .mu.m.
6. The layered substrate for the OLED device of claim 1, wherein
the density of the scattering elements gradually decreases as it
goes from the interface to a boundary of the free area.
7. The layered substrate for the OLED device of claim 1, wherein
the solid particles comprises at least one selected from the group
consisting of SiO.sub.2, TiO.sub.2, and ZrO.sub.2.
8. The layered substrate for the OLED device of claim 1, wherein
the internal extraction layer comprises a glass material.
9. The layered substrate for the OLED device of claim 8, wherein
the glass material comprises about 55 to 84 wt % Bi.sub.2O.sub.3,
about 0 to 20 wt % BaO, about 5 to 20 wt % ZnO, about 1 to 7 wt %
Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2, and about 5 to 20 wt
% B.sub.2O.sub.3 and optionally further comprises about 0.05 to 3
wt % Na.sub.2O and/or about 0 to 0.3 wt % CeO.sub.2.
10. The layered substrate for the OLED device of claim 1, further
comprising a light-transmissive barrier layer formed on the
internal extraction layer.
11. The layered substrate for the OLED device of claim 10, wherein
the barrier layer comprises at least one selected from the group
consisting of SiO.sub.2 and Si.sub.3N.sub.4 and is formed as a
monolayer or multi-layer.
12. The layered substrate for the OLED device of claim 10, wherein
the barrier layer has a thickness of about 5 to 50 nm.
13. An organic light-emitting diode (OLED) device comprising: a
light-transmissive substrate; an internal extraction layer formed
on the light-transmissive substrate and comprising a scattering
area containing scattering elements composed of solid particles and
pores, the solid particles having a density that decreases as it
goes away from the interface with the light-transmissive substrate,
and the pores having a density that increases as it goes away from
an interface with the light-transmissive substrate, and a free area
where no scattering elements are present, formed from a surface of
the internal extraction layer, which is opposite to the interface,
to a predetermined depth; a light-transmissive electrode layer
formed on the internal extraction layer; an organic layer formed on
the light-transmissive electrode layer, and a reflective electrode
formed on the organic layer.
14. The OLED device of claim 13, wherein more than about 90% of all
solid particles are present in a first area corresponding to
one-half or two-thirds of an entire thickness of the internal
extraction layer from the interface.
15. The OLED device of claim 14, wherein the density of the pores
in a second area is higher than that of the pores in the first
area, the second area being defined between a boundary of the first
area and a boundary of the free area.
16. The OLED device of claim 13, wherein the density of the
scattering elements gradually decreases as it goes from the
interface to a boundary of the free area.
17. The OLED device of claim 13, wherein the internal extraction
layer comprises a glass material comprising about 55 to 84 wt %
Bi.sub.2O.sub.3, about 0 to 20 wt % BaO, about 5 to 20 wt % ZnO,
about 1 to 7 wt % Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2,
and about 5 to 20 wt % B.sub.2O.sub.3 and optionally further
comprises about 0.05 to 3 wt % Na.sub.2O and/or about 0 to 0.3 wt %
CeO.sub.2.
18. The OLED device of claim 13, further comprising a barrier layer
comprising at least one selected from the group consisting of
SiO.sub.2 and Si.sub.3N.sub.4 and formed as a monolayer or
multi-layer between the internal extraction layer and the
light-transmissive electrode layer.
19. The OLED device of claim 18, wherein the barrier layer has a
thickness of about 5 to 50 nm.
20. A layered structure for an OLED device, the layered structure
comprising a light-transmissive substrate and an internal
extraction layer formed on one side of the light-transmissive
substrate, wherein the internal extraction layer comprises a glass
material comprising about 55 to 84 wt % Bi.sub.2O.sub.3, about 0 to
20 wt % BaO, about 5 to 20 wt % ZnO, about 1 to 7 wt %
Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2, and about 5 to 20 wt
% B.sub.2O.sub.3.
21. The layered structure of claim 20, wherein the glass material
comprises about 0.05 to 3 wt % Na.sub.2O.
22. The layered structure of claim 20, wherein the glass material
does not contain any of TiO.sub.2 or ZrO.sub.2, except for
unavoidable traces.
23. The layered structure of claim 20, wherein the glass material
comprises about 65 to 80 wt % Bi.sub.2O.sub.3.
24. An organic light-emitting diode (OLED) device comprising: a
layered structure of claim 20; a light-transmissive electrode layer
formed on the internal extraction layer; an organic layer formed on
the light-transmissive electrode layer, and a reflective electrode
formed on the organic layer.
25. The layered structure of claim 23, wherein the glass material
comprises about 0 to 5 wt % BaO.
Description
TECHNICAL FIELD
[0001] The present invention relates to a layered structure for an
organic light-emitting diode (OLED) device and, more particularly,
to a layered structure for an OLED device, the layered structure
comprising an internal extraction layer (IEL) which can effectively
extract light, which is lost by a waveguide effect caused by a
difference in refractive index between a glass substrate, an ITO
layer, and an organic layer and by a total reflection effect caused
by a difference in refractive index between the glass substrate and
air, to the outside, a method for manufacturing the same, and an
OLED device having the same.
BACKGROUND ART
[0002] An organic light-emitting diode (OLED) is a device in which
organic layers are sandwiched between two electrodes and, when an
electric field is applied to the organic layers, electrons and
holes are injected from the electrodes and recombine in the organic
layer to form excitons, and the excitons decay to the ground state
and emit light. The structure of the OLED is relatively simple,
requires fewer types of parts, and is advantageous for mass
production. The OLEDs have been developed for display purposes, and
the field of OLED lighting that uses white OLEDs has recently
attracted much attention.
[0003] Unlike an OLED panel, an OLED lighting panel does not have
separate red, green, and blue (RGB) pixels and emits white light
using multiple organic layers. Here, the organic layers used in the
OLED lighting panel include a hole injection layer, a hole
transporting layer, an emission layer, an electron transporting
layer, an electron injection layer, etc. according to their
functions.
[0004] The OLEDs may be classified into various types depending on
the materials used, light-emitting mechanisms, light-emitting
directions, driving methods, etc. Here, the OLEDs may be classified
according to the light-emitting structure into a bottom emission
type OLED that emits light toward a glass substrate and a front
emission type OLED that emits light in a direction opposite to the
glass substrate. In the case of the bottom emission type OLED, a
metal thin film such as aluminum, etc. is used as a cathode to
serve as a reflective plate, and a transparent conductive oxide
film such as ITO, etc. is used as an anode to serve as a path
through which light emits. In the case of the front emission type
OLED, the cathode is composed of multilayer thin films including a
silver thin film, and the light is emitted through the cathode.
However, the front emitting structure is rarely used as the
lighting panel, except for a transparent panel that emits light
from both sides, and the bottom emission structure is most widely
used.
[0005] Meanwhile, a phosphorescent OLED can use all excitons, which
are formed by recombination of electrons and holes, in the light
emission, and thus its theoretical internal quantum efficiency
approaches 100%. However, even if the internal quantum efficiency
is close to 100%, about 20% of light is emitted to the outside, and
about 80% of light is lost by a waveguide effect caused by a
difference in refractive index between a glass substrate, an ITO
layer, and an organic layer and by a total reflection effect caused
by a difference in refractive index between the glass substrate and
air.
[0006] The refractive index of the inner organic layer is about 1.7
to 1.8, and the refractive index of the ITO layer (i.e., a
transparent electrode) generally used as the anode is about 1.9.
The thickness of these two layers is as small as about 200 to 400
nm, the refractive index of the glass substrate is about 1.5, and
thus a planar waveguide is naturally formed in the OLED. According
to the calculation, the amount of light lost by the waveguide
effect appears to be about 45%.
[0007] Moreover, the refractive index of the glass substrate is
about 1.5 and the refractive index of external air is about 1.0. As
a result, when light escapes from the glass substrate to the
outside, the light incident beyond the critical angle causes total
reflection and is trapped in the glass substrate, and the light
trapped in this manner amounts to about 35%.
[0008] As a result, only about of 20% of light is emitted to the
outside due to the waveguide effect between the glass substrate,
the ITO layer, and the organic layer and due to the total
reflection effect between the glass substrate and the air layer,
and thus the external light efficiency of the OLED remains in a low
level due to the low light extraction efficiency.
[0009] Therefore, a technology for extracting light trapped in the
OLED is desired to improve the external light efficiency of the
OLED. Here, a technology for extracting light trapped between the
organic layer and the ITO layer to the outside is called internal
light extraction, and a technology for extracting light trapped in
the glass substrate to the outside is called external light
extraction. The light extraction technologies have attracted much
attention as a core technology that can improve the efficiency,
brightness, and lifespan of the OLED lighting panel. In particular,
the internal light extraction technology is evaluated as an
effective technology that can theoretically achieve an improvement
of external light efficiency of more than three times, but it
sensitively affects the internal interface of the OLED. Thus, the
internal light extraction technology needs to satisfy electrical,
mechanical, and chemical properties in addition to the optical
effect.
[0010] At present, the external light extraction technology, which
attaches a micro-lens array (MLA) film, a light-scattering film,
etc. to the external surface of the OLED panel, has already been
established, but the internal light extraction technology has not
yet reached a practical stage.
[0011] According to research reports, it is known that the internal
light extraction technologies such as inner light-scattering
layers, substrate surface deformation, refractive index modulation
layers, photonic crystals, nanostructure formation, etc. have an
effect on the internal light extraction. The key point of the
internal light extraction technology is to scatter, diffract or
refract the light trapped by the waveguide effect to form an
incident angle smaller than the critical angle such that the light
is extracted to the outside of an optical waveguide.
[0012] However, the above technologies introduced as the internal
light extraction technologies are still in a laboratory stage, and
thus the development of an internal light extraction technology
applicable to mass production is urgently desired.
DISCLOSURE OF INVENTION
Technical Problem
[0013] An aspect of the present invention is to provide a layered
structure for an OLED device, which can effective extract light
trapped in an optical waveguide and a glass substrate in the OLED
device to significantly improve the external light efficiency of
the OLED device, thus improving the efficiency, brightness, and
lifespan of the OLED device.
[0014] Another aspect of the present invention is to provide an
OLED device having the layered structure for the OLED device.
Solution to Problem
[0015] According to an aspect of the present invention, there is
provided a layered structure for an organic light-emitting diode
(OLED) device, the layered structure comprising a
light-transmissive substrate and an internal extraction layer
formed on one side of the light-transmissive substrate, wherein the
internal extraction layer may comprise: a scattering area
containing scattering elements composed of solid particles and
pores, the solid particles having a density that decreases as it
goes away from the interface with the light-transmissive substrate,
and the pores having a density that increases as it goes away from
the interface with the light-transmissive substrate; and a free
area where no scattering elements are present, formed from the
surface of the internal extraction layer, which is opposite to the
interface, to a predetermined depth.
[0016] Here, more than about 90% of all solid particles may be
present in a first area corresponding to one-half or two-thirds of
the entire thickness of the internal extraction layer from the
interface.
[0017] In an embodiment, the density of the pores in a second area
may be higher than that of the pores in the first area, the second
area being defined between the boundary of the first area and the
boundary of the free area.
[0018] In an embodiment, the first area may have a thickness of
about 5 to 15 .mu.m, the second area may have a thickness of about
3 to 10 .mu.m, and thus the entire thickness of the internal
extraction layer may be about 8 to 25 .mu.m.
[0019] In an embodiment, the free area may have a thickness of
about 0.5 to 2.0 .mu.m.
[0020] In an embodiment, the density of the scattering elements may
gradually decrease as it goes from the interface to the boundary of
the free area.
[0021] In an embodiment, the solid particles may comprise at least
one selected from the group consisting of SiO.sub.2, TiO.sub.2 and
ZrO.sub.2.
[0022] In an embodiment, the internal extraction layer may comprise
a glass material.
[0023] The glass material may comprise about 55 to 84 wt %
Bi.sub.2O.sub.3, about 0 to 20 wt % BaO, about 5 to 20 wt % ZnO,
about 1 to 7 wt % Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2,
and about 5 to 20 wt % B.sub.2O.sub.3. The glass material may
optionally further comprise about 0.05 to 3 wt % Na.sub.2O and/or
about 0 to 0.3 wt % CeO.sub.2.
[0024] The layered substrate for the OLED device may further
comprise a light-transmissive barrier layer formed on the internal
extraction layer.
[0025] The barrier layer may comprise at least one selected from
the group consisting of SiO.sub.2 and Si.sub.3N.sub.4. The barrier
layer can be formed as a monolayer or multi-layer (for example,
alternating SiO.sub.2 and Si.sub.3N.sub.4 layers).
[0026] In an embodiment, the barrier layer may have a thickness of
about 5 to 50 nm, especially 10 to 30 nm.
[0027] According to another aspect of the present invention, there
is provided an organic light-emitting diode (OLED) device
comprising: a light-transmissive substrate; an internal extraction
layer formed on the light-transmissive substrate and comprising a
scattering area containing scattering elements composed of solid
particles and pores, the solid particles having a density that
decreases as it goes away from the interface with the
light-transmissive substrate, and the pores having a density that
increases as it goes away from the interface with the
light-transmissive substrate, and a free area where no scattering
elements are present, formed from the surface of the internal
extraction layer, which is opposite to the interface, to a
predetermined depth; a light-transmissive electrode layer formed on
the internal extraction layer; an organic layer formed on the
light-transmissive electrode layer; and a reflective electrode
formed on the organic layer.
[0028] Here, more than about 90% of all solid particles may be
present in a first area corresponding to one-half or two-thirds of
the entire thickness of the internal extraction layer from the
interface.
[0029] In an embodiment, the density of the pores in a second area
may be higher than that of the pores in the first area, the second
area being defined between the boundary of the first area and the
boundary of the free area.
[0030] In an embodiment, the density of the scattering elements may
gradually decrease as it goes from the interface to the boundary of
the free area.
[0031] In an embodiment, the internal extraction layer may comprise
a glass material comprising about 55 to 84 wt % Bi.sub.2O.sub.3,
about 0 to 20 wt % BaO, about 5 to 20 wt % ZnO, about 1 to 7 wt %
Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2, and about 5 to 20 wt
% B.sub.2O.sub.3. The glass material may optionally further
comprise about 0.05 to 3 wt % Na.sub.2O and/or about 0 to 0.3 wt %
CeO.sub.2.
[0032] The OLED device may further comprise a barrier layer
comprising at least one selected from the group consisting of
SiO.sub.2 and Si.sub.3N.sub.4 and formed between the internal
extraction layer and the light-transmissive electrode layer. The
barrier layer can be formed as a monolayer or multilayer (for
example, alternating SiO.sub.2 and Si.sub.3N.sub.4 layers).
[0033] In an embodiment, the barrier layer may have a thickness of
about 5 to 50 nm, especially 10 to 30 nm.
[0034] According to still another aspect of the present invention,
there is provided a layered structure for an OLED device, the
layered structure comprising a light-transmissive substrate and an
internal extraction layer formed on one side of the
light-transmissive substrate, wherein the internal extraction layer
comprises a glass material comprising about 55 to 84 wt %
Bi.sub.2O.sub.3, about 0 to 20 wt % BaO, about 5 to 20 wt % ZnO,
about 1 to 7 wt % Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2,
and about 5 to 20 wt % B.sub.2O.sub.3. The glass material may
optionally further comprise about 0.05 to 3 wt % Na.sub.2O and/or
about 0 to 0.3 wt % CeO.sub.2.
[0035] In an embodiment, the glass material may not contain any of
TiO.sub.2 or ZrO.sub.2, except for unavoidable traces.
[0036] In an embodiment, the glass material may comprise about 65
to 80 wt % Bi.sub.2O.sub.3 and preferably about 0 to 5 wt %
BaO.
[0037] According to a further aspect of the present invention,
there is provided an organic light-emitting diode (OLED) device
comprising: a layered structure of any one of aforementrioned, a
light-transmissive electrode layer formed on the internal
extraction layer; an organic layer formed on the light-transmissive
electrode layer; and a reflective electrode formed on the organic
layer.
Advantageous Effects of Invention
[0038] The layered structure for the OLED device according to an
embodiment of the present invention can effectively extract light
trapped in the optical waveguide and the glass substrate in the
OLED device to significantly improve the external light efficiency
of the OLED device, thus improving the efficiency, brightness, and
lifespan of the OLED device.
BRIEF DESCRIPTION OF DRAWINGS
[0039] The above and other features and benefits of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0040] FIG. 1 is a cross-sectional view showing the structure of a
layered structure for an OLED device and an OLED device having the
same according to an embodiment of the present invention;
[0041] FIG. 2 is a schematic diagram showing the light-scattering
effect according to the structure of an internal extraction layer
provided in the layered structure for the OLED device of FIG.
1;
[0042] FIG. 3 is a graph showing the density distribution of all
scattering elements contained in the internal extraction layer of
FIG. 2, which is normalized to the thickness of the internal
extraction layer;
[0043] FIG. 4 is an SEM image of the internal extraction layer of
FIG. 3;
[0044] FIG. 5 is graphs showing changes in light diffusion and
light absorbance according to the density of solid particles
contained in the internal extraction layer;
[0045] FIG. 6 is graphs showing changes in light absorbance and
light transmittance according to a change in thickness of the
internal extraction layer;
[0046] FIG. 7 is a graph showing a difference in light absorbance
according to whether a frit as a material for the internal
extraction layer contains a transition metal; and
[0047] FIG. 8 is a flowchart showing a method for manufacturing a
layered structure for an OLED device according to an embodiment of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0048] Reference will now be made in detail to the embodiments of
the present general inventive concept, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals refer to like elements throughout. The embodiments are
described below in order to explain the present general inventive
concept by referring to the figures. In the drawings, the
thicknesses of layers and regions are exaggerated for clarity.
Throughout the specification, like reference numerals represent the
same components.
[0049] Hereinafter, a layered structure 20 for an OLED device and
an OLED device 10 having the same according to an embodiment of the
present invention will be described with reference to the
accompanying drawings.
[0050] [Layered Structure for OLED Device]
[0051] A layered structure 20 for an OLED device according to an
embodiment of the present invention is formed on a
light-transmissive electrode layer 300 of an OLED device 10 (in
particular, with a bottom emission structure) to improve the
efficiency of extracting light generated in the OLED device 10 to
the outside.
[0052] FIG. 1 schematically shows the structure of the layered
structure 20 for the OLED device and the OLED device 10 having the
same according to an embodiment of the present invention. The
layered structure 20 for the OLED device generally comprises a
light-transmissive substrate 100 and an internal extraction layer
200 formed on one side of the light-transmissive substrate 100.
[0053] The light-transmissive substrate 100 is formed of a material
having a high transmittance to visible light, and a glass substrate
or a plastic substrate may be used as the high transmittance
material. However, the glass substrate, whose refractive index can
be easily adjusted, and which can withstand high temperature when a
frit paste, which will be described later, is applied thereto and
fired at a high temperature of 500 to 750.degree. C., is desirable
in an embodiment of the present invention. Here, an inorganic glass
such as alkali glass, alkali-free glass, high strain point glass,
quartz glass, etc. may be used for the glass substrate. However,
the use of the plastic substrate is not excluded as long as the
above conditions are satisfied.
[0054] In an embodiment, the glass substrate has a refractive index
of about 1.5 to 1.6, because the higher the refractive index, the
smaller the critical angle, thus causing the total reflection even
at a small incident angle, which is thus not desirable.
[0055] The internal extraction layer 200 formed on one side of the
light-transmissive substrate 100 is a kind of scattering layer
provided to prevent light, which is generated by recombination of
electrons and holes in an organic layer 400 of the OLED device 10,
from being lost by the waveguide effect in the light-transmissive
substrate 100, and belongs to the technology for improving the
light extraction efficiency of the OLED device 10 through the
above-described internal light extraction. The internal extraction
layer 200 may also be made of a glass material and may be formed,
for example, by applying a frit paste to one side of the
light-transmissive substrate 100 and firing the resulting
light-transmissive substrate 100 at a high temperature.
[0056] Scattering elements 210 are contained in the internal
extraction layer 200 and are composed of solid particles 211
comprising at least one selected from the group consisting of
SiO.sub.2, TiO.sub.2, and ZrO.sub.2, for example, and pores 212
comprising air or gas bubbles. The light incident into the internal
extraction layer 200, i.e., the light incident directly from the
organic layer 400 as well as the light totally reflected from the
interface between the light-transmissive substrate 100 and air and
fed back to the internal extraction layer 200 are randomly
scattered by the plurality of scattering elements 210 and, during
this process, the light having an incident angle smaller than the
critical angle exits to the outside of the light-transmissive
substrate 100, thus improving the light extraction efficiency.
[0057] In particular, in the layered structure 20 for the OLED
device according to an embodiment of the present invention, the
internal extraction layer 200 is broadly divided into two regions,
in more detail, three regions, which are schematically shown in the
partially enlarged view of FIG. 1.
[0058] The structure of the internal extraction layer 200 may be
broadly divided into a scattering region D, which comprise the
scattering elements 210 composed of the solid particles 211 and the
pores 212, and a free region F where no scattering elements 210 are
present, formed from the surface of the internal extraction layer
200, which is opposite to the interface with the light-transmissive
substrate 100, to a predetermined depth. As mentioned above, the
scattering area D is an area where the light incident into the
internal extraction layer 200 is scattered in various ways, and the
free area F is a kind of buffer zone to prevent the flatness of the
surface of the internal extraction layer 200 from being degraded by
the scattering elements 210.
[0059] A significant feature of an embodiment of the present
invention is that the scattering area D comprises both the solid
particles 211 and the pores 212, whose individual and overall
densities are uniformly distributed over the depth of the internal
extraction layer 200.
[0060] First, the individual density of the solid particles 211 and
the pores 212 will be described below. Based on the interface
between the light-transmissive substrate 100 and the internal
extraction layer 200, the density of the solid particles 211
decreases as it goes away from the interface, while the density of
the pores 212 increases as it goes away from the interface. This
complex distribution of the solid particles 211 and the pores 212
is provided in view of the properties of the different types of
scattering elements 210. The pores 212 are formed by oxygen gas
generated during reduction of Bi.sub.2O.sub.3 and BaO contained in
the frit paste as the material for the internal extraction layer
200 and provide a strong scattering effect. However, the pores 212
tend to be concentrated at the top of the internal extraction layer
200 due to the nature of the gas, which makes it difficult to
obtain a desired distribution of the pores 212. To make up for the
drawback of the pores 212, the solid particles 211 are controlled
to have a higher density distribution as they are closer to the
interface between the light-transmissive substrate 100 and the
internal extraction layer 200. Since it is easier to control the
density distribution of the solid particles 211 than that of the
pores 212, it is possible to artificially control the distribution
of the scattering elements 210 in the above manner.
[0061] The free area F configured to prevent the flatness of the
surface of the internal extraction layer 200 from being degraded by
the scattering elements 210 has a thickness range of about 0.5 to
2.0 .mu.m. Due to the presence of the free area F, the flatness of
the surface of the internal extraction layer 200 satisfies the
surface roughness conditions of .DELTA.Ra<1 nm and
.DELTA.Rpv<15 nm, where .DELTA.Ra represents the center line
average roughness and .DELTA.Rpv represents the maximum height
roughness. If the surface roughness of this level is not satisfied,
sparks are produced along the surface shape of the internal
extraction layer 200 when the light-transmissive electrode layer
300, the organic layer 400, etc. are deposited on the internal
extraction layer 200, thus causing defects such as short-circuit,
etc.
[0062] Next, when the structure of the internal extraction layer
200 is divided into three areas in detail, the scattering area is
divided into two areas such as a first area D1 and a second area D,
which are related to the frit paste for controlling the density of
the solid particles 211 and the pores 212, respectively.
[0063] The first area D1 is an area where more than about 90% of
all solid particles 211 are present and corresponds to one-half or
two-thirds of the entire thickness of the internal extraction layer
200 from the interface. That is, most of the solid particles 211
are present in the first area D1, which is formed by a first frit
paste containing the solid particles 211, which will be described
later.
[0064] The second area D2 refers to the middle area between the
boundary of the first area D1 and the boundary of the free area F,
and the density of the pores 212 in the second area D2 is higher
than that of the pores 212 in the first area D1. That is, in
addition to a small amount of solid particles 211, most of the
pores 212 are contained in the second area D2, which is mainly
formed by a second frit paste containing no solid particles
211.
[0065] Meanwhile, the distribution of all scattering elements 210
is also relevant in addition to the individual density of the solid
particles 211 and the pores 212 which constitute the scattering
elements 210. The density of the scattering elements 210 gradually
decreases as it goes from the interface between the
light-transmissive substrate 100 and the internal extraction layer
200 to the boundary of the free area F. The graph of FIG. 3 shows
the density of the scattering elements 210 normalized with respect
to the thickness of the internal extraction layer 200. Moreover,
FIG. 4 is an SEM image of the internal extraction layer
corresponding to the density distribution of the scattering
elements 210 of FIG. 3, in which the elements that appear darker
are the solid particles 211 and the elements that appear lighter
are the pores 212.
[0066] The overall distribution pattern of the scattering elements
210 is controlled mainly by the density of the solid particles 211.
Moreover, the highest density of the scattering elements 210 in the
area adjacent to the boundary is formed for the purpose of
providing a smaller path of light which is scattered by the
scattering elements 210 after being extracted from the internal
extraction layer 200 to the light-transmissive substrate 100,
reflected from the interface between the light-transmissive
substrate 100 and air, and incident into the internal extraction
layer 200. That is, as shown schematically in FIG. 2, in the
internal extraction layer 200 of structure (b) having a higher
density of scattering elements 210, in particular, solid particles
211 on the interface, compared to structure (a) on the left side,
most light is scattered near the interface between the
light-transmissive substrate 100 and the internal extraction layer
200, not in the deep inner area, and thus it is possible to reduce
the loss of light due to the extension of the optical path as much
as possible, which results in an improvement of the light
extraction efficiency.
[0067] The following table 1 shows the optical efficiency and its
increase rate of the internal extraction layer 200 formed in the
OLED device 10 with respect to the OLED device 10 having no
internal extraction layer 200. In Examples 1 and 2 shown in table
1, TiO.sub.2 and SiO.sub.2 were used as the solid particles 211,
respectively, the same glass material made of a frit comprising
about 55 to 84 wt % Bi.sub.2O.sub.3, about 0 to 20 wt % BaO, about
5 to 20 wt % ZnO, about 1 to 7 wt % Al.sub.2O3, about 5 to 15 wt %
SiO.sub.2, about 5 to 20 wt % B 203, about 0.1 to 3 wt % Na.sub.2O,
and about 0 to 0.3 wt % CeO.sub.2 (which will be described in
detail later) was used as the light-transmissive substrate 100, and
the density (2 wt %) of the solid particles 211 was controlled to
be the same.
TABLE-US-00001 TABLE 1 Measured values of the increase in optical
efficiency due to the formation of the internal extraction layer
Measured values Optical Efficiency (lm/W) Increased rate (%) In the
In the In the glass In the glass Measured Position air substrate
air substrate Reference 37.1 68.4 -- -- Example 1 60.9 90.1 +64 +32
Example 2 63.8 92.8 +72 +36
[0068] Measurement of the optical efficiency was performed on the
light extracted to the outside of the glass substrate (expressed as
"in the air") and the light extracted from the glass substrate
before exiting to the air (expressed as "in the glass substrate")
in accordance with Examples 1 and 2 of the OLED devices 10 each
having the internal extraction layer 200 compared to the Reference
of the OLED device 10 having no internal extraction layer 200. As
the solid particles 211, TiO.sub.2 was used in Example 1 and
SiO.sub.2 was used in Example 2.
[0069] As can be seen from table 1, due to the presence of the
internal extraction layer 200 in the OLED device 10 according to an
embodiment of the present invention, the optical efficiency of the
light extracted to the air was increased more than 60%.
[0070] Moreover, it should be noted that the optical efficiency of
the light extracted to the air was increased about two times
compared to the optical efficiency of the light extracted from the
glass substrate. This fact shows that the layered structure 20 for
the OLED device according to an embodiment of the present invention
make a significant contribution to the external light extraction as
well as the internal light extraction, which results from the fact
the scattering elements 210 contained in the internal extraction
layer 200 have a higher density as they are closer to the interface
with the light-transmissive substrate 100 (i.e., the glass
substrate) as shown in FIGS. 2 and 3.
[0071] Moreover, most of the scattering elements 210, which are
contained in the internal extraction layer 200 to shorten the path
of the light scattered near the interface between the
light-transmissive substrate 100 and the internal extraction layer
200, are the solid particles 211, and thus the density of the solid
particles 211 also affects the optical efficiency. FIG. 5 is a
graph showing the changes in light diffusion and light absorbance
obtained when the density of TiO.sub.2 particles as the solid
particles 211 was changed to 1 wt % and 2 wt %, respectively. As
expected, it can be seen that the increase in the density of the
solid particles 211 increases the amount of light diffused, which
in turn increases the optical path in the internal extraction layer
200 to increase the light absorbance, which is unfavorable for the
light extraction. Thus, it can be seen that there is a density
range of the solid particles 211, which is suitable for the light
extraction, and this density range can be obtained
experimentally.
[0072] Here, the thickness of the internal extraction layer 200
that constitutes the layered structure 20 for the OLED device
according to an embodiment of the present invention will be
described. The thickness of the first area D1 is about 5 to 15
.mu.m, the second area D2 is about 3 to 10 .mu.m, and thus the
entire thickness of the internal extraction layer 200 is about 8 to
25 .mu.m. The reason that the entire thickness of the internal
extraction layer 200 is selected as about 8 to 25 .mu.m is as
follows. As can be seen from the graph of FIG. 5, when the
scattering elements 210 of the same content are present, as the
thickness of the internal extraction layer 200 is smaller, the
light absorbance decreases (as shown in the left graph of FIG. 5)
and the light transmittance increases (as shown in the right graph
of FIG. 5), which is desirable; however, it is necessary to
consider the minimum thickness desired to maintain the flatness of
the surface of the internal extraction layer 200. That is, the
thickness of about 8 .mu.m is the minimum margin for the flatness,
and the thickness of about 25 .mu.m is the upper limit for the
light transmittance.
[0073] Meanwhile, a light-transmissive barrier layer 250 may be
further formed on the internal extraction layer 200 of the layered
structure 20 for the OLED device, the barrier layer 250 comprising
at least one selected from the group consisting of SiO.sub.2 and
Si.sub.3N.sub.4 (i.e., SiO.sub.2, Si.sub.3N.sub.4, and a mixture
thereof) and formed as a monolayer or multi-layer.
[0074] The barrier layer 250 is to protect the internal extraction
layer 200 from an etching solution when the light-transmissive
electrode layer 300, for example, ITO is deposited on the internal
extraction layer 200 and patterned. When the barrier layer 250 is
employed, it is easier to use a wet etching process, which is
relatively inexpensive.
[0075] Moreover, the barrier layer 250 can reduce the light
absorbance to improve the optical properties of the
light-transmissive electrode layer 300. However, the refractive
index of SiO.sub.2 is about 1.45, which is lower about 0.4 times
than that of ITO and thus may cause the total reflection, which is
problematic.
[0076] However, when the barrier layer 250 composed of SiO.sub.2 is
controlled to have a small thickness, the light transmission occurs
even at an incident angle greater than the critical angle due to
optical tunneling, and thus it is possible to minimize the optical
loss caused by the total reflection and compensate for some optical
loss by improving the optical properties of the light-transmissive
electrode layer 300.
[0077] A range of about 5 to 50 nm is established as a desired
thickness of the barrier layer 250 based on the above-described
theoretical background. With the thickness smaller than the lower
limit, it is difficult to expect the effect as an etching barrier,
and when the thickness exceeds the upper limit, the optical loss
caused by the total reflection increases rapidly. In particular,
the thickness of the barrier layer 250 may preferably be in the
range of 10 to 50 nm for the effect as an etching barrier.
[0078] However, the refractive index of Si.sub.3N.sub.4 is about
2.05, which is higher about 0.2 times than that of ITO, and thus
the possibility that the total reflection occurs is relatively low.
Accordingly, the upper limit of the thickness can be increased
slightly when the barrier layer 250 is formed of
Si.sub.3N.sub.4.
TABLE-US-00002 TABLE 2 Chemical resistance test of the barrier
layer with respect to chemical etching Immer- sion time Amount of
removal (Depth of etching) (min) Layer With SiO.sub.2 Barrier layer
With SiO.sub.2 Barrier layer 5 ITO 70 nm 70 nm IEL x x 10 ITO 150
nm(Residues observed) 150 nm(Residues observed) IEL x IEL exposed
15 ITO Completely removed Completely removed IEL x Completely
removed 20 ITO Completely removed -- IEL x --
[0079] The above table 2 shows the results of etching obtained by
immersing a layered structure, in which an SiO.sub.2 barrier layer
of 10 nm in thickness is formed between an internal extraction
layer of about 20 .mu.m in thickness formed on a soda lime glass
substrate of about 0.7 nm in thickness and an ITO layer of about
140 nm in thickness, and a layered structure, in which no SiO.sub.2
barrier layer is formed, in a dilute hydrochloric acid solution (4
wt % HCl+96 wt % distilled water at 25.degree. C.), respectively,
and observing the degree of etching as the immersion time goes.
[0080] As shown in table 2, about half the thickness of the ITO
layer was etched at an immersion time of about 1 minute, and the
internal extraction layer was completely removed after the lapse of
the immersion time of 15 minutes in the layered structure without
the SiO.sub.2 barrier layer. Compared to this, in the layered
structure with the SiO.sub.2 barrier layer, the internal extraction
layer was not exposed even after the lapse of the immersion time of
20 minutes, from which it could be seen that the SiO.sub.2 barrier
layer could effectively protect the internal extraction layer from
the chemical etching.
[0081] Moreover, in order to examine the improvement of the optical
properties of the light-transmissive electrode layer 300, the light
transmittance and light absorbance of a layered structure, in which
an SiO.sub.2 barrier layer of about 10 nm in thickness is formed
between an ITO layer of about 140 nm in thickness and a soda lime
glass substrate of about 0.7 nm in thickness, and a layered
structure, in which no SiO.sub.2 barrier layer is formed, were
measured. As a result, while the light transmittance and light
absorbance of the layered structure without the SiO.sub.2 barrier
layer were 85.9% and 2.6%, the light transmittance was increased to
87.1% and the light absorbance was reduced to 2.3% due to the
SiO.sub.2 barrier layer interposed therebetween. That is, the
optical properties of the ITO layer were significantly improved
owing to introduction of the SiO.sub.2 barrier layer.
[0082] Accordingly, the barrier layer 250 of about 5 to 50 nm in
thickness formed on the internal extraction layer 200 can protect
the internal extraction layer 200 from the chemical etching and
further increase the overall light extraction effect of the layered
structure 20 for the OLED device.
[0083] [Composition of Glass Material or Frit]
[0084] A relevant element of the layered structure 20 for the OLED
device, which is configured to improve the efficiency of extracting
light generated in the OLED device 10 to the outside, is the
internal extraction layer 200. In particular, in the present
embodiment, the internal extraction layer 200 is made of a glass
material so as to control the density and distribution of the
scattering elements 210 composed of the solid particles 211 and the
pores 212 during the manufacturing process.
[0085] In particular, in the present embodiment, the internal
extraction layer 200 is made of a glass material using a glass
frit, and it is possible to obtain appropriate optical properties
by controlling the composition of the frit. In the following
description of the embodiments of the present invention, the glass
frit will be simply referred to as the "frit".
[0086] The frit is especially well adapted as a raw material to the
formation of the glass material comprised in the internal
extraction layer 200 of an embodiment of the present invention.
Thanks to its high refractive index, the frit can also be
beneficially used as a raw material in the formation of any glass
material comprised in an internal extraction layer for any OLED
device. As a consequence, the desired features of the frit
disclosed in an embodiment of the present invention can be
associated with any internal extraction layer comprising a glass
material. When using a glass frit to obtain the glass material, the
composition of the frit is the same as the composition of the glass
material. Consequently, the desired compositional features of the
frit given here below also correspond to desired compositional
features of the glass material comprised in the internal extraction
layer.
[0087] In an embodiment, the internal extraction layer comprises an
area containing (in addition to the glass material) scattering
elements, especially solid particles and/or pores, and a free area
where no scattering elements are present, composed of the glass
material. The free area forms the surface of the internal
extraction layer which is opposite to the interface between the
internal extraction layer and the light-transmissive substrate. In
an embodiment, the thickness of the free area is of at least 1
.mu.m, or even 3 .mu.m or else 5 .mu.m. It is preferably of at most
20 or even 15 .mu.m.
[0088] The main component of the frit as a raw material for the
formation of the internal extraction layer 200 of an embodiment of
the present invention is Bi.sub.2O.sub.3 (or
Bi.sub.2O.sub.3+BaO)--ZnO--B.sub.2O.sub.3--Al.sub.2O.sub.3--SiO.sub.2--Na-
.sub.2O, in which Bi.sub.2O.sub.3 (or Bi.sub.2O.sub.3+BaO) is the
major component, and in particular, the frit should not contain any
transition metals having a high light absorbance such as Fe, Cu,
Mn, Co, V, Cr, Ni, etc., except for unavoidable traces. Moreover,
the frit should not contain any of TiO.sub.2 or ZrO.sub.2, except
for unavoidable traces.
[0089] The composition of the frit for the internal extraction
layer 200 should meet the conditions such as a refractive index of
about 1.7 to 2, for example at least 1.8 or even 1.9 in an
embodiment, a firing temperature of 500 to 570.degree. C., and a
thermal expansion coefficient of 70 to 90.times.10.sup.-7/.degree.
C. The range of the refractive index corresponds to the refractive
indices of the light-transmissive electrode layer 300 and the
organic layer 400 and is established to minimize the effect that
the difference in the refractive index has on the light extraction
efficiency. Moreover, the ranges of the firing temperature and the
thermal expansion coefficient are set to prevent the glass
substrate corresponding to the light-transmissive substrate, which
is the basis for the formation of the internal extraction layer
200, from being deformed or deteriorated during the firing process
of the frit.
[0090] The composition of the frit (or of the glass material)
comprises about 55 to 84 wt % Bi.sub.2O.sub.3, about 0 to 20 wt %
BaO, about 5 to 20 wt % ZnO, about 1 to 7 wt % Al.sub.2O.sub.3,
about 5 to 15 wt % SiO.sub.2, and about 5 to 20 wt %
B.sub.2O.sub.3. The composition may optionally further comprise
about 0.05 to 3 wt % Na.sub.2O and/or about 0 to 0.3 wt %
CeO.sub.2.
[0091] The composition of the frit (or of the glass material) may
consist essentially of (or consist of) about 55 to 84 wt %
Bi.sub.2O.sub.3, even 65 to 80 wt % Bi.sub.2O.sub.3, about 0 to 20
wt % BaO, about 5 to 20 wt % ZnO, about 1 to 7 wt %
Al.sub.2O.sub.3, about 5 to 15 wt % SiO.sub.2, about 5 to 20 wt %
B.sub.2O.sub.3, about 0.05 to 3 wt % Na.sub.2O, and about 0 to 0.3
wt % CeO.sub.2.
[0092] Moreover, the composition of the frit (or of the glass
material) may consist essentially of (or consist of) about 65 to 80
wt % Bi.sub.2O.sub.3 and preferably about 0 to 5 wt % BaO.
[0093] Bi.sub.2O.sub.3 is a component for reducing the softening
point of the frit and increasing the refractive index, and BaO is
an auxiliary component that may be contained together with
Bi.sub.2O.sub.3. Here, the content of Bi.sub.2O.sub.3 should be
controlled to about 55 to 84 wt %, especially 55 to 83.95 wt %, and
the content of BaO should be controlled to about 0 to 20 wt %. In
an embodiment, the content of Bi.sub.2O.sub.3 is at least about 60
wt % or 62 wt % or even 65 wt %. It may especially be about 60 to
80 wt % or even 62 to 78 wt % or 65 to 75 wt %. In an embodiment,
the content of BaO may be about 0 to 10 wt %, especially 0 to 5 wt
%, even 0 to 2 wt %. In some embodiments, the content of BaO can be
zero. If the content of Bi.sub.2O.sub.3 is less than the lower
limit, the refractive index decreases, which makes it difficult to
satisfy the range of the refractive index of about 1.7 to 2.0, and
the firing temperature also increases, which makes it difficult to
apply an alkali glass to the substrate. If the content of
Bi.sub.2O.sub.3 exceeds the upper limit, light in the blue range is
strongly absorbed, and the thermal stability decreases during
firing, thus deteriorating the surface of the light extraction
layer. BaO has a slight effect of reducing the softening point of
the frit and thus can substitute for some Bi.sub.2O.sub.3. However,
if the content of BaO exceeds the upper limit, the firing
temperature may exceed a permissible range, which is
problematic.
[0094] ZnO is a component for reducing the softening point of the
frit. The content of ZnO should be controlled to about 5 to 20 wt
%, especially up to 15 wt % or 13 wt %, even 12 wt % or 10 wt %.
The content of ZnO is about 8 to 15 wt % or 9 to 13 wt %. If the
content of ZnO is less than the lower limit, the firing temperature
of the frit increases, whereas, if it exceeds the upper limit, the
phase of the frit becomes unstable, the chemical resistance
decreases, and light in the green range is strongly absorbed, which
is thus not desirable.
[0095] B.sub.2O.sub.3 is a component for reducing the thermal
expansion coefficient and stabilizing the phase of the frit. The
content of B.sub.2O.sub.3 should be controlled to about 5 to 20 wt
%, especially up to 15 wt % or 12 wt %. The content of
B.sub.2O.sub.3 is about 6 to 15 wt % or 7 to 12 wt %. If the
content of B.sub.2O.sub.3 is less than the lower limit, the phase
of the frit becomes unstable, whereas, if it exceeds the upper
limit, the water resistance of the light extraction layer
decreases, which is thus not desirable.
[0096] Al.sub.2O.sub.3 is a component for stabilizing the phase of
the frit. The content of Al.sub.2O.sub.3 should be controlled to
about 1 to 7 wt %, for example at least 1.5 or 2 wt % in an
embodiment. In an embodiment, it is about 1.5 to 5 wt %, especially
2 to 4 wt %. If the content of Al.sub.2O.sub.3 is less than the
lower limit, the phase of the frit becomes unstable and the
chemical resistance decreases, whereas, if it exceeds the upper
limit, the refractive index of the frit decreases and the firing
temperature increases, which is thus not desirable.
[0097] SiO.sub.2 is a component for stabilizing the phase of the
frit. The content of SiO.sub.2 should be controlled to about 5 to
15 wt %, for example up to 14 wt % in an embodiment or 12 wt %,
especially 6 to 14 wt % or 7 to 12 wt %. If the content of
SiO.sub.2 is less than the lower limit, the phase of the frit
becomes unstable, whereas, if it exceeds the upper limit, the
refractive index of the frit decreases and the firing temperature
increases, which is thus not desirable.
[0098] Na.sub.2O is an optional component for reducing the
softening point of the frit. The content of Na.sub.2O should be
controlled to about 0.05 to 3 wt %, especially at least 0.1 wt %.
In an embodiment, it is about 0.1 to 2 wt % or 0.5 to 1.5 wt %. If
the content of Na.sub.2O is less than the lower limit, the firing
temperature of the frit increases, whereas, if it exceeds the upper
limit, the chemical resistance decreases, which is thus not
desirable.
[0099] In an embodiment, the TiO.sub.2 content is up to about 1 wt
%, or even 0.5 wt %, or 0.1 wt %. In an embodiment, the ZrO.sub.2
content is also up to about 1 wt %, or even 0.5 wt %, or 0.1 wt %.
In an embodiment, the frit does even not contain any of TiO.sub.2
or ZrO.sub.2, except for unavoidable traces (for example lower than
0.05 wt %), since the oxides have proven to promote the
crystallization of the glass material.
[0100] In an embodiment, the frit does not contain any of Nb, P,
Pb, Ta, Y, Sn, Gd, La, V, or Mo.
[0101] Here, the frit according to the embodiment of the present
invention should not contain any transition metals chosen from Fe,
V, Cr, Mn, Ni, Co, Cu, Pd, Ag, Au, Pt, Cd (however, ZnO, an
essential component for reducing the softening point of the frit
should not be included in the transition metals). However, the frit
may optionally contain a trace of Ce. The transition metal serves
to inhibit the reduction of Bi.sub.2O.sub.3, etc. at a high
temperature, thus preventing yellowing of films. Accordingly, a
transition metal is generally added to the frit containing
Bi.sub.2O.sub.3. However, these transition metals exhibit strong
absorption properties in a specific wavelength region. In
particular, when the optical path is increased due to the
scattering in the internal extraction layer 200, the light
absorption by the transition metal may cause a significant optical
loss, and thus it is necessary to eliminate the addition of the
transition metal to the first. However, the light absorption
properties of an oxide of Ce, a lanthanide, is limited to a dark
blue region, and thus the optical effect on an OLED lighting device
having a fluorescent blue light source is insignificant. Moreover,
the oxide of Ce facilitates the complete combustion of organic
components during burnout process in the manufacturing of the light
extraction layer, and thus CeO.sub.2 may be added in an amount less
than 0.3 wt %, for example 0.1 wt % in an embodiment. The CeO.sub.2
content can be zero in some embodiments.
[0102] FIG. 7 is a graph comparing the light absorbance of Example
1 being a frit containing 70 wt % Bi.sub.2O.sub.3 (0 wt % BaO), 10
wt % ZnO, Al.sub.2O.sub.3 3 wt %, SiO.sub.2 7 wt %, 9 wt %
B.sub.2O.sub.3, and 1 wt % Na.sub.20, Example 2 in which 0.1 wt %
CeO.sub.2 is added to the above frit, and Comparative Example 1 in
which 0.1 wt % CuO+MnO+CoO is added to the above frit of Example 1.
As shown in FIG. 7, it can be seen that the light absorbance is
increased when the transition metals are added to the frit.
Comparative Example 1, where the oxides of Cu, Mn, and Co are
added, shows a surprisingly high increase in light absorbance over
a wide wavelength range. Compared to this, Example 2, where 0.1 wt
% CeO.sub.2 is added, shows good results of a slight increase in
light absorbance in a dark blue region where the wavelengths are
below about 400 nm. Example 1 is therefore preferred.
[0103] When comparing the results of FIG. 7 to those of FIG. 5, the
optical path is increased by the increase in light scattering due
to the addition of the solid particles 211, and when the transition
metals such as Fe, Mn, Cu, Mo, etc. are added to the frit, the
light absorption effect of the transition metals according to the
increase in the optical path is further increased, which will
clearly have a significant adverse effect on the light
extraction.
[0104] [Method for Manufacturing Layered Structure for OLED
Device]
[0105] A method for manufacturing a layered structure 20 for an
OLED device in accordance with an embodiment of the present
invention will be described below.
[0106] The method for manufacturing the layered structure 20 for
the OLED device according to an embodiment of the present invention
comprises a process of preparing a light-transmissive substrate
100, a process of coating a first frit paste comprising a frit and
solid particles 211 on the light-transmissive substrate 100 and
drying the resulting substrate 100, a process of coating a second
frit paste comprising the frit on the coating layer of the first
frit paste, a process of smoothing the surface of the coating layer
of the second frit paste by keeping the resulting substrate 100, on
which the first and second frit pastes are coated, for a
predetermined time and then drying the resulting substrate 100, and
a process of heating the light-transmissive substrate 100 on which
the first and second frit pastes are coated.
[0107] The process of preparing the light-transmissive substrate
100 is to prepare a substrate, which is the basis for the formation
of an internal extraction layer 200, the substrate being formed of
a material having a high transmittance to visible light as
mentioned above and, in particular, corresponding to a glass
substrate. The basic properties such as the firing temperature,
refractive index, etc., which are needed for the light-transmissive
substrate 100, are the same as previously described.
[0108] The process of coating the first frit paste comprising the
frit and the solid particles 211 on the light-transmissive
substrate 100 and drying the resulting substrate 100 corresponds to
a process for forming a first area D1 comprising most of the solid
particles 211 in the internal extraction layer 200.
[0109] The first frit paste comprises 70 to 80 wt % frit and 0.5 to
6 wt % solid particles 211, and the remainder thereof comprises a
binder and a solvent. The components of the frit are the same as
previously described, and the solid particles 211 comprise at least
one selected from the group consisting of SiO.sub.2, TiO.sub.2, and
ZrO.sub.2.
[0110] In the present embodiment, ethyl cellulose is used as the
binder, pine oil and butyl cellosolve acetate (BCA) are used as the
solvent, and the frit, the solid particles 211, the binder, and the
solvent are uniformly mixed by stirring.
[0111] The first frit paste having the above-described composition
is coated on the light-transmissive substrate 100 by slit coating
or screen printing and dried in a convection oven at about
150.degree. C. for about 20 minutes to significantly reduce the
fluidity, thus facilitating the process of coating the second frit
paste, which will be described in more detail below.
[0112] After coating and drying the first frit paste, the process
of coating the second frit paste on the coating layer of the first
frit paste continues.
[0113] The second frit paste is prepared by mixing a frit, a
binder, and a solvent which are the same as those used in the first
frit paste. The difference of the second frit paste from the first
frit paste is that the second frit pate contains no solid particles
211. The second frit paste comprises 66 to 76 wt % frit, and the
remainder thereof comprises a binder and a solvent. Moreover, the
second frit paste is coated by the same method as the first frit
paste.
[0114] As can be expected from the fact that the second frit paste
contains no solid particles 211, this process corresponds to a
process for forming a second area D2 having a high density of pores
212 in the internal extraction layer 200 and a free area F where no
scattering elements 210 are present from the surface of the
internal extraction layer 200 to a predetermined depth.
[0115] When the process of coating the first and second frit pastes
is completed, the resulting light-transmissive substrate 100 is
left for a predetermined time, for example, about 30 minutes to 2
hours such that the surface of the coating layer of the second frit
paste is smoothed by gravity.
[0116] Meanwhile, during the above process, it is possible to
facilitate the smoothing of the surface of the second frit paste
coating layer by irradiating ultrasonic waves to the coating layers
of the first and second frit pastes. In particular, when the
surface of the second frit paste coating layer smoothed by the
ultrasonic irradiation, it is possible to obtain an effect that a
diffusion area of the solid particles 211 between the coating
layers of the first and second frit pastes is activated. When the
diffusion area of the solid particles 211 is activated, the
non-uniform density distribution of the solid particles 211, formed
between the first frit paste and the second frit paste, decreases,
thus compensating for the sudden change in physical properties such
as refractive index, hardness, etc.
[0117] When the coating layer of the second frit paste is smoothed,
the resulting light-transmissive substrate 100 is also dried in a
convection oven at about 150.degree. C. for about 20 minutes.
[0118] The light-transmissive substrate 100 on which the first and
second frit pastes are coated by the above processes is fired in a
convection oven at a high temperature to form the internal
extraction layer 200.
[0119] The light-transmissive substrate 100 coated with the frit
pastes is first heated in a convection oven at about 350 to
430.degree. C. for about 20 minutes such that the binder is burned
out and then reheated at a higher temperature of 520 to 570.degree.
C. such that the frit pastes are fired, thus forming the internal
extraction layer 200.
[0120] During the above firing process of the frit pastes, oxygen
gas is dissociated from the oxide contained in the frit, in
particular, from Bi.sub.2O.sub.3 contained in a large amount, thus
forming pores 212 in the internal extraction layer 200. Here, the
dissociated oxygen gas rises up by buoyancy, and thus the density
of the pores 212 in an upper area (i.e., the second area) in the
internal extraction layer 200 increases higher than a lower area
(i.e., the first area).
[0121] The thickness of the free area F, which is the uppermost
area of the internal extraction layer 200 where no scattering
elements, in particular, pores 212 are present, is controlled by
the firing temperature, time, etc. Moreover, the thickness of the
free area F depends on the size of the frit. That is, the smaller
the frit, the larger the surface area, and thus the thickness of
the free area F is reduced even under the same firing
conditions.
[0122] Meanwhile, it is possible to protect the internal extraction
layer 200 from the chemical etching and increase the light
extraction effect by adding a process of depositing an SiO.sub.2 or
Si.sub.3N.sub.4 barrier layer of 5 to 50 nm in thickness on the
internal extraction layer 200 prepared by the process of coating
and firing the first and second frit pastes.
[0123] As such, the method for manufacturing the layered structure
20 for the OLED device according to an embodiment of the present
invention has significant benefits in that it is possible to easily
control the density of the scattering elements 210 composed of the
solid particles 211 and the pores 212 by separately using two types
of frit pastes, such as the first frit pate containing the solid
particles 211 and the second frit pate containing no solid
particles 211, and by adding a large amount of Bi.sub.2O.sub.3 or
Bi.sub.2O.sub.3+BaO, which generated oxygen gas during the firing
process, to the frit.
[0124] [OLED Device]
[0125] An OLED device 10 provided with the layered structure 20 for
the OLED device according to an embodiment of the present invention
is shown in FIG. 1.
[0126] The layered structure 20 for the OLED device comprises the
above-described internal extraction layer 200 interposed between
the light-transmissive substrate 100 and the light-transmissive
electrode layer 300 of the existing OLED device. The layered
structure 20 can be directly applied to the conventional OLED
device, and thus the OLED device will be described in brief.
[0127] The OLED device 10 of an embodiment of the present invention
comprises the light-transmissive substrate 100 on which the
above-described internal extraction layer 200 is formed, the
light-transmissive electrode layer 300 formed on the internal
extraction layer 200, the organic layer 400 formed on the
light-transmissive electrode layer 300, and a reflective electrode
500 formed on the organic layer 400. It will be appreciated that
the above-described barrier layer 250 may be further formed on the
internal extraction layer 200.
[0128] The light-transmissive electrode layer (anode) 300 has a
light transmittance of about 80% or higher so as to extract light
generated in the organic layer 400 to the outside. Moreover, the
light-transmissive electrode layer 300 has a high work function so
as to inject a great amount of holes. In detail, various materials
such as indium tin oxide (ITO), SnO.sub.2, zinc oxide (ZnO), indium
zinc oxide (IZO), ZnO--Al.sub.2O.sub.3 (AZO), ZnO--Ga.sub.2O.sub.3
(GZO), etc. are used.
[0129] The light-transmissive electrode layer 300 may be formed by
forming an ITO layer on the internal extraction layer 200 and
etching the ITO layer. The ITO layer may be formed by sputtering or
deposition, and an ITO pattern is formed by photolithography and
etching. This ITO pattern is transferred into the
light-transmissive electrode layer (anode) 300.
[0130] The organic layer 400 is composed of a hole injection layer
410, a hole transporting layer 420, an emission layer 430, an
electron transporting layer 440, and an electron injection layer
450. The refractive index of the organic layer 400 is about 1.7 to
1.8.
[0131] The organic layer 400 may be formed by both coating and
deposition. For example, when one or more layers of the organic
layer 400 are formed by the coating, the other layers are formed by
the deposition. When a layer is formed by the coating and then
another layer is formed thereon by the deposition, the coated layer
is dried and cured by concentration before forming the organic
layer by the deposition.
[0132] The hole injection layer 410 has a small difference in
ionization potential so as to reduce the hole injection barrier
from the anode. Improvement of hole injection efficiency from the
electrode interface in the hole injection layer 410 reduces the
driving voltage of the device and further increases the hole
injection efficiency. In high molecular materials, polyethylene
dioxythiophene doped with polystyrene sulfonic acid (PSS)
(PEDOT:PSS) is widely used, and in low molecular materials,
phthalocyanine type copper phthalocyanine (CuPc) is widely
used.
[0133] The hole transporting layer 420 serves to transport holes
injected from the hole injection layer 410 to the emission layer
430. The hole transporting layer 420 has appropriate ionization
potential and hole mobility. For the hole transporting layer 420,
triphenylamine derivatives,
N,N'-bis(1-naphthyl)-N,N-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD),
N,N'-diphenyl-N,N'-bis[N-phenyl-N-(2-naphthyl)-4'-amino-biphenyl4--
yl]-1,1'-biphenyl-4,4'-diamine (NPTE),
1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (HTM2),
N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine
(TPD), etc. are used.
[0134] The emission layer 430 provides a space where the injected
electrons and holes recombine and is formed of a material having
high light-emitting efficiency. A light-emitting host material used
in the emission layer and a doping material of a light-emitting dye
function as a recombination center of holes and electrons injected
from the anode and cathode. The doping of the light-emitting dye to
the host material in the emission layer 430 obtains a high
light-emitting efficiency and further converts the emission
wavelength. The light-emitting material as the organic material
includes low molecular weight materials and high molecular weight
materials and are classified into fluorescent materials and
phosphorescent materials based on the light-emitting mechanism.
Examples of materials for the emission layer 430 may include metal
complexes of quinoline derivatives, such as
tris(8-quinolinolato)aluminum complexes (Alq3),
bis(8-hydroxy)quinaldine aluminum phenoxide (Alq'2OPh),
bis(8-hydroxy)quinaldine aluminum-2,5-dimethylphenoxide (BAlq),
mono(2,2,6,6-tetramethyl-3,5-heptanedionate)lithium complex (Liq),
mono(8-quinolinolato)sodium complex (Naq),
mono(2,2,6,6-tetramethyl-3,5-heptanedionate)lithium complex,
mono(2,2,6,6-tetramethyl-3,5-heptanedionate)sodium complex, and
bis(8-quinolinolato)calcium complex (Caq2); tetraphenylbutadiene,
phenylquinacridone (QD), anthracene, perylene, and fluorescent
materials such as coronene. As the host material, quinolinolate
complexes may be used, and for example 8-quinolinol and aluminum
complexes having its derivative as a ligand may be used.
[0135] The electron transporting layer 440 serves to transport
electrons injected from the electrode. For the electron
transporting layer 440, quinolinol aluminum complexes (Alq3),
oxadiazole derivatives (e.g., 2,5-bis(1-naphthyl)-1,3,4-oxadiazole
(BND) and 2-(4-t-butylphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole
(PBD)), triazole derivatives, bathophenanthroline derivatives,
silole derivatives, etc. are used.
[0136] The electron injection layer 450 increases the injection
efficiency of electrons. In the electron injection layer 450, a
layer is formed of an alkali metal such as lithium (Li), cesium
(Cs), etc. on a cathode interface.
[0137] For the reflective electrode (cathode) 500, a metal having a
small work function or its alloy is used. Examples of materials for
the cathode may include alkali metals, alkaline earth metals, and
metals of group III of the periodic table. Of those, in an
embodiment, aluminum (Al), magnesium (Mg), silver (Ag) or alloys
thereof are used as inexpensive materials with good chemical
stability. Moreover, in a polymer system, a laminate of calcium
(Ca) or barium (Ba) and aluminum (Al), etc. may be used.
[0138] As described above, the layered structure for the OLED
device according to an embodiment of the present invention can
effectively extract light trapped in the optical waveguide and the
glass substrate in the OLED device to significantly improve the
external light efficiency of the OLED device, thus improving the
efficiency, brightness, and lifespan of the OLED device.
[0139] Moreover, the method for manufacturing the layered structure
for the OLED device which can manufacture the layered structure for
the OLED device in mass production with a simple process and low
cost.
[0140] While the invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the invention as defined by the
following claims.
[0141] It is to be understood that the present invention
contemplates that, to the extent possible, one or more features of
any embodiment can be combined with one or more features of any
other embodiment.
INDUSTRIAL APPLICABILITY
[0142] The present invention is applicable to a layered structure
for an organic light-emitting diode (OLED) device.
* * * * *