U.S. patent application number 11/011588 was filed with the patent office on 2005-05-05 for light-emitting polymer composition and organic el display device using the same.
Invention is credited to Kim, Mu-Hyun, Kwon, Jang-Hyuk, Suh, Min-Chul.
Application Number | 20050095357 11/011588 |
Document ID | / |
Family ID | 36787494 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050095357 |
Kind Code |
A1 |
Kim, Mu-Hyun ; et
al. |
May 5, 2005 |
Light-emitting polymer composition and organic EL display device
using the same
Abstract
A light-emitting polymer composition for a light-emitting layer
in an organic EL display device includes at least first and second
light-emitting polymers having different interfacial
characteristics which lower a cohesion between elements of the
first and second light-emitting polymers.
Inventors: |
Kim, Mu-Hyun; (Suwon-city,
KR) ; Kwon, Jang-Hyuk; (Suwon-city, KR) ; Suh,
Min-Chul; (Sungnam-city, KR) |
Correspondence
Address: |
MCGUIREWOODS, LLP
1750 TYSONS BLVD
SUITE 1800
MCLEAN
VA
22102
US
|
Family ID: |
36787494 |
Appl. No.: |
11/011588 |
Filed: |
December 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11011588 |
Dec 15, 2004 |
|
|
|
10172001 |
Jun 17, 2002 |
|
|
|
Current U.S.
Class: |
427/66 ;
252/301.35; 313/504; 313/506; 428/690; 428/917 |
Current CPC
Class: |
H01L 51/0013 20130101;
H01L 51/0037 20130101; C09K 11/06 20130101; C09K 2211/1408
20130101; C09K 2211/14 20130101; H01L 51/0039 20130101; H05B 33/14
20130101; H01L 51/5012 20130101; C09K 2211/1441 20130101; H01L
51/0038 20130101; Y10S 428/917 20130101; H01L 51/56 20130101 |
Class at
Publication: |
427/066 ;
252/301.35; 428/690; 428/917; 313/504; 313/506 |
International
Class: |
H05B 033/10; H05B
033/14; C09K 011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2001 |
KR |
2001-66880 |
Claims
1-22. (canceled)
23. A method for fabricating an organic EL display device,
comprising: providing a substrate; forming an anode on the
substrate; forming a hole transporting layer over the anode;
forming a light-emitting layer comprising a light-emitting polymer
composition including first and second light-emitting polymers
having elements by Laser Induced Thermal Imaging method (LITI); and
forming a cathode over the light-emitting layer, wherein the first
and second light-emitting polymers have different interfacial
characteristics which lower a cohesion between the elements of the
first and second light-emitting polymers, and wherein a
corresponding wavelength spectrum of the first light-emitting
polymer overlaps a corresponding wavelength spectrum of the second
light-emitting polymer, so as to allow an energy transfer in the
light-emitting polymer composition.
24. The method of claim 23, wherein the light-emitting polymer
composition further comprises an additive which improves adhesion
of the light-emitting composition to a substrate and lowers the
cohesion between the elements of the first and second
light-emitting polymers.
25. The method of claim 24, wherein the additive is one of an
optically inert polymer, an optically inert low-molecular material,
a polymer having a carrier transporting ability, and a
low-molecular material having a carrier transporting ability.
26. The method of claim 24, wherein the optically inert polymer is
selected from a group consisting of a polystyrene, a
poly(styrene-butadione) copolymer, a polymethylmethacrylate, a
polyalphamethylstyrene, a styrene-methylmethacrylate copolymer, a
polybutadiene, a polycarbonate, a polyethyleneterephthalate, a
polyestersulfonate, a polysulfonate, a polyarylate, a
fluorinepolyimide, a transparent fluoric resin, and a transparent
acrylic resin.
27. The method of claim 24, wherein the polymer having the carrier
transporting ability is selected from a group consisting of an
arylamine, a perylrene group and a pyrrole-based polymer.
28. The method of claim 24, wherein the low-molecular material
having the carrier transporting ability is one of an arylamine, a
hydrazone, a carbazole, a stylbene, a staburst group, and an
oxadiazole.
29. The method of claim 24, wherein: the first light-emitting
polymer has a mixing mass ratio in a range between 0.3 and 0.8, and
the second light-emitting polymer has a mixing mass ratio in a
range between 0.2 and 0.7.
30. The method of claim 23, wherein the additive has a mixing mass
ratio of less than 0.7.
31. A method for fabricating an organic EL display device,
comprising: providing a substrate; forming an anode on the
substrate; forming a hole transporting layer over the anode;
forming a light-emitting layer by Laser Induced Thermal Imaging
(LITI) method; and forming a cathode over the light-emitting layer,
wherein the light-emitting layer comprises a light-emitting polymer
composition including: a light-emitting polymer having elements;
and an additive which improves adhesion of the light-emitting
composition to a substrate and lowers a cohesion between the
elements of the light-emitting polymer, wherein the additive is one
of an optically inert polymer, an optically inert low-molecular
material, a polymer having a carrier transporting ability, and a
low-molecular material having a carrier transporting ability.
32. The method of claim 31, wherein the optically inert polymer is
selected from a group consisting of a polystyrene, a
poly(styrene-butadione) copolymer, a polymethylmethacrylate, a
polyalphamethylstyrene, a styrene-methylmethacrylate copolymer, a
polybutadiene, a polycarbonate, a polyethyleneterephthalate, a
polyestersulfonate, a polysulfonate, a polyarylate, a
fluorinepolyimide, a transparent fluoric resin, and a transparent
acrylic resin.
33. The method of claim 31, wherein the polymer having the carrier
transporting ability is selected from a group consisting of an
arylamine, a perylrene group and a pyrrole-based polymer.
34. The method of claim 31, wherein the low-molecular material
having the carrier transporting ability is one of an arylamine, a
hydrazone, a carbazole, a stylbene, a staburst group, and an
oxadiazole.
35. The method of claim 31, wherein the additive has a mixing mass
ratio in a range between 0.375 and 0.667.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 2001-66880 filed on Oct. 29, 2001, in the Korean
Industrial Property Office, the disclosure of which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a light-emitting polymer
composition and an organic electroluminescent (EL) display device
using the same.
[0004] 2. Description of the Related Art
[0005] An organic EL display device includes an anode, a hole
injection layer, a hole transportation layer, a light-emitting
layer, an electron transporting layer, an electron injection layer,
and a cathode, which are sequentially stacked on a substrate.
[0006] The above-described layers of the organic EL display device
are made of a low-molecular organic material or a high-molecular
organic material (i.e., a polymer). The layers of the organic EL
display device comprising a low-molecular organic material are
formed by, for example, a vacuum deposition technique, while the
layers of the organic EL display comprising a high-molecular
organic material are formed by, for example, a spin coating
technique.
[0007] In general, an organic EL display device having a
light-emitting layer of one color made of a high-molecular organic
material is easy to manufacture and is lower in driving voltage
than that of a low-molecular organic material. However, an organic
EL display device having a light-emitting layer of one color made
of the high-molecular organic material is lower in light-emitting
efficiency and shorter in life span than that of the low-molecular
organic material.
[0008] On the other hand, in forming a light-emitting layer of a
full color, an organic EL display device having the high-molecular
organic material has difficulties in patterning red, green and blue
light-emitting layers using an ink jet technique or a laser
transfer technique, leading to a low light-emitting efficiency and
a short life span.
[0009] Conventional light-emitting polymer materials are patterned
by the ink-jet technique or the laser transfer technique. However,
in most cases, light-emitting polymer materials are not transferred
using the laser transfer technique, which is a kind of a thermal
transfer technique.
[0010] The thermal transfer technique requires at least a light
source, a transfer film, and a substrate. Light emitted from the
light source is absorbed into a light absorbing layer of the
transfer film and then converted into heat energy. An image forming
material of the transfer film is transferred to the substrate by
the heat energy, thereby forming a desired image on the substrate.
The thermal transfer technique is also used to form a color filter
of a liquid crystal display (LCD) device.
[0011] FIG. 1 shows a schematic view illustrating a laser transfer
operation for patterning a light-emitting layer of a conventional
organic EL display device.
[0012] Referring to FIG. 1, an organic film S.sub.2 is formed on a
substrate S.sub.1. A laser beam is irradiated to the substrate
S.sub.1 to separate the organic film S.sub.2 from the substrate
S.sub.1 and transfer it to a substrate S.sub.3.
[0013] Here, parameters that determine a transfer characteristic
include an adhesion W.sub.12 between the substrate S.sub.1 and the
organic film S.sub.2, a cohesion W.sub.22 between elements of the
organic films S.sub.2, and an adhesion W.sub.23 between the organic
film S.sub.2 and the substrate S.sub.3.
[0014] The adhesion W.sub.12 and W.sub.23 and the cohesion W.sub.22
can be described by a surface tension and an interfacial tension as
follows:
W.sub.12=.gamma..sub.1+.gamma..sub.2-.gamma..sub.12;
W.sub.22=2.gamma..sub.22; and
W.sub.23=.gamma..sub.2+.gamma..sub.3-.gamma..sub.23,
[0015] where .gamma..sub.1 denotes a surface tension of the
substrate S.sub.1, .gamma..sub.2 denotes a surface tension of the
organic film S.sub.2, .gamma..sub.3 denotes a surface tension of
the substrate S.sub.3, .gamma..sub.12 denotes an interfacial
tension between the substrate S.sub.1 and the substrate S.sub.2,
Y.sub.22 denotes an interfacial tension between the elements of the
organic film S.sub.2 and Y.sub.23 denotes an interfacial tension
between the substrate S.sub.2 and the substrate S.sub.3.
[0016] As the cohesion between the elements of the organic film
S.sub.2 becomes smaller than the adhesion between the respective
substrates S.sub.1 and S.sub.3 and the organic film S.sub.2, the
laser transfer characteristic improves.
[0017] However, a lighting-emitting layer of the conventional
organic EL display device is usually made of a polymer film which
has a high molecular weight. Therefore, the cohesion between
elements of the polymer film is relatively large. Accordingly, the
polymer film shows a bad transfer characteristic in the
conventional organic EL display device.
[0018] That is, the conventional art does not disclose a technique
that can improve a transfer characteristic where the light-emitting
layer is formed using the laser transfer technique.
SUMMARY OF THE INVENTION
[0019] Accordingly, it is an object of the present invention to
provide a light-emitting polymer composition which can improve a
transfer characteristic where a light-emitting layer of an organic
EL display device is formed using a laser transfer technique.
[0020] It is another object of the present invention to provide a
light-emitting polymer composition which can improve a
light-emitting efficiency of an organic EL display device.
[0021] Additional objects and advantages of the invention will be
set forth in part in the description which follows and, in part,
will be obvious from the description, or may be learned by practice
of the invention.
[0022] To achieve the above and other objects of the present
invention, there is provided a light-emitting polymer composition
for a light-emitting layer in an organic EL display, comprising at
least first and second light-emitting polymers having elements,
wherein the first and second light-emitting polymers have different
interfacial characteristics which lower a cohesion between the
elements of the first and second light-emitting polymers, and a
corresponding wavelength spectrum of the first light-emitting
polymer overlaps a corresponding wavelength spectrum of the second
light-emitting polymer, so as to have an energy transfer in the
light-emitting polymer composition.
[0023] The light-emitting polymer composition further includes an
additive which improves adhesion of the light-emitting composition
to a substrate and lowers the cohesion between the elements of the
first and second light-emitting polymers. The additive is
"optically inert." That is, the addition of the additive to the
light-emitting polymer composition does not affect a final emitting
spectrum and a color index of the light-emitting polymer
composition in a range of visible light region of 400 nm to 800 nm,
wherein the range is a emitting light region of the light-emitting
polymer composition.
[0024] The additive is one of an optically inert polymer, an
optically inert low-molecular material, a polymer having a carrier
transporting ability, and a low-molecular material having a carrier
transporting ability.
[0025] The optically inert polymer is selected from a group
consisting of a polystyrene, a poly(styrene-butadione) copolymer, a
polymethylmethacrylate, a polyalphamethylstyrene, a
styrene-methylmethacrylate copolymer, a polybutadiene, a
polycarbonate, a polyethyleneterephthalate, a polyestersulfonate, a
polysulfonate, a polyarylate, a fluorinepolyimide, a transparent
fluoric resin, and a transparent acrylic resin.
[0026] The polymer having the carrier transporting ability is
selected from a group consisting of an arylamine, a perylrene group
and a pyrrole-based polymer. The low-molecular material having the
carrier transporting ability is, for example, an arylamine, a
hydrazone, a carbazole, a stylbene, a staburst group, and an
oxadiazole. A mixing mass ratio of the first light-emitting polymer
is in a range between 0.3 and 0.8, and a mixing mass ratio of the
second light-emitting polymer is in a range between 0.2 and 0.7. A
mixing mass ratio of the additive is less than 0.7.
[0027] To achieve the above and other objects according to another
aspect of the present invention, there is provided a light-emitting
polymer composition for a light-emitting layer of an organic EL
display, comprising a light-emitting polymer having elements and an
additive which improves adhesion of the light-emitting composition
to a substrate of the organic EL display, and lowers a cohesion
between the elements of the light-emitting polymers.
[0028] The additive is one of an optically inert polymer, an
optically inert low-molecular material, a polymer having a carrier
transporting ability, and a low-molecular material having a carrier
transporting ability.
[0029] The optically inert polymer is selected from a group
consisting of a polystyrene, a poly(styrene-butadione) copolymer, a
polymethylmethacrylate, a polyalphamethylstyrene, a
styrene-methylmethacrylate copolymer, a polybutadiene, a
polycarbonate, a polyethyleneterephthalate, a polyestersulfonate, a
polysulfonate, a polyarylate, a fluorinepolyimide, a transparent
fluoric resin, and a transparent acrylic resin.
[0030] The polymer having the carrier transporting ability is
selected from a group consisting of an arylamine, a perylrene group
and a pyrrole-based polymer. The low-molecular material having the
carrier transporting ability is, for example, an arylamine, a
hydrazone, a carbazole, a stylbene, a staburst group, and an
oxadiazole. A mixing mass ratio of the additive is in a range
between 0.375 and 0.667.
[0031] To achieve the above and other objects according to yet
another aspect of the present invention, there is provided an
organic EL display device comprising an anode, a hole transporting
layer formed on the anode, a light-emitting layer comprising a
light-emitting polymer composition including at least first and
second light-emitting polymers having elements, wherein the first
and second light-emitting polymers have different interfacial
characteristics which lower a cohesion between the elements of the
first and second light-emitting polymers, and a cathode formed on
the light-emitting layer.
[0032] A corresponding wavelength spectrum of the first
light-emitting polymer overlaps a corresponding wavelength spectrum
of the second light-emitting polymer so as to have an energy
transfer in the light-emitting polymer composition.
[0033] The light-emitting polymer composition further comprises an
additive which improves adhesion of the light-emitting composition
to a substrate of the organic display device, and lowers the
cohesion between the elements of the first and second
light-emitting polymers.
[0034] To achieve the above and other objects according to still
another aspect of the present invention, there is provided an
organic EL display device comprising an anode, a hole transporting
layer formed on the anode, a light-emitting layer comprising a
light-emitting polymer composition including a light-emitting
polymer having elements, and an additive which improves adhesion of
the light-emitting composition to a substrate and lowers a cohesion
between the elements of the light-emitting polymer, and a cathode
formed on the light-emitting layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] These and other objects and advantages of the present
invention will become apparent and more readily appreciated from
the following description of the embodiments, taken in conjunction
with the accompanying drawings of which:
[0036] FIG. 1 is a schematic view illustrating a laser transfer
operation for patterning a light-emitting layer of a conventional
organic EL display device;
[0037] FIG. 2 is a cross-sectional view illustrating an organic EL
display device according to an embodiment of the present
invention;
[0038] FIG. 3 is a mixing mass ratio graph showing a mixing mass
ratio of a light-emitting polymer composition according to the
present invention;
[0039] FIG. 4 Is a graph illustrating a wavelength spectrum of the
organic EL display device of FIG. 2 having a light-emitting polymer
composition of the present invention;
[0040] FIG. 5 is a graph illustrating a wavelength spectrum of the
organic EL display device of FIG. 2 according to variations of a
mixing mass ratio of the light-emitting polymer composition;
[0041] FIG. 6 is a CIE color coordinate of the organic EL display
device having a mixing mass ratio of SUPER
YELLOW:RED-B:polystyrene=0.64:0.28:0.- 08, respectively, according
to the present invention; and
[0042] FIG. 7 is a wavelength spectrum of the organic EL display
device of FIG. 6 having the light-emitting polymer composition of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Reference will now be made in detail to the embodiments of
the present invention, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to the
like elements throughout. The embodiments are described below in
order to explain the present invention by referring to the
figures.
[0044] A transfer characteristic of a polymer film can be improved
by lowering a cohesion between elements of the polymer film and/or
raising an adhesion between a substrate and the polymer film.
[0045] A light-emitting polymer composition according to an
embodiment of the present invention includes at least two kinds of
light-emitting polymers having different interfacial
properties.
[0046] Two kinds of light-emitting polymers having different
interfacial properties are mixed to prepare a polymer film. When a
laser beam is irradiated to the polymer film, a phase separation
occurs. The polymer film begins to transfer to a substrate from a
portion of the polymer film in which the phase separation occurs.
The phase separation lowers a cohesion between elements of the
polymer film without greatly lowering an adhesion between the
substrate and the polymer film. Consequently, a transfer
characteristic of the polymer film can be improved. As the polymers
have a greater difference in interfacial characteristic, the
polymer film is transferred more efficiently.
[0047] However, when the two kinds of polymers are mixed, a
light-emitting efficiency of an organic EL display device may be
lowered. Therefore, the light-emitting polymer composition of the
present invention has a structure that efficiently performs an
energy transfer. That is, an energy received by one polymer
(hereinafter, host polymer) is momentarily transferred to the other
polymer (hereinafter, a dopant polymer). Therefore, wavelength
spectrums of the host polymer and the dopant polymer overlap each
other.
[0048] For example, a yellow light-emitting polymer, in which a
wavelength of absorbed light is relatively small (i.e., has a
relatively high energy), receives energy to emit yellow light, and
a red light-emitting polymer, in which a wavelength of absorbed
light is large (i.e., has a relatively low energy), receives the
energy from the yellow light-emitting polymer to finally emit red
light. In other words, since the energy transfer occurs
momentarily, only the wavelength spectrum of the red light-emitting
polymer is finally observed.
[0049] The light-emitting polymer composition can be prepared to
emit R, G and B colors as well as a single color in the
above-described method.
[0050] The light-emitting polymer composition may further include
an additive which improves the adhesion between the polymer film
and the substrate, and simultaneously lowers the cohesion between
elements of the polymer film. The additive is "optically inert."
That is, the addition of the additive to the light-emitting polymer
composition does not affect a final emitting spectrum and a color
index of the light-emitting polymer composition in a range of
visible light region of 400 nm to 800 nm, wherein the range is a
emitting light region of the light-emitting polymer
composition.
[0051] The additive includes an optically inert polymer, an
optically inert low-molecular material, a polymer having a carrier
transporting ability, or a low-molecular material having a carrier
transporting ability.
[0052] The optically inert polymer includes a polystyrene, a
poly(styrene-butadione)copolymer, a polymethylmethacrylate, a
polyalphamethylstyrene, a styrene-methylmethacrylate copolymer, a
polybutadiene, a polycarbonate, a polyethyleneterephthalate, a
polyestersulfonate, a polysulfonate, a polyarylate, a
fluorinepolyimide, a transparent fluoric resin, and a transparent
acrylic resin. The polymer having the carrier transporting ability
includes an arylamine, a perylrene group and a pyrrole-based
polymer. The low-molecular material having a carrier transporting
ability includes one of an arylamine, a hydrazone, a carbazole, a
stylbene, a staburst group, and an oxadiazole.
[0053] A mixing mass ratio of the two kinds of light-emitting
polymers of the light-emitting polymer composition is as follows:
0.3<first polymer<0.8; and 0.2<second polymer<0.7. A
mixing mass ratio of the additive is less than 0.7.
[0054] A light-emitting polymer composition according to another
embodiment of the present invention can include one kind of polymer
and an additive. The additive is one of the above-described
additives. In this case, since the energy transfer does not occur,
a light-emitting efficiency is not improved, but the adhesion
between a substrate and a polymer film prepared using the
light-emitting polymer composition is improved. A large amount of
the additive may reduce the light-emitting efficiency. Accordingly,
a mixing mass ratio of the additive in this case is in a range
between 0.375 and 0.667.
[0055] The mixing mass ratios depend on pattern characteristics and
a color purity of a resulting device.
[0056] A method of manufacturing an organic EL display device
according to the present invention is described below.
[0057] A substrate having an anode is cleaned in, for example, an
acetone and an isopropylalcohol in sequence and is
UV/ozone-treated. A hole transporting layer is, for example,
spin-coated on the substrate and then baked. A light-emitting
polymer composition of the present invention is deposited on a
transfer substrate to tens of nanometers (nm) to thereby form a
transfer film. A light-emitting layer having R, G and B color
patterns is patterned on the hole transporting layer by using a
laser transfer technique. A cathode is formed on the light-emitting
layer. Finally, an encapsulating process is performed to complete
the organic EL display device.
[0058] The organic EL display device of the present invention has
an excellent transfer characteristic, thereby forming the
light-emitting layer having an edge roughness of less than 5
.mu.m.
[0059] FIG. 2 shows a cross-sectional view illustrating an organic
EL display device according to the present invention. In FIG. 2,
reference numerals 100, 200, 300 and 400 denote a cathode, a
light-emitting layer, a hole transporting layer, and an anode,
respectively.
[0060] Example 1 below describes a light-emitting polymer
composition having two kinds of light-emitting polymers and an
additive, and an organic EL display device using the same according
to the present invention:
EXAMPLE 1
[0061] The two kinds of light-emitting polymers and the additive
are mixed in an appropriate mass ratio and dissolved in a single
solvent to prepare the light-emitting polymer composition. One
light-emitting polymer is a PPV-based yellow electrolight-emitting
polymer available under the trade name "SUPER YELLOW" from Covion
Organic Semiconductors GmbH. The other light-emitting polymer is a
PFO-based red electrolight-emitting polymer available under the
trade name "RED-B" from Dow Chemical Company. The additive is a
polystyrene having a molecular weight of 2,500 available from
Sigma-Aldrich Corporation.
[0062] The light-emitting polymer composition is sufficiently
stirred at a temperature of 60.degree. C. for at least three hours.
The light-emitting polymer composition is deposited on a transfer
substrate to a thickness 80 nm to thereby form a transfer film. A
substrate having an anode electrode pattern is cleaned and then
UV/ozone-treated. A hole transporting layer made of a "PEDOT/PSS"
from Bayer AG is coated on the substrate to a thickness of 50 nm.
The transfer film undergoes a laser transfer technique to thereby
form a light-emitting layer of the organic EL display device. A
cathode electrode including an LiF layer of 1 nm and an Al layer of
150 nm is formed on the light-emitting layer. Finally, an
encapsulating process is performed to complete the organic EL
display device.
[0063] A mixing mass ratio of the above light-emitting polymer
composition which satisfies a Commission Internationale de
I'Eclairage (CIE) color coordinate and have an improved transfer
characteristic is as follows: 0.3<SUPER YELLOW<0.8,
0.2<RED-B<0.7, and polystyrene<0.7.
[0064] One of the optimum mixing mass ratio of the above
light-emitting polymer composition is as follows: SUPER
YELLOW:RED-B:polystyrene=0.64:0.- 28:0.08. In this case, a
light-emitting efficiency is 1.25 cd/A, and a color coordinate is
x=0.66 and y=0.33 (CIE1931, 300 Cd/m.sup.2 at a voltage of 6.5
volts).
[0065] In the above light-emitting polymer composition, where the
organic EL display device emits a red light, which is a finally
observed light, SUPER YELLOW is a host polymer and RED-B is a
dopant polymer.
[0066] FIG. 3 shows a mixing mass ratio graph of a light-emitting
polymer composition of the present invention which satisfies a CIE
color coordinate and have an improved transfer characteristic. A
non-dotted region (a region not filled with dots) is a feasible
region that can satisfy the CIE coordinate and has the laser
transfer characteristic.
[0067] FIG. 4 shows a graph illustrating a wavelength spectrum of
an organic EL display device according to the present invention. As
shown in FIG. 4, a wavelength spectrum of emitted light overlaps a
wavelength spectrum of absorbed light in a wavelength range between
500 nm and 700 nm. Therefore, an energy transfer from i.e., SUPER
YELLOW to RED-B occurs momentarily, so that only a wavelength
spectrum of red light is observed.
[0068] FIG. 5 shows a graph illustrating a wavelength spectrum of
an organic EL display device of the present invention according to
variations of a mixing mass ratio of a light-emitting polymer
composition used in the organic EL display device. As shown in FIG.
5, a wavelength spectrum of an organic EL display device having a
mixing mass ratio of RED-B of 25% is almost identical to that of
where a mixing mass ratio of RED-B is 100%.
[0069] FIGS. 6 and 7 show a CIE color coordinate and a wavelength
spectrum of an organic EL display device having a light-emitting
polymer composition with a mixing mass ratio of SUPER
YELLOW:RED-B:polystyrene=0.- 64:0.28:0.08, respectively.
[0070] Example 2 below describes a light-emitting polymer
composition having one light-emitting polymer and an additive, and
an organic EL display device using the same according to the
present invention.
EXAMPLE 2
[0071] The light-emitting polymer is a red electrolight-emitting
polymer available under the trade name "AEF 2009 & 2045" from
Covion Organic Semiconductors GmbH. The additive is a polystyrene
available from Sigma-Aldrich Corporation. The molecular weight of
the polystyrene is in a range between 2,000 and 2,500. The closer
the molecular weight of the polystyrene is to 2,000, better the
edge roughness of the light-emitting layer.
[0072] The light-emitting polymer and the additive are mixed in an
appropriate mixing mass ratio and dissolved in a toluene to prepare
the light-emitting polymer composition.
[0073] The light-emitting polymer composition is sufficiently
stirred at a temperature of 60.degree. C. for at least three hours.
The light-emitting polymer composition is deposited on a transfer
substrate to a thickness 80 nm to thereby form a transfer film. A
substrate having an anode is cleaned and then UV/ozone-treated for
fifteen minutes. A hole transporting layer made of "PEDOT/PSS" from
Bayer AG is coated on the substrate to a thickness of 50 nm. The
transfer film undergoes a laser transfer technique to thereby form
a light-emitting layer of the organic EL display device. A cathode
electrode is formed on the light-emitting layer. Finally, an
encapsulating process is performed to complete the organic EL
display device.
[0074] The mixing mass ratio of the light-emitting polymer
composition is as follows: 0.333<AEF 2009 or 2045<0.675, and
0.375<polystyrene<0.667. The light-emitting layer has an edge
roughness of less than 5 .mu.m.
[0075] Tables 1 and 2 below show the light emitting efficiency and
the CIE color coordinate of the organic EL display device
manufactured in the above-described condition.
[0076] An organic EL display device of Table 1 has the following
structure: substrate having anode/hole transporting layer of 50
nm/AEF2009:polystyrene(1:1)/cathode having a Ca layer of 30 nm and
an Ag layer of 250 nm.
1TABLE 1 Spincoating Turn-on Voltage (V) Efficiency speed Thickness
voltage at 100 at 100 CIE (1931) (rpm) (.ANG.) (V) Cd/ Cd/ X Y
CR/PS 2000 800 4.5 7.5 0.78 0.6601 0.3383 (#1) CR/PS 2000 800 4.0
7.0 0.83 0.6628 0.3354 (#2) CR/PS 2000 800 4.0 6.5 0.77 0.6605
0.3376 (#3)
[0077] An organic EL display device of Table 2 has the following
structure: substrate having anode/hole transporting of 50
nm/AEF2045:polystyrene(1:2)/cathode having a Ca layer of 30 nm and
a Ag layer of 250 nm.
2TABLE 2 Voltage Turn-on (V) Efficiency Thickness voltage at 100 at
100 CIE (1931) (.ANG.) (V) Cd/ Cd/ x Y CR/PS 700 3.5 5.5 0.79
0.6658 0.3342 (#1) CR/PS 800 3.5 6.0 1.34 0.6682 0.3309 (#2) CR/PS
850 3.5 6.5 1.22 0.6682 0.3309 (#3) CR/PS 900 4.0 7.0 0.51 0.6675
0.3316 (#4)
[0078] According to the present invention, a transfer
characteristic of a light-emitting layer of an organic EL display
device, formed using a laser transfer technique, is improved.
Accordingly, a resulting pattern of the light-emitting layer is
improved. In addition, the organic EL display device of the present
invention shows an improved light-emitting efficiency, as compared
to a conventional, i.e., pure red light-emitting polymer in the
same luminance condition.
[0079] Although a few embodiments of the present invention have
been shown and described, it will be appreciated by those skilled
in the art that changes may be made in these embodiments without
departing from the principles and spirit of the invention, the
scope of which is defined in the appended claims and their
equivalents.
* * * * *