U.S. patent application number 16/811315 was filed with the patent office on 2020-09-17 for flexible light-emitting device including conductive fiber.
The applicant listed for this patent is DAEGU GYEOGBUK INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Chang Hee CHO, Soon Moon JEONG, Sang Kyoo LIM, Bo Kyung SONG, Seong Kyu SONG.
Application Number | 20200292140 16/811315 |
Document ID | / |
Family ID | 1000004702148 |
Filed Date | 2020-09-17 |
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United States Patent
Application |
20200292140 |
Kind Code |
A1 |
JEONG; Soon Moon ; et
al. |
September 17, 2020 |
FLEXIBLE LIGHT-EMITTING DEVICE INCLUDING CONDUCTIVE FIBER
Abstract
Provided is a flexible light-emitting device including: a
light-emitting complex medium including a polymer matrix, and a
nano light-emitting material dispersed therein, the light-emitting
complex medium generating light via application of an electric
field thereto; a plurality of first fiber electrodes extending in a
first direction and disposed within the light-emitting complex
medium, wherein the plurality of first fiber electrodes are
arranged along a first imaginary plane and are spaced apart from
each other, wherein a first voltage is applied to the plurality of
first fiber electrodes; and a plurality of second fiber electrodes
extending in the first direction and disposed within the
light-emitting complex medium, wherein the plurality of first fiber
electrodes are alternated with the plurality of second fiber
electrodes, wherein a second voltage different from the first
voltage is applied to the plurality of second fiber electrodes.
Inventors: |
JEONG; Soon Moon; (Daegu,
KR) ; SONG; Seong Kyu; (Daegu, KR) ; SONG; Bo
Kyung; (Daegu, KR) ; LIM; Sang Kyoo; (Daegu,
KR) ; CHO; Chang Hee; (Daegu, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAEGU GYEOGBUK INSTITUTE OF SCIENCE AND TECHNOLOGY |
Daegu |
|
KR |
|
|
Family ID: |
1000004702148 |
Appl. No.: |
16/811315 |
Filed: |
March 6, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/0888 20130101;
F21S 4/24 20160101; H01L 51/502 20130101; C09K 11/54 20130101; C08L
83/04 20130101; G02B 6/0005 20130101 |
International
Class: |
F21S 4/24 20060101
F21S004/24; H01L 51/50 20060101 H01L051/50; C09K 11/08 20060101
C09K011/08; C09K 11/54 20060101 C09K011/54; C08L 83/04 20060101
C08L083/04; F21V 8/00 20060101 F21V008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2019 |
KR |
10-2019-0027916 |
Claims
1. A flexible light-emitting device comprising: a light-emitting
complex medium including a polymer matrix, and a nano
light-emitting material dispersed therein, the light-emitting
complex medium generating light via application of an electric
field thereto; a plurality of first fiber electrodes extending in a
first direction and disposed within the light-emitting complex
medium, wherein the plurality of first fiber electrodes are
arranged along a first imaginary plane and are spaced apart from
each other, wherein a first voltage is applied to the plurality of
first fiber electrodes; and a plurality of second fiber electrodes
extending in the first direction and disposed within the
light-emitting complex medium, wherein the plurality of first fiber
electrodes are alternated with the plurality of second fiber
electrodes, wherein a second voltage different from the first
voltage is applied to the plurality of second fiber electrodes.
2. The flexible light-emitting device of claim 1, wherein the
second fiber electrodes are arranged along the first imaginary
plane.
3. The flexible light-emitting device of claim 1, wherein the
second fiber electrodes are arranged along a second imaginary plane
different from the first imaginary plane.
4. The flexible light-emitting device of claim 1, wherein the
polymer matrix includes at least one selected from a group
consisting of polydimethylsiloxane (PDMS), polymethylmethacrylate
(PMMA), polycarbonate (PC), polyimide (PI), polyethylene (PE),
polypropylene (PP), methacrylic, ployurethane, and polyethylene
terephthalate (PET).
5. The flexible light-emitting device of claim 4, wherein the nano
light-emitting material includes a quantum dot.
6. The flexible light-emitting device of claim 1, wherein each of
the first fiber electrodes and the second fiber electrodes includes
a conductive fiber having electrical conductivity.
7. The flexible light-emitting device of claim 1, wherein the
flexible light-emitting device further comprises: a first voltage
application member electrically connected to the first fiber
electrodes for applying the first voltage to the first fiber
electrodes; and a second voltage application member electrically
connected to the second fiber electrodes for applying the second
voltage to the second fiber electrodes.
8. The flexible light-emitting device of claim 7, wherein the first
voltage is an alternating current (AC) voltage and the second
voltage is a ground voltage.
9. The flexible light-emitting device of claim 1, wherein the
polymer matrix is made of polydimethylsiloxane (PDMS), wherein the
nano light-emitting material includes a zinc sulfide (ZnS) quantum
dot, wherein the light-emitting complex medium generates first
light using the electric field applied thereto and generates second
light using mechanical stimulus applied thereto.
10. A flexible light-emitting device comprising: a light-emitting
complex medium including: a first medium layer including a first
polymer matrix, and a first nano light-emitting material dispersed
therein; and a second medium layer including a second polymer
matrix, and a second nano light-emitting material dispersed
therein, wherein the second medium layer is stacked on the first
medium layer; a plurality of first fiber electrodes extending in a
first direction and disposed within the first medium layer, wherein
the plurality of first fiber electrodes are arranged along a first
imaginary plane and are spaced apart from each other, wherein a
first voltage is applied to the plurality of first fiber
electrodes; a plurality of second fiber electrodes extending in the
first direction and disposed within the first medium layer, wherein
the plurality of first fiber electrodes are alternated with the
plurality of second fiber electrodes, wherein a second voltage
different from the first voltage is applied to the plurality of
second fiber electrodes; and a third fiber electrode located within
the second medium layer, wherein a third voltage is applied to the
third fiber electrode.
11. The flexible light-emitting device of claim 10, wherein the
first polymer matrix and the second polymer matrix are made of the
same material.
12. The flexible light-emitting device of claim 10, wherein the
first voltage is an alternating current voltage, the second voltage
is ground voltage, and the third voltage is one of the alternating
current voltage and the ground voltage.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims a benefit under 35 U.S.C. .sctn.
119(a) of Korean Patent Application No. 10-2019-0027916 filed on
Mar. 12, 2019, on the Korean Intellectual Property Office, the
entire disclosure of which is incorporated herein by reference for
all purposes.
BACKGROUND
1. Field
[0002] The present disclosure relates to a flexible light-emitting
device having surface light emission.
2. Description of Related Art
[0003] A conventional electroluminescence element has a structure
in which two planar electrodes face each other with a
light-emitting layer interposed therebetween. Light is emitted from
the light-emitting layer when an electric field generated by the
two planar electrodes is applied to the light-emitting layer.
[0004] In the electroluminescence element having such a structure,
a technique for forming the electrodes using silver nanowires
(AgNW), carbon nanotubes (CNT), etc. has been developed to improve
flexibility. However, in order to increase an electrical
conductivity of the electrode made of such materials, it is
necessary to increase a density of the material or increase a
thickness of the electrode. In this case, there is a problem that
light transmittance of the electrode is lowered, thereby reducing
light extraction efficiency of the electroluminescence element.
Further, in the electroluminescence element having such a
structure, light generated from the light-emitting layer must pass
through one of the electrodes in order to be extracted to an
outside. Thus, the electrode through which light passes must be
made of a material having very high light transmittance, and as a
result, a type of the material applicable to the electrode is
limited.
[0005] In a light-emitting element capable of electroluminescence
(EL) and mechanical light emission (ML) simultaneously, in order to
apply a strong electric field to the light-emitting layer, a
thickness of the light-emitting layer must be reduced. In this
case, there is a problem that performance of the mechanical light
emission is reduced due to the reduced thickness of the
light-emitting layer. Increasing the thickness of the
light-emitting layer causes a problem that performance of the
electroluminescence is degraded.
[0006] Therefore, there is a need for development of a
light-emitting element having a structure that may fundamentally
solve the problem as described above.
SUMMARY
[0007] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
all key features or essential features of the claimed subject
matter, nor is it intended to be used alone as an aid in
determining the scope of the claimed subject matter.
[0008] One purpose of the present disclosure is to provide a
flexible light-emitting device in which fiber electrodes disposed
inside a light-emitting complex medium are used to generate an
in-plane electric field, which in turn allows the light-emitting
complex medium to emit light, thereby to generate light with high
efficiency regardless of a material of the fiber electrode or a
thickness of light-emitting complex medium.
[0009] Purposes in accordance with the present disclosure are not
limited to the above-mentioned purpose. Other purposes and
advantages in accordance with the present disclosure as not
mentioned above may be understood from following descriptions and
more clearly understood from embodiments in accordance with the
present disclosure. Further, it will be readily appreciated that
the purposes and advantages in accordance with the present
disclosure may be realized by features and combinations thereof as
disclosed in the claims.
[0010] In a first aspect of the present disclosure, there is
provided a flexible light-emitting device comprising: a
light-emitting complex medium including a polymer matrix, and a
nano light-emitting material dispersed therein, the light-emitting
complex medium generating light via application of an electric
field thereto; a plurality of first fiber electrodes extending in a
first direction and disposed within the light-emitting complex
medium, wherein the plurality of first fiber electrodes are
arranged along a first imaginary plane and are spaced apart from
each other, wherein a first voltage is applied to the plurality of
first fiber electrodes; and a plurality of second fiber electrodes
extending in the first direction and disposed within the
light-emitting complex medium, wherein the plurality of first fiber
electrodes are alternated with the plurality of second fiber
electrodes, wherein a second voltage different from the first
voltage is applied to the plurality of second fiber electrodes.
[0011] In one implementation of the first aspect, the second fiber
electrodes are arranged along the first imaginary plane.
[0012] In one implementation of the first aspect, the second fiber
electrodes are arranged along a second imaginary plane different
from the first imaginary plane.
[0013] In one implementation of the first aspect, the polymer
matrix includes at least one selected from a group consisting of
polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA),
polycarbonate (PC), polyimide (PI), polyethylene (PE),
polypropylene (PP), methacrylic, ployurethane, and polyethylene
terephthalate (PET).
[0014] In one implementation of the first aspect, the nano
light-emitting material includes a quantum dot.
[0015] In one implementation of the first aspect, each of the first
fiber electrodes and the second fiber electrodes includes a
conductive fiber having electrical conductivity.
[0016] In one implementation of the first aspect, the flexible
light-emitting device further comprises: a first voltage
application member electrically connected to the first fiber
electrodes for applying the first voltage to the first fiber
electrodes; and a second voltage application member electrically
connected to the second fiber electrodes for applying the second
voltage to the second fiber electrodes.
[0017] In one implementation of the first aspect, the first voltage
is an alternating current (AC) voltage and the second voltage is a
ground voltage.
[0018] In one implementation of the first aspect, the polymer
matrix is made of polydimethylsiloxane (PDMS), wherein the nano
light-emitting material includes a zinc sulfide (ZnS) quantum dot,
wherein the light-emitting complex medium generates first light
using the electric field applied thereto and generates second light
using mechanical stimulus applied thereto.
[0019] In a second aspect of the present disclosure, there is
provided a flexible light-emitting device comprising: a
light-emitting complex medium including: a first medium layer
including a first polymer matrix, and a first nano light-emitting
material dispersed therein; and a second medium layer including a
second polymer matrix, and a second nano light-emitting material
dispersed therein, wherein the second medium layer is stacked on
the first medium layer; a plurality of first fiber electrodes
extending in a first direction and disposed within the first medium
layer, wherein the plurality of first fiber electrodes are arranged
along a first imaginary plane and are spaced apart from each other,
wherein a first voltage is applied to the plurality of first fiber
electrodes; a plurality of second fiber electrodes extending in the
first direction and disposed within the first medium layer, wherein
the plurality of first fiber electrodes are alternated with the
plurality of second fiber electrodes, wherein a second voltage
different from the first voltage is applied to the plurality of
second fiber electrodes; and a third fiber electrode located within
the second medium layer, wherein a third voltage is applied to the
third fiber electrode.
[0020] In one implementation of the second aspect, the first
polymer matrix and the second polymer matrix are made of the same
material.
[0021] In one implementation of the second aspect, the first
voltage is an alternating current voltage, the second voltage is
ground voltage, and the third voltage is one of the alternating
current voltage and the ground voltage.
[0022] Effects in accordance with the present disclosure may be as
follows but may not be limited thereto.
[0023] In the flexible light-emitting device in accordance with the
present disclosure, the in-plane electric field generated between
the fiber electrodes disposed inside the light-emitting complex
medium may be used to generate light and, further, the generated
light does not have to pass through the fiber electrodes when the
generated light is emitted to an outside. Thus, even when the fiber
electrode is made of a material with low light transmittance, the
device may emit the light at high efficiency. Further, the light
may be generated at high efficiency regardless of a thickness of
the light-emitting complex medium. Those are advantages over the
conventional light-emitting device in which the light-emitting
layer is disposed between the two electrodes having the planar
structure, and thus, when light generated from the light-emitting
layer is emitted to the outside, the light must pass through one of
the two planar electrodes.
[0024] In addition to the effects as described above, specific
effects in accordance with the present disclosure will be described
together with the detailed description for carrying out the
disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1A is a plan view illustrating a flexible
light-emitting device according to an embodiment of the present
disclosure.
[0026] FIG. 1B and FIG. 1C are cross-sectional views of different
embodiments as taken along a cut line A-A' shown in FIG. 1A.
[0027] FIG. 2 is a perspective view illustrating a flexible
light-emitting device according to another embodiment of the
present disclosure.
[0028] FIG. 3 is a view for illustrating a method of manufacturing
a light-emitting device according to Present Example 1.
[0029] FIG. 4 is a view for illustrating a method for manufacturing
a light-emitting device according to Present Example 2.
[0030] FIG. 5A shows optical and SEM cross-sectional images (b) of
a light-emitting device of Present Example 1 and a photograph (c)
showing electroluminescence under 500 Vrms voltage application
condition at 1 KHz frequency of Present Example 1.
[0031] FIG. 5B shows optical and SEM images (d, e) and EDS images
(f, g) of 130 .mu.m diameter Ag-coated nylon fiber having dozens of
nylon yarns and a 200 nm thick Ag coating layer.
[0032] FIG. 5C shows photographs showing ML light emission (h)
induced by pen stimulation to the light-emitting device of Present
Example 1, and EL light emission (i) while the light-emitting
device of Present Example 1 is wound around the pen.
[0033] FIG. 6 shows a photograph (a) of ML light emission induced
by pulling of the light-emitting device of Present Example 1 by
hand, ML light-emission spectrum (b) based on a
stretching-releasing (S-R) rate increasing from 100 cpm (cycles per
minute) to 500 cpm (cycles per minute), and ML intensity (c) over
time as obtained by integrating an spectral intensity from 400 nm
to 800 nm over 5000 cycles, and a magnified graph (d) thereof.
[0034] FIG. 7 shows a photograph (a) of EL light-emission as
measured in the light-emitting device in Present Example 1, a graph
(b) showing a voltage-luminance relationship under conditions of
various frequencies (100, 500, 1000 and 2000 Hz), and a
voltage-luminance graph (c) and a voltage-current graph (d) based
on a bending cycle.
[0035] FIG. 8A shows images showing simulated electric field
distribution (a) and optical field distribution (b) in a
light-emitting element with a pair of fiber electrodes, and images
showing simulated electric field distribution (f) and optical field
distribution (g) in a light-emitting element having a plurality of
pairs of fiber electrodes.
[0036] FIG. 8B shows a cross-sectional image (c) when AC voltage is
applied to the light-emitting device of Present Example 1 having
multiple of pairs of fiber electrodes, and a cross-sectional image
(d) when the AC voltage is not applied thereto, and a contour image
(e) evaluated in terms of a light intensity thereof.
[0037] FIG. 8C shows images of light emission of the light-emitting
device of Present Example 1.
[0038] FIG. 9 shows schematic images (a, b) of a light emitting
device of Present Example 2, an orange background light-emission
image (d), a green zig-zag pattern light-emission image (e),
simultaneous light-emission images (f and g) of an orange
background and a green zig-zag pattern, and EL spectrum (h) and CIE
coordinates at positions I, II and III shown in (d) to (f).
DETAILED DESCRIPTIONS
[0039] For simplicity and clarity of illustration, elements in the
figures are not necessarily drawn to scale. The same reference
numbers in different figures denote the same or similar elements,
and as such perform similar functionality. Further, descriptions
and details of well-known steps and elements are omitted for
simplicity of the description. Furthermore, in the following
detailed description of the present disclosure, numerous specific
details are set forth in order to provide a thorough understanding
of the present disclosure. However, it will be understood that the
present disclosure may be practiced without these specific details.
In other instances, well-known methods, procedures, components, and
circuits have not been described in detail so as not to
unnecessarily obscure aspects of the present disclosure.
[0040] Examples of various embodiments are illustrated and
described further below. It will be understood that the description
herein is not intended to limit the claims to the specific
embodiments described. On the contrary, it is intended to cover
alternatives, modifications, and equivalents as may be included
within the spirit and scope of the present disclosure as defined by
the appended claims.
[0041] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to limit the
present disclosure. As used herein, the singular forms "a" and "an"
are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises", "comprising", "includes", and
"including" when used in this specification, specify the presence
of the stated features, integers, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, integers, operations, elements, components,
and/or portions thereof. As used herein, the term "and/or" includes
any and all combinations of one or more of the associated listed
items. Expression such as "at least one of" when preceding a list
of elements may modify the entire list of elements and may not
modify the individual elements of the list.
[0042] It will be understood that, although the terms "first",
"second", "third", and so on may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section described below could be termed
a second element, component, region, layer or section, without
departing from the spirit and scope of the present disclosure.
[0043] In addition, it will also be understood that when a first
element or layer is referred to as being present "on" or "beneath"
a second element or layer, the first element may be disposed
directly on or beneath the second element or may be disposed
indirectly on or beneath the second element with a third element or
layer being disposed between the first and second elements or
layers.
[0044] It will be understood that when an element or layer is
referred to as being "connected to", or "coupled to" another
element or layer, it may be directly on, connected to, or coupled
to the other element or layer, or one or more intervening elements
or layers may be present. In addition, it will also be understood
that when an element or layer is referred to as being "between" two
elements or layers, it may be the only element or layer between the
two elements or layers, or one or more intervening elements or
layers may also be present.
[0045] Further, as used herein, when a layer, film, region, plate,
or the like is disposed "on" or "on a top" of another layer, film,
region, plate, or the like, the former may directly contact the
latter or still another layer, film, region, plate, or the like may
be disposed between the former and the latter. As used herein, when
a layer, film, region, plate, or the like is directly disposed "on"
or "on a top" of another layer, film, region, plate, or the like,
the former directly contacts the latter and still another layer,
film, region, plate, or the like is not disposed between the former
and the latter. Further, as used herein, when a layer, film,
region, plate, or the like is disposed "below" or "under" another
layer, film, region, plate, or the like, the former may directly
contact the latter or still another layer, film, region, plate, or
the like may be disposed between the former and the latter. As used
herein, when a layer, film, region, plate, or the like is directly
disposed "below" or "under" another layer, film, region, plate, or
the like, the former directly contacts the latter and still another
layer, film, region, plate, or the like is not disposed between the
former and the latter.
[0046] Unless otherwise defined, all terms including technical and
scientific terms used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
inventive concept belongs. It will be further understood that
terms, such as those defined in commonly used dictionaries, should
be interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0047] FIG. 1A is a plan view illustrating a flexible
light-emitting device according to an embodiment of the present
disclosure. FIG. 1B and FIG. 1C are cross-sectional views of
different embodiments as taken along a cut line A-A' shown in FIG.
1A.
[0048] Referring to FIG. 1A to FIG. 1C, a flexible light-emitting
device 100 according to one embodiment of the present disclosure
includes a light-emitting complex medium 110, a plurality of first
fiber electrodes 120, a plurality of second fiber electrodes 130, a
first voltage application member 140 and a second voltage
application member 150.
[0049] The light-emitting complex medium 110 may include a polymer
matrix and a nano light-emitting material dispersed therein, and
may generate light via application of an electric field
thereto.
[0050] A material of the polymer matrix is not particularly limited
as long as it is transparent and flexible. For example, the polymer
matrix may be made of polydimethylsiloxane (PDMS),
polymethylmethacrylate (PMMA), polycarbonate (PC), polyimide (PI),
polyethylene (PE), polypropylene (PP), methacrylic, ployurethane,
polyethylene terephthalate (PET), etc. The polymer matrix may have
a sheet structure with a constant thickness. The thickness of the
polymer matrix may be appropriately changed depending on an
application to which the polymer matrix is applied.
[0051] The nano light-emitting material may be uniformly dispersed
within the polymer matrix and may generate light in a particular
wavelength range via application of an electric field thereto. In
one embodiment, the nano light-emitting material may include a
quantum dot as a semiconductor nanocrystal.
[0052] The quantum dot refers to a semiconductor nanocrystal
particle of several to tens of nanometers in size. The quantum dot
has a band gap discontinuously quantized by a quantum confinement
effect. When energy above the band gap is applied thereto, the
quantum dot absorbs the energy to emit light having a wavelength
corresponding to the band gap. A wavelength of the light generated
from the quantum dot may be controlled by a size, composition, etc.
of the quantum dot.
[0053] The quantum dot may include a known quantum dot without
limitation. For example, the quantum dot may be made of II-VI group
compound, II-V group compound, III-V group compound, III-IV group
compound, III-VI group compound, IV-VI group compound or mixtures
thereof. The "mixture" includes not only simple mixtures of the
compounds, but also ternary compounds, quaternary compounds, and
the mixtures having dopants doped therein.
[0054] Examples of the II-VI group compounds may include magnesium
sulfide (MgS), magnesium selenide (MgSe), magnesium telluride
(MgTe), calcium sulfide (CaS), calcium selenide (CaSe), calcium
telluride (CaTe), strontium sulfide (SrS), strontium selenide
(SrSe), strontium telluride (SrTe), cadmium sulfide (CdS), cadmium
selenide (CdSe), tellurium cadmium (CdTe), zinc sulfide (ZnS), zinc
selenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS),
mercury selenide (HgSe), mercury telluride (HgTe), etc.
[0055] Examples of the II-V group compounds may include zinc
phosphide (Zn.sub.3P.sub.2), zinc arsenide (Zn.sub.3As.sub.2),
cadmium phosphide (Cd.sub.3P.sub.2), cadmium arsenide
(Cd.sub.3As.sub.2), cadmium nitride (Cd.sub.3N.sub.2) or zinc
nitride (Zn.sub.3N.sub.2).
[0056] Examples of the III-V group compounds may include boron
phosphide (BP), aluminum phosphide (AlP), aluminum arsenide (AlAs),
antimony monoxide (AlSb), gallium nitride (GaN), gallium phosphide
(GaP), gallium arsenide (GaAs), gallium antimony (GaSb), indium
nitride (InN), indium phosphide (InP), indium arsenide (InAs),
indium antimony (InSb), aluminum nitride (AlN), boron nitride (BN),
etc.
[0057] Examples of the III-IV group compounds may include boron
carbide (B.sub.4C), aluminum carbide (Al.sub.4C.sub.3), gallium
carbide (Ga.sub.4C), and the like.
[0058] Examples of the III-VI group compounds may include aluminum
sulfide (Al.sub.2S.sub.3), aluminum selenide (Al.sub.2Se.sub.3),
aluminum telluride (Al.sub.2Te.sub.3), gallium sulfide
(Ga.sub.2S.sub.3), gallium selenide (Ga.sub.2Se.sub.3), indium
sulfide (In.sub.2S.sub.3), indium selenide (In.sub.2Se.sub.3),
gallium telluride (Ga.sub.2Te.sub.3), indium telluride
(In.sub.2Te.sub.3). Etc.
[0059] Examples of the IV-VI group compound may include lead
sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), tin
sulfide (SnS), tin selenide (SnSe), tin telluride (SnTe), and the
like.
[0060] In one example, the quantum dot may have a single core
structure having a single core or a core/shell structure including
a core and a shell surrounding the core.
[0061] Each of the core and the shell of the quantum dot may be
made of the compounds as exemplified above. For example, the above
compounds may constitute the core or shell alone or in combination
of two or more thereof. A bandgap of the compound constituting the
core may be narrower than a bandgap of the compound constituting
the shell. However, the present disclosure is not limited thereto.
When the quantum dot has the core/shell structure, the compound
constituting the shell may be different from the compound
constituting the core.
[0062] In one example, the nano light-emitting material may further
include a ligand coupled to a surface of each of the quantum dots
to prevent the quantum dots from agglomerating with each other and
quenching. The ligand may include any known quantum dot ligand
without limitation. For example, the ligand may include an alkyl
group having 6 to 30 carbon atoms, an amine compound having an
alkenyl group, a carboxylic acid compound, a phosphine oxide
compound, a pyridine compound, a thiophene compound, and the
like.
[0063] The plurality of first fiber electrodes 120 and the
plurality of second fiber electrodes 130 may extend in parallel
with each other in a first direction X in the light-emitting
complex medium 110 and may be alternately arranged with each other.
Each of the plurality of first and second fiber electrodes 120 and
130 may include a conductive fiber having electrical conductivity.
The conductive fiber may be made of a conductive material or may be
made of a complex material including an insulating core fiber and a
conductive coating covering a surface thereof. For example, the
conductive material may include a conductive polymer, a metal wire,
or the like. The complex material may include a polymer fiber made
of an insulating polymer material such as nylon, polyester,
vinylon, and acryl, etc. and a conductive metal coating layer
coating a surface of the polymer fiber and made of silver (Ag),
gold (Au), copper (Cu), or aluminum (Al), etc. In this case, the
polymer fiber may be manufactured by twisting a plurality of yarns
and includes a fiber having a diameter of several mm or smaller,
for example, about 1 mm or smaller.
[0064] A first voltage may be applied to the first fiber electrodes
120 and a second voltage may be applied to the second fiber
electrodes 130. For example, an AC voltage may be applied to the
first fiber electrodes 120, and a ground voltage may be applied to
the second fiber electrodes 130. In this case, inside the
light-emitting complex medium 110, an electric field may be
generated between the first fiber electrodes 120 and the second
fiber electrodes 310, such that light may be generated inside the
light-emitting complex medium 110 via the electric field.
[0065] In one embodiment, as shown in FIG. 1B, the plurality of
first fiber electrodes 120 and the plurality of second fiber
electrodes 130 may be arranged at an imaginary same plane "a"
located within the light-emitting complex medium 110.
[0066] In another embodiment, as shown in FIG. 1C, the plurality of
first fiber electrodes 120 may be arranged at an imaginary first
plane "a", while the plurality of second fiber electrodes 130 may
be arranged at an imaginary second plane "a" parallel to and
different from the first plane "a". The second fiber electrodes 130
may be alternately arranged with the first fiber electrodes
120.
[0067] The first voltage application member 140 may apply the first
voltage to the first fiber electrodes 120, and the second voltage
application member 150 may apply the second voltage to the second
fiber electrodes 130.
[0068] The first voltage application member 140 may be electrically
connected to one ends of the first fiber electrodes 120, and the
second voltage application member 150 may be electrically connected
to one ends of the second fiber electrodes 130. In one example,
FIG. 1A shows that the first and second voltage application members
140 and 150 are disposed outside the light-emitting complex medium
110. Alternatively, at least one of the first and second voltage
application members 140 and 150, for example, both of the first and
second voltage application members 140 and 150 may be embedded
within the light-emitting complex medium 110.
[0069] In one embodiment, when the polymer matrix is made of
polydimethylsiloxane (PDMS), and the nano light-emitting material
includes a zinc sulfide (ZnS) quantum dot, the flexible
light-emitting device 100 may perform electroluminescence (EL) by
the electric field generated between the first and second fiber
electrodes 120 and 130 as described above and ML
(mechano-luminescence) by mechanical stress applied to the
light-emitting complex medium 110.
[0070] FIG. 2 is a perspective view illustrating a flexible
light-emitting device according to another embodiment of the
present disclosure.
[0071] Referring to FIG. 2, a flexible light-emitting device 200
according to another embodiment of the present disclosure may
include a light-emitting complex medium 210, a plurality of first
fiber electrodes 220, a plurality of second fiber electrodes 230, a
third fiber electrode 260, a first voltage application member 240,
a second voltage application member 250, and a third voltage
application member 270. The components except for the
light-emitting complex medium 210 and the third fiber electrode 260
are substantially the same as or similar to those of the flexible
light-emitting device 100 as described with reference to FIG. 1A to
FIG. 1C. Thus, duplicate detailed descriptions thereof will be
omitted below.
[0072] The light-emitting complex medium 210 may include a first
medium layer 121 that generates light of a first wavelength and a
second medium layer 122 that is stacked on the first medium layer
121 and generates light of a second wavelength that is different
from the first wavelength.
[0073] The first medium layer 121 may include a first polymer
matrix and a first nano light-emitting material dispersed therein.
The second medium layer 122 may include a second polymer matrix and
a second nano light-emitting material dispersed therein.
[0074] The first polymer matrix and the second polymer matrix may
be made of different polymer materials, but may be made of the same
polymer material. In the latter case, a single polymer matrix may
be formed.
[0075] The first nano light-emitting material may include a first
quantum dot that generates light of the first wavelength, and the
second nano light-emitting material may include a second quantum
dot that generates light of the second wavelength.
[0076] Since the materials of the first and second polymer matrices
and the materials of the first and second nano light-emitting
materials have already been described above, redundant descriptions
thereof are omitted.
[0077] Each of the first and second fiber electrodes 220 and 230
may include a conductive fiber having electrical conductivity. The
first and second fiber electrodes 220 and 230 may extend in
parallel to each other in the first direction X in the first medium
layer 211 and may be alternately arranged with each other.
[0078] A first voltage may be applied to the first fiber electrodes
220 and a second voltage may be applied to the second fiber
electrodes 230. For example, an alternating voltage may be applied
to the first fiber electrodes 220, and a ground voltage may be
applied to the second fiber electrodes 230. In this case, inside
the first medium layer 211, an electric field may be generated
between the first fiber electrodes 220 and the second fiber
electrodes 230, such that the electric field may allow generating
light of the first wavelength in the first medium layer 211.
[0079] The first and second fiber electrodes 220 and 230 are
substantially the same as the first and second fiber electrodes 120
and 130 of the flexible light-emitting device 100 as described with
reference to FIG. 1A to FIG. 1C. Thus, redundant descriptions
thereof are omitted.
[0080] The third fiber electrode 260 may be disposed inside the
second medium layer 212, and a third voltage may be applied
thereto. In this case, the third voltage may be a voltage different
from the first and second voltages, or may be the same voltage as
one of the first and second voltages.
[0081] When the third voltage different from the first and second
voltages is applied to the third fiber electrode 260, a vertical
electric field may be generated between the first fiber electrode
220 and the third fiber electrode 260 and between the second fiber
electrode 230 and the third fiber electrode 260. This vertical
electric field may allow generating light of the first wavelength
in a portion of the first medium layer 211 and light of the second
wavelength in a portion of the second medium layer 212.
[0082] In one example, when the third voltage equal to one of the
first and second voltages is applied to the third fiber electrode
260, a vertical electric field may be generated between the third
fiber electrode 260 and one of the first and second fiber
electrodes 220 and 230 to which a voltage different from the third
voltage is applied. The vertical electric field may allow
generating light of the first wavelength in a portion of the first
medium layer 211 and light of the second wavelength in a portion of
the second medium layer 212.
[0083] In an embodiment, a first AC voltage and a ground voltage
may be applied to the first and second fiber electrodes 220 and
230, respectively, while the ground voltage may be applied to the
third fiber electrode 260.
[0084] The first and second voltage application members 240 and 250
may apply the first voltage and the second voltage to the first
fiber electrodes 220 and the second fiber electrodes 230,
respectively. The third voltage application member 270 may apply
the third voltage to the third fiber electrode 260.
[0085] In one embodiment, when the third voltage different from the
first and second voltages is applied to the third fiber electrode
260, the third voltage application member 270 may be an independent
component insulated from the first and second voltage application
members 240 and 250. Alternatively, when the third voltage equal to
one of the first and second voltages is applied to the third fiber
electrode 260, one of the first and second voltage application
members 240 and 250 to which the same voltage as the third voltage
is applied may function as the third voltage application member
270.
[0086] In one embodiment, the third fiber electrode 260 may include
a conductive fiber patterned to have a predetermined shape. In this
case, in the light-emitting complex medium 210, the first medium
layer 211 may emit background light in a surface light emission
manner, and, at the same time, the second medium layer 212 may emit
light in a shape corresponding to a shape of the second fiber
electrode 260.
[0087] In another embodiment, the third fiber electrode 260 may
include a plurality of conductive fibers extending in the first
direction (X) or in a direction perpendicular to the first
direction (X) and arranged in parallel with each other. In this
case, the light-emitting complex medium 210 may emit a mixture of
light generated in the first medium layer 211 and light generated
in the second medium layer 212 in a surface light emission
manner
[0088] In the flexible light-emitting device in accordance with the
present disclosure, the in-plane electric field generated between
the fiber electrodes disposed inside the light-emitting complex
medium may be used to generate light and, further, the generated
light does not have to pass through the fiber electrodes when the
generated light is emitted to an outside. Thus, even when the fiber
electrode is made of a material with low light transmittance, the
device may emit the light at high efficiency. Further, the light
may be generated at high efficiency regardless of a thickness of
the light-emitting complex medium. Those are advantages over the
conventional light-emitting device in which the light-emitting
layer is disposed between the two electrodes having the planar
structure, and thus, when light generated from the light-emitting
layer is emitted to the outside, the light must pass through one of
the two planar electrodes.
[0089] Hereinafter, Present Examples and Experimental Examples of
the present disclosure will be described in detail. However, the
following Examples are merely one embodiment of the present
disclosure, and a scope of the present disclosure is not limited to
the following Examples.
Present Example 1
[0090] FIG. 3 is a view for illustrating a method of manufacturing
a light-emitting device according to Present Example 1.
[0091] As shown in FIG. 3, 16 Ag-coated nylon fibers were disposed
onto a glass substrate in a fully stretched manner while
maintaining a gap of about 300 .mu.m from the glass substrate such
that the 16 Ag-coated nylon fibers are embedded in a center of the
light-emitting complex medium layer. Subsequently, in order to form
the light-emitting complex medium layer, liquid PDMS containing a
curing agent at a weight ratio of 9:1 and a green light-emitting
ZnS phosphor were mixed with each other at a weight ratio of 7:3.
The uncured PDMS+ZnS(G) mixture was dropped onto the glass
substrate on which the fibers were placed, and then the mixture was
cured for 30 minutes in an oven at 70.degree. C. Then, a copper
tape was attached to each of exposed ends of first fiber electrodes
to which the AC voltage is applied and the second fiber electrodes
to which the ground voltage is applied. In this way, a
light-emitting device of Present Example 1 was manufactured.
Present Example 2
[0092] FIG. 4 is a view for illustrating a method for manufacturing
a light-emitting device according to Present Example 2.
[0093] As shown in FIG. 4, 16 Ag-coated nylon fibers were disposed
onto a glass substrate in a fully stretched manner while a gap
between the fibers and the glass substrate is absent such that the
16 Ag-coated nylon fibers are embedded in a center of the
light-emitting complex medium layer. Subsequently, in order to form
a first medium layer, liquid PDMS containing a curing agent in a
weight ratio of 9:1 and a green light-emitting ZnS phosphor were
mixed with each other at a weight ratio of 7:3. The uncured
PDMS+ZnS (G) mixture was dropped onto the glass substrate on which
the fibers were placed, followed by curing the mixture for 30
minutes in an oven at 70.degree. C. Subsequently, a zig-zag
pattern-shaped fiber was placed such that a gap of about 200 .mu.m
between the fiber and the first medium layer was maintained. Liquid
PDMS containing the curing agent in a weight ratio of 9:1 and
orange light-emitting ZnS phosphor were mixed with each other in a
weight ratio of 7:3. The uncured PDMS+ZnS (O) mixture was dropped
onto the first medium layer on which the patterned fiber was placed
and was cured under an ambient atmosphere at room temperature for
24 hours. Then, a copper tape is attached to each of exposed ends
of alternately arranged first and second fiber electrodes fixed
inside the first medium layer and receiving an AC voltage and a
ground voltage respectively. A copper tape was attached to an
exposed end of the patterned third fiber electrode fixed in the
second medium layer. In this way, the light-emitting device of
Present Example 2 was manufactured.
Experimental Example
[0094] FIG. 5A shows optical and SEM cross-sectional images (b) of
a light-emitting device of Present Example 1 and a photograph (c)
showing electroluminescence under 500 Vrms voltage application
condition at 1 KHz frequency of Present Example 1. FIG. 5B shows
optical and SEM images (d, e) and EDS images (f, g) of 130 .mu.m
diameter Ag-coated nylon fiber having dozens of nylon yarns and a
200 nm thick Ag coating layer. FIG. 5C shows photographs showing ML
light emission (h) induced by pen stimulation to the light-emitting
device of Present Example 1, and EL light emission (i) while the
light-emitting device of Present Example 1 is wound around the
pen.
[0095] Referring to FIG. 5A, the conductive fiber is embedded in
the center of the light-emitting complex medium. After applying the
AC voltage thereto, the in-plane AC field generated between the
first fiber electrodes and the second fiber electrodes excites the
ZnS phosphor such that the EL has been effectively generated.
[0096] Referring to FIG. 5B, it may be seen that a silver coating
layer of about 200 nm thickness is formed on a surface of a nylon
fiber of about 130 .mu.m in diameter composed of dozens of silver
coated nylon yarns of about 20 .mu.m in diameter.
[0097] Referring to FIG. 5C, the complex of PDMS and ZnS is widely
known as an ML source. The light-emitting device of Present Example
1 achieved ML light emission via pen writing thereon, and EL light
emission stably without loss of luminance even when the pen was
wound around the device. In the light-emitting device of Present
Example 1, most of ML emission is generated from the surface of the
light-emitting complex medium. Thus, ML performance is not hindered
by the embedded fiber electrodes. Further, PDMS is a soft and
flexible matrix. Thus, the light-emitting device of Present Example
1 exhibits high flexibility.
[0098] FIG. 6 shows a photograph (a) of ML light emission induced
by pulling of the light-emitting device of Present Example 1 by
hand, ML light-emission spectrum (b) based on a
stretching-releasing (S-R) rate increasing from 100 cpm (cycles per
minute) to 500 cpm (cycles per minute), and ML intensity (c) over
time as obtained by integrating an spectral intensity from 400 nm
to 800 nm over 5000 cycles, and a magnified graph (d) thereof.
[0099] Referring to (a) of FIG. 6, the light-emitting device of
Present Example 1 achieved ML of the same green color as the color
of PL and EL when the device has been stretched by hand.
[0100] Referring to (b) to (d) of FIG. 6, when the light-emitting
device of Present Example 1 is periodically stretched or released
using a stretching-releasing system with a stretching condition of
10%, an intensity of the green ML spectrum increased as the S-R
rate increases from 100 cpm (cycles per minute) to 500 cpm. The CIE
coordinates of the ML spectrum were (0.23, 0.58), representing a
typical green color emission.
[0101] A time-resolution ML intensity of a S-R motion (40 cpm,
integration time=10 ms) over 5000 cycles was investigated. ML
intensity was kept without degradation for 5000 cycles of S-R
motion. Slight increase in the ML intensity seen in an initial
state is believed to be due to rearrangement of ZnS particles
between adjacent fiber electrodes. However, this change has been
stabilized after 500 cycles. In one example, as shown in (d) of
FIG. 6, ML emission was generated during the stretching and
releasing motion.
[0102] The above results are consistent with previous reports. It
is determined that the fiber electrodes generate multiple emissions
in the light-emitting device without reducing the ML performance of
the light-emitting device of Present Example 1.
[0103] FIG. 7 shows a photograph (a) of EL light-emission as
measured in the light-emitting device in Present Example 1, a graph
(b) showing a voltage-luminance relationship under conditions of
various frequencies (100, 500, 1000 and 2000 Hz), and a
voltage-luminance graph (c) and a voltage-current graph (d) based
on a bending cycle.
[0104] Referring to FIG. 7, when an electric field is generated by
applying the AC voltage to the first fiber electrodes and the
ground voltage to the second fiber electrodes, the light-emitting
device of Present Example 1 effectively generates green light. In
this connection, luminance increases as the electric field and
frequency increase. Further, in the light-emitting device of
Present Example 1, a luminance value changed over a range of
several tens of cd/m.sup.2 as typically observed under frequency
conditions of several kHz in an alternating current-driven EL
element based on a conventional PDMS+ZnS complex. From these
results, it may be seen that the AC field applied between the
parallel electrodes of the light-emitting device of Present Example
1 exhibits a comparable voltage-current relationship as compared
with a conventional EL element employing flat electrodes.
[0105] Further, as shown in (c) and (d) of FIG. 7, it was
identified that the light-emitting device of Present Example 1
exhibited stable voltage-luminance and voltage-current behavior
after 10,000 bending cycles (bending radius=3 mm). From these
results, it may be seen that the light-emitting device of Present
Example 1 does not generate any electrical short during 10,000
bending cycles, and has excellent flexibility and durability.
[0106] FIG. 8A shows images showing simulated electric field
distribution (a) and optical field distribution (b) in a
light-emitting element with a pair of fiber electrodes, and images
showing simulated electric field distribution (f) and optical field
distribution (g) in a light-emitting element having a plurality of
pairs of fiber electrodes. FIG. 8B shows a cross-sectional image
(c) when AC voltage is applied to the light-emitting device of
Present Example 1 having multiple of pairs of fiber electrodes, and
a cross-sectional image (d) when the AC voltage is not applied
thereto, and a contour image (e) evaluated in terms of a light
intensity thereof. FIG. 8C shows images of light emission of the
light-emitting device of Present Example 1.
[0107] Referring to FIG. 8A to FIG. 8C, when only a pair of fiber
electrodes are used to generate an electric field therebetween, the
fiber electrodes may affect the extraction of light to the outside
(see (a) and (b) in FIG. 8A) due to opaque and non-light-emitting
properties of the fiber electrodes. When a plurality of pairs of
fiber electrodes are used, light is generated radially around each
fiber electrode due to a complex electric field formed between
neighboring fiber electrodes (see (d) and (e) in FIG. 8B).
[0108] Simulation of a light-emitting element having a plurality of
pairs of fiber electrodes was performed to identify such a
light-emitting profile. From the simulation result, it was found
that the highest electric and optical fields originate from the
fiber electrodes (see (f) and (g) in FIG. 8A). A result of
simulation of the light-emitting element having only the pair of
fibers did not show such a trend. Thus, this suggests that the
higher electric field in the radial direction is caused by the
influence between the neighboring fiber electrodes. Since the
number of electric field lines depends on a charge amount of each
electrode, and a density of the electric field lines is inversely
proportional to a distance, the density of the spatially defined
electric field lines is the highest at the fiber electrode surface.
Further, because of the interaction between neighboring fiber
electrodes, the density of the total electric field lines was high
in an upward direction and the electric field in the radial
direction was generated. Therefore, luminescence occurred mainly
near the fiber electrodes.
[0109] The magnified light-emitting photograph identifies such
light-emitting properties. A linear light-emitting region coincided
with positions of the fiber electrodes (see (h) and (I) in FIG.
8C).
[0110] From the above results, it may be seen that in the
light-emitting device according to the present disclosure, the
light-emitting region originates from the high radial electric
field generated near the surfaces of the fiber electrodes, and the
fiber electrodes do not affect the extraction of the generated
light to the outside. As a result, it is determined that when
adjusting the distance between the fiber electrodes, the light
emission device in accordance with the present disclosure may
realize uniform surface light emission.
[0111] FIG. 9 shows schematic images (a, b) of a light emitting
device of Present Example 2, an orange background light-emission
image (d), a green zig-zag pattern light-emission image (e),
simultaneous light-emission images (f and g) of an orange
background and a green zig-zag pattern, and EL spectrum (h) and CIE
coordinates at positions I, II and III shown in (d) to (f).
[0112] Referring to FIG. 9, the patterned third fiber electrode
disposed inside the second medium layer and receiving the ground
voltage interacts with the first fiber electrodes disposed in the
first medium layer and receiving the AC voltage to generate a
vertical electric field, thereby to realize independent light
emission. Specifically, the in-plane electric field formed between
the first and second fiber electrodes in the first medium layer
induced orange emission. The vertical electric field formed between
the third fiber electrode inside the second medium layer and the
first fiber electrode inside the first medium layer mainly
generates green light when the first fiber electrode is disposed on
a bottom of the first medium layer. Further, when the in-plane
electric field formed between the first and second fiber electrodes
and the vertical electric field formed between the third fiber
electrode and the first fiber electrode were simultaneously
applied, yellowish-colored pattern light emission appeared.
[0113] Although described above with reference to the preferred
embodiments of the present disclosure, those skilled in the art
will appreciate that various modifications and changes may be made
in the present disclosure without departing from a spirit and scope
of the present disclosure set forth in the following claims.
* * * * *