U.S. patent application number 17/004786 was filed with the patent office on 2021-07-22 for light emitting element and display device including the same.
This patent application is currently assigned to Samsung Display Co., LTD.. The applicant listed for this patent is Samsung Display Co., LTD.. Invention is credited to Ilhun CHO, Hyomin KO, Bora LEE.
Application Number | 20210226086 17/004786 |
Document ID | / |
Family ID | 1000005077565 |
Filed Date | 2021-07-22 |
United States Patent
Application |
20210226086 |
Kind Code |
A1 |
LEE; Bora ; et al. |
July 22, 2021 |
LIGHT EMITTING ELEMENT AND DISPLAY DEVICE INCLUDING THE SAME
Abstract
Provided is a light emitting element including a first
electrode, a hole transport region disposed over the first
electrode, an emission layer disposed over the hole transport
region, an electron transport region disposed over the emission
layer, and a second electrode disposed over the electron transport
region, wherein the hole transport region includes a first hole
transport layer disposed adjacent to the first electrode and having
a first refractive index, a second hole transport layer disposed
adjacent to the emission layer and having a second refractive
index, and a third hole transport layer disposed between the first
hole transport layer and the second hole transport layer and having
a third refractive index greater than each of the first refractive
index and the second refractive index, thereby achieving high light
extraction efficiency and high luminous efficiency.
Inventors: |
LEE; Bora; (Hwaseong-si,
KR) ; KO; Hyomin; (Suwon-si, KR) ; CHO;
Ilhun; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Display Co., LTD. |
Yongin-si |
|
KR |
|
|
Assignee: |
Samsung Display Co., LTD.
Yongin-si
KR
|
Family ID: |
1000005077565 |
Appl. No.: |
17/004786 |
Filed: |
August 27, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/14 20130101;
H01L 33/60 20130101; G02F 1/133603 20130101 |
International
Class: |
H01L 33/14 20060101
H01L033/14; G02F 1/13357 20060101 G02F001/13357; H01L 33/60
20060101 H01L033/60 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2020 |
KR |
10-2020-0007949 |
Claims
1. A light emitting element comprising: a first electrode; a hole
transport region disposed over the first electrode; an emission
layer disposed over the hole transport region; an electron
transport region disposed over the emission layer; and a second
electrode disposed over the electron transport region, wherein the
hole transport region comprises: a first hole transport layer
disposed adjacent to the first electrode and having a first
refractive index; a second hole transport layer disposed adjacent
to the emission layer and having a second refractive index; and a
third hole transport layer disposed between the first hole
transport layer and the second hole transport layer and having a
third refractive index greater than each of the first refractive
index and the second refractive index.
2. The light emitting element of claim 1, wherein a difference
between the third refractive index and the first refractive index
is greater than about 0.1, and a difference between the third
refractive index and the second refractive index is greater than
about 0.1.
3. The light emitting element of claim 2, wherein the first
refractive index is in a range of about 1.2 to about 1.7, the
second refractive index is in a range of about 1.2 to about 1.7,
and the third refractive index is in a range of about 1.7 to about
2.2.
4. The light emitting element of claim 2, wherein the first
refractive index and the second refractive index are equal.
5. The light emitting element of claim 1, wherein the second hole
transport layer is directly disposed under the emission layer.
6. The light emitting element of claim 5, wherein a refractive
index of the emission layer is greater than the first refractive
index of the first hole transport layer, and a difference between
the refractive index of the emission layer and the first refractive
index is greater than about 0.1.
7. The light emitting element of claim 6, wherein the refractive
index of the emission layer is in a range of about 1.7 to about
2.2.
8. The light emitting element of claim 1, wherein the first hole
transport layer is directly disposed over the first electrode.
9. The light emitting element of claim 8, wherein a refractive
index of the first electrode is greater than the first refractive
index of the first hole transport layer, and a difference between
the refractive index of the first electrode and the first
refractive index is greater than about 0.1.
10. The light emitting element of claim 9, wherein the refractive
index of the first electrode is in a range of about 1.7 to about
2.2.
11. The light emitting element of claim 1, wherein a ratio of a
thickness of the first hole transport layer to a thickness of the
third hole transport layer to a thickness of the second hole
transport layer is in a range of about 0.1:0.8:0.1 to about
0.45:0.1:0.45.
12. The light emitting element of claim 1, wherein the first
electrode is a reflective electrode, and the second electrode is a
transmissive electrode or a transflective electrode.
13. The light emitting element of claim 1, wherein the emission
layer emits light having a central wavelength in a range of about
430 nm to about 470 nm.
14. The light emitting element of claim 13, wherein a ratio of a
thickness of the first hole transport layer to a thickness of the
third hole transport layer to a thickness of the second hole
transport layer is about 1:1:1.
15. The light emitting element of claim 1, wherein the first hole
transport layer and the second hole transport layer each
independently comprise at least one of the compounds represented by
Formulae 1-1 to 1-4: ##STR00024## wherein in Formulae 1-1 to 1-4,
A.sub.1 to A.sub.5 are each independently a hydrogen atom, a
deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a
nitro group, an amino group, a substituted or unsubstituted silyl
group, a substitution or unsubstituted oxy group, a substituted or
unsubstituted alkyl group having 1 to 60 carbon atoms, a
substituted or unsubstituted aryl group having 6 to 60 ring-forming
carbon atoms, or a substituted or unsubstituted heteroaryl group
having 2 to 60 ring-forming carbon atoms, a is an integer from 0 to
5, b is an integer from 0 to 4, and c is an integer from 0 to
6.
16. The light emitting element of claim 1, wherein the third hole
transport layer comprises a compound represented by Formula 2:
##STR00025## wherein in Formula 2, Ar.sub.1 and Ar.sub.2 are each
independently a hydrogen atom, a deuterium atom, a halogen atom, a
substituted or unsubstituted alkyl group having 1 to 30 carbon
atoms, a substituted or unsubstituted aryl group having 6 to 30
carbon atoms, a substituted or unsubstituted heteroaryl group
having 2 to 30 ring-forming carbon atoms, or bonded to an adjacent
group to form a ring, Ar.sub.3 is a substituted or unsubstituted
aryl group having 6 to 30 ring-forming carbon atoms, or a
substituted or unsubstituted heteroaryl group having 2 to 30
ring-forming carbon atoms, a and b are each independently 0 or 1,
L.sub.1 and L.sub.2 are each independently a substituted or
unsubstituted cycloalkylene group having 3 to 10 ring-forming
carbon atoms, a substituted or unsubstituted heterocycloalkylene
group having 2 to 10 ring-forming carbon atoms, a substituted or
unsubstituted cycloalkenylene group having 3 to 10 ring-forming
carbon atoms, a substituted or unsubstituted arylene group having 6
to 30 ring-forming carbon atoms, or a substituted or unsubstituted
heteroarylene group having 2 to 60 ring-forming carbon atoms, p and
s are each independently an integer from 0 to 4, q and r are each
independently an integer from 0 to 3, and R.sub.1 to R.sub.5 are
each independently a hydrogen atom, a deuterium atom, a halogen
atom, a hydroxyl group, a cyano group, a nitro group, an amino
group, a substituted or unsubstituted silyl group, a substituted or
unsubstituted oxy group, a substituted or unsubstituted alkyl group
having 1 to 60 carbon atoms, a substituted or unsubstituted
heterocycloalkyl group having 3 to 60 ring-forming carbon atoms, a
substituted or unsubstituted aryl group having 6 to 60 ring-forming
carbon atoms, or a substituted or unsubstituted heteroaryl group
having 2 to 60 ring-forming carbon atoms.
17. The light emitting element of claim 1, wherein the third hole
transport layer comprises at least one of Compounds 1 to 69:
##STR00026## ##STR00027## ##STR00028## ##STR00029## ##STR00030##
##STR00031## ##STR00032## ##STR00033## ##STR00034## ##STR00035##
##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040##
##STR00041## ##STR00042## ##STR00043##
18. A display device comprising: a plurality of light emitting
elements, each of the light emitting elements comprising: a first
electrode; a hole transport region disposed over the first
electrode; an emission layer disposed over the hole transport
region; an electron transport region disposed over the emission
layer; and a second electrode disposed over the electron transport
region, wherein the hole transport region of at least one of the
plurality of light emitting elements comprises: a first hole
transport layer disposed adjacent to the first electrode and having
a first refractive index; a second hole transport layer disposed
adjacent to the emission layer and having a second refractive
index; and a third hole transport layer disposed between the first
hole transport layer and the second hole transport layer and having
a third refractive index greater than each of the first refractive
index and the second refractive index.
19. The display device of claim 18, wherein a difference between
the third refractive index and the first refractive index is
greater than about 0.1, and a difference between the third
refractive index and the second refractive index is greater than
about 0.1.
20. The display device of claim 18, wherein the first electrode is
a reflective electrode, and the second electrode is a transmissive
electrode or a transflective electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to and benefits of Korean
Patent Application No. 10-2020-0007949 under 35 U.S.C. .sctn. 119,
filed on Jan. 21, 2020 in the Korean Intellectual Property Office,
the entire contents of which are incorporated herein by
reference.
BACKGROUND
1. Technical Field
[0002] The disclosure herein relates to a light emitting element
and a display device including the same, and more particularly, to
a light emitting element including hole transport layers having
different refractive indices and a display device including the
same.
2. Description of the Related Art
[0003] Various types of display devices used in multimedia devices
such as televisions, cellular phones, tablet computers, navigations
and game consoles are being developed. In such display devices, a
so-called self-luminescent display element accomplishing display by
causing a light emitting material including organic compounds or
quantum dots in an emission layer disposed between electrodes
facing each other to emit light is used.
[0004] In the application of a light emitting element to a display
apparatus, there is a demand for a light emitting element having
high luminous efficiency and a long life, and development on
materials and structures, for a light emitting element, capable of
stably attaining such characteristics is being continuously
required.
SUMMARY
[0005] The disclosure provides a light emitting element having
excellent light extraction efficiency.
[0006] The disclosure also provides a display device including a
light emitting element having high luminous efficiency.
[0007] An embodiment of the inventive concept provides a light
emitting element including a first electrode, a hole transport
region disposed over the first electrode, an emission layer
disposed over the hole transport region, an electron transport
region disposed over the emission layer, and a second electrode
disposed over the electron transport region, wherein the hole
transport region includes a first hole transport layer disposed
adjacent to the first electrode and having a first refractive
index, a second hole transport layer disposed adjacent to the
emission layer and having a second refractive index, and a third
hole transport layer disposed between the first hole transport
layer and the second hole transport layer and having a third
refractive index greater than each of the first refractive index
and the second refractive index.
[0008] A difference between the third refractive index and the
first refractive index may be greater than about 0.1, and a
difference between the third refractive index and the second
refractive index may be greater than about 0.1.
[0009] The first refractive index may be in a range of about 1.2 to
about 1.7, the second refractive index may be in a range of about
1.2 to about 1.7, and the third refractive index may be in a range
of about 1.7 to about 2.2.
[0010] The first refractive index and the second refractive index
may be equal.
[0011] The second hole transport layer may be directly disposed
under the emission layer.
[0012] The refractive index of the emission layer may be greater
than the first refractive index of the first hole transport layer,
and a difference between the refractive index of the emission layer
and the first refractive index may be greater than about 0.1.
[0013] The refractive index of the emission layer may be in a range
of about 1.7 to about 2.2.
[0014] The first hole transport layer may be directly disposed over
the first electrode.
[0015] The refractive index of the first electrode may be greater
than the first refractive index of the first hole transport layer,
and a difference between the refractive index of the first
electrode and the first refractive index may be greater than about
0.1.
[0016] The refractive index of the first electrode may be in a
range of about 1.7 to about 2.2.
[0017] The ratio of a thickness of the first hole transport layer
to a thickness of the third hole transport layer to a thickness of
the second hole transport layer may be in a range of about
0.1:0.8:0.1 to about 0.45:0.1:0.45.
[0018] The first electrode may be a reflective electrode, and the
second electrode may be a transmissive electrode or a transflective
electrode.
[0019] The emission layer may emit light having a central
wavelength in a range of about 430 nm to about 470 nm.
[0020] The ratio of a thickness of the first hole transport layer
to a thickness of the third hole transport layer to a thickness of
the second hole transport layer may be in a range of about
1:1:1.
[0021] The first hole transport layer and the second hole transport
layer may each independently include at least one of the compounds
represented by Formulae 1-1 to 1-4.
##STR00001##
[0022] In Formulae 1-1 to 1-4, A.sub.1 to A.sub.5 may each
independently be a hydrogen atom, a deuterium atom, a halogen atom,
a hydroxyl group, a cyano group, a nitro group, an amino group, a
substituted or unsubstituted silyl group, a substitution or
unsubstituted oxy group, a substituted or unsubstituted alkyl group
having 1 to 60 carbon atoms, a substituted or unsubstituted aryl
group having 6 to 60 ring-forming carbon atoms, or a substituted or
unsubstituted heteroaryl group having 2 to 60 ring-forming carbon
atoms. In Formulae 1-1 to 1-4, a is an integer of 0 to 5, b is an
integer of 0 to 4, and c is an integer of 0 to 6.
[0023] The third hole transport layer may include a compound
represented by Formula 2.
##STR00002##
[0024] In Formula 2, Ar.sub.1 and Ar.sub.2 may each independently
be a hydrogen atom, a deuterium atom, a halogen atom, a substituted
or unsubstituted alkyl group having 1 to 30 carbon atoms, a
substituted or unsubstituted aryl group having 6 to 30 carbon
atoms, a substituted or unsubstituted heteroaryl group having 2 to
30 ring-forming carbon atoms, or bonded to an adjacent group to
form a ring, and Ara may be a substituted or unsubstituted aryl
group having 6 to 30 ring-forming carbon atoms or a substituted or
unsubstituted heteroaryl group having 2 to 30 ring-forming carbon
atoms. In Formula 2, a and b are each independently 0 or 1, and
L.sub.1 and L.sub.2 may each independently be a substituted or
unsubstituted cycloalkylene group having 3 to 10 ring-forming
carbon atoms, a substituted or unsubstituted heterocycloalkylene
group having 2 to 10 ring-forming carbon atoms, a substituted or
unsubstituted cycloalkenylene group having 3 to 10 ring-forming
carbon atoms, a substituted or unsubstituted arylene group having 6
to 30 ring-forming carbon atoms, or a substituted or unsubstituted
heteroarylene group having 2 to 60 ring-forming carbon atoms. In
Formula 2, p and s are each independently an integer of 0 to 4, q
and r are each independently an integer of 0 to 3, and R.sub.1 to
R.sub.5 may each independently be a hydrogen atom, a deuterium
atom, a halogen atom, a hydroxyl group, a cyano group, a nitro
group, an amino group, a substituted or unsubstituted silyl group,
a substituted or unsubstituted oxy group, a substituted or
unsubstituted alkyl group having 1 to 60 carbon atoms, a
substituted or unsubstituted heterocycloalkyl group having 3 to 60
ring-forming carbon atoms, a substituted or unsubstituted aryl
group having 6 to 60 ring-forming carbon atoms, or a substituted or
unsubstituted heteroaryl group having 2 to 60 ring-forming carbon
atoms.
[0025] In an embodiment of the inventive concept, a display device
includes light emitting elements, each of the light emitting
elements including a first electrode, a hole transport region
disposed over the first electrode, an emission layer disposed over
the hole transport region, an electron transport region disposed
over the emission layer, and a second electrode disposed over the
electron transport region, and wherein the hole transport region of
at least one of the light emitting elements includes a first hole
transport layer disposed adjacent to the first electrode and having
a first refractive index, a second hole transport layer disposed
adjacent to the emission layer and having a second refractive
index, and a third hole transport layer disposed between the first
hole transport layer and the second hole transport layer and having
a third refractive index greater than each of the first refractive
index and the second refractive index.
[0026] A difference between the third refractive index and the
first refractive index may be greater than about 0.1, and a
difference between the third refractive index and the second
refractive index may be greater than about 0.1.
[0027] The first electrode may be a reflective electrode, and the
second electrode may be a transmissive electrode or a transflective
electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings are included to provide a further
understanding of the inventive concept, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the inventive concept and, together with the
description, serve to explain principles of the inventive concept.
In the drawings:
[0029] FIG. 1 is a perspective view of an electronic device
according to an embodiment;
[0030] FIG. 2 is a plan view of a display device according to an
embodiment;
[0031] FIG. 3 is a schematic cross-sectional view of a display
device of an embodiment corresponding to line I-I' of FIG. 2;
[0032] FIG. 4 is a schematic cross-sectional view of a light
emitting element according to an embodiment;
[0033] FIG. 5 is a schematic cross-sectional view illustrating a
part of a light emitting element according to an embodiment;
and
[0034] FIG. 6 is a graph showing the comparison of efficiency
characteristics in a light emitting element of Example and
Comparative Example.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] The inventive concept may have various modifications and may
be embodied in different forms, and example embodiments will be
explained in detail with reference to the accompany drawings. The
inventive concept may, however, be embodied in different forms and
should not be construed as being limited to the embodiments set
forth herein. Rather, all modifications, equivalents, and
substituents which are included in the spirit and technical scope
of the inventive concept should be included in the inventive
concept.
[0036] It will be understood that when an element or layer is
referred to as being "on", "disposed on", "connected to", or
"coupled to" another element or layer, it can be directly on,
disposed, connected, or coupled to the other element or layer or
intervening elements or layers may be present.
[0037] Like numbers refer to like elements throughout. Also, in the
drawings, the thickness, the ratio, and the dimensions of elements
are exaggerated for an effective description of technical
contents.
[0038] The term "and/or," includes all combinations of one or more
of which associated configurations may define. For example, "A
and/or B" may be understood to mean "A, B, or A and B." The terms
"and" and "or" may be used in the conjunctive or disjunctive sense
and may be understood to be equivalent to "and/or". Throughout the
disclosure, the expression "at least one of A, B, or C" may
indicate only A, only B, only C, both A and B, both A and C, both B
and C, all of A, B, and C, or variations thereof.
[0039] The term "at least one of" is intended to include the
meaning of "at least one selected from the group consisting of" for
the purpose of its meaning and interpretation. For example, "at
least one of A and B" may be understood to mean "A, B, or A and B."
When preceding a list of elements, the term, "at least one of,"
modifies the entire list of elements and does not modify the
individual elements of the list.
[0040] It will be understood that, although the terms "first",
"second", etc. may be used herein to describe various elements,
these elements should not be limited by these terms. These terms
are only used to distinguish one element from another. For example,
a first element could be termed a second element, and, similarly, a
second element could be termed a first element, without departing
from the scope of example embodiments of the inventive concept. The
terms of a singular form may include plural forms unless the
context clearly indicates otherwise.
[0041] Terms such as "below," "lower," "under," "above," "upper,"
and the like are used to describe the relationship of the
configurations shown in the drawings. The terms are used as a
relative concept and are described with reference to the direction
indicated in the drawings. The invention may also be oriented in
other directions and thus the spatially relative terms may be
interpreted differently depending on the orientations.
[0042] 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 the
inventive concept pertains. It is also to be understood that terms
defined in commonly used dictionaries should be interpreted as
having meanings consistent with the meanings in the context of the
related art, and are expressly defined herein unless they are
interpreted in an ideal or overly formal sense.
[0043] It should be understood that the terms "comprise",
"include", "contain", or "have" are intended to specify the
presence of stated features, integers, steps, operations, elements,
components, or combinations thereof in the disclosure, but do not
preclude the presence or addition of one or more other features,
integers, steps, operations, elements, components, or combinations
thereof.
[0044] Hereinafter, a light emitting element according to an
embodiment of the inventive concept and a display device including
the same will be described with reference to the accompanying
drawings.
[0045] FIG. 1 is a perspective view of an electronic device
according to an embodiment. FIG. 2 is a plan view of a display
device according to an embodiment. FIG. 3 is a schematic
cross-sectional view illustrating a part of a display device
corresponding to line I-I' of FIG. 2.
[0046] In an embodiment, an electronic device ED may be a small-
and medium-sized electronic device such as a smart phone, a tablet,
a personal computer, a notebook computer, a personal digital
terminal, a car navigation unit, a game console, and a camera. The
electronic device ED may be a large-sized electronic device such as
a television set, a monitor, or an outdoor billboard. These are
merely presented as an example, and thus it may be adopted for
other electronic devices without departing from the inventive
concept.
[0047] The electronic device ED may include a display device DD and
a housing HAU. The display device DD may display an image IM
through a display surface IS. FIG. 1 illustrates that the display
surface IS is parallel to a plane defined by a first direction axis
DR1 and a second direction axis DR2 crossing the first direction
axis DR1. However, this is an example, and in another embodiment,
the display surface IS of the display device DD may have a curved
shape.
[0048] Among the normal directions of the display surface IS, for
example, the thickness directions of the display device DD, a
direction in which the image IM is displayed is indicated by a
third direction axis DR3. A front surface (or an upper surface) and
a rear surface (or a lower surface) of each member may be defined
by the third direction axis DR3. The directions indicated by the
first to third direction axes DR1, DR2, and DR3 are relative
concepts, and may thus be changed to other directions.
[0049] The housing HAU may hold the display device DD. The housing
HAU may be disposed to cover the display device DD so that an upper
surface which is the display surface IS of the display device DD is
exposed. The housing HAU may cover a side surface and a bottom
surface of the display device DD and may expose the entire upper
surface. However, the embodiment of the inventive concept is not
limited thereto, and the housing HAU may cover a portion of the
upper surface as well as the side surface and the bottom surface of
the display device DD.
[0050] The display device DD may include a base substrate BS, a
circuit layer DP-CL disposed on the base substrate BS, and a
display element layer DP-OEL. The display element layer DP-OEL may
include a pixel defining layer PDL, light emitting elements OEL-1,
OEL-2 and OEL-3 disposed between the pixel defining layer PDL, and
an encapsulation layer TFE disposed on the light emitting elements
OEL-1, OEL-2 and OEL-3.
[0051] The base substrate BS may be a member that provides a base
surface where the display element layer DP-OEL is disposed. The
base substrate BS may be a glass substrate, a metal substrate, a
plastic substrate, etc. However, the embodiment of the inventive
concept is not limited thereto, and the base substrate BS may be an
inorganic layer, an organic layer, or a composite material
layer.
[0052] In an embodiment, the circuit layer DP-CL may be disposed on
the base substrate BS, and the circuit layer DP-CL may include
transistors (not shown). The transistors (not shown) each may
include a control electrode, an input electrode, and an output
electrode. For example, the circuit layer DP-CL may include a
switching transistor and a driving transistor to drive the light
emitting elements OEL-1, OEL-2, and OEL-3 of the display element
layer DP-OEL.
[0053] Each of the light emitting elements OEL-1, OEL-2 and OEL-3
may include a first electrode EL1, a hole transport region HTR,
emission layers EML-R, EML-G and EML-B, an electron transport
region ETR, and a second electrode EL2.
[0054] Each of the light emitting elements OEL-1, OEL-2, and OEL-3
included in the display device DD of an embodiment may have a
structure of a light emitting element (OEL, FIG. 4) of an
embodiment, which will be described later. The hole transport
region HTR included in each of the light emitting elements OEL-1,
OEL-2, and OEL-3 included in the display device DD of an embodiment
may include hole transport layers having different refractive
indices.
[0055] FIG. 3 illustrates an embodiment that light emitting layers
EML-R, EML-G, and EML-B of light emitting elements OEL-1, OEL-2,
and OEL-3 are disposed in an opening OH defined in a pixel defining
layer PDL, and a hole transport region HTR, an electron transport
region ETR, and a second electrode EL2 are provided as a common
layer in all the light emitting elements OEL-1, OEL-2, and OEL-3.
However, the embodiment of the inventive concept is not limited
thereto, and unlike the one shown in FIG. 3, in an embodiment, the
hole transport region HTR or the electron transport region ETR is
separated by the pixel defining layer PDL, and provided by being
patterned inside the opening OH defined in the pixel defining layer
PDL.
[0056] In an embodiment, the hole transport region HTR, the
emission layer EML-R, EML-G, and EML-B, the electron transport
region ETR, etc. of the light emitting elements OEL-1, OEL-2, and
OEL-3 may be provided using various methods such as a vacuum
deposition method, a spin coating method, a cast method, a
Langmuir-Blodgett (LB) method, an inkjet printing method, a laser
printing method, and a laser induced thermal imaging (LITI)
method.
[0057] An encapsulation layer TFE may cover the light emitting
elements OEL-1, OEL-2, and OEL-3. The encapsulation layer TFE may
seal the display element layer DP-OEL. The encapsulation layer TFE
may be disposed on the second electrode EL2, and fill the opening
OH.
[0058] The encapsulation layer TFE may be a thin film encapsulation
layer. The encapsulation layer TFE may be one layer or a laminated
layer of multiple layers. The encapsulation layer TFE includes at
least one insulating layer. The encapsulation layer TFE according
to an embodiment of the inventive concept may include at least one
inorganic film (hereinafter, an encapsulating inorganic film). The
encapsulation layer TFE according to an embodiment of the inventive
concept may include at least one organic film (hereinafter, an
encapsulating organic film) and at least one encapsulating
inorganic film.
[0059] The encapsulating inorganic film protects the display
element layer DP-OEL from moisture/oxygen, and the encapsulating
organic film protects the display element layer DP-OEL from foreign
substances such as dust particles. The encapsulating inorganic film
may include a silicon nitride layer, a silicon oxynitride layer, a
silicon oxide layer, a titanium oxide layer, an aluminum oxide
layer, etc., but is not limited thereto. The encapsulating organic
film may include an acryl-based organic film but is not limited
thereto.
[0060] Although not shown, a capping layer may be further disposed
on the second electrode EL2 in an embodiment. For example, the
capping layer (not shown) may be disposed between the second
electrode EL2 and the encapsulation layer TFE.
[0061] Referring to FIGS. 2 and 3, the display device DD may
include a non-light emitting region NPXA and light emitting regions
PXA-B, PXA-G and PXA-R. Each of the light emitting regions PXA-B,
PXA-G and PXA-R may be a region emitting light generated from the
light emitting elements ED-1, ED-2, and ED-3, respectively. The
light emitting regions PXA-B, PXA-G and PXA-R may be spaced apart
from each other on a plane.
[0062] Each of the light emitting regions PXA-R, PXA-G and PXA-B
may be a region separated by a pixel defining layer PDL. The
non-light emitting regions NPXA may be regions between neighboring
light emitting regions PXA-R, PXA-G and PXA-B, and may correspond
to the pixel defining layer PDL. Each of the light emitting regions
PXA-B, PXA-G and PXA-R may correspond to a pixel. The pixel
defining layer PDL may separate the light emitting elements OEL-1,
OEL-2, and OEL-3. The emission layers EML-R, EML-G and EML-B of the
light emitting elements OEL-1, OEL-2, and OEL-3 may be disposed and
separated in the opening OH defined in the pixel defining layer
PDL. The emission layers EML-R, EML-G, and EML-B separated by the
pixel defining layer PDL may be formed through a method such as
inkjet printing.
[0063] The pixel defining layer PDL may be formed of a polymer
resin. For example, the pixel defining layer PDL may be formed
including a polyacrylate-based resin or a polyimide-based resin.
The pixel defining layer PDL may be formed by further including an
inorganic material in addition to the polymer resin. The pixel
defining layer PDL may be formed including a light absorbing
material, or may be formed including a black pigment or a black
dye. The pixel defining layer PDL formed including a black pigment
or a black dye may implement a black pixel defining film. When
forming the pixel defining layer PDL, carbon black may be used as
the black pigment or the black dye, but the embodiment of the
inventive concept is not limited thereto.
[0064] The pixel defining layer PDL may be formed of an inorganic
material. For example, the pixel defining layer PDL may be formed
including silicon nitride (SiNx), silicon oxide (SiOx), silicon
oxynitride (SiOxNy), etc. The pixel defining layer PDL may define
light emitting regions PXA-R, PXA-G, and PXA-B. The light emitting
regions PXA-R, PXA-G, and PXA-B and a non-light emitting region
NPXA may be separated by the pixel defining layer PDL.
[0065] The light emitting regions PXA-R, PXA-G and PXA-B may be
divided into groups according to the color of light generated from
the light emitting elements OEL-1, OEL-2, and OEL-3. In the display
device DD of an embodiment illustrated in FIGS. 2 and 3, three
light emitting regions PXA-R, PXA-G and PXA-B which emit red light,
green light, and blue light, respectively are illustrated. For
example, the display device DD of an embodiment may include a red
light emitting region PXA-R, a green light emitting region PXA-G
and a blue light emitting region PXA-B, which are distinguished
from each other.
[0066] The display device DD according to an embodiment includes
light emitting elements OEL-1, OEL-2, and OEL-3, and the light
emitting elements OEL-1, OEL-2, and OEL-3 may emit light in
different wavelength ranges. For example, in an embodiment, the
display device DD may include a first light emitting element OEL-1
emitting red light, a second light emitting element OEL-2 emitting
green light, and a third light emitting element OEL-3 emitting blue
light. However, the embodiment of the inventive concept is not
limited thereto, and the first to third light emitting elements
OEL-1, OEL-2, and OEL-3 may emit light in a same wavelength range
or emit light in at least one different wavelength range. For
example, the blue light emitting region PXA-B, the green light
emitting region PXA-G, and the red light emitting region PXA-R of
the display device DD may correspond to the first light emitting
element OEL-1, the second light emitting element OEL-2, and the
third light emitting element OEL-3, respectively.
[0067] In an embodiment, the first to third light emitting elements
OEL-1, OEL-2, and OEL-3 may all emit light in a blue wavelength
range. The display device DD may further include a color control
layer on an upper part of the display element layer DP-OEL. The
color control layer may be a portion that transmits light provided
by the light emitting elements OEL-1, OEL-2, and OEL-3 or converts
wavelength.
[0068] Referring to FIG. 2, the blue light emitting regions PXA-B
and the red light emitting regions PXA-R may be alternately
arranged in a first direction axis DR1 to form a first group PXG1.
The green light emitting regions PXA-G may be arranged in the first
direction axis DR1 to form a second group PXG2. The first group
PXG1 may be disposed to be spaced apart from the second group PXG2
in a second direction axis DR2. The first group PXG1 and the second
group PXG2 each may be provided in plural. The first groups PXG1
and the second groups PXG2 may be alternately arranged in the
second direction axis DR2.
[0069] One green light emitting region PXA-G may be disposed to be
spaced apart from one blue light emitting region PXA-B or one red
light emitting region PXA-R in a fourth direction axis DR4. The
fourth direction axis DR4 may be a direction between the first
direction axis DR1 and the second direction axis DR2.
[0070] The arrangement structure of the light emitting regions
PXA-B, PXA-G, and PXA-R shown in FIG. 2 may have a pantile
structure. However, the arrangement structure of the light emitting
regions PXA-B, PXA-G, and PXA-R in the display device DD according
to an embodiment is not limited to the arrangement structure shown
in FIG. 2. For example, in an embodiment, the light emitting
regions PXA-B, PXA-G, and PXA-R may have a stripe structure where
the blue light emitting region PXA-B, the green light emitting
region PXA-G, and the red light emitting region PXA-R are
alternately arranged in the first direction axis DR1.
[0071] FIG. 4 is a schematic cross-sectional view of a light
emitting element according to an embodiment. FIG. 5 is a schematic
cross-sectional view illustrating a part of a light emitting
element according to an embodiment. FIG. 5 is a schematic
cross-sectional view illustrating a part corresponding to region AA
in FIG. 4. As described above, each of the light emitting elements
OEL-1, OEL-2, and OEL-3 included in the display device DD shown in
FIG. 3, etc. has a structure of a light emitting element OEL shown
in FIGS. 4 and 5.
[0072] The light emitting element OEL of an embodiment includes a
first electrode EL1, a hole transport region HTR disposed over the
first electrode EL1, an emission layer EML disposed over the hole
transport region HTR, an electron transport region ETR disposed
over the emission layer EML, and a second electrode EL2 disposed
over the electron transport region ETR. In the light emitting
device OEL of an embodiment, the hole transport region may include
a first hole transport layer HTL1 disposed adjacent to the first
electrode EL1, a second hole transport layer HTL2 disposed adjacent
to the emission layer EML, and a third hole transport layer HTL3
disposed between the first hole transport layer HTL1 and the second
hole transport layer HTL2.
[0073] In an embodiment, the first hole transport layer HTL1 and
the second hole transport layer HTL2 may be layers having a smaller
refractive index than the third hole transport layer HTL3. The
first refractive index of the first hole transport layer HTL1 is
less than the third refractive index of the third hole transport
layer HTL3, and the second refractive index of the second hole
transport layer HTL2 is less than the third refractive index of the
third hole transport layer HTL3.
[0074] In the light emitting element OEL of an embodiment, the
first electrode EL1 has conductivity. The first electrode EL1 may
be formed of a metal alloy or a conductive compound. The first
electrode EL1 may be an anode. The first electrode EL1 may be a
pixel electrode. The first electrode EL1 may be a reflective
electrode. When the first electrode EL1 is the reflective
electrode, the first electrode EL1 may include Ag, Mg, Cu, Al, Pt,
Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF/Ca, LiF/Al, Mo, Ti, a compound
thereof, or a mixture thereof (e.g., a mixture of Ag and Mg). In an
embodiment, the first electrode EL1 may have a structure in which
multiple layers are stacked. When the first electrode EL1 has a
structure in which multiple layers are stacked, at least one layer
may be a reflective film formed of a reflective electrode material.
When the first electrode EL1 has a structure in which multiple
layers are stacked, at least one layer may include a transparent
conductive film formed of indium tin oxide (ITO), indium zinc oxide
(IZO), zinc oxide (ZnO), indium tin zinc oxide (ITZO), etc. For
example, the first electrode EL1 may have a three-layer structure
of ITO/Ag/ITO, but it is not limited thereto. A thickness of the
first electrode EL1 may be in a range of about 1,000 .ANG. to about
10,000 .ANG.. For example, the thickness of the first electrode EL1
may be in a range of about 1,000 .ANG. to about 3,000 .ANG..
[0075] The hole transport region HTR is provided on the first
electrode EL1. The hole transport region HTR may include first to
third hole transport layers HTL1, HTL2, and HTL3. The first hole
transport layer HTL1 may be disposed under the third hole transport
layer HTL3 and the second hole transport layer HTL2 may be disposed
over the third hole transport layer HTL3 with respect to the third
hole transport layer HTL3 having a relatively greater refractive
index compared to other hole transport layers HTL1 and HTL2. In the
light emitting element OEL of an embodiment, the hole transport
region HTR may include hole transport layers HTL1, HTL2, and HTL3
arranged in the order of a low refractive hole transport layer/high
refractive hole transport layer/low refractive hole transport layer
in the thickness direction.
[0076] A difference between the first refractive index of the first
hole transport layer HTL1 and the third refractive index of the
third hole transport layer HTL3 may be greater than about 0.1. For
example, a difference between the first refractive index and the
third refractive index may be greater than or equal to about 0.2. A
difference between the second refractive index of the second hole
transport layer HTL2 and the third refractive index of the third
hole transport layer HTL3 may be greater than about 0.1. For
example, a difference between the second refractive index and the
third refractive index may be greater than or equal to about
0.2.
[0077] The first refractive index of the first hole transport layer
HTL1 may be in a range of about 1.2 to about 1.7, and the second
refractive index of the second hole transport layer HTL2 may be in
a range of about 1.2 to about 1.7. The third refractive index of
the third hole transport layer HTL3 may be in a range of about 1.7
to about 2.2. For example, the first refractive index of the first
hole transport layer HTL1 may be in a range of about 1.4 to about
1.6, and the second refractive index of the second hole transport
layer HTL2 may be in a range of about 1.4 to about 1.6, and the
third refractive index of the third hole transport layer HTL3 may
be in a range of about 1.9 to about 2.0.
[0078] A thickness of the hole transport region HTR may be in a
range of about 50 .ANG. to about 15000 .ANG.. For example, the
thickness of the hole transport region HTR may be in a range of
about 100 .ANG. to about 5000 .ANG.. The thickness ratio (D1:D3:D2)
of a thickness of the first hole transport layer HTL1 to a
thickness of the third hole transport layer HTL3 to a thickness of
the second hole transport layer HTL2 included in the hole transport
region HTR may be in a range of about 0.1:0.8:0.1 to about
0.45:0.1:0.45. For example, in an embodiment, the thickness D1 of
the first hole transport layer and the thickness D2 of the second
hole transport layer are substantially equal, and the thickness D3
of the third hole transport layer may be different from the
thickness D1 of the first hole transport layer and the thickness D2
of the second hole transport layer. However, the embodiment of the
inventive concept is not limited thereto, and the thickness D1 of
the first hole transport layer and the thickness D2 of the second
hole transport layer may be different from each other. The
thickness ratio (D1:D3:D2) of the thickness of the first hole
transport layer HTL1 to the thickness of the third hole transport
layer HTL3 to the thickness second hole transport layer HTL2 may be
optimally adjusted according to wavelength range of light emitted
from an emission layer EML, display quality required in the display
device DD (FIG. 2), and the type of a hole transport material used
in each of the hole transport layers HTL1, HTL2, and HTL3 of the
hole transport region HTR.
[0079] For example, in the light emitting element OEL of an
embodiment, when the emission layer EML emits blue light having a
central wavelength in a wavelength range of about 430 nm to about
470 nm, the thickness ratio (D1:D3:D2) of the thickness of the
first hole transport layer HTL1 to the thickness of the third hole
transport layer HTL3 to the thickness of the second hole transport
layer HTL2 may be about 1:1:1.
[0080] The light emitting element OEL of an embodiment may include
hole transport layers HTL1, HTL2, and HTL3 arranged in the order of
a low refractive hole transport layer/high refractive hole
transport layer/low refractive index hole transport layer, thereby
achieving improved luminous efficiency characteristics. The light
emitting element OEL of an embodiment may include the hole
transport layers HTL1, HTL2, and HTL3 of the hole transport region
HTR having different refractive indices to minimize light emitted
from functional layers inside to disappear due to destructive
interference, and to create constructive interference by the hole
transport layers HTL1, HTL2, and HTL3 having different refractive
indices, thereby achieving high light extraction efficiency.
[0081] In an embodiment, the first hole transport layer HTL1 may be
directly disposed over the first electrode EL1. The second hole
transport layer HTL2 may be directly disposed under the emission
layer EML.
[0082] In the description, "directly disposed" may mean that there
is no layer, film, region, plate or the like added between a
portion of a layer, a film, a region, a plate or the like and other
portions. For example, "directly disposed" means disposing without
additional members, such as an adhesive member between two
layers.
[0083] In the light emitting element OEL of an embodiment, the
refractive index of the first electrode EL1 may be in a range of
about 1.7 to about 2.2. For example, the refractive index of the
first electrode EL1 may be in a range of about 1.9 to about 2.0.
For example, the refractive index of the first electrode EL1 may be
greater than the first refractive index of the first hole transport
layer HTL1, and a difference in the refractive index between the
first hole transport layer HTL1 and the first electrode ELL which
are adjacent to each other, may be greater than about 0.1.
[0084] In the light emitting element OEL of an embodiment, the
refractive index of the emission layer EML may be in a range of
about 1.7 to about 2.2. For example, the refractive index of the
emission layer EML may be in a range of about 1.9 to about 2.0. For
example, the refractive index of the emission layer EML may be
greater than the second refractive index of the second hole
transport layer HTL2, and a difference in the refractive index
between the second hole transport layer HTL2 and the emission layer
EML, which are adjacent to each other, may be greater than about
0.1.
[0085] For example, the light emitting element OEL of an embodiment
includes a hole transport region HTR, in which hole transport
layers HTL1 and HTL2 having different refractive indices from the
adjacent first electrode EL1 or the emission layer EML are
disposed, to achieve light extraction efficiency characteristics
and improved luminous efficiency characteristics.
[0086] The first hole transport layer HTL1 and the second hole
transport layer HTL2 may each independently include at least one of
the compounds represented by Formulas 1-1 to 1-4 below. The
compounds represented by Formulas 1-1 to 1-4 may have a refractive
index in a range of about 1.2 to about 1.7. The first hole
transport layer HTL1 and the second hole transport layer HTL2 each
may each independently be formed of any one of the compounds
represented by Formulas 1-1 to 1-4, or mixtures thereof.
##STR00003##
[0087] In Formulas 1-1 to 1-4 above, A.sub.1 to A5 may be each
independently a hydrogen atom, a deuterium atom, a halogen atom, a
hydroxyl group, a cyano group, a nitro group, an amino group, a
substituted or unsubstituted silyl group, a substituted or
unsubstituted oxy group, a substituted or unsubstituted alkyl group
having 1 to 60 carbon atoms, a substituted or unsubstituted aryl
group having 6 to 60 ring-forming carbon atoms, a substituted or
unsubstituted heteroaryl group having 2 to 60 ring-forming carbon
atoms. In Formula 1-2, a may be an integer from 0 to 5, and in
Formula 1-3, b may be an integer from 0 to 4, and in Formula 1-4, c
may be an integer from 0 to 6.
[0088] In the description, the term "substituted or unsubstituted"
may indicate that one is substituted or unsubstituted with at least
one substituent selected from the group consisting of a deuterium
atom, a halogen atom, a cyano group, a nitro group, an amino group,
a silyl group, oxy group, thio group, sulfinyl group, sulfonyl
group, carbonyl group, a boron group, a phosphine oxide group, a
phosphine sulfide group, an alkyl group, an alkenyl group, an
alkynyl group, an alkoxy group, a hydrocarbon ring group, an aryl
group, and a heterocyclic group. Each of the substituents recited
above may be substituted or unsubstituted. For example, a biphenyl
group may be interpreted as an aryl group or a phenyl group
substituted with a phenyl group.
[0089] In the description, the term "bonded to an adjacent group to
form a ring" may indicate that one is bonded to an adjacent group
to form a substituted or unsubstituted hydrocarbon ring, or a
substituted or unsubstituted heterocycle. The hydrocarbon ring
includes an aliphatic hydrocarbon ring and an aromatic hydrocarbon
ring. The heterocycle includes an aliphatic heterocycle and an
aromatic heterocycle. Rings formed by being bonded to an adjacent
group may be monocyclic or polycyclic. The rings formed by being
bonded to each other may be connected to another ring to form a
spiro structure.
[0090] In the description, the term "an adjacent group" may mean a
substituent substituted for an atom which is directly connected to
an atom substituted with a corresponding substituent, another
substituent substituted for an atom which is substituted with a
corresponding substituent, or a substituent sterically positioned
at the nearest position to a corresponding substituent. For
example, two methyl groups in 1,2-dimethylbenzene may be
interpreted as mutually "adjacent groups" and two ethyl groups in
1,1-diethylcyclopentane may be interpreted as mutually "adjacent
groups".
[0091] In the description, examples of a halogen atom may include a
fluorine atom, a chlorine atom, a bromine atom, and an iodine
atom.
[0092] In the description, an alkyl group may be a linear,
branched, or cyclic type. The number of carbon atoms in the alkyl
group is 1 to 50, 1 to 30, 1 to 20, 1 to 10, or 1 to 6. Examples of
the alkyl group may include a methyl group, an ethyl group, an
n-propyl group, an isopropyl group, an n-butyl group, a s-butyl
group, a t-butyl group, an i-butyl group, a 2-ethylbutyl group, a
3,3-a dimethylbutyl group, an n-pentyl group, an i-pentyl group, a
neopentyl group, a t-pentyl group, a cyclopentyl group, a
1-methylpentyl group, a 3-methylpentyl group, a 2-ethylpentyl
group, a 4-methyl-2-pentyl group, an n-hexyl group, a 1-methylhexyl
group, a 2-ethylhexyl group, a 2-butylhexyl group, a cyclohexyl
group, a 4-methylcyclohexyl group, a 4-t-butylcyclohexyl group, an
n-heptyl group, a 1-methylheptyl group, a 2,2-dimethylheptyl group,
a 2-ethylheptyl group, a 2-butylheptyl group, an n-octyl group, a
t-octyl group, a 2-ethyloctyl group, a 2-butyloctyl group, a
2-hexyloctyl group, a 3,7-dimethyloctyl group, a cyclooctyl group,
an n-nonyl group, an n-decyl group, an adamantyl group, a
2-ethyldecyl group, a 2-butyldecyl group, a 2-hexyldecyl group, a
2-octyldecyl group, an n-undecyl group, an n-dodecyl group, a
2-ethyldodecyl group, a 2-butyldodecyl group, a 2-hexyldocecyl
group, a 2-octyldodecyl group, an n-tridecyl group, an n-tetradecyl
group, an n-pentadecyl group, an n-hexadecyl group, a
2-ethylhexadecyl group, a 2-butylhexadecyl group, a
2-hexylhexadecyl group, a 2-octylhexadecyl group, an n-heptadecyl
group, an n-octadecyl group, an n-nonadecyl group, an n-eicosyl
group, a 2-ethyleicosyl group, a 2-butyleicosyl group, a
2-hexyleicosyl group, a 2-octyleicosyl group, an n-henicosyl group,
an n-docosyl group, an n-tricosyl group, an n-tetracosyl group, an
n-pentacosyl group, an n-hexacosyl group, an n-heptacosyl group, an
n-octacosyl group, an n-nonacosyl group, an n-triacontyl group,
etc., but are not limited thereto.
[0093] In the description, an aryl group means any functional group
or substituent derived from an aromatic hydrocarbon ring. The aryl
group may be a monocyclic aryl group or a polycyclic aryl group.
The number of ring-forming carbon atoms in the aryl group may be 6
to 30, 6 to 20, or 6 to 15. Examples of the aryl group may include
a phenyl group, a naphthyl group, a fluorenyl group, an anthracenyl
group, a phenanthryl group, a biphenyl group, a terphenyl group, a
quaterphenyl group, a quinquephenyl group, a sexiphenyl group, a
triphenylenyl group, a pyrenyl group, a benzofluoranthenyl group, a
chrysenyl group, etc., but are not limited thereto.
[0094] In the description, a fluorenyl group may be substituted,
and two substituents may be bonded to each other to form a spiro
structure. An example that the fluorenyl group is substituted is as
follows. However, the embodiment of the inventive concept is not
limited thereto.
##STR00004##
[0095] In the description, a heteroaryl group may include at least
one of B, O, N, P, Si, or S as a hetero atom. When the heteroaryl
group contains two or more hetero atoms, the two or more hetero
atoms may be the same as or different from each other. The
heteroaryl group may be a monocyclic heteroaryl group or a
polycyclic heteroaryl group. The number of ring-forming carbon
atoms in the heteroaryl group may be 2 to 30, 2 to 20, or 2 to 10.
Examples of the heteroaryl group may include a thiophene group, a
furan group, a pyrrole group, an imidazole group, a triazole group,
a pyridine group, a bipyridine group, a pyrimidine group, a
triazine group, a triazole group, an acridyl group, a pyridazine
group, a pyrazinyl group, a quinoline group, a quinazoline group, a
quinoxaline group, a phenoxazine group, a phthalazine group, a
pyrido pyrimidine group, a pyrido pyrazine group, a pyrazino
pyrazine group, an isoquinoline group, an indole group, a carbazole
group, an N-arylcarbazole group, an N-heteroarylcarbazole group, an
N-alkylcarbazole group, a benzoxazole group, a benzoimidazole
group, a benzothiazole group, a benzocarbazole group, a
benzothiophene group, a dibenzothiophene group, a thienothiophene
group, a benzofuran group, a phenanthroline group, a thiazole
group, an isoxazole group, an oxazole group, an oxadiazole group, a
thiadiazole group, a phenothiazine group, a dibenzosilole group, a
dibenzofuran group, etc., but are not limited thereto.
[0096] In the description, the above description on the aryl group
may be applied to an arylene group, except that the arylene group
is a divalent group. The above description on the heteroaryl group
may be applied to a heteroarylene group, except that the
heteroarylene group is a divalent group.
[0097] In the description, a silyl group includes an alkyl silyl
group and an aryl silyl group. Examples of the silyl group include
a trimethylsilyl group, a triethylsilyl group, a
t-butyldimethylsilyl group, a vinyldimethylsilyl group, a
propyldimethylsilyl group, a triphenylsilyl group, a diphenylsilyl
group, a phenylsilyl group, etc., but are not limited thereto.
[0098] In the description, the number of carbon atoms in an amino
group is not particularly limited, but may be 1 to 30. The amino
group may include an alkyl amino group, an aryl amino group, or a
heteroaryl amino group. Examples of the amino group include a
methylamino group, a dimethylamino group, a phenylamino group, a
diphenylamino group, a naphthylamino group, a
9-methyl-anthracenylamino group, a triphenylamino group, etc., but
are not limited thereto.
[0099] The third hole transport layer HTL3 may include a compound
represented by Formula 2 below. The compound represented by Formula
2 may have a refractive index in a range of about 1.7 to about
2.2.
##STR00005##
[0100] In Formula 2 above, Ar.sub.1 and Ar.sub.2 may be each
independently a hydrogen atom, a deuterium atom, a halogen atom, a
substituted or unsubstituted alkyl group having 1 to 30 carbon
atoms, a substituted or unsubstituted aryl group having 6 to 30
carbon atoms, a substituted or unsubstituted heteroaryl group
having 2 to 30 ring-forming carbon atoms, or bonded to an adjacent
group to form a ring. Ara may be a substituted or unsubstituted
aryl group having 6 to 30 ring-forming carbon atoms or a
substituted or unsubstituted heteroaryl group having 2 to 30
ring-forming carbon atoms. In Formula 2, a and b may be each
independently 0 or 1, and L.sub.1 and L.sub.2 may be each
independently a substituted or unsubstituted cycloalkylene group
having 3 to 10 ring-forming carbon atoms, a substituted or
unsubstituted heterocycloalkylene group having 2 to 10 ring-forming
carbon atoms, a substituted or unsubstituted cycloalkenylene group
having 3 to 10 ring-forming carbon atoms, a substituted or
unsubstituted arylene group having 6 to 30 ring-forming carbon
atoms, or a substituted or unsubstituted heteroarylene group having
2 to 60 ring-forming carbon atoms. In Formula 2, p and s may be
each independently an integer from 0 to 4, q and r may be each
independently an integer from 0 to 3, and R.sub.1 to R.sub.5 may be
each independently a hydrogen atom, a deuterium atom, a halogen
atom, a hydroxyl group, a cyano group, a nitro group, an amino
group, a substituted or unsubstituted silyl group, a substituted or
unsubstituted oxy group, a substituted or unsubstituted alkyl group
having 1 to 60 carbon atoms, a substituted or unsubstituted
heterocycloalkyl group having 3 to 60 ring-forming carbon atoms, a
substituted or unsubstituted aryl group having 6 to 60 ring-forming
carbon atoms, or a substituted or unsubstituted heteroaryl group
having 2 to 60 ring-forming carbon atoms.
[0101] The compound for the third hole transport layer HTL3
represented by Formula 2 may be represented by any one of the
compounds of Compound Group 1 below, which contains Compounds 1 to
69. The third hole transport layer HTL3 in the light emitting
element OEL of an embodiment may include at least one of Compounds
1 to 69 of Compound Group 1.
##STR00006## ##STR00007## ##STR00008## ##STR00009## ##STR00010##
##STR00011## ##STR00012## ##STR00013## ##STR00014## ##STR00015##
##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020##
##STR00021## ##STR00022## ##STR00023##
[0102] The hole transport region HTR of the light emitting element
OEL of an embodiment may only include three hole transport layers
HTL1, HTL2, and HTL3. The light emitting element OEL of an
embodiment may include hole transport layers in which the first
hole transport layer HTL1/third hole transport layer HTL3/second
hole transport layer HTL2 are stacked in order between the first
electrode EL1 and the emission layer EML, thereby achieving
excellent luminous efficiency characteristics. In an embodiment,
the refractive indices of the first hole transport layer HTL1 and
the second hole transport layer HTL2 are less than the refractive
index of the third hole transport layer HTL3, and a difference in
the refractive index may be greater than about 0.1.
[0103] The emission layer EML is provided on the hole transport
region HTR. A thickness of the emission layer EML may be, for
example, in a range of about 100 .ANG. to about 1000 .ANG.. For
example, the thickness of the emission layer EML may be in a range
of about 100 .ANG. to about 300 .ANG.. The emission layer EML may
have a single layer formed of a single material, a single layer
formed of different materials, or a multilayer structure having
multiple layers formed of different materials.
[0104] The emission layer EML may emit one of red, green, blue,
white, yellow, or cyan light. The emission layer EML may include a
fluorescence light emitting material or a phosphorescence light
emitting material. In an embodiment, the emission layer EML may
include quantum dots.
[0105] In the light emitting element OEL of an embodiment, the
emission layer EML may include an anthracene derivative, a pyrene
derivative, a fluoranthene derivative, a chrysene derivative, a
dihydrobenzanthracene derivative, a triphenylene derivative, etc.
For example, the emission layer EML may include an anthracene
derivative, a pyrene derivative, etc. However, the embodiment of
the inventive concept is not limited thereto, and the emission
layer EML may include a known light emitting material.
[0106] In the light emitting element OEL of an embodiment, the
electron transport region ETR is provided on the emission layer
EML. The electron transport region ETR may include at least one of
a hole blocking layer, an electron transport layer, or an electron
injection layer, but the embodiment of the inventive concept is not
limited thereto.
[0107] The electron transport region ETR may have a single layer
formed of a single material, a single layer formed of different
materials, or a multilayer structure including layers formed of
different materials.
[0108] For example, the electron transport region ETR may have a
single layer structure of an electron injection layer EIL or an
electron transport layer ETL, and may have a single layer structure
formed of an electron injection material and an electron transport
material. The electron transport region ETR may have a single layer
structure formed of different materials, or may have a structure in
which an electron transport layer/electron injection layer and a
hole blocking layer/electron transport layer/electron injection
layer are stacked in order from the emission layer EML, but is not
limited thereto. The thickness of the electron transport region ETR
may be, for example, in a range of about 1,000 .ANG. to about 1,500
.ANG..
[0109] When the electron transport region ETR includes the electron
injection layer, the electron transport region ETR may be a
halogenated metal such as LiF, NaCl, CsF, RbCl, RbI, and Cul, a
lanthanide metal such as Yb, a metal oxide such as Li.sub.2O, BaO,
or lithium quinolate (LiQ), but is not limited thereto. The
electron injection layer may also be formed of a mixture material
of an electron transport material and an insulating organo-metal
salt. The organo-metal salt may be a material having an energy band
gap of greater than or equal to about 4 eV. For example, the
organo-metal salt may include, metal acetates, metal benzoates,
metal acetoacetates, metal acetylacetonates, or metal stearates.
When the electron transport region ETR includes the electron
transport layer, the electron transport region ETR may include an
anthracene-based compound. However, the embodiment of the inventive
concept is not limited thereto, and the electron transport region
ETR may include a known electron transport material.
[0110] The second electrode EL2 is provided on the electron
transport region ETR. The second electrode EL2 may be a common
electrode or a cathode. The second electrode EL2 may be a
transmissive electrode or a transflective electrode. If the second
electrode EL2 is the transmissive electrode, the second electrode
EL2 may include a transparent metal oxide, for example, indium tin
oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium tin
zinc oxide (ITZO), etc. If the second electrode EL2 is the
transflective electrode, the second electrode EL2 may include Ag,
Mg, Cu, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF/Ca, LiF/Al, Mo,
Ti, a compound thereof, or a mixture thereof (e.g., a mixture of Ag
and Mg). The second electrode EL2 may have a multilayer structure
including a reflective film or a transflective film formed of the
above-described materials, and a transparent conductive film formed
of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide
(ZnO), indium tin zinc oxide (ITZO), etc.
[0111] A capping layer (not shown) may be disposed on the second
electrode EL2 of the light emitting element OEL of an embodiment.
The capping layer (not shown) may include, for example,
.alpha.-NPD, NPB, TPD, m-MTDATA, Alq.sub.3, CuPc,
N4,N4,N4',N4'-tetra(biphenyl-4-yl) biphenyl-4,4'-diamine (TPD15),
4,4',4''-tris(carbazol sol-9-yl)triphenylamine (TCTA), N,
N'-bis(naphthalen-1-yl), etc.
[0112] A display device of an embodiment may include light emitting
elements, and at least one light emitting element among the light
emitting elements may have a configuration of the light emitting
element according to an embodiment described above.
[0113] Referring back to FIG. 3, the display device DD of an
embodiment includes first to third light emitting elements OEL-1,
OEL-2, and OEL-3 separated by a pixel defining layer PDL and the
first to third light emitting elements OEL-1, OEL-2, and OEL-3 have
different configurations of emission layers EML-B, EML-G, and
EML-R, and thus may emit light in different wavelength ranges. One
of the first to third light emitting elements OEL-1, OEL-2, and
OEL-3 may have the configuration of the light emitting element of
FIGS. 4 and 5 described above. In an embodiment, two light emitting
elements selected from the first to third light emitting elements
OEL-1, OEL-2, and OEL-3 or all three light emitting elements may
have the configuration of the light emitting element of FIGS. 4 and
5 described above.
[0114] When all three light emitting elements OEL-1, OEL-2, and
OEL-3 in the display device DD of an embodiment have the
configuration of the light emitting element of FIGS. 4 and 5
described above, the hole transport region HTR may be provided as a
common layer in all of the first to third light emitting elements
OEL-1, OEL-2, and OEL-3. For example, the hole transport region HTR
provided as the common layer may have a structure including the
first to third hole transport layers HTL1, HTL2, and HTL3.
[0115] In the display device of an embodiment, unlike the one
illustrated in FIG. 3, the hole transport region HTR is disposed in
an opening OH defined in the pixel defining layer PDL, and may be
provided to be separated to correspond to the emission layers
EML-B, EML-G, and EML-R. The hole transport regions HTR included in
each of the light emitting elements OEL-1, OEL-2, and OEL-3 have a
structure including the first to third hole transport layers HTL1,
HTL2, and HTL3. When the hole transport region HTR is provided to
be separated to correspond not to the common layer but to the light
emitting elements OEL-1, OEL-2, and OEL-3, the thickness ratio of
the first to third hole transport layers HTL1, HTL2, and HTL3
included in each of the light emitting element OEL-1, OEL-2, and
OEL-3 may be controlled to vary according to the wavelength range
of light emitted from each of the light emitting elements OEL-1,
OEL-2, and OEL-3.
[0116] In the display device DD of another embodiment, the first
light emitting element OEL-1 emitting blue light may have a light
emitting element structure including first to third hole transport
layers HTL1, HTL2, and HTL3. However, the embodiment of the
inventive concept is not limited thereto.
[0117] FIG. 6 is a graph showing comparison of luminous efficiency
of Comparative Examples and Examples. Example shows evaluation
results for light emitting elements having a hole transport region
structure of the light emitting element of an embodiment described
above, and Comparative Examples 1 to 4 show evaluation results for
light emitting elements having a hole transport region
configuration which is different from Example. The configuration of
other functional layers of the light emitting elements was the same
in Comparative Examples and Example, except the configuration of
the hole transport region. Comparative Examples and Example are
light emitting elements emitting blue light having a central
wavelength in the vicinity of 464 nm.
[0118] Comparative Examples 1 and 2 are the cases in which the hole
transport region is formed of one hole transport layer,
respectively. Comparative Example 1 is the case of including only
one hole transport layer having a refractive index of about 1.9,
and Comparative Example 2 is the case of including only one hole
transport layer having a refractive index of about 1.4.
[0119] Comparative Examples 3 and 4 are the cases where the hole
transport region is formed of two-layered hole transport layers,
respectively. In Comparative Example 3, the refractive index of the
hole transport layer adjacent to the first electrode was about 1.4,
and the refractive index of the hole transport layer adjacent to
the emission layer was about 1.9. In Comparative Example 4, the
refractive index of the hole transport layer adjacent to the first
electrode was about 1.9, and the refractive index of the hole
transport layer adjacent to the emission layer was about 1.4. For
example, Comparative Examples 3 and 4 are the cases where the
stacking order of the low-refractive hole transport layer and the
high-refractive hole transport layer is different.
[0120] Example has the structure of the hole transport region of
the light emitting element described above, which is the case where
three-layered hole transport layers are included, the refractive
indices of the first hole transport layer adjacent to the first
electrode and the second hole transport layer adjacent to the
emission layer are about 1.4, respectively, the refractive index of
the third hole transport layer disposed between the first hole
transport layer and the second hole transport layer is about
1.9.
[0121] In FIG. 6, the horizontal axis refers to a color coordinate
value and corresponds to a "y" value of the color coordinate of
light emitted from a light emitting element. The value shown in the
horizontal axis in FIG. 6 corresponds to a y value in CIE color
coordinates. The graph of FIG. 6 shows luminous efficiency
according to the color coordinate of emitted light. Referring to
the results of FIG. 6, it is seen that in a color coordinate value
of 0.04 to 0.1, the light emitting element of Example showed higher
luminous efficiency than those of Comparative Example. Example
showed improved luminous efficiency of about 34% compared to
Comparative Example 1.
[0122] The light emitting element of an embodiment includes a hole
transport region having a stacked structure of a low-refractive
hole transport layer/high-refractive hole transport
layer/low-refractive hole transport layer to exhibit a high light
extraction effect, thereby achieving excellent luminous efficiency
characteristics. The di splay device of an embodiment may include a
light emitting element having a hole transport region in which hole
transport layers having different refractive indices are stacked,
thereby having high luminance characteristics.
[0123] A light emitting element of an embodiment may achieve
improved light extraction characteristics by including hole
transport layers having different refractive indices.
[0124] A light emitting element of an embodiment may achieve
excellent light luminous efficiency by including a light emitting
element containing hole transport layers having different
refractive indices.
[0125] Although the inventive concept has been described with
reference to embodiments of the inventive concept, it will be
understood that the inventive concept should not be limited to
these embodiments, but various changes and modifications can be
made by those skilled in the art without departing from the spirit
and scope of the inventive concept.
[0126] Accordingly, the technical scope of the inventive concept is
not intended to be limited to the contents set forth in the
detailed description of the specification, but is intended to be
defined by the appended claims.
* * * * *