U.S. patent application number 14/884952 was filed with the patent office on 2016-06-09 for organic light emitting display device.
This patent application is currently assigned to LG DISPLAY CO., LTD.. The applicant listed for this patent is LG Display Co., Ltd.. Invention is credited to Jaeseung JANG, DongHyuk KIM, Jaeil SONG.
Application Number | 20160163771 14/884952 |
Document ID | / |
Family ID | 54251383 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160163771 |
Kind Code |
A1 |
JANG; Jaeseung ; et
al. |
June 9, 2016 |
ORGANIC LIGHT EMITTING DISPLAY DEVICE
Abstract
An organic light emitting display device is disclosed. The
organic light emitting display device includes a first light
emitting part between an anode and a cathode, the first light
emitting part having a first light emitting layer, and a second
light emitting part between the first light emitting part and the
cathode, the second light emitting part having a second light
emitting layer and a third light emitting layer, wherein the second
light emitting layer includes a hole-type host and a first
electron-type host, and the third light emitting layer includes a
first electron-type host and a second electron-type host.
Inventors: |
JANG; Jaeseung; (Seoul,
KR) ; SONG; Jaeil; (Gyeonggi-do, KR) ; KIM;
DongHyuk; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Display Co., Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG DISPLAY CO., LTD.
Seoul
KR
|
Family ID: |
54251383 |
Appl. No.: |
14/884952 |
Filed: |
October 16, 2015 |
Current U.S.
Class: |
257/40 |
Current CPC
Class: |
H01L 51/5004 20130101;
H01L 2251/552 20130101; H01L 51/5092 20130101; H01L 2251/5384
20130101; H01L 2251/55 20130101; H01L 51/504 20130101; H01L 27/3206
20130101; H01L 27/3209 20130101; H01L 51/5278 20130101 |
International
Class: |
H01L 27/32 20060101
H01L027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2014 |
KR |
10-2014-0175347 |
Claims
1. An organic light emitting display device, comprising: a first
light emitting part between an anode and a cathode, the first light
emitting part having a first light emitting layer; and a second
light emitting part between the first light emitting part and the
cathode, the second light emitting part having a second light
emitting layer and a third light emitting layer, wherein the second
light emitting layer includes a hole-type host and a first
electron-type host, and the third light emitting layer includes a
first electron-type host and a second electron-type host.
2. The organic light emitting display device of claim 1, wherein
the LUMO (lowest unoccupied molecular orbital) level of the first
electron-type host is within a range from -2.3 eV to -2.5 eV, and
the LUMO (lowest unoccupied molecular orbital) level of the second
electron-type host is within a range from -2.6 eV to -2.8 eV.
3. The organic light emitting display device of claim 2, wherein
the difference in LUMO levels between the first electron-type host
and the second electron-type host is equal to or less than 0.5
eV.
4. The organic light emitting display device of claim 1, wherein
the HOMO level of the first electron-type host and the second
electron-type host is within a range from -5.4 eV to -5.8 eV.
5. The organic light emitting display device of claim 1, wherein
the electron mobility of the first electron-type host is equal to
or lower than 1.times.10.sup.-5 cm.sup.2/Vs, and the electron
mobility of the second electron-type host is within a range from
1.times.10.sup.-5 cm.sup.2/Vs to 1.times.10.sup.-4 cm.sup.2/Vs.
6. The organic light emitting display device of claim 1, wherein
the second light emitting layer and the third light emitting layer
includes a yellow-green light emitting layer.
7. The organic light emitting display device of claim 1, further
comprising a third light emitting part between the second light
emitting part and the cathode, the third light emitting part having
a fourth light emitting layer.
8. The organic light emitting display device of claim 1, wherein an
occupied volume ratio of the first electron-type host in the third
light emitting layer is equal to or larger than an occupied volume
ratio of the second electron-type host in the third light emitting
layer.
9. The organic light emitting display device of claim 1, wherein an
occupied volume ratio of the first electron-type host adjacent to
the second light emitting layer is equal to or larger than an
occupied volume ratio of the second electron-type host adjacent to
the cathode.
10. An organic light emitting display device, comprising: a first
light emitting part between an anode and a cathode, the first light
emitting part having a first light emitting layer; and a second
light emitting part over the first light emitting part, the second
light emitting part having a second light emitting layer, wherein
the second light emitting layer includes two regions so that light
emission occurs within the second light emitting layer, one of the
two regions having a hole-type host and a first electron-type host
to adjust electron injection into the second light emitting layer
and improve the lifetime of the second light emitting layer, and
the other one of the two regions having a first electron-type host
and a second electron-type host, the first electron-type host and
the second electron-type host having different electron mobilities
from each other.
11. The organic light emitting display device of claim 10, wherein
the second light emitting layer includes a yellow-green light
emitting layer.
12. The organic light emitting display device of claim 10, wherein
the electron mobility of the first electron-type host is lower than
the electron mobility of the second electron-type host so as to
improve electron injection into the second light emitting
layer.
13. The organic light emitting display device of claim 12, wherein
the electron mobility of the first electron-type host is equal to
or lower than 1.times.10.sup.-5 cm.sup.2/Vs, and the electron
mobility of the second electron-type host is within a range from
1.times.10.sup.-5 cm.sup.2/Vs to 1.times.10.sup.-4 cm.sup.2/Vs.
14. The organic light emitting display device of claim 10, wherein
the difference in LUMO (lowest unoccupied molecular orbital) levels
between the first electron-type host and the second electron-type
host is small so as to improve electron injection into the second
light emitting layer.
15. The organic light emitting display device of claim 14, wherein
the difference in LUMO (lowest unoccupied molecular orbital) levels
between the first electron-type host and the second electron-type
host is equal to or less than 0.5 eV.
16. The organic light emitting display device of claim 10, wherein
an organic light emitting display device including one of the two
regions of the second light emitting layer having a hole-type host
and a first electron-type host and the other one of the two regions
having first and second electron-type hosts having a different
electron mobility has increased lifetime of the organic light
emitting display device, as compared with an organic light emitting
display device having a hole-type host and an electron-type
host.
17. The organic light emitting display device of claim 10, further
comprising a third light emitting part having a third light
emitting layer between the second light emitting part and the
cathode.
18. The organic light emitting display device of claim 10, wherein
an occupied volume ratio of the first electron-type host in the
other region is equal to or larger than an occupied volume ratio of
the second electron-type host in the other region.
19. The organic light emitting display device of claim 1, wherein
an occupied volume ratio of the first electron-type host adjacent
to the anode is equal to or larger than an occupied volume ratio of
the second electron-type host adjacent to the cathode.
Description
[0001] This application claims the priority benefit of Korean
Patent Application No. 10-2014-0175347 filed on Dec. 8, 2014, which
is incorporated herein by reference for all purposes as if fully
set forth herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an organic light emitting
display device, and more particularly, to an organic light emitting
display device which is capable of improving lifetime.
[0004] 2. Discussion of the Related Art
[0005] Image displays used for displaying a variety of information
on the screen are one of the core technologies of the information
and communication era. Such image displays have been developed to
be thinner, lighter, and more portable, and furthermore to have
high performance. With the development of the information society,
various demands for display devices are on the rise. To meet these
demands, research on panel displays such as liquid crystal displays
(LCD), plasma display panels (PDP), electroluminescent displays
(ELD), field emission displays (FED), organic light emitting diodes
(OLED), etc is actively under way.
[0006] Among these types of panel displays, the OLED devices are a
type of devices that, when a charge is injected into an organic
light emitting layer formed between an anode and a cathode, emit
light as electron-hole pairs are produced and dissipated. The OLED
devices are advantageous in that they can be formed on a flexible
transparent substrate such as plastic, can be driven at relatively
low voltage, less power consumption, and excellent color
sensitivity, as compared to plasma display panels or inorganic EL
displays. Especially, white OLED devices are used for various
purposes in lighting, thin light sources, backlights for liquid
crystal displays, or full-color displays employing color
filters.
[0007] A typical organic light emitting display device is formed of
organic materials stacked between an anode and a cathode. When a
voltage is applied to the organic light emitting display device,
holes are injected from the anode, and electrons are injected from
the cathode. The injected charges move to the opposite electrode
according to the energy levels of the organic layers, and are
combined together in a light emitting layer of organic materials to
form excitons. When the excitons fall to the ground state, they
decay into thermal energy or emit light. As recent research into
high-efficiency organic light emitting display devices continues,
phosphorescent devices using two types of host and one type of
dopant are becoming a mainstream through improvements to the light
emitting layer. Especially, materials for the two types of host are
chosen in consideration of the properties of each charge of
hole-type and electron type.
[0008] However, phosphorescent devices using two types of host and
one type of dopant have not achieved improvements in lifetime
though phosphorescent devices have done in efficiency. The reason
of this is that a light emission area formed between a hole
transport layer and a light emitting layer causes an interface
degradation and an exciton-polaron interaction leads to a lifetime
reduction. The cause of the interface degradation and lifetime
reduction is the high electron density in the light emission area.
High electron densities move the light emission area toward the
hole transport layer and exert electric stress on the dopant, thus
accelerating the degradation. As a result, the lifetime of the
organic light emitting display device is reduced.
SUMMARY
[0009] Accordingly, the present invention is directed to an organic
light emitting display device that substantially obviates one or
more of the problems due to limitations and disadvantages of the
related art.
[0010] An object of the present invention is to provide an organic
light emitting display device which is capable of improving the
lifetime of the device.
[0011] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
[0012] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described, an
organic light emitting display device comprises a first light
emitting part between an anode and a cathode, the first light
emitting part having a first light emitting layer, and a second
light emitting part between the first light emitting part and the
cathode, the second light emitting part having a second light
emitting layer and a third light emitting layer, wherein the second
light emitting layer includes a hole-type host and a first
electron-type host, and the third light emitting layer includes a
first electron-type host and a second electron-type host.
[0013] The LUMO (lowest unoccupied molecular orbital) level of the
first electron-type host is within a range from -2.3 eV to -2.5 eV,
and the LUMO (lowest unoccupied molecular orbital) level of the
second electron-type host is within a range from -2.6 eV to -2.8
eV.
[0014] The difference in LUMO levels between the first
electron-type host and the second electron-type host is equal to or
less than 0.5 eV.
[0015] The HOMO level of the first electron-type host and second
electron-type host is within a range from -5.4 eV to -5.8 eV.
[0016] The electron mobility of the first electron-type host may be
equal to or lower than 1.times.10.sup.-5 cm.sup.2/Vs, and the
electron mobility of the second electron-type host is within a
range from 1.times.10.sup.-5 cm.sup.2/Vs to 1.times.10.sup.-4
cm.sup.2/Vs.
[0017] The second light emitting layer and the third light emitting
layer include yellow-green light emitting layers.
[0018] The organic light emitting display device further comprises
a third light emitting part between the second light emitting part
and the cathode, the third light emitting part having a fourth
light emitting layer.
[0019] An occupied volume ratio of the first electron-type host in
the third light emitting layer may be equal to or larger than an
occupied volume ratio of the second electron-type host in the third
light emitting layer.
[0020] An occupied volume ratio of the first electron-type host
adjacent to the second light emitting layer may be equal to or
larger than an occupied volume ratio of the second electron-type
host adjacent to the cathode.
[0021] In another aspect, an organic light emitting display device
comprises a first light emitting part between an anode and a
cathode, the first light emitting part having a first light
emitting layer, and a second light emitting part between the first
light emitting part and the cathode, the second light emitting part
having a second light emitting layer, wherein the second light
emitting layer includes two regions so that light emission occurs
within the second light emitting layer, one of the two regions
having a hole-type host and a first electron-type host to adjust
electron injection into the second light emitting layer and improve
the lifetime of the second light emitting layer, and the other one
of the two regions having a first electron-type host and a second
electron-type host the first electron-type host and the second
electron-type host having a different electron mobility from each
other.
[0022] The second light emitting layer includes a yellow-green
light emitting layer.
[0023] The electron mobility of the first electron-type host is
lower than the electron mobility of the second electron-type host
so as to improve electron injection into the second light emitting
layer.
[0024] The electron mobility of the first electron-type host is
equal to or lower than 1.times.10.sup.-5 cm.sup.2/Vs, and the
electron mobility of the second electron-type host is within a
range from 1.times.10.sup.-5 cm.sup.2/Vs to 1.times.10.sup.-4
cm.sup.2/Vs.
[0025] The difference in LUMO (lowest unoccupied molecular orbital)
levels between the first electron-type host and the second
electron-type host is small so as to improve electron injection
into the second light emitting layer.
[0026] The difference in LUMO (lowest unoccupied molecular orbital)
levels between the first electron-type host and the second
electron-type host is equal to or less than 0.5 eV.
[0027] An organic light emitting display device includes one of two
regions of the second light emitting layer having a hole-type host
and a first electron-type host and the other one of the two regions
having first and second electron-type hosts having a different
electron mobility has increased lifetime of the organic light
emitting display device, as compared with the second light emitting
layer having a hole-type host and an electron-type host.
[0028] The organic light emitting display device further comprises
a third light emitting part having a third light emitting layer
between the second light emitting part and the cathode.
[0029] An occupied volume ratio of the first electron-type host in
the other region may be equal to or larger than an occupied volume
ratio of the second electron-type host in the other region.
[0030] An occupied volume ratio of the first electron-type host
adjacent to the anode may be equal to or larger than an occupied
volume ratio of the second electron-type host adjacent to the
cathode.
[0031] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0033] FIG. 1 is a cross-sectional view showing an organic light
emitting display device according to a first exemplary embodiment
of the present invention;
[0034] FIG. 2 is a cross-sectional view showing an organic light
emitting display device according to a second exemplary embodiment
of the present invention;
[0035] FIG. 3 is an energy band diagram of an organic light
emitting display device according to the present invention;
[0036] FIG. 4 is a graph of the current density vs. operating
voltage of devices according to Comparative Example and Embodiments
1 to 3 of the present invention;
[0037] FIG. 5 is a graph of the efficiency vs. luminance of devices
according to Comparative Example and Embodiments 1 to 3 of the
present invention;
[0038] FIG. 6 is a graph of the quantum efficiency vs. luminance of
devices according to Comparative Example and Embodiments 1 to 3 of
the present invention; and
[0039] FIG. 7 is a graph of the rate of decrease in luminance over
time of devices according to Comparative Example and Embodiments 1
to 3 of the present invention.
DETAILED DESCRIPTION
[0040] The advantages and features of the present invention and
methods for accomplishing the same may be understood more readily
by reference to the following detailed descriptions of exemplary
embodiments and the accompanying drawings. The present invention
may, however, be embodied in many different forms and should not be
construed as being limited to the exemplary embodiments set forth
herein. Rather, these exemplary embodiments are provided so that
this disclosure will be thorough and complete and will fully convey
the concept of the present invention to those skilled in the art,
and the present invention is defined by the appended claims
[0041] The shapes, sizes, percentages, angles, numbers, etc shown
in the figures to describe the exemplary embodiments of the present
invention are merely examples and not limited to those shown in the
figures. Like reference numerals denote like elements throughout
the specification. In describing the present invention, detailed
descriptions of related well-known technologies will be omitted to
avoid unnecessary obscuring the present invention. When the terms
`comprise`, `have`, `consist of` and the like are used, other parts
may be added as long as the term `only` is not used. The singular
forms may be interpreted as the plural forms unless explicitly
stated.
[0042] The elements may be interpreted to include an error margin
even if not explicitly stated.
[0043] When the position relation between two parts is described
using the terms `on`, `over`, `under`, `next to` and the like, one
or more parts may be positioned between the two parts as long as
the term `immediately` or `directly` is not used.
[0044] When the temporal relationship between two events is
described using the terms `after`, `following`, `next`, `before`
and the like, the two events may not occur in succession as long as
the term `immediately` or `directly` is not used.
[0045] It will be understood that, although the terms first,
second, etc., may be used to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another element. Thus, a first
element discussed below could be termed a second element without
departing from the technical spirit of the present invention.
[0046] The features of various exemplary embodiments of the present
invention may be combined with one another either partly or wholly,
and may technically interact or work together in various ways. The
exemplary embodiments may be carried out independently or in
combination with one another.
[0047] Hereinafter, various exemplary embodiments of the present
invention will be described in detail with reference to the
accompanying drawings.
[0048] FIG. 1 is a cross-sectional view showing an organic light
emitting display device according to a first exemplary embodiment
of the present invention.
[0049] Referring to FIG. 1, an organic light emitting display
device 100 of the present invention comprises light emitting parts
ST1, ST2, and ST3 between an anode 110 and a cathode 260, and
charge generation layers 160 and 210 between the light emitting
parts ST1, ST2, and ST3. Although this exemplary embodiment has
been illustrated and described with an example where three light
emitting parts are between the anode 110 and the cathode 260, the
present invention is not limited to this example and four or more
light emitting parts may be between the anode 110 and the cathode
260.
[0050] The anode 110 is a hole injection electrode, and may be
formed of ITO (indium tin oxide), IZO (indium zinc oxide), or ZnO
(zinc oxide) having a high work function. Also, if the anode 110 is
a reflective electrode, the anode 110 may further comprise a
reflective layer formed of aluminum (Al), silver (Ag), or nickel
(Ni) under a layer formed of ITO, IZO, or ZnO.
[0051] The first light emitting part ST1 is a single light emitting
diode unit, and comprises a first hole injection layer 120, a first
hole transport layer 130, a first light emitting layer 140, and a
first electron transport layer 150.
[0052] The first hole injection layer 120 may function to
facilitate hole injection from the anode 110 to the first light
emitting layer 140, and may be formed of, but are not limited to,
one among CuPc (copper phthalocyanine), PEDOT
(poly(3,4)-ethylenedioxythiophene), PANI (polyaniline), and NPD
((N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine).
The first hole injection layer 120 may be 1 to 150 nm thickness. If
the first hole injection layer 120 is 1 nm thickness or greater,
the hole injection properties may be improved, or if the first hole
injection layer 120 is 150 nm thickness or less, an increase in the
thickness of the first hole injection layer 120 may be prevented
and a rise in operating voltage may be therefore prevented. The
first hole injection layer 120 may not be included in the
composition of the organic light emitting display device, depending
on the structure or characteristics of the device.
[0053] The first hole transport layer 130 may function to
facilitate hole transport, and may be formed of, but are not
limited to, one of NPD
(N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine),
TPD (N,N'-bis-(3-methylphenyl)-N,N'-bis(phenyl)-benzidine),
spiro-TAD
(2,2'7,7'-tetrakis(N,N-diphenylamino)-9,9'-spirofluorene), and
MTDATA
(4,4',4''-tris(N-3-methylphenyl-N-phenylamino)-triphenylamine). The
first hole transport layer 130 may be 1 to 150 nm thickness. If the
first hole transport layer 130 is 1 nm thickness or greater, the
hole transport properties may be improved, or if the first hole
transport layer 130 is 150 nm thickness or less, an increase in the
thickness of the first hole transport layer 130 may be prevented,
and a rise in operating voltage may be therefore prevented.
[0054] The first light emitting layer 140 may emit light of red,
green, or blue. For example, it may be a blue light emitting layer
in this exemplary embodiment. The blue light emitting layer
comprises one among a blue light emitting layer, a dark blue light
emitting layer, or a sky blue light emitting layer. The blue light
emitting layer may be formed of, but are not limited to, a
phosphorescent material comprising a host material such as CBP
(4,4'-bis(carbazol-9-yl)biphenyl) and a dopant material having an
iridium-based material. Alternatively, the blue light emitting
layer may be formed of, but are not limited to, a fluorescent
material comprising any one among spiro-DPVBi, spiro-CBP,
distyrylbenzene (DSB), distyrylarylene (DSA), a PFO polymer, and a
PPV polymer.
[0055] The first electron transport layer 150 functions to
facilitate electron transport, and affects the lifetime or
efficiency of the organic light emitting display device. The first
electron transport layer 150 may be formed of, but are not limited
to, one among Alq.sub.3(tris(8-hydroxyquinolinato)aluminum), PBD
(2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), TAZ
(3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole), and
BAlq(bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminum).
The first electron transport layer 150 may be 1 to 150 nm
thickness. If the first electron transport layer 150 is 1 nm
thickness or greater, a degradation of the electron transport
properties may be prevented, or if the first electron transport
layer 150 is 150 nm thickness or less, an increase in the thickness
of the first electron transport layer 150 may be prevented, and a
rise in operating voltage may be therefore prevented.
[0056] A first charge generation layer (CGL) 160 is over the first
light emitting part ST1. The first light emitting part ST1 and the
second light emitting part ST2 are connected by the first charge
generation layer 160. The first charge generation layer 160 may be
a PN-junction charge generation layer formed by joining an N-type
charge generation layer 160N and a P-type charge generation layer
160P. The PN junction charge generation layer 160 generates a
charge, or injects the charge, i.e., electrons and holes,
separately into the light emitting layers. That is, the N-type
charge generation layer 160N supplies electrons to the blue light
emitting layer 140 adjacent to the anode, and the P-type charge
generation layer 160P supplies holes to the light emitting layer of
the second light emitting part ST2. As such, the organic light
emitting display device with a plurality of light emitting layers
can further increase its emission efficiency and lower its
operating voltage.
[0057] The N-type charge generation layer 160N may be formed of a
metal or an N-doped organic material. The metal may be one material
among Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Sm, Eu, Tb, Dy,
and Yb. An N-type dopant and host for the N-doped organic material
may be commonly-used materials. For example, the N-type dopant may
be an alkali metal, an alkali metal compound, an alkali earth
metal, or an alkali earth metal compound. Specifically, the N-type
dopant may be one among Li, Cs, K, Rb, Mg, Na, Ca, Sr, Eu, and Yb.
The percentage of the dopant to be mixed is between 0.5 and 10%
relative to 100% for the host. The dopant may have a work function
of 2.5 eV or higher. The host material may be an organic material
that has a hetero-ring having nitrogen atom, with 20 to 60 carbon
atoms, for example, one material among
Alq.sub.3(tris(8-hydroxyquinoline)aluminum), triazine, a
hydroxyquinoline derivative, a benzazole derivative, and a silole
derivative.
[0058] The P-type charge generation layer 160P may be formed of a
metal or a P-doped organic material. The metal may be one or more
alloys among Al, Cu, Fe, Pb, Zn, Au, Pt, W, In, Mo, Ni, and Ti. A
P-type dopant and host for the P-doped organic material may be
commonly-used materials. For example, the P-type dopant may be one
material among F.sub.4-TCNQ
(2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodemethane), a
derivative of tetracyanoquinodemethane, iodine, FeCl.sub.3,
FeF.sub.3, and SbCl.sub.5. The host may be one material among NPB
(N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine), TPD
(N,N'-bis-(3-methylphenyl)-N,N'-bis(phenyl)-benzidine), and TNB
(N,N,N'N'-tetranaphthalenyl-benzidine).
[0059] The second light emitting part ST2 comprising a second hole
injection layer 170, a second hole transport layer 180, a second
light emitting layer 190, a third light emitting layer 195, and a
second electron transport layer 200 is over the first charge
generation layer 160. The second hole injection layer 170, the
second hole transport layer 180, and the second electron transport
layer 200 may have the same composition as the first hole injection
layer 120, the first hole transport layer 130, and the first
electron transport layer 150 of the above-described the first light
emitting part ST1, respectively, or have different compositions
from their compositions.
[0060] The second light emitting layer 190 and the third light
emitting layer 195 of the present invention each may emit light of
red, green, or blue. In this exemplary embodiment, the second light
emitting layer 190 and the third light emitting layer 195 both may
be yellow light emitting layers; that is, the second light emitting
layer 190 may be a first yellow light emitting layer and the third
light emitting layer 195 may be a second yellow light emitting
layer. A yellow light emitting layer may be a light emitting layer
that emits yellow-green light.
[0061] The yellow light emitting layer is a light emitting layer
that emits yellow light as a hole injected from the anode 110 and
an electron injected from the cathode 260 are bound together and
form an excited state. If the yellow light emitting layer's light
emission area is formed between a hole transport layer and a light
emitting layer, this leads to an interface degradation and a
lifetime reduction. Also, high electron densities in the light
emission area of the yellow light emitting layer cause the light
emission area to be formed between the hole transport layer and the
light emitting layer, resulting in an interface degradation and a
lifetime reduction. In view of this, the present inventors have
formed a yellow light emitting layer comprising a first yellow
light emitting layer and a second yellow light emitting layer, in
order to form the yellow light emitting layer's light emission area
in the middle part of the light emitting layer. Or the present
inventors have formed a yellow light emitting layer having two
regions so that light emission occurs within the yellow light
emitting layer. The two regions includes the first yellow light
emitting layer and the second yellow light emitting layer,
respectively. The yellow light emitting layer includes a
yellow-green light emitting layer. Also, hosts in the first and
second yellow light emitting layers may have different
compositions, in order to adjust electron injection into the yellow
light emitting layer and improve the lifetime of the yellow light
emitting layer. Or hosts in the two regions may have different
compositions, in order to adjust electron injection into the yellow
light emitting layer and improve the lifetime of the yellow light
emitting layer. The first yellow light emitting layer comprises a
hole-type host and a first electron-type host, and the second
yellow light emitting layer comprises a first electron-type host
and a second electron-type host. Or, one of the two regions is
configured to comprise a hole-type host and a first electron-type
host, and the other region is configured to comprise a first
electron-type host and a second electron-type host, with the first
electron-type host and the second electron-type host having a
different electron mobility. The first electron-type host and the
hole-type host are adjusted balance of the hole and electron in the
first yellow light emitting layer or one of the two regions. The
second yellow light emitting layer or the other one of the two
regions is configured to have a small difference in LUMO (lowest
unoccupied molecular orbital) level between the first electron-type
host and the second electron-type host, in order to improve
electron injection ability. The LUMO (lowest unoccupied molecular
orbital) level of the first electron-type host is within a range of
-2.3 eV to -2.5 eV, and the LUMO (lowest unoccupied molecular
orbital) level of the second electron-type host is within a range
of -2.6 eV to -2.8 eV, and the difference in LUMO (lowest
unoccupied molecular orbital) levels between the first
electron-type host and the second electron-type host is no more
than 0.5 eV. The HOMO (highest occupied molecular orbital) level of
the first electron-type host and second electron-type host is
within a range of -5.4 eV to -5.8 eV.
[0062] Moreover, the electron mobility of the first electron-type
host is lower than the electron mobility of the second
electron-type host, in order to improve electron injection into the
yellow light emitting layer. By using materials with low electron
mobility as the first electron-type host and materials with
relatively high electron mobility as the second electron-type host,
the movement of electrons within the second yellow light emitting
layer is adjusted. Hence, the electron mobility of the first
electron-type host is equal to or lower than 1.times.10.sup.-5
cm.sup.2/Vs, and the electron mobility of the second electron-type
host is within a range of 1.times.10.sup.-5 cm.sup.2/Vs to
1.times.10.sup.-4 cm.sup.2/Vs. Also, since the first electron-type
host and second electron-type host of the second yellow light
emitting layer are not damaged by electrons, the second yellow
light emitting layer can improve stability, thereby preventing or
minimizing degradation of the light emitting layer. Therefore, in
the present invention, the first yellow light emitting layer
comprises a hole-type host and a first electron-type host, and the
second yellow light emitting layer comprises a first electron-type
host and a second electron-type host.
[0063] CBP (4,4'-bis(carbazol-9-yl)biphenyl), NPB
(N,N'-bis(naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine),
TcTa(4,4',4''-tris(carbazol-9-yl)triphenylmine, etc may be applied
as the hole-type host.
##STR00001##
[0064] B3PYMPM
(4,6-bis(3,5-di(pyridine-3-yl)phenyl)-2-methylpyrimidine),
TPBi(2,2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole),
3TPYMB (tris(2,4,6-trimethyl-3-(pyridine-3-yl)phenyl)borane),
BmPyPhB (1,3-bis[3,5-di(pyridine-3-yl)phenyl]benzene, etc. may be
applied as the first electron-type host and the second
electron-type host. The first electron-type host may be formed of
one among these materials, and the second electron-type host may be
formed of another among the unselected materials. For example, the
first electron-type host and the second electron-type host may be
formed of one among B3PYMPM and TPBi, respectively, 3TPYMB and
BmPyPhB, respectively, or TPBi and 3TPYMB, respectively.
##STR00002##
[0065] Although materials of the hole-type host and electron-type
hosts of the present invention have been listed as above, the
present invention is not limited thereto and other well-known
hole-type materials or electron-type materials may be used so long
as host material properties such as HOMO (highest occupied
molecular orbital), LUMO (lowest unoccupied molecular orbital), and
electron mobility satisfy the aforementioned conditions.
[0066] The second charge generation layer 210 is over the second
light emitting part ST2. The second charge generation layer 210 is
a PN-junction charge generation layer, formed by joining an N-type
charge generation layer 210N and a P-type charge generation layer
210P, which generates a charge, or injects the charge, i.e.,
electrons and holes, separately into the light emitting layers. The
N-type charge generation layer 210N has the same composition as the
N-type charge generation layer 160N of the first charge generation
layer 160, so its description will be omitted. The P-type charge
generation layer 210P also has the same composition as the
aforementioned P-type charge generation layer 160P of the first
charge generation layer 160.
[0067] The third light emitting part ST3 comprising a fourth light
emitting layer 230 is over the second charge generation layer 210.
The fourth light emitting layer 230 may emit light of red, green,
or blue. For example, it may be a blue light emitting layer in this
exemplary embodiment. The blue light emitting layer comprises a
blue light emitting layer, a dark blue light emitting layer, or a
sky blue light emitting layer. The third light emitting part ST3
further comprises a third hole transport layer 220 between the
second charge generation layer 210 and the fourth light emitting
layer 230, and a third electron transport layer 240 and an electron
injection layer 250 that are over the fourth light emitting layer
230.
[0068] The electron injection layer 250 functions to facilitate
electron injection, and may be formed of, but are not limited to,
Alg.sub.3 (tris(8-hydroxyquinolinato)aluminum), PBD
(2-4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), TAZ
(3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole), or
BAlq(bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminum). On
the other hand, the electron injection layer 250 may be formed of a
metal compound, and the metal compound may be, for example, but are
not limited to, one or more among LiQ, LiF, NaF, KF, RbF, CsF, FrF,
BeF.sub.2, MgF.sub.2, CaF.sub.2, SrF.sub.2, BaF.sub.2, and
RaF.sub.2. The electron injection layer 250 may be 1 to 50 nm
thickness. If the electron injection layer 250 is 1 nm thickness or
greater, a degradation of the electron injection properties may be
prevented, or if the electron injection layer 250 is 50 nm
thickness or less, an increase in the thickness of the electron
injection layer 250 may be prevented, and a rise in operating
voltage may be therefore prevented. The electron injection layer
250 may be omitted depending on the configuration of the
device.
[0069] The cathode 260 is over the third light emitting part ST3 to
constitute the organic light emitting display device according to
the first exemplary embodiment of the present invention. The
cathode 260 is an electron injection electrode, and may be formed
of one among magnesium (Mg), calcium (Ca), aluminum (Al), silver
(Ag), or an alloy thereof, having a low work function. If the
organic light emitting display device is a top-emission type or a
dual-emission type, the cathode 260 may be formed thin enough to
pass light therethrough. If the organic light emitting display
device is a bottom-emission type, the cathode 260 may be formed
thick enough to reflect light.
[0070] As discussed above, the organic light emitting display
device according to the first exemplary embodiment of the present
invention comprises a first yellow light emitting layer and a
second yellow light emitting layer. Or the organic light emitting
display device according to the first exemplary embodiment of the
present invention comprises a yellow light emitting layer having
two regions so that light emission occurs within the yellow light
emitting layer. The two regions include the first yellow light
emitting layer and the second yellow light emitting layer. The
yellow light emitting layer comprises a yellow-green layer. The
first yellow light emitting layer or one of the two regions is
configured to comprise a first electron-type host and a hole-type
host, in order to adjust the hole-electron balance in the first
yellow light emitting layer. The second yellow light emitting layer
or the other one of the two regions is configured to have a small
difference in LUMO (lowest unoccupied molecular orbital) level
between the first electron-type host and the second electron-type
host, in order to improve electron inject ability from the cathode.
The electron mobility of the first electron-type host is lower than
the electron mobility of the second electron-type host, in order to
improve electron injection into the yellow light emitting layer. By
forming the second yellow light emitting layer with low electron
mobility as the first electron-type host and materials with
relatively high electron mobility as the second electron-type host,
the movement of electrons within the second yellow light emitting
layer is adjusted. Also, since the first electron-type host and
second electron-type host of the second yellow light emitting layer
are not damaged by electrons, the second yellow light emitting
layer can improve stability, thereby preventing or minimizing
degradation of the light emitting layer. As such, the lifetime of
the device can be improved.
[0071] FIG. 2 is a view showing an organic light emitting display
device according to a second exemplary embodiment of the present
invention. The same elements as the first exemplary embodiment are
denoted by the same reference numerals, so descriptions of these
elements will be omitted below.
[0072] Referring to FIG. 2, an organic light emitting display
device 100 of the present invention comprises a plurality of light
emitting parts ST1 and ST2 between an anode 110 and a cathode 260,
and a charge generation layer 160 between the light emitting parts
ST1 and ST2.
[0073] More specifically, the first light emitting part ST1 is a
single light emitting diode unit, and comprises a first light
emitting layer 140. The first light emitting layer 140 may emit
light of red, green, or blue: for example, it may be a blue light
emitting layer in this exemplary embodiment. The first light
emitting part ST1 further comprises a hole injection layer 120 and
a first hole transport layer 130 that are between the anode 110 and
the first light emitting layer 140. Also, the first light emitting
part ST1 further comprises a first electron transport layer 150
over the first light emitting layer 140. Accordingly, the first
light emitting part ST1 comprising the hole injection layer 120,
the first hole transport layer 130, the first light emitting layer
140, and the first electron transport layer 150 is formed over the
anode 110. The hole injection layer 120 and the first hole
transport layer 130 may not be included in the composition of the
first light emitting part ST1, depending on the structure or
characteristics of the device.
[0074] The charge generation layer 160 is over the first light
emitting part ST1. The charge generation layer 160 is a PN-junction
charge generation layer, formed by joining an N-type charge
generation layer 160N and a P-type charge generation layer 160P,
which generates a charge, or injects the charge, i.e., electrons
and holes, separately into the light emitting layers.
[0075] The second light emitting part ST2 comprising a second light
emitting layer 190 and a third light emitting layer 195 is over the
charge generation layer 160. The second light emitting layer 190
and the third light emitting layer 195 may emit light of red,
green, or blue, and they may be yellow light emitting layers, for
example, in this exemplary embodiment. Each yellow light emitting
layer may comprise a yellow-green light emitting layer.
[0076] In the present invention, the second light emitting layer
190 may be a first yellow light emitting layer, and the third light
emitting layer 195 may be a second yellow light emitting layer. The
first yellow light emitting layer or one of the two regions is
configured to comprise a hole-type host and a first electron-type
host, and the second yellow light emitting layer is configured to
comprise a first electron-type host and a second electron-type
host. The first electron-type host and hole-type host are adjusted
the hole-electron balance in the first yellow light emitting layer
or one of the two regions. The second yellow light emitting layer
or the other one of the two regions is configured to have a small
difference in LUMO (lowest unoccupied molecular orbital) levels
between the first electron-type host and the second electron-type
host, in order to improve electron inject ability. The LUMO (lowest
unoccupied molecular orbital) level of the first electron-type host
is within a range of -2.3 eV to -2.5 eV, and the LUMO (lowest
unoccupied molecular orbital) level of the second electron-type
host is within a range of -2.6 eV to -2.8 eV, and the difference in
LUMO (lowest unoccupied molecular orbital) levels between the first
electron-type host and the second electron-type host is no more
than 0.5 eV. The HOMO (highest occupied molecular orbital) level of
the first electron-type host and second electron-type host is
within a range of -5.4 eV to -5.8 eV.
[0077] Moreover, the electron mobility of the first electron-type
host is lower than the electron mobility of the second
electron-type host, in order to improve electron injection into the
yellow light emitting layer. By using materials with low electron
mobility as the first electron-type host and materials with
relatively high electron mobility as the second electron-type host,
the movement of electrons within the second yellow light emitting
layer or the other one of the two regions is adjusted. Hence, the
electron mobility of the first electron-type host is not less than
1.times.10.sup.-5 cm.sup.2/Vs, and the electron mobility of the
second electron-type host is within a range of 1.times.10.sup.-5
cm.sup.2/Vs to 1.times.10.sup.-4 cm.sup.2/Vs. Also, since the first
electron-type host and second electron-type host of the second
yellow light emitting layer are not damaged by electrons, the
second yellow light emitting layer can improve stability, thereby
preventing or minimizing degradation of the light emitting layer.
Therefore, in the present invention, the first yellow light
emitting layer or one of the two regions comprises a hole-type host
and a first electron-type host, and the second yellow light
emitting layer or the other one of the two regions comprises a
first electron-type host and a second electron-type host.
[0078] The second light emitting part ST2 further comprises a
second hole transport layer 180 between the charge generation layer
160 and the second light emitting layer 190, and a second electron
transport layer 200 and an electron injection layer 250 that are
over the third light emitting layer 195. The cathode 260 is formed
over the second light emitting part ST2 to constitute the organic
light emitting display device according to the second exemplary
embodiment of the present invention.
[0079] As discussed above, the organic light emitting display
device according to the second exemplary embodiment of the present
invention comprises a first yellow light emitting layer and a
second yellow light emitting layer. The first yellow light emitting
layer or one of the two regions is configured to comprise a first
electron-type host and a hole-type host, in order to adjust the
hole-electron balance in the first yellow light emitting layer or
one of the two regions. The second yellow light emitting layer or
the other one of the two regions is configured to have a small
difference in LUMO (lowest unoccupied molecular orbital) levels
between the first electron-type host and the second electron-type
host, in order to improve electron inject ability from the cathode.
By using materials with low electron mobility as the first
electron-type host and materials with relatively high electron
mobility as the second electron-type host, the movement of
electrons within the second yellow light emitting layer or the
other one of the two regions is controlled. Also, since the first
electron-type host and second electron-type host of the second
yellow light emitting layer are not damaged by electrons, the
second yellow light emitting layer can improve stability, thereby
preventing or minimizing degradation of the light emitting layer.
As such, the lifetime of the device can be improved.
[0080] FIG. 3 is an energy band diagram of a second yellow light
emitting layer of an organic light emitting display device
according to the present invention.
[0081] Referring to FIG. 3, a yellow light emitting layer of the
present invention comprises a first yellow light emitting layer and
a second yellow light emitting layer, and the first yellow light
emitting layer comprises a hole-type host H-Host and a first
electron-type host E-Host-1, and the second yellow light emitting
layer comprises a first electron-type host E-Host-1 and a second
electron-type host E-Host-2. The first yellow light emitting layer
and the second yellow light emitting layer both comprise the same
yellow dopant. Or, the yellow light emitting layer has two regions
so that light emission occurs within the yellow light emitting
layer. The two regions can be regarded as the first yellow light
emitting layer and the second yellow light emitting layer,
respectively. The yellow light emitting layer comprises a
yellow-green light emitting layer. Also, hosts in the first and
second yellow light emitting layers may have different
compositions, in order to adjust electron injection into the yellow
light emitting layer and improve the lifetime of the yellow light
emitting layer. Or, hosts in the two regions may have different
compositions, in order to adjust electron injection into the yellow
light emitting layer and improve the lifetime of the yellow light
emitting layer.
[0082] With the use of a hole-type host H-Host and a first
electron-type host E-Host-1 as the first yellow light emitting
layer, the hole-type host H-Host and the first electron-type host
E-Host-1 can improve hole inject ability and electron inject
ability, respectively, thereby adjusting the hole-electron
balance.
[0083] With the use of a first electron-type host E-Host-1 and a
second electron-type host E-Host-2 as the second yellow light
emitting layer, electron inject ability can be improved because the
difference in LUMO (lowest unoccupied molecular orbital) levels
between the first electron-type host E-Host-1 and the second
electron-type host E-Host-2 is small. By using materials with low
electron mobility as the first electron-type host E-Host-1 and
materials with relatively high electron mobility as the second
electron-type host E-Host-2, the movement of electrons is
controlled. Although it is possible to slow down the electron
mobility of the hole-type host H-Host, the hole-type host H-Host
can be easily degraded compared to the electron-type hosts because
it is poor in terms of damage by injected electrons or in terms of
stability. Hence, in the present invention, the electron mobility
of the electron-type hosts is adjusted. Moreover, electrons moving
into the dopant can be trapped in the hosts, and this reduces
degradation of the dopant and improves lifetime of the device.
[0084] Hereinafter, an embodiment for the manufacture of an organic
light emitting display device according to the present invention
will be disclosed. However, the following materials for the light
emitting layer do not limit the scope of the present invention.
Comparative Example
[0085] An organic light emitting display device was manufactured by
forming, on a substrate, a hole injection layer, a hole transport
layer, a yellow light emitting layer, an electron transport layer,
an electron injection layer, and a cathode. The yellow light
emitting layer was formed by mixing a CBP host and a B3PYMPM host.
The yellow light emitting layer includes the yellow-green light
emitting layer.
Embodiment 1
[0086] The organic light emitting display device has the same
composition as Comparative Example, and includes a first yellow
light emitting layer and a second yellow light emitting layer
instead of the yellow light emitting layer. The first yellow light
emitting layer is formed of a mixture of a CBP host and a B3PYMPM
host (the ratio of the CBP host and the B3PYMPM host is 1:1), and
the second yellow light emitting layer is formed of a mixture of a
B3PYMPM host and a 3TPYMP host (the ratio of the B3PYMPM host and
the 3TPYMP host is 3:7). The first and second yellow light emitting
layer includes the first and second yellow-green light emitting
layer. In the embodiments, the first electron-type host of the
first yellow light emitting layer and the first electron-type host
of the second yellow light emitting layer include the same
material, but are not limited thereto. The first electron-type host
of the first and second light emitting layers may be applied the
same material or the different material having the range of the
LUMO levels and the electron mobility of the embodiments.
Embodiment 2
[0087] The organic light emitting display device has the same
composition as Embodiment 1. The first yellow light emitting layer
is formed of a mixture of a CBP host and a B3PYMPM host (the ratio
of the CBP host and the B3PYMPM host is 1:1), and the second yellow
light emitting layer is formed of a mixture of a B3PYMPM host and a
3TPYMP host (the ratio of the B3PYMPM host and the 3TPYMP host is
5:5). The first and second yellow light emitting layer includes the
first and second yellow-green light emitting layer. In the
embodiments, the first electron-type host of the first yellow light
emitting layer and the first electron-type host of the second
yellow light emitting layer include the same material, but are not
limited thereto. The first electron-type host of the first and
second light emitting layers may be applied the same material or
the different material having the range of the LUMO levels and the
electron mobility of the embodiments.
Embodiment 3
[0088] The organic light emitting display device has the same
composition as Embodiment 1. The first yellow light emitting layer
is formed of a mixture of a CBP host and a B3PYMPM host (the ratio
of the CBP host and the B3PYMPM host is 1:1), and the second yellow
light emitting layer is formed of a mixture of a B3PYMPM host and a
3TPYMP host (the ratio of the B3PYMPM host and the 3TPYMP host is
7:3). The first and second yellow light emitting layer includes the
first and second yellow-green light emitting layer. In the
embodiments, the first electron-type host of the first yellow light
emitting layer and the first electron-type host of the second
yellow light emitting layer include the same material, but are not
limited thereto. The first electron-type host of the first and
second light emitting layers may be applied the same material or
the different material having the range of the LUMO levels and the
electron mobility of the embodiments.
[0089] The materials for the light emitting layer used in the above
Comparative Example and Embodiments 1 to 3 do not limit the scope
of the present invention.
[0090] The operating voltage, efficiency, external quantum
efficiency, and lifetime of the devices manufactured according to
Comparative Example and Embodiments 1 to 3 were measured and shown
in the following Table 1. Also, the current density vs. operating
voltage of the devices was measured and shown in FIG. 4, the
efficiency vs. luminance was measured and shown in FIG. 5, the
external quantum efficiency vs. luminance was measured and shown in
FIG. 6, and the rate of decrease in luminance over time was
measured and shown in FIG. 7 (the operating voltage, efficiency,
external quantum efficiency, and lifetime measurements taken in the
embodiments were expressed as a percentage relative to those taken
in Comparative Example corresponding to 100%).
TABLE-US-00001 TABLE 1 External Operating quantum voltage
Efficiency efficiency Lifetime (%) (%) (EQE, %) (%) Comparative 100
100 100 100 Example Embodiment 102 103 102 121 1 Embodiment 105 101
100 133 2 Embodiment 107 98 98 145 3
[0091] Referring to Table 1 and FIGS. 4 to 7, Embodiments 1 to 3
using a first yellow light emitting layer formed of a mixture of a
hole-type host and an electron-type host and a second yellow light
emitting layer formed of a mixture of two electron-type hosts
showed equivalent levels of operating voltage, efficiency, and
external quantum efficiency and a remarkable increase in lifetime
of the device, compared to Comparative Example using a single
yellow light emitting layer formed of a mixture of a hole-type host
and an electron-type host.
[0092] As illustrated in FIG. 4, it can be seen that Embodiments 1
to 3 have similar levels of current density vs. operating
voltage.
[0093] As illustrated in FIGS. 5 to 7, Embodiment 1 using the first
yellow light emitting layer formed of the mixture of the hole-type
host and the first electron-type host (the ratio of the hole-type
host and the first electron-type host is 1:1), and the second
yellow light emitting layer formed of the mixture of the
electron-type host and the first electron-type host (the ratio of
the second electron-type host and the electron-type host is 3:7)
showed a 2% increase in operating voltage, a 2% increase in
external quantum efficiency, a 3% increase in efficiency, and a 21%
increase in lifetime, compared to Comparative Example. Also,
Embodiment 2 using the first yellow light emitting layer formed of
the mixture of the hole-type host and the first electron-type host
(the ratio of the hole-type host and the first electron-type host
is 1:1) and the second yellow light emitting layer formed of the
mixture of the first electron-type host and the second
electron-type host (the ratio of the first-electron host and the
second-electron host is 5:5) showed a 5% increase in operating
voltage, the same level of external quantum efficiency, a 1%
increase in efficiency, and a 33% increase in lifetime, compared to
Comparative Example. Also, Embodiment 3 using the first yellow
light emitting layer formed of the mixture of the hole-type host
and the first electron-type host (the ratio of the hole-type host
and the first electron-type host is 1:1) and the second yellow
light emitting layer formed of the mixture of the first
electron-type host and the second electron-type host (the ratio of
the first electron-type host and the second electron-type host is
7:3) showed a 7% increase in operating voltage, a 2% decrease in
external quantum efficiency, a 2% decrease in efficiency, and a 45%
increase in lifetime, compared to Comparative Example.
[0094] From these results, it can be found out that the lifetime of
a device comprising a single yellow light emitting layer having a
mixture of a hole-type host and an electron-type host is shorter
than the lifetime of a device having a first yellow light emitting
layer having a mixture of a hole-type host and an electron-type
host and a second yellow light emitting layer having a mixture of
two electron-type hosts. Also, it can be found out that the
lifetime of a device is longer when a device having the second
yellow light emitting layer includes a mixture of two electron-type
hosts (the ratio of the two electron-type host is 7:3) rather than
a device having the second yellow light emitting layer formed of a
mixture of two electron-type hosts (the ratio of the two
electron-type hosts is 3:7). And an organic layer of the organic
light emitting display device is formed by thermal evaporation
method. Generally, the thermal evaporation method forms an organic
material to a thickness of lA in a second. For example, if a volume
ratio of the first electron-type host and the second electron-type
host is 3:7 on the basis of the thermal evaporation method having a
thickness of 1 .ANG. in a second, the first electron-type host is
formed a thickness of 0.3 A in a second and the second
electron-type host is formed a thickness of 0.7 A in a second. And,
it can be found out that the lifetime of a device is longer when a
device having the second yellow light emitting layer includes an
occupied volume ratio of the electron-type host adjacent to the
first yellow light emitting layer is equal to or larger than an
occupied volume ratio of the electron-type host adjacent to the
electron transport layer or the cathode. Also, an occupied volume
ratio of the first electron-type host in the second light emitting
layer is equal to or larger than an occupied volume ratio of the
second electron-type host in the second light emitting layer,
thereby increasing the lifetime of the organic light emitting
display device. Occupied volume ratio may refer to the portion or
part of volume occupied by a respective material in a certain
layer. That is, an occupied volume ratio in the third light
emitting layer may be based on a sum of the occupied volumes of
first electron-type host and the second electron-type host.
[0095] Accordingly, it can be concluded that the organic light
emitting display device including one of the two regions of the
yellow light emitting layer having a hole-type host and a first
electron-type host and the other one of the two regions having
first and second electron-type hosts having a different electron
mobility has increased lifetime of the organic light emitting
display device, as compared with the yellow light emitting layer
comprises a hole-type host and an electron-type host. The first and
second yellow light emitting layer includes the first and second
yellow-green light emitting layer.
[0096] As discussed above, an organic light emitting display device
according to an exemplary embodiment of the present invention
comprises a first yellow light emitting layer and a second yellow
light emitting layer. The first yellow light emitting layer or one
of the two regions is configured to comprise a first electron-type
host and a hole-type host, in order to adjust the hole-electron
balance in the first yellow light emitting layer or one of the two
regions. The second yellow light emitting layer or the other one of
the two regions is configured to have a small difference in LUMO
(lowest unoccupied molecular orbital) levels between the first
electron-type host and the second electron-type host, in order to
improve electron inject ability from the cathode. Moreover, the
electron mobility of the first electron-type host is lower than the
electron mobility of the second electron-type host, in order to
improve electron injection into the yellow light emitting layer. By
using materials with low electron mobility as the first
electron-type host and materials with relatively high electron
mobility as the second electron-type host, the movement of
electrons within the second yellow light emitting layer or the
other one of the two regions is adjusted. Also, since the first
electron-type host and second electron-type host of the second
yellow light emitting layer are not damaged by electrons, the
second yellow light emitting layer can improve stability, thereby
preventing or minimizing degradation of the light emitting layer.
As such, the lifetime of the device can be improved. Also, an
occupied volume ratio of the first electron-type host in the one
region of the yellow light emitting layer is equal to or larger
than an occupied volume ratio of the second electron-type host in
the another region of the yellow light emitting layer, thereby
increasing the lifetime of the organic light emitting display
device. And, an occupied volume ratio of the first electron-type
host adjacent to the anode is equal to or larger than an occupied
volume ratio of the second electron-type host adjacent to the
cathode, thereby increasing the lifetime of the organic light
emitting display device.
[0097] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *