U.S. patent application number 16/353578 was filed with the patent office on 2020-07-16 for organic light-emitting diode.
This patent application is currently assigned to Yuan Ze University. The applicant listed for this patent is Yuan Ze University Nichem Fine Technology Co, Ltd. WISECHIP SEMICONDUCTOR INC. Tetrahedron Technology Corporation SHINE MATERIAL. Invention is credited to Chia-Hsun Chen, Tien-Lung Chiu, Jiun-Haw Lee, Pei-Hsi Lee.
Application Number | 20200227671 16/353578 |
Document ID | 20200227671 / US20200227671 |
Family ID | 71125228 |
Filed Date | 2020-07-16 |
Patent Application | download [pdf] |
United States Patent
Application |
20200227671 |
Kind Code |
A1 |
Lee; Jiun-Haw ; et
al. |
July 16, 2020 |
ORGANIC LIGHT-EMITTING DIODE
Abstract
An organic light-emitting diode including an anode, a cathode,
and a luminescent layered structure is provided. The luminescent
layered structure is disposed between the anode and the cathode.
The luminescent layered structure has a luminescent layer and a
sensitizer layer. The luminescent layer has a luminescent-layer
ground state, a luminescent-layer singlet state and a
luminescent-layer triplet state, in which two times of the
luminescent-layer triplet state is higher than the
luminescent-layer singlet state. The sensitizer layer has a
sensitizer-layer triplet state, which is between the
luminescent-layer singlet state and the luminescent-layer triplet
state. The molecules of the sensitizer layer at the sensitizer
layer triplet layer transfers energy to the molecules of the
luminescent layer at the luminescent-layer triplet state and
triggers triplet-triplet annihilation upconversion in the
luminescent layer such that the luminescent layer emits light of a
first color
Inventors: |
Lee; Jiun-Haw; (Chung-Li,
TW) ; Chiu; Tien-Lung; (Chung-Li, TW) ; Chen;
Chia-Hsun; (Chung-Li, TW) ; Lee; Pei-Hsi;
(Chung-Li, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yuan Ze University
Nichem Fine Technology Co, Ltd.
WISECHIP SEMICONDUCTOR INC.
Tetrahedron Technology Corporation
SHINE MATERIALS TECHNOLOGY CO., LTD. |
Chung-Li
Jhubei City
Zhunan Township
Zhunan Township
Kaohsiung City |
|
TW
TW
TW
TW
TW |
|
|
Assignee: |
Yuan Ze University
Chung-Li
TW
Nichem Fine Technology Co, Ltd.
Jhubei City
TW
WISECHIP SEMICONDUCTOR INC.
Zhunan Township
TW
Tetrahedron Technology Corporation
Zhunan Township
TW
SHINE MATERIALS TECHNOLOGY CO., LTD.
Kaohsiung City
TW
|
Family ID: |
71125228 |
Appl. No.: |
16/353578 |
Filed: |
March 14, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G 3/2003 20130101;
H01L 51/5206 20130101; H01L 51/5072 20130101; H01L 51/5056
20130101; H01L 51/5221 20130101 |
International
Class: |
H01L 51/52 20060101
H01L051/52; H01L 51/50 20060101 H01L051/50; G09G 3/20 20060101
G09G003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2019 |
TW |
108101237 |
Claims
1. An organic light-emitting diode, comprising: an anode; a
cathode; and a luminescent layered structure disposed between the
anode and the cathode, including a luminescent layer having a
luminescent-layer ground state, a luminescent-layer singlet state
and a luminescent-layer triplet state, in which two times of the
luminescent-layer triplet state is higher than the
luminescent-layer singlet state; and a sensitizer layer having a
sensitizer-layer triplet state, which is between the
luminescent-layer singlet state and the luminescent-layer triplet
state, wherein molecules of the sensitizer layer at the
sensitizer-layer triplet state transfer energy to molecules of the
luminescent layer at the luminescent-layer triplet state and
triggers triplet-triplet annihilation upconversion in the
luminescent layer such that the luminescent layer emits light of a
first color.
2. The organic light-emitting diode according to claim 1, further
comprising: a hole transport layer disposed between the anode and
the luminescent layered structure; and an electron transport layer
disposed between the cathode and the luminescent layered
structure.
3. The organic light-emitting diode according to claim 1, wherein
the sensitizer layer is an electron transport layer, and the
organic light-emitting diode further comprises a hole transport
layer disposed between the anode and the luminescent layered
structure.
4. The organic light-emitting diode according to claim 1, wherein
the sensitizer layer is a hole transport layer, and the organic
light-emitting diode further comprises an electron transport layer
disposed between the cathode and the luminescent layered
structure.
5. The organic light-emitting diode according to claim 1, wherein
the sensitizer layer includes one of a (8-hydroxyquinoline) metal
complex and a 10-hydroxybenzo [h] quinoline-metal complex.
6. The organic light-emitting diode according to claim 5, wherein
the sensitizer layer includes one of
tris(8-hydroxyquinoline)aluminum and
bis(10-hydroxybenzo[h]quinolinato)beryllium.
7. The organic light-emitting diode according to claim 1, wherein
the sensitizer layer includes
1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene.
8. The organic light-emitting diode according to claim 1, wherein
the emissive layer is selected from the group consisting of an
anthracene derivative, a pyrene derivative and a perylene
derivative.
9. The organic light-emitting diode according to claim 8, wherein
the anthracene derivative is selected from the group consisting of
9,10-Di(2-naphthyl)anthracene,
2-methyl-9,10-D(2-naphthyl)anthracene,
2-tert-butyl-9,10-Di(2-naphthyl)anthracene, and
9,9'-dianthracene.
10. The organic light-emitting diode according to claim 1, wherein
the sensitizer layer further includes a sensitizer-layer singlet
state and a sensitizer-layer ground state, in which the molecules
of the sensitizer layer at the sensitizer-layer singlet state
returns to the sensitizer-layer ground state and emits light of a
second color.
11. The organic light-emitting diode according to claim 10, wherein
white light can be generated by mixing light of the first color and
light of the second color.
12. The organic light-emitting diode according to claim 1, wherein
the luminescent layered structure further includes a blocking layer
disposed between the sensitizer layer and the luminescent layer, in
which the blocking layer has a blocking-layer ground state and a
blocking-layer triplet state, the blocking-layer singlet state
being higher than the luminescent-layer singlet state, and the
blocking-layer triplet state being higher than the
luminescent-layer triplet state.
13. The organic light-emitting diode according to claim 12, wherein
the blocking layer is selected from the group consisting of
1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene and
1,3,5-Tri(1-pyrenyl)benzene.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a light-emitting diode, and
specifically to an organic light-emitting diode.
BACKGROUND OF THE INVENTION
[0002] A conventional organic light-emitting diode (OLED) is formed
of several stacked nano-size layers including an anode, a hole
transport layer (HTL), a luminescent layer, an electron transport
layer (ETL) and a cathode in spatial order. When a voltage is
applied to an OLED, a current of holes flows from the anode to the
highest occupied molecular orbitals (HOMO) of the HTL, thus
generating positive polarons, and at the same time a current of
electrons flows from the cathode to the lowest unoccupied molecular
orbitals (LUMO) of the ETL, thus generating negative polarons. The
positive polarons and the negative polarons recombine in the
luminescent layer, thereby generating singlet excitons and triplet
excitons. Thereafter, the singlet excitons return to the ground
state, upon which light is emitted.
[0003] In the evolution of OLEDs, extending the lifetime of blue
OLEDs has been a key issue, the reason being that the energy of
blue photons is relatively high, which results in the property of
rapid degradation. To be specific, active exciton-polaron
annihilation exists in blue OLEDs since excitons possess long
lifespan and thus tend to react with excitons and form high energy
polarons that break molecular bonds in the luminescent material and
consequently reduce the lifetime of blue OLEDs.
[0004] In addition, light is emitted when singlet excitons return
to the ground state, while triplet excitons in fluorescent
materials cannot return to the ground state with photon emission.
That is to say, a considerable amount of energy is wasted taking
into consideration of the fact that triplet excitons account for 75
percent of excited excitons as a result of the recombination
between the positive polarons and the negative polarons.
[0005] Therefore, in light of the above-mentioned drawbacks, OLEDs
of the prior art still have room for improvement.
SUMMARY OF THE INVENTION
[0006] One of the objectives of the present invention is to provide
an organic light-emitting diode which emits light utilizing the
triplet energy thereof, thereby extending the lifetime of the
organic light-emitting diode.
[0007] One embodiment of the present embodiment provides an organic
light emitting diode including an anode, a cathode and a
luminescent layered structure. The luminescent layered structure is
disposed between the anode and the cathode. The luminescent layered
structure has a luminescent layer and a sensitizer layer. The
luminescent layer has a luminescent-layer ground state, a
luminescent-layer singlet state and a luminescent-layer triplet
state, in which two times of the luminescent-layer triplet state is
higher than the luminescent-layer singlet state. The sensitizer
layer has a sensitizer-layer triplet state, which is between the
luminescent-layer singlet state and the luminescent-layer triplet
state. The molecules of the sensitizer layer at the sensitizer
layer triplet layer transfers energy to the molecules of the
luminescent layer at the luminescent-layer triplet state and
triggers triplet-triplet annihilation upconversion in the
luminescent layer such that the luminescent layer emits light of a
first color.
[0008] To further understand the features and technical content of
the present invention, please refer to the following detailed
descriptions and drawings related to the present invention.
However, the provided drawings are used only for providing
reference and descriptions, and are not intended to limit the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic view illustrating an organic
light-emitting diode according to a first embodiment of the present
invention.
[0010] FIG. 2 illustrates a variant embodiment of the organic
light-emitting diode according to the first embodiment of the
present invention.
[0011] FIG. 3 illustrates another variant embodiment of the organic
light-emitting diode according to the first embodiment of the
present invention.
[0012] FIG. 4 is an energy level diagram of the luminescent layered
structure of a first experimental example according to the first
embodiment of the present invention.
[0013] FIG. 5 is a diagram illustrating the transient
electroluminescence of the first experimental example according to
the first embodiment of the present invention.
[0014] FIG. 6 illustrates the transient electroluminescence of the
luminescent layer of the first experimental example according to
the first embodiment of the present invention.
[0015] FIG. 7 is a diagram illustrating the external quantum
efficiency of the first experimental example according to the first
embodiment and those of comparative examples.
[0016] FIG. 8 illustrates an energy level diagram of the
luminescent layered structure of a second experimental example
according to the first embodiment of the present invention.
[0017] FIG. 9 illustrates the transient electroluminescence of the
luminescent layer of the second experimental example according to
the first embodiment of the present invention.
[0018] FIG. 10 is a diagram illustrating the external quantum
efficiency of the second experimental example according to the
first embodiment and those of the comparative examples.
[0019] FIG. 11A is a schematic view of the organic light-emitting
diode according to the second embodiment of the present
invention.
[0020] FIG. 11B illustrates an energy level diagram of the
luminescent layered structure according to the second embodiment of
the present invention.
[0021] FIG. 12 is a diagram illustrating the external quantum
efficiency of a first experimental example, a second experimental
example and a third experimental example according to the second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Embodiments of the present invention are described below
with reference to FIG. 1 to FIG. 12. A person skilled in the art
can understand the advantages and effects of the present invention
from the description disclosed below. However, the content
disclosed below is not intended to limit the protection scope of
the present invention. The present invention can be implemented by
a person skilled in the art based on different perspectives and
applications without departing from the concept and spirit of the
present invention. In addition, it should be stated in advance that
the accompanying drawings of the present invention are merely used
for illustration, and are not drawn according to actual dimensions
for sake of clear illustration. Moreover, the same reference number
corresponds to the same component. It should also be understood
that expressions such as one component is "connected to" or
"disposed on" another may mean that the former is either directly
or indirectly connected to or disposed on the latter, wherein
"connected" may refer to either physical or electrical
connection.
First Embodiment
[0023] The organic light-emitting diode Z according to the first
embodiment of the present invention is described between with
reference to FIG. 1 to FIG. 7. First of all, referring to FIG. 1,
the organic light-emitting diode Z provided by the first embodiment
of the present invention includes an anode 1, a cathode 2, a
luminescent layered structure 3, a hole transport layer 4 and an
electron transport layer 5. The hole transport layer 4 is disposed
between the anode 1 and the luminescent layered structure 3, and
the electron transport layer 5 is disposed between the cathode 2
and the luminescent layered structure 3.
[0024] As shown in FIG. 1, the luminescent layered structure 3 has
a luminescent layer 31 and a sensitizer layer 32. The luminescent
layer 31 includes a luminescent-layer ground state, a
luminescent-layer singlet state and a luminescent-layer triplet
state. Specifically, in the present embodiment, the luminescent
layer 31 is a TTA material layer, that is to say, two times of the
luminescent-layer triplet state is higher than the
luminescent-layer singlet state. More specifically, the luminescent
layer 31 is preferably made of an anthracene derivative, a pyrene
derivative or a perylene derivative; however, the present invention
is not limited thereto. The anthracene derivative may be but not
limited to 9,10-Di(2-naphthyl)anthracene (ADN),
2-methyl-9,10-D(2-naphthyl)anthracene,
2-tert-butyl-9,10-Di(2-naphthyl)anthracene, or
9,9'-dianthracene.
[0025] In the embodiment shown in FIG. 1, the sensitizer layer 32
is disposed between the luminescent layer 31 and the hole transport
layer 4. However, the present invention is not limited thereto. In
other embodiments, the position of the luminescent layer 31 and
that of the sensitizer layer 32 are interchangeable. That is to
say, in other embodiments, the sensitizer layer 32 can be disposed
between the luminescent layer 31 and the electron transport layer
5. The sensitizer layer 32 has a sensitizer-layer triplet state,
which is between the luminescent-layer singlet state and the
luminescent-layer triplet state. In the present embodiment, the
material of the sensitizer layer 32 is preferably a
(8-hydroxyquinoline) metal complex or a 10-hydroxybenzo [h]
quinoline-metal complex. More specifically, examples of the
(8-hydroxyquinoline) metal complex may include but not limited to
tris(8-hydroxyquinoline)-aluminium (Alq.sub.3) and
tris-(8-hydroxyquinoline)gallium (Gaq.sub.3), and examples of
10-hydroxybenzo [h] quinoline-metal complex may include but not
limited to bis(10-hydroxybenzo[h]quinolinato)beryllium.
[0026] In a variant embodiment of the present embodiment, the
sensitizer layer 32 can transport electron holes and acts as a hole
transport layer disposed between the luminescent layer 31 and the
anode 1, as shown in FIG. 2. In another variant embodiment, the
sensitizer layer 32 can transport electrons and serve as an
electron transport layer disposed between the luminescent layer 31
and the cathode 2, as shown in FIG. 3. Furthermore, in other
embodiments, the sensitizer layer 32 can be added to the
luminescent layer 31 as a dopant. It should be noted that the
present invention is not limited to any of the above examples.
[0027] The light emitting mechanism of the organic light-emitting
diode of a first experimental example according to the present
embodiment is described below with reference to FIG. 4, which shows
an energy level diagram of the luminescent layered structure 3 of
the first experimental example. In FIG. 4, the luminescent-layer
singlet state S1, the sensitizer-layer triplet state T1 and the
sensitizer-layer ground state G1 of sensitizer layer 32 and the
luminescent-layer singlet state S2, the luminescent-layer triplet
state T2, and the luminescent-layer ground state G2 of the
luminescent layer 31 are shown. As shown in FIG. 4, the triplet
state T1 of the sensitizer layer 32 is between the
luminescent-layer singlet state S2 and the luminescent-layer
triplet state T2. To be specific, the material of the luminescent
layer 31 of the first experimental example is ADN, and that of the
sensitizer layer 32 is Alq.sub.3, in which the energy level of the
luminescent layered structure 3 is shown in Table 1 below.
TABLE-US-00001 TABLE 1 Sensitizer Luminescent layer 32 layer 32
Singlet state (eV) 2.3 2.83 Triplet state (eV) 2.0 1.67
[0028] In the present embodiment, through the technical solution
that the sensitizer layer 32 is disposed next to the luminescent
layer 31 such that triplet-triplet energy transfer mechanism (TTET)
between the sensitizer layer 32 and the luminescent layer 31 can
occur, i.e. the molecules of the sensitizer layer 32 at the
sensitizer-layer triplet state T1 transfer energy to the molecules
of the luminescent layer 31 at the luminescent-layer triplet state
T2 in a manner such that triplet-triplet annihilation upconversion
mechanism (TTAUC) is triggered in the luminescent layer 31
thereafter.
[0029] Specifically, the aforementioned TTAUC mechanism occurs
among excited triplet state molecules, wherein one excited triplet
state molecule transfers energy to another excited triplet state
molecule and returns to the ground state, and the excited triplet
state molecule that receives the energy is raised to the singlet
state. Next, molecules of the luminescent layer 31 that arc raised
to the singlet state return to the luminescent-layer ground state
G2, thereby emitting light of a first color L1.
[0030] Referring to FIG. 4, in the present embodiment, molecules of
the sensitizer layer 32 at the sensitizer-layer singlet state S1
emit light of a second color L2 when returning to the
sensitizer-layer ground state G1. Furthermore, in the present
embodiment, white light can be generated by mixing the first color
light L1, the second color light L2, and light of a third color.
For example, when using Alq.sub.3 as the sensitizer layer 32 and
ADN as the luminescent layer 31, then with an added light-emitting
material that emits red light, a white light can be obtained by
mixing the blue light emitted by ADN, the green light emitted by
Alq.sub.3 and the red light. However, the present invention is not
limited thereto. For instance, in other embodiments, the material
of the luminescent layer 31 and that of the sensitizer layer 32 are
selected based on a predetermined color of light emitted by the
organic light-emitting diode Z, thereby generating light of the
predetermined color by mixing the first color light L1 and the
second color light L2.
[0031] Please refer to FIG. 5 and FIG. 6, wherein FIG. 5 shows a
diagram illustrating the electroluminescent property of the first
experimental example according to the present embodiment, and FIG.
6 shows a diagram illustrating the transient electroluminescence of
the luminescent layer of the first experimental example according
to the present embodiment. Specifically, in the first experimental
example, indium tin oxide (ITO) is used as the anode 1, and LiF/Al
is used as the cathode 2. The thickness of the hole transport layer
4 is 50 nm, and the material thereof is
N,N'-di(1-naphthyl)-N,N'-diphenyl benzidine (NPB). The thickness of
the electron transport layer 5 is 65 nm, and the material thereof
is 4,7-diphenyl-1,10-phenanthroline (Bphen). The thickness of the
sensitizer layer 32 is 5 nm, and the material thereof is Alq.sub.3.
The thickness of the luminescent layer 31 is 10 nm, and the
material thereof is ADN. It should be noted that the above
description regarding the materials used and the specifications
thereof are the exemplary embodiment of the present invention; the
present invention is not limited thereto.
[0032] In the experimental example shown in FIG. 5 and FIG. 6, the
transient electroluminescence of the organic light-emitting diode Z
is measured by first applying an electro-pulse to the organic
light-emitting diode Z, and the light emitted by the organic
light-emitting diode Z in response to the electro-pulse is gauged
and converted into electric output with a photomultiplier. The
curves shown in FIG. 5 respectively represent the electric signals
outputted by the organic light-emitting diode Z in response to an
input voltage of 5 V, 4.6 V, 4.2 V, 3.8 V and 3.4 V. As shown in
FIG. 5, when each applied voltage is turned off at 0 second, the
speed at which the organic light-emitting diode Z of the first
experimental example emits light is of microsecond-scale. In
general, the speed at which singlet excitons emit light is of
nanosecond-scale, and that of triplet excitons is of
microsecond-scale since triplet excitons decay slower owing to the
spin conservation. That is to say, FIG. 5 shows that in the first
experimental example the triplet excitons contribute to a larger
percentage of total emission than organic light-emitting diodes in
the prior art. The curves shown in FIG. 6 respectively represent
the electric signals outputted by the luminescent layer 31
corresponding to an input electro-pulse of 5 V, 4.6 V, 4.2 V, 3.8 V
and 3.4 V. It can be seen from FIG. 6 that in the first
experimental example of the present embodiment, the first color
light L1 emitted by the luminescent layer 31 (ADN) is mainly from
the triplet excitons thereof.
[0033] FIG. 7 illustrates the external quantum efficiency of the
first experimental example (shown with the curve marked as
Alq.sub.3/ADN) according to the present embodiment and those of a
first comparative example (shown with the curve marked as ADN) and
a second comparative example (shown with the curve marked as
Alq.sub.3). The difference between the first experimental example
and the first and second comparative examples lies in that the
first experimental example has a sensitizer layer and a luminescent
layer, whereas the first comparative example has only ADN as the
luminescent layer and does not have a sensitizer layer; the second
comparative example has only Alq.sub.3 as the luminescent layer and
does not have a sensitizer layer. As shown in FIG. 7, the first
experimental example exhibits higher external quantum efficiency
than the first comparative example and the second comparative
example do within most part of the operational current density. As
stated in the background of the invention, 75% of recombined
positive polarons and negative polarons transform into triplet
excitons, which means the waste in energy in the prior art. In the
present embodiment, by adding the sensitizer layer 32 in the
organic light-emitting diode Z and adjusting the thicknesses of the
hole transport layer 4 and the electron transport layer 5, the
negative polarons and the positive polarons recombine in the
sensitizer layer 32 instead of the luminescent layer 31 so that
singlet excitons and triplet excitons can be generated in the
sensitizer layer 32, which triggers triplet-triplet energy transfer
mechanism (TTET) between the luminescent layer 31 and the
sensitizer layer 32 and then triplet-triplet annihilation
upconversion mechanism (TTAUC) in the luminescent layer 31
thereafter. In this way, most of the triplet energy in the
sensitizer layer 32 and the triplet energy in the luminescent layer
31 are converted to light emitted by the organic light-emitting
diode Z, thereby increasing the external quantum efficiency of the
organic light-emitting diode Z.
[0034] The second experimental example of the organic
light-emitting diode Z of the present embodiment is described below
with reference to FIG. 8 to FIG. 10. The second experimental
example has a structure that is similar to that of the first
experimental example with the main difference being that the
material of the sensitizer layer 32 of the second experimental
example is 1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene (DMPPP). FIG.
8 shows the energy level diagram of the luminescent layered
structure 3 of the second experimental example. As shown in the
figure, the sensitizer-layer triplet state T3 of the sensitizer
layer 32 (DMPPP) is higher than the luminescent-layer triplet state
T2 of the luminescent layer 31, and the sensitizer-layer singlet
state S3 of the sensitizer layer 32 is higher than the
luminescent-layer singlet state S2 of the luminescent layer 31.
More specifically, the energy level of the luminescent layered
structure 3 is shown in Table 2 below.
TABLE-US-00002 TABLE 2 Sensitizer Luminescent layer 32 layer 31
Singlet state (eV) 3.15 2.83 Triplet state (eV) 2.01 1.67
[0035] Please refer to FIG. 9. FIG. 9 illustrates the transient
electroluminescence of the luminescent layer of the first
experimental example according to the present embodiment. The
curves shown in FIG. 9 respectively represent the electric signals
outputted by the luminescent layer 31 (ADN) in response to an input
voltage of 5.5 V-6 V, 5.5 V, 5.0 V, 4.5 V, and 4.0 V. As shown in
FIG. 9, when each applied voltage is turned off at 0 second, the
speed at which the organic light-emitting diode Z of the second
experimental example emits light is of microsecond-scale, which
indicates that a larger percentage of the total emission of the
second experimental example is converted from the triplet energy as
compared to a conventional organic light-emitting diode.
[0036] FIG. 10 illustrates the external quantum efficiency of the
second experimental example (shown with the curve marked as
DMPPP/ADN) according to the present embodiment and those of a third
comparative example (shown with the curve marked as ADN) and a
fourth comparative example (shown with the curve marked as DMPPP).
The difference between the second experimental example and the
third and fourth comparative examples lies in that the second
experimental example has a sensitizer layer 32 and a luminescent
layer 31, whereas the third comparative example has only ADN has
only the luminescent layer and does not have a sensitizer layer;
the fourth comparative example has only DMPPP as the luminescent
layer and does not have a sensitizer layer either. As shown in FIG.
10, the second experimental example, which includes DMPPP as the
sensitizer layer 32 and ADN as the luminescent layer 31, exhibits
higher external quantum efficiency than the third comparative
example and the fourth comparative example.
[0037] It should be noted that the relative difference between the
sensitizer-layer singlet state and the luminescent-layer singlet
state is not limited in the present invention. A person skilled in
the art can select the material of the sensitizer layer and that of
the luminescent layer according to actual needs. For instance, when
in a condition that ADN which emits blue light has been determined
to be the material of the luminescent layer 31, the material of the
sensitizer layer 32 can be decided based on the predetermined light
color of the organic light-emitting diode Z. Specifically, when in
one embodiment the predetermined light color is white, a material
that has a singlet state lower than the luminescent-layer singlet
state S2 can be selected as the material of the sensitizer layer
32, as in the case of the first experimental example, so that the
second color light L2 is green. In this way, with a doped red
light-emitting material the organic light-emitting diode Z can emit
white light. When in another embodiment the predetermined light
color of the organic light-emitting diode Z is blue, then a
material that has a singlet state higher than the luminescent-layer
singlet state S2 can be chosen to be the material of the sensitizer
layer 32, as in the case of the second experimental example, so
that the second color light L2 and the first light color L1 are
both blue light.
[0038] In summary, the first embodiment of the present invention
uses mainly the triplet energy thereof to emit light utilizing the
technical solution of the sensitizer layer 32, which serves as the
place the recombination between the positive polarons and the
negative polarons takes place such that triplet-triplet
annihilation upconversion mechanism can be triggered in the
luminescent layer 31 by the triplet excitons in the sensitizer
layer 32 generated from the recombination. Since the sensitizer
layer 32 acts as the recombination zone in the present embodiment,
high energy polarons are prevented from reacting with the excitons
in the luminescent layer 31. Therefore, the triplet energy in the
sensitizer layer 32 can be utilized to emit light by being
transferred to the luminescent layer 31 and converted through TTAUC
mechanism, thereby enhancing the illumination efficiency of the
organic light-emitting diode Z and extending the lifetime
thereof.
Second Embodiment
[0039] Referring to FIG. 11A, the main difference between the
present embodiment and the first embodiment lies in that the
organic light-emitting diode Z of the second embodiment further
includes a blocking layer 33 between the luminescent layer 31 and
the sensitizer layer 32. With reference to FIG. 11B, the blocking
layer 33 has a blocking-layer singlet state S4 and a blocking-layer
triplet state T4, in which the blocking-layer singlet state S4 is
higher than the luminescent-layer singlet state S2, and the
blocking-layer triplet state T4 is higher than the
luminescent-layer triplet state T2.
[0040] With the blocking layer 33, the triplet energy of the
sensitizer layer 32 can be transferred to the triplet state of the
luminescent layer 31. At the same time, the quenching effects
between the sensitizer layer 32 and the luminescent layer 31 can be
reduced. In this way, the illumination efficiency of the organic
light-emitting diode Z can be further improved.
[0041] Furthermore, the material of the blocking layer 33 can be
1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene (DMPPP) or
1,3,5-Tri(1-pyrenyl)benzene (TPB3). However, the present invention
is not limited thereto. Specifically, the blocking layer 33 of the
present embodiment is DMPPP, whose energy level is shown in Table 3
below.
TABLE-US-00003 TABLE 3 Sensitizer Blocking Luminescent layer 32
layer 33 layer 31 Singlet state (eV) 2.8 3.15 2.83 Triplet state
(eV) 2.0 2.05 1.67
[0042] Please refer to FIG. 12, which shows a diagram illustrating
the external quantum efficiency of a first experimental example, a
second experimental example and a third experimental example
according to the second embodiment of the present invention. The
first experimental example of the present embodiment uses ADN as
the luminescent layer, Alq.sub.3 as the sensitizer layer, and the
first experimental example has no blocking layer. The second
experimental example is shown with a curve marked as 5 nm in FIG.
12. The difference between the first experimental example and the
second experimental example is that the second experimental example
has a blocking layer 33 with a thickness of 5 nm between the
luminescent layer 31 and the sensitizer layer 32. The material of
the blocking layer 33 is DMPPP. The third experimental example is
shown with a curve marked as 10 nm in FIG. 12. The difference
between the first experimental example and the third experimental
example is that the third experimental example has a blocking layer
33 with a thickness of 10 nm between the luminescent layer 31 and
the sensitizer layer 32. The material of the blocking layer 33 of
the third experimental example is DMPPP. As shown in FIG. 12, the
third experimental example exhibits higher external quantum
efficiency than the second experimental example, which in turn
offers higher external quantum efficiency than the first
experimental example. Therefore, the present embodiment shows that
adding a blocking layer 33 to the organic light-emitting diode Z
(as in the second experimental example and third experimental
example of the present embodiment compared to the first
experimental example) can effectively enhance the efficiency of the
organic light-emitting diode Z.
[0043] In summary, the embodiments of the present invention
achieves "the molecules of the sensitizer layer at the
sensitizer-layer triplet layer transfers energy to the molecules of
the luminescent layer at the luminescent-layer triplet state and
triggers triplet-triplet annihilation upconversion in the
luminescent layer such that the luminescent layer emits light of a
first color" through the technical solutions that "two times of the
luminescent-layer triplet state is higher than the
luminescent-layer singlet state" and "the sensitizer-layer triplet
state is between the luminescent-layer singlet state and the
luminescent-layer triplet state".
[0044] Through the aforementioned technical solutions, the organic
light-emitting diode Z of the present embodiments utilizes the
sensitizer layer 32 to perform triplet-triplet energy transfer
between the sensitizer layer 32 and the luminescent layer 31,
thereby triggering triplet-triplet annihilation upconversion
mechanism in the luminescent layer 31. In this way, triplet energy
of the luminescent layer 31 and that of the sensitizer layer 32 can
be converted into light emitted by the organic light-emitting diode
Z, thereby effectively enhancing the illumination efficiency and
the lifespan of the organic light-emitting diode Z.
[0045] In addition, in some embodiments, a blocking layer can be
added to the organic light-emitting diode Z, in which the singlet
state of the blocking layer is higher than the singlet state of the
luminescent layer, and the triplet state of the blocking layer is
higher than the triplet state of the luminescent layer. In this
way, the illumination efficiency of the organic light-emitting
diode can be further increased.
[0046] The present invention has been described with reference to
the above embodiments, but the above embodiments are merely
examples for implementing the present invention. It should be noted
that the disclosed embodiments are not intended to limit the scope
of the present invention. On the contrary, any modification and
equivalent configuration within the spirit and scope of the
appended claims shall fall within the scope of the present
invention.
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