Organic Light-Emitting Diode with Enhanced Light-Emitting Efficiency and Color Purity
An organic light-emitting diode including an anode, a cathode, and a luminescent layered structure disposed between the anode and the cathode. The luminescent layered structure has a luminescent layer, a sensitizer layer and a guiding material. The luminescent-layer singlet state is two times higher than the luminescent-layer triplet state. The sensitizer layer has a sensitizer-layer triplet state between the luminescent-layer singlet state and the luminescent-layer triplet state. The guiding material has a guiding-material triplet state between the sensitizer-layer singlet state and the sensitizer-layer triplet state. The energy of molecules at the sensitizer-layer singlet state is transferred to the guiding-material triplet state and then to the sensitizer-layer triplet state, which is then transferred to 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.
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The present invention relates to a light-emitting diode, and specifically to an organic light-emitting diode.
BACKGROUND OF THE INVENTIONA typical 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 a current of electrons flow 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.
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 tends to react with excitons, forming high energy polarons that break molecular bonds in the luminescent material and consequently reduce the lifetime of blue OLEDs.
In addition, light is emitted when singlet excitons return to the ground state, while triplet excitons in fluorescent materials cannot return to 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 of positive polarons and negative polarons.
Therefore, OLEDs of prior art still have room for improvement.
SUMMARY OF THE INVENTIONThe objective 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. Furthermore, the organic light-emitting diode transfers singlet state energy to triplet state energy, which contributes to the light emission as well, thereby further enhancing the light-emitting efficiency and color purity.
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, a sensitizer layer, and a guiding material. The luminescent layer has a luminescent-layer ground state, a luminescent-layer singlet state and a luminescent-layer triplet state, in which the luminescent-layer singlet state is two times higher than the luminescent-layer triplet 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 guiding material has a guiding-material triplet state between the sensitizer-layer singlet state and the sensitizer-layer triplet state. The molecules of the sensitizer layer at the sensitizer-layer singlet state transfer energy to the molecules of the guiding material at the guiding-material triplet state, in which the transferred energy is further transferred to the molecules of the sensitizer layer at the sensitizer-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.
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.
Embodiments of the present invention are described below with reference to
The organic light-emitting diode Z according to the first embodiment of the present invention is described between with reference to
As shown in
In the embodiment shown in
More specifically, with reference to
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
As shown in
In the present embodiment, through the technical solution that the sensitizer layer 32 doped with the guiding material 33 is disposed next to the luminescent layer 31 such that the molecules of the sensitizer layer 32 at the sensitizer-layer singlet state S2 transfer energy to the molecules of the guiding material 33 at the guiding-material triplet state T3, in which the transferred energy is further transferred to the molecules of the sensitizer layer 32 at the sensitizer-layer triplet state T2. Next, the triplet-triplet energy transfer mechanism (TTET) between the sensitizer layer 32 and the luminescent layer 31 occurs, i.e. the molecules of the sensitizer layer 32 at the sensitizer-layer triplet state T2 transfers energy to that of the luminescent layer 31 at the luminescent-layer triplet state T1. Thereafter, triplet-triplet annihilation upconversion mechanism (TTAUC) in triggered in the luminescent layer 31.
Specifically, the aforementioned TTAUC mechanism occurs among excited triplet state molecules, wherein one excited triplet state molecule transfer energy to another excited triplet state molecule and returns to the ground state, whereas the excited triplet state molecule that receives energy is raised to the singlet state. Thereafter, molecules of the luminescent layer 31 that are raised to the singlet state return to the luminescent-layer ground state G1, thereby emitting light of a first color L1.
Referring to
Through the aforementioned technical solution, the present invention enables the energy at the sensitizer-layer singlet state S2 to participate in the light-emitting mechanism of the organic light-emitting diode Z with the guiding material 33, thereby increasing the efficiency of the organic light-emitting diode Z. On the other hand, the material of the sensitizer layer 32 of the present experimental example is Alq3 that emits green light, and that of the luminescent layer 31 is ADN, which emits blue light; therefore, in order to prevent the green second color light L2 emitted when molecules at the sensitizer-layer singlet state S2 return to ground state from affecting the blue first color light L1, the present embodiment enables at least part of the energy at the sensitizer-layer singlet state S2 to be transferred to the sensitizer-layer triplet state T2 through the luminescent layer 31 such that the color purity of the first color light L1 is enhanced.
It should be noted that the present invention is not limited to the above description. For instance, when in other embodiments, the predetermined emission color of the organic light-emitting diode Z is not the first color light L1, 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 the 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 S1 can be chosen 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. With 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 S1 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.
In summary, the first embodiment of the present invention uses mainly the triplet energy thereof to emit light through the technical solution of the sensitizer layer 32 doped with the guiding material 33, 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 that are generated from the recombination. Since the sensitizer layer 32 acts as the recombination zone in the present embodiment, high energy polarons in the luminescent layer 31 are prevented from reacting with the excitons. Therefore, the triplet energy in the sensitizer layer 32 can be utilized by being transferred and converted to emit light, thereby enhancing the illumination efficiency of the organic light-emitting diode Z and extending the lifetime thereof. In addition, the guiding-material triplet state T3 of the guiding material 33 is between the sensitizer-layer singlet state S2 and the sensitizer-layer triplet state T2, thereby enabling the energy at the sensitizer-layer singlet state S2 to be transferred to the guiding-material triplet state T3 of the guiding material 33, and then to the sensitizer-layer triplet state T2 of the sensitizer layer 32. In this way, the efficiency of the organic light-emitting diode Z can be enhanced. On the other hand, under the condition that the second color light L2 is different from the first color light L1, the color purity of the first color light L1 can be increased.
Second EmbodimentReferring to
With the blocking layer 34, 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.
Furthermore, the material of the guiding material 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 guiding material 33 of the present experimental example is DMPPP, and the materials of the luminescent layer 31, the sensitizer layer 32, and the guiding material 33 are ADN, Alq3, and Ir(ppy)3 respectively. The energy level of
Please refer to
In the experimental example shown in
Please refer to
Please further refer to
In summary, the embodiments of the present invention achieves “the molecules of the sensitizer layer at the sensitizer-layer singlet state transfer energy to the molecules of the guiding material at the guiding-material triplet state, in which the transferred energy is further transferred to the molecules of the sensitizer layer at the sensitizer-layer triplet state” through the technical solutions of “the luminescent layered structure includes the guiding material” and “the guiding-material triplet state is between the sensitizer-layer singlet state and the sensitizer-layer triplet state”.
Through the aforementioned technical solutions, the organic light-emitting diode Z of the present embodiments utilizes the guiding-material triplet state T3 of the guiding material 33 to transfer energy from the sensitizer-layer singlet state S2 to the sensitizer-layer triplet state T2 so that the energy at the sensitizer-layer singlet state S2 can contribute to light emission, thereby enhancing the efficiency of the organic light-emitting diode Z and increasing the color purity of the first color light L1. Next, the sensitizer layer 32 performs triplet-triplet energy transfer with 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 lifespan of the organic light-emitting diode Z.
In addition, in some embodiments, a blocking layer 34 can be added in the organic light-emitting diode Z, in which the singlet state of the blocking layer 34 is higher than that of the luminescent layer 31, and the triplet state of the blocking layer 34 is higher than that of the luminescent layer 31. In this way, the illumination efficiency of the organic light-emitting diode Z can be further increased.
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.
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 the luminescent-layer singlet state is two times higher than the luminescent-layer triplet state; a sensitizer layer having a sensitizer-layer singlet state and a sensitizer-layer triplet state, which is between the luminescent-layer singlet state and the luminescent-layer triplet state, and a guiding material having a guiding-material triplet state between the sensitizer-layer singlet state and the sensitizer-layer triplet state, wherein molecules of the sensitizer layer at the sensitizer-layer singlet state transfer energy to molecules of the guiding material at the guiding-material triplet state, in which the transferred energy is further transferred to the molecules of the sensitizer layer at the sensitizer-layer triplet state, wherein the molecules of the sensitizer layer at the sensitizer-layer triplet state transfers 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, wherein the guiding material is a dopant in the sensitizer layer.
3. The organic light-emitting diode according to claim 1, wherein the guiding material forms a guiding material layer, in which the sensitizer layer is situated between the guiding material layer and the luminescent layer.
4. The organic light-emitting diode according to claim 1, wherein the guiding material is one of a phosphorescent material and a thermally activated delayed fluorescence material.
5. The organic light-emitting diode according to claim 4, wherein the guiding material is an iridium complex.
6. 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.
7. 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.
8. 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.
9. 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.
10. The organic light-emitting diode according to claim 9, wherein the sensitizer layer includes one of a tris(8-hydroxyquinoline)aluminum and bis(10-hydroxybenzo[h]quinolinato)beryllium.
11. The organic light-emitting diode according to claim 1, wherein the sensitizer layer includes 1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene.
12. The organic light-emitting diode according to claim 1, wherein the luminescent layer is selected from the group consisting of an anthracene derivative, a pyrene derivative and a perylene derivative.
13. The organic light-emitting diode according to claim 12, 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.
14. 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.
15. The organic light-emitting diode according to claim 14, wherein a white light can be generated by mixing light of the first color and light of the second color.
16. 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 singlet 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.
17. The organic light-emitting diode according to claim 16, 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.
Type: Application
Filed: Mar 15, 2019
Publication Date: Sep 17, 2020
Applicants: Yuan Ze University (Chung-Li), Nichem Fine Technology Co, Ltd. (Jhubei City), WISECHIP SEMICONDUCTOR INC. (Zhunan Township), Tetrahedron Technology Corporation (Zhunan Township), SHINE MATERIALS TECHNOLOGY CO., LTD. (Kaohsiung City)
Inventors: Jiun-Haw LEE (Chung-Li), Tien-Lung CHIU (Chung-Li), Chia-Hsun CHEN (Chung-Li), Pei-Hsi LEE (Chung-Li)
Application Number: 16/354,826