Light-emitting element, display device, method for manufacturing light-emitting element, and light emission method

Patent metadata

Field	Value
Publication number	US-10658607-B2
Application number	US-201916459648-A
Country	US
Kind code	B2
Filing date	Jul 2, 2019
Priority date	Nov 10, 2015
Publication date	May 19, 2020
Grant date	May 19, 2020

Abstract

An organic EL element ( 10 ) includes a first light-emitting layer ( 33 a ) having the shortest emission peak wavelength of a light-emitting layer ( 33 ) and containing a host material and a TTF material or at least the TTF material, a second light-emitting layer ( 33 b ) containing at least a TADF material, a third light-emitting layer ( 33 c ) having the longest emission peak wavelength of the light-emitting layer ( 33 ) and containing at least fluorescent material. The excited triplet level of the TTF material is lower than the excited triplet level of the TADF material.

First claim

The invention claimed is:

1. A light-emitting element comprising;
a first electrode;
a second electrode; and
a functional layer containing at least a first light-emitting layer and a second light-emitting layer, the functional layer being disposed between the first electrode and the second electrode, wherein
the first light-emitting layer has an emission peak wavelength shorter than an emission peak wavelength of the second light-emitting layer, and contains a host material and a triplet-triplet-fusion (TTF) material or at least the TTF material, the TTF material being a delayed fluorescent material that causes a TTF phenomenon by the TTF material alone or in cooperation with the host material,
the second light-emitting layer is adjacent to the first light-emitting layer, and contains at least a thermally activated delayed fluorescent material, the thermally activated delayed fluorescent material being a delayed fluorescent material in which reverse intersystem crossing occurs from an excited triplet level to an excited singlet level by thermal activation, and
an excited triplet level of at least one of the host material and the TTF material contained in the first light-emitting layer is lower than the excited triplet level of the thermally activated delayed fluorescent material contained in the second light-emitting layer.

2. The light-emitting element according to claim 1 , wherein
energy of excitons generated in the second light-emitting layer is transferred to the first light-emitting layer due to a Dexter energy transfer, and
each of the first light-emitting layer and the second light-emitting layer emits light.

3. The light-emitting element according to claim 2 , wherein
the Dexter energy transfer occurs from the excited triplet level of the thermally activated delayed fluorescent material in the second light-emitting layer to an excited triplet level of the TTF material in the first light-emitting layer, and
re-excitation occurs from the excited triplet level of the TTF material to an excited singlet level of the TTF material.

4. The light-emitting element according to claim 1 , wherein the second light-emitting layer has a thickness of not greater than 20 nm.

5. The light-emitting element according to claim 1 , wherein
the first electrode includes a positive electrode,
the first light-emitting layer, the second light-emitting layer, and a third light-emitting layer are layered in this order from a first electrode side,
the first light-emitting layer contains a material having a hole mobility higher than an electron mobility,
the second light-emitting layer contains a material having an electron mobility higher than a hole mobility, and
the third light-emitting layer contains a material having an electron mobility higher than a hole mobility.

6. The light-emitting element according to claim 1 , wherein
the first electrode is a negative electrode,
the first light-emitting layer, the second light-emitting layer, and a third light-emitting layer are layered in this order from a first electrode side,
the first light-emitting layer contains a material having an electron mobility higher than a hole mobility,
the second light-emitting layer contains a material having a hole mobility higher than an electron mobility, and
the third light-emitting layer contains a material having a hole mobility higher than an electron mobility.

7. The light-emitting element according to claim 1 , wherein a highest occupied molecular orbital (HOMO) level of a material contained in the second light-emitting layer at least at a highest mixing ratio is higher than a HOMO level of a material contained in the first light-emitting layer at least at the highest mixing ratio.

8. The light-emitting element according to claim 1 , wherein a lowest unoccupied molecular orbital (LUMO) level of a material contained in the second light-emitting layer at least at the highest mixing ratio is lower than a LUMO level of a material contained in the first light-emitting layer at least at the highest mixing ratio.

9. The light-emitting element according to claim 1 , wherein
the first light-emitting layer has a thickness of less than 5 nm, and
the second light-emitting layer has a thickness which is not greater than 20 nm.

10. The light-emitting element according to claim 9 , wherein
the functional layer contains at least one layer on the first light-emitting layer such that the first light-emitting layer is interposed between the second light-emitting layer and the at least one layer,
the at least one layer contains a fourth layer on the first light-emitting layer such that the first light-emitting layer is interposed between the second light-emitting layer and the fourth layer, and
a highest occupied molecular orbital (HOMO) level of a material contained in the fourth layer is lower than a HOMO level of a material contained in the second light-emitting layer at least at a highest mixing ratio.

11. The light-emitting element according to claim 9 , wherein
the functional layer contains at least one layer on the first light-emitting layer such that the first light-emitting layer is interposed between the second light-emitting layer and the at least one layer,
the at least one layer contains a fourth layer on the first light-emitting layer such that the first light-emitting layer is interposed between the second light-emitting layer and the fourth layer, and
a lowest unoccupied molecular orbital (LUMO) level of a material contained in the fourth layer is higher than a LUMO level of a material contained in the second light-emitting layer at least at a highest mixing ratio.

12. The light-emitting element according to claim 1 , wherein
the first light-emitting layer contains the host material,
the excited triplet level of the host material contained in the first light-emitting layer is higher than the excited triplet level of the TFT material, and
the host material contained in the first light-emitting layer has a hole mobility higher than an electron mobility.

13. The light-emitting element according to claim 1 , wherein
the second light-emitting layer contains a host material,
an excited triplet level of the host material contained in the second light-emitting layer is higher than the excited triplet level of the thermally activated delayed fluorescent material, and
the host material contained in the second light-emitting layer has an electron mobility higher than a hole mobility.

14. The light-emitting element according to claim 1 , wherein a content of the TTF material in the first light-emitting layer and a content of the thermally activated delayed fluorescent material in the second light-emitting layer are not less than 10 wt %, respectively.

15. A display device comprising a plurality of the light-emitting elements recited in claim 1 , the display device further comprising:
(i) a first pixel being provided with one of the plurality of the light-emitting elements, the first pixel emits light of a first color, and
(ii) a second pixel being provided with another one of the plurality of the light-emitting elements, the second pixel emits light of a second color which is different from the first color, wherein
the one of the plurality of the light-emitting elements and the another one of the plurality of the light-emitting elements emits a same monochromatic light,
the first pixel modulates the monochromatic light into the first color, and
the second pixel modulates the monochromatic light into the second color.

16. The display device according to claim 15 , wherein
the first pixel

Assignees

• Sharp Kk

Inventors

• Tsukamoto Yuto
• Kikuchi Katsuhiro
• Kawato Shinichi
• Niboshi Manabu
• Koike Eiji
• ITO Asae

Classifications

• H01L51/50

  Electricity · mapped topic

• H01L51/5028 Primary

  Electricity · mapped topic

• H01L2251/558

  Electricity · mapped topic

• H01L51/504

  Electricity · mapped topic

• H01L51/56

  Electricity · mapped topic