Light-emitting element, display device, electronic device, and lighting device

• US 9,941,481 B2
• Filed: 03/04/2016
• Issued: 04/10/2018
• Est. Priority Date: 03/09/2015
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Hosoumi, Shunsuke, Ishisone, Takahiro, Takahashi, Tatsuyoshi, Seo, Satoshi
• Primary Examiner(s): Shamsuzzaman, Mohammed
• Application Number:
  US15/060,657
• Publication Number:
  US 20160268534A1
• Time in Patent Office: 767 Days
• Field of Search: 257 40, 25230116, 313504
• CPC Class Codes: H10K 2101/90 Multiple hosts in the emissive layer
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 85/633 comprising polycyclic condensed aromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: H10K 85/636 comprising heteroaromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: H10K 85/6572 comprising only nitrogen in the heteroaromatic polycondensed ring system, e.g. phenanthroline or carbazole
• CPC Class Codes: H10K 85/6576 comprising only sulfur in the heteroaromatic polycondensed ring system, e.g. benzothiophene
• CPC Class Codes: Y02P 20/582 Recycling of unreacted starting or intermediate materials

Abstract

A light-emitting element containing a fluorescent material and having high emission efficiency is provided. The light-emitting element contains the fluorescent material and a host material. The host material contains a first organic compound and a second organic compound. The first organic compound and the second organic compound can form an exciplex. The minimum value of a distance between centroids of the fluorescent material and at least one of the first organic compound and the second organic compound is 0.7 nm or more and 5 nm or less.

Claims

1. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer between the pair of electrodes,

wherein the light-emitting layer comprises;

a fluorescent material as a guest material; and

a first organic compound and a second organic compound capable of forming an exciplex as a host material, and

wherein a minimum value of a distance between a centroid of the fluorescent material and a centroid of the first organic compound or the second organic compound is larger than or equal to 0.7 nm and smaller than or equal to 5 nm;

wherein the minimum value of the distance between the centroids is a distance at the time when a running coordination number calculated by a classical molecular dynamics method exceeds 0.

2. The light-emitting element according to claim 1, wherein the minimum value of the distance between the centroids corresponds to a distance between the centroid of the fluorescent material and the centroid of the first organic compound or the second organic compound nearest to the fluorescent material.

3. The light-emitting element according to claim 1, wherein a minimum value of a distance between the centroid of the fluorescent material and a centroid of the first organic compound and a minimum value of a distance between the centroid of the fluorescent material and a centroid of the second organic compound are each larger than or equal to 0.7 nm and smaller than or equal to 5 nm.

4. The light-emitting element according to claim 1, wherein the fluorescent material comprises at least two alkyl groups each having 2 or more carbon atoms.

5. The light-emitting element according to claim 1, wherein the fluorescent material comprises at least two branched alkyl groups each having 3 to 10 carbon atoms.

6. The light-emitting element according to claim 1, wherein the fluorescent material comprises at least two cyclic hydrocarbon groups each having 3 to 10 carbon atoms or at least two bridged cyclic hydrocarbon groups each having 3 to 10 carbon atoms.

7. The light-emitting element according to claim 1, wherein the fluorescent material comprises condensed aromatic hydrocarbon having 3 to 12 carbon atoms.

8. The light-emitting element according to claim 1, wherein light emitted from the exciplex has a region overlapping with an absorption band of the fluorescent material on the lowest energy side.

9. The light-emitting element according to claim 1,

wherein a proportion of a delayed fluorescence component in light emitted from the exciplex is higher than or equal to 10%, and

wherein the delayed fluorescence component contains a delayed fluorescence component whose fluorescence lifetime is 10 ns or longer and 50 μ

s or shorter.

10. The light-emitting element according to claim 1,

wherein one of the first organic compound and the second organic compound has a function of transporting electrons, and

wherein the other of the first organic compound and the second organic compound has a function of transporting holes.

11. The light-emitting element according to claim 1,

wherein one of the first organic compound and the second organic compound comprises a π

-electron deficient heteroaromatic ring skeleton, and

wherein the other of the first organic compound and the second organic compound comprises a π

-electron rich heteroaromatic ring skeleton or an aromatic amine skeleton.

12. A display device comprising:

the light-emitting element according to claim 1; and

at least one of a color filter and a transistor.

13. An electronic device comprising:

the display device according to claim 12; and

at least one of a housing and a touch sensor.

14. A lighting device comprising:

the light-emitting element according to claim 1; and

at least one of a housing and a touch sensor.

15. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer between the pair of electrodes, wherein the light-emitting layer comprises;

a fluorescent material as a guest material; and

a first organic compound and a second organic compound capable of forming an exciplex as a host material,

wherein the fluorescent material has a fluorescence quantum yield of 70% or higher, and wherein a minimum value of a distance between a centroid of the fluorescent material and a centroid of the first organic compound or the second organic compound is larger than or equal to 0.7 nm and smaller than or equal to 5 nm;

wherein the minimum value of the distance between the centroids is a distance at the time when a running coordination number calculated by a classical molecular dynamics method exceeds 0.

16. The light-emitting element according to claim 15, wherein the minimum value of the distance between the centroids corresponds to a distance between the centroid of the fluorescent material and the centroid of the first organic compound or the second organic compound nearest to the fluorescent material.

17. The light-emitting element according to claim 15, wherein a minimum value of a distance between the centroid of the fluorescent material and a centroid of the first organic compound and a minimum value of a distance between the centroid of the fluorescent material and a centroid of the second organic compound are each larger than or equal to 0.7 nm and smaller than or equal to 5 nm.

18. The light-emitting element according to claim 15, wherein the fluorescent material comprises at least two alkyl groups each having 2 or more carbon atoms.

19. The light-emitting element according to claim 15, wherein the fluorescent material comprises at least two branched alkyl groups each having 3 to 10 carbon atoms.

20. The light-emitting element according to claim 15, wherein the fluorescent material comprises at least two cyclic hydrocarbon groups each having 3 to 10 carbon atoms or at least two bridged cyclic hydrocarbon groups each having 3 to 10 carbon atoms.

21. The light-emitting element according to claim 15, wherein the fluorescent material comprises condensed aromatic hydrocarbon having 3 to 12 carbon atoms.

22. The light-emitting element according to claim 15, wherein light emitted from the exciplex has a region overlapping with an absorption band of the fluorescent material on the lowest energy side.

23. The light-emitting element according to claim 15,

wherein a proportion of a delayed fluorescence component in light emitted from the exciplex is higher than or equal to 10%, and

wherein the delayed fluorescence component contains a delayed fluorescence component whose fluorescence lifetime is 10 ns or longer and 50 μ

s or shorter.

24. The light-emitting element according to claim 15,

wherein one of the first organic compound and the second organic compound has a function of transporting electrons, and

wherein the other of the first organic compound and the second organic compound has a function of transporting holes.

25. The light-emitting element according to claim 15,

wherein one of the first organic compound and the second organic compound comprises a π

-electron deficient heteroaromatic ring skeleton, and

wherein the other of the first organic compound and the second organic compound comprises a π

-electron rich heteroaromatic ring skeleton or an aromatic amine skeleton.

26. A display device comprising:

the light-emitting element according to claim 15; and

at least one of a color filter and a transistor.

27. An electronic device comprising:

the display device according to claim 26; and

at least one of a housing and a touch sensor.

28. A lighting device comprising:

the light-emitting element according to claim 15; and

at least one of a housing and a touch sensor.