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

• US 10,454,052 B2
• Filed: 04/03/2018
• Issued: 10/22/2019
• Est. Priority Date: 03/09/2015
• Status: Expired due to Fees

• 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:
  US15/944,013
• Publication Number:
  US 20180226598A1
• Time in Patent Office: 567 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 device comprising:

a pair of electrodes over a substrate; and

a first light-emitting layer and a second light-emitting layer between the pair of electrodes,

a charge generation layer between the first light-emitting layer and the second light-emitting layer,

wherein at least one of the first light-emitting layer and the second 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 comprises at least two substituents and condensed aromatic hydrocarbon having at least three rings,

wherein the two substituents comprise any one of branched alkyl groups each having 3 to 10 carbon atoms, cyclic hydrocarbon groups each having 3 to 10 carbon atoms, bridged cyclic hydrocarbon groups each having 3 to 10 carbon atoms, and

wherein light emitted from the exciplex has a region overlapping with an absorption band of the fluorescent material on the lowest energy side.

2. The light-emitting device 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.

3. The light-emitting device 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.

4. The light-emitting device 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.

5. The light-emitting device according to claim 1,

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, and

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.

6. The light-emitting device according to claim 5, 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.

7. The light-emitting device according to claim 5, 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.

15. The light-emitting device according to claim 1, wherein the condensed aromatic hydrocarbon is one selected from the group consisting of an anthracene skeleton, a phenanthren skeleton, a fluorine skeleton, an indacene skeleton, a tetracene skeleton, a triphenylen skeleton, a chrysene skeleton, a pyrene skeleton, a fluoranthene skeleton, a pentacene skeleton, a perylene skeleton, a rubicene skeleton, a trinaphthylene skeleton, and a dibenzoperiflanthene skeleton.

16. The light-emitting device according to claim 1, wherein each of the two substituents is a tert-butyl group.

8. A light-emitting device comprising:

a pair of electrodes over a substrate; and

a first light-emitting layer and a second light-emitting layer between the pair of electrodes,

a charge generation layer between the first light-emitting layer and the second light-emitting layer,

wherein at least one of the first light-emitting layer and the second 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 the fluorescent material comprises at least two substituents and condensed aromatic hydrocarbon having at least three rings,

wherein the two substituents comprise any one of branched alkyl groups each having 3 to 10 carbon atoms, cyclic hydrocarbon groups each having 3 to 10 carbon atoms, bridged cyclic hydrocarbon groups each having 3 to 10 carbon atoms, and

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 device according to claim 8,

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 device according to claim 8,

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 device according to claim 8,

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. The light-emitting device according to claim 8,

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, and

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.

13. The light-emitting device according to claim 12, 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.

14. The light-emitting device according to claim 12, 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.

17. The light-emitting device according to claim 8, wherein the condensed aromatic hydrocarbon is one selected from the group consisting of an anthracene skeleton, a phenanthren skeleton, a fluorine skeleton, an indacene skeleton, a tetracene skeleton, a triphenylen skeleton, a chrysene skeleton, a pyrene skeleton, a fluoranthene skeleton, a pentacene skeleton, a perylene skeleton, a rubicene skeleton, a trinaphthylene skeleton, and a dibenzoperiflanthene skeleton.

18. The light-emitting device according to claim 8, wherein each of the two substituents is a tert-butyl group.