Light-emitting element

• US 9,276,228 B2
• Filed: 08/02/2013
• Issued: 03/01/2016
• Est. Priority Date: 08/03/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Seo, Satoshi, Seo, Hiromi, Takahashi, Tatsuyoshi
• Primary Examiner(s): Green, Telly
• Application Number:
  US13/957,612
• Publication Number:
  US 20140034930A1
• Time in Patent Office: 942 Days
• Field of Search: 257/40, 313/504, 428/690
• US Class Current: 1/1
• CPC Class Codes: C09K 11/02 Use of particular materials as binders, particle coatings or suspension media therefor
• CPC Class Codes: C09K 11/06 containing organic luminescent materials
• CPC Class Codes: C09K 2211/1007 Non-condensed systems
• CPC Class Codes: C09K 2211/1011 Condensed systems
• CPC Class Codes: C09K 2211/1014 bridged by heteroatoms, e.g. N, P, Si or B
• CPC Class Codes: C09K 2211/1029 containing one nitrogen atom as the heteroatom
• CPC Class Codes: C09K 2211/1044 containing two nitrogen atoms as heteroatoms
• CPC Class Codes: C09K 2211/1092 containing sulfur as the only heteroatom
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 2101/30 Highest occupied molecular orbital [HOMO], lowest unoccupied molecular orbital [LUMO] or Fermi energy values
• CPC Class Codes: H10K 2101/40 Interrelation of parameters between multiple constituent active layers or sublayers, e.g. HOMO values in adjacent layers
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: H10K 85/321 Metal complexes comprising a group IIIA element, e.g. Tris (8-hydroxyquinoline) gallium [Gaq3]
• CPC Class Codes: H10K 85/611 Charge transfer complexes
• CPC Class Codes: H10K 85/615 Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
• CPC Class Codes: H10K 85/622 containing four rings, e.g. pyrene
• CPC Class Codes: H10K 85/624 containing six or more rings
• 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 85/654 : comprising only nitrogen as heteroatom H10K85/652 takes precedence
• 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

Abstract

To provide a light-emitting element which uses a fluorescent material as a light-emitting substance and has higher luminous efficiency. To provide a light-emitting element which includes a mixture of a thermally activated delayed fluorescent substance and a fluorescent material. By making the emission spectrum of the thermally activated delayed fluorescent substance overlap with an absorption band on the longest wavelength side in absorption by the fluorescent material in an S₁ level of the fluorescent material, energy at an S₁ level of the thermally activated delayed fluorescent substance can be transferred to the S₁ of the fluorescent material. Alternatively, it is also possible that the S₁ of the thermally activated delayed fluorescent substance is generated from part of the energy of a T₁ level of the thermally activated delayed fluorescent substance, and is transferred to the S₁ of the fluorescent material.

Claims

1. A light-emitting element comprising:

a pair of electrodes; and

an EL layer between the pair of electrodes,

wherein the EL layer comprises a light-emitting layer,

wherein the light-emitting layer comprises a first organic compound, a second organic compound, and a fluorescent material,

wherein the first organic compound and the second organic compound form an exciplex which exhibits thermally activated delayed fluorescence, and

wherein, in the exciplex, a difference between levels of a triplet excited state and a singlet excited state is 0.2 eV or less.

2. The light-emitting element according to claim 1, wherein light emission of the exciplex is overlapped with an absorption band on a lowest energy side of the fluorescent material.

3. The light-emitting element according to claim 2, wherein a difference in energy between a peak wavelength of the absorption band on the lowest energy side of the fluorescent material and a peak wavelength of the exciplex is 0.2 eV or less.

4. The light-emitting element according to claim 2, wherein a peak wavelength of light emission of the exciplex is longer than or equal to a peak wavelength of the absorption band on the lowest energy side of the fluorescent material.

5. The light-emitting element according to claim 2, wherein a difference between a peak wavelength of light emission of the exciplex and a peak wavelength of light emission of the fluorescent material is 30 nm or less.

6. The light-emitting element according to claim 1, wherein one of the first organic compound and the second organic compound is a material having an electron-transport property and the other is a material having a hole-transport property.

7. The light-emitting element according to claim 1, wherein one of the first organic compound and the second organic compound is a n-electron deficient heteroaromatic compound and the other is a n-electron rich heteroaromatic compound or an aromatic amine compound.

8. The light-emitting element according to claim 1, wherein the first organic compound is different from the second organic compound.

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

wherein the exciplex generates the singlet excited state from the triplet excited state, and

wherein an energy is transferred to from a level of the singlet excited state of the exciplex to a level of a single exited state of the fluorescent material.

10. A light-emitting element comprising:

a pair of electrodes; and

an EL layer between the pair of electrodes,

wherein the EL layer comprises a light-emitting layer,

wherein the light-emitting layer comprises a thermally activated delayed fluorescence substance and a fluorescent material,

wherein the thermally activated delayed fluorescence substance comprises a first organic compound and a second organic compound, wherein the first organic compound and the second organic compound form and exciplex which exhibits thermally activated delayed fluorescence, and wherein, in the exciplex, a difference between levels of a triplet excited state and a singlet excited state is 0.2 eV or less.

11. The light-emitting element according to claim 10, wherein light emission of the exciplex is overlapped with an absorption band on a lowest energy side of the fluorescent material.

12. The light-emitting element according to claim 11, wherein a difference in energy between a peak wavelength of the absorption band on the lowest energy side of the fluorescent material and a peak wavelength of the exciplex is 0.2 eV or less.

13. The light-emitting element according to claim 11, wherein a peak wavelength of light emission of the exciplex is longer than or equal to a peak wavelength of the absorption band on the lowest energy side of the fluorescent material.

14. The light-emitting element according to claim 11, wherein a difference between a peak wavelength of light emission of the exciplex and a peak wavelength of light emission of the fluorescent material is 30 nm or less.

15. The light-emitting element according to claim 10, wherein one of the first organic compound and the second organic compound is a material having an electron-transport property and the other is a material having a hole-transport property.

16. The light-emitting element according to claim 10, wherein one of the first organic compound and the second organic compound is a π

-electron deficient heteroaromatic compound and the other is a π

-electron rich heteroaromatic compound or an aromatic amine compound.

17. The light-emitting element according to claim 10, wherein the first organic compound is different from the second organic compound.

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

wherein the exciplex generates the singlet excited state from the triplet excited state, and

wherein an energy is transferred to from a level of the singlet excited state of the exciplex to a level of a single exited state of the fluorescent material.