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

• US 9,059,421 B2
• Filed: 07/31/2013
• Issued: 06/16/2015
• 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, Ishisone, Takahiro
• Primary Examiner(s): Vu, David
• Assistant Examiner(s): NGUYEN, CUONG B
• Application Number:
  US13/955,904
• Publication Number:
  US 20140034927A1
• Time in Patent Office: 685 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 2101/20 Delayed fluorescence emission
• CPC Class Codes: H10K 2101/25 using exciplex
• CPC Class Codes: H10K 2101/27 Combination of fluorescent and phosphorescent emission
• 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 50/13 comprising stacked EL layers within one EL unit
• CPC Class Codes: H10K 50/81 Anodes
• CPC Class Codes: H10K 50/82 Cathodes
• CPC Class Codes: H10K 85/341 Transition metal complexes, e.g. Ru(II)polypyridine complexes H10K85/331 takes precedence
• CPC Class Codes: H10K 85/342 comprising iridium
• CPC Class Codes: H10K 85/346 comprising platinum
• CPC Class Codes: H10K 85/615 Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
• CPC Class Codes: H10K 85/624 containing six or more rings
• CPC Class Codes: H10K 85/626 containing more than one polycyclic condensed aromatic rings, e.g. bis-anthracene
• 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

Abstract

A multicolor light-emitting element using fluorescence and phosphorescence, which has a small number of manufacturing steps owing to a relatively small number of layers to be formed and is advantageous for practical application can be provided. In addition, a multicolor light-emitting element using fluorescence and phosphorescence, which has favorable emission efficiency is provided. A light-emitting element which includes a light-emitting layer having a stacked-layer structure of a first light-emitting layer exhibiting light emission from a first exciplex and a second light-emitting layer exhibiting phosphorescence is provided.

Claims

1. A light-emitting element comprising:

a first electrode,

a second electrode, and

an electroluminescence layer interposed between the first electrode and the second electrode,

wherein the electroluminescence layer comprises a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked,

wherein the first light-emitting layer contains a first organic compound and a second organic compound,

wherein the second light-emitting layer contains a third organic compound and a phosphorescent substance,

wherein a combination of the first organic compound and the second organic compound forms a first exciplex,

wherein the first light-emitting layer is in contact with the second light-emitting layer,

wherein the first light-emitting layer is a fluorescent layer,

wherein the second light-emitting layer is a phosphorescent layer, and

wherein the first organic compound and the second organic compound are mixed in the first light-emitting layer to form a single light-emitting layer.

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

wherein light emission spectrum of the first exciplex has a peak on a shorter wavelength side than light emission spectrum of the phosphorescent substance.

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

wherein a difference in energy between a triplet excited level and a singlet excited level of the first exciplex is greater than or equal to 0 eV and less than or equal to 0.2 eV.

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

wherein the first light-emitting layer further contains a fluorescent substance.

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

wherein white light emission is exhibited.

6. A light-emitting module comprising:

the light-emitting element according to claim 1, and

a means controlling the light-emitting element.

7. A light-emitting device comprising:

the light-emitting element according to claim 1, and

a means controlling the light-emitting element.

8. An electronic appliance comprising the light-emitting element according to claim 1.

9. A light-emitting element comprising:

a first electrode,

a second electrode, and

an electroluminescence layer interposed between the first electrode and the second electrode,

wherein the electroluminescence layer comprises a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked,

wherein the first light-emitting layer contains a first organic compound and a second organic compound,

wherein the second light-emitting layer contains a third organic compound, a fourth organic compound, and a phosphorescent substance,

wherein a combination of the first organic compound and the second organic compound forms a first exciplex,

wherein a combination of the third organic compound and the fourth organic compound forms a second exciplex,

wherein the first light-emitting layer is in contact with the second light-emitting layer,

wherein the first light-emitting layer is a fluorescent layer, and

wherein the second light-emitting layer is a phosphorescent layer.

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

wherein a light emission spectrum of the first exciplex has a peak on a shorter wavelength side than a light emission spectrum of the phosphorescent substance.

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

wherein a difference in energy between a triplet excited level and a singlet excited level of the first exciplex is greater than or equal to 0 eV and less than or equal to 0.2 eV.

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

wherein a lowest-energy-side absorption band of the phosphorescent substance overlaps with an emission spectrum of the second exciplex.

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

wherein a difference in equivalent energy values between a peak wavelength of the lowest-energy-side absorption band of the phosphorescent substance and a peak wavelength of the emission spectrum of the second exciplex is less than or equal to 0.2 eV.

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

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, and

wherein one of the third organic compound and the fourth organic compound is a material having an electron-transport property and the other is a material having a hole-transport property.

15. The light-emitting element according to claim 14,

wherein one of the first electrode and the second electrode functions as an anode and the other functions as a cathode,

wherein one of the first light-emitting layer and the second light-emitting layer, which is positioned on the side where the electrode functioning as the anode is formed, contains a large amount of the material having the hole-transport property, and

wherein the other of the first light-emitting layer and the second light-emitting layer, which is positioned on the side where the electrode functioning as the cathode is formed, contains a large amount of the material having the electron-transport property.

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

wherein a combination of the first organic compound and the second organic compound is the same as a combination of the third organic compound and the fourth organic compound.

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

wherein light emission spectrum of the first exciplex has a peak on a shorter wavelength side than light emission spectrum of the second exciplex.

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

wherein the first light-emitting layer further contains a fluorescent substance.

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

wherein white light emission is exhibited.