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

• US 9,362,517 B2
• Filed: 11/20/2014
• Issued: 06/07/2016
• Est. Priority Date: 12/02/2013
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Ohsawa, Nobuharu, Nonaka, Yusuke, Ishisone, Takahiro, Seo, Satoshi, Kawata, Takuya
• Primary Examiner(s): Garber, Charles
• Assistant Examiner(s): Seven, Evren
• Application Number:
  US14/548,947
• Publication Number:
  US 20150155511A1
• Time in Patent Office: 565 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 2101/27 Combination of fluorescent and phosphorescent emission
• CPC Class Codes: H10K 2101/90 Multiple hosts in the emissive layer
• CPC Class Codes: H10K 2102/351 Thickness
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/121 for assisting energy transfer, e.g. sensitization
• CPC Class Codes: H10K 50/131 with spacer layers between the electroluminescent layers
• CPC Class Codes: H10K 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: H10K 59/32 Stacked devices having two or more layers, each emitting at different wavelengths
• CPC Class Codes: H10K 85/342 comprising iridium
• 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 85/626 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 85/654 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
• CPC Class Codes: Y02B 20/00 : Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

An object of one embodiment of the present invention is to provide a multicolor light-emitting element that utilizes fluorescence and phosphorescence and is advantageous for practical application. The light-emitting element has a stacked-layer structure of a first light-emitting layer containing a host material and a fluorescent substance, a separation layer containing a substance having a hole-transport property and a substance having an electron-transport property, and a second light-emitting layer containing two kinds of organic compounds that form an exciplex and a substance that can convert triplet excitation energy into luminescence. Note that a light-emitting element in which light emitted from the first light-emitting layer has an emission spectrum peak on the shorter wavelength side than an emission spectrum peak of the second light-emitting layer is more effective.

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

wherein an emission spectrum of the first light-emitting layer is in a shorter wavelength region than an emission spectrum of the second light-emitting layer,

wherein the first light-emitting layer comprises a fluorescent substance and a host material,

wherein the fluorescent substance emits light in the first light-emitting layer,

wherein the second light-emitting layer comprises a substance capable of converting triplet excitation energy into light emission, a first organic compound, and a second organic compound, and

wherein the first organic compound and the second organic compound form a first exciplex.

2. The light-emitting element according to claim 1, wherein the first layer comprises a substance having a hole-transport property and a substance having an electron-transport property.

3. The light-emitting element according to claim 2, wherein the substance having a hole-transport property and the substance having an electron-transport property form a second exciplex.

4. The light-emitting element according to claim 1, wherein a thickness of the first layer is greater than 0 nm and less than or equal to 20 nm.

5. The light-emitting element according to claim 1, wherein a thickness of the first layer is greater than or equal to 1 nm and less than or equal to 10 nm.

6. The light-emitting element according to claim 2, wherein the first organic compound is the substance having a hole-transport property and the second organic compound is the substance having an electron-transport property.

7. The light-emitting element according to claim 1, wherein energy is transferred from the first exciplex to the substance capable of converting triplet excitation energy into light emission.

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

wherein a singlet excited level of the host material is higher than a singlet excited level of the fluorescent substance, and

wherein a triplet excited level of the host material is lower than a triplet excited level of the fluorescent substance.

9. The light-emitting element according to claim 2, wherein a triplet excited level of the host material is lower than a triplet excited level of the substance having a hole-transport property and a triplet excited level of the substance having an electron-transport property.

10. The light-emitting element according to claim 1, wherein the host material is an organic compound having a condensed aromatic ring skeleton.

11. The light-emitting element according to claim 1, wherein the host material is an organic compound having an anthracene skeleton.

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

wherein the host material is an organic compound having an anthracene skeleton, and

wherein the fluorescent substance is an organic compound having a pyrene skeleton.

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

wherein the second light-emitting layer comprises n layers,

wherein n is an integer of 2 or larger, and

wherein the n layers contain n kinds of substances having different emission spectra and capable of converting triplet excitation energy into light emission.

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

wherein the second light-emitting layer comprises a first phosphorescent substance and a second phosphorescent substance as the substance capable of converting triplet excitation energy into light emission, and

wherein the first phosphorescent substance and the second phosphorescent substance have different emission spectra.

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

wherein the first phosphorescent substance emits light in a red region,

wherein the second phosphorescent substance emits light in a green region, and

wherein the fluorescent substance emits light in a blue region.

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

wherein the first phosphorescent substance has a peak of an emission spectrum of 580 nm to 680 nm,

wherein the second phosphorescent substance has a peak of an emission spectrum of 500 nm to 560 nm, and

wherein the fluorescent substance has a peak of an emission spectrum of 400 nm to 480 nm.

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

wherein the second light-emitting layer comprises a first phosphorescent layer and a second phosphorescent layer,

wherein the first phosphorescent layer comprises the first phosphorescent substance, and

wherein the second phosphorescent layer comprises the second phosphorescent substance.

18. The light-emitting element according to claim 17, wherein the first phosphorescent substance exhibits a carrier-trapping property in the first phosphorescent layer.

19. The light-emitting element according to claim 18, wherein the carrier-trapping property is an electron-trapping property.

20. A display module comprising the light-emitting element according to claim 1.

21. A lighting module comprising the light-emitting element according to claim 1.

22. A light-emitting device comprising:

the light-emitting element according to claim 1; and

a unit for controlling the light-emitting element.

23. A display device comprising:

the light-emitting element according to claim 1 in a display portion; and

a unit for controlling the light-emitting element.

24. A lighting device comprising:

the light-emitting element according to claim 1 in a lighting portion; and

a unit for controlling the light-emitting element.

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