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

• US 10,374,186 B2
• Filed: 05/18/2018
• Issued: 08/06/2019
• 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): Seven, Evren
• Application Number:
  US15/983,223
• Publication Number:
  US 20180269418A1
• Time in Patent Office: 445 Days
• Field of Search: None
• 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 device comprising:

an anode, a plurality of light-emitting layers, a first layer and a cathode,

wherein the plurality of light-emitting layers comprises;

a first light-emitting layer over the anode, the first light-emitting layer comprising a fluorescent substance and a host material;

a second light-emitting layer over the first light-emitting layer; and

a third light-emitting layer over and in contact with the second light-emitting layer; and

wherein the first layer is positioned between the first light-emitting layer and the second light-emitting layer,

wherein the cathode is positioned over the third light-emitting layer,

wherein one of the second light-emitting layer and the third light-emitting layer comprises;

a first light-emitting substance which is configured to convert triplet excitation energy into light emission;

a first organic compound; and

a second organic compound,

wherein the first organic compound and the second organic compound are configured to form an exciplex, and

wherein a difference between an energy value of a peak wavelength of an emission spectrum of the exciplex and an energy value of a peak wavelength of a lowest-energy absorption band of the first light-emitting substance is 0.2 eV or less.

2. The light-emitting device according to claim 1, wherein the second light-emitting layer comprises a second light-emitting substance which is configured to convert triplet excitation energy into light emission.

3. The light-emitting device according to claim 1, wherein the first light-emitting substance is a phosphorescent material.

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

wherein the second light-emitting layer comprises a second light-emitting substance which is configured to convert triplet excitation energy into light emission, and

wherein each of the first light-emitting substance and the second light-emitting substance is a phosphorescent material.

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

wherein a peak wavelength of a spectrum emitted from the first light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the second light-emitting layer, and

wherein the peak wavelength of the spectrum emitted from the first light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the third light-emitting layer.

6. The light-emitting device according to claim 1, wherein a peak wavelength of a spectrum emitted from the third light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the second light-emitting layer.

7. The light-emitting device according to claim 1, wherein a triplet excited level of the host material is lower than a triplet excited level of the fluorescent substance.

8. The light-emitting device according to claim 1, wherein the host material has an anthracene skeleton.

9. The light-emitting device according to claim 1, wherein the fluorescent substance is a pyrenediamine compound.

10. A light-emitting device comprising:

a first light-emitting element, a second light-emitting element, a third light-emitting element and a fourth light-emitting element, each comprising an anode, a plurality of light-emitting layers, a first layer and a cathode,

wherein the plurality of light-emitting layers each comprises;

a first light-emitting layer over the anode and between the anode and the first layer, the first light-emitting layer each comprising a fluorescent substance and a host material;

a second light-emitting layer over the first layer; and

a third light-emitting layer over and in contact with the second light-emitting layer and between the second light-emitting layer and the cathode,

wherein one of the second light-emitting layer and the third light-emitting layer each comprises;

a first light-emitting substance which is configured to convert triplet excitation energy into light emission;

a first organic compound; and

a second organic compound,

wherein the first organic compound and the second organic compound are configured to form an exciplex, and

wherein a difference between an energy value of a peak wavelength of an emission spectrum of the exciplex and an energy value of a peak wavelength of a lowest-energy absorption band of the first light-emitting substance is 0.2 eV or less,

wherein the first light-emitting element and a red color filter overlap each other,

wherein the second light-emitting element and a green color filter overlap each other,

wherein the third light-emitting element and a blue color filter overlap each other, and

wherein the fourth light-emitting element has a region which overlap none of the red color filter, the green color filter or the blue color filter.

11. The light-emitting device according to claim 10, wherein the second light-emitting layer comprises a second light-emitting substance which is configured to convert triplet excitation energy into light emission.

12. The light-emitting device according to claim 10, wherein the first light-emitting substance is a phosphorescent material.

13. The light-emitting device according to claim 10,

wherein the second light-emitting layer comprises a second light-emitting substance which is configured to convert triplet excitation energy into light emission, and

wherein each of the first light-emitting substance and the second light-emitting substance is a phosphorescent material.

14. The light-emitting device according to claim 10,

wherein a peak wavelength of a spectrum emitted from the first light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the second light-emitting layer, and

wherein the peak wavelength of the spectrum emitted from the first light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the third light-emitting layer.

15. The light-emitting device according to claim 10, wherein a peak wavelength of a spectrum emitted from the third light-emitting layer is shorter than a peak wavelength of a spectrum emitted from the second light-emitting layer.

16. The light-emitting device according to claim 10, wherein a triplet excited level of the host material is lower than a triplet excited level of the fluorescent substance.

17. The light-emitting device according to claim 10, wherein the host material has an anthracene skeleton.

18. The light-emitting device according to claim 10, wherein the fluorescent substance is a pyrenediamine compound.