Light-emitting element

• US 8,981,355 B2
• Filed: 02/06/2013
• Issued: 03/17/2015
• Est. Priority Date: 02/09/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Seo, Satoshi
• Primary Examiner(s): Stark, Jarrett
• Assistant Examiner(s): Ahmed, Shahed
• Application Number:
  US13/760,301
• Publication Number:
  US 20130207088A1
• Time in Patent Office: 769 Days
• Field of Search: 257/50, 257/40, 257/79, 257/E51.002, 313/504
• US Class Current: 257/40
• 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 2211/1029 containing one nitrogen atom as the heteroatom
• CPC Class Codes: C09K 2211/1059 containing three nitrogen atoms as heteroatoms
• CPC Class Codes: C09K 2211/185 of the platinum group, i.e. Os, Ir, Pt, Ru, Rh or Pd
• CPC Class Codes: C09K 2211/188 of other metals not provided for in one of the previous groups
• CPC Class Codes: H01L 31/02322 comprising luminescent members, e.g. fluorescent sheets upon the device
• 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 2101/30 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 2102/00 Constructional details relating to the organic devices covered by this subclass
• CPC Class Codes: H10K 50/00 Organic light-emitting devices integrated devices or assemblies of multiple devices H10K59/00, H10K65/00; organic semiconductor lasers H01S5/36
• 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 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: H10K 50/17 Carrier injection layers
• CPC Class Codes: H10K 50/171 : Electron injection layers
• CPC Class Codes: H10K 85/30 : Coordination compounds
• CPC Class Codes: H10K 85/346 : comprising platinum
• CPC Class Codes: H10K 85/649 : Aromatic compounds comprising a hetero 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

Abstract

Provided is a light-emitting element with high external quantum efficiency and a low drive voltage. The light-emitting element includes a light-emitting layer which contains a phosphorescent compound and a material exhibiting thermally activated delayed fluorescence between a pair of electrodes, wherein a peak of a fluorescence spectrum and/or a peak of a phosphorescence spectrum of the material exhibiting thermally activated delayed fluorescence overlap(s) with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound, and wherein the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes.

Claims

1. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer between the pair of electrodes,

wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and

wherein a peak of a fluorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.

2. The light-emitting element according to claim 1, wherein a difference between an energy value of the peak of the fluorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less.

3. The light-emitting element according to claim 1, wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.

4. The light-emitting element according to claim 1, wherein the phosphorescent compound is an organometallic complex.

5. The light-emitting element according to claim 1, wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·

cm.

6. The light-emitting element according to claim 1, wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π

-electron excess heteroaromatic ring and a π

-electron deficient heteroaromatic ring.

7. The light-emitting element according to claim 6, wherein in the thermally activated delayed fluorescence material, the π

-electron excess heteroaromatic ring is directly bonded to the π

-electron deficient heteroaromatic ring.

8. A light-emitting device comprising the light-emitting element according to claim 1.

9. An electronic device comprising the light-emitting element according to claim 1.

10. A lighting device comprising the light-emitting element according to claim 1.

32. The light-emitting element according to claim 1, wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.

11. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer between the pair of electrodes,

wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and

wherein a peak of a phosphorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.

12. The light-emitting element according to claim 11, wherein a difference between an energy value of the peak of the phosphorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less.

13. The light-emitting element according to claim 11, wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.

14. The light-emitting element according to claim 11, wherein the phosphorescent compound is an organometallic complex.

15. The light-emitting element according to claim 11, wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·

cm.

16. The light-emitting element according to claim 11, wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π

-electron excess heteroaromatic ring and a π

-electron deficient heteroaromatic ring.

17. The light-emitting element according to claim 16, wherein in the thermally activated delayed fluorescence material, the π

-electron excess heteroaromatic ring is directly bonded to the π

-electron deficient heteroaromatic ring.

18. A light-emitting device comprising the light-emitting element according to claim 11.

19. An electronic device comprising the light-emitting element according to claim 11.

20. A lighting device comprising the light-emitting element according to claim 11.

33. The light-emitting element according to claim 11, wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.

21. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer between the pair of electrodes,

wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and

wherein a peak of a fluorescence spectrum and a peak of a phosphorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.

22. The light-emitting element according to claim 21,

wherein a difference between an energy value of the peak of the fluorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less, and

wherein a difference between an energy value of the peak of the phosphorescence spectrum and the energy value of the peak of the lowest-energy-side absorption band is 0.3 eV or less.

23. The light-emitting element according claim 21, wherein a difference between the energy value of the peak of the fluorescence spectrum and the energy value of the peak of the phosphorescence spectrum is 0.3 eV or less.

24. The light-emitting element according to claim 21, wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.

25. The light-emitting element according to claim 21, wherein the phosphorescent compound is an organometallic complex.

26. The light-emitting element according to claim 21, wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·

cm.

27. The light-emitting element according to claim 21, wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π

-electron excess heteroaromatic ring and a π

-electron deficient heteroaromatic ring.

28. The light-emitting element according to claim 27, wherein in the thermally activated delayed fluorescence material, the π

-electron excess heteroaromatic ring is directly bonded to the π

-electron deficient heteroaromatic ring.

29. A light-emitting device comprising the light-emitting element according to claim 21.

30. An electronic device comprising the light-emitting element according to claim 21.

31. A lighting device comprising the light-emitting element according to claim 21.

34. The light-emitting element according to claim 21, wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.