Light-emitting element

• US 9,604,928 B2
• Filed: 02/10/2012
• Issued: 03/28/2017
• Est. Priority Date: 02/16/2011
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Shitagaki, Satoko, Seo, Satoshi, Ohsawa, Nobuharu, Inoue, Hideko, Suzuki, Kunihiko
• Primary Examiner(s): Maldonado, Julio J
• Assistant Examiner(s): RAHMAN, MOIN M
• Application Number:
  US13/370,679
• Publication Number:
  US 20120205632A1
• Time in Patent Office: 1,873 Days
• Field of Search: 257/40, 257642-643, 257/759, 257/E51.001, 257/E51.052, 257E25008-E25009
• US Class Current: 1/1
• CPC Class Codes: C07D 209/86 with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to carbon atoms of the ring system
• CPC Class Codes: C07D 239/26 with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to ring carbon atoms
• CPC Class Codes: C07D 241/12 with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to ring carbon atoms
• CPC Class Codes: C07D 333/76 Dibenzothiophenes
• CPC Class Codes: C07D 409/10 linked by a carbon chain containing aromatic rings
• CPC Class Codes: C07D 471/04 Ortho-condensed systems
• CPC Class Codes: C07F 15/0033 Iridium compounds
• CPC Class Codes: C09K 11/025 non-luminescent particle coatings or suspension media
• CPC Class Codes: C09K 11/06 containing organic luminescent materials
• CPC Class Codes: C09K 2211/1007 Non-condensed systems
• CPC Class Codes: C09K 2211/1074 containing more than 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: H10K 2101/10 Triplet 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 2101/90 Multiple hosts in the emissive layer
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 85/342 comprising iridium
• 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 85/631 : Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine
• 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 light-emitting element having high external quantum efficiency is provided. A light-emitting element having a long lifetime is provided. A light-emitting element is provided which includes a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, in which a combination of the first organic compound and the second organic compound forms an exciplex (excited complex). The light-emitting element transfers energy by utilizing an overlap between the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound and thus has high energy transfer efficiency. Therefore, a light-emitting element having high external quantum efficiency can be obtained.

Claims

1. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer comprising a phosphorescent compound, a first organic compound, and a second organic compound between the pair of electrodes,

wherein the first organic compound, the second organic compound, and the phosphorescent compound are mixed in the light-emitting layer,

wherein the first organic compound and the second organic compound are selected so as to form an exciplex, and

wherein a peak of an emission spectrum of the exciplex overlaps with an absorption based on a triplet metal-to-ligand charge transfer of the phosphorescent compound.

2. The light-emitting element according to claim 1, wherein a molar absorption coefficient of the absorption is 2000 M⁻

1•

cm<sup>−

1</sup> or more.

3. The light-emitting element according to claim 1, wherein a molar absorption coefficient of the absorption is 5000 M⁻

1•

cm<sup>−

1</sup> or more.

4. The light-emitting element according to claim 1, wherein an excitation energy of the exciplex is transferred to the phosphorescent compound so that the phosphorescent compound emits phosphorescence.

5. The light-emitting element according to claim 1, wherein at least one of the first organic compound and the second organic compound is a fluorescent compound.

6. The light-emitting element according to claim 1, wherein the phosphorescent compound is selected from bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium(III), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III), and (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III).

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

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

26. The light-emitting element according to claim 1, wherein the first organic compound is a heteroaromatic compound and the second organic compound is an aromatic amine compound.

27. The light-emitting element according to claim 1, wherein the first organic compound is a heteroaromatic compound and the second organic compound is a carbazole compound.

9. A light-emitting element comprising:

a pair of electrodes; and

an EL layer between the pair of electrodes, the EL layer comprising;

a hole-injection layer;

a hole-transport layer over the hole-injection layer;

a light-emitting layer over the hole-transport layer, the light-emitting layer comprising a phosphorescent compound, a first organic compound, and a second organic compound;

an electron-transport layer over the light-emitting layer; and

an electron-injection layer over the electron-transport layer,

wherein the first organic compound, the second organic compound, and the phosphorescent compound are mixed in the light-emitting layer,

wherein the first organic compound and the second organic compound are selected so as to form an exciplex, and

wherein a peak of an emission spectrum of the exciplex overlaps with an absorption based on a triplet metal-to-ligand charge transfer of the phosphorescent compound.

10. The light-emitting element according to claim 9, wherein a molar absorption coefficient of the absorption is 2000 M⁻

1•

cm<sup>−

1</sup> or more.

11. The light-emitting element according to claim 9, wherein a molar absorption coefficient of the absorption is 5000 M⁻

1•

cm<sup>−

1</sup> or more.

12. The light-emitting element according to claim 9, wherein an excitation energy of the exciplex is transferred to the phosphorescent compound so that the phosphorescent compound emits phosphorescence.

13. The light-emitting element according to claim 9, wherein at least one of the first organic compound and the second organic compound is a fluorescent compound.

14. The light-emitting element according to claim 9, wherein the phosphorescent compound is selected from bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium(III), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium((III)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)indium((III)), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)indium(III), and (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)indium(III).

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

16. A lighting device comprising the light-emitting element according to claim 9.

28. The light-emitting element according to claim 9, wherein the first organic compound is a heteroaromatic compound and the second organic compound is an aromatic amine compound.

29. The light-emitting element according to claim 9, wherein the first organic compound is a heteroaromatic compound and the second organic compound is a carbazole compound.

17. A light-emitting element comprising:

a pair of electrodes;

a first EL layer;

a second EL layer; and

a charge-generation layer between the first EL layer and the second EL layer,

wherein the first EL layer, the second EL layer, and the charge-generation layer are stacked between the pair of electrodes,

wherein at least one of the first EL layer and the second EL layer comprises a light-emitting layer which comprises a phosphorescent compound, a first organic compound, and a second organic compound,

wherein the first organic compound, the second organic compound, and the phosphorescent compound are mixed in the light-emitting layer,

wherein the first organic compound and the second organic compound are selected so as to form an exciplex, and

wherein a peak of an emission spectrum of the exciplex overlaps with an absorption based on a triplet metal-to-ligand charge transfer of the phosphorescent compound.

18. The light-emitting element according to claim 17, wherein a molar absorption coefficient of the absorption is 2000 M⁻

1•

cm<sup>−

1</sup> or more.

19. The light-emitting element according to claim 17, wherein a molar absorption coefficient of the absorption is 5000 M⁻

1•

cm<sup>−

1</sup> or more.

20. The light-emitting element according to claim 17, wherein an excitation energy of the exciplex is transferred to the phosphorescent compound so that the phosphorescent compound emits phosphorescence.

21. The light-emitting element according to claim 17, wherein at least one of the first organic compound and the second organic compound is a fluorescent compound.

22. The light-emitting element according to claim 17, wherein the phosphorescent compound is selected from bis(3,5-dimethyl-2-phenylpyrazinato)(dipivaloylmethanato)iridium((III)), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III), and (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III).

23. The light-emitting element according to claim 17, wherein emission colors of the first and the second EL layers are complementary to each other so that the light-emitting element emits white light.

24. An electronic device comprising the light-emitting element according to claim 17.

25. A lighting device comprising the light-emitting element according to claim 17.

30. The light-emitting element according to claim 17, wherein the first organic compound is a heteroaromatic compound and the second organic compound is an aromatic amine compound.

31. The light-emitting element according to claim 17, wherein the first organic compound is a heteroaromatic compound and the second organic compound is a carbazole compound.