Light-emitting element

• US 10,573,829 B2
• Filed: 05/21/2018
• Issued: 02/25/2020
• 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): Rahman, Moin M
• Application Number:
  US15/984,825
• Publication Number:
  US 20180269410A1
• Time in Patent Office: 645 Days
• 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 method of emitting light from a light-emitting element comprising a first compound, a second compound, and a phosphorescent compound between a pair of electrodes, the method comprising:

forming an exciplex between the first compound and the second compound; and

transferring an excitation energy from the exciplex to the phosphorescent compound,

wherein the phosphorescent compound has an absorption spectrum comprising absorption bands, an emission spectrum of the exciplex overlaps with the absorption band having the longest wavelength, and a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band having the longest wavelength is 0.2 eV or less, and

wherein each of a level of a triplet excitation energy of the first compound and a level of a triplet excitation energy of the second compound is higher than a level of a triplet excitation energy of the phosphorescent compound.

2. The method according to claim 1, wherein the difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band having the longest wavelength is 0.1 eV or less.

3. The method according to claim 1, wherein the emission spectrum is a fluorescence spectrum.

4. The method according to claim 1, wherein the phosphorescent compound is an organometallic complex.

5. The method according to claim 1, wherein the phosphorescent compound is an iridium complex.

6. The method according to claim 1, wherein a molar absorption coefficient of the absorption band having the longest wavelength is 2000 M⁻

1·

cm<sup>−

1</sup> or higher.

7. The method according to claim 1,

wherein the first compound comprises a heterocyclic compound, and

wherein the second compound comprises a carbazole compound.

8. The method according to claim 1,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes, and

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

9. The method according to claim 1,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes,

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

wherein the hole-injection layer comprises an organic compound and an electron acceptor.

10. A method of emitting light from a light-emitting element comprising a first compound, a second compound, and a phosphorescent compound between a pair of electrodes, the method comprising:

applying a voltage between the pair of electrodes to form an exciplex between the first compound and the second compound,

wherein an excitation energy of the exciplex is transferred to the phosphorescent compound,

wherein the phosphorescent compound has an absorption spectrum comprising absorption bands, an emission spectrum of the exciplex overlaps with the absorption band having the longest wavelength, and a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band having the longest wavelength is 0.2 eV or less, and

wherein each of a level of a triplet excitation energy of the first compound and a level of a triplet excitation energy of the second compound is higher than a level of a triplet excitation energy of the phosphorescent compound.

11. The method according to claim 10, wherein the difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band having the longest wavelength is 0.1 eV or less.

12. The method according to claim 10, wherein the emission spectrum is a fluorescence spectrum.

13. The method according to claim 10, wherein the phosphorescent compound is an organometallic complex.

14. The method according to claim 10, wherein the phosphorescent compound is an iridium complex.

15. The method according to claim 10, wherein a molar absorption coefficient of the absorption band having the longest wavelength is 2000 M⁻

1·

cm<sup>−

1</sup> or higher.

16. The method according to claim 10,

wherein the first compound comprises a heterocyclic compound, and

wherein the second compound comprises a carbazole compound.

17. The method according to claim 10,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes, and

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

18. The method according to claim 10,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes,

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

wherein the hole-injection layer comprises an organic compound and an electron acceptor.

19. A method of using a light-emitting element comprising a first compound, a second compound, and a phosphorescent compound between a pair of electrodes, the method comprising:

forming an exciplex between the first compound and the second compound; and

transferring an excitation energy from the exciplex to the phosphorescent compound,

wherein the phosphorescent compound has an absorption spectrum comprising absorption bands, an emission spectrum of the exciplex overlaps with the absorption band having the longest wavelength, and a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band having the longest wavelength is 0.2 eV or less, and

wherein each of a level of a triplet excitation energy of the first compound and a level of a triplet excitation energy of the second compound is higher than a level of a triplet excitation energy of the phosphorescent compound.

20. The method according to claim 19, wherein the difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band having the longest wavelength is 0.1 eV or less.

21. The method according to claim 19, wherein the emission spectrum is a fluorescence spectrum.

22. The method according to claim 19, wherein the phosphorescent compound is an organometallic complex.

23. The method according to claim 19, wherein the phosphorescent compound is an iridium complex.

24. The method according to claim 19, wherein a molar absorption coefficient of the absorption band having the longest wavelength is 2000 M⁻

1·

cm<sup>−

1</sup> or higher.

25. The method according to claim 19,

wherein the first compound comprises a heterocyclic compound, and

wherein the second compound comprises a carbazole compound.

26. The method according to claim 19,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes, and

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

27. The method according to claim 19,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes,

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

wherein the hole-injection layer comprises an organic compound and an electron acceptor.

28. The method according to claim 19, wherein the light-emitting element emits light.

29. A method of using a light-emitting element comprising a first compound, a second compound, and a phosphorescent compound between a pair of electrodes, the method comprising:

applying a voltage between the pair of electrodes to form an exciplex between the first compound and the second compound,

wherein an excitation energy of the exciplex is transferred to the phosphorescent compound,

wherein the phosphorescent compound has an absorption spectrum comprising absorption bands, an emission spectrum of the exciplex overlaps with the absorption band having the longest wavelength, and a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the absorption band having the longest wavelength is 0.2 eV or less, and

wherein each of a level of a triplet excitation energy of the first compound and a level of a triplet excitation energy of the second compound is higher than a level of a triplet excitation energy of the phosphorescent compound.

30. The method according to claim 29, wherein the difference between the energy value of the peak of the emission spectrum and the energy value of a peak of the absorption band having the longest wavelength is 0.1 eV or less.

31. The method according to claim 29, wherein the emission spectrum is a fluorescence spectrum.

32. The method according to claim 29, wherein the phosphorescent compound is an organometallic complex.

33. The method according to claim 29, wherein the phosphorescent compound is an iridium complex.

34. The method according to claim 29, wherein a molar absorption coefficient of the absorption band having the longest wavelength is 2000 M⁻

1·

cm<sup>−

1</sup> or higher.

35. The method according to claim 29,

wherein the first compound comprises a heterocyclic compound, and

wherein the second compound comprises a carbazole compound.

36. The method according to claim 29,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes, and

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

37. The method according to claim 29,

wherein the light-emitting element comprises a light-emitting layer and a hole-injection layer between the pair of electrodes,

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

wherein the hole-injection layer comprises an organic compound and an electron acceptor.

38. The method according to claim 29, wherein the light-emitting element emits light.