Light-emitting element
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.
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 −1 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 −1 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 −1 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 −1 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.