Light-emitting element, light-emitting device, display device, electronic device, and lighting device
An object is to provide a light-emitting element which uses a plurality of kinds of light-emitting dopants and has high emission efficiency. In one embodiment of the present invention, a light-emitting device, a light-emitting module, a light-emitting display device, an electronic device, and a lighting device each having reduced power consumption by using the above light-emitting element are provided. Attention is paid to Förster mechanism, which is one of mechanisms of intermolecular energy transfer. Efficient energy transfer by Förster mechanism is achieved by making an emission wavelength of a molecule which donates energy overlap with the longest-wavelength-side local maximum peak of a graph obtained by multiplying an absorption spectrum of a molecule which receives energy by a wavelength raised to the fourth power.
1. A light-emitting device comprising a light-emitting layer,
the light-emitting layer comprising:
a phosphorescent compound as a guest material; and
a first organic compound and a second organic compound as a host material,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein an emission spectrum of the exciplex has an overlap with a wavelength of a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
2. A light-emitting device comprising a light-emitting layer,
the light-emitting layer comprising:
a phosphorescent compound as a guest material; and
a first organic compound and a second organic compound as a host material,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein a band having a maximum value of an emission spectrum of the exciplex has an overlap with a band having a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
3. A light-emitting device comprising a light-emitting layer,
the light-emitting layer comprising:
a phosphorescent compound as a guest material; and
a first organic compound and a second organic compound as a host material,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein a wavelength range having half of intensity of a maximum value of an emission spectrum of the exciplex has an overlap with a wavelength range having half of intensity of a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
4. The light-emitting device according to claim 1 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and the wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
5. The light-emitting device according to claim 2 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and a wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
6. The light-emitting device according to claim 3 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and a wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
7. The light-emitting device according to claim 1 ,
wherein the phosphorescent compound is an iridium complex.
8. The light-emitting device according to claim 2 ,
wherein the phosphorescent compound is an iridium complex.
9. The light-emitting device according to claim 3 ,
wherein the phosphorescent compound is an iridium complex.
10. The light-emitting device according to claim 1 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
11. The light-emitting device according to claim 2 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
12. The light-emitting device according to claim 3 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
13. The light-emitting device according to claim 1 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
14. The light-emitting device according to claim 2 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
15. The light-emitting device according to claim 3 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
16. A material comprising a first organic compound and a second organic compound,
wherein the material is used in a light-emitting layer including a phosphorescent compound,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein an emission spectrum of the exciplex has an overlap with a wavelength of a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
17. A material comprising a first organic compound and a second organic compound,
wherein the material is used in a light-emitting layer including a phosphorescent compound,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein a band having a maximum value of an emission spectrum of the exciplex has an overlap with a band having a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
18. A material comprising a first organic compound and a second organic compound,
wherein the material is used in a light-emitting layer including a phosphorescent compound,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein a wavelength range having half of intensity of a maximum value of an emission spectrum of the exciplex has an overlap with a wavelength range having half of intensity of a longest-wavelength-side peak of a function ε(λ)λ 4 of the phosphorescent compound,
wherein λ denotes a wavelength, and
wherein ε(λ) denotes a molar absorption coefficient of the phosphorescent compound and is a function of the wavelength λ.
19. The material according to claim 16 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and the wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
20. The material according to claim 17 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and a wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
21. The material according to claim 18 ,
wherein a difference between a peak wavelength of the emission spectrum of the exciplex and a wavelength of the longest-wavelength-side peak of the function ε(λ)λ 4 of the phosphorescent compound is less than or equal to 0.2 eV.
22. The material according to claim 16 ,
wherein the phosphorescent compound is an iridium complex.
23. The material according to claim 17 ,
wherein the phosphorescent compound is an iridium complex.
24. The material according to claim 18 ,
wherein the phosphorescent compound is an iridium complex.
25. The material according to claim 16 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
26. The material according to claim 17 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
27. The material according to claim 18 ,
wherein at least one of the first organic compound and the second organic compound is a heterocyclic compound.
28. The material according to claim 16 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
29. The material according to claim 17 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
30. The material according to claim 18 ,
wherein at least one of the first organic compound and the second organic compound is an aromatic amine compound or a carbazole derivative.
31. The material according to claim 18 ,
wherein the material is used as a host material in the light-emitting layer including the phosphorescent compound as a guest material.
32. A light-emitting device comprising the light-emitting layer,
the light-emitting layer comprising:
the material according to claim 18 as a host material; and
the phosphorescent compound as a guest material.