Light-emitting element, display device, electronic device, and lighting device
A light-emitting element having low driving voltage and high emission efficiency is provided. In the light-emitting element, a combination of a guest material and a host material forms an exciplex. The guest material is capable of converting triplet excitation energy into light emission. Light emission from the light-emitting layer includes light emission from the guest material and light emission from the exciplex. The percentage of the light emission from the exciplex to the light emission from the light-emitting layer is greater than 0 percent and less than or equal to 60 percent. The energy after subtracting the energy of light emission from the exciplex from the energy of light emission from the guest material is greater than 0 eV and less than or equal to 0.23 eV.
1. A light-emitting element comprising:
a light-emitting layer comprising:
a first organic compound; and
a second organic compound,
wherein the first organic compound has a LUMO level higher than or equal to a LUMO level of the second organic compound, and has a HOMO level higher than or equal to a HOMO level of the second organic compound,
wherein the first organic compound is a phosphorescent compound, and
wherein a relation 0 eV<E G_abs −ΔE Ex ≤0.23 eV is satisfied where E G_abs is transition energy calculated from an absorption edge of an absorption spectrum of the first organic compound and ΔE Ex is an energy difference between the HOMO level of the first organic compound and the LUMO level of the second organic compound.
2. The light-emitting element according to claim 1 , wherein the second organic compound comprises at least one of a pyridine skeleton, a diazine skeleton, and a triazine skeleton.
3. The light-emitting element according to claim 1 , wherein the first organic compound comprises iridium.
4. The light-emitting element according to claim 1 , wherein the first organic compound and the second organic compound form a first exciplex.
5. The light-emitting element according to claim 4 ,
wherein light emission from the light-emitting layer comprises light emission from the first organic compound and light emission from the first exciplex, and
wherein the light emission from the light-emitting layer comprises an emission component whose time in which emission intensity is reduced to lower than or equal to 1% is shorter than or equal to 37 μs.
6. The light-emitting element according to claim 4 , wherein a lowest triplet excitation energy level of the second organic compound is higher than or equal to a lowest triplet excitation energy level of the first organic compound.
7. The light-emitting element according to claim 4 , wherein a lowest triplet excitation energy level of the first organic compound is higher than or equal to a lowest triplet excitation energy level of the first exciplex.
8. The light-emitting element according to claim 1 ,
wherein the light-emitting layer further comprises a third organic compound,
wherein one of the LUMO level of the second organic compound and a LUMO level of the third organic compound is higher than or equal to the other of the LUMO level of the second organic compound and the LUMO level of the third organic compound,
wherein one of the HOMO level of the second organic compound and a HOMO level of the third organic compound is higher than or equal to the other of the HOMO level of the second organic compound and the HOMO level of the third organic compound.
9. The light-emitting element according to claim 8 , wherein the second organic compound and the third organic compound form a second exciplex.
10. A display device comprising the light-emitting element according to claim 1 , and a transistor.
11. A light-emitting element comprising:
a light-emitting layer comprising:
a first organic compound; and
a second organic compound,
wherein one of the first organic compound and the second organic compound has a LUMO level higher than or equal to a LUMO level of the other of the first organic compound and the second organic compound, and has a HOMO level higher than or equal to a HOMO level of the other of the first organic compound and the second organic compound,
wherein the first organic compound is a phosphorescent compound, and
wherein a relation 0 eV<E G_abs −ΔE Ex ≤0.18 eV is satisfied where E G_abs is transition energy calculated from an absorption edge of an absorption spectrum of the first organic compound and ΔE Ex is an energy difference between the HOMO level of the one of the first organic compound and the second organic compound and the LUMO level of the other of the first organic compound and the second organic compound.
12. The light-emitting element according to claim 11 , wherein the first organic compound comprises iridium.
13. The light-emitting element according to claim 11 , wherein the first organic compound and the second organic compound form a first exciplex.
14. The light-emitting element according to claim 13 ,
wherein light emission from the light-emitting layer comprises light emission from the first organic compound and light emission from the first exciplex, and
wherein the light emission from the light-emitting layer comprises an emission component whose time in which emission intensity is reduced to lower than or equal to 1% is shorter than or equal to 37 μs.
15. The light-emitting element according to claim 13 , wherein a lowest triplet excitation energy level of the second organic compound is higher than or equal to a lowest triplet excitation energy level of the first organic compound.
16. The light-emitting element according to claim 13 , wherein a lowest triplet excitation energy level of the first organic compound is higher than or equal to a lowest triplet excitation energy level of the first exciplex.
17. The light-emitting element according to claim 11 ,
wherein the light-emitting layer further comprises a third organic compound,
wherein one of the LUMO level of the second organic compound and a LUMO level of the third organic compound is higher than or equal to the other of the LUMO level of the second organic compound and the LUMO level of the third organic compound,
wherein one of the HOMO level of the second organic compound and a HOMO level of the third organic compound is higher than or equal to the other of the HOMO level of the second organic compound and the HOMO level of the third organic compound.
18. The light-emitting element according to claim 17 , wherein the second organic compound and the third organic compound form a second exciplex.
19. A display device comprising the light-emitting element according to claim 11 , and a transistor.
20. A light-emitting element comprising:
a light-emitting layer comprising:
a first organic compound;
a second organic compound; and
a third organic compound,
wherein one of the first organic compound and the second organic compound has a LUMO level higher than or equal to a LUMO level of the other of the first organic compound and the second organic compound, and has a HOMO level higher than or equal to a HOMO level of the other of the first organic compound and the second organic compound,
wherein an energy difference between the HOMO level of the first organic compound and a HOMO level of the third organic compound is greater than or equal to 0 eV and smaller than or equal to 0.3 eV,
wherein the first organic compound is a phosphorescent compound, and
wherein a relation 0 eV<E G_abs −ΔE Ex ≤0.23 eV is satisfied where E G_abs is transition energy calculated from an absorption edge of an absorption spectrum of the first organic compound and ΔE Ex is an energy difference between the HOMO level of the one of the first organic compound and the second organic compound and the LUMO level of the other of the first organic compound and the second organic compound.
21. The light-emitting element according to claim 20 , wherein the first organic compound comprises iridium.
22. The light-emitting element according to claim 20 , wherein the first organic compound and the second organic compound form a first exciplex.
23. The light-emitting element according to claim 22 ,
wherein light emission from the light-emitting layer comprises light emission from the first organic compound and light emission from the first exciplex, and
wherein the light emission from the light-emitting layer comprises an emission component whose time in which emission intensity is reduced to lower than or equal to 1% is shorter than or equal to 37 μs.
24. The light-emitting element according to claim 22 , wherein a lowest triplet excitation energy level of the second organic compound is higher than or equal to a lowest triplet excitation energy level of the first organic compound.
25. The light-emitting element according to claim 22 , wherein a lowest triplet excitation energy level of the first organic compound is higher than or equal to a lowest triplet excitation energy level of the first exciplex.
26. The light-emitting element according to claim 20 ,
wherein one of the LUMO level of the second organic compound and a LUMO level of the third organic compound is higher than or equal to the other of the LUMO level of the second organic compound and the LUMO level of the third organic compound, and
wherein one of the HOMO level of the second organic compound and the HOMO level of the third organic compound is higher than or equal to the other of the HOMO level of the second organic compound and the HOMO level of the third organic compound.
27. The light-emitting element according to claim 26 , wherein the second organic compound and the third organic compound form a second exciplex.
28. A display device comprising the light-emitting element according to claim 20 , and a transistor.