Light-emitting element, display device, electronic device, and lighting device
A light-emitting element with high luminous efficiency is provided. The light-emitting element contains a first organic compound and a second organic compound. The first and second organic compounds form an exciplex. The first organic compound emits no fluorescence but phosphorescence at a temperature ranging from low temperature to normal temperature. The luminescence quantum yield of the first organic compound is higher than or equal to 0% and lower than or equal to 40% at room temperature. Light emitted from the light-emitting element includes light emitted from an exciplex formed by the first organic compound and the second organic compound.
1. A light-emitting element comprising a light-emitting layer comprising a first organic compound and a second organic compound,
wherein a LUMO level of one of the first organic compound and the second organic compound is higher than or equal to a LUMO level of the other of the first organic compound and the second organic compound,
wherein a HOMO level of the one of the first organic compound and the second organic compound is higher than or equal to a HOMO level of the other of the first organic compound and the second organic compound,
wherein a combination of the first organic compound and the second organic compound is capable of forming an exciplex,
wherein the first organic compound is capable of converting triplet excitation energy into light emission,
wherein the first organic compound has a luminescence quantum yield higher than or equal to 0% and lower than or equal to 40% at room temperature, and
wherein light emitted from the light-emitting layer comprises light emitted from the exciplex.
2. The light-emitting element according to claim 1 , 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 second organic compound.
3. The light-emitting element according to claim 1 , wherein the first organic compound comprises a ligand coordinated to Ir.
4. The light-emitting element according to claim 3 , wherein the ligand comprises a nitrogen-containing five-membered heterocyclic skeleton.
5. The light-emitting element according to claim 1 ,
wherein the second organic compound is capable of transporting an electron, and
wherein the second organic compound comprises a π-electron deficient heteroaromatic skeleton.
6. The light-emitting element according to claim 1 , wherein the exciplex is capable of emitting light with luminous efficiency higher than luminous efficiency of light emitted from the first organic compound.
7. A display device comprising:
the light-emitting element according to claim 1 ; and
at least one of a color filter and a transistor.
8. A light-emitting element comprising a light-emitting layer comprising a first organic compound and a second organic compound,
wherein a LUMO level of one of the first organic compound and the second organic compound is higher than or equal to a LUMO level of the other of the first organic compound and the second organic compound,
wherein a HOMO level of the one of the first organic compound and the second organic compound is higher than or equal to a HOMO level of the other of the first organic compound and the second organic compound,
wherein a combination of the first organic compound and the second organic compound is capable of forming an exciplex,
wherein the first organic compound is capable of not emitting fluorescence,
wherein the first organic compound is capable of emitting phosphorescence,
wherein the first organic compound has a luminescence quantum yield higher than or equal to 0% and lower than or equal to 40% at room temperature, and
wherein light emitted from the light-emitting layer comprises light emitted from the exciplex.
9. The light-emitting element according to claim 8 , 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 second organic compound.
10. The light-emitting element according to claim 8 , wherein the first organic compound comprises a ligand coordinated to Ir.
11. The light-emitting element according to claim 10 , wherein the ligand comprises a nitrogen-containing five-membered heterocyclic skeleton.
12. The light-emitting element according to claim 8 ,
wherein the second organic compound is capable of transporting an electron, and
wherein the second organic compound comprises a π-electron deficient heteroaromatic skeleton.
13. The light-emitting element according to claim 8 , wherein the exciplex is capable of emitting light with luminous efficiency higher than luminous efficiency of light emitted from the first organic compound.
14. A display device comprising:
the light-emitting element according to claim 8 ; and
at least one of a color filter and a transistor.
15. A light-emitting element comprising a light-emitting layer comprising a first organic compound and a second organic compound,
wherein a LUMO level of one of the first organic compound and the second organic compound is higher than or equal to a LUMO level of the other of the first organic compound and the second organic compound,
wherein a HOMO level of the one of the first organic compound and the second organic compound is higher than or equal to a HOMO level of the other of the first organic compound and the second organic compound,
wherein a combination of the first organic compound and the second organic compound is capable of forming an exciplex,
wherein the first organic compound comprises Ru, Rh, Pd, Os, Ir, or Pt,
wherein the first organic compound has a luminescence quantum yield higher than or equal to 0% and lower than or equal to 40% at room temperature, and
wherein light emitted from the light-emitting layer comprises light emitted from the exciplex.
16. The light-emitting element according to claim 15 , 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 second organic compound.
17. The light-emitting element according to claim 15 , wherein the first organic compound comprises a ligand coordinated to Ir.
18. The light-emitting element according to claim 17 , wherein the ligand comprises a nitrogen-containing five-membered heterocyclic skeleton.
19. The light-emitting element according to claim 15 ,
wherein the second organic compound is capable of transporting an electron, and
wherein the second organic compound comprises a π-electron deficient heteroaromatic skeleton.
20. The light-emitting element according to claim 15 , wherein the exciplex is capable of emitting light with luminous efficiency higher than luminous efficiency of light emitted from the first organic compound.
21. A display device comprising:
the light-emitting element according to claim 15 ; and
at least one of a color filter and a transistor.