Light-emitting element, display device, electronic device, and lighting device
A light-emitting element having high emission efficiency which includes a fluorescent material as a light-emitting substance is provided. A light-emitting element includes a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a light-emitting layer. The light-emitting layer includes a host material and a guest material. The host material has a difference of more than 0 eV and less than or equal to 0.2 eV between a singlet excitation energy level and a triplet excitation energy level. The guest material is capable of emitting fluorescence. The triplet excitation energy level of the host material is higher than a triplet excitation energy level of the guest material.
1. A light-emitting element comprising:
a pair of electrodes;
a first electroluminescence layer and a second electroluminescence layer between the pair of electrodes; and
a charge generation layer between the first electroluminescence layer and the second electroluminescence layer,
wherein the first electroluminescence layer comprises a light-emitting layer,
wherein the light-emitting layer comprises a first material and a second material,
wherein the second material is capable of emitting fluorescence,
wherein a difference between a singlet excitation energy level and a triplet excitation energy level of the first material is more than 0 eV and less than or equal to 0.2 eV, and
wherein the triplet excitation energy level of the first material is higher than a triplet excitation energy level of the second material.
2. The light-emitting element according to claim 1 , wherein the singlet excitation energy level of the first material is higher than a singlet excitation energy level of the second material.
3. The light-emitting element according to claim 1 , wherein a difference between the lowest singlet excitation energy level and the lowest triplet excitation energy level in the first material is more than 0 eV and less than or equal to 0.2 eV.
4. The light-emitting element according to claim 1 ,
wherein the first material is capable of exhibiting thermally activated delayed fluorescence at room temperature, and
wherein a thermally activated delayed fluorescence emission energy of the first material is higher than a phosphorescence emission energy of the second material.
5. The light-emitting element according to claim 1 ,
wherein the first material is a first organic compound, and
wherein the second material is a second organic compound.
6. The light-emitting element according to claim 1 ,
wherein a weight ratio of the second material to the first material is more than 0 and less than or equal to 0.05.
7. The light-emitting element according to claim 1 , wherein the first electroluminescence layer comprises at least one selected from a hole-injection layer, a hole-transport layer, an electron-transport layer, and an electron-injection layer.
8. A display device comprising:
the light-emitting element according to claim 1 ; and
a color filter overlapping with the light-emitting element.
9. An electronic device comprising:
the display device according to claim 8 ; and
a housing or a touch sensor.
10. A lighting device comprising:
the light-emitting element according to claim 1 ; and
a housing or a touch sensor.
11. A light-emitting element comprising:
a pair of electrodes;
a first electroluminescence layer and a second electroluminescence layer between the pair of electrodes; and
a charge generation layer between the first electroluminescence layer and the second electroluminescence layer,
wherein the first electroluminescence layer comprises a first light-emitting layer,
wherein the first light-emitting layer comprises a first material and a second material,
wherein the second material is capable of emitting fluorescence,
wherein a difference between a singlet excitation energy level and a triplet excitation energy level of the first material is more than 0 eV and less than or equal to 0.2 eV,
wherein the triplet excitation energy level of the first material is higher than a triplet excitation energy level of the second material, and
wherein an emission spectrum of the first material comprises a region overlapping with an absorption band on a longest wavelength side in an absorption spectrum of the second material.
12. The light-emitting element according to claim 11 , wherein the singlet excitation energy level of the first material is higher than a singlet excitation energy level of the second material.
13. The light-emitting element according to claim 11 , wherein a difference between the lowest singlet excitation energy level and the lowest triplet excitation energy level in the first material is more than 0 eV and less than or equal to 0.2 eV.
14. The light-emitting element according to claim 11 ,
wherein the first material is capable of exhibiting thermally activated delayed fluorescence at room temperature, and
wherein a thermally activated delayed fluorescence emission energy of the first material is higher than a phosphorescence emission energy of the second material.
15. The light-emitting element according to claim 11 ,
wherein the first material is a first organic compound, and
wherein the second material is a second organic compound.
16. The light-emitting element according to claim 11 ,
wherein a weight ratio of the second material to the first material is more than 0 and less than or equal to 0.05.
17. The light-emitting element according to claim 11 , wherein the first electroluminescence layer comprises at least one selected from a hole-injection layer, a hole-transport layer, an electron-transport layer, and an electron-injection layer.
18. A display device comprising:
the light-emitting element according to claim 11 ; and
a color filter overlapping with the light-emitting element.
19. An electronic device comprising:
the display device according to claim 18 ; and
a housing or a touch sensor.
20. A lighting device comprising:
the light-emitting element according to claim 11 ; and
a housing or a touch sensor.