Light-emitting element, light-emitting device, display device, electronic appliance, and lighting device
A multicolor light-emitting element using fluorescence and phosphorescence, which has a small number of manufacturing steps owing to a relatively small number of layers to be formed and is advantageous for practical application can be provided. In addition, a multicolor light-emitting element using fluorescence and phosphorescence, which has favorable emission efficiency is provided. A light-emitting element which includes a light-emitting layer having a stacked-layer structure of a first light-emitting layer exhibiting light emission from a first exciplex and a second light-emitting layer exhibiting phosphorescence is provided.
1. A light-emitting element comprising:
a first electrode,
a second electrode, and
an electroluminescence layer interposed between the first electrode and the second electrode,
wherein the electroluminescence layer comprises a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked,
wherein the first light-emitting layer contains a first organic compound, a second organic compound, and a fluorescent substance,
wherein the second light-emitting layer contains a third organic compound and a phosphorescent substance,
wherein a combination of the first organic compound and the second organic compound forms a first exciplex,
wherein the first light-emitting layer is a fluorescent layer,
wherein the second light-emitting layer is a phosphorescent layer, and
wherein the first organic compound and the second organic compound are mixed in the first light-emitting layer to form a single light-emitting layer.
2. The light-emitting element according to claim 1 , wherein a light emission spectrum of the first exciplex has a peak on a shorter wavelength side than a light emission spectrum of the phosphorescent substance.
3. The light-emitting element according to claim 1 , wherein a difference in energy between a triplet excited level and a singlet excited level of the first exciplex is greater than or equal to 0 eV and less than or equal to 0.2 eV.
4. The light-emitting element according to claim 1 , wherein white light emission is exhibited.
5. A light-emitting module comprising:
the light-emitting element according to claim 1 , and
a means controlling the light-emitting element.
6. A light-emitting device comprising:
the light-emitting element according to claim 1 , and
a means controlling the light-emitting element.
7. An electronic appliance comprising the light-emitting element according to claim 1 .
8. A light-emitting element comprising:
a first electrode,
a second electrode, and
an electroluminescence layer interposed between the first electrode and the second electrode,
wherein the electroluminescence layer comprises a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked,
wherein the first light-emitting layer contains a first organic compound, a second organic compound, and a fluorescent substance,
wherein the second light-emitting layer contains a third organic compound, a fourth organic compound, and a phosphorescent substance,
wherein a combination of the first organic compound and the second organic compound forms a first exciplex,
wherein a combination of the third organic compound and the fourth organic compound forms a second exciplex,
wherein the first light-emitting layer is a fluorescent layer, and
wherein the second light-emitting layer is a phosphorescent layer.
9. The light-emitting element according to claim 8 , wherein a light emission spectrum of the first exciplex has a peak on a shorter wavelength side than a light emission spectrum of the phosphorescent substance.
10. The light-emitting element according to claim 8 , wherein a difference in energy between a triplet excited level and a singlet excited level of the first exciplex is greater than or equal to 0 eV and less than or equal to 0.2 eV.
11. The light-emitting element according to claim 8 , wherein a lowest-energy-side absorption band of the phosphorescent substance overlaps with an emission spectrum of the second exciplex.
12. The light-emitting element according to claim 8 , wherein a difference in equivalent energy values between a peak wavelength of a lowest-energy-side absorption band of the phosphorescent substance and a peak wavelength of an emission spectrum of the second exciplex is less than or equal to 0.2 eV.
13. The light-emitting element according to claim 8 ,
wherein one of the first organic compound and the second organic compound is a material having an electron-transport property and the other is a material having a hole -transport property, and
wherein one of the third organic compound and the fourth organic compound is a material having an electron-transport property and the other is a material having a hole-transport property.
14. The light-emitting element according to claim 13 ,
wherein one of the first electrode and the second electrode functions as an anode and the other functions as a cathode,
wherein one of the first light-emitting layer and the second light-emitting layer, which is positioned on the side where the electrode functioning as the anode is formed, contains a large amount of the material having the hole-transport property, and
wherein the other of the first light-emitting layer and the second light-emitting layer, which is positioned on the side where the electrode functioning as the cathode is formed, contains a large amount of the material having the electron-transport property.
15. The light-emitting element according to claim 8 , wherein a combination of the first organic compound and the second organic compound is the same as a combination of the third organic compound and the fourth organic compound.
16. The light-emitting element according to claim 8 , wherein a light emission spectrum of the first exciplex has a peak on a shorter wavelength side than a light emission spectrum of the second exciplex.
17. The light-emitting element according to claim 8 , wherein white light emission is exhibited.
18. A light-emitting module comprising:
the light-emitting element according to claim 8 , and
a means controlling the light-emitting element.
19. A light-emitting device comprising:
the light-emitting element according to claim 8 , and a means controlling the light-emitting element.