Light-emitting element, light-emitting device, display device, electronic appliance, and lighting device
View Patent ↗A multicolor light-emitting element in which light-emitting layers emitting light of different colors are stacked and color adjustment is easily made is provided. A multicolor light-emitting element which is inexpensive and has favorable emission efficiency is provided. A light-emitting element in which at least two light-emitting layers emitting light of different colors are formed in contact with each other and the light emitted from the two light-emitting layers is obtained from exciplexes is provided. In addition, the light-emitting element in which the exciplexes emit delayed fluorescence is provided.
1. A light-emitting element comprising:
a first electrode;
a second electrode; and
an EL layer interposed between the first electrode and the second electrode,
wherein the EL layer comprises a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked in direct contact with each other,
wherein the first light-emitting layer contains a first organic compound and a second organic compound,
wherein the second light-emitting layer contains a third organic compound and a fourth organic compound,
wherein the first organic compound and the second organic compound are mixed in the first light-emitting layer and form a first exciplex in the first light-emitting layer, and
wherein the third organic compound and the fourth organic compound are mixed in the second light-emitting layer and form a second exciplex in the second light-emitting layer.
2. The light-emitting element according to claim 1 ,
wherein light emission is obtained from the first exciplex and the second exciplex.
3. The light-emitting element according to claim 1 ,
wherein a difference in energy between a singlet excited level and a triplet excited level of at least one of the first exciplex and the second exciplex is 0.2 eV or lower.
4. The light-emitting element according to claim 1 ,
wherein at least one of the first exciplex and the second exciplex exhibits delayed fluorescence.
5. The light-emitting element according to claim 1 ,
wherein an electron-hole recombination region in the light-emitting layer is arranged to be positioned at an interface between the first light-emitting layer and the second light-emitting layer.
6. The light-emitting element according to claim 1 ,
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.
7. The light-emitting element according to claim 6 ,
wherein the first electrode functions as an anode, and the second electrode functions as a cathode,
wherein the first light-emitting layer is positioned on the first electrode side,
wherein the first light-emitting layer contains a larger amount of the material having the hole-transport property than the second light-emitting layer, and
wherein the second light-emitting layer contains a larger amount of the material having the electron-transport property than the first light-emitting layer.
8. The light-emitting element according to claim 1 ,
wherein the first exciplex and the second exciplex emit light having peaks at different wavelengths.
9. The light-emitting element according to claim 1 ,
wherein an emission spectrum of the light-emitting layer has two peaks.
10. The light-emitting element according to claim 1 ,
wherein one of the first organic compound and the second organic compound is the same as one of the third organic compound and the fourth organic compound.
11. The light-emitting element according to claim 1 ,
wherein the light-emitting layer exhibits white light emission.
12. A light-emitting module comprising:
the light-emitting element according to claim 1 ; and
a means controlling the light-emitting element.
13. A lighting device comprising the light-emitting element according to claim 1 .
14. A light-emitting device comprising:
the light-emitting element according to claim 1 ; and
a means controlling the light-emitting element.
15. An electronic appliance comprising the light-emitting element according to claim 1 .