Light-emitting element, light-emitting device, electronic device, and lighting device
A light-emitting element with high reliability that can keep favorable characteristics after long-time driving is provided. In addition, a light-emitting device having a long lifetime including the light-emitting element is provided. Moreover, an electronic device and a lighting device having a long lifetime are provided. In a light-emitting element including an EL layer between a pair of electrodes, a light-emitting layer included in the EL layer has a stacked-layer structure which is different from the conventional structure, whereby the light-emitting element can keep favorable characteristics after long-time driving even in the case where carrier balance is changed over time due to driving of the light-emitting element or a light-emitting region is shifted due to the change.
1. A light-emitting device comprising:
a first electrode;
a first light-emitting layer over the first electrode and comprising a first light-emitting material and a first organic compound which is different from the first light-emitting material;
a second light-emitting layer over and in direct contact with the first light-emitting layer and comprising a second light-emitting material and a second organic compound which is different from the second light-emitting material;
a third light-emitting layer over and in direct contact with the second light-emitting layer and comprising the first light-emitting material and a third organic compound which is different from the first light-emitting material; and
a second electrode over the third light-emitting layer,
wherein:
the first light-emitting material and the second light-emitting material are different from each other,
the first light-emitting layer and the third light-emitting layer exhibit first emission, and
second emission from the second light-emitting layer has an emission peak at a longer wavelength than the first emission.
2. The light-emitting device according to claim 1 ,
wherein:
the first light-emitting layer comprises the first organic compound and a fourth organic compound which form an exciplex,
the second light-emitting layer comprises the second organic compound and a fifth organic compound which form an exciplex, and
the third light-emitting layer comprises the third organic compound and a sixth organic compound which form an exciplex.
3. The light-emitting device according to claim 2 ,
wherein:
each of the first organic compound, the second organic compound, and the third organic compound has hole-transport property, and
each of the fourth organic compound, the fifth organic compound, and the sixth organic compound has electron-transport property.
4. The light-emitting device according to claim 2 , wherein at least one of the first emission and the second emission is phosphorescence.
5. The light-emitting device according to claim 3 ,
wherein:
the first emission is green light, and
the second emission is red light.
6. An electronic device comprising the light-emitting device according to claim 1 .
7. A lighting device comprising the light-emitting device according to claim 1 .
8. The light-emitting device according to claim 1 , wherein the first light-emitting material and the second light-emitting material individually are any one of a substance emitting fluorescence, a substance emitting phosphorescence and a thermally activated delayed fluorescence material.
9. The light-emitting device according to claim 2 ,
wherein:
the first organic compound, the second organic compound, and the third organic compound are the same as each other, and
the fourth organic compound, the fifth organic compound, and the sixth organic compound are the same as each other.
10. A light-emitting device comprising:
a first electrode;
a first light-emitting layer over the first electrode;
a second light-emitting layer over the first light-emitting layer;
a third light-emitting layer over the second light-emitting layer; and
a second electrode over the third light-emitting layer,
wherein:
the first light-emitting layer and the third light-emitting layer exhibit green light,
the second light-emitting layer exhibits red light, and
each of the first light-emitting layer, the second light-emitting layer, and the third light-emitting layer comprises a first organic compound and a second organic compound which form an exciplex.
11. The light-emitting device according to claim 10 ,
wherein:
the first organic compound has hole-transport property, and
the second organic compound has electron-transport property.
12. The light-emitting device according to claim 10 , wherein at least one of the green light and the red light is phosphorescence.
13. An electronic device comprising the light-emitting device according to claim 10 .
14. A lighting device comprising the light-emitting device according to claim 10 .