LIGHT-EMITTING ELEMENT, LIGHT-EMITTING DEVICE, DISPLAY DEVICE, ELECTRONIC DEVICE, AND LIGHTING DEVICE
Provided is a light-emitting element which includes a first electrode, a second electrode over the first electrode, and first and second light-emitting layers therebetween. The first light-emitting layer contains a first host material and a first light-emitting material, and the second light-emitting layer contains a second host material and a second light-emitting material. The first light-emitting material is a fluorescent material, and the second light-emitting material is a phosphorescent material. The level of the lowest triplet excited state (T 1 level) of the first light-emitting material is higher than the T 1 level of the first host material. A light-emitting device, an electronic device, and a lighting device including the light-emitting element are further provided.
1 . A light-emitting element comprising:
a first electrode;
a second electrode over the first electrode; and
a first light-emitting layer and a second light-emitting layer between the first electrode and the second electrode,
wherein the first light-emitting layer comprises a first host material and a first light-emitting material,
wherein the second light-emitting layer comprises a second host material and a second light-emitting material,
wherein the first light-emitting material is a fluorescent material, and the second light-emitting material is a phosphorescent material, and
wherein a T 1 level of the first light-emitting material is higher than a T 1 level of the first host material.
2 . The light-emitting element according to claim 1 ,
wherein the first light-emitting layer and the second light-emitting layer are in contact with each other.
3 . The light-emitting element according to claim 1 ,
wherein the first light-emitting layer and the second light-emitting layer are separated from each other.
4 . The light-emitting element according to claim 1 , further comprising a layer between the first light-emitting layer and the second light-emitting layer,
wherein the layer comprises a hole-transport material and an electron-transport material.
5 . The light-emitting element according to claim 1 ,
wherein the second light-emitting layer is located over the first light-emitting layer.
6 . A light-emitting device comprising the light-emitting element according to claim 1 .
7 . A lighting device comprising the light-emitting element according to claim 1 .
8 . A light-emitting element comprising:
a first electrode;
a second electrode over the first electrode;
a first light-emitting unit and a second light-emitting unit between the first electrode and the second electrode; and
an interlayer between the first light-emitting unit and the second light-emitting unit,
wherein the first light-emitting unit comprises a first light-emitting layer and a second light-emitting layer,
wherein the first light-emitting layer comprises a first host material and a first light-emitting material,
wherein the second light-emitting layer comprises a second host material and a second light-emitting material,
wherein the first light-emitting material is a fluorescent material and the second light-emitting material is a phosphorescent material, and
wherein a T 1 level of the first light-emitting material is higher than a T 1 level of the first host material.
9 . The light-emitting element according to claim 8 ,
wherein the first light-emitting layer and the second light-emitting layer are in contact with each other.
10 . The light-emitting element according to claim 8 ,
wherein the first light-emitting layer and the second light-emitting layer are separated from each other.
11 . The light-emitting element according to claim 8 , further comprising a layer between the first light-emitting layer and the second light-emitting layer,
wherein the layer comprises a hole-transport material and an electron-transport material.
12 . The light-emitting element according to claim 8 ,
wherein the second light-emitting layer is located over the first light-emitting layer.
13 . The light-emitting element according to claim 8 ,
wherein the second light-emitting unit is located over the first light-emitting unit.
14 . The light-emitting element according to claim 8 ,
wherein the second light-emitting unit comprises a third light-emitting layer which comprises a third host material and a third light-emitting material.
15 . A light-emitting device comprising the light-emitting element according to claim 8 .
16 . A lighting device comprising the light-emitting element according to claim 8 .