Light-emitting element, light-emitting device, display device, electronic device, and lighting device

Abstract

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.

What is claimed is: 
     
         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 .