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

Abstract

It is an object to provide an element structure which is suitable for a light-emitting element using a phosphorescent compound. It is another object to provide a light-emitting element with high luminous efficiency by using the element structure. In particular, it is another object to provide a light-emitting element with high luminous efficiency and long life. A light-emitting element is manufactured, which includes a first light-emitting layer and a second light-emitting layer provided to be in contact with each other between a first electrode and a second electrode, where the first light-emitting layer includes a hole transporting host material and a phosphorescent compound, and the second light-emitting layer includes an electron transporting host material and the phosphorescent compound.

1 . (canceled) 
     
     
         2 . A light-emitting element comprising:
 a first light-emitting layer and a second light-emitting layer being in contact with each other between a first electrode and a second electrode, and   a hole transporting layer between the first electrode and the first light-emitting layer, and   an electron transporting layer between the second electrode and the second light-emitting layer,   wherein the first light-emitting layer comprises a first host material and a phosphorescent compound,   wherein the second light-emitting layer comprises a second host material and the phosphorescent compound, and   wherein the first host material is a first heteroaromatic compound.   
     
     
         3 . The light-emitting element according to  claim 2 , wherein at least one of the first light-emitting layer and the second light-emitting layer emits green light or yellowish green light. 
     
     
         4 . The light-emitting element according to  claim 2 ,
 wherein the second host material is a second heteroaromatic compound, and   wherein the second heteroaromatic compound is different from the first heteroaromatic compound.   
     
     
         5 . The light-emitting element according to  claim 2 , wherein the first host material has a higher hole transporting property than an electron transporting property. 
     
     
         6 . The light-emitting element according to  claim 2 , wherein the second host material has a higher electron transporting property than a hole transporting property. 
     
     
         7 . The light-emitting element according to  claim 2 ,
 wherein the hole transporting layer comprises a hole transporting material,   wherein the electron transporting layer comprises an electron transporting material,   wherein the hole transporting layer is in contact with the first light-emitting layer,   wherein each of the hole transporting material and the electron transporting material has triplet excitation energy lower than that of the phosphorescent compound.   
     
     
         8 . The light-emitting element according to  claim 2 ,
 wherein the second light-emitting layer comprises a first region and a second region,   wherein the first region comprises the phosphorescent compound, and   wherein the second region does not comprise the phosphorescent compound.   
     
     
         9 . The light-emitting element according to  claim 2 , wherein energy gap of the second host material is 3.3 eV or less. 
     
     
         10 . The light-emitting element according to  claim 2 , wherein the phosphorescent compound is a guest material. 
     
     
         11 . A light-emitting device comprising the light-emitting element according to  claim 2 . 
     
     
         12 . An electronic device comprising the light-emitting device according to  claim 11 . 
     
     
         13 . A light-emitting element comprising:
 a first light-emitting layer and a second light-emitting layer being in contact with each other between a first electrode and a second electrode, and   a hole transporting layer between the first electrode and the first light-emitting layer, and   an electron transporting layer between the second electrode and the second light-emitting layer,   wherein the first light-emitting layer comprises a first host material and a phosphorescent compound,   wherein the second light-emitting layer comprises a second host material and the phosphorescent compound,   wherein the first host material is a first heteroaromatic compound, and   wherein the second host material is a second heteroaromatic compound.   
     
     
         14 . The light-emitting element according to  claim 13 , wherein at least one of the first light-emitting layer and the second light-emitting layer emits green light or yellowish green light. 
     
     
         15 . The light-emitting element according to  claim 13 , wherein the first host material has a higher hole transporting property than an electron transporting property. 
     
     
         16 . The light-emitting element according to  claim 13 , wherein the second host material has a higher electron transporting property than a hole transporting property. 
     
     
         17 . The light-emitting element according to  claim 13 ,
 wherein the hole transporting layer comprises a hole transporting material,   wherein the electron transporting layer comprises an, electron transporting material,   wherein the hole transporting layer is in contact with the first light-emitting layer,   wherein each of the hole transporting material and the electron transporting material has triplet excitation energy lower than that of the phosphorescent compound.   
     
     
         18 . The light-emitting element according to  claim 13 ,
 wherein the hole transporting layer comprises a hole transporting material,   wherein the electron transporting layer comprises an electron transporting material,   wherein the hole transporting layer is in contact with the first light-emitting layer,   wherein each of the hole transporting material and the electron transporting material has triplet excitation energy lower than that of the phosphorescent compound.   
     
     
         19 . The light-emitting element according to  claim 13 ,
 wherein the second light-emitting layer comprises a first region and a second region,   wherein the first region comprises the phosphorescent compound, and   wherein the second region does not comprise the phosphorescent compound.   
     
     
         20 . A light-emitting device comprising the light-emitting element according to  claim 13 . 
     
     
         21 . An electronic device comprising the light-emitting device according to  claim 20 .