Light emitting element and display device including the same

Abstract

Provided is a light emitting element including a first electrode, a hole transport region disposed over the first electrode, an emission layer disposed over the hole transport region, an electron transport region disposed over the emission layer, and a second electrode disposed over the electron transport region, wherein the hole transport region includes a first hole transport layer disposed adjacent to the first electrode and having a first refractive index, a second hole transport layer disposed adjacent to the emission layer and having a second refractive index, and a third hole transport layer disposed between the first hole transport layer and the second hole transport layer and having a third refractive index greater than each of the first refractive index and the second refractive index, thereby achieving high light extraction efficiency and high luminous efficiency.

What is claimed is: 
     
         1 . A light emitting element comprising:
 a first electrode;   a hole transport region disposed over the first electrode;   an emission layer disposed over the hole transport region;   an electron transport region disposed over the emission layer; and   a second electrode disposed over the electron transport region,   wherein the hole transport region comprises:
 a first hole transport layer disposed adjacent to the first electrode and having a first refractive index; 
 a second hole transport layer disposed adjacent to the emission layer and having a second refractive index; and 
 a third hole transport layer disposed between the first hole transport layer and the second hole transport layer and having a third refractive index greater than each of the first refractive index and the second refractive index. 
   
     
     
         2 . The light emitting element of  claim 1 , wherein
 a difference between the third refractive index and the first refractive index is greater than about 0.1, and   a difference between the third refractive index and the second refractive index is greater than about 0.1.   
     
     
         3 . The light emitting element of  claim 2 , wherein
 the first refractive index is in a range of about 1.2 to about 1.7,   the second refractive index is in a range of about 1.2 to about 1.7, and   the third refractive index is in a range of about 1.7 to about 2.2.   
     
     
         4 . The light emitting element of  claim 2 , wherein the first refractive index and the second refractive index are equal. 
     
     
         5 . The light emitting element of  claim 1 , wherein the second hole transport layer is directly disposed under the emission layer. 
     
     
         6 . The light emitting element of  claim 5 , wherein
 a refractive index of the emission layer is greater than the first refractive index of the first hole transport layer, and   a difference between the refractive index of the emission layer and the first refractive index is greater than about 0.1.   
     
     
         7 . The light emitting element of  claim 6 , wherein the refractive index of the emission layer is in a range of about 1.7 to about 2.2. 
     
     
         8 . The light emitting element of  claim 1 , wherein the first hole transport layer is directly disposed over the first electrode. 
     
     
         9 . The light emitting element of  claim 8 , wherein
 a refractive index of the first electrode is greater than the first refractive index of the first hole transport layer, and   a difference between the refractive index of the first electrode and the first refractive index is greater than about 0.1.   
     
     
         10 . The light emitting element of  claim 9 , wherein the refractive index of the first electrode is in a range of about 1.7 to about 2.2. 
     
     
         11 . The light emitting element of  claim 1 , wherein a ratio of a thickness of the first hole transport layer to a thickness of the third hole transport layer to a thickness of the second hole transport layer is in a range of about 0.1:0.8:0.1 to about 0.45:0.1:0.45. 
     
     
         12 . The light emitting element of  claim 1 , wherein
 the first electrode is a reflective electrode, and   the second electrode is a transmissive electrode or a transflective electrode.   
     
     
         13 . The light emitting element of  claim 1 , wherein the emission layer emits light having a central wavelength in a range of about 430 nm to about 470 nm. 
     
     
         14 . The light emitting element of  claim 13 , wherein a ratio of a thickness of the first hole transport layer to a thickness of the third hole transport layer to a thickness of the second hole transport layer is about 1:1:1. 
     
     
         15 . The light emitting element of  claim 1 , wherein the first hole transport layer and the second hole transport layer each independently comprise at least one of the compounds represented by Formulae 1-1 to 1-4: 
       
         
           
           
               
               
           
         
         wherein in Formulae 1-1 to 1-4, 
         A 1  to A 5  are each independently a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substitution or unsubstituted oxy group, a substituted or unsubstituted alkyl group having 1 to 60 carbon atoms, a substituted or unsubstituted aryl group having 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 60 ring-forming carbon atoms, 
         a is an integer from 0 to 5, 
         b is an integer from 0 to 4, and 
         c is an integer from 0 to 6. 
       
     
     
         16 . The light emitting element of  claim 1 , wherein the third hole transport layer comprises a compound represented by Formula 2: 
       
         
           
           
               
               
           
         
         wherein in Formula 2, 
         Ar 1  and Ar 2  are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 2 to 30 ring-forming carbon atoms, or bonded to an adjacent group to form a ring, 
         Ar 3  is a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 30 ring-forming carbon atoms, 
         a and b are each independently 0 or 1, 
         L 1  and L 2  are each independently a substituted or unsubstituted cycloalkylene group having 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted heterocycloalkylene group having 2 to 10 ring-forming carbon atoms, a substituted or unsubstituted cycloalkenylene group having 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted arylene group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroarylene group having 2 to 60 ring-forming carbon atoms, 
         p and s are each independently an integer from 0 to 4, 
         q and r are each independently an integer from 0 to 3, and 
         R 1  to R 5  are each independently a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted oxy group, a substituted or unsubstituted alkyl group having 1 to 60 carbon atoms, a substituted or unsubstituted heterocycloalkyl group having 3 to 60 ring-forming carbon atoms, a substituted or unsubstituted aryl group having 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 60 ring-forming carbon atoms. 
       
     
     
         17 . The light emitting element of  claim 1 , wherein the third hole transport layer comprises at least one of Compounds 1 to 69: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
         18 . A display device comprising:
 a plurality of light emitting elements, each of the light emitting elements comprising:
 a first electrode; 
 a hole transport region disposed over the first electrode; 
 an emission layer disposed over the hole transport region; 
 an electron transport region disposed over the emission layer; and 
 a second electrode disposed over the electron transport region, 
   wherein the hole transport region of at least one of the plurality of light emitting elements comprises:
 a first hole transport layer disposed adjacent to the first electrode and having a first refractive index; 
 a second hole transport layer disposed adjacent to the emission layer and having a second refractive index; and 
 a third hole transport layer disposed between the first hole transport layer and the second hole transport layer and having a third refractive index greater than each of the first refractive index and the second refractive index. 
   
     
     
         19 . The display device of  claim 18 , wherein
 a difference between the third refractive index and the first refractive index is greater than about 0.1, and   a difference between the third refractive index and the second refractive index is greater than about 0.1.   
     
     
         20 . The display device of  claim 18 , wherein
 the first electrode is a reflective electrode, and   the second electrode is a transmissive electrode or a transflective electrode.