Organic light emitting element

Abstract

An organic light emitting device having a light emitting layer that contains first to fourth organic compounds satisfying the following formulae can realize long-life emission with high color purity. The second and the third organic compounds are delayed fluorescent materials, and the emission amount from the fourth organic compound is the maximum. E S1 is a lowest excited singlet energy, E T1 is a lowest excited triplet energy and C onc is a concentration in the light emitting layer. E S1 (1)>E S1 (2)>E S1 (4)>E S1 (3), E S1 (2)−E S1 (3)<0.30 eV, E T1 (1)>E T1 (2)>E T1 (3). Conc(1)>Conc(2)>Conc(3), Conc(3)≤20 wt %

1 . An organic light emitting device having a light emitting layer that contains a first organic compound, a second organic compound, a third organic compound and a fourth organic compound satisfying the following requirements (a) to (e), wherein:
 the second organic compound and the third organic compound are delayed fluorescent materials each having a different structure, and   the maximum component of light emission from the organic light emitting device is light emission from the fourth organic compound:
     E   S1 (1)> E   S1 (2)> E   S1 (4)> E   S1 (3)  Requirement (a):
 
     E   S1 (2)− E   S1 (3)<0.30 eV  Requirement (b):
 
     E   T1 (1)> E   T1 (2)> E   T1 (3)  Requirement (c):
 
   Conc(1)>Conc(2)>Conc(3)  Requirement (d):
 
   Conc(3)≤20 wt %  Requirement (e):
 
   
       wherein:
 E S1 (1) represents a lowest excited singlet energy of the first organic compound, 
 E S1 (2) represents a lowest excited singlet energy of the second organic compound, 
 E S1 (3) represents a lowest excited singlet energy of the third organic compound, 
 E S1 (4) represents a lowest excited singlet energy of the fourth organic compound, 
 E T1 (1) represents a lowest excited triplet energy of the first organic compound, 
 E T1 (2) represents a lowest excited triplet energy of the second organic compound, 
 E T1 (3) represents a lowest excited triplet energy of the third organic compound, 
 Conc(1) represents a concentration of the first organic compound in the light emitting layer, 
 Conc(2) represents a concentration of the second organic compound in the light emitting layer, 
 Conc(3) represents a concentration of the third organic compound in the light emitting layer. 
 
     
     
         2 . The organic light emitting device according to  claim 1 , further satisfying the following requirement (c1):
     E   T1 (1)> E   T1 (2)> E   T1 (4)> E   T1 (3)  Requirement (c1):
   
       wherein:
 E T1 (4) represents a lowest excited triplet energy of the fourth organic compound. 
 
     
     
         3 . The organic light emitting device according to  claim 1 , further satisfying the following requirement (d1):
   Conc(1)>Conc(2)>Conc(3)>Conc(4)  Requirement (d1):
   
       wherein:
 Conc(4) represents a concentration of the fourth organic compound in the light emitting layer. 
 
     
     
         4 . The organic light emitting device according to  claim 3 , further satisfying the following requirement (f):
   Conc(3)/Conc(4)>5  Requirement (f):
   
     
     
         5 . The organic light emitting device according to  claim 1 , further satisfying the following requirement (e2):
   Conc(4)≤1 wt %  Requirement (e2):
   
     
     
         6 . The organic light emitting device according to  claim 1 , wherein the second organic compound is such that the energy difference ΔE st  between the lowest excited single state and the lowest excited triplet state at 77 K is 0.3 eV or less. 
     
     
         7 . The organic light emitting device according to  claim 1 , wherein the third organic compound is such that the energy difference ΔE st  between the lowest excited single state and the lowest excited triplet state at 77 K is 0.3 eV or less. 
     
     
         8 . The organic light emitting device according to  claim 1 , wherein the light emitting layer is composed of a compound alone formed of atoms selected from the group consisting of a carbon atom, a hydrogen atom, a nitrogen atom, a boron atom, an oxygen atom and a sulfur atom. 
     
     
         9 . The organic light emitting device according to  claim 1 , wherein the first organic compound, the second organic compound and the third organic compound each are independently a compound formed of atoms selected from the group consisting of a carbon atom, a hydrogen atom and a nitrogen atom. 
     
     
         10 . The organic light emitting device according to  claim 10 , wherein the second organic compound and the third organic compound both contain a cyanobenzene structure.