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

Abstract

A novel light-emitting element or a highly reliable light-emitting element is provided. The light-emitting element includes an anode, a cathode, and an EL layer between the anode and the cathode. The EL layer includes at least a light-emitting layer. The light-emitting layer includes at least a first organic compound and a second organic compound. The energy for liberating halogen from a halogen-substituted product of the first organic compound in a radical anion state and in a triplet excited state is less than or equal to 1.00 eV. The amount of halogen-substituted product in the second organic compound is not increased with an increase in driving time of the light-emitting element.

What is claimed is: 
     
         1 . A light-emitting element comprising:
 an anode;   a cathode; and   an EL layer including a light-emitting layer between the anode and the cathode,   wherein the light-emitting layer comprises a first organic compound and a second organic compound, and   wherein neither an amount of a halogen-substituted product of the first organic compound nor an amount of a halogen-substituted product of the second organic compound is increased with an increase in driving time of the light-emitting element.   
     
     
         2 . The light-emitting element according to  claim 1 ,
 wherein an energy for liberating halogen from the halogen-substituted product of the first organic compound in a radical anion state and in a triplet excited state is less than or equal to 1.00 eV.   
     
     
         3 . The light-emitting element according to  claim 2 , wherein the energy for liberating halogen from the halogen-substituted product of the first organic compound is less than or equal to 0.87 eV. 
     
     
         4 . The light-emitting element according to  claim 1 , wherein the second organic compound is a light-emitting substance. 
     
     
         5 . The light-emitting element according to  claim 1 , wherein the first organic compound is a host material. 
     
     
         6 . A light-emitting element comprising:
 an anode;   a cathode; and   an EL layer including a light-emitting layer between the anode and the cathode,   wherein the light-emitting layer comprises a first organic compound and a second organic compound, and   wherein neither an amount of a halogen-substituted product of the first organic compound nor an amount of a halogen-substituted product of the second organic compound is increased at the time when luminance of the light-emitting element becomes less than or equal to 80% of an initial luminance.   
     
     
         7 . The light-emitting element according to  claim 6 ,
 wherein an energy for liberating halogen from the halogen-substituted product of the first organic compound in a radical anion state and in a triplet excited state is less than or equal to 1.00 eV.   
     
     
         8 . The light-emitting element according to  claim 7 , wherein the energy for liberating halogen from the halogen-substituted product of the first organic compound is less than or equal to 0.87 eV. 
     
     
         9 . The light-emitting element according to  claim 6 , wherein the second organic compound is a light-emitting substance. 
     
     
         10 . The light-emitting element according to  claim 6 , wherein the first organic compound is a host material. 
     
     
         11 . A light-emitting element comprising:
 an anode;   a cathode; and   an EL layer including a light-emitting layer between the anode and the cathode,   wherein the light-emitting layer comprises a first organic compound and a second organic compound, and   wherein a concentration of a halogen atom used for the first organic compound is less than or equal to 20 ppm.   
     
     
         12 . The light-emitting element according to  claim 11 , wherein the concentration of the halogen atom in the first organic compound is less than or equal to 10 ppm. 
     
     
         13 . The light-emitting element according to  claim 11 ,
 wherein an energy for liberating halogen from a halogen-substituted product of the first organic compound in a radical anion state and in a triplet excited state is less than or equal to 1.00 eV.   
     
     
         14 . The light-emitting element according to  claim 13 , wherein the energy for liberating halogen from the halogen-substituted product of the first organic compound is less than or equal to 0.87 eV. 
     
     
         15 . The light-emitting element according to  claim 11 , wherein the second organic compound is a light-emitting substance. 
     
     
         16 . The light-emitting element according to  claim 11 , wherein the first organic compound is a host material.