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

Abstract

Provided is a light-emitting element including a fluorescence-emitting material with high emission efficiency. The light-emitting element includes a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a first organic compound, a second organic compound, and a guest material. The first organic compound has a function of emitting a thermally activated delayed fluorescence at room temperature. The guest material has a function of emitting fluorescence. A HOMO level of the first organic compound higher than or equal to a HOMO level of the second organic compound. A LUMO level of the first organic compound is lower than or equal to a LUMO level of the second organic compound.

1 . A light-emitting element comprising:
 a pair of electrodes; and   an EL layer between the pair of electrodes,   wherein the EL layer comprises a first organic compound, a second organic compound, and a guest material,   wherein the first organic compound has a function of emitting a thermally activated delayed fluorescence at room temperature,   wherein the guest material has a function of emitting fluorescence,   wherein a HOMO level of the first organic compound is higher than or equal to a HOMO level of the second organic compound, and   wherein a LUMO level of the first organic compound is lower than or equal to a LUMO level of the second organic compound.   
     
     
         2 . The light-emitting element according to  claim 1 , wherein a difference between a singlet excitation energy level of the first organic compound and a triplet excitation energy level of the first organic compound is larger than 0 eV and smaller than or equal to 0.2 eV. 
     
     
         3 . The light-emitting element according to  claim 1 , wherein the guest material emits light. 
     
     
         4 . The light-emitting element according to  claim 1 ,
 wherein the first organic compound comprises a first π-electron deficient heteroaromatic skeleton and a first π-electron rich heteroaromatic skeleton, and   wherein the second organic compound comprises a second π-electron deficient heteroaromatic skeleton and a second π-electron rich heteroaromatic skeleton.   
     
     
         5 . The light-emitting element according to  claim 4 ,
 wherein the first π-electron deficient heteroaromatic skeleton comprises a diazine skeleton or a triazine skeleton,   wherein the first π-electron rich heteroaromatic skeleton comprises any one or more of an acridine skeleton, a phenoxazine skeleton, or a 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton,   wherein the second π-electron deficient heteroaromatic skeleton comprises a pyridine skeleton or a diazine skeleton, and   wherein the second π-electron rich heteroaromatic skeleton comprises any one or more of a furan skeleton, a thiophene skeleton, a fluorine skeleton, and a pyrrole skeleton.   
     
     
         6 . The light-emitting element according to  claim 1 ,
 wherein a weight ratio of the second organic compound to the first organic compound is from 1:0.05 to 1:0.5, and   wherein a weight ratio of the second organic compound to the guest material is from 1:0.001 to 1:0.01.   
     
     
         7 . A display device comprising:
 the light-emitting element according to  claim 1 ; and   a color filter, a sealant, or a transistor.   
     
     
         8 . An electronic device comprising:
 the display device according to  claim 7 , and   a housing or a function of a touch sensor.   
     
     
         9 . A lighting device comprising:
 the light-emitting element according to  claim 1 , and   a housing or a function of a touch sensor.   
     
     
         10 . A light-emitting element comprising:
 a pair of electrodes; and   an EL layer between the pair of electrodes,   wherein the EL layer comprises a first organic compound, a second organic compound, and a guest material,   wherein the first organic compound has a function of emitting a thermally activated delayed fluorescence at room temperature,   wherein the guest material has a function of emitting fluorescence,   wherein an oxidation potential of the first organic compound is lower than or equal to an oxidation potential of the second organic compound, and   wherein a reduction potential of the first organic compound is higher than or equal to a reduction of the second organic compound.   
     
     
         11 . The light-emitting element according to  claim 10 , wherein a difference between a singlet excitation energy level of the first organic compound and a triplet excitation energy level of the first organic compound is larger than 0 eV and smaller than or equal to 0.2 eV. 
     
     
         12 . The light-emitting element according to  claim 10 , wherein the guest material emits light. 
     
     
         13 . The light-emitting element according to  claim 10 ,
 wherein the first organic compound comprises a first π-electron deficient heteroaromatic skeleton and a first π-electron rich heteroaromatic skeleton, and   wherein the second organic compound comprises a second π-electron deficient heteroaromatic skeleton and a second π-electron rich heteroaromatic skeleton.   
     
     
         14 . The light-emitting element according to  claim 13 ,
 wherein the first π-electron deficient heteroaromatic skeleton comprises a diazine skeleton or a triazine skeleton,   wherein the first π-electron rich heteroaromatic skeleton comprises any one or more of an acridine skeleton, a phenoxazine skeleton, or a 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton,   wherein the second π-electron deficient heteroaromatic skeleton comprises a pyridine skeleton or a diazine skeleton, and   wherein the second π-electron rich heteroaromatic skeleton comprises any one or more of a furan skeleton, a thiophene skeleton, a fluorine skeleton, and a pyrrole skeleton.   
     
     
         15 . The light-emitting element according to  claim 10 ,
 wherein a weight ratio of the second organic compound to the first organic compound is from 1:0.05 to 1:0.5, and   wherein a weight ratio of the second organic compound to the guest material is from 1:0.001 to 1:0.01.   
     
     
         16 . A display device comprising:
 the light-emitting element according to  claim 10 ; and   a color filter, a sealant, or a transistor.   
     
     
         17 . An electronic device comprising:
 the display device according to  claim 16 , and   a housing or a function of a touch sensor.   
     
     
         18 . A lighting device comprising:
 the light-emitting element according to  claim 10 , and   a housing or a function of a touch sensor.