Light-emitting element, light-emitting device, electronic appliance, and lighting device
View Patent ↗A light-emitting element which has low driving voltage and high emission efficiency is provided. The light-emitting element includes, between a pair of electrodes, a hole-transport layer and a light-emitting layer over the hole-transport layer. The light-emitting layer contains a first organic compound having an electron-transport property, a second organic compound having a hole-transport property, and a light-emitting third organic compound converting triplet excitation energy into light emission. A combination of the first organic compound and the second organic compound forms an exciplex. The hole-transport layer is formed using two or more kinds of organic compounds and contains at least the second organic compound.
1. A light-emitting element comprising:
a hole-transport layer; and
a light-emitting layer over the hole-transport layer,
wherein the light-emitting layer includes a first organic compound having an electron-transport property, a second organic compound having a hole-transport property, and a third organic compound converting triplet excitation energy into light emission,
wherein a combination of the first organic compound and the second organic compound forms an exciplex, and
wherein the hole-transport layer comprises the second organic compound and an organic compound having a hole-transport property.
2. The light-emitting element according to claim 1 , wherein the hole-transport layer further comprises a fourth organic compound whose T 1 level is higher than that of the first organic compound.
3. The light-emitting element according to claim 1 , wherein the hole-transport layer further contains a fourth organic compound whose T 1 level is higher than that of the second organic compound.
4. The light-emitting element according to claim 1 ,
wherein the first organic compound is a n-electron deficient heteroaromatic compound,
wherein the second organic compound is a n-electron rich heteroaromatic compound or an aromatic amine compound, and
wherein the third organic compound is a phosphorescent organometallic complex.
5. A light-emitting device comprising the light-emitting element according to claim 1 .
6. An electronic appliance comprising the light-emitting device according to claim 5 .
7. A lighting device comprising the light-emitting device according to claim 5 .
8. A light-emitting element comprising:
a hole-injection layer;
a hole-transport layer over the hole-injection layer;
a light-emitting layer over the hole-transport layer;
an electron-transport layer over the light-emitting layer; and
an electron-injection layer over the electron-transport layer,
wherein the light-emitting layer includes a first organic compound having an electron-transport property, a second organic compound having a hole-transport property, and a third organic compound converting triplet excitation energy into light emission,
wherein a combination of the first organic compound and the second organic compound forms an exciplex, and
wherein the hole-transport layer comprises the second organic compound and a fourth an organic compound having a hole-transport property.
9. The light-emitting element according to claim 8 , wherein the hole-transport layer further comprises a fourth organic compound whose T 1 level is higher than that of the first organic compound.
10. The light-emitting element according to claim 8 , wherein the hole-transport layer further contains a fourth organic compound whose T 1 level is higher than that of the second organic compound.
11. The light-emitting element according to claim 8 ,
wherein the first organic compound is a π-electron deficient heteroaromatic compound,
wherein the second organic compound is a π-electron rich heteroaromatic compound or an aromatic amine compound, and
wherein the third organic compound is a phosphorescent organometallic complex.
12. A light-emitting device comprising the light-emitting element according to claim 8 .
13. An electronic appliance comprising the light-emitting device according to claim 12 .
14. A lighting device comprising the light-emitting device according to claim 12 .