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

摘要

To increase emission efficiency of a fluorescent light-emitting element by efficiently utilizing a triplet exciton generated in a light-emitting layer. The light-emitting layer of the light-emitting element includes at least a host material and a guest material. The triplet exciton generated from the host material in the light-emitting layer is changed to a singlet exciton by triplet-triplet annihilation (TTA). The guest material (fluorescent dopant) is made to emit light by energy transfer from the singlet exciton. Thus, the emission efficiency of the light-emitting element is improved.

主权项

1. A light-emitting element comprising:
a hole-transport layer comprising a hole-transport material over a first electrode; a light-emitting layer comprising a guest material and a host material over the hole-transport layer; an electron-transport layer comprising an electron-transport material over and in contact with the light-emitting layer; and a second electrode over the electron-transport layer, wherein the host material is an anthracene compound, wherein the guest material is a pyrene compound, wherein a T1 level of the host material is lower than a T1 level of the guest material, wherein a T1 level of the hole-transport material is higher than the T1 level of the host material, wherein the host material and the electron-transport material are same compound, and wherein the hole-transport material is a phenanthrene compound.