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

摘要

A light-emitting element having high external quantum efficiency is provided. A light-emitting element having a long lifetime is provided. A light-emitting element includes a light-emitting layer between a pair of electrodes. The light-emitting layer contains at least a phosphorescent compound, a first organic compound (host material) having an electron-transport property, and a second organic compound (assist material) having a hole-transport property. The light-emitting layer has a stacked-layer structure including a first light-emitting layer and a second light-emitting layer, and the first light-emitting layer contains a higher proportion of the second organic compound than the second light-emitting layer. In the light-emitting layer (the first light-emitting layer and the second light-emitting layer), a combination of the first organic compound and the second organic compound forms an exciplex.

主权项

1. A light-emitting device comprising:
a first light-emitting layer over an anode, the first light-emitting layer comprising a first compound, a first organic compound, and a second organic compound; a second light-emitting layer over the first light-emitting layer, the second light-emitting layer comprising a second compound, the first organic compound, and the second organic compound; and a cathode over the second light-emitting layer, wherein an emission spectrum of an exciplex of the first organic compound and the second organic compound overlaps with an absorption spectrum of the first compound so as to transfer an excited energy of the exciplex to the first compound, wherein the emission spectrum of the exciplex of the first organic compound and the second organic compound overlaps with an absorption spectrum of the second compound so as to transfer the excited energy of the exciplex to the second compound, wherein a region of the first light-emitting layer comprises a higher proportion of the second organic compound than a region of the second light-emitting layer, and wherein at least one of the first organic compound and the second organic compound is a fluorescent compound.