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

摘要

A light-emitting element with improved emission efficiency is provided. The light-emitting element includes a light-emitting layer in which a first light-emitting layer and a second light-emitting layer are stacked in contact with each other over an anode, and a first substance serving as an emission center substance in the second light-emitting layer is the same as a main substance in the first light-emitting layer. Note that a second substance is added to the first light-emitting layer for stabilization of film quality, and a third substance serving as a host material to disperse the first substance serving as an emission center substance is included in the second light-emitting layer. In the light-emitting element, the second substance and the third substance are substances having energy gaps (or triplet energy) larger than the first substance.

主权项

1. A light-emitting element comprising:
an anode; a hole-transporting layer over the anode; a first light-emitting layer over and in direct contact with the hole-transporting layer, the first light-emitting layer comprising a first substance and a second substance; a second light-emitting layer over and in direct contact with the first light-emitting layer, the second light-emitting layer comprising the first substance and a third substance; and a cathode over the second light-emitting layer, wherein the third substance is a maximum component in the second light-emitting layer, wherein an amount of the first substance is larger than an amount of the second substance in weight in the first light-emitting layer, wherein the second substance and the third substance each have an energy gap larger than the first substance, wherein the first substance in the first light-emitting layer is 70 wt % or higher and lower than 100 wt %, and wherein the first substance in the second light-emitting layer serves as an emission center substance, the first substance in the second light-emitting layer being the same as the first substance in the first light-emitting layer.