Patent ID: 8916897

Claim:
A light-emitting element comprising: a first electrode; a first light-emitting layer over the first electrode comprising: a first phosphorescent compound; and a first host material; a second light-emitting layer over the first light-emitting layer comprising: a second phosphorescent compound; and a second host material; a third light-emitting layer over the second light-emitting layer comprising: a third phosphorescent compound; and a third host material; and a second electrode over the third light-emitting layer, wherein light emitted from the second phosphorescent compound has a longer wavelength than light emitted from the first phosphorescent compound, wherein a longest-wavelength-side peak of a function ε(λ)λ 4 of the second phosphorescent compound overlaps with a phosphorescence spectrum F(λ) of the first phosphorescent compound, wherein light emitted from the third phosphorescent compound has a longer wavelength than the light emitted from the second phosphorescent compound, wherein a longest-wavelength-side peak of a function ε(λ)λ 4 of the third phosphorescent compound overlaps with a phosphorescence spectrum F(λ) of the second phosphorescent compound, wherein the second light-emitting layer has a thickness of less than 5 nm and greater than or equal to 1 nm, wherein λ denotes a wavelength, and wherein ε(λ) denotes a molar absorption coefficient at the wavelength λ.