Light-emitting element, light-emitting device, display device, electronic device, and lighting device
First Claim
1. A light-emitting device comprising:
- an anode;
a first light-emitting layer over the anode, the first light-emitting layer comprising a first phosphorescent compound and a first host material;
a second light-emitting layer between the anode and the first light-emitting layer and in contact with the first light-emitting layer, the second light-emitting layer comprising a second phosphorescent compound, a first electron-transport compound, and a first hole-transport compound; and
a cathode over the first light-emitting layer,wherein an emission wavelength of the second phosphorescent compound is longer than an emission wavelength of the first phosphorescent compound,wherein a triplet excitation energy of the first host material is higher than or equal to a triplet excitation energy of the first electron-transport compound or the first hole-transport compound,wherein the first electron-transport compound and the first hole-transport compound form an exciplex, andwherein a difference in energy between an emission peak wavelength of the exciplex and a peak wavelength of an absorption band of the second phosphorescent compound which originates from a triplet metal to ligand charge transfer transition, is 0.2 eV or less.
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Accused Products
Abstract
A light-emitting element which uses a plurality of kinds of light-emitting dopants emitting light in a balanced manner and has high emission efficiency is provided. Further, a light-emitting device, a display device, an electronic device, and a lighting device each having reduced power consumption by using the above light-emitting element are provided. A light-emitting element which includes a plurality of light-emitting layers including different phosphorescent materials is provided. In the light-emitting element, the light-emitting layer which includes a light-emitting material emitting light with a long wavelength includes two kinds of carrier-transport compounds having properties of transporting carriers with different polarities. Further, in the light-emitting element, the triplet excitation energy of a host material included in the light-emitting layer emitting light with a short wavelength is higher than the triplet excitation energy of at least one of the carrier-transport compounds.
106 Citations
16 Claims
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1. A light-emitting device comprising:
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an anode; a first light-emitting layer over the anode, the first light-emitting layer comprising a first phosphorescent compound and a first host material; a second light-emitting layer between the anode and the first light-emitting layer and in contact with the first light-emitting layer, the second light-emitting layer comprising a second phosphorescent compound, a first electron-transport compound, and a first hole-transport compound; and a cathode over the first light-emitting layer, wherein an emission wavelength of the second phosphorescent compound is longer than an emission wavelength of the first phosphorescent compound, wherein a triplet excitation energy of the first host material is higher than or equal to a triplet excitation energy of the first electron-transport compound or the first hole-transport compound, wherein the first electron-transport compound and the first hole-transport compound form an exciplex, and wherein a difference in energy between an emission peak wavelength of the exciplex and a peak wavelength of an absorption band of the second phosphorescent compound which originates from a triplet metal to ligand charge transfer transition, is 0.2 eV or less. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A light-emitting device comprising:
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an anode; a first light-emitting layer over the anode, the first light-emitting layer comprising a first phosphorescent compound and a first host material; a second light-emitting layer between the first light-emitting layer and the anode and in contact with the first light-emitting layer, the second light-emitting layer comprising a second phosphorescent compound, a first electron-transport compound, and a first hole-transport compound; a third light-emitting layer between the second light-emitting layer and the anode and in contact with the second light-emitting layer, the third light-emitting layer comprising a third phosphorescent compound, a second electron-transport compound, and a second hole-transport compound; and a cathode over the first light-emitting layer, wherein an emission wavelength of the second phosphorescent compound is longer than an emission wavelength of the first phosphorescent compound, wherein an emission wavelength of the third phosphorescent compound is longer than the emission wavelength of the second phosphorescent compound, wherein a triplet excitation energy of the first host material is higher than or equal to a triplet excitation energy of the first electron-transport compound or the first hole-transport compound, wherein the first electron-transport compound and the first hole-transport compound form an exciplex, and wherein a difference in energy between an emission peak wavelength of the exciplex and a peak wavelength of an absorption band of the second phosphorescent compound, which originates from a triplet metal to ligand charge transfer transition is 0.2 eV or less. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification