Light-emitting element, display module, lighting module, light-emitting device, display device, electronic appliance, and lighting device
A multicolor light-emitting element that utilizes fluorescence and phosphorescence and is advantageous for practical application is provided. The light-emitting element has a stacked-layer structure of a first light-emitting layer containing a host material and a fluorescent substance and a second light-emitting layer containing two kinds of organic compounds and a substance that can convert triplet excitation energy into luminescence. Note that light emitted from the first light-emitting layer has an emission peak on the shorter wavelength side than light emitted from the second light-emitting layer.
1. A light-emitting device comprising:
an anode;
a first light-emitting layer;
a second light-emitting layer; and
a cathode in this order,
wherein the second light-emitting layer comprises a first substance which is capable of converting triplet excitation energy into luminescence, a first organic compound, and a second organic compound,
wherein the first organic compound and the second organic compound are configured to form an exciplex,
wherein a peak wavelength of light emitted from the first light-emitting layer is shorter than a peak wavelength of light emitted from the second light-emitting layer,
wherein an energy value of peak wavelength of an emission spectrum of the exciplex is a first energy value,
wherein an energy value of a peak wavelength of a lowest-energy-side absorption band of the first substance is a second energy value,
wherein a difference between the first energy value and the second energy value is smaller than 0.2 eV,
wherein the first organic compound comprises a first carbazole skeleton, and
wherein the second organic compound comprises a second carbazole skeleton.
2. A lighting device comprising:
a first light-emitting device;
a second light-emitting device;
a third light-emitting device; and
a fourth light-emitting device,
wherein each of the first light-emitting device, the second light-emitting device, the third light-emitting device, and the fourth light-emitting device comprises the light-emitting device according to claim 1 ,
wherein the first light-emitting device overlaps with a red color filter,
wherein the second light-emitting device overlaps with a green color filter,
wherein the third light-emitting device overlaps with a blue color filter, and
wherein the fourth light-emitting device comprise a region which overlaps with none of the red color filter, the green color filter, and the blue color filter.
3. The light-emitting device according to claim 1 ,
wherein the fluorescent substance comprises a pyrenediamine compound.
4. A lighting device comprising:
a first light-emitting device;
a second light-emitting device;
a third light-emitting device; and
a fourth light-emitting device,
wherein each of the first light-emitting device, the second light-emitting device, the third light-emitting device, and the fourth light-emitting device comprises the light-emitting device according to claim 3 ,
wherein the first light-emitting device overlaps with a red color filter,
wherein the second light-emitting device overlaps with a green color filter,
wherein the third light-emitting device overlaps with a blue color filter, and
wherein the fourth light-emitting device comprise a region which overlaps with none of the red color filter, the green color filter, and the blue color filter.
5. The light-emitting device according to claim 1 , wherein the first light-emitting layer comprises a fluorescent substance and a host material.
6. The light-emitting device according to claim 5 , wherein a triplet excitation level (a T1 level) of the host material is lower than a T1 level of the fluorescent substance.