Light-emitting element comprising stacked light-emitting layers, light-emitting device, electronic device, and lighting device
A light-emitting element with a high current efficiency is provided. A low-power consumption light-emitting device is also provided. In addition, low-power consumption electronic device and lighting device are provided. The light-emitting element includes an EL layer between a pair of electrodes. The EL layer includes a light-emitting layer. The light-emitting layer includes a first light-emitting layer and a second light-emitting layer. The emission peak of the second light-emitting layer is at a shorter wavelength than that of the first light-emitting layer. The first light-emitting layer includes a host material and a guest material. The LUMO level of the guest material is in the range of ±0.1 eV of the LUMO level of the host material.
1. A light-emitting element comprising:
a first EL layer between an anode and a cathode; and
a light-emitting layer between the anode and the cathode,
wherein the first EL layer includes a first light-emitting layer and a second light-emitting layer,
wherein the first light-emitting layer is located between the cathode and the second light-emitting layer,
wherein the first light-emitting layer is in contact with the second light-emitting layer,
wherein the light-emitting layer is spaced from the first light-emitting layer and the second light-emitting layer,
wherein the first light-emitting layer includes a first host material and a first guest material,
wherein the second light-emitting layer includes a second host material and a second guest material, the first host material and the second host material are the same host material,
wherein an emission peak of the second guest material is at a shorter wavelength than an emission peak of the first guest material,
wherein a guest material of the light-emitting layer emits fluorescence,
wherein a lowest unoccupied molecular orbital level of the first guest material is in a range of higher than 0 eV and lower than 0.1 eV of a lowest unoccupied molecular orbital level of the first host material,
wherein each of the first guest material and the second guest material is a phosphorescent organometallic iridium complex, and
wherein the first guest material is different from the second guest material.
2. The light-emitting element according to claim 1 , further comprising:
a second EL layer between the anode and the cathode; and
a charge-generation layer between the first EL layer and the second EL layer.
3. The light-emitting element according to claim 2 , wherein the first EL layer is located between the charge-generation layer and the cathode.
4. The light-emitting element according to claim 2 , wherein the first EL layer is located between the charge-generation layer and the anode.
5. The light-emitting element according to claim 1 , further comprising a third light-emitting layer,
wherein the third light-emitting layer is located between the first light-emitting layer and the cathode,
wherein the third light-emitting layer is in contact with the first light-emitting layer, and
wherein the second light-emitting layer and the third light-emitting layer include the same material.
6. The light-emitting element according to claim 1 ,
wherein emission in the first light-emitting layer has a peak at a wavelength from 560 nm to 700 nm, and
wherein emission in the second light-emitting layer has a peak at a wavelength from 500 nm to 560 nm.
7. A light-emitting device comprising:
the light-emitting element according to claim 1 ; and
a flexible printed circuit.
8. An electronic device comprising:
the light-emitting device according to claim 7 ; and
an operation key, a speaker, a microphone, or an external connection portion.
9. A lighting device comprising:
the light-emitting device according to claim 7 ; and
a housing.
10. The light-emitting element according to claim 1 , wherein the first guest material is an organometallic iridium complex in which a ligand is a phenylpyrazine derivative having an alkyl group.
11. The light-emitting element according to claim 1 ,
wherein the first guest material is an organometallic iridium complex in which a ligand is a phenylpyrazine derivative having an alkyl group, and
wherein the first host material is an electron-transport host material including a quinoxaline derivative.
12. The light-emitting element according to claim 1 ,
wherein the first guest material exhibits red emission, and
wherein the second guest material exhibits green emission.
13. A light-emitting element comprising:
a first EL layer between an anode and a cathode; and
a light-emitting layer between the anode and the cathode,
wherein the first EL layer includes a first light-emitting layer and a second light-emitting layer,
wherein the first light-emitting layer is located between the cathode and the second light-emitting layer,
wherein the first light-emitting layer is in contact with the second light-emitting layer,
wherein the light-emitting layer is spaced from the first light-emitting layer and the second light-emitting layer,
wherein the first light-emitting layer includes an electron-transport material, and a hole-transport material, and a first guest material,
wherein the second light-emitting layer includes a host material and a second guest material, the host material and the one of the electron-transport material and the hole-transport material are the same host material,
wherein an emission peak of the second guest material is shorter than an emission peak of the first guest material,
wherein a guest material of the light-emitting layer emits fluorescence,
wherein a lowest unoccupied molecular orbital level of the first guest material is in a range of higher than 0 eV and lower than 0.1 eV of a lowest unoccupied molecular orbital level of one of the electron-transport material and the hole-transport material,
wherein each of the first guest material and the second guest material is a phosphorescent organometallic iridium complex, and
wherein the first guest material is different from the second guest material.
14. The light-emitting element according to claim 13 , further comprising:
a second EL layer between the anode and the cathode; and
a charge-generation layer between the first EL layer and the second EL layer.
15. The light-emitting element according to claim 14 , wherein the first EL layer is located between the charge-generation layer and the cathode.
16. The light-emitting element according to claim 14 , wherein the first EL layer is located between the charge-generation layer and the anode.
17. The light-emitting element according to claim 13 , further comprising a third light-emitting layer,
wherein the third light-emitting layer is located between the first light-emitting layer and the cathode,
wherein the third light-emitting layer is in contact with the first light-emitting layer, and
wherein the second light-emitting layer and the third light-emitting layer include the same material.
18. The light-emitting element according to claim 13 ,
wherein emission in the first light-emitting layer has a peak at a wavelength from 560 nm to 700 nm, and
wherein emission in the second light-emitting layer has a peak at a wavelength from 500 nm to 560 nm.
19. A light-emitting device comprising:
the light-emitting element according to claim 13 ; and
a flexible printed circuit.
20. An electronic device comprising:
the light-emitting device according to claim 19 ; and
an operation key, a speaker, a microphone, or an external connection portion.
21. A lighting device comprising:
the light-emitting device according to claim 19 ; and
a housing.
22. The light-emitting element according to claim 13 , wherein the first guest material is an organometallic iridium complex in which a ligand is a phenylpyrazine derivative having an alkyl group.
23. The light-emitting element according to claim 13 ,
wherein the first guest material is an organometallic iridium complex in which a ligand is a phenylpyrazine derivative having an alkyl group, and
wherein the electron-transport material includes a quinoxaline derivative.
24. The light-emitting element according to claim 13 ,
wherein the first guest material exhibits red emission, and
wherein the second guest material exhibits green emission.