Light-emitting element, light-emitting device, lighting device, and electronic appliance
View Patent ↗A light-emitting element whose lifetime is improved. In addition, a light-emitting device, a lighting device, and an electronic appliance in which the light-emitting element is used. A light-emitting element including, between an anode and a cathode, a hole-transport layer and a layer containing a light-emitting substance provided to be in contact with a cathode side surface of the hole-transport layer, in which the hole-transport layer includes a first organic compound and an anti-reduction substance, and in which the layer containing a light-emitting substance includes a second organic compound and a light-emitting substance and has at least an electron-transport property is provided. In addition, a light-emitting device including the light-emitting element, or a lighting device or an electronic appliance including the light-emitting device is provided.
1. A light-emitting element comprising:
an anode;
a hole-transport layer over the anode;
a first light-emitting layer over and in contact with the hole-transport layer;
a second light-emitting layer over and in contact with the first light-emitting layer; and
a cathode over the second light-emitting layer,
wherein the hole-transport layer includes a first organic compound and an anti-reduction substance,
wherein an electron-accepting property of the anti-reduction substance is higher than an electron-accepting property of the first organic compound,
wherein the first light-emitting layer includes a first host material having an electron-transport property and a first light-emitting material,
wherein the second light-emitting layer includes a second host material having an electron-transport property and a second light-emitting material having a hole-trapping property,
wherein the LUMO level of the anti-reduction substance is lower than the LUMO level of the first organic compound and the LUMO level of the first light-emitting layer, and
wherein the LUMO level of the first light-emitting layer is lower than the LUMO level of the first organic compound.
2. The light-emitting element according to claim 1 ,
wherein the anode and the hole-transport layer are in contact with each other.
3. The light-emitting element according to claim 1 ,
wherein the first light-emitting layer and the second light-emitting layer are formed by a wet method.
4. A light-emitting device comprising the light-emitting element according to claim 1 .
5. A lighting device comprising the light-emitting device according to claim 4 .
6. An electronic appliance comprising the light-emitting device according to claim 4 .
7. The light-emitting element according to claim 1 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material.
8. The light-emitting element according to claim 1 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material, and
wherein a difference between an absolute value of the HOMO level of the second host material and an absolute value of the HOMO level of the second light-emitting material is greater than 0.2 eV.
9. A light-emitting element comprising:
an anode;
a hole-transport layer over the anode;
a first light-emitting layer over and in contact with the hole-transport layer;
a second light-emitting layer over and in contact with the first light-emitting layer; and
a cathode over the second light-emitting layer,
wherein the hole-transport layer includes a first organic compound and an anti-reduction substance,
wherein an electron-accepting property of the anti-reduction substance is higher than an electron-accepting property of the first organic compound,
wherein the first light-emitting layer includes a first host material having an electron-transport property and a first light-emitting material,
wherein the second light-emitting layer includes a second host material having an electron-transport property and a second light-emitting material having a hole-trapping property,
wherein the LUMO level of the anti-reduction substance is lower than the LUMO level of the first organic compound and the LUMO level of the first light-emitting layer,
wherein the LUMO level of the first light-emitting layer is lower than the LUMO level of the first organic compound, and
wherein a concentration of the first light-emitting material included in the first light-emitting layer is higher than a concentration of the second light-emitting material included in the second light-emitting layer.
10. The light-emitting element according to claim 9 ,
wherein the anode and the hole-transport layer are in contact with each other.
11. The light-emitting element according to claim 9 ,
wherein the first light-emitting layer and the second light-emitting layer are formed by a wet method.
12. A light-emitting device comprising the light-emitting element according to claim 9 .
13. A lighting device comprising the light-emitting device according to claim 12 .
14. An electronic appliance comprising the light-emitting device according to claim 12 .
15. The light-emitting element according to claim 9 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material.
16. The light-emitting element according to claim 9 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material, and
wherein a difference between an absolute value of the HOMO level of the second host material and an absolute value of the HOMO level of the second light-emitting material is greater than 0.2 eV.
17. A light-emitting element comprising:
an anode;
a hole-transport layer over the anode;
a first light-emitting layer over and in contact with the hole-transport layer;
a second light-emitting layer over and in contact with the first light-emitting layer; and
a cathode over the second light-emitting layer,
wherein the hole-transport layer includes a first organic compound and an anti-reduction substance,
wherein an electron-accepting property of the anti-reduction substance is higher than an electron-accepting property of the first organic compound,
wherein the first light-emitting layer includes a first host material having an electron-transport property and a first light-emitting material,
wherein the second light-emitting layer includes a second host material having an electron-transport property and a second light-emitting material having a hole-trapping property,
wherein the LUMO level of the anti-reduction substance is lower than the LUMO level of the first organic compound and the LUMO level of the first light-emitting layer,
wherein the LUMO level of the first light-emitting layer is lower than the LUMO level of the first organic compound, and
wherein the anti-reduction substance includes metal oxide.
18. The light-emitting element according to claim 17 ,
wherein a concentration of the metal oxide included in the first organic compound is greater than or equal to 67 wt % and less than 100 wt % in the hole-transport layer.
19. The light-emitting element according to claim 17 ,
wherein the anode and the hole-transport layer are in contact with each other.
20. The light-emitting element according to claim 17 ,
wherein the first light-emitting layer and the second light-emitting layer are formed by a wet method.
21. A light-emitting device comprising the light-emitting element according to claim 17 .
22. A lighting device comprising the light-emitting device according to claim 21 .
23. An electronic appliance comprising the light-emitting device according to claim 21 .
24. The light-emitting element according to claim 17 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material.
25. The light-emitting element according to claim 17 ,
wherein the HOMO level of the second host material is lower than the HOMO level of the second light-emitting material, and
wherein a difference between an absolute value of the HOMO level of the second host material and an absolute value of the HOMO level of the second light-emitting material is greater than 0.2 eV.