Light-emitting element, light-emitting device, electronic device, and lighting device
To increase emission efficiency of a fluorescent light-emitting element by efficiently utilizing a triplet exciton generated in a light-emitting layer. The light-emitting layer of the light-emitting element includes at least a host material and a guest material. The triplet exciton generated from the host material in the light-emitting layer is changed to a singlet exciton by triplet-triplet annihilation (TTA). The guest material (fluorescent dopant) is made to emit light by energy transfer from the singlet exciton. Thus, the emission efficiency of the light-emitting element is improved.
1. A light-emitting element comprising:
a hole-transport layer comprising a hole-transport material over a first electrode;
a light-emitting layer comprising a guest material and a host material over the hole-transport layer;
an electron-transport layer comprising an electron-transport material over and in contact with the light-emitting layer; and
a second electrode over the electron-transport layer,
wherein the host material is an anthracene compound,
wherein the guest material is a pyrene compound,
wherein a T1 level of the host material is lower than a T1 level of the guest material,
wherein a T1 level of the hole-transport material is higher than the T1 level of the host material,
wherein the host material and the electron-transport material are same compound, and
wherein the hole-transport material is a phenanthrene compound.
2. The light-emitting element according to claim 1 , wherein the guest material is a fluorescent material.
3. A light-emitting device comprising the light-emitting element according to claim 1 .
4. An electronic device comprising the light-emitting element according to claim 1 .
5. A lighting device comprising the light-emitting element according to claim 1 .
6. The light-emitting element according to claim 1 , wherein the pyrene compound is a pyrene diamine compound.
7. The light-emitting element according to claim 1 ,
wherein the anthracene compound comprises a carbazole group, and
wherein the pyrene compound is a pyrene diamine compound.
8. A light-emitting element comprising:
a hole-transport layer comprising a hole-transport material over a first electrode;
a light-emitting layer comprising a guest material and a host material over the hole-transport layer;
an electron-transport layer comprising an electron-transport material over and in contact with the light-emitting layer; and
a second electrode over the electron-transport layer,
wherein the host material is an anthracene compound,
wherein the guest material is a pyrene compound,
wherein a T1 level of the host material is lower than a T1 level of the guest material,
wherein a T1 level of the hole-transport material is higher than the T1 level of the guest material and the T1 level of the host material,
wherein the host material and the electron-transport material are same compound, and
wherein the hole-transport material is a phenanthrene compound.
9. The light-emitting element according to claim 8 , wherein the guest material is a fluorescent material.
10. A light-emitting device comprising the light-emitting element according to claim 8 .
11. An electronic device comprising the light-emitting element according to claim 8 .
12. A lighting device comprising the light-emitting element according to claim 8 .
13. The light-emitting element according to claim 8 , wherein the pyrene compound is a pyrene diamine compound.
14. The light-emitting element according to claim 8 ,
wherein the anthracene compound comprises a carbazole group, and
wherein the pyrene compound is a pyrene diamine compound.
15. A light-emitting element comprising:
a hole-transport layer comprising a hole-transport material over a first electrode;
a light-emitting layer comprising a guest material and a host material over the hole-transport layer;
an electron-transport layer comprising an electron-transport material over and in contact with the light-emitting layer; and
a second electrode over the electron-transport layer,
wherein the host material is an anthracene compound,
wherein the guest material is a pyrene compound,
wherein a T1 level of the host material is lower than a T1 level of the guest material,
wherein a T1 level of the hole-transport material is higher than the T1 level of the host material,
wherein a shape of a spectrum of delayed fluorescence is the same as a shape of a fluorescent spectrum of the guest material,
wherein a period where a ratio of an intensity of the delayed fluorescence with respect to an emission intensity during steadily injecting carriers is higher than or equal to 0.01 is 1×10 −6 sec or longer,
wherein the host material and the electron-transport material are same compound, and
wherein the hole-transport material is a phenanthrene compound.
16. A light-emitting device comprising the light-emitting element according to claim 15 .
17. An electronic device comprising the light-emitting element according to claim 15 .
18. A lighting device comprising the light-emitting element according to claim 15 .
19. The light-emitting element according to claim 15 , wherein the pyrene compound is a pyrene diamine compound.
20. The light-emitting element according to claim 15 ,
wherein the anthracene compound comprises a carbazole group, and
wherein the pyrene compound is a pyrene diamine compound.
21. A light-emitting element comprising:
a hole-transport layer comprising a hole-transport material over a first electrode;
a light-emitting layer comprising a guest material and a host material over the hole-transport layer;
an electron-transport layer comprising an electron-transport material over and in contact with the light-emitting layer; and
a second electrode over the electron-transport layer,
wherein the host material is an anthracene compound,
wherein the guest material is a pyrene compound,
wherein a T1 level of the host material is lower than a T1 level of the guest material,
wherein a T1 level of the hole-transport material is higher than the T1 level of the guest material and the T1 level of the host material,
wherein a shape of a spectrum of delayed fluorescence is the same as a shape of a fluorescent spectrum of the guest material,
wherein a period where a ratio of an intensity of the delayed fluorescence with respect to an emission intensity during steadily injecting carriers is higher than or equal to 0.01 is 1×10 −6 sec or longer,
wherein the host material and the electron-transport material are same compound, and
wherein the hole-transport material is a phenanthrene compound.
22. A light-emitting device comprising the light-emitting element according to claim 21 .
23. An electronic device comprising the light-emitting element according to claim 21 .
24. A lighting device comprising the light-emitting element according to claim 21 .
25. The light-emitting element according to claim 21 , wherein the pyrene compound is a pyrene diamine compound.
26. The light-emitting element according to claim 21 ,
wherein the anthracene compound comprises a carbazole group, and
wherein the pyrene compound is a pyrene diamine compound.