Light-emitting element
View Patent ↗Provided is a light-emitting element with high external quantum efficiency and a low drive voltage. The light-emitting element includes a light-emitting layer which contains a phosphorescent compound and a material exhibiting thermally activated delayed fluorescence between a pair of electrodes, wherein a peak of a fluorescence spectrum and/or a peak of a phosphorescence spectrum of the material exhibiting thermally activated delayed fluorescence overlap(s) with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound, and wherein the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes.
1. A light-emitting element comprising:
a pair of electrodes; and
a light-emitting layer between the pair of electrodes,
wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and
wherein a peak of a fluorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.
2. The light-emitting element according to claim 1 , wherein a difference between an energy value of the peak of the fluorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less.
3. The light-emitting element according to claim 1 , wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.
4. The light-emitting element according to claim 1 , wherein the phosphorescent compound is an organometallic complex.
5. The light-emitting element according to claim 1 , wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·cm.
6. The light-emitting element according to claim 1 , wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π-electron excess heteroaromatic ring and a π-electron deficient heteroaromatic ring.
7. The light-emitting element according to claim 6 , wherein in the thermally activated delayed fluorescence material, the π-electron excess heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring.
8. A light-emitting device comprising the light-emitting element according to claim 1 .
9. An electronic device comprising the light-emitting element according to claim 1 .
10. A lighting device comprising the light-emitting element according to claim 1 .
11. A light-emitting element comprising:
a pair of electrodes; and
a light-emitting layer between the pair of electrodes,
wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and
wherein a peak of a phosphorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.
12. The light-emitting element according to claim 11 , wherein a difference between an energy value of the peak of the phosphorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less.
13. The light-emitting element according to claim 11 , wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.
14. The light-emitting element according to claim 11 , wherein the phosphorescent compound is an organometallic complex.
15. The light-emitting element according to claim 11 , wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·cm.
16. The light-emitting element according to claim 11 , wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π-electron excess heteroaromatic ring and a π-electron deficient heteroaromatic ring.
17. The light-emitting element according to claim 16 , wherein in the thermally activated delayed fluorescence material, the π-electron excess heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring.
18. A light-emitting device comprising the light-emitting element according to claim 11 .
19. An electronic device comprising the light-emitting element according to claim 11 .
20. A lighting device comprising the light-emitting element according to claim 11 .
21. A light-emitting element comprising:
a pair of electrodes; and
a light-emitting layer between the pair of electrodes,
wherein the light-emitting layer comprises a phosphorescent compound and a thermally activated delayed fluorescence material, and
wherein a peak of a fluorescence spectrum and a peak of a phosphorescence spectrum of the thermally activated delayed fluorescence material overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound.
22. The light-emitting element according to claim 21 ,
wherein a difference between an energy value of the peak of the fluorescence spectrum and an energy value of a peak of the lowest-energy-side absorption band is 0.3 eV or less, and
wherein a difference between an energy value of the peak of the phosphorescence spectrum and the energy value of the peak of the lowest-energy-side absorption band is 0.3 eV or less.
23. The light-emitting element according claim 21 , wherein a difference between the energy value of the peak of the fluorescence spectrum and the energy value of the peak of the phosphorescence spectrum is 0.3 eV or less.
24. The light-emitting element according to claim 21 , wherein the lowest-energy-side absorption band comprises an absorption band based on a triplet MLCT transition.
25. The light-emitting element according to claim 21 , wherein the phosphorescent compound is an organometallic complex.
26. The light-emitting element according to claim 21 , wherein a molar absorption coefficient of the lowest-energy-side absorption band is higher than or equal to 5000/M·cm.
27. The light-emitting element according to claim 21 , wherein the thermally activated delayed fluorescence material is a heterocyclic compound comprising a π-electron excess heteroaromatic ring and a π-electron deficient heteroaromatic ring.
28. The light-emitting element according to claim 27 , wherein in the thermally activated delayed fluorescence material, the π-electron excess heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring.
29. A light-emitting device comprising the light-emitting element according to claim 21 .
30. An electronic device comprising the light-emitting element according to claim 21 .
31. A lighting device comprising the light-emitting element according to claim 21 .
32. The light-emitting element according to claim 1 , wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.
33. The light-emitting element according to claim 11 , wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.
34. The light-emitting element according to claim 21 , wherein in the light-emitting layer, the phosphorescent compound functions as a guest material and the thermally activated delayed fluorescence material functions as a host material.