Light-emitting element, light-emitting device, display device, lighting device, and electronic device
Provided is a light-emitting element which has an anode, a light-emitting layer over the anode, an electron-transport layer over and in contact with the light-emitting layer, an electron-injection layer over and in contact with the electron-transport layer, and a cathode over and in contact with the electron-injection layer. The light-emitting layer has an electron-transport property, and the electron-transport layer includes an anthracene derivative. The light-emitting layer further includes a phosphorescent substance. This device structure allows the formation of a highly efficient blue-emissive light-emitting element even though the phosphorescent substance has higher triplet energy than the anthracene derivative which directly contacts with the light-emitting layer.
1. A light-emitting device comprising:
an anode;
a light-emitting layer over the anode, the light-emitting layer comprising a host material and a phosphorescent substance;
an electron-transport layer over and in contact with the light-emitting layer, the electron-transport layer comprising a first organic compound which has an anthracene skeleton and one of a carbazolyl skeleton and a dibenzo[c,g]carbazolyl skeleton;
an electron-injection layer over and in contact with the electron-transport layer, the electron-injection layer comprising a second organic compound which is different from the first organic compound; and
a cathode over and in contact with the electron-injection layer,
wherein the host material is a π-electron deficient heteroaromatic compound, and
wherein the electron-injection layer comprises:
a first layer comprising the second organic compound; and
a second layer over the first layer, the second layer comprising any one of lithium fluoride, cesium fluoride and calcium fluoride.
2. The light-emitting device according to claim 1 , wherein the π-electron deficient heteroaromatic compound has one of a pyridine group, a 2,2′-bipyridine group, and a pyrimidine group to which a carbazolyl group is bonded through a phenylene group or a biphenylene group.
3. The light-emitting device according to claim 1 , wherein the anthracene skeleton and the one of the carbazolyl skeleton and the dibenzo[c,g]carbazolyl skeleton are bonded to each other through a para-phenylene group.
4. The light-emitting device according to claim 1 , wherein the second layer is in contact with the first layer.
5. The light-emitting device according to claim 1 , wherein the host material is represented by any one of the following formulae:
6. The light-emitting device according to claim 1 , wherein the first organic compound is represented by any one of the following formulae:
7. A lighting device comprising the light-emitting device according to claim 1 .
8. A display device comprising the light-emitting device according to claim 1 .
9. An electronic device comprising the light-emitting device according to claim 1 .
10. The light-emitting device according to claim 1 ,
wherein the light-emitting layer comprises a first light-emitting layer and a second light-emitting layer,
wherein the first light-emitting layer comprises the phosphorescent substance, and
wherein the second light-emitting layer comprises the phosphorescent substance and the host material.
11. The light-emitting device according to claim 10 , wherein the first light-emitting layer further comprises the host material and a second host material.
12. The light-emitting device according to claim 1 ,
wherein the host material has an electron transport property higher than a hole-transport property, and
wherein the phosphorescent substance is capable to emit phosphorescence with a peak in a range from 420 nm to 530 nm.
13. A light-emitting device comprising:
an anode;
a light-emitting layer over the anode, the light-emitting layer comprising a host material and a phosphorescent substance;
an electron-transport layer over and in contact with the light-emitting layer, the electron-transport layer comprising a first organic compound which has an anthracene skeleton;
an electron-injection layer over the electron-transport layer, the electron-injection layer comprising:
a first layer comprising a second organic compound; and
a second layer over the first layer, the second layer comprising any one of lithium fluoride, cesium fluoride and calcium fluoride; and
a cathode over the electron-injection layer.
14. The light-emitting device according to claim 13 , wherein the electron-injection layer is in contact with the electron-transport layer and the cathode.
15. The light-emitting device according to claim 13 , wherein the second organic compound is different from the first organic compound.
16. The light-emitting device according to claim 14 , wherein the second layer is in contact with the first layer.
17. A lighting device comprising the light-emitting device according to claim 13 .
18. A display device comprising the light-emitting device according to claim 13 .
19. An electronic device comprising the light-emitting device according to claim 13 .
20. The light-emitting device according to claim 13 ,
wherein the light-emitting layer comprises a first light-emitting layer and a second light-emitting layer,
wherein the first light-emitting layer comprises the phosphorescent substance, and
wherein the second light-emitting layer comprises the phosphorescent substance and the host material.
21. The light-emitting device according to claim 20 , wherein the first light-emitting layer further comprises the host material and a second host material.
22. The light-emitting device according to claim 13 ,
wherein the host material has an electron transport property higher than a hole-transport property,
wherein the host material is a π-electron deficient heteroaromatic compound, and
wherein the phosphorescent substance is capable to emit phosphorescence with a peak in a range from 420 nm to 530 nm.