Light-Emitting Element, Light-Emitting Device, and Method for Manufacturing the Same

• US 20110057178A1
• Filed: 09/01/2010
• Published: 03/10/2011
• Est. Priority Date: 09/04/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Shitagaki, Satoko, Seo, Satoshi
• Granted Patent: US 9,209,415 B2
• Time in Patent Office: Days
• US Class Current: 257/40
• CPC Class Codes: H10K 2101/30 Highest occupied molecular orbital [HOMO], lowest unoccupied molecular orbital [LUMO] or Fermi energy values
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/13 comprising stacked EL layers within one EL unit
• CPC Class Codes: H10K 50/14 Carrier transporting layers
• CPC Class Codes: H10K 85/324 comprising aluminium, e.g. Alq3
• CPC Class Codes: H10K 85/633 comprising polycyclic condensed aromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: H10K 85/6572 comprising only nitrogen in the heteroaromatic polycondensed ring system, e.g. phenanthroline or carbazole

Abstract

Disclosed is a light-emitting element which includes a first light-emitting layer over and in contact with a hole-transport layer and a second light-emitting layer over and in contact with the first light-emitting layer. The first and the second light-emitting layers contain a bipolar host material and an emissive guest material. The guest material in the first light-emitting layer has a lower ability for capturing a hole than a guest material in the second light-emitting layer; therefore, the hole-transport property of the first light-emitting layer can be controlled to be higher than that of the second light-emitting layer. The difference in hole-transport property between the first and second light-emitting layers allows a recombination region to be widely spread in the light-emitting layers. An anti-reducing material may be provided in the hole-transport layer, which prevents the hole-transport layer from being reduced by electrons which fail to undergo recombination in the light-emitting layers.

Claims

1. A light-emitting device 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 first light-emitting layer contains a first host material and a first light-emitting material,

wherein the second light-emitting layer contains a second host material and a second light-emitting material, and

wherein a hole-transport property of the first light-emitting layer is higher than a hole-transport property of the second light-emitting layer.

2. The light-emitting device according to claim 1,

wherein a difference between HOMO levels of the second host material and the second light-emitting material is larger than a difference between HOMO levels of the first host material and the first light-emitting material.

3. The light-emitting device according to claim 1,

wherein an electron-transport property of the first light-emitting layer is lower than an electron-transport property of the second light-emitting layer.

4. The light-emitting device according to claim 1,

wherein a difference between LUMO levels of the first host material and the first light-emitting material is larger than a difference between LUMO levels of the second host material and the second light-emitting material.

5. The light-emitting device according to claim 1,

wherein the first host material and the second host material are bipolar.

6. The light-emitting device according to claim 1,

wherein the first host material and the second host material are the same.

7. The light-emitting device according to claim 1,

wherein at least one of the first host material and the second host material is an anthracene derivative.

8. The light-emitting device according to claim 1,

wherein at least one of the first host material and the second host material is an anthracene derivative having a carbazolyl group.

9. The light-emitting device according to claim 1,

wherein the hole-transport layer is in contact with the anode.

10. The light-emitting device according to claim 1,

wherein emission color of the first light-emitting material is different from emission color of the second light-emitting material.

11. The light-emitting device according to claim 1,

wherein the hole-transport layer comprises a first organic compound and an anti-reducing material which is reduced more easily than the first organic compound.

12. The light-emitting device according to claim 11,

wherein the anti-reducing material is an oxide of any of Group 4 to 8 metals.

13. The light-emitting device according to claim 11,

wherein the first organic compound is the same as at least one of the first host material and the second host material.

14. An electric device comprising the light-emitting device according to claim 1.

15. A lighting device comprising the light-emitting device according to claim 1.

16. A light-emitting device 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;

a third light-emitting layer over and in contact with the second light-emitting layer; and

a cathode over the third light-emitting layer,

wherein the first light-emitting layer contains a first host material and a first light-emitting material,

wherein the second light-emitting layer contains a second host material and a second light-emitting material,

wherein the third light-emitting layer contains a third host material and a third light-emitting material,

wherein a hole-transport property of the first light-emitting layer is higher than or equal to a hole-transport property of the second light-emitting layer, and

wherein the hole-transport property of the second light-emitting layer is higher than a hole-transport property of the third light-emitting layer.

17. The light-emitting device according to claim 16,

wherein a difference between HOMO levels of the second host material and the second light-emitting material is equal to or larger than a difference between HOMO levels of the first host material and the first light-emitting material, and

wherein a difference between HOMO levels of the third host material and the third light-emitting material is larger than a difference between HOMO levels of the second host material and the second light-emitting material.

18. The light-emitting device according to claim 16,

wherein the first host material, the second host material, and the third host material and are bipolar.

19. The light-emitting device according to claim 16,

wherein at least two of the first host material, the second host material, and the third host material are the same.

20. The light-emitting device according to claim 16,

wherein at least one of the first host material, the second host material, and the third host material is an anthracene derivative.

21. The light-emitting device according to claim 16,

wherein at least one of the first host material and the second host material is an anthracene derivative having a carbazolyl group.

22. The light-emitting device according to claim 16,

wherein the hole-transport layer is in contact with the anode.

23. The light-emitting device according to claim 16,

wherein mission colors of the first light-emitting layer 113a, the second light-emitting layer 113b, and the third light-emitting layer 113c are different.

24. The light-emitting device according to claim 16,

wherein the hole-transport layer comprises a first organic compound and an anti-reducing material which is reduced more easily than the first organic compound.

25. The light-emitting device according to claim 24,

wherein the anti-reducing material is an oxide of any of Group 4 to 8 metals.

26. The light-emitting device according to claim 24,

wherein the first organic compound is the same as at least one of the first host material, the second host material, and the third host material.

27. An electric device comprising the light-emitting device according to claim 16.

28. A lighting device comprising the light-emitting device according to claim 16.