Light-emitting element, light-emitting device, display device, electronic device, and lighting device

• US 8,916,897 B2
• Filed: 05/29/2013
• Issued: 12/23/2014
• Est. Priority Date: 05/31/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei, Seo, Satoshi
• Primary Examiner(s): Nguyen, Dao H
• Assistant Examiner(s): Nguyen, Tram H
• Application Number:
  US13/904,396
• Publication Number:
  US 20130320377A1
• Time in Patent Office: 573 Days
• Field of Search: 257/88, 257/13, 257 79-103, 257/918, 257/40, 257/191, 257E51018-E51022, 257E33001-E33077, 257/E33.054, 257/E25.028, 257/E25.032, 257/E31.058, 257/E31.063, 257/E31.115, 257E27133-E27139, 257/116, 257/117, 257/432, 257/437, 257/749, 257E31056-E33059, 438 22- 47, 438/69
• US Class Current: 257/98
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 2101/40 Interrelation of parameters between multiple constituent active layers or sublayers, e.g. HOMO values in adjacent layers
• 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 50/80 Constructional details
• CPC Class Codes: H10K 85/342 comprising iridium

Abstract

An object is to provide a light-emitting element which uses a plurality of kinds of light-emitting dopants and has high emission efficiency. In one embodiment of the present invention, a light-emitting device, a light-emitting module, a light-emitting display device, an electronic device, and a lighting device each having reduced power consumption are provided by using the above light-emitting element. Focus is placed on Förster mechanism, which is one of mechanisms of intermolecular energy transfer. Efficient energy transfer by Förster mechanism is achieved by employing a combination of molecules which makes it possible to obtain an overlap between an emission spectrum band of the molecule which donates energy and the longest-wavelength-side peak of a characteristic curve obtained by multiplying an absorption spectrum of the molecule which receives energy by a wavelength raised to the fourth power.

Claims

1. A light-emitting element comprising:

a first electrode;

a first light-emitting layer over the first electrode comprising;

a first phosphorescent compound; and

a first host material;

a second light-emitting layer over the first light-emitting layer comprising;

a second phosphorescent compound; and

a second host material;

a third light-emitting layer over the second light-emitting layer comprising;

a third phosphorescent compound; and

a third host material; and

a second electrode over the third light-emitting layer,

wherein light emitted from the second phosphorescent compound has a longer wavelength than light emitted from the first phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the second phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the first phosphorescent compound,

wherein light emitted from the third phosphorescent compound has a longer wavelength than the light emitted from the second phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the third phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the second phosphorescent compound,

wherein the second light-emitting layer has a thickness of less than 5 nm and greater than or equal to 1 nm,

wherein λ

denotes a wavelength, and

wherein ε

(λ

) denotes a molar absorption coefficient at the wavelength λ

.

2. The light-emitting element according to claim 1, wherein the second light-emitting layer has a thickness of less than or equal to 2 nm and greater than or equal to 1 nm.

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

wherein the first host material has an electron-transport property, and

wherein the second host material and the third host material each have a hole-transport property.

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

wherein the first host material has a hole-transport property, and

wherein the second host material and the third host material each have an electron-transport property.

5. The light-emitting element according to claim 1, wherein the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the third phosphorescent compound is larger than the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the second phosphorescent compound.

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

7. A light-emitting device comprising:

the light-emitting element according to claim 1; and

a driver circuit configured to control the light-emitting element.

8. A display device comprising:

the light-emitting element according to claim 1 in a display portion; and

a driver circuit configured to control the light-emitting element.

9. An electronic device comprising the light-emitting element according to claim 1.

10. A light-emitting element comprising:

a first electrode;

a first light-emitting layer over the first electrode comprising;

a first phosphorescent compound; and

a first host material;

a plurality of second island-like light-emitting regions over the first light-emitting layer comprising;

a second phosphorescent compound; and

a second host material;

a third light-emitting layer over the plurality of second island-like light-emitting regions comprising;

a third phosphorescent compound; and

a third host material; and

a second electrode over the third light-emitting layer,

wherein light emitted from the second phosphorescent compound has a longer wavelength than light emitted from the first phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the second phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the first phosphorescent compound,

wherein light emitted from the third phosphorescent compound has a longer wavelength than the light emitted from the second phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the third phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the second phosphorescent compound,

wherein λ

denotes a wavelength, and

wherein ε

(λ

) denotes a molar absorption coefficient at the wavelength λ

.

11. The light-emitting element according to claim 10,

wherein the first host material has an electron-transport property, and

wherein the second host material and the third host material each have a hole-transport property.

12. The light-emitting element according to claim 10,

wherein the first host material has a hole-transport property, and

wherein the second host material and the third host material each have an electron-transport property.

13. The light-emitting element according to claim 10, wherein the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the third phosphorescent compound is larger than the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the second phosphorescent compound.

14. A lighting device comprising the light-emitting element according to claim 10.

15. A light-emitting device comprising:

the light-emitting element according to claim 10; and

a driver circuit configured to control the light-emitting element.

16. A display device comprising:

the light-emitting element according to claim 10 in a display portion; and

a driver circuit configured to control the light-emitting element.

17. An electronic device comprising the light-emitting element according to claim 10.

18. A light-emitting element comprising:

a first electrode;

a first light-emitting layer over the first electrode comprising;

a first phosphorescent compound; and

a first host material;

a mixed layer over the first light-emitting layer comprising;

a plurality of second island-like light-emitting regions comprising;

a second phosphorescent compound; and

a second host material;

a plurality of third island-like light-emitting regions comprising;

a third phosphorescent compound; and

a third host material; and

a second electrode over the mixed layer,

wherein light emitted from the second phosphorescent compound has a longer wavelength than light emitted from the first phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the second phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the first phosphorescent compound,

wherein light emitted from the third phosphorescent compound has a longer wavelength than light emitted from the second phosphorescent compound,

wherein a longest-wavelength-side peak of a function ε

(λ

)λ

⁴ of the third phosphorescent compound overlaps with a phosphorescence spectrum F(λ

) of the second phosphorescent compound,

wherein λ

denotes a wavelength, and

wherein ε

(λ

) denotes a molar absorption coefficient at the wavelength λ

.

19. The light-emitting element according to claim 18,

wherein the first host material has an electron-transport property, and

wherein the second host material and the third host material each have a hole-transport property.

20. The light-emitting element according to claim 18,

wherein the first host material has a hole-transport property, and

wherein the second host material and the third host material each have an electron-transport property.

21. The light-emitting element according to claim 18, wherein the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the third phosphorescent compound is larger than the longest-wavelength-side peak of the function ε

(λ

)λ

⁴ of the second phosphorescent compound.

22. A lighting device comprising the light-emitting element according to claim 18.

23. A light-emitting device comprising:

the light-emitting element according to claim 18; and

a driver circuit configured to control the light-emitting element.

24. A display device comprising:

the light-emitting element according to claim 18 in a display portion; and

a driver circuit configured to control the light-emitting element.

25. An electronic device comprising the light-emitting element according to claim 18.