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

• US 9,082,994 B2
• Filed: 03/20/2014
• Issued: 07/14/2015
• Est. Priority Date: 03/26/2013
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Watabe, Takeyoshi, Seo, Satoshi
• Primary Examiner(s): VU, HUNG K
• Application Number:
  US14/220,535
• Publication Number:
  US 20140291642A1
• Time in Patent Office: 481 Days
• Field of Search: 257/40, 257/103, 257/E51.022, 257/E51.026
• US Class Current: 1/1
• CPC Class Codes: C09K 11/025 non-luminescent particle coatings or suspension media
• CPC Class Codes: C09K 11/06 containing organic luminescent materials
• CPC Class Codes: C09K 2211/1007 Non-condensed systems
• CPC Class Codes: C09K 2211/1044 containing two nitrogen atoms as heteroatoms
• CPC Class Codes: C09K 2211/185 of the platinum group, i.e. Os, Ir, Pt, Ru, Rh or Pd
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 2101/30 Highest occupied molecular orbital [HOMO], lowest unoccupied molecular orbital [LUMO] or Fermi energy values
• 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 50/125 specially adapted for multicolour light emission, e.g. for emitting white light
• CPC Class Codes: H10K 50/13 comprising stacked EL layers within one EL unit
• CPC Class Codes: H10K 85/342 comprising iridium
• CPC Class Codes: H10K 85/615 Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
• CPC Class Codes: H10K 85/633 comprising polycyclic condensed aromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: H10K 85/636 comprising heteroaromatic 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
• CPC Class Codes: H10K 85/6576 comprising only sulfur in the heteroaromatic polycondensed ring system, e.g. benzothiophene

Abstract

Provided is a light-emitting element having a light-emitting layer which contains at least a host material and a plurality of guest materials, where the host material has a lower T1 level than that of at least one of the plurality of guest materials. The emission of the one of the plurality of guest materials exhibits a multicomponent decay curve, and the lifetime thereof is less than or equal to 15 μsec, preferably less than or equal to 10 μsec, more preferably less than or equal to 5 μsec, where the lifetime is defined as a time for the emission to decrease in intensity to 1/100 of its initial intensity.

Claims

1. A light-emitting device comprising:

a first electrode;

a light-emitting layer over the first electrode, the light-emitting layer comprising a host material, a first guest material, and a second guest material; and

a second electrode over the light-emitting layer,

wherein the light-emitting layer comprises a first light-emitting layer and a second light-emitting layer which are in contact with each other,

wherein the host material and the first guest material are included in the first light-emitting layer,

wherein the host material and the second guest material are included in the second light-emitting layer,

wherein a T1 level of the host material is lower than a T1 level of the first guest material and higher than a T1 level of the second guest material, and

wherein a difference in T1 level between the host material and the first guest material is larger than 0 eV and less than or equal to 0.2 eV.

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

wherein the first guest material and the second guest material each are an organometallic compound.

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

wherein a rate constant of a radiative transition of the second guest material is larger than 5×

10⁵ sec<sup>−

1</sup>.

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

wherein a rate constant of a non-radiative transition of the host material is smaller than 1×

10² sec<sup>−

1</sup>.

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

wherein an emission from the light-emitting layer exhibits a multicomponent decay curve, and

wherein a lifetime of the emission is less than or equal to 15 μ

sec where the lifetime is a time required for the emission to decrease in intensity to 1/100 of an initial value thereof.

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

wherein the lifetime of the emission is less than or equal to 10 μ

sec.

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

wherein the lifetime of the emission is less than or equal to 5 μ

sec.

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

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

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

wherein the light-emitting layer further comprises an organic compound,

wherein a T1 level of the organic compound is lower than the T1 level of the first guest material and higher than the T1 level of the second guest material.

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

wherein the first light-emitting layer consists of the host material and the first guest material, and

wherein the second light-emitting layer consists of the host material and the second guest material.

12. A light-emitting device comprising:

a first electrode;

a first EL layer over the first electrode;

a charge generation layer over the first EL layer;

a second EL layer over the charge generation layer; and

a second electrode over the second EL layer,

wherein at least one of the first EL layer and the second EL layer comprises a light-emitting layer which comprises a host material, a first guest material, and a second guest material,

wherein the light-emitting layer comprises a first light-emitting layer and a second light-emitting layer which are in contact with each other,

wherein the host material and the first guest material are included in the first light-emitting layer,

wherein the host material and the second guest material are included in the second light-emitting layer,

wherein a T1 level of the host material is lower than a T1 level of the first guest material and higher than a T1 level of the second guest material, and

wherein a difference in T1 level between the host material and the first guest material is larger than 0 eV and less than or equal to 0.2 eV.

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

wherein the first guest material and the second guest material each are an organometallic compound.

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

wherein a rate constant of a radiative transition of the second guest material is larger than 5×

10⁵ sec<sup>−

1</sup>.

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

wherein a rate constant of a non-radiative transition of the host material is smaller than 1×

10² sec<sup>−

1</sup>.

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

wherein an emission from the light-emitting layer exhibits a multicomponent decay curve, and

wherein a lifetime of the emission is less than or equal to 15 μ

sec where the lifetime is a time required for the emission to decrease in intensity to 1/100 of an initial value thereof.

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

wherein the lifetime of the emission is less than or equal to 10 μ

sec.

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

wherein the lifetime of the emission is less than or equal to 5 μ

sec.

19. An electronic device comprising the light-emitting device according to claim 12.

20. A lighting device comprising the light-emitting device according to claim 12.

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

wherein the light-emitting layer further comprises an organic compound,

wherein a T1 level of the organic compound is lower than the T1 level of the first guest material and higher than the T1 level of the second guest material.

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

wherein the first light-emitting layer consists of the host material and the first guest material, and

wherein the second light-emitting layer consists of the host material and the second guest material.