Light-emitting element

• US 8,994,263 B2
• Filed: 02/10/2012
• Issued: 03/31/2015
• Est. Priority Date: 02/16/2011
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Shitagaki, Satoko, Seo, Satoshi, Ohsawa, Nobuharu, Inoue, Hideko, Takahashi, Masahiro, Suzuki, Kunihiko
• Primary Examiner(s): COUGHLIN, ANDREW J
• Application Number:
  US13/370,676
• Publication Number:
  US 20120206035A1
• Time in Patent Office: 1,145 Days
• Field of Search: 313/498, 313/504
• US Class Current: 313/504
• 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: H05B 33/14 characterised by the chemical or physical composition or the arrangement of the electroluminescent material , or by the simultaneous addition of the electroluminescent material in or onto the light source
• CPC Class Codes: H10K 2101/00 Properties of the organic materials covered by group H10K85/00
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: H10K 50/17 Carrier injection layers
• CPC Class Codes: H10K 50/171 Electron injection layers
• CPC Class Codes: H10K 50/818 Reflective anodes, e.g. ITO combined with thick metallic layers
• CPC Class Codes: H10K 50/828 Transparent cathodes, e.g. comprising thin metal layers
• 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 85/624 containing six or more rings
• CPC Class Codes: H10K 85/626 containing more than one polycyclic condensed aromatic rings, e.g. bis-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 with high external quantum efficiency, or a light-emitting element with a long lifetime. The light-emitting element includes, between a pair of electrodes, a light-emitting layer including a guest material and a host material, in which an emission spectrum of the host material overlaps with an absorption spectrum of the guest material, and phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material. By using the overlap between the emission spectrum of the host material and the absorption spectrum of the guest material, the energy smoothly transfers from the host material to the guest material, so that the energy transfer efficiency of the light-emitting element is high. Accordingly, a light-emitting element with high external quantum efficiency can be achieved.

Claims

1. A light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer comprising a guest material and a host material between the pair of electrodes,

wherein an emission spectrum of the host material overlaps with a longest-wavelength-side absorption band in an absorption spectrum of the guest material, and

wherein phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material, and

wherein a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the lowest-energy-side absorption band in the absorption spectrum is 0.3 eV or less.

2. The light-emitting element according to claim 1, wherein the longest-wavelength-side absorption band includes an absorption based on a triplet MLCT transition.

3. The light-emitting element according to claim 1, wherein the emission spectrum is a fluorescent spectrum.

4. The light-emitting element according to claim 1, wherein the guest material is an organometallic complex.

5. The light-emitting element according to claim 4, wherein the guest material is an iridium complex.

6. The light-emitting element according to claim 1, wherein a molar absorption coefficient of the longest-wavelength-side absorption band in the absorption spectrum is 5000 M⁻

1·

cm<sup>−

1</sup> or higher.

7. An electronic device comprising a light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer comprising a guest material and a host material between the pair of electrodes,

wherein an emission spectrum of the host material overlaps with a longest-wavelength-side absorption band in an absorption spectrum of the guest material, and

wherein phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material, and

wherein a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the lowest-energy-side absorption band in the absorption spectrum is 0.3 eV or less.

8. The electronic device according to claim 7, wherein the longest-wavelength-side absorption band includes an absorption based on a triplet MLCT transition.

9. The electronic device according to claim 7, wherein the emission spectrum is a fluorescent spectrum.

10. The electronic device according to claim 7, wherein the guest material is an organometallic complex.

11. The electronic device according to claim 7, wherein the guest material is an iridium complex.

12. The electronic device according to claim 7, wherein a molar absorption coefficient of the longest-wavelength-side absorption band in the absorption spectrum is 5000 M⁻

1 ·

cm<sup>−

1</sup> or higher.

13. A lighting device comprising a light-emitting element comprising:

a pair of electrodes; and

a light-emitting layer comprising a guest material and a host material between the pair of electrodes,

wherein an emission spectrum of the host material overlaps with a longest-wavelength-side absorption band in an absorption spectrum of the guest material, and

wherein phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material, and

wherein a difference between an energy value of a peak of the emission spectrum and an energy value of a peak of the lowest-energy-side absorption band in the absorption spectrum is 0.3 eV or less.

14. The lighting device according to claim 13, wherein the longest-wavelength-side absorption band includes an absorption based on a triplet MLCT transition.

15. The lighting device according to claim 13, wherein the emission spectrum is a fluorescent spectrum.

16. The lighting device according to claim 13, wherein the guest material is an organometallic complex.

17. The lighting device according to claim 13, wherein the guest material is an iridium complex.

18. The light-emitting element according to claim 13, wherein a molar absorption coefficient of the longest-wavelength-side absorption band in the absorption spectrum is 5000 M⁻

1·

cm<sup>−

1</sup> or higher.