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

• US 9,219,243 B2
• Filed: 07/31/2013
• Issued: 12/22/2015
• Est. Priority Date: 08/03/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Matsubara, Tomoe, Seo, Satoshi
• Primary Examiner(s): Vu, David
• Assistant Examiner(s): NGUYEN, CUONG B
• Application Number:
  US13/955,813
• Publication Number:
  US 20140034926A1
• Time in Patent Office: 874 Days
• US Class Current: 1/1
• 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 2102/311 Flexible OLED
• 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 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: H10K 85/611 Charge transfer complexes

Abstract

A multicolor light-emitting element in which light-emitting layers emitting light of different colors are stacked and color adjustment is easily made is provided. A multicolor light-emitting element which is inexpensive and has favorable emission efficiency is provided. A light-emitting element in which at least two light-emitting layers emitting light of different colors are formed in contact with each other and the light emitted from the two light-emitting layers is obtained from exciplexes is provided. In addition, the light-emitting element in which the exciplexes emit delayed fluorescence is provided.

Claims

1. A light-emitting element comprising:

a first electrode;

a second electrode; and

an EL layer interposed between the first electrode and the second electrode,

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

wherein the first light-emitting layer contains a first organic compound and a second organic compound,

wherein the second light-emitting layer contains a third organic compound and a fourth organic compound,

wherein the first organic compound and the second organic compound are mixed in the first light-emitting layer and form a first exciplex in the first light-emitting layer, and

wherein the third organic compound and the fourth organic compound are mixed in the second light-emitting layer and form a second exciplex in the second light-emitting layer.

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

wherein light emission is obtained from the first exciplex and the second exciplex.

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

wherein a difference in energy between a singlet excited level and a triplet excited level of at least one of the first exciplex and the second exciplex is 0.2 eV or lower.

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

wherein at least one of the first exciplex and the second exciplex exhibits delayed fluorescence.

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

wherein an electron-hole recombination region in the light-emitting layer is arranged to be positioned at an interface between the first light-emitting layer and the second light-emitting layer.

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

wherein one of the first organic compound and the second organic compound is a material having an electron-transport property and the other is a material having a hole-transport property, and

wherein one of the third organic compound and the fourth organic compound is a material having an electron-transport property and the other is a material having a hole-transport property.

7. The light-emitting element according to claim 6,

wherein the first electrode functions as an anode, and the second electrode functions as a cathode,

wherein the first light-emitting layer is positioned on the first electrode side,

wherein the first light-emitting layer contains a larger amount of the material having the hole-transport property than the second light-emitting layer, and

wherein the second light-emitting layer contains a larger amount of the material having the electron-transport property than the first light-emitting layer.

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

wherein the first exciplex and the second exciplex emit light having peaks at different wavelengths.

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

wherein an emission spectrum of the light-emitting layer has two peaks.

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

wherein one of the first organic compound and the second organic compound is the same as one of the third organic compound and the fourth organic compound.

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

wherein the light-emitting layer exhibits white light emission.

12. A light-emitting module comprising:

the light-emitting element according to claim 1; and

a means controlling the light-emitting element.

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

14. A light-emitting device comprising:

the light-emitting element according to claim 1; and

a means controlling the light-emitting element.

15. An electronic appliance comprising the light-emitting element according to claim 1.