Light-Emitting Element

• US 20140084274A1
• Filed: 09/18/2013
• Published: 03/27/2014
• Est. Priority Date: 09/21/2012
• Status: Abandoned Application

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei, Seo, Satoshi, Shitagaki, Satoko, Ohsawa, Nobuharu, Inoue, Hideko, Kadoma, Hiroshi, Osaka, Harue
• Application Number:
  US14/030,554
• Publication Number:
  US 20140084274A1
• Time in Patent Office: Days
• US Class Current: 257/40
• 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 2101/90 Multiple hosts in the emissive layer
• CPC Class Codes: H10K 30/865 Intermediate layers comprising a mixture of materials of the adjoining active layers
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers

Abstract

A light-emitting element with high emission efficiency is provided. The light-emitting element includes, between a pair of electrodes, a layer containing a p-type host, a light-emitting layer containing a guest, the p-type host, and an n-type host, and a layer containing the n-type host. A combination of the p-type host and the n-type host forms an exciplex. Among the layer containing the p-type host, the light-emitting layer, and the layer containing the n-type host, the light-emitting layer has the highest secondary ion intensity of the n-type host, the layer containing the n-type host has the second-highest secondary ion intensity of the n-type host, and the layer containing the p-type host has the lowest secondary ion intensity of the n-type host in analysis by a time-of-flight secondary ion mass spectrometer.

Claims

1. A light-emitting element comprising:

a first electrode;

a light-emitting layer comprising a phosphorescent compound and an organic compound over the first electrode;

a first layer comprising the organic compound over the light-emitting layer; and

a second electrode over the first layer,

wherein, in the light-emitting layer, a concentration of the organic compound is higher than a concentration of the phosphorescent compound, and

wherein secondary ion intensity of the organic compound detected by a time-of-flight secondary ion mass spectrometer is higher in the light-emitting layer than in the first layer.

2. The light-emitting element according to claim 1, wherein the organic compound has an electron-transport property.

3. The light-emitting element according to claim 1, wherein the organic compound is a nitrogen-containing heteroaromatic compound.

4. The light-emitting element according to claim 1, wherein the organic compound is a six-membered heteroaromatic compound.

5. The light-emitting element according to claim 1, wherein the phosphorescent compound is an organometallic complex.

6. A light-emitting element comprising:

a first electrode;

a first layer comprising a first organic compound over the first electrode;

a light-emitting layer comprising a phosphorescent compound, the first organic compound, and a second organic compound over the first layer;

a second layer comprising the second organic compound over the light-emitting layer; and

a second electrode over the second layer,

wherein, in the light-emitting layer, a concentration of the second organic compound is higher than a concentration of the first organic compound and a concentration of the phosphorescent compound, and

wherein secondary ion intensity of the second organic compound detected by a time-of-flight secondary ion mass spectrometer is higher in the light-emitting layer than in the second layer.

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

wherein the first organic compound has a hole-transport property, and

wherein the second organic compound has an electron-transport property.

8. The light-emitting element according to claim 6, wherein the first organic compound is an aromatic amine compound.

9. The light-emitting element according to claim 6, wherein the second organic compound is a nitrogen-containing heteroaromatic compound.

10. The light-emitting element according to claim 6, wherein the second organic compound is a six-membered heteroaromatic compound.

11. The light-emitting element according to claim 6, wherein the phosphorescent compound is an organometallic complex.

12. The light-emitting element according to claim 6, wherein the first organic compound and the second organic compound form an exciplex in the light-emitting layer.

13. A light-emitting element comprising:

a first layer comprising a first organic compound;

a light-emitting layer comprising a phosphorescent compound, the first organic compound, and a second organic compound over and in contact with the first layer; and

a second layer comprising the second organic compound over and in contact with the light-emitting layer,

wherein the first organic compound has a hole-transport property,

wherein the second organic compound has an electron-transport property,

wherein an energy difference between a LUMO level of the phosphorescent compound and a LUMO level of the second organic compound is equal to or less than 0.3 eV, and

wherein secondary ion intensity of the second organic compound detected by a time-of-flight secondary ion mass spectrometer is higher in the light-emitting layer than in the second layer.

14. The light-emitting element according to claim 13,

wherein the light-emitting layer comprises a first region and a second region,

wherein, in the first region, a concentration of the second organic compound is higher than a concentration of the first organic compound, and

wherein, in the second region, a concentration of the second organic compound is lower than a concentration of the first organic compound.

15. The light-emitting element according to claim 13, wherein the first organic compound is an aromatic amine compound.

16. The light-emitting element according to claim 13, wherein the second organic compound is a nitrogen-containing heteroaromatic compound.

17. The light-emitting element according to claim 13, wherein the second organic compound is a six-membered heteroaromatic compound.

18. The light-emitting element according to claim 13, wherein the phosphorescent compound is an organometallic complex.

19. The light-emitting element according to claim 13, wherein the first organic compound and the second organic compound form an exciplex in the light-emitting layer.

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