Light emitting element and light emitting device using the same

• US 7,893,427 B2
• Filed: 07/15/2005
• Issued: 02/22/2011
• Est. Priority Date: 07/23/2004
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kumaki, Daisuke, Seo, Satoshi
• Primary Examiner(s): Cao; Phat X
• Application Number:
  US10/582,249
• Publication Number:
  US 20070114512A1
• Time in Patent Office: 2,048 Days
• Field of Search: 257/40, 257/79
• US Class Current: 257/40
• CPC Class Codes: H01L 27/15 including semiconductor components having potential barriers, specially adapted for light emission
• CPC Class Codes: H01L 33/00 Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof H10K50/00 takes precedence; devices consisting of a plurality of semiconductor components formed in or on a common substrate and including semiconductor components having potential barriers, specially adapted for light emission H01L27/15; semiconductor lasers H01S5/00
• CPC Class Codes: H01L 33/0008 having p-n or hi-lo junctions
• CPC Class Codes: H01L 33/42 Transparent materials
• CPC Class Codes: H01L 33/60 Reflective elements
• CPC Class Codes: H10K 2102/351 Thickness
• CPC Class Codes: H10K 50/155 comprising dopants
• CPC Class Codes: H10K 50/157 between the light-emitting layer and the cathode
• CPC Class Codes: H10K 50/165 comprising dopants
• CPC Class Codes: H10K 50/30 Organic light-emitting transistors
• CPC Class Codes: H10K 50/852 comprising a resonant cavity structure, e.g. Bragg reflector pair
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 85/324 comprising aluminium, e.g. Alq3

Abstract

An object of the prevent invention is to provide a light emitting element having slight increase in driving voltage with accumulation of light emitting time. Another object of the invention is to provide a light emitting element having slight increase in resistance value with increase in film thickness. A light emitting element of the invention includes a first layer for generating holes, a second layer for generating electrons and a third layer comprising a light emitting substance between first and second electrodes. The first and third layers are in contact with the first and second electrodes, respectively. The second and third layers are connected to each other so as to inject electrons generated in the second layer into the third layer when applying the voltage to the light emitting element such that a potential of the second electrode is higher than that of the first electrode.

Claims

1. A light emitting element comprising:

a first layer for generating a hole;

a second layer for generating an electron; and

a third layer comprising a light emitting substance,

wherein the first layer, the second layer and the third layer are interposed between a first electrode and a second electrode;

wherein the second layer is interposed between the first layer and the third layer;

wherein the first layer is physically in contact with the first electrode; and

wherein the light emitting element emits light when a voltage is applied between the first electrode and the second electrode such that a potential of the second electrode is higher than that of the first electrode.

2. A light emitting device comprising the light emitting element according to claim 1.

3. The light emitting element according to claim 1, wherein the light emitting element is incorporated into a display portion of an electronic appliance.

4. The light emitting element according to claim 1, wherein the third layer is in contact with the second electrode.

5. The light emitting element according to claim 1,

wherein the first layer comprises a first substance having a hole transporting property and a second substance having an electron accepting property to the first substance;

and

wherein a molar ratio of the second substance to the first substance is 0.5 to 2.

6. The light emitting element according to claim 1, wherein the first layer comprises DNTPD.

7. The light emitting element according to claim 1, wherein the first layer is in contact with the second layer.

8. The light emitting element according to claim 1, wherein the second layer is in contact with the third layer.

9. A light emitting element comprising:

a first layer comprising a first substance and a second substance;

a second layer comprising a third substance and a fourth substance; and

a third layer comprising a light emitting substance,

wherein a hole transporting property of the first substance is stronger than an electron transporting property thereof;

wherein the second substance has an electron accepting property to the first substance;

wherein an electron transporting property of the third substance is stronger than a hole transporting property thereof;

wherein the fourth substance has an electron donating property to the third substance;

wherein the first layer, the second layer and the third layer are interposed between a first electrode and a second electrode;

wherein the second layer is interposed between the first layer and the third layer;

wherein the first layer is physically in contact with the first electrode; and

wherein the light emitting element emits light when a voltage is applied between the first electrode and the second electrode such that a potential of the second electrode is higher than that of the first electrode.

10. The light emitting element according to claim 9, wherein a molar ratio of the second substance to the first substance is 0.5 to 2.

11. A light emitting device comprising the light emitting element according to claim 9.

12. The light emitting element according to claim 9, wherein the light emitting element is incorporated into a display portion of an electronic appliance.

13. The light emitting element according to claim 9, wherein the third layer is in contact with the second electrode.

14. The light emitting element according to claim 9, wherein the first substance is DNTPD.

15. The light emitting element according to claim 9, wherein the first layer is in contact with the second layer.

16. The light emitting element according to claim 9, wherein the second layer is in contact with the third layer.

17. A light emitting element comprising:

a first layer comprising a p-type semiconductor;

a second layer comprising an n-type semiconductor; and

a third layer comprising a light emitting substance,

wherein the first layer, the second layer and the third layer are interposed between a first electrode and a second electrode;

wherein the second layer is interposed between the first layer and the third layer;

wherein the first layer is physically in contact with the first electrode; and

wherein the light emitting element emits light when a voltage is applied between the first electrode and the second electrode such that a potential of the second electrode is higher than that of the first electrode.

18. A light emitting device comprising the light emitting element according to claim 17.

19. The light emitting element according to claim 17, wherein the light emitting element is incorporated into a display portion of an electronic appliance.

20. The light emitting element according to claim 17, wherein the third layer is in contact with the second electrode.

21. The light emitting element according to claim 17, wherein the first layer is in contact with the second layer.

22. The light emitting element according to claim 17, wherein the second layer is in contact with the third layer.

23. A light emitting element comprising:

a first layer comprising 4, 4′

-bis[N-(1-naphthyl)-N-phenylamino]biphenyl and molybdenum oxide;

a second layer comprising tris(8-quinolinolato)aluminum and lithium; and

a third layer comprising a light emitting substance,

wherein the first layer, the second layer and the third layer are interposed between a first electrode and a second electrode;

wherein the second layer is interposed between the first layer and the third layer;

wherein the first layer is physically in contact with the first electrode; and

wherein the light emitting element emits light when a voltage is applied between the first electrode and the second electrode such that a potential of the second electrode is higher than that of the first electrode.

24. The light emitting element according to claim 23, wherein a molar ratio of molybdenum oxide to 4, 4′

-bis[N-(1-naphthyl)-N-phenylamino]biphenyl is 0.5 to 2.

25. A light emitting device comprising the light emitting element according to claim 23.

26. The light emitting element according to claim 23, wherein the light emitting element is incorporated into a display portion of an electronic appliance.

27. The light emitting element according to claim 23, wherein the third layer is in contact with the second electrode.

28. The light emitting element according to claim 23, wherein, the first layer is in contact with the second layer.

29. The light emitting element according to claim 23, wherein the second layer is in contact with the third layer.

30. A light emitting element comprising:

a first layer comprising a first substance and a second substance;

a second layer comprising a third substance and a fourth substance; and

a third layer comprising x pieces of layers (x is a given positive integer),

wherein the first layer, the second layer and the third layer are interposed between a first electrode and a second electrode;

wherein the first electrode comprises a conductive material which is capable of reflecting light;

wherein the second electrode comprises a conductive material that can transmit a visible light;

wherein the x pieces of layers comprises a light emitting layer;

wherein the second layer is interposed between the first layer and the third layer;

wherein a hole transporting property of the first substance is stronger than an electron transporting property thereof;

wherein the second substance has an electron accepting property to the first substance;

wherein an electron transporting property of the third substance is stronger than a hole transporting property thereof;

wherein the fourth substance has an electron donating property to the third substance;

wherein the first layer is in contact with the first electrode;

wherein one layer of the x pieces of layers is in contact with the second layer;

wherein y pieces of layers (y <

x, and y is a positive integer) are provided between the light emitting layer and the second layer;

wherein the light emitting element emits light when a voltage is applied thereto such that a potential of the second electrode is higher than that of the first electrode; and

wherein a thickness of the first layer and a thickness of the second layer satisfy expressions 1, 2 and 3 below;

31. A light emitting device comprising the light emitting element according to claim 30.

32. The light emitting element according to claim 30, wherein the light emitting element is incorporated into a display portion of an electronic appliance.

33. The light emitting element according to claim 30, wherein the conductive material has a reflectance of 50 to 100%.

34. The light emitting element according to claim 30, wherein an X^th layer comprised in the third layer is in contact with the second electrode.

35. The light emitting element according to claim 30, wherein a molar ratio of the second substance to the first substance is 0.5 to 2.

36. The light emitting element according to claim 30, wherein the first substance is DNTPD.

37. The light emitting element according to claim 30, wherein the first layer is in contact with the second layer.

38. The light emitting element according to claim 30, wherein the second layer is in contact with the third layer.