VISIBLE LIGHT EMITTING DIODES FABRICATED FROM SOLUBLE SEMICONDUCTING POLYMERS

• US 20020022284A1
• Filed: 02/02/1999
• Published: 02/21/2002
• Est. Priority Date: 02/27/1991
• Status: Active Grant

• Current Assignee: Alan J. Heeger, David Braun
• Original Assignee: Alan J. Heeger, David Braun
• Inventors: HEEGER, ALAN J., BRAUN, DAVID
• Granted Patent: US 6,534,329 B2
• Time in Patent Office: Days
• US Class Current: 438/22
• CPC Class Codes: H10K 2102/311 Flexible OLED
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/805 Electrodes
• CPC Class Codes: H10K 50/81 Anodes
• CPC Class Codes: H10K 50/82 Cathodes
• CPC Class Codes: H10K 50/868 Arrangements for polarized light emission H10K50/86 takes precedence
• CPC Class Codes: H10K 71/00 Manufacture or treatment specially adapted for the organic devices covered by this subclass
• CPC Class Codes: H10K 71/191 characterised by provisions for the orientation or alignment of the layer to be deposited
• CPC Class Codes: H10K 85/114 Poly-phenylenevinylene; Derivatives thereof

Abstract

Visible light LEDs are produced having a layer of conjugated polymer which is cast directly from solution or formed as a gel-processed admixture with a carrier polymer. The LEDs can be formed so as to emit polarized light.

Claims

1. A process for fabrication of a light-emitting diode which emit visible light, which process comprises the steps of:

i) precoating a substrate with a transparent conducting first layer, said first layer having high work function and serving as an ohmic hole-injecting electrode;

ii) casting upon said first layer directly from solution, a thin transparent layer of a soluble conjugated polymer; and

iii) fabricating onto the conjugated polymer film from a low work function metal, a negative, electron-injecting contact, said electron-injecting contact acting as the rectifying contact in the diode structure.

2. The process of claim 1, wherein the substrate is a rigid, transparent, inorganic substrate.

3. The process of claim 1, wherein the substrate is a flexible, transparent, organic polymer substrate.

4. The process of claim 1, wherein he conducting first layer is an electronegative metal.

5. The process of claim 1, wherein the conducting first layer is a conductive metal oxide.

6. The process of claim 1, wherein the conjugated polymer film comprises poly(2-methoxy,5-(2′

-ethylhexyloxy)-1,4-phenylenevinylene), MEH-PPV.

7. The process of claim 1, wherein the low work function metal is calcium.

8. A light-emitting diode comprising a substrate, a transparent conducting first layer, said first layer deposited upon said substrate and having a high work function and serving as a ohmic hole-injecting electrode, a film of conjugated polymer present upon said conducting first layer, said film of conjugated polymer having been cast directly from solution as a thin, transparent layer onto said first layer, and a negative, electron-injecting contact fabricated onto said film of said conjugated polymer, said contact being formed from a low work function metal and acting as the rectifying contact in the diode structure.

9. The light-emitting diode of claim 8, further characterized by emitting visible light and by turning on at voltages below 5 volts.

10. The light-emitting diode of claim 9, wherein the substrate is a rigid, transparent, inorganic substrate.

11. The light-emitting diode of claim 8, wherein the substrate is a flexible, transparent, organic polymer substrate.

12. The light-emitting diode of claim 8, wherein the conducting first layer is an electronegative metal.

13. The light-emitting diode of claim 12, wherein the electronegative metal comprises gold.

14. The light-emitting diode of claim 8, wherein the conducting first layer is a conductive metal oxide.

15. The light-emitting diode of claim 8, wherein the conductive metal oxide is indium/tin oxide.

16. The light-emitting diode of claim 8, wherein the conjugated polymer film comprises MEH-PPV.

17. The light-emitting diode of claim 16, wherein the substrate is polyethyleneterephthalate.

18. The light-emitting diodes of claim 16 wherein the low work function metal is calcium.

19. The light-emitting diode of claim 16, wherein the substrate is an orientation-inducing substrate by which the MEH-PPV is chain-aligned and oriented thereupon, thus yielding a light-emitting diode which emits polarized light.

20. A process for fabrication of a light-emitting diode which emits visible light, which process comprises the steps of:

i) casting a free-standing, semitransparent film of a soluble conjugated polymer from solution, said film serving as a luminescent, semiconducting polymer and simultaneously as a substrate;

ii) coating the free-standing, conjugated polymer film on one side with a transparent conducting first layer, said transparent conducting first layer having a high work function and serving as the ohmic hole-injecting electrode; and

iii) fabricating a negative electron-injecting contact onto the other side of the conjugated polymer film from a low work function metal, said contact acting as the rectifying contact in the diode structure.

21. The process of claim 20, wherein the conducting first layer is an electronegative metal.

22. The process of claim 20, wherein the conducting first layer is a conductive metal oxide.

23. The process of claim 20, wherein the conjugated polymer film is poly(2-methoxy,5-(2′

-ethylhexyloxy)-1,4-phenylenevinylene), MEH-PPV.

24. The process of claim 20, wherein the low work function metal is calcium.

26. The light-emitting diode of claim 24, further characterized by emitting visible light and by turning on at voltages below 5 volts.

27. The light-emitting diode of claim 25, wherein the conducting first layer is an electronegative metal.

28. The light-emitting diode of claim 26, wherein the electronegative metal is gold.

29. The light-emitting diode of claim 24, wherein the conducting first layer is a conductive metal oxide.

30. The light-emitting diode of claim 24, wherein the conductive metal oxide is indium/tin oxide.

31. The light-emitting diode of claim 24, wherein the conjugated polymer comprises MEH-PPV.

32. The light-emitting diode of claim 24 wherein the low work function metal is calcium.

25. A light-emitting diode comprising a free-standing, semitransparent semiconducting film of a soluble conjugated polymer, said film having been cast directly from a solution of said polymer, said film serving as a luminescent, semiconducting polymer and simultaneously as a substrate;

a transparent conducting first layer coated upon one side of said free-standing, transparent film, said first layer having high work function and serving as an ohmic hold-injecting electrode, and a negative electron-injecting contact fabricated onto the other side of the conducting polymer film, said contact formed from a low work function metal and acting as the rectifying contact in the diode structure.

33. A process for fabrication of a light-emitting diode which emits polarized visible light, said process comprising the steps:

i) gel-processing a soluble conjugated polymer in admixture with an ultra-high molecular weight carrier polymer, an oriented, free-standing film in which the conjugated polymer is chain-aligned, said chain-aligning resulting in polarized luminescence,

ii) coating said oriented free-standing film on one side with a transparent, conducting first layer, said first layer, having high work function and serving as an ohmic hole-injecting electrode, and

iii) fabricating a negative, electron-injecting contact-onto the other side of the oriented free-standing film, said contact fabricated from a low work function metal and acting as the rectifying contact in the diode structure.

34. The process of claim 33, wherein the carrier polymer is polyethylene.

35. The process of claim 33, wherein he conducting first layer is an electronegative metal.

36. The process of claim 33, wherein the conducting first layer is a conductive metal oxide.

37. The process of claim 33, wherein the conjugated polymer is poly(2-methoxy,5-(2′

-ethylhexyloxy)-1,4-phenylenevinylene), MEH-PPV.

38. The process of claim 33 wherein the low work function metal is calcium.

40. The light-emitting diode of claim 39, further characterized by emitting visible light and by turning on at voltages below 5 volts.

41. The light-emitting diode of claim 39, wherein the conducting first layer is an electronegative metal.

42. The light-emitting diode of claim 41, wherein the electronegative metal is gold.

43. The light-emitting diode of claim 39, wherein the conducting first layer is a conductive metal oxide.

44. The light-emitting diode of claim 43, wherein the conductive metal oxide is indium/tin oxide.

45. The light-emitting diode of claim 39, wherein the conjugated polymer film is MEH-PPV.

46. The light-emitting diode of claim 45, wherein the carrier polymer is polyethylene.

47. The process of claim 39, wherein the low work function metal is calcium.

39. A light-emitting diode comprising an oriented, free-standing film formed from a gel-process admixture of soluble conjugated polymer with ultra-high molecular weight carrier polymer in which the conjugated polymer is chain-aligned, said chain-aligning resulting in polarized luminescence, said film serving as a luminescent, semiconducting polymer and simultaneously as a substrate, a transparent, conducting, first layer coated upon one side of said free-standing, transparent film, said first layer;

having high work function and serving as an ohmic hold-injecting electrode and a negative electron-injecting contact fabricated onto the other side of the semiconducting film, said contact formed from a low work function metal and acting as the rectifying contact in the diode structure.