Non-degenerate wide bandgap semiconductors as injection layers and/or contact electrodes for organic electroluminescent devices

• US 6,433,355 B1
• Filed: 02/08/1999
• Issued: 08/13/2002
• Est. Priority Date: 06/05/1996
• Status: Expired due to Term

• Current Assignee: InnoLux Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Strite, Samuel C., Riess, Walter
• Primary Examiner(s): Lee, Eddie
• Assistant Examiner(s): BAUMEISTER, BRADLEY W
• Application Number:
  US09/155,591
• Time in Patent Office: 1,282 Days
• Field of Search: 257/40, 257/76-78, 257/88, 257/94, 257/96, 257/97, 257/103, 313/503, 313/504
• US Class Current: 257/40
• CPC Class Codes: H10K 2102/3026 Top emission
• CPC Class Codes: H10K 2102/3031 Two-side emission, e.g. transparent OLEDs [TOLED]
• CPC Class Codes: H10K 2102/321 Inverted OLED, i.e. having cathode between substrate and anode
• CPC Class Codes: H10K 50/81 Anodes
• CPC Class Codes: H10K 50/828 Transparent cathodes, e.g. comprising thin metal layers

Abstract

An organic light emitting device is provided having a substrate (60), an anode contact electrode (64), a cathode contact electrode (61), and an organic region (62, 63) in which electroluminescence takes place if a voltage is applied between the anode (64) and cathode (61). At least one of the electrodes (61, 64) comprises a non-degenerate wide bandgap semiconductor.

Claims

1. An organic light emitting device comprising:

a substrate;

two contact electrodes, one thereof serving as an anode and the other one serving as a cathode; and

an organic region in which electroluminescence takes place if a voltage is applied between the contact electrodes,

wherein at least one of the contact electrodes comprises a non-degenerate wide bandgap semiconductor, such that,

if that contact electrode serves as a cathode, the non-degenerate wide bandgap semiconductor conduction band is essentially aligned with respect to the LUMO of the organic region for injection of electrons from the conduction band (CB) of the non-degenerate wide bandgap semiconductor into the LUMO of the organic region, or such that,

if that contact electrode serves as an anode, the non-degenerate wide bandgap semiconductor valence band is essentially aligned with respect to the HOMO of the organic region for injection of holes from the valence band (VB) of the non-degenerate wide bandgap semiconductor into the HOMO of the organic region.

2. The organic light emitting device of claim 1, wherein each of the contact electrodes comprises a non-degenerate wide bandgap semiconductor.

3. The organic light emitting device of claim 1, wherein the sequence of layers is:

substrate/cathode/organic region/anode.

4. The organic light emitting device of claim 3, wherein light generated by said electroluminescence is either emitted from said organic region through said anode, or from said organic region through said cathode and substrate.

5. The organic light emitting device of claim 1, wherein the sequence of layers is:

substrate/anode/organic region/cathode.

6. The organic light emitting device of claim 5, wherein light generated by said electroluminescence is either emitted from said organic region through said cathode, or from said organic region through said anode and substrate.

7. The organic light emitting device of claim 1, wherein said organic region comprises a single organic layer or a stack of organic layers.

8. The organic light emitting device of claim 1, wherein said non-degenerate wide bandgap semiconductor is alloyed introducing a semiconductor.

9. The organic light emitting device of claim 8 wherein the semiconductor differs by an isoelectronic element.

10. The organic light emitting device of claim 1, wherein said contact electrode comprising a non-degenerate wide bandgap semiconductor further comprises an interlayer.

11. The organic light emitting device of claim 10, wherein said interlayer is either in direct contact with said organic region, or embedded within said non-degenerate wide bandgap semiconductor.

12. The organic light emitting device of claim 10 wherein the interlayer is a metal interlayer.

13. The organic light emitting device of claim 1, wherein said organic region comprises an electron transport layer being in direct contact with said cathode and/or a hole transport layer being in direct contact with said anode.

14. The organic light emitting device of claim 1, wherein said substrate is transparent or semitransparent.

15. The organic light emitting device of claim 1, wherein said substrate comprises glass or plastic.

16. The organic light emitting device of claim 1, wherein said substrate is flexible.

17. The organic light emitting device of claim 1, wherein said substrate comprises silicon and includes at least one integrated circuit.

18. The organic light emitting device of claim 1, wherein at least one of said contact electrodes comprises an Indium-Tin-Oxide (ITO) layer.

19. The organic light emitting device of claim 1, wherein said organic region further comprises one of:

a stack of more than one organic emission layer;

an organic compound doped with one or more impurities, organic or inorganic, chosen to dominate and enhance the electroluminescence;

a stack of more than one organic emission layer, some of which may be doped to dominate or enhance the electroluminescence of that particular organic emission layer ;

and

a stack of more than one organic layer, in which the role of one or more of said organic layers is to electrically confine one or more carrier types to improve the emission of an adjacent organic layer.

20. An organic light emitting device of claim 1, wherein said non-degenerate semiconductor is a III-N compound.

21. An organic light emitting device of claim 1, wherein said non-degenerate semiconductor is a II-VI compound.

22. An organic light emitting device of claim 1, wherein said non-degenerate semiconductor is one of diamond, SiC, ZnGaSSe, CaF₂, and AIP.

23. The light emitting device of claim 1, wherein said non-degenerate wide bandgap semiconductor comprises at least one of the following:

a wide bandgap III-N compound comprising GaN, AlN, BN, AlGaN, InGaN, or InAlGaN;

a wide bandgap II-VI compound comprising ZnS, MgS, ZnSe, MgSe, ZnMgSSe, CdS, ZnO or BeO; and

diamond, SiC, ZnGaSSe, CaF2, or AIP.

24. The organic light emitting device of claim 1, wherein a threshold voltage value causing a light emission of said device is ten volts or less.

25. The organic light emitting device of claim 1, wherein said alignment is achieved by a gradation of values of conduction bands if said cathode comprises said non-degenerate wide bandgap semiconductor and said alignment is achieved by a gradation of values of valence bands if said anode comprises said non-degenerate wide bandgap semiconductor.

26. An organic light emitting array or display comprising more than one organic light emitting device pursuant to claim 1.

27. The organic light emitting array or display of claim 26, wherein said more than one organic light emitting device shares the same substrate and said substrate additionally contains at least one of:

at least one other device,

at least one circuit, and

at least one electrical connector.

28. The organic light emitting array or display of claim 27, wherein said at least one other device said at least one circuit, or said at least one electrical connector drive or control at least one of said more than one organic light emitting device.

29. The organic light emitting array or display of claim 27, wherein said light emitting devices are deposited cathode first or anode first onto said substrate.

30. The organic light emitting array or display of claim 26, further comprising at least one of:

at least one color filter and

at least one color converter, thereby providing for the emission of light at different wavelengths.

31. An organic light emitting device comprising:

a substrate;

two contact electrodes, one thereof serving as an anode and the other one serving as a cathode; and

an organic region in which electroluminescence takes place if a voltage is applied between the contact electrodes,

wherein at least one of the contact electrodes comprises a non-degenerate wide bandgap semiconductor having a bandgap of at least 2.5 eV, such that,

if that contact electrode serves as a cathode, the non-degenerate wide bandgap semiconductor conduction band is aligned with respect to the LUMO of the organic region for injection of electrons from the conduction band (CB) of the non-degenerate wide bandgap semiconductor into the LUMO of the organic region, thereby essentially eliminating an electron-injection energy barrier, or such that,

if that contact electrode serves as an anode, the non-degenerate wide bandgap semiconductor valence band is aligned with respect to the HOMO of the organic region for injection of holes from the valence band (VB) of the non-degenerate wide bandgap semiconductor into the HOMO of the organic region, thereby essentially eliminating a hole-injection energy barrier.

32. A method of reducing a threshold voltage for electroluminescence in an organic light emitting device having an anode, a cathode, and an organic region in which electroluminescence takes place if a voltage is applied between said anode and said cathode, wherein at least one of said anode and said cathode comprises a non-degenerate wide bandgap semiconductor, said organic region having a highest occupied molecular orbital (HOMO) and a lowest unoccupied molecular orbital (LUMO), said non-degenerate wide bandgap semiconductor having a valence band (VB) and a conduction band (CB), said threshold value being a minimum value of said applied voltage to cause said electroluminescence, said method comprising at least one of the following:

aligning said LUMO of said organic region approximately to said CB of said non-degenerate wide bandgap semiconductor; and

aligning said HOMO of said organic region approximately to said VB of said non-degenerate wide bandgap semiconductor.

33. The method of claim 32, wherein a threshold voltage value causing a light emission of said device is ten volts or less.

34. The method of claim 32, wherein said threshold voltage is six volts or less.