STABLE BLUE PHOSPHORESCENT ORGANIC LIGHT EMITTING DEVICES

• US 20090121624A1
• Filed: 11/05/2008
• Published: 05/14/2009
• Est. Priority Date: 11/09/2007
• Status: Active Grant

• Current Assignee: Universal Display Corporation
• Original Assignee: Universal Display Corporation
• Inventors: MacKenzie, Peter B., D'Andrade, Brian, Weaver, Michael S., Brown, Julia J.
• Granted Patent: US 8,557,399 B2
• Time in Patent Office: Days
• US Class Current: 313/504
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 2101/30 Highest occupied molecular orbital [HOMO], lowest unoccupied molecular orbital [LUMO] or Fermi energy values
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/18 Carrier blocking layers
• CPC Class Codes: H10K 71/10 Deposition of organic active material
• CPC Class Codes: H10K 71/311 Purifying organic semiconductor materials
• CPC Class Codes: H10K 85/342 comprising iridium
• CPC Class Codes: H10K 85/657 Polycyclic condensed heteroaromatic hydrocarbons
• CPC Class Codes: H10K 85/6572 comprising only nitrogen in the heteroaromatic polycondensed ring system, e.g. phenanthroline or carbazole

Abstract

Novel combination of materials and device architectures for organic light emitting devices are provided. In some aspects, specific charge carriers and solid state considerations are features that may result in a device having an unexpectedly long lifetime. In some aspects, emitter purity is a feature that may result in devices having unexpectedly long lifetime. In some aspects, structural and optical considerations are features that may result in a device having an unexpectedly long lifetime. In some aspects, an emissive layer including an organic phosphorescent emissive dopant and an organic carbazole host material results in devices having an unexpectedly long lifetime.

Claims

1. An organic light emitting device, comprising:

an anode;

a cathode;

an emissive layer disposed between the anode and the cathode, the emissive layer including a host having a triplet energy and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm;

an exciton blocking layer at least 5 nm thick disposed between the emissive layer and the cathode and adjacent to the emissive layer, the exciton blocking layer consisting essentially of materials having a triplet energy greater than or equal to the triplet energy of the host of the emissive layer;

wherein

the emissive layer is at least 40 nm thick;

electrons in the emissive layer are carried predominantly by the host;

the HOMO of the phosphorescent emissive dopant is at least 0.5 eV higher than the HOMO of the host;

the concentration of the phosphorescent emissive dopant in the emissive layer is at least 9 wt %;

the phosphorescent emissive dopant comprises a cyclometallated N,C-donor imidazophenanthridine ligand comprising at least one 2,2,2-trialklethyl substituent.

2. The device of claim 1, wherein the emissive layer is at least 50 nm thick.

3. The device of claim 1, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

0-8 Torr to about 1×

10<sup>−

12</sup> Torr.

4. An organic light emitting device, comprising:

an anode;

a cathode;

an emissive layer disposed between the anode and the cathode, the emissive layer including a host and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm;

wherein

the phosphorescent emissive dopant is deposited from a source that has a purity in excess of 99.5% as determined by high pressure liquid chromatography, the source further having a combined concentration of halide and metal impurities below 100 ppm;

the phosphorescent emissive dopant leaves a residue corresponding to less than 5 wt % of the original charge in the sublimation crucible; and

the phosphorescent emissive dopant has a sublimation temperature less than 350°

C. and is deposited via sublimation.

5. The device of claim 4, wherein the phosphorescent emissive dopant is deposited in an environment having less than 10 ppm oxygen, and in the near absence of light having a wavelength<

600 nm.

6. The device of claim 4, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level less than about 1×

10<sup>−

8</sup> Torr.

7. The device of claim 4, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

8</sup> Torr to about 1×

10<sup>−

12</sup> Torr.

8. The device of claim 4, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

9</sup> Torr to about 1×

10<sup>−

12</sup> Torr.

9. The device of claim 4, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

10</sup> Torr to about 1×

10<sup>−

12</sup> Torr.

10. The device of claim 5, wherein the phosphorescent emissive dopant comprises a cyclometallated N,C-donor imidazophenanthridine ligand comprising at least one 2,2,2-trialklethyl substituent.

11. A method of depositing an emissive layer for an organic light emitting device, comprising:

providing a source of a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm, wherein

the source has a purity in excess of 99.5% as determined by high pressure liquid chromatography;

the source further has a combined concentration of halide and metal impurities below 100 ppm;

the source being sufficiently pure that a residue corresponding to less than 5 wt % of the original charge in the sublimation crucible remains after the original charge is fully depleted; and

the phosphorescent emissive dopant has a sublimation temperature less than 350°

C. and is deposited via sublimation;

depositing the phosphorescent emissive dopant via sublimation, along with a host.

12. The method of claim 11, wherein the phosphorescent emissive dopant is deposited in an environment having less than 10 ppm oxygen, and in the near absence of light having a wavelength less than 600 nm.

13. The device of claim 11, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level less than 1×

10<sup>−

8</sup> Torr.

14. The device of claim 11, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

8</sup> Torr to 1×

10<sup>−

12</sup> Torr.

15. The device of claim 11, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

9</sup> Torr to 1×

10<sup>−

12</sup> Torr.

16. The device of claim 11, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

10</sup> Torr to 1×

10<sup>−

12</sup> Torr.

17. The method of claim 12, wherein the phosphorescent emissive dopant comprises a cyclometallated N,C-donor imidazophenanthridine ligand comprising at least one 2,2,2-trialklethyl substituent.

27. The device of claim 15, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

0-8 Torr to about 1×

10<sup>−

12</sup> Torr.

18. An organic light emitting device, comprising:

an anode;

a cathode; and

an emissive layer disposed between the anode and the cathode, the emissive layer including a host and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm;

wherein, when a voltage is applied across the device, electrons in the emissive layer are carried predominantly by the host;

wherein the HOMO of the phosphorescent dopant is at least 0.5 eV higher than the HOMO of the host; and

wherein the phosphorescent emissive dopant has a concentration of at least 9 wt % in the emissive layer.

19. The device of claim 18, wherein the emissive dopant has a stable anion state.

20. The device of claim 18, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

8</sup> Torr to about 1×

10<sup>−

12</sup> Torr.

21. An organic light emitting device, comprising:

an anode;

a cathode;

a CuPc hole injection layer disposed between the anode and the cathode and adjacent to the anode;

an emissive layer disposed between the anode and the cathode, the emissive layer including a host having a triplet energy and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm; and

an exciton blocking at least 5 nm thick disposed between the emissive layer and the cathode and adjacent to the emissive layer, the exciton blocking layer consisting essentially of materials having a triplet energy greater than or equal to the triplet energy of the host of the emissive layer;

wherein the emissive layer is at least 40 nm thick; and

wherein the recombination zone is at least 40 nm from the cathode.

22. The device of claim 21, wherein the emissive layer is at least 40 nm from the cathode.

23. The device of claim 21, wherein the emissive layer is at least 50 nm thick.

24. The device of claim 21, wherein the phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

8</sup> Torr to about 1×

10<sup>−

12</sup> Torr.

25. An organic light emitting device, comprising:

an anode;

a cathode;

a CuPc hole injection layer disposed between the anode and the cathode and adjacent to the anode;

an emissive layer disposed between the anode and the cathode, the missive layer including a host having a triplet energy and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm; and

an exciton blocking at least 5 nm thick disposed between the emissive layer and the cathode and adjacent to the emissive layer, the exciton blocking layer consisting essentially of materials having a triplet energy greater than or equal to the triplet energy of the host of the emissive layer;

wherein the emissive layer is at least 40 nm thick; and

wherein the surface plasmon mode is less than 30%.

26. The device of claim 25, wherein the emissive layer is at least 50 nm thick.

28. An organic light emitting device, comprising:

an anode;

a cathode;

an emissive layer disposed between the anode and the cathode, the emissive layer including;

an organic carbazole host material, having the structure;

29. The device of claim 28, wherein the organic phosphorescent dopant has a peak emissive wavelength less than 500 nm.

30. The device of claim 29, wherein the organic carbazole host material is

31. The device of claim 30, wherein the carbazole host has a triplet energy corresponding to a wavelength less than 480 nm.

32. The device of claim 31, wherein the organic carbazole host material is mCBP, having the structure:

33. The device of claim 29, wherein the organic phosphorescent emissive dopant is organometallic.

34. The device of claim 33, wherein the organic phosphorescent dopant is an organometallic material having at least one organic ligand coordinated to an Ir atom.

35. The device of claim 34, wherein the organic phosphorescent emissive dopant has the structure:

36. The device of claim 28, wherein the organic phosphorescent emissive dopant is deposited in a vacuum system having a pressure level in the range of about 1×

10<sup>−

8</sup> Torr to about 1×

10<sup>−

12</sup> Torr.