OLEDs utilizing direct injection to the triplet state

• US 20060279204A1
• Filed: 11/16/2005
• Published: 12/14/2006
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: The Trustees of Princeton University (Princeton University), Universal Display Corporation, University of Southern California
• Original Assignee: The Trustees of Princeton University (Princeton University)
• Inventors: Forrest, Stephen, Thompson, Mark E., Brown, Julia J.
• Granted Patent: US 7,683,536 B2
• Time in Patent Office: Days
• US Class Current: 313/506
• 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 2101/40 Interrelation of parameters between multiple constituent active layers or sublayers, e.g. HOMO values in adjacent layers
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/15 Hole transporting layers
• CPC Class Codes: H10K 50/16 Electron transporting layers
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree

Abstract

The present invention relates to OLEDs utilizing direct injection to the triplet state. The present invention also relates to OLEDs utilizing resonant injection and/or stepped energy levels.

Claims

1. An organic light emitting device comprising:

a) an anode;

b) a cathode;

c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising

i) a phosphorescent dopant having a phosphorescent dopant HOMO energy level, a phosphorescent dopant LUMO energy level, a triplet energy, and a singlet energy; and

ii) an emissive layer host having an emissive layer host HOMO energy level and an emissive layer host LUMO energy level; and

d) a transport layer disposed adjacent to the emissive layer, the transport layer comprising a first material having a first material HOMO energy level and a first material LUMO energy level, wherein an electron-hole pair directly recombine across an energy separation that is at least about equal to the triplet energy of the phosphorescent dopant.

2. The device of claim 1, wherein the energy separation between the emissive layer host LUMO and the phosphorescent dopant HOMO is at least about equal to the triplet energy of the phosphorescent dopant.

3. The device of claim 1, wherein the energy separation between the emissive layer host HOMO and the phosphorescent dopant LUMO is at least about equal to the triplet energy of the phosphorescent dopant.

4. The device of claim 1, wherein the transport layer is an electron transport layer, and wherein the energy separation between the first material LUMO and the phosphorescent dopant HOMO is at least about equal to the triplet energy of the phosphorescent dopant.

5. The device of claim 1, wherein the transport layer is a hole transport layer, and wherein the energy separation between the first material HOMO and the phosphorescent dopant LUMO is at least about equal to the triplet energy of the phosphorescent dopant.

6. The device of claim 1, comprising two transport layers:

an electron transport layer comprising an electron transport material, and a hole transport layer comprising a hole transport material, wherein the energy separation between the electron transport material LUMO and the hole transport material HOMO is at least about equal to the triplet energy of the phosphorescent dopant.

7. The device of claim 6, wherein the energy separation is at least about 0.2 eV less than the singlet energy of the phosphorescent dopant.

8. The device of claim 1, wherein the phosphorescent dopant has a peak in the emission spectra that is less than about 500 nm.

9. An organic light emitting device comprising:

a) an anode;

b) a cathode;

c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising

i) a phosphorescent dopant having a phosphorescent dopant HOMO energy level, a phosphorescent dopant LUMO energy level, a triplet energy, and a singlet energy; and

ii) an emissive layer host having an emissive layer host HOMO energy level and an emissive layer host LUMO energy level; and

d) a transport layer disposed adjacent to the emissive layer, the transport layer comprising a plurality of materials, each material having a HOMO energy level and a LUMO energy level, wherein at least one energy level of each of the plurality of materials together form a series of energy steps leading to at least one energy level in the emissive layer, wherein each step in the series of energy steps is no more than about 0.2 eV.

10. The device of claim 9, wherein the transport layer is a hole transport layer and the HOMO energy levels of the plurality of materials form a series of energy steps leading to the emissive layer host HOMO or the phosphorescent dopant HOMO, wherein each step in the series of energy steps is no more than about 0.2 eV.

11. The device of claim 10, wherein the series of energy steps leads to the emissive layer host HOMO, and the energy separation between the emissive layer host HOMO and the phosphorescent dopant LUMO is at least about equal to the triplet energy of the phosphorescent dopant.

12. The device of claim 10, wherein the series of energy steps leads to the phosphorescent dopant HOMO, and the energy separation between the phosphorescent dopant HOMO and the emissive layer host LUMO is at least about equal to the triplet energy of the phosphorescent dopant.

13. The device of claim 9, wherein the transport layer is an electron transport layer and the LUMO energy levels of the plurality of materials form a series of energy steps leading to the emissive layer host LUMO or the phosphorescent dopant LUMO, wherein each step in the series of energy steps is no more than about 0.2 eV.

14. The device of claim 13, wherein the series of energy steps leads to the emissive layer host LUMO, and the energy separation between the emissive layer host LUMO and the phosphorescent dopant HOMO is at least about equal to the triplet energy of the phosphorescent dopant.

15. The device of claim 13, wherein the series of energy steps leads to the phosphorescent dopant LUMO, and the energy separation between the phosphorescent dopant LUMO and the emissive layer host HOMO is at least about equal to the triplet energy of the phosphorescent dopant.

16. The device of claim 9, wherein the transport layer comprises a sublayer disposed adjacent to the emissive layer, wherein the sublayer comprises a transport layer host that is doped with a mixture of more than one material of the plurality of materials.

17. The device of claim 16, wherein the transport layer host is doped with a mixture of all of the plurality of materials.

18. The device of claim 17, wherein the transport layer host is doped with a mixture of all of the plurality of materials in about equal proportions.

19. The device of claim 9, wherein the transport layer comprises a plurality of adjacent sublayers, each sublayer comprising a transport layer host doped with a single material of the plurality of materials.

20. The device of claim 9, wherein the entire transport layer is doped with one or more materials of the plurality of materials.

21. The device of claim 9, wherein the transport layer comprises:

a) an un-doped sublayer disposed adjacent to

b) a doped sublayer comprising one or more materials of the plurality of materials, the doped sublayer disposed adjacent to

c) the emissive layer.

22. The device of claim 9, wherein one or more materials of the plurality of materials is deposited as a neat layer to form the series of energy steps.

23. A method comprising:

a) depositing an anode over a substrate;

b) depositing an emissive layer over the anode, wherein the emissive layer comprises

i) a phosphorescent dopant having a phosphorescent dopant HOMO energy level, a phosphorescent dopant LUMO energy level, a triplet energy, and a singlet energy; and

ii) an emissive layer host having an emissive layer host HOMO energy level and an emissive layer host LUMO energy level;

c) depositing an electron transport layer over the emissive layer, wherein the electron transport layer comprises an electron transport material having an electron transport material LUMO energy level; and

d) depositing a cathode over the electron transport layer, wherein the energy separation between i) the electron transport material LUMO or the emissive layer host LUMO, and ii) the phosphorescent dopant HOMO is at least about equal to the triplet energy of the phosphorescent dopant and at least about 0.2 eV less than the singlet energy of the phosphorescent dopant.