Radiation Emitting Device

• US 20120153305A1
• Filed: 02/28/2012
• Published: 06/21/2012
• Est. Priority Date: 08/07/2007
• Status: Active Grant

• Current Assignee: OSRAM OLED GMBH (Ams-Osram AG)
• Original Assignee: Osram Opto Semiconductors GmbH (Ams-Osram AG)
• Inventors: Choulis, Stelios A., Mathai, Matthew K., CHOONG, Vi-En
• Granted Patent: US 8,610,114 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• 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 2102/103 comprising indium oxides, e.g. ITO
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/125 specially adapted for multicolour light emission, e.g. for emitting white light
• CPC Class Codes: H10K 50/18 Carrier blocking layers
• CPC Class Codes: H10K 50/181 Electron blocking layers
• CPC Class Codes: H10K 85/1135 Polyethylene dioxythiophene [PEDOT]; Derivatives thereof
• CPC Class Codes: H10K 85/342 comprising iridium
• CPC Class Codes: H10K 85/6565 Oxadiazole compounds
• CPC Class Codes: H10K 85/6574 comprising only oxygen in the heteroaromatic polycondensed ring system, e.g. cumarine dyes

Abstract

A radiation emitting device comprising a first electrode, which emits first charge carriers having a first charge during operation, a first charge carrier transporting layer, which comprises a fluorescent substance, a second charge carrier transporting layer, which contains a phosphorescent substance, and a second electrode, which emits second charge carriers having a second charge during operation, wherein during operation the second charge carrier transporting layer is largely free of first charge carriers.

Claims

1. A radiation emitting device comprising:

a first electrode, which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer, which comprises a fluorescent substance and is arranged on the first electrode;

a second charge carrier transporting layer, which contains a phosphorescent substance and is arranged on the first charge carrier transporting layer; and

a second electrode, which emits second charge carriers having a second charge during operation and is arranged on the second charge carrier transporting layer;

wherein during operation the second charge carrier transporting layer is largely free of first charge carriers emitted by the first electrode.

2. The radiation emitting device as claimed in claim 1, wherein the second charge carrier transporting layer is unipolar and can transport only second charge carriers, or blocks first charge carriers.

3. The radiation emitting device as claimed in claim 1, wherein a unipolar charge carrier transporting layer, which blocks the charge carriers having the first charge or can transport only charge carriers having the second charge, is arranged between the first charge carrier transporting layer and the second charge carrier transporting layer.

4. The radiation emitting device as claimed in claim 1, embodied as an organic light emitting diode, wherein the first charge carrier transporting layer, the second charge carrier transporting layer, the phosphorescent substance or the fluorescent substance comprise organic materials.

5. The radiation emitting device as claimed in claim 1, wherein a recombination of charge carriers having the first charge and charge carriers having the second charge can result in the formation of excitons as excited electronic states, which comprise singlet and triplet excitons.

6. The radiation emitting device as claimed claim 1, wherein a recombination of charge carriers having the first charge and charge carriers having the second charge takes place only in the first charge carrier transporting layer.

7. The radiation emitting device as claimed in claim 5, wherein the excitons formed in the first charge carrier transporting layer comprise triplet excitons, and wherein the phosphorescent substance emits phosphorescent radiation upon excitation by the energy of the triplet excitons formed in the first charge carrier transporting layer.

8. The radiation emitting device as claimed in claim 1, wherein the first electrode is an anode, the first charge carrier transporting layer is a hole transporting and electron transporting layer, the second charge carrier transporting layer is an electron transporting layer, and the second electrode is a cathode.

9. The radiation emitting device as claimed in claim 8, wherein the second charge carrier transporting layer is a hole blocking, or exclusively electron transporting layer.

10. The radiation emitting device as claimed in claim 1, wherein the first electrode is a cathode, wherein the first charge carrier transporting layer is a hole transporting and electron transporting layer, wherein the second charge carrier transporting layer is a hole transporting layer, and wherein the second electrode is an anode.

11. The radiation emitting device as claimed in claim 10, wherein the second charge carrier transporting layer is an electron blocking or exclusively hole transporting layer.

12. The radiation emitting device as claimed in claim 1, wherein an exciton blocking layer is situated between the second charge carrier transporting layer and the second electrode.

13. The radiation emitting device as claimed in claim 1, wherein the fluorescent substance comprises an organic material.

14. The radiation emitting device as claimed in claim 1, wherein the fluorescent substance is present as a dopant in a charge carrier transporting matrix material.

15. The radiation emitting device as claimed in claim 1, wherein the phosphorescent substance comprises an organic material.

16. The radiation emitting device as claimed in claim 1, wherein the phosphorescent substance is present as a dopant in a charge carrier transporting matrix material.

17. The radiation emitting device as claimed in claim 16, wherein at least two different phosphorescent substances are situated as dopants in the second charge carrier transporting layer.

18. The radiation emitting device as claimed in claim 17, wherein the phosphorescent substances emit with different wavelengths.

19. The radiation emitting device as claimed in claim 18, wherein the second charge carrier transporting layer has partial regions which each comprise a substance that is phosphorescent at different wavelengths, and the wavelength of the emitted radiation of the phosphorescent substance increases with greater distance from the first charge carrier transporting layer.

20. The radiation emitting device as claimed in claim 1, wherein the HOMO/LUMO levels of the second charge carrier transporting layer are coordinated with the HOMO/LUMO levels of the first charge carrier transporting layer such that no charge carriers having the first charge can pass into the second charge carrier transporting layer.

21. The radiation emitting device as claimed in claim 1, wherein the HOMO/LUMO levels of the second charge carrier transporting layer are coordinated with the HOMO/LUMO levels of the first charge carrier transporting layer such that triplet excitons can pass from the first into the second charge carrier transporting layer.

22. The radiation emitting device as claimed in claim 1, wherein the thickness of the second charge carrier transporting layer is coordinated with the diffusion length of the triplet excitons, such that the triplet excitons can diffuse through the entire second charge carrier transporting layer.

23. The radiation emitting device as claimed in claim 1, wherein at least two second charge carrier transporting layers are present and the total thickness of all the second charge carrier transporting layers is less than or equal to the diffusion length of the triplet excitons.

24. The radiation emitting device as claimed in claim 1, wherein each second charge carrier transporting layer comprises a phosphorescent substance that emits at a different wavelength.

25. The radiation emitting device as claimed in claim 24, wherein the second charge carrier transporting layers are arranged such that the wavelength of the emitted radiation increases with greater distance from the first charge carrier transporting layer.

26. The radiation emitting device as claimed in claim 1, wherein the HOMO/LUMO levels of all the second charge carrier transporting layers are coordinated with one another such that an exciton transfer through all the charge carrier transporting layers can be effected from the first charge carrier transporting layer.

27. The radiation emitting device as claimed in claim 1, wherein a charge carrier transport path for transporting the first and second charge carriers during operation runs through the device and the charge carrier transport path for the first charge carriers is restricted to that region of the device which is delimited by the first electrode and the first charge carrier transporting layer and the charge carrier transport path of the second charge carriers runs at least through the second charge carrier transporting layer and the first charge carrier transporting layer.

28. The radiation emitting device as claimed in claim 1, wherein the first charge carrier transporting layer is an electron transporting layer and the second charge carrier transporting layer is a hole transporting layer, and wherein the LUMO of the second charge carrier transporting layer is at least 300 meV above the HOMO of the first charge carrier transporting layer.

29. The radiation emitting device as claimed in claim 23, wherein the at least two second charge carrier transporting layers have different matrix materials.

30. The radiation emitting device as claimed in claim 24, wherein the layer of the at least two second charge carrier transporting layers, which has the phosphorescent dopant having the lowest T₁ level is furthest away from the first charge carrier transporting layer.

31. A radiation emitting device comprising:

a first electrode, which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer, which comprises a fluorescent substance and is arranged on the first electrode;

a second charge carrier transporting layer, which contains a phosphorescent substance and is arranged on the first charge carrier transporting layer; and

a second electrode, which emits second charge carriers having a second charge during operation and is arranged on the second charge carrier transporting layer;

wherein during operation, the transport of first charge carriers emitted by the first electrode contributes to less than 0.1% of the entire charge transport in the second charge carrier transport layer.

32. A radiation emitting device comprising:

a first electrode, which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer, which comprises a fluorescent substance and is arranged on the first electrode;

a second charge carrier transporting layer, which contains a phosphorescent substance and is arranged on the first charge carrier transporting layer;

a second electrode, which emits second charge carriers having a second charge during, operation and is arranged on the second charge carrier transporting layer; and

a unipolar charge carrier transporting layer, which blocks the charge carriers having the first charge or can transport only charge carriers having the second charge is arranged between the first charge carrier transporting layer and the second charge carrier transporting layer;

wherein during operation the second charge carrier transporting layer is largely free of first charge carriers emitted by the first electrode.