MICROCAVITY OLED DEVICE WITH NARROW BAND PHOSPHORESCENT EMITTERS

• US 20150008419A1
• Filed: 02/26/2013
• Published: 01/08/2015
• Est. Priority Date: 02/27/2012
• Status: Active Grant

• Current Assignee: Arizona Board of Regents (University of Arizona)
• Original Assignee: Jian Li
• Inventors: Li, Jian
• Granted Patent: US 9,318,725 B2
• Time in Patent Office: Days
• US Class Current: 257/40
• CPC Class Codes: H10K 2101/10 Triplet emission
• CPC Class Codes: H10K 50/11 characterised by the electroluminescent [EL] layers
• CPC Class Codes: H10K 50/12 comprising dopants
• CPC Class Codes: H10K 50/125 specially adapted for multicolour light emission, e.g. for emitting white light
• CPC Class Codes: H10K 50/81 Anodes
• CPC Class Codes: H10K 50/82 Cathodes
• CPC Class Codes: H10K 50/828 Transparent cathodes, e.g. comprising thin metal layers
• CPC Class Codes: H10K 50/852 comprising a resonant cavity structure, e.g. Bragg reflector pair
• CPC Class Codes: H10K 50/856 comprising reflective means
• CPC Class Codes: H10K 85/346 comprising platinum

Abstract

A microcavity organic light emitting diode (OLED) device is disclosed having a narrow-band phosphorescent emitter.

Claims

1. A microcavity narrow band organic light emitting diode (OLED) device having enhanced light emission, comprising,

a) a substrate;

b) a microcavity having a selected cavity length defined over one substrate by, in sequence, a dielectric minor made with a quarter wave stack (QWS), a metallic transmissive electrode, an organic electroluminescent (EL) layer comprising of a hole injection layer (HIL), a hole transporting layer (HTL), an emissive layer (EML), an electron transporting layer (ETL), an electron injection layer (EIL), and a metal electrode,

wherein the QWS comprises of a defined number of alternating high refractive index and low refractive index QWS pairs and wherein a maximum reflectivity of QWS mirrors is provided by selection of dielectric materials;

wherein one metallic electrode layer is light transmissive and the second metal electrode layer is substantially opaque and reflective;

wherein the organic electroluminescent (EL) layer comprises at least one host material selected from the class of aryl amines and aryl-substituted carbazole compounds, aryl substituted oxadiazoles, aryl-substituted triazoles, aryl substituted phenanthrolines and metal quinoxolates and at least one phosphorescent emitter material dispersed in the at least one host material and selected from the class of phosphorescent dyes comprising derivatives of cyclometalated metal complexes having a narrow emission spectrum bandwidth, and wherein a full width at a half maximum emission intensity is less than 40 nm, so that one of red, green, or blue light is generated in the EML layer.

wherein the position of the EML to the metal electrode layer that is opaque and reflective is defined;

wherein the selected cavity length of the microcavity OLED device is tuned to provide a resonance condition for emission of one of red, green, or blue light through the light transmissive electrode layer and having the improved light extraction efficiency;

wherein the light extraction efficiency of the device is tuned by adjusting the spacing between a metallic transmissive electrode and the metal electrode layer that is opaque and reflective, and the selected cavity length is modified by adjusting a thickness of the light transmissive electrode layer and a thickness of the organic electroluminescent layer (EL), or a combination thereof.

2. The microcavity narrow band OLED device according to claim 1, wherein the bottom metallic light transmissive electrode comprises of Indium Tin Oxide (ITO), zinc tin oxide (ZTO), tin oxide (SnO_x), indium oxide (InO_x), molybdenum oxide (MoO_x), carbon nanotubes, and the thickness of the metallic light transmissive electrode is between 10 nm and 100 nm;

3. The microcavity narrow band OLED device according to claim 1, wherein the top metal electrode layer that is opaque and reflective comprises of Al, Ag, Au or alloys thereof and the thickness of the metal electrode is between 20 nm to 300 nm.

4. The microcavity narrow band OLED device according to claim 1, wherein the bottom metallic light transmissive electrode is an anode and the top metal electrode that is opaque and reflective is a cathode.

5. The microcavity narrow band OLED device according to claim 1, wherein the alternating QWS pairs have a high index of refraction between 2 to 3.5, and a low index of refraction between 1 to 2.

6. The microcavity narrow band OLED device according to claim 1,wherein the QWS comprises the alternating high refractive index materials comprising TiO₂, TaO_x, amorphous Si or a combination thereof, and the low refractive index materials comprising SiO₂, SiN_x, and LiF pairs or a combination thereof. The DBR is designed to provide a high reflectivity at a desired (or design) wavelength. Without wishing to be bound by theory, the design wavelength is typically chosen to be close to the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, or close to the emission wavelength at the desired temperature of operation of the device. The optical layer thickness of each layer in the DBR corresponds to one-quarter of the design wavelength, wherein the wavelength is taken to be the wavelength within the material (that is, the wavelength of the light, as measured in free space, divided by the refractive index of the material). In some embodiments, the thickness of each layer can be chosen to be an odd integer multiple of the quarter-wavelength thickness.

7. The microcavity narrow band OLED device according to claim 1, wherein the cavity length is defined as the spacing between the high refractive index material layer (the closest one to the metallic transmissive electrode layer) and the top metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal or slightly longer than integer multiple of half-value of the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

8. The microcavity narrow band OLED device according to claim 1, wherein the light extraction efficiency of the device is tuned by adjusting a thickness of the light transmissive electrode layer and a thickness of the organic electroluminescent layer (EL), or a combination thereof.

9. The microcavity narrow band OLED device according to claim 1, wherein the phosphorescent emitter material comprises an emitter with full-width-half-maxim (FWHM) of emission spectra between 5-40 nm.

10. The microcavity narrow band OLED device according to claim 1, wherein the white OLED device can be fabricated by coating the opposite side of blue-emitting microcavity narrow band OLED device with green, yellow, orange and red phosphors, or a combination thereof.

11. The microcavity narrow band OLED device according to claim 7, wherein the cavity length is defined as the spacing between the high refractive index material layer (the closest one to the metallic transmissive electrode layer) and the top metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal to or slightly longer than half-value of the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

12. The microcavity narrow band OLED device according to claim 7, wherein the cavity length is defined as the spacing between the high refractive index material layer (the closest one to the metallic transmissive electrode layer) and the top metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal to or slightly longer than the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

13. The microcavity narrow band OLED device according to claim 9, wherein the composition of the phosphorescent emitter comprises of the general formula:

14. The microcavity narrow band OLED device according to claim 9, wherein the composition of the phosphorescent emitter comprises of one or more of the formulas:

15. The microcavity narrow band OLED device according to claim 13, wherein the phosphorescent emitter comprises one or more of the formulas:

16. A microcavity narrow band organic light emitting diode (OLED) device having enhanced light emission, comprising,

a) a substrate;

b) a microcavity having a selected cavity length defined over one substrate by, in sequence, a metal electrode, an organic electroluminescent (EL) layer comprising of a hole injection layer (HIL), a hole transporting layer (HTL), an emissive layer (EML), an electron transporting layer (ETL), an electron injection layer (EIL), and a second metal electrode;

wherein one metallic electrode layer is light transmissive and the second metal electrode layer is substantially opaque and reflective;

wherein the organic electroluminescent layer comprises at least one host material selected from the class of aryl amines and aryl-substituted carbazole compounds, aryl substituted oxadiazoles, aryl-substituted triazoles, aryl substituted phenanthrolines and metal quinoxolates and at least one phosphorescent emitter material dispersed in the at least one host material and selected from the class of phosphorescent dyes comprising derivatives of cyclometalated metal complexes having a narrow emission spectrum bandwidth, and wherein a full width at a half maximum emission intensity is less than 40 nm, so that one of red, green, or blue light is generated in the EML layer.

wherein the position of the EML to the metal electrode layer that is opaque and reflective is defined;

wherein the selected cavity length of the microcavity OLED device is tuned to provide a resonance condition for emission of one of red, green, or blue light through the light transmissive electrode layer and having the improved light extraction efficiency;

wherein the light extraction efficiency of the device is tuned by adjusting the spacing between a metallic transmissive electrode and the metal electrode layer that is opaque and reflective, and the selected cavity length is modified by adjusting a thickness of the light transmissive electrode layer and a thickness of the organic electroluminescent layer (EL), or a combination thereof.

17. The microcavity narrow band OLED device according to claim 16, wherein the metallic light transmissive electrode comprises of Indium Tin Oxide (ITO), zinc tin oxide (ZTO), tin oxide (SnO_x), indium oxide (InO_x), molybdenum oxide (MoO_x), carbon nanotubes, Al, Ag, Au or alloys thereof, and the thickness of the metallic light transmissive electrode is between 10 nm and 100 nm;

18. The microcavity narrow band OLED device according to claim 16, wherein the metal electrode layer that is opaque and reflective comprises of Al, Ag, Au or alloys thereof and the thickness of the metal electrode is between 50 nm to 300 nm.

19. The microcavity narrow band OLED device according to claim 16, wherein the bottom metallic electrode is light transmissive and the top metal electrode is opaque and reflective.

20. The microcavity narrow band OLED device according to claim 16, wherein the top metallic electrode is light transmissive and the bottom metal electrode is opaque and reflective.

21. The microcavity narrow band OLED device according to claim 16, wherein the cavity length is defined as the spacing between the metallic transmissive electrode layer and the metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal to or slightly longer than integer multiple of half-value of the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

22. The microcavity narrow band OLED device according to claim 16, wherein the light extraction efficiency of the device is tuned by adjusting a thickness of the light transmissive electrode layer, and a thickness of the organic electroluminescent layer (EL), or a combination thereof.

23. The microcavity narrow band OLED device according to claim 16, wherein the phosphorescent emitter material comprises an emitter with full-width-half-maxim (FWHM) of emission spectra between 5-40 nm.

24. The microcavity narrow band OLED device according to claim 21, wherein the cavity length is defined as the spacing between the metallic transmissive electrode layer and the metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal to or slightly longer than the half-value of the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

25. The microcavity narrow band OLED device according to claim 21, wherein the cavity length is defined as the spacing between the metallic transmissive electrode layer and the metal electrode layer that is opaque and reflective. The cavity length is chosen to be equal to or slightly longer than the peak emission wavelength of an emissive material, such as narrow band phosphorescent emitters, wherein the light extraction efficiency of the device is optimized.

26. The microcavity narrow band OLED device according to claim 23, wherein the composition of the phosphorescent emitter comprises of the general formula:

27. The microcavity narrow band OLED device according to claim 23, wherein the composition of the phosphorescent emitter comprises of one or more of the formulas:

28. The microcavity narrow band OLED device according to claim 26, wherein the phosphorescent emitter comprises one or more of the formulas: