High performance light-emitting devices

• US 7,863,632 B2
• Filed: 08/23/2004
• Issued: 01/04/2011
• Est. Priority Date: 08/23/2004
• Status: Expired due to Fees

• Current Assignee: National Research Council Canada
• Original Assignee: National Research Council Canada
• Inventors: Dobrowolski, Jerzy, Li, Li, Poitras, Daniel
• Primary Examiner(s): Lee; Hsien-ming
• Assistant Examiner(s): PARENDO, KEVIN A
• Application Number:
  US11/573,774
• Publication Number:
  US 20070246705A1
• Time in Patent Office: 2,325 Days
• Field of Search: 438/29, 257/E51.022, 257/98
• US Class Current: 257/98
• CPC Class Codes: H10K 50/852 comprising a resonant cavity structure, e.g. Bragg reflector pair
• CPC Class Codes: H10K 85/311 Phthalocyanine
• CPC Class Codes: H10K 85/324 comprising aluminium, e.g. Alq3
• CPC Class Codes: H10K 85/631 Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine

Abstract

An organic light emitting device consists of a layered structure including a top multilayer stack, a bottom multilayer stack, a cavity layer between the top multilayer stack and the bottom multilayer stack, and an organic light emitting region within the cavity layer. The layered structure is constructed such that the product of phase factors ξ₁ and ξ₂ is. greater than 80% at the center of at least one emitting wavelength region and for a normal viewing angle, wherein where R_a⁻ and R_b⁺ are the reflectance of the top and bottom multilayer stacks respectively, φ_a⁻ and φ_b⁺ are the phase changes on reflection for the top and bottom multilayer stacks respectively, α₁ β₁ are respectively the real and imaginary parts of the phase thickness of the cavity layer, α₂ and β₂ are respectively the real and imaginary parts of the phase thickness of the light-emitting region at the operating wavelength of the device, x is the mean distance of light emitting region from the bottom multilayer stack, n and k are the refractive index and absorption coefficient of the cavity layer, θ_cavity is the emitting angle inside the cavity layer, and d is the physical thickness of said cavity layer. This condition improves the light output efficiency of the device.

Claims

1. A light emitting device comprising:

a layered structure comprising a cavity layer containing a light emitting region sandwiched between passive bottom and top multilayer stacks, said passive bottom and top multilayer stacks being devoid of a light emitting layer;

wherein the passive bottom multilayer stack includes a cathode and the passive top multilayer stack includes a hole transport layer and a transparent anode,

wherein the passive top multilayer stack includes an additional functional layer group for increasing an internal reflectance of the passive top multilayer stack and the passive bottom multilayer stack includes an additional functional layer group for reducing reflectance from the cathode;

wherein a top transparent substrate through which light is emitted from the device is located above the top multilayer stack; and

wherein said layered structure is constructed such that the product of phase factors ξ

₁ and ξ

₂ is greater than 80% at the center of at least one light emitting region and for a normal viewing angle, wherein

2. The light emitting device as claimed in claim 1, wherein said product is greater than or equal to 90% at the center of at least one emitting region and for the normal viewing angle.

3. The light emitting device as claimed in claim 1, wherein said product is greater than or equal to 95% at the center of at least one emitting region and for the normal viewing angle.

4. The light emitting device as claimed in claim 1, wherein the passive top multilayer stack has the structure Al/LiF/Alq3/NPB/CuPc/ITO.

5. The light emitting device as claimed in claim 4, further comprising a glass substrate.

6. The light emitting device as claimed in claim 1, wherein said at least one additional functional layer group in the top multilayer stack includes a dielectric layer between said anode and the top transparent substrate.

7. The light emitting device as claimed in claim 6, wherein said at least one additional functional layer group in the top multilayer stack comprises alternating layers of dielectric material of different refractive index.

8. The light emitting device as claimed in claim 7, wherein said alternating layers comprise SiO₂ and TiO₂.

9. The light emitting device as claimed in claim 1, wherein said at least one additional functional layer group in the top multilayer stack comprises a layer of conductive material with a reflection and an absorption between said anode and said cavity layer.

10. The light emitting device as claimed in claim 9, wherein said layer of conductive material is a metal.

11. The light emitting device as claimed in claim 9, wherein said layer of conductive material is silver.

12. The light emitting device as claimed in claim 1, wherein said passive top multilayer stack includes an absorbent layer group above said anode to decrease the external reflectance of said top multilayer stack.

13. The light emitting device as claimed in claim 12, wherein said absorbent layer group comprises a mixture of metal and dielectric.

14. The light emitting device as claimed in claim 12, wherein said absorbent layer group comprises a semiconductor.

15. The light emitting device as claimed in claim 12, wherein said absorbent layer group comprises alternate alternating layers of metal and dielectric.

16. The light emitting device as claimed in claim 12, further comprising a layer of conductive material with an absorption and a reflectance in said top multilayer stack adjacent said cavity layer.

17. The light emitting device as claimed in claim 16, wherein said conductive material is silver.

18. The light emitting device as claimed in claim 15, wherein said alternating dielectric layers comprise nickel alloy and SiO₂.

19. The light emitting device as claimed in claim 1, wherein said light emitting device is an OLED.

20. A method of making a light emitting device comprising:

providing a layered structure comprising a cavity layer containing an active light emitting region sandwiched between passive bottom and top multilayer stacks, said passive top and bottom multilayer stacks being devoid of a light emitting layer, wherein the passive bottom multilayer stack includes a cathode and the passive top multilayer stack includes a hole transport layer and a transparent anode layer, the passive top multilayer stack includes an additional functional layer group for increasing an internal reflectance of the top layer stack and the passive bottom multilayer stack includes an additional functional layer group for reducing reflectance from the cathode; and

providing, above the passive top multilayer stack, a top transparent substrate through which light is emitted from the device; and

wherein thicknesses of said layered structure are selected such that the product of phase factors ξ

₁ and ξ

₂ is greater than 80% at the center of at least one light emitting region and for a normal viewing angle, wherein

21. The method as claimed in claim 20, wherein said product of the phase factors ξ

₁ and ξ

₂ is greater than or equal to 90% at the center of at least one emitting wavelength region and for the normal viewing angle.

22. The method as claimed in claim 20, wherein said product of the phase factors ξ

₁ and ξ

₂ is greater than or equal to 95% at the center of at least one emitting wavelength region and for the normal viewing angle.

23. The method as claimed in claim 20, wherein the reflectance of the passive top multilayer stack and phase changes occurring upon reflection from said passive top multilayer stack in said cavity layer are controlled with said additional functional layer group in said passive top multilayer stack.

24. The method as claimed in claim 23, wherein said additional functional layer group in said passive top multilayer stack comprises alternating dielectric layers above the transparent anode layer in said passive top multilayer stack.

25. The method as claimed in claim 24, wherein said alternating dielectric layers are SiO₂ and TiO₂.

26. The method as claimed in claim 20, comprising reducing the external reflectance of the passive top multilayer stack with at least one absorption layer group in said top multilayer stack.

27. The method as claimed in claim 26, further comprising including a reflective conductive layer on the inside of said passive top multilayer stack to enhance the reflectance within said cavity layer and compensate for a reduction in efficiency caused by said absorption layer group.

28. The method as claimed in claim 27, wherein said at least one absorption layer group comprises a mixture of metal and dielectric.

29. The method as claimed in claim 28, wherein said at least one absorption layer group comprises a semiconductor.

30. The method as claimed in claim 26, wherein said at least one absorption layer group comprises alternating dielectric and metal layers.

31. The method as claimed in claim 27, wherein said reflective conductive layer is a metal.

32. The method as claimed in claim 31, wherein said metal is silver.