High Performance Light-Emitting Devices

• US 20070246705A1
• Filed: 08/23/2004
• Published: 10/25/2007
• Est. Priority Date: 08/23/2004
• Status: Active Grant

• Current Assignee: National Research Council Canada
• Original Assignee: National Research Council Canada
• Inventors: Dobrowolski, Jerzy, Li, Li, Poitras, Daniel
• Granted Patent: US 7,863,632 B2
• Time in Patent Office: Days
• US Class Current: 257/40
• 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 top multilayer stack, a bottom multilayer stack, and a cavity layer between said top multilayer stack and said bottom multilayer stack;

an organic light emitting region within said cavity layer; 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 emitting wavelength region and for a normal viewing angle, wherein

${\mathrm{\xi <br><br>}}_1={\left(1+\frac{4<br><br>\sqrt{R_a^{-}<br><br>R_b^{+}}<br><br>{\sin }^2<br><br>\left({\mathrm{\alpha <br><br>}}_1-\frac{{\mathrm{\phi <br><br>}}_a^{-}+{\mathrm{\phi <br><br>}}_b^{+}}{2}\right)<br><br>{\mathrm{e<br><br>}}^{-2<br><br>{\mathrm{\beta <br><br>}}_1}}{{\left(1-\sqrt{R_a^{-}<br><br>R_b^{+}}<br><br>{\mathrm{e<br><br>}}^{-2<br><br>{\mathrm{\beta <br><br>}}_1}\right)}^2}\right)}^{-1}$${\mathrm{\xi <br><br>}}_2=1-\frac{4<br><br>\sqrt{R_b^{+}}<br><br>{\sin }^2<br><br>\left({\mathrm{\alpha <br><br>}}_2-\frac{{\mathrm{\phi <br><br>}}_b^{+}}{2}\right)<br><br>{\mathrm{e<br><br>}}^{-2<br><br>{\mathrm{\beta <br><br>}}_2}}{{\left(1+\sqrt{R_b^{+}}<br><br>{\mathrm{e<br><br>}}^{-2<br><br>{\mathrm{\beta <br><br>}}_2}\right)}^2}$$\{\begin{array}{c}{\mathrm{\delta <br><br>}}_1=\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(n-\mathrm{ik}\right)<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}=\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\mathrm{nd}<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}-i<br><br>\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\mathrm{kd}<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}={\mathrm{\alpha <br><br>}}_1-{\mathrm{i\beta <br><br>}}_1\\ {\mathrm{\delta <br><br>}}_2=\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(n-\mathrm{ik}\right)<br><br>x<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}=\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\mathrm{nx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}-i<br><br>\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\mathrm{kx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{cavity}}={\mathrm{\alpha <br><br>}}_2-{\mathrm{i\beta <br><br>}}_2\end{array}$

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, α

₁ β

₁ are respectively the real and imaginary parts of the phase thickness of said cavity layer, α

₂ and β

₂ are respectively the real and imaginary parts of the phase thickness of said 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 said cavity layer, θ

_cavity is the emitting angle inside the cavity layer, and d is the physical thickness of said cavity layer.

2. A 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 wavelength region and for a normal viewing angle.

3. A 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 wavelength region and for a normal viewing angle.

4. A light emitting device as claimed in claim 1, having the structure Al/LiF/Alq3/NPB/CuPc/ITO.

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

6. A light emitting device as claimed in claim 1, wherein said top multilayer stack includes an anode and a hole transport layer and at least one additional layer to increase the reflectance of the top multilayer stack and to control the phase change on reflection.

7. A light emitting device as claimed in claim 6, wherein said at least one additional layer group is a dielectric layer between said anode and a substrate.

8. A light emitting device as claimed in claim 7, wherein said at least one additional layer group comprises alternate layers of dielectric material of different refractive index.

9. A light emitting device as claimed in claim 8, wherein said alternate layers comprise SiO₂ and TiO₂.

10. A light emitting device as claimed in claim 6, wherein said at least one additional layer comprises a layer of conductive material with high reflection and low absorption between said anode and said cavity layer.

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

12. A light emitting device as claimed in claim 10, wherein said layer of conductive material is silver.

13. A light emitting device as claimed in claim 6, wherein said top multilayer stack includes an absorbent layer group above said anode to decrease the external reflectance of said multilayer stack.

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

15. A light emitting device as claimed in claim 13, wherein said absorbent layer group comprises a semiconductor.

16. A light emitting device as claimed in claim 13, wherein said absorbent layer group comprises alternate layers of metal and dielectric.

17. A light emitting device as claimed in claim 13, further comprising a layer of conductive material of low absorption and high reflectance in said top multilayer stack adjacent said cavity layer.

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

19. A light emitting device as claimed in claim 18, wherein said alternate metal and dielectric layers comprise SiO₂ and Inconel™

.

20. A light emitting device as claimed in claim 1, wherein said light emitting device is an OLED.

21. A light emitting device in the form of a layered structure comprising:

a bottom multilayer stack including a cathode layer;

a cavity layer including a light emitting region;

a top multilayer stack including a hole transport layer, a transparent anode layer, a transparent substrate; and

at least one additional layer group in said top multilayer stack controlling the reflectance of the top multilayer stack and phase changes occurring upon reflection from said top multilayer stack in said cavity layer.

22. A light emitting device as claimed in claim 21, wherein said at least one additional layer comprises alternate dielectric layers above said transparent anode layer.

23. A light emitting device as claimed in claim 22, wherein said alternate dielectric layers are SiO₂ and TiO₂.

24. A light emitting device as claimed in claim 21, wherein said light emitting device is an OLED.

28. A light emitting device as claimed in claim 24, wherein said at least one additional absorptive layer group comprises alternate dielectric and metal layers.

29. A light emitting device as claimed in claim 23, wherein said conductive layer is a metal.

30. An organic light emitting device as claimed in claim 29, wherein said metal is silver.

25. A light emitting device in the form of a layered structure comprising:

a bottom multilayer stack including a cathode layer;

a cavity layer including a light emitting region;

a top multilayer stack including a hole transport layer, a transparent anode layer, a transparent substrate;

at least one additional absorptive layer group in said top multilayer stack reducing the external reflectance of the top multilayer stack; and

a layer of conductive material having high reflectance and low absorption on the inside of said multilayer stack to increase the internal reflectance of said top multilayer stack.

26. A light emitting device as claimed in claim 25, wherein said absorbent layer group comprises a mixture of metal and dielectric.

27. A light emitting device as claimed in claim 25, wherein said absorbent layer group comprises a semiconductor.

31. A light emitting device as claimed in claim 25, wherein said light emitting device is an OLED.

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

designing a layered structure including a plurality of layers and an organic light emitting material within said layered structure;

creating an optical model of said layered structure that takes into account at least phase changes on reflection occurring within said structure;

determining suitable layer thicknesses from said optical model to optimize light emission efficiency; and

fabricating said layered structure with said layers having said layer thicknesses determined from said optical model.

33. A method as claimed in claim 32, wherein said layered structure includes top and bottom multilayer stacks, and a cavity layer including a light-emitting region, and said layer thicknesses 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 emitting wavelength region and for a normal viewing angle, wherein

34. A method as claimed in claim 33, wherein said product is greater than or equal to 90% at the center of at least one emitting wavelength region and for a normal viewing angle.

35. A method as claimed in claim 33, wherein said product is greater than or equal to 95% at the center of at least one emitting wavelength region and for a normal viewing angle.

36. A method as claimed in claim 32, wherein said layered structure includes top and bottom multilayer stacks, and a cavity layer including a light-emitting region, said method further comprising controlling the reflectance of the top multilayer stack and phase changes occurring upon reflection from said top multilayer stack in said cavity layer with at least one additional layer group in said multilayer stack.

37. A method as claimed in claim 36, wherein said at least one additional layer group comprises alternate dielectric layers above a transparent anode layer in said top multilayer stack.

38. A method as claimed in claim 37, wherein said alternate dielectric layers are SiO₂ and TiO₂.

39. A method as claimed in claim 32, wherein said layered structure includes top and bottom multilayer stacks, and a cavity layer including a light-emitting region, said method further comprising reducing the external reflectance of the top multilayer stack with at least one absorption layer group in said multilayer stack.

40. A method as claimed in claim 39, further comprising including a reflective conductive layer on the inside of said top multilayer stack to enhance the reflectance within said cavity and compensate for a reduction in efficiency caused by said absorption layer group.

41. A method as claimed in claim 40, wherein said at least one absorption layer group comprises a mixture of metal and dielectric.

42. A method as claimed in claim 41, wherein said at least one absorption layer group comprises a semiconductor.

43. An organic light emitting device as claimed in claim 39, wherein said at least one absorption layer group comprises alternate dielectric and metal layers.

44. A method as claimed in claim 40, wherein said conductive layer is a metal.

45. A method as claimed in claim 44, wherein said metal is silver.