Color organic light emitting diode display with improved lifetime

• US 20040036421A1
• Filed: 08/20/2002
• Published: 02/26/2004
• Est. Priority Date: 08/20/2002
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Miller, Michael E., Arnold, Andrew D., Murdoch, Michael J.
• Granted Patent: US 6,747,618 B2
• Time in Patent Office: Days
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3225 using an active matrix
• CPC Class Codes: H10K 50/19 Tandem OLEDs
• CPC Class Codes: H10K 59/351 comprising more than three subpixels, e.g. red-green-blue-white [RGBW]
• CPC Class Codes: H10K 59/353 characterised by the geometrical arrangement of the RGB subpixels

Abstract

An improved OLED color display device, in which a display pixel has a plurality of subpixels of different colors, wherein the areas of the subpixels are different in size based on the emission efficiency of the emissive elements and the chromaticity of a target display white point, thereby protecting the subpixels whose emission efficiency is low from prematurely deteriorating, wherein the improvement comprises the relative sizes of the subpixels being further based on the relative luminance stability over time of the subpixels, thereby further extending the useful lifetime of the display.

Claims

1. An improved OLED color display device, in which a display pixel has a plurality of subpixels of different colors, wherein the areas of the subpixels are different in size based on the emission efficiency of the emissive elements and the chromaticity of a target display white point, thereby protecting the subpixels whose emission efficiency is low from prematurely deteriorating, wherein the improvement comprises:

the relative sizes of the subpixels being further based on the relative luminance stability over time of the subpixels, thereby further extending the useful lifetime of the display.

2. The color display device claimed in claim 1, wherein the relative sizes of the subpixels are determined according to the equation:

A_i=f(E_i,T_i,Y_i)

where A_i are the sizes of the subpixels;

E_i are the material efficiencies for the differently colored subpixels;

T_i are the luminance stability over time for the differently colored subpixels; and

Y_i are the luminances of the differently colored subpixels for a given target display white and the chromaticity coordinates of the subpixels.

3. The color display device claimed in claim 2, wherein the luminance stability over time are defined as:

T_i=cI^d

where c and d are constants and I is the current density through the subpixel.

4. The color display device claimed in claim 1, wherein the differently colored subpixels emit red, green and blue light.

5. The color display device claimed in claim 1, wherein more than three colored subpixels are used to form the color display device.

6. The color display device claimed in claim 4, wherein the area of the blue subpixels is substantially larger than the area of the red and green subpixels to compensate for the relatively short lifetime of the blue subpixels.

7. The color display claimed in claim 1, wherein the subpixels are stacked on top of one another.

8. The color display claimed in claim 1, wherein layers of light emitting material of the same color are stacked on top of one another to form a subpixel having an effective area proportional to the number of layers.

9. The color display claimed in claim 1, wherein different numbers of different colored light emitting layers are stacked on top of one another to provide the different subpixel areas.

10. The color display claimed in claim 1, wherein the subpixels having the largest size are located on one plane, and subpixels having a plurality of different sizes are located on another plane.

11. The color display claimed in claim 10, wherein the subpixels emit red, green and blue light, the blue subpixels are located in the one plane and the red and green subpixels are located in the other plane.

12. The color display claimed in claim 1, wherein at least one of the subpixels is subdivided into visually distinct regions.

13. A method of determining the relative sizes of subpixels in a OLED display device of the type having a display pixel that includes a plurality of subpixels of different colors, wherein the subpixels are different in size based on the emission efficiency of the subpixels, the chromaticity of a target display white, and the relative luminance stability over time of the subpixels thereby protecting the subpixels whose emission efficiency is low from prematurely deteriorating, comprising the steps of:

a) measuring chromaticity coordinates for the subpixels;

b) selecting aim chromaticity coordinates and luminance of a target display white point;

c) calculating a required luminance for each subpixel using the chromaticity coordinates of the subpixels, and the aim chromaticity coordinates and the luminance of the target display white point;

d) selecting an initial light emissive area for each subpixel;

e) providing an optical transmission factor for each subpixel;

f) calculating an actual luminance for each subpixel using the initial areas and optical transmission factors for the subpixel;

g) determining a functional relationship between current density and luminance output for each subpixel;

h) calculating an aim current density for each subpixel;

i) determining a functional relationship between current density and a luminance stability over time for each subpixel;

j) calculating a lifetime for each subpixel using the aim current density and the luminance stability functions; and

k) if the lifetimes are unequal, modifying the light emissive areas of the subpixels and repeating steps h, j, and k until the lifetimes are substantially equal.

14. The method claimed in claim 13, wherein the relative sizes are determined according to the equation:

A_i=f(E_i,T_i,Y_i)

where A_i are the areas of the subpixels;

E_i are the material efficiencies for the differently colored subpixels;

T_i are the luminance stabilities over time for the differently colored subpixels; and

Y_i are the luminances of the differently colored subpixels for a given target display white and the chromaticity coordinates of the subpixels.

15. The method claimed in claim 14, wherein the luminance stability for each of the materials over time are defined as:

T_i=cI^d

where c and d are constants and I is the current density through the subpixels.

16. The method claimed in claim 13, wherein the differently colored subpixels emit red, green and blue light.

17. The method claimed in claim 13, wherein more than three colored subpixels are used to form the color display device.

18. The method claimed in claim 16, wherein the area of the blue subpixel is substantially larger than the area of the red and green subpixels to compensate for the relatively short lifetime of the blue subpixels.

19. The method claimed in claim 13, wherein the subpixels are stacked on top of one another.

20. The method claimed in claim 19, wherein layers of light emitting material of the same color are stacked on top of one another to form a subpixel.

21. The method claimed in claim 20, wherein different numbers of layers of different colored light emissive materials are stacked on top of one another to provide the different sized subpixels.

22. The method claimed in claim 19, wherein the subpixels having the largest size are located on one plane, and subpixels having a plurality of different sizes are located on another plane.

23. The method claimed in claim 22, wherein the subpixels are red, green and blue, the blue emissive elements are located in the one plane and the red and green subpixels are located in the other plane.

24. The method claimed in claim 13, wherein at least one of the subpixels is subdivided into visually distinct regions.

25. A method of determining the relative sizes of subpixels in an OLED display device of the type having a display pixel that includes a plurality of subpixels of different colors, wherein sizes of the subpixels are different based on the emission efficiency of the subpixels, the chromaticity of a target display white, and the relative luminance stability over time of the subpixels, thereby protecting the subpixels whose emission efficiency is low from prematurely deteriorating, comprising the steps of:

a) providing chromaticity coordinates for the subpixels;

b) selecting aim chromaticity coordinates and luminance of a target display white point;

c) calculating a required luminance for each subpixel using the chromaticity coordinates of the subpixels, and the aim chromaticity coordinates and the luminance of the target display white point;

d) determining a functional relationship between current and luminance output for each subpixel;

e) calculating a required current for each subpixel to produce the required luminance using the functional relationships between current and luminance;

f) determining a functional relationship between current density and a luminance stability over time for each subpixel;

g) selecting a target useful lifetime;

h) calculating a current density that will obtain the selected useful lifetime for each subpixel using the relationships between current density and luminance stability over time; and

i) calculating a size for each subpixel by dividing the required currents by the respective calculated current densities.

26. The method claimed in claim 25, wherein the relative sizes are determined according to the equation:

A_i=f(E_i,T_i,Y_i)

where A_i are the areas of the subpixels;

E_i are the material efficiencies for the differently colored subpixels;

T_i are the luminance stability over time for the differently colored subpixels; and

Y_i are the luminances of the differently colored subpixels for a given target display white and the chromaticity coordinates of the subpixels.

27. The method claimed in claim 26, wherein the luminance stability over time are defined as:

Ti=cI^d

where c and d are constants and I is the current density through the subpixels.

28. The method claimed in claim 25, wherein the differently colored subpixels emit red, green and blue light.

29. The method claimed in claim 25, wherein more than three colored subpixels are used to form the color display device.

30. The method claimed in claim 28, wherein the area of the blue subpixel is substantially larger than the area of the red and green subpixels to compensate for the relatively short lifetime of blue subpixels.

31. The method claimed in claim 25, wherein the subpixels are stacked on top of one another.

32. The method claimed in claim 31, wherein layers of the same color light emitting materials are stacked on top of one another to form a subpixel.

33. The method claimed in claim 32, wherein different numbers of different colored light emitting materials are stacked on top of one another to provide the different sized subpixels.

34. The method claimed in claim 31, wherein the subpixels having the largest size are located on one plane, and subpixels having a plurality of different sizes are located on another plane.

35. The method claimed in claim 34, wherein the subpixels emit red, green and blue light, the blue subpixels are located in the one plane and the red and green subpixels are located in another plane.

36. The method claimed in claim 25, wherein at least one of the subpixels is subdivided into visually distinct regions.