COLOR ELECTRO-LUMINESCENT DISPLAY WITH IMPROVED EFFICIENCY

• US 20080238829A1
• Filed: 03/30/2007
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: Nanoco Technologies Limited (Nanoco Group Plc)
• Original Assignee: Eastman Kodak Company
• Inventors: Miller, Michael E., Kane, Paul J.
• Granted Patent: US 7,851,987 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: H10K 59/351 comprising more than three subpixels, e.g. red-green-blue-white [RGBW]

Abstract

A full-color electroluminescent display with improved efficiency and increased color gamut that includes substantially complementary yellow and blue light-emitting elements, the chromaticity coordinates of which define the endpoints of a line that intersects a Planckian locus within the interval 0.175<=u′<=0.225 within the Commission Internationale de l'"'"'Eclairage (CIE) 1976 u′v′ chromaticity space. Also included in the display is a green light-emitting element of spectrum having a dominant wavelength between 500 nm and 540 nm and a full width, half maximum spectral bandwidth of 50 nm or less; and a red light-emitting element.

Claims

1. A full-color electroluminescent display with improved efficiency and increased color gamut, comprising:

a. substantially complementary yellow and blue light-emitting elements, the chromaticity coordinates of which define the endpoints of a line that intersects a Planckian locus within the interval 0.175<

=u′

<

=0.225 within the Commission Internationale de l'"'"'Eclairage (CIE) 1976 u′

v′

chromaticity space;

b. a green light-emitting element of spectrum having a dominant wavelength between 500 nm and 540 nm and a full width, half maximum spectral bandwidth of 50 nm or less; and

c. a red light-emitting element.

2. The color electroluminescent display device of claim 1, wherein combinations of the substantially complementary yellow and blue light-emitting elements, which lie along the line in the CIE chromaticity space, produce any colors along the line between them with greater luminous efficiency than other combinations of the four light-emitting elements (red, green, yellow, and blue).

3. The color electroluminescent display device of claim 1, wherein the red and green light-emitting elements have emission characteristics that are selected to produce a display having a color gamut of at least 0.14 units in the CIE 1976 u′

v′

chromaticity space.

4. The color electroluminescent display device of claim 1, wherein the blue light-emitting element emits light having a dominant wavelength between 440 and 460 nm.

5. The color electroluminescent display device of claim 1, wherein the yellow light-emitting element emits light having a dominant wavelength between 565 and 575 nm.

6. The color electroluminescent display device of claim 1, wherein the yellow light-emitting element produces a peak luminance of at least 20 times a peak luminance produced by the blue light-emitting element when forming a 6500K white point.

7. The color electroluminescent display device of claim 1, wherein the red light-emitting element emits light having a dominant wavelength between 650 nm and 670 nm.

8. The color electroluminescent display device of claim 1, wherein the light-emitting elements are formed from different species of inorganic light-emitting particles, each species emitting a different color of light, the electroluminescence spectrum of each species having a full-width half maximum of 50 nm or less.

9. The color electroluminescent display device of claim 8, wherein the spectrum of each species further has full-width half maximum of 30 nm or less.

10. The color electroluminescent display device of claim 8, wherein the inorganic light-emitting particles are quantum dots and wherein emission characteristics of the light-emitting elements are altered by forming quantum dots of different sizes.

11. A method of making a color electroluminescent display device, comprising the steps of:

a. forming a first electrode over a substrate;

b. selecting at least two different electroluminescent materials that provide substantially complementary yellow and blue light emission, having chromaticity coordinates that define endpoints of a line that intersects a Planckian locus within the interval 0.175<

=u′

<

=0.225 within CIE 1976 u′

v′

chromaticity space;

c. selecting a green electroluminescent material having a dominant wavelength between 500 nm and 540 nm and a full width, half maximum spectral bandwidth of 50 nm or less;

d. selecting a red electroluminescent material;

e. forming a light-emitting layer over the first electrode, wherein the light-emitting layer is formed as a patterned array of the yellow, blue, green, and red electroluminescent materials; and

f. forming a second electrode over the light-emitting layer, wherein at least one of the first or second electrodes are patterned, and are aligned to the patterned array of the yellow, blue, green, and red electroluminescent materials to form light-emitting elements.

12. The method claimed in claim 11, wherein at least one of the first and second electrodes is transparent or semi-transparent.

13. The method claimed in claim 11, wherein each of the light-emitting materials are comprised of inorganic light-emitting particles.

14. The method claimed in claim 13, wherein the step of forming a light-emitting layer over the first electrode, further comprises forming a colloidal mixture of the inorganic light-emitting particles and an additional electrically conductive particle.

15. The method of making the light-emitting device of claim 11, wherein the step of forming the light-emitting layer over the first electrode further comprises coating at least one common inorganic transport layer within the area of each of the light-emitting elements.

16. The method of making the light-emitting device of claim 11, wherein the step of forming a light-emitting layer further comprises coating at least one common inorganic transport layer over the first electrode prior to coating the electroluminescent materials and forming at least a second common inorganic transport layer over the electroluminescent materials, prior to forming the second electrode.

17. A color electroluminescent display system having at least four differently colored light-emitting elements, comprising:

a. substantially complementary yellow and blue light-emitting elements having chromaticity coordinates that define endpoints of a line that intersects a Planckian locus within the interval 0.175<

=u′

<

=0.225 within the Commission Internationale de l'"'"'Eclairage (CIE) 1976 u′

v′

chromaticity space,;

b. a green light-emitting element of spectrum having a dominant wavelength between 500 nm and 540 nm and a full width, half maximum spectral bandwidth of 50 nm or less;

c. a red light-emitting element; and

d. a controller that is electrically connected to the light-emitting elements and that selectively applies a drive signal to the light-emitting elements to preferentially apply the yellow and blue light-emitting elements when forming near-neutral colors to improve the luminous efficiency of the display while maintaining a large color gamut.