Utilizing gradient refractive index films for light extraction and distribution control in OLED
View Patent ↗The present invention relates to an electro-optical device, wherein the device is a light source, for example an OLED. The OLED includes at least a substrate, a cathode, an anode, one or more organic light-emissive materials disposed between the cathode and anode, and a gradient refractive index film disposed on an external, light emitting surface of the device, for example on the substrate layer. Alternatively, the device may be constructed with the gradient refractive index film as the substrate, and/or the gradient refractive index film may be applied to more than one light-emitting surface of a device.
1. An OLED including a gradient refractive index film, wherein the gradient refractive index film comprises a composite film having a reducing refractive index from a first surface of the film to a second surface of the film, wherein the gradient refractive index film comprises at least two materials that, with reference to one another, exhibit a reduction in refractive index value as the materials progress away from the external light emissive surface upon which the film is disposed.
2. The OLED of claim 1 wherein the OLED is a light source.
3. The OLED of claim 1 wherein the OLED is a display.
4. The OLED of claim 1 wherein a critical angle of incidence between the second surface of the gradient refractive index film and an external environment is from at least about 45° and up to about 90°.
5. The OLED of claim 1 wherein a critical angle of incidence between any two internal materials within the gradient refractive index film is at least about 65° and up to about 90°.
6. The OLED of claim 1 wherein the gradient refractive index film shifts the color coordinates (ccx and ccy) of the OLED by no more than 10%.
7. The OLED of claim 1 wherein the on-axis luminance of the light source is increased by at least 4% as compared to the on-axis luminance of the same light source without the multi-layer film.
8. The OLED of claim 1 wherein the first surface is directly adjacent a light emitting surface of the OLED.
9. The OLED of claim 1 wherein the second surface is exposed to air or another environment external to the gradient refractive index film.
10. The OLED of claim 1 wherein the OLED comprises at least a cathode, one or more organic light-emissive materials, an anode, and a light-transmissive substrate, and the gradient refractive index film is disposed adjacent the substrate.
11. The OLED of claim 10 wherein the substrate comprises glass or a light-transmissive polymer, and the gradient refractive index film is applied to an external surface of the substrate with an index matching adhesive.
12. The OLED of claim 1 wherein the OLED comprises a cathode, one or more light-emissive materials, and an anode, disposed on the gradient refractive index film.
13. The OLED of claim 1 wherein the OLED has more than one light-emitting surface, and the gradient refractive index film is disposed on at least one light emitting surface.
14. The OLED of claim 1 wherein the OLED has more than one light-emitting surface, and the gradient refractive index film is disposed on at least two light emitting surfaces, and the gradient refractive index film may or may not be the same on each of the at least two light emitting surfaces.
15. The OLED of claim 1 wherein the gradient refractive index film further includes a material that scatters light within the gradient refractive index film to increase light emission from the OLED.
16. The OLED of claim 15 wherein the material that scatters light within the gradient refractive index film comprises alumina.