Light extraction film with nanoparticle coatings
A multifunctional optical film for enhancing light extraction includes a flexible substrate, a structured layer having nanoparticles of different sizes, and a backfill layer. The structured layer effectively uses microreplicated diffractive or scattering nanostructures located near enough to the light generation region to enable extraction of an evanescent wave from an organic light emitting diode (OLED) device. The backfill layer has a material having an index of refraction different from the index of refraction of the structured layer. The backfill layer also provides a planarizing layer over the structured layer in order to conform the light extraction film to a layer of an OLED display device. The film may have additional layers added to or incorporated within it to an emissive surface in order to effect additional functionalities beyond improvement of light extraction efficiency.
1. A multifunctional optical film for enhancing light extraction from a self-emissive light source having a surface that outputs light, comprising:
a flexible substrate substantially transmissive to light emitted by the self-emissive light source;
a structured layer of extraction elements having a first index of refraction,
wherein the extraction elements comprise nanoparticles disposed in a surface layer manner on the substrate, and the extraction elements form a non-planar surface of the structured layer, and
wherein the nanoparticles comprise first nanoparticles having diameters within a first range and second nanoparticles added to the first nanoparticles and having diameters in a second range less than and non-overlapping with the first range; and
a backfill layer comprising a material having a second index of refraction different from the first index of refraction, wherein the backfill layer forms a planarizing layer over the nanoparticles on the non-planar surface of the structured layer, forming a planar surface on a side of the backfill layer opposite the nanoparticles,
wherein a substantial portion of the extraction elements are in optical communication with the light output surface of the self-emissive light source when the planar surface of the backfill layer is located against the light output surface of the self-emissive light source,
wherein the structured layer and backfill layer are in sufficient proximity to the light output surface of the self-emissive light source when the planar surface of the backfill layer is located against the light output surface of the self-emissive light source in order to at least partially enhance the extraction of light from the light output surface, and
wherein the first range of diameters is 60 nm to 10 microns, and the second range of diameters is 3 nm to 40 nm.
2. The multifunctional optical film of claim 1 , wherein the extraction elements comprise a multi-layer of the nanoparticles.
3. The multifunctional optical film of claim 1 , wherein a portion of the extraction elements are in contact with a surface of the substrate and the substantial portion of the extraction elements are proximate but not in contact with the surface of the substrate.
4. The multifunctional optical film of claim 1 , further comprising an optical coupling layer located on the planar surface of the backfill layer, wherein the optical coupling layer comprises an adhesive providing for optical coupling between the light output surface of the self-emissive light source and the backfill layer.