Methods for reducing diffuse reflection of nanostructure-based transparent conductive films and touch panels made of the same
View Patent ↗The present disclosure relates to optical stacks having nanostructure-based transparent conductive films and low diffuse reflection. Also described are display devices that incorporate the optical stacks.
1. An optical stack comprising:
at least one nanostructure layer;
an overcoat immediately overlying the nanostructure layer, wherein the overcoat comprises a plurality of porous nanoparticles;
at least one substrate adjacent to the nanostructure layer; and
an outermost cover layer that is most proximate to an incident light, wherein:
the outermost cover layer is made of polyimides or clear polymers embedded with high refractive index particles selected from ZnO, ZrO 2 , or TiO 2 , and has a refractive index of at least 1.7,
the nanostructure layer comprises a plurality of conductive nanostructures embedded in an insulating medium,
a diffuse reflection of the incident light, as viewed from a same side of the optical stack as the incident light, is less than 6% of the incident light, and
the nanostructure layer is more proximate to the incident light than the substrate.
2. The optical stack of claim 1 , wherein the insulating medium has a refractive index of less than 1.5.
3. The optical stack of claim 2 , wherein the insulating medium is air.
4. The optical stack of claim 1 , wherein the plurality of conductive nanostructures do not individually have an organic coating or have a low-index organic coating.
5. The optical stack of claim 1 wherein:
the insulating medium is HPMC,
the plurality of conductive nanostructures are silver nanowires,
a weight ratio of the HPMC and the plurality of conductive nanostructures is about 1:1, and
the nanostructure layer has a sheet resistance of less than 100 ohms/sq.
6. The optical stack of claim 1 , wherein the overcoat has a refractive index of less than 1.55.
7. The optical stack of claim 6 , wherein the overcoat is a low-index optically clear adhesive (OCA) layer having a refractive index of 1.45 or less.
8. The optical stack of claim 6 , wherein the overcoat further comprises a low-index binder.
9. The optical stack of claim 8 , wherein the plurality of porous nanoparticles are silica nanoparticles having an internal void volume of 50-90%.
10. The optical stack of claim 9 , wherein the plurality of porous nanoparticles are present at 20-80% by volume of the overcoat.
11. The optical stack of claim 8 , wherein the low-index binder is a UV-curable resin having a refractive index of less than 1.5.
12. The optical stack of claim 11 , wherein the low-index binder is an acrylic or polyurethane resin.
13. The optical stack of claim 8 , wherein the overcoat has a refractive index of 1.22.
14. The optical stack of claim 1 , further comprising an undercoat interposed between the substrate and the nanostructure layer, wherein:
the undercoat immediate underlies the nanostructure layer, and
the undercoat has a higher refractive index than that of the insulating medium and that of the substrate.
15. The optical stack of claim 14 , wherein the undercoat is made of TiO 2 , SiO 2 , or polyimide independently, and has a refractive index of at least 1.65.
16. The optical stack of claim 1 , wherein the outermost cover layer is a TiO 2 layer.
17. The optical stack of claim 1 , wherein:
the plurality of conductive nanostructures has a first sheet resistance,
the insulating medium has a second sheet resistance, and
the first sheet resistance is at least 10 3 more than the second sheet resistance.
18. The optical stack of claim 1 , further comprising an undercoat interposed between the substrate and the nanostructure layer, wherein a refractive index of the nanostructure layer is less than a refractive index of the undercoat.
19. The optical stack of claim 18 , wherein the refractive index of the undercoat is greater than a refractive index of the substrate.
20. The optical stack of claim 18 , wherein a refractive index of the overcoat is less than or equal to the refractive index of the nanostructure layer.