Electroluminescent device having improved light output

1. An electroluminescent device comprising a transparent substrate, a securing layer, a light scattering layer, an electroluminescent unit including a transparent electrode layer, a light emitting element including at least one light emitting layer, and a reflecting electrode layer in that order, wherein the light scattering layer includes one monolayer of inorganic particles having an index of refraction larger than that of the light emitting layer and wherein the securing layer holds the inorganic particles in the light scattering layer; further including a surface smoothing layer between the light scattering layer and the transparent electrode layer wherein the surface smoothing layer includes nanoparticles of high index metal oxide materials dispersed in a polymer matrix.

2. The electroluminescent device of claim 1 further including a short reduction layer disposed in the electroluminescent unit between the transparent electrode layer and the light emitting element.

3. The electroluminescent device of claim 1 wherein the securing layer includes a photo-polymerizable material, a heat-polymerizable material, an epoxy, or an adhesive.

4. The electroluminescent device of claim 2 wherein the securing layer includes a photo-polymerizable material, a heat-polymerizable material, an epoxy, or an adhesive.

5. The electroluminescent device of claim 1 wherein the inorganic particles in the light scattering layer includes titanium oxide, tantalum oxide, niobium oxide, zirconium oxide, aluminum oxide, tungsten oxide, antimony oxide, vanadium oxide, molybdenum oxide, or mixtures thereof.

6. The electroluminescent device of claim 2 wherein the inorganic particles in the light scattering layer includes titanium oxide, tantalum oxide, niobium oxide, zirconium oxide, aluminum oxide, tungsten oxide, antimony oxide, vanadium oxide, molybdenum oxide, or mixtures thereof.

7. The electroluminescent device of claim 1 wherein the size of the inorganic particles is between 0.1 μm and 10 μm.

8. The electroluminescent device of claim 2 wherein the size of the inorganic particles is between 0.1 μm and 10 μm.

9. The electroluminescent device of claim 1 wherein the light scattering layer further contains a binder material.

10. The electroluminescent device of claim 2 wherein the light scattering layer further contains a binder material.

11. The electroluminescent device of claim 9 wherein the binder material is polyurethane.

12. The electroluminescent device of claim 10 wherein the binder material is polyurethane.

13. The electroluminescent device of claim 1 wherein the refractive index of the surface smoothing layer is higher than that of the light emitting layer.

14. The electroluminescent device of claim 2 wherein the refractive index of the surface smoothing layer is higher than that of the light emitting layer.

15. The electroluminescent device of claim 1 wherein the nanoparticles include titanium oxide, tantalum oxide, niobium oxide, zirconium oxide, aluminum oxide, tungsten oxide, antimony oxide, vanadium oxide, molybdenum oxide, or mixtures thereof.

16. The electroluminescent device of claim 1 wherein the polymer matrix material includes polyvinylpyrrolidone.

17. The electroluminescent device of claim 1 wherein the surface smoothing layer includes polyvinylcarbazole.

18. The electroluminescent device of claim 1 wherein the thickness of the surface smoothing layer is less than 0.5 μm.

19. The electroluminescent device of claim 1 wherein the securing layer is an UV-curable polymer including polyurethanes, epoxies, polyesters, acrylates, or acrylics, or pressure sensitive adhesives.

20. The electroluminescent device of claim 1 wherein the securing layer has an index of refraction equal to or less than that of the substrate.

21. The electroluminescent device of claim 2 wherein the short reduction layer has a thickness between 10 nm and 200 nm.

22. The electroluminescent device of claim 2 wherein the short reduction layer has a sheet resistivity between 1×10 6 ohms/square to about 1×10 12 ohms/square.

23. The electroluminescent device of claim 2 wherein the material for the short reduction layer includes molybdenum oxide, vanadium oxide, antimony oxide, bismuth oxide rhenium oxide, tantalum oxide, tungsten oxide, niobium oxide, nickel oxide, or mixtures thereof.

24. The electroluminescent device of claim 2 wherein the material for the short reduction layer includes a mixture of a conductive oxide including indium oxide, gallium oxide, zinc oxide, tin oxide, aluminum doped zinc oxide, and mixtures thereof and an insulating material selected from oxides, fluorides, nitrides, sulfides and mixtures thereof.

25. The electroluminescent device of claim 2 wherein the material for the short reduction layer includes a mixture of indium-tin oxide and zinc sulfide or of indium-tin oxide and zinc sulfide-silicon oxide mixture.

26. The electroluminescent device of claim 2 wherein the material for the short reduction layer includes organic materials including PEDOT/PSS, polythiophene, or polyaniline.

27. The electroluminescent device of claim 1 wherein the electroluminescent unit is a stacked OLED device.

28. The electroluminescent device of claim 1 wherein the material for the reflecting electrode layer is selected from Ag, Au, Al, or alloys thereof.

29. An electroluminescent device comprising a transparent substrate, a securing layer, a light scattering layer, an electroluminescent unit including a transparent electrode layer, a light emitting element including at least one light emitting layer, and a reflecting electrode layer in that order, wherein the light scattering layer includes one monolayer of inorganic particles having an index of refraction larger than that of the light emitting layer and wherein the securing layer holds the inorganic particles in the light scattering layer wherein the securing layer is an acrylate based UV-curable polymer that further contains silane.