Electroluminescent devices with improved optical out-coupling efficiencies

Abstract

An electroluminescent (EL) device is disclosed. An optically reflective concave structure includes a first surface and a second surface that lies at an angle relative to the first surface, wherein at least the first and second surfaces are optically reflective. One or more functional layers include a light emitting layer, disposed over the surfaces of the optically reflective concave structure, wherein at least one electroluminescent area of the light emitting layer is defined on the first surface. Especially, the ratio between the width of the first surface and the thickness of the one or more functional layers in the optically reflective concave structure is smaller than a constant value.

What is claimed is: 
     
         1 . An electroluminescent (EL) device, comprising:
 an optically reflective concave structure, including a first surface, a second surface that lies at an angle relative to the first surface, and a third surface parallel to the first surface, wherein at least the first and second surfaces of the optically reflective concave structure are optically reflective; and   one or more functional layers including a light emitting layer, disposed over the surfaces of the optically reflective concave structure, wherein at least one electroluminescent area of the light emitting layer is defined on the first surface of the optically reflective concave structure;   wherein the ratio between the maximum width of the first surface of the optically reflective concave structure and the thickness of the one or more functional layers in the optically reflective concave structure is smaller than 200.   
     
     
         2 . The electroluminescent device of  claim 1 , wherein the one or more functional layers including a patterned interlayer formed between the optically reflective concave structure and the other functional layers, and the at least one electroluminescent area is defined by the patterned interlayer. 
     
     
         3 . The electroluminescent device of  claim 1 , further comprising a bend of the one or more functional layers formed at the angle between the first surface and the second surface, wherein the light emitted from the electroluminescent area is re-directed and out-coupled to air by the bend, when propagating in the one or more functional layers. 
     
     
         4 . The electroluminescent device of  claim 1 , further comprising:
 a first portion of the one or more functional layers, disposed over the first surface; and   a second portion of the one or more functional layers, disposed over the second surface,   wherein the light emitted from the electroluminescent area is re-directed and out-coupled to air by the variation of the thicknesses between the first portion and the second portion of the one or more functional layers, when propagating from the first portion to the second portion in the one or more functional layers.   
     
     
         5 . The electroluminescent device of  claim 1 , further comprising an index-matching material that is mostly filled on the first and second surfaces of the optically reflective concave structure and over the one or more functional layers. 
     
     
         6 . The electroluminescent device of  claim 5 , wherein the ratio between the maximum width of the first surface of the optically reflective concave structure and the total thickness of the one or more functional layers and the index-matching material in the optically reflective concave structure is smaller than 60. 
     
     
         7 . The electroluminescent device of  claim 5 , wherein the light emitted from the electroluminescent area is re-directed and out-coupled to air, and the number of reflection of the reflected or total internal reflected light and corresponding optical loss is reduced before being re-directed and out-coupled, when propagating in the one or more functional layers and the index-matching material. 
     
     
         8 . The electroluminescent device of  claim 5 , wherein the refractive indices of the other functional layers and the index-matching material within the optically reflective concave structure are kept within ±0.2 of that of the light emitting layer or higher than that of the light emitting layer, and the other functional layers and the index-matching material within the optically reflective concave structure have relatively high transparency of more than 75% in the wavelength range of the light emitted from the electroluminescent area. 
     
     
         9 . The electroluminescent device of  claim 5 , wherein the exposed surface of the index-matching material within the optically reflective concave structure is flat or curved. 
     
     
         10 . The electroluminescent device of  claim 1 , wherein the optically reflective concave structure is directly formed by an optically reflective material, the optically reflective material is selected from the group consisting of metal and scattering reflector. 
     
     
         11 . The electroluminescent device of  claim 1 , wherein the optically reflective concave structure is composed of a concave structure and an optically reflective surface, the material of the optically reflective surface is selected from the group consisting of metal, transparent conductive metal-oxide, transparent dielectric, scattering reflector, distributed Bragg reflector formed by alternate stacking of high-index/low-index materials, their stacking and their combinations. 
     
     
         12 . The electroluminescent device of  claim 1 , wherein the material of the first surface is the same as that of the second surface of the optically reflective concave structure. 
     
     
         13 . The electroluminescent device of  claim 1 , wherein the material of the first surface is different from that of the second surface of the optically reflective concave structure. 
     
     
         14 . The electroluminescent device of  claim 1 , wherein the electroluminescent area of the light emitting layer is extended to the intersection of the second and third surfaces of the optically reflective concave structure. 
     
     
         15 . The electroluminescent device of  claim 1 , wherein the optically reflective surfaces of the optically reflective concave structure have a relatively high optical reflectance more than 80% in the wavelength range of the light emitted from the electroluminescent area. 
     
     
         16 . The electroluminescent device of  claim 1 , wherein the functional layers in the optically reflective concave structure have a relatively high transparency more than 75% in the wavelength range of the light emitted from the electroluminescent area. 
     
     
         17 . A display including said electroluminescent (EL) device of  claim 1 , wherein the display comprising:
 a substrate;   a thin-film transistor formed on the substrate; and   an interconnection conductor, being electrical contact to the thin-film transistor,   wherein said electroluminescent device electrically contacts to the interconnection conductor via the first surface of the optically reflective concave structure.   
     
     
         18 . The display of  claim 17 , wherein the interconnection conductor also serves as the first surface of the optically reflective concave structure in said electroluminescent device. 
     
     
         19 . The display of  claim 17 , wherein the surfaces of the optically reflective concave structure in said electroluminescent device is non-conductive, and the one or more functional layers include a first electrode disposed between the other functional layers and the optically reflective concave structure, wherein the first electrode is electrically connected to the interconnection conductor and the one or more functional layers. 
     
     
         20 . A display including said electroluminescent (EL) device of  claim 1 , wherein the display comprising:
 a substrate;   a thin-film transistor formed on the substrate; and   an interconnection conductor, being electrical contact to the thin-film transistor,   wherein said electroluminescent device electrically contacts to the interconnection conductor via the third surface of the optically reflective concave structure.   
     
     
         21 . The display of  claim 20 , wherein the interconnection conductor also serves as the surfaces of the optically reflective concave structure.