Highly Bright Flexible Electroluminescent Devices with Retroreflective Electrodes

Flexible and stretchable light-emitting films using phosphor powders for electroluminescent (EL) devices offer the advantages of low cost and high durability under deformation. However, their low brightness is a significant disadvantage. A device structure adapting a light-transmission emitting layer and a retroreflective electrode to boost the brightness of EL device films is presented. The EL devices are fabricated by sandwiching the ZnS-particle-doped transparent resin emission layer between indium tin oxide and prismatic Ag thin film retroreflector electrodes. The ZnS particles, which are on the scale of tens of micrometers, dispersed in the emission layer induce light reflection over a wide viewing angle. However, at a high particle loading, the reflection rate is drastically decreased by the closed microstructure of the phosphor/resin emission layer. By optimizing the device structure and the composition of the emission layer consisting of phosphors, dielectric nanoparticles, and resin, a device is fabricated exhibiting a luminance of 1017 cd m⁻² (6.67 V µm⁻¹ at 10 kHz), which is 442% brighter than that of a conventional EL device.