Highly efficient flexible OLEDs based on double-sided nano-dimpled substrate (PVB) with embedded AgNWs and TiO₂ nanoparticle for internal and external light extraction

A light extraction structure and a flexible electrode have been developed to enhance the electroluminescence (EL) efficiency of flexible organic light-emitting diodes (FOLEDs). However, these structures are still influenced by optical losses, poor electrical stability, and low throughput, and are not suitable to be adopted into FOLEDs due to the surface roughness problem, low flexibility/adhesion, complicated process, and high temperature/pressure process. Here, to solve these problems, we demonstrate embedded Ag nanowires (AgNWs) in flexible substrate and highly flexible random nano pattern via easy/low-cost solution form process at atmospheric pressure and low temperature without any additional material. This study demonstrates an internal and external light extraction structure composed of double-sided nano-dimpled substrate PVB (DndP), which is directly fabricated on both sides of a flexible substrate (polyvinyl butyral, PVB) only in itself without additional material via the easy/low-cost transferring process using the anodic aluminum oxide (AAO) template by an anodization process-based solution form at atmospheric pressure and low temperature. Therefore, because the DndP and the substrate are composed of the same material, PVB, there is no light loss between their interfaces. In addition, a high-refractive-index TiO₂ nanoparticle, for the scattering effect, and AgNWs, for electrode flexibility, are embedded into the DndP via the covering method using the solution form. Such structures exhibit extraordinary mechanical flexibility due to the AgNWs embedded in the PVB substrate. Therefore, FOLEDs using such structures can be well adapted to flexible/rollable/foldable displays and wearable application devices. Moreover, the corrugated surface of FOLEDs by such structures can improve the current flow through increased surface area of electrodes and extract the trapped light through the scattering effect (Rayleigh, Mie), reducing the total reflection and coupled photon in metal/dielectric. In addition, the FOLEDs with such structures show color/spectrum-stable property and independence of viewing angles owing to their random nature. The final green FOLEDs with DndP, embedded scattering TiO₂ nanoparticle, and embedded AgNWs&PEDOT:PSS demonstrate an outstanding EL efficiency enhancement ratio of 2.23 time via internal and external light extraction without electrical short.