Fabrication of junction-free Ag fiber electrodes for flexible organic light-emitting diodes (OLEDs) is demonstrated. The junction-free Ag fiber electrodes are fabricated by electrospun polymer fibers used as an etch mask and wet etching of Ag thin film. This process facilitates surface roughness control, which is important in transparent electrodes based on metal wires to prevent electrical instability of the OLEDs. The transmittance and resistance of Ag fiber electrodes can be independently adjusted by controlling spinning time and Ag deposition thickness. The Ag fiber electrode shows a transmittance of 91.8% (at 550 nm) at a sheet resistance of 22.3 Ω □ , leading to the highest OLED efficiency. In addition, Ag fiber electrodes exhibit excellent mechanical durability, as shown by measuring the change in resistance under repeatable mechanical bending and various bending radii. The OLEDs with Ag fiber electrodes on a flexible substrate are successfully fabricated, and the OLEDs show an enhancement of EQE (≈19%) compared to commercial indium tin oxide electrodes.

We demonstrated light extraction improvement by applying a scattering layer of Ag nanoparticles physically synthesized through a low-temperature annealing process to flexible organic light-emitting diodes (OLEDs). In general, increasing the size of Ag nanoparticles is preferred to increase light scattering, but a high-temperature annealing process (∼400 °C) is required to produce them. However, flexible substrates generally cannot withstand high-temperature processes. In this study, we formed Ag nanoparticles at a low temperature of ∼200 °C by inserting a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate buffer layer, thus promoting Ag dewetting. As a result, the scattering layer of enlarged Ag nanoparticles formed at low temperatures increased the external quantum efficiency by 24% in a flexible OLED compared to a reference device.

The world first flexible full color 5.6‐inch active matrix organic light emitting diode (AMOLED) display with top emission mode on stainless steel foil is demonstrated. The active matrix back planes were fabricated using low temperature poly‐Si (LTPS). The p‐channel poly‐Si TFTs on the stainless steel foil exhibited the field‐effect mobility of 71.2 cm2/Vs, threshold voltage of −2.7 V, off current of 6.7× 1013 A/um, and subthreshold slope of 0.63 V/dec. These TFT performances made it possible to integrate scan driver circuit on the panel. A low‐cost planarization techniqe of stainless steel foil was developed to replace the expensive chemical mechanical planarization (CMP) method, which was the most critical barrier against mass production. The full color flexible AMOLED display on the stainless steel foil will be promising for mobile applications because of its thin, light, rugged, and design‐free properties.