Transparent ultra-thin silver electrodes formed via a maskless evaporation process for applications in flexible organic light-emitting devices

We have fabricated flexible, transparent, ultra-thin silver (Ag) electrodes by using a maskless deposition process and applied them to organic light-emitting devices (OLEDs). A selective ultraviolet/ozone (UV/O₃) treatment was performed on the polyethylenimine (PEI) polymer layer, which contained amine groups and was coated onto a silicon substrate, in order to form an electrode pattern. An ultra-thin Ag film was deposited in vacuum on the UV/O₃-treated substrate without a mask, resulting in the formation of a flexible, transparent, ultra-thin Ag electrode pattern. The optimum PEI concentration and the optimum UV/O₃ treatment time for the formation of flexible, transparent, Ag electrode patterns were determined from their sheet resistances, optical transmittances, Fourier-transform infrared spectra and X-ray photoelectron spectra. The sheet resistance of the ultra-thin Ag electrode transferred to an epoxy substrate changed within 5% only when the bending diameter of curvature and the number of bending cycles were 5 mm and 3000, respectively. The current density and the luminance of an OLED with a flexible, transparent, ultra-thin Ag electrode deposited on an epoxy substrate were larger than those of an OLED with an indium-tin-oxide (ITO) electrode formed on a polyethylene naphthalate substrate. We have confirmed that the flexible, transparent, ultra-thin Ag electrodes hold promise for use in the fabrication of flexible OLEDs.