Polymer Electrodes for Flexible Organic Light-Emitting Devices

We report a high luminance and low operating voltage molecular organic light-emitting diode (MOLED) using a conducting polymer hole-injecting electrode (anode) on a plastic substrate. A dramatic improvement in the rectification ratio is observed upon the insertion of a buffer layer between the conducting polymer anode and the organic hole-transporting layer (HTL). Micro-shorts leading to a leakage current caused by the non-uniformity of the polymer film are greatly reduced. Atomic force microscope (AFM) images show a much smoother surface of the polymer anode/buffer layer relative to that of the bare polymer film. A slight increase (0.3eV ± 0.2eV) in the work function of the polymer anode upon the addition of the buffer layer is also measured. A simple method of patterning the conducting polymer electrode on various substrates including plastics is also reported. This approach conveniently provides finely patterned conducting polymer films with νm resolution while maintaining their intrinsic electrical and optical properties such as the surface sheet resistance and the optical transmittance.