Experimental study of chemical reaction between LiF and polyflourene interface during sputtering indium-tin oxide cathode for top emission polymer light emitting devices

Top emission polymer light-emitting devices (PLEDs) with different heat treatments are investigated. Due to the high work function of an indium-tin-oxide (ITO) cathode as a top electrode, LiF is employed as an interlayer to increase electron injection. The PLEDs fabricated at room temperature show better electrical and optical characteristics such as current density-voltage, luminance, and current efficiency, etc., than that of PLED devices with heat treatment. To investigate the Li diffusion in the polyfluorene layer, X-ray photoelectron spectroscopy measurement before and after heat treatment is performed. The poor performance of PLEDs with heat treatments is observed due to the high trap density generated in the film because of the Li diffusion in the polyfluorene layer.