Nickel as an alternative semitransparent anode to indium tin oxide for polymer LED applications

We report on the possibility of using a thin Ni layer, instead of ITO, as a semitransparent hole-injecting electrode for bottom polymer LEDs. Thin metal layers of Ni were deposited by a sputtering technique and their electrical and optical properties with different deposition times have been investigated. Both square resistance and transmittance were seen to decrease with deposition time (thickness). The films showed a transmittance of around 30-40%, which is quite low compared to the 86% of ITO, while their square resistance was higher than that of ITO. Nevertheless, diodes based on a blue emitting polymer, polyfluorene (PFO), showed the same efficiency for either ITO or thin Ni electrodes, although the Ni transmittance is around 2.5 times lower than the ITO transmittance. Such preliminary results definitively suggest that indium-free organic devices can be achieved.