Electroluminescence lifetime and efficiency of polymer LEDs with surface-treated anodes

We studied the influence of wet (aquaregia, ultrasonication, RCA) and dry (oxygen- and argon-plasmas) treatments of ITO anodes on single- and double-layer LEDs based on PPV or PDPV, in terms of the electroluminescence (EL) lifetimes, efficiencies (Cd/A and Im/W), luminances and driving voltages. Oxygen plasma treatment yields the highest efficiencies, luminances, and the lowest driving voltages. We measured the lifetimes (time to half luminance at constant V) of ITO/PPV/Ca devices, all driven with an initial current density of 10 mA/cm2. Oxygen plasma treatment increases significantly the EL lifetime by an order of magnitude with respect to the untreated ITO, and removes the occasional occurrence of low-voltage current anomalies.