Doping front propagation in light-emitting electrochemical cells

Observations of the expansion of the p- and n-doped regions in planar (lateral) polymer light-emitting electrochemical cells with large (mm-sized) interelectrode gaps driven with 5 to 50 V have inspired a model describing the doping front propagation. We find that the propagation is limited by the movement of ions in the electronically insulating region between the p- and n-doped regions. Two consequences of an ion-limited front propagation are that the doping fronts accelerate as they approach each other, and that fingerlike protrusions are formed, particularly at larger drive voltages.