Anomalous conduction current in PEO

Thin films of the ion-conducting polymer polyethylene oxide (PEO) are used to investigate the transient current density through the samples after application of a voltage step. Applying the same voltage it is found experimentally that the long-term conduction current density response through the PEO is independent of the sample length. Qualitatively comparable results are obtained from computer simulations using a three-dimensional hopping model. This model takes into account the movement of intrinsic ions as well as the injection of extrinsic electrons from the electrodes. It turns out that the width of a depletion zone at the negative electrode is responsible for the length independence of the current. This width mainly defines the long-term current and depends only on the applied voltage. The depletion zone can be determined experimentally with surface potential measurements performed with a scanning Kelvin probe.