Anomalous current-voltage and impedance behaviour in doped Poly 3-methylthiophene devices

Current-voltage (I-V) and impedance measurements are performed on electrochemically-doped poly(3-methylthiophene) (P3MeT) devices in metal/polymer/metal sandwich geometry. The detailed investigation shows the presence of negative differential resistance (NDR) in the sandwich devices with different metals in action as substrate and top electrode. It is found that the reiteration of I-V measurements significantly enhances the NDR. The P3MeT devices shows a considerable switching behaviour with ON to OFF ratio varying between two to three order but lacks the consistency in bias stress test. An anomalous behaviour in the impedance measurements in the form of a prolonged tail is observed in Cole-Cole plots towards lower frequency region, which gets more prominent with applied bias. This impedance anomaly is explained in terms of large distribution of relaxation times arising due to long lived trap states at the bulk and interface which is correlated with the NDR observed in P3MeT devices.