The stability of conductance in electropolymerized insulating polypyrrole under application of a high voltage was investigated using a metal-insulator-metal-type diode device. The conductance varied over time due to application of the voltage, and the current-time profiles were classified into three types according to the level of the applied voltage. In the very low voltage region the conductance was stable; in the middle voltage region the conductance increased to a stable value; and in the high voltage region the conductance first increased and then decreased. The mechanism of the change in conductance, the UV-Vis absorption spectra and the photo-radiated current behaviour are dismissed.
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