Electric-field-controlled conductance of “metallic” polymers in a transistor structure

Abstract

It was recently reported that use of a doped ``metallic'' polymer as the active channel in a field effect transistor structure results in unexpected ``normally on'' transistorlike behavior. We report here the role of ion migration in transistors based on metallic polymer [poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS)]. The analysis of the ion flow into the active channel due to the gate voltage suggests that for the transistors studied compensating $\ensuremath{\sim}2$ counterions per 100 dopant molecules suppresses PEDOT conductance up to three orders of magnitude. We determine from the temperature dependence of the conductivity of the active channel that the change in conductance of the active channel is throughout the channel in contrast to confinement of gate field induced charge carriers to the channel/dielectric interface in conventional transistors. The decrease of channel conductance reflects an increase of activation energy of carriers. Therefore, we propose that removal of intermediate hopping sites in the disoriented PEDOT:PSS by a small fraction of ion charge compensation causes carriers to anisotropically hop over longer distance leading to a conductor-nonconductor transition.