ESR Study of Electric-Field Controlled Conductance of Fully-doped Polymers in a Transistor Structure

It was recently reported that use of doped ``metallic'' polymer as the active channel in a field effect transistor structure results in unexpected ``normally on`` transistor-like behavior. Epstein \textit{et al}. proposed [1] that ion motion is involved in the conductance modulation of the ``metallic'' polymer. We study here the role of ion migration in the ``metallic'' polymer (poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS)) based transistors by employing ESR spectroscopy. We found that approximately 18{\%} reduction of localized polaron concentration in PEDOT:PSS caused by ions insertion results in 10$^{3}$ times decrease in the polymer conductance. The $N(E_{F})$ determined from the Pauli susceptibility remains essentially unchanged after ions are inserted into the active channel. This indicates that the major conductance suppression in PEDOT:PSS occurs in the disordered regions. We proposed that the inserted ions modulate the charge carrier hopping distance in the disordered regions of the PEDOT:PSS resulting in a conductor-nonconductor transition. [1]A. J. Epstein \textit{et al.}, Curr. Appl. Phys. \textbf{2}, 339 (2002).