New scenarios of charge transport in PEDT:PSS conducting polymer: From hole resonant tunneling to cationic motion and relaxation

This work reports a series of distinct current density∼field (JE) characteristics of the poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) (or PDET:PSS) conducting polymer system. Symmetrical and asymmetrical negative differential resistance (NDR) behaviors are observed for metal/PEDT:PSS/metal sandwich devices, and these novel behaviors are related to hole injection and resonant tunneling, hole blockage and extraction, and ionic motion in the PEDT:PSS films. Both the PEDT:PSS/metal interface configuration and film thickness have strong effect on the manifestation of the NDR characteristic. It is proposed that phase segregation in μm-thick PEDT:PSS films could lead to the conversion of hole-dominated transport to ionic motion-dominated conduction, thus causing a drastic change in JE characteristics of films with different thickness. Our results highlight the important effect of PEDT:PSS/metal interface and PEDT:PSS film thickness on charge conduction, and broaden our current understanding of this model organic system with both electronic and ionic conducting components.