Role of Confinement in Enhancing Electrical Transport of Conducting Polymers

Confined conducting polymers (CPs) such as in nanocylinder geometries have been shown to exhibit enhanced conductance that is primarily attributed to factors such as chain alignment, increased crystallinity, and/or pi-pi stacking. We address the significance of these factors of polymers confined in alumina nanocylinders of diameters ranging from 20 nm to 100 nm and compare them with properties of bulk films. A conducting substrate of suitable work function and a common top contact was used to examine the macroscopic electrical transport of the CPs in these regularly patterned structures. Isolated nanopores were examined using conducting atomic force microscopy methods. A series of conducting polymers that include in-situ polymerized PEDOT:Tos, other forms of PEDOT from aqueous dispersion, and n-type doped polymers were examined. The enhanced vertical conductivity that is normally not observed in thick PEDOT films due to the transport barriers also points to the reduced degree of disorder. The difference in electrical charge transport of polymer blend PEDOT:PSS and polymer-monomer blend PEDOT:Tos in alumina scaffold in terms of σ as a function of ω and T highlights the efficacy of this approach to reduce disorder in tailored systems. The high-resolution transmission electron microscopic technique illustrates the picture of structural disorder present in the nanochannels and the variation of connecting pathways between the ordered regions on an amorphous matrix in two types of CPs with similar electronic PEDOT backbone. The confinement facilitates microstructures as the in-situ polymerization of PEDOT:Tos proceeds. The utility of these geometry-induced properties is demonstrated in the context of photodetection and thermoelectric applications.