Electrochemistry of conductive polymers. 45. Nanoscale conductivity of PEDOT and PEDOT:PSS composite films studied by current-sensing AFM

[Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] (PEDOT:PSS, Baytron P) composite films were prepared under various conditions and their conductivities were studied by the current-sensing atomic force microscopy (CS-AFM) technique. Topographic and current images of pristine and additive-treated PEDOT: PSS as well as electrochemically synthesized PEDOT films were obtained in nanoscale using the CS-AFM. The as-prepared pristine PEDOT:PSS films showed a low population of conductive spots isolated by large insulating regions; both their population and the conductivities increased upon addition of a few additives to the PEDOT:PSS solution before spin-coating. From the current-voltage (I-V) traces recorded at a few representative spots of different electronic states, much improved pathways for charge percolation appeared to have been established in the additive-treated films. Electrochemically prepared PEDOT films showed much better electrical properties compared with spin-casted films of chemically prepared polymers. The conductivity of all these films was shown to be significantly enhanced by the electrochemical doping process.