Anisotropic hopping conduction in spin-coated PEDOT:PSS thin films

The charge transport in spin-coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been investigated as a function of temp. and elec. field. Both the magnitude and the transport mechanism are found to be strongly anisotropic. This striking behavior is quant. explained in terms of a morphol. model in which flattened, quasimetallic PEDOT-rich grains are organized in horizontal layers that are sepd. by continuous insulating PSS lamellas. In this model, the in-plane cond. is described by three-dimensional variable range hopping between .apprx.25 nm sized PEDOT-rich particles sepd. by subnanometer PSS barriers, while the out-of-plane cond. is described by nearest-neighbor hopping between more widely spaced mol. sites. These length scales are supported by previously reported scanning probe measurements.