A possible phase transition in metallic polythiophene and poly(3-methylthiophene) at low temperature

We have an experimental study on the transport properties in as-grown polythiophene and poly(3-methylthiophene) films doped with PF6−. Precise measurements were made of the four-terminal DC resistivity, the Voltage-Shorted-Compaction resistivity and the absolute thermoelectric power between 1.6–300K with an aim to abstract the transport properties inherent to the crystallized regions of polymeric materials. The results are strongly indicative of the occurrence of a metal-insulator transition within the crystallized (metallic) regions at low temperatures. The difference in the transport property of bulk materials is understood by their different transition temperatures.