Electrical Conductivity of Polypyrrole Films at a Temperature Range of 70 K to 350 K

The dc conductivity of electrochemically synthesized polypyrrole films doped from light to intermediate levels with p-toluene sulfonic acid was measured in the temperature range of 77 to 300 K, using a modified four-probe rig. Plots of dc conductivity vs. temperature were parameterized by fitting Mott’s Variable Range Hopping conduction model. The localization length of localized electrons was assumed to be 3 Å, which is approximately equal to the length of a pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300 and 10 K. Results were found to be consistent with Mott’s requirement that αR ⪢ 1. Microwave (10 GHz) conductivity measurements were carried out on the same set of polypyrrole samples at a temperature range of 90 to 473 K. Both microwave and dc conductivities were found to increase with temperature. The large values of microwave conductivity compared to dc conductivity over the temperature range tested suggests the existence of more charge hopping that does not contribute to the dc conductivity.