  The semiconducting properties of regioregular poly(3-hexylthiophene) are
characterized by impedance measurements, from 40 Hz to 100 MHz. X-ray
diffraction shows the presence of both ordered and disordered regions. The
analysis of impedance data by Nyquist plots show two semi-circular arcs, and
its size is reduced by d.c. bias. Also, the carrier variation by light and
chemical doping alters the shape and size of arcs. The fits to the data and
equivalent circuits show considerable changes in the resistive, capacitive and
constant-phase element parameters as the carrier density increases. The
increase in carrier density reduces the relaxation time in ordered regions, and
it does not alter much in disordered regions.
