Structure–conductivity correlation in ferric chloride-doped poly(3-hexylthiophene)

Abstract

Poly(3-hexylthiophene) (P3HT) matrix has been chemically doped (redox doping) by ferric chloride (FeCl₃) with different molar concentrations to get P3HT–FeCl₃ charge-transfer complexes. The effect of redox doping on photo-physical, structural, and morphological properties and dc electrical conductivity of P3HT matrices has been examined. The dc conductivity has been measured on films of pristine P3HT and P3HT–FeCl₃ charge-transfer complexes in the temperature range 6–300 K. Analysis of dc conductivity data reveals that in the temperature range 40–300 K, the dc conductivity is predominantly governed by Mott's 3-dimensional variable range hopping (3D-VRH); however, below 40 K tunnelling seems to dominate. A slight deviation from 3D-VRH to 1D-VRH is observed with an increase in doping level or precisely with an increase in the extent of P3HT–FeCl₃ charge-transfer complexes. We attribute this deviation to the induced expansion in crystallographic lattices as revealed by x-ray diffraction data and formation of discrete conducting domains as observed by atomic force microscope imaging.