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

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 3dimensional 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. 3 Author to whom any correspondence should be addressed. New Journal of Physics 8 (2006) 112 PII: S1367-2630(06)24510-5 1367-2630/06/010112+21$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft 2 Institute of Physics DEUTSCHE PHYSIKALISCHE GESELLSCHAFT