NATURE OF IMPURITIES IN PI-CONJUGATED POLYMERS PREPARED BY FERRIC-CHLORIDE AND THEIR EFFECT ON THE ELECTRICAL-PROPERTIES OF METAL-INSULATOR-SEMICONDUCTOR STRUCTURES
Msa. Abdou et al., NATURE OF IMPURITIES IN PI-CONJUGATED POLYMERS PREPARED BY FERRIC-CHLORIDE AND THEIR EFFECT ON THE ELECTRICAL-PROPERTIES OF METAL-INSULATOR-SEMICONDUCTOR STRUCTURES, Chemistry of materials, 7(4), 1995, pp. 631-641
Poly(3-hexylthiophene), prepared by oxidative coupling using ferric ch
loride, has been purified to different extents so as to yield a series
of samples with identical chemical structure and molecular weight but
containing varying levels of residual iron impurity (0.05-3.2 wt % Fe
). The polymers were analyzed by Mossbauer, UV-vis, IR, and EPR spectr
oscopies. The impurity is an octahedral iron(III) complex. The electri
cal response of thin polymer films was investigated in the form of met
al-insulator-semiconductor (MIS) structures. Analysis of MIS field eff
ect transistors (MISFETs) shows that both field effect mobility and bu
lk conductivity decrease as a function of impurity concentration. Capa
citance-voltage (C-V) measurements performed on MIS structures show th
at the concentration of immobile, and ionized, electron-acceptor impur
ities increases with concentration of residual iron complexes. Evidenc
e is provided for the formation of a relatively ''thick'' accumulation
layer at the polymer/insulator interface. The thickness of the accumu
lation layer was found to be field dependent.