ELECTRIC AND MAGNETIC-FIELD DEPENDENCE OF THE CONDUCTIVITY IN POLY(3-HEXYLTHIOPHENE)LANGMUIR-BLODGETT FILMS

The conductivity of undoped and NOPF6-doped Langmuir-Blodgett thin fil ms of poly(3-hexylthiophene) has been studied under strong electric (u p to 60 kV/cm) and magnetic (up to 15 T) fields at low temperatures (d own to 4.3 K). The electric-field dependence of the conductivity in do ped films fits the theory of charging-energy-limited tunneling between highly conducting regions. In the electric-field-induced conduction m ode, the magnetoresistance adopts a positive B2 dependence which is ar gued to arise from the geometrical contribution corresponding to an ex tremely high and bias-dependent Hall mobility, over 103 cm2/Vs below 4 0 K. However, the high Hall mobility was not measurable using a conven tional four-point technique. The results can be reproduced in free-sta nding films of doped poly(3-hexylthiophene). Undoped Langmuir-Blodgett films show a linearly varying positive magnetoresistance the magnitud e of which increases with decreasing temperature.