DOPING STUDIES OF HETEROGENEOUS LANGMUIR-BLODGETT THIN-FILMS CONTAINING POLY(3-HEXYL THIOPHENE)

Langmuir-Blodgett multilayer thin films fabricated from mixed monolayers containing poly(3-hexyl thiophene) and stearic acid were rendered electrically conductive with strong oxidizing agents such as SbCl5, I2 and NOPF6. In-situ doping studies using dopants introduced in the gas phase revealed that the increase in conductivity was due to the formation of bipolaron-type charged defect sites on the polymer backbone. The highest level of conductivity was achieved by doping with NOPF6 from solution (about 3 S/cm). Solution phase doping, however, was found to disrupt the molecular organization of the multilayer film completely. In contrast, doping could be accomplished with retention or modification of the original molecular organization if carried out in the gas phase using either SbCl5 or I2. The resultant in-plane conductivities were a few orders of magnitude lower than films doped from solution due to the heterogeneous nature of the doped multilayer film. The conductivity of multilayer films doped with SbCl5 was found to be stable in vacuum whereas the conductivity of films doped with I2 decayed rapidly in either vacuum or air.