An FT-IR investigation of the influence of doping on the molecular organization of Langmuir-Blodgett thin films containing poly(3-hexylthiophene)

Abstract

The influence that various doping treatments have on the molecular structure and organization of mixed Langmuir-Blodgett films comprised of poly(3-hexylthiophene) and deuterated stearic acid was investigated using reflection-absorption infrared spectroscopy. The molecular organization and electrical properties of these films were found to depend strongly on the type of dopant used and its method of introduction. When doped from solution with NOPF 6 and SbCl 5, the original molecular organization of the multilayer film was significantly disrupted and the deuterated stearic acid molecules were extracted into the doping solution. In some cases, this extraction process produced uniform thin films of poly(3-hexylthiophene) with conductivities comparable to free-standing films. Gas-phase doping with I 2 and SbCl 5, on the other hand, could be accomplished without significantly altering the molecular morphology of the film. The heterogeneous two-phase nature of the multilayer films in this case resulted in lower conductivities.