Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase

A method is demonstrated by which liquid-crystalline self-organization in rigid-rod nematic conjugated polymers can be used to control the microstructure of the active semiconducting layer in solution-processed polymer thin-film transistors (TFTs). Enhanced charge carrier mobilities of 0.01–0.02 cm2/V s and good operating stability have been achieved in polyfluorene copolymer TFTs by preparing the polymer in a nematic glassy state and by aligning the polymer chains parallel to the transport direction with the help of an alignment layer. Mobility anisotropies of 5–8 for current flow parallel and perpendicular to the alignment direction have been observed that are of the same order of magnitude as optical dichroic ratios.