Nanoscale thin-film morphologies and field-effect transistor behavior of oligothiophene derivatives

The field-effect transistor (FET) performances of two thiophene-based semiconducting materials (T2TT and T2FL) were examined. Through studies of the thin-film morphology using X-ray diffraction (XRD) and atomic force microscopy (AFM), we could access the behavior and structure of the thin-film devices at the nanoscale level in single molecular layers and determine the correlation between molecular alignment and device performance. Due to the extended π-conjugation, efficient hole injection, and good molecular alignment, the T2TT and T2FL FET devices exhibited hole mobilities of up to 0.03 cm² V^-1 s^-1, when the films were deposited at T_sub = RT and 80 °C, respectively. In spite of the large number of small grains in the film deposited at room temperature, the T2TT molecules were aligned perpendicular to the substrate when deposited at this low substrate temperature, which favored π-π overlap between adjacent molecules, resulting in high OFET performance.