Hydrogen-bonding-facilitated layer-by-layer growth of ultrathin organic semiconducting films

We demonstrated that the layer-by-layer growth of thin film crystals of conjugated organic molecules is facilitated by their hydrogen-bonding capabilities. We synthesized bis(3-hydroxypropyl)-sexithiophene (bHP6T), which includes two hydroxyalkyl groups that promote interlayer and intermolecular molecular interactions during the crystal growth process. Under the optimal deposition conditions, the crystals grew in a nearly perfect layer-by-layer mode on the solid substrate surfaces, enabling the formation of uniform charge transporting films as thin as a few monolayers. A thin film transistor device prepared from a bHP6T film only 9 nm thick exhibited a charge carrier mobility well above 1 × 10(-2) cm(2)/(V s) and an on/off ratio exceeding 1 × 10(4). These properties are better than the properties of other sexithiophene-based devices yet reported. The devices exhibited enhanced stability under atmospheric conditions, and they functioned properly, even after storage for more than 2 months.