Controlling Grain Size in Solution-Processed Organic Semiconductors for Thin-Film Transistors

We present a novel method for controlling the grain size in solution-processed triethylsilylethynyl anthradithiophene (TES-ADT) films through the addition of fractional amounts of fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (FTES-ADT). FTES-ADT can seed the crystallization of TES-ADT during solvent-vapor annealing. The grain size in these films follows an exponential dependence on the concentration of FTES-ADT; varying the FTES-ADT concentration by 2-fold induces a 3-order of magnitude change in the grain size. For channels in which the average grain size is 29 $\mu $m, device mobility of the organic thin-film transistors (OTFTs) is 0.05 cm$^{2}$/V-s. For channels in which the average grain size is 2700 $\mu $m, the device mobility is 0.35 cm$^{2}$/V-s. The relationship between device mobility and grain size is well described by a composite mobility model, which assumes a high intrinsic grain mobility and a low grain boundary mobility. Grazing incidence x-ray diffraction indicates that the crystal lattice of TES-ADT is preserved despite the addition of FTES-ADT.