Three orders of magnitude is the range over which the grain size (see figure) can be tuned in solution-processed organic semiconductor thin films for TFTs. Fluorinated triethylsilyl anthradithiophene (FTES-ADT) is added in fractional amounts to seed crystallization of TES-ADT Correlation between device mobility and grain size in the active layer is described by a composite mobility model that assumes charge-carrier traps are located at grain boundaries.