A simple and straightforward processing methodology for tuning the grain size over three orders of magnitude in the active layer of OTFTs in length has been demonstrated. The characteristics of solution-processed OTFTs can also vary dramatically depending on the morphology of the active layer. The goal of controlling the crystallization of TES-ADT, fluorinated 5, 11- bis(triethylsilylethynyl) anthradithiophene (FTES-ADT) to seed the nucleation of the active layer. OTFT were fabricated in a bottom-contact geometry, using phosphor- doped silicon as the gate electrode and a 300 nm thermally grown Si02 layer as the gate dielectric. This process involves the addition of fractional quantities 'impurities' that is capable of seeding the crystallization the organic semiconductor. This method of seeding the crystallization of solution processed organic semiconductors effectively eliminates grain size variation in the active layers of OTFT, thus providing a robust route to fabricating reliable and reproducible devices.