Morphology of quaterthiophene thin films in organic field effect transistors

The morphology of vacuum evaporated unsubstituted quaterthiophene films is studied as a function of the evaporation parameters. X-ray diffraction and AFM studies show that the thin film has a layered structure. Upon increasing the substrate temperature an increase in size of the single crystallites forming the film is observed together with a more uniform orientation. Larger crystals can be obtained by evaporating at a non- constant increasing deposition rate. Field-effect transistor devices fabricated at room temperature and 100°C reveal an increase in the field-effect mobility by a factor of 100 to a value of μFET=4.8 *10−4 cm2V−1S−1