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 degrees C reveal an increase in the field-effect mobility by a factor of 100 to a value of mu(FET)=4.8*10(4) cm(2)V(-1)s(-1).