Vapor sensing with α,ω-dihexylquarterthiophene field-effect transistors:: The role of grain boundaries

We have investigated the channel-length dependence of responses to a vapor analyte with a series of alpha,omega-dihexylquarterthiophene (DHalpha4T) field-effect transistors (FETs). Single-crystalline DHalpha4T devices deposited by vacuum sublimation at substrate temperatures of 70 degreesC are compared with polycrystalline DHalpha4T films deposited at room temperature. By changing the length of FET channels and/or the size of polymer grains, the number of grain boundaries per device is changed systematically. A larger response to vapor analyte is obtained by increasing the number of grain boundaries per device, showing that vapor sensing occurs mainly at grain boundaries. (C) 2002 American Institute of Physics.