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 α,ω-dihexylquarterthiophene (DHα4T) field-effect transistors (FETs). Single-crystalline DHα4T devices deposited by vacuum sublimation at substrate temperatures of $\text{70\hspace{0.05em}°}\mathrm{C}$ are compared with polycrystalline DHα4T 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.