Environmental Effects on the Performance of Small-Molecule Organic Thin-Film Transistors

Electrical measurements are performed on a bottom-gate bottom-contact organic thin-film transistor with 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES ADT) (diF-TES ADT) as the active layer, varying the relative humidity of the environment surrounding the transistor. The results strongly indicate that water negatively impacts the electrical performance of the transistor and that the ingress of water is dynamic provided that the organic semiconductor layer is not encapsulated. It is found that the change can be reversed and the performance restored by removing the source of water. The drain current and threshold voltage of the transistor varied linearly when the relative humidity is changed from 35% to 7%, suggesting that the transistor can be used as a humidity sensor. Water decreases the drain current and carrier mobility of organic thin-film transistors by increasing the number of carriers trapped near the gate dielectric. Electrical experiments versus relative humidity on diF-TES-ADT transistors suggest that this behavior enables such a device to function as a humidity sensor, as the output current and threshold voltage respond linearly with relative humidity. image