Effect of postfabrication thermal annealing on the electrical performance of pentacene organic thin-film transistors

We report the results of a systematic investigation of the electrical and physical modifications to pentacene organic thin-film transistors (OTFT) that result from postfabrication thermal annealing. The thermally induced electrical modifications of the performance of the pentacene OTFTs were explored, and the morphology and structure of the pentacene films were investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. We found that postfabrication thermal annealing at 50 °C significantly improved the mobility, from 0.19 to 0.36 cm2/Vs, and increased the on/off ratio to almost twice that of the non-annealed device. We also found that annealing increased the pentacene grain size and enhanced the 0 0 1 peak intensity in the XRD pattern, indicating greater molecular ordering. At postfabrication thermal annealing temperatures of 70 °C and above, the pentacene films lose their crystallinity and the OTFT performance is decreased.