Performance of Organic Field-Effect Transistor Based on Poly(3-hexylthiophene) as a Semiconductor and Titanium Dioxide Gate Dielectrics by the Solution Process

Organic field-effect transistors (OFETs) were fabricated with a high-dielectric-constant and high-permittivity titanium dioxide (TiO 2 ) as a gate insulator and regioregular poly(3-hexylthiophene-2,5-diyl) (RR-P3HT) as the electronically active semiconductor. Positive OFET characteristics were obtained with a low threshold voltage (+3 V) and high field-effect mobility (3.73 × 10 -3 cm 2 V -1 s -1 ). The dielectric material (TiO 2 ) was prepared by the sol–gel technique and the gate insulator layer was fabricated by spin coating. The RR-P3HT thin films were fabricated by drop casting with different solution concentrations. The thickness of the thin films was measured using the surface profile measuring system. The fabricated thin film structure was analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD), and UV–visible absorption spectra. The X-ray result shows that the drop-cast RR-P3HT thin film has a high crystallinity on the TiO 2 surface, which leads to the high field-effect mobility of the OFET. The results show that the OFET performances are not only dependent on the orientation and crystallinity of the polymer semiconductor, but that also the gate dielectric properties, surface roughness, and interface properties between the gate and semiconductor layers are very important for the efficient performance of the OFET.