Fabrication and characterization of organic field effect transistors with poly(3-hexylthiophene) thin films

In this study, we fabricated Organic Field Effect Transistors (OFETs) using an Au/P3HT/SiO2/n⁺⁺-Si structure. The organic poly(3-hexylthiophene) (P3HT) films with various thickness, which were controlled by changing weight concentration of P3HT in chloroform (CHCl₃) solvent, have been fabricated using a solgel method. The correlations of mobility and on/off current ratio depend on various thickness of P3HT films are revealed. The mobility of the P3HT films were about 1.1, 2.2, and 2.8 × 10^-3 [cm²V^-1 s^-1] for 0.4, 0.7, and 1.0 wt%, respectively. We also observed the trade off relation on mobility and on/off ratio with increasing anneal temperature from 100 to 140°C. The surface morphology with various thicknesses was scanned by using atomic force microscopy (AFM) in order to verify the relations between the thickness of film and device performance. We observed the increase of on current with thickness of active layer. These results indicate that the accumulated carriers between semiconductor and insulator are strongly affected by the degree of molecular packing and size of molecular bonding.