Morphology, Electrical Performance and Potentiometry of PDIF-CN2 Thin-Film Transistors on HMDS-Treated and Bare Silicon Dioxide

In this work, the electrical response of n-type organic field-effect transistors, achieved by evaporating PDIF-CN2 films on both bare and Hexamethyldisilazane (HMDS) treated SiO2 substrates, was investigated by standard electrical characterization and potentiometry. Morphological and charge transport characterizations demonstrated that the hydrophobic degree of the substrate surface has a huge impact on the final response of the devices. The PDIF-CN2 transistors on HMDS-treated substrates show a maximum mobility of 0.7 cm2/Volt·s, three orders of magnitude greater than in the case of the device without surface functionalization. The scanning Kelvin probe microscopy technique was used to perform surface potentiometry to image the local surface potential inside the channel during the transistor operation and has allowed us to identify the film morphological disorder as the primary factor that could compromise the effectiveness of the charge injection process from gold contacts to PDIF-CN2 films. For optimized devices on HMDS-treated substrates, SKPM was also used to analyze, over time, the evolution of the potential profile when negative VGS voltages were applied. The findings of these measurements are discussed taking into account the role of VGS-induced proton migration towards SiO2 bulk, in the operational stability of the device