Scanning Kelvin Probe Microscopy investigation of the contact resistances and charge mobility in n-type PDIF-CN2 thin-film transistors

In this paper, Scanning Kelvin Probe Microscopy (SKPM) was applied in combination with standard current-voltage measurements to assess the contact resistance (R-C) effects and to estimate the contact-free charge carrier mobility in n-type transistors based on evaporated films of PDIF-CN2. This analysis was carried out in particular as a function of the applied polarization voltages. The separate contributions to the R-C phenomenon coming from the injecting (source) and extracting (drain) electrodes were investigated with the possibility to separately analyze the specific electrical behaviour of these two regions. In agreement with previous results, the experimental data here discussed show that the devices under analysis are not simply injected limited. Voltage drops at both the injecting and extracting contacts must be taken into consideration. However, it is worth to mention that for the bottom-contact devices here investigated, a minimum R-C of 5.5 k Omega cm was found in linear regime. These values are significantly lower (i.e. by a factor 5x) than those previously reported for other perylene dimiide thin-film devices with bottom-contact configuration.