The effect of MWCNTs on the performance of α-sexithiophene OTFT device and its gas-sensing property

Abstract

In this paper, bottom contact organic thin-film transistor (OTFT) gas sensors were prepared. Silicon dioxide (SiO2) and titanium/aurum (Ti/Au) were used as the insulating layer and the electrode for the device, respectively. The multi-walled carbon nanotubes (MWCNTs)/α-sexithiophene (α-6T) bilayer films were used as the active layer, and α-6T single layer sensitive film was also prepared for comparison purpose. The electrical and trace NO2-sening properties of these two OTFT gas sensors were tested and analyzed. The results showed that, the OTFT device based on MWCNTs/α-6T bilayer had obviously better electrical properties, better stabilities and higher NO2-sening response values than the device with α-6T single layer, in which both the carrier mobility (μ) and on/off current ratio enhanced two order of magnitude. The improved performance of bilayer OTFT can be explained that MWCNTs acted as highly conducting bridges connecting the crystalline terraces in the α-6T film. Threshold voltage (VT), carrier mobility, on/off current ratio and grid current which showed extremely similar variation trend as source-drain current, were optional parameters to reveal the gas-sensing characteristic of OTFT gas sensors. Morphology analysis showed that the special feature of MWCNTs had certain influence on the gas-sensing properties.