Abstract
Organic thin-film transistors (OTFTs), based on two n-type structures of fullerene (C-60) and N,N '-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), are investigated. The two OTFT devices reveal a negative differential resistance (NDR) behavior in the saturation region of the output curves. The OTFT based on C-60 shows a more pronounced NDR than that based on PTCDI-C8. The main origin of the NDR is ascribed to the trapping states. In addition, the contact resistance (R-c) of the two devices, extracted using the developed voltage transition method (V-tr method), as well as the obtained values of R-c, are in fair agreement with the experimental values extracted using the total resistance. The device based on C-60 exhibits a higher R-c than that based on PTCDI-C8. OTFT parameters, such as transconductance (g(m)), mobility (mu(max)), threshold voltage (V-th,V-), turn-on voltage (V-on), ratio current I-on/I-off, and subthreshold slope (SS), are obtained in the linear and saturation regimes. The extracted value of SS for the OTFT based on C-60 is very small compared with that of the device based on PTCDI-C8, which indicates an increase in the density of trapping states in the C-60 film.