Degradation study and calculation of density-of-states in PTCDI-C8 channel layer from the electrical characteristics of thin-film transistors

Abstract

N-type organic thin film transistor (OTFT) with a top-contact structure was fabricated by thermal vapour deposition using N,N′-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as an n-channel layer on Si/SiO2 substrate. The density of localised states (DOS) in the gap of PTCDI-C8 is estimated by studying the temperature dependence of the electrical characteristics of OTFT. The measurements were done immediately after the devices fabrication (non-degraded devices) and also after 2 h of exposure to air (degraded devices). The extracted field effect mobility decreased from 0.02 to 0.004 cm2 V−1 s−1 and threshold voltage increased from 25.3 to 40.5 V for the degraded OTFT. The degradation of OTFTs was due to the trapping of majority charge carriers in the localised trap states created by adsorbed oxygen in the PTCDI-C8 layer. These localised trap states were found to be situated at around 0.15 eV above the lowest unoccupied molecular orbit level. The study of DOS in OTFTs gives a complete understanding of trap-limited transport in organic thin film semiconductors.