Effects of interfacial modification on the performance of an organic transistor based on TCNQ LB films

The influence of interfacial modifications of n-type organic-based thin-film transistors (OTFTs), using low work-function metal electrodes and self-assembled monolayers (SAMs), were analyzed by electrical and structural measurements. We employed ultra thin films of long-alkyl-chained tetracyanoquinodimethane (C18-TCNQ) Langmuir–Blodgett (LB) films as the n-type semiconducting layer with nano-scale thickness. A significant increase in the drain current was observed for the OTFT with low work-function metal electrodes, and this current increase was consistent with the decrease in the injection barrier height for carrier electrons to transfer from the electrodes into the LB films. On the other hand, it was found that the density of interfacial trapping sites decreased with the SAMs treatment, even though no structural modification was induced by the SAM. This behavior is considered to be due to the elimination of active SiOH groups on the SiO2 substrate by the SAMs treatments. It was also found that the device parameters strongly depend on the alkyl chain length of the SAMs. In order to explain this phenomenon clearly, a new interfacial model based on the interaction between carrier electrons and interfacial SiOH groups is proposed.