Stable peri-Xanthenoxanthene Thin-Film Transistors with Efficient Carrier Injection
journal contributionposted on 10.02.2009, 00:00 by Norihito Kobayashi, Mari Sasaki, Kazumasa Nomoto
We have synthesized and characterized stable organic semiconductors, 3,9-diphenyl-peri-xanthenoxanthene (Ph-PXX) and its soluble derivative for organic thin-film transistors (OTFTs). A π-system is stabilized against oxidation by introduction of heteroatoms into the reactive sites in the π-system. This strategy for stabilization does not suffer from the conventional tradeoff between environmental stability and efficient carrier injection, which appears when OSCs with deeper highest occupied molecular orbitals (HOMOs) are applied. UV−vis spectra of an air-saturated solution of Ph-PXX were unchanged over 120 h, indicating that it has an environmental stability. A HOMO level of Ph-PXX molecule was estimated to be only 5.1 eV below vacuum level, achieving efficient carrier injection. In fact, OTFTs with Ph-PXX showed high apparent mobility over 0.4 cm2/(V s) without demonstrating nonlinear behavior of source-drain ohmic contacts and have been shown to be stable for 5 months under ambient conditions. In addition, the OTFTs showed great thermal stability at temperatures up to 150 °C in air. These characteristics have been also achieved with a solution-processed OTFT with a soluble 3,9-bis(p-propylphenyl)-peri-xanthenoxanthene (PrPh-PXX). These results show that molecular design with passivation of the reactive cites is useful to make stable molecules with efficient carrier injection.