| Organic thin-film transistors (OTFTs) are a promising alternative technology to amorphous silicon devices. Pentacene-based organic thin-film transistors have been fabricated using various phosphonate-linked self-assembled monolayers (SAMs) as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region to explore the relationship between film structure and device performance. Improvements in the subthreshold slope and threshold voltage are observed compared to control devices fabricated without the buffer, and are related to structural motif similarities between the pentacene semiconductor and the SAMs. Both observations are consistent with a greatly reduced density of charge trapping states at the semiconductor-dielectric interface that is effected by introduction of the self-assembled monolayer. The alignment of molecular energy levels between a self-assembled monolayer of 9-phosphonoanthracene formed on silicon dioxide and pentacene has been studied using photoelectron spectroscopies. The semiconducting band gap of pentacene was found to be nested within that of the monolayer; the monolayer presents a significant energetic barrier to hole injection from a pentacene overlayer, but only a small to moderate barrier to electrons. Additionally, a scheme was devised that utilized self-limiting interlayer chemistry that deposited linear polyacenes in a controlled, layer-by-layer fashion to produce smooth multilayered constructions. Transistor devices were fabricated on these multilayer constructions, but failed to show any measurable performance, most likely due to chemical interactions of the linking groups or device geometry constraints. |
