Tailored interfaces for self-patterning organic thin-film transistors

Patterning organic thin-film transistors (OTFTs) is critical in achieving high electronic performance and low power consumption. We report on a high-yield, low-complexity patterning method based on exploiting the strong tendency of halogen-substituted organic semiconductors to crystallize along chemically tailored interfaces. We demonstrate that the organic semiconductor molecules self-align on the contacts, when the halogen-halogen interaction is allowed by the chemical structures and conformations of the self-assembled monolayer and organic semiconductor. The ordered films exhibit high mobilities and constrain the current paths. The regions surrounding the devices, where the interaction is inhibited, consist of randomly oriented molecules, exhibiting high-resistivity and electrically insulating neighboring devices. To identify the role of F-F interactions in the development of crystalline order, we investigate OTFTs fabricated on mono-fluorinated benzene thiol treated contacts, which allows us to isolate the interactions between the F originating from the organic semiconductor and the F in each position on the benzene ring of the thiol, and to selectively study the role of each interaction. Combining the results obtained from quantitative grazing incidence X-ray diffraction and Kelvin probe measurements, we show that the surface treatments induce structural changes in the films, but also alter the injection picture as a result of work function shifts that they introduce. We show that both effects yield variations in the field-effect transistor characteristics, and we are able to tune the field-effect mobility more than two orders of magnitude in the same material.