Enhancing charge carrier transport in solution-processed organic field-effect transistors by control of fluid dynamics

Abstract

Meniscus-guided coating (MGC) is a promising technique for depositing highly crystalline organic semiconductor (OSC) thin films. MGC enables unidirectional crystal growth of OSC, which is advantageous when used as an active layer in organic field effect transistors (OFETs). This is because efficient charge transport in OFETs is also unidirectional, from source to drain. In this thesis, firstly, the effect of casting speed, concentration and their combined relation on the crystallization and the morphology of OSC have been investigated. The resulting morphologies were electrically evaluated in OFETs and an optimal processing window for efficient charge transport was defined. Numerical simulations of both the fluid dynamics in the coating bead and the crystallization were used to explain the morphological transitions. Secondly, the role of meniscus shape on the crystallization of OSC was investigated to determine an ideal coating height between the substrate and the coating head that also provides an enhanced charge transport in OFETs. The fluid dynamics simulation in the coating bead was used to explain the morphological transitions depending on the coating height and the casting speed. Thirdly, precise allocation of OSC during MGC was investigated by controlling the substrate wettability via self-assembled monolayer. In particular, future of OFET circuitry relies on minimizing the crosstalk between neighbor devices. Precisely positioning OSC during MGC offers a solution for reducing the crosstalk. Finally, the findings in the thesis have the potential to upscale the MGC techniques, playing a significant role in understanding the crystallization behavior of OSCs.