Gate‐Dielectric Surface Engineering With Fluorinated Monolayers: Minimizing Contact Resistance and Nonidealities in OFETs

Organic field‐effect transistors (OFETs) hold great potential for flexible, large‐area electronics, but face challenges related to hysteresis in the transfer characteristics, contact resistance, and charge trapping. This study examines the growth and electrical properties of 2‐decyl‐7‐phenyl[1]benzothieno[3,2‐b][1]benzothiophene (Ph‐BTBT‐10) organic‐semiconductor films on Al2O3 as gate dielectric, focusing on the effects of surface functionalization with a self‐assembled monolayer (SAM) of either a non‐fluorinated or a more or less strongly fluorinated phosphonic acid. This functionalization of the gate dielectric surface is found not to significantly affect the structural organization of Ph‐BTBT‐10 thin films grown at room temperature. Thin films grown at room temperature exhibit a single‐layer lamella with a step height of 26.7 Å, although there is evidence of a bilayer arrangement at the semiconductor‐dielectric interface. Remarkably, the use of Al2O3 functionalized with a fluorinated SAM leads to significant improvements in OFET performance, including near‐zero threshold voltages, reduced hysteresis, reduced contact resistance, and more ideal electrical characteristics compared to bare Al2O3. This work highlights the significant yet non‐trivial benefits of gate‐dielectric surface functionalization in reducing contact resistance and mitigating non‐ideal behaviors in OFETs, offering an alternative to traditional approaches like contact doping or functionalization of the source/drain contacts in bottom‐contact organic thin‐film transistors (TFTs).