High-Performance Organic Field-Effect Transistors Based on a Self-Assembled Polar Dielectric Monolayer

A high-performance bottom-gate organic field-effect transistor (OFET) is proposed and demonstrated based on a polymer-based self-assembled monolayer (SAM) of poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3HT-COOH) as the gate insulator. The P3HT-COOH molecules have a significant portion of side chains with carboxylic acid groups anchored on the ITO gate electrode, resulting in an ordered arrangement and the formation of a polar monolayer. The fabricated OFETs based on the P3HT active channel exhibit outstanding electrical properties, including a high field-effect mobility (7.21 × 10^–2 cm² V^–1 s^–1), high on/off ratios (∼10⁴), reduced trap density (5.36 × 10¹¹ cm^–2), extremely low threshold voltage (−0.2 V), and low subthreshold swing (113 mV decay^–1). Particularly, the threshold voltage of the studied devices sets the lowest record compared to previous studies. The exceptionally good performance can be attributed to the fact that in addition to the inherent polar field, the ultrathin SAM dielectric with periodic packing enables a much smoother surface texture and simultaneously promotes polymer chain alignment of the active channel with enhanced crystallinity, which highlights the role of the P3HT-COOH polar monolayer in optimizing the structure and electronic properties of the active channel. Thus, those organic thin-film transistors incorporating polar SAMs as dielectrics offer a promising strategy for enhancing performance and expanding applications in low-power electronic technologies.