Solvent-Resistant Organic Transistors and Liquid-Phase Sensors Based on Cross-Linked Semiconducting Layers

Abstract

Sensor applications based on organic field-effect transistor (OFET) platforms have attracted increasing interest because of their advantages such as light-weight, low-cost, and flexibility. Various OFET-based sensors have been demonstrated for sensing a various types of stimuli including chemical/biological species, pressure, and light. Nonetheless, there is a substantial drawback for practical applications of OFET-based sensors; the poor resistance of organic semiconductors in common organic solvents. Although OFET-based sensors for detecting vaporized organic solvents and aqueous-phase analytes have been reported, the direct detection of the liquid-phase analytes, i.e., organic solvents, has not yet been demonstrated. Herein, we demonstrate solvent-resistant OFET-based sensors with high sensitivity and selectivity using photo-cross-linkable organic semiconductor, azide-functionalized poly(3-hexylthiophene) (P3HT) copolymers. P3HT-azide copolymers have been introduced to enhance the chemical resistance of semiconducting layer in common organic solvents. Moreover, calixarene derivatives have been adopted on the top of the semiconducting layer to increase the sensitivity and selectivity of the sensors toward target analytes. Various liquid-phase organic solvents were tested using solvent-resistant OFET-based sensors and well-defined sensing results were obtained owing to the combined effects between the liquid-phase analytes and sensors; the interactions between calixarene/analytes and the enhanced electron-withdrawing/donating characteristics depending on the liquid-phase analytes. The OFET-based sensors showed low detection limits (≈ 1 vol %) toward a complex solutions of organic solvents. The experimental results agreed with the computational study at the atomistic level via both molecular dynamics (MD) and density functional theory (DFT). The sensing demonstration for various pH solutions has also been conducted. Furthermore, flexible OFET-based sensors have been fabricated with a polymer dielectric and a flexible substrate. This report provides a novel approach for the fabrication of OFET-based sensors that can detect liquid-phase organic solvents and substantially expands possibility of their practical use.