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MXene–organic semiconductor blends for high-mobility printed organic electronic devices

Subject Area Polymer Materials
Term from 2018 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 399684426
 
Final Report Year 2021

Final Report Abstract

Two-dimensional (2D) transition metal carbides or carbonitrides (MXenes) are one of the latest additions to the family of 2D materials. Due to their hydrophilicity, metallic conductivity (>6000 S cm-1) and tuning surface chemistry, MXenes show promise in a broad range of applications including energy storage, electromagnetic interference shielding, water purification, gas- and biosensors, lubrication, and catalysis. A novel approach to exploit excellent charge transport properties of MXenes was explored by the project MX-OSMOPED in which MXene flakes are used as additives to organic semiconductors (OSs). These materials are becoming increasingly popular as a staple ingredient of advanced flexible organic electronic devices, which can be fabricated by mass-production methods such as printing or spraying. However, OSs suffer from low charge carrier mobility which precludes their use in high-speed electronics. The consortium within the MX-OSMOPED project concentrated on research of the role of micron-size MXene flakes as boosters of charge carrier mobility in thin OS layers. Firstly, we have focused on the preparation of MXenes, which presents a hot topic. However, the mainstream synthetic methods rely on the chemical etching of MAX powders (e.g., Ti3AlC2) using hazardous HF or alike, leading to MXene sheets with fluorine termination and poor ambient stability in colloidal dispersions. Therefore, we have developed a completely new method that uses iodine etching in anhydrous acetonitrile followed by the delamination in HCl solution, and yields highly stable colloidal dispersions. Secondly, by adding MXenes to solutions of conjugated polymers we obtained blended layers, which exhibit significantly higher charge carrier mobilities than neat OS layers. Organic thin film transistors were realized on rigid and flexible substrates. Moreover, by functionalizing MXenes with didecyldimethyl ammonium bromide and blending it with a conjugated polymer we have realized layers with an increased hole and electron mobility. We have used these layers to fabricate logical AND and NAND gate devices on polyethylene terephthalate substrates. Our theoretical efforts based on density-functional theory calculation provide important insight into dependence of MXene work function on the surface composition. Calculations also show that conductivity in Ti3C2X2 and Nb4C3X2; X=O/OH MXenes is governed by the electron-LO-phonon coupling. MX-OSMOPED was also concentrated on multiscale characterization of charge transport properties, morphology, structure, chemical composition and electronic properties of thin layers of MXenes as well as blended OS/MXene layer. This resulted in a rich data library obtained by the state-of-the art characterization techniques.

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