Large-Area Vacuum-Filtrated 2D MXene (Ti₃C₂T_x) Contacts for Flexible Monolayer Organic Field-Effect Transistors

High-quality monolayer-based organic field-effect transistors (OFETs) have shown great progress to serve as the building blocks of next-generation flexible electronics. Traditional metal evaporation could cause thermal damage on the organic active layer, thus limiting their electrical performance. MXene (Ti₃C₂T_x), a two-dimensional transition metal carbides and nitrides, have high conductivity and compatibility with low-cost solution-processed electrode deposition without inducing thermal damage. By vacuum-filtrated assistance, MXene can achieve lower electrical resistivity due to a tighter layer-by-layer structure compared with other deposition methods. The MXene layer can be patterned by a conformal mask that attached to the printing stamp directly and form a high-resolution electrodes array by direct transfer without a lift-off process. The patterning, deposition of MXene, and subsequent electrodes-transfer are all chemical-free processes, which avoid the chemical damage of the organic active layer and make them extremely suitable for the large-area mass production.<br/>In this work, Meniscus-guided coating is used to grow 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) organic semiconductor monolayer on gate dielectric as the active channel, then transferred vacuum-filtrated MXene electrodes (15 μm channel length, which cannot be achieved without photolithography-patterning in previous study) to form the bottom-gate top-contact structure. The Ti₃C₂T_x nanoflakes alignment was improved during the transfer process from cross-sectional SEM and XRD characterization. A subthreshold swing of ~72 mV/decade and field-effect mobility of ~4.2 cm²/V/s were achieved on high-κ dielectric HfO₂ by decent contact of HfO₂/C₁₀-DNTT/MXene interface, and the I_ON/I_OFF ratio reached ~10⁸. We further fabricated OFETs on an ultra-thin conformal flexible substrate and realized uniform electrical performance. Compared with other MXene contacts, our current work shows comparable mobility with the shortest channel length, which expanded the application range of low-dimensional conductors as the patterning electrodes. We believe this processing approach of the 2D carbon-based MXene is extremely suitable for the layer-by-layer assembly of the next-generation large-area flexible electronics.