Lithography-Free Electrical Contact Method for Optoelectronic and Flexible Devices Based on Mechanically Exfoliated 2D Materials

We report a tabletop, versatile and lithography-free electrical contacting method for two-dimensional (2D) materials and van der Waals (vdW) heterostructures based on silver paint micromanipulation (SPMM). Operated under an ambient optical microscope, this additive, room-temperature approach circumvents the chemical solvents and high temperatures associated with conventional cleanroom processing used in electrode fabrication. We validate the efficacy of this strategy by fabricating devices based on high-quality mechanically exfoliated thin flakes on both rigid SiO2/Si and flexible polycarbonate substrates. On rigid supports, SPMM-contact multilayer graphene devices exhibit linear Ohmic behavior with excellent environmental stability over multiple days and an ambipolar field effect. Gate-tunable multilayer graphene/few-layer MoS2/multilayer graphene field-effect transistors demonstrate n-type gating with a two-terminal carrier mobility of 60 cm2Vs and time-resolved photoresponse under 660 nm and 415 nm illumination, with responsivities as high as 10 A/W at the lowest incident powers. The SPMM method can also be carried out on flexible polymeric substrates such as polycarbonate, which is notoriously difficult to work with in microfabrication. We demonstrate a flexible multilayer graphene device that functions as highly responsive piezoresistive strain sensors at low deformations with a gauge factor of 50. Finally, a fully integrated flexible vdW photodetector is tested up to 1.2% uniaxial tensile strain. Despite experiencing local micro-fracturing of the MoS2 channel, the localized vdW junctions maintain robust charge collection, yielding photodetecting capabilities under tensile strain. This simple and cost-effective electrical contacting technique establishes a highly accessible platform for the rapid prototyping and mechanical testing of next-generation optoelectronics and flexible electronics based on 2D materials and vdW heterostructures.