Ultrahigh Photoresponse in Double-Strained Monolayer MoS₂ Films with Domain Adjustments

Strain engineering of two-dimensional (2D) transition metal chalcogenides, which aims primarily to tune the bandgap of a semiconductor with modulations of lattice strain, has emerged as a practical way to enhance their electrical and optical properties. Herein, we propose a flexible optoelectronic device based on large-scale monolayer MoS₂ film optimized with maximum tensile strain (via double strain engineering) and domain orientation (relative to the parallel electrodes). Controllable in situ strain spanning a compressive-to-tensile strain range of ±1.27% was applied to the domain-aligned MoS₂ monolayer as the 2D layer were transferred onto a polymer substrate bent concavely or convexly. To extend the benefit by the in situ tensile strain, we applied second strain by post-bending the resulting photodetectors to produce the final tensile strain of +1.80%. Another key achievement is the adjustment of electrode positions depending on the domain orientation to produce maximum polarization field with minimum energy bandgap. As an optimal light-sensing performance, the maximum photoresponsivity of 1142 A W^-1 was attained for the double-strained sample, representing a ~130-fold increase relative to that for the unstrained one. This value corresponds to the highest value compared to those for any reported 2D-material-based visible photodetectors.