Macroscopic Janus Transition Metal Dichalcogenide Single Crystals With Enhanced Piezoelectricity and Carrier Mobility.

Abstract

Janus transition metal dichalcogenides (TMDCs), featuring intrinsic out-of-plane symmetry breaking and permanent electrical dipole moments, open novel avenues for atomic-scale symmetry control. However, the absence of high-quality, macroscopic single crystals has hindered the exploration of their predicted intriguing properties and practical applications. Herein, we demonstrate the synthesis of millimeter-scale single-crystal Janus TMDC monolayers, including MoSSe, WSSe, MoSeS, and WSeS. A combination of spectroscopic, microscopic, and electrical measurements confirms their exceptional crystallinity and spatial homogeneity over large areas. Notably, in contrast to conventional TMDC monolayers, the obtained Janus materials exhibit a strong out-of-plane piezoelectric response, with record experimental 𝑑₃₃ value of ∼2.06 pm/V for WSSe and ∼1.56 pm/V for MoSSe, representing an enhancement of over 15 times compared to previously reported experimental results. Moreover, field-effect transistors (FETs) based on Janus MoSSe achieve an exceptional carrier mobility of ∼13 cm²·V^-1·s^-1, along with a device yield of 95% across an array of 100 devices. This work provides a feasible pathway for the scalable production of high-quality, single-crystal Janus materials and highlights their promise for integration into next-generation electronic and optoelectronic devices.