High-Performance Electromechanical Power Generation of Lithography-Free Large-Scale MoS₂ Monolayer Film Harvesters

Recently, two-dimensional (2D) transition metal dichalcogenide (TMD) materials have been recognized to possess high piezoelectricity due to the lack of inversion symmetry. Because of the limited availability of large-area MoS₂ monolayer, however, the energy-harvesting performance of 2D TMD materials has not been fully understood. Only single-crystalline TMD with dimensions on the order of a few micrometers has been investigated as an electromechanical energy harvesting device so far. Here, we introduce a defect-controlled synthesis of centimeter-scale polycrystalline MoS₂ monolayers with the assistance of a Na₂S film. Beyond the known effect of Na as a growth promoter, extra sulfur supplied by the Na₂S critically passivates sulfur vacancies, enabling the preparation of a high-quality monolayer film. As a result, a millimeter-scale energy harvester with nonconventional interdigitated electrodes, which was fabricated without e-beam lithography, exhibited the unexpectedly high piezoelectric energy harvesting performance of ~402.9 mV output voltage and ~41.2 nA output current under a bending strain of ~0.47 %. These values are ~20 and ~1,370 times greater, respectively, than the reported best values for single-crystal 2D TMD materials.