Tunable piezoelectric nanogenerators using flexoelectricity of well-ordered hollow 2D MoS2 shells arrays for energy harvesting

Highlights: • Novel piezoelectric nanogenerators (PNGs) consisting of 2D piezoelectric MoS₂ shells were fabricated. • The effect of the MoS₂ shell size on power generation characteristics was investigated. • The output voltage of 1.2 V was measured under the pressure of 4.2 kPa by using MoS₂ shell-based PNGs. • High-power generation properties and nonlinear hysteresis behavior were observed for the micrometer-scale MoS₂ shells. -- Abstract: Piezoelectric two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS₂) have recently attracted significant attention owing to their applicability for fabrication of flexible power generators. In this study, novel piezoelectric nanogenerators (PNGs) consisting of 2D piezoelectric MoS₂ shells are fabricated where an Al₂O₃ thin layer deposited on the surface of polystyrene (PS) beads is used to avoid collapse of the spherical MoS₂ shells under the high growth temperature. In addition, the MoS₂ shell size is controlled by adjusting the PS bead size and the effects of the MoS₂ shell size on power generation characteristics are investigated. Our PNG based on the piezoelectric MoS₂ shells produces a peak output voltage of approximately 1.2 V at a pressure of 4.2 kPa. The minimum pressure for power generation by tapping is 0.3 kPa. This novel method is very promising for development of the next-generation PNGs based on 2D semiconductor piezoelectric materials.