Two-Dimensional Vanadium-Doped ZnO Nanosheet-Based Flexible Direct Current Nanogenerator

Here, we report the synthesis of lead-free single-crystalline two-dimensional (2D) vanadium(V)-doped Zn0 nanosheets (NSs) and their application for high-performance flexible direct current (DC) power piezoelectric nanogenerators (NGs). The vertically aligned Zn0 nanorods (NRs) converted to NS networks by V doping. Piezoresponse force microscopy studies reveal that vertical V-doped Zn0 NS exhibit typical ferroelectricity with clear phase loops, butterfly, and well-defined hysteresis loops with a piezoelectric charge coefficient of up to 4 pm/V, even in 2D nanostructures. From pristine In NR-based NGs, alternating current (AC)-type output current was observed, while from V-doped Zn0 NS-based NGs, a DC-type output current density of up to 1.0 mu Acm(-2) was surprisingly obtained under the same vertical compressive force. The growth mechanism, ferroelectric behavior, charge inverted phenomena, and high piezoelectric output performance observed from the V-doped Zn0 NS are discussed in terms of the formation of an ionic layer of [V(0H)(4)(-)], permanent electric dipole, and the doping-induced resistive behavior of Zn0 NS.