Performance Optimization of Vertical Nanowirebased Piezoelectric Nanogenerators

is among the most abundant and reliable energy sources in our daily life, regardless of weather or temperature conditions, in contrast with solar [ 2 ] and thermoelectric energies. [ 3 ] New materials, structures and technologies have been subjects of active research and development. [ 4–7 ] Likewise, at the nanoscale, energy harvesting nanotechnologies based on the piezoelectric effect have been developed to harvest small-scale and irregular sources of mechanical energy present in our living environment, such as air fl ow [ 8 ] or heart beating, [ 9 ] among others. Moreover, due to their small size, energy harvesting devices can be effectively integrated with other nano/micro scale functional devices to build self-powered systems. [ 10 ] Thus, over the past few years, semiconductor piezoelectric nanowires (piezo NWs) have been extensively investigated as the building blocks of piezoelectric mechanical energy harvesters called nanogenerators (NG) [ 11–13 ] as well as for sensors. [ 12,14–17 ]