Piezoelectric nanogenerators (PENGs) are considered as attractive devices to harvest and supply energy to low-power autonomous systems. The use of ZnO nanowires (NWs) in those devices is very promising as they combine a strong piezoelectric response and the possibility to be grown by low-cost and low temperature techniques such as chemical bath deposition (CBD). In the widely used vertically integrated architecture, the bottom electrode plays a crucial role as it acts as a nucleation layer for the ZnO NW growth. Au electrodes are typically used as they result in the formation of relatively dense arrays of NWs while keeping a Schottky contact at the interface, which is essential to the device performances. Another critical aspect to efficiently integrate ZnO NWs in PENGs is to be able to precisely control their morphological and electrical properties, in order to have high aspect ratios, good verticality, and high resistivity. In this context, several studies have been performed, focusing respectively on i) the elucidation of the nucleation mechanisms of ZnO NWs onto Au seed layers ii) the modelisation of the elongation of the NWs using a predictive approach, iii) the use of chemical additives during CBD including Cu nitrate to compensate for the high electrical conductivity of the NWs, and iv) the control of the NW morphology through selective area growth. These results provide key elements to achieve the fabrication of highly efficient ZnO NWs, which should be taken into account for their subsequent integration into PENGs.
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