Since the development of the first Zinc Oxide Nanowire (ZnO NW) based piezoelectric nanogenerator (PNG) by Z. Wang and J. Song in 2006,^[1] the energy harvesting field has been revolutionized owing to the ability of ZnO NWs to convert mechanical energy into electrical energy. Nowadays, ZnO NW arrays are found to be integrated into electronic devices for efficient and sustainable sources.

This thesis focuses on enhancing the performance of PNGs based on vertically integrated ZnO NW arrays grown in an aqueous medium by chemical bath deposition (CBD). The latter, a green chemistry process, offers potential industrial viability at a large scale for the growth of ZnO NWs at low temperatures (60 – 100 °C) on flexible and rigid substrates. However, the unintentional formation of mainly hydrogen-related defects in ZnO NWs grown by CBD results in a high density of free electrons in their bulk (5 × 10¹⁷ – 1.5 × 10¹⁹ cm^-3),^[2] leading to the detrimental screening effect of piezoelectric potential. This screening effect originates from electrostatic interactions between free electrons and the positive poles created within bent ZnO NWs.^[3]

This thesis explores distinct approaches for boosting the energy conversion efficiency of PNGs based on ZnO NWs grown by CBD. The first strategy involves developing electrically resistive ZnO NWs through compensatory Cu-doping and thermal annealing processes, followed by their integration into PNGs to evaluate their piezoelectric properties. The second approach modifies the surface properties of ZnO NWs by coating them with Alumina (Al₂O₃) shell and parylene-C layers, assessing their effects on piezoelectric properties through PNG characterizations. Finally, the thesis examines the synthesis of ZnO NWs on Aluminum-doped ZnO and gold seed layers, aiming to create, respectively, Ohmic and Schottky interfaces with ZnO NWs for piezoelectric applications.

This fully experimental work provides promising ways to enhance ZnO NW-based PNGs, offering potential possibilities for sustainable energy harvesting applications.

[1] Z. L. Wang, J. Song, Science (80-. ). 2006, 312, 242–246.

[2] A. J. L. Lopez Garcia, M. Mouis, V. Consonni, G. Ardila, Nanomaterials 2021, 11, 941.

[3] R. K. Pandey, J. Dutta, S. Brahma, B. Rao, C. P. Liu, JPhys Mater. 2021, 4, DOI 10.1088/2515-7639/ac130a.