Characteristics of Piezoelectric Nanogenerators Based on Cr-Doped ZnO Nanorods for NO Gas Sensing

In this investigation, chromium-doped ZnO nanorod (NR) arrays were grown on ITO/PET substrates using a hydrothermal method. Subsequently, self-powered gas sensors based on piezoelectric nanogenerators (PENGs) were fabricated and characterized. The chromium doping concentration in the ZnO NRs was estimated to be 0.26 at% measured by energy-dispersive X-ray spectroscopy (EDS). Additionally, transmission electron microscope (TEM) results revealed that the as-grown ZnO NRs exhibited a hexagonal wurtzite structure. During the device fabrication process, the top electrode patterns were defined through laser engraving, and silver thin films were deposited on the ITO-PET substrates using the RF-sputtering technique. The piezoelectric nanogenerators (PENGs) were composed of the silver top electrodes and the bottom of chromium-doped ZnO NRs. A specialized impacting system has been employed to drive the fabricated PENGs with a fixed frequency. By the doping concentration of 0.5 mM chromium nitrate, it can be found that the output voltages of the PENG were measured at 1.447 V and 2.323 V respectively, without and with introducing 100 ppm of nitric oxide (NO). Clearly, such a PENG device exhibits an excellent self-powered characteristic and demonstrates a good sensitivity to NO gas.