Investigating the impact of different growth temperatures on the photoelectrochemical, and optical properties of zinc oxide nanorod for electrical and optoelectronic applications

In the current study, zinc oxide nanorod (ZnO NR) thin films were successfully synthesized using a simple and cost-effective hydrothermal method at various growth temperatures (100 °C, 110 °C, 120 °C, 130 °C, and 140 °C). The properties of the fabricated ZnO NR thin films were investigated using various analytical techniques, including X-ray diffraction (XRD), Mott–Schottky (MS) analysis, electrochemical impedance spectroscopy (EIS), photocurrent (PC) measurements, dark current–voltage (I–V) analysis,, photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), Raman spectroscopy, transmission electron microscopy (TEM), and UV–vis spectroscopy. XRD analysis confirmed that the ZnO NRs possess a hexagonal polycrystalline structure with a preferred orientation along the (002) plane. The average crystal size increased with rising growth temperature, which enhances the electron transport properties. SEM analysis revealed that the ZnO NRs grown at different temperatures exhibited various orientations,, forming flower-like structures while maintaining hexagonal morphology. PL analysis revealed two distinct emission peaks in the ZnO NR spectra, confirming their optical activity. Raman spectroscopy further confirmed the formation of ZnO nanorods with a wurtzite crystal structure. UV–vis spectroscopy showed an optical absorption edge at 382 nm, corresponding to the material’s band gap energy. Photocurrent (PC) measurements, electrochemical impedance spectroscopy (EIS), and Mott–Schottky (MS) analysis demonstrated enhanced electrical properties and confirmed the N-type conductivity of the ZnO NRs. Samples fabricated at 140 °C exhibited the highest carrier concentration (3.58 × 10²¹ cm⁻³) and the most negative flat-band potential (-0.95 V), indicating superior electronic performance. Our findings suggest that ZnO NRs thin films synthesized at 140 °C are promising candidates for optoelectronic applications, particularly as electron transport layers (ETLs) in solar cell devices.