Insight into Co concentrations effect on the structural, optical, and photoelectrochemical properties of ZnO rod arrays for optoelectronic applications

Abstract

Using a cost-effective and time-efficient chemical bath deposition (CBD) approach, zinc oxide (ZnO) nanorod doped with various cobalt concentrations ranged from 2% to 8% have been synthesized on ITO substrates. Different methods: including X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy, photoluminescence spectrometry (PL), current-voltage (I–V), and photocurrent were employed to investigate the structural, morphological, optical, and photoelectrochemical. XRD results confirmed that rod arrays formed in hexagonal structure with favorite orientated in (002) plane. SEM images revealed at all doping levels that there were hexagonally shaped nanorods of ZnO, which agreed with XRD measurements. UV–visible measurements indicate an absorption band edge at 381 nm which, is mainly recognized as a characteristic direct bandgap for ZnO arrays. In doped samples; other absorption band edges observed at 562, 605, and 654 nm correspond to the d-d transformation of Co2+ ions. The calculated value of band gap energy (Eg) reduced with the increasing of the Co dopant ions. The PL spectra exposed near band edge emission and defect-related visible emission band. Photocurrent analysis showed that the fabricated arrays have an n-type conductivity. Moreover, the photocurrent enhancement with increasing doping concentration where 6% Co ions have the highest value. The results show that Co doped ZnO nanorods are talented candidates for solar cells and biosensors applications.