Impact of zinc concentration and annealing temperature on the structural, optical, and photoelectrochemical properties of nickel oxide thin films synthesized by electrodeposition method

Abstract

In this study, Zinc (Zn)- doped nickel oxide (NiO) thin films were fabricated via the electrodeposition method. The synthesized films were created with different concentrations of Zn (2 %, 4 %, 6 %, and 8 %) after that annealed at two different temperatures (300 °C and 500 °C). The prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RAM), UV–vis spectrophotometry, photocurrent (PC), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), Energy-Dispersive X-ray spectroscopy (EDX), photocurrent (PC), and Mott-Schottky (MS) analysis. XRD patterns indicate that Zn: NiO thin films have a cubic phase, with the (111) direction as the preferred orientation. Various structural parameters such as dislocation density, stacking fault, lattice strain, and crystallite size have been determined. The presence of Zn doping in NiO has been confirmed by EDX analysis. The EDX mapping of elements revealed the uniform distribution of Ni, Zn, and O in the sample. The optical transmittance and absorbance were analyzed using a UV–vis spectrophotometer. The lowest transmittance values were found for 8 % Zn: NiO thin films annealed at 300 °C and 500 °C. The absorption edge corresponding to pure NiO-300 °C and NiO-500 °C has been observed at 300 and 320 nm, respectively. The band gap energy (Eg) decreased to 3.88 eV for 8 %Zn: NiO (300 °C) and 3.71 eV for 8 %Zn: NiO (500 °C). The Raman analysis showed three distinct peaks at 590 cm−1, 705 cm−1, and 1172 cm−1, which correspond to the vibration of Ni—O bonds. The SEM results indicated that increasing the doping concentration and annealing temperature resulted in larger grain sizes in the manufactured samples. Furthermore, the PL spectra analysis of the synthesized films revealed two distinct emission peaks at around 400 and 490 nm. PC analysis confirmed the p-type conductivity of manufactured arrays. From MS measurements, the highest carrier concentration (NA) values of 8.81×1018 cm−3 and 9.41×1019 cm−3 were obtained for 8 %Zn: NiO (300 °C) and 8 %Zn: NiO (500 °C), respectively. EIS analysis confirmed the highest conductivity and enhanced electrochemical activity for 6 % Zn: NiO (500 °C) and 8 % Zn: NiO (300 °C). These results suggest that Zn-doped NiO is suitable for optoelectronic applications.