Hydrophobic nickel doped Co₃O₄ sprayed thin films as solar absorber

As part of this study, we elaborated and characterized samples of thin layers of cobalt oxide, doping them with different concentrations of nickel (2%, 4% and 6%). These films were deposited on ordinary glass substrates at a temperature of 400 °C, with a deposition time of 5 min, using the spray pyrolysis technique. The main objective of this research was to explore the influence of nickel doping on the physical properties of cobalt oxide. The results obtained by Raman spectroscopy confirmed the presence of Co⁺² cations located in tetrahedral sites and Co⁺³ in octahedral sites, thus validating the spinel-type cubic structure. Morphological analysis revealed that the incorporation of nickel into the Co₃O₄ thin films, synthesized by spray pyrolysis, resulted in a significant transformation of the porous surface morphology. This transformation resulted in the transition from a porous structure to a dense and uniform configuration, characterized by nanoflower grains. Analyzes by EDS spectrometry revealed peaks associated with the elements Co and O, thus confirming the composition of the films. An improvement in the durability and overall performance of the solar device in humid environments by obtaining the hydrophobic character (CA = 99°) for the Co₃O₄/6%Ni film. The transmittance decreased with increased as a function of Ni concentration. Optical studies show direct band gaps E_g1 and E_g2 varying between 1.41 and 1.3 eV and between 2.09 and 1.99 eV respectively. Notably, the electrical resistivity experienced a significant decrease from 28.39 to 0.178 Ω.cm for the undoped and 2% Ni-doped films, respectively. However, for Ni concentrations ≥ 4%, the electrical resistivity increased from 3.47 to 10.2 Ω cm.