The study of structural, optical and electrochromic properties of WO3:Co:Ni thin films deposited by spray pyrolysis

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In this study, WO3:Ni (0 at.%, 10 at.%, 20 at.%, and 30 at.%) and WO3:Co20 at.%: Ni (0%, 5%, 10%, 20%, and 30%) thin films were deposited on glass substrates by pyrolysis spray technique and then annealed at T = 500 °C. For the preparation of thin films, the initial solution of 0.1 M tungsten oxide and the precursors of nickel sulfate and 6-hydrate cobalt chloride were used. After preparing thin films, the effect of the presence of Ni impurities on the structural, morphology, optical and electrochromic properties of WO3:Ni and WO3:Co 20 at.%–Ni thin films was studied. The results of the X-ray diffraction showed that the structure of thin films after annealing has a polycrystalline structure with the combined phases of CoWO4, NiWO4, and W17O49 with monoclinic and hexagonal structures. As the amount of Ni impurities increases, the grain size of the WO3:Ni thin films increases and ranges from 8 to 36 nm. Also, for WO3 thin films:Co20 at.%:Ni, the CoWO4 and NiWO4 phases have been seen and the grain size was in the range from 35 to 39 nm. The voltametric cycle diagrams of WO3:Ni and WO3:Co20 at.%:Ni thin films showed that the electrochromic behavior improves with increasing nickel impurity. The morphology of the thin films was studied by field emission electron microscopy (FESEM). Also, the energy band gap of thin films with the addition of nickel and cobalt impurities was calculated using UV–Vis diagrams. The energy gap is decreased for both WO3:Ni and WO3:Co (20%):Ni thin films.