Chemical bath deposition and characterization of electrochromic thin films of sodium vanadium bronzes

Thin yellow-orange films of sodium vanadium oxide bronzes have been prepared from a sodium–vanadium solution (1:1) at 75 °C and pH = 3. The composition, structure and morphology of the films have been studied by XRD, IR spectroscopy, TG and SEM–EDX analyses. It has been established that the prepared films are a phase mixture of hydrated NaV6O15 (predominant component) and Na1.1V3O7.9 with total water content of 10.58%.The sodium vanadium bronze thin films exhibit two-step electrochromism followed by color change from yellow-orange to green, and then from green to blue. The cyclic voltammetry measurements on the as-deposited and annealed vanadium bronze films reveal the existence of different oxidation/reduction vanadium sites which make these films suitable for electrochromic devices. The annealing of the films at 400 °C changes the composition, optical and electrochemical properties

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► We report a new chemical bath method for the deposition of vanadium bronze thin films.
► The films are phase mixture of NaV6O15 and Na1.1V3O7.9 with 10.58% lattice water.
► The as-deposited vanadium bronze films exhibit two-step electrochromism.
► They change their yellow-orange color to green and then from green to blue color.
► The method allows the preparation of films on substrates with low melting point.