Solvothermal growth of Nb2O5 films on FTO coated glasses and their electrochromic properties

We have demonstrated that niobium pentoxide (Nb2O5) films can be directly grown on fluorine-doped tin oxides (FTO) coated glasses by a simple solvothermal process. The effect of ethanol concentration in precursor solution on the structure and electrochromic properties of Nb2O5 films was investigated. The XRD patterns show that the as-grown Nb2O5 films are polycrystalline. When the ethanol volume percentage in precursor solution is 30% or 40%, the prepared Nb2O5 films display [040] preferred orientation and reticular structure. The research results on the electrochromic properties reveal that the Nb2O5 film prepared with an ethanol volume percentage of 30% presents the largest optical modulation of 69.0% at the wavelength of 800 nm. For the film, fast switching from colorless state to blue-black state (coloration time: 10.7 s) and then to colorless state (bleaching time: 0.7 s) were observed. The coloration efficiency reaches 85.9 cm2 C−1. The results of cyclic voltammetry tests further demonstrate that the electrochromic properties of the film prepared with an ethanol volume percentage of 30% remain stable within 400 cycles.