Effect of H₂Te₂O₆ and TeO₂ phases on structural and electrochromic properties of WO₃–TeO₂ nanostructured binary thin films

Abstract

In this paper, WO₃–TeO₂ binary thin films were deposited by spray pyrolysis. By changing the stoichiometry between WO₃ and TeO₂ in initial solution, three samples with various molar ratios were prepared including: (a) WO₃ (0.15 M)–TeO₂ (0.05 M), (b) WO₃ (0.1 M)–TeO₂ (0.1 M), and (c) WO₃ (0.05 M)–TeO₂ (0.15 M). Then, deposited binary thin films were characterized by XRD, FE-SEM, and I–V cyclic voltammetry to study electrochromic and coloration properties of the thin films before and after annealing at T = 500 °C. The XRD analysis of the samples shows the formation of the H₂Te₂O₆ phase with the preferred peak of (2 0 0), which increased with TeO₂ content after annealing. The WO₃–TeO₂ thin films were used as a binary combination of n-type (WO₃) and p-type (TeO₂) semiconductors to investigate the change in electrochromic properties before and after annealing at T = 500 °C. The results of the hysteresis I–V curve of the WO₃–TeO₂ binary combination showed that by increasing the H₂Te₂O₆ phase, the electron–hole exchange and, consequently, the coloration/bleaching process are improved. The area under the hysteresis curve varies in the range of 11.02 $\times {10}^{-3}$ to 88.32 $\times {10}^{-3}$ A.V. The diffusion coefficient also varies in the range of 1.96 $\times {10}^{-12}$ to 7.09 $\times {10}^{-12}$ cm²/s.

Graphical abstract