Surface, optical and electrochemical performance of indium-doped ZnO/WO 3 nano-composite thin films

Great demand on replacing emission and pollution-free materials for energy storage by traditional fossil fuels has led to investigating of high-performance electrochromic materials. Nano-composite for electrochromic device may be a good choice. In this paper, stack-structured indium-doped ZnO/WO3 nano-composite thin films were deposited on glass, indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO)-coated glass substrates, respectively. Surface, optical and electrochromic (EC) performance of the prepared nano-composite films has been investigated. Electrochromic impedance spectroscopy (EIS), cyclic voltammetry, repeating chronoamperometry (CA) and chronocoulometry (CC) measurements were taken. The Raman spectroscopy measurement shows that high-intensity peaks are related to ZnO wurtzite structure for all substrates. In the CA measurement, the rate of Li+ transfer between surface and electrolyte was faster for films coated onto ITO substrate. In addition, the intercalation/deintercalation of Li+ was obviously found faster for films onto ITO substrate due to roughness, structure differences than the other sample. As an advantage of our nano-composite material, the absence of current decay in the both coloration and bleaching stages has proved superiority and stability of films as well as indium contribution. The reversibility of stack-structured InZnO/WO3 nano-composite films was computed as 30 and 50% for the film with ITO and FTO substrates. The highest coloration efficiency value has calculated as 80 and 69 cm2/C for nano-composite thin films deposited onto FTO substrate @ 632 and 550 nm, respectively. Warburg impedance element values were determined from the equivalent circuit model. Also, calculated charges were determined for bleaching or coloring process for all films.