Regulating the growth of WO3 thin films using ammonium acetate as structure directing agent

Abstract

The optimization of morphology and structure of tungsten trioxide (WO3) needs to be performed to target some specific applications. In fields such as electrochromics and sensing, the study of electrochemical reaction kinetics is important as it defines the rate of reaction occurring on the WO3 surface. In the present study, WO3 thin films are grown on fluorine-doped tin oxide (FTO) glass by in-situ hydrothermal technique. To regulate the growth of the WO3 layer employing the hydrothermal method, ammonium acetate has been used as a capping agent (CA) and its molar ratio for tungsten, i.e., CA/W, was varied from 0 to 6. Cyclic voltammetry (CV) revealed that the thin film prepared with CA/W of 4 has improved Li+ ions intercalation/deintercalation which leads to fast reaction kinetics. Better electrochemical reaction kinetics in WO3 thin film with a CA/W ratio of 4 compared with the samples having CA/W of 0 and 2 is ascribed to its improved morphology and phase. X-ray diffraction and scanning electron microscopy analysis showed negligible thin film growth with a CA/W ratio of 6. Overall, WO3 thin film with a CA/W ratio of 4 showed excellent performance, making it a good candidate for electrochromics or other related applications.