Influence of applied voltage on optimal performance and durability of tungsten and vanadium oxide co-sputtered thin films for electrochromic applications

Highlights: • Effect of potential on durability of undoped and V doped WO₃ electrochromic films. • Enhanced electrochromic features including much reduced bleaching time. • More than 50% of transmission modulation between colored and bleached phases. In this research, tungsten and vanadium oxide co-sputtered thin films are evaluated for electrochromic properties based on the effects of applied cyclic voltages of −0.7 V, −1.0 V and −1.3 V for 9600 s. XRD patterns reveal the appearance of new peaks after completion of −1.3 V cycles, these peaks are not seen after lower voltage scans. SEM images also verify severely damaged morphologies. Chronoamperometry (CA) scan of −1.3 V shows a drastic reduction in current density value to as low as 32% for bleaching and 26% for coloring respectively. This is because of the lesser intercalation and de-intercalation as a result of damaged and disturbed orientation. Whereas the films with −1.0 V testing cycles shows the current density drop to 93% and 88% for bleaching and coloring respectively. A remarkable discovery in switching times of WO₃-V₂O₅ co-sputtered thin films is also achieved. Coloring and bleaching times are drastically reduced to 5.5 s and ‹1.3 s as compared to only WO₃ films having these values as 13.4 and 4.1 s respectively. We further investigates electrochromic films for different states and concentrations by XPS, electrochemical impedance spectroscopy (EIS) for electronic/ionic conductivity comparison and visible spectroscopy to verify optical modulation and calculation of some optical constants.