Enhancement of long-term cyclic durability of electrochromic WO3 thin films via Ta2O5 passivation

In this study, we investigated the degradation mechanisms affecting the electrochromic performance of sputtered WO₃ thin films during cyclic testing in a Li-based liquid electrolyte. We introduced a chemically and thermally stable Ta₂O₅ passivation layer to enhance the sustainability and durability of electrochromic devices. Although the stacking of the Ta₂O₅ layer onto the WO₃ thin film slightly reduced the current density, transmittance modulation, coloration efficiency, and switching speed, it significantly improved the long-term cyclic durability by preventing crystallization and the morphological degradation of WO₃ in half cells. An electrochromic device comprising the 50 nm-thick Ta₂O₅-passivated WO₃ thin film exhibited excellent durability and maintained nearly identical transmittance modulation even after 8000 cycles at room temperature. The current density of the electrochemical device with the nonpassivated WO₃ film decreased, whereas that of the device with the passivated film remained stable when tested at 50 °C. Furthermore, the Ta₂O₅ passivation layer suppressed surface morphology degradation in heated water. This study presents a promising approach for fabricating electrochromic devices with superior long-term cyclic durability in Li-based electrolytes as well as in high-temperature and high-humidity environments by using a Ta₂O₅ passivation layer. •Degradation mechanisms of WO₃ thin films during cyclic testing were investigated.•Ta₂O₅ passivation layer was introduced to enhance the sustainability and durability of WO3.•Electrochromic full cell comprising Ta₂O₅-passivated WO₃ exhibited excellent durability.•Ta₂O₅ passivation layer suppressed surface morphology degradation in heated water.