Electrochromic properties of sputter-grown Nb18W16O93 thin films

Large-area electrochromic films with high stability under high temperatures and humid conditions are essential for the commercialization of smart windows. In this paper, we introduce a new cathodic coloration Nb18W16O93 thin film produced using sputtering that exhibits excellent electrochromic modulation, superior chemical stability, and cyclic durability owing to its stable host structure for ion intercalation. The electrochemical properties of the as-grown Nb18W16O93 thin films, including charge density and transmittance modulation, were enhanced with increasing deposition temperatures. The annealed Nb18W16O93 thin films (grown at room temperature) exhibited comparable electrochromic performances to films grown at high temperatures. Electrochromic devices composed of annealed and high-temperature-grown Nb18W16O93 thin films exhibited excellent durability and nearly identical transmittance modulation, even after 10,000 test cycles. Furthermore, degradation of the surface morphology of the Nb18W16O93 thin films after etching in heated water was alleviated, suggesting high stability under hot and humid conditions, whereas the flat surface of the room-temperature-grown WO3 thin films degraded significantly.