Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability

Highlights: • Long-time durability is vital for electrochromic smart windows. • Potentiostatic pretreatment of WO₃ sputtered films enhances durability • The pretreated WO₃ films maintain good electrochromic performance under harsh electrochemical cycling. - Abstract: Electrochromic WO₃ thin films have important applications in devices such as smart windows for energy-efficient buildings. Long-term electrochemical cycling durability of these films is essential and challenging. Here we investigate reactively sputter-deposited WO₃ films, backed by indium–tin oxide layers and immersed in electrolytes of LiClO₄ in propylene carbonate, and demonstrate unprecedented electrochemical cycling durability after straight-forward electrochemical pretreatments by the application of a voltage of 6 V vs. Li/Li⁺ for several hours.