Effects of hydrothermal temperature and coloring/bleaching voltage on the electrochromic performance of WO3

Tungsten oxide (WO₃) is a promising electrochromic material for energy-efficient smart windows, yet its commercial viability is hindered by the inherent trade-off between optical contrast (ΔT) and cycling stability. Herein, by systematically tuning hydrothermal temperatures (120–180°C), the ΔT of WO₃ films reached 82.52 % and 74.6 % retention after 1000 cycles. XPS analysis reveals W⁵⁺/W⁶⁺ redox dynamics under varying voltages (-1.5 to +1.5 V), demonstrating that excessive Li⁺ injection at −1.5 V induces lattice distortion. The different coloring/bleaching voltage identified that −1.2 V was the optimal voltage balancing ΔT (73.1 %) and cycling stability (74.41 % retention after 1000 cycles), which aligns with the national standard for smart window durability. This study provides a scalable synthesis strategy to guide the design of next-generation electrochromic materials.