Impact of switching potential and time on the optical performance of Nickel/Tungsten oxide-based electrochromic devices

Abstract

This study investigates the effects of switching potential and switching time on the optical performance of electrochromic devices (ECDs). Full-cell ECDs were assembled into sandwich-type cells, with nickel hydroxide (NiO_xH_y) as the anodic and tungsten oxide (WO₃) as the cathodic layers. A conductive layer of 0.5 M lithium perchlorate in propylene carbonate was used, with all layers positioned between fluorine-doped tin oxide-coated glass. NiO_xH_y and WO₃ thin films were deposited via reactive direct current magnetron sputtering under optimized conditions. The optical performance was evaluated under switching potentials (± 0.5 to ± 2.5 V) and switching times (5 to 35 s). Optimal switching conditions were achieved at ± 2.0 V and 30 s, yielding a visible transmittance change (Δ%T_vis) of 63.2%, a transmittance change at 550 nm (Δ%T₅₅₀) of 65.6%, a contrast ratio of 7.02, and an optical density change of 0.85. Under these conditions, either or both NiO_xH_y and WO₃ layers approached saturation, with nearly all sites occupied by the injected Li⁺ ions. They also exhibited excellent optical memory, with %T₅₅₀ increasing by only 2.9% over 6,200 s. Stable performance was observed at ± 1.5 V and 20 s, with Δ%T₅₅₀ maintained between 44 and 49% for over 12,600 s. These findings highlight the importance of optimizing switching potential and time for enhanced ECD performance. The results are particularly relevant for smart windows, energy-efficient buildings, and automotive glass. Fast switching reduces glare in windshields, improving driving safety, while moderate switching in buildings enhances energy efficiency and occupant comfort.