Influence of Ta2O5 electrolyte thickness on the electro-optical performance of all-solid-state electrochromic devices

In this study, inorganic all-solid-state electrochromic devices (ECDs) with the structure of glass/ITO/WO3/Li/Ta₂O₅/NiO/ITO were fabricated. The influence of the Ta₂O₅ solid electrolyte thickness on the electro-optical performance of ECDs was systematically investigated. For this purpose, amorphous Ta₂O₅ films of varying thicknesses were deposited via reactive pulsed DC magnetron sputtering. The optical properties and morphology of the films were characterized using a UV–Vis–NIR spectrophotometer, SEM, and AFM. All Ta₂O₅ films exhibited high transparency, uniform and flat surfaces, and surface roughness below 2 nm. The electro-optical properties of the ECDs were evaluated through cyclic voltammetry and chronoamperometry, revealing a strong dependence on Ta₂O₅ film thickness. Results indicate that Ta₂O₅ films with thinner layers (<305 nm) demonstrate relatively weak electron-blocking capability, leading to high leakage currents in the corresponding ECDs. This resulted in degraded optical memory effects, cycling stability, and coloration efficiency. As the Ta₂O₅ thickness increased, leakage currents gradually decreased and stabilized. ECDs with thicker Ta₂O₅ layers (≥450 nm) displayed superior electro-optical performance. Notably, Ta₂O₅ thickness showed no significant impact on device response time, with all ECDs achieving rapid switching speeds (coloration time <9 s, bleaching time <2 s). This study contributes to a deeper understanding of oxide electrolyte-based ECDs and provides critical insights for improving their electro-optical performance.