Lithiation of WO₃ films by evaporation method for all-solid-state electrochromic devices

Lithium (Li) electrolyte plays an important role in the electrochromic devices (ECDs), however, there are few studies on the matching between Li content and electrochromic layer in all-solid-state ECDs. In this work, lithiation WO₃ films with different Li thickness were prepared by evaporation method to investigate the effect of Li thickness on the optical properties of WO₃ films. Meanwhile, the Li storage capacity of WO₃ in liquid electrolyte was calculated. The results showed that the optimal thickness of Li for 450 nm WO₃ film prepared by evaporation was 42 nm. All-solid-state ECD glass/ITO/NiO/ZrO₂/Li/WO₃/ITO with optimal Li thickness exhibited large optical transmittance modulation (64.9% at 680 nm and 52.5% at 550 nm), high coloration efficiency (CE, 106.6 cm²/C at 550 nm) and superior cycle stability (98% retention of the maximum optical modulation after 4000 cycles). This work provides a new idea for the design and preparation of all-solid state ECDs.