The effect of humidity control on all-thin-film electrochromic devices and their superior sustainable recoverability

In this paper, the all-thin-film electrochromic devices (ECDs) with well-designed structure of glass/ITO/NiO_x/Ta₂O₅/WO₃/ITO are fabricated by e-beam evaporation method. In particular, the ECDs are placed in the different-humidity environment to absorb water as the electrolyte. We reported for the first time about the influence of humidity during humidification process on electrochromic performance of the ECDs. The research results demonstrate that the humidity has a significant influence on transmittance modulation and coloration efficiency (CE) of the as-prepared ECDs. The ECD humidified at 50-60% humidity environment shows optimal electrochromic performance containing large optical transmittance modulation (69.1% at 633 nm) and high coloration efficiency (90.74 cm²·C⁻¹ at 633 nm). Furthermore, a novel mechanism, water-decreasing-induced degradation, is proposed to explain the degradation of the ECDs with water as electrolyte during repeated electrochemical cycle. Encouragingly, their electrochromic performance has a significant recovery when the degraded ECDs are humidified again. Importantly, the recovery process can be repeated many times. This means that the electrochromic performance of this ECD is recoverable, and their long-term performance degradation can be successfully avoided. Our results will open avenues for designing and developing superior electrochromic devices.