Electrically Activated UV‑A Filters Based on Electrochromic MoO_3–x

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO₃ and WO₃ are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO_3–x-based electrically activated ultraviolet (UV) filters. The MoO_3–x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H⁺ injection/extraction in MoO_3–x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325–800 nm), with a peak of ∼60% in the UV-A range (350–392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm² C^–1 are achieved.