In Operando Ultraviolet Illumination Enables Self‐Healing Electrochromic Response

ABSTRACT Ion trappinginduced performance degradation hinders the widespread adoption of cathodic electrochromic materials and associated devices. Although recent studies demonstrate that post‐treatment combining constant bias with ultraviolet illumination can rejuvenate the single electrochromic layer, this approach damages counter electrodes in full devices owing to extended bias durations. Here, we demonstrate a self‐restoration of electrochromic performance by in operando ultraviolet illumination. This approach is highly efficient and safe for both single cathodic electrochromic layers and full devices. Meanwhile, it is found in operando ultraviolet illumination has to be ceased once the full rejuvenation is achieved. Prolonged in operando ultraviolet illumination leads to persistent degradation of the electrochromic layer which can no longer be rejuvenated due to the formation of hexagonal Li 2 WO 4 . The approach of in operando ultraviolet illumination paves the way for electrochromic devices with superior long‐span life.