Electrochromic Performance Fading and Restoration in Amorphous TiO2 Thin Films

Electrochromic performance fading is inevitable upon extended cycling, and the limited lifetime greatly prevents large-scale commercialization of electrochromism-based devices. Here the origin of the performance degradation is uncovered and the performance restoration in TiO2 thin films is explored. It is shown that, depending on the applied potential windows, the inserted ions are immobilized in alpha-traps resulting in a monotonous degradation of colored state, or immobilized in b- and modified alpha-traps leading to mutual degradation of colored and bleached state of the films. It is found by releasing the resided ions in various traps, the initial performance can be restored accordingly. Moreover, reversible sites and all traps are demonstrated to be interconvertible through an ion trapping and detrapping process. These results provide a general scope in understanding the electrochromism in oxide thin films and offer the scheme for potential traps control or even elimination, aiming at superior electrochromic devices.