In situ formation of solid electrolyte interphase for improved cyclability of electrochromic tungsten oxide thin films

Tungsten oxide (WO3) is highly regarded as one of the most promising working electrodes for electrochromic devices due to its large optical modulation, however, it suffers from degradation at the WO3/electrolyte interface. Herein, we developed an ALD-Al2O3/Li-based electrolyte hybrid layer as organic/inorganic solid electrolyte interphase (SEI) to improve the cyclic stability of the WO3 thin films. In situ formation of SEI has been confirmed by an analysis of components (such as Li2CO3, Li2O, and PC) of the electrochromic WO3 thin films with the ALD-Al2O3 interface layer after electrochemically cyclic treatment. As for comparative analysis of microstructural and electrochemical properties of the electrochromic WO3 thin films with and without the ALD-Al2O3 interface layer, we emphasize that the SEI, introduced by the ALD-Al2O3 interface layer and produced by electrochemical cycling, embodies its optimality properties. With the introduction of SEI, the cyclic stability of the WO3 thin film can be significantly enhanced, allowing for a stable transmittance modulation (1500 cycles with 94 % retention). This work offers a new strategy to improve the cyclic stability of WO3 thin films and enlightens the design on stable interface for electrochromic electrodes.