The Counterbalancing Role of Oxygen Vacancy between the Electrochromic Properties and the Trapping Effect Passivation for Amorphous Tungsten Oxide Films.

Defect engineering of electrode materials is considered highly effective in regulating their performance, among which oxygen vacancies play a vital role. Thereupon, comprehensively understanding effects of oxygen vacancy in electrochemical processes of transition metal oxides stays hot and controversial, representatively for amorphous tungsten oxide films and their electrochromic (EC) behaviors. Upon long-term cycling, amorphous tungsten oxide suffers from the universal trapping effect governed by the intrinsic host microstructure and transport kinetics of the inserted ions, implying that manipulating oxygen vacancies could be a potential solution to the ion-trapping problem. Hence, systematic work is urgent for not only tackling the trapping effect but also understanding the effect of oxygen vacancies on EC behaviors. Herein, the concentration of oxygen vacancies in the amorphous tungsten oxide films is modulated over a wide range. In combination with comprehensive experiments and first-principles calculations, the presence of oxygen vacancy is detrimental to the EC properties, but it greatly attenuates the trapping effect. Excellent cyclic stability is achieved with a 100% optical modulation rate and charge capacity retention after 5000 cyclic voltammetry cycles. This study elucidates understanding of oxygen vacancy engineering in transition metal oxides, particularly regarding trapping effect passivation.