Porous fluorine-doped tin oxide-anchored vanadium oxide films for multi-functional highly capacitive electrochromic layers

Electrochromic (EC) devices have been studied in recent decades as devices for optical property changes and energy-saving technologies, which has broadened their applications to include smart windows, sunglasses, and rear-view mirrors. Recently, multifunctional EC energy storage devices have attracted global attention because they can store and release energy during color changes. Herein, we demonstrate a hybrid composite structure of porous fluorine-doped tin oxide (FTO) microspheres on vanadium oxide films. Porous FTO microspheres were successfully synthesized using solvent-assisted ultrasonic spray pyrolysis. Vanadium oxide precursor solutions for the spin-coating process were prepared with porous FTO microsphere contents of 0, 1, 2, and 3 wt%. The hybrid composite EC energy storage film with 2 wt% porous FTO (V₂O₅-FTO2) exhibited superior EC and energy storage performances of widened transmittance modulation (53.79 % at 415 nm) and competitive specific capacitance (486.3 F/g at a high current density of 10 A/g) with high cyclic stability of 87.96 % up to 500 cycles. Thus, the suggested V₂O₅-FTO hybrid structure demonstrates feasibility as a promising research strategy for developing multifunctional highly capacitive electrochromic layers.