In situ efficient growth of Rubik nanocube WO3·0.33H2O array films for high-performance electrochromic energy storage devices

Abstract

Tungsten trioxide (WO₃)-based electrochromic devices have attracted considerable attention due to their promising applications in smart windows, energy-efficient displays, and sunglasses. However, it is still challenging to fabricate high-performance WO₃ electrochromic films using an efficient and facile wet method. Here, we report a one-step strategy for the in situ growth of WO₃·0.33H₂O Rubik nanocube films on fluorine-doped tin oxide (FTO) conducting substrates in hydrogen peroxide (H₂O₂) and an ethylene glycol (EG)-containing hydrothermal system that is seed layer-free. The complexing effect of H₂O₂ results in the highly efficient formation of WO₃·0.33H₂O films with good interface stability and a porous structure formed by the stacked Rubik nanocubes. Benefiting from the porous structure, the obtained WO₃·0.33H₂O film delivers outstanding electrochromic and electrochemical energy storage performance, such as large optical modulation over the wide-band visible-near-infrared (Vis-NIR) range (up to 80% at 633 nm and 90% at 1000 nm), high coloration efficiency (65.6 cm² C⁻¹), high rate capability as well as good cycling stability (with 80% transmittance retention over 1000 cycles). Furthermore, as a demonstration, a complementary electrochromic device was assembled based on the WO₃·0.33H₂O film, which offers a high coloration efficiency (92.6 cm² C⁻¹), optical modulation in the visible range (up to 70% at 633 nm), and large energy storage of 27.4 mA h m⁻² at 0.07 mA cm⁻². We believe that this efficient and facile wet method for preparing electrochromic films will provide a fresh approach to investigating high-performance electrochromic systems.