Electrochromic properties of three-colour prussian green ECDs and the evolution of Fe ions during the discoloration process

Prussian green (PG) film was directly grown on FTO glass by one-step hydrothermal process for excellent electrochromic performance. The electrochromic devices (ECDs) based on as-grown PG film can show reversible color changes between green, blue and colorless states. The existence state of iron elemental in PG film at different color states was studied by X-ray photoelectron spectroscopy. Compared with the traditional Prussian blue ECDs, PG ECDs achieve a higher optical modulation range (42.7%) and a shorter switching time (t c /t b =1.0/7.4 s). This study provides a novel method for preparing high-performance three-color ECDs by a simple hydrothermal method, and clearly shows the evolution of Fe ions during the discoloration process.