Reversible electrochromism in α-In₂Se₃ through ferroelectric switching induced phase transition

Electrochromic materials change color or opacity when subjected to electrical stimuli, often through reversible chemical reactions or phase transitions. Their optical switch capabilities make them promising for applications like smart windows and glasses, thus garnering widespread attention in recent years. Van der Waals layered ferroelectric α-In₂Se₃, known for its rich polymorphs, is a promising candidate for exploring physical property modulation via phase transformations. However, the discovery of electrochromism in In₂Se₃ has been impeded by similar optical constants among its polymorphs. Herein, we report the experimental observation of reversible electrochromism in α-In₂Se₃ thin flakes accompanied by ferroelectric polarization switching. Microscopic structural characterizations reveal that the color change stems from a crystalline-to-amorphous phase transition. An improved Kramer-Kronig analysis was employed to quantify the change in optical constants of the flake. A disordered polarization switching model, inherent to the crystal symmetry of α-In₂Se₃, was proposed to explain the electrically driven amorphization. This work delivers distinct insight into the unique electrochromic behavior and unveils opportunities of relevant applications for the van der Waals layered ferroelectric.