A Lithium‐Salt‐Free, Hydrophobic, Solid‐State Poly(Ionic Liquid) Electrolyte Enables Rapid Assembly of Unencapsulated, Removable Electrochromic "Window Tint Film".

Electrochromic technology that enables modulation of a material's optical properties by application of an applied voltage is utilized in smart windows. However, avoiding water absorption by lithium salt in the electrolyte necessitates complex encapsulated device assemblies that must be constructed under strict atmosphere conditions and are largely unrepairable. Herein, a lithium‐salt‐free, hydrophobic, solid‐state poly(ionic liquid) electrolyte based on strong C─F bonds that exhibits low polarizability, low moisture absorption, and a wide electrochemical window, allowing the fabrication of unencapsulated electrochromic devices with outstanding long‐term cycling and environmental stability are presented. Intimate contact between the electrolyte and the electrode is achieved through integrated in situ polymerization, providing an interface with multiple molecular interactions that impart robust adhesion, efficient ion transport, and excellent stability. To demonstrate the potential of this electrolyte for cost‐effective electrochromic smart windows, low‐cost (≈110 USD m−2), unencapsulated, removable, electrochromic "window tint film" with customizable dimensions and shapes are fabricated. [ABSTRACT FROM AUTHOR]