In Situ Fabricated Self‐Healing, Highly Stretchable Sb 3+ ‐Doped Non‐Lead Double Perovskite Halide COFs Exhibits Narrow‐Band Emission Properties

Abstract In situ fabrication techniques enable the synthesis of non‐lead double perovskite halide composite optical films (COFs) with excellent optical properties at low temperatures via simple processes. However, most studies are based on rigid polymers as matrices, and there is a lack of exploration on narrow‐band emission COFs. This study proposes an improved in situ growth strategy, successfully synthesizing Sb 3 ⁺‐doped Cs 2 KTbCl 6 lead‐free double perovskite halide COFs within a self‐healing polyurethane (ISSPU) matrix featuring synergistic dynamic disulfide bonds and high‐density hydrogen bonds. These films achieving narrow‐band emission with a full width at half maximum (FWHM) of 7.54 nm and a maximum photoluminescence quantum yield (PLQY) of 27.08%, also exhibits excellent tensile strength (31.13 MPa), fracture elongation (987%), and cyclic tensile stability, along with thermal‐induced self‐healing capability. Leveraging the excellent narrow‐band green luminescence and self‐healing properties of the COFs, this material demonstrates significant application potential in optical anti‐counterfeiting and flexible wearable devices.