High‐Efficiency Luminescence and Robust Thermal Quenching Resistance in Organic–Inorganic Hybrid Indium‐Based Metal Halides

Abstract Low‐dimensional lead‐free metal halide perovskites have attracted considerable attention for the development of multifunctional optoelectronic materials owing to their extensive structural diversity and adjustable optical properties. However, organic cation‐based low‐dimensional metal halides often exhibit limited thermal stability, while inorganic cations‐based ones have a poor solution processability. To address these challenges, this study proposes a hybrid organic–inorganic cation approach by utilizing both 4,4‐difluoropiperidine (DFPD) and cesium (Cs⁺) to prepare low‐dimensional metal halides: (DFPD)₂CsInCl₆. Two isostructural metal halides are developed: α‐(DFPD)₂CsInCl₆ and β‐(DFPD)₂CsInCl₆, which exhibit different space group symmetries. This strategy ensures both thermal stability and introduces structural diversity. Doping (DFPD)₂CsInCl₆ with antimony (Sb³⁺) enhances its PLQY from 0% to 100%. The emission centers of both materials exhibit temperature‐insensitive behavior and maintain efficient and stable PL emission even at high temperatures (up to 400 K), making them excellent candidates as thermally stable phosphor materials for solid‐state lighting applications. This work thus expands the scope of developing multifunctional low‐dimensional metal halides.