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

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.