F-Substitution for Achieving Multiferroicity in In (III)-Based Two-Dimensional Organic–Inorganic Hybrid Halogen Double Perovskites

Two-dimensional halogen hybrid double perovskite (HHDP) multiferroic materials have drawn significant interest due to their applications in information storage, sensors, actuators, photoelectric devices, etc. However, optimizing performance based on nonferroic materials aiming to realize multiferroicity remains a major challenge. Here, a ferroelectric-ferroelastic multiferroic (3,3-difluorocyclobutanaminium)4AgInBr8 (FCAIB) was successfully obtained from a nonferroic HHDP (cyclobutylaminium)4AgInBr8 (CAIB). Compared with CAIB, FCAIB shows a much higher phase transition temperature (ΔT = 113 K). It is worth noting that FCAIB exhibits a large spontaneous polarization as high as 8.08 μC cm–2. In addition, the FCAIB demonstrates excellent photoelectric detection stability and a light-dark current switching ratio of 7. Our research provides profound insights into achieving multiferroicity and performance optimization in hybrid double perovskite materials and presents a practical approach for exploring new photoelectric functional materials.