Dimensionality Engineering: A Pathway to Ferroelectric Halide Perovskites

Metal halide perovskites have emerged as a versatile materials platform that uniquely combines semiconducting and ferroelectric functionalities, enabled by their exceptional structural and chemical tunability. Unlike conventional oxide ferroelectrics, halide perovskites offer rich design freedom through dimensionality control, organic–inorganic coupling, and compositional engineering. In this review, we highlight recent progress in ferroelectric halide perovskites from the perspective of dimensionality, with particular emphasis on how reduced dimensionality stabilizes intrinsic ferroelectricity. We first introduce early studies on three‐dimensional halide perovskites, highlighting the ferroelectric‐like response in prototypical systems such as MAPbI 3 and clarifying the distinction between intrinsic ferroelectricity and extrinsic effects arising from ionic migration and leakage currents. We then focus on low‐dimensional halide perovskites and discuss key design strategies, including spacer cation engineering, B‐site cation engineering, and polar‐axis control, in relation to their underlying ferroelectric mechanisms. Finally, we review emerging applications of ferroelectric halide perovskites in self‐powered photodetectors, solar cells, and neuromorphic devices, where polarization‐induced internal electric fields enable novel device functionalities. We conclude by outlining critical challenges and future directions, including ferroelectric switching dynamics, lead‐free material development, and polarization control for scalable device integration.