Realization of Tunable Ferroelectricity in Perovskite Crystals for Multidirectional Self‐Driven Photodetection

Abstract Halide perovskite ferroelectrics endowed with a distinctive spontaneous polarization effect have been regarded as prospective electroactive materials and are prevalently utilized in solar cells, photoelectric detection, and other domains. Among them, multipolar‐axis ferroelectrics featuring multiple equivalent polarization directions are particularly desirable for diverse areas of applications. Nevertheless, the design and regulation of multipolar axis perovskite ferroelectrics remains a significant challenge. Here, guided by the strategy of layer regulation, we successfully designed and regulated a series of 2D homologous perovskites OA 2 Cs n ‐1 Pb n Br 3 n +1 (OA =  n ‐octylammonium, n  = 1–3). Notably, OA 2 Cs n ‐1 Pb n Br 3 n +1 exhibits layer‐dependent ferroelectricity: OA 2 PbBr 4 exhibits non‐ferroelectricity, OA 2 CsPb 2 Br 7 displays uniaxial ferroelectricity, while OA 2 Cs 2 Pb 3 Br 10 has multiaxial ferroelectricity. Moreover, the devices fabricated based on OA 2 Cs 2 Pb 3 Br 10 achieve high‐performance self‐driven photodetection in multiple directions. This precise layer‐regulation strategy offers an efficient approach to obtaining and regulating multipolar‐axis perovskite ferroelectrics, presenting the potential for next‐generation optoelectronic devices.