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

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 OA2Csn‐1PbnBr3n+1 (OA = n‐octylammonium, n = 1‐3). Notably, OA2Csn‐1PbnBr3n+1 exhibits layer‐dependent ferroelectricity: OA2PbBr4 exhibits non‐ferroelectricity, OA2CsPb2Br7 displays uniaxial ferroelectricity, while OA2Cs2Pb3Br10 with multiaxial ferroelectricity. Moreover, the devices fabricated based on OA2Cs2Pb3Br10 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.