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 OA₂Cs_n _-1Pb_nBr₃ _n ₊₁ (OA = n-octylammonium, n = 1-3). Notably, OA₂Cs_n _-1Pb_nBr₃ _n ₊₁ exhibits layer-dependent ferroelectricity: OA₂PbBr₄ exhibits non-ferroelectricity, OA₂CsPb₂Br₇ displays uniaxial ferroelectricity, while OA₂Cs₂Pb₃Br₁₀ has 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.