One‐Dimensional Ferroelectric CsCu ₂ Br ₃ Single‐Crystal Enables UVB Polarization‐Sensitive Photodetector for Encryption Wireless Communications

Abstract Perovskite ferroelectrics with switchable spontaneous polarization have aroused widespread attention due to their potential applications in nonvolatile memory, optoelectronic detection, and so forth, yet they face challenges like insufficient thermal stability, structural brittleness, lead toxicity concerns, and other aspects. This paper presents the first well‐defined synthesis of one‐dimensional (1D) lead‐free ferroelectric CsCu ₂ Br ₃ single‐crystals (SCs), which possess a wide bandgap (≈4.1 eV), high Curie temperature, in‐plane ferroelectric self‐polarization, prominent optical anisotropy, and other notable properties. These characteristics enable the samples to sensitively detect weak ultraviolet‐B (UVB) signals and precisely discriminate linear polarization states. A prototype polarization‐sensitive UVB photodetector based on 1D CsCu ₂ Br ₃ SCs is successfully fabricated, demonstrating exceptional photoresponse performance with a photoresponsivity of 400 mA W ^{− 1} , a specific detectivity of 1.12 × 10 ¹² Jones, a rapid response characteristic with rise/fall times of 1.2/1.6 ms, and a high polarization ratio of 4.3 under 320 nm linearly polarized light illumination. By leveraging a dual‐parameter optoelectronic signal‐polarization encoding technology, the detector realizes encryption communication, with the channel capacity being augmented by 1.45 times. This work establishes CsCu ₂ Br ₃ SCs as eco‐benign perovskite platforms for probing ferroelectricity and multi‐physical coupling phenomena, demonstrating their critical role in advancing cross‐disciplinary functional material research.