Ultrawide‐Bandgap Rb ₂ AgCl ₃ Perovskite Single Crystals Enabling Self‐Powered Solar‐Blind UV Polarization‐Sensitive Photodetection for Intelligent Imaging and Encryption

Solar‐blind ultraviolet polarization detection is critically hindered by the intrinsic isotropy, complex fabrication, and insufficient polarization sensitivity of conventional ultrawide‐bandgap (UWBG) semiconductors such as Ga 2 O 3 and h‐BN. Here, we break this deadlock by introducing a rationally designed lead‐free perovskite analogue, one‐dimensional Rb 2 AgCl 3 single crystals, which were synthesized via a spatially confined cooling method. Its unique chain‐like lattice endows an ultrawide bandgap of 4.83 eV, exceptional thermal stability up to 934 K, and pronounced in‐plane optical anisotropy. Enabled by these attributes, a Schottky‐junction self‐powered photodetector achieves unprecedented solar‐blind ultraviolet performance: a responsivity of 0.2 A/W, specific detectivity of 3.46 × 10 12 Jones, external quantum efficiency of 96%, ultrafast response of 7.9/17.5 µs, and a record dichroic ratio of 15.8 at 255 nm. These metrics not only surpass all reported perovskite‐based devices but also rival, and even outperform, state‐of‐the‐art UWBG semiconductors. Furthermore, the detector enables high‐fidelity polarization imaging, convolutional neural network integration with >99% recognition accuracy, and a 6 × 6 array encryption system based on physically unclonable function keys. This work elevates low‐dimensional lead‐free perovskites from mere substitutes to genuine rivals, establishing a transformative platform for intelligent, self‐powered solar‐blind optoelectronics.