CVD‐Synthesized CsAg₂I₃ Single Crystals toward Polarization UV Photodetection and Anti‐Counterfeiting Identification

Abstract Low‐dimensional ternary silver halide (CsAg₂I₃), an emerging inorganic lead‐free perovskite, has garnered significant scientific attention due to its strong quantum confinement effects, wide bandgaps, non‐toxicity, and others. However, the photophysical properties and optoelectronic performance of CsAg₂I₃ materials and devices are significantly compromised by crystal quality and defects arising from liquid‐phase preparation. Herein, 1D CsAg₂I₃ single crystals newly grown by the chemical vapor deposition method are reported. These crystals display exceptional quality and stability over a 3‐month period despite exposure to air and moisture. The high in‐plane anisotropic structure, phonon vibrations, and refractive index of CsAg₂I₃ crystals are also experimentally elucidated. Polarization‐sensitive ultraviolet photodetector based on the CsAg₂I₃ monocrystal features a responsivity of 139 mA W⁻¹, a specific detectivity of 1.05 × 10¹¹ cm Hz^1/2 W⁻¹, an ultra‐fast photoresponse speed of 48.2/69.1 µs, and a dichroic ratio of 2.66 upon 360 nm irradiation at −5.0 V bias. The photodetector excels amongst its competitors, moving toward the potential application of rapid optical anti‐counterfeiting identification. This work, which leverages grown high‐crystalline and highly stable CsAg₂I₃ monocrystals, holds promises for advancing this functional material into a robust next‐generation optoelectronic devices capable of probing sensitive optical sensing and specific azimuth recognition.