Ultrawide-Bandgap CsAgCl ₂ Layered Single Crystals for Bifunctional Solar-Blind UV Polarimetry and X-ray Detection

The monolithic integration of solar-blind ultraviolet polarization sensitivity and high-energy X-ray detection into a single semiconductor platform is urgently demanded for next-generation multimodal smart sensing, yet remains unattainable with mainstream ultrawide bandgap materials (e.g., Ga 2 O 3, hBN, diamond, and others) due to their inherent trade-offs among bandgap, stopping power, and anisotropy. Here, we break this deadlock by developing lead-free layered CsAgCl 2 perovskite single crystals via a well-controlled chemical solution deposition method. This material features an ultrawide indirect bandgap of 4.29 eV, a Cs/Ag heavy-atom constituent, and pronounced optical anisotropy. The developed Ag/CsAgCl 2 /Ag device architecture delivers a comparable polarization-sensitive solar-blind ultraviolet photodetector with a dichroic ratio of 4.6, responsivity of 560 mA/W, specific detectivity of 2.3 × 10 13 Jones, and fast response (300/270 μs) at 250 nm, outperforming all reported leadfree perovskite deepultraviolet detectors. Concurrently, leveraging a large mobility–lifetime product (μτ ∼ 2.8 × 10 –4 cm 2 V –1 ) and ultralow dark current drift (1.25 × 10 –4 μA cm –1 s –1 V –1 ), the same device showcases ultrahigh sensitivity of 10563 μC·Gy –1 ·cm –2, incredibly low detection limits of 28.7 nGy air ·s –1, and high-resolution imaging at 50 V for 50 keV X-ray photons, rivaling commercial directconversion materials. Boasting outstanding ambient stability and ultralow dark current, this CsAgCl 2 platform uniquely unifies two incompatible functions, delivering an eco-friendly, transformative paradigm for compact multimodal sensing with profound scientific and practical implications.