High-Quality Wide-Bandgap 0D Cs _<b>4</b> PbI _<b>6</b> Perovskite Single Crystal for High-Performance Ultraviolet Photodetectors and X-ray Detectors

All-inorganic perovskites, renowned for their superior photoelectric properties, have found extensive applications across diverse fields. Among these, perovskite-based visible-blind ultraviolet photodetection and X-ray detection have emerged as rapidly evolving research hotspots. Herein, the accumulation of PbI₂ on the crystal surface is observed and verified for the first time. Through the slow solvent evaporation method at 70 °C to avoid PbI₂ accumulation, a high-quality transparent colorless Cs₄PbI₆ single crystal with low defect density and high phase purity can be successfully fabricated, which exhibits excellent detection properties due to its wide bandgap of 3.3 eV. The zero-dimensional transparent colorless Cs₄PbI₆ single-crystal-based visible-blind ultraviolet photodetector shows a high responsivity as much as 35.10 A/W, an external quantum efficiency as high as 1.07 × 10⁴%, and a detectivity as large as 2.45 × 10¹⁴ Jones, with an extremely fast response speed of ∼40 μs and excellent long-term stability. In addition, transparent and colorless Cs₄PbI₆ is also used in direct-type X-ray detectors exhibiting high sensitivity. Under the irradiation of an X-ray source energy (160 keV) close to that of medical CT, the sensitivity of the device can reach 154.84 μC·Gy_air ^-1·cm^-2, with the detection limit lower than the safe value required for medical diagnosis.