Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs 3 Bi 2 Br 9 (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 10 12 Ω cm and a mobility lifetime product of 8.32 × 10 −4 cm 2 V −1 . The Au/CBB/Au singlecrystal device exhibits a high sensitivity of 1705 μC Gy air −1 cm −2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGy air s −1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10 −10 nA cm −1 s −1 V −1 and long-term air environment reliability under a high electric field of 10 000 V cm −1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics. KEYWORDS: lead-free perovskites, two-dimensional perovskites, Cs 3 Bi 2 Br 9 single crystal, ultralow detection limit, X-ray imaging

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These results suggest that different acupoints on the same meridian may activate certain similar areas of the brain. In addition, acupoints that are commonly used in clinical practice might modulate a greater extent of cortical areas than uncommonly used acupoints.