Single-Step Synthesis of Cs₃Bi₂I₉ Nanocrystals for Scalable Direct X‑ray Detectors

Lead-free perovskite-inspired materials have emerged as promising candidates for direct X-ray detection. However, in the early exploration of emerging materials, the focus was on large single crystals. Herein, we report a facile, scalable, single-step synthesis of high-quality Cs₃Bi₂I₉ nanocrystals (NCs) directly from their precursor powders through an ultrasonication approach. The large-scale synthesis of the NCs allowed for the production of 0.78 cm² pellets used in the fabrication of X-ray detection devices, which exhibit a high bulk resistivity of 1 × 10¹¹ Ω cm and a low dark current density of 3.3 nA cm^-2 under an applied bias of 50 V (357 V cm^-1 electric field). These devices achieve a limit detection of 108 nGy_air s^-1, an order of magnitude improvement over the a-Se used in commercial medical imaging, along with stable current under continuous X-ray exposure with a peak energy of 35 keV_p. Finally, we demonstrate the scale-up of these detectors by producing thick films 9 cm² in area, achieving a performance comparable to that of the detectors based on pellets.