Halogen (Cl, Br, I) tuning of 3-Methylpiperidine Bismuth Halides for Highly Sensitive, Low-Dose, and Stable X-ray Detection

Abstract X-ray detection has extensive applications in medical imaging, scientific research, and security inspection. Despite the superior radiation detection properties of lead-based perovskites, including high carrier mobility and superior attenuation efficiency, their toxicity and instability arising from ion migration hinders further development. To address these challenges, a series of halogen-tuned lead-free 3-methylpiperidine bismuth halides, (C6H14N)3Bi2I9, (C6H14N)2BiBr5 and (C6H14N)2BiCl5 (C6H14N = 3-methylpiperidine) single crystals were grown and systematically characterized. 3-methylpiperidine was selected for their steric effect stabilizing the lattice, and the synergistic tuning through halogen variation enabled a structural transition along with modulation of their properties. Notably, lateral-structured (C6H14N)3Bi2I9 single crystal-based X-ray detectors achieved remarkable sensitivity of 388.05 μC Gy⁻¹ cm⁻², a low detection limit of 71.05 nGy s⁻¹ and a dark current drift of 2.16 × 10⁻8 nA cm⁻¹ s⁻¹ V⁻¹. Importantly, the material retained its original morphology after eight months of ambient storage. Furthermore, flexible X-ray devices fabricated via spin-coating (C6H14N)3Bi2I9 exhibited excellent X-ray response with a sensitivity of 121.48 μC Gy⁻¹ cm⁻² and outstanding mechanical stability. This work reveals that halogen tuning effectively optimizes the structure and performance of Bi-based perovskites, providing valuable insights for advancing them in X-ray detection applications.