Tailoring Multi-Phenyl Ring Cation for Stable Scalable Hybrid Bismuth Iodide Amorphous Film: Enabling Record...

The 329-type bismuth (Bi)-based metal halide (MH) polycrystalline films have potential to be applied in the new generation of X-ray imaging technology owing to high X-ray absorption coefficients and excellent detection properties. However, the mutually independent [Bi₂X₉]^3- units and numerous grain boundaries in the material lead to low carrier transport and collection capabilities, severe ion migration, large dark currents, and poor response uniformity. Here, a new multi-phenyl ring methyltriphenylphosphonium (MTP) is designed to optimize the energy band structure. For the first time, the coupling between the A-site cation and [Bi₂X₉]^3- is realized, making it the main contributor to the conduction band minimum (CBM), getting rid of dilemma that carrier transport is confined to [Bi₂X₉]^3-. Further, the preparation of MTP₃Bi₂I₉ amorphous large-area wafer is achieved by melt-quenching; the steric hindrance effect improves stability, increases ion migration energy, and promotes response uniformity (14%). Moreover, the amorphous structure takes advantage of A-site cation participation in the conductivity, achieving a record sensitivity (7601 µC Gy^-1 cm^-2) and low dark current (≈0.11 nA) in the field of amorphous X-ray detection, and features low-temperature large-area preparation. Ultimately, designing amorphous array imaging devices that exhibit excellent response uniformity and potential imaging capabilities is succeeded here.