Influence of Cation on X‐Ray Detection Performance in Mixed‐Halide 2D Ruddlesden–Popper Perovskite

The strategic development of core sensing materials is intrinsically linked to the transformative capabilities of X‐ray detectors, directly governing the efficiency, sensitivity, and long‐term operational stability. This study investigates the X‐ray photodetection capability of 2D mixed‐halide perovskites, BA 2 PbBr 2 I 2 (BA = Butylammonium, C 4 H 9 NH 3 ) and PEA 2 PbBr 2 I 2 (PEA = Phenethylammonium, C 6 H 5 C 2 H 4 NH 3 ), emphasizing the impact of their organic spacer cations. The antisolvent vapor‐assisted crystallization method is employed for halide perovskites synthesis, yielding structural and elemental integrity. A comprehensive investigation into the influence of aliphatic (BA) and aromatic (PEA) organic spacers on the X‐ray photodetection performance is conducted using a custom‐designed X‐ray source with various dose rates (≈95 to 287 mGy s −1 ). The carrier mobility‐lifetime ( μτ ) product, a critical figure of merit for detector performance, is measured as 1.824 × 10 −6 cm 2 V −1 for BA 2 PbBr 2 I 2 and 1.479 × 10 −6 cm 2 V −1 for PEA 2 PbBr 2 I 2 . The sensitivity of the detectors is calculated to be 272 and 373 μC Gy air −1 cm −2 for BA 2 PbBr 2 I 2 and PEA 2 PbBr 2 I 2 , respectively, for a dose rate of 95.5 mGy s −1 . The enhanced sensitivity, corroborated with the type of aromatic spacers, is attributed to improved π–π stacking between successive layers, increased structural rigidity, and higher defect formation energy. The favorable electrical and optoelectronic attributes position these materials as exceptionally compelling contenders for next‐generation, high‐sensitivity X‐ray detection platforms.