Tailoring a Two-Dimensional Halide Perovskite Composed of the Secondary Amine Cation for Anisotropic X-ray Responses

Two-dimensional (2D) metal-halide perovskites have shown broad application prospects in the field of optoelectronic detection. The presence of the natural quantum-well structure results in strong anisotropy of physical properties, while studies on anisotropic X-ray responses remain insufficient. Here, we present an intriguing anisotropy of X-ray-responsive behaviors in a 2D halide perovskite, (t-ACH)₂(DMA)Pb₂Br₇ (1, where t-ACH is trans-4-(aminomethyl)cyclohexanecarboxylate and DMA is dimethylamine), in which the secondary amine DMA⁺ cation with a large ionic radius locates inside the perovskite cage to form inorganic frameworks. The alternative alignment of inorganic slabs and organic bilayers creates a typical quantum-well architecture, which accounts for the generation of photoelectronic anisotropy. High-quality crystals of 1 exhibit notable semiconducting properties with a large μτ product (1.9 × 10^-4 cm² V^-1). Intriguingly, 1 has better X-ray detection sensitivity (∼569.9 μC Gy_air^-1 cm^-2) along the in-plane direction, which is attributed to its excellent charge carrier transport performance in this direction. Conversely, the higher resistance stemming from the organic barrier results in a lower detection limit along the out-of-plane direction (∼78.1 nGy_air s^-1), much lower than the medical diagnostic criteria (∼5.5 μGy_air s^-1). This work might open up new possibilities for the creative use of hybrid perovskites in direct X-ray detection.