Revealing the Sensitivity-Stability Trade-Off in Quasi-2D Perovskite Single-Crystal X-ray Detectors

Quasi-2D perovskites (Q2D PVSKs) are promising candidates for direct X-ray detection because of their environmental robustness and ability to suppress dark current and ion migration. By varying the organic spacers and the number of inorganic octahedral layers, commonly described by the phase n-value, Q2D PVSKs provide a rich structural library and an ideal platform for balancing bandgap, absorption, carrier mobility, and ionic stability. Substantial efforts have been devoted to improving sensitivity and detection limits in X-ray detectors based on Q2D PVSKs. However, a systematic understanding of how the phase n-value governs the performance-stability trade-off in Q2D PVSK X-ray detectors remains limited. Here we systematically and quantitatively investigate the dimensionality-dependent performance and operational stability of X-ray detectors based on FPEA2MAn-1PbnI3n+1 single crystals (n = 1-3). As n increased from 1 to 3, the detector sensitivity increased from 28.9 to 55.2 μC Gy-1 cm-2 at a low electric field of 12 V mm-1. The largely improved sensitivity is attributed to a cooperative effect of enhanced X-ray absorption, narrower bandgaps, improved mobility-lifetime product, and reduced radiative recombination. In parallel, the ion-migration activation energy decreased from 0.85 to 0.55 eV, resulting in the current drift increasing by about 3-fold. These findings establish the phase n-value as a critical structural parameter governing the sensitivity-stability trade-off in Q2D PVSK X-ray detectors, offering a practical design principle for optimizing dimensionality toward high-performance and operationally stable devices.