Bipyridine-Based One-Dimensional Perovskites with Type-II Band Alignment Enables High-Sensitivity Direct X-ray Detection

Low-dimensional hybrid perovskites are considered strong contenders for direct X-ray detection due to their enhanced environmental stability and suppressed ion migration. However, their performance is often limited by inefficient carrier transport. Herein, we synthesized two one-dimensional lead iodide perovskites, 44DPPbI₄ and 22DP₂Pb₃I₁₀, using 4,4'-bipyridine (44DP) and 2,2'-bipyridine (22DP) as organic cations, respectively. Density functional theory (DFT) calculations demonstrate that both materials exhibit type-II band alignment, enabling effective charge separation and reducing recombination. A larger energy offset between the conduction band maximum (CBM) and the lowest unoccupied molecular orbital (LUMO) in 44DPPbI4 favors interfacial charge separation, giving rise to a larger carrier mobility-lifetime product. Consequently, the 44DPPbI₄-based device exhibits a high sensitivity of 5631.81 μC Gy^-1 cm^-2 and a low detection limit of 4.40 nGy s^-1. Both materials also exhibit high ionic activation energies and high resistivity, indicating suppressed ion migration. Our results demonstrate a new strategy in material design for achieving a high-performance X-ray detector.