Sensitive and Stable Tandem X‐Ray Detectors Achieved by High‐Quality 2D Perovskite Single Crystals

2D perovskite single crystals (SCs) demonstrate significant potential for developing low-cost, stable, and low dose X-ray detection. However, the large interlayer spacing in 2D perovskite results in low carrier mobility, limiting the sensitivity enhancement of X-ray detection. Herein, a tandem detector is designed and assembled for the first time to solve the critical issue of low carrier transport efficiency in 2D perovskite SCs. The tandem SC detector establishes efficient cross-layer charge transport channels through a "layered synchronous collection" strategy, enabling a "short-range transport" mechanism. The unique "longitudinal short-range transport" reduces carrier transport distance and then decreases recombination and trap capture, thus significantly enhanced carrier collection efficiency. Consequently, these detectors not only maintain low dark current but also exhibit a higher response current than single-junction counterparts, resulting in superior X-ray detection performance. Specifically, the tandem SC detectors achieved a high sensitivity of 5218 µC Gy^-1 cm^-2, a low detection limit of 2.2 n Gy s^-1, and a short response time of 1.8 ms. Furthermore, the tandem detectors retain original response after continuous X-ray irradiation with a high dose of 2.4 Gy. The combination of high stability and sensitivity enables the tandem SC detectors achieved high-definition imaging at 12.5 lp mm^-1.