Distorted Lead‐Free Germanium‐Based Perovskite Single‐Crystals for Stable and Efficient X‐Ray Detection and Imaging

3D metal halide perovskite X‐ray detectors have become the focus of research in recent years due to their superior sensitivity. However, the reported efficient perovskite X‐ray detectors all contain highly toxic lead and worrisome stability, which greatly limits their wide application and promotion. In this study, a distorted 3D germanium perovskite MAGeI3 single crystal (SC) is designed and grown by gradient cooling method. Due to its distorted octahedral structure, the MAGeI3 SCs not only possess high sensitivity but also have superior long‐term working stability. Specifically, the MAGeI3 SC X‐ray detectors achieve a record sensitivity of 42825 µC Gy−1 cm−2 and an impressive low detection limit of 4.1 nGy s−1, both of them are far better than the state‐of‐the‐art lead‐free perovskite SC X‐ray detectors. Moreover, the unencapsulated SC detector still maintains the original response even at high applied electric field and high dose rate X‐ray irradiation for several hours. Eventually, a high resolution of 7.2 lp mm−1 in X‐ray imaging is demonstrated on the MAGeI3 SC detector under a low dose rate of 478 nGy s−1 and at a low electric field of 1 V mm−1. This work provides a new pathway to design high‐performance and low‐toxicity X‐ray detectors. A distorted 3D perovskite MAGeI3 single crystal (SC) is designed and grown by gradient cooling method. The unencapsulated MAGeI3 SC detectors not only possess high sensitivity but also have superior long‐term working stability. Moreover, the detectors achieve a high resolution of 7.2 lp mm−1 in X‐ray imaging even under a low dose rate and at low electric field.