As‐Grown CsPbBr 3 Single Crystal With Atomically Smooth Surface Enabling High‐Performance X‐ray Detection

Solution‐grown metal halide perovskite single crystals show great promise for X‐ray detection, yet their performance is limited by surface defects generated during crystal growth. Herein, an as‐grown CsPbBr 3 single crystal, obtained by incorporating decyltrimethylammonium bromide (DTAB) as an additive, exhibits an atomically smooth surface due to the synergistic modulation of DTAB through weak coordination and hydrophobic effects. The as‐grown CsPbBr 3 ‐DTAB single crystal exhibits an extremely uniform surface with low roughness of 4.5 Å, a significantly extended charge carrier lifetime increasing from 4.53 to 263.52 ns, and a reduced trap density lowered from 7.78 × 10 9 to 8.17 × 10 8 cm −3 . X‐ray detectors based on CsPbBr 3 single crystals achieve a high sensitivity of 45 780 µC·Gy −1 ·cm −2 and a practically measurable X‐ray dose rate down to 0.618 nGy air ·s −1 with an extrapolated detection limit of 0.03 nGy air ·s −1 . The detectors exhibit remarkable operational stability maintained over 10 000 s, outperforming most reported inorganic perovskite detectors. This work provides an effective approach for mitigating surface defects in perovskite single crystals and demonstrates significant potential for high‐performance radiation detection applications.