Reveal the Humidity Effect on the Phase Pure CsPbBr3 Single Crystals Formation at Room Temperature and Its Application for Ultrahigh Sensitive X‐Ray Detector

Generally, growing phase pure CsPbBr3 single crystals is challenging, and CsPb2 Br5 or Cs4 PbBr6 by-products are usually formed due to the different solubilities of CsBr and PbBr2 in the single solvent. Herein, the growth of high-quality phase pure CsPbBr3 perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr3 to two dimensional (2D) layered tetragonal CsPb2 Br5 and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic-inorganic perovskite, the prepared CsPbBr3 single crystals are much more stable under high humidity, which satisfies the long-term working conditions of X-ray detectors. The X-ray detectors based on CsPbBr3 single crystals show a high sensitivity and a low detection limit of 1.89 μGyair s-1 , all of which meet the needs of medical diagnosis.