High‐Performance Industrial‐Grade CsPbBr(3) Single Crystal by Solid–Liquid Interface Engineering

All‐inorganic metal halide perovskite CsPbBr(3) crystal is regarded as an attractive alternative to high purity Ge and CdZnTe for room temperature γ‐ray detection. However, high γ‐ray resolution is only observable in small CsPbBr(3) crystal; more practical and deployable large crystal exhibits very low, and even no detection efficiency, thereby thwarting prospects for cost‐effective room temperature γ‐ray detection. The poor performance of large crystal is attributed to the unexpected secondary phase inclusion during crystal growth, which traps the generated carriers. Here, the solid–liquid interface during crystal growth is engineered by optimizing the temperature gradient and growth velocity. This minimizes the unfavorable formation of the secondary phase, leading to industrial‐grade crystals with a diameter of 30 mm. This excellent‐quality crystal exhibits remarkably high carrier mobility of 35.4 cm(2) V(−1) s(−1) and resolves the peak of (137)Cs@ 662 keV γ‐ray at an energy resolution of 9.91%. These values are the highest among previously reported large crystals.