Unveiling the Monoclinic Phase in CsPbBr<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> Perovskite Crystals, Phase Transition Suppression and High Energy Resolution γ-Ray Detection
Adam Balvanz, Khasim Saheb Bayikadi, Zhifu Liu, Thomas S. Ie, John A. Peters, Mercouri G. Kanatzidis
Abstract
All-inorganic CsPbBr 3 and CsPbCl 3 perovskites are promising materials for high-performance solar cells and advanced radiation detection technologies with high stability. Here we report that CsPbBr 3– x Cl x ( x = 0–3) crystals exhibit eutectoid behavior for the melting points and phase transition temperatures. The well-known halide perovskite cubic phase transition temperature shifts near room temperature (∼37 °C for CsPbBr 2 Cl). We conducted an extensive crystallographic analysis on single crystals of 7 different compositions, including the end members CsPbBr 3 and CsPbCl 3 . Contrary to previous beliefs, we discovered they exhibit a monoclinic structure with space group symmetry P 2 1 / m at room temperature, rather than the orthorhombic Pnma . This new structural model is more precise and features a unit cell volume that is four times larger than that of the orthorhombic model. From high-quality single crystals of CsPbBr 2 Cl, grown by the Bridgman method, we constructed γ-ray detectors achieving an energy resolution of 7.2% at 200 V for 57 Co radiation. Thermally stimulated current spectroscopy of the CsPbBr 2 Cl samples revealed that the defect densities in crystals from different regions of the ingot were relatively uniform, with values of ∼4.72 × 10 12 and ∼5.09 × 10 12 cm –3 . These findings indicate that low deep-level defect densities can be achieved that are consistent with the notable performance of the CsPbBr 2 Cl perovskite as a high-energy γ radiation detector.