Suppression of Impurity Phase in Cesium Halide Perovskites by using Pressure

Cesium halide perovskites, Cs₄PbBr₆ are new promising candidates for the applications of wide band gap semiconductors. However, the unavoidable appearance of CsPbBr₃, during the growth of the host crystal significantly hinders the optical and electrical properties of the materials. We report the suppression of the CsPbBr₃ phase by applying pressure in an order of giga-pascal scale.
The results of XRD revealed that the CsPbBr₃ phase disappeared at 2.6 GPa. No PL and band edge peak of CsPbBr₃ was observed at 3.0 GPa, which demonstrates the disappearance of the fluorescence from the UV irradiated sample. With further pressure, the XRD data showed a reversible phase transition from rhombohedral to monoclinic of Cs₄PbBr₆ at 2.6 GPa. The main peaks were stable under pressure up to 20.0 GPa. After releasing the pressure, a very small intensity of PL peak, the band edge, and XRD peaks for CsPbBr₃ phase were observed. The Cs₄PbBr₆ phase was recovered at ambient conditions. It is speculated that CsPbBr₃ crystals are sensitive to pressure with the distortion of [PbBr₆]^-4 network at moderately low pressure (<3.0 GPa), while Cs₄PbBr₆ crystals are much stable at high pressure (up to 20.0 GPa) due to the isolated octahedral PbBR₆^–4 ions interspersed Cs⁺ cations.