Compositional degradation with Br content in Cesium lead halide CsPbBrxI3-x

The inorganic cesium lead halide CsPbX3 (where X ​= ​I, Br, Cl) are reported to possess good stability than that of organic-inorganic hybrid halides. CsPbI3 is reported to have four phases: perovskite black phase (cubic (α), tetragonal (β), orthorhombic(γ)) and non-perovskite yellow orthorhombic (δ). With band gap of ∼ 1.73eV, CsPbI3-α is most suitable phase among all-inorganic lead halide Perovskites. However, in ambient atmosphere (almost instantly) the perovskite black phase convert into non-perovskite yellow orthorhombic phase. At the same time CsPbBr3 remains in the orthorhombic phase at room temperature. Thus, in the present investigation, compositional variation of Br in Cesium lead iodide CsPbBrxI3-x (x ​= ​0.0 to 3.0 ​at the step of 0.5) samples synthesized by cold sintering technique is studied. The XRD patterns showed the orthorhombic phase for CsPbBr3. Further, CsPbBrxI3-x (x ​≤ ​1.0) have shown double phase corresponding to CsPbI3 (Pnma) ​+ ​PbI2 ( R3¯m). However, the compound with 1.5 ≤ x ​< ​3.0 showed the presence of various phases with and without oxygen including the CsPbBr3 (orthorhombic, Pnma) phase which has also been confirmed through UV–visible spectroscopy, impedance and Schottky anomaly. This compositional failure is also suggested by deviation from Vegards law showing volumetric expansion. The role of oxygen vacancy has been probed for the compositional failure for 1.5 ≤ x ​< ​3.0 using XPS characterization and Raman spectroscopy.